Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-12-22
2001-12-18
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S340000, C523S351000, C524S386000, C524S487000, C524S904000, C525S934000
Reexamination Certificate
active
06331581
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, and to a process for the preparation thereof.
Conventionally the 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 raise the problem that the 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 component and a decrease in thermal flowability of granulated powder coating composition and leading to the impairment of film properties such as smoothness of coating surface, specular reflectance and the like.
An object of the present invention is to provide a method for color matching of a powder coating composition and a production process, the method or process being capable of giving a powder coating composition which forms a film improved in finished appearance without flooding and excellent in properties such as smoothness of coating surface, specular reflectance, adhesion and the like, and the method or process 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, the method comprising the steps of: dryblending two or more kinds of starting colored thermosetting powder coating compositions of different colors having an average particle size of 10 &mgr;m or less to achieve color matching, and granulating the dryblend to a particle size in the range which is suitable for coating, by adding at least one binder selected from the group consisting of an aqueous solution of polyethylene glycol and an aqueous dispersion of paraffin wax.
According to the present invention, there is also provided a process for preparing a color-matched thermosetting powder coating composition, the process including the above-mentioned color matching step and granulation step.
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 accomplish color match, and granulating the dryblend by adding a specific binder. The method makes it easy to match the color of coating compositions and produces a colored thermosetting powder coating composition excellent in finished appearance and film properties. The present invention was accomplished based on these novel findings.
Starting Colored Thermosetting Powder Coating Composition
Colored thermosetting powder coating compositions for use as the starting materials in the color matching method and the production process of the present invention 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 said thermosetting powder resins include resins having a functional group which reacts with a curing agent when heated. Specific examples of such resins are acrylic resins, polyester resins, epoxy resins, fluorine-containing resins, silicone resins and hybrids of these resins. Suitable functional groups include hydroxyl, carboxyl, epoxy, blocked isocyanate, etc.
The curing agent which is useful herein includes one having a functional group which reacts with the functional group in the powder resin to form a cured coating film or one capable of initiating polymerization of the functional group in the powder resin. Examples of curing agents for hydroxyl-containing powder resins include amino resins and blocked isocyanate compounds. Examples of curing agents for carboxyl-containing powder resins include polyepoxides and B-hydroxyethyl alkylamides. Examples of curing agents for epoxy-containing powder resins include polycarboxylic acids, initiators for cationic polymerization of epoxy groups, etc. Examples of curing agents for blocked isocyanate-containing powder resins include polyols.
Examples of amino resins include hexamethoxymelamine resins, hexaethoxymelamine resins, “Cymel 303” (tradename, a product of Mitsui Cytec. Co., Ltd.) and “Sumimal M-55” (tradename, a product of Sumitomo Chemical Co., Ltd.). Examples of blocked isocyanate compounds include those prepared by blocking an aliphatic, alicyclic or aromatic polyisocyanate with a blocking agent such as a phenol, &egr;-caprolactam or alcohol. The aliphatic, alicyclic or aromatic polyisocyanate may be isophorone diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, tolylene diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diusocyanate or the like. Examples of polyepoxides include homopolymers and copolymers of triglycidyl isocyanurate or glycidyl (meth)acrylate, and “Celoxide 2021” (tradename) and “EHPE-3150” (tradename) both manufactured by Daicel Industries, Co., Ltd. Examples of &bgr;-hydroxyethyl alkylamides include &bgr;-hydroxyethyl propylamide. Examples of polycarboxylic acids include adipic acid, sebacic acid, suberic acid, succinic acid, glutaric acid, maleic acid, fumaric acid, dodecanedioic acid, pimelic acid, azelaic acid, itaconic acid, citraconic acid and like aliphatic polycarboxylic acids and their anhydrides; terephthalic acid, isophthalic acid, phthalic ac
Kawamoto Yugen
Ohnishi Kazuhiko
Takanashi Hidefumi
Armstrong Westerman Hattori McLeland & Naughton LLP
Kansai Paint Co. Ltd.
Yoon Tae H.
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