JPS6026006A - Coagulation of polymer latex - Google Patents

Abstract

PURPOSE:To achieve energy preservation and upgrading of product properties by process rationalization, by recirculating a filtrate obtained form solid/liquid separation to a pH adjustment tank for reuse. CONSTITUTION:A polymer latex (e.g., a latex obtained by emulsion-polymerizing an ethylenic monomer) is fed to a coagulation tank 1, where it is treated with a coagulating agent (e.g., sulfuric acid). The formed slurry is fed to a pH adjustment tank 2, where its pH is adjusted with a pH adjusting agent (e.g., sodium hydroxide). This slurry is then fed to a solidification tank 3, where it is treated at a predetermined solidification temperature, and then fed to a solid/liquid separation tank 4. The filtrate obtained here is recirculated through a line 5 to the pH adjustment tank 2. At this time, an alkaline substance is supplied from an alkali reservoir 6. By the recirculation and reuse of the filtrate, the process can be rationalized and at the same time, energy necessary for solid/liquid separation or the like, can reduced. In addition, it is possible to obtain a product property which is better than that obtained when an alkaline substance is added directly to the pH adjustment tank.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention 1] The present invention relates to a method for coagulating a polymer latex, and more particularly to a method for coagulating a polymer latex by improving the coagulating step in an emulsion polymerization method.

[Technical background of the invention and its problems J Conventionally, thermoplastic resins produced by emulsion polymerization method are
After going through a series of steps such as polymerization, coagulation, dehydration during washing, and drying, it was turned into a dry powder. Regarding these processes, we will focus on product properties such as surface shape, color, and gloss, as well as process rationalization.
Many studies are being conducted from the perspective of energy conservation, etc. Generally, by improving the polymerization/coagulation process, subsequent washing, dehydration, and drying processes can be significantly improved.

However, in the coagulation process, no satisfactory improvement method has yet been found for streamlining the process, saving energy, etc. Furthermore, regarding the physical properties of the product, it is necessary to adjust the pH using an alkaline substance in the pH adjustment treatment step after coagulation, but at this time, the soft aggregation state of the polymer particles is maintained and the particles are It is difficult to prevent re-emulsification of the polymer, and there are also drawbacks such as the heat resistance of the polymer being locally reduced by alkaline substances, making it difficult to obtain good product properties.

[Objective of the invention 1 The present invention can achieve process rationalization and energy saving,
[1] It is an object of the present invention to provide a method for coagulating a polymer latex which can also provide good physical properties of the product.

[Summary of the Invention] The present invention provides a method for reusing a polymer slurry discharged from a solidification tank by separating solid and liquid in a coagulation process of polymer latex, and then circulating the obtained filtrate to a pH adjustment tank. It is characterized by

The present invention will be explained in more detail below.

The polymer latex used in the present invention is an emulsion latex in a broad sense and may be of any type.

The solidification process of the present invention will be explained based on a block diagram. The latex obtained by the polymerization reaction is supplied to a coagulation tank 1,
After being treated with a coagulant, the generated slurry is supplied to the pH adjustment tank 2. A pH adjuster is added to the tank 2 to adjust the pH, and then supplied to the solidification tank 3 where it is treated at a predetermined solidification temperature, and then supplied to the solid-liquid separation tank 4. The filtrate obtained by solid-liquid separation is circulated to the 1-nominal pH adjustment tank 2 through the circulation line 5. Note that during filtrate circulation, an alkaline substance is supplied to the circulation line 5 from the alkaline tank 6 .

Coagulants used in the coagulation operation include, for example, sulfuric acid, hydrochloric acid, (acids such as 6-acid, phosphobutyric acid, sulfite, etc.; magnesium sulfate, 1j, magnesium chloride, calcium 11,
Aluminum sulfate, aluminum monoxide, potassium chloride
Examples include polyvalent metals such as

An alkaline substance is used as the pH adjusting agent supplied to the pH adjusting tank, and the substance includes, for example, alkali metal hydroxide such as hydroxide, potassium hydroxide, calcium hydroxide, Hydroxides of alkaline earth metals such as magnesium hydroxide; oxides of alkali metals or alkaline earth metals; salts of weak acids such as sodium carbonate, potassium carbonate, sodium bicarbonate, phosphoric acid, and aqueous ammonia; Examples include water-soluble amines, and all those that can make the pH of the aqueous solution 7.0 or higher can be used. The amount of these alkaline substances added depends on the pH
Adjustment 41! From the pH value of the coagulated slurry supplied to 0
．． It is preferable that the amount is in a range of 1 to 1-higher and that the pH value of the entire coagulated slurry after adding the alkaline substance is 7.0 or less. When added within this range, the alkaline substance acts effectively, maintains the soft agglomeration state of the polymer particles, and effectively prevents re-emulsification of the particles. Furthermore, it is also possible to prevent hydrolysis of the polymer.

When carrying out the present invention, the temperature during the coagulation operation and the temperature during pH adjustment will vary slightly depending on the type of latex used. For example, as a monomer component, either ethyl acrylate or butyl acrylate, or a mixture thereof is more than 0 and 25% by weight or less, and either methyl methacrylate and styrene, or a mixture thereof is 7% by weight.
In the case of a copolymer latex composed of 5% by weight or more and less than 100% by weight, the temperature is preferably in the range of 0 to 92°C. Butyl acrylate is 35-45
In the case of a copolymer latex consisting of 65 to 55% by weight of either methyl methacrylate or styrene, or a mixture thereof, the temperature range is preferably from 0 to 83 °C. . In addition, copolymer latex streaks consisting of butyl acrylate and styrene 0% to 0% by weight (
In the case of a copolymer latex obtained by polymerizing methyl methacrylate (solid content) and 50 to 30% methyl methacrylate,
0-82°C is preferred.

In the case of copolymer latex consisting of 40-60% butyl acrylate, 14% by weight of acrylonitrile, 10-20% by weight of acrylonitrile, and 30-40% by weight of methi-1 fufu, the temperature is 0-88°C.
is preferred.

The slurry supplied to the solidification tank is preferably treated within a predetermined solidification temperature range. This is to harden the polymer particles in the coagulated slurry and mechanically stabilize them. This temperature range must be higher than the temperature during the coagulation operation and the temperature during pH adjustment since the polymer particles in the coagulation slurry are in a soft agglomerated state. If the solidification temperature is lower than the temperature during coagulation and the temperature during adjustment, the coagulated particles will be completely solidified and the polymer particles will be fused together and stabilized mechanically and chemically. Therefore, the effect of adding an alkaline substance cannot be obtained, and the effect of the present invention cannot be achieved.

1-! As a one-liquid method, for example, gravity filtration using gravity, i! I! Vacuum filtration method suitable for continuous operation, centrifugal separation method using specific gravity difference, and pressure filtration V with high filtration speed.
etc., and solid-liquid separation is performed according to conventional methods. The filtrate 111 is again circulated to the pH adjustment tank via the circulation line connected to the solid-liquid separator, and at this time, the alkaline substance is supplied from the alkali tank to the circulation line. As described above, the amount of the substance added is 0.1 or more higher than the pH value of the coagulated slurry supplied to the pH adjustment tank, and the pH value of the entire coagulated slurry after adding the alkaline substance is 7. The amount is preferably within a range of .0 or less. On the other hand, the solid content obtained by solid-liquid separation is
For example, after adding a stabilizer and the like, pelletizing with a screw extruder, it is made into a molded product using an injection molding machine or the like.

[Effect of the invention 1 According to the present invention, the filtrate obtained by solid-liquid separation can be recycled and reused, so the process can be rationalized and the energy required for solid-liquid separation etc. can be significantly reduced. There will be 11 Noh plays. In addition, by supplying an alkaline substance to the circulation line, it is possible to improve product physical properties by 1+j compared to when the substance is directly added to the pH adjustment tank.
It becomes t7 Noh. Furthermore, by adding an alkaline substance in an amount within the predetermined range, it is possible to maintain the agglomerated state of the polymer particles and prevent re-emulsification of the particles, and also to reduce the heat-reducing properties of the polymer. It becomes possible to achieve defense 11-.

[Example 1 of the Invention Example 1 A water-based latex with a solid content of 42 wt.
It was supplied to the coagulation tank at a flow rate of min. Also, at the same time, 5
% sulfuric acid and water at 1.41/ff1in and 41/in, respectively.
It was supplied to the coagulation tank at a flow rate of 11 in., and the pH was maintained at 1.5 and the temperature at 40°C. i in nuclide! IX Continuously coagulated slurry with a solid content concentration of 10% is subjected to solid-liquid separation, and the solid content is
It was supplied to the H adjustment tank. The solids concentration at the time of feeding was approximately 35% by weight. The pH adjustment tank contains the filtrate that was resupplied via the circulation line, and the nuclide was adjusted to pH 2, 0, and 70°C by the thorium hydroxide supplied from the alkaline tank through the circulation line. is maintained.

Next, the slurry discharged from the pH adjustment tank was supplied to a solidification tank, heated to 82°C, and then supplied to a solid-liquid separator. After solid-liquid separation, the filtrate was re-supplied to the pH adjustment tank via the circulation line, while the solid content was recovered. After drying the obtained solid content, a small amount of stabilizer was added thereto, and it was molded into pellets using a screw extruder, and test pieces were created using an injection molding machine. When we observed the appearance of this test piece, we found that
Both appearance and color tone were extremely good.

Also, without using a circulation line, solid content of 10
A comparison of the test piece obtained by supplying the slurry directly to the adjustment tank and the test piece above showed that if the filtrate was circulated, energy savings of approximately 60% could be achieved in terms of calorific value. Ta.

On the other hand, when a test piece was prepared in the same manner as above by supplying sodium hydroxide directly to the pH adjustment tank without using a circulation line, a portion of the test piece turned yellow and the color tone and appearance changed. It was extremely bad. This is presumed to be because sodium hydroxide was locally absorbed into the polymer, resulting in deterioration.

Example 2 Methyl methacrylate 2 on polybutadiene 50 binding part
A water-based latex with a solid content of 38 double star shape obtained by graft polymerizing 0 parts by weight and 30 parts by weight of styrene was mixed at 3.51/m
was fed to the coagulation tank at a flow rate of in. Also, at the same time, 10%
Sulfuric acid and water at 1.51/win and 51/win respectively
It is supplied to the coagulation tank at a flow rate of
maintained. Solid content concentration 10% continuously coagulated with nuclides
The slurry was subjected to solid-liquid separation, and the solid content was supplied to a pH adjustment tank. The solids concentration at the time of feeding was approximately 35% by weight. Note that the pH adjustment tank contains the filtrate that was resupplied via the circulation line, and the nuclide was
H2, 5, 65° maintained at 0. Then P H
The slurry discharged from the adjustment tank is supplied to the solidification tank, and 83
After heating to 0°, it was fed to a solid-liquid separator. After solid-liquid separation, the filtrate was re-supplied to the pH adjustment tank via the circulation line, while the solid content was recovered.

A test piece was prepared from the obtained solid fraction in the same manner as in Example 1, and the appearance of this test piece was observed, and the appearance and color tone were both extremely good.

Also, without using a circulation line, solid content lO can be removed from the coagulation tank.
A comparison of the above test piece with a test piece obtained by directly supplying % slurry to the pH adjustment tank revealed that when the filtrate was circulated, energy savings of about 60% could be achieved in terms of calorific value.

On the other hand, when a test piece was prepared in the same manner as above by supplying sodium hydroxide directly to the pH adjustment tank without using a circulation line, a part of the test piece turned yellow, and the color tone and appearance was extremely bad.

[Brief explanation of the drawing]

The drawing shows a block diagram of the solidification process of the present invention. ■... Coagulation tank 2... pH adjustment tank 1 3... Solidification tank 4... Solid-liquid separation tank 5... Circulation line 6... Alkali tank 2

Claims (2)

[Claims] (1) In the polymer latex coagulation process, after solid-liquid separation of the polymer slurry discharged from the solidification tank, fjJ
A method for coagulating polymer latex, characterized in that the collected filtrate is recycled by circulating it in a pH adjustment tank. (2) The method for coagulating a polymer latex according to claim 1, characterized in that an alkaline substance is supplied to the circulation path.