Acrylic rubber and crosslinkable composition thereof

Abstract

An acrylic rubber that is a copolymer in which 1 to 4 wt. % of a reactive halogen group-containing vinyl monomer is copolymerized as a crosslinkable comonomer, wherein 45 to 65 wt. % of n-butyl acrylate, 10 to 35 wt. % of 2-methoxyethyl acrylate and 8 to 30 wt. % of ethoxyethoxyethyl acrylate are copolymerized in 100 wt. % of comonomers other than the crosslinkable comonomer. This ethoxyethoxyethyl acrylate-copolymerized acrylic rubber can suppress the reduction of oil resistance while improving cold resistance represented by a TR-10 value, and by compounding it with a vulcanizing agent corresponding to the crosslinkable group thereof, a crosslinkable composition is formed.

Claims

1. An acrylic rubber that is a copolymer in which 1.09 to 1.43 wt. % of vinyl monochloroacetate is copolymerized as a crosslinkable comonomer, wherein 55.7 to 61.2 wt. % of n-butyl acrylate, 12.0-32.6 wt. % of 2-methoxyethyl acrylate and 10.1 to 26.8 wt. % of ethoxyethoxyethyl acrylate are copolymerized in 100 wt. % of comonomers other than the vinyl monochloroacetate.

2. The acrylic rubber according to claim 1, wherein 1.09 to 1.36 wt. % of the vinyl monochloroacetate is copolymerized as the crosslinkable comonomer in the copolymer.

3. The acrylic rubber according to claim 1, wherein 2 wt. % or less of a vinyl monomer or olefin monomer is further copolymerized.

4. The acrylic rubber according to claim 1, wherein the Mooney viscosity ML.sub.1+4 (100° C.) is 5 to 100.

5. A crosslinkable acrylic rubber composition comprising the acrylic rubber according to claim 1, and a vulcanizing agent that reacts with the vinyl monochloroacetate.

6. The crosslinkable acrylic rubber composition according to claim 5, wherein the vulcanizing agent that reacts with the reactive halogen group is sulfur, a sulfur donator, or a triazine compound.

Description

EXAMPLES

(1) The following describes the present invention with reference to Examples.

Examples 1 to 6 and Reference Example

(2) (1) In a separable flask equipped with a thermometer, a stirrer, a nitrogen gas inlet tube, and a Dimroth condenser tube, the following components were charged:

(3) TABLE-US-00001 Water 187 parts by weight Sodium lauryl sulfate 1.6 parts by weight Polyoxyethylene lauryl ether 1.6 parts by weight n-Dodecyl mercaptan (chain transfer agent) 0.0035 parts by weight Charged monomer mixture 100 parts by weight After nitrogen gas substitution was carried out to sufficiently remove oxygen from the system, a redox initiator comprising:

(4) TABLE-US-00002 Sodium formaldehyde sulfoxylate (Rongalite, 0.011 parts by weight produced by Wako Pure Chemical Industries, Ltd.) Tertiary butyl hydroperoxide (Perbutyl H, 0.0063 parts by weight produced by NOF Corporation)
was added to initiate the polymerization reaction under room temperature conditions, and the reaction was continued until the polymerization conversion rate become 90% or more. The formed aqueous latex was coagulated with a 10 wt. % sodium sulfate aqueous solution, washed with water, and dried, thereby obtaining an acrylic rubber.

(5) Table 1 below shows the amount of the charged monomer mixture used (parts by weight) and the amount of the produced acrylic rubber (parts by weight).

(6) TABLE-US-00003 TABLE 1 Charged Example monomer mixture 1 2 3 4 5 6 n-BA 55.0 55.0 55.0 54.7 54.4 60.0 2-MEA 22.5 32.5 17.5 22.4 22.3 12.5 EEEA 19.0 9.0 24.0 18.9 18.8 24.0 St 1 1 1 1 1 1 Cl-VAc 2.5 2.5 2.5 3.0 3.5 2.5 Amount of the 94.8 94.3 94.8 94.1 93.7 94.8 produced acrylic rubber Notes: n-BA: n-butyl acrylate 2-MEA: 2-methoxyethyl acrylate EEEA: ethoxyethoxyethyl acrylate St: styrene Cl-VAc: vinyl monochloroacetate

(7) Table 2 shows the copolymerization ratio, Mooney viscosity ML.sub.1+4 (100° C.), and Tg value of the obtained acrylic rubbers. The total amount of the monomer components, i.e., n-butyl acrylate, 2-methoxyethyl acrylate, and ethoxyethoxyethyl acrylate, is shown as 100 wt. % or 100 mol %.

(8) TABLE-US-00004 TABLE 2 Copolymerization ratio as Example measured by .sup.1H-NMR 1 2 3 4 5 6 n-BA wt. % 57.3 57.3 56.8 55.7 56.1 61.2 mol % 61.7 58.5 62.1 60.5 60.8 67.1 2-MEA wt. % 21.6 32.6 17.7 20.4 20.6 12.0 mol % 22.8 33.3 19.2 21.8 22.0 12.9 EEEA wt. % 21.1 10.1 25.1 23.9 23.4 26.8 mol % 15.5 7.1 18.6 17.7 17.2 20.0 Cl-Vac Notes) wt. % 1.26 1.09 1.22 1.36 1.43 1.22 chlorine content wt. % 0.37 0.32 0.36 0.40 0.42 0.36 Mooney viscosity (point) 23 24 22 21 21 22 ML.sub.1+4 (100° C.) Polymer Tg (° C.) −48.2 −45.6 −50.0 −48.8 −48.8 −50.5 Notes: Using a Total Organic Halogen Analyzer (Model TOX-2100, produced by Mitsubishi Chemical Analytech Co., Ltd.), the content of organic chlorine in the acrylic rubber was measured, and the copolymerization ratio of Cl-VAc was calculated from the obtained chlorine content.

(9) (2) Using the acrylic rubber obtained in each Example, the following components were kneaded with an internal mixer.

(10) TABLE-US-00005 Acrylic rubber 100 parts by weight FEF carbon black 60 parts by weight Stearic acid 1 part by weight Antioxidant (Nocrac CD, produced by 2 parts by weight Ouchi Shinko Chemical Industrial Co., Ltd.; 4,4′-bis(α,α-dimethylbenzyl)diphenylamine)
Subsequently, the following components were added.

(11) TABLE-US-00006 Vulcanization accelerator (NS Soap, produced by 3 parts by weight Kao Corporation) Vulcanization accelerator (Nonsoul SK-1, 0.25 parts by weight produced by NOF Corporation) Vulcanizing agent (sulfur) 0.3 parts by weight
The resulting mixture was kneaded with an open roll to prepare a crosslinkable acrylic rubber composition. This composition was subjected to press vulcanization at 180° C. for 8 minutes, and then to oven vulcanization (secondary vulcanization) at 175° C. for 4 hours, thereby obtaining an acrylic rubber molded article.

(12) The acrylic rubber molded article was measured for each of the following items.

(13) Normal state physical properties: According to JIS K-6253 (2010) corresponding to ISO 7619-1: 2010, and JIS K-6251 (2010) corresponding to ISO 37: 2005

(14) Oil swelling resistance test: According to JIS K-6258 (2010) corresponding to ISO 1817: 1999 IRM 903 oil was used, and volume changes ΔV100 after being immersed at 150° C. for 70 hours were measured

(15) TR test: According to JIS K-6261 (2006) corresponding to ISO 2921: 1997 TR-10 values were measured

(16) Compression set: According to JIS K-6262 (2013) corresponding to ISO 815-1: 2008 and ISO 815-2: 2008, measurement values at 150° C. for 70 hours

(17) Table 3 below shows the above measurement results. The target for acceptance of each physical property value is as follows: tensile strength: 11.5 MPa or more, elongation at break: 130% or more, oil swelling resistance (ΔV100): 38% or less, TR-10: −42° C. or lower, and compression set: 35% or less. The Reference Example shows the measurement values (TR-10 value: according to JIS K-6301) of the blend (TR-10: −44° C.) of Example 4 of Patent Document 3.

(18) TABLE-US-00007 TABLE 3 Example Measurement item 1 2 3 4 5 6 Reference Example Normal state physical properties Hardness (Duro A) 64 60 62 61 60 62 71 Mo 100 (MPa) 9.7 8.0 8.0 9.1 8.6 8.5 6.1 Tensile (MPa) 12.1 12.1 11.6 12.3 12.5 11.9 7.3 strength Elongation (%) 140 140 140 140 140 140 124 at break ΔV100 (%) 33.7 29.9 36.2 33.9 34.1 37.1 — TR-10 (° C.) −44.3 −42.1 −45.5 −45.3 −45.0 −46.0 (−44) Compression (%) 33 32 35 29 28 35 59 set

Comparative Examples 1 to 9

(19) (1) In the Examples, the amounts of the charged monomer mixtures used (parts by weight) were each changed as follows.

(20) TABLE-US-00008 TABLE 4 Charged monomer Comparative Example mixture 1 2 3 4 5 6 7 8 9 n-BA 55 55 55 54.5 54.5 55 55 55 55.8 2-MEA 12.5 2.5 36.5 22.5 18.0 12.5 21.5 41.5 22.9 HA — — — — — 29 — — — OA — — — — — — 20 — — EEEA 29.0 39.0 5.0 — — — — — 19.3 MTGA — — — 19.5 24 — — — — ST 1 1 1 1 1 1 1 1 1 Cl-VAc 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 1.0 Amount of the 94.4 94.1 94.6 92.4 91.5 94.1 93.7 95.0 94.5 produced acrylic rubber Notes: HA: n-hexyl acrylate OA: n-octyl acrylate MTGA: methoxyethoxyethoxyethyl acrylate

(21) Table 5 below shows the copolymerization ratio, Mooney viscosity ML.sub.1+4 (100° C.), and Tg value of the obtained acrylic rubbers. In Comparative Examples 4 and 5, the .sup.1H-NMR peak of MTGA overlaps with that of 2-MEA, and in Comparative Example 6, the .sup.1H-NMR peak of HA overlaps with that of n-BA; thus, their determination is not possible. Therefore, the copolymerization ratios are unknown.

(22) TABLE-US-00009 TABLE 5 Copolymerization ratio as Comparative Example measured by .sup.1H-NMR 1 2 3 4 5 6 7 8 9 n-BA wt. % 58.6 56.3 57.7 — — — 57.1 57.4 56.7 mol % 58.1 59.5 59.1 — — — 61.1 57.8 61.3 2-MEA wt. % 11.3 3.2 36.8 — — — 22.5 42.6 20.8 mol % 12.3 3.6 37.1 — — — 23.7 42.2 22.2 HA wt. % — — — — — — — — — mol % — — — — — — — — — OA wt. % — — — — — — 20.4 — — mol % — — — — — — 15.2 — — EEEA wt. % 30.1 40.5 5.5 — — — — — 22.5 mol % 22.7 31.7 3.8 — — — — — 16.5 MTGA wt. % — — — — — — — — — mol % — — — — — — — — — Cl-Vac wt. % 1.09 1.05 1.09 1.08 1.05 1.09 1.22 1.26 0.58 chlorine content wt. % 0.32 0.31 0.32 0.32 0.31 0.32 0.36 0.37 0.17 Mooney viscosity (point) 21 15 26 28 25 22 23 29 20 ML.sub.1+4 (100° C.) Polymer Tg (° C.) −52.5 −55.1 −44.2 −51.1 −51.0 −50.0 −48.6 −43.0 −50.1

(23) (2) Using the acrylic rubbers obtained in Comparative Examples 1 to 9, vulcanization and measurement of each item were performed in the same manner as in Examples 1 to 6. Table 6 below shows the measurement results.

(24) TABLE-US-00010 TABLE 6 Comparative Example Measurement item 1 2 3 4 5 6 7 8 9 Normal state physical properties Hardness (Duro A) 61 62 60 64 67 58 61 64 51 Mo 100 (MPa) 8.3 7.5 8.3 9.8 6.9 4.3 7.5 8.6 3.8 Tensile (MPa) 11.2 9.7 12.5 11.0 9.5 10.9 12.0 13.9 10.9 strength Elongation (%) 140 120 150 110 110 210 150 160 210 at break ΔV100 (%) 39.2 43.5 28.1 28.2 29.0 98.7 80.1 26.3 35.9 TR-10 (° C.) −46.9 −48.8 −41.4 −46.1 −47.7 −45.5 −44.1 −39.5 −43.1 Compression (%) 37 39 32 33 42 29 30 32 46 set

(25) The above results indicate the following. (1) The cold resistance (TR10) of the conventional acrylic rubber can be improved by copolymerizing 8 to 30 wt. % of ethoxyethoxyethyl acrylate [EEEA] (each Example). (2) When the amount of EEEA is large, the cold resistance is improved; however, the normal state values and the compression set are deteriorated, and the oil swelling resistance increases (Comparative Examples 1 and 2). (3) When the amount of EEEA is too low, the effect of improving cold resistance is not sufficiently exhibited (Comparative Example 3). (4) When methoxy triethylene glycol acrylate [MTGA], which is an alkoxy acrylate with a long chain, is used, the cold resistance is improved; however, the normal state physical properties (tensile strength and elongation) are deteriorated (Comparative Examples 4 and 5). (5) When an alkyl acrylate with a longer chain compared with n-BA is used instead of alkoxy acrylate, the cold resistance is improved; however, the oil swelling resistance significantly increases, which is not practical (Comparative Examples 6 and 7). (6) When the amount of crosslinkable monomer is too low, the compression set is deteriorated due to the reduction of crosslinking density (Comparative Example 9).