WO2001038404A1

WO2001038404A1 - Method for production of porous cross-linked polymer material

Info

Publication number: WO2001038404A1
Application number: PCT/JP2000/008055
Authority: WO
Inventors: Koichi Yonemura; Akiko Mitsuhashi
Original assignee: Nippon Shokubai Co., Ltd.
Priority date: 1999-11-19
Filing date: 2000-11-15
Publication date: 2001-05-31
Also published as: JP4766812B2; JP2003514963A; AU1412701A

Abstract

For the production of a porous cross-linked polymer material formed of a water-in-oil high internal phase emulsion, a method is provided which comprises mixing and emulsifying an oil phase containing a monomer component and a water phase containing water thereby obtaining a water-in-oil high internal phase emulsion, partly polymerizing the resultant emulsion, imparting a prescribed shape to the partly polymerized emulsion, and subsequently causing the after-polymerization in process to be completed. This method is capable of continuously producing a porous cross-linked polymer material excelling absorption properties and mechanical strength in a short period of time.

Description

DESCRIPTION METHOD FOR PRODUCTION OF POROUS CROSS-LINKED POLYMERMATERIAL

Technical Field This invention relates to a method for the production of a porous cross-linked polymer which comprises a step of polymerizing a water-in-oil type high internal phase emulsion (hereinafter referred to briefly as "HIPE") and a step of after-polymerizing the HIPE in a very short period of time thereby producing a porous cross-linked polymer having continuous cells having communicating pores formed in the surface and the interior thereof (hereinafter referred to also as "open cells"). More particularly, this invention relates to a method for the production of a porous cross-linked polymer which carries out continuously the component steps thereof ranging from a step of supplying the HIPE through a step of polymerizing the HIPE, and can be widely applied to (1) liquid absorbent materials such as, for example, ® core materials in disposable diapers to be used for absorbing body fluid such as urine and blood; and (2) absorbing materials of water, oil and organic solvent to be used for disposing of a waste oil a waste solvent and waste organic solvents; (2) energy absorbent materials such as, for example, sound insulating materials and heat insulators in automobiles and buildings to be used for absorbing sound and heat; and (3) chemical impregnating substrates such as, for example, products of domestic use impregnated with an aromatic agent, a detergent, a lustering agent, a surface protecting agent, and a flame-retarding agent.

Background Art

The term "HIPE" refers to an emulsion wherein the ratio of a water phase, i.e. a dispersed phase (inner phase), to an oil phase, i.e. an outer phase is not less than about 3/1. It is known to produce a porous cross-linked polymer material by polymerizing this HIPE. The porous cross-linked polymer material produced by using a foaming agent without preparing an HIPE (hereinafter occasionally referred to simply as "foam") is disposed to afford a foam of closed cells of a comparatively large diameter. In contrast, the method for producing a porous cross-linked polymer material from an HIPE (hereinafter occasionally referred to briefly as "HIPE method" ) excels in capability of producing a low-density foam of open cells having a minute diameter.

Methods for producing porous cross-linked polymer materials from HIPE's are disclosed in the official gazette of U.S.P.No.4,522,953, 093/24,535 and U.S.P. No.5,290,820, for example.

The official gazette of U.S.P.NO. 4,522,953 discloses a method which comprises preparing an HIPE containing a water-soluble and/or an oil-soluble polymerization initiator and thermally polymerizing the HIPE at 50°C or 60°C for a period in the range of eight hours to 72 hours . The official gazette of W093/24,535 discloses a method which comprises forming a gel possessing a prescribed dynamic modulus of elasticity in shear from an emulsion at a temperature less than 65°C and thereafter polymerizing the gel at a temperature of not less than 70°C. Then, the official gazette of U.S.P. No.5,290,820 discloses a method which, in view of the fact that a gaseous monomer such as butadiene is not easily introduced into an HIPE because it continues to exist in the gaseous state dependent on the volatility during the course of the preparation of the HIPE, comprises preparatorily emulsifying a partly polymerized monomer and then polymerizing the emulsified monomer.

The method which is disclosed in the official gazette of U.S.P.NO. 4,522,953, however, is deficient in efficiency of production because of an unduly long polymerization time. The official gazette of U.S.P. No.5,290,820 further discloses amethodwhich comprises partly polymerizing a gaseous monomer such as butadiene with a view to allowing easy handling of the monomer and emulsifying the resultant partial polymer thereby producing an HIPE. This method can be expected to shorten the time for the polymerization of the HIPE because the time required for polymerizing the HIPE corresponds to the time needed for polymerizing the monomer remaining in a not polymerized state. It has been ascertained to the inventors that an effort to form an HIPE by emulsifying the partly polymerized monomer, however, entails such disadvantages as requiring an unduly long time for the emulsification, imparting pores of an unduly large diameter to the texture of the HIPE, rendering the difficulty to the emulsification because of a limit on the water phase/oil phase ratio, and preventing the produced HIPE from acquiring sufficient stability because of the advance of oil/water separation with the elapse of time.

The official gazette of W093/24,535, in the production of a low-density foambythepolymerizationof anHIPE, concerns a method for producing a porous cross-linked polymer material by preparatorily causing the HIPE to form at a temperature in the range of 20 - 65°C a gel possessing a dynamic modulus of elasticity in shear (rheometric index) of 500 pascals and thereafter heating the monomer at a temperature of at least 70°C thereby polymerizing and cross-linking the monomer. The polymerization of a HIPE requires the monomer to stand at 60°C for 16 hours and, meanwhile, the polymerization at the elevated temperature forms a cause for deficiency of the HIPE in stability. The invention of interest, therefore, contemplates preparatorily heating the HIPE to 20 - 65°C thereby forming a gel of prescribed modulus of elasticity and polymerizing the monomer to a certain degree and subsequently polymerizing at least not less than 85% of the monomer at a higher temperature, with the result that the over all polymerization time will be shortened.

The method disclosed in the official gazette, however, is targeted at hardening the HIPE in the form of a block as is plain from the fact that the working examples invariably illustrate the hardening of the HIPE in the form of a block. When the hardening is attained in the form of a block, the operation can be simplified and the polymerization time can be shortened because the gel is formed in a hardening column having the internal temperature thereof adjusted to a level in the range of 20 - 65°C and thereafter the gel retained in the resultant state is heated to a temperature of not less than 70°C to polymerize the residual monomer. in contrast, an effort to obtain a porous cross-linked polymer material in the form of a sheet by the method which is disclosed in the official gazette requires an operation of supplying an HIPE onto a polymerizing bed of a flat surface thereby imparting the form of a sheet to the HIPE, causing the sheet of HIPE to form a gel at a temperature in the range of 20 - 65°C, and subsequently polymerizing the residual monomer in the sheet at a temperature of not less than 70°C. The porous cross-linked polymer material in the form of a sheet is efficiently produced by continuously supplying the HIPE to the polymerizing bed and continuously hardening the layer of the HIPE as formed on the bed. This procedure is impracticable because it requires to keep the HIPE shaped in the form of a sheet mounted on the polymerizing base till completion of the polymerization and retain the HIPE in that shape till completion of the hardening and, therefore, demands the polymerizing base to possess a great length. It is, therefore, an object of this invention to solve the technical task mentioned above and provide a method for production which is capable of polymerizing a porous cross-linked polymer material in a very short period of time without impairing the stability of an HIPE and shortening the polymerizing bed necessary for obtaining a porous cross-linked polymer material in the form of a sheet and, therefore, is particularly suitable for a continuous process of polymerization.

Disclosure of the Invention

The present inventor has pursued a diligent study with a view to developing an HIPE method for continuous production of porous cross-linked polymer material in a very short period of time and has consequently discovered that a method which comprises partly polymerizng a water-in-oil emulsion, then shaping the resultant polymer as in a polymerizing tank or a polymerizing bed, and subsequently bringing the polymerization in process to completion, can produce a porous cross-linked polymer material possessing satisfactory mechanical strength in a short period of time and, in the case of the porous cross-linked polymer material produced continuously in the form of a sheet, can permit a reduction in the length of the polymerizing bed and, moreover, can allow the produced porous cross-linked polymer material to acquire excellent absorption properties. This invention has been perfected as a result.

The object of this invention mentioned above is accomplished by this invention providing for the production of a porous cross-linking polymer material formed of a water-in-oil high internal phase emulsion with a method for theproduction of a porous cross-linkedpolymermaterialwhich comprises mixing and emulsifying an oil phase containing a monomer component and a water phase containing water thereby obtaining a water-in-oil high internal phase emulsion, partly polymerizing the resultant emulsion, imparting a prescribed shape to the partly polymerized emulsion, and subsequently causing the after-polymerization in process to be completed.

According to this invention, a porous cross-linked polymer material excelling in absorption properties and mechanical strength can be efficiently produced in a very short period of time by subjecting a water-in-oil emulsion to partial polymerization (hereinafter occasionally referred to as "preparatory polymerization") and thereafter casting the resultant partial polymer in the form of a sheet on a polymerizing bed having a flat surface, for example.

The method of this invention is particularly advantageous for application to continuous polymerization and is capable of producing a material of a prescribed performance in a short period of time as compared with the method involving no preliminary polymerization. When this production is implemented by the use of a belt conveyor type apparatus for continuous polymerization, for example, the method can shorten the belt conveyor part, miniaturize the apparatus, and decrease the space for production.

Brief Description of the Drawings Fig. 1 is a schematic side view illustrating a typical mode of embodying an apparatus for continuous polymerization which is suitable for a method for producing a porous cross-linked polymer material according to this invention.

Best Mode of Embodying the Invention

This invention relates, in the production of a porous cross-linked polymer material formed of a water-in-oil high internal phase emulsion, to a method characterized by mixing and emulsifying an oil phase containing a monomer component and a water phase containing water thereby obtaining a water-in-oil high internal phase emulsion, partly polymerizing the resultant emulsion, imparting a prescribed shape to the partly polymerized emulsion, and subsequently causing the after-polymerization in process to be completed. Heretofore, the impartation of a form to an HIPE has been attained by using the HIPE in a liquid state from the viewpoint of facilitating the impartation of form and the practice of partly polymerizing an HIPE and subsequently effecting the impartation of form to the resultant polymer has never been put to practice. This invention, however, has accompanied a discovery that the form can be imparted even after the HIPE has been polymerized and this impartation of form can shorten the time of polymerization subsequent to the impartation of form. Generally, the porous cross-linked polymer material using an HIPE is polymerized by going through the steps of preparing an HIPE in an emulsifying device, adding a polymerization initiator to the HIPE, and forming and polymerizing the HIPE in a polymerizing device.

Now, one example of the mode of continuously producing a porous cross-linked polymer by polymerizing an HIPE will be described below with reference to the process flow illustrated in Fig. 1. As illustrated in Fig.1, an HIPE 101 is continuously supplied from an HIPE supplying part 119 onto a sheet material 203 and formed in the shape of a sheet of a prescribed thickness by adjusting the set height of a roller 209. An unwinding roller 208 and a rewinding roller 212 have their rotational speeds adjusted so that the sheet material 203 may be synchronized with a conveyor belt 201. The sheet material 205 held under such tension as to impart a fixed thickness to the HIPE 101 is advanced at a rotational speed which is controlled by rollers 209 and 211 and an unwinding roller 207 and a rewinding roller 213. Inside a polymerizing oven 215, the HIPE 101 is polymerized by a heating means 219 formed of a hot water shower and disposed under the conveyor belt 201 and a hot air circulating device disposed above the conveyor belt 201 to afford a porous cross-linked polymer 102. The porous cross-linked polymer 102 is stripped of the upper and lower sheet materials 203 and 205, then, the porous cross-linked polymer 102 is mounted on a belt rotated by a conveyor 302 operated by the rolls of a dehydrating device 303. It is nipped between pressing rolls 301 opposed vertically to each other across the belt and dehydrated by virtue of the rotation of the rolls 303. Optionally, the dehydrated porous cross-linked polymer 102 is transferred to a continuously disposed endless band knife type slicer 401 and is sliced in the direction of thickness by a band knife 402 kept in rotation.

Now, the method for production in the present invention will be described below along the flow of the steps thereof. [I] Preparation of HIPE

(1) Raw material used for HIPE

The rawmaterials to be used for an HIPE are only required to include (a) a polymerizing monomer, (b) a cross-linking monomer, and (c) a surfactant as essential components for forming an oil phase and (d) water as an essential component for a water phase. They may optionally include further (e) a polymerization initiator, (f) a salt, and (g) other additive as arbitrary components for forming an oil phase and/or a water phase.

(a) Polymerizing monomer The monomer composition essential for the composition of the HIPE mentioned above is a polymerizing monomer possessing one polymerizing unsaturated group inthemolecule thereof. Though it does not need to be particularly discriminated but has only to be capable of being polymerized in a dispersion or a water-in-oil type high internal phase emulsion and allowed to form an emulsion consequently. It preferably contains a (meth)acrylic ester at least partly, more preferably contains not less than 20 mass % of the (meth) acrylic ester, and particularly preferably contains not less than 35 mass % of the (meth)acrylic ester. When the (meth)acrylic ester is contained as a polymerizing monomer possessing one polymerizing unsaturated group in the molecule thereof proves advantageous because the produced porous cross-linked polymer abounds in flexibility and toughness. As concrete examples of the polymerizable monomer which is used effectively in this invention, allylene monomers such as styrene; monoalkylene allylene monomers such as ethyl styrene, a-methyl styrene, vinyl toluene, and vinyl ethyl benzene; (meth)acrylic esters such as methyl (meth) aerylate, ethyl (meth) aerylate, butyl (meth) aerylate, isobutyl (meth)acrylate, isodecyl (meth)acrylate, 2-ethylhexyl (meth) aerylate, lauryl (meth)aerylate, stearyl (meth)acrylate, cyclohexyl (meth)aerylate, and benzyl (meth)aerylate; chlorine-containing monomers such as vinyl chloride, vinylidene chloride, and chloromethyl styrene; acrylonitrile compounds such as acrylonitrile and methacrylonitrile; and vinyl acetate, vinyl propionate, N-octadecyl acrylamide, ethylene, propylene, and butene may be cited. These polymerizable monomers may be used either singly or in the form of a combination of two or more members . The content of the polymerizing monomer is preferred to be in the range of 10 - 99.9 mass %, based on the total mass of themonomer composition consisting of the polymerizing monomerand a cross-linkingmonomer. The reason forthis range is that the produced porous cross-lined polymer is enabled to acquire pores of minute diameters . The range is more preferably 30 - 99 mass % and particularly preferably 30 - 70 mass % . If the content of the polymerizing monomer is less than 10 mass %, the produced porous cross-linked polymer will be possibly friable and deficient in water absorption ratio. Conversely, if the content of the polymerizingmonomer exceeds 99.9 mass %, the porous cross-linked polymer consequently produced will be possibly deficient in strength and elastic recovery power and incapable of securing sufficient amount of water absorbed and sufficient velocity of water absorption.

(b) Cross-linking monomer The other monomer composition essential for the composition of the HIPE mentioned above is a cross-linking monomer possessing at least two polymerizing unsaturated groups inthemolecule thereof . Similarly to the polymerizing monomer mentioned above, it does not need to be particularly discriminated but has only to be capable of being polymerized in a dispersion or a water-in-oil type high internal phase emulsion and allowed to form an emulsion consequently.

As concrete examples of the cross-linking monomer which is effectively usable herein, aromatic monomers such as divinyl benzene, trivinyl benzene, divinyl toluene, divinyl xylene, p-ethyl-vinyl benzene, divinyl naphthalene, divinyl alkyl benzenes, divinyl phenanthrene, divinyl biphenyl, divinyl diphenyl methane, divinyl benzyl, divinyl phenyl ether, and divinyl diphenyl sulfide; oxygen-containing monomers such as divinyl furan; sulfur-containing monomers such as divinyl sulfide and divinyl sulfone; aliphatic monomers such as butadiene, isoprene, and pentadiene; and esters of polyhydric alcohols with acrylic acid ormethacrylic acid such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butane diol di(meth)acrylate, 1,4-butane diol di(meth)acrylate, 1,6-hexane diol di(meth)acrylate, octane diol di(meth)acrylate, decane diol di(meth)acrylate, trimethylol propane di(meth)aerylate, trimethylol propane tri(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol di(meth) aerylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, N,N'-methylene bis (meth) acryl amide, triallyl isocyanurate, triallyl amine, tetraallyloxy ethane, hydroquinone, catechol, resorcinol, and sorbitol may be cited. These cross-linking monomers may be used either singly or in the form of a combination of two or more members.

The content of the cross-linked monomer is properly in the range of 0.1 - 90 mass %, preferably 1 - 70 mass %, and particularly preferably 30 - 70 mass %, based on the total mass of themonomer composition consisting of the polymerizing monomer mentioned above and the cross-linking monomer mentioned above. If the content of the cross-linked monomer is less than 0.1 mass %, the produced porous cross-linked polymer will possibly be deficient in strength and elastic recovery force, unable to effect absorption sufficiently per unit volume or unit mass , and incapable of securing absorption in a sufficient amount at a sufficient velocity. Conversely, if the content of the cross-linked monomer exceeds 90 mass %, the porous cross-linked polymer produced consequently will possibly be friable and deficient in water absorption ratio. (c) Surfactant

The surfactant which is essential for the composition of the HIPE mentioned above does not need to be particularly discriminated but has only to be capable of emulsify a water phase in an oil phase forming the HIPE. It is not limited to the specific examples cited above but may be selected from the nonionic surfactants, cationic surfactants, amphoteric surfactants and ampholytic surfactants heretofore known to the art.

Among these surfactants, as concrete examples of the nonionic surfactant, nonyl phenol polyethylene oxide adduct; block polymer of ethylene oxide and propylene oxide; sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monomyristylate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, sorbitan sesquioleate, and sorbitan distearate; glycerin fatty acid esters such as glycerol monostearate, glycerol monooleate, diglycerol monooleate, and self-emulsifying glycerol monostearate; polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, and polyoxyethylene higher alcohol ethers; polyoxyethylene alkylaryl ethers such as polyoxyethylene nonyl phenyl ether; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monomyristylate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan trioleate; polyoxyethylene sorbitol fatty acid esters such as tetraoleic acid polyoxyethylene sorbit; polyoxyethylene fatty acid esters such as polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, and polyethylene glycol monooleate; polyoxyethylene alkyl amines; hydrogenated polyoxyethylene castor oil; and alkyl alkanol amides may be cited. These nonionic surfactants having HLB values of not more than 10, more preferably in the range of 2 - 6, prove preferable. It is permissible to use two or more such nonionic surfactants in combination. The combined use possibly results in stabilizing the HIPE.

As concrete examples of the cationic surfactant, quaternary ammonium salts such as stearyl trimethyl ammonium chloride, ditallow dimethyl ammonium methyl sulfate, cetyl trimethyl ammonium chloride, distearyl dimethyl ammonium chloride, and alkylbenzyl dimethyl ammonium chloride; alkyl amine salts such as coconut amine acetate and stearyl amine acetate; alkyl betaines such as lauryl trimethyl ammonium chloride, lauryl betaine, stearyl betaine, and lauryl carboxymethyl hydroxyethyl imidazolinium betaine; and amine oxides such as lauryl dimethyl amine oxide may be cited. The use of the cationic surfactant can impart excellent antibacterial properties to the porous cross-linked polymer whenthepolymer is used for an absorbentmaterial, for example.

The anionic surfactant of a kind possessing an anionic moiety and an oil-soluble moiety can be advantageously used.

As concrete examples of anionic surfactant, such reactive anion emulsifiers possessed of a double bond as, for example, alkyl sulfates such as sodium dodecyl sulfate, potassium dodecyl sulfate, and ammonium alkyl sulfate; sodium dodecyl polyglycol ether sulfate; sodium sulforicinoate; alkyl sulfonates such as sulfonated paraffin salts; sodiumdodecyl benzene sulfonate, alkyl sulfonates such as alkali metal sulfates of alkali phenol hydroxyethylene; higher alkyl naphthalene sulfonates; fatty acid salts such as naphthalene sulfonic acid formalin condensate, sodium laureate, triethanol amine oleate, and triethanol amine apiate; polyoxyalkyl ether sulfuric esters; sulfuric esters of polyoxyethylene carboxylic ester and polyoxyethylene phenyl ether sulfuric esters; succinic acid dialkyl ester sulfonates; and polyoxy ethylene alkyl aryl sulfates may be cited . An HIPE may be prepared by using an anionic surfactant in combination with a cationic surfactant.

The combined use of the nonionic surfactant and the cationic surfactant may possibly improve the HIPE in stability.

The content of the surfactant mentioned above is properly in the range of 1 - 30 mass parts, preferably 3 - 15 mass parts , based on 100 mass parts of the total mass of the monomer composition consisting of the polymerizing monomer and the cross-linked monomer. If the content of the surfactant is less than 1 mass part, the shortage will possibly deprive of the HIPE of stability of dispersion and prevent the surfactant from manifesting the effect inherent therein sufficiently. Conversely, if the content of the surfactant exceeds 30 mass parts, the excess will possibly render the produced porous cross-linked polymer unduly friable and fail to bring a proportionate addition to the effect thereof and do any good economically. (d) Water

The water essential for the composition of the HIPE mentioned above may be city water, purified water or deionized water. Alternatively, with a view to utilizing to advantage the waste water resulting from the production of the porous cross-linked polymer, this waste water may be adopted in its unmodified form or after undergoing a prescribed treatment. The content of the water may be suitable selected, depending on the kind of use ( such as , for example, an absorbent material, sound insulation material, or filter) for which the porous cross-linked polymer possessing continuous cells is intended. Since the hole ratio of the porous cross-linked polymer material is decided by varying the water phase/oil phase (W/O) ratio of the HIPE, the amount of water to be used is automatically decided by selecting theW/O ratio calculated to produce a hole ratio which conforms to the use and the purpose of the produced material. (e) Polymerization initiator

For the purpose of accomplishing the polymerization of an HIPE in a very short period of time as aimed at by this invention, it is advantageous to use a polymerization initiator. Thepolymerization initiator is onlyrequired to be suitable for use in the reversed phase emulsion polymerization. It is not discriminated between the water-soluble type and the oil-soluble type.

As concrete examples of thewater-solublepolymerization initiator which is used effectively herein, azo compounds such as 2,2 ' -azobis (2-amidinopropane) dihydrochloride; persulfates suchas ammoniumpersulfate, potassiumpersulfate, and sodium persulfate; peroxides such as potassiumperacetate, sodiumperacetate, sodiumpercarbonate, potassiumperacetate may be cited. As concrete example of the oil-soluble polymerization initiator which is used effectively herein, peroxide suchas, cumenehydroperoxide, t-butyl ydroperoxide, t-butylperoxide-2-ethylhexyanoate di-t-butyl peroxide, diisopropyl benzene hydroperoxide, p-methane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide,

2,5-dimethylhexane-2,5-dihydroperoxide, benzoyl peroxide, and methylethyl ketone peroxide may be cited. These polymerization initiators may be used either singly or in the form of a combination of two or more members .

Combined use of two or more kinds of polymerization initiator having different 10 hour half period temperatures, i.e. the temperatures at which the concentrations of the relevant initiators are halved in 10 hours proves advantageous . As a matter of course, it is permissible to use in combination the water-soluble polymerization initiator and the oil-soluble polymerization initiator.

The content of the polymerization initiator mentioned above is properly in the range of 0.05 - 25 mass parts, preferably 1.0 - 10 mass parts, based on 100 mass parts of the total mass of the monomer composition consisting of a polymerizing monomer and a cross-linking monomer, though it is variable with the combination of the polymer composition and the polymerization initiator. If the content of the polymerization initiator is less than 0.05 mass part, the shortage will be at a disadvantage in increasing the amount of the unaltered monomer component and consequently increasing the residual monomer content in the produced porous cross-linked polymer. Conversely, if the content of the polymerization initiator exceeds 25 mass parts, the excess will be at a disadvantage in rendering the polymerization difficult to control and degrading the mechanical property of the produced porous cross-linked polymer. Alternatively, a redox polymerization initiator formed by combining the polymerization initiator mentioned above with a reducing agent may be used. In this case, the polymerization initiator to be used herein does not need to be discriminated between the water-soluble type and the oil-soluble type. It is permissible to use a water-soluble redox polymerization initiator and an oil-soluble redox polymerization initiator in combination.

In the reducing agents, as concrete examples of the water-soluble reducing agents, sodium hydrogen sulfite, potassium hydrogen sulfite, sodium thiosulfate, potassium thiosulfate, L-ascorbic acid, ferrous salts, formaldehyde sodium sulfoxylate, glucose, dextrose, triethanol amine, and diathanol amine may be cited. As concrete examples of the oil-soluble reducing agent, dimethyl aniline, tin octylate, and cobalt naphthenate may be cited. These redox polymerization initiator type reducing agents may be used either singly or in the form of amixture of two ormoremembers .

The ratio of the reducing agent contained in the redox polymerization initiator mentioned above (mass ratio), i.e. the polymerization initiator (oxidizing agent) /reducing agent, is in the approximate range of 1/0.01 - 1/10, preferably 1/0.2 - 1/5.

The polymerization initiator (inclusive of the redox polymerization initiator) is only required to be present at least during the course of the polymerization of an HIPE. It may be added to the oil phase and/or the water phase prior to the formation of an HIPE, (2) simultaneously with the formation of an HIPE, or ® after the formation of an HIPE. In the case of the redox polymerization initiator, the polymerization initiator (oxidizing agent) and the reducing agent may be added at different times. (f) Salt

The salt as an arbitrary component for the composition of the HIPE mentioned above may be used when it is necessary for improving the stability of the HIPE.

As concrete examples of the salt of this nature, halogenides , sulfates, nitrates, and other similar water-soluble salts of alkalimetals and alkaline earthmetalε such as calcium chloride, sodium sulfate, sodium chloride, and magnesium sulfate may be cited. These salts may be used either singly or in the form of a combination of two or more members. Such a salt is preferred to be added in the water phase. Among other salts mentioned above, polyvalent metal salts prove particularly advantageous from the viewpoint of the stability of the HIPE during the course of polymerization.

The content of the salt mentioned above is proper in the range of 0.1 - 20 mass parts, preferably 0.5 - 10 mass parts, based on 100 mass parts. If the content of the salt exceeds 20 mass parts, the excess will be at a disadvantage in suffering thewastewater squeezed out of the HIPE to contain the water in an unduly large amount, boosting the cost for thedisposal ofthewastewater, failingto bringaproportional addition to the effect, and not doing any good economically. If the content is less than 0.1 mass part, the shortage will possibly prevent the effect of the addition of the salt from being fully manifested, (g) Other additive Varying other additive which are capable of improving the conditions of production, the property of HIPE, and the performance of the porous cross-linked polymer by imparting the performance and the function of their own, they may be suitably used herein. For example, a base and/or a buffer may be added for the purpose of adjusting the pH value. The content of the other additive may be selected within such a range that the additive used may fully manifest the performance, function, and further the economy commensurate with the purpose of addition. As such additives, activated carbon, inorganic powder, organic powder, metallic powder, deodorant, antibacterial agent, antifungi agent, perfume and other highly polymerized compounds may be cited. (2) Method for preparation of HIPE

The method for production of the HIPE which can be used in this invention does not need to be particularly discriminated. Any of the methods for production of HIPE heretofore known to the art may be suitably used. A typical method for the production of interest will be specifically described below.

First, a polymerizing monomer, a cross-linking monomer, and a surfactant as essential components and further an oil-soluble polymerization initiator (inclusive of an oil-soluble redox polymerization initiator) and other additive as optional components for the formation of an oil phase prepared in respectively specified amounts mentioned above are stirred at a prescribed temperature to produce a homogeneous oil phase. Meanwhile, water as an essential component and further a water-soluble polymerization initiator (inclusive of a water-soluble redox polymerization initiator), salts, and other additive as optional components for the formation of a water phase prepared in respectively specified amounts are stirred and heated to a prescribed temperature in the range of 30 - 95°C to produce a homogeneous water phase.

Then, the oil phase which is the mixture of the monomer component, surfactant, etc. and the water phase which is the mixture of water, water-soluble salt, etc., both prepared as described above are joined, mixed and stirred efficiently for exertion of proper shearing force and induction of emulsification at the temperature for the formation of an HIPE (emulsifying temperature) which will be described specifically hereinbelow to accomplish stable preparation of an HIPE. As a means for stirring and mixing the water phase and the oil phase particularly for the table preparation of the HIPE, the method which comprises keeping the oil phase stirred and continuously adding the water phase to the stirred oil phase over a period of several minutes to some tens of minutes. Alternatively, the HIPE aimed at may be produced by stirring and mixing part of the water phase component and the oil phase component thereby forming an HIPE resembling yogurt and continuing the stirring and mixing operation while adding the remaining portion of the water phase component to the yogurt-like HIPE.

(3) Water phase/oil phase (W/O) ratio The water phase/oil phase (W/O) ratio (mass ratio) of the HIPE which is obtained as described above does not need to be particularly limited but may be properly selected to suit the purpose for which the porous cross-linked polymer material possessed of open cells is used (such as, for example, water absorbent, oil absorbent, sound insulating material, and filter). It is only required to be not less than 3/1 as specified above and is preferred to fall in the range of 10/1 - 250/1, particularly 10/1 - 100/1. If the W/O ratio is less than 3/1, the shortage will be possibly at a disadvantage in preventing the porous cross-linked polymer material from manifesting a fully satisfactory ability to absorb water and energy, loweringthe degree of opening, andcausingthe surface of theproduced porous cross-linkedpolymermaterial to suffer from unduly low degree of opening and fail to exhibit a fully satisfactory permeability to liquid. The hole ratio of the porous cross-linked polymer material is decided by varying the W/O ratio . Thus , the W/O ratio is preferred to be selected so as to impart to the produced porous cross-linked polymer material a hole ratio conforming to the use and the purpose. When the product is used as a varying absorbent material such as disposable diaper or sanitary article, for example, the W/O ratio is preferred to fall in the approximate range of 10/1 - 100/1. Incidentally, the HIPE which is obtained by stirring and mixing the water phase and the oil phase is generally a white highly viscous emulsion.

(4) Apparatus for production of HIPE The apparatus for the production of the HIPE mentioned above does not need to be particularly discriminated. Any of the apparatuses for the production of the porous cross-linked polymer material which have been heretofore known to the artmay beused. For example, the stirring device ( emulsifier) to be used for mixing and stirring the water phase and the oil phase may be selected from among the stirring devices and the kneading devices which have been heretofore known to the art. As concrete examples of the stirring device, stirring devices using vanes of the propeller type, the paddle type, and the turbine type, homomixers, line mixers, and pin mills may be cited.

(5) Temperature for forming HIPE

The temperature for forming an HIPE (hereinafter refers to emulsifying temperature) is generally in the range of 20 - 100°C. From the viewpoint of the stability of the HIPE, the temperature is preferably in the range of 30 - 95°C, more preferably 40 - 95°C, particularly preferably 40 - 85°C, and most preferably 55 - 70°C. If the temperature for forming the HIPE is less than 20°C, the shortage will possibly result in unduly elongating the time for heating, depending on the temperature of hardening. Conversely, if the temperature exceeds 100°C, the excess will possibly result in degrading the stability of the formed HIPE. Incidentally, it is commendable to adjust preparatorily the temperature of the oil phase and/or the water phase to the prescribed emulsifying temperature and then stir and mix the two phases till emulsification and form the HIPE as expected. Since the preparation of the HIPE uses thewater phase in a larger amount, the preparatory adjustment of the temperature of at least the water phase to the prescribed emusifying temperature may well be rated as more favorable. If the polymerizing monomer or the cross-linking monomer begins to polymerize and forms a polymer while the emulsification is in progress, the formed polymer will possibly impair the stability of the HIPE . When a polymerization initiator (inclusive of a redox polymerization initiator) is incorporated in the rawmaterial for the preparation of the HIPE, therefore, the emulsifying temperatureof theHIPE is preferredto be incapableof inducing the polymerization initiator (oxidizing agent) to undergo substantial thermal decomposition enough to initiate polymerization of the HIPE. Morepreferably, the emulsifying temperature is lower than the temperature at which the half-life of the polymerization initiator (oxidizing agent) is 10 hours (10-hour half-life temperature). [II] Production of Porous Cross-linked Polymer Material (1) Addition of polymerization initiator (a) Time for addition of polymerization initiator

This invention contemplates adding a polymerization initiator to the water phase and/or the oil phase and mixing them prior to the formation of an HIPE, (2) simultaneously adding the polymerization initiator with the formation of the HIPE, or making this addition subsequently to the formation of the HIPE. Even in the case of the addition of ©, a redox polymerization initiator may be used similarly in the case of φ described above regarding the method for forming the HIPE.

(b) Method for addition of polymerization initiator It is convenient to add preparatorily the polymerization initiator to the oil phase when the polymerization initiator or the reducing agent is an oil-soluble type or to the water phase when it is in a water-soluble type. Alternatively, the oil-soluble polymerization initiator (oxidizing agent) or the reducing agent may be added in an emulsified form, for example, to the water phase.

(c) Form of use of polymerization initiator

The polymerization initiator may be used in an undiluted form, in the form of a solution in water or an organic solvent , or in the form of a dispersion. When the addition is made either simultaneously with or subsequently to the formation of the HIPE, it is important that the added polymerization initiator be quickly and homogeneously mixed with the HIPE for the purpose of avoiding the otherwise possible heterogeneous polymerization of the monomer component. Further, the HIPE which has been mixed with the polymerization initiator is quickly introduced into a polymerization vessel or a continuous polymerizing device as means for polymerization. It is commendable from this point of view to insert a path for the introduction of a polymerization initiator such as a reducing agent or an oxidizing agent in the path extending from the emulsifying device for preparing the HIPE through the polymerization vessel or the continuous polymerizing device, adding the polymerization initiator via the path to the HIPE, and mix them by means of a line mixer. If the HIPE which contains the polymerization initiator has a small difference between the emulsifying temperature and the polymerizing temperature thereof, the closeness of the emulsifying temperature to the polymerizing temperature will possibly set the polymerizing monomer or the cross-linking monomer polymerizing during the course of the emulsification and suffer the resultant polymer to impair the stability of the produced HIPE. Thus, themethod of adding the reducing agent or the oxidizing agent or other polymerization initiator to the HIPE immediately prior to the polymerization, i.e. themethod of (2) or(3) mentioned above, proves advantageous . The amount of the polymerization initiator to be used herein equals that in the method described above under the title of the method for preparation of HIPE. (2) Preparatory polymerization of HIPE (a) Method for preparatory polymerization The operation of polymerizing part of the HIPE, namely the method for preparatory polymerization in this invention, does not need to be particularly discriminated. A tank, a vessel provided with a stirrer, a static mixer, etc. which are known to the art may be used threfor. Optionally, the preparatory polymerization may be implemented by retaining the HIPE for a prescribed length of time in a pipe, a hopper, or a die which are adapted to lead the HIPE to the polymerizing device. These devices are preferred to be furnishedwith such heating means as a hot water jacket, for example. In the preparatory polymerization by this invention, the "ratio of gelation" serves as the index of the ratio of polymerization of the HIPE . The ratio of gelation ( % ) in this invention is the numerical value represented as (weight of a sample after drying/weight of sample before washing) ^χl00, which is calculated in accordance with the method for determination of the ratio of gelation described in the paragraph covering working examples. The HIPE, after adding the polymerization initiator, continues to polymerize so long as it retains a temperature which fits the polymerization. The term "ratio of gelation" as used in this invention, therefore, is interpreted as referringto the ratio of gelation intheHIPE immediatelybeforethe impartation of formthereof . The preparatory polymerization by this invention generally continues till the ratio of gelation reaches a level in the range of 1 - 40%. From the viewpoint of shortening the time for the subsequent step of polymerization, the ratio of gelation is preferably in the range of 5 - 35% , more preferably 10 - 30%, and particularly preferably 15 - 25%. If the ratio of gelation is less than 1%, the shortage will be at a disadvantage in preventing the effect of shortening the time of the subsequent step of polymerization from being fully manifested. If the ratio of gelation exceeds 40%, the excess will be at a disadvantage in degrading the flowability of the HIPE and encountering difficulty in imparting an expected form to the HIPE.

This invention preparatorily polymerizes the HIPE and does not polymerize the monomer which is contained in the oil phase prior to the preparation of the HIPE. If only the monomer in the oil phase is polymerized, it will possibly result in impairing the stability of the produced HIPE. The polymerization of part of the HIPE prior to the impartation of form is aimed at enabling the HIPE to retain the flowability thereof intact during the course of the impartation of form and meanwhile shortening the time required for the subsequent polymerization and consequently promoting the reduction in length of the polymerizing apparatus to be used for the subsequent polymerization.

(b) Temperature of preparatory polymerization

The temperature of the HIPE of this invention during the course of the preparatory polymerization may be properly selected, depending on the kind of the polymerization initiator to be used and the amount of this initiator to be incorporated in the raw material. Generally, it is in the range of room temperature - 100°C. From the viewpoint of stability of the HIPE and the polymerization velocity, it is preferably in the range of 50 - 100°C, more preferably 65

- 95°C, and particularly preferably 80 - 95°C. If the temperature of the preparatory polymerization is less than the normal temperature, the shortage will be commercially at a disadvantage in suffering the preparatory polymerization to consume an unduly long time. Conversely, if this temperature exceeds 100°C, the excess will be possibly at a disadvantage in causing the produced porous cross-linked polymer material to acquire pores not unequal in diameter further suffering the porous cross-linked polymer material to be deficient in strength. The temperature of the preparatory polymerization may be varied in two stages or more stages during the course of the preparatory polymerization. This invention does not need to exclude the preparatory polymerization which is performed in this manner. (c) Time for preparatory polymerization The time for the preparatory polymerization of the HIPE contemplated by the present inventionmay be properly selected, depending on the kind of the polymerization initiator to be used and the amount of incorporation of this initiator in the rawmaterial . Generally, it is inthe rangeof five seconds

- six hours. It is preferably in the range of five seconds

- one hour, more preferably 10 seconds - 30 minutes, and particularly preferably 10 seconds - 15 minutes. If the time for the preparatory polymerization exceeds six hours, the excess will be commercially at a disadvantage in impairing the productivity. If the time is less than five seconds, the shortage will be possibly at a disadvantage in preventing the ratio of gelation from sufficiently rising.

(3) After-polymerization of preparatorily polymerized HIPE

(a) Method for polymerization

The HIPE which has been preparatorily polymerized is subjected to impartation of an expected form and then to polymerization of the residual monomer in the HIPE. The present invention designates the polymerization of the HIPE followed the preparatory polymerization as "after-polymerization" for the sake of convenience of discrimination thereof from the preparatory polymerization. The after-polymerization may be effected by a batch method or a continuous method after the impartation of form to the HIPE. The term "continuous method" as used in the present specification refers to an operation of continuously supplying the HIPE at least after the preparatory polymerization to a device for impartation of form and then after-polymerizing the HIPE continuously in a polymerizing device which will be specifically described herein below and the term "batch method" refers to an operation of subjecting the HIPE after the preparatory polymerization to impartation of a prescribed form and then collecting the formed pieces of HIPE into groups of a proper number and after-polymerizing the groups of HIPE pieces in a polymerizing device.

The method of continuous polymerization which consists in continuously polymerizing the HIPE proves advantageous because it excels in efficiency of production and most effectively utilizes the effect of shortening the time of polymerization due to the preparatory polymerization of the HIPE according to this invention and the effect of shortening of the polymerizing bed as well. To be specific, the continuous polymerization of a porous cross-linked polymer in the form of a sheet is implemented, for example, by continuously supplying a preparatorily polymerized HIPE onto a belt conveyor in motion which is adapted to have the surface thereof heated with a heating device, imparting a form of smooth sheet to the HIPE carried on the belt, and meanwhile subjecting the HIPE sheet to after-polymerization. When the conveyor has a smooth surface for contact with the emulsion, the product of the formof a continuous sheet having an expected thickness can be obtained by supplying the preparatorily polymerized HIPE in a prescribed thickness onto the belt.

For the purpose of producing a porous cross-linked polymer in a three-dimensional form, the cast polymerization, i.e. a method which comprises casting a HIPE in a mold having a relevant form and polymerizing the HIPE in the mold, can be adopted. Incidentally, the cast polymerization may be carried out by a batch method or by a continuous method using a mold on a die in continuous motion. (b) Temperature for after-polymerization

The temperature for the after-polymerization of an HIPE according to this invention may be properly selected to suit the ratio of gelation of the preparatory polymerization, the kind of a polymerization initiator to be incorporated in the rawmaterial, andtheamountofthe initiatortobe incorporated. Generally, it is in the range of normal room temperature - 150°C. From the viewpoint of the stability of the HIPE and the polymerization velocity, it is preferably in the range of 60 - 110°C, more preferably 80 - 110°C, and particularly preferably 90 - 100°C. If the temperature for after-polymerization is less than normal room temperature, the shortage will be at a disadvantage in unduly elongating the time required for the after-polymerization and possibly rendering the after-polymerization itself unfit for commercial production. Conversely, if the temperature of after-polymerization exceeds 150°C, the excess will be possibly at a disadvantage in causing the produced porous cross-linked polymer material to form pores not uniform in diameter and betray deficiency in strength. The temperature of the after-polymerization may be varied in two stages or more stages during the course of the after-polymerization. This invention does not need to exclude the polymerization which is performed in this manner.

(c) Time for after-polymerization

The time for the after-polymerization of a partly hardened HIPE in this invention likewise may be properly selected to suit the ratio of gelation of the preparatory polymerization, the kind of a polymerization initiator to be incorporated in the raw material, and the amount of the initiator so incorporated. It is generally in the range of one minute - 20 hours, preferably within one hour, more referably within 30 minutes, and particularly preferably in the range of one - 20 minutes. If the time for the after-polymerization exceeds 20 hours, the excess will be possibly at a disadvantage in degrading the productivity and rendering the after-polymerization unfit for commercial operation. Conversely, if this time is less than one minute, the shortage will be at a disadvantage in preventing the produced porous cross-linked polymer material from acquiring sufficient strength. Naturally, this invention does not preclude the adoption of a longer time for the after-polymerization than the upper limit specified above. This invention effects the impartation of a form to an HIPE after the HIPE has undergone the preparatory polymerization and, owing to the selection of this process, attains the reduction of the time required for the after-polymerization. Even when the after-polymerization is carried out under the conditions which are similar to those prevalent heretofore, therefore, the time which is required for the after-polymerizationcanbe shortenedbecausethepreparatory polymerization has reducedthe amount of the residual monomer. Particularly, since the after-polymerization is performed after the impartation of a form and consequently enabled to exalt the efficiency of the polymerizing tank subsequently to the impartation of the form, the length of the polymerizing bed to be used in the production of a continuous sheet can be shortened.

After the after-polymerization, the HIPE is cooled occasionally slowly to a prescribed temperature, though not compulsively. Alternatively, the after-polymerized porous cross-linked polymer material may be transferred in its uncooled stateto the subsequent step of such an aftertreatment as dehydration or compression which will be specifically described herein below.

(d) Apparatus for after-polymerization The apparatus for after-polymerization which can be used in this invention does not need to be particularly discriminated. For example, a belt conveyor type continuous polymerizing machine provided with a temperature adjusting device and a continuous cast polymerizing machine can be used . The continuous polymerizing machine requires a length commensurate with the time for polymerization. The method of this invention, however, does not unduly elongate the polymerization linebut allows the apparatus to enjoy a compact construction because the preparatory polymerization performed on a HIPE permits a decrease in the time for polymerization. It is naturally permissible to use a batch type polymerization tank or a batch type cast polymerizing machine.

(4) Step of aftertreatment (conversion into finished product) after formation of porous cross-linked polymer material

(a) Dehydration

The porous cross-linked polymer material formed in consequence of the completion of polymerization is normally dehydratedbycompression, aspirationunderreducedpressure, or the combination thereof. By this dehydration, generally

50-98% of the water used is removed and the remainder thereof is left adhering to the porous cross-linked polymer material .

The ratio of dehydration is properly set to suit the purpose for which the produced porous cross-linked polymer material is used. Generally, the water content in the porous cross-linked polymer material in a perfectly dried state is set at a level in the range of 1 - 10 g, preferably 1 - 5 g, per g of the polymer material. (b) Compression

The porous cross-linked polymer of this invention can be obtained in a form compressed to one of several divisions of the original thickness . The compressed sheet has a smaller inner volume than the original porous cross-linked polymer andpermits adecrease inthecostoftransportationor storage. The porous cross-linked polymer in the compressed state is characterized by being disposed to absorb water when exposed to a large volume of water and resume the original thickness and exhibiting the ability to absorb water at a higher speed than the original polymer.

Fromtheviewpoint of savingthe space fortransportation or storage and facilitating the handling, it is effective to compress the polymer to not more than 1/2 of the original thickness. Preferably, the compression is made to not more than 1/4 of the original thickness.

(c) Cleaning For the purpose of improving the surface condition of the porous cross-linked polymer, the porous cross-linked polymer may be washed with pure water, an aqueous solution containing an arbitrary additive, or a solvent.

(d) Drying The porous cross-linked polymer obtained by the preceding steps, when necessary, may be dried by heating as with hot air or microwaves or may be moistened for adjustment of the water content.

(e) Cutting The porous cross-linked polymer obtained by the preceding steps, when necessary, may be cut in expected shape and size and fabricated into a finished product fitting the purpose of use.

(f) Impregnation The polymer may be endowed with functionality by being impregnated with a detergent or an aromatic agent.

Now, this invention will be described more specifically below with reference to working example. The properties of the porous cross-linked polymer material reported in these working examples were determined and rated as follows.

(1) About 30 g of a sample was weighed out accurately, placed in a plastic vessel having an inner volume of 1 liter, and washed therein by being stirred with 500 mL of acetone for 16 hours. (2) The sample washed with acetone was separated by filtration, placed in a plastic vessel having an inner volume of 1 liter, and washed two times therein by being stirred with 500 mL of deionized water for 1.5 hours. (3) The sample washed with the deionized water was separated by filtration, placed in a plastic vessel having an inner volume of 1 liter, and again washed therein by being stirred with 500 mL of acetone for three hours.

(4) The sample again washed with acetone was separted by filtration and dried under a reduced pressure at 60°C for

16 hours by the use of a vacuum drier (made by Tabai and sold under trademark designation of "Vacuum Oven LHV-122").

(5) The sample thus dried was accurately weighed.

( 6 ) The ratio of gelation ( % ) was calculated in accordance with the formula 1 shown below using the accurate weight found as above.

Formula 1: Ratio of gelation (%) = [ (Mass of sample after drying) /(Weight of sample before washing) ]^χ 100

A sample cut in the cube of 1 cm was dried and weighed and immersed in an ample amount of purified water. The sample swelled by absorbing the purified water was left standing and draining for 30 seconds on a glass filter 120 mm in diameter and 5 mm in thickness (made by Duran Corp. and sold under theproduct code of "#0" ) . The sample nowwetwiththe absorbed water was weighed. The ratio of free swelling (g/g) of the porous cross-linked polymer material was calculated in accordance with the formula 2 shown below using the weight found as above.

Formula 2 : Ratio of free swelling = (Mass of sample after absorbing water - Weight of sample before absorbing water) /(Mass of sample before absorbing water)

A sample was cut to obtain a disc 5 mm in thickness and 2.87 cm in diameter. The disc was immersed in a physiological saline solution at 32°C. The disc in the immersed state was tested for thickness under no load by the use of a dead-load thickness meter (made by Ono Sokkiseizo K.K. and sold under the trademark designation of "Digital Linear Gauge Model EG-225"). After the elapse of 15 minutes then, the sample was held under a load of 5.1 kPa. When the mass of the sample reached the state of equilibrium, the thickness of the sample under the load was measured. The resistance to compression strain (RTCD) ( % ) was calculated in accordancewiththe formula 3 shown below.

Formula 3: RTCD (%) = [ (Thickness under no load -Thickness under load) /(Thickness under no load)] * 100

Example of Preparation of HIPE A water phase to be used in a process of continuous emulsification for the formation of an HIPE was prepared by dissolving 36.3 kg of calcium chloride anhydride and 568 g ofpotassiumpersulfate in3781itersofpurifiedwater. Then, an oil phase was obtained by adding 960 g of diglycerin monooleate to a mixture consisting of 1600 g of styrene, 4800 g of 2-ethyl hexyl acrylate and 1600 g of 55% divinyl benzene. The water phase was supplied at a temperature of 75°C and a flow volume of 56.5 cm³/s and the oil phase at a temperature of 22°C and a flow volume of 1.13 g/s respectively to a dynamic mixing device. In the dynamic mixing device, they were thoroughly mixed by means of a pin impeller rotated at 1800 rpm and the formed mixture was partly circulated to obtain an HIPE at a ratio of 57.6 cm³/s.

Example 1

The HIPE obtained in the example mentioned above was retained for 10 minutes in a hopper kept at 75°C to obtain a partly polymerized water-in-oil emulsion having a ratio of gelation of 15% . This emulsion was cast on a beltlike plate of an apparatus illustrated in Fig. 1. The emulsion on the beltlike plate was passed at a rate of travel of 20 cm/min through a polymerizing oven having the inner temperature kept at 120°C so as to be after-polymerized for 20 minutes to afford a hardened HIPE.

The HIPE having the ratio of gelation of 15%, when cast onto the beltlike plate, could be easily shaped in the form of a sheet owing to the proper flowability thereof.

The produced polymer, namely the porous cross-linked polymer material, was found to have a ratio of free swelling of 47 g/g and a RTCD of 6%. Thus, the product showed only small strain under load and exhibited excellent properties under load.

Comparative Example 1

The HIPE obtained in the example mentioned above and not subjected subsequently to preparatory polymerization was cast onto the beltlike plate of the apparatus of Fig. 1 as used in Example 1. The HIPE on the beltlike plate was passed at a rate of travel of 20 cm/min through a polymerizing oven having the inner temperature kept at 120°C so as to be after-polymerized for 30 minutes to afford a porous cross-linked polymer material. The polymer material thus obtained was found to have a ratio of free swelling of 47 g/g and a RTCD of 35%. An increase in the time for polymerization required to elongate the polymerizing oven by 50%.

Example 2 An HIPE was obtained by repeating the procedure of the example mentioned above while changing the temperature of the water phase during the preparation of an HIPE to 95°C and using 2270 g of sodium persulfate in the place of 568 g of potassium persulfate. This HIPE was passed through a static mixer kept at 95°C over a period of 20 seconds to obtain a partly polymerized HIPE having a ratio of gelation of 6%. The produced HIPE was cast onto the beltlike plate of the apparatus of Fig.1. The HIPE on the beltlike plate was passed at a rate of travel of 30 cm/min through a polymerizing oven having the inner temperature thereof kept at 120°C so as to be after-polymerized for six minutes.

The HIPE having the ratio of gelation of 6%, when cast onto the beltlike plate, could be easily shaped in the form of a sheet owing to the proper flowability thereof. The produced porous cross-linked polymer material was found to have a ratio of free swelling of 47 g/g and a RTCD of 8% . Thus , the product showed only small strain under load and exhibited excellent properties under load.

Comparative Example 2

An HIPE obtained by following the procedure of Example 2 and not subjected subsequently to preparatory polymerization was cast onto the beltlike plate of the apparatus of Fig. 1 in the same manner as in Example 2. The HIPE on the beltlike plate was passed at a rate of travel of 30 cm/min through a polymerizing oven having the inner temperature kept at 120°C so as to be after-polymerized for six minutes. The produced porous cross-linked polymer material was found to have a ratio of free swelling of 47 g/g and a RTCD of 13%. This productwas deficient inproperties under load.

Example 3

A partly polymerized HIPE having a ratio of gelation of 15% obtained in the same manner as in Example 1 was packed in a mold in the shape of a rectangular solid, 3 5 10 cm. The HIPE in the mold was left standing for 20 minutes in a constant temperature bath having the inner temperature kept at 120°C so as to be after-polymerized.

The HIPE having the ratio of gelation of 15% could be easily supplied to a constant temperature bath owing to the proper flowability and then hardened into a porous block of a homogeneous texture throughout the entire volume.

The porous cross-linked polymer material thus obtained was found to have a ratio of free swelling of 47 g/g and a RTCD of 6%. This product showed only small strain under load and exhibited fine properties under load.

Comparative Example 3

The HIPE obtained in the example mentioned above and not subjected subsequently to preparatory polymerization was packed in the same mold in the shape of a rectangular solid, 3 x 5 x 10 cm, as used in Example 3. The HIPE in the mold was left standing for 20 minutes in a constant temperature bath having the inner temperature thereof kept at 120°C so as to be after-polymerized. The porous cross-linked polymer material thus obtained was found to have a ratio of free swelling of 47 g/g and a RTCD of 30% . The product was deficient in properties under load. Comparative Example 4

The oil phase cited in the example of preparation of theHIPEmentionedaboveand 80 gofmethylethyl ketoneperoxide added thereto were heated together to 60°C so as to polymerize themonomerpartly in advance and prepare a polymer-containing oil phase (ratio of gelation 10%) . This oil phase was mixed with a water phase. When an attempt was made to subject the produced HIPE to preparatory polymerization, it barely resulted in forming a heterogeneous HIPE containing freewater. The preparatory polymerization could not be attained.

Industrial Applicability

This invention resides in a method for quickly producing a porous cross-linked polymer material excelling in absorption properties andmechanical strength. It is capable of exalting the efficiency of production and useful for commercial production. Particularly, in the case of continuous production, the method shows an unusually outstanding industrial applicability because it permits miniaturization of the polymerizing part of the apparatus and allows the production to be carried out efficiently even in a narrow space.

Claims

1. In the production of a porous cross-linked polymer material formed of awater-in-oil high internal phase emulsion, a method which comprises mixing and emulsifying an oil phase containing a monomer component and a water phase containing water thereby obtaining a water-in-oil high internal phase emulsion, partly polymerizing the resultant emulsion, imparting a prescribed shape to the partly polymerized emulsion, and subsequently causing the after-polymerization in process to be completed.

2. A method according to claim 1, wherein said partial polymerization proceeds till a ratio of gelation in the range of 1 - 40%.

3. A method according to claim 1 or claim 2, wherein the partly polymerized emulsion is continuously supplied to a conveyor and then subjected to impartation of a prescribed shape and after-polymerization.

4. A method according to claim 3 , wherein the surface of said conveyor for contact with the emulsion is a flat sheet andthepartlypolymerized emulsion is supplied in a prescribed thickness on the conveyor and subjected to after-polymerization.

5. A method according to claim 3, wherein the surface of said conveyor for contact with the emulsion is possessed of a mold and said partly polymerized emulsion is supplied to the mold and then subjected to after-polymerization.

6. A method according to claim 1 or claim 2, wherein the emulsion which has undergone partial polymerization is supplied to a mold and then subjected to after-polymerization in the mold.