JPH0140843B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing powdered rubber that is soluble in rubber-based organic solvents. More specifically, a rubber latex containing a water-soluble polymer containing a carboxyl group is dropwise mixed into an aqueous solution of a higher amine salt under acidic conditions, and then a synthetic resin emulsion is added to the resulting powdered rubber slurry, and a fatty acid soap is added to the slurry. In addition, the present invention relates to a method for producing powdered rubber soluble in rubber-based organic solvents, which is characterized in that it is acid-formed, aged at 50 to 100°C, and then treated with alkali at 30°C or lower. Conventionally, rubber is often isolated from rubber latex, and its shape is relatively large lumps (blocks or veils) or chips. However, depending on its use or application, it may be necessary to shred it. Particularly in the field of solvent-based adhesives, a melting operation is essential, and in this case, if the rubber is in the form of blocks or chips, the surface area is small compared to its weight, so it takes a long time to melt. do. If it is in powder form, it can be dissolved in a short time when producing an adhesive liquid, making it industrially very advantageous as a rubber material for solvent-based adhesives. Despite such huge demands,
Rubber is still supplied in bales or chips. This is because rubber, by its very nature, has high stickiness and elasticity even at room temperature, and even once powdered, these particles stick to each other and form lumps. For this reason, various studies have been made on methods for producing powdered rubber that does not adhere to each other and form lumps. Such methods include a physical-mechanical method in which the rubber is physically or mechanically crushed and an anti-blocking agent such as talc, silica or calcium carbonate is added, and an aqueous solution of a polyvalent metal salt, such as an aluminum salt, which is a coagulant for rubber latex. There is a chemical method in which rubber latex is added and the rubber is chemically separated into powder form. However, in these methods of manufacturing powdered rubber, large amounts of anti-blocking agents and coagulants are mixed into the powdered rubber, so even if an adhesive liquid is prepared, these are insoluble in the solvent, so two layers cannot be separated. It has the disadvantage that it does not form a homogeneous liquid, which is industrially disadvantageous as a rubber material for rubber-based solvent-based adhesives. The present inventors have previously invented a method for manufacturing powdered rubber that essentially does not contain inorganic substances.
Publication No. 9562 (Patent Application No. 148732 of 1975). According to this method, a mixture of an anionic or nonionic rubber latex and an anionic water-soluble polymer that dissociates in water and has a negative charge undergoes coacelvation with the anionic water-soluble polymer under acidic conditions. Powdered rubber is produced by mixing dropwise into an aqueous solution containing an acidic, water-soluble cationic polymer or cationic surfactant, separating the rubber into powder, then adding a synthetic resin emulsion, dehydration, and drying. can do. However, such powdered rubber was found to contain a component (hereinafter referred to as gel) that is insoluble in rubber solvents, and was found to be unsuitable as a rubber material for rubber solvent-based adhesives. As a result of intensive research taking these points into consideration, we have developed a powder rubber slurry obtained by using a water-soluble polymer having a carboxyl group and a higher amine salt as a substance that causes coacervation under acidic conditions with the water-soluble polymer. By adding fatty acid soap to the liquid, converting it into acid form, aging it at 50-100℃, and treating it with alkali at below 30℃, it becomes soluble in rubber-based organic solvents.
In addition, we succeeded in producing powdered rubber with excellent free-flowing properties. That is, the present invention uses a mixture of an anionic or nonionic rubber latex and a water-soluble polymer containing 0.1 to 10% by weight of carboxyl groups based on the dry solid content of the rubber latex, and a mixture of water-soluble polymers containing 0.1 to 10% by weight of carboxyl groups based on the dry solid content of the rubber latex. Dry solids of rubber latex are mixed dropwise into an aqueous solution containing an amine salt under acidic conditions, and then 1 to 30% by weight of a synthetic resin is added as an emulsion based on the dry solids of rubber latex to a powdered rubber slurry liquid. Production of powdered rubber soluble in rubber-based organic solvents, which is characterized by adding 0.5 to 5% by weight of fatty acid soap per minute, forming the acid form, aging at 50 to 100°C, and treating with alkali at 30°C or less. It is about law. The rubber targeted in the present invention can be any rubber that can be obtained as an anionic or nonionic latex, including natural rubber and polyisoprene, which is a homopolymer of conjugated diene compounds produced by conventional emulsion polymerization. Rubber, polybutadiene rubber, polychloroprene rubber, the above conjugated diene compound and styrene, acrylonitrile,
Styrene-butadiene rubber, acrylonitrile-butadiene rubber, which is a copolymer with vinyl compounds such as vinyl pyridine, acrylic acid, methacrylic acid, alkyl acrylate, and alkyl methacrylate;
Vinylpyridine butadiene styrene rubber, acrylic acid butadiene rubber, methacrylic acid butadiene rubber, methyl acrylate butadiene rubber, methyl methacrylate butadiene rubber, or isobutylene isoprene rubber, which is a copolymer of olefins such as ethylene, propylene, isobutylene, and a conjugated diene compound. etc. The preferred rubber is
Polychloroprene rubber, which is often used as a rubber-based solvent-based adhesive, and at least 50% by weight contains 2
- Refers to a rubber made of chloro-1,3-butadiene (hereinafter abbreviated as chloroprene). Typical copolymerizable monomers that can be used with chloroprene include styrene, acrylonitrile, vinyl acetate, alkyl esters of acrylic and methacrylic acids, butadiene, isoprene,
1-chloro-1,3-butadiene, 2,3-dichloro-1,3-butadiene, 2-cyano-1,3
-butadiene, etc., and these rubber latexes can be easily produced according to known emulsion polymerization techniques. In particular, it is preferable to use polychloroprene rubber latex, which is polymerized at low temperatures and has a high degree of crystallinity. The water-soluble polymer used in the present invention has a carboxyl group, and includes natural products such as sodium alginate and gum arabic, sodium carboxymethylcellulose, acrylic acid/methyl acrylate copolymer, and methacrylic acid/methyl acrylate copolymer. , vinyl acetate/crotonic acid copolymer, styrene/maleic acid copolymer, etc., per dry solid content of rubber latex.
It is used in a range of 0.1 to 10% by weight, preferably 1 to 5% by weight, and is preferably added to the rubber latex in the form of an aqueous solution. The higher amine salts that cause coacervation under acidic conditions with the water-soluble polymer used in the present invention are acetates, hydrochlorides, sulfates, nitrates, etc. of higher amines. Dodecyldimethylamine, cetyldimethylamine, coconut alkyldimethylamine, hydrogenated tallow alkyldimethylamine, stearylmethylbenzylamine, dodecylmethylbenzylamine, polyoxyethylene tallow alkylpropylene diamine, dodecyldiethanolamine, coconut alkylamine, tallow alkylamine, cetylamine, Examples include stearylamine and hardened tallow alkylamine. These higher amine salts are used in an amount of 0.1 to 10% by weight, preferably 1 to 5% by weight, based on the dry solid content of the rubber latex.
Used within the range of In the present invention, the rubber latex containing a water-soluble polymer is mixed dropwise into an aqueous solution of a higher amine salt under acidic conditions to separate the rubber into powder. The ratio of the polymer and the higher amine salt to be used can be easily determined by conducting preliminary experiments in advance. Separation of rubber latex into powdered rubber in the present invention can occur only under acidic conditions, and it is necessary to control the pH. this
Acids used to adjust pH include hydrochloric acid, sulfuric acid,
An inorganic acid such as nitric acid or an organic acid such as acetic acid is used, and there are no restrictions on the method of addition, as long as the pH at the end of powder separation is kept acidic, preferably 4 to 5. In the above operation, it is sufficient to simply mix each solution under stirring at room temperature, and the rubber can be quickly and easily separated into powder form from the rubber latex.
In this case, the amount of water or stirring strength is affected, but it is not an important factor, and the suitable amount of water or stirring strength can be easily determined in advance by conducting preliminary experiments in each case. A synthetic resin is then added and mixed as an emulsion to the powdered rubber dispersion thus obtained. The powdered rubber obtained in the above step can be easily separated and washed with a cotton cloth, etc., but when dehydrated under load,
After dehydration, they tend to stick together and form clumps, making it difficult to obtain rubber in powder form. In the present invention, this problem has been solved by adding a synthetic resin as an emulsion, and the rubber has fluidity that does not form into agglomerates even after dehydration, or it can be made into a powdered rubber by mild pulverization. The synthetic resins used here are those with a glass transition temperature of 30°C or higher, such as polystyrene, polymethyl methacrylate, polyvinyl chloride, styrene/acrylonitrile copolymer, styrene/methyl methacrylate copolymer, styrene/butadiene. Examples include copolymers, styrene/vinyl chloride copolymers, vinyl chloride/vinylidene chloride copolymers, and these synthetic resins are used as emulsions. These synthetic resins need to be selected in consideration of the solvent used for producing the rubber solvent-based adhesive liquid, and it is preferable to use synthetic resins that are soluble in the solvent. These synthetic resins are used in an amount of 1 to 30% by weight, preferably 3 to 15% by weight, based on the dry solid content of the rubber latex. If this amount is less than 1% by weight, it will not be sufficiently effective in preventing agglomeration after dehydration, and if it exceeds 30% by weight, the properties as a rubber will be impaired, which is not preferable. The powdered rubber slurry obtained by adding the synthetic resin to the powdered rubber dispersion as an emulsion and mixing sufficiently, preferably for at least 10 minutes, can be easily dehydrated using a centrifugal separator or the like, and has fluidity or It can be ground into wet powder rubber with mild force. However, when the powdered rubber obtained by drying is dissolved in a rubber-based organic solvent such as toluene or benzene, it does not dissolve completely, and
A gel content of 20% by weight precipitated and separated into two layers. This phenomenon is very disadvantageous when considering the use of rubber-based solvent-based adhesives as rubber materials, and it is necessary to remove the gel content in order to obtain a uniform rubber solution. As a result of intensive research focusing on this point, it was found that this gel component is soluble in an aqueous alkaline solution. In the present invention, if an alkaline aqueous solution is immediately added to the powder rubber slurry obtained by adding the synthetic resin to make it alkaline, the powder state will be destroyed and the rubber will coagulate into lumps. In order to prevent this problem, that is, to prevent the powder rubber from agglomerating in the powder rubber slurry by adding an alkaline aqueous solution, fatty acid soap is added to the powder rubber slurry to make it into an acid form. It must be made. The fatty acid soap used here is a sodium salt or potassium salt of a fatty acid having 12 to 20 carbon atoms, and the fatty acids include lauric acid,
Examples include myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, etc. After adding these fatty acid soaps, hydrochloric acid, sulfuric acid,
It is converted into acid form by inorganic acids such as nitric acid or organic acids such as acetic acid. In this case, it is desirable that the fatty acid soap be uniformly dispersed in the powdered rubber slurry.
In addition, when adding acid, it is sufficient to use more than the equivalent mole of fatty acid soap to be added.
Since fatty acid soap is essentially an alkaline substance, it must be added so that the pH of the powdered rubber slurry does not become alkaline, preferably to a pH of 6 or less. Instead of acids, neutralization with polyvalent metal salts such as calcium chloride, barium sulfate, magnesium chloride, zinc sulfate, aluminum chloride, etc. is also possible, and agglomeration of powdered rubber slurry does not occur during alkali treatment. No, but in this case,
There is a gel component in the final powdered rubber,
It has the disadvantage that a uniform rubber solution cannot be obtained even when dissolved in a rubber-based organic solvent. The fatty acid soap used in the present invention is 0.5 to 5% by weight based on the dry solid content of the rubber latex.
It is preferably used in a range of 1 to 2% by weight,
If it is less than 0.5% by weight, it will not be possible to prevent the powder rubber slurry from agglomerating in the subsequent alkali treatment process, and if it is used in excess of 5% by weight, it will cause vulcanization delays and deteriorate the physical properties of the rubber. This is not desirable because it impairs the In the present invention, fatty acid soap is added to make it into an acid form, and then it is aged at 50 to 100°C, but the aging time varies depending on the temperature. For example, at 80°C, 10
It is sufficient to perform the test for at least 2 hours at 50°C.
It can be changed arbitrarily depending on the temperature. This aging is essential in the present invention, and if it is not carried out, the powdered rubber slurry tends to agglomerate during alkali treatment or become blocks during dehydration, which is undesirable. Also, the aging temperature is 50℃.
At temperatures below this temperature, it is impossible to prevent the tendency toward block formation during dehydration even if the aging is carried out for a long time. Next, an alkaline aqueous solution is added to the powdered rubber slurry at a temperature below 30°C to make it alkaline.If the above treatment has been carried out, even if an alkaline substance is added, the powdered rubber will not aggregate at all, and the powdered rubber slurry will be made alkaline. The fluidity of the liquid is not lost. It is preferable that the alkaline treatment temperature is low;
A temperature of 30° C. or lower is sufficient, but a temperature higher than this temperature is not preferable because the powdered rubber slurry tends to aggregate during alkali treatment. The materials used to make the powdered rubber slurry liquid used here include sodium hydroxide, potassium hydroxide, aqueous ammonia,
There are sodium bisulfite, sodium carbonate, potassium carbonate, etc., and it is sufficient to add them until the pH of the powdered rubber slurry becomes alkaline, preferably 9 or higher, and after addition, stir and mix for at least 5 minutes, preferably 15 minutes. The gel content can be removed by performing this for a few minutes. The powdered rubber slurry liquid obtained by the above operations is
It can be easily dehydrated using a centrifugal separator or the like, and can be made into wet powder rubber by being fluid or pulverized with light force. Next, the drying method is not particularly limited, and methods such as ventilation drying, hot air drying, vacuum drying, and fluidized drying can be freely selected and used. In order to obtain a dry powdered rubber having a uniform particle size, it is preferable to use a fluidized drying method or a flash drying method that allows drying in a state of motion. The present invention is a method for producing a powdered rubber having the above-mentioned structure, which is soluble in an organic solvent. Moreover, powdered rubber that dissolves quickly can be easily, quickly, and efficiently produced. In order to make the present invention easier to understand, the present invention will be described below with reference to examples, but the present invention is not limited thereto. Unless otherwise specified in the examples, parts and %
All values are by weight. Polychloroprene rubber used in the examples (hereinafter
(abbreviated as CR) latex 100 parts of chloroprene and dodecyl mercaptan
Contains 0.115 parts, 3.6 parts of rosin potassium soap, and 0.4 parts of formaldehyde/naphthalene sulfonate soda.
A stabilized alkaline aqueous emulsion was prepared in 1 part. Polymerization was carried out by setting the temperature of the emulsion at 12° C., adding a portion of a 1.5% aqueous solution of hydrosulfite, and then continuously dropping a 1% aqueous potassium persulfate solution. Polymerization has a conversion rate of 70
%, 0.1 part of t-butylcatechol and
Polymerization was stopped by adding 0.1 part of phenothiazine,
Unreacted chloroprene was stripped and distilled off using a conventional method to obtain CR latex with a dry solid content of about 37%. Examples 1 to 3 800 g of a 1% aqueous solution of sodium carboxymethyl cellulose (viscosity at 25°C: 113 cps) was added to 2000 g of CR latex and mixed to form a homogeneous solution.
This was then mixed with polyoxyethylene tallow alkylpropylene diamine acetate containing 12 g of acetic acid.
It was added to 2000 g of a 0.8% aqueous solution over 5 minutes with stirring. The rubber immediately separated into powder, and the pH at that time was 4.8. Next, polystyrene emulsion (product name LX303, approximately 45%) manufactured by Japan Synthetic Rubber Co., Ltd.
Add 100g of solid content over 1 minute, then
Mixing continued for 10 minutes. Next, 200 g of a 4% aqueous solution of fatty acid soap as shown in Table 1 was added, neutralized with equimolar hydrochloric acid, and then aged under the respective conditions.
Thereafter, the temperature was lowered to 25° C., the pH of the powdered rubber slurry was adjusted to 9 with 2% potassium hydroxide, and an alkali treatment was performed for 15 minutes. During this period, the dispersion state of the powder rubber slurry liquid was good. After dehydration and washing in a centrifuge, the mixture was crushed and fluidized at 40° C. for 40 minutes to obtain a free-flowing powder rubber as shown in Table 1. This powdered rubber was placed in a basket made of 200 mesh wire mesh, and immersed in benzene at room temperature for 40 hours. When the gel content insoluble in benzene was measured, all of the powdered rubber was dissolved, and the gel content was measured. was 0%.

[Table] As shown in Comparative Examples 1 and 3, if the aging conditions are insufficient, blocks will form during dehydration.
Even after crushing, a uniform powdered rubber could not be obtained, and when treated with alkali without adding fatty acid soap, the powdered rubber slurry agglomerated during the addition of an aqueous potassium hydroxide solution. In addition, as in Comparative Example 2, when no alkali treatment was performed, powdered rubber with 99% of the particle size of 1.5 mm or less was obtained, but when the gel content was measured in the same manner as in Example 1, it was found that it contained 3.86% of gel. Therefore, it was not possible to obtain a uniform rubber solution, and the gel component precipitated and separated into two layers. Comparative Example 4 The same procedure as in Example 1 was carried out except that the alkali treatment temperature was changed to 40°C. When alkaline treatment was carried out at 40°C, there was no change in the dispersion state of the powdered rubber slurry in the potassium hydroxide aqueous solution, but after 5 minutes of mixing, the dispersion state worsened, and after 10 minutes, the dispersion state deteriorated. This resulted in agglomeration. Example 4 Instead of CR latex in Example 1,
Styrene-butadiene rubber latex made using potassium oleate as an emulsifier (23% bound styrene, 38% dry solids, Mooney viscosity)
Powdered rubber was produced in the same manner as in Example 1 except that 2000 g of ML _1+4,60 ) was used. 95% less than 1.5mm
A free-flowing powder rubber was obtained, and when dissolved in toluene, a homogeneous rubber solution with a gel content of 0% was obtained. Example 5 Acrylonitrile-butadiene rubber latex (bound acrylonitrile content 33%, dry solid content 40%,
A powdered rubber was produced in the same manner as in Example 1, except that 2000 g of Mooney viscosity ML ₁₊₄ , 46) was used instead of CR latex. A free-flowing rubber of 97% less than 1.5 mm was obtained, and when dissolved in methyl ethyl ketone, there was no undissolved matter and a uniform rubber solution could be obtained.

Claims (1)

[Claims] 1 Rubber latex containing a water-soluble polymer containing a carboxyl group is dropwise mixed into an aqueous solution of a higher amine salt under acidic conditions, and then a synthetic resin is added as an emulsion, and a fatty acid soap is added to the powdered rubber slurry obtained. , make this into acid form, 50~
A method for producing powdered rubber soluble in organic solvents, which comprises aging at 100°C and then alkali treatment at 30°C or lower.