There are many faults in gravure printing of flexible package, such as the printing product is flowery and glossy, there are different depth of shadow and knife line, etc. These faults may come from the film itself, or from mechanical rotation, operator technology, indoor temperature and humidity, most of which are closely related to the doctor blade. Therefore, the correct selection, installation and use of the doctor blade will greatly reduce the failure rate. The squeegee plays an important role in gravure printing. The correct use of the squeegee can not only make the ink color bright and saturated, but also reduce the printing quality accident to the lowest point. When gravure press is driven by the motor at high speed, the squeegee also swings accordingly. Different manufacturers of gravure printing machine, the scraper swing mechanism is different. For example, the ys620 rotary gravure printing machine produced by Guangdong Shanzhang Light Industry Machinery Factory is used by our company, and the scraper swing is driven by a special micro motor, while the scraper swing of model 800 gravure printing machine produced by Haining people's machinery factory in Zhejiang Province is driven by transmission gear. No matter what kind of swing structure, it is necessary to achieve a goal: to scrape off the excess ink, and at the same time reduce the friction between the blade and the plate, so as to prolong the service life of the squeegee and the plate. 1、 Selection of scraper blade if there is no flexibility, the blade can not be quickly restored to its original position, and will leave on the plate when the knife wire, scraper powder, copper plate powder, have a great impact on the color of printed matter. The doctor blade with a certain proportion of C, Cr, Mn and Si should be selected. The thickness of the scraper is usually 0.1-0.18mm. The scraper is too thick and inflexible to scrape the ink cleanly. The reaction on the printed matter often presents fog, which not only affects the next color overprint, but also the quality of the same batch of printed matter before and after is very related. If the scraper is too thin, the blade is easy to leave a knife mark on the plate, under the action of friction, the scraper will gradually wear, which will inevitably affect the quality of the printed matter. We have noticed that when printing a large area of full-scale white background, the use of a too thin scraper often causes longitudinal streaks. The hardness of the squeegee also affects the quality of the printed matter. The scraper is made of iron, while the gravure is made of copper. The hardness of copper is hv200-hv300, and the hardness of inscription is hv700-hv900. Therefore, it is better to choose a scraper with hardness of hv450-hv600. In this way, the printing plate will not be damaged and knife marks will not be left, and the extra ink in the layout can be scraped. The blade of the scraper should be arc-shaped, which is conducive to the protection of the plate. Because the printing plate surface is arc-shaped, if the blade edge is also arc-shaped, it is not easy to damage the plate, but also easy to clean the ink, to ensure that the non graphic layout is clean and free of ink stagnation. If the blade tip is flat, because the flat edge is very sharp, not only easy to damage the plate, but also affect the scraping effect, thus affecting the printing quality. 2、 When installing the doctor blade, it is often supported by a secondary blade. The secondary blade is generally made of hard steel, and the thickness of the secondary blade selected by our company is 120-150 μ M. The general 8 ᦇ nut of the secondary blade is clamped in the center of the doctor blade, about 8mm away from the back of the doctor blade and about 7mm away from the edge of the blade (the specific position should be determined by test). When the scraper is installed too much, it is easy to deform and wave. In high-speed printing, some places can be scraped clean, and some places can not be scraped clean. This will not only affect the printing quality, but also wear easily. Scraper out too short, and lack of the necessary flexibility, you must increase the pressure in order to clean the non graphic part (no net hole) ink, but also damage the plate. Therefore, it is very important to install the scraper properly, which should be adjusted according to the actual situation. The installation position of the squeegee (the distance between the contact point of the squeegee and the plate cylinder and the imprint point of the imprint cylinder) has a great influence on the quality of the printed matter. Most gravure presses can adjust and adjust the scrapers by adjusting the adjusting nuts of the auxiliary scrapers. If the adjustment is not good, it will make the printed matter dull and unclear. In printing, there will be dry plate, blocking plate, no coloring, false edge, ink layer with poor fastness and other phenomena. The installation position of the doctor blade is related to printing speed and ink drying speed. The drying speed of the ink can be adjusted according to the printing speed, so the installation position of the squeegee should be adjusted according to the printing speed. Generally, a plate cylinder with a diameter of about 15cm is used. When the machine speed is about 60m / min, the distance between the squeegee and the impression point is 6cm. The printing speed is fast, the distance is better, the printing speed is slow, and the distance should be closer.3、 Before installing the doctor blade, both the new blade and the old blade should be grinded to ensure that there is no gap and burr. The blade angle should be 25 degrees. Our factory usually add a few drops of oil on the stone for rough grinding, and then use 1000 pieces of water-resistant abrasive cloth to add a few drops of oil for fine grinding. Add a few drops of oil can play a lubricating role, reduce friction, grinding effect is generally good, peers may wish to try. Most printing plants often encounter the phenomenon of ink color or light and thick, especially when printing screen adjustment products, this is not only related to the ink transfer, but also the angle between the scraper and the plate cylinder can not be ignored. Most gravure presses can choose the angle of 45 ° to 65 °. The angle is small, the ink layer is dark and glossy, but the scraping effect is poor, and it is easy to scratch and blur the picture and text. If the included angle is too large, the shallow part of the screen may not be able to transfer ink, such as the main pattern with shadow is printed, but its shadow is not. The solution is to adjust the position of the scraper, and adjust the position of the turret to make the ink transfer to the substrate as much as possible. To adjust to the best angle, but also consider the depth of the mesh, scraper position and printing speed and other factors. If the net point is too deep, the angle should be larger. The pressure of the squeegee also has a very important impact on the quality of the printed matter. The pressure can be adjusted according to the depth of the mesh and the level of text. If the plate cylinder is too long, and corrosion gravure, then the pressure will be greater. Because of corrosion gravure mesh hole deep, but the edge of the pattern is prone to burr and other phenomena. However, if the pressure is too high, it is easy to scrape off the ink in the shallow screen hole, resulting in the printing failure of the shallow screen part; moreover, if the pressure is too high, the contact angle will become smaller, and it is difficult to scrape the excess ink in the layout, resulting in ink accumulation under the scraper, resulting in knife line. In general, the contact angle of the scraping system with good working condition should be about 60 degrees. If the pressure of the scraper is too light, it will cause scuffing and other faults. The solution is to blow air to the blade of the blade, that is, the interface between the blade and the printing plate. The blowing can be carried out with special blowing facilities. When the doctor blade is used for a period of time, there will be burr, crack and other phenomena. The doctor blade can not work effectively. At this time, it is necessary to grind the blade or replace it with a new one. In the actual work, sometimes the scraper appears fracture phenomenon, and the service life can be extended by grinding or adding cushion, so as to save the scraper cost and solve the corresponding quality failure. After use, the doctor blade should be kept clean and lubricated. The usual method is as follows: (1) clean the used scraper with solvent. (2) After drying, apply engine oil, put into plastic bags, and store in ventilation. The polyester blade is usually coated with 6 × 10 oil. (3) Keep them by category for future use. To sum up, the correct selection and use of squeegee is very important to improve the quality of gravure products.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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