JPS5825500B2 - water absorbing agent - Google Patents

Description

[Detailed description of the invention] The present invention relates to a water absorbing agent.

More specifically, the present invention relates to a water-absorbing agent that absorbs aqueous substances to a high degree when it comes into contact with an aqueous substance, and has a high water-retaining property even under pressure.

Conventionally, attempts have been made to use water-absorbing resins as a constituent material in sanitary cotton, disposable diapers, and other sanitary materials that absorb thin body fluids.

Examples of such absorbent resins include hydrolysates of starch-acrylonitrile graft polymers and starch-acrylonitrile graft polymers.
Neutralized products of acrylic acid graft polymers, saponified products of vinyl acetate-acrylic acid ester copolymers, hydrolyzed products of acrylonitrile copolymers or acrylamide copolymers, and crosslinked products thereof, or obtained by reverse phase emulsion polymerization. Self-crosslinking sodium polyacrylate and the like are known.

However, since these absorbent resins are manufactured by a method that involves complicated steps and low productivity, the resulting absorbent resins are susceptible to contamination with impurities and are also expensive.

Therefore, in actual use, there are problems such as the amount of use is limited due to cost.

Furthermore, because these absorbent resins have a low degree of polymerization in their main chains, even if they have a crosslinked structure, they still have a large amount of water soluble content, and generally 2
Contains water-soluble components in a proportion of 0 to 50% by weight.

Therefore, when these absorbent resins come into contact with menstrual blood, urine, or other body fluids, there are problems such as a low initial absorption rate, a low saturated absorption amount, and stickiness.

Furthermore, since it contains a large amount of water-soluble matter, there is also a problem in terms of safety for the skin and mucous membranes of the human body.

Furthermore, many of these absorbent resins have low heat resistance and cause deterioration in quality and performance due to heat when molded into absorbent sheets.

Furthermore, when these absorbent resins are powdered, they tend to generate dust, which harms the working environment, and when the resulting powder comes into contact with aqueous substances, it tends to become lumpy and its initial absorption capacity is extremely reduced. There is also a drawback.

The present inventors have conducted intensive research to solve the above-mentioned problems with conventionally known absorbent resins. ,
The alkali metal salt crosslinked polyacrylic acid obtained by copolymerizing an acrylate monomer and a crosslinking monomer at a relatively high concentration in an aqueous solution to form a gel-like hydropolymer, and then drying by heating, The present invention has been completed based on the discovery that all of the above-mentioned problems of conventional absorbent resins have been solved and that the absorbent resin has various excellent effects.

Therefore, the object of the present invention is to provide a drug that has a low aqueous content, does not become sticky even when it comes into contact with the absorbed liquid, has excellent absorbency, and is capable of adjusting the pH to a range that is safe for human skin. The present invention provides a water-absorbing agent that generates almost no dust when molded into an absorbent sheet either alone or in combination with a fibrous material, and has excellent heat resistance and stability.

That is, the water absorbing agent of the present invention comprises an acrylate-based monomer consisting of 0 to 50 mol% of acrylic acid and 50 to 100 mol% of an alkali metal acrylate in the presence of a water-soluble and/or water-dispersible surfactant A. 100 parts by weight of polymer B and crosslinkable monomer C0,
001 to 5 parts by weight is copolymerized with an aqueous solution at a concentration of 25% by weight or more to obtain a gel-like hydrous polymer, which is further heat-dried to obtain a polyacrylic alkali metal salt crosslinked product. be.

The water-soluble or water-dispersible surfactant A used in the present invention needs to be compatible with or disperse in the aqueous solution of the acrylate monomer B.

Examples of such surfactant A include polyoxyethylene alkyl ether, holoxyethylene alkylphenol ether, sorbitan fatty acid ester, polyoxyethylene sorbicun fatty acid ester, polyoxyethylene acyl ester, oxyethylene oxypropylene block copolymer, and sucrose. One or more types selected from nonionic surfactants or anionic surfactants such as fatty acid esters, higher alcohol sulfate ester salts, alkylbenzene sulfonates, or polyoxyethylene sulfate salts can be used. can.

Among these, water-soluble or water-dispersible nonionic surfactants having an HLB of 7 or more are particularly preferred in the present invention.

The amount of water-soluble and/or water-dispersible surfactant A used in the present invention is in the range of 0.01 to 10 parts by weight based on 100 parts by weight of acrylate monomer B. Things are good.

The amount of water-soluble and/or water-dispersible surfactant A used is 0.
If the amount is less than 1 part by weight, the compatibility between the aqueous solution of acrylate monomer B and crosslinkable monomer C will be poor, and a uniform crosslinked polymer will not be obtained. becomes lower.

Moreover, the gel-like hydrous polymer obtained has a high stickiness, which makes it difficult to release it from the polymerization container.

In addition, the workability during cutting in the pretreatment process for heating and drying the gel-like hydropolymer or when molding with an extruder, etc. is poor, and as a result, it is susceptible to mechanical crosstalk due to adhesiveness, resulting in the cutting of molecules, etc. This causes a decrease in physical properties, resulting in a decrease in absorption capacity.

Furthermore, when a gel-like hydrous polymer is made into a powder after heating and drying, dust easily accumulates, and the initial absorption rate for aqueous substances is low.

Also, when molded into an absorbent sheet, caking occurs easily due to moisture absorption.

On the other hand, if the amount exceeds 10 parts by weight, surfactant A will be removed during polymerization.
The molecular weight of the main chain of the crosslinked polymer decreases due to chain transfer to the crosslinked polymer, and the resulting gel-like hydrous polymer becomes soft and difficult to handle.

Moreover, when it is made into a powder after being heated and dried, its absorption capacity is reduced when it comes into contact with an aqueous substance.

The water-soluble and/or water-dispersible surfactant A is completely dissolved or finely emulsified and dispersed in the aqueous solution of the acrylate monomer B before polymerization.

Then, crosslinkable monomer C, which has poor compatibility with the aqueous solution of acrylate monomer B, is solubilized in the aqueous solution of acrylate monomer B, and crosslinkable with acrylate monomer B. Monomer C
It has the effect of increasing the copolymerization reactivity with the polymer and causing uniform crosslinking.

As the polymerization progresses, such surfactant A
The resulting gel-like hydropolymer undergoes phase separation and becomes a milky-white, uniformly dispersed state.

Fine particles or droplets of surfactant A are present on the surface and inside of the obtained gel-like hydropolymer.

This reduces the amount of adhesion of the hydrogel polymer to the polymerization vessel it comes in contact with, and the mold releasability is greatly improved.

Furthermore, when cutting or molding a gel-like hydropolymer, if it comes into contact with a metal cutter, kneader, screw, or nozzle, or if a new cut surface is formed by cutting, fine surfactant particles or Because the micro droplets are uniformly present inside the gel-like hydropolymer, it always has good mold releasability, and even when the gel-like hydropolymer is subjected to mechanical crosstalk, slippage occurs and molecular chain scission occurs. Deterioration is less likely to occur, and as a result, when the crosslinked polyacrylic acid alkali metal salt obtained is used as a water absorbing agent, the decrease in absorption capacity is significantly smaller than when surfactant A is not used.

The acrylate monomer B used in the present invention contains 0 to 50 mol% of acrylic acid and 50 to 50 mol% of an alkali metal acrylate.
It consists of 100 mol%.

If the proportion of the alkali metal acrylic acid salt is less than 50 mol %, the resulting gel-like hydropolymer will have a high stickiness, making it impossible to produce a water absorbing agent with good workability.

From the viewpoint of the safety of the water-absorbing agent of the present invention against human skin, it is preferable that the acrylate monomer B consists of 10 to 40 moles of acrylic acid and 60 to 90 moles of an alkali metal acrylate. .

If the composition is within this range, the pH value of the resulting water-absorbing agent when it comes into contact with an aqueous liquid to be absorbed will be within a safe range for human skin, and it can be suitably used as a water-absorbing agent.

As the acrylic acid used in the present invention, commercially available acrylic acid can be used.

Also, if necessary, a part of the acrylic acid can be replaced with another water-soluble polymerizable carboxylic acid such as methacrylic acid.

As the alkali metal of the alkali metal acrylate salt, commonly used alkali metals such as lithium, sodium, potassium, etc. can be used.

In particular, regarding sodium, sodium polyacrylate is approved as a food additive, and is preferable from a safety point of view.
).

The crosslinkable monomer C used in the present invention has at least two polymerizable double bonds in one molecule, and is compatible with the acrylate monomer B and surfactant A in an aqueous solvent. It is essential that it be soluble, have good copolymerizability with acrylate monomer B, and form a crosslinked structure efficiently.

Such crosslinking monomers include ethylene glyco-
diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, penta One or more selected from erythritol trimethacrylate, N,N'=methylenebisacrylamide, triallyl incyanurate, pentaerythritol diacrylate, pentaerythritol dimethacrylate, etc. can be used.

The amount of crosslinkable monomer C used in the present invention is 0.001 to 5 parts by weight per 100 parts by weight of acrylate monomer B.
It is necessary that the proportions be in the range of parts by weight.

If the amount of crosslinkable monomer C used exceeds 5 parts by weight, the crosslinking density will become too high, and the absorption capacity will decrease.

On the other hand, if the amount is less than 0.001 parts by weight, the crosslinking density is too low, resulting in stickiness when it comes into contact with the liquid to be absorbed, and the initial absorption rate is also low.

In the absorbent of the present invention, the amount of crosslinkable monomer C used is 0.001 to 5 parts by weight per 100 parts by weight of acrylate monomer B.
parts by weight, and thus a relatively small amount of crosslinking monomer C
Even when using surfactant A in combination with aqueous solution copolymerization at high concentration, it is possible to copolymerize uniformly and efficiently with acrylate monomer B, resulting in a crosslinked polymer with a uniform crosslinked structure. .

When performing aqueous copolymerization according to the present invention, acrylate monomer B, crosslinkable monomer C, and surfactant A may be mixed in a conventional manner or in any order prior to polymerization.

Moreover, other components can be added and used in combination as necessary.

Examples of such other components include polyhydric alcohols such as diethylene glycol and glycerin.

If such a polyhydric alcohol is used in combination, crosslinking is also carried out by the reaction between the carboxyl groups in the polymer and the polyhydric alcohol at the stage of heating and drying the resulting gel-like hydrous polymer.

That is, it is also possible to coexist crosslinking by the crosslinkable monomer C and crosslinking by a polyhydric alcohol in the crosslinked polymer.

The aqueous solution polymerization method employed in the present invention involves uniformly mixing the water-soluble and/or water-dispersible surfactant A, the acrylate monomer B, the crosslinkable monomer C1, and the initiator. A method in which an aqueous solution or aqueous dispersion containing a mixture of acrylate monomer B and crosslinkable monomer C at a concentration of 25% by weight or more is subjected to bulk polymerization or cast polymerization in a nitrogen atmosphere is preferred.

In order to eliminate heat generated by polymerization and to easily control the reaction temperature, it is preferable to carry out the polymerization in a closed container with a relatively large heat transfer area.

For such aqueous solution polymerization, for example,
The polymerization vessel described in Japanese Patent No. 42466 is suitable.

When the monomer concentration during polymerization is less than 25% by weight, the molecular weight of the main chain of the crosslinked polymer is difficult to increase, and therefore the water-soluble content of the resulting absorbent increases and the initial absorption rate decreases.

The initiator used in the aqueous solution polymerization is not particularly limited as long as it is a common water-soluble radical generating initiator.

Examples include ammonium persulfate, potassium persulfate, hydrogen peroxide, etc., and redox initiators made by combining these with reducing agents such as sodium bisulfite, t-ascorbic acid, and ferrous salts are also used. It will be done.

Regarding the polymerization temperature during polymerization, a relatively low temperature is preferable because it increases the molecular weight of the main chain of the crosslinked polymer obtained, but in order to complete the polymerization, it should be within the range of 10 ° C. or higher and 80 ° C. or lower. is preferred.

When drying by heating the gel-like hydropolymer of the crosslinked polymer obtained by aqueous solution copolymerization based on the present invention, it is desirable to dry it as efficiently and in a short time as possible to prevent deterioration due to excessive heat.

As such a drying method, the surface area per unit volume is reduced to 9 cr by cutting or extruding the gel-like hydrous polymer.
After subdividing into ri2/crrt” or more,
Particularly preferred is a method of drying by heating with hot air at a temperature of 100 to 230°C.

In the present invention, after polymerizing a mixed aqueous solution of acrylate monomer B and crosslinkable monomer C without using a surfactant, a surfactant is added at the stage of forming a gel-like hydropolymer. If it is added, uniform copolymerization and crosslinking of acrylate monomer B and crosslinkable monomer C cannot be carried out.

Furthermore, it is impossible to uniformly distribute the surfactant into the interior of the gel-like hydrous polymer, and therefore it is impossible to prevent sticking during cutting or extrusion and to prevent deterioration due to crosstalk.

Furthermore, even if the obtained crosslinked polymer is powdered, the surfactant is not uniformly distributed in such powder, and it is difficult to improve dust generation or to reduce the ” cannot be expected to be effective in preventing occurrence.

The alkali metal salt polyacrylic acid crosslinked product obtained in this way is used as an absorbent in various forms such as powder, granules, and coarse granule tubes, but when used as a powder, it has particularly excellent initial absorbency. Shows high absorption capacity.

There are no particular restrictions on the method of pulverization, and conventionally known methods can be used as appropriate.

In the heat-dried gel-like hydropolymer obtained by aqueous solution copolymerization in the present invention, fine particles or droplets of surfactant A are uniformly dispersed on the surface and inside.
Can be crushed in a short time.

In addition, even if fine powder is generated in this pulverization process, the fine powder tends to aggregate in longitude due to the fine particles or fine droplets of surfactant A that are uniformly dispersed on and inside the particles. Therefore, it has the advantage of not accumulating dust.

The water-absorbing agent of the present invention is composed of the alkali metal salt cross-linked polyacrylic acid obtained in this way, and has superior performance compared to conventionally known absorbent resins. can be considered as follows.

In other words, since aqueous solution copolymerization is carried out at a relatively high concentration to form a gel-like hydropolymer, the degree of polymerization is high.Furthermore, crosslinking is carried out moderately efficiently and uniformly, so that the water-soluble content contained in the water-absorbing agent is extremely low. In addition, it has a high degree of swelling when absorbing aqueous substances.

Therefore, it is less sticky and has a high initial absorption rate and a high saturated absorption amount.

In addition, since there is almost no water-soluble content, there is little irritation when it comes into contact with human skin, and when the water-absorbing agent comes into contact with aqueous substances, the pH value of the system can be adjusted to a safe range, which improves safety. This is preferable.

Furthermore, since the polymerization is carried out in the presence of surfactant A, the relatively hydrophobic surfactant A is evenly distributed on the powder particle surface, resulting in a high initial absorption rate and a high initial absorption rate. Even when fine powder is generated during the pulverization process when used as a powder, the fine powders are slightly agglomerated together, so dust is less likely to be generated, and caking is less likely to occur even when humidity is high.
Excellent workability when processing water absorbing agents into absorbent sheets 1st grade,
Does not harm the working environment.

And when the water-absorbing agent powder comes into contact with an aqueous substance, it is less likely to become lumpy.

In addition, the water absorbing agent of the present invention has very high heat resistance, and even if it is heated when processed into an absorbent sheet or the like, there will be no deterioration in absorption capacity or change in quality.

Furthermore, the water absorbing agent of the present invention does not contain any impurities such as organic solvents or inorganic salts.

As described above, the water-absorbing agent of the present invention has excellent performance, and can be manufactured industrially with high productivity, so it can be supplied at a relatively low cost. Therefore, it can be used as a water-absorbing agent for sanitary cotton and disposable diapers Absorption capacity per price will be dramatically improved.

The water-absorbing agent of the present invention can be used for a wide range of purposes; for example, when used as a water-absorbing agent for sanitary cotton, disposable diapers, etc.
Because it quickly absorbs menstrual blood, urine, and other body fluids, and also absorbs a large amount of liquid, the absorbed liquid hardly oozes out even after long-term use or when pressure is applied.

At this time, the water absorbing agent may be used as it is in the form of powder or granules, or may be formed into a sheet.

The water-absorbing agent can be formed into a sheet by stacking multiple sheets of paper or non-woven fabric, scattering the water-absorbing agent powder between them to form a sandwich shape, and then pressing it with an embossing roll or the like; There is a method in which the mixture is mixed with pulp cotton that has been pulverized into short fibers and pressed together, and a method in which the mixture is mixed with pulp cotton and pressed and then further sandwiched between paper or nonwoven fabric to form a sandwich.

Furthermore, in these sheet-form press-bonding methods, water or steam, a low-melting thermoplastic resin, an adhesive resin, or the like can be used in combination as a binder.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the scope of the present invention is not limited by these Examples.

Example 1 5US2 whose inner surface was lined with 47 fluoride ethylene resin
7 made 300m71LX300mlLX501117
In an openable and closable airtight container with an internal volume of Add the indicated amounts of various crosslinking monomers C and surfactant A, and bring the temperature of the solution to 4.
After the temperature was lowered to 0°C, 0.61% of ammonium persulfate and 0.21% of sodium bisulfite were added and uniformly dissolved.

Polymerization proceeded slowly and became a cloudy gel with the generation of heat.

The temperature of the reaction system became 55 to 80°C 2 to 5 hours after the start of polymerization.

After 7 hours from the start of polymerization, the sealed container was opened and the gel-like hydrous polymer produced was taken out.

Then, each of the gel-like hydrous polymers taken out was cut into a 1m71L square using a steel cutter.

Next, the cut 1 mm square gel-like hydropolymer was cut into pieces, each with a contact part made of 5US32 and a screw diameter of 3077J.
Using a screw extruder with L/D=17 and a screw rotation speed of 45 rpm, it was extruded from a perforated nozzle with a diameter of 1.5 to obtain a string-like gel with a diameter of about 2 threads.

The surface area per unit volume of this string-like gel is approximately 20 dΔ
It was thin 3.

This string-like gel was dried in a hot air dryer at 180° C. for 90 minutes to obtain alkali metal acrylate crosslinked polymers (crosslinked polymers 1 to 4).

Each of the obtained crosslinked polymers was made into powder using a vibrating pulverizer.

Transfer 0.21 of this powder to a non-woven tea bag type bag (40
mm x 150 mrrt), immersed in 0.9% saline, and weighed 3 minutes and 5 minutes later, respectively.

Using the absorbed weight of only the tea bag type bag as a blank, the swelling ratio of the crosslinked polymer was determined according to the following formula.

The results are shown in Table 1. Weight after absorption (Me-Blank F
) Swelling ratio -□ Weight of powder ('?) 20 g of the obtained powder was placed in a 1001 nZ glass sample bottle, and after shaking for a certain period of time, dust generation was examined.

The results are also shown in Table 1. All of the water-absorbing agents of the present invention exhibited excellent initial absorbency, and the swollen gel formed by the water-absorbing agent powder absorbing the liquid to be absorbed was not sticky.

In addition, there is almost no dust generation, and the pH of a single-width aqueous dispersion of these crosslinked polymers is 7.0, and the pH of a single-width aqueous solution of commercially available high molecular weight sodium polyacrylate is 9.6. It showed a pH value that is safer for human skin than that of

Comparative Example 1 A polymer (comparative polymer 1) was obtained in the same manner as in Example 1, except that crosslinkable monomer C was not used.

This Comparative Polymer 1 contained a large amount of soluble matter even after being made into a powder, and as shown in Table 1, its absorption capacity was low, making it unsuitable as a water-absorbing agent.

Comparative Example 2 A polymer (comparative polymer 2) was obtained in the same manner as in Example 1 except that surfactant A was not used.

In Comparative Polymer 2, the crosslinkable monomer C was not uniformly dissolved in the pre-polymerization stage, and it deteriorated due to mechanical crosstalk in the post-polymerization stage, so the absorption capacity was poor as shown in Table 1. It was low, and the dust generation of the powder was also high.

Comparative Example 3 The proportion of sodium acrylate in the acrylate monomer A was 40 mol and the crosslinkable monomer B was set, and the addition rate of pentaerythritol trimethacrylate was 0.1 part (based on 100 parts of monomer). As surfactant A, 1 part of "Neoperex 05" manufactured by Kao Atlas ■ (100%
Polymerization was attempted in the same manner as in Example 1, except that part) was used.

However, since polymerization did not start, rapid polymerization occurred when the temperature of the system was raised to 60"C.

Furthermore, when the swelling ratio of the powder obtained in the same manner as in Example 1 in 0.9% saline solution was measured, it showed a small value of 24 times in 3 minutes and 26 times in 5 minutes.

Furthermore, the pH of this 1% aqueous powder dispersion was as low as 5.2.

Example 2 Physiological cotton was prepared using the powders of crosslinked polymers 1 and 3 obtained in Example 1 as water absorbing agents, and the absorbent capacity was measured.

Do you want to uniformly disperse the powder of crosslinked polymer 1 or 3 between two sheets of absorbent paper? /i absorbent paper) and pressed with an embossing roll to create an absorbent sheet.

Cut this sheet into 6c1rL x 16cm, absorbent sheet, absorbent paper, cotton valve and polyethylene laminate I.
・Overlap the ends one after another, wrap the whole thing with non-woven fabric, and crimp both ends to make a total of 60'? (Physiological cotton 1 and 2)
) The sanitary cotton was placed on a 10-mesh wire mesh of known weight with the use side up, tap water was poured for 5 minutes, the needle was tilted for 1 minute, and then the weight was measured.

25'i on sanitary cotton that has absorbed water again? The weight after applying a pressure of /d was measured.

All results are shown in Table 2.

For comparison, the absorbent capacity was similarly measured for sanitary cotton (comparison sanitary cotton) which was prepared in the same manner without using an absorbent sheet, but with absorbent paper added instead, and the total amount was 6.0 y.

As shown in Table 2, the sanitary cotton using the water-absorbing agent of the present invention has excellent absorbency and excellent water retention even under pressure.

Claims (1)

[Claims] 1. In the presence of water-soluble and/or water-dispersible surfactant A,
Acrylate monomer B consisting of 0 to 50 mol % of acrylic acid and 50 to 100 mol % of an alkali metal acrylic salt
A mixture of 100 parts by weight and 0,001 to 5 parts by weight of the crosslinkable monomer C is copolymerized with an aqueous solution at a concentration of 25% by weight or more to obtain a gel-like hydropolymer, and the resulting polyester is further heated and dried. A water absorbing agent made of a crosslinked alkali metal acrylic acid salt. 2 The amount of surfactant A used is acrylate monomer B1
The water-absorbing agent according to claim 1, wherein the amount is in the range of 0.01 to 10 parts by weight to 0.00 parts by weight. 3. The water absorbing agent according to claim 1 or 2, wherein surfactant A is a water-soluble and/or water-dispersible surfactant and a nonionic surfactant with an HLB of 7 or more. 4. Claim 1, 2 or 3, wherein the acrylate monomer B consists of 10 to 40 mol% of acrylic acid and 60 to 90 mol% of an alkali metal acrylate. water absorbing agent.