JPH0344580B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a rubber composition for a rubber cup for a brake cylinder that has excellent durability. Prior Art Conventional rubber cup compositions include natural rubber (NR), styrene-butadiene rubber (SBR), and in some cases ethylene-propylene-nonconjugated diene terpolymer rubber (EPDM). Although these rubbers have sufficient performance, in recent years,
There is a growing demand for rubber cups that have higher heat resistance than conventional rubber cups, specifically, that have less tendency to sag at high temperatures. Therefore, it is necessary to use EPDM material with high heat resistance as the rubber cup material, but conventional
1,1-bis(t-
Peroxides with relatively short half-lives, such as (butylperoxy) 3,3,5-trimethylcyclohexane and dicumyl peroxide, have been used. Regarding this point, as a result of numerous studies by the present inventors, it was found that when such a peroxide with a short half-life is used, the crosslinking efficiency is low and the stiffness is insufficient. DISCLOSURE OF THE INVENTION The present invention focuses on the above-mentioned problems, and uses a peroxide whose half-life of 1 minute is 175 to 200°C to produce ethylene-propylene copolymer rubber or ethylene-propylene-nonconjugated rubber. A rubber composition for a rubber cup for a brake cylinder that is efficiently crosslinked by crosslinking diene ternary copolymer rubber with or without an appropriate crosslinking aid, and has improved practical durability as a rubber cup with excellent stiffness. It is something that provides something. Carbon black, which is the main component of the rubber composition of the rubber cup for brake cylinders of the present invention, is preferably mixed in an amount of 15 to 70 parts by weight with respect to 100 parts by weight of the above copolymer rubber. If it exceeds 70 parts by weight, the rubber hardness becomes too large to be used as a rubber cup. Further, carbon black preferably has a high reinforcing property, that is, a particle size of 50 mμ or less, and a particle size larger than this is not preferable from the viewpoint of durability, as the reinforcing property becomes low and it becomes easily worn. The peroxide, which is another component of the rubber composition of the present invention, must have a half-life of 1 minute at a temperature of 175 to 200°C, and below 175°C, it has poor stiffness at the same crosslink density ratio. undesirable and
At 200°C or higher, the vulcanization temperature during rubber crosslinking (usually referred to as vulcanization press) is too high to be practical. The peroxides that can be used in the present invention include, for example, di-t-butylperoxy-diisopropylbenzene (trade name "Peroximon F"),
(manufactured by NOF Corporation) (temperature to obtain a half-life of 1 minute: 175
°C), 2,5-dimethyl-2,5-di-(t-butyl)peroxyhexane (trade name:
25B”, manufactured by NOF Corporation) (179℃) and 2,5-
Dimethyl-2,5-(t-butyl)peroxyhexine (trade name "Perhexine 25B", NOF Corporation)
(193°C), and mixtures thereof. Furthermore, in addition to the above-mentioned constituent components of the rubber composition of the present invention, crosslinking aids such as sulfur, dipentamethylene thiuram, ethylene dimethacrylate, dicyclohexyl phthalate, etc. are added to 100 parts of the copolymer rubber to effectively crosslink the rubber. It can be used in a proportion of 0.01 to 5.0 parts by weight. The crosslinking conditions for obtaining the rubber composition of the present invention are as follows:
The vulcanization temperature is preferably in the range of approximately 140 to 220°C; outside this range, crosslinking of EPDM will not proceed.
If the temperature exceeds this level, the decomposition of EPDM will proceed, which is not preferable.
Further, the vulcanization time is preferably about 1 to 120 minutes.
If the vulcanization time is less than 1 minute, crosslinking will not proceed;
If the temperature exceeds 10 minutes, heat aging will occur, making it undesirable as a rubber. The rubber composition of the present invention produced as described above has a network chain concentration in the range of 5 x 10 ^-5 to 9 x 10 ^-4 mol/cc as measured using the method for measuring network chain concentration shown by the following formula. It has concentration. If the network chain concentration is below this lower limit, it will lack setting properties and cannot be used as a rubber cup, and if it is above the upper limit, it will lack chipping resistance and breaking strength. Network chain concentration = -g/α [l _o (1-V _R ) + V _R + μV ² / _R / g ² / ₃
V ¹ / ₃ - ^{V R} / ₂ ] g = (W ₃ - W ₁ ') / (W ₀ - W ₁ ) V _R = (W ₃ - W ₁ ) / (W ₂ - W ₁ ) W ₀ : Rubber initial weight (g) W ₁ : Weight of the rubber in water (g) W ₂ : Weight of the rubber when the rubber is immersed in benzene at 40°C and swelling reaches equilibrium (g) W ₁ ′: The above-mentioned swollen rubber Weight in water (g) W ₃ : Rubber weight after completely removing benzene from the above swollen rubber (g) α : Molecular volume of benzene (cm ³ /mol) μ : Solvent-rubber interaction coefficient Next, The present invention will be described in detail with reference to examples. Test Example Sample preparation was performed as follows. First, the gap between the rolls is set to 0.3 to 0.8 mm, and the copolymer rubber (EPM or EPDM) is thinly passed through the roll at a roll temperature of 50°C.Then, the gap is widened to 2 to 4 mm, and the copolymer rubber is wrapped around the roll. Added fillers such as Next, carbon black was added little by little, and when the addition was completed, the carbon black was cut back. A crosslinking aid (for example, sulfur) was then added, and finally peroxide was added to complete the kneading to obtain a rubber composition of the present invention and a comparative rubber composition for comparative purposes. In each sample preparation described above, various rubber composition samples were made based on the following basic formulations: EPDM copolymer rubber 100 (parts by weight) EAF carbon black 45 Zinc white 5 Stearic acid 1 Peroxide 7 As the above peroxide Various peroxides shown in Table 1 below were used.

[Table] First, the crosslinking efficiency of each sample with the above basic formulation was calculated using the following formula, and the results are shown in Figure 1: Crosslinking efficiency = V _e /P _p V _e : Network chain density of EPDM after crosslinking (Calculated from the benzene swelling ratio) P _p : Number of moles of peroxide used Figure 1 shows the temperature (℃) required to obtain a half-life of peroxide of 1 minute on the horizontal axis and the peroxide on the vertical axis. of things
The crosslinking efficiency for EPDM was plotted. From this figure 1, the longer the half-life of the peroxide, the more EPDM
It is clear that the crosslinking efficiency is high. From this fact, in the present invention, EPM or EPDM can be efficiently crosslinked by using a peroxide with a long half-life, that is, a peroxide whose temperature required to obtain a half-life of 1 minute is 175°C or higher. I know what I can do. Furthermore, compression set (CS) was measured using the same sample, and the results are shown in FIG. In FIG. 2, the network chain concentration is plotted on the horizontal axis and the compression set (measured based on JIS K6301: heated and compressed at 70° C. for 22 hours) is plotted on the vertical axis. As is clear from Figure 2, there is a good correlation between the network chain concentration of EPDM and CS. This shows that there is a significant difference in the above relationship between EPDM cross-linked using a peroxide with a long decomposition half-life and EPDM cross-linked using a peroxide with a short decomposition half-life. In other words, EPDM cross-linked using a peroxide with a long decomposition half-life in the present invention has a lower cross-linking rate and excellent stiffness than when cross-linked with a peroxide with a short half-life shown for comparison purposes. It can be seen that a rubber composition is obtained. Furthermore, using the same sample, the tensile strength (Kg/
cm ² ) and the results are shown in FIG.
In Figure 3, the horizontal axis is the EPDM network chain concentration (mol/cc).
And the tensile strength (Kg/cm ² ) was plotted on the vertical axis. From FIG. 3, it can be seen that EPDM crosslinked using a peroxide with a long decomposition half-life in the present invention has a greater tensile strength than one with a short half-life. Summarizing the above test results, it can be seen that in the present invention, EPDM crosslinked using a dialkyl peroxide whose temperature for obtaining a decomposition half-life of 1 minute is in the range of 175 to 200 °C has the following advantages: (1 ) The crosslinking efficiency is high, so sufficient crosslinking points can be created with a small amount of peroxide, which reduces costs. (2) Low network chain concentration (low crosslinking density) and low stiffness. (3) A rubber composition with high breakability can be obtained; and (4) A rubber composition with a better balance of physical properties than in (2) and (3) above can be obtained. Examples In this example, various rubber compositions of unvulcanized rubber were prepared as described in the test examples using the compounds and amounts shown in Tables 2 and 3, and these rubber compositions were heated at 170°C. Press vulcanization was carried out for 40 minutes to produce test pieces and rubber cups for the purpose of the present invention, as well as comparative test pieces and rubber cups for comparative purposes. The physical properties of the formed rubber cups of the present invention and comparative rubber cups were measured, and an operational durability test was conducted.The results of these tests are shown in the lower rows of Tables 2 and 3.

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[Table] In Tables 2 and 3, Comparative Examples 1 to 4 are comparative examples of comparative rubber cups made from EPDM rubber compositions using peroxides with short decomposition half-lives. None of the rubber cups had a very high crosslinking density and had poor stiffness (CS value reference).
Furthermore, Comparative Examples 4 and 5 are rubber cups made from compositions containing a large amount of "Percyl D" as a peroxide, and although these comparative rubber cups have improved stiffness, they are inferior in breaking material and have scratches on the rubber cups. It was confirmed that the rubber cup sticks easily and causes cracks (the "clunk" described here refers to the phenomenon in which a rubber cup gets stuck between the cylinder and the piston and is torn off). On the other hand, the rubber cup made using peroximone F, a peroxide used in the present invention in the test example, was acceptable for use in brake cylinders with some scratches.
The rubber cups made using the peroxides ``Perhexa 25B'' and ``Perhexin 25B'' of No. 7 have sufficient crosslinking density, excellent stiffness, and good breaking performance, with almost no scratches. It turns out that there isn't. In Table 3, Examples 8 to 13 show test results for rubber cups made from rubber compositions made by crosslinking EPDM by adding a crosslinking aid to the peroxide of the present invention. When sulfur or the product name ``TRA'' (dipentamethylene lentithurum) is added as a crosslinking agent, it becomes a rubber cup with excellent breakability, which helps the product name ``DCHP'' (dicyclohexyl phthalate) and the product name ``EDMA'' (ethylene dimethacrylate). It can be seen that when used as an agent, a rubber cup with excellent stiffness can be obtained. Comparative Example 5 in Table 3 shows the rubber physical properties of a rubber cup manufactured using styrene-butadiene copolymer rubber (SBR) as the raw polymer and data obtained from a cup operation durability test. The EPDM rubber cup of the present invention is improved over the SBR rubber cup in all of the characteristics required for a rubber cup, such as low settability, abrasion resistance, and high breakage.
It can be seen that the rubber cup according to the present invention is superior. Effects of the Invention In the present invention, a peroxide having a half-life of 1 minute within the range of 175 to 200°C is used as a crosslinking agent for ethylene-propylene copolymer rubber or ethylene-propylene non-conjugated diene terpolymer rubber. By developing a new rubber composition for a rubber cup for brake cylinders, which uses NR, SBR, and other rubber materials, and further contains appropriate inorganic fillers and crosslinking aids as necessary, we have developed a new rubber composition for rubber cups for brake cylinders. We were able to produce a well-balanced rubber cup that has superior settling properties and breakability compared to the rubber cup produced from the above. Furthermore, since the peroxide used in the present invention has a high crosslinking efficiency, sufficient crosslinking points can be formed with a small amount of peroxide, and an excellent rubber cup at low cost can be produced with reduced costs.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the half-life temperature and crosslinking efficiency of EPDM made with various peroxides used in the present invention and for comparison purposes, and Figure 2 is the network of EPDM made with various peroxides used in the present invention and for comparison purposes. Graph showing the relationship between chain concentration and CS, and the third
The figure is a graph showing the relationship between the network chain concentration and tensile strength of EPDM made of various peroxides shown in FIG. 2.

Claims (1)

[Claims] 1 Ethylene/propylene copolymer rubber or ethylene/propylene/nonconjugated diene ternary copolymer rubber
0.1 to 5.0 parts by weight of a peroxide having a half-life of 1 minute at a temperature of 175 to 200°C, in a rubber composition containing 100 parts by weight and 15 to 70 parts by weight of carbon black;
Or a rubber composition for a rubber cup for a brake cylinder, characterized in that it is vulcanized with the peroxide and 0.01 to 5.0 parts by weight of a crosslinking aid.