JP4992309B2 - Rubbery elastic coating agent - Google Patents

Description

  The present invention relates to a coating agent for a rubber-like elastic body. More specifically, the present invention relates to a coating agent for a rubber-like elastic body that does not cause peeling of a coating film due to adhesion during high-temperature compression or friction and wear at high surface pressure.

  Conventionally, a graphite coating film has been applied to the surface of rubber-like elastic bodies that constitute a part of rubber-coated metal gaskets, bearing seals, oil seals, etc. for the purpose of preventing sticking, blocking, and improving wear resistance. In addition, coating films such as fatty acid metal salts, fatty acid amides, waxes such as paraffin, silicone oil, etc., or coating films containing ethyl cellulose, phenol resin, etc. as a binder are formed. If the engine is further subjected to vibration under high surface pressure or high temperature conditions such as the above, the surface rubber coating layer such as a gasket may be worn and gas leakage may occur. In addition, the rubber coating layer of the rubber-like elastic sliding portion such as a bearing seal or an oil seal may be worn due to repeated sliding and cause oil leakage.

Therefore, the present applicant firstly wears or breaks the rubber coating layer on the gasket surface even under severe conditions such as high surface pressure and high temperature that are the usage environment of the engine head gasket, and further vibration is applied. As a coating agent for rubber-like elastic bodies that can form a gasket and the like effective for gas sealing with almost no phenomenon, a liquid resin containing hydroxyl group of 1,2-polybutadiene and 1,2-polybutadiene isocyanate compound curing agent A surface treatment agent for vulcanized rubber to which an aqueous dispersion of the above is added is proposed.
JP-A-3-252442

  Although the proposed coating agent for rubber-like elastic material achieves the intended purpose of improving the abrasion resistance of the rubber coating layer, water is used in 1,2-polybutadiene because an aqueous dispersion is used. Promotes the reaction between the hydroxyl group of the crosslinking agent and the isocyanate group of the cross-linking agent, and also the water itself reacts with the isocyanate group, leading to an increase in viscosity and gelation of the surface treatment dispersion, and poor workability during coating processing. There was a problem. Furthermore, as a result of the reaction between water and isocyanate groups, the high molecular weight of 1,2-polybutadiene is hindered, and there are still problems to be improved in terms of wear resistance, peeling resistance and slipperiness of the surface treatment layer. It was.

In order to solve this problem, the present applicant has further proposed a surface treatment agent for vulcanized rubber in which the aqueous dispersion of polyolefin is changed to an organic solvent dispersion. However, the proposed coating agent for rubber-like elastic bodies still has a problem that the coating film is peeled off due to adhesion during high-temperature compression and friction / wear at high surface pressure.
Japanese Patent Laid-Open No. 7-165953

Further, the applicant of the present invention contains an isocyanate group-containing 1,2-polybutadiene or a 1,2-polybutadiene mixture obtained by blending a hydroxyl group-containing 1,2-polybutadiene with a wax having a softening point of 40 to 160 ° C. and a fluororesin. A surface treatment agent for vulcanized rubber made of an organic solvent solution has been proposed, but it was also observed that the wax and polybutadiene resin may stick at high temperatures in the proposed coating agent for rubbery elastic bodies. .
JP 2003-213122 A

  The object of the present invention is to prevent adhesion and high pressure during high-temperature compression without impairing the performances conventionally required for coating agents for rubber-like elastic bodies, such as prevention of sticking and adhesion, prevention of blocking, and improvement of wear resistance. An object of the present invention is to provide a coating agent for a rubber-like elastic body that does not cause peeling of a coating film due to friction and wear at surface pressure.

The purpose of such invention, powdery fluorine resin, and also contains a polycarbonate resin and an isocyanate group-containing compound 1,2-polybutadiene, for the additional inclusion of preferably further softening point 40 to 160 ° C. of the wax, the silicone-based polymer This is achieved by a rubber-like elastic body coating agent not contained .

The coating agent for rubber-like elastic body according to the present invention is capable of adhesion and high surface pressure during high temperature compression without impairing conventionally required performance such as prevention of sticking and adhesion, prevention of blocking, and improvement of wear resistance. Although there is an effect that the coating film is not peeled off due to friction and wear, the following effects can be given in more detail.
(1) Excellent applicability of coating agent.
(2) Even if the coating thickness is reduced to, for example, 5 μm or less, there is no coating unevenness and it can be processed at low cost. The surface-treated rubber-like elastic body is flexible without being inferior in lubricity or non-adhesiveness. Since the original physical properties of rubber are not impaired, the sealing performance is excellent in the case of sealing parts.
(3) There is no blocking between the surface-treated rubber-like elastic bodies.
(4) The surface of the surface-treated rubber-like elastic body has low friction and low sliding, and is excellent in mounting workability.
(5) On the surface of the surface-treated rubber-like elastic body, many chemical bonds are formed between the functional group of the rubber-like elastic body and the coating agent component. It is durable and can reduce the wear of the rubber-like elastic body.
(6) As a result of the formation of many chemical bonds, the surface-treated rubber-like elastic body exhibits durability and non-adhesiveness at high temperatures, and has low adhesiveness and adhesion to metal, Similar effects are seen at high temperatures.
(7) Since the coating agent is made of a fluororesin and a polybutadiene derivative (and wax), there is no risk of outgassing or contamination, and it can be used for IT-related parts.
(8) Since it does not contain silicone polymers such as silicone resin, silicone rubber, silicone oil, etc., it can also be used in areas where there is a risk of electrical contact problems.
(9) By containing the isocyanate group-containing 1,2-polybutadiene, the adhesiveness to the fluororesin or wax is good, and there is no particle contamination caused by dropping of the fluororesin particles or wax particles.
(10) Conventional treatment films containing fluororesin are hard, and in the case of seal parts, problems such as deterioration of seal performance and occurrence of cracks and peeling of the film due to repeated compression-release are observed. In the rubber-like elastic body coating agent, by adding a polybutadiene derivative (and wax), flexibility is imparted to the film, and such a problem is effectively solved.

  The coating agent for rubber-like elastic body of the present invention having such properties is a seal material made of rubber-like elastic body such as O-ring, square ring, D-ring, V-packing, oil seal, gasket and packing, and dust such as constant velocity joint. For rubber products such as boots, various valves, diaphragms, wiper blades, storage devices such as engines, motors and hard disks, various anti-vibration rubbers such as optical disks, storage device heads such as hard disks, and shock absorbing stopper parts such as printer heads. It is effectively applied to this.

  Fluorocarbon resins include polytetrafluoroethylene [PTFE], tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, polyvinylidene fluoride, polyvinyl fluoride, ethylene / tetra A fluoroethylene copolymer is exemplified, and PTFE is preferably used.

These fluororesin particles are obtained by classifying a fluororesin obtained by a bulk polymerization method , a suspension polymerization method , a solution polymerization method , an emulsion polymerization method or the like into a particle size of about 0.1 to 5 μm, a suspension polymerization method , Dispersions obtained by solution polymerization method , emulsion polymerization method, etc. are dispersed in fine particles to about 0.1-5μm by shearing stirring, etc., and those obtained by these polymerization methods are coagulated and dried, then dry pulverized by and cooling grinding, such as those micronized is used to 10μm or less. When the particle size is set to 0.1 to 10 μm, if the particle size is smaller, there is a merit that the coating thickness can be reduced, but the contact area is reduced by reducing the unevenness of the coating surface, and friction is caused at low surface pressure. When the particle size is larger, on the other hand, when the particle size is larger, the coating thickness becomes larger and the cost for coating increases, but the unevenness becomes larger, and the contact area with the counterpart material becomes smaller at low surface pressure. Thus, the friction coefficient is lowered. Accordingly, the particle diameter is appropriately adjusted according to the usage requirements, and for example, seal parts are determined in consideration of these advantages and disadvantages, and those having a particle size of about 0.5 to 2 μm are preferably used.

As the polycarbonate resin, a fragrance derived from a commercially available resin having a melting point of about 220 to 230 ° C. and a glass transition temperature Tg of about 150 ° C., for example, 4,4′-dihydroxydiphenyl-2,2-propane (bisphenol A). A group polycarbonate is used. Fluorine resin used in combination with this
(And wax) have high adhesive strength at a high temperature of about 150 to 200 ° C., but a polycarbonate resin having a melting point of about 220 to 230 ° C. does not have high adhesive strength even at a high temperature of about 150 to 200 ° C.

As the isocyanate group-containing 1,2-polybutadiene, a molecular weight of about 1,000 to 3,000 with an isocyanate group added as a terminal group is used, which is a commercial product such as Nippon Soda product Nisso TP-1001 (butyl acetate 50 wt. % -Containing solution) can be used as they are. This polybutadiene resin has better compatibility and compatibility with rubber than polyisocyanate resin that reacts with the same isocyanate group to polymerize it, so it has good adhesion to rubber and especially good anti-friction and wear properties. It is a feature.

  Further, since this isocyanate group-containing 1,2-polybutadiene has an isocyanate group added to the terminal group, it is allowed to react with the functional group, hydroxyl group and / or carboxyl group-containing 1,2-polybutadiene on the surface of the rubber-like elastic body. And can be used as a curing agent for 1,2-polybutadiene containing a hydroxyl group and / or a carboxyl group. As the hydroxyl group and / or carboxyl group-containing 1,2-polybutadiene having a hydroxyl group and / or carboxyl group added as a terminal group, a molecular weight of about 1,000 to 3,000 is used. Use G series (containing hydroxyl group) such as Nisso G-1000, C series (containing carboxyl group) such as C-1000, GQ series (containing hydroxyl group and carboxyl group) such as GQ-1000, GQ-2000, etc. I can do it.

  When the isocyanate group-containing 1,2-polybutadiene and the hydroxyl group and / or carboxyl group-containing 1,2-polybutadiene are used in combination, the isocyanate group-containing 1,2-polybutadiene is 25% by weight or more, preferably 40% by weight. As described above, the hydroxyl group and / or carboxyl group-containing 1,2-polybutadiene is used in a proportion of 75% by weight or less, preferably 60% by weight or less. If the amount of isocyanate group-containing 1,2-polybutadiene is less than this, the adhesion to rubber will be lowered, and consequently the slipping property and non-adhesive performance will be lowered, and the friction and wear resistance will be lowered.

  As the wax, vegetable waxes, petroleum waxes, synthetic waxes and the like having a softening point of 40 to 160 ° C, preferably 60 to 120 ° C are used. Plant waxes include carnauba wax, candelilla wax, and rice wax, petroleum waxes include paraffin wax and microcrystalline wax, and synthetic waxes include polyethylene wax, Fischer-Tropsch wax, fatty acid amide, and various modified waxes. Usually, commercially available waxes and resins can be used as they are. If a softening point higher than this is used, slipperiness and non-adhesive performance will be reduced. On the other hand, when a material having a softening point lower than this is used, the adhesion between the rubber and the treatment agent and the friction and wear resistance are lowered.

The above components are used in the following weight ratios in the coating agent composition comprising these components.
Powdery fluororesin: about 10 to 70%, preferably about 15 to 60%
Polycarbonate resin: about 5-60%, preferably about 10-50%
Isocyanate group-containing 1,2-polybutadiene (or hydroxyl and / or
Or a mixture with carboxyl group-containing 1,2-polybutadiene):
About 20-70%, preferably about 30-60%
Wax: 0 to about 50%, preferably about 5 to 20%

  If the proportion of powdered fluororesin is used more than this, the adhesion to the rubbery elastic body, friction / wear resistance, sealability, etc. will be reduced, and the flexibility of the coating will be impaired, resulting in a cured coating. Cracks occur and the appearance is impaired. On the other hand, if it is used in a smaller proportion, slipperiness and non-adhesiveness will decrease.

  As for the polycarbonate resin, the higher the ratio, the lower the adhesive strength at high temperature, but the wear resistance and sealability are reduced, so that the ratio is preferably about 10 to 50% by weight.

  If the proportion of the isocyanate group-containing 1,2-polybutadiene is used more than this, the adhesion to the rubber-like elastic body will be good, but the slipping property and the adhesive force will become high. On the other hand, if it is used in a smaller proportion, the adhesion to the rubber-like elastic body will be lowered, and as a result, the slipperiness will be lowered due to peeling or abrasion.

  With regard to the wax, by blending this, the effect of further reducing the adhesive strength with the metal at high temperature can be obtained, but when used in a proportion higher than this, the adhesion to the rubber-like elastic body is improved. The slipperiness decreases due to peeling and friction.

  The coating agent comprising the above components is used as a dispersion or solution of an organic solvent or an aqueous dispersion. Organic solvents include aromatic hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, di-n-propyl ketone, cyclohexanone, phorone (diisopropylideneacetone), isophorone Ketones such as (3,5,5-trimethyl-2-cyclohexenone) and ethers such as methyl cellosolve and ethyl cellosolve are used.

  The amount of dilution with an organic solvent is appropriately selected depending on the coating thickness and coating method, but the solid content concentration is generally set in the range of about 2 to 20% by weight. The coating thickness is usually 1 to 10 μm, preferably 2 to 5 μm. When the coating thickness is smaller than this, it is not possible to cover the entire surface of the rubber-like elastic body, resulting in slipperiness and non-adhesiveness. It may be damaged. On the other hand, if the coating thickness is larger than this, the rigidity of the coating surface increases, and the sealing performance and flexibility may be impaired. For use applications such as seal parts, about 1 to 5 μm is preferable.

  Examples of rubber-like elastic bodies that can be treated with such a surface treating agent include fluorine rubber, nitrile rubber, hydrogenated nitrile rubber, ethylene-propylene (-diene) rubber, sterene-butadiene rubber, acrylic rubber, chlorobrene rubber, butyl rubber, General rubber materials such as natural rubber can be mentioned. Of these, rubber-like elastic materials with less blooming to the rubber-like elastic surface layer such as anti-aging agents and oils are preferably used. It is done. Depending on the rubber material and purpose, the blending ratio of the above components, the type of organic solvent, the amount of organic solvent, and the organic solvent mixing ratio are appropriately selected.

  Examples of the method for applying the rubber-like elastic body coating agent to the surface of the rubber-like elastic body include application methods such as dipping, spraying, roll coater, flow coater, and inkjet, but are not limited to these methods. . At this time, it is preferable to remove the dirt or the like on the surface of the rubber-like elastic body beforehand by washing before applying the surface treatment agent. In particular, when a bloom or bleed material is deposited on the surface from a rubber-like elastic body, washing and drying with water, a detergent, a solvent, or the like is performed.

  After coating the rubber-like elastic body coating agent on the surface of the rubber-like elastic body, it is heat-treated at about 150 to 250 ° C. for about 10 minutes to 24 hours. When the heating temperature is lower than this and the heating time is shorter than this, the coating is not sufficiently cured and the adhesiveness with the rubber-like elastic body is insufficient, and the non-adhesiveness and slipperiness are deteriorated. On the other hand, when the heating temperature is higher than this and the heating time is longer than this, heat aging of the rubber-like elastic body occurs. Therefore, it is necessary to appropriately set the heating temperature and the heating time according to the heat resistance of various rubber-like elastic bodies.

  For items that require a reduction in the outgas amount, heat treatment, reduced pressure treatment, extraction treatment, etc. can be carried out alone or in combination. The heat treatment is preferably performed at about 150 to 250 ° C. for about 1 to 24 hours, and the temperature is high in order to gasify the low molecular components in the rubber-like elastic body and the low molecular components contained in the wax and polybutadiene in the coating. The longer the time, the more effective.

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

Examples 1-5, Comparative Examples 1-5
When the following components are mixed and each component to be dispersed or dissolved is added directly to toluene, heat is generated at the time of addition, and it becomes easy to react or aggregate in the coating agent. Used after being dispersed or dissolved in
Particulate polytetrafluoroethylene [PTFE]: particle size 1 μm, toluene 85 wt% polycarbonate resin [PC]: Mitsubishi Chemical S-3000R
30% toluene, 53% xylene, 10% cyclohexanone content Isocyanate group-containing 1,2-polybutadiene [PB-NCO]: Nippon Soda TP1001
Containing 50% by weight of butyl acetate Hydroxyl / carboxyl group-containing 1,2-polybutadiene [PB-OH, -COOH]:
Company product GQ1000, xylene 55 wt% polyethylene wax [PE Wax]: molecular weight about 2000, melting point 110 ° C, particle size 1μm
Toluene 85% by weight Toluene The toluene solution with a solid content concentration of 5% by weight was applied to a compression molded vulcanized fluororubber with a thickness of 4μm and heat treated at 230 ° C for 3 hours. The items were measured.

Dynamic friction measurement test: For a 2mm fluororubber sheet surface-treated as described above, according to JIS K7125, P8147, using a surface testing machine (manufactured by Shinto Kagaku), a 10 mm diameter chrome steel ball friction element Measure the dynamic friction coefficient under the conditions of a moving speed of 50 mm / min and a load of 50 g using the above. Static friction coefficient test: vulcanized fluoro rubber O-ring (dimensions: inner diameter 7.8 mm, thickness 1.9 mm, nominal number P8) Surface treatment was performed and the O-ring was placed on an aluminum plate according to JIS P8147, the aluminum plate was tilted, the angle θ at which the O-ring began to move was measured, and the static friction coefficient was evaluated as tanθ. Adhesion test between rubbers: Vulcanization Fluoro rubber sheet (60 × 25 × 2mm) is subjected to the above surface treatment, and the rubber is bonded to each other in a constant temperature and humidity chamber at 40 ° C and 95% humidity for 24 hours at a surface pressure of 0.15kg / cm ² , then at room temperature Under the tensile shear bond strength test piece according to JIS K6850 tensile shear bond strength test method Measure the tensile strength and evaluate the adhesive strength of the surface. High temperature adhesion test with metal: Vulcanized fluororubber O-ring (inner diameter 7.8mm, thickness 1.9mm diameter, nominal number P8) is subjected to the above surface treatment, The O-ring is compressed 25% with a JIS K6301 compressor (compressed surface is polished with stainless steel buff), left in a constant temperature bath at 120 ° C for 24 hours, cooled to room temperature, cooled for 3 hours, and adhered to the compressed surface. Force measurement High surface pressure abrasion test: 2mm fluororubber sheet surface-treated as described above, made of stainless steel as a counterpart material using a surface testing machine (manufactured by Shinto Kagaku) according to JIS K7125, P8147 Using a scratching needle with a diameter of 0.4 mm, a high load reciprocating test was performed under the conditions of a moving speed of 400 mm / min, a reciprocating moving width of 30 mm, and a load of 300 g. The surface wear state is determined by microscopic observation in the following three stages. ○: The surface of the rubber substrate is exposed. NOT △: surface treatment agent is worn, the exposed rubber substrate wear surface portion ×: surface treatment agent is worn, the rubber base material is entirely exposed wear surface,
Or, rubber base wear is observed. Leak test of sealing material: O-ring (inner diameter 119.6mm, thickness 7mm, nominal number P120) made of vulcanized fluoro rubber is subjected to the above surface treatment, and the O-ring is compressed 5%. Measure the amount of helium leak 3 minutes after helium gas injection with the helium leak detector

The obtained results are shown in the following Table 1 (Example) and Table 2 (Comparative Example) together with the composition of each component.
Table 1
Example
1 2 3 4 5
[Coating agent component: parts by weight]
PTFE 150 150 150 85 60
PC 110 110 110 285 60
PB-NCO 50 27.5 50 50 50
PB-OH, -COOH − 25 − − −
PE Wax − − 60 40 25
Toluene 800 800 920 820 640
Total 1100 1112.5 1290 1280 835
[Same solid content; parts by weight]
PTFE 22.5 22.5 22.5 12.75 9
PC 7.7 7.7 7.7 19.95 4.2
PB-NCO 25 13.75 25 25 25
PB-OH, -COOH − 11.25 − − −
PE Wax − − 9 6 3.75
Total 55.2 55.2 64.2 63.7 41.95
[Solid content weight ratio;%]
PTFE 40.8 40.8 35.0 20.0 21.5
PC 13.9 13.9 12.0 31.3 10.0
PB-NCO 45.3 24.9 38.9 39.2 59.6
PB-OH, -COOH − 20.4 − − −
PE Wax − − 14.0 9.4 8.9
[Measurement and evaluation results]
Coefficient of dynamic friction 0.2 0.2 0.2 0.2 0.4
Coefficient of static friction 0.2 0.2 0.2 0.2 0.5
Rubber-to-rubber adhesion (kg / cm ² ) <0.1 <0.1 <0.1 <0.1 <0.1
Adhesion with metal at high temperature (kg) 8 8 6 4 12
High surface wear test ○ ○ ○ ○ ○
Leakage rate (Pa ・ m ³ / sec) 5 × 10 ^-11 5 × 10 ^-11 5 × 10 ^-11 5 × 10 ^-10 5 × 10 ^-10
Note) <0.1 indicates below detection limit ( 0.1 is measurable)

Table 2
Comparative example
1 2 3 4 5
[Coating agent component: parts by weight]
PTFE 125 15 30 250 −
PC − − − − 240
PB-NCO 50 50 50 50 50
PE Wax 125 15 200 − −
Toluene 950 500 950 1000 1000
Total 1250 590 1250 1250 840
[Same solid content; parts by weight]
PTFE 18.75 2.25 4.5 37.5 −
PC----16.8
PB-NCO 25 25 25 25 25
PE Wax 18.75 2.25 33 − −
Total 62.5 29.5 62.5 62.5 41.8
[Solid content weight ratio;%]
PTFE 30.0 7.6 7.2 60.0 −
PC − − − − 40.2
PB-NCO 40.0 84.7 40.0 40.0 59.8
PE Wax 30.0 7.6 52.8 − −
[Measurement and evaluation results]
Coefficient of dynamic friction 0.2 0.7 0.7 0.2 0.5
Coefficient of static friction 0.2 0.8 0.8 0.2 0.4
Adhesive strength between rubbers (kg / cm ² ) <0.1 5.0 3.0 <0.1 <0.1
Adhesion with metal at high temperature (kg) 20 40 30 15 17
High surface pressure wear test ○ × × △ ×
Leakage rate (Pa ・ m ³ / sec) 5 × 10 ^-11 1 × 10 ^-9 5 × 10 ^-11 1 × 10 ^-7 1 × 10 ^-8

Claims (5)

Powdery fluororesin, Ri name contains polycarbonate resin and an isocyanate group-containing 1,2-polybutadiene, rubbery elastomer coating containing no silicone polymer.   The coating agent for rubber-like elastic bodies according to claim 1, wherein the powdery fluororesin is polytetrafluoroethylene particles having a particle diameter of 0.1 to 10 µm.   The coating agent for a rubber-like elastic body according to claim 1 or 2, comprising 10 to 70% by weight of a powdery fluorine-based resin, 5 to 60% by weight of a polycarbonate resin, and 20 to 70% by weight of an isocyanate group-containing 1,2-polybutadiene.   The coating agent for a rubbery elastic body according to claim 3, further comprising a wax having a softening point of 40 to 160 ° C in a proportion of 50% by weight or less. Isocyanate group-containing 1,2-polybutadiene is used in combination with hydroxyl group and / or carboxyl group-containing 1,2-polybutadiene, and in the total amount of both, hydroxyl group and / or carboxyl group-containing 1,2-polybutadiene is 75% by weight or less. The coating agent for rubber-like elastic bodies according to claim 1 used.