Color management of the hottest sheet gravure prin

2022-07-26
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Color management of paper gravure printing spot color is widely used in gravure printing. Spot color ink is generally prepared by the ink factory according to the color samples provided by the printing factory, the paper used for printing, the depth of intaglio holes, etc. Even so, the spot color ink will produce the phenomenon that the printing hue is different from the color sample when it is printed on the machine. Although we can contact the ink factory for further adjustment, this is not a long-term solution after all. Because the paper used by the printing plant is not very fixed, the whiteness, smoothness and tightness of different batches of paper are also different, and the depth of the printing plate hole is also different. At present, there are more and more kinds of inks, and the hues of some inks are very similar, which brings a lot of inconvenience to the storage and storage of inks

therefore, relying on the existing large coal industrial base, gravure printing manufacturers must strengthen the color management of printing. From the determination of printing color samples to the monitoring of color management process, how to establish an excellent color management system is very important

selection of base inks

in order to solve the problem caused by the wide variety of spot color inks for gravure printing, generally classify the types of inks, find out several commonly used reference inks as base inks, and use color difference meter or spectrophotometer for measurement and monitoring

common inks and toner inks include sky blue, peach red, medium yellow, black, crimson, golden red, rose red, scarlet, radiant blue, special purple, special green, special blue, transparent yellow, orange, white ink, diluent, gold blending oil, etc. After the technologist has identified the required base ink, it is necessary to pre adjust the hue of each color ink before the product is printed, and try to find the closest spot color ink. The less the ink components, the better, so as not to affect the saturation and brightness of the ink and lead to the increase of variable factors of the allocated ink. Rough adjustment can be directly observed after scraping with an ink scraping stick. If possible, a large area of main color ink can be slightly adjusted with the help of a color difference meter or a spectrophotometer when the product is proofed on the machine to determine the ink allocation ratio

color matching skills

next, take the deployment of large red ink and light green ink as an example to introduce the deployment skills of spot color ink

1. Deployment of large red ink

for a certain large red, in the ciel*a*b* color space, l*=40.80, a*=59.80, b*=42.11. Thus, we generally know its position in the color space

the base ink to be selected for blending this color is mainly bright red, and the toner inks are dark red, golden red, black and diluent

in comparative measurement, when one of △ l*, △ a*, △ b* is close to Z or greater than or equal to Z in the tristimulus value, the color difference will be obvious when observed with the naked eye. Therefore, l* is a key chromaticity index. The products of some foreign manufacturers determine the main position of color in ciel*a*b* color space

(1) if △ l*> 0 and △ l* value is large, the color is too bright, and the ink layer appears thin from the perspective of printing; From the composition of ink, the proportion of dark red ink in ink is less

there are two ways to adjust this. One is to increase the ink layer thickness by increasing the printing viscosity and reducing the printing speed; The other is to increase the proportion of dark red ink. At this time, a very small amount of purple ink or black ink can be used to adjust, and the yellow phase can be adjusted with golden red ink

(2) if △ l* < 0 and the absolute value of △ l* is large, the color is dark and there are too many pigment components in the ink

when adjusting brightness, it will have some influence on the saturation of color. Therefore, while adjusting the brightness, a little golden red ink can be added for fine adjustment, but the red phase and yellow phase in the color cannot be greatly affected. Of course, the hue cannot be adjusted solely. When adjusting the yellow phase in red ink, orange ink or golden red ink can be used to replace yellow ink for fine adjustment

2. Deployment of light green ink

light green ink in ciel*a*b* color space, l*=81.69, a*=-11.06, b*=4.00. The color is mainly white ink and adjusted with a small amount of special green ink. The blue phase and red phase can be adjusted by sky blue ink, medium yellow ink or transparent yellow ink. In addition, when the color is mixed, the problem of reading the cursor should also be considered. In the blue phase, it is difficult to read the optical logo, and in the yellow phase, it is normal to read the optical logo. Therefore, the proportion of yellow ink can be appropriately increased to make light green with yellow

determination of the first sample and sealing and distribution of the standard sample

since the printing factory can only carry out mass production after the customer approves the first sample, the determination of the first sample has become a very important link in color management

in gravure printing, the determination of the first sample has its particularity. In particular, for cigarette labels and wine labels with large quantities (from tens of thousands to hundreds of thousands, or even millions, which are increasingly widely used in machine tool processing, testing instruments and other industries), the printing resistance of printing plates is generally required to reach about 1million. If some printing plates are properly operated and properly kept, their printing resistance can even reach 2million ~ 3million. However, with the increase of the number of printing, the printing plate holes will gradually become lighter, the ink layer thickness will continue to decrease, and the color saturation will also decrease. Compared with the samples printed with the new version, the color will have a grade difference

to keep the color fluctuation of the whole batch of products small, according to the printing adaptability of each kind of paper, when printing for the first time with the new version, add about 20% diluent in the ink, and adjust the viscosity appropriately, so as to directly reduce the color saturation slightly. With the shallower depth of the printing plate hole, the proportion of diluent can be continuously reduced, or even no diluent can be added, so as to relatively improve the color concentration of the ink. At the same time, the viscosity of the ink can be properly adjusted to keep the ink transfer stable

after the first sample standard is confirmed, the quality control department can seal and mark the off machine printed color samples for later process processing and sample retention. The color manager of the quality control department shall establish a standard color sample file folder and distribute it to the process department and the production workshop. In addition, the process department shall be informed immediately of any deviation during the printing process to adjust the process formula and printing parameters, and the printing bench shall be informed of the changed process instructions

the multi rib structure of the printing machine table is 10% lighter than the traditional thermosetting resin matrix composite sandwich plate structure; At the same time, process management and color difference detection

after the paper, printing plate, ink formula and standard color sample are determined, the printing machine shall strictly implement the following process requirements within a relatively stable time

(1) ink color concentration. By scraping the ink sample, you can check whether the prepared ink formula is stable

(2) ink printing viscosity. Controlling the printing viscosity of the ink is helpful to the wetting of the ink on the printing plate during ink scraping and reduce the wear of the doctor blade on the printing plate

(3) press speed. Controlling the machine speed helps to stabilize the ink transfer

(4) drying temperature. The drying temperature of the printed matter should not be too low, otherwise the ink film that is not completely dry and not firmly attached will adhere to the cooling roller

(5) ambient temperature and humidity. The temperature and humidity of the environment have a direct impact on the temperature and moisture content of the ink

the printing machine shall be sampled for self inspection at a certain frequency, and the quality control department shall monitor and measure the continuous operation of the machine. The color difference shall be detected at least once within 30 minutes. Under the condition that the process parameters remain unchanged, if there is obvious color change, the color manager shall coordinate with the technologist to make on-site process adjustment, record the changes and send them to the printing machine

it is worth mentioning that the state of the color difference meter determines whether the detected data is accurate and reliable. Therefore, it is necessary to ensure that several important indicators of the color difference meter, such as fatigue characteristics, stability, repeatability, reproducibility and accuracy, meet the use requirements

establish the inspection system of printing plate, paper and ink

the key to color management is compliance, consistency and durability. Paper should be used together with printing plate and ink. The physical and chemical properties of paper determine the depth of printing plate holes and the viscosity of ink. In color management, first of all, we should check the material inspection, and conduct physical and chemical tests on its important indicators, such as the whiteness, smoothness, tightness and other indicators of the paper, the hue, viscosity, fineness and other indicators of the ink, and the depth and shape of the printing plate hole. The supplier is required to provide materials with stable quality. If the materials are to be replaced, they shall be tested by the quality control department, the process department and the marketing personnel, and tested on the computer if necessary. For example, each kind of paper has its corresponding printing speed, printing pressure, ink viscosity, drying temperature, etc., and some paper color areas are also different, and the packaging suitability is also different. Mass printing is not allowed without customer approval. After small batch printing samples are printed, they are sent to customers for packaging tests, and mass production can be carried out after customers' approval

in a word, color management is a systematic science, and every link is crucial. Training an excellent color administrator and constantly maintaining the established color quality control system are the most important

reprinted from: Printing Technology

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