A Brief Talk on the Knowledge of Printing White Iron Coatings

First, the composition and performance of white paint used for printing

The white paint used for printing iron requires good whiteness and strong hiding power, and its color is not yellowed after baking at high temperature. The coating film has flexibility and strong adhesion, and it is suitable for stamping and processing of cans or other packages. The film has good gloss. White paint usually consists of four parts, namely titanium dioxide, resins, auxiliaries and diluents. The molecular formula of titanium dioxide is TiO2, which is extracted from ilmenite and is currently the most widely used white pigment in the world. At present, China is more used in Japan, the United States, France and other imported titanium dioxide. The pigment has the advantages of strong hiding power, no yellowing, and is the protagonist in the white pigment. Titanium dioxide has two types of anatase and rutile. The former has a whiter color, but is easily pulverized; the latter has a strong hiding power and is relatively stable. When used in combination, they can be used alone or mixed. The white-lacquer resin consists of a non-dried modified alkyd resin, an ethylene-modified epoxy resin, an acrylic resin, and a polyester resin. The auxiliary agent is divided into a touch-up agent (or additive) and a toner. The retouching agent plays a role in improving the surface properties of the paint after application of the paint and formation of the paint film.

Second, the hue characteristics of white paint

The hue of white paint can be described as ever-changing, but it can be broadly divided into three categories: blue phase, red phase, and white phase. The so-called blue phase is mainly white, revealing blue hue in white. The red phase is dominated by white, revealing a red hue in white. The white phase is the original white hue. In fact, the hue of white is far more than the above three. Some white paints have a blue-red composition, and the proportion of the white paint also affects the hue effect of white. The choice of white hue should be determined based on the basic color sample of the product pattern. Normally, the warm-colored pattern can use a bluish white paint, while the cool-colored pattern is intended to use a red-white paint. A large area of ​​the cool tone pattern would be quite satisfactory if combined with a large red phase white paint. Therefore, the hue choice of the white paint should be determined by the color effect of the trademark pattern.

Third, the need for attention in the construction of white paint

[I] Strengthen the inspection of paint hue before construction

At present, paint suppliers still have a large gap in the hue control of white paint, which is related to the factors of change in the raw and auxiliary materials of paint manufacturers. Such as different batches of titanium dioxide, different country differences. The hue changes of resins and additives all directly affect the hue change of white paint. Even some international well-known manufacturers of coating materials often experience large fluctuations in the control of hue. This is not only related to the accurate weighing of the components when they are compatible with pigments, but also directly related to changes in pigments, resins, auxiliaries, and diluents, so this fluctuation also exists. Therefore, it is very important for us to use the unit to strengthen the inspection work before feeding. In addition to conventional inspection items, such as hardness testing after film formation, adhesion fastness testing, impact strength testing, sulfur resistance, acid resistance, corrosion resistance, and retort resistance tests, a hue test of white paint is also added. The basis for the hue inspection is the paint supplier, and the use unit confirms the hue model. If there is a difference in hue, the paint supplier should be immediately required to negotiate, if necessary, adjust the hue or return the paint supplier.

(2) Strictly control the thickness of coating film during construction

After the physical and chemical indicators of white paint pass the inspection, construction can begin. The viscosity, speed, and drying temperature of the coating must be strictly controlled during construction, and the most important is the thickness of the coating. The viscosity of the coating often determines the quality of the coating. The viscosity is too high and the poor leveling property is caused during construction; the viscosity is too low and the coating film thickness required for the process cannot be achieved during construction. The speed is usually controlled at 70-90 sheets/min. Too fast, the film is not completely dry; too slow, too dry, and can easily cause yellowing in the white paint. The drying temperature must be strictly in accordance with the white coating construction process. The temperature is too low, and the cross-linking between the resin molecules in the white paint is insufficient, which affects the quality of the formed film. When the temperature is too high, the resin becomes brittle, and the intrinsic quality of the white paint film is affected. Kind of malady. In the construction of printing iron, the control of coating film thickness is the key. Normally, before the official opening of the seal, one sheet is painted. After drying, quality inspection personnel perform the inspection of the dry film thickness. After passing the inspection, the film can be boot-coated. If it is too thick or too thin, it must be re-adjusted and confirmed before production. If the coating is too thick or too thin, it will directly affect the hue of the coating and affect the quality of the entire product.