Color print images through the green, magenta, yellow three primary colors superimposed printing ink and show all kinds of colors, so that the original color image reproduction received. In reproduction, for a variety of technology and the impact of factors of production, printing color images can not be good to restore the original color. In order to be satisfied with the image quality printing, production must be in the printing of color images to detect, and by regulating certain variables to control the printing quality of color reproduction.
1, affecting the quality of color reproduction a major factor
By the printing press on reproduction, the impact of color copying images a number of factors, such as: network expansion, color printing sequence and Dieyin, ink hue and field density, temperature and viscosity of ink, water supply (Offset), paper nature, India Version of deep space, printing pressure.
1. Network expansion
In printing, the network expansion will occur, but the expansion of more than a certain range when a lot of quality problems. This network expansion will lower the contrast between the image and to change the whole image deep, dark-death outlets paste, copy dramatic changes in hue, when the printing of colored images outlets at the same time expanding, deepening the overall image. When only one color of a network expansion, will have a color cast copy images, such as: red version for network coverage expansion occurred in the transfer, 50 percent of the network into 55 percent, the reddish color printing images, a partial Rouse Red, a light neutral colors red, green change dirty. Printing ink pressure and density can affect the ground network expansion. Small changes in pressure will print the entire printing images produced significant changes; field ink density increases, expansion of networks to increase the image and dark-color have a great impact.
2. Color printing sequence and Dieyin
Color image printing, the ink is Yiseyise Dieyin, Dieyin will have adverse deviation color, blending and levels of disturbance. Color printing sequence with the color effect of Dieyin great. The multi-color printing presses, ink printing colored short time interval, after the color ink is printed Dieyin first printed color ink surface, a "wet stacked wet" in the printing status. China and India in Dieyin color of ink on paper than the surface layers of ink printed on the wet ink an advantage. Two colors of ink color as long as the reversal of the order, Dieyin colored hue, saturation and brightness may be different. Goods such as green and red ink Dieyin, the first after India Green and India magenta, Dieyinsepian green, magenta and India after the first printed blue, red Dieyinsepian. Dieyin in order to obtain good results, even after the color sequence scheduled reasonable arrangements for the colored ink viscosity.
3. Color ink density and field
Printing ink used in the production there are different degrees of Sepian so that the printed images produced color cast, as far as possible using less color of ink for color printing. Printing images on the ground decided to printing ink density image reproduction of the color bands to reconcile. The higher the density of the field, color reproduction order to reconcile the wide scope. Field density so that the image color saturation lower Dieyin color weakened.
4. Ink temperature and viscosity
Printed copy of the image, ink viscosity is a very important parameter. General printed using liquid ink, the loser in the device does not absorb ink Mexico and channeling Mexican institutions, through ink viscosity ink tank add to the amount of solvent control. Offset and the general Tuyin viscous ink, the ink viscosity great. In order to make ink evenly from the surface of paper printed version to the transfer, offset and Tuyin machine has absorbed Mexico and Mexican channeling devices. Ink in these devices pass between the roller and the fight absorbed in the process of being squeezed, shear and separation. Ink roller to overcome the friction within the power and make due to ink roller surface temperature increases, the transmission was beaten and absorbed in the process of being squeezed, shear and separation. Roller In order to overcome the friction within the ink to work and due to ink roller surface temperature increases, the transfer of ink viscosity declined. Ink-thinning, the roller surface contained less ink, paper delivered to the surface to reduce the volume of ink, printing images order to reconcile the change in color printing and undermines the image of consistency. Some research shows that: start up the printing presses after printing a color image deviation of 60 percent for ink roller temperature caused by the change.
5. Offset ink balance
Offset production direct impact on the balance of ink image reproduction quality. Small water from the dirty plates would, paste version; Ambassador water emulsion ink, printing images to reduce the color saturation.
Second, the printing color images of detection
Color printing images from the color yellow, magenta, blue ink by RGB different proportion of the composite form. Measuring general printing color images on the screen, instead of measuring the color, but measurement and printing images at the same time the quality control of the printing. Control of the print runs were generally placed in the trailer shoot at. Detection of measuring instruments used control of the corresponding color printing quality of information available, such as the primary color ink density in the field, Dieyin rate, the network expansion, network density, neutral gray reduction, contrast and other parameters to determine the color copying images order to reconcile the situation.
Measurement of printing color images at the three measurement methods, namely, density measurements and color measurement meters and the spectrophotometer measurements.
1. Density measurements
Density is the separation, platemaking and printing equipment in the main, this measurement is the printing industry has been the most commonly used in the form of an objective evaluation of the quality, density of cheap, widely used. Color density measured at the surface, can only be a primary color ink printing in the relative volume, it can not indicative of the measured color hue. Density measurements of various forms and not linked to color system, which can not be used colorful language description of the tested color. In color measurement and evaluation, the density of a certain limitations, it is not a standard color measuring instruments.
2. Color color measurement meters
Color meter is measured by the color of the surface was measured directly with the three colors stimulate the value of X, Y, Z proportional to the visual response, after conversion that measured color X, Y, Z values, these values can also be converted Other color space absorbed into the color parameters. Color is a subject with three broadband Lvse Pian density of the special. As their own devices and equipment in principle to a certain thickness of the error so that the color of the absolute accuracy of measurements bad. However, due to its cheaper price, is still widely used in color measurement instruments.
3. Spectrophotometer (spectrum spectrophotometer) color measurement
Spectrophotometer to measure the surface color of the visible spectrum wavelengths of light reflectivity. Will be visible spectrum of light to a certain distance (5 nm, 10nm, 20nm) irradiation color surface, and then measuring reflectance point by point. Various wavelengths of light reflectance value and the relationship between the depiction of the wavelength point will be measured by the color of the surface brightness curve. Spectrophotometric every one of the only express a color. Can also be measured values into other forms of color systems. Spectrophotometer is a flexible, the ideal color measurement instruments. At present, some foreign printing presses equipped with the Printing color quality testing of color measurement equipment is used spectrophotometer.
Third, control the quality of color printing method
Production of printing, paper, ink and printing plates, and other image quality constraints. When these factors have determined the circumstances, the printing press on the image copy production and how to control the quality of printing color images? »
1. According upper body production, printing pressure regulation
According to copy the image quality printing, paper thickness, plates and other printing conditions regulating the pressure so that the network get the best image reproduction.
2. Reasonable arrangements for color sequence
At present, the general use of multi-color printing ink, blue, magenta and yellow sequence or blue, magenta, yellow and black sequence. This color sequence so that accurate color reproduction more easily realized. Thick layers of ink are steeled, such as offset the use of black, blue, magenta and yellow sequence, the ink layer thickness are: Heimo to 0.8 ¦Ì m, green ink to 0.9 ¦Ì m, for a magenta ink. 0¦Ì m, yellow ink to 1.1 ¦Ì m; ink viscosity Youtaidaoxiao order, such as Heimo 1188 Pa, Green Mexico 488 Pa, magenta ink for the 477 Pa, yellow ink for the 147 Pa. Ink viscosity can not meet the requirements of order, the ink viscosity can be adjusted in advance.
3. Printer calibration
According to a Sample and established conditions for adjustment of the printing presses to print images and print runs were the same.
Fourth, the process of printing presses and color reproduction quality control
Printing process, the impact on the quality of the printed image a lot of variables, in order to compensate for these variables the adverse effects, such as more advanced printing press Heidelberg, Germany, and Japan's Mitsubishi Roland production such as the printing press adjust three major parameters: Inking The temperature devices, for Mexico and the volume of supply of water.
1. Inking temperature control device
Some of the printing press or can be equipped with matching Inking device temperature control devices. Mexico lost in the process of channeling ink roller both rotation and rocky ledge, thus increasing its maximum temperature, temperature control, generally in channeling ink rollers to the core-cooling water to reduce the temperature, the ink roller surface temperature remains stable , Thus ensuring the stability of Mexico for. In addition to channeling some printer ink roller, also Modou roll in the cooling water-cooling.
2. For control of Mexico
Printing ink image density of the ground surface size directly affect the quality of color reproduction, the field size of the ink for ink density of (the surface layers of ink printing images thickness) size impact. With the ink layer thickness of the field to increase density is increasing. To a certain point field density will not increase the thickness of the layers of ink on the increase. Images can be printed on the basis of the quality of information control to adjust volume for Mexico (ink layer thickness) size.
Mexico presses the current volume of automatic adjustment mainly includes two parts, Jimo struggle to roll the overall volume of ink and ink roller in the local area Mexican regulation. Mexican ensure that the overall regulation of the entire screen image printing order to reconcile the right color reproduction, because the printing images on the distribution of the entire layout different from the ink of the regional demand for different, so roll down the roll axis direction will be divided into several Modou Mexican small areas, different areas of Mexico sent the Mexican to meet the different images of the local area to the different needs of Mexico.
3. Water Control
Offset printed version of the size of water must be controlled. With the size of water should speed printing presses for Mexico differ by volume, to ensure that the balance of ink, printing images is not Fahua, color saturation, and not paste version. Adjust the size of water is by changing the speed roller Shuidou achieved.
V. Conclusion
To meet the color image printed copy quality requirements, the need for printing images to detect and control. Through the modern printing press ink temperature, for the Mexican volume of water supplied to the control of image quality to meet the printing requirements. |
