JP2001011372A - Paint composition and painted article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paint composition that shows high adhesion to substrates, particularly adhesion to aluminum alloy and gives the paint film of excellent sliding properties, for example, resistance to abrasion, seize, and a low friction coefficient. SOLUTION: This paint composition comprises 100 pts.wt. of polytetrafluoroethylene and polyamideimide at a weight ratio of (5-10)/(95-90) and 5-10 pts.wt. of alumina particles, or 1-10 pts.wt. of silicon nitride whiskers or particles. This paint composition is used as a paint film for the sliding part in an internal combustion engine, for example, pistons.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition which gives a coating film having excellent adhesion to a substrate and sliding properties, and a coated article having the coating film on the surface. When the coating film of the coating composition of the present invention is provided on the outer peripheral surface of the piston skirt, a piston for an internal combustion engine having excellent heat resistance, seizure resistance, and wear resistance and a low coefficient of friction can be obtained.

[0002]

2. Description of the Related Art In internal combustion engines, it is necessary to improve the sliding characteristics such as abrasion resistance and seizure resistance on sliding component surfaces more than ever in order to improve the rotation speed, the compression ratio, the weight, and the fuel efficiency. Is growing. In such sliding members for internal combustion engines, attempts have been made to form a resin coating layer on the outer peripheral surface of a piston skirt, for example. And
Various compositions containing a solid lubricant have been proposed as means for improving the sliding characteristics of the resin coating layer.

For example, Japanese Patent No. 25552523 discloses a resin coating layer obtained by adding a fluororesin powder such as polytetrafluoroethylene, a molybdenum disulfide powder, a boron nitride powder and a graphite powder to a heat-resistant resin such as a polyamideimide resin. There is a disclosure relating to a piston of an internal combustion engine having an outer peripheral surface. However, in order to reduce the friction coefficient of the resin coating layer, it is necessary to increase the mixing ratio of the fluororesin. There is a disadvantage that the amount of wear of the layer increases.

[0004] Japanese Patent Application Laid-Open No. 1-317663 discloses an abrasion-resistant and non-adhesive smooth sheet material comprising a fluorine resin, an inorganic powder such as alumina, and a binder.
The composition of the fluororesin, polyamideimide, and alumina is described in the text. However, there is no description of a specific composition range or an example.

Japanese Patent Application Laid-Open No. 1-261514 discloses that 11.8 to 74.1% by weight of polyamideimide (PAI) and 13.5% of polytetrafluoroethylene (PTFE).
There is a disclosure of a sliding material comprising ５４54.8% by weight and 1.1 to 38.3% by weight of alumina. However, a resin composition in this composition range does not have sufficient abrasion resistance, and requires steps such as surface roughening of a base material and pressure molding to form a sliding resin layer. Further, the PTFE used here is a high-molecular-weight PTFE having a number average molecular weight of 1,000,000 or more, which is used for molding called fine powder or molding powder.

JP-A-3-181558 discloses a melt-flowable PAI 80 to 99 having a specific chemical structure.
There is a disclosure of a resin composition consisting of 20% by weight and 20 to 1% by weight of PTFE. However, the abrasion resistance of the resin composition in this composition range is not sufficient, and when producing a resin molded product,
It is necessary to perform compression molding at high temperature. There is a description that alumina fiber or the like may be added at the time of molding, but there is no description of a specific addition amount or an example.

Japanese Patent Application Laid-Open No. Hei 8-127753 discloses a furan resin precursor which becomes furan resin by curing either furfural or furfuryl alcohol or both as a starting material, and powdered PTFE having an average particle diameter of 20 μm or less.
And a coating composition comprising a spherical alumina having an average particle diameter of 10 μm or less is disclosed. In Comparative Example 2, 54% by weight of PAI, 33% by weight of PTFE, 10.5% by weight of alumina, 1.0% by weight of carbon, and 1.0% by weight of silica A coating composition consisting of 0.5% by weight of surfactant and 0.5% by weight of surfactant is described. However, a coating composition having this composition range does not have good abrasion resistance.

[0008]

As described above, in order to lower the friction coefficient of the resin coating layer, it is necessary to increase the compounding ratio of the fluororesin. Since the heat-resistant resin has no bonding force, the amount of wear of the resin coating layer increases, and it has been difficult to achieve both a low friction coefficient and wear resistance.

In order to solve the above problems, the present inventors have:
It can be fired at 200 ° C or less, which is applicable to aluminum alloy pistons of internal combustion engines, and has heat resistance, oil resistance,
PAI capable of achieving a good balance of coating properties such as adhesion to aluminum alloy base material and abrasion resistance, and PTF capable of improving the low wear coefficient and seizure resistance of the coating surface
E and a study of the composition of fillers such as alumina particles and silicon nitride whiskers used for the purpose of improving the abrasion resistance of the coating film. The present invention has been found to be excellent in adhesion to steel and sliding characteristics (low friction coefficient, abrasion resistance, seizure resistance), and has completed the present invention.

[0010]

That is, the present invention provides a PT
Consisting of FE, PAI, and alumina particles, PTFE and P
The composition of AI is 5 to 10/95 to 90 by weight,
The present invention also relates to a coating composition containing 5 to 10 parts by weight of alumina particles based on 100 parts by weight of the total of PTFE and PAI.

Further, the present invention comprises whiskers or particles of PTFE, PAI and silicon nitride, wherein the composition of PTFE and PAI is 5 to 10/95 to 90 by weight and the total of PTFE and PAI is The present invention relates to a coating composition containing 1 to 10 parts by weight of whiskers or particles of silicon nitride based on 100 parts by weight.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS PTFE used in the present invention has a function of imparting lubricating properties to a sliding surface and improving a low friction coefficient and seizure resistance. PTFE is industrially produced by suspension polymerization or emulsion polymerization. PTFE as a molding raw material as used in the above-mentioned JP-A 1-261514
Has a high number-average molecular weight of 1,000,000 or more and has non-melt processability (melt viscosity at 380 ° C. of 10 ⁸ poises or more), so that it is difficult to disperse or blend it in other melt-processable resins. The major reason why this high molecular weight PTFE powder is not suitable for dispersion and blending is that high molecular weight PTFE
This is because the E powder causes fibrillation during the dispersion and blending steps. Therefore, when the number average molecular weight obtained by emulsification or suspension polymerization under low
Fine particles and powder of low molecular weight PTFE having a molecular weight of less than 1,000,000 are preferably used in the coating composition of the present invention. Further, the average particle diameter is preferably 0.01 to 20 μm, particularly 0.1 to 1 due to the good dispersion stability in the coating and the smoothness of the formed coating film surface.
A powder of 0 μm is preferable.

In the present invention, as a matrix for forming a coating film, the coating film properties such as resin heat resistance, oil resistance, adhesion to a metal substrate, and abrasion resistance are well-balanced and can be fired at 200 ° C. or lower. PAI is used for that reason. When the substrate (object to be coated) is an aluminum alloy, the firing temperature is 200
If the temperature exceeds 100 ° C., the dimensional accuracy of the aluminum alloy is degraded due to thermal expansion, which is inconvenient especially when coating a substrate which requires strict dimensional accuracy such as a piston of an internal combustion engine. PAI is characterized by having both an amide bond and an imide bond in the molecular structure. For example, the reaction of an aromatic diamine having an amide group in the molecule with an aromatic tetravalent carboxylic acid such as pyromellitic acid, trimellitic anhydride Produced by the reaction of an aromatic trivalent carboxylic acid such as a diamine such as 4,4-diaminophenyl ether or a diisocyanate such as diphenylmethane diisocyanate, or a reaction between a dibasic acid having an aromatic imide ring in a molecule and a diamine. High molecular weight polymer.

The alumina particles used in the present invention for the purpose of improving abrasion resistance are preferably in the form of powder of aluminum oxide having an average particle diameter of 0.1 to 20 μm. The average particle diameter is 0.1 to 1.0 from the viewpoint that the dispersion stability in the paint and the smoothness of the formed coating film surface are good.
Those having a range of μm are particularly preferred. It is also known to use hard silicon carbide or the like as a filler other than the alumina particles, but in these cases, the abrasion resistance of the coating film obtained is inferior to that of the alumina particles.

The composition of PTFE and PAI is 5 to 5 by weight.
10/95 to 90. PTFE / PAI is 5/95
When smaller, the coefficient of friction of the obtained coating film increases,
Also, the seizure resistance decreases. If it is larger than 10/90, the abrasion resistance of the coating film obtained will decrease.

The alumina particles are blended in an amount of 5 to 10 parts by weight based on 100 parts by weight of the total of PTFE and PAI. If the amount is too small, the effect of improving the wear resistance is insufficient, and if it is too large, the wear resistance is reduced.

As with the alumina particles, whiskers or particles of silicon nitride may be blended for the purpose of improving the wear resistance. Whiskers are usually 1-500μ in length
m and an aspect ratio of 10 to 500.
It is not limited to these. As the particles, those having an average particle diameter of about 0.1 to 5.0 μm are suitable. The compounding amount is 1 to 10 parts by weight, preferably 3 to 8 parts by weight based on 100 parts by weight of the total amount of PTFE and PAI. When it is within this range, the effect of improving the wear resistance is high.

In carrying out the present invention, the above-mentioned PTFE,
In addition to PAI and alumina particles or silicon nitride whiskers or particles, solvents, solid lubricants, pigments, dispersion stabilizers, surface conditioners, thixotropic agents, defoamers, and viscosities for the purpose of improving coating properties and coating properties Regulators, anti-gelling agents, UV absorbers, light stabilizers, plasticizers, anti-segregation agents, anti-skinning agents, anti-scratch agents, fungicides, antibacterial agents, antioxidants, antistatic agents, silanes Various additives such as coupling agents can be used.

The solvent that can be used in the present invention is not particularly limited as long as it can dissolve the resin for forming the coating film. For example, nitrogen-containing solvents such as N-methyl-2-pyrrolidone and dimethylacetamide that dissolve PAI;
Other oxygen-containing solvents such as γ-butyrolactone; aromatic hydrocarbons such as xylene and toluene; esters such as butyl acetate; ketones such as methyl isobutyl ketone; glycol ethers such as butyl cellosolve;
Alcohols such as butanol; hydrocarbon solvents such as mineral spirits and petroleum mixed solvents represented by Solvesso (manufactured by Exxon Chemical Co., Ltd.).

Examples of the solid lubricant include sulfides such as molybdenum disulfide and tungsten disulfide, fluorinated graphite and graphite.

Examples of the pigment that can be used in the present invention include carbon, titanium oxide, iron oxide, and calcium carbonate.

Examples of the dispersion stabilizer include surfactants, more specifically, anionic surfactants, cationic surfactants, amphoteric surfactants and nonionic surfactants. Those are recommended, but not limiting.

The surface conditioner is used for the purpose of preventing leveling and cissing, and examples thereof include acrylic oligomer-based polymers and polysiloxane-based polymers such as dimethylpolysiloxane.

Examples of the thixotropic agent include bentonite, metal soap, oxidized polyethylene wax, polyamide wax, silica (silicon dioxide) and the like.

As a coating method, a conventionally known coating method can be adopted. For painting, brush, roller, roll coater, air spray, airless spray, electrostatic coating machine,
Conventionally known coating equipment such as a dip coating machine, an electrodeposition coating machine, and a screen printing machine can be used.

The coating composition of the present invention is prepared by a conventional method using PTF
It is prepared by mixing and dispersing E, PAI, alumina particles, silicon nitride whiskers or particles, and if necessary, a dispersion stabilizer, a pigment, a solvent and the like.

The coating composition of the present invention is applicable to metal substrates such as aluminum, iron and alloys thereof. Further, if necessary, the substrate may be subjected to a preliminary treatment such as alkali degreasing, shot blasting, etching, or a surface treatment such as a chemical conversion treatment. be able to. After coating, the coating is
Dry for 60 minutes, 160-280 ° C, preferably 16
The baking is performed in a temperature range of 0 to 200 ° C. for 10 to 180 minutes. The thickness of the coating film after firing is not particularly limited, but is usually 1 to
It is about 100 μm, preferably about 5 to 50 μm.

The coating thus obtained is excellent in heat resistance, oil resistance and sliding characteristics (seizure resistance, low friction coefficient, wear resistance) and is suitably applied to the outer peripheral surface of a piston skirt of an internal combustion engine. , Electrical products (microwave oven, toaster, washing machine, hair dryer, cassette deck, compact disc player, video camera, VCR, air conditioner indoor unit, outdoor unit, air purifier, etc.), office equipment (facsimile, copying) Machines, cameras, chairs, clocks, electronic whiteboards, scissors, etc., automobiles, kitchen appliances (range hoods, ventilation fans, etc.), building materials for houses (shutters, blinds, curtain rails, accordion curtains, gates, keys, roll screens, etc.) ),
It can also be used for sliding parts such as hydraulic equipment.

[0029]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Examples 1 to 3 and Comparative Examples 1 to 6 PTFE, PAI, alumina particles and silicon nitride whiskers were set in the weight ratio shown in Table 1, and the polyamideimide resin (weight parts) was used in accordance with the composition (parts by weight) shown in Table 2. PAI)
A coating composition was prepared by mixing and dispersing varnish, fluororesin, carbon black, methyl isobutyl ketone, N-methyl-2-pyrrolidone, and other additives in a sand mill for 2 hours.

[0031]

[Table 1]

[0032]

[Table 2]

Varnish: resin solid content 27% (solvent component: N
-Methyl-2-pyrrolidone: 54.75% by weight, xylene: 18.25% by weight) Fluororesin: low molecular weight PTFE powder (number average molecular weight of about 2)
0,000, average particle size about 10 μm. However, the fluororesin used in Example 3 was a mixture of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and high molecular weight PTFE. Silica: average particle diameter 7 nm Silicone oil solution: 10% by weight toluene solution Fluorinated surfactant: DS-451 (manufactured by Daikin Industries, Ltd.)

The obtained coating composition was applied to a test piece made of an aluminum alloy for measuring sliding characteristics, which had been subjected to a degreasing treatment in advance, by an air spray, and was applied at 80 to 100 ° C. for 60 hours.
After drying for 200 minutes, it was baked at 200 ° C. for 60 minutes to form a coating film having a thickness of about 20 μm to obtain a coated product.

The sliding properties of the coating films formed in Examples 1 to 3 and Comparative Examples 1 to 6 were examined by the following method.

(1) Wear Depth Using a high surface pressure abrasion tester, the wear depth after abrasion in lubricating oil for 30 minutes at a load of 30 kg under a load of 30 kg was measured using an aluminum alloy as a mating material. Wear depth is 5.0
When it was less than μm, it was judged that the abrasion resistance was good.

(2) Seizure Load (Seizure Resistance) Using a pin-on-disk wear tester with an aluminum alloy as a mating material, the load was increased by 25 kg / min at 1,000 revolutions per minute, and the load at which seizure occurred was measured. When seizure did not occur at a load of 500 kg, the seizure resistance was judged to be good.

(3) Dynamic friction coefficient The load was 200 kg, and the measurement was carried out under the same conditions as in (2).
When the dynamic friction coefficient was 0.03 or less, it was determined that the friction characteristics were good.

(4) Overall Evaluation of Sliding Characteristics When all of the evaluation results (1) to (3) were good, the overall evaluation of sliding characteristics was judged to be good.

[0040]

[Table 3]

[0041]

The coating composition of the present invention has excellent adhesion to a substrate, especially an aluminum alloy, and can provide a coating film having good seizure resistance and abrasion resistance and a low coefficient of friction.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Koichiro Ogita 1-1, Nishiichitsuya, Settsu-shi, Osaka Daikin Industries, Ltd. Yodogawa Works (72) Inventor Shinji Kato 1-Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Automobile Stocks F term in the company (reference) 4J038 CD122 DJ051 HA166 HA436 KA06 KA08 MA14 NA04 NA11 NA12 NA14 PA19 PB02 PB06 PB07 PB09 PB11 PC02

Claims (5)

[Claims] 1. A composition comprising polytetrafluoroethylene, polyamideimide and alumina particles, wherein the composition of polytetrafluoroethylene and polyamideimide is 5 to 1 in weight ratio.
A coating composition which is 0/95 to 90 and contains 5 to 10 parts by weight of alumina particles based on 100 parts by weight of the total amount of polytetrafluoroethylene and polyamideimide. 2. A composition comprising polytetrafluoroethylene, polyamideimide, and silicon nitride whiskers or particles, wherein the composition of polytetrafluoroethylene and polyamideimide is 5 to 10/95 to 90 by weight, and A coating composition comprising 1 to 10 parts by weight of silicon nitride whiskers or particles based on 100 parts by weight of the total amount of tetrafluoroethylene and polyamideimide. 3. The coating composition according to claim 1, wherein the polytetrafluoroethylene is a powder having a number average molecular weight of 1,000 to less than 1,000,000 and an average particle diameter of 0.01 to 20 μm. object. 4. A coated article having a coating film of the coating composition according to claim 1 on the surface. 5. A piston of an internal combustion engine having a coating film of the coating composition according to claim 1 on an outer peripheral surface of a piston skirt.