ETHYLENE/PROPYLENE-BASED COPOLYMER RUBBER COMPOSITION

Abstract

An ethylene/propylene-based copolymer rubber composition having excellent mold contamination resistance obtained by adding a primary antioxidant, a secondary antioxidant, and a plasticizer to ethylene/propylene-based copolymer rubber, wherein based on 100 parts by weight of the ethylene/propylene-based copolymer rubber, 0.3 parts by weight or more of the benzimidazole-based antioxidant (A) is contained as the secondary antioxidant, less than 10 parts by weight of the ether ester-based plasticizer (B) is contained as the plasticizer, and the (B)/(A) ratio is 4.0 times or more.

Claims

1-10. (canceled)

11. An ethylene/propylene-based copolymer rubber composition obtained by adding a primary antioxidant, a secondary antioxidant, a plasticizer, and an acid acceptor to an ethylene/propylene-based copolymer rubber, wherein based on 100 parts by weight of the ethylene/propylene-based copolymer rubber: 0.3 parts by weight or more of the benzimidazole-based antioxidant (A) is contained as the secondary antioxidant, less than 10 parts by weight of the ether ester-based plasticizer (B) is contained as the plasticizer, 0.1 to 10.0 parts by weight of the oxide or hydroxide of a divalent metal or hydrotalcite is contained as the acid acceptor, and the (B)/(A) ratio is 4.0 times or more.

12. The ethylene/propylene-based copolymer rubber composition according to claim 11, wherein 0.3 to 1.5 parts by weight of the benzimidazole-based antioxidant is used.

13. The ethylene/propylene-based copolymer rubber composition according to claim 11, wherein 1 to 8 parts by weight of the ether ester-based plasticizer is used.

14. The ethylene/propylene-based copolymer rubber composition according to claim 11, wherein the (B)/(A) ratio is 4 to 10.

15. The ethylene/propylene-based copolymer rubber composition according to claim 11, wherein the ether ester-based plasticizer is a plasticizer represented by the general formula:
R(OC.sub.2H.sub.4).sub.nOCO(CH.sub.2).sub.mCOO(C.sub.2H.sub.4O).sub.nR wherein: R is a lower alkyl group having 1 to 5 carbon atoms, m is an integer of 4 to 8, and n is an integer of 2 or more.

16. The ethylene/propylene-based copolymer rubber composition according to claim 11, wherein the primary antioxidant is an amine-based antioxidant.

17. The ethylene/propylene-based copolymer rubber composition according to claim 11, wherein an organic peroxide crosslinking agent is further added.

18. A crosslinked molded product of the ethylene/propylene-based copolymer rubber composition according to claim 17.

19. The crosslinked molded product according to claim 18, which is O rings or gaskets.

Description

EXAMPLES

[0049] The following describes the present invention with reference to Examples.

Example 1

[0050]

TABLE-US-00001 EPDM (EPT4045H, produced by Mitsui 100 parts by weight Chemicals, Inc., ethylene content: 54 wt. %, diene content: 8.1 wt. %, Vm(125° C.)28) SRF carbon black 60 parts by weight Zinc oxide 5 parts by weight Stearic acid 0.5 parts by weight Paraffinic process oil (Diana PW380, produced by 3 parts by weight Idemitsu Kosan Co., Ltd.) Dicumyl peroxide (Percumyl D, produced by 4 parts by weight NOF Corporation) 4,4′-bis(α,α-dimethylbenzyl)diphenylamine 0.2 parts by weight (Nocrac CD, produced by Ouchi Shinko Chemical Industrial Co., Ltd.) Mercaptobenzimidazole 0.3 parts by weight (Nocrac MB, produced by Ouchi Shinko Chemical Industrial Co., Ltd.) Ether ester-based plasticizer (ADK-CIZER 1.3 parts by weight RS735, produced by ADEKA Corporation)
Each of the above components was kneaded with a kneader and an open roll, and the obtained kneaded product (composition) was crosslinked using a vulcanizing press or an injection molding machine at 180° C. for 6 minutes, followed by oven crosslinking (secondary crosslinking) at 150° C. for 5 hours.

[0051] The evaluation was carried out on a crosslinked test sheet having a thickness of 2 mm or an O ring having a diameter of 3.10 (for measuring compression set) according to the JIS standard corresponding to ISO 188 and 815-1.

[0052] Heat resistance: Normal state physical property values at 150° C. after 500 hours were calculated. A hardness change of less than +9 was evaluated as ◯, and +9 or more as X.

[0053] Compression set: Changes in values at 120° C. after 150 hours were calculated. A change of less than 23% was evaluated as ◯, 23% or more and less than 33% as Δ, and 33% or more as X.

[0054] Mold contamination: Using a mold after crosslinking formation 300 times under the predetermined crosslinking condition, the presence or absence of contamination that could be visually confirmed was determined in comparison with a mold immediately after cleaning. The absence of mold contamination was evaluated as ◯, and the presence of mold contamination as X.

[0055] Kneading processability: The presence or absence of bagging was visually determined. The absence of bagging was evaluated as ◯, and the presence of bagging as X.

Examples 2 to 4 and Comparative Examples 1 to 4

[0056] In Example 1, the amounts of mercaptobenzimidazole as a secondary antioxidant, and the amounts of ether ester-based plasticizer were changed in various ways. In addition, the zinc oxide was not used in Comparative Example 4.

Comparative Example 5

[0057] In Example 2, in place of the ether ester-based plasticizer, the same amount (3 parts by weight) of ester-based plasticizer (dioctyl sebacate) was used.

[0058] Following table shows the measurement evaluation results obtained, together with the amount of secondary antioxidant and the amount of plasticizer.

TABLE-US-00002 TABLE Example Comparative Example 1 2 3 4 1 2 3 4 5 [amount of component, parts by weight] (A) Secondary antioxidant 0.3 0.7 1.4 0.3 1.0 0.7 0.1 1.0 0.7 (B) Ether ester-based 1.3 3.0 6.0 3.0 3.0 10.0 3.0 3.0 (B) Ester-based 3.0 (B) Plasticizer/(A)antioxidant 4.3 4.3 4.3 10.0 3.0 14.3 30.0 3.0 4.3 [Measurement .Math. Evaluation] Normal state physical properties Hardness 77 74 75 74 74 71 75 68 71 Tensile strength (MPa) 18.3 17.1 16.8 17.3 17.3 14.9 18.3 18.5 16.8 Elongation at break (%) 170 180 190 180 180 200 160 240 210 Heat resistance Hardness change +4 +5 +8 +5 +5 +12 +9 +24 +10 Tensile strength change −40 −31 −19 −35 −44 −30 −42 −77 −34 Elongation change −42 −33 −29 −36 −42 −44 −50 −90 −56 Evaluation ◯ ◯ ◯ ◯ ◯ X X X X Compression set Value 20 17 31 18 17 38 25 52 27 Evaluation ◯ ◯ Δ ◯ ◯ X Δ X Δ Mold contamination Presence or absence none none none none yes none none none yes Evaluation ◯ ◯ ◯ ◯ X ◯ ◯ ◯ X Kneading processability Presence or absence none none none none none yes none none none Evaluation ◯ ◯ ◯ ◯ ◯ X ◯ ◯ ◯

[0059] The above results demonstrate the following. [0060] (1) It can be understood from the results of each Example that the ethylene/propylene-based copolymer rubber composition of the present invention not only has excellent mold contamination resistance, but also satisfies compression set characteristics and composition kneading processability, which are essential for seal parts. [0061] (2) In Comparative Example 1, in which the (B)/(A) ratio is 3.0, the mold contamination resistance is deteriorated. [0062] (3) In Comparative Example 2, in which the amount of plasticizer is 10 parts by weight and the (B)/(A) ratio is 14.3, the mold contamination resistance is excellent, whereas none of the heat resistance, compression set characteristics, and composition kneading processability is satisfied. [0063] (4) Although the mold contamination resistance can be improved by reducing the amount of secondary antioxidant or by not using zinc oxide, the deterioration of heat resistance and compression set characteristics is unavoidable (Comparative Examples 2 to 4). [0064] (5) Compounding an ester-based plasticizer deteriorates not only mold contamination resistance, but also heat resistance and compression set characteristics (Comparative Example 5).