JP4642343B2 - Continuous production method for water-absorbent resin products - Google Patents

Description

The present invention relates to a continuous production method for a water-absorbing resin product having high physical properties, and relates to a continuous production method for obtaining a water-absorbing resin product having high physical properties simply and inexpensively with a stable and constant quality .

In recent years, hygroscopic materials such as disposable diapers and sanitary napkins, so-called incontinence pads, have widely used water-absorbing resins for the purpose of absorbing bodily fluids as constituent materials. Examples of the water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product, a hydrolyzate of starch-acrylic acid graft polymer, a saponified vinyl acetate-acrylic acid ester copolymer, an acrylonitrile copolymer or an acrylamide copolymer. Known are hydrolysates of polymers or cross-linked products of these, and cross-linked polymers of cationic monomers.
Such a water-absorbent resin has excellent liquid absorption amount, water absorption speed, gel strength, gel permeability, suction force for sucking water from a substrate containing an aqueous liquid, etc. when in contact with an aqueous liquid such as body fluid. It is required to have excellent physical properties. Furthermore, in recent years, water-absorbing resin powders with a very narrow particle size distribution and water-absorbing resin powders with high absorption capacity and low water-soluble content have been demanded, and the absorption capacity under pressure and liquid permeability under pressure are high. It has come to be required.

Many parameters and measurement methods defining various properties of these water-absorbing resins are disclosed in the following patent documents.
For example, a water absorbent resin excellent in gel strength, soluble content, and water absorption magnification has been proposed (see, for example, Patent Document 1). In addition, a water-absorbing resin excellent in liquid permeability under no pressure, water absorption speed, and water absorption magnification has been proposed (see, for example, Patent Document 2). Furthermore, a technique for defining a specific particle size distribution has also been proposed (see, for example, Patent Document 3. In addition, US Pat. No. 5,051,259, US Pat. No. 5,419,956, European Patent No. 6,294,441, etc.).
In addition, many water-absorbing resins having excellent water absorption capacity under pressure under various loads and methods for measuring the same have been proposed, and water-absorbing resins combined with other physical properties are proposed (for example, patents). See Reference 4. Besides these, European Patent No. 0707603, European Patent No. 0712659, European Patent No. 1029886, US Patent No. 5462972, US Patent No. 5453323, US Patent No. 5797893, US Patent No. 6127454, US Pat. Issued patent Re37021 etc.).

  Further, a water-absorbing resin excellent in impact resistance has been proposed (see, for example, Patent Document 5; in addition, US Pat. No. 5140076, etc.). Furthermore, a water-absorbing resin that defines the amount of dust has been proposed (see, for example, Patent Document 6), and a water-absorbing resin with less coloring has been proposed (for example, see Patent Document 7). As for urine resistance, a water-absorbing resin excellent in gel durability and water-absorbing ability to an L-ascorbic acid aqueous solution has been proposed (for example, see Patent Document 8; in addition, European Patent 0940148 and the like). An excellent water-absorbing resin has been proposed (see, for example, Patent Document 9). Further, a water-absorbing resin with little residual monomer has been proposed (see, for example, Patent Document 10).

Further, it has been proposed that a water-absorbing resin having specific physical properties is suitable for a water-absorbing article (diaper) having specific physical properties, constitution or polymer concentration (see, for example, Patent Document 11. In addition, US Pat. No. 5,147,343). No., US Pat. No. 5,149,335, European Patent 532002, US Pat. No. 5,601,452, US Pat. No. 5,562,646, US Pat. No. 5,669,894, International Publication No. WO 02/053198, and the like.
In recent years, as the production amount of the water-absorbent resin increases, the production steps such as polymerization and surface treatment are continued (for example, see Patent Document 12). When water-absorbing resin is continuously produced, it is desirable that all have the same high physical properties, but in reality, there may be variations in physical properties between lots of water-absorbing resin that are produced continuously. Water-absorbing resin that greatly exceeds or falls below the physical properties is mixed (see, for example, Patent Documents 13 and 14). And the higher the physical properties are required, the longer the manufacturing process is continued, and the larger the manufacturing scale is, the smaller the variation in physical properties in each step gives a large variation in the properties of the final water absorbent resin product. In addition, surface cross-linking described below, particularly dehydration esterification, affects the dispersion of physical properties in the final water absorbent resin product. In order to suppress such variations in physical properties, conventionally, there has been often a reduction in productivity. In addition, a wide variety of water-absorbing resins that meet user demands are required. As a result, there are problems that it takes a long time to stabilize physical properties when changing the product number (type), and that the manufacturing process is complicated. It was.

In recent years, sanitary materials for absorbing feces, urine, and blood represented by paper diapers (also known as absorbent articles) have increased the concentration (amount used) of the water-absorbent resin, and the physical properties of such water-absorbent resin products are slightly lower. Such a variation has a problem of having a great influence on the final water-absorbent article.
US Reissue Patent No. 32649 British Patent No. 2267094 US Pat. No. 6,087,002 US Pat. No. 6,297,335 US Pat. No. 6,414,214 US Pat. No. 5,994,440 US Pat. No. 6,444,744 US Pat. No. 6,194,531 European Patent No. 1153656 European Patent No. 0605215 US Pat. No. 6,150,582 European Patent No. 093739 International Publication No. 2002/10451 Pamphlet JP-A-11-349625

Therefore, the problem to be solved by the present invention is to provide a continuous production method of a water-absorbent resin product with stable quality, which can easily and inexpensively continuously produce a water-absorbent resin product with high physical properties at a stable and constant quality. It is .

The present inventor has intensively studied to solve the above problems. As a result, the polymerization step, drying step, classification step, the surface modification step and the surface modification step after the second classification step continuously produced by the incoming water absorbent resin via the after after the second classification step Measures predetermined physical properties and / or predetermined component amounts, for example, absorption capacity under no pressure, absorption capacity under pressure, liquid permeability, particle size, etc., and values of predetermined physical properties and / or predetermined component amounts are above a certain level and / or below a certain level the separated water-absorbing resin showing, in the same manufacturing line or another production line, and the surface modification step a through by continuous-produced come the second classification step prior to the water-absorbent resin mixture As a result, it was found that the final product should be obtained, and the present invention was completed.
That is, the continuous production method of the water absorbent resin product according to the present invention is continuously produced through the polymerization step, the drying step, the classification step, the surface modification step, and the second classification step after the surface modification step. For the water-absorbent resin, the step (A) of measuring predetermined physical properties and / or predetermined component amounts after the second classification step , and the predetermined physical properties and / or predetermined component amounts are a certain level and / or below a certain level according to the measurement results A step (B) of separating a predetermined amount of the water-absorbent resin (a) showing the value of the water-absorbent resin continuously produced, and at least part of the separated predetermined amount of the water-absorbent resin (a) , in the same manufacturing line or another production line, and a step (C) to be mixed with the surface modification step of pre said second classification step coming is produced continuous manner through the water-absorbing resin.

  In the present invention, a water-absorbent resin product having high physical properties can be continuously produced easily and inexpensively with a stable and constant quality.

Hereinafter, the present invention will be described in detail. However, the scope of the present invention is not limited to these descriptions, and modifications other than the following examples can be made as appropriate without departing from the spirit of the present invention.
[Continuous production of water-absorbent resin products]
The method for producing a water-absorbent resin product according to the present invention comprises drying the hydrogel crosslinked polymer obtained in the polymerization step in the drying step, then pulverizing in the pulverization step as necessary, and then classifying step. In this method, the water-absorbent resin product is continuously produced through the surface modification step and the second classification step after the surface modification step . Moreover, a transportation process and a storage process are included as needed.

In the present invention, “manufacturing continuously” does not require all processes to be continuous processes, and even if batch processes such as polymerization and surface treatment are included, they may be substantially connected to form a series of continuous flows. For example, it is continuously manufactured. In the case of including a batch process in the present invention, a storage hopper or the like may be appropriately provided in the middle for the connection as necessary.
The continuous production method of a water absorbent resin product according to the present invention is suitably used for industrial production and continuous production of a water absorbent resin product on a plant scale. Preferably, the production amount of the water absorbent resin product is 5 t ( (metric ton) / day or more, more preferably 10 t / day or more, and particularly preferably 20 t / day or more, and is preferably applied to large-scale continuous production. The upper limit of the production amount is not particularly limited, but is usually preferably 1000 t / day or less, and more preferably 500 t / day or less. In the following, unless otherwise specified, t means weight ton and metric ton, and weight and mass are synonymous.

(Polymerization process)
In the present invention, the water-absorbing resin is a water-swellable and substantially water-insoluble crosslinked polymer, and is a conventionally known water-swellable crosslinked polymer that forms an anionic, nonionic or cationic substantially water-insoluble hydrogel. It is. In the present invention, “water swellability” refers to absorption of a large amount of water in ion-exchanged water that is essentially 5 times or more of its own weight, preferably 50 to 1000 times. In the present invention, “substantially water-insoluble” means that the water-soluble component (water-soluble polymer) in the water-absorbent resin is 0 to 50% by mass, preferably 25% by mass or less, more preferably 20% by mass or less, and still more preferably. Means 15% by mass or less, particularly preferably 10% by mass or less.

In the present invention, the water-absorbent resin is used alone or as a mixture. Among these, an acid group-containing water-absorbent resin is preferable, and one of the carboxyl group-containing water-absorbent resins, which are carboxylic acids or salts thereof, or a mixture thereof. More preferred are mixtures. Typically, a cross-linked polymer obtained by cross-linking polymerization of a monomer mainly composed of acrylic acid and / or a salt thereof (neutralized product), for example, a polyacrylate cross-linkage optionally containing a graft component It is preferable to have a polymer as a main component.
In the present invention, the water-absorbent resin has a constitutional unit in the range of 0 to 50 mol% acrylic acid and 100 to 50 mol% acrylate (however, the total amount of both is 100 mol% or less). Preferably, those in the range of 10 to 40 mol% acrylic acid and 90 to 60 mol% acrylate (however, the total amount of both is 100 mol% or less) are more preferable. The molar ratio of acid to salt (the ratio of salt to the total molar amount of acid and salt) is called the neutralization rate.

Neutralization of the water-absorbing resin for forming the salt may be performed in the monomer state before polymerization, or may be performed in the polymer state during or after the polymerization, or they may be used in combination. May be. Examples of the neutralization salt include alkali metal salts such as sodium, potassium and lithium of (poly) acrylic acid, ammonium salts and amine salts.
In addition, the acrylic acid that can be used in the present invention preferably contains p-methoxyphenol (also referred to as hydroquinone monomethyl ether) from the viewpoints of stabilization of physical properties, reduction of residual monomers, acceleration of polymerization, and low coloration. The content is preferably 200 ppm by mass or less, more preferably 10 to 160 ppm by mass, further preferably 20 to 140 ppm by mass, further preferably 30 to 120 ppm by mass, and more preferably 40 to 100 ppm by mass with respect to acrylic acid. ppm, more preferably 50 to 90 ppm by mass. The content of protoanemonin and / or furfural in acrylic acid that can be used in the present invention is preferably 0 to 20 ppm by mass, more preferably 0 to 10 ppm by mass, and particularly preferably 0 to 5 ppm. Mass ppm.

  The monomer for obtaining the water absorbent resin in the present invention may be substantially acrylic acid (salt) alone, or may be obtained using an unsaturated monomer other than the above acrylic acid (salt). Further, another unsaturated monomer may be used in combination with acrylic acid (salt) to obtain a water absorbent resin. Although it does not specifically limit as monomers other than acrylic acid (salt), Specifically, for example, methacrylic acid, maleic acid, vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamide- Anionic unsaturated monomers such as 2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) Acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene Glycol (meth) acrylate, poly Nonionic hydrophilic group-containing unsaturated monomers such as tylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, N-vinylacetamide; N, N-dimethylamino Cations such as ethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and quaternary salts thereof Unsaturated unsaturated monomers. These monomers may be used alone or in combination of two or more as appropriate.

In the present invention, from the viewpoint of physical properties, acrylic acid and its salt used as a main component are used, and if necessary, it is usually preferably 0 to 30 mol%, more preferably 0 to 10 mol% in all monomers. What is necessary is just to use another monomer together.
When polymerizing the above-mentioned monomers in order to obtain the water-absorbent resin in the present invention, bulk polymerization or precipitation polymerization can be performed. However, performance and ease of control of polymerization, and absorption of swollen gel are also possible. From the viewpoint of characteristics, it is preferable to perform aqueous solution polymerization or reverse phase suspension polymerization by using the monomer as an aqueous solution, and it is more preferable to perform aqueous solution polymerization suitable for continuous polymerization. The concentration of the monomer in the aqueous solution (hereinafter referred to as the monomer aqueous solution) when the monomer is used as an aqueous solution is determined by the temperature of the aqueous solution and the type of monomer and is particularly limited. However, it is preferably in the range of 10 to 70% by mass, and more preferably in the range of 20 to 60% by mass. Moreover, when performing the said aqueous solution polymerization, you may use together solvents other than water as needed, and the kind of solvent used together is not specifically limited.

The method for aqueous solution polymerization is not particularly limited. For example, the aqueous monomer solution is polymerized while crushing the resulting hydrogel crosslinked polymer in a uniaxial or multiaxial (preferably double-armed) kneader. Examples thereof include a method (kneader polymerization), a method in which a monomer aqueous solution is supplied in a predetermined container or on a driving belt for polymerization (belt polymerization), and the resulting gel is pulverized with a meat chopper or the like. Such kneader polymerization and belt polymerization can be preferably applied in order to exert the effects of the present invention most, and these continuous polymerizations are particularly preferably used.
When starting the above polymerization, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2'-azobis (2-amidinopropane) dihydrochloride, etc. Photopolymerization initiators such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one and 1-hydroxycyclohexyl phenyl ketone can be used. Furthermore, it is good also as a redox type | system | group initiator by using together the reducing agent which accelerates | stimulates decomposition | disassembly of these polymerization initiators, and combining both. Examples of the reducing agent include (bi) sulfurous acid (salt) such as sodium sulfite and sodium bisulfite, L-ascorbic acid (salt), reducing metal (salt) such as ferrous salt, amines, and the like. Although it is mentioned, it is not particularly limited. The amount of these polymerization initiators used is preferably from 0.001 to 2 mol% (based on monomer), more preferably from 0.01 to 0.1 mol% (based on the physical properties such as residual monomer and water absorption properties). Monomer).

Further, the polymerization reaction may be initiated by irradiating the reaction system with active energy rays such as radiation, electron beam, and ultraviolet rays, and the above polymerization initiator may be used in combination. The reaction temperature in the polymerization reaction is not particularly limited, but the temperature range from the lowest temperature to the highest temperature (peak temperature) of the polymerization reaction is preferably in the range of 15 to 130 ° C. More preferably, it is in the range of ˜120 ° C. Further, the reaction time and the polymerization pressure are not particularly limited, and may be appropriately set according to the type of monomer or polymerization initiator, the reaction temperature, and the like.
The water-absorbent resin in the present invention has a crosslinked structure inside (so-called internal crosslinking).

The internal crosslinking may be one formed without using a crosslinking agent (self-crosslinking type), but has two or more polymerizable unsaturated groups or two or more reactive groups in one molecule. More preferably, a crosslinking agent (internal crosslinking agent) is formed by copolymerization or reaction.
Specific examples of these internal crosslinking agents include, for example, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri ( (Meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, tri Allylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene Examples include lenglycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, and glycidyl (meth) acrylate. These internal cross-linking agents may be used alone, or two or more types as appropriate. May be used in combination. These internal cross-linking agents may be added to the reaction system all at once or in divided portions. When using at least one kind or two or more kinds of internal cross-linking agents, the compound having two or more polymerizable unsaturated groups is polymerized in consideration of the absorption characteristics of the water absorbent resin product finally obtained. Sometimes it is essential to use it.

The amount of these internal crosslinking agents used is preferably 0.001 to 2 mol%, more preferably 0.005 to 0.5 mol%, more preferably 0.005 to 0.5 mol%, based on the physical properties, relative to the monomer (excluding the crosslinking agent). Preferably it is 0.01-0.2 mol%, Especially preferably, you may be in the range of 0.03-0.15 mol%.
When using the internal cross-linking agent to introduce a cross-linked structure into the water-absorbent resin, the internal cross-linking agent is added to the reaction system before, during or after the polymerization of the monomer or after the polymerization or neutralization. You just have to do it.
In the polymerization, 0-50% by mass (based on monomer) of starch / cellulose, starch / cellulose derivative, polyvinyl alcohol, polyacrylic acid (salt), polyacrylic acid (salt) Various foaming agents such as hydrophilic polymers such as cross-linked products and others, carbonic acid (hydrogen) salts, carbon dioxide, azo compounds, inert organic solvents, and the like, and various surface activity. Agents; chelating agents; chain transfer agents such as hypophosphorous acid (salts) may be added.

  In the present invention, the water-absorbing resin is preferably produced by reverse phase suspension polymerization or aqueous solution polymerization, and particularly preferably produced by aqueous solution polymerization. The reverse phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent. For example, U.S. Pat. Nos. 4,093,764, 4,367,323, 4,446,261, 4,683,274, and 5,244,735. Are described in US patents. Aqueous polymerization is a method in which an aqueous monomer solution is polymerized without using a dispersion solvent. For example, US Pat. US Pat. No. 5,264,495, US Pat. No. 5,145,906 and US Pat. No. 5,380,808, European patents such as European Patents 081636, 09555086, and 0922717, and international publications such as WO 01/16197. In addition, the polymerization conditions described in the above-described patent documents and the like used in the description of the prior art can also be suitably applied to the present invention.

(Drying process)
The water-containing gel-like cross-linked polymer obtained in the polymerization step is made into a water-absorbing resin having a desired water content by a drying step. From the viewpoint of color reduction and residual monomer reduction, drying is performed after completion of polymerization (after discharge from the polymerization machine), preferably within 2 hours, more preferably within 1 hour, even more preferably within 0.5 hour, and particularly preferably 0.8. Start (put into dryer) within 2 hours.
Drying is usually performed in a temperature range of 60 to 250 ° C, preferably 100 to 220 ° C, more preferably 120 to 200 ° C. The drying time depends on the surface area of the polymer, the moisture content, the type of the dryer, etc., and is selected to achieve the desired moisture content.However, from the viewpoint of physical properties such as residual monomer reduction, it preferably contains water vapor and has a dew point. Hot air drying is performed with hot air of 50 to 100 ° C., more preferably with hot water containing water vapor and a dew point of 60 to 90 ° C., preferably for 0.1 to 5 hours.

The water content of the water-absorbent resin in the present invention (specified by the amount of water contained in the water-absorbent resin / measured by loss on drying at 180 ° C. for 3 hours) is not particularly limited, but from the physical properties of the resulting water-absorbent resin product, It is preferable that the powder exhibits fluidity even at room temperature, more preferably 0.2 to 30% by mass, still more preferably 0.3 to 15% by mass, and particularly preferably 0.5 to 10% by mass. .
(Crushing process)
The production method according to the present invention includes a pulverization step in which the hydrogel crosslinked polymer obtained in the polymerization step is dried in the drying step and then pulverized by a pulverizer to form a particulate water-absorbing resin, if necessary. May be included. In particular, when aqueous solution polymerization is performed in the polymerization step, it is preferable to include a pulverization step.

Examples of the pulverizer used in the pulverization step include a roller mill, a knife mill, a hammer mill, a pin mill, a jet mill, and the like, and may include a means for heating the inner wall surface of the pulverizer itself.
A gel-like material obtained without pulverization or a gel-like material obtained without pulverization, that is, a material having a mass average particle diameter exceeding 1000 μm may be used. When aqueous solution polymerization is performed in the process, it is generally preferable to form a powder by a pulverization process.
The particle shape of the water-absorbent resin thus obtained is not particularly limited to a spherical shape, a crushed shape, an indeterminate shape or the like, but an indeterminate crushed shape obtained through a pulverization step can be preferably used.

(Classification process)
In the present invention, it is adjusted to a powder particle size in accordance with the purpose by carrying out classification by classification step further. Classification step, after about dry 燥工, after good Mashiku grinding process, and is provided in front of the more surface modification Engineering. In the present invention, Ru second classification step to after said surface modification step is provided.
As the particle diameter of the water-absorbent resin obtained in the present invention, after classification or as a final product, the mass average particle diameter is preferably in the range of 200 to 700 μm, more preferably in the range of 300 to 600 μm, and particularly preferably in the range of 400 to 500 μm. It is a range.

  The water-absorbent resin obtained in the present invention is 850 to 150 μm (after passing through the 850 μm standard sieve and the non-passed product of the 150 μm standard sieve / standard sieve is JIS or its equivalent) after classification or as a final product. What contains 95-100 mass% of resin powder is preferable. The water-absorbent resin obtained in the present invention preferably has a smaller proportion of fine powder (for example, preferably less than 100 μm, more preferably less than 150 μm), specifically less than 5.0% by mass, and more preferably 3.0%. It is less than mass%, especially less than 1.0 mass%. In addition, the water-absorbent resin obtained in the present invention preferably has a smaller proportion of coarse particles (eg, preferably substantially 1000 μm sieve or more, more preferably 850 μm sieve or more), specifically 5.0 mass% or less. Preferably, 1.0 mass% or less is more preferable.

(Surface modification process)
In the present invention, it is et modifying the surface by surface modification process.
Surface modification of the water-absorbent resin includes (i) surface crosslinking with a surface crosslinking agent, (ii) surface coating with water-insoluble fine particles, (iii) surface coating with a surfactant, and (iv) hydrophilicity or hydrophobicity. Surface coating with a polymer, (v) surface coating with an antibacterial agent or deodorant, and (vi) surface coating with a hydrophilic or hydrophobic organic compound. More than one species are applied, preferably (i) surface cross-linking with a surface cross-linking agent and / or (ii) surface coating with water-insoluble fine particles, most preferably (i) and (ii) Is also applied.

In consideration of physical properties, the amount of the surface modifier (surface crosslinking agent, water-insoluble fine particles, etc.) used is 100 parts by mass of the water absorbent resin (preferably 100 parts by mass of the water absorbent resin that is a dry body). Preferably it is the range of 0.001-10 mass parts, More preferably, it is the range of 0.01-8 mass parts, More preferably, it is 0.05-5 mass parts, Most preferably, it is the range of 0.1-2 mass parts. .
Surface cross-linking is an operation for improving various physical properties by increasing the cross-linking density in the vicinity of the surface of the water-absorbent resin from the inside of the particle. In addition to internal cross-linking, various surface cross-linking agents ( 2) is added to the water-absorbent resin to crosslink only the surface or surface layer.

The surface cross-linking agent is not particularly limited, but a cross-linking agent that reacts with a carboxyl group, particularly a dehydration reactive cross-linking agent is preferably used. Here, the dehydration reactivity means that a functional group (particularly a functional group near the surface) of the water-absorbent resin undergoes a dehydration reaction, preferably dehydration esterification and / or dehydration amidation, more preferably Dehydration esterification. Although the water-absorbent resin surface-crosslinked by dehydration esterification has high physical properties, it is difficult to control the reaction in continuous production. In order to eliminate this problem and stabilize the physical properties, the present invention is preferably applied.
As such a dehydration-reactive crosslinking agent, specifically, for example, when the water absorbent resin contains a carboxyl group, a hydroxyl group-containing crosslinking agent such as a polyhydric alcohol; an amino group-containing crosslinking agent such as a polyvalent amine. A crosslinking agent; a cyclic crosslinking agent such as an alkylene carbonate, a mono-, di- or polyoxazolidinone compound, or an oxetane compound such as 3-methyl-3-oxetanemethanol. Examples thereof include a cyclic crosslinking agent that generates an amino group and causes the hydroxyl group or amino group to undergo a crosslinking reaction;

  More specifically, the dehydration-reactive cross-linking agent is described, for example, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, glycerin, 1,4-butanediol, 1,5- Polyhydric alcohol compounds such as pentanediol; alkylene carbonate compounds of 1,3-dioxolan-2-one and 4-methyl-1,3-dioxolan-2-one; oxetane compounds such as 3-methyl-3-oxetanemethanol and many others Among these, a dehydration reactive crosslinking agent selected from polyhydric alcohols, alkylene carbonates, oxazolidinone compounds, and (polyvalent) oxetane compounds in order to maximize the effects of the present invention. The above is preferable, and it is particularly preferable to use a polyhydric alcohol.

  As the surface cross-linking agent, in addition to these dehydration-reactive cross-linking agents, non-dehydration-reactive cross-linking agents, for example, epoxy compounds such as ethylene glycol diglycidyl ether and γ-glycidoxypropyltrimethoxysilane; 2,4-tri Polyisocyanate compounds such as range isocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; silane coupling agents such as γ-aminopropyltrimethoxysilane; 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate] and the like; and polyvalent metals such as beryllium, magnesium, calcium, strontium, zinc, aluminum, iron, chromium, manganese, titanium, and zirconium;

When mixing the surface cross-linking agent with the water absorbent resin, water and / or a hydrophilic organic solvent may be used.
The amount of water used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass with respect to 100 parts by mass of the water absorbent resin (preferably 100 parts by mass of the water absorbent resin which is a dry body). More preferably, it is the range of 1-5 mass parts.
Examples of the hydrophilic organic solvent include alcohols such as ethyl alcohol, propyl alcohol and isopropyl alcohol; ketones such as acetone; ethers such as dioxane, alkoxy (poly) ethylene glycol and tetrahydrofuran; amides of ε-caprolactam; dimethyl Examples thereof include sulfoxides such as sulfoxide, and the use amount thereof is preferably in the range of 0 to 10 parts by mass, more preferably in the range of 0 to 5 parts by mass, with respect to 100 parts by mass of the water absorbent resin. Preferably it is the range of 0-3 mass parts.

The method for mixing the surface cross-linking agent is not particularly limited. Therefore, water, hydrophilic organic solvent, inorganic powder, etc. may be mixed separately with respect to the water-absorbent resin, may be mixed together, or may be mixed in several times. Preferably, it is more preferable that after mixing all of these in advance, this mixture is added to the water-absorbent resin, and at that time, an aqueous solution is prepared.
In mixing, the water-insoluble fine particle powder and the surfactant may be allowed to coexist in a range not impeding the effects of the present invention, for example, in a range of 0 to 10 parts by mass (for a water-absorbing resin).
Among the above-mentioned various mixing methods, a method in which a surface cross-linking agent and, if necessary, water and / or a hydrophilic organic solvent are dropped and mixed in a water-absorbent resin is preferable, and a spraying method is more preferable. The size of the droplets to be sprayed is preferably 0.1 to 300 μm in terms of average particle size, and more preferably 0.1 to 200 μm in terms of average particle size. In this case, the temperature of the aqueous solution is preferably 0 ° C. to boiling point, more preferably 5 to 50 ° C., and further preferably 10 to 30 ° C. from the viewpoint of mixing property and stability. The temperature of the water absorbent resin powder before mixing is preferably 0 to 80 ° C., more preferably 40 to 70 ° C., from the viewpoint of mixing properties.

A suitable mixing device used for the mixing is a device capable of producing a large mixing force to ensure uniform mixing. Examples of such a mixing apparatus include a cylindrical mixer, a double wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluidized furnace rotary disk. Type mixer, airflow type mixer, double arm type kneader, internal mixer, pulverizing type kneader, rotary mixer, screw type extruder, etc., preferably mixing within 3 minutes in high speed stirring type mixer Is done. In particular, the mixing is preferably continuous mixing.
In this step, when heat treatment is performed, the treatment time is preferably 1 to 180 minutes, more preferably 3 to 120 minutes, and particularly preferably 5 to 100 minutes. The heat treatment temperature (specified by heat medium temperature or material temperature) is preferably in the range of 100 to 250 ° C, more preferably in the range of 140 to 220 ° C, further preferably in the range of 150 to 220 ° C, and in the range of 160 to 220 ° C. Particularly preferred.

The heat treatment can be performed using a normal dryer or a heating furnace, and examples include a grooved mixed dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, and an infrared dryer. The
In the surface modification step preferably included in the production method according to the present invention, in addition to surface cross-linking, or inactive surface activity in the sense that it does not react with water-absorbent resin without causing surface cross-linking. An agent, an inert deodorant, an inert inorganic fine particle powder, or the like may be used. As the surfactant and inert inorganic fine particle powder used in this case, preferably, ultrafine particles and inorganic fine particles described later are used, and in this case, the surface crosslinking is preferably performed simultaneously or separately.

  In the present invention, the cationic polymer compound as an additive used for modifying the surface of the water-absorbent resin can improve the fixability to hygienic materials, and preferably has a mass average molecular weight of 2000 or more, more preferably 5000. Above, most preferably 10,000 or more. The upper limit of the mass average molecular weight is not particularly limited, but is preferably 10 million or less, more preferably 1 million or less from the viewpoint of physical properties. The amount used is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and still more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the water absorbent resin. Mixing of the cationic polymer compound is added alone or in solution (aqueous solution), preferably after surface crosslinking. Specific examples of the cationic polymer compound include polyethyleneimine, polyvinylamine, polyallylamine, polyamidoamine and epichlorohydrin condensate, polyamidine, partial hydrolyzate of poly (N-vinylformaldehyde), or salts thereof. The

  In the present invention, when water-insoluble fine particles are used as an additive, it is possible to improve the liquid permeability of the water-absorbent resin and the blocking resistance during moisture absorption. As the water-insoluble fine particles, inorganic or organic water-insoluble fine particles having a mass average particle size of preferably 10 μm or less, more preferably 1 μm or less, particularly preferably 0.1 μm or less are used, and the lower limit of the mass average particle size is particularly limited. However, usually 0.1 nm or more is preferable. Specifically, silicon oxide (for example, trade name: Aerosil, manufactured by Nippon Aerosil Co., Ltd.), titanium oxide, aluminum oxide, or the like is used. The mixing is performed by powder mixing (Dry-Blend) or slurry mixing. The amount used is preferably 10 parts by mass or less, more preferably 0.001 to 5 masses per 100 parts by mass of the water absorbent resin. Parts, more preferably 0.01 to 2 parts by mass.

These surface cross-linking methods are various European patents such as European Patent Nos. 0349240, 0605150, 0450923, 0818733, 0450924, 0668080, and US Pat. Nos. 5,409,771, 5597873, Various US patents such as US Pat. No. 5,385,983, US Pat. No. 5,610,220, US Pat. No. 5,633,316, US Pat. No. 5,674,633, US Pat. No. 5,462,972, and international publications such as WO 99/42494, WO 99/43720, The surface crosslinking method can also be applied to the present invention.
In the present invention, in addition to the surface crosslinking as the surface treatment, an additive may be further added as necessary. Deodorants, antibacterial agents, fragrances, foaming agents, pigments, dyes, hydrophilic short fibers, plasticizers, adhesives, surfactants, fertilizers, oxidizing agents, reducing agents, water, salts, chelating agents, bactericides Various functions for water-absorbent resins such as addition of hydrophilic polymers such as polyethylene glycol, paraffin, hydrophobic polymers, thermoplastic resins such as polyethylene and polypropylene, thermosetting resins such as polyester resins and urea resins, etc. It may include an addition step for imparting, preferably an addition step to the surface.

The amount of these additives to be used is preferably in the range of 0 to 30 parts by mass, more preferably in the range of 0 to 10 parts by mass, and still more preferably in the range of 0 to 1 part by mass with respect to 100 parts by mass of the water absorbent resin. It is. In addition, after surface cross-linking and / or addition of an additive to the water-absorbent resin, the present invention is generically referred to as a water-absorbent resin as long as the water-absorbent resin is a main component and is substantially integrated. The content of these additives is applied as a measurement target in the step (A) for measuring the predetermined physical properties and / or the predetermined component amounts in the present invention.
(Transport process)
The transport process included as necessary in the production method according to the present invention links each process such as a polymerization process, a drying process, a pulverization process, a classification process, and a surface modification process. Although a transporting step is not always necessary, it is preferable to include a step of transporting at least the dried particulate water-absorbing resin with a transporter.

In the transportation process, transportation is carried out continuously or batchwise, preferably continuously. Examples of the transport machine used in the transport process include a belt conveyor, a screw conveyor, a chain conveyor, a vibration conveyor, a pneumatic conveyor, and the like, and includes a means for heating and / or keeping warm the inner wall surface from the outside. Things can be mentioned. Of these transporters, chain conveyors or pneumatic conveyors are preferred.
In the transportation process, it is preferable to perform at least a part of the process by pneumatic transportation. In order to reduce damage due to transportation of water-absorbent resin powder with high physical properties, which is a dry product powder, and also to suppress contamination with metallic foreign matter, at least a part of the transportation process may be performed by pneumatic transportation. preferable.

In this transportation process, it is preferable that the inner wall surface of the transport machine is heated from the outside and / or kept warm. This is because there is a tendency that aggregation in the transport aircraft can be effectively prevented.
(Storage process)
The production method according to the present invention may include a storage step of storing the dried particulate water-absorbing resin in a storage tank.
Examples of the storage tank used in this storage step include a silo, a hopper, and the like, and preferably a tank equipped with a means for heating the inner wall surface thereof. In the particulate water-absorbing resin, a storage tank having a metallic inner surface, for example, an inner surface made of iron or stainless steel, is preferred from the viewpoint of the wearability and chargeability of the particulate water-absorbing resin. In addition to the storage of the final product, a storage step (intermediate hopper) may be separately provided in the middle of each step, and each step may be connected by a buffer hopper and a quantitative supply hopper for continuous production.

(Other processes)
It is also preferable to irradiate the resulting water absorbent resin, particularly the final water absorbent resin product, with magnetic field lines. Gel deterioration is prevented by irradiation with such magnetic field lines, and a water-absorbing resin that is excellent in durability and substantially free from metallic foreign matters can be obtained. The magnetic flux density of the magnetic field lines used is preferably 0.05 Wb / m ² (500 gauss) or more, more preferably 0.5 Wb / m ² or more, particularly preferably 1.0 Wb / m ² or more, preferably a permanent magnet. And / or an electromagnet is used, and more preferably, the magnets are arranged in a lattice shape and the water-absorbing resin is passed between the lattices.

[Stabilization of water-absorbent resin product quality]
In the continuous production method of a water absorbent resin product according to the present invention, water absorption continuously produced through a polymerization step, a drying step, a classification step, a surface modification step, and a second classification step after the surface modification step. The predetermined physical property and / or the predetermined component amount is not less than a certain value and / or not more than a certain amount in accordance with the step (A) of measuring the predetermined physical property and / or the prescribed component amount after the second classification step and the measurement result. A step (B) of separating a predetermined amount of the water absorbent resin (a) showing a value from the continuously produced water absorbent resin, and at least a part of the separated predetermined amount of the water absorbent resin (a), in the same manufacturing line or another production line, and a step (C) to be mixed with the surface modification step of pre said second classification step coming is produced continuous manner through the water-absorbent resin, It is characterized by.

Hereinafter, these steps (A) to (C) will be described.
(Process (A))
In the continuous production method of a water absorbent resin product according to the present invention, water absorption continuously produced through a polymerization step, a drying step, a classification step, a surface modification step, and a second classification step after the surface modification step. With respect to the functional resin , the predetermined physical properties and / or the predetermined component amounts are measured after the second classification step.
The polymerization step, drying step, classification step, the surface modification step and the surface modification step after the second classification step continuously produced by the incoming water absorbent resin via the, in the after the second classification step, not particularly limited as long as it is water-absorbent resin after about the second classification Engineering is performed, specifically, the second classification Engineering higher the instrumentation placed al classifier water-absorbent resin which is performed discharged It means the water absorbent resin present in the production line after the outlet or the water absorbent resin product finally obtained.

That is, the water-absorbent resin of measuring the predetermined physical properties, water-absorbing resin in which the second classification Engineering higher the instrumentation placed al classifier water-absorbent resin is carried out is present in the production line after the outlet to be discharged It may be the water-absorbent resin product finally obtained, but it exists in the final storage step of the continuous production line and / or immediately before and / or around from the viewpoint of ease of measurement. It is preferable that the water absorbent resin product finally obtained. When the second classification Engineering higher the instrumentation placed al classifier water-absorbent resin is carried out to measure the predetermined property for the water-absorbing resin present in the production line after the outlet to be discharged, the measurement location is not particularly limited, it may be a close location to the outlet where the second classification Engineering higher the instrumentation placed al classifier water-absorbent resin to be performed is discharged, the end of the production line (outlet as a product) The location close to

The measurement of the predetermined physical property and / or the predetermined component amount may be continuous measurement, or may be performed by sampling at a predetermined output every predetermined time and / or predetermined time. Here, for each predetermined production amount, for example, it may be for each lot (Lot), or a sampling inspection may be performed for each production amount in the lot. More specifically, for example, when the final product is bag-packed (drum-packed or container-packed) every predetermined amount, a sampling inspection is performed on the product bag corresponding to the predetermined output and / or predetermined time. Or sample the line flow for that lot. The lot size and definition will be described later.
The predetermined physical properties and / or the predetermined component amounts are not particularly limited as long as they are physical properties and component amounts that affect the quality of the water absorbent resin product. For example, the absorption capacity under no pressure, the absorption capacity under pressure, the liquid permeability ( Flow rate), water content, pH, residual monomer, bulk specific gravity, content of various components (additives, etc.), gel strength, water-soluble component amount, air permeability, gel durability (light resistance, heat resistance, resistance) Examples include various known and novel physical properties and component amounts including urinary properties, LA resistance), deodorizing ability, antibacterial ability, and object color. These measuring methods are also known in the above-mentioned various patents, EDNA (European Disposable And Non-Woven Association) and JIS (Japan Industrial Standard). Among these, preferably, from the stability of physical properties and the magnitude of influence, the particle size represented by the amount of fine powder, the absorption capacity under no pressure represented by CRC, the absorption capacity under pressure represented by AAP or AUL, It is at least one physical property selected from gel strength and liquid permeability (liquid flow rate), more preferably two or more physical properties, more preferably three or more physical properties, and particularly preferably four or more physical properties. is there.

The physical properties and component amounts measured in the present invention are not limited to the methods described in the examples of the present application, and known physical properties may be measured by known measuring methods, and improvements in these known physical property measuring methods. However, it may be a completely new measurement method, or may have completely new physical properties and component amounts.
The particle size measurement method is not particularly limited, such as sieving classification, airflow classification, wet classification, and dry classification, and may be measured by weight (mass) or volume may be measured by a laser or the like. In particular, it is one of the preferred embodiments in the present invention that the particle size is measured by a laser diffraction scattering method .

  Laser diffraction scattering is a method that uses the light scattering principle to measure the particle size distribution from the pattern of light scattered from particles suspended in liquid (wet) or dry powder particles (dry). is there. The sample concentration of the particles is appropriately determined, but is preferably 1 to 90% by mass, more preferably 2 to 70% by mass. As a measurement principle, it is preferable to use at least one selected from the Mie scattering method, the Fraunhofer analysis method, and the polarized differential scattering method (PIDS). When measuring wet, a non-absorbing solvent (non-aqueous solvent) that is transparent and has low viscosity and is inert to the water-absorbent resin is appropriately selected. For example, lower alcohols such as methanol, ethanol, and propanol; hexane, etc. Are used as dispersion solvents. When measuring by a dry method, as a dispersion method, a free fall is mentioned preferably, for example, and a tornado method is especially preferable.

  Preferred lasers for measuring the particle size by laser diffraction scattering include single wave or multiwave, preferably 50 to 3000 nm, more preferably 100 to 1000 nm, and even more preferably 350 to 900 nm. A diode laser (750 nm), a tungsten halogen lamp (450 nm, 600 nm, 900 nm), and a red semiconductor laser (for example, 690 nm). The laser diffraction scattering of the particle size may be performed by batch measurement based on partial sampling of the water-absorbing resin, or may be continuously measured by attaching a laser diffraction scattering apparatus in the middle of the production line. The measurement may be either a wet measurement or a dry measurement. In the dry measurement, the water-absorbent resin powder may be dropped freely or may be an injection type. From the viewpoint of accuracy with respect to the water-absorbent resin and application to the present invention, dry measurement is preferred. The measurement is preferably performed under conditions of a temperature of 0 to 100 ° C., more preferably 10 to 60 ° C., and preferably a relative humidity of 10 to 100%, more preferably 10 to 60%. In addition, when measuring a particle size by a laser diffraction scattering method, it is common to obtain | require a particle size by volume (%), However, You may convert into mass (weight)% suitably compared with sieve classification. In order to convert the particle size expressed by volume (%) to mass (weight)%, the particle size is compared using a standard sample of a water-absorbent resin having the desired physical properties and component amounts, and based on the results. What is necessary is just to convert by a fixed ratio.

  The particle size measured by the laser diffraction scattering method is preferably the particle size of the water-absorbent resin product as the final product, and its physical properties and component amounts (absorption capacity under no pressure, absorption capacity under pressure, liquid permeability, particle size, etc.) ) Is high and controlled as described later. For example, the mass average particle diameter is in the range of 300 to 600 μm, and 850 to 150 μm (passing through the 850 μm standard sieve and not passing through the 150 μm standard sieve) Preferably, the surface-crosslinked water-absorbent resin powder containing 95 to 100% by mass of the water-absorbent resin powder is JIS or its equivalent). Also, the particle size of the water-absorbent resin measured by the laser diffraction scattering method (the particle size represented by volume (%) or the particle size represented by mass (weight)% by sieving may be used) and other physical properties In addition, the component amount is a measurement target of the predetermined physical property and / or the predetermined component amount in the present invention, and may be used as a test result or a catalog description item indicating the performance of the water absorbent resin product as a final product.

  As a measurement other than the measurement of particle size by laser diffraction scattering method, in the measurement of absorption capacity under no pressure, absorption capacity under pressure, liquid permeability, the particle size (specified by the whole water-absorbent resin or specific particle size), measurement temperature, The measurement time and the absorbing solution are appropriately selected. Examples of the absorbing solution are not limited to ion-exchanged water and physiological saline, but include various concentrations of saline, artificial or natural urine, blood, drainage, wastewater, seawater, and water mixed with organic solvent / water. Illustrated and used according to purpose. The measurement temperature is appropriately selected in the range of the freezing point and below the boiling point, but is preferably controlled as narrow as possible in the range of 0 to 50 ° C, more preferably in the range of 10 to 44 ° C, and further in the range of 20 to 40 ° C. . Moreover, the measurement time may be measured instantaneously in a continuous manner, or the measurement time may be preferably measured by batch measurement within 16 hours, more preferably within 3 hours, and even more preferably within 1 hour. .

The measurement time does not necessarily need to reach equilibrium or saturation, and by measuring in a very short time of about 1 second to 10 minutes, the saturated value or 1 hour value may be inferred from past experience values, You may manage by a short time value. Using such a short-time measurement, the water-absorbent resin is separated (for example, separated on the line) by continuously measuring predetermined physical properties and / or predetermined component amounts during the production flow of the water-absorbent resin. May be.
The absorption capacity under no pressure in the present invention is a method in which the water-absorbent resin is freely swollen in a large excess of the liquid to be absorbed, for example, CRC (Centrifuge Retention Capacity), Blue Dextran Method, TB Method (Tea Bag), etc. It has been known.

As the method for measuring the absorption capacity under pressure in the present invention, AAP (Absorbency Against Pressure), AUL (Absorbency under load), demand method, and the like are known depending on various loads and measured concentrations.
In determining the water-absorbing resin (a) having a predetermined physical property and / or a predetermined component amount that is greater than or equal to a certain value and / or less than a certain value, the predetermined physical property value and / or the predetermined component amount value are What is necessary is just to determine suitably from the physical property of the water absorbing resin to perform.
A method for determining the predetermined physical property value and / or the predetermined component amount value is not particularly limited. For example, a target physical property value or a target component value of a water absorbent resin product to be finally obtained is a predetermined physical property value. The method employ | adopted as a value and a predetermined component amount value is mentioned.

  Further, predetermined physical properties and / or predetermined component amounts are measured for each of a predetermined number of lots produced, and a predetermined number of lots with higher measured values (higher lots) are separated in order from the highest measured value or measured. There is also a method in which a predetermined number of lots with lower values (lower lots) are separated in descending order of measured values. Both the upper level and the lower level may be separated, or only one of them may be separated. More preferably, only the lower order separation is performed. In the case of this method, the amount to be separated is preferably the upper and / or lower 30 to 0.0001% by mass, more preferably 20 to 0.001% by mass, and still more preferably the total amount of the predetermined number of lots produced. Is in the range of 10 to 0.01% by mass, particularly preferably 5 to 0.05% by mass.

Specifically, for example, when the purpose is to produce a water-absorbent resin having a predetermined range of absorption capacity under no pressure, absorption capacity under pressure, liquid permeability, particle size, and the like, Predetermined absorption capacity under no pressure, absorption capacity under pressure, liquid permeability, particle size deviating from a predetermined value from a predetermined component amount value, or a predetermined upper or lower fixed amount is determined in advance, and the predetermined What is necessary is just to send the water absorption resin below it or more to a process (B) on the basis of a physical-property value and / or a predetermined component amount value.
On the basis of the target physical property value of such a water absorbent resin product, it is preferable to separate those that deviate from the target physical property value in the step (B).

  As a specific example of the separation standard in the step (B), since it is appropriately determined in accordance with the intended water absorbent resin product, it cannot be said unconditionally, but for CRC, for example, preferably 10 to 50 g / g Those that fall outside the range, more preferably those that fall outside the range of 25 to 48 g / g, and even more preferably those that fall outside the range of 28 to 45 g / g are separated. For AAP at 1.9 kPa, preferably out of the range of 20-40 g / g, more preferably out of the range of 30-38 g / g, still more preferably out of the range of 33-37 g / g. Isolate things. For AAP at 4.9 kPa, it is preferably out of the range of 10-30 g / g, more preferably out of the range of 20-28 g / g, still more preferably out of the range of 23-27 g / g. Isolate things. The liquid permeability is preferably out of the range of 360 seconds or less, more preferably out of the range of 240 seconds or less, still more preferably out of the range of 1 to 180 seconds, and still more preferably 2 to 2. Separate out of 120 seconds range. Regarding the particle size, the content of the water-absorbent resin powder having a mass average particle size of 300 to 600 μm and 850 to 150 μm (passing 150 μm through a 850 μm standard sieve) is preferably out of the range of 90 to 100% by mass. From the range of 95 to 100% by mass, more preferably from the range of 98 to 100% by mass. Regarding the particle size, the amount of fine powder of less than 150 μm is preferably out of the range of less than 10% by mass, more preferably out of the range of less than 5% by mass, further preferably from the range of less than 2% by mass. Isolate what has come off.

These physical properties may be measured by other measurement methods. For example, a water absorbent resin product that gives a physical property of CRC = 50 g / g is CRC = 50 g / g when measured by other measurement methods. The value corresponding to is given.
In the present invention, the CRC value for the non-pressurized water absorption ratio and the AAP value for the pressurized water absorption ratio may be controlled by other measurement methods. Various physical properties of water absorption magnification under pressure are a concept including the ranges of CRC and AAP as referred to in the present invention.
When the amount of separation in the step (B) is too large, the productivity is lowered and the contribution to the physical property stability is small for the cost. Moreover, when there is too little separation amount in a process (B), there is little contribution to physical property stability. Therefore, in the production method of the present invention, the predetermined physical property values necessary for determining the water absorbent resin (a) in the step (B) and the amount of separation in the step (B) are not too much or too little. It is necessary to determine a predetermined component quantity value.

In the present invention, in accordance with the results you measure the predetermined property and / or the predetermined component content for the second classification step and / or a surface-modifying step through the coming continuously produced water-absorbent resin, production conditions Can also be changed.
In the present invention, the production conditions are preferably changed in accordance with the analyzed particle size. Preferably, the measurement of the predetermined physical properties such as the particle size and / or the predetermined component amount is performed automatically and continuously, and in accordance with the measurement result, the programmed manufacturing conditions are changed, for example, the step (B) or the step The condition change in (C) may be performed. Conventionally, in the production of a water-absorbing resin, temperature and flow rate have been measured. However, in the present invention, by measuring predetermined physical properties and / or predetermined component amounts of the water-absorbing resin, higher water-absorbing properties are obtained. Resin products can be manufactured more stably and with stable quality.

A suitable example of the change in the manufacturing conditions is separation in the step (B) described later and mixing in the step (C). For example, when the production method according to the present invention includes a step of measuring the particle size of the water-absorbent resin by the laser diffraction / scattering method, it does not require a classification time of several tens of minutes in batch analysis such as conventional sieve classification. Because the particle size is automatically and continuously determined instantly, monitoring can be performed in the middle of the manufacturing line, and the manufacturing conditions can be automatically changed by humans at any time according to the particle size distribution. Therefore, as the production conditions change in accordance with the laser diffraction scattering of the particle size as long as it depends on the particle size or concerns, condition change of surface modification depends on the adjustment and the particle size of the particle size distribution (eg if the temperature , Amount), etc., and can be applied in each step such as grinding, classification, and surface treatment. Examples of the method of monitoring in the middle or at the end of the production line include a method of sampling in a batch manner automatically or manually and a method of continuous measurement.

(Process (B))
In the method for producing a water-absorbent resin product according to the present invention, the water-absorbent resin (a) exhibits a predetermined physical property and / or a predetermined component amount that is a certain value and / or a certain value in accordance with the measurement result in the step (A). (B) which isolate | separates predetermined amount from the water absorbent resin produced continuously.
As a specific form, for example, when measuring predetermined physical properties and / or predetermined component amounts of the finally obtained water-absorbent resin product, the predetermined physical properties and / or predetermined component amounts are a certain level and / or below a certain level. A predetermined amount of the water absorbent resin (a) showing the value of is separated from the water absorbent resin product itself produced continuously.

Further, measuring a predetermined physical properties and / or the predetermined component content for the water-absorbing resin in which the second classification Engineering higher the instrumentation placed al classifier water-absorbent resin is carried out is present in the production line after the outlet to be discharged In some cases, the water-absorbent resin product is produced by separating directly from the middle of the flow, or the predetermined physical properties and / or the amount of the predetermined component is a certain value and / or a certain value from the transportation speed of the production line. Estimate the time coming out from the end of the line (the product outlet), and separate the water-absorbent resin product obtained at the appropriate time. Separation may be done in batches for each container stored in a bag or tank as a final product such as for each lot, or separated by flowing in one or two lines after continuous flow, such as in the continuous automatic measurement shown below. May be.

That is, in continuous production, continuously measure the physical properties and particle size of the water-absorbent resin that flows to each step or final product, and continue to flow only a certain standard or more from the bifurcated line to the line. Alternatively, a water-absorbing resin less than a certain standard may be separated from the line. In addition, when separation is performed in a batch manner, the separation may be performed while the container is stored or taken out from the container.
As a preferred method, the particle size of the continuously flowing water-absorbing resin is continuously measured by laser wet or dry, preferably dry, so that the particle size is less than a certain level (for example, a water-absorbing resin with a large amount of fine powder or a broad particle size distribution). A sequence that automatically separates the water-absorbent resin from the line may be used. Specifically, a form in which the particle size is measured by a laser diffraction scattering method and automatically separated in conjunction with the measurement result is preferable.

(Process (C))
In the method for producing a water-absorbent resin product according to the present invention, at least a part of the predetermined amount of the water-absorbent resin (a) separated in the step (B) is transferred to the surface in the same production line or another production line. comprising the step (C) to be mixed with the second classification step prior to the water-absorbent resin comes being produced continuous manner through a reforming process.
That is, the total amount or at least a part of the predetermined amount of the water absorbent resin (a) separated in the step (B) (preferably 50 to 100% by mass, more preferably 80 to 100% by mass, particularly preferably 95% of the separated amount). the 100 wt%), in the same manufacturing line or another production line, and later exit before Symbol table Men'aratameshitsu steps that take place counter応器or al table Men'aratame reformed water absorbent resin is discharged Then, it is mixed with the water-absorbent resin existing in the production line before the second classification step or the finally obtained water-absorbent resin product. Since steps (B) and (C) are performed when necessary, they may be batch-type or continuous. The transport of the water-absorbent resin in the steps (B) and (C) may be connected by the above-described transporter, or in the case of a batch type, may be performed for each container or bag. In addition, it is preferable that the water-absorbent resin in the steps (B) and (C) is mixed as it is without being particularly modified (for example, surface treatment or granulation) between the steps, and as it is, dry mixing (powder) More preferably, the body is mixed).

The mixing in the step (C) is preferably performed in the middle of the production line. In the middle of the production line, the water-absorbing resin (a) is mixed during the normal flow (classification and transportation) of continuous production without substantially providing a new mixing device for the step (C). It shows that.
In the same manufacturing line or another production line, water absorption before Symbol Table Men'aratameshitsu steps that take place counter応器or al table Men'aratame reformed water absorbent resin is present in the production line after the outlet to be discharged when mixed sex resins, but before the second classification step may be introduced at any point of such a production line, for example, in the same manufacturing line or another production line, before Symbol table Men'aratame it anti応器or al table Men'aratame reformed water absorbent resin quality step that is performed may be at a point close to the outlet to be discharged, even at a point close to the edge end of the production line and before the second classification step Good.

When mixing with the water absorbent resin product finally obtained, it mixes with the water absorbent resin product.
Although the form of mixing in the step (C) is not particularly limited, in order to enhance the stabilization of quality, the predetermined physical properties and / or the amount of the predetermined component separated in the step (B) are a certain value and / or a certain value. It is preferable to add or mix the water-absorbent resin (a) having a small amount continuously or intermittently. When the water-absorbing resin (a) is added and mixed, the amount of the added mixture is preferably 10% by mass or less, and more preferably 0.01 to 5% by mass.
The mixing of the two is preferably carried out by wet mixing or dry mixing, more preferably by dry mixing, and the various mixers exemplified above are used. In the middle of the production flow, it is also preferable to mix after the surface treatment, and to mix by using the powder flow in various transport steps and classification steps instead of the mixer.

That is, in order to easily and inexpensively continuous production with a constant quality of the water-absorbent resin product of high properties stable, step mixing in (C) is a water-absorbent resin comes being continuously produced via the surface modification step It is preferable to be performed in the middle of the production line before the second classification step .
In the present invention, continuous production means production of a water-absorbent resin product continuously for 24 hours or more in one line or one day or more in 5 tons (metric ton) / day. The production time is preferably 10 days or more, more preferably 100 days or more, and the production amount per line is preferably 20 t / day or more, more preferably 50 t / day or more. In addition, in the continuous production system, polymerization, drying, pulverization, surface modification, etc., which are basic steps of the method for producing a water-absorbent resin product, each step may be a continuous type or a batch type (for example, a polymerization step). In this case, the interval between each step is preferably 24 hours or less, more preferably 12 hours or less, still more preferably 6 hours or less, and particularly preferably 3 hours or less.

[Water-absorbent resin products with stable quality]
According to the production method of the present invention, a water-absorbent resin product having excellent physical properties such as absorption capacity under no pressure, absorption capacity under pressure, liquid permeability, particle size and the like, and a stable quality can be obtained continuously with high productivity. It is done. Moreover, by mixing a plurality of water-absorbing resins (preferably dry mixing in the middle of the production line), the desired physical properties can be adjusted.
The physical properties of the water-absorbent resin product obtained in the present invention are preferably 25.0 g / g or more as the CRC value for the absorption capacity under no pressure, and the AAP value at 1.9 kPa or 4.9 kPa for the absorption capacity under pressure. Preferably, it is 20.0 g / g or more, and the liquid permeability is preferably 240 seconds or less. As for the particle size, preferably, the content of the water-absorbent resin powder having a mass average particle diameter of 300 to 600 μm and 850 to 150 μm (passing 150 μm through a 850 μm standard sieve) is 95 to 100% by mass, or The amount of fine powder of less than 150 μm is less than 5% by mass. (In the following description, regarding the physical property values, 25.0 is omitted when the decimal point is one digit, such as 25.)
In addition, CRC, 1.9kPa, or 4.9kPa AAP is a representative example of a method for measuring the absorption capacity under no pressure and the absorption capacity under pressure, respectively, and in the present invention, it is not necessarily measured by that measurement method. Alternatively, another absorption capacity without pressure (for example, TB method, dextran method, filtration method) or another absorption capacity under pressure (for example, AUL, APPUP) may be used.

The CRC of the water-absorbent resin product obtained in the present invention is more preferably 28 to 65 g / g, further preferably 30 to 60 g / g, further preferably 32 to 58 g / g, and still more preferably 34 to It is 56 g / g, particularly preferably in the range of 36 to 54 g / g.
The AAP of the water absorbent resin product obtained by the present invention at 1.9 kPa or 4.9 kPa is more preferably 23 g / g or more, further preferably 25 g / g or more, and particularly preferably 27 g / g or more. The upper limit of the AAP at 1.9 kPa or 4.9 kPa of the water absorbent resin product obtained in the present invention is not particularly limited, but is preferably 50 g / g or less.
The liquid permeability of the water absorbent resin product obtained in the present invention is more preferably 1 to 180 seconds, further preferably 2 to 120 seconds, and particularly preferably 3 to 60 seconds.

The bulk specific gravity of the water absorbent resin product obtained in the present invention is preferably 0.30 to 0.90, more preferably 0.50 to 0.80, and still more preferably 0.60 to 0.75.
The particle size of the water-absorbent resin product obtained in the present invention is a water-absorbent resin powder having a mass average particle diameter of 300 to 600 μm and 850 to 150 μm (passing 150 μm through a 850 μm standard sieve), more preferably 97 It is a particle size containing -100 mass%, More preferably, it is a particle size containing 99-100 mass%. Moreover, as for the particle size of the water-absorbent resin product obtained in the present invention, the amount of fine powder of less than 150 μm is more preferably less than 3% by mass, and still more preferably less than 1% by mass. (If the particle size is measured by volume by the laser diffraction scattering method, it may be appropriately converted to mass (weight)% if necessary.)
Moreover, as shown in the below-mentioned Example and the subject of this invention mentioned above, the water-absorbent resin product obtained by this invention is low coloring (no yellowing), and there are few residual monomers. Specifically, the coloring state is preferably 0 to 15, more preferably 0 to 13, more preferably 0 to 10, and most preferably 0 to 0 in terms of YI value (see Yellow Index / European Patent Nos. 0942014 and 1108745). 5 and almost no yellowing. Further, the residual monomer is preferably 500 ppm or less, more preferably 400 ppm or less, further preferably 300 ppm or less, and the standard deviation thereof is preferably 30 or less, more preferably 20 or less, and further preferably 10 or less.

Moreover, pH becomes like this. Preferably it is the range of 4.0-9.0, More preferably, it is the range of 5.0-8.0.
Conventionally, when trying to stabilize and increase the physical properties of the water-absorbent resin, careful production is necessary, and it has been necessary to sacrifice the productivity. High-productivity resin products. Further, as described above, when a dehydration-reactive crosslinking agent is used in surface crosslinking, high physical properties can be expressed and safety is high, but it becomes difficult to control the reaction and it is difficult to stabilize the physical properties of the water-absorbent resin product. However, according to the present invention, the physical properties can be stabilized while maintaining the high physical properties, and the productivity is not affected or rather improved. In the present invention, when a dehydration-reactive crosslinking agent is used, it may be allowed to act as a solvent (for example, a solvent for another crosslinking agent) without acting as a crosslinking agent, but is usually subjected to heat treatment at 160 to 220 ° C. It is preferable to act as a surface cross-linking agent for surface cross-linking.

That is, the present invention provides a novel water absorbent resin product having high physical properties and stable quality.
The water-absorbent resin product according to the present invention is a water-absorbent resin product obtained by cross-linking a monomer mainly composed of acrylic acid and / or a salt thereof and then surface cross-linking using a dehydration-reactive cross-linking agent. Because
(1) The mass average particle diameter is 300 to 600 μm,
(2) The residual monomer amount is 500 ppm or less,
(3) The average value of the absorption capacity without load measured with an analysis point n = 3 is 25 g / g or more, the standard deviation is 0 to 0.50,
(4) The average value of the absorption capacity under pressure at 1.9 kPa or 4.9 kPa measured with an analysis point n = 3 is 20 g / g or more, the standard deviation is 0 to 0.35,
(5) The average value of the amount of fine powder of less than 150 μm measured with the number of analysis points n = 3 is less than 5.0% by mass, the standard deviation is 0 to 0.50,
It is characterized by being.

Furthermore, the dehydration-reactive crosslinking agent is preferably a polyhydric alcohol.
Since the water-absorbent resin product according to the present invention has almost no physical property fluctuation at an analysis point n = 3 and has high physical properties, it is extremely unprecedented even in actual use (for example, use as an actual diaper). Gives excellent performance.
Here, the number of analysis points n means that samples of n points are arbitrarily extracted and various physical properties are measured for the water absorbent resin product. The larger the number of analysis points n, the more accurately the fluctuation of physical properties can be recognized. n is preferably 3 or more, more preferably 5 or more, further preferably 10 or more, and particularly preferably 20 or more. Although the upper limit of n is not particularly limited, it is usually preferably 5000 or less, more preferably 1000 or less, further preferably 500 or less, and particularly preferably 100 or less.

The amount of one analysis point n is not particularly limited because it depends on the form of the water absorbent resin product. For example, in the case of a product in a water absorbent resin production plant, 1 kg or more is a lot. Preferably, 10 kg or more is more preferable, 20 kg or more is more preferable, 100 kg or more is further preferable, and 500 kg or more is particularly preferable. Although an upper limit is not specifically limited, Usually, 500 t or less is preferable, 100 t or less is more preferable, 50 t or less is more preferable, 25 t or less is especially preferable.
The form for extracting n analysis points is not particularly limited. For example, in the case of a product in a water absorbent resin production plant, n points of lots are extracted for each production lot, and one lot is selected. The form which extracts n samples is mentioned. In the case of a commercially available product in the form of a water-absorbent resin product, a mode in which n commercial products are extracted for each production lot, and a mode in which n samples are extracted from commercial products of the same lot. , Etc. In the case of a final product such as a diaper, n samples are extracted from the water-absorbent resin product taken out from the final product of the same lot in a form in which the water-absorbent resin product is taken out from n final products for each production lot. Form, etc. When the lot is unknown in these commercially available products, for example, it is considered that the same lot is used for each sales unit, and n points may be extracted. The extraction of the n analysis points may be performed in units of final product shipping containers (for example, bags) or in units of production batches, times, days, or the like.

  In addition, when taking out a water absorbent resin product from a final product such as a diaper and measuring various physical properties, the water absorbent resin product is taken out from the final product and dried to such a degree as not to cause damage (for example, reduced pressure at 50 ° C. or lower). It is preferable to measure after drying. Since the water absorption characteristics of a water absorbent resin product depend on its moisture content, it is sufficient to measure the water absorbent resin product immediately after production because it has a specific moisture content. The water content of the water-absorbent resin product that has absorbed moisture is determined by drying at a constant water content (the water content in the case of drying at 180 ° C. for 3 hours, preferably 1 to 8% by mass, more preferably 3 to 6% by mass). %) Is preferably measured.

The water-absorbent resin product according to the present invention has an average value of the absorption capacity under no pressure measured with an analysis point n = 3 is 25 g / g or more, but the average value is preferably 28 to 65 g / g, More preferably, it is 30-60 g / g, More preferably, it is 32-58 g / g, More preferably, it is 34-56 g / g, Most preferably, it is the range of 36-54 g / g.
The water-absorbent resin product according to the present invention has a standard deviation of the absorption capacity under no pressure measured with an analysis point n = 3, but the standard deviation is preferably 0 to 0.40. Preferably it is 0-0.30, More preferably, it is 0-0.20, Most preferably, it is 0-0.10.

The water-absorbent resin product according to the present invention has an average value of the absorption capacity under pressure at 1.9 kPa or 4.9 kPa measured with an analysis point n = 3, but the average value is preferably It is 23 g / g or more, more preferably 25 g / g or more, and particularly preferably 27 g / g or more. Although an upper limit is not specifically limited, Preferably it is 50 g / g or less.
The water-absorbent resin product according to the present invention has a standard deviation of the absorption capacity under pressure at 1.9 kPa or 4.9 kPa measured with an analysis point n = 3, and such standard deviation is preferably Is 0 to 0.30, more preferably 0 to 0.20, and still more preferably 0 to 0.10.

In the water-absorbent resin product according to the present invention, the average value of the amount of fine powder of less than 150 μm measured with an analysis point n = 3 is less than 5.0% by mass, but such average value is preferably less than 3.0% by mass. More preferably, it is less than 1.0 mass%.
In the water-absorbent resin product according to the present invention, the standard deviation of the amount of fine powder of less than 150 μm measured with an analysis point n = 3 is 0 to 0.50, preferably 0 to 0.40, more preferably 0 to 0. .30, more preferably 0 to 0.20, and particularly preferably 0 to 0.10.
The water-absorbent resin product according to the present invention preferably has an average value of liquid permeability measured with an analysis point n = 3 of 240 seconds or less, more preferably 1 to 180 seconds, and still more preferably 2 to 120. Seconds, particularly preferably 3 to 60 seconds. Moreover, Preferably, the liquid-permeability standard deviation measured by the analysis score n = 3 is 0-10, More preferably, it is 0-5, More preferably, it is 0-3.

The water-absorbent resin product according to the present invention preferably has the above-mentioned pH, bulk specific gravity, mass average particle diameter, and residual monomer, and in these various properties, the standard deviation of pH measured with an analysis point n = 3 is preferable. Is 0 to 0.01, the standard deviation of the bulk specific gravity measured at the analysis point n = 3 is preferably 0 to 0.01, and the standard deviation of the mass average particle diameter measured at the analysis point n = 3 is preferable. Is 0 to 20, more preferably 0 to 10, and the standard deviation of the residual monomer measured with an analysis point n = 3 is preferably 0 to 20, more preferably 0 to 10.
In the present invention, the standard deviation represents variations in various physical property values at the number of analysis points n. When the standard deviation is within the above range, a water-absorbent resin product with stable quality is obtained. The number of analysis points n is preferably in the above range.

Standard deviations such as CRC, AAP, liquid permeability, and particle size are defined by the following formula (1), and can be calculated by, for example, commercially available calculation software (for example, STDEV of Microsoft Excel).
Standard deviation = Standard deviation of physical properties at n analysis points (1)
Further, according to the present invention, other physical properties of the water absorbent resin product can be similarly controlled. For example, the content of coarse particles of 850 μm or more can be controlled within a standard deviation, preferably in the range of 0 to 1.00, more preferably 0 to 0.50, and still more preferably 0 to 0.20. In addition, various physical properties such as additive content, residual monomer, coloring, pH, and water-soluble content can be stably controlled.

In the present invention, as one of the preferred embodiments, in the surface modification step, a dehydration-reactive cross-linking agent that has conventionally been difficult to control physical properties is used, more preferably dehydration esterification, and still more preferably Use monohydric alcohol. That is, the present invention is preferably a novel production method that imparts physical property stability (the above standard deviation) to a water absorbent resin product with such a surface cross-linking agent. The preferred particle size, water-soluble content, residual monomer, coloring, etc. of the water-absorbent resin product are within the above ranges, and the preferred monomer in the polymerization step is mainly composed of acrylic acid and / or a salt thereof.
[Uses of water-absorbing resin products]
ADVANTAGE OF THE INVENTION According to this invention, the water-absorbent resin product excellent in the stable physical property without the dispersion | variation in the quality in the case of continuous manufacture can be manufactured simply. By mixing different water-absorbing resins, a water-absorbing resin having any desired physical property can be obtained. The water-absorbent resin product obtained by the present invention is widely used in agricultural and horticultural water retention agents, industrial water retention agents, hygroscopic agents, dehumidifying agents, building materials, etc., particularly preferably represented by paper diapers, sanitary napkins, Used as sanitary material for absorption of feces, urine or blood.

  That is, the water-absorbent resin product obtained by the present invention is excellent in balance and stable in various physical properties. Can be used at a high concentration, preferably 30 to 100% by mass, more preferably 40 to 100% by mass, and still more preferably 50 to 95% by mass. Further, the structure of the water absorbent body (absorbing core) in the sanitary material is not particularly limited as long as it is a structure used for general water absorbent articles. For example, a water absorbent resin is formed between hydrophilic fiber materials formed into a sheet shape. A so-called sandwich structure water-absorbing body, and a so-called blended structure water-absorbing body formed by mixing a hydrophilic fiber material and a water-absorbing resin.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Hereinafter, for convenience, “parts by mass” may be simply referred to as “parts”. In addition, “mass%” may be simply written as “%”.
(1) Absorption capacity under no pressure by CRC The following measurement was performed according to European Patent No. 1153656. That is, 0.200 g of the water-absorbing resin was uniformly placed in a non-woven bag (60 mm × 60 mm) and immersed in 0.9% by mass physiological saline at room temperature. After 30 minutes, the bag was pulled up, drained at 250 G for 3 minutes using a centrifuge, and then the mass W1 (g) of the bag was measured. Further, the same operation was performed without using the water absorbent resin, and the mass W0 (g) at that time was measured. And the absorption capacity (g / g) under no pressure by CRC was calculated from these W1 and W0 according to the following formula.

Absorption capacity without pressure by CRC (g / g) = (W1 (g) −W0 (g)) / mass of water absorbent resin (g)
(2) Absorption capacity under pressure by AAP The following measurement was performed according to US Pat. No. 5140076. Specifically, a stainless steel wire mesh (mesh size: 38 μm) was fused to the bottom of a plastic support cylinder having an inner diameter of 60 mm, and 0.900 g of a water-absorbing resin was uniformly dispersed on the mesh. In addition, the outer diameter is slightly smaller than 60 mm, adjusted so that a load of 4.9 kPa can be uniformly applied to the water-absorbent resin, and there is no gap between the inner wall surface of the support cylinder, and A piston and a load that are not hindered from moving up and down were placed in this order, and the mass Wa (g) of this measuring device set was measured. A glass filter with a diameter of 90 mm was placed inside a petri dish with a diameter of 150 mm, and 0.90% by mass physiological saline (25 ° C.) was added to the same level as the glass filter. A filter paper having a diameter of 90 mm was placed thereon so that the entire surface was wetted, and excess liquid was removed. The set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load. After 1 hour, the measuring device set was lifted and its mass Wb (g) was measured. And the absorption capacity | capacitance under pressure by AAP (g / g) was computed from Wa and Wb according to following Formula.

Absorption capacity under pressure with AAP (g / g)
= (Wa (g) -Wb (g)) / mass of water absorbent resin ((0.9) g)
(3) Water-soluble component (sometimes abbreviated as soluble component)
500 mg of water-absorbent resin was dispersed in 1000 ml of deionized water at room temperature, stirred for 16 hours with a 40 mm magnetic stirrer, and the swollen gel was separated with a filter paper (TOYO, No. 6) and filtered. Next, the water-soluble polymer in the filtrate eluted from the water-absorbent resin was subjected to colloidal titration to determine the mass% of water-soluble content in the water-absorbent resin (vs. water-absorbent resin).
(4) Residual monomer In the above (3), the amount of residual monomer in the water-absorbing resin (ppm / water-absorbing resin) is also analyzed by UV analysis of the separately prepared filtrate after stirring for 2 hours by liquid chromatography. did.

(5) Particle size and mass average particle size When continuously measuring, the particle size distribution of the water-absorbent resin was measured by free-falling dry measurement of the water-absorbent resin powder using an infrared semiconductor laser (wavelength 690 nm, AC 100 V).
As another method, 10.0 g of a water-absorbent resin under the conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH% and having an opening of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm (THE IIDA TESTING SIEVE: diameter 8 cm), and classified for 10 minutes using a vibration classifier (IIDA SIEVE SHAKER, TYPE: ES-65 type, SER No. 0501). The residual percentage R was plotted on a logarithmic probability paper, thereby reading the mass average particle size (D50).

(6) Coloring evaluation of water-absorbent resin (hunter whiteness)
According to European Patent Nos. 942014 and 1108745. That is, a color spectrophotometer SZ-Σ80 COLOR MEASURING SYSTEM manufactured by Nippon Denshoku Industries Co., Ltd. was used for coloring evaluation of the water absorbent resin powder. Under setting conditions (reflection measurement / attached powder / paste sample stand (inner diameter 30 mm) / standard round white plate for powder / paste No. 2/30 mmΦ floodlight pipe), about 6 g of water-absorbing resin is provided on the provided sample stand. The surface color (hunter whiteness (WB) and YI (Yellow) is filled with the above spectrocolor difference meter under conditions of room temperature (20 to 25 ° C.) and humidity of 50 RH%. Index)) was measured. Note that the larger WB and the smaller YI, the lower the color and the closer to the substantially white color.

(7) pH
According to US Pat. No. 6,444,744, the pH of 100 mg water-absorbing resin dispersion (23 ± 2 ° C.) in 100 g of physiological saline was measured.
(8) Liquid permeability under pressure (fluid speed)
In accordance with US Pat. No. 5,985,944, the liquid permeability to physiological saline (about 25 ml) at a load of 24.5 g / cm ² was measured using 0.5 g of water absorbent resin. In addition, the higher the liquid permeability under pressure, the shorter the liquid transmission speed (seconds).
(9) Volume-mass conversion in laser diffraction / scattering method The particle size distribution of the surface-crosslinked water-absorbent resin powder (1) obtained in Production Example 1 described later is measured for each batch using the laser diffraction / scattering method. While measuring by volume, separately, the particle size distribution of 100 points was measured by mass by sieving, and the conversion formula of both (volume-mass) was obtained. Using the obtained conversion formula, the volume particle size measured by the laser diffraction scattering method was converted to mass particle size (sieve particle size).

[Production Example 1]
By connecting devices consisting of a metering pump, belt polymerization machine, gel crusher, belt dryer, powder crusher, classifier, humidifier (mixer of surface cross-linking agent), and heat treatment machine with a conveyor, FIG. As shown in the flow chart, water-absorbing resin products are continuously produced by a continuous manufacturing method of water-absorbing resin products including a polymerization process, a drying process, a pulverization process, a classification process, a surface modification process, a transportation process, and a storage process. Manufactured. The production amount was 300 kg / hr. Details are as follows.
(Polymerization process)
A sodium acrylate aqueous solution in which 71 mol% of acid groups were neutralized at a concentration of 41 mass%, and 0.05 mol% of polyethylene glycol diacrylate (average number of added moles of ethylene oxide n = 9) as an internal crosslinking agent (vs. Monomer) was prepared as monomer (1). After the monomer (1) was kept at 20 ° C. and continuously deaerated with nitrogen, 0.12 g / monomer mole of sodium persulfate and 0.005 g / monomer mole of L-ascorbic acid were each continuously in an aqueous solution. Immediately after mixing, the mixture was continuously fed to a thickness of 20 mm on an endless belt sealed with nitrogen by a metering pump. Polymerization started in about 1 minute, and the hydrogel crosslinked polymer (1) was continuously discharged from the end of the moving belt in about 20 minutes.

(Drying process)
Next, the crosslinked polymer (1) was continuously crushed into particles of about 1 mm with a connected meat chopper and then placed on a perforated plate of a band dryer at a thickness of 3 to 5 cm. When hot air of 170 ° C. was passed up and down and dried with continuous hot air for 30 minutes, a block-shaped dry polymer (1) was obtained at the outlet of the dryer.
(Crushing and classification process)
The dry polymer (1) was taken out and crushed at the same time, and the resulting particulate dried product was a three-stage roll granulator at a rate of 300 kg / hr (the roll gap was 1.0 mm / 0.55 mm / 0.42 mm from the top). The powder was pulverized by continuously feeding to the slab. The obtained particulate water-absorbing resin powder at about 60 ° C. was continuously classified with a JIS 850 μm standard sieve to obtain a water-absorbing resin base polymer (1) having a size of 90% by mass or more and less than 850 μm and a size of 150 μm or more.

(Surface modification process)
Further, the water-absorbent resin base polymer (1) was continuously supplied to a high-speed continuous mixer (turbulator / 1000 rpm), and 1,4-butanediol / propylene glycol / water / 24% aqueous sodium hydroxide solution = 0. A surface cross-linking agent aqueous solution composed of 39 / 0.62 / 3.39 / 0.3 (mass% / base polymer) was sprayed and mixed with a spray that averaged about 200 μm droplets. Next, the obtained mixture (1) was continuously heat-treated at 195 ° C. for 40 minutes with a paddle dryer, and further classified (second classification step) with a sieving device having a screen mesh of 850 μm. By storing, surface-crosslinked water-absorbing resin powder (1) was obtained.

[Production Example 2]
Instead of the monomer (1) in the polymerization step of Production Example 1, a sodium acrylate aqueous solution in which 75 mol% of acid groups were neutralized at a concentration of 38% by mass, and trimethylolpropane triacrylate as an internal cross-linking agent was used. By using 0.02 mol% (based on monomer) as the monomer (2), a hydrogel crosslinked polymer (2) is obtained, and then dried, ground and classified in the same manner. A water absorbent resin base polymer (2) was obtained.
The water-absorbent resin base polymer (2) is continuously fed with a high-speed continuous mixer (turbulator / 1000 rpm), and ethylene glycol diglycidyl ether / propylene glycol / water / isopropanol = 0.1 / 0.9. A surface cross-linking agent aqueous solution composed of /3.0/0.5 (mass% / base polymer) was sprayed and mixed with a spray that averaged about 200 μm droplets. Next, the obtained mixture (2) was subjected to continuous heat treatment with a paddle dryer at 195 ° C. for 40 minutes, and further classified (second classification step) with a sieving device having a screen mesh of 850 μm. By storing, a surface-crosslinked water-absorbent resin powder (2) was obtained.

[Production Example 3]
The following conditions were changed in the continuous production of Production Example 2 to obtain a water absorbent resin powder (3).
That is, the surface cross-linking agent aqueous solution mixed with the water absorbent resin base polymer (2) was changed to propylene glycol / water / isopropanol = 0.5 / 2.0 / 0.5 (mass% / base polymer) to obtain. The obtained mixture (3) was heat-treated at 210 ° C. for 30 minutes. Furthermore, the surface-crosslinked water-absorbent resin powder (3) was obtained by classification and storage in the same manner.
[Comparative Example 1]
In Production Example 1, the above process was performed continuously for 24 weeks with a 24-hour operation, and the physical properties of the water-absorbent resin were measured every 1 ton (about 3.3 hours), and the average value and standard deviation of the physical property values for each lot. (Number of analysis points n: about 100). The results are shown in Table 1.

[Comparative Example 2]
In Production Example 2, the above process was performed continuously for 24 hours with a 24-hour operation, and the physical properties of the water-absorbent resin were measured every 1 ton (about 3.3 hours), and the average value and standard deviation of the physical property values for each lot. (Number of analysis points n: about 100). The results are shown in Table 1.
[Example 1]
In the lot of the water absorbent resin obtained in Comparative Example 1, only the upper and lower 10% of the AAP value was separated in a batch system, and the separated upper and lower 10% of the water absorbent resin was subjected to second crosslinking after surface crosslinking. After 20% dry mixing with the water-absorbent resin before the classification step, the average value and standard deviation of the physical property values for each lot were determined. The results are shown in Table 1.

[Example 2]
In the lot of the water-absorbent resin obtained in Comparative Example 1, only the lower 10% of the AAP value was batch-separated, and the separated lower 10% water-absorbent resin was subjected to surface crosslinking and before the second classification step. After 10% dry mixing with the water-absorbent resin, the average value and standard deviation of the physical property values for each lot were determined. The results are shown in Table 1.
Example 3
In Comparative Example 2, when the particle size distribution of the water-absorbing resin in which the particle size of the water-absorbing resin falls freely from the line before the final storage step is continuously dry measured with an infrared semiconductor laser (wavelength 690 nm), the amount of fine powder exceeds 2% by mass The second line was automatically separated into two parts. The water-absorbing resin thus separated was dry-mixed with the water-absorbing resin after surface crosslinking and before the second classification step, and the average value and standard deviation of the physical property values for each lot were determined. The results are shown in Table 1.

Example 4
In the lot of the water-absorbent resin obtained in Comparative Example 2, only the lower 1% of liquid permeability under pressure was separated in a batch system, and the lower 1% of the separated water-absorbent resin was subjected to the second classification after surface crosslinking. After 1% dry mixing with the water-absorbent resin before the process, the average value and standard deviation of the physical property values for each lot were determined. The results are shown in Table 1.
[Comparative Example 3]
In Production Example 3, the above steps were performed continuously for 24 weeks with a 24-hour operation, and the physical properties of the water-absorbent resin were measured every 1 ton (about 3.3 hours), and the average value and standard deviation of the physical property values for each lot. (Number of analysis points n: about 100). The results are shown in Table 1.

Example 5
In the lot of the water-absorbent resin obtained in Comparative Example 3, only the lower 1% of liquid permeability under pressure was separated in a batch system, and the separated lower 1% water-absorbent resin was subjected to the second classification after surface crosslinking. After 1% dry mixing with the water-absorbent resin before the process, the average value and standard deviation of the physical property values for each lot were determined. The results are shown in Table 1.
Example 6
In the Lot of the water absorbent resin obtained in Comparative Example 3, only the lower 2% of the CRC value was separated in a batch system, and the separated lower 2% of the water absorbent resin was subjected to surface crosslinking and before the second classification step. After 1% dry mixing with the water-absorbent resin, the average value and standard deviation of the physical property values for each lot were determined. The results are shown in Table 1.

  The results of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1, and the standard deviation (s) of various physical properties is very small in the method of the present invention. Even if productivity (cost) is not sacrificed for physical property control as in the prior art, the present invention can stabilize the physical property even in continuous production and multi-product production on a huge scale. Further, according to the present invention, productivity may be improved. Moreover, the water absorption characteristic of the sanitary material (absorbent articles such as diapers) using the water absorbent resin product obtained in the present invention can be very stabilized.

  According to the present invention, it is possible to easily produce a water-absorbing resin product having excellent physical properties with no variation in quality during continuous production, and the water-absorbing resin product obtained by the present invention is an agricultural and horticultural water retaining agent. It is widely used in industrial water-retaining agents, hygroscopic agents, dehumidifying agents, building materials, etc., and particularly preferably used as sanitary materials for absorbing feces, urine or blood, represented by paper diapers, sanitary napkins and the like.

The flowchart which shows an example of embodiment of the manufacturing method of this invention.

Claims (10)

The water-absorbent resin continuously produced through the polymerization step, the drying step, the classification step, the surface modification step, and the second classification step after the surface modification step , has predetermined physical properties and / or after the second classification step. Or step (A) of measuring a predetermined component amount;
In accordance with the measurement result, a step of separating a predetermined amount of the water absorbent resin (a) having a predetermined physical property and / or a predetermined component amount of a certain value and / or a certain value from a continuously produced water absorbent resin ( B) and
Wherein at least a portion of the separated predetermined amount of water-absorbent resin (a), in the same manufacturing line or another production line, the second classification coming is produced continuous manner through the surface modification step Including the step (C) of mixing with the water-absorbent resin before the step ,
Continuous production method for water-absorbent resin products. The continuous production method of a water absorbent resin product according to claim 1, wherein the mixing in the step (C) is dry mixing. The mixing in the step (C) is a water-absorbing resin according to claim 1 or 2 , wherein the water-absorbing resin (a) separated in the step (B) is mixed as it is without being modified. A continuous production method for products. The continuous production of the water absorbent resin product according to any one of claims 1 to 3 , wherein the mixed amount in the step (C) is an amount that is 10% by mass or less of the continuously produced water absorbent resin. Method. The water absorption property according to any one of claims 1 to 4 , wherein the predetermined physical property and / or the amount of the predetermined component is at least one selected from absorption capacity under no pressure, absorption capacity under pressure, liquid permeability, and particle size. Continuous production method of resin products. The continuous production method of a water absorbent resin product according to claim 5 , wherein the particle size is measured by a laser diffraction scattering method. The method for continuously producing a water absorbent resin product according to any one of claims 1 to 6 , wherein the amount of the water absorbent resin (a) separated in the step (B) is 30 to 0.0001 mass%. The continuous production method of a water absorbent resin product according to any one of claims 1 to 7 , wherein the water absorbent resin obtained as a final product contains 95 to 100% by mass of a water absorbent resin powder having a particle diameter of 850 to 150 µm. The continuous production method of a water-absorbent resin product according to any one of claims 1 to 8 , wherein the polymerization in the polymerization step is aqueous solution polymerization using a monomer as an aqueous solution. The surface modification in the surface modification step includes (i) surface crosslinking with a surface crosslinking agent, (ii) surface coating with water-insoluble fine particles, (iii) surface coating with a surfactant, and (iv) hydrophilicity or hydrophobicity. 1 or 2 or more types selected from (v) surface coating with an antibacterial agent or deodorant, (vi) surface coating with a hydrophilic or hydrophobic organic compound A method for continuously producing a water absorbent resin product according to any one of claims 1 to 9 .

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