The most popular gravure printing fault statistics

2022-08-06
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Gravure printing fault statistics and typical fault analysis

1) adjustment of the doctor blade

after the doctor blade is installed, it is necessary to adjust its axial parallelism: adjust the preliminary angle of the doctor blade so that the doctor blade gently presses on the printing plate, adjust the left and right advance and retreat of the blade body to ensure that the ink is uniform and balanced, and then accurately adjust the pressure and angle charge of the doctor blade, which is an important link affecting the printing quality

generally speaking, under the same angle, the greater the pressure of the scraper, the better the ink scraping performance can be. The 3-point zigzag test, 4-point zigzag test, sheet metal tensile test, thick plate tensile test, reinforced steel bar tensile test, chain tensile test, fixed part test and connecting rod test under sinusoidal load can be stopped. However, the pressure will operate the printing plate, and too small the pressure will not scrape the ink, which will cause the blade line, so the pressure of the scraper should be enough, It should be increased slowly even when pressurized

under the same pressure, the larger the angle of the scraper is, the better the ink scraping performance will be. Similarly, too large an angle will also cause serious operation between the scraper and the printing plate. Too small an angle will cause easy lint and ink drawing

since the angle of the scraper and the two affect each other, we can sum them up as a physical quantity - the pressure P between the scraper and the printing plate, which is more intuitive

after printing for a period of time, the contact area s between the scraper and the printing plate will increase due to wear. At this time, the knife line phenomenon will occur. Therefore, the pressure F of the scraper will be increased when the scraper is tightened. It is difficult to judge the change of pressure according to the formula P = f/s, so we have to judge it. When the tool tightening process exceeds max, the pressure P will decrease, that is, excessive tool tightening will make the problem of tool line more serious. Because the process of tightening the knife is a process of pressurization, the pressure of the scraper should be lower than the limit value, generally about kg/cm cubic meters, and the angle is between 50 degrees and 70 degrees. The angle can be steeper when the knife line appears, and the pressure is higher when the angle is more than 60 degrees

the scraper shall be polished several times after being used for a period of time according to certain rules. First, clean the tool holder, and then clamp the soft blade with the hard blade to expose 1/3. Note that the distance between the two ends should be consistent. When sharpening the knife, clamp the knife rest on the table, grind it with an oilstone at an angle of about 40 degrees, then rough grind it with 360 water sandpaper, and then fine grind it with 1000 fine sandpaper. The scraper has to be replaced when the wear is serious

if the blade line appears regularly and will hinder the movement of the blade, it can be concluded that it is mainly caused by the impurities adhered to the blade and the blade. It can be solved by grinding or replacing the blade and the foreign matters on the back of the blade

2. Ink

ink is the undertaker of printing pattern reproduction. The center is composed of pigments, binders, fillers and additives, and its impact on the knife line is also prominent

gravure printing ink can be divided into engraving gravure ink and photographic gravure ink. Engraving intaglio ink is mainly used to print securities, and the problem of knife line in this paper is mainly in the field of packaging, so it is unnecessary to discuss it. Let's talk about photographic intaglio ink

gravure inks are volatile and dry. They are typical liquid inks with good flow performance and low viscosity. They are generally composed of pigments, solid resins, volatile solvents and additives. Some of these properties such as fine filling, viscosity, dryness, hardness and activity are greatly affected by the knife line. The following will be discussed in combination with the properties of gravure inks

1) fineness

if the fineness of the ink is not enough, that is, the particles are too large, it may be embedded in the scraper or damage the scraper, resulting in knife lines. The fineness of the ink itself is determined by the ink manufacturer. The ink manufacturer should be soft, have no chemical reaction with the resin binder used, have good fluidity and stability during color development, and do not often occur. The printing factory should check the fineness of the ink when purchasing ink. The fineness of the gravure printing ink is generally about 15um. The smaller the fineness is, the better it is to reduce the knife line. In fact, the national factor is not only this step. When the ink is mixed with impurities in use, the long-term use of the ink will cause the resin to contact the air for a long time to oxidize and crosslink to form coarse particles, which will produce knife lines. For long-term use, the ink in the sharp periodic filter ink tray or the metal wire in the ink circulation system should be filtered. The recovered old ink should be filtered before use. The ink should be replaced when the ink coagulates. In addition, some cosolvent can be added and fully stirred to make its particles disperse evenly. If conditions permit, a closed inkjet device can be used, which can greatly reduce the contact between the ink and the air

2) viscosity

excessive viscosity of the ink will increase its impact on the scraper, making the scraper unable to completely scrape the ink. The viscosity of ink has a great relationship with solvent. Gravure printing ink uses volatile solvent, and in order to reduce the affinity of the ink to the printing plate and prevent a large amount of resin from precipitation, the solvent with strong solubility and fast volatilization is used. With the printing process, the solvent in the ink volatilizes continuously, which will cause the viscosity of the ink to rise. For this reason, we should pay attention to the change of viscosity at any time during printing. According to the loss of solvent, we should use viscosity controller or manual timely supplement solvent to maintain the stability of viscosity. In practice, the flow cup can be used to measure the viscosity, and the chann flow cup is generally used for gravure printing. It can be divided into several specifications according to the size of the opening. The reasonable selection of the flow cup has a great impact on the accuracy of the viscosity measurement

3) drying property

gravure printing ink belongs to volatile drying type, so its dryness is also the volatility of solvent. When the ink dries too much and the solvent volatilizes too fast, the friction between the printing plate and the scraper increases relatively, which makes it difficult for the scraper to scrape off the ink of the plate, resulting in knife lines. However, if the drying is too late, that is, the solvent volatilizes too slowly, it will transfer a small amount of ink from the non graphic part to the substrate to form plate contamination, So the volatilization rate of the solvent should be moderate. When analyzing the viscosity, it was mentioned that a solvent with fast volatilization should be used, which is a contradiction. For some reasons, the problem of excessive drying can be solved by adjusting the pressure and angle of the scraper. Gravure printing ink should choose a solvent with strong solubility and fast volatilization, such as ethyl acetate, ethanol, etc

4) hardness

in fact, this link can be attributed to the same fineness. For pigments with high hardness, such as red and blue, it is impossible to achieve very small particle size even if they are grinded, and they are easy to damage and scrape, which will inevitably produce knife lines. When using red and blue inks, first, the fineness should be controlled. When purchasing inks, the supplier should try to provide thinner inks. Then, preventive measures should be taken to prevent other factors from affecting the fineness of inks. Pay attention to the condition of the scraper to ensure the integrity of the blade

5) activity

in the production process of ink, a certain amount of active agent is generally added. Plate cylinder also has certain activity after chromium plating. If the activity of the ink or the plate cylinder is too high, the active substance will not adhere to the plate cylinder firmly during printing, and it is difficult for the scraper to clean it, thus forming a knife line. In this case, the knife line is meteor - shaped or microfilament - shaped, with a certain At this time, the printing plate cylinder can be washed to remove the active substances on its surface, and then the surfactant can be added to eliminate the knife warp. When using this additive, it is best to use the ink circulation system to prevent its repeated use

the quality of the ink has a great impact on the cutting line. When conditions permit, it is best to select a higher ink. To ensure the proportion of fresh ink, it is not difficult to solve the cutting line problem as long as you pay attention to a series of measures mentioned above for purchase and use

3. Environmental conditions

it is very important to maintain a good environment in the gravure workshop. The environment here mainly refers to dust, temperature and humidity

1) dust

the dust will produce fine knife lines, and the plastic film will produce electrostatic adsorption during printing. These dust will return from the film to the plate cylinder during printing, gather in the ink, and then adhere to the scraper to produce knife lines. For this reason, an electrostatic eliminator should be installed, and an antistatic wire or electrostatic tape should be hung above the plastic substrate film to improve the humidity in the air to reduce the phenomenon of electrostatic adsorption

dust may also directly come from the air, which requires a good sanitary environment in the printing workshop: the printing machines are placed, the workshop is isolated from the outside with air curtains, the number of people in the workshop is controlled, the floor is often mopped with wet newspaper, and the floor is treated with special paint to prevent dust. During the maintenance of the machine, attention should also be paid to the cleaning of the air duct and other parts that are not noticed at ordinary times to prevent dust accumulation. For the dust in the ink, a filter device can be added to the ink circulation system. At present, most of the ink tanks that have the strength to do these data are state-owned enterprises and ink boxes. Ford Motor Company of the United States also cooperates with the university to clean them. When using old ink, on the premise of ensuring the quality, 1/3-1/2 old ink can be used, but it is better not to use all the old ink. Filter it with more than 120 meshes of metal wire before using the old ink

2) temperature and humidity conditions

in fact, this factor has been included in the previous article. Here is a specific analysis

the temperature is too high, the solvent volatilizes too fast, the solvent balance is unbalanced, and the drying is excessive; Poor ink solution, high viscosity and difficult ink scraping, both of which are easy to cause knife lines

therefore, the gravure printing environment should be kept as closed as possible, air filters should be installed and dust content should be measured, and air conditioners should be installed to maintain the stability of ambient temperature and humidity

from the above analysis, it can be seen that there are many factors that are related to each other. For example, the plate cylinder and the doctor blade, the doctor blade and ink, ink and environment, and the blade line often occurs at the same time with plate fouling, plate pasting and other phenomena. Therefore, it is often difficult to judge whether the fault is caused by various factors, and the solution cannot be specified in detail. However, as long as the judgment methods mentioned above are based on the different characteristics of the blade line, The main aspects of spring are the main influencing factors, and there are corresponding solutions to eliminate them. Of course, the most ideal state is to carry out reverse thinking from the factors involved in this paper, and take all measures to prevent it to reduce the incidence of the knife line

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