JPH1045929A - Production of porous crosslinked polymer material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a low-density porous crosslinked polymer material having improved absorption capacity in a state in which a water-in-oil type high disperse phase emulsion at high water to oil ratio is maintained. SOLUTION: This polymer material is produced from a water-in-oil type emulsion obtained by mixing a monomer component comprising essentially a crosslinking monomer having at least two polymerizable unsaturated groups in the molecule with water in the presence of a surfactant comprising essentially a pentaerythritol ester of a fatty acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for obtaining a water-in-oil emulsion used in producing a porous cross-linked polymer material by a highly dispersed phase water-in-oil emulsion polymerization method.

[0002]

BACKGROUND OF THE INVENTION Polymer foams can be classified as either closed-cell foams or open-cell foams. Open cell foams can be used as a matrix to contain various liquids and gases. These are variously industrially applicable, for example, as wipes and diapers, as carriers and ion exchange resins. For some of these applications, it is desirable to form porous cross-linked polymer blocks that have very low density and high capacity to absorb and retain liquids. Such high absorption capacity, low density polymer blocks are known as highly dispersed phase emulsions (HIPEs) having a relatively small amount of continuous oil phase and a relatively large amount of internal or dispersed aqueous phase, Of water-in-oil emulsions. Generally, these high absorption capacity, low density foams form a highly dispersed phase water-in-oil emulsion with a weight ratio of water to oil phase greater than 9: 1 in the presence of a surfactant, It is produced by polymerizing the monomers in the oil phase at about 60 ° C. with a polymerization initiator for about 8 hours. However, the stability of the emulsion at high water-to-oil ratios, eg, above 30: 1, is poor and sometimes emulsion breakage can occur.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an oil having high stability even at high water to oil ratios in order to obtain a low density, porous, crosslinked polymer material having improved absorption capacity. It is an object of the present invention to provide a method for producing using a water-in-water type high dispersion phase emulsion.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and found that, in the presence of a surfactant containing pentaerythritol fatty acid ester as an essential component,
By forming a water-in-oil emulsion, a stable water-in-oil emulsion that could not be obtained by the conventional method of producing a porous cross-linked polymer material is formed, and the porous cross-linking having an improved absorption capacity is obtained in a subsequent step. The inventors have found that a polymer material can be provided, and have completed the present invention.

Hereinafter, the present invention will be described in detail.

For the production of the porous polymer material, various vinyl monomers can be used as long as they can be dispersed in a water-in-oil type high-dispersion phase emulsion or can form the oil phase of the emulsion. Crosslinkable monomers having at least two polymerizable unsaturated groups in the molecule can be used. Vinyl monomers used in the present invention include, for example, styrene,
Monoalkenyl arene monomers such as α-methylstyrene, chloromethylstyrene, vinylethylbenzene and vinyltoluene: for example, 2-ethylhexyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, hexyl acrylate, n -Acrylates or methacrylate ethers such as butyl methacrylate, lauryl notacrylate and isodecyl methacrylate: and mixtures thereof.

[0007] In the molecule used in the present invention, at least two
Examples of the crosslinkable monomer having one polymerizable unsaturated group include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and polyethylene glycol-polypropylene glycol di (meth). Acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate,
1,6-hexanediol di (meth) acrylate, N,
N'-methylenebisacrylamide, N, N'-propylenebisacrylamide, glycerin tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, polyhydric alcohol (for example, glycerin, trimethylol Examples thereof include polyfunctional (meth) acrylates and divinylbenzenes obtained by esterification of an alkylene oxide adduct of propane or tetramethylolmethane with (meth) acrylic acid. One or more of these may be used. be able to. Among these, a crosslinkable monomer suitable for use in the present invention is divinylbenzene.

Further, the ratio of the crosslinkable monomer having at least two polymerizable unsaturated groups in the molecule used in the present invention to the total monomer component is 1 to 5 in the total monomer component.
0% by weight, preferably 5 to 45% by weight, more preferably 10 to
It is in the range of 40% by weight. If the amount of the crosslinkable monomer used is less than 1% by weight, it becomes difficult to form a porous molded body having continuous pores due to stickiness of the crosslinked polymer, or the crosslinked polymer itself during liquid absorption becomes difficult. It may be easily dissolved and may not exhibit sufficient liquid absorption performance. On the other hand, if it exceeds 50% by weight, the absorption amount per unit volume or unit weight of the obtained liquid absorbing material may be insufficient.

The pentaerythritol fatty acid ester used in the present invention may be any ester of pentaerythritol and a fatty acid. Among them, pentaerythritol monolaurate, pentaerythritol monopalmitate, pentaerythritol monostearate and pentaerythritol monooleate are preferred. These pentaerythritol fatty acid esters may be used alone or in admixture with two or more kinds to improve the liquid absorption rate, or in combination with other surfactants such as sorbitan fatty acid esters.

[0010] The total amount of the surfactant containing pentaerythritol fatty acid ester as an essential component is usually 100
It is in the range of 1 to 40 parts by weight based on parts by weight. Preferably 5 to
It is in the range of 30 parts by weight. When the amount of the surfactant containing pentaerythritol fatty acid ester as an essential component is less than 1 part by weight, the water-in-oil emulsion may become unstable. If the amount is more than 40 parts by weight, the effect corresponding to the amount used may not be exhibited.

[0011] A good water-in-oil emulsion with a high disperse phase is
An emulsion as obtained without substantial degradation of the emulsion. The unabsorbed free water present on the emulsion surface after the formation of the emulsion indicates the decomposition or deterioration of the emulsion. Thus, when a good emulsion cures, no or little water is not absorbed after curing. An emulsion is substantially degraded when the amount of unabsorbed free water is generally greater than 5% by weight, based on the total amount of water used to make the emulsion. That is, during curing, the decomposition of the emulsion should be less than 10% by weight, more preferably less than 5% by weight of the total water, based on the total water used to make the emulsion.

Further, in the present invention, various stabilizers can be added to the oil phase or the aqueous phase in advance for the purpose of stabilizing the water-in-oil emulsion at the time of polymerization. Suitable as a stabilizer are water-soluble inorganic salts, which are preferably added to the aqueous phase. Such water-soluble inorganic salts include, for example, water-soluble salts such as potassium, sodium, calcium, magnesium, and aluminum, and polyvalent metal salts are particularly preferable. The addition amount of the water-soluble inorganic salt is preferably 0.1 to 20 parts by weight, particularly preferably 0.3 to 10 parts by weight, per 100 parts by weight of water.

As the polymerization initiator used in the present invention, a conventionally known radical generator may be used. For example, monomer-soluble organic peroxides such as benzoyl peroxide, lauroyl peroxide and cumene hydroperoxide may be used. 2,2′-azobisisobutyronitrile,
Monomer-soluble azo compounds such as 2,2′-azobisdimethylvaleronitrile; potassium persulfate, sodium persulfate,
Water-soluble persulfates such as ammonium persulfate; water-soluble azo compounds such as 2,2'-azobis (N, N-dimethyleneisobutylamidine) dihydrochloride and 2,2'-azobis (2-amidinopropane) dihydrochloride These can be used alone or in combination of two or more. Further, it can be used as a redox polymerization catalyst in combination with a reducing agent such as sodium thiosulfate and sodium sulfite. In particular, in order to control the pore size, it is preferable to use a redox polymerization catalyst that can be polymerized at a low temperature. These polymerization initiators are used in the form of a mixture with a monomer or water. The amount of the polymerization initiator to be used is preferably 0.05 to 5% by weight, more preferably 0.1 to 3% by weight, based on the monomer components.

In obtaining the porous crosslinked polymer material of the present invention, first, a vinyl monomer, an oil phase component comprising a crosslinkable monomer having at least two polymerizable unsaturated groups in a molecule, and water Must be mixed in the presence of a surfactant essentially containing pentaerythritol fatty acid ester to form a water-in-oil emulsion having a large amount of water as an internal discontinuous phase. The preferred mixing ratio of the oil phase component and water is in the range of 99 to 90% by weight of water to 1 to 10% by weight of the oil phase component. More preferably 1 to 5 parts by weight of oil phase component with water
It ranges from 99 to 95% by weight. If the amount of the oil phase component is less than 1% by weight, the strength of the obtained porous cross-linked polymer material may be reduced, which may cause a problem in handleability. When the amount of the oil phase component is more than 10% by weight, the liquid absorption of the obtained porous cross-linked polymer material may decrease.

In the present invention, as a method of forming a water-in-oil emulsion by mixing an oil phase component with water in the presence of a surfactant essentially containing a pentaerythritol fatty acid ester, a large amount of water is immiscible. There is no particular limitation as long as a water-in-oil emulsion having a continuous phase can be formed. For example, 1) a method in which an oil phase in which a pentaerythritol fatty acid ester is dissolved is added to water with stirring, 2)
A method in which water is added to an oil phase in which pentaerythritol fatty acid ester is dissolved while stirring, 3) A method in which water is added to an oil phase in which pentaerythritol fatty acid ester is dissolved and stirred, 4) An oil in which pentaerythritol fatty acid ester is dissolved in water And a method in which the oil phase in which the pentaerythritol fatty acid ester is dissolved and water are continuously fed and mixed. Further, in each method, a surfactant that essentially requires a pentaerythritol fatty acid ester may be previously dissolved in an oil phase as in the above method, or may be previously dispersed in water, or an oil phase component, Water and a surfactant essentially containing pentaerythritol fatty acid ester can be separately supplied and mixed. A preferred method from an economic viewpoint is a method in which a surfactant essentially containing pentaerythritol fatty acid ester is dissolved in the oil phase component in advance.

As the mixing or stirring device that can be used in the present invention, a conventionally known mixing or worling device can be used.
Examples thereof include a tank-type stirring device equipped with various stirring blades, a static mixer, a neader, and a homogenizer.

In the method of the present invention, the water-in-oil emulsion formed by the above method is used in the presence of a polymerization initiator in the range of 15 to 90.
Aged at a temperature of ℃ to obtain a porous cross-linked polymer. In the polymerization, the water-in-oil emulsion is preferably subjected to static polymerization under conditions in which the internal aqueous phase is not destroyed.For example, cast polymerization is performed while feeding the water-in-oil emulsion batchwise or continuously. Can be. In the polymerization, by forming the polymerization container into an arbitrary shape, the porous cross-linked polymer obtained by the polymerization can be formed and polymerized into an arbitrary shape, for example, particles, fibers, mats, sheets, blocks, and the like. It is possible. Of course, a continuous polymerization method can be employed as the polymerization method. Polymerization temperature is 15-90
° C, preferably in the range of 20 to 50 ° C. It is also possible to carry out the first half of the polymerization in a temperature range of 20 to 50 ° C. and the second half in a temperature range of 50 to 90 ° C. The polymerization time is suitably about 1 to 30 hours. If the polymerization temperature is lower than 15 ° C., it takes a long time for polymerization and is not industrially preferable.If the polymerization temperature is higher than 90 ° C., it becomes difficult to control the pore size of the obtained porous cross-linked polymer, and the liquid absorption of the liquid absorbing material Decrease.

The porous crosslinked polymer produced by the method of the present invention can be washed and dried to obtain an absorbent block that is particularly useful for absorbing liquids. In order to reduce the electrolyte content of the porous crosslinked polymers, these porous crosslinked polymers are generally washed with a solvent. Suitable solvents are, for example, alcohols, low-concentration electrolyte solutions (lower than the aqueous phase), such as 1% calcium chloride solution or deionized water. The washed porous cross-linked polymer can be dried by squeezing water and / or solvent from the porous cross-linked polymer and / or by using air drying, heat drying or vacuum drying.

According to the production method of the present invention, it is possible to produce a low-density porous crosslinked polymer material having a small amount of syneresis after curing and therefore having a high absorption capacity. The low-density porous crosslinked polymer material of the present invention thus obtained is
It can be cut into any shape, such as sheet, block, fiber, film, powder, etc., according to the purpose, and it comes in contact with liquids such as water, alcohol, petroleum, etc. Since it is made of a porous molded body having a large number of continuous pores in which the liquid permeates into the molded body when it is made, the liquid absorption capacity is remarkably excellent. Although the porous molded article of the present invention may be used as it is as a liquid absorbing material, at least a part of the porous molded article is sandwiched by a liquid-permeable film, or the porous molded article is made of a liquid-permeable material. It is also possible to fill a container and use it as a liquid absorbing article.

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. In the examples, unless otherwise specified, parts mean parts by weight. The water separation rate and the absorption per unit weight of the low-density porous crosslinked polymer material for various liquids in the present invention were measured by the following methods.

(Water separation rate) The weight of water not absorbed after curing was measured, and the water separation rate (% by weight) was determined by the following equation. Water separation rate = weight of water not absorbed after curing / total amount of water used in emulsion production (absorbed amount per unit weight) Use a pre-weighed dry sample cut to 1 cm square with a thickness of about 10 mm, and a sufficient amount of various The sample was immersed in the liquid. The sample that has absorbed the liquid and expanded has a diameter of
After leaving it on a glass filter (# 0: manufactured by Duran) having a height of 120 mm and a height of 5 mm for 30 seconds to drain the liquid, the weight of the absorbed sample was measured, and the absorption amount of various liquids was calculated by the following formula ( g / g)
I asked.

Absorption amount = (weight of sample after liquid absorption−weight of sample before liquid absorption) / weight of sample before liquid absorption

[0023]

Next, the present invention will be described more specifically with reference to examples.

Example 1 A 1000 ml cylindrical polypropylene container was charged with 30 g of calcium chloride, 4.8 g of sodium persulfate and 312 g of pure water as an aqueous phase. Then, 1.3 g of styrene and 2-ethylhexyl acrylate were used as the oil phase.
4.0 g, 55 g divinylbenzene 1.3 g, and pentaerythritol monooleate (trade name: Exepearl PE-M
O, manufactured by Kao Corporation) was added into a container with stirring at room temperature. After 4 hours, the polymerization system became yogurt-like and a good emulsion was obtained. When the polymerization system became yogurt, stirring was stopped, a solution of 0.11 g of sodium bisulfite dissolved in 5.0 g of pure water was added, and the mixture was stirred again until the emulsion became uniform. After completion of the stirring, polymerization was carried out for 3 hours while keeping the vessel at room temperature, and then the vessel was placed in a 60 ° C water bath for 2 hours to complete the polymerization. At this time, the amount of water separation was 11.1 g, the water separation rate was 3.5% by weight, and a cured product with a small amount of water separation was obtained. The cured product is washed with hot water at 60 ° C., sliced in a water-containing state into a size of 10 mm in thickness, and further compressed and dehydrated in the thickness direction between perforated plates. Then 60
Swell and dehydrate twice with 1% calcium chloride aqueous solution at ℃
It was dried in a hot air dryer at 60 ° C. for 10 hours to obtain a porous crosslinked polymer material (1) of the present invention. The porous cross-linked polymer material (1) had an absorption amount of 19.6 g / g of ethanol (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd., purity: 99.5% or more) at 25 ° C. The porous crosslinked polymer material (1) had an absorption amount of water at 60 ° C. of 19.5 g / g.

Example 2 A 1000 ml cylindrical polypropylene container was charged with 30 g of calcium chloride, 4.8 g of sodium persulfate and 312 g of pure water as an aqueous phase. Then, 0.9 g of styrene and 2-ethylhexyl acrylate were used as the oil phase.
4.2 g, 1.5 g of 55% divinylbenzene, and pentaerythritol monooleate (trade name: Exepearl PE-M
O, manufactured by Kao Corporation) was added into a container with stirring at room temperature. Two hours later, the polymerization system became a yogurt state, and a good emulsion was obtained. When the polymerization system became yogurt, stirring was stopped, a solution of 0.11 g of sodium bisulfite dissolved in 5.0 g of pure water was added, and the mixture was stirred again until the emulsion became uniform. After completion of the stirring, polymerization was carried out for 3 hours while keeping the vessel at room temperature, and then the vessel was placed in a 60 ° C water bath for 2 hours to complete the polymerization. At this time, the amount of syneresis was 9.3 g, the syneresis rate was 2.9% by weight, and a cured product with less syneresis was obtained. The cured product is washed with hot water at 60 ° C., sliced in a water-containing state into a size of 10 mm in thickness, and further compressed and dehydrated in the thickness direction between perforated plates. Then 60
Swell and dehydrate twice with 1% calcium chloride aqueous solution at ℃
It was dried in a hot air dryer at 60 ° C. for 10 hours to obtain a porous crosslinked polymer material (2) of the present invention. The porous crosslinked polymer material (2) had an absorption amount of 22.7 g / g of ethanol at 25 ° C. (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd., purity: 99.5% or more). The porous cross-linked polymer material (2) had an absorption amount of water at 60 ° C. of 19.7 g / g.

Claims (4)

[Claims] In producing a porous cross-linked polymer material from a water-in-oil emulsion, the water-in-oil emulsion requires a cross-linkable monomer having at least two polymerizable unsaturated groups in a molecule. A method for producing a porous cross-linked polymer material, characterized by being obtained by mixing a monomer component to be obtained with water in the presence of a surfactant containing a pentaerythritol fatty acid ester as an essential component. 2. The process according to claim 1, wherein the water-in-oil emulsion contains at least 90% by weight, based on the emulsion, of water as a disperse phase. 3. The process for producing a porous cross-linked polymer material according to claim 1, wherein the amount of the surfactant containing pentaerythritol fatty acid ester as an essential component is 1 to 40% by weight based on the monomer component. . 4. The pentaerythritol fatty acid ester is at least one selected from pentaerythritol monolaurate, pentaerythritol monopalmitate, pentaerythritol monostearate and pentaerythritol monooleate. A method for producing a porous crosslinked polymer material according to claim 1.