Water quality film product quality control points
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The laminating process, also known as post-printing, post-press, post-press, is one of the most important processes in post-press processing, and an effective means to improve the quality and quality of printed products. It is often used in the decorative processing of pre-printed carton paper, paper boxes, handbags, covers and other products. After the film is coated, it can be waterproof, stain-proof, anti-color, heat-resistant and anti-friction. It can also enhance the gloss, beauty, puncture 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 coating film damages the health of the operator due to the use of the solvent containing benzene, pollutes the environment of the workshop, and the concentration of the organic solvent increases continuously, causing a fire, and the paper and film materials after lamination are difficult to be used. Recycling, waste of resources and other shortcomings are gradually replaced by high-strength, high-grade, easy-to-recycle, non-polluting characteristics of coated printing products, which are deeply replaced by the water-based laminating process favored by customers. The water-based film can not only improve the environmental problems in the production process, but also avoid the physical injury to the operator, reduce the production cost, and is widely used for the high strength of the easy-to-recycle and laminating products. The process flow is shown in Figure 1. . The quality of printed products after water-based coating is also affected by many factors. This paper will discuss the control points of the quality of coated products in the water-based coating process.
1. Self-quality of laminating adhesive
The water-based coating glue is a white emulsion type adhesive composed of water as a dispersing agent and a high molecular polymer as a dispersed phase. The aqueous film-forming resin of water-based film adhesive affects and controls the gloss, adhesion, abrasion resistance, water resistance, flexibility and drying properties of the film coating layer, and protects the surface of paper and ink. Functional additives are used to improve the transferability, leveling, drying performance, slipperiness, viscosity adjustment, gloss improvement, etc. of water-based coating rubber. Water-based glue has a certain ability to "powder" on the powder on the printed matter, which can improve the gloss of the film. However, if there is too much powder, a snowflake-like white spot will appear. At the same time, when printing with gold or silver ink, if the amount of glue is too large, the water will wet the gold and silver ink, causing the black and silver ink to be black. Therefore, the good quality aqueous coating glue should be free of organic solvents, the residual organic monomer should be less than 0.1%, smell odorless or slightly alcohol or ester scent, and absorb and distribute the paper fibers after film mulching. Moisture makes the glue dry and transparent, and it is firmly bonded to the plastic film. The film product has good gloss and strong adhesion.
2. Paper material
After the aqueous coating, the initial viscosity of the water-based adhesive is poor, the viscosity is small when it is not dried, and the paper is deformed by the adsorption of moisture. After the film is coated, the paper and the film are released due to the deformation of the paper. The phenomenon that causes bubbles after drying. At the same time, when the paper is thicker or has a higher stiffness, the water-based film is slightly longer than the film, which will affect the post-process paper. Therefore, the water-based coating process requires paper and paperboard to be quantitatively 100-400 g/m2, and it is relatively difficult to apply a water-based coating to a coated paper having a basis weight of 100 g/m2 or less and a paperboard having a basis weight of 400 g/m2 or more, especially for offset paper. Sizing. Practice has proved that the film coated on the offset paper product, the product of the water-based film is easy to cause the paper and plastic to be detached, and sometimes the film is gently separated, and the film and the printed product are completely separable, which is easy to cause a quality accident. At the same time, the lower bound paper coated film is easy to be folded and overflowed, and the higher the weight of the cardboard film, the easy to degumming at the indentation during die cutting.
3. Film material
The plastic film used for the aqueous film is basically the same as the conventional oil film, and is mainly a polypropylene film, and a polyvinyl chloride film, a polyethylene film, a polyester film or the like can also be used. The thickness of the film is generally 0.01 to 0.02 mm, and the transparency is required to be high, the light transmittance is above 90%, and it is required to be resistant to light, chemical corrosion, geometrical stability, and certain mechanical strength. In the coating process, the adhesive used for the aqueous coating is an aqueous film-forming resin, which requires less corona treatment and longer storage time after film coating. At the same time, the initial adhesiveness of the water-based coating rubber is poor, and the tensile force and pressure of the film are small. If the wrinkles and the rewinding of the film are different, the paper will be pulled at the time of lamination, and the like. The quality of the film product.
4. Printed ink layer condition
The condition of the ink layer of the printed matter mainly refers to the size of the image on the paper, the thickness of the ink layer and the ink properties. The influence of the ink layer on the film is mainly reflected on the adhesion strength of the printed matter and the film. When the printed matter is in the field, the ink layer is thick, and the image area is large, the ink changes the surface characteristics of the paper with many voids, hinders the penetration and diffusion of the adhesive, makes the printed matter and the plastic difficult to adhere, and is prone to quality problems such as delamination and drying. . In the water-based coating process, the coating glue contains a certain amount of moisture. When used for large-area (solid) graphic products, it will present a large area of snow-like spots on the surface of the graphic, resulting in discoloration of the graphic and affecting the appearance of the product. quality. Therefore, the aqueous film is not suitable for a large-area printed film, and in particular, a printed film of gold or silver ink is coated.
5. Laminating equipment
The water-based laminating machine is composed of a paper feeding portion, a paper conveying positioning portion, a gumming portion, a pressing portion, a winding portion, a slitting portion and the like. After the film is coated, it does not need to be heated and dried, and the roll is directly received, so the machine speed is fast, and the maximum speed can reach 80 m/min (about 7,000 sheets/hour), and the machine speed is equivalent to that of the ordinary glue printing machine. The paper feeding portion and the paper conveying positioning portion are the same as the general paper offset printing machine. The water-based laminating machine does not heat the drying tunnel, the distance between the gluing part and the pressing part is relatively close, the gluing part is relatively simple, the glue liquid mainly passes through the osmotic drying, the pressing part is normal temperature, there is no pressure roller, and the pressure is small, so the pressure is small, so the pressure is small, so the pressure is small Not suitable for lamination of gold, silver cardboard and hot stamping products. The special water-based laminating machine is equipped with a drying tunnel, similar to an oil-based laminating machine, which can cover gold and silver cardboard, but at a lower speed.
6. Bump embossing
The embossing is also one of the important processes for finishing the surface of the printed product, but the printed product after the aqueous coating is not easy to be processed by the concave and convex. When the product of the water-based film is pressed and embossed, white spots and wrinkles are formed on the contact surface, the sticking is not firm, and when it is severe, foaming occurs, and the paper is more prominent on the coated paper. For example, some cover book covers, the cover side rubber bar line after water-based lamination is not very straight, and there are embossed marks with unevenness, which seriously affects the appearance of the product.
7. Other factors
In the water-based coating process, the factors affecting the quality of the product film include the dilution agent and the drying of the ink. Under normal circumstances, if the ink is used as a thinner in the ink, the white powder has obvious powdery particles, which makes it not tightly bonded to the binder, which hinders the adhesion, which may result in poor adhesion and affect the quality of the printed product. At the same time, when the film is coated when the ink is not completely dried, the product after the film is blistered and delaminated, which affects the appearance of the product.
In short, in the laminating process, the water-based coating uses water-based environmentally friendly glue, does not require heating and drying equipment, high-speed energy saving and high gloss, and is welcomed by many manufacturers, and is gradually replacing the traditional oil-based laminating process. However, the water-based film coating effect is not perfect, and the quality of the printed film after the film coating is also affected by many factors, and the research on the water-based film coating process still needs to be continued. Today, after the post-press processing technology has attracted much attention, with the improvement of the laminating process, the complete production equipment, the relevant properties of the printing paper and the film material, the printed products after the water-based lamination will exhibit higher quality. The water-based laminating process, which represents the development direction of the laminating process, will usher in a broader future.