How to ensure the printing effect of the high-line flexo carton?
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The flexible printing of high-network corrugated paper is a comprehensive system coordination process, which requires adjustment and cooperation of various related links to achieve a relatively optimal value. Such as plate making, ink, corrugated paper and cardboard, printing equipment, printing technology and other aspects are very important, we must cooperate. How to achieve flexible printing of high-network corrugated paper? The key technologies are:
First, the flexible plate making aspect, determine the best solution that can be suitable for printing and can reflect the product design effect.
1. Determine print suitability conditions
The first thing to know about printing equipment. Such as the unit color, the type and number of anilox rolls, the paper feeding system, the basic situation of the scraper system. There are also paper types, such as white paper or coated paper. Conditionally, a set of test plates for testing the printability of the printer can be provided. The utility model comprises a ladder strip for testing the expansion of different network lines of the flexographic version, a color block for measuring the solid density value of the ink, a simple chromatogram for overprinting different dot ratios, a yin and yang character and a straight line with different font sizes, a module for measuring the color registration error, and a module. To observe the pressure of the printing balance pressure and so on. Test plates are required to be produced under normal production conditions such as normal paperboard, standard water-based ink production, normal printing pressure and vehicle speed. Of course, some printing conditions can be changed to get different test samples. Through the analysis of the test samples, we can get the printability of the press under normal conditions. It can be found that the dot expansion, curve, the solid density of the water-based ink, the hue value, the mesh hitting net condition, the influence of the color sequence, the reduction of the fine lines, the overprinting error, and the printing balance pressure.
2. Determine the plate making process, color separation scheme
In the flexographic printing plate, the determination of the color separation process plan is a key factor, and it can play a certain decisive role to some extent for the success of high-line products. The color separation of flexible printing is done with as little color as possible, and the color is superimposed as purely as possible, which is very helpful for printing and reducing costs.
3. Plate selection and number of angles
The number of screens added to the plate is limited by the number of mesh roller lines, and the ratio between the two is required to be 1:5 or more. The 400L/in anilox roller can achieve a printing plate of up to 80L/in, and the number of lines is too high to paste and produce moiré. Therefore, the number of screen lines is not as high as possible. Moreover, the printing effect of 80L/in and 75L/in is not much different from the fineness.
The screen angle of flexo printing mainly adopts two angles of 7, 37, 67, 82, and 7, 22, 52, and 82 depending on the angle of the anilox roller. However, the angle of the screen should be based on the actual product, and it cannot be cut across the board. For example, the linear pattern of the monochromatic hanging net must be 45 degrees or 0 degrees for the hanging net angle, otherwise the edge of the hanging net pattern will appear more jagged. The angle of the color pattern should be selected based on the principle that the hue angle of the main color of the product pattern differs by 30 degrees. If the portrait skin is dominated by yellow, then the color difference between magenta and yellow should be above 30 degrees; if the landscape is dominated by green, then the color difference between cyan and yellow should be above 30 degrees, otherwise it will be prone to moiré. . Perform proofing simulations before screening to determine the best screening method. Discrete outlets use a certain amount of screening technology to increase the anti-counterfeiting of products.
4. At present, the direct plate making system mainly adopts the extremely high transfer technology, and the image is directly imaged on the resin plate after the color separation imposition. The digital printing plate has the advantages of complete dot type, high light spot loss, low printing dot expansion rate, long order adjustment, large dot, and no paste. It is the best choice for flexo printing.
Second, high network cable flexible printing requirements for sheet, paper, cardboard, water-based inks and equipment
1. High-network-line plate selection: For plates with high-line printing, the hardness should be slightly higher than that of general printing. This is because the amount of ink required for this printing process is small in order to accurately represent the fine dots. If the printing plate is too soft, the amount of ink transferred will be too large, which is not conducive to the control of the amount of ink, and it is prone to malfunctions such as color cast and blockage. In addition, the plate material is required to have a good dot reproduction range, and can produce fine high-gloss dots; uniform thickness, good flatness, easy to realize light pressure printing, and easy reproduction of the original; Elasticity, after being pressed, it can restore the original thickness and the plate material must have a certain toughness, and the small mesh points are not easy to wear. The plates currently used for such printing are DuPont's TDR and the like.
2. Cardboard: It is best to use coated white paper to achieve the same effect as offset printing. Because the coated white paper has a good finish, the print is more glossy and bright. The surface of ordinary whiteboard paper has poor gloss and the color of the imprint is dull. In addition, coated whiteboard paper is different from offset paper and coated paper, which retains some of the original characteristics of whiteboard paper - permeability and adhesion, which is beneficial to the printing of water-based inks. Cardboard can be made of cardboard with uniform thickness, flat paper surface, moisture control of 9+2% and good hardness. E-type, F-type or G-type corrugated with 180g/m2 facial tissue. Such a cardboard corrugation is low, the cardboard is flat, can withstand more pressure, reduce the phenomenon of ribs, imprinting, etc., and improve the quality of printed products.
3. Ink: Ink is a key factor in the entire printing process. The water-soluble acrylic acid is mixed with the acrylic emulsion, and a high-linking agent is added. For four-color overprinted high-web jobs, it is important to 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 dots, delicate pattern; high gloss - bright color, bright; low viscosity - no blocking net, ink stick , graphic is clean and refreshing; high color content - full color, rich in content; good adhesion - anti-wear, no fading; good leveling - uniform color, no exposed bottom; fast drying - good color stacking effect, no drag Flowers; good overprinting - good compatibility between colors, natural color, harmony, rich layers.
4. Equipment requirements: (1) Scraper: The printing machine capable of high-line printing must have a scraper. It also requires a sealed double scraper and maintains the effectiveness of the scraper to accurately control ink transfer. (2) Closed-loop ink Road: Closed ink path is good for preventing excessive contact between ink and air, preventing some components of ink from volatilizing, oxidizing, dissolving bubbles, etc., and maintaining the stability of ink composition to successfully complete high-quality printing; (3) High-net mesh transmission Ink roller: This is one of the most important conditions for high-speed screen printing. The higher the number of mesh lines, the higher the network cable that can be printed, and the smaller the amount of ink transferred, which helps to reproduce small high-gloss dots; (4) ) suction paper feeding, full-process adsorption paper: can improve the flatness of the paperboard, smooth paper feeding, ensure the accuracy, ensure the registration accuracy; (5) liner (lined between the printing plate and the plate roller): better lining The pad cushions and regulates pressure, protects small dots and improves plate life.