Principles of Printing and Packaging-Process-Technology: How to determine the edge of the mouth when installing the plate? How to determine the width of the gripping edge of the printing plate during loading? What is the printing positioning system ... The following will introduce you to the common problems and solutions in packaging offset printing. The following content is organized by editors for your reference.
Common problems and solutions of packaging offset printing
How to determine the edge of the mouth when installing the version?
Which side of the original version is used as the mouth side should be considered from the needs of printing and post-press processing.
â‘ Considering the specifications and positioning accuracy of the printing machine, the general rectangular original version should use the long side as the mouth edge.
â‘¡ Considering the accuracy of overprinting, since the paper deformation at the gripping edge is small and the paper deformation at the trailing edge is large, the side with the higher overprinting requirements on the original plate should be used as the gripping edge.
â‘¢ From the perspective of saving paper, because the 1cm wide position of the mouth edge cannot be printed, sometimes the paper width is very tight, and it is necessary to make full use of this part of the white edge, then the blank edge on the finished product or the paper tongue of the paste box Be a mouth.
â‘£ From the perspective of post-press processing, the choice of gripping edge should be conducive to die cutting processing.
How to determine the width of the grip edge of the printing plate when installing the plate?
When installing a plate, the distance between the original image and the edge of the printing plate should be within a certain range. If the distance between the image on the original plate and the edge of the plate is c, the distance between the image on the original plate and the edge of the paper is a, and the distance between the edge of the paper and the plate is b, then c = a + b. The size of b is determined by the position of the plate cylinder relative to the impression cylinder and the amount of gripping paper brought forward by the front ruler. The effect of adjusting the front rule on b is very small. The amount of adjustment of the position of the plate cylinder relative to the impression cylinder is different, generally around 5 cm.
The printed plate, that is, when c has been determined, adjusting the size of b can change the front and back positions of the printed image on the paper, commonly known as "borrowing the cylinder". But if you need to rely on "borrow cylinder" to adjust the position of the image on the paper when printing, it will obviously affect the production efficiency. A more reasonable approach is to choose a roughly centered b0 value for a certain type of printing press. If you want the image to be printed on the paper at a distance of a from the grip edge, then determine the image according to c = a ten b0 The distance c from the edge of the printing plate. Every time this method is used to determine the position of the original plate relative to the grip edge of the printing plate during printing, there is no need to "borrow the cylinder" when printing. If there is a corner line on the original, usually use the corner as a reference to determine the distance between the original and the edge of the plate.
What is a printing positioning system?
From the original manuscript to the printed matter, it has to undergo color separation, imposition, and copying. Exposure, printing and other production processes. In order to ensure that the color-separated images can achieve overprinting in the fastest way in the production of various processes, the positioning pin and the positioning hole can be used to achieve the goal through a series of operations. This system is called the printing positioning system. Since the desktop system is now commonly used for layout production, it can automatically output accurate color separation film for overprinting, so the positioning system is mainly used in the process of printing and printing.
What constitutes a positioning system?
The positioning system is mainly composed of printing plates. The film punch is composed of positioning pins and positioning pins on the plate cylinder.
What are the benefits of using a positioning system?
â‘ Greatly shorten the time to install and adjust the version. If you can reasonably arrange the position of the original plate relative to the printing plate when printing. And the positioning system is used correctly, so the registration can be achieved basically without adjusting the plates between the color groups of the printing machine, which greatly improves the production efficiency.
â‘¡The printing plate no longer needs to be pulled repeatedly for many times, reducing the overprinting caused by the stretching deformation of the printing plate and improving the printing quality of the product.
How to use the positioning system correctly?
At present, the multi-color printing and printing positioning system is adopted in China, and the correct method of use is as follows:
â‘ Cut the polyester film base, the width should be less than the distance of the image of the grip edge of the original plate from the grip edge of the printing plate, and punch the polyester film base with a punching machine.
â‘¡Take the perforated edge of the polyester film base as the reference of the mouth of the printing plate, and use the oblong hole in the middle of the polyester film base as the center line of the printing plate to fix the negative of the first color plate on the film base. Note that the film base should be attached to the non-drug film side of the film.
â‘¢ Put the base of the polyester film of the first color version of the fixed number on the positioning pin, and register the second color version negative film with the first color version negative film. At the same time, the second polyester film base is sleeved on the positioning pin, and the second color plate negative film and the second polyester film base are fixed together when the second and first color plate negative films are registered. Process the remaining negatives of the other color plates by processing the negative plates of the second color plate.
â‘£Perforate each printing plate to be printed, align the negatives of each color plate and the positioning holes of the printing plate with positioning pins, and then print the plate.
⑤When installing the plate, first of all, the plate clamp of the plate cylinder of each unit should be retracted to the same reference position, the two U-shaped holes on the printing plate should be hung on the positioning pins, and the u-shaped holes and the positioning pins should be closely connected. Then tighten the clip on the trailing edge first, and then tighten the clip on the edge of the mouth.
What are the requirements for the exposure light source for the PS version?
â‘ The spectrum of the light source of the plate-making machine should be consistent with the photosensitive spectrum of the PS plate sensitizer. The photosensitive spectrum of the PS version is about 350-450nm, which requires the light source to have a high-energy peak in this wavelength range to shorten the exposure time and achieve a good exposure effect.
â‘¡ The illuminance of the light source should be uniform. The illuminance can be used to detect the illuminance of each point in the middle and the periphery of the printing platform.
â‘¢ The power of the light source should be around 3000W, and the voltage fluctuation value should be less than 10%. Before exposure, the light source should be preheated to ensure stable light intensity during exposure.
How to determine the exposure time of the PS version?
The exposure time of the PS version mainly depends on the photosensitive range of the PS version. Factors such as sensitivity and the spectral characteristics of the light source, the strength of the light source, and so on. Therefore, every time you replace the PS version of a different brand or replace the light source, you need to use a series of tests on the PS version to determine the correct exposure time.
The test method is as follows: choose a transmission gray scale with a continuous density adjustment difference of 0.15 and Brunel or other similar test strips with small dots and thin lines in the positive picture. Use two test strips to gradually increase on the PS version. Expose the exposure time, record the corresponding exposure time of each piece, observe it with a magnifying glass after development, check each test strip that is exposed, the exposure time corresponding to the test strip that meets the conditions can be used as the normal exposure time. When drying ordinary mesh-adjusted products, the first 4 levels of gray ladders are required to be sunburned; 1% 6 of the dots are sunned, 2% of the dots are aligned; 11μm wide thin lines are retained, 8μm wide thin lines are sunned .
How to adjust the exposure time of the PS version according to specific conditions?
â‘ There are no outlets, only thicker text. The original version of the lines and the ground can increase the exposure time and remove the small dirty spots and stains to reduce the time for removing dirt.
â‘¡The negative film has been stored for a long time, the blank part is yellowed, or after manual imposition, there are two or three layers of blank film bases stacked together, which can slightly increase the exposure time; the original part of the field is not high enough density can reduce the exposure time.
â‘¢ The pressure of the proofing machine is less than that of the printing machine, so the increase of the proofing dot is smaller than the increase of the printing dot, so the exposure time of the proofing plate should be less than the exposure time of the printing plate. The proofing version is generally done with 0.5% of the dots, and 1% of the dots are reserved.
Strictly speaking, for the color separation of the gradation draft. When determining the tone replication curve, it should have taken into account the difference in dot gain in various situations and compensated. In fact, the domestic standardization of this process is not very good, so according to the production conditions of the respective printing plants. Adjust the exposure time. If the dot increase rate is large during our printing process. The exposure time can be increased. According to different substrates to be printed, when printing plates for printing offset paper, the exposure time should be longer than printing plates for printing coated paper.
Why do I need to pump down when exposure is made?
Take the production of positive PS version as an example. When printing, if the film surface of the negative film is not in close contact with the photosensitive coating of the PS version. There is a gap in the middle, and there will be light obliquely from the edge of the blank part of the negative film to the photosensitive coating directly below the graphic part, causing the edge of the graphic part to decompose in light. Make the image dry. The dots become smaller, and small dots and thin lines are lost.
Because one side of the printing frame is transparent glass, the other side is a rubber pad. When the vacuum pump evacuates the air in the printing frame, the air pressure inside is low, and the rubber pad will press the PS version under the external atmospheric pressure. The original negatives face the glass and are tightly connected.
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