NITRILE RUBBER-BASED COMPOSITION

Abstract

A nitrile rubber-based composition comprising 1,000 to 2,500 parts by weight of a magnetic powder or silylated magnetic powder having a compressed density of 3.4 to 3.7 g/cm.sup.3, 0.5 to 20 parts by weight of alkoxyalkylsilane, and 8 to 40 parts by weight of a plasticizer, based on 100 parts by weight of nitrile rubber, hydrogenated nitrile rubber, or blend rubber thereof. The nitrile rubber-based composition that does not cause deterioration in roll processability and in adhesion between an adhesive applied to a metal plate and the rubber, even when a magnetic powder is added at a ratio as high as 1,000 parts by weight or more based on 100 parts by weight of nitrile rubber, hydrogenated nitrile rubber, or blend rubber thereof.

Claims

1. A nitrile rubber-based composition comprising 1,000 to 2,500 parts by weight of a magnetic powder or silylated magnetic powder having a compressed density of 3.4 to 3.7 g/cm.sup.3, 0.5 to 20 parts by weight of alkoxyalkylsilane, and 8 to 40 parts by weight of a plasticizer, based on 100 parts by weight of nitrile rubber, hydrogenated nitrile rubber, or blend rubber thereof.

2. The nitrile rubber-based composition according to claim 1, wherein alkoxyalkylsilane is used at a ratio of 0.5 to 1.0 parts by weight based on 1,000 parts by weight to less than 1300 parts by weight of the magnetic powder.

3. The nitrile rubber-based composition according to claim 1, wherein alkoxyalkylsilane is used at a ratio of 1.0 to 2.0 parts by weight based on 1,300 parts by weight to less than 1700 parts by weight of the magnetic powder.

4. The nitrile rubber-based composition according to claim 1, wherein alkoxyalkylsilane is used at a ratio of 2.0 to 10 parts by weight based on 1,700 parts by weight to less than 2,000 parts by weight of the magnetic powder.

5. The nitrile rubber-based composition according to claim 1, wherein alkoxyalkylsilane is used at a ratio of 10 to 20 parts by weight based on 2,000 to 2,500 parts by weight of the magnetic powder.

6. The nitrile rubber-based composition according to claim 1, wherein millable type nitrile rubber having a Mooney viscosity ML.sub.1+4 (100 C.) of 20 to 50 is used.

7. The nitrile rubber-based composition according to claim 1, wherein a magnetic powder having two particle size distribution peaks at 1 to 2 m and 2 to 4 m is used.

8. The nitrile rubber-based composition according to claim 1, wherein the magnetic powder having a compressed density of 3.4 to 3.7 g/cm.sup.3 is at least one of a ferrite magnet and a rare-earth magnet.

9. The nitrile rubber-based composition according to claim 8, wherein the ferrite magnet is a strontium ferrite or a barium ferrite.

10. The nitrile rubber-based composition according to claim 1, wherein alkoxyalkylsilane is trialkoxyoctylsilane.

11. The nitrile rubber-based composition according to claim 1, which is applied as a vulcanization molding material of rubber magnet for sensor used in magnetic encoders.

12. A rubber magnet for sensor, which is a vulcanization-molded product of the nitrile rubber-based composition according to claim 11.

13. A magnetic encoder composed of the rubber magnet for sensor according to claim 12.

14. The magnetic encoder according to claim 13, which is used in an encoder part of a wheel speed sensor.

15. The magnetic encoder according to claim 14, wherein the encoder comprises an annular magnetic rubber molded product mounted on a support member capable of being attached to a rotating body, and single or multiple N pole and S pole are magnetized in the circumferential direction.

16. A method for producing a rubber magnet for sensor, comprising vulcanizing a nitrile rubber-based composition in a mold to which a magnetic field is applied, wherein the composition comprises 1,000 to 2,500 parts by weight of a magnetic powder or silylated magnetic powder having a compressed density of 3.4 to 3.7 g/cm.sup.3, 0.5 to 20 parts by weight of alkoxyalkylsilane, and 8 to 40 parts by weight of a plasticizer, based on 100 parts by weight of nitrile rubber, hydrogenated nitrile rubber, or blend rubber thereof.

Description

EXAMPLES

[0023] The following describes the present invention with reference to Examples.

Example 1

[0024]

TABLE-US-00001 Nitrile rubber (DN219, produced by JSR; 70 parts by weight Mooney viscosity ML.sub.1+4 (100 C.): 27) Hydrogenated nitrile rubber 30 parts by weight (Zetpol 2020L, produced by Zeon Corporation; Mooney viscosity ML.sub.1+4 (100 C.): 57.5) Strontium ferrite magnetic powder 1,000 parts by weight (SF-D630, produced by Dowa F-Tec Co., Ltd.; compressed density: 3.59 g/cm.sup.3; particle size distribution peaks: 1.7 m and 3.3 m) Active zinc oxide 3 parts by weight (produced by Seido Chemical Industry Co., Ltd.) Fatty acid amide (Diamide O-200, produced by 2 parts by weight Nippon Kasei Chemical Co., Ltd.) Antioxidant (Nocrac CD, produced by 2 parts by weight Ouchi Shinko Chemical Industrial Co., Ltd.; 4,4-bis(,-dimethylbenzyl)diphenyl amine) Antioxidant (Nocrac MBZ, produced by 0.5 parts by weight Ouchi Shinko Chemical Industrial Co., Ltd.; zinc salt of 2-mercaptobezimidazole) Stearic acid (produced by Miyoshi Oil & Fat Co., 2 parts by weight Ltd.) Paraffin wax (produced by Nippon Seiro Co., 2 parts by weight Ltd.) Sulfur (produced by Tsurumi Chemical Industry 2 parts by weight Co., Ltd.) Tetramethylthiuram disulfide (Nocceler TT, 2 parts by weight produced by Ouchi Shinko Chemical Industrial Co., Ltd.) N-cyclohexy1-2-benzothiazyl sulfenamide; 1 part by weight (Nocceler CZ, produced by Ouchi Shinko Chemical Industrial Co., Ltd.) Plasticizer (C-9N, produced by ADEKA 8 parts by weight Corporation) Alkoxyalkylsilane 0.5 parts by weight (OCTEO produced by Evonik Industries)
The above components were kneaded by a closed type kneader (pressurizing type kneader) and an open roll, and the kneaded product was compression-molded at 180 C. for 4 minutes, thereby vulcanization-molding a two mm thick test rubber sheet.

[0025] The compressed density (CD value) of the magnetic powder was calculated in such a manner that 10 g of the magnetic powder sample was placed in a cylindrical mold having a diameter of 25.4 mm, and compressed by a press at an effective pressure of 1,000 kgf/cm.sup.2 (98 MPa), and the compressed density was calculated from the measured value of the sample thickness (h) after compression using the following formula:

CD (g/cm.sup.3)=10/(1.27).sup.2h

[0026] Using the kneaded product and test rubber sheet, the following evaluations and measurements were each carried out.

[0027] Compound processability: A rubber composition that could be fed as a sheet after it was wound around a roll, followed by addition kneading was evaluated as , and a rubber composition that could not be fed as a sheet was evaluated as X.

[0028] TP moldability: A test rubber sheet that could be released smoothly from the mold without sticking to the mold or damaging the rubber itself was evaluated as , and a test rubber sheet that was difficult to release from the mold was evaluated as X.

[0029] Adhesion: A kneaded sheet compound was vulcanized and bonded to a SUS plate coated with a phenolic adhesive, and the adhesion state when this was peeled using pincers was observed. A rubber remaining ratio of 70% or more was evaluated as , and less than 70% as X.

[0030] Compound fluidity: According to JIS K6300-1: 2001 corresponding to ISO 289-1: 1994 and 289-2: 1994, the minimum Mooney viscosity Vm was measured under a temperature condition of 125 C. using a Mooney viscometer (AM-3, produced by Toyo Seiki Seisaku-sho, Ltd.). A Vm of 80% or more was evaluated as , and less than 80% as X.

[0031] Normal state physical properties (hardness): According to JIS K6253: 1997 corresponding to ISO 7619: 1997, the instant hardness Hs was measured using a type A durometer.

[0032] Normal state physical properties (tensile strength, elongation): According to JIS K6251: 2010 corresponding to ISO 37, the tensile strength (MPa) and elongation at break (%) were measured.

[0033] Magnetic force: The magnetic force of a sample with a thickness of 2 mm, a length of 3 mm, and a width of 5 mm was measured using a vibrating sample magnetometer (VSM-5, produced by Toei Industry Co., Ltd.) under the conditions of an applied magnetic field of 1.510.sup.4 Oe and a frequency of 80 Hz, and the saturation magnetization Ms (unit: mT), residual magnetization Mr (unit: mT), and coercive force iHc (unit: kA/m) were determined from the magnetic force curve.

Comparative Example 1

[0034] In Example 1, alkoxyalkylsilane was not used.

Comparative Example 2

[0035] When the amount of magnetic powder was changed to 2,000 parts by weight in Comparative Example 1, kneading and molding could not be performed.

Comparative Example 3

[0036] When the plasticizer was not used in Example 1, the resultant became sandy during kneader kneading, and molding could not be performed.

Example 2

[0037] In Example 1, the amount of magnetic powder was changed to 2,000 parts by weight, the amount of alkoxyalkylsilane was changed to 5 parts by weight and the amount of plasticizer was changed to 40 parts by weight, respectively.

Comparative Example 4

[0038] In Example 2, the amount of alkoxyalkylsilane was changed to 12.5 parts by weight and the amount of plasticizer was changed to 60 parts by weight, respectively.

Comparative Example 5

[0039] In Example 2, the amount of plasticizer was changed to 80 parts by weight.

Comparative Example 6

[0040] In Comparative Example 5, the amount of alkoxyalkylsilane was changed to 20 parts by weight.

Comparative Example 7

[0041] When the amount of plasticizer was changed to 16 parts by weight in Example 2, kneading and molding could not be performed.

Example 3

[0042] In Example 1, the amount of magnetic powder was changed to 2,000 parts by weight, the amount of alkoxyalkylsilane was changed to 10 parts by weight and the amount of plasticizer was changed to 30 parts by weight, respectively.

Comparative Example 8

[0043] In Example 3, the amount of alkoxyalkylsilane was changed to 30 parts by weight.

Comparative Example 9

[0044] In Example 3, the same amount (10 part by weight) of mercapto-based silane coupling agent was used in place of alkoxyalkylsilane.

Comparative Example 10

[0045] In Example 3, the same amount (10 part by weight) of sulfur-based silane coupling agent was used in place of alkoxyalkylsilane.

Example 4

[0046] In Example 1, the amount of magnetic powder was changed to 2,500 parts by weight, the amount of alkoxyalkylsilane was changed to 20 parts by weight and the amount of plasticizer was changed to 40 parts by weight, respectively.

Comparative Example 11

[0047] When the amount of alkoxyalkylsilane was changed to 5 parts by weight in Example 4, molding could not be performed.

Comparative Example 12

[0048] When the amount of magnetic powder was changed to 3,000 parts by weight, the amount of alkoxyalkylsilane was changed to 30 parts by weight, and the amount of plasticizer was changed to 50 parts by weight, respectively in Example 1, kneading and molding could not be performed.

[0049] Results of evaluations and measurements obtained in the foregoing Examples and Comparative Examples are given in the following Table.

TABLE-US-00002 TABLE Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Measurement item Ex. 1 Ex. 1 Ex. 2 Ex. 4 Ex. 5 Ex. 6 Ex. 3 Ex. 8 Ex. 9 Ex. 10 Ex. 4 Ex. 11 [Before vulcanization] Compound processability kneadability evaluation [After vulcanization] Moldability Tp moldability evaluation X X X Adhesion Rubber remaining ratio (%) 80 60 90 10 10 50 90 40 60 60 70 50 Evaluation X X X X X X X X Compound fluidity Mooney viscosity Vm 107.8 117 94.8 44.5 43.2 30.6 93.7 50 179.6 Normal state physical properties Hardness (Duro A, peak) 89 90 93 82 74 61 91 84 92 Tensile strength (MPa) 2.6 2.5 3.7 1.1 0.95 0.34 1.5 1.2 3.9 Elongation (%) 200 180 6 30 30 30 90 40 3 Magnetic force Saturation magnetization Ms (mT) 248 253 293 292 282 285 295 290 299 Residual magnetization Mr (mT) 201 205 242 240 229 234 238 236 245 Coercive force iHc (kA/m) 141 143 126 146 154 128 129 119 122

[0050] The above results demonstrate the following.

[0051] (1) In Examples 1 to 4, the compound processability, moldability, adhesion to the metal plate, and compound fluidity are all excellent. Since a large amount of magnetic powder is compounded, molded products having a high magnetic force can be produced.

[0052] (2) When alkoxyalkylsilane is not used, the adhesion to the metal plate is reduced (Comparative Example 1), or in the first place, kneading and molding cannot be performed (Comparative Example 2).

[0053] (3) When a plasticizer is not used, molding cannot be performed (Comparative Example 3).

[0054] (4) When a prescribed amount or more of alkoxyalkylsilane is used, the adhesion to the metal plate is reduced (Comparative Example 8).

[0055] (5) When an insufficient amount of alkoxyalkylsilane is compounded based on the amount of magnetic powder, kneading and molding cannot be performed (Comparative Example 7). Even if the amount of plasticizer is increased to allow kneading, molding cannot be performed, and the adhesion to the metal plate is reduced (Comparative Example 11).

[0056] (6) When a silane coupling agent other than alkoxyalkylsilane is used, moldability deteriorates, and adhesion to the metal plate cannot be ensured (Comparative Examples 9 and 10).

[0057] (7) If the amount of plasticizer is too large, the adhesion to the metal plate is reduced (Comparative Examples 4 to 6).

INDUSTRIAL APPLICABILITY

[0058] The nitrile rubber-based composition according to the present invention can be effectively used as a vulcanization molding material of rubber magnet for sensor and the like applied to magnetic encoders for wheel speed sensors etc.