Lamination of paper prints is one of the steps in post-press processing. Refers to the paper after printing and the adhesive-coated plastic film is bonded together by the pressure of the rubber roller and the electric heating roller to form a paper-plastic product. After the paper printed matter is covered with a film, a thin and transparent plastic film is added to the surface, and the surface of the printed matter appears smoother and brighter, which greatly improves the gloss and fastness of the printed matter, extends the service life of the product, and plays a waterproof, Protection against dirt, abrasion, folds, and chemical corrosion. After the film is printed, the graphic color of the printed product is brighter and more beautiful, and it is more full of three-dimensional texture. Therefore, this process is currently used in many graphic magazines, books, and packaging products.
Brief introduction of laminating process
According to the different raw materials and equipment used, the paper film coating method can be divided into three ways: coated film, pre-coated film, water-based film.
That is, the thin film adhesive used in the coating film process is now coated, and the adhesives used are solvent-based and emulsion-based, which can be formulated at any time. That is, there are many preliminary preparations for the operation of coating the film. The first is the metering of the solvent and solution to make them fully mixed. Then raise the temperature of the drying tunnel of the laminating machine, and then adjust the wind speed, temperature, air volume and the pressure and temperature of the pressing roller in the drying tunnel. After all the preparations are correct, carry out the laminating operation. After the lamination is completed, the laminating machine should be thoroughly cleaned with alcohol. The process flow is: unwinding of plastic film-gluing and coating of glue-drying in drying tunnel-lamination of paper printing products-winding of finished products.
The film used in the pre-coated film process is a rolled film coated with adhesive that is produced and supplied by a special manufacturer. The adhesive used is generally hot melt and solvent volatile. The pre-preparation of the pre-coated film is relatively simple, there is no need to prepare a binder solution, and there is no need to increase the temperature of the drying tunnel. It is only necessary to adjust the pressure, lamination temperature, and lamination speed of the pressure roller to adjust to the best state. The laminating operation can be carried out. Its technological process is: unwinding of plastic film-laminating of paper printing products-winding of finished products.
The water-based film lamination process is a cold lamination operation, and the complexity is between the coated film and the pre-coated film. It does not need a drying tunnel, no need to increase the temperature of the pressure roller and heating roller, as long as the pressure of the pressure roller, the speed of lamination, and the large amount of sizing are controlled
small. After the film is wound up, it can be cut in about 15 minutes. After the laminating is completed, the laminating machine should be cleaned with clean water. The process flow is: unwinding of plastic film-gluing and coating of glue-lamination of paper printing products-winding of finished products.
Laminated machinery
The laminating machinery and equipment are divided into two types: instant coating laminating machine and pre-coating laminating machine.
The composition of instant coating laminating machine includes three parts: gluing, drying and hot pressing. The gluing part is equipped with an adjusting device to adjust the amount of gluing to meet the requirements of different printed parts. The rubber roller is a chrome-plated steel roller. The drying tunnel in the drying tunnel is generally about 2-3 meters long. The opening of the drying tunnel is equipped with an infrared lamp and an electric fan to dry the adhesive and eliminate exhaust gas. The hot pressing part is composed of a rubber roller and a metal roller. The metal roller is hollow, with an electric heating tube inside, and the temperature can be automatically controlled. The pressure of this group of rollers can be adjusted. It is the key part of the film, which is directly related to the adhesion fastness of the product film. Instant coating laminating machine is the most widely used laminating equipment so far.
Pre-coating laminating machine, it has no glue device and drying device, small size, extremely flexible and convenient operation, stable performance and wide range of application, it is not only suitable for laminating processing of large quantities of printed products, but also particularly suitable for automated office Laminating of small batches of printed materials such as systems.
Laminated plastic film
The plastic films commonly used in the laminating process are polypropylene film (PP), polyvinyl chloride film (PVC), polyethylene film (PE), polyester film (PET) and so on.
In order to meet the requirements for the use of printed materials, plastic films should meet the following conditions:
1. The thickness of the film used for laminating is generally from 0 · 01 to 0 · 02 mm, and the appearance should be smooth, without unevenness, wrinkles, bubbles, shrinkage holes, pinholes, pits and other defects.
2. After the corona discharge treatment of the plastic film used for coating, the treatment surface effect should be uniform, the light transmittance should be above 90%, the higher the transparency, the better, to ensure that the printed matter covered has the best clear effect. The surface tension of the plastic film after corona treatment should meet the requirements of the film, and it has good wetting performance and adhesion performance.
3. The film used for coating should have good light resistance, chemical resistance, stable geometric dimensions, and certain mechanical strength properties to ensure that it is not easy to change color under long-term light irradiation, and the geometric dimensions remain stable, while ensuring plastic The film has certain chemical stability in contact with chemicals such as solvents, adhesives, and inks.
4. Most of the plastic films used for coating are non-polar, low-surface-energy, hard-to-stick materials. In addition, due to factors such as poor cleanliness of the surface layer of the plastic film, it is difficult for the plastic film to adhere well to the coated substrate, so the surface of the plastic film must be pre-treated to clean the surface to enhance the adhesive Wetting ability and adhesion ability to the surface of plastic film.
Laminated adhesive
The adhesive used for laminating is the intermediate substance covered by the printed matter and the plastic film, which mainly plays a role of bonding, allowing the organic combination of the plastic film and the paper printed matter. Adhesives are generally composed of main materials and auxiliary materials; the main materials are synthetic resins, synthetic rubbers, natural macromolecules and inorganic compounds; auxiliary materials are used in adhesives to improve the performance of main materials or to facilitate construction. Substances mainly include curing agents, plasticizers, fillers, solvents, etc. The adhesive used for coating is generally a solvent-based adhesive.
That is, in the coating film process, the solvent-based adhesive is used. In the emulsion adhesive, the solid content is 30%-50%, and the remaining 50%-70% are the solvent dispersed phase, the adhesive and the thinning water The proportion of preparation must be strictly controlled. During the laminating process, the adhesive can form a strong bond only after direct volatilization and indirect volatilization.
In the water-based film coating process, water-based (emulsion-type) adhesives using water as a solvent. This water-based (emulsion) adhesive is an organic liquid formed by 55% water or aqueous solution (aqueous phase) and 45% organic phase (oil phase) under the action of an emulsifier. This water-based adhesive is non-toxic, pollution-free, and non-flammable. The main material of this adhesive is limited to polymer resins that can be dispersed in water. Therefore, it requires higher requirements for plastic films and film coating equipment. , And the stability of the adhesion performance is not ideal.
In the pre-coating film laminating process, the adhesive has a melting type and a solvent evaporation type. The pre-coating film is supplied by a special manufacturer. At present, the adhesive layer of the pre-coating film in the domestic market is mainly composed of hot-melt adhesive or polymer low-temperature resin. According to the different processing equipment and process conditions, different thicknesses of adhesive layer films are often selected. The thickness of the adhesive layer is generally between 6 and 15 microns. The hot sol is made by blending and modifying several materials such as main tackifier resin, tackifier, regulator, etc. The organic polymer resin is a single polymer low-temperature copolymer. Since the hot melt adhesive is composed of a mixture of several materials, the transparency of the printed product after film coating is significantly lower than that of the low-temperature pure resin-based pre-coated film.
The main points of the control of laminating process operation
Paper-plastic lamination is the comprehensive result of the physical function of thermocompression bonding, and the lamination temperature, lamination pressure, and lamination speed are the basic conditions for achieving this physical synthesis. Correctly handling the film temperature, film pressure, and film speed is essential to ensure the quality of the film and bring a good operating interface to the next process.
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