Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1998-06-17
2003-04-22
Wilson, D. R. (Department: 1713)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S407000, C525S199000, C525S200000, C525S309000, C525S934000
Reexamination Certificate
active
06551708
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a powder coating composition. Further in detail, the powder coating composition of the present invention is suitable for coating of a precoat metal (hereinafter referred to as “PCM”).
BACKGROUND ART
Hitherto, there have been many proposals as to a powder coating composition. In JP-A-1-103670, for example, there is described a thermosetting powder coating composition comprising a fluorine-containing copolymer containing chlorotrifluoloethylene as the main component and a curing agent.
A coating film obtained from the powder coating composition described in the above-mentioned publication has high gloss and good weather resistance. There is a problem, however, that the coating film is inferior in bending resistance because the fluorine-containing copolymer is crosslinked by the curing agent, and thus the coating film is difficult to be employed for an application such as PCM which need to be subjected to post processing such as bending.
The present inventors have found that a powder coating composition comprising a specific powder which contains specific amounts of a specific vinylidenefluoride copolymer and a specific methyl methacrylate copolymer can provide a coating film being excellent particularly in bending resistance.
Namely, an object of the present invention is to provide a powder coating composition which is superior in dispersibility of pigment, weather resistance, appearance and stain-proofing property and particularly excellent in bending resistance, which makes it possible to give a coating film being hardly cracked during bending process of the metal plate with the film thereon in the application for PCM.
DISCLOSURE OF THE INVENTION
The present invention relates to a powder coating composition comprising a powder which contains
100 parts by weight of a vinylidene fluoride copolymer having a melting point of not higher than 150° C., a crystallinity of not higher than 35% and a weight average molecular weight of from 1×10
4
to 5×10
5
and 10 to 400 parts by weight of a methyl methacrylate copolymer having a glass transition temperature of not higher than 110° C. and a weight average molecular weight of from 1×10
4
to 5×10
5
;
an average particle size of particles constituting the powder being from 1 to 100 &mgr;m and an apparent density of the powder being from 0.2 to 1 g/ml.
BEST MODE FOR CARRYING OUT THE INVENTION
As the specific vinylidene fluoride (VdF) copolymer which can be employed in the present invention, there is, for example, a copolymer obtained by copolymerizing VdF as an essential component with one or more monomers copolymerizable with VdF, for example, a fluoroolefine monomer such as tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE) or hexafluoropropylene (HFP) or a monomer having an unsaturated bond such as perfluorobutenoic acid, maleic acid or vinyl acetate. By using such a copolymer, there are superior effects, which cannot be obtained by VdF homopolymer, that a coating film can be obtained at a relatively low temperature of not higher than 200° C. and occurrence of crack at the time of post processing of a coated metal plate can be prevented.
Among the VdF copolymers, from the viewpoints of good copolymerizability, weather resistance and thermal stability, VdF-TFE copolymer, VdF-TFE-HFP copolymer, VdF-TFE-CTFE copolymer, VdF-TFE-TrFE copolymer, VdF-CTFE copolymer, VdF-HFP copolymer, VdF-TFE-perfluorobutenoic acid copolymer and VdF-TFE-maleic acid copolymer are preferable, and VdF-TFE-HFP copolymer and VdF-TFE-CTFE copolymer are further preferable. Particularly by using a copolymer containing CTFE, balance between hardness of a coating film and post-processability can be improved.
A copolymerization ratio of VdF in the VdF copolymer is, from the viewpoint of good compatibility with methyl methacrylate copolymer, not less than 60% by mole, preferably not less than 70% by mole. From the viewpoint of post processability, the upper limit is preferably 98% by mole.
A melting point of the VdF copolymer is not higher than 150° C., preferably 40° to 120° C. from the viewpoints that leveling property is good and superior appearance, gloss and workability in coating can be obtained even if the powder coating composition obtained from the copolymer is not heated to a high temperature.
A crystallinity of the VdF copolymer is, due to the same reason mentioned above with respect to the melting point, not higher than 35%, preferably from 0 to 10%.
A weight average molecular weight of the VdF copolymer is not less than 1×10
4
, from the viewpoints that in application such as PCM, crack hardly occurs during bending and post processability is not lowered, and is preferably not more than 5×10
5
from the viewpoints that flowability of the powder coating composition is not easy to be lowered and appearance of the coating film is not easy to be damaged.
As the specific methyl methacrylate copolymer which can be employed in the present invention, there are, for example, homopolymer of methyl methacrylate (MMA), a copolymer obtained by copolymerizing MMA as the main component with one or more monomers copolymerizable with MMA such as acrylic acid ester monomer and methacrylic acid ester monomer, and the like.
As the acrylic acid ester monomer, there are, for example, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, benzyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate and the like.
As the methacrylic acid ester monomer, there are, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate (t-BMA), n-hexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate and the like.
As the monomer copolymerizable with the above-mentioned MMA, there are, for example, further to the above-mentioned monomers, conjugated diene compounds such as 1,3-butadiene, isoprene and chloroprene; aromatic vinyl compounds such as styrene, &agr;-methylstyrene, halogenated styrene and divinylbenzene; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; and the like.
By using such a copolymer, good effects can be obtained in appearance, thermal stability and weather resistance of the coating film.
In the present invention, the purposes are accomplished even if crosslinking is not carried out and, however, the powder coating composition of the present invention can be used in the form of a crosslinkable type by addition of a crosslinkable group and a curing agent in an amount where post processability which is characteristic of the present invention is not damaged.
Further in the present invention, as the monomer copolymerizable with MMA, further to the above-mentioned monomers, for example, a monomer containing one or more reactive groups such as
can be used.
As the above R, there are, for example, a saturated hydrocarbon residue having 1 to 3 carbon atoms and the like.
Among the above-mentioned reactive groups, —OH, —COOH and
are preferable.
A MMA copolymer obtained by copolymerizing a monomer having such a reactive group can be used as thermosetting powder coating composition, for example, when used in combination with a curing agent.
As the monomer having such a reactive group, there are, for example, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and crotonic acid; amide compounds such as acrylamide, methacrylamide N-methyl acrylamide, N-methyl methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N-alkyl acrylamide, N-alkyl methacrylamide, N,N-dialkyl acrylamide and N,N-dialkyl methacrylamide; acrylic acid esters such as 2-hydroxyethyl acrylate, N,N-dialkylaminoethyl acrylate and glycidyl acrylate; methacrylic acid esters such as 2-hydroxyethyl methacrylate, N,N-dialkylaminoethyl methacrylate, glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate; vinyl ether compounds such
Iwakiri Ryuzi
Tsuda Nobuhiko
Armstrong Westerman & Hattori, LLP
Daikin Industries Ltd.
Wilson D. R.
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