Why is there a color difference in plastic flexible packaging? (on)

Why is there a color difference in plastic flexible packaging? (on)

How to make the ink color of a batch of printed products or batches of printing consistent in printing is a basic requirement and an important problem. For the manufacturer, the color of the packaging used in the product has become an important means and symbol for identifying the product (even the logo of the company).

If the appearance of the product packaging looks different, the consumer may think that the quality of the product is unstable, and even suspect the authenticity of the product. Therefore, these well-known enterprises pay great attention to the color of product packaging, and require that their ink color must be consistent.

How to make the ink color of a batch of printed products or batches of printing consistent in printing is a basic requirement and an important problem. For the manufacturer, the color of the packaging used in the product has become an important means and symbol for identifying the product (even the logo of the company). If the appearance of the product packaging looks different, the consumer may think that the quality of the product is unstable, and even suspect the authenticity of the product. Therefore, these well-known enterprises pay great attention to the color of product packaging, and require that their ink color must be consistent.

The consistency of color can only be said to be relative. Strict control of the same batch of color difference is more difficult, and strict control of color difference between large batches or batches is more difficult. Plastic flexible packaging gravure printing is mostly multi-batch printing and high-volume printing, controlling color difference, is a very important issue for plastic flexible packaging printing enterprises.

First, the ink

Ink is one of the main factors determining the color consistency of a print. The ink itself also has the same batch color difference and chromatic aberration between different batches, which is an important indicator reflecting the quality of the ink.

To solve the problem of chromatic aberration of plastic gravure, it is first necessary to select an ink with stable quality and no deviation in hue. It is best to use the same batch of ink (the best one-time modulation when preparing the spot color ink) for a batch of prints, because it is difficult to ensure that the hue is different for different batches of ink. If the ink hue deviation is too large, it is difficult to control the consistency of the printing ink by other methods, especially when printing the layered version.

Second, the amount of ink added to the ink tank each time during the printing process is required to keep the new ink added frequently. Especially for a pattern with a small amount of ink, if the amount of ink applied is too much at one time, the ink will be oxidized and become old after being exposed to the air for a long time, for example, the long black ink is gray, and the new ink is not black; The long red ink will turn dark red, not as bright as new ink. In the printing process, the volatilization speed of the mixed solvent used in the ink is strictly controlled. When the volatilization speed is too fast, the transfer rate of the ink may be lowered, thereby affecting the color of the printed product.

In addition, when using the two-component ink, it should be fully stirred and less matched. Otherwise it is difficult to maintain the stability of the ink viscosity, and may also cause other printing failures.

Second, the scraper

The contact position, angle and pressure of the scraper and the plate cylinder have a great influence on the ink color of the print, especially the light of the shallow layer, so the ideal state is that the scraper is in the same position from beginning to end. However, for various reasons, the position, angle and pressure of the blade have to be adjusted during the printing process, so we must understand the influence of the change on the color of the printed product and take corresponding measures.

The contact position of the scraper with the plate cylinder determines the distance between the contact point of the knife and the plate and the imprinting point. The length of the distance should be adjusted according to the printing speed, ink viscosity, cell depth, and plate quality. In general, the longer the distance, the greater the degree of drying of the ink in the cells and the lower the transfer rate of the ink. In terms of its effect on the printing effect, it is equivalent to the partial withdrawal of the ink color. At the same time, this distance is also a test of ink adaptability. Conversely, when the distance is short, the transfer rate of the ink is relatively high, and at the same time, some fine lines on the plate are transferred to the printing material.

The blade angle is the angle between the tangent of the contact point of the doctor blade and the plate cylinder and the blade. Increasing the blade angle makes it easy to scrape the ink on the plate to make the image clear, but it may also cause the ink layer to be too thin, the ink film to have poor gloss, and the like, and it is easy to damage the plate cylinder. Conversely, the blade angle is reduced, the ink layer is thickened, and the print gloss is good, but the corners of the image are easily blurred.

The blade pressure also has a certain influence on the ink color. When the pressure becomes large, the ink color becomes shallow; when the pressure becomes shallow, the ink color of the printed product tends to become darker.