Oil seal coating

Abstract

DEPCT65 Oil-sealing coatings containing 10 to 90 parts by weight of filler. And 10 to 40 parts by weight of beeswax, relying on 100 parts by weight of isocyanates composed of... 1,2-polybutadiene and its prepared solution in an organic solvent which serves as a filler. Silicone resin particles with particle sizes of 0.5 to 10 micrometers and fluororesin particles of a certain size. Particles of 0.1 to 2 micrometers were used at a ratio of 20 to 80 percent by weight of the substance. Adding all the coatings for oil-resistant seals can demonstrate the excellent sealing performance inherent in the seals. It is oil-resistant while maintaining the excellent spreading ability of the coating and can also... It has the characteristic of low torque. -----------------------------------------------------------

Description

Oil seal coating agent

[0001] The present invention relates to a coating agent for oil seals, and more particularly to a coating agent for oil seals that has excellent dispersibility of fillers.

[0002] Oil seals are widely used as important mechanical elements in fields such as automobiles and industrial machinery. Oil seals are used for moving and sliding applications, but in these applications, problems often arise, such as deterioration of the sealing oil and sealing materials due to frictional heat in the seal, and energy loss in the equipment due to frictional resistance.

[0003] To reduce the torque of an oil seal, it is preferable to retain oil on the sliding surface, which requires increasing the roughness of the sliding surface to improve its oil wettability.However, conventional coating agents that contain only small particle diameter fluororesin particles of approximately 0.1 to 10 μm as filler have difficulty significantly improving oil wettability due to the high surface energy of the fluororesin, and it is also difficult to increase the roughness of the coating surface due to the small particle diameter.

[0004] On the other hand, by forming a coating of a material with a lower friction coefficient than the seal material on the sliding surface of the oil seal lip, the oil seal can be made low-friction, but if the coating peels off due to sliding, the low-friction effect will be lost.

[0005] The present applicant has previously proposed in Patent Documents 1 and 2 a surface treatment agent for vulcanized rubber prepared as an organic solvent solution by adding 10 to 160 parts by weight of a wax having a softening point of 40 to 160°C and a fluororesin or both of such a wax and a polyethylene resin to 100 parts by weight of isocyanate group-containing 1,2-polybutadiene. These are said to be effectively applied to oil seals and the like, but further low torque properties are desired.

[0006] In response to this problem, the present applicant has further proposed a coating agent for oil seals, which is prepared as an organic solvent solution by adding 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 to 100 parts by weight of isocyanate group-containing 1,2-polybutadiene, and which results in a contact angle of less than 35° between the coated substrate surface and engine oil. However, further improvement in the dispersibility of the PTFE filler, which is a fluororesin, is desired (Patent Document 3).

[0007] In order to improve the dispersibility of PTFE, dispersants are added, but adding too much dispersant reduces the strength of the film formed from the coating agent. On the other hand, using fillers other than PTFE reduces the abrasion resistance. Therefore, it has been difficult to balance the strength of the coating agent with its dispersibility.

[0008] Patent No. 3893985 Patent No. 4873120 WO 2016 / 132982 A1

[0009] An object of the present invention is to provide a coating agent which maintains good dispersibility of the coating agent, allows the excellent sealing performance inherent to an oil seal to be exhibited, and also enables low torque to be achieved.

[0010] The object of the present invention is achieved by a coating agent for oil seals, which is prepared as an organic solvent solution containing 10 to 90 parts by weight of a filler and 10 to 40 parts by weight of a wax per 100 parts by weight of isocyanate group-containing 1,2-polybutadiene, and which uses as fillers silicone resin particles having a particle size of 0.5 to 10 μm and fluororesin particles having a particle size of 0.1 to 2 μm, each in a proportion of 20 to 80% by weight of the total filler amount.

[0011] The use of a combination of fluororesin particles and silicone resin particles as fillers in the coating agent ensures the dispersibility of the coating agent, and by using silicone resin particles with a large particle size and selecting particles that will result in a contact angle of less than 35° between the coated oil seal surface and engine oil, the roughness of the coating surface is increased while improving wettability with oil and reducing the coefficient of dynamic friction in oil, resulting in the excellent effect of achieving low torque for the oil seal.

[0012] Isocyanate-containing 1,2-polybutadiene resins with molecular weights of approximately 1,000 to 3,000 and terminal isocyanate groups are commonly used. Commercially available products, such as Nippon Soda's Nisso TP-1001 (a solution containing 50% by weight of butyl acetate), can be used as is. The isocyanate groups added as terminal groups react with functional groups and hydroxyl-containing components on the surface of vulcanized rubber, allowing for adhesion and curing. This polybutadiene resin has better compatibility and solubility with rubber than polyurethane resins, which also react with isocyanate groups and polymerize. Therefore, it has excellent adhesion to rubber and excellent friction and wear resistance.

[0013] The fillers used are fluororesin particles with particle diameters (measured by image analysis) of 0.1 to 2 μm, preferably 0.1 to 0.5 μm, and silicone resin particles with particle diameters of 0.5 to 10 μm, preferably 0.5 to 5 μm, each used at a ratio of 20 to 80 wt% of the total filler. The fluororesin particles enable the formation of a coating film with excellent abrasion resistance, and even a small amount can achieve this effect, improving the durability of the coating agent. Furthermore, silicone resin particles are characterized by their resistance to aggregation and low specific gravity, which allows for good dispersibility in the coating liquid, eliminating the need for a dispersant.

[0014] If the particle size of the fluororesin particles is larger than this, the particles will aggregate to a large extent, making it difficult to control the roughness of the coating film surface. In particular, if the size of the aggregates exceeds 30 μm, the coating surface will become rough, the sealing performance will deteriorate, and oil leakage will occur. Furthermore, because the specific gravity of fluororesin particles is high, if the particle size is large, the dispersant effect will not be exerted, resulting in precipitation and compromising the stability of the coating liquid.

[0015] If the particle size of the silicone resin particles is smaller than this, the roughness of the coating surface will be small, the oil retention effect will not be maintained, and the torque of the seal sliding surface will increase.On the other hand, if the particle size is larger than this, the settling speed will be fast, and after leaving it for a long time, a precipitate called a hard cake will be formed.

[0016] If the proportion of fluororesin particles is less than this, the abrasion resistance will deteriorate, while if it is used in a higher proportion, the surface roughness of the coating film will decrease, the oil retention ability will decrease, the oil repellency will increase, and the torque will increase.In addition, the contact angle with engine oil and the friction coefficient will tend to increase.

[0017] Examples of fluororesins include polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, polyvinylidene fluoride, polyvinyl fluoride, ethylene / tetrafluoroethylene copolymer, etc. Examples of these fluororesin particles include those obtained by classifying fluororesins obtained by bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, etc. into particles with a particle size of about 0.1 to 2 μm, those obtained by dispersing dispersions obtained by suspension polymerization, solution polymerization, emulsion polymerization, etc. into fine particles with a size of about 0.1 to 2 μm by shear stirring, etc., and those obtained by coagulating and drying the products obtained by the above polymerization methods, followed by dry grinding or cold grinding to fine particles of about 2 μm or less.

[0018] The silicone resin may be a condensation reaction type, addition reaction type, ultraviolet or electron beam curable type, or other silicone resin, such as polymethylsilsesquioxane (methyltrimethoxysilane polymer). In the present invention, these are not particularly limited as long as they have a specified particle size, and commercially available products can be used as they are.

[0019] In addition to fluororesin particles and silicone resin particles, fillers such as silica and polycarbonate particles can also be used in combination, provided that the intended purpose of the present invention is not impaired. These fillers are used in a total amount of 10 to 90 parts by weight, preferably 40 to 80 parts by weight, per 100 parts by weight of isocyanate group-containing 1,2-polybutadiene. If the total amount of filler exceeds this limit, the coating film's adhesion to rubber and its friction and wear resistance properties will be impaired, the coating film's flexibility will be impaired, and the cured film will crack. On the other hand, if the total amount of filler is less than this limit, the slipperiness will be impaired, the coating film's surface roughness will be reduced, the oil retention capacity will be reduced, and torque will increase.

[0020] The coating agent further contains 10 to 40 parts by weight, preferably 10 to 30 parts by weight, of wax per 100 parts by weight of isocyanate group-containing 1,2-polybutadiene. If the wax is used in a proportion less than this, abrasion resistance decreases, and it becomes difficult to control the settling of fluororesin particles and the formation of precipitates of silicone resin particles. On the other hand, if the wax is used in a proportion greater than this, the coating agent softens, resulting in a decrease in abrasion resistance.

[0021] The use of wax improves the abrasion resistance of the coating film, and because of its low specific gravity, mixing it with fluororesin can prevent the aggregation and precipitation of fluororesin particles and suppress the formation of hard cakes (sediments) of silicone resin particles.

[0022] As the wax, vegetable waxes, petroleum waxes, synthetic waxes, etc., having a melting point of 40 to 160° C., preferably 60 to 120° C., are used. Vegetable waxes include carnauba wax, candelilla wax, rice wax, etc., petroleum waxes include paraffin wax, microcrystalline wax, etc., and synthetic waxes include polyethylene wax, Fischer-Tropsch wax, fatty acid amides, various modified waxes, etc., and generally, commercially available waxes with a predetermined melting point can be used as is.

[0023] If a wax with a melting point of 40 to 160°C is used, the wax will melt when the coating is baked and will be uniformly dispersed within the binder resin. If a wax with a higher melting point is used, the wax may not melt after the coating is baked, resulting in clumps of wax that may reduce adhesion to the substrate. On the other hand, if a wax with a lower melting point is used, the wax component may come off in the high temperature environment during product use, reducing the coating's abrasion and wear resistance.

[0024] The above components are prepared as a solution (dispersion) in an organic solvent and used as a coating agent for oil seals. Examples of organic solvents that can be used include toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, and methyl isobutyl ketone. Commercially available solvents can be used as is. The amount of dilution with organic solvent is selected appropriately depending on the coating thickness and coating method. The coating thickness is typically about 1 to 30 μm, preferably about 3 to 20 μm. If the coating thickness is less than this, the rubber surface may not be completely coated, resulting in a loss of slipperiness and non-stick properties. On the other hand, if the coating thickness is greater than this, the rigidity of the coated surface may increase, resulting in a loss of sealing properties and flexibility. For applications such as sealing parts, a thickness of about 3 to 20 μm is preferred.

[0025] In the present invention, a coating agent is used that is finally prepared as an organic solvent solution, and that after coating the oil seal surface, the contact angle between the coated oil seal surface and engine oil, such as engine oil OW-20, is less than 35°. If filler particles that result in a contact angle greater than this after coating are used, the filler will repel oil, impairing the oil retention ability of the oil seal sliding surface and making it difficult to achieve the desired low torque.

[0026] Examples of rubbers constituting oil seals that can be treated with such coating agents include common rubber materials such as fluororubber, nitrile rubber, hydrogenated nitrile rubber, ethylene-propylene rubber, styrene-butadiene rubber, acrylic rubber, chloroprene rubber, butyl rubber, and natural rubber, and among these, rubber materials that cause little blooming of rubber compounding agents such as antioxidants and oils compounded into the rubber onto the rubber surface layer are preferably used. Note that the compounding ratio of each of the above components and the type, amount, and mixing ratio of the organic solvent are appropriately selected depending on the rubber material and purpose.

[0027] Methods for applying the coating agent to the surface of an oil seal include, but are not limited to, immersion, spraying, roll coating, and flow coating. It is preferable to remove any dirt or other impurities from the rubber surface by cleaning before applying the coating agent. In particular, if bloom or bleed material has precipitated on the surface from the rubber, the surface is washed with water, detergent, solvent, or the like, followed by drying.

[0028] After the coating agent is applied to the oil seal surface, it is heat-treated at approximately 150-250°C for approximately 10 minutes to 24 hours. If the heating temperature is lower or the heating time is shorter, the coating will not harden sufficiently and its adhesion to the rubber will be insufficient, resulting in poor non-stickiness and slipperiness. On the other hand, if the heating temperature is higher or the heating time is longer, the rubber will begin to age due to heat. Therefore, the heating temperature and heating time must be set appropriately depending on the heat resistance of each type of rubber.

[0029] Furthermore, for items that require a reduction in outgassing, heat treatment, decompression treatment, extraction treatment, etc. can be carried out alone or in combination, but heat treatment is the most economical option. To reduce the amount of outgassing, heat treatment at approximately 150 to 250°C for approximately 1 to 24 hours is preferred, and the higher the temperature and the longer the time, the more effective it is at gasifying the low molecular weight components in the rubber and the low molecular weight components contained in the polybutadiene in the coating.

[0030] Next, the present invention will be described with reference to examples.

[0031] Example 1 200 parts by weight of isocyanate group-containing 1,2-polybutadiene (Nippon Soda product TP1001; contains 50% butyl acetate) (100 parts by weight) Polymethylsilsesquioxane particles 30 parts by weight (Momentive Tospearl 130; particle size 3 μm) Polytetrafluoroethylene particles 30 parts by weight (AGC Sei Chemical product Fluon 172J; particle size 0.2 μm) Paraffin wax (melting point 100°C) 20 parts by weight Butyl acetate (balance) Total 2000 parts by weight

[0032] The above components were mixed, and the resulting butyl acetate solution was sprayed onto a 2 mm thick vulcanized rubber surface to a thickness of 10-30 μm. After heat treatment at 200°C for 10 hours, the surface roughness, contact angle, dynamic friction coefficient in oil, and abrasion resistance were measured and evaluated. The dispersibility and redispersibility of the coating solution were also evaluated. Note that each weight part is shown as a solution weight part, and the actual weight part of each component is shown in parentheses (this also applies to the following examples and comparative examples).

[0033] Dispersibility: After preparing the coating liquid, the settling speed of the silicone resin particles or fluororesin particles is checked visually, and if no settling is observed after 10 minutes, it is evaluated as ○, and if settling is observed in less than 10 minutes, it is evaluated as ×. Redispersibility: After preparing the coating liquid, the hard cake (sediment) is left to stand for one day, and if the sediment is redispersed after one hour of stirring, it is evaluated as ○, and if there is any residue, it is evaluated as ×. Surface roughness Rz: Compliant with JIS B0601 (1994), using Accretech Surfcom 1400A manufactured by Tokyo Seimitsu. Contact angle: Using Drop Master 500 manufactured by Kyowa Interface Science, the contact angle against engine oil OW-20 is measured, and if less than 35° is evaluated as ○, if 35° or more is evaluated as ×. Dynamic friction coefficient in oil: Using a HEIDON TYPE14DR surface property tester manufactured by Shinto Scientific, a reciprocating motion is performed under the following conditions, and the dynamic friction on the outward path is evaluated as ○. The coefficient of dynamic friction was measured, and a value of less than 0.2 was evaluated as ○, and a value of 0.2 or more as ×. Load: 50g Speed: 50mm / min Reciprocating distance: 50mm Indenter: 10mm diameter steel ball Oil type: Engine oil OW-20 Note) The coefficient of dynamic friction in oil is an evaluation that correlates with the evaluation of an actual oil seal; if the coefficient of dynamic friction in oil using the above test piece is low, the evaluation of an actual oil seal will also be good. Abrasion resistance: Using a Friction Player FPR-2000 manufactured by Rhesca, a 0.4mm diameter SUS pin was pressed against the coating surface in a dry state at 80°C with a load of 300g, and rotated at a linear speed of 400mm / sec. The distance until the coating peeled off and the rubber was exposed was measured, and a value of 0.1km or more was evaluated as ○, and less than 0.1km as ×.

[0034] Example 2 In Example 1, the same amount (30 parts by weight) of XC99-A8808 (particle diameter: 0.7 μm) manufactured by Momentive Corporation was used as polymethylsilsesquioxane particles.

[0035] Example 3 In Example 1, the same amount (30 parts by weight) of Tospearl 1100 (particle diameter: 10 μm) manufactured by Momentive Corporation was used as polymethylsilsesquioxane particles.

[0036] Example 4 In Example 1, the amount of polymethylsilsesquioxane particles was changed to 56 parts by weight, and the amount of polytetrafluoroethylene particles was changed to 24 parts by weight.

[0037] Example 5 In Example 1, the amount of polymethylsilsesquioxane particles was changed to 24 parts by weight, and the amount of polytetrafluoroethylene particles was changed to 56 parts by weight.

[0038] Comparative Example 1 In Example 1, the same amount (30 parts by weight) of Tospearl 3120 (particle diameter 12 μm) manufactured by Momentive Corporation was used as polymethylsilsesquioxane particles.

[0039] Comparative Example 2 In Example 1, the amount of polymethylsilsesquioxane particles was changed to 40 parts by weight, and no polytetrafluoroethylene particles were used.

[0040] Comparative Example 3 In Example 1, the amount of polymethylsilsesquioxane particles was changed to 45 parts by weight, and the amount of polytetrafluoroethylene particles was changed to 5 parts by weight.

[0041] Comparative Example 4 In Example 1, the amount of polymethylsilsesquioxane particles was changed to 10 parts by weight, and the amount of polytetrafluoroethylene particles was changed to 55 parts by weight.

[0042] Comparative Example 5 In Example 1, no polymethylsilsesquioxane particles were used, and the amount of polytetrafluoroethylene particles was changed to 40 parts by weight.

[0043] Comparative Example 6 In Example 1, the amount of polymethylsilsesquioxane particles was changed to 50 parts by weight, and the amount of polytetrafluoroethylene particles was changed to 50 parts by weight.

[0044] Comparative Example 7 In Example 1, the polymethylsilsesquioxane particles and the polytetrafluoroethylene particles were not used.

[0045] Comparative Example 8 In Example 1, the amount of paraffin wax used was changed to 5 parts by weight.

[0046] Comparative Example 9 In Example 1, the amount of paraffin wax used was changed to 60 parts by weight.

[0047] Comparative Example 10 In Example 1, 30 parts by weight of Fluon 150J (particle diameter 10 μm) manufactured by AGC Sei Chemical Co., Ltd. was used as polytetrafluoroethylene particles, and no paraffin wax was used.

[0048] The results obtained in the above examples and comparative examples are shown in the following Tables 1 and 2. Table 1 Example Measurement / Evaluation Item 1 2 3 4 5 Dispersibility of silicone resin particles ○ ○ ○ ○ ○ Redispersibility of silicone resin particles ○ ○ △ ○ ○ Dispersibility of fluororesin particles ○ ○ ○ ○ ○ Surface roughness (μm) 16.5 5.6 21.5 10.5 12.7 Contact angle (°) 21.3 25.3 14.5 19.4 20.8 ○ ○ ○ ○ ○ Dynamic friction coefficient in oil 0.18 0.20 0.18 0.18 0.19 ○ ○ ○ ○ ○ Abrasion resistance ○ ○ ○ ○ ○

[0049] The above results suggest the following: (1) The coating agents obtained in each example maintain good dispersibility while exhibiting the excellent sealing performance inherent to oil seals and achieving low torque. (2) When large-sized silicone resin particles are used, redispersibility is poor, hindering application (Comparative Example 1). (3) When the proportion of fluororesin particles in the total filler is low, abrasion resistance deteriorates (Comparative Examples 2-3). Conversely, when the proportion is high, oil repels, resulting in a high contact angle and a high coefficient of friction in oil (Comparative Examples 4-5). (4) When the total filler content is high, the surface roughness of the coating film increases, causing oil starvation on convex parts. When the total filler content is low, the surface roughness decreases. In both cases, abrasion and abrasion resistance are reduced (Comparative Examples 6-7). (5) When the wax content is low, the dispersibility of the fluororesin particles is not ensured (Comparative Example 8). (6) When the wax content is high, the coating film softens, resulting in poor abrasion and abrasion resistance (Comparative Example 9). (7) If wax is not used, the dispersibility deteriorates and the desired contact angle cannot be achieved (Comparative Example 10).

[0050] The coating agent of the present invention achieves low torque while maintaining the excellent sealing performance inherent to oil seals, and therefore can be effectively used not only for oil seals but also for preventing adhesion, reducing friction, and preventing wear of rubber parts such as rubber rolls for copiers, rubber belts for copiers, industrial rubber hoses, industrial rubber belts, wipers, automotive weather strips, and glass runs.

Claims

DEPCT651. Oil-sealing coatings composed of 10 to 90 parts by weight of filler and 10 to 40 parts by weight of wax containing 100 parts by weight of isocyanate groups composed of 1,2-polybutadiene and prepared as an organic solvent solution as filler, silicone resin particles with particle size of 0.5 to 10 µm and fluororesin particles with particle size of 0.1 to 2 µm are used at a ratio of 20 to 80 percent by weight of the total filler amount.

2. Oil-sealing coatings according to claim 1. Where silicone resin particles are polymethylsilses chioxane particles.

3. Oil-sealing coatings under claim 1 where silicone resin particles with a particle size of 0.5 to 5 micrometers are used.

4. Oil-sealing coatings under claim 1 where fluororesin particles with a particle size of 0.1 to 0.5 micrometers are used.

5. Oil-sealing coatings under claim 1 where filler in the amount of 40 to 80 parts by weight is used.

6. Oil-sealing coatings under claim 1 where wax in the amount of 10 to 30 parts by weight is used. 7.Oil seals that change according to the coating using the coating according to claim 18. Oil seals according to claim 7 in which, after the coating is applied, are heated to 150 to 250 degrees Celsius for 10 minutes to 24 hours. Oil seals according to claim 7 or 8 in which the contact angle between the surface of the oil seal and the engine oil is less than 35 degrees.