CA1190343A

CA1190343A - Rubber composition

Info

Publication number: CA1190343A
Application number: CA000382103A
Authority: CA
Inventors: Hiroji Enyo; Teizo Kotani; Yoshiaki Kato; Masaaki Watanabe; Yasuhiko Takemura
Original assignee: Japan Synthetic Rubber Co Ltd
Current assignee: JSR Corp
Priority date: 1980-07-22
Filing date: 1981-07-21
Publication date: 1985-07-09
Also published as: IT8148937A0; IT1171404B; FR2487369B1; FR2487369A1; JPS6123935B2; DE3128993A1; DE3128993C2; JPS5725342A

Abstract

Abstract of the Disclosure A rubber composition comprising (A) 10-90% by weight of a terpolymer consisting of a conjugated diole-fin, an .alpha., .beta.-unsaturated nitrile and an .alpha., .beta.-unsaturated carboxylic ester (preferably, a terpolymer consisting of 20-50% by weight of a conjugated diolefin, 10-40% by weight of an .alpha., .beta.-unsaturated nitrile and 10-70% by weight of an .alpha., .beta.-unsaturated carboxylic ester), (B) 10-90% by weight of acrylic rubber vulcanizable with sulfur and (C) 0-40% by weight of a copolymer consisting of a conjugated diolefin and an .alpha. ,.beta.-unsaturated nitrile having a combined .alpha. ,.beta.-unsaturated nitrile content of 10-60% by weight. Said rubber composition is inexpen-sive, excellent in processability, oil resistance, heat resistance and ozone resistance and small in mold-contamination and has a small compression set.

Description

o~ f3k3 1 This invention relates to a vulcanizable rubber composition, and more particularly to a rubber composition excellen-t in oil resistance, heat resistance and ozone resistance having a small compression set.
Hitherto, acrylic rubber has been used in packings, O-rings, gaskets and the like which are required to have oil resistance, heat resistance and ozone resistance. Although acrylic rubber satisfies the required performances in respect oE oil resistance, heat resistance and ozone resistance, it has faults that it is poor in processability in the steps of blending and kneading, the vulcanizate obtained by vulcanizing the composition in a conventional manner has so great a compression set that a secondary vulcanization is required, and the composition contaminates the mold in the step of molding, and is expensive. Therefore, its improvement is desired.
In order to improve these properties, there has been proposed the sulfur-vulcanizable acrylic rubber obtained by copolymerizing an acrylic ester with a crosslinking component such as cyclopentadiene, ethylidenenorbornene, vinylidenenorbornene, allyl acrylate, 2-butenyl acrylate, 3-methyl-2-butenyl acry-late or the iike. Even in this caser however, a suf-ficient:Ly small compression set cannot be ob-tained without seconclary vulcani.zation and the price is high, so that it is no-t broadly used in prac-tice.
Fur-ther, in order to overcome these disadvantages, i-t has also been studied to improve -the compression se-t by blending an acrylic rubber wi-th a butadiene-acrylonitril.e co-polymer. ~-lowever, a sufficiently satisfac-to:ry produc-t has not been ob-tained because of rnarked reduction in hea-t resistance and deterioration in ozone resistance~
The present inven-tors have conducted extensive re~
search Eor the purpose of improviny these properties. As a result, it has been found -that the purpose can be achieved by blending a conjugated diolefin-unsatura-ted nitri.le-unsaturated carboxylic ester terpolymer in-to an acrylic rubber.
According to this inven-tion, there is provided a rubber composition comprising (A) 10-90% by weight of a ter-polymer consisting of a conjugated diolefin, an ~,~-unsatur-ated nitrile and an ~,~-unsaturated carboxylic es-ter, (B) 10-90% by weight of a sulfur--vulcanizable acrylic rubber and (C) 0-40% by weight of a copolymer consisting of a conjugated diolefin and an ~ unsaturated nitrile having a combined ~,~-unsa-turated nitrile content of 10-60% by weight.
Another aspect of the inven-tion provides a rubber vulcanizate based on -the above-mentioned rubber composi-tion.
Still another aspect of the invention provides a method for produci.ng a rubber vulcanizate, -the method com-prising vulcanizing the above-men-tioned rubber composition by heating a-t a -temperature of 100 -to 210C, for abou-t 0.5 to 120 minu-tes.
~ ccording -to this invention, -the disadvan-taye of the conven-tional acrylic rubber tha-t it has a hiyh - 2a -1 compression set can be overcome without impairing the advan-tages of the conventional acrylic rubber, namely, the heat resistance, oil resistance and ozone resistance, and there can be obtained an inexpensive rubber composition good in processability and small in mold contamination.
As a result of overcoming the above-mentioned disadvantages, vulcaniæates of the rubber composition obtained can be used as extrusion-molded products such as hose and gasket; composite structures such as fiber cloth-reinforced hose and belt; and other various molded products such as O-ring and the like.
Though in this invention the method of pre-paring the terpolymer (A) is not critical, an emulsion polymerization is preferable. As the conjugated diole-fin which is one of the copolymerizing components of the terpolymer (A), 1,3-butadiene, 1,3-isoprene and the like may be used. As the ~ unsaturated nitrile which is another copolymeriæing component, there may be used acrylonitrile, methacrylonitrile and the like. As the ~,~-unsaturated carboxylic ester which is the other copolymerizing component, there may be used methyl esters, ethyl esters, n-butyl esters, 2-ethylhexyl esters and the like of acrylic acid, methacrylic acid and the like.
The content of conjugated diolefin in the ter-polymer (A) is preferably in the range of 20-50% by 1 weight~ more preferably 30 - 45 % by weight. If it exceeds 50~ by weight, the heat resistance canno-t be suf~iciently exhibited. On the other hand, from the viewpoint of obtaining good sulfur-vulcanizability and good resistance to low temperature, the content is pre-ferably kept at 20% by weight or more. The content of ,~-unsaturated nitrile in the terpolymer (A) is pre-ferably in the range of 10-40~ by weight, more preerably 20 - 30% by weight. If it exceeds 40% by weight, the resistance to low temperature becomes unsatisfactory.
On the other hand, from the viewpoint of maintaining the oil resistance satisfactory, the content is preferably kept at 10~ by weight or more. The content of ~
unsaturated carboxylic ester in the terpolymer (A) is preferably 10 - 70% by weight, more preferably 25 - 50 by weight.
The sulur-vulcanizable acrylic rubber (B) used in this invention is a sulfur-vulcanizable acrylic copolymer comprising as its main component, at least one member selected from an alkyl acrylate such as ethyl acrylate, butyl acrylate or the like; an alkoxy alkyl acryla-te such as ethoxyethyl acrylate, methoxyethyl acrylate or the like; an alkylthioalkyl acry]ate such as methylthioethyl acrylate, ethylthioethyl acrylate or the like; and a cyanoalkyl acrylate, and also comprising a small amount of cyclopentadiene, ethylidenenorbornene, vinylidenenorbornene, 2-butenyl acrylate, 3-methyl-2-1 butenyl acrylate or the li]ce as a crosslinking component, and optionally a small amount of a vinyl compound such as acrylonitrile, acrylamide or the like. The sulfur-vulcanizable acrylic rubber (B) is preferably a copolymer consisting of 90-95% by weight of ethyl acry-late, butyl acrylate, methoxyethyl acrylate, or a mix-ture thereof and 5~10% by weight of ethylidenenorbornene.
The copolymer (C) used in this invention is produced according to the recipe of emulsion polymeriza-tion. Among the copolymerizing components of the copo-lymer (C), the conjugated diolefin includes, for exampler 1,3-butadiene, 1,3 isoprene and the like, and the ~ unsatura-ted nitrile includes, for example, acry lonitrile, methacrylonitrile and the like. The content of a, 3-unsaturated nitrile in the copolymer (~) is pre-ferably 10-60% by weight, more preferably 20 - 40% by weight, from the viewpoint of oil resistance and physical properties of rubber. If it is less than 10~ by weight, the composition is inferior in oil resistance. If it is more than 60% by weight, the composition is inferior in resistance to low temperature.
In this invention, the proportion of the ter-polymer (A) in the rubber composition is 10-90~ by weight, preferably 20-80% by weight, and more preferably 30-60% by weight. If the proportion of the terpolymer (A) is less than 10% by weight, the compression set, processability and mold-contamination are not improved.
If it exceeds 90~ by weight, the ozone resistance beco-1 mes unsatisfactory. In this invention, the proportion of the acrylic rubber (B) is 10-90~ by weight, pre~
ferably 20 ~0% by weight. If it i5 less than 10~ by weight, the ozone resistance becomes unsatisfactory. If it exceeds 90% by weight, the compression set is not improved.
In the rubber composition of this invention, the proportion of the copolymer (C) is 0~40% by weight.
Although a higher proportion oE the copolymer ~C) gives a less expensive composition having better oil resistance, the ozone resistance becomes unsatisfactory if its proportion exceeds 40% by weight. From these viewpoints, it is more preferable that the proportion of the copolymer (C) in the composition is ~-35~ by weight.
In this invention, as the means or kneading polymers and the like, there can be used conventional mixing means such as roll mill, Banbury mixer and ex~ruder, as well as other internal mixers capable of mixing the components without unduly heating them.
Into the rubber composition of this invention may be incorporated compounding agents which are conven-tionally used such as filler (carbon black, calcium car--bonate, hydrocarbon resin, phenolic resin and the like), vulcanizing agent, vulcanizing assistantr antioxidant, softening agent and the like.
In general, the vulcanization is effected by heating the composition at a temperature of 100-210C for about 0.5-120 minutes by means of steam, a high tem-perature fluld or micro-wa~7e.
This invention will be explained below more spe-cifically referring to Examples. This invention is not limited to these Examples.
In the Examples, the measurements of physical properties were conducted in ~he following manner:
I) Physical properties of vulcanizate (tensile strength, elongation and hardness): They were measured according to the tensile test and hardness test defined 10 in JIS K 630L.
II) Heat resistance: It was measured according to the aging test defined in JIS K 6301. It was the Geer oven heat aging test and the conditions were as follows:
temperature, 130C; time, 120 hours.
15 III) Ozone resistance: It was measured according to the ozone deterioration test defined in JIS K 6301.
The test conditions were as follows: ozone concentration, 50 pphm; temperature, 40C; elongation 2096.
IV) Compression set: It was measured according to the compression set test defined in JIS K 6301.
The test conditions were as follows: tem-perature, 120C; compression, 25%; time, 70 hours.
V) Oil resistance: It was measured according to the 25 immersion test defined in JIS K 6301.
The test conditions were as follows: oil, testing oil Wo. 3; temperature, 120C; time, 70 hours.
VI) Processability: A mixturé according to the com-l pounding recipe me~tioned in Table l was kneaded with a Banbury mixer and rolls. If a composition showed a great winding tendency to the Banbury rotor and a great stickiness to roll, and accordingly the composition was inferior in processability, its processability was expressed "bad". If a composition showed a small ten-dency of winding and stickiness, its processability was expressed "good".
VII) Mold-contamination property: A kneaded mixture with the compounding recipe mentioned in Table l was press-vulcanized 50 times on one metallic plate and the state of contamination was observed. When contamination was found, it was expressed '~contaminated"~

Examples 1-5 Mixtures with the compounding recipes (parts by weight) mentioned in Table l were kneaded with a Banbury mixer and open rolls and thereafter press-vulcanized at 150C for 30 minutes. The results obtained are shown in Table 2.

Compara-tive Examples 1-5 Mixtures with the compounding recipes shown in Table 1 were kneaded with a Banbury mixer and open rolls, and thereafter press-vulcanized at 150C for 30 minutes. The results obtained are shown in Table 2.

ar ~

Table 1 \ No. Example _ Compound ~ 1 2 3 4 5 _ ingredients ~ __ _ _ ~ _ Terpolymer (A) (1) 25 50 75 30 20 Acrylic rubber (8) (~)75 50 25 50 50 Copolymer (C) (3) _ _ _ ~ 20 30 _ Zinc o~ide 3 3 3 3 3 Stearic acid 1 1 1 1 MAF Carbon 45 45 45 45 45 Vulcanization accelerator TT (4) 2 2 2 2 2 Vulcanization accelerator CBS (5) 2 2 2 2 2 Sulfur 0.5 0 5 0.5 0.50.5 _ (continued) aS~
Table 1 (Cont'd) _ Comparative Example _ _ ._ _ _ 100 _ 3 3 3 3 3

2 2 2 2 2 _ 0.5 0.5 0.5 0.5 l Note:
(1) Butadiene-acrylonitrile-butyl acrylate terpolymer obtained by emulsion polymerization process (acrylonitrile content 25% by weight, butadiene content 40~ by weight).
(2) Sulfur-vulcanizable acrylic rubber (butyl acrylate/
ethylidenenorbornene (90/10) copolymer).

(3) JSR N230S manufactured by Japan Synthetic Rubber Co., Ltd. (butadiene-acrylonitrile copolymer having a combined acrylonitrile content of 35~ by weight)

(4) Tetramethylthiuram disulEide.

(5) N-cyclohexyl-2~benzothiazolyl sulfenamide.

Table 2 ~ _ _ No.
~~
Item of test ~---_ _ . ~
Physical properties of vulcanizate Tensile strength (kgf/cm2) Elongation (~) Hardness (JIS A) _' _ _ _ _ _ Heat resistance (130C x 120 hrs) Percentage of change in tensile s-trength (%) Percentage o change in elongation (%) _ _ _ _ Ozone resistance (40C x 50 pphm x 20% elongation) Crack initiation time (hr) _ __ _ Compression set (120C x 70 hrs x 25% compression) (%) ~ _ Oil resistance (120 C x 70 hrs, No. 3 oil) Percentage o change in volume (%) _ _ Processability _ _ Mold-con-tamination _ Table 2 (Cont'd) _ _ __ _ Example _ _ _ _ . _ l 2 3 4 5 _ llO 136 18~ 152 130 350 320 320 3~0 400 _ . ____ _ _ +30 +13 -13 ~10 ~3 _ _ _ . . _ _ _ or more or more or more or more _ _ _ _ _ _ _ __ __ ~_ _ _ _ _ Good Good GoodGood Good _ _ _ _ None None NoneNone None _ Table 2 (Cont'd) Comparative Example _ ~ _ _ _ - ~ 1 300 370 490 ~20 390 _ _ _ _ +69 +80 +38 +~0 +25 -82 -80 -80 -14 -Sl _ _ _. _ Breakdown 5 1 200 at chuck or more _ _ _ __ _ _ _ _ _ .
. Good Good Good Bad Good _ _ _ None None None Comtami- None _ nated 1 It is apparent from the results in Table 2 that when Examples 1-3 are compared with Comparative Examples 1-4, the heat resistance and ozone resistance are markedly lower in Comparative Examples 1-3 in which a mixed system of the acrylic rubber (B) and the copo-lymer (C) is used, while the heat resistance is not impaired and the ozone resistance is good in ~xamp]es 1-3 in which the mixed system of this invention con-sisting of the terpolymer (A) and the acrylic rubber (~) is used. Further, the compression set is also remarkably improved as compared with Comparative Example 4 in which a single system of the acrylic rubber (B) is used. Thus, it i5 understandable that a practically useful and less expensive rubber composition can be obtained according to this invention without secondary vulcanization.
When Examples 4 and 5 are compared with Comparative Example 2, Examples 4 and 5, in which a ter-nary mixture system of the terpolymer (A), the acrylic rubber (B) and the copolymer (C) is used, are good in ozone resistance withou-t great deterioration of heat resistance as compared with Comparative Example 2 in which a system free from the terpolymer (A) is used.
Further, they are remarkably improved in compression set as compared with Comparative Example 4 in which a single system of the acrylic rubber (B) is used. Thus, it is understandabLe that a practically useful and less expen-l sive rubber composition can be obtained according to this invention wil:hout secondary vulcanization.

Example 6 The same procedure as in Example 2 was repeated, except that the terpolymer (A) was replaced by a butadiene-acrylonitrile~butyl acrylate terpolymer having a butadiene content of 30% by weiyht and an acry-lonitrile content of 20% by weight obtained by emulsion polymerization process, to obtain the results shown in Table 3.

Example 7 The same procedure as in Example 4 was repeated, except that the copolymer (C) was replaced by JSR N241H manufactured by Japan Synthetic Rubber Co., Ltd. (butadiene-acrylonitrile copolymer having a com-bined acryloni-trile content of 29% by weight), to obtain the results shown in Table 3.

Example 8 The same procedure as in Example 2 was repeated, except that the terpolymer (A) was replaced by a butadiene-acrylonitrile-ethyl acrylate terpolymer having an acrylonitrile content of 25% by weight and a butadiene content of 40% by weight obtained by emulsion polymerization process, to obtain the results shown in Table 3.

1 Example 9 The same procedure as in Exarnple 2 was repeated~ except that the terpolymer (A) was replaced by a butadiene-acrylonitrile-methoxyethyl acrylate ter-polymer having an acrylonitrile content of 25% by weightand a butadiene content of 40% by weight obtained by emulsion polymerization process, to obtain the results shown in Table 3.

Example lO
The same procedure as in Example 2 was repeated, except that the acrylic rubber (B) was replaced by a butyl acrylate/methoxyethyl acrylate/ethyl acrylate/ethylidenenorbornene (40/25/25/lO by weight) rubber, to obtain the results shown in Table 3.

Table 3 _ ~--______ Example No.

Item of test ~ _ _ Physical properties of vulcanizate Tensile strength (kgf/cm2) Elongation (%) Hardness (JIS A) __ _ Heat resistance (130 C x 120 hrs) Percentage oE change in tensile strength (%) Percentage of change in elongation (%) _ Ozone resistance (40C x 50 pphm x 20% elongation) Crack initiation time (hr) _ _ Compression set (120C x 70 hrs x 25% compression) (%) . . . _ Oil resistance (120 C x 70 hrs, No. 3 oil) Percentage of change in volume (%) _ __ _ _ _ Processability _ Mold-contamination Table 3 (Cont'd) ____ .___ __ ___ 74 73 7~ 74 7 _ +19 +11 +12 +18 +15 _ _ 200 200 ~00 200 200 or more or more or more or more or more _ _ _ ~ _ _ , 42 39 ~0 40 40 _ _ . i Good Good Good Good Good _ _ _._____ ;
None NoD~ None None None -

Claims

What is claimed is:

1. A rubber composition consisting essentially of (A) 10-90% by weight of a terpolymer consisting of a conjugated diolefin, an .alpha., .beta.-unsaturated nitrile and an .alpha., .beta.-unsaturated carboxylic ester, (B) 10-90% by weight of a sulfur-vulcanizable acrylic rubber and (C) 0-40% by weight of a copolymer consisting of a conjugated diole-fin and an .alpha., .beta.-unsaturated nitrile having a combined .alpha., .beta.-unsaturated nitrile content of 10-60% by weight.

2. A rubber composition according to Claim 1, wherein said terpolymer (A) consists of 20-50% by weight of a conjugated diolefin, 10-40% by weight of an .alpha., .beta.-unsaturated nitrile and 10-70% by weight of an .alpha., .beta.-unsaturated carboxylic ester.

3. A rubber composition according to Claim 1, wherein said terpolymer (A) consists of 30 - 45% by weigh of a conjugated diolefin, 20 - 30% by weight of an .alpha., .beta.-unsaturated nitrile and 25 - 50% by weight of an .alpha., .beta.-unsaturated carboxylic ester.

4. A rubber composition according to Claim 1, 2 or 3, wherein the conjugated diolefin of the terpolymer (A) is 1,3-butadiene or 1,3-isoprene, the .alpha., .beta.-unsaturated nitrile of the terpolymer (A) is acrylonitrile or metha-crylonitrile, and the .alpha., .beta.-unsaturated carboxylic ester of the terpolymer (A) is methyl acrylate, ethyl acry-late, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate or 2-ethylhexyl methacrylate.

5. A rubber composition according to claim 1, 2 or 3, wherein said ter-polymer (A) is butadiene-acrylonitrilebutyl acrylate terpolymer.

6. A rubber composition according to claim 1, 2 or 3, wherein said ter-polymer (A) is butadiene-acrylonitrilebutyl acrylate terpolymer and the content of acrylonitrile in the terpolymer (A) is 25% by weight and the content of butadiene in the terpolymer (A) is 40% by weight.

7. A rubber composition according to claim 1, 2 or 3, wherein the proportion of the terpolymer (A) is 20 to 80% by weight.

8. A rubber composition according to claim 1, 2 or 3, wherein the proportion of the terpolymer (A) is 30 to 60% by weight.

9. A rubber composition according to claim 1, wherein said sulfur-vulcanizable acrylic rubber (B) comprises at least one member selected from an alkyl acrylate, an alkoxyalkyl acrylate, an alkylthioalkyl acrylate and a cyanoalkyl acrylate as its main component, and also comprises cyclopentadiene, ethylidenenorbornene, vinylidenenorbornene, 2-butenyl acrylate or 3-methyl-2-butenyl acrylate as its crosslinking component, and optionally a small amount of a vinyl compound.

10. A rubber composition according to claim 9, wherein said sulfur-vulcanizable acrylic rubber (B) contains ethyl acrylate, butyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, an alkylthioalkyl acrylate or a cyanoacrylate as its main component, and also contains cyclopentadiene, ethyl-idenenorbornene, vinylidenenorbornene, 2-butenyl acrylate or 3-methyl-2-butenyl acrylate as its crosslinking component, and acrylonitrile or acrylamide as the vinyl compound.

11. A rubber composition according to claim 9, wherein said sulfur-vulcanizable acrylic rubber (B) is a copolymer consisting of 90 to 95% by weight of ethyl acrylate, butyl acrylate, methoxyethyl acrylate or a mixture thereof and 5 to 10% by weight of ethylidenenorbornene.

12. A rubber composition according to claim 9, wherein said sulfur-vulcanizable acrylic rubber (B) is a copolymer consisting of 90% by weight of butyl acrylate and 10% by weight of ethylidenenorbornene.

13. A rubber composition according to claim 1, 2 or 3, wherein the pro-portion of the acrylic rubber (B) is 20 to 80% by weight.

14. A rubber composition according to claim 1, 2 or 3, wherein the copolymer (C) is contained in a proportion of 5 to 35% by weight.

15. A rubber composition according to claim 1, 2 or 3, wherein the copolymer (C) is contained in a proportion of 5 to 35% by weight, and the con-tent of .alpha.,.beta.-unsaturated nitrile in the copolymer (C) is 10 to 60% by weight.

16. A rubber composition according to claim 1, 2 or 3, wherein the copolymer (C) is contained in a proportion of 5 to 35% by weight, and the con-tent of .alpha.,.beta.-unsaturated nitrile in the copolymer (C) is 20 to 40% by weight.

17. A rubber composition according to claim 1, 2 or 3, wherein the copolymer (C) is contained in a proportion of 5 to 35% by weight, and wherein said copolymer (C) is a copolymer of 1,3-butadiene or 1,3-isoprene and acrylo-nitrile or methacrylonitrile.

18. A rubber composition according to claim 1, 2 or 3, wherein the copolymer (C) is contained in a proportion of 5 to 35% by weight, and wherein said copolymer (C) is a butadiene-acrylonitrile copolymer having a combined acrylonitrile content of 35% by weight.

19. A rubber composition according to claim 1, 2 or 3, wherein said rubber composition additionally contains at least one compounding agent selected from the group consisting of filler, vulcanizing agent, vulcanizing assistant, antioxidant and softening agent.

20. A rubber vulcanizate based on the rubber composi-tion as defined in claim 1, 2 or 9.

21. A method for producing a rubber vulcanizate, which method comprises vulcanizing the rubber composition as defined in claim 1, 2 or 9 by heating at a temperature of 100 to 210°C
for about 0.5 to 120 minutes.