JP2001270902A - Method for manufacturing rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a mixed composition comprising a filler providing a colored product with a high lightness and containing uniformly dispersed fine fillers, without applying a mastication process as well as a method for manufacturing a vulcanized rubber using the composition SOLUTION: A natural rubber latex and a wet-ground calcium carbonate slurry are blended together in a vessel with an agitator. The rubber and calcium carbonate are coprecipitated from the mixture by adding an inorganic salt such as calcium nitrate, and then, the precipitate is coagulated, washed, dried, and vulcanized by kneading it with a vulcanizing agent, a vulcanization accelerator, etc., to form a vulcanized rubber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rubber composition for producing a vulcanized rubber having excellent mechanical strength such as tensile strength, abrasion resistance and heat aging resistance by blending a filler with rubber. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Natural rubber raw materials used for tires and industrial rubber products are produced by coagulating latex collected from a rubber tree. Since this raw material has a molecular weight of 1,000,000 or more, it is difficult to process it as it is. Therefore, in order to improve the processability, a mastication step for reducing the molecular weight is performed. However, a decrease in the molecular weight in this mastication step results in a decrease in mechanical properties at the same time. Therefore,
A processing method that does not require a mastication step is required.

[0003] In rubber products, a filler is generally compounded and used. Calcium carbonate is also widely used as a filler for rubber. Generally, the smaller the particle size, the better the compounding effect such as the reinforcing effect. Heavy calcium carbonate produced by dry grinding of mined raw materials by a mechanical method is difficult to produce those of 1 μm or less due to the limitations of grinding technology. It is not so desired and is merely used as a bulking agent for cost reduction.

[0004]

[0003] Carbon black is widely used as a reinforcing agent for vulcanized rubber. However, since the rubber product is blackened and the brightness and coloring cannot be expected, it has the second highest reinforcing property next to carbon black. Fine powder silica reinforcing agents (so-called white carbon) are used but are expensive.
Therefore, the use of calcium carbonate as a reinforcing agent, which has been used only as a filler for the purpose of simply lowering the unit price (volume unit price) of a product, has been studied.

In the wet pulverization in which calcium carbonate is pulverized in water, fine particles having a particle size of about 0.2 μm can be produced due to the development of a dispersant (Japanese Patent Application Laid-Open No. 9-150072). Although it is expected to be an effect as a vulcanized rubber reinforcing filler at a lower cost than the fine particle sedimentable calcium carbonate produced in the above, the fine particles are remarkably agglomerated in the drying step and cannot be taken out as a powder. . Therefore, a conventional method of mechanically kneading a filler using a closed kneader such as a Banbury mixer, a roll machine or the like cannot be applied to solid raw material rubber, so that a new method must be developed.

[0006]

The object of the present invention is to employ a method for producing a rubber composition, which comprises co-precipitating a rubber latex and a calcium carbonate slurry to obtain a rubber dough. . More specifically, a natural rubber latex and a calcium carbonate slurry are mixed, and a rubber and a filler are coprecipitated and coagulated with a neutral salt solution to obtain a rubber paste.

[0007] The kneaded dough prepared by the above method is kneaded with a compounding agent such as a vulcanizing agent such as sulfur or peroxide, a vulcanization accelerator or an antioxidant, and vulcanized rubber is obtained by a conventional method.

[0008] For this reason, if a natural pulverized calcium carbonate slurry is mixed with natural rubber latex as it is, a simple kneading machine without a long mastication process over a long period of time using a Banbury mixer or a roll machine. Allows the mixing of the filler.

It has been confirmed that the surface of the natural rubber latex is negatively charged, and that the surface charge of the wet-ground calcium carbonate is also negative. is there.

[0010] The concentration of the natural rubber latex is about 60%, but it may be used as it is or may be moderately puffed. From the viewpoint of preventing mechanical destruction and aggregation of the latex, the number of times of stirring and the time are 100 to 500 rpm, 5 to 20 minutes, especially 250 rp.
m, preferably about 10 minutes.

Usually, an acid such as formic acid is used for coagulating the natural rubber latex, but if an acid is used, it cannot be used because calcium carbonate dissolves. for that reason,
In the present invention, coprecipitation by salting out by adding a neutral inorganic salt solution,
An aqueous calcium nitrate solution which is coagulated but does not have a detrimental effect by remaining in the vulcanized rubber such as chloride ions or transition metal ions is preferable as the coagulant. As the solvent, methanol and ethanol can be used in addition to water.

The coagulated rubber-calcium carbonate is preferably washed with water and dried at 50 to 90 ° C. for 2 to 10 hours, particularly at about 80 ° C. for 6 hours. In this step, the water content is reduced to about 0.5%. If the temperature is 90 ° C. or higher, the rubber tends to age.

The dried coagulated product is kneaded with a compounding chemical by a kneading mixer. If the temperature is lower than 80 ° C., the molecular weight is significantly reduced due to the shearing force.

The compounding chemicals used for the production of vulcanized rubber are generally used crosslinking agents, vulcanization accelerators, antioxidants and processing aids. The crosslinker may be either sulfur or peroxide. Further, depending on the use, ordinary light / heavy calcium carbonate powder, clay, diatomaceous earth, barium sulfate or the like may be mixed as a filler.

The coagulated product after drying is preformed by a roll machine or the like, and vulcanized at a predetermined temperature to obtain a vulcanized rubber.

The method of the present invention can be applied to synthetic rubber latex such as styrene-butadiene rubber and nitrile-butadiene rubber latex, but is most suitably applied to natural rubber latex.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 Using an ammonia-stabilized natural rubber latex having a rubber content of 60% and a calcium carbonate slurry having an average particle diameter of 0.6 μm, the amount of calcium carbonate was 50 to 100 parts per 100 parts of solid rubber. 1
The latex and the slurry were weighed to 50 parts, mixed using a vessel equipped with a stirrer, and stirred at 250 rpm for 10 minutes.
Next, a 0.7 wt% aqueous solution of calcium nitrate was dropped and stirred to coprecipitate and solidify. The coagulated product was washed with water and dried at 80 ° C. for 6 hours. The kneading of the vulcanizing agent and the like was performed using a mixer attached to a Brabender plastic coder set at 80 ° C. After preforming into a sheet, it was press-vulcanized to obtain a vulcanized rubber. The formulation is as shown in Table 1.

[0018]

[Table 1]

FIG. 1 shows the tensile strength (T _B ), elongation (E _B ),
It is the result of comparing the dependency of the 0% elongation modulus (M ₃₀₀ ) on the blending amount with that prepared by a conventional method using dry-ground calcium carbonate having an average particle diameter of 1 μm. In natural rubber, in general, the tensile strength and elongation decrease and the elongation modulus increases as the amount of the filler increases. The product prepared by the present invention does not differ from the conventional product in the tendency of decrease in elongation, but has a small decrease in tensile strength. On the other hand, the extension modulus was remarkably improved, and at 150 parts, it was twice that of the conventional product, indicating that the effect of reinforcing the modulus was large. FIG. 2 is a scanning electron micrograph showing the state of dispersion of calcium carbonate in the vulcanized rubber. No agglomerates were observed, indicating good dispersibility.

Example 2 A vulcanized rubber was prepared in the same manner as in Example 1 using a calcium carbonate slurry having a finer average particle diameter of 0.2 μm than that of Example 1. As shown in FIG. 3, even if the particle diameter becomes finer, the dispersion state is good. Table 2 shows these Examples 1 and 2 and a conventional dry-pulverized calcium carbonate (Comparative Example 1).
It is the result of comparing various physical property values with those of the compound containing carbon black (Comparative Example 2) and the like. Various properties are improved by pulverization, and the values are almost equal to those of carbon black except for the tear strength.

[0021]

[Table 2]

Further, as shown in Table 3, after the heat aging test (100
(72 ° C., 72 hours) is smaller than that of carbon black, and is characterized by improved heat resistance. This is because the calcium carbonate acts as a reinforcing agent even after the heat aging test, resulting in a vulcanized rubber having excellent heat resistance.

[0023]

[Table 3]

[0024]

The filler-mixed kneaded dough using the rubber latex and the filler slurry of the present invention and the method for producing a vulcanized rubber using the same can be compounded in rubber with fine particles dispersed therein. Good dispersion of the filler.
For this reason, calcium carbonate acts as a reinforcing agent, not just a filler, improving mechanical strength and sufficiently exhibiting a vulcanized rubber reinforcing effect.

Further, due to this reinforcing effect, the thermal properties are also improved, and a vulcanized rubber having excellent heat resistance can be produced.

Since a rubber having good strength can be produced by blending bright colors, the variety in product design is increased. Unlike carbon black, the rubber composition can maintain lightness without being blackened, and if a pigment is blended, the rubber composition can enjoy many colorful colorings with lightness.

Since the mastication step is not required, there is no decrease in physical properties due to the decrease in molecular weight due to mastication. Further, the energy required in the mastication step can be saved.

[Brief description of the drawings]

FIG. 1 is a comparison graph of the dependence of the properties of vulcanized rubber prepared by the method of the present invention on the blending of calcium carbonate and the blending amount of dry-ground calcium carbonate prepared by a conventional method.

FIG. 2 is a scanning electron microscope photograph of a cross section of a vulcanized rubber blended with calcium carbonate having an average particle diameter of 0.6 μm according to the method of the present invention, which was broken by cooling with liquid nitrogen.

FIG. 3 is a scanning electron micrograph of a cross section of a vulcanized rubber blended with calcium carbonate having an average particle diameter of 0.2 μm according to the method of the present invention, which is broken by cooling with liquid nitrogen.

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[Procedure amendment]

[Submission date] March 31, 2000 (200.3.3.
1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

[0023]

[Table 3]

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Katsushi Nishi 5301 Haga, Okayama City, Okayama Prefecture Inside the Industrial Technology Center, Okayama Prefecture (72) Yumiko Takase 2-8-6 Nishi-Shimbashi, Minato-ku, Tokyo (72) Inventor Ryoji Ito 2-8-6 Nishi-Shimbashi, Minato-ku, Tokyo F-Tech Co., Ltd. F-term (reference) 4F070 AA04 AA05 AC16 AE01 DA32 DA38 DA39 4J002 AC001 AC011 DE236 FD016

Claims (2)

[Claims] 1. A method for producing a rubber composition, comprising co-precipitating a rubber latex and a calcium carbonate slurry to obtain a kneaded rubber dough. 2. A natural rubber latex and a calcium carbonate slurry are mixed, and a rubber and a filler are coprecipitated with a neutral salt solution.
A method for producing a rubber composition, comprising coagulating into a kneaded rubber dough.