JPS5946963B2 - Polymer recovery method from latex - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering pomer from sticky polymer latex.

More specifically, the present invention relates to a method for obtaining aggregates having a particle size that is easy to dehydrate and dry from an ethylene/vinyl ester copolymer latex. A copolymer of ethylene and vinyl ester (hereinafter referred to as EVE) has high elasticity, excellent durability, and good compatibility with other resins, and is attracting attention as a material for waterproof sheets, rubber parts, and electric wire coatings. There is.

EVE can be produced by bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, and the like. The emulsion polymerization method requires post-treatments such as aggregation to remove impurities such as emulsifiers, but EVs with relatively high molecular weight
E is obtained, making it suitable for rubber applications where mechanical strength is important. However, EVs that are rubbery at room temperature
It was very difficult to precipitate E from latex, dehydrate and dry it because of its stickiness. That is, when attempting to agglomerate, dehydrate, and dry the particles using known agglomeration methods, the particles either coalesce together and form lumps during aggregation, or coalesce during the centrifugal dehydration process or drying process to form lumps. It is from. In order to prevent sticking during the centrifugal dehydration process and drying process, it has been proposed to add anti-sticking agents such as hard resins and various powders such as inorganic substances. However, the prevention of adhesion during the aggregation process was not sufficient. Even when attempting to mechanically crush the EVE once agglomerated in the agglomeration process, the frictional heat generated during crushing increases the adhesiveness of the layer, making it difficult to pulverize. Furthermore, the particle size and shape of the aggregates greatly affect the dehydration rate in the dehydration process and the drying rate in the drying process. For these reasons, it has been strongly desired to obtain aggregates having a constant particle size distribution from the viewpoint of EVE productivity. Ethylene content is 10-50% by weight, which is suitable for rubber applications.
EVE having a Mooney viscosity of 5 to 40 is extremely sticky at temperatures above room temperature, and when agglomerated using a coagulant by a known method at a coagulation temperature of 50° C. or higher, it is obtained as a lump in which particles coalesce together.

In addition, even if a coagulant is added at a temperature below 50°C, the polymer may not coagulate completely and the waste liquid remains cloudy, or it may be necessary to use many times the amount of coagulant to completely precipitate the polymer. I needed it. Japanese Patent Publication No. 47-36010 describes a method of salting out a water-insoluble inorganic substance having an average particle size of 10 microns or less to an ethylene copolymer latex. However, in the case of latexes using anionic emulsifiers commonly used in the rubber industry, it is disadvantageous to add inorganic substances that destabilize the latex before aggregation from the viewpoint of controlling the shape of the agglomerated particles. Furthermore, these inorganic substances have the disadvantage of lowering the transparency and thermal stability of EVE, thereby lowering its commercial value. The present inventors have investigated an economical method for recovering polymers that does not reduce the transparency or thermal stability of products, and as a result, they have discovered a method for recovering polymers that yields aggregates with a particle size distribution that is easy to dehydrate and dry. , led to the present invention.

That is, the present invention has an ethylene content of 10 to 50% by weight.
[Me] General formula for EVE latex with a viscosity of 5 to 40 (where M is Ca.Ba.Zn.Cd.Pb.Al.N
H4, Na. K. n is an integer of 1 to 3 depending on the charge of M,
R is a hydrocarbon having 11 to 31 carbon atoms.

) is added in an amount of 0.2 to 5% by weight (based on the solid content of the latex), then heated to 50°C or higher, and an aqueous coagulant solution is added to coagulate the copolymer. A method for recovering polymers from latex is provided. According to the polymer recovery method of the present invention, the compound represented by the above general formula (hereinafter referred to as a fatty acid salt) rather stabilizes the EVE latex until it reaches the aggregation temperature, and after the E has coagulated by adding a coagulant. It adheres to the surface of the nascent agglomerated particles to prevent the particles from coalescing with each other due to adhesion, and the interaction between the amount of the fatty acid salt added and the temperature at which the coagulant is added produces agglomerates with the desired particle size distribution. I can do it.

According to the method of the present invention, not only the dehydration and drying speeds are improved, but also the amount of polymer deposits on the stirring blades and walls of the coagulation pot is greatly reduced, thereby improving productivity. In the present invention, when the fatty acid salt is added before coagulating the latex, the residual rate is much higher than when it is added after coagulating, and it is also effective in preventing adhesion during dehydration and drying processes.

The EVE aqueous solution used in the present invention is obtained from polyethylene and vinyl ester, and contains EVE whose particles are usually 10 microns or less. Ru.

Examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl pivalate, vinyl versatate, and the like. Note that EVE may be copolymerized with other vinyl monomers that can react with ethylene and vinyl ester. For example, examples of such vinyl monomers include acrylic acid, methacrylic acid and its esters, vinyl chloride, styrene, acrylonitrile, and olefin compounds, and one or more of these monomers can be copolymerized. The EVE has an ethylene content of 10 to 50% by weight.
Particularly effective is 10 to 40% by weight, and less than 10% by weight is not preferred because it has low rubber elasticity and is not suitable for rubber applications.

Further, if the amount exceeds 50% by weight, the polymer has little tackiness and there is no need to use the method of the present invention. Furthermore, those with a Mooni viscosity of less than 5 tend to form lumps when agglomerated and have low mechanical strength, making them unsuitable for rubber applications, while those with a Mooni viscosity of less than 40 tend to form lumps during agglomeration even without using the method of the present invention. It is excluded because it is possible to recover the polymer without it. The fatty acid salt of the present invention has a chemical structure represented by the following formula.

[However, R: Hydrocarbon having 11 to 31 carbon atoms M: CalB
a,. ZnlCdlPblNH4, Al. ．． NalKl
n: 1 to 3 (depending on the number of M) If the number of carbon atoms in R in the above general formula is less than 11, there will be no adhesion prevention effect during dehydration or drying, and if it is more than 31, the number of carbon atoms in the latex at the time of addition will be reduced. This is not preferable because it impairs stability and makes the EVE particle size after aggregation non-uniform.

The amount of such fatty acids added is 0 based on the solid content of the latex.
, 2 weights Shima to 5 weights.

If the amount is less than 0.2% by weight, there will be no effect on adjusting the diameter of the aggregated particles, and if it exceeds 5% by weight, the aggregated particles will be so fine that they will clog the centrifugal dehydrator, making post-treatment difficult. Although the emulsion polymerization method shows the advantage of improving the molecular weight when synthesizing EVE compared to other polymerization methods, there is a problem in removing impurities such as emulsifiers. The agglomerated particle size of EVE can be controlled to be easily washable and dehydrated. The coagulant used in the present invention may be any commonly used coagulant, such as inorganic acids,
These include organic acids, inorganic salts, and polymer flocculants, and specific examples include hydrochloric acid, sulfuric acid, sodium chloride, calcium chloride, and aluminum chloride.

The amount of such a coagulant added is usually 0.0% based on the solid content of EVE.
It is 5 to 3% by weight. As mentioned above, the EVE-containing latex of the present invention is usually obtained by emulsion polymerization and has a solid content of 10 to 50% by weight.
Of course, EVE latexes synthesized by other polymerization methods can also be used as long as they can achieve the effects according to the method of the present invention. At this time, it is necessary to use an anionic emulsifier due to the relationship with the coagulant, but it is also possible to use mainly anionic emulsifiers in combination with nonionic emulsifiers. In the present invention, the flocculated and precipitated EVE is then dehydrated and dried to obtain a homogeneous product having approximately 5 to 200 meshes.

Antioxidants, anti-blocking agents, etc. may be added during these steps. Incidentally, the obtained EVE may be further pulverized using a pulverizer if necessary. The EVE recovered in the present invention is effectively used as a powdery elastomer in addition to rubber applications such as heat-resistant and oil-resistant packings, as well as for the modification of other resins.

Other resins include polyvinyl chloride, polystyrene, polypropylene, etc., and their impact resistance and moldability can be improved by adding the EVE obtained in the present invention. Furthermore, since the EVE obtained by the present invention is in the form of powder, it is of great industrial significance in terms of ease of weighing and blending. The method of the present invention is also applicable to elastomers other than EVE.

Examples of elastomers other than EVE include natural rubber latex, which is a rubbery polymer with a glass transition temperature at room temperature, and synthetic rubber latex, such as known rubber latexes such as acrylic rubber latex, nitrile rubber latex, and polychloroprene latex. The present invention will be explained below with reference to Examples. All percentages in the examples are percentages by weight. Example 1, Comparative Example 1 The following raw materials were charged into an electromagnetic rotary autoclave having an internal volume of 21 cm.

Next, ethylene was blown into the reaction vessel twice to remove air, and then heated to 40°C, and the ethylene pressure was 65kg/CrIL.
Pressure was applied.

A catalyst solution in which 2f1 of potassium persulfate was dissolved in 50I of water was mixed with 6
The mixture was added dropwise for a certain period of time to carry out the reaction. The resulting latex contained 39% copolymer with an ethylene content of 30%, a Mooney viscosity of 35, and a particle size of 0.2 microns. Water 10009 was added to 1000 g of the latex, and hydrated calcium stearate (manufactured by Dainippon Ink & Chemicals Co., Ltd., W
- 30C, purity 30%) 69 was added and mixed. This was heated to 80° C., and an aqueous solution of 8 g of calcium chloride dissolved in 42 g of water was gradually added to coagulate the latex. The particle size distribution of the obtained aggregates was determined using a JIS standard sieve. Next, a small centrifugal dehydrator (manufactured by Mori Seisakusho) with a capacity of 11
The aggregate was dehydrated for 2 minutes at 2000 times/min using a 0-mesh filter cloth, and its water content was measured.

Further, the dehydrated product was spread to a thickness of 20 mm in a soaking dryer (manufactured by Satake Seisakusho) heated to 60° C., and the drying time was measured until the moisture content became 0.5% or less. After drying, the EVE was white particles with no stickiness. In order to evaluate thermal stability, the thermal decomposition temperature was measured in a nitrogen stream using a differential thermal balance manufactured by Shimadzu Corporation. The obtained results are summarized in Table 1. In Comparative Example 1, the same operation as in Example 1 was performed except that calcium stearate was not added to the EVE latex obtained in Example 1.

The results are also shown in Table 1. According to the above table, compared to the comparative example, aggregates with a uniform particle distribution were obtained in the example, and dehydration and drying were easier.

Example 2 The same raw materials as in Example 1 were used, but in addition carbon tetrachloride 49
Polymerization was carried out in the same manner as in Example 1.

The obtained latex had an ethylene content of 30% and a viscosity of 11. It contained 40% of EVE (particle size distribution of aggregates) with a particle size of 0.3 microns.

To the latex 10009 was added 10009 of water, and further 69 of hydrated calcium stearate (purity equivalent) was added and mixed. This was heated to 80° C., and an aqueous solution of 8 g of calcium chloride dissolved in 429 g of water was gradually added to coagulate the latex. The particle distribution of the obtained aggregate was measured using a sieve and found to be as follows. Examples 3 to 6, Comparative Example 2
~6 Example 3 was prepared by using the latex obtained in Example 2 and changing the amount of calcium stearate (purity) from Example 2 to 109.

Further, in place of the calcium stearate in Example 2, barium stearate, zinc laurate, and calcium montanate were used as Examples 4, 5, and 6, respectively. Example 1
Table 2 shows the results of evaluation using the same method as above. Comparative Example 2 was prepared by using the latex obtained in Example 2 and changing the amount of calcium stearate in Example 2 to 249. Comparative Examples 3, 4, 5, and 6 were prepared by adding talc, polyethylene wax, vinyl chloride resin, and calcium acetate instead of calcium stearate.

Claims (1)

[Scope of Claims] 1. 0.2 to 5% of a compound represented by the following general formula is added to a latex of an ethylene/vinyl ester copolymer having an ethylene content of 10 to 50% by weight and a Mooney viscosity of 5 to 40.
1. A method for recovering a polymer from latex, which comprises adding % by weight (based on the solid content of latex), followed by heating to 50° C. or higher, and adding an aqueous coagulant solution to coagulate the copolymer. [General formula M(OOCR)n where M is Ca, Ba, Zn, Cd, Pb, Al, NH
_4, Na, and Kn are integers of 1 to 3 depending on the charge of M, and R is a hydrocarbon having 11 to 31 carbon atoms. ]