JPH0464620B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing granular rubber that is resistant to blocking. (Prior Art) Rubber is usually used in the form of bales or chips of a certain size during processing. However, in recent years, granular rubber has been increasingly used because it is blended with plastics or inorganic materials (magnetic powder, asbestos, etc.), or dissolved in a solvent to make a rubber solution. Conventionally, methods for producing granular rubber include pulverizing rubber chips or pellets in a pulverizer with the addition of an anti-blocking agent, or mixing rubber latex with an anti-blocking agent and drying the mixture in a spray dryer. It is being said. However, the granular rubber produced by these methods has poor powder properties and is prone to blocking.
Furthermore, it has drawbacks such as high energy costs for crushing and drying. (Problems to be Solved by the Invention) As a result of intensive research in order to solve these drawbacks, the present inventors have succeeded in obtaining granular rubber from rubber latex with good powder properties and resistance to blocking by a specific method. The present invention was completed based on this finding. (Means for Solving the Problems) That is, the present invention involves mixing rubber latex, a solvent for dissolving or swelling the rubber, and a dispersant, then adding an anti-blocking agent, recovering the solvent, dehydration,
The present invention provides a method for producing granular rubber by drying. Examples of the rubber latex used in the present invention include natural rubber latex, synthetic rubber latex obtained by emulsion polymerization, and synthetic rubber latex obtained by emulsifying a polymer solution obtained by solution polymerization with water and an emulsifier. In addition, synthetic rubber latexes include polybutadiene rubber, polyisoprene rubber, polyisobutylene rubber, acrylic rubber, chloroprene rubber, epichlorohydrin rubber,
Examples include butadiene-styrene copolymer rubber and butadiene-acrylonitrile copolymer rubber. Further examples include rubber latexes containing plasticizers, stabilizers, ultraviolet absorbers, antioxidants, vulcanizing agents, lubricants, pigments, fillers, reinforcing agents, and the like.
It is also possible to use a mixture of two or more rubber latexes. In the present invention, the rubber concentration of the rubber latex is
It is preferably 70% by weight or less. If the amount exceeds 70% by weight, the rubber will stick and become block-like, making it impossible to obtain the desired granular composite. The lower limit of the rubber concentration is not particularly limited, but in general, when the concentration is low, such as less than 10% by weight, the efficiency is poor because the amount of granular rubber obtained in one production process is small. The solvent used in the present invention is not particularly limited as long as it dissolves or swells the rubber of the rubber latex, and examples include butane, pentane, hexane,
Alkanes such as octane, alkenes such as butene, pentene, and hexene, dienes such as butadiene and isoprene, alcohols such as octyl alcohol and decyl alcohol, methyl ethyl ketone,
Examples include ketones such as isobutyl methyl ketone, aromatics such as benzene, toluene, and xylene, and vinyl halides such as vinyl chloride, vinyl fluoride, and vinyl bromide. Of course, it is also possible to use two or more of these in combination. Among these, those with low boiling points such as butadiene, isoprene, and vinyl chloride are difficult to remain in the polymer;
Moreover, it is extremely preferable because it is easy to recover. The amount of the solvent used is at least 10 parts by weight, preferably at least 30 parts by weight, per 100 parts by weight of rubber in the rubber latex. When the amount of the solvent used is less than 10 parts by weight, the rubber latex becomes block-like or crumb-like, and the desired granular rubber cannot be obtained. The upper limit of the amount of solvent is not particularly limited, but in general, if a large amount exceeding 500 parts by weight is used, the efficiency is poor because it takes time to recover the solvent. Dispersants used in the present invention include, for example, partially saponified polyvinyl acetate, cellulose derivatives such as alkylcellulose, polymer electrolytes such as polyvinylpyrrolidone, polyacrylic acid, and polyacrylates, and maleic anhydride-vinyl acetate copolymer. Examples include synthetic water-soluble polymeric substances such as polymers, natural polymeric substances such as starch, gelatin, gum tragacanth, and inorganic compounds such as barium sulfate, calcium sulfate, calcium carbonate, magnesium carbonate, or mixtures of one or more thereof. It will be done. The amount of dispersant used is 0.05 to 10 parts by weight, preferably 0.1 parts by weight per 100 parts by weight of rubber in the rubber latex.
~5 parts by weight. If the amount of the dispersant used is less than 0.05 parts by weight, the rubber latex will become block-like or crumb-like, making it impossible to obtain the desired granular rubber. Furthermore, if the amount of dispersant used exceeds 10 parts by weight, the quality of the product will deteriorate, which is not preferable. In the present invention, an emulsifier may be used in an amount of 0 to 5 parts by weight, preferably 0.001 to 2 parts by weight, per 100 parts by weight of rubber in the rubber latex, in combination with a dispersant.
Emulsifiers include partial esters of polyhydric alcohols such as sorbitan monolaurate, sorbitan triolate, and glyceryl monostearate, ethers such as polyoxyethylene nonyl phenyl ether, polypropylene glycol-polyethylene glycol block copolymers, and higher Nonionic surfactants such as alcohols; higher fatty acid salts such as sodium stearate and potassium oleate, sodium alkyl sulfates such as sodium lauryl sulfate, sodium alkylaryl sulfonates and alkyls such as sodium dodecylbenzenesulfonate. Examples include anionic surfactants such as sodium succinate. The anti-blocking agents used in the present invention include inorganic compounds such as silica, talc, and calcium carbonate, lubricants based on organic compounds such as polyethylene wax, higher alcohols, and higher fatty acids, polyethylene, polystyrene, polyvinyl chloride, and crosslinked materials thereof. Examples include fine powder. The amount of anti-blocking agent used varies depending on the tackiness of the rubber in the rubber latex, but is 1 to 30 parts by weight, preferably 2 to 20 parts by weight, per 100 parts by weight of rubber. If the amount of anti-blocking agent used is less than 1 part by weight, the obtained granular rubber tends to block, which is not preferable. or,
If the amount of anti-blocking agent used exceeds 30 parts by weight, the quality of the product will deteriorate, which is not preferable. In addition, in the present invention, in order to obtain powder of an appropriate size, 0% per 100 parts by weight of rubber in the rubber latex is used.
~5 parts by weight of coagulating agents such as acids, alkalis, salts, etc. can be added. In the present invention, an autoclave equipped with a stirrer is used as a container for mixing the rubber latex, solvent, dispersant, and anti-blocking agent. The mixing temperature varies depending on the type and amount of polymer, but is usually between room temperature and 80°C. Furthermore, stirring conditions do not need to be particularly limited, and conditions may be selected that allow the mixture to flow and disperse. The mixing time is not particularly limited, but is usually 30 minutes to 3 hours. The method of mixing the rubber latex, solvent and dispersant in the present invention is not particularly limited; for example, they may be charged into an autoclave all at once and mixed with stirring, or may be sequentially charged and mixed with stirring. However, it is preferable to mix the anti-blocking agent with other substances before charging it into the autoclave. If the anti-blocking agent is added at the same time as other substances, it will be incorporated into the droplets of the rubber solution latex composed of the other substances, and the anti-blocking effect will be lost or significantly reduced. or,
In order to uniformly adhere the anti-blocking agent to the surface of the rubber droplets, it is preferable to gradually add the anti-blocking agent as a solution such as an aqueous solution to a mixture of other substances while stirring. (Effects of the Invention) In this way, according to the present invention, a granular rubber with good powder properties and less blocking can be obtained by a relatively simple mixing operation. (Example) The present invention will be described in more detail with reference to Examples below. Parts in Examples and Comparative Examples are by weight unless otherwise specified. The following measurement method was used as a measure of the resistance to blocking of the samples in the Examples and Comparative Examples. Fill a cylinder with an inner diameter of 3 inches and a depth of 3 inches with the sample, and remove the excess sample with a blade. At a temperature of 30°C, a load of 5 kg was applied to the top of the sample for 5 minutes.
After applying the load for a minute, remove the load and gently tilt the cylinder sideways. Measure the time from when the sample collapses until the bottom of the cylinder is visible, and define this as the collapse time. The shorter the decay time, the less likely the sample is to block. Example 1 A butadiene styrene copolymer rubber latex (solid content 50%) with a styrene content of 40% (solid content 50%) 100 was prepared using a rosin acid mixture and an oleic acid mixture in a stainless steel autoclave equipped with a stirrer.
(in terms of solid content), 1.1 parts of partially saponified polyvinyl acetate, 30 parts of butadiene monomer, and 2 parts of magnesium sulfate, and after stirring at 60°C for 1 hour, the particle size was determined.
0.1μ cross-linked polystyrene latex (solids content 40
%) and stirred for 30 minutes, the butadiene monomer was recovered and dehydrated and dried to obtain granular rubber. Examples 2 to 4 and Comparative Examples 1 to 2 The amount of butadiene monomer in Example 1 was 0 parts (Comparative Example 1) per 100 parts of rubber latex (solid content);
When the same method as in Example 1 was used except that the amounts were changed to 5 parts (Comparative Example 2), 50 parts (Example 2), 100 parts (Example 3), and 150 parts (Example 4), butadiene monomer Particulate rubber was obtained with 50, 100, and 150 parts of body weight, but crumb-like was obtained with the others, and the desired granular rubber could not be obtained. Examples 5 to 7 and Comparative Examples 3 to 4 In Example 1, the partially saponified product of polyvinyl acetate was
1 part (Comparative Example 3), 0.02 parts (Comparative Example 4), 0.2 parts (Example 5), 0.5 parts (Example 6), and 2 parts (Example 7). When used, granular rubber was obtained when 0.2 part or more of partially saponified polyvinyl acetate was used, but in other cases, the latex became crumb-like and the desired granular rubber could not be obtained. Example 8 100 parts of a butadiene-acrylonitrile copolymer rubber latex with a solid content of 35% and acrylonitrile of 41%, which was produced using rosin acid soap in a stainless steel autoclave equipped with a stirrer (in terms of solid content), 2 parts of hydroxypropyl methyl cellulose,
Add 0.1 part of sodium dodecylbenzenesulfonate, 1 part of calcium chloride, and 100 parts of vinyl chloride monomer,
After stirring at 40° C. for 30 minutes, a slurry containing 5 parts of calcium carbonate was added, and after stirring for 30 minutes, the vinyl chloride monomer was recovered and dehydrated and dried to obtain granular rubber. Examples 9 to 10 and Comparative Example 5 Example 8 except that the amount of calcium carbonate in Example 8 was changed to 0 parts (Comparative Example 5), 10 parts (Example 9), and 15 parts (Example 10). Granular rubber was obtained in the same manner. Example 11 Granular rubber was prepared using the same method as in Example 8, except that 20 parts of vinyl chloride polymer latex (solid content 50%) with a particle size of 0.2μ was added together with calcium carbonate as an anti-blocking agent. I got it. Comparative Example 6 Granular rubber was obtained in the same manner as in Example 1, except that the crosslinked polystyrene fine powder of Example 1 was charged at the same time as the other materials, and stirred at 60° C. for 1 hour and 30 minutes. Comparative Example 7 Granular rubber was obtained in the same manner as in Example 8, except that the calcium carbonate in Example 8 was charged at the same time as the other ingredients, and the mixture was stirred at 40° C. for 1 hour. Comparative Example 8 The butadiene-acrylonitrile copolymer rubber latex used in Example 8 was coagulated into crumbs, which were dehydrated and dried, and 10 parts of calcium carbonate were added thereto and ground in a grinder to obtain granular rubber. The properties of the granular rubber prepared in each of the above examples are shown in Tables 1-
It is summarized in 4. From each table, it can be seen that the granular rubber obtained in each example provides a particle size rubber that is less likely to block than the comparative example.

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Claims (1)

[Claims] 1. A method for producing granular rubber, which comprises mixing rubber latex, a solvent, and a dispersant, then adding and mixing an anti-blocking agent, recovering the solvent, dehydrating, and drying.