JP2753679B2 - Manufacturing method of heat resistant rubber products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-resistant rubber product which is excellent in heat resistance and has a small compression set and is suitable as a heat exchanger and other sealing materials used at high temperatures.

[0002]

2. Description of the Related Art For example, a rubber sealing material used in a heat exchanger is required to have a small compression set, excellent heat resistance, and good sealing properties. However, since the conventional rubber composition has a large compression set and insufficient heat resistance, the rubber seal material undergoes permanent set during use, causing so-called settling, fluid leakage, and prolonged use at high temperatures. Due to exposure to time, compression cracking occurred and could not withstand long-term use. For this reason, it is necessary to design the compression ratio of the packing to be low or to lower the operating temperature, and it has not been possible to satisfy the market requirements.

[0003] As a means for improving the heat resistance of rubber, it is common to employ peroxide crosslinking instead of sulfur vulcanization. However, peroxide crosslinking reduces the rubber strength required for sealing materials. There is a drawback to make it. Further, the peroxide crosslinking agent is likely to remain in the rubber after the primary vulcanization, and when this peroxide crosslinking agent remains in the rubber, the residual peroxide is gradually decomposed in a high temperature atmosphere during use. Since the cross-linking proceeds, there are drawbacks such as settling of the sealing material, an extremely low strength, and eventually breaking. Further, there was a problem that the rubber composition obtained by peroxide crosslinking had an odor.

It is known that an antioxidant is added as a means for preventing cross-linking occurring during use, ie, a reduction in strength due to secondary vulcanization, and improving heat resistance during use. The effect obtained with the agent was not sufficient. As a means for preventing curing by heat, there is a means for reducing the volatile content by stopping the blending of a softener or a plasticizer which is usually added to rubber, but a sufficient effect was not obtained. As a means for reducing the compression set, it is known to increase the amount of a peroxide crosslinking agent.
In this case, the odor increases, and the heat resistance deteriorates due to the increase in the residual peroxide.

[0005]

The present invention does not cause compression cracking even when subjected to long-term compression at a high temperature, has a small compression set, sufficiently satisfies the function as a sealing material, and has an odor. It is intended to provide a method for producing a rubber product which does not generate any rubber.

[0006]

SUMMARY OF THE INVENTION The present invention provides an ethylene
4,4- (α, α-dimethylbenzyl) diphenylamine and 2-mercaptobenzimidazole or a zinc salt of 2-mercaptobenzimidazole in a mixing ratio of 1: 1 to 0.05: 1 with 100 parts by weight of propylene rubber. 0.1 to 6 parts by weight of the antioxidant, 0.5 to 10 parts by weight of the crosslinking assistant, 0.01 parts by weight of the peroxide crosslinking agent
０．０５0.05 mol and a reinforcing agent such as carbon black and the like are added, kneaded, and subjected to primary vulcanization by a conventional method to a rubber composition formed into a desired shape.
A method for producing a heat-resistant rubber product, comprising performing secondary vulcanization at 30C for 30 minutes to 6 hours.

In the present invention, ethylene-propylene rubber having basically good heat resistance is used as the rubber. However, the ethylene-propylene rubber referred to in the present invention includes ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene terpolymer rubber (EPDM) and E
It contains a mixed rubber in which PM and EPDM are mixed at an arbitrary ratio.

As antiaging agents, 4,4- (α, α-
Mixtures of (dimethylbenzyl) diphenylamine with 2-mercaptobenzimidazole or the zinc salt of 2-mercaptobenzimidazole are used. The mixing ratio (weight ratio) of the former and the latter is set in the range of 1/1 to 0.05 / 1, and a total of 0.1 to 6 parts by weight of both is added to the rubber. The former is too large and the mixing ratio is 1
If it exceeds / 1, the compression set becomes large, and if it is too small and the mixing ratio becomes less than 0.05 / 1, sufficient heat aging resistance cannot be obtained. Further, the amount added to the rubber is 0.1.
If the amount is less than 1 part by weight, the desired effect cannot be obtained,
On the other hand, if it exceeds 6 parts by weight, bloom is generated.

[0009] As crosslinking aids, N, N-m-phenylenedimaleimide, triallyl isocyanate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, polyfunctionality generally used in peroxide crosslinking are used. Methacrylate monomers and the like can be used. The addition amount is 0.5 to 10 parts by weight. When the addition amount is less than 0.5 part by weight, heat resistance is reduced, the compression set becomes large, and when it exceeds 10 parts by weight, However, depending on the intended function, the amount is small when the amount of the crosslinking agent is large, and is large when the amount of the crosslinking agent is small.

As the peroxide crosslinking agent, 1,1-di-t is used.
-Butylperoxy-3,3,5-trimethylcyclohexane, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5
-Dimethyl-2,5-di (t-butylperoxy) hexane, 1,3 bis (t-butylperoxyisopropyl) benzene and the like can be used. The amount added is 0.
When the amount is less than 0.01 mol, the compression set becomes large. On the other hand, when the amount exceeds 0.05 mol, the composition becomes hard, the elongation is reduced, and the material is easily cracked.

In addition, compounding chemicals commonly used in the rubber industry, such as reinforcing agents such as carbon black, zinc oxide, softeners, plasticizers, tackifiers, and white fillers, may be appropriately added or omitted. can do.

In the present invention, the above rubber, antioxidant, crosslinking aid, peroxide crosslinking agent, carbon black, etc. are kneaded in a conventional manner, molded into a desired shape, and subjected to primary vulcanization. After application, it is necessary to perform secondary vulcanization. The conditions of the secondary vulcanization are set in the range of 150 to 200 ° C. for 30 minutes to 6 hours depending on the shape and thickness of the product. If the temperature of the secondary vulcanization is less than 150 ° C., or if the vulcanization time is less than 30 minutes, bloom tends to occur and the compression set becomes large,
On the other hand, when the vulcanization temperature exceeds 200 ° C. or the vulcanization time exceeds 6 hours, heat aging proceeds and the deterioration of physical properties becomes excessive. In particular, when the vulcanization temperature is low, the decomposition of the residual peroxide is delayed, and it takes a long time to volatilize the decomposition products.

[0013]

According to the present invention, an ethylene / propylene rubber having excellent heat resistance is used, and a larger amount of a peroxide crosslinking agent and the like are added together with a crosslinking aid than before, and 4,4- (Α, α-dimethylbenzyl) diphenylamine and 2-mercaptobenzimidazole or 2-
Since a mixture with a zinc salt of meltcaptobenzimidazole is added, the heat resistance can be improved and the compression set can be reduced without lowering the strength of the product made of ethylene / propylene rubber. And the temperature 15
Since the secondary vulcanization is carried out at 0 to 200 ° C. for 30 minutes to 6 hours, the residual peroxide disappears, no odor is generated, the physical properties after aging of the product are improved, and the compression set is further reduced. can do. The compression set can be further reduced by adding zinc oxide.

[0014]

Example: EPDM as ethylene / propylene rubber
(Mitsubishi Petrochemical Co., Ltd., trade name "EPT3045")
, Zinc oxide as an auxiliary agent, nickel diethyldithiocarbamate (trade name “Nocrack NBC”, manufactured by Ouchi Shinko Chemical Co., Ltd.) as an antioxidant, 2-mercaptobenzimidazole (Ouchi Shinko Chemical Industry Co., Ltd.) (Trade name "Nocrack MB"), zinc salt of 2-mercaptobenzimidazole (trade name "Nocrack MBZ" manufactured by Ouchi Shinko Chemical Co., Ltd.) and 4,4- (α, α-dimethylbenzyl) diphenylamine ( Ouchi Shinko Kagaku Kogyo Co., Ltd., trade name "Nocrack CD"), calcium stearate as an internal mold release agent, and carbon black (Tokai Carbon Co., Ltd., trade name "Seast 3") as a filler. Triallyl isocyanate (manufactured by Nippon Kasei Co., Ltd., trade name "Tyke") as the oiling agent and paraffinic oil as the oiling agent Process oil (manufactured by Idemitsu Kosan Co., Ltd., trade name "PW-380") is used as a peroxide crosslinking agent, 1,3-bis (tert-butylperoxyisopropyl)
Using benzene, trade name “Parcadox 14/40”), kneading with the composition shown in Table 1 below (unit: parts by weight) to form a sheet having a thickness of 2 mm, followed by primary vulcanization and secondary vulcanization Samples of Examples 1 to 3 and Comparative Examples 1 to 4 were obtained by performing sulfuration. In Table 1, "Percadox 14/40" of the peroxide crosslinking agent is a 40% mixed powder of 1,3-bis (tert-butylperoxyisopropyl) benzene, and 1,3-bis (third Since the molecular weight of butylperoxyisopropyl) benzene is 338.49, the compounding ratio of 4 parts by weight and 10 parts by weight of
It corresponds to 05 mol and 0.012 mol.

Table 1 Comparative Example Example 1 2 3 4 1 2 3 EPDM 100 100 100 100 100 100 100 Zinc oxide 0 0 0 10 10 10 10 Nocrack NBC 1.5 1.5 1.5 0 0 0 0 Nocrack MB 0 0 0 2 2 2 0 Nocrack MBZ 0 0 0 0 0 0 2 Nocrack CD 0 0 0 0.5 0.5 0.5 0.5 Calcium stearate 1 1 1 1 1 1 1 Carbon black 60 60 60 50 50 50 50 Crosslinking aid 0 0 0 3 3 3 3 Process oil 5 5 5 0 0 0 0 Peroxide crosslinker 4 4 4 10 10 10 10 Total 171.5 171.5 171.5 176.5 176.5 176.5 176.5

For these samples, JIS-K-63
The initial physical properties were measured according to No. 01. Next, the sample was left in an atmosphere at a temperature of 180 ° C. for 96 hours, and the physical properties after aging were measured in the same manner. The results are shown in Tables 2 and 3 below. Further, the above Examples 1 to 3 and Comparative Example 1
29mm diameter, 12.7mm height with rubber compound of ~ 4
, And then subjected to primary vulcanization and secondary vulcanization, and then to a compression set (temperature 180 ° C., standing time 72 hours, compression ratio 25) according to JIS-K-6301.
%) Was measured. The results are shown in Tables 2 and 3. However, the vulcanization conditions are as follows: primary vulcanization only 170 ° C x 3
Changed to 0 minutes.

Table 2 Comparative Example 1 2 3 4 Primary vulcanization (° C × min) 170 ° C × 25 minutes 〃 〃 次 Secondary vulcanization (° C × H) None 130 ° C × 5H 180 ° C × 5H None Initial physical properties Tensile strength Sa (kgf / cm ² ) 170 167 90 161 Elongation at break (%) 250 210 170 230 Tensile product 42500 35070 15300 37030 Odor Yes Yes No Yes Physical properties after aging (180 ℃ × 96H) Tensile strength (kgf / cm ² ) 30 50 35 168 Elongation at break (%) 50 80 50 110 Tensile product 1500 4000 1750 18480 Rate of change of tensile product (%) -96.4 -88.5 -88.5 -50.0 Compression set (%) 35.6 30.3 22.7 17.3

Table 3 Example 1 2 3 Primary vulcanization (° C × min) 170 ° C × 25 minutes 〃 〃 Secondary vulcanization (° C × H) 180 ° C × 5H 180 ° C × 8H 180 ° C × 5H Initial physical properties Tensile strength Sa (kgf / cm ² ) 170 180 172 Elongation at break (%) 130 110 130 Tensile product 22100 19800 22360 Odor None None None Physical properties after aging (180 ℃ × 96H) Tensile strength (kgf / cm ² ) 175 183 175 Elongation (%) 130 110 130 Tensile product 22750 20130 22750 Rate of change of tensile product (%) + 2.9 + 1.6 + 1.7 Compression set (%) 12.5 11.2 12.8

As is apparent from the above Tables 1 to 3, all of Examples 1 to 3 have no odor, have good physical properties after aging, and have a small compression set. . On the other hand, in Comparative Example 1 in which the secondary vulcanization was omitted in the conventional formulation, the decrease in strength due to aging was remarkably large, and the compression set was too large to be practical. In Comparative Example 2 in which the temperature of the secondary vulcanization was set lower and the time was set shorter in the conventional formulation, the physical properties after aging are slightly improved compared to Comparative Example 1 by performing the secondary vulcanization. However, the temperature is low and the time is short, so that this is not practical. Also,
Comparative Example 3 in which the time of secondary vulcanization was set shorter with the conventional formulation
The antiaging agent is unsuitable, so that aging proceeds by secondary vulcanization, physical properties are low, and the compression set is large because the amount of the peroxide crosslinking agent is small. In Comparative Example 4, which had the same composition as that of the example but omitted the secondary vulcanization, the peroxide crosslinking agent remained, so that the physical properties after aging were low, the compression set was large, and the odor was present.

[0020]

As described above, the present invention relates to 100 parts by weight of ethylene-propylene rubber,
(Α, α-dimethylbenzyl) diphenylamine and 2-
Mercaptobenzimidazole or zinc salt of 2-mercaptobenzimidazole with 1: 1 to 0.05:
Antioxidants mixed in a mixing ratio of 1 to a total of 0.1 to 6
Parts by weight, a crosslinking aid of 0.5 to 10 parts by weight, a peroxide crosslinking agent of 0.01 to 0.05 mol and a reinforcing agent such as carbon black and the like are added, kneaded and molded into a desired shape. After primary vulcanization of the resulting rubber composition in a conventional manner,
Since it is a method for producing a heat-resistant rubber product characterized by performing a secondary vulcanization at 50 to 200 ° C. for 30 minutes to 6 hours,
Without reducing the strength of the product, it can improve its heat resistance, reduce compression set, and eliminate residual peroxide to eliminate odor and improve the physical properties of the product after aging. Can be. The compression set can be further reduced by adding zinc oxide as described in the examples.

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein 100 parts by weight of ethylene / propylene rubber are mixed with 4,4- (α, α-dimethylbenzyl) diphenylamine and 2-mercaptobenzimidazole or 2-mercaptobenzimidazole.
1: 1 with zinc salt of meltcaptobenzimidazole
0.1 to 6 parts by weight of the antioxidant obtained by mixing at a mixing ratio of ~ 0.05: 1, 0.5 to 10 parts by weight of the crosslinking aid,
A peroxide crosslinking agent was added in an amount of 0.01 to 0.05 mol and a reinforcing agent such as carbon black and the like, kneaded, and subjected to primary vulcanization by a conventional method to a rubber composition formed into a desired shape. Thereafter, a secondary vulcanization is performed at a temperature of 150 to 200 ° C. for 30 minutes to 6 hours, thereby producing a heat-resistant rubber product.