Causes and solutions of the cutting line of the ho

Causes and solutions of plastic intaglio printing knife line

there are often many quality faults in intaglio printing with plastic film, among which the knife line is one of the most common faults. The production of knife thread makes the product scrapped, which is easy to cause economic losses. As a printing enterprise engaged in flexible packaging, it is urgent to analyze and summarize its causes and find corresponding solutions, so as to finally reduce the knife line fault to the lowest point

first, the relationship between the generation of knife line and ink viscosity

the generation of knife line is directly related to ink viscosity. In actual production, the higher the viscosity of ink, the easier it is to produce knife line in printing. This kind of knife line roughly presents two forms in printing. The first kind of knife line is in the shape of fine flow silk, which generally does not drag too long, but appears intermittently on the printed matter. The starting point of the fine flow silk knife line is mostly close to the printing pattern, and the starting point of the knife line is generally thicker than the end. In actual production, if you do not carefully observe, this fine flow silk knife line is easy to be ignored. This kind of filiform cutting line is often the root cause of quality accidents, which must be paid attention to. There are several methods to solve this problem, which is also commonly used by printing staff, but it should also be determined according to the actual situation

a. grind a soft blade with a width of 5cm, a length of 15cm and a thickness of 140um to be very smooth. Gently pick it at the place where the knife line appears. Under normal circumstances, this kind of tiny flow filiform knife line will be improved. This operation is generally completed when the machine is running, which requires familiar operators to complete, so as not to be easy to outsmart oneself and cause unnecessary losses

b. the most fundamental solution is to add an appropriate amount of suitable solvent to the ink to reduce the viscosity of the ink. After the viscosity of the ink is reduced, the small flow filiform knife lines will generally be eliminated. This is because after the solvent is added, the viscosity of the ink decreases and the fluidity increases accordingly. Therefore, the small flow filiform knife line is also related to the poor fluidity, which should be noted

the second kind of knife line takes the printed pattern as the starting point, but the knife line is concentrated, rough, and appears regularly in the same position of the printed matter, often continuing to the next color. This kind of knife line is easy to be found. The reason for this kind of knife line is that the viscosity of the ink is too high, the point transfer on the printing plate is poor, and the internal auxiliary agent of the ink is damaged with the change of the ambient temperature. Especially when the temperature is too high, a thin dry solid layer will be formed on the surface of the ink. After a long time, the ink layer accumulated between the printing plate and the doctor blade will jack up the doctor blade, resulting in this knife line. The way to solve this kind of knife line is to adjust the angle of the doctor blade first. Generally, the angle between the doctor blade and the printing plate is 60, but sometimes the angle between the doctor blade and the printing plate can be increased to about 65, so the pressure of the doctor blade increases correspondingly. At the same time, add an appropriate amount of corresponding additives or solvents to the ink with high viscosity to reduce the viscosity of the ink and increase the fluidity of the ink. When adding solvent, the ink should be stirred with the trend of the solvent. Another solution is to put stirring in the ink tank; The mixing roller rotates with the rotation of the cylinder. It can prevent the ink surface from forming layers, and it is also a method to reduce the generation of knife lines. The above two solutions are used together. In the absence of special circumstances, the above centralized knife lines of different thickness will be effectively restrained. It must be noted that the angle of the doctor blade should not be increased too much to prevent damage to the brand drum

second, the relationship between the generation of knife lines and ink particle size

the thickness of ink particles is closely related to the generation of knife lines. The thinner the ink, the better the print quality, and the corresponding reduction of knife lines and probability. There are strict requirements on the particle size of the ink, usually requiring the ink fineness to be 15um. The oil can be used for later design optimization. The reference ink fineness cannot meet the requirements. The rough particles will jack up the scraper, resulting in knife lines. At the same time, too rough ink particles will cause great damage to the scraper and printing plate. The ink thickness should be moderate, and too fine is not good

causes and solutions of plastic gravure printing knife line (2)

after long-term observation of this kind of knife line, it is found that the direction of knife line caused by rough ink particles on the print is also different, mainly in three forms. 1. There are irregular knife lines of different thickness on the printing of the first knife line, which extends from the printed pattern to the place without pattern. The knife line is long, and as the doctor blade swings left and right, the knife line also moves, sometimes one, two, sometimes many. The solution is to adjust the position of the doctor blade up and down, and observe whether the printing has color depth aliasing. 2. The direction of the second knife line is very regular. It appears in the printing pattern part of the same printing plate, and it is in the same position. With the left and right swing of the doctor blade, there is basically no big change. This is because the coarse particles in the ink push up the doctor blade, and the left and right swing of the doctor blade can't drive it at all. If it appears in the middle color, the next color ink will fill these knife lines, that is, the next color ink will appear at the knife line. 3. The third kind of knife line is easy to appear on the last color. When printing in the plastic film, it usually appears on the white plate. Such a knife line or two will run through the whole print. When viewed from the front of the print, if the knife line is not rough, it is not easy to find it. When viewed from the back of the print, you can find the trace formed by the knife line throughout. This trace will appear undoubtedly when compounding, especially in the composite aluminum coating, It can be seen more clearly

no matter what kind of knife line above, the solution is to stop printing and filter the ink. Usually, the ink used in the first and second colors is filtered before printing on the machine. 140 mesh metal screen is selected for filtering. After long-term practice, it has achieved initial results, which is worth learning and reference from peers

III. The relationship between the generation of knife line and plate cylinder

the generation of knife line is inextricably linked with the surface finish and coating quality of plate roller. The printing plate is divided into manual 4. The metal tensile testing machine engraves the plate and electric engraving plate before holding the test piece. The manual engraving intaglio plate is not smooth, and knife lines are easy to appear; The surface of electric engraving intaglio is smooth, and the probability of generating knife lines is much lower than that of manual engraving. When printing with hand carved intaglio, use 1000 # water-resistant sandpaper to polish the layout before the first time on the machine. The specific method is to drive the printing speed faster, run the machine empty, and move the sandpaper back and forth during grinding, but do not use too much force, otherwise the hole will be damaged. After polishing, use a soft cloth to wipe the drum clean before printing. The knife line phenomenon is reduced a lot. It should be noted that this work needs to be undertaken by experienced personnel. If such a knife line appears during printing, the method is the same as before

the hardness of the coating is also related to the generation of knife lines. If the hardness of the coating is not enough, it is easy to be damaged under the action of the scraper, and knife lines will also be generated. This kind of knife line sometimes does not exist, which is also called hidden knife line, and often appears in the absence of printed patterns. This kind of knife line is easy to be found only under the irradiation of the reverse side of the fluorescent lamp. There are two solutions for this kind of knife line: one is to gently grind the coating with 1000 × water-resistant sandpaper after this situation occurs, Generally, it will improve, but often it will appear again after printing for a period of time, so it is best to remove the plating, and when it is more serious, it is necessary to remake the plate; The second is to adjust the doctor blade, increase the pressure of the doctor blade, and blow to the layout at the same time, which also has a good effect

IV. The relationship between the generation of the knife line and the doctor blade

the generation of the knife line has a great relationship with the quality and installation of the doctor blade. The grinding quality of the doctor blade has a lot to do with the knife line. If it is properly ground, it is not easy to produce knife lines, otherwise it is easy to produce knife lines. When grinding, usually use oilstone to grind, and then use 1000 # water-resistant sandpaper and 6 # engine oil to grind it smooth. The ash on the back of the knife is grinded into a 25 slope. If the scraper has a serious gap, it should be replaced with a new blade. At the same time, it should also be noted that if the blade is imported soft and elastic, it is not easy to produce knife line. If it is domestic blade, it is easy to produce knife line. The blade must have a certain elasticity. Hard and inelastic is the main reason for the knife line. There are other reasons, such as scraping the excess ink on the printing plate, resulting in fog and affecting the quality. Generally, the hardness of copper is between 200hv-300hv, the hardness of chromium is between 800hv-900hv, and the hardness of scraper should be between 450hv- (900+300)/2, so as not to damage the printing plate, leave no knife marks, and reduce the probability of knife lines. The tip of the doctor blade should be arc-shaped, which can protect the printing plate, because the plate is circular and the doctor blade is arc-shaped. It does not damage the printing plate, and it is easy to scrape the ink away. Keep the place without pattern clean without stagnant ink during printing. If the knife tip is flat, because the flat tip is very sharp, it will not only hurt the printing plate but also affect the printing, and the dirty scraping will produce knife lines. During installation, the scraper should be protected between 0.5cm-1.2cm with the small flat plate in the lithography frame under the scraper. If the scraper is installed too prominently, the scraper is easy to deform and take on a wavy shape, which affects the ink scraping effect, resulting in quality accidents. If the installation is too short, the ink is very easy to scrape out, but there will be many knife marks on the plate, and as long as the knife is loose, the printed pattern becomes thicker or so Purell kt mr07 can be applied to a large number of fields and can't be used repeatedly. In addition, if the weight of the hammer is too heavy and the pressure of the scraper is too large, the knife line will be generated. The solution is to reduce the weight of the hammer and blow the layout properly, which will also effectively reduce the generation of the knife line

causes and solutions of plastic gravure printing knife line (3)

v. the relationship between the production of knife line and the environment

the production of knife line has a great relationship with the quality of the environment. If there is dust in the operating environment, the dust will enter the ink and cause knife lines. 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. At work, filter the ink of the first color sequence and the second color before printing on the machine. Before going to work, remove dust. When going off duty, there are special health personnel to clean. The environment must be kept clean

the knife line is produced in a variety of forms, which requires the operator to form the habit of summarizing experience and actively cooperate with the factory management to minimize the knife line fault