JPS6222811A - Production of water-absorptive composite - Google Patents

Abstract

PURPOSE:To obtain a composite excellent in water absorptivity, handleability, etc., expensively, by applying an aqueous solution containing a (meth)acrylate salt, a crosslinking monomer having a plurality of double bonds and a radical polymerization initiator to a molded fibrous base and polymerizing the monomers. CONSTITUTION:An aqueous solution containing an alkali metal or ammonium salt of (meth)acrylic acid (A), a crosslinking monomer (B) having at least two double bonds in the molecule and being copolymerizable therewith (e.g., ethylene glycol diacrylate or diallyl phthalate) and a radical polymerization initiator (C) (e.g., t-butyl hydroperoxide) is prepared. This aqueous solution is applied to a molded fibrous base (e.g., paper or cotton gauze) and the component A is polymerized to form a highly water-absorptive polymer. In this way, the purpose water-absorptive composite is obtained. This composite can be suitably used for a variety of sanitary materials, soil conditioners, etc.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing a water-absorbing composite.

More specifically, an aqueous solution containing (meth)acrylic acid and/or an alkali salt of (meth)acrylic acid and a crosslinkable monomer is applied to the molded fibrous substrate, and polymerized in the presence of a radical polymerization initiator. , relates to a method for producing a water-absorbing composite in which a superabsorbent polymer is fixed to a molded fibrous substrate.

The water-absorbent composite obtained by the production method of the present invention has excellent water absorption and a high water absorption rate, and also has a high strength polymer gel that swells upon water absorption. Since it is stably fixed to the surface, it can be widely used in the production of various water-absorbing materials.

[Prior art]

Conventionally, paper, pulp, nonwoven fabric, sponge-like urethane resin, and the like have been used as water-retaining agents in various sanitary materials such as sanitary napkins and paper diapers, and in various agricultural materials. However, these materials absorb only 10 to 50 times their own weight of water, so in order to absorb or retain a large amount of water, a large amount of material is required.
Not only does it become extremely bulky, but it also has drawbacks such as the fact that when a material that has absorbed water is pressurized, the water easily separates.

In order to improve the above-mentioned drawbacks of this type of water-absorbing material, various highly water-absorbing polymeric materials have been proposed in recent years. For example, starch graft polymers (Japanese Patent Publication No. 53-46199, etc.), modified cellulose (Japanese Patent Publication No. 50-80376, etc.)
(Japanese Patent Publication No. 43-23), cross-linked water-soluble polymers (Japanese Patent Publication No. 43-23)
462, etc.), self-crosslinking type acrylic acid alkali metal salt polymers (Japanese Patent Publication No. 54-30710, etc.), and the like have been proposed.

However, although these superabsorbent polymer materials have a fairly high level of water absorption performance, most of them are obtained in the form of powder, so they cannot be used for example in sanitary napkins,
In order to use it in sanitary materials such as paper diapers, it is necessary to disperse it evenly onto a base material such as tissue, nonwoven fabric, or cotton.

However, it is difficult to stably fix the polymer powder dispersed by this method on the substrate, and it often aggregates locally after dispersion, and the swollen gel after water absorption also does not stably fix on the substrate. It is not fixed and easily moves from the base material and is stored away. For this reason, when used in paper diapers, for example, the absorbent material becomes "stiff" after urinating, making it extremely uncomfortable to wear. However, the above-mentioned method of dispersing powdered polymer in a base material to obtain an absorbent body is difficult.
The cost is extremely high due to the complexity associated with handling the powder and process problems in achieving uniform dispersion efficiently.

[Problem that the invention seeks to solve]

Recently, one method to solve these problems has been to manufacture a composite by applying an aqueous solution of acrylic acid monomer to a molded fibrous substrate in a predetermined pattern, and then irradiating this with electromagnetic radiation or particulate ionizing radiation. A method for producing a water-absorbing composite by converting an acrylic acid monomer into a superabsorbent polymer has been reported (Japanese Patent Publication No. 57-50054).
Publication No. 6). According to this method, the uniform dispersion and stable immobilization on the substrate when handling the above-mentioned powder are considerably improved, but when converting into a super absorbent polymer, electromagnetic radiation or fine particles Because ionizing radiation is used, the self-crosslinking reaction of the superabsorbent polymer is extremely easy to proceed, and as a result, its performance as an absorber, especially its water absorption capacity, is extremely low. There is a drawback that the amount is less than half compared to the case. In addition, it is difficult to say that this is an inexpensive method in terms of the safety and cost involved in handling the radiation generating device as described above.

[Means for solving problems]

(Object of the invention) The present invention improves the method for producing a water-absorbing composite described in Japanese Patent Publication No. 57-500546 and provides a method for producing a water-absorbing composite with even better water-absorbing performance. That is.

As a result of various studies aimed at solving the above-mentioned problems, the present inventors discovered that by polymerizing acrylic acid-based monomers, a water-absorbing composite with significantly improved water-absorbing performance can be obtained. , the present invention has been achieved.

(Structure of the Invention) That is, the method for producing a water-absorbing composite of the present invention uses an alkali metal salt or ammonium salt of acrylic acid and/or methacrylic acid. ) is applied to a molded fibrous substrate, and then an acrylic acid monomer is polymerized to produce a water-absorbent composite consisting of a superabsorbent polymer and a molded fibrous substrate. This is a method for producing a water-absorbing composite characterized by using a crosslinkable monomer having two or more double bonds in a molecule copolymerizable with a monomer and a radical polymerization initiator.

(Background and Features of the Invention) The method for producing the water-absorbing composite of the present invention is disclosed in Japanese Patent Publication No. 57-500.
This is an improved method of the method described in Publication No. 546, and both methods have many things in common in terms of the monomers used, the fibrous substrate, and the method of impregnating the fibrous substrate with an aqueous monomer solution. There is no essential difference in this respect.

However, when a crosslinkable monomer having two or more double bonds is present in a molecule that can be copolymerized with a Kinesulfuric acid monomer,
The purpose is to carry out polymerization using a water-soluble radical polymerization initiator. To this end, the production method of the present invention can yield a polymer with significantly superior water absorption performance than the superabsorbent polymer obtained by the method described in the above-mentioned publication, and can yield a low-cost, high-performance water-absorbent composite. This is possible.

(Detailed Description of the Invention) (1) Monomer The monomer used in the present invention is acrylic acid and/or methacrylic acid, and 2 of the total carboxyl groups are
0 to 1001, preferably 40 to 95, partially neutralized with an alkali metal salt, or 20 to 100,
Preferably, 40 to 100 salts are neutralized with ammonium salt. In the case of alkali metal salts, if the degree of neutralization is too high, the hydrous gel will exhibit weak alkalinity, which poses a safety problem when used in sanitary materials and the like.

Furthermore, if the degree of neutralization is too low, the amount of water absorbed by the polymer will drop significantly. On the other hand, in the case of ammonium salts, if the degree of neutralization is too low, the water-containing gel will exhibit weak acidity, and furthermore, the amount of water absorption will decrease significantly, causing problems in terms of both safety and performance.

Examples of the alkali metal salts used include sodium salts, potassium salts, lithium salts, etc., and sodium salts and potassium salts are preferred from the viewpoint of industrial availability, cost, and safety.

The higher the concentration of these acrylic acid monomers, the better. That is, by increasing the heptamer concentration, the degree of polymerization increases, and the amount of highly water-absorbing polymer filled per unit surface area of the molded fiber substrate increases, making it possible to obtain a composite with excellent water absorption performance. Furthermore, by increasing the monomer concentration, or conversely speaking, by decreasing the water concentration, it is possible to reduce the energy required for drying, which is advantageous in terms of cost. Specifically, a disaturated solubility at the working temperature is advantageously used, for example, in the case of IJium acrylate, it is about 45% by weight at room temperature.

(2) Crosslinkable monomer The crosslinkable monomer having two or more double bonds in the molecule copolymerizable with the acrylic acid monomer used in the present invention exhibits a certain degree of water solubility and It must be copolymerizable with acrylic acid monomers. Specific examples of such crosslinkable monomers include ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, propylene glycol diacrylate, and propylene glycol diacrylate. methacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, glycerin triacrylate, glycerin trimethacrylate), N,N'-methylenepisacrylamide, N,N'-methylenepismethacrylamide, diallyl phthalate, diallylmalate, diallyl Examples include terephthalate, triallyl cyanurate, triallyl isocyanurate, triallyl isocyanurate, triallyl phosphate, among others, polyethylene glycol di(meth)acrylate, N, N'
- Methylenepisacrylamide is preferred. The amount of these crosslinking monomers used is 0 parts by weight per 100 parts by weight of acid monomer.
．． 0.001 to 5 parts by weight, preferably 0.01 to 1 part by weight.

If the amount is less than 0.001 parts by weight, the water absorption capacity will be significantly increased, but the water-absorbed gel will become paste-like and the shape retention of the gel will be extremely poor, which is not preferable.

On the other hand, when 5 parts by weight or more is used, although the shape retention of the gel is significantly improved, the water absorption performance becomes considerably low, which poses a practical problem.

(3) Radical polymerization initiator The radical polymerization initiator used in the production method of the present invention includes:
- Hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide,
Azo hydrogen peroxide such as azobisinobutyronitrile and 2,2'-7zobis(amidinopropane) dihydrochloride, and persulfates such as potassium persulfate and ammonium persulfate are used. These radical polymerization initiators may also be used as a redox type initiator in combination with reducing substances such as sulfites, amines, and the like. The amount of these radicals used varies depending on the type of radical polymerization initiator used, polymerization temperature, etc., but generally it is 0.01 to 21 to 2 parts by weight or 1 to 2 parts by weight based on the acrylic acid monomer. It is 1% by weight. 0. If the amount of O used is less than 11 parts by weight, the polymerization reaction time will be too long;
The above methods hardly improve the performance of the superabsorbent polymer and are not very advantageous in terms of cost.

(4) Application method An acrylic acid monomer as described above, and a crosslinkable monomer having two or more double bonds in the molecule that can be copolymerized with the monomer,
Furthermore, an aqueous solution containing a radical polymerization initiator is applied to the molded fibrous substrate. In this case, it may be applied separately. At this time,
It is preferable to form a periodic pattern in the form of small dots or lines. For example, if there is a continuous line of cross-linked absorbent polymer around the edges of the absorbent padding part of a diaper, this diaper has the advantage that leakage around the edges is minimized. .

In general, it is preferred to employ a pattern of very finely divided, discrete sections in order to maximize the ratio of polymer surface area to mass. An example of a method for applying it to a fibrous substrate is printing (pr
int ing, spraying, flowing, kiss coating, saturati
ng), etc. Further, if desired, the aqueous solution can be applied to the fibrous substrate in an all-over pattern, whereupon the aqueous solution may be applied in an amount sufficient to simply coat one side of the fibrous substrate, or the aqueous solution may be applied in an amount sufficient to simply coat one side of the fibrous substrate. It can also be used in an amount sufficient to penetrate the thickness of the substrate.

The amount of impregnation of the aqueous solution applied to the fibrous substrate is not particularly limited and can vary widely depending on the product use of the water-absorbing composite used. Generally, 1 to 1000 parts by weight of the sail per 1 part by weight of the fibrous base, usually 0.5 to 50 parts by weight.
] i quantity parts are adopted.

(5) Fibrous substrate The fibrous substrate used in the present invention includes a pad made of loosely formed fibers, a carded or air-laid web, tissue paper, woven fabric such as cotton gauze,
It may be knitted fabric or non-woven fabric. A "molded" fibrous substrate is defined as a fibrous substrate that is used to incorporate the fibrous substrate into an article.
Although cutting, joining, shaping, etc. may be required, web forming operations do not require further processing.

It is generally preferred to use absorbent fibers for the fibrous substrate, such as wood pulp, rayon, cotton or other cellulosic fibers or polyester fibers. However, other types of fibers may be embedded in the shaped fibrous substrate.

(6) Polymerization Condition When applying the aqueous solution to a quality substrate to produce a water-absorbing composite consisting of a superabsorbent polymer and a molded fibrous substrate, the aqueous solution is prepared at room temperature or heated to a predetermined temperature. put. Preferably, the polymerization is carried out batchwise in a box-type reaction tank at a predetermined polymerization temperature, or the polymerization is sufficiently degassed.

The temperature inside the reaction tank is generally 20-150℃,
Preferably, the temperature is 40 to 100°C. In addition, when heating the aqueous solution to a predetermined temperature in advance, the temperature is as follows:
The polymerization temperature at this time is equal to or slightly lower than y, for example, a lower temperature of about 5 to 10°C.

The polymerization time varies depending on the polymerization temperature used, etc.
Generally, it is several seconds to 2 hours, preferably several seconds to 10 minutes.

After the polymerization is complete, if necessary, the composite is dried to remove moisture, for example by passing it through a series of drying baths or using a forced draft oven.

As mentioned above, in the method of the present invention, instead of using electromagnetic radiation or particulate ionizing radiation as shown in the above-mentioned Japanese Patent Publication No. 57-500546 for polymerization, acrylic acid-based monomers are used. The most important feature and advantage of this method is that a crosslinkable monomer having two or more double bonds is present in the molecule that can be copolymerized with the polymer, and a radical initiator is used. That is, in the former method using radiation, there is little flexibility in the polymerization conditions for crosslinking, and it is possible to easily change the high water absorbency or the reaction temperature over a wide range. A highly absorbent polymer with high properties can be obtained at low cost, and an excellent water absorbent composite can be obtained.

〔Example〕

Hereinafter, the present invention will be further explained in detail by giving Examples and Comparative Examples. In addition, the physiological saline water absorption capacity described in these examples refers to the value measured by the following test method. 2007 was weighed and added to each, and the polymer was left to stand for about 4 hours to allow the polymer to sufficiently swell with the saline solution. Next, drain the water using a 100 mesh sieve, weigh the amount of filtered saline, and calculate the physiological saline water absorption capacity according to the following formula.

Example 1 Sodium hydroxide (purity 95% by weight) in a 100cc conical flask 13. Take IP and cool with pure water 3
9. Melted with Of. To this, 30 liters of acrylic acid was injected under water cooling to neutralize it. The degree of neutralization of acrylic acid was about 75 degrees, and the monomer concentration in the aqueous solution was about 45 times ffk.

N,N'-methylenepisacrylamide as a crosslinking monomer was dissolved in this in an amount of o,oO5i, radically polymerized, and deaeration was performed.

Separately polyester non-woven fabric (2 denier) 0.12731
The raw material was applied to the entire surface of the nonwoven fabric to impregnate it. The amount of monomer impregnated was 9.0 times the weight of the nonwoven fabric. This was degassed with N2 in advance and heated to 50°C.
The mixture was placed in a constant-temperature reaction tank at a temperature of 100° C., and the temperature was further raised to 90° C. in about 10 minutes. Polymerization occurred immediately to obtain a water-absorbing composite in which a super-absorbent polymer consisting of partially neutralized sodium polyacrylate crosslinked with N,N'-methylenepisacrylamide was stably fixed to the polyester nonwoven fabric.

As a result of measuring the physiological saline water absorption capacity of the above-mentioned water-absorbing composite, 3
It was 6.0.

Example 2 Acrylic acid 30 F was taken in a 100 cc conical flask, and 9.32 g of pure water was added thereto and mixed. To this was gradually added 20.62 g of potassium hydroxide (85 wt. 4) under water cooling for neutralization. The degree of neutralization was about 754, and the monomer concentration in the aqueous solution was about 74 parts. This was combined with N as a crosslinking monomer, and 0.
0083f was dissolved and kept at 50°C.

2. Separately as a radical polymerization initiator. Cuazobis (2-
Amidinopropane) dihydrochloride (0.2 f) was dissolved in 12 g of pure water, and this was applied to the entire surface of a polyester nonwoven fabric (1,4 denier) 0.135 Of.

The raw material monomer solution was quickly applied to the entire surface of the nonwoven fabric, and the fabric was placed in a reaction tank that had been previously degassed with N2 and maintained at 70°C. Polymerization occurred immediately to obtain a water-absorbing composite in which a super-absorbent polymer consisting of partially neutralized potassium polyacrylate crosslinked with N,N'-methylenepisacrylamide was stably fixed to the polyester nonwoven fabric. The amount of monomer impregnated into the nonwoven fabric was 10 times the weight of the nonwoven fabric.

As a result of measuring the physiological saline water absorption capacity of the above water-absorbing composite, 4
It was 5.2.

Example 3 100 cc conical flask 1 IC25 weight 4 ammonia water 26.9 f was taken, and acrylic acid 302 was added dropwise to it while cooling it on ice to neutralize it. Acrylic acid neutralization degree is approximately 95
Unfortunately, the monomer concentration in the aqueous solution was about 95 parts.

0.029 g of N,N'-methylenepisacrylamide as a crosslinking monomer and 0.1 g of potassium persulfate as a radical polymerization initiator were dissolved in this at room temperature and thoroughly degassed. .

Separately, a 0.1970 f polyester nonwoven fabric was taken, and the entire surface of the fabric was coated and impregnated with the raw material monomer aqueous solution. The amount of impregnated 7-mer was about 27 times that of the nonwoven fabric. This was previously degassed with N2, placed in a constant temperature reaction tank set at 50°C, and further heated to 90°C in about 10 minutes. Polymerization occurred immediately to obtain a water-absorbing composite in which a super-absorbent polymer consisting of partially neutralized ammonium polyacrylate crosslinked with N,N'-methylenepisacrylamide was stably fixed to the polyester nonwoven fabric.

As a result of measuring the physiological saline water absorption capacity of the above water-absorbing composite,
It was 43.9.

Example 4 A water-absorbing composite was obtained in the same manner as in Example 3, except that the rayon nonwoven fabric was 0.14472 and the raw material monomer impregnation was 12 times that of the nonwoven fabric.

The physiological saline water absorption capacity of the water-absorbing composite was 39.0.

Example 5 A water-absorbing composite was obtained in the same manner as in Example 3, except that the raw monomer aqueous solution was sprayed from a spray nozzle for coating and impregnation, and the amount of impregnation was 5.4 times that of the nonwoven fabric.

The physiological saline water absorption capacity of this water-absorbing composite was 40.4.

In addition, the above-mentioned water-absorbing composite has extremely finely divided super-absorbent polymers fixed on the fibers with good stability, and its texture is extremely soft, making it suitable for sanitary materials such as sanitary napkins and paper diapers. .

Comparative Example 1 By the same operation as shown in Example 2, a partially neutralized potassium acrylate aqueous solution having a degree of neutralization of 75 degrees and a monomer concentration in the aqueous solution of about 74 parts by weight is prepared. This was sprayed onto a polyester nonwoven fabric from a spray nozzle to coat and impregnate it. The amount of impregnated monomer is approximately 1 per nonwoven fabric.
It was 0 times.

The nonwoven fabric impregnated with this partially neutralized potassium acrylate monomer aqueous solution was irradiated with an electron beam at a dose of 10 megarads from an electron beam apparatus equipped with a dynamidron accelerator.

A water-absorbing composite was obtained in which a super-absorbent polymer made of a self-crosslinked partially neutralized potassium polyacrylate was stably fixed to a polyester nonwoven fabric.

Results of measuring the physiological saline water absorption capacity of the above water-absorbing composite 1
It was quite small at 8.5.

Comparative Example 2 A water-absorbing composite was obtained using the same formulation and operation as in Comparative Example 1, except that the amount of impregnation with the nonwoven material was 0.8 times by weight and the amount of electron beam irradiation was 4 megarads. As a result of measuring the physiological saline water absorption capacity of the superabsorbent polymer in the water-absorbent composite obtained by this operation, it was found to be quite small at 22.5 P per superabsorbent polymer.

〔Effect of the invention〕

The water-absorbing composite obtained by the production method of the present invention has extremely high water-absorbing performance, which is more than twice that of the method disclosed in Japanese Patent Publication No. 57-500546.

Furthermore, since it is in the form of a sheet, it is easier to handle and cheaper than the conventionally used powdered superabsorbent resin, so it is used in sanitary napkins, paper diapers, etc., and various other sanitary materials. It can be advantageously used in the production of Furthermore, by utilizing its excellent water absorption performance and ease of handling, it can be used to manufacture various materials for horticultural and agricultural purposes, including soil conditioners and water retention agents, which have recently attracted attention.

Claims (1)

[Scope of Claims] 1) Applying an aqueous solution containing an alkali metal salt or ammonium salt of acrylic acid and/or methacrylic acid (hereinafter referred to as an acrylic acid monomer) to a molded fibrous substrate,
Next, when the acrylic acid monomer is polymerized to produce a water absorbent composite consisting of a super absorbent polymer and a molded fibrous substrate, a double bond is formed in a molecule copolymerizable with the acrylic acid monomer. 1. A method for producing a water-absorbing composite comprising using a crosslinking monomer having two or more of the above and a radical polymerization initiator. 2) The production method according to claim 1, wherein 20 to 100% of the total carboxyl groups of the acrylic acid monomer are partially neutralized with an alkali metal salt or an ammonium salt. 3) The manufacturing method according to claim 1, wherein the alkali metal salt is a sodium salt or a potassium salt. 4) The crosslinkable monomer is ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,
Propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, glycerin tri(meth)acrylate, N,N'-methylenepis(meth)acrylamide, diallyl phthalate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, tri- The manufacturing method according to claim 1, wherein the manufacturing method is one or more selected from the group consisting of allyl isocyanurate and triallyl phosphate. 5) The manufacturing method according to claim 1, wherein the fibrous substrate contains cellulose fibers or polyester fibers. 6) The manufacturing method according to claim 5, wherein the fibrous substrate is a loose pad of fibers, a carded web, an air-laid web, paper, a nonwoven fabric, a woven fabric, or a stockinated fabric.