Choosing an ink suitable for specialized applications is very important for all printing processes. Professional screen printing workers generally use thicker ink film printing process, which is different from other printing processes in the printing industry. No other printing process has such good light resistance, wear resistance and durability. As a thick ink film printing process, it has obvious advantages in printing rigid or soft products. In order to help choose the ink suitable for a certain substrate, the following introduces the basic functions of the commonly used ink system.
1. UV ink
Among all the ink systems currently used, the UV ink series has had a huge impact on the optical media market in the past 10 years.
Compared with solvent-based inks and evaporative drying inks, UV inks are photoreactive inks. In the solvent system, once the solvent leaves the ink, it becomes a dry ink film. The UV chemical composition contains oligomers, monomers and photoinitiators. Solvent-based inks contain resins, while UV inks contain oligomers—a very different resin than solvent-evaporative coatings. Oligomers will chemically react with monomers in the chemical composition. In UV inks the monomer is the solvent equivalent. The monomer as a carrier can provide the ink viscosity required for printing.
In UV inks, the coating is 100% curable, because everything in this coating will change from liquid to solid.
The curing process is stimulated by the photoinitiator. The photoinitiator is a co-catalyst for the chain reaction, and in this reaction, the radicals or molecules are joined by chains to other molecules, resulting in polymerization of the entire UV ink layer. UV ink can withstand die cutting, bending and forming, and can maintain good resistance and bending resistance, can withstand at least 5 years of outdoor natural environment. Compared with solvent evaporation inks, UV inks have many excellent characteristics. In printing production, 8-10 feet long UV reactors have taken 60 feet long gas drying devices, which can greatly reduce costs. At present, the printing problems of UV inks are gradually reduced. Not only will the ink viscosity not change, but the ink will not evaporate. Due to the perfect management of ink in production, four-color printing is easier.
2. Water-based UV ink
Some successful printing has used water-based UV inks, the solid content of this ink meets the requirements for printing on non-coated paper. The high ratio of moisture greatly reduces the thickness of the cured ink film. This ink can be diluted with water, and the screen can also be washed with water.
Compared with ordinary high-solids UV inks, water-based UV inks require lower energy of ultraviolet light.
The disadvantage of using water-based UV ink is that it is difficult to handle this lightweight paper or porous paper. Paper edge warping is a common problem, this paper absorbs water quickly. The resin system needs to release water quickly without affecting the cross-linking function of the resin.
3. Ordinary water-based ink
Water-based inks have not been greatly improved. The most commonly used are image printing factories, especially those that use paper weighing more than 80 pounds. When the ink film is dry, the printed paper rarely creases or curls. Vinyl and metal substrates are used in very limited applications. Chemical hardeners are often used in production to improve their appearance performance, but when considering die cutting, ink debris is easily caused, so the flexibility of the ink must also be taken into account.
The common fields of water-based ink are styrene, polyolefin, lightweight paper, etc., which can be used to make products with good durability as well as products resistant to chemicals and water.
4. Epoxy resin ink
If the epoxy resin is properly mixed, it will have excellent characteristics of resistance to various substrates, such as glass, metal, ceramic, wood, plastic and many other materials.
Epoxy resin inks are divided into two categories: single-component and two-component. Single-component ink systems are formulated with thermosetting resins. They must be baked and not air-dried. Two-component systems require the addition of catalysts or film hardeners, and have the advantage of air drying. There are currently ink systems for baking formulations.
There are several catalysts that can be added to epoxy resin inks to make them compatible with almost any substrate. Two-component epoxy resin systems have a much longer shelf life than single-component epoxy resins, and color inks do not deteriorate quickly. The "pot life" is a limit for the ink to remain usable. The time limit for the viscosity of the ink on the screen is usually expressed in hours or minutes. Changing the epoxy resin with a solvent will not affect or extend the pot life.
5. Gold and silver powder ink
When considering the use of gold and silver powder inks for decoration, gold and silver powder pigments with connecting materials must be used. The gold and silver powder pigments must float on the surface of the ink film and overprint on it during the drying and curing process. The process of overlapping gold and silver powders is called metal powder suspension.
Currently, gold and silver powder components can be added to solvent-based, water-based and UV inks. Gold and silver powder can maintain its good brightness in acrylic resin and vinyl resin. Since gold and silver powders oxidize when exposed to water, they can cause problems for water-based inks. For UV inks, the stability of the mixed ink lasts very short. It is well known that 0mm zinc, copper and other dry ground metal powder are made. However, the phenomenon of darkening of gloss often occurs, mainly due to improper ink mixing. Gold and silver powder is not suitable for long-term outdoor exposure, because it will eventually lead to a decrease in the gloss of the metal. There is currently a transparent laminated film that can protect gold and silver powder pigments. In the case of gold and silver powder can not maintain the required brightness and temperature, printing workers sometimes use pearlescent pigment instead. Unfortunately, pearlescent pigments do not have the hiding power of gold and silver powder pigments.
6. Plastic, paper and metal printing inks
Plastic, paper and metal printing inks make up most of the inks used by image printing and industrial screen printing workers. If you are not currently using these three inks for printing, but plan to use them in the future, you can look at the knowledge introduced below, it will help you make a choice.
1. Plastic printing ink
Plastic printing inks are dried by evaporation, oxidation or polymerization, and form a physicochemical bond that dissolves the plastic surface, similar to corrosion. On the other hand, oxidized and polymerized inks will bond into a highly adhesive agent called mechanical tack. This type of ink can be used for thermoplastic substrates that are highly resistant to solvents, such as polyethylene and polyester.
Varnish-type screen printing inks are mainly used for printing thermoplastic materials such as acrylic acid, cellulose acetate, butyrate, nitrocellulose, polyvinyl chloride, and combinations thereof. This type of ink system is mainly used for vacuum-forming hard plastics, but it must be regularly checked for aging, because they will lose their adhesion after long-term exposure to light and heat. Some plastic films, such as acrylic and styrene, will crack on the surface when using active solvents in varnishes. The crack may be discovered very late, sometimes until the print is completely completed. When printing on acrylic or styrene materials, specially formulated inks should be used to prevent this from happening.
UV drying on polyethylene can be completed in a few seconds. There is no UV-curable ink that can meet the user's requirements for a wide range of plastics. Polystyrene and PVC use one ink system, while polyethylene and polypropylene use a different ink system.
The functional component in the diffusion ink series is a dye that can penetrate or diffuse onto certain compatible substrates. These dyes can be handled by traditional screen printing methods and placed in an oven at 180 ° F for 30 minutes. Thermal diffusion melts the dye into the plastic, making it an integral part of the plastic.
There are four advantages of the ink system: the ink does not dry on the screen; the ink can be adjusted with water or glycerin; the screen can be washed with water;
2. Paper printing ink
Among all the above ink systems, advertising printing inks are the easiest to use. This ink can be printed on various coating and non-coated papers. This kind of ink is used to print the advertisements of purchase points, information advertisements, corrugated boxes, signs and greeting cards, etc., and the decoration effect is very good. The finish is the degree of gloss. The gloss is usually determined by the type of ink, but if it needs to be changed to a certain degree, it is necessary to add a matte medium or special ink to the ink. If you change from high gloss to standard gloss, such as silk, eggshell and other matte surfaces, it is best to use advertising printing ink.
At present, the most representative inks are advertising inks, nitrocellulose paint and multifunctional inks. Before printing these inks, diluent or retarder should be added to make them have good ink flow performance. For most ink systems, thinner fluids in the form of thinners, retarders / fillers make advertising printing inks relatively cheaper per gallon.
Standard gloss or flat tone advertising inks need to be air-dried for 15--20 minutes, and only a few seconds under the conditions of air-jet drying. Using a 200-260 line / inch screen, for prints with good hiding power, an average of about 1500 square feet per gallon of ink can be printed (1 square foot = 0.0929 square meters).
3. Metal printing ink
Pre-coated metal does not require additional processing of the material. The surface has been treated and coated with a coating. Polyester coating and acrylic coating are the two most commonly used metal coatings, but the metal must be pre-determined. In order to obtain the required adhesion properties, the metal surface and ink must reach 265-280 ° F.
Metal printing inks can be air-dried, or thermoset or catalytically dried. To coat the primer on the metal surface, methods such as roller coating, spray coating or printing can be used. After applying this primer, the metal is resistant to shearing, punching, and forming operations. The color of the bottom layer also protects the bottom coating. The primer coating resin will age under UV light. A transparent layer is printed on it to protect its surface. Other coatings must be compatible to ensure the adhesion between the coatings.
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