Concept and function of film covering and troubleshooting

一、 Concept and function of film covering

1. The concept of lamination lamination, which can also be called plastic lamination, glue mounting and film pasting, is a post press processing process in which a transparent plastic film is pasted to the surface of a print by hot pressing to form a film with a thickness of 10 ~ 20um.

There are two cases of film covering:

(1) After printing pictures and texts on the surface of the plastic film, it is covered with paper.

(2) After printing pictures and texts on paper, a layer of plastic film is covered on it.

This paper mainly discusses the second case.

2. Function of film covering

(1) Protect the printed matter from wear and tear.

(2) It can make up for the quality defects of printed matter.

(3) Increase the strength of prints, such as puncture strength, tensile strength, etc.

(4) Extend the storage time of prints. For example, the photos will not fade and remain yellow after plastic packaging, which increases the storage life.

(5) Increase the gloss of the printed matter and make the pattern color more bright and full.

二、 Film covering process and quality inspection method

The film covering process is carried out according to the following steps:

1. Preparation.

(1) Check the printed matter to be coated. The inspection contents include:

① Whether the ink is sufficiently dry.

② Whether the printed matter is flat.

③ Whether there is powder spraying on the surface. The addition of dusting can solve the problem of rubbing dirt on the back of the printed matter, but dusting 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 coarse particles float on the surface of the printed matter, and the adhesive is bonded with this layer of powder during coating, resulting in false adhesion and affecting the coating quality. Therefore, if the film is coated, attention should be paid to controlling the amount of powder sprayed.

(2) Select film.

(3) Choose an adhesive.

2. Install the film drum.

Cut the drum into appropriate format and then put it 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 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. Film pressing.

Pay attention to control the hot pressing temperature and the pressure between the rollers. The temperature is too low, the coating is not firm, and it is easy to delaminate. When the pressure is too high, the paper surface is slightly uneven or the film tension is inconsistent, there will be wrinkles or stripes.

6. Slitting and finalization.

After the sample meets the test standard, it can be cut and finalized. There are often some quality problems after the printed matter is coated. In order to find problems before the product flows into the market, it needs to be inspected in advance. The inspection methods are as follows:

1. Knead.

Knead the film covered sample 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 sheet, and the ink layer should be attached to the film, or tear the paper base.

3. Pressurize.

Press the sample with a relief press, and there should be no whitening.

4. Heating.

Place the sample in a high temperature environment of 65 degrees, and it should not peel off, blister or wrinkle.

5. Immerse in water.

After immersing the sample sheet in constant temperature water for about 1 hour, there should be no separation between the film and the printing paper.

三、 Faults and Solutions

1. Crack and treatment of indentation line after coating

Lamination can improve the folding resistance of the surface of the printed matter, which has a good protective effect on the printed matter. However, if the quality of the plastic film is poor, there will be indentation line cracking during indentation, which will not only affect the appearance, but also fail to play the role of the film. Generally speaking, cracking only occurs in the film layer, and the underlying paper generally will not break.

terms of settlement:

(1) Replace with film raw materials with better quality and folding resistance.

(2) Change the paper direction of the lamination.

(3) Modify the die cutting version.

2. Peeling

The cover of a book or the surface of a paper with a large printing surface often breaks away from 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 film coating is difficult to evenly wet, resulting in weak bonding. It is necessary to check whether the glue has quality problems, whether it is in accordance with the technical indicators of the glue during the operation, or replace the glue with a more suitable viscosity, increase the amount of glue, and also increase the printing pressure.

(2) The diluent has problems because the alcohol and water contained in it cause the hydroxyl group not to react. The solution is to replace high-purity ethyl acetate.

(3) If the film has quality problems or the surface treatment is not enough, 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 printed matter is not dry, it should be hot pressed before gluing, or choose an adhesive with high solid content to increase the coating thickness.

(6) When the film is dried, improving the humidity of the surrounding environment and increasing the drying time are conducive to improving the film quality.

3. Tensile deformation of film

For the phenomenon of film tensile deformation, the following aspects can be solved:

(1) Reduce the amount of glue. Because if the amount of gluing is too large, the paper will still absorb the moisture in the glue after covering the film, resulting in expanded deformation. After drying, the film will stretch and deform under the influence of the paper with larger sizing. Therefore, on the premise of ensuring the product quality, the amount of gluing should be reduced as much as possible.

(2) The smaller the tension, the better. Film and paper have different properties and strong deformation ability.

(3) During the transfer process of the product, the temperature and humidity of the external environment will change greatly, and the thermal expansion and cold contraction will also cause the deformation of the film.

4. There are bubbles between paper and film

The causes and solutions are as follows:

(1) If the printing ink layer is not completely dry, the solution is: press the printed matter hot and then glue it, or postpone the film covering date.

(2) The printing ink layer is too thick, which makes it difficult for the paper and film to fit together. The coating amount of adhesive can be appropriately increased, and the pressure and composite temperature can be increased.

(3) Top paper. There are bubbles at the lap of the two sheets of paper because the front and back sheets of paper are pressed together when laminating. Bubbles will appear in the gap between them after the film is applied. Pressure or more glue should be applied at the top of the 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 drying and compound roll temperature should be reduced.

(5) The film itself is uneven or curled. Replace the film or adjust the tension.

(6) Dust and impurities on the film surface should be removed in time.

(7) The amount of adhesive is small or the coating is uneven (if the adhesive is too thick, it is not easy to apply evenly). The coating amount and uniformity should be improved.

(8) Printed matter has ruffles. The printed matter with ruffles should be humidified or scattered to dry.

5. Film wrinkling and edge warping

Wrinkling may be caused by the following reasons:

(1) The film tension is inconsistent due to the imbalance of the film transfer roll or the imbalance between the two ends of the electric heating roll and the rubber roll, and the unequal linear speed. It should be adjusted to balance.

(2) The film is uneven, such as inconsistent tightness at both ends or wavy edges. Replace the qualified film.

(3) There is sliding between the paper and the film. This may be caused by the thick adhesive layer. Adjust the gluing amount or increase the drying speed. Main causes and suggestions of edge warping fault:

(1) Film carrier is too thin: film covering should be avoided for too thin paper.

(2) Tension imbalance: adjust the film tension.

(3) The composite pressure is too high and the temperature is too high. The composite pressure and temperature should be appropriately reduced.

(4) The tension of the film is too large (including the winding tension). The film has anelastic deformation, causing the product to curl to one side of the film. The solution is to adjust the screw depth of the film feeding expansion screw and reduce the winding tension.

(5) Film covered products will curl if they are not fully dried. The solution is to control the humidity of the workshop and extend the drying time.