The hottest perspective film covering technology I

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Perspective film coating technology (II)

IV. composite strength is the main index to measure the quality of film coating. The so-called composite strength of film coated products, simply speaking, refers to the adhesion fastness between plastic film and paper (board) printing in film coated products. Its size depends on the adhesion between plastic film, paper (board) printing and adhesive (or hot melt adhesive). The primary significance of lamination is the protection of printed matter. If the lamination is not strong, processing has no practical significance. Any kind of film covering process is all about fastness. When laminating, the adhesion mainly comes from the mechanical and physical-chemical adhesion between plastic film, paper (board) printing and adhesive (or hot melt adhesive). There are many factors that affect the composite strength of coated products, including both objective factors brought by production materials such as paper, printing ink, plastic film, adhesive (or hot melt adhesive), and subjective factors that can be artificially controlled such as coating process parameters and printing process.

the key to film fastness lies in the affinity between glue and printed matter (ink and substrate). As a film industry, printing ink is not optional, that is, only the film covering suitable for the ink market is the only choice. Therefore, as a pre coating, it can be regarded as an excellent product only if it adapts to the performance of all inks. To improve the affinity between adhesive layer and printed matter, it is necessary to understand the bonding mechanism. The mechanism of bonding can be discussed in two aspects: physical bonding and chemical bonding. Physical bonding can be regarded as anchoring effect, that is, the bonding surface is rough. When pressing, both sides penetrate into each other's interface to form overlapping and mutual bonding. Chemical bonding involves intermolecular force, chemical strength, electrostatic attraction and van der Waals force. Practice shows that the generation of adhesive force is mainly composed of chemical bonding. The surface of the bonded adhesive layer is activated to produce chemical groups with high intermolecular force, chemical strength and electrostatic attraction, so as to improve the surface energy of the adhesive layer, so as to effectively improve the chemical adhesive force of the adhesive layer.

as the lamination process is a surface finishing process for further processing of printed matter after printing, the composite strength of the lamination product is affected by the process parameters in the lamination production process, such as the temperature, pressure, speed of the lamination process, the coating condition of the adhesive, film tension and environmental factors; At the same time, it is also affected by the printing process, that is, the surface state of the printed matter formed after printing, such as the thickness of the ink layer, the area and distribution of graphics and texts, the characteristics of the ink, the use of diluents, the use of powder spraying, the drying of the ink layer, and so on. All these factors will affect the formation conditions of mechanical and physical-chemical bonding between paper (board), plastic film and adhesive (or hot melt adhesive), cause the change of bonding state between printed matter and plastic film, and thus affect the composite strength of coated products. In addition, the following factors are also factors to measure the quality of film covering: ① surface quality. The surface quality is the visual effect of people. The coated surface should be flat, bright and clean, without protrusions, folds and spots. To achieve such an effect, in addition to the factors of the substrate, the single material, uniform thickness and good transparency of the adhesive layer are indispensable elements; ② Low temperature composite performance. Whether from the perspective of energy saving or damage to printed matter, low-temperature pre coating is always popular; ③ Machinability. Some products, especially advertising materials, need to be UV polished or bronzed on the surface after coating, which puts forward higher requirements for the performance of the substrate surface.

v. factors affecting the quality of film coating

1. The condition of ink layer of printed matter

the condition of ink layer of printed matter mainly refers to the nature of paper, ink performance, thickness of ink layer, image and text area and density of printed image and text. Their impact on the quality of film coating is mainly the impact on the adhesion strength between printed matter and film. When the ink layer of the printed matter is thick and the image and text area is large, the ink changes the porous surface characteristics of the paper, seals many paper fiber pores, hinders the penetration and diffusion of the adhesive, makes it difficult for the printed matter to bond with the plastic film, and is prone to delamination, blistering and other failures. Offset printing adopts powder spraying process to avoid printing crystal rubbing dirty, and powder spraying forms a layer of fine particles on the surface of the ink layer. When laminating, the adhesive is not bonded with the ink layer everywhere, but with these powders, forming a false adhesion phenomenon, which seriously affects the quality of lamination. When the ink is not completely dry, the high boiling solvent contained in the ink is very easy to make the plastic film expand and elongate, which is the main reason for the foaming and delamination of the product after coating.

2 environmental humidity

the environmental humidity of the film coating workshop has an impact on the film coating quality. It is mainly because the water content between adhesive and plastic film and printing changes with the change of air relative humidity. Printing materials sensitive to humidity will produce internal stress due to size changes. For example, the longitudinal expansion rate of printed matter is 0.5%, and the longitudinal thermal shrinkage of BOPP film is 4%. If the printed matter is stretched due to excessive water absorption, it will cause internal stress between the printed matter and the heating shrinkage of the film, which will lead to the crimping, tendency and poor adhesion of the film covered products. In addition, in the environment with high humidity, the equilibrium moisture value of the printed matter will also change. A large amount of moisture absorbed from the air medium will be released from the surface during the hot pressing process, stagnate at the bonding interface, and form a non bonding phenomenon locally. Moreover, the change of the equilibrium moisture value of the printed matter (moisture absorption from the air medium or moisture release to the air medium) mostly occurs at the edge of the printed matter, making it form a ruffled edge or tight edge. It is not easy to form a good adhesion with the film and produce wrinkles in the hot pressing composite, so that the production cannot proceed smoothly

3 temperature control

humidification can soften the film and bond the paper with the plastic film. However, if the temperature is too high, the film is easy to break, which will seriously affect the product quality. Measures such as fan cooling and turning off the electric heating wire shall be taken.

VI. The green development trend of plastic mulching

plastic mulching is favored by the printing industry and consumers because of its folding resistance, wear resistance, protection of prints, increased gloss and low cost. However, the coated paper becomes a kind of white pollution because it cannot be recycled, and toxic substances such as toluene and Tianna water volatilize during the coating process, which damage people's health. Today, when we advocate "protecting the environment and protecting data", the plastic film covering process has been eliminated in Europe and the United States. Europe and the United States even refuse to import all kinds of packaging materials with plastic film covering. Although there are water-based plastic film covering process and hot melt adhesive pre coating dry plastic compound process, these two types of film covering are called "environmental protection film covering machine", However, the former still fails to solve the problem that the waste of film coated printing materials cannot be degraded and recycled. The latter requires a lot of heat in the production process if the swing rod does not stop in the middle position, which consumes a lot of energy and has a poor working environment. The removed lubricating oil is burned into ashes for chemical analysis or spectral analysis. Moreover, the waste needs to be separated from paper and plastic in 60 ℃ water, which leads to a high separation cost.

with the renewal of environmental protection awareness, health awareness and business philosophy, the popularity will also be further expanded and developed. New scientific and technological achievements will eliminate the products of the old process, resulting in qualitative changes in the coating process. "Non toxic, harmless, green and environmental protection" has become the inevitable development trend of the coating process. For example, water-based film covering adhesive, which uses water-soluble polymer polyester materials and takes water as solvent, is basically an environmental protection product. At present, domestic water-based film covering adhesive has the problem of poor stability, but wdt-3300, wdt-220, wdt-1100 made in Korea have solved these defects, and can completely replace oil-based film covering adhesive products. In terms of machinery, the laminating machine manufacturers in Guangdong, Hebei and Zhejiang have successively launched several semi-automatic desktop dry laminating machine products. South Korea Yongxin also launched four full-automatic water-based dry laminating machine products flcd-s1020, 1090, 1350 and 1450 to the Chinese market. Its operation process is fully automated, which greatly reduces the human-machine contact time, and the use of glue is non-toxic, harmless, green and environmental friendly. These new products have been used by the domestic leading and highly modern Benxi Steel Group, and will also be the world's first high-strength hot stamping steel phs2000 generation awareness business community, Such as Haier Fengcai, HK, etc. It can really be said that "little lotus just shows its sharp corners, and dragonflies have long stood on its head". Glazing technology is therefore also favored. Glazing is to add a layer of colorless and transparent paint, namely glazing oil, on the surface of the print by coating, spraying or printing. After calendering and drying, a colorless and transparent bright layer is formed on the surface of the print, which increases the gloss of the print surface and also improves the stiffness of the print. It also plays a role in protecting the print and increasing the beauty. However, the printing waste after polishing can be recycled or decomposed by itself, which does not pollute the environment. Therefore, it is a surface decoration processing technology with great development potential, which is likely to gradually occupy the plastic coating process market. Although toluene and alcohol are the diluents used in oily and alcohol glazing on the market at present, they are harmful to human body and environmental protection. However, water-based glazing has gradually become the mainstream of glazing technology, although this technology needs further development to make it more suitable for the dual requirements of environmental protection and printing quality. At present, the water-based UV glazing process that has been developed is an ideal environmental friendly glazing process, and it is also the development direction of glazing process in the future

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