Problems to be Noted in Vacuum Aluminized Paper Printing

1. Prepress process design

Due to the poor wear resistance of vacuum aluminized printing products, the low glossiness, the easy breakage of materials, and the fact that practical problems such as the crease lines are easily exposed, it will directly result in poor product molding, poor material stiffness, and poor printing ink. Cracks and other issues. Therefore, in addition to the selection of high-quality aluminized paper, in the design of the printing process, the characteristics of the aluminized paper should be used as far as possible to avoid weaknesses. For the design of printing and graphic design, the pattern text should avoid the use of a large area of ​​opaque ink as the background color, and use the exposed bottom effect to highlight the unique metallic luster color of the aluminized paper. For offset dot images, the area is preferably small, large areas of four-color overprinting are avoided, and spot color printing is often used to increase color saturation. The color chosen should try to highlight the metallic luster and gloss of the aluminized paper and use less contrasting spot colors. Choosing inks should also be printed with as good transparency as possible. Pay attention to the effect of the metal luster of the aluminized paper on the ink, and the different background colors of the paper will have different color effects. If printed on the aluminum layer transparent yellow, golden yellow. Small texts and lines should avoid overprinting so as not to expose the bottom or color, increase overprinting difficulties, and increase the rejection rate. Try not to print a large-area spot color block at the crease line to prevent the appearance of white or crease lines, and make up for the lack of material folding. Learn more about the printing performance of the aluminized paper, the post-press processing technology and the requirements of the customer's packaging process on the machine, fully consider the printing special characteristics of the aluminized paper, and use the extreme colors together.

2. Selection of ink

Vacuum aluminum-plated paper is suitable for UV ink printing, offset printing, screen printing, gravure, etc., but different printing methods require different inks. Ten vacuum aluminum-plated papers are not resistant to friction. Therefore, during the printing process, attention should be paid to minimizing the number of overprints, and the speed should not be too fast. In addition, the technological formula of the aluminum-plated materials can be adjusted according to specific conditions, and when the paper is hard, it is easy to crack. When the paper is soft, it is not wearable; generally, the viscosity of the ink should be lowered to avoid affecting the composite effect of the product. The selection of ink should pay attention to the matching of the ink and the printing material. The surface coating of the aluminized paper is suitable for water-based coating; the water content of the aluminized paper is controlled at 5%-6%. For the cracking problem of vacuum aluminized paper, this usually occurs only one or two months after printing or even packaging. In order to avoid the occurrence of such a situation, a printing test is generally required to be performed for a period of time in order to detect it. Material stability, mass production after the material is qualified.

(1) offset printing, screen printing. The aluminum layer ink of vacuum aluminum-plated paper has poor ink adsorption, especially when the offset printing is performed, the process of ink penetration, polymerization, oxidation, conjunctiva, and drying on the vacuum aluminum-plated paper is longer. Due to poor adhesion, ink breakage at the folds can sometimes occur. UV offset inks can be tested for POP inks, and the viscosity of the inks should also be noted. Offset and screen printing should be based on the drying speed of the ink to determine the boot speed, offset water control to the dirty version prevail. Many vacuum aluminum coated paper manufacturers often back coat water for the purpose of facilitating final drying, but do not perform backwater treatment before providing them to the printing company, making the aluminum coated paper easy to curl during the printing process. The surface of the aluminized paper itself has a certain amount of fine pores. Water can penetrate into the paper and the importance of moisture control can be seen. Aluminized paper printing should pay special attention to the fastness and color of the ink. For the fastness of the ink, there are mainly two cases. First, the ink after printing is used to pull off the ink to be printed first; the second is after printing. The ink layer on the surface of the paper is not firm enough to pull off. For the solution, the former proposes to increase the UV curing intensity of color shades or use wet and wet overprinting to complete the curing process at the delivery site at one time; the latter uses high-toughness UV-curing inks and adds special varnish to the ink. Adjust its viscosity. As for the problem of color explosion, the general solutions are: first, the use of water-based varnish before UV printing; second, the use of special color blocks to increase the thickness of the ink layer twice to increase the folding resistance; the third is to choose the high toughness Ink.

In the process of offset printing and screen printing vacuum aluminum plating, due to the poor adhesion of UV offset ink to the paper surface, sometimes ink breakage occurs at the folds. Pay attention to its ink adhesion, and also pay attention to the viscosity of the ink. . Offset and screen printing should be based on the drying speed of the ink to determine the boot speed, offset water control to the dirty version prevail. Because the surface of vacuum aluminized paper is not like composite aluminum foil paper and PET paper, it has certain fine pores, water can penetrate into the paper, so the control of moisture is very important; 3 the printing of vacuum aluminized paper can not stack too much The maximum number of paper jams is no more than 3,000, because the surface of the vacuum aluminized paper is not resistant to abrasion, and stacking too much will damage the surface of the print. 4 Note that the vacuum aluminized paper should not be stored for too long. It is better not to exceed two months because For a long time, the surface will adhere to the back of the paper, causing the paper surface to bloom. 5 The printing of vacuum aluminum-plated paper should pay attention to the temperature during thermal curing is not too high, the high temperature will affect the surface of the vacuum aluminum-coated paper, make it become flowers , And too hot paper shrinkage deformation is too big, a great impact on post-processing.

(2) Gravure. From the adaptability of aluminized paper and gravure printing, today's requirements for ink are mainly focused on solving the problem of ink adhesion and burst color. To achieve good adhesion between the aluminized paper and the gravure ink, the medium between the two, varnish, is the key. It can neither corrode the plating but also has a good affinity, but it will not affect the subsequent printing. Leveling. According to industry insiders, the use of 300-mesh anilox rolls for aluminum-plated paper, followed by uniform water-based varnish to increase the surface tension of the paper to 38 dyne or more, can achieve the desired effect, and initially solve the problem of gravure ink adhesion. . Once the aluminized paper is not properly controlled, it is easy to explode. This is related to many factors such as the paper itself, PET film, glue, ink, and temperature control operation. In the case of inks, the ink binder consists of a resin and a solvent. The resin has the ability to contain and release pigments, and the solvent acts to disperse and dissolve. Different resin and solvent varieties and ratios can determine the ink transferability, drying, ink layer fastness and other performance indicators. General gravure inks are composed of two or three kinds of resins and two or three kinds of corresponding additives with pigments and mixed solvents.

In the use of ink, according to the characteristics of the aluminized paper, increase the proportion of flexible resin in the ink and the corresponding solvent, and pay attention to control the fineness of the pigment particles in the ink (usually to control in the 3 microns to 8 microns). If the pigment is in the form of a sheet, the color paste can be subjected to a quick sanding treatment to refine the soft particles that are difficult to filter in the original color paste, and to optimize the properties without changing the characteristics of high transparency and high gloss. You can get the desired result. In addition, we must pay attention to adjust the viscosity of the control ink, improve the binding force and anti-explosive color ability of the resin and the pigment. The hue, saturation, and transparency of the ink have a great effect on the color rendering effect of the aluminized paper. The common 3 to 4 sanding pigments can reduce the fineness, but it is easy to make the pigment in the ink black and dark. , and there is a phenomenon of back thickening. To solve this problem, it is recommended to use pigment color chips (ie, ink chips, such as those produced by Zhuhai Fangdi Ink Co., Ltd.). This kind of color pre-dispersed pigments can use special production techniques to enable the pigment itself to be used. The shade of light plays its best. The mirror-like light transmission effect is also an important factor for guaranteeing metallic luster on pure aluminum foil and aluminized paper products. It does not affect the unique effects of the aluminum-plated laser paper, but also makes the ink transfer smoothly, to adapt to overprinting, stacking flexibility, friction resistance, heat resistance, resistance to post-processing operations and other needs.



Reprinted from: China Packaging News

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