JPH05178916A - Production of self-crosslinkable polymer emulsion - Google Patents

Abstract

PURPOSE:To efficiently produce the title emulsion which has good stability and quality and is free from coagulates unlike the self-crosslinkable polymer emulsion produced by the conventional process. CONSTITUTION:A liquid mixture of a water-soluble crosslinkable monomer and a monomer copolymerizable therewith is pre-emulsified in the presence of an emulsifying agent and a polymerization catalyst to prepare a monomer emulsion. This emulsion is dropped into a polymerization system where neither an initiator nor an emulsifying agent is present, and polymerization is initiated at a concentration not higher than the critical micelle concentration to thereby produce the desired emulsion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a self-crosslinking polymer emulsion having good quality and excellent polymerization stability.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
An aqueous resin dispersion is generally produced by an emulsion polymerization method. However, when a hydrophilic monomer such as N-methylol acrylamide is copolymerized, there is a problem that the polymerization stability is significantly lowered and gelation occurs. there were.

As a method for solving these problems, for example, in JP-A-2-233711, a polymerizable monomer and a monomer having a crosslinking property with the monomer are made into a monomer emulsion, and the emulsion is prepared in an aqueous phase. A method for producing a self-crosslinking plastic dispersion liquid using a pre-emulsion addition polymerization method in which emulsion polymerization is carried out in two steps is described. This pre-emulsion addition polymerization method is a method in which monomers containing a hydrophilic monomer are emulsified with a surfactant and then added dropwise to a polymerization system in which water, an initiator and an emulsifier are mixed, but decomposed. It was difficult to control the polymerization rate by the initiator, and there was a problem that aggregates were by-produced. In addition, since the emulsifier is added to the continuous phase side in advance, the polymerization system becomes the critical micelle concentration (hereinafter, abbreviated as CMC concentration) or more, and the hydrophobic monomer is preferentially polymerized to form a hydrophilic monomer. There is a problem that the copolymerizability is lowered.

Further, in JP-A-58-185668, a mixture prepared by dissolving or dispersing a tackifier resin in a mixture of monomers is made into an emulsified mixture prepared by dispersing it in water containing an emulsifier, and water, the emulsifier and the polymerization are polymerized. A method for producing a water-resistant copolymer emulsion type adhesive is described, which comprises continuously adding and polymerizing a polymerization liquid containing a catalyst. However, even in this polymerization operation, the emulsifier is previously added to the continuous phase side, which is not preferable for the same reason as described above.

On the other hand, in such a polymerization system, a seed polymerization method has also been proposed, and in JP-A-2-80482, a mixture of monomers, a tackifier resin, and a mixture of monomers in an emulsion of a polymer such as vinyl ester. A method is described in which a pre-emulsion containing an emulsifier and water is sequentially added to carry out emulsion polymerization in the presence of a polymerization catalyst. Further, JP-A-57-16082 discloses a method for producing an emulsion-type pressure-sensitive adhesive by a two-step polymerization method in which an emulsified monomer is dropped and polymerized in a polymer emulsion, and these methods have two steps. Therefore, there is a problem that not only the operation becomes complicated, but also the cost becomes disadvantageous because the reaction of is required.

As described above, in the conventional method for producing a polymer emulsion, the polymerization stability is lowered, a by-product of agglomerates, the copolymerizability is lowered, or the operation is complicated. The advent of methods for producing coalesced emulsions has been strongly desired in the art. The present invention provides a method for producing a simple self-crosslinking polymer emulsion, which is easy to control the polymerization rate, does not generate coagulates as a by-product, and has excellent copolymerizability, as a solution to such problems. With the goal.

[0007]

Means for Solving the Problems The present inventors have solved the above-mentioned problems and, in order to efficiently obtain an aqueous resin dispersion obtained by copolymerizing a hydrophilic monomer such as N-methylolacrylamide, As a result of earnest research, the present invention has been completed, focusing on a method of dropping a monomer emulsion into a polymerization system containing no emulsifier. In the present invention, the liquid side on which the monomer emulsion is dropped is called a polymerization system. That is,
The gist of the present invention is a method for producing a self-crosslinking polymer emulsion in which a water-soluble monomer having crosslinkability and a monomer copolymerizable with the monomer are copolymerized, and a water-soluble monomer having crosslinkability is used. A liquid mixture of the body and a monomer copolymerizable with the monomer,
A monomer emulsion is prepared by pre-emulsifying in the presence of an emulsifier and a polymerization catalyst, and the monomer emulsion is added dropwise to a polymerization system in which an initiator and an emulsifier do not exist, and polymerization is performed at a critical micelle concentration or less in the initial stage of polymerization. The present invention relates to a method for producing a self-crosslinking polymer emulsion, which is characterized by being started.

In the production method of the present invention, first, a mixed solution of a water-soluble monomer having crosslinkability and a monomer copolymerizable with the monomer is mixed with a dispersion medium in the presence of an emulsifier and a polymerization catalyst. And preliminarily emulsified to prepare a monomer emulsion. Examples of the crosslinkable water-soluble monomer (hydrophilic monomer) used in the present invention include amide groups such as N-methylol acrylamide, acrylamide, methacrylamide, and diacetone acrylamide, and a monomer having a methylol group. The body may be mentioned, and these may be used alone or in combination of two or more. At this time, the concentration of the water-soluble monomer is preferably 20 wt% or less with respect to the total weight of the monomers (the weight of the mixed solution of the cross-linkable water-soluble monomer and the copolymerizable monomer). If the concentration of water-soluble monomer is more than 20 wt%,
In the polymerization system, the amount of the water-soluble monomer eluted from the droplets of the monomer into the dispersion medium increases, and the polymerization of the water-soluble monomer proceeds in the dispersion medium to form a gelled product, which is not preferable.

Examples of the copolymerizable monomer used in the present invention include the following acrylic acid esters, vinyl esters, and styrene-based monomers. Examples of the acrylic acid esters include acrylic acid or methacrylic acid methyl, ethyl, propyl, butyl, isobutyl, t-butyl, cyclohexyl, 2-
Examples thereof include alkyl esters of ethylhexyl, isononyl, lauryl, stearyl and the like (having 1 to 18 carbon atoms in the alkyl group), and (meth) acrylates of aromatic alcohols such as benzyl (meth) acrylate. These are one or two kinds. The above is used in combination. Examples of the vinyl esters include vinyl acetate, vinyl propionate, tertiary vinyl nonanoate, vinyl stearate, vinyl monochloroacetate, vinyl benzoate and the like, and these are used alone or in combination of two or more. Examples of the styrene-based monomer include styrene and chloromethylstyrene, which may be used alone or in combination of two or more. In the present invention, among the above-mentioned copolymerizable monomers, acrylic acid esters are preferably used from the viewpoint of polymerization stability (when the polymerization stability is good, the formation of aggregates is less likely to occur).

Examples of the emulsifier (surfactant) used in the present invention include alkylbenzene sulfonates, sodium dialkylsulfosuccinates, higher alcohol sulfates, polyoxyethylene alkylphenyl ether sulfates, sodium styrene sulfonates, allyl alkyls. Emulsion polymerization of anionic surfactants such as sodium sulfosuccinate, nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene polyoxypropylene alkyl ether, and amphoteric surfactants such as carbobetaine and sulfobetaine. Examples thereof include known ones, and these are used alone or in combination of two or more. At this time, the emulsifier amount is 10w based on the total weight of the monomers.
t% or less is preferable. When the amount of the emulsifier is more than 10 wt%, the micelles increase, whereby the polymerization of the hydrophobic monomer in the micelle progresses and the copolymerizability with the hydrophilic monomer decreases, which is not preferable.

Examples of the polymerization catalyst (water-soluble initiator) used in the present invention include peroxides such as ammonium persulfate, potassium persulfate and hydrogen peroxide, and 2,2'-azobis (2-amidinopropane) hydrogen. A water-soluble radical polymerization catalyst such as an azo polymerization catalyst such as chloride can be used. At this time, the amount of the polymerization catalyst is 5 wt with respect to the total weight of the monomers.
% Or less is preferable. If the amount of the polymerization catalyst is more than 5 wt%, the by-product of the aggregate will proceed, which is not preferable. Further, in the present invention, water is usually used as the dispersion medium of the monomer emulsion to be preliminarily emulsified, but hydrophilic solvents such as methanol, ethanol, n-propanol, i-propanol and acetone may be used together. At this time, the amount of water charged is usually 20 to 300 wt% with respect to the total weight of the monomers. Two
If it is less than 0 wt%, an O / W type emulsion is not formed, and if it is more than 300 wt%, productivity is lowered, which is not preferable.

In the present invention, a monomer emulsion is prepared by mixing and stirring the above components to carry out preliminary emulsification. Examples of the pre-emulsification method include a method using a batch homomixer, an ultrasonic emulsifier, a high-pressure homogenizer, etc., and a change in stirring speed, a change in frequency, a change in pressure, etc. The diameter can be adjusted. At this time, the smaller the particle size of the monomer emulsion is, the more stable the monomer emulsion becomes, which is preferable, but it is difficult to set the particle size to 0.5 μm or less in a usual emulsification operation. Therefore, the average particle size range of the monomer droplets in the monomer emulsion is preferably 0.5 to 30 μm. When it is larger than 30 μm, the storage stability of the polymer emulsion after the completion of the polymerization is deteriorated, and separation due to by-production of coarse particles occurs, which is not preferable.

In the method for producing a self-crosslinking polymer emulsion of the present invention, the monomer emulsion obtained as described above is added dropwise to a polymerization system in which neither an initiator nor an emulsifier is present, and polymerization is carried out at a CMC concentration or less. Let it start. That is, in the present invention, the initiator is not added to the polymerization system, but when the initiator is added in advance, thermal decomposition proceeds from the temperature rising stage before dropping the monomer emulsion, and excess radicals are generated in the initial stage of polymerization. Is generated and it becomes difficult to control the polymerization rate. Further, the polymerization of the water-soluble monomer alone easily occurs and the copolymerizability decreases, so that the polymerization stability deteriorates and the amount of aggregates increases.

Further, in the present invention, the emulsifier is not previously added to the polymerization system in order to start the polymerization at a CMC concentration or lower in the initial stage of the polymerization. As described above, since the polymerization system does not include an initiator and an emulsifier, it takes time to reach the CMC concentration in the initial stage of dropping, during which the hydrophilic monomer is diffused outside the monomer droplets and the radical is contacted. Then, the polymerization is started.
Since the polymer serves as a nucleus and particle growth occurs, a polymer having a relatively narrow particle size distribution is obtained, and the polymerization stability is also excellent. Further, from the aspect of particle size distribution, the storage stability of the polymer of which polymerization is completed is also good. On the other hand, in the polymerization in the state where the micelle concentration is increased by adding the emulsifier to the polymerization system in advance, the hydrophobic monomer is selectively polymerized in the micelle and lacks the copolymerizability with the hydrophilic monomer. Therefore, the polymerization stability is deteriorated due to the generation of aggregates.

In the present invention, the concentration of the copolymer in the obtained polymer emulsion can be arbitrarily set according to the charged amount of the raw materials (monomer, polymerization catalyst, emulsifier) according to the purpose. The concentration of the copolymer in the polymer emulsion obtained from the viewpoint of stability is preferably 70 wt% or less. The amount of water used as the dispersion medium for the polymerization system is set so that the concentration of the copolymer in the obtained polymer emulsion is 70 wt% or less. When the copolymer concentration in the polymer emulsion is more than 70 wt%, the polymerization stability is lowered, which is not preferable. In the present invention, a one-step reaction is adopted in order to simplify the reaction operation, but the polymerization temperature here is usually 60 to 90 ° C, preferably 70 to 85 ° C. 60
When the temperature is lower than 0 ° C, the amount of radicals generated is small, the number of core particles is small, and the polymer particles become coarse, which is not preferable. Further, at a temperature higher than 90 ° C., the polymerization rate is high, it is difficult to control the nucleation rate, and a gelled product is easily generated, which is not preferable.

The average particle size of the polymer emulsion obtained by the method for producing a self-crosslinking polymer emulsion of the present invention as described above is 100 to 600 nm, preferably 120 to 500 nm, depending on the purpose.

[0017]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 100 parts by weight of a monomer mixture consisting of 60 parts by weight of ethyl acrylate, 15 parts by weight of butyl acrylate, 10 parts by weight of methyl methacrylate, 10 parts by weight of 80% acrylic acid and 5 parts by weight of N-methylolacrylamide. Emulgen 150 in parts by weight
3.5 parts by weight of 20% aqueous solution of nonionic emulsifier (manufactured by Kao Corporation), 4 parts by weight of 25% aqueous solution of neoperex F-25 (manufactured by Kao Corporation) anionic emulsifier and 0.5 parts by weight of ammonium persulfate. Then, 47 parts by weight of water was charged into a batch type homomixer and preliminarily emulsified at 8000 rpm for several minutes to prepare a monomer emulsion.

Next, 55 parts by weight of water was charged into a 5 L stainless steel polymerization vessel equipped with a stirrer, a thermometer and a reflux condenser, and the mixture was stirred and purged with nitrogen, and the temperature was raised to 85 ° C. over 2 hours. Then, the above monomer emulsion was continuously added dropwise. The temperature inside the polymerization vessel during the polymerization was kept at 85 ° C., and after completion of dropping, aging was carried out at 85 ° C. for 2 hours. The average particle size of the monomer particles in the pre-emulsified monomer emulsion during dropping was 2 μm as measured by a micrograph. The obtained polymer emulsion particles have an average particle size of 200 nm as measured by a light scattering method (used by Coulter N4, manufactured by Coulter Electronics Co.).
Met. Further, the polymerization stability was good, and the total amount of the polymerized product was filtered through a wire mesh of 150 mesh, and the wire mesh was dried, and then the dry weight of the polymer of 150 mesh or more was calculated. It was 5% by weight.
Further, even in the storage stability for 6 months (encapsulated in a glass container and stored in a sealed state at 25 ° C.), the polymer did not separate and showed homogeneous stability.

Example 2 Polymerization was carried out in the same manner as in Example 1. However, the number of revolutions of the batch type homomixer was set to 2000 rpm, and the obtained monomer particles were subjected to polymerization using a monomer emulsion having an average particle size of 10 μm. The obtained polymer emulsion had an average particle size of 350 nm, and the stability of the polymer was good as in Example 1. The amount of aggregate was 0.7% by weight of the total polymer.

Example 3 Polymerization was carried out in the same manner as in Example 1. However, the composition of the monomer was 62 parts by weight of butyl acrylate, 32 parts by weight of methyl methacrylate, 4 parts by weight of 80% acrylic acid, and 100 parts by weight of a mixed solution of 2 parts by weight of diacetone acrylamide. The rotation speed was 4000 rpm, and polymerization was performed using a monomer emulsion having an average particle diameter of the obtained monomer particles of 6 μm. The obtained polymer emulsion had an average particle size of 270 nm, and the stability of the polymer was good. The amount of aggregate was 0.6% by weight of the total polymer.

Comparative Example 1 A monomer emulsion was prepared by charging a batch homomixer with the same composition and the same amount as in Example 1 in advance and pre-emulsifying at 8000 rpm for several minutes. Then, in a polymerization vessel similar to that of Example 1, 55 parts by weight of water and further 150 Emulgen were added.
0.35 parts by weight of 20% aqueous solution of nonionic emulsifier (manufactured by Kao Corporation), 0.4 parts by weight of 25% aqueous solution of neoperex F-25 (manufactured by Kao Corporation) anionic emulsifier, and ammonium persulfate of 0. The temperature was raised to 85 ° C. while charging 05 parts by weight, stirring and purging with nitrogen. The previously prepared monomer emulsion was continuously dropped into this polymerization container over 2 hours. The temperature inside the polymerization vessel during the polymerization was kept at 85 ° C., and after completion of dropping, aging was carried out at 85 ° C. for 2 hours. During the dropping, the average particle size of the monomer particles of the monomer emulsion was 2 μm. The obtained polymer emulsion particles had an average particle size of 100 nm and the amount of aggregates was 7.0% by weight of the total polymer. In the storage stability (encapsulated in a glass container and stored in a sealed state at 25 ° C.), separation occurred in 3 days, and coarse particles were precipitated.

[0023]

EFFECTS OF THE INVENTION According to the method for producing a self-crosslinking polymer emulsion of the present invention, unlike the conventional production method, a self-crosslinking polymer emulsion having excellent polymerization stability and good quality and free of agglomerates is obtained. It can be manufactured efficiently.

Claims (4)

[Claims] 1. A method for producing a self-crosslinking polymer emulsion comprising copolymerizing a water-soluble monomer having crosslinkability and a monomer copolymerizable with the monomer, wherein a water-soluble monomer having crosslinkability is used. A liquid mixture of the body and a monomer copolymerizable with the monomer,
A monomer emulsion is prepared by pre-emulsifying in the presence of an emulsifier and a polymerization catalyst, and the monomer emulsion is added dropwise to a polymerization system in which an initiator and an emulsifier do not exist, and polymerization is performed at a critical micelle concentration or less in the initial stage of polymerization. A method for producing a self-crosslinking polymer emulsion, which comprises starting. 2. The monomer emulsion is 0.5 to 30 μm.
The method according to claim 1, wherein the average particle size is m. 3. The method according to claim 1, wherein the copolymerizable monomer is an acrylic acid ester. 4. The production method according to claim 1, wherein the water-soluble monomer having crosslinkability is a monomer having an amide group or a methylol group.