1 Scope
This standard is applicable to the determination and evaluation of the coating performance of prepainted steel sheet (hereinafter referred to as "prepainted steel sheet").
2 Normative References
The following normative documents contain provisions which, through reference in this text, constitute provisions of this standard. For dated references, subsequent amendments to (excluding corrections to), or revisions of, any of these publications do not apply. However, all parties coming to an agreement according to this standard are encouraged to study whether the latest editions of these documents are applicable. For undated references, the latest edition of the normative document referred to applies.
GB/T 1766-1995 Paint and Varnish - Rating Schemes of Degradation of Coats
GB/T 12754 Prepainted Steel Sheet
3 Terms and Definitions
For the purposes of this standard, the terms and definitions given in GB/T 12754 and the following apply.
3.1
Relative luminous reflectance factor
The ratio of the luminous flux reflected by the specimen to the luminous flux reflected by standard plane under the identical geometric conditions.
3.2
Specular gloss
The relative luminous reflectance factor of specimen in the specular reflection direction.
3.3
Tristimulus values
The amounts of three kinds of reference stimulus necessary to reach color matching with the to-be-tested light in trichromatic system.
3.4
Color space
Chroma space
A kind of most uniform color space which is searched continuously in order to reduce the copy error caused by spatial nonuniformity, it has corresponding color difference visually at different positions, in different directions but at an equal geometrical distance, and the spatial distance that is easy to measure is taken as the magnitude of color sense difference.
3.5
T-bend
T-bend is the minimum n value when the coating does not crack or shed in 180° reverse bend test by taking n (n=0, 1, 2…) times of the thickness of tested specimen as the curvature radius.
3.6
Pencil hardness
The coating's scratch resistance judged by using a group of pencils (with specified lead dimension, shape and hardness) to scratch on the coating surface.
3.7
Cupping height
The height of the cup body which is deformed by punching at the end point of test.
3.8
Blank plate
The flat plate of identical size as the specimen, being used for covering the empty space of specimen holder to prevent light leakage under the condition that the specimen holder is not fully hung with specimens.
4 Determination of Coating Thickness
