Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-07-16
2003-10-21
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S421100
Reexamination Certificate
active
06635312
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a method for improving crater resistance of paint films.
(2) Description of the Related Art
Cratering in paint films, which occurs with the application of a paint, is a serious paint film defect and has been a problem to be overcome in the paint industry.
Cratering is a phenomenon in which bowl shaped depressions are formed on the surface of a paint film when a liquid paint is applied to a substrate. When severe, cratering produces holes so deep as to expose the substrate. Various factors cause cratering. It is generally believed that factors, such as 1) rapid evaporation of a solvent from part of the wet paint film immediately after application of a paint, 2) influence of residual monomers and additives contained in the paint, 3) contaminant dusts in the film from the atmosphere, and 4) oil fouling on the substrate, cause the formation of a lower surface tension “trigger” portion on the film surface, and expansion of this trigger portion results in cratering.
With respect to crater resistance of paint films, Satoh et al., “Journal of the Japan Society of Colour Material”, Vol. 47, No. 9, pp. 19-26 (1974) describes the following: The cratering tendency of a paint depends on its flow properties. The lower the residual viscosity is and the larger the yield value K is, the stronger the cratering tendency is.
E. Kuwano et al., “Research on Coatings”, No. 136, April, pp. 9-16 (2001) describes the following: Continuous surface film with a large storage modulus G′ is resistant to cratering. When paint additives such as leveling agents are added, the surface storage modulus G′ increases.
A. Hiwara et al., “Research on Coatings”, No. 127, October, pp. 2-9 (1996) describes the following: The storage modulus/loss modulus (G′/G″) ratio of a paint relates to cratering tendency of the paint. The higher this ratio is, the higher the crater resistance is.
However, there is no known method that can effectively improve the crater resistance of a paint film, regardless of the kind of liquid paint used.
BRIEF SUMMARY OF THE INVENTION
An object of the invention is to provide a novel method for improving crater resistance of the paint films of various liquid paints which vary in their resin component, pigment component, etc.
The present inventors carried out a variety of studies on the effects of viscosity and elasticity of liquid paints on the occurrence or degree of cratering in the paint films. The inventors found that in the application of a liquid paint to a substrate, when adjustments are made in such a manner a wet paint film immediately after application has a specific level of viscosity and a storage modulus (G′)/loss modulus (G″) ratio within a specific range, the paint film exhibits highly improved crater resistance. The present invention was accomplished based on this finding.
The present invention provides the following methods for improving the crater resistance of paint films.
1. A method for providing a paint film with improved cratering resistance, comprising making adjustments in the application of a liquid paint to a substrate in such a manner that the wet paint film immediately after application has a viscosity of 0.2 to 1.0 Pa·s at a strain rate of 5 sec
−1
at 20° C., as measured by the static flow method, and has a storage modulus/loss modulus (G′/G″) ratio within the range of 0.1 to 0.25 at an angular frequency of 10 rad/sec at 20° C., as measured by the oscillation method.
2. The method according to item 1 wherein the viscosity and the G′/G″ ratio are measured at a point of time from about 0.5 minutes to about 3 minutes after application.
3. The method according to item 1 wherein the adjustments are made by at least one of the following means: modification of the liquid paint composition before application; modification of the coating process; and modification of coating conditions.
4. The method according to item 1 wherein the adjustments are made in such a manner that the wet paint film immediately after application has a viscosity of 0.4 to 1.0 Pa·s and a storage modulus/loss modulus (G′/G″) ratio within the range of 0.12 to 0.22.
5. The method according to item 3 wherein the modification of the liquid paint composition before application of the paint is carried out using at least one of the following means: addition of a fluidity regulator; addition of a solvent; and adjustment of the paint pigment concentration.
6. The method according to item 3 wherein the modification of the coating process is the use of spray coating in place of other processes.
DETAILED DESCRIPTION OF THE INVENTION
There is no limitation on the substrate used in the method of the invention. Examples of substrates include metal substrates (sheets, plates or molded articles) such as iron plates, aluminium plates, stainless steel plates, zinc plated steel sheets, zinc alloy plated steel sheets and tin plates; surface treated metal substrates formed by treating the surface of the above-mentioned metal substrates with phosphate, chromate, complex oxide or the like; plastic substrates; inorganic ceramic substrates such as glass, cement, slate, mortar, concrete and tile; paper; and coated substrates produced by coating the above-mentioned substrates. Examples of zinc alloy plated steel sheets are steel sheets plated with an alloy such as iron/zinc, nickel/zinc or aluminium/zinc.
The liquid paint used in the invention can be an organic solvent paint or an aqueous paint comprising a resin, optionally with a curing agent.
Usable as the resin of the liquid paint is any known paint resin. Representative examples include acrylic resins, polyester resins, alkyd resins, epoxy resins, polyamide resins, silicone polyester resins, silicone acrylic resins, fluorine resins, epoxy resins, and modified resins thereof. These resins can be used singly or in combinations of two or more, and can be used in combination with curing agents. Examples of curing agents include amino resins such as melamine resins, epoxy compounds, polyamine compounds, polyisocyanate compounds and blocked polyisocyanate compounds. It is also possible to use a combination of an epoxy-containing acrylic resin and a carboxyl-containing acrylic resin.
The paint can be a clear paint or a colored paint comprising a coloring pigment and/or a luster pigment. If necessary, the paint may contain other pigments such as extender pigments.
Examples of coloring pigments include inorganic pigments such as titanium dioxide and iron oxide; and organic pigments such as phthalocyanine blue, quinacridone red, perylene red and phthalocyanine green. Examples of luster pigments include aluminium flakes and mica flakes. Examples of extender pigments include barium sulfate, calcium carbonate, talc and clay.
When the liquid paint is an organic solvent paint, useful organic solvents include, for example, xylene, toluene, ethyl acetate, isobutyl acetate, ethanol, butanol, cyclohexanol, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol monobutyl ether and propylene glycol monomethyl ether. It is usually appropriate that the solids concentration of the organic solvent paint be about 20 wt. % to about 70 wt. %.
When the liquid paint is an aqueous paint, water or a mixed solvent of water and an aqueous organic solvent can be used as the solvent. Examples of aqueous organic solvents include ethylene glycol monobutyl ether, propylene glycol monomethyl ether, ethanol, butanol and isopropanol. It is usually appropriate that the solids concentration of the aqueous paint be about 20 wt. % to about 70 wt. %.
In the method of the invention, the liquid paint can be applied to a substrate by a coating process such as air spray coating, rotary spraying, airless spray coating, roll coating, brush coating, curtain coating and dip coating. Particularly preferred are spray coating processes such as air spray coating, rotary spraying and airless spray coating. These spray coating processes can be carried out by electros
Fujitani Toshihide
Hiwara Atsunao
Armstrong Westerman & Hattori, LLP
Cameron Erma
Kansai Paint Co. Ltd.
LandOfFree
Method for improving crater resistance of paint films does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for improving crater resistance of paint films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for improving crater resistance of paint films will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3151795