In the past decade or so, the printing of newspapers in China has developed extremely rapidly. From 1998 to 1993, during the five years of public use, nearly 1,800 newspapers from all provinces, cities, and counties nationwide eliminated outdated and polluted lead discharge operations and realized offset offset printing.
In 1994, China began to issue color newspapers. In 1996, there were about 50 kinds of color newspapers in the country. By the end of 1998, it had soared to about 400 types. In the past two years, high-quality color newspapers printed with coated paper also have a certain number of listings. Industry insiders predict that in the next few years, the circulation of color newspapers will continue to increase, and there will be higher requirements for the printing quality of color newspapers.
The color newspaper is formed by printing an Y (yellow) M (magenta) C (cyan) K (black) four-color ink on an offset printing press. Compared with black-and-white newspapers, the effect of color reproduction is the most important indicator for evaluating the printing quality of color newspapers. Therefore, to improve the printing quality of color newspapers, in addition to focusing on the prepress processing, printing equipment, paper, ink and many other aspects, but also must be based on the nature of printing presses, paper, ink, and reasonable choice of printing color sequence.
1. Color Printing Sequence of General Color Offset Printing Products The so-called general color offset printing products refer to single-color or multi-color offset printing presses.
A single-color offset press can only print one type of ink on the substrate at one time of delivery and delivery (ie, a printing process). Therefore, if a monochrome offset press prints a color print, the second, third, and fourth colors must be printed after the first color is printed. The interval between printing inks is relatively long, ranging from a few hours to long hours to tens of hours. The first printing ink is fixed on the paper, and when it is nearly dried, the ink of the latter color is printed and adhered thereon, which is a characteristic of the transfer of the multi-color printing ink. Since the ink is overprinted with the latter color of wet ink imprinted on the previous color of dry ink, this type of overprinting is referred to as work printing. In the case of overprinting, the adhesiveness of the previous color ink is greater than the adhesiveness of the latter color, the color ink of the latter color adheres well to the ink film of the previous color ink, and the overprinting effect is good; conversely, if the adhesiveness of the latter color ink is greater than The adhesiveness of the previous color ink, the latter color ink not only cannot adhere well to the ink film of the previous color ink, but also sticks away part or all of the previous color ink film, and the overprint effect is naturally not good, even can not achieve. It can be seen that the adhesion of the ink is critical to the overprinting of the ink.
The drying method used for the printing ink used in sheet-fed offset printing is mainly oxidative polymerization, and the penetration is secondary. In the drying process of the ink, the adhesiveness of the ink will also change, first it will rise, reach a certain maximum value and then will drop, and when the ink is completely dry, the formed ink film will lose its adhesiveness. According to the above-mentioned law of ink adhesiveness changing with drying time, as long as the time interval for ink printing is mastered, when the ink of the previous color sticks with a large amount of ink after printing, a good overprint effect can be obtained. Due to the long time required for the offset ink to dry completely, reverse overprinting or crystallization failure of the ink generally does not occur. Therefore, the single color offset press is more flexible in the selection of the color sequence for printing, and the color sequence during printing is usually selected from the aspects of overprint accuracy, ease of operation, and printing cost. For example, considering that the deformation of the paper during the printing process will gradually become stable, you can print yellow ink with a low requirement for overlay accuracy, or print ink with a smaller area on the first image, so that the printing sequence can be arranged. The purpose of reducing the degree of inaccuracy of the ink after printing is also reduced. For example, if the printing color sequence is arranged from light to dark, it is easier to replace the ink and the operation is more convenient; and the inexpensive opaque chrome yellow ink is placed first Color printing can reduce printing costs.
When printing with a multicolor adhesive machine, two or more colors of ink can be printed on the substrate during a single printing and delivery process. If a four-color offset press is used, the input paper feeding mechanism is a white paper, and the output from the delivery mechanism is a color print. When using a multi-color offset printing machine, the printing interval between colors is very short. The first printing ink has just been printed for a fraction of a second, and then the ink of the same color is overprinted. Therefore, the ink transfer feature is that the ink of the previous color is not used yet. When it is too dry, the ink of the next color is overprinted. Since the overprinting of the ink is such that the latter wet ink is imprinted on the previous color ink, this overprinting method is called wet printing. Since the wet printing is always performed in the wet and wet manner at the moment of overprinting, the adhesiveness of the previous color ink does not increase with the drying time. In order for the overprinting to proceed normally, the adhesiveness of the colored inks must be The order from front to back in the printing unit gradually decreases.
When printing with a multicolor offset press, the ink overlay rate is lower than when using a monochrome offset press, because in the dry printing, the post-printing ink is transferred to the pre-printed ink that has been fixed and gradually dried. After the ink is printed, it splits from the middle of the ink film to a part of the ink film, and part of the ink remains on the surface of the printing plate. However, wet printing is not the case. The latter color ink is generally split between the ink films of the two color inks. A small part of the ink is transferred to the wet ink film of the previous color, most of which remains on the printing plate, and the wet printing. From the position where the ink film is split, the thickness of the ink film increases in order from the front to the back of the printing unit, which is favorable for the overprinting of the wet printing ink.
The density of the ink has a certain relationship with the degree of the ink film. Generally, as the value of the ink density increases, the thickness of the ink film also gradually increases. China's printing industry standard CY/T5-99 stipulates that the field density range of fine prints (generally coated with coated paper) is 0.85-1.10 for yellow, 1.25-1.5 for magenta, 1.30-1.55 for cyan and 1.40-1.75 for black . If all are calculated according to the upper limit of the standard range, the experimental results show that when the density of the yellow ink is 1.10, the thickness of the ink film is about 1.43m, when the magenta ink density is 1.50, the ink film thickness is about 0.96m, and the ink density is 1.55. The film thickness was 0.82 m, and the ink film thickness was 0.75 m when the black ink density was 1.75. (To be continued)
In 1994, China began to issue color newspapers. In 1996, there were about 50 kinds of color newspapers in the country. By the end of 1998, it had soared to about 400 types. In the past two years, high-quality color newspapers printed with coated paper also have a certain number of listings. Industry insiders predict that in the next few years, the circulation of color newspapers will continue to increase, and there will be higher requirements for the printing quality of color newspapers.
The color newspaper is formed by printing an Y (yellow) M (magenta) C (cyan) K (black) four-color ink on an offset printing press. Compared with black-and-white newspapers, the effect of color reproduction is the most important indicator for evaluating the printing quality of color newspapers. Therefore, to improve the printing quality of color newspapers, in addition to focusing on the prepress processing, printing equipment, paper, ink and many other aspects, but also must be based on the nature of printing presses, paper, ink, and reasonable choice of printing color sequence.
1. Color Printing Sequence of General Color Offset Printing Products The so-called general color offset printing products refer to single-color or multi-color offset printing presses.
A single-color offset press can only print one type of ink on the substrate at one time of delivery and delivery (ie, a printing process). Therefore, if a monochrome offset press prints a color print, the second, third, and fourth colors must be printed after the first color is printed. The interval between printing inks is relatively long, ranging from a few hours to long hours to tens of hours. The first printing ink is fixed on the paper, and when it is nearly dried, the ink of the latter color is printed and adhered thereon, which is a characteristic of the transfer of the multi-color printing ink. Since the ink is overprinted with the latter color of wet ink imprinted on the previous color of dry ink, this type of overprinting is referred to as work printing. In the case of overprinting, the adhesiveness of the previous color ink is greater than the adhesiveness of the latter color, the color ink of the latter color adheres well to the ink film of the previous color ink, and the overprinting effect is good; conversely, if the adhesiveness of the latter color ink is greater than The adhesiveness of the previous color ink, the latter color ink not only cannot adhere well to the ink film of the previous color ink, but also sticks away part or all of the previous color ink film, and the overprint effect is naturally not good, even can not achieve. It can be seen that the adhesion of the ink is critical to the overprinting of the ink.
The drying method used for the printing ink used in sheet-fed offset printing is mainly oxidative polymerization, and the penetration is secondary. In the drying process of the ink, the adhesiveness of the ink will also change, first it will rise, reach a certain maximum value and then will drop, and when the ink is completely dry, the formed ink film will lose its adhesiveness. According to the above-mentioned law of ink adhesiveness changing with drying time, as long as the time interval for ink printing is mastered, when the ink of the previous color sticks with a large amount of ink after printing, a good overprint effect can be obtained. Due to the long time required for the offset ink to dry completely, reverse overprinting or crystallization failure of the ink generally does not occur. Therefore, the single color offset press is more flexible in the selection of the color sequence for printing, and the color sequence during printing is usually selected from the aspects of overprint accuracy, ease of operation, and printing cost. For example, considering that the deformation of the paper during the printing process will gradually become stable, you can print yellow ink with a low requirement for overlay accuracy, or print ink with a smaller area on the first image, so that the printing sequence can be arranged. The purpose of reducing the degree of inaccuracy of the ink after printing is also reduced. For example, if the printing color sequence is arranged from light to dark, it is easier to replace the ink and the operation is more convenient; and the inexpensive opaque chrome yellow ink is placed first Color printing can reduce printing costs.
When printing with a multicolor adhesive machine, two or more colors of ink can be printed on the substrate during a single printing and delivery process. If a four-color offset press is used, the input paper feeding mechanism is a white paper, and the output from the delivery mechanism is a color print. When using a multi-color offset printing machine, the printing interval between colors is very short. The first printing ink has just been printed for a fraction of a second, and then the ink of the same color is overprinted. Therefore, the ink transfer feature is that the ink of the previous color is not used yet. When it is too dry, the ink of the next color is overprinted. Since the overprinting of the ink is such that the latter wet ink is imprinted on the previous color ink, this overprinting method is called wet printing. Since the wet printing is always performed in the wet and wet manner at the moment of overprinting, the adhesiveness of the previous color ink does not increase with the drying time. In order for the overprinting to proceed normally, the adhesiveness of the colored inks must be The order from front to back in the printing unit gradually decreases.
When printing with a multicolor offset press, the ink overlay rate is lower than when using a monochrome offset press, because in the dry printing, the post-printing ink is transferred to the pre-printed ink that has been fixed and gradually dried. After the ink is printed, it splits from the middle of the ink film to a part of the ink film, and part of the ink remains on the surface of the printing plate. However, wet printing is not the case. The latter color ink is generally split between the ink films of the two color inks. A small part of the ink is transferred to the wet ink film of the previous color, most of which remains on the printing plate, and the wet printing. From the position where the ink film is split, the thickness of the ink film increases in order from the front to the back of the printing unit, which is favorable for the overprinting of the wet printing ink.
The density of the ink has a certain relationship with the degree of the ink film. Generally, as the value of the ink density increases, the thickness of the ink film also gradually increases. China's printing industry standard CY/T5-99 stipulates that the field density range of fine prints (generally coated with coated paper) is 0.85-1.10 for yellow, 1.25-1.5 for magenta, 1.30-1.55 for cyan and 1.40-1.75 for black . If all are calculated according to the upper limit of the standard range, the experimental results show that when the density of the yellow ink is 1.10, the thickness of the ink film is about 1.43m, when the magenta ink density is 1.50, the ink film thickness is about 0.96m, and the ink density is 1.55. The film thickness was 0.82 m, and the ink film thickness was 0.75 m when the black ink density was 1.75. (To be continued)
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