Cover film after printing process

Laminating technology is a post-press processing technology that has attracted much attention at present. It has many advantages and many problems. It is widely used and the prospects are not optimistic.

One. The concept and role of the film

1. The concept of laminating film The laminating film can also be referred to as laminating, laminating, and laminating. It is a post-printing process in which a thin transparent plastic film is applied to the surface of a printed product by hot-pressing to form a thin film having a thickness of 10 to 20 μm.
Film coating two cases:
(1) After printing the graphic on the surface of the plastic film, it is laminated with the paper.
(2) After printing the graphic on the paper, cover it with a layer of plastic film.
This article focuses on the second case.

2. The role of the film
(1) Protect prints from abrasion.
(2) It can make up for the quality defects of printed materials.
(3) Increase the strength of printed products, such as puncture strength, tensile strength, and so on.
(4) Extend the storage time of printed products. If the photo is plastic, it does not fade or yellow, which increases the shelf life.
(5) Increase the luster of printed materials to make the pattern more bright and full.

II. Film Lamination Process and Quality Inspection Methods <br> Lamination Process Follow these steps:

1. Preparations.
(1) Check the printed matter to be coated. The inspection includes:
1 whether the ink is sufficiently dry.
2 whether the print is smooth.
3 Does the surface have dusting? The application of dusting can solve the problem of dirt on the back of the printed matter, but the dusting will form an irreversible mat on the surface of the ink layer, thereby reducing the viscosity of the paper. If too much dust is sprayed during the printing process, these coarser particles float on the surface of the printed product. When the film is coated, the adhesive adheres to the layer of dust, causing false sticking and affecting the quality of the film. Therefore, if the film is covered, the amount of dusting should be controlled.
(2) Select the film.
(3) Select adhesives.

2. Install the film roll.
After cutting the roll into a suitable format, go to the machine.

3. Coating adhesives.
Pay attention to the viscosity and thickness of the adhesive.

4. Drying.
The purpose of drying is to remove the solvent from the binder and retain the solids content of the binder. When the dryness of the adhesive layer reaches 90 to 95%, the adhesive force is maximum.

5. Pressure film.
Pay attention to control the hot press temperature and the pressure between the rollers. The temperature is too low, the film is not strong, and it is easy to delaminate. If the pressure is too high, if the paper surface is slightly uneven or the film tension is not uniform, creasing or streaking may occur.

6. Splitting and shaping.
After the proofs meet the test standards, they can be cut and shaped. After the film is printed, some quality problems often occur. In order to detect problems before the product enters the market, inspections must be performed in advance. The inspection methods are as follows:
1. Rub it.
Before and after rubbing the cover sheet, there should be no peeling or blistering between the film and the paper.
2. Tear off.
Uncover and tear off the proof film layer. The ink layer should adhere to the film or tear the paper base.
3. Pressurize.
Pressing the proofs with a letterpress printer should be no whitening.
4. Warm up.
Put the proofs in a high-temperature environment at 65 degrees. Do not peel, blistering, or wrinkle.
5. Soak in water.
After soaking the proof in room temperature water for about one hour, there should be no separation between the film and printed paper.

Three. Faults and solutions

1. The cracking of the indentation line after the film coating and the treatment of the film can improve the folding endurance of the printed matter, and has a good protection effect on the printed matter. However, if the quality of the plastic film is poor, the indentation line will crack when the indentation occurs. Phenomenon, not only affects the appearance, but also does not achieve the role of the film. In general, cracking only occurs in the thin film layer, and the underlying paper is generally not broken.
Solution:
(1) Replaced with thin film materials with better quality and better folding resistance.
(2) Change the direction of film feeding.
(3) modify the die-cut version.

2. The cover of a peeling book or the surface of a paper with a large printing surface is often covered by a film that leaves the paper. The causes and solutions are as follows:
(1) Because the ink layer on the surface of the printed matter is thick, the glue used for the film coating is difficult to be uniformly wetted, resulting in poor adhesion. It is necessary to check whether the glue has quality problems. Whether or not the glue is used in the operation process is based on the technical specifications of the glue, or the viscosity is changed. Suitable glue to increase the amount of glue can also increase the printing pressure.
(2) The diluent is problematic because the alcohol and water contained therein cause the hydroxyl group to not react. The solution is to replace high-purity ethyl acetate.
(3) The film has a quality problem or the surface treatment is insufficient, and the film should be refreshed.
(4) The surface of the printed matter is dusted. Wipe it with a dry cloth.
(5) The ink layer of the printed matter is not dry, it should be hot-pressed again and then glued, or the adhesive with high solid content should be selected to increase the coating thickness.
(6) When the membrane is dried, the humidity in the surrounding environment will be increased and the drying time will be increased, which will help improve the quality of the coating.

3. Tensile Deformation of Thin Films The phenomenon of tensile deformation of the film can be resolved from the following aspects:
(1) reduce the amount of glue. Because if the amount of glue is too large, the paper still absorbs the water in the glue after the film is overlaid, resulting in enlarged deformation. After the film is dried, the film will be stretched and deformed due to the large size of the paper, so under the premise of ensuring the quality of the product , should minimize the amount of glue.
(2) The smaller the tension, the better the film and winding. Thin film and paper performance is different, deformation ability.
(3) During the transfer process, the temperature and humidity of the external environment change greatly, and thermal expansion and contraction can also cause deformation of the film.

4. The causes of air bubbles between the paper and the film are as follows:
(1) When the printing ink layer is not completely dried, it is covered with a film. The solution is to press the printed product after hot pressing, and it is also possible to postpone the coating date.
(2) The printing ink layer is too thick and the paper and film are difficult to seal. The coating amount of the adhesive can be appropriately increased to increase the pressure and the composite temperature.
(3) Top paper. The laps of the two sheets of paper are bubbly because the two sheets of paper are topped together. The air bubbles appear behind the membrane. Pressure should be applied to the top paper or fill the gap with sizing.
(4) The drying temperature or the surface temperature of the composite roll is too high, and the surface of the adhesive is crusted. Drying and compound roll temperatures should be reduced.
(5) The film itself is uneven or curled. Replace the film or adjust the tension.
(6) Dust and impurities on the surface of the film should be promptly removed.
(7) The amount of adhesive is small or the coating is not uniform (such as the adhesive is too thick, not easy to uniform coating). Should increase the amount of coating and uniformity.
(8) The printed matter has a lotus leaf. The printed matter with flounces should be humidified or scattered to dry.

5. The wrinkling and wrinkling of the film may be caused by the following reasons:
(1) The film transfer roller is unbalanced or the electric roller and the rubber roller are unbalanced at both ends. The line speed is not equal and the film tension is inconsistent. Should adjust to balance.
(2) The film is not uniform, such as inconsistent or waved edges at both ends. Replace qualified film.
(3) Sliding between paper and film. This may be caused by the thick glue layer. Should adjust the amount of glue or increase the drying speed. The main cause of edge failure and suggestions:
(1) The upper film carrier is too thin: Too thin paper should be avoided as much as possible.
(2) Tension imbalance: Adjust the film tension.
(3) The compound pressure is too high and the temperature is too high. The composite pressure and temperature should be appropriately reduced.
(4) The film is subjected to excessive tension (including rolling tension). The film undergoes an anisotropic deformation causing the product to curl on one side of the film. The solution is to adjust the screw depth of the film expansion screw and reduce the retracting tension.
(5) The coated product is not sufficiently dried and curled. The solution is to control the humidity in the workshop and extend the drying time.

IV. Future Prospects

The issue of environmental protection can be said to be the biggest problem currently existing in the coating process. Covered film pollution mainly includes pollution of workers' health, environmental pollution, and "white pollution" caused by waste.
Many film laminating plants have introduced oily laminating machines in order to save costs. The adhesives contain a large amount of chemical thinners such as benzene and alcohol, which are toxic and cause health damage to workers. Long-term filming work may even cause life-threatening hazards.
During the lamination process, most volatiles such as benzene and alcohol are volatilized, but a small amount remains in the product and slowly evaporates after being stored and distributed to the reader.
At present, China's film market is still a faction of "prosperity". To talk about books and magazines decoration, we must talk about the film coating process. This status quo has its inevitability:
(1) Film-covered products have many advantages. See the role of the laminate (in the previous section of this article).
(2) After years of development and improvement, the film-covering equipment and technology have been quite mature.
(3) The laminating machine is relatively cheap, and the printing factory is willing to introduce it. The cost of the coating process is not high, and the publisher is willing to improve the performance and aesthetics of all aspects of the book by laminating. Both printers and publishers can obtain certain benefits from the film.
With the development of science and technology and the enhancement of human environmental protection awareness, “green environmental protection” will become an inevitable trend in the development of the lamination process. To be sure, in the future development process, the film coating technology will face more and more tests, how it will develop, and how to survive better. These are problems that cannot be avoided in the development of the film coating process.

Author: Sun Yanhua
Reprinted from: Print Quality and Standardization