How to effectively use existing equipment conditions to improve the printing quality of corrugated boxes

For a long time, I had the privilege of contacting the captains of the carton printers and production managers. When the quality of the printing products could not be improved, they often complained about obsolete equipment, poor printing plate production, poor ink quality, and poor paper quality. In fact, the majority of industry (investors) consider the market demand and produce products that meet the needs of customers with the lowest cost.

The development of corrugated cartons flexographic printing started relatively late in China, and many factors determine the quality of prints.

Factors that affect the flexographic printing of corrugated boxes are:

First, the market demand: China is a developing country, the economy does not fully integrate into the international community, and due to regional development imbalances and differences between urban and rural areas, and produce different market needs.

The introduction of flexo-printed corrugated cartons into China was only a matter of nearly ten years. Due to the different aesthetic perceptions of corrugated cartons and the low market demand for corrugated cartons on the domestic market, the awareness of cartons as a product brand was particularly blurred. Therefore, it will take a long process to popularize high-end cartons. As the Chinese economy and the world converge, especially with the increase in economic exchanges with Europe and the United States, this process may be shortened. However, the unbalanced development of the Chinese economy and the unbalanced demand for products determine Multiple levels of packaging requirements.

Second, the existing restrictions on environmental conditions: Flexographic printing in China's development late, flexographic printing machinery and supporting materials localization is slow, in quality and imported products have a quality gap.

Although there are indeed many good quality corrugated box printers, there is a process of digestion, absorption, and improvement after all. There are also gaps in domestic equipment. Plates, which depended on imports in the early days, have developed in the near future, but they are still a long way from foreign technology levels. As for the rapid development of ink and wash, there is a trend that compares favorably with that of imported products.

What is particularly important is that the flexographic printing process is immature, and there is no training material for the training of flexo employees in the country. Colleges and universities have not yet set up such a specialty and they lack a theoretical basis. Therefore, according to the actual needs of the training of relevant personnel, as soon as possible to improve the level of operation and management of employees, so as to give full play to the effectiveness of flexographic equipment.

Third, restrictions on economic development conditions: The early investment in corrugated cartons often uses screen printing and offset printing before they are smeared. Even if there are rudimentary offset printing methods, most of them use rubber plates and many plants have large investment scale. Elimination is not very realistic.

Therefore, I believe that we can effectively use the existing equipment conditions, fully improve the quality of employees, give full play to the organic combination of human and machine, and improve the printing quality of corrugated boxes. Of course, it does not rule out the conditions for companies to introduce equipment and technology to the next level.

I seek organic integration of the five elements of corrugated box printing presses in order to make full use of existing conditions, tap potentials, and improve printing quality. What are the five elements of carton printing? - (1) equipment conditions (2) printing plates (3) ink (4) paper (5) five factors of the operator's technical level are indispensable, now the printing equipment conditions and plate elements analysis For the reference of the industry.

1. Printing equipment, focusing on the selection of anilox roller and control of printing pressure for corrugated box printing equipment.
The choice of anilox roller has a wrong view in the flexo printing industry. The core of the flexo printing machine is the anilox roller. The higher the better the anilox roller is, the higher the cable is, the better the cable is.

Need to consider according to the type of printing press, printed graphics, substrates and economic factors. Corrugated box printing generally adopts a unit type printing machine, the graphic cable is not very high, corrugated board surface roughness and other factors determine that you do not need to use expensive ceramic anilox roller and use general metal anilox roller to meet the need. The number of corrugated box printing lines is generally 55-65 lines/in, some are as high as 85 lines/in, and the relationship between the selected anilox roller and the printing plate network line is 4:1. 200 lines/in, 300 lines/in can be used. A 150 line/in anilox roll can be provided if there is a coating or a large solid print.

Therefore, 150 lines/in anilox roller can be considered for large field printing, 200 lines/in for daily general corrugated box printing, and 300 lines/in for high-precision color overprinting.

In general, the higher the number of anilox roller lines, the smaller the amount of ink transferred, and the lower the number of lines, the greater the amount of ink transferred. In actual operation, the slower the printing speed is, the larger the ink transfer amount is, and the larger the viscosity is, the larger the ink transfer amount is. It can be seen that when performing on-the-spot or block-printing, thinner lines of anilox rollers can be considered, inks with higher viscosity can be used, and printing speeds that are slightly slower can be combined. On the other hand, when performing high-line and color gradation printing. A higher number of anilox rollers can be used, lower-year inks are used, and faster printing speeds are used, which of course can be used in combination with actual conditions.

Anilox roller and printing moiré (regular non-ideal stripes or patterns in printing images in color carton printing), in flexo printing, in addition to the improper relationship between the angles of the various printing plate screen lines can cause moire, the anilox roller and Improper relationship between the angle of the printing plate network cable and the number of lines may also cause moiré. This phenomenon is rare if the film is produced by flexographic software (the printing plate has been avoided). In reality, most cardboard boxes go out when the color is overprinted. The output of the film, and most of the output companies use Offset software, plate angle may be hit with the anilox roller corner. (The ink hole on the anilox roller is generally sculpted in a direction of 45o with respect to the axis, which is the same as the angle of the screen on the black version in general offset printing.) For flexo printing, the plate should avoid the 45o angle of the screen. In practice, there are two methods to solve, one is to avoid the plate, try to use flexographic software, and the second is to require the anilox roller to avoid 45o.

2. Printing pressure. The poor printing quality of corrugated cartons is currently caused by improper printing pressure. For example: the text is not clear, there are spots in the field but not full, double eyelid (heavy) flash, color cast and other serious impact on print quality. The flexo pressure is generally 1-3kg/cm2 and the corrugated box printing pressure is generally 1-2kg/cm2. The printing pressure conditions are: the plate cylinder and plate, the stress (hardness) and elastic force of the plate, and the reaction of the impression cylinder. force.

The size of the embossing force is related to the hardness of the plate and the degree of deformation of the plate under pressure. Internationally, there is an increasing tendency to use thin plates, especially when printing screen plates, because it is possible to limit the distance between the plate cylinder and the pressure roller to reduce the compression deformation of the plate and reduce the change in the platen force, thereby controlling the enlargement and hardness of the print edge. Mouth to stabilize print quality. In this area, R/bat air cushions or simple j-rb sponge cushions are attached to the back of the plate to cushion the plate. In the printing process, when the amount of ink is "insufficient", the printing pressure of the printing plate tends to increase, attempting to achieve the ink color requirement, resulting in a serious edge effect, dot expansion, text blurring, and pushing the limited ink volume to unnecessary Parts. When printing on corrugated paper, the high part of the corrugation appears to have a washboard-like groove due to the pressure; fortunately, it can be avoided with a flexible cushion. When printing at the level, the dot gain value is serious, which will cause the full-page dot to develop to a high profile, and the dark tone to become a serious color cast on the field, resulting in the entire picture layer being unclear, three-dimensional, and strong, with edge effects in the field, lines, and text. It doesn't look full, it's not solid, it's typeface stencil, so it's critical to use the right amount of embossing.

In actual operation, in addition to the use of elastic cushioning force, more attention should be paid to the adjustment and balance of the press pressure. In general, the pressure should be adjusted to extend the dot, and the edge effect is not obvious.

3. Printing plate. For flexo, there is a limitation on the resolution. In general, the carton printing plate lines are all below 120 lines/M, so the fineness cannot be overemphasized. Film production requirements:
(1) Consider manuscripts that require film “black and white” to be distinct, with the black level reaching 3.5 or more, the white level reaching 0.06 or less, clear writing, no flash and trachoma and meeting production requirements (2) film deformation according to the deformation of the printing plate, In order to meet the requirements of the reproduction (3) The angle of the screen of the separation is to avoid the angle of the anilox roller as much as possible so as to avoid moiré. Consider the matching of the plate line and the anilox roller (approximately 1:4).

The choice of printing plate: In the production of high network cable overprint version, can be properly considered to use 2.84mm version, for example: KY2.84JM network cable can be up to 120 lines / in, and the hardness is moderate to reach A42o Shore, thin line, stand upright, clear, The dot gain is smaller, and a thicker elastic pad is used to cushion the pressure, resulting in a better overprint effect. In general mechanical pressure balance is poor, slow speed of the press can be considered using KY3.94JM-A, hardness to shoreA38o, you can minimize the network to expand and reduce the print ghosting, so as to achieve the desired printing effect. If the printing equipment has good balance force, the ink transfer and printing speed is faster and better. The printing operator can use KY3.94S-A hardness shore-A35o. Of course, the choice of printing plate should be based on actual needs, such as: high network line overprinting With KY2.84JM, KY3.94JM-A with fewer dot gains is generally used for color printing or line printing, and KY3.94S-A can be used for general printing or more in the field. In fact, what type of plate can be used depends on the condition of the printing equipment, the printing graphics and the operator's habits.

The above analysis of the two elements of the five elements of corrugated paper printing, in fact, the choice of ink and the choice of paperboard used, are all related to the company's customer requirements cost.

I personally believe that it is necessary to fully grasp and be able to operate the existing printing equipment, give full play to the optimal part of the existing conditions, and realize the effective combination of human and machine. This is a relatively successful enterprise.