JP2890022B2 - Water-absorbing resin particles and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to modified water-absorbent resin particles and a method for producing the same. More specifically, the present invention relates to a water-absorbent resin particle having an improved absorption rate (particularly, an initial absorption amount under pressure), an absorption capacity under pressure, and resistance to moisture absorption blocking, and a method for producing the same.

[0002]

Conventionally, water-absorbing resins have been widely used for sanitary products, sanitary materials such as disposable diapers, soil water retention agents, and the like. However, although conventional water-absorbent resins have high absorption capacity, they are not sufficiently satisfactory for use in applications such as disposable diapers and sanitary products that require a high absorption rate. It is generally used in combination with a fibrous material such as pulp having a high speed. In other words, the higher the absorption capacity of the water-absorbing resin, the stronger the affinity with water as it increases, so that when the resin particles come into contact with water, gelation occurs at the contact portion and uniform penetration of water into the inside of the particles is hindered. As a result, there has been a problem that the absorption rate is reduced. In order to improve this drawback, attempts have been made to increase the absorption rate by increasing the surface area by making the water-absorbent resin particles finer and increasing the contact area with water. The absorption rate is somewhat faster due to the increased surface area. However, since a film is formed on the surface of the resin particles in contact with water, and the particles adhere to each other and uniform water penetration is impaired, it is necessary to improve the essential absorption rate only by making the particles finer. Did not connect. In addition to the above problems, the conventional water-absorbent resin particles absorb the moisture and block the resin particles in the process of storing the resin under high humidity or supplying the resin to a manufacturing machine such as a disposable diaper because of its high absorbency. Therefore, there are problems such as that the resin adheres to the machine, and the moisture absorption blocking makes it impossible to discharge the resin from the hopper or to continuously supply the resin to the machine.
As a method of improving the moisture absorption blocking property, the following methods have been proposed. A method in which fine powdered hydrophobic silica having an average particle diameter of 0.05 μm or less and a specific surface area of 50 m ² / g or more is mixed with the water-absorbent resin particles (JP-A-56-133028).
No.). A method in which inorganic powders such as hydrous silicon dioxide, hydrous aluminum hydroxide, and hydrous titanium oxide are added to the water-absorbent resin particles (JP-A-59-80459). Mix stearic acid and inorganic powder with water-absorbent resin particles,
A method of coating the surface of a resin with stearic acid (JP-A-63
-105064). However, in the above method, although the moisture absorption blocking property can be improved by the addition of the hydrophobic silica, the surface of the resin particles is covered with the hydrophobic silica, so that the absorption rate (the initial absorption amount under pressure, etc.) and the absorption under pressure are increased. There are problems such as a reduction in magnification and generation of a large amount of dust due to the mixing of finely divided silica. In the above method, when the inorganic powder is not hydrophobic, the absorption rate (initial absorption amount under pressure, etc.) and the absorption capacity under pressure do not decrease much, but the improvement in the moisture absorption blocking resistance is insufficient. In addition, since the inorganic powder is in the form of fine powder, there is a problem that a large amount of dust is generated as in the above case. In the above method, since the surface of the resin particles is covered with a hydrophobic high-melting organic compound or stearic acid, it is possible to improve the moisture absorption blocking resistance to some extent, but it is not sufficient, and the high-melting organic compound or stearic acid is not used. However, there is a problem that the absorption rate (initial absorption amount under pressure, etc.) and the absorption capacity under pressure are reduced because the absorption of water-absorbent resin particles is impaired. As described above, in many cases, the moisture-absorbing blocking imparting agent is often hydrophobic, and the absorption rate (initial absorption under pressure, etc.) and the absorption capacity under pressure are reduced, so that the moisture-absorbing blocking ability and absorption are reduced. It was difficult to balance the speed and the absorption capacity under pressure.

[0003]

Means for Solving the Problems The present inventors have sought to improve these problems, that is, the absorption resistance (particularly the initial absorption amount under pressure) and the anti-moisture blocking property while maintaining the absorption capacity under pressure. As a result of intensive studies aimed at obtaining good water-absorbent resin particles, it was possible to obtain water-absorbent resin particles having improved absorption rate and absorption capacity under pressure and good moisture-absorption blocking properties. .

That is, the present invention relates to modified water-absorbent resin particles obtained by treating particles of a water-absorbent resin (A) with a silicone-based surfactant (B), wherein HLB of (B) is 7 to 18; (B) a viscosity at 25 ° C. of 10 to 2,000 centistokes (cst); and (B) an amount of 0.001 to 3% by weight based on the amount of (A).
Water-absorbent resin particles; and a water-absorbent resin (A) particle comprising a silicone-based surfactant (B).
Wherein the HLB of (B) is 7 to 18, the viscosity at 25 ° C. of (B) is 10 to 2,000 centistokes (cst), The amount of (B) is 0.001 to 3% by weight based on the amount of (A).
A method for producing modified water-absorbent resin particles, characterized in that:

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a water absorbent resin (A)
Is a water-swellable crosslinked polymer capable of absorbing pure water 50 to 1000 times its own weight. Examples of the water-absorbing resin that can be suitably used in the present invention include JP-B-53-46199 and JP-B-53-46200.
Of starch-acrylic acid (salt) graft copolymer described in Japanese Patent Application Laid-Open No. 55-133413, etc., and crosslinking obtained by aqueous solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization, etc.) described in JP-A-55-133413 Polyacrylic acid (salt), JP-B-54-30710, JP-A-56-26909
JP-A-52-14689, JP-A-52-27455, crosslinked or self-crosslinked polyacrylic acid (salt) described in Japanese Patent Application Laid-Open Publication No.
And saponified copolymers of a vinyl ester and an unsaturated carboxylic acid or a derivative thereof described in JP-A-58-231, and acrylic acid (salt) described in JP-A-58-2312 and JP-A-61-36309. Sulfonic acid (salt)
Examples thereof include a water-absorbent resin obtained by copolymerizing a group-containing monomer, a crosslinked product of an isobutylene-maleic anhydride copolymer, a hydrolyzate of a starch-acrylonitrile copolymer, and a crosslinked carboxymethylcellulose derivative. Two or more of the above water-absorbing resins may be used in combination. Among these, preferred are water-absorbing resins containing a polymerizable unsaturated carboxylic acid and / or a water-soluble salt thereof (Na salt, K salt, etc.) as a main constituent unit. Particularly preferred are:
A crosslinked product of a starch-acrylic acid (salt) graft copolymer, a crosslinked polyacrylic acid (salt) obtained by aqueous solution polymerization, and reverse-phase suspension polymerization, in that a water-absorbing resin having high absorption performance can be produced at low cost. Is a cross-linked or self-cross-linked polyacrylic acid (salt) obtained in (1).

Further, when the water-absorbent resin (A) is a water-absorbent resin having a polymerizable unsaturated carboxylic acid and / or a water-soluble salt thereof as a main constituent unit, the vicinity of the surface of the above-mentioned water-absorbent resin particles is a carboxylic acid. Surface-crosslinked type water-absorbent resin particles having a structure crosslinked with a crosslinking agent having at least two functional groups capable of reacting with a group and / or a water-soluble base thereof have a further improved absorption rate and a higher gel strength. So
It can be suitably used in the present invention. Examples of the crosslinking agent used for surface crosslinking include polyglycidyl ether compounds (ethylene glycol diglycidyl ether, glycerin-1,3-diglycidyl ether, glycerin triglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc.). Polyamine compounds (e.g., ethylenediamine, diethylenetriamine); polyamine resins (e.g., polyamide polyamine epichlorohydrin resin, polyamine epichlorohydrin resin); polyol compounds (glycerin, ethylene glycol, polyethylene glycol, etc.); Among these, preferred crosslinking agents form a strong covalent bond with a carboxylic acid (salt) group to obtain a water-absorbent resin excellent in both absorption rate and gel strength,
The polyglycidyl ether compound and the polyamine resin are economical in that the crosslinking reaction can be carried out at a relatively low temperature and are economical.

The amount of the cross-linking agent in the surface cross-linking treatment is not particularly limited since it can be variously changed depending on the type of the cross-linking agent, cross-linking conditions, target performance, and the like. 001 to 3% by weight, preferably 0.01 to 2% by weight, more preferably 0.05 to 1% by weight. When the amount of the crosslinking agent is less than 0.001% by weight, there is no great difference in performance from the water-absorbing resin which is not subjected to the crosslinking treatment. On the other hand, if it exceeds 3% by weight, the gel after water absorption becomes too hard, becomes brittle, and the absorption performance is undesirably reduced. This surface cross-linking may be performed at any stage before (A) is treated with the silicone surfactant (B), simultaneously with (B) or after treatment with (B). Although good, it is preferable that the surface of the water-absorbent resin (A) is treated with the silicone-based surfactant (B) in that the surface of the water-absorbent resin (A) can be efficiently treated with the silicone-based surfactant (B). ) Is a stage before being processed.

The shape of the particles of the water-absorbent resin (A) is not particularly limited as long as it is in the form of powder, and may be any of granular, granular, granulated, scaly, massive, pearl, fine powder and the like. The shape may be as follows. The particle size distribution of the particles of the water-absorbent resin (A) is not particularly limited, and is usually from 1 to 1,000.
The content of micron, preferably 50-850 micron, particles is 95% by weight or more.

The water-absorbent resin (A) particles have an absorbency against normal saline (0.9% sodium chloride aqueous solution) under normal pressure of 30 times or more of its own weight, preferably 35 to 80 times.
And more preferably 40-70 times. The absorbency against physiological saline under pressure is 20 times or more of its own weight, preferably 25 to 60 times.

As the silicone surfactant (B) in the present invention, polyethylene oxide-modified silicone, polyethylene oxide / polypropylene oxide-modified silicone and the like can be mentioned, and among them, polyethylene oxide-modified silicone is preferable. Further, a form in which (B) is dissolved in water or a volatile solvent or emulsified in water can be suitably used in the present invention.

The HLB of the silicone surfactant (B) is usually from 7 to 18, preferably from 10 to 18. If the HLB is more than 18, the hydrophilicity is too high and the effect of improving the moisture absorption blocking resistance is poor, and in order to achieve the improvement, a large amount of (B) must be added, which is not economical. On the other hand, when the HLB is less than 7, the water repellency of (B) becomes strong, resulting in impeding water absorption. Therefore, when the HLB is 7 to 18, the initial absorption under pressure and the absorption capacity under pressure are improved, and water-absorbent resin particles having good moisture absorption blocking performance can be obtained.

The viscosity of (B) at 25 ° C. is usually 10
~ 2,000 centistokes (cst). Preferably, there is no need to dilute with water or solvents, and (A)
20 to 1,000 cst from the viewpoint that mixing with C is easy. Those having a viscosity of more than 2,000 cst must be diluted with water or a low-viscosity solvent (eg, methyl ethyl ketone, cellosolves, lauryl alcohol, etc.) before use, and a step of removing the solvent from the water-absorbent resin particles is required. Not as economical. Further, there is a problem that the powder fluidity deteriorates. On the other hand, 10 centistokes (cst)
If it is less than (B), the water-absorbent resin (A) easily penetrates into the inside of the particles, and the desired effect is poor.

The amount of (B) used relative to the particles of (A) is usually from 0.001 to 3% by weight, preferably from 0.005 to 2% by weight, particularly preferably from 0.01 to 1% by weight.
When the amount of (B) used is less than 0.001% by weight, there is no great difference from the water-absorbent resin particles not treated with (B). On the other hand, if it exceeds 3% by weight, another problem such as deterioration of powder fluidity occurs.

In the present invention, the stage of treating the particles of (A) with (B) includes a stage during pulverization and a stage before the product is obtained after pulverization. Preferably, it is a stage after pulverization and before reaching a product. After the pulverization and before reaching the product, the particles of the water-absorbent resin (A) are converted into a silicone-based surfactant (B).
Industrial equipment for treating with a conical blender, Nauter mixer, double-arm kneader, V-type mixer,
Examples include a mechanical mixing device such as a fluidized bed mixer, a turbulizer, a screw type line blender, a ribbon mixer, and a mortar mixer. As a specific method of processing with these mixing apparatuses, a master batch is prepared by adding and mixing (B) in a high concentration (for example, 5 to 20% by weight based on the particles of (A)) with (A) in advance. A method in which the masterbatch is added to (A) and mixed so as to have a predetermined addition amount as (B), and (B) is added or sprayed while stirring (A) in the mixing apparatus described above. And the like. Alternatively, (B) may be dissolved in water or a volatile solvent or emulsified in water and then added to (A). The viscosity of (B) is 1,000 to 2,000.
In the case of relatively high 0 cst, the particles of the water-absorbent resin (A) and / or the particles of the (A) are heated and then the particles of the (A) are changed to the (B)
, Uniform processing is achieved. In the case where the particles of (A) are particles of a water-absorbent resin whose surface has been cross-linked with a cross-linking agent, (B) may be added to the cross-linking agent solution used for the cross-linking treatment.

[0015] Fine powder (D) of inorganic silicon dioxide can be added to the modified water-absorbent resin particles of the present invention at any stage. By adding (D), the normal pressure absorption rate can be further improved. Also, improvement in powder fluidity can be expected. An example of (D) is a dry inorganic silica produced by hydrolyzing silicon tetrachloride in a flame in which oxygen and hydrogen are burned at a high temperature.
and silica having an alkyl group introduced by further reacting a silanol group on the surface of the inorganic silica with monomethyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, or the like. Specifically, the specific surface area is 50 to 500.
Silicon dioxide with a primary particle size of 5 to 50 nm at m ² / g. A preferred example of (D) is a so-called hydrophilic silicon dioxide having the above specific surface area and particle size and having a hydrophilicity of 70% or more. Here, the degree of hydrophilicity refers to water /
The ratio of silicon dioxide suspended colloidally in a mixture of methanol = 70/30. The smaller the value, the stronger the hydrophobicity. When the hydrophobicity increases, the initial absorption rate of the water-absorbent resin particles under pressure and the absorption capacity under pressure decrease.

The amount of (D) is usually from 0.001 to 2% by weight, preferably from 0.01 to 1% by weight, based on the amount of (A).
It is. When the amount of (D) is less than 0.001% by weight,
There is not much difference from the water-absorbent resin particles not containing (D). On the other hand 2
If the amount exceeds 10% by weight, the absorption capacity under pressure is significantly reduced.
Further, another problem such as dust generation due to the added (D) occurs.

The modified water-absorbent resin particles of the present invention to which (D) is added include, for example, a method in which (D) is added to and mixed with the particles of (A) in advance. (B) adding and mixing (D), (A) adding (D) while mixing particles (B), (A) treating particles (B) with (B) Later add (D)
Mixing method and the like can be mentioned. The preferred methods are and methods.

In the modified water-absorbent resin particles of the present invention, organic powders (for example, pulp powder, cellulose derivatives, natural polysaccharides, etc.), inorganic powders and the like may be added as extenders or additives within a range not to impair the effects of the present invention. Powders (zeolites, silica, alumina, bentonite, activated carbon, etc.), antioxidants, preservatives, bactericides, other surfactants, coloring agents, fragrances, and the like can be added as necessary. 10% by weight of the modified water-absorbent resin particles
% By weight or less.

[0019]

The present invention will be further described with reference to the following examples and comparative examples, but the present invention is not limited to these examples. The initial absorption amount of the water-absorbent resin and the water-absorbent resin particles under pressure, the absorption capacity under pressure, the moisture absorption blocking rate, and the degree of dust generation were measured by the following methods. Hereinafter, unless otherwise specified,% indicates% by weight.

Initial absorption amount under pressure and absorption capacity under pressure:
0.1 g of water-absorbent resin particles are uniformly placed in a cylindrical plastic tube (inner diameter 30 mm, height 60 mm) having a 250 mesh nylon net attached to the bottom surface, and a load of 20 g / cm ² is placed on the resin particles. A weight with an outer diameter of 30 mm is placed on the balance. A plastic tube containing water-absorbent resin particles is immersed in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline with the nylon mesh side facing down, and left. The weight of the water-absorbent resin particles increased by absorbing the physiological saline is measured after 10 minutes and 60 minutes. The 10-fold value of the increased weight after 10 minutes was defined as the initial absorption under pressure to physiological saline, and the 10-fold value of the increased amount after 60 minutes was defined as the absorption capacity under pressure to physiological saline. Moisture absorption blocking ratio: 10 g of water-absorbent resin particles having a particle size of 20 mesh or less are uniformly placed in an aluminum dish having a diameter of 5 cm, and left for 3 hours in a thermo-hygrostat at 40 ° C. and a relative humidity of 80%. The water-absorbent resin particles after standing were lightly sieved with a 12-mesh wire net, and blocked by moisture absorption. The weight of the resin particles having a size of 12 mesh or more was measured, and the moisture absorption blocking ratio was determined by the following formula. Moisture absorption blocking ratio (%) = (weight of resin particles of 12 mesh or more / total weight of resin particles after standing) × 100 Dust generation degree: suction port of a 1-liter suction bottle and inhalation of a digital dust meter (manufactured by Shibata Kagaku) The mouth is connected with a glass tube having an inner diameter of 7 mm and a length of 10 cm. 20 g of water-absorbent resin particles are dropped from the upper mouth of the suction bottle using a funnel into the suction bottle. The number of dust particles generated in one minute from the dropped water-absorbent resin particles was measured using a digital dust meter, and this value was defined as the degree of dust generation (unit: CPM).

Comparative Example 1 A 1-liter glass reactor was charged with 95 g of sodium acrylate, 27 g of acrylic acid, 0.3 g of N, N'-methylenebisacrylamide and 430 g of deionized water, and the contents were stirred and mixed. Was kept at 5 ° C. After flowing nitrogen into the contents to reduce the amount of dissolved oxygen to 1 ppm or less, 1 g of a 1% aqueous solution of hydrogen peroxide and 1 g of a 0.3% aqueous solution of ascorbic acid are added to initiate polymerization, and polymerization is performed for about 5 hours. Thereby, a hydrogel polymer was obtained. This hydrogel polymer was dried with hot air at 130 to 150 ° C. and pulverized to adjust the particle size to obtain water-absorbent resin particles of 105 to 850 μm. While stirring 100 g of the obtained water-absorbent resin particles at high speed, 1 g of a 10% aqueous solution of ethylene glycol diglycidyl ether is sprayed and heat-treated at about 140 ° C. for 30 minutes to crosslink the surface of the water-absorbent resin particles. I got This was used as a comparative water-absorbent resin (b
1). Incidentally, the particle size distribution of (b1) is almost the same as before the surface crosslinking. Table 1 shows the performance measurement results of the water absorbent resin (b1).

Example 1 100 g of the water-absorbent resin particles (b1) obtained in Comparative Example 1 was put into a V-type mixer, and polyethylene oxide-modified silicone oil [KF353A, Shin-Etsu Chemical Co., Ltd .:
HLB = 10.0, viscosity = 400 cst] was added and mixed well to obtain the modified water-absorbent resin particles (a1) of the present invention. Table 1 shows the performance evaluation of this product.

Example 2 100 g of the water-absorbent resin particles (b1) obtained in Comparative Example 1 were put into a V-type mixer, and polyethylene oxide-modified silicon oil [KF351A, Shin-Etsu Chemical Co., Ltd .:
0.02 g of HLB = 14.5, viscosity = 100 cst] was added and mixed well to obtain modified water-absorbent resin particles (a2) of the present invention. Table 1 shows the performance evaluation of this product.

Comparative Example 2 100 g of the water-absorbing resin particles (b1) obtained in Comparative Example 1 was put into a V-type mixer, and polyethylene oxide-modified silicone oil [KF945A, Shin-Etsu Chemical Co., Ltd .:
HLB = 4.5, viscosity = 150 cst] was added and mixed well to obtain comparative water-absorbent resin particles (b2). Table 1 shows the performance evaluation of this product.

Comparative Example 3 100 g of the water-absorbent resin particles (b1) obtained in Comparative Example 1 were put into a V-type mixer, and hydrophobic silica (Aerosil-972) was used.
0.5 g was added to obtain comparative water-absorbent resin particles (b3). Table 1 shows the performance evaluation of this product.

Comparative Example 4 100 g of the water-absorbent resin particles (b1) obtained in Comparative Example 1
Was added with 1 g of titanium oxide having a particle size of 30 microns to obtain comparative water-absorbent resin particles (b4). Table 1 shows the performance evaluation of this product.

Comparative Example 5 100 g of the water-absorbent resin particles (b1) obtained in Comparative Example 1
Then, 1 g of stearic acid was added, and the mixture was heated to 80 ° C. to melt the stearic acid and stirred at this temperature for 10 minutes. Next, 3 g of silicon dioxide was added thereto, mixed well, and cooled to room temperature to obtain comparative water-absorbent resin particles (b5). Table 1 shows the performance evaluation of this product.

[0028]

[Table 1]

As can be seen from Table 1, the water-absorbent resin particles of the present invention maintain the absorption capacity under pressure and exhibit good moisture-absorbing blocking resistance as compared with Comparative Example 1. In addition, the initial absorption under pressure is improved. In addition, less dust is generated.

[0030]

The water-absorbent resin particles of the present invention have the following effects. Conventionally, water-absorbent resin particles have been improved due to the problem of blocking between particles under high humidity due to their high water absorption, but without impairing their high absorption performance, improve the moisture absorption blocking resistance. There aren't too many effective methods. The present invention solves this. That is, the modified water-absorbent resin particles of the present invention have improved absorption speed (especially, initial absorption amount under pressure) essential for the water-absorbent resin, and have a moisture absorption blocking property while maintaining the absorption capacity under pressure. Is an improvement. Further, an effect of improving dust generation can be obtained.

Due to the above effects, the water-absorbent resin particles of the present invention can be used in sanitary diapers (child diapers and adult paper diapers), sanitary napkins, incontinence pads, breast milk pads, surgical underpads, pet sheets and the like. It can be used particularly suitably for articles and absorbent materials. In addition, powdery and granular materials such as cold insulators, desiccants, water retention agents for plants and soil, coagulants such as sludge, waterproofing materials and packing materials for civil engineering construction, waterproofing materials for electric cables and optical fiber cables, artificial snow, etc. It is useful for various applications utilizing a water-absorbing resin.

──────────────────────────────────────────────────続 き Continuing from the front page Examiner Ryuichi Ide (56) References JP-A-5-70625 (JP, A) JP-A-5-156034 (JP, A) (58) Fields studied (Int. Cl. ⁶⁾ , DB name) C08J 3/12 C08K 3/36 C08L 101/14 B01J 20/26

Claims (6)

(57) [Claims] 1. A modified water-absorbent resin particle obtained by treating a particle of a water-absorbent resin (A) with a silicone-based surfactant (B), wherein the HLB of (B) is 7 to 18. The viscosity of (B) at 25 ° C. is 10 to 2,000 centistokes (cst), and the amount of (B) is 0.001 to 3% by weight based on the amount of (A).
Water-absorbing resin particles, characterized in that: 2. The water-absorbent resin particles according to claim 1, wherein (B) is a polyethylene oxide-modified silicone. 3. The water-absorbent resin particles according to claim 1, wherein (A) is a water-absorbent resin having a polymerizable unsaturated carboxylic acid and / or a water-soluble salt thereof as a main constituent unit. 4. The method according to claim 1, wherein the particles of (A) are treated with (B), simultaneously with (B) or after (B), after which the carboxylic acid groups and / or The water-absorbent resin particles according to claim 3, wherein the cross-linking agent (C) having at least two functional groups capable of reacting with a water-soluble base further crosslinks the vicinity of the surface of the particles (A). 5. The water-absorbent resin particles according to claim 1, wherein 0.001 to 2% by weight of the fine powder of silicon dioxide (D) is added to (A). 6. A method for producing modified water-absorbent resin particles, wherein particles of the water-absorbent resin (A) are treated with a silicone-based surfactant (B), wherein the HLB of (B) is 7 to 18. The viscosity of (B) at 25 ° C. is 10 to 2,000 centistokes (cst), and the amount of (B) is 0.001 to 3% by weight based on the amount of (A).
A method for producing modified water-absorbent resin particles, characterized in that: