JPS61264006A - Production of highly water-absorbing polymer - Google Patents

Abstract

PURPOSE:To obtain a highly water-absorbing polymer having high rate of water- absorption and giving a water-absorbed gel having high gel strength, easily, by crosslinking the surface of a highly water-absorbing polymer having carboxyl group, etc., with a silane coupling agent in the presence of a silanol condensation catalyst. CONSTITUTION:The surface of a highly water-absorbing polymer having carboxyl group and/or carboxylate group (e.g. acrylic acid polymer) is crosslinked with a silane coupling agent of formula XRSiYn (X is group reactive with the functional group of the above polymer; R is organic group; Y is hydrolyzable group; n is 1-3) (e.g. r-glycidoxypropyl trimethoxysilane) in the presence of a silanol condensation catalyst (e.g. dibutyltin dilaurate) in the absence or presence of an inert solvent (e.g. n-heptane) with controlling the water-content of the system to 10-50wt% based on the polymer. USE:A sanitary material such as paper diaper, a material for agricultural and horticultural use, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (al) Object of the Invention The present invention relates to a method for producing a super absorbent polymer that has a high water absorption rate and high water absorption gel strength.

(Field of Industrial Application) The superabsorbent polymer obtained by the production method of the present invention absorbs a large amount of water in a short period of time and swells, but it is insoluble in water, and the polymer gel that swells after absorbing water is Because of its high strength, it can be advantageously used in the production of various water-absorbing materials or materials that are used in a swollen state after absorbing water.

(Prior Art) Conventionally, paper, valves, nonwoven fabrics, sponge-like urethane resins, 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, multi-lobed materials are required.
Not only did it become extremely bulky, but it also had the disadvantage of separating moisture when pressurizing the material that had absorbed water.
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 polymer
No. 6199, etc.), cellulose modified products (JP-A-1989-1999),
80376, etc.), crosslinked water-soluble polymers (Japanese Patent Publication No. 43-23462, etc.), self-crosslinking alkali metal acrylate polymers (Japanese Patent Publication No. 54-30710, etc.), and the like have been proposed.

However, these superabsorbent polymer materials either have low water absorption capacity, or even if they have high water absorption capacity, the water absorption rate is slow, or when mixed with water, they exhibit so-called ``as-is'' (i.e., uneven water absorption when wet). ), it is not possible to absorb water efficiently and it takes a long time to absorb water. For this reason, such conventional superabsorbent polymer materials are unsuitable for applications such as sanitary napkins and paper diapers that absorb a large amount of water at once and require instantaneous water absorption ability. .

Generally, in order to improve the dispersibility, solubility, or water absorption rate of a hydrophilic polymer in water, a surfactant such as sorbitan monostearate, a non-volatile hydrocarbon, or calcium stearate powder is added to the hydrophilic polymer. A known method is to make the surface of a polymer hydrophobic by adding a substance such as The effect of improving the speed could not be expected to be very high, and on the contrary, it had the disadvantage of causing a problem of 11.

It is also known that in order to increase the water absorption rate of superabsorbent polymers, the hydrophilicity of the polymer is reduced by increasing the crosslinking density, but this method can slightly improve the water absorption rate, but the improvement The effect could not be said to be significant, and on the contrary, it had the disadvantage of significantly lowering the water absorption capacity.

In order to overcome the above-mentioned drawbacks of conventional water-absorbing materials, the present inventors have already published Japanese Patent Application No. 60-52357 (where X represents a functional group capable of reacting with a functional group of a superabsorbent polymer). ,R
represents an organic group, Y represents a hydrolyzable group, and n is 1 to 3
indicates an integer. ) We have proposed a method for producing a superabsorbent polymer with improved water absorption rate and gel strength, which is characterized by treatment with a silane coupling agent represented by: Although this method significantly improves water absorption rate and gel strength,
As a result of a more detailed study of this, it was found that under certain controlled conditions as described in the above publication, it was extremely effective, and under these conditions the water absorption rate was high with good reproducibility, causing "mamako". It has been found that a superabsorbent polymer with no water absorption can be obtained.

(Problems to be Solved by the Invention) The present invention improves the method for producing a super absorbent polymer described in the above-mentioned Makigan No. 60-52357, and further increases the water absorption rate while maintaining the water absorption performance. The object of the present invention is to provide a method for producing an improved superabsorbent polymer with good reproducibility.

(b) Structure of the Invention (Means for Solving Problems) As a result of various studies to solve the above problems, the present inventors have developed a super absorbent polymer containing carboxyl groups and/or carboxylate groups. , 1 to the polymer
The water content was controlled to 10 to 50% by weight, and in the presence of a silanol condensation catalyst, the general formula % formula % (wherein, X represents a functional group capable of reacting with the functional group of the superabsorbent polymer, R represents an organic group, Y represents a hydrolyzable group, and n represents an integer from 1 to 3) By crosslinking the surface with a silane coupling agent, the water absorption rate is significantly increased. It was found that the "mamako" phenomenon could be prevented. That is, the present invention is based on the aforementioned Japanese Patent Application No. 60-52357.
This is an improved method of the method described in the publication, and is considered to be a difference.5
The purpose is to control the weight ratio to zero and to make the silanol condensation catalyst exist as an essential component. For this reason, the production method of the present invention makes it possible to obtain, with good reproducibility, a polymer with a significantly higher water absorption rate than the polymer obtained by the method described in the above-mentioned publication.

As the raw material superabsorbent polymer in the production method of the present invention, any superabsorbent polymer containing carboxyl groups and/or carboxylate groups can be used. Examples of such superabsorbent polymers include acrylic acid (@polymer), methacrylic acid (salt) polymer, acrylic acid (salt)/methacrylic acid (salt) copolymer,
Starch/acrylic acid (salt) graft copolymer, starch/
saponified product of acrylic acid ester graft copolymer, saponified product of starch/methyl methacrylate graft copolymer,
saponified product of methyl methacrylate/vinyl acetate copolymer,
Saponified products of methyl acrylate/vinyl acetate copolymer, saponified products of starch/acrylonitrile graft copolymer,
Saponified product of starch/acrylamide graft copolymer, starch/acrylonitrile-2-acrylamide-2
- Crosslinked products of various polymers such as a saponified product of a methyl/L/propanesulfonic acid graft copolymer, a saponified product of a starch/acrylonitrile/vinyl sulfonic acid graft copolymer, and polyethylene oxide crosslinked with acrylic acid; Examples include crosslinked sodium carboxymethylcellulose. In addition, the above-mentioned acrylic acid (salt) and methacrylic acid (
Polymers (including copolymers) of acrylic acid (salts)
or methacrylic acid (salt), maleic acid (salt), itaconic acid (salt), acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-'7 in an amount that does not reduce the performance of the water-absorbing polymer produced. A copolymer obtained by copolymerizing a comonomer such as chloroylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-hydroxyethyl acrylate, or 2-hydroxyethyl methacrylate may be used without any problem.

The crosslinked products of the various polymers described above used as the raw material superabsorbent polymer in the present invention can be made into crosslinked products by various means. Crosslinking means include, for example, entanglement of molecular chains by high-level polymerization of polymer molecules, self-crosslinking by pseudo-crosslinking, or divinyl compounds copolymerizable with the above-mentioned various hexamers, such as N,N'-methylenebis( Crosslinking with meth)acrylamide, (poly)ethylene glycol di(meth)acrylates, etc., and polyfunctional compounds that react with functional groups of polymers, such as carboxylate groups, such as (poly)glycidyl ethers, haloepoxy compounds, Examples include crosslinking by adding and reacting polyaldehydes, polyols, polyamines, etc., and crosslinking based on reactions between functional groups present in the polymer, such as esterification with carboxyl groups and hydroxyl groups. .

In addition, when the superabsorbent polymer used as the raw material of the present invention is a carboxylate type, that is, a salt type, it may be an alkali metal salt type such as sodium or potassium, an alkaline earth metal salt type such as magnesium or calcium, or an ammonium salt type. and amine salt types, but particularly preferred are alkali metal salt types.

Examples of the functional group X in the silane coupling agent represented by the general formula (1) used in the production method of the present invention include a glycidyl group, an amine 7 group, and a mercapto group, and the hydrolyzable group Y Examples of such groups include alkoxy groups and acetoxy groups. Specific examples of the silane coupling agent (1) include r-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyljethoxysilane, β-(3,4-
epoxycyclohexyl)ethyltrimethoxysilane,
γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-aminoprohyltriethoxysilane, N-phenyl-γ--l〇-aminopropyltri methoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, octadecyldimethykc3-()rimethoxysilyl)
Examples include [propyl] ammonium chloride.

Among these, silane coupling agents having a glycidyl group as the functional group X, such as γ-glycidoxypropyltrimethoxysilane, are particularly preferred.

In the present invention, the treatment of a superabsorbent polymer with a silane coupling agent must be carried out in the presence of a well-controlled moisture content and a silanol condensation catalyst. Even if the silane coupling treatment is performed without a well-controlled water content and/or in the absence of a silanol condensation catalyst, a highly water-absorbing polymer with good reproducibility, a high water absorption rate, and no "remains" can be obtained. .

The treatment with a silane coupling agent in the presence of a silanol condensation catalyst and its controlled moisture content can be carried out in various embodiments. As an example of the treatment mode, for example, a mixture of a silane coupling agent, water in an amount to be decomposed and a silanol condensation catalyst is added to a dried superabsorbent polymer, and the water is evaporated by heating I2. Good [2,
Adding a superabsorbent polymer powder into an inert solvent to form a slurry, adding a mixture of a silane coupling agent and a controlled amount of water and a silanol condensation catalyst to the slurry, and heating under reflux; Alternatively, a mixture of a silane coupling agent and a controlled amount of water and a silanol condensation catalyst may be added to the slurry to evaporate the water and inert solvent. A controlled amount of water is added from the reaction product solution containing the superabsorbent polymer and water, to which a silane coupling agent and a silanol condensation catalyst are added and heated under reflux or L< may be heated and evaporated.

Inert solvents used in each of the above treatments include, for example, alcohols such as methanol and ethanol; ethers such as acetone, ketyloxane such as methyl ethyl ketone, and tetrahydrofuran; n-pentane, n-hexane, n-hebutane, and cyclohexane. , benzene, toluene, xylene, and other hydrocarbons; carbon tetrachloride, methylene chloride, chloroform, ethylene dichloride), etc.
Examples include 'y'nated hydrocarbons. Among these, aliphatic or aliphatic saturated hydrocarbons such as n-hexane, n-heptane, and cyclohexane can particularly effectively achieve the object, and are listed as preferred examples.

The amount of silane coupling agent used in the above treatment is:
Although it varies somewhat depending on the type of super absorbent polymer, the amount of water present, the type and amount of inert solvent, etc., it is usually 0.001 to 1 O10 weight per liter of super absorbent polymer, preferably 0. .01 to 3% by weight. If the amount used is too small, the effect of improving the water absorption rate and gel strength will not be obtained, and if it is too large, the water absorption ability of the treated polymer will decrease.

Furthermore, the amount of water present in the above treatment is an extremely important point in the present invention.
It is necessary to set the amount to 10 to 50% by weight based on the superabsorbent polymer. If the amount of water is less than 10 liters by weight, the superabsorbent polymer is likely to become swollen during treatment, and the reaction with the silane coupling agent will not proceed effectively, making it difficult to carry out effective treatment. On the other hand, when the water value exceeds 50Ji, the superabsorbent polymer becomes too swollen and the silane coupling agent penetrates into the resin, making it impossible to crosslink only the resin surface layer. Although the gel strength is improved, the effect on improving the water absorption rate is reduced.

The inert solvent used in the above treatment may be used alone or in combination of two or more as appropriate.The amount of inert solvent used depends on the type of superabsorbent polymer and the inert solvent. Although it varies depending on the type, etc., it is usually 10 to 5000 weight-Jit%, preferably 5% to the superabsorbent polymer.
It is 0 to 500% by weight. If the inert solvent is used with less noise, the amount of material handled during treatment will be reduced and the volumetric efficiency of the treatment equipment will be improved, but the dispersibility of the superabsorbent polymer during treatment will be poor, making the treatment reaction less effective. It stops progressing. In addition, if too much inert solvent is used, the processing reaction will proceed more easily, but at the same time, it will increase the number of materials to be handled, reduce the volumetric efficiency of the equipment, etc., and increase the processing cost. It will be disadvantageous.

In the present invention, as the silanol condensation catalyst that must be used together with the silane coupling agent, any of the commonly known dibutyltin silaurylate, diptyltin diacedate, diptyltin dioctoate, etc. can be used. 0.1 to 1000 weight, preferably 1 to 500 for the used i1 hasilane coupling agent
The weight is %. If it is less than o, i% by weight, the effect of its addition is small, and if it is more than 1000% by weight, it is not advantageous enough to further increase the effect, and the cost is high industrially, so it is not very meaningful.0 The present invention allows smooth reaction treatment. The temperature conditions under which the process is carried out cannot be generalized as they vary depending on the type of silane coupling agent used, the type and condition of the inert solvent, the water droplets present, the type of superabsorbent polymer, etc. The temperature is normally selected from the range of 20 to 180°C, preferably 50 to 150°C.

(Examples, etc.) The following is a more detailed description of the invention by giving Examples and Comparative Examples.

Example 1 A super absorbent polymer was manufactured based on Example 1 of Japanese Patent Application No. 59-275308. After adding 4.5 f of cyclohexane (375v, sorbitan monostear) to the bottom flask and dissolving it, nitrogen gas was blown in to drive out the dissolved oxygen. In a flask containing 50011Ig, add 201v of water to acrylic acid 751F while cooling it with water from the outside.
31.2 μl of caustic soda dissolved in was added to neutralize 74.9% of the carboxyl groups. In this case, the monomer concentration with respect to water corresponds to 30% as a monomer concentration after medium filtration.

Next, add 0.050% of N,N'-methylenebisacrylamide to this. After adding and dissolving 0.26 F of potassium persulfate, nitrogen gas was blown in to drive out dissolved oxygen.

The contents of this 500-ml flask were added to the contents of the four-bottomed flask, stirred and dispersed, and the temperature inside the flask was raised in an oil bath while bubbling nitrogen gas, resulting in a temperature of 60°C. After reaching this point, the internal temperature rose rapidly, reaching 72°C several tens of minutes later. Next, the internal temperature was maintained at about 64° C., and the reaction was allowed to proceed for 3 hours while stirring.

Note that stirring was performed at 250 rpm.

When the stirring was stopped after the reaction was completed, the wet polymer particles settled to the bottom of the flask and could be easily separated from the cyclohexane phase by decantation. The separated wet polymer was transferred to a vacuum dryer and heated to 80-90° C. to remove adhering cyclohexane and water. The resulting dry polymer was a powder containing free-flowing, easily grindable lumps.

=17- Next, the dry polymer obtained in the above treatment is pulverized to give 25
409 was taken into a 300-den eggplant-shaped flask. Next, cyclohexane 392 was added to form a slurry. While stirring this slurry, a mixture of 0.085 W of r-glycidiglopyltrimethoxy 7ran dissolved in 92 ml of water (22.5 ml of superabsorbent polymer) and 10 ml of cyclohexane were added. −
0.2ft of butyltin: The dissolved mixture was added and stirred at room temperature for about 30 minutes.

Next, the flask was immersed in an oil bath at 80°C, the temperature was raised to 105°C, the temperature was maintained for about 1 hour, and then evaporated to dryness under reduced pressure to obtain a dry polymer. Water was distilled out from the polymerization reaction solution obtained in the same manner as in Example 1 by azeotropic dehydration with cyclohexane (i.e., 25 tons of water remained in the polymer, which corresponds to 11 it% by weight of the superabsorbent polymer). ) After removing the solution, add 0.2f of r-glycidoxypropyltrimethoxysilane and 0.4f of di-n-butyltin dilaurate, mix thoroughly, and then place in an oil bath at 80°C. Immerse and set the oil bath temperature to 10
After raising the temperature to 5° C., the mixture was evaporated to dryness under reduced pressure while maintaining the same oil bath temperature to obtain a dry polymer.

Comparative Example 1 Dry polymer 409 obtained by removing cyclohexane and water from the polymerization reaction solution obtained in the same manner as in Example 1 was placed in a 300-inch eggplant-shaped flask. Next, cyclohexane 391F was added to form a slurry. While stirring this slurry, water 3R (to super absorbent polymer 7.5 weight iii)
A mixture of 0.0859 of r-glycidoxyglobyltrimethoxysilane dissolved in 102% of cyclohexane and 0.22 of di-n-butyltin dilaurate in 102 of cyclohexane were added to The mixture was stirred and mixed for 30 minutes. The flask was then immersed in an 80°C oil bath and heated to 105°C.
After raising the temperature to °C, it was maintained at the same temperature for about 1 hour, and then evaporated to dryness under reduced pressure to obtain a dry polymer.

Comparative Example 2 A dry polymer was obtained in the same manner as in Comparative Example 1 except that the amount of water added was changed to 4of (corresponding to 100% of the superabsorbent polymer).

Comparative Example 3 Dry polymer 40r obtained by removing cyclohexane and water from the polymerization reaction solution obtained in the same manner as in Example 1 was placed in a 300-inch eggplant-shaped flask. Next, 49 tons of cyclohexane was added to form a slurry. While stirring this slurry, water 9F (22.5 wt% based on the super absorbent polymer) was added.
A mixture of 0.0857 r-glycidogyciprobyltrimethoxysilane was added to the mixture (equivalent to
The mixture was stirred and mixed for 0 minutes. Next, the flask was immersed in an oil bath at 80°C, and the temperature was raised to 105°C, maintained at the same temperature for about 1 hour, and then evaporated to dryness under reduced pressure to obtain a dry polymer.

The saline water absorption capacity and water absorption rate of the polymers obtained in the above-mentioned Tani Examples and Comparative Examples were measured based on the following method.

The results are shown in Table 1.

In a beaker with an A1 saline water absorption capacity of 300, about 0.5 of the polymer was added and the concentration was 0.
Weigh and add 20 of 9% salt salt to each,
After mixing, the mixture was allowed to stand for about 60 minutes to allow the saline solution to fully swell the polymer. Next, after draining with a 100-mesh filter, the filtered saline solution was weighed, and the water absorption capacity of the saline solution was calculated according to the following formula.

B. 0.9 xi-% saline solution 50- in a beaker with a water absorption rate of 100-
was added, the stirrer was rotated using a magnetic stirrer, and the time from when Polymer 2 was added to when the stirrer stopped was measured to determine the water absorption rate.

(C) As is clear from the above Examples and Comparative Examples, the production method of the present invention not only has a high water absorption capacity, but also has a high initial water absorption rate, and when water is absorbed, It can absorb water quickly without causing the phenomenon, and can be easily produced using a simple method. Utilizing its excellent performance, this super absorbent polymer can be used for various sanitary materials such as sanitary napkins and paper diapers, as well as for horticultural and agricultural purposes such as soil conditioners and water retention agents. It can be advantageously used in the production of various materials such as.

Table 1

Claims (1)

[Scope of Claims] 1) Controlling the water content of a super absorbent polymer containing carboxyl groups and/or carboxylate groups to 10 to 50% by weight relative to the polymer in the presence or absence of an inert solvent. and in the presence of a silanol condensation catalyst, the general formula XRSiYn (wherein, n is an integer of 1 to 3. 2) The production method according to claim 1, wherein the superabsorbent polymer is a polymer containing a carboxyl group based on acrylic acid/methacrylic acid and/or an alkali metal carboxylate group. 3) The production method according to claim 1, wherein the inert solvent is an aliphatic or alicyclic saturated hydrocarbon. 4) The manufacturing method according to claim 1, which is a silane coupling agent in which X is a glycidyl group in the general formula.