JPH0311282B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a porous polymer having internal pores,
In particular, the present invention relates to a method for producing a water-absorbing polymer that has a low apparent specific gravity and is rich in water absorption, air permeability, and elasticity. [Prior Art] Various methods are known for producing water-absorbing resins by polymerizing ethylenically unsaturated monomers such as acrylic acid and alkali metal acrylates using a reversed-phase suspension polymerization method. For example, by employing reverse phase suspension polymerization or reverse phase emulsion polymerization, a polymer dispersant (Japanese Unexamined Patent Publication No. 57-167307) or a surfactant (Japanese Unexamined Patent Publication No. 58-32641) is added to an aqueous vinyl monomer solution. Efforts have been made to improve the wettability of water-absorbing polymers. However, when the above-mentioned water-absorbing polymer is used as a water-absorbing agent for sanitary napkins, disposable diapers, etc., it needs to be more elastic, have a small apparent specific gravity and be easily mixed with cotton-like pulp, etc., have water absorbency, and have good breathability. Practical properties such as excellent properties are required, but water-absorbing polymers produced by conventional methods do not necessarily satisfy the above-mentioned required performance. On the other hand, when a hydrophobic monomer is polymerized in an aqueous dispersion medium, a nonionic surfactant is contained in the monomer phase and an ionic surfactant is contained in the aqueous phase to form a water phase/monomer phase/aqueous phase type. , so-called W/O/
There is a method of forming a W-type emulsion and then polymerizing it to obtain a spherical polymer having spherical vacuoles with an average particle size of 0.5 to 50μ, particularly a material used for cosmetics, etc. (Japanese Patent Application Laid-Open No. 193901/1982). Are known. However, when polymerizing water-soluble monomers, even if this method is used as is, it has not been possible to produce a water-absorbing polymer having the above-mentioned practical properties. [Problems to be Solved by the Invention] An object of the present invention is to produce a polymer having internal pores, particularly a polymer having a small apparent specific gravity and high water absorption, air permeability, and elasticity. A further object of the present invention is to produce a spherical water-absorbing polymer having the above physical properties. [Means for Solving the Problems] The present invention provides, when polymerizing water-soluble polymerizable monomers, not just reverse phase suspension or reverse emulsion polymerization, but an O This was done based on the knowledge that a porous polymer can be efficiently obtained by forming a /W/O type emulsion and performing polymerization. That is, in producing a porous polymer, the present invention includes the following steps: (1) Using a water-soluble surfactant or a water-soluble polymer dispersant, the inner phase is a hydrophobic phase and the outer phase is at least one kind of (2) adding the O/W emulsion to a hydrophobic dispersion medium containing an oil-soluble surfactant or an oil-soluble polymer dispersant; (3) producing an O/W/O emulsion; and (3) polymerizing a monomer. Examples of water-soluble polymerizable monomers used in the present invention include vinyl monomers having polymerizable unsaturated groups such as olefinic unsaturated carboxylic acids, olefinic unsaturated sulfonic acids, olefinic unsaturated amines, and olefinic unsaturated ethers. It will be done. Among these, examples of vinyl monomers having a sulfonic acid group include unsaturated sulfonic acids such as acrylamide methylpropanesulfonic acid and allylsulfonic acid, and examples of vinyl monomers having an amino group include acrylamide, dimethylaminoethyl methacrylate, etc. unsaturated amines. Examples of the vinyl monomer having a carboxyl group or a carboxylate group include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid; Acid esters such as methoxypolyethylene glycol methacrylate and phenoxypolyethylene glycol methacrylate, and water-soluble salts of acrylic acid and methacrylic acid include unsaturated carboxylic acids such as alkali metal salts, alkaline earth metal salts, and ammonium salts. Examples include salt. In the present invention, it is preferable to use only the above-mentioned water-soluble monomers as polymerizable monomers, but water-insoluble monomers that can be copolymerized with water-soluble vinyl monomers, such as acrylic acid and methacrylic acid having an alkyl group having 1 to 18 carbon atoms, are preferred. acid,
An unsaturated carboxylic acid ester monomer such as maleic acid or fumaric acid may be used in combination in an amount of 50% by weight (hereinafter abbreviated as %) or less, for example, 1 to 50% of the total monomer weight. In the present invention, in the first step (1), the above polymerizable monomer and a water-soluble surfactant or a water-soluble polymer dispersant are used, so that the inner phase is a hydrophobic phase and the outer phase is an aqueous phase containing the above polymerizable monomer. O/W emulsion (so-called oil in water emulsion)
form. As the water-soluble surfactant, any surfactant can be used as long as it is water-soluble. Specifically, anionic surfactants such as sulfates having 10 to 18 carbon atoms such as sodium lauryl sulfate and sodium polyoxyethylene lauryl sulfate;
Examples of nonionic surfactants with an HLB of 7.0 or higher include fatty acid esters such as polyoxyethylene glycerin monostearate, polyoxyethylene glycerin monoisostearate, rosin ester, and polyoxyethylene rosin ester. In addition, as a water-soluble polymer dispersant, saponification degree is 60-95 mol% and polymerization degree is 100-95 mol%.
Examples include 3000 polyvinyl alcohol, modified polyvinyl alcohol in which a sulfonic acid group or a carboxylic acid group is introduced into polyvinyl alcohol, polyethylene oxide, hydroxyethyl cellulose, and gum arabic. In the present invention, the O/W type emulsion may be produced in any way, but for example, if the concentration of the polymerizable monomer is 30% or more, preferably 35 to 50%,
0.001 to 20 of water-soluble surfactant to monomer
%, preferably 0.01 to 10%,
Add a hydrophobic organic compound to this and stir O/W.
Form a mold emulsion. The hydrophobic organic compounds used here include aliphatic hydrocarbons such as n-pentane, cyclopentane, n-hexane, cyclohexane, n-heptane, and methylcyclohexane; aromatic hydrocarbons such as benzene and toluene;
Examples include aliphatic alcohols having 4 to 6 carbon atoms such as n-butyl alcohol and n-amyl alcohol, aliphatic ketones such as methyl ethyl ketone, and aliphatic esters such as ethyl acetate.
These can be used alone or as a mixture of two or more. Further, the amount of the hydrophobic organic compound added is preferably in the range of 1 to 150% based on the monomer aqueous solution. In the present invention, it is desirable to add a polymerization initiator to the O/W emulsion in advance before starting polymerization. As a polymerization initiator,
Ketone peroxides such as methyl ethyl ketone peroxide and methyl isobutyl ketone peroxide; dialkyl peroxides such as di-t-butyl peroxide and t-butylcumyl peroxide; t-butyl peracetate; t-butyl perisobutyrate; - Alkyl peresters such as butyl pivalate, persulfates such as hydrogen peroxide, potassium persulfate, and ammonium persulfate, perchlorates such as potassium perchlorate and sodium perchlorate, and halogens such as potassium chlorate and potassium bromate. Acid acid, 2-(carbamoylazo)-isobutyronitrile, 2,2'-azobis(N,N'-dimethyleneiso-butyramidine) dihydrochloride, 2,2'-
Azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutyramidine), 4,4'-azopis(4-cyanopentanoic acid), azobisisobutyronitrile , 2,2'-azobis(4-methoxy-
2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), (1
-phenylethyl)azodiphenylmethane, 2,
2'azobisisobutyronitrile, dimethyl-2,
2'-azobisisobutyrate, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(1-cyclo-hexanecarbonitrile), 2,
2'-azobis(2,4,4'-trimethylpentane), 2-phenylazo-2,4-dimethyl-4
Examples include azo compounds such as -methoxyvaleronitrile and 2,2'-azobis(2-methylpropane). The above polymerization initiator is one or two
It can be used as a mixture of more than one species. still,
The polymerization initiator is 0.001 to 10% based on the monomer,
Preferably it is used in an amount of 0.01-5%. In step (2) of the present invention, the O/W emulsion is added to a hydrophobic dispersion medium containing an oil-soluble surfactant or an oil-soluble polymer dispersant to form an O/W/O type emulsion. In other words, the above O/W is dispersed in the hydrophobic phase (O). Dispersion can be carried out by adding the O/W emulsion all at once and then stirring, or by stirring while dropping the O/W emulsion. The oil-soluble surfactant used here is
Nonionic surfactants with an HLB of 7 or less, such as sorbitan fatty acid esters such as sorbitan oleate, sorbitan stearate, and sorbitan laurate, and phthalates such as hexadecyl sodium phthalate and cetyl stearyl sodium phthalate are preferred. In addition, oil-soluble polymer dispersants include cellulose ethers such as ethyl cellulose, ethyl hydroxyethyl cellulose, and benzyl cellulose, cellulose esters such as cellulose acetate, cellulose butyrate, and butyl cellulose acetate, mylenated polybutadiene, mylenated polyethylene, and mylenated α. - Olefin etc. can be used. These oil-soluble surfactants or polymeric dispersants are added in a proportion of 0.1 to 25% in a hydrophobic dispersion medium.
It is best to add it in advance so that
Incidentally, as the hydrophobic dispersion medium, the hydrophobic organic compounds exemplified in the above section of O/W emulsion can be used. At this time, the same hydrophobic organic compound used for the innermost phase can also be used as the hydrophobic dispersion medium. Further, the amount of the hydrophobic dispersion medium to be used is arbitrary, but it is preferably 10 to 500 parts by weight per 100 parts by weight of the O/W emulsion from the viewpoint of economy and workability. In the present invention, in step (3), polymerization is started after or simultaneously with the formation of the O/W/O emulsion. Polymerization can be initiated by a conventional method, but the polymerization temperature should be 50°C or higher and the reaction time should be 30 minutes or more.
A range of 6 hours is preferred. The present invention is based on the above steps, but in carrying out the method of the present invention, a known crosslinking agent may be added either before, during or after polymerization. For example, as a crosslinking agent, N,
N′-diallylacrylamide, diallylamine,
Polyallyl compounds such as diallyl methacrylamide, diallyl phthalate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, triallyl phosphate, divinylbenzene, N,N'-methylenebisacrylamide, ethylene glycol diacrylate, ethylene glycol dimethacrylate, Polyvinyl compounds such as glycerin trimethacrylate, polyglycidyl ethers such as ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether, haloepoxy compounds such as epichlorohydrin and α-methylchlorohydrin, polyaldehydes such as glitaraldehyde and glyoxal, glycerin, etc. Polyols such as ethylenediamine, polyamines such as ethylenediamine, hydroxyvinyl compounds such as 2-hydroxyethyl methacrylate, and inorganic or organic metal salts that generate polyvalent ions such as calcium, magnesium, zinc, and aluminum can be mentioned. Moreover, monoglycidyl compounds such as phenol polyoxyethylene glycidyl ether can be used as a modifier. When using the above-mentioned crosslinking agent or monoglycidyl compound, it can be used in any amount depending on the desired properties of the final product polymer, but usually
It is preferably in the range of 0.01 to 10%. Furthermore, a compound such as a polymerization accelerator may be added to each phase of the O/W/O emulsion. The polymer produced as described above is dried directly after polymerization or after removing the solvent by decantation or centrifugation, using a means such as a vacuum dryer or fluidized fluid dryer, and is pulverized and manufactured as necessary. It can be used after grain treatment. [Effects of the Invention] According to the method of the present invention, a porous spherical polymer having a small apparent specific gravity, high elasticity, and excellent water absorption and air permeability can be produced. Therefore, the porous spherical polymer produced according to the present invention has particularly good water absorbency, so it can be used in various sanitary materials that come into contact with the human body, such as sanitary napkins, disposable diapers, patient sheets, tampons, and sanitary cotton. Can be used for In addition, because the gel structure does not easily deteriorate even after long-term use, it can be used for a variety of purposes, such as water retention agents for agriculture and horticulture, and water stop agents for civil engineering and construction. It can also be applied to cosmetics where properties and breathability are important. Furthermore, it can also be used for applications such as anti-condensation agents and ion exchange resins where hygroscopicity and breathability are important. In addition to the above-mentioned uses, the water-absorbing resin produced according to the present invention can be added with additives such as colorants and fragrances, fillers, and used in combination with different materials such as paper and fibers. Furthermore, depending on the nature of the polymerizable monomer, it is possible to create porous polymers that have other properties than water-absorbing resins. Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto. [Example] Example 1 300 g of cyclohexane and 3 g of ethyl cellulose (manufactured by Hercules, trade name N-50) were added to a four-necked flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a nitrogen gas introduction tube. The mixture was stirred with water, nitrogen gas was blown in to drive out dissolved oxygen, and the temperature was raised to 70°C. In another flask, 43 g of sodium hydroxide was dissolved in 130 g of water, and 100 g of acrylic acid (AA) was added to the resulting aqueous solution. , product name oks−3266)
4 g of ethylene glycol diglycidyl ether, 25 mg of ethylene glycol diglycidyl ether, and 54 g of hexane were added, stirred, and nitrogen gas was blown to drive out dissolved oxygen to prepare an aqueous monomer solution (O/W emulsion). Next, while thoroughly stirring the dispersion medium in the four-necked flask at a speed of 400 rpm, add 1 portion of the O/W emulsion.
The mixture was added dropwise over a period of time, and polymerization was further continued for 3 hours. Thereafter, these were directly dried at 80°C under reduced pressure to obtain porous spherical polymers. Example 2 Polymerization was carried out in the same manner as in Example 1, except that 50 mg of sodium dodecyl sulfonate was used instead of modified polyvinyl alcohol and 27 g of ethyl acetate was used instead of hexane, to obtain a porous spherical polymer. Example 3 Partially saponified vinyl alcohol (manufactured by Nippon Gosei Co., Ltd., trade name GH) was used instead of modified polyvinyl alcohol.
-17) 4g, cyclohexane instead of hexane
Polymerization was carried out in the same manner as in Example 1 except that 81 g was used to obtain a porous spherical polymer. Example 4 80g of acrylic acid instead of 100g of acrylic acid
and 20 g of sodium acrylamide methylpropanesulfonate (AMPS), 34 g of sodium hydroxide instead of 43 g of sodium hydroxide, and 4 g of rosin (EO) ₁₅ ester instead of modified polyvinyl alcohol. Example 1
Polymerization was carried out in the same manner as above to obtain a porous spherical polymer. Note that (EO) ₁₅ above means addition of an average of 15 moles of ethylene oxide. Example 5 80g of acrylic acid instead of 100g of acrylic acid
and dimethylaminoethyl methacrylate (DM)
20g of sodium hydroxide, 34g of sodium hydroxide instead of 43g of sodium hydroxide, 54g of cyclohexane instead of hexane, and 0.2g of isostearic acid (EO) ₃₀ glycerin ester instead of modified polyvinyl alcohol. Polymerization was carried out in the same manner as in Example 1 to obtain a porous spherical polymer. Comparative Example 1 300 g of cyclohexane and 3.0 g of ethyl cellulose were added to a four-necked flask (No. 1) equipped with a stirrer, reflux condenser, dropping funnel, and nitrogen gas inlet tube, stirred, nitrogen gas was blown in to drive out dissolved oxygen, and the mixture was heated to 70°C. The temperature rose to Also, in another flask,
Dissolve 43 g of sodium hydroxide in 130 g of water and add 100 g of acrylic acid to the resulting aqueous solution. Add and dissolve 0.16 g of ammonium persulfate (APS) and 25 mg of ethylene glycol diglycidyl ether to expel dissolved oxygen to prepare a monomer solution. did. Next, the monomer aqueous solution was added dropwise into the four-necked flask over 1 hour while the system was thoroughly stirred at a speed of 400 rpm, and polymerization was continued for an additional 3 hours. After polymerization, it was directly dried at 80°C under reduced pressure to obtain a spherical polymer. Comparative Example 2 A spherical polymer was obtained by polymerization in the same manner as in Comparative Example 1, except that 4 g of modified polyvinyl alcohol was added to the monomer aqueous solution. The performances of the polymers obtained in Examples 1 to 4 and Comparative Examples 1 to 2 are summarized in Table 1. In addition, the initial water absorption rate in the table was measured using the following method. Γ Initial water absorption rate Polymer in a 6 x 8 cm paper tea bag type bag
0.3g was added, the bag was stood upright, and the bottom was lightly stuffed with polymer. This was immersed in physiological saline in a 300 ml beaker for 1 minute with the bag upright. After soaking for 1 minute, the water was drained and the weight was measured. The amount of water absorbed by the tare was subtracted from this value and converted into the amount of water absorbed per 1 g of polymer.

【table】

[Table] Next, in Example 1, the O/W emulsion produced after starting dropping the O/W emulsion into cyclohexane
An optical micrograph of the W/O emulsion particle structure is shown in FIG. 1, and an optical micrograph of the O/W/O emulsion particle structure produced after the start of dropping the O/W emulsion in Example 5 is shown in FIG. Further, optical micrographs of the W/O emulsion particle structure formed after dropping the monomer aqueous solution in Comparative Examples 1 and 2 are shown in FIGS. 4 and 3, respectively. From the results in Table 1 and FIGS. 1 to 4, it can be seen that when an O/W/O emulsion is formed and polymerized according to the present invention, a polymer having extremely excellent performance can be obtained.

[Brief explanation of the drawing]

Figures 1 and 2 are optical micrographs of the O/W/O emulsion particle structure produced after the start of dropping the O/W emulsion according to the present invention, and Figures 3 and 4 are optical micrographs of the monomer aqueous solution obtained by the conventional method. It is an optical micrograph of the W/O emulsion particle structure after dropping.

Claims (1)

[Claims] 1. In producing a porous polymer, the following steps: (1) Using a water-soluble surfactant or a water-soluble polymer dispersant, the inner phase is a hydrophobic phase and the outer phase is a hydrophobic phase. A step of creating an O/W emulsion, which is an aqueous phase containing various water-soluble polymerizable monomers, (2) converting the O/W emulsion into a hydrophobic dispersion medium containing an oil-soluble surfactant or an oil-soluble polymer dispersant; A method for producing a porous polymer, further comprising the steps of: creating an O/W/O emulsion; and (3) polymerizing a monomer. 2. The manufacturing method according to claim 1, wherein the water layer containing the water-soluble monomer contains a polymerization initiator.