Technical parameters and influencing factors of perspective coating technology (in)

Coated material plastic film

Commonly used plastic films are: polyvinyl chloride (PVC), polypropylene (BOPP) and polyester (PET) films. Among them, BOPP film (15 ~ 20pm) is flexible, non-toxic, and has good flatness, high transparency, good lightness, and is resistant to abrasion, water, heat and chemicals. In addition, it is cheap and it is covered. The ideal composite material in the membrane process.

Film coating process has three requirements on the quality of plastic film: 1 The thickness directly affects the transparency, refractive index, fastness and mechanical strength of the film. According to the film's own performance and purpose, the thickness of the film is 0.01. Between ～0.02mm is appropriate. 2 Subject to corona or other methods, the surface tension of the treated surface should reach 4Pa in order to have good wettability and adhesion performance, and the corona treatment surface should be uniform. 3 The higher the transparency, the better so as to ensure the best clarity of the printed material.

Transparency is expressed as the percentage of transmitted light, ie, transmitted light and projected light; the transmittance of PET film is generally 88% to 90%, and the transmittance of other kinds of films is usually between 92% and 93%. Good light resistance, that is, it is not easy to discolor under long-term irradiation of light, and has certain mechanical strength and flexibility characteristics. The mechanical strength of the film includes tensile strength, elongation at break, elastic modulus, impact strength, and the number of folding times. Technical indicators. The geometric size should be stable, and the coefficient of hygroscopic expansion coefficient, thermal expansion coefficient, heat distortion temperature and other indicators should be used. Coated film should be in contact with solvents, adhesives, inks, etc., must have a certain degree of chemical stability. The appearance of the film surface should be smooth, without unevenness and wrinkles, and the film should be free from bubbles, shrinkage holes, pinholes, and pits, etc. The film surface should be free from contamination such as dust, impurities, and grease. Uniform thickness, small deviation in vertical and horizontal thickness; due to the limited adjustment ability of the laminating machine, it is also required that the cover be neat and the two ends should be loose and uniform to ensure uniform coating. Of course, the lower the cost, the better.

The quality inspection method of plastic film, in addition to the above surface treatment of the film surface, etc., can also be detected by hand or visual inspection. The wide-barrel film roll must also be slit into narrow rolls in accordance with the required width to be used for coating. After the slitting, the narrow roll requires that the edges be flush, aligned at both ends, and have the same curling tension.

Measure the quality of the film

The so-called laminating product's composite strength, simply speaking, refers to the lamination product in the plastic film and paper (board) prints between the fastness, its size depends on the plastic film, paper (board) print and adhesion The size of the adhesive (or hot melt adhesive). The overriding significance of the film is the protection of the printed matter. If the film is not strong, processing will have no practical significance. Any kind of lamination process must work hard and fast. When the film is coated, the adhesive force mainly comes from the mechanical bonding force and physicochemical bonding force between the plastic film, the paper (plate) print and the adhesive (or hot melt adhesive). There are many factors that affect the composite strength of film-covered products, including objective factors such as paper, printing inks, plastic films, adhesives (or hot-melt adhesives) and other production materials, as well as coating process parameters and printing processes. Can subjective factors such as human control.

The key to film fastness lies in the affinity between the adhesive and the printed material (ink and substrate). As the film coating industry, the printing ink is not optional, that is, only the film that meets the ink market is the only choice. Therefore, as a precoat film, only the performance of all inks is superior. To improve the affinity between the adhesive layer and the printed material, we must understand the principle of bonding. The principle of bonding can be easily discussed from both physical and chemical bonding. Physical bonding can be considered as an anchoring effect, that is, the bonding surface is rough, and when pressed together, both sides penetrate into each other's interface to form a lap and adhere to each other. Chemical bonding involves intermolecular forces, chemical bonds, electrostatic attraction, van der Waals forces. Practice has proved that the adhesive force is mainly composed of chemical bonding, and the surface of the adhesive layer is activated to produce a chemical group having intermolecular force, chemical bond force, electrostatic attraction and increase the surface energy of the adhesive layer, thereby Improve the chemical bonding of the adhesive layer.

Since the lamination process is a surface finishing process for the printed matter after printing, the composite strength of the laminating product is affected not only by the process parameters in the lamination production process, such as the temperature, pressure, and speed of the lamination process. , adhesive coating conditions, film tension and environmental factors, etc.: At the same time, it is also affected by the printing process, that is, the surface state of the printed product formed after printing, such as ink layer thickness, graphic area and distribution, ink Characteristics, use of diluting agents, dusting application, ink drying, etc. All of these factors can affect the mechanical bonding and physical and chemical bond formation conditions between paper (plates), plastic films and adhesives (or hot melt adhesives), and cause changes in the bonding state between prints and plastic films. , thereby affecting the composite strength of film products.

In addition, the following factors are also factors to measure the quality of the film: 1 Surface quality. The surface quality is the visual effect of humans. The surface of the film should be smooth, smooth, no protrusions, no creases, and no spotted spots. To achieve this effect, in addition to the factors of the substrate, the adhesive layer has a single material, uniform thickness, and good transparency, and is an indispensable element. 2 low-temperature composite properties. Precoat Films Low-temperature precoat films are always popular, regardless of energy conservation or the reduction of damage to prints. 3 processability. Some products, especially advertising products, must be UV-coated or gilded on the surface after lamination, which puts higher requirements on the performance of the substrate surface.

(to be continued)