The printing process is an extremely complicated process. In this process, with the transfer of ink, various problems often occur. These problems are closely related to the quality of the printed matter. In multi-color printing, if the overprint of each color ink is not controlled well, it will cause the color of the printed matter to change, thereby causing the quality problem of the printed matter. Therefore, we must analyze and study the overprinting of ink.
In actual printing production, the biggest printing defect caused by poor overprinting is exposed white. According to practical experience, the main causes of multi-color overprinting in color image printing are ink viscosity, printing pressure, printing speed, paper surface strength, printing interval time, etc. Any of these factors are not well controlled, which will affect the final color printed matter. The printing quality is very easy to cause dew failure. This article is based on the above factors that affect the effect of overprinting, to study and discuss the law of multicolor overprinting in color printing. In order to achieve the above purpose, this article focuses on performing overprinting experiments from factors that affect the effect of overprinting, such as changing ink viscosity, printing pressure and printing speed, and analyzes the relationship between the experimental results and overprinting whiteness, and at the same time analyzes other factors that cause printing whitening, such as paper surface performance , Overprint time interval, printing color sequence, etc., and finally get the rule of multi-color overprint in color printing.
1. The effect of ink viscosity on overprinting
1. Ink viscosity
It has a great influence on the effect of wet overprinting. The viscosity of the ink is large, and the ink layer shows a large cohesion. If the viscosity of the first printing ink is lower than the viscosity of the post-printing ink, the post-printing ink will rely on its own cohesion to change the ink of the first printing Sticking away, resulting in "reverse overprinting" causing color mixing. Therefore, it is very important to control the viscosity.
2. Experiment of the effect of ink viscosity on overprinting effect
Experimental equipment: S-1000 water-based four-color printing slotting machine produced by Changsheng Industry Co., Ltd., 4 # viscosity test cup
Experimental agent: thickener, thinner, leveling agent
Experimental steps: â‘ Overprint black on blue, the viscosity of blue ink is 11.3s, the viscosity of black ink is 13s, the initial printing speed is 40 rpm, the printing pressure is 3.6mm, and the substrate used is white Cardboard B-type corrugated paper, under this printing condition, the initial whiteness is 10%.
â‘¡ Change the viscosity of the black ink, keep the other initial conditions unchanged for printing, observe the dew and record the data.
â‘¢ Through the experimental data in the table, draw a graph of the relationship between ink viscosity and overprint.
Second, the impact of printing pressure on overprinting
1. Printing pressure
The printing process is, in a sense, a process to resolve the contradiction between ink and paper. To transfer the ink on the printing plate to the substrate, a certain force must be applied, the so-called printing pressure. It has an important role in printing.
Printing pressure control is not easy. If the printing pressure is too large or too small, it will lead to a reduction in print quality. Especially when the pressure is too great, it brings more disadvantages. It often causes graphic distortion, local accumulation of ink, paper roughening, expanded dots on the imprint, and unclear printed product levels. On the contrary, if the printing pressure is too small, it will also cause many failures such as incomplete transfer of printed graphics, inaccurate dots, and more obvious defect exposure. Therefore, in the printing process, it is very critical to control the printing pressure in a more appropriate range.
2. Experiment of the influence of printing pressure on overprinting
Experimental equipment: S-1000 water-based four-color printing slotting machine produced by Changsheng Industrial Co., Ltd.
Experimental steps: â‘ Overprint black on blue, the viscosity of blue ink is 11.3s, the viscosity of black ink is 13s, the initial printing speed is 40 rpm, the printing pressure is 3.6mm, and the substrate used is white Cardboard B-type corrugated paper, under this printing condition, the initial whiteness is 10%.
â‘¡ Change the printing pressure, keep other initial conditions unchanged for printing, observe the dew and record the data.
â‘¢ Through the experimental data in the table, plot the relationship between printing pressure and overprint. [next]
3. The effect of printing speed on overprinting
1. Printing speed
From the point of view of the performance of the printing press, the printing speed can be easily adjusted within a relatively large range, but the printing pressure cannot automatically follow the change according to a certain functional relationship with the speed change. Therefore, in actual production, it is always used to fix the printing pressure first, and then adjust the amount of ink to adapt to the change of printing speed. Studying the effect of printing speed on ink transfer has certain guiding significance for the adjustment of water ink volume, printing speed, printing pressure, etc. in production.
2. Experiment of the effect of printing speed on overprinting
Experimental equipment: S-1000 water-based four-color printing slotting machine, stopwatch produced by Changsheng Industrial Co., Ltd.
Experimental steps: â‘ Overprint black on blue, the viscosity of blue ink is 11.3s, the viscosity of black ink is 13s, the initial printing speed is 40 rpm, the printing pressure is 3.6mm, and the substrate used is white Cardboard B-type corrugated paper, under this printing condition, the initial whiteness is 10%.
â‘¡ Change the printing speed, keep other initial conditions unchanged, print, observe the dew and record the data.
â‘¢ Through the experimental data in Table 3, plot the relationship between printing speed and overprint.
4. Analysis of other factors
1. Ink film thickness and color sequence
As the density of the ink film increases, the thickness of the ink film also gradually increases, and printing is performed in the order in which the thickness of the ink film increases in sequence, and the overprint effect is the best. The final printing of the ink with high brightness can make the whole picture bright and bright; and the density is the lowest, as the ink with thicker color for the outline of the picture should be printed afterwards. Multi-color printing adopts the cyan → product → yellow color sequence that gradually increases the thickness of the ink film, which is beneficial to improve the overprint effect of multi-color printed products.
2. Overprint time interval
When two-color overprinting is required, the first printed color must have a certain drying time, otherwise, the next color printing will cause sticking, dot expansion and other failures. Therefore, dry overprinting should control the time interval of overprinting. If the time interval is too long, the first printing color is dried quickly, and then the printing color has not begun to overprint, then the post-printing ink cannot be attached to the pre-printing ink, forming ink spots; If the time interval is too short, overprinting after printing is too late to dry, the dry overprinting of the ink cannot be completed well.
3. Paper surface properties
â‘ Ink absorption of paper. The ink absorption of paper is the performance of fiber properties, reflecting the interweaving conditions between fibers, the nature and content of fillers and gums, etc. Its essence is the capillary adsorption of pores between fibers to the ink binder. The absorption of ink by paper is related to the pressure of the printing machine, the length of the printing time, the viscosity of the ink, and the structure of the paper itself. Paper with a lot of lignin has high ink absorption, such as newsprint with less filler and glue, good ink absorption, and easy to adjust the pressure, which can appropriately reduce the pressure, which can increase the printing plate's durability. However, if the paper is too slack and the fiber gap is too large, a "brushing" phenomenon will occur when the ink viscosity is large; if the ink viscosity is low, the binder will quickly penetrate into the paper fibers, resulting in a "through-printing" phenomenon. Therefore, it is necessary to properly adjust the viscosity of the ink to avoid the ink from falling off the surface after the ink binder penetrates, which will cause the product to lose its gloss and affect the printing quality.
â‘¡Elastoplasticity and smoothness of paper. The elasticity of the paper refers to the degree to which the paper can recover after the printing pressure disappears. The plasticity of the paper refers to the degree of deformation caused by the printing pressure. The elasticity of the paper affects the ink absorption performance; the paper has good plastic properties to ensure the elasticity of the paper, which directly affects the printing pressure and the amount of ink supply. Depending on the nature of the paper, different operations should be applied. The printing pressure of paper with higher elasticity should be higher, and the ink supply can be smaller; on the contrary, the printing pressure of paper with lower elasticity should be lower, and the ink supply can be increased. The smoothness of the paper has a great influence on the overprinting effect. The smoothness is high. The graphics and text of the layout after overprinting can be well expressed, especially the small dots can be restored well when the dots are overprinted. The paper with low smoothness is due to the surface of the paper. Trapped, it is easy to make the dot printing unclear, and the level of the printing plate is not clear.
V. Conclusion
In summary, there are many and complex factors that affect the overprinting effect of color printing. Any poor control of the factors will affect the quality of the final printing. Based on the above discussion and experiments, we have summarized the following multi-color overprinting rules for color printing:
â‘ The viscosity of the ink should be reduced in sequence, and the difference between the viscosity of the two stacked inks is generally 4s. â‘¡According to the difference of the viscosity of the ink and the surface properties of the paper, the printing speed should be mastered reasonably. Generally, it should be controlled at 80-120 rpm. â‘¢ Control the printing pressure according to the viscosity of the ink and the different surface properties of the paper. If the ink and the selected paper are better, the printing pressure should be increased without affecting the expansion of the dot.
Dining chair is a common seat in restaurants, bars, cafes and other places for people to use when dining. According to different design styles, materials, functions and uses, dining chairs can be divided into a variety of categories. The following will be a brief introduction to the product classification of dining chairs.
First, according to the design style classification
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Second, according to the material classification
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Third, according to the use of classification
Generally, it can be divided into two uses: domestic and commercial.
1. Home dining chair: Home dining chair pays attention to comfort and beauty, common dining table chair, folding chair and bar chair.
2. Commercial dining chairs: Commercial dining chairs pay attention to durability and practicality, common bar chairs, cafe chairs and fast food restaurant chairs.
In general: dining chair as one of the important furniture in restaurants, bars, cafes and other places, according to the design style, material and use of different, can be divided into a variety of categories. Choosing a dining chair that suits your place and needs can enhance the comfort and beauty of the dining environment.
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