Small cartons and carton products often have various structural layouts coexisting. For example, there are not only layouts based on solid printing, but also printing layouts where mesh, text, lines and solid patterns coexist; there are both gold and silver layouts that cannot be displayed in spectral colors, and there are layouts where spot colors and four primary colors coexist. If the offset printing, embossing (or gravure, etc.) process is used for different printing methods, the printed products have their own advantages in process characteristics, and the combination of multiple processes for printing cartons, cartons and other packaging products can improve the intrinsic quality of the products.
The offset printing process has a good printing reproduction effect, soft tones, clear dots, and rich printing layers. The large-area printing area is not easy to appear dirty products. The embossing and gravure printing processes have the advantages of thick and full ink layer, bright colors and high gloss.
Therefore, use the advantages of different printing processes to print products that have both mesh, text, lines and solid patterns, as well as various color layouts, and combine the advantages of different printing methods, and use the process to “synthesize” to print the same product. The product can not only make full use of equipment utilization, but also improve product quality and economic benefits simultaneously.
A variety of reasonable arrangements combined with printing processes
The offset printing process has the advantages of light printing pressure, relatively small printing deformation value, and the product is not easy to be dirty and over-bottomed. Therefore, it is suitable for printing over-color anilox plates, lines, small text, negative images and large-area solid layouts.
The embossing process can achieve a larger ink supply at one time, and is more suitable for printing gold and silver ink layouts, solid, line or text layouts. From the characteristics of printing, the ink layer of the offset printing process is thin, the ink is also easy to dry, and the product does not produce bumps, which does not affect the normal overprinting of embossing. However, the ink color of the embossing process is slow to dry, which will cause some adverse effects on the normal color registration.
Therefore, the overprinting sequence of rubber-convex products should generally be: offset printing first, relief printing second; small printing first, large-area printing second; strong hiding ink color first, strong transparency ink second Printing, such as red and yellow (except for white ink dilution), overprint black text or patterns on the layout. You can print the black layout first, and then print other colors. In this way, due to the strong transparency of the overprint color, the black can still show pure black Color.
The technical control essentials of printing with multiple processes combined
1. Do a good job in the process technology control of pre-press design
The embossed solid layout should avoid the small negative lines and text in the same color plate, so as not to fully take into account the pressure and ink supply, it is easy to cause paste and uneven pressure, which will affect the printing quality of the product. The overprinted parts of the rubber letterpress should be as far apart as possible to leave a certain gap around the edges of the overprinted layout or appropriately expand the edge of the light-colored layout (so that the edge of the overprinted layout can be overlaid and covered), so that the slight overprinting is inaccurate. It is not easy to detect with the naked eye.
2. Do a good job in technical control of the imposition process
The overprinted parts of the layout should be placed as close as possible to the bite and the drawing rule (side rule) to avoid inaccurate overprinting due to the expansion and contraction of the paper. In addition, the layout of the “gehe” (separation core) larger or multi-section overprinting layout should not be combined into separate overprinting with two processes.
3. Pay attention to the reasonable selection of offset printing plates
The PS plate has a thinner plate. After it is installed on the surface of the cylinder, its wrap angle is relatively small, and the elongation of the printing plate is also small, and it can maintain close contact with the cylinder, which is beneficial to improve the overprinting of the rubber convex product. Therefore, the offset printing process should choose PS plate for printing.
4. Pay attention to the process technology control of the bottom support of the printing plate
Small-size packaging products are often printed on a letterpress printing machine with a quarto or split-circle flattening structure. The characteristics of the base material of the printing plate have a greater impact on the printing pressure, overprint accuracy, and ink quality effects. effect. The traditional wooden backing has poor material, squareness, flatness and stability. It is prone to bowing and deformation, and the printing quality is difficult to guarantee. Therefore, letterpress printing should use a solid, flat, square, stable aluminum or cast iron magnetic plate base and other metallic materials, which is the basis for improving the registration and ink quality of the product.
5. Pay attention to the control technology of printing pressure
The printing pressure should be adjusted uniformly and moderately. Excessive pressure can easily stretch and deform the printed sheet and cause inaccurate overprinting. Therefore, the printing pressure of the embossing process must not be too large, and the lightest printing pressure should be used to meet the requirements. Ideal printing under the premise of uniform and full ink color.
6. Pay attention to the technical control of the lining process
The lining is the medium that realizes the transfer of pressure and imprinting. Its characteristics also affect the registration and ink quality of the product. Therefore, the deformation coefficient of the lining material should be as small as possible, and the material should be neutral and hard. At the same time, the thickness of the lining must be determined in strict accordance with the technical parameters of the equipment specification. In addition, the lining must be tightly packed, and there must be no looseness or bulging. The embossed lining must not be repeatedly patched or hollowed out to prevent inaccurate overprinting and ghosting.
7. Pay attention to the technical control of the balance of ink and wash
In the offset printing process, to control the ink and water balance, it is necessary to use the smallest possible amount of fountain solution to print while maintaining the ink and water balance. The abnormal balance method of “big ink and water” should be avoided for printing to prevent deformation due to excessive water absorption on the paper surface.
8. Pay attention to control the temperature and humidity of the printing environment
Controlling the temperature and humidity of the printing workshop is an important part of improving the accuracy of product overprinting. The temperature and humidity of the offset printing and embossing workshops should be kept relatively balanced, and there should be no large disparity between heights and lows. Otherwise, it will easily cause inaccurate overprinting. . Generally, most small and medium-sized printing companies are limited by conditions and cannot effectively and accurately control the temperature and humidity of the production site. They often use experience to control doors and windows or use simple methods such as splashing water on the ground. A certain effect.
9. Pay attention to the technical control before the cardboard is put into use
Cardboard is very sensitive to changes in temperature and humidity of the external environment, especially white paperboard that has just been produced, which is most likely to undergo expansion and contraction due to changes in temperature and humidity, resulting in inaccurate product overprinting. In order to reduce the chance of this situation, the newly produced white paperboard is usually stored for a period of time after it is shipped back from the printing plant. After the paperboard is relatively stable, the overprinting phenomenon is not easy to occur after it is put into use. In addition, the cut cardboard should be sent to the printing workshop immediately to balance the temperature and humidity of the printing workshop, and then printing will help improve the registration accuracy of the product.
10. Pay attention to the technical barriers of the paper cutting process
The accuracy of the cardboard specifications will also affect the overprinting of the product. Because of different machine structures, their front and drawing positions are not the same. In this way, if the edge of the cardboard is not cut square enough, there is a bevel or wavy edge, it will cause inaccurate registration. This requires the product of the glue-convex combination, the sides of the cardboard must be cut into right angles, straight lines, and there must be no bevel or wavy edges. In order to improve the cutting precision of the cardboard, the cutting thickness must be strictly controlled, because the thicker the paper stack, the softer the paper, the more deformed the paper surface will be when the paper press is pressed down. Therefore, the cutting thickness of each stack of cardboard The smaller the amount, the more helpful it is to improve the cutting accuracy of the cardboard. In addition, the cutting edge of the knife should be kept sharp, and the appropriate blade angle should be selected according to the hardness of the paper, which is also an important measure to improve cutting accuracy.
11. Pay attention to the production cycle of product overprinting
When the first color or several colors of the printed product are printed, the overprinting should be done immediately, so as to avoid the stretching and variation of the printed product due to too long time delay, resulting in inaccurate overprinting.
12. Pay attention to the protection of semi-finished printed products
The final semi-finished product should be sealed with plastic film to prevent the cardboard from absorbing or losing moisture from the outside air, so as to avoid or reduce the undesirable phenomenon of expansion and variation of the semi-finished product.
To sum up, packaging products such as cartons and cartons, no matter what process is used for printing, it does not matter whether one printing process is used for printing alone, or multiple processes are combined for printing; multi-color printing machines are used for printing and production. Or use a monochrome printing machine for printing production; use an advanced multi-function printing machine for printing production, or use a simple and ordinary printing machine for printing production. No matter what the situation, the most important and most critical link is According to the characteristics of the product, control the operation technology and process technology, and use the appropriate printing pressure to print with the appropriate amount of ink; based on the characteristics of the ink, printing plate and cardboard, printing at the appropriate speed can be used. So that the printing quality and production efficiency are better improved.