JPH0129801B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the production of powdered chloroprene rubber (hereinafter simply referred to as powder CR), and more specifically to the production of anionic chloroprene polymer latex (hereinafter simply referred to as powder CR).
By dispersing an alkali metal salt of metasilicic acid in (referred to as CR latex) and mixing it with a coagulant,
This invention relates to a method for obtaining powder CR by precipitating fine particulate chloroprene polymer with low stickiness. In recent years, rubber processing technology has become more sophisticated, and efforts are being made to save labor and energy during processing. In order to cope with these technologies, the form of raw rubber has been changed from the conventional veil shape (large block shape).
Alternatively, there is a strong demand for so-called powdered rubber in the form of fine particles with a particle size of several mm or less, instead of in the form of chips. The same applies to chloroprene rubber (hereinafter referred to as CR), and there is an urgent need to develop a stable manufacturing method for powdered CR. A common method for producing powdered rubber is to mechanically pulverize bale or chip rubber into fine particles using a pulverizer or the like. However, in the case of CR,
As a characteristic of CR itself, it is highly adhesive, and even if one simply tries to make it into fine particles, the particles will stick to each other, resulting in so-called blocking. This phenomenon becomes a big problem when producing powdered CR or processing the produced product, as the properties of the powder are lost. As a result of research into improving this problem, it was found that the adhesiveness was significantly improved by dispersing an alkali metal salt of metasilicic acid in anionic CR latex and mixing it with an alkaline earth metal salt, an aluminum salt, or an acid. The present inventors have discovered that it is possible to obtain CR in the form of fine particles, leading to the present invention. The method according to the invention is to prepare an anionic CR latex with the formula M ₂ SiO ₃ , where M is an alkali metal.
After dispersing the metasilicate represented by 2 to 50 parts by weight, preferably 5 to 30 parts by weight, per 100 parts by weight of the chloroprene polymer in the CR latex, alkaline earth metal salts and aluminum salts are dispersed. This is a method in which fine particulate chloroprene polymer is precipitated by mixing with a coagulant selected from acids and a coagulating agent selected from acids, and by separating and recovering the fine particulate chloroprene polymer from a dispersion of this fine particulate chloroprene polymer and drying it. , a powder CR with improved stickiness is obtained. In this case, the separation method may be a known method such as static separation, centrifugation, cloth separation, etc., and the drying method may be a known method such as a fluidized bed dryer or a paddle dryer, and if necessary, the fine particles may be washed. We can also use powdered rubber fillers such as talc, clay, calcium carbonate, silicic acid, and carbon black, salts of higher fatty acids such as calcium stearate and barium stearate, synthetic resins such as powdered PVC and phenolic resin, MgO, ZnO, etc. may be added before and after the dispersion operation or before and after the drying operation in order to further enhance the anti-sticking effect. In the present invention, anionic CR latex refers to anionic emulsifiers, such as sodium salts and potassium salts of rosin acid mainly composed of asymmetric products of abietic acid, or sodium salts of fatty acids having about 12 to 30 carbon atoms; CR latex is obtained by homopolymerizing chloroprene monomer or copolymerizing monomer copolymerizable with chloroprene monomer using potassium salt, etc. Examples of compounds include compounds containing at least one reactive double bond in the molecule, and preferred examples include vinyl compounds such as styrene, methacrylic acid, and acrylonitrile;
Conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dichloro-1,3-butadiene and other examples include sulfur. Therefore, in the present invention, CR or chloroprene polymer naturally includes not only chloroprene homopolymers but also chloropyrene copolymers. Unreacted volatile monomers in CR latex are usually removed by a known method such as steam stripping. The amount of chloroprene polymer in CR latex is usually about 20 to 60% by weight. The compound represented by the formula M ₂ SiO ₃ (wherein M is an alkali metal) used in the present invention is usually called a metasilicate, and sodium metasilicate represented by Na ₂ SiO ₃ is particularly preferably used. . Sodium metasilicate has various amounts of crystal water in the form of Na ₂ SiO ₃ .nH ₂ O, and any of them can be used, but those without crystal water (n = 0) form orthorhombic crystals at room temperature. The nonahydrate salt with n=9 is also crystalline at room temperature and can be used as a solid, but it is preferable to use it as an aqueous solution. The amount of metasilicate added is chloroprene polymer 100
The amount is 2 to 50 parts by weight, preferably 5 to 30 parts by weight.If it is less than 2 parts by weight, the effect will be little, and if it exceeds 50 parts by weight, it is possible to make CR into fine particles, but the product The non-rubber content increases, which is disadvantageous because it greatly affects the physical properties of the rubber, complicates the cleaning operation, and increases the amount of coagulant required. The method for dispersing metasilicate in CR latex is not particularly limited, but it can preferably be dispersed under stirring. The coagulants selected from alkaline earth metal salts, aluminum salts, and acids used in the present invention include alkaline earth metal chlorides, nitrates, aluminum chlorides, sulfates, nitrates, and inorganic acids. It is a compound that has the ability to coagulate water-soluble and anionic CR latex such as acids, and preferable examples include
CaCl ₂ , BaCl ₂ , MgCl ₂ , AlCl ₃ , Ca(NO ₃ ) ₂ , Ba
(NO ₃ ) ₂ Mg (NO ₃ ) ₂ Al (NO ₃ ) ₃ , Al ₂ (SO ₄ ) ₃ , aluminum hydroxychlorides, hydrochloric acid, sulfuric acid,
These include nitric acid and acetic acid, which can be used alone or in combination of two or more compounds. Salts are usually 0.1 to 10% by weight of these coagulants.
It is possible to make an aqueous solution of 100 parts by weight of the CR latex and mix it in a high proportion of 5 to 500 parts by weight, but it is not a good idea to mix it with a large amount of coagulant liquid at a low concentration and it is 30 to 200 parts by weight. It is preferable to use parts. Acids are usually controlled by the pH of the coagulation system,
The pH value is 5 or less, preferably 2 or less. In the case of an acid, it may be used alone, but it is preferably used in combination with a salt. In the case of a combination system, the pH of the coagulation system is adjusted to 8 or less, preferably 6.5 or less. The method of mixing the CR latex and coagulant aqueous solution is not particularly limited, but a method of mixing the two under forced stirring is preferred. This is because the degree of stirring affects the particle size of the precipitated particles, and if the stirring is good, the distribution width of the particle size will be small, and if the stirring is insufficient, the distribution width will be wide, and in extreme cases, it will become partially blocked. . In the present invention, the size of the chloroprene polymer particles to be produced is controlled by the amount of metasilicate dispersed in the CR latex, the degree of stirring of the CR latex and coagulant aqueous solution, and the temperature of the system during the coagulation reaction. It is possible to adjust accordingly. The temperature of the system is not particularly limited, and may range from room temperature to a high temperature of about 90°C, and in some cases may be lower than room temperature, for example, from 0 to 5°C. Regarding the effect that temperature has on the size of particles, the particles tend to be larger and the particles themselves tend to be stronger when the temperature is higher. Another method for controlling the size of chloroprene polymer particles is to include in the coagulation system a nonionic surfactant or an anionic surfactant selected from alkyl sulfates and salts of sulfonic acids directly linked to aromatic rings. let When these surfactants are present in the coagulation system, the size of the precipitated polymer particles becomes smaller. Preferred examples of the surfactants to be used include the following. Examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenol ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid ester,
Examples of glycerin fatty acid esters include polyoxyethylene cetyl ether, polyoxyethylene nonylphenol ether, sorbitan monolaurylate, polyoxyethylene sorbitan trioleate, polyoxyethylene stearate, stearic acid monoglyceride, and alkyl sulfates. Examples of salts of sulfonic acid directly linked to an aromatic ring include sodium dodecylbenzenesulfonate, sodium dodecylnaphthalenesulfonate, and a formalin condensate of naphthalenesulfonic acid. The amount used varies depending on the coagulation system, but in general, it is 0.01 parts by weight per 100 parts by weight of CR latex.
~5 parts by weight, preferably 0.01 to 1 part by weight, if too little, there will be no substantial effect; if it is too much, precipitation of the chloroprene polymer will be inhibited, and in extreme cases, the precipitation of the chloroprene polymer may not occur. There is also. The surfactant can be used by pre-dispersing it in the CR latex, by adding it at the same time as the coagulant aqueous solution, or by adding it to the coagulant aqueous solution if it has no substantial effect when coexisting with the coagulant aqueous solution. It may be dispersed. Examples are shown below to further specifically explain the present invention. Parts or percentages used in the examples are expressed on a weight basis unless otherwise specified. In the present Examples and Comparative Examples, CR latex produced by the method described below was used. CR latex manufacturing method Latex (A) a Prescription Chloroprene 100 parts Water 124〃 Disproportionated rosin acid 3〃 n-dodecyl mercaptan 0.25〃 Salt of condensate of naphthalene sulfonic acid and formaldehyde 0.6〃 Sodium hydroxide 0.7〃 b Polymerization Catalyst Potassium persulfate 0.5% and anthraquinone-β-
An aqueous solution containing 0.05% sodium sulfonate was used. c Polymerization temperature 40°C d Termination of polymerization When the polymerization rate reached 65%, 0.2 part of p-tert-butylcatechol was added to terminate the polymerization. e. Removal of remaining monomers The remaining monomers were removed by a steam stripping method to obtain an anionic CR latex (A) with a chloroprene polymer content of 35%. Latex (A)
The pH was 12.0. Latex (B) a Prescription Chloroprene 100 parts Water 124〃 Hyamine 2389 ^* 4〃 n-dodecyl mercaptan 0.25〃 Sodium formaldehyde sulfoxylate
0.03 b Polymerization catalyst A 0.05% aqueous solution of t-butyl hydroperoxide was used. c Polymerization temperature 40°C d Termination of polymerization When the polymerization rate reached 65%, 0.2 part of p-tert-butylcatechol was added to terminate the polymerization. e. Removal of remaining monomers The remaining monomers were removed by a steam stripping method to obtain a cationic CR latex (B) with a chloroprene polymer content of 37%. Latex (B)
The pH was 4.5. *Quaternary ammonium salt type surfactant manufactured by Rohm and Haas Example 1 After adding acetic acid to the latex (A) to adjust the pH to 7, Na ₂ 15 parts of SiO ₃ (sodium metasilicate)
After dissolving in 45 parts of warm water at 70°C, it was added to the latex under stirring and dispersed for 5 minutes, and then stirred and mixed for 10 minutes with a 1% BaCl ₂ aqueous solution of 5 times the amount of the latex to break the granules (rubber). I let it out. This granular material dispersion is dehydrated using a centrifuge equipped with Saran cloth, and then water is sprayed onto the granular material in the centrifuged state, and the granular material is taken out.
After dispersing and mixing 5 parts of Hakuenka CC (activated calcium carbonate fine powder manufactured by Shiraishi Industries), it was dried in a fluidized bed dryer with stirring blades on the floor, processed with a standard 10-mesh sieve, and then A powdered rubber having a fluidity of 5% or less by weight was obtained. Using the obtained powdered rubber, the formulations shown in Table 1 were prepared, and the Mooney viscosity and physical properties of the rubber of the vulcanizate were measured, and the results are shown in Table 1. For comparison in Table 1, a portion of latex (A) was frozen and solidified, and the physical properties of rubber chips produced by drying with hot air were measured, and the results are also listed.

[Table] Example 2 The latex and silicates shown in Table 2 were used, and the treatment was carried out according to the procedure of Example 1, except that a 1% aqueous CaCl ₂ solution was used as the coagulation liquid. Got the results. However, the pH of the latex was not adjusted. As is clear from this, the method according to the present invention has a remarkable effect.

[Table] The parts of silicate in Table 2 are expressed based on 100 parts of chloroprene polymer in the latex. Examples 3 to 6 Using latex (A), 15 parts of Na ₂ SiO ₃ and the surfactants shown in Table 3 were dispersed in the latex based on 100 parts of chloroprene polymer in the latex. % hydrochloric acid to lower the PH to 5.6,
Next, a 0.5% CaCl ₂ aqueous solution was added to obtain a dispersion containing particulate matter, and the mixture was treated according to Example 1 to obtain a powdered rubber. This powdered rubber was processed through a standard sieve with 42 meshes, and the weight on the sieve was measured and shown in Table 3.

[Table] The amount of surfactant dispersed in Table 3 is expressed in parts per 100 parts of rubber in the latex.

Claims (1)

[Scope of Claims] 1 An anionic chloroprene polymer latex is added with methane represented by the formula M ₂ SiO ₃ (wherein M is an alkali metal) based on 100 parts by weight of the chloroprene polymer in the latex. A powder characterized in that it is made into fine particulate chloroprene polymer by dispersing 2 to 50 parts by weight of silicate and mixing it with a coagulant selected from alkaline earth metal salts, aluminum salts, and acids. A method for producing chloroprene rubber. 2 Anionic chloroprene polymer latex
0.01 of a nonionic surfactant or an anionic surfactant selected from alkyl sulfates and salts of aromatic sulfonic acids per 100 parts by weight.
~5 parts by weight of a metasilicate of _the formula _M2SiO3 , where M is an alkali metal, for every 100 parts by weight of chloroprene polymer in the latex. 1. A method for producing powdery chloroprene rubber, which comprises dispersing the chloroprene rubber and mixing it with a coagulant selected from alkaline earth metal salts, aluminum salts, and acids to obtain fine particulate chloroprene polymers.