Put a good corrugated carton flexographic printing quality (a)

Flexo printing is one of the four major printing processes in China. It is compatible with the advantages of letterpress, lithographic, and gravure printing processes. It has the advantages of convenient operation, short production cycle, clear product marking, light printing pressure, high printing plate printing rate, and stable product quality. The good advantages. The flexographic printing process can not only print substrates with good surface glossiness, but also can print rough surface materials; it can print non-absorbent substrates and can print a variety of materials with strong absorption; it can be used to print internal packaging. Products, but also print packaging cartons, cartons products. The good process characteristics of flexographic printing make it widely used in printing paper, paperboard, plastic film, cellophane, stickers and aluminized materials, etc. It is a production with wide market prospects for printing and packaging, commercial and other products. Process. However, as with other printing processes, the flexographic printing process inevitably causes some print quality problems and affects the quality of the product. One of the most common problems with print quality is the loss of dots, the enlargement of dots, the distortion of the printing plate size, and the print bar marks.

A flexographic printing quality problem

Reticle version is a common product form of flexographic printing. In the printing production process, if the production process is not properly controlled, quality problems such as dot loss, deformation, and enlargement are prone to occur. For example, the small dot of the layout highlight area is easy to lose, and dark dot network parts It is prone to enlargement, affixing, and becoming real. Due to the expanded distortion of outlets, the printing layout lacks a sense of hierarchy and the quality of printing is significantly reduced. The printing plate is soft and flexible, which is the main reason why the quality of the flexographic printing screens is prone to quality problems. Process analysis shows that in the flexographic printing process, under the effect of pressure, the graphic size of the printing plate becomes larger, so that the dot area becomes larger, and the fine dots are easily lost due to wear or uneven pressure. On the other hand, due to the flexographic printing, using a low-viscosity ink, when the contact pressure between the surface of the plate and the print is slightly larger, the ink on the plate will spread outward, making the ink layer in the middle of the expanded dot thinner. The edge of the ink layer is thick, forming a tired-like hollow point, with a magnifying glass to observe the edge of the dot visible paste, which is the basic characteristics of the flexographic printing dot increase. The production process also shows that the higher the dot number of the flexographic plate, the larger the dot gain; the coarser the ink particles used, the larger the dot enlargement; the larger the ink volume on the plate or the ink is too thin, and the dots are also enlarged. The larger the printing pressure and the pressure of the anilox roller, the larger the dot enlargement: the softer the substrate, the rubber roller, the pad or the flexible plate, the bigger the dot enlargement; the worse the machine is in using the aging, and the dot gain is also larger. The bigger. In addition, the thickness of the printing plate is inconsistent and it is easy to make the printing dot enlarge or lose. Therefore, to prevent the emergence of flexographic printing quality problems, it is necessary to pay attention to good process technology and operation technology, but also to select good quality, high precision media, but also pay attention to good equipment maintenance, can be better Guarantee the printing quality of outlet products.

Second printing plate size deformation problem

The deformation of the flexographic layout is an inevitable phenomenon. This is because the flexographic printing press is a high-speed rotary press. The radius of the printing roller is small, so the bending deformation of the printing plate is large. After the printing plate is pasted on the surface of the cylindrical roller, the printing plate is along the circumference of the roller. The surface of the bending deformation, so that the print image size changes are more obvious. In addition, the characteristics of the web printing material are soft, and the stretching change easily occurs under the action of the tension and the printing pressure during printing, so that the substrate in the axial direction of the cylinder has a shrinkage phenomenon. In addition, the flexographic print graphic part is convex structure, and the non-text area is concave, so that if the printing speed is adjusted lower, the printing pressure is adjusted, the precision of the machine is lower, and the blank layout area is larger. The greater the relief depth of the graphic and text, the more distortion occurs in the printing layout. Variations in the specifications of the printing plate graphic text make the printed semi-finished products not meet the requirements of the process design. This has a great influence on the print products with higher quality requirements, such as inaccurate overprinting. After the semi-finished products have been die-cut, slit, or trimmed into single-structured products, deviations from the layout of printed graphics and texts occur, especially the printed layouts of multi-imprinted structures. This phenomenon is particularly severe, and the finished products often fail to meet quality standards. Or process design requirements. In view of the above-mentioned quality defects, it is necessary to take measures to overcome the changes in the printing size.

Firstly, the printing plate should be flattened, and the contact between the printing plate and the surface of the roller must be tight. When the printing plate is glued, it must be used once.

The second is to control the appropriate printing pressure; the pressure must not be too great;

The third is to control the tension of the roll material when it is conveyed, and there must be no looseness or tightness;

Fourth, the printing speed should not be too fast or too slow, and maintain a constant printing speed;

Fifth, it is necessary to pay attention to the maintenance of the machine, do a good job of lubrication of the various components, to prevent the wear and tear of the critical components, to the printing accuracy;

Sixthly, according to the usual accumulated production experience, the layout specifications should be properly adjusted in the process of plate making so that the distorted layout after printing can meet the quality requirements for overprinting, die-cutting and trimming.

Lack of mark on three printing plates

Print bar marks are a common type of printing failure. If a resin plate is printed on a TL2640 type letterpress two-color rotary press, if the machine or the ink has a bad phenomenon, it is also easy to produce print mark defects.

Roller shaft head, bearing wear loosening phenomenon

When the embossing roller or the plate roller shaft head and bearing bush are lubricated badly and wear and looseness occurs, fluttering or slipping is likely to occur during the printing process, so that the print layout horizontally appears a mark, and the screen dot area is enlarged. Phenomenon, it should usually pay attention to do a good job of equipment lubrication, to prevent the failure of the problem.

Worn out of roller gear or eccentric components

When the roller gear or plate roller eccentric wear loosening, the roller is also prone to chattering or sliding phenomenon during the printing process, so that the printing plate surface out of the horizontal bar marks, the dots on the print product is also likely to expand In this case, corresponding measures should be taken to repair the mechanical components.

Ink roller colloids are hard or eccentric

When the ink roller is hard (such as a rubber roller), the adhesiveness is poor, and the friction is also small. In the process of printing the ink on the layout, it is prone to the situation of slippage or rubber dispensing, so that a horizontal mark is produced in the horizontal direction of the layout, so the printed layout is printed. The best use of polyurethane rubber roller or castor oil roller, its texture is relatively soft, and has a certain degree of viscosity, brushing ink is more uniform, it can better avoid the production of print marking phenomenon.

Ink roller position adjustment is not suitable

When the position of the ink roller is unsuitable for adjustment, and there is a bad contact between it and the iron roller, it is easy to cause a transverse delineation phenomenon in the process of rolling the ink. Therefore, the height of the ink roller must be adjusted to the plate. To maintain the proper contact state, the contact pressure with the stringer iron roller should also be appropriate. A 10-thread gauge can be used to insert between the ink roller and the plate surface; drawing between the ink roller and the ink roller is tested and drawn. It is appropriate to have a slight sense of resistance

Instable ink viscosity

When the viscosity of the ink is insufficient, and the fluidity is too large, the ink roller is likely to slip on the platen ink, causing a transverse bar mark phenomenon on the plate. Therefore, the printing ink should maintain a certain viscosity to prevent the production of a print bar mark.

(to be continued)