JP4553610B2 - Concentration method of rubber latex - Google Patents

Description

  The present invention relates to a method for concentrating rubber latex. More specifically, the present invention relates to a method of concentrating rubber latex by treating rubber latex with carbon dioxide and / or carbonated water to cause phase separation.

  The rubber latex may be used as it is as a raw material for industrial products, or may be used as a solid rubber after coagulation. For example, rubber gloves, catheters, foams, rubber threads, adhesives, paper processing coating agents, etc. are produced from rubber latex as a raw material. Solid rubber is widely used as industrial products such as tires and belts.

  When rubber latex, particularly natural rubber latex is used as a raw material, the rubber content is generally concentrated from about 30% at the time of collection to about 60%. As the concentration method, for example, centrifugal separation, heating evaporation method, electric gradient method, dialysis method and the like have been used. In the case of natural rubber latex, the latex contains many non-rubber components such as proteins, carbohydrates, phospholipids, ash, and enzymes. Concentration methods such as centrifugation and electric gradient methods can be used during concentration. These non-rubber components can also be removed to some extent. However, these concentrating methods require a lot of energy and require a large apparatus. In addition, the heat evaporation method simply evaporates moisture and cannot remove non-rubber components. Furthermore, the dialysis method is not a practical method as an industrial means. Therefore, a continuous centrifugation method is generally employed for producing concentrated latex from natural rubber. As a result, the cream phase (dry rubber content (DRC) 60 wt%) containing the desired rubber component is separated from the serum phase (DRC 3-8 wt%). However, in addition to this, the bottom fraction remains in the continuous centrifuge, and it is necessary to stop the operation once every 1-2 hours and remove this bottom fraction. For this reason, the production efficiency of the continuous centrifugation method is considerably low. On the other hand, the serum phase containing a small amount of rubber contains fine rubber particles having a particle size of 1 micron or less that were not separated by centrifugation. In order to recover the fine particle rubber, a technique of acid coagulation by adding a large amount of sulfuric acid to the serum phase is generally used. However, skim rubber obtained by coagulation with sulfuric acid from the serum phase is a low-quality natural rubber containing many impurities, and its commercial value is low. In the case of serum that has been stored for a long time, it may not solidify even with the addition of sulfuric acid, and its treatment is quite difficult.

  On the other hand, for solid natural rubber, fresh latex (about 30% by weight of DRC) collected from rubber trees is diluted with water twice and then formic acid is added to solidify the rubber component. And purified. A large amount of mechanical energy is required for cutting the solidified rubber, and even if it is used with a large amount of water, sufficient washing with water cannot be expected simply by washing the outside of the solid rubber. Therefore, it is said that the purity of the rubber content in the obtained solid natural rubber is about 94%.

  An object of the present invention is to provide a method for concentrating and washing rubber latex.

  Another object of the present invention is to provide a method that, unlike the conventional methods as described above, can not only easily concentrate the rubber latex, but also obtain a purified rubber component by washing the rubber latex.

  Still other objects and advantages of the present invention will become apparent from the following description.

  According to the present invention, the above objects and advantages of the present invention are achieved by a method of concentrating rubber latex characterized by bringing rubber latex into contact with carbonic acid.

  According to the present invention, rubber latex can be phase-separated by an easy method, and the cream phase containing the separated rubber component remains in a stable colloidal state, and the separated aqueous phase (serum phase) is removed. The phase separation can be performed again by newly adding water to the cream phase, so latex can be easily concentrated, washed with water, etc.

  The inventor blows carbon dioxide into a rubber latex or mixes and agitates the latex with carbonated water, and when left for a certain period of time, the latex separates into two phases, and after removing the lower serum phase, the concentrated latex It was found that the latex was phase-separated again by adding water or carbonated water. Of course, there is no problem even if carbon dioxide is introduced into latex mixed with carbonated water.

  Hereinafter, the present invention will be described in detail. The latex used in the present invention may be natural rubber latex or synthetic rubber latex. Examples of natural rubber latex include fresh natural rubber latex, high ammonia natural rubber latex, saponification natural rubber latex (PCT / JP03 / 09880) already filed by the present inventor and natural rubber deproteinized with a proteolytic enzyme. Latex (JP-A-6-56902) can be mentioned.

  The present inventors phase-separated the latex by a simple method, and the cream phase portion containing the separated rubber component is maintained in a stable colloidal state, and the separated aqueous phase is removed and a new water phase is removed. Alternatively, the present inventors have found a method in which phase separation occurs again and the latex can be washed by adding carbonated water. The present invention will be described in detail. When carbon dioxide is blown into the latex or the latex is mixed and stirred with carbonated water and left for a certain period of time, the latex is phase-separated and separated into two phases. After removing the lower serum phase, the phase is separated again by adding water or carbonated water to the concentrated latex phase (cream phase). At this time, there is no problem even if carbon dioxide is introduced into the latex mixed with carbonated water. This is a characteristic action of carbon dioxide or carbon dioxide gas. Even if other acids such as formic acid are used, the latex does not cause only phase separation into the cream phase and the serum phase. Wake up. Carbon dioxide is gaseous and only needs to be blown into the latex, and the concentration of carbonated water is not limited. Saturated carbonated water is preferable. Of course, you may use both together. The treatment temperature is not particularly limited, but there is no problem at room temperature to about 80 ° C.

If the rubber latex is preliminarily adjusted to a pH of preferably 5 to 8 before coming into contact with carbonic acid, phase separation can easily proceed.

  For example, carbon dioxide gas or carbonated water having a saturated concentration or less is used at a ratio of 50 to 400 parts by weight of saturated carbonated water with respect to 100 parts by weight of rubber latex. When the rubber latex is a natural rubber latex, the collected fresh natural rubber latex may be diluted with water in advance, for example, twice before concentration, and used for concentration.

If this method is used, the latex can be easily concentrated, washed with water, etc. by a simple method, which has great industrial significance. In the case of producing solid natural rubber, water-soluble impurities such as proteins, sugars and inorganic salts can be easily removed by washing thoroughly in the latex state before coagulation treatment. Since fine rubber is washed, its washing efficiency is so large that it cannot be compared with the conventional water washing treatment of solid rubber after coagulation. Furthermore, even if the concentration is low and concentration and coagulation are difficult due to the fine particles, such as fine rubber contained in the serum phase of the by-product generated in the conventional continuous centrifugation process, it is concentrated in advance by the method of the present invention. And washing can be easily coagulated to recover high purity solid natural rubber.
The reason why the latex is phase-separated by this method has been confirmed by experiments that the latex particle size is enlarged by the treatment of the latex with carbon dioxide or carbon dioxide.
As a result, this method is also effective as a method for enlarging the particle size of latex.

  EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Example 1
4, 6, 8, 10 mL of commercially available carbonated water for beverages was added to 2 mL of fresh natural rubber latex (DRC about 30% by weight, containing a small amount of ammonia), and the mixture was stirred at 15 ° C. for 24 hours. Let stand for hours. The pH of the carbonated water used was 4.9. Both mixtures separated into a cream phase and a nearly clear serum phase. None of the cream phases contained coagulum. Further, when each separated mixture was stirred, the cream phase and the serum phase were uniformly dispersed, but after several hours to 24 hours, the same separated state as before the dispersion was obtained again. The state of phase separation is shown in FIG. This state was stable and kept in a separated state even after 1 week or more. The cream phase one week after mixing with carbonated water was collected, and the particle size distribution was measured with a Coulter 230 light scattering particle size distribution analyzer. As shown in FIG. 2, mixing fresh latex with carbonated water increases large particle size of 2 microns or more, and average particle size 0.83 microns found in fresh latex is doubled and quadrupled. It was found that all treated with carbonated water increased to 2.5 microns.

Reference Example 2
To 40 mL of fresh natural rubber latex (DRC about 30% by weight, containing a small amount of ammonia), 200 mL of water in which about 100 mL of carbon dioxide gas was blown into ion-exchanged water at 15 ° C. was added and stirred. Let stand for hours. The pH of the carbonated water used was 4.7. After removing the serum phase separated from the cream phase with a siphon, 80 mL of ion-exchanged water was added and allowed to stand for 48 hours. The resulting cream phase contained no coagulum. Further, when the separated mixture was stirred, the cream phase and the serum phase were uniformly dispersed, but after several hours to 24 hours, the same separated state as before the dispersion was obtained again. The state of phase separation is shown in FIG.

Reference example 3
200 mL of ion-exchanged water was added to 100 mL of fresh natural rubber latex (DRC about 30% by weight, containing a small amount of ammonia), and about 2000 L of carbon dioxide gas was blown into this at 30 ° C. The pH changed from the initial 9.4 to 6.9. This latex was allowed to stand at 30 ° C. for 24 hours, and then separated into a transparent aqueous phase and a cream phase.

  In addition, after adjusting the pH to 6.5 by adding 0.1% (w / v) formic acid with stirring to a mixture obtained by adding 200 mL of ion exchange water to 100 mL of the same fresh latex as above, Carbon dioxide gas was blown in the same way. Latex foaming during carbon dioxide blowing was reduced from the previous case. This latex was allowed to stand at 30 ° C. for 24 hours, and then separated into a transparent aqueous phase and a cream phase. The degree of separation was improved. FIG. 4 shows the state of latex phase separation that was allowed to stand for 3 days after carbon dioxide blowing.

Comparative Example 1
6 mL of an aqueous solution having a formic acid concentration of 0.08% to 0.83% (w / v concentration) was added to 3 mL of fresh natural rubber latex (DRC about 30% by weight), and the mixture was stirred at 30 ° C. for 24 hours. Let stand for hours. The pH of the formic acid aqueous solution used was 2.2 to 2.7. When mixed with 0.83% and 0.67% aqueous formic acid, the latex immediately became partially coagulated and after 24 hours separated into a coagulated rubber and a clear serum phase. When 0.50%, 0.33%, 0.17%, and 0.08% formic acid aqueous solution was mixed, each mixture kept a uniform latex state even after mixing, and after 48 hours, the coagulum Formation and separation of the serum phase were not observed. The state of phase separation is shown in FIG.

Photo showing phase separation of a mixture of natural rubber fresh latex and carbonated water Particle size distribution of the mixture after 1 week of mixing natural rubber fresh latex and carbonated water Photograph showing phase separation of natural rubber fresh latex and carbonated water mixture, reseparation after redispersion Photograph showing phase separation after injecting carbon dioxide gas into natural rubber fresh latex and standing for 3 days Photograph showing phase separation when various concentrations of formic acid are added to natural rubber fresh latex

Explanation of symbols

A: Mixture of 2 mL of fresh latex and 4 mL of carbonated water B: Mixture of 2 mL of fresh latex and 6 mL of carbonated water C: Mixture of 2 mL of fresh latex and 8 mL of carbonated water D: Mixture of 2 mL of fresh latex and 10 mL of carbonated water a: In fresh latex Rubber particle size distribution b: Size distribution of rubber particles in the cream phase obtained for a mixture of fresh latex and 2 volumes of carbonated water c: Obtained for a mixture of fresh latex and 4 volumes of carbonated water Particle size distribution E of the rubber particles in the cream phase: Carbon dioxide gas was blown into a mixture (pH 9.4) of 100 mL of fresh latex and 200 mL of ion-exchanged water F: To a mixture (pH 6.5) of 100 mL of fresh latex and 200 mL of ion-exchanged water Carbon dioxide gas blowing G: 3 mL fresh latex and 0.83% (w / v) formic acid aqueous solution 6 Mixture of mL H: Mixture of 3 mL of fresh latex and 6 mL of 0.67% (w / v) aqueous formic acid I: Mixture of 3 mL of fresh latex and 6 mL of 0.50% (w / v) aqueous formic acid J: 3 mL of fresh latex and 0 Mixture of 6 mL of 33% (w / v) formic acid aqueous solution K: Mixture of 3 mL of fresh latex and 6 mL of 0.17% (w / v) aqueous formic acid L: 3 mL of fresh latex and 0.08% (w / v) aqueous formic acid solution 6 mL of mixture

Claims (5)

Concentration method of a natural rubber latex, characterized in that brought into contact with natural rubber latex and carbonated water collected from trees of the rubber. Before brought into contact with natural rubber latex and carbonated water collected from trees of the rubber, the method according to claim 1 for adjusting the advance 5-8 the pH of natural rubber latex. Particle diameter increment Dafa latex particles characterized in that it contacted the natural rubber latex and carbonated water collected from trees of the rubber increases the particle size of the latex particles of a natural rubber latex. A method for producing solid natural rubber using the method according to claim 1, 2 or 3. Relative to 100 parts by weight of rubber latex at a rate of saturated carbonated water is 50 to 400 parts by weight, claim 1 of the following carbonated water saturation concentration is used, 3 or 4 the method described.