The pre-coating film coating is to bond the pre-coated film with the adhesive to the paper product after being pressed and heated by the rubber roller and the heating roller to form a paper-plastic bond.
Preparation before lamination
(1) The thickness of the BOPP film used for lamination should generally be between 0.01 and 0.02mm, the transparency should be above 90%, and the thermal shrinkage should be small.
(2) Before putting on the machine, you should check whether the BOPP film is within the shelf life, whether the coating layer on the film is uniform, and whether the surface is scratched or crushed. The glued side of the film is passed through the heated cylinder and faces the print.
(3) The rubber roller and heating roller must be kept clean, and the pressure balance rollers on both sides must rotate flexibly.
(4) Adjust and determine the gap between the feeding rollers according to the thickness of the paper.
(5) Select BOPP films of different widths according to the product size, and adjust the side gauges according to the requirements of the product.
(6) Adjust the film guide roller so that the tension on both sides of the film is consistent, and the surface of the film is flat and wrinkle-free.
Key points of pre-coating and laminating process control
The key technologies of the pre-coating lamination process are mainly the control of lamination temperature, lamination pressure and lamination speed.
1. Lamination temperature
Temperature is the primary factor for pre-coating film lamination, because the adhesive on the pre-coating film is a hot melt adhesive, and the temperature determines the melting state of the hot melt adhesive, which determines the direction of the hot melt adhesive molecules to BOPP film, printed ink layer, paper, etc. penetration and diffusion capacity. Although the increase of the lamination temperature helps to enhance the bonding strength, the excessive temperature will cause the film to shrink, the surface of the product will be shiny and blistered, and the product will be wrinkled. According to practical experience, the coating temperature should be controlled between 70 and 100 °C.
2. Lamination pressure
The surface of the paper is not smooth, only under the appropriate pressure, the hot melt adhesive in the molten state can completely cover the surface of the printed matter, and the lamination product will be bright and the bonding effect is good. Smaller pressure will lead to weaker bonding; higher pressure will help to improve the bonding force between film and paper products. However, if the pressure is too large, it is easy to make the product wrinkle, and it is easy to damage and deform the surface of the rubber roller, reducing the service life of the rubber roller. As the pressure increases, the contact pressure between the rubber roller and the heating roller increases, which increases the load on the shaft heads and bearings of the two rollers, increases the wear, and increases the load on the transmission system. Therefore, too much pressure will affect the whole machine. service life.
In actual production, the pressure should be adjusted according to the paper. For example, for loose paper, the pressure is greater, and vice versa. According to experience, the film pressure is generally set to 8-25MPa.
3. Lamination speed
The speed of lamination determines the melting time of the adhesive on the pre-coated film on the heated roller and the contact time between the film and the paper. The lamination speed is slow, the heating time of the adhesive on the BOPP film is relatively long, the lamination time of the film and the paper is long, and the bonding effect is good, but the production efficiency is low. The lamination speed is fast, the heating time of the adhesive on the BOPP film on the heating roller is short, the contact time between the film and the paper is short, and the bonding effect is poor. The production speed of domestic pre-coating and laminating equipment is generally controlled between 5 and 30 m/min.
The above three key process technologies in pre-coating film coating – coating temperature, coating pressure and coating speed are briefly analyzed, but the adjustment and cooperation between the three should be based on the different equipment used, coating The actual situation of the different types of products and the types of films used can be flexibly grasped, and only in this way can high-quality lamination products be obtained.
4. Parameter control of lamination for special printed matter
Special printed matter refers to the printed matter with large printing area, thick ink layer, dark color, large paper moisture content and large paper size. When laminating such prints, the lamination parameters are generally controlled as follows.
Lamination temperature: 95～115℃
Lamination pressure: 16～25Mpa
Lamination speed: 5～10m/min
Other Factors Affecting Lamination Quality
1. Ink
For products that need to be pre-coated and coated, it is best to use bright and fast-drying ink for printing, but it is not advisable to put more catalysts in use, otherwise the surface of the ink layer will crystallize. In addition, the difference in ink viscosity and oil content will affect the lamination effect.
2. Coating situation of adhesive
The adhesive layer on the BOPP film is required to be thin and uniform. On the premise of ensuring firm adhesion, a pre-coating film with a thinner adhesive coating should be selected as much as possible, otherwise the melting effect will be affected.
Problems and solutions in the production
1. Snowflakes appear on the product
(1) The pressure of the rubber roller is not enough, and the pressure should be increased appropriately.
(2) The glue on the pre-coating film is not completely melted, which can be solved by the following methods.
① Properly increase the coating temperature.
②Increase the contact area between the film and the heating roller, so that the heating and melting degree of the adhesive on the film increases at the same speed.
③ Decrease the lamination speed.
(3) There is dust and impurities on the glued surface of the pre-coating film, which should be removed in time.
2. The product appears wrinkled
(1) The pressure of the rubber roller is too large, causing the film to deform, and the pressure should be appropriately reduced.
(2) The surface of the rubber roller is damaged and uneven, and the rubber roller should be replaced.
(3) The pressure between the rubber roller and the heating roller is unbalanced and should be adjusted appropriately.
(4) If the tension on both sides of the film is inconsistent, or there are wavy edges, the film material should be replaced.
3. The product is curled after slitting
(1) The tension of the film is too large, causing the film to stretch and deform, so the tensioning screw for the film should be adjusted.
(2) The winding tension is large, which deforms the film and paper at the same time, and the winding tensioning mechanism should be adjusted.
(3) The ambient humidity is high, and the humidity in the production workshop should be controlled at about 60%.
(4) The drying time is short, and the drying time should be appropriately extended. After the coated product is completely dried and cooled on the winding roller, the film is cut and cut.
4. The adhesion is not strong and the film is released
(1) If the pre-coating film exceeds the shelf life, replace it with a new pre-coating film.
(2) When the ink layer of the printed matter is not dry, the drying time of the printed matter should be extended, especially when laminating special printed matter.
(3) The coating pressure is small, the speed is fast, and the temperature is low. The coating pressure can be appropriately increased, the coating speed can be reduced, and the coating temperature can be increased.
