JPH029601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for coagulating and enlarging small particle size rubber latex to a particle size suitable for manufacturing ABS resin and the like.

"Conventional technology" Styrene-acrylonitrile-butadiene graft copolymer (so-called ABS resin), styrene-
When producing butadiene graft copolymer (so-called high impact polystyrene) etc. by emulsion polymerization method,
The appropriate rubber particle size is 0.2 to 0.7 μm. Rubber latex produced by emulsion polymerization, such as styrene-butadiene copolymer (SBR) latex, polybutadiene latex, etc., usually contain rubber particles with a particle size of 0.2 μm or less.
It is about 0.1 μm. Since it is not preferable to use latex containing rubber with such a small particle size for ABS resin production, an operation is performed to agglomerate the rubber latex particles and increase the particle size prior to the emulsion graft polymerization step. .

The agglomeration and enlargement of particle size is caused by adding acidic substances such as sulfuric acid and acetic anhydride to rubber latex that uses surfactants as emulsifiers, such as fatty acid soaps, which are composed of salts of weak acids and strong bases and lose their emulsifying effect in acidic regions. In addition,
This is generally done by making the liquid of latex acidic.

By making the liquid of the latex acidic, the emulsifying effect of the fatty acid soap is weakened, and as a result, the rubber latex particles coagulate with each other, resulting in large-sized rubber latex particles. After the particle size of the latex particles has been agglomerated and enlarged to a desired size, a method is usually adopted in which a basic substance such as caustic potash is added to restabilize the latex.

``Problems to be Solved by the Invention'' However, this operation of agglomerating and enlarging the particle size is carried out while the emulsifying effect of the emulsifier is temporarily weakened, which causes the latex to become unstable and stick to the walls of the reaction vessel. There were problems such as the formation of coagulum and adhesion, and the production of latex particles with abnormally large particle sizes.

The present inventors have arrived at the present invention as a result of extensive research aimed at solving these problems and providing a method for stably increasing the particle size of rubber latex. .

``Means for Solving the Problems'' The gist of the present invention is to add acid to rubber latex that has been emulsified with a surfactant containing fatty acid soap as a main component and has an average particle size of 0.2 μm or less. When adding a substance to make the liquid of the latex acidic and coagulate and enlarge the rubber latex particles, the rubber latex particles are The average particle size is 0.2~0.4μm
A method for coagulating and enlarging rubber latex particles is provided.

The present invention will be explained in detail below. The rubber latex used in the present invention is suitably one emulsified with fatty acid soap. Examples of the rubber latex used include styrene-butadiene copolymer (SBR) latex and polybutadiene latex. The average particle size of the rubber latex particles contained in these rubber latexes is 0.2 μm or less before the agglomeration and enlargement operation.
It is about 0.1 μm.

As the fatty acid soap used in the method of the present invention, higher fatty acid soaps such as sodium stearate and potassium oleate are particularly preferred.

If a small amount of a surfactant, which will be described later, is added as an emulsifier together with fatty acid soap, the operation of agglomerating and enlarging latex particles can be carried out in a more stable state. This is because, when phosphoric acid is added, the surfactant added with the fatty acid soap does not lose its emulsifying effect, and even if the liquid of the latex becomes acidic, especially when the pH value becomes 4 or less, The generation of giant latex particles as described in Japanese Patent Publication No. 47-49191 is not observed.

In the method of the present invention, the agglomeration and enlargement of latex particles is carried out by adding phosphoric acid to make the latex acidic. In this case, it is particularly preferable that the pH value of the latex is 4 or less.

That is, by adding phosphoric acid to rubber latex,
By keeping the pH value below 4, the emulsifying effect of fatty acid soap is reduced. In this case, phosphoric acid (100 parts by weight) per 100 parts by weight of rubber latex (total amount including water) is used.
% conversion amount) is in the range of 0.4 to 0.8 parts by weight,
The PH value of the latex becomes 4 or less, and the particle size of the enlarged rubber latex remains stable within the desired range and hardly changes, making the operation of the particle size enlargement process extremely easy. It is more preferable that the amount of phosphoric acid added is in the range of 0.45 to 0.65 parts by weight, since the particle size will be substantially uniform and constant within the desired range.

In addition, if phosphoric acid is added in the form of an aqueous solution of about 3 to 10% by weight, the amount added can be easily controlled, and furthermore, local aggregation of the rubber latex can be prevented, thereby avoiding the generation of coagulum etc. This is preferable because it can be done.

When phosphoric acid is added to latex, as mentioned above,
The emulsifying ability of the fatty acid soap is reduced, resulting in a state where the stability of the rubber latex is reduced. When adding phosphoric acid, if it is injected directly into the gas phase from the top of a container containing latex through a nozzle with a hole diameter of about 1 inch or more, as is usually done without special consideration, the emulsified state of the latex will be destroyed. This causes problems such as the formation of coagulum, the adhesion of rubber to the walls of the reaction vessel, and the formation of large particles that are inconvenient for the production of ABS resin.

Therefore, when adding phosphoric acid according to the method of the present invention, it is necessary to add the phosphoric acid in the form of a shower or mist without giving a severe impact to the liquid surface of the latex.

In the method of the present invention, the term "shower form" or "mist form" means that an aqueous solution of phosphoric acid is dispersed in the gas phase into droplets with a diameter of about 0.5 mm to 5 mm in a shower form, and as droplets with a diameter of about 5 mm or less in a mist form. It refers to the state in which

To make phosphoric acid into a shower, for example, place an acid-resistant water nozzle with dozens of well-known pores with a diameter of about 0.5 mm to 5 mm above the container containing the rubber latex, and let the water flow out from the water nozzle. This is done by letting

To make it into a mist, for example, the end of a pipe is closed using a known method, and an acid-resistant spray nozzle with a notch of about 1 mm to 5 mm square is placed above the container containing the rubber latex. This is carried out by spraying phosphoric acid under pressure from this spray nozzle.

When adding phosphoric acid, do not perform strong stirring that mechanically applies a high shear rate using a stirring blade or the like installed in the container containing the rubber latex; for example, the added phosphoric acid should be dispersed only by stopping stirring. There are two methods: mixing the latex with the latex using a drying method, and a gentle mixing method such as bubbling an inert gas such as nitrogen into the latex. These methods make the particle size of the latex uniform. The effect of doing so can be further demonstrated. By adding this phosphoric acid, the average particle size of rubber latex particles in the rubber latex exceeds 0.2 μm and becomes 0.4 μm.
It will be in the range below. The rubber latex thus obtained having an average particle diameter within this range is suitable as a raw material for rubber such as ABS resin produced by an emulsion polymerization method.

After the addition of phosphoric acid is finished, e.g. caustic soda,
A method can be adopted in which phosphoric acid is neutralized by adding an aqueous solution of a basic substance such as caustic potash. In this case, the basic substance should be added in an amount sufficient to restore the original PH value of the rubber latex, thereby restoring the emulsifying ability of the fatty acid soap. The basic substance is preferably added directly into the liquid of the rubber latex, such as by injecting it from the bottom of the reaction vessel. It is not preferable to drop an aqueous solution of a basic substance from the gas phase at the top of the reaction vessel because the impact may destroy the emulsified state of the latex.

When adding a basic substance to the latex after the particle size has been enlarged, if a surfactant is added that does not reduce the emulsifying ability even when the liquid is made acidic, the latex can be further stabilized and the formation of coagulum can be reduced. Furthermore, if an appropriate amount of such a surfactant is added to the latex before adding phosphoric acid, for example, about 0.1% by weight or less of the solid content of the latex, the operation of coagulating and enlarging the particle size can be carried out stably. With,
The particle size of the latex can be controlled within the desired range of 0.2-0.4μm. In this case, the larger the amount of the surfactant added, the smaller the particle size becomes.

Further, it is also possible to stabilize the latex after the coagulation and enlargement operation by adding only the above-mentioned surfactant without adding the above-mentioned basic substance.

Examples of surfactants that can be added to the fatty acid soap in the method of the present invention include alkylbenzene sulfonates such as sodium naphthalene sulfonate and sodium dodecylbenzenesulfonate, sulfonates such as formalin polycondensates, and alkylphenol-type phosphates. Examples include nonionic surfactants such as acid esters.

"Effects of the Invention" According to the method of the present invention, rubber latex with a small particle size of 0.2 μm or less can be turned into an enlarged rubber latex with a particle size of 0.2 to 0.4 μm suitable for producing graft copolymers such as ABS resin. At this time, the formation of coagulated substances is small, and furthermore, the coagulated substances do not adhere to the walls of the reaction vessel. Therefore, the enlargement operation of latex particles can be carried out in a stable state.
Furthermore, it is possible to stabilize the emulsified state of the rubber latex after the coagulation and enlargement operation.

"Examples" Next, the method of the present invention will be explained in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

In addition, in Examples and Comparative Examples, the average particle size refers to the number average particle size.

Example 1 In a reaction vessel with a capacity of 300 and equipped with a jacket and a stirrer, solids content 23.5% by weight, pH 9.9, particle size 0.07 μm
128 kg of styrene-butadiene copolymer (SBR, bound styrene 23% by weight) latex (emulsifier sodium stearate) was charged. 8 g of sodium dodecylbenzenesulfonate was added to this reaction vessel, and the internal temperature was raised to 60° C. while stirring using a stirring blade. After the temperature was raised, stirring was stopped, and 15 kg of a phosphoric acid aqueous solution having a concentration of 5% by weight was showered onto the liquid surface from a nozzle provided with 50 holes each having a diameter of 1 mm. The time required was approximately 5 minutes, and the pH value was 3.
After the addition of phosphoric acid was completed, 1.7 kg of aqueous caustic soda solution with a concentration of 25% by weight was added through the charging port opened at the bottom of the can, and gentle stirring was started again.

The average particle size of the rubber latex obtained is
The solid content was 21.7% by weight, and the coagulum was 0.32% by weight of the resulting latex.

Example 2 The particle size coagulation and enlargement operation of the latex was carried out in the same manner as in Example 1, except that sodium dodecylbenzenesulfonate was not added.

The average particle size of the obtained latex was 0.331 μm, and the solid content was 21.6% by weight.

Example 3 In the example described in Example 2, the amount of added phosphoric acid aqueous solution with a concentration of 5% by weight was 12.8Kg, and the amount of caustic soda (concentration
Except for the addition amount of 1.4 kg of 25% aqueous solution),
The particle size agglomeration and enlargement operation was carried out in the same manner as in the same example.

The average particle size of the obtained latex was 0.331 μm, and the solid content was 22.1% by weight.

Example 4 In a reaction vessel with the same capacity of 300 as used in Example 1,
120 kg of SBR latex (bonded styrene 10% by weight, solid content 25% by weight, emulsifier sodium stearate) having an average particle size of 0.07 μm and a pH value of 11.7 was charged, and 45 g of sodium dodecylbenzenesulfonate was added thereto. After raising the temperature inside the reaction vessel to 50°C while stirring, the stirring was stopped and 9.6 kg of phosphoric acid aqueous solution with a concentration of 5% by weight was injected in 3 minutes through a nozzle equipped with 50 holes with a diameter of 1 mm. It was added to the liquid surface of the latex in a shower-like manner. Thereafter, 3.3 kg of a caustic potassium aqueous solution (concentration 10% by weight) was injected from the bottom of the can.
Then, gentle stirring was started again.

The average particle size of the obtained latex was 0.26μm,
The coagulum was 0.3% by weight of the latex obtained. The solid content was 22.6% by weight.

Example 5 In the example described in Example 4, the phosphoric acid aqueous solution was
Close the tip of a 10mm diameter pipe and attach 2mm x 2 to the side.
The particle size was agglomerated and enlarged in the same manner as in the same example, except that the particles were atomized and dropped onto the liquid surface from a nozzle with one mm-sized notch.

The average particle size of the obtained latex was 0.26μm,
The coagulum was 0.2% by weight.

Example 6 In the example described in Example 5, the particle size of the latex was coagulated and enlarged in the same manner as in Example 5, except that nitrogen was bubbled from the bottom of the can when the aqueous phosphoric acid solution was made into a mist and fell onto the liquid surface. performed the operation.

The average particle size of the obtained latex was 0.32 μm, and the amount of coagulum formed was 0.3% by weight.

Example 7 In the example described in Example 6, the amount of the 5% by weight phosphoric acid aqueous solution added was 15.6 kg, and the amount of the caustic potassium aqueous solution (concentration 10
The particle size was agglomerated and enlarged in the same manner as in the same example, except that the weight percentage was 5.4 kg.

The average particle size of the obtained latex was 0.32 μm, and the amount of coagulum was 0.3% by weight.

Example 8 In the example described in Example 6, the amount of the 5 wt% phosphoric acid aqueous solution added was 19.2 kg, and the amount of the caustic potassium aqueous solution (concentration 10
Particle size agglomeration and enlargement operation was carried out in the same manner as in the same example except that the amount of added amount (% by weight) was 6.6 kg.

The average particle size of the obtained latex was 0.33 μm, and the amount of coagulum was 0.34% by weight.

Comparative Example 1 The particle size agglomeration and enlargement operation was carried out in the same manner as in Example 4, except that an aqueous phosphoric acid solution with a concentration of 5% by weight was added from a nozzle with a diameter of 1 inch. .

The average particle size of the obtained latex was 0.23 μm, and the amount of coagulated material was 2% by weight.

Comparative Example 2 In the example described in Example 5, except that the latex was stirred continuously without stopping stirring.
Particle size enlargement was carried out as in the same example.

The average particle size of the obtained latex was 0.31 μm, and the amount of coagulum formed reached 2.5% by weight.

Comparative Example 3 In the example described in Example 1, 11.5 kg of sulfuric acid aqueous solution (concentration 2% by weight) and 25% by weight were used instead of phosphoric acid.
Particle size enlargement was carried out in the same manner as in the same example except that 1.26 kg of an aqueous solution of caustic soda was added.

The average particle size of the obtained latex was 0.218 μm, and the amount of coagulum formed was 3.5% by weight.

Comparative Example 4 In the example described in Comparative Example 3, the amount of sulfuric acid aqueous solution added was 13.8 kg, and the amount of caustic soda aqueous solution added was 1.51 kg.
The procedure was the same as in the same example except that Kg was used.

The average particle size of the obtained latex was 0.275 μm, and the amount of coagulum formed was 5% by weight.

Claims (1)

[Claims] 1. An acidic substance is added to rubber latex that has been emulsified with a surfactant containing fatty acid soap as a main component and the average particle size of the rubber latex particles is 0.2 μm or less to acidify the liquid properties of the latex. When coagulating and enlarging the rubber latex particles, the average particle diameter of the rubber latex particles is 0.2 to 0.4 μm by adding phosphoric acid as an acidic substance in the form of a shower or mist onto the liquid surface of the latex.
A method for coagulating and enlarging rubber latex particles, characterized by obtaining rubber latex having the following properties. 2. The method for coagulating and enlarging rubber latex particles according to claim 1, wherein the PH value of the rubber latex is 4 or less. 3 The range of the amount of phosphoric acid added is 100%
The method for coagulating and enlarging rubber latex particles according to claim 1, wherein the amount is 0.4 to 0.8 parts by weight.