In recent years, with the continuous emergence of new equipment, new materials, and new technologies, the printing technology of corrugated board is maturing and progressing. The carton packaging production process featuring direct printing on corrugated board and off-line pre-printing has been widely used in the packaging field due to its advantages of high quality, low long-term comprehensive cost, short cycle efficiency, and environmental protection. To some extent, it has replaced offset printing and become a trend.
In the past two years, people have mostly seen high-line water-based direct prints (some of them up to 110 lines) or some off-line pre-printed products at participating in exhibitions or from printed samples. And several well-known domestic machinery and equipment manufacturers are promoting. Water-based direct printing equipment factories such as Nanhai Dongfang, Shanghai Dinglong, Beijing Dobbek, and Taiwan's Longsheng, TCY, etc.; off-line preprinted machinery manufacturers such as Qingzhou Yigaofa, Guangzhou Kesi High. It is inconceivable that such a high-line screen print should be realized with domestic equipment several years ago.
The water-based printing of high-line corrugated paper is an integrated system. It does not depend on which link does a good job. She needs to adjust and cooperate with each other to achieve a relative best value in order to print an exquisite one. product. Such as plate making, ink painting, corrugated paper and cardboard, printing equipment, printing technology and other links are all very important and must be well coordinated. The following is a brief discussion on how to realize the water-based printing of high-line corrugated paper.
First, in terms of flexible platemaking, determine the best solution that can be suitable for printing and reflect the product design effect.
1, determine the printability conditions
First of all, we must understand the customer's printing equipment, such as the unit color number, type and number of anilox roller, the paper feeding system, the basic situation of the scraper system. There are paper types, white paper or coated paper. Conditional plate makers generally provide a set of test plates for testing the printability of printers. It includes a ladder strip for testing the expansion of different flexographic screen points, a color patch for measuring the density of ink in the field, a simple chromatogram for the overprinting of different dot proportions, a yin and yang character and straight line with different font sizes, and a module for measuring trapping errors. To observe the pressure balance of printing pressure bar and so on. Test plates are required to be completed under normal printing board, standard production water-based inks, normal printing pressure and vehicle speed. Of course, you can change some of the printing conditions to get different test samples. Through the analysis of the test sample, we can get the printability of this type of printing press under this condition. The dot expansion curve for each color, the density of water-based ink, the hue value, the impact of the dots, the influence of the color sequence, the reduction of fine lines, the overprint error, and the balance pressure of printing can be obtained.
Combining the test data obtained above and the test results of the control test samples, the plate-making company can establish a color matching management system for the printer, such as creating a dot compensation curve for dot gain, screen color and gamma curve correction, and a proofer. Color simulation and matching and more.
2, determine the plate making process, color separation program
In the flexo platemaking, the determination of the color separation process plan is a key factor. To a certain extent, whether or not a high-line cable product can be printed successfully plays a decisive role. Yingjie plate making company has been devoted to the research and promotion of carton color water-based high-speed line plate for many years. It was the biggest winner in the 2004 and 2005 China Flexographic Association and DuPont Wolverine Competitions, and won the "Outstanding Contribution Award" of the platemaking industry. Below is a description of the specific details of the two winning entries.
The foreground of the "JVC" sound box is a clear speaker, and the background is an effect of gradual change to netting, which is slightly embarrassing. This gradual to net effect should be relatively easy to achieve for offset printing, but it is more difficult for watermarks such as conventional dot-based methods. Discrete FM dots will destroy the details of the image, but it is not easy for the large-area pitted surface printing of the corrugated box to print ribs. In addition, it is natural for the net to be absent, and no hard mouth will appear. So we decided to use the usual dot network for the foreground sound, and the background is to use a discrete FM network, and the product tone will be combined with the appropriate range of the network and the absolute sequence of the various colors. The watermark effect obtained in this way is due to the fact that the foreground and the background adopt different mesh types, so that the foreground effect is more prominent, and the background gradient is natural and reasonable, highlighting the sense of embarrassment and well embodying the designer's design ideas. On the other hand, discrete networks use a certain amount of screening technology to increase the security of products. So the customer is very satisfied, the sample was successful, and all the series of "JVC" were all transferred to the watermark.
Another example is the determination of the color separation scheme for the 'e-can body' on the outer box of "Yashu" brand coconut milk. This box originally used the offset printing method. The easy-pull can body was made of four-color overprint. The four-color network Chengdu was relatively close to the field. If you simply apply these data to the watermark, the effect of the four-color overprinting part will be neither black nor false, and it will be a far cry from offset printing. This is due to the fact that printers that print this product do not have a direct drying system. With the short distance between the color groups and the fast printing speed, the former color of the larger ink volume is still dry in the future, and the latter color has been imprinted. This will not only make it difficult to re-adhere to the back of the color, the printing plate will also stick back to the printing plate without drying the front color ink. This is not only a waste of ink, of course, the result is not ideal. Therefore, the total amount of ink printed by the watermarking machine must be taken into account when separating the color of this part (from the test version can be analyzed). The black can body part mainly uses black to reflect the level, so the black version strengthens the tone level, and uses special black ink, the other three colors of the net into a substantial reduction, magenta and yellow only retained one percent outlets, cyan in order to ensure The blackness of the can and the amount of color retained some. For accurate color registration, other colors on the edge of the can slightly receded slightly from the can body. The transition between black and colored patterns in black cans is a natural process. As a result, the effect of such separation printing is very hierarchical and three-dimensional, and the picture of the pattern is clear and clean, full of colors.
There are many examples of such separations. The color separation of water-based printing requires the use of as little color as possible and the color as pure as possible to complete the color superposition. This is very helpful for printing and reduces costs, reflecting the packaging effect.
3, the choice of printing plate screen number and angle
The number of screen printing screens is limited by the number of lines of the screen roller, requiring a ratio of 1:5 or more. The 400L/in anilox roller can achieve a maximum of 80L/in plate, and the number of lines is too high to paste and produce moire. Therefore, the higher the number of screens, the better. Moreover, the printing effect of 80L/in and 75L/in will not be much different from the fineness.
The watermarking angle of the watermark mainly adopts 7, 37, 67, 82 and 7, 22, 52, 82 angles according to the different anilox roller angles. However, the screen angle must be based on the actual product, and it cannot be cut across the board. If the monochromatic pattern is hung in a straight line, the angle of the hanging net must be 45 degrees or 0 degrees, otherwise the edge of the hanging pattern will appear more jagged. The selection of the overlapping pattern angle should be based on the principle that the hue angle of the main hue of the product pattern is different by 30 degrees. If the portrait is yellow, then the color difference between magenta and yellow should be more than 30 degrees; if the scenery is mainly green, then the color difference between cyan and yellow should be above 30 degrees, otherwise it will easily produce moire . Conditional plate-making companies will perform screening simulations to determine the best screening method.
4, high network plate plate selection
The printing plate used for high-line printing has a slightly higher hardness than the printing plate required for general printing. This is because such a printing process requires a small amount of ink in order to accurately represent fine dots. If the printing plate is too soft, it will lead to excessive transfer of ink, which is unfavorable to the control of the amount of ink, and is prone to defects such as color cast, blocking of the net, and the like. In addition, it is also required that the plate material has a good dot reproduction range, can produce fine high-gloss dots; has a uniform thickness, good flatness, easy to achieve light pressure printing, easy reproduction of the original; very good flexibility , After the pressure can be restored to the original thickness and plate material must have a certain degree of toughness, fine mesh is not easy to wear and so on. The plates commonly used for such printing are DuPont's TDR.
Second, high-line water-based printing on paper, cardboard, water-based ink requirements
1, cardboard
To achieve the same effect as offset printing, coated whiteboard paper is the best choice. Because the coated white paper has a better finish, the print is more glossy and bright. Ordinary white paper surface gloss is poor, the color of the imprint is dull. In addition, coated white paper is different from offset paper and coated paper, which retains part of the original characteristics of white paper - permeability and adhesion, and is conducive to the printing of water-based ink. The paperboard can be used for cardboard with uniform thickness, smooth paper surface, moisture control of 9±2%, and good hardness. E-type, F-type or G-type corrugated, with 180g/m2 gram weight of face paper. Such paperboard has low corrugation and flat cardboard, which can withstand greater pressure, reduce the appearance of lines and imprints, and improve the quality of printed products. At present, white coated paper can be supplied by Finnish paper companies, and there are also several domestic manufacturers in Guangdong.
2. Ink
Ink is a key factor in the entire printing process. For four-color overprinted high-line live work, we must pay attention to the choice of ink. This has little to do with the past experience of printing manufacturers. The ink for printing coated paper is different from ordinary ink. It mainly requires the following features.
Good fineness - clear dots, exquisite patterns; high gloss - bright colors, glossy; low viscosity - no blocking nets, ink bars, clean and fresh graphics; high color content - full color, rich content; Good—anti-wear, no discoloration; good leveling—uniform color, no exposed bottom; fast drying—good stacking effect, no trailing; good printability—good compatibility between colors, natural, harmonious, and hierarchical rich. At present, inks that can be widely used for coating paper printing include Guangdong Mingfeng ink, Yingjie ink, and Oriental ink.
Third, high-line water-based printing equipment, printing operation requirements
1, equipment requirements
scraper. The printing machine that can complete the high-line printing must have a scraper. It also requires a sealed double scraper and maintains the effectiveness of the scraper scraping so that the ink can be accurately controlled.
drying. Drying equipment is a more important configuration of new printing equipment. Because the ink on the coated paper is significantly slower than ordinary white paper by infiltration, multi-color inlays require that the previous color ink be dried as quickly as possible, and the next color can be smoothly stacked. Therefore, the advanced printing machine adopts either cold air drying or larger units. The distance is such that the board has enough time to dry, or it is equipped with drying devices such as infrared rays, UV, and the like.
Closed circulation ink circuit. Closing the ink path will help to prevent excessive contact between ink and air and prevent certain components of ink from volatilizing, oxidizing, and dissolving bubbles. To maintain the stability of the ink composition can be successfully completed high-quality printing.
High mesh screen ink transfer roller. This is one of the most important conditions for realizing high-line printing. The higher the number of reticulation lines, the higher the number of screen lines that can be printed, and the smaller the amount of ink transferred, which helps to reproduce fine high-gloss dots.
Suction and paper feeding, adsorption of the whole paper. It can improve the flatness of paperboard, steadily move the paper, ensure the accuracy, and ensure the accuracy of registration. Liner (lined between plate and plate roller). A good cushion cushions and regulates pressure, protects fine dots, and improves plate life.
2, printing operation
Stress - Pressure is the most critical control factor in the printing process. Pressure adjustment must be just right, the pressure is too light: the lack of ink, the color is light, uneven color, exposed at the end, virtual edge; pressure is too large: block nets, dirty version, flash, dot expansion, darker color, dark images.
Ink transfer - The amount of ink transferred can be adjusted by controlling the pressure, changing the viscosity and transferability of the ink. In addition to affecting the accuracy of color, the amount of ink transferred also has a direct relationship with the drying, stacking, leveling, and adhesion properties of the imprint, and must be carefully handled to make a quality product.
Color Sequence - When the four primary color gradation plates are superimposed on coated paper, the best color sequence is usually: C, M, Y, K.
1. Black is the complementary color that adjusts the light and shade levels and enhances the three-dimensional sense, usually at the end;
2, yellow transparency is better than C, M, so on the post-print;
3. The water-based ink blotting gloss is worse than that of the oil-based ink, which is also a weakness compared with flexo printing. The color sequence is printed from light to dark, and the overall effect of the product will be even more dim. From dark to light printing, the color will appear glossy and bright;
4, to prevent the "color", we put the printing process in the color of the latter group, picked up to the former color group of the ink bucket to the phenomenon called "dark color." The dark "brown" to light color, light-colored ink scrap; light-colored "brown" to dark color, little effect, so to use from dark to light color sequence.
Machine speed - due to the specific circumstances of the various equipment, can not be generalized, we generally in practice, according to the actual situation, the machine speed is controlled at 6000-9000pcs / h. The speed is too slow: the ink is large, the color is dark, and the drying is excessive; the speed is too fast, the drying is insufficient, the color stacking is difficult, the dirt is dragged, and the nesting is not allowed.
Use a specially-washed liquid ring to rub the printing plate - to prevent the dried ink from corroding the printing plate, keep the printing plate clean; the dots are circular, so use the rubbing method; the dot of the high screen version is very young, use the special Wash solution, wipe carefully.
The above is a variety of factors that should be taken into consideration when realizing fine-line water-based prints. With the maturation and improvement of various supporting technologies and equipment, it is believed that this technology will be applied more widely.