The secret of Packaging Boxes printing color difference control

The secret of Packaging Boxes printing color difference control

About the Packaging Boxes control of printing color difference

The chromatic aberration problem of packaging printed products has always plagued printing workers. Whether the chromatic aberration problem can be effectively controlled is a measuring rod that reflects the company's product quality, reputation and the skill level of the operator. issues that the company must pay attention to.

The chromatic aberration of Packaging Boxes is roughly divided into two phenomena, one refers to: the color of the same batch of products is the same, but there is a chromatic aberration with the color of the sample. The second refers to: there is a color difference in the same batch of colors, some are consistent with the sample, but some are inconsistent with the sample.

Now we will discuss and analyze with you from the following aspects.

1. The first phenomenon (the color of the same batch of products is the same, but there is a color difference with the color of the sample)

1. Human factors:

It has nothing to do with the captain's skill level, but it has something to do with the captain's sense of responsibility. Since the colors of the same batch of products can be kept the same, it means that the captain's skill level is not low, but why do you dare to print it if it is inconsistent with the sample? Did you sign the first one? This is entirely a matter of the captain's sense of responsibility. (It does not rule out the mistake of signing the sample, if so, it is related to the responsibility of the person who signed the sample).

2. Paper color:

Papers with different whiteness have different effects on the color of the printed ink layer. Because the difference in whiteness is equivalent to adding different black, red, blue or yellow to the ink, although the amount of ink and hue have not changed during printing, the actual ink has a certain degree of transparency, and the effect of color varies with the whiteness of the paper. Different and displayed, resulting in different color differences. When opening the material, the same batch of paper must be used. Because the gram weight, specification and size are the same, but the production batch number date is different, the whiteness of the paper will have a certain difference, which will lead to the color difference of the printed product. Therefore, paper of the same whiteness must be used as the printing paper for the same product.

3. The gloss and smoothness of the paper:

The gloss of the printed matter depends on the gloss and smoothness of the paper. Offset color printing is when the light is incident on the surface of the paper, the light is reflected to the retina of the human eye, and the color is seen through the photosynthesis received by the color-sensitive cells. If the gloss and smoothness of the paper is high, the color we observe is basically the color reflected through the ink layer, and the main color light saturation is high. If the surface of the paper is rough and the gloss is low, diffuse reflection will occur, which will reduce the saturation of the main color light, making the color perception of the printed matter lessened by the human eye. The same amount of ink was used to measure the density with a densitometer. Paper with high smoothness and gloss with high density values. Paper with low smoothness gloss and low density value.

4. Surface treatment of printed sheets:

After the Packaging Boxes is surface treated by laminating, glazing, calendering, oiling, and printing, there will be varying degrees of hue changes. Some of these changes are physical changes and some are chemical changes. The physical change is mainly reflected in the increase of specular reflection on the surface of the product, which has a certain impact on the color density. For example, compound light film, UV varnish, calendering, etc., the color density will increase. The color density of the printed product after complex sub-film and matt oil is reduced. The chemical changes are mainly from laminating glue, varnish, UV oil and so on. These materials contain a variety of solvents, which will cause a chemical reaction in the color of the printing ink layer to cause color changes. Therefore, as a printed product for packaging offset printing, if there is a post-press processing process during printing, the physical and chemical changes of post-press processing must be taken into account to determine the density value and Lab value of the ink layer during printing.

5. Dry retreat density value:

Immediately after the offset printing product is printed, the ink is still in a wet state, and the density value measured at this time is different from the density value measured after the print is dried. The density value is high when wet, and the density value is low when dry, which is the phenomenon of dry back density value. This is because the ink layer just printed has a certain leveling. It is mainly reflected in the specular reflection of the surface, which looks bright and shiny. When the ink layer is dry, there is diffuse reflection on the surface, and the natural luster is duller than when it was just printed. In order to ensure that the color difference of batch products is reduced as much as possible during normal printing, we use the same wet density test method to control. That is to say, the first time the printed product is in the wet state, the wet density value and L*a*b* value are measured immediately after the customer signs and agrees. When printing the product later (wet state), control the color according to the density value and L*a*b* value measured for the first time. Of course, if a densitometer with a polarizer device is used, it can eliminate the light generated by the specular reflection on the surface of the ink layer. The wet density measured by it is relatively close to the dry density, and it can also help control the reduction of chromatic aberration.

6. Printing pressure:

Printing pressure is one of the conditions for ink transfer. Since the surface of the printing plate and the blanket cannot be absolutely flat, the surface of the paper is inevitably uneven or uneven. If the printing pressure is insufficient or uneven, the ink layer is prone to uneven shades, so it is required to achieve "three levels" in the process, that is, the surface of the printing plate, the blanket, the substrate and the lining surface are required to be relatively flat. Under the conditions, only a thinner ink layer can obtain a more uniform ink color on the printed matter through a balanced printing pressure.

When the printing pressure is insufficient or uneven, and there is poor contact between the lining body and the printing plate, it is necessary to increase the amount of ink input to meet the visual effect of inking on the plate. However, this will not only increase the consumption of ink, but also easily cause the color difference of printing and the sticking of printed products, so do a good job of "three levels" (ink roller level, horizontal roller level, roller level) and use uniform and constant printing. Pressure can prevent the color difference caused by improper pressure.

7. Look at the light source of the sample table:

Offset printed products must have a light source when observing the color, and no color can be seen without light, but if the characteristics of the light source are different, then the color difference will be very large. Generally, we require that the color be viewed under the condition of natural light (that is, the standard light source). If an ordinary light bulb is used as the light source to observe the color, the color will appear yellow, it is difficult to accurately identify the color, and the final printed product will have a serious color cast. In addition, the intensity of light and the angle of illumination will also affect color identification. Under the same light source, the intensity of light reflected on the illuminated proof is mainly determined by the distance between the proof and the light source. Those who are near are strong, those who are far are weaker. Therefore, we usually pay attention to two points in our work, whether it is day or night: one is to use a standard light source (about 400-700 wavelength), and the other is to pay attention to the equal intensity of the light source and the angle of illumination. For products with high color requirements, the ink color sample of the printed sheet should be placed on the standard sample for comparison, so that due to the small difference in observation angle, the color identification is relatively accurate. Therefore, the process practice tells us that the difference in the characteristics of the light source and the observation angle will directly affect the accurate identification of colors (yinshua96.cn).

2. The second phenomenon (there is color difference in the same batch of colors, some are consistent with the sample, but some are inconsistent with the sample)

1. Human factors:

It is believed that the hue of the first few sheets is accurate. When the ink and water are not balanced, they start to open all the way. During the printing process, the amount of water and ink is constantly adjusted, and the color is opened while adjusting, which will inevitably cause the color difference of the same batch of printed products. This has a lot to do with the captain's skill level, experience, and personality, and both belong to the color difference of the same batch of products caused by lack of ability.

2. Fountain solution:

Offset printing is based on the principle of repulsion between oil and water. This water refers to the fountain solution. Its size directly affects the color of the ink layer. The color of the large ink layer is light, and the color of the small ink layer will be darker. The greater the water, the more serious the emulsification of the ink. Emulsified inks are dull and light in color. The printed products of emulsified ink not only have serious color difference, but also have quality problems such as stickiness, non-drying, and weak printing. Therefore, in printing and operation, the size of the wetting liquid on the printing plate layout must be strictly controlled, and the balance of ink and water must be done well.

3. Printing speed:

The speed of the vehicle in printing will affect the color depth of the Packaging Boxes. This is because the speed of the vehicle will affect the balance of the ink. The moisture content of the express plate and the moisture content of the slow plate vary differently. The water volatilization of the express printing plate is small, and the water volatilization of the slow printing plate is large. Due to the change in the size of the water, the ink and water are unbalanced, and the color of the ink will inevitably change. Therefore, we must pay attention to the constant speed when printing, and we must not drive fast for a while. Drive slowly for a while, so the printed products will have color difference. At the same time, it must be adjusted to a most stable speed according to the condition of the machine. For example, some imported offset presses indicate the maximum speed of 16,000 sheets/hour, and the maximum speed of domestic machines is 8,000 sheets/hour. These speeds are not stable speeds. Generally speaking, whether it is an imported machine or a domestic machine, it is ideal that the stable speed is 70% of the maximum speed, that is, the imported machine is about 11,000 sheets/hour, and the domestic machine is about 5,600 sheets/hour. Such a speed can be easily controlled. Ink balance to reduce chromatic aberration.

4. Bad ink roller:

In the offset printing process, whether the Packaging Boxes can obtain uniform ink color, the quality of the rubber roller plays a very important role. Generally, there are three types of rubber rollers: ink transfer roller, ink distribution roller and inking roller, which have a great influence on the shade of ink. The elasticity, viscosity, circularity, hardness and surface finish of the ink roller largely determine the ink quality of the printed product. If the elasticity of the inking roller is poor, the viscosity is insufficient, and the roller body is eccentric. When the colloid is too hard and the colloid is aging, it is easy to cause uneven or unstable inking during the printing process, making the printing ink color of the prepared sheet inconsistent. Therefore, it is necessary to ensure the quality of the rubber roller during printing to ensure that the ink applied to the printing plate is basically the same in each printing cycle. Therefore, the rubber roller should be cleaned in the usual work, so that the paper dust and impurities remaining on the rubber roller can be removed to ensure the uniform transmission of ink. At the same time, the contact pressure between the ink rollers and between the ink roller and the printing plate should also be adjusted, otherwise it will cause uneven ink transfer and serious color difference. (yinshua96.cn)

5. Maintenance of equipment:

Maintaining the good performance of the machine is a reliable guarantee for improving the quality of printing ink. If the machine is unstable, such as inconsistent pressure, unstable paper feeding, and frequent empty sheets and multiple sheets during printing. It is bound to cause color difference in printing. Therefore, we usually do a good job in the maintenance of the equipment, pay attention to the lubrication of the key parts of the machine, prevent the aggravation of wear, and keep the equipment in a stable state. As an offset printer, we must do "three good" (good management, good use, and good repair) and "four meetings" (will use, maintain, inspect, and troubleshoot).

There are many reasons for the formation of printing color difference, and the control methods are not limited to these. This requires us to continuously explore and accumulate in the printing operation, and develop a good habit of taking notes, which is conducive to the improvement of our own ability, and watch more in our spare time. Books about printing theory, with theories to guide, can avoid many detours. Customers have higher and higher requirements for the quality of Packaging Boxes. For us, it is pressure and motivation. Face it, and you will go smoother and smoother on the road to success.

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