Key Technology of Stereo Printing and Its Application Analysis (two)
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At present, there are two methods commonly used for photographing three-dimensional printed originals, namely, circular stereo photography and shutter movement. Arc motion shooting: The cylindrical lens plate is directly attached to the front of the photosensitive film, and is shot with a camera. The optical axis of the camera is always facing the center of the subject. The total distance of camera motion is subject to the requirements of the reproduced image, and is generally controlled at an angle of 3°-10°. The grating plate in front of the camera's photosensitive film moves synchronously with the photosensitive film. Each exposure is focused into one pixel under each half cylinder of the grating plate. When the camera finishes shooting at a predetermined distance, the pixels fill the entire pitch. A stereo photo can be obtained by rinsing. Shutter movement shooting: When shooting, the distance from the end of the lens to the other end is 60mm, which is equivalent to the distance between the eyes of the person. At the same time, the grid plate in front of the photosensitive sheet also moves correspondingly, and the moving distance is a pitch of 0.6 mm.
2, plate making and printing process
Due to the fineness of the stereo image pixels and the magnification of the lenticular grating, the number of plate-making screen lines must be above 120 lines/cm. Three-dimensional printing and ordinary color printing have different angles, and the same mesh angle is used for the blue and black versions. In addition, the three-dimensional printing of different pitches has different combinations of network lines of yellow, magenta, cyan and black to avoid the generation of interference fringes. Nowadays, the netting angle used by general manufacturers at home and abroad is: 0.6 pitch/cm, 100 lines/cm color separation, then the degree of screen angle is Y81, M36, C66, K66; 0.44 pitch/cm, 58 lines/ For the color separation of cm, the degree of the screen angle is Y50, M20, C65, K65; 0.31 pitch/cm, 81 line/cm color separation, then the degree of the screen angle is Y66, M22, C51, K51.
Since the three-dimensional original is composed of a series of closely arranged pixels, after the plate making and printing, the cylindrical mirror plate is also to be combined. Therefore, when selecting the angle of the wire, in addition to considering the formation of the moire between the screens, it is also necessary to pay attention to the nets. The screen angle is formed by the moiré lines formed by the pixel lines and the column mirror lines. For example, stereo printing is not suitable for 0 degree, because the horizontal network cable is the most obvious, and 0 degree is orthogonal to the pixel line and the cylindrical line, which interferes with the sharpness and depth of the image. In the three-dimensional printing, the angles of the blue and black screens are the same, which is determined by its own characteristics. Since the three-dimensional printed matter is finally combined with the plastic plate, the cylindrical mirror plate mostly has a certain gray scale, and because the three-dimensional printing uses a very fine 300-line screen, it only needs to be dried to 8.5 or 9 during the printing. Into the point, otherwise it is easy to paste the plate when printing, so you need to increase the amount of color in the dark area to achieve a 9-9.5 point effect. Therefore, the three-dimensional printing has a higher density in the field than the four-color printing. Generally: lithographic offset printing: Y: 1-1.1, M: 1.4-1.5, C: 1.5-1.6; three-dimensional printing: Y: 1.33-1.35, M: 1.31-1.33, C: 2. If the three-color ink is close to the neutral gray after overprinting, in order to reduce the error caused by the fourth overprint, it is not necessary to print the black version, and the black version and the green version can be taken at the same angle for flexibility. In the case of small-format continuous exposure, the temperature of the exposure light source will cause the film to shrink, causing the pitch of the front and back webs to change, which affects the accuracy of the printing orientation. Therefore, it is most ideal to make the color separation sheet into a whole film for printing. When copying the positive image, it is necessary to close the film with the same width as the pitch between the negative film and the photosensitive film. The printing plate should use a PS version with better level of performance. The printing method selected for three-dimensional printing should ensure that the three-dimensional feeling is not lost due to printing, the overprinting precision is good, and mass printing is suitable. Offset offset printing: plate making, printing overprinting precision, and printing durability are better, printing three-dimensional feeling is better, plate making is stable, and mass production; gravure: plate making, printing overprinting precision is not good, printing resistance is better, printing The three-dimensional effect is good, but the multi-color printing effect is not good; the 珂罗版: the plate making modulation is unstable, the printing durability is low, the printing precision of the printed product is good, and the three-dimensional feeling is better, but it is not suitable for mass production. Three-dimensional printing is generally printed using a lithographic offset printing process. The quality of three-dimensional printing has a significant impact on the visual effect of stereoscopic images. Due to the focusing and obstruction of the grating, the network cable is required to be clear and the overprinting is accurate, and the color registration error is not allowed to exceed 0.02 mm, and the ink is required to be clean and not faded. Printed with a high-precision four-color press, the rule lines must be strictly met, and the workshop must have constant temperature and constant humidity conditions. For the above conditions, stereo photographs are usually made by offset printing. The stereoscopic image film taken is subjected to color separation by electronic color separation or direct screening process.
3, three-dimensional printing materials and technology
(1) Paper. Printing paper is required to be compact, smooth, flat, and less stretchable; usually coated paper or cardboard.
(2) Grating sheet material. There are mainly hard plastic three-dimensional grating sheets. The polystyrene raw material is subjected to injection molding to form a concave-convex cylindrical mirror-shaped grating sheet. Polystyrene is colorless and transparent (transparency is 88%-92%), refractive index is 1.59-1.6, no ductility and flammability. Due to such a high refractive index, it has a good gloss. The processing of transparent plastics produces birefringent stress-optical effects. It has a tensile strength of 3.52-6.33 MPa, a flexural strength of 6.12-9.84 MPa, and a heat distortion temperature of 70-98 °C. The chemical properties of polystyrene are resistant to certain mineral oils, organic acids, bases, salts, lower alcohols and aqueous solutions thereof. It is softened by the attack of hydrocarbons, ketones, higher fatty esters, etc., and is soluble in aromatic hydrocarbons and toluene, ethylbenzene and styrene monomers. In some cases, the degree of corrosion of polystyrene by chemical agents can be reduced by annealing, stress relieving, and the like. Soft plastic three-dimensional lenticular sheet. The soft plastic three-dimensional grating sheet is mainly pressed by a polyvinyl chloride sheet base through a metal grating roller or a grating plate. Polyvinyl chloride is a polymer compound obtained by polymerizing chlorinated olefins and is difficult to burn. Although polyvinyl chloride and polyethylene are both milky white, polyvinyl chloride can be made into a colorless, transparent and glossy film, and can produce various soft films according to the plasticizer content. This material is also subjected to pulse heat sealing, high frequency heat sealing, and bonding fastness. The chemical properties of polyvinyl chloride have good chemical resistance, but the thermal stability and light resistance are poor. Hydrogen chloride is decomposed at 140 ° C, and a stabilizer is required for the production. Polyvinyl chloride has a chlorine content of 56% to 58%, and is low in molecular weight and easily soluble in ketones, esters and chlorinated hydrocarbon solvents. High relative molecular mass is difficult to dissolve.
(3) Ink. At present, some ink manufacturers can provide inks and additives suitable for three-dimensional (three-dimensional) printing, and some manufacturers have developed new ink production lines. However, it should be noted that the three-dimensional printing ink is not a foaming ink, and virtually any visible degree of foaming will affect the sharpness and three-dimensional effect. Three-dimensional printing inks have a curing temperature within the curing range of standard plastic inks (149 ° C - 171 ° C), but must be increased to a curing temperature suitable for ultra-thick ink layers. If the ink layer is fully cured, the three-dimensional ink will have the same elasticity as a standard plastic ink. Although three-dimensional printing inks are not common, this ink is quite different from the thicker plastic ink layers that people often have. If done correctly, the 3D printed image will have sharp subtle layers and sharp edges, the printed edges will bulge vertically from the fabric surface, and the ink walls will be smooth. Although the ink is thick and the ink plate is thick, 3D printing can still produce exciting subtle layers and screened prints.
(4) Adhesive. The role of the adhesive is to enable the print and the lenticular sheet to be firmly adhered together; secondly, it can protect the ink layer from discoloration at high temperatures.
The problems to be noticed in three-dimensional printing are as follows: the single-lens or multi-lens camera is used for photography, and the camera is required to have high precision to avoid errors caused by vibration. And accurately adjust the focal length, angle and grating data movement spacing; improve the accuracy of plate-making color separation and copying, 300-line dot requirements are strong, the image of the scene remains rich; color printing must be carried out according to the plan to avoid production The paper is stretched, resulting in inaccurate overprinting; the grating spacing and angle have higher precision, and the composite molding requires accurate positioning. The transparency of soft plastic and soft plastic is better.