Ghost trouble of the hottest printing press and it

2022-08-07
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The ghost image of printing machine is one of the most troublesome problems in printing. For small format offset printing machines with short ink path, the ghost image mainly appears in the parts that should not have graphics and text. There are several types of ghosts, which usually appear on a large area of the field or in a small blank area

1. types of ghosts

ghosts can be divided into craft ghosts and mechanical ghosts

(L) process ghost

process ghost is mainly caused by the chemical changes of the ink during the drying process. It usually occurs when printing bright ink on matte paper or matte ink on bright paper. The appearance of such ghosts is irregular and difficult to control and avoid. Sometimes it occurs after live printing and ink drying

it is almost impossible to completely eliminate the ghost of this kind of process, but the printing factory can adopt 2 The binder shall take corresponding measures to avoid ghosts, such as improving the ventilation conditions of the paper receiving department and keeping the temperature of the processing workshop and the storage workshop constant. If there is still a ghost, you can also polish the picture and text

(2) mechanical ghost

mechanical ghost is the most common ghost, which is mainly caused by the mechanical reasons of the printing press. The mechanical ghost is affected by the ink roller, blanket and printing plate on the printing machine. The ghost caused by blanket and printing plate needs to be eliminated by the printer; The ghost caused by the ink roller, also known as the ghost of lack of ink, is mainly due to the unreasonable prepress design

the ghost of ink shortage is mostly caused by the fact that a certain part of the printing picture requires a large amount of ink, and the ink roller cannot supply ink in time. For example, large bold characters of the same color are designed above a large area of the field. The part on the ink roller used to print bold characters does not have enough time to ink before the field behind the printing, so the field part behind the bold characters is slightly shallower than the field of other parts

2. elimination of ghosting

there is a lack of other ink ghosting, which is more likely to occur when using transparent ink for printing, but rarely when using opaque ink and proofing. The greater the value of kn, the higher the rigidity (not easy to be twisted). In cooperation with the experimental mechanism printing process marked as a good platform, some measures can be taken to reduce the ghost of ink shortage. First of all, attention should be paid to avoiding the use of designs that are easy to produce ghost shadows of ink shortage, such as large borders, large fields, etc. If such a design must be adopted, the following measures can be taken:

(L) pictures shall be used as much as possible in the design. For eye tone printing that does not involve the field, generally there will be no ghost phenomenon

(2) change the design. Reduce the density of large borders or large fields, balance the density gap between the eye-catching pictures on the page and the field parts, and try to balance the ink volume of the whole page to reduce the appearance of ghosts. For example, if you put two pictures on the right side of the printed sheet, it is easy to produce ghosts when printing; If the design is changed so that two pictures are placed separately, one on the left and one on the right, and the ink amount of the whole page is balanced, the ghost of rabbits can be avoided

(3) reasonably design the layout during typesetting. Proper layout can ensure that the ink roller has enough inking time to avoid ghost. For example, if a design is to place a large picture on the field, when making up, if the printing press is large enough, it can be placed behind two pictures on a white background

(4) use the color bar placed at the cutting part other than the graphic part to transfer the excess ink on the ink roller. These color bars are called ink transfer bars

(5) adjust the printer to increase the ink supply to the ink bucket of the ghost part. Moreover, some printing machines are equipped with inclined ink leveling rollers, which can effectively solve the ghost of ink shortage. That is, different parts of the ink roller are used to print different parts of a large area of the field, so that the ink roller will not lack ink

(6) rotate the design layout by 90 °. Take printing large bold words on the field as an example. If the ink roller inks large bold words first, and then inks the field, printing one by one, it is easy to cause the ghost of ink shortage. However, if the printing sheet is rotated 90 ° so that one part of the ink roller inks the font and the other part inks the field, the ghost of ink shortage can be effectively avoided

the ghost phenomenon of light ink color in some parts of the field border is mainly caused by design reasons, that is, the ink roller can not quickly supplement enough ink to meet the needs of field printing. Due to the large amount of printing ink required for the field frame, ink shortage is easy to occur in the circumferential direction of the drum, resulting in that the ink color of the field frame printed along the circumferential direction is shallower than that printed along the axial direction

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