JPH031321B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel emulsion polymerization process for producing highly concentrated latex.

Polymer latexes are widely used industrially in the fields of paints, adhesives, paper processing agents, fiber processing agents, etc., either as they are or in combination with various additives. Furthermore, polymers obtained by salting out and drying polymer latex are widely used industrially in the rubber industry and plastics industry. Examples of polymers include acrylic monomers such as alkyl acrylates and alkyl methacrylates, vinyl esters such as vinyl acetate, vinyl halides such as vinyl chloride and vinylidene chloride, vinylidene halides, isoprene, butadiene, isobutylene, styrene, acrylonitrile, etc. There are homopolymers and copolymers made from monomers.

These latexes are made by emulsion polymerization methods well known in the art. In other words, it is a method in which a monomer is added to an aqueous medium containing a surfactant, and polymerization is stably carried out using a polymerization catalyst that generates radicals, and the polymer is produced as particles with a diameter of 0.1 to 1 micron. Exists in a stably dispersed state in an aqueous medium.

By the way, in this emulsion polymerization, the polymer content of the final latex product is usually limited to 60% by weight. The reason why this 60% limit is set is that if you try to increase the concentration higher than this, the distance between the polymer particles will become too close and the entire system will aggregate, or a large amount of coarse particles that can be seen with the naked eye will be generated. Alternatively, the viscosity of the latex may increase significantly, making it impossible to put it into practical use. Solving these problems and stably producing latex with a polymer concentration of over 60% has been a long-standing challenge in the industry. In other words, high-concentration latex has many advantages, such as improving plant productivity, reducing transportation and storage costs, shortening the drying time of latex, forming a thick coating film in one go, and reducing volumetric shrinkage due to drying. This is because it has

[Problems to be solved by conventional technology and invention]

Although several methods have been proposed for producing high-concentration latex, no method has been found that can be carried out stably and efficiently and that does not involve excessive reinforcement of plant equipment.

There is a method of producing latex by emulsion polymerization and then removing water by distillation to make it highly concentrated. However, this method has many problems, such as excessive distillation costs, foaming that requires a large amount of antifoaming agent, easy generation of coarse particles, and surface skinning.

U.S. Patent No. 4,130,523 discloses that in order to widen the particle size distribution of the polymer and lower the viscosity of the latex to facilitate emulsion polymerization at high concentrations, a portion of the latex is extracted from the polymerization pot during the middle stage of polymerization. proposed a method to complete the reaction by continuously reintroducing this into the polymerization tank at the final stage of polymerization. However, this method presents various problems due to the withdrawal of a portion of the latex during the intermediate stages of polymerization.
That is, there is an excessive investment in equipment such as the need for a transfer pump to draw out the latex and the need to install a storage tank with an agitation device and a temperature control device. An even bigger problem is that the extracted latex contains a large amount of unreacted monomer and lacks stability, so the quality and properties of the final latex are likely to change.

In JP-A-56-157401, an emulsion of a specific monomer mixture containing a relatively large amount of a polymerization inhibitor is introduced into an aqueous phase containing an anionic emulsifier and a water-soluble salt to cause polymerization. He proposes a manufacturing method to obtain concentrated latex. However, since this method combines monomers that do not copolymerize and also contains a relatively large amount of polymerization inhibitor, a major problem is that a large amount of unreacted monomers remains in the final latex. It is. The conversion rate of monomer to polymer calculated from the results of the examples is at most 95%, and in fact tens of thousands of ppm of monomer is contained in the latex. Naturally, such latexes are unacceptable in terms of odor and safety.

[Means to solve the problem]

The present inventors have conducted extensive studies on a high-concentration latex emulsion polymerization method to overcome this situation.
The present invention has now been completed.

That is, the present invention provides the following methods: (1) A saturated ethylenically unsaturated monomer having no carboxyl group in an aqueous medium containing a surfactant, a polymerization catalyst, and a water-soluble salt selected from sodium bicarbonate or phosphate. The first step of obtaining seed latex by polymerizing one or more monomers and one or more ethylenically unsaturated monomers having a carboxyl group, (2) adding water to the seed latex in (1); sodium oxide,
A second step of mixing one or more basic compounds selected from potassium hydroxide and ammonium hydroxide, (3) substantially surface active in the presence of the seed latex prepared in (2). This is a highly concentrated latex emulsion polymerization method characterized by comprising a third step in which an ethylenically unsaturated monomer containing no agent is introduced and polymerized. Note that, in the present invention, the second step of mixing the basic compound is not limited to the first step or the third step.

The surfactant used in the present invention is a conventional anionic or nonionic surfactant or a mixture of both. Examples of anionic acids include fatty acids, alkyl sulfonates, alkylaryl sulfonates, alkyl sulfosuccinates,
There are polyoxyethylene alkyl sulfates, polyoxyethylene alkylaryl sulfates, etc., and nonionic types include polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether, polyoxyethylene sorbitan fatty acid ester, oxyethylene oxypropylene block polymer, etc. . The preferred amount of these surfactants added is 0.2 to 4% by weight based on the monomer.

In the present invention, the water-soluble salt selected from sodium bicarbonate or phosphate used in each step serves as a buffer to maintain polymerization stability and appropriately adjust the particle size of the polymer. Examples of phosphates include potassium hydrogen phosphate, potassium dihydrogen phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate. The amount of these water-soluble salts added is based on the monomer.
A preferred range is 0.2 to 3% by weight.

The polymerization color medium used in the present invention is one that performs addition polymerization of monomers by radical decomposition using heat or a reducing substance, and contains water-soluble or oil-soluble persulfates, peroxides, and azobis compounds. be. Examples include potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, benzoyl peroxide, t-butyl hydroperoxide, t-butyl peroxybenzoate,
2,2-Asobisisobutyronitrile, 2,2-
Examples include azobis(2-amidinopropane) hydrochloride and 2,2-azobis(2,4-dimethylvaleronitrile), and the amount thereof is usually 0.1 to 1% by weight based on the monomer. Note that when it is desired to accelerate the polymerization rate or to perform polymerization at a lower temperature, reducing substances such as sodium bisulfite, ferrous chloride, ascorbic acid, and sodium formaldehyde sulfoxylate are often combined with the polymerization catalyst.

Examples of ethylenically unsaturated monomers without carboxyl groups used in the present invention include aromatic monomers such as styrene and vinyltoluene, methyl acrylate, ethyl acrylate, butyl acrylate,
Acrylic esters such as 2-ethylhexyl acrylate, dodecyl acrylate, stearyl acrylate, methacrylic esters such as methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, stearyl methacrylate, vinyl acetate , vinyl esters such as vinyl propionate and vinyl versatate, vinyl cyanides such as acrylonitrile and methacrylonitrile, vinyl halides such as vinyl chloride and vinylidene chloride, as well as ethylene, butadiene, chloroprene, isoprene, isobutylene, etc. is also added as an example.
In addition, there are monomers with various other functional groups. For example, acrylamide, methacrylamide, diacetone acrylamide, glycidyl acrylate, glycidyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, N-methylol-acrylamide,
N-butoxymethacrylamide, phosphooxyethyl methacrylate, methacrylic acid 3
-chloro-2-acidphosphooxypropyl,
Methylpropanesulfonic acid acrylamide, divinylbenzene, allyl acrylate, allyl methacrylate, ethylene glycol acrylate, ethylene glycol methacrylate, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, styrene Examples include sodium sulfonate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, sodium vinyl sulfonate, and sodium alkylaryl sulfosuccinate.

Examples of the ethylenically unsaturated monomer having a carboxyl group used in the present invention include acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, and monobutyl maleate. These monomers are usually
It is blended in an amount of 0.5 to 7% by weight, preferably 1 to 4% by weight.

The basic compound mixed in the two steps of the present invention has the effect of suppressing the increase in viscosity of the latex and the generation of coagulum during the subsequent polymerization, and a specific example thereof is sodium hydroxide. , potassium hydroxide, and ammonium hydroxide. The preferred amount of these additives is such that the pH of the seed latex is adjusted to 4-8.

In the three stages of the present invention, it is important that substantially no additional surfactant be added when the ethylenically unsaturated monomer is introduced. This means that the polymerization of the ethylenically unsaturated monomers introduced in the three stages proceeds substantially only in the seed latex particles. Therefore, this does not limit the addition of small amounts of surfactant that do not substantially generate new polymer particles.
Note that if a substantial amount of surfactant is included, the viscosity of the latex will increase significantly, making polymerization difficult.

〔Effect of the invention〕

The present invention is capable of stably and efficiently producing a low-viscosity latex with a solid content of more than 60% by weight and free of coarse particles and coagulums, and does not require any new equipment expansion, and does not require the usual industrial production. It can be carried out in plant facilities constructed for emulsion polymerization, which is carried out in

〔Example〕

The present invention will be specifically explained below based on Examples and Comparative Examples, but it goes without saying that the scope of the present invention is not limited only to these Examples. Note that parts and percentages in the text are based on weight.

Example 1 374 parts of water was charged into the pressure-resistant reaction kettle shown in FIG. 1 and heated to a temperature of 80°C. Below, the temperature is controlled at 80°C. Next, a 5% aqueous solution of ammonium persulfate
After adding 26 parts, a monomer emulsion prepared in advance and having the following composition was flowed in at a constant rate for 1.5 hours.

Water 164.8 parts 25% aqueous solution of polyoxyethylene nonyl phenyl ether 20.8 parts 26% aqueous solution of sodium polyoxyethylene nonyl phenyl sulfate 20.0 parts Disodium hydrogen phosphate 5.2 parts Sodium persulfate 1.6 parts Styrene 509.6 parts Methacrylic acid 10.4 parts Thirty minutes after the inflow of the bulk emulsion is finished, 5.1 parts of a 25% aqueous solution of ammonia is added. Next, a monomer mixture of 764.4 parts of styrene and 15.6 parts of methacrylic acid and 46.8 parts of a 5% aqueous solution of sodium persulfate were separately introduced at a constant rate over a period of 2 hours and a period of 2.5 hours. Thirty minutes after this inflow was completed, the temperature was cooled to 60°C. Then t-
1 part of butyl hydroperoxide was added, and an aqueous solution consisting of 1 part of sodium formaldehyde sulfoxylate and 5 parts of water was flowed in over a period of 30 minutes. After 30 minutes, the mixture was cooled to room temperature and taken out from the reaction vessel through an 80-mesh filter cloth.The filter cloth contained almost no coarse particles or coagulated substances, indicating good polymerization stability.

The obtained latex had a solid content concentration of 67.0% and a viscosity of
It was a uniform aqueous dispersion of 3500 cps.

Example 2 The composition of the monomer emulsion in the first stage is as follows: 164.8 parts of water 25% aqueous solution of polyoxyethylene nonyl phenyl ether 20.8 parts 26% aqueous solution of sodium polyoxyethylene nonyl phenyl sulfate 20.0 parts Sodium hydrogen carbonate 5.2 parts Ammonium persulfate 1.6 parts Methyl methacrylate 509.6 parts Methacrylic acid 10.4 parts The third stage mixed monomer is methyl methacrylate
Polymerization was carried out in the same manner as in Example 1 except that 764.4 parts of methacrylic acid and 15.6 parts of methacrylic acid were used.

The obtained latex had a solid content concentration of 67.1% and a viscosity of
It was a uniform aqueous dispersion with coarse particles of 2000 cps and no coagulum.

Example 3 The composition of the monomer emulsifier in each step is as follows: 164.8 parts of water 25% aqueous solution of polyoxyethylene nonyl phenyl ether 20.8 26% aqueous solution of sodium polyoxyethylene nonyl phenyl sulfate 20.0 parts Disodium hydrogen phosphate 5.2 parts ammonium persulfate 1.6 parts styrene 296.4 parts 2-ethylhexyl acrylate 210.6 parts methacrylic acid 10.4 parts acrylamide 2.6 parts, the third stage mixed monomer is styrene 444.6 parts,
Polymerization was carried out in the same manner as in Example 1, except that 319.8 parts of 2-ethylhexyl acrylate and 15.6 parts of methacrylic acid were used.

The obtained latex had a solid content concentration of 67.1% and a viscosity of
It was a uniform aqueous dispersion with coarse particles of 1300 cps and no coagulum.

Example 4 The composition of the monomer emulsifier in the first stage is: 168.0 parts of water 25% aqueous solution of polyoxyethylene nonyl phenyl ether 20.8 26% aqueous solution of sodium polyoxyethylene nonyl phenyl sulfate 20.0 parts Disodium hydrogen phosphate 2.1 Parts Sodium persulfate 1.6 parts N-methylolacrylamide 6.4 parts Acrylonitrile 20.6 parts n-Butyl acrylate 361.4 parts Methyl methacrylate 121.3 parts Methacrylic acid 10.3 parts The third stage mixed monomer is acrylonitrile
Polymerization was carried out in the same manner as in Example 1, except that 31.4 parts of n-butyl acrylate, 548.7 parts of n-butyl acrylate, 184.2 parts of methyl methacrylate, and 15.7 parts of methacrylic acid were used.

The obtained latex had a solid content concentration of 66.9% and a viscosity of
It was a uniform aqueous dispersion with coarse particles of 1000 cps and no coagulum.

Example 5 The same procedure as in Example 1 was carried out until the monomer emulsion was finished flowing. After the monomer emulsion has finished flowing in
After 30 minutes, 5.0 parts of a 25% aqueous solution of sodium hydroxide is added. Next, a monomer mixture consisting of 560.0 parts of styrene, 537.6 parts of butadiene, 17.9 parts of methacrylic acid, 4.5 parts of acrylic acid, 1.0 part of lauryl mercaptan and 5% sodium persulfate.
67 parts of an aqueous solution separately, the former for 3 hours,
The latter flows at a constant rate over a period of 3.5 hours.

Thirty minutes after this inflow was completed, the temperature was cooled to 60°C. Then, 1 part of t-butyl hydroperoxide was added, and an aqueous solution consisting of 1 part and 5 parts of sodium formaldehyde sulfoxylate was added over a period of 30 minutes. After 30 minutes, the mixture was cooled to room temperature and taken out from the reaction vessel through an 80-mesh filter cloth.

The obtained latex had a solid content concentration of 70.6% and a viscosity of
It was a uniform aqueous dispersion with coarse particles of 3800 cps and no coagulum.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that 5.2 parts of disodium hydrogen phosphate was excluded from the monomer emulsion formulation in Example 1. As a result, as the monomer mixture of the third stage was introduced, the viscosity of the latex increased significantly, making it impossible to continue the polymerization.

Comparative Example 2 All polymerization was carried out according to Example 1, except that the addition of 5.1 parts of a 25% aqueous solution of ammonia was added after the monomer emulsion of Example 1 was introduced. As a result, a large amount of coarse particles and coagulation were generated as the monomer mixture of the third stage was introduced. Filtration of the obtained latex was extremely difficult.

Comparative Example 3 Polymerization was carried out in the same manner as in Example 1 except that methacrylic acid in the monomer emulsion formulation in Example 1 was omitted. As a result, similar to Comparative Example 2, a large amount of coarse particles,
Occurrence of coagulum was observed, and filtration of the coagulum was difficult.

Comparative Example 4 Similarly to Comparative Examples 1, 2 and 3, Example 2 was prepared by excluding either the water-soluble salt, the basic compound or the ethylenically unsaturated monomer having a carboxyl group.
As a result of carrying out the polymerizations of 5 to 5, it was observed that the viscosity of the latex significantly increased and a large amount of coarse particles and coagulates were generated, making filtration difficult.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of emulsion polymerization equipment used in Examples and Comparative Examples for explaining the present invention. In the figure, 1 is a pressure-resistant reaction vessel, 2 is a stirrer, 3 is a sulfur condenser, 4 is a thermometer, 5 is a temperature control jacket, 6 is a metering feed pump, and 7 is a mixing tank.

Claims (1)

[Scope of Claims] 1. One or more ethylenically unsaturated monomers having no carboxyl group in an aqueous medium containing a surfactant, a polymerization catalyst, and a water-soluble salt selected from sodium bicarbonate or phosphate. and a monomer consisting of one or more types of ethylenically unsaturated monomers having a carboxyl group to obtain a seed latex, a first step of obtaining a seed latex, 2 adding sodium hydroxide to the seed latex of (1),
A second step of mixing one or more basic compounds selected from potassium hydroxide and ammonium hydroxide, in which substantially a surfactant is mixed in the presence of the seed latex prepared in steps up to 3 (2). A highly concentrated latex emulsion polymerization method comprising a third step of injecting and polymerizing free ethylenically unsaturated monomers.