ACRYLIC RUBBER, RUBBER COMPOSITION, AND CROSSLINKED PRODUCT THEREOF, RUBBER HOSE, AND SEAL PART

Abstract

An aspect of the present invention is an acrylic rubber containing an alkyl acrylate, ethylene and vinyl acetate as monomer units, wherein a content of a polyvinyl alcohol in the acrylic rubber is 0.5 to 2% by mass.

Claims

1. An acrylic rubber comprising an alkyl acrylate, ethylene and vinyl acetate as monomer units, wherein a content of a polyvinyl alcohol in the acrylic rubber is 0.5 to 2% by mass.

2. The acrylic rubber according to claim 1, wherein the alkyl acrylate comprises an alkyl acrylate having an alkyl group having 4 to 8 carbon atoms.

3. The acrylic rubber according to claim 2, wherein the alkyl acrylate further comprises an alkyl acrylate having an alkyl group having 1 to 3 carbon atoms.

4. The acrylic rubber according to claim 1, wherein a content of the alkyl acrylate is 60 to 90% by mass based on a total amount of the monomer units.

5. The acrylic rubber according to claim 1, wherein a content of the ethylene is 0.5 to 5% by mass based on a total amount of the monomer units.

6. The acrylic rubber according to claim 1, wherein a content of the vinyl acetate is 8 to 25% by mass based on a total amount of the monomer units.

7. The acrylic rubber according to claim 1, further comprising a crosslinking monomer as a monomer unit.

8. The acrylic rubber according to claim 7, wherein the crosslinking monomer is a crosslinking monomer having an epoxy group.

9. The acrylic rubber according to claim 7, wherein the crosslinking monomer is a crosslinking monomer having a carboxyl group.

10. The acrylic rubber according to claim 7, wherein a content of the crosslinking monomer is 0.5 to 10% by mass based on a total amount of the monomer units.

11. A rubber composition comprising the acrylic rubber claim 1.

12. A crosslinked product of the rubber composition according to claim 11.

13. A rubber hose comprising the crosslinked product according to claim 12.

14. A seal member comprising the crosslinked product according to claim 12.

Description

EXAMPLES

[0062] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0063] A pressure-resistant reactor having an internal volume of 40 liters was charged with 11 kg of a monomer mixed liquid containing monomers shown in Tables 1 to 3 (excluding ethylene), 17 kg of 4% by mass of an aqueous polyvinyl alcohol solution (degree of saponification of the polyvinyl alcohol: 88% by mole), and 22 g of sodium acetate, and these were thoroughly mixed in advance with a stirrer to prepare uniform suspensions. Then, after the upper portion of the reactor was replaced with nitrogen, ethylene was injected into the upper portion of the reactor by 3 MPa. After stirring was continued and the temperature in the reactor was maintained at 55° C., 2 liters of an aqueous t-butyl hydroperoxide solution (0.25% by mass) was added to initiate polymerization. The temperature inside the reactor was maintained at 55° C. and the reaction was terminated after 6 hours. To the obtained copolymer, 7 liters of an aqueous sodium borate solution (3.5% by mass) was added to solidify the copolymer. Next, a step of adding 450 parts h mass of pure water having a temperature shown in Tables 1 to 3 to 100 parts by mass of the solidified copolymer, stirring the mixture in the reactor for 5 minutes, and discharging the water from the reactor was repeated 4 times to perform water washing. Thereafter, dehydration and drying were performed to obtain an acrylic rubber.

[0064] The compositions of the monomer units contained in the obtained acrylic rubbers are shown in Tables 1 to 3. The content of the monobutyl maleate monomer unit was measured by dissolving the acrylic rubber in toluene and performing neutralization titration using potassium hydroxide, The contents of the other monomer units were measured by nuclear magnetic resonance spectroscopy.

[0065] In addition, the content of the polyvinyl alcohol and boron in the obtained acrylic rubber and the Mooney viscosity ML (1+4) 100° C. were measured. The results are shown in Tables 1 to 3.

[0066] The content of the polyvinyl alcohol in the acrylic rubber was measured by a pyrolysis GC-MS. More specifically, the acrylic rubber was thermally decomposed at 550° C. by a double shot pyrolyzer (PY-2020D manufactured by Frontier Laboratories Inc.), and crotonaldehyde, which was a decomposition product of polyvinyl alcohol, was quantitatively determined by gas chromatography mass spectrometry (JMS-DX303 manufactured by JEOL Ltd., agilent capillary column DB-5, carrier gas: helium, inlet temperature: 280° C., temperature rising condition: holding at 70° C. for 2 minutes and then rising to 280° C. at 12° C./min) using an absolute calibration curve method, thereby measuring the content of the polyvinyl alcohol in the acrylic rubber. The content of boron was measured by ICP emission spectrometry. The Mooney viscosity ML (1+4) 100° C. was measured according to the method specified in JIS K6300.

[0067] Subsequently, each of the obtained acrylic rubbers and each component shown below were used in the compositions shown in Tables 1 to 3, and kneading was performed with an 8-inch open roll to obtain a rubber composition. [0068] Filler: carbon black (Seast SO manufactured by Tokai Carbon Co., Ltd.) [0069] Lubricant a: stearic acid (Lunac S-90 manufactured by Kao Corporation) [0070] Lubricant b: stearylamine (Farmin 80 manufactured by Kao Corporation) [0071] Anti-aging agent: 4,4′-bis(α,α-dimethylbenzyl) diphenylamine (Naugard #445 manufactured by Addivant) [0072] Surfactant: sodium laurylsulfate (Emal 0 manufactured by Kao Corporation) [0073] Crosslinking agent a: 1-(2-cyanoethyl)-2-methylimidazole (CN-25 manufactured by Shikoku Chemicals Corporation) [0074] Crosslinking agent b: 2,2-bis[4-(4-aminophenoxy) phenyl] propane (BAPP manufactured by Wakayama Seika Kogyo Co., Ltd.) [0075] Crosslinking agent c: n-butyl 4,4-di(t-butylperoxy) valerate PERHEXA V-40 manufactured by NOF Corporation) [0076] Crosslinking agent d: trimethylolpropane trimethacrylate (Monosizer TD-1500 manufactured by DIC Corporation) [0077] Crosslinking accelerator a: ammonium benzoate (VALKNOCK AB manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) [0078] Crosslinking accelerator b: 1,3-di-o-tolylguanidine (NOCCELER DT manufactured by Ouchi Shinko Chemical industrial Co., Ltd.) [0079] Crosslinking accelerator c: trimethylthiourea (NOCCELER TMU manufactured by Ouchi Shinko Chemical industrial CO., Ltd.) [0080] Crosslinking accelerator d: phenothiazine (Manufactured by Seiko Chemical Co., Ltd.)

[0081] The obtained rubber composition was dispensed into a sheet having a thickness of 2.4 mm, and then heated and pressurized at 170° C. and 10 MPa for 20 minutes using a press vulcanizer. Subsequently, heating was carried out in a gear oven at 170° C. for 4 hours to obtain a crosslinked product of the rubber composition.

[0082] (Evaluation of Properties of Crosslinked Product)

[0083] The tensile strength and elongation of the crosslinked product were. measured in accordance with JIS K6251-2010, Further, the hardness of the crosslinked product was measured using a type A durometer in accordance with JIS K6253-2006.

[0084] (Evaluation of Water Resistance)

[0085] In accordance with the “immersion test” of JIS K6258-2010, the crosslinked product was subjected to an immersion test with pure water, and the volume change rate of the crosslinked product before and after the test was calculated based on the following formula.

Volume change rate (%)=(volume after test−volume before test)/volume before test×100

[0086] (Evaluation of Copper Damage Resistance)

[0087] A crosslinked product molded into a No. 3 dumbbell shape was used as a test piece. 5 g of a slurry obtained by mixing engine oil (Mobil 1 5W-30 manufactured by EMG Lubricanz Performance Materials Inc.) and copper powder (CE-1110 manufactured by Fukuda Metal Foil & Powder Co., Ltd.) at a ratio of engine oil/copper powder=3/1 (mass ratio) was applied using a brush so as to completely cover the marked lines of the test piece, and dried at room temperature for 12 hours. Subsequently, the copper damage resistance test was performed by heating the test piece in a gear oven at 150° C. for 500 hours. Thereafter, the copper-containing paste was peeled off from the test piece using a spatula, and the elongation of the test piece was measured in accordance with JIS K6251-2010, The elongation change rate (%) before and after the test was calculated based on the following formula.

Elongation change rate (%)=(elongation after test−elongation before test)/elongation before test×100

TABLE-US-00001 TABLE 1 Comp. Comp. Example Example Example Example Example Example 1-1 1-1 1-2 1-3 1-2 1-4 Monomer composition Ethyl acrylate 45.6 45.6 45.6 45.6 45.6 — (parts by mass) n-Butyl acrylate 36.9 36.9 36.9 36.9 36.9 83 Ethylene 3 3 3 3 3 3.4 Vinyl acetate 13.1 13.1 13.1 13.1 13.1 12.1 Glycidyl Methacrylate 1.48 1.48 1.48 1.48 1.48 1.16 Allyl glycidyl ether — — — — — 0.29 Temperature of pure water (° C.) 95 70 50 30 10 50 Content of polyvinyl alcohol (parts, by mass) 0.4 0.6 1.1 1.6 2.5 1.1 Content of boron (ppm by mass) 21 26 37 43 46 65 Mooney viscosity 48 48 48 48 48 26 Composition of rubber Acrylic rubber 100 100 100 100 100 100 composition Filler 50 50 50 50 50 50 (parts by mass) Lubricant a 1 1 1 1 1 1 Lubricant b 0.3 0.3 0.3 0.3 0.3 — Anti-aging agent 1 1 1 1 1 1 Surfactant 1 1 1 1 1 1 Crosslinking agent a 1.4 1.4 1.4 1.4 1.4 1.4 Crosslinking accelerator a 0.3 0.3 0.3 0.3 0.3 0.3 Properties of crosslinked Tensile strength (MPa) 13.8 13.9 14 13.8 13.9 9.8 product Elongation (%) 310 320 320 330 310 290 Hardness 65 66 65 65 65 66 Water resistance Volume change rate (%) 9 11 12 13 16 8 Copper damage resistance Elongation change rate (%) −51 −39 −35 −29 −28 −32

TABLE-US-00002 TABLE 2 Comp. Comp. Example Example Example Example Example 2-1 2-1 2-2 2-3 2-2 Monomer composition Ethyl acrylate 45.6 45.6 45.6 45.6 45.6 (parts by mass) n-Butyl acrylate 36.9 36.9 36.9 36.9 36.6 Ethylene 3 3 3 3 3 Vinyl acetate 13.1 13.1 13.1 13.1 13.1 Monobutyl maleate 1.28 1.28 128 1.28 1.28 Temperature of pure water (° C.) 95 70 50 30 10 Content of polyvinyl alcohol (parts by mass) 0.3 0.7 1.2 1.6 2.2 Content of boron (ppm by mass) 34 43 58 72 81 Mooney viscosity 43 43 43 43 43 Acrylic rubber 100 100 100 100 100 Composition of Filler 50 50 50 50 50 rubber composition Lubricant a 1 1 1 1 1 (parts by mass) Lubricant b 0.3 0.3 0.3 0.3 0.3 Anti-aging agent 1 1 1 1 1 Crosslinking agent b 0.8 0.8 0.8 0.8 0.8 Crosslinking accelerator b 1 1 1 1 1 Properties of crosslinked Tensile strength (MPa) 10.1 10.0 10.2 10.2 10.3 product Elongation (%) 290 300 290 280 290 Hardness 64 64 64 64 64 Water resistance Volume change rate (%) 8 10 8 13 16 Copper damage resistance Elongation change rate (%) −55 −32 −23 −19 −17

TABLE-US-00003 TABLE 3 Example Example Example 3-1 3-2 3-3 Monomer Methyl acrylate 11 — — composition Ethyl acrylate — — 38.6 (parts by mass) n-Butyl acrylate 73.4 83 34.2 Ethylene 2 2 2.6 3.6 Vinyl acetate 11.8 12.8 23.6 Temperature of pure water (° C.) 50 50 50 Content of polyvinyl alcohol 1.2 1.1 1.2 (pans by mass) Content of boron (ppm by mass) 30 75) 16 Mooney viscosity 43 38 48 Composition of Acrylic rubber 100 100 100 rubber Filler 50 50 50 composition Lubricant a 1 1 1 (parts by mass) Lubricant b — — 0.5 Anti-aging agent 1 1 1 Surfactant 1 1 — Crosslinking agent a 1.4 1.4 — Crosslinking agent b — — — Crosslinking agent c — — 7 Crosslinking agent d — — 7 Crosslinking 0.3 0.3 — accelerator a Crosslinking — — — accelerator b Crosslinking — — 0.5 accelerator c Crosslinking — — 0.5 accelerator d Properties of Tensile strength 12.1 11.5 11.6 cross linked (MPa) product Elongation (%) 280 240 410 Hardness 67 61 58 Water resistance Volume change rate 12 12 9 (%) Copper damage Elongation −35 −37 −39 resistance change rate (%)

[0088] As can be seen from Table 1, in the acrylic rubber in which the crosslinking monomer having an epoxy group is used as the crosslinking monomer, when the content: of the poly vinyl alcohol in the acrylic rubber is within the specific. range, both of the water resistance and copper damage resistance can be achieved (any one of them is not excessively deteriorated). Similarly, as can be seen from Table 2, in the acrylic rubber in which the crosslinking monomer having a carboxyl group is used as the crosslinking monomer, when the content of the polyvinyl alcohol in the acrylic rubber is within the specific range, both of the water resistance and copper damage resistance can be achieved (any one of them is not excessively deteriorated). In addition, as can be seen from Table 3, in the acrylic rubber in which the crosslinking monomer is not used, when the content of the polyvinyl alcohol in the acrylic rubber is within the specific range, both of the water resistance and copper damage resistance can be achieved (any one of them is not excessively deteriorated).