CN111995706B

CN111995706B - Absorbent resin particle, preparation method thereof and absorbent product

Info

Publication number: CN111995706B
Application number: CN202010801153.1A
Authority: CN
Inventors: 张建国; 肖晨
Original assignee: China Chemical Co ltd
Current assignee: China Chemical Co ltd
Priority date: 2020-08-11
Filing date: 2020-08-11
Publication date: 2022-06-21
Anticipated expiration: 2040-08-11
Also published as: CN111995706A

Abstract

The invention relates to the field of high polymer materials, in particular to an absorbent resin particle, a preparation method thereof and an absorbent product. The water-absorbent resin particles of the present invention comprise a crosslinked polymer having a water-soluble vinyl monomer and/or a hydrolyzable vinyl monomer and an internal crosslinking agent as essential constituent units, and at least a part of the surface of the crosslinked polymer is covered with a covering layer formed of a surface crosslinking agent. The absorbent resin particles of the present invention satisfy: the water retention under no-load pressure is 20-25 g/g, the absorption under load pressure is 0.8-1.2 times of the absorption under no-load pressure, and the passing rate of the gel liquid is at least 250 ml/min.

Description

Absorbent resin particle, preparation method thereof and absorbent product

Technical Field

The invention relates to the field of high polymer materials, in particular to an absorbent resin particle, a preparation method thereof and an absorbent product.

Background

Water-absorbent resins or water-absorbent resin compositions are widely used as main components of disposable diapers, sanitary napkins, incontinence pads, and other sanitary materials (absorbent articles) for the purpose of absorbing body fluids (urine, blood, etc.).

The water-absorbent resin composition contains a water-absorbent resin as a main component. Known water-absorbent resin compositions include: a crosslinked product of a partially neutralized product of polyacrylic acid, a hydrolyzed product of a starch-acrylonitrile graft polymer, a neutralized product of a starch-acrylic acid graft polymer, a saponified product of a vinyl acetate-acrylic acid ester copolymer, a crosslinked product of carboxymethyl cellulose, a hydrolyzed product of an acrylonitrile copolymer or an acrylamide copolymer, and a crosslinked product of the hydrolyzed product, a crosslinked product of a cationic monomer, a crosslinked isobutylene-maleic acid copolymer, and a crosslinked product of 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid.

In recent years, as for these sanitary materials, high functionalization and thinning thereof are progressing, so there is a tendency to increase the amount of the water-absorbent resin used in each sheet of sanitary material and the ratio of the water-absorbent resin to the whole absorbent structure comprising the water-absorbent resin and the hydrophilic fiber. Specifically, by decreasing the amount of the hydrophilic fiber (which has a low bulk density) and increasing the amount of the water absorbent resin (which has excellent water absorbency and a large bulk density), the ratio of the water absorbent resin in the absorbent structure is increased. Thus, the sanitary material can be thinned without reducing the water absorption amount.

Such a thin sanitary material is required to prevent "leakage" of the absorbent article and "fogging", that is, rewet phenomenon, which occurs when the absorbent article is pressurized and the liquid is not reversed. As absorbent resin particles. It is conventional to increase the rate of absorption to prevent "leakage" and increase the amount of absorption to prevent "fogging". However, in the conventional absorbent resin particles, the absorption amount under no load pressure is higher than that under load pressure, and the former is generally 1.5 to 2 times as high as that of the latter. In a case such as sitting or lying down, the surface-drying sensation may deteriorate after the absorbent article is subjected to pressure.

Disclosure of Invention

The primary object of the present invention is to provide absorbent resin particles.

The second object of the present invention is to provide a method for producing the absorbent resin particles.

A second object of the present invention is to provide an absorbent article containing the absorbent resin particles.

In order to realize the purpose of the invention, the technical scheme is as follows:

the present invention relates to an absorbent resin particle comprising a crosslinked polymer containing a water-soluble vinyl monomer and/or a hydrolyzable vinyl monomer and an internal crosslinking agent as essential constituent units, at least a part of the surface of the crosslinked polymer being coated with a coating layer formed of a surface crosslinking agent;

the absorbent resin particles satisfy the following conditions (i) to (iii):

the water retention under no load pressure is 20-25 g/g,

② the absorption capacity under load pressure is 0.8 to 1.2 times, preferably 0.9 to 1.05 times, the absorption capacity under no load pressure,

③ the passing rate of the gel liquid is at least 250 ml/min.

Optionally, the surface cross-linking agent is selected from a polyglycidyl compound, a polyol, a polyamine, a polyaziridine, a polyisocyanate, a silane coupling agent, or a polyvalent metal salt;

preferably polyglycidyl compounds, polyols and polyamines,

more preferably a polyglycidyl compound, most preferably ethylene glycol diglycidyl ether.

Optionally, the weight ratio of the surface cross-linking agent to the cross-linked polymer is 0.001-3: 100, preferably 0.005 to 2: 100, more preferably 0.01 to 1: 100.

the present invention also relates to a method for producing the absorbent resin particles described above, comprising at least the steps of;

(1) preparing to obtain water-containing cross-linked polymer particles;

(2) subjecting the surface cross-linking agent to a cross-linking reaction with the aqueous cross-linked polymer particles;

(3) drying to obtain the absorbent resin particles.

Optionally, in the step (1), the water content of the water-containing crosslinked polymer particles is 35 to 60 wt%, preferably 45 to 55 wt%.

Alternatively, in step (1), the method for preparing the aqueous crosslinked polymer particles comprises the following means:

i. firstly, preparing blocks of the water-containing crosslinked polymer, and then crushing the blocks to obtain water-containing crosslinked polymer particles;

ii. The aqueous crosslinked polymer particles are directly prepared.

Optionally, in the mode i, the temperature of the water-containing crosslinked polymer before crushing is 60-120 ℃, and preferably 65-110 ℃;

more preferably, in mode ii, the method for directly preparing the water-containing crosslinked polymer particles comprises: a kneading polymerization method and a reverse suspension method;

still more preferably, in the reverse suspension method, when an aqueous monomer solution containing a crosslinking agent is added dropwise, the concentration of the crosslinking agent in the aqueous monomer solution gradually increases.

Optionally, the weight average particle size of the water-containing crosslinked polymer particles is 100 to 800 μm, more preferably 200 to 600 μm, and particularly preferably 300 to 500 μm.

Optionally, in the step (2), the heating temperature during the crosslinking reaction is 100 to 300 ℃, preferably 110 to 180 ℃, more preferably 120 to 160 ℃, and particularly preferably 130 to 150 ℃.

The present invention also relates to an absorbent article comprising the above absorbent resin particles or the absorbent resin particles produced by the above production method.

The invention has at least the following beneficial effects:

the absorbent resin particles of the present invention have an absorption capacity under load pressure close to that under no load pressure, and have a high gel liquid passage rate, and the absorbent article using the absorbent resin particles of the present invention has an excellent surface dry feel even when the absorbent article is pressurized.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Detailed Description

Hereinafter, the method for producing the absorbent of the present invention will be described in detail. However, the scope of the present invention is not limited to the description, and may be modified as appropriate without departing from the scope of the present invention, in addition to the following examples. Specifically, the present invention is not limited to the embodiments described below, and various modifications can be made within the scope shown in the claims, and embodiments obtained by appropriately combining the technical means disclosed in the respective embodiments are also included in the technical scope of the present invention. In the present invention, the meaning of weight and mass, weight% and mass%, and weight part and mass part are the same, and the meaning of mass, mass% and mass part is unified in the present specification.

In the conventional absorbent resin pellets, the absorption amount under no-load pressure is higher than that under load pressure, the former is generally 1.5 to 2 times as high as the latter, and in a case such as sitting or lying down, the absorbent article is pressurized, and therefore the surface-dry feeling of the absorbent article under pressure may be deteriorated. In view of the drawbacks of the prior art, embodiments of the present invention provide absorbent resin particles that have an absorption capacity under load pressure close to that under no load pressure, have a high gel liquid passage rate, and dry the surface of an absorbent article under pressure.

The embodiment of the present invention provides an absorbent resin particle comprising a crosslinked polymer having a water-soluble vinyl monomer a1 and/or a hydrolyzable vinyl monomer a2 and an internal crosslinking agent b1 as basic constituent units, at least a part of the surface of the crosslinked polymer being coated with a coating layer formed of a surface crosslinking agent, and preferably all of the surface of the crosslinked polymer being coated with a coating layer formed of a surface crosslinking agent,

the absorbent resin particles of the embodiments of the present invention satisfy the following conditions (i) to (iii):

the water retention under no load pressure is 20-25 g/g,

② the absorption capacity under the load pressure is 0.8-1.2 times of the absorption capacity under the no-load pressure,

③ the passing rate of the gel liquid is at least 250 ml/min.

The water retention capacity of the absorbent resin particles under no load under pressure is preferably 20 to 25 from the viewpoint of the feeling of dryness of the surface of the absorbent article under pressure when the absorbent article is mixed (bonded) with the absorbent article. If it is outside this range, the surface-dry feeling of the absorbent article under pressure becomes poor. The water retention under no load pressure is correlated with the crosslink density of the crosslinked polymer, and the value thereof can be adjusted by adjusting the amount of the crosslinking agent added.

The absorbent resin particles absorb under a load pressure (0.9psi), and the amount of absorption under a load pressure is preferably 0.8 to 1.2 times, and particularly preferably 0.9 to 1.05 times, the amount of absorption under a no-load pressure, from the viewpoint of the feeling of surface dryness under pressure applied to an absorbent article. If the absorption amount under the load pressure is less than 0.8 times the absorption amount under the no-load pressure, the dry feeling of the surface of the absorbent article under pressure deteriorates. The absorption amount under load pressure is correlated with the crosslink density of the crosslinked polymer, and can be adjusted by adjusting the addition amount of the crosslinking agent. In general, the absorption capacity under no load pressure is higher than that under load pressure in absorbent resin particles, and the former is usually 1.5 to 2 times as high as that of the latter. In a case such as sitting or lying down, the absorbent article is applied with pressure, and therefore the surface-drying sensation of the absorbent article under pressure may be deteriorated. The absorbent resin particles of the examples of the present invention have an absorption capacity under load pressure close to an absorption capacity under no load pressure, and the surface of the absorbent article is dried under pressure.

The higher the passing rate of the gel liquid, from the viewpoint of the feeling of surface dryness under pressure applied to the absorbent article, without affecting other properties of the absorbent resin particles, the more favorable the liquid is to be uniformly diffused and infiltrated in the absorbent body, and further, the influence of the local absorption transition of the absorbent body on the feeling of dryness on the surface of the absorbent article can be avoided.

The absorbent resin particles of the embodiment of the invention are obtained by crosslinking and drying hydrogel particles having a water content of 35 to 60 wt% with a surface crosslinking agent.

[ MONOMER ]

The water-soluble vinyl monomer means a vinyl monomer having at least 100g dissolved in 100g of water at 25 ℃. The term "hydrolyzable" refers to a property of being hydrolyzed by the action of water and, if necessary, a catalyst (acid or base, etc.) at 50 ℃. The hydrolysis of the hydrolyzable vinyl monomer may be performed before and/or during and/or after the polymerization process, but is preferably performed after the polymerization from the viewpoint of the molecular weight of the resulting absorbent resin particles.

From the viewpoint of absorption characteristics, the water-soluble vinyl monomer a1 is preferably a vinyl monomer substituted with a carboxyl group and a salt thereof, a sulfo group and a salt thereof, or an amino group, more preferably a vinyl monomer substituted with a carboxyl group and a salt thereof, or a carbamoyl group, and particularly preferably acrylic acid and a salt thereof, methacrylic acid and a salt thereof, acrylamide and methacrylamide, and most preferably an acrylate salt. "carboxy salt" means a "carboxylate group","Sulfonyl salt" refers to "sulfonate". Examples of the salt include alkali metal (lithium, sodium, potassium and the like) salts, alkaline earth metal (magnesium, calcium and the like) salts, ammonium (NH)₄) Salts and the like. Among these salts, from the viewpoint of absorption characteristics, alkali metal salts and ammonium salts are preferable, alkali metal salts are more preferable, and sodium salts are particularly preferable.

When either the water-soluble vinyl monomer a1 or the hydrolyzable vinyl monomer a2 is used as a structural unit, the structural units may be used alone or two or more monomers may be used as a structural unit, if necessary. When the water-soluble vinyl monomer a1 and the hydrolyzable vinyl monomer a2 are used as the constituent units, the ratio of a 1: the molar ratio of a2 is 75-99: 1-25, preferably 85-95: 5-15, more preferably 90-93: 7 to 10, most preferably 91 to 92: 8-9. Within this range, the absorption performance is further improved.

As the structural unit of the absorbent resin particles, other vinyl monomer a3 copolymerizable with the above-mentioned vinyl monomer may be used as a structural unit in addition to the water-soluble vinyl monomer a1 and the hydrolyzable vinyl monomer a 2. The copolymerizable vinyl monomer a3 is not particularly limited, and the following vinyl monomers (i) to (iii) and the like can be used:

i. an aromatic vinyl monomer having 8 to 30 carbon atoms, for example: styrene, alpha-methylstyrene, and the like.

ii. Aliphatic vinyl monomers having 2 to 20 carbon atoms, for example: ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, butadiene, isoprene and the like.

iii an alicyclic vinyl monomer having 5 to 15 carbon atoms, for example: pinene, limonene, indene, cyclopentadiene, dicyclopentadiene, ethylidene norbornene, and the like.

When the other vinyl monomer a3 is used as a structural unit, the molar ratio of the a3 unit to the sum of the water-soluble vinyl monomer a1 unit and the hydrolyzable vinyl monomer a2 unit (i.e., a 3: a1+ a2) is 0.01 to 5: 100, more preferably 0.05 to 3: 100, preferably 0.08-2: 100, particularly preferably 0.1 to 1.5: 100. from the viewpoint of absorption characteristics and the like, it is most preferable that the content of the unit of the other vinyl monomer (a3) is 0 mol%.

The internal crosslinking agent b1 is not particularly limited, and a polyglycidyl compound or a crosslinking agent having two or more ethylenically unsaturated groups can be used from the viewpoint of absorption characteristics. The polyglycidyl compound is preferably ethylene glycol diglycidyl ether; the crosslinking agent having two or more ethylenically unsaturated groups may be N, N' -methylenebisacrylamide, or poly (meth) allyl ether of a polyhydric alcohol (polyol) having 2 to 10 carbon atoms, and particularly preferably triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane, and pentaerythritol triallyl ether. The molar ratio of the internal crosslinking agent b1 unit to the sum of the water-soluble vinyl monomer a1 unit and the hydrolyzable vinyl monomer a2 unit (i.e., b 1: a1+ a2) is 0.001-5: 100, more preferably 0.005 to 3: 100, particularly preferably 0.01 to 1: 100. within this range, the absorption characteristics will be further improved.

[ POLYMER ]

The polymerization methods used to obtain the crosslinked polymers of the examples of the present invention are: spray polymerization, drop polymerization, bulk polymerization, precipitation polymerization, aqueous solution polymerization, reversed-phase suspension polymerization, or the like. The embodiment of the present invention is preferably aqueous solution polymerization or reversed phase suspension polymerization performed as an aqueous monomer solution. Among the polymerization methods, the aqueous solution polymerization method is preferable because it is advantageous in terms of safe production and cost control because it does not require the use of an organic solvent. In the aqueous solution polymerization, a water-soluble vinyl monomer (a1) and/or a hydrolyzable vinyl monomer (a2), an internal crosslinking agent (b1), and water are used to prepare an aqueous solution (hereinafter referred to as a monomer solution). The monomer solution may be polymerized to obtain a bulk aqueous crosslinked polymer (hereinafter referred to as an aqueous gel).

The concentration of the monomer solution during polymerization is not particularly limited, but is preferably 20 mass% to the saturated concentration or less, more preferably 25 to 80 mass%, and still more preferably 30 to 70 mass%. If the concentration is less than 20 mass%, the productivity may be lowered. It is preferable to carry out the polymerization at a concentration of less than the saturation concentration because it is found that the physical properties are reduced when the monomer is polymerized in a slurry (aqueous dispersion of an acrylic acid salt).

In the reversed-phase suspension polymerization method, when an aqueous monomer solution containing a crosslinking agent is dropped, the concentration of the crosslinking agent in the aqueous monomer solution gradually increases. For example, the aqueous monomer solution containing the crosslinking agent may be divided into 2 to 10 parts, preferably 4 to 6 parts, and the concentration of the crosslinking agent is 0%, 0.5%, 1.5%, and 3% in this order in 4 parts. The method is favorable for obtaining a gradient core-shell structure, has hard outside and soft inside, and can realize the balance between the gel strength and the absorption capacity.

In addition, in order to promote the polymerization and to improve the physical properties of the water-absorbing agent, a degassing step of dissolved oxygen (for example, a substitution step of substitution with an inert gas) may be provided as necessary at the time of polymerization. In addition, in order to increase the water absorption rate of the water absorbing agent and increase the surface area or increase the drying rate, bubbles (particularly, inert gas) or various foaming agents (for example, organic or inorganic carbonates, azo compounds, urea compounds) may be contained during polymerization to foam so that the volume is increased by, for example, 1.001 to 10 times during polymerization or drying.

The polymerization step of the embodiment of the present invention may be carried out under normal pressure, reduced pressure, or increased pressure, preferably normal pressure (101.3kPa, 1 atm); or its neighborhood value (normal pressure. + -. 10%)). The temperature at the start of the polymerization varies depending on the kind of the polymerization initiator used, but is preferably 15 to 130 ℃, and more preferably 20 to 120 ℃.

The polymerization initiator used in the examples of the present invention may be suitably determined depending on the polymerization form, and is not particularly limited, and examples thereof include a photodecomposition type polymerization initiator, a thermal decomposition type polymerization initiator, and a redox type polymerization initiator. By these polymerization initiators, the polymerization in the present invention can be started. Examples of the photolytic polymerization initiator include benzoin derivatives, benzil derivatives, acetophenone derivatives, benzophenone derivatives, and azo compounds. Examples of the thermal decomposition type polymerization initiator include: persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide; azo compounds such as 2,2 '-azobis (2-amidinopropane) dihydrochloride and 2,2' -azobis [2- (2-imidazolin-2-yl) propane ] dihydrochloride. Examples of the redox polymerization initiator include a system using a persulfate and a peroxide in combination with a reducing compound such as L-ascorbic acid and sodium hydrosulfite.

[ GEL CRUSHING ]

The embodiment of the present invention can directly produce the water-containing crosslinked polymer having a certain particle diameter by the kneading polymerization method and the reversed-phase suspension polymerization method, or can produce the water-containing crosslinked polymer particles (hereinafter referred to as hydrogel particles) by crushing (chopping) the bulk water-containing crosslinked polymer.

The hydrogel crusher usable in the present invention is not particularly limited, and examples thereof include: a gel mill, a single-screw extruder, a twin-screw extruder, a meat chopper, and the like, each of which is provided with a plurality of rotating stirring blades, such as a batch-type or continuous double-arm kneader. Among these, a screw extruder having a perforated plate at the head end is preferable. In the gel pulverization step of the present invention, the temperature of the water-containing gel before the gel pulverization (gel temperature) is preferably 60 to 120 ℃, more preferably 65 to 110 ℃ from the viewpoints of the particle size control of the particulate water-containing gel and the physical properties of the water-absorbent resin. If the gel temperature is less than 60 ℃, the aqueous gel may have increased hardness in its properties and it is difficult to control the particle shape and particle size distribution when the gel is crushed. In addition, if the gel temperature exceeds 120 ℃, the softness of the aqueous gel may increase and it may be difficult to control the particle shape and particle size distribution well. Here, the gel temperature can be controlled by the temperature at the time of polymerization, heating or cooling after polymerization, or the like.

The size of the hydrogel particles after crushing is preferably 50 μm to 10cm, more preferably 100 μm to 2cm, and particularly preferably 1mm to 1 cm. In addition, the crushing (chopping) can be carried out during the polymerization, in which case the polymerization heat is easily released.

First, the water retention capacity, which is a main property of the absorbent resin particles, is generally proportional to the crosslink density of the crosslinked polymer. When the crosslink density of the crosslinked polymer is low, the water retention is high, and when the crosslink density of the crosslinked polymer is high, the water retention is low. It is generally desirable that absorbent articles are capable of absorbing large amounts of absorbed liquids, and in order to meet this requirement it is desirable to keep the crosslink density as low as possible. However, when the crosslinking density is low, the strength of a gel swollen by absorbing an absorbed liquid is significantly reduced, and under pressure, there is a problem that the absorbed liquid cannot be absorbed because the gel strength is low. To overcome this problem, surface crosslinking known in the art increases the crosslinking density near the surface of the absorbent resin particles, forming a core-shell structure having different crosslinking densities on the inside and the surface, which in part achieves a balance of the water retention under no load pressure and the absorption under load pressure. By carrying out this technique, the absorption capacity under no-load pressure is higher than that under load pressure, and the former is usually 1.5 to 2 times as high as the latter. But in cases such as sitting or lying down, the absorbent article is in fact subjected to pressure, and therefore the feeling of surface dryness of the absorbent article under pressure may deteriorate.

[ surface Cross-linking ]

In order to suppress an increase in surface moisture feeling under the application of pressure, the present embodiment achieves a good surface-dry feeling under pressure of an absorbent article by optimizing the water content of the water-containing crosslinked polymer particles in the surface crosslinking step. Namely: controlling the water content of the hydrogel particles within the range of 35-60 wt%, and carrying out surface crosslinking to realize the following steps: comprising a water-soluble vinyl monomer a1 and/or a hydrolyzable vinyl monomer a2, a crosslinked polymer having an internal crosslinking agent b1 as a main constituent unit, and water, wherein the water content is 35 to 60% by weight. The aqueous crosslinked polymer particles were further crosslinked with a surface crosslinking agent (b2) to give' aqueous crosslinked polymer particles having a coating layer.

The water content of the hydrogel is preferably 35 to 60%, more preferably 45 to 55%. Within this range, the absorbent article has a good surface-dry feel under pressure. The surface crosslinker b2 may be the same as or different from the internal crosslinker b 1. As the surface cross-linking agent, a polyglycidyl compound (polyglycidyl), a polyol, a polyamine, a polyaziridine, a polyisocyanate, a silane coupling agent, a polyvalent metal salt, or the like can be used. Among the above surface-crosslinking agents, from the viewpoint of economy and absorption characteristics, a polyglycidyl compound, a polyhydric alcohol, and a polyamine are preferred, a polyglycidyl compound and a polyhydric alcohol are more preferred, a polyglycidyl compound is particularly preferred, and ethylene glycol diglycidyl ether is most preferred.

The amount (wt%) of the surface-crosslinking agent b2 used is not particularly limited, and may be variously changed depending on the kind of the surface-crosslinking agent, the crosslinking condition, the target performance, and the like, but from the viewpoint of absorption characteristics and the like, the ratio of the amount of the surface-crosslinking agent b2 used to a1+ a2+ b1 is 0.001 to 3: 100, preferably 0.005-2: 100, more preferably 0.01 to 1: 100. within this range, the surface-dry feel of the absorbent article under pressure will be good. The surface-crosslinking agent b2 may be added by spraying and kneaded after being mixed with the hydrogel by means of spraying under high-speed stirring, or while crushing the hydrogel. Mixing and kneading devices such as a uniaxial extruder, a ribbon mixer, a double arm kneader and an SV mixer can be used. In addition to the direct mixing described above, the hydrogel may also be dispersed in a solvent, and then the surface cross-linking agent b2 may be dissolved or dispersed in the solvent to achieve uniform coating. A device with a high stirring force, such as a homomixer or a biological mixer, may be used.

When the hydrogel particles and the surface-crosslinking agent b2 are reacted by heating, the heating is preferably conducted by heat conduction and/or heat transfer by hot air. The surface cross-linking step need not be a constant temperature throughout. However, in order to prevent local overheating, it is preferable that the temperature of the heating device is 100 to 300 ℃, more preferably 110 to 180 ℃, more preferably 120 to 160 ℃, and particularly preferably 130 to 150 ℃ during 70% or more of the time from the beginning to the end of the step, particularly 90% or more of the time, and substantially the entire time.

If necessary, known additives may be added to the absorbent resin particles of the present invention at any stage. As the additives, preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet absorbers, colorants, perfumes, deodorants and organic fibrous substances can be used. When the additive is added, the total amount (wt%) of the additive varies depending on the use.

[ DRY ] A

The hydrogel particles subjected to surface crosslinking can be obtained by hot air drying (paddle dryer, belt dryer, floating dryer, etc.), azeotropic dehydration drying, freeze drying, far infrared ray drying, etc. to obtain absorbent resin particles. The drying temperature is preferably 100 to 300 ℃, and more preferably 120 to 180 ℃. The drying time is not particularly limited, and is, for example, preferably 1 minute to 5 hours, and more preferably 5 minutes to 1 hour, because it depends on the surface area and water content of the hydrogel, the type of the drying agent, and the like. The resin solid content, which is determined from the amount of reduction after drying (mass change between before and after drying 1g of powder or granule at 180 ℃ for 3 hours), is preferably 80 mass% or more, more preferably 85 to 99 mass%, and still more preferably 90 to 98 mass%.

The parameter detection method in the embodiment of the invention comprises the following steps:

water retention under no load pressure

A tea bag (length: 20cm, width: 10cm) made of a nylon mesh having a pore diameter of 63 μm was immersed in 1,000ml of physiological saline (salt concentration: 0.9 wt%) for 1 hour without stirring after adding 1.00g of a measurement sample, and then suspended for 15 minutes to remove water. Then, each tea bag was put into a centrifugal separator, centrifuged at 150G for 90 seconds, the remaining physiological saline was removed, and the weight including the tea bag was measured (h1), and the weight of the tea bag after centrifugal dehydration was measured as (h2) in the same manner as described above except that the measurement sample was not used. The water retention was determined by the following equation. In addition, the temperature of the physiological saline used and the measurement environment was 25 ℃. + -. 2 ℃.

Water retention (g/g) ═ h1 (h2)

Absorption capacity under load pressure

The measurement sample was placed in a cylindrical plastic tube (inner diameter 30mm, height 60mm) equipped with a nylon mesh on the bottom surface thereof and having a pore diameter of 63 μm. Weighing 1g, vertically placing a plastic pipe, and placing a measurement sample on a nylon net to ensure that the measurement sample has a substantially uniform thickness; a metal load-bearing compact (load pressure 0.9psi) having an outer diameter of 29.5mm was applied to the measurement specimen. In a petri dish (diameter: 12cm) containing 60ml of physiological saline (saline concentration: 0.9 wt%), a plastic tube containing a measurement sample was erected with the nylon mesh side being the lower surface, and the porous ceramic plate was immersed and left to stand. After 60 minutes, the plastic tube containing the sample is weighed to obtain the mass increased by absorption of physiological saline. The temperature of the physiological saline used and the measuring atmosphere were 25 ℃. + -. 2 ℃.

Gel liquid passage rate

The aqueous gel particles were prepared by immersing 0.32g of the test sample in 80ml of physiological saline for 2 hours. On the other hand, a stopcock (inner diameter: 4mm, length: 8cm) of a closed column (inner diameter: 25.4mm, length: 35cm) having a plug and a filter (mesh opening: 8 μm to 10 μm) with a capacity scale was closed, and the column was fixed vertically (in the direction of gravity) with the stopcock set to the lower side. Next, the above hydrogel particles were transferred to a column together with physiological saline, and a pressing shaft (weight: 18g, length: 34cm) vertically provided at one end with a circular wire net (diameter: 25mm) having a mesh opening of 180 μm was put in such a manner that the wire net was positioned on one side of the hydrogel particles, and a weight (100g) was put thereon and left to stand for 1 minute. The stopcock at the lower part of the column was opened, and the time (T1; sec) required for the liquid level in the column to change from 60ml to 40ml was measured to determine the gel liquid passage rate (Y, ml/min) by the following equation. In addition, the temperature of the physiological saline used and the measurement environment was 25 ℃. + -. 2 ℃.

(Y)＝20(ml)×60/(T1-T2)

T2 is the time determined by performing the same operation as described above for the case where the test sample is not contained. That is, 50ml of physiological saline was added to a filter-closed type column with a plug and a volume scale, and the time (T2; sec) required for the liquid level in the column to change from 60ml to 40ml was measured.

Surface dryness value

Calibrating the tester: the diaper was soaked in artificial urine (0.03 wt% of potassium chloride, 0.08 wt% of magnesium sulfate, 0.8 wt% of sodium chloride, and 99.09 wt% of deionized water), left for 60 minutes, and then the detector of the temperature and humidity sensing tester was placed on the fully wetted diaper, and a dryness value of 0% was set. Next, the detector of the temperature and humidity sensor tester was placed on the dried diaper (the diaper was dried by heating at 80 ℃ for 2 hours), and the dryness of 100% was set.

A metal ring (inner diameter 80mm, length 40mm) was placed at the center of the paper diaper to be measured, 90ml of artificial urine was injected, the metal ring was removed immediately after the artificial urine was absorbed, 3 detectors of temperature and humidity sensor testers were placed at the center and the left and right sides of the paper diaper to start measuring the surface dryness, values 5 minutes after the start of the measurement were respectively designated as MO-1 (center), MO-2 (left side), and MO-3 (right side), and the average value of the three values was taken as the test result.

The absorbent resin particles of the present invention can be used as an absorbent body together with a fibrous material. The absorbent body preferably constitutes an absorbent article (disposable diaper, sanitary napkin, etc.). The present invention will be further described below by way of preparation examples, examples and comparative examples, but the present invention is not limited thereto.

Preparation example 1:

77 parts by weight of sodium acrylate, 22.9 parts by weight of acrylic acid, 0.10 part by weight of N, N' -methylenebisacrylamide, 110 parts by weight of deionized water and 0.001 part by weight of ferrous sulfate were placed in a glass reaction vessel. The monomer solution temperature was maintained at 3 ℃ while stirring. Nitrogen gas was introduced into the monomer solution so that the dissolved oxygen amount was 1ppm or less, and 0.3 parts by weight of a 1% aqueous hydrogen peroxide solution, 0.8 parts by weight of a 0.2% aqueous ascorbic acid solution and 0.8 parts by weight of 2% 2,2' -azobisamidopropane dihydrochloride were added to the monomer solution to start the polymerization reaction, and after the reaction solution reached 98 ℃, polymerization was performed at a polymerization temperature of 98 ± 2 ℃ for about 3 hours. Hydrogel (1) having a water content (120. + -. 5 ℃ C.. times.30 minutes) of 52% by weight was obtained.

300 parts by weight of hydrogel (1) was pulverized at 70 ℃ in a chopper having a pore size of 4.5mm to obtain hydrogel particles (1).

Preparation example 2:

the hydrogel particles (1) were dried at 135 ℃ and a wind speed of 1.9 m/sec using a vented belt dryer to obtain a dried product. The dried product was crushed with a commercially available juice extractor, and the particle diameter thereof was adjusted to a particle size range of 850 to 150 μm using sieves having mesh openings of 850 μm and 150 μm to obtain absorbent resin particles H1.

Preparation example 3:

81.8 parts by weight of acrylic acid and 0.10 part by weight of N, N' -methylenebisacrylamide were mixed, 110 parts by weight of deionized water and 0.001 part by weight of ferrous sulfate were added, and the monomer solution temperature was maintained at 3 ℃ while stirring. Nitrogen gas was introduced into the monomer solution so that the dissolved oxygen amount was 1ppm or less, and 0.3 parts by weight of a 1% aqueous hydrogen peroxide solution, 0.8 parts by weight of a 0.2% aqueous ascorbic acid solution and 0.8 parts by weight of 2% 2,2' -azobisamidopropane dihydrochloride were added to the monomer solution to start the polymerization reaction, and the reaction solution reached 94 ℃. Hydrogel particles were obtained by polymerization and mixing at 94 ± 2 ℃ for about 1 hour. Further, 32.77 parts of sodium hydroxide was added, stirring was continued, and the mixture was kneaded for 30 minutes to obtain hydrogel particles (2) having a water content (120 ± 5 ℃ c. × 30 minutes) of 54 wt%.

Preparation example 4:

145.4 parts by weight of acrylic acid were diluted with 9.4 parts by weight of water, and 242.3 parts by weight of a 25% aqueous solution of sodium hydroxide was added to neutralize while cooling to 20 ℃. To the solution were added 0.09 parts by weight of ethylene glycol diglycidyl ether, 0.0146 parts by weight of sodium hypophosphite monohydrate, and 0.0727 parts by weight of potassium persulfate, and mixed with stirring at 25 ℃ for 2 minutes to obtain an aqueous monomer solution (1). Then, 624 parts by weight of cyclohexane was placed in a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen introduction tube, and 1.56 parts by weight of polyoxyethylene octylphenyl ether phosphate (trade name: Prysurf A210G) was added, the atmosphere was replaced with nitrogen while stirring, and the temperature was raised to 70 ℃ and maintained, and the aqueous monomer solution (1) was added dropwise at a rate of 6.6 parts by weight/min for 6 minutes and then maintained at 75 ℃ for 15 minutes. The remaining aqueous monomer solution (1) was added dropwise at 6.6 parts by weight/min over 54 minutes. Then, the mixture was aged at 75 ℃ for 30 minutes to obtain hydrogel particles (3) having a water content (120. + -. 5 ℃ C.. times.30 minutes) of 55% by weight.

Preparation example 5:

water was removed from the hydrogel particle (3) of production example 4 by azeotropic distillation of water and cyclohexane, and the water content of the resin (120. + -. 5 ℃ C. for 30 minutes) was about 5% by weight. The mixture was cooled to 30 ℃ and the stirring was stopped, the resin particles settled, the resin particles and cyclohexane layer were separated by decantation, and then filtered and dried under reduced pressure at 80 ℃ to obtain dried polymer particles, the particle size thereof was adjusted to a particle size range of 850 to 150 μm using sieves having mesh openings of 850 μm and 150 μm to obtain absorbent resin particles.

Example 1:

1.8 parts by weight of ethylene glycol diglycidyl ether was added by spraying to 300 parts by weight of the hydrogel particles (1) obtained in production example 1, followed by further kneading with a chopper, and then the hydrogel particles were dried using the drying conditions of production example 2, thereby obtaining absorbent resin particles (1) of the present invention having a weight-average particle diameter of 400 μm.

Example 2:

in the same manner as in example 1 except for changing "1.8 parts by weight of ethylene glycol diglycidyl ether" to "3.6 parts by weight of ethylene glycol diglycidyl ether", absorbent resin particles (2) of the present invention were obtained, the weight-average particle diameter of which was 410 μm.

Example 3:

to 400 parts by weight of the hydrogel particle (2) obtained in preparation example 3, 2 parts by weight of ethylene glycol diglycidyl ether was added, and the mixture was stirred in a general mixer for 15 minutes to obtain a hydrogel particle. The hydrogel particles were then dried using the drying conditions of preparation example 2, thereby obtaining absorbent resin particles (3) of the present invention having a weight-average particle diameter of 380 μm.

Example 4:

in the same manner as in example 3 except that "2 parts by weight of ethylene glycol diglycidyl ether" was changed to "3 parts by weight of glycerol triglycidyl ether", absorbent resin particles (4) of the present invention were obtained, the weight average particle diameter of which was 400 μm.

Example 5:

to 400 parts by weight of the hydrogel particle (3) obtained in production example 4, 5 parts by weight of ethylene glycol diglycidyl ether was added, and the mixture was continuously stirred and held at 75 ℃ for 30 minutes, after which the hydrogel particle was dried according to the procedure in production example 5, thereby obtaining an absorbent resin particle (5) of the present invention. The weight average particle size was 350. mu.m.

Example 6:

400 parts by weight of the aqueous monomer solution (1) prepared in preparation example 4 was divided into 4 equal parts, and 0 part by weight, 0.5 part by weight, 1.5 parts by weight and 3 parts by weight of ethylene glycol diglycidyl ether were added, respectively. Then, the mixture was stirred at 25 ℃ for 2 minutes by a biological mixer (ABM-2, manufactured by Nippon Seikagaku Kogyo Co., Ltd.) to obtain aqueous monomer solutions (2) to (5). Next, 624 parts of cyclohexane was placed in a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen introduction tube, and 1.56 parts by weight of polyoxyethylene octylphenyl ether phosphate (trade name: PRYSURF a210G, manufactured by Dai-ichi industrial pharmaceutical co., ltd.) was added thereto, followed by nitrogen substitution with stirring and temperature increase to 70 ℃. Then, while keeping the temperature at 70 ℃, the aqueous monomer solution (2) was dropped at a rate of 6.6 parts by weight/min for 6 minutes and kept at 75 ℃ for 15 minutes, and then the remaining aqueous monomer solution (2) was dropped at a rate of 6.6 parts by weight/min, and immediately after completion of the dropping, the aqueous monomer solution (3) was dropped at a rate of 6.6 parts by weight/min. Thereafter, similarly, the aqueous monomer solutions (4) and (5) were successively dropped. Then, the mixture was aged at 75 ℃ for 30 minutes to obtain hydrogel particles (4). The water content (120. + -. 5 ℃ C.. times.30 minutes) was 55% by weight. Thereafter, the same operation as in production example 5 was performed, thereby obtaining absorbent resin particles (6) of the present invention having a weight average particle diameter of 350 μm.

Comparative example 1:

the absorbent resin particles H1 obtained in preparation example 2 were used as comparative absorbent resin particles, and the weight-average particle diameter thereof was 400 μm.

Comparative example 2:

to 100 parts by weight of the absorbent resin particles H1 obtained in comparative example 1, 4 parts by weight of a 50 wt% ethylene glycol diglycidyl ether solution was added by spraying under high-speed stirring (high-speed stirring turbulizer by michelson corporation: rotation speed 2000rpm) in a solvent of a mixed solution of water and methanol in a mass ratio of 70: 30 and then left to stand at 140 c for 30 minutes for surface crosslinking, to thereby obtain comparative absorbent resin particles H2 having a weight-average particle diameter of 400 μm.

Comparative example 3:

300 parts by weight of water was added to 300 parts by weight of the hydrogel particle (1) obtained in production example 1, and the hydrogel particle was kneaded twice with a chopper to obtain a hydrogel having a water content (120. + -. 5 ℃ C.. times.30 minutes) of 85% by weight. Further, 1.8 parts by weight of ethylene glycol diglycidyl ether was added, and after thoroughly mixing by hand, the mixture was kneaded again with a chopper to obtain water-containing gel particles. Then, the same operation as in production example 2 was performed, thereby obtaining comparative absorbent resin particles H3 having a weight-average particle diameter of 400 μm.

Comparative example 4:

77 parts by weight of sodium acrylate, 22.85 parts by weight of acrylic acid, 0.15 part by weight of N, N' -methylenebisacrylamide, 220 parts by weight of deionized water, 2 parts by weight of diglycidyl ether, and 0.001 part by weight of ferrous sulfate were charged into a glass reaction vessel. The monomer solution temperature was maintained at 3 ℃ with stirring. Nitrogen gas was introduced into the reactor so that the dissolved oxygen amount was 1ppm or less, and 0.3 parts by weight of a 1% aqueous hydrogen peroxide solution, 0.8 parts by weight of a 0.2% aqueous ascorbic acid solution and 0.8 parts by weight of 2% 2,2' -azobisamidopropane dihydrochloride were added to the monomer solution to start the polymerization reaction, and after the reaction solution reached 85 ℃, polymerization was carried out at a polymerization temperature of 85 ± 2 ℃ for about 5 hours. A gel of polymer is obtained with a water content (120. + -. 5 ℃ C.. times.30 minutes) of 70% by weight. 300 parts by weight of hydrogel were crushed at 25 ℃ with a chopper (plate pore size: 6mm, 12VR-400K manufactured by Iizuka Industry Co., Ltd.) to obtain hydrogel particles (6). Thereafter, the same operation as in production example 2 was performed, thereby obtaining comparative absorbent resin particles (H4) having a weight-average particle diameter of 380 μm.

For the absorbent resin particles obtained in examples and comparative examples, the water retention under unloaded pressure and the absorption under loaded pressure and the gel liquid passage rate were measured, and the results thereof are shown in table 1.

TABLE 1

Example 7:

100 parts by weight of fluff pulp and 200 parts by weight of the absorbent resin particles (1) of the present invention obtained in example 1 were mixed with an air-flow mixing device to have a basis weight of about 300g/m²And at 5kg/cm²Is pressed for 30 seconds under pressure to obtain the absorbent body (1). The absorbent body (1) was cut into a rectangular shape of 14 cm. times.36 cm, and absorbent paper (basis weight 15.5 g/m) of the same size as the absorbent body was placed above and below the absorbent body, respectively²Napier Tissue Soft Slim). Further, a polyethylene sheet (Kanno Shokai co., ltd., poly sheet, thickness of 0.03mm) was placed on the back face, and a polyethylene nonwoven fabric (basis weight 20.0 g/m) was placed²DuPont co., ltd., Tyvek) was placed on the front face to make a disposable diaper (1).

Examples 8 to 12:

disposable diapers (2) to (6) were produced in the same manner as in example 7, except that the absorbent resin particles (1) were changed to the absorbent resin particles (2) to (6), respectively.

Comparative examples 5 to 8:

the disposable diaper of the comparative example was produced in the same manner as in example 7, except that the absorbent resin particles (1) were changed to the absorbent resin particles (H1) to (H4), respectively.

The results of the surface dryness test of the disposable diaper are shown in Table 2.

TABLE 2

As understood from the results of the paper diaper using these absorbent resin particles, when absorbent resin particles satisfying the requirements of the present invention are used, a high surface dryness value can be obtained. These results show that artificial urine injected into a disposable diaper is dispersed throughout the disposable diaper due to the high gel permeability of the absorbent resin particles, and that the artificial urine is absorbed by the absorbent resin particles even if pressure is applied. That is, the absorbent article using the absorbent resin particles of the present invention has a good surface dry feeling both under pressure and without pressure, and can reduce the problems such as fogging.

Industrial applicability of the invention

By applying the absorbent resin particles of the present invention to various absorbents, absorbent articles having excellent surface-dry feeling can be obtained. In particular diapers (children's and adults, etc.), sanitary towels, pads (incontinence pads and surgical pads). The absorbent resin particles of the present invention are not only sanitary products, but also pet urine absorbents, urine gelling agents for mobile toilets, antistaling agents for fruits and vegetables, drip absorbents for meat and seafood, cold storage agents, disposable heaters, and the like. It can also be used for various other purposes, for example: gelling agent for battery, water-retaining agent for plant and soil, anti-dewing agent, water-blocking material, packaging material and artificial snow.

Although the present application has been described with reference to the preferred embodiments, it is not intended to limit the scope of the claims, and many possible variations and modifications may be made by one skilled in the art without departing from the spirit of the present application.

Claims

1. A method for producing absorbent resin particles comprising a crosslinked polymer having a water-soluble vinyl monomer and/or a hydrolyzable vinyl monomer and an internal crosslinking agent as essential constituent units, at least a part of the surface of the crosslinked polymer being coated with a coating layer formed of a surface crosslinking agent;

the absorbent resin particles satisfy the following conditions (i) to (iii):

the water retention under no load pressure is 20-25 g/g,

③ the passing rate of the gel liquid is at least 250 ml/min;

the method is characterized by at least comprising the following steps:

(1) preparing to obtain water-containing cross-linked polymer particles, wherein the water content of the water-containing cross-linked polymer particles is 35-60 wt%;

(3) drying to obtain the absorbent resin particles.

2. The method according to claim 1, wherein the surface cross-linking agent is selected from a polyglycidyl compound, a polyol, a polyamine, a polyaziridine, a polyisocyanate, a silane coupling agent, and a polyvalent metal salt.

3. The method according to claim 1, wherein the surface cross-linking agent is selected from the group consisting of polyglycidyl compounds, polyhydric alcohols, and polyamines.

4. The method of claim 1, wherein the surface cross-linking agent is ethylene glycol diglycidyl ether.

5. The method according to claim 1, wherein the weight ratio of the surface crosslinking agent to the crosslinked polymer is 0.001 to 3: 100.

6. the method according to claim 5, wherein the weight ratio of the surface-crosslinking agent to the crosslinked polymer is 0.005 to 2: 100.

7. the method according to claim 6, wherein the weight ratio of the surface cross-linking agent to the cross-linked polymer is 0.01 to 1: 100.

8. the method according to claim 1, wherein the water content of the water-containing crosslinked polymer particles is 45 to 55 wt%.

9. The production method according to claim 1, wherein in the step (1), the method for producing the aqueous crosslinked polymer particles comprises the following means:

ii. The aqueous crosslinked polymer particles are directly prepared.

10. The production method according to claim 9, wherein in the mode i, the temperature of the aqueous crosslinked polymer before pulverization is 60 to 120 ℃.

11. The production method according to claim 10, wherein in the mode i, the temperature of the aqueous crosslinked polymer before pulverization is 65 to 110 ℃.

12. The method according to claim 9, wherein in mode ii, the method for directly preparing the aqueous crosslinked polymer particles comprises: a kneading polymerization method and a reverse suspension method.

13. The production method according to claim 12, wherein in the reverse suspension method, when an aqueous monomer solution containing a crosslinking agent is added dropwise, the concentration of the crosslinking agent in the aqueous monomer solution gradually increases.

14. The method according to claim 1, wherein the water-containing crosslinked polymer particles have a weight average particle diameter of 100 to 800 μm.

15. The method according to claim 14, wherein the water-containing crosslinked polymer particles have a weight average particle diameter of 200 to 600 μm.

16. The method according to claim 15, wherein the water-containing crosslinked polymer particles have a weight average particle diameter of 300 to 500 μm.

17. The production method according to claim 1, wherein in the step (2), the heating temperature at which the crosslinking reaction is performed is 100 to 300 ℃.

18. The production method according to claim 17, wherein in the step (2), the heating temperature at which the crosslinking reaction is performed is 110 to 180 ℃.

19. The production method according to claim 18, wherein in the step (2), the heating temperature at which the crosslinking reaction is performed is 120 to 160 ℃.

20. The production method according to claim 19, wherein in the step (2), the heating temperature at which the crosslinking reaction is performed is 130 to 150 ℃.