What is Direct to Plate?
Direct printing is a printing method in which the ink on the printing portion of the printing plate is directly transferred to the surface of the substrate. Direct printing is the printing ink in contact with the material being printed, and the printing ink is transferred to the material being printed. All letterpress printing machines (including the latest rubber or plastic rotary presses) and gravure printing presses, as well as the hand-held lithographs in the oldest lithographic printing processes, are directly printed.
Direct printing
Printing press printing
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Early decal printing has just begun
Color printing directly on the container-with the advancement of screen printing equipment technology, printing
Direct printing
Machine speed, reliability, overprinting capabilities and other technologies have made printing more traditional from direct to direct printing. At the same time, automation has become one of the current development trends. If screen printing manufacturers want to be invincible in the competition, they must produce products that meet customer needs and high quality. One of the ways to improve competitiveness is to print directly in color, and container printing is no exception. But at present, with the exception of some screen printing manufacturers in the United States, many people think that it is impossible to directly print the primary color on the container (using yellow, magenta, cyan, black or more color printing). In fact, there is not much difference between printing on containers and printing on flat substrates. Although container printing machinery and printing systems have been greatly developed in the past decade, few manufacturers have adopted them. This article analyzes the changes in the market and the opportunities facing container manufacturers, describes the process of direct printing on containers, and the reasons why many container decoration manufacturers are reluctant to print halftone images directly on containers. First, the reasons why many manufacturers do not use direct printing. Because the substrates in container printing have curved surfaces or other irregular shapes, it is necessary to print graphics on them, which brings some difficulties to printing. In fact, there is not much difference between curved surface printing and flat surface printing. The most obvious difference is that the container itself must be pre-treated before it can easily accept the ink. Secondly, the place where the doctor blade passes is an uneven curved surface, which has special printing pressure Claim. Therefore, in container decoration, the handling of substrates is a key issue. In addition to understanding the subtle differences between container printing and offset printing, the printer must also be able to deal with the diversity of prints. This diversity includes differences in highlight areas, dark areas, and midtone areas. Space instability and other problems caused by container manufacturing. It should also be noted that increasing the printing speed will also be more difficult due to the curved shape of the container. These factors are not easy to overcome and need to be compensated with stable, high-quality printing equipment.
Second, the application of direct printing in other aspects Screen printing has been used in glass and plastic container printing
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Occupies a dominant position, but since the late 1980s, many people believe that pressure-sensitive ribbon transfer and thermal transfer will replace screen printing. But this is not the case. At least for spot color printing, screen printing still plays an important role. But for color printing, ribbon transfer and thermal transfer methods are preferred. In the printing field, because customers need to print directly, it is used in almost all aspects: offset printing, flexo printing, embossing and screen printing. We can see printed products such as T-shirts, posters, banners, etc. on screen printing everywhere, but also on decals and transfer ribbons, and then applied to containers. Manufacturers of flat screen printing and fabric products are aware that the multicolor printing process is not mysterious, but it is currently difficult to see the use of overprint technology in the decoration of plastic or glass containers. In the development of printing technology, the role of digitization cannot be ignored. The meaning of digitization is huge. It does not need to go through plate-making (for screen printing, it does not need screen), shortens the production cycle, and can respond to customer needs in a timely manner. Already manufacturers use digital methods for container printing, but there are many shortcomings in printed products: the visual effect of image color is poor, and the created image is unstable and durable. Although the digitalization of container printing is still in its infancy, it will soon develop. For screen printing, since the ink can produce good visual effects and can also resist harsh environmental conditions, we can't help asking: Why should we use separate processing when we have the ability to print the image directly on the container? Method? Direct printing
Third, the market needs of overprint printing and its superiority The needs of customers force the container to adopt a four-color overprint method. Although everyone's appreciation level and taste are different, in most cases, consumers tend to choose products with beautifully designed appearance. For example, when people buy a CD, although they have not seen the images on the CD, they are happy to choose products with beautifully printed pictures. Satisfying the needs of customers is one of the reasons for direct printing, but other factors cannot be ignored, which are introduced separately below.
1. Can save costs In the process of loading, printing, unloading and selling to the customer from the container, we should consider how to save material and labor. From the perspective of time and material, the additional process, such as printing labels, thermal transfer, and then used for container decoration, is costly. If the color pattern is directly printed on the container, the investment will be reduced.
2. Direct printing can be delivered in time, container decoration no longer needs to produce labels, and production is more free, especially when the delivery date is approaching, this advantage is more obvious.
3. Get high-quality products. The images obtained by multi-color screen printing directly on the container are more stable and durable than the images obtained on the label.
4. There is no obvious label edge on the container, which makes the whole picture more attractive.
5. Improve the overall effect Without using labels or other thermal transfer materials, there is no need to specifically reserve a large space to store these materials, and there is no need to consider problems such as label damage or expiration, which reduces waste and improves the overall production efficiency.
Fourth, conditions are mature It is easy to enter the field of container decoration, but in order to get more orders,
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The competition is fierce, unless there is a strong advantage. How can we gain a competitive position in a mature field? The answer is: Dividing funds or increasing investment, and direct screen printing is an ideal way. For example, many European decoration manufacturers have successfully used the direct decoration method adopted by flat printing manufacturers in production practice and achieved good results. "Tomography" usually refers to the combination of the original color and the black plate to obtain a color print. The basis of overprinting is color separation, that is, it is divided into two colors, three colors, four colors, and even more colors. The basic principle is that the tiny half-tone ideas printed are very close to each other. The image seen by the human eye is a superposition of many ideas, and the reflected light is formed by incident on the human eye according to the principle of color addition. Usually people think that it is impossible to directly print colors on curved surfaces, but in fact, the procedures used in flat printing have many similarities on curved substrates. In order to obtain high-quality prints, there are many aspects to consider, and effective control of these changing factors can lead to better products. The main factors that should be considered are film, screen, stencil, exposure, printing process, and machine characteristics, which are described below. (1) In the decoration of the film, the film should be properly separated first. This is the key to determining the print quality, because once the separation is completed, it cannot be compensated in the screen production or printing stage. Therefore, if the company does not have good color separation ability, it is recommended to find a manufacturer specializing in the production of four-color screen printing film for color separation. Screen printing four-color separations are different from lithographic offset printing, so the lithographic separation process is not suitable for screen printing. This is because the printing plate is manufactured in different ways, and during screen printing, paper or substrates are deposited. More ink than lithography. In order to obtain a better reproduction effect, various parameters need to be considered in color separation. First of all, it is necessary to understand the tone range and the shape of the halftone dots. In the offset printing, the entire tone range can be printed from 1% to 100%, and for container printing, the tone can only be printed from 15% to 85%. In container halftone printing, the best dot shape is oval. This is because when the square dots are expanded, the four corners of the dots spread and interconnect with each other to expand the range. The oval dots are only connected in two directions to expand the range. Relatively much smaller. In addition, the image area of the color separation film must have obvious edges and the density must be at least 4.0. If you print very high-quality products, the required film output machine should have a resolution of more than 240dpi and the network cable must reach 85 to 100 lines / inch. In most cases, the original document provided by the customer is usually a digitized document. The output film is overprinted accurately and should have overprint marks. Note that these marks or overprint lines must be removed before printing. (2) After the screen color separation is completed, the manufacturing method of the screen plate should be considered. First consider
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Screen and screen tension. For the above-mentioned number of network lines (85-100 lines / inch), use a plain weave screen of 380-390 mesh / inch. In addition, please ask the screen manufacturer to provide other parameters such as the diameter of the network cable and the influence of the type of ink used. Dyeing screens can also be used. Dyeing screens can prevent excess light when exposed, so as not to damage the neat edges of the stencil. Many theories currently state that proper tension can provide the desired mesh distance. Although proper screen pitch will improve edge sharpness and prevent smudging, it is important to know that the rotation of the substrate during container printing has unique cutting characteristics. At the extruded contact point, the curved surface and the screen should be printed with less force than the flat printing. The most suitable screen tension is 18-20N / cm, and the tension is allowed to drop to 15-16N / cm within 24h. It is necessary to purchase a good tensiometer. Achieving the right tension is important, but it is more critical to maintain a consistent and consistent tension value for all screens in production, because if the screen tensions are different, the product may fail. Another factor to consider is the consistency or thickness of the printing ink. In offset printing, when the ink is very thin, it can still reflect the expected color after overprinting. For screen printing, if it is too thick, the result of ink accumulation will be offset. When outputting film, the more technical screen-separating personnel can choose a certain method to compensate. (III) Screen printing stencils The manufacturing requirements for screen printing stencils are the same as for spot color printing, but for four-color printing
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, The requirements for template manufacturing are higher. Regardless of whether you choose a direct emulsion or a capillary photosensitive film to make a stencil, the final printing plate must fulfill two functions: first, a flat print must be left during printing to prevent the screen lines from showing; in addition, the ink must May be thin, minimizing ink buildup. When the screen is made, the emulsion is thickly applied, and a flatter stencil will be easily obtained, but this will make the stencil thicker and the ink accumulation larger. Use a higher quality direct emulsion or choose a capillary photosensitive film that matches the number of screens to compensate. In the stencil manufacturing process, the emulsion coating technology plays a key role in the quality of the stencil, which requires continuous practice, and the application of the capillary photosensitive film is the same. If you want to measure and control the thickness and surface roughness of the stencil, you can purchase measurement equipment such as Deltascope and Rzmeter to measure the surface characteristics or roughness of the stencil. (D) Exposure For halftone printing, correct exposure is important, because underexposure or overexposure will affect the dot shape, and then affect the quality and color of the printed image. These aspects are not valued in spot color printing. In spot color printing, the real area of color is little affected by small changes in image size. In general, sufficient exposure is necessary. The use of a light integrator will help to compensate for energy loss and reduced light intensity. In order to maintain the most stable results, the exposure should be tested regularly using an exposure device.
(5) When screen printing is used, pay attention to the problem of moire. When printing halftone screen prints,
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Due to the appearance of moire in the area, the difference between the original and the screen print can be clearly seen. The following describes how to reduce its impact. We know that each color separation film has a certain screen angle during color separation, of which the yellow version is the smallest and the black version is the largest. What needs to be dealt with in color separation is that each color is not affected by the previous printing color when printing, so it is necessary to specify the angle that is most favorable for printing in screen printing. However, in screen printing, even if an appropriate halftone angle is selected, problems will still occur. This is because the screen is acting strangely, and screen interference on the screen will cause moire. In some cases, some container printers use oblique stretch screens to solve this problem, but this is not easy to do, unless stretch screen frames are used, and it will increase the consumption of silk screen. On the other hand, the angle of the substrate cannot be set on a container printer, so the angle of the stretched screen must be set at the screen printing stage. The correct setting method is: Put each color separation film on the tight screen and rotate it until the moire is the smallest, note the relationship between the screen line and the screen angle, and tighten the screen at this angle. The same measurement is performed for each color separation sheet. Such a screen angle is also suitable for other printing. In addition, it should be noted that if you choose an oblique stretch screen, you cannot consider the issue of recycling. (VI) Machine characteristics In the past ten years, many container decoration (printing) manufacturers have focused on
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Investment in machinery and equipment, they invested hundreds, sometimes even millions, of printing equipment, and also slowly transitioned from single-color two-color to four-color and five-color printing. However, not all container printing machines can produce high-quality color products. The most important thing for color printing is to have a stable machine that can maintain overprint accuracy of + -0.005 inches. In addition, the right tools are also important. The tools and stable machines used are important for container printing to control overprint accuracy. In theory, each container printed is heavy enough and does not need to be inflated to suit the printing, but it is not the case. It is still necessary to ensure that the pressure is stable when inflated, because too much inflation will make the printing like printing on a balloon, but the pressure is insufficient It is printed on the pillow. Machine manufacturers have perfected their printing systems to efficiently adapt to a variety of substrates. Even though the same image cannot be represented exactly from one bottle to another (due to the small differences between containers), it maintains roughly stable results and meets the overprint requirements. Concluding remarks Although there are so many applications for four-color (or more color) printing of containers, why does container decoration technology still lag behind this development trend? This is a question worth pondering. Container decoration faces special challenges, but these challenges are not insurmountable. In all the process of container decoration, control is the key: control runs through the whole process from design to printing. If you think about the needs of your customers, you may be tempted to believe that accepting this challenge will pay off.
