New technology equipment to improve the printing quality of color corrugated boxes
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Corrugated boxes can protect and facilitate the transportation of goods during the transportation of goods. With the progress of carton printing process and packaging machinery, how to improve the printing quality of color corrugated boxes has been paid more and more attention by carton enterprises.
With the improvement of the technical strength of the packaging machinery industry, some imperfect technologies have made great breakthroughs. The application in the production of color corrugated box shows superior performance, guarantees the printing quality of corrugated boxes, and prints the packaging. The development of the industry has produced a huge boost.
1. Carbide corrugated roll
As a corrugating roller for the heart of a single-sided machine, it plays a decisive role in the quality of corrugated board. The carbide corrugating roller is coated with a high-density, high-hardness, and high-wear-resistant carbide alloy powder, and this fluidity coating is sprayed onto the finished and finely processed cylinder by thermal spraying.
Compared to ordinary corrugating rolls, carbide corrugating rolls have the following advantages:
1.1 can get the optimal tooth design to get the ideal shape.
1.2 can ensure that the tooth height and the top circle remain unchanged for a long time, ensuring the smooth quality of the cardboard.
1.3 Reduce the amount of core paper by 2% to 8%, reduce the amount of adhesive, reduce waste, reduce the number of replacement of corrugating rolls, and reduce damage to other units.
1.4 Easy to repair, the diameter of the corrugated roller after repair is almost unchanged.
2. Reverse (reverse) squeegee inking system
The mounting direction of the system squeegee is opposite to the direction of rotation of the anilox roller. Compared with the conventional angle, the pressure between the squeegee and the anilox roller is lighter, the loss is smaller, and the accuracy is more accurately transmitted. Control ink to meet high quality printing requirements (as shown in Figure 1)
Figure 1 Reverse (reverse) doctor blade system
3. trapping technology
Trap is also called trapping, also known as expansion and contraction, mainly to compensate for the whitening between two adjacent different colors due to inaccurate printing overprinting. When people face the printed matter, they always feel that the dark color is close to the human eye, and the light color is far from the human eye. Therefore, when trapping the original, it is always trying to prevent the light color under the dark color from being exposed. The dark color above remains the same to ensure that it does not affect the visual effect.
In the process of printing corrugated cardboard boxes, the implementation of trapping processing must follow certain principles. Under normal circumstances, the color is not expanded, the color is not expanded, and the color is expanded without expanding the ground. Sometimes, mutual expansion is also possible. In special cases, reverse trapping is required, and even a gap is added between the two adjacent colors to compensate for the overprinting error, so that the printed matter is beautiful.
The amount of trapping amount depends on the characteristics of the printing material and the overprinting precision of the printing system. Generally, the offset of the offset printing is smaller, and the amount of trapping of the gravure and flexo printing is larger, generally 0.2 to 0.3 mm. According to the customer's printing accuracy or requirements.
There are four main methods of trapping:
3.1 Monochrome line overprint method: add light lines on the edge of the color block and select the line attribute as overprint.
3.2 synthetic line method: add a synthetic line on the side of the color block, the line attribute is not selected as overprint.
3.3 layering method: trapping is achieved by retracting or expanding the elements on different layers.
3.4 Shift method: Retract or expand by moving the position of the inflection point in the color block, generally used in the trapping related to the gradient.
Figure 2 trapping (trapping)
When the color block is adjacent to the color block, the monochromatic line superimposition method or the synthetic line method is mainly used. If the color block is formed by superimposing two primary colors or spot colors of the same size and position, there are transparent colors or white surrounding, Preventing overprinting from leaking out of the next color and causing unsightlyness, you can take the next color shrinking method to trap. If the color patch is overprinted by two flat-grid hues, or if the previous color is a flat net and the next color is a solid, trapping is generally not required unless printing has special requirements. When the continuous tone image is adjacent to the color block, there are two types of trapping: one is to expand the color block into the image, and the other is to extend the edge of the image into the color block. When expanding the edge of the image, you can slightly enlarge the image according to the actual situation, or use the image editing software to enlarge the edge of the image or enlarge the mask of the image. When a four-color image is adjacent to one or several of the primary colors, trapping is generally not required. If the hue of the patch differs greatly from the hue of the image, trapping is required. For example, when a red tomato pattern is adjacent to a green block, the green block must be expanded into the tomato pattern. When the four-color image is adjacent to the spot color, it must be trapped.
4. Air cushion lining technology
Corrugated board is easily damaged during flexographic printing, and the difference in mechanical properties of the rollers and bearings on the press, variations in the thickness of the plates and corrugated board, ink viscosity, temperature changes in the printing shop, etc. Printing quality. Table 1 lists the general machining characteristics of common corrugated board.
Table 1 General mechanical processing characteristics of common corrugated boxes
If the corrugated board is compressed so much that the corrugated wall is bent more than the board breaking strength, the corrugated board will not return to its original thickness, ie the board will be damaged when it exceeds the compressible limit. The compressibility of corrugated board in printing is related to the amount of compression of the nip, but it is not equal. The compressive amount of corrugated cardboard is often less than the amount of compression of the nip between the embossing cylinder and the plate cylinder. During the printing process, when the embossing cylinder and the plate cylinder are squeezed, the plates and corrugations The cardboard will be compressed.
If a thin plate printed corrugated cardboard is used on the liner, the three layers of corrugated cardboard, printing plate, and liner will be compressed by an amount equal to the sum of the compressions of the layers. As can be seen from Figure 3, with the R/bak liner technology, the amount of compression of the plates and corrugated cardboard is reduced, while the liner absorbs a large amount of compression.
Figure 3. Effect of the R/bak padding technique: the amount of compression of the plates and paperboard is reduced, while the pad absorbs a greater amount of compression.
Plasticity is a measure of the softness of a material, and plasticity is comparable to hardness. Thin corrugated board is generally less practicable in terms of compressibility, while thicker corrugated board is more malleable and should be printed on thicker plastic substrates, preferably using a softer resin plate. High-quality flexographic printing requires that the plate be adapted to the thickness of the board. To achieve this, the plate plasticity should be comparable to or higher than the plasticity of the board.
Damaged cardboard
(When the printing pressure is too small, the printed substrate is prone to corrugated and washboard-like patterns, and affects the printing on the ground and fine lines;
When the printing pressure is too large, the printed substrate is easily deformed or even destroyed, and at the same time, the resin plate is deformed and the printing dot is enlarged. )
Figure 4: Compensation of padding technology
In the traditional flexo printing, 7mm thick printing plate is used. When the printing plate is pressed, the convex part of the graphic is strongly pressed, first compressed, the dots and text lines are easily deformed, the dot expansion is intensified, and the plate making cost is also high. If the 4mm thin plate plus 3mm R/bak air cushion is used to replace the 7mm printing plate, the hardness of the air cushion lining is 20-25 Shore, which is lower than the hardness of the printing plate (the commonly used printing plate hardness is 35). When the printing is pressed, the air cushion lining is first compressed, so the printing plate is small in deformation, the printing quality is greatly improved, and the plate making cost can be reduced. This thin plate process combined with R/bak air-cushion lining technology is more suitable for printing fine images and is gradually replacing traditional thick plates.
R/bak is a polyurethane type material with the following main features: it can reduce the printing surface pressure, effectively control the expansion of the dot; avoid the deformation of the printing plate and prolong the service life of the printing plate; and have unique compensation for the excessively large plate roller. Function; good printability for low-quality corrugated paper, and can avoid damage to corrugated paper; can improve the printing grade of traditional printing equipment.
R/bak air-cushion lining technology is a mature technology widely used in corrugated box printing. It is regarded as the most direct and most effective solution to improve the printing quality of corrugated boxes.
5. Thin cardboard thin printing technology
In the color corrugated box printing, on the basis of thin cardboard, the role of the thin flexo plate is also fully exerted. With the continuous improvement of the flexographic plate making process, the high resolution image is transferred by the excellent ink transfer performance of the plate itself. Finally, the high added value of corrugated boxes is realized.
Flat on-the-spot printing, smaller bar code areas, and more elaborate gradual transitions reduce the phenomenon of smashing clothes and achieve accurate registration. Such high-quality prints not only establish a corporate image, but also expand the business of the enterprise.
However, the application of thin cardboard/thin plate technology is also a challenge for the corrugated box printing industry itself, and the low price short version has become the mainstream of the corrugated box printing industry.
6. Summary
While having high quality equipment, the precision of the equipment and the operator adjustment technology are the most important factors in determining print quality. A good quality corrugated carton product must have accurate processing position and fine and clear printing. The processing position includes printing position, coloring position, coloring position, slotting position and emptying position, which not only requires high precision and operation of the equipment. The person must have an in-depth understanding of the equipment, and can find the answers in time for the analysis of the bad causes, and correctly eliminate and correct them. The operation of the printing press is a team performance. Everyone should understand their work and responsibilities, and cooperate with each other to achieve the ultimate in processing quality and efficiency.