Select Ink: Basic Functions of Common Ink Systems

Choosing an ink suitable for a specific application is important for all printing processes. Professional screen printing workers generally use a thick ink film printing process, which is different from other printing processes in the printing industry. No other printing process has such good light resistance, abrasion resistance and durability. As a thick ink film printing process, there is a clear advantage in printing rigid or soft products. To help select the inks that are suitable for a particular substrate, here are the basic functions of the currently used ink systems.

First, UV ink

Of 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 those based on solvent-based inks and evaporation-drying inks. In solvent systems, the solvent forms a dry ink film upon leaving the ink. UV chemistry contains oligomers, monomers, and photoinitiators. Solvent-based inks contain resins, and UV inks contain oligomers—a distinct resin that is used in solvent-evaporated coatings. The oligomers will chemically react with the monomers in the chemical composition. Monomers are equivalents of solvents in UV inks. The monomer as a carrier provides the viscosity of the ink required for printing.

In UV inks, the coating is 100% curable because all of the material in the coating will change from liquid to solid.

The curing process is exacerbated by photoinitiators. Photoinitiators are the cocatalysts of the chain reaction, and in this reaction, the free radicals or the side chains of the molecules are bordered with 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, and can withstand at least 5 years of outdoor natural environment. Compared with solvent evaporation inks, UV inks have many excellent properties. In print production, 8-10 foot long UV reactors have taken 60-foot gas drying units, which can greatly reduce costs. At present, the printing problem of UV ink is gradually reduced, not only the ink viscosity will not change, but the ink will not evaporate. Due to the perfect management of the ink in production, four-color printing is easier.

Second, water-based UV ink

Some successful prints have used water-based UV inks, the solid content of which meets the requirements for printing on non-coated paper. A high percentage of moisture greatly reduces the thickness of the cured ink film, which can be diluted with water, or it can be washed with water.

Water-based UV inks require lower UV energy than ordinary high-solid UV inks.

The disadvantage of using a water-based UV ink is that it is difficult to handle a lightweight paper or porous paper. Paper edge warpage is a common problem, and the paper absorbs water very 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 is an image printing factory, especially a paper printing factory that often uses more than 80 pounds. When the ink film is dried, the printed paper rarely wrinkles or curls. Vinyl and metal substrates are used in very limited applications. Chemical hardeners are often used in production to improve the appearance of the film. However, considering the fact that die cutting is likely to cause ink debris, the softness of the ink must also be taken into consideration.

Water-based inks are commonly used in the fields of styrene, polyolefins, lightweight papers, etc. They can be used to make durable products and chemical and water-resistant products.

Fourth, epoxy ink

If the epoxy resin is properly mixed, it will have excellent properties that are resistant to various substrates such as glass, metal, ceramics, wood, plastics, and many other materials.

Epoxy inks fall into two main categories: single-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 the baking system of the ink system.

Several catalysts can be added to epoxy inks to make it compatible with almost any substrate. Two-component epoxy resin systems have a much longer shelf life than single components, and colored inks do not degrade quickly. The "pot life" is a limit to the extent that the ink can be used, and the time limit of ink viscosity on the screen is usually expressed in units of hours or minutes. Changing the epoxy resin with a solvent does not affect or extend the pot life.

Five, gold and silver ink

When considering the use of gold and silver ink for decoration, it is necessary to use gold-silver 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 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 maintains its good brightness in acrylic and vinyl resins. Oxidation occurs when gold and silver powder is exposed to water, thus causing problems for water-based inks. For UV inks, the stability of the mixed ink is very short. It is well known to be made of various dry-milled metal powders such as 0mm zinc and copper. However, the phenomenon of gloss dimming 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 luster. Currently there is a transparent laminated film that can protect gold and silver powder pigments. In the case where the powder of gold and silver cannot 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.

Six, plastic, paper and metal printing ink

Plastic, paper and metal printing inks constitute the majority of inks used by image printing and industrial screen printing workers. If you do not currently use these three types of inks for printing, but you plan to use them in the future, you can take a look at the following information, which will help you to make a choice.

1, plastic printing ink

Plastic printing inks are dried by evaporation, oxidation or polymerization and form a physical chemical binder that dissolves the plastic surface similar to corrosion. On the other hand, oxidized and polymeric inks will bond to a highly adhesive known as mechanical gluing. This type of ink can be used for highly solvent-resistant thermoplastic substrates such as polyethylene and polyester.

Varnish screen printing inks are mainly used for printing thermoplastic materials such as acrylic, cellulose acetate, butyrate, nitrocellulose, polyvinyl chloride and combinations thereof. This type of ink system is mainly used for vacuum-molded rigid plastics, but its aging must be checked frequently because they lose their adhesion due to prolonged exposure to light and heat. Some plastic films, such as acrylic, styrene, etc., crack on the surface when the active solvent is used in the varnish. Cracks may be discovered late, sometimes until the print is completed. When printing on acrylic or styrenic materials, specially formulated inks should be used to prevent this from happening.

UV drying on polyethylene can be completed in seconds. No UV-curable ink can 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 compatible substrates. These dyes can be processed by conventional screen printing methods and placed in a 180°F oven 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 does not dry on the screen; the ink can be adjusted with water or glycerin; the screen can be cleaned 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 the inks can be printed on a variety of paints and non-coated papers. The printing of point-of-purchase advertisements, information advertisements, corrugated cartons, signage, and greeting cards are all printed using this kind of ink, and the decorative effect is very good. Finish is the degree of gloss, 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 matting medium or special varnish to the ink. If you change from high light to standard gloss, such as silk, eggshell, and other non-glossy surfaces, it is best to use advertising printing inks.

At present, the most representative inks are advertising inks, nitrocellulose paints and multi-functional inks. These inks are added with a diluent or retarder before printing to give them good ink flow properties. For most ink systems, thinning fluids in the form of diluents, retarders, or fillers make advertising inks cost-per-gallon relatively inexpensive.

Standard glossy or flat-advertisement advertising inks require air drying for 15- 20 minutes, and in jet-dried conditions, it takes only a few seconds. Using a screen of 200-260 lines per inch, for prints with good hiding power, an average of 1,500 square feet per gallon of ink can be printed (1 square foot = 0.0929 square meters).

3, metal printing ink

Precoat metal does not require additional processing of the material. Its 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-measured. In order to obtain the required adhesion performance, the metal surface and ink must reach 265-280°F.

Metal printing inks can be air-drying, thermosetting or catalytic drying. The primer coating on the metal surface can be applied by roll coating, spraying or printing. After applying this primer, the metal is resistant to shearing, punching, molding and other operations. The underlying color also protects the primer. Undercoat resins age under UV light and a clear layer is printed on top to protect the surface. Other coatings must be compatible to ensure adhesion between layers.