When packaging and printing companies undertake a batch of transparent film-packed jobs, they need to use white ink for the bottom, but the problem of insufficient white ink coverage is believed to plague many companies. On this issue, we should first understand the main factors that affect the hiding power of ink, such as: ink color density. The thickness of the ink layer, the degree of pigment dispersion, etc., then the corresponding test analysis.
1. Ink concentration
Increasing the ink color density is one of the main methods to increase the hiding power of ink. When printing, the ink of titanium dioxide with a color density of 55% is used in the ink factory (normal white ink concentration is 25%, titanium dioxide pigment is currently the most white The white pigment with the best hiding power. After the printing, although its hiding power is better than ordinary white ink, it still does not meet the requirements. Due to high color concentration, low solvent, and quick drying, it is easy to cause blockage, and the leveling property of the ink after printing is not. Well, there is chalking, so other methods should be considered.
2. Ink thickness
We know that the thickness of the gravure ink layer can reach 8-15μm, but if the gravure ink layer is only 3-4μm, it will cause problems. Can be investigated from the following aspects.
(1) Roller production. The engraving depth of the supplier's plate cylinder has reached the maximum (60
Îœm), but because of its technical limitations, the engraved cells have a pyramidal shape, and the pyramidal cells are easy to block, causing poor transmission of ink. Therefore, although the ink storage capacity increases, it does not increase the amount of ink transferred. At this stage, For better transmission of ink, the network points should be pyramid-shaped or honeycomb-shaped. These two types of meshes have a large amount of ink storage and are easy to transmit ink. In addition, the smoothness of the edge of the cell and the thickness of the chrome plating also affect the transfer of ink, so the printing method can be considered twice to solve the problems caused by the plate cylinder.
(2) The hardness of the embossing roller is too high, and the printing material is soft. As a result, the amount of ink transferred in the cell is too small, and a softer embossing roller should be replaced.
(3) The printing pressure is relatively small, resulting in the ink in the cells being squeezed by the small force and poor transfer. At this time, the imprinting force should be increased.
(4) The film is stored for a long time after surface treatment, resulting in poor wetting and adhesion of the ink. Therefore, it should be printed immediately after surface treatment of the printing material.
(5) Ink pigment concentration is too high, resulting in too fast drying rate, affect the ink situation, should be appropriate to adjust the pigment concentration and viscosity.
(6) When the static electricity of the film is too large during printing, electrostatic discharge should be considered, and then the ink transfer rate can be increased by the electrostatic ink absorber.
(7) Consider the performance of the press.
After the above measures were taken, the thickness of the ink layer of the ink was significantly increased, but the hiding power of the white ink still did not meet the expected requirements. Therefore, the problem of the gravure ink itself must be considered again.
3. Pigment dispersion
The hiding power of the ink essentially depends on the ratio of the refractive index of the pigment to the refractive index of the binder. When this ratio is 1, the pigment is transparent; if the ratio is greater than 1, the pigment is opaque, that is, it has hiding power. The refractive index of a pigment is in turn affected by the degree of pigment dispersion and the difference in refractive index between the pigment and the binder. The higher the degree of dispersion of the pigment, the smaller the above difference, the better the transparency of the pigment.
The test white ink pigment is titanium dioxide. Titanium dioxide is a white crystalline powder that is the most opaque of all white pigments, with a refractive index of 1.84-2.55, a large dispersion, and lightfastness. Heat resistance and alkali resistance are all better.
Other printing methods use ordinary pigments. A thinner ink layer and a lower color density can achieve the desired hiding effect. Gravure cannot. Gravure ink pigment particle size should be less than 5
Îœm, and the gravure ink is thinner than other printing inks, so the dispersion is large and the transparency is high (ie, the hiding power is low). Therefore, if the titanium dioxide particles used are fine and have a large dispersion, the resulting hiding power will not be strong. If the desired hiding effect cannot be achieved by increasing the particle size, other printing methods can only be used.
If the ink is prepared using a titanium dioxide powder with an appropriately increased particle size, the hiding power of the white ink is increased. This method is more time- and labor-saving than increasing the ink color density and the ink layer thickness, and is also willing to reduce the production cost.
