JPH04202541A - Composite absorbent and its production - Google Patents

Abstract

PURPOSE:To obtain a composite absorbent resistant to twist, having excellent absorption performance and feeling and useful for paper diaper, etc., by impregnating a cellulosic sponge with an aqueous solution of a water-absorbing polymer and a crosslinking agent or a self-crosslinking polymer and heating the impregnated product. CONSTITUTION:The objective composite absorbent suitable as an absorbent of paper diaper, etc., is produced by (1) impregnating a cellulosic sponge having an absorption ratio of >=5 and a water-content of 50-300wt.% with an aqueous solution of a water-absorbing polymer (preferably salt of a copolymer of acrylic acid and methyl acrylate) and a crosslinking agent (preferably diglycidyl ethers) or an aqueous solution of a self-crosslinking polymer and (2) heating the impregnated product at >=50 deg.C to crosslink the polymer. The amount of the crosslinked polymer attached to the matrix of the cellulosic sponge is <=100wt.%, preferably 10-100wt.%, more preferably 10-70wt.% based on the cellulosic sponge.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a composite absorbent material, and more specifically, the present invention relates to a composite absorbent material, and more specifically, a cellulose sponge is impregnated with an aqueous solution of a polymer and a crosslinking agent, or a self-crosslinking type polymer aqueous solution, and then crosslinked. A polymeric substance attached to a sponge matrix prevents the absorbent material from twisting during use, uneven distribution of the polymer, and falling off.It also has excellent absorption capacity and texture, and is suitable for absorbing sanitary napkins, disposable diapers, etc. The present invention relates to a composite absorbent material that can be suitably used as a body. [Prior Art] Conventionally, fluff pulp, absorbent paper, nonwoven rayon fabric, etc. have been used as materials for absorbent materials such as sanitary napkins and disposable diapers. Absorbent polymers are used that can absorb hundreds of times more water. Since this absorbent polymer is generally in the form of granules, it is often used by sandwiching it with absorbent paper or by mixing it into fluff pulp. However, since absorbent bodies made of these materials are made of intertwined fibers, the absorbent body may twist during use, resulting in leakage of liquids such as blood and urine. Furthermore, when a granular polymer is used, there are drawbacks such as the polymer becoming unevenly distributed due to body movements, resulting in a decrease in absorption capacity, and the gel-like polymer falling off after absorbing liquid.

In order to improve these drawbacks, many proposals have been made to prevent the absorber from twisting and the polymer from becoming unevenly distributed and falling off. For example, Japanese Patent Application Laid-Open No. 56-97448 proposes a method of interposing flat pulp and polymer in the voids of the foam to prevent the absorbent from twisting and the polymer from falling off. This method is still insufficient and has the disadvantage of slowing down the manufacturing process. Furthermore, JP-A-59-204975 discloses a method in which a water-soluble monomer that can be converted into a water-absorbing polymer, such as (meth)acrylic acid or a salt thereof, is applied to a cellulose fiber base material and then polymerized. It is presented. However, since this material is a fiber-based material, there are still problems such as the absorbent material twisting when used, the capillary tubes between the fibers becoming smaller, reducing the absorption rate, and poor texture. .

[Problem to be solved by the invention]

The present invention overcomes the drawbacks of the prior art, and provides a composite absorbent material that does not cause uneven distribution of absorbent polymers, prevents the polymers from falling off during use, and has excellent absorbent performance and texture.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies and found that a composite absorbent material in which a water-absorbing polymer is attached to a cellulose sponge matrix can prevent the absorbent material from twisting during use and the uneven distribution of the polymer. The present inventors have also discovered that it has excellent absorption performance and texture, and have completed the present invention.

That is, according to the present invention, a composite absorbent body is provided in which a cellulose sponge matrix is impregnated with a water-absorbing polymer (hereinafter simply referred to as polymer).

In the present invention, the cellulose sponge refers to a sponge made of a material having a cellulose skeleton, and includes sponges made of cellulose itself,
Cellulose derivatives, e.g.

There are sponges made of viscose, cellulose ethers, cellulose esters, etc., or sponges made of mixtures thereof. Such a sponge, for example, a viscose sponge, is manufactured as follows.

First, cellulose is made into alkali cellulose with an alkali, then sulfurized with carbon dioxide to produce cellulose xanthate, and further a sodium hydroxide solution is added to prepare viscose. Glauber's salt is added to viscose, which is a dissolved product of cellulose, solidified by heating, washed with water, treated with dilute sulfuric acid solution, washed again with water, further neutralized with soda carbonate, washed with water, dried, and made into viscose. , Sponge.

The cellulose sponge used in the present invention has a density of 0.01-0.8 g/am' when uncompressed, and a compression deformation rate of 10 to 60% under a load of 45 g/an2.
shows.

The water-absorbing polymers to be attached to the matrix of the cellulose sponge used in the present invention include polyacrylates, polymethacrylates, salts of copolymers of acrylic acid and methacrylic acid, and salts copolymerizable with (meth)acrylic acid. There are salts of copolymers with monomers, etc.

As copolymerizable monomers, (
There is no particular restriction as long as it becomes water-soluble by neutralizing the meth)acrylic acid moiety, such as (meth)acrylamide, dimethyl(meth)acrylamide, alkoxypolyethylene glycol (meth)acrylate, vinylpyrrolidone,
Maleic acid, fumaric acid, crotonic acid, itaconic acid, styrene sulfonic acid, acrylamide propane sulfonic acid,
Examples include vinyl acetate and (meth)acrylic acid ester.

In the case of hydrophobic monomers such as vinyl acetate and (meth)acrylic acid ester, the copolymerization ratio thereof is preferably 75 mol% or less. Furthermore, when copolymerizing (meth)acrylic acid ester, methyl ester and ethyl ester are preferred for the same reason.

Among the above polymers, polyacrylates, salts of copolymers of acrylic acid and methyl acrylate, and salts of copolymers of acrylic acid and ethyl acrylate are preferred in terms of absorption performance and texture of the resulting composite absorbent. Preferred are salts of copolymers of acrylic acid and methyl acrylate.

The amount of polymer attached should be 1% to the weight of the cellulose sponge, considering the absorption performance and texture of the composite absorbent material.
00% or less, preferably 10-100%, more preferably 10-70%.

The crosslinking agent used in the present invention is not particularly limited as long as it is a bifunctional compound that is water-soluble and reacts with carboxylic acid, and includes diglycidyl ethers such as ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether, and ethylene diamine. , propylene diamine,
Polyamines such as diethylenetriamine, polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol are used, but diglycidyl ethers are preferred.

The amount of crosslinking agent used is 0.2 to 3% by weight based on the polymer.
, preferably 0.5 to 2% by weight.

The self-crosslinking water-soluble polymer used in the present invention includes (
meth)acrylic acid and hydroxyethyl (meth)acrylate, polyethylene glycol (meth)acrylate,
Glycidyl (meth)acrylate, methylol (meth)
Examples include salts of acrylamide or copolymers with butoxymethyl (meth)acrylamide.

The copolymerization ratio of (meth)acrylic acid and comonomer is (meth)acrylic acid/comonomer = 8/2-2-8 (molar ratio), preferably 7/3-3-7 (molar ratio). .

Among the above polymers, acrylic acid and hydroxyethyl (
meth)acrylate or polyethylene glycol (
A copolymer with meth)acrylic acid is preferred, and a copolymer of acrylic acid and hydroxyethyl (meth)acrylate is particularly preferred.

The salts of the polymer used in the present invention include alkali metal salts,
The neutralization rate of ethanolamines is not particularly limited and is determined in consideration of absorption performance, but is usually 50 mol% or more, preferably 60 to 80 mol%.

When the above polymer is used in the production of the composite absorbent body of the present invention, ethylene glycol, glycerin, polyethylene glycol, etc. may be used in combination as a plasticizer. The above polymer is manufactured by known solution radical polymerization. The appropriate molecular weight of the polymer used is 5,000 to 200,000. If the molecular weight is too small, the absorption performance of the composite absorbent will be insufficient, and if the molecular weight is too high, when impregnating a cellulose sponge with an aqueous polymer solution, the polymer concentration must be lowered from the viewpoint of workability, resulting in problems. It becomes the economy.

To obtain the composite absorbent of the present invention, for example, a cellulose sponge whose water content has been adjusted in advance to 50-300% by weight is impregnated with an aqueous solution of a polymer and a crosslinking agent or an aqueous solution of a self-crosslinking polymer, and heated to a temperature of 50°C or higher. Just be silent.

By this method, a composite absorbent body in which cellulose fibers and absorbent polymer are integrated can be suitably produced.

The cellulose sponge used in the present invention preferably has a water content of 50-300%. If the water content is less than 50%, the penetration of the polymer into the interior of the cellulose sponge will be insufficient, and the absorbent performance of the composite absorbent will deteriorate, which is not preferable. Furthermore, if the water content exceeds 300%, no improvement in the absorption performance of the composite absorbent material will be observed, and on the contrary, a disadvantage arises in that the drying process requires a long time, which is undesirable.

The heating temperature needs to be 50° C. or higher to promote the crosslinking reaction. The suitable heat treatment temperature varies depending on the crosslinking method of the polymer used, but is 50 to 100°C for a system using a combination of an aqueous polymer and a crosslinking agent, and 80 to 120°C for a system using a self-crosslinking type polymer.

If the heating temperature is less than 50°C, the crosslinking reaction will not occur, which is not preferable. Furthermore, if the temperature exceeds 120°C, the cellulose sponge will deteriorate, which is not desirable.

The time required to cause the crosslinking reaction varies depending on the heating temperature and the moisture content of the cellulose sponge, but it is from 30 minutes to
2 hours. The heating treatment method is not particularly limited, and a drum dryer, hot air dryer, etc. can be used.

In addition, in the present invention, the method of impregnating a cellulose sponge with an aqueous solution of Volize and a crosslinking agent or an aqueous solution of a self-crosslinking type polymer is not particularly limited. Any method can be used as long as the amount of polymer impregnated can be controlled, such as a method of extruding an aqueous solution or a method of immersing a cellulose sponge in an aqueous polymer solution and then squeezing it through a drum to a predetermined amount.

C Effects of the Invention] Since the composite absorbent body of the present invention impregnates the matrix of the cellulose sponge with a water-absorbing polymer, there is no twisting of the absorbent body, and uneven distribution and shedding of the polymer can be prevented.
Moreover, it has excellent absorption performance and texture. Therefore, the composite absorbent material of the present invention is suitably used as an absorbent material for sanitary napkins, disposable diapers, and the like.

〔Example〕

Next, embodiments of the present invention will be described in detail.

[Production Example-1] Into an IQ five-piece separable flask equipped with a stirrer, nitrogen inlet tube, reflux condenser, and thermometer, add 2 ounces of ion-exchanged water.
]0.5g was added, nitrogen was introduced for 20 minutes while stirring, and then heating was started using an oil bath. Internal temperature is 9
When the temperature reached 0°C, a solution of 9.54 g of sodium hypophosphite (I hydrate) dissolved in 216 g of 80% acrylic acid and a solution of 4.08 g of potassium persulfate dissolved in 100 g of ion-exchanged water were added. Each was added dropwise over 3 hours using a metering pump to perform polymerization. 95-100 after completion of dripping
The polymerization was completed by aging at ℃ for 2 hours. After cooling to 70° C., a solution of 96.8 g of sodium hydroxide (93%) dissolved in 135 g of ion-exchanged water was added to perform neutralization.

The obtained polymer aqueous solution had a solid content of 36% and a pH of 5.5.
, the viscosity was 32θcp, and the weight average molecular weight of the obtained polymer was 10,000.

[Production Example-2] Add 3 parts of ion-exchanged water to an IQ 5-piece separable flask equipped with a stirrer, nitrogen inlet tube, reflux condenser, and thermometer.
Add 2g and 128g of methanol, and add 2g while stirring.
After introducing nitrogen for 0 minutes, heating was started using a 75°C water bath. When the internal temperature reached 60°C, a monomer solution of 108 g of 80% acrylic acid and 103.2 g of methyl acrylate dissolved in 10.4 g of ion-exchanged water and 128 g of methanol was added; 2. An initiator solution in which 1.30 g of barazobisamidinopropane hydrochloride was dissolved in 10 g of ion-exchanged water and 40 g of methanol was added dropwise over 3 hours using a metering pump to effect polymerization.

After the dropwise addition was completed, the mixture was further stirred for 2 hours in a water bath at 75°C and then aged to complete the polymerization. After cooling to 30° C., a solution of 54.9 g of monoethanolamine dissolved in 83.5 g of ion-exchanged water was added to perform neutralization.

The obtained polymer aqueous solution had a solid content of 36.1% and a viscosity of 6.
80 cP, and the weight average molecular weight of the obtained copolymer is
It was 15,000.

[Production Example-3] Add 4 quarts of ion-exchanged water to an IQ 5-piece separable flask equipped with a stirrer, nitrogen inlet tube, reflux condenser, and thermometer.
Add 1 g and 164 g of methanol, and add 2.
After introducing nitrogen for 0 minutes, heating was started using a 75°C water bath. When the internal temperature reaches 60°C, add 90g of 80% acrylic acid and 11 2-hydroquine ethyl acrylate.
6g and a monomer solution in which 72g of methanol was uniformly dissolved; 2. Barazobisamidinopropane hydrochloride 1.0
An initiator solution in which 8 g was dissolved in 10 g of ion-exchanged water and 40 g of methanol was prepared using a metering pump.
The mixture was added dropwise over 3 hours to carry out polymerization. After the dripping is finished,
Stirring was further continued for 2 hours in a water bath at 75°C to effect aging and complete polymerization. After cooling to 30° C., a solution of 28 g of sodium hydroxide (93%) dissolved in 252 g of ion-exchanged water was added to perform neutralization.

The obtained polymer solution had a solid content of 26.0% and a viscosity of 96.
It was 0 cp.

[Example-1] A cellulose sponge (weight 4.3 g) cut into 7aaXI4cm and 1-thickness was immersed in ion-exchanged water, and then the water content was adjusted to 100% using a hand-cranked drum.

3゜g of the sodium polyacrylate aqueous solution obtained in Production Example-1
-ethylene glycol diglycidyl ether 0
．． Ig was added, and 79 g of ion-exchanged water was added to dilute. (Solid content concentration 1O%) Place a vat on a balance and place a wet cellulose sponge in the vat. A mixed solution of Na polyacrylate and ethylene glycol diglycidyl ether was placed in a sprayer, and while measuring the weight, log was sprayed onto the surface of the cellulose sponge so as to be as uniform as possible.

Next, the composite absorbent was kept in a hot air dryer at 80° C. for 3 hours to obtain a composite absorbent in a dry state. The absorption performance of the obtained composite absorbent body was measured according to the following test method, and the absorption amount was 51 g, the reversion amount was Ilg, and the absorption rate was 6 seconds.

On the other hand, the absorption performance of cellulose sponge alone without polymeric impregnation is: Hlg, 18g, 12g, respectively.
It was seconds.

Approximately 2Q of physiological saline is placed in a stainless steel vat with an absorption capacity of 23cm x 30an, and the weighed composite absorbent body is immersed therein.

A 1oool x 20c11 3m thick acrylic plate is placed on top of the composite absorbent body, and a weight is placed on top of the composite absorbent body, so that a total load of 45 g/am2 is applied to the composite absorbent body. After being immersed for 5 minutes, the sample was taken out and placed on an 8-mesh wire mesh for 3 minutes to drain water, then the weight was measured, and the weight before immersion was subtracted to obtain the absorbed amount.

30g of return volume physiological saline was absorbed into the composite absorbent material, left for 2 minutes, placed 30 sheets of No. 2 filter paper cut into 30-mouth corners, placed a weight to give a load of 45g/aa2, and left for 2 minutes. The amount of liquid absorbed by the filter paper was measured and determined as the amount of liquid returned.

Z in the center of an acrylic plate with an absorption rate of 5cm x 16an and a thickness of 3ao
Drill a hole mXIO- and attach a cylinder with an inner diameter of 2 am and a height of lO-. Place this device so that the opening of the acrylic plate is in the center of the composite absorbent body, and pour 20 tnQ of physiological saline into the cylindrical part at once. Using a stopwatch, pour the physiological saline completely into the composite absorbent body. The time taken for the substance to be absorbed was measured and defined as the absorption rate.

A composite absorbent material adjusted to a texture of 10cm x IOcm and a thickness of 3 lbs was evaluated by sensory evaluation.

[Example-2] Take 30 g of the copolymer solution obtained in Production Example-2,
0.16 g of ethylene glycol diglycidyl ether was added, and 126 g of ion-exchanged water was added to dilute the mixture (solid content concentration: 7%). This solution was put into a sprayer, and a composite absorbent body was obtained in the same manner as in Example-1. However, the weight of the cellulose sponge used was 4.5 g, and the amount of the sprayed solution was 15 g.

The absorption performance of the obtained composite absorbent body was an absorption amount of 52 g, a reversion amount of 12 g, and an absorption speed of 7 seconds.

[Example-3] Take 20 g of the copolymer solution obtained in Production Example-3,
Diluted by adding 84 g of ion-exchanged water (solid content concentration 5%).
). This solution was put into a sprayer to obtain a composite absorbent according to Example-1. However, the weight of the cellulose sponge used was 4.2 g, the amount of the sprayed solution was 20 g, and the treatment conditions in the hot air dryer were 120° C. for 1 hour.

The absorption performance of the obtained composite absorbent body was that the absorption amount was 50 g, the reversion amount was 11 g, and the absorption speed was 7 seconds.

[Example 4] A monoethanolamine salt of a copolymer was synthesized in the same manner as Production Example 2, except that 40 g of ethyl acrylate was used instead of the methyl acrylate used in Production Example 2.

A portion of the monoethanolamine salt solution of this copolymer was taken, 2vt% of ethylene glycol diglycidyl ether was added to the copolymer, and the mixture was further diluted with ion-exchanged water to form a spray with a solid content concentration of 7%. I got it. Using this solution, a composite absorbent body was produced in the same manner as in Example-1. However, the cellulose sponge used weighed 4.3g,
The amount of solution sprayed was 20 g.

The absorption performance of the obtained composite absorbent body was an absorption amount of 54 g, a reversion amount of 11 g, and an absorption speed of 7 seconds.

[Example 5] According to Production Example 3, copolymers were synthesized with different molar ratios of acrylic acid, 2- and droxyethyl acrylate, and the neutralization rate of the acrylic acid moiety. A composite absorbent body was produced in the same manner as in Example 3, and its absorption performance was measured. The results are shown in Table-1.

[Example-6] Take 80 g of the copolymer solution obtained in Production Example-3,
Diluted by adding 24g of ion-exchanged water (solid content 20%)
. After immersing a cellulose sponge in this solution, a composite absorbent body was produced in the same manner as in Example 3 by changing the amount of impregnation, and the absorbent performance and texture were evaluated. Table 2 of the results
Shown below.

Claims (3)

[Claims] (1) A composite absorbent material characterized by having a water-absorbing polymer attached to a cellulose sponge matrix. (2) A cellulose sponge with an absorption capacity of 5 times or more and a water content of 50-300% by weight is impregnated with an aqueous solution of a polymer and a crosslinking agent or an aqueous solution of a self-crosslinking polymer, and then heated to a temperature of 50°C or more. The method for producing a composite absorbent body according to claim (1). (3) The composite absorbent body according to claim (1), wherein the amount of the water-absorbing polymer attached is 100% or less based on the weight of the cellulose sponge.