Development of UV ink for screen printing
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Compared with offset printing, printing and other printing processes, screen printing is a small industry, but screen printing is developing faster than other printing processes, and it will be developed in the direction of cutting-edge, mechanization and specialization. As an ink manufacturer, it is also part of the paint, paint and varnish production industry. There are many manufacturing processes. The raw materials produced under certain conditions can be used for the production of screen printing inks, and may be high quality inks.
The raw materials for the production of screen inks are basically the raw materials, resins and the like required for the production of other printing inks, house paintings. These raw materials and resins can be used for screen printing by mixing them in one package. As a screen printer, the most prominent advantage is that it can push the squeegee to print on very long materials. When we analyze the substrate and the chemical components contained in it, we find that the content of these chemicals 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, so it is difficult for us to produce various types 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, and they have been around for a few years. Can UV inks be used as general-purpose products in other printing? Most offset printing factories now print, dry and stack prints at the same speed as the substrate. Just speed, UV ink is not the best choice for offset printing. Most roller color offset presses are not equipped with UV curing reactors or The space of the UV lamp, the offset printing factory prefers to purchase equipment for the purchase of UV ink, because the price of UV ink is very expensive.
There are certain aspects of offset printing using UV inks, such as metal surface decoration printing, which still uses thermosetting inks, but requires a long transfer for curing. Now, like the production of beer cans, UV inks are used. From the standpoint of screen printing and the ink manufacturer's point of view, UV inks are very suitable 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 in the process from ink to solid state (curing process). Commonly used screen printing inks, the variations can be divided into two basic types: solvent volatilization and chemical reaction.
Solvent-evaporable inks consist of three parts: resin, solvent and additives. Most of the resins are ethylene, propylene and materials or paints. All solvent-evaporable coatings are classified as varnishes. The powdered or solid resin is dissolved in a solvent, and then a solvent is added. The solvent may be a mixture of two or three different components, and finally the additive may be a pigment, a plasticizer or the like. This type of ink evaporates from the solvent and changes from a liquid to a solid. Once the solvent has evaporated, the ink becomes a dry film and the resin returns to a solid state.
The chemically reactive ink consists of four parts: a resin, a solvent, an additive, and a drying oil/catalyst. The resin is also dissolved in a solvent, the solvent is added to the ink to achieve a printing viscosity, and then the additive and the drying oil are added. The process in which the ink changes from a solid to a liquid is a process of oxidation, that is, a chemical reaction between oxygen, a dry oil, and a resin, producing a very active, unstable atomic group that reacts rapidly and undergoes polymerization, in other words, The radical reacts with oxygen molecules in the dried oil. After the polymerization, the ink becomes a dry film, and the solvent is volatilized and released, which only plays a role of increasing the viscosity in printing, and is independent of curing and drying. There are also differences in this type of chemical reaction, and a catalyst can be added. For example, thermosetting enamels rely on heat to promote the use of right, some require air drying, some require thermal drying, some require heat combined with air or oxygen and catalyst, the ink becomes a dry film, the solvent is released and it is printed. It only plays a role in increasing the viscosity, and has nothing to do with curing and drying. There are also differences in this type of chemical reaction, and a catalyst can be added. For example, thermosetting enamels rely on heat to promote the reaction, some require air drying, some require thermal drying, and some require heat in combination with air or oxygen and catalyst.
UV photocuring is a new chemical reaction. The structure of the UV ink includes a resin, a monomer instead of a solvent, an additive, and a photoinitiator. The resin in the UV ink is quite different from the resin of the solvent-evaporable ink. It is reactive and can react with a certain product in other chemical reactions. In the UV ink, it can react with the monomer. A monomer is a low molecular weight chemical that, to some extent, replaces the solvent, which reduces the viscosity for printing. But in addition to acting as a solvent or diluent, it has a very important role - to participate in chemical reactions. Each component in the UV ink can react chemically because it is 100% cured and all components will become solid by chemical reaction.
The additive in the UV ink means a pigment or the like. The curing process of the UV ink is the reaction process of the photoinitiator. The photoinitiator acts as a radical, which produces a chain reaction. It has photosensitivity. After receiving light, it becomes an excited molecule. The excited molecule spontaneously splits into two or more atomic groups. These atomic groups undergo chain polymerization, which is the curing process of UV ink.
Solvents are an important part of screen printing inks. The resin, plasticizer and pigment are mixed in the correct proportion to achieve a certain viscosity, which is suitable for the printing of certain types of printing materials. The solvent is very important here, and 90% of the problems are related to the dissolution. A large amount of petrochemical is used in the production of inks. Users will complain that the ink does not dry after passing through the conveyor belt. The ink is different from day to day. The ink is dried on the screen, and the substrate absorbs all the solvent. How to solve it is related to the solvent. Different regions, different temperatures and humidity, different ink properties; different altitudes, different boiling points of the solvent, different ink properties, which are related to solvents.
Now the government prohibits us from using too much solvent because the solvent evaporates into the air, causing environmental pollution. We can only use 5% solvent content, so in the future there will be petrochemical solvents that are difficult to obtain, expensive, and solvent-free, the government will make us unemployed, we have to work hard to develop a new ink system. , Photoreactive inks - the production of UV inks is a viable route.
As a screen printer, not only do you want the color of the printing ink to be beautiful, because the ink plays a decorative role in many aspects, which requires the ink to be able to withstand the process of die cutting, bending and molding. The ink is resistant to gasoline, chemical solvents and resistant. Wear, weather resistance, long life and inks can be printed on a variety of materials. It takes time to ensure that the ink has the above properties. The adhesion of the ink is good on the one hand, so that the ink has the properties of solvent resistance, wear resistance, etc., and the printability meets the user's requirements and is another aspect. The advantages of UV ink are not explained here. UV ink saves a lot of space, which is very important today. The automatic printing equipment used by the printing factory is equipped with 12, 15 and 18 meters long conveyor belts. It is very expensive to start the gas dryer. Now the UV ink can be used only. 2, 2.5, 3 meter long conveyor belt. The speed of the machine is not as important as the speed of the entire printing process. We can place the print in a box not far from the press. We often talk about preserving energy and will speculate on this. Ink with high solvent content requires a lot of gas, air, electricity and money, U The use of V ink will greatly reduce these consumptions.
The term "printability" is specifically formulated for solvent based inks. As long as the UV ink is used, the printing quality is as good as that of the screen. Since the UV ink is 100% solid and has no volatile solvent, the ink viscosity does not change. In the past, printers had to finish a long period of printing, especially when printing fine patterns. They always encountered the problem of viscosity change. They would apply ink before and after, volatilize the solvent, change the viscosity, and print every 50 to 75 sheets. When the thickness of the ink layer is different, the UV ink, the quality of the printed day is exactly the same. Cleaning is a big problem, especially in factories that are shorter than those that print enamel or have a long drying cycle. There is a lot of dust in the air. When printing with UV ink, the printed products will be put into the curing equipment and dried immediately. Therefore, the printed matter is not exposed to impurities. many.
UV inks are expensive and cost two to five times more per gallon than regular inks. The general ink, whether it is a solvent volatilization type or a chemical reaction type, has a solid content of about 40%, in other words, 60% is a solvent, and a UV ink solid content is 100%, which is 2 to 5 times that of a general ink. If a general solvent volatilization ink is applied to a 70 line/cm screen, the dried ink layer is only 13 microns thick, and is printed on the same screen with UV ink, and the thickness of the ink layer after curing is 25 to 37 microns. Therefore, in order to obtain a multiple thickness of the ink layer, the UV ink is printed with a very fine screen.
So how do you prepare for using UV ink? First, a reaction or curing device is required. We call the curing equipment a reactor because the UV ink does react chemically during the curing process from liquid to solid. To accommodate special needs, care should be taken when purchasing curing equipment. Care should be taken to ensure the unique properties of any heat sensitive material. From the energy released from the UV ink tube, many devices operate at high temperatures and can distort the substrate, so designing and producing a UV reactor is more common than placing a UV tube on a conveyor belt. The use of UV inks requires tight controls and procedures. When printing black vinyl ink, a 67-122 line/cm screen can be used, and the mesh size is different, resulting in the best print quality and ink hiding power, so the printer has to use and must use the screen. A coarse mesh or blunt scraper will thicken the ink layer but will not cure. Since the UV light source cannot penetrate into the thick film layer regardless of the exposure time, the surface of the ink layer is cured, and the adhesion of the ink is also lowered because the bottom of the ink layer is not cured.
The photosensitive film plays a very important role in the use of UV ink. The film is thick and the printed ink layer is thick. A 25 to 37 micron thick indirect stencil that prints very fine graphics and feels as clear as Braille. Since the UV ink does not dry on the screen, it can print small pinholes on the plate. UV inks are expensive, so it is important to keep inventory and color control in strict condition. After printing, the screen should be cleaned. If there is a little UV ink left on the screen, and this screen is placed in a well-lit room, this piece will not be used for printing.
For solvent-based inks, a production line costs $50,000, while UV inks, which cost the same amount of ink, cost $150,000 due to the high cost of raw materials. We must have the right product and guarantee the sales volume in order to change the production line to balance the difference between the two. Due to the complex application range of inks and the variety of substrates, we have to choose several applications. Even UV inks can't do all the work.
As an ink manufacturer, the target is to use a large amount of customers, such as UV reactors, new screens, etc., and can require a large amount of UV ink for long-term printing of certain types of products. In the case of small-scale screen printers, it is impossible for producers to produce specially formulated UV inks for printing on a variety of materials. UV ink is an effective solution to improve product quality and simplify production processes. The use of UV ink is also a good way to protect natural energy in accordance with product production rules. Using UV ink to get the paper out of the high-speed printing press, it is 2 to 3 meters high, which is what we dream of.