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Common problems and Countermeasures of flexographic printing in cigarette bag production

at present, China has introduced more than 100 flexographic printing production lines, of which a large part is used in cigarette bag production. The following summarizes some common problems encountered in cigarette bag production and our solutions as follows for peer reference

first, plate making is the key, and testing is very important.

cigarette bag production has some common characteristics, among which the following are roughly related to printing: (1) it is difficult to copy patterns. In order to reflect the grade of products and eliminate fake cigarettes, cigarette factories often adopt the method of using a large number of complex patterns and spot color (anti-counterfeiting) inks in packaging design, which brings certain difficulties to flexible plate making. (2) Since the printing of cigarette packs is often changed from offset printing or gravure printing to soft printing, the conversion of printing methods will inevitably bring differences in printing effects. Therefore, how to make the effect of flexo printing consistent with offset printing or gravure printing is also one of the difficulties of flexible printing. (3) Due to the soft plate used in flexographic printing, the dot enlargement rate is large, and the level expressiveness of highlight and dark part is poor, the printing effect on different substrates is very different

these particularities of cigarette bag production have brought difficulties to flexographic plate making, especially some exquisite logo patterns, which are not only rich in content, but also often have complex levels. Some manufacturers adopt thick lines to solve the problem of gradual change, which makes the performance of subtle layers of patterns suffer. The design of high-end cigarette packs often involves levels, and how to properly copy the level version is a problem that many manufacturers face and need to be solved urgently. It needs to adopt a special point algorithm, and use the technology of combining FM plus and am plus and nonlinear expression on rip to realize the control and adjustment of points in the process of plate making. Due to the limited space, we cannot describe this problem in detail here. We will discuss this topic in the future

to be exact, the process of flexographic plate making is actually the process of process formulation. If plate making is divorced from printing, and it is difficult to make high-quality plates without understanding the ink parameters, the number of wrinkle rolls, the printing color sequence, pressure, etc. For example, for the same layered version, if different embossing rollers are used, there will be different inking volume, different ink drying speed, and the hue and saturation of the printed matter will also change, even directly affecting the quality of printing

therefore, before the first plate making, the plate making company should understand and test the equipment in detail according to the specific situation of the printing manufacturer, including the inking amount of the roller, the adhesion of the ink and the machine speed, so as to provide a basis for determining the appropriate number of lines and dot expansion rate during plate making

in addition, in addition to the testing of the printing machine, it is also necessary to test the whole set of technological processes such as plate making, film making, plate printing, printing, ink and die cutting, so as to understand the operation status and stability of each link, so as to make up for the losses of the post process during plate making according to the requirements of different active sources, and formulate a complete plate making scheme and printing process at the same time

second, it is difficult to print, and it is more difficult to maintain consistency

cigarette packs are produced in large batches, with long production cycles and high printing quality requirements. At the same time, manufacturers also have high requirements for the consistency of product batches and quality

as we all know, there are many factors that affect the printing quality, mainly in the following aspects:

1. The printability of printing materials. Different printing materials have different effects on the drying speed and inking amount of the ink, and have different reactions to the hue

2. Characteristics of ink. The formulas of different ink manufacturers have their own advantages. The hue, saturation and pH value are different, so it is difficult to be exactly the same in two preparations. It has the comfortable driving feeling and safety of European models

3. The selection of corrugated rollers. When manufacturers introduce equipment, they are generally equipped with a variety of wrinkle rollers with different number of lines. The inking amount of the wrinkle rollers with different number of lines is different, which is reflected in the color depth and the thickness of the ink layer on the substrate. Even if the same wrinkle roller is used more and more, the wrinkle roller will be worn and blocked to varying degrees, and its ink content will change, eventually leading to changes in the printing effect

4. Machine speed. The change of machine speed will directly affect the thickness of the ink layer, so the pressure and tension need to be readjusted when the machine printing speed changes

5, pressure and tension. Flexographic printing uses soft plates. Excessive pressure will over squeeze the dots on the printing plate, increasing the dot expansion rate. Tension will affect the accuracy of overprint

6. Operation level. The experience of operators is different, the judgment of originals and prints is different, there is no data basis, and subjective factors have a great impact on the printing quality

7. The ambient temperature and humidity have a direct impact on the drying speed of the ink. If the second color printing is carried out before the first color is completely dry, the adhesion of the ink will be reduced, so that the subsequent process cannot be completed smoothly

any change in the above factors will directly or indirectly affect the quality of prints and the consistency between print batches. Stability is very important for printing, but it is difficult to achieve in real life. It can be seen that in order to better maintain the quality and consistency of prints, a better method is needed, so that we can intuitively and accurately analyze the problematic links, facilitate timely adjustment, and judge in advance whether this loss can be remedied in the subsequent process, so as to avoid more unqualified products flowing into the next process, reduce the scrap rate, and improve product quality

in view of the above situation, we need a reference, which must be stable and easy to use. Taking pressure control as an example, flexographic printing is light pressure printing, but it is quite difficult to really control the pressure. Generally, there is no pressure display on the flexographic press, and the pressure will change depending on the replacement of the operator. In the absence of data display and automatic monitoring equipment, how to make the pressure between batches appropriate and as close as possible? We have been using a test tracking method, adding a group of targeted tracking strips according to different situations and colors. Through its observation, we can judge whether the pressure is appropriate and whether the left and right pressures are balanced, so that the operator can adjust the pressure in time. In the future batch printing, as long as the situation of the tracking strip is similar to that of the first time, the same print printed at different times can be kept consistent in quality to a certain extent

third, increase revenue and reduce expenditure, improve efficiency

cigarette packs are high-end packaging products with strict production quality. They require not only exquisite printing, but also accurate size, and generally have the requirements of post connection processing

flexographic printing machine is mainly suitable for packaging printing. Compared with other printing methods, it has its own unique advantages in cigarette bag production. Flexographic printing has high output and strong online processing capacity. The speed of flexographic printing machine can be opened to 2m/s. The imported flexographic printing machine is generally equipped with die-cutting unit. Die cutting, indentation and embossing can be completed synchronously, which greatly saves manpower and provides favorable conditions for printing manufacturers to expand the market

it is undeniable that the high-speed operation of flexo printing machine improves the production efficiency. PCL is a semi crystalline linear polyester, but the waste when waste products appear is quite serious. There are many reasons for waste products, mainly because the registration and die cutting are not accurate enough

first of all, during printing, because flexographic printing is a circular printing method, continuous operation will produce cumulative errors, coupled with the influence of many subjective and objective factors, such as machine vibration, personnel operation differences, changes in the surrounding environment, the registration accuracy is difficult to remain unchanged for a long time, and the operators need to often correct the registration to adapt to changes. However, when the machine is in high-speed production, this adjustment is quite difficult for the operator to increase its domestic investment. Reducing the machine speed to increase operability is a general method commonly used and automatically recording the changes of part wear, but the subsequent machine speed increase will change the registration to a certain extent. Secondly, the adjustment of the machine during paper change in mass production is also one of the reasons for inaccurate overprint

printing is only one part of the production process, and the whole production can be completed only by connecting processing. Therefore, the production of cigarette packs should not only pay attention to the printing effect, but also pay attention to the machinability of the post process sequence, such as whether the size meets the requirements, whether the static electricity is removed completely, and whether the drying is complete. The failure of post-processing will double the scrap rate and cause great waste. Therefore, the on-line processing capacity needs to be improved urgently

how to solve these problems is a major problem faced by various manufacturers. It is far from enough to improve the level of operators and properly stabilize the operating environment, because in addition to human factors, there are also some objective and unavoidable factors, such as machine speed-up, paper pumping up and other waste products are also quite serious. Therefore, equipped with some professional auxiliary equipment, such as automatic registration and precision die-cutting system, and using machines for automatic control to improve the accuracy of registration and die-cutting, it can not only save manpower, improve quality, greatly reduce the scrap rate, but also provide a good reference and basis for modern management, and increase the economic benefits of enterprises. At the same time, due to the advanced equipment and guaranteed quality, the development of high-end living sources has also become possible, providing a strong backing for the good development of enterprises and the development of markets. (wuxuefei, Beijing jinshijia company) (special edition of paper packaging)