JP5843466B2 - Absorbent resin particles and method for producing the same - Google Patents

Description

  The present invention relates to an absorbent resin particle containing a surfactant.

  The absorber used for paper diapers or the like is usually a combination of a laminate of cotton-like pulp and absorbent resin particles, a nonwoven fabric, and the like. However, in recent years, due to demands for comfort in use, ease of portability, etc., the amount of cotton-like pulp used has been reduced to make the absorbent body thinner and lighter. However, since this impairs the flexibility of the absorber at the same time, studies have been made on improving flexibility by improving the material and structure of the absorber.

  Conventionally, for improving the flexibility of an absorbent body including absorbent resin particles, a cushion layer made of a fiber layer laminate in which high-density fiber layers and low-density fiber layers are alternately laminated in an absorbent layer ( Patent Document 1) and a surface sheet have been proposed that use a nonwoven fabric in which ridges and grooves extending in one direction are alternately arranged and the amount of fibers in the buttock is substantially increased (Patent Document 2).

JP 2008-229033 A JP 2010-106430 A

  However, the conventional method has a drawback of high cost due to changes in materials and processes. Then, an object of this invention is to provide the absorbent resin particle which improves the softness | flexibility of an absorber, without changing the raw material and structure of a surface sheet or an absorption layer.

  The inventor of the present invention has arrived at the present invention as a result of studies to achieve the above object. That is, the present invention provides a crosslinked polymer (A) comprising water-soluble vinyl monomer (a1) and / or hydrolyzable vinyl monomer (a2), internal crosslinking agent (a3) and surface crosslinking agent (a4) as essential constituent units. And a nonionic surfactant (B) which is a polyoxyethylene polyoxypropylene block copolymer, and (B) is present on the surface of the absorbent resin particles. In the absorbent resin particles, the amount of (B) present on the surface is 0.01 to 1% by weight based on the weight of (A).

  The absorptive resin particle of this invention has an effect which improves the softness | flexibility of the absorber containing this.

  The absorbent resin particles of the present invention are absorbent resin particles comprising a crosslinked polymer (A) and a nonionic surfactant (B). The crosslinked polymer (A) comprises a water-soluble vinyl monomer (a1) and / or a hydrolyzable vinyl monomer (a2), an internal crosslinking agent (a3) and a surface crosslinking agent (a4) as essential constituent units.

<Crosslinked polymer (A)>
The water-soluble vinyl monomer (a1) means a vinyl monomer having a property (solubility) of dissolving at least 100 g in 100 g of water at 25 ° C.
The solubility is measured by the method described in “Revised 3rd edition, Chemical Handbook, Basic Edition II (pages II-166 to II-175)”.
The hydrolyzable vinyl monomer (a2) means a vinyl monomer that becomes a water-soluble vinyl monomer (a1) by hydrolysis.

Although there is no limitation in particular as a water-soluble vinyl monomer (a1) and / or a hydrolysable vinyl monomer (a2), For example, the water-soluble radical polymerization monomer as described in Unexamined-Japanese-Patent No. 2005-075982 is mentioned. Among these, from the viewpoint of absorption performance {absorption rate, diffusion area, surface dryness, SDME dryness, etc.}, the water-soluble vinyl monomer (a1) is preferable, more preferably an anionic vinyl monomer, and particularly preferably 3 carbon atoms. -30 vinyl group-containing carboxylic acid (salt) {unsaturated monocarboxylic acid (salt) ((meth) acrylic acid, crotonic acid, cinnamic acid and salts thereof); unsaturated dicarboxylic acid (salt) (maleic acid, Fumaric acid, citraconic acid, itaconic acid and their salts, etc.); and monoalkyl (carbon number 1 to 8) ester of unsaturated dicarboxylic acid (monobutyl maleate, monobutyl ester of fumaric acid, ethyl carbitol of maleic acid) Monoester, ethyl carbitol monoester of fumaric acid, citraconic acid monobutyl ester and itaconic acid Recall monoesters}, then preferably the unsaturated monocarboxylic acid (salt), most preferably acrylic acid (salt).

  Each of the water-soluble vinyl monomer (a1) and / or the hydrolyzable vinyl monomer (a2) may be a single structural unit or two or more structural units. Of the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), the water-soluble vinyl monomer (a1) is preferable from the viewpoint of absorption performance and the like, and more preferably (a1) is used alone as a structural unit. It is.

  When both the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as constituent units, the molar ratio {(a1) / (a2)} of these vinyl monomer units is 75/25 to 99 / 1, more preferably 85/15 to 95/5, particularly preferably 90/10 to 93/7, and most preferably 91/9 to 92/8. Within this range, the absorption performance is further improved.

The crosslinked polymer (A) can further comprise other vinyl monomers copolymerizable with the water-soluble vinyl monomer (a1) and / or the hydrolyzable vinyl monomer. Is preferably not included.
The other vinyl monomer is not limited as long as it is a monomer that can be copolymerized with the water-soluble vinyl monomer (a1) and the like, and examples thereof include a vinyl monomer described in JP-A-2003-225565.
When other vinyl monomer is used as the constituent unit, the content (mol%) of the other vinyl monomer unit is selected from the water-soluble vinyl monomer (a1) unit and hydrolyzable vinyl monomer (a2) unit from the viewpoint of absorption performance. Based on the total number of moles, 0.01 to 30 is preferable, 0.05 to 20 is more preferable, and 0.1 to 15 is particularly preferable.

  As the internal crosslinking agent (a3), a known internal crosslinking agent, for example, an internal crosslinking agent described in JP-A-2003-225565 can be used. Of these internal cross-linking agents, an internal cross-linking agent having two or more ethylenically unsaturated groups is preferable from the viewpoint of absorption performance, and more preferably triallyl cyanurate, triallyl isocyanurate, and those having 2 to 10 carbon atoms. Poly (meth) allyl ethers of polyols, particularly preferably triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane and pentaerythritol triallyl ether, most preferably pentaerythritol triallyl ether.

  The content (mol%) of the internal crosslinking agent (a3) is preferably 0.001 to 5, more preferably, based on the number of moles of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit. Is 0.005 to 3, particularly preferably 0.01 to 1. Within this range, the absorption characteristics are further improved.

  As the surface crosslinking agent (a4), a known surface crosslinking agent, for example, a surface crosslinking agent described in JP-A-2003-225565 can be used. Among these surface cross-linking agents, from the viewpoint of water absorption performance and the like, the water-soluble substituent {carboxy group, hydroxyl group, etc.} of the water-soluble vinyl monomer (a1) unit and / or the hydrolysis of the hydrolyzable vinyl monomer (a2) unit. Is preferably a cross-linking agent having at least two functional groups capable of reacting with water-soluble substituents {carboxy group, hydroxyl group, etc.} generated by the above, more preferably polyvalent glycidyl, particularly preferably ethylene glycol diglycidyl ether and glycerin diglycidyl. Ether, most preferably ethylene glycol diglycidyl ether.

  The content (% by weight) of the surface cross-linking agent (a4) is based on the number of moles of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit, from the viewpoint of discomfort to the human body. 0.01-0.1 is preferable, More preferably, it is 0.03-0.08, Most preferably, it is 0.05-0.06.

  The crosslinked polymer (A) is prepared in the same manner as in known methods {Japanese Patent Laid-Open No. 2003-225565 and Japanese Patent Laid-Open No. 2005-075982 etc.} and a water-soluble vinyl monomer (a1) and / or a hydrolyzable vinyl monomer ( a2) and the internal cross-linking agent (a3) are polymerized to prepare a hydrogel, and if necessary, the hydrogel is chopped and then dried to prepare dry particles. The dry particles and the surface cross-linking agent (a4) Can be obtained by reacting.

  As the method of the surface crosslinking reaction, known methods (for example, Japanese Patent No. 3648553, Japanese Patent Application Laid-Open No. 2003-165883, Japanese Patent Application Laid-Open No. 2005-75982, Japanese Patent Application Laid-Open No. 2005-95759) can be applied.

<Nonionic surfactant (B)>
The nonionic surfactant (B) means a surfactant having a hydroxyl group or an ether bond that is not ionically dissociated in water as a hydrophilic group.
The nonionic surfactant (B) is a polyoxyethylene polyoxypropylene block copolymer, and propylene oxide (hereinafter abbreviated as PO) ethylene oxide (hereinafter abbreviated as EO) is added as PO, EO to the active hydrogen compound. These are compounds added in block order.
The polyoxyethylene polyoxypropylene block copolymer which is a high molecular weight type as the nonionic surfactant (B) has high safety in use and little influence on the absorption performance after addition.

  The amount of the nonionic surfactant (B) present on the surface of the absorbent resin particles is 0 based on the weight of the crosslinked polymer (A) from the viewpoint of the softening effect by the surfactant and the absorption performance after the addition. 0.01 to 1, preferably 0.03 to 0.5, and more preferably 0.05 to 0.2.

The amount of the nonionic surfactant (B) present on the surface of the absorbent resin particles is the amount of (B) recovered from the surface of the absorbent resin particles by the following method.
<Method for measuring the amount of nonionic surfactant (B) present on the surface>
Add the absorbent resin particles in an organic solvent in which the nonionic surfactant (B) is soluble, stir, extract (B) from the surface of the absorbent resin particles, separate this, and evaporate the organic solvent. The evaporation residue is the amount of (B).

  The ratio of EO to PO (number of moles of EO / number of moles of PO) of the nonionic surfactant (B) is preferably 0.1 to 10, more preferably 1 to 10, from the viewpoint of the softening effect of the surfactant. 10, particularly preferably 5-10.

The number average molecular weight of the nonionic surfactant (B) is preferably 2,000 to 30,000, more preferably 10,000 to 30,000, and particularly preferably 20, from the viewpoint of the softening effect due to the surfactant. 000-30,000.
The number average molecular weight is measured by gel permeation chromatography (GPC).

  The absorbent resin particles of the present invention can be obtained by mixing the absorbent resin particles (C) comprising the crosslinked polymer (A) and the nonionic surfactant (B). As a step of mixing (C) and (B), from the viewpoint of allowing (B) to be present on the surface of (C), immediately before the surface cross-linking step, during the surface cross-linking step, and immediately after the surface cross-linking step is more preferable. Is immediately after the surface crosslinking step.

  The water content (% by weight) of (C) when mixing the absorbent resin particles (C) and the nonionic surfactant (B) is (C) from the viewpoint of the breakability and absorption performance of (C). ) Based on the weight of 1), preferably 1 to 10, more preferably 2 to 8, particularly preferably 3 to 6.

  Although it does not specifically limit as temperature (degreeC) which mixes an absorbent resin particle (C) and a nonionic surfactant (B), From a viewpoint of deterioration prevention of the crosslinked polymer (A) contained in (C), 10-150 are preferable, More preferably, it is 15-140, Most preferably, it is 20-130.

  When it is desired to mix the nonionic surfactant (B) as a liquid, it can be used as a liquid by dissolving (B) in water or by heating (B) to a melting point or higher of the solid.

When mixing the nonionic surfactant (B) as a liquid, after spraying the liquid onto the absorbent resin particles (C) or bringing the solid (B) into contact with (C), the (B) It is also possible to mix by heating above the melting point.
Examples of the mixing device applicable to spraying or contact include a turbulizer and a double-armed bench kneader.

In the absorbent resin particles of the present invention, if necessary, any stage {among the production process of the crosslinked polymer (A), a polymerization process, a shredding process, a drying process, a pulverizing process, a surface crosslinking process and / or a process Before and after and after the step of mixing (A) and (B), etc.}, additives can be added.
As additives, known additives (for example, Japanese Patent Application Laid-Open No. 2003-225565) {preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet absorbers, colorants, fragrances, deodorants, and organic fibers Etc.}, etc., and one or more of these may be used in combination.

By applying the absorbent resin particles of the present invention to various absorbers, an absorbent article excellent in the flexibility of the absorber can be produced. The absorber and the absorbent article are manufactured by a known method (for example, Japanese Patent Application Laid-Open No. 2005-186016).
Absorbent articles include sanitary products {paper diapers (children's disposable diapers and adult disposable diapers, etc.), napkins (sanitary napkins, etc.), vomiting absorption etiquette bags, paper towels, pads (incontinence pads and surgical underpads) Etc.) and pet sheets (pet urine absorption sheets, heat insulation sheets, etc.)} and various household and industrial absorption sheets {freshness maintenance sheets, drip absorption sheets, paddy rice seedling sheets, concrete curing sheets and cables, etc. Running prevention sheet, etc.}.
Among these, the absorbent resin particles of the present invention are suitable for sanitary goods from the viewpoint of the flexibility of the absorbent body, and further suitable for paper diapers, pads and sanitary napkins, especially paper diapers and sanitary napkins.

  Hereinafter, although an example and a comparative example explain the present invention further, the present invention is not limited to these. Hereinafter, unless otherwise specified, “%” represents “% by weight” and “parts” represents “parts by weight”.

Example 1
Water-soluble vinyl monomer (a1-1) {acrylic acid, manufactured by Mitsubishi Chemical Corporation} 135 parts (1.87 mole parts), internal cross-linking agent (a3-1) {pentaerythritol triallyl ether, manufactured by Daiso Corporation} While stirring and mixing 0.37 parts (0.0014 mol parts) and 352.28 parts deionized water, the temperature was maintained at 3 ° C. Nitrogen was introduced into the mixed solution so that the amount of dissolved oxygen in the mixed solution was 1 ppm or less, and then 0.54 parts of 1% aqueous hydrogen peroxide solution, 1.0125 parts of 2% aqueous ascorbic acid solution, and 2% of 2% , 2′-azobis (2-methylpropionamidine) dihydrochloride aqueous solution 10.125 parts was added and mixed to initiate polymerization, and after the reaction temperature reached 90 ° C., the polymerization temperature was 90 ± 2 ° C. and about 5 Water-containing gel (1) was obtained by time polymerization.
The water-containing gel (1) was shredded to a size of 3 to 7 mm with a mincing machine (12VR-400K, Iizuka Kogyo Co., Ltd.) to obtain a shredded gel, and then 48% of the shredded gel was added to 400 parts. 89.1 parts of an aqueous sodium hydroxide solution was added to neutralize 72 equivalent% of the carboxyl groups to obtain a neutralized chopped gel. The neutralization degree of the neutralized chopped gel calculated from the acid value measured by JIS K0113-1997 {0.1 N potassium hydroxide aqueous solution as titrant, potentiometric titration method, inflection point method} Was 70.1 equivalent%.
Next, this neutralized chopped gel is applied to a stainless steel tray with a height of 20 cm, a width of 20 cm, a height of 10 cm, a top plate, and a mesh with a mesh opening of 4 mm. It laminated | stacked and dried with the ventilation type | mold band dryer (made by Inoue Metal Industry) on 150 degreeC and the wind speed of 2.0 m / s, and the dry polymer (2) was obtained.
The dried polymer (2) was pulverized with a juicer mixer (MX-X53, manufactured by Matsushita Electric Industrial Co., Ltd.) and adjusted to a particle size range of 150 to 710 μm using a sieve having openings of 150 and 710 μm. 2% water / methanol mixture of surface cross-linking agent (a4-1) {ethylene glycol diglycidyl ether, manufactured by Nagase ChemteX Corporation} while stirring at 2000 rpm with a high-speed stirring turbulizer mixer (manufactured by Hosokawa Micron Corporation) Absorbent resin particles (C-) were added and mixed with 3.5 parts of a solution (weight ratio of water / methanol = 60/40) by spraying, left standing at 140 ° C. for 30 minutes, and subjected to heat crosslinking (surface crosslinking). 1) was obtained. When the moisture content of (C-1) was measured with a heat drying moisture meter (MS-70, manufactured by A & D Co., Ltd.), it was 3.5% based on the weight of (C-1). .
Nonionic surfactant (B-1) which is a polyoxyethylene polyoxypropylene block copolymer (B-1) {number average molecular weight 25,000 (EO455 mol-PO86 mol adduct)), product By adding 0.2 parts of name New Pole PE-128 (manufactured by Sanyo Chemical Industries Co., Ltd.)} and mixing at 130 ° C. for 20 minutes with a double-arm bench kneader (PNV-1, manufactured by Irie Shokai Co., Ltd.) The absorbent resin particles (D-1) of the present invention were obtained.

Example 2
In Example 1, the nonionic surfactant is changed from “(B-1)” to “Nonionic surfactant (B-2) {number average molecular weight 16,000 (EO 300 mol-PO 55 mol adduct), trade name New Except having changed to "Pole PE-108 (made by Sanyo Chemical Industries Ltd.)}", operation similar to Example 1 was performed and the absorbent resin particle (D-2) of this invention was obtained.

Example 3
In Example 1, the nonionic surfactant is changed from “(B-1)” to “nonionic surfactant (B-3) {number average molecular weight 9,400 (EO 150 mol-PO35 mol adduct), trade name New Except for changing to "Pole PE-78 (manufactured by Sanyo Chemical Industries, Ltd.)}", the same operation as in Example 1 was performed to obtain absorbent resin particles (D-3) of the present invention.

Example 4
In Example 1, the nonionic surfactant is changed from “(B-1)” to “nonionic surfactant (B-4) {number average molecular weight 3,100 (EO 30 mol-PO35 mol adduct), trade name New Except for changing to "Pole PE-74 (manufactured by Sanyo Chemical Industries, Ltd.)}", the same operation as in Example 1 was performed to obtain absorbent resin particles (D-4) of the present invention.

Example 5
In Example 1, the nonionic surfactant is changed from “(B-1)” to “nonionic surfactant (B-5) {number average molecular weight 2,200 (EO5 mol-PO35 mol adduct), trade name New Except for changing to "Pole PE-71 (manufactured by Sanyo Chemical Industries Co., Ltd.)}", the same operation as in Example 1 was performed to obtain absorbent resin particles (D-5) of the present invention.

Example 6
In Example 1, the same operation as in Example 1 was performed except that the addition amount of the nonionic surfactant (B-1) was changed from “0.2 part” to “0.3 part”. Absorbent resin particles (D-6) were obtained.

Example 7
In Example 1, the same operation as in Example 1 was performed except that the addition amount of the nonionic surfactant (B-1) was changed from “0.2 part” to “0.05 part”. Resin particles (D-7) were obtained.

Example 8
In Example 1, “adding 0.2 part of nonionic surfactant (B-1)” was changed to “spray spraying 4 parts of 5% aqueous solution of nonionic surfactant (B-1)”, “ The same operation as in Example 1 except that “mixing at 130 ° C. for 20 minutes in a double-arm bench kneader” is changed to “heating at 80 ° C. for 30 minutes in a safety oven (SPHH-201, manufactured by Espec Corp.)”. The absorbent resin particles (D-8) of the present invention were obtained.

Comparative Example 1
In Example 1, the same operation as Example 1 was performed except not having added nonionic surfactant (B-1), and the comparative absorbent resin particle (D-9) was obtained.

  Using the absorbent resin particles (D-1) to (D-8) of the present invention prepared in Examples 1 to 8 and the comparative absorbent resin particles (D-9) prepared in Comparative Example 1, The absorber was prepared by the method shown in Fig. 5 and its flexibility was measured and evaluated. The results are shown in Table 1.

<Preparation of absorber>
On the pulp layer (weight per unit area 213 g / cm ² ) cut to 8 cm × 12.5 cm, 0.71 part of the absorbent resin particles (weight per unit area 213 g / cm 2) was evenly dispersed. Furthermore, in the order of pulp and absorbent resin particles, 4 layers of pulp layers and 3 layers of water-absorbent resin particles are finally laminated, and this is pressed by a roll press machine (CR-200, manufactured by Toyo Design Co., Ltd.). The absorber was prepared by pressing under conditions of a speed of 20 m / min and a clearance of 1 mm.

<Measurement of absorber flexibility>
Using an automated compression tester (KFSFB3-AUTO-A, manufactured by Kato Tech Co., Ltd.), the absorber is compressed under the conditions of a compression deformation rate of 0.05 mm / sec and a compression maximum load condition of 50 gf / cm ² . The compression energy was measured. The softer the material, the easier it is to compress and the higher the compression energy value.

  From the results in Table 1, it can be seen that the absorbent resin particles of the present invention are superior in absorber softness during the preparation of the absorber as compared with the comparative example. And from this result, the absorbent article (paper diaper etc.) using the absorbent resin particles of the present invention has a feeling of use in a state that the user wears it without changing the material and structure of the surface sheet and the absorbent layer. It can be seen that is improved.

  The absorbent resin particles of the present invention can be applied to an absorbent body containing absorbent resin particles and fibrous materials, and since this absorbent body is excellent in flexibility, the absorbent body provided with this absorbent body. Useful for articles {paper diapers, sanitary napkins, etc.}.

Claims (1)

Absorbency comprising a cross-linked polymer (A) comprising water-soluble vinyl monomer (a1) and / or hydrolyzable vinyl monomer (a2), internal cross-linking agent (a3) and surface cross-linking agent (a4) as essential constituent units. Resin particles (C) and a nonionic surfactant (B) which is a polyoxyethylene polyoxypropylene block copolymer, the water content of (C) is 1 to 10 weights based on the weight of (C) %, And the amount of (B) used is 0.01 to 1% by weight based on the weight of (A).