Corrugated box dot printing experience
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With the prosperity of the commodity economy, the market competition has become increasingly fierce, prompting commodity manufacturers to strive to improve the quality of outer packaging, and beautifying packaging has become an effective means of product promotion and promotion. The quality of corrugated carton packaging and printing has been increasingly valued by commodity manufacturers and consumers. In order to enhance the competitiveness of products and improve the packaging grade of products, many corrugated carton layouts have begun to use dot patterns to highlight products and enrich the layout.
In the packaging design, the expressiveness and visual impact of the graphics are relatively strong, which is very easy to attract people's attention. The graphics printed by the dot are difficult to counterfeit, the anti-counterfeiting performance is good, and the layered and three-dimensional sense is pleasing to the eye. To get a high-quality dot effect, you must first work on the design draft. The dot is the basic unit that realizes the change of the publishing level, the tone of the tone, and the natural boundary. It plays a role in determining the color, level and image outline of the print. The degree of shading of the printed graphic is expressed by the size of the dot. The larger the number of dots, the thicker the ink of the graphic printing, and the lighter the opposite. For corrugated box printing, the dot is too dense and easy to cause paste phenomenon; if the dot is too thin, the graphic details will be lost, affecting the graphic effect, and the production must be accurate. The graphics are divided into vector and bitmap, and their processing methods are different.
Vector point processing method
For vector graphics, you need to control the grayscale, and the grayscale changes to reflect the graphics level. The size of the grayscale determines the dot size and thickness. When the vector image is output, the number of output lines determines the number of graphics points. The larger the number of network lines, the more the number of network points. The output must be selected with the appropriate number of network lines. Only by considering the grayscale graphics of the vector image and the number of output network lines, a satisfactory dot effect can be obtained.
Bitmap image dot processing method
1. The most basic processing method of bitmap images
PhotoShop is currently widely used image processing software. For bitmaps, after scanning the image, the most basic processing method is to remove the dots first. Perform Filter-->Noise--->Despeckle in PhotoShop. Then sharpen Filter--->Shaper--->unsharp mask sharpen, then adjust the overall contrast of the image, execute Image--->Adjust--->levels, the usual way is to put the left side Pull the triangle to the middle.
2. Create and select the desired dot image
After processing the scanned image, select show paths from windows, use the pen tool to draw the path to the portion of the dot image that needs to be created, keep the path (name), and then cut the defined path (clipping path) ), save the image as (save as) Photoshop EPS format, you can place the required image part in the drawing software such as Freehand, Pagemake.
3. Bitmap formation
First convert the processed image to grayscale mode (Grayscale), execute Image--->mode---> Grayscale, then convert to bitmap modebitmap, enter the bitmap dialog box. , where the output (output line number) data in the resolution is generally the same as the input (input line number) data, then select the halftone screen from the mothod (method), and then enter the halfone screen dialog box. According to customer needs, you can choose Round, Diamond, Ellipse, Line, Square, Cross, etc. The circular dot with the largest connotation capacity to reduce the dot enlargement rate in printing. The angle of the selected dot must avoid the angle of the mesh line of the anilox roller, and the size of the dot is thickened by the parameters in the frequency to obtain the dot pattern suitable for the printing condition. The formed dot pattern can be printed in advance in a 1:1 ratio to check the dot effect for adjustment or delivery to the customer for approval.
Production of dot printing resin plate
After the design draft is output into a film, the plate can be plated. The photosensitive resin plate used to make the dot pattern requires a high hardness. It is suitable for 45~50o Shore A, and the material has low elasticity and slow recovery. Reproducibility.
The production of the resin plate on the same product packaging is carried out as much as possible at the same time. Once completed, it is very easy to appear the difference in dot printing and the different effects. If the photosensitive resin plate of the dot pattern cannot be processed at one time, the back exposure, main exposure, rinsing, drying, de-bonding and post-processing time must be strictly controlled during the plate making, and the recording should be made so that the data is consistent for each processing. Dot pattern photosensitive resin version of the same effect.
Correct choice of anilox roller
When designing dot patterns, consider the anilox roll of the corporate press. Anilox roller is the "heart" of corrugated carton printing machine. Carton manufacturers are constantly improving the grade of anilox roller in response to the market demand for the exquisite printing of corrugated carton.
At present, the metal mesh transfer roller is commonly used on corrugated box printing machines, and its precision is mainly ensured by the manufacturing process and extrusion technology of the netting cutter and the roller. When performing graphic dot printing, the number of mesh lines, the shape of the mesh and the arrangement angle of the metal mesh transfer roller should be considered as follows:
Number of lines in the net
The mesh of the metal mesh transfer roller is composed of the mesh and the mesh wall. In order to obtain sufficient storage and delivery of ink, the mesh must be at the best depth during processing under the premise of ensuring the accuracy of the tool. The narrower the better, the better the volume is required. The choice of the mesh of the metal mesh transfer roller depends mainly on the actual ink demand for corrugated carton printing. In corrugated carton printing, it is generally between 150 and 300 lines/inch. For large-area solid printing, 165 lines/inch can be used. For network cable, graphic dot printing should use an anilox roller of 180 to 300 lines/inch. The selection of the number of lines of the printing resin plate has an important relationship with the number of lines of the anilox roll. The ratio of the number of printed resin plates to the number of lines of the anilox roll should be 1:3.5 to 4, so as to ensure the high light area in the printed resin plate. The minimum dot does not fall into the cell of the anilox roll to create dots, which affects the print quality.
Netting shape and arrangement angle
The different mesh shapes on the metal mesh transfer roller determine different volumes and stored ink quantities. The shape of the mesh is mostly square prismatic, hexagonal, pyramidal, hexagonal connected, diamond shaped, and the like. The same number of lines, the shape of the netting is different, and the volume is different. With the same number of lines, choose the appropriate mesh shape to get better printing results.
The mesh alignment angle of the metal anilox roller refers to the angle between the axis of the roller and the axis of the roller. Under normal circumstances, the square prismatic shape, the pyramid shape is 45", and the hexagonal shape, the hexagonal connection shape, the diamond shape is 60", and there are also 30". If the printed resin plate and the anilox roller are in the same angle or printed on the resin plate The number of lines does not match the line number of the anilox roll or the dot shape of the printed resin plate matches the mesh shape of the anilox roll, and the pattern will produce a moiré, which must be avoided when designing the dot pattern.
Good quality of water-based inks
In order to obtain high-quality dot printing, it is necessary to master the pH, color density, hue, drying performance and flow properties of water-based inks.
The pH of the water-based ink should be controlled at 8.5-9. Because the corrugated carton area is relatively large, the plate roller is exposed to a lot of air, and the printing speed is slow. The water-based ink should choose a slower drying speed. Otherwise, the ink is easy to dry on the printing plate, so that the solid printing is not true. Version. When a stop ink is dry and is not easily rubbed off with water, it is necessary to exchange the aqueous ink when this occurs. When printing the stacked ink, the fluidity of the ink is relatively strict. It should be noted that the latter color is slower than the liquid of the previous color, otherwise the ink of the overlapping color is not good. The ink contains yeast and amine, which is easy to volatilize, which makes the ink thicker. It is easy to cause the dot printing plate to strengthen the graphic dot printing process control. Under normal circumstances, the dot pattern and the large area ink block are printed together as much as possible. Dot pattern and large area ink block need different ink volume and pressure during printing. It is often not easy to master when printing together. If large-area ink blocks are taken care of, it will produce dot enlargement or paste; if you take care of the dot pattern A large area of ink will appear to be under pressure, resulting in a false impression on the ground. Pressure adjustment and color control are much simpler if large areas of ink and dot patterns are printed separately.
However, at present, most corrugated box printing layouts either have gradient dots or large-area mesh lines, a small number of ink blocks, or large-area ink blocks and a small number of network cables. It is difficult to separate the two. In this case, the thickness of the solid part can be increased by 0.15-0.30mm to improve the plate pressure and printing pressure. If it is a gradient dot, when the paper is partially stuck in the field, pay attention to the transition between the ground and the cable. The paper should be cut into a zigzag shape to avoid a hard mouth.
Effectively control the expansion of outlets
In the process of printing, a certain degree of dot enlargement must exist. What is important is how to control it. This requires the printer to adjust the pressure as lightly as possible to obtain the minimum dot gain and make adjustments to the parameters of the press. Record in detail so that the same printing effect can be tracked later.
Master the printing pressure
Appropriate printing pressure is very important for printing quality. Corrugated box flexographic printing is light pressure printing, and the contact pressure between the rollers must be strictly adjusted according to requirements to ensure uniform line pressure. If the pressure is too large, it will cause abnormal wear, mechanical fatigue, deformation, and even journal fracture of the roller, which will damage the printing plate, and the phenomenon of printing dot enlargement and printing blurring will affect the printing quality of the corrugated carton.
Ensure the normal speed of the press
The running speed has a certain relationship with the amount of ink transferred. The running speed is slow, the ink transfer amount is large, the running speed is fast, the ink transfer amount is small, and the stable running speed can obtain a stable ink transfer amount. Since the viscosity of the aqueous ink has a certain proportional relationship with the amount of ink transferred, large-area solid printing can use a slightly slower running speed and a slightly higher viscosity aqueous ink and a lower number of netting. Screen printing requires faster running speeds and low-concentration aqueous inks and higher line counts.
Strictly clean the anilox roller and dot printing plate
The biggest characteristic of water-based inks is that it is extremely difficult to clean after drying, and cleaning work is particularly important. The metal mesh transfer roller should be disengaged from the plate roller during the temporary shutdown, but the mesh transfer roller should continue to contact with the rubber wiper roller to prevent the ink from drying on the bottom of the mesh. When the metal mesh transfer roller is finished and the machine is stopped for a long time, the ink transfer system must be thoroughly cleaned and wiped clean with a clean cloth instead of just using water. If you do not accidentally block it, you should use regular cleaning agents or even a washing machine for large washing, but this is a last resort. The cost of washing is high, and it may not be successful every time. If you do not pay attention to the maintenance of the anilox roller, you will find a way to get it after the blockage.
After the printing is completed, the resin printing plate of the dot printing is immediately cleaned to prevent the ink from drying on the plate surface, causing the dot to become clogged, resulting in a bad plate.