There are many quality problems in gravure printing with plastic film, among which the tool line is one of the most common faults. The production of cutter line makes the products scrapped, which is easy to cause economic losses. As a printing enterprise engaged in flexible packaging, it is urgent to analyze and summarize the causes and find corresponding solutions to reduce the knife line fault to the lowest point.
In the process of gravure printing production, the problem of cutter line (thin knife line also known as cutter wire) has been bothering operators. The frequent occurrence of tool line makes many products scrapped, resulting in economic losses. As enterprises and operators engaged in flexible packaging printing, it is necessary to analyze and summarize the causes and find corresponding solutions to reduce the occurrence of knife line quality problems as far as possible.
1、 Relationship between the generation of cutter line and ink viscosity
In production, the higher the viscosity of the ink, the easier to produce knife line in printing.
The first kind of tool line is in the form of fine flow filaments, which generally does not drag too long, but intermittently appears on the printed matter. In actual production, if you do not observe carefully, this kind of fine flow thread is easy to be ignored. The most fundamental solution to solve this problem is to add a suitable amount of solvent to the ink to reduce the viscosity of the ink. After the viscosity of the ink is reduced, the fine flow thread will be eliminated. This is because the viscosity of the ink decreases after the solvent is added, and the flow performance is improved accordingly. Therefore, the small flow thread is also related to the poor flow performance.

The second kind of cutting line is based on the printing pattern, but it is concentrated and rough. It appears regularly in the same position of the printed matter, and often continues to the next color. This kind of knife line is easy to find. The reason for this kind of knife line is that the ink viscosity is too high, the printing plate is not well transferred to the net point, and the ink auxiliary agent is damaged with the change of ambient temperature. Especially when the temperature is too high, a thin layer of dry solid will be formed on the surface of the ink. After a long time, the accumulated ink layer between the printing plate and the squeegee will jack up the scraping knife, thus producing this kind of knife line. The solution to this problem is: first, adjust the blade angle and add appropriate additives or solvents to the ink with high viscosity, so as to reduce the viscosity of the ink and increase the fluidity of the ink. When adding solvent, the ink should be stirred with the direction of the solvent. Another solution is to put the mixing roller into the ink tank. With the rotation of the cylinder, the mixing roller also rotates accordingly. There is a way to prevent the ink surface layer, but also to reduce the knife line. The above two solutions cooperate with each other. In the absence of special circumstances, the above concentrated knife lines with different thicknesses will be effectively restrained. It must be noted that the angle of a little bit of the doctor blade should not be increased too much to prevent damage to the cylinder.

The third kind of knife line is easy to appear in the last color. When printing in plastic film, it usually appears on the white plate. Such one or two knife lines will run through the whole print. From the front of the print, if the knife line is not rough, it is not easy to detect. From the back of the print, you can find that the trace of the knife line runs through, and always forms a long "mark". This kind of trace will appear no doubt when it is combined, especially when the composite aluminum coating is applied, it is more clear and distinguishable in the large area of white. No matter which knife line is above, the solution is to stop printing and filter the ink. Generally, the ink used in the first and second color sequence is filtered before printing on the machine. The effect will be much better. The selection of filter screen is different due to different manufacturers. Some factories can also filter household stockings. We recommend a metal mesh of 140. After long-term practice, it has achieved initial results, which is worthy of learning and learning from peers. At the same time, the third kind of tool line mostly occurs in white version, because white version contains titanium dioxide, the thickness of titanium dioxide is very important. In addition, in the development of ink, grinding is not in place is the root cause of this phenomenon.
2、 The relationship between the generation of knife line and the particle size of ink
The thickness of ink particles is closely related to the generation of knife line. The thinner the ink is, the better the quality of printed products is, and the probability of knife line generation is correspondingly reduced. There are strict requirements on the size of the ink, usually requires the ink fineness of 15 μ m, the ink fineness can not meet the requirements, the coarse particles will lift the scraper, resulting in knife line, at the same time, too rough ink particles damage the scraper and printing plate greatly, the ink thickness should be moderate, too fine is not good.
3、 Relationship between the generation of cutter line and plate cylinder
The generation of knife line is closely related to the surface smoothness and coating quality of plate cylinder. Printing plate is divided into manual engraving plate and electric engraving plate. Manual engraving gravure surface finish is poor, the probability of generating knife line is more than that of electric engraving plate, on the contrary, the electric engraving roller is much lower than manual engraving plate. When engraving gravure by hand, use 1000 ? water-resistant emery cloth to polish the layout before the first printing, and the probability of knife line in printing is low, which is mainly reflected in pre press processing. The specific practice of sanding, but the sanding machine will not be damaged after high-speed running. After grinding, stick it with soft cloth and wipe it with solvent. It should be noted that it is better to do it by skilled workers. The hardness of coating is also related to the generation of knife line. If the coating hardness is not enough, it is easy to be damaged under the action of scraper, and knife line will also be produced. This kind of knife line is sometimes absent, which is called "hidden knife line". It often appears in the part without printing pattern. This kind of knife line can be easily found only under the reflection of fluorescent lamp. There are two ways to solve this problem: 1) in this case, grind the coating lightly with 1000 mm water resistant sandpaper, which will generally improve. However, printing often occurs after a period of time, so it is best to remove the plating treatment, more serious of this phenomenon needs to be re plate. ② Adjust the scraper, increase the pressure of the blade, and blow to the layout at the same time, it can also achieve good results. Air blowing should be noted that the air volume should not be too large, so as to avoid the leakage of printing plate pattern.
4、 The relationship between the generation of knife line and the doctor blade
The production of knife line is closely related to the quality and installation of the doctor blade. The quality of scraping blade grinding is closely related to the cutting line. If it is properly ground, it is not easy to produce knife line, otherwise it is easy to produce knife line. When grinding, the oil stone is usually used for grinding, and then 1000 water-resistant sandpaper and 6 engine oil are used for grinding. The ash on the back of the knife is ground into a 25 ° inclined edge. If there is a serious gap in the scraper, a new blade should be replaced. At the same time, it should also be noted that if the blade is imported soft elastic, it is not easy to produce cutter line, and if it is domestic blade, it is easy to produce cutter line. The blade must have a certain flexibility, hard and inelastic is the main cause of knife line, and there are other reasons, such as scraping the excess ink on the printing plate, causing fog effect on the quality, etc. Generally, the hardness of copper is between 200hv-300hv, and that of chromium is 800hv-900hv. The hardness of scraper should be 450hv - (900 + 300) / 2, which will not damage the printing plate and leave no knife marks, but also reduce the probability of knife line. The blade tip of the squeegee should be arc-shaped, so as to protect the printing plate, because the plate is circular and the scraper is circular. Do not damage the plate, and easy to clean the ink. If the knife tip is flat, because the flat is very sharp, it will not only damage the printing plate, but also affect the printing. If the blade tip is flat, it will not only damage the printing plate, but also affect the printing. When installing, the scraper should be protected between 0.5cm-1.2cm between the small plate in the platen frame under the scraper. If the scraper is too prominent, the scraper is easy to deform and wave shape, which will affect the scraping effect, thus causing quality accidents. If the installation is too short, the ink is easy to be wiped out, but there will be a lot of knife marks on the plate, and as long as the knife is loose, the pattern printed will become thick or light, which can not be repeated Use. In addition, if the weight of the hammer is too heavy and the pressure of the scraper is too large, the cutter line will be generated. The solution is to reduce the weight of the hammer, and at the same time, appropriate air blowing to the layout will effectively reduce the production of knife line.
5、 The relationship between tool line generation and environment
The generation of cutter line is closely related to the environment. If the operating environment has dust, dust into the ink will cause knife line. The workshop should first isolate the printing unit to reduce the flow of personnel. The room is equipped with air conditioning facilities and dust removal equipment. When going to work, the first color sequence and the second color ink are filtered and then printed on the machine. Before going to work, dust is removed. When off duty, there are special health personnel to clean up. The environment must be kept clean.
There are many kinds of tool line, and the form is not limited to one pattern. This requires the operator to form the habit of summing up experience, and actively cooperate with the management of the factory to reduce the cutter line fault to the minimum.
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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