Laminating technology is a post-press processing technology that is currently receiving much attention. It has many advantages and many problems. It is widely used, but the prospects are not optimistic.
1. The concept and function of film
1. The concept of lamination Lamination is also called over-plastic, laminating, and sticking. It is a post-printing process in which a transparent plastic film is applied to the surface of a printed product by hot pressing to form a film with a thickness of 10-20um.
Two cases of lamination:
(1) After printing graphics on the surface of the plastic film, cover it with paper.
(2) After printing graphics on the paper, overlay a layer of plastic film on it.
This article mainly discusses the second situation.
2. The role of film
(1) Protect printed matter from abrasion.
(2) It can make up for the quality defects of printed matter.
(3) Increase the strength of printed products, such as piercing strength and tensile strength.
(4) Extend the storage time of printed products. For example, after the photo is sealed, it will not fade or turn yellow, which will increase the shelf life.
(5) Increase the gloss of the printed matter and make the pattern color brighter and fuller.
2. Laminating process and quality inspection methods
The laminating process is carried out as follows:
1. Preparation.
(1) Check the printed matter to be coated. The inspection content includes:
â‘ Whether the ink is sufficiently dry.
â‘¡Whether the printed matter is smooth.
â‘¢ Whether there is dust on the surface. The addition of powder spray can solve the problem of dirt on the back of the printed matter, but the powder spray will form an irreversible cushion on the surface of the ink layer, thereby reducing the viscosity of the paper. If too much powder is sprayed during the printing process, these coarser particles will float on the surface of the printed product, and the adhesive will adhere to this layer of powder sprayed during the coating, which will cause false sticking and affect the quality of the coating. Therefore, if the film is covered, attention should be paid to control the amount of powder sprayed.
(2) Select the film.
(3) Choose the adhesive.
2. Install the film reel.
After cutting the reel into a suitable format, start 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 in the adhesive and retain the solid content of the adhesive. When the dryness of the adhesive layer reaches 90-95%, the bonding force is the largest.
5. Lamination.
Pay attention to control the hot pressing temperature and the pressure between the rollers. If the temperature is too low, the coating is not strong, and it is easy to delaminate. When the pressure is too large, the paper surface is slightly uneven or the film tension is inconsistent, it will produce wrinkles or stripes.
6. Slitting and shaping.
After the sample meets the test standard, it can be cut and shaped. Some quality problems often occur after the printed matter is covered with film. In order to find the problem before the product flows into the market, you need to check in advance. The inspection methods are as follows:
1. Rub it. Rub the film proofs back and forth back and forth, there should be no separation or blistering between the film and the paper.
2. Tear off. Peel and tear off the film layer of the proof, the ink layer should be attached to the film, or tear the paper base.
3. Pressurize. Use a letterpress printing machine to press the sample, there should be no whitish phenomenon.
4. Heat up. Place the proof sheet in a 65-degree high-temperature environment and bake it without peeling off, blistering or wrinkling.
5. Soak in water. After soaking the sample in normal temperature water for about 1 hour, there should be no separation between the film layer and the printing paper.
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3. Faults and solutions
1. Cracking and treatment of indentation line after coating
Laminating film can improve the folding resistance of the surface of the printed matter, and has a good protective effect on the printed matter, but if the quality of the plastic film is poor, the indentation line cracks will occur during the indentation, which not only affects the appearance, but also does not play the film Due role. In general, cracking only occurs in the film layer, and the bottom paper generally does not break.
Solution:
(1) Change to a film material with better quality and better folding endurance.
(2) Change the paper feeding 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 printing surface often appears to be covered with a film to separate from the paper. There are several reasons and solutions:
(1) Because the ink layer on the surface of the printed matter is thick, it is difficult to evenly wet the glue used for the film, resulting in poor adhesion. It is necessary to check whether the glue has quality problems, whether it is in accordance with the technical specifications of the glue during the operation, or change the viscosity Suitable glue, increase the amount of glue, can also increase the printing pressure.
(2) The diluent is problematic because the alcohol and water contained in it cause the hydroxyl groups to not react. The solution is to replace high-purity ethyl acetate.
(3) If the film has quality problems or insufficient surface treatment, the film should be renewed.
(4) There is dusting on the surface of the printed matter. Wipe it off with a dry cloth.
(5) The ink layer of the printed matter is not dry, it should be hot pressed once before gluing, or choose a high solid content adhesive to increase the coating thickness.
(6) When the film is dried, increase the humidity of the surrounding environment and increase the drying time, which is conducive to improving the quality of the film.
3. The film is stretched and deformed
For the film stretching deformation phenomenon, it can be solved from the following aspects:
(1) Reduce the amount of glue. If the amount of glue is too large, the paper still absorbs the moisture in the glue after the film is coated, resulting in expanded deformation. After drying, the film is stretched and deformed by the larger paper, so under the premise of ensuring product quality , Should minimize the amount of glue.
(2) The smaller the tension during film and winding, the better. The properties of film and paper are different, and the deformability is strong.
(3) During the transfer of the product, the temperature and humidity of the external environment change greatly, and the thermal expansion and contraction will also cause the deformation of the film.
4. There are bubbles between the paper and the film
The causes and solutions are as follows:
(1) The printing ink layer is coated before the film is completely dried. The solution is to heat-press the printed product and then apply the glue. The coating date can also be postponed.
(2) The printing ink layer is too thick, and the paper and the film are difficult to close together. It is possible to increase the coating amount of the adhesive, increase the pressure and compound temperature.
(3) Top paper. There is air bubbles at the overlap of the two papers because the two papers are pressed together when laminating. Bubbles will appear after the film is applied to the gap between them. Should pressurize or apply more glue at the top paper to fill the gap.
(4) The drying temperature or the surface temperature of the composite roller is too high, and the surface of the adhesive is skinned. The temperature of drying and compound rolls should be reduced.
(5) The film itself is uneven 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 dosage of the adhesive is small or the coating is uneven (such as the adhesive is too thick, it is difficult to coat evenly). The coating amount and uniformity should be improved.
(8) The printed matter has ruffles. The printed matter with ruffles should be humidified or spread out to dry.
5. The film is wrinkled and warped
Wrinkling may be caused by the following reasons:
(1) The film transfer roller is unbalanced or the electric heating roller and the rubber roller are unbalanced, and the linear speed is not equal, which causes the film tension to be inconsistent. Should be adjusted to balance.
(2) The film is uneven, such as inconsistent tightness at both ends or wavy edges. Qualified film should be replaced.
(3) There is slippage between the paper and the film. This may be caused by too thick glue layer. Should adjust the amount of glue or increase the drying speed. The main reasons and suggestions for the edge curling failure:
(1) The film carrier is too thin: Too thin paper should avoid laminating as much as possible.
(2) Unbalanced tension: adjust film tension.
(3) The compound pressure is too high and the temperature is too high. The compound pressure and temperature should be reduced appropriately.
(4) The tensile force on the film is too large (including rewinding tension). The film is elastically deformed, causing the product to curl to the side of the film. The solution is to adjust the screw-in depth of the screw for tightening the film and reduce the winding tension.
(5) The film-coated product will not be fully dried and will curl. The solution is to control the humidity in the workshop and extend the drying time.
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4. Future prospects
The environmental protection problem can be said to be one of the biggest problems currently existing in the laminating process. Film pollution mainly includes workers' health pollution, environmental pollution, and "white pollution" caused by waste.
In order to save costs, many laminating factories introduce oil-based laminating machines. The glue contains a large amount of chemical thinners such as benzene and alcohol, which are highly toxic and cause health damage to the staff.
During the lamination process, most of the volatiles such as benzene and alcohol are volatilized, but a small amount remains in the product, and slowly volatilizes after being stored and circulated to the reader.
At present, China's film market is still a scene of "prosperity", to talk about the decoration of books and periodicals, we must talk about the process of film. This status quo has its inevitability:
(1) Laminated products have many advantages. For details, see the role of lamination (the previous part of this article).
(2) After years of development and improvement, the laminating equipment and technology have become quite mature.
(3) The laminating machine is cheaper and the printing plant is willing to introduce it. The cost of the lamination process is not high. The publisher is willing to improve the performance and aesthetics of all aspects of the book through lamination. Both printing houses and publishing houses can obtain certain benefits from lamination.
With the development of science and technology and the enhancement of human awareness of environmental protection, "green environmental protection" will become an inevitable trend in the development of laminating processes. To be sure, in the future development process, the lamination technology will face more and more tests, how will it develop, and how can it survive better, these are problems that cannot be avoided in the development of the lamination process.
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