Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1998-10-22
2000-10-24
Thibodeau, Paul
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
4284258, 428458, 428422, 428484, 427379, 427409, 525440, 525437, 528 45, 528176, 528272, 528298, 528307, B32B 1500
Patent
active
06136455&
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thermosetting coating composition for precoated steel sheets which are required to have high hardness, good workability and stain resistance, to a precoated steel sheet having a film of the coating composition, and to a method for producing such precoated steel sheets. The precoated steel sheet of the invention is suitable for use in household electric appliances and as construction materials, and also can be used in producing vehicles.
BACKGROUND ART
Coating compositions for precoated steel sheets are required to have various properties, such as high hardness, good workability, stain resistance, chemical resistance, water-proofness and distinction of image. Of these, the hardness and the workability are important characteristics, which, however, are contradictory to each other but the levels of which are required to be high. The workability as referred to herein indicates that, when flat, precoated steel sheets are worked into various shaped structures through bending, cutting or drawing, the paint films are damaged slightly. Therefore, it shall be said that the larger the degrees of elongation and flexibility of paint films themselves, the better the workability of the paint films. In particular, the bending workability (flexibility) of paint films varies, depending on the thickness of the steel sheets coated with the films.
In the T-shape bending test (according to 12.2.2 in JIS G3312) which is generally used in evaluating the flexibility of precoated steel sheets, a precoated steel sheet to be tested is bent, with putting a plural number, n, of specimen plates all having the same thickness inside the sheet being bent, and the bent part of the sheet is observed under a magnifier as to whether or not the paint film on that part is cracked. In the test, the smallest number of the specimen plates as put inside the precoated steel sheet being tested with no paint film cracking is determined as 1T, 2T, and this indicates the tested steel sheet flexibility. In this T-shape bending work, the degree of elongation of the outermost periphery of the sheet being bent is represented by the following equation:
Accordingly, where precoated steel sheets as tested in the T-shape bending test give the same value, those having a thinner thickness shall have a larger elongation strain (%) at their outermost periphery and have a smaller curvature at their bent part, indicating that they have good workability.
To evaluate the workability of precoated steel sheets, the T-shape bending test noted above is generally employed. However, stamping and roll forming which are generally effected in industrial production of household electric appliances by manufacturers differ from the working in the T-shape bending test in the working history and the working speed, and the former require severer working conditions than the latter. The working history includes the working steps up to the final working level. For precoated steel sheets worked up to the same final working level, those as worked to have a large value R in the initial working stage shall receive a small degree of stress at their paint films as the strain resulting from the initial working may disperse throughout the part as bent to have the value R, while those as worked to have a small value R in the initial working stage shall receive a large degree of stress at their paint films as the strain resulting from the initial working may concentrate in the limited area of the part as bent to have the value R. Therefore, as compared with precoated steel sheets tested in the T-shape being test comprising U-shape bending followed by contact bending, those as tested by V-shape bending followed by contact bending shall receive a larger degree of stress at their paint films even though they are all worked up to the same final working level. Accordingly, the latter testing method is useful for simple evaluation of severe working.
On the other hand, it is desirable that the hardness of paint films is higher in ord
REFERENCES:
patent: 5817731 (1998-10-01), Yoshida et al.
Anyashiki Takashi
Ehara Mamoru
Kajita Yasuyuki
Kato Hiroyuki
Kotani Keiichi
NKK Corporation
Thibodeau Paul
Zacharia Ramsey
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