JPH0721012B2 - Polymer latex coagulation method - Google Patents

Description

The present invention relates to a method for aggregating a polymer latex for providing a high-concentration large particle size polymer latex in a short time without producing coagulated particles as a by-product in the aggregating step. .

[Conventional technology]

Resins obtained by emulsion polymerization using rubber latex as a substrate are often important as engineering plastics, and the main examples are ABS resins obtained by graft polymerization of styrene and acrylonitrile onto polybutadiene or styrene to polybutyl acrylate. As an example, an ASA resin in which acrylonitrile is graft-polymerized can be used.

Generally, a polymer containing grafted rubber particles as a component has its physical properties changed by a graft polymerization method, but the physical properties of the polymer also greatly change by changing the particle size and distribution of the rubber matrix particles, so that an appropriate particle size and It is well known that it is necessary to use a rubber matrix having a distribution state.

For example, in the case of ABS resin, it is generally difficult to obtain good physical properties unless the particle diameter is at least 2500 Å or more, and it is more preferable that particles of 5000 Å or more are contained.

However, the production of polymer particles having such a large particle size by emulsion polymerization is industrially disadvantageous because the polymerization rate is remarkably reduced, as easily derived from the general theory of emulsion polymerization.

Various methods for aggregating a small particle size polymer latex have been known so far.

For example, US Pat. No. 2,446,101 and US Pat.
94,002 discloses a method of adding ammonium chloride to a latex, but in the method of performing aggregation using such a water-soluble salt, in order to enhance the particle size enlargement effect because the effect is small. Must be added in large amounts. Moreover, it is necessary to add a large amount of emulsifier in order to re-stabilize the polymer latex after aggregation.

Furthermore, these low molecular weight components added in large amounts in the aggregating step may cause problems with stability in the later step,
Further, it may remain in the final polymer to impair the quality of the product, which is not preferable.

U.S. Pat.No. 3,281,386, No. 3,551,370 or and No. 3,652,721 describes a method of aggregating latex particles by deactivating the surfactant activity of an emulsifier with acetic acid or acetic anhydride. Proposed.
However, in this method, the step of adding an acid to the latex is the most unstable, and the coagulated particles (coagulate until the particles reach 10 μm or more at the boundary surface where the added acid diffuses in the latex,
Particles that are enlarged and can no longer return to an emulsified state, and are often referred to as "core guillum"), and it is necessary to make the acid concentration sufficiently low to prevent the formation of such particles. The use of a high concentration of acid can be said to be a disadvantageous method because not only the final latex concentration is lowered, but also the effect of enlarging the particle size itself is reduced.

On the other hand, having a hydrophilic group and a hydrophobic group in one molecule, a method using a so-called polymer flocculant, U.S. Pat.No. 3,049,500, No. 3,056,758, No. 3,330,795, No. 3,288,741. And the Japanese Patent Publication No. 46-14539.

In these methods, the polymer coagulant is used as it is or after being partially modified and used alone or in combination with a specific salt.

However, the method using a polymer flocculant requires a long time for the flocculation step, the particle size is not very large, and it is difficult to stop the flocculation. Has the major drawback of

By the way, as a method currently used industrially,
A method using a high-pressure homogenizer and a method of adding a solvent having a good affinity for the polymer latex can be mentioned. In the former case, a latex having a uniform particle diameter can be obtained only by aggregating a part of the latex particles. In the latter case, the solvent needs to be distilled off as a pre-stage of the graft polymerization, and there is a lot of room for improvement.

[Problems to be solved by the invention]

An object of the present invention is to provide an industrially advantageous method for aggregating polymer latex, which does not produce core guillum in the agglomeration process, has a large particle size enlarging effect on the polymer latex, and has a uniform particle size distribution in a short aggregating time. Especially.

[Means for solving problems]

The method for aggregating a polymer latex of the present invention is a method of aggregating latex particles by adding an acid to a small particle size polymer latex obtained by an emulsion polymerization method using an emulsifier mainly composed of an emulsifier which is acidic and has a reduced surface activity. , An acidic emulsifier having good surface activity is added to the polymer latex in advance, then an excess amount of acid is added to the polymer latex as the first step, and then the polymer latex is added to the polymer latex as the second step. It is characterized in that the polymer latex of the first stage having a higher concentration than this is added and mixed to keep the mixed polymer latex at pH 6 or less.

The small particle size polymer latex used in the present invention is mainly composed of an emulsifier which is acidic and decreases in surface activity, and is composed of monomers, water
The emulsifier which is produced by a conventional emulsion polymerization using an initiator or the like and is not particularly limited as an emulsifier whose surface activity is reduced by acid, but is represented by, for example, an emulsifier having a carboxylic acid group and a salt of an alkali metal. However, anionic emulsifiers such as potassium laurate, sodium oleate, mixed fatty acid potassium, and potassium rosinate can be used. The amount of addition may be the amount necessary to maintain the stability of the latex when polymerizing the small particle size polymer latex used for aggregation, and is not particularly limited, but generally the polymer
It can be used in the range of 0.5 to 5 parts with respect to 100 parts (weight basis).

The small particle size polymer latex used in the present invention is not particularly limited, and examples thereof include polybutadiene latex, polystyrene-butadiene copolymer latex, polyacrylonitrile-butadiene copolymer latex,
A soft polymer latex such as polybutyl acrylate latex is suitable, and a hard polymer latex such as polystyrene latex or polyacrylonitrile-styrene copolymer latex can also be used.

In the present invention, before adding an acid to the small particle size polymer latex, an emulsifier having an acidic and good surface-active ability is added in advance. As the emulsifier, an acid group having a higher ionization constant than the acid described later is used. Can be used as the emulsifier composed of a salt of a sulfonic acid group and an alkali metal, for example, sodium alkylbenzenesulfonate, sodium alkylnaphthalenesulfonate, potassium alkyldiphenylethersulfonate,
Sodium lauryl sulfate can be used. The addition amount varies depending on the type and concentration of the acid described below, and the type and concentration of the small particle size polymer latex, and therefore cannot be limited, but is generally in the range of 0.01 to 1.0 part per 100 parts of the polymer, and the addition amount is If it is too small, coagulum may occur in the acid addition step, and if it is too large, the effect of increasing the particle size becomes small. The emulsifier may be added at the time of polymerizing the small particle size latex used for aggregation or after the polymerization.

Next, an acid to be added as a first step in the present invention can be used as long as it has an ionization constant higher than that of an acid group of an emulsifier which is acidic and reduces surface activity.
A strong acid such as hydrochloric acid or sulfonic acid, or a weak acid such as maleic acid, itaconic acid or acetic acid, or a mixed solution of two or more thereof can be used. However, its concentration needs to be as high as possible under the condition that coagulum is not formed in the aggregation step.

The amount of acid added to the small particle size polymer latex cannot be limited because it changes depending on the type and amount of the emulsifier used, but at least the latex at the end of the second stage
The pH needs to be 6 or less.

The concentration of the polymer latex used in the first step is important because if it is too high, coagulum is generated in the step of adding an acid, and if it is too low, the effect of particle size enlargement becomes small. However, the concentration range varies depending on the type and concentration of the acid used and the type and addition amount of the emulsifier which is acidic and has good surface-active ability, and therefore the range cannot be limited. However, for industrial purposes, the latex concentration
It is preferable to adjust other conditions so that it can be 30% or more.

Next, the polymer latex added as the second step in the present invention is because the concentration of the acid to be contact-mixed with the polymer latex is sufficiently diluted in the first step, and the viscosity of the polymer latex after the step of the first step is finished. Since the difference is small, it is possible to use a polymer latex having a higher concentration than that used in the first step, and thus it is possible to enhance the particle size enlargement effect. For example, if the particle size is 1000Å or more, it can be used at a concentration of 40% or more.

The ratio of the polymer latex used in the first step and the second step can be in a wide range, and the polymer latex used in the first step occupies 1/10 to 9/10 of the whole in comparison with the solid content. Is possible. In order to lower the pH of the polymer latex to 6 or lower at the end of the second step, the emulsifier and the electrolyte contained in the latex used in the first step and the second step are mixed with an acid in an amount sufficient to neutralize them. Must be added in the first stage.

In the present invention, adding a water-soluble salt to the starting material in advance is effective for enhancing the stability when polymerizing a small particle size polymer latex or controlling the particle size, and further for the particle size in the aggregating step. It is effective in enhancing the hypertrophic effect. The type of salt used is required to be water-soluble and is not particularly limited as long as it does not generate an insoluble salt or gas by reacting with an acid to be added, and examples thereof include sodium chloride, potassium sulfate and acetic acid. There are sodium, potassium phosphate, tetrapotassium pyrophosphate, etc., which may be used alone,
You may mix and use 2 or more types.

The polymer latex after the completion of the second stage is extremely unstable, and it is difficult to transfer and store it for a long time as it is. Therefore, a means for stabilizing it is needed. There are a method using an alkali and a method using a surfactant. The former method is to add, for example, sodium hydroxide, potassium hydroxide or ammonium hydroxide.
The amount added is appropriate to neutralize the acid added in the aggregating step, and if the concentration is too high, core gillum is formed in the adding step, so 15% or less is preferable.

The latter method is a method of adding a stable emulsifier at a pH of 5 or less, not to mention the above-mentioned emulsifier having an acidic and good surface-active ability, in addition to that, polyoxyethylene lauryl ether, polyoxyethylene octyl phenyl ether Nonionic surfactants such as sorbitan monooleate can also be used.

〔Example〕

Next, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1 100 parts of butadiene monomer, 85 parts of deionized water, 1.6 parts of potassium oleate, sodium sulfonate (TAMOL-SNT)
R Rohm and Haas) 0.3 part, sodium sulfate 0.8
Parts, potassium persulfate 0.2 parts, tert-lead decyl mercaptan 0.15 parts, and potassium hydroxide 0.18 parts were placed in a pressure vessel equipped with a stirrer and the temperature was raised to 60 ° C. to start polymerization.

After the polymerization was started, 5 parts of deionized water in which 0.1 part of potassium sulphate was dissolved was added to the pressure vessel at a polymerization rate of 65% to raise the polymerization temperature to 65 ° C. After a polymerization time of 26 hours, a polybutadiene latex having a polymerization rate of 88%, an average particle size of 1850Å, a solid content of 50.4% and a viscosity of 200 centipoise was obtained. This is designated as latex A.

Next, 0.1 part of the organic sulfonic acid soda was added to the latex A and 1000 parts of the solid content of the latex A and deionized water to make the concentration 40%, and the latex was converted into the solid content.
In addition to 50 parts, a container equipped with a stirrer, 18 parts of 2% sulfuric acid was added with stirring.

Further, while continuing stirring, 50 parts of the latex A was converted to a solid content and gently added. Then, the above sulfuric acid and an equivalent amount of 5% sodium hydroxide were added to obtain a stable latex.

This latex had a particle size of 3000Å, did not form coagulum and was a high-concentration latex with a solid content of 41.2%.

Example 2 Latex A diluted to 40% concentration after the production of latex A
A stable latex was obtained in the same manner as in Example 1 except that the amount of the solid content was 29 parts and the amount of the latex A added later was 71 parts in terms of the solid content.

This latex had a mean particle size of 3600Å, did not form coagulum and was a stable agglomerated latex.

Example 3 Latex A diluted to 40% concentration after the production of Latex A
Is converted to solids to make 24 parts and latex A added later
A stable latex was obtained in the same manner as in Example 1 except that the solid content was converted to 76 parts.

This latex has an average particle size of 3700Å and a solid content of 4
At 3.5%, coagulum was not produced as a by-product, and it was a large particle size latex with high solid content.

Comparative Example 1 Budadiene monomer 100 parts, deionized water 85 parts, potassium oleate 1.7 parts, organic sulfonic acid sodium 0.1 part, pyrophosphate tetrapotassium salt 2.0 parts, tassia reed decyl mercaptan 0.3 parts, potassium persulfate 0.2 parts The product was placed in a pressure-resistant container equipped with and the temperature was raised to 60 ° C. to start polymerization.

After the polymerization was started, when the polymerization rate was 65%, 5 parts of deionized water and 0.1 part of potassium persulfate were added to the pressure vessel to adjust the polymerization temperature to 6%.
Raised to 5 ° C. A polybutadiene latex having an average particle size of 1900Å was obtained with a polymerization time of 22 hours.

This is designated as latex B.

Next, deionized water was added to latex B to make a 40% concentration, and 44 parts of 2% sulfuric acid was added to 100 parts of the solid content. The liquidity at this time is pH 3.2, and after 5 minutes, 5
% Sodium hydroxide was added to raise the pH to 11.5 to obtain a stable latex. Coagulum was not produced as a by-product during the coagulation process, but the average particle size of the latex was 2400Å and the solid content was low at 31.7%.

Comparative Example 2 Comparative Example 1 except that the concentration of sulfuric acid in Comparative Example 1 was increased to 4% and 22 parts was added for the purpose of increasing the solid content concentration of the latex obtained by further increasing the particle size and re-stabilizing. The same operation was performed. However, a large amount of coagulum was produced as a by-product in the process of adding the sulfuric acid. This core guayrum was filtered with two pieces of gauze, and the dry weight was measured to be 2.0 parts.

〔The invention's effect〕

According to the method for aggregating a polymer latex of the present invention, a core latex is not produced as a by-product in the aggregating step, and a polymer latex having a large particle size can be obtained at a high concentration in a short aggregating time. Therefore, the present invention provides an industrially advantageous method for aggregating polymer latex.

Claims (1)

[Claims] 1. A method of aggregating latex particles by adding an acid to a small particle size polymer latex obtained by an emulsion polymerization method using an emulsifier mainly composed of an emulsifier which is acidic and decreases in surface activity, and the polymer latex is previously prepared. To the polymer latex is added an acidic emulsifier having good surface activity, then an excess amount of acid is added to the polymer latex as a first step, and then a higher concentration of the polymer latex is added as a second step. Add and mix the above small particle size polymer latex and adjust the pH of the polymer latex after mixing.
A method for aggregating a polymer latex, which is characterized by keeping at 6 or less.