JPS61213206A - Production of polymer having high water-absorptivity - Google Patents

Abstract

PURPOSE:To obtain a polymer having remarkably excellent rate of water- absorption and gel strength, and useful as a water-absorbing material for paper diaper, etc., by crosslinking the surface of a highly water-absorbing polymer with a specific crosslinking agent in the presence of water, and at the same time, introducing OH group to the surface of the polymer. CONSTITUTION:The surface of a highly water-absorbing polymer containing carboxyl group and/or carboxylate group as a constituent component of the (co)polymer (e.g. acrylic acid, alkali metal methacrylate, etc.) is treated with one or more crosslinking agents selected from trimethylolpropane diglycidyl ether, diglycerol diglycidyl ether, diglycerol triglycidyl ether, and sorbitol di(or tri or tetra)glycidyl ether, in the presence of water. The surface is crosslinked and at the same time, OH group is introduced to the surface of the polymer by this process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a superabsorbent polymer having extremely excellent water absorption rate and gel strength.

(Industrial Application Field) The 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 is insoluble in water and has excellent gel strength as a swollen polymer. It is advantageous for manufacturing various water-absorbing materials or materials that absorb water and swell to be used in good condition. can be used.

(Prior Art) Conventionally, paper, pulp, nonwoven fabric, sponge-like urethane resin, etc. have been used as water-retaining agents in sanitary napkins, paper diapers, various sanitary materials, and various industrial materials. However, these materials absorb only about 10 to 50 times their own weight, so in order to absorb or retain a large amount of water, a large amount of material is required, which not only makes them extremely bulky, but also There were drawbacks, such as the fact that if a material that had absorbed water was pressurized, the water would easily separate.

To improve the above-mentioned drawbacks of this type of water-absorbing material,
In recent years, various highly absorbent polymer materials have been proposed. For example, starch gujift polymer (!!#Koshō 53-461
No. 99, etc.), cellulose modified products (!! #Kaisho 50-
80376, etc.), crosslinked water-soluble polymers (Japanese Patent Publication No. 43-23462, etc.), self-crosslinking type alkali gold acrylate polymers (Japanese Patent Publication No. 54-30710, etc.), etc. have been proposed. Ta.

However, these super absorbent polymer materials have low water absorption capacity, or even if they have high water absorption capacity, the water absorption rate is slow, and when they come into contact with an object to be absorbed, so-called "mamako" is generated and the water is not absorbed efficiently. , it takes a long time to absorb the desired amount of water. Therefore, it is particularly unsuitable for applications such as sanitary napkins, paper diapers, etc., which absorb a large amount of water-absorbing material at once and require instantaneous water-absorbing ability, and have many problems.

(Problems to be Solved by the Present Invention) The present invention addresses the above-mentioned problems in super absorbent materials, namely, provides a method for producing a super absorbent polymer that has significantly improved water absorption rate and gel strength, particularly water absorption rate. This is what I am trying to do.

(Means for Solving the Problems) As a result of various studies aimed at solving the above-mentioned problems, the present inventors have discovered that super absorbent polymers containing carboxyl groups or carboxylate groups as constituent components of polymers or copolymers In the presence of water, one or more selected from trimethylolpropane diglycidyl ether, diglycerol diglycidyl ether, diglycerol triglycidyl ether, sorbitol diglycidyl ether, nrubitol triglycidyl ether, and flubitol tetracricidyl ether. By carrying out surface crosslinking treatment with a crosslinking agent and simultaneously introducing hydroxyl groups onto the polymer surface, a super absorbent polymer with an extremely high water absorption rate can be obtained by a simple treatment method. This led to the discovery of this fact and the completion of the present invention.

Generally, a method of making the surface of a hydrophilic polymer hydrophobic is known as method 1-i of improving the water dispersibility and dissolution or water absorption rate of a hydrophilic polymer.

That is, by mixing a surfactant such as sorbitan monostearate, a non-volatile hydrocarbon, calcium stearate, etc. into a powdered hydrophilic polymer, the dispersibility in water was improved. However, even if this method is applied to superabsorbent polymers, although the dispersibility in water is improved in the very early stage, the water absorption rate is slow, and if this is not improved, so-called "one-piece strands" will be generated during the water absorption process. However, sufficient effects are not achieved.

Another method for increasing the water absorption rate of superabsorbent polymers is to increase the crosslinking density to reduce the hydrophilicity of the polymer. However, if this method is carried out, the water absorption rate will be slightly improved, but it will not have a very noticeable effect, and in this case, the water absorption capacity will be significantly reduced, and the original performance of the super absorbent polymer will be impaired, so it is not the preferred method. It's hard to say.

On the other hand, 2-
A compound having a hydroxyl group such as hydroxyethyl acrylate is copolymerized as the above-mentioned comonomer (Japanese Patent Laid-Open No. 57
-168921 '4) It has been reported that the water absorption rate is significantly improved by the polymers added as comonomers, although the water absorption rate is slightly improved in polymers obtained by mainstream production methods. Since the compound having a hydroxyl group is uniformly distributed in the polymer, it is not sufficient, and the dispersibility in water is poor and ζ tends to occur.

Also, a method of coating a superabsorbent polymer with a water-soluble polymer or a water-soluble surfactant (JP-A-57-1J89)
21, etc.), but mainstream treatments do not provide a sufficient water absorption rate, and when some types of water-soluble surfactants are used, the product polymer may develop cracks. , it becomes difficult to use.

The present invention has a high water absorption rate without impairing the water absorption ability of the super absorbent polymer containing a carboxyl group or a carboxylate group as a component of the polymer or copolymer, and produces 1 mako As a result of various studies with the aim of preventing these superabsorbent polymers, we found that these superabsorbent polymers were treated in the presence of water with trimethylolpropane diglycidyl ether, diglycerol diglycidyl ether, diglycerol triglycidyl ether, sorbitol dicrycidyl ether,
At the same time, surface crosslinking treatment is performed using one or more crosslinking agents selected from sorbitol triglycidyl ether and sorbitol tetraglycidyl ether, utilizing the reactivity between the glycidyl groups in the crosslinking agent and the functional groups in the superabsorbent polymer,
It has been found that by introducing hydroxyl groups onto the polymer surface, a superabsorbent polymer with a significantly high water absorption rate can be obtained using a simple processing method.

As the superabsorbent polymer that can be used in the present invention, any polymer or copolymer containing a carboxyl group or carboxylate group as a constituent component can be used, and the type of polymer and polymerization The method doesn't matter. Examples of these superabsorbent polymers include acrylic acid (salt) polymer, methacrylic acid (salt) polymer, acrylic acid (salt)/methacrylic acid (salt) copolymer, and starch/acrylic acid (salt) graft copolymer. Polymer, saponified starch/ethyl acrylate graft copolymer, saponified starch/methyl methacrylate graft copolymer, saponified methyl methacrylate/vinyl acetate copolymer, methyl acrylate/vinyl acetate copolymer Saponified product of union, saponified product of starch/acrylonitrile graft copolymer, saponified product of starch/acrylamide graft copolymer, saponified product of starch/acrylonitrile-2-acrylamido-2-methylpropanesulfonic acid graft copolymer, starch Examples include crosslinked products of saponified products of /acrylonitrile/vinyl sulfonic acid graft copolymers, polyethylene oxide crosslinked with acrylic acid, and crosslinked products of sodium carboxymethyl cellulose. Also, acrylic acid (salt) or methacrylic acid (salt), maleic acid (salt), itacon shunji (salt),
Comonomers such as acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2-(meth)acryloylethanesulfonic acid, and 2-hydroxyethyl(meth)acrylate are copolymerized within a range that does not reduce the performance of water-absorbing borimani. Polymers may also be used in the method of the invention.

The crosslinking agent used in the present invention is a compound having two or more glycidyl groups and one or more hydroxyl group in one molecule. It crosslinks by reacting with a group such as a carboxyl group, and at the same time introduces a hydroxyl group onto the polymer surface.

Examples of such crosslinking agents include trimethylolpropane diglycidyl ether, diglycerol diglycidyl ether, diglycerol triglycidyl ether, nlupitol diglycidyl ether, sorbitol triglycidyl ether, sorbitol tetraglycidyl ether, etc. These can be used alone or as a mixture of two or more. Generally, these are produced by forming an adduct with a polyhydric alcohol containing three or more hydroxyl groups in one molecule and epichlorohydrin in a stoichiometric amount lower than the number of hydroxyl groups according to a known method, and then adding caustic soda to close the ring. The resulting sodium chloride is obtained after separation.

In order to react these crosslinking agents with the superabsorbent polymer, water is first required, and this is an essential condition for achieving the object of the present invention. As an example of a specific method,
For example, a mixed solution of the above-mentioned crosslinking agent and water is added to a dry polymer and evaporated by heating, or alcohols such as methanol and ethanol, ketones such as methyl ethyl ketone, ethers such as diethyl ether, dibutyl ether, dioxane, and tetrahydrofuran are used. Hydrocarbons such as n-pentane, n-hexane, n-hebutane, cyclohexane, benzene, toluene, xylene, carbon tetrachloride, methylene chloride, chloroform, ethylene dichloro2
The slurry is made into a slurry with an inert solvent such as halogenated hydrocarbons such as hydride, etc., and a mixed solution of the above-mentioned cross-linking agent and water is added thereto, and then heat-treated preferably under reflux, or the slurry liquid after adding the cross-linking agent. or by adding a crosslinking agent to the above-mentioned inert solvent and water, or to the reaction solution obtained from the reaction step containing water and heating preferably under reflux, or after adding the crosslinking agent. The reaction treatment can be carried out by heating and evaporating the slurry liquid.

Needless to say, after the reaction treatment, the product is manufactured by evaporation/drying.

The amount of the crosslinking agent used in the present invention varies slightly depending on the type of superabsorbent polymer, the amount of water present, the type and amount of inert solvent, etc., but it is usually 0% to the superabsorbent polymer. A suitable range is often .001 to 10 weight percent. Generally, the amount of crosslinking agent used is 0.001
If it is less than the weight percent, the addition effect will not be expressed,
If the amount is more than 10.0% by weight, the water absorption capacity will be significantly lowered, which is not preferable.

In addition, in the reaction treatment in the present invention, the amount of water present is O,S~3
00 parts by weight is suitable. If the amount of water is less than 0.5 parts by weight, the superabsorbent polymer will be in a non-swollen state, the reaction with the crosslinking agent will be difficult to proceed, and a long reaction time will be required, which is industrially disadvantageous. On the other hand, if the amount of water is 300 parts by weight or more, although the gel strength of the superabsorbent polymer obtained is improved, it is not very effective in improving the water absorption rate.
In order to improve the water absorption rate, a large amount of crosslinking agent is required, and as a result, the water absorption capacity is significantly reduced, which is not preferable.

In the reaction treatment of the present invention, when using the above-mentioned inert solvent shown in the specific example, it goes without saying that it is a solvent that does not have any influence on the superabsorbent polymer, and it is not necessary to use it alone. Maku can also be used by mixing two or more types. The amount used varies depending on the type of superabsorbent polymer and inert solvent used, but generally the superabsorbent polymer is 100%
10 to 5000 parts by weight, preferably 50 parts by weight
Good results are obtained when used in parts by weight of ~SOO.

The smaller the amount of inert solvent, the better the volumetric efficiency, but the dispersibility of the superabsorbent polymer will be poor, making it difficult for the reaction treatment to proceed.

On the other hand, if the amount of inert solvent is large, it will be easier to disperse and the reaction will proceed more easily, but the volumetric efficiency will be poor and the cost will be high, which is not very good from an industrial perspective. Therefore, in the reaction treatment according to the present invention, the inert solvent is preferably present within the above concentration range, and the reaction treatment is preferably carried out with respect to the type of crosslinking agent used, the type of inert solvent, and the like. Although it is difficult to generalize because it varies depending on the amount of water present and the type of superabsorbent polymer, it is usually 20 to 1
The reaction is preferably carried out at 80°C, preferably from 50 to 150°C. At temperatures below 20°C, the reaction rate is too slow and takes a long time; at temperatures above 180°C, the hydroxyl cliff in the crosslinking agent reacts with, for example, the carboxyl group in the superabsorbent polymer, resulting in esterification. This tends to cause problems such as thermal deterioration of superabsorbent polymers and a decrease in water absorption performance.

(Effects of the Invention, etc.) The features of the present invention are that the treatment method is simple, dust and water absorption ability is maintained, and the water absorption rate is significantly improved by preventing "stickiness" that tends to occur during water absorption, and the gel strength is improved. You can get something excellent.

Therefore, the polymer obtained by the production method of the present invention can be advantageously used in the production of sanitary napkins, paper towels, etc. and other sanitary materials by taking advantage of its excellent water absorption performance and water absorption rate.

Furthermore, by taking advantage of its excellent water absorption performance and gel strength, it can also be used to manufacture various materials for horticultural and agricultural purposes, including soil conditioners and water retention agents, which have recently become popular. can.

The present invention will be explained in further detail below with reference to Examples and Comparative Examples.

Note that the pure water absorption capacity, saline water absorption capacity, and water absorption rate described in these examples were measured by the following test method and are indicated by rounded numbers.

A. Approximately 0.5 f of polymer and approximately IL of pure water in a beaker with a pure water absorption capacity of 1 t.
were weighed and mixed, and then left to stand for about 60 minutes to allow the polymer to sufficiently swell with water. Next, after draining with a 100-mesh filter, the amount of the filtrate is weighed, and the pure water absorption capacity is calculated according to the following formula.

B. Weigh and mix about 0.51F of polymer and about 20of of saline with a concentration of 0.9% in a beaker with a saline water absorption capacity of 300d, and then leave it for about 60 minutes to fully absorb the polymer with the saline. swelled to. Next, after draining with a 100-mesh filter, the amount of filtered saline solution is weighed, and the water absorption capacity of the saline solution is calculated according to the following formula.

C0 water absorption rate 300 m Add saline solution with a concentration of 0.9% by weight to a beaker for about 20 minutes.
About 0.5 f of polymer is weighed out, added and dispersed, and left to swell for a predetermined period of time (1 minute, 3 minutes, 5 minutes). After a predetermined period of time, weigh the volume of the filtrate using a 100 mesh sieve, and calculate the amount of water absorbed using the formula shown in B.

The results of the actual example and comparative example are summarized in Table 1 below.

Comparative Example-1 A super absorbent polymer was produced based on Example 1 of Japanese Patent Application No. 59-236685. i.e. stirrer, reflux condenser,
Put 375f of cyclohexane into a 1 ton capacity four-necked round bottom flask equipped with a thermometer and a nitrogen gas inlet tube, add 4.52% of sorbitan monostearate and dissolve it, then blow in nitrogen gas to remove dissolved oxygen. kicked out.

Separately, in a flask with a capacity of 500 wj, 75 f of acrylic acid was dissolved in 201 @ of water while cooling with ice from the outside.
Add 1.2f of caustic soda to remove 74% of the carboxyl group.
Neutralized 9%. In this case, the monomer concentration relative to water corresponds to 300% by weight. Next, 0.259 g of potassium persulfate was added and dissolved, and then nitrogen gas was blown in to drive out dissolved oxygen. The contents of this 500-ml flask were added to the interior of the four-bottomed flask, stirred to disperse them, and the temperature inside the flask was raised in an oil bath while bubbling nitrogen gas, resulting in a temperature around 60°C. After reaching the temperature, the internal temperature rose rapidly and reached 75°C several tens of minutes later. Next, one of them was kept at 60 to 65°C and reacted for 4 hours while stirring. Note that stirring was performed at 250 rpm.

When stirring was stopped after 4 hours of reaction, 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 dried at 80-90%
The adhering cyclohexane and water were removed by heating to 0.degree. C., resulting in a powdered polymer containing free-flowing, easily grindable lumps.

Comparative Example 2 A superabsorbent polymer was produced based on Example 1 of Japanese Patent Publication No. 54-30710. i.e. stirrer, reflux condenser,
Add 22B of n-hexane to a 500D four-necked round bottom flask equipped with a nitrogen gas inlet tube, add and dissolve 1.8F of sorbitan monostearate, and then blow in nitrogen gas to drive out the dissolved oxygen. Ta. Separately, in an Erlenmeyer flask, 75% of the carboxyl groups were neutralized with 13.1 f095% caustic soda dissolved in 39 f of water while cooling 30 f of acrylic acid with ice from the outside. The monomer concentration in the aqueous phase is 4
I lost 5 weight. Next, 0.19 g of potassium persulfate was added and dissolved, and nitrogen gas was blown into the solution to remove oxygen present in the solution. The contents of the Erlenmeyer flask were added to the above-mentioned four-hole flask and dispersed, a slight amount of nitrogen gas was introduced, and the internal temperature of the flask was maintained at 60 to 65° C. in an oil bath to continue the reaction for 6 hours. When the stirring was stopped, the reaction system became a suspension system in which the swollen polymer particles easily sedimented and separated. n
- Hexane was distilled off under reduced pressure, and a portion of the remaining swollen polymer was dried under reduced pressure at 80-90° C. The polymer was obtained as a free-flowing powder containing lumps that could be easily powdered.

Comparative Example-3 A superabsorbent polymer was produced based on Example 1 of JP-A-56-131608. That is, 30f of acrylic acid is
00- flask, and while cooling and stirring, 58.72% of a 22.6% by weight aqueous solution of caustic soda was added dropwise to neutralize the solution to 80% by mole, then 0.11% of potassium persulfate was added, and the mixture was stirred. Continued dissolution at room temperature.

500m equipped with a reflux condenser that replaced the system with nitrogen in advance
Cyclohexane 163.4f and HL B 8 in the flask
．． After the surfactant was dissolved at room temperature under stirring, the above-mentioned aqueous solution of partially neutralized acrylic acid salt was added dropwise and suspended. After sufficiently purging the system with nitrogen again, the temperature is raised and the oil bath is heated! ! The polymerization reaction was carried out for 3 hours while maintaining the temperature at 55 to 60°C.

The produced polymer solution was evaporated to dryness under reduced pressure to obtain a dry polymer in the form of fine granules.

Comparative Example-4 A super absorbent polymer was produced based on Example 9 of JP-A-52-25886. That is, 1st corn starch ('1159 water) was charged into a reaction vessel equipped with a stirring rod, a nitrogen blowing tube, and a thermometer, stirred at 80°C for 1 hour under a nitrogen stream, cooled to 30°C,
f acrylic acid %15f acrylamide)', 0.15
Calcium oxide of F, and o, i as a polymerization catalyst
St of ammonium persulfate and 0.0152 of sodium bisulfite were added, and the mixture was stirred at 40°C for 3 hours to polymerize. The reaction solution becomes an elastic white solid.9. The obtained white solid was dried under reduced pressure at 80 to 90°C, pulverized,
It was made into a powder.

This powder was added to a 5% sodium hydroxide water/methanol mixed bath WL (water to methanol weight ratio 1:5), 146.5f.
After adding tft& and leaving it for 1 hour at room temperature, it was dried under reduced pressure at 80 to 90°C and crushed to obtain a slightly colored powder.

Comparative Example-5 A superabsorbent polymer was produced based on Example 3 of JP-A-52-27455. That is, 0.5 t of benzoyl peroxide was added as a polymerization initiator to 60 t of vinyl acetate and 40 F of methyl acrylate, and this was dispersed in 300 d of water containing 3 t of partially saponified polyvinyl alcohol as a dispersion stabilizer, and polymerized at 65° C. for 6 hours. After cooling, the resulting copolymer was filtered and dried.

Next, the copolymer 259 was dissolved in 800 methanol, and 58.1+d of 40% aqueous sodium hydroxide solution was added thereto, followed by saponification at 60°C for 5 hours. After the reaction was completed, the saponified product was washed with methanol and then dried under reduced pressure to obtain a powder.

Comparative Example-6 A super absorbent polymer was produced based on Example 11 of JP-A-58-71907. That is, 309 acrylic acid was added to 9.24 t of deionized water, and to this was added 20.6 f of potassium hydroxide with a purity of 85% as a neutralizing agent, N, N'
- Methinone bisacrylamide 0.00832 f is sequentially added to prepare a potassium acrylate aqueous solution (neutralization degree 75%) with a mixed monomer concentration of 70% by weight.

The aqueous solution prepared above was kept warm at 70°C, and 1 part of water was added to it.
．． Of 2,2'-azobis(2-amidinopropane)
Polymerization starts after a few seconds and is completed within about 1 minute, resulting in a dry polymer foamed by the heat of polymerization. It was made into a powder.

Example-1 Dry polymer 201 obtained with the same formulation as Comparative Example-1 was
t# eggplant flask. Then methanol 259
was added to form a slurry, and while stirring, a mixed solution of trimethylolpropane diglycidyl ether o and osr dissolved in 4.5 t of water was added, and stirring was continued for about 30 minutes at room temperature. Next, the above contents were placed in an oil bath at 80°C and heated to 110°C.
The temperature was raised to 100°C, and heat treatment was performed. After raising the temperature to 110°C, the pressure was further reduced and evaporated to dryness to obtain a dry polymer.

Example 2 Using a dry polymer obtained using the same recipe as in Comparative Example 1, and using sorbitol diglycidyl ether as a crosslinking agent, a dry polymer was obtained using the same recipe as in Example 1.

Example-3 Water was added to 180? After distillation, there is 0 sorbitol diglycidyl ether in it.
．． After adding 359 and thoroughly mixing, the mixture was placed in an 80°C oil bath and heated to 110°C for heat treatment. 11011::
After raising the temperature to , the pressure was reduced and the mixture was evaporated to dryness to obtain a dry polymer.

Comparative Example 7 A super absorbent polymer was produced based on Example 1 of JP-A-56-161413. That is, n-hexane 230111j was placed in the same flask as used in comparison column-2.
After removing the water and dissolving 1.8 F of sorbitan monostearate, nitrogen gas was blown into the solution to drive out dissolved oxygen. Separately, in an Erlenmeyer flask, acrylic acid 301 was cooled with ice from the outside and neutralized with 13.81095% caustic soda dissolved in water 469, and then 1.592% of 2-hydroxy 7-ethyl acrylate was added and dissolved. Next, 0.19% of potassium persulfate was added and dissolved, and then nitrogen gas was blown into the aqueous solution to remove oxygen present in the aqueous solution. Add the contents of the Erlenmeyer flask to the above flask, disperse, and bring the internal temperature of the flask to 60 to 65°C in an oil bath while introducing a small amount of nitrogen gas.
The reaction was continued for 3 hours.

After the reaction was completed, n-hexane was distilled off under reduced pressure, and a portion of the remaining swollen polymer was dried under reduced pressure at 80 to 90°C to obtain a powdery polymer.

Comparative Example-8 A super absorbent polymer was produced based on the contents of JP-A-57-168921. That is, polyethylene glycol (
Daiichi Kogyo Yakuhin ■, P, EG-NO154G) 1.4
A mixture of F and methanol 234f is added, and the mixture is stirred at room temperature for 10 minutes. After filtration with a glass filter and drying under reduced pressure, a dry polymer was obtained.

(Left below) 1) Place 0.5 t of polymer in a Petri dish and drop 20 m of saline solution with a pipette for 2 seconds and judge.

2) Judgment is made using a gel after absorbing 200 times the weight of pure water of the polymer.

X2 weak Δ: Slightly weak ○: Normal (standard) ■＝Slightly strong 02 strong

Claims (2)

[Claims] (1) Trimethylolpropane diglycidyl ether, diglycerol diglycidyl ether, diglycerol triglycidyl is added to a superabsorbent polymer containing a carboxyl group or/and a carboxylate group as a component of a polymer or copolymer in the presence of water. A super absorbent polymer characterized by surface crosslinking treatment with one or more crosslinking agents selected from ether, sorbitol diglycidyl ether, sorbitol triglycidyl ether, and sorbitol tetraglycidyl ether, and at the same time, hydroxyl groups are introduced onto the polymer surface. manufacturing method. (2) The superabsorbent polymer is (meth)acrylic acid or/
The method according to claim 1, which is a polymer containing an alkali metal salt of (meth)acrylic acid as a constituent component of the polymer.