Application of screen printing process in the field of self-adhesive labels
Screen printing belongs to stencil printing, which is called four printing methods together with offset printing, embossing and gravure printing. The principle of screen printing is that when the printing plate is printed, the ink is transferred to the substrate through the perforations of the stencil through a certain pressure to form an image or text. In the field of adhesive label printing, screen printing is not a major printing process, but according to the recent development of the international and domestic packaging market, screen printing has a relatively stable growth.
Advantages of screen printing
Compared with other printing methods, screen printing has the following main features:
1. Strong printing adaptability. The three printing methods of offset printing, embossing and gravure printing can generally only be performed on flat substrates. The screen printing can not only print on the plane, but also print on the curved surface, spherical surface and uneven surface of the substrate;
2. Thick ink layer, strong three-dimensional sense and rich texture. The thickness of the ink layer for offset printing and relief printing is generally 5 microns, the thickness for gravure printing is about 12 microns, the thickness of the ink layer for flexographic printing is 10 microns, and the thickness of the ink layer for screen printing far exceeds the thickness of the above ink layer Up to about 30 microns. The screen printing ink layer is thick, the printing quality is rich, and the three-dimensional feeling is strong, which is incomparable to other printing methods. At the same time, silk screen printing can not only print in monochrome, but also register and screen color printing;
3. The layout is soft. The screen printing plate is soft and has a certain elasticity. It is not only suitable for printing on soft items such as Paper and cloth, but also suitable for printing on hard items, such as glass and ceramics.
4. Various types of inks can be used for screen printing. Namely: oily, water-based, synthetic resin emulsion type, powder and other types of ink;
5. The embossing force of screen printing is small. Due to the low pressure used in printing, it is also suitable for printing on fragile objects.
Self-adhesive label printing method classification
At present, global sticker label printing can be divided into the following camps according to the different printing methods used:
1. Mainly flexo printing
The North America region represented by the United States and Canada is a typical representative of the use of flexographic printing stickers. The equipment is a unit-type printing unit, mainly based on water-based ink, and adopts round die cutting.
2. Half for embossing and flexo printing
This processing method is mostly in Europe, and the application of flexographic printing is basically the same as that in the United States. Relief printing also occupies 50% of the proportion, and all of the relief printing uses UV ink, and most of the equipment is laminated or satellite.
3. Mainly with relief printing
This approach is based on the Asia-Pacific region. Most developing countries in the Asia-Pacific region are still lagging behind in label printing. Even if they use letterpress printing, only a few use UV ink equipment. Most label printing still uses resin ink, roll-to-roll printing and sheet printing. Coexistence; Due to the high proportion of manual labeling, single-sheet offset printing stickers are widely used; flat die-cutting is the main method in die cutting.
4. Offset printing
Offset printing is the main method for printing paper stickers in Chinese label printing factories. The characteristics of offset printing are fine graphics and rich layers, suitable for mass printing, and the printing equipment can be used in one machine, suitable for the characteristics of the Chinese label market. However, sheet-fed offset printing is not suitable for printing films with no absorption on the surface, because film labels are mostly roll-to-roll printing, which requires volatile dry ink. Offset printing can print thicker plastic materials, such as in-mold labels and label hang tags, but UV curing devices must be added to the machine, which requires a large fee.
5. Screen printing
Screen printing is the most adaptable printing method for substrates. At present, many screen printing factories use low-cost screen printing equipment to undertake the printing business of self-adhesive labels and film labels. The characteristics of screen-printed labels are thick ink color and strong three-dimensional sense. UV ink can be used to print film products. In addition to the few types of rotary screen printing equipment that can be competent for roll-to-roll label printing, most screen printing equipment is semi-automatic flat screen printing machines, which can only print single-sheet products. The accuracy of overprinting is not high, which is not suitable for the production line. Film label production equipment. Moreover, while the post-press processing technology is transforming its business, it should also pay attention to the corresponding changes in the post-press processing of the label. For example, when printing the self-adhesive label, the post-press processing of the sticker is divided into single sheets according to the application form of the label Paper processing and web processing. [next]
Application of screen printing in the field of stickers
Screen printing stickers are mainly used in the electronic machinery industry, and membrane switches are typical products. The advantages of screen printing are thick ink layer, colorful colors, bumpy feeling, and strong visual impact. It is suitable for the restoration of simple lines, color blocks, text and other patterns, and the general total number of printed colors does not exceed 4 colors. The disadvantage is that the printing gradient color The effect is poor, and the beautiful multi-color printing effect cannot be achieved.
The current label market requires higher and higher printing technology. The main requirements for label product printing are: must be eye-catching, have a strong visual impact, have subtle performance in local details, and have a three-dimensional finish on the surface; can produce higher added value and have better anti-counterfeiting effects. Obviously, a single printing method simply cannot meet these requirements for label product printing.
The combination printing method meets the needs of modern printing industry development, layout design, and brings huge profits to the printing manufacturers, so it has developed rapidly. In foreign countries, more than 10% of label products have been printed using combination printing. Such as transparent material labels. Transparent material labels often need to be screen printed with a background color, and then used for color printing or letterpress printing of logos and patterns. The printing effect of this method is different from the general label printing, it can improve the grade of the product well.
From the market development trend, this printing method will become more and more popular. The excellent coverage effect of screen printing is not only applied to the printing of transparent materials, but also used to print gold ink silver ink and hot stamping fields.
Silk and flexible combination printing
At present, the most commonly used joint method is screen printing combined with flexible printing. The rotary screen printing unit cooperates with the flexographic printing machine for printing, and has the following applications:
1. In order to enhance the attractiveness of the product, use the penetration effect design, such as the use of very heavy colors or luminous ink;
2. Labels used in relatively harsh environments, such as battery labels, lubricating oil barrel labels, paint poke labels;
3. Products that need to emphasize product names and logos, such as drug labels, injections, etc .;
4. Certain ingredients need to be warned to users according to the law, including blind people;
5. Need to obtain metallic effects such as gold and silver;
6. A simpler printing process is needed, such as large-area printing using silk screen, only missing text is printed instead of printing fine text on blank substrates;
7. Relief and matte effect are required on some cigarette packs or cosmetic packaging.
In flexo-screen printing combined printing, because there are many factors that affect the printing quality, in addition to mastering the operating skills of screen printing and flexo printing, we must also pay attention to the characteristics of different printing methods, so that the two truly achieve advantages Complement each other to form a good combination, such as the use of printing materials and inks, speed matching, standardization, and problems with screen printing itself.
With the application of new materials and new processes, label printing technology will continue to improve, combination printing will gradually become the mainstream method of label printing; combination printing can not only complement the advantages of multiple printing methods, but also create new D. The future market is vast, and I believe that flexo-screen printing combined printing will be the preferred method for future label combined printing.
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