When packaging and printing companies undertake a batch of jobs with transparent film packaging, they need to use white ink as the primer, but the problem of insufficient white ink hiding power has plagued many companies. On this issue, we should understand the main factors that affect the hiding power of ink, such as: ink color density, ink layer thickness, pigment dispersion, etc., and then conduct the corresponding test analysis.
1. Improve ink color density
Increasing the color density of the ink is a major method of increasing the hiding power of the ink. During printing, a specially configured titanium white ink with a color density of 55% is used (common white ink has a color density of 25%, and the titanium white pigment is currently the most white and covering The most powerful white pigment), although its hiding power is better than ordinary white ink after printing, it still does not meet the requirements. Due to the high color density, less solvent, and fast drying, it is easy to cause blockage, and the ink has poor leveling after printing. Pulverization occurs, so other methods should be considered.
2. Make sure the thickness of the ink layer meets the standard
We know that the thickness of the gravure ink layer can reach 8-15μm, but if the gravure white ink layer is only 3-4μm, the problem will occur. You can check from the following aspects.
(1) Production of plate roller. The engraving depth of the supplier's plate cylinder has reached the maximum (60μm), but due to its technical limitations, the engraved cells are pyramid-shaped, and the pyramid-shaped cells are easy to block the plate and cause poor ink transfer, so although the amount of ink storage is increased However, it cannot increase the amount of ink transfer. At this stage, in order to better transfer ink, the cells should be prismatic or honeycomb. The two types of cells have large ink storage capacity and are easy to transfer ink. In addition, the smoothness of the edge of the mesh and the thickness of the chrome plating also affect the transfer of ink, so you can consider the method of printing twice to solve the problems caused by the plate cylinder.
(2) The hardness of the embossed rubber roller is too large, and the printing material is relatively soft, which results in too little ink transfer in the cell. The embossed rubber roller with a softer hardness should be replaced.
(3) The printing pressure is small, which causes the ink in the mesh to be squeezed with low pressure and poor transfer. At this time, the embossing force should be increased.
(4) The film is stored for a long time after surface treatment, which results in poor ink wetting and adhesion, so it should be printed in time after the surface treatment of the printing material.
(5) The concentration of ink pigment is too large, which causes the drying speed to be too fast and affects the inking situation. The concentration and viscosity of the pigment should be adjusted appropriately.
(6) The static electricity of the film is too large during printing. After the static electricity is eliminated, the electrostatic transfer device should be used to increase the ink transfer rate.
(7) Consider the performance of the printing press.
After taking the above measures for printing, the thickness of the ink layer has increased significantly, but the hiding power of the white ink still does not meet the expected requirements, so the problem of gravure ink itself must be considered again.
3. Control the dispersion of pigments
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 the 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 the pigment is affected by the dispersion of the pigment and the difference between the refractive index of the pigment and the binder. The higher the dispersion of the pigment and the smaller the above difference, the better the transparency of the pigment.
The pigment of the white ink for the test is titanium dioxide. Titanium dioxide is a white crystalline powder, the most opaque of all white pigments, with a refractive index of 1.84-2.55, a large degree of dispersion, good light resistance, heat resistance and alkali resistance.
Other printing methods use ordinary pigments, and the thinner ink layer and lower color density can achieve the required hiding effect, while gravure printing cannot. The particle size of the gravure ink pigment should be less than 5 μm, and the gravure ink is thinner than other printing methods, so the dispersion is large and the transparency is high (that is, the hiding power is low). If the titanium dioxide particles used are finer and more dispersed, it will result in less hiding power. If the desired hiding effect cannot be achieved by increasing the granularity, other printing methods can only be used.
If the printing ink is prepared with titanium dioxide powder with an appropriately increased particle size, the hiding power of the white ink is increased. This method is more time-saving and labor-saving than increasing the ink color density and ink layer thickness, and can also reduce production costs.
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