BACK TRAP stains are usually produced only on coated paper, but not on offset paper. This is due to the fact that the paper structure of the offset paper is rough and loose, and its ink absorption is good. In addition, its printing pressure is usually larger. Therefore, when entering the jaw group, the ink (including ink particles and binders) of the front color is printed. ) A considerable portion has already penetrated into the paper. Therefore, even if uneven BACK TRAP occurs, it will not affect the color depth of each point on the paper. In addition, the double offset printing itself is rough and it is impossible to use it for fine prints. Therefore, the impact of BACK TRAP on offset paper is negligible.
In the case of coated papers, since most of the coated papers are now coated with multiple coats and subjected to super light treatment, ultra-fine calcium carbonate and china clay are used as pigments in paints, and synthetic latexes are used as adhesives, so coatings are compared. Closed, which leads to slower penetration of the binder in the coating after printing, a large number of pigment particles and binders are regulated on the surface of the paper. A closer coating on the surface of the paper can, of course, produce a higher gloss of printing, but on the other hand, when the paper enters the latter color group from the former color group, BACK TRAP will inevitably occur in a large area. In addition, because the coated paper surface is smooth and the blanket is in uniform contact with the paper surface, the BACK TRAP phenomenon may occur in the subsequent color group in any multi-color printing.
Why do some coated papers produce uneven BACK TRAP, which in turn causes BACK TRAP pigmentation? This is because the root cause of the BACK TRAP stain is the uneven absorption of the coated paper. If the coating absorbs the ink evenly, then the blanket will peel off the ink on the paper very evenly and will not have any adverse effect on the effect of the print screen, thus printing a perfect print. However, if the coating absorbs ink unevenly, it will result in uneven ink drying speed on the paper surface. When entering the follow-up color group, the ink is peeled off by the blanket in the slow-drying area more than in the fast-drying area. This difference in quantity may be due to a stripping action, or it may be due to multiple stripping effects. When the difference in the amount of peeling was so large that it could be observed by the human eye, there was a case where the printing color was different, that is, the BACK TRAP color was generated. In the area where the BACK TRAP pigmentation occurs, lighter areas indicate poor paper absorption performance and darker areas indicate better paper absorption performance.
It should be noted that when using offset fast-drying inks, the amount of stripping of the ink on the surface of the blanket relative to the amount of ink remaining on the surface of the paper is relatively small, and these traces of ink transferred to the blanket have not yet been found to be printed. It has caused obvious effects. Practice has proved that it is impossible to judge the degree of BACK TRAP from the shape of the dot under normal printing conditions. Even in the presence of BACK TRAP stains, it is now macroscopic. At this time, even if the blanket has more or less stripping of the ink, the volume of ink remaining on the paper is still only a small part. There are no obvious differences in the shades of the different areas in the shape of the dots, but some of the more serious BACK TRAP spots may have different shades of dots. The reason why these dots can be kept intact is probably due to the fact that during the period when the paper entered the printing group from the last printing group, many contraceptives and pigment particles penetrated into the coating of the paper. Therefore, even if it is strongly affected by the blanket, it is impossible for the dot to break.
The reason for the uneven absorption of coated paper is very complicated. Some people think that due to the influence of various factors in the coating process, the adhesive and other substances in the coated paper coating are unevenly distributed, which eventually leads to the absorption of ink by the coating. The unevenness; there are also views that the coating thickness affects the ink absorption. At present, the international papermaking industry is still deeply studying this topic.
Third, the identification of BACK TRAP stains In the printing, if there is a printing color class, how to determine its cause? For the several stains mentioned at the beginning of this article, the stains caused by excessive dampening solution and reversed overprinting are well-known and have accumulated rich experience in dealing with such problems. For BACK TRAP stains and wet repellent colors Because of its many similarities in macroscopic performance, speckles are not well distinguished. However, they still have some differences in the following aspects. Due to the fact that many domestic four-color offset presses are used for printing, we will discuss the KMCY color sequence of four-color machines below.
1. The appearance of the BACK TRAP stain on the surface form is macroscopic and usually appears on a single page with a large area of ​​color, but no obvious difference is observed on the microscopic site pattern.
For wet-repellent stains, the reason for this is that the fountain solution of the previous color hinders the transfer of the ink of the next color. Therefore, when wet repulsion occurs, not only macroscopic large-area flowers but also microscopic appearances appear on the printed samples. Looking at outlets is usually incomplete, as shown in Figure 4.
2, the order of appearance of stains due to the BACK TRAP stain is the paper surface of the ink is stripped by the subsequent color group blanket caused by, so from the first color to the penultimate color may occur, that is, K, M, C BLACK TRAP spots appear to be unhelpful. If black spots appear on the black screen during the actual printing process, you should pay special attention to whether it is a BACK TRAP spot. However, because of the final printing of yellow, BACK TRAP spots cannot occur.
For wet repellency, its appearance is ...C. Y three colors appear, and the first color K side can not appear wet repulsion.
3. Occurrence area Any area on the paper that has been transferred to the text, except for the dots that are superimposed on the sequence ink, the rest of the mesh may be affected by BACK TRAP. As long as there is a large degree of non-uniform absorption of the ink by the coating, BACK TRAP spots may appear.
For wet repulsion, it can only occur in the space of the previous color. The magenta stain due to wet repellency is the area on the black plate with fountain solution. If superimposed on the previous solid, no wet repellent stains will appear. (To be continued)
In the case of coated papers, since most of the coated papers are now coated with multiple coats and subjected to super light treatment, ultra-fine calcium carbonate and china clay are used as pigments in paints, and synthetic latexes are used as adhesives, so coatings are compared. Closed, which leads to slower penetration of the binder in the coating after printing, a large number of pigment particles and binders are regulated on the surface of the paper. A closer coating on the surface of the paper can, of course, produce a higher gloss of printing, but on the other hand, when the paper enters the latter color group from the former color group, BACK TRAP will inevitably occur in a large area. In addition, because the coated paper surface is smooth and the blanket is in uniform contact with the paper surface, the BACK TRAP phenomenon may occur in the subsequent color group in any multi-color printing.
Why do some coated papers produce uneven BACK TRAP, which in turn causes BACK TRAP pigmentation? This is because the root cause of the BACK TRAP stain is the uneven absorption of the coated paper. If the coating absorbs the ink evenly, then the blanket will peel off the ink on the paper very evenly and will not have any adverse effect on the effect of the print screen, thus printing a perfect print. However, if the coating absorbs ink unevenly, it will result in uneven ink drying speed on the paper surface. When entering the follow-up color group, the ink is peeled off by the blanket in the slow-drying area more than in the fast-drying area. This difference in quantity may be due to a stripping action, or it may be due to multiple stripping effects. When the difference in the amount of peeling was so large that it could be observed by the human eye, there was a case where the printing color was different, that is, the BACK TRAP color was generated. In the area where the BACK TRAP pigmentation occurs, lighter areas indicate poor paper absorption performance and darker areas indicate better paper absorption performance.
It should be noted that when using offset fast-drying inks, the amount of stripping of the ink on the surface of the blanket relative to the amount of ink remaining on the surface of the paper is relatively small, and these traces of ink transferred to the blanket have not yet been found to be printed. It has caused obvious effects. Practice has proved that it is impossible to judge the degree of BACK TRAP from the shape of the dot under normal printing conditions. Even in the presence of BACK TRAP stains, it is now macroscopic. At this time, even if the blanket has more or less stripping of the ink, the volume of ink remaining on the paper is still only a small part. There are no obvious differences in the shades of the different areas in the shape of the dots, but some of the more serious BACK TRAP spots may have different shades of dots. The reason why these dots can be kept intact is probably due to the fact that during the period when the paper entered the printing group from the last printing group, many contraceptives and pigment particles penetrated into the coating of the paper. Therefore, even if it is strongly affected by the blanket, it is impossible for the dot to break.
The reason for the uneven absorption of coated paper is very complicated. Some people think that due to the influence of various factors in the coating process, the adhesive and other substances in the coated paper coating are unevenly distributed, which eventually leads to the absorption of ink by the coating. The unevenness; there are also views that the coating thickness affects the ink absorption. At present, the international papermaking industry is still deeply studying this topic.
Third, the identification of BACK TRAP stains In the printing, if there is a printing color class, how to determine its cause? For the several stains mentioned at the beginning of this article, the stains caused by excessive dampening solution and reversed overprinting are well-known and have accumulated rich experience in dealing with such problems. For BACK TRAP stains and wet repellent colors Because of its many similarities in macroscopic performance, speckles are not well distinguished. However, they still have some differences in the following aspects. Due to the fact that many domestic four-color offset presses are used for printing, we will discuss the KMCY color sequence of four-color machines below.
1. The appearance of the BACK TRAP stain on the surface form is macroscopic and usually appears on a single page with a large area of ​​color, but no obvious difference is observed on the microscopic site pattern.
For wet-repellent stains, the reason for this is that the fountain solution of the previous color hinders the transfer of the ink of the next color. Therefore, when wet repulsion occurs, not only macroscopic large-area flowers but also microscopic appearances appear on the printed samples. Looking at outlets is usually incomplete, as shown in Figure 4.
2, the order of appearance of stains due to the BACK TRAP stain is the paper surface of the ink is stripped by the subsequent color group blanket caused by, so from the first color to the penultimate color may occur, that is, K, M, C BLACK TRAP spots appear to be unhelpful. If black spots appear on the black screen during the actual printing process, you should pay special attention to whether it is a BACK TRAP spot. However, because of the final printing of yellow, BACK TRAP spots cannot occur.
For wet repellency, its appearance is ...C. Y three colors appear, and the first color K side can not appear wet repulsion.
3. Occurrence area Any area on the paper that has been transferred to the text, except for the dots that are superimposed on the sequence ink, the rest of the mesh may be affected by BACK TRAP. As long as there is a large degree of non-uniform absorption of the ink by the coating, BACK TRAP spots may appear.
For wet repulsion, it can only occur in the space of the previous color. The magenta stain due to wet repellency is the area on the black plate with fountain solution. If superimposed on the previous solid, no wet repellent stains will appear. (To be continued)