The pre-coating film coating film is a paper-plastic product formed by bonding a pre-coated adhesive film with a pressure and a heat of a rubber roller and a heating roller, and adhering to a paper product.
The process flow of pre-film coating is roughly as follows: paper feeding at the feeding station→printing film press→recovering the finished product.
Pre-film preparation
(1) The thickness of the BOPP film used for laminating should generally be between 0.01 and 0.02 mm, the transparency should be above 90%, and the heat shrinkage rate should be small.
(2) Before applying the machine, check whether the BOPP film is in the shelf life, whether the coating layer on the film is even and whether the surface is scratched or crushed. The adhesive surface of the film passes through the heating roller and faces the print.
(3) The rubber roller and heating roller must be kept clean, and the pressure balance rollers on both sides must be flexible.
(4) Adjust and determine the gap of the paper feed roller according to the paper thickness.
(5) Select BOPP film with different width according to the product size, and adjust the side gauge according to the requirements of the product.
(6) Adjust the guide roller so that the tension on both sides of the film is the same, and the surface of the film is flat and free from wrinkles.
Pre-coated film coating process control points
The key technologies of the precoating film coating process are mainly the control of the coating temperature, the coating pressure and the coating speed.
1. Film temperature Temperature is the primary factor for film lamination because the adhesive on the film is a hot melt adhesive. The temperature determines the melting state of the hot melt adhesive and determines the hot melt adhesive to BOPP film and prints. Infiltration capacity and diffusion ability of ink layer, paper, etc. Although the increase in film temperature contributes to the enhancement of the bond strength, excessively high temperatures will cause shrinkage of the film, and the surface of the product will be shiny and blistering, causing the product to wrinkle. According to practical experience, the film temperature should be controlled between 70 ~ 100 °C.
2. Lamination pressure The surface of the paper is not even. Only under the appropriate pressure, the hot-melt adhesive in the molten state can completely cover the surface of the printed product. The film-covered product is bright and has good bonding effect. The pressure is small and the adhesiveness is not strong; the pressure is higher, which helps to improve the binding force between the film and the paper product. However, if the pressure is too high, it is easy to make the product wrinkle, and it is easy to make the surface of the rubber roller injure and deform and reduce the service life of the rubber roller. With the increase of pressure, the contact pressure between the rubber roller and the heating roller is increased, the axle head and bearing load of the two rollers are increased, the wear is aggravated, and at the same time, the load of the transmission system is aggravated, so too much pressure will affect the whole machine. Service life.
In actual production, the pressure should be adjusted according to the different paper. For example, for paper with loose paper, the pressure is greater, and vice versa. According to experience, the film pressure is generally set to 8 ~ 25MPa is appropriate.
3. Coating speed The speed of the coating speed determines the melting time of the adhesive on the pre-coated film on the heating roller and the contact time between the film and the paper. With slow lamination, 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 film coating 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 adhesive effect is poor. The production speed of domestic pre-film coating equipment is generally controlled between 5 and 30 m/min.
Above the three key technologies in the pre-coating film coating - the coating temperature, the coating pressure and the coating speed have been simply analyzed, but the adjustment coordination between the three should be based on the different equipment used, film Different types of products and different types of films used are flexible, and only in this way can high-quality coated products be obtained.
4.Special Print Film Parameters Control Special prints are printed materials with large printing area, thick ink layer, deep color, large paper moisture content, and large paper size. When laminating such prints, the lamination parameters are generally controlled as follows.
Film temperature: 95~115°C
Film coating pressure: 16～25Mpa
Film speed: 5 ~ 10m/min
Other factors affecting film quality
1. Ink It is necessary to use a pre-film coated product. It is best to use bright light and fast dry ink for printing. However, it is not appropriate to put more catalyst when using it, otherwise the surface of the ink layer will crystallize. In addition, ink viscosity, oil content, etc. will affect the coating effect.
2. Application of Adhesives The adhesive layer on the BOPP film is required to be thin and uniform. Under the premise of ensuring firm bonding, the precoat film with thinner adhesive coating should be selected as far as possible, otherwise it will affect the melting effect.
Laminated film common problems and solutions
1. The product has a snow point (1) The rubber roller pressure is not enough and the pressure should be increased appropriately.
(2) The glue on the precoat film is not completely melted and can be solved by the following method.
1 properly increase the film temperature.
2 increase the contact area between the film and the heating roller, so that at the same speed of the adhesive on the film to increase the degree of heating.
3 reduce the film speed.
(3) Dust and impurities on the coating surface of the precoat film shall be promptly removed.
2. The product is wrinkled (1) The pressure of the rubber roller is so great that the film is deformed and the pressure should be reduced appropriately.
(2) The surface of the rubber roller is damaged and uneven, and the rubber roller should be replaced.
(3) The pressure imbalance between the rubber roller and the heated roller should be properly adjusted.
(4) The tension on both sides of the film is inconsistent, or there are wavy edges. Replace the film material.
3. Product curl after slitting (1) If the film tension is too large and the film is stretched and deformed, adjust the tension screw to the film.
(2) The winding tension is large, so that the film and the paper are deformed simultaneously, and the winding tension mechanism should be adjusted.
(3) The humidity in the environment should be controlled at about 60% in the production workshop.
(4) The drying time is short, and the drying time should be appropriately extended. After the film product is completely dried and cooled on the winding roller, the film is cut.
4. Insufficient bonding, stripping (1) The pre-painted film exceeds the shelf life, replace the new pre-coated film.
(2) The ink layer of the printed matter is not dry, and the drying time of the printed matter should be extended, especially when laminating special prints.
(3) With low film pressure, high speed, and low temperature, the film pressure can be appropriately increased, the film speed can be reduced, and the film temperature can be increased.