Waterborne film product quality control points

The lamination process, also known as post-press lamination, post-printing laminating, and post-printing foil, is one of the most important processes in the post-printing process, and is an effective means of improving the grade and value of printed products. It is often used in pre-printed carton paper, carton, handbag, cover and other products in the decorative processing technology. After being coated, the printed product can be waterproof, anti-fouling, anti-fading, heat-resisting, and friction-resistant. At the same time, it can enhance the glossiness, aesthetics, puncture strength, and tensile strength of the product, and increase the service life and packaging of the product. quality. In the lamination process, the solvent-based coating is due to the use of benzene-containing solvents that impair the health of the operators, pollutes the workshop environment, and the concentration of organic solvents increases, causing fires. The coated paper and film materials are difficult to apply. Recycling, waste of resources and other shortcomings have been gradually replaced by high-strength, high-grade, easy-to-recover, non-pollution, and other features of film-covered products. The water-based film can not only improve the environmental problems in the production process, avoid the physical injury to the operators, but also reduce the production cost, easy recovery and the high strength of the film products and is widely used. The process flow is shown in Figure 1. . The quality of printed products after water-based film coating is also influenced by many factors. This article will discuss the control points of the quality of film-covered products in the water-based film coating process.

1. The quality of the plastic film

The water-based film adhesive is a white emulsion adhesive consisting of water as a dispersant and a high molecular polymer as a dispersed phase. The aqueous film-forming resin of the water-based film adhesive affects and dominates the gloss, adhesion, wear resistance, water resistance, flexibility, and drying performance of the film coating film layer, and plays a role in the protection of paper and ink surfaces. Functional additives are used to improve the transferability, leveling properties, drying properties, slip properties, viscosity adjustment, gloss enhancement and the like of water-based film adhesives. The water-based glue has a certain “powder eating” ability for the powder on the print and can improve the gloss of the film. However, if you spray too much, there will be snow-white spots. At the same time, when gold or silver ink is used for printing, if the amount of glue is too large, the water will wet the gold and silver inks, causing black ink and silver ink to be black. Therefore, a good quality water-based film adhesive should contain no organic solvent, and the residual monomer should be less than 0.1%. It smells odorless or slightly alcohol or ester-like, and absorbs and releases paper fibers after coating. The moisture makes the glue dry and transparent, and it is firmly bonded with the plastic film, and the film product has good glossiness and strong adhesive force.

2. Paper material

After waterborne coating, due to the poor initial viscosity of the water-based adhesive, the viscosity of the water-free adhesive is very small, and the paper is deformed due to moisture adsorption. After the film is coated, the paper and the film will be separated from the unevenness due to the deformation of the paper. The phenomenon causes air bubbles after drying. At the same time, when the paper is thicker or has a higher stiffness, the water-borne film dragging film is slightly longer, which will affect the subsequent process of aligning the paper. Therefore, the water-based film coating process requires the quantitative determination of paper and paperboard at 100-400 g/m2. It is relatively difficult to apply water-based film to coated paper with a basis weight of 100 g/m2 or less and paperboard with a basis weight of 400 g/m2 or more, especially for offset paper. Sizing. Practice has proved that, in the offset film products, water-based film products can easily cause paper and plastic detachment, sometimes gently tear, film and print products can be completely separated, easy to cause quality accidents. At the same time, the coated paper with lower quantification is easy to be folded and overflowed when coated, and the cardboard with higher quantitation is easy to debond at the indentation at the time of die cutting.

Film material

The plastic film used for water-based film coating is basically the same as the conventional oil-based film, and is mainly a polypropylene film, and a polyvinyl chloride film, a polyethylene film, a polyester film, and the like can also be used. Film thickness is generally 0.01 ~ 0.02mm, requires high transparency, light transmittance of more than 90%, and must be light resistance, chemical resistance, geometric dimensions, a certain degree of mechanical strength. In the film coating process, the adhesive used for the aqueous film is an aqueous film-forming resin, and the corona treatment of the film is required to be low, and the film storage time is longer. At the same time, the initial viscosity of the water-based film adhesive is poor, and the tension and pressure on the film are relatively small. If the film has different wrinkles and rewinding, the board will fail at the time when the film is covered, and the failure will be caused. Film product quality.

4. Printing ink layer condition

The condition of the ink layer in the printed matter mainly refers to the size of the image area on the paper, the thickness of the ink layer, and the performance of the ink. Their influence on the film is mainly reflected in the influence on the adhesive strength of the printed matter and the film. When the printed matter is in the field, the ink layer is thick, and the area of ​​the graphic is large, the ink changes the surface characteristics of the paper with many voids, hinders the penetration and diffusion of the adhesive, makes the print and the plastic difficult to be bonded, and is prone to delamination and difficult drying and other quality problems. . In the water-based film coating process, the film adhesive contains a certain amount of moisture, and when used in a large area (field) graphic product, a large area of ​​snowflake-like spots appears on the surface of the graphic, resulting in discoloration of the graphic and affecting the appearance of the product. quality. Therefore, the water-based film is not suitable for the printing of large-area films, especially the printing of gold and silver inks.

5. Laminating equipment

The water-based laminating machine consists of a paper feeding section, a paper conveying positioning section, a gluing section, a pressure combining section, a winding section, and a slitting section. After the film is covered, it does not need to be heated and dried, and the film is wound directly. Therefore, the machine speed is fast, and the maximum speed can reach 80 meters/minute (about 7,000 sheets/hour). The speed is comparable to that of a common adhesive printing machine. The paper feeding section and the paper conveying positioning section are the same as the general paper offset printing machine. The water laminating machine does not have a heating tunnel, the distance between the gluing part and the pressure part is relatively short, the gluing part is relatively simple, the glue liquid is mainly through the osmotic drying, the pressure part is at room temperature, there is no pressure roller, and the pressure is also small, so Not suitable for overlaying gold, 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 cover the gold and silver cardboard, but the speed is low.

6. Embossing

Embossing and embossing are also one of the important processes for finishing the surface of the printed product. However, the printed product after the waterborne coating is not easy to be processed with irregularities. When the waterborne film product is pressed and embossed, it will produce white spots and bow wrinkles on its contact surface, and the paste will be weak. When it is severe, it will blistering, and it will be prominent on the coated paper. For some rubber book covers, the glue line on the cover side of the water-based film is not very straight, and it has uneven marks, which seriously affects the appearance of the product.

7. Other factors

In the water-based film coating process, the factors that affect the film quality of the product include the diluting agent and the drying of the ink. Under normal circumstances, if white ink is used as a diluting agent in the ink, the obvious silty particles in the white ink will not bind tightly to the binder, which will have an obstructive effect on the adhesion and will result in poor adhesion and affect the quality of the printed product. At the same time, when the ink is not fully dried, it will also cause blistering and delamination of the product after the film is covered, which will affect the appearance of the product.

In short, in the laminating process, the water-based laminating film uses water-based environmental protection glue, does not require heating and drying devices, high-speed energy-saving and high gloss, and is welcomed by many manufacturers, and is gradually replacing the traditional oil film coating process. However, the effect of the water-based coating is not perfect, and the quality of the printed product after the coating is also affected by many factors. Research on the aqueous coating process still needs to continue. In the aftermath of the post-press processing technology, with the improvement of the laminating process, the completeness of the production equipment, the improvement of the properties related to the printing paper and film materials, and the higher quality of the printed products after water-based lamination, To better enhance the value of the product, the water-based laminating process, which represents the direction of the development of the lamination process, will usher in a broader tomorrow.

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