BE1020479A5 - PROCESS FOR THE CONTINUOUS PRODUCTION OF POLYACRYLIC ACID WATER ABSORBING RESIN (SEL) - Google Patents

Description

Process for the continuous production of polyacrylic acid (salt) water-absorbent resin /

BACKGROUND

1. Technical field

The present invention relates to a process for producing a polyacrylic acid (salt) water-absorbent resin. More particularly, the present invention relates to a process for producing a polyacrylic acid (salt) water-absorbent resin, by means of which a water-absorbent resin having superior physical properties can be stably and continuously produced in washing a continuous production apparatus for a water-absorbent resin periodically with water.

2. Description of the Related Art

A water-absorbent resin (PSA / Superabsorbent Polymer) is a water-swellable and water-insoluble polymeric gelling agent, and has been frequently used primarily in disposable applications, as absorbent articles such as disposable diapers and sanitary napkins, water retention agent for gardening and agriculture, industrial water stop material, and the like. As such a water-absorbing resin, those utilizing many hydrophilic monomers or polymers as raw materials have been proposed. Of these, in particular, a polyacrylic acid (salt) water-absorbent resin obtained using acrylic acid and / or a salt thereof as a monomer has been used industrially in most case in light of its high performance of water absorption.

Such a water-absorbing resin is produced by means of a polymerization step, a drying step, a sputtering step, a classification step, a surface crosslinking step, and the like (US Pat. Nos. 6,727,345, 7,193,006 and 6,716,894). Accompanying the higher performance of disposable diapers as a main application, a water-absorbent resin has also been required for many functions. Specifically, it has been required that many physical properties including not only high water absorption capacity alone, but also gel strength, water soluble content (US Patent Reissue No. 32,649), velocity of water absorption, pressure absorption (US Patent No. 5,149,335), liquid permeability, particle size, urine resistance, antibiotic property, resistance to impact, powder fluidity, deodorant property, color fastness, low powder dust, and the like are imparted to a water-absorbent resin. For this reason, many proposals such as surface crosslinking technology, additives, modification of production steps have been proposed also in other documents in addition to US Pat. Nos. 6,727,345, 7,193,006, 6,716,894, U.S. Patent Reissue No. 32,649, U.S. Patent Nos. 5,149,335 and 5,562,646, U.S. Patent Application Publication No. 2005/02556469, U.S. Patents

Nos. 7,169,843, 7,173,086, 6,414,214, 6,849,665, US Patent Application Publication Nos. 2008/0125,533, 2007/0293,617, 2002/0128,618, 2005/0,245,684. , application WO 2006/082197, US Patent Application Publication No. 2008/202 987, WO 2006/082189, WO 2008/025652, WO 2008/025656, WO 2008/025655. , U.S. Patent Application Publication Nos. 2010/041 550, 2010/042 612.

In recent years, as the amount of water absorbent resin used in disposable diapers has increased (eg, 50% or more by weight), liquid permeability has been considered a factor. most important. In addition, many improvement processes or modification technologies for fluid permeability under load or unloaded liquid permeability, such as SFC (salt flow conductivity / US Patent No. 5,562,646) and GBP ( gel bed permeability / US Patent Application Publication No. 2005/0256,469, US Pat. Nos. 7,169,843 and 7,173,086) and the like have been proposed.

In such physical properties, many combinations of a plurality of parameters including liquid permeability have also been proposed, and a technology is known to specify a Frangibility Index (FI) (US Patent No. 6,414,214). , a technology for specifying a water absorption rate (FSR / Vortex) or the like (US Patent No. 6,849,665), and a technology for specifying a salt flux conductivity (SFC) product and absorption by capillarity after 60 minutes (DA60) (US Patent Application Publication No. 2008/0125,533).

In addition, as a method for improving liquid permeability, such as salt flow conductivity and gel bed permeability, there is known a technology for adding gypsum before or during polymerization (US Patent Application Publication No. 2007/0 293 617), a technology for adding a spacer group (US Patent Application Publication No. 2002/0128,618), a technology using a nitrogen polymer having 5 to 17 [moles / kg] of an atom. protonating nitrogen (US Patent Application Publication No. 2005/0245684), a technology for using a polyamine and a polyvalent metal ion or a polyvalent anion (WO 2006/082197), a coating technology a water-absorbent resin having a pH of less than 6 with a polyamine (US Patent Application Publication No. 2008/202 987), and a technology for using a polyammonium carbonate (WO 2006/082 189). In addition to these technologies, there is known a technology for using a polyamine in a base polymer having an extractable material amount greater than 3% by weight, and a technology for specifying a capillarity index (WI) or a gel strength (WO applications). 2008/025652, WO 2008/025656, WO 2008/025655). In addition, to improve color and liquid permeability, there is also known a technology for using a polyvalent metal salt while controlling methoxyphenol which is a polymerization inhibitor in the polymerization (US Patent Application Publication No. 2010/041 550 and 2010/042 612). In addition, there is also known a technology for electrostatic charge elimination focused on the classification step (U.S. Patent Application Publication No. 2011/116,300). In addition, there is also known a technology for improving liquid permeability focused on the classification step (WO 2011/115 216 and WO 2011/115 221).

In addition, attention was drawn to the rate of water absorption (eg, FSR and Vortex) as a physical property other than liquid permeability, and foaming polymerization (which will be described below) has been proposed as a method for improving a water absorption rate. However, it is generally difficult to obtain at the same time a water absorption rate and a liquid permeability. A water-absorbent resin in a spherical form, as well as in an irregular shape, is known for a form of a water-absorbent resin. The spherical water-absorbent resin is produced with difficulty because of its shape (which will be described below). Although droplet polymerization (which will be described below) has been proposed as a method for improving liquid permeability, it is difficult to improve liquid permeability because the water-absorbing resin obtained by the polymerization of droplets has a spherical shape.

summary

Many of the surface crosslinking techniques, additives, and variations in the preparation steps have been proposed in US Pat. Nos. 6,727,345, 7,193,006, and 6,716,894, US Pat. 32,649, U.S. Patent Nos. 5,149,335, 5,562,646, U.S. Patent Application Publication No. 2005/02556,469, U.S. Patent Nos. 7,169,843, 7,173,086, 6,414,214 and 849,665, US Patent Application Publication Nos. 2008/0125,533, 2007/0293,617, 2002/0128,618 and 2005/0245,684, WO 2006/082197, patent application publication. U.S. Patent Application Serial No. 2008 / 02,0987 WO 2006/082189, WO 2008/025652, WO 2008/025656, WO 2008/025655, US Patent Application Publication Nos. 2010/041 550, 2010. / 042 612 and 2011/116 300, WO 2011/115 216 and WO 2011/115 221, and the like to improve the physical properties of a water-absorbent resin.

However, a change or addition of raw materials of a water-absorbent resin, such as a surface-crosslinking agent or an additive (polyamine polymer, inorganic fine particle, or thermoplastic polymer) have sometimes caused not only a decrease in the safety of raw materials or an increase in cost, but also a deterioration of other physical properties. In addition, the addition of a new production process not only provided a cost increase factor due to the costly investment of the facility or energy for it, but also contrary a deterioration of productivity or physical properties, because of the requirement for an operation industrially complicated in some cases.

For this reason, an object of the present invention is, in order to solve the problems, to provide a method for improving and stabilizing the physical properties (e.g., liquid permeability) of a water-absorbent resin by a simple technique. and advantageous without requiring modification of raw materials or expensive installation investment. The foregoing problems tend to be remarkably present for a water-absorbent resin having a high water absorption rate and a spherical water-absorbent resin, typically a spherical water-absorbent resin obtained by suspension polymerization. reverse phase or droplet polymerization. Thus, the present invention may be advantageously applied to the production of a water-absorbent resin as mentioned above.

The present inventors have found that in the production, in particular, in a continuous production of a water-absorbent resin, even in a continuous production at a flow rate equal to or greater than 1 [t / h], even when the techniques in US patents

Nos. 6,727,345.7,193,006 and 6,716,894, US Patent Reissue No. 32,649, US Patent Nos. 5,149,335,5,562,646, US Patent Application Publication No. 2005/0256,469, US Patent Application Serial Nos. U.S. Patent Nos. 7,169,843, 7,173,086, 6,414,214 and 6,849,665, U.S. Patent Application Publication Nos. 2008/0125,533, 2007/0293,617, 2002/0128,618 and 2005/0. 245,684, WO 2006/082197, US Patent Application Publication No. 2008/202 987, WO 2006/082189, WO 2008/025652, WO 2008/025656, WO 2008/025655. , US Patent Application Publication Nos. 2010/041 550, 2010/042 612 and 2011/116 300, WO 2011/115 216 and WO 2011/115 221, in particular WO 2011/115 216 and WO 2011/115 221, are adopted, one can observe a deterioration of the physical properties. Thus, they have studied a cause of such deterioration and, therefore, they have found that even when there is no problem in continuous operation, the capacity of the apparatus itself deteriorates, forming a small amount of an adhering product or a collapsible thin film comprising a mixture of water-absorbent resin powder or water-absorbent resin fine powder with water at a contact surface with a water-absorbent resin in a production apparatus after a drying step. They further found that as a method for removing aggregates, a washing method other than washing with water results in insufficient recovery of physical properties. For this reason, they have found such problems and discovered solutions for them by subjecting the contact surface with the water-absorbent resin in the production apparatus after the washing step with water washing.

Specifically, in order to solve the problems described above, the present invention relates to a process for the continuous production of a polyacrylic acid (salt) water-absorbent resin, comprising successively a polymerization step of polymerizing an aqueous acid solution. (salt) acrylic to obtain a gel-like crosslinked polymer containing water; a drying step of drying the gel-like crosslinked polymer containing water to obtain a dried water-absorbent resin; a classification step of classifying the dried water absorbent resin to obtain water-absorbent resin particles; and a surface crosslinking step of subjecting the water-absorbing resin particles to surface crosslinking before and / or after the classification step, a surface of a device that is used in one or more of the steps after The drying step and the contacts with the water-absorbent resin being washed with water.

According to a second aspect of the invention which has the same spirit as in the preceding invention, the present invention relates to a process for the continuous production of a polyacrylic acid (salt) water-absorbent resin, comprising successively a step polymerization process comprising polymerizing an aqueous (salt) acrylic acid solution to obtain a gel-like crosslinked polymer containing water; a drying step of drying the gel-like crosslinked polymer containing water to obtain a dried water-absorbent resin; a classification step of classifying the dried water absorbent resin to obtain water-absorbent resin particles; and a surface crosslinking step of subjecting the water-absorbent resin particles to surface crosslinking before and / or after the classification step, wherein the water-absorbent resin has a rate of absorption of (FSR) equal to or greater than 0.30 [g / g / s], and a surface of a device that is used in one or more of the steps after the drying step and contacts with the water-absorbent resin is washed with water.

According to a third aspect of the invention which has the same spirit as in the preceding invention, the present invention relates to a process for the continuous production of a polyacrylic acid (salt) water-absorbent resin, comprising successively a step polymerization process comprising polymerizing an aqueous (salt) acrylic acid solution to obtain a gel-like crosslinked polymer containing water; a drying step of drying the gel-like crosslinked polymer containing water to obtain a dried water-absorbent resin; a classification step of classifying the dried water absorbent resin to obtain water-absorbent resin particles; and a surface crosslinking step of subjecting the water-absorbent resin particles to surface crosslinking before and / or after the classification step, wherein the water-absorbing resin is a spherical water-absorbent resin or a granulated substance thereof, and a surface of a device that is used in one or more of the steps after the drying step and the contacts with the water-absorbent resin is washed with water.

According to the present invention, in the process for producing a water-absorbent resin, comprising a polymerization step, a drying step, a classification step, and a surface-crosslinking step, the physical properties (e.g. permeability to liquids) after surface crosslinking can be maintained to be superior.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a flowchart schematically illustrating a continuous production step for obtaining a water-absorbent resin of the present invention.

DETAILED DESCRIPTION

Hereinafter, the continuous production process of a polyacrylic acid (salt) water-absorbent resin according to the present invention will be described in detail. However, a scope of the present invention should not be limited to these descriptions, and embodiments other than the following exemplifications may also be modified according to the situation and carried out in a range not affecting the essential point of the invention. the present invention. Specifically, the present invention should not be limited to each of the following embodiments, and various variations are possible within a scope defined in the claims, and embodiments achieved by combining the situation with Each of the various technological embodiments are also encompassed within the technological scope of the present invention.

[1] Definition of terms (1-1) "Water-absorbing resin" and "water-absorbing resin powder"

The "water-absorbent resin" in the present invention refers to a water-swellable and water-insoluble polymeric gelling agent. The "swelling property in water" means that the no-load absorption capacity (CRC) as specified in ERT441.2-02 is substantially equal to or greater than 5 [g / g], preferably 10 to 100 [g / g], and more preferably 20 to 80 [g / g]. In addition, the "insolubility property in water" means that the Ext (water-soluble content) as specified in ERT470.2-02 is substantially equal to or less than 50% by weight (lower limit: 0% by weight ), preferably equal to or less than 30% by weight, more preferably equal to or less than 20% by weight, and still more preferably equal to or less than 10% by weight.

In addition, "water-absorbent resin powder" refers to a water-absorbent resin having a certain degree of fluidity as a powder. For example, it refers to a water-absorbing resin whose flow rate (fluidity) as specified in ERT450.2-02 can be measured, or which can be graded with a sieve by PSD (particle size) as specified in ERT420. .2-02. Specifically, it refers to a water-absorbent resin having a particle diameter equal to or less than 5 mm, as specified by sieve classification.

The water-absorbent resin is suitably designed for the applications. It is not particularly limited, but is preferably a hydrophilic crosslinked polymer obtained by crosslinking polymerization of an unsaturated monomer having a carboxyl group. The water-absorbent resin is not limited to a form in which the total amount (100% by weight) is a polymer, and may include an additive and the like in a range to maintain performance. That is, even a water-absorbent resin composition containing a water-absorbent resin and an additive is generically referred to as "the water-absorbing resin in the present invention".

When the water-absorbent resin is a water-absorbent resin composition, the content of the water-absorbent resin (a polyacrylic acid (salt) water-absorbent resin) is preferably from 70 to 99.9. % by weight, more preferably from 80 to 99.7% by weight, and still more preferably from 90 to 99.5% by weight. As a component other than the water-absorbing resin, in the light of the rate of water absorption or the impact resistance of the powder (particles), water, and the additives are preferred. to be described later can be contained as needed.

(1-2) "Continuous production process"

The term "continuous" in the continuous production process of the present invention means that the production steps according to the present invention (e.g., a polymerization step, a drying step, a classification step, and a crosslinking step of surface) are carried out continuously for a day or more to produce a water-absorbent resin. In this case, not all production steps need to be performed continuously, and the continuous production method of the present invention includes an embodiment where the production steps that are performed in batches are repeated (batch extension). ) and an embodiment where only a part of the production steps is stopped. In addition, an idle period (e.g., a period to cool an apparatus) and the like may be provided when the production steps are performed in batches. In the present invention which includes a batch extension embodiment, 50% or more of the entire production process is preferably operated.

During the production period in the present invention, the production is substantially continuously carried out preferably for 30 days or more, more preferably 50 days or more, and particularly preferably 100 days or more, to produce an absorbent resin. water. In addition, an upper limit of the production period is preferably long, and thus the upper limit is not particularly limited, but is preferably equal to or less than 365 days, more preferably 300 days or less, and in particular preferably equal to or less than 200 days.

(1-3) "Polyacrylic acid (salt thereof)" "Polyacrylic acid (salt thereof)" in the present invention refers to a polymer having acrylic acid and / or a salt thereof (hereinafter referred to as "acrylic acid (or one thereof)" in some cases) as the main component as a repeating unit and optionally comprising a graft component. Specifically, it denotes a polymer containing acrylic acid (or a salt thereof) of substantially 50 to 100% by mole, preferably 70 to 100% by mole, more preferably 90 to 100% by mole, and more preferably more preferably substantially 100% per mole, as a monomer excluding a crosslinking agent. The salt as a polymer contains substantially a water-soluble salt, and is preferably a monovalent salt, more preferably an alkali metal salt or an ammonium salt, still more preferably an alkali metal salt, and particularly preferably a salt thereof. sodium. In addition, although the shape is not particularly limited, a particulate form or a powder form is preferred.

(1-4) "EDANA" and "ERT" "EDANA" is an abbreviation for European Disposables and Nonwovens Associations (European associations of disposables and nonwovens). "ERT" is an abbreviation of a measurement method (ERT / EDANA recommended test method) of a water-absorbent resin based on European standards (practically worldwide standards). In addition, in the present invention, unless otherwise indicated, the physical properties of a water-absorbent resin are measured in accordance with the original ERT text (known document: revised 02 02).

(a) "CRC" (ERT441.2-02)

"CRC" is an abbreviation for centrifugal retention capacity and refers to the no-load absorption capacity (hereinafter referred to as "absorption capacity" in some cases). Specifically, CRC is the absorbency (unit; [g / gl) after 0.2 g of a water-absorbent resin in a nonwoven fabric is freely swollen in an excess amount of an aqueous solution. 0.9% by weight of sodium chloride for 30 minutes, and is dehydrated by a centrifuge.

(b) "AAP" (ERT442.2-02) "AAP" is an abbreviation for Absorption Against Pressure and refers to the absorption capacity under load. Specifically, the AAP is the absorption capacity (unit; [g / g]) after 0.9 g of a water-absorbent resin is swollen in an excess amount of 0.9 aqueous solution. % by weight of sodium chloride for 1 hour under a load of 2.06 kPa (0.3 psi, 21 [g / cm 2]). Moreover, in ERT442.2-02, it is called Absorption Under Pressure, but is defined essentially the same as AAP. In the present invention, the measurement was made with the change in the load condition to 4.83 kPa (0.7 psi, 50 [g / cm 2]).

(c) "Ext" (ERT470.2-02) "Ext" is an abbreviation for Extractives and refers to a water-soluble content (content of water-soluble products). Specifically, the measurement is made by adding 1.0 g of a water-absorbent resin to 200 ml of 0.9% by weight aqueous sodium chloride solution, stirring the mixture at 500 rpm for one hour. 16 hours, then measuring the amount of a dissolved polymer by pH titration (unit:% by weight).

(d) "Residual Monomers" (ERT410.2-02)

"Residual monomers" refers to a quantity of monomers remaining in a water-absorbent resin. Specifically, the amount of monomers is a value (unit; ppm) measured by adding 1.0 g of a water-absorbent resin to 200 ml of a 0.9% by weight aqueous solution of sodium chloride, stirring the mixture at 500 rpm for 1 hour and then measuring the amount of residual monomers dissolved in the solution using high performance liquid chromatography (HPLC).

(e) "PSD" (ERT420.2-02) "PSD" is an abbreviation for Particle Size Distribution and refers to a particle size measured by sieve classification. An average particle diameter by weight (D50), and a particle diameter distribution and a width thereof (logarithmic standard deviation σζ) can be measured by the method described in "(1) average particle diameter and particle size distribution. In addition, in the case of a measurement of a particle diameter of a particulate gel-like particulate crosslinked polymer containing water, the measurement is carried out in accordance with US Pat. No. 1,594,556. to the process described in JP-A-2000-063 527.

(f) Other physical properties specified in EDANA

"PH" (ERT400.2-02) refers to the pH of a water-absorbent resin.

"Moisture content" (ERT 430.2-02) refers to a moisture content of a water-absorbent resin.

"Flow" (ERT 450.2-02) refers to the downward flow rate of a water-absorbing resin.

"Density" (ERT 460.2-02) means the specific bulk density of a water-absorbing resin.

"Respirable particles" (ERT480.2-02) means a respirable dust of a water-absorbent resin.

"Dust" (ERT490.2-02) refers to dust embedded in a water-absorbent resin.

(1-5) "Liquid Permeability"

"Liquid permeability" in the present invention refers to the flow property of a liquid flowing between charged or unloaded swollen gel particles. "Liquid permeability" can be measured for SFC (salt flow conductivity) or GBP (gel bed permeability) as a representative measurement method.

"SFC (Saline Flow Conductivity)" means a liquid permeability of 0.9 g of a water-absorbent resin to an aqueous solution of 0.69% by weight of sodium chloride under a load of 2.06 kPa ( 0.3 psi), and is measured according to the SFC test method described in US Pat. No. 5,669,894. In addition, "GBP (gel bed permeability)" refers to the liquid permeability of an absorbent resin. the water to a 0.69 wt.% aqueous solution of sodium chloride under load or free expansion, and is measured in accordance with the GBP test method described in WO 2005/016393.

(1-6) Others

In this description, "X to Y" indicating a range means "equal to or greater than X and equal to or less than Y". In addition, the unit of weight "t (ton)" means a "metric ton". Unless otherwise indicated, "ppm" refers to "ppm by weight" or "ppm by mass". In addition, "weight" and "mass", "% by weight" and "% by weight", and "part by weight" and "part by mass" are used interchangeably with the same meanings. In addition, "-acid (salt)" refers to "-acid and / or salt thereof", "(meth) acryl" refers to "acryl and / or methacryl", respectively. In addition, the measurement of physical and similar properties is carried out under ambient temperature conditions (20 to 25 ° C) / relative humidity of 40 to 50% unless otherwise indicated.

[2] Water washing process for production apparatus for polyacrylic acid (salt) water-absorbent resin (2-1) Washing with water

The present invention relates to a process for the continuous production of a polyacrylic acid (salt) water-absorbent resin, comprising successively a polymerization step of polymerizing an aqueous solution of acid (salt) acrylic so as to obtain a polymer cross-linked gel-like material containing water; a drying step of drying the gel-like crosslinked polymer containing water to obtain a dried water-absorbent resin; a classification step of classifying the dried water absorbent resin to obtain water-absorbent resin particles; and a surface crosslinking step of subjecting the water-absorbing resin particles to surface crosslinking before and / or after the classification step, a surface of a device that is used in one or more of the steps after the drying step and the contacts with the water-absorbent resin being washed with water. Hereinafter, washing with water in the present invention will be described in detail.

The present invention has a water wash feature of a contact surface with a water-absorbent resin of a continuous production apparatus after the drying step. The "water wash" in the present invention may be carried out continuously together with the production of the water-absorbent resin or intermittently periodically, but is preferably carried out intermittently periodically. In the case where no washing with water or in the case of washing other than washing with water is carried out, the physical properties (in particular the permeability to liquids and the quantity of fine powder ) would be altered over time or not sufficiently recovered after washing, which is not preferable.

A material to be washed away with water may usually be a water-absorbent resin powder (typically one that passes through a JIS standardized sieve having a mesh size of 1000 μτη), particularly a fine powder of water-absorbent resin (typically one which passes through a JIS standardized sieve having a sieve mesh size of 150 μτη) or aggregates thereof, or aggregates consisting of a mixture of resin powder absorbing the water or fine powder of water-absorbent resin with water that is attached to a production apparatus for a water-absorbent resin. The aggregates are generated in a step of adding water or an aqueous solution to a water-absorbent resin or derived from dew condensation water formed in the apparatus.

The present inventors have found that in the production, in particular, in the continuous production of a water-absorbent resin, further in a continuous production equal to or greater than 1 [t / h], even when the techniques in the patents US No.

6,727,345, 7,193,006, and 6,716,894, US Patent Reissue No. 32,649, US Patent Nos. 5,149,335, 5,562,646, US Patent Application Publication No. 2005/0256,469, U.S. Patent Nos. 7,169,843, 7,173,086, 6,414,214 and 6,849,665, U.S. Patent Application Publication Nos. 2008/0125,533, 2007/0293,617, 2002/0128,618 and 2005 / 0 245 684, WO 2006/082197, US Patent Application Publication No. 2008/202 987, WO 2006/082189, WO 2008/025652, WO 2008/025656, WO 2008/025. 655, US patent application publications NO. 2010/041 550, 2010/042 612 and 2011/116 300, the applications WO 2011/115 216 and WO 2011/115 221 are adopted, we see that the physical properties deteriorate gradually. In this sense, they have studied that the capacity of the apparatus itself deteriorates, by fixing a small amount of water-absorbent resin powder or aggregates consisting of a mixture of fine powder of resin absorbing the water. water with water at a contact surface with a water-absorbent resin in a production apparatus after a drying step. In addition, they have found that by washing processes other than washing with water as a method for removing aggregates, the physical properties are insufficiently recovered.

Thus, the continuous production process of the present invention can be appropriately controlled on a very large scale. From this point of view, in the present invention, the productivity of a water-absorbing resin per line is preferably equal to or greater than 1 [t / h], more preferably equal to or greater than 1.5 [t / h]. ], still more preferably equal to or greater than 2 [t / h], and in particular preferably equal to or greater than 3 [t / h]. The upper limit of productivity is not particularly limited, but it can be suitably determined, and can be, for example, 10 [t / h], and the like. The term "one line" refers to series production steps for the production of a water-absorbent resin, and in the case of a division of the steps, it is defined as the amount of treatment in a step surface crosslinking (a device).

(Wash cycle with water)

In the case of carrying out intermittently periodically washing with water, a wash cycle with water is not particularly limited, but it can be suitably selected from, for example, every 12 hours, every day, every 10 days, every 30 days, every 40 days, every 45 days, every 60 days, every 75 days, every 120 days, every 150 days, and the like. In addition, the upper limit of the latter corresponds to a large-scale maintenance of a production apparatus which is carried out once a year, but it can be appropriately selected from, for example, every 300 days, all 200 days, and the like, depending on the amount of production, the number of products, or the like.

For this reason, the water wash cycle in the present invention can be determined in advance from the cycles described above, but is preferably determined based on a decrease or change in properties. while confirming the physical properties of the resulting water-absorbent resin. The decrease or change in physical properties can be determined by various physical properties as described later in [4], in particular, the absorption capacity under load (eg, AAP), liquid permeability (e.g. SFC), the particle size (in particular, the amount of fine powder, moreover one that passes through a standardized JIS sieve having a sieve mesh size of 150 μιη), or the like, and typically by particle size or liquid permeability. Preferably, a time when washing with water is performed is determined by a change in particle size (particle size) or a change in liquid permeability. More specifically, the water wash cycle in the classification step is determined by a change in particle size (particle size) or a change in liquid permeability after the classification step.

During washing with water, the operation of a production apparatus for washing with water can be stopped temporarily or the production of a water-absorbent resin can be continued by replacement with a replacement apparatus. In addition, the water wash may be performed in the intact apparatus, or may be performed with the decomposition of part or all of the device, such as a revision. During continuous production, the same water-absorbing resin can be produced substantially under the same production conditions, or a different water-absorbing resin can be produced by modifying the production conditions.

(Wash water) The water used for washing with water in the present invention (hereinafter referred to as "wash water" in some cases) is not limited to water alone (100% by weight of water). water), but in order to improve the effects by washing, a small amount of a solvent or an additive may be incorporated. The water content is preferably equal to or greater than 90% by weight, more preferably equal to or greater than 95% by weight, still more preferably equal to or greater than 99% by weight, in particular preferably equal to or greater than 99.9% by weight. % by weight, and most preferably substantially 100% by weight. The water may suitably be selected from industrial pure water, tap water, groundwater, distilled water, deionized water, rainwater, and the like. Of these, industrial pure water and tap water are preferably used, and industrial pure water is more preferably used.

The additive (solvent) is not particularly limited, but examples thereof include water-soluble organic solvents such as methanol, ethanol, isopropanol, and acetone, and even more preferably organic solvents. water-soluble having a low boiling point of 30 to 100 ° C; alkali metal salts such as sodium chloride, sodium sulfate, and potassium chloride; alkaline earth metal salts such as calcium chloride and magnesium chloride; trivalent or higher valence polyvalent metal salts such as aluminum sulphate; bases such as sodium carbonate, sodium bicarbonate and sodium hydroxide; various surfactants; and adjuvants, and the like. A combination of the inorganic salts and / or alkaline aqueous solutions may be used, but the water is used in an amount within the previously described range of profitability and contamination in the water-absorbent resin, and the like.

(Washing water temperature)

A form of wash water used in the water wash of the present invention is not particularly limited, but water in the form of gas or liquid can be used, but water under the liquid form is particularly preferable. A wash water temperature is suitably determined in the higher range than that from a freezing point to a boiling point. However, warm water is preferred from the effect point of view by washing. Specifically, a hot water temperature is preferably higher than room temperature (20 to 25 ° C) to the boiling point, more preferably 30 to 100 ° C, still more preferably 35 to 100 ° C. in particular preferably from 40 to 95 ° C, and most preferably from 45 to 90 ° C. Moreover, in the case of the use of steam as water in the form of gas, the water is used in the form of steam heated to normal pressure with a temperature preferably equal to or lower than 500 ° C, more preferably equal to or less than 300 ° C, and still more preferably equal to or less than 200 ° C. In the case where a washing water temperature is too low, the effects by washing would be deteriorated, which is not preferable. On the other hand, in the case where the washing water temperature is too high, an effect proportional to the adaptation of a means of increase of energy or of boiling point (use of an increase of pressure or additive) can not be obtained, and the workability during washing with water would be deteriorated or a worker could be burned and the like, which is not preferable.

(Pressure during washing with water)

The water wash in the present invention can be carried out under any pressure of normal pressure, increased pressure, and reduced pressure, and is not particularly limited. In the case of the use of water in the form of a liquid, the boiling point of the water (the highest temperature of the water in the form of liquid) may be increased or decreased from 100 ° C by the pressure and additives described above. From the point of view of cost-effectiveness, washing with water is preferably carried out under normal pressure or normal pressure ± 5%, or normal pressure ± 1% (in the ordinary range of atmospheric pressure fluctuation).

(Washing process with water)

The water-washing process for a continuous production apparatus of a water-absorbent resin in the present invention is not particularly limited, but the water-washing can be carried out while continuing the production of the water-absorbing resin. water-absorbent resin, or water-washing may be performed while stopping temporarily or periodically the production of water-absorbent resin. Examples of the method for washing with water while continuing the production of water-absorbent resin include a method which comprises continuously spraying a stream of water on a production apparatus, and a method which includes spraying a stream of water while continuously drying, and the like. In addition, examples of the method for effecting a water wash while temporarily or periodically stopping the production of water-absorbent resin include a method which comprises washing with water of part or all of the water-absorbing resin. a device after temporary or periodic shutdown of the device, and the like. In addition, the water washing process is not particularly limited, but examples thereof include a method of spraying water directly onto a production apparatus, a method of showering water on an apparatus process, a method of immersing a production apparatus in water, a method of wiping a production apparatus with water, and a method of brushing a production apparatus with water water, and the like. These methods can be used in combination with each other, and can be repeated several times. However, it is preferable to subject a contact surface to a water-absorbent resin of the production apparatus after the drying step to a water wash by immersion in water or vaporization with water .

In addition, the washing with water can be carried out at one place, and preferably in a plurality of places, and in particular preferably, the washing with water is carried out in other production apparatus including a classification apparatus (in particular, a metal screen) used in the classification step or apparatus used in the surface crosslinking step. That is, the water wash is preferably carried out at least in the classification step or the surface crosslinking step, and more preferably at least in the classification step.

(Immersion)

In the present invention, "immersion" refers to a process in which all or part of the production apparatus or a decomposition product thereof is immersed in a large amount of excess water (wash water ) to inflate a fixed water-absorbent resin in a location where physical removal of the water-absorbent resin is difficult, such as dead volume, thereby facilitating the removal of the water-absorbent resin .

In the present invention, "immersion" includes an embodiment where water is "filled" in an apparatus for reaction, filling, storage and the like of a water-absorbent resin (for example, a hopper, a conduit, a heat treatment apparatus, a cooling apparatus, and the like) for washing, which is sometimes referred to as "water injection and filling". Specifically, the water wash according to the present invention is performed by immersing an apparatus in water or by injecting (filling) water into an apparatus, which is collectively referred to as water immersion.

In the present invention, the immersion time is not particularly limited, but is preferably 1 minute to 10 days, more preferably 1 hour to 5 days, and still more preferably 1 hour to 3 days. The immersion time is appropriately selected in the range described above.

The wash water during the immersion may be either static (without agitation) or dynamic (agitation including a stream of water and the like). The wash water after the immersion may be suitably exchanged or partially exchanged (weir), or reused several times.

(Pressurized water stream) The wash water used in the water wash of the present invention may be under pressure (hereinafter referred to as "pressurized water stream"). Concerning the degree of pressurization, it is possible to use a stream of water under pressure with an ultra-high pressure (relative pressure equal to or greater than 500 [kg / cm 2]), but from the point of view of the effects by washing, it is preferable to use a pressurized water stream preferably having a relative pressure of from 1 to 400 [kg / cm 2], and more preferably a relative pressure of about 5 to 200 [kg / cm 2]. Thus, there is no need for expensive equipment to obtain an ultra-high pressure water stream. The relative pressure may be appropriately selected depending on a production apparatus structure to be washed with water. For example, in the case where the production apparatus to be washed with water is a device having a weak or weak structure (for example, a sieve), it is preferable to carry out the washing with water at a relative pressure equal to or less than 200 [kg / cm2]. Thus, one can prevent the deformation or the corruption of the apparatus. On the other hand, in the case where the production apparatus to be washed with water is a device having a high intensity structure (for example, a vane dryer and a spraying device), washing with water can be performed at a higher relative pressure (for example, equal to or less than 400 [kg / cm 2]). When the pressurized water stream is sprayed, a flat nozzle, a rotary nozzle, or a forced suction type nozzle may be used.

An apparatus for generating a stream of water under pressure is not particularly limited, but a commercially available device may be used. Specific examples thereof include a high pressure washer manufactured by Sugino Machine Co., Ltd., an ultra-high pressure static wash unit manufactured by Isuzu Motor Syutoken Co., Ltd., Tokyo, Japan. automated high pressure washing manufactured by KIT Co., Ltd., a cleaning system manufactured by URACA Co., Ltd., and a hot water high pressure cleaner manufactured by Karcher Japan Co., Ltd, and the like. Depending on the production unit to be washed with water, the appropriate equipment can be selected.

(Production apparatus to be washed with water)

The water wash in the present invention is carried out for the apparatus for producing the water-absorbent resin after the drying step, in particular the production apparatus after the spraying step. From the point of view of effects by washing, the washing with water is preferably carried out for a production apparatus which is operated by heating, more preferably for the production apparatus which is operated by heating at 35 to 150 ° C, and still more preferably at 40 to 100 ° C. For the production apparatus which is operated in the temperature range described above, several tenths of% to several% by weight of moisture evaporate from a water-absorbent resin and collect, and this moisture forms aggregates together with the water-absorbent resin powder or the fine water-absorbent resin powder. The aggregates are probably attached to an internal surface or a dead volume of the production apparatus. On the other hand, in the case of the production apparatus to be heated to 100 ° C, or even to a high temperature exceeding 150 ° C, the water is evaporated and removed to the outside of the system, and there is a small occurrence of the problems described previously. In addition, in the case of the production apparatus which is operated at a temperature below 35 ° C and even below 40 ° C, the operating stability is insufficient, which is not preferable.

According to another possibility, it is preferable to carry out the washing with water in an agitator or vibrating device. The aggregates with the water-absorbent resin powder or the water-absorbent resin fine powder are easily attached to the inner surface or dead volume of the stirring or vibrating device. Thus, by performing a water wash for the device, the effects of the present invention (improving or stabilizing the physical properties, in particular liquid permeability, of a water-absorbing resin) can be effectively achieved. Here, the stirring or vibrating device is not particularly limited, but is preferably a mixing device used in the mixing step for mixing the water-absorbent resin with water or an aqueous solution; or a classification device used in the classification step. Here, examples of the mixing device include a mixing device and the like described below in the section of "(d) Mixing device in the mixing step (surface crosslinking step)". In addition, examples of the classification device include the following classification device (in particular of the vibrating type), the dryer (in particular, agitator-type or vibrating type), described in the section of "(3-2) Step of drying ", and the heat treatment device and the like, described below in the section of" (b) Heat treatment device in the heat treatment step (surface crosslinking step) ".

For the production apparatus to be washed with water, the contact surface with the water-absorbent resin may be coated with resin, but the surface is preferably made of stainless steel (materials; SUS304 or the like) with a surface roughness (Rz) preferably equal to or less than 150 nm, more preferably equal to or less than 100 nm, and still more preferably equal to or less than 50 nm. The lower limit of the surface roughness (Rz) is preferably 0 nm, but a value of about 10 nm would make a small difference, and even about 20 nm is sufficient. The surface roughness (Rz) designates a maximum height (nm) of surface irregularity. Another surface roughness (Ra) is also defined in JIS B 0601-2001. Hereinafter, the production apparatus to be washed with water will be described. The operating conditions and the like in each step will be described later in (3).

Hereinafter, the steps in which it is preferable to carry out the water wash step of the present invention will be described. In addition, the present invention is not limited to the following steps.

(a) Drying device in the drying step

Water washing in the present invention can be carried out for a drying device in the drying step in some cases. That is, the drying temperature (operating temperature) in the drying step is usually higher than the temperature range as previously described, and for this reason, it is believed that there is a small possibility that aggregates of a water-absorbent resin with water are attached to the drying device. However, when drying a water-absorbent resin, a cross-flow continuous band dryer or the like is usually used, and the gel-like fine particles containing water of a water-absorbent resin penetrate in an opening (holes or slots having a size ranging from several tenths to several tens of mm 2, preferably 0.2 to 10 mm 2) of a metal mesh, a punching plate, or the like used in the drying device . The particles are dried as they are, and thus, the openings are permanently sealed, resulting in deterioration of the dryer capacity, non-uniform local drying, or production of undried materials (rubbery materials during drying). ) in some cases. Water-gel-like fine particles which cause a permanent impediment are heated for a long period of time until they are colored in many cases. When these colored foreign materials are removed by chance, and incorporated into a water-absorbent resin as a product, the effects on the production apparatus are small, but the colored foreign materials are detected. For this reason, there is a risk that shipping of the product is not allowed.

As a countermeasure in this regard, in the present invention, an entire drying device, within a drying device (in particular, the contact surface with a water-absorbing resin), in particular , a metal mesh, a punch plate (porous plate), or the like, is preferably washed with water. The shape and the like of the metal mesh and punch plate (shape and pore size) is not particularly limited, and the metal mesh and the punch plate may have protruding or convex-concave portions.

Specifically, the water wash in the drying step of the present invention is performed for a metal mesh or a punch metal (punch plate) of a drying device to prevent pores from clogging. In particular, the water wash is more suitably applied to a water-absorbent resin having a high rate of water absorption (free swelling rate) and a spherical water-absorbing resin which induces significant clogging of the water. pores. As used herein, the term "spherical" is not limited to an absolute spherical shape, and includes a flattened, convexo-concave spherical shape and aggregates. It indicates a form of water-absorbing resin to be obtained by spray polymerization in a gaseous phase or by droplet polymerization. The metal to be punched is preferably used in a fluidized bed drier or a carpet dryer.

(b) Heat treatment device or cooling device in a heat treatment step or a cooling step (surface crosslinking step)

The water wash in the present invention can be carried out for a heat treatment device or a cooling device in the heat treatment step or the cooling step (surface crosslinking step) in some cases. The heat treatment step is a heat treatment step for further crosslinking reaction and modification of the resulting water-absorbent resin particles, for which ordinary kilns or furnaces may be used. Examples of the heat treatment device or cooling device used herein include, for example, a slotted mixing dryer, a tumble dryer, a vane dryer, a disk dryer, a fluid bed dryer, an air dryer, air stream, an infrared dryer, and the like.

Specifically, the water wash is preferably performed for an inner surface of at least one of a mixing device (described below in (d)), a heat treatment device and a cooling device in the surface crosslinking step. An additive other than a surface crosslinking agent may be added in the heat treatment device and the cooling device. Similarly, the heat treatment device and the cooling device can be used as the mixing device described below (see the section of (d) below). Preferably, an additive and a second surface crosslinking agent are added, in particular, preferably added with water.

In a manner similar to the drying step, the heat treatment temperature (operating temperature) in the heat treatment step is usually higher than the temperature ranges described above, and for this reason, it is believed that there is a slight possibility that aggregates of a water-absorbent resin with water are attached to the heat treatment device. However, a material to be heated (usually a mixture of a water-absorbent resin with a surface-crosslinking agent) is retained in a dead volume or the like in the device for a long time, to the point of being colored. When removed, the same colored foreign material as in the drying step is detected, and there is a risk that shipping of the product will not be allowed. As a countermeasure, the present invention is preferably applied.

(c) Classification scheme in the classification stage

The washing with water of the present invention is mainly carried out for a production apparatus after the drying step with stirring or vibration, in particular, for a production apparatus after a spraying step, as well as, for a production device classification in a classification step, in particular, a metal screen having a mesh size of 45 to 2000 μιη. Hereinafter, the classification device will be described in the classification step.

The classification step in the present invention is a step in which the particle size of the water-absorbent resin is controlled in a desired range with a sieve, and is performed before and / or after the surface-crosslinking step. In the present invention, a step of classifying into a predetermined particle size before the surface crosslinking is designated first classification step, a step of performing a classification after the surface crosslinking step is referred to as the second classification step ( granulation stage). In the present invention, it is preferable to perform both of these classification steps. That is, it is preferable to carry out the classification step before and after the surface crosslinking step.

In the classification step of the water-absorbent resin, a water-absorbent resin is placed in an opening of a used metal screen, which would cause a decrease in the classification efficiency, and an increase in the amount of fine powder and deterioration of physical properties. As a countermeasure, the present invention is preferably applied.

(Classification mesh)

In the present invention, a water-absorbent resin is classified using a metal screen. In the present invention, a metal screen is suitably washed with water.

As the metal screen to be washed with water, various standardized screens may be exemplified, for example, in JIS, ASTM, TYLER, or the like. These sieves may be a plate screen or a mesh screen. The shape of the mesh screen can be selected according to the situation with reference to JIS Z8801-1 (2000) or the like. A size of standardized sieve mesh is preferably from 10 μτη to 100 mm, more preferably from 20 μm to 10 mm, still more preferably from 45 to 2000 μτη, even more preferably from 50 μτη to 1 mm. One or more types of sieves are used, in particular metal sieves.

Specifically, in the present invention, a metal mesh is preferably washed with water, more preferably, a metal mesh having a mesh size of 50 μm to 1 mm is washed with water, more preferably preferably, a metal mesh used for drying or classification is washed with water, and in particular preferably, a metal mesh (mesh of sieve) used for the classification is washed with water.

The area of the screen mesh area (mesh area of a metal screen) is preferably from 1 to 10 [m2 / sheet], and more preferably from 1.5 to 7 [m2 / sheet], from point of view of classification efficiency.

By sieve classification, only the upper part, or only the lower part can be obtained by classification. The upper and lower parts are preferably obtained by classification at the same time. That is, a plurality of sieves are preferably used at the same time, and even more preferably, in the light of improved physical properties, sieves with at least three types of mesh size are used. sieve. As such technique, in addition to the predetermined sieves for the upper and lower portions, an intermediate sieve or an upper sieve is preferably used. A suitable sieve is, for example, a sieve having an upper sieve size limit of 850 to 1000 μπι, 710 to 850 μιη, or 600 to 710 μιη, and a lower sieve mesh size limit of 150 to 225 μτη. Even more preferably, depending on the situation, it is possible to add a sieve at a central or upper part. (Classification device)

A classification device for use in the present invention is not particularly limited so long as it has a sieve mesh surface, and may include, for example, those classified as a vibrating screen and a shifter. The vibrating screen may include an inclined type, a low head shape, Hum-sea, Rhewum, Ty-Rock, Gyrex, Eliptex, and the like. The shifter may comprise a reciprocating type, Exolon-grader, Traversator-sieb, Sauer-meyer, Gyratory shifter, Gyro-shifter, a Ro-tex screen, and the like. They are more precisely sorted on the basis of a type of movement (circle, ellipse, rectilinear line, arc, pseudo-ellipse, spiral, spiral type) of a mesh surface, of a vibration system (free vibration, forced vibration), of a type of drive (eccentric axis, fall of unbalanced weight, electromagnet, and impact), of the inclination (horizontal system, inclined system) of a mesh surface, of an installation method (type installed and suspended type), and the like. Among these, a classification device having a screen mesh surface moving in a three-dimensional orbit including an eccentric radial inclination (inclination of a mesh screen which disperses a material from the center to the periphery), or a tangential inclination (inclination of a mesh screen which controls a speed of evacuation on the mesh).

Among these, in the light of the effects of the present invention, there is preferably used a classification device having a screen mesh surface moving in a spiral by a combination of radial inclination and tangential inclination, as a type. with vibration (shifter or grooving machines).

(d) Mixing device in the mixing step (surface crosslinking step)

The washing with water of the present invention is mainly carried out for a production apparatus after the drying step with stirring or vibration, in particular, for a production apparatus after a spraying step, and it is further carried out in a mixing device in a mixing step of mixing water or an aqueous solution with a water-absorbing resin (preferably a surface-crosslinking step or a subsequent step). Hereinafter, the mixing device will be described in the mixing step. The mixture of an additive is also described in the section of (3-8).

The mixing step in the present invention is a step of adding an additive, water, or an aqueous solution for further crosslinking reaction and modification of the water-absorbent resin, and it can be carried out by using an ordinary dynamic or static mixer. In addition, even in the case of adding an additive during cooling in the surface crosslinking step, such an addition is involved in the present mixing step.

Specifically, in the present invention, an inner surface of a mixing device for mixing a water-absorbent resin with water, an aqueous solution, or an aqueous dispersion is preferably washed with water. More preferably, an inner surface of a mixing device in a surface crosslinking step or a subsequent mixing step is washed with water.

In the mixing step for a water-absorbent resin, water or an aqueous solution is mixed with the water-absorbing resin, and thus, the moisture content of the resin is expected water absorbing increases to induce an increase in viscosity. For this reason, there are many instances where the high viscosity water absorbing resin is attached to a dead volume and the like in a mixing device and is held for a long time until it is colored. When these colored foreign materials are removed by some equipment and are incorporated into a water-absorbing resin as a product, although the effects on a production apparatus are small, since the colored foreign materials are detected, the product presents a risk of not being shipped. For this reason, as a counter-measure to this problem, the present invention is preferably applied to washing the mixing device with water.

Examples of the mixing device used in the present invention include a high speed stirring type mixer (high speed continuous mixer), a plow mixing device, a cylindrical mixing device, a double walled conical mixer, V-shaped mixer, ribbon type mixer, screw type mixer, fluidized furnace rotary disk type mixer, air flow type blender, twin cell mixer, internal mixer, blender grinding type, a road stabilizer, a screw extruder, and the like. Of these, a high speed stirring mixer having a stirring axis equipped with a plurality of stirring panels or stirring blades is preferred, and a high speed stirring mixer having a spindle is more preferred. agitator equipped with a stirring blade (for example, a Turbulizer or Proshare mixer).

The high speed stirring mixer designates a mixer in which a stirring shaft equipped with a plurality of stirring panels is rotated at a speed of usually 100 to 5000 rpm, preferably 200 to 4000 rpm, and more preferably 500 to 3000 rpm to generate a mixing force. In the present invention, the mixture is preferably carried out in the high speed stirring mixer within 3 minutes, and more preferably within 1 minute (with the lower limit of about 1 second), and continuous mixing is particularly preferable. .

(e) Spray device in the spraying step

The water wash of the present invention can also be performed for a spraying device in the spraying step. The spraying step is a step of spraying the dried water-absorbent resin or coarse particles that do not pass through a metal screen in the classification step, and the like, so as to obtain an absorbent resin. water spray. It may also comprise a step of spraying the aggregates obtained in the mixing step or in the heat treatment step.

Examples of the spraying device used in the present invention include a knife mill, hammer mill / pin mill / jet mill, roller mill, hammer mill, roller granulator, mill crusher. jaws, a gyratory crusher, a cone crusher, a roller crusher, a grinder, and the like, and a spraying device known in the prior art can also be used. In addition, those equipped with means for heating the inner wall of the spray device are preferred.

The spraying step is preferably carried out in an external heating state of the inner wall of the spraying device, in a state of adjusting the temperature of an inner wall of the spraying device at 30 to 150 ° C, or in a state where the temperature of an inner wall of the spray device is prevented from being lowered by at least 20 ° C with respect to the powder temperature of the water-absorbent resin.

(f) Transport device in the transport stage

Washing with water in the present invention can be carried out for a transport device in a transport step, in some cases. The transporting step is a step of conveying the water-absorbent resin such as the dried water-absorbent resin after drying, the water-spray-absorbing resin after spraying, and the like.

Examples of the transportation device used in the present invention include an air conveyor, a belt conveyor, a screw conveyor, a chain conveyor, a vibrating conveyor, a pneumatic conveyor, and the like, and those equipped with a means of transportation. external heating of an inner wall and / or a heating means of an inner wall are preferable. Among these, an air conveyor is particularly preferable.

(g) Storage device in the storage step

Water washing in the present invention can be performed for a storage device in a storage step. The storage step is a step of storing a water-absorbent resin such as a dried water-absorbent resin after drying and a water-spray-absorbed resin after spraying. That is, the storage step is a step between each step of producing a water-absorbent resin, wherein the water-absorbent resin is stored during or after production.

Examples of the storage device used in the present invention include silos, hoppers, tanks, and the like, and those preferably equipped with external heating means of an inner wall surface and / or a means warming an inner wall surface. From the point of view of abrasion and loading ability, a storage tank having an inner surface made of steel or stainless steel is preferable.

In points (a) to (g) above, it is preferable to carry out the washing with water for at least one device, more preferably a plurality of devices selected from devices (a) to (e). Here, in the case of carrying out the water wash in the spraying step (e), the present process more preferably comprises one or more additional spraying steps after the drying step and before the classification step. . Particularly preferably, the water wash is carried out in the spraying step or the drying step. When the water washing is performed in a plurality of steps (a) to (g), the water washing can be carried out simultaneously or separately (at different times).

(a) Drying device in the drying step (b) Heat treatment device or cooling device in a heat treatment step or a cooling step (surface crosslinking step) (c) Classification device in the classification step (d) Mixing device in the mixing step (step of mixing water, an aqueous solution, or an aqueous dispersion, in particular the surface crosslinking step) (e) Device spraying in the spraying step (Apparatus for production after washing with water)

In the present invention, a production apparatus is preferably used after washing with water after removal of moisture, in particular after drying. A method for removing moisture is not particularly limited, but the moisture can be wiped with a water-absorbent material such as a cloth, and a production apparatus can be naturally dried at room temperature (20). at 25 ° C) or in the sun. However, moisture is preferably removed using a hot air dryer or an air stream (eg, a high pressure gas), thereby drying the apparatus.

(Prior art)

As a method of producing a water-absorbent resin in the prior art, the washing of a monomer is well known. In addition, JP-A-20 0616 0 846 and Figure 2 in the document; and U.S. Patent No. 6,667,372 and Figure 1 in the document; and JP-A-2006-199862 disclose washing pipes or the like to prevent clogging of the pipes during transport of a monomer or polymerization at an outlet of the pipe. JP-A-2006-199862 discloses washing a monomer in a gas stream.

U.S. Patent Application Publication No. 2009/0,315,204 and WO 2009/001,954 disclose the washing of a polymerization tape. WO 2009/001 954 discloses washing a polymerization belt or meat grinder, and recycling the hydrogel. JP-A-6-328,044 below describes the washing of water-absorbing resin deposits due to the high-pressure water flow on a surface of an inner wall of a polymerization reactor for polymerization. by reversed phase suspension, as well as a surface of an agitator, an inner wall surface of a transport pipe, and the like. JP-A-1-242602 discloses a method for removing deposited polymers from a surface of a main member of a polymer production equipment, which comprises treating a water-soluble polymer and / or swellable polymer deposits in water with an aqueous solution of inorganic salt and / or an aqueous alkaline solution.

Although JP-A-2006-160846, US Patent No. 6,667,372, JP-A-2006-199862, US Patent Application Publication No. 2009/0,315,204, WO 2009/001 954, EP-A-2,066,737, JP-A-6-328,044, JP-A-1-242,602 describe the washing of a polymerized monomer or gel, they do not describe not washing a production apparatus after the drying step, in particular after the spraying step, in particular washing in a classification step, and the problems and effects of the present invention.

In the prior art, a water-absorbent resin after drying has been manipulated at low humidity so as to avoid water, and generally a vacuum of dried powder or dust is used to a large extent for the removal. under vacuum. However, the present inventors have found that liquid permeability can be improved by washing with water. Also in the present invention, it is possible to wash a polymerization vessel, a monomer transport pipe, and the like described in JP-A-2006-160846, US No. 6 667,372, JP-A-2006-199862, US Patent Application Publication No. 2009/0,315,204, WO 2009/001,954, EP-A-2,066,737, JP-A-6; 328,044, JP-A-1-242602, but such washing does not contribute substantially to a solution to the problems of the present invention.

For example, WO 2010/032694 and others, and US Patent No. 6,164,455, US Patent Application Publication Nos. 2008/0202,987, 2009/0261,023, 2009/0194. 462, 2009/0266,747, and 2010/0101,982 describe a sieve classifying method of a water-absorbent resin. None of the documents from WO 2010/032 694, US Patent No. 6,164,455, US Patent Application Publication Nos. 2008/0202,987, 2009/0261,023, 2009/0194,462, 2009 / 0 266 747, and 2010/0 101 982 does not propose water washing or the problems and effects of the present invention. In addition, none of US Pat. Nos. 6,727,345, 7,193,006, 6,716,894, US Patent Reissue No. 32,649, US Patent Nos. 5,149,335 and 5,562,646, the publication of US Pat. U.S. Patent Application No. 2005/0256469, U.S. Patent Nos. 7,169,843, 7,173,086, 6,414,214, 6,849,665, U.S. Patent Application Publication Nos. 2008/0125,533, 2007 / 0 293 617, 2002/0 128 618, 2005/0 245 684, WO 2006/082 197, US Patent Application Publication No. 2008/202 987, WO 2006/082 189, WO 2008/025 652, WO 2008/025656, WO 2008/025655, US Patent Application Publication No. 2010/041 550, 2010/042 612 discloses a method of classification comprising washing with water of the present invention. In addition, aspiration of dried powder or vacuum dust for removal is generally used to a large extent, but WO 2011/115 216 and WO 2011/115 221 disclose the use of a ball of knock or air brush as sieve. The present inventors have found that permeability to liquids or the like can be improved by washing with water.

[3] Process for producing polyacrylic acid (salt) water-absorbent resin

Hereinafter, in [3], there will be described a method for producing a polyacrylic acid (salt) water-absorbent resin by focusing on the operating conditions in the respective preparation steps.

Among the processes for producing a water-absorbent resin, described in US Patent Application Publication No. 2011/116,300, WO 2011/115 216 and WO 2011/115 221, the polymerization to the surface crosslinking step may be applied because they are in the polymerization step (3-1) to the surface crosslinking step (3-6) in the present invention.

As described in [2] above, washing with water in the polymerization step (3-1) or the fine spraying step of the gel (3-2) does not contribute substantially to a solution to the problems of the present invention, and is not within the scope of the present invention. For this reason, in the present invention, after the drying step (3-3), in particular after the spraying step (3-4), washing with water is carried out.

(3-1) Polymerization Stage

The present step is a step of polymerizing an aqueous (salt) acrylic acid solution so as to obtain a crosslinked gel-like polymer containing water.

(Monomer (crosslinking agent excluded))

For the water-absorbent resin according to the present invention, an aqueous (salt) acrylic acid solution is used as raw materials (monomer) thereof. The aqueous solution contains acrylic acid (salt) as the main component in the used range of (1-2) above. A partially neutralized salt of acrylic acid is not particularly limited, but from the point of view of the water-absorbing performance of the water-absorbing resin, it is preferably a monovalent salt of acid acrylic acid selected from alkali metal salts, ammonium salts, and amine salts of acrylic acid, more preferably alkali metal salts of acrylic acid, and still more preferably acrylates selected from sodium salt , the lithium salt, and the potassium salt of acrylic acid, and particularly preferably the sodium salt of acrylic acid.

Neutralization may be carried out as a monomer prior to polymerization or may be carried out as a gel containing water (hydrogel) after the polymerization, and a combination thereof may be permitted. The neutralization ratio is preferably from 10 to 100% by mole, more preferably from 30 to 95% by mole, still more preferably from 50 to 90% by mole, and particularly preferably from 60 to 80% by mole.

The aforementioned monomer (including the following crosslinking agent) may be usually polymerized as an aqueous solution, and its solids content is usually 10 to 90% by weight, preferably 20 to 80% by weight, more preferably 30 to 70% by weight, still more preferably 35 to 60% by weight, and particularly preferably 35 to 55% by weight.

In order to improve various physical properties of the resulting water-absorbent resin, a water-soluble resin or a water-absorbent resin such as starch, polyvinyl alcohol, and a polyacrylic acid (salt) can be added, additives which will be described later such as various foaming agents (carbonate, azo compounds, bubbles, and the like), a surfactant, and a chelating agent as an arbitrary component, to an aqueous solution of acrylic acid (salt) or of gel containing water (hydrogel) after polymerization, dried materials or powder. The amount of water-soluble resin or water-absorbent resin to be added is preferably from 0 to 50% by weight, more preferably from 0 to 20% by weight, still more preferably from 0 to 10% by weight, and more preferably most preferred, 0 to 3% by weight, based on the monomers. In addition, the amount of the non-polymeric additive such as a foaming agent and a surfactant to be added is preferably from 0 to 5% by weight, and more preferably from 0 to 1% by weight, based on the monomers. In addition, when the additive is added, the lower limit of the amount of additives to be added is not particularly limited so long as it does not adversely affect, in particular, various physical properties of the absorbent resin. water obtained, but it is preferably 0.1% by weight, and more preferably 0.5% by weight relative to the monomers.

In the present invention, when an acrylic acid (salt) is used as the main component in the range described in (1-2) above, a hydrophilic or hydrophobic unsaturated monomer other than acrylic acid (salt) may be contained . Such other monomer is not particularly limited, and examples thereof include methacrylic acid, maleic (anhydride) acid, itaconic acid, cinnamic acid, vinylsulfonic acid, acid, and the like. allyl toluene sulphonic acid, vinyl toluene sulphonic acid, styrene sulphonic acid, 2- (meth) acrylamido-2-methylpropanesulphonic acid, 2- (meth) acryloyl ethanesulionic acid, 2- (meth) acryloylpropanesulfonic acid, 2-hydroxyethyl (meth) acryloyl phospate, (meth) acryloxyalkanesulfonic acid, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-ethyl (meth) acrylamide N-isopropyl (meth) acrylamide, Ν, Ν-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, 1 stearyl acrylate, and salts thereof, and the like. (Crosslinking agent (internal crosslinking agent))

In the present invention, it is particularly preferable to use a crosslinking agent (hereinafter referred to as "internal crosslinking agent" in some cases) from the point of view of the physical properties of water absorption. An amount of the internal crosslinking agent used is preferably from 0.001 to 5% by mole, preferably from 0.005 to 2% by mole, more preferably from 0.01 to 1% by physical properties. per mole, and in particular preferably from 0.03 to 0.5% per mole, relative to the monomer, excluding the crosslinking agent.

The internal crosslinking agent that can be used is not particularly limited, and examples thereof include crosslinking agents capable of being polymerized with acrylic acid, crosslinking agents capable of reacting with a carboxylic group, crosslinking agents having both capabilities, and the like. Specific examples of the polymerizable crosslinking agent include compounds having at least two polymerizable double bonds in their molecule, such as N, N1-methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (polyoxyethylene) trimethylolpropane tri (meth) acrylate, and poly (meth) allyoxyalkane. Examples of the reactive crosslinking agent include covalent crosslinking agents such as a polyglycidyl ether (ethylene glycol diglycidyl ether or the like), a polyhydric alcohol (propane-diol, glycerin, sorbitol, or the like), and crosslinking agents having an ionic binding property, such as polyvalent metal compounds including aluminum. Among these, from the point of view of the physical properties of water absorption, crosslinking agents capable of being polymerized with acrylic acid may be used preferably, and in particular, polymerizable crosslinking agents of the type acrylate, allyl type and acrylamide type can be used appropriately. These internal crosslinking agents can be used individually or in combination of two or more of their types.

(Polymerization inducer)

A polymerization inducer that can be used in the present invention may be considered appropriate depending on the type of polymerization. Examples of the polymerization inducer include photodecomposition polymerization inducers, thermal decomposition type polymerization inducers and redox type polymerization inducers, and the like. The amount of the polymerization initiator used is preferably from 0.0001 to 1% per mole, and more preferably from 0.001 to 0.5% per mole, based on the monomer.

Examples of the photodecomposition inducer include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds, and the like. In addition, examples of the thermal decomposition inducer include persulfates (such as sodium persulfate, potassium persulfate, and ammonium persulfate), peroxides (such as hydrogen peroxide, t-butyl peroxide, and methyl-ethyl ketone peroxide), azo compounds (such as 2,2'-azobis (2-amidinopropane) dihydrochloride, and 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, and the like.

Examples of the redox polymerization inducer include a system using in combination persulfate or peroxide with a reducing compound such as L-ascorbic acid and sodium bisulfite. In addition, a combination of the photodecomposition inductor and the thermal decomposition inductor may also be included in a preferable embodiment.

(Polymerization process)

The polymerization process according to the embodiment of the present invention can be carried out, from the point of view of the polymerization control performance, usually by. spray polymerization, droplet polymerization, aqueous solution polymerization (static or continuous aqueous solution polymerization), or phase inversion suspension polymerization. Preferably, the polymerization process can be carried out by aqueous solution polymerization, and more preferably by continuous polymerization in aqueous solution. Since a water-absorbing resin obtained by aqueous solution polymerization or continuous polymerization in aqueous solution in the prior art has an irregular particle shape, improvement in liquid permeability has been difficult, but in the present invention the Liquid permeability can be improved considerably, even in the case of an irregular particle.

As a preferable embodiment of the continuous polymerization in aqueous solution, for example, continuous polymerization in a kneader (described in US Patent No. 6,987,151, US Patent No. 6,710,141, and the like), and Continuous web polymerization (described in US Patent No. 4,893,999, US Patent No. 6,241,928, and US Patent Application Publication No. 2005/215734, and the like) may be exemplified. By continuous polymerization in aqueous solution, a water-absorbent resin can be produced in high yield. Thus, the dried water-absorbent resin is preferably in an irregular crushed form obtained by continuous polymerization in a kneader or continuous polymerization on a web. A polymerization device used in the present polymerization step is not particularly limited so long as the various previous types of polymerization can be carried out, but, for example, in the case of continuous strip polymerization, preferably a continuous strip reaction device, and in the case of continuous polymerization in a kneader, a continuous kneader is preferably used.

Since the present invention can provide a monomer having excellent stability even in a polymerization at such a high concentration or at such a high temperature, and can also provide a water-absorbent resin with a high whiteness, the present invention can exert its effects more significantly under such conditions. Such high temperature initiated polymerization has been exemplified in U.S. Patent No. 6,906,159 and U.S. Patent No. 7,091,253, or the like. In the present invention, however, production on an industrial scale can be easily achieved since the process of the present invention is also superior in monomer stability prior to polymerization.

Although the polymerization can be carried out even in an air atmosphere, from the point of view of improving the coloring, it is preferable to carry it out in an inert gas atmosphere such as nitrogen and carbon dioxide. argon (for example, having an oxygen concentration equal to or less than 1% by volume). It is also preferable that dissolved oxygen in a monomer or monomer-containing solution is sufficiently replaced by an inert gas (for example, at an oxygen concentration (amount of dissolved oxygen) of less than 1 [mg / L]) before polymerization.

The polymerization can be carried out at any of normal pressure, reduced pressure, and increased pressure, but preferably under normal pressure (or its vicinity, usually, atmospheric pressure ± 10 mm Hg). In addition, in order to promote the polymerization and to improve the physical properties, if necessary, a degassing step of the oxygen dissolved in the polymerization can be provided (for example, an inert gas replacement step). In addition, the temperature at the beginning of the polymerization may vary depending on the type of polymerization inducer used, but is preferably 15 to 130 ° C, and more preferably 20 to 120 ° C.

(Particularly preferable polymerization process)

The water-wash in the present invention may in particular preferably be applied to a water-absorbent resin having a high water absorption rate (particularly a free swelling rate of 0.30 g). / g / s] or more) "or" a spherical water-absorbent resin or a granulated substance thereof ".

It has been found that the physical properties of the water-absorbent resin having a high water absorption rate or a spherical water-absorbent resin decrease over time in a production step using a powdery water-absorbent resin such as a step of mixing an aqueous solution (for example, the surface crosslinking step) and a classification step. Then, it was found that the above problem could be solved by washing with water of a device in the classification step (in particular a metal screen) and a device in the surface crosslinking step. .

As used herein, the term "spherical water-absorbent resin" refers to a water-absorbent resin having a sphericity defined in WO 2008/009 580 equal to or greater than 0.80, equal to or greater than at 0.84, equal to or greater than 0.87, equal to or greater than 0.90, preferably equal to or greater than 0.93 in this order, particularly preferably equal to or greater than 0.96. The spherical water-absorbent resin can be typically obtained by reversed phase suspension polymerization in a hydrophobic organic solvent (eg, cyclohexane, n-heptane) containing a surfactant (e.g. sucrose), gas phase sputtering polymerization, or droplet polymerization.

In addition, reverse phase suspension polymerization as previously mentioned is described in US Patent No. 4,973,632 and the like, while droplet polymerization or spray polymerization is described in WO 2008/095901, WO 2009/027 356, WO 2010/003 855, WO 2010/003 897, WO 2010/057 912, WO 2011/023 572, WO 2011/026 876, and the like.

The spherical water-absorbent resin can be obtained by reverse phase suspension polymerization, spray polymerization, or droplet polymerization, to form a spherical particle in the polymerization. Thus, no spraying operation is required after the polymerization, the bulk density of the water-absorbent resin thus obtained is increased to make the resin compact, and the impact resistance of the powder is improved. However, as previously mentioned, a metal mesh or punch metal is easily clogged, a problem that could be solved by water washing in accordance with the present invention.

As used herein, the term "water-absorbent resin having a high rate of water absorption" refers to a water-absorbing resin having a water absorption rate (FSR) equal to or greater than 0.30 [g / g / sec], preferably equal to or greater than 0.32 [g / g / sec], more preferably equal to or greater than 0.35 [g / g / sec]. Such a water-absorbent resin can typically be obtained by foaming polymerization or granulation of fine powder. As used herein, the term "foaming polymerization" refers to polymerization of an aqueous monomer solution using a foaming agent (eg, carbonate and azo compounds) or a gas dispersed therein in the polymerization. Foaming polymerization is described in WO 97/017397, WO 97/031 971, WO 00/052 087, and WO 2009/062902.

The water-absorbent resin having a high water absorption rate has an increased particle surface area ([m 2 / g]) of a water-absorbent resin. As a means for this purpose, fine spraying and granulation of a water-absorbent resin and foaming polymerization as mentioned above can be carried out. The foaming polymerization in the polymerization step is preferably used, and the polymerization of an aqueous monomer solution with a gas dispersed therein is more preferably used. The gas dispersion is preferable so that no residue remains in a water-absorbent resin, when compared to the case where a foaming agent is used.

The water-absorbent resin having a high water absorption rate often forms aggregates in a step of adding an aqueous solution because of its high water absorption rate, to the point of adhering to an internal surface of a device, which easily causes clogging in a metal mesh or punch metal, but a problem could be solved by water washing in accordance with the present invention.

(3-2) Fine spray stage of the gel

The gel-like cross-linked polymer containing water (hydrogel) obtained in the polymerization step may be dried as it is, or the water-containing gel may be optionally crushed into a gel in particulate form using a gel grinding machine (a kneader, a meat grinder, or the like) during the polymerization or after the polymerization. Specifically, the present process may comprise a step of fine spraying of the water-containing gel (also hereinafter referred to as "gel grinding") between the polymerization step by continuous strip polymerization or continuous polymerization in a kneader, and the drying step.

The temperature of the gel containing water in the gel grinding may be maintained or raised preferably between 40 and 95 ° C, and more preferably 50 to 80 ° C, in light of the physical properties. The resin solids content of the water-containing gel is not particularly limited, but from the point of view of the physical properties, it is preferably from 10 to 70% by weight, more preferably from 15 to 65% by weight. and still more preferably from 30 to 55% by weight. In the gel containing water, water or a polyhydric alcohol, a mixed liquid of water and polyhydric alcohol, a solution of a polyvalent metal in water, or a vapor thereof may be added. ci, or the like.

The average particle diameter by weight (as specified by sieve classification) of the gel containing particulate water after the gel grinding is preferably in the range of 0.2 to 10 mm, more preferably 0.3 to 10 mm. 5 mm, and in particular preferably 0.5 to 3 mm. The gel ratio containing particulate water having a particle diameter equal to or greater than 5 mm is preferably 0 to 10% by weight, and more preferably 0 to 5% by weight, based on the total amount. The particle diameter of the gel containing particulate water is measured by a wet type classification method described in JP-A-2000-63,527, paragraph [0091].

(3-3) Drying step

The drying process is not particularly limited as long as the gel-like cross-linked polymer containing water obtained in the polymerization step or the gel containing particulate water obtained in the spraying step gel can be dried to a desired resin solids content. For example, various drying methods may be adopted, such as heated drying, hot air drying, reduced pressure drying, infrared drying, microwave drying, tumble dryer drying, azeotropic dehydration with a hydrophobic organic solvent, and a high humidity drying using high temperature steam. Of these, hot air drying is preferred, hot air drying using a gas having a dew point temperature of 0 to 100 ° C is more preferred, and air drying. The use of a gas having a dew point temperature of 20 to 90 ° C is even more preferred.

The drying process for obtaining the spherical water-absorbent resin is not particularly limited, but azeotropic dehydration in an organic solvent (particularly reverse phase suspension polymerization), or fluidized bed drying is preferably , applied.

The drying temperature is not particularly limited, but is preferably in the range of 100 to 300 ° C, and more preferably in the range of 150 to 250 ° C. In order to satisfy both the superior physical properties and the whiteness of the water-absorbing resin obtained, it is preferred that the drying temperature be from 165 to 230 ° C and that the drying time be less than 50 minutes, and it is particularly preferred that the drying time be from 20 to 40 minutes. The drying temperature or the drying time outside these ranges could result in a reduction of the no-load absorption capacity (CRC), an increase in extractables, a decrease in the whiteness of the water-absorbing resin, and for this reason, is not preferable.

Resin solids content determined from a reduced amount of gel containing dried water (a change in weight when 1 g of a powder or particle is heated to 180 ° C for 3 hours) is preferably 80% or more by weight, more preferably 85 to 99% by weight, still more preferably 90 to 98% by weight, and particularly preferably 92 to 97% by weight. In the drying step, a dried water-absorbent resin can be obtained with a dry weight adjusted in the preceding ranges.

(3-4) Spraying step (optional)

The spraying process is not particularly limited so long as a dried water absorbent resin obtained in the drying step can be sprayed. However, it is possible, for example, to use the spraying device of point [2] previously (the spraying device in the spraying step). The spraying device is optionally subjected to the washing with water described in [2], in the present invention. Among these, from the point of view of controlling the particle size, it is particularly preferable to use a multi-phase roller mill or roller granulator.

By the spraying step, the dried water-absorbent resin obtained in the drying step is pulverized to give a water-spray-absorbent resin (water-spray-absorbent resin particles in an irregular crushed form). Since the physical properties of the water-absorbent resin particles can be improved by the spraying step, the spraying step can be suitably applied.

In the case of reverse phase suspension polymerization, spray polymerization, and droplet polymerization, as mentioned above, the spraying step is not particularly necessary because particularly spherical particle in the polymerization. This step may be judged appropriate depending on the form of polymerization.

(3-5) Classification stage

The process for the present step is not particularly limited so long as it can classify the water-spray absorbent resin to be obtained by the spraying step as mentioned above, but a classification device is used, for example shown in [2] previously (classification device in the classification step), and the device in the classification step is most preferable, and in the present invention, the classification device is preferably washed at the water described in [2] above.

In the present invention, it may be sufficient for the classification step to be performed at least once (in one place) in the entire steps. However, two classification steps twice (in two or more places) are preferably performed in the entire steps, and the classification step is performed even more preferably at least once (at one place) before and after the step. surface crosslinking. Depending on the need, the classification steps can be carried out 3 to 6 times.

The elimination of electricity classification is described in U.S. Patent Application Publication No. 2011/116,300.

(Classification vibration)

A sieve classifier suitable for the classification method according to the present invention is not specifically limited. A flat surface classification method is preferably used, and a timbal sieve classifier is particularly preferable. This sieve classification device is typically vibrated to support classification. The vibration is preferably performed to a degree such that a product to be classified is guided in a spiral (helical) direction on the screen. This forced vibration typically has a vibration width of 0.7 to 40 mm, and preferably 1.5 to 25 mm, and a vibration number of 60 to 6000 rpm, and preferably 100 to 600 rpm.

(Particle size)

In the present invention, a particle size is specified by a standard screen (JIS Z8801-1 (2000)). An average particle diameter by weight (D50) of the water-absorbent resin particles obtained in the sputtering step, or even in the classification step, is preferably from 200 to 600 μτη, more preferably from 200 to 550 μτη , still more preferably from 200 to 500 μτη, even more preferably from 250 to 500 μτη, and in particular preferably from 350 to 450 μτη. It is more preferred that the number of particles having a particle diameter of less than 150 μτη be less, and it is desirable that the content of fine particles having a particle diameter of less than 150 μπτ is usually equal to or less than 5% by weight, more preferably equal to or less than 3% by weight, and in particular preferably equal to or less than 1% by weight. The lower limit of the content of fine particles is not particularly limited, but so that it does not take too much time in the classification operation, the content is preferably equal to or greater than 0.1% by weight. weight. By the method of the present invention, even when fine particles having a particle diameter of less than 150 μτη, which are an opportunity for device adhesion, are included, stable operation can be achieved. In addition, it is more preferable that the number of particles having a particle diameter greater than 850 μτη is less, and it is desirable that a content of particles having a particle diameter greater than 850 μιη is usually 0 to 5% by weight, more preferably 0 to 3% by weight, and particularly preferably 0 to 1% by weight. That is, the average particle diameter by weight (D50) of the water-absorbent resin particles prior to surface crosslinking is from 200 to 500 μιη, and the fine particles having a particle diameter of less than 150 μτη are preferably included at a content equal to or greater than 0.1% by weight.

A logarithmic standard deviation (σζ) of the particle size is preferably from 0.25 to 0.45, and more preferably from 0.30 to 0.40. These values can be measured by a method described, for example, in WO 2004/069 915 and a method described in EDANA-ERT420.2-02 ("PSD") using the standard screen.

In the present invention, a ratio of particles having a particle diameter equal to or greater than 150 μιη and less than 850 μτη is preferably equal to or greater than 95% by weight, and more preferably equal to or greater than 98% by weight ( upper limit of 100% by weight), based on the total number of particles. It is preferable to subject the dried material or powder having such a ratio to surface crosslinking. In addition, particle size prior to surface crosslinking is preferably applied to a product after surface crosslinking, and further applied to a final product.

(Other classification conditions)

A suitable classification method is a method described in WO 2011/115 216 and WO 2011/115 221, and the conditions for it are the same as those described in the present invention.

In the step of classifying a water-absorbent resin according to the present invention, it is necessary that at least one, or even two or more, constructions selected from the group consisting of the following constructions (i) to (iii) described in applications WO 2011/115 216 and WO 2011/115 221 are satisfied.

(i) Use of a stamping material in a lower part of the mesh of a metal screen used in the classification step.

(ii) Tensile strength (tension) of a metal screen mesh used in the classification step of 35 to 100 [N / cm].

(iii) Using an air brush in a lower part of the mesh of a metal screen used in the classification step.

In the following, the points (i) to (iii) above will be described in detail.

(i) Typing material (see WO 2011/115 216 and WO 2011/115 221)

From the point of view of the classification efficiency of a water-absorbing resin powder or the physical properties of the resulting water-absorbent resin, a stamping material is used in a lower part of the meshes of a screen. metal. The impact material is an elastic material used to prevent clogging of a classification device, and any shape of the impact material can be used without limitation, any wavy shape such as spherical shapes, ellipsoid and polyhedron. Preferably, use is made of at least one element selected from a ball (spherical), a strike block (spherical), and a striking brush; a ball of striking or a striking block is more preferably used; and even more preferably, a ball of typing. In addition, the case where the impact material is used on the meshes of a metal screen or in which the striking material is not used would cause a decrease in the physical properties (for example, liquid permeability) of the water-absorbent resin, in particular, a decrease over time, or an increase in fine powder or dust.

The method of using the impact material in the present invention in a lower portion of a mesh of the metal screen is not particularly limited, but examples thereof include a method which further comprises providing in a lower part of the mesh of the metal screen, metal screen mesh or punch metal having a mesh size or pore size equal to or greater than the mesh size of the screen mesh metal, and by placing (for example, loading) a stamping material (preferably a stamping ball or a stamping block) on the mesh of the metal screen or the metal to be punched. From the point of view of classification efficiency, it is preferable to use a stamping material on a metal to be punched.

The impact material is preferably a resin, and examples thereof include natural rubber, urethane, chloroprene rubber, silicone resins, and the like. Of these, taking into account attachment or contamination, and the like in a white water-absorbent resin, it is preferable to use white or milky white stripping material, in particular, white natural rubber. , white urethane, or the like. In addition, the elastic modulus of elasticity (Young's modulus) of the resin is preferably from 0.05 to 1.0 GPa, and more preferably from 0.06 to 0.5 GPa.

The size or shape of the impact material is suitably determined depending on the physical properties of a desired water-absorbent resin, but is preferably a block shape or a spherical shape, and its diameter is preferably from 5 to 200 mm, still more preferably from 10 to 100 mm, and particularly preferably from 20 to 60 mm. Within the range described above, it is possible to use in combination striking balls or striking blocks having different diameters. In addition, when using a striking block, the diameter is determined by taking a volume as if it were a sphere.

In the present invention, a plurality of striking materials (punching balls, striking blocks, or the like) is preferably used. The amount of impact materials used of the present invention is defined as a cross-sectional area of one or more impact balls relative to the area of a mesh of the metal screen. The amount is preferably equal to or greater than 1%, more preferably equal to or greater than 5%, still more preferably equal to or greater than 10%, particularly preferably 15% or more, and most preferably equal or greater than 20%. The upper limit is preferably less than a tightly compressed amount taking into account a gap between the impact balls, and more preferably equal to or less than 70%. The amount can be appropriately determined in the meantime.

In the present invention, from the point of view of improving the physical properties or productivity of the resulting water-absorbent resin, the impact material during classification is preferably heated. The heating temperature is preferably equal to or greater than 40 ° C, more preferably equal to or greater than 50 ° C, and still more preferably equal to or greater than 60 ° C. The upper limit of the heating temperature can be set appropriately. Taking into account that excessive heating would reduce effects by the impact material, further reducing the life of the impact material, the heating temperature is usually preferably equal to or lower than 150 ° C, more preferably equal to or lower than at 120 ° C, still more preferably at or below 100 ° C, in particular preferably at or below 90 ° C, and most preferably at or below 80 ° C. For this reason, the temperature of the impact material may be selected from range temperatures, for example from 40 to 100 ° C, 50 to 100 ° C, 60 to 100 ° C, and the like, although not limited to these ranges and may be defined in any of the upper and lower limits of the heating temperature.

In order to heat a striking material according to the present invention in the temperature range described above, the striking material can be heated outside. The interior of a sieve, a sieve surface, and a water-absorbent resin may be heated as a heat source at a predetermined temperature, and a contact time or contact value with a sanding material ( for example, a volume flow of hot air on a screen, and a flow rate or retention value of a water-absorbent resin in a screen, and the like) can be controlled.

(ii) Tensile force (tension) (see WO 2011/115 216 and WO 2011/115 221)

The "tensile force (tension)" in the present invention refers to a load applied when a mesh of a metal screen used in the classification step is stretched. A voltage of a classification mesh (metal mesh) in the present invention is preferably equal to or greater than 35 [N / cm], more preferably equal to or greater than 40 [N / cm], still more preferably equal to or greater at 45 [N / cm], and in particular preferably equal to or greater than 50 [N / cm]. The upper limit of the tension is preferably equal to or less than 100 [N / cm], more preferably equal to or less than 80 [N / cm], and still more preferably equal to or less than 60 [N / cm]. When the tension is equal to or greater than 35 [N / cm], a reduction in the classification efficiency of a water-absorbent resin powder can be prevented, and the liquid permeability of the absorbent resin can be improved. water obtained. In addition, when the tension is equal to or less than 100 [N / cm], the durability of a metal mesh can be ensured, allowing continuous operation. In this case, the tension can be measured with a tensiometer with respect to a web portion of a screen when placing a metal mesh on a classification screen. The measurement theory is based on the "mechanical measurement of sagging tissue under constant force". Various tensiometers are commercially available, for example, by TEKOMAT, and the like, and these commercially available products can be used in the present invention.

(iü) Air brush (air gap) (see WO 2011/115 216 and WO 2011/115 221)

From the point of view of the classification efficiency of a water-absorbent resin powder and the physical properties of the resulting water-absorbent resin, an air brush (air gap) is used in a lower part. mesh of the metal sieve.

In the present invention, an air brush means an instrument for spraying a gas (air) such as compressed air, and is also referred to as an air knife.

Examples of the air brush (air knife) include an air jet cleaner and an air jet brush cleaner, and the like.

The air brush (air knife) can be used with respect to either one part or all the sieves, but it can preferably be used with at least a portion of the sieves (sieves having an equal mesh size or less than 300 μπι), and the air brush (air knife) is used with respect to an amount equal to or greater than 30%, more preferably equal to or greater than 50%, even more preferably equal to or greater than 70 %, in particular preferably equal to or greater than 90%, and most preferably 100% of the sieves.

The air brush in the present invention is preferably used, in particular, during the classification of the fine powder, and is preferably installed in a lower portion of a screen having a screen mesh size of 200 or less. μτη, and more preferably a sieve having a sieve mesh size equal to or less than 150 μτη. The lower limit of the screen mesh size is preferably equal to or greater than 30 μηι, more preferably equal to or greater than 45 μτη, and still more preferably equal to or greater than 75 μτη. The air brush may be preferably used for the classification of the fine powder as a substitute for the impact material to improve the liquid permeability (SFC or GBP) of the resulting water-absorbent resin.

From the point of view of the stable preservation of the excellent physical properties of the water-absorbing resin powder and the suppression of the clogging phenomenon, in the air brush of the present invention, dried air is preferably used. as primary air and secondary air. The dew point of the dried air is preferably equal to or less than 0 ° C, more preferably equal to or less than -30 ° C, still more preferably less than or equal to -35 ° C, and particularly preferably equal to or less than -40 ° C. Examples of the method for adjusting the dew point include a method using a membrane dryer, a method using a cooling-adsorption dryer, a method using a diaphragm dryer, and a method with a combination of these methods. In the case of the use of an adsorption type dryer, it may be of a cyclic heating type, of a non-heating cyclic type, or of a non-cyclic type.

In addition to the dried gas, a heated gas may be used. The heating method for heated air is not particularly limited, but the air can be heated directly using a heat source and can be heated indirectly by heating a device or a pipe. The temperature of the heated gas is preferably equal to or greater than 30 ° C, more preferably equal to or greater than 50 ° C, and still more preferably equal to or greater than 70 ° C.

(Guide)

In the present invention, a sieve of a classification device preferably has a guide of the water-absorbent resin powder.

(Heating temperature)

A classification device (sieve temperature to be used) is preferably used at a temperature equal to or greater than 40 ° C, and in the temperature range of 40 to 80 ° C, and more preferably about 45 to 60 ° C. When the temperature is equal to or greater than 40 ° C, deterioration of the physical properties can be prevented. When the temperature is below 100 ° C or 80 ° C, the economic disadvantages due to higher temperature manufacture can be prevented and the influence on the classification efficiency can also be prevented.

The classification device is preferably used at a temperature not lower than 20 ° C, and preferably 10 ° C, relative to the temperature of the water-absorbent resin powder.

When the water-absorbent resin powder is handled, the temperature of the water-absorbing resin powder introduced into the

Classification is defined at a temperature equal to or greater than room temperature, and preferably equal to or greater than 40 ° C. It is preferable to heat the water-absorbent resin powder, for example, to 40 to 100 ° C, and more preferably 50 to 80 ° C. In order to obtain the water-absorbent resin at this temperature, heating may be suitably carried out or the water-absorbent resin may be kept hot after the drying step or heating in the surface-crosslinking step. , for example.

(Reduced pressure)

In the present invention, the lower limit of reduced pressure is preferably greater than 0 kPa, more preferably equal to or greater than 0.01 kPa, and still more preferably equal to or greater than 0.05 kPa, in the light of efficiency. classification. In order to prevent a flotation of a powder in a classification device, and to reduce the cost of an exhaust device, the upper limit of reduced pressure is preferably equal to or less than 10 kPa, more preferably equal to or less than 8 kPa, still more preferably equal to or less than 5 kPa, and in particular preferably equal to or less than 2 kPa. The preferable range of the reduced pressure degree can be arbitrarily selected between the lower limit and the upper limit. (Air flow)

In the classification step, a stream of gas may preferably be passed through a water-absorbent resin powder. In particular preferably, the gas stream is typically heated to a temperature equal to or greater than 40 ° C, preferably 50 ° C or more, more preferably 60 ° C or higher, still more preferably equal to or greater than 60 ° C. 65 ° C, and in particular preferably equal to or greater than 70 ° C, before being loaded into a sieve classifier. The temperature of the gaseous stream may be usually equal to or less than 120 ° C, preferably equal to or less than 110 ° C, more preferably equal to or less than 100 ° C, still more preferably equal to or less than 90 ° C, and in particular preferably at least 80 ° C.

(Dew point of the atmosphere)

A dew point of the atmosphere (air) in the classification step or a dew point of the gas flow is preferably equal to or less than 15 ° C, more preferably equal to or less than 10 ° C, still more preferably equal to or less than 5 ° C, and in particular preferably equal to or less than 0 ° C. Although the lower limit of the dew point is not particularly limited, it is preferably equal to or greater than -10 ° C and more preferably equal to or greater than -5 ° C, if cost-effectiveness is taken into account. The temperature of the gas is preferably from 5 to 40 ° C, and more preferably from 10 to 35 ° C.

(Form of water-absorbent resin and classification)

The water-wash according to the present invention is preferably applied in the classification of a water-absorbent resin having a large number of convex-concave portions on the surface of its particles and a water-absorbent resin having a practically spherical shape. Specifically, this is because the shape of such water-absorbing resins easily causes clogging of the sieve meshes.

The water-absorbent resin having a large number of convex-concave portions on the surface of its particles can be produced by conventional methods such as foaming polymerization using a foaming agent or a surfactant (US Patent No. 6,100). 305) or by spraying gel under specific conditions (WO 2011/126 079). The polymerization is generally carried out in order to improve the rate of water absorption. The water-absorbent resin having a substantially spherical shape can be obtained by reverse phase suspension polymerization, spray polymerization, or droplet polymerization, as previously mentioned.

(3-6) Surface crosslinking step

The present step is a step for surface crosslinking of the water-absorbent resin particles obtained in the foregoing steps (the drying step, the spraying step, or the classification step). As used herein, the term "surface crosslinking" refers to a crosslinking of a surface or adjacent the surface of the water-absorbent resin particles. The term "surface or vicinity of the surface" as used herein means a surface layer portion with a thickness usually equal to or less than several tens of μτη from the surface, or a portion of a surface layer with a thickness equal to or less than 1/10 of the entire thickness from the surface. The thickness can be determined according to the situation according to the objects. In the production process of the present invention, the liquid permeability or the load absorption capacity can be improved by surface crosslinking.

The surface crosslinking process is not particularly limited, but examples thereof include a method of crosslinking a surface of water-absorbent resin particles using a surface crosslinking agent (Japanese Patent No. 2,530,668). In particular, surface crosslinking can be suitably applied under high temperature heat.

(Surface crosslinking agent)

As the surface crosslinking agent which can be used in the present invention, various organic or inorganic surface crosslinking agents can be exemplified, and organic surface crosslinking agents are preferably used. As organic surface crosslinking agent, polyhydric alcohol compounds such as mono-, di-, tri-, or tetrapropylene glycol, 1,3-propane-diol, glycerin, can be included. 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, and sorbitol; epoxy compounds such as ethylene glycol diglycidyl ether and glycidol; polyvalent amino compounds or condensed compounds thereof with a halo-epoxy compound, oxazoline compounds; compounds (mono-, di- or poly-) oxazolidinone; alkylene carbonate compounds such as ethylene carbonate; oxetane compounds; cyclic urea compounds such as 2-imidazolidinone, and the like, for example. Among them, one or more surface crosslinking agents having an esterification reactivity of dehydration, selected from polyhydric alcohol compounds, alkylene carbonate compounds, oxazolidinone compounds, and the like, each of which requires a reaction at a high temperature, can be preferably and in particular used in combination. These surface crosslinking agents can be used individually or in combination of two or more of their types.

Because the surface crosslinking agent having a dehydration esterification reactivity has a low reactivity, it has high safety, but a stable reaction control is difficult on the other hand. On the other hand, in the present invention, even in continuous production using such a surface-crosslinking agent having dehydration esterification reactivity, the water-absorbent resin can be continuously produced with little variation (deviation). physical property and a small standard variation. More specifically, the compounds exemplified in U.S. Patent Nos. 6,228,930, 6,071,976, and 6,254,990, or the like may be included.

Examples of inorganic surface-crosslinking agents are salts (organic salts or inorganic salts) or hydroxides, for example divalent or higher valence polyvalent metals, preferably trivalent or tetravalent. Examples of the polyvalent metal include aluminum, zirconium and the like, and examples of the polyvalent metal salt include aluminum lactate and aluminum sulfate. These inorganic surface crosslinking agents are used at the same time as or independently of the organic surface crosslinking agent. Surface crosslinking using the polyvalent metal has been described in WO 2007/121 037, WO 2008/09 843, WO 2008/09 842, US Pat. Nos. 7,157,141, 6,605,673 and 6,620,889, US Patent Application Publication Nos. 2005/0288182, 2005/0 070 671, 2007/0106 013, and 2006/0 073 969.

In addition, liquid or similar permeability of the water-absorbent resin can be improved by using polyamine polymers, in particular, polyamine polymers having a weight average molecular weight of about 5,000 to 1,000,000, other than organic surface crosslinking agent, at the same time or separately. Polyamine polymers have been described, for example, in US Pat. No. 7,098,284, WO 2006/082,188, WO 2006/082,189, WO 2006/082,197, WO 2006/111,402, WO 2006/111. 403, and WO 2006/111404, and the like.

In the present invention, in addition to the surface crosslinking agent with a covalent bonding property, as an organic surface crosslinking agent, a surface crosslinking agent with an ionic bonding property, among them the polyvalent metal salt or the polyamine polymer may be further used in combination to improve liquid permeability. In order to improve liquid permeability, other than the organic surface crosslinking agent, an inorganic surface crosslinking agent may preferably be used, and may be further used in combination. When these various surface-crosslinking agents are used in combination, they can be added to the water-absorbent resin at the same time (once), or they can be added separately (several times).

The amount of surface crosslinking agent used may be selected depending on the situation depending on the compounds to be used or a combination thereof, or the like. It is preferably from 0.001 to 10 parts by weight, and more preferably from 0.01 to 5 parts by weight, based on 100 parts by weight of the water-absorbent resin particles. When the organic surface crosslinking agent and the inorganic surface crosslinking agent are used in combination, or when the surface crosslinking agent with a covalent bonding property and the surface crosslinking agent with a crosslinking property ionic bond are used in combination, their amount used in combination may be in the foregoing range. The amount of solvent used can also be selected within the next range. (Mixed solvent)

When the surface crosslinking agent is used, water is preferably used. The amount of water used is not particularly limited, but preferably ranges from 0.5 to 20 parts by weight, and more preferably from 0.5 to 10 parts by weight, based on 100 parts by weight of the particles. of water-absorbing resin.

In this case, a hydrophilic organic solvent can be used. In the case of the use of the hydrophilic organic solvent, the amount of the hydrophilic organic solvent used is not particularly limited, it is preferably greater than 0 and equal to or less than 10 parts by weight, and more preferably greater than 0 and equal to or less than 5 parts by weight, based on 100 parts by weight of the water-absorbent resin particles.

Examples of the hydrophilic organic solvent include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, and t-butyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as dioxane, alkoxy (poly) ethylene glycol, and tetrahydrofuran; amides such as ε-caprolactam and N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; and polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propane-diol, dipropylene glycol, 2,2,4-trimethyl-1 , 3-pentanediol, glycerine, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1, 2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylol propane, diethanolamine, triethanolamine, polyoxypropylene, pentaerythritol, sorbitol, and the like. One or more types of these solvents can be used.

(Other components)

In the present step, by mixing the surface-crosslinking agent solution with the water-absorbing resin particles, a water-insoluble fine particle powder or surfactant may coexist in an amount such that does not inhibit the effects of the present invention. The type or amount of water-insoluble fine particle powder or surfactant to be used is not particularly limited. The range given by way of example can be applied in the specification of application WO 2005/075 070.

In the present step, in addition to the surface crosslinking agent, acidic materials such as organic acid (lactic acid, citric acid, or p-toluenesulphonic acid) or a sodium salt may be used as required. these, and an inorganic acid (phosphoric acid sulfuric acid, or sulfurous acid) or a salt thereof, basic materials such as caustic soda and sodium carbonate, a polyvalent metal salt such as aluminum, and the like in an amount of preferably 0 to 10% by weight, still more preferably 0 to 5% by weight, and particularly preferably about 0 to 1% by weight, based on the absorbent resin powder 1 ' water.

(Temperature and reaction time)

After mixing the surface-crosslinking agent with the water-absorbing resin particles, the mixture may preferably be subjected to a heat treatment and then, as necessary, subjected to a cooling treatment. The heating temperature in the heat treatment is not particularly limited so long as it is a temperature at which the surface crosslinking reaction takes place. It is preferably 70 to 30 ° C, more preferably 120 to 250 ° C, and still more preferably 150 to 250 ° C. The heating time is preferably in the range of 1 minute to 2 hours. The water-absorbent resin after the heat treatment may be optionally subjected to a cooling treatment, in order to stop the surface crosslinking reaction.

(Other surface crosslinking)

In the present invention, surface crosslinking can be carried out without the use of a surface crosslinking agent. For example, surface crosslinking by a radical polymerization inducer (for example, US Pat. No. 4,783,510), surface crosslinking by activated energy beams (for example, EP-A-1,506,788). surface crosslinking by surface polymerization (e.g., US Patent No. 7,201,941), or the like can also be applied to the present invention.

(3-7) Rehumidification Stage or Additive Addition Step

In the present invention, a step of adding water or an additive, or a step of adding a second surface crosslinking agent may optionally be provided after the surface crosslinking step (a rewetting step or a adding additive step).

As an additive, there may be mentioned a chelating agent, a reducing agent, an anti-dyeing agent, a deodorant, an antifungal agent, a dust control agent, an agent for reducing the residual monomers, a water-soluble polymer, a hydrophobic polymer, a water insoluble fine particle, and the like. The added amount of these is preferably from 0 to 5 parts by weight, more preferably from 0.001 to 1 part by weight, based on 100 parts by weight of a water-absorbent resin. Although no solvent in the addition is a problem, water is preferably used as the solvent. In this case, the water is mixed in an amount of preferably from 0.1 to 20 parts by weight, more preferably from 0.5 to 10 parts by weight, based on 100 parts by weight of an absorbent resin. water.

In the rehumidification step or the additive addition step, the physical properties of the resulting water-absorbent resin can be maintained or stabilized by performing the water wash in accordance with the present invention.

(3-8) Other steps

In addition to the foregoing steps, a step of recycling the evaporated monomer, a granulation step, an iron removal step, a transport step, a fine powder removal step, a step of recycling fine powders, or the like. In addition, examples of the additive include a deodorant, antifungal agent, inorganic fine particles, a chelating agent, a reducing agent, an anti-dye, and the like, which can be used in the range of 0.001 to 5 parts by weight, based on the water-absorbent resin powder.

[4] Physical properties of polyacrylic acid (salt) water-absorbent resin

The production method of the present invention may be suitably applied particularly in the case where at least three or more physical properties of the water-absorbent resin are controlled. Effects by controlling each physical property can be suitably exercised in the production process for the water-absorbent resin with many functions and superior physical properties such as preferably 4 or more, 5 or more, or 6 or more. more. As a physical property to be controlled, the following can be exemplified: (a) Pressure Absorption (AAP), (b) Liquid Permeability (SFC), (c) Absorption Capacity no-load (CRC), (d) water-soluble (extractable) content, (e) residual monomers, (f) initial staining, (g) moisture content, and still free swelling capacity (FSC), (h) particle size ( particle diameter), pH, fluidity (throughput), bulk density (density), respirable particles, dust, and the like. They can be applied to the production process by being highly controlled. The physical properties to be controlled or the measurement methods thereof may be determined according to the situation, and the EDANA measurement methods and the like are applicable to the preparation of the water-absorbent resin in the following range.

When the water-absorbent resin according to the present invention is intended to be used in hygiene materials, in particular in disposable diapers, at least one physical property of the following points (a) to (g), and furthermore , two or more physical properties including pressure absorption, and in particular, three or more physical properties can preferably be controlled within a desired range. If the following physical property is not satisfied, the effects by the present invention may not be sufficiently achieved or sufficient performance may not be achieved in high concentration layers which will be described later.

(a) Pressure Absorption (AAP)

In the water-absorbent resin obtained by the production method of the present invention, in order to prevent leakage in the disposable diapers, the pressure absorption (PAA) for an aqueous solution at 0, 9% by weight of sodium chloride under a pressure of 2.06 kPa or a pressure of 4.83 kPa may be controlled, preferably to be equal to or greater than 20 [g / g], more preferably equal to or greater than 22 [g / g], and still more preferably equal to or greater than 23 [g / g]. The upper limit of pressure absorption (PAA) is not particularly limited, and a higher value is better. In light of the compromise with other physical properties or cost, the upper limit of the pressure absorption at a pressure of 2.06 kPa may be about 40 [g / g] and that at a pressure of 4.83 kPa can be about 30 [g / g], and even about 28 [g / g]. In the present description, unless otherwise indicated, the absorption against a pressure is a value under a pressure of 4.83 kPa as defined in ERT442.2-02.

The water-absorbent resin obtained by the production method of the present invention preferably satisfies the no-load absorption capacity as described below and more preferably satisfies the no-load absorption capacity and the salt-flow conductivity such as described below, while satisfying the absorption vis-à-vis a pressure as described above.

(b) Liquid Permeability (Saline Flow Conductivity)

In the water-absorbent resin obtained by the production method of the present invention, in order to prevent leakage in the disposable diapers, the 0.69% by weight saline flux conductivity (SFC), which indicates liquid permeability under pressure, may be controlled to be equal to or greater than 1 [x 10'7 · cm3 · s · g'1], preferably equal to or greater than 10 [x 10'7 · cm3 · s · g'1], more preferably equal to or greater than 20 [x 10'7 · cm3 · s · g'1], still more preferably equal to or greater than 30 [x 10'7 cm3 · s · g'1], even more preferably still equal or greater than 50 [x 10'7 · cm3 · s · g'1], even more preferably greater than or equal to 70 [x 10'7 · cm3 · s · g'1], particularly preferably greater than or equal to 100 [x 10 -7 · cm3 · s · g'1], and most preferably equal to or greater than 110 [x 10'7 · cm3 · s · g'1]. Since a higher value of the upper limit is preferable, it is not particularly limited. In general, it may be equal to or less than 1000 [x 10-7 · cm3 · s · g'1], and more preferably equal to or less than 500 [x 10 * 7 'cm3 · s · g-1].

By the production method of the present invention, a surface-crosslinked water-absorbent resin having the desired salt-flow conductivity value exemplified above can be obtained.

(c) Absorption capacity without load (CRC)

In the water-absorbent resin obtained by the production process of the present invention, the no-load absorption capacity (CRC) may be preferably controlled to be equal to or greater than 10 [g / g], more preferably equal or greater than 20 [g / g], still more preferably equal to or greater than 25 [g / g], and in particular preferably greater than or equal to 27 [g / g]. A higher value of absorption capacity without load is preferable, and therefore the upper limit value is not particularly limited. In the light of a compromise with other physical properties, it may be 50 or less [g / g], more preferably. equal to or less than 45 [g / g], and still more preferably equal to or less than 40 [g / g].

The water-absorbent resin obtained by the production method of the present invention preferably satisfies the salt-flow conductivity and the pressure-absorption as described below, while still satisfying the capacity. absorption without charge as described above.

(d) Water-soluble content (Ext)

The water-absorbent resin obtained by the production method of the present invention may have a water-soluble content (Ext), preferably equal to or less than 35% by weight, more preferably equal to or less than 25% by weight, even more preferably equal to or less than 15% by weight, and in particular preferably equal to or less than 10% by weight.

(e) Residual monomers

The water-absorbent resin obtained by the production method of the present invention may have residual monomers preferably ranging from 0 to 700 ppm by weight, more preferably from 0 to 600 ppm by weight, and particularly preferably from 0 to 500 ppm. in weight.

(f) Initial color

The production method of the present invention can inhibit and prevent the production of brown foreign materials in the water-absorbent resin. A lower rate of production of the brown foreign materials in the water-absorbent resin is preferred, but of the 1000 water-absorbent resin particles obtained by the production method of the present invention, the production of about 5 particles or less (lower limit: 0) of brown particles is acceptable. The water-absorbent resin obtained by the production process of the present invention can be excellent in initial coloring and coloring over time, and can exhibit sufficient whiteness even at high temperature and high humidity in an acceleration test ( model) for a long storage period.

The water-absorbent resin obtained by the production process of the present invention may be excellent in initial coloring. For example, in a Hunter Lab surface color system, the L (clarity) value may preferably be 85 or more, more preferably 87 or greater, and still more preferably 89 or greater; the value b may preferably range from -5 to 10, more preferably from -5 to 5, and still more preferably from -4 to 4; and the value a may preferably range from -2 to 2, more preferably from -1 to 1, still more preferably from -0.5 to 1, and most preferably from 0 to 1. The YI (yellow index ) may preferably be equal to or less than 10, still more preferably equal to or less than 8, and in particular preferably equal to or less than 6; . The WB (white balance) may preferably be 70 or more, more preferably 75 or more, and more preferably 77 or greater. In addition, the water-absorbing resin may be better as well. in coloring over time, and may have sufficient whiteness even at high temperature and high humidity in an acceleration test (model) for a long period of storage.

(g) Moisture content

The moisture content of the water-absorbent resin obtained by the production method of the present invention may be preferably 5% by weight or less, and still more preferably 1% by weight or less. In particular, when the classification step is carried out after the surface crosslinking step, the classification method according to the present invention is preferred because it can significantly exert its effects for such a water-absorbing resin having a low humidity. Although the lower limit of the moisture content is not particularly limited, it may preferably be equal to or greater than 0.1% by weight, and still more preferably equal to or greater than 0.5% by weight.

(h) Particle size and particle shape

In the present invention, a particle size is specified by a standard screen (JIS Z8801-1 (2000)). The average particle diameter by weight (D50) of the water-absorbent resin particles obtained in the pulverization step and the classification step is preferably 200 to 600 μτη, more preferably 200 to 550 μτη, still more preferably from 200 to 500 μτη, in particular preferably from 250 to 500 μιη, and most preferably from 350 to 450 μτη. It is more preferred that the content of particles having a particle diameter of less than 150 μπτ be less, and it is desirable that the content of fine particles having a particle diameter of less than 150 μτη is usually equal to or less than 5% by weight, more preferably equal to or less than 3% by weight, and in particular preferably equal to or less than 1% by weight. The lower limit of the content of fine particles is not particularly limited, but so that it does not take too much time in the classification operation and the like, the content is preferably equal to or greater than 0.1% by weight. weight. By the process of the present invention, even when fine particles having a particle diameter of less than 150 μπι, which are responsible for adhesion to an apparatus, are incorporated, stable operation can be achieved. In addition, it is more preferable that the content of particles having a particle diameter greater than 850 μπι is less, and it is desirable that a content of particles having a particle diameter greater than 850 μπι is usually 0 to 5% by weight, more preferably 0 to 3% by weight, and particularly preferably 0 to 1% by weight. That is, the average particle diameter by weight (D50) of the water-absorbent resin particles prior to surface-crosslinking is from 200 to 500 μπι, and the fine particles having a smaller particle diameter at 150 μτη are preferably included at a content equal to or greater than 0.1% by weight.

The logarithmic standard deviation (σζ) of the particle size is preferably from 0.25 to 0.45, and more preferably from 0.30 to 0.40. These physical property values are measured using a standardized sieve, for example, by the method described in WO 2004/069 915 or in EDANA-ERT42 0.2-02 ("PSD").

In the present invention, a proportion of particles having a particle diameter equal to or greater than 150 μττι and less than 850 μπι is preferably equal to or greater than 95% by weight, and more preferably equal to or greater than 98% by weight ( upper limit of 100% by weight), based on the total number of particles. It is preferable to subject the dried product or the powder having such a particle size to surface crosslinking. The same particle size is preferably also applied to a powder after surface crosslinking, as well as to a final product.

The particle form of the water-absorbent resin according to the present invention is not particularly limited, and there may be mentioned an irregular shape, a (substantially) spherical shape, a fibrous form, a granular substance thereof , and the like. As mentioned above, the particle form is preferably applied to a process for producing a spherical water-absorbent resin and a water-absorbent resin having a high water-absorbing rate (absorbent resin). porous water).

(i) Water absorption rate (FSR)

The water absorption rate (FSR) of the water-absorbent resin obtained by the production process of the present invention is preferably not less than 0.2 [g / g / sec], more preferably not less than 0.3 [g / g / sec], still more preferably not less than 0.35 [g / g / sec], and particularly preferably not less than 0.4 [g / g / sec], of perspective of the absorption capacity of disposable diapers.

According to the second aspect of the invention, from the point of view of placing the focus on the rate of water absorption, it is not less than 0/30 [g / g / s], preferably not less than 0.40 [g / g / s].

The method for producing the water-absorbent resin of the present invention may preferably be applied to improve the rate of water absorption (free swelling rate), best applied to achieve high salt flow conductivity. and is a method for obtaining a water absorption rate (free swelling rate) and a high liquid permeability (salt flow conductivity) at the same time. Preferably, the free swelling ratio is not less than 0.35 [g / g / sec] and the salt flow conductivity is not less than 20 [x 10 7 · cm 3 · s · g x], and ideally, the production process can be applied in the range described above.

[5] Applications of polyacrylic acid (salt) water-absorbent resin

Applications of the water-absorbent resin of the present invention are not particularly limited, but the water-absorbent resin may be preferably used in absorbent articles such as disposable diapers, sanitary napkins, and protective towels against urinary leakage. In particular, superior performance can be achieved, particularly when used in high concentration layers (those where a significant amount of a water-absorbent resin is used in a part of the layers), where the odor or coloring or the like derived from the raw materials of the water-absorbent resin has been conventionally a problem, especially when used at a top layer portion of an absorbent body in articles absorbents.

The content (core concentration) of the water-absorbent resin in an absorbent body arbitrarily containing another absorbent material (pulp fibers and the like) in absorbent articles may preferably be from 30 to 100% by weight. more preferably from 40 to 100% by weight, still more preferably from 50 to 100% by weight, even more preferably from 60 to 100% by weight, particularly preferably from 70 to 100% by weight, and most preferably from 75 to 95% by weight.

[6] Examples

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but is not intended to be limited thereto. In addition, for convenience, "liter (s)" and "% by weight" are described as "L" and "% by weight", respectively, in some cases. In addition, for the water-absorbent resin obtained by the present invention, various physical properties described in the claims or examples, unless otherwise indicated, have been determined under ambient temperature conditions (20 to 25 ° C) and humidity. 50% RH, according to an EDANA method and the following measurement examples. In addition, for the water-absorbing resins obtained, a water-absorbent resin before surface crosslinking is referred to as water-absorbent resin particles; and a water-absorbent resin after surface cross-linking is referred to as water-absorbent resin powder for convenience.

(6-1) Process for measuring physical properties (a) Solid content of resin (solids content)

1.00 g of a water-absorbent resin was weighed into an aluminum cup having a diameter of about 50 mm less, and the total weight W1 [g] of a sample (the resin) was accurately measured. absorbing water and aluminum cup).

Then, the sample was allowed to stand in an oven at an atmosphere temperature of 180 ° C to dry the water-absorbent resin. After 3 hours, the sample was taken out of the oven and cooled to room temperature in a desiccator. Then, the total weight W2 [g] of the sample (the water-absorbent resin and the aluminum cup) was measured after drying, and a solids content (unit, [% by weight]) was calculated according to the following formula.

[Equation 1]

In order to measure the resin solids content of the gel-like particulate crosslinked polymer containing water (particulate gel containing water or particulate hydrogel), the measurement was made by a similar operation except that the amount of the particulate gel containing water was changed from 2 to 4 g and the drying time was changed to 24 hours.

(b) SFC (salt flow conductivity)

The SFC (salt flow conductivity) of a water-absorbent resin obtained in the present invention was measured by the method described in U.S. Patent Specification No. 5,669,894.

(c) Other physical properties

Physical properties such as CRC (Absorption Capacity Without Load, see "CRC" section previously: the method described in ERT441.2-02), AAP (Pressure Absorption; see the "AAP" section previously: the method described in ERT441.2-02 with the charge condition changed to 4.83 kPa), the particle size (see section "PSD" previously: the method described in ERT420.2 -02), pH-soluble content (water soluble content, see "Ext" section above: the process described in ERT470.2-02), and the amount of residual acrylic acid (residual monomers) (see section " Residual monomers "above: the method described in ERT410.2-02) of a water-absorbent resin obtained in the present invention have been measured according to EDANA's EDERT as previously described or the description of the application publication. U.S. Patent No. 2006/204,755; The FSR (free swelling rate (water absorption rate)) was measured by reference to the "FSR" described in US Patent Application Publication No. 2007/225,422 (corresponding to the Japanese document open to the US Pat. Inspection No. 2007-284 675).

(6-2) Examples [Production example 1-ld]

In the production condition 1 of the water-absorbent resin according to the present invention, a water-absorbent resin has been continuously produced by the technique as described below.

Specifically, as a continuous production apparatus for a water-absorbent resin according to the present invention (a production capacity of 1500 [kg / h]), an apparatus has been provided which consists of a polymerization step, a fine gel spraying step, a drying step, a spraying step, a first classification step, a surface crosslinking step (a mixing step, a heat treatment step, and a cooling step), a step of second classification step, a transport step connecting the steps to each other, and an intermediate reservoir that temporarily preserves and stores an intermediate product, and an intermediate hopper (see Figure 1). For the transport step connecting the first classification step and the surface crosslinking step, and the transport step connecting the surface crosslinking step and the second classification step, air transport was used. using dry air with a dew point of 10 ° C or by heating the air to 60 ° C. By bringing the continuous production apparatus under the following conditions, the continuous production of a water-absorbent resin was started.

More specifically, a partially neutralized aqueous sodium acrylate solution having a neutralization ratio of 75% per mole (monomer concentration of 37% by weight) and containing 0.06% per mole (based on the monomer) was prepared. of polyethylene glycol diacrylate (average degree of polymerization of 9) as an internal crosslinking agent as an aqueous monomer solution.

Then, when the aqueous monomer solution was fed continuously to a polymerization apparatus using a metering pump, a dissolved oxygen amount of 0.5 or less [mg / L] was defined by injecting gaseous nitrogen in the middle of the transport conduit, then 0.14 g of sodium persulfate and 0.005 g of L-ascorbic acid (relative to 1 mole of the monomer, respectively) were added continuously separately as the polymerization, and mixed with an in-line mixture. Subsequently, the aqueous monomer solution was fed to a flat steel strip (polymerization apparatus) having dams at either end thereof to give a thickness of about 30 mm, effecting therefore static polymerization in aqueous solution continuously at 95 ° C for 30 minutes. By the above operations, a gel-like crosslinked polymer containing water (polymerization step) was obtained.

Then, the gel-like crosslinked polymer containing water (solids content 45% by weight) obtained in the polymerization step was fed continuously to a meat grinder with a pore diameter of 7 mm under an atmosphere of 60 ° C to effect a gel spray, thereby obtaining a particulate, gel-like, particulate crosslinked polymer having a particle diameter of about 1 mm (fine spray step of the gel) .

Then, the gel-like particulate, gel-like, water-containing polymer was dispersed and mounted on a movable porous plate of a continuous cross-flow carpet dryer to give a thickness of 50 mm, dried with hot air at a temperature of 185 ° C with a dew point of 30 ° C for 30 minutes, then cooled by being exposed to the open air, thereby obtaining a dried water-absorbent resin (96% solids content) by weight, powder temperature 60 ° C) (drying step).

Then, the dried water-absorbent resin was fed continuously to a three-stage roller mill (roll gap, from the top, 1.0 mm / 0.7 mm / 0.5 mm) to perform spraying, thereby obtaining a water-spray-absorbing resin (spraying step).

Subsequently, the water-spray-absorbent resin was continuously fed to and classified with a vibration-type circular classification device with a sieve opening diameter of 1600 mm, having metal screens each having a mesh size. of sieve 1000 μπι, 850 μτη and 150 μιη while maintaining the powder temperature at 60 ° C. The water-absorbent resin remaining on the metal screen having a sieve mesh size of 150 μπι was collected as water-absorbing resin particles. The metal screen was formed of SUS304, and had a tensile force of 50 [N / cm], a surface roughness Rz of the inner surface of the sieve of 50 nm, a surface roughness Ra of the inner surface of the sieve of 4.8 nm, and a sieve area of 2 [m2 / sheet]. The classification device was maintained at 60 ° C, and had a dew point of atmosphere in the device of 13 ° C, a vibration number of 230 rpm, a radial inclination (gradient) of 11 mm, a tangential inclination (gradient) of 11 mm, and an eccentricity value of 35 mm. The classification device was subjected to electrostatic charge elimination with a grounding resistance of 5 Ω. By an exhaust system installed with a bag filter, the pressure in the classification device was reduced to 0.11 kPa, and dry air (a temperature of 60 ° C, a dew point of 10 ° C) was passed through the classification device at 2 [m3 / h] (first classification step).

With regard to the physical properties at the first day of operation, the water-absorbent resin particles had a no-load absorption capacity of 36 [g / g], a solids content of 96% by weight, an average particle diameter of weight (D50) of 450 μτη, a σζ of 0.35, and a proportion of particles having a particle diameter equal to or greater than 150 μπι and less than 850 μιη of approximately 98% by weight. In addition, the water-absorbent resin particles included fine particles having a particle diameter of less than 150 μιη at a proportion of 2% by weight (the proportion of particles having a particle diameter equal to or greater than 850 μπι was 0% in weight).

Then, a surface crosslinking agent solution was prepared which consisted of 0.3 part by weight of 1,4-butanediol, 0.5 part by weight of propylene glycol, and 2.7 parts by weight of pure water relative to 100 parts by weight of the water-absorbent resin particles. Then, the solution was sprayed onto the water-absorbent resin particles using a spray and mixed with a high speed continuous mixer (Turbulizer 1000 rpm) for 6 seconds (mixing step). The mixture was fed to a vane dryer for heating and heat treated at 198 ° C for 40 minutes (heat treatment step). Subsequently, the mixture was forcibly cooled to give a powder temperature of 60 ° C using a vane dryer to cool having the same structure (cooling step), thereby obtaining a powder of water-absorbent resin (surface crosslinking step).

Then, the water-absorbent resin powder obtained by the surface-crosslinking step was continuously fed to and classified with a vibration-type circular classification device with a sieve opening diameter of 1600 mm, comprising a metal sieve having a sieve mesh size of 850 μτη while maintaining the powder temperature at 60 ° C. The metal screen was formed of SUS304, and had a tensile force of 50 [N / cm], a surface roughness Rz of the inner surface of the sieve of 50 nm, a surface roughness Ra of the inner surface of the sieve of 4.8 nm, and a sieve area of 2 [m2 / sheet]. In addition, a punch metal made of stainless steel having a pore diameter of 20 mm (SUS 304 material, 40% opening porosity) was installed in a lower portion of the metal screen (50 mm in diameter). below the surface of the sieve), and a 30 mm diameter ball (consisting of urethane resin, white (milky white), a cross sectional area ratio (ratio of the cross-sectional area of the metal stamping ball (16%), a temperature (an equilibrium heating temperature from hot air, sieve surface, and water-absorbing resin) about 60 ° C) was placed on it. The classification device was maintained at 60 ° C, and had a dew point of atmosphere in the device of 13 ° C, a vibration number of 230 rpm, a radial inclination (gradient) of 11 mm, a tangential inclination (gradient) of 11 mm, and an eccentricity value of 35 mm. The classification device was subjected to electrostatic charge elimination with a grounding resistance of 5 Ω. By an exhaust system installed with a bag filter, the pressure in the classification device was reduced to 0.11 kPa, and dry air (a temperature of 60 ° C, a dew point of 10 ° C) was passed through the classification device at 2 [m3 / h] (second classification step).

In this case, a portion remaining on the metal sieve having a sieve mesh size of 850 μπι was again sprayed, and mixed with a portion which had passed through a metal sieve having a mesh size of sieve 850 μιη, so as to obtain a granular water-absorbent resin having a particle diameter of less than 850 μιη. With regard to the physical properties on the first day of operation, the water-absorbent resin had a moisture content of 1.5% by weight, a water-soluble content of 8.8% by weight, and an average particle diameter by weight (D50 ) of 450 μιη, and a σζ of 0.36.

While continuously producing a water-absorbing resin under the operating conditions described above, a sample was taken each time 1 tonne of the product was reached to measure the physical properties (no-load absorption capacity). absorption versus a salt flow pressure / conductivity) of the water-absorbent resin for a total quantity of 20 tons. For the data of the samples obtained, the averages and their standard deviations were determined and evaluated as water-absorbing resin (1-ld) on the first day of operation. The results are shown in Table 1.

[Production example l-30d]

In the production condition 1 described above, the continuous production apparatus for a water-absorbent resin has been used continuously, to continuously produce a water-absorbing resin.

In order to study the change in performance of the water-absorbent resin over time, a sample thereof was taken every time 1 tonne of the product was reached to measure the physical properties of the absorbent resin. the water for a total quantity of 20 tons, by the same method as in the production example 1-ld from the thirtieth day of continuous operation. For the water-absorbent resin (1-3d) at the thirtieth day of operation, the results are shown in Table 1.

The water-absorbing resin (1-3 Od) was found to have a salt flow conductivity of 28 [x 10 -7 · cm3 · s · g'1], to confirm that there was a decrease in conductivity in saline flow (from 36 to 28) compared to the first day of operation (water-absorbing resin (1-ld)).

In studying a cause of the decrease in saline flux conductivity, it was noted that in the first classification step, the proportion of particles having a particle diameter equal to or greater than 150 μπι and less than 850 μτη was reduced to about 94% in weight compared to about 98% by weight on the first day of operation. That is, it is believed that with an increase in the amount of fine powder, the porosity of the water-absorbing resin decreases to induce a decrease in salt flow conductivity.

[Comparative Example 1]

In order to resolve the decrease in salt flow conductivity that occurred in Production Example I-30d, the first classification step was temporarily stopped, and a vacuum wash (suction) was carried out in the device.

Circular classification of vibration type. Vacuum (suction) washing was performed using a commercially available vacuum machine to a point where foreign materials such as solid material can not be visually confirmed. Steps other than the first classification stage were used without stopping while the utilization rate was slightly lowered.

After washing under vacuum, the vibration-type circular classification device was recovered to restart 1 Operation, but the proportion of particles having a particle diameter equal to or greater than 150 μτα and less than 850 μιη in the first classification step was of about 95% by weight, the salt flow conductivity was 29 [x 10 7 · cm 3 · s · g -1], and recovery of physical properties was not observed. The results with the comparative water-absorbing resin (1) are shown in Table 1.

[Example 1] Since in the vacuum (suction) washing of Comparative Example 1, no recovery of physical properties was observed, the first classification step was again stopped, and the classification device circular vibration type was subjected to a water wash. In the water wash, the metal screen was first removed from the classification device and immersed in a hot water bath (industrial pure water) at 60 ° C for 1 hour. Then, large amounts of the water-absorbing resins that had penetrated the sieve openings were swollen, which could be observed visually. This phenomenon was particularly noticeable with a metal screen having a sieve mesh size of 150 μτη. That is, in the vacuum (suction) wash of Comparative Example 1, it can be seen that the removal of the water-absorbent resin was insufficient.

Subsequently, industrial pure water at 50 ° C was discharged at a discharge pressure (relative pressure) of 200 [kg / cm 2] with a high pressure cleaner manufactured by Karcher Japan Co., Ltd., to completely eliminate the water-absorbent resin that had penetrated the sieve openings and the foreign material that was present in the dead volume of the classification device.

After washing with water, the classification device was dried by high pressure air, and recovered to restart the operation. Therefore, the proportion of particles having a particle diameter equal to or greater than 150 μτη and less than 850 μηι in the first classification step was about 98% by weight, the salt flux conductivity was 36 [x 10 '7 · cm3 · s · g'1], which were recovered at the same level as those on the first day of the operation. The results with the water-absorbent resin (1) are shown in Table 1.

From the results of Production Example I-30d, Comparative Example 1, and Example 1, it is necessary to wash with water a circular classification device of vibration type (in particular, a metal sieves having a sieve mesh size of 150 μιη) in a first classification step about every 30 days in continuous operation.

[Production example l-120d]

Subsequently to Example 1, the continuous production apparatus for a water-absorbent resin in the production condition 1 described above was used continuously, to continuously produce a water-absorbing resin. For the first classification step, the vibration type circular classification device was washed with water about every 30 days during continuous operation.

During the continuous operation by the above method, brown foreign materials were detected in the water-absorbent resin (about 30 to 40 particles in 1000 particles of the water-absorbent resin) after the 120th day from the production example 1-ld (the first day of operation). As a result of the analysis, the brown foreign materials were found to be sodium polyacrylate, a discolored water-absorbing resin. The water-absorbent resin in which the brown foreign material has been detected is designated water-absorbing resin (1-120d) for convenience.

The vane dryer for heating (heat treatment device) used in the surface crosslinking step (heat treatment step) was opened to be studied internally, and hence foreign materials (agglomerates) with discolouration to blackish brown was confirmed in the dead volume of the vane dryer. [Example 2]

In order to remove blackish brown foreign materials generated in Production Example I-120d, the surface crosslinking step was temporarily stopped, and the vane dryer for heating was washed. During washing, the blackish brown foreign materials were removed using a spatula to a point where blackish brown foreign materials were no longer visually observable (spatula wash). The steps other than the surface crosslinking step were operated without stopping while the utilization rate was slightly lowered.

After completion of washing, the device was recovered to restart operation. However, blackish brown foreign materials in the water-absorbent resin were not completely removed, and were detected (about 10 to 20 particles in 1000 particles of the water-absorbent resin). The water-absorbent resin obtained in Example 2 is designated water-absorbent resin (2) for convenience.

[Example 3] Since in the spatula wash in Example 2, blackish brown foreign materials were not sufficiently removed, the surface crosslinking step was stopped again, and the paddle dryer for heating was subjected to washing with water. The water wash was performed by introducing hot water (industrial pure water) at 60 ° C into the vane dryer, immersing in for 1 hour, then washing the inside of the device using the device. high pressure washing with industrial pure water. By immersion with hot water, it was confirmed that the water-absorbent resin was swollen from the dead volume or the like. That is, in the washing of Example 2, it was found that the removal of foreign matter was insufficient.

Subsequently, the interior of the device was washed with water using a high pressure washer made by Sugino Machine Ltd. For washing with water, hot water (industrial pure water) at 60 ° C was discharged at a flow pressure (relative pressure) of 400 [kg / cm 2], and the water-absorbent resin that had entered the dead volume of the vane dryer was completely eliminated.

After washing with water, the vane dryer was dried and recovered to restart operation. As a result, brown foreign materials have disappeared. The results with a water-absorbent resin (3) are shown in Table 1.

From the results of Example 1-120d, Example 2, and Example 3, it is considered that it is preferable to subject the vane dryer for heating (heat treatment device) in the Surface cross-linking step with water wash about every 12 days in continuous operation.

[Production example l-150d]

Subsequent to Example 3, the continuous production apparatus for a water-absorbent resin in the production condition 1 described above was used continuously, to continuously produce a water-absorbing resin. For the first classification step, the vibration type circular classification device was washed with water about every 30 days during continuous operation. In addition, for the surface crosslinking step, the vane dryer for heating (heat treatment device) was washed with water about every 120 days during continuous operation.

During the continuous operation by the above method, an abnormal noise occurred in the three-stage roller mill in the spraying step after the 150th day from the production example 1-ld (FIG. first day of operation), to the point of rendering the particle size of the water-spray-absorbent resin unstable. The water-absorbent resin having an unstable particle size is referred to as water-absorbing resin (1-150d) for convenience.

The three-stage roller mill was opened for internal study to find that a significant amount of undried material (rubbery materials during drying, which was not completely dried) was fixed in the opening of the three-stage roller mill. The cross flow continuous belt dryer of the previous step, the drying step, was also opened, to be studied internally, to find that part of the opening of the porous plate was obstructed, which was supposed to cause a decrease in drying efficiency.

[Example 4]

In order to remove the undried materials generated in Production Example I-150d, the cross-flow continuous belt dryer and the three-stage roller mill were washed. In the wash, undried materials were removed using a cloth to a point where the undried materials were no longer visually observable (rag wash). Steps other than the drying step and the spraying step were operated without stopping while the utilization rate was slightly lowered.

After completion of washing, the device was recovered to restart operation. However, the undried materials were generated to make the size of the particles of the water-spray-absorbent resin slightly unstable. The water-absorbent resin obtained in Example 4 is designated water-absorbent resin (4) for convenience. [Example 5] Since in the rag wash of Example 4 the undried materials were not sufficiently removed, the drying step and the spraying step were stopped again, and the plate porous continuous cross flow belt dryer and three-stage roller mill was washed with water. The water wash was carried out by introducing hot water (industrial pure water) at 60 ° C under a flow pressure (relative pressure) of 400 [kg / cm 2 2 using a high pressure washing device. manufactured by Sugino Machine Ltd., to completely remove undried materials.

After washing with water, the dryer and a roller mill were dried with high pressure air to restart the operation. As a result, there was no production of undried materials and the condition was recovered to that of the first day of operation. The results with a water-absorbent resin (5) are shown in Table 1.

From the results of Production Example I-150d, Example 4, and Example 5, it is considered that it is preferable to subject a continuous cross flow carpet dryer to the drying step. and a three-stage roller mill in the spraying step to wash with water about every 150 days in continuous operation.

[Production example 2-ld]

In the production condition 2 of the water-absorbent resin according to the present invention, the water-absorbent resin has been continuously produced by the technique as described below.

Specifically, a water-absorbing resin (2-ld) was obtained by the same operation in the same conditions as in the 1-ld production example, except that the ball has not been used in the second classification step in production example 1-ld.

With regard to the physical properties on the first day of operation, the water-absorbent resin has a moisture content of 1.5% by weight, a water-soluble content of 8.7% by weight, and an average particle diameter by weight (D 50 ) of 445 μπι, and a σζ of 0.39.

While continuously producing a water-absorbing resin under the operating conditions described above, a sample was taken each time 1 tonne of the product was reached to measure the physical properties (no-load absorption capacity). absorption versus a salt flow pressure / conductivity) of the water-absorbent resin for a total quantity of 20 tons. For the data of the 20 samples obtained, the means and their standard deviations were determined and evaluated as water-absorbing resin (2-ld) on the first day of operation. The results are shown in Table 1.

[Production example 2-45d]

In the production condition 2 described above, the continuous production apparatus for a water-absorbent resin has been used continuously, to continuously produce a water-absorbing resin. For the vibration type circular classification device in the first classification step, the vane dryer for heating (heat treatment device) in the surface cross-linking step, and the dryer and the three-stage roller mill in the drying step / spraying step, it is provided in advance the periodic performance of washing with water.

After performing continuous operation by the above method, a significant decrease in salt flow conductivity at day 45 was observed from the 2-ld production example (the first day of operation). For a water-absorbent resin (2-45d) at day 45 of operation, the results are shown in Table 1.

The water-absorbent resin (2-45d) had a salt flux conductivity of 27 [x 10 -7 · cm3 · s · g-1], to confirm that there was a decrease in salt-flow conductivity (from 34 to 27) compared to the first day of operation (water-absorbing resin (2-ld)).

In studying a cause of salt flux conductivity decrease, it was noted that in the second classification step, an obstruction was observed in the metal screen having a mesh size of 850 μιη.

[Example 6]

In order to solve the problems encountered in production example 2-45d, the second classification step was stopped temporarily, and the vibration type circular classification device (metal screen having a mesh size of 850 μτη). has been washed. For washing, the metal screen was tapped with the hands to remove obstruction materials to a point where they were no longer visually observable (hand wash). Steps other than the second classification stage were used without stopping while the utilization rate was slightly lowered.

After completion of washing, the device was recovered to restart operation, but it was found that the salt flow conductivity was 30 [x 10 7 · cm 3 · s · g -1] to find that the physical properties of The results with a water-absorbent resin (6) are shown in Table 1.

[Example 7] Since in the washing of Example 6, a recovery of the physical properties was not sufficiently observed, the second classification step was again stopped, and the vibration-type circular classification device was been washed with water. In the water wash, the metal screen was first removed from the classification device and immersed in a hot water bath (industrial pure water) at 60 ° C for 1 hour. Then, large amounts of the water-absorbing resins that had penetrated the sieve opening were swollen, which could be observed visually. That is, in the wash of Example 7, it can be seen that removal of the water-absorbent resin was not sufficient to completely eliminate clogging of the metal screen.

Subsequently, hot water (industrial pure water) at 50 ° C was discharged at a discharge pressure (relative pressure) of 200 [kg / cm 2] with a high pressure cleaner manufactured by Karcher Japan Co. , Ltd., to completely eliminate the water-absorbent resin that had penetrated the sieve opening and the foreign material that was present in the dead volume of the classification device.

After washing with water, the classification device was dried by high pressure air, and recovered to restart the operation. As a result, the salt flow conductivity was found to be 34 [x 10'7 · cm3 · s · g'1], which was restored to the same level as the first day of operation. The results with a water-absorbent resin (7) are shown in Table 1.

From the results of production example 2-45d, example 6, and example 7, it is observed that it is preferable to wash with water a circular classification device of vibration type (in in particular, a metal sieve having a sieve mesh size of 850 μτη) in the second classification step about every 45 days in continuous operation, in the case where a ball of striking is omitted.

[Production example 3-ld]

In the production condition 3 of the water-absorbent resin according to the present invention, the water-absorbent resin has been continuously produced by the technique as described below.

Specifically, as a continuous production apparatus for a water-absorbent resin according to the present invention (a production capacity of 1500 [kg / h]), an apparatus which consists of a polymerization step, a step of fine spray of the gel, a drying step, a spraying step, a first classification step, a surface crosslinking step (a mixing step, a heat treatment step, and a cooling step), a second step of classification, a transport step connecting the steps to each other, and an intermediate tank which temporarily preserves and stores an intermediate product, and an intermediate hopper (see Figure 1) has been provided. For the transport step connecting the first classification step and the surface crosslinking step, and the transport step connecting the surface crosslinking step and the second classification step, air transport was used. using dry air with a dew point of 10 ° C or by heating the air to 60 ° C. By bringing the continuous production apparatus under the following conditions, the continuous production of a water-absorbent resin has been started.

More specifically, a partially neutralized aqueous sodium acrylate solution having a neutralization ratio of 73% per mole (monomer concentration of 38% by weight) and containing 0.09% per mole (based on the monomer) was prepared. of polyethylene glycol diacrylate (average degree of polymerization of 9) as an internal crosslinking agent as an aqueous monomer solution.

Then, when the aqueous monomer solution was fed continuously to a polymerization apparatus using a metering pump, a dissolved oxygen amount of 0.5 or less [mg / L] was defined by injecting gaseous nitrogen in the middle of the transport conduit, then 0.14 g of sodium persulfate and 0.005 g of L-ascorbic acid (relative to 1 mole of the monomer, respectively) were added continuously separately as the polymerization, and mixed with an in-line mixture. Subsequently, the aqueous monomer solution was fed to a flat steel strip (polymerization apparatus) having dams at either end thereof to give a thickness of about 30 mm. thereby performing static aqueous solution polymerization continuously at 97 ° C for 30 minutes. By the above operations, a gel-like crosslinked polymer containing water (polymerization step) was obtained.

Then, the gel-like crosslinked polymer containing water (solids content 46% by weight) obtained in the polymerization step was fed continuously to a meat grinder with a pore diameter of 7 mm under an atmosphere of 60 ° C to effect a gel spray, thereby obtaining a particulate, gel-like, particulate crosslinked polymer having a particle diameter of about 1 mm (fine spray step of the gel).

Then, the gel-like particulate, gel-like, water-containing polymer was dispersed and mounted on a movable porous plate of a continuous cross-flow carpet dryer to give a thickness of 50 mm, dried with hot air at a temperature of 190 ° C with a dew point of 30 ° C for 30 minutes, then cooled by being exposed to the open air, thereby obtaining a dried water-absorbent resin (solids content of 96, 5% by weight, powder temperature 60 ° C) (drying step).

Then, the dried water absorbent resin was fed continuously to a three-stage roller mill (roll gap, from the top, 1.0 mm / 0.6 mm / 0.48 mm) to perform spraying, thereby obtaining a water-spray-absorbing resin (spraying step).

Subsequently, the water-spray-absorbent resin was continuously fed to and classified with a vibration-type circular classification device with a sieve opening diameter of 1600 mm, having metal screens each having a mesh size. sieve size of 850 μτη, 710 μτη and 150 μτη while maintaining the powder temperature at 60 ° C. The water-absorbent resin remaining on the metal screen having a mesh size of 150 μτη was collected as water-spray-absorbent resin particles. The metal screen was formed of SUS304, and had a tensile force of 50 [N / cm], a surface roughness Rz of the inner surface of the sieve of 50 nm, a surface roughness Ra of the inner surface of the sieve of 4.8 nm, and a sieve area of 2 [m2 / sheet]. The classification device was maintained at 60 ° C, and had a dew point of atmosphere in the device of 13 ° C, a vibration number of 230 rpm, a radial inclination (gradient) of 11 mm, a tangential inclination (gradient) of 11 mm, and an eccentricity value of 35 mm. The classification device was subjected to electrostatic charge elimination with a grounding resistance of 5 Ω. By an exhaust system installed with a bag filter, the pressure in the device of

Classification was reduced to 0.11 kPa, and dry air (a temperature of 60 ° C, a dew point of 10 ° C) was passed through the classification device at 2 [m3 / h] (first classification step).

With regard to the physical properties at the first day of operation, the water-absorbent resin particles had a no-load absorption capacity of 33 [g / g], a solids content of 96% by weight, an average particle diameter of weight (D50) of 400 μπι, a σζ of 0.36, and a proportion of particles having a particle diameter equal to or greater than 150 μιη and less than 850 μτη of about 98% by weight. In addition, the water-absorbent resin particles included fine particles having a particle diameter of less than 150 μπι at a proportion of 2% by weight (the proportion of particles having a particle diameter equal to or greater than 850 μπι was 0% in weight).

Then, a surface crosslinking agent solution was prepared which consisted of 0.36 part by weight of 1,4-butanediol, 0.6 part by weight of propylene glycol, and 3.24 parts by weight of pure water relative to 100 parts by weight of the water-absorbent resin particles. Then, the solution was sprayed onto the water-absorbent resin particles using a spray and mixed with a high speed continuous mixer (Turbulizer 1000 rpm) for 6 seconds (mixing step). The mixture was fed to a vane dryer for heating and heat treated at 199 ° C for 40 minutes (heat treatment step).

Subsequently, the mixture was forcibly cooled to 60 ° C using a vane dryer for cooling having the same structure (cooling step). In this case, 1.5 parts by weight of an aluminum sulfate treating liquid were added to 100 parts by weight of the water-absorbent resin which had been subjected to heat treatment (surface crosslinking), to obtain a water-absorbent resin powder having its surface coated with aluminum sulfate. The aluminum sulfate treating liquid was prepared by mixing 0.3 part by weight of a 50% by weight aqueous solution of sodium lactate (manufactured by Musashino Chemical Laboratory Ltd.) and 0.1 part by weight. propylene glycol relative to 1 part by weight of a 27% by weight aqueous solution of aluminum sulfate for water supply (manufactured by Asada Chemical Industry Co., Ltd.) (surface crosslinking step) .

Then, the water-absorbent resin powder obtained by the surface-crosslinking step was continuously fed to and classified with a vibration-type circular classification device with a sieve opening diameter of 1600 mm, comprising a metal sieve having a sieve mesh size of 710 μνα while maintaining the powder temperature at 60 ° C. The metal screen was formed of SUS304, and had a tensile force of 50 [N / cm], a surface roughness Rz of the inner surface of the sieve of 50 nm, a surface roughness Ra of the inner surface of the sieve of 4.8 nm, and a sieve area of 2 [m2 / sheet]. In addition, a punch metal made of stainless steel having a pore diameter of 20 mm (SUS 304 material, 40% opening porosity) was installed in a lower portion of the metal screen (50 mm in diameter). below the surface of the sieve), and a 30 mm diameter ball (consisting of urethane resin, white (milky white), a cross sectional area ratio (ratio of the cross-sectional area of the metal stamping ball (16%), a temperature (an equilibrium heating temperature from hot air, sieve surface, and water-absorbing resin) about 60 ° C) was placed on it. The classification device was maintained at 60 ° C, and had a dew point of atmosphere in the device of 13 ° C, a vibration number of 230 rpm, a radial inclination (gradient) of 11 mm, a tangential inclination (gradient) of 11 mm, and an eccentricity value of 35 mm. The classification device was subjected to electrostatic charge elimination with a grounding resistance of Q. By an exhaust device installed with a bag filter, the pressure in the classification device was reduced to 0.11. kPa, and dry air (a temperature of 60 ° C, a dew point of 10 ° C) was passed through the classification device at 2 [m3 / h] (second stage of classification ).

In this case, a portion remaining on the metal sieve having a sieve mesh size of 710 μιη was again pulverized, and mixed with a portion which had passed through a metal sieve having a sieve mesh size of 710 μτη, so as to obtain a granular water-absorbent resin having a particle diameter of less than 710 μτη. With regard to the physical properties on the first day of operation, the water-absorbent resin particles had a moisture content of 1.4% by weight, a water-soluble content of 6.3% by weight, an average particle diameter by weight (D50) of 401 μτη, and a σζ of 0.36.

While continuously producing a water-absorbing resin under the operating conditions described above, a sample was taken each time 1 tonne of the product was reached to measure the physical properties (no-load absorption capacity). absorption versus a salt flow pressure / conductivity) of the water-absorbent resin for a total quantity of 20 tons. For the data of the samples obtained, the averages and their standard deviations were determined and evaluated as water-absorbing resin (3-ld) on the first day of operation. The results are shown in Table 2.

[Production example 3-75d]

In the production condition 3 described above, the continuous production apparatus for a water-absorbent resin has been used continuously, to continuously produce a water-absorbing resin. For the vibration type circular classification device in the first classification step, the vane dryer for heating (heat treatment device) in the surface cross-linking step, and the dryer and the three-stage roller mill in the drying step / spraying step, it is provided in advance the periodic performance of washing with water.

After performing continuous operation by the above method, there was a significant decrease in salt flow conductivity at day 75 from the 3-ld production example (the first day of operation). For a water-absorbent resin (3-75d) at the 75th day of operation, the results are shown in Table 2.

The water-absorbing resin (3-75d) had a salt flow conductivity of 60 [x 10'7 · cm3 · s · g'1], to confirm that there was a decrease in saline flux conductivity (from 110 to 60) compared to the first day of operation (water-absorbent resin (3-ld)).

In studying a cause of the decrease in salt flow conductivity, it was noted that agglomerates of the aluminum sulfate treatment liquid and the water-absorbent resin adhered to the surface of the pallet in the pallet dryer. the cooling step, to the point of preventing the added aluminum sulphate treatment liquid from being effectively mixed with the water-absorbing resin. [Example 8]

In order to remove the agglomerates from the aluminum sulfate treatment liquid and the water-absorbing resin generated in Production Example 3-75d, the surface crosslinking step was stopped temporarily, and the drier was dried. pallets for cooling was washed. During washing, the agglomerates were removed using a spatula to a point where agglomerates were no longer visually observable (spatula wash). The steps other than the surface crosslinking step were operated without stopping while the utilization rate was slightly lowered.

After completion of washing, the device was recovered to restart operation, but the salt flow conductivity was not recovered. The results with a water-absorbent resin (8) are shown in Table 2.

[Example 9] Since in the spatula wash of Example 8, the agglomerates of the aluminum sulfate treating liquid and the water-absorbing resin were not sufficiently removed, the surface crosslinking was again stopped, and the vane dryer for cooling was washed with water. The water wash was performed by introducing hot water (industrial pure water) at 60 ° C into the vane dryer, immersing in for 1 hour, then washing the inside of the device using the device. high pressure washing with industrial pure water. By immersion with hot water, it was confirmed that the water-absorbent resin was swollen from the dead volume or the like. That is, in the washing of Example 8, it was found that the removal of the agglomerates from the aluminum sulfate treating liquid and the water-absorbing resin was insufficiently removed.

Subsequently, the interior of the device was washed with water using a high pressure washer made by Sugino Machine Ltd. For washing with water, hot water (industrial pure water) at 60 ° C was discharged at a flow pressure (relative pressure) of 400 [kg / cm 2], and the agglomerates of the process liquid Aluminum sulfate and the water-absorbent resin that had entered the dead volume of the vane dryer were completely removed.

After washing with water, the vane dryer was dried and recovered to restart operation. As a result, the salt flow conductivity was found to be 110 [x 10 "7 · cm3 · s · g" 1], which was restored to the same level as the first day of operation. The results with the water-absorbent resin (9) are shown in Table 2.

From the results of Production Example 3-75d, Example 8, and Example 9, it is observed that it is necessary to wash with water a paddle dryer for cooling in the water. surface crosslinking step about every 75 days during continuous operation, in the case of carrying out an aluminum treatment.

[Production example 4-ld]

In the production condition 4 of the water-absorbent resin according to the present invention, a water-absorbent resin has been continuously produced by the technique as described below.

Specifically, a water-absorbing resin (3-ld) was obtained by the same operation in the same conditions as in the 3-ld production example, except that the ball has not been used in the second classification step in production example 3-ld. With regard to the physical properties on the first day of operation, the water-absorbent resin has a moisture content of 1.4% by weight, a water-soluble content of 6.4% by weight, and an average particle diameter by weight (D50 ) of 394 μιη, and a σζ of 0.39.

While continuously producing a water-absorbing resin under the operating conditions described above, a sample was taken each time 1 tonne of the product was reached to measure the physical properties (no-load absorption capacity). absorption versus a salt flow pressure / conductivity) of the water-absorbent resin for a total quantity of 20 tons. For the data of the 20 samples obtained, the means and their standard deviations were determined and evaluated as water-absorbing resin (4-ld) on the first day of operation. The results are shown in Table 2.

[Production example 4-40d]

In the production condition 4 described above, the continuous production apparatus for a water-absorbent resin has been used continuously, to continuously produce a water-absorbing resin. For the vibration type circular classification device in the first classification step, the vane dryer for heating (heat treatment device) in the surface cross-linking step, and the dryer and the three-stage roller mill in the drying step / spraying step, it is provided in advance the periodic performance of washing with water. In addition, in the case of carrying out an aluminum treatment during the surface crosslinking step, it is necessary to previously manage the periodic washing of the vane dryer for cooling with water.

After performing continuous operation by the above method, a decrease in saline flow conductivity at day 40 was observed from the 4-ld production example (the first day of operation). For a water-absorbent resin (4-40d) at the 40th day of operation, the results are shown in Table 2.

The water-absorbing resin (4-40d) had a salt flux conductivity of 93 [x 10'7 · cm3 · s · g-1], to confirm that there was a decrease in saline flux conductivity (from 103 to 93) compared to the first day of operation (water-absorbing resin (4-ld)).

In studying a cause of the salt flux conductivity decrease, it was noted that in the second classification step, an obstruction was observed in the metal screen having a mesh size of 710 μτη.

[Example 10]

In order to solve the problems encountered in the 4-40d production example, the second step of

Classification was stopped temporarily, and the vibrating circular classification device (metal sieve having a sieve mesh size of 710 μιη) was washed. For washing, the metal screen was tapped with the hands to remove obstruction materials to a point where they were no longer visually observable (hand wash). Steps other than the second classification stage were used without stopping while the utilization rate was slightly lowered.

After completion of washing, the device was recovered to restart operation, but it was found that the salt flux conductivity was 94 [x 10 7 · cm 3 · s · g -1] to find that the physical properties did not improve. The results with a water-absorbent resin (10) are shown in Table 2.

[Example 11] Since in the wash of Example 10, a recovery of physical properties was not sufficiently observed, the second classification step was again stopped, and the vibration-type circular classification device was been washed with water. In the water wash, the metal screen was first removed from the classification device and immersed in a hot water bath (industrial pure water) at 60 ° C for 1 hour. Then, large amounts of the water-absorbing resins that had penetrated the sieve opening were swollen, which could be observed visually. That is, in the wash of Example 10, it can be seen that the removal of the water-absorbent resin was slightly insufficient to completely eliminate clogging of the metal screen.

Subsequently, hot water (industrial pure water) at 50 ° C was discharged at a discharge pressure (relative pressure) of 200 [kg / cm 2] with a high pressure cleaner manufactured by Karcher Japan Co. , Ltd., to completely eliminate the water-absorbent resin that had penetrated the sieve opening and the foreign material that was present in the dead volume of the classification device.

After washing with water, the classification device was dried by high pressure air, and recovered to restart the operation. Therefore, the salt flow conductivity was found to be 104 [x 10-7 cm3 · s · g'1], which was restored to the same level as the first day of operation. water (11) are shown in Table 2.

From the results of production example 4-40d, example 10, and example 11, it is observed that it is preferable to wash with water a circular classification device of vibration type (in in particular, a metal sieve having a sieve mesh size of 710 μιη) in the second classification step about every 40 days in continuous operation, in the case of carrying out an aluminum treatment in the same way. cooling step.

[Production example 5-ld]

In the production condition of the water-absorbent resin according to the present invention, a water-absorbent resin has been continuously produced by the technique as described below.

Specifically, in the surface crosslinking step of Production Example 3-ld, the mixing step was carried out for 2 minutes with a Proshare mixer (manufactured by Pacific Machinery & Engineering Co., Ltd.; rotations of 300 rpm) instead of a Turbulizer (mixing step). With regard to the physical properties on the first day of operation, the water-absorbent resin has a moisture content of 1.4% by weight, a water-soluble content of 6.3% by weight, and an average particle diameter by weight (D50 ) of 408 μπι, and a σζ of 0.35.

While continuously producing a water-absorbing resin under the operating conditions described above, a sample was taken each time 1 tonne of the product was reached to measure the physical properties (no-load absorption capacity). absorption versus a salt flow pressure / conductivity) of the water-absorbent resin for a total quantity of 20 tons. For the data of the 20 samples obtained, the means and their standard deviations were determined and evaluated as water-absorbing resin (5-ld) on the first day of operation. The results are shown in Table 2.

[Production example 5-20d]

In the previously described production condition, the continuous production apparatus for a water-absorbent resin has been used continuously, to continuously produce a water-absorbing resin. For the circular classification device of vibration type in the first classification step, the vane dryer for heating (heat treatment device) in the surface crosslinking step, the vane dryer for cooling and the dryer and the Three-stage roller mill in the drying step / spraying step, the periodic execution of the water wash is provided in advance.

After running the continuous operation by the above method, a decrease in 20-day salt water pressure and conductivity absorption was observed from the 5-ld production example (FIG. the first day of operation). In addition, the current value of the Proshare mixer has increased compared to the first day of operation. A water-absorbing resin (5-20d) was evaluated on the 20th day of operation, and the results are shown in Table 2.

[Example 12]

When the Proshare mixer was stopped in the 5-20d production example and the interior of it was checked, a strong adhesion of the water-absorbent resin to a rotating paddle was seen. and so the washing was done with a spatula. After washing, the operation was restarted, but the current value of the Proshare mixer was immediately reduced to that before washing, and the absorption values for salt-flow pressure and conductivity were decreased. The results of a water-absorbent resin (12) are shown in Table 2.

[Example 13] Since in Example 12 the washing was insufficient, the Proshare mixer was stopped again, and industrial pure water was sprayed onto it to swell the absorbent resin. glued water and to wipe it precisely. After washing, operation was restarted, and the absorption values for salt flow pressure and conductivity were recovered. The results of a water-absorbent resin (13) are shown in Table 2.

From the results of Production Example 5-20d, Example 12, and Example 13, it is observed that it is preferable to wash with water a high speed mixer in step Surface crosslinking approximately every 20 days in continuous operation.

[Production example 6-ld]

In the production condition 6 of the water-absorbent resin according to the present invention, a water-absorbent resin has been continuously produced by the technique as described below.

Specifically, a water-absorbing resin particle and a water-absorbing resin were obtained by the method described in Example 3 of WO 2011/126,079.

More specifically, as a production apparatus for a polyacrylic acid (salt) type water-absorbent resin, there is provided a continuous production apparatus which consists of a polymerization stage, a fine-stage spraying step, gel, a drying step, a spraying step, a classification step, a surface crosslinking step, a cooling step, a granulating step, and a step of transport stage linking the steps to each other. The production capacity of the continuous production apparatus was about 3500 [kg / h]. The steps can be respectively in one line or separated into two lines. In the case of two lines, the production capacity is represented as the total capacity of these. Using the continuous production apparatus, a polyacrylic acid (salt) water-absorbent resin has been continuously produced.

First, an aqueous monomer solution consisting of 193.3 parts by weight of acrylic acid, 64.4 parts by weight of a 48% by weight aqueous solution of sodium hydroxide, 1.26 was prepared. part by weight of polyethylene glycol diacrylate (average degree of polymerization of 9), 52 parts by weight of a 0.1% by weight aqueous solution of pentasodium salt of ethylene diamine tetrakis (methylenephosphonic acid), and 134 parts by weight of deionized water.

Then, after the aqueous monomer solution maintained at 40 ° C. was fed continuously using a metering pump, 97.1 parts by weight of a 48% by weight aqueous solution was added continuously. sodium hydroxide with an online mixture. At this time, the temperature of the aqueous monomer solution is raised to 85 ° C by the heat of neutralization.

Then, after continuous addition of 8.05 parts by weight of a 4 wt% aqueous solution of sodium persulfate with an in-line mixture, the aqueous monomer solution was fed continuously to a continuous polymerization apparatus. having a flat polymerization band equipped with dams at either end thereof to give a thickness of about 7.5 mm. Subsequently, the polymerization (polymerization time 3 minutes) was carried out continuously, so as to obtain a cross-linked gel-like polymer containing band-type water (polymerization step).

The gel-like cross-linked polymer containing band-type water to be obtained in the polymerization step was cut continuously in the width direction with respect to the direction of travel of the polymerization strip at intervals to give a cut length of 200 mm.

The gel-like crosslinked polymer containing water having the cut length of 200 mm was fed to a screw extruder to be sprayed with gel. As a screw extruder, a meat grinder having a screw axis with a diameter of 152 mm and equipped at its end with a porous plate having a diameter of 340 mm, a pore diameter of 22 mm, 105 pores was used. , a hole ratio of 52%, and a thickness of 20 mm. The gel-like crosslinked polymer containing water was fed at a speed of 132,800 [g / min] while controlling the speed of rotation of the screw axis of the meat grinder at 153 rpm, thereby obtaining a particulate water-gel-like particulate crosslinked polymer (fine gel spraying step).

Then, the gel-like, particulate, water-containing, crosslinked polymer was dispersed on an air strip within one minute after the grinding of the gel had been completed, and dried at 185 ° C for 30 minutes, obtaining so a dried water-absorbent resin (powder temperature of about 60 ° C) (drying step).

Then, the total amount of the dried water-absorbent resin obtained in the drying step was fed continuously to a three-stage roller mill for spraying (spraying step). Then, the water-spray-absorbent resin was classified through JIS standardized screens having a mesh size of 850 μτα and 150 μπι, thereby obtaining irregularly-absorbed water-absorbent resin particles ( first stage of classification).

Regarding the physical properties at the first day of operation, the water-absorbent resin particles had a no-load absorption capacity of 31.5 [g / g], a solids content of 93.6% by weight, a diameter weight average particle weight (D50) of 356 μτη, a σζ of 0.34, and a proportion of particles having a particle diameter equal to or greater than 150 μτη and less than 850 μιη of approximately 99.4% by weight. In addition, the water-absorbent resin particles included fine particles having a particle diameter of less than 150 μτη at a proportion of 0.6% by weight (the proportion of particles having a particle diameter equal to or greater than 850 μπι was 0% by weight).

Then, a solution of covalent surface crosslinking agent which consisted of 0.3 part by weight of 1,4-butanediol, 0.6 part by weight of propylene glycol, and 3.0 parts by weight was uniformly mixed. of pure water with 100 parts by weight of the water-absorbent resin particles (mixing step). The mixture was subjected to heat treatment at 208 ° C for 40 minutes (heat treatment step). Subsequently, the mixture was cooled, and uniformly mixed with a solution of a surface crosslinking agent having an ion binding property which consisted of 1.17 parts by weight of a 27 aqueous solution, 5% by weight of aluminum sulphate (8% by weight as reduced to aluminum oxide), 0.196 part by weight of a 60% by weight aqueous solution of sodium lactate and 0.029 part by weight of propylene glycol (cooling step).

Then, the cooled water-absorbent resin particles were crushed so as to pass through a standardized JIS screen having a mesh size of 850 μm (second classification step), thereby obtaining an absorbent resin. 'water.

While continuously producing a water-absorbing resin under the operating conditions described above, a sample was taken each time 1 tonne of the product was reached to measure the physical properties (no-load absorption capacity). absorption versus salt-flow pressure / conductivity / free swelling ratio) of the water-absorbent resin for a total amount of 20 tons. For the data of the samples obtained, the averages and their standard deviations were determined and evaluated as water-absorbing resin (6-ld) on the first day of operation. The results are shown in Table 3.

The water-absorbing resin (6-1d) was observed by scanning electron microscope, and it was found that there were a large number of convex-concave portions on the surface of the water-absorbent resin, by comparison with the water-absorbing resin (1-ld).

[Production example 6-25d]

In the production condition 6 described above, the continuous production apparatus for a water-absorbent resin has been used continuously, to continuously produce a water-absorbing resin.

In order to study the change in performance of the water-absorbent resin over time, a sample thereof was taken every time 1 tonne of the product was reached to measure the physical properties of the absorbent resin. water for a total quantity of 20 tons, by the same method as in the production example 6-ld from the twenty-fifth day of continuous operation. For the water-absorbent resin (6-25d) at the twenty-fifth day of operation, the results are shown in Table 3.

The water-absorbing resin (6-25d) was found to have a salt flow conductivity of 110 [x 10 7 · cm 3 · s · g -1], to confirm that there was a decrease in conductivity in salt flow (from 116 to 110) compared to the first day of operation (water-absorbing resin (6-ld)).

In studying a cause of the decrease in saline flux conductivity, it was noted that in the first classification step, the proportion of particles having a particle diameter equal to or greater than 150 μιη and less than 850 μιη was reduced to about 96% by weight relative to about 99.4% by weight on the first day of operation. That is, it is believed that with an increase in the amount of fine powder, the porosity of the water-absorbing resin decreases to induce a decrease in salt flow conductivity.

[Comparative Example 2]

In order to resolve the salt flow conductivity decrease that occurred in Production Example 6-25d, the first classification step was temporarily stopped, and a vacuum wash (suction) was performed in the device. classification. Vacuum (suction) washing was performed using a commercially available vacuum machine to a point where foreign materials such as solid material can not be visually confirmed. Steps other than the first classification stage were used without stopping while the utilization rate was slightly lowered.

After washing under vacuum, the classification device was recovered to restart the operation, but the proportion of particles having a particle diameter equal to or greater than 150 μπι and less than 850 μτη in the first classification step was approximately 97% by weight, the salt flow conductivity was 112 [x 10 7 · cm 3 · s · g -1], and the recovery of the physical properties was not observed. comparative water (2) are shown in Table 3.

[Example 14] Since in the vacuum (suction) washing of Comparative Example 2, no recovery of physical properties was observed, the first classification step was again stopped, and the classification device was washed with water. In the water wash, the JIS standardized sieves were first removed from the classification device and immersed in a hot water (industrial pure water) bath at 60 ° C for 1 hour. Then, large amounts of the water-absorbing resins that had penetrated the sieve openings were swollen, which could be observed visually. This phenomenon was particularly noticeable with a metal screen having a sieve mesh size of 150 μτη. That is, in the vacuum (suction) wash of Comparative Example 2, it can be seen that the removal of the water-absorbent resin was insufficient.

Subsequently, industrial pure water at 50 ° C was discharged at a discharge pressure (relative pressure) of 200 [kg / cm 2] with a high pressure cleaner manufactured by Karcher Japan Co., Ltd., to completely eliminate the water-absorbent resin that had penetrated the sieve openings and the foreign material that was present in the dead volume of the classification device.

After washing with water, the classification device was dried by high pressure air, and recovered to restart the operation. Therefore, the proportion of particles having a particle diameter equal to or greater than 150 μτη and less than 850 μτη in the first classification step was approximately 99% by weight, the salt flow conductivity was 116 [x 10 '7 · cm3 · s · g'1], which were recovered at the same level as those on the first day of the operation. The results with the water-absorbent resin (14) are shown in Table 3.

From the results of Production Example 6-25d, Comparative Example 2, and Example 14, it is observed that it is necessary to wash with water a classification device (in particular a standardized JIS sieve having a sieve mesh size of 150 μηι) in a first classification step approximately every 25 days of continuous operation in the production condition 6.

Although washing with water for the sieve was more often carried out when compared to Example 1, the cause for this is believed to be that a ratio of sprayed substance having a particle diameter of about mesh size is large (in Example 14, with respect to a sieve mesh size of 175 μιη, an average particle diameter by weight (D50) of 356 μιη, and a σζ of 0.34; Example 1, with respect to a mesh size of 150 μιη sieve, a mean particle diameter by weight (D50) of 450 μιη, and a σζ of 0.35), and that the convexo-concave shape of the water-absorbent resin would easily produce clogging of the sieve.

[Production example 7-ld]

In the production condition 7 of the water-absorbent resin according to the present invention, a water-absorbent resin has been continuously produced by the technique as described below.

Specifically, a water-absorbent resin particle and a water-absorbent resin were obtained by the method described in Example 3 of U.S. Patent No. 6,100,305 (corresponding Japanese Patent No. 4,286,335).

Specifically, an aqueous monomer solution was prepared by mixing 83.2 parts of an acrylic acid, 1662.8 parts of a 37% by weight aqueous solution of sodium acrylate, 5.5 parts of polyethylene diacrylate. glycol (an average number of moles of ethylene oxide (EO) added of 8), and 654.5 parts of deionized water. The neutralization ratio of the acrylic acid in the aqueous monomer solution was 85%, and the monomer concentration was 30%.

Then, the dissolved oxygen was removed from the aqueous monomer solution by blowing nitrogen gas into the aqueous monomer solution while maintaining the temperature of the aqueous monomer solution at 24 ° C. Subsequently, 77 parts of a 10% by weight aqueous solution of 2,2'-azobis (2-methylpropionamidine) dihydrochloride were added with stirring of the aqueous monomer solution.

When 3 minutes had elapsed from priming the stirring, the aqueous monomer solution containing 2,2'-azobis (2-methylpropionamidine) dihydrochloride appeared cloudy and white, and a white particulate solid with a diameter Average particle size of about 9 μχη was generated. The particulate solid was 2,2'-azobis (2-methylpropionamidine) diacrylate as a foaming agent.

After 5 minutes have elapsed from the initiation of stirring, 10.8 parts of a 10% by weight aqueous solution of sodium persulfate and 0.5 part of a 1% aqueous solution are added. by weight of L-ascorbic acid as a radical polymerization inducer under agitation of the aqueous monomer solution under the nitrogen atmosphere. After sufficient stirring of the aqueous monomer solution, it was allowed to stand.

When 3 minutes have elapsed since the addition of the 10 wt% aqueous solution of sodium persulfate and the 1 wt% aqueous solution of L-ascorbic acid, the polymerization was started. The polymerization was carried out in a hot water bath while controlling the temperature of the hot water bath to monitor the temperature increase of the aqueous monomer solution. When 26 minutes had elapsed since the addition of the 10 wt% aqueous solution of sodium persulfate to the aqueous monomer solution, the temperature of the aqueous monomer solution reached 97 ° C. Subsequently, the aqueous monomer solution was allowed to stand for a further 20 minutes while maintaining the temperature thereof in the range of 70 ° C to 90 ° C, so that the polymerization reaction of the monomer of Acrylic acid salt was finished. As a result, a gel-like crosslinked polymer containing water having cells as a porous cross-linked polymer was obtained.

The gel-like cross-linked polymer containing water thus obtained was ground continuously by a rotary mill. The average residence time of the gel-like crosslinked polymer containing water in the rotary mill during milling, i.e., the milling time, was about 0.25 minutes. A particulate gel-like cross-linked polymer containing water after milling had a particle diameter of from about 1 mm to 15 mm.

The particulate gel-like crosslinked polymer containing water after milling was dried at 160 ° C for 1 hour using a circulating hot air dryer. Subsequently, the water-absorbent resin dried after drying was pulverized with a roller mill, and classified with JIS standardized sieves, thereby obtaining water-absorbent resin particles which passed through the screen. of metal having a sieve mesh size of 850 μτη and remain on the metal screen having a sieve mesh size of 150 μτη.

With regard to the physical properties of the first day of operation, the water-absorbent resin particles had a no-load absorption capacity of 45.5 [g / g], a solids content of 95.1% by weight, a diameter weight average particle weight (D50) of 43 0 μτη, a σζ of 0.36, and a proportion of particles having a particle diameter equal to or greater than 150 μπι and less than 850 μιτι of approximately 97.4% by weight. In addition, the water-absorbent resin particles included fine particles having a particle diameter of less than 150 μτη at a proportion of 2.6% by weight (the proportion of particles having a particle diameter equal to or greater than 850 μπι was 0% by weight).

The water-absorbent resin particles thus obtained were subjected to a secondary crosslinking treatment. Specifically, a treatment solution for the secondary crosslinking treatment was prepared by mixing 0.05 part of ethylene glycol diglycidyl ether, 0.5 part of lactic acid, 0.02 part of polyoxyethylene sorbitan monostearate, 0 75 parts of isopropyl alcohol and 3 parts of water.

Then, the water-absorbent resin was obtained by mixing 100 parts of the water-absorbing resin thus obtained with the treatment solution for the secondary crosslinking treatment, and the resulting mixture was heated at 195 ° C for 30 minutes.

While continuously producing a water-absorbing resin under the operating conditions described above, a sample was taken each time 1 tonne of the product was reached to measure the physical properties (no-load absorption capacity). absorption versus a salt flow pressure / conductivity) of the water-absorbent resin for a total quantity of 20 tons. For the data of the samples obtained, the averages and their standard deviations were determined and evaluated as water-absorbing resin (7-1d) on the first day of operation. The results are shown in Table 3.

The water-absorbing resin (7-1d) was observed by scanning electron microscope, and it was found that there were a large number of convex-concave portions on the surface of the water-absorbent resin, by comparison with the water-absorbing resin (1-ld).

[Production example 7-20d]

In the production condition 7 described above, the continuous production apparatus for a water-absorbent resin has been used continuously, to continuously produce a water-absorbing resin.

In order to study the change in performance of the water-absorbent resin over time, a sample thereof was taken every time 1 tonne of the product was reached to measure the physical properties of the absorbent resin. the water for a total quantity of 20 tons, by the same method as in the production example 7-ld from the twentieth day of continuous operation. For the water-absorbent resin (7-20d) on the twentieth day of operation, the results are shown in Table 3. In this example, the water-absorbing resin produced in the production condition 7 was examined for the Absorption against pressure by changing the load condition to 2.06 kPa.

The pressure absorption of the water-absorbing resin (7-20d) was found to be 29 [g / g], to confirm that there was a decrease in pressure (from 32 to 29) compared to the first day of operation (water-absorbing resin (7-ld)).

In studying a cause of the decrease in absorption with respect to a pressure, it was noted that in the first classification step, the proportion of particles having a particle diameter equal to or greater than 150 μτα and less than 850 μιη was reduced to about 92% by weight relative to about 96% by weight on the first day of operation. That is, it is believed that with an increase in the amount of fine powder, the mixing property with a surface crosslinking agent is degraded in the surface crosslinking treatment.

[Comparative Example 3]

In order to solve the decrease in pressure absorption that occurred in the 7-20d production example, the first classification step was stopped temporarily, and a vacuum wash (suction) has been carried out in the classification device. Vacuum (suction) washing was performed using a commercially available vacuum machine to a point where foreign materials such as solid material can not be visually confirmed. Steps other than the first classification stage were used without stopping while the utilization rate was slightly lowered.

After washing under vacuum, the classification device was recovered to restart the operation, but the proportion of particles having a particle diameter equal to or greater than 150 μιη and less than 850 μm in the first classification step was about 93% by weight, pressure absorption was 29 [g / g], and recovery of physical properties was not observed. The results with the comparative water-absorbent resin (3) are shown in Table 3.

[Example 15] Since in the vacuum (suction) washing of Comparative Example 3, no recovery of physical properties was observed, the first classification step was again stopped, and the classification device was washed with water. In the water wash, the JIS standardized sieves were first removed from the classification device and immersed in a hot water (industrial pure water) bath at 60 ° C for 1 hour. Then, large amounts of the water-absorbing resins that had penetrated the sieve openings were swollen, which could be observed visually. This phenomenon was particularly noticeable with a metal screen having a sieve mesh size of 150 μιη. That is, in the vacuum (suction) wash of Comparative Example 3, it can be seen that the removal of the water-absorbent resin was insufficient.

Subsequently, industrial pure water at 50 ° C was discharged at a discharge pressure (relative pressure) of 200 [kg / cm 2] with a high pressure cleaner manufactured by Karcher Japan Co., Ltd., to completely eliminate the water-absorbent resin that had penetrated the sieve openings and the foreign material that was present in the dead volume of the classification device.

After washing with water, the classification device was dried by high pressure air, and recovered to restart the operation. Therefore, the proportion of particles having a particle diameter equal to or greater than 150 μτη and less than 850 μπι in the first classification step was about 96% by weight, the absorption against a pressure was 32 [g / g], which was recovered at the same level as those on the first day of the operation. The results with the water-absorbent resin (15) are shown in Table 3.

From the results of Production Example 7-20d, Comparative Example 3, and Example 15, it is observed that it is necessary to wash with water a classification device (in particular a JIS standardized sieve having a sieve mesh size of 150 μιη) in a first classification step about every 20 days of continuous operation in the production condition 7.

Although washing with water is more often performed compared to Example 1, it is believed that the reason for this is that the convexo-concave shape of the water-absorbent resin would easily cause clogging of the sieve. .

H

tn

CD

m

B

ü r *

- OH

d 'o · - *

H

not! not a word

H ® U 0)

O

ta.

3 u

u you CO

Ö

• H

ORP

rtf

CD

rH "IW

Ö

D

"U

not a word

• H

>

H

not a word

U

% Ö

O

U

ω ΰ να) dd

H

G G

I-I

H

BOY WUT

(Ö aj _

( "H

A ~ (d

H

H

tr1 m ΓΠ £ ü P * o

H

X

4J

m <u ü

Cu m ö H r-1 nj in s

ORP

4-1 Ö

QJ

M) 4-1 ri>

• H

4-1 α C3 T3 Ö O u tt) n

'<U' 4J H

- ö 04 0

3 hours

tö (U • I-I

Λ -

Iti H

H - ΰ

o • ri m co

(U

s-i ft p <l) 1 fi

Cn fi. m 'd ra? ? ? Λ0

O I

h ra * H * *> & o ^ JJ o ra -H "0) w o - u? u o fe to ^ ra λ -? δι -S - g pH Λ (Ö p. Ο ra

, JS

a § ^

Where ή Ο .9 Η π g i ij ® S · 2 S Λ Ο Η α, ο • η 10 <ö

jj rH

u 5 2 2 ti Ό ri g fi -Η?.

ϋ ö ö>> g fi fi

U

\ QJ fi ΐ) Η Ö • Η 0) ΰ ra 3 fi α)

- CU

Η Q Μ fi .. .. ra 0)

~ ~ E

H 05

- UL

r-, 4J

ro \ (u 5 ω _ t s (Summary)

As shown in the tables. 1 to 3 above, although a decrease in physical properties, the incorporation of brown foreign materials, the production of undried materials, or the like can be observed by continuous operation over time, a water-absorbing resin having higher physical properties can be stably produced continuously without the problems described above, periodically washing with water.

By the present method, the physical properties of a water-absorbent resin can be improved, and stable continuous production can be achieved.

The full disclosure of Japanese Patent Application No. 2011-200221 filed September 14, 2011 including the description, claims, drawings and abstract is hereby incorporated by reference in its entirety.

Claims (96)

A method of continuously producing a polyacrylic acid (salt) water-absorbent resin, comprising successively: a polymerization step of polymerizing an aqueous (salt) acrylic acid solution to obtain a similar cross-linked polymer a gel containing water; a drying step of drying the gel-like crosslinked polymer containing water to obtain a dried water-absorbent resin; a classification step of classifying the dried water absorbent resin to obtain water-absorbent resin particles; and a surface crosslinking step of subjecting the water-absorbing resin particles to surface crosslinking before and / or after the classification step, wherein a surface of a device that is used in one or more of steps after the drying step and the contacts with the water-absorbent resin is washed with water. A process for continuously producing a polyacrylic acid (salt) water-absorbent resin, comprising successively: a polymerization step of polymerizing an aqueous acid (salt) acrylic solution to obtain a similar cross-linked polymer a gel containing water; a drying step of drying the gel-like crosslinked polymer containing water to obtain a dried water-absorbent resin; a classification step of classifying the dried water absorbent resin to obtain water-absorbent resin particles; and a surface crosslinking step of subjecting the water-absorbent resin particles to surface crosslinking before and / or after the classification step, wherein the water-absorbent resin has a rate of absorption of water (FSR) equal to or greater than 0.30 [g / g / s], and a surface of a device that is used in one or more of the steps after the drying step and contacts with the absorbent resin. water is washed with water. A process for continuously producing a polyacrylic acid (salt) water-absorbent resin, comprising successively: a polymerization step of polymerizing an aqueous acid (salt) acrylic solution to obtain a similar cross-linked polymer a gel containing water; a drying step of drying the gel-like crosslinked polymer containing water to obtain a dried water-absorbent resin; a classification step of classifying the dried water absorbent resin to obtain water-absorbent resin particles; and a surface crosslinking step of subjecting the water-absorbent resin particles to surface crosslinking before and / or after the classification step, wherein the water-absorbing resin is a spherical water-absorbent resin or a granulated substance thereof and a surface of a device that is used in one or more of the steps after the drying step and the contacts with the water-absorbent resin are washed with water. The method of any one of claims 1 to 3, wherein the washing with water is performed in the classification step or the surface crosslinking step. The method of any one of claims 1 to 4, wherein the washing with water is performed in the classification step. The method of any one of claims 1 to 5, wherein the washing with water is carried out intermittently periodically. The method of any one of claims 1 to 6, wherein the washing with water is carried out with hot water. The process of claim 7, wherein the hot water temperature is 30 to 100 ° C. The process of claim 7 wherein the hot water temperature is 35 to 100 ° C. The method of claim 7, wherein the hot water temperature is 40 to 95 ° C. 11. The method of claim 7, wherein the hot water temperature is 45 to 90 ° C. The method according to any one of claims 1 to 11, wherein the washing with water is carried out with a stream of water under pressure. The method of claim 12, wherein the stream of pressurized water has a relative pressure of from 1 to 400 kg / cm 2. The method of claim 12, wherein the stream of pressurized water has a relative pressure of 5 to 200 kg / cm 2. The method of any one of claims 1 to 14, wherein the washing with water is performed by immersing an apparatus in water or by injecting water into an apparatus. 16. The method of claim 15, wherein the dipping is performed by immersing all or part of the production apparatus or one of its compounds in a quantity of excess water. 17. A method according to claim 15 or 16, wherein the immersion time of the apparatus in water or the injection of water into the apparatus is from one minute to 10 days. 18. The method of claim 15 or 16, wherein the immersion time of the apparatus in water or the injection of water into the apparatus is from 1 hour to 5 days. 19. The method of claim 15 or 16, wherein the immersion time of the apparatus in water or the injection of water into the apparatus is from 1 hour to 3 days. 20. Method according to one of claims 1 to 6, wherein the washing with water is carried out by steam. 21. The method of claim 20, wherein the vapor as water in the form of gas heated to normal pressure with a temperature equal to or less than 500 ° C. 22. The method of claim 20, wherein the vapor as water in the form of gas heated to normal pressure with a temperature equal to or lower than 300 ° C. 23. The method of claim 20, wherein the vapor as water in the form of gas heated to normal pressure with a temperature equal to or less than 200 ° C. 24. The method of any one of claims 3 to 23, wherein the spherical water-absorbent resin is obtained by reverse phase suspension polymerization. 25. A process according to any one of claims 3 to 23, wherein the spherical water-absorbent resin is obtained by gas phase sputtering polymerization, or droplet polymerization. 26. A process according to any one of claims 3 to 25, wherein the spherical water-absorbent resin has a sphericity equal to or greater than 0.80. The method of any one of claims 3 to 25, wherein the spherical water-absorbent resin has a sphericity equal to or greater than 0.84. 28. A process according to any one of claims 3 to 25, wherein the spherical water-absorbent resin has a sphericity equal to or greater than 0.87. The method of any one of claims 3 to 25, wherein the spherical water-absorbent resin has a sphericity equal to or greater than 0.90. 30. The method of any of claims 3 to 25, wherein the spherical water-absorbent resin has a sphericity equal to or greater than 0.93. 31. The method of any one of claims 3 to 25, wherein the spherical water-absorbent resin has a sphericity equal to or greater than 0.96. The method of any one of claims 2 to 31, wherein the water-absorbent resin has a water absorption rate (FSR) equal to or greater than 0.32 [g / g / sec]. The method of any one of claims 2 to 31, wherein the water-absorbent resin has a water absorption rate (FSR) equal to or greater than 0.35 [g / g / sec]. The process of any one of claims 1 to 33, wherein foaming polymerization is used in the polymerization step. The method of claim 34, wherein the foaming polymerization is carried out by polymerizing an aqueous monomer solution with a gas dispersed therein. 36. A method according to any one of claims 1 to 35, wherein the washing with water is used for at least one device selected from the following devices (a) to (e): (a) a drying device in the drying step, (b) a heat treatment device or a cooling device in the heat treatment step or the cooling step (surface crosslinking step), (c) a classification device in the classification step, (d) a mixing device in the mixing step (step of mixing water, an aqueous solution, or an aqueous dispersion, in particular the surface-crosslinking step), and (e) a spraying device in the spraying step. The method of claim 36, wherein the water washing is performed for a plurality of devices selected from devices (a) to (e). 38. A process according to any one of claims 1 to 37, wherein the apparatus for producing after washing with water is used after removal of the moisture. The method of claim 38, wherein the moisture is removed using a hot air dryer or an air stream. 40. The method of claim 39, wherein the air stream is a high pressure gas. 41. The method of claims 39 or 40, wherein the air stream is high pressure air. 42. A process according to any one of claims 1 to 41, wherein the washing with water is carried out by sieves of a metal sieve or a metal to be punched. 43. The method of claim 42, wherein the mesh of the metal screen has a mesh size of 50 μπι to 1 mm. 44. The method of claim 42, wherein the metal to be punched is a metal to be punched in a carpet dryer or a metal to be punched in a fluid bed dryer. The method of any one of claims 1 to 44, wherein the washing with water is performed for an inner surface of a mixing device for mixing the water-absorbing resin with water, at a aqueous solution, or an aqueous dispersion. 46. A method according to any one of claims 1 to 45, wherein the washing with water is carried out for an internal surface of at least one device selected from a mixing device, a heat treatment device and a device for cooling in the surface crosslinking step. 47. A method according to any one of claims 1 to 46, wherein the production apparatus to be washed with water is stainless steel. 48. A method according to any one of claims 1 to 47, wherein the production apparatus to be washed with water at a surface roughness (Rz) of contact surface with the water-absorbing resin equal to or less than 150nm. 49. A method according to any one of claims 1 to 47, wherein the production apparatus to be washed with water at a surface roughness (Rz) of contact surface with the water-absorbing resin equal to or less than lOOnm. A method according to any of claims 1 to 47, wherein the production apparatus to be washed with water at a surface roughness (Rz) of contact area with the water-absorbing resin equal to or less than 50nm. 51. The method of any one of claims 1 to 50, wherein the device having a temperature during operation of 40 to 100 ° C is washed with water. 52. A method according to any one of claims 1 to 51, wherein in the classification step, a classification device comprising metal screen mesh having a sieve mesh size of 45 to 2000 μm is used. 53. The method of any one of claims 1 to 53, wherein a time when the water wash is performed is determined by a change in a particle size or a change in liquid permeability. The method of any one of claims 1 to 53, wherein the classifying step is performed before and after the surface crosslinking step. 55. Process according to any one of claims 1 to 54 for which the water-absorbing resin particle before the surface-crosslinking step has a mean particle diameter by weight (D50) of between 200 and βΟΟμπι and comprises fine particles having a particle diameter of less than 150 μm in a content of between 0.1% by weight and 5% by weight. The process of any one of claims 1 to 54 wherein the water-absorbent resin particle prior to the surface-crosslinking step has an average particle diameter by weight (D50) of from 200 to 550 μm and comprises fine particles having a particle diameter of less than 150 μm in a content of between 0.1% by weight and 5% by weight. The method of any one of claims 1 to 54, wherein the water-absorbent resin particles prior to the surface-crosslinking step have an average particle diameter by weight (D50) of from 200 to 500 μm and contain fine particles having a particle diameter of less than 150 μm in a proportion of 0.1% by weight to 5% by weight. The method of any one of claims 1 to 54 wherein the water-absorbent resin particle prior to the surface-crosslinking step has an average particle diameter by weight (D50) of between 250 and 500 μm and comprises fine particles having a particle diameter of less than 150 μm in a content of between 0.1% by weight and 5% by weight. The method of any one of claims 1 to 54 wherein the water-absorbent resin particle prior to the surface-crosslinking step has a weight average particle diameter (D50) of between 350 and 450 μm and comprises fine particles having a particle diameter of less than 150 μm in a content of between 0.1% by weight and 5% by weight. 60. A process according to any one of claims 1 to 59, wherein a salt flux conductivity (SFC) of the water-absorbent resin is equal to or greater than 10 [x 10 -7 · cm3 · s · g'1 ]. 61. A process according to any one of claims 1 to 59, wherein the salt flux conductivity (SFC) of the water-absorbent resin is equal to or greater than 20 [x 10 -7 · cm 3 · s · g-1] . 62. A process according to any one of claims 1 to 59, wherein the salt flux conductivity (SFC) of the water-absorbent resin is equal to or greater than 30 [x 10 -7 · cm 3 · s · g -1] . 63. A process according to any one of claims 1 to 59, wherein the salt flux conductivity (SFC) of the water-absorbent resin is equal to or greater than 50 [x 10 -7 · cm 3 · s · g-1] . 64. A process according to any one of claims 1 to 59, wherein the salt flux conductivity (SFC) of the water-absorbent resin is equal to or greater than 70 [x 10 -7 · cm 3 · s · g -1] . 65. A process according to any one of claims 1 to 59, wherein the salt flux conductivity (SFC) of the water-absorbent resin is equal to or greater than 100 [xl0 ~ 7 · cm3 · s · g-1] . The method of any one of claims 1 to 65, wherein the non-load absorbing capacity (CRC) of the water-absorbent resin is 20 or more [g / g], and a flow conductivity. The saline (SFC) of the water-absorbent resin is equal to or greater than 110 [x 10 -7 · cm3 · s · g-1]. The process of any one of claims 1 to 61, wherein the water absorption rate (FSR) of the water-absorbent resin is equal to or greater than 0.35 [g / g / sec], and a salt flux conductivity (SFC) of the water-absorbent resin is equal to or greater than 20 [x 10 ~ 7 · cm 3 · s · g-1]. 68. The process of any one of claims 1 to 67, further comprising one or more spraying steps after the drying step and before the classifying step. 69. The method of claim 68, wherein the washing with water is carried out in the spraying step or the drying step. The method of any one of claims 1 to 69, wherein the dried water absorbent resin has an irregular crushed form obtained by continuous polymerization in a kneader or web continuous polymerization. The method of any one of claims 1 to 70, wherein in the surface crosslinking step, a covalently bonded surface crosslinking agent and an ionically bonded surface crosslinking agent are used in combination. The method of claim 71, wherein the surface crosslinking agents having a dehydration esterification reactivity and the polyvalent metals are used in combination. The method of any one of claims 1 to 71, wherein the dried water absorbent resin introduced in the classification step comprises a surfactant and the temperature is raised to or maintained at or above 40 ° C. The method of any one of claims 1 to 73, wherein in the classification step, a sieve classifier vibrates at a vibration width of 0.7 to 40 mm and a vibration number of 60 to 6000 rpm. The method of any one of claims 1 to 74, wherein in the classification step, a sieve classifier vibrates at a vibration width of 1.5 to 25 mm and a vibration number of 100 to 600 rpm. / min. 76. A method according to any one of claims 1 to 75, wherein in a lower part of the mesh of the metal screen used in the classification step, a striking material is installed. The method of claim 76, wherein the temperature of the impact material is from 40 to 100 ° C. The method of any one of claims 1 to 35, wherein the tensile force (tension) of a metal screen mesh used in the classification step is from 35 to 100 [N / cm]. 79. The method of any one of claims 1 to 78, wherein in the classification step, an air brush is used in a lower portion of the mesh of the metal screen used in the classification step. 80. A process according to any one of claims 1 to 79, wherein the continuous production is carried out for 30 to 365 days. 81. A process according to any one of claims 1 to 80, wherein the continuous production is carried out for 50 to 300 days. 82. A process according to any one of claims 1 to 81, wherein the continuous production is carried out for 100 to 200 days. The method of any one of claims 1 to 82, wherein the productivity of a water-absorbing resin per line is 1 to 10 [t / h]. The method of any one of claims 1 to 83, wherein the productivity of a water-absorbing resin per line is 1.5 to 10 [t / h]. The process of any one of claims 1 to 84, wherein the productivity of a water-absorbent resin per line is 2 to 10 [t / h], 86. A process according to any one of claims 1 to 85, wherein the productivity of a water-absorbent resin per line is 3 to 10 [t / h]. 87. A process according to any one of claims 1 to 86, wherein the water used for washing with water has a water content equal to or greater than 90% by weight. 88. A process according to any one of claims 1 to 87, wherein the water used for washing with water has a water content equal to or greater than 95% by weight. 89. A process according to any one of claims 1 to 88, wherein the water used for washing with water has a water content of 99% or more by weight. 90. A process according to any one of claims 1 to 89, wherein the water used for washing with water has a water content equal to or greater than 99.9% by weight. 91. A process according to any one of claims 1 to 90, wherein the water used for washing with water has a water content of substantially 100% by weight. 92. A method according to any one of claims 1 to 91, wherein the water used for washing with water is selected from industrial pure water, tap water, groundwater, water distilled, deionized water, rainwater. 93. A method according to any one of claims 1 to 92, wherein the water used for washing with water is selected from industrial pure water and tap water. 94. Process according to any one of claims 1 to 93, wherein the water used for washing with water is industrial pure water. 95. A process according to any one of claims 1 to 94, wherein during washing with water, the operation of a production apparatus for washing with water is stopped temporarily. 96. A process according to any one of claims 1 to 94, wherein during washing with water, the production of a water-absorbent resin is continued by replacement with a replacement apparatus.