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Analysis of the problem of ink drop in label printing

Source:Dongguan Deli Intelligent Technology Co., Ltd.      Time:2021-04-25 17:41:10

In the label printing process of film materials, it is easy to cause the problem of ink loss in the surface layer printing, which greatly affects the quality of the printed products and even delays the delivery date. This article attempts to summarize and enumerate the common causes of ink drop and improvement methods from the daily printing experience, for the industry to discuss together in order to find the best solution.

Problem 1: Coating defects

Conventional films are divided into two types: coated and uncoated. The causes of ink drop due to film coating defects are also divided into two situations: For coated film materials, if the surface coating is not strong enough , It will cause poor ink adhesion; and uncoated film materials are often due to the poor fastness of the surface layer to the ink, causing the ink to drop.

The ink drop caused by coating defects can be solved by the following methods: use varnish printing treatment on the surface layer to protect the surface of the ink and prevent ink drop; use corona reprocessing on the surface layer, and corona on the surface of the material The dyne value should not be less than 38mm/m. If the dyne value is less than 36mm/m, it will directly affect the firmness of the printing ink; the surface layer is primed or the ink adhesion enhancer is used (the blending ratio is about 3% ), it can also improve the ink retention of the film surface layer; some subsurface synthetic paper materials are not suitable for testing with 3M tape because the surface coating has certain characteristics of paper coating.

Problem 2: Tension

For the film material with corona treatment on the printing surface, in order to achieve good ink wetting, the dyne value usually needs to be above 38mm/m, and the ink drop problem is likely to occur if it is less than 36mm/m; at the same time, the dyne value of this material It will gradually fade over time, and the printing ink problem will occur. The essence of this problem is tension.

For the ink drop caused by this situation, there are the following solutions: use a satellite rotary machine with on-line corona function to perform on-line corona treatment to improve the surface energy of film materials; use an intermittent printing machine to perform surface primer coating Treatment is used to improve the surface printing adhesion; when the dyne value fades, it needs to be treated with corona during printing, but the dyne value does not completely represent the adhesion between the ink and the surface material, generally dyne The decay cycle of the value is 3 months-6 months, so it is recommended to minimize the long-term storage of stock materials.

 Finally, it is recommended to use ink with higher adhesion, and it is recommended to consult the ink supplier.

Problem 3: Ink drying and tension

In the printing process, the reasons of ink drying and tension may also cause ink drop. It is divided into: printing ink layer is too thick, resulting in incomplete drying; UV lamp energy is insufficient, lamp tube aging, lamp reflector aging, resulting in insufficient drying and curing of UV lamp, and ink layer not drying; ink excessive drying, resulting in material deformation and formation The ink layer comes off.

This ink drop problem can be solved in the following three ways:

First, the use of deep ink thin printing is commonly known as reducing ink volume, such as spot color Dizi ink, which can be darker, and the ink volume is smaller in formal printing to achieve the sample effect, and the output power of the UV lamp can be increased at the same time. , Reduce the printing speed, increase the exposure time of the UV lamp, and achieve the drying effect. This solution is suitable for old intermittent or satellite rotating machines and old UV lamp solutions.

Second, check whether the UV lamp tube is aging and clean the reflector. Usually the domestic UV lamp has a service life of about 500-1000 hours, and the imported lamp has a service life of about 1000-2500 hours. For details, please refer to the actual usage. It is recommended that the printing factory should clean the UV lamp every six months or so to ensure normal use.

Third, reduce the output power of the UV lamp. The specific operation is for printing jobs in general printing plants. The first few groups of colors in the color sequence are mostly logos or small prints. The light required is limited. Do not over-exposure at high-end, because the film material absorbs limited heat energy. Excessive exposure will cause the film material to curl, deform and become brittle, and decrease the ink adhesion. You can follow the principle of using low-end UV lamps first.

Question 4: The matching of ink and material

Finally, the matching degree of the ink and the material will also cause ink drop to a certain extent. For example, the molecular tension of the ink used is too large to form a uniform ink layer on the surface of the substrate material; or the use of ink models that have exceeded the shelf life or inferior domestic brand inks will cause ink to be printed.

In the case of the above, you can switch to inks that match the printing material, such as special film inks and lightfast and lightfast inks (consult the ink manufacturer for specific); and for expired inks, you need to check before printing. Do printing tests, or print some simple text or small logos, and some low-end products; print large-area solid and full-page dot and line patterns, and it is recommended to use inks with good brand and high adhesion (such as Hanghua ink, etc.).

Summary of factors affecting ink drop

Through the above analysis, we can summarize the eight major reasons for ink drop:

1. Coated film materials have poor surface coating fastness;

2. Uncoated film material, resulting in poor fastness to ink after printing;

3. Low dyne value. For the corona-treated film material on the printing surface, in order to achieve good ink wetting, the dyne value usually needs to be above 38mm/m;

4. The dyne value fades, and the printing surface is a corona-treated film material, and its dyne value may gradually fade over time, and the fade cycle is 3-6 months;

5. Too thick printing ink layer and insufficient UV lamp power cause insufficient curing of the ink layer;

6. The ink tension is too large to form a uniform solidified ink layer on the surface of the printing material;

7. Use expired ink or inferior domestic ink;

8. The ink is over-exposed and over-dried

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