Printing contrast is the most important indicator for evaluating the quality of printing. It is the ratio of the difference between the solid density and the wire density and the solid density. Usually, the solid density of the dots with a dot area of ​​75% is selected. It is mainly expressed in the level of printed matter. The higher the contrast of the printing, the more the level of the printed matter is pulled apart, the greater the visual impact. On the contrary, it makes the level of the printed matter graded, without spirit, color deviation, and gives the human eye the feeling very bad.
Printing contrast is so important for printed matter, how can we control it well? In the following, based on the problems and solutions encountered in the production process, combined with some theoretical knowledge, we briefly analyzed several factors that affect the printing contrast of tinplate printing products. I hope that it will be helpful for future production control.
1. Original quality
The effect of the quality of the original on the K value is mainly reflected in the linearity of the printing film and the development of the film.
Film linearity refers to the consistency of the actual number of dots on the pattern of the film and the number of dots required by the pattern itself, which can be checked with a standard ladder. If the linearity is not correct, the product produced cannot correspond to the original manuscript at all, and the K value data has no guiding significance.
The development of the film is mainly due to the influence of the development quality on the dot quality during the output of the film. Insufficient development will cause the edge of the dot to be unclear. The K value will become smaller than normal, and excessive development will cause the dot to become virtual and lost. The K value Will become larger than normal. It can be checked by observing the control strip with 40 times magnifying glass.
Second, printing quality
The effect of printing quality on the K value is mainly reflected in the quality control during exposure and development. Excessive exposure and development will lead to loss of dots and lead to a larger K value. The level of the bright tone (low dots) part is not delicate enough; insufficient exposure and development will lead to a lower K value of the high-level dots and gradation level, and the level of dark tone is poor. . The quality of the printing quality can be accurately judged through the printing and measuring control strip.
3. Ink suitability
The effect of ink suitability on the K value is mainly due to the emulsification performance of the ink. Excessive emulsification will cause ink accumulation on the ink path and the water path, causing paste plates to reduce the K value; insufficient emulsification will make the transferability of the ink worse, and the ink cannot be transferred evenly. On the substrate, the K value is unstable. The emulsification performance of the ink is mainly affected by the quality of the ink itself, and is related to the ink's binder and additives. The difference in the suitability of different inks varies greatly.
4. Printing pressure
The effect of printing pressure on the K value is mainly reflected through the two aspects of ink transfer and dot quality. The printing pressure includes: the pressure between the ink rollers on the ink path, the pressure between the plate ink roller and the printing plate, the water pressure, the pressure between the printing plate and the blanket, and the pressure between the rubber cylinder and the impression cylinder. Abnormal pressure in any of the above will cause the network to expand abnormally, causing the K value to decrease.
Five, white cod
From the experiments we have done so far, the difference in the color of white codine will have a greater impact on the K value of one or two colors. The reddish phase of Butin has a greater influence on the K value of the red ink, and the K value of the red ink will drop more, but the effect on other colors is relatively small. Yu Pu has a background red. When the overall red reaches the desired density, the density of the red ink does not really reach. That is, when we remove the background red, its density is less than the density when there is a background red (that is, the same density Under, the thickness of the ink layer with bottom red is thinner than the thickness of the ink layer without bottom red), and at the same time, bottom red has a greater impact on the dots than on the ground. It also has the same effect on other hues, except that the affected colors are different.
Six, fountain solution
The pH value of the fountain solution has a great influence on the ink transfer of our offset printing, which is a necessary condition for the formation of an inorganic salt layer in the blank part. In theory, when the pH value of the fountain solution is greater than 6, the ability of the printing plate to form an inorganic salt layer is greatly reduced. The hydrophilic capacity of the blank part is greatly reduced, and the ink expands above the graphic part, and even causes the blank part to become dirty. Therefore, under the same solid density, the dot expansion rate value is larger than that under normal printing conditions. Its K value also fell. Similarly, if the pH value of the fountain solution is less than 4.5, the ink is easily emulsified, resulting in paste, resulting in an increase in the dot expansion rate, resulting in a decrease in the K value.
The influence of alcohol in fountain solution on K value is no less than the influence of PH value on K value. As we all know, the main role of alcohol in printing is to reduce the surface tension of water and reduce the temperature of the ink roller. If the alcohol concentration is too low, the surface tension of the water cannot be effectively reduced, the fountain solution cannot be spread well in the blank part of the printing plate, and the ink can easily enter the blank area, resulting in an increase in the dot expansion rate, followed by ineffective The cooling effect leads to excessive emulsification of the ink and easy expansion of the dots, which makes the K value drop.
7. Blanket
Blanket is the intermediate of our lithographic (offset) ink transfer. When printing, the blanket is in contact with the ink in the graphic part of the printing plate, and also in contact with the water in the blank part of the printing plate. Therefore, the blanket is mainly composed of rubber of non-polar material to ensure that the blanket absorbs the ink to the maximum extent and transfers the ink, and absorbs the moisture to the minimum. If the performance of the blanket is not good, it will cause the ink to not transfer well to the iron skin, causing irregular changes in the K value.
In order to obtain the ideal K value for the printed matter, it depends largely on the performance of the blanket. The performance indicators of the blanket are mainly: ink transmission, elongation, elasticity, flatness, etc. If the performance of the blanket If the index is not good, it will not be possible to print out the formed dots, which directly affects the K value of the product.
At present, the blankets we use all use air cushion blankets, which have two types of air cushion layers. Generally speaking, the thicker air cushion layer is more conducive to printing dot products, and its K value is also higher, but it is not conducive to printing products on the ground. On the contrary, the thin air cushion blanket is very suitable for printing solid products but not suitable for printing dot products. The K value is not easy to be high.
8. The temperature and humidity of the environment
When the temperature in the printing workshop increases, the viscosity of the ink decreases and the fluidity increases. At the same time, the dry vegetable oil also separates more free fatty acids, which causes the hydrophilicity of the blank part to decrease. The ink in the graphic part spreads outward, resulting in dots. Unusual expansion causes the K value to decrease. If the temperature in the printing workshop decreases, the yield value of the ink increases, the transfer capacity decreases, and the water volatilization capacity of the printing plate decreases, causing the K value of the printed product to change irregularly.
When the humidity in the printing workshop is unstable, the production operator cannot correctly control the water volume of the printing plate, which causes the water volume of the printing plate to be large and small, causing the color difference of the printed product and other defects, and the K value of the printed product will also change irregularly.
In summary, in order to have an ideal K value for printed products, strict control must be taken from the above aspects. Any poor control will result in unsatisfactory K value and affect the quality of the final product.
Storage Jar,Lunch Box With Lock,Plastic Jar Set,Kitchen Storage Set
Ningbo DSS Intelligent Technology Co., Ltd , https://www.dsscosmetics.com