Mirror ink is a kind of screen printing ink with special effects, especially mirror photochromic ink. The ink is printed on the back of transparent plastic material by screen printing. When viewed from the front, due to the interference of light, the printed image is with the viewing angle. Changes can produce holographic images. Mirror light and mirror photochromic inks can be printed on a variety of substrates for unique decorative effects.
In recent years, more and more products have been printed using mirror photochromic inks, such as the keys of mobile phones, the panels of electronic products, and plastic signs, which have increased the value and selling points for screen printing products and are welcomed by users. However, compared with ordinary printing inks, mirror color ink in the printing technology and technical requirements are relatively high, and difficult to control, the following will briefly describe the characteristics of mirror ink, printing methods, storage and precautions, I hope to correctly use the mirror ink Help.
1. The type of mirror ink
Mirror inks include common mirror inks (silver and metallic colors) and mirror light color inks. At present, the scope of the use of ordinary mirror ink is very wide, such as the use of IMD technology to create mobile phone keys, washing machines and other electrical appliances operating panel and electronic products on the decorative parts, etc.; the use of mirror light color ink is focused on decorative, printed products look better than General mirror ink grade is higher.
2. Mirror type ink substrate
Mirror-type inks are mainly used for the printing of transparent sheets, that is, printing on the reverse side (back side) of the material, and show the effect from the front.
Commonly used transparent sheets are: PC (polycarbonate), PMMA (acrylic or plexiglass), hard PVC (polyvinyl chloride), and treated PET (polyester).
Mirror ink has good adhesion to the above transparent sheet, and it can get mirror and mirror color change effect. However, it is worth noting that for PC or PMMA materials, due to processing technology, material purity, molecular weight differences, and material density, some products may not achieve the desired mirror or mirror change due to poor solvent resistance. Must be tested before use, quality can be confirmed before production.
Not only that, in order to get a mirror effect, in addition to the above factors, the mirror ink is composed of a special aluminum powder pigment and a small amount of resin and other basic materials, and the aluminum powder pigment is a sheet, can be obtained in parallel with the surface of the substrate Because of the mirror reflection effect, materials with poor surface smoothness (substrates) and materials that are not resistant to solvents in the ink do not achieve the desired mirror effect.
3. The key points of screen printing ink
(1) In addition to a small amount of resin and flake aluminum pigment in the mirror ink, the solvent accounts for a large proportion in the mirror ink, so the viscosity of the mirror ink is very low, and a screen printing machine of the opening and closing type cannot be used when printing to avoid the mirror ink. When the screen is tilted, excessive flow occurs. Therefore, regardless of manual or machine printing, an elevating screen printing machine should be used so that the thin ink can evenly cover the screen plate. This can prevent screen printing from affecting normal screen printing.
(2) If a screen printing machine is used, the metal re-inking scraper should be replaced with a rubber material, which will facilitate uniform ink coating on the screen.
(3) When printing with mirror ink, the range of ink distribution on the web should be controlled as close as possible to the printing area of ​​the effective graphics. Otherwise, if the coating area is too large, the solvent in the mirror ink quickly volatilizes, easily causing blocking of the web and affecting the ink. Continuous printing.
(4) The solvent of the mirror-like ink is quickly volatilized on the screen. To prevent blocking of the screen, printing must be done continuously while printing. At the same time, care must be taken to avoid air convection and to speed up screen drying.
(5) The printing ink layer should not be too thick. The ink should be printed as thin as possible. Otherwise, the aluminum pigment in the ink will peel off. Remember that mirror inks are not suitable for multicolor overprinting.
(6) The mirror type ink itself has poor shielding performance. In order to obtain a good mirror and mirror color change effect, it is necessary to add a layer of cover type ink. The printed cover type ink should be selected to have good adhesion to the mirror surface and mirror color ink. It does not produce solvent-eroded ink. Such as Seiko mirror silver ink, available cover ink as shown in Table 1. However, there are fewer cover inks that can be used by Seiko mirror photochromic inks. For example, when printing PET materials, only SG700 BLACK inks are provided with T-912 solvent.
4. Printing process of mirror photochromic ink
(1) Types of specular photochromic inks
Divided by color: 641- wide music silver; 642- wide music gold; 643- wide Le Mantao color; 644- deep music deep blue stone and so on. Each ink has A, B, C three particle sizes:
A, 100 μm×100 μm; B, 100 μm×50 μm; C, 50 μm×50 μm.
(2) Selecting mesh according to particle size
A(100μm×100μm) 80 mesh/cm wire mesh
B(100μm×50μm) 100 mesh/cm wire mesh
C(50μm×50μm) Uses 150 Mesh/cm Wire Mesh
(3) Printing process conditions of commonly used substrates
Substrate: Surface treated PET;
Ink: Use SG700 series mirror photochromic ink, diluted with solvent T-912 to 20%;
Screen mesh number: A type, 80 mesh/cm
Class B, 100 mesh/cm
Class C, 150 mesh/cm
Drying conditions: 60 °C temperature, 60 minutes;
Back cover ink: SG700-710 BLACK ink; diluted to 20% with solvent T-912; dried at 60°C for 30 minutes;
Squeegee hardness: control in SH80 ~ 85, thickness 10mm.
5. Mirror ink printing techniques
(1) The tension of the screen is slightly reduced, and the squeegee pressure of the doctor blade is reduced;
(2) The network distance is as small as possible;
(3) ensure continuous printing;
(4) The printing environment should be kept dry, if the air humidity is high, dehumidification measures should be taken, otherwise the printing ink will become jelly in the wet state;
(5) When the ink pigment aggregates and agglomerates, the added solvent will not recover, and it is better not to continue to use it;
(6) The dry conditions of mirror ink printing have a great influence on the mirror effect. Drying at 60-80°C for 10 minutes is more effective than natural drying. After the mirror ink is printed on the glass, it must be dried at a temperature of 100°C or higher. The ink has good adhesion.
In short, the mirror ink is a high-grade decorative ink, its ink is thin as water, screen printing is very volatile, if the printing environment is not good, printing technology is not in place, in the printing prone to blocking the network, the substrate is not dense ink layer, The mirror effect is not ideal. At present, operators who are already using mirror inks should pay attention to understanding the printing conditions of inks and master screen printing techniques so as to ensure that the printed materials meet the expected quality requirements in mass production.
(Author: Sanwa International Printing Equipment Co., Ltd. Chen Shan)
Source: "Printing Technology - Equipment and Special Printing"
Heat Press Machine,Manual Heat Press Co., Ltd. , http://www.china-presses.com