Rubber composition for dust cover boots

This invention relates to a rubber composition for dust cover boots which comprises an epichlorohydrin/propylene oxide copolymer rubber as a main component and has overall excellent properties.
Among existing oil-resistant rubbers, chloroprene rubber (to be sometimes referred to as CR) is an excellent synthetic rubber having balanced properties, and finds widespread uses in hose covers, dust cover boots and belts of automobiles. CR has been used particularly in dust cover boots (to be sometimes referred to simply as boots) for ball joints used in the power transmission system of automobiles, which require many properties such as grease (oil) resistance, heat resistance, cold resistance, water resistance, weatherability, ozone resistance and bending resistance. As engines have been improved to meet the regulations of motor exhaust gases which came into enforcement in order to control atmospheric pollution, the dust cover boots have been required to have higher heat resistance than before. CR, however, cannot possibly meet the new requirement for higher heat resistance. In particular, since CR undergoes heat hardening-induced degradation, it cannot withstand use for a long period of time, and this may involve a danger of leading to a serious accident. Furthermore, since CR has a crystalline structure, it is regarded as unsuitable for use in districts of cold climate, and it is further suspected of having unsatisfactory dynamic ozone resistance.
On the other hand, an epichlorohydrin/ethylene oxide copolymer rubber (to be referred to as CHC) has better heat resistance, grease (oil) resistance, cold resistance and dynamic ozone resistance than CR, but poor bending resistance, and is unsuitable as a material for boots. No rubber material has been developed which can satisfy the various properties required of recent boot materials.
It is an object of this invention to provide a rubber composition for dust cover boots which retains grease (oil) resistance and bending resistance equivalent to CR and has improved heat resistance, cold resistance and dynamic ozone resistance over CR.
This object of the invention is achieved by a rubber composition for dust cover boots comprising a copolymer rubber composed of 10 to 60 mole% of epichlorohydrin, 30 to 90 mole% of propylene oxide or both propylene oxide and ethylene oxide with the propylene oxide/ethylene oxide mole ratio being at least 1, and 0 to 15 mole% of an unsaturated epoxide, and a vulcanization agent for the copolymer rubber.
The copolymer rubber used in this invention is obtained by copolymerizing epichlorohydrin and either propylene oxide or both propylene oxide and ethylene oxide, and as required an unsaturated epoxide.
Examples of the unsaturated epoxide include allyl glycidyl ether, glycidyl methacrylate, glycidyl acrylate and butadiene monoxide. By using the unsaturated epoxide as a comonomer, the heat softening-induced degradation and dynamic ozone resistance of the rubber vulcanizate are improved. If the amount of the unsaturated epoxide exceeds 15 mole%, the rubber vulcanizate undergoes heat hardening-induced degradation, loses rubbery elasticity, and becomes brittle. The suitable amount of propylene oxide or the total amount of propylene oxide and ethylene oxide is within the range of 30 to 90 mole% according to the cold resistance required of the boot. If this amount is less than 30 mole%, the cold resistance of the rubber vulcanizate becomes unsatisfactory. If it exceeds 90 mole%, the rubber vulcanizate has reduced grease resistance and has a large degree of swelling. The especially preferred proportions of the copolymer components are 15 to 55 mole% for epichlorohydrin, 35 to 85 mole% of propylene oxide or propylene oxide plus ethylene oxide, and 2 to 10 mole% for the unsaturated epoxide. If the mole ratio of propylene oxide to ethylene oxide is less than 1, the bending resistance of the rubber vulcanizate becomes insufficient. The Mooney viscosity [ML.sub.1+4 (100.degree. C.)] of the copolymer rubber is 10 to 100.
Typical vulcanization agents used in this invention are polythiols and thioureas normally used for CHC. When the copolymer rubber contains 1 to 15 mole% of the unsaturated epoxide as a copolymer component, sulfur and sulfur donors normally used for diene-type rubbers can also be used as the vulcanization agents.
Examples of the polythiols include di- or tri-mercapto-s-triazine compounds (described, for example, in U.S. Pat. No. 3,787,376), 2,5-dimercapto-1,3,4-thiadiazole compounds (described, for example, in U.S. Pat. No. 4,288,576), 2,3-dimercaptopyrazine compounds (described, for example, in Japanese Patent Publication No. 14468/1983), 2,3-dimercaptoquinoxaline compounds (described, for example, in Japanese Patent Publication No. 14469/1983), and 3,5-dimercapto-1,2,4-triazole compounds (described, for example, in Japanese Patent Publication No. 46463/1982). Examples of the thioureas include 2-mercaptoimidazoline (ethylenethiourea) compounds, and 2-mercaptopyrimidine compounds (described, for example, in U.S. Pat. No. 3,341,490).
Typical examples of the sulfur-donors are thiuram compounds such as morpholine disulfide, tetramethylthiuram monosulfide, tetramethyl thiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, dipentamethylenethiuram tetrasulfide, and dimethyldiphenylthiuram disulfide. Since as is well known the sulfur donor has the action of promoting sulfur vulcanization, it can of course be used together with sulfur.
The amount of the vulcanization agent is 0.1 to 10 parts by weight per 100 parts by weight of the copolymer rubber. Needless to say, two or more vulcanization agents may be used in combination.
The rubber composition of this invention is prepared by mixing the copolymer rubber composed of epichlorohydrin, propylene oxide or both propylene oxide and ethylene oxide and optionally the unsaturated epoxide with ordinary rubber compounding agents such as a vulcanizing agent, a reinforcing agent, a filler, a plasticizer and an antioxidant by an ordinary mixer such as a roll or a Banbury mixer.
By heating the rubber composition in a mold usually at 100.degree. to 250.degree. C., a rubber vulcanizate is obtained. The vulcanizate has excellent grease resistance, bending resistance, heat resistance, cold resistance and dynamic ozone resistance in a well-balanced state, and is useful as a material for a dust cover boot for automobiles.

The following examples illustrate the present invention more specifically.
EXAMPLE 1
An epichlorohydrin/propylene oxide copolymer rubber prepared by a known solution polymerization method using an organoaluminum compound-type polymerization catalyst was mixed with other compounding agents in accordance with the following compounding recipe by a cold roll, and heated at 160.degree. C. under pressure for 30 minutes to prepare a vulcanizate.
______________________________________Compounding recipe______________________________________Epichlorohydrin/propylene 100oxide copolymer rubber (parts by weight)Stearic acid 1FEF carbon black 40Red lead 52-Mercaptoimidazoline 1.2Nickel dibutyldithiocarbamate 1.5______________________________________
The properties of the vulcanizate were measured in accordance with JIS K-6301. The grease immersion test was carried out in accordance with the immersion test set forth in JIS K-6301 using MOLIREX No. 2 (a product of Kyodo Oils and Fats Co., Ltd.).
The results are given in Table 1. The results in Table 1 show that the vulcanizate of Run No. 1 (comparison) had poor cold resistance, and the vulcanizate of Run No. 6 (comparison) had poor grease resistance, and they are not suitable for dust cover boots.
TABLE 1__________________________________________________________________________ Run No. Comparison Invention ComparisonTest item 1 2 3 4 5 6__________________________________________________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin 70 50 40 30 40 8Propylene oxide 30 50 60 70 40 92Ethylene oxide -- -- -- -- 20 --Properties in a normalconditionTensile strength (kg/cm.sup.2) 130 121 115 106 126 90Elongation (%) 460 500 540 590 520 640Hardness (JIS) (point) 64 62 60 58 62 55Heat aging test in air[After 144 hours at 135.degree. C.)Tensile strength change (%) +2 -8 -17 -32 -6 -41Hardness change (point) +6 +5 +4 +1 +5 +1Grease immersion test[After 70 hours at 135.degree. C.]Volume change (%) +14 +23 +28 +36 +20 +55Hardness change (point) -6 -9 -10 -13 -7 -23Gehman T.sub.10 (.degree.C.) -27 -34 -39 -44 -40 -59__________________________________________________________________________
EXAMPLE 2
Example 1 was repeated using each of copolymer rubbers having the compositions indicated in Table 2. The dynamic ozone degradation test was carried out in an atmosphere having a temperature of 40.degree. C. and an ozone concentration of 50 ppm under dynamic conditions which gave an elongation of 0 to 30% to a test specimen, and the state of tearing was observed 200 hours later.
A chloroprene rubber composition prepared in accordance with the following compounding recipe was also tested.
______________________________________Compounding recipe______________________________________Neoprene WXJ (a product of 100Showa Neoprene Co., Ltd.) (parts by weight)Stearic acid 1FEF carbon black 40Zinc oxide 5Magnesium oxide 4Aromatic softening agent (FFlexM, 10a product of Fuji Kosan Co., Ltd.)2-Mercaptoimidazoline 0.5Octylated diphenylamine 1N--phenyl-N-- isopropyl-p-phenylenediamine 1______________________________________
The results are shown in Table 2. It is seen from the table that the chloroprene rubber vulcanizate had poor heat resistance and dynamic ozone resistance, and a vulcanizate of the epichlorohydrin homopolymer had poor cold resistance and bending resistance.
TABLE 2__________________________________________________________________________ Run No. Comparison Invention ComparisonTest item 7 8 9 10 11 12__________________________________________________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin Chloro- 40 40 50 50 100Propylene oxide prene 60 57 50 47 --Allyl glycidyl ether rubber -- 3 -- 3 --Properties in a normalconditionTensile strength (kg/cm.sup.2) 197 112 124 119 133 150Elongation (%) 350 590 590 570 560 430Hardness (JIS) (point) 65 60 60 63 59 60Heat aging test in air[After 144 hours at 135.degree. C.)Tensile strength change (%) -41 -14 -17 -2 -9 +25Elongation change (%) -86 -59 -66 -60 -68 -58Hardness change (point) +23 +4 +7 +8 +12 +7[After 72 hours at 150.degree. C.)Tensile strength change (%) -- -26 -26 -13 -21 +12Elongation change (%) -- -58 -66 -61 -68 -58Hardness change (point) +28 +3 +7 +7 +10 +10180.degree. Bending test Broken No crack occurred. Grease immersion test[After 70 hours at 135.degree. C.]Volume change (%) +38 +21 +20 +17 +16 +7Hardness change (point) -10 -8 -7 -5 -2 -1Gehman T.sub.10 (.degree.C.) -34 -39 -40 -35 -35 -21Dynamic ozone resistance testAfter 200 hours * No crackingDe Mattia bending testNumber of bendings which More than 500,000 200,000caused cracking__________________________________________________________________________ *Innumerable deep cracks, less than 1 mm, occured.
EXAMPLE 3
Each of polymer rubbers having the compositions indicated in Table 3 was tested in the same way as in Example 2 in accordance with the following compounding recipe.
______________________________________Compounding recipe______________________________________Polymer rubber 100 (parts by weight)Stearic acid 3FEF carbon black 40Magnesium oxide 3Calcium carbonate 52,4,6-Trimercapto-s-triazine 0.9Nickel dibutyldithiocarbamate 1.5Cyclohexyl thiophthalimide 1______________________________________
In Run No. 13 (comparison), 1 part by weight of cyclohexyl thiophthalimide in the above compounding recipe was replaced by 0.3 part by weight of 1,3-diphenylguanidine in order to make the vulcanization speed agree with that of the composition of the present invention.
The results are shown in Table 3. It is seen from the table that the vulcanizate of epichlorohydrin homopolymer had poor cold resistance and bending strength.
TABLE 3______________________________________ Run No. Compar- ison InventionTest item 13 14 15______________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin 100 40 50Propylene oxide -- 57 47Allyl glycidyl ether -- 3 3Properties in a normal conditionTensile strength (kg/cm.sup.2) 119 102 106Elongation (%) 450 610 560Hardness (JIS) (point) 71 61 62Heat aging test in air[After 144 hours at 135.degree. C.)Tensile strength change (%) +11 -17 -5Elongation change (%) -53 -59 -59Hardness change (point) +4 +3 +4[After 72 hours at 150.degree. C.)Tensile strength change (%) +8 -32 -18Elongation change (%) -53 -62 -63Hardness change (point) +5 +2 +3180.degree. Bending test No crack occurred. Grease immersion test[After 70 hours at 135.degree. C.]Volume change (%) +9 +21 +18Hardness change (point) 0 +2 +3Gehman T.sub.10 (.degree.C.) -20 -38 -35Dynamic ozone resistance testAfter 200 hours No crackingDe Mattia bending testNumber of bendings which 220,000 More thancaused cracking 500,000______________________________________
EXAMPLE 4
Each of copolymer rubbers having the compositions indicated in Table 4 was tested in the same way as in Example 2 in accordance with the compounding recipe shown below. Vulcanizates were prepared by heating the compositions at 170.degree. C. under pressure for 15 minutes.
______________________________________Compounding recipe (Run No. 16)Epichlorohydrin/propylene oxide/ 100allyl glycidyl ether terpolymer (parts by weight)Stearic acid 1HAF carbon black 40Zinc oxide 5Sulfur 1Tetramethylthiuram disulfide 1.5Cyclohexyl benzothiazyl sulfenamide 1.5Nickel dibutyldithiocarbamate 1.5Compounding recipe (Runs Nos. 17 and 18)Epichlorohydrin/propylene oxide/ 100allyl glycidyl ether terpolymer (parts by weight)Stearic acid 3HAF carbon black 40Magnesium oxide 32,4,6-Trimercapto-s-triazine 0.91,3-Diphenylguanidine 0.5Nickel dibutyldithiocarbamate 1.5______________________________________
The results are shown in Table 4. It is seen from the table that the polythiol-vulcanized product had better heat resistance and compression set than the sulfur-vulcanized product.
TABLE 4______________________________________ Run No. InventionTest item 16 17 18______________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin 30 30 30Propylene oxide 67 67 64Allyl glycidyl ether 3 3 6Properties in a normal conditionTensile strength (kg/cm.sup.2) 168 153 143Elongation (%) 560 770 700Hardness (JIS) (point) 65 59 61Heat aging test in air[After 72 hours at 150.degree. C.)Tensile strength change (%) -36 -38 -41Elongation change (%) -53 -58 -62Hardness change (point) +5 +1 +3[After 120 hours at 150.degree. C.)Tensile strength change (%) -69 -45 -48Elongation change (%) -64 -58 -63Hardness change (point) -4 0 +1180.degree. Bending test No crack occurred. Grease immersion test[After 70 hours at 135.degree. C.]Volume change (%) +33 +34 +33Hardness change (point) - 15 -5 -6Gehman T.sub.10 (.degree.C.) -46 -45 -45Dynamic ozone resistance testAfter 200 hours No crackingDe Mattia bending testNumber of bendings which More than 500,000caused crackingCompression set (%) after 93 58 5870 hours at 135.degree. C.______________________________________
EXAMPLE 5
Each of copolymer rubbers having the compositions indicated in Table 5 was tested in the same way as in Example 4.
A chloroprene rubber composition prepared in accordance with the following compounding recipe was also tested.
______________________________________Compounding recipe______________________________________Neoprene WXJ (given hereinabove) 100 (parts by weight)Stearic acid 1HAF carbon black 40Zinc oxide 5Magnesium oxide 4Aromatic softening agent 10(given hereinabove)2-Mercaptoimidazoline 0.5Octylated diphenylamine 1N--phenyl-N-- isopropyl-p-phenylenediamine 1______________________________________
The results are shown in Table 5. It is seen from the table that the chloroprene rubber vulcanizate had poor heat resistance, cold resistance and dynamic ozone resistance.
TABLE 5______________________________________ Run No. Compar- ison InventionTest item 19 20 21 22______________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin Chloro- 30 40 30Propylene oxide prene 66 56 66Allyl glycidyl ether rubber 4 4 --Glycidyl methacrylate -- -- 4Properties in a normal conditionTensile strength (kg/cm.sup.2) 238 154 151 134Elongation (%) 390 770 620 710Hardness (JIS) (point) 64 61 63 60Heat aging test in air[After 240 hours at 135.degree. C.)Tensile strength change (%) -- -36 -29 -37Elongation change (%) -- -61 -54 -65Hardness change (point) +31 +2 +3 +2180.degree. Bending test Broken No crack occurred. Grease immersion test[After 70 hours at 135.degree. C.]Volume change (%) +36 +36 +29 +37Hardness change (point) -11 -8 -5 - 9Gehamn T.sub.10 (.degree.C.) -32 -45 -38 -44Dynamic ozone resistance testAfter 200 hours (*) No crackingDe Mattia bending testNumber of bendings which More than 500,000caused cracking______________________________________ (*): Innumerable deep cracks, less than 1 mm, occurred.
EXAMPLE 6
An epichlorohydrin/propylene oxide/allyl glycidyl ether copolymer rubber prepared by a known solution polymerization method using an organoaluminum compound polymerization catalyst was mixed with compounding agents in accordance with the following compounding recipe by a cold roll, and heated at 160.degree. C. under pressure for 30 minutes to prepare a vulcanizate.
______________________________________Compounding recipe______________________________________Epichlrohydrin/propylene oxide/allyl 100glycidyl ether copolymer rubber (parts by weight)Stearic acid 1FEF carbon black 40Zinc oxide 5Sulfur 1Tetramethylthiuram disulfide 1.5Cyclohexyl benzothiazyl sulfenamide 1.5Nickel dibutyldithiocarbamate 1.5______________________________________
The properties of the vulcanizate were measured as described hereinabove, and the results obtained are shown in Table 6.
TABLE 6__________________________________________________________________________ Run No. Comparison Invention ComparisonTest item 23 24 25 26 27 28 29 30__________________________________________________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin -- 20 30 40 50 55 30 70Propylene oxide 97 77 67 57 47 42 40 27Ethylene oxide -- -- -- -- -- -- 27 --Allyl glycidyl ether 3 3 3 3 3 3 3 3Properties in a normalconditionTensile strength (kg/cm.sup.2) 93 110 116 127 136 140 125 142Elongation (%) 440 410 420 430 450 440 430 460Hardness (JIS) (point) 61 64 65 65 65 66 65 67Heat aging test in air[After 144 hours at 135.degree. C.)Tensile strength change (%) -6 -8 -9 -14 -20 -22 -10 -31Hardness change (point) +5 +7 +8 +9 +11 +14 +8 +16Grease immersion testVolume change (%) +56 +33 +28 +23 +18 +15 +20 +11Hardness change (point) -28 -15 -11 -5 -3 0 -4 0Gehman T.sub.10 (.degree.C.) -64 -49 -44 -38 -34 -32 -50 -26Dynamic ozone resistance test No crackingAfter 200 hoursDe Mattia bending test More than 500,000Number of bendings whichcaused cracking__________________________________________________________________________
EXAMPLE 7
Each of epichlorohydrin/propylene oxide/allyl glycidyl ether copolymer rubbers having the compositions indicated in Table 7 was tested in the same way as in Example 6.
A chloroprene rubber composition prepared in accordance with the following compounding recipe was also tested. The results are shown in Table 7.
______________________________________Compounding recipe______________________________________Neoprene WXJ (described hereinabove) 100 (parts by weight)Stearic acid 1FEF carbon black 40Zinc oxide 5Magnesium oxide 4Aromatic softening agent 10(described hereinabove)2-Mercaptoimidazoline 0.5Octylated diphenylamine 1N--phenyl-N--isopropyl-p-phenylenediamine 1______________________________________
TABLE 7______________________________________ Run No. Compar- ison InventionTest item 31 32 33______________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin Chloro- 40 40Propylene oxide prene 55 53Allyl glycidyl ether rubber 5 7Properties in a normal conditionTensile strength (kg/cm.sup.2) 197 129 126Elongation (%) 350 360 290Hardness (JIS) (point) 65 65 66Heat aging test in air[After 144 hours at 135.degree. C.)Tensile strength change (%) -41 -15 -14Elongation change (%) -86 -67 -69Hardness change (point) +23 +12 +13After 240 hours at 135.degree. C.)Tensile strength change (%) -- -33 -32Elongation change (%) -- -72 -76Hardness change (point) +28 +12 +13180.degree. Bending test Broken No crack occurred. Grease immersion test[After 70 hours at 135.degree. C.]Volume change (%) +38 +22 +20Hardness change (point) -10 -4 -1Gehman T.sub.10 (.degree.C.) -34 -39 -39Dynamic ozone resistance testAfter 200 hours (*) No crackingDe Mattia bending testNumber of bendings which More than 500,000caused cracking______________________________________ (*): Innumerable deep cracks, less than 1 mm, occurred.
EXAMPLE 8
Each of copolymer rubbers having the compositions indicated in Table 8 was tested in the same way as in Example 6 in accordance with the following compounding recipe. The results are shown in Table 8.
______________________________________Compounding recipe______________________________________Epichlorohydrin/propylene oxide/ 100allyl glycidyl ether terpolymer (parts by weight)Stearic acid 1HAF carbon black 40Zinc oxide 5Sulfur 1Tetramethylthiuram disulfide 1.5Cyclohexylbenzothiazyl sulfenamide 1.5Nickel dibutyldithiocarbamate 1.5______________________________________
TABLE 8______________________________________ Run No. Compar- ison InventionTest item 34 35 36 37______________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin -- 30 30 40Propylene oxide 97 68.5 64 58Allyl glycidyl ether 3 1.5 6 2Properties in a normal conditionTensile strength (kg/cm.sup.2) 140 176 148 170Elongation (%) 560 640 350 510Hardness (JIS) (point) 61 62 68 66Heat aging test in air[After 120 hours at 135.degree. C.]Tensile strength change (%) -22 -17 -11 -19Hardness change (point) +8 +8 +10 +9Grease immersion test[After 70 hours at 135.degree. C.]Volume change (%) +54 +29 +27 +25Hardness change (point) -29 -14 -10 -11Gehman T.sub.10 (.degree.C.) -62 -44 -44 -36______________________________________
EXAMPLE 9
Each of copolymer rubbers having the compositions indicated in Table 9 was tested in the same way as in Example 8.
For comparison, a chloroprene composition prepared in accordance with the following compounding recipe was also tested.
The results are shown in Table 9.
______________________________________Compounding recipe______________________________________Neoprene WXJ (given hereinabove) 100 (parts by weight)Stearic acid 1FEF carbon black 40Zinc oxide 5Magnesium oxide 4Aromatic softening agent 10(given hereinabove)2-Mercaptoimidazoline 0.5Octylated diphenylamine 1N--phenyl-N--isopropyl-p-phenylenediamine 1______________________________________
TABLE 9______________________________________ Run No. Compar- ison InventionTest item 38 39 40 41______________________________________Composition (mole %) ofthe copolymer rubberEpichlorohydrin Chloro- 29 39 29Propylene oxide prene 67 57 67Allyl glycidyl ether rubber 4 4 --Glycidyl methacrylate -- -- 4Properties in a normal conditionTensile strength (kg/cm.sup.2) 255 147 167 126Elongation (%) 370 380 430 340Hardness (JIS) (point) 65 67 66 64Heat aging test in air[After 240 hours at 135.degree. C.)Tensile strength change (%) -- -23 -32 -39Elongation change (%) -- -53 -65 -54Hardness change (point) +30 +9 +12 +10180.degree. Bending test Broken No crack occurred. Grease immersion test[After 70 hours at 135.degree. C.]Volume change (%) +35 +28 +24 +29Hardness change (point) -10 -14 -9 -15Gehman T.sub.10 (.degree.C.) -32 -45 -37 -44Dynamic ozone resistance testAfter 200 hours (*) No crackingDe Mattia bending testNumber of bendings which More than 500,000caused cracking______________________________________ (*): Innumerable deep cracks, less than 1 mm, occurred.

Number	Date	Country	Kind
59-148090	Jul 1984	JPX
59-213208	Oct 1984	JPX

Number	Name	Date
3201367	Smith	Aug 1965
3285893	Vandenberg	Nov 1966
3453357	Logan	Jul 1969
4251648	Oetzel	Feb 1981
4268644	Maeda et al.	May 1981
4299944	Maeda et al.	Nov 1981
4310643	Maeda et al.	Jan 1982

Rubber composition for dust cover boots

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