Some technical problems often occur in the use of coatings on color coated sheets. This paper briefly introduces several common problems.
1: Visual Error of Flash Paint
There are two types of coatings for color coated panels: plain paint and flash paint (flash paint is also divided into metal paint and pearlescent paint). Unlike plain paint, which produces color through selective absorption and diffuse reflection of light by pigment particles, metals and pearlescent pigments are arranged in layers in the same orientation parallel to the paint film. When light shines on the surface of the paint film, part of the light is hardly absorbed due to the direct reflection of aluminium powder. Some of the light is particularly bright, which gives a very bright feeling and part of the light. The wire is reflected by aluminum powder for many times, and the light is darker. Therefore, different visual effects can be observed from different angles.
The sketch of flash paint light reflection shows that the light produced by the same incident light source darkens with the increase of reflection times. The effect seen in the observation angle A and B varies with the brightness of light, so the visual effect of flash paint varies with the incident angle of light (corresponding to the change of morning and evening in nature) and the observer's observation position. Therefore, the chromatic aberration of flash paint is more difficult to control, and users sometimes reflect the phenomenon of visual chromatic aberration in use.
On the one hand, in the management of flash paint coatings, steel mills should select the same paint supplier and batch of coatings at the same time as far as possible in the same user contract in the production control, so as to avoid the color difference caused by the difference of different coatings and processes, and at the same time, use multi-angle color difference meter which is closer to the effect of human eye measurement to compare the color difference. On the other hand, the user is guided to avoid the problem of chromatic aberration caused by different material installation directions.
2: Coating Bonding Problem
When color coated panels are used as sandwich panels, one of the common problems is poor bonding or foaming. Because when the coating is used to make sandwich panels, the coating must be effectively combined with foaming agent to ensure the integrity of the sandwich panels. Generally speaking, the main problems that users encounter in their use include "not sticking" and "surface hole".
2.1 "Can't Stick"
Pictures of poor adhesion of coating on the back of color coated panel. The main reasons for these problems are as follows:
(1) Glue reaction time: The length of glue reaction time during processing affects the foaming effect. The foaming effect will not be ideal if the time is too long or too short. As shown in Figure 2-(a), it is an inappropriate template for foaming time.
(2) Coating quality: The types of coatings determine the surface activity of the coatings after curing, which will affect the foaming effect of color coated sheets and foaming agents. If the active group of the coating is less, the foaming property will be affected. It is a poor foaming template for coatings with less active groups.
(3) Glue quality: Foaming glue is generally composed of black glue and white glue. White glue is polyether polyol with hydroxyl group, and black glue is cyanate ester. After mixing in a certain proportion, the two glues react to form polyurethane, that is, foaming material. The effective ingredients in the glue seriously affect the foaming effect of the product. Poor foaming may occur if other substances are added to white gum to reduce cost or polyether polyols are replaced by lower-priced polyester polyols.
(4) Other factors: foaming process and production environment are also important factors affecting the quality of sandwich panel products.