Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-10-13
2002-11-19
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S458000, C428S460000, C428S461000, C428S624000
Reexamination Certificate
active
06482536
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a non-chrome based coating composition capable of forming a coating film having good properties in corrosion resistance, fabrication properties, adhesion properties, and boiling water resistance, and a coated metal plate having a coating film formed from the coating composition.
BACKGROUND ART
A precoated metal plate such as a precoated steel sheet prepared by coil coating or the like has widely been used in the art as building materials such as roofs, walls, shutters, garages and the like for an architectural structure, and as housing-related goods such as various kinds of household appliances, panel boards, refrigerated show cases, steel furniture, kitchen furniture, and the like.
The above housing-related goods are prepared from the precoated steel sheet by a process which comprises cutting the precoated steel sheet, followed by press molding and joining, and may have a metal-exposed area as a cut surface and a crack-developed area due to press molding. Since the metal-exposed area and the crack-developed area may show poorer corrosion resistance compared with other areas, inclusion of a chrome based anticorrosive pigment into a primer coating film of the precoated steel sheet has been carried out in the art for the purpose of improving corrosion resistance.
However, the chrome based anticorrosive pigment may contain or produce a hexavalent chromium showing good corrosion resistance but imparting harmful effect to the human body, resulting in producing problems from the standpoint of an environmental protection.
Many non-chrome based anticorrosive pigments, for example, zinc phosphate, aluminum tripolyphosphate, zinc molybdate, etc., have been marketed, but may show poorer corrosion resistance compared with the chrome based anticorrosive pigment and poor boiling water resistance in a large amount, resulting in being incapable of substitute it for the chrome based anticorrosive pigment in the preparation of the precoated steel sheet.
DISCLOSURE OF THE INVENTION
The present inventors made intensive studies for the purpose of obtaining a non-chrome based coating composition capable of forming a coating film showing good properties in corrosion resistance, fabrication properties, adhesion properties and boiling water resistance to find out that the above purpose can be achieved by use of a coating composition containing specified ones of the silica fine particles used as a matting agent or the like in such an amount that a cured coating film formed therefrom may have a specified range of glass transition temperature, resulting in accomplishing the present invention.
That is, the present invention provides a coating composition containing 8 to 130 parts by weight, preferably 30 to 80 parts by weight of (B) silica fine particles having an oil absorption in the range of 30 to 200 ml/100 g and a pore volume in the range of 0.05 to 1.2 ml/g per 100 parts by weight of (A) a coating film-forming resin, a cured coating film formed from the coating composition having a glass transition temperature in the range of 40 to 125° C.
The coating film-forming resin (A) in the present invention, in a first preferable embodiment, is a mixture of 40 to 95 parts by weight of an organic resin containing hydroxyl group or epoxy group with 5 to 60 parts by weight of at least one curing agent selected from the group consisting of an amino resin, blocked polyisocyanate compound and polyvalent carboxylic acid curing agent.
The coating film-forming resin (A) of the present invention, in a preferable second embodiment, is a mixture obtained by mixing 5 to 90 parts by weight of hydroxyl group-containing polyester resin, 5 to 70 parts by weight of novolak type epoxy resin and 5 to 40 parts by weight of at least one curing agent selected from the group consisting of amino resin and blocked polyisocyanate compound based on 100 parts by weight of a total solid content.
The present invention also provides a coated metal plate having a coating film formed from the above coating composition on the surface of a metal plate optionally surface-treated.
The present invention further provides a coated metal plate prepared by forming a topcoating film having a glass transition temperature in the range of 20 to 80° C. on the surface of the coating film formed from the above coating composition on the surface of a galvanized sheet, a zinc alloy-plated steel sheet, aluminum-plated steel sheet or an aluminum plate optionally surface-treated respectively.
The coating composition of the present invention is explained more in detail hereinafter.
In the coating composition of the present invention, the film-forming resin as the component (A) may include any film-forming resins without particular limitations, and typically may include, for example, at least one resin selected from polyester resin, epoxy resin, acrylic resin, fluorocarbon resin, vinyl chloride resin and the like; mixtures of the above resin with a curing agent, and the like.
Of the above resins, in a first preferable embodiment, the film-forming resin (A) includes a mixture of a hydroxyl group or epoxy group-containing organic resin with at least one curing agent selected from amino resin, blocked polyisocyanate compound and polyvalent carboxylic acid curing agent. The hydroxyl group or epoxy group-containing organic resin particularly includes at least one resin selected from hydroxyl group-containing polyester resin and epoxy resin. The above organic resin usually has a resin acid value less than 50 mg KOH/g.
The hydroxyl group-containing polyester resin as the preferable organic resin may include an oil-free polyester resin, oil-modified alkyd resin, modified products thereof, for example, urethane-modified polyester resin, urethane-modified alkyd resin, epoxy-modified polyester resin and acrylic-modified polyester resin, and the like. The hydroxyl group-containing polyester resin may preferably have a number average molecular weight in the range of 1,500 to 35,000, preferably 2,000 to 25,000, a glass transition temperature (Tg) in the range of 10 to 100° C., preferably 20 to 80° C., and a hydroxyl value in the range of 2 to 100 mg KOH/g, preferably 5 to 80 mg KOH/g.
In the present invention, the glass transition temperature (Tg) of the resin is measured by the differential scanning calorimeter (DSC), and the number average molecular weight is measured by use of a calibration curve of a standard polystyrene in accordance with the gel permeation chromatography (GPC).
The oil-free polyester resin consists of an esterified product between a polybasic acid component and a polyhydric alcohol component. The polybasic acid component may include, as the major component, for example, at least one dibasic acid selected from phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, sebacic acid and maleic anhydride, and lower alkyl esterified products thereof, and in addition to the above acids, may optionally include monobasic acid such as benzoic acid, crotonic acid, p-t-butyl benzoic acid and the like, trivalent or higher polybasic acid such as trimellitic anhydride, methylcyclohexene tricarboxylic acid, pyromellitic anhydride and the like, and the like. The polyhydric alcohol may include, as the major component, for example, dihydric alcohol such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butane diol, neopentyl glycol, 3-methylpentane diol, 1,4-hexane diol, 1,6-hexane diol and the like, and, in addition to the above acid, may optionally include trihydric or higher polyhydric alcohol such as glycerine, trimethylol ethane, trimethylol propane, pentaerythritol and the like. These polyhydric alcohols may be used alone or in combination. Esterification or ester exchange reaction between both components may be carried out by a process known per se. The acid component may particularly include isophthalic acid, terephthalic acid, and lower alkyl esterified products thereof.
The alkyd resin may be prepar
Nakano Takashi
Ooshima Takao
Tada Masahiro
Tanaka Shoichi
Kansai Paint Co. Ltd.
Turner Archene
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