Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-01-28
2002-02-19
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S934000, C524S904000
Reexamination Certificate
active
06348520
ABSTRACT:
The present invention relates to a novel method for color matching of a thermosetting powder coating composition, the method being capable of color matching with ease.
Conventionally, color matching of powder coating compositions have been made as by the following method to realize the color specified by the user. For example, a coloring pigment is mixed with and dispersed in a powder resin, a curing agent and the like, and the obtained dispersion is mixed to melt and disperse the coloring pigment, the curing agent and the like in the powder resin using, e.g., a twin-screw dispersing device, followed by cooling, coarse grinding, fine grinding and sieving, thereby giving the contemplated color-matched powder coating composition.
The above-mentioned preparation of color-matched powder coating compositions poses no problem in preparing a large amount of powder coating composition with a specified color. However, when powder coating compositions of various colors are prepared in small amounts, namely, in the case of small-lot manufacture of paints with different colors, numerous problems are entailed which include a great loss of powder coating compositions, considerable labor, intensified contamination and so on.
In order to overcome the above-mentioned problems, a variety of methods for color matching of powder coating compositions have been proposed. For instance, WO90/06345 discloses a method wherein two or more kinds of powder coating compositions with different colors are mixed together and granulated with an aqueous acrylic resin as a granulating agent to provide a color-matched powder coating composition. Japanese Unexamined Patent Publication No.188586/1995 describes a method wherein two or more kinds of powder coating compositions are dryblended for color matching, and the dryblend is granulated with a synthetic resin as a binder. However, these conventional methods necessitate the use of an aqueous acrylic resin and a resin binder both having a high molecular weight to prevent the degradation of film properties, resulting in irregular granules due to a high viscosity of the resin components and in decrease of thermal flowabillty of the granulated powder coating composition which leads to the impairment of film properties such as surface smoothness, specular reflectance and the like.
An object of the present invention is to provide a method for color matching of a powder coating composition, the method being capable of giving a powder coating composition which achieves good finished appearance without flooding and is excellent in film properties such as surface smoothness, specular reflectance, adhesion and the like, and the method being capable of facilitating color matching and small-lot manufacture of powder coating compositions with different colors.
Other objects and features of this invention will become apparent from the following description.
According to the present invention, there is provided a method for color matching of a thermosetting powder coating composition (hereinafter referred to as “color matching method I”), the method comprising the steps of: (1) dryblending two or more kinds of starting colored thermosetting powder coating compositions of different colors having an average particle size of 20 &mgr;m or less to achieve color matching, and (2) granulating the dryblend to a particle size in the range suitable for powder coating, by heating the dryblend with agitation to a temperature at which the dryblend melts at the particle surfaces but does not melt in the particle interiors.
According to the present invention, there is also provided a method for color matching of a thermosetting powder coating composition (hereinafter referred to as “color matching method II”), the method comprising the steps of: (1) dryblending two or more kinds of starting colored thermosetting powder coating compositions of different colors having an average particle size of 20 &mgr;m or less to achieve color matching, and (2) granulating the dryblend to a particle size in the range suitable for powder coating, by (i) adding a solid binder having an average particle size of 20 &mgr;m or less and a lower melting point than the starting powder coating compositions and then (ii) heating the resulting mixture to a temperature at which the binder melts but the starting powder coating compositions do not melt.
According to the present invention, there is further provided a method for color matching of a thermosetting powder coating composition (hereinafter referred to as “color matching method III”), the method comprising the steps of: (1) dryblending two or more kinds of starting colored thermosetting powder coating compositions of different colors having an average particle size of 20 &mgr;m or less with a solid binder having an average particle size of 20 &mgr;m or less and a lower melting point than the starting powder coating compositions to achieve color matching, and (2) granulating the dryblend to a particle size in the range suitable for powder coating, by heating the dryblend to a temperature at which the binder melts but the starting powder coating compositions do not melt.
According to the present invention, there is further provided a method for color matching of a thermosetting powder coating composition (hereinafter referred to as “color matching method IV”), the method comprising the steps of: (1) dryblending two or more kinds of starting colored thermosetting powder coating compositions of different colors having an average particle size of 20 &mgr;m or less to achieve color matching, and (2) granulating the dryblend to a particle size in the range suitable for powder coating, by (i) compressing the dryblend at a pressure sufficient to melt the particle surfaces of the dryblend for forming a sheet or grains, and then (ii) grinding and classifying the sheet or grains.
The present inventors conducted extensive research to overcome the foregoing problems of the prior art and found the following solution. The solution is a method comprising dryblending two or more kinds of starting thermosetting powder coating compositions of different colors with a specific particle size to achieve color matching, and granulating the dryblend to a particle size suitable for coating, by heating and agitating the dryblend, or by adding a specific solid binder, or by grinding and classifying a sheet or grains formed by compressing the dryblend. The method makes it easy to match the color of a coating composition and produces a colored thermosetting powder coating composition excellent in application characteristics, finished appearance and film properties. The present invention was accomplished based on these novel findings.
As used herein, the term “granulate” is intended to mean “to agglomerate powder particles into granules or agglomerates having a greater diameter”.
Starting Colored Thermosetting Powder Coating Composition
Colored thermosetting powder coating compositions for use as the starting materials in the color matching method of the invention each comprise a coloring pigment and a resin component comprising a curing agent and a thermosetting powder resin which is melted and fluidized when heated. The thermosetting powder resin has a softening temperature of about 30 to about 100° C.
The coloring pigment to be used herein is at least one pigment selected from white pigments, black pigments, red pigments, yellow pigments, blue pigments, green pigments, scaly aluminum powders, colored mica powders, copper powders, tin powders, and stainless steel powders. The amount of the coloring pigment to be used can be suitably selected to impart satisfactory film properties such as hiding power and surface smoothness to the film formed from the obtained powder coating composition. Although variable with the type of the pigment used, the amount of the pigment is about 0.1 to about 100 parts by weight, preferably about 1 to about 80 parts by weight, per 100 parts by weight of the powder resin component.
Examples of thermosetting powder resins include resins having a functional group which
Kawamoto Yugen
Ohnishi Kazuhiko
Takanashi Hidefumi
Armstrong Westerman Hattori McLeland & Naughton LLP
Jagannathan Vasu
Kansai Paint Co. Ltd.
Shosho Callie E.
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