Flexo printing

Before 1920, flexo printing was also called aniline printing because the ink used in this printing method was aniline ink and was used in the food packaging industry. However, the ink color component of this aniline ink is a coal tar dye, which contains toxins. So soon, the U.S. printers gave up the ink and changed it to use water-based ink for printing. This printing method is also called flexographic printing. Until 1952, the American Flexographic Printing Association (FTA) was established. This kind of printing method has been greatly developed in the United States. The so-called flexographic printing refers to a printing method of transferring ink through an anilox roller. Flexo is a general name for a letterpress made of a rubber plate, a photosensitive resin plate, and the like. one. There are two kinds of relief printing plates used for flexographic printing: rubber printing plates and polyester printing plates. The rubber plate is produced by natural synthesis or artificial synthesis, and plated by casting and engraving; the polyester plate is made of a photosensitive resin. Different from the production method of the polyester plate and the rubber plate, the plate material of the polyester plate is directly exposed to ultraviolet rays to harden the polyester. Because polyester plates are mostly made by photolithography, they are often referred to by the industry as photosensitive resin plates. There are two kinds of polyester plate materials: one is a prefabricated, single-sheet polyester plate, which is called a solid-state flexographic plate, and the other is a liquid polyester, also called a liquid-sensitized flexographic plate. Either flexible printing of rubber or polyester printing plates are flexible and have the ability to coat ink onto a variety of different substrates. The rubber plate making rubber plate has three basic steps: (1) it is made into a corrosion engraving plate from a negative film; (2) a model or a word template base is made from an engraving plate; (3) a rubber plate is made from a character plate base. In the rubber plate making process, an alloy coated with a sensitized emulsion is placed in a specially designed vacuum frame, and the plated film is placed on the alloy plate for exposure. Next, the non-imprinted and non-hardened emulsion is washed away, the non-printed portion is eroded, and the image portion is projected. Under the control of heat and pressure, the mold is pressed against the relief, and the material is melted on the alloy relief to form a mold. Under control of heat and pressure, a piece of rubber is pressed against the mold to create a rubber plate. Since the rubber plate was made of an etched plate, any layout problems were found during proofreading, and the etch plate was re-created to increase the manufacturing cost. Polyester plate-making polyester plates are different in platemaking methods, so they produce plates in different forms, both in solid and liquid form. The flexible polyester plate is made of prefabricated solid polyester or coated with liquid polyester with the required thickness, and forms a printing plate after curing. Production of Solid Polyester Plates In the production of rubber plates, lithograph plates should be used to make engravings first. Solid polyester plates are used to make plates directly from negative films without intermediate steps. Each plate is made of negative film. Made directly into thickness. First, the unexposed solid polyester plate was cut to the size required for the process, placed in a vacuum rack, and fully exposed to ultraviolet light to harden or cure the plate. After exposure, the negative film was placed on the photosensitive resin plate, and exposed in a clean vacuum frame with ultraviolet rays. Light enters the graphic portion (blank portion) of the negative film to cause hardening of the graphic portion of the polyester plate. In this way, the graphic image of the negative image is printed and copied by the printer. The next step is: the exposed plate is washed by a plate processor, the non-graphic portion of the plate is cleaned, the uncured non-hardened polyester is washed away, and the plate surface is concave; while the convex hardened graphic is left. section. The plate is then sent to a dryer and blown dry for further hardening and drying. After being rinsed and dried, the plate is exposed again with ultraviolet rays. After this exposure, a completely processed plate is obtained. In addition, flexographically-printed rubber plates and polyester plates are more printable than other comparable cost printing plates, and their throughput for smooth-surfaced printing often exceeds five million sheets, such as polyethylene, Printed materials such as coated paper. Therefore, flexible printing is economical and practical, and has a longer life than gravure cylinders. The production cost of flexible printing plates is lower, the production is simpler and faster than offset printing plates, and the amount of discharged ink is less than that of offset printing. There is no need to flush the printing plates during printing. The water balance problem in offset printing. The production of liquid polyester plate Liquid polyester plate has three methods of coating, molding and roll forming. In the production process, the negative image is first placed on the parallel glass of the plate making machine, and then the liquid photosensitive resin plate is laid on the protected vulgar picture, and the substrate is covered at the same time, and the upper and lower exposure molding is performed, followed by washing and drying, and the subsequent exposure treatment. Exposure molding is an important part of the plate making process. If the exposure is excessive, it will increase the slope, resulting in the gap between the text strokes is too shallow, or the dark points of the photo dark tone will enlarge, affecting the printing effect. In fact, copy the half-tone draft, you can first reverse transfer version, do a short time to the bottom of the exposure, so that the plate version of the base plate has a smaller range of light, and then exposure, can make the print deeper. After rinsing with the rinsing liquid after exposure, the uncured resin can be completely eliminated from the plate. The higher the alkalinity of the weak sodium acid, is beneficial to the flushing work, but too high will damage the imprint, so the concentration must maintain a reasonable range. When rinsing treatment, it is also necessary to control the rinsing temperature. If the temperature is too high, it will damage the high light positions and the horizontal fine strokes. The rinsing pressure should also be kept under control, and the pressure is too large to damage the printed portion. The purpose of drying is to bake out all the moisture absorbed during the printing process in order to facilitate the effective exposure. Therefore, strictly control the process, otherwise it will affect the opacity of the network and the decline in the resistance force. Second, the performance of the plate material has evolved from the traditional rubber plate embossing rubber relief to the photosensitive resin plate, solving many problems. At present, the highest resolution of the photosensitive resin plate has exceeded the highest resolution of three hundred and fifty lines per inch, dot reproducibility of 1 to 95%, plate material flatness of ± 0.013mm. Solid flexo plate making is very simple. The obvious advantage is that the thickness is very uniform, the latitude is very large, it can accommodate very fine high light levels, and it has less shrinkage than the rubber plate and liquid plate. High print rate. Liquid flexo plates can have different hardness. In recent years, with the development of technology, liquid multi-layer flexographic plates can also be produced, and foamed plastic films can be used instead of polyester films. three. Types of Flexible Printing Materials In the packaging industry, nearly half of packaging products are produced using paper and paper. Today, more than 85% of packaging products are made using flexible printing methods. Why the flexible printing can be used in the packaging industry, the main use of the printing process, the main reason lies in the versatility of flexible printing. In fact, it can be printed on any kind of substrate used for packaging. For flexible printing, the main substrates are: (1) paper and cardboard; (2) film; (3) metal foil and plastic film. Paper and paper flexo printing does not require much paper. It can be applied to the printing of various kinds of paper and paperboard. Among the accepted wrapping papers, the simplest but the most widely used paper type is the use of kraft paper. The resulting brown food bag is printed flexibly. In addition, the most popular flexible printed paper products and cardboard products are some of the daily necessities. Such as: shopping bags, sugar bags, flour bags, potatoes, onion heads and pet food bags. Paperbacks, canned labels, pressure sensitive materials, labels, and gift wraps. Film film printing materials are the most commonly used flexible printing materials. Actually, as early as the 1930 film revolution, cellophane was used, and cellophane printing required fluid dry ink. This type of ink can only be printed flexographically or by photogravure printing. The photogravure process is costly and is limited by the engraving and more cumbersome operating procedures of large format gravure cylinders. Polyethylene, which began to be promoted in 1950, is another versatile film that is widely used in the packaging industry. Flexible printing is used to pack the most common products for daily use, including: fresh and frozen vegetable packaging, fresh or frozen bread packaging, candy cheese, meat, baking food packaging, dry cleaning bags, bed sheets, textiles , shirts and other retail fabric packaging. All of these everyday items were turned into rayon for printing. Many of the characteristics of yamlon made it an ideal packaging material. Metal foils for flexible printing are shafted lead coils or lead alloys. Metal foil printing is very similar to film printing. When metal foil printing is used for packaging, always put paper or film together. For food packaging, packs for ice cream, candy, frozen foods, tobacco, and mixed food packages. After the introduction of metal foil blister packaging, the production of flat pellets and the production of capsule pills have increased. Metal foil gift wraps are also printed flexibly and are often used in combination with base adhesives. The composite metal foil, film, plastic wax and paper can all be compounded together, and can be recombined either in a cyclic manner or as desired. Compounding can be done without limitation. Five or more substrates can be successfully combined and printed. Usually when printing a substrate, the surface of the printed material is the front or back of another substrate. The upper or outer layer is used to protect the printing environment while the inner layer is used to protect the content of the desired package. Some packaging products using composite materials: fast food, cheese, meat packaging, ketchup packaging, mustard, soy sauce and fruit juice and so on. four. There are five major printing processes that characterize flexible printing inks. They are: offset printing, gravure printing, flexographic printing, embossing, and screen printing. Special inks need to be formulated to suit various process requirements. The pigments of flexographic printing inks can be organic or inorganic, natural or synthetic materials. These pigments must be finely ground particles. They can provide inks with pigments, and enhance the strength of the ink film to improve the hiding power, transparency and gloss of the ink film. The binder in the ink can be used to fix the pigment particles and can adhere to the surface of the printed material. Resin. The solvent of the ink can change the solid part of the ink into a liquid suitable for printing. In order to improve the adhesion of the ink, the softness and abrasion resistance of the ink film, additives may be added therein. Flexographic printing inks are mainly water-based inks, solvent inks, and UV inks. Water-based inks are suitable for absorbing pit paper, wrapping paper and newspaper printing. It has two basic features. Namely: The liquidity and fast fixing of the flexible printing ink. Unlike paste inks used for embossing and flat printing, flexo printing inks (like gravure inks) are thin and can be poured—it is fluid. The low viscosity and fluidity of flexible inks are the reasons why such ink rollers are available on flexographic presses. As inks improve, flexible printing inks have fast fixing properties. This makes it ideal for printing on non-absorbent printing materials. For example: transparent film, polyethylene and ethylene resins. In addition, the flexible ink requires a simple drying system and uses a relatively simple design of the printer connection. Therefore, the flexible printing of a low-energy hot-gas dryer can reduce the cost of energy consumption. A simple printer design keeps the price of the presses always lower than other printing machines. In the packaging printing process, UV ink is often used to make the print quickly dry. With the other benefit of using UV ink, the machine can be stopped at any time. The anilox roller does not need to be cleaned immediately, and it will not affect the printing quality. In addition, the ink particles are fine, the concentration is high, the stability, and the ink curing is a chemical reaction, there is no evaporation of the solvent, and there is no air pollution. In spite of this, due to the high ink concentration, it is necessary to use a closed type ink tank, and at the same time increase the temperature control system for adjusting the viscosity, and in order to prevent the thermal shrinkage of the substrate, it is necessary to introduce the cooling system of the printer and the UV lamp. Fives. The broad market for flexographic printing includes a wide range of flexographic printing, including inserts, business forms, packaging cardboard, pit paper, trademarks, film packaging, paper flexible packaging, paper bags, plastic bags, containers, fiberboard, and adhesive tape. There are about 4,000 flexo printing companies in Europe, of which 450 are engaged in carton production; soft packaging companies are about 900; and bagging factories are about 1,000. Because the flexographic printing machine's ink transfer device is simple; the cost of printing presses is less than that of the gravure printing machine, and gravure printing can be done; the production accuracy of the flexographic printing press is improved, the printing pressure is accepted without pressure printing, and the machine noise is small. , High speed; For high-speed printing smooth operation, low paper loss rate. consumption