JPH0639544B2 - Rubber composition for seals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to heat resistance, cold resistance, compression set, oil resistance,
The present invention also relates to a rubber composition for sealing, which has excellent wear resistance and is used in fluid pressure equipment, particularly in hydraulic equipment for automobiles.

(Prior Art) Conventionally, for example, acrylonitrile butadiene rubber (NB
R) is used, but rubber having excellent heat resistance is being demanded due to an increase in operating environment temperature due to exhaust gas regulations and the like. To meet this demand, some synthetic rubbers with excellent heat resistance such as acrylic rubber and fluorine rubber are used, but these rubbers do not always have sufficient performance in terms of cold resistance, compression set, and wear resistance. Not obtained.

On the other hand, a highly saturated nitrile rubber has a performance close to that of a conventional NBR and excellent heat resistance, but a rubber composition for sealing,
In particular, it is not always satisfactory in terms of cold resistance and compression set as a seal for a hydraulic system for automobiles.

(Problems to be Solved by the Invention) By the way, hydraulic systems for automobiles are typically used for brakes and power steerings, and are safety parts related to the operation of those systems. There is a serious relationship with sex. Due to today's safety standards, automotive hydraulics generally must be operable in the temperature range of -30 to + 150 ° C. In particular, the low temperature limit differs depending on the destination, and special specifications below -30 ° C must be considered for extremely cold regions. Therefore, the most necessary properties as a rubber for sealing a hydraulic system used at such a high temperature and a low temperature are that stress relaxation is not performed over the entire operating temperature range and that rubber elasticity is not lost at a low temperature.

It is an object of the present invention to provide a rubber composition for sealing which has improved stress relaxation resistance and cold resistance of a highly saturated nitrile rubber which is said to have excellent oil resistance.

(Means for Solving Problems) Therefore, the present inventor has noticed that rubber elasticity at low temperature is realized by preventing vitrification and crystallization of the rubber, and there is a high saturated nitrile rubber. Blending rubbers composed of different hydrocarbons increases the crosslink density, lowers the crystallization rate at low temperatures, and increases the crosslink rate, thus eliminating the need for secondary crosslinks after product molding and plasticizing. The inventors have completed the present invention, knowing that it is possible to prevent scattering of agents and the like and improve flexibility at low temperatures.

Therefore, the gist of the present invention is that 50 to 99 parts by weight of the highly saturated nitrile rubber is a rubber which is hard to be compatible with the highly saturated nitrile rubber and which is composed of a hydrocarbon and is ethylene-propylene copolymerized. Improved resistance to cold, consisting of a mixture of 1 to 50 parts by weight of at least one rubber selected from the group consisting of rubber, ethylene-propylene-non-conjugated diene terpolymer, natural rubber, isoprene rubber and butyl rubber. A rubber composition for sealing.

As described above, according to the present invention, it is difficult to be compatible with the highly saturated nitrile rubber, and the rubber composed of the above-mentioned hydrocarbons is blended, so that a heterogeneous state is caused, which prevents crystallization at a low temperature. A rubber composition for sealing having improved flexibility at low temperature can be obtained.

According to one embodiment of the present invention, the highly saturated nitrile rubber is 50 to 99 parts by weight, preferably 70 to 95 parts by weight, and 1 to 50 parts by weight of a rubber composed of the above hydrocarbons, preferably 5 parts by weight. It is obtained by mixing a mixture with up to 30 parts by weight of peroxide and a crosslinking aid and vulcanizing it, and has excellent heat resistance, cold resistance, compression set, oil resistance, and abrasion resistance, especially for automobiles. -30 to + as sealing material for various hydraulic devices including
It is a rubber composition for sealing that can be used in a wide range of 150 ° C. and has performance exceeding that of conventional NBR.

It is said that the highly saturated nitrile rubber shows almost no compatibility with the rubber composed of the above-mentioned hydrocarbons, and it has been unexpectedly expected that even those skilled in the art would mix these in the past. is there. However, according to the present invention, the exact mechanism is unknown, but rather it does not exhibit compatibility, so that it is possible to appropriately set the dispersed state, and thereby it is possible to maintain that state unexpectedly and stably. It is thought that it effectively works to maintain elasticity at low temperatures.

(Function) The highly saturated nitrile rubber used in the rubber composition for sealing according to the present invention has a double bond portion of the butadiene unit of NBR in an amount of about 20%.
It is 80-100% hydrogenated, and commercially available products include Zetpol (trade name) of Nippon Zeon Co., Ltd.

The rubber composed of the hydrocarbon used in the rubber composition for sealing of the present invention includes cold resistance (elasticity at low temperature),
Excellent compression set characteristics such as ethylene-propylene copolymer rubber (EPM), ethylene-propylene-non-conjugated diene terpolymer rubber (EPDM), natural rubber (NR), isoprene rubber (IR), butyl rubber (IIR ) And the like.

Although various peroxides can be used for vulcanization, for example, 1,3 bis- (t-butylperoxy-isopropyl) benzene is the most preferable for obtaining a low compression set, and it is preferable to use 100 parts by weight of the rubber mixture. Add 1 to 15 parts by weight. In that case, if the compounding amount is less than 1 part by weight, the vulcanization will not be sufficiently carried out, and if it exceeds 15 parts by weight, the flexibility as a rubber will be insufficient and not practical.

More preferably, the mixture together with the aforementioned peroxide in the mixture as a crosslinking aid, trimethylolpropane trimethacrylate (TMPTMA), ethylene dimethacrylate (EDMA),
By adding 0.01 to 15 parts by weight of triallyl isocyanurate (TAIC) and the like to 100 parts by weight of the rubber mixture, a vulcanized product having excellent compression set and abrasion resistance can be obtained. In that case, if the cross-linking aid is blended in an amount of more than 15 parts by weight, the scorch progresses rapidly, and it becomes difficult to store the unvulcanized blend.

In the rubber composition for sealing of the present invention, as a reinforcing agent, carbon black may be used in an amount of 10 to 150 parts by weight based on 100 parts by weight of the rubber mixture, and further, a reinforcing fiber such as carbon fiber or glass fiber may be used in an amount of 0.01 to 5 parts by weight. They can be used in combination in parts by weight, and if necessary, in addition to the above-mentioned compounding agents, antiaging agents, plasticizers, lubricants and the like may be further compounded.

The conditions of vulcanization are not particularly limited, but it is carried out, for example, at 180 ° C. for about 5 to 20 minutes.

(Examples) Next, the present invention will be described using examples and comparative examples.

Table 1 shows that a rubber composition for sealing, which is a mixture of various rubbers composed of a highly saturated nitrile rubber and a hydrocarbon according to the present invention, contains carbon black as a reinforcing agent, an antiaging agent, and a plasticizer. Examples 1 and 2 in which an oxide and further a crosslinking aid are added and the material test results of these examples are shown.

For comparison with these Examples, Table 1 shows a typical NBR (33% by weight of nitrile), which generally has oil resistance and heat resistance, as Comparative Example 1, and a highly saturated nitrile rubber as a reinforcing agent. As Comparative Examples 2 and 3 in which carbon black, an antioxidant and a plasticizer were mixed and vulcanized only with peroxide, the material test results of these Comparative Examples are shown.

The material test was conducted by preparing rubber compositions having the compounding components and compounding amounts (parts by weight, phr) of the examples and comparative examples shown in Table 1, and the rubber compositions of Examples 1 and 2 at 180 ° C. for 10 minutes. The rubber composition of Comparative Example 1 was vulcanized at 160 ° C. for 10 minutes, and the rubber compositions of Comparative Examples 2 to 3 were vulcanized at 180 ° C. for 10 minutes.

As can be seen by comparing the examples and the comparative examples in Table 1, according to the present invention, the following effects are recognized.

(1) Comparing compression set as an index of stress relaxation resistance, the example is smaller. In other words, there is little "fatigue".

(2) Comparing the TR50 / 10 value (° C) as an index of cold resistance, the example is lower. That is, according to the present invention, rubber elasticity is maintained up to a low temperature of -29 ° C.

Note) TR means Temperature Retraction, and TR50 / 10 means that the length of the stretched rubber test piece is 50% stretched at room temperature and frozen (vitrification) at low temperature. The temperature at which it shrinks by 10% (becomes 45% elongation).

(3) The results of the oil resistance test are within a practically sufficiently acceptable range for both Comparative Examples and Examples, and it can be said that equivalent effects can be obtained in that range. In particular, it can be said that the same effect can be obtained in the case of ATF dexylone II used as a lubricating oil for PS. It can be said that this effect was unexpected because it was obtained by blending non-oil resistant BR.

(Effects of the Invention) As described in detail above, according to the present invention, a rubber from a hydrocarbon and a highly saturated nitrile rubber, which are not compatible with each other and were not considered to be used in combination with each other, are rather mixed. As a result, it can be seen that sufficient rubber elasticity can be obtained even at a low temperature of about -30 ° C. In particular, the effect of having both the oil resistance and the cold resistance, which are contradictory properties, to a practically acceptable level is remarkable.

Claims (1)

[Claims] 1. A rubber composed of a hydrocarbon, which is hard to be compatible with 50 to 99 parts by weight of a highly saturated nitrile rubber, and is highly compatible with the highly saturated nitrile rubber, which is an ethylene-propylene copolymer rubber,
Ethylene-propylene-non-conjugated diene terpolymer rubber,
A sealing rubber composition having improved cold resistance, which comprises a mixture containing 1 to 50 parts by weight of at least one rubber selected from the group consisting of natural rubber, isoprene rubber and butyl rubber.