Development of UV inks for screen printing

Compared with offset printing, lead printing and other printing processes, screen printing belongs to a small industry, but screen printing is developing faster than other printing processes, and it will develop in the direction of cutting-edge, mechanization and specialization. As an ink manufacturer, it is also a part of the paint, paint and varnish production industries. There are many manufacturing processes. The raw materials produced under certain conditions can be used for the production of screen printing inks, and they may be high quality inks.

The raw materials for the production of screen inks are basically the raw materials and resins needed for the production of other printing inks, house paintings, and the like. Mixing these raw materials and resins in a packaging can be used for screen printing. As a screen printer, its most prominent advantage is that it can push the squeegee to print on very long materials. When we analyze the printed materials and the chemical components contained in them, we find that the content of these chemical components far exceeds the amount used to produce the ink. As a manufacturer, we are faced with raw material problems and need to produce inks suitable for various materials. In fact, our production scale is small. Therefore, it is very difficult for us to produce various kinds of inks suitable for printing on various materials. Our increase in sales is also insufficient for researchers to research and develop in this area because we are still small producers.

UV inks are not new products. It has been a few years old. Can UV inks be used as a universal product in other printing? Most offset printing plants now print, dry, and stack prints at the same speed as substrates, just speed, and UV inks are not the best choice for offset printing. Most cylinder offset press designs are not equipped with UV curing reactors or With the UV lamp space, the offset printing factory would rather purchase the UV inks for the purchase of equipment because UV inks are expensive.

Right now, there are certain aspects of offset printing that use UV inks, such as metal surface decoration printing, and still use plastisol inks. However, they require very long conveyors for curing. Now, UV inks are used to make beer cans. From the perspective of screen printing and ink manufacturers, UV inks are well suited for screen printing.

Before talking about the characteristics and structure of UV inks, it is important to understand the physical or chemical changes that occur during the process of ink change from liquid to solid (curing process). The commonly used screen printing inks, its change can be divided into two basic types: solvent volatile type and chemical reaction type.

Solvent-evolving inks consist of three parts: resins, solvents, and additives. Most of the resins are ethylene, propylene and materials or paints. All solvent-evaporated coatings are classified as varnish. The powdered or solid resin is dissolved in a solvent and then added to the solvent. This solvent may be a mixture of two or three different components. Finally, additives may be added. The additives may be pigments, plasticizers or other additives. This type of ink is volatilized by a solvent and changes from a liquid state to a solid state. Once the solvent is completely evaporated, the ink becomes a dry film and the resin returns to the solid state.

Chemically reactive inks consist of four parts: resins, solvents, additives, and drying oils/catalysts. The resin is also dissolved in the solvent, the solvent is added to achieve the printing viscosity using the ink, and then the additive and the drying oil are added. The process of changing the ink from a solid to a liquid is an oxidation reaction, ie, a chemical reaction occurs between oxygen, a drying oil, and a resin to generate very active and unstable atomic groups, and these radicals rapidly react and polymerize, in other words, The radical reacts with oxygen molecules in the drying oil. After the polymerization reaction, the ink becomes a dry film and the solvent is volatilized and released. It only plays a role in increasing the viscosity in the printing, regardless of the curing and drying. There are also differences in this type of chemical reaction and catalysts can be added. Such as heat-curing enamel, rely on heat to promote the use of the right reaction, some need air drying, some need heat drying, some need heat and air or oxygen and catalyst, the ink becomes a dry film, the solvent volatilizes, it prints It only plays a role in increasing the viscosity, regardless of curing drying. There are also differences in this type of chemical reaction and catalysts can be added. Such as heat-curing enamel, by heat to promote the reaction, some need air drying, some need heat drying, some need heat and air or oxygen and catalyst

UV light curing reaction is a new chemical reaction. The structures of UV inks include resins, monomers instead of solvents, additives and photoinitiators. The resin in the UV ink is very different from the resin of the solvent-volatile ink. It is reactive and it can react with a certain product in other chemical reactions. In the UV ink, it reacts with the monomer. The monomer is a low molecular weight chemical that can replace the solvent to some extent and it can reduce the viscosity for printing. But in addition to serving as a solvent or diluent, it also has a very important role to play in chemical reactions. Each component of the UV ink can react chemically because it is 100% cured and all components will become solid by chemical reaction.

Additives in UV inks are pigments and the like. The UV ink curing process is the photoinitiator reaction process. The photoinitiator acts as an atomic group, which produces a chain reaction. It has photosensitivity, and after being exposed to light, it becomes an excited molecule, and the excited molecule spontaneously splits into two or more atomic groups. These atomic groups undergo chain polymerization and this is the curing process of the UV ink.

Solvents are an important part of screen printing inks. The resins, plasticizers, and pigments are mixed in the correct proportions to achieve a certain viscosity that is suitable for the printing of a certain type of printing materials. Solvents are critical here, and 90% of the problems are related to solvents. In the production of inks, a large number of petrochemicals were used. The user will complain that the ink does not dry after passing through the conveyor belt. The nature of the ink varies from day to day. The ink is dried on the screen, and the substrate absorbs all the solvent. How to solve these problems is related to the solvent. Different regions, different temperature and humidity, ink performance is different; different elevations, different solvent boiling point, ink performance is also different, which are related to solvents.

The government now prohibits us from using too much solvent because the solvent evaporates into the air and causes environmental pollution. We can only use 5% solvent content, so in the future there will be petrochemical solvents not only difficult to obtain, expensive, but also in the situation where we can not use solvents, the government will make us unemployed, we have to work hard to develop a new ink system , Photoreactive ink - UV ink production is a feasible way.

As a screen printer, not only does the printing ink have beautiful colors, because the ink plays a decorative role in many aspects. This requires the ink to withstand the process of die cutting, bending, and forming. The ink is resistant to gasoline, chemical solvents, and resistance. Wear, weather resistance, and long life performance, and the ink can be printed on a variety of materials. It takes time to ensure that the ink has the above properties. Adhesion is good on the one hand, so that the ink has solvent resistance, wear resistance and other properties, printability to meet user requirements is another aspect. Here is no more explanation of the advantages of UV ink. UV ink can save a lot of space, which is very important today. The fully automatic printing equipment used in printing plants is equipped with 12, 15, 18-meter-long conveyor belts. The cost of starting gas dryers is very high. The UV inks used today can only be used. 2,2.5,3 meters long conveyor belt. The speed of the machine is not as important as the speed of the entire printing process. We can transport the prints in a box not far from the printing press. We often talk about saving energy, and we will use this as a speculation. Drying high-solvent inks requires a lot of gas, air, electricity, and money. The use of UV inks will greatly reduce these costs.

The term "printability" was coined for solvent-based inks. As long as the UV ink is used, the printing quality is as good as the screen printing plate. Since the UV ink is 100% solid and there is no volatilizable solvent, the ink viscosity does not change. In the past, printers had to complete a very long cycle of printing, especially when printing fine patterns, and they always encountered the problem of viscosity change. They would apply ink to the front and back to volatilize the solvent and change the viscosity. Every 50 to 75 prints. At that time, the thickness of the ink layer will be different, while the UV ink, the quality of the work day is exactly the same. Cleaning is a big problem, especially in factories where there is a long period of time between printing enamels or drying. There is a lot of dust in the air. When printing with UV inks, the prints will be immediately put into the curing equipment to dry, so the prints are not exposed to impurities. many.

UV inks are expensive and are 2 to 5 times more expensive per gallon than regular inks. General inks, whether solvent-evaporating or chemical-reactive, have a solid content of about 40%, in other words 60% are solvents, and UV inks have a solid content of 100%, which is 2 to 5 times that of general inks. If a 70-thread/cm wire mesh is coated with a general solvent-evolving ink, the thickness of the dried ink layer is only 13 μm, and UV ink is used to print on the same screen. After curing, the thickness of the ink layer reaches 25 to 37 μm. Therefore, in order to obtain a doubled ink layer thickness, a very fine screen printing UV ink is used.

So how to prepare for using UV ink? First, you need a reaction or curing device. We call the curing device a reactor because the UV ink actually did undergo a chemical reaction during the solidification process from liquid to solid. To meet special needs, care should be taken when purchasing curing equipment. For any heat-sensitive material, care should be taken to ensure its unique properties. Looking at the energy released from UV ink tubes, many devices operate at high temperatures and can deform the substrate. Therefore, UV reactors are more commonly designed and placed than on conveyor belts. Using UV inks requires rigorous controls and procedures. When printing black vinyl ink, you can use 67 - 122 lines / cm mesh screen, mesh screen number, resulting in the best print quality, ink hiding power, then the printer must use and must use the screen. A coarse mesh screen or a blunt squeegee thickens the ink layer but does not cure. Because no matter how much the exposure time, UV light source can not penetrate into the thick film layer, so the ink layer surface is cured, because the ink layer is not cured at the bottom, will also make the ink adhesion.

The photosensitive film plays a very important role in the use of UV ink. The diaphragm is thick and the printed ink layer is thick. A 25 to 37-micron thick indirect template can print very fine text and feel as clear as Braille. Since the UV ink does not dry on the screen, it prints the tiny pinholes on the plate. UV inks are expensive, so it is very important to keep inventory and color controls tightly. After printing, make sure that the screen is clean. If there is a little UV ink remaining on the screen, and this screen is placed in a well-lit room, this block will not be used for printing.

For solvent-based inks, a production line costs $50,000, while UV inks cost $150,000 for the same amount of ink production lines due to the high cost of raw materials. We must have suitable products and guarantee sales to change the production line in order to balance the difference between the two. Due to the complex range of ink applications and the variety of substrates, we must choose several applications. Even UV inks cannot do all the work.

As an ink manufacturer, the target is for a large amount of customers, such as UV reactors, new screens, and the like, and can require a large amount of UV inks for long-term printing of a certain type of product. If it is a small-scale silk screen printer, it is impossible for the manufacturer to produce specially formulated UV inks suitable for the printing of various materials. UV ink is an effective way to improve product quality and simplify production processes. The use of UV ink is also a good way to protect the natural energy source according to the production rules of the product. Using UV ink can make the paper leave the high-speed printing machine and stack it into 2 to 3 meters high, which is our dream.