Select ink: basic functions of common ink systems
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Choosing an ink for a specific application is important for all printing processes. Professional screen printers generally use a thicker ink film printing process, which is different from other printing processes in the printing industry. No other printing process has such good light fastness, abrasion resistance and durability. As a thick ink film printing process, it has obvious advantages in printing rigid or soft products. To help select inks for a certain substrate, the basic functions of the currently used ink systems are described below.
First, UV ink
Among all the ink systems currently in use, the UV ink series has had a huge impact in the optical media market over the past 10 years.
UV inks are photoreactive inks compared to solvent based inks and evaporative drying inks. In a solvent system, the solvent becomes a dry ink film once it leaves the ink. The UV chemical composition contains oligomers, monomers and photoinitiators. The solvent-based ink contains a resin, and the UV ink contains an oligomer - a completely different resin from that used for solvent evaporation type coatings. The oligomer will chemically react with the monomer in the chemical composition. Monomers are equivalents of solvents in UV inks. The monomer acts as a carrier to provide the viscosity of the ink required for printing.
In UV inks, the coating is 100% curable because everything in the coating will change from liquid to solid.
The curing process is intensified by a photoinitiator. The photoinitiator is a cocatalyst for the chain reaction, in which the free radical or the pendant chain of the molecule is flanked by other molecules, resulting in polymerization of the entire UV ink layer. UV inks can withstand die cutting, bending and forming, and maintain good resistance and bending resistance, at least for five years of outdoor natural environment. UV inks have many excellent properties compared to solvent evaporative inks. In print production, the 8-10 foot long UV reactor has taken 60 feet of gas drying equipment, which greatly reduces costs. At present, the printing problem of UV inks is gradually reduced, not only the viscosity of the ink does not change, but also the ink does not evaporate. Four-color printing is made easier by the perfect management of the inks in production.
Second, water-based UV ink
Some successful printing uses water-based UV inks that have a solids content that 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 or the screen can be washed with water.
Water-based UV inks require less UV energy than conventional high-solids UV inks.
A disadvantage of using water-based UV inks is that it is difficult to handle one such lightweight paper or porous paper. Paper edge warping is a common problem and the paper absorbs water quickly. The resin system needs to release water quickly without affecting the cross-linking function of the resin.
Third, ordinary water-based ink
Water-based inks have not been greatly improved. The most commonly used image printing factory, especially paper printing plants that often use more than 80 pounds. When the ink film is dried, the printed paper is rarely wrinkled or curled. Vinyl and metal substrates are used in very limited applications. Chemical hardeners are often used in production to improve the appearance of the film, but it is easy to cause ink crumbs when considering die-cutting, so the softness of the ink must also be taken into account.
Water-based inks are commonly used in the fields of styrene, polyolefins, lightweight paper, etc., and they can be used to produce durable products as well as chemical and water resistant products.
Fourth, epoxy resin ink
If the epoxy resin is properly mixed, it will have excellent properties against various substrates, such as glass, metal, ceramics, wood, plastic, and many other materials.
Epoxy resins are divided into two broad categories: one-component and two-component. One-component ink systems are formulated with thermosetting resins that must be baked and not air dried. Two-component systems require the addition of a catalyst or hardener and have the advantage of air drying, which is currently available in baking formulations.
Several catalysts can be added to epoxy inks to bond to virtually any substrate. Two-component epoxy systems have a much longer shelf life than single components, and color inks do not deteriorate quickly. The "pot life" is a limit on which the ink can be used. The time limit of the viscosity of the ink on the screen is usually expressed in hours or minutes. Changing the epoxy resin with a solvent does not affect or extend the pot life.
Fifth, gold and silver powder ink
When considering the use of gold and silver powder ink for decoration, it is necessary to use a gold and silver powder pigment with a binder. The gold-silver pigment must float on the surface of the ink film and be superimposed on it during drying and curing. The process in which gold and silver powders overlap each other is called metal powder suspension.
Gold and silver powder components can now be added to solvent based, water based and UV inks. Gold and silver powder maintains its good brightness in acrylic and vinyl resins. Since gold and silver powder will oxidize when exposed to water, it will cause some problems for water-based inks. For UV inks, the stability of the mixed ink lasts for a very short time. It is well known that 0mm zinc, copper and other dry-grinding metal powders are used. However, the phenomenon of gloss darkening often occurs, mainly due to improper ink mixing. Gold and silver powders are not suitable for long-term outdoor exposure because they eventually lead to a decrease in metallic gloss. There is currently a transparent laminate film that protects gold and silver pigments. In the case where the gold and silver powder does not maintain the required brightness and temperature, the printer sometimes replaces it with a pearlescent pigment. Unfortunately, pearlescent pigments do not have the hiding power of gold and silver pigments.
Sixth, plastic, paper and metal printing inks
Plastic, paper and metal printing inks make up most of the ink used in image printing and industrial screen printing workers. If you don't currently use these three inks for printing, but you have plans to use them in the future, you can take a look at the knowledge described below, which will help you make your choice.
1, plastic printing ink
The plastic printing ink is dried by evaporation, oxidation or polymerization and forms a physicochemical bond that dissolves the surface of the plastic, similar to corrosion. On the other hand, oxidized and polymeric inks will bond into a highly adherent agent called mechanical gluing. These inks can be used in highly solvent resistant thermoplastic substrates such as polyethylene and polyester.
Varnish-based screen printing inks are primarily used to print thermoplastic materials such as acrylic acid, cellulose acetate, butyrate, nitrocellulose, polyvinyl chloride, and combinations thereof. These ink systems are mainly used for vacuum-formed rigid plastics, but their aging must be checked frequently because they lose their adhesion due to prolonged exposure to light and heat. Some plastic films, such as acrylic acid, styrene, etc., have cracks on the surface when the active solvent is used in the varnish. Cracks may be discovered very late, sometimes until the prints are all completed. When printing on acrylic or styrene materials, specially formulated inks should be used to prevent this from happening.
UV drying on the polyethylene can be done in a few seconds. No UV-curable inks meet the user's requirements for a wide range of plastics. Polystyrene and PVC use an ink system, while polyethylene and polypropylene use a different ink system.
The functional component of the diffusion ink series is a dye that can penetrate or diffuse onto certain substrates. These dyes can be manipulated by conventional 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.
The ink system has four advantages: the ink is not dried on the screen; the ink can be adjusted with water or glycerin; the screen can be washed with water; and the print is resistant to fading.
2, paper printing ink
In all of the above ink systems, advertising printing inks are the easiest to use and can be printed on a variety of coatings and non-coated papers. Purchase point advertisements, information advertisements, corrugated boxes, signs and greeting cards are all printed using this ink, and the decoration effect is very good. The finish is the degree of gloss, which is usually determined by the type of ink, but if it needs to be changed to a certain degree, a matte medium or a special varnish is added to the ink. If it is changed from high light to standard gloss, such as silk, eggshell and other matt surfaces, it is best to use advertising printing ink.
The most representative inks currently available are advertising inks, cotton varnishes and multi-functional inks. These inks are added with a diluent or retarder prior to printing to provide good ink flow properties. For most ink systems, thinners in the form of diluents, retarders/fillers make advertising printing inks relatively cheaper per gallon.
Standard gloss or flat-adjusted advertising inks require air drying for 15-20 minutes, in jet-dry conditions, in just a few seconds. With a 200-260 wire/inch screen, the average print per liter of ink is about 1500 square feet (1 square foot = 0.0929 square meters) for prints with good hiding power.
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 coatings and acrylic coatings are the two most common metal coatings, but metals must be pre-measured. In order to achieve the desired adhesion properties, the metal surface and ink must reach 265-280 °F.
The metallic printing ink can be air dried or thermoset or catalytically dried. The primer may be applied to the metal surface by roll coating, spraying or printing. After applying this primer, the metal is resistant to shearing, punching, forming, and the like. The underlying color also protects the primer. The primer resin ages under UV light, and a transparent layer is applied to protect the surface. Other coatings must be compatible to ensure adhesion between the coatings.