About the Color Difference Control of Ink (I)

First, the relationship between intaglio network points and colors

From the principle of intaglio printing, it can be known that the amount of gravure ink is mainly determined by the shape, size, depth and depth of the printing roller, which is determined by the volume of the mesh ink in the unit area, and the printing capacity of the printing plate is accompanied by the printing plate cylinder. The change in the change, so when the large print volume and the need to use multiple sets of plate cylinder to complete the task of the same product (such as smoke packaging), you need to strictly control the process parameters when making the same color plate cylinder, For example, the number of screen lines, screen angles, depths, passage grooves, and even the hardness of the engraved copper layer should be kept consistent so as to minimize the color difference caused by the replacement of the plate cylinder. Once this happens, it has to be adjusted in the ink. When the new version is used, a suitable amount of diluting ink is used to reduce the coloring power of the ink and make it similar to the original color.

With the increase of the number of prints in the same printing plate cylinder, the surface chrome layer gradually wears under the action of the ink squeegee to gradually change the cell site, and the amount of ink on the plate cylinder also becomes smaller, and the color of the print is also changed. It gradually fades, although this is an unavoidable process, but due to the gravure cylinder in the copper layer after the 0.08-0.10mm hard chromium plating layer, this layer of chromium has a good rub resistance, generally The normal service life (in the case of a full version dark version) is between 1.5 and 2 million revolutions. Therefore, the color difference of the gravure product in the small batch printing is not easy to detect, and only in the large-volume printing, the later product will have a perceptible color difference compared with the previous product. Some ink suppliers have a special supply of color-reducing agents, which can compensate for the coloring power of certain spot colors to delay the process of color differences caused by the shallowing of the cell's holes, which in essence extends the service life of the plate cylinder. Of course, Make fine adjustments during operation. For a worn plate cylinder, it is confirmed that if the cell wall is not damaged, it can be re-chromed and then chrome plated, and it can be reused. If the cell wall is damaged, the plate cylinder must be re-created. There is a difference between the depth of the newly made printing plate and the old version, and the printing ink should be adjusted according to the actual printing.

The influence of the ink concentration on the color difference is mainly caused by the change of the ink pigment content per unit volume. The main factor that causes this change in the printing process is that the gravure ink continuously circulates in the ink supply system, causing the solvent in the ink to continuously evaporate, causing the ink to become more and more concentrated, and then adding the solvent to adjust the ink to the initial setting. The process of setting the concentration is often short-lived, and sometimes an excess of solvent is added and the adjustment is repeated. This kind of frequent adjustment often reflects the color difference on the products. Therefore, when formulating the relevant operating regulations, the addition of solvent is more appropriate and less appropriate, and the conditional unit is better to use an automatic solvent adding device on the unit. The ink concentration in the ink tank is detected and adjusted at any time, which is very good for reducing the color difference in batch printing.

Second, the main factors affecting color difference

The first is the influence of ink, which is the main factor that determines the consistency of the print color. The hue of printing ink should be stable. The color difference between the same batch and different batch should be kept as small as possible; new ink should be added frequently during printing; for spot color ink ( In particular, some spot colors formulated with white ink should be stirred frequently to prevent the separation of these composite colors; the ink should preferably remain sticky during printing; the solvent added during printing should not be contaminated by other colors.

In addition, the ink used for printing should be the same as that used for proofing (same manufacturer, same series, same model) so as to ensure uniform color.

The second is the effect of the squeegee. This is because the material of the squeegee, the assembly size, the position of the contact plate, the angle and the pressure have a great influence on the color of the print, especially the light color of the shallow screen. The softer the squeegee (or when the assembly is long), the darker the print. The larger the distance between the contact point of the doctor blade and the printing plate and the printing point, the lighter the color of the printed product. The greater the pressure of the blade, the lighter the color of the print.

The third is the effect of the plate roller, because the plate roller will become light after use for a period of time, and the amount of ink will reduce the color deviation. Therefore, after a certain number of prints, consider replating rolls. In addition, the color will become lighter if blocking occurs.

The fourth is the influence of the light source. It is best to use a standard light source (D65) or daylight as the light source. The light source should be located directly above the light source. Because of the difference in the spectral band of the light source, the hue of some colors will change. The difference in light source angle also affects the hue of the color.

Fifth, the impact of other printing conditions, such as the temperature and humidity of the printing shop, the printing speed and solvent drying speed changes, printing pressure, the hardness of the imprinting roller will affect the color of the print.

In the final analysis, when the color of a printed product deviates, it is necessary to consider several factors, such as the amount of ink applied to the ink, the amount of transfer, the color of the ink itself, and the condition of the light source during observation.

Third, the ink manufacturer and printing plant color difference exists

The first is the printing method. Most ink factories use the British import small printing machine. The mesh of this machine is on the flat version, and the printing is completed by the circular embossing roller and the printing film. The printing machine is round. In the circular press mode, the mesh hole is on the rotating peripheral roller. The number of lines and angles of these two kinds of meshes are quite different, which makes the same ink, in the two kinds of printing methods, there is not a small difference, and sometimes it is not only the problem of dark color, but also It is the effect that hue, lightness, etc. will bring about greater differences. Some small factories use the ink stick to make it worse. Using the proofing machine of the plate making factory for the color, the effect will be much better than the imported small printing machine, and the price is almost the same. This kind of proofing machine can be made into the same version as the printing factory, and can design different levels and depths of printing according to the needs. Patterns, which make the printing method basically the same as the printing plant, and an important factor that affects the hue - the printing plate, is also the same as the printing plant.

Followed by the version depth, different prints have different depths. The ink factory's understanding or estimation of the version depth used in the prints also affects the accuracy of the color correction. Obviously, if the ink factory prints with a 45-μm-thick plate, and the customer's version is much smaller than 45 μm, the printed color becomes lighter, and vice versa, it becomes darker. Some people think that according to the standard ink provided by the user to adjust the ink, the version depth can not be considered, in fact, this is a theoretical view, but in practice it is not the case. Theoretically speaking, two identical inks (such as dividing a glass of ink into two parts) are consistent in their darkness and lightness (other conditions are the same). However, in actual color mixing, it is not possible to formulate exactly the same ink, so there is often such a phenomenon; sometimes the printed version of the color is more similar (according to customer requirements), but if the deep printing version, the color is A lot worse, so it is very important to grasp the depth of the edition. If the version of the client is too deep, it is necessary to use a deep version to print the right color.

Once again, we have to say the viscosity. The printing viscosity of the ink in the ink factory should be consistent with the printing viscosity of the printer when printing the ink. The farther the difference between the two, the larger the color difference. The ink factory uses 22s for coloring, and the customer uses 35s. At this time, the color is definitely much darker, but it is much lighter. Some ink factories do not pay much attention to this issue. Regardless of the viscosity of the printing factory, they all compare the customer's standard with the uniform viscosity (ink-like and print-like), which causes a large color difference.

Another point is the printed material. Ink factories use different materials (including other processes) for coloring and printing.

Some inks are printed with a layer of white ink that is closer to the customer's print, and some are the opposite. Some ink customers have not changed much after compounding, but some have changed very much, such as some transparent colors. Therefore, when tinting the ink factory, we must be clear about the customer's technological situation. The most basic ones include whether or not the white ink underlay is printed and what material is compounded. Whether it is coated with oil.

Theoretically speaking, the closer the printing conditions during the coloring of the ink factory to the conditions used by the printing house using the ink, the higher the accuracy of the recalled ink. However, due to the limitations of the conditions, there are still many differences between the two. For example, the printing speed, the environment for watching colors, the pressure of the printing roller, etc., cannot be unified. As long as these four parts are well controlled, they can certainly be greatly improved. The color accuracy of the ink factory.

In the printing process, how to keep a hue consistent with a batch of prints or batches of prints is a basic requirement and an important problem. Hue's - can only be said to be relative, the absolute color consistency is impossible, especially when the number of printed times, this batch of a batch of possible hue with him is far worse.

Fourth, how to control the hue in the maximum consistency

As an ink, it is required that there is no deviation in the hue of the ink, and it is preferable to use the same batch of ink first. Because of the different batches of inks, although there are few changes in some hue, but some have changed, which requires a good supply of raw materials. The consistency of the ink hue is the most basic requirement and is also an important condition. If the hue deviation of the ink is too large, it is difficult to control the hue consistency through other methods. When several colors are stacked together or the ink layer is thick, hue The difference is obvious. Secondly, the amount of ink added to the ink tray each time is required to be less, in order to keep adding new ink frequently, especially some patterns with less ink. If too much ink is added at a time, the ink will be used for a long time without adding new ink. The hue will change. For example, with a long black ink, it will be gray, and if it is not new, it will be black. If you use a long red ink, it will become dark red, and it will not be as bright as a new ink. The third is to require that the viscosity of the ink be consistent from beginning to end, preferably with a viscosity controller.

In the same important position is the scraper. The position of the doctor blade in contact with the printing plate has a great influence on the hue of the hue, especially the shallow web, so that it is required that the doctor blade be substantially in the same position throughout. The pressure of the squeegee has little effect on the hue and can be varied within a certain range. However, if the change is too large, it is also influential, especially for the printing of shallow webs.

The third aspect is the plate factor. The influence of the printing plate on the hue is mainly manifested in: the first is easy to block the plate, at this time the amount of ink transfer is reduced, thereby affecting the hue. So clean the plate with detergent and print it in normal condition. The second is the wear of the printing plate. When the number of printing plates is large, the hue changes as the degree of wear increases, and overall it becomes lighter. To solve this problem, if the printing batch is large, and often printed varieties, you can dilute some of the ink in the new version, and then gradually reduce the degree of dilution as the print volume increases, until no longer dilute.