The laminating process, also known as post-press lamination, post-press laminating, and post-press film, is one of the most important processes in post-press processing and is an effective means to improve the quality of printed products and the value of commodities. It is often used in the decorative processing technology of preprinted carton facial paper, carton, handbag, cover and other products. After the printed product passes through the film, it can have waterproof, anti-fouling, anti-fading, heat resistance, and friction resistance. At the same time, it can enhance the gloss, aesthetics, piercing strength and tensile strength of the product, and improve the service life and packaging of the product. quality. In the laminating process, the solvent-based ready-to-coated laminating film damages the health of the operator due to the use of benzene-containing solvents, pollutes the workshop environment, and the concentration of organic solvents continues to increase to cause fires. The paper and film materials after laminating are difficult The shortcomings of recycling and waste of resources are gradually replaced by the water-based laminating process favored by the majority of customers due to the high-strength, high-grade, easy to recycle, and non-pollution characteristics of the laminated printed matter. The water-based coating can not only improve the environmental problems in the production process, avoid the physical harm to the operator, but also reduce the production cost. It is easy to recycle and the high strength of the coating product is widely used. Its process is shown in Figure 1. . The quality of the printed product after water-based coating is also affected by many factors. This article will discuss the key points of the quality control of the product in the water-based coating process.
1. The quality of the film adhesive
The water-based film adhesive is a white emulsion adhesive composed of water as a dispersant and a polymer as a dispersed phase. The water-based film-forming resin of the water-based film adhesive affects and controls the gloss, adhesion, abrasion resistance, water resistance, flexibility and drying performance of the film coating layer of the film adhesive, and plays a protective role on the surface of paper and ink. Functional additives are used to improve the transferability, leveling, drying performance, and slip properties of water-based film adhesives, adjust viscosity, and improve gloss. The water-based adhesive has a certain "powder-eating" ability to spray powder on the printed matter, which can improve the gloss of the film. However, if too much powder is sprayed, snowflake-like white spots will appear. At the same time, when printing with gold and silver ink, if the amount of glue applied is too large, the water will soak the gold and silver ink, causing the gold and silver ink marks to blacken. Therefore, a good quality water-based film adhesive should be free of organic solvents, and the residual body monomer should be less than 0.1%. It smells odorless or has a slight alcohol or ester flavor. After the film is absorbed and emitted by paper fibers Moisture makes the glue dry and transparent, firmly adheres to the plastic film, the gloss of the coated product is good, and the adhesion is strong.
2. Paper materials
After the water-based coating, the initial viscosity of the water-based adhesive is poor, and the viscosity is very small when not dried. The paper is deformed due to the absorption of moisture. After the film is coated, the paper and the film will peel off due to the deformation of the paper. The phenomenon caused bubbles after drying. At the same time, when the paper is thicker or has a higher stiffness, the water-based film trailing tape film is slightly longer, which will affect the subsequent process of flushing the paper. Therefore, the water-based coating process requires the paper and cardboard to have a basis weight of 100-400g / m2. It is relatively difficult to apply water-based coating to the coated paper with a basis weight of less than 100g / m2 and the board with a basis weight of 400g / m2, especially for offset paper Sizing. Practice has proved that the film coated on the offset paper products, the water-based film products are easy to cause the paper and plastic to detach, sometimes gently torn, the film and the printed product can be completely separated, which is easy to cause quality accidents. At the same time, the coated paper with lower basis weight is easy to be broken and overflowed, and the cardboard with higher basis weight is easily degummed at the indentation area during die cutting.
3. Film materials
The plastic film used for water-based coating is basically the same as the traditional oil-based coating, mainly polypropylene film, but also polyvinyl chloride film, polyethylene film, polyester film, etc. The thickness of the film is generally 0.01 ~ 0.02mm, which requires high transparency, light transmittance of more than 90%, and must be resistant to light, chemical corrosion, stable geometric dimensions, and a certain mechanical strength. In the laminating process, the adhesive used for the aqueous coating is an aqueous film-forming resin, which requires less corona treatment for the film and a longer storage time after coating. At the same time, the initial viscosity of the water-based laminating adhesive is poor, and the tension and pressure on the film are small. If the wrinkles and rewinding of the film are different, it will cause failures such as emptying of the cardboard overlap during lamination. The quality of coated products.
4. The condition of the ink layer of the printed product
The condition of the ink layer of the printed matter mainly refers to the size of the graphic area on the paper, the thickness of the ink layer, and the performance of the ink. Their impact on the film is mainly manifested as the effect of the adhesion strength between the printed matter and the film. When the printed matter is solid, the ink layer is thick, and the graphic area is large, the ink changes the surface characteristics of the paper with many voids, which hinders the penetration and diffusion of the adhesive, making the printed matter difficult to bond with the plastic, and is prone to quality problems such as delamination and drying. . In the water-based laminating process, the laminating adhesive contains a certain amount of moisture. When used for large-area (field) graphic products, a large area of ​​snowflake-like spots will appear on the surface of the graphic, which will cause the discoloration of the graphic and affect the appearance of the product. quality. Therefore, the water-based coating is not suitable for large-area printing, especially for printing gold and silver ink.
5. Laminating equipment
The water-based film laminating machine is composed of a paper feeding part, a paper conveying and positioning part, a gluing part, a pressing part, a winding part, and a slitting part. It does not need to be heated and dried after being coated, and is directly wound up, so the machine speed is relatively fast, and the maximum speed can reach 80 meters / minute (about 7000 sheets / hour), which is comparable to ordinary offset printing machines. The paper feeding part and the paper conveying positioning part are the same as the general paper offset press. The water-based laminating machine does not have a heating and drying tunnel, and the gluing part is close to the pressing part. The gluing part is relatively simple. The glue liquid is mainly dried by infiltration. The pressing part is normal temperature, there is no pressure roller, and the pressure is also small, so Not suitable for laminating gold and silver cardboard and hot stamping products. The special water-based laminating machine is equipped with a drying tunnel, similar to the oil-based laminating machine, which can coat gold and silver cardboard, but the speed is lower.
6. Embossing
Concavo-convex embossing is also one of the important processes for finishing the surface of printed products, but the printed products after water-based coating are not easy to be processed. When the concave-convex embossing is carried out on the water-based coated products, white spots and bow wrinkles will appear on the contact surface, the adhesion is not firm, and it will blister in severe cases, and it is more prominent on coated paper. For example, some glue binding book covers, the rubber line on the cover side after water-based coating is not very straight, and there are uneven imprint marks, which seriously affects the appearance of the product.
7. Other factors
In the water-based coating process, the factors that affect the quality of the product coating also include the dilution agent and the drying condition of the ink. Normally, if white ink is used as a diluent in the ink, there are obvious powdery particles in the white ink, which makes it not tightly bound to the bonding material, which hinders the adhesion, and will cause the adhesion to be weak and affect the quality of the printed product. At the same time, when the ink is coated before the ink is completely dried, it will also cause foaming and delamination of the product after coating, which will affect the appearance of the product.
In short, in the coating process, the water-based coating uses water-based environmentally friendly glue, does not require a heating and drying device, and has high speed, energy saving and high gloss. It is welcomed by many manufacturers and is gradually replacing the traditional oily coating process. However, the effect of water-based film coating is not perfect. The quality of the printed film after the film coating is also affected by many factors. The related research on the water-based film coating process still needs to be continued. Today, after the attention of post-press processing technology, with the improvement of the lamination process, the production equipment is complete, the performance of the printing paper and film materials is improved, and the printed products after water-based lamination will show higher quality. To better enhance product value, the water-based film process, which represents the development direction of the film process, will usher in a broader tomorrow.
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