Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2000-07-28
2003-01-21
Boykin, Terressa M. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamidoester
Reexamination Certificate
active
06509099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phosphate-treated steel plate with a substrate of zinc-base plated steel plate, which is used for body plates of automobiles and for household electric appliances, and the like.
2. Description of the Related Arts
Main stream of surface-treated steel plates for body plates of automobiles in prior art was electrolytic Zn—Ni alloy plated steel plates, organic composite coating steel plates (electrolytic Zn—Ni alloy plating+chromate coating+organic coating), and alloyed hot dip galvanized steel plates. In recent years, automobile manufacturers have tried to use inexpensive 100% zinc plated steel plates as the body plates of automobiles in view of cost reduction. The 100% zinc plated steel plates have, however, a plating layer in soft and with low melting point, so that the 100% zinc plated steel plates tend to induce fusion between plating layer and tool during press-forming, which raises a problem of easy occurrence of press-crack at portions of complex shapes. Accordingly, development of materials having superior lubrication performance was waited. In this regard, there have been introduced responding technologies given below.
(1) JP-A-7-138764, (the term “JP-A-” referred to herein signifies “Unexamined Japanese Patent Publication”), (hereinafter referred to as the “Prior Art 1”), discloses a zinc phosphate-treated steel plate which comprises: a zinc-containing metal plated steel plate; a zinc phosphate coating layer having a specified weight ratio of zinc to phosphorus and having a specified weight ratio of a specified metal, formed on the zinc-containing metal plated plate; and a lubricant oil layer on the zinc phosphate coating layer.
(2) JP-A-9-049086, (hereinafter referred to as the “Prior Art 2”), discloses a method for manufacturing an electroplated steel plate having high whiteness degree and excellent coatability, which method comprises the step of treating an electrolytically galvanized steel plate using a treatment solution containing specified amount of phosphoric acid ion, zinc ion, magnesium ion, nickel ion, and other ions, under a specified condition.
The zinc phosphate-treated steel plates which are disclosed in above-given Prior Arts 1 and 2 show an improvement in lubrication to some degree. The improvement effect is, however, not a satisfactory level. Furthermore, the zinc phosphate coating on these steel plates has a porous structure, so that the steel plates show poor corrosion resistance at portions where the electrodeposition coating cannot fully cover and where substrate steel plate is likely left exposed even after the electrodeposition coating, which portions include flange section and hem section observed at joints of body plates of automobiles. In addition, the electroplated steel plates which are manufactured by the technology disclosed in the Prior Art 2 give not satisfactory level of coating adhesiveness and of post-coating corrosion resistance in the case of two or more coating layers which are applied to the steel plates for body plates of automobiles.
As for the technology to improve the corrosion resistance of zinc phosphate-treated steel plates, prior art in the household electric appliances applied the zinc phosphate treatment followed by sealing treatment using a chromate-base aqueous solution. The conventional sealing technology for the zinc phosphate-treated steel plates uses hexavalent chromium which is a substance under environmental regulations. Therefore, technology which does not use chromium was wanted. Responding to the need, the following-listed technologies have been proposed.
(3) JP-A-56-136979, (hereinafter referred to as the “Prior Art 3”), discloses a treatment method applying phosphate treatment to a cold-rolled steel plate or a galvanized steel plate, then immediately applying a post-treatment using a treatment solution consisting mainly of a chelating agent.
(4) JP-A-58-197284, (hereinafter referred to as the “Prior Art 4”), discloses a method of treament before coating for zinc-base plated steel plates, which method comprises the steps of: applying phosphate treatment to the zinc plated steel plates, then applying treatment using an aqueous solution containing a polyacrylic acid and a aromatic polyhydric alcohol.
(5) JP-B-63-4916, (the term “JP-B-” referred to herein signifies “Examined Japanese Patent Publication”), (hereinafter referred to as the “Prior Art 5”), discloses a composite plated steel plate having excellent durability, which steel plate comprises a steel plate, a Zn—Ni alloy plating, a phosphoric acid coating at coating weights of from 1 to 2 g/m
2
on the Zn—Ni alloy plating, and a polymer coating having thicknesses of from 5 to 10 &mgr;m on the phosphoric acid coating.
The above-described conventional zinc phosphate-treated steel plates have, however, problems given below. That is, the zinc phosphate-treated steel plates in the Prior Arts 3 and 4 use ordinary zinc phosphate coating, so that these steel plates have no coating adhesiveness that is required as the steel plates for automobiles. In addition, the organic sealing which is disclosed in these prior arts is dissolved or degraded owing to the contact with alkaline or acidic solution met in the process of automobile body assembly: [shearing→pressing→welding alkali degreasing→chemical conversion electrodeposition coating→intermediate coating and top coating]. As a result, the corrosion resistance of these steel plates is poor.
The zinc phosphate-treated steel plate of the Prior Art 5 uses ordinary zinc phosphate coating, similar with that of the Prior Arts 3 and 4, so that the steel plate has no coating adhesiveness that is required as the steel plates for automobiles. In addition, since the organic coating is very thin, 5 to 10 &mgr;m, the spot welding is very difficult, and the coating is easily peeled during the press-forming stage owing to the bending and unbending at bead portions, (resulting in poor anti-powdering performance), further the peeled coating degrades the lubricant performance, which results in poor press-formability.
Consequently, prior arts fail to satisfy all of the required performance of: corrosion resistance, anti-powdering performance, lubrication, coating adhesiveness, and weldability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an environmentally friendly surface-treated steel plate which has excellent corrosion resistance, anti-powdering performance, lubrication, coating adhesiveness, and weldability, and which contains no chromium.
To achieve the above-given object, the present invention provides a phosphate-treated steel plate which comprises: a zinc-base plated steel plate; a zinc phosphate coating layer formed on the surface of the zinc-base plated steel plate; and an organic coating formed on the zinc phosphate coating layer.
The zinc phosphate coating layer contains at least one substance selected from the group consisting of nickel, manganese, and magnesium, at coating weights of from 0.2 to 2.5 g/m
2
.
The organic coating consists of at least one organic resin selected from the group consisting of an ethylene-base resin, an epoxy-base resin, a urethane-base resin, and an acrylic-base resin.
The epoxy-base resin is preferably a block urethane-modified resin prepared by mixing a modified epoxy resin (A) comprising an epoxy resin, a multifunctional amine, and a monoisocyanate, and a block urethane (B) comprising a polyol, a polyisocyanate, and a block agent, at mixing rates (A/B) of from 95/5 to 50/50 (weight ratio of nonvolatile matter).
The epoxy-base resin is preferably an epoxy-base resin prepared by mixing 5 to 80 parts by weight (solid content) of a polyisocyanate compound having at least two isocyanate groups in a single molecule thereof, and 100 parts by weight (solid content) of a substrate resin in which at least one basic nitrogen atom and at least two primary hydroxide groups are added to a terminal of the molecular chain of the epoxy resin.
The present
Ando Satoru
Kubota Takahiro
Miyoshi Tatsuya
Sagiyama Masaru
Urata Kazuya
Boykin Terressa M.
Frishauf Holtz Goodman & Chick P.C.
NKK Corporation
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