JPS6021601B2 - Manufacturing method of powdered rubber - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing powdered rubber.

More specifically, polymethyl vinyl ether and an alkali metal sulfate or carbonate are added to a rubber latex, the resulting mixture is added to an aqueous solution of an alkali metal chloride or nitrate, and the rubber The present invention relates to a method for producing powdered rubber from rubber latex, which comprises precipitating rubber from latex into powder, and then adding a synthetic resin emulsion thereto to adsorb the synthetic resin onto the surface of the powdered rubber particles. Conventionally, rubber is often produced singly from rubber latex, and the rubber is supplied in the form of relatively large lumps (blocks or bales) or chips.

However, when using it or depending on the application, it is necessary to cut it into pieces.

For example, when molding a block-shaped synthetic rubber, the block-shaped rubber is cut into pieces, weighed, and then kneaded using a kneading method such as a Banbury mixer or roll mixing.

In such cases, if the rubber is in powder form and is supplied in the form of pellets, the shredding process can be omitted, and the feeding to the weighing machine or processing machine prior to processing can be automated. can. Furthermore, during processing, if the rubber is in powder form, it will be easier to knead it with various compounded chemicals or fillers. Furthermore, in recent years, with the expansion of rubber applications, rubber has been increasingly used in blends with various thermoplastic resins.

These synthetic resins are generally in powder form and are often supplied in pellet form, and the various rubbers used for the above purposes must be in powder form from the viewpoint of dispersibility with the synthetic resin. is desirable.

Also, when preparing a rubber solution for use as a rubber adhesive, if the rubber is in powder form or pellet form, the time required for dissolution can be greatly shortened due to the increased surface area. Therefore, it is very advantageous industrially.

However, despite such demands, various rubbers are still currently supplied in the form of blocks or chips. This is because rubber, by its very nature, is highly adhesive or elastic even at room temperature, and once formed into pellets, the pellets stick to each other and form blocks during storage or transportation.

For this reason, in order to produce powdered rubber that does not stick to each other and form blocks, various studies have been made on methods for producing powdered rubber.

A common method is to grind rubber in an attrition mill, suspend it in air, add an aqueous dispersion of an anti-blocking agent such as talc or calcium carbonate, dehydrate it to form a powdered rubber, and then dust it. A method in which rubber is treated with rubber powder, or a method in which the rubber is treated with liquid nitrogen or the like to bring it below the temperature at which it forms into arms, and then pulverized by spraying with a jet stream or irradiated with ultrasonic waves, and then powdered by applying an anti-blocking agent. There is a method of simultaneously spraying rubber latex and an anti-blocking agent dispersion into a heating chamber to form powdered rubber.

However, all of these methods rely on physical means, and a large amount of heat is generated due to the friction between the rubbers due to the elasticity or viscosity of the rubber. There are problems such as difficulty in pulverizing rubber into powder, high economic cost, and limited ability to process rubber into powder. It is disadvantageous in that components may be mixed in. The inventors of the present invention have conducted extensive research into a new method for producing powdered rubber that is different from conventional methods and does not have such drawbacks.As a result, the present inventors have found that powdered rubber can be produced directly from rubber latex through a simple chemical treatment. The company succeeded in producing rubber. Further, the powdered rubber obtained in the present invention can be directly dissolved in an organic solvent to prepare a uniform rubber solution. In the present invention, 5 to 2% by weight of polymethyl vinyl ether and 5 to 2% by weight of an alkali metal sulfate or carbonate are added to anionic or nonionic rubber latex in the form of an aqueous solution based on the dry weight of the rubber latex. The rubber latex mixture obtained by adding and thoroughly mixing is mixed by passing it under an aqueous solution containing an alkali metal chloride or nitrate in an amount of 5 to 20% by weight based on the dry weight of the rubber latex. By separating the rubber from the rubber latex into a powder, which is then added with a glass transition temperature of 30% by weight, based on the dry weight of the rubber latex.
The present invention relates to a method for producing powdered rubber, which is characterized by adding a synthetic resin as an emulsion at a temperature of 0.degree. C. or higher, dehydrating and drying.

The target rubber of the present invention can be any rubber that can be bound as an anionic or nonionic latex. Polyisoprene rubber (IR), polychloroprene rubber (CR), and polybutadiene rubber (B
R), the conjugated diene compound and styrene, acrylonitrile, vinylpyridine, acrylic acid, methacrylic acid,
Styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), vinylpyridine-butadiene-styrene copolymer rubber, and acrylic acid-ptadiene copolymer rubber, which are copolymers with vinyl compounds such as alkyl acrylates and alkyl methacrylates. Rubber, methacrylate butadiene copolymer rubber, methyl acrylate butadiene copolymer rubber, methyl methacrylate butadiene copolymer rubber, and inbutylene isoprene copolymer, which is a copolymer of olefins such as ethylene, propylene, isobutylene, and a diene compound. There are rubber etc.

These rubber latexes usually contain from 10 to 6% by weight of rubber, based on the total amount of latex. In the present invention, polymethyl vinyl ether and an alkali metal sulfate or carbonate are first added to rubber latex. Polymethyl vinyl ether is an amorphous atactic polymer that is soluble in water as well as organic solvents such as methanol, ethanol, acetone, benzene, toluene, and ethyl acetate. It is preferably added as 5 to 2% by weight, preferably 8% by weight, based on the dry weight of the rubber latex.
It is used in a range of 15% by weight. It is not necessary to use more than 2% by weight, but if it is less than 5% by weight, the rubber will become lumpy and will not separate into powder.

Further, the polymethyl vinyl ether aqueous solution must be kept at a temperature of 32° C. or lower; if the temperature is higher than 320° C., polymethyl vinyl ether will precipitate from the aqueous solution and cannot be used in the present invention. Alkali metal sulfates or carbonates added to the rubber latex together with polymethyl vinyl ether include, for example, K2S04, Na2S04,
K2C03, Na2C03, etc., in an amount of 5 to 2% by weight, preferably 8 to 2% by weight, based on the dry weight of the rubber latex.
It is used in a range of 15% by weight.

It is not necessary to use more than 2% by weight, but if it is less than 5% by weight, the rubber will become lumpy and will not separate into powder.

The polymethyl vinyl ether and the alkali metal sulfate or carbonate may be added to the rubber latex separately as an aqueous solution, or they may be added as an aqueous polymethyl vinyl ether solution in which the alkali metal salt is dissolved. . This mixing operation can be easily carried out at room temperature, and the pH of the resulting mixture is 7 or higher. The rubber latex mixture is then mixed dropwise into an aqueous alkali metal chloride or nitrate solution using a rope pestle. By doing so, the rubber is precipitated into powder and separated into two phases: powdered rubber and an aqueous phase. Examples of the alkali metal nitrates used here include M, 12, CaC12, &C
I2, mother (C03)2, Mg (N03)2, Ca (N0
3) 2nd grade, 5 to 5 per dry weight of rubber latex
It is used in an amount of 20% by weight, preferably 8 to 15% by weight.

It is not necessary to use more than 2% by weight, but if it is less than 5% by weight, the rubber becomes lumpy and cannot be separated into powder.

Further, it is preferable that these alkali metal salts are used in an equimolar amount or a ratio close to that of the alkali metal salt. The volume of the aqueous alkali metal salt solution is not particularly limited, but it is preferably used within a range of 1 to 1 volume larger than the volume of the rubber latex. The above operation can be easily carried out at room temperature, but this alkali metal salt aqueous solution may be heated, and the amount can be freely selected within the range of 0 to 100 qo.

By mixing in this manner, the rubber can be precipitated into powder form from the rubber latex and separated into two phases: a powdered rubber particle phase and an aqueous phase. In this mixing, the liquid p
CaS04, which is usually called a soluble salt from alkali metal salts and alkali metal salts, because H' is above 7;
Water-irresolvable salts such as CaC03, European S04, and MgC03 are formed.

In the present invention, this unnecessary salt in the water formed during mixing combines with the thermal gelation property of polymethyl vinyl ether to separate the rubber from the rubber latex into powder, and prevents adhesion between the separated rubber particles. It is assumed that this is working effectively.

In addition, since this water-insoluble salt quickly dissolves in dilute acids such as hydrochloric acid, sulfuric acid, and acetic acid, it can be finally removed by washing and does not remain in the final powdered rubber. The powdered rubber particles obtained by the above procedure can be easily filtered and washed using cotton cloth, etc. However, since dehydration using methods such as centrifugation places a load on the rubber particles, the rubber particles are The particles tend to stick to each other and form blocks, making it difficult to obtain rubber in powder form.

In the present invention, this problem was solved by adding a synthetic resin emulsion, and by adsorbing the synthetic resin emulsion particles to the surface of the rubber particles and dehydrating and drying them, adhesion between the rubber particles was prevented and fluidity was improved. Powdered rubber can be obtained. The synthetic resin emulsion used herein refers to an emulsion in which synthetic resin particles having a glass transition temperature of 30 qo or higher are dispersed in an aqueous medium.
Examples of such synthetic resin emulsions include polystyrene emulsion, polymethyl methacrylate emulsion, methyl methacrylate/methyl acrylate copolymer emulsion, polyvinyl chloride emulsion, vinyl chloride/vinylidene chloride copolymer emulsion, and polyacetic acid pinylate emulsion. , styrene/acrylonitrile copolymer emulsion, styrene/itaconic acid copolymer emulsion, styrene/methyl methacrylate copolymer emulsion, styrene/vinyl chloride copolymer emulsion, fluororesin emulsion such as polyvinyl fluoride and polychlorotrifluoroethylene. There is. These synthetic resin emulsions are added to a system in which rubber is dispersed in powder form by two-phase separation so that the dry weight is 1 to 40% by weight, preferably 3 to 15% by weight, based on the dry weight of the rubber latex. If the amount of synthetic resin is less than 1% by weight, it is difficult to obtain a sufficient effect, and the rubber cannot be obtained in a powdered state, which tends to form blocks. Moreover, if it is used in an amount exceeding 4% by weight, the properties as a rubber may be impaired, which is not preferable. In order to sufficiently adsorb the synthetic resin emulsion particles onto the surface of the rubber particles dispersed in powder form in water, it is necessary to mix thoroughly after adding the synthetic resin emulsion, but mixing for 30 minutes or more is sufficient. .

The powdered rubber obtained by the above procedure is filtered, thoroughly washed, and then easily dehydrated by centrifugation, but the synthetic resin adsorbs to the surface of the powdered rubber particles and sticks between the rubber particles. Therefore, even if a rotating load of several thousand to tens of thousands is applied, there will be no sticking to each other and forming blocks, and it can be easily crushed using powdered rubber with fluidity or light crushing Powdered rubber is obtained.

Next, the drying method is not particularly limited, and any drying method such as ventilation drying, hot air drying, vacuum drying, fluidized drying, etc. can be freely selected and used. To obtain dry powder rubber with uniform powder rubber particle size,
It is preferable to use a method such as fluidized drying or vibration drying that allows drying in a moving state. The present invention is a method for producing powdered rubber having the above-mentioned structure, and according to the present invention, powdered rubber having a particle size of about 3 ribs or less can be easily and efficiently produced.

The powdered rubber obtained by the present invention can be directly and easily dissolved in organic solvents such as benzene, toluene, and tetrahydrofuran, and can be made into a uniform rubber solution, and the undissolved portion is JIS
When measured according to standard K6388, it is as small as 2% by weight or less. For example, it takes only several tens of minutes to produce a rubber solution with a concentration of 1% by weight. This is industrially advantageous compared to the conventional process, which takes several hours to a day to turn rubber chips or bales into a rubber solution. Rubber adhesives are used as rubber solutions, and the present invention can be said to be particularly suitable for powdering polychloroprene rubber, which is widely used in this field. Examples will be described below, but the invention is not limited thereto.

Unless otherwise specified in the examples, parts represent parts by weight.
Rubber latex and synthetic resin emulsion used in the examples Polychloroprene rubber latex (abbreviated as CR) 4.0 parts of rosin potassium soap, 0.4 part of caustic soda, sodium form-7-rudehyde-naphthalene sulfonate in a nitrogen stream 0.4 parts of the condensate was dissolved in 10 parts of water, and then chloroprene in which 0.12 parts of n-dodecylmecaptan and 0.1 parts of 2,6-di-t-butyl-p-cursol were dissolved was added. The mixture was emulsified, and 0.006 part of disodium ethylenediaminetetraacetate and 0.004 part of iron sulfate were added at 10°C, followed by polymerization while dropping a 1% aqueous solution of potassium persulfate.

The polymerization was stopped at 70% conversion, and unreacted chloroprene was distilled off to obtain a polychloroprene rubber latex with a dry weight of 35%. 'B} Acrylonitrile butadiene copolymer rubber latex (abbreviated as NBR) High acrylonitrile butadiene copolymer rubber latex (trade name Nipol 1571) manufactured by Nippon Zeon Co., Ltd. with a dry weight of 3
The content was adjusted to 5% by weight.

■Polyptadiene rubber latex (abbreviated as BR) Polyptadiene rubber latex (trade name JSR7000) manufactured by Japan Synthetic Rubber Co., Ltd. was adjusted to have a dry weight of 35% by weight.

Dissolved polymethyl methacrylate emulsion (abbreviated as PMMA) In a nitrogen stream, dissolve 20 parts of water, 7.5 parts of sodium alkylaryl polyoxyethylene sulfonate, and 0.75 parts of sodium dodecylbenzenesulfonate, and then 15 parts of methyl methacrylate were added and polymerization was carried out at 760° C. using potassium persulfate as an initiator.

The dry weight of the polymethyl methacrylate emulsion obtained was 42% by weight. {Machi Polyvinyl chloride emulsion (abbreviated as PVC) manufactured by Nippon Zeon Co., Ltd. (product name: Wo
A polyvinyl chloride emulsion (n151) was used.

The dry weight was 47% by weight. Examples 1 to 3 and Comparative Examples 1 to 2 An aqueous solution of polymethyl vinyl ether (25 qo of a 3% by weight aqueous solution of PS with a viscosity of 300) was added to polychloroprene rubber latex in the proportions shown in Table 1 at room temperature. Then, an aqueous sodium sulfate solution was added and mixed uniformly.

When this mixture was added dropwise to an aqueous solution of calcium chloride at room temperature while stirring, the rubber immediately became powder and separated. Next, polymethyl methacrylate was added as an emulsion to the aqueous solution in which the powdered rubber was dispersed to give a concentration of 6% by weight based on the dry weight of the rubber latex.
Continued mixing for an hour. After filtering and washing with a cotton cloth, it was dehydrated in a centrifugal separator and dried to obtain a fluid powdered rubber. On the other hand, as shown in Comparative Example 1, polymethylpinyl ether and Na2S0 added to rubber latex
When the amount of No. 4 and the amount of CaC12 were less than the predetermined amounts, the rubber did not separate into powder, but precipitated in the form of agglomerated lumps. In addition, as shown in Comparative Example 2, if polymethyl methacrylate emulsion was not added, the powdered rubber would stick to each other and form blocks after dehydration in a centrifugal chick machine.

Table 2 shows the particle size and insoluble portion of the powdered rubber obtained in these Examples, and the results of an adhesion test using the rubber.

The particle size was mostly 14 mesh or less, and the insoluble portion in toluene was small at 2% by weight or less, making it possible to form a uniform rubber solution. Also, only 20 minutes was required to form a toluene solution containing 1% by weight of rubber.
The adhesion test consisted of 10 parts of the powdered rubber, 8 parts of magnesium oxide, 5 parts of activated zinc white, 2 parts of anti-aging agent (Nocrac 200 manufactured by Ouchi Shinko), and phenolic resin (CKM 1634 manufactured by Showa Union Gosei). After mixing 3 groups in a high-speed mixer, the solid content obtained by dissolving in toluene is 25% by weight.
The rubber solution was applied to a No. 9 cotton canvas at a concentration of 50 M/l, glued together, and dried. As a result, 20
It was found that it had a peel strength of k9/i or higher. Table 2 a) According to JIS standard K6388, b) Measurement example after bonding and drying at 23°C for 7 days. The same procedure was used as in Example 1 except that 98.3% by weight of 1
42.6 parts of powdered polychloroprene rubber having a mesh size of 4 mesh or less and 83.4 weight % of a powder polychloroprene rubber of 2 mesh or less was obtained.

The normal temperature peel strength for canvas/canvas measured according to Example 1 was 21.3 k9/i. Example 5 In Example 3, potassium sulfate was used instead of sodium sulfate,
In the same manner as in Example 3 except that barium nitrate was used instead of calcium chloride, 45% of powdered rubber containing 97.7% by weight of 14 mesh or less and 80.1% by weight of 2 skin mesh or less was prepared.
．． Guo got it.

The insoluble portion of the powdered rubber in toluene is 1. When a canvas/canvas adhesion test was conducted in the same manner as in Example 1, it was found to have a peel strength of 20.9 k9/in2. Example 6 BR latex (3% by dry weight) 10% by total weight
At room temperature, add 10 parts of polymethyl vinyl ether (3% by weight aqueous solution has a viscosity of 300% by weight) at room temperature, then add 8 parts of a 5% by weight aqueous solution of sodium sulfate, and mix uniformly. did.

When this mixed latex was added dropwise to 500 parts of a 3% by weight aqueous calcium chloride solution at room temperature while stirring, the rubber immediately separated into powder. A polyvinyl chloride emulsion was added to the aqueous solution in which the powdered rubber was dispersed in an amount of 5% by weight based on the dry weight of the rubber latex, and mixing was continued for 1 hour. Next, filtration,
After washing, dehydration, and drying, 40.3 parts of fluid powder rubber containing 98.7% by weight of 14 mesh or less and 90.3% by weight of 2 mesh or less was obtained. Example 7 39.8 parts of powdered NBR was obtained in the same manner as in Example 6 except that NBR latex (dry weight 35% by weight) was used instead of BR latex.

Claims (1)

[Claims] 1 Anionic or nonionic rubber latex,
A mixture obtained by adding 5 to 20% by weight of polymethyl vinyl ether and 5 to 20% by weight of an alkali metal sulfate or carbonate as an aqueous solution, based on the dry weight of the rubber latex, is added in an amount of 5 to 20% by weight, based on the dry weight of the rubber latex. The rubber is separated from the rubber latex into a powder by mixing it in an aqueous solution containing an alkaline earth metal chloride or nitrate, and then the glass transition temperature is 1 to 40% by weight based on the dry weight of the rubber latex. A method for producing powdered rubber, which comprises adding a synthetic resin having a temperature of 30° C. or higher as an emulsion, dehydrating it, and drying it.