Selecting an ink for a specific application is important for all printing processes. No other printing process has such good lightfastness, abrasion 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 systems.
1. Water-based UV ink
Some successful printing has used water-based UV inks that have a solids content suitable for printing on uncoated papers. 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-solid UV inks, water-based UV inks require lower UV energy.
The disadvantage of using water-based UV inks is that it is difficult to handle a lightweight or porous paper. Paper edge warping is a common problem, and this paper absorbs water very quickly. The resin system needs to release water quickly without affecting the crosslinking function of the resin.
2. Ordinary water-based ink
Water-based inks haven't been much improved. The most commonly used is the image printing factory, especially the paper printing factory that often uses more than 80 pounds. When the ink film dries, the printed paper rarely wrinkles or <edges. Vinyl and metal substrates are used in a very limited number of applications. In production, chemical hardening agents are often used to improve its appearance performance, but it is easy to cause ink debris when die-cutting is considered, so the softness of the ink should also be taken into account.
Water-based inks are commonly used in styrene, polyolefin, lightweight paper, etc. They can be used to make products with good durability and chemical and water-resistant products.
3. UV ink
Of all the ink systems in use today, the UV ink family has had a huge impact in the optical media market over the past 10 years.
Compared with those solvent-based inks and evaporative drying inks, UV inks are photoreactive inks. In solvent systems, the solvent forms a dry ink film once it leaves the ink. The UV chemistry contains oligomers, monomers and photoinitiators. Solvent-based inks contain resins, while UV inks contain oligomers—a very different resin than those used in solvent-evaporating coatings. The oligomer will chemically react with the monomers in the chemical composition. Monomers are the equivalent of solvents in UV inks. Monomer as a carrier can provide ink viscosity required for printing.
In UV inks, the coating is 100% curable because everything in this coating will transform from liquid to solid.
The curing process is activated by photoinitiators. The photoinitiator is a co-catalyst for the chain reaction, and in this reaction, the free radical or the edge of the molecule connects to the chain and connects with other molecules, resulting in the 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 outdoor natural environments for at least 5 years. Compared with solvent evaporation ink, UV ink has many excellent characteristics. In printing production, the 8-10 feet long UV reactor has replaced the 60 feet long gas drying device, which can greatly reduce the cost. At present, the printing problems of UV ink are gradually reduced, not only the viscosity of the ink will not change, but also the ink will not evaporate. Four-color printing is easier due to the perfect management of ink in production.
4. Epoxy resin ink
When properly mixed, epoxies have excellent resistance to a wide variety of substrates such as glass, metal, ceramics, wood, plastics, and many other materials.
Epoxy inks fall into two broad categories: one-component and two-component. One-component ink systems are formulated with thermoset resins, they need to be baked and cannot be air dried. The two-component system needs to add a catalyst or hardener, and has the advantage of air drying. There are currently baked ink systems for this ink system.
There are several catalysts that can be added to epoxy inks to allow them to be bonded to almost any kind of substrate. Two-part epoxy systems have a much longer pot life than one-part, and the colored inks will not deteriorate as quickly. "Pot life" is a limit for the ink to remain usable, and the time limit for ink viscosity on the screen is usually expressed in hours or minutes. Altering epoxies with solvents will not affect or extend pot life.
5. Gold and silver powder ink
When considering the use of gold and silver powder inks for decoration, it is necessary to use gold and silver powder pigments with binders. Gold and silver powder pigments need to float on the surface of the ink film and overprint on it during the drying and curing process. The process of gold and silver powder overlapping each other is called metal powder suspension phenomenon.
At present, gold and silver powder components can be added to solvent-based, water-based and UV inks. Gold and silver powder retains its brilliance well in acrylics and vinyls. Since gold and silver powder oxidizes when exposed to water, it can cause some problems for water-based inks. For UV inks, the stability of mixed inks lasts very short. It is well known that 0mm zinc, copper and other dry-ground metal powders are made. However, the phenomenon of darkening of gloss often occurs, mainly due to improper mixing of inks. Gold and silver powder is not suitable for long-term outdoor exposure, because it will eventually lead to a loss of metallic luster. There is currently a clear laminating film that protects gold and silver powder pigments. In the case that gold and silver powder cannot maintain the required brightness and temperature, printing workers sometimes use pearlescent pigments instead. Unfortunately, pearlescent pigments do not have the hiding power of gold and silver powder pigments.
6. Plastic, paper and metal printing ink
Plastic, paper and metal printing inks make up the majority of inks used by graphic and industrial screen printers. If you do not currently use these three inks for printing, but you plan to use them in the future, you can take a look at the knowledge introduced below, which will help you make a choice.
1. Plastic printing ink
Plastic printing inks dry by evaporation, oxidation or polymerization and form a physicochemical bond that dissolves the plastic surface, similar to corrosion. Oxidative and polymeric inks, on the other hand, will bond into a highly adhesive form known as mechanical tack. These inks can be used on 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 their combinations. These ink systems are primarily used for vacuum-formed rigid plastics, but their aging needs to be checked frequently, as they lose adhesion with prolonged exposure to light and heat. Some plastic films, such as acrylic, styrene, etc., crack the surface when active solvents are used in the varnish. Cracks may not be discovered until late, sometimes not until after the print is fully finished. When printing on acrylic or styrene materials, inks specially formulated should be used to prevent this from happening.
UV drying on polyethylene can be done in seconds. None of the UV-curable inks 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 range is a dye that penetrates or diffuses onto certain compatible substrates. These dyes can be processed by traditional screen printing methods and baked 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 advantages of this ink system are fourfold: the ink does not dry on the screen; the ink can be adjusted with water or glycerin; the screen can be washed with water; and the printed matter is fade-resistant.
2. Paper printing ink
Of all the above ink systems, advertising printing inks are the easiest to use and can be printed on a variety of coated and uncoated papers. Point-of-purchase advertisements, informational advertisements, corrugated boxes, signs and greeting cards are all printed with this ink for decorative effect. 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, a matte medium or a special varnish must be added to the ink. If you change from high gloss to standard gloss, it is better to use advertising printing ink for various matte surfaces such as silk and eggshell.
At present, the most representative inks are advertising inks, nitrocellulose paints and multifunctional inks. These inks are added with diluents or retarders before printing to give them good ink flow properties. Thinning fluids in the form of thinners, retarders/fillers make advertising printing inks relatively inexpensive per gallon for most ink systems.
Standard glossy or flat-tone advertising inks need to be air-dried for 15--20 minutes, and it only takes a few seconds for air-jet drying.
3. Metal printing ink
Prepainted metals require no additional treatment of the material. Its surface has been treated and coated with a coat. Polyester coatings and acrylic coatings are two commonly used metal coatings, but require pre-measurement of the metal. Metal surfaces and inks need to be at 265-280°F to obtain the required adhesion properties.
Metallic printing inks can be air dry, heatset or catalytically dry. Coating the primer on the metal surface can adopt methods such as roller coating, spraying or printing. When this primer is applied, the metal resists operations such as shearing, punching, forming, etc. The underlying color also protects the underlying paint. The primer resin will age under UV light, and a transparent layer is printed on it to protect its surface. Other coatings need to be compatible to ensure the adhesion between the coatings.
