JPH033697B2 - - 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 mixed dropwise into an aqueous solution of a higher amine salt under acidic conditions, and then a synthetic resin emulsion is added to obtain a powdered rubber slurry, which is then mixed with water. The present invention relates to a method for producing powdered rubber soluble in rubber-based organic solvents, which is characterized in that it is made alkaline after being treated with a rubber poor solvent.

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. especially,
In the field of solvent-based adhesives, a dissolving 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, and therefore a large amount of time is required for dissolution. 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 it is powdered, these particles stick to each other and form into 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 physical-mechanical methods in which rubber is physically or mechanically crushed and anti-blocking agents such as talc, silica or calcium carbonate are added, and polyvalent metal salts such as aluminum salts are coagulants for rubber latex. There is a chemical method in which rubber latex is added to an aqueous solution and the rubber is chemically separated into powder form. However, in these methods of manufacturing powdered rubber, a large amount of anti-blocking agents and coagulants are mixed into the powdered rubber, so even if the adhesive liquid is prepared, these are insoluble in the solvent, so the two layers cannot be separated. It has the disadvantage that it does not form a homogeneous liquid, making it industrially disadvantageous as a rubber material for rubber-based solvent-based adhesives.

The inventors have previously devised a process for producing powdered rubber that is essentially free of inorganic materials. (Patent Application No. 148732 of 1978) 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 is prepared under acidic conditions. Drop-mixed into an aqueous solution containing an acidic water-soluble cationic polymer or a cationic surfactant that can cause coacervation with a water-soluble polymer,
Powdered rubber can be produced by separating rubber into powder, then adding a synthetic resin emulsion, dehydrating and drying. 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 powdered rubber 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. After treating the slurry liquid with a rubber poor solvent that mixes with water, it is further made alkaline.
We have succeeded in producing powdered rubber that is soluble in rubber-based organic solvents and has excellent free-flowing properties.

That is, the present invention uses a mixture of 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 higher amine of 0.1 to 10% by weight based on the dry solid content of the rubber latex. A powdered rubber slurry liquid obtained by dropwise mixing under acidic conditions into an aqueous salt-containing solution and then adding 1 to 30% by weight of a synthetic resin based on the dry weight of the rubber latex as an emulsion is used to reduce the amount of rubber that is mixed with water. The present invention relates to a method for producing powdered rubber soluble in rubber-based organic solvents, which comprises making the slurry liquid alkaline after treatment with a solvent.

As used herein, processing means uniformly mixing the powdered rubber slurry or filtrate with a water-miscible rubber poor solvent.

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, polyptadiene rubber, polychloroprene rubber, the 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.

A preferred rubber is polychloroprene rubber, which is often used as a rubber-based solvent-based adhesive, and refers to a rubber containing at least 50% by weight of 2-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, isobrene, 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, methacrylic acid, methyl acrylate copolymer, Synthetic products such as vinyl acetate/crotonic acid copolymer, styrene/maleic acid copolymer, etc. are included, and the amount per dry solid content of rubber latex is 0.1~
It is used in an amount of 10% by weight, preferably in the range 1-5% by weight, and is preferably added to the rubber latex in the form of an aqueous solution.

The water-soluble polymer used in the present invention and the higher amine salts capable of causing coacervation under acidic conditions include acetates, hydrochlorides, sulfates of higher amines;
Nitrates, etc., and higher amines include dodecyldimethylamine, cetyldimethylamine, coconut alkyldimethylamine, hardened tallow alkyldimethylamine, stearylmethylbenzylamine,
Examples include dodecylmethylbenzylamine, polyoxyethylene tallow alkylpropylene diamine, dodecyl diethanolamine, coconut alkylamine, tallow alkylamine, cetylamine, 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.

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 to 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 adjust the Hz. This PH
The acids used to adjust the pH include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, or organic acids such as acetic acid, and there are no restrictions on the method of addition. The pH should be kept between 4 and 5.

The above operation only requires mixing 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, it is affected by the amount of water or the strength of stirring.
The suitable amount of water or stirring strength is not a critical factor and can be easily determined in each case by conducting preliminary experiments.

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 if it is dehydrated under load, it tends to stick to each other and form lumps after dehydration.
It becomes 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 must 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 as an emulsion to the powdered rubber dispersion and mixing sufficiently, preferably for at least 10 minutes, can be easily dehydrated using a centrifugal separator and has fluidity. Alternatively, it can be ground into a wet powder rubber using 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;
It precipitated as a gel fraction of ~20% by weight 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. prevent such points,
That is, in order to prevent agglomeration of the powder rubber in the powder rubber slurry liquid by adding an alkaline aqueous solution, it is necessary to treat the powder rubber slurry liquid with a poor rubber solvent that is miscible with water. The treatment described here with a poor solvent for rubber that mixes with water means that a slurry of powdered rubber containing a synthetic resin or a wet powder rubber obtained by decantation or other methods is treated with a poor solvent for rubber that mixes with water. This means mixing and dropping into a solvent, and by these treatments, the powdered rubber can be uniformly dispersed without agglomeration.

It is sufficient to carry out this treatment for several minutes, and the poor solvents used here for rubber that mix with water include lower alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, and acetone. It is sufficient to use an amount that can be freely dispersed. The amount can be selected arbitrarily, but preferably 0.5 of the rubber latex used.
~5 times the volume is used.

In the present invention, an alkaline aqueous solution is added to the powdered rubber slurry liquid that has been treated with the rubber poor solvent that mixes with water to make it alkaline. There is no agglomeration, and the fluidity of the powdered rubber slurry is not lost. The substances used to make the PH of the powdered rubber slurry liquid used here alkaline include sodium hydroxide,
Potassium hydroxide, aqueous ammonia, sodium bisulfite, sodium carbonate, potassium carbonate, etc.
It is sufficient to add until the pH of the powdered rubber slurry becomes alkaline, preferably 9 or higher. After addition, the gel content can be removed by stirring and mixing for 5 minutes or more, preferably 15 minutes.

The powdered rubber slurry liquid obtained by the above operations can be easily dehydrated using a centrifugal separator or the like, and can be made into wet powdered rubber with fluidity or by being crushed with a 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 powdered rubber which is soluble in an organic solvent and has the above-mentioned structure. Powdered rubber that dissolves quickly and 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. All parts and percentages are by weight unless otherwise stated in the examples.

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 potash and 0.4 parts of formaldehyde naphthalene sulfonic acid leader.
A stabilized alkaline aqueous emulsion was prepared. Polymerization was carried out by setting the temperature of the emulsion at 12° C., adding one part 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%.

Example 1 800 g of a 1% aqueous solution of sodium carboxymethylcellulose (viscosity at 25° C., 113 cps) was added to 2000 g of CR latex and mixed to form a uniform mixture. Next, this was mixed with polyoxyethylene tallow alkylpropylene diamine containing 12 g of acetic acid.
It was added to 2000 g of a 0.8% aqueous solution of acetate over 5 minutes under stirring. The rubber immediately separated into powder, and the pH at that time was 4.8. Next, 100 g of polystyrene emulsion (trade name: LX303, approximately 45% solids) manufactured by Nihon Gosei Rubber Co., Ltd. was added over 1 minute, and mixing was continued for an additional 10 minutes. Then,
After removing water by decantation, 1.8
of ethyl alcohol was added and mixing continued for 3 minutes. Then, 2% sodium hydroxide was added, the pH was adjusted to 9, and the mixture was mixed for 30 minutes. The powder rubber slurry did not aggregate, and the powder rubber was well dispersed. Next, dehydrate with a centrifuge, crush, and store at 40°C.
Fluid drying was carried out for 30 minutes to obtain a free-flowing powder rubber with a particle size of 98% less than 1.5 mm. 200mesh of this powdered rubber
When the powdered rubber was placed in a cage made of wire mesh and immersed in benzene for 40 hours at room temperature, the gel content insoluble in benzene was measured, and the powdered rubber was all dissolved and the gel content was 0%. . Furthermore, when a rubber solution containing 5% toluene was prepared, a uniform and transparent rubber solution could be obtained.

Comparative Example 1 When the powdered rubber slurry obtained by adding polystyrene emulsion in Example 1 was immediately added with 2% sodium hydroxide without being treated with ethyl alcohol, when the pH reached 7, the powdered rubber began to aggregate. When the pH was 9, the powdered rubber agglomerated into lumps, making it impossible to obtain powdered rubber.

Comparative Example 2 In Example 1, the powdered rubber slurry obtained by adding polystyrene emulsion was treated with ethyl alcohol, dehydrated with a centrifuge, and crushed.
After fluidized drying at 40°C for 30 minutes, it was possible to obtain a powdered rubber with 98% free-flowing properties of 1.5 mm or less. However, when the gel content was measured in the same manner as in Example 1, it was found that the gel content was 3.86%. Furthermore, when a rubber solution containing 5% toluene was prepared, gel components precipitated at the bottom, making it impossible to obtain a uniform rubber solution.

Example 2 1200 g of a 2% aqueous solution of gum arabic (viscosity 5 cps at 25° C.) was added to 3000 g of CR latex to form a homogeneous mixture. Then adjust the pH with 10% acetic acid aqueous solution.
6.5 was added to 5000 g of a 0.8% aqueous solution of polyoxyethylene tallow alkylpropylene diamine acetate containing 6 g of acetic acid over 10 minutes with stirring. The pH of the powder separated liquid after addition is
It was 4.6. Next, 150 g of polystyrene emulsion (trade name LX303, approximately 45% solids) was added over 3 minutes and mixing continued for an additional 10 minutes.
Then remove the water with a cotton cloth and apply wet powdered rubber to 1.8
of methyl alcohol under stirring. The dispersion state is good, and the pH can be reduced to 9 with 2% ammonia water.
and continued mixing for 30 minutes. Dehydrated in a centrifuge,
After crushing, fluidized drying was performed at 35°C for 45 minutes. A 95% free-flowing powder rubber having a diameter of 1.5 mm or less was obtained, and its gel content was measured in the same manner as in Example 1. It was found that there was no insoluble matter and the gel content was 0%.

Comparative Example 3 In Example 2, when no treatment with aqueous ammonia was performed, a powdered rubber with 96% free-flowing properties of 1.5 mm or less could be obtained, but the gel content was measured in the same manner as in Example 1. The gel content was found to be 3.91%.

Example 3 Powder separation was carried out in the same manner as in Example 2, except that 1200 g of a 1% aqueous solution of sodium alginate (viscosity at 25°C: 355 cps) was used instead of gum arabic, and polystyrene emulsion was added. 1.5 after removing water by decantation
of isopropanol was added and mixed uniformly.
The powdered rubber slurry liquid was stable, and after mixing for 3 minutes, the pH was adjusted to 12 with a 1% aqueous potassium hydroxide solution, and mixing was continued for 15 minutes. After dehydration and crushing, at 40℃
The powdered rubber obtained by fluidized drying for 30 minutes was 98% free-flowing with a diameter of 1.5 mm or less, and was as follows.
The gel % measured in the same manner as above was 0.

Comparative Example 4 In Example 3, the powder rubber that was not subjected to alkali treatment with potassium hydroxide had a diameter of 1.5 mm or less.
However, the gel content measured in the same manner as in Example 3 was 4.33%, which contained insoluble matter.

Example 4 900 g of a 2% aqueous solution of carboxymethylcellulose sodium (viscosity 18 cps at 25° C.) was added to 3000 g of CR latex to form a homogeneous mixture. This was added to 5000 g of an aqueous solution containing 18 g of acetic acid and 36 g of coconut alkylamine hydrochloride over 10 minutes with stirring. After the addition was completed, the pH of the powder separated liquid was 4.9. Then, 180 g of high styrene butadiene emulsion (trade name Nipol 2507, manufactured by Nippon Zeon Co., Ltd., dry solids 47%) was added over 2 minutes, and mixing was continued for an additional 5 minutes. Remove the water by decantation, add 1.5 ml of acetone, and mix for 10 minutes. The rubber did not aggregate and was well dispersed. Next, the pH was adjusted to 9 with 2% potassium hydroxide and treated with an alkali for 10 minutes, followed by dehydration and crushing in a centrifuge, and fluidized drying at 40°C for 30 minutes. 1.5mm
A free-flowing powdered rubber with 97% or less was obtained, and when this powdered rubber was dissolved in toluene, it was completely dissolved, there was no undissolved matter, and the gel% was 0. On the other hand, when no alkali treatment was performed, 97% free-flowing rubber with a diameter of 1.5 mm or less could be obtained;
This rubber contained 5.33% of a toluene-insoluble component, that is, a gel component, and it was not possible to uniformly dissolve the rubber.

Example 5 In Example 3, instead of CR latex,
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 3 except that 3000 g of ML ₁₊₄ =60) was used. 94% are 1.5mm or less
A free-flowing powder rubber was obtained which, when dissolved in toluene, was completely dissolved, no undissolved matter was present, and the gel content was 0%. In addition, in the example, when the alkali treatment with potassium hydroxide was not performed, a powdered rubber with a free-flowing size of 94% of 1.5 mm or less was produced, but this rubber had a gel content that is insoluble in toluene. It contained 4.51%.

Example 6 In Example 3, instead of CR latex,
Acrylonitrile-butadiene rubber latex prepared using sodium oleate as an emulsifier (33% bound acrylonitrile content, 40% dry solids)
%, Mooney viscosity ML ₁₊₄ =46) Powdered rubber was produced in the same manner as in Example 3 except that 3000 g was used.
A 97% free-flowing rubber was obtained except for 1.5 mm.
When dissolved in methyl ethyl ketone, no insoluble matter was present, and a uniform rubber solution could be obtained. In addition, in the example, when the alkaline treatment with potassium hydroxide was not performed, it was possible to obtain a free-flowing powder rubber with a size of 97% or less of 1.5 mm, but this rubber contained a gel content that is insoluble in methyl ethyl ketone. It was not possible to obtain a uniform rubber solution.

Claims (1)

[Claims] 1. A powdered rubber slurry liquid obtained by dropping a mixture of rubber latex and a water-soluble polymer containing a carpoxyl group into an aqueous solution of a higher amine salt under acidic conditions, and then adding a synthetic resin as an emulsion, or a wet powder obtained from the liquid. A method for producing powdered rubber soluble in organic solvents, which comprises treating the powdered rubber with a rubber poor solvent that mixes with water and then making it alkaline.