The flexible printing of high screen corrugated paper is a comprehensive system cooperation process, which requires the adjustment and mutual cooperation of various relevant links to achieve a relatively optimal value. Functional High Dot Flexographic Overprint Carton Solution
Such as plate making, ink, corrugated paper and paperboard, printing equipment, printing technology and other links are very important and should be well coordinated. How to realize flexible printing of high screen corrugated paper?Functional High Dot Flexographic Overprint Carton Solution
The key technologies are:
（1） In terms of flexible plate making, determine the best solution that can not only be suitable for printing, but also reflect the effect of product design
1. Determine printability conditions
First of all, we should understand the situation of printing equipment. For example, the color number of the unit, the type and number of lines of anilox roller, the basic situation of paper feeding system and scraper system.Functional High Dot Flexographic Overprint Carton Solution
There are also paper types, such as whiteboard or coated paper. If possible, a set of test plates for testing the printing suitability of the printer can be provided. Functional High Dot Flexographic Overprint Carton Solution
It includes a ladder bar for testing the dot expansion of different screen lines of flexo, a color block for measuring the field density value of ink, a simple chromatography for overprinting with different dot ratios, yin-yang characters and straight lines of different font sizes, a module for measuring the chromatic error, a pressure bar for observing the printing balance pressure, etc. Functional High Dot Flexographic Overprint Carton Solution
The test printing plate is required to be completed under the production conditions of normal printing board, standard production water-based ink, normal printing pressure and speed. Of course, some printing conditions can be changed to get different test samples. Functional High Dot Flexographic Overprint Carton Solution
Through the analysis of the test samples, we can get the printability of this type of printer under normal conditions. The dot expansion, curve, field density of water-based ink, hue value, dot collision, influence of color sequence, reduction of fine lines, overprint error and printing balance pressure of each color can be obtained.
Combined with the above test data and the printing effect of the test sample, a set of color matching management system for this printer can be established, such as establishing dot compensation curve for dot expansion, correcting screen color and gannina curve, color simulation and matching of proofing, etc.
2. Determine the plate making process and color separation scheme
In flexographic plate making, the determination of color separation process scheme is a key factor, which plays a decisive role in the success of high screen products. The color separation of flexible printing should use as few colors as possible and use as pure colors as possible to complete the color superposition, which is very helpful to printing and reduce the cost.
3. Selection of screen line number and angle of printing plate
The number of screen lines of printing plate is restricted by the number of screen lines of anilox ink transfer roller, and the ratio between them is required to be more than 1:5. The anilox roller of 400L / in can achieve the printing plate of 80L / in at most. If the number of lines is too high, it is easy to paste the plate and produce moire. Therefore, the higher the number of network cables, the better. Moreover, the printing effect of 80L / in and 75L / in will not be much different in terms of fineness.
The screening angle of flexo printing mainly adopts two angles: 7, 37, 67, 82 and 7, 22, 52 and 82 according to the angle of anilox roller. However, from the perspective of screening, we should start from the reality of the product, not one size fits all. For example, for the monochrome screen linear pattern, the screen angle must be 45 degrees or 0 degrees, otherwise there will be obvious sawtooth at the edge of the screen pattern.
The selection of overlapping pattern angle shall be based on the principle that the hue angle difference of the main tone of the product pattern is 30 degrees. If the portrait skin is mainly yellow, the color difference between magenta and yellow should be more than 30 degrees;
If the landscape is mainly green, the color difference between cyan and yellow should be more than 30 degrees, otherwise it will be easy to produce moire. Before plate making, the proofing simulation of screening is carried out to determine the best screening method. Discrete outlets adopt certain screening technology to increase the anti-counterfeiting of products.
4. At present, the direct plate making system mainly adopts extremely high transfer technology, which can directly image on the resin plate after color separation and plate making. Digital printing plate has the advantages of complete dot type, high light spot is not easy to lose, low printing dot expansion rate, step length, large dot and no paste. It is the best choice for flexographic high screen plate making.
（2） Requirements of high screen wire flexible printing for plate, paper, paperboard, water-based ink and equipment
1. Plate material selection for high screen plate making: the plate used for high screen printing shall have a hardness slightly higher than that required for general printing. This is because this printing process requires a small amount of ink to accurately reflect small dots. The printing plate is too soft, which will lead to excessive ink transfer, which is not conducive to ink control, and is prone to color deviation, screen blocking and other faults.
In addition, it is also required that the plate should have a good dot reproduction range and be able to make small high gloss dots; With uniform thickness and good flatness, it is easy to realize light press printing and easily reproduce the original;
It has good elasticity, can return to the original thickness after compression, and the plate should have a certain toughness, and the small dot is not easy to wear, etc. At present, the plates commonly used in this kind of printing include DuPont TDR, etc.
2. Paperboard: to achieve the effect comparable to offset printing, it is best to use Coated Whiteboard. Because the Coated Whiteboard has a good finish, the imprint is more shiny and bright. The surface gloss of ordinary whiteboard is poor, and the imprinted color is dim. In addition, coated whiteboard is different from offset paper and coated paper.
It retains some of the original characteristics of whiteboard – permeability and adhesion, which is conducive to the printing of water-based ink. Paperboard with uniform thickness, flat paper surface, moisture controlled at 9 + 2% and good hardness can be selected. E-type, F-type or G-type corrugated with 180g / m2 face paper. This kind of paperboard has low corrugation and flat paperboard, which can withstand greater pressure, reduce ribs and false imprinting, and improve the quality of printing.
3. Ink: ink is a key factor in the whole printing process. Water soluble acrylic acid and acrylic emulsion were added to join high coupling agent. For high screen movable parts with four-color overprint, we must pay attention to the choice of ink. The ink of printing coated paper is different from ordinary ink. It mainly requires the following characteristics: good fineness – clear dot and fine pattern;
High Gloss – bright color and luster; Low viscosity – no blocking screen and ink bar, clean and refreshing graphics and texts; High color content – full color and rich connotation; Good adhesion – anti-wear and no fading; Good leveling – uniform color without bottom exposure; Fast drying – good color stacking effect, no drag flower; Good overprint – good compatibility among colors, natural and harmonious colors and rich levels.
4. Equipment requirements:
(1) scraper: the printer that can complete high screen printing must have a scraper. It also requires sealed double scraper and maintain the effectiveness of the scraper, so as to accurately control ink transfer;
(2) Closed circulating ink path: the closed ink path is conducive to prevent excessive contact between ink and air, prevent some components of ink from volatilizing, oxidizing and dissolving into bubbles, and maintain the stability of ink components in order to successfully complete high-quality printing;
(3) High screen line anilox ink transfer roller: This is one of the most important conditions for high screen line printing. The higher the number of anilox lines, the higher the screen line that can be printed, and the smaller the ink transfer volume, which is helpful to reproduce small high gloss dots;
(4) Suction paper feeding and whole process adsorption paper feeding: it can improve the flatness of paperboard, smooth paper feeding, ensure accuracy and registration accuracy;
(5) Liner (liner between plate and plate roller): a better liner can buffer and adjust the pressure, protect small dots and improve the service life of the plate