JPS6143606A - Preparation of highly water absorbing resin - Google Patents

Abstract

PURPOSE:To obtain the titled resin satisfying various performances such as water absorption capacity and water absorption rate, etc. at the same time, by dispersing an aqueous solution of an alkali metal acrylate containing a water- soluble polymerization initiator in a hydrophobic organic solvent in the presence of a special dispersing agent and polymerizing the salt. CONSTITUTION:An aqueous solution of an alkali metal acrylate containing a water-soluble polymerization initiator, e.g. ammonium persulfate, is dispersed in a hydrophobic organic solvent, preferably a solvent, e.g. cyclohexane, in the presence of sucrose ester of a fatty acid as a dispersing agent to carry out the reversed phase suspension polymerization. The amount of the above-mentioned dispersing agent ot be used is 0.1-5wt% based on the alkali metal acrylate.

Description

DETAILED DESCRIPTION OF THE INVENTION L1LL Mori 111 The present invention is to produce a water-absorbing resin, especially water-absorbing capacity, water-absorbing rate, gel strength, etc., by a reverse phase suspension polymerization method from an aqueous rB solution of an alkali metal acrylate. The present invention relates to a method for obtaining a water-absorbing resin having excellent properties and a substantially uniform particle size.

Water-absorbing resins are used in sanitary products such as sanitary products, diapers, and disposable rags, as well as agricultural and gardening products such as water retention agents, and are also used for purposes such as coagulating sludge, preventing condensation on building materials, and dehydrating oils. It is being

Examples of this water-absorbing resin include carboxymethylcellulose crosslinked products, polyoxyethylene partially crosslinked products, starch-7crylonitrile graft copolymer hydrolysates, polyacrylate partially crosslinked products, vinyl alcohol-acrylate copolymers, etc. It has been known. The performance of these water-absorbing resins is
In particular, it depends greatly on the manufacturing method, but none of them can simultaneously satisfy all required performances such as water absorption capacity, water absorption rate, gel strength, etc. For example, the water absorption capacity may be low, or even if the water absorption capacity is high. However, the gel strength after water absorption is weak, the gel after water absorption feels sticky, and there is no so-called smooth feeling, and the resin after water absorption becomes sticky. .

A known method for improving the gel strength of the above-mentioned water-absorbent resin after water absorption is to increase the crosslinking density of the water-absorbent resin. There are certain shortcomings.

Furthermore, the disadvantage that the resin becomes lumpy after water absorption can be overcome by surface-modifying the water-absorbing resin using a crosslinking agent such as ethylene glycol diglycidyl ether. However, the crosslinking agent itself has risks such as skin irritation, and when it remains in the resin, new safety and health problems arise.

In addition, in recent years, as a method for producing water-absorbent resins with high water absorption capacity, a method of inverting an aqueous solution of alkali metal acrylic salt by using a combination of two specific initiators and using a specific sorbitan fatty ester as a dispersant has been developed. A technique for conducting a polymerization reaction according to the phase suspension polymerization method was proposed (Japanese Patent Application Laid-Open No. 161408/1983).
(see publication).

However, even with the method proposed above, it is still not possible to obtain a polymer that fully satisfies the various performances required of water-absorbing resins, and its water-absorbing ability, water-absorbing rate, gel strength, viscosity, etc. have not been improved. There is room for

Problems to be Solved by Akira In view of the above-mentioned circumstances, the present inventors have developed a water-absorbing resin that satisfies all of the required performances of water-absorbent resins, such as water-absorbing ability, water-absorbing speed, gel strength, and viscosity. We conducted intensive research with the aim of developing a synthetic resin. As a result, M1, which has never been used in the above reversed-phase suspension polymerization method! It has been found that when a fatty acid ester is used as a dispersant, all the problems seen in the prior art can be solved and a water-absorbing resin having excellent performance that meets the above objectives can be obtained. The present invention was completed based on this new knowledge.

In order to determine this, the present invention involves dispersing an aqueous alkali metal acrylate salt solution containing a water-soluble polymerization initiator in a hydrophobic organic solvent in the presence of a sucrose fatty acid ester and carrying out reverse phase suspension polymerization. It is related to the manufacturing method of the characteristic super absorbent resin.

In the method of the present invention, as mentioned above, the use of sucrose fatty acid ester as a dispersant is an essential requirement, and based on this, the properties required for the water absorbent resin, especially water absorption capacity, water absorption rate, gel strength, and It is possible to obtain the desired water-absorbing resin which has excellent viscosity, is relatively uniform, has an appropriate particle size, and is highly safe. In particular, the sucrose fatty acid ester used as the above-mentioned dispersant is known as a food emulsifier and is safe, meeting all the specifications of the Japanese Food Additives Standards. It is suitable for manufacturing resin. The sucrose fatty acid ester is usually obtained by transesterifying sucrose and a lower ester of fatty acid, and those having an HLB of 1 to 15 are commercially available. Its fatty acid components are generally stearic acid,
Valmitic acid, oleic acid, etc. are the main ones, and these are usually contained in the product in the form of a mixture because they are made from oils, fats, hydrogenated oils, etc. In the present invention, any of such commercially available sucrose fatty acid esters can be used. The amount of the sucrose fatty acid ester to be used is determined as appropriate, but it is generally preferably selected from a range of about 0.1 to 5% by weight of the monomer to be polymerized, that is, the alkali metal acrylate salt. If this is less than 0.1% by weight, the desired water-absorbent resin may not be obtained or the particle size of the obtained polymer (water-absorbent resin) tends to be uneven, and if it exceeds 5% by weight, However, the effect is not particularly noticeable, and it is economically disadvantageous.

In the present invention, the monomer to be polymerized in the presence of the Nts fatty acid ester is an alkali metal salt of acrylic acid, taking into consideration the water absorption capacity, safety, rot resistance, etc. of the resulting water absorbent resin. use

This monomer can be obtained by neutralizing acrylic acid with an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.

The degree of neutralization does not need to be 100%, but is usually 50%.
% to 95%. If the degree of neutralization is too much less than 50%, the polymerization rate tends to decrease and the water absorption capacity tends to be poor, whereas there is no particular advantage if the degree of neutralization is more than 95%.

The above monomer is subjected to the reversed-phase suspension polymerization reaction of the present invention in the form of an aqueous solution. The monomer concentration in the aqueous solution is the polymerization stability during suspension polymerization, and the molecules of the resulting polymer! (degree of crosslinking), usually up to a saturation concentration of 35% or more, preferably 4
It is preferable to adjust it to 0-70%. If this concentration is less than 35%, suspension polymerization stability may decrease and aggregates may be produced as by-products.

In the reverse phase suspension polymerization of the monomer aqueous solution in the presence of sucrose fatty acid ester in the present invention, a water-soluble polymerization initiator is added and dissolved in the monomer aqueous solution in advance. As the water-soluble polymerization initiator, any of various conventionally known initiators can be used.

Examples include water-soluble persulfate m salts such as ammonium persulfate and potassium persulfate, and water-soluble azo initiators such as azobis-(2-amidinopropane) hydrochloride. These polymerization initiators are usually selected from a range of about 0.001 to 5.0!1 ffi%, preferably about 0.01 to 2.0% by weight, based on the alkali metal salt of acrylic acid. .

Note that when the above monomers are polymerized using a water-soluble oversulfurization salt, the self-crosslinking reaction proceeds without using any crosslinking agent, but when using a water-soluble azo initiator, the self-crosslinking reaction proceeds. may be difficult to progress or may not progress. In this case, the acrylic wave alkali metal uAl! It is necessary to further add a crosslinking agent component to the fli body aqueous solution. This crosslinking agent component is already known in this field, and typically, bisacrylamides such as methylenebisacrylamide and methylenebismethacrylamide, divinyl compounds shown below, etc. can be used. .

〇 General formula (in the formula, X is ethylene, propylene, 2-hydroxypropylene, □ +CH2CH204-CH2CH2- group or 5-
Indicates an integer of 40. ] Diacrylic (or methacrylic) acid esters represented by The compound of general formula (1) can be obtained, for example, by reacting polyols such as ethylene glycol, propylene glycol, glycerin, polyethylene glycol, polypropylene glycol, and acrylic acid or methacrylic acid.

〇General formula % formula % [In the formula, Q represents 2 or 3. ] Diacrylamides represented by. The compound of general formula (2) can be obtained, for example, by reacting polyalkylene polyamines such as diethylenetriamine and triethylenetetramine with acrylic acid. Among these, especially N, N'
Bisacrylamides such as -methylenebisacrylamide and N,N'-methylenebismethacrylamide are preferred.

The above-mentioned crosslinking agent component contributes to a certain degree of improvement in the gel strength of 1g2 of the combined product, and is usually about 0.001 to 0.3% by weight, preferably about 0.00% by weight, based on the alkali metal acrylate salt used as the monomer. It is used in a range of 0.005 to 0.1% by weight.

Hydrophobic tampon used as a dispersion medium in the present invention
ttg influences the stability of the polymer produced by reverse phase suspension polymerization and is usually selected from aliphatic or alicyclic hydrocarbon solvents. Specific examples thereof include n-pentane, n-hexane, n-hebutane, cyclohexane, ligroin, etc., especially cyclohexane, n-
Pentane and n-hexane are preferred. The ratio of the dispersion medium to the monomer aqueous solution can be varied over a wide range of t! Although the volume ratio can be varied depending on the environment, it is usually appropriate to set the volume ratio of monomer aqueous solution to dispersion medium in the range of 1:2 to 5:1.

The reverse phase suspension polymerization method of the present invention can be basically carried out according to conventionally known methods, except for using the above-mentioned specific sucrose fatty acid ester. As a specific example, for example, the hydrophobic Ti-containing solvent and the sucrose fatty acid ester are added and dissolved in a suitable reaction vessel, and a water-soluble polymerization initiator and, if necessary, a crosslinking agent are added in advance under a nitrogen stream. After adding a predetermined amount of the prepared aqueous solution of alkali metal acrylic acid salt and raising the temperature in the system to 40 to 80°C, the system was maintained for a predetermined time, water was distilled off under azeotropy, and the contents were then filtered. Then, a method of drying under reduced pressure can be adopted. In this way, it is possible to obtain the desired polymer in the form of beads, usually having an average particle size of about 0.01 to 2 mm.

According to the above-described method of the present invention, the polymerization reaction can be carried out stably based on the use of a specific sucrose fatty acid ester as a dispersant, and therefore bead-shaped polymers having an appropriate particle size can be obtained. Furthermore, the polymer thus obtained has excellent properties such as water absorption capacity, water absorption rate, and gel strength, and has features such as no fusion between particles during water absorption (mamako phenomenon) and no sticky feeling. Moreover, the dispersant used in the method of the present invention is safe in itself and does not contain any other substances that may cause skin irritation, so the resulting polymer also poses safety and health problems. Not at all. This is an excellent advantage especially when the obtained polymer is used for purposes such as sanitary product materials.

The water-absorbing resin obtained by the method of the present invention can be similarly used in various fields in which conventional water-absorbing resins of this kind are used, and can be used particularly effectively because it has the above-mentioned properties.

Examples are given below to explain the method of the present invention in more detail, but the present invention is not limited thereto.

Example 1 1 equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube
350 cyclohexane in a four-volume rosette flask
g, and 0.60 g of sucrose fatty acid ester was added and dispersed therein. Next, nitrogen gas was blown in to drive out the dissolved oxygen in the system, and the temperature was raised to 60°C. Sugar fatty acid ester (manufactured by Dai-Kogyo Seiyaku Co., Ltd., trade name rDK Ester F
-50J, HLB6) was dissolved. 11. Separately, 18.9 g of acrylic acid was placed in an Erlenmeyer flask, and this was dissolved in 30 g of ion-exchanged water while cooling with ice from the outside.
10 96% water-broken potassium water-soluble 8! (corresponding to 72 mol% based on acrylic acid), N,N'-
Methylenebisacrylamide 0.004Q and 2.2'
-7 Zobisu (2-Amizip O Pan) 2 Salt Shun Salt 0.0
3 g was added and nitrogen gas was blown into the system to remove oxygen present in the aqueous solution in the system. The contents of the Erlenmeyer flask were added to and dispersed in the four rosetteable flasks, the internal temperature of the flask was maintained at 60°C for 1 hour with stirring, the reaction was completed, and cyclohexane and water were azeotropically distilled. After removal, the temperature inside the system was cooled to 40° C. or lower, and the contents were filtered and dried under reduced pressure to obtain a spherical polymer (water-absorbing resin A) with a center particle diameter of 0.01 to 0.211.

Example 2 In the same manner as in Example 1 except that 0.3 g of M sugar fatty acid ester was used, the center particle size was 0.01 to 0.2011.
A spherical polymer (water absorbent resin B) was obtained.

Example 3 In the same manner as in Example 1, except that 0.06a of sucrose fatty acid ester was used, the center particle size was 0.01 to 1.011.
An m-spherical polymer (water absorbent resin C) was obtained.

Example 4 In the same manner as in Example 1, except that ethylene glycol diallyl ester 0.0049 was used instead of N,N=-methylenebisacrylamide as a crosslinking agent, a material having a center particle diameter of 0.01 to 0.21111 was prepared in the same manner as in Example 1. A spherical polymer (water absorbent resin D) was obtained.

Example 5 In the same manner as in Example 1, except that 0.004 g of diethylenetriamine diacrylamide was used instead of N,N''-methylenebisacrylamide as the crosslinking agent,
A spherical polymer (water-absorbing resin E) having a central particle diameter of o, oi to 0.2 square meters was obtained.

Example 6 In Example 1, the shochu fat ester was manufactured by Dai-Kogyo Seiyaku Co., Ltd., trade name rDK ester F-204 (
Similarly, using HLB6), the central particle size was 0.01 to 0.
．． A spherical polymer of No. 21111 (water absorbent resin F) was obtained.

Example 7 In Example 1, the sucrose fatty ester was manufactured by Dai-Kogyo Seiyaku Co., Ltd., trade name rDK ester F-1404.
(HLB13) in the same manner, the center particle diameter was 0.01.
A spherical polymer (water-absorbing resin G) having a particle size of 0.21 was obtained.

Example 8 Same as Example 1 except that 0.03111 potassium persulfate was used instead of 2.2-1azobis-(2-amidinopropane) dihydrochloride as the polymerization initiator and no crosslinking agent was used. A spherical polymer (water absorbent resin H) having a center particle diameter of 0.01 to 0.21 m1 was obtained.

Comparative Example 1 The same procedure as in Example 1 was repeated except that 0.3 g of sorbitan monostearate was used instead of the sucrose fatty acid ester, but the central particle diameter was 0.01 to . 0.1111 g of a spherical polymer (comparative water absorbent resin a) was obtained.

For each of the water absorbent resins obtained in the above Examples and Comparative Examples, the water absorption capacity, water absorption ia, gel strength and viscosity after water absorption were measured by the following methods.

(Water absorption capacity) (a) 150g of ion-exchanged water in a 200-inch beaker
and 0.12 g of a water-absorbing resin sample were added, and after being allowed to stand for 30 minutes, it was separated in a furnace using a 200-mesh wire mesh, 1ffi of the flowing water was measured, and the water absorption capacity was calculated using the following formula.

(The weight of the water-absorbing resin sample added at the beginning - (the water absorption capacity that flows out - the weight of water!11)) (b) In the above (a), 0.9% saline was used instead of ion-exchanged water. A similar test was conducted to determine the water absorption capacity.

[Water absorption speed]

In advance, add physiological saline (0
, 9% saline solution) and a stirring bar were stirred at a speed of 600 rpm using a magnetic stirrer, and water absorbent resin sample 2. When Oa is added, gelation occurs due to water absorption and swelling, fluidity decreases, and the water vortex at the stirring center disappears. Measure the time required for the vortex to disappear after adding the water-absorbing resin sample, and use this as the water absorption rate.

[Gel strength]

A gel (hereinafter referred to as 30x gel) was prepared by mixing 60 g of physiological saline and 2.0 g of a water-absorbing resin sample, and
The hardness (surface hardness and internal hardness) of the gel is measured using a Neocard meter manufactured by Iki Co., Ltd. Here, the surface hardness is expressed as a resistance force that prevents the pressure-sensitive shaft from pushing away the gel and entering the sample surface. On the other hand, internal hardness is expressed as the resistance force of the pressure-sensitive shaft to cause the gel to flow inside the gel.

[Gel viscosity 11'1K] The viscosity of the 30x gel was determined using a Neocard meter, and the stickiness of the gel was evaluated based on these measured values. The viscosity force here refers to the apparent viscosity that acts in the form of wm force to cause the gel to flow.

The results obtained according to each of the above test methods are shown in Table 1 below.

Table 1

Claims (1)

[Claims] (1) A superabsorbent resin characterized by dispersing an aqueous alkali metal acrylic salt solution containing a water-soluble polymerization initiator in a hydrophobic organic solvent in the presence of a sucrose fatty acid ester and subjecting it to reverse phase suspension polymerization. manufacturing method.