Packing, decorating and printing products such as cigarette packs, wine boxes and food boxes are often printed with white paper and card paper of 250-400 g/m2. The maximum paper thickness that an offset press can print is 0.9 mm, but generally Under the circumstances, the thickness of paper to be printed is often only between 0.04 and 0.3 mm. The difference between white paper and coated paper, offset paper and letterpress paper lies in the thickness of the paper. During the process of offset printing of whiteboard paper, the paper feeding section, the imprinted part of the offset printing press, the color arrangement of printing, and the balance of water and ink are all part Adjust accordingly.
A roller lining and pressure regulation
When printing white board paper, the center distance between the plate cylinder and the blanket cylinder does not change, only the center of the impression cylinder and the blanket cylinder need to be adjusted. The center distance between the printing roller and the blanket cylinder can be increased by 0.20-0 at 250-450g/m2. .4mm, due to the poor smoothness of the surface of the white paper, rough, the paper is also much less tight than the coated paper, printed paper also pay attention to the printing pressure is also a little more.
Such as India 400g/m2 whiteboard paper, plate cylinder and rubber roller gap 3.95mm, rubber roller and the impression roller gap 3.40mm, plate roller village total package 0.65-0.75mm The total pad of the blanket cylinder is 3.15-3.35mm (measured with a micrometer). If the sheet is thick or thin, the reduced thickness, that is, the thickness of the liner removed from the pad of the plate should be added. In the blanket cylinder, if the paper is printed at a thin thickness, a certain thickness is subtracted from the blanket cylinder and a corresponding thickness is added to the pad of the plate cylinder.
Second, offset printing part of the adjustment
1. When the white paper is printed, the air volume of the suction nozzle and the blowing nozzle of the paper feeding section must be adjusted accordingly.
2. The paper suction nozzle and paper feeding nozzle need to replace the rubber apron with larger diameter and larger thickness. The pull gauge pressure spring can be replaced with a wire with a diameter of 1.5mm; by removing the paper feed roller and the shaft The coupling pin, or remove the roller on the pendulum, in order to achieve the purpose of the feed roller does not swing, smooth paper.
3. When printing whiteboard paper, the double-sheet control or gap of the offset printing press must be increased accordingly; the distance between the paper-pressure tongue of the side-gauge and the front gauge and the paper-feeding board, and the distance between the safety bar and the paper-feeding board must be Increase some.
4. The distance between the transfer tooth pad and the impression cylinder surface and between the transfer tooth pad and the transfer plate should be increased, and the distance should be approximately equal to the thickness of the paper plus 0.3 mm.
Third, the color sequence when printing
1. The products printed on white paper have Hong Kong version on the spot, and they have text, lines and patterns. Such as: the postal department express delivery envelopes, wine boxes, cigarette packaging (barrels) and other printed products, printing the color sequence is best to print text, lines, patterns, and then put the full version on the last machine printing , This can avoid due to the thick white paper, the paper is not dry when the imprint is caused by the collision of the paper caused by the collision, the back of the dirty phenomenon.
2, the dark color on the front printing, light color on the back of India, due to the dark color ink strong hiding power, adhesion, placed in front of the first printing, easy to overprint accurate; light color ink hiding power is weak, It's not easy to observe the rules when you run the printing on the back side. The effect of overprinting is much better.
3, often in a printed product, there are halftone four-color electric points of the network, there are continuous adjustment of patterns, text, lines. The four-color electricity network points should be printed first, which is conducive to overprinting accurately and reducing the impact of paper stretching. Then continue to print a continuous pattern, text, lines, in the arrangement of the printing color sequence to look for the primary and secondary, the first difficult to be more appropriate.
4, such as hot weather, white paper printing monochrome encounter uneven paper moisture content, wrinkling is not smooth, poor paper surface strength caused by falling powder, hair loss, etc., can also be the first air to print a blank, you can Solve the phenomenon.
Fourth, printing white paper how to prevent dirt
1, when the full version of the original version of the field as far as possible with the original barrel of ink, without adding 6 # ink, plus some appropriate de-adhesive, anti-adhesive agent; do not add dry oil when the weather is hot. The full-fill version of the field is often prone to dirt on the back, and is often solved by dusting. Although the printed anti-adhesive dirty dusting agent contains pure plant material, the dispersion and fluidity are good, but the use of dusting agent will directly affect the printing product. The surface gloss makes the ink color unlit and pollutes the environment, and has an impact on the accuracy of the offset press.
2, white paper surface roughness, loose quality and poor ink absorption, flatness is poor, so the full-print version should be printed on the ground background, dark color after printing, background color to be deeper, printed thin, ink should not be too Big. If the flatness of the white paper is good, then when the full-print version is on the ground, the dark color should be printed first, and the amount of ink should be printed to ensure that the back surface is not dirty, and then the background color is overprinted so that the print product finish will be compared. Well, at the same time, pay attention to the balance of ink and water and control the size of the printing plate layout.
In addition, when the offset printing machine prints whiteboard paper, because the paper is thicker, multiple sheets of white paper jam into the embossing and the rubber cylinder, which may cause â€œstingy carsâ€. Therefore, it is necessary to carefully control the double-sheet control and skew before printing. Equipment such as control, front control and other electrical appliances are properly adjusted. The distance between the double sheet control roller and the paper feed roller during double sheet control must not be less than two paper thicknesses, but it must not be more than three paper thicknesses, or the paper of the arches will pass through. When the controller will stop; or double sheets have been passed from the controller above, and the controller power supply contacts have not touched, do not control the purpose of double sheet. Timely clean the dirt and dirt or insulation on the surfaces of the two-sheet control roller and the feed roller or the two contact surfaces of the power supply control unit to prevent the failure of the double-sheet control system and the â€œstingy carâ€, the traffic jam and the pressure The failure of the drum occurred.
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