Commodity Packaging and Printing Process (2)

Domestic multicolor gravure printing press meets market challenges

With the improvement of people’s material and cultural living standards and changes in consumer attitudes, the domestic packaging market has grown at a rate of over 20% every year for the past ten years. Its packaging and printing market has grown faster, and the quality and grade of printing have also been constantly improving. Now that entrepreneurs have had a refreshed understanding of the role of packaging and printing, packaging printing is no longer a simple description and text, but rather the most effective carrier of corporate culture, corporate identity, and product brand, and also the intrinsic quality of products. The appearance of the product is a perfect unity of image; at the same time, the design is novel, and the printing and exquisite packaging printing gives the customer a more profound impression and great attraction. With the continuous development of domestic flexible packaging materials, the variety, quality, and quantity of its packaging products are increasing, and the performance of gravure printing machines for printing soft films is also increasing and the number is increasing. Around 90 years ago, large-scale packaging and printing companies in China have introduced a number of multicolor intaglio printing press production lines from Italy, Germany, Japan and other famous printing equipment manufacturers according to the development of the packaging printing market, which satisfies the needs of the domestic market at that time. However, in recent years, the rapid growth of the medium and high-grade packaging printing market, relying solely on those imported equipment can not meet the needs, and the introduction of imported equipment is generally unable to withstand the economic capacity of enterprises (requires 12 million -30 million yuan). As a result, a large number of small and medium-sized printing companies have sought out multicolor intaglio printing machines suitable for themselves and the packaging printing market in the domestic gravure printing machines. This is both an opportunity and a challenge for gravure printing machinery manufacturers. Now I will talk about several technical aspects of domestic gravure printing machines for commercial consideration.

A. Mechanical Structure and System The mechanical structure and system of domestic multicolor gravure printing presses and imported multicolor gravure printing presses are similar. Some of us abroad have us. However, in actual use, we have found that the quality of printed matter and machine stability are far from each other. The reasons are mainly due to the following aspects: tension control of retracting and unwinding, stability of printed circuit, circulation of ink supply system, and drying system , Control of the embossing force, mechanical transmission, and machining accuracy and assembly accuracy of the complete machine parts. Such as: (1) In the machine (some not installed) installed with the tension control system, although the tension of the front and rear rolls is controlled, the damping of the paper roll is large and the dynamic balance is neglected. In this way, the tension between different units at different times and at different speeds is not the same, and the instability of the tension directly affects the accuracy of overprinting of printed products and reduces the requirement for the orderliness of the winding. (2) In gravure printing, due to the large embossing force and high operating speed, people always try to increase the module of the gear to ensure the mechanical strength when designing the transmission gear, which causes the error of the gear to increase and the vibration to increase. Intensified, so that the layout of the units at different times and different imprinting force, which directly affect the overprint accuracy and ink stability. (3) Air distribution in the drying system. Non-uniformity of the drying air flow makes the ink drying speed inconsistent, the whitening of the resin occurs when the temperature is too high, the oil film is not dried when the temperature is too low, and the bleed and the passing roller fouling are generated. All of this is something that we should consider and solve when designing the machine as a whole.

B, automatic overprinting system gravure gravure printing due to the longer lines, easy stretch film and other characteristics, so in the high-grade soft film printing press control becomes very important. Low registration accuracy is also one of the main factors in the low level of domestic gravure printing presses. From an economic point of view, increasing the high-performance overprint control system is one of the effective ways to improve the quality of domestic-made machine products, and it is also one of the ways to invest less effectively. In solving the automatic overprint system, introducing and learning advanced foreign technology is an important aspect, but we must understand its principles and combine with the actual situation in China. Now the automatic overprinting system used on imported gravure printing machines adopts the principle of measuring the actual overprinting error, and then adjusting the overprinting error. Due to the high precision of the machining of the imported machine, the design is reasonable, and the tension change is small, its overprinting error is The change is small and regular, so that it will adjust the error to zero if it does not exceed the specified error range, so it is well used on imported machines. When used on domestic machines, it shows a certain degree of irrationality. Because the performance of domestic machine is very difficult compared with the imported machine, its overprinting error is large and the regularity is bad, sometimes the measured error is already bad (unqualified), and then the overprinted product is already in the whole adjustment. In a roll, it cannot be excluded from subsequent processing. In view of this situation, we must first consider two aspects in principle. One is to be able to predict possible overprint errors, and the other is to make zero adjustments before actual printing.

In the theory of overprinting error, our predecessors have used a lot of experiments and arguments to show that the generation of overprinting errors is a multi-element random function whose error distribution follows the law of normal distribution; in multi-color printing, the accuracy of overprinting The calculation results are the same for any color. In this way, we use the first color in multicolor gravure printing as the standard for overprinting errors compared with other colors, calculate the size of overprint error, and then adjust the overprint error to zero. The first color is already printed. It can be easily measured by using an image sensor before printing in different colors. Where can other color positions be predicted? In gravure printing, the ink transfer is directly transferred from the gravure cylinder. For the print carrier, we only need to know that at a certain moment, the first color signal strip and a certain fixed position of a plate cylinder can reach the printing position at the same time, and we can know that the overprint is accurate after printing, otherwise the time when they arrive is inconsistent. Certainly there will be overprinting errors, so that we can easily use the adjustment of the length of the paper path so that they arrive at the same time without overprinting errors. We use two image sensors in the first unit, one to test the printed signal strip of the first color, one to test the fixed position signal of the plate cylinder, compare the two signals, and then compare and control the circuit. The computer overprint adjustment system composed of circuits, command signal generators, stepping motors, etc., can complete overprint error prediction and automatic zero adjustment. This will fundamentally solve the problem of rapid increase in the overprint level of domestic gravure printing presses and economical and practical.

C. Quality Monitoring of Dynamic Prints 软 Soft-film gravure printing machines are generally high-speed printing of reels, and operators cannot accurately judge the quality of prints during the printing process, especially drawing, swimming, and dot coarsening. Net wrinkles, uneven ink and other minor changes. Due to the poor stability of domestic gravure printing presses, slight deviations in printed matters are often inevitable. If problems are not discovered in time, it is possible to form batch scraps of printed products. Now the imported image detection and control system can basically solve the problem. It can accurately capture clear images at a printing speed of about 200m/min, and can freely zoom in and out for print quality within a range of 3 to 20 times. Inspections can also be compared with stored standard images (or customer-approved images) at any time to determine whether the current print product meets the customer's requirements. Of course, this system also needs to conduct a comprehensive digital comparison of the manual and automatic data processing, printing quality indicators, automatic alarm when the printed product fails, and guides the operator to adjust the problems.

In short, there is a lot of work that needs to be done, but we must base ourselves on the domestic situation and seize this opportunity to improve the quality and level of domestic multicolor intaglio printing machines as soon as possible so as to meet the requirements of flexible packaging printing in the domestic market.

Author: Ren Jiping machinery of the Beijing Institute of Printing Machinery)