Acrylic rubber and crosslinkable composition thereof

Abstract

An acrylic rubber that is a copolymer in which 1 to 3 wt. % of a fumaric acid monoalkyl ester monomer containing an alkyl group having 1 to 8 carbon atoms is copolymerized as a crosslinkable comonomer, wherein 45 to 65 wt. % of n-butyl acrylate, 12 to 32 wt. % of 2-methoxyethyl acrylate, and 11 to 30 wt. % of ethoxyethoxyethyl acrylate are copolymerized in 100 wt. % of comonomers other than the crosslinkable comonomer. This acrylic rubber can suppress the reduction of oil resistance while improving cold resistance represented by a TR-10 value.

Claims

1. An acrylic rubber that is a copolymer in which 1.01 to 2.31 wt. % of a fumaric acid monoalkyl ester monomer containing an alkyl group having 1 to 8 carbon atoms is copolymerized as a crosslinkable comonomer, wherein 56.9 to 61.9 wt. % of n-butyl acrylate, 12.6 to 22.9 wt. % of 2-methoxyethyl acrylate, and 19.9 to 25.6 wt. % of ethoxyethoxyethyl acrylate are copolymerized in 100 wt. % of comonomers other than the crosslinkable comonomer.

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

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

4. A crosslinkable acrylic rubber composition comprising the acrylic rubber according to claim 1, and an aromatic diamine vulcanizing agent.

5. The crosslinkable acrylic rubber composition according to claim 4, wherein a guanidine compound vulcanization aid is further comprised.

6. A crosslinked molded product crosslinked and molded from the crosslinkable acrylic rubber composition according to claim 4.

7. The crosslinked molded product according to claim 6, which has a TR-10 value of 41 C. or lower.

8. The crosslinked molded product according to claim 6, which is used as a sealing material.

9. The crosslinked molded product according to claim 7, which is used as a sealing material.

Description

EXAMPLES

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

Comparative Example 1 and Examples 1 to 7

(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) 0.01 parts by weight Charged monomer mixture 100 parts by weight

(4) After nitrogen gas substitution was carried out to sufficiently remove oxygen from the system, a redox initiator comprising:

(5) TABLE-US-00002 Sodium formaldehyde sulfoxylate 0.011 parts by weight (Rongalite, produced by Wako Pure Chemical Industries, Ltd.) Tertiary butyl hydroperoxide 0.0063 parts by weight (Perbutyl H, 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 reaches 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.

(6) 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).

(7) TABLE-US-00003 TABLE 1 Comp. Charged Ex. 1 Example monomer mixture 1 1 2 3 4 5 6 n-BA 55.0 55.0 55.0 55.2 54.8 54.4 60.0 2-MEA 32.5 22.5 17.5 22.7 22.3 22.3 12.5 EEEA 9.5 19.5 24.5 19.6 19.4 18.8 24.5 St 1 1 1 1 1 1 1 MBF 2.0 2.0 2.0 1.5 2.5 3.5 2.0 Amount of the 94.7 94.7 94.9 94.4 94.2 94.2 94.7 produced acrylic rubber Notes: n-BA: n-butyl acrylate 2-MEA: 2-methoxyethyl acrylate EEEA: ethoxyethoxyethyl acrylate St: styrene MBF: mono-n-butyl fumarate

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

(9) TABLE-US-00004 TABLE 2 Comp. Copolymerization ratio as Ex. 1 Example measured by .sup.1H-NMR 1 1 2 3 4 5 6 n-BA wt. % 57.2 57.3 56.9 57.2 57.0 57.6 61.9 mol % 59.4 61.7 62.1 61.3 61.4 62.0 67.5 2-MEA wt. % 32.6 21.6 17.9 22.9 21.5 21.2 12.6 mol % 33.4 22.8 19.2 24.2 22.8 22.5 13.5 EEEA wt. % 10.2 21.1 25.2 19.9 21.5 21.2 25.6 mol % 7.2 15.5 18.7 14.5 15.8 15.5 19.0 MBF Notes) wt. % 1.34 1.35 1.33 1.01 1.71 2.31 1.35 Mooney viscosity (point) 24 22 22 21 21 22 22 ML.sub.1+4 (100 C.) Polymer Tg ( C.) 45.6 48.1 50.2 48.5 48.6 48.5 50.3 Note) The amount of MBF (the amount of carboxyl groups) in the acrylic rubber was quantified by neutralization titration.

(10) (2) Using the acrylic rubber obtained in Comparative Example 1 and each Example, the following components were kneaded by using a closed type kneading machine.

(11) TABLE-US-00005 Acrylic rubber 100 parts by weight FEF carbon black 60 parts by weight Stearic acid 2 parts by weight Antioxidant (Nocrac CD, produced by 2 parts by weight Ouchi Shinko Chemical Industrial Co., Ltd.; 4,4-bis(,-dimethylbenzyl)diphenylamine) Lubricant (Phosphanol RL-210, produced by 1 part by weight Toho Chemical Industry Co., Ltd.) Subsequently, the following components were added. Vulcanizing agent (Cheminox CLP 5250, 2.5 parts by weight produced by Unimatec Co., Ltd. Vulcanization accelerator (Nocceler DT, 1.0 part by weight produced by Ouchi Shinko Chemical Industrial Co., Ltd.)
The resulting mixture was kneaded using an open roll to prepare a crosslinkable acrylic rubber composition. This composition was subjected to press crosslinking at 180 C. for 8 minutes and then to oven crosslinking (secondary crosslinking) at 175 C. for 4 hours, and thereby an acrylic rubber molded article was obtained.

(12) The acrylic rubber crosslinked 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 V100 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 permissible standard targets for acceptance of each physical property value are as follows: tensile strength: 10.0 MPa or more, elongation at break: 130% or more, oil swelling resistance (V100): 38% or less, TR-10: 41 C. or lower, and compression set: 15% or less.

(18) TABLE-US-00006 TABLE 3 Comp. Example Measurement item Example 1 1 2 3 4 5 6 Normal state physical properties Hardness (Duro A) 61 63 61 60 64 65 62 Mo 100 (MPa) 5.0 5.2 5.0 3.6 7.1 8.1 5.2 Tensile strength (MPa) 11.1 10.5 10.2 10.2 10.5 10.5 10.2 Elongation at break (%) 160 150 140 190 150 140 140 V100 (%) 29.5 33.8 35.9 31.8 27.4 26.5 36.9 TR-10 ( C.) 40.0 42.1 43.2 42.8 42.8 42.5 43.5 Compression set (%) 13 13 13 13 13 13 13

Comparative Examples 2 to 10

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

(20) TABLE-US-00007 TABLE 4 Charged Comparative Example monomer mixture 2 3 4 5 6 7 8 9 10 n-BA 55.8 54 55 55 55 55 55 54.5 54.5 2-MEA 22.9 21.5 36.5 12.5 2.5 12.5 21.5 22.5 18.5 HA 29.5 OA 20.5 EEEA 19.3 18.5 5.5 29.5 39.5 MTGA 20.0 24 ST 1 1 1 1 1 1 1 1 1 MBF 1.0 5.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Amount of the 94.2 94.5 94.8 94.5 94.5 94.2 93.8 92.5 91.7 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 rubber. In Comparative Example 7, the .sup.1H-NMR peak of HA overlaps with that of n-BA, and in Comparative Examples 9 and 10, the .sup.1H-NMR peak of MTGA overlaps with that of 2-MEA; thus, their determination is not possible. Therefore, their copolymerization ratios are unknown.

(22) TABLE-US-00008 TABLE 5 Copolymerization ratio as Comparative Example measured by .sup.1H-NMR 2 3 4 5 6 7 8 9 10 n-BA wt. % 57.2 56.8 58.7 57.9 57.1 50.1 mol % 61.3 61.2 60.1 64.3 65.5 56.0 2-MEA wt. % 22.9 21.7 35.7 11.6 2.83 20.8 mol % 24.2 23.0 36.0 12.7 3.2 22.5 HA wt. % mol % OA wt. % 28.2 mol % 21.5 EEEA wt. % 19.9 21.5 5.6 30.4 40.1 mol % 14.5 15.8 3.9 23.0 31.3 MTGA wt. % mol % MBF wt. % 0.70 3.25 1.34 1.33 1.31 1.34 1.35 1.34 1.33 Mooney viscosity (point) 20 22 27 20 15 22 23 28 26 ML.sub.1+4 (100 C.) Polymer Tg ( C.) 48.4 48.5 44.1 52.4 55.0 49.9 48.7 51.0 50.9

(23) (2) Using the acrylic rubbers obtained in Comparative Examples 2 to 10, crosslinking and measurement of each item were carried out in the same manner as in Comparative Example 1 and Examples 1 to 6. Table 6 below shows the measurement results.

(24) TABLE-US-00009 TABLE 6 Comparative Example Measurement item 2 3 4 5 6 7 8 9 10 Normal state physical properties Hardness (Duro A) 50 75 63 60 62 59 61 63 67 Mo 100 (MPa) 2.1 11.1 5.0 5.2 5.0 2.8 4.8 5.7 4.0 Tensile strength (MPa) 9.1 11.1 11.0 9.2 7.8 10.9 11.2 9.4 8.2 Elongation at break (%) 210 100 160 140 120 200 160 110 110 V100 (%) 35.5 22.9 28.0 39.0 43.1 97.2 79.5 28.0 28.7 TR-10 ( C.) 42.0 42.1 39.1 44.4 46.2 43.0 42.1 43.7 45.2 Compression set (%) 16 20 12 14 15 12 12 12 15

(25) The above results demonstrate the following. (1) The cold resistance (TR-10) of conventional acrylic rubber can be improved by copolymerizing 11 to 30 wt. %, preferably 19 to 26 wt. %, of ethoxyethoxyethyl acrylate [EEEA] (each Example). (2) If the amount of crosslinkable monomer is too low, the compression set is deteriorated due to a decrease in crosslink density (Comparative Example 2). (3) If the amount of crosslinkable monomer is too large, the rubber composition gets hardened, and the elongation and compression set are deteriorated (Comparative Example 3). (4) If the amount of EEEA is too low, the effect of improving cold resistance is not sufficiently exhibited (Comparative Examples 1 and 4). (5) If the amount of EEEA is too high, the cold resistance is improved; however, the normal state value (and compression set) are deteriorated, and the oil swelling resistance increases (Comparative Examples 5 and 6). (6) The use of an alkyl acrylate with a longer chain than n-BA in place of ethoxyethoxyethyl acrylate improves cold resistance, but significantly increases oil swelling resistance, which is impractical (Comparative Examples 7 and 8). (7) The use of methoxytriethylene glycol acrylate [MTGA], which is a long-chain alkoxy acrylate, improves cold resistance, but deteriorates normal state physical properties (tensile strength and elongation at break) (Comparative Examples 9 and 10).