Acrylic rubber

Abstract

An acrylic rubber contains a copolymer of a monomer mixture of: 25 to 46 wt. % of alkoxyalkyl acrylate, 23 to 37 wt. % of 2-ethylhexyl acrylate, 9 to 17 wt. % of alkyl methacrylate, 1 to 3 wt. % of monoalkyl fumarate and the remaining amount is ethyl acrylate. This acrylic rubber improves hydrolysis resistance by introducing a specific alkyl acrylic monomer with extremely low hydrolysis property i.e. low hydrophilicity, and at the same time satisfies all of oil resistance, cold resistance, and hydrolysis resistance in a well-balanced manner.

Claims

1. An acrylic rubber comprising a copolymer of a monomer mixture comprising: 28.2 to 44.2 wt. % of 2-methoxyethyl acrylate; 24.2 to 35.2 wt. % of 2-ethylhexyl acrylate; 10 to 16 wt. % of methyl methacrylate; 1.6 wt. % of monobutyl fumarate; and 12 to 23 wt. % of ethyl acrylate, wherein the weight percentages of the monomers are based upon the total weight of the monomer mixture, and the weight percentages of the monomers add up to 100%.

2. The acrylic rubber according to claim 1, which has a weight average molecular weight M.sub.w of 1,000 to 8,000,000.

3. An acrylic rubber composition comprising the acrylic rubber according to claim 1 and a crosslinking agent for carboxyl group.

4. The acrylic rubber composition according to claim 3, which is used as a crosslinking molding material for sealing materials.

5. A sealing material being obtained by crosslinking molding of the acrylic rubber composition according to claim 4.

Description

EXAMPLES

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

Example 1

(2) 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-00002 Water 187 parts by weight Sodium lauryl sulfate 1.6 parts by weight Polyoxyethylene lauryl ether 1.6 parts by weight n-Dodecyl mercaptan 0.01 parts by weight Charged monomer mixture Ethyl acrylate [EA] 15 parts by weight 2-Methoxyethyl acrylate [MEA] 34.2 parts by weight 2-Ethylhexyl acrylate [EHA] 34.2 parts by weight Methyl methacrylate [MMA] 15 parts by weight Monobutyl fumarate [MBF] 1.6 parts by weight
After oxygen was sufficiently removed from the system by replacement with nitrogen gas, the following components were added.

(4) TABLE-US-00003 Sodium formaldehyde sulfoxylate (Rongalite, 0.0088 parts by weight produced by Wako Pure Chemical Industries, Ltd.) Tertiary butyl hydroperoxide (Perbutyl P, 0.0050 parts by weight produced by NOF Corporation)
Then, a polymerization reaction was initiated at room temperature, and the reaction was continued until the polymerization conversion rate reached 90% or more. In this polymerization conversion rate, the proportion of the charged monomer mixture approximately corresponds to the proportion of monomers in the produced copolymer.

(5) The formed aqueous latex was coagulated with a 10 wt. % sodium sulfate aqueous solution, followed by water washing and drying, thereby obtaining an acrylic rubber.

Example 2

(6) In Example 1, the amount of the MEA and EHA were changed to 44.2 parts by weight and 24.2 parts by weight, respectively.

Example 3

(7) In Example 1, the amount of the EA and MMA ere changed to 20 parts by weight and 10 parts by weight, respectively.

Example 4

(8) In Example 1, the amount of the EA was changed to 12 parts by weight, the amount of the MEA and EHA were changed to 35.2 parts by weight, respectively, and the amount of the MMA was changed to 16 parts by weight.

Example 5

(9) In Example 1, the amount of the EA was changed to 23 parts by weight, the amount of the MEA was changed to 28.2 parts by weight, and the amount of the MMA was changed to 13 parts by weight.

Comparative Examples 1 to 11

(10) In Example 1, the charged monomer mixture (part by weight) was changed a shown in Table 1 below.

(11) TABLE-US-00004 TABLE Comparative Example EA BA MEA DIA MMA MBF 1 15 (34.2) 34.2 — 15 1.6 2 20 (34.2) 34.2 — 10 1.6 3 15 — (24.2) (44.2) 15 1.6 4 15 — (49.2) (19.2) 15 1.6 5 22 — 34.2 34.2  (8) 1.6 6 19.7 — 29.5 29.5   (19.7) 1.6 7 20 — (22.2) (41.2) 15 1.6 8 15 — (48.2) 25.2 10 1.6 9 20 — 43.2 (20.2) 15 1.6 10 15 — 28.2 (45.2) 10 1.6 11 20 — 26.2 (40.2) 12 1.6 Note 1) BA: n-butyl acrylate Note 2) Numerical values in parentheses are outside the scope of the claims
Preparation of Acrylic Rubber Composition

(12) The following components were kneaded using a sealed kneader.

(13) 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 Ouchi 2 parts by weight Shinko Chemical Industrial Co., Ltd.) Processing aid (Paraffin 70S, produced by 2 parts by weight Sanko Chemical Industry Co., Ltd.)
Then, the following components were added using an open roll to prepare a crosslinkable acrylic rubber composition.

(14) TABLE-US-00006 Vulcanization accelerator (Vulcofac ACT55, 1 part by weight producedby Safic-Alcan) Vulcanizing agent (CHEMINOX AC6, produced by 0.6 parts by weight Nisso Fine Chemicals Co., Ltd.)
Production of Acrylic Rubber Crosslinked Product

(15) The crosslinkable acrylic rubber composition was press vulcanized at 180° C. for 10 minutes, followed by oven vulcanization (secondary vulcanization) at 175° C. for 4 hours, thereby obtaining m acrylic rubber crosslinked product.

(16) Physical Property Test of Acrylic Rubber Crosslinked Product

(17) Normal physical properties: according to JIS K6253 corresponding to ISO 7619-1: 2010, and JIS K6251 corresponding to ISO 37: 2005 Hydrolysis resistance test: according to JIS K6258 corresponding to ISO 1817: 2015

(18) A tensile test specimen and a volume change specimen ware each prepared in the same manner as for the normal physical property specimen. These specimens ware suspended on a stainless steel wire, ad placed in a PTFE beaker (117 mm in diameter and 146 mm in depth) by hanging. A test liquid (1 wt. % zinc chloride aqueous solution) was put therein so that the entire specimens were dipped. The beaker was placed in a stainless steel pressure-resistant container, and the container was sealed with a flange with packing. The container was placed in a oven, heated at 120° C. for 480 hours, and then allowed to cool to near room temperature. The extracted specimens were placed in a gear-type oven and dried at 120° C. for 70 hours. The thus-treated specimens ware determined for hardness, breaking strength, elongation at break, and volume change. Oil resistance test: according to JIS K6258 corresponding to ISO 1817: 2015 Using IRM903 oil, the volume change at 150° C. after 70 hours was measured Low temperature test: according to JIS K6261 corresponding to ISO 2921: 1997 TR10 value was measured

(19) The following table 2 (Examples) ad table 3 (Comparative Examples) show the results of the above test of physical properties.

(20) TABLE-US-00007 TABLE 2 Example Measurement item 1 2 3 4 5 Normal physical properties Hardness (Duro A) 69 66 67 68 64 Breaking strength 11.8 12.5 11.2 11.0 11.0 (MPa) Elongation at break 195 190 170 180 160 (%) Hydrolysis resistance test Hardness (Duro A) 88 93 88 87 85 Breaking strength 11.7 14.4 10.8 13 13 (MPa) Elongation at break 95 80 65 120 110 (%) Volume change (%) −7.0 −9.8 −9.0 −8.0 −8.2 Oil resistance Volume change (%) +36.3 +19.3 +35.5 +36.2 +36.5 Low temperature test TR10 (° C.) −25.8 −24.7 −29.8 −26.7 −27.1

(21) TABLE-US-00008 TABLE 3 Comparative Example Measurement item 1 2 3 4 5 6 Normal physical properties Hardness (Duro A) 66 65 63 65 64 68 Breaking strength 12.8 12.1 11.1 13.2 10.5 12.8 (MPa) Elongation at break 185 160 200 175 140 240 (%) Hydrolysis resistance test Hardness (Duro A) 96 97 82 90 93 90 Breaking strength 19.1 25.3 11.3 14 17.2 13.4 (MPa) Elongation at break 90 50 125 45 80 115 (%) Volume change (%) −11.3 −14.1 −6.2 −10.1 −12.6 −6.2 Oil resistance Volume change (%) +14.8 +14.6 +57.4 +13.5 +34.6 +29.0 Low temperature test TR10 (° C.) −21.4 −25.5 −29.2 −23.9 −31.5 −19.9 Comparative Example Measurement item 7 8 9 10 11 Normal physical properties Hardness (Duro A) 63 65 68 62 64 Breaking strength 10.6 11.3 12.1 9.6 10.2 (MPa) Elongation at break 180 145 180 160 170 (%) Hydrolysis resistance test Hardness (Duro A) 81 94 94 82 88 Breaking strength 13.0 17.0 16.4 12.0 13.1 (MPa) Elongation at break 165 60 75 135 120 (%) Volume change (%) −6.9 −13.4. −10.4 −8.5 −8.8 Oil resistance Volume change (%) +53.3 +19.2 +16.2 +56.8 +48.7 Low temperature test TRW (° C.) −27.5 −29.2 −22.8 −33.9 −30.0

(22) The above results suggest the following.

(23) (1) In each Example, the volume change after the hydrolysis resistance test is small, and oil resistance and cold resistance are well balanced.

(24) (2) Comparative Examples 1 and 9 are superior in oil resistance, but inferior in hydrolysis resistance and cold resistance.

(25) (3) Comparative Examples 2, 4, and 8 are superior in oil resistance, but inferior in hydrolysis resistance.

(26) (4) Comparative Examples 3, 7, 10, and 11 are superior in hydrolysis resistance and cold resistance, but inferior in oil resistance.

(27) (5) Comparative Example 5 is superior in cold resistance, but inferior in hydrolysis resistance.

(28) (6) Comparative Example 6 is superior in hydrolysis resistance and oil resistance, but inferior in cold resistance.