Method of forming porcelain enamels on aluminized steel
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorsAtsushi Nishino, Kazunori Sonetaka, Kunio Kimura, Yoshihiro Watanabe
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Abstract
In a method of forming porcelain enamel layer on a metal substrate, the method comprises steps of applying a first coating for an underlying ground layer and a second coating for overlying self-cleaning layer or coloring layer, and the method is characterized by firing both of said first coating and said second coating at the same time, forming a double layered porcelain enamel layer having an inter-layer wherein both layers are mixed, thus giving a sufficient bonding force inbetween as well as strong corrosion resistivity of the substrate due to few pinholes and bubbles in the underlying ground coating.
Claims22
A method of forming porcelain enamels on a dip aluminized steel sheet comprising the sequential steps of:
- (a) applying a first coating of a first slip adapted to form a first layer, said first slip containing a frit and a binder selected from the group consisting of an alkali silicate, colloidal silica, colloidal alumina, silicone resins, organic binders, and mixtures thereof;
- (b) drying said first coating at a temperature below the softening point of said frit in said first slip at a temperature less than 350.degree. C.;
- (c) applying a second coating of a second slip adapted to form a second layer;
- and
- (d) firing said first and second coatings in a single firing step after the application of all the slip coatings.
A single step firing method of forming a porcelain enamel coating on a dip-aluminized steel sheet substrate comprising, in combination, the successive steps of:
- (a) applying an aqueous coating composition of a first slip to form a first layer onto said steel substrate, said aqueous coating composition containing a frit having a softening point greater than 350.degree. C.;
- (b) drying the thus applied first coating at a temperature less than 350.degree. C. to remove a substantial portion of the water from said aqueous coating composition and retain said first coating on said steel substrate;
- (c) applying a catalyst-containing aqueous coating composition of a second slip containing both a catalyst and a frit which when heated forms a second layer on the dried first layer;
- and thereafter
- (d) heating said first and second coatings on said steel substrate in a single firing step to a temperature in the range of about 520.degree. C. to about 820.degree. C. for a period of time sufficient to soften said first layer thereby forming a pore-free corrosion-resistant layer and a mixture of said first and second layers at their point of contact, the two layers thus formed being strongly bonded together.
A method of forming a self-cleaning, multilayered, corrosion-resistant porcelain enamel on an aluminized steel sheet using a single firing step, said method consisting essentially of the following successive steps:
- (a) applying an aqueous slurry of a first slip adapted to form a ground coat enamel layer on said aluminized steel sheet, said first slip containing a frit and a binder selected from the group consisting of an alkali silicate, colloidal silica, colloidal alumina, a silicone resin, an organic binder, or mixtures thereof, said binder capable of bonding the aluminum surface of said aluminized steel sheet;
- (b) drying the thus-applied first coating at a temperature below the softening point of said frit in said first slip at a temperature below 350.degree. C. thereby setting said first slip and adhering same to said aluminized steel sheet;
- (c) applying as a second coating a second aqueous slurry of a second slip adapted to form a smooth, self-cleaning layer on said ground coat, said second slip coating containing at least one frit and an oxidizing catalyst,
- provided that the frit contained in said second slip has a softening point higher than the softening point of the frit contained in said first slip;
- (d) drying the thus-applied second slip;
- and
- (e) firing the first and second dried coatings in a single firing step thereby providing an irregular interface and a strong bonding force between the two coatings and a smooth, self-cleaning, corrosion-resistant porcelain enamel layer substantially free from pinholes and bubbles on said steel sheet.
Dependencies are inferred from the claim text.