Flexo printing

Overview: Flexographic printing uses blankets, plastics, or other soft materials as the media. The ink is attached to the raised portion of the plate and the image is transferred to the substrate. The use of quick-drying inks makes flexo printing an ideal way to print on plastics and foils. It is the preferred method of producing packaging for handbags, wrappers, or similar materials, and has advantages over other printing methods. Soft skin prints are also suitable for printing on thick, compressible materials, such as cardboard for packaging. The ink used in flexo printing may be a water-based ink or a solvent-based ink. As with letterpress printing, the inking portion of flexographic printing is more prominent, mainly the graphic area to be printed, and the graphic is transferred to the substrate by pressure during printing. The depressed area on the plate is not a graphic part and it is not inked and therefore will not be copied. Flexographic printing can be either sheet-fed printing or web-fed printing. According to need, the characters and pictures on the manuscript are transferred by photography to the negative or positive image film for plate making, and finally the picture and text are copied to the substrate. The process uses sensitive chemicals, paper and film. The photolithographic process is used to image soft materials (such as plastics and rubbers) coated with a photosensitive formulation, and some water-insoluble areas are formed after the development. The waste water generated in this process contains acid, alkali, solvent, coating liquid and developer on the plate. If a metal plate is used, the non-image area is corroded with an acid liquid, so that the heavy metal concentration in the waste water is high. If rubber or plastic plates are used, no metal will enter the wastewater. Lots of waste paper, waste ink, and cleaning solvents are generated during the flexo process. Most of the VOC toxic gases emitted into the air are volatilized from inks and cleaning solvents. The main raw materials used for flexographic printing are offset and photopolymer plates, solvent-based inks, hydrocarbon solvents and various types of substrates, which have a considerable impact on the environment. Printers select and configure various chemical agents to suit the prepress and pressroom applications. Chemical reactions, plate making, inks and solvents, and maintenance in darkrooms require the help of chemicals to achieve the ultimate goal of printing the best images on substrates. Traditional flexographic processes require the use of large, open containers for various inks and solvents. They will volatilize some harmful gases in the workshop, which is extremely unfavorable to the health of the operators. The industrial wastewater discharged from the darkroom, cleaning tank and cooling system will cause environmental pollution. Wastewater from cleaning inks may enter sewers or sewage pipes. For flexo printing, the entire process waste must be closely monitored to minimize harm to the human body and the environment. Prepress - Platemaking Printing plants using photopolymer plates have gradually replaced traditional chloride solvents with Citrus-based solvents and other acceptable solvents. Photoresin platemaking systems that can be washed with water are already available. They are non-toxic, do not contain carcinogens, and are non-corrosive. In the process of making a rubber plate, a photopolymer-coated base plate was used. Hard lithographic photopolymer plates are etched rather than metal plates using laser engraving, a non-chemical platemaking method. The future development trend may be in the recovery and reuse of photopolymer plates, residual scrap and polyester photosensitive coating. A link mechanism system has now been added to the printing press with a microprocessor-controlled exposure unit and a development and drying unit. The highly automated and computer-controlled UV light source ensures plate-making accuracy and reduces the operator's labor intensity. The system also has a very good device for the treatment of solvents. Printing-ink water-based inks are widely used in flexo printing, especially during the printing of corrugated boxes. The transition from solvent-based inks to water-based inks began with white ink, which is the largest amount of ink used in flexographic printing. There are many problems at the beginning, such as poor adhesion, poor moisture resistance, insufficient gloss, and low print speeds. Poor adhesion makes its use in frozen food packaging very limited. Now water-based ink technology has greatly improved and gradually become the mainstream of plastic film printing. The color of the product is more vivid and vivid than the solvent-based oil base. Plastic films also need to be further improved to suit the wettability and adhesion of water-based inks. In order to make the ink transfer, dry, ink supply, and drying system, the drying system must be improved accordingly. In addition, there is also a need for a cleaning system that allows the ink components to be fully utilized and remove residual ink in a timely manner so that the service life of the anilox roller and the doctor blade system can be extended. Surface tension can cause beads to form on the surface of water-based inks, causing the loss of small dots. Printer manufacturers are actively developing ceramic anilox rollers and printing plates that can easily transfer water-based inks onto substrates. Good ink overprinting can ensure the smooth progress of four-color printing. Since the surface tension of water is higher than that of alcohol, in order to obtain a good dry superimposition effect, the relative pressure between the two drying rollers must be reduced, so that the hot air flow between the rollers can be more circulated to speed up the drying. The ink supply system and the ink temperature control system can reduce the volatilization of the amine and ensure the vividness of the color. The drying of a water-based ink is divided into three steps: water evaporates from the ink; amines are also separated from the ink to render the ink water-resistant; the polymer particles must be joined to form a film on the surface of the dried ink layer. In wet environments, the stability of water-based inks is better, and unlike solvent-based inks, viscosity changes due to the volatilization of solvents. To ensure the quality of water-based ink printing, excessive mechanical agitation must be prevented, the pH value should be kept stable, the temperature should be controlled below 110°F, and the water-based ink should be sampled and ceramic anilox roll should be used. A new type of polymer resin dispersed in water is applied to water resistant flexo inks and overprinting varnishes. While other water-based ink systems rely primarily on resins with higher acidity to achieve dispersibility in water, this resin does not need to be used to neutralize liquid media to maintain the dispersibility of the resin in water, such as ammonia and amine. Therefore, in the printing process, it is not necessary to maintain the balance of the PH value of the ink, nor to emit the odor of the amine. This type of resin has a very fast drying rate on the substrate, which greatly increases the printing speed, does not require too high a drying temperature, and has a rewetting property (drum, plate, and anilox roller). The development of the squeegee technology has improved the quality of flexo printing and effectively controlled the contamination of the ink when the ink was transferred from the ink fountain to the surface of the substrate. The common two cylinder ink supply system (ink fountain roller, anilox roller) with ink tank is a completely open, large amount of solvent is in direct contact with the air and it is very volatile. The box-type squeegee system controls this volatilization. The oil pump transfers the ink from the ink tank to the tank so that most of the area where the ink is located is sealed and only a very small portion of the anilox roller is exposed. When the anilox roll is rotated into position, the scraper scrapes the excess ink and sends it back to the tank. There is also a plastic or metal scraper inside the tank. The tank is completely closed so there is no ink leakage. The anilox roller technology has long been adapted to this type of doctor blade system. When cleaning the anilox roller, an automatic system with ultrasonic or high pressure is used. Liquid cleaning (rather than mechanical cleaning) reduces the damage to the anilox roller and the dot. The chrome roll has been replaced by a laser-engraved ceramic roll. With the application of the box type scraper system and other related performance improvements, the volatilization of the solvent is greatly reduced. The ink is only volatilized when it is transferred from the anilox roll to the plate and then transferred to the substrate. Regardless of the printing speed, the amount of ink left by the scraper is fixed. Squeegee systems with an automatic cleaning system (automated squeegee cleaning and ink adjustment) solve the residual ink recovery problem and reduce the amount of water used to clean the printing system. Of course, the squeegee system also has some problems: oil leakage from the seal, ink splashing from the drum plate, installation and cleaning of the box system, and local corrosion caused by the water-based ink. Several new drying technologies have been developed that can save energy and adapt to new ink formulations. Infrared drying utilizes electromagnetic radiation and high energy concentration, with moderate investment costs but high operating costs; it is often used in conjunction with an air convection dryer to provide sufficient heat on the coated drum. The radio frequency drying method uses high frequency electron energy to dry the moisture and solvent on the coating material. Its investment costs are high, but operating costs are moderate. Relief Printing Like flexographic printing, letterpress printing utilizes raised portions of metal or plastic plates. It used to be the main printing method; it is mainly used today to print books, business cards and brochures. The market share of letterpress printing is rapidly being lithographed, gravure and flexo imprinted. Now the three types of letterpress printing are flat-press, flat-press and round presses. Flat-press type printing machine, the surface of the raised plate is fixed on a flat surface. The substrate is placed on another plane and then printed with the inked plate. The process of transferring the printed sheets of the flattening-type printing machine from the paper transporting pile to the paper receiving pile is a process in which the printing plate cylinder rotates, and the printing process is performed on the printed sheets. These two kinds of printing machines are relatively lithographic, flexographic and The gravure press is very slow. The most important printing machine is a round press type printing machine.