JPH051176A - Rubber composition - Google Patents

Abstract

PURPOSE:To provide a rubber composition having an excellent scorchpreventing property and capable of being vulcanized at low temperatures in short time when the vulcanization is once started. CONSTITUTION:A rubber composition containing a dienic rubber, a vulcanizing agent, soft carbon as a reinforcing agent, an aliphatic hydrocarbon as a tackifier, a mixture of a thiazole vulcanization accelerator and a dithiocarbamic acid vulcanization accelerator as a vulcanization accelerator, and a processing auxiliary for lowering the viscosity of the composition, characterized in that the content of the processing auxiliary is 5-10 pts.wt. per 100 pts.wt. of the dienic rubber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition which must be vulcanized at a low temperature in a short time, for example, a rubber composition used for a cushion sheet used for laminating a base tire and a tread portion in the production of a retreaded tire. Regarding things.

[0002]

2. Description of the Related Art Generally, a retreaded tire is manufactured by sequentially stacking an unvulcanized cushion sheet and a prevulcanized tread portion as an adhesive medium on a base tire and then vulcanizing and molding the same. During vulcanization molding, the cushion sheet forms a cross-link bond with the base tire and the tread portion, respectively, and bonds the base tire and the tread portion together.

[0003]

As such a cushion sheet, in the vulcanization molding, it is possible to vulcanize at low temperature and in a short time in order to prevent deterioration of physical properties of the base tire and the tread portion, and further, the base tire and the tread. It is required that the natural vulcanization does not proceed so much during storage so that the adhesive strength with the parts does not decrease. That is, although the rubber composition of the cushion sheet does not easily undergo vulcanization during storage (in other words, it has excellent scorch prevention properties), once vulcanization starts, vulcanization ends in a short time. Therefore, the composition must have a fast vulcanization rate.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a rubber composition having excellent scorch-preventing properties and a high vulcanization rate.

[0005]

The rubber composition of the present invention comprises:
Diene rubber, vulcanizing agent, soft carbon as a reinforcing agent, aliphatic hydrocarbon as a tackifier, a mixture of a thiazole vulcanization accelerator and a dithiocarbamic acid vulcanization accelerator as a vulcanization accelerator, and a viscosity A rubber composition containing a processing aid for decreasing the amount of the processing aid, wherein the content of the processing aid is 5 to 10 parts by weight based on 100 parts by weight of the diene rubber.

[0006]

EXAMPLE The type of the diene rubber which is the main component of the rubber composition is appropriately selected according to the form of the rubber product. Natural rubber is generally used in a cushion sheet for an adhesive medium used for manufacturing a retreaded tire. In the rubber composition of the present invention, a diene rubber is mixed with a vulcanizing agent, a reinforcing agent, a tackifier, a vulcanization accelerator, a processing aid, and other appropriate compounding agents.

Sulfur is generally used as the vulcanizing agent.

Soft carbon is used as a reinforcing agent. Carbon black as a reinforcing agent is generally classified into hard carbon and soft carbon based on the particle size. Soft carbon has a particle size of FEF or more, and has a low reinforcing property to rubber. Hard carbon has a particle size of HAF or less than channel black and has a strong reinforcing property against rubber. Since hard carbon has a functional group such as a carboxyl group or a hydroxyl group, vulcanization proceeds even at room temperature to easily form a crosslinked structure. Therefore, a rubber composition containing hard carbon is inferior in scorch preventiveness and tends to have a low degree of vulcanization with an adherend, which is not preferable.

Examples of soft carbon used in the present invention include FEF, GPF and SRF. Of these, FEF is particularly preferably used. The soft carbon content can be appropriately selected depending on the type of rubber component, the form of the rubber product, and the like. For example, with cushion rubber,
About 30 to 50 parts by weight is preferably contained with respect to 100 parts by weight of the diene rubber.

The tackifier is blended to increase the tackiness of the compounded rubber and uses an aliphatic hydrocarbon. A compound having an aromatic ring such as a phenol resin is not preferable because it has relatively high activity and is likely to undergo a vulcanization reaction during storage. The type of the aliphatic hydrocarbon is not particularly limited, and may have a double bond or a triple bond in the molecule, and includes both linear and branched ones. The content of the aliphatic hydrocarbon can be appropriately selected depending on the type of rubber component, the form of the rubber product, and the like. For example, in the cushion seat,
It is preferably 5 parts by weight or more based on 100 parts by weight of the diene rubber.

As the vulcanization accelerator, a mixture of a thiazole vulcanization accelerator and a dithiocarbamic acid vulcanization accelerator is used. Despite the high vulcanization rate of this mixture, the accelerator itself is inactive and therefore does not promote spontaneous vulcanization during storage. Examples of the thiazole vulcanization accelerator used in the present invention include mercaptobenzothiazole and zinc salt of mercaptobenzothiazole. Examples of the dithiocarbamic acid vulcanization accelerator include zinc ethylphenyldithiocarbamate and zinc dimethyldithiocarbamate. The content of vulcanization accelerator,
The amount of the mixture is generally 0.5 to 2 parts by weight with respect to 100 parts by weight of natural rubber, although it depends on the type of rubber to be adhered. The content ratio of the thiazole-based vulcanization accelerator and the dithiocarbamic acid-based vulcanization accelerator in the mixture is not particularly limited.

[0012] The processing aid is a mixture of fatty acid soaps, etc., which are blended to reduce the rubber viscosity and facilitate the processing operation in the production of rubber products, and are generally used as lubricants. The content of the processing aid is preferably 5 to 10 parts by weight with respect to 100 parts by weight of the diene rubber. 5
If it is less than 10 parts by weight, a sufficient lubricating effect cannot be obtained, and if it exceeds 10 parts by weight, the rubber viscosity becomes too low and the workability is deteriorated.

Rubber compositions in which the above-mentioned compounding agents and compounding agents such as antiaging agents and plasticizers are appropriately compounded do not readily undergo natural vulcanization at room temperature (excellent in scorch resistance), and are vulcanized. Since the speed is high, vulcanization can be completed in a short time at low temperature.

[Specific Examples] Examples 1 and 2 Escoletz 1102B, which is 100 parts by weight of a natural rubber as a diene rubber and an aliphatic hydrocarbon as a tackifier.
(Trade name of Exxon Chemical Co., Ltd.), a mixture of zinc-2-mercaptobenzothiazole (ZnMBT) and zinc dimethyldithiocarbamate (ZnMDC) as a mixture of a thiazole vulcanization accelerator and a dithiocarbamic acid vulcanization accelerator, and Structor 40MS (trade name of Columbia Carbon Co., Ltd.) was added as a processing aid in the amounts shown in Table 1, and the following compounding agents were further added to prepare the rubber compositions of Examples 1 and 2. .. This rubber composition was extruded with an extruder to prepare a cushion sheet.

Zinc white 5 parts by weight Stearic acid 2 parts by weight Anti-aging agent (IPPD) 3 parts by weight Aroma oil 5 parts by weight Sulfur 2 parts by weight

Comparative Examples 1 to 10 Except that the types and / or amounts of carbon black, tackifier, vulcanization accelerator and processing aid were changed as shown in Table 1.
A rubber composition was prepared and a cushion sheet was prepared in the same manner as in the example. In Comparative Examples 1, 2, 8 and 9, HAF which is hard carbon was used. Comparative Examples 1, 2,
Nos. 3 and 8 used SP1068 (manufactured by Nippon Shokubai Co., Ltd.) which is a phenolic hydrocarbon as a tackifier. Further, in Comparative Examples 1 and 6, N was used as the vulcanization accelerator instead of ZnMDC.
-Cyclohexyl-2-benzothiazyl sulfenamide (CBS) was used and in Comparative Example 7 only ZnMDC was used.

[0017]

[Table 1]

[Evaluation Method] (a) Scorchability: For the cushion sheet immediately after preparation and for the cushion sheet left at 50 ° C. for 10 days,
The minimum viscosity (unit: M) at 135 ° C. was measured with a Mooney viscometer. The results are shown in Table 2.

(B) Vulcanization degree: The cushion sheet immediately after preparation and the cushion sheet left at 50 ° C. for 10 days were vulcanized at 100 ° C. until the start of vulcanization (t ₀ ) and The time required for 90% vulcanization (t ₉₀ ) was measured with a rheometer. The results are shown in Table 2.

[0020]

[Table 2]

[Evaluation Results] Comparing Example 1 with Comparative Example 9, soft carbon was used because Example 1 showed a smaller increase in viscosity upon standing and a shorter initial vulcanization start time. It can be seen that the scorch prevention property and the vulcanization property are better.

Comparing Example 1 and Comparative Example 8, Example 1 has a smaller increase in viscosity upon standing and has a shorter initial vulcanization start time. Therefore, one using an aliphatic hydrocarbon is preferred. However, it is found that the scorch prevention property and the vulcanization property are excellent.

Comparing Example 1 with Comparative Examples 1, 6 and 7, Example 1 showed a smaller increase in viscosity upon standing,
Since the time required for 90% vulcanization (t ₉₀ ) is also short, it can be seen that the combination of the thiazole-based vulcanization accelerator and the dithiocarbamic acid-based vulcanization accelerator is excellent in the scorch prevention property and the vulcanization property.

Comparing Examples 1 and 2 with Comparative Examples 2 to 5, 10 shows that Examples 1 and 2 show a small increase in viscosity upon standing and have a short initial vulcanization start time (t ₀ ). ,
It can be seen that when the content of the processing aid is within the range of the present invention, the anti-scorch property and the vulcanization property are excellent.

[0025]

EFFECTS OF THE INVENTION The rubber composition of the present invention has little progress of natural vulcanization at room temperature, so that even if it is stored for a long period of time, the increase in viscosity is small and the vulcanization rate is fast. ,
Vulcanization molding can be completed in a short time. Therefore, adhesion to rubber products whose physical properties will deteriorate unless vulcanized at low temperature for a short time,
For example, it is preferably used for a rubber composition of a cushion sheet of a retreaded tire.

Claims (1)

Claims: 1. A diene rubber, a vulcanizing agent, a soft carbon as a reinforcing agent, an aliphatic hydrocarbon as a tackifier,
A rubber composition containing a mixture of a thiazole-based vulcanization accelerator and a dithiocarbamic acid-based vulcanization accelerator as a vulcanization accelerator, and a processing aid for reducing viscosity, wherein the content of the processing aid is Is 5 to 10 parts by weight with respect to 100 parts by weight of the diene rubber.