Paper is the most important substrate for printing. The quality of paper directly affects the quality of printed matter. There are big differences in gloss, surface strength, whiteness, absorbency, smoothness, and stretchability of different paper surfaces. Even if the printing conditions are the same, the same ink will be printed on different papers. Produces different color effects. The surface properties of the paper directly represent the tone level and color of the image, and determine the positive data of the plateau and color. Therefore, in actual operation, the printing characteristics of the paper should be fully grasped, and the printing parameters should be determined according to the performance of the paper to improve the quality of the printed matter.
Determine the number of screen lines based on paper performance
The number of commonly used screen lines is 80, 100, 120, 133, 150, 175, 200, 300lpi, etc. In actual selection, paper performance is an important factor. The surface properties such as the smoothness and roughness of the paper determine that they have different requirements for the number of screen lines.
Coated paper or high-grade calendered white paperboard has high surface smoothness and can reproduce finer dots, so the number of screen lines is higher, generally can be set to 175 ~ 300lpi;
The surface of the offset paper is thicker than the coated paper, and the number of screen lines can be between 120 and 150 lpi;
The surface of the newsprint is rougher. Too small dots will form broken edges or fall completely in the recessed area. Therefore, larger dot printing should be used, and the number of screens can be between 80 and 33 lpi.
Determine black/white field based on paper performance
In the highlight of the printed image, generally 3% to 5% of the highlight area is not printed, that is, the highlight portion of the printed matter is formed by the color of the paper. If the whiteness of the paper is different, it will affect the color brightness and saturation of the main bright spot of the picture, which will affect the color contrast of the picture. Similarly, the texture of the paper is also very relevant. The newsprint is a porous material, the ink is easily absorbed by the fiber, causing a high degree of light scattering on the printed surface, reducing the printing density, black is not black, and the smooth, coated Paper, the ink is absorbed on the surface, and the light is scattered very little, making the dark tone darker.
The printing gloss of newsprint is poor, which directly affects the drift of printing ink color; the surface whiteness is low, the printing contrast is small; the smoothness is low, and the ink diffusibility is strong, so that the number of good newsprint screens does not exceed 133lpi.
In view of these characteristics, the black/white field calibration value, the white field can be networked in a small area (C=0%, M=0%, Y=0%, K=0%), and the black field can be scaled to C=62. %, M=Y=56%, K=75%, and the total amount of ink overprint is also smaller, 250.
The surface of the coated paper has good smoothness, whiteness and light reflection ability. The ink printed on the coated paper has small diffusion, the dot shape is good, the dot enlargement rate can be controlled at about 15%; the color of the printed matter printed on the coated paper Good, good saturation, bright colors, can reflect better levels and contrasts. High light can print 2% of the dots, and the total number of dot-tone overlays can reach 340 or so. The number of screen lines can reach 200lpi or more, and the density contrast can reach 1.8.
Therefore, for coated paper, some manufacturers set the white field dot value to C=95%, M=Y=3%, which is the minimum number of dots that can be dried by the printing plate and the minimum number of dots printed on the printing paper. All have a relationship, the black field calibration is roughly C = 95%, M = Y = 85%, K = 75%.
It should be noted that if there is no white field point on the image, the paper color can be used as the reference point for adjusting the white field, and the paper can be reversely adjusted to less than 3% of the CMYK color dots.
Determine color separation parameters based on paper properties
First, the compensation sample of the dot increase is being set
When the ink is transferred to the surface of the paper under pressure, the ink diffuses to the periphery as it penetrates due to the absorption of the paper, resulting in an increase in dots and making the entire image darker. Obviously, different dot gain effects will be produced for different quality papers. The stronger the paper absorbency, the larger the dot gain value. Specifically, the newsprint is the largest and the coated paper is the smallest. The increase in the dot size formed by the paper properties generally exhibits an exponential expansion law. In the prepress process, it is necessary to compensate for the influence of the dot gain.
For different sizes of dots, the dot gain value is different. Generally, the high-adjustment and dark-adjusted dot gain values ​​are small, and the mid-tone dot gain value is large. It is generally recommended to use the default settings better, such as the default value of coated paper printing is about 17%, offset paper is about 22%, and newsprint is about 30%.
Second, choose the color separation type GCR, UCR
The use of GCR makes it easy to maintain gray balance, reduce the total amount of ink overprint, make the ink dry faster, and increase the printing speed. The quality of the black version plays a decisive role in the entire printing. For general manuscripts, GCR is recommended. Special originals, such as high-grade color, dark and rich images, can also use UCR. In short, we must be flexible.
Third, the total ink setting
The printing characteristics of the paper, as well as the high speed of the rotary printing, determine that the total ink volume cannot be too high.
Foreign data shows:
The total black quantity of newsprint printing is generally controlled at 240% to 260%;
The total ink volume of coated paper printing is generally controlled at 280% to 320%;
The total ink volume of offset paper printing is generally controlled at 300% to 340%.
The setting of this value is determined by each process and is completely dependent on the dot enlargement rate at the time of printing. If the network expansion is serious, the value needs to be reduced. Otherwise, the dark adjustment will be dead, and the dark shadow level will be seriously lost. If the network expansion is basically normal, the value can be appropriately increased to ensure that the dark color is full and full performance. Dark-tuning the regional level is conducive to the reproduction of the entire tone. In addition, you should choose the ink that suits your paper, depending on the paper.
Paper is the most important substrate for printing. The quality of paper directly affects the quality of printed matter. There are big differences in gloss, surface strength, whiteness, absorbency, smoothness, and stretchability of different paper surfaces. Even if the printing conditions are the same, the same ink will be printed on different papers. Produces different color effects. The surface properties of the paper directly represent the tone level and color of the image, and determine the positive data of the plateau and color. Therefore, in actual operation, the printing characteristics of the paper should be fully grasped, and the printing parameters should be determined according to the performance of the paper to improve the quality of the printed matter.
Determine the number of screen lines based on paper performance
The number of commonly used screen lines is 80, 100, 120, 133, 150, 175, 200, 300lpi, etc. In actual selection, paper performance is an important factor. The surface properties such as the smoothness and roughness of the paper determine that they have different requirements for the number of screen lines.
Coated paper or high-grade calendered white paperboard has high surface smoothness and can reproduce finer dots, so the number of screen lines is higher, generally can be set to 175 ~ 300lpi;
The surface of the offset paper is thicker than the coated paper, and the number of screen lines can be between 120 and 150 lpi;
The surface of the newsprint is rougher. Too small dots will form broken edges or fall completely in the recessed area. Therefore, larger dot printing should be used, and the number of screens can be between 80 and 33 lpi.
Determine black/white field based on paper performance
In the highlight of the printed image, generally 3% to 5% of the highlight area is not printed, that is, the highlight portion of the printed matter is formed by the color of the paper. If the whiteness of the paper is different, it will affect the color brightness and saturation of the main bright spot of the picture, which will affect the color contrast of the picture. Similarly, the texture of the paper is also very relevant. The newsprint is a porous material, the ink is easily absorbed by the fiber, causing a high degree of light scattering on the printed surface, reducing the printing density, black is not black, and the smooth, coated Paper, the ink is absorbed on the surface, and the light is scattered very little, making the dark tone darker.
The printing gloss of newsprint is poor, which directly affects the drift of printing ink color; the surface whiteness is low, the printing contrast is small; the smoothness is low, and the ink diffusibility is strong, so that the number of good newsprint screens does not exceed 133lpi.
In view of these characteristics, the black/white field calibration value, the white field can be networked in a small area (C=0%, M=0%, Y=0%, K=0%), and the black field can be scaled to C=62. %, M=Y=56%, K=75%, and the total amount of ink overprint is also smaller, 250.
The surface of the coated paper has good smoothness, whiteness and light reflection ability. The ink printed on the coated paper has small diffusion, the dot shape is good, the dot enlargement rate can be controlled at about 15%; the color of the printed matter printed on the coated paper Good, good saturation, bright colors, can reflect better levels and contrasts. High light can print 2% of the dots, and the total number of dot-tone overlays can reach 340 or so. The number of screen lines can reach 200lpi or more, and the density contrast can reach 1.8.
Therefore, for coated paper, some manufacturers set the white field dot value to C=95%, M=Y=3%, which is the minimum number of dots that can be dried by the printing plate and the minimum number of dots printed on the printing paper. All have a relationship, the black field calibration is roughly C = 95%, M = Y = 85%, K = 75%.
It should be noted that if there is no white field point on the image, the paper color can be used as the reference point for adjusting the white field, and the paper can be reversely adjusted to less than 3% of the CMYK color dots.
Determine color separation parameters based on paper properties
First, the compensation sample of the dot increase is being set
When the ink is transferred to the surface of the paper under pressure, the ink diffuses to the periphery as it penetrates due to the absorption of the paper, resulting in an increase in dots and making the entire image darker. Obviously, different dot gain effects will be produced for different quality papers. The stronger the paper absorbency, the larger the dot gain value. Specifically, the newsprint is the largest and the coated paper is the smallest. The increase in the dot size formed by the paper properties generally exhibits an exponential expansion law. In the prepress process, it is necessary to compensate for the influence of the dot gain.
For different sizes of dots, the dot gain value is different. Generally, the high-adjustment and dark-adjusted dot gain values ​​are small, and the mid-tone dot gain value is large. It is generally recommended to use the default settings better, such as the default value of coated paper printing is about 17%, offset paper is about 22%, and newsprint is about 30%.
Second, choose the color separation type GCR, UCR
The use of GCR makes it easy to maintain gray balance, reduce the total amount of ink overprint, make the ink dry faster, and increase the printing speed. The quality of the black version plays a decisive role in the entire printing. For general manuscripts, GCR is recommended. Special originals, such as high-grade color, dark and rich images, can also use UCR. In short, we must be flexible.
Third, the total ink setting
The printing characteristics of the paper, as well as the high speed of the rotary printing, determine that the total ink volume cannot be too high.
Foreign data shows:
The total black quantity of newsprint printing is generally controlled at 240% to 260%;
The total ink volume of coated paper printing is generally controlled at 280% to 320%;
The total ink volume of offset paper printing is generally controlled at 300% to 340%.
The setting of this value is determined by each process and is completely dependent on the dot enlargement rate at the time of printing. If the network expansion is serious, the value needs to be reduced. Otherwise, the dark adjustment will be dead, and the dark shadow level will be seriously lost. If the network expansion is basically normal, the value can be appropriately increased to ensure that the dark color is full and full performance. Dark-tuning the regional level is conducive to the reproduction of the entire tone. In addition, you should choose the ink that suits your paper, depending on the paper.
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