JPH02167351A - Diene-based rubber excellent in ozone resistance - Google Patents

Abstract

PURPOSE:To obtain the subject diene-based rubber improved in ozone resistance in a state of an imposed dynamic strain by blending a diene-based rubber with ethylene propylene rubber having a specific Mooney viscosity and vulcanizing only the diene-based rubber. CONSTITUTION:An ozone-resistant diene-based rubber obtained by blending (A) 100 pts.wt. diene-based rubber material (e.g. NR, IR or SBR) with (B) 15-25 pts.wt. ethylene propylene rubber material (which may be EPDM that is a terpolymer containing a small amount of a diene component) having >=80, preferably >=90 Mooney viscosity (100 deg.C) and further blending the resultant unvulcanized rubber with sulfur as a vulcanizing agent and N-cyclohexyl-2- benzothiazyl.sulfenamide and tetramethylthiuram disulfide as a vulcanization accelerator, zinc flower, reinforcing material, etc., molding the prepared blend, carrying out sulfur vulcanizing and vulcanizing only the component (A) without vulcanizing the component (B).

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a diene rubber having excellent ozone resistance, and particularly to a diene rubber having excellent ozone resistance under conditions of dynamic strain without significant deterioration of physical properties. This invention relates to a diene rubber that has been effectively improved and has excellent ozone resistance.

(Background Art) Conventionally, one of the drawbacks of rubber materials is that they are vulnerable to ozone, especially NR, IRBRSSBR,
Diene-based rubbers with double bonds (unsaturation) in the main chain, such as NBR, tend to crack due to ozone deterioration under strain, so these rubber materials are used as the main materials. It is well known that ozone resistance must be considered for most rubber products.

In order to improve the ozone resistance of such diene rubber, it is common practice today to coat the surface of the rubber product with a material that has excellent ozone resistance, or to add an amine-based crack preventive agent to wax. This is dealt with by using them together.

However, even with such crack preventive agents, they migrate to the rubber surface and form a film to physically and chemically prevent cracks caused by ozone deterioration, so the strain caused in rubber products is static. Although it is effective in some cases, if continuous or intermittent dynamic strain is generated, such a film will be destroyed and ozone attack will be concentrated in the destroyed area. However, its effectiveness was low, and it was extremely difficult to protect against ozone deterioration.

(Solution Section B) Here, the present invention has been made against the background of the above-mentioned circumstances, and the problems to be solved are:
Ozone resistance can be improved without significant deterioration of physical properties, and cracks due to ozone deterioration can be effectively prevented not only under static strain but also under dynamic strain. The purpose of the present invention is to provide a diene rubber with excellent properties.

(Solution Means) In order to solve this problem, in the present invention, ethylene having a Mooney viscosity: M L , , 3 (at 100° C.) of 80 or more is added to 100 parts by weight of the diene rubber material. It is formed by sulfur vulcanization of unvulcanized rubber containing 15 to 25 parts by weight of propylene rubber material, and the ethylene propylene rubber material is substantially not vulcanized. , a diene rubber with excellent ozone resistance obtained by vulcanizing only the diene rubber material,
This is its characteristic.

(Specific explanation of the structure) First, the present invention focuses on the elasticity and hardness of the diene rubber material,
The purpose is to improve the ozone resistance while maintaining physical properties such as strength, and therefore, any known diene rubber material can be used as the diene rubber material used in the present invention. Yes, NR, IR,, BR,, SB
R, NBR, or a blend of them, etc.
As in the past, it is used as appropriate depending on the physical properties required of the product, the conditions of use of the product, etc.

In addition, the ethylene propylene rubber material (hereinafter referred to as EPR) added to the diene rubber material may be EPM, which is a copolymer of ethylene and propylene, or a small amount of ethylene and propylene. EPDM, which is a terpolymer with a diene component, can be used, but its polymer viscosity is Mooney viscosity: MLl. It is necessary to use a material having a Mooney viscosity of 80 or more at (100° C.), and preferably a Mooney viscosity of 90 or more. Note that if the Mooney viscosity of the EPR polymer is less than 80, the desired effect of improving ozone resistance cannot be sufficiently achieved.

Further, in the present invention, such PR is added in a proportion of 15 to 25 parts by weight based on 100 parts by weight of the diene rubber material.

However, if the amount of EPR added is too small, the desired effect of improving ozone resistance cannot be fully achieved; on the other hand, if it is too large, the effect of improving ozone resistance cannot be achieved. However, the physical properties of the resulting rubber product are significantly deteriorated.

The diene rubber material to which a predetermined amount of EPR has been added is treated with commonly used known rubber compounding materials, such as reinforcing agents, townizing agents, vulcanizing agents, vulcanization accelerators, and vulcanization accelerators. An unvulcanized rubber material is prepared by appropriately blending an auxiliary agent, an anti-aging agent, and, if necessary, a filler, a tackifier, and the like.

In addition, the unvulcanized rubber thus prepared is subjected to a molding process and a vulcanization process in accordance with conventional methods.
In particular, in the present invention, only the diene polymer is vulcanized in the vulcanization process, and the EPR polymer is not substantially vulcanized. A vulcanization operation will be performed.

Specifically, when EPM is used as an EPR, it is possible to vulcanize only diene polymers by using sulfur as a vulcanizing agent, and EPM can be used as an EPR.
When PDM is used, it is possible to vulcanize only the diene polymer by selecting the vulcanization accelerator and adjusting the amount used.

For rubber products mainly made of diene rubber materials obtained by performing such vulcanization operations,
without impairing the physical properties of diene rubber materials.
The present inventor has confirmed that the dynamic ozone resistance can be improved and that it exhibits excellent ozone resistance not only under static strain but also under dynamic strain. .

(Examples) In order to clarify the present invention more specifically, some examples of the present invention will be shown below. Needless to say, this is not something that can be accepted.

In addition to the following examples and the above-mentioned specific description, the present invention includes various changes, modifications, and changes based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention. It should be understood that the present invention may be implemented in a modified form.

In order to make the effects of the present invention more clear, some comparative examples conducted by the present inventor are also shown below together with Examples of the present invention.

First, for a diene rubber material having a compounding composition as shown in Table 1 below, E
By adding a predetermined amount of PDM, kl
Various unvulcanized rubbers shown in items 1 to 11 were obtained.

As is clear from Table 1, the Mooney viscosity of EPDM added is outside the range of the present invention in Nα5 to Nα7 as comparative examples, and Nα8 as comparative examples
In samples 1 to 11, the amount of EPDM added is outside the range of the present invention.

For each 100 parts by weight of these unvulcanized rubbers, 1.0 parts by weight of sulfur as a vulcanizing agent and N-cyclohexyl-2-benzothiazyl as a vulcanization accelerator were added.・Blending 1.5 parts by weight of sulfenamide, 0.5 parts by weight of tetramethylthiuram disulfide, and 5.0 parts by weight of zinc white as a vulcanization accelerator, and FEF carbon black as a reinforcing material. 50 parts by weight, 1.5 parts by weight of N-phenyl-N'-isopropyl P-phenylene cyano as an antiaging agent, 1.5 parts by weight of 2,2°4-trimethyl-1,2-dihydroquinoline polymer. 0 parts by weight, 2.0 parts by weight of wax, 2.0 parts by weight of stearic acid as a processing aid, and 10.0 parts by weight of aromatic oil as a softener, kneaded, and molded. A vulcanization operation was performed at 150° C. for 20 minutes according to the method described in .

In addition, the scorch time (Mooney scorch time) under normal conditions maintained at 121°C was measured for each kneaded product of unvulcanized rubber to which the various compounded materials mentioned above were added, and the results are also shown in Table 1. .

Further, for each of the vulcanized rubbers obtained as described above, ozone concentration: 50 pptv, temperature: 40 ° C.
Under the following environment, dynamic strain with an elongation rate of 0-10% is continuously generated, and static strain with an elongation rate of 50% is continuously generated, respectively, until cranking occurs. The results are shown in Table 2 below.
The results are shown as dynamic test results and static test results, respectively.

Furthermore, for each such vulcanized rubber, J Is
- A normal state physical property test was conducted in accordance with -6301, and tensile stress crab M. . , tensile strength: TI, elongation: E6, spring hardness: H8 and tear strength (B type): T,
The results are shown in Table 2.

As is clear from the above explanation, a predetermined amount of EPR having a specific polymer viscosity is added to a diene-based rubber material, and only the diene-based polymer is added without substantially co-curing the EPR. In the vulcanized diene rubber according to the present invention, the ozone resistance can be extremely effectively improved without impairing the inherent physical properties of the diene rubber material. The greatest technical significance of the present invention resides in that it is possible to advantageously prevent the occurrence of cracks due to ozone deterioration under conditions of dynamic strain, which has been difficult.

Applicant: Tokai Rubber Industries Co., Ltd.

Claims (1)

[Claims] An unvulcanized rubber made by blending 15 to 25 parts by weight of an ethylene propylene rubber material with a Mooney viscosity of ML_1_+_3 (100°C) of 80 or more to 100 parts by weight of a diene rubber material is sulfur-vulcanized. A diene with excellent ozone resistance, characterized in that the ethylene propylene rubber material is not substantially vulcanized and only the diene rubber material is vulcanized. Rubber.