The control of the quality of printing products in various process links of window coating

Window mulching is a special kind of mulching technology, which not only has the advantages of mulching products, but also makes the packaged goods visible. Mainly used in carton packaging, in the food, medicine, light industrial products, in the export of goods is increasingly widely used in packaging. In actual production, due to a variety of uncertainties, product quality fluctuates greatly, and defects such as blistering, stripping, wrinkles, snow spots, aprons, and roll paper are prone to occur.

After the window is opened, the printed matter is coated with glue by a coating roller along the paper path, and the laminating process is completed by pressing the upper and lower pressure rollers together with the plastic film. There are two differences in the working principle. In the process of window coating, all aspects may affect the quality of finished products.

(1) The adhesive is first applied to the printed surface of the printed product, and then the plastic film is covered on the surface of the printed product, and finally pressed into a finished product.

(2) Window coating is performed on a print with a window.

printed matter

(1) If the ink on the surface of the printed matter is too thick or is not dry, the coated adhesive cannot normally penetrate through the pores between the ink layer and the paper to cause a false bond, resulting in the finished film. Blisters in a short time.

(2) It is unavoidable to use chemical liquids during the printing process, and it is easy to change the surface structure of the paper so that the adhesive does not make good contact with the paper, causing the product to foam after being left for a long time.

(3) The surface of the film print is dried to the initial dryness, and the thickness is about 0.002 to 0.003mm. Therefore, if the dust on the substrate is too thick, the thin film will appear on the product due to the false pressure on the film. spot.
(4) After the product is printed, it should be stored for a period of time to facilitate the volatilization of the paper moisture. Otherwise, after the film is coated, as the moisture evaporates, the paper fiber shrinks, causing wrinkling of the film.

(5) The high surface roughness of the printed matter will affect the flowability (leveling and spreading) of the adhesive, resulting in uneven application of the adhesive, and the occurrence of bright spots or “fogging” on the surface of the product after the film is covered.

(6) Prints with poor flatness are liable to wrinkle when they are covered with film, and due to unevenness of the paper, the adhesive cannot be evenly coated on the paper, resulting in phenomena such as release and blistering.

Adhesive

1. Adhesive viscosity

If the viscosity of the adhesive is too high, the fluidity and wettability of the adhesive will be reduced, and the adhesive coating will not be uniformly applied, resulting in the coating layer becoming flowered, and the coating layer will produce snow spots. At the same time, during the coating process, excessively high viscosity makes it easy for prints to stick on the coating roller (coil roller) and is rolled up with the rotation of the coating roller. If the viscosity of the adhesive is too low, the solvent in the adhesive cannot be fully volatilized in the drying process, so that the solid content of the adhesive is reduced, and the phenomenon that the film is not strong, film peeling, blistering, etc. easily occurs.

2. Thickness of adhesive coating layer

If the amount of adhesive applied is too small and the thickness is too thin, the adhesive force will be insufficient and the film will easily fall off. However, if the coating layer is too thick, the effect is even worse. For example, the volatilization of the solvent in the adhesive is slowed down, and the product is easily foamed after being placed; the moisture content of the paper is affected, and the paper fiber shrinks and folds at the window opening. Even squeeze out the apron at the window. All of these can cause fatal damage to the quality of the coating.

3. Mixing ratio of adhesive and thinning water

The proportion of adhesive and thinning water must be strictly in accordance with the requirements of the film and adhesive, otherwise it will result in poor adhesion.

film

Because the essence of the film is to bond the printed matter and the plastic film together with the adhesive, the quality of the film is not only related to the nature of the adhesive, but also has a close relationship with the surface properties of the plastic film. Enhancing the surface roughness of the plastic film, improving its surface crystallinity, increasing the cohesive strength of the surface layer, or removing the weak surface layer can effectively improve the film quality. In addition, since the film is subjected to a mechanical force during the film coating process, it must have a certain mechanical strength and flexibility. If the film is too soft, wrinkles are easily generated during the pressing process.

Drying temperature

If the temperature of the drying tunnel is too low, the solvent in the adhesive cannot be fully volatilized, which will affect the fastness of the coating film, and it is easy to produce blisters and release film. The temperature of the drying tunnel is too high, and the surface after coating may produce many folds.

Lamination

1. Pressing pressure

The large pressure helps to improve the adhesion of the film and the print, but the pressure is too large to cause the plastic film to deform and wrinkle, and it is easy to squeeze out the apron at the window opening. And because the bottom of the floor has a window, so the floor will inevitably be uneven force, the window will have a stress change, the plastic film is easy to wrinkle. If the pressure is too low, the adhesion is not strong and it is easy to produce release film. The uneven pressure on the left and right sides of the lamination roller can easily cause deformation and wrinkling of the film.

2. Film speed

The filming speed is affected by the pressure of the pressing force. If the pressure is large, the filming speed can be appropriately faster, but if the filming speed is too high, the time for pressing the paper and the plastic film becomes shorter and the adhesion is liable to be caused.
Use raw materials rationally.