Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-05-12
2002-07-16
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C427S372200, C427S385500, C428S423100, C524S507000, C524S589000, C524S591000, C524S839000, C524S840000, C525S123000, C525S455000
Reexamination Certificate
active
06420477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an aqueous coating composition for metal sheets, and surface-treated metal sheets and a surface treating method using the same. More detailedly, this invention relates to an aqueous coating composition capable of forming a film giving good adhesion of UV-curable paints, UV-curable inks or UV-curable adhesives, corrosion resistance, formability, and durability with injury when applied onto the surface of a metal sheet, and surface-treated metal sheets and surface treating method for metal sheets using the same.
2. Statement of Related Art
Workpieces and formed products using metal sheets, for example aluminum or aluminum alloy sheets have hithereto been utilized in broad fields, and there are many techniques for forming resin film on their surfaces in order to give formability, corrosion resistance, durability with injury, etc. For example, JP-A-8/127735 discloses an aluminum sheet for lubricating treatment which comprises an aluminum sheet having chromate film provided thereon and having lubricity film composed of a water dispersion-type polyurethane resin, particles of a silicon compound and a lubricant formed on the chromate film, JP-A-7/228828 discloses a resin-coated aluminum alloy material excellent in lubricity and excellent in corrosion resistance which makes press forming of strong processing possible, produced by forming resin film using a composition wherein particles of a polyethylene wax are dispersed in a resin. Further, JP-A-7/195031 discloses, as a surface-treated aluminum sheet material capable of having excellent formability and durability with injury, a surface-treated aluminum sheet material having a friction coefficient controlled to be 0.15 or less, which comprises an aluminum alloy sheet material having a coating containing 5 to 40% SiO
2
having a particle size of 0.1 &mgr;m or less and 5 to 60% a lubricant applied thereon with a thickness of 0.5 to 10 &mgr;m.
All these metal sheets of prior art are materials having good formability, corrosion resistance, etc. given by forming resin film containing a lubricant such as wax particles, and as to painting adhesion after formation, it is mentioned that painting adhesion can be ensured by anchor effect by pinholes in JP-A-7/228828, by specifying especially the combination of the particle size of the silicon compound in the lubrication treating agent, the kind and compounding amount of the lubricant and the particle size of the resin wax in JP-A-8/127735, and by limiting the amount of film formed on the surface in JP-A-7/195031.
In recent years, from compliance with controls on solvent effluence and advantages of work, cases where as paints for top coating or inks, UV-curable ones are used have been increasing. However, in UV-curable top coating, the volumetric shrinkage rate between before and after curing is large due to radical polymerization, and as a result, the cured film has remaining large internal stress. Therefore, the film of UV-curable top coatings is inferior to the film of usual solvent-type or aqueous top coatings in adhesion to the base material, and there arise many cases where base material design taking UV-curable top coatings into account is made necessary. The surface of sheets treated by the above-exemplified prior art is often poor in adhesion of UV-curable top coatings.
DESCRIPTION OF THE INVENTION
Object of the Invention
As stated above, film satisfying adhesion of UV-curable top coatings has not been obtained by usual surface treating methods wherein resin film is formed for giving formability, corrosion resistance, durability with injury, etc. onto the surface of metal sheets. This invention aims to solve this problem, and provides such an aqueous coating composition appliable to the surface of metal sheets such as aluminum or aluminum alloy sheets that the coating film shows good adhesion of UV-curable top coatings, in addition to the above various characteristics, and surface-treated metal sheets and a surface treating method for metal sheets using the same.
SUMMARY OF THE INVENTION
The invention for solving the above problem relates to an aqueous coating composition for metal sheets which comprises, as indispensable components, the following (C) alone or two or more of the following (A), (B) and (C), and water, and does not contain a photopolymerization initiator:
(A) a polyurethane resin having an elongatedness of dry film of 100% or more (excluding the following (C))
(B) a synthetic resin having at least one ethylenic double bond (excluding the following (C))
(C) a polyurethane resin having an elongatedness of dry film of 100% or more and having at least one ethylenic double bond.
The invention also relates to a metal sheet having thereon film formed by applying and drying the aqueous coating composition.
The invention also relates, as a method for effectively using the above aqueous coating composition for metal sheets, to a surface treating method for a metal sheet which comprises coating the surface of a metal sheet with the aqueous coating composition for metal sheets, drying the applied composition and forming a film of a UV-curable paint, a UV-curable ink or a UV-curable adhesive on the whole or part of the resultant surface.
The invention also relates to a metal sheet having thereon composite film formed by the surface treating method.
When the composition and the surface treating method are used, good adhesion of UV-curable top coatings is obtained in addition to good formability, good corrosion resistance and good durability with injury.
When, in the composition and method, the composition contains (D) a water dispersible wax in the range of 0.1 to 20% by weight of the total solid components, good formability in strong forming is obtained in addition to the above various characteristics, and when the composition contains (E) a water insoluble fine particles having a Mohs hardness of 2.5 or more in a rate of 30% by weight or less of the total solid components, better durability with injury is obtained in addition to the above various characteristics.
DESCRIPTION OF PREFERRED EMBODIMENT
The invention is detailedly described below. In the invention, (A) the polyurethane resin having an elongatedness of dry film of 100% or more is assumed to mean such a polyurethane resin that when an aqueous dispersion thereof is applied onto a support sheet, dried at room temperature for 24 hours and further dried at 120° C. for 10 minutes, and the resultant dry film (150 &mgr;m thick×10 mm wide) is stretched at 300 mm/min, elongatedness at breaking is 100% or more. When the elongatedness is less than 100%, the film is poor in following characteristic to deformation in the case where the metal sheet after the coating and drying is processed, and cracks are liable to be generated at the processed part, and thereby corrosion resistance lowers. The upper limit of the elongatedness is not particularly limited, but when it goes beyond 800%, film hardness generally gets too low and the practical range gets narrow in durability with injury, and the elongatedness is preferably 800% or less.
As the above polyurethane resin, general polyurethane resins can be used so long as the elongatedness is satisfied. Namely, the above polyurethane resin of the invention can be a polyurethane resin obtained by polyaddition reaction between a polyisocyanate having two or more (usually two) isocyanato groups and a polyol having two or more (usually two) hydroxyl groups.
As the polyisocyanate, aromatic, alicyclic and aliphatic polyisocyanates are mentioned, and, specifically, aromatic polyisocyanates include tolylene diisocyanate (TDI)(2,4- or 2,6-TDI), diphenylmethane diisocyanate (MDI)(4,4′- or 2,4′-MDI), polymeric MDI, xylylene diisocyanate (XDI), naphthylene diisocyanate (NDI)(usually 1,5-NDI), paraphenylene diisocyanate (PPDI), tetramethylxylylene diisocyanate (TMXDI), tolidine diisocyanate (TODI), 3,3′-dimethoxy-4,4′-biphenylene diisocyanate, etc., alicyclic polyisocyanates include dicyclohexylmetha
Hamamura Kazunari
Morita Ryoji
Nihon Parkerizing Co. Ltd.
Niland Patrick D.
Nixon & Vanderhye
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