Precoat film refers to the pre-plastic film on the plastic rewinding and then printed with the paper composite process. It first by the pre-coated film processing plant according to the use of different specifications of the adhesive coating on the film after the rewinder for the use of manufacturers to choose, and then combined with the printed matter. Film, that is, the film is coated with plastic film adhesive, and paper printed by the heating, pressure together so that together, forming a paper-in-one product processing technology. As a result of the surface of a thin, transparent plastic film, the surface more smooth and bright, so as to improve the gloss and fastness of printed materials, graphic colors more vibrant, rich three-dimensional, but also play a waterproof, Anti-fouling, wear-resistant, folding, resistance to chemical corrosion and so on.
In the pre-coated film process, many factors will be more or less the impact of film quality, here, for you in the pre-filming process affect the quality of the "seven sins." These seven points are: prepress design, paper characteristics, ink characteristics, equipment selection, environmental conditions, film speed and film pressure.
1. Prepress design
In the beginning of print design, it should take into account the film that link, that is, designers in the design of printed matter, should take into account the printed matter in the follow-up printing, printing process which needs to process, what kind of Technology, the choice of what paper and ink.
Books, magazines and other publications cover the use of pre-coated film, the film is often due to insufficient conditions and film, leading to the cover failed. In the cover design, if our designers in the rolling line at the color design is light-colored or even colorless, making the adhesion here exclude ink interference, then there is no problem from the film. Similarly, pre-coated film is not suitable for metal inks, prone to film from the phenomenon. Therefore, for the problem of film, first of all, the designer of the printed product should know how many processing steps the printed product needs to undergo, and what effect each processing procedure will have on the film, and how to avoid such an influence. This requires designers to master the design of printing, bronzing, local UV, rolling line, bump and other processes on the impact of film.
Paper characteristics
Pre-coated film on the paper have certain requirements, due to improper selection of paper, can also cause pre-coated film coating after the bad. According to experience, short fiber tensile strength of the paper is low, in the rolling line or the use of pre-coated film after the film is easy to break, so that the ink along the paper rupture, resulting in local separation of the film and printed material, especially when rolling direction This problem is more likely to occur when the paper is in the same longitudinal direction. In addition, coated coated paper, especially thick coated coated paper, the use of pre-coated film and there is no problem, but if the film after the rolling line, bump and other processes will appear in the rolling line and bump at the film Phenomenon, which is mainly due to coated paper coated with high polymer added less inorganic components and encountered external force when the coating is easy to fall off into powder, so after the film rolling or rolling in the process caused by the pre- The adhesive layer of the coating film is separated from the printing paper.
Another problem with paper is that the surface is too rough, and if the precoated film device used does not have a flattening system, the surface of the retroperitoneal print may be unsightly.
3. Ink selection
In the actual work, often this happens, the same pre-coated film, the same film equipment, the same film process conditions, the two prints have the opposite two results: one is 100% bonding qualified, The other is unqualified. Such a result had to be cause for concern.
A wide variety of printing inks, the performance difference. After years of practice found that the surface properties of the printed ink after the impact of the results of pre-coating a greater impact on the pre-coating film on the ink fastness of the composite or fastness. The need to check the ink surface wetting tension approach to determine the different surface properties of the ink and pre-coating composite fastness, and to detect the problem of film-like proofs. When the ink surface energy at 34dyn / cm or more, the pre-coating film on the ink adhesion is poor, the ink surface energy increased to 38dyn / cm or more, the qualified film products to the normal rolling line and convex.
When the printing ink surface wax precipitation, silicon organic substances or too much mineral oil drying is not sufficient, will lead to printing after the surface can be reduced. Since the binding force between the precoat film and the ink is achieved by attraction between the molecules at a close distance, the adhesion of the precoated film to the ink is small, and the adhesion between the ink and the ink is low. Adhesive layer can only adsorb this layer of material, and can not pass through the layer and the ink in the bonding material combined, resulting in pre-coated film can not be firmly bonded with the print.
Four. Film equipment
In the actual choice of pre-coating equipment, the need to consider many factors, the main points to note:
1. Heating roller temperature uniformity
During the coating process, the surface temperature of the heated roller through which the coated product passes and the non-coated product pass varies greatly, often when the coated temperature is sufficient, and when the coated film is rolled, But from the membrane phenomenon. Since the sensor for detecting the heating roller is fixed to the edge of the heating roller, the temperature seen by the operator is not just the true temperature of the film, which tends to confuse the operator. Therefore, it is preferable to place the induction temperature means at a position close to the intermediate surface.
2. The surface state of the steel drum
Conventional oily film or water-based coating of the roller surface requires the more smooth the better, can make the film after the BOPP gloss better, but such conditions are not appropriate pre-coating. The precoat film requires a roll surface temperature of about 110 ° C, and at such a temperature, the rollability of the film after the film formation deteriorates with the progress of the process. Therefore, the surface of the steel bar used for the precoated film should be finely scratched. The surface condition of the steel drum also requires no pits, drums, scratches and the like.
3. Uniformity of the rubber roller
The homogeneity of the rubber roller mainly includes the outer dimension and the material uniformity.
V. Environmental conditions
For the film environment, mainly related to the plant temperature and humidity changes.
As in the cold winter, films and prints can not be processed immediately after they are transferred from the outside to the inside, and can not be processed until the temperature of the raw materials and the ambient temperature are in balance.
After the completion of the coating, since the moisture can not be evaporated from the film surface, but to the edge of the movement and precipitation, so easy to edge separation of the phenomenon of paper, when the humidity exceeds 90%, such problems will be very prominent.
Six. Film speed
The speed of laminating determines the melting time of the adhesive on the pre-coated film on the heating roller and the contact time of the film and paper, the coating speed is slow, the adhesive time of the adhesive on the BOPP film is relatively long, the film and paper Lamination of a long time, the bonding effect is good, but the production efficiency is low. The speed of film coating, BOPP film adhesive on the heating roller heating time is short, thin film and paper contact time is short, the bonding effect is poor. Therefore, the domestic production rate of pre-coated film coating equipment is generally controlled between 5-30m / min.
7. Film pressure
In fact, the paper surface is not smooth, only in the appropriate pressure, the molten state of the hot melt adhesive to completely cover the surface of the print. If the pressure is small, bonding is not strong; pressure, and easy to produce wrinkles, and easy to make rubber roller surface injury, deformation, reduce the life of rubber roller. And as the pressure increases, the contact pressure between the rubber roller and the heating roller increases, the two rollers of the shaft head, bearing load increases, wear increased, while increasing the load of the transmission system, so the pressure will affect the machine too much Service life.
In actual production, the pressure should be adjusted according to the different paper.
For example, loose paper for the paper, the pressure should be larger, and vice versa smaller. According to experience, film pressure is generally set to 8 ~ 25MPa is appropriate.
In addition, for some special printing materials, such as printing area, ink layer thickness, color depth, paper water content, paper size of the printed matter, we also give them in the film when the temperature, pressure and speed control parameters :
Film temperature: 95 to 105 ° C
Film pressure: 16 a 25Mpa
Coating speed: 5-10m / min
More than seven for the pre-film process to be noted that the technical points to help colleagues in India will be covered with the use of more complete process.
