Corrugated carton printing
A prepress design
Corrugated cartons were mostly transport packages. With the development of the market economy, corrugated cartons have also begun to favor sales packages. Therefore, higher requirements have been placed on the layout and printing of cartons.
Prior to 1995, most carton makers used a rubber plate printing process. At present, flexographic printing occupies a very important position, so how to improve the quality of flexographic printing is a very important issue. I think that the quality of printing depends on factors such as printing color sequence, pre-press film, flexographic plate making, and printing ink.
(a) printing color sequence
In flexo printing, the various plates are often field versions, and the aqueous ink used is generally not very transparent. Therefore, when arranging the overprinting sequence of various printing plates, it is necessary to consider whether or not the color after stacking can meet the requirements of the original and achieve a good overprinting effect. It directly relates to the quality of printed products.
The printing color sequence is mainly based on the order selected by the original design and the plate making. However, depending on product features and process requirements, there are often changes. The color sequence in general flexographic printing is governed by the following conditions.
1. The first printing of strong ink hiding power. Generally, light ink is printed first and dark ink is printed afterwards.
2. When the number of overprinting colors is large and dark rules are not used for overprinting rules, dark outlines should be printed first.
3. It is necessary to cover the inner edge of the outline of the image with the darkest color. When the burr of the outline is eliminated, the dark color must be overprinted. But sometimes this dark color is a color code. At this time, a part of the dark color may be printed first as the specifications of the various colors. Finally overprint dark outlines.
4. The main colors of the picture patterns are generally arranged in the final overprint.
5. For the same color of both existing outlets and on-site full editions, in order to meet the requirement that the outlets do not paste version and the full edition on the ground does not produce flowers, the screen edition and the full edition on the ground shall be printed separately. In this way, the printing pressure can be adjusted individually and different inks can be used to ensure the printing quality.
(b) Plates
The printing plate is mainly based on the original and process requirements.
1. Different print sequences of prints have a certain influence on films and flexographic plates. For example, print first light color, and then print dark color to cover the light color deeply. If the center circle is black, the outer circle is yellow. For example, when printing yellow and then printing black, when the film is out, the yellow is the same size as the original, and the black version is the same circle as the original. The black overprint yellow can hide the yellow black. If printed in black and then printed in yellow, the inner diameter of the yellow circle should be 1 to 2 mm smaller than the inner diameter of the original yellow circle when the film is produced. Black is a circle of the same size as the original. In other words, the yellow circle and the black circle overlap by 1 to 2 mm. This guarantees accurate yellow and black overprint.
2. Flexographic printing often involves patterns with dots. With the continuous improvement of the plate making process and the gradual improvement of product quality, in order to meet people's requirements for beautiful colors, fresh, clear and elegant appearance, there are new requirements for the choice of network line angle. Most of the main color screen network screen angle is 45 degrees. Because from the visual effect, the dots arranged at a 45-degree line angle have a dynamic sense of beauty and look particularly comfortable; the 90-degree line angles are sluggish and look uncomfortable; the dots are at 15 degrees or 75 degrees. The dots arranged from an angle have a visual effect in between. Therefore, the dot pattern angle of the dots is 45 degrees, followed by 15 degrees or 75 degrees.
3. Most carton manufacturers use round press printing. The plate is affixed to the drum. The thickness of the flexo plate is 3.94mm. Because the printing plate thickness, hanging film, etc. cause the printing pattern to extend in the circumferential direction of the drum, such as the circle will become an ellipse. Therefore, the paper feed direction should be taken into account when the film is taken out, and the shrinkage amount is calculated according to the diameter of the plate cylinder and the thickness of the resin plate. The corresponding reduction in the circumferential direction to ensure that the printed product pattern does not deform. For the plate-hanging operation on the plane, the amount of shrinkage should also be taken into consideration when hanging the plate.
(III) Printing ink
Most corrugated cartons manufacturing companies use water-based inks, and the performance of water-based inks determines the printing quality of corrugated cartons. The tinting power of ink is a scalar term that reflects the degree of ink dispersion and how much the pigment is in the ink. In general, when printing thin cable products, the ink concentration should be selected higher; the printed field products can be lower in concentration. Under high speed, high pressure, and high temperature conditions, the concentration is higher; on the contrary, it may be lower.
Ink viscosity is the ability of the ink to block its molecular motion under the influence of external forces. That is, the mutual adhesion of molecules inside the ink. The viscosity of the ink has a great relationship with the production process and the quality of the printed product. If the viscosity is too large, it may cause uneven transmission of ink, netting and pulling, and may also result in a flower pattern due to the nakedness of the graphic and textual basis. If the viscosity is too small, it may cause ink emulsification, and the printing area may become ink. Therefore, the above-mentioned dot printing and field printing should be separated from each other. The dot printing should use high-concentration and low-viscosity inks to ensure that the dots are clear. The viscosity is 18 to 25 seconds. For the field version, the low concentration is high. Sticky ink, viscosity of 35 ± 5 seconds to ensure printing does not bloom.
(to be continued)
