Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-08-16
2002-01-01
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S100000, C524S101000, C524S102000, C524S109000
Reexamination Certificate
active
06335389
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resin composition for powdery coatings, which utilizes a carboxyl group-containing resin and a curing agent having a &bgr;-methylglycidyl group, and which provides coating films having high impact resistance, weather resistance, heat yellowing resistance, etc., useful for outdoor uses.
BACKGROUND ART
As resins for powdery coatings, e.g. epoxy resins, polyester resins, polyacrylic resins, polyvinyl chloride resins and polyethylene resins are used at the present time.
In recent years, thermosetting resins are mainly used from the viewpoint of physical properties and smoothness of the coating films. However, thermosetting resins have a drawback such that in a case of using a condensation resin or in a case of using a block isocyanate as a curing agent, a condensation desorption component or a blocking agent may gasify to form bubbles in the coating films.
Accordingly, as a preferred curing agent to be used for powdery coatings, a polyglycidyl compound having no desorption component during the curing reaction may be mentioned. However, if a conventional glycidyl compound such as a bisphenol type diglycidyl ether is used as a curing agent, it has been known that the resin may decompose when used outdoors, due to unstableness to light derived from its phenyl ether structure, and the glossiness of the surface will disappear very early. Further, the use of a polyglycidyl compound having a skeleton other than the bisphenol type as a curing agent is imperfect, since a demand for the weather resistance is increasing in recent years. With respect to such a demand, it has been known that a coating film having an excellent weather resistance will be obtained by using as a crosslinking agent a poly-&bgr;-methylglycidyl compound instead of the polyglycidyl compound.
As examples of using said poly-&bgr;-methylglycidyl compound as a curing agent for powdery coatings, JP-A-49-24244 discloses a resin composition for powdery coatings, which comprises a polyester resin having an acid value of from 30 to 200, synthesized from e.g. an aromatic dicarboxylic acid or its ester, a dihydroxy alcohol and a polyhydric carboxylic acid, and tris(&bgr;-methylglycidyl)isocyanurate.
JP-A-49-94722 discloses a method for producing a resin composition for powdery coatings which comprises a free hydroxyl group-containing polyester resin, an acid anhydride and an epoxy compound such as tris(&bgr;-methylglycidyl)isocyanurate.
JP-A-50-19832 discloses a method for producing a resin composition for powdery coatings which comprises a polyester resin containing a carboxyl group on its side chain by means of an ester linkage, and an epoxy compound such as tris(&bgr;-methylglycidyl)isocyanurate. The composition may contain an additive such as an ultraviolet light absorber or an antioxidant.
JP-A-51-44130 discloses a resin composition for powdery coatings, which comprises a polyester resin having a free phenolic hydroxyl group, and a compound having at least two glycidyl groups and having a melting point of from 30 to 250° C., a monomer radical-copolymerizable with a compound having an epoxy group, or an epoxy compound such as tris(&bgr;-methylglycidyl)isocyanurate. To this composition, a tetraalkylammonium salt such as tetrabutylammonium bromide or tetraethylammonium chloride, an imidazole such as imidazole, 2-methyl-4-ethyl-imidazole or 2-methyl-imidazole, a tertiary amine such as triethylenediamine or N-methyl morpholine, or an organic carboxylic acid such as cobalt naphthenate or zinc naphthenate, may be added as a catalyst.
JP-A-51-12823 discloses a composition for powdery coatings, which has a polyhydric carboxylic acid mixed with a polymer comprising a vinyl monomer having a (methyl)glycidyl group, an unsaturated polyester having a (methyl)glycidyl group and another vinyl monomer. To said composition, e.g. an alkali or an amine may be added so as to accelerate the curing reaction.
JP-A-52-69935 discloses a composition for powdery coatings, which has a specific polyester having a low acid value added to a carboxyl group-containing polyester, and triglycidyl isocyanurate or tris(&bgr;-methylglycidyl)isocyanurate. Said composition may contain an additive such as an antioxidant.
JP-A-57-51760 discloses a composition for powdery coatings to be used for topcoats for automobiles, obtained by combining an acrylic copolymer comprising an unsaturated monomer having an epoxy group, a carboxyl-terminated crosslinking agent, a supplementary crosslinking agent or a modifying agent and an ultraviolet light deterioration inhibitor.
JP-A-4-63872 discloses a composition for powdery coatings, which contains a carboxyl group-containing resin, and a polyglycidyl compound having from 2 to 6 glycidyl groups in one molecule, obtained by adding an epoxy compound such as tris(&bgr;-methylglycidyl)isocyanurate to a polyester oligomer having at least two carboxyl groups in its molecule. Said composition may contain an additive such as an ultraviolet light absorber or an antioxidant.
JP-A-4-288373 discloses a composition for powdery coatings, which comprises a base resin and a curing agent and a curing catalyst as well. The base resin is a resin having at least two carboxyl groups in one molecule. As the curing agent, triglycidyl isocyanurate or a polyglycidyl compound having from 2 to 6 glycidyl groups on the average in one molecule, obtained by adding tris(&bgr;-methylglycidyl)isocyanurate to a polyester oligomer having at least two carboxyl groups in one molecule. Said composition may contain an additive such as an ultraviolet light absorber or an antioxidant.
WO-93/04122 discloses a composition comprising a carboxyl group-containing polyester, an epoxy curing agent such as triglycidyl isocyanurate or a methyl-substituted triglycidyl isocyanurate, and a phosphonium salt catalyst. As the resin for powdery coatings, an epoxy resin, a polyester resin, a polyacrylic resin, a polyvinyl chloride resin or a polyethylene resin may, for example, be used at the present time.
U.K. Patent No. 1,266,066 discloses a thermosetting resin composition which comprises a &bgr;-methylglycidyl ester compound and an amine or a polycarboxylic acid.
JP-A-49-24244 discloses a technique utilizing as a curing agent which places emphasis mainly on the storage stability of the powder, a polyglycidyl ester and/or poly-&bgr;-methylglycidyl ester of an aromatic polyhydric carboxylic acid having a melting point of from 30 to 250° C. and having at least two glycidyl ester groups and/or &bgr;-methylglycidyl ester groups in its molecule.
WO-97/44400 discloses a resin composition for powdery coatings, which contains a carboxyl group-containing resin and bis(&bgr;-methylglycidyl)terephthalate as a curing agent, as the main components, and a ring-opening polymerization inhibitor for effective curing reaction, and which provides a coating film having an excellent weather resistance.
Conventionally, a baking-curable powdery coating is usually baked in line, and from its nature, its color may turn yellow relative to the adjusted color during baking, i.e. so-called heat yellowing may occur, for reasons such that the temperature distribution in an oven or the baking time is not constant. This heat yellowing will deteriorate the design of the coating film, and accordingly the powdery coating is required not to undergo heat yellowing, i.e. it is required to have an excellent heat yellowing resistance, even if the baking conditions such as the temperature and the time for baking are severe. However, the poly-&bgr;-methylglycidyl compound used as a crosslinking agent is known to be poor in view of heat yellowing resistance as compared with a polyglycidyl compound. Conventionally, it is a sterically-hindered phenol that is used for the purpose of decreasing the heat yellowing of a polymer. The heat yellowing will somewhat decrease by using it, however, when the baking is carried out in a gas oven which is conventionally employed for baking of powdery coatings, the sterically-hindered phenol tends to be oxidized by NOX generated in the gas ove
Hidaka Motohiko
Ikeda Hisao
Nissan Chemical Industries Ltd.
Sanders Kriellion A.
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