What factors will affect the color difference of Folding Drawer Boxes printing?

What factors will affect the color difference of Folding Drawer Boxes printing?

How to keep the ink color of a batch of prints or several batches of prints consistent in printing is a basic requirement and an important problem. For manufacturers, the color of the packaging used by the product has become an important means and symbol to identify the product (even the logo color of the company). No matter where they are, consumers will recognize the red of Coca-Cola, the orange-yellow of Tide laundry detergent, and the colors of many products. If the appearance of the product packaging looks different, consumers may perceive the product as inconsistent quality or even doubt the authenticity of the product. Therefore, these well-known enterprises attach great importance to the color of product packaging, and require that the ink color must be stable and consistent.

The consistency of color can only be said to be relative. It is more difficult to strictly control the color difference in the same batch, and it is even more difficult to strictly control the color difference between large batches or different batches. The gravure printing of Folding Drawer Boxes is mostly multi-batch printing and large-scale printing. Controlling color difference is a very important topic for Folding Drawer Boxes printing enterprises.

1. Ink

Ink is one of the main factors that determine the color consistency of printed products. The ink itself also has the color difference of the same batch and the color difference between different batches, which is an important indicator reflecting the quality of the ink.

To solve the chromatic aberration problem of gravure printing, we must first select inks with stable quality and no deviation in hue. It is best to use the same batch of inks for a batch of printed products (it is best to prepare a sufficient amount at one time when preparing spot color inks), because it is difficult to ensure that there is no difference in hue between different batches of inks. If the ink hue deviation is too large, it is difficult to control the consistency of the printed ink color by other methods, especially when printing a layered version.

Secondly, the amount of ink added to the ink tank each time during the printing process is required to be less, so as to keep adding new ink frequently. Especially for patterns with a small amount of ink, if too much ink is added at one time, the ink will oxidize and become stale when exposed to the air for a long time. For example, the black ink that has been used for a long time is gray, not as black as new ink; Red ink that has been used for a long time will turn dark red, not as bright red as new ink. In the printing process, the volatilization speed of the mixed solvent used in the ink should be strictly controlled. When the volatilization speed is too fast, the transfer rate of the ink may be reduced, which will affect the color of the printed product.

In addition, when using two-component ink, it should be fully stirred and less frequent. 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 printed product, especially the ink color of the shallow layer, so the ideal state is that the scraper is in the same position from beginning to end. However, due to various reasons, the position, angle and pressure of the scraper have to be adjusted during the printing process, so we must understand the influence of its changes on the color of the printed product and take corresponding measures.

The contact position of the scraper and the plate cylinder determines the distance between the contact point of the knife and the plate and the imprinting point. The length of this distance should be adjusted according to the printing speed, ink viscosity, cell depth, and layout quality. In general, the longer the distance, the more dry the ink in the cells and the lower the transfer rate of the ink. As far as its influence on the printing effect is concerned, it is equivalent to the partial fade of the ink color. At the same time, when the distance is long, it is also a test for the adaptability of the ink. On the contrary, when the distance is short, the transfer rate of the ink is relatively high, and at the same time, some fine lines on the layout are transferred to the printing material.

The scraper angle is the angle between the tangent of the contact point between the scraper blade and the plate cylinder and the scraper. Increasing the angle of the scraper can easily scrape off the ink on the layout and make the pictures and texts clear, but it may also cause the phenomenon that the ink layer is too thin, the gloss of the ink film is poor, and it is easy to damage the printing plate cylinder. On the contrary, if the angle of the scraper is reduced, the printing ink layer becomes thicker and the printed product has good gloss, but the edges and corners of the pictures and texts are easily blurred.

Scraper pressure also has a certain influence on the ink color. When the pressure becomes larger, the ink color becomes lighter; when the pressure becomes lighter, the ink color of the printed product tends to become darker.

3. Plate cylinder

The influence of the printing plate cylinder on the consistency of ink color is mainly manifested in the following aspects:

1. Blocking: Blocking is a phenomenon in which the cells are blocked for some reason (caused by solidified substances in the ink, high-viscosity substances or insoluble substances of foreign substances, etc.) and the transfer rate is reduced. At this time, the transfer amount of ink is reduced, which affects the hue. When the plate is blocked, use a solvent or special cleaning agent (using general decontamination powder can easily cause other failures) to clean the plate cylinder, and take corresponding measures for the cause of the plate blocking to make it back to normal.

There are many factors that affect the blocking of the plate. In addition to the insoluble factors caused by chemical changes when using inks that are prone to chemical reactions, such as two-component inks, other reasons can be summarized as the ink drying and solidifying on the layout, mixing impurities, and poor quality of plate making, etc. factor. In addition, during the printing process, if water or other types of ink are mixed into the ink, it will affect the fluidity of the ink, cause the re-agglomeration of the pigment, and also cause the blockage failure.

In addition, the plate cylinder should be inspected in detail before printing. If the plate cylinder adheres to oil, etc., it will cause printing failures similar to plate blocking during printing.

2. Wear of the plate cylinder

When the printing volume of the printed product is large, the degree of wear of the printing plate cylinder is large, and the printing ink color will change, generally speaking, it tends to become lighter (because the cells become lighter and the amount of ink applied is reduced). Therefore, after a certain number of prints, it needs to be re-plated. Although the cells of the plate cylinder become lighter, other process adjustments can be used to maintain the color stability, but after excessive use, the value of re-plating will be lost, and only re-plates will be made.

Various failures and damages may also occur to the plate cylinder during use. Due to many factors influencing plate making, it is almost impossible to completely repeat the original plate making process conditions when re-making a plate, so it is often difficult to obtain the same printing effect as the original even under the same printing conditions after re-making. In order to solve this problem, if the printing batch is large and it is a job that is often printed, the method of making two or even multiple sets of versions can be considered.

3. Plate design and color management

When designing the printing plate, the influence of printing and post-press processing technology should be fully considered. For example, the colors in some dot areas are prone to gradation, which should be handled well when making plates. Many plate-making enterprises have begun to use color management software, which has played a positive role in improving the quality of color reproduction.

4. Printing conditions and environment

In the printing process, the color of the ink film mainly depends on the concentration and transfer rate of the ink. For specific substrates and specific inks, the concentration of the ink is relatively fixed, and the transfer rate depends on factors such as ink viscosity, dryness, and the condition of the layout cells, as well as printing speed, printing pressure, doctor blade pressure, doctor blade The influence of factors such as position, blade angle and environmental conditions (temperature and humidity). It should be pointed out here that when these conditions change, the degree of influence on the highlights, shadows, and midtones of the printed product is different.

1. The viscosity and drying speed of the ink change:

Changes in ink viscosity can directly affect the color of the printed product. When the viscosity is high, the color density is relatively high, and conversely, when the viscosity is low, the color density is relatively low. This effect is sometimes very obvious and must be taken seriously. According to the requirements of the printing process, the viscosity of the ink should be moderate. If the viscosity is too large, it is not conducive to the transfer of the ink, and it is easy to produce the phenomenon of smearing;

Changes in ink viscosity have a subtle effect on the migration area generated by ink migration or dot flow, especially in multi-color printing. Therefore, when the printing speed is constant, the viscosity of the ink is required to be consistent from beginning to end, and it is best to use an automatic viscosity controller.

When the solvent ratio in the ink changes, the drying speed of the ink will change, which in turn affects the transfer rate of the ink and the color of the printed product. For some inks with a small amount, after being placed in the ink tank and used for a period of time, due to the automatic volatilization of the solvent, it will not only affect the viscosity of the ink, but also affect the proportion and volatilization speed of the solvent, so the solvent should be replenished in time.

2. Changes in ambient temperature and humidity

If the room temperature and the liquid temperature of the ink change greatly, the ink migration state will change, and the color tone will also change.

This is because the temperature change affects the viscosity of the ink. At the same time, high temperature and low temperature will have a significant impact on the ink transfer rate of the high-gloss parts. Therefore, when printing high-end products, the temperature and humidity of the printing workshop should be controlled anyway. In addition, when using ink in winter, it should be preheated in advance to reduce the temperature change of the ink itself.

3. Separation of synthetic colors:

This phenomenon is easy to occur in light colors and in mixtures of various colors such as organic pigments and inorganic pigments with very different specific gravity. Especially when the ink in the ink tank is not very flowing, the precipitation will promote the separation of the synthetic color, so pay attention to make the ink circulation smooth. In addition, if the stirring is not sufficient during toning, the concentration of a certain color tends to increase as the printing progresses, so the ink should be fully stirred with a machine such as a dissolver or other methods before the actual printing.

4. The deterioration of the ink makes the color development worse

Due to long-term printing, the solvent composition of the ink changes, or the moisture in the air is mixed into the ink to cause the ink to deteriorate, making the color development worse.

In order to prevent the ink temperature from dropping due to the heat of vaporization, a slow-drying solvent can be used together. In high temperature and high humidity weather, a certain amount of water may be mixed into the ink. In the event of an abnormality, new ink should be added, or all of them should be replaced. The remaining ink that has been used for many times should be filtered or discarded regularly due to the inclusion of a lot of dust. .

5. Other printing conditions

Due to the overlapping of dots and the irregular wind blowing on the layout, or the change of printing speed and drying speed, the printing discoloration will occur.

5. The influence of post-press processing

1. Changes in post-press processing technology:

The use of different post-press processing (such as extrusion lamination and dry lamination) also has a certain impact on the hue of the printed product. At the same time, the high temperature of extrusion compounding sometimes causes the change of the pigment. In addition, when heat-sealing is performed at a temperature of 200 degree or higher, the hue of the heated part may become darker. This is because the colorant is melted by heating and recrystallized by cooling, resulting in the formation of microcrystals and an increase in coloring strength.

2. Changes in post-press processing substrates:

The change of the post-press processing substrate, such as the change of the aluminum layer of the aluminized film, will directly affect the overall hue. Of course, the color cast of the printed substrate will also have a slight impact on the overall hue.

3. Photochemical reaction:

When the light resistance and weather resistance of the ink colorant are poor, the color of the printed product may change due to photochemical reaction.

4. Influence of package contents:

When the contents contain volatile and migratory active substances, the color of the package print may also change due to corrosion. Therefore, the appropriate ink should be selected and used according to the end use of the packaging print (or negotiated with the ink manufacturer).

6. Visual color observation and color control instrument detection

Customers expect a high degree of consistency in the ink color of packaged printed products, but not everyone observes the same color results. What customers need is persuasive data, that is, quantitative data on color. Although the naked eye is good at seeing color, it is not good at memorizing color (if the products are not placed side by side, the naked eye cannot accurately measure the color), so the naked eye is no longer considered a reliable guarantee for judging ink color, and the instrument shows its unique importance. From the naked eye to the densitometer, colorimeter and then to the spectrophotometer, to the current desktop spectrophotometer, the color measurement results are more accurate, which is enough to compensate for the fatigue effect of the human eye, visual persistence, visual memory, etc. adverse effects. Of course, it will take time to widely use color control instruments in our country.

As part of the color management process, color detection is an indispensable step and the first step in color management. At the same time, since the color stability will be affected at any time during the operation of the printing press, it will be an important development trend to use the online color control device to measure and monitor the color stability.

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