Reasons for the poor adhesion of plastic gravure ink

Editor's note: The method of judging the adhesion fastness of ink printing is generally determined by the glass paper pressure sensitive adhesive tape. The printing fastness varies with the ink type. Careful reference should be made to the specific solution. The main reasons are:

First, misuse ink type or mixed with different inks.

There are many types of inks, suitable for different substrates. If you use the wrong ones, there will be loose adhesion. For example, the gravure ink of cellophane is nitrocellulose, and the ink of printing paper is rosin. If it is used wrongly, it will produce The phenomenon of poor adhesion makes the ink also play a decisive role in the problem of the fastness of the printing ink layer. For different substrates, the corresponding ink should be used. For cellophane, nitro-Silicon resin ink can be used. For polypropylene film, chlorinated polypropylene resin ink can be used. For polyethylene film, polyamide resin can be used. Ink and so on.

In actual production, in order to adjust the viscosity and volatilization rate of the ink, a certain amount of solvent is often added. However, when using solvents, mixed solvents are often used. Several problems should be noted:

(1) When adding the solvent, the solvent with lower surface tension should be used as far as possible in order to reduce the surface tension of the entire ink system, thereby improving the wettability of the printing film;

(2) When the solid content of the work is too high, the wetting effect will be relatively low, thereby affecting the ink fastness. On the contrary, if too much solvent is added, the effective components that the ink adheres to the film will be relatively reduced. Fastness decreased. In order to solve the contradiction between the fastness of the ink layer and the volatilization rate of the ink, a resin (rubber) or other suitable compatible adhesive resin or rubber corresponding to the ink may be added to the diluent or the ink. This can also improve the fastness of the ink layer to a certain extent. At the same time, the ink is left for a long time, or mixed with impurities, which can cause deterioration of the connecting material. Therefore, fresh ink should be used as much as possible or the changed ink should be replaced in time.

Second, the ink swollen , or solid material precipitation caused by weak adhesion, to prevent the ink from swell, you can not use excessively quick-drying solvents, should be combined with the right amount of slow-drying solvents, to minimize the opportunity for ink and air contact, The moisture in the air invades the ink, increasing the viscosity of the ink and allowing the resin to precipitate and gel.

In the printing, there is a drop in gloss, a decrease in the concentration, a poor transfer, and a failure in plugging the plate. Therefore, the ink tank should be sealed and the air blower should not leak to the printing roller. When the printing pattern is extremely low, the ink consumption is particularly low. Use new inks as much as possible. For example: When the ink is a polyamide resin ink, usually toluene:isopropanol:ethyl ester 5:3:2 or Alkaline:xylene:isopropanol 20%:50%:30% , Can effectively prevent the ink from bloating, usually when the room temperature is higher than 25 °C printing, the chance of ink swelling is higher, the best indoor temperature is 21 °C - 23 °C printing, relative humidity 65%, are conducive to printing , reduce the probability of poor adhesion, and if the chlorinated polypropylene resin ink using toluene: xylene 80%: 20%, or toluene: ethyl ester: butanone 70%: 20%: 10% are conducive to increase its viscosity It also effectively prevents the bloating factor. In the printing process, if the supply solvent evaporates before the ink is dried, the condition is good, the heat provided by the drying is insufficient, the distance from the entrance of the drying tunnel, or the printing speed is too slow, so that the material is partially printed and goes into the drying process. If the time of the road is dragged on too long, it will be prone to "whitening" failures, and will also affect the problem of poor adhesion. ("Blank" first, the ink is cold, the water vapor in the air becomes a drop and mixes with the ink, causing the gelatinization to become turbid and precipitated. The "whitening" product has significantly reduced gloss, transparency, and adhesion.) It is to increase the printing speed and make the printing roller close to the baking mouth. If the above conditions cannot be achieved, a slow-drying solvent can be used to make the drying time slow. However, when a large amount of slow-drying solvents are used, problems such as residual odor and adhesion of the printed materials are apt to occur, but they cannot be added too much. Therefore, in order to improve the adhesion of the ink, the actual operating conditions and printing effects should be adjusted?

How to measure the gray balance?

The gray balance was subjectively evaluated by comparing the overprinting color of cyan, magenta, and yellow with the black having the same gradation value. The gray balance must be evaluated under standard observation conditions. Densitometers can also be used to objectively evaluate gray balance. The absolute density of each main filter must be approximately equal.

Grey ruler

Each print must have a gray ladder or a series of objective solid or light-colored marks. These color patches must appear on every page or on as many pages as possible. The target densities in the above three tables represent the density of patches measured using each filter.

The total range of the three ink densities in the table cannot exceed +/-0.03.

Color code

In addition to the gray scale, color patches should also be used where possible. Color patches should include the following sections:

1. Four colors (CMYK) in the field

2. Color blocks when the percentage of four color dots is 50%

3. Any two colors of solid overprint

If space allows, it is best to add 45% color and 25% color blocks. Gray scales and color scales should be as large as possible for measurement. The recommended height and width (or diameter) of the color block is 3/8 inch. Smaller patches can also be used if the printer or the newspaper agrees. The color scale does not require a continuous tone, and the color scale can be designed creatively on the page width.

Use gray ruler rules?

1. Use a projection densitometer to periodically check the imagesetter and the film processor to ensure that they can output the correct film dot percentage/tone value for the gray scale.

2. The gray scale width and densitometer window (projection or reflection) should be the same width to ensure correct density readings.

3. Check the densitometer calibration every day, but recalibrate only when necessary.

4. The change in the internal density of the press must be within the density tolerances in the above table.

5. If necessary, make a dark to light adjustment of the ash scale on the press because the ink color is not pure. Cyan and magenta include those that can affect the yellow readings in the grey scale. After adjusting a color, you should recheck the other two colors.

6. It is best to read in the same place as the gray scale or plate to reduce the density change due to imprinting on the ink or on the press.

7. When using grayscale filters for red, green, and blue measurements, the three density values ​​cannot differ by more than +/- 0.03.

8. When starting up, follow these steps

Register the paper.

Make the page horizontally reach a visual gray balance.

Use a reflection densitometer to check the ash scale.

Adjust density if needed.

After a few minutes, check the density again at the same location and adjust the density if necessary.