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Introduction to Printing and Lamination

        The film covering effect is not only related to the film covering raw materials and film covering operation methods, but also related to the ink layer condition of the pasted printed matter. The condition of ink layer of printed matter is mainly determined by the nature of paper, ink performance, ink layer thickness, graphic area and integrated density of printed graphic.Introduction to Printing and Lamination

        These factors affect the formation conditions of bonding mechanical adhesion and physical-chemical adhesion, resulting in the change of surface adhesion of printed matter.Introduction to Printing and Lamination 

Introduction to Printing and Lamination

       Ink layer thickness of printed matter. Field printed matter with thick ink layer is often difficult to bond with plastic film, and will soon delamination and blister. Introduction to Printing and Lamination

      This is because the thick ink layer changes the porous surface characteristics of the paper, closes the pores of the paper fibers, and seriously hinders the penetration and diffusion of the adhesive. The penetration of adhesive to a certain extent is beneficial to film bonding.Introduction to Printing and Lamination

 

       In addition, if the ink layer and the area of the ink layer on the surface of the printed matter are different, the adhesion and wettability are also different. Experiments show that the surface tension decreases significantly with the increase of ink layer thickness or graphic area. Therefore, both monochrome printing and laminated printing should strive to control the ink layer to a thinner extent.Introduction to Printing and Lamination

 

      The thickness of the printing ink layer is also directly related to the printing method. The thickness of the ink layer is also different with different printing methods. For example, the ink layer thickness of lithographic products is about L-2 μ m. Introduction to Printing and Lamination

       When embossing, it is about 2-5 μ m. Up to 10% in gravure printing μ m。 From the perspective of film coating, lithographic printing is ideal, and its ink layer is very thin.Introduction to Printing and Lamination

 Introduction to Printing and Lamination

 

      Type of printing ink. The printed matter to be coated shall adopt fast fixing bright offset printing ink. The binder of the ink is composed of synthetic resin, dry vegetable oil, high boiling point kerosene and a small amount of gum.Introduction to Printing and Lamination

       The synthetic resin molecule contains polar groups, which are easy to diffuse and penetrate with the polar groups in the adhesive molecule, and produce cross-linking to form physical and chemical binding force, which is conducive to film covering;Introduction to Printing and Lamination

       Fast fixing this photo offset printing ink also has the advantage of rapid drying of the ink layer after printing, which is also very beneficial to the coating. However, it is not appropriate to add too much desiccant when using, otherwise, the surface of the ink layer will crystallize, which will affect the coating effect.Introduction to Printing and Lamination

 

      Use of ink diluent. Ink diluent is a kind of substance that can lighten the color of ink. The commonly used ink diluents are white ink, Willy oil and gloss oil.Introduction to Printing and Lamination

 

      White ink is an ink, which is composed of white ink pigment, binder and auxiliary materials. It is commonly used in light color field printing, spot color printing and trademark pattern printing. Poor quality white ink has obvious powder particles, which is not tightly combined with the binder. Introduction to Printing and Lamination

      After printing, the binder will quickly penetrate into the paper, and the pigment floats on the paper to hinder the adhesion. This is the reason why some light color field printed materials are often easy to be covered with film.Introduction to Printing and Lamination

 

      Self ink should be carefully selected before printing, and self ink with uniform, fine and no obvious particles should be selected as diluent as far as possible.Introduction to Printing and Lamination

 

      Willy oil is a paste transparent body made of aluminum hydroxide and dry vegetable oil binder. It can be used to increase the gloss of the surface of printed products and has excellent printing performance. However, aluminum hydroxide is light and will float on the surface of the ink layer after printing.Introduction to Printing and Lamination

      During coating, an imperceptible isolation layer is formed between the adhesive and the ink layer, resulting in poor adhesion or blistering. Its own slow drying, but also has the characteristics of inhibiting ink drying, which is also difficult to adapt to film coating.Introduction to Printing and Lamination

 

         Gloss oil is a kind of fast drying diluent from inside to outside. It is a colloidal transparent material made of resin, flat vegetable oil and desiccant. It has fine texture, bright conjunctiva, good affinity and can firmly adsorb polypropylene film on the surface of ink layer. Introduction to Printing and Lamination

       At the same time, gloss oil can make the imprinting shiny, accelerate the drying speed and have good printing performance. Therefore, it is an ideal ink diluent.Introduction to Printing and Lamination

 

        Powder spraying. In order to adapt to multi-color high-speed printing, powder spraying process is often used in offset printing to solve the problem of dirty back. Powder spraying is mostly composed of cereal starch and natural suspended substances. Introduction to Printing and Lamination

       The anti sticking effect of powder spraying is mainly to form an irreversible cushion on the surface of the ink layer, so as to reduce adhesion.Introduction to Printing and Lamination 

      Due to the coarse particles, if too much powder is sprayed during the printing process, these particles float on the surface of the printed matter. During film coating, the adhesive is not bonded with the ink layer everywhere, but with this layer of powder spraying, resulting in false adhesion and seriously affecting the film coating quality.Introduction to Printing and Lamination

       Therefore, if the post press products need to be coated, the amount of powder spraying should be controlled as much as possible during printing.Introduction to Printing and Lamination

 

      The surface and inner layer of printed matter are dry. Poor drying of printing ink layer does great harm to the quality of film coating. The factors affecting the drying of the ink layer are not only the type of ink, the amount and type of drying agent in the printing process, and the ambient temperature and humidity in the printing and storage room.Introduction to Printing and Lamination

      But also the structure of the paper itself. If the structure of coated paper and offset paper is different, the drying condition of ink layer is also different.Introduction to Printing and Lamination