However, the screen printing of such color blocks is increasingly unable to meet the demand for the fine screen printing market, especially the demand for the halftone screen printing market.
Because halftone screen printing can be used in many fields, such as advertising paintings, textile printing, T-shirts, ceramic glass printing, ceramic decal printing, CD printing, and the like. Half-tone screen printing can even be used in unexpected areas such as surface decoration of aerospace, aerospace and electrical products.
In recent years, the screen printing industry has generated a great interest in performing color halftone reproduction on different substrates. The ability of screen printing to perform color reproduction on substrates of different shapes and materials has been recognized by many graphic designers, advertising manufacturers, packaging and decorators, and printers, and has received more and more attention. Its market is very competitive. force.
At present, in China, halftone screen printing technology can be used not only for small-format screen printing, but also for half-tone screen printing of large-scale outdoor advertising, showing screen printing-specific functions, such as: for printing bus stop cards and The screen printing of subway advertisements and outdoor advertisements has gradually become popular, and the application field is expanding. As a result, half-tone screen printing is also attracting textiles, plastics, glass, metal printers, and large-scale advertising and decoration companies. They have conducted research and explorations in terms of process, technology and materials. There are also many fine-printing half-tone printing products available.
However, it is not easy to grasp the process of halftone screen printing. Because when you look deep into the halftone screen printing process, you will find that the process itself is much more complicated than expected. There are many variables in the overall halftone screen printing process, and each variable factor affects the quality of the final screen printing product.
Halftone screen printing should consider the question: In short, what is the final product? What is printed on the substrate? What kind of ink is used? How many colors should be printed? Determine, requirements for positive drawing base, selection of screen, determination of stretching tension, quality requirements for templates, requirements and control of exposure, such as requirements and control of screens in screen printing, templates Variable control, the control of the amount of ink transfer, and the impact of printing materials on the accuracy of the ship and the prevention of static electricity, half-tone screen printing and color registration order and registration requirements. This chapter analyzes and discusses the factors affecting quality in the above-mentioned halftone screen printing, so as to arouse the attention of screen printers and improve the quality of halftone screen printing products.
Four-color original for screen printing
One, four color screen printing tone
There are many ways to express levels in printing. There are two common methods: one is continuous halo staining and hierarchical expression; the other is halftone hierarchical expression.
The image of the reflected manuscript, from the highlights to the shades of the color shades, is formed continuously and uninterruptedly from deep to shallow or from shallow to deep even density, and is called continuous tone. For example, the colorless shade diagram baseplate without the net, the black and white photographs of the bottom edition and the drafts and photographs are continuously adjusted. Regardless of whether the image of the negative or positive image is from the highlight to the shadow, the shades of the image are represented by halftones, which are called halftones.
Second, four-color screen printing level representation method
The representation of the halftone gradation is to divide the continuous halo staining into different lines, such as coarse, short, and short, or small dots of varying sizes. There are three main methods of general expression:
The first is the line representation, which is the high, medium, and low tone levels of the manuscript. It is expressed in terms of thickness, density, and length. The lines are thick and dense, and the lines are thin and sparse. The disadvantage of this method of expression is that it is relatively rough, and the expression of the tone levels of the continuous blooming is not fine. Moreover, it can only appear in black and white or a single color, there is no color change, and the rich colors of the original cannot be reflected by the overlap color.
The second is the AM representation. The shades of the manuscript are represented by small dots and regular dots.
The third is the FM network representation. This method is rather special, with some irregularly arranged fine points to express the level of color, dense performance of dark and deep levels, point evacuation performance light and bright level.
Screen printing, in addition to the field color block patterns, text, lines, are halftone dot size, reproduction shades of gray tone level, instead of the original continuous blooming color, to complete the copy of the original image.
What is commonly used now is the amplitude modulation point. This kind of dot is the basic unit that constitutes an image on a screen printing plate. It is a real point of a regular arrangement with an equal center distance and an unequal area. Dots are the basis of the screen printing reproduction process. The correct transmission of screen dots in screen printing and printing is the most basic requirement for halftone screen printing. In screen printing, the dots play the following roles:
(1) The task of presenting hue, brightness, and saturation is imposed on the printing effect.
(2) In the printing process, it is the basic element of image transmission.
(3) In color synthesis is the organizer of image color, gradation, and outline.
As we all know, the halftone screen printing graphic is done by the dot. After coating the sensitized film, printing plate, and other series of treatments on the screen, the dots are made into the image part, and the remaining part of the image part except the screen dots penetrates the mesh and seals the ink.
In this sense, halftone screen printing is called dot printing. Then, why can the outlets realistically reproduce the continuous tone level on the original? This is because once the original image is screened, the original image is divided into countless mesh dots, that is, the continuous tone image information is converted into a dot image. information. When the color is synthesized, since the dots of different sizes are printed at different angles or close together, the ink on the dots selectively absorbs and reflects the light under the action of light. The reflected part of the light passes through the light. Space mixing, acting on human eyes (colored nerves), creating illusions in people's eyes, looks like continuous tone. In fact, the space occupied by each dot on screen printing products is equal. The difference in color tone seen by people is due to the difference in the size of the space occupied by each dot, and the depth of tone is caused by The dot space reflects the reflected light intensity.
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