JP2013249411A - Natural rubber reduced in odor, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a natural rubber remarkably reduced in odor, and prevented from decrease in the plasticity remaining index (PRI).SOLUTION: A natural rubber remarkably reduced in odor, and prevented from decrease in the plasticity remaining index (PRI) is obtained by crushing a solidified material of a natural rubber latex, immersing the obtained crushed material in a sodium hydroxide aqueous solution, thereafter adding an antioxidant such as 2,2,4-trimethyl-1,2-dihydroquinoline or its polymer, and drying the mixture at 75°C to 140°C.

Description

  The present invention relates to natural rubber with reduced odor and a method for producing the same.

  Natural rubber is widely used in large quantities in the rubber industry because of its excellent physical properties and low cost. Natural rubber is made from rubber sap (natural rubber latex) collected by tapping at a rubber plantation. As a production method thereof, a method is generally employed in which an acid such as formic acid is added to a latex to coagulate, and after dehydration, drying and smoking, measurement and molding are performed. In addition to this, rubber called tree lace solidified in the form of string in the cut groove of rubber trees, rubber called cup lamp in which latex flowing out from the cut groove collected in the cup and naturally solidified, or unsmoked sheet or wet rubber (Slabs), semi-processed products such as RSS scraps, etc. are pulverized, washed, dried, weighed, and molded.

  However, natural rubber produced by these conventional methods emits a peculiar odor due to rot during storage of the raw material or in the manufacturing process due to the characteristic that the raw material is a natural product. As well as worsening the environment, the impact on the factory surroundings was also a problem. In addition, odors are generated during the processing of the natural rubber obtained, especially during the mastication process, among manufacturers of rubber products including tires that use this natural rubber. As a countermeasure, huge investments such as the installation of deodorizing equipment have been forced, and there has been an urgent need for non-bromination of natural rubber.

Therefore, Patent Document 1 below discloses a method for producing natural rubber in which natural rubber latex is brought into contact with an alkaline solution before or after coagulation.
However, the odor reduction effect of the prior art is still insufficient, and there is a problem that the plasticity residual index (PRI) is lowered, and there is room for improvement.

JP-A-8-81504

  An object of the present invention is to provide a natural rubber in which odor is remarkably reduced and a decrease in plasticity residual index (PRI) is prevented, and a method for producing the same.

As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by pulverizing a natural rubber latex coagulum and immersing it in an aqueous sodium hydroxide solution and then adding an antioxidant. The present invention has been completed.
That is, the present invention is as follows.
1. Natural rubber latex coagulated product is pulverized, and the resulting pulverized product is immersed in an aqueous sodium hydroxide solution, followed by adding an antioxidant and drying at 75 ° C to 140 ° C to reduce the odor obtained. Rubber.
2. 2. The natural rubber according to 1 above, wherein the antioxidant is an amine / ketone-based anti-aging agent.
3. 3. The natural rubber as described in 2 above, wherein the amine / ketone antioxidant is 2,2,4-trimethyl-1,2-dihydroquinoline or a polymer thereof.
4). 4. The natural rubber according to any one of 1 to 3, wherein the concentration of the aqueous sodium hydroxide solution is 0.1 N or less.
5. 5. The natural rubber according to any one of 1 to 4, wherein the addition amount of the antioxidant is 0.1 parts by mass or more with respect to 100 parts by mass of the natural rubber.
6). Natural rubber with reduced odor comprising pulverizing a coagulated product of natural rubber latex, immersing the obtained pulverized product in an aqueous sodium hydroxide solution, subsequently adding an antioxidant and drying at 75 ° C. to 140 ° C. Manufacturing method.

ADVANTAGE OF THE INVENTION According to this invention, the natural rubber by which odor was reduced significantly and the fall of the plasticity residual index (PRI) was prevented, and its manufacturing method can be provided.
In particular, in the form in which the antioxidant is specified, the odor reduction effect and the plasticity residual index (PRI) decrease prevention effect are further enhanced.
Further, even in the form in which the concentration of the aqueous sodium hydroxide solution and / or the amount of addition of the antioxidant is specified, the odor reducing effect and the plasticity residual index (PRI) lowering preventing effect are further enhanced.

Hereinafter, the present invention will be described in more detail.
As described above, the natural rubber with reduced odor of the present invention coagulates and pulverizes the natural rubber latex, immerses the obtained pulverized product in an aqueous sodium hydroxide solution, and then adds an antioxidant, 75 It is obtained by drying at a temperature of from 140C to 140C.

  The natural rubber latex coagulated product used in the present invention is not particularly limited, and examples thereof include latex coagulated rubber, cup lamps, slabs, unsmoked sheets, and mixtures thereof.

  The natural rubber latex coagulum is subsequently pulverized into a pulverized product. The particle size of the pulverized product is preferably 10 mm or less, and preferably 2 to 5 mm from the viewpoint of easy hot-air drying.

  Subsequently, the obtained pulverized product is washed with water and immersed in an aqueous sodium hydroxide solution. The concentration of the sodium hydroxide aqueous solution is preferably 0.1 N or less, more preferably 0.05 to 0.1 N, from the viewpoint of the odor reducing effect. Moreover, immersion time is 30 minutes-60 minutes, for example.

Next, the pulverized product after the immersion is taken out, preferably washed with water, and an antioxidant is added. The antioxidant may be appropriately selected from known ones, but from the viewpoint of improving the effect of the present invention, for example, an amine / ketone antioxidant which is a reactive product of amines and acetones is preferable.
Examples of the amine / ketone antioxidant include 2,2,4-trimethyl-1,2-dihydroquinoline or a polymer thereof, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, diphenylamine. Among them, 2,2,4-trimethyl-1,2-dihydroquinoline or a polymer thereof is preferable from the viewpoint of improving the effect of the present invention.

  From the viewpoint of improving the effect of the present invention, the addition amount of the antioxidant is preferably 0.1 parts by mass or more, more preferably 0.1 to 0.5 parts by mass with respect to 100 parts by mass of natural rubber.

  The method of adding the antioxidant to the pulverized product is not particularly limited as long as it is performed using a known kneading means. Antioxidants can produce desired effects even when added in powder form. Apart from this, an antioxidant may be added as an aqueous solution or an aqueous suspension to the pulverized product by means such as spraying.

Subsequently, the pulverized product to which the antioxidant is added is dried at a drying temperature in the range of 75 ° C to 140 ° C. When the drying temperature is less than 75 ° C., the water used in the water washing hardly evaporates. On the other hand, if it exceeds 140 ° C., the physical properties of the natural rubber may be deteriorated, which is not preferable.
The drying time is, for example, 40 to 120 minutes.

  The natural rubber of the present invention thus obtained has a significant reduction in odor and prevents a decrease in plasticity residual index (PRI). Therefore, the generation of bad odor during the mastication process of natural rubber is suppressed, and the odor derived from natural rubber is reduced in various rubber production processes after the mastication process. The antioxidant is generally added after the mastication step in the rubber manufacturing industry, and the addition time and the purpose of addition are different from those of the present invention, and both are distinguished.

  The natural rubber of the present invention includes fillers such as carbon black and silica, vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, various oils, anti-aging agents, plasticizers, vulcanization aids, processing aids, etc. And it can use suitably for the raw material of various rubber products, for example, the rubber composition for tires.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited to the following example.

Examples 1-4 and Comparative Examples 1-5
The natural rubber latex collected by tapping was naturally coagulated in a cup to prepare a cup lamp (CL). Subsequently, the CL was pulverized, washed with water, dehydrated, and molded into a sheet.
Separately, natural rubber latex collected by tapping was coagulated with formic acid to remove water-soluble non-rubber components, and the rubber was dried for about 1 week to 10 days to prepare an unsmoked sheet (USS).
Next, the CL and USS were mixed, pulverized, washed with water at a mass ratio of CL: USS = 6: 4, and finally pulverized to a particle size of 10 mm or less with a shredder machine to prepare a pulverized product.
The obtained pulverized product was immersed in an aqueous sodium hydroxide solution having a concentration shown in Table 1 for 1 hour or not, and after washing with water, the amount of antioxidant (2,2,4-trimethyl-1) shown in Table 1 was obtained. , 2-dihydroquinoline polymer (Nocrack 224 manufactured by Ouchi Shinko Kogyo Co., Ltd.) (hereinafter referred to as RD) is added or is not added and dried at 130 ° C. for 30 minutes and passed through a roll once. Thereafter, the sample was further dried at 130 ° C. for 15 minutes to obtain each natural rubber sample, and each of the obtained natural rubber samples was subjected to the following odor test and measurement of plasticity residual index (PRI).

Odor test: 50 g of a natural rubber sample was placed in a polyvinyl chloride bag and heated at 100 ° C. for 1 hour, and then the panel was checked for odor. Ten panelists evaluated the odor level in 6 stages, and the average value was taken as the result of the odor test. The odor level means that the lower the numerical value, the less the odor. In addition, the natural rubber sample having a low numerical value in this odor test generates little odor in the subsequent mastication process.
Residual plasticity index (PRI): Measured according to JIS K6300-1. PRI represents the ratio of plasticity after aging to natural aging when a natural rubber sample is aged by air heating. The result was expressed as an index with the value of Comparative Example 1 being 100. The lower this index, the greater the heat aging.
The results are also shown in Table 1. In Table 1, phr means parts by mass of each used component with respect to 100 parts by mass of the natural rubber sample.

From the results of Table 1, the natural rubbers of Examples 1 to 4 were obtained by pulverizing a coagulated product of natural rubber latex, immersing the obtained pulverized product in an aqueous sodium hydroxide solution, and subsequently adding an antioxidant. Since it is obtained by drying at a temperature of from 140 ° C. to 140 ° C., the odor is remarkably reduced and the decrease in the plasticity residual index (PRI) is also prevented.
On the other hand, Comparative Examples 2 to 3 were only immersed in a sodium hydroxide aqueous solution, so that the odor was improved, but the PRI was confirmed to be lowered, and a high normality sodium hydroxide aqueous solution was used ( Comparative example 3), the tendency is remarkable.
In Comparative Example 4, since only the antioxidant was added, the effect of improving odor was not confirmed.

Claims (6)

  Natural rubber latex coagulated product is pulverized, and the resulting pulverized product is immersed in an aqueous sodium hydroxide solution, followed by adding an antioxidant and drying at 75 ° C to 140 ° C to reduce the odor obtained. Rubber.   The natural rubber according to claim 1, wherein the antioxidant is an amine / ketone-based anti-aging agent.   The natural rubber according to claim 2, wherein the amine / ketone antioxidant is 2,2,4-trimethyl-1,2-dihydroquinoline or a polymer thereof.   The natural rubber according to any one of claims 1 to 3, wherein the concentration of the aqueous sodium hydroxide solution is 0.1 N or less.   The natural rubber according to any one of claims 1 to 4, wherein an addition amount of the antioxidant is 0.1 parts by mass or more with respect to 100 parts by mass of the natural rubber.   Natural rubber with reduced odor comprising pulverizing a coagulated product of natural rubber latex, immersing the obtained pulverized product in an aqueous sodium hydroxide solution, subsequently adding an antioxidant and drying at 75 ° C. to 140 ° C. Manufacturing method.