The production of knife line has a great relationship with the quality of ink. Ink viscosity, surfactant, ink fineness, drying speed and so on may lead to knife line.
1. Viscosity of ink
The production of knife line is directly related to the viscosity of ink. Generally speaking, the higher the viscosity of the ink in printing production, the more likely to cause knife line fault in printing. Therefore, properly reducing the viscosity of printing ink is conducive to the scraper to clean the printing ink, so as to prevent knife line.
There are two main types of cutter line fault caused by high ink viscosity in printed matter. One is that the cutter line is in the form of fine flow filament, which generally does not drag too long, but appears intermittently on the printed matter. The starting point of the micro flow thread is mostly close to the printing pattern, and the starting point of the knife line is generally thicker than the end, It is easy to ignore the fine flow thread. However, this kind of flow thread is often the root cause of quality accidents, so we must pay attention to it. There are many ways to solve the problem, but the best method should be chosen according to the actual situation.
The specific prevention and control methods are as follows:
① In general, this tiny flow thread will be improved by gently picking at the cutter line. This kind of operation is generally completed under the condition of machine operation, which requires skilled operators to complete, so as to avoid unnecessary losses
② As the knife line is related to the viscosity and fluidity of the ink, the basic method to eliminate the knife line is to add appropriate amount of solvent into the ink to reduce the ink viscosity and improve the fluidity of the ink. After the ink viscosity decreases and the ink fluidity increases, the fine flow thread will be eliminated.
Another kind of knife line caused by the high viscosity of ink is the printing pattern as the starting point, but the knife line is concentrated, relatively rough, and regularly appears in the same position of the printed matter, and often continues to the next color, which is easy to find. The reason is that the ink viscosity is too high, the printing plate dot transfer is not good, the ink auxiliary agent with the change of ambient temperature is destroyed, especially when the temperature is too high, the ink surface will form a thin layer of dry solid layer, a long time between the plate and the doctor blade will scrape up the blade, resulting in this kind of knife line.
The method to solve the problem is as follows:
① Adjust the angle of the squeegee. Generally, the angle between the squeegee and the plate is 60 degrees, but sometimes the angle between the blade and the plate can be increased to about 65 degrees, so that the pressure of the doctor blade will be increased accordingly, and the scraping effect will also be enhanced accordingly. However, it should be noted that the angle of the doctor blade should not be increased too much, and the pressure of the scraper should not be too high, otherwise it is easy to cause damage to the plate cylinder and affect the service life.
② In order to reduce the viscosity of the ink and increase the fluidity of the ink, appropriate additives or solvents are added to the high viscosity ink. When adding solvent, the ink should be stirred with the direction of solvent.
③ The mixing roller is added into the ink tank. With the rotation of the plate cylinder, the mixing roller also rotates correspondingly to prevent the ink surface from scaling, which is also a method to prevent the generation of knife line. With the rapid development of printing press, now medium and high-speed machines have been equipped with circulating ink adding device, which is also a method to reduce the surface crust of ink, which has a great effect on reducing the probability of knife line. All of the above solutions can be used in cooperation with each other. In general, after the above-mentioned solutions, the centralized and different thickness of cutter lines will be completely or largely restrained.
2. Surfactant

In the production process of ink, it is generally necessary to add a certain amount of surfactant. The plate cylinder after chromium plating has a certain adsorption due to the porous metal. If there are too many surfactants in the ink or the adsorption of the cylinder is too high, the active substances will adhere to the cylinder firmly during the printing process, making it difficult for the scraper to completely scrape clean, thus forming a knife line in printing. This kind of knife line is mainly in the shape of meteor or microfilament. If you wipe the layout and scraper in time after the knife line appears, the knife line will disappear temporarily. However, due to the surfactant problem in the ink, the knife line will reappear quickly. Although there is a certain rule, it is not completely repeated. In this case, you can first clean the plate cylinder, remove the active substances on the cylinder, and then add a special surfactant to the ink, which will achieve a more obvious effect. If the retarder is added before printing, it can play a preventive role.

3. Ink fineness
Knife line fault is closely related to the thickness of ink particles. Generally speaking, the thinner the ink, the better the quality of the printed matter, the lower the probability of knife line. At the same time, the finer the ink particles, the better the covering power. However, the smaller the ink fineness, the better, too fine ink will also cause other printing problems. In gravure or other printing, there are strict requirements on the size of the ink particles. Generally, the ink particle size should be moderate. Generally, the ink fineness should be about 15 μ M. Foreign matter mixed in the ink, or the auxiliaries in the ink precipitate with the change of temperature, and the pigment agglomerates, etc., can produce coarse-grained foreign matter, making the ink particles rough. Foreign matter is mostly brought in by the film, due to the static electricity of the plastic film substrate, the adsorbed dust and the additives in the plastic film precipitate into the ink, which are the main reasons for the appearance of foreign matter. When using pigment with high hardness, even after grinding, it may cause knife line: for example, red and blue ink are easier to produce knife line, because red and blue pigments are the most difficult to grind, and it is difficult to ensure that they have appropriate particle size. In addition, the use of hydrophilic pigments is also easy to appear knife line. Ink fineness can not meet the requirements, rough particles will lift the scraper, resulting in knife line. In addition, the rough ink particles have a greater damage to the scraper, plate, etc. through the careful observation of the knife line fault caused by the unqualified ink fineness, it is found that the direction of the knife line on the printed matter caused by the unqualified ink particle size is not the same. There are three main forms
① The knife line on the printed matter is irregular and of different thickness. This kind of knife line extends from the printing pattern part to the non pattern part. The knife line is longer. With the swing of the doctor blade, the knife line also moves, sometimes one or two, sometimes even many. For the elimination of this kind of knife line, the position of the squeegee can be adjusted up and down properly. When adjusting the trial printing, attention should be paid to observe the phenomenon that the printed matter has five color depth and light color difference, so as to ensure the normal printing color. Due to the up and down adjustment of the squeegee, it is easy to cause the color difference of the printed matter, especially when the printing plate is a shallow screen, which must be paid attention to.
② The direction of the knife line on the printed matter is very regular. This kind of knife line appears in the printing pattern part of the same plate, and is in the same position. With the left and right swing of the squeegee, there is basically no big change. This is because the coarse particles in the ink lift the blade, and the left and right swing of the scraper can not drive it at all. If it appears in the intermediate color, the next color ink will fill these knife lines, that is, the next color ink color phase appears at the knife line.
③ The cutting line on the printed matter mostly appears in the last color. When printing in plastic film, it usually appears on the white plate, such a knife line, two or more lines will run through the whole print. If you observe from the front of the print, the knife line is not rough, and it is not easy to detect. If you observe from the back of the print, you can find that the knife line always runs through the track, forming one, two or more long traces. This kind of trace will appear undoubtedly when the composite aluminum coating is applied, especially when it is coated with aluminum, it will be more clearly seen in the large area of white. At the same time, the third kind of knife line mostly occurs in white plate, because white ink 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. For the knife line caused by ink fineness, the solution is to stop printing, filter the ink, and then print on the machine after filtering the ink used, which has a good effect on preventing knife line. The selection of filter screen is different due to different manufacturers. Some manufacturers even use silk stockings to filter. According to the practical experience of some manufacturers, the effect of using 140 mesh metal screen is ideal.
4. Ink drying speed
The ink drying speed is too fast, so that the ink drying is excessive, the friction between the plate roller and the scraper is relatively increased, and the scraper is difficult to clean the ink in the layout. When the drying is too slow, the micro ink attached to the non graphic part of the plate cylinder will be transferred to the substrate, forming plate pollution, resulting in knife line during printing. Therefore, attention should be paid to the adjustment and control of ink drying speed.
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.
We uphold the integrity of cooperation, good quality, good service business philosophy, won the industry's approval, products sold to all over the world; welcome friends from all walks of life to inquire, visit our factory to investigate guidance and business negotiations.