Discussion on the law of multicolor overprinting in color printing
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
The printing process is an extremely complicated process. In the process, various problems often occur with the transfer of ink. These problems are closely related to the quality of printed matter. In multi-color printing, if the overprinting of each color ink is not well controlled, the color of the printed matter will change, resulting in quality problems 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 white. According to practical experience, the main causes of multicolor overprinting in color image printing are ink viscosity, printing pressure, printing speed, surface strength of paper, printing interval, etc. Any one of the factors is not well controlled, which will affect the final color print. Printing quality, it is easy to cause whitening failure. This paper starts from the above factors affecting the overprinting effect, and studies and discusses the law of multicolor overprinting in color printing. In order to achieve the above objectives, this paper focuses on the overprinting experiment by changing the factors affecting the overprinting effect such as ink viscosity, printing pressure and printing speed, and analyzes the relationship between the experimental results and the overprinting whiteness, and analyzes other factors causing the printing whiteness, such as the surface properties of the paper. , overprinting time interval, printing color sequence, etc., finally get the law of multi-color overprinting in color printing.
First, the effect of ink viscosity on overprinting
1. Viscosity of the ink
It has a great influence on the wet overprinting effect. The viscosity of the ink is large, and the ink layer exhibits a large cohesive force. If the viscosity of the first printing ink is lower than the viscosity of the printing ink, the printing ink will rely on its own cohesive force to print the ink first. Sticking away, creating "reverse overprinting" causes color mixing. So controlling viscosity is crucial.
2. 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: tackifier, thinner, leveling agent
Experimental procedure: 1 Overprint black on blue, blue ink viscosity is 11.3s, black ink viscosity is 13s, initial printing speed is 40rpm/min, printing pressure is 3.6mm, and the substrate used is white paper. The paper-type B-type corrugated paper has an initial whiteness of 10% under the printing conditions.
2 Change the viscosity of the black ink, keep the other initial conditions unchanged, observe the whiteness, and record the data.
3 Through the experimental data in the table, draw a graph of ink viscosity and overprint relationship.
Second, the impact of printing pressure on overprinting
Printing pressure
The printing process, in a sense, is the process of solving the contradiction between ink and paper. To transfer the ink at the image on the plate to the substrate, a certain amount of force must be applied, the so-called printing pressure. It plays an important role in printing.
Control of printing pressure is not an easy task. If the printing pressure is too large or too small, the quality of the printed product will be reduced. In particular, if the pressure is too large, it will bring more disadvantages. It often causes distortion of graphics and text, local accumulation of ink, paper pulling, imprinting of dots, and unclear prints. On the contrary, when the printing pressure is too small, it will also cause many problems such as incomplete transfer of printed graphics, inaccurate dot and dot defects, and more obvious defects. Therefore, it is very important to control the printing pressure within a relatively appropriate range during the printing process.
2. The effect of printing pressure on overprinting
Experimental equipment: S-1000 water-based four-color printing slotting machine produced by Changsheng Industry Co., Ltd.
Experimental procedure: 1 Overprint black on blue, blue ink viscosity is 11.3s, black ink viscosity is 13s, initial printing speed is 40rpm/min, printing pressure is 3.6mm, and the substrate used is white paper. The paper-type B-type corrugated paper has an initial whiteness of 10% under the printing conditions.
2 Change the printing pressure, keep the other initial conditions unchanged, print the film, observe the whitening situation, and record the data.
3 Through the experimental data in the table, draw a graph of printing pressure and overprint relationship.
Article keyword search: color printing overprint
Third, the impact of printing speed on overprinting
Printing speed
From the performance of the printing press, the printing speed can be easily adjusted within a large range, and the printing pressure cannot automatically follow the change according to a function relationship with the change of the speed. Therefore, in actual production, it is always customary to fix the printing pressure first, and then adjust the amount of ink to adapt to changes in printing speed. Studying the influence of printing speed on ink transfer has certain guiding significance for the adjustment of ink quantity, printing speed and printing pressure in production.
2. The effect of printing speed on overprinting
Experimental equipment: S-1000 water-based four-color printing slotting machine and stopwatch produced by Changsheng Industry Co., Ltd.
Experimental procedure: 1 Overprint black on blue, blue ink viscosity is 11.3s, black ink viscosity is 13s, initial printing speed is 40rpm/min, printing pressure is 3.6mm, and the substrate used is white paper. The paper-type B-type corrugated paper has an initial whiteness of 10% under the printing conditions.
2 Change the printing speed, keep the other initial conditions unchanged, observe the whiteness, and record the data.
3 Through the experimental data in Table 3, draw a graph of printing speed and overprint relationship.
Fourth, 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 the printing is performed in the order in which the thickness of the ink film is sequentially increased, and the overprinting effect is the best. The final printing of the ink with high brightness can make the whole picture bright and bright; the lowest concentration, as the ink with thicker outline of the picture, should be printed later. Multi-color printing adopts the color sequence of green→product→yellow which gradually increases the thickness of the ink film, which is advantageous for improving the overprinting effect of multi-color prints.
2. Overprint time interval
When the two-color overprinting is performed, the color to be printed first is required to have a certain drying time, otherwise, the printing of the next color may cause problems such as sticking and dot enlargement. Therefore, the dry overprinting should control the time interval of the overprinting. If the time interval is too long, the first printing color is quickly dried, and the back printing color has not started to be overprinted, then the back printing ink cannot adhere to the first printing ink to form an ink spot; If the time interval is too short, the ink is overprinted and the ink is overprinted, and the dry overprint of the ink cannot be completed well.
3. Surface properties of paper
1 The ink absorbency of the paper. The ink absorbing property of paper is the expression of fiber properties, which is a reflection of the interweaving condition between fibers, the nature and content of fillers and rubber compounds, and the essence is the capillary adsorption of the pores between fibers to the ink binder. The absorption of ink by the paper is related to the pressure of the printing machine, the length of the embossing time, the viscosity of the ink, and the structure of the paper itself. The paper containing lignin has a large ink absorption property, such as a filler for newsprint, a small amount of rubber, good ink absorption, easy adjustment of pressure, and appropriate pressure reduction, thereby increasing the printing durability of the printing plate. However, if the paper is too slack, the fiber gap is too large, when the viscosity of the ink is large, the phenomenon of "pulling" will occur; if the viscosity of the ink is small, the binder will quickly penetrate into the paper fibers, resulting in a "print-through" phenomenon. Therefore, it is necessary to appropriately adjust the viscosity of the ink to prevent the surface ink from falling off after the ink binder is infiltrated, thereby causing the product to lose its luster and affecting the printing quality.
2 Paper elastoplasticity and smoothness. Paper elasticity refers to the extent to which paper can be recovered after printing pressure has disappeared. The plasticity of the paper refers to the degree of deformation produced 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. Different operations should be applied depending on the nature of the paper. The paper with a slightly larger elasticity should have a larger printing pressure, and the ink supply amount can be smaller; on the contrary, the printing pressure of the paper with less elasticity should be smaller, and the ink supply amount can be increased. The smoothness of the paper has a great influence on the overprinting effect, and the smoothness is high. The image of the post-stacked layout can be well performed, especially when the dot is overprinted, the small dots can be well restored, and the paper with low smoothness is present due to the surface of the paper. It is easy to make the dot printing unclear, and the layout of the printing plate is not clear.
V. Conclusion
In summary, the factors affecting the effect of color printing overprinting are more and more complicated, and the poor control of any one factor will affect the quality of the final printing. Based on the above discussion and experiments, we have summarized the following color printing multicolor overprinting rules:
1 The ink viscosity should be reduced in turn, and the viscosity of the two-phase stack ink is generally 4 s. 2 According to the viscosity of the ink and the surface properties of the paper, the printing speed is reasonably mastered. Generally should be controlled at 80-120 rev / min as well. 3 According to the viscosity of the ink and the different surface properties of the paper, the printing pressure is controlled, and the printing pressure should be made larger when the ink and the selected paper are better without affecting the expansion of the dot.