For multi-color offset printing of coated paper, printing stains (MOTTLE, commonly known as "printing," "printing," "ink misrepresentation," etc.) are one of the most common problems that arise today. A major topic for research in the international papermaking and printing industries. This article will initially discuss the causes of the stain, but its solution still needs further study.
First, the type of printing spots Printing spots usually refers to the color of the print appears on the normal, uneven shades or streaks. It is usually irregularly arranged and the boundaries are not clear. In general, the stains on printed products can generally be divided into the following three categories:
1, BACK TRAP MOTTLE (BTM stains)
It refers to the color spot produced by the peeling of the blanket (ie, BACK TRAP) in the subsequent color group in the multi-color printing. This blemishes will be the focus of this article. Due to the fact that no Chinese translation has been found in China, the divestment phenomenon, BACK TRAP, will not be translated in this article to avoid confusion.
2. WATER INTERFERENCE MOTTLE (WIM stains)
It contains two kinds of stains, one is the "wet repellent" stain, which appears in the multi-color printing of coated paper. The reason for this is that the surface coating of the coated paper is too closed and the dampening fluid cannot fully respond. , resulting in the next color of ink can not be divided into color space to form a stain; the other kind of stain is caused by the problem of fountain solution (such as fountain solution is too much, fountain solution is not properly configured, etc.) The appearance of this type of WIM is not limited by the type of paper and can occur in a single color.
3, WET INK TRAP MOTTLE (WTM stains)
Domestic data is generally referred to as “reverse overprint†or “mixed colorâ€. In multi-color printing, since the viscosity of the latter color ink is greater than the viscosity of the previous color ink, the ink of the previous color is stuck by the ink of the latter color. Spots. The emergence of WTM is not limited by the type of paper.
In addition, if the paper surface is too rough to cause uneven ink transfer during printing, stains may also be formed. This stain is called "ConTACT MOTTLINT". With the advancement of papermaking technology, this phenomenon has rarely happened.
At present, the domestic printing industry generally attaches great importance to anti-overprinting and ink-water balance. The papermaking industry always pays more attention to wet repulsion and has made a certain level of in-depth research. The national standard for coated paper has also made relevant provisions on wet exclusion. For BACK TRAP pigmentation, there have been no reports of in-depth studies in the country.
Second, the cause of BACK TRAP stains BACK TRAP is a multi-color offset press (especially more than 4 colors models) unique to the printing process. For multi-color offset presses, the BACK TRAP phenomenon is inevitable as long as it is a wet-press print and a blanket exists.
In the modern multi-color printing process, with the increase of printing speed, the time for the paper to pass between adjacent two color groups is as long as 1-2 seconds, and the total time for passing through several color groups is only 2-3 seconds. In such a short period of time, the ink is not dry. While printing, the blanket has a certain pressure applied to the paper. Therefore, during the printing process, when the paper is moved from the previous color group to the subsequent color group, the blanket and the sheet of the subsequent color group are replaced with each other. In addition to the transfer of ink ink and fountain solution to the paper surface, there is also the possibility that the blanket of the subsequent color group sticks off the part of the ink printed on the front color group, thus creating a BACK TRAP phenomenon. For blankets of the subsequent color group, any blank areas on the blanket may peel off the unbleached ink on the paper. This phenomenon does not occur when blankets are not used during dry printing or printing.
In the printing process of the 4-color machine or the 6-color machine, after carefully observing the blank areas of the blankets of the following color groups, it can be seen that more or less of the patterns on the preceding color groups are transferred. This is because the blanket of the subsequent color group causes a BACK TRAP effect on the ink transferred from the front color group to the paper.
The BACK TRAP stain is a product of BACK TRAP that does not occur uniformly on paper. If BACK TRAP occurs evenly, there will be no adverse effect on the printed product. The appearance of BACK TRAP stains is different shades of print. Usually occurs easily in a single color, such as a large area of ​​gray, blue, red or color overlay area on the print. Figure 3 shows an enlargement of the BACK TRAP stain in 70% magenta. (To be continued)
First, the type of printing spots Printing spots usually refers to the color of the print appears on the normal, uneven shades or streaks. It is usually irregularly arranged and the boundaries are not clear. In general, the stains on printed products can generally be divided into the following three categories:
1, BACK TRAP MOTTLE (BTM stains)
It refers to the color spot produced by the peeling of the blanket (ie, BACK TRAP) in the subsequent color group in the multi-color printing. This blemishes will be the focus of this article. Due to the fact that no Chinese translation has been found in China, the divestment phenomenon, BACK TRAP, will not be translated in this article to avoid confusion.
2. WATER INTERFERENCE MOTTLE (WIM stains)
It contains two kinds of stains, one is the "wet repellent" stain, which appears in the multi-color printing of coated paper. The reason for this is that the surface coating of the coated paper is too closed and the dampening fluid cannot fully respond. , resulting in the next color of ink can not be divided into color space to form a stain; the other kind of stain is caused by the problem of fountain solution (such as fountain solution is too much, fountain solution is not properly configured, etc.) The appearance of this type of WIM is not limited by the type of paper and can occur in a single color.
3, WET INK TRAP MOTTLE (WTM stains)
Domestic data is generally referred to as “reverse overprint†or “mixed colorâ€. In multi-color printing, since the viscosity of the latter color ink is greater than the viscosity of the previous color ink, the ink of the previous color is stuck by the ink of the latter color. Spots. The emergence of WTM is not limited by the type of paper.
In addition, if the paper surface is too rough to cause uneven ink transfer during printing, stains may also be formed. This stain is called "ConTACT MOTTLINT". With the advancement of papermaking technology, this phenomenon has rarely happened.
At present, the domestic printing industry generally attaches great importance to anti-overprinting and ink-water balance. The papermaking industry always pays more attention to wet repulsion and has made a certain level of in-depth research. The national standard for coated paper has also made relevant provisions on wet exclusion. For BACK TRAP pigmentation, there have been no reports of in-depth studies in the country.
Second, the cause of BACK TRAP stains BACK TRAP is a multi-color offset press (especially more than 4 colors models) unique to the printing process. For multi-color offset presses, the BACK TRAP phenomenon is inevitable as long as it is a wet-press print and a blanket exists.
In the modern multi-color printing process, with the increase of printing speed, the time for the paper to pass between adjacent two color groups is as long as 1-2 seconds, and the total time for passing through several color groups is only 2-3 seconds. In such a short period of time, the ink is not dry. While printing, the blanket has a certain pressure applied to the paper. Therefore, during the printing process, when the paper is moved from the previous color group to the subsequent color group, the blanket and the sheet of the subsequent color group are replaced with each other. In addition to the transfer of ink ink and fountain solution to the paper surface, there is also the possibility that the blanket of the subsequent color group sticks off the part of the ink printed on the front color group, thus creating a BACK TRAP phenomenon. For blankets of the subsequent color group, any blank areas on the blanket may peel off the unbleached ink on the paper. This phenomenon does not occur when blankets are not used during dry printing or printing.
In the printing process of the 4-color machine or the 6-color machine, after carefully observing the blank areas of the blankets of the following color groups, it can be seen that more or less of the patterns on the preceding color groups are transferred. This is because the blanket of the subsequent color group causes a BACK TRAP effect on the ink transferred from the front color group to the paper.
The BACK TRAP stain is a product of BACK TRAP that does not occur uniformly on paper. If BACK TRAP occurs evenly, there will be no adverse effect on the printed product. The appearance of BACK TRAP stains is different shades of print. Usually occurs easily in a single color, such as a large area of ​​gray, blue, red or color overlay area on the print. Figure 3 shows an enlargement of the BACK TRAP stain in 70% magenta. (To be continued)
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