JP6234668B2 - Method for producing polyacrylic acid (salt) water-absorbing resin - Google Patents

Description

  The present invention relates to a method for producing a polyacrylic acid (salt) water-absorbing resin. More specifically, a polyacrylic acid (salt) -based water-absorbing resin that can stably produce a water-absorbing resin having high physical properties stably by washing the water-absorbing resin continuous production apparatus at regular intervals. It relates to a manufacturing method.

  Water-absorbent resin (SAP / Super Absorbent Polymer) is a water-swellable, water-insoluble polymer gelling agent, such as absorbent articles such as paper diapers and sanitary napkins, water retention agents for agriculture and horticulture, industrial waterstop materials, etc. , Mainly used in disposable applications. As such a water-absorbent resin, those using many monomers and hydrophilic polymers as raw materials have been proposed. Among them, in particular, polyacrylic acid (salt) water-absorbing resin using acrylic acid and / or a salt thereof as a monomer is most frequently used industrially because of its high water absorption performance.

  Such a water absorbent resin is manufactured through a polymerization process, a drying process, a pulverization process, a classification process, a surface cross-linking process, and the like (Patent Documents 1 to 3). With the improvement in performance of paper diapers, which are the main application, water-absorbing resins are also required to have many functions. Specifically, the gel strength, water-soluble component (Patent Document 4), water absorption speed, water absorption capacity under pressure (Patent Document 5), liquid permeability, particle size distribution, urine resistance Many properties of the water-absorbing resin are required, such as properties, antibacterial properties, impact resistance, powder flowability, deodorant properties, coloring resistance, and low dust. Therefore, many proposals have been made in addition to Patent Documents 1 to 23, such as surface cross-linking techniques, additives, and changes in the manufacturing process.

  In recent years, as the amount of water-absorbent resin used in paper diapers increases (for example, 50% by weight or more), liquid permeability has been seen as a more important factor. And many improvement methods and improvement techniques of liquid permeability under load and no-load liquid permeability such as SFC (Saline Flow Conductivity / Patent Document 6) and GBP (Gel Bed Permeability / Patent Documents 7 to 9) have been proposed. Yes.

  In addition, in the above physical properties, many combinations of a plurality of parameters including liquid permeability have been proposed, and a technique for defining impact resistance (FI) (Patent Document 10), a water absorption speed (FSR / Vortex), and the like are defined. A technique (Patent Document 12) that defines the product of a technology (Patent Document 11), a liquid diffusion performance (SFC), and a core absorption amount (DA60) after 60 minutes is known.

  Furthermore, as a method for improving liquid permeability such as SFC and GBP, a technique of adding gypsum before or during polymerization (Patent Document 13), a technique of adding a spacer (Patent Document 14), 5 to 17 [mol / kg] ] Using a nitrogen-containing polymer having a protonizable nitrogen atom (Patent Document 15), a technique using a polyamine and a polyvalent metal ion or polyvalent anion (Patent Document 16), a water-absorbing resin having a pH of less than 6 Are known (Patent Document 17) and polyammonium carbonate (Patent Document 18). In addition to this, a technique using polyamine with a soluble content of 3% by weight or more, and a technique (Patent Documents 19 to 21) for defining the wicking index (WI) and gel strength are known. Moreover, in order to improve coloring and liquid permeability, the technique (patent document 22, 23) which uses a polyvalent metal salt after controlling the methoxyphenol which is a polymerization inhibitor at the time of superposition | polymerization is also known. Moreover, the technique (patent document 24) which performs static elimination as a technique which paid its attention to the classification process is also known. Further, a technique for improving liquid permeability focusing on the classification process (Patent Documents 25 and 26) is also known.

  Further, as a physical property other than liquid permeability, attention is also paid to a water absorption rate (for example, FSR and Vortex), and foam polymerization (described later) is also proposed as a method for improving the water absorption rate. However, in general, it has been difficult to achieve both water absorption speed and liquid permeability. Furthermore, as the particle shape of the water-absorbing resin, a spherical water-absorbing resin is also known in addition to the indefinite shape. The spherical water-absorbing resin is difficult to manufacture because of its shape (described later). In addition, although droplet polymerization (described later) has been proposed as a method for improving liquid permeability, the shape of the particles obtained by droplet polymerization is spherical, and it is difficult to improve liquid permeability. Met.

US Pat. No. 6,727,345 US Pat. No. 7,193,006 US Pat. No. 6,716,894 US Reissue Patent No. 32649 US Pat. No. 5,149,335 US Pat. No. 5,562,646 US Patent Application Publication No. 2005/0256469 US Pat. No. 7,169,843 US Pat. No. 7,173,086 US Pat. No. 6,414,214 US Pat. No. 6,894,665 US Patent Application Publication No. 2008/0125533 US Patent Application Publication No. 2007/0293617 US Patent Application Publication No. 2002/0128618 US Patent Application Publication No. 2005/0245684 International Publication No. 2006/082197 US Patent Application Publication No. 2008/202987 International Publication No. 2006/082189 International Publication No. 2008/025652 International Publication No. 2008/025656 International Publication No. 2008/025655 US Patent Application Publication No. 2010/041550 US Patent Application Publication No. 2010/042612 US Patent Application Publication No. 2011/116300 Specification International Publication No. 2011/115216 International Publication No. 2011/115221

  In order to improve the physical properties of the water-absorbent resin, such as Patent Documents 1 to 26, many surface cross-linking techniques, additives, and manufacturing process changes have been proposed.

  However, changing or adding water-absorbing resin raw materials such as surface cross-linking agents and additives (polyamine polymers, inorganic fine particles, thermoplastic polymers) not only lowers the safety and cost of raw materials but also lowers other physical properties. Could cause. In addition, the addition of a new manufacturing process not only causes high capital investment and increased costs due to its energy, but also requires industrially complicated operation, which may cause a decrease in productivity and physical properties. there were.

  Accordingly, the present invention improves and stabilizes the physical properties (for example, liquid permeability) of the water-absorbent resin by a simple method without the need for changing raw materials or expensive capital investment in order to improve the above problems. It aims to provide a method. The above-mentioned problems are high water absorption type water-absorbing resins and spherical water-absorbing resins, typically spherical water-absorbing resins obtained by reverse phase suspension polymerization or droplet polymerization, and tend to be noticeable. is there. Therefore, the present invention is preferably applied to the production of the water-absorbent resin described above.

  The inventors of the present invention may employ the methods of Patent Documents 1 to 26, particularly Patent Documents 25 and 26 in the production of water-absorbent resins, particularly continuous production, and further in continuous production of 1 [t / hr] or more. As the cause of the deterioration was gradually observed, the cause was investigated. Even if there was no problem in the continuous operation, the water-absorbent resin powder or the water-absorbent resin was in contact with the water-absorbent resin in the production apparatus after the drying process. It has been found that the original ability of the apparatus is reduced by a small amount of agglomerates composed of a mixture of resin fine powder and water forming a thin film. Furthermore, it has been found that recovery of physical properties is insufficient by a washing method other than water washing as a method for removing the aggregate. Then, the problem and cause were solved by performing the water washing of the contact surface with the water absorbing resin in the manufacturing apparatus after the drying process.

  That is, in order to solve the above-described problems, the present invention provides a polymerization step for polymerizing an acrylic acid (salt) aqueous solution to obtain a hydrogel crosslinked polymer, and drying the hydrogel crosslinked polymer to obtain a water-absorbing resin. A drying step for obtaining a dried product, a classification step for classifying the dried water-absorbing resin product to obtain water-absorbing resin particles, and a surface crosslinking step for surface-crosslinking the water-absorbing resin particles before and / or after the classification step. Is a continuous production method of polyacrylic acid (salt) -based water-absorbing resin, comprising the step of contacting the water-absorbing resin with respect to the apparatus used in each step in one or more steps after the drying step A method for continuously producing a polyacrylic acid (salt) -based water-absorbing resin, in which the surface is washed with water.

  A second invention having the same idea as the above invention is a polymerization step of polymerizing an acrylic acid (salt) aqueous solution to obtain a hydrogel crosslinked polymer, and drying the hydrogel crosslinked polymer to absorb water. A drying step for obtaining a dried resin product, a classification step for classifying the dried water-absorbent resin product to obtain water-absorbing resin particles, and a surface cross-linking for surface-crosslinking the water-absorbent resin particles before and / or after the classification step. A process for continuously producing a polyacrylic acid (salt) -based water absorbent resin, wherein the water absorbent rate (FSR) of the water absorbent resin is 0.30 [g / g / s] or more, In one or more steps after the drying step, there is provided a continuous production method of a polyacrylic acid (salt) -based water-absorbent resin, in which a contact surface with the water-absorbent resin is washed with water for an apparatus used in each step.

  A third invention having the same idea as the above invention is a polymerization step of polymerizing an acrylic acid (salt) aqueous solution to obtain a hydrogel crosslinked polymer, and drying the hydrogel crosslinked polymer to absorb water. A drying step for obtaining a dried resin product, a classification step for classifying the dried water-absorbent resin product to obtain water-absorbing resin particles, and a surface cross-linking for surface-crosslinking the water-absorbent resin particles before and / or after the classification step. A continuous production method of a polyacrylic acid (salt) -based water-absorbent resin, comprising the steps, wherein the water-absorbent resin is spherical, or a granulated product thereof, and in one or more steps after the drying step, Provided is a continuous production method of a polyacrylic acid (salt) -based water-absorbing resin, in which a contact surface with the water-absorbing resin is washed with water for an apparatus used in each step.

  According to the present invention, in a method for producing a water absorbent resin including a polymerization step, a drying step, a classification step, and a surface cross-linking step, the physical properties (for example, liquid permeability) after surface cross-linking can be maintained high.

FIG. 1 is a flowchart schematically showing a continuous production process for obtaining the water absorbent resin of the present invention.

  Hereinafter, although the continuous production method of the polyacrylic acid (salt) -based water-absorbing resin according to the present invention will be described in detail, the scope of the present invention is not limited to these descriptions, and the present invention is not limited to the following examples. The present invention can be changed and implemented as appropriate without departing from the spirit of the present invention. Specifically, the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the claims, and technical means disclosed in different embodiments are appropriately combined. Embodiments obtained in this manner are also included in the technical scope of the present invention.

[1] Definition of terms (1-1) "Water absorbent resin" and "Water absorbent resin powder"
The “water-absorbing resin” in the present invention means a water-swellable water-insoluble polymer gelling agent. “Water swellability” means that the CRC (water absorption capacity without pressure) defined by ERT441.2-02 is essentially 5 [g / g] or more, preferably 10 to 100 [g / g. ], More preferably 20 to 80 [g / g]. In addition, “water-insoluble” means that Ext (water-soluble matter) defined by ERT470.2-02 is essentially 50% by weight or less (lower limit: 0% by weight), preferably 30% by weight. Hereinafter, it is more preferably 20% by weight or less, and further preferably 10% by weight or less.

  The “water absorbent resin powder” refers to a water absorbent resin having a certain fluidity as a powder. For example, a water absorbent resin capable of measuring a flow rate (flow rate) defined by ERT450.2-02. It refers to a water-absorbing resin that can be classified by a sieving resin or a PSD (particle size distribution) defined by ERT420.2-02. Specifically, it means a water-absorbing resin having a particle diameter of 5 mm or less as defined by sieve classification.

  The water-absorbing resin can be appropriately designed according to its use and is not particularly limited, but may be a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group. preferable. Further, the total amount (100% by weight) is not limited to a form of a polymer, and may contain an additive or the like as long as the above performance is maintained. That is, even a water-absorbing resin composition containing a water-absorbing resin and an additive is generically referred to as a 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 (polyacrylic acid (salt) -based water absorbent resin) is preferably 70 to 99.9% by weight, and 80 to 99.7% by weight. % Is more preferable, and 90 to 99.5% by weight is still more preferable. As other components other than the water-absorbent resin, water is preferable from the viewpoint of the water absorption speed and the impact resistance of the powder (particles), and if necessary, additives described later are included.

(1-2) “Continuous Manufacturing Method”
“Continuous” in the continuous production method of the present invention means that the production process according to the present invention (for example, a polymerization process, a drying process, a classification process, a surface crosslinking process) is continuously performed for 1 day or longer, This means that all manufacturing processes do not have to be continuous, and even when batch is repeated (continuous batch) or only part of the manufacturing process is stopped, it corresponds to “continuous” of the present invention. To do. Further, a pause period (for example, cooling of the apparatus) or the like may be installed during the batch period, and it is preferable that 50% or more of all the process sections including the batch are in operation.

  The production period in the present invention is preferably 30 days or more, more preferably 50 days or more, particularly preferably 100 days or more, and is carried out substantially continuously to produce a water absorbent resin. The upper limit of the production period is not particularly limited because it is preferably long, but is preferably 365 days or less, more preferably 300 days or less, and particularly preferably 200 days or less.

(1-3) "Polyacrylic acid (salt)"
The “polyacrylic acid (salt)” in the present invention includes an optional graft component, and is a heavy component mainly composed of acrylic acid and / or a salt thereof (hereinafter referred to as “acrylic acid (salt)”) as a repeating unit. Means coalescence. Specifically, as a monomer excluding the crosslinking agent, acrylic acid (salt) is essentially 50 to 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, still more preferably substantially 100. A polymer containing mol% is meant. The salt as a polymer essentially includes a water-soluble salt, preferably a monovalent salt, more preferably an alkali metal salt or an ammonium salt, still more preferably an alkali metal salt, particularly preferably a sodium salt. The shape is not particularly limited, but is preferably in the form of particles or powder.

(1-4) “EDANA” and “ERT”
“EDANA” is an abbreviation for European Disposables and Nonwovens Associations, and “ERT” is an abbreviation for ERT / EDANA Recommended Test Method which is a European standard (almost world standard). is there. In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the ERT original (known document: revised in 2002).

(A) "CRC" (ERT441.2-02)
“CRC” is an abbreviation for Centrifugation Retention Capacity (centrifuge retention capacity) and means water absorption capacity without pressure (hereinafter also referred to as “water absorption capacity”). Specifically, after 0.2 g of the water-absorbing resin in the nonwoven fabric was freely swollen for 30 minutes with respect to a large excess of 0.9 wt% sodium chloride aqueous solution, the water absorption capacity after draining with a centrifuge ( Unit; [g / g]).

(B) “AAP” (ERT442.2-02)
“AAP” is an abbreviation for Absorption Against Pressure, which means water absorption capacity under pressure. Specifically, 0.9 g of the water-absorbent resin is loaded with 2.06 kPa (0.3 psi, 21 [g / cm ² ]) for 1 hour with respect to a large excess of 0.9 wt% sodium chloride aqueous solution. It is the water absorption capacity (unit: [g / g]) after swelling below. In ERT442.2-02, “Absorption Under Pressure” is described, but it is substantially the same as AAP. In the present invention, the load condition was changed to 4.83 kPa (0.7 psi, 50 [g / cm ² ]).

(C) "Ext" (ERT470.2-02)
“Ext” is an abbreviation for Extractables and means a water-soluble component (water-soluble component amount). Specifically, 1.0 g of a water-absorbing resin was added to 200 ml of a 0.9 wt% sodium chloride aqueous solution and stirred for 16 hours at 500 rpm, and then the amount of dissolved polymer was measured by pH titration (unit: weight). %).

(D) “Residual Monomers” (ERT410.2-02)
“Residual Monomers” means the amount of monomer remaining in the water-absorbent resin. Specifically, after adding 1.0 g of water-absorbing resin to 200 ml of 0.9 wt% sodium chloride aqueous solution and stirring for 1 hour at 500 rpm, the amount of dissolved residual monomer is measured by high performance liquid chromatography (HPLC). Value (unit: ppm).

(E) "PSD" (ERT420.2-02)
“PSD” is an abbreviation for Particle Size Distribution, and means a particle size distribution measured by sieving classification. The weight average particle size (D50), the particle size distribution and its width (logarithmic standard deviation σζ) are measured by the method described in European Patent No. 1594556 “(1) Average Particle Diameter and Distillation of Particle Diameter”. Is done. Moreover, when measuring the particle diameter of a particulate hydrogel crosslinked polymer, it measures according to the method disclosed by Unexamined-Japanese-Patent No. 2000-063527.

(F) Other physical properties defined by EDANA “pH” (ERT400.2-02); means the pH of the water-absorbent resin.

  “Moisture Content” (ERT430.2-02); means the water content of the water-absorbent resin.

  “Flow Rate” (ERT450.2-02); means the flow rate of the water-absorbent resin.

  “Density” (ERT460.2-02); means the bulk specific gravity of the water-absorbent resin.

  “Respirable Particles” (ERT480.2-02): Respirable area dust of water absorbent resin.

  “Dust” (ERT490.2-02): means dust contained in the water absorbent resin.

(1-5) “Liquid permeability”
“Liquid permeability” in the present invention refers to the fluidity of a liquid passing between particles of a swollen gel under load or no load. As a representative measurement method, SFC (Saline Flow Conductivity / physiology) Saline flow conductivity) and GBP (Gel Bed Permeability / gel bed permeability).

  “SFC (Saline Flow Inducibility)” refers to the liquid permeability of a 0.69 wt% sodium chloride aqueous solution to 0.9 g of water absorbent resin at a load of 2.06 kPa (0.3 psi). US Pat. No. 5,669,894 Measured in accordance with the SFC test method disclosed in the issue. “GBP (gel bed permeability)” refers to the liquid permeability of a 0.69 wt% sodium chloride aqueous solution to a water absorbent resin under load or free expansion, and is disclosed in International Publication No. 2005/016393. Measured according to GBP test method.

(1-6) Others In this specification, “X to Y” indicating a range means “X or more and Y or less”. Further, “t (ton)” as a unit of weight means “Metric ton”, and “ppm” means “weight ppm” or “mass ppm” unless otherwise noted. Furthermore, “weight” and “mass”, “wt%” and “mass%”, “part by weight” and “part by mass” are treated as synonyms. Further, “˜acid (salt)” means “˜acid and / or salt thereof”, and “(meth) acryl” means “acryl and / or methacryl”. Furthermore, regarding measurement of physical properties and the like, unless otherwise noted, measurement is performed at room temperature (20 to 25 ° C.) / Relative humidity 40 to 50%.

[2] Water washing method of polyacrylic acid (salt) water-absorbing resin production apparatus (2-1) Water washing The present invention comprises a polymerization step of polymerizing an acrylic acid (salt) aqueous solution to obtain a hydrogel crosslinked polymer, A drying step for drying the hydrogel crosslinked polymer to obtain a dried water absorbent resin, a classification step for classifying the dried water absorbent resin to obtain water absorbent resin particles, and / or before the classification step. A method for continuously producing a polyacrylic acid (salt) -based water-absorbing resin, which sequentially includes a surface-crosslinking step of surface-crosslinking the water-absorbent resin particles, and in each step in one or more steps after the drying step Provided is a continuous production method of a polyacrylic acid (salt) -based water-absorbing resin, in which a contact surface with the water-absorbing resin is washed with water for an apparatus to be used. Hereinafter, the water washing of the present invention will be described in detail.

  The present invention is characterized in that the contact surface with the water absorbent resin in the continuous production apparatus after the drying step is washed with water. “Washing” in the present invention may be performed continuously at the same time as the production of the water-absorbent resin or intermittently at regular intervals, but is preferably intermittently performed at regular intervals. It should be noted that washing without water or washing other than water is not preferable because physical properties (particularly liquid permeability and fine powder amount) may deteriorate with time and may not be recovered after washing.

  The substance to be removed by washing with water is typically a water absorbent resin powder (typically passed through a JIS standard sieve having an opening of 1000 μm), particularly a water absorbent resin fine powder (typically a JIS standard sieve having an opening of 150 μm). Passing material), or aggregates thereof, or agglomerates made of a mixture of water-absorbent resin powder or water-absorbent resin fine powder and water are attached to the water-absorbent resin production apparatus. In addition, the said aggregate is produced by the process of adding water and aqueous solution to a water absorbing resin, or the dew condensation water in an apparatus.

  In the production of a water-absorbent resin, particularly continuous production, and further in continuous production of 1 [t / hr] or more, the present inventors can gradually reduce physical properties even if the methods of Patent Documents 1 to 26 are adopted. Therefore, when the cause was sought, a small amount of agglomerates composed of a mixture of water absorbent resin powder or fine powder and water adhered on the contact surface with the water absorbent resin in the manufacturing apparatus after the drying process, so It has been found that the performance of is reduced. Furthermore, it has been found that recovery of physical properties is insufficient by a washing method other than water washing as a method for removing the aggregate.

  Thus, the continuous production method of the present invention can be suitably controlled in the production of a huge scale. From this viewpoint, in the present invention, the production amount of the water absorbent resin per line is preferably 1 [t / hr] or more, more preferably 1.5 [t / hr] or more, and further 2 [t / hr] or more. It is preferably 3 [t / hr] or more. The upper limit of the production amount is not particularly limited, and can be appropriately determined, for example, 10 [t / hr]. One line refers to a series of manufacturing steps of the water-absorbent resin, and when the step is branched, it is defined by the processing amount in the surface cross-linking step (one apparatus).

(Rinse cycle)
When water is washed intermittently at regular intervals, the water washing cycle is not particularly limited, and 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, etc. The upper limit corresponds to a large-scale maintenance of the manufacturing apparatus performed once a year, but may be appropriately determined every 300 days, every 200 days, etc. depending on the production amount, the manufactured product number, and the like.

  Therefore, although the period of the water washing in the present invention may be determined in advance by the above period, it is preferable to determine by the deterioration or change of the physical properties while confirming the physical properties of the obtained water absorbent resin. The decrease or change in the physical properties is due to various physical properties described later in [4], in particular water absorption capacity under pressure (for example, AAP), liquid permeability (for example, SFC), particle size distribution (in particular, fine powder amount, and further 150 μm opening JIS standard). Etc., and typically can be determined by particle size distribution or liquid permeability. Preferably, the washing time is determined based on a change in particle size (particle size distribution) or a change in liquid permeability. More specifically, the period of water washing in the classification process is determined by the change in particle size (particle size distribution) or liquid permeability after the classification process.

  During the washing period, the production apparatus to be washed may be temporarily stopped, or the production of the water-absorbent resin may be continued by replacing with a spare machine. The washing with water may be performed as it is, or may be performed by disassembling part or all of the apparatus, such as during overhaul. During continuous production, the same water absorbent resin may be produced under substantially the same production conditions, or different water absorbent resins may be produced by changing the production conditions.

(Washing water)
The water used in the water washing of the present invention (hereinafter sometimes referred to as “washing water”) is not limited to water alone (100% by weight of water), and a small amount of solvent or additive is used to enhance the washing effect. The content of water is preferably 90% by weight or more, more preferably 95% by weight or more, still more preferably 99% by weight or more, particularly preferably 99.9% by weight or more, and substantially 100% by weight. Most preferred. The water can be appropriately selected from industrial pure water, tap water, ground water, distilled water, ion-exchanged water, rainwater, and the like. Of these, industrial pure water and tap water are preferably used, and industrial pure water is more preferably used.

  Although it does not specifically limit as said additive (solvent), For example, water-soluble organic solvents, such as methanol, ethanol, isopropanol, and acetone, More preferably, the low boiling-point water-soluble organic solvent whose boiling point is 30-100 degreeC; Sodium chloride, sulfuric acid Alkali metal salts such as sodium and potassium chloride; alkaline earth metal salts such as calcium chloride and magnesium chloride; trivalent or higher polyvalent metal salts such as aluminum sulfate; bases such as sodium carbonate, sodium hydrogen carbonate and sodium hydroxide; Various surfactants; builder and the like. Although these inorganic salts and / or alkaline aqueous solutions may be used in combination, water within the above-described range is used from the viewpoint of cost-effectiveness and contamination to the water-absorbent resin.

(Washing water temperature)
The form of the washing water used in the water washing of the present invention is not particularly limited, and gas or liquid water can be used, but liquid water is particularly preferable. The temperature of the washing water is appropriately determined within the range from the freezing point to the boiling point, but warm water is preferable from the viewpoint of the washing effect. Specifically, the temperature of the hot water is preferably higher than room temperature (20 to 25 ° C.) to the boiling point, more preferably 30 to 100 ° C., further preferably 35 to 100 ° C., particularly preferably 40 to 95 ° C., 45 -90 ° C is most preferred. Moreover, when using water vapor | steam as gaseous water, as the temperature, 500 degrees C or less is preferable, 300 degrees C or less is more preferable, The atmospheric pressure heating water vapor of 200 degrees C or less is still more preferable. When the temperature of the washing water is low, the washing effect is inferior, which is not preferable. On the other hand, if the temperature of the washing water is high, an effect commensurate with the means for increasing energy and boiling point (pressurization and use of additives) cannot be obtained, and there is a risk of deterioration in workability and burns during washing. Absent.

(Pressure during washing)
The water washing of the present invention can be performed under normal pressure, under pressure, or under reduced pressure, and is not particularly limited. When liquid water is used, the boiling point of water (maximum temperature in liquid water) may be raised or lowered from 100 ° C. depending on pressure and the above-mentioned additives. It is preferably performed under a pressure of ± 5% before and after that, and further ± 1% (within the range of daily atmospheric pressure change).

(Washing method)
The method of washing the water-absorbing resin continuous production apparatus in the present invention with water is not particularly limited, and the water-absorbing resin may be washed while continuing to produce the water-absorbing resin, or the production of the water-absorbing resin may be temporarily or periodically. You may stop and wash with water. Examples of the method of washing with water while continuing the production of the water-absorbent resin include a method of continuously injecting a water flow into the production apparatus, a method of injecting a water flow while continuously drying, and the like. In addition, examples of the method of temporarily or periodically stopping the production of the water-absorbing resin and washing with water include a method of periodically stopping the device and washing part or all of the device with water. In addition, the method for washing with water is not particularly limited, and water injection, showering, dipping, water wiping, water brushing, and the like can be given directly to the manufacturing apparatus. These methods may be used in combination or repeated multiple times. However, it is preferable that the contact surface with the water-absorbent resin in the manufacturing apparatus after the drying step is washed with water by water immersion or water injection.

  Moreover, although the place which performs water washing may be one place, Preferably water washing is carried out with other manufacturing apparatuses including a plurality of places, especially a classification device (especially a metal sieve) in the classification process or an apparatus used in the surface cross-linking process. It is preferable. That is, washing with water is preferably performed at least in a classification step or a surface crosslinking step, and more preferably performed in at least a classification step.

(Immersion)
In the present invention, “immersion” refers to water absorption adhering to a place where physical removal is difficult, such as dead space, by immersing all or part of the manufacturing apparatus or decomposition products in a large excess of water (washing water). It means a method of making the resin easily swelled and removed.

  Also, in the present invention, the case where the inside of an apparatus (for example, a hopper, a pipe, a heat treatment apparatus, a cooling apparatus, etc.) in which a water-absorbing resin is reacted, filled, stored, etc. is “filled” with water and washed. Although it is classified as “immersion”, it may be referred to as “water injection and filling” if necessary. That is, the water washing of the present invention is performed by immersing the apparatus in water or injecting (filling) water into the apparatus, and is generally performed by immersing water.

  Although it does not specifically limit as immersion time in this invention, 1 minute-10 days are preferable, 1 hour-5 days are more preferable, 1 hour-3 days are still more preferable. It determines suitably within the said range.

  Further, the washing water during the immersion may be static (no stirring) or dynamic (stirring including a water flow). The washing water after the immersion may be appropriately replaced or partially replaced (overflow), or may be reused a plurality of times.

(Pressurized water flow)
The washing water used in the water washing of the present invention may be used under pressure (hereinafter referred to as “pressurized water flow”). In this case, the degree of pressurization may be a pressurized water flow of ultra-high pressure (gauge pressure of 500 [kg / cm ² ] or more), but preferably a gauge pressure of 1 to 400 [kg / cm ² ] from the viewpoint of cleaning effect. Preferably, a pressurized water flow having a gauge pressure of about 5 to ²⁰⁰ [kg / cm ² ] may be used. Therefore, expensive equipment for obtaining an ultra-high pressure water stream is not required. The gauge pressure can be appropriately selected according to the structure of the manufacturing apparatus to be washed. For example, when the manufacturing device to be washed is a device having a delicate structure or low strength (for example, a sieve), it is preferable to perform washing with a gauge pressure of 200 [kg / cm ² ] or less. Thereby, the deformation | transformation and damage of an apparatus can be prevented. On the other hand, when the manufacturing apparatus to be washed is a high-strength apparatus (for example, a paddle dryer or a pulverizing apparatus), the apparatus may be washed with a higher gauge pressure (for example, 400 [kg / cm ² ] or less). . Moreover, when injecting the said pressurized water flow, a flat nozzle, a rotation nozzle, or a push-in type nozzle can be utilized.

  In addition, it does not specifically limit as an apparatus which generates a pressurized water flow, A commercially available apparatus can be utilized. Specifically, Sugino Machine Co., Ltd. high pressure cleaning equipment, Tokyo Isuzu Motors Co., Ltd. stationary ultra high pressure cleaning unit, KIT Co., Ltd. automatic high pressure cleaning system, URACA Co., Ltd. cleaning system, Kercher Japan ( And hot water high pressure washer. Appropriate equipment can be selected depending on the manufacturing equipment to be washed.

(Manufacturing equipment to be washed)
Washing with water in the present invention is performed on a water-absorbent resin production apparatus after the drying process, particularly a production apparatus after the crushing process. From the viewpoint of the cleaning effect, washing with water is preferably performed on a production apparatus that is operated by heating, more preferably 35 to 150 ° C., and even more preferably 40 to 100 ° C. In the manufacturing apparatus that operates in the above temperature range, the water-absorbing resin is reduced to 0.00%. There is a high possibility that several to several weight% of water volatilizes and aggregates, and this moisture forms an aggregate with the water absorbent resin powder or the water absorbent resin fine powder, which adheres to the inner surface and dead space of the production apparatus. On the other hand, in the case of a manufacturing apparatus that is heated to a high temperature exceeding 100 ° C., and moreover 150 ° C., water is evaporated and released out of the system, so that such problems are few. Further, in the case of a manufacturing apparatus that operates at a temperature lower than 35 ° C. or even lower than 40 ° C., it is not preferable because it lacks the stability of the operation.

  Or it is preferable that water washing is performed with respect to the apparatus stirred or vibrated. Aggregates with the water absorbent resin powder or the water absorbent resin fine powder are likely to adhere to the inner surface or dead space of the stirring or vibrating device. For this reason, the effect (improvement and stability of the physical properties of the water-absorbent resin, particularly the liquid permeability) can be effectively achieved by washing the apparatus with water. Here, the device for stirring or vibrating is not particularly limited, but is preferably a mixing device used in a mixing step of mixing water or an aqueous solution with a water absorbent resin; or a classification device used in a classification step. Here, examples of the mixing device include a mixing device described in the following “(d) mixing device in mixing step (surface crosslinking step)”. Further, as the classifier, the following classifier (particularly vibration type), the dryer (particularly stirring or vibration type) described in the following section “(3-2) Drying step”, the following “(b) Heat treatment” Examples include the heat treatment apparatus described in the section “Heat treatment apparatus in step (surface crosslinking step)”.

  Further, the manufacturing apparatus to be washed may have a resin-coated contact surface with the water-absorbing resin, but is preferably made of stainless steel (material: SUS304 or the like), and its surface roughness (Rz) is preferably 150 nm. In the following, smoothing is more preferably performed to 100 nm or less, and further preferably to 50 nm or less. Further, the lower limit of the surface roughness (Rz) is preferably 0 nm, but there is no great difference even if it is about 10 nm, and about 20 nm is sufficient. The surface roughness (Rz) means the maximum value of the maximum height (nm) of the surface irregularities. Other surface roughness (Ra) is also defined by JIS B 0601-2001. Hereinafter, the manufacturing apparatus to be washed will be described. The operation conditions for each step will be described later in [3].

  Below, the process in which it is preferable to perform the water washing process which concerns on this invention is demonstrated. In addition, this invention is not limited to the following process.

(A) Drying device in the drying step The water washing of the present invention may be performed on the drying device in the drying step. That is, since the drying temperature (operating temperature) in the drying step is usually higher than the above-described temperature range, it is considered that there is a low possibility that aggregates of water-absorbing resin containing water adhere to the drying device. However, a water-absorbing resin is usually dried using a ventilation band type continuous dryer or the like, and an opening such as a metal net or a punching plate used for the drying device (a hole or slit of several to several tens of mm ² ). , Preferably 0.2 to 10 mm ² ), the water-absorbent resin hydrogel finely divided product enters, is dried as it is, and permanently closes the opening, resulting in reduced performance of the drying device and local drying unevenness, Or generation | occurrence | production of an undried material (rubber-like material in the middle of drying) may be caused. In addition, the hydrogel fine particles that have been permanently clogged are often colored because they are heated for a long time. If the colored foreign matter is detached due to some kind of trigger and mixed into the water-absorbent resin as a product, the product is detected as a colored foreign matter with little influence on the manufacturing apparatus, and there is a risk that the product cannot be shipped.

  Therefore, as these countermeasures, in the present invention, the entire drying device, the inside of the drying device (particularly the contact surface with the water-absorbing resin), particularly a metal net, a punching plate (perforated plate) and the like are preferably washed with water. The shape of the metal net or punching plate (the shape or size of the hole) is not particularly limited, and may have protrusions or irregularities.

  That is, the water washing in the drying process of the present invention is performed on the metal net or punching metal (punching plate) of the drying device to prevent clogging of the holes. Among them, the present invention is more preferably applied to a water-absorbing resin or a spherical water-absorbing resin having a particularly high water absorption rate (FSR) in which pores are severely clogged. The “spherical shape” is not limited to a true sphere, and is a concept including a flat spherical shape, irregularities and aggregates, and refers to the shape of a water-absorbent resin obtained by spray polymerization or droplet polymerization into a gas phase. The punching metal is preferably used in a fluidized bed dryer or a band dryer.

(B) Heat treatment device or cooling device in heat treatment step or cooling step (surface crosslinking step) The water washing of the present invention is relative to the heat treatment device or cooling device in the heat treatment step or cooling step (surface crosslinking step). May also be performed. The said heat processing process is a process of performing the heat processing for the further crosslinking reaction and modification | reformation of the obtained water absorbing resin particle, and can use a normal dryer or a heating furnace. Examples of the heat treatment apparatus or cooling apparatus used include a groove type mixing dryer, a rotary dryer, a paddle dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, and an infrared dryer.

  That is, preferably, washing with water is performed on the inner surface of at least one of a mixing device (described later (d)), a heat treatment device, and a cooling device in the surface crosslinking step. In addition, in the said heat processing apparatus and cooling device, additives other than a surface crosslinking agent can be added, and it can also be used as a mixer (refer the following (d) term) mentioned later. Preferably, an additive and a second surface cross-linking agent are added, and particularly preferably added with water.

  Similar to the drying step, the heat treatment temperature (operating temperature) in the heat treatment step is usually higher than the above-described temperature range, so that the water-absorbent resin aggregate containing water may adhere to the heat treatment apparatus. Is considered low. However, the object to be heated (mainly a mixture of the water-absorbent resin and the surface cross-linking agent) is colored by staying in a dead space or the like in the apparatus for a long time, and if this is detached, the same colored foreign matter as in the drying step There is a risk that the product will not be shipped. The present invention is preferably applied as a countermeasure.

(C) Classifying device in the classification step The water washing of the present invention is mainly performed on a manufacturing device after the drying step that is stirred or vibrated, particularly on a manufacturing device after the pulverization step, and further, a classification device in the classification step, in particular Opening is performed on a metal sieve having a mesh size of 45 to 2000 μm. Hereinafter, the classification apparatus in the classification process will be described.

  The classification step in the present invention is a step of sieving the particle size distribution of the water-absorbent resin into a desired range, and is performed before and / or after the surface cross-linking step. The step of classifying to a predetermined particle size before surface crosslinking is referred to as the first classification step, and the step of classification after the surface crosslinking step is referred to as the second classification step (granulation step). In the present invention, both of these classification steps are performed. preferable. That is, it is preferable to perform the classification step before and after the surface crosslinking step.

  In the step of classifying the water-absorbent resin, the water-absorbent resin enters the opening of the metal sieve to be used, which causes a decrease in classification efficiency, which may cause an increase in the amount of fine powder and a decrease in physical properties. The present invention is preferably applied as a countermeasure.

(Classification network)
In the present invention, the water absorbent resin is classified using a metal sieve. In the present invention, the metal sieve is preferably washed with water.

  Examples of the metal sieve to be washed with water include various standard sieves such as JIS, ASTM and TYLER. These sieves may be plate sieves or mesh sieves. The shape of the mesh screen is appropriately selected with reference to JIS Z8801-1 (2000) and the like. The opening of the standard sieve is preferably 10 μm to 100 mm, more preferably 20 μm to 10 mm, still more preferably 45 to 2000 μm, still more preferably 50 μm to 1 mm, and one or more kinds of sieves, particularly metal sieves. Is used.

  That is, in the present invention, the metal mesh is preferably washed with water, more preferably the metal mesh with an opening of 50 μm to 1 mm is washed with water, more preferably the metal mesh for drying or classification is washed with water, particularly preferably for classification. The metal net (sieving net) is washed with water.

In addition, the area of the screen surface (the area of the metal screen) is preferably 1 to 10 [m ² / sheet] and more preferably 1.5 to 7 [m ² / sheet] from the viewpoint of classification efficiency.

  In the sieving classification, only the upper part may be classified or only the lower part may be classified, but it is preferable to classify the upper and lower limits simultaneously. That is, a plurality of sieves are preferably used at the same time, and more preferably at least three types of sieves are used from the viewpoint of improving physical properties. As such a method, it is preferable to use an intermediate sieve or an upper sieve in addition to the upper and lower predetermined sieves. As a suitable sieve, for example, the upper limit is a sieve of 850 to 1000 μm, 710 to 850 μm, and 600 to 710 μm, and the lower limit is a sieve of 150 to 225 μm. More preferably, a sieve may be appropriately added in the middle or upper part.

(Classification device)
The classifying device used in the present invention is not particularly limited as long as it has a sieve screen surface, and examples thereof include those classified as a vibrating screen or a shifter. Vibrating screens include tilted, low-head, Hum-mer, Rheum, Ty-Rock, Gyrex, and elliptical vibration (Eliptex). The shifter includes a reciprocating type, Exonon-grader, Traversator-sieb, Sauer-meyer, a gyratory shifter (Gyratory), a gyroshifter and a rotex screen (Ro-tex). These are the movement shape of the mesh surface (circle, ellipse, straight line, arc, pseudo ellipse, spiral, spiral), vibration method (free vibration, forced vibration), drive method (eccentric shaft, unbalanced weight, electromagnet, impact ), Inclination of the mesh surface (horizontal type, inclined type), installation method (floor type, hanging type), etc. Above all, the metal sieve mesh has a three-dimensional motion trajectory consisting of eccentric inclination, radial inclination (inclination of the sieve mesh that disperses the material from the center to the periphery) or tangential inclination (inclination of the sieve mesh that controls the discharge speed on the mesh). What is drawn is preferred.

  In particular, from the viewpoint of the effect of the present invention, a classifier that moves the screen surface in a spiral manner by a combination of radial inclination and tangential inclination, such as a swing type (Tumbler-Screening machines), is preferable.

(D) Mixing device in the mixing step (surface cross-linking step) The water washing of the present invention is mainly performed on the manufacturing device after the drying step, which is stirred or vibrated, in particular, on the manufacturing device after the pulverization step, and further absorbs water. It is performed on a mixing apparatus in a mixing step (preferably a surface cross-linking step or a subsequent step) in which water or an aqueous solution is mixed with the resin. Hereinafter, the mixing apparatus in the mixing step will be described. In addition, about mixing of an additive, it describes also in (3-8).

  The mixing step in the present invention is a step of mixing an additive, water, or an aqueous solution for further crosslinking reaction or modification of the water-absorbent resin, and can be performed using a normal dynamic or static mixer. . In addition, the case where an additive is added at the time of cooling in the surface cross-linking step is also included in the mixing step.

  That is, in the present invention, the inner surface of a mixer that preferably mixes water, an aqueous solution or an aqueous dispersion with a water absorbent resin is washed with water. More preferably, water washing is performed on the inner surface of the mixer in the surface cross-linking step or a subsequent mixing step.

  In the water-absorbing resin mixing step, water or an aqueous solution is mixed with the water-absorbing resin, so that it is expected that the water content of the water-absorbing resin increases and the viscosity increases. For this reason, the highly viscous water-absorbing resin adheres to the dead space of the mixing apparatus and stays for a long time, and is often colored. If the colored foreign matter is detached due to some kind of trigger and mixed into the water-absorbent resin as a product, the product is detected as a colored foreign matter with little influence on the manufacturing apparatus, and there is a risk that the product cannot be shipped. Therefore, the present invention is preferably applied to water washing of the mixing device as a countermeasure against these.

  The mixing apparatus used in the present invention includes, for example, a high-speed stirring mixer (high-speed continuous mixer), a vertical mixer, a cylindrical mixer, a double-wall cone mixer, a V-shaped mixer, and a ribbon-type mixer. Machine, screw type mixer, fluidized-type furnace rotary disk type mixer, airflow type mixer, twin-type kneader, internal mixer, pulverizing type kneader, rotary mixer, screw type extruder, etc. A high-speed agitation type mixer having a stirring shaft equipped with a stirring blade or a stirring blade is preferable, and a high-speed stirring type mixer having a stirring shaft equipped with a stirring blade (for example, a turbulizer or a proshear mixer) is more preferable.

  In addition, the said high-speed stirring type mixer means the mixer which the mixing axis | shaft provided with the several stirring board rotates at 100-5000 rpm normally, Preferably it is 200-4000 rpm, More preferably, it produces a mixing force by 500-3000 rpm. To do. In the present invention, the mixing is preferably within 3 minutes, more preferably within 1 minute (lower limit is about 1 second) in a high-speed stirring mixer, and continuous mixing is particularly preferable.

(E) Pulverizing device in the pulverizing step The water washing of the present invention may be performed on the pulverizing device in the pulverizing step. The said grinding | pulverization process is a process of grind | pulverizing the water-absorbent-resin dried material for obtaining the water-absorbent-resin pulverized material, the coarse particle | grains etc. which do not pass the metal sieve in a classification process, and is obtained by the said mixing process or heat processing process. Also included is a step of grinding the agglomerates.

  Examples of the pulverizer used in the present invention include a knife mill, a hammer mill, a pin mill, a jet mill, a roll mill, a hammer mill, a roll granulator, a joke crusher, a gyle crusher, a cone crusher, a roll crusher, and a cutter mill. Conventionally known grinding devices can be used. In addition, what is equipped with the means to heat the inner wall face of a grinding | pulverization apparatus is preferable.

  In the pulverization step, the inner wall surface of the pulverizer is heated from the outside, the inner wall surface temperature of the pulverizer is set to 30 to 150 ° C., or the inner wall surface temperature of the pulverizer is set to the powder temperature of the water absorbent resin. It is preferable not to lower the temperature by 20 ° C. or more.

(F) Transportation device in the transportation process The water washing of the present invention may be performed on the transportation device in the transportation process. The said transporting process is a process of transporting the water absorbent resin such as dried water absorbent resin after drying, pulverized water absorbent resin and the like.

  Examples of the transportation apparatus used in the present invention include pneumatic transportation, belt conveyor, screw conveyor, chain conveyor, vibration conveyor, pneumatic conveyor, etc., and means for heating and / or keeping the temperature of the inner wall surface from the outside. Those provided are preferred. Among these, pneumatic transportation is particularly preferable.

(G) Storage device in storage step The water washing of the present invention may be performed on a storage device in the storage step. The said storage process is a process of storing water absorbent resin, such as dried water absorbent resin dried product and pulverized water absorbent resin pulverized product. That is, the said storage process is a process installed between each manufacturing process of a water absorbing resin, and storing the water absorbing resin during manufacture or after manufacture.

  Examples of the storage device used in the present invention include a silo, a hopper, a tank and the like, and those having a means for heating the inner wall surface from the outside and / or a means for keeping warm are preferable. Furthermore, a storage tank having an inner surface made of iron or stainless steel is preferable from the viewpoint of wearability and chargeability.

  Of the above (a) to (g), it is preferable that at least one device selected from (a) to (e), more preferably a plurality of devices, be washed with water. Here, in the case where (e) the pulverization step is washed with water, it is more preferable to further include one or more pulverization steps before the classification step after the drying step. Particularly preferably, washing with water is performed in a pulverization step or a drying step. In addition, when performing water washing by the several process of (a)-(g), water washing can be performed simultaneously or separately (separate time).

(A) Drying device in the drying step (b) Heat treatment device or cooling device in the heat treatment step or cooling step (surface crosslinking step) (c) Classification device in the classification step (d) Mixing step (water, aqueous solution or Mixing device in water dispersion mixing process, especially surface cross-linking step) (e) Grinding device in pulverization process (manufacturing device after washing with water)
In this invention, it is preferable to use the manufacturing apparatus after water washing, after removing water | moisture content, especially after drying. The method for removing moisture is not particularly limited, but may be wiped with a water-absorbing material such as cloth, or may be left to dry naturally at room temperature (20 to 25 ° C.) or in the sun. The apparatus may be dried by removing moisture using a hot air dryer or an air flow (for example, high pressure gas).

(Conventional technology)
As a conventional method for producing a water-absorbent resin, the cleaning of the monomer is well known, and the pipes and the like are washed in order to prevent clogging due to polymerization in the monomer transfer pipe or at the pipe outlet, as described in the following patent document. 27 and its FIG. 2, the following patent document 28, its FIG. 1, and the following patent document 29. U.S. Pat. No. 6,057,059 discloses the cleaning of monomers with a gas stream.

  In addition, cleaning the polymerization belt is disclosed in Patent Documents 30 and 31 below. Patent Document 31 discloses cleaning of a polymerization belt and a meat chopper and recycling of a hydrogel. The following Patent Document 33 discloses cleaning of water-absorbing resin deposits by a high-pressure water stream such as a polymerization reactor inner wall surface of reverse phase suspension polymerization, a stirrer surface, a transfer line inner wall surface, and the like. Patent Document 34 discloses a method for removing an adhering polymer from a main surface of a polymer production apparatus, characterized by treating a water-soluble polymer and / or a water-swellable polymer adhering substance with an inorganic salt aqueous solution and / or an alkaline aqueous solution. Disclosure.

  Although these patent documents 27-34 have the indication about the washing | cleaning of a monomer or a polymer gel, about the manufacturing apparatus after a drying process, especially a grinding | pulverization process, the washing | cleaning of an apparatus, especially the washing | cleaning in a classification process, and this invention Disclose issues and effects.

Conventionally, handling of the water-absorbent resin after drying is performed at low humidity because it dislikes water, and in general, suction by dry powder or dust vacuum has been frequently used for its removal. It has been found that liquid permeability is improved by washing with water. In the present invention, it is also possible to clean the polymerization vessel and the monomer transfer pipe described in Patent Documents 27 to 34. However, such cleaning is substantially effective for solving the problems of the present invention. Does not contribute.
The method for sieving and classifying the water-absorbent resin is disclosed in, for example, Patent Document 24 (International Publication No. 2010/032694) and the following Patent Documents 35 to 40. These Patent Documents 24 and 35 to 40 do not suggest any problems or effects of washing with water or the present invention. Moreover, also in the said patent documents 1-23, the classification method including the water washing of this invention is not disclosed at all. In general, the suction of dry powder or dust with vacuum has been frequently used for the removal. However, the above Patent Documents 25 and 26 disclose the use of a tapping ball or an air brush as a sieve. Have found that the liquid permeability is improved by washing with water.

(Patent Document 27) JP-A-2006-160844 (Patent Document 28) US Pat. No. 6,667,372 (Patent Document 29) JP-A-2006-199862 (Patent Document 30) US Patent Application Publication No. 2009/0315204 Description (Patent Document 31) Pamphlet of International Publication No. 2009/001954 (Patent Document 32) European Patent Application Publication No. 2066737 (Patent Document 33) JP-A-6-328044 (Patent Document 34) JP-A-1- No. 242602 (Patent Document 35) US Pat. No. 6,164,455 (Patent Document 36) US Patent Application Publication No. 2008/0202987 (Patent Document 37) US Patent Application Publication No. 2009/0261023 (Patent Document) 38) US Patent Application Publication No. 2009/0194462 (Patent Document 39) US Patent Application Publication No. 2009/0266747 (Patent Document 40) US Patent Application Publication No. 2010/0101982 [3] Method for Producing Polyacrylic Acid (Salt) Water Absorbing Resin In [3], a method for producing a polyacrylic acid (salt) water-absorbing resin will be described with a focus on operating conditions in each production process.

  In addition, among the manufacturing methods of the water-absorbent resin described in Patent Documents 24-26, the polymerization step to the surface cross-linking step are the same as the (3-1) polymerization step to (3-6) surface cross-linking step of the present invention. Can be applied.

  In addition, as described in [2] above, the water washing in the (3-1) polymerization step and (3-2) gel atomization step does not substantially contribute to the solution of the problem of the present invention. It is outside the scope of the invention. Therefore, in the present invention, water washing is performed after (3-3) the drying step, particularly after (3-4) the pulverization step.

(3-1) Polymerization step This step is a step of polymerizing an acrylic acid (salt) aqueous solution to obtain a hydrogel crosslinked polymer.

(Monomer (excluding crosslinking agent))
The water absorbent resin according to the present invention uses an aqueous solution of acrylic acid (salt) as a raw material (monomer). The aqueous solution contains acrylic acid (salt) as a main component within the above range (1-2). The partially neutralized salt of acrylic acid is not particularly limited, but a monovalent salt of acrylic acid selected from alkali metal salts, ammonium salts, and amine salts of acrylic acid is preferable from the viewpoint of water absorption performance of the water absorbent resin. An alkali metal salt of an acid is more preferable, an acrylate selected from a sodium salt, a lithium salt, and a potassium salt is further preferable, and a sodium salt is particularly preferable.

  The neutralization may be performed with a monomer before polymerization, may be performed with a hydrogel after polymerization, or may be used in combination. The neutralization rate is preferably 10 to 100 mol%, more preferably 30 to 95 mol%, still more preferably 50 to 90 mol%, and particularly preferably 60 to 80 mol%.

  The above-mentioned monomers (including the following crosslinking agent) are usually polymerized in an aqueous solution, and the solid content thereof is usually 10 to 90% by weight, preferably 20 to 80% by weight, more preferably 30 to 70% by weight. More preferably, it is 35 to 60% by weight, particularly preferably 35 to 55% by weight.

  Furthermore, in order to improve various physical properties of the water-absorbing resin obtained, aqueous solution such as starch, polyvinyl alcohol, polyacrylic acid (salt) is added to acrylic acid (salt) aqueous solution or water-containing gel, dried product or powder after polymerization. Additives described later such as a water-soluble resin or a water-absorbing resin, various foaming agents (carbonates, azo compounds, bubbles, etc.), surfactants, chelating agents and the like may be added as optional components. The amount of the water-soluble resin or water-absorbent resin is preferably 0 to 50% by weight, 0 to 20% by weight, 0 to 10% by weight, and 0 to 3% by weight with respect to the monomer. Moreover, 0-5 weight% is preferable with respect to a monomer and non-polymeric additives, such as the said foaming agent and surfactant, 0-1 weight% is more preferable. The lower limit of the additive amount when the additive is added is not particularly limited as long as the physical properties of the obtained water-absorbent resin are not particularly impaired, but 0.1% by weight with respect to the monomer. Preferably, 0.5% by weight is more preferable.

  Moreover, in this invention, when using acrylic acid (salt) as a main component in the range as described in said (1-2), the other hydrophilic or hydrophobic unsaturated monomer may be included. Examples of such other monomers include, but are not limited to, methacrylic acid, (anhydrous) maleic acid, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfone. Acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2-hydroxyethyl (meth) acryloyl phosphate, (meth) acrylic Roxyalkanesulfonic acid, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N , N-dimethylaminopropyl (me ) Acrylamide, 2-hydroxyethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate , Stearyl acrylate and salts thereof.

(Crosslinking agent (internal crosslinking agent))
In the present invention, it is particularly preferable to use a crosslinking agent (hereinafter sometimes referred to as “internal crosslinking agent”) from the viewpoint of water absorption characteristics. The amount of the internal crosslinking agent used is preferably from 0.001 to 5 mol%, more preferably from 0.005 to 2 mol%, more preferably from 0.01 to 1 with respect to the above monomer excluding the crosslinking agent, from the viewpoint of physical properties. The mol% is more preferable, and 0.03 to 0.5 mol% is particularly preferable.

  The internal crosslinking agent that can be used is not particularly limited, and examples thereof include a polymerizable crosslinking agent with acrylic acid, a reactive crosslinking agent with a carboxyl group, and a crosslinking agent having both of them. Specifically, N, N′-methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (polyoxyethylene) trimethylolpropane tri (meth) acrylate, poly (meth) are used as the polymerizable crosslinking agent. Examples include compounds having at least two polymerizable double bonds in the molecule, such as allyloxyalkanes. The reactive crosslinking agent is a polyglycidyl ether (such as ethylene glycol diglycidyl ether), a covalent crosslinking agent such as a polyhydric alcohol (such as propanediol, glycerin, or sorbitol), or a polyvalent metal compound such as aluminum. An ion-bonding crosslinking agent can be exemplified. Among these, from the viewpoint of water absorption properties, a polymerizable crosslinking agent with acrylic acid is preferable, and acrylate-based, allyl-based, and acrylamide-based polymerizable crosslinking agents are particularly preferably used. These internal crosslinking agents may be used alone or in combination of two or more.

(Polymerization initiator)
The polymerization initiator used in the present invention is appropriately selected depending on the form of polymerization. Examples of such polymerization initiators include photodegradable polymerization initiators, thermal decomposition polymerization initiators, and redox polymerization initiators. The amount of the polymerization initiator used is preferably 0.0001 to 1 mol% and more preferably 0.001 to 0.5 mol% with respect to the monomer.

  Examples of the photodegradable polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds, and the like. Examples of the thermal decomposition type polymerization initiator include persulfates (sodium persulfate, potassium persulfate, ammonium persulfate), peroxides (hydrogen peroxide, t-butyl peroxide, methyl ethyl ketone peroxide), and azo compounds. (2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, etc.) and the like.

  Examples of the redox polymerization initiator include a system in which a reducing compound such as L-ascorbic acid or sodium hydrogen sulfite is used in combination with the persulfate or peroxide and the both are combined. Moreover, it can also be mentioned as a preferable aspect to use together the said photodegradable polymerization initiator and a thermal decomposition type polymerization initiator.

(Polymerization method)
The polymerization method according to the embodiment of the present invention is usually performed by spray polymerization, droplet polymerization, aqueous solution polymerization (stationary or continuous aqueous solution polymerization) or reverse phase suspension polymerization from the viewpoint of performance and polymerization control, preferably It is carried out by aqueous solution polymerization, more preferably by continuous aqueous solution polymerization. Conventionally, the water-absorbent resin obtained by aqueous solution polymerization or continuous aqueous solution polymerization has been difficult to improve the liquid permeability because its shape becomes irregularly shaped particles, but in the present invention, in the case of irregularly shaped particles, However, the liquid permeability is significantly improved.

  Preferable forms of the above-mentioned continuous aqueous solution polymerization include, for example, continuous kneader polymerization (described in US Pat. Nos. 6,987,151 and 6,710,141), continuous belt polymerization (US Pat. Nos. 4,893,999 and 6,241,928, and published US patent applications). No. 2005/215734 etc.). In these continuous aqueous solution polymerizations, a water-absorbing resin can be produced with high productivity. For this reason, it is preferable that the shape of the dried water-absorbent resin is an irregularly crushed shape obtained by continuous kneader polymerization or continuous belt polymerization. The polymerization apparatus used in this polymerization step is not particularly limited as long as the above various polymerizations can be performed. For example, a continuous belt reactor is preferably used for continuous belt polymerization, and continuous kneader polymerization may be used. Preferably, a continuous kneader is used.

  In the present invention, even when polymerization is carried out at a high concentration or at a high temperature, since the water-absorbent resin having excellent monomer stability and high whiteness can be obtained, the effect is more remarkably exhibited under such conditions. Such high temperature initiation polymerization is exemplified in U.S. Pat. Nos. 6,906,159 and 7,091,253, etc., but the method of the present invention is excellent in stability of the monomer before polymerization, so that it is on an industrial scale. Is easy to produce.

  These polymerizations can be carried out in an air atmosphere, but from the viewpoint of improving coloring, it is preferable to carry out in an inert gas atmosphere (for example, oxygen concentration of 1% by volume or less) such as nitrogen or argon. In addition, the dissolved oxygen in the monomer or the solution containing the monomer is sufficiently substituted with an inert gas (for example, oxygen (the amount of dissolved oxygen) is less than 1 [mg / L]), and then used for polymerization. It is preferred that

  The polymerization can be carried out at normal pressure, reduced pressure, or increased pressure, but preferably at normal pressure (or in the vicinity thereof, usually atmospheric pressure ± 10 mmHg). Moreover, in order to accelerate | stimulate superposition | polymerization and to improve a physical property, you may provide the deaeration process (for example, substitution process with an inert gas) of dissolved oxygen as needed at the time of superposition | polymerization. Further, the temperature at the start of polymerization depends on the kind of polymerization initiator used, but is preferably 15 to 130 ° C, more preferably 20 to 120 ° C.

(Particularly preferred polymerization method)
The water washing in the present invention is particularly effective for “a water-absorbing resin having a high water absorption rate (particularly, FSR of 0.30 [g / g / s] or more)” or “a water-absorbing resin that is spherical or a granulated product thereof”. Preferably applied.

  It has been found that the physical properties of the water-absorbing resin having a high water absorption rate and the spherical water-absorbing resin decrease with time in powder-based manufacturing processes such as an aqueous liquid mixing process (for example, a surface crosslinking process) and a classification process. It was done. Then, it discovered that the said problem was solved by performing the apparatus washing in the classification process (especially metal sieve) and the apparatus washing in the surface cross-linking process.

  The “spherical water-absorbing resin” preferably has a “sphericity” as defined in International Publication No. 2008/009580, preferably 0.80 or more, and in order, 0.84 or more, 0.87 or more, 0 .90 or more, 0.93 or more is preferable, and particularly preferably, the water-absorbing resin is 0.96 or more. The spherical water-absorbing resin typically includes reverse phase suspension polymerization in a hydrophobic organic solvent (for example, cyclohexane, n-heptane) in which a surfactant (for example, sucrose fatty acid ester) is selected, It can be obtained by spray polymerization in the phase, droplet polymerization.

  The reverse phase suspension polymerization is described in, for example, U.S. Pat. No. 4,973,632, and the spray polymerization or droplet polymerization is performed in, for example, International Publication Nos. 2008/095901, 2009/027356, 2010/003855, 2010/003897, 2010/057912, 2011/023572, 2011/0268776 and the like.

  The spherical water-absorbing resin is obtained by reverse phase suspension polymerization, spray polymerization, or droplet polymerization, and has a spherical particle shape during the polymerization. Therefore, the pulverization operation after polymerization is unnecessary, the resulting water-absorbent resin has a high bulk specific gravity, becomes compact, and the powder has excellent impact resistance. However, as described above, clogging with a metal net or punching metal was likely to occur, but this problem was solved by the water washing of the present invention.

  In addition, the “high water absorption rate water-absorbing resin” means that the water absorption rate (FSR) is 0.30 [g / g / s] or more, preferably 0.32 [g / g / s] or more, more preferably It refers to a water-absorbing resin of 0.35 [g / g / s] or more, and can be typically obtained by foam polymerization or fine powder granulation. The “foaming polymerization” refers to the use of a foaming agent (for example, carbonate or azo compound) at the time of polymerization, or polymerization of an aqueous monomer solution in which a gas is dispersed. The foam polymerization is described in WO 97/017397, 97/031971, 00/052087, and 2009/069022.

The water-absorbing resin having a high water absorption rate is achieved by improving the particle surface area ([m ² / g]) of the water-absorbing resin. It can also be performed by granulation. Preferred is foam polymerization in the polymerization step, and polymerization of a monomer aqueous solution in which a gas is dispersed is more preferable. Dispersion of the gas is preferable because no residue remains in the water-absorbent resin as compared with the case where a foaming agent is used.

  Since the water-absorbing resin having a high water absorption rate has a high water absorption rate, in the addition step of the aqueous liquid, agglomerates are often generated and adhere to the inner surface of the apparatus, and clogging is likely to occur in the metal net or punching metal. However, this problem was solved by the water washing of the present invention.

(3-2) Gel Fine Granulation Step The hydrogel crosslinked polymer (hydrogel) obtained in the above polymerization step may be dried as it is, but if necessary during gelation or after polymerization, a gel crusher ( Gel crushing using a kneader, meat chopper, etc.) to form particles. That is, a hydrated gel refinement (hereinafter also referred to as “gel crushing”) step may be further included between the polymerization step by continuous belt polymerization or continuous kneader polymerization and the drying step.

  The temperature of the hydrogel at the time of gel crushing is preferably 40 to 95 ° C., more preferably 50 to 80 ° C., from the viewpoint of physical properties. The resin solid content of the hydrous gel is not particularly limited, but is preferably 10 to 70% by weight, more preferably 15 to 65% by weight, and still more preferably 30 to 55% by weight from the viewpoint of physical properties. You may add water, a polyhydric alcohol, the liquid mixture of water and a polyhydric alcohol, the solution which melt | dissolved the polyvalent metal in water, these vapors, etc. to the said hydrogel.

  The weight-average particle size (specified by sieving classification) of the particulate hydrogel after the gel crushing is preferably in the range of 0.2 to 10 mm, more preferably 0.3 to 5 mm, particularly preferably 0.5 to 3 mm. It is. Moreover, 0-10 weight% of the whole is preferable, and, as for the ratio whose particle diameter of a particulate hydrous gel is 5 mm or more, 0-5 weight% is more preferable. The particle diameter of the particulate hydrous gel can be determined by the wet classification method described in paragraph [0091] of JP-A No. 2000-63527.

(3-3) Drying step If the hydrated gel-like crosslinked polymer obtained in the polymerization step or the particulate hydrated gel obtained in the gel atomization step can be dried to a desired resin solid content, The method is not particularly limited, but for example, heat drying, hot air drying, reduced pressure drying, infrared drying, microwave drying, drum dryer drying, dehydration drying by azeotropy with a hydrophobic organic solvent, high humidity drying using high temperature steam For example, various drying methods can be employed. Among these, hot air drying is preferable, hot air drying with a gas having a dew point temperature of 0 to 100 ° C. is more preferable, and hot air drying with a gas having a dew point temperature of 20 to 90 ° C. is more preferable.

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

  The drying temperature is not particularly limited, but is preferably 100 to 300 ° C, more preferably 150 to 250 ° C. However, in order to achieve both high physical properties and whiteness of the obtained water-absorbent resin, the drying temperature is 165 to 230 ° C., the drying time is preferably within 50 minutes, and particularly preferably 20 to 40 minutes. If the drying temperature or the drying time is out of this range, it is not preferable because it may cause a decrease in water absorption capacity (CRC) of the water absorbent resin under no pressure, an increase in soluble content, and a decrease in whiteness.

  Further, the resin solid content obtained from the loss on drying of the hydrogel (weight change when 1 g of powder or particles is heated at 180 ° C. for 3 hours) is preferably 80% by weight or more, more preferably 85 to 99% by weight, 90% -98 wt% is more preferable, and 92-97 wt% is particularly preferable. In the drying step, a dried water-absorbent resin product having a dry weight adjusted within the above range is obtained.

(3-4) Grinding step (optional)
The method is not particularly limited as long as the dried water-absorbent resin obtained in the drying step can be pulverized. For example, the pulverizing device shown in (2) (Crushing device in the pulverizing step) is used. In the present invention, these pulverizers are washed with water as described in [2] above if necessary. Among these, it is particularly preferable to use a roll mill or a roll granulator in multiple stages from the viewpoint of particle size control.

  By the pulverization step, the dried water-absorbent resin obtained in the drying step is pulverized to obtain a pulverized water-absorbent resin (amorphous crushed water-absorbent resin particles). Since the physical properties of the water-absorbent resin particles are improved by the pulverization step, the pulverization step is preferably applied.

  In the above-described reversed-phase suspension polymerization, spray polymerization, and droplet polymerization, particularly spherical particles are obtained in the polymerization, so that the pulverization step is not particularly necessary and may be appropriately selected depending on the polymerization form.

(3-5) Classification step If the pulverized water-absorbent resin obtained in the pulverization step can be classified, the method is not particularly limited. For example, in (2) (Classification device in the classification step) The classifier shown is used, and the apparatus in these classification steps is most preferable. In the present invention, it is preferable that the water washing described in the above [2] is performed.

  In the present invention, the classification step may be performed at least once (one place) on all steps, but preferably twice (two places) or more on all steps, more preferably before and after the surface crosslinking step. It is sufficient that it can be performed at least once (one place). Furthermore, you may provide the classification process 3-6 times as needed.

  The neutralization classification is described in Patent Document 24.

(Classification vibration)
The sieving apparatus suitable for the classification method according to the present invention is not limited at all, but preferably uses a plane classification method, and particularly preferably a tumble-type sieving apparatus. This sieving device is typically vibrated to support classification. The vibration is preferably performed to such an extent that the product to be classified is guided spirally (spiral) on the sieve. These forced vibrations typically have a runout of 0.7-40 mm, preferably 1.5-25 mm, and a frequency of 60-6000 rpm, preferably 100-600 rpm.

(Granularity)
In the present invention, the particle size is defined by a standard sieve (JIS Z8801-1 (2000)), but the weight average particle size (D50) of the water-absorbent resin particles obtained in the pulverization step and the classification step is 200 to 600 μm. Is preferable, 200 to 550 μm is more preferable, 200 to 500 μm is more preferable, 250 to 500 μm is still more preferable, and 350 to 450 μm is particularly preferable. Further, the smaller the fine particles having a particle size of less than 150 μm, the better. The content of fine particles having a particle size of less than 150 μm is usually preferably 5% by weight or less, more preferably 3% by weight or less, and particularly preferably 1% by weight or less. At this time, the lower limit of the content of the fine particles is not particularly limited, but is preferably 0.1% by weight or more in consideration of the fact that the classification operation is not troublesome in a transient manner. According to the method of the present invention, a stable operation can be achieved even if fine particles having a particle diameter of less than 150 μm that may cause adhesion to the apparatus are included. Furthermore, the smaller the particles exceeding 850 μm, the better, and the content of particles exceeding 850 μm is usually preferably 0 to 5% by weight, more preferably 0 to 3% by weight, and particularly preferably 0 to 1% by weight. That is, it is preferable that the water-absorbent resin particles before surface cross-linking contain 0.1% by weight or more of fine particles having a weight average particle diameter (D50) of 200 to 500 μm and a particle diameter of less than 150 μm.

  The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.25 to 0.45, and more preferably 0.30 to 0.40. These physical property values are measured by a method described in, for example, International Publication No. 2004/069915 or EDANA-ERT420.2-02 (“PSD”) using a standard sieve. In the present invention, the proportion of particles having a particle diameter of 150 μm or more and less than 850 μm is preferably 95% by weight or more, more preferably 98% by weight or more (upper limit 100% by weight) with respect to the whole. It is preferable to surface-crosslink the dried product or powder having this ratio. The particle size before the surface crosslinking is preferably applied to the final product after the surface crosslinking.

(Other classification conditions)
A suitable classification method is the method described in Patent Documents 25 and 26, and such conditions are directly described in the present invention.

  In the step of classifying the water absorbent resin according to the present invention, it is necessary to satisfy at least one selected from the group consisting of the following configurations (i) to (iii) described in Patent Documents 25 and 26, and further two or more. .

  (I) A tapping material is used in the lower part of the metal screen used in the classification process.

  (Ii) The tension of the metal sieve mesh used in the classification step is 35 to 100 [N / cm].

  (Iii) Use an air brush at the lower part of the metal screen used in the classification step.

  The above (i) to (iii) will be described in detail below.

(I) Tapping material (refer to Patent Documents 25 and 26)
From the viewpoint of the classification efficiency of the water-absorbent resin powder and the properties of the water-absorbent resin obtained, a tapping material is used in the lower part of the metal sieve mesh. The tapping material refers to an elastic material used for preventing clogging of the sieving device, and the tapping material can be any shape as long as it rolls, such as a sphere, a spheroid, and a polyhedron. . Preferably, at least one selected from a tapping ball (spherical), a tapping block (spherical), and a tapping brush is used, more preferably a tapping ball or a tapping block, and further preferably a tapping ball is used. In addition, when the tapping material is used on a metal sieve mesh or when the tapping material is not used, the physical properties (for example, liquid permeability) of the water-absorbent resin are deteriorated, particularly the deterioration with time, fine powder And problems such as increased dust.

  The method of using the tapping material of the present invention at the lower part of the metal sieve mesh is not particularly limited. For example, the metal sieve mesh having an opening larger than the opening of the metal sieve mesh at the lower part of the metal sieve mesh or There is a method in which a punching metal having a hole diameter is further installed, and a tapping material (preferably a tapping ball or a tapping block) is disposed (for example, filled) on the metal sieve mesh or the punching metal. From the viewpoint of classification efficiency, it is preferable to use a tapping material on the punching metal.

  The tapping material is preferably made of resin, and examples thereof include natural rubber, urethane, chloroprene rubber, and silicone resin. Among these, it is preferable to use a white or milky white tapping material, in particular, natural white rubber, white urethane or the like in consideration of adhesion to a white water-absorbing resin or mixing. In addition, the compression elastic modulus (Young's modulus) of these resins is preferably 0.05 to 1.0 GPa, more preferably 0.06 to 0.5 GPa.

  The size and shape of the tapping material are appropriately determined according to the desired physical properties of the water-absorbent resin, but are preferably block-shaped or spherical, and the diameter (diameter) is preferably 5 to 200 mm, and 10 to 100 mm. Is more preferable, and 20 to 60 mm is particularly preferable. Furthermore, if it is in the said range, you may use together a tapping ball or a tapping block of a different diameter. In addition, when using a tapping block, the volume is converted into a sphere and used as a diameter.

  In the present invention, it is preferable to use a plurality of tapping materials (such as tapping balls or tapping blocks). The amount of the tapping material of the present invention is defined by the cross-sectional area of the tapping ball with respect to the area of the metal sieve mesh, and the amount is preferably 1% or more, and in the following order, 5% or more, 10% or more, 15% or more. 20% or more is preferable, and the upper limit is preferably less than the closest packing in consideration of the gap between the tapping balls, and more preferably 70% or less. It is determined appropriately within these ranges.

  In the present invention, it is preferable that the tapping material at the time of classification is heated from the viewpoint of improving the physical properties and productivity of the obtained water absorbent resin. As heating temperature, 40 degreeC or more is preferable, 50 degreeC or more is more preferable, and 60 degreeC or more is further more preferable. Although the upper limit of the heating temperature is set as appropriate, excessive heating is likely to reduce the effect of the tapping material and further shorten the life of the tapping material. Is more preferable, 100 ° C. or lower is further preferable, 90 ° C. or lower is particularly preferable, and 80 ° C. or lower is most preferable. Accordingly, the temperature of the tapping material can be selected, for example, from 40 to 100 ° C., 50 to 100 ° C., 60 to 100 ° C., but is not limited to these ranges, and is selected from the upper limit value and the lower limit value of the heating temperature. Specified in any range.

  In order to heat the tapping material according to the present invention to the above-described temperature range, the tapping material may be heated from the outside. As the heat source, the inside of the screen, the surface of the screen, the water absorbent resin are heated to a predetermined temperature, The contact time and the contact amount (for example, the flow rate of hot air to the sieve, the flow rate of the water-absorbing resin in the sieve, the residence amount, etc.) may be controlled.

(Ii) Tension (tension) (see Patent Documents 25 and 26)
“Tension tension” in the present invention refers to a load applied when a net of a metal sieve used in the classification process is stretched. The tension of the classification network (metal network) of the present invention is preferably 35 [N / cm] or more, more preferably 40 [N / cm] or more, still more preferably 45 [N / cm] or more, and particularly preferably. 50 [N / cm] or more. The upper limit of the tension is preferably 100 [N / cm] or less, more preferably 80 [N / cm] or less, and further preferably 60 [N / cm] or less. If the tension is 35 [N / cm] or more, a decrease in the classification efficiency of the water absorbent resin powder can be prevented, and the liquid permeability of the resulting water absorbent resin is improved. Further, if the tension is 100 [N / cm] or less, the durability of the metal net can be ensured and continuous operation is possible. The tension is measured with a tension meter at the center of the screen when the metal net is stretched on the classification screen. The measurement principle is “Mechanical measuring of the fabric's sagging under a constant force”. Various tension meters are commercially available, such as those sold by TEKOMAT, etc., and in the present invention, these commercially available products can be used.

(Iii) Airbrush (air knife) (see: Patent Documents 25 and 26)
From the viewpoint of the classification efficiency of the water absorbent resin powder and the properties of the water absorbent resin obtained, an air brush (air knife) is used below the metal sieve mesh. In the present invention, the air brush refers to an instrument that ejects 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.

  The air brush (air knife) may be applied to a part or all of the sieve, but is preferably used in at least a part of the sieve (a sieve having an opening of 300 μm or less), and more than 30% of the whole, In the following order, it is preferable to use an air brush (air knife) with a sieve of 50% or more, 70% or more, 90% or more, or 100%.

  The air brush of the present invention is preferably used particularly when fine powder is classified, and is preferably installed under a sieve having an opening of 200 μm or less, more preferably 150 μm or less. As a sieve opening, the lower limit is preferably 30 μm or more, more preferably 45 μm or more, and further preferably 75 μn or more. The air brush is preferably used for classification of fine powder as an alternative to the tapping material, and can improve the liquid permeability (SFC and GBP) of the resulting water-absorbent resin.

  In the air brush of the present invention, it is preferable to use dry air as primary air and secondary air from the viewpoint that the excellent physical properties of the water-absorbent resin powder can be stably maintained and the blocking phenomenon can be suppressed. The dew point of the dry air is preferably 0 ° C. or lower, more preferably −30 ° C. or lower, still more preferably −35 ° C. or lower, and particularly preferably −40 ° C. or lower. Examples of the method for controlling 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 using them in combination. When an adsorption dryer is used, it may be a heat regeneration type, a non-heat regeneration type, or a non-regeneration type.

  Moreover, you may use heated air other than dry air. A method for heating the heated air is not particularly limited, but the air may be directly heated using a heat source, or indirect heating may be performed by heating the device or the pipe. As temperature of this heating air, 30 degreeC or more is preferable, 50 degreeC or more is more preferable, and 70 degreeC or more is further more preferable.

(guide)
In the present invention, it is also preferable that the sieve of the classifier has a guide for the water-absorbent resin powder.

(Heating temperature)
Such a classifier (temperature of the sieve to be used) is preferably used in a temperature range of 40 ° C. or higher, and further 40 to 80 ° C. More preferably, it is the temperature range of 45-60 degreeC. If the temperature is 40 ° C. or higher, deterioration of physical properties is prevented. On the other hand, if the temperature is 100 ° C. or even less than 80 ° C., economic disadvantages due to high temperatures can be prevented, and the classification efficiency is adversely affected. Can be prevented.

  The classifier is preferably used at a temperature not lower than 20 ° C. with respect to the temperature of the water absorbent resin powder. More preferably, the temperature is not lower than 10 ° C.

  Further, when the water absorbent resin powder is handled, the water absorbent resin powder introduced into the classification step is set to a temperature of room temperature or higher, preferably 40 ° C. or higher. For example, it is preferable to heat to 40 to 100 ° C., more preferably 50 to 80 ° C. In order to obtain a water-absorbing resin at such a temperature, the water-absorbing resin after heating in the drying step or the surface cross-linking step is appropriately heated. You may use it by keeping warm.

(Decompression)
In the present invention, from the viewpoint of classification efficiency, the lower limit of the degree of reduced pressure is preferably more than 0 kPa, more preferably 0.01 kPa or more, and further preferably 0.05 kPa or more. In addition, from the viewpoint of suppressing powder lifting in the system and cost reduction for the exhaust device, the upper limit of the degree of vacuum is preferably 10 kPa or less, more preferably 8 kPa or less, further preferably 5 kPa or less, and particularly preferably 2 kPa or less. A preferable numerical range of the degree of reduced pressure can be arbitrarily selected between the lower limit value and the upper limit value.

(air flow)
In the classification step, it is preferable that the air flow passes through the water-absorbent resin powder, and particularly preferably, the gas flow is typically 40 ° C. or higher, preferably 50 ° C. or higher, before charging the gas flow into the sieving device. Preferably it heats to 60 degreeC or more, More preferably, it is 65 degreeC or more, Most preferably, it heats to 70 degreeC or more. The temperature of the gas stream is usually 120 ° C. or lower, preferably 110 ° C. or lower, more preferably 100 ° C. or lower, still more preferably 90 ° C. or lower, and particularly preferably 80 ° C. or lower.

(Atmosphere dew point)
The dew point of the atmosphere (air) in which the classification step is performed and the dew point of the gas flow are preferably 15 ° C. or less, more preferably 10 ° C. or less, still more preferably 5 ° C. or less, and particularly preferably 0 ° C. or less. The lower limit of the dew point is not particularly limited, but is preferably −10 ° C. or higher, more preferably −5 ° C. or higher in consideration of cost performance. Furthermore, the gas temperature is preferably 10 to 40 ° C, more preferably 10 to 35 ° C.

(Shape and classification of water-absorbing resin)
The water washing of the present invention is preferably applied when classifying a water-absorbing resin having many irregularities on the particle surface or a substantially spherical water-absorbing resin. That is, the shape of these water-absorbing resins is likely to cause clogging of the sieve screen.

  In addition, the water-absorbent resin with many unevenness | corrugations on the particle | grain surface is the method of performing foaming polymerization (US Pat. No. 6,100,305) using said foaming agent and surfactant, or gel grinding | pulverization on specific conditions (International Publication No. 2011/126079). Etc.) can be produced by a known method. The polymerization is usually performed for the purpose of improving the high water absorption rate. Further, as described above, the substantially spherical water-absorbing resin can be obtained by reverse phase suspension polymerization, spray polymerization, or droplet polymerization.

(3-6) Surface Crosslinking Step This step is a step of surface cross-linking the water-absorbent resin particles obtained in the above step (drying step, pulverizing step or classification step). In the present specification, “surface crosslinking” refers to crosslinking the surface of the water absorbent resin particles or the vicinity of the surface. “Surface or near the surface” usually means a surface layer portion having a thickness of 10 μm or less, or a surface layer portion having a thickness of 1/10 or less of the total thickness, and these thicknesses are appropriately determined according to the purpose. . In the production method of the present invention, liquid permeability and water absorption capacity under pressure are improved by surface crosslinking.

  Although it does not restrict | limit especially as this surface crosslinking method, For example, the method (Japanese Patent 2530668) which bridge | crosslinks the surface of a water absorbing resin particle using a surface crosslinking agent is mentioned. In particular, surface crosslinking by high-temperature heating is preferably applied.

(Surface cross-linking agent)
Examples of the surface cross-linking agent that can be used in the present invention include various organic or inorganic surface cross-linking agents, but organic surface cross-linking agents can be preferably used. Examples of the organic surface crosslinking agent include mono-, di-, tri- or tetra-propylene glycol, 1,3-propanediol, glycerin, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, Polyhydric alcohol compounds such as 1,6-hexanediol and sorbitol; epoxy compounds such as ethylene glycol diglycidyl ether and glycidol; polyhydric amine compounds or condensates thereof with haloepoxy compounds; oxazoline compounds; (mono, di, or poly ) Oxazolidinone compounds; alkylene carbonate compounds such as ethylene carbonate; oxetane compounds; cyclic urea compounds such as 2-imidazolidinone. Among these, one or more dehydrating esterification reactive surface cross-linking agents such as polyhydric alcohol compounds, alkylene carbonate compounds and oxazolidinone compounds, which require a reaction at a high temperature, and a combination of a plurality of them can be particularly preferably used. The said organic surface crosslinking agent may be used independently and may use 2 or more types together.

  The dehydrated esterification reactive surface cross-linking agent is low in reactivity and thus high in safety, but it is difficult to control stable reaction accordingly. However, in the present invention, even if such a dehydration esterification reactive surface cross-linking agent is used for continuous production, it is possible to continuously produce a water-absorbing resin with small physical deviation and small standard deviation. More specifically, compounds exemplified in U.S. Pat. Nos. 6,228,930, 6071976, 6254990 and the like can be mentioned.

  Examples of the inorganic surface cross-linking agent include divalent or higher, preferably trivalent or tetravalent polyvalent metal salts (organic salts or inorganic salts) or hydroxides. Examples of the polyvalent metal include aluminum and zirconium, and examples of the polyvalent metal salt include aluminum lactate and aluminum sulfate. These inorganic surface cross-linking agents are used simultaneously or separately with the organic surface cross-linking agent. Regarding surface cross-linking with a polyvalent metal, International Publication Nos. 2007/121037, 2008/09843, 2008/09842, U.S. Pat. Nos. 7,157,141, 6,605,673, and 6620889, U.S. Pat. Patent Application Publication Nos. 2005/0288182, 2005/0070671, 2007/0106013, and 2006/0073969.

  Furthermore, in addition to the organic surface cross-linking agent, a polyamine polymer, particularly a polyamine polymer having a weight average molecular weight of about 5,000 to 1,000,000 may be used simultaneously or separately to improve the liquid permeability of the water absorbent resin. As for the polyamine polymer, for example, U.S. Patent No. 7098284, International Publication No. 2006/082188, No. 2006/082189, No. 2006/082197, No. 2006/111402, No. 2006/111403, No. 2006/111404 and the like.

  In the present invention, in addition to the covalent surface crosslinking agent that is the organic surface crosslinking agent, in order to improve liquid permeability, an ion binding surface crosslinking agent, among them, the polyvalent metal salt and the polyamine polymer are used. Can also be used together. Further, in order to improve the liquid permeability, an inorganic surface cross-linking agent is preferably used in addition to the organic surface cross-linking agent, and can be used in combination. When these various surface cross-linking agents are used in combination, they may be added to the water-absorbent resin simultaneously (once) or separately (multiple times).

  Although the usage-amount of the said surface crosslinking agent is suitably determined by the compound to be used, those combinations, etc., 0.001-10 weight part is preferable with respect to 100 weight part of water absorbent resin particles, 0.01-5 weight Part is more preferred. When using an organic surface crosslinking agent and an inorganic surface crosslinking agent in combination, or when using a covalent bonding surface crosslinking agent and an ionic bonding surface crosslinking agent in combination, the amount used thereof is used within the above-mentioned range. The The amount of solvent used is also determined within the following ranges.

(Mixed solvent)
When using the surface cross-linking agent, water is preferably used. Although there is no restriction | limiting in particular as the usage-amount of this water, 0.5-20 weight part is preferable with respect to 100 weight part of water absorbing resin particles, and 0.5-10 weight part is more preferable.

  At this time, a hydrophilic organic solvent may be used. The amount of the hydrophilic organic solvent used in the case of using the hydrophilic organic solvent is not particularly limited, but is preferably more than 0 part by weight and 10 parts by weight or less, based on 100 parts by weight of the water-absorbent resin particles. More than 5 parts by weight is more preferable.

  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; dioxane, alkoxy (poly ) Ethers such as ethylene glycol and tetrahydrofuran; Amides such as ε-caprolactam and N, N-dimethylformamide; Sulphoxides such as dimethyl sulfoxide; Ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, glycerin, 2-butene-1, -Diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, And polyhydric alcohols such as diethanolamine, triethanolamine, polyoxypropylene, pentaerythritol, sorbitol; and the like, and one or more of these can be used.

(Other ingredients)
In this step, when the surface cross-linking agent solution is mixed with the water-absorbent resin particles, a water-insoluble fine particle powder or a surfactant may be allowed to coexist in a range not impeding the effects of the present invention. The type and amount of water-insoluble fine particle powder and surfactant used are not particularly limited, and the range exemplified in International Publication No. 2005/077500 can be applied.

  Furthermore, in this step, in addition to the surface cross-linking agent, if necessary, an organic acid (lactic acid, citric acid, p-toluenesulfonic acid) or a salt thereof, an inorganic acid (phosphoric acid, sulfuric acid, sulfurous acid) or a salt thereof. Acid substances such as caustic soda and sodium carbonate, polyvalent metal salts such as aluminum sulfate, etc., preferably 0 to 10% by weight, more preferably 0 to 5% by weight, based on the water-absorbent resin powder, Particularly preferably, 0 to 1% by weight may be used in combination.

(Reaction temperature and time)
After the surface cross-linking agent is mixed with the water-absorbent resin particles, the mixture is preferably subjected to a heat treatment and, if necessary, a cooling treatment thereafter. Although it will not restrict | limit especially if the heating temperature at the time of the said heat processing will be a surface crosslinking reaction, 70-300 degreeC is preferable, 120-250 degreeC is more preferable, 150-250 degreeC is still more preferable. The heating time is preferably in the range of 1 minute to 2 hours. The water-absorbing resin after the heat treatment may be subjected to a cooling treatment as necessary in order to stop the surface crosslinking reaction.

(Other surface cross-linking)
In the present invention, surface crosslinking can be performed without using a surface crosslinking agent. For example, surface cross-linking with a radical polymerization initiator (eg, US Pat. No. 4,783,510), surface cross-linking with active energy rays (European Patent Publication No. 1506788), surface cross-linking by polymerization on the surface (eg, US Pat. No. 7,201,941) Etc. are also applicable to the present invention.

(3-7) Re-humidification step or additive addition step In the present invention, a step of adding water or an additive or a step of adding a second surface cross-linking agent may optionally be provided after the surface cross-linking step. Good (rehumidification step or addition step).

  Examples of the additive include chelating agents, reducing agents, anti-coloring agents, deodorants, antibacterial agents, dust control agents, residual monomer reducing agents, water-soluble polymers, hydrophobic polymers, and water-insoluble fine particles. These addition amounts are preferably 0 to 5 parts by weight, more preferably 0.001 to 1 part by weight with respect to 100 parts by weight of the water absorbent resin. In addition, there is no problem even if no solvent is added, but water is preferably used as the solvent. In that case, it is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, with respect to 100 parts by weight of the water absorbent resin.

  Also in the rehumidification step or the addition step, it is possible to achieve maintenance or stabilization of the properties of the water-absorbent resin obtained by washing with water according to the present invention.

(3-8) Other steps In addition to the above steps, an evaporation monomer recycling step, granulation step, iron removal step, transport step, fine powder removal step, fine powder recycling step, and other additive addition steps are provided as necessary. May be. In addition, as an additive, it is the range of 0.001-5 weight part with respect to water absorbing resin powder, such as a deodorizer, an antibacterial agent, an inorganic fine particle, a chelating agent, a reducing agent, and a coloring inhibitor.

[4] Physical properties of polyacrylic acid (salt) -based water-absorbing resin The production method of the present invention is suitably applied particularly when at least three or more physical properties of the water-absorbing resin are controlled. The effect of controlling each physical property is preferably exhibited by a method for producing a water-absorbing resin having a multifunctional and high physical property of preferably 4 or more, 5 or more, 6 or more. The physical properties to be controlled are as follows: (a) Water absorption capacity under pressure (AAP), (b) Liquid permeability (SFC), (c) Water absorption capacity without pressure (CRC), (d) Water acceptable In addition to the amount of extractables (Extractables), (e) residual monomers (Residual Monomers), (f) initial coloration, (g) moisture content (Moisture Content), free swelling ratio (FSC), (h) particle size distribution (particle diameter) (Particle Size Distribution), pH, flow rate (Flow Rate), bulk density (Density), Respirable Particles, Dust, and the like, which can be suitably applied in a production method in which these are highly controlled. The physical properties to be controlled and the measuring method thereof are appropriately determined, but the above-described EDANA measuring method can be applied to the production of the water-absorbing resin in the following range.

  When the water-absorbent resin of the present invention is intended for use in sanitary materials, especially paper diapers, at least one of the following (a) to (g), and further two or more, particularly three or more including AAP: It is preferable that the physical properties are controlled within a desired range. If the following conditions are not satisfied, the effects of the present invention may not be sufficiently obtained, or the high-concentration diapers described below may not exhibit sufficient performance.

(A) Absorption capacity under pressure (AAP)
The water-absorbent resin obtained by the production method of the present invention is based on a 0.9% by weight sodium chloride aqueous solution under a pressure of 2.06 kPa, and further under a pressure of 4.83 kPa, in order to prevent leakage of paper diapers. The water absorption capacity under pressure (AAP) is preferably controlled to 20 [g / g] or more, more preferably 22 [g / g] or more, and further preferably 23 [g / g] or more. The upper limit of water absorption capacity under pressure (AAP) is not particularly limited and is preferably as high as possible. However, from the balance with other physical properties and costs, the upper limit of AAP is 40 [g / g] under pressure of 2.06 kPa, 4 Under a pressure of .83 kPa, it is about 30 [g / g], and further about 28 [g / g]. In the present specification, unless otherwise specified, AAP indicates a value under a pressure of 4.83 kPa at ERT442.2-02.

  Furthermore, the water absorbent resin obtained by the production method of the present invention preferably satisfies the following AAP, preferably satisfies the following CRC, and further preferably satisfies the following SFC.

(B) Liquid permeability (SFC)
The water-absorbent resin obtained by the production method of the present invention has a 0.69% by weight physiological saline flow conductivity (SFC), which is a liquid passage property under pressure, in order to prevent leakage in paper diapers. [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more, preferably 10 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more, more preferably 20 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more, more preferably 30 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more, and even more preferably 50 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more. Even more preferably 70 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more, particularly preferably 100 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more, most preferably 110) [ × 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more. Since the upper limit of SFC is preferably as high as possible, it is not particularly limited, but is generally 1000 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or less, more preferably 500 [× 10 ⁻⁷ · cm ^3. s · g ⁻¹ ] or less.

  By the production method of the present invention, a surface-crosslinked water-absorbing resin having the desired SFC value mentioned above can be obtained.

(C) Absorption capacity without pressure (CRC)
The water-absorbing resin obtained by the production method of the present invention preferably has a water absorption capacity (CRC) under no pressure of 10 [g / g] or more, more preferably 20 [g / g] or more, and further preferably 25 [g / g]. g / g] or more, particularly preferably 27 [g / g] or more. The higher the CRC, the more preferable the upper limit value is not particularly limited, but from the balance of other physical properties, it is preferably 50 [g / g] or less, more preferably 45 [g / g] or less, and still more preferably 40 [g / g]. It is as follows.

  Furthermore, the water-absorbent resin obtained by the production method of the present invention preferably satisfies the CRC, and preferably satisfies the SFC and AAP.

(D) Water soluble content (Ext)
The water-absorbent resin obtained by the production method of the present invention has a water-soluble content (Ext) of preferably 35% by weight or less, more preferably 25% by weight or less, still more preferably 15% by weight or less, and particularly preferably 10% by weight. It is as follows.

(E) Residual monomer The water-absorbent resin obtained by the production method of the present invention preferably has a residual monomer amount of 0 to 700 ppm, more preferably 0 to 600 ppm, and particularly preferably 0 to 500 ppm.

(F) Initial coloring According to the production method of the present invention, it is possible to suppress and prevent the generation of brown foreign matters in the water-absorbent resin. Here, the ratio of occurrence of brown foreign matter in the water absorbent resin is preferably as small as possible, but it is sufficient if it is about 5 or less (lower limit: 0) in 1000 water absorbent resins obtained by the production method of the present invention. It is. Further, the water-absorbent resin obtained by the production method of the present invention is excellent in initial coloring and coloring over time, and can exhibit sufficient whiteness even at high temperature and high humidity, which is a long-term accelerated test (model).

  The water-absorbent resin obtained by the production method of the present invention is excellent in initial coloring. For example, in the Hunter Lab surface color system, the L value (Lightness) is preferably 85 or more, more preferably 87 or more, and still more preferably 89 or more. Yes, the b value is preferably -5 to 10, more preferably -5 to 5, further preferably -4 to 4, and the a value is preferably -2 to 2, more preferably -1 to 1, further preferably. Is -0.5 to 1, most preferably 0 to 1. YI (yellowness) is preferably 10 or less, more preferably 8 or less, particularly preferably 6 or less, and WB (white balance) is preferably 70 or more, more preferably 75 or more, particularly preferably 77 or more. is there. Furthermore, such a water-absorbent resin is excellent in coloration with time, and exhibits sufficient whiteness even at high temperature and high humidity, which is an accelerated test (model) for long-term storage.

(G) Water content The water content of the water-absorbent resin obtained by the production method of the present invention is preferably 5% by weight or less, more preferably 1% by weight or less. In particular, when the classification step is performed after the surface cross-linking step, the classification method of the present invention is preferable because it exerts a more remarkable effect on the water-absorbent resin having a low water content. The lower limit of the moisture content is not particularly limited, but is preferably 0.1% by weight or more, more preferably 0.5% by weight or more.

(H) Particle size distribution and particle shape In the present invention, the particle size is defined by a standard sieve (JIS Z8801-1 (2000)), but the weight average particle diameter of the water-absorbent resin particles obtained in the pulverization step and the classification step. (D50) is preferably 200 to 600 μm, more preferably 200 to 550 μm, still more preferably 200 to 500 μm, particularly preferably 250 to 500 μm, and most preferably 350 to 450 μm. Further, the smaller the fine particles having a particle size of less than 150 μm, the better. The content of fine particles having a particle size of less than 150 μm is usually preferably 5% by weight or less, more preferably 3% by weight or less, and particularly preferably 1% by weight or less. At this time, the lower limit of the content of the fine particles is not particularly limited, but is preferably 0.1% by weight or more in consideration of the fact that the classification operation is not troublesome in a transient manner. According to the method of the present invention, a stable operation can be achieved even if fine particles having a particle diameter of less than 150 μm that may cause adhesion to the apparatus are included. Furthermore, the smaller the particles exceeding 850 μm, the better, and the content of particles exceeding 850 μm is usually preferably 0 to 5% by weight, more preferably 0 to 3% by weight, and particularly preferably 0 to 1% by weight. That is, it is preferable that the water-absorbent resin particles before surface cross-linking contain 0.1% by weight or more of fine particles having a weight average particle diameter (D50) of 200 to 500 μm and a particle diameter of less than 150 μm.

  The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.25 to 0.45, and more preferably 0.30 to 0.40. These physical property values are measured by a method described in, for example, International Publication No. 2004/069915 or EDANA-ERT420.2-02 (“PSD”) using a standard sieve. In the present invention, the proportion of particles having a particle diameter of 150 μm or more and less than 850 μm is preferably 95% by weight or more, more preferably 98% by weight or more (upper limit 100% by weight) with respect to the whole. It is preferable to surface-crosslink the dried product or powder having this particle size distribution. The particle size before the surface crosslinking is preferably applied to the powder after the surface crosslinking and further to the final product.

  The particle shape of the water-absorbent resin of the present invention is not particularly limited, and examples thereof include indefinite shapes, (substantially) spherical, fibrous, and granulated products thereof. It is preferably applied to a method for producing a water-absorbing resin (porous water-absorbing resin) having a high water absorption rate.

(I) Water absorption rate (FSR)
The water absorption rate (FSR) of the water absorbent resin obtained by the production method of the present invention is preferably 0.2 [g / g / s] or more, more preferably 0.3 [g / g] from the viewpoint of water absorption performance of the paper diaper. g / s] or more, more preferably 0.35 [g / g / s] or more, and particularly preferably 0.4 [g / g / s] or more.

In the second invention, from the viewpoint of emphasizing the water absorption rate, it is 0.30 [g / g / s] or more, preferably 0.40 [g / g / s] or more.
The method for producing a water absorbent resin of the present invention is preferably applied to the improvement of the water absorption rate (FSR), more preferably applied to the high SFC, and achieves both the water absorption rate (FSR) and the liquid permeability (SFC). It is a manufacturing method. Preferably, FSR: 0.35 [g / g / s] or more and SFC: 20 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more, more preferably applied to the production method in the above range. Is done.

[5] Use of polyacrylic acid (salt) water-absorbent resin The use of the water-absorbent resin of the present invention is not particularly limited, but is preferably used for absorbent articles such as paper diapers, sanitary napkins, incontinence pads, etc. obtain. In particular, when used in high-concentration diapers (a large amount of water-absorbent resin is used in one diaper), which has been problematic in the past due to the odor, coloring, etc. derived from the raw material of the water-absorbent resin, the absorptivity is particularly good. Particularly excellent performance is exhibited when used for the upper layer portion of the absorber in the article.

  In this absorbent article, the content (core concentration) of the water-absorbent resin in the absorbent body optionally containing other absorbent materials (such as pulp fibers) is preferably 30 to 100% by weight, and 40 to 100% by weight. More preferably, 50 to 100% by weight is further preferable, 60 to 100% by weight is even more preferable, 70 to 100% by weight is particularly preferable, and 75 to 95% by weight is most preferable.

  EXAMPLES Hereinafter, although this invention is demonstrated according to an Example and a comparative example, this invention is limited to these and is not interpreted. For convenience, “liter” may be described as “L” and “wt%” may be described as “wt%”. The physical properties described in the claims and examples of the water-absorbent resin obtained in the present invention are the EDANA method under conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH% unless otherwise specified. It was determined according to the following measurement example. Hereinafter, for the water-absorbing resin obtained, the water-absorbing resin before surface cross-linking is referred to as water-absorbing resin particles, and the water-absorbing resin after surface cross-linking is referred to as water-absorbing resin powder for convenience.

(6-1) Physical property measurement method (a) Resin solid content (solid content)
Into an aluminum cup having a bottom diameter of about 50 mm, 1.00 g of the water absorbent resin was weighed, and the total weight W1 [g] of the sample (water absorbent resin and aluminum cup) was accurately weighed.

  Next, the sample was allowed to stand in an oven having an atmospheric temperature of 180 ° C., and the water absorbent resin was dried. After 3 hours, the sample was taken out of the oven and cooled to room temperature in a desiccator. Thereafter, the total weight W2 [g] of the dried sample (water absorbent resin and aluminum cup) was weighed, and the solid content (unit: [wt%]) was calculated according to the following formula.

  In addition, when measuring the resin solid content of the particulate hydrogel crosslinked polymer (particulate hydrogel), the sampling amount of the particulate hydrogel was changed to 2 to 4 g, and the drying time was changed to 24 hours. .

(B) SFC (saline flow inductivity)
The SFC (saline flow conductivity) of the water-absorbent resin obtained in the present invention was measured according to the description of US Pat. No. 5,669,894.

(C) Other physical properties CRC of the water-absorbent resin obtained in the present invention (water absorption capacity without pressure; see the above "CRC" section: method described in ERT441.2-02), AAP (water absorption capacity under pressure; See section “AAP”: In the method described in ERT441.2-02, the load condition was changed to 4.83 kPa), particle size distribution (see section “PSD” above: method described in ERT420.2-02), pH-soluble component (water-soluble component; see “Ext” above: method described in ERT470.2-02), residual acrylic acid amount (residual monomer) (see “Residual Monomers” above: ERT410.2) The physical properties such as the method described in -02) were measured according to ERT of EDANA described above or US Patent Application Publication No. 2006/204755. Further, FSR (Free Swell Rate) was measured with reference to “FSR” of US Patent Publication No. 2007/225422 (corresponding Japanese Patent Publication No. 2007-284675).

(6-2) Example [Production Example 1-1d]
As manufacturing condition 1 of the water absorbent resin according to the present invention, the water absorbent resin was continuously produced by the following method.

  That is, as a water-absorbent resin continuous production apparatus (production capacity 1500 [kg / hr]) according to the present invention, a polymerization process, a gel granulation process, a drying process, a pulverization process, a first classification process, a surface crosslinking process (mixing) Process, heat treatment process and cooling process), second classification process, transport process connecting each process, intermediate tank for temporarily storing and storing intermediate products, and an intermediate hopper (see FIG. 1) ) Was prepared. In addition, the transportation process which connects a 1st classification process and a surface crosslinking process, and the transportation process which connects a surface crosslinking process and a 2nd classification process are the air using dew point 10 degreeC dry air or 60 degreeC heated air, respectively. Adopted transportation. The continuous production apparatus was operated under the following conditions, and continuous production of the water absorbent resin was started.

  First, as an aqueous monomer solution, an aqueous solution of partial sodium salt of acrylic acid having a neutralization rate of 75 mol% (monomer concentration: 37% by weight) and polyethylene glycol diacrylate as an internal crosslinking agent (average degree of polymerization: 9) 0 What added 0.06 mol% (with respect to monomer) was prepared.

  Next, when the monomer aqueous solution is continuously supplied to the polymerization apparatus using a metering pump, nitrogen gas is blown in the middle of the transport pipe so that the dissolved oxygen amount is 0.5 [mg / L] or less. Then, 0.14 g of sodium persulfate as a polymerization initiator and 0.005 g of L-ascorbic acid (one mole of monomer) were continuously added separately and mixed by line mixing. Thereafter, the aqueous monomer solution was supplied onto a flat steel belt (polymerization apparatus) having weirs at both ends so that the thickness was about 30 mm, and a stationary aqueous solution polymerization was performed at 95 ° C. for 30 minutes. Through the above operation, a hydrogel crosslinked polymer was obtained (polymerization step).

  Subsequently, the hydrogel crosslinked polymer (solid content: 45% by weight) obtained in the polymerization step was continuously supplied to a meat chopper having a pore diameter of 7 mm under an atmosphere of 60 ° C., and the gel was pulverized. A particulate hydrogel crosslinked polymer having a particle size of about 1 mm was obtained (gel refinement step).

  Next, the particulate hydrogel crosslinked polymer was placed on a perforated plate on which a continuous aeration band dryer moves so as to have a thickness of 50 mm, and dried with hot air at a temperature of 185 ° C. and a dew point of 30 ° C. for 30 minutes. . Then, it cooled with external air and obtained the water-absorbent resin dried material (solid content; 96 weight%, powder temperature; 60 degreeC) (drying process).

  Next, the dried water absorbent resin was continuously supplied to a three-stage roll mill (roll gap; 1.0 mm / 0.7 mm / 0.5 mm from the top) and pulverized to obtain a pulverized water absorbent resin (pulverization step). ).

Subsequently, the water-absorbent resin pulverized product is continuously supplied to an oscillating circular classifier having a sieve opening diameter of 1600 mm having a metal sieve with openings of 1000 μm, 850 μm and 150 μm while maintaining the powder temperature at 60 ° C. After classifying, the water absorbent resin remaining on the metal sieve having an opening of 150 μm was collected as water absorbent resin particles. The metal sieve has a material of SUS304, a tension tension of 50 [N / cm], a surface roughness Rz of the sieve inner surface of 50 nm, a surface roughness Ra of the sieve inner surface of 4.8 nm, and a sieve area of 2 [m ² / Sheet]. The classifier was kept at 60 ° C., the atmospheric dew point in the device was 13 ° C., the frequency was 230 rpm, the radial inclination (gradient) was 11 mm, the tangential inclination (gradient) was 11 mm, and the eccentric amount was 35 mm. Further, the classifier is subjected to static elimination with a ground resistance of 5Ω, depressurized to 0.11 kPa by an exhaust device with a bag filter, and ventilated with dry air (temperature 60 ° C., dew point 10 ° C.) 2 [m ³ / hr]. (First classification step).

  The physical properties of the water-absorbent resin particles on the first day of operation were CRC: 36 [g / g], solid content: 96% by weight, weight average particle size (D50): 450 μm, σζ: 0.35, particle size The ratio of particles that are 150 μm or more and less than 850 μm was about 98% by weight. The water-absorbent resin particles contained 2% by weight of fine particles having a particle size of less than 150 μm (0% by weight for particles having a particle size of 850 μm or more).

  Next, a surface cross-linking agent solution consisting of 0.3 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol and 2.7 parts by weight of pure water is prepared with respect to 100 parts by weight of the water-absorbent resin particles. Then, the water-absorbent resin particles were sprayed using a spray and mixed for 6 seconds with a high-speed continuous mixer (turbulizer; 1000 rpm) (mixing step). Subsequently, the mixture is supplied to a heating paddle dryer and heated at 198 ° C. for 40 minutes (heating treatment step), and then forcedly cooled with a cooling paddle dryer of the same specification until the powder temperature reaches 60 ° C. (Cooling step), water absorbent resin powder was obtained (surface cross-linking step).

Subsequently, the water-absorbent resin powder obtained in the surface cross-linking step was continuously applied to an oscillating circular classifier having a sieve mouth diameter of 1600 mm having a metal sieve having an aperture of 850 μm while maintaining a powder temperature of 60 ° C. To be classified. The metal sieve has a material of SUS304, a tension tension of 50 [N / cm], a surface roughness Rz of the sieve inner surface of 50 nm, a surface roughness Ra of the sieve inner surface of 4.8 nm, and a sieve area of 2 [m ² / Sheet]. Furthermore, a stainless steel punching metal (material: SUS304, open area ratio: 40%) with a hole diameter of 20 mm is placed under the metal sieve (50 mm below the sieve surface), and a tapping ball (urethane resin) with a diameter of 30 mm is placed thereon. Manufactured, white (milky white), cross-sectional area ratio (ratio of tapping ball cross-sectional area to metal sieve area); 16%, temperature (hot air, sieve surface, heating equilibrium temperature from water absorbent resin); Arranged. The classifier was kept at 60 ° C., the atmospheric dew point in the device was 13 ° C., the frequency was 230 rpm, the radial inclination (gradient) was 11 mm, the tangential inclination (gradient) was 11 mm, and the eccentric amount was 35 mm. Further, the classifier is subjected to static elimination with a ground resistance of 5Ω, depressurized to 0.11 kPa by an exhaust device with a bag filter, and ventilated with dry air (temperature 60 ° C., dew point 10 ° C.) 2 [m ³ / hr]. (Second classification step).

  The residue on the metal sieve having an aperture of 850 μm is pulverized again, and then mixed with the material passing through the metal sieve having an aperture of 850 μm, so that the total amount is a sized water-absorbing resin having a particle size of less than 850 μm Got. The physical properties on the first day of operation of the water-absorbent resin were as follows: water content: 1.5% by weight, water-soluble content: 8.8% by weight, weight average particle size (D50): 450 μm, σζ: 0.36 It was.

  While continuously producing a water-absorbent resin under the operating conditions described above, sampling was performed for every ton of product, and the physical properties (CRC / AAP / SFC) were measured for a total of 20 tons. About the obtained 20 points | piece data, the average value and standard deviation were calculated | required, and it evaluated as the water absorbing resin (1-1d) of the driving | operation 1st day. The results are shown in Table 1.

[Production Example 1-30d]
The continuous production apparatus of the water absorbent resin was operated without stopping the production condition 1 described above, and continuous production of the water absorbent resin was continued.

  In order to investigate the change with time of the water-absorbent resin performance, from the 30th day of continuous operation, samples were sampled for every 1 ton of products and measured for a total of 20 tons by the same method as in Production Example 1-1d. The results are shown in Table 1 as the water absorbent resin (1-30d) on the 30th day of operation.

The SFC of the water absorbent resin (1-30d) is 28 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], compared with the first day of operation (water absorbent resin (1-1d)), A decrease in SFC (36 → 28) was confirmed.

  As a result of investigating the cause of the SFC decrease, the ratio of particles having a particle diameter of 150 μm or more and less than 850 μm was reduced to about 94% by weight with respect to about 98% by weight on the first day of operation in the first classification step. There was found. That is, it is presumed that the porosity in the water-absorbent resin decreases with an increase in the amount of fine powder, and the SFC decreases.

[Comparative Example 1]
In order to eliminate the SFC drop that occurred in Production Example 1-30d, the first classification step was temporarily stopped, and vacuum (suction) cleaning of the oscillating circular classifier was performed. The vacuum (suction) cleaning was performed using a commercially available suction machine to the extent that no foreign matter such as solid matter could be visually confirmed. In addition, it was made to drive | operate in the state which slightly reduced the operation rate, without stopping processes other than a 1st classification process.

After the vacuum cleaning, the oscillating circular classifier was restored and the operation was resumed. The ratio of particles having a particle diameter of 150 μm or more and less than 850 μm in the first classification process was about 95% by weight, and the SFC was 29 [× 10 ^−7. · Cm ³ · s · g ^-1 ], and no recovery of physical properties was observed. The results are shown in Table 1 as a comparative water absorbent resin (1).

[Example 1]
In the vacuum (suction) cleaning of Comparative Example 1, no physical property recovery was observed, so the first classification process was stopped again and the oscillating circular classifier was washed with water. In the water washing, the metal sieve was first removed from the classifier and immersed in a hot water bath at 60 ° C. for 1 hour. As a result, a large number of water-absorbing resins that had entered the opening of the sieve swelled and became visible. This phenomenon was particularly remarkable with a metal sieve having an opening of 150 μm. That is, it can be said that the vacuum (suction) cleaning of Comparative Example 1 was insufficient in removing the water absorbent resin.

Subsequently, industrial pure water at 50 ° C. was ejected at a discharge pressure (gauge pressure) of 200 [kg / cm ² ] with a high pressure washer manufactured by Kärcher Japan Co., Ltd. and entered the opening of the sieve. Foreign matter that was present in the dead space of the water-absorbent resin and the classifier was removed cleanly without a trace.

After the washing with water, the classifier was dried by high-pressure air, recovered, and restarted. As a result, the ratio of particles having a particle diameter of 150 μm or more and less than 850 μm in the first classification step was about 98% by weight, and the SFC was 36 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], and recovered to the same level as on the first day of operation. The results are shown in Table 1 as the water absorbent resin (1).

  In addition, from the results of Production Example 1-30d, Comparative Example 1 and Example 1, the oscillating circular classifier (especially a metal sieve having an opening of 150 μm) in the first classification process was washed with water every 30 days or so for continuous operation. There is a need to do.

[Production Example 1-120d]
Subsequent to Example 1 described above, the continuous production apparatus for water absorbent resin was operated under the production condition 1 described above without stopping, and continuous production of the water absorbent resin was continued. In addition, about the 1st classification process, the water washing of the rocking | swiveling circular classifier was repeated about every 30 days of continuous operation.

  When continuous operation was performed by the above method, brown foreign matter was detected in the water-absorbent resin on the 120th day from Production Example 1-1d (first day of operation) (about 30 to 40 particles in 1000 particles of the water-absorbent resin). It was. As a result of analysis, the brown foreign matter was sodium polyacrylate, and the water-absorbent resin was discolored. In addition, the water absorbent resin in which the brown foreign material was detected is described as a water absorbent resin (1-120d) for convenience.

  Therefore, when the heating paddle dryer (heat treatment machine) used in the surface cross-linking process (heat treatment process) was opened and the inside was inspected, the dead space of the paddle dryer was confirmed to have a foreign substance (lumps) that turned black-brown. It was done.

[Example 2]
In order to remove the black-brown foreign matter generated in Production Example 1-120d, the surface cross-linking process was temporarily stopped and the heating paddle dryer was washed. The said washing | cleaning removed to the grade which cannot confirm black-brown foreign material visually using a spatula (spatula washing | cleaning). In addition, processes other than the said surface crosslinking process were made to drive | operate in the state which reduced the operation rate slightly, without stopping.

  After completion of the washing, the apparatus was restored and the operation was resumed. However, the black-brown foreign matter in the water-absorbent resin was not completely eliminated and was detected (about 10 to 20 particles in 1000 particles of the water-absorbent resin). In addition, the water absorbing resin obtained in Example 2 is described as a water absorbing resin (2) for convenience.

[Example 3]
Since the removal of black-brown foreign matters was insufficient in the spatula cleaning of Example 2, the surface cross-linking process was stopped again, and the heating paddle dryer was washed with water. The water washing was performed by putting warm water (industrial pure water) at 60 ° C. into a paddle dryer and immersing the paddle dryer for about 1 hour, and then washing the inside of the apparatus with industrial pure water with a high-pressure washing device. In addition, it was confirmed that the water-absorbing resin swelled from dead space or the like due to immersion of warm water. In other words, it was found that the water-absorbent resin was not sufficiently removed by the cleaning of Example 2 to completely remove the brown coloration.

Subsequently, the inside of the apparatus was washed with water using a high pressure washing apparatus manufactured by Sugino Machine Co., Ltd. The washing is performed by jetting warm water (industrial pure water) at 60 ° C. at a discharge pressure (gauge pressure) of 400 [kg / cm ² ] to clean the water-absorbing resin that has entered the dead space of the paddle dryer. Removed without.

  After the washing with water, the paddle dryer was dried and restored, and the operation was resumed. As a result, the brown foreign matter had disappeared. The results are shown in Table 1 as the water absorbent resin (3).

  In addition, from the results of Production Example 1-120d, Example 2 and Example 3, it was considered that the heating paddle dryer (heat treatment machine) in the surface cross-linking step is preferably washed with water every 120 days or so. The

[Production Example 1-150d]
Subsequent to Example 3, the continuous production apparatus for the water absorbent resin was operated under the production condition 1 described above without stopping, and continuous production of the water absorbent resin was continued. In addition, about the 1st classification process, the water washing of the rocking | swiveling circular classifier was repeated about every 30 days of continuous operation. In addition, in the surface cross-linking step, it is necessary to wash the heating paddle dryer (heat treatment machine) every 120 days of continuous operation.

  When continuous operation was performed by the above method, abnormal noise was generated from the three-stage roll mill in the pulverization process on the 150th day from Production Example 1-1d (operation first day), and the particle size of the water absorbent resin pulverized product was unstable. became. For the sake of convenience, the water-absorbing resin whose particle size has become unstable is referred to as a water-absorbing resin (1-150d).

  Therefore, when the three-stage roll mill was opened and the inside was inspected, a large amount of undried material (rubber-like dry product that had not been completely dried) adhered to the inlet portion of the three-stage roll mill. Therefore, when the continuous ventilation band dryer of the drying process, which is the previous process, was opened and the inside was inspected, it was estimated that a part of the opening of the perforated plate was blocked and the drying efficiency was reduced. It was.

[Example 4]
In order to remove the undried material generated in Production Example 1-150d, the continuous aeration band dryer and the three-stage roll mill were washed. In the cleaning, wastes were removed to the extent that undried materials could not be visually confirmed using wastes (waste cleaning). In addition, the processes other than the drying process and the pulverizing process were operated with a slightly reduced operation rate without stopping.

  After completion of the washing, the apparatus was restored and the operation was resumed. However, an undried product was still generated, and the particle size of the water-absorbent resin pulverized product was slightly unstable. In addition, for the sake of convenience, the water-absorbing resin (4) is referred to as the water-absorbing resin obtained in Example 4.

[Example 5]
Since removal of undried material was insufficient in the waste cleaning of Example 4, the drying step and the pulverization step were stopped again, and the perforated plate of the continuous aeration band dryer and the three-stage roll mill were washed with water. The water washing is performed by using a high-pressure washing device manufactured by Sugino Machine Co., Ltd. and jetting warm water (industrial pure water) at 60 ° C. at a discharge pressure (gauge pressure) of 400 [kg / cm ² ]. Was removed cleanly and without traces.

  After the washing with water, the dryer and the roll mill were dried with high-pressure air, and the operation was resumed. The results are shown in Table 1 as the water absorbent resin (5).

  In addition, from the results of Production Example 1-150d, Example 4 and Example 5, it is preferable that the continuous aeration band dryer in the drying process and the three-stage roll mill in the pulverization process are washed with water every 150 days or so for continuous operation. Is considered.

[Production Example 2-1d]
As production conditions 2 of the water absorbent resin according to the present invention, the water absorbent resin was continuously produced by the following method.

  That is, except having not used a tapping ball at the 2nd classification process in manufacture example 1-1d, the same conditions and operation as manufacture example 1-1d were performed, and water absorbing resin (2-1d) was obtained. The physical properties on the first day of operation of the water-absorbent resin were as follows: water content: 1.5% by weight, water-soluble content: 8.7% by weight, weight average particle size (D50): 445 μm, σζ: 0.39. It was.

  While continuously producing a water-absorbent resin under the operating conditions described above, sampling was performed for every ton of product, and the physical properties (CRC / AAP / SFC) were measured for a total of 20 tons. About the obtained 20 points | piece data, the average value and the standard deviation were calculated | required, and it evaluated as the water absorbing resin (2-1d) of the driving | operation 1st day. The results are shown in Table 1.

[Production Example 2-45d]
The continuous production apparatus of the water absorbent resin was operated without stopping the production condition 2 described above, and continuous production of the water absorbent resin was continued. In addition, the swinging circular classifier in the first classification process, the heating paddle dryer (heat treatment machine) in the surface cross-linking process, the dryer in the drying process and the pulverizing process, and the three-stage roll mill are each in a fixed period. The washing was controlled in advance.

  When continuous operation was performed by the above method, a sharp decrease in SFC was observed on the 45th day from Production Example 2-1d (first operation day). The results are shown in Table 1 as the water absorbent resin (2-45d) on the 45th day of operation.

The SFC of the water absorbent resin (2-45d) is 27 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], compared with the first day of operation (water absorbent resin (2-1d)), A decrease in SFC (34 → 27) was confirmed.

  When the cause of SFC reduction was investigated, clogging was confirmed in the metal sieve having an opening of 850 μm in the second classification step.

[Example 6]
In order to eliminate the problem that occurred in Production Example 2-45d, the second classification step was temporarily stopped, and the oscillating circular classification device (metal sieve having an opening of 850 μm) was cleaned. The cleaning was performed by hitting a metal sieve with a human hand to remove cloggings to the extent that it could not be visually confirmed (hand washing). In addition, it was made to drive | operate in the state which slightly reduced the operation rate, without stopping processes other than the said 2nd classification process.

After the completion of the washing, the apparatus was restored and the operation was resumed. However, the SFC was 30 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], and sufficient recovery of physical properties was not recognized. The results are shown in Table 1 as the water absorbent resin (6).

[Example 7]
Since the physical properties were not sufficiently recovered in the cleaning of Example 6, the second classification process was stopped again, and the oscillating circular classification device was washed with water. In the water washing, the metal sieve was first removed from the classifier and immersed in a 60 ° C. warm water (industrial pure water) bath for 1 hour. As a result, a large number of water-absorbing resins that had entered the opening of the sieve swelled and became visible. That is, in the cleaning of Example 7, it can be said that the water-absorbing resin was not sufficiently removed to completely remove the clogging of the metal sieve.

Subsequently, hot water (industrial pure water) at 50 ° C. was ejected at a discharge pressure (gauge pressure) of 200 [kg / cm ² ] with a high pressure washer manufactured by Kärcher Japan Co., Ltd. The water-absorbing resin that had entered and the foreign substances present in the dead space of the classifier were removed cleanly without a trace.

After washing with water, the classifier was dried and recovered by high-pressure air, and the operation was resumed. As a result, the SFC was 34 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], the same level as the first day of operation. Was recovering. The results are shown in Table 1 as the water absorbent resin (7).

  From the results of Production Example 2-45d, Example 6 and Example 7, when tapping balls are not used, the swinging circular classifier (especially metal sieve having an aperture of 850 μm) in the second classifying process is operated continuously. It is considered preferable to wash with water every 45 days or so.

[Production Example 3-1d]
As production condition 3 of the water absorbent resin according to the present invention, the water absorbent resin was continuously produced by the following method.

  That is, as a water-absorbent resin continuous production apparatus (production capacity 1500 [kg / hr]) according to the present invention, a polymerization process, a gel granulation process, a drying process, a pulverization process, a first classification process, a surface crosslinking process (mixing) Process, heat treatment process and cooling process), second classification process, transport process connecting each process, intermediate tank for temporarily storing and storing intermediate products, and an intermediate hopper (see FIG. 1) ) Was prepared. In addition, the transportation process which connects a 1st classification process and a surface crosslinking process, and the transportation process which connects a surface crosslinking process and a 2nd classification process are the air using dew point 10 degreeC dry air or 60 degreeC heated air, respectively. Adopted transportation. The continuous production apparatus was operated under the following conditions, and continuous production of the water absorbent resin was started.

  First, as an aqueous monomer solution, an aqueous solution of partial sodium salt of acrylic acid having a neutralization rate of 73 mol% (monomer concentration: 38% by weight) and polyethylene glycol diacrylate as an internal cross-linking agent (average polymerization degree: 9) 0 What added 0.09 mol% (with respect to monomer) was prepared.

  Next, when the monomer aqueous solution is continuously supplied to the polymerization apparatus using a metering pump, nitrogen gas is blown in the middle of the transport pipe so that the dissolved oxygen amount is 0.5 [mg / L] or less. Then, 0.14 g of sodium persulfate as a polymerization initiator and 0.005 g of L-ascorbic acid (one mole of monomer) were continuously added separately and mixed by line mixing. Thereafter, the aqueous monomer solution was supplied onto a flat steel belt (polymerization apparatus) having weirs at both ends so that the thickness was about 30 mm, and a stationary aqueous solution polymerization was performed at 97 ° C. for 30 minutes. Through the above operation, a hydrogel crosslinked polymer was obtained (polymerization step).

  Subsequently, the hydrogel crosslinked polymer (solid content: 46% by weight) obtained in the polymerization step was continuously supplied to a meat chopper having a pore diameter of 7 mm under an atmosphere of 60 ° C., and the gel was pulverized. A particulate hydrogel crosslinked polymer having a particle size of about 1 mm was obtained (gel refinement step).

  Next, the particulate hydrogel cross-linked polymer was placed on a perforated plate moved by a continuous aeration band dryer so as to have a thickness of 50 mm, and dried with hot air at a temperature of 190 ° C. and a dew point of 30 ° C. for 30 minutes. . Then, it cooled with external air and obtained the water-absorbent resin dried material (solid content; 96.5 weight%, powder temperature; 60 degreeC) (drying process).

  Next, the dried water absorbent resin was continuously supplied to a three-stage roll mill (roll gap; 1.0 mm / 0.6 mm / 0.48 mm from the top) and pulverized to obtain a pulverized water absorbent resin (pulverization step). ).

Subsequently, the water-absorbent resin pulverized product is continuously supplied to an oscillating circular classifier having a sieve opening diameter of 1600 mm having a metal sieve with openings of 850 μm, 710 μm and 150 μm while maintaining the powder temperature at 60 ° C. After classifying, the water absorbent resin remaining on the metal sieve having an opening of 150 μm was collected as water absorbent resin particles. The metal sieve has a material of SUS304, a tension tension of 50 [N / cm], a surface roughness Rz of the sieve inner surface of 50 nm, a surface roughness Ra of the sieve inner surface of 4.8 nm, and a sieve area of 2 [m ² / Sheet]. The classifier was kept at 60 ° C., the atmospheric dew point in the device was 13 ° C., the frequency was 230 rpm, the radial inclination (gradient) was 11 mm, the tangential inclination (gradient) was 11 mm, and the eccentric amount was 35 mm. Further, the classifier is subjected to static elimination with a ground resistance of 5Ω, depressurized to 0.11 kPa by an exhaust device with a bag filter, and ventilated with dry air (temperature 60 ° C., dew point 10 ° C.) 2 [m ³ / hr]. (First classification step).

  The physical properties of the water-absorbent resin particles on the first day of operation were CRC: 33 [g / g], solid content: 96% by weight, weight average particle size (D50): 400 μm, σζ: 0.36, particle size The ratio of particles that are 150 μm or more and less than 850 μm was about 98% by weight. The water-absorbent resin particles contained 2% by weight of fine particles having a particle size of less than 150 μm (particles having a particle size of more than 850 μm were 0% by weight).

  Next, a surface cross-linking agent solution comprising 0.36 parts by weight of 1,4-butanediol, 0.6 parts by weight of propylene glycol and 3.24 parts by weight of pure water with respect to 100 parts by weight of the water absorbent resin particles is prepared. Then, the water-absorbent resin particles were sprayed using a spray and mixed for 6 seconds with a high-speed continuous mixer (turbulizer; 1000 rpm) (mixing step). Subsequently, the mixture was supplied to a heating paddle dryer and heat-treated at 199 ° C. for 40 minutes (heat treatment step).

  Thereafter, forced cooling was performed with a cooling paddle dryer having the same specifications until the powder temperature reached 60 ° C. (cooling step). At that time, by adding 1.5 parts by weight of the aluminum sulfate treatment liquid to 100 parts by weight of the heat-treated (surface-crosslinked) water-absorbent resin, a water-absorbent resin powder having a coated surface was obtained. . The above-mentioned aluminum sulfate treatment solution is a 50% by weight sodium lactate aqueous solution (produced by Musashino Chemical Laboratory Co., Ltd.) with respect to 1 part by weight of a 27% by weight liquid aluminum sulfate aqueous solution (produced by Asada Chemical Industry Co., Ltd.). ) 0.3 parts by weight and propylene glycol 0.1 parts by weight (surface crosslinking step).

Subsequently, the water-absorbent resin powder obtained in the surface cross-linking step was continuously applied to an oscillating circular classifier having a sieve mouth diameter of 1600 mm having a metal sieve having a mesh size of 710 μm while maintaining a powder temperature of 60 ° C. To be classified. The metal sieve has a material of SUS304, a tension tension of 50 [N / cm], a surface roughness Rz of the sieve inner surface of 50 nm, a surface roughness Ra of the sieve inner surface of 4.8 nm, and a sieve area of 2 [m ² / Sheet]. Furthermore, a stainless steel punching metal (material: SUS304, open area ratio: 40%) with a hole diameter of 20 mm is placed under the metal sieve (50 mm below the sieve surface), and a tapping ball (urethane resin) with a diameter of 30 mm is placed thereon. Manufactured, white (milky white), cross-sectional area ratio (ratio of tapping ball cross-sectional area to metal sieve area); 16%, temperature (hot air, sieve surface, heating equilibrium temperature from water absorbent resin); Arranged. The classifier was kept at 60 ° C., the atmospheric dew point in the device was 13 ° C., the frequency was 230 rpm, the radial inclination (gradient) was 11 mm, the tangential inclination (gradient) was 11 mm, and the eccentric amount was 35 mm. Further, the classifier is subjected to static elimination with a ground resistance of 5Ω, depressurized to 0.11 kPa by an exhaust device with a bag filter, and ventilated with dry air (temperature 60 ° C., dew point 10 ° C.) 2 [m ³ / hr]. (Second classification step).

  The residue on the metal sieve having a mesh size of 710 μm is pulverized again and then mixed with the material passing through the metal sieve having a mesh size of 710 μm, so that the total amount of the water-absorbent resin is less than 710 μm. Got. The physical properties of the water-absorbent resin on the first day of operation were water content: 1.4% by weight, water-soluble content: 6.3% by weight, weight average particle size (D50): 401 μm, σζ: 0.36. It was.

  While continuously producing a water-absorbent resin under the operating conditions described above, sampling was performed for every ton of product, and the physical properties (CRC / AAP / SFC) were measured for a total of 20 tons. About the obtained 20 points | pieces data, the average value and the standard deviation were calculated | required, and it evaluated as the water absorbing resin (3-1d) of the driving | operation 1st day. The results are shown in Table 2.

[Production Example 3-75d]
The continuous production apparatus of the water absorbent resin was operated without stopping the production condition 3 described above, and continuous production of the water absorbent resin was continued. In addition, the swinging circular classifier in the first classification process, the heating paddle dryer (heat treatment machine) in the surface cross-linking process, the dryer in the drying process and the pulverizing process, and the three-stage roll mill are each in a fixed period. The washing was controlled in advance.

  When continuous operation was performed by the above method, a sharp decrease in SFC was observed on the 75th day from Production Example 3-1d (first operation day). The results are shown in Table 2 as the water absorbent resin (3-75d) on the 75th day of operation.

The SFC of the water-absorbent resin (3-75d) is 60 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], compared with the first day of operation (the water-absorbent resin (3-1d)), A significant decrease in SFC (110 → 60) was confirmed.

  When the cause of the SFC drop was investigated, in the paddle dryer in the cooling process, a lump of aluminum sulfate treatment liquid and water absorbent resin adhered to the paddle surface, and the added aluminum sulfate treatment liquid was effectively mixed with the water absorbent resin. It turned out that it was not.

[Example 8]
In order to remove the lump of aluminum sulfate treatment liquid and water absorbent resin generated in Production Example 3-75d, the surface cross-linking process was temporarily stopped, and the cooling paddle dryer was washed. The said washing | cleaning removed to the grade which cannot confirm the said lump with a spatula visually (spatula washing | cleaning). In addition, processes other than the said surface crosslinking process were made to drive | operate in the state which reduced the operation rate slightly, without stopping.

  After completion of the cleaning, the apparatus was recovered and the operation was resumed, but SFC did not recover. The results are shown in Table 2 as the water absorbent resin (8).

[Example 9]
In the spatula cleaning of Example 8, the removal of the aluminum sulfate treatment liquid and the mass of the water-absorbing resin was insufficient, so the surface crosslinking step was stopped again and the cooling paddle dryer was washed with water. The water washing was performed by putting warm water (industrial pure water) at 60 ° C. into a paddle dryer and immersing the paddle dryer for about 1 hour, and then washing the inside of the apparatus with industrial pure water with a high-pressure washing device. In addition, it was confirmed that the water-absorbing resin swelled from dead space or the like due to immersion of warm water. That is, it was found that the cleaning of Example 8 was insufficient to remove the aluminum sulfate treatment liquid and the water-absorbent resin lump.

Subsequently, the inside of the apparatus was washed with water using a high pressure washing apparatus manufactured by Sugino Machine Co., Ltd. The water washing is performed by jetting warm water (industrial pure water) at 60 ° C. at a discharge pressure (gauge pressure) of 400 [kg / cm ² ], and the aluminum sulfate treatment liquid and water absorption that have entered the dead space of the paddle dryer. The resin mass was removed cleanly and without traces.

After the washing with water, the paddle dryer was dried and restored, and the operation was resumed. As a result, the SFC was 110 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], which was recovered to the same level as the first day of operation. . The results are shown in Table 2 as the water absorbent resin (9).

  In addition, from the results of Production Example 3-75d, Example 8, and Example 9, it is preferable that the cooling paddle dryer in the surface cross-linking process is washed with water every 75 days or so when the aluminum treatment is performed. Is considered.

[Production Example 4-1d]
As the production condition 4 of the water absorbent resin according to the present invention, the water absorbent resin was continuously produced by the following method.

  That is, a water-absorbent resin (4-1d) was obtained by performing the same conditions and operations as in Production Example 3-1d except that no tapping ball was used in the second classification step in Production Example 3-1d. The physical properties of the water-absorbent resin on the first day of operation were as follows: water content: 1.4% by weight, water-soluble content: 6.4% by weight, weight average particle size (D50): 394 μm, σζ: 0.39 It was.

  While continuously producing a water-absorbent resin under the operating conditions described above, sampling was performed for every ton of product, and the physical properties (CRC / AAP / SFC) were measured for a total of 20 tons. About the obtained 20 points | piece data, the average value and the standard deviation were calculated | required, and it evaluated as the water absorbing resin (4-1d) of the 1st driving | operation. The results are shown in Table 2.

[Production Example 4-40d]
The continuous production apparatus of the water absorbent resin was operated without stopping the production condition 4 described above, and continuous production of the water absorbent resin was continued. In addition, the swinging circular classifier in the first classification process, the heating paddle dryer (heat treatment machine) in the surface cross-linking process, the dryer in the drying process and the pulverizing process, and the three-stage roll mill are each in a fixed period. The washing was controlled in advance. Further, when aluminum treatment is performed in the surface cross-linking step, it is necessary to previously manage the water washing every predetermined period for the cooling paddle dryer.

  When continuous operation was performed by the above method, a decrease in SFC was observed on the 40th day from Production Example 4-1d (first operation day). The results are shown in Table 2 as the water absorbent resin (4-40d) on the 40th day of operation.

The SFC of the water-absorbent resin (4-40d) is 93 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], compared with the first day of operation (water-absorbent resin (4-1d)), A decrease in SFC (103 → 93) was confirmed.

  When the cause of the SFC drop was investigated, clogging was confirmed in the metal sieve having an opening of 710 μm in the second classification step.

[Example 10]
In order to eliminate the problem that occurred in Production Example 4-40d, the second classifying step was temporarily stopped, and the oscillating circular classifier (metal sieve having a mesh size of 710 μm) was cleaned. The cleaning was performed by hitting a metal sieve with a human hand to remove cloggings to the extent that it could not be visually confirmed (hand washing). In addition, it was made to drive | operate in the state which slightly reduced the operation rate, without stopping processes other than the said 2nd classification process.

After completion of the washing, the apparatus was restored and the operation was resumed. However, the SFC was 94 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], and physical properties were hardly recovered. The results are shown in Table 2 as the water absorbent resin (10).

[Example 11]
Since the physical properties were not much recovered in the cleaning of Example 10, the second classification step was stopped again, and the oscillating circular classification device was washed with water. In the water washing, the metal sieve was first removed from the classifier and immersed in a 60 ° C. warm water (industrial pure water) bath for 1 hour. As a result, a large number of water-absorbing resins that had entered the opening of the sieve swelled and became visible. That is, it can be said that the water-absorbing resin was removed slightly in the cleaning of Example 10.

Subsequently, hot water (industrial pure water) at 50 ° C. was ejected at a discharge pressure (gauge pressure) of 200 [kg / cm ² ] with a high pressure washer manufactured by Kärcher Japan Co., Ltd. The water-absorbing resin that had entered and the foreign substances present in the dead space of the classifier were removed cleanly without a trace.

After washing with water, the classifier was dried and recovered by high-pressure air, and the operation was resumed. As a result, the SFC was 104 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], the same level as the first day of operation. Was recovering. The results are shown in Table 2 as the water absorbent resin (11).

  In addition, from the results of Production Example 4-40d, Example 10 and Example 11, the oscillating circular classifier (especially a metal sieve having a mesh size of 710 μm) in the second classification process is used when aluminum treatment is performed in the cooling process. It is considered that it is preferable to wash with water every 40 days or so.

[Production Example 5-1d]
As manufacturing condition 5 of the water absorbent resin according to the present invention, the water absorbent resin was continuously produced by the following method.

  That is, in the surface cross-linking step in Production Example 3-1d, the mixture was mixed for 2 minutes with a proshear mixer (manufactured by Taiheiyo Kiko; rotational speed 300 rpm) instead of the turbulizer. The physical properties of the water-absorbent resin on the first day of operation were as follows: water content: 1.4% by weight, water-soluble content: 6.3% by weight, weight average particle size (D50): 408 μm, σζ: 0.35 It was.

  While continuously producing a water-absorbent resin under the operating conditions described above, sampling was performed for every ton of product, and the physical properties (CRC / AAP / SFC) were measured for a total of 20 tons. About the obtained 20 points | piece data, the average value and standard deviation were calculated | required, and it evaluated as the water absorbing resin (5-1d) of the driving | operation 1st day. The results are shown in Table 2.

[Production Example 5-20d]
The continuous production apparatus of the water absorbent resin was operated without stopping the production condition 5 described above, and continuous production of the water absorbent resin was continued. In addition, about the swinging circular classifier in the first classifying process, the paddle dryer for heating (heat treatment machine) in the surface cross-linking process, the paddle dryer for cooling, the dryer in the drying and grinding processes, and the three-stage roll mill, In each case, the process was controlled in advance for washing with water at regular intervals.

  When continuous operation was carried out by the above method, a decrease in the values of AAP and SFC was observed on the 20th day from Production Example 5-1d (first operation day). In addition, the current value of the pro-shear mixer was larger than the first day of operation. Evaluation was made as a water absorbent resin (5-20d) on the 20th day of operation, and the results are shown in Table 2.

[ Reference Example 12]
In Production Example 5-20d, the proshear mixer was stopped and the inside was confirmed. As a result, a strong water-absorbing resin adhered to the rotating paddle, and thus spatula cleaning was performed. After the washing, the operation was resumed. However, the current value of the proshear mixer immediately returned to the level before washing, and the values of AAP and SFC were lowered. The results are shown in Table 2 as the water absorbent resin (12).

[Example 13]
In Reference Example 12, since the washing was insufficient, the pro-shear mixer was stopped again, and industrial pure water was sprayed to swell the adsorbed water-absorbing resin and wiped cleanly. When the operation was resumed after the washing, the values of AAP and SFC were recovered. The results are shown in Table 2 as the water absorbent resin (13).

In addition, from the results of Production Example 5-20d, Reference Example 12 and Example 13, it is considered that the high-speed mixer in the surface crosslinking step is preferably washed with water every 20 days or so of continuous operation.

[Production Example 6-1d]
As manufacturing condition 6 of the water absorbent resin according to the present invention, the water absorbent resin was continuously produced by the following method.

  That is, Example 3 of International Patent Publication No. 2011/126079 was re-examined to obtain water-absorbing resin particles and a water-absorbing resin.

  Specifically, as a production apparatus for polyacrylic acid (salt) water-absorbing resin, a polymerization process, a gel fine granulation process, a drying process, a pulverization process, a classification process, a surface crosslinking process, a cooling process, a sizing process, and each A continuous manufacturing apparatus composed of a transport process for connecting the processes was prepared. The production capacity of the continuous production apparatus is about 3500 [kg / hr], and the above steps may be one series or two series, respectively. In the case of two or more series, the production capacity is indicated by the total amount of each series. A polyacrylic acid (salt) water-absorbing resin was continuously produced using the continuous production apparatus.

  First, 193.3 parts by weight of acrylic acid, 64.4 parts by weight of 48% by weight aqueous sodium hydroxide, 1.26 parts by weight of polyethylene glycol diacrylate (average polymerization degree 9), 0.1% by weight of ethylenediaminetetra (methylenephosphonic acid) ) A monomer aqueous solution consisting of 52 parts by weight of a 5 sodium aqueous solution and 134 parts by weight of deionized water was prepared.

  Next, after continuously supplying the monomer aqueous solution adjusted to 40 ° C. with a metering pump, 97.1 parts by weight of an aqueous 48 wt% sodium hydroxide solution was continuously line-mixed. At this time, the temperature of the aqueous monomer solution rose to 85 ° C. due to heat of neutralization.

  Further, after continuously mixing line of 5.04 parts by weight of a 4% by weight aqueous sodium persulfate solution, a continuous polymerization apparatus having a planar polymerization belt with weirs at both ends is provided with a thickness of about 7.5 mm. Continuously fed. Thereafter, polymerization (polymerization time 3 minutes) was continuously performed to obtain a band-shaped hydrogel crosslinked polymer (polymerization step).

  The band-shaped hydrogel crosslinked polymer obtained in the polymerization step was continuously cut at equal intervals in the width direction with respect to the traveling direction of the polymerization belt so that the cutting length was 200 mm.

  The hydrogel crosslinked polymer having a cutting length of 200 mm was supplied to a screw extruder and gel crushed. As the screw extruder, a meat chopper having a diameter of 340 mm, a hole diameter of 22 mm, a hole number of 105, a hole plate of 52%, a thickness of 20 mm, and a screw shaft diameter of 152 mm was used. . In the state where the screw shaft rotation speed of the meat chopper was set to 153 rpm, the hydrogel crosslinked polymer was supplied at 132800 [g / min] to obtain a particulate hydrogel crosslinked polymer (gel refinement step). ).

  Next, the particulate water-containing gel-like cross-linked polymer is sprayed on the ventilation belt within 1 minute after the completion of the gel pulverization, dried at 185 ° C. for 30 minutes, and dried water absorbent resin (powder temperature; about 60 ° C.). Obtained (drying step).

  Next, the entire amount of the dried water absorbent resin obtained in the drying step is continuously supplied to a three-stage roll mill and pulverized (pulverization step), and then further classified by JIS standard sieves having openings of 850 μm and 150 μm. Regularly crushed water-absorbing resin particles were obtained (first classification step).

  The physical properties on the first day of operation of the water absorbent resin particles were as follows: CRC: 31.5 [g / g], solid content: 93.6% by weight, weight average particle diameter (D50): 356 μm, σζ: 0.34 The ratio of particles having a particle diameter of 150 μm or more and less than 850 μm was 99.4% by weight. The water-absorbent resin particles contained 0.6% by weight of fine particles having a particle size of less than 150 μm (0% by weight for particles having a particle size of 850 μm or more).

  Next, covalently bonded surface cross-linking comprising 0.3 parts by weight of 1,4-butanediol, 0.6 parts by weight of propylene glycol and 3.0 parts by weight of deionized water with respect to 100 parts by weight of the water-absorbent resin particles. The agent solution was mixed uniformly (mixing step) and heat-treated at 208 ° C. for 40 minutes (heat treatment step). Thereafter, cooling is performed, and the composition consists of 1.17 parts by weight of a 27.5% by weight aqueous aluminum sulfate solution (8% by weight in terms of aluminum oxide), 0.196 parts by weight of 60% by weight aqueous sodium lactate and 0.029 parts by weight of propylene glycol. The ion binding surface cross-linking agent solution was uniformly mixed (cooling step).

  Thereafter, the mixture was pulverized until it passed through a JIS standard sieve having an opening of 850 μm (second classification step) to obtain a water absorbent resin.

  In addition, while continuously producing a water-absorbent resin under the above operating conditions, sampling was performed for every 1 ton of product, and the physical properties (CRC / AAP / SFC / FSR) were measured for a total of 20 tons. About the obtained 20 points | piece data, the average value and standard deviation were calculated | required, and it evaluated as the water absorbing resin (6-1d) of the driving | operation 1st day. The results are shown in Table 3.

  In addition, when this water absorbing resin (6-1d) was observed by SEM, many unevenness | corrugations were seen on the surface of the water absorbing resin compared with the water absorbing resin (1-1d).

[Production Example 6-25d]
Under the production condition 6 described above, the water absorbent resin continuous production apparatus was operated without being stopped, and continuous production of the water absorbent resin was continued.

  In order to investigate the change with time of the water-absorbent resin performance, from the 25th day of continuous operation, samples were sampled for every 1 ton of products by the same method as in Production Example 6-1d, and the physical properties were measured for a total of 20 tons. The results are shown in Table 3 as the water absorbent resin (6-25d) on the 25th day of operation.

The SFC of the water absorbent resin (6-25d) is 110 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], and compared with the first day of operation (the water absorbent resin (6-1d)), A decrease in SFC (116 → 110) was confirmed.

  As a result of investigating the cause of the SFC decrease, in the first classification step, the proportion of particles having a particle size of 150 μm or more and less than 850 μm was reduced to about 96% by weight with respect to 99.4% by weight on the first day of operation. It has been found. That is, it is presumed that the porosity in the water-absorbent resin decreases with an increase in the amount of fine powder, and the SFC decreases.

[Comparative Example 2]
In order to eliminate the SFC drop that occurred in Production Example 6-25d, the first classification process was temporarily stopped, and the classifier was vacuumed (suctioned). The vacuum (suction) cleaning was performed using a commercially available suction machine to the extent that no foreign matter such as solid matter could be visually confirmed. In addition, it was made to drive | operate in the state which slightly reduced the operation rate, without stopping processes other than a 1st classification process.

After the vacuum cleaning, the classifier was restored and the operation was resumed. The ratio of particles having a particle diameter of 150 μm or more and less than 850 μm in the first classification process was about 97% by weight, and the SFC was 112 [× 10 ⁻⁷ · cm ^3. s · g ⁻¹ ], and no recovery of physical properties was observed. The results are shown in Table 3 as a comparative water absorbent resin (2).

[Example 14]
In the vacuum (suction) cleaning of Comparative Example 2, recovery of physical properties was not recognized, so the first classification step was stopped again and the classification device was washed with water. In the water washing, first, the JIS standard sieve was removed from the classifier and immersed in a hot water bath at 60 ° C. for 1 hour. As a result, a large number of water-absorbing resins that had entered the opening of the sieve swelled and became visible. This phenomenon was particularly remarkable with a metal sieve having an opening of 150 μm. That is, it can be said that the water-absorbing resin was not sufficiently removed by the vacuum (suction) cleaning of Comparative Example 2.

Subsequently, industrial pure water at 50 ° C. was ejected at a discharge pressure (gauge pressure) of 200 [kg / cm ² ] with a high pressure washer manufactured by Kärcher Japan Co., Ltd. and entered the opening of the sieve. Foreign matter that was present in the dead space of the water-absorbent resin and the classifier was removed cleanly without a trace.

After the water washing, the classifier was dried and recovered by high-pressure air, and the operation was restarted. As a result, the ratio of particles having a particle diameter of 150 μm or more and less than 850 μm in the first classification step was about 99% by weight, and the SFC was 116 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ], and recovered to the same level as on the first day of operation. The results are shown in Table 3 as the water absorbent resin (14).

  In addition, from the results of Production Example 6-25d, Comparative Example 2 and Example 14, the classification device in the first classification process (particularly the JIS standard sieve having a mesh size of 150 μm) is about every 25 days of continuous operation in the case of production condition 6. It is necessary to wash with water.

  The washing frequency of the sieve is higher than that in Example 1, but the cause is a large proportion of the pulverized product having a particle size of about the degree of opening of the sieve (Example 14: weight average particle with respect to 175 μm of opening of the sieve) The diameter (D50) is 356 μm, σζ: 0.34, Example 1: The sieve opening is 150 μm, the weight average particle diameter is 450 μm, σζ; 0.35), and the unevenness of the water-absorbent resin is the sieve mesh This is probably because clogging is likely to occur.

[Production Example 7-1d]
As manufacturing condition 7 of the water absorbent resin according to the present invention, the water absorbent resin was continuously produced by the following method.

  That is, Example 3 of US Pat. No. 6,100,305 (corresponding Japanese Patent No. 4286335) was re-examined to obtain water-absorbing resin particles and water-absorbing resin.

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

  While maintaining the monomer aqueous solution at a temperature of 24 ° C., nitrogen gas was blown into the liquid to expel dissolved oxygen in the monomer aqueous solution. Subsequently, 77 parts of a 10 wt% aqueous 2,2'-azobis (2-methylpropionamidine) dihydrochloride solution was added to the aqueous monomer solution with stirring.

  Three minutes after the start of stirring, the monomer aqueous solution to which 2,2′-azobis (2-methylpropionamidine) dihydrochloride was added became cloudy and a white fine particle solid having an average particle diameter of about 9 μm was formed. did. The fine particulate solid was 2,2'-azobis (2-methylpropionamidine) diacrylate as a foaming agent.

  Furthermore, 5 minutes after the start of stirring, 10.8 parts of a 10% by weight sodium persulfate aqueous solution and 0.5 part of a 1% by weight L-ascorbic acid aqueous solution as radical polymerization initiators were added while stirring in a nitrogen atmosphere. It added to the said monomer aqueous solution. The aqueous solution was sufficiently stirred and then allowed to stand.

  The polymerization reaction started 3 minutes after the addition of the 10 wt% aqueous sodium persulfate solution and the 1 wt% L-ascorbic acid aqueous solution. The polymerization reaction was carried out in a hot water bath, with the temperature of the hot water bath following the temperature rise of the aqueous solution. 26 minutes after the addition of the 10% by weight aqueous sodium persulfate solution, the temperature of the aqueous solution to which the aqueous sodium persulfate solution was added reached 97 ° C. Thereafter, the aqueous solution was allowed to stand for another 20 minutes while maintaining the temperature in the range of 70 ° C. to 90 ° C. to complete the polymerization reaction of the acrylate monomer. As a result, a water-containing gel-like crosslinked polymer having air bubbles, which is a porous crosslinked polymer, was obtained.

  Next, the hydrogel crosslinked polymer was continuously crushed by a rotary crusher. The average residence time of the hydrogel crosslinked polymer in the rotary crusher during crushing, that is, the crushing time was about 0.25 minutes. The size of the particulate hydrogel crosslinked polymer after pulverization was in the range of about 1 mm to 15 mm in particle diameter.

  The pulverized particulate hydrogel crosslinked polymer was dried with a circulating hot air dryer at 160 ° C. for 1 hour. Next, the dried water-absorbent resin dried product is pulverized by a roll mill, and further passed through a sieve having a mesh size of 850 μm by a JIS standard sieve, and the water-absorbent resin particles having a particle diameter remaining on the 150 μm sieve. Got.

  The physical properties on the first day of operation of the water-absorbent resin particles were as follows: CRC: 45.5 [g / g], solid content: 95.1% by weight, weight average particle diameter (D50): 430 μm, σζ: 0.36 The ratio of particles having a particle diameter of 150 μm or more and less than 850 μm was 97.4% by weight. The water-absorbent resin particles contained 2.6% by weight of fine particles having a particle size of less than 150 μm (0% by weight for particles having a particle size of 850 μm or more).

  Next, secondary crosslinking treatment was performed on the water-absorbent resin particles obtained above. That is, the treatment liquid for secondary crosslinking treatment was 0.05 part of ethylene glycol diglycidyl ether, 0.5 part of lactic acid, 0.02 part of polyoxyethylene sorbitan monostearate, 0.75 part of isopropyl alcohol and 3 parts of water. Was adjusted by mixing.

  Subsequently, 100 parts of the obtained water-absorbing resin particles and the treatment liquid were mixed, and the obtained mixture was heat-treated at 195 ° C. for 30 minutes to obtain a water-absorbing resin.

  In addition, while continuously producing a water-absorbent resin under the above operating conditions, sampling was performed for every 1 ton of product, and the physical properties (CRC / AAP / SFC) were measured for a total of 20 tons. About the obtained 20 points | piece data, the average value and standard deviation were calculated | required, and it evaluated as the water absorbing resin (7-1d) of the driving | operation 1st day. The results are shown in Table 3.

  In addition, when this water absorbing resin (7-1d) was observed by SEM, many unevenness | corrugations were seen on the surface of the water absorbing resin compared with the water absorbing resin (1-1d).

[Production Example 7-20d]
Under the production condition 7 described above, the continuous production apparatus for the water absorbent resin was operated without being stopped, and the continuous production of the water absorbent resin was continued.

  In order to investigate the time-dependent change of the water-absorbing resin performance, from the 20th day of continuous operation, samples were sampled for every 1 ton of products by the same method as in Production Example 7-1d, and the physical properties were measured for a total of 20 tons. The results are shown in Table 3 as the water absorbent resin (7-20d) on the 20th day of operation.

  However, the water-absorbent resin produced under production condition 7 was measured by AAP with the load condition changed to 2.06 kPa.

  The AAP of the water absorbent resin (7-20d) is 29 [g / g], and compared with the first day of operation (water absorbent resin (7-1d)), a decrease in AAP (32 → 29) was confirmed. It was done.

  As a result of investigating the cause of the decrease in AAP, the ratio of particles having a particle diameter of 150 μm or more and less than 850 μm in the first classification step was reduced to about 92% by weight from about 96% by weight on the first day of operation. There was found. Furthermore, it became clear that the mixing property of the surface cross-linking agent deteriorated in the surface cross-linking step as the amount of fine powder increased.

[Comparative Example 3]
In order to eliminate the decrease in AAP that occurred in Production Example 7-20d, the first classification step was temporarily stopped, and the classifier was vacuumed (suctioned). The vacuum (suction) cleaning was performed using a commercially available suction machine to the extent that no foreign matter such as solid matter could be visually confirmed. In addition, it was made to drive | operate in the state which slightly reduced the operation rate, without stopping processes other than a 1st classification process.

  After the vacuum cleaning, the classifier was restored and the operation was resumed. The ratio of particles having a particle size of 150 μm or more and less than 850 μm in the first classification step was about 93% by weight, and AAP was 29 [g / g]. Recovery was not observed. The results are shown in Table 3 as a comparative water absorbent resin (3).

[Example 15]
In the vacuum (suction) cleaning of Comparative Example 3, no physical property recovery was observed, so the first classification step was stopped again and the classification device was washed with water. In the water washing, first, the JIS standard sieve was removed from the classifier and immersed in a hot water bath at 60 ° C. for 1 hour. As a result, a large number of water-absorbing resins that had entered the opening of the sieve swelled and became visible. This phenomenon was particularly remarkable with a metal sieve having an opening of 150 μm. That is, it can be said that the water-absorbing resin was not sufficiently removed by the vacuum (suction) cleaning of Comparative Example 3.

Subsequently, industrial pure water at 50 ° C. was ejected at a discharge pressure (gauge pressure) of 200 [kg / cm ² ] with a high pressure washer manufactured by Kärcher Japan Co., Ltd. and entered the opening of the sieve. Foreign matter that was present in the dead space of the water-absorbent resin and the classifier was removed cleanly without a trace.

  After the water washing, the classifier was dried and recovered by high-pressure air, and the operation was restarted. As a result, the ratio of particles having a particle size of 150 μm or more and less than 850 μm in the first classification step was about 96% by weight, and AAP was 32 [g. / G] and recovered to the same level as the first day of operation. The results are shown in Table 3 as the water absorbent resin (15).

  In addition, from the results of Production Example 7-20d, Comparative Example 3 and Example 15, the classification device in the first classification process (especially the metal sieve having a mesh size of 150 μm) is in the production condition 7 every about 20 days of continuous operation. It is necessary to wash with water.

  The frequency of washing the screen with water is higher than that in Example 1, but the cause is thought to be because the unevenness of the water-absorbent resin tends to cause clogging of the screen.

(Summary)
As shown in Tables 1 to 3 above, deterioration of physical properties, contamination with brown foreign matters, generation of undried material, etc. are observed in continuous operation over a long period of time, but there is no such problem by washing with water every certain period, and high A water-absorbing resin having physical properties can be stably and continuously produced.

  Improves physical properties of water-absorbent resin and enables stable continuous production.

Claims (36)

A polymerization step of polymerizing an acrylic acid (salt) aqueous solution to obtain a hydrogel crosslinked polymer;
A drying step of drying the hydrogel crosslinked polymer to obtain a dried water-absorbent resin;
A classification step of classifying the dried water absorbent resin to obtain water absorbent resin particles;
A method for continuously producing a polyacrylic acid (salt) water-absorbing resin, which includes a surface cross-linking step for surface cross-linking the water-absorbent resin particles before and / or after the classification step,
The continuous production means that the polymerization step, the drying step, the classification step and the surface cross-linking step are continuously performed for 1 day or more to produce a water-absorbent resin, and 50% or more of all the process sections are in operation. In a state where the batch is repeated (batch continuation), only a part of the manufacturing process is stopped, and a pause period is set during the batch period,
In one or more steps after the drying step, for the device used in each step, the contact surface with the water absorbent resin is washed with water ,
The method for continuously producing a polyacrylic acid (salt) water-absorbent resin, wherein the water washing is performed with a pressurized water flow having a gauge pressure of 1 to 400 [kg / cm ² ] . A polymerization step of polymerizing an acrylic acid (salt) aqueous solution to obtain a hydrogel crosslinked polymer;
A drying step of drying the hydrogel crosslinked polymer to obtain a dried water-absorbent resin;
A classification step of classifying the dried water absorbent resin to obtain water absorbent resin particles;
A method for continuously producing a polyacrylic acid (salt) water-absorbing resin, which includes a surface cross-linking step for surface cross-linking water-absorbent resin particles before and / or after the classification step,
The continuous production means that the polymerization step, the drying step, the classification step and the surface cross-linking step are continuously performed for 1 day or more to produce a water-absorbent resin, and 50% or more of all the process sections are in operation. In a state where the batch is repeated (batch continuation), only a part of the manufacturing process is stopped, and a pause period is set during the batch period,
The water absorption rate (FSR) of the water absorbent resin is 0.30 [g / g / s] or more,
In one or more steps after the drying step, for the device used in each step, the contact surface with the water absorbent resin is washed with water ,
The method for continuously producing a polyacrylic acid (salt) water-absorbent resin, wherein the water washing is performed with a pressurized water flow having a gauge pressure of 1 to 400 [kg / cm ² ] . A polymerization step of polymerizing an acrylic acid (salt) aqueous solution to obtain a hydrogel crosslinked polymer;
A drying step of drying the hydrogel crosslinked polymer to obtain a dried water-absorbent resin;
A classification step of classifying the dried water absorbent resin to obtain water absorbent resin particles;
A method for continuously producing a polyacrylic acid (salt) water-absorbing resin, which includes a surface cross-linking step for surface cross-linking water-absorbent resin particles before and / or after the classification step,
The continuous production means that the polymerization step, the drying step, the classification step and the surface cross-linking step are continuously performed for 1 day or more to produce a water-absorbent resin, and 50% or more of all the process sections are in operation. In a state where the batch is repeated (batch continuation), only a part of the manufacturing process is stopped, and a pause period is set during the batch period,
The water-absorbent resin is spherical or a granulated product thereof,
In one or more steps after the drying step, for the device used in each step, the contact surface with the water absorbent resin is washed with water ,
The method for continuously producing a polyacrylic acid (salt) water-absorbent resin, wherein the water washing is performed with a pressurized water flow having a gauge pressure of 1 to 400 [kg / cm ² ] .   The continuous production method according to any one of claims 1 to 3, wherein the water washing is performed in the classification step or the surface crosslinking step.   The continuous manufacturing method of any one of Claims 1-4 with which the said water washing is performed for every fixed period.   The continuous production method according to any one of claims 1 to 5, wherein the washing with water is performed with warm water. The continuous production method according to any one of claims 1 to 6 , wherein the washing with water is performed by immersion in water or injection of water into the apparatus. The continuous production method according to any one of claims 3 to 7 , wherein the spherical water-absorbing resin is obtained by reverse phase suspension polymerization. The continuous production method according to any one of claims 3 to 8 , wherein the spherical water-absorbing resin is obtained by spray polymerization into a gas phase or droplet polymerization. The continuous production method according to any one of claims 1 to 9 , wherein the water absorption rate (FSR) of the water absorbent resin is 0.35 [g / g / s]. The continuous production method according to any one of claims 1 to 10 , wherein the polymerization step is foam polymerization. The continuous production method according to claim 11 , wherein the foam polymerization is performed by polymerization of an aqueous monomer solution in which a gas is dispersed. The continuous production method according to any one of claims 1 to 12 , wherein the water washing is performed by at least one apparatus selected from the following (a) to (e).
(A) Drying device in the drying step (b) Heat treatment device or cooling device in the heat treatment step or cooling step (surface crosslinking step) (c) Classification device in the classification step (d) Mixing step (water, aqueous solution or (E) Grinding device in the grinding step The continuous production method according to claim 13 , wherein washing with water is performed in a plurality of steps (a) to (e). The continuous production method according to any one of claims 1 to 14 , wherein the water washing is performed on a metal sieve net or a punching metal. The continuous production method according to claim 15 , wherein the metal sieve mesh is a classified sieve mesh having an opening of 50 μm to 1 mm. The continuous manufacturing method according to claim 15 , wherein the punching metal is a punching metal of a band dryer or a punching metal of a fluidized bed dryer. The continuous production method according to any one of claims 1 to 17 , wherein the water washing is performed on an inner surface of a mixing apparatus that mixes water, an aqueous solution, or an aqueous dispersion with a water absorbent resin. The continuous production method according to any one of claims 1 to 18 , wherein the water washing is performed on an inner surface of at least one of a mixing device, a heat treatment device, and a cooling device in the surface crosslinking step. The continuous manufacturing method according to any one of claims 1 to 19 , wherein water washing is performed on an apparatus having an operating temperature of 40 to 100 ° C. 21. The continuous production method according to any one of claims 1 to 20 , wherein in the classification step, a classification device including a metal sieve mesh having an opening of 45 to 2000 [mu] m is used. The continuous production method according to any one of claims 1 to 21 , wherein the timing of washing with water is determined by a change in particle size or a change in liquid permeability. The continuous production method according to any one of claims 1 to 22 , wherein a classification step is performed before and after the surface crosslinking step. A weight average particle diameter (D50) 200~500μm prior water-absorbent resin particles subjected to surface cross-linking, particle size containing fine particles of less than 150 [mu] m 0.1 wt% or more, or any claim 1-23 1 The continuous manufacturing method as described in a term. 25. The continuous production method according to any one of claims 1 to 24, wherein a saline flow conductivity (SFC) of the water-absorbent resin is 10 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more. . The water absorption capacity (CRC) of the water absorbent resin is 20 [g / g] or more, and the saline flow conductivity (SFC) is 110 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more. Item 26. The continuous production method according to any one of Items 1 to 25 . The water absorption rate (FSR) of the water absorbent resin is 0.35 [g / g / s] or more, and the saline flow conductivity (SFC) is 20 [× 10 ⁻⁷ · cm ³ · s · g ⁻¹ ] or more. The continuous production method according to any one of claims 1 to 25 , wherein The continuous production method according to any one of claims 1 to 27 , further comprising one or more pulverization steps before the classification step after the drying step. The continuous production method according to claim 28 , wherein the water washing is performed in the pulverization step or the drying step. 30. The continuous production method according to any one of claims 1 to 29 , wherein the dried water-absorbent resin has an irregularly crushed shape obtained by continuous kneader polymerization or continuous belt polymerization. The continuous production method according to any one of claims 1 to 30 , wherein in the surface cross-linking step, a covalent bond surface cross-linking agent and an ionic bond surface cross-linking agent are used in combination. The continuous production method according to any one of claims 1 to 31 , wherein the dried water-absorbent resin introduced into the classification step contains a surfactant and is heated or kept at a temperature of 40 ° C or higher. 33. The continuous production method according to any one of claims 1 to 32 , wherein in the classification step, a tapping material is installed at a lower part of a metal sieve screen to be used for classification. The continuous production method according to claim 33 , wherein the temperature of the tapping material is 40 to 100 ° C. The continuous production method according to any one of claims 1 to 34 , wherein the tension of the metal sieve mesh used in the classification step is 35 to 100 [N / cm]. The continuous production method according to any one of claims 1 to 35 , wherein continuous production for 30 days or more is performed.