3D Printing
In simple terms, three-dimensional printing creates a sense of three-dimensionality on a flat surface, making the image appear lifelike and seemingly within reach. Because of this characteristic, it has always occupied an important position in the printing industry since its introduction to the market, and many fields use three-dimensional printing products. Its novelty, uniqueness, and realistic effects make it memorable, allowing more companies to effectively promote their products.
The principle of three-dimensional printing is to simulate the distance between human eyes. By capturing images from different angles of left and right eyes, recording left and right pixels on photosensitive materials, and viewing, the left eye sees the left pixels, and the right eye sees the right pixels. Products made according to this principle are called three-dimensional printing. Three-dimensional printing can realistically reproduce objects, and because the original manuscript is designed or photographed scenery, high-quality copper plate paper and heat-resistant ink are generally selected for printing. Therefore, the glossiness is good, the colors are bright, not easy to fade, and the printed product's surface is covered with a layer of concave-convex cylindrical grating, allowing direct viewing of panoramic images in three dimensions, among other characteristics. The effect of three-dimensional images must be demonstrated by display technology. Here, three-dimensional display refers to the reproduction of three-dimensional spatial information of images, which is another basic condition for obtaining three-dimensional vision. There are mainly two methods to achieve three-dimensional display: bidirectional display and multidirectional display.
Since the original manuscript of the three-dimensional printing consists of closely arranged pixels, after plate making and printing, it needs to be compounded with a grating plate. Therefore, when selecting the screen angle, in addition to considering the moiré pattern formed between the screen plates, attention should also be paid to the moiré pattern formed by the angles of each screen and the pixel lines and grating plate lines. For example, it is not suitable to choose 0 degrees in three-dimensional printing because the horizontal screen lines are the most obvious, and 0 degrees are orthogonal to the pixel lines and grating lines, which interfere with the clarity and depth of the image. In three-dimensional printing, the angles for cyan and black plates are the same, determined by their characteristics. Since three-dimensional printing products need to be compounded with plastic plates, and most of these grating plates have a certain degree of grayscale, when using a fine 300-line screen, only about 85% to 90% exposure is needed during plate making; otherwise, it is prone to plate blur, and it is necessary to increase the ink quantity in the dark tone areas to achieve a 90% to 95% effect. Therefore, the color ink density of three-dimensional printing is higher than that of flat four-color printing. Generally, for flat offset printing: Y: 1-1.1, M: 1.4-1.5, C: 1.5-1.6; for three-dimensional printing: Y: 1.33-1.35, M: 1.31-1.33, C: 2. If the three-color ink overlay approaches neutral gray, to reduce the error caused by the fourth overlay, there is no need to print a black plate again, and the same angle can be used for both cyan and black plates for flexible control. During small-format continuous exposure, the temperature of the exposure light source may cause film shrinkage, resulting in changes in the screen distance between the front and back exposures, affecting printing orientation accuracy. Therefore, it is ideal to use a continuous film composed of sub-color films for exposure. When copying the positive, it is necessary to have a line film that is tightly matched with the film and the photosensitive film, including the same moiré distance. Phototypesetting plates with good expressive power should be used for plate making. The printing method selected for three-dimensional printing must ensure that the three-dimensional sense is not lost due to printing, the overlay accuracy is good, and it is suitable for mass production. For flat offset printing: plate making, printing overlay accuracy, and printing endurance are relatively good, the printed products have a better three-dimensional sense, the plate making is stable, and mass production is possible; photogravure: plate making and printing overlay accuracy are not good, but the printing endurance is relatively good, the printed products have a good three-dimensional effect, but the multi-color printing effect is not good; collotype: plate making modulation is unstable, the printing endurance is low, the printing accuracy of printed products is relatively good, the three-dimensional sense is better, but it is not suitable for mass production. Three-dimensional printing generally uses flat offset printing technology. The quality of three-dimensional printing has a significant impact on the visual effect of three-dimensional images. Due to the focusing and hindering effects of the grating, clear screen lines and accurate overlay are required, with a color registration error of no more than 0.02 mm, and the ink must be clean and not prone to fading. High-precision four-color printing presses are used for printing, and the registration lines must strictly converge. Additionally, the workshop must have constant temperature and humidity conditions. Compared with the above conditions, three-dimensional photographs usually adopt offset printing plate making methods. The film of the photographed three-dimensional image is electronically color-separated or directly screened.
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