Patent ID: 6015628
Filing Date: 2000-01-18
Classification: B05D,Y10T

Abstract:
An organic composite coated steel sheet with press formability and perforation corrosion resistance, which comprises a zinc or zinc alloy plated steel sheet having on at least one of its surfaces a first chromate layer having a coating weight of from 5 to 200 mg/m.sup.2 in terms of metallic chromium, and a second layer of an organic film having a thickness of from 0.1 to 3.0 .mu.m, in that order, and in which said organic film comprises an epoxy resin mixture (i), a lubricant (ii) and a rust preventive additive, in such a ratio by weight, in terms of the non-volatile contents, that the epoxy resin mixture is from 30 to 80% by weight, the lubricant is from 8 to 50% by weight and the rust preventive additive is from 3 to 50% by weight; wherein(i) is an epoxy resin mixture composed of a base resin (A) as prepared by adding at least one basic nitrogen atom and at least two primary hydroxyl groups to the ends of an epoxy resin, and a curing agent for (A) of a polyisocyanate compound (B), as mixed in a ratio by weight, A/B, of being from 95/5 to 55/45 (in terms of the non-volatile contents); and(ii) is a composite lubricant composed of a polyethylene wax (C) having a molecular weight of from 700 to 4500 and a softening point of from 100 to 140.degree. C. as prepared through coordination-anionic polymerization using a Ziegler catalyst, and a powder of a fluorine resin (D), as mixed in a ratio by weight, C/D, of being from 10/90 to 90/10, wherein said fluorine resin (D) to be in the organic film is a powder of a tetrafluoroethylene resin having a mean particle size of from 0.1 to 5 .mu.m that satisfies the following conditions (a) and (b):(a) When tested in a method for testing its flow properties with a capillary rheometer under the conditions mentioned below, in accordance with JIS K7199, the apparent melt viscosity and the apparent rate of shear of the resin powder satisfy the following equation (1):log .eta..ltoreq.A-B log .gamma. (1)in which:A is 5.45;B is 0.64;.eta. is the apparent melt viscosity (poise) of the resin, provided that .eta.>0; and.gamma. is the apparent rate of shear of the resin (sec.sup.-1), provided that 5.ltoreq..gamma..ltoreq.1300,Test Conditions:Temperature: 330.degree. C.Diameter of Barrel: 9.55 mmDimension of Capillary:Diameter, d=1 mmLength, 1=10 mmInlet of Capillary: flat(b) The resin has a specific surface area of 11 m.sup.2 /g or smaller.