Overprinting process
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The laminating process is a post-press processing technology that has received much attention at present. It has many advantages, and there are also many problems. The application is extensive and the prospects are not optimistic.
I. The concept and role of film
1. Concept of lamination The film can also be called over-plastic, silicone, and film. It is a post-press process that forms a film with a thickness of 10-20 um by heat-pressing a transparent plastic film onto the surface of the printed matter.
Two cases of filming:
(1) After printing on the surface of the plastic film, it is covered with paper.
(2) After printing the graphic on the paper, a plastic film is laminated thereon.
This article focuses on the second case.
2. The role of the film
(1) Protect printed matter from abrasion.
(2) can make up for the quality defects of printed matter.
(3) Increase the print strength, such as puncture strength, tensile strength, etc.
(4) Extend the time of printing. If the photo is plasticized, it will not fade or yellow, and will increase the shelf life.
(5) Increase the gloss of the print to make the pattern color brighter and fuller.
2. Film coating process and quality inspection method
The lamination process is carried out as follows:
1. Prepare for work.
(1) Check the printed matter to be coated. The inspection contents include:
1 Whether the ink is sufficiently dry.
2 Whether the print is flat.
3 Whether there is powder on the surface. The addition of dusting can solve the smearing of the back of the printed matter, but the dusting will form an irreversible mat on the surface of the ink layer, thereby reducing the stickiness of the paper. If too much dust is sprayed during the printing process, these coarse particles float on the surface of the printed matter, and the adhesive adheres to the sprayed powder when the film is coated, thereby causing a false sticking phenomenon and affecting the quality of the film. Therefore, if the film is covered, care should be taken to control the amount of dust sprayed.
(2) Select a film.
(3) Select a binder.
2. Install the film roll.
After cutting the roll into a suitable format, it is put on the machine.
3. Apply adhesive.
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 rubber layer reaches 90 to 95%, the bonding force is the largest.
5. Pressing the film.
Take care to control the hot pressing temperature and the pressure between the rollers. The temperature is too low, the film is not strong, and it is easy to delamination. If the pressure is too large, the paper surface is slightly uneven or the film tension is inconsistent, wrinkles or streaks may occur.
6. Cutting and shaping.
The sample can be cut and shaped after it meets the test standard. There are often some quality problems after the film is printed. In order to find the problem before the product enters the market, it needs to be inspected in advance. The inspection methods are as follows:
1. Hey. The film sample should be smashed back and forth, and there should be no separation or blistering between the film and the paper.
2. Tear off. Uncover and tear off the film layer of the sample, the ink layer should be attached to the film, or the paper base should be torn.
3. Pressurization. Pressurize the proof with a letterpress press and there should be no whitening.
4. Warm up. The sample should be baked in a high temperature environment of 65 degrees, and should not be stripped, blistered, or wrinkled.
5. Soak in water. After the sample is placed in normal temperature water for about 1 hour, the film layer and the printing paper should be separated.
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3. Faults and solutions
1. Cracking and treatment of indentation line after filming
The film can improve the folding resistance of the printed surface and has a good protective effect on the printed matter. However, if the quality of the plastic film is poor, the cracking of the indentation line will occur during the indentation, which not only affects the appearance but also prevents the film from being formed. The role it should have. Generally, cracking only occurs in the film layer, and the underlying paper generally does not break.
Solution:
(1) Replace the film raw material with better quality and folding resistance.
(2) Change the paper feed direction of the film.
(3) Modify the die cut version.
2. Peeling phenomenon
The cover of the book or the surface of the paper with a large print surface often shows a film that is covered with paper. The reasons 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 is difficult to be uniformly wetted, resulting in poor bonding. It is necessary to check whether the glue has quality problems, whether the glue is used according to the technical specifications, or the viscosity is changed. Suitable glue, 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 the high purity ethyl acetate.
(3) If the film has quality problems or the surface treatment is insufficient, the film should be renewed.
(4) There is dusting on the surface of the printed matter. Wipe it off with a dry cloth.
(5) If the ink layer of the printed matter is not dry, it should be hot pressed once and then glued, or the adhesive with high solid content should be selected to increase the coating thickness.
(6) When the film is dried, the humidity of the surrounding environment is increased, and the drying time is increased, which is advantageous for improving the film quality.
3. The film undergoes tensile deformation
For the phenomenon of tensile deformation of the film, it can be solved from the following aspects:
(1) Reduce the amount of glue applied. Because if the amount of glue is too large, the paper will still absorb the moisture in the glue after the film is finished, and the deformation will be expanded. After the film is dried, the film is affected by the deformation of the paper, and the tensile deformation is caused, so the product quality is guaranteed. Should minimize the amount of glue applied.
(2) When the film is wound and wound, the tension is as small as possible. The film has different properties from paper and has strong deformability.
(3) During the transfer process, the temperature and humidity of the external environment change greatly, and the thermal expansion and contraction will also cause deformation of the film.
4. There are bubbles between the paper and the film.
The reasons and solutions are as follows:
(1) The printing ink layer is not completely dried to cover the film. The solution is to heat the film and then apply the glue, and the filming date can be postponed.
(2) The printing ink layer is too thick, and the paper and the film are difficult to be closely adhered. The amount of adhesive coating can be appropriately increased to increase the pressure and the composite temperature.
(3) Top paper. There are bubbles in the overlap of the two sheets of paper because the top and bottom of the paper are together when the film is covered. In the gap between them, bubbles appear on the film. The gap should be filled by pressing or applying glue at the top paper.
(4) The drying temperature or the surface temperature of the composite roll is too high, and the surface of the adhesive is crusted. The drying and compound roll temperatures should be reduced.
(5) The film itself is not flat or curled. Replace the film or adjust the tension.
(6) There are dust impurities on the surface of the film, which should be removed in time.
(7) The amount of binder is small or the coating is not uniform (if the binder is too thick, it is not easy to coat evenly). The amount of coating and uniformity should be increased.
(8) The printed matter has a ruffled edge. The printed matter with ruffles should be humidified or spread out to dry.
5. Film wrinkles, curled edges
Wrinkling can be caused by the following reasons:
(1) The film transfer roller is unbalanced or the electric heating roller and the rubber roller are unbalanced at both ends, and the line speeds are not equal, resulting in inconsistent film tension. It should be adjusted to make it balanced.
(2) The film is not uniform, such as inconsistent or wavy edges at both ends. The qualified film should be replaced.
(3) Sliding between the paper and the film. This may be caused by the glue layer being too thick. The amount of glue should be adjusted or the drying speed should be increased. The main causes and suggestions for the edge failure:
(1) The upper film carrier is too thin: too thin paper should avoid filming as much as possible.
(2) Tension imbalance: adjust the film tension.
(3) The composite pressure is too large and the temperature is too high. The combined pressure and temperature should be appropriately reduced.
(4) The film is subjected to excessive tensile force (including winding tension). The film undergoes elastic deformation, causing the product to curl toward one side of the film. The solution is to adjust the screwing depth of the film expansion screw and reduce the winding tension.
(5) The film product is not sufficiently dried and will curl. The solution is to control the humidity in the workshop and prolong the drying time.
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Future prospects
Environmental protection can be said to be one of the biggest problems in the laminating process. Membrane pollution mainly includes workers' health pollution, environmental pollution, and "white pollution" caused by waste.
Many laminating factories have introduced oil-based laminating machines to save costs. The rubber contains a large amount of chemical diluents such as benzene and alcohol, which is very toxic and causes health damage to workers. Long-term exposure to laminating work may cause life-threatening.
During the laminating process, most of the volatiles such as benzene and alcohol are volatilized, but a small part remains in the product and slowly evaporates after being stored and distributed to the reader.
At present, China's film market is still a "prosperous" scene. To talk about the decoration of books and periodicals, we must talk about the filming process. This status quo has its inevitability:
(1) Film products have many advantages. See the role of the film (top part of this article).
(2) After years of development and improvement, film coating 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 laminating process is not high, and the publisher is willing to improve the performance and aesthetics of all aspects of the book through filming. Printing houses and publishing houses can get some benefits from the film.
With the development of science and technology and the strengthening of human environmental awareness, “green environmental protection” will become an inevitable trend in the development of film coating technology. It is certain that in the future development process, the laminating technology will face more and more tests, how will it develop, and how to survive better. These are the problems that cannot be avoided in the development of the laminating process.