When the packaging and printing enterprises undertake a batch of transparent film packaging of live parts, they need to use white ink as the backing, but the problem of insufficient white ink coverage perplexes many enterprises. On this issue, we should understand the main factors that affect the covering power of ink, such as: ink color concentration, ink layer thickness, pigment dispersion, and then carry out the corresponding experimental analysis.
1. It is a main method to increase the covering power of ink by improving the color density of ink. In printing, titanium white ink with 55% ink color concentration (ordinary white ink concentration is 25% and titanium white pigment is the whitest and best covering pigment) is used in printing. Although its covering power is better than that of ordinary white ink, it still fails to meet the requirements High concentration, less solvent, fast drying, easy to cause blocking, poor leveling of ink after printing, powdering phenomenon, so other methods should be considered.
2. We know that the thickness of gravure ink layer can reach 8-15 μ m, but if gravure white ink layer only 3-4 μ M can not meet the standard, there will be problems. The investigation can be carried out from the following aspects.
(1) Plate cylinder production. The engraving depth of the supplier's plate cylinder has reached the maximum (60 μ m). However, due to its technical limitations, the engraving mesh hole is pyramid shaped, which is easy to block the plate, resulting in poor ink transfer. Therefore, although the ink storage capacity is increased, the ink transfer capacity cannot be increased. At present, for better ink transmission, the mesh points should be pyramid shaped or honeycomb shaped, which have large ink storage capacity and easy transmission Ink. In addition, the smoothness of the mesh edge and chromium plating thickness also affect the transfer of ink, so we can consider printing twice to solve the problem caused by the cylinder.
(2) The hardness of the imprint cot is too large, and the substrate material is soft, resulting in the transfer of ink in the mesh is too small, so the soft roller should be replaced.
(3) The printing pressure is small, which causes the ink in the screen hole to be squeezed and transferred poorly. At this time, the embossing force should be increased.
(4) Film after surface treatment storage time is too long, resulting in poor ink wetting and adhesion, so it should be printed in time after the surface treatment of substrate materials.
(5) Ink pigment concentration is too high, resulting in drying speed is too fast, affecting the ink situation, should be appropriate to adjust the pigment concentration and viscosity.
(6) When printing film static electricity is too large, we should consider to eliminate the static electricity, and then through the electrostatic ink absorption device to improve the ink transfer rate.
(7) Consider the performance of the printing press.
After taking the above measures, the ink layer thickness has increased significantly, but the white ink coverage still does not meet the expected requirements, so the gravure ink itself should be considered again.
3. Controlling the dispersion of pigment, the covering power of ink depends on the ratio of pigment refractive index and binder refractive index. When the ratio is 1, the pigment is transparent; if the ratio is greater than 1, the pigment is opaque, that is, it has covering power. The refractive index of pigment is affected by the dispersion of pigment and the difference of refractive index between pigment and binder. The higher the dispersion of pigment is, the smaller the difference is, the better the transparency of pigment is.
The pigment of white ink is titanium dioxide. Titanium dioxide is a white crystalline powder, which is the most opaque of all white pigments. Its refractive index is 1.84-2.55. It has large dispersion, good light resistance, heat resistance and alkali resistance.
Other printing methods use common pigments, thinner ink layer and lower color density can achieve the required covering effect, but gravure printing can not. Gravure ink pigment particle size should be less than 5 μ m, and gravure ink is thinner than other printing methods, so it has high dispersion and high transparency (i.e. low covering power). If the titanium dioxide particles used are fine and dispersive, the covering power is not strong. If the expected covering effect can not be achieved by increasing the particle size, other printing methods can only be used.
If the ink prepared by properly increasing the particle size of titanium dioxide is used, the covering power of white ink will be increased. This method is more time-saving and labor-saving than increasing the ink color concentration and ink layer thickness, and also can reduce the production cost.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, a world famous manufacturing city, is a subsidiary company of Beite packaging (China) Co., Ltd
With an area of 6000 square meters, it is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of advanced production equipment in China
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The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for food, daily chemicals, and other special-shaped bags
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