JPS6338377B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition in which granular vulcanized rubber is mixed into an unvulcanized rubber composition. Rubber products such as tires are shipped after removing so-called spill rubber, which is formed by flowing into the vent holes of a mold during vulcanization. Traditionally, this spew rubber was disposed of as industrial waste, such as by landfill or incineration, but as the production of rubber products increases, the amount of spew rubber generated has increased, and as a result, social issues such as consideration for environmental pollution and effective use of resources are being made. Considering the request, it is hard to say that this is a preferable method. The present inventors conducted various studies on the reuse of spilled rubber, and as a result, mixed granular vulcanized rubber smaller than a certain specific surface area into an unvulcanized rubber composition matrix containing polybutadiene as an essential component,
The present invention has been accomplished by discovering that a rubber composition obtained by vulcanization has excellent physical properties even when the proportion of granular rubber is extremely high. That is, the present invention provides an unvulcanized rubber containing 20 to 85% by weight of polybutadiene as an essential component and mixed with at least one of natural and/or synthetic cis-1,4-polyisoprene and styrene-butadiene copolymer. In the composition matrix, 1000 to 4000 parts by weight of granular vulcanized rubber with a specific surface area of 50 cm ² /g or less and 3 parts by weight of sulfur are added per 100 parts by weight of the unvulcanized rubber component.
It relates to a rubber composition characterized by being blended with ~40 parts by weight and vulcanized. The rubber composition of the present invention differs from conventional rubber compositions formed by mixing granular or powdered rubber,
Even if a large amount of granular rubber is mixed in, the physical properties such as abrasion resistance, bending resistance, and breaking strength can be maintained at a satisfactory level, so the spew rubber is of high value in terms of reuse. The rubber composition of the present invention is suitable for various uses, but especially when used as the sole of men's shoes, it exhibits superior abrasion resistance and crack resistance for long-term use compared to conventional shoe soles. It has excellent flexibility and is comfortable to wear, reducing fatigue when walking. In addition to shoe soles, the rubber composition of the present invention can also be used for elastic mats, railway slab mats, and the like. The present invention will be explained in detail below. The unvulcanized rubber composition matrix contains 20 to 85% by weight of polybutadiene as an essential component and is a mixture of at least one of natural or synthetic cis-1,4-polyisoprene and styrene-butadiene copolymer. As the polybutadiene, cis-1,4-polybutadiene and syndiotactic 1,2-polybutadiene are preferably used, but trans-1,4-polybutadiene is preferably used.
Polymers containing 30% by weight or less of structures other than the above, such as the 1,4-structure, can also be used in the same manner. Preferably used as natural and/or synthetic cis-1,4-polyisoprene are natural rubber,
and synthetic polyisoprene containing 90% or more of cis-1,4 bonds. Furthermore, a styrene-butadiene copolymer having a styrene component content of 10 to 70% by weight is generally used, and among them, a styrene component content of 25% by weight is preferably used. The above unvulcanized rubber composition has 20 to 85% as an essential component.
% by weight of polybutadiene. If the polybutadiene content is less than 20% by weight, the bending resistance will be poor, and if it is more than 85% by weight, the breaking strength will be poor, which is not preferable. In addition, when the content of natural and/or synthetic cis-1,4-polyisoprene is 50% by weight or less, and the content of styrene-butadiene copolymer is also 50% by weight or less, the content of the mixed granular vulcanized rubber is It has good adhesion and an excellent balance of mechanical properties such as abrasion resistance, bending resistance, and breaking strength. Among these ranges, polybutadiene 30~
80% by weight, natural and/or synthetic cis-1,4
- The balance of the above properties is the best when polyisoprene is 20 to 40% by weight and styrene-butadiene rubber is 0 to 40% by weight. The granular vulcanized rubber mixed into the unvulcanized rubber composition must have a specific surface area of 50 cm ² /g or less.
When the specific surface area is 50 cm ² /g or less, even if 1,000 parts by weight or more of granular vulcanized rubber is mixed into 100 parts by weight of the rubber component of the unvulcanized rubber matrix, the abrasion resistance will not decrease, and the bending resistance will not decrease. The toughness and breaking strength can also be maintained at a satisfactory level. However, if the granular vulcanized rubber exceeds 4000 parts by weight, the adhesion between the vulcanized rubbers will not be good, so the granular vulcanized rubber is blended in an amount in the range of 1000 to 4000 parts by weight. When the specific surface area of the granular vulcanized rubber is 50 cm ² /g or more, there is no noticeable deterioration in physical properties when a small amount is incorporated, but when 1000 parts by weight or more is mixed, various physical properties are significantly deteriorated. The granular vulcanized rubber preferably has at least one selected from natural rubber, polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber as a main component. Vulcanized rubbers containing other rubber components such as ethylene-propylene rubber, acrylonitrile-butadiene rubber, etc. within 20% by weight of the total rubber components are also suitably used as described above. As these granular vulcanized rubbers, granules obtained by crushing rubber products such as spew rubber and waste tires are usually used. The rubber composition of the present invention is vulcanized with sulfur. Unlike ordinary unvulcanized rubber, in the present invention, sulfur is impregnated into the granular vulcanized rubber during vulcanization, reducing the concentration of sulfur in the unvulcanized rubber matrix, resulting in insufficient vulcanization. The amount of sulfur required varies depending on the amount of granular vulcanized rubber blended, but it is necessary to blend 3 to 40 parts by weight of sulfur. Compounding agents commonly added to rubber, such as vulcanization accelerators, softeners, anti-aging agents, resins, waxes, carbon black, and inorganic fillers, can be appropriately added to the unvulcanized rubber composition. The unvulcanized rubber and the granular vulcanized rubber can be kneaded using a conventional kneading device such as a Banbury mixer, a kneader, or an open roll. Since the kneaded rubber contains many particulate vulcanized rubber components, it is easy to form into pellets, which improves workability in the next vulcanization step. Vulcanization can be carried out using normal equipment, but when vulcanizing an integral object such as the sole of a shoe, transfer molding or injection molding is more suitable for producing products with better dimensional accuracy than flat molding. It is. Example 1 The specific surface area of an unvulcanized rubber composition containing equal amounts of natural rubber, styrene-butadiene rubber, and polybutadiene rubber as shown in Table 1, mainly composed of natural rubber and styrene-butadiene rubber from a tire factory, was Approximately 23cm ² /g of Spiyu rubber (average size, diameter 2mm, length 10mm) and sulfur (Table 2) were kneaded and then vulcanized for 20 minutes at a temperature of 160°C and a press pressure of 50Kg/cm ^{2 .} A vulcanized rubber sheet with a thickness of 2 mm, a sample for a bending test, and a sample for an abrasion test were obtained.

[Table] Physical properties of the vulcanizate were evaluated in accordance with JIS K-6301. The bending test was conducted under the following conditions. Usually, this is done by making a scratch on a Demartya-type sample, but in this method, we use a bending tester (maximum distance 7.48 cm,
Minimum distance 1.88cm, 300 bends/min) 1
After 10,000 cycles, the test pieces were classified into the following 7 grades depending on the presence or absence of cracks and the size of the scratches. Rating situation 7: No cracks 6: 0.1~0.2mm cracks (1 crack occurred) 5: 0.3~0.5mm 〃 (1 crack occurred) 4: 0.6~1.0mm 〃 (1~3 cracks occurred) 3: 1.0~ 5.0mm 〃 (1 to 5 pieces occur) 2: 5.0 to 20mm 〃 (1 to 10 pieces occur) 1: All cuts The abrasion test was performed using a Lambourn type abrasion tester.
Measure the volume change of the sample per minute after 30 seconds of preliminary polishing and 180 seconds of main polishing under the conditions of load 5 kg, grinder rotation speed 380 times/minute, sample rotation speed 540 times/minute, and slip ratio +40%. did. The above results are shown in Table 2.

[Table] Comparative Example 1 A specific surface area of approximately 60 obtained by crushing used passenger car tires into an unvulcanized rubber composition having the formulation shown in Table 1.
cm ² /g granular powder rubber (average size 30 mesh)
and sulfur were kneaded, and vulcanization and evaluation were performed under the same conditions as in Example 1. The results are shown in Table 3.

【table】

[Table] Examples 2 and 3 and Comparative Examples 2 to 4 Compound compositions were prepared in which the polymer components of the unvulcanized rubber composition for matrix were changed, and Example 1
Vulcanization and evaluation were carried out under the same conditions as above. The formulation and results are shown in Table 4.

[Table] Example 4 As shown in Table 5, two types of rubber compositions were prepared by mixing spew rubber with a specific surface area of 23 cm ² /g and sulfur into an unvulcanized rubber composition for matrix at 160°C using a transfer mold. Rubber soles were created by vulcanization for 30 minutes. Using the rubber soles, 10 pairs of men's leather shoes were manufactured and evaluated by wearing them for one year.

【table】

[Table] Heel wear, which is noticeable in synthetic rubber (styrene-butadiene rubber) soles, was extremely low in the soles of the present invention, and uneven wear was also small. In addition, there were no problems such as cracks in the arch of the foot, which is severely bent. In addition, its cushioning, fit, and feel as a shoe sole were also well-received.

Claims (1)

[Claims] 1 20-85% by weight of polybutadiene as an essential component
and natural and/or synthetic cis-1,
100% unvulcanized rubber component in a matrix of an unvulcanized rubber composition prepared by mixing at least one of 4-polyisoprene and a styrene-butadiene copolymer.
1. A rubber composition comprising 1000 to 4000 parts by weight of granular vulcanized rubber having a specific surface area of 50 cm ² /g or less per part by weight and 3 to 40 parts by weight of sulfur and vulcanized.