JP2000230067A - Foamed rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition which can give a seal having a lip slide part having microscopic irregularities and therefore showing improved performances by compounding a nitrile rubber with a specified combination of blowing agents or with specified microspheres. SOLUTION: This composition comprises 100 pts.wt. synthetic rubber, especially, nitrile rubber and either a combination of 1-3 pts.wt. dinitrosopentamethylenetetramine(DPT) with azodicarbonamide(AZC) or 5-10 pts.wt. thermally expandable microspheres, especially, ones made from a vinylidene chloride/acrylonitrile copolymer and containing isobutane. The use of the DPT/AZC combination realizes an unvulcanized raw rubber stock and a rubber vulcanizate having stable and fine closed cells. When the temperature of the microspheres rises, the shell polymer softens and the contained isobutane is gasified to form voids of 50 μm in size on the average.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for improving the sealing performance by forming irregularities on a lip sliding portion of a sealing material such as a bearing seal, a wheel seal or an oil seal.

[0002]

2. Description of the Related Art Conventionally, as a means for improving sealing performance, there has been known a method of kneading additives such as PTFE resin, graphite, molybdenum, and cellulose fiber into a rubber material. There are many problems that need to be resolved. Also, techniques for modifying the lip surface have been studied. The method is as follows: (1) A method of applying a fluorine coating treatment to the lip surface. (2) A method of forming a spiral groove on the lip. And so on.

[0003]

However, the above-described method of modifying the lip surface presents various disadvantages as described below. That is, the method (1) of applying a fluorine coating to the lip surface has problems in terms of cost and molding method, and the method (2) of forming a spiral groove on the lip has a problem in the right and left directions of rotation. give a big limitation to the point-of-use and requires absolutely right and left two types of products for which there is. In view of the above, the present invention has conceived of forming micro unevenness on the lip surface as a method of modifying the lip surface easily and easily without being affected by physical properties.

[0004]

According to the present invention, as a method of modifying the surface of a seal lip, a number of foaming agents and microspheres have been studied in order to form micro unevenness on the seal lip. We have found a rubber composition that can form micro unevenness on the lip surface of the seal by using a combination of agents and specific microspheres.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventionally known blowing agents include (a) inorganic blowing agents (sodium bicarbonate, ammonium nitrite, etc.) (b) nitroso compounds: N, N'-dinitrosopentamethylene Tetramine (DPT) is generally used. (C) Azo compound: azodicarbonamide (AZC),
Azobisisobutyronitrile (ABIN) (d) Sulfonyl hydrazide compound: benzenesulfonyl hydrazide (BSH), toluenesulfonyl hydrazide (TSH), derivatives thereof, and the like. For the purposes of the present invention, the decomposition temperature is limited to a range of 180 ° C. to 200 ° C. and is fine and capable of forming closed cells. As the blowing agent meeting the conditions, the DPT of (b) and the A of (c)
There is ZC. However, when DPT is used alone, the unvulcanized dough changes with time, the scorch time is shortened, and foaming is not performed. On the other hand, when AZC is used alone, the scorch time of the unvulcanized dough becomes longer, causing a reduction in vulcanization. Therefore, by using DPT and AZC together, it is possible to reduce the change with time of the unvulcanized dough and to produce a stable, fine, vulcanized rubber having closed cells.

Various hollow microspheres have been industrialized for a long time, and inorganic microspheres such as shirasu balloons obtained by processing shirasu produced in Minamikyushu, microballoons obtained from borosilicate glass, and alumina balloons. Materials include organic materials such as carbon spheres having a carbon composition and phenol balloons comprising a foaming agent and a phenol resin.

[0007] As a result of studying such various microspheres, it is the Expancel manufactured by Expellcel that forms micro unevenness on the cross section of the rubber vulcanizate.
The most uniform one was obtained. The Expancel is a thermo-expandable microsphere. The polymer of the outer shell (vinylidene chloride / acrylonitrile copolymer) increases when the temperature is increased.
Is softened, the contained isobutane is gasified, and swells like a balloon ball with a true sphere and no internal pressure, forming a central cavity of 50 μm on average. Du5 with a particularly high temperature range for foaming
51 and 091 are optimal.

[0008]

EXAMPLES <Example 1> Nitrile rubber: 100 Stearin sun: 1 Active zincation: 5 Antioxidant ODP: 3 MAF carbon: 60 Plasticizer DOP: 10 Sulfur: 0.5 Accelerator (A): 2 0 Accelerator (B): 1.5 Cell microphone A (DPT): 1.5 AZC: 1.5

<Example 2> Nitrile rubber: 100 Stearin sun: 1 Active zincation: 5 Antioxidant ODP: 3 MAF carbon: 60 Plasticizer DOP: 10 Sulfur: 0.5 Accelerator (A): 2.0 Accelerator (B): 1.5 Du551: 5

[0010] Table 1 shows the rotational torque value in the dry state in comparison with the conventional one.

[Table 1] The prior art shows that the rotational torque value decreases with an increase in the number of revolutions, and the lip gradually stops following the shaft. However, in the case of the embodiment, almost constant value is maintained regardless of the rotation speed. It is considered that the formation of micro unevenness on the sliding surface of the lip increases the contact area and makes the shaft more closely contact with the shaft, and as a result, maintains a high rotational torque value.

Claims (1)

[Claims] 1. A combination of (A) 1 to 3 parts by weight of dinitrosopentamethylenetetramine (DPT) and azodicarbonamide (AZC) with 100 parts by weight of synthetic rubber, particularly nitrile rubber, and (B) thermal expansion Microspheres, especially vinylidene chloride containing isobutane
A microsphere formed of an acrylonitrile copolymer: a foamed rubber composition characterized by containing 5 to 10 parts by weight, either (A) or (B).