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Corrugated cartons are made from relatively heavy cardboard after being slotted and high-quality surface finishes. In order to increase the sales volume of products, manufacturers have been making constant efforts to increase the attractiveness of the outer packaging of the products. Therefore, cartons have become increasingly packaged and commercialized.
Corrugated board color half-tone printing has also become more and more common. The improvement of paperboard production process, improvement of ink quality and improvement of anilox roller processing technology lay a certain foundation for the application of thin plate technology, and effectively promoted the application of thin plate technology in flexographic printing technology.
Demand Creation Market In the printing of corrugated board, the media system used is very extensive, such as various types of plates, plates with different thicknesses, plates with different substrates, double-stick tapes with different adhesiveness, and different elasticity. Liner materials, etc., can be combined to form a variety of different combinations. Most corrugated board printers have tried to test various combinations of different types of plates, tapes, gaskets, and inks, and analyzed the results obtained.
For a long time, corrugated board manufacturers have been eager to have a special plate, do not need any special materials, apply to all plate-making equipment, and can adapt to tropical, subtropical and continental climatic conditions. It is based on this demand that the structure and properties of the photopolymer have been greatly improved, and it has also been able to have a very stable operating performance under different climatic conditions. Moreover, even after printing several million times, the ink The transfer performance can still be kept constant and consistent. What customers need is a plate that is more flexible and printable. Therefore, this market demand has promoted the development of thin corrugated plates.
In addition, the latest digital media has also become an important issue in corrugated box printing. The new, thinner plate for corrugated board printing has a black protective layer on the surface, and this protective layer can be ablated by the laser light emitted by the CTP device.
According to the development of market demand, the supplier of plates has increased the size of the plates. The new thin flexible plate material has a layer of photopolymer layer, and the types are increasingly complete. Due to the use of a softer plate, the transfer properties of the ink are very good, the consistency is good, and the halftone image after printing works well. Therefore, there are also many printing companies who have given up their original hard plates and have changed. Printed with a soft plate. As a result, the plate-making time is saved, which shortens the entire production cycle and at the same time reduces the production costs (including the costs of the materials themselves and the costs associated with plate processing).
Control of brush plate influence and dot gain When printing corrugated cardboard with flexographic printing, in order to eliminate the influence of the brush plate (rinsing and developing), it is necessary to adjust the printing pressure slightly higher, which inevitably results in the expansion of the dot. In general, the greater the deformation of the printing plate, the more serious the dot expansion phenomenon after printing and the quality of the final printing product, so it is only possible to print low-line images and thicker negative texts, and it is impossible to carry out printing. Fine graphic printing.
In response to this situation, in order to reduce the amount of deformation of the printing plate and improve the quality of the final print, people have taken corresponding measures. The first is to use thin-plate technology in the printing of corrugated cardboard.
Secondly, it is the improvement of the photopolymer and the standardization of the media system. At present, this kind of plate material used in corrugated board printing has already been put on the market, and has been constantly improving and perfecting in terms of exposure latitude, thus improving the quality of cardboard print. This makes the thin plate technology of corrugated cardboard favored by people.
Applications in the field of plate making and printing In general, thin plates with hardness between 32 and 34 Shore hardness can basically meet the requirements of corrugated board printing. This plate is designed for color halftone printing, line and field printing (suitable for various substrates). After the main exposure, there is a clear color difference between the exposed portion and the unexposed portion of the printing plate, and the contrast is relatively strong. In this way, the quality of the raised portion (text portion) on the printing plate can be easily controlled.
This new type of photopolymer plate also has other advantages. For example, the printability is very good, even on very rough, uneven bags, cardboard or other substrates can get a good printing effect; Independent points print accurately, single points are not lost; small texts and UPC barcodes are very clear and accurate. The gradation reproduction range is very wide, and if the plate is made under standard conditions, the tone reproduction range can be optimized very conveniently. All in all, the exposure latitude of this new photopolymer plate is very large.
From F-flute and E-flute up to N-flute and G-flute, the requirements for color, hiding power, contrast, etc. are becoming increasingly stringent. The printer began accepting and adopting thin technology. The technical differences between corrugated board printing and folding carton printing are becoming more and more blurred and less obvious.
Choosing the right plate material The manufacturer has made great improvements in the performance of the plate, the dot gain rate has been reduced, the ink transfer performance has been improved, and the negative effects of the plate (wash development) have been reduced, and The contrast of halftone printing is also improved. When printing fine halftone images or lines, the consistency of the printed matter must be guaranteed. In this case, a new thin flexible plate or other thin hard standard plate is recommended. Under the effect of pressure, the plate must have high elasticity and have a strong resistance to deformation.
Elastic compressible sticker material is a good choice. When a thin plate is used for printing, a large amount of printing pressure is absorbed by the foam pad, so that the printed dot is very clean and the edge contour is also very clear. This requires a correspondingly suitable pressure depending on the type of corrugated board to be printed, that is, the pressure applied between the thinner and harder plates and the softer plate is different.
Based on the reduction in the diameter of the cylinder and the type of corrugated board, the best plate-pad combination was determined through testing. The plate-making time required for the thin plate material is relatively short, and the deformation amount of the film and the plate is also relatively small. The embossed depth of the thin plate must not be less than 0.039 inches, because if the relief depth is too small, a large printing pressure must be used. However, a large printing pressure may result in a small embossed (or shaded) paste. . Therefore, when printing thin corrugated board, it is advisable to keep the relief height of the plate between 0.039 and 0.042 inches.
In order to meet some special requirements for heavy-duty bag printing (for example, printing on film or paper) or printing on rough-surfaced substrates, another hardness between 42 and 44 Shore hardness can be used. Thicker plates may have good results.
The choice of anilox roller The role of the anilox roller is to ink the printing plate, must choose the appropriate anilox roller, can not only ensure that the small dot is not lost, but also can guarantee the ink from the plate to the substrate on the transfer rate comparison High, and the ink's color intensity is also relatively high. Corresponding anilox rollers are listed below for different quality grade corrugated board printing requirements:
1. B-flute, coated paper: 356 lines/inch anilox roll, the theoretical ink transfer amount is 4.20 to 4.52 BCM (6.5 to 7.0 cm 3/m 2), halftone The overall printing of text, text, and lines is good.
2. B-flute, non-coated paper: The amount of ink transferred is largely influenced by the thickness of the plate and the liner material used with it. It is recommended to use an anilox roller of 305 threads/inch. The theoretical ink transfer amount is 5.81 to 6.13 BCM (9.0 to 9.5 cm 3/m 2 ).
3, E-flute, coated paper: For this printing material, different types of plates, the results produced are very different. It is mainly influenced by the type of plate material, such as the hardness of the plate, the matching of the gasket, etc. These are all very important and have a direct impact on the final result. Therefore, here we can only provide you with a rough, rough recommended value, you can use an anilox roller between 356 ~ 405 lines / inch, transfer ink volume in the 3.23 ~ 4.52BCM (5.0 Between 7.0 cm 3/m 2).
In addition, the composition of the ink and its viscosity have a great influence on the ink transfer performance. When choosing a plate that is suitable for all applications, it is important to keep in mind that the various components of the system, including plates, plate materials, ink rollers, and the ink itself, are very important. If you choose the right one with the right mix, you can get high-quality, consistent prints.
The post-press processing and pre-press processing of corrugated board printing are in a period of rapid development, and great changes have taken place. The monochromatic printing business has become less and less, and it has gradually disappeared. Instead, the rise of color printing has taken off. Moreover, the flexo platemaking process has also made great progress, and can effectively control and eliminate the brush plate inherent in the process itself ( Rinse development) has a negative effect.