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EP-4006114-B1 - COATING AGENT FOR OIL SEAL

EP4006114B1EP 4006114 B1EP4006114 B1EP 4006114B1EP-4006114-B1

Inventors

  • YASUNAGA, Natsumi

Dates

Publication Date
20260513
Application Date
20200630

Claims (7)

  1. A coating agent for oil seal comprising 10 to 90 parts by weight in total of fluororesin particles having a particle size of 0.5 µm or less and filler particles other than fluororesin particles having a particle size of 1 to 20 µm, and 10 to 40 parts by weight of a wax having a melting point of 40 to 160°C, based on 100 parts by weight of isocyanate group-containing 1,2-polybutadiene, and being prepared as an organic solvent solution, wherein the fluororesin particles are used at a ratio of 20 to 80 wt.% of the total filler amount; and wherein the particle size of the filler particles is measured according to JIS Z8825 corresponding to ISO 13320.
  2. The coating agent for oil seal according to claim 1, wherein all the fillers are used at a rate of 40 to 80 parts by weight.
  3. The coating agent for oil seal according to claim 1, wherein the fluororesin particles are used at a rate of 30 to 70 wt.% of the total filler amount.
  4. The coating agent for oil seal according to claim 1, wherein the wax is used at a rate of 10 to 30 parts by weight.
  5. An oil seal, which is subjected to coating treatment using the coating agent according to claim 1.
  6. The oil seal according to claim 5, wherein after coating treatment, heat treatment is performed at 150 to 250°C for 10 minutes to 24 hours.
  7. The oil seal according to claim 5 or 6, wherein a contact angle between an oil seal surface and engine oil is less than 35°.

Description

TECHNICAL FIELD The present invention relates to a coating agent for oil seal. More particularly, the present invention relates to a coating agent for oil seal having excellent dispersibility for fillers. BACKGROUND ART Oil seal is widely used as an important machine element in the field of vehicles, industrial machines, and the like. Oil seal is used for the purpose of movement and sliding; however, in that case, deterioration of the seal oil and the sealing material due to the frictional heat of the seal, and energy loss in devices due to frictional resistance are often problematic. In order to reduce the torque of the oil seal, it is preferable for oil to be held on the sliding surface. To satisfy this purpose, it is required to improve wettability with oil by increasing the roughness of the sliding surface. Here, in the case of a coating agent comprising, as a filler, only fluororesin particles having a low particle size of about 0.1 to 10 µm, which are conventionally used in coating agents, the surface energy of fluororesin is high, so that it is difficult to improve wettability with oil significantly. Further, because of its small particle size, it is also difficult to increase the roughness of the coating surface. For this reason, it is considered to use a coating agent containing a filler with a large particle size. However, when a filler other than PTFE is used, abrasion resistance is lowered. When only PTFE is used, the amount of aggregation is large, resulting in deterioration of liquid stability and deterioration of the coating surface state due to aggregates. The present applicant has previously proposed, in Patent Documents 1 and 2, surface-treating agents for vulcanized rubber comprising 10 to 160 parts by weight respectively of a wax having a softening point of 40 to 160°C and a fluororesin, or 10 to 160 parts by weight respectively of a fluororesin and a polyethylene resin, based on 100 parts by weight of isocyanate group-containing 1,2-polybutadiene, wherein the surface-treating agents are prepared as organic solvent solutions. These surface-treating agents are supposed to be effectively applicable to oil seal and the like; however, further lower torque characteristics are demanded. To address this problem, the present applicant has further proposed a coating agent for oil seal comprising 10 to 160 parts by weight of a fluororesin, silica, silicone resin, or polycarbonate filler having a particle size of 0.5 to 30, µm based on 100 parts by weight of isocyanate group-containing 1,2-polybutadiene, and being prepared as an organic solvent solution, wherein a contact angle between a substrate surface coated with the coating agent and engine oil is less than 35°. However, further improvements are required for the dispersibility of the PTFE filler, which is a fluororesin (Patent Document 3). Here, a dispersant is added to improve the dispersibility of PTFE; however, if a large amount of dispersant is added, the strength of a film formed from the coating agent is reduced. Therefore, it was difficult to obtain a balance between the strength of the coating agent and its dispersibility. JP 2008 189892 A aims to provide a surface treating agent for a vulcanized rubber, which satisfies performances required to a coating agent for a rubbery elastomer etc., such as anti-fixation, anti-adhesion, anti-blocking and wear-resistance improvement and prevents peeling of a coating film caused by adhesion at hot-pressing or frictional wear under a high contact pressure. As a solution to the problem, the document describes a coating agent which comprises (a) a cellulose derivative, (b) 1,2-polybutadiene containing an isocyanate group and (c) at least one chosen from a wax having a softening point of 40-160°C, graphite and a fluororesin. JPH09 109703 A aims to provide a paint composition manufactured by including solid lubricating material in fluororubber and having not only excellency in flexibility, slidability and wear resisting property but also possibility of provision of sealing property and anti-gas permeability, particularly provide a paint composition used for a fuel cap packing for the purpose of gasoline, etc., and provide a fuel cap packing coated with the abovementioned paint composition. As a solution to the problem, the document describes a fuel cap packing coated with paint composition including one or more kinds of solid lubricating material out of a group consisting of molybdenum disulfide, graphite, and silicone rubber powder and paint composition including one or more kinds of solid lubricating material selected out of a group consisting of polytetrafluoroethylene, molybdenum disulfide, graphite and the silicone rubber powder. CN 108 587 404 A describes an oil seal coating agent, a spraying method thereof and an oil seal prepared therefrom. The oil seal coating agent is composed of a component A, a component B and a component C according to a mass proportion of 100:7-8:100, wherein the componen