Roll-to-roll wide-width flexo preprint management

The roll-to-roll wide-width flexo preprinting of this emerging corrugated box printing process has been made by several parties in the printing industry in China for several years and has made unremitting efforts. Now it has been developed in some printing manufacturers and has achieved better results. Economic benefits. In major domestic supermarkets, high-quality colored beer corrugated boxes are everywhere. The colorful color packaging of Budweiser, Tsingtao Brewery, China Resources, Blue Sword Beer and other manufacturers attracted numerous customers, strongly stimulating people’s desire to purchase, and playing a promotional role in packaging. It can be said that the quality of pre-printed color corrugated boxes in China's roll-to-roll flexo printing presses is comparable to lithographic printing and gravure printing. The development space is very broad. Few people are now doubtful about the feasibility of volume-to-volume flexo preprinting, and their full benefits are fully affirmed.

However, there are still many manufacturers who have already introduced flexographic printing presses to prepare for the pre-printing of color paper cartons. Due to lack of management, the equipment is difficult to operate normally, product quality cannot be guaranteed, and economic benefits cannot be discussed. The author's company has also experienced these phenomena. However, after several years of unremitting efforts and the close cooperation of related cooperative units, coupled with proper and reasonable management, our company's roll-to-roll flexographic preprinting has been on the right track, achieving mass production.

In the following, the author will summarize some of the experiences and lessons learned in the management of roll-to-roll flexo pre-printing, discuss it with colleagues, and hope to help counterparts who are engaged in flexo pre-printing, so that packaging and printing companies are engaged in flexo printing. In the preprinting process, you can take some detours.

First, manuscript review and printing plate

The first of the five elements of printing is the manuscript. After obtaining the sample draft (generally offset printing) provided by the customer, the pre-printed team (preferably the head of the factory department and other related technical and technical departments) should study the sample draft together so as to pre-print according to flexo. Features to determine the requirements for the next step of color separation for reference by the platemaking company. If the printing factory does not raise technical requirements, professional plate-making companies generally perform color separation and plate-making after accepting the printing manuscript. Since the degree of understanding of printed manuscripts is not the same, and the degree of familiarity with flexographic preprinting and the degree of understanding of actual use are different, there is a large unrealistic situation between printing plate production and printing production. Repeatedly revising or recreating the situation, resulting in material and time waste. In addition, many people in the industry wrote that they should establish a technician, but for those who just started to print flexographic preprints, because no one would dare to say very familiar, so it is best to study the manuscript together, and then make the plate for the plate making company If you do not understand, you can communicate with the plate-making companies and discuss with each other to ensure that the success of the plate production is beneficial to both parties. However, in the process of developing and researching flexo preprints, it is necessary to consciously train specialized craftsmen to lay the foundation for future mass production.

When studying and analyzing manuscripts, you should pay attention to the following items:

1 dot text lines and field editions must be separated from each other, even if they are the same color. This is because the dot text lines and the amount of ink needed in the field are not the same. If it is on the same plate, after the anilox roller quantitatively transmits the ink, it meets the ink demand of dot and text lines, and it cannot meet the ink demand of the field version. In turn, to meet the on-demand version of the ink demand, outlets, text lines will be bound to paste. In addition, small lines and large lines should also be divided into two editions.

(2) For continuous screen drafting, the highlights of the pattern are markedly polarized. Small outlets (about 8% or less) are either lost during the printing process and become an absolute net; or the outlets are severely enlarged. Tuning outlets. In the dark tone part, more than 90% of the tone points will be connected to the network and become the field. Therefore, we must consider the pitfalls of this flexo when we are making plates, and we cannot fall into it. The general treatment method is to use the amplitude modulation network point and the frequency modulation network point in the making of the plate, continuously adjust the transition network in the network point greater than 10%, adopt the amplitude modulation network point, the network point less than or equal to 10% adopts the frequency modulation network point.

3. Can use spot colors, try to use spot colors, use less or no four-color dot overprint. Special eye-catching spot colors should use special color overprinting, but the two plates should be clearly identified, one main color and one sub-color when processing. In the sub-color version, some text lines and lines can be taken into consideration. Doing so can achieve the purpose of superimposition, and does not increase the color number of the printing plate.

4 Because there is an inevitable overprint error in printing, the trapping problem needs to be considered. If the overprinting accuracy of the flexographic printer is 0.2 mm, the trapping amount should be set to 0.25-1.00 mm. This is because general flexo preprinting machines have more color groups and faster speeds. In order to reduce the difficulty of printing and avoid trapping, it is necessary to add a little trapping amount.

5 Note the size of the layout. In the large format, both vertical and horizontal dimensions should be taken into account. The circumference of the plate cylinder should be determined longitudinally, ie, the circumference of the plate should be repeated and the width of the printing surface should be determined horizontally. Because printing cylinders and their associated gears are relatively expensive and difficult to process, manufacturers generally only prepare 2 to 3 plate cylinders and associated gears. Therefore, when calculating large sizes, priority must be given to whether they can be used. The circumference of the existing plate cylinders is based on this consideration of the lateral width of the web. Of course, if the width of the transverse web exceeds the web width of the machine, only the processing of the plate cylinder and its associated gears will be considered. In addition, try not to repeat the perimeter. Practice has proved that the larger the repeat perimeter, the larger the printing plate area. When a large amount of printing is performed, it is easy to cause problems such as foaming of the printing plate due to the problem of sticking, and thus the printed matter is scrapped.

After analyzing the manuscript, you can submit the plate to the plate making company. It is important to note that when making plates, the pressure and tension characteristics of the printing press are different, and the technical level of the printing workers is also different. The changes in the printing will be different. Therefore, when determining a certain plate-making company to conduct plate-making, the plate-making company must be required to do a set of test-type printing on the machine to detect various information such as printing pressure, printing tension and machine overprint, and determine the deformation amount of the plate so as to facilitate Appropriate compensation is given for prepress processing. In addition, the plate-making company must first make digital samples, check various indicators, and check for errors or other errors. Although the current digital proofing cannot fully reflect the true situation of flexo printing, it can still serve as a reference for obvious problems. Now a set of flexo-printed preprints is expensive, and it costs more than 10,000 yuan in six-color calculations, reducing the number of re-copying and saving a lot of money.

Second, the printing plate management and raw and auxiliary materials testing

Prior to printing, a full-scale process quality inspection of the prepared printing plate is required. The content of the inspection is almost the same as that of the offset printing film, that is, the number of printing plates, bar code, finished product size and component size, whether the unfolding size is consistent with the length and width of the paper, whether there is any error in the graphic and graphics, and whether there is an imposition method or not. Whether the scratches and separations meet the requirements. Different from the content of the offset printing film detection, it is necessary to pay attention to whether or not the photoelectric eye controls the cross-cut mark and its position is correct. Because the corrugated paperboard production line with flexographic preprinting is equipped with a photoelectric eye tracking and crosscutting control system, the main principle is that the photoelectric eye recognizes the crosscut marking on the corrugated cardboard printing pattern, and marks the moment of cross-cutting to the photoelectric eye. It is transmitted to the control computer, and then the control computer controls the cutting time of the cross cutter, so as to accurately cut the corrugated cardboard at the boundary of the pattern. If the position of the cross-cut mark is inaccurate, the corrugated cardboard line of the roll pre-printed face sheet will be cut at a wrong position, resulting in the carton being scrapped.

As with other printing methods, raw and auxiliary materials such as paper and ink used for flexo preprinting should also be inspected. Flexographic preprinting is web printing. It is necessary to first detect whether the paper width is the width of the order, whether the weight of the paper roll is the weight marked on the label, and then check the water content, the quantitative, and the resistance that affect the corrugated box. Penetration, ring pressure index, tightness and folding tolerance and other indicators. It should be noted that the folding resistance is divided into the longitudinal folding resistance and the horizontal folding resistance, and the folding resistance is not the same. The general manufacturers only detect one direction index. In fact, the folding resistance in both directions affects the corrugated box.

The quality of the flexographic preprinted aqueous ink directly affects the correctness and stability of the print color. Preprinted inks mainly detect hue and viscosity. Hue is the basic item for ink detection and it has a great influence on the color of the ink. The correctness of the hue of the ink is very important for controlling the color of the print. It is generally detected with a color wheel. The viscosity of preprinted inks is relatively low and is generally measured with a viscosity cup. Printing companies use high-quality, good-applicability papers and water-based inks in the initial stage of flexo-printing to avoid the printing defects caused by the printability of paper and ink, and to focus on mastering skills to ensure that the products are qualified. On this basis, we can explore how to reduce the production costs of certain materials.

Third, prepress preparation

Before printing, as with other printing methods, the machine operators should first understand the production and construction orders, process planning books, proofs and sample boxes, specifications and dimensions, repeat perimeters, anilox roller configurations, models of ink varnish, and the place of production. Color order, color number and print number and other requirements.

Prepress printing pre-press printing is the key to normal printing.

The first is the affixation of the printing plate. The flexo-printing of the preprinted printing plate requires a special double-sided tape to be affixed to the surface of the plate cylinder to form a complete printing cylinder. The quality of double-sided tape directly affects the printing quality of EIJ brush products. Currently, this type of tape is also mainly imported. The method of pasting plates is much the same as ordinary flexographic printing. Since the printing plate is pasted on the machine, the plate cylinder can only be moved longitudinally and laterally, and it is incapable of force on the printing plate, and can only be re-posted. Therefore, when attaching a printing plate, it is necessary to pay attention to that the printing plate cannot be skewed. However, it is necessary to accurately affix the printing plate depending on the proficiency of the operator.

After the plate is attached, the plate cylinder is suspended on the machine according to a predetermined color sequence. When determining the printing color sequence, the common color sequence for the normal four-color dot version is yellow, magenta, cyan, and black; for the spot color version, the color sequence of the first lighter and deeper color is generally used, and the light color ink is first printed, which can make The dark ink superimposed ink has a bright effect, and the spot color printed by the superimposed method is generally the primary color after the primary color.

After the plate cylinder is placed on the machine, it is necessary to prepare each plate with the corresponding anilox roller. The selection of the anilox roller is mainly determined according to the amount of ink to be printed on each plate of the printed matter (that is, the image area of ​​each plate). From our practical experience, the field version uses 250~400 lpi, the text and line version use 400~600 lpi, and the dot version uses 550~800 lpi. In addition, when selecting the anilox roller, not only the number of roller lines should be taken into consideration, but also the comparison of the BCM (cell volume) of the same line of anilox rollers. Before using the anilox roller, check carefully whether the surface of the anilox roller has any oil, dust or powder. If the above material is present, it must be cleaned to avoid abrasion of the anilox roller.

The rollers of the flexographic preprinting machine are all driven by gears. Therefore, the installation of the gears associated with each roller cannot be neglected. In particular, they cannot be interchanged. Otherwise, the subsequent printing operations will be affected. When we once produced Budweiser laminating paper, due to the negligence of the operators, we exchanged the gears of the two printing plates. All the rollers had been installed before we discovered it. We all felt that the problem was not significant. As a result, the machine was printed on the machine. The printing plate will be beaten, so that there will be regular uneven pressure on the printed products, until the gears are exchanged to print properly.

Also pay attention to the installation of the squeegee. Since the squeegee is relatively sharp, it must be kept safe during installation. If it touches the skin a little, it will bleed. Therefore, it is best to wear gloves.

Nearly all of the products processed by flexo preprinting involve spot colors. The deployment of spot color inks is generally first deployed with the color wheel, and the basic ink color meets the requirements of the machine to determine the applicable formula. After the spot color ink is tested on the printer and confirmed by the customer, it needs to be archived so that the required spot color ink can be quickly adjusted when printing again to improve production efficiency and ensure accuracy and continuity. General formula should be dated, product name, customer name, proportion of various inks, used