ACRYLIC RUBBER, ACRYLIC RUBBER COMPOSITION AND CROSSLINKED PRODUCT OF SAME

Abstract

An acrylic rubber containing 100 parts by mass of an alkyl acrylate and 30 parts by mass or more of an alkyl methacrylate, as monomer units.

Claims

1. An acrylic rubber comprising 100 parts by mass of an alkyl acrylate and 30 parts by mass or more of an alkyl methacrylate, as monomer units.

2. The acrylic rubber according to claim 1, wherein the alkyl methacrylate is n-butyl methacrylate.

3. The acrylic rubber according to claim 1, wherein the alkyl acrylate is one or more selected from the group consisting of ethyl acrylate and n-butyl acrylate.

4. The acrylic rubber according to claim 1, further comprising a crosslinking monomer having a carboxy group as the monomer units.

5. The acrylic rubber according to claim 1, further comprising ethylene as the monomer units.

6. The acrylic rubber according to claim 1, wherein a content of the alkyl methacrylate is 30 parts by mass or more and 60 parts by mass or less.

7. An acrylic rubber composition comprising the acrylic rubber according to claim 1.

8. The acrylic rubber composition according to claim 7, further comprising one or more selected from the group consisting of a crosslinking agent and a crosslinking accelerator.

9. The acrylic rubber composition according to claim 7, further comprising one or more selected from the group consisting of a filler, a reinforcing agent, a plasticizer, a lubricant, an anti-aging agent, a stabilizer, and a silane coupling agent.

10. A crosslinked product of the acrylic rubber composition according to claim 7.

11. A hose member comprising the crosslinked product according to claim 10.

12. A sealing member comprising the crosslinked product according to claim 10.

13. A vibration-proof rubber member comprising the crosslinked product according to claim 10.

Description

EXAMPLES

[0065] Hereinafter, the present invention will be more specifically described based on Examples, however, the present invention is not limited by these Examples.

[0066] Six types of acrylic rubbers A to F were produced in the conditions shown below.

[0067] <Acrylic rubber A>

[0068] pressure-resistant reaction container having an internal volume of 40 liters, 17 kg of 4% by mass aqueous solution of partially saponified polyvinyl alcohol and 56 g of sodium formaldehyde sulfoxylate were charged, and the whole was thoroughly mixed with a stirrer in advance, thereby preparing a homogeneous suspension. The air in the upper part of the container was replaced with nitrogen, then 0.9 kg of ethylene was injected under pressure into the upper part of the container, and the pressure was adjusted at 3.5 MPa. Under stirring, the temperature in the container was maintained at 55° C., and 5.2 kg of ethyl acrylate, 2.9 kg of n-butyl acrylate, 3.1 kg of n-butyl methacrylate, 0.22 kg of monobutyl fumarate, and a 0.5% by mass aqueous solution of t-butyl hydroperoxide were separately injected under pressure from an inlet to start polymerization. The temperature in the container during the reaction was maintained at 55° C., and the reaction was performed until the polymerization conversion ratio reached 95%. To the resulting polymerization liquid, 20 kg of 0.3% by mass aqueous solution of sodium borate was added to solidify the polymer, and the polymer was dehydrated and dried to obtain an acrylic rubber A.

[0069] This acrylic rubber A had a copolymer composition of 45 parts by mass of the ethyl acrylate unit, 24 parts by mass of the n-butyl acrylate unit, 28 parts by mass of the n-butyl methacrylate unit, 1.5 parts by mass of the ethylene unit, and 1.5 parts by mass of the monobutyl fumarate unit. These respective monomer components were quantitatively determined using a nuclear magnetic resonance spectrum method.

[0070] <Acrylic rubber B>

[0071] The same method as in the acrylic rubber A was performed to obtain an acrylic rubber B, except that n-butyl acrylate and monobutyl fumarate were not used, and monomers to be used were changed to 7.6 kg of ethyl acrylate, 3.6 kg of n-butyl methacrylate, 0.9 kg of ethylene, and 0.28 kg of monobutyl maleate.

[0072] This acrylic rubber B had a copolymer composition of 67 parts by mass of the ethyl acrylate unit, 30 parts by mass of the n-butyl methacrylate unit, 1.6 parts by mass of the ethylene unit, and 1.5 parts by mass of the monobutyl maleate unit.

[0073] <Acrylic rubber C>

[0074] The same method as in the acrylic rubber A was performed to obtain an acrylic rubber C, except that n-butyl acrylate and monobutyl fumarate were not used, and monomers to be used were changed to 8.3 kg of ethyl acrylate, 2.9 kg of n-butyl methacrylate, 0.9 kg of ethylene, and 0.28 kg of monobutyl maleate.

[0075] This acrylic rubber C had a copolymer composition of 72% by mass of the ethyl acrylate unit, 25% by mass of the n-butyl methacrylate unit, 1.7% by mass of the ethylene unit, and 1.6% by mass of the monobutyl maleate unit, with respect to the whole monomer units (100% by mass).

[0076] <Acrylic rubber D>

[0077] The same method as in the acrylic rubber A was performed to obtain an acrylic rubber D, except that n-butyl acrylate and monobutyl fumarate were not used, and monomers to be used were changed to 7.2 kg of ethyl acrylate, 4.0 kg of n-butyl methacrylate, 0.9 kg of ethylene, and 0.28 kg of monobutyl maleate.

[0078] This acrylic rubber D had a copolymer composition of 63% by mass of the ethyl acrylate unit, 34% by mass of the n-butyl methacrylate unit, 1.5% by mass of the ethylene unit, and 1.4% by mass of the monobutyl maleate unit, with respect to the whole monomer units (100% by mass).

[0079] <Acrylic rubber E>

[0080] The same method as in the acrylic rubber A was performed to obtain an acrylic rubber E, except that n-butyl methacrylate and monobutyl fumarate were not used, and monomers to be used were changed to 7.8 kg of ethyl acrylate, 3.4 kg of n-butyl acrylate, 0.9 kg of ethylene, and 0.28 kg of monobutyl maleate.

[0081] This acrylic rubber E had a copolymer composition of 68% by mass of the ethyl acrylate unit, 29% by mass of the n-butyl acrylate unit, 1.6% by mass of the ethylene unit, and 1.5% by mass of the monobutyl maleate unit, with respect to the whole monomer units (100% by mass).

[0082] <Acrylic rubber F>

[0083] The same method as in the acrylic rubber A was performed to obtain an acrylic rubber F, except that n-butyl methacrylate and monobutyl fumarate were not used, and monomers to be used were changed to 6.2 kg of ethyl acrylate, 3.9 kg of n-butyl acrylate, 1.1 kg of methyl methacrylate, 0.9 kg of ethylene, and 0.28 kg of monobutyl maleate.

[0084] This acrylic rubber F had a copolymer composition of 53% by mass of the ethyl acrylate unit, 34% by mass of the n-butyl acrylate unit, 1.6% by mass of the ethylene unit, 9.7% by mass of the methyl methacrylate unit, and 1.6% by mass of the monobutyl maleate unit, with respect to the whole monomer units (100% by mass).

[0085] <Acrylic rubber G>

[0086] The same method as in the acrylic rubber A was performed to obtain an acrylic rubber G, except that n-butyl methacrylate and monobutyl fumarate were not used, and monomers to be used were changed to 6.2 kg of ethyl acrylate, 3.9 kg of n-butyl acrylate, 1.1 kg of methyl methacrylate, 0.9 kg of ethylene, and 0.40 kg of monobutyl maleate.

[0087] This acrylic rubber G had a copolymer composition of 53% by mass of the ethyl acrylate unit, 34% by mass of the n-butyl acrylate unit, 1.5% by mass of the ethylene unit, 9.6% by mass of the methyl methacrylate unit, and 2.2% by mass of the monobutyl maleate unit, with respect to the whole monomer units (100% by mass).

[0088] <Acrylic rubber H>

[0089] same method as in the acrylic rubber A was performed to obtain an acrylic rubber H, except that the amounts of monomers to be used were changed to 7.7 kg of ethyl acrylate, 2.4 kg of n-butyl acrylate, 1.1 kg of n-butyl methacrylate, 0.9 kg of ethylene, and 0.28 kg of monobutyl fumarate.

[0090] This acrylic rubber H had a copolymer composition of 68% by mass of the ethyl acrylate unit, 19% by mass of the n-butyl acrylate unit, 1.5% by mass of the ethylene unit, 9.7% by mass of the n-butyl methacrylate unit, and 1.5% by mass of the monobutyl fumarate unit, with respect to the whole monomer units (100% by mass).

[0091] The monomer compositions of the acrylic rubbers A to H are shown in Table 1 below. Note that, in Table 1, values converted when the alkyl acrylate unit is regarded as 100 parts by mass.

TABLE-US-00001 TABLE 1 Example Comparative Example Acrylic rubber A B C D E F G H Monomer Ethyl acrylate unit Parts by 65 100 100 100 70 61 61 78 composition n-Butyl acrylate unit mass 35 — — — 30 39 39 22 Methyl methacrylate unit — — — — — 11 11 — n-Butyl methacrylate unit 41 45 35 55 — — — 11 Ethylene unit 2.2 2.4 2.4 2.4 1.6 1.8 1.7 1.7 Monobutyl maleate unit — 2.2 2.2 2.2 1.5 1.8 2.5 — Monobutyl fumarate unit 2.2 — — — — — — 1.7

[0092] The above-described acrylic rubbers A to H and other materials were kneaded using an 8-inch open roll at blending in Table 2, thereby obtaining acrylic rubber compositions of Examples 1 to 4 and Comparative Examples 1 to 4. These acrylic rubber compositions (non-crosslinked) were molded into a thickness of 2 mm and subjected to a heating treatment with a hot press at 170° C.×20 minutes to obtain primary crosslinked products, and then the primary crosslinked products were subjected to a heating treatment with hot air (geer oven) at 170° C.×4 hours, thereby obtaining crosslinked products of the acrylic rubber compositions.

[0093] Reagents shown in Table 2 are as follows.

[0094] Carbon black: SEAST SO manufactured by TOKAI CARBON CO., LTD.

[0095] Lubricant A: Liquid paraffin (manufactured by KANEDA Co., Ltd.)

[0096] Lubricant B: Stearic acid (manufactured by NOF CORPORATION)

[0097] Lubricant C: Stearylamine (FARMIN 80 manufactured by Kao Corporation)

[0098] Anti-aging agent: 4,4′-Bis(α,α-dimethylbenzyl) diphenylamine (NAUGARD 445 manufactured by Addivant USA LLC)

[0099] Crosslinking agent: Hexamethylendiamine carbamate (Diak#1 manufactured by DuPont)

[0100] Crosslinking accelerator: XLA-60 manufactured by LANXESS

[0101] Heat resistance, oil resistance, and cold resistance of the obtained crosslinked products of the acrylic rubber compositions were evaluated under the following conditions.

[0102] (Heat resistance test)

[0103] The crosslinked product of the acrylic rubber composition was subjected to a thermal treatment at a test temperature of 190° C. for a test time of 504 hours according to JIS K6257:2017. The elongation at break of each of the crosslinked products before and after the thermal treatment was measured using No. 3 dumbbell according to JIS K6251:2017. The elongation at break after the thermal treatment and a change ratio in the elongation at break before and after the thermal treatment were obtained. As the value of the change ratio is close to 100, there is no change before and after the thermal treatment, and it indicates that heat resistance is high.

[0104] (Oil resistance test)

[0105] Regarding Examples 1 to 4, ΔV (volume change ratio) and ΔW (mass change ratio) of the crosslinked products were also measured according to JIS K6258:2016.

[0106] (Cold resistance test)

[0107] Regarding Examples 1 to 4, T.sub.100 of the crosslinked products were measured according to JIS K6261:2006. Herein, T.sub.100 is a temperature at which the modulus (specific modulus) with respect to the modulus of the crosslinked product at 23° C. becomes 100 times.

TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 3 4 1 2 3 4 Type of acrylic rubber A B C D E F G H Blending Acrylic rubber 100 100 100 100 100 100 100 100 (parts by Carbon black: SEAST SO 45 50 50 50 50 50 45 50 mass) Lubricant A: liquid paraffin 1 1 1 1 1 1 1 1 Lubricant B: stearic acid 1 1 1 1 1 1 1 1 Lubricant C: stearylamine 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Anti-aging agent: NAUGARD 445 1.0 1.0 1 1 1.0 1.0 1.0 1.0 Crosslinking agent: Diak#1 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Crosslinking accelerator: XLA-60 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Evaluation Heat Elongation at break [%] 194 226 201 247 42 106 123 33 results resistance after thermal treatment Change ratio in [%] 60 65 59 71 14 27 34 10 elongation at break Oil ΔV [%] 56 35 31 42 — — — — resistance ΔW [%] 42 25 21 29 — — — — Cold T.sub.100 [° C.] −25 −16 −19 −15 — — — — resistance

[0108] As shown in Table 2, the crosslinked products of the acrylic rubber compositions of Examples exhibited excellent heat resistance as compared to the crosslinked products of the acrylic rubber compositions of Comparative Examples.