Pre-coated film is the process of pre-gluing and rewinding plastic film and then laminating it with paper prints. It is first applied by the pre-coated film processing factory according to the use of specifications and width, the glue is coated on the film rewinding for the use of manufacturers to choose, and then laminated with printed materials. Laminating, or laminating, is a processing technology in which plastic film is coated with adhesive and bonded with paper printed materials after heating and pressure to form a paper-plastic product. By the lamination of printed materials, due to the surface of a thin and transparent plastic film, the surface is smoother and brighter, thereby improving the gloss and fastness of the printed materials, the graphic color is more vivid, three-dimensional, while more waterproof, stain-resistant, wear-resistant, folding, chemical corrosion resistance.
It consists of a substrate and adhesive adhesive layer, usually a polyester (PET) film and a biaxially oriented polypropylene (BOPP) film. BOPP film has the characteristics of high transparency, good brightness, non-toxic and odorless, water resistance, heat resistance, low price, soft texture, etc., and is an ideal material in the lamination process, with a thickness of about 12-20um. The thickness of the adhesive layer is 5-15um. Therefore, from the perspective of material cost and processing technology, most of the pre-coated film substrates use BOPP films. According to the different processing equipment and process conditions, different thicknesses of adhesive layer will be selected. The adhesive layer is divided into hot melt adhesive and organic polymer low temperature resin, the difference between the two is: hot melt adhesive is made of the main adhesive resin and tackifier, regulator and several kinds of material blending modification, while the organic polymer resin is a single polymer low temperature copolymer.
(1) The film thickness is between 0.01-0.02mm, and the surface tension should reach 4.0 x 10-2N/m after corona or other methods of treatment in order to have better wetting performance and adhesion performance.
(2) The film corona treatment surface is uniform and consistent, and the higher the transparency, the better, to ensure the best clarity of the covered print.
(3) The film should have good light resistance, not easy to change color under prolonged exposure to light, and the geometric size should remain stable
(4) The film should be in contact with solvents, adhesives, inks and other chemical substances, and the film should have a certain chemical stability.
(5) The appearance of the film should be flat, without unevenness and wrinkles, without bubbles, shrinkage holes and pockmarks and other defects.
Factors affecting pre-coated films：
1. Temperature
It is the first key to lamination, the adhesive used for pre-coating film is hot melt adhesive, the temperature determines the melting state of hot melt adhesive, determines the leveling performance of hot melt adhesive, determines the diffusion ability of hot melt adhesive molecules to BOPP film, printing ink layer, paper substrate and other three substances between molecules, and also determines the crystallinity of hot melt adhesive, only the correct control of the temperature of the working area, in order to make the pre-coating film on the film solid Hot melt adhesive layer thoroughly melted into a viscous flow state, with suitable fluidity to achieve wetting and bonding of the printed surface, while ensuring immediate curing after lamination, so that the composite film products to achieve a flat appearance, bright enough, good degree of melting of the adhesive layer, no creases. And can be stripped of ink. The temperature control of the laminating process also affects and determines the change when the hot melt adhesive for laminating is solved by heat, and the strength of resistance to the new heat. Therefore, strict control of temperature is the primary key to pre-coated film lamination. According to our practice. Temperature control in the range of about 80 to 100 ℃ is more appropriate.
2. Pressure
In the correct control of the laminating temperature at the same time should also use the appropriate pressure, because the surface of the paper itself is not very flat, only under pressure, the viscous flow state of the hot melt adhesive will be in the process of driving away the air on the surface of the printed material fully wetted paper printed surface.
Produce colloidal molecules to the paper print ink layer, paper molecules between the diffusion, dislocation, to achieve good bonding, the formation of a complete coverage of the entire surface of the print, so that the print to bright, non-foggy, glue layer flow flat, no crease, good bonding effect, in the case of no crease, the appropriate increase in pressure, in order to make the thermoplastic curing function of hot melt adhesive can be fully expressed to ensure that the laminate products in the composite and then add The process, the impact of various physical stripping, impact forces and other influences have a strong resistance, (such as indentation, hot stamping, etc.) to achieve a perfect unified speed of the internal structure and surface state of composite printed products.
3. Speed
Paper surface lamination is a composite movement in the dynamic process, its movement speed determines the paper-plastic composite in the hot pressing body in the hot pressing work interface stay time, also determines the input temperature and pressure of the laminating machine and in the actual production process on the actual value of the paper-plastic composite knot out. When the laminating temperature and pressure is fixed, the change of speed will make the laminating effect change, and because of the upper limit of temperature and pressure supply, only by less than the set value of the direction of change, and with the speed of speed, the drop is obvious, the decline in the force of hot pressing, so that the composite effect deteriorates, running speed is too fast, bonding is not firm, there will be fog, too slow is not efficient, or even blistering. So composite running speed, determine the time to achieve bonding of pre-coated film and paper printed materials. According to our experience, the general speed control in the folio paper a minute about 10-20 sheets more appropriate. (Electronic laminating machine speed due to the hot press cylinder is small, the speed should be slower).
