Three-dimensional printing principle and process technology
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In the field of printing, the three-dimensional reproduction of the three-dimensional image of the object printing - three-dimensional printing, has become an important content in the special printing industry, the following will talk about the technical characteristics and development prospects.
The principle and characteristics of three-dimensional printing
The principle of three-dimensional printing is to simulate the distance between two eyes of the human being. Shooting from different angles, the left and right pixels are recorded on the photosensitive material. When viewing, the left eye sees the left pixel and the right eye sees the right pixel. The printed matter produced according to this principle is called For three-dimensional printing.
The three-dimensional printing has the following characteristics: (1) The object can be reproduced realistically, and has a strong three-dimensional feeling. The product image is clear, the layer is rich, the image is realistic, and the artistic conception is deep; (2) the manuscript of the three-dimensional printing is often formed by the design or the scene, and the printed matter is generally selected as high-quality coated paper and high-temperature ink printing, so the gloss is good. The color is bright and not easy to fade; (3) The surface of the printed product is covered with a layer of concave and convex mirror-shaped grating plate, which can directly view the stereoscopic effect of the panoramic picture. From the perspective of stereoscopic vision of objects, the stereoscopic vision of objects is mainly derived from human physiological factors, experience and psychological factors. In fact, stereo vision is the stereoscopic information that people combine to form these complex factors of appeal in the visual process. From the physiological point of view, there are parallax (two-eye parallax and monocular motion parallax), convergence, and regulation. Specifically, binocular parallax is the fundamental factor for people to obtain stereoscopic vision. In daily life, when people observe an object, the image of the object seen by the left and right eyes will be different due to the angle of view between the two eyes. Parallax, it gives people a three-dimensional sense.
The effect of a stereoscopic image must be reflected by the display technology. The stereoscopic display referred to herein refers to the reproduction of stereoscopic information in the three-dimensional space of an image, which is another basic condition for obtaining stereoscopic vision. There are two main methods for realizing stereoscopic display, namely, two-way display method and multi-directional display method.
(1) Two-way display method. Can be divided into stereoscopic method, two-color filter method, polarized color filter method and alternating segmentation method. Regardless of which method is adopted, stereoscopic vision is obtained by separately observing the image by using the left and right parallax eyes. Stereoscopic method: The basic principle of the stereoscopic method is to use a stereoscopic mirror to observe the left and right patterns to form a three-dimensional effect. This method has been widely used since the advent of the 19th century, but special stereoscopes must be used, otherwise there will be no stereoscopic vision. Two-color filter method: a method in which left and right images are printed in the same plane with red and blue inks, and the printed image is observed through red and blue color filters. Since the color filter and the ink are complementary to each other, the image observed through the color filter is not red and blue but black. Therefore, this method is limited to black and white photographs and is not suitable for color prints. In addition, light of different wavelengths enters both eyes, which is easy to cause eye fatigue. Therefore, this method is rarely used except for the use of aerial maps. Polarized color filter method: The left and right images are respectively projected on the same plane through polarized color filters that are orthogonal to each other, and the left and right eyes are also observed by the same polarizing filter. Although this method requires special glasses, it has been widely used in stereoscopic movies and stereoscopic televisions. Alternate segmentation method: The left and right images are alternately presented on the same plane and the unnecessary portions of the same period are masked, thereby generating a stereoscopic effect. Since the afterimage effect causes flashing, and the glasses for shielding are expensive, this method has not been popularized so far.
(2) Multi-directional display method. There are mainly parallax shielding methods and cylindrical lens methods. Parallax screening method: Parallax shielding method, also known as parallax slit method, was invented by FELves in 1930. Its working principle is to divide the left eye image and the right eye image by slit and expose it on the film, and then develop it. , printing and printing. If you place it in the same position at the time of shooting, and both eyes are placed at the position where the image is placed, the stereoscopic image can be seen. By applying the parallax slit method, if two images are combined, a parallax stereoscopic image can be obtained. If the aperture ratio of the slit is lowered, the synthesis of a plurality of images can be completed, and a parallax panoramic image can be obtained. The parallax slit method is essentially inevitable in that the amount of light is decremented. Therefore, it is currently rarely used except for use in the photography of the cylindrical lens method. Cylindrical lens method: A cylindrical lens can be seen as a lens plate composed of a plurality of convex lens sheets side by side, which has a focusing effect. The back side of the lens coincides with the focal plane. Due to the image separation effect of the lens, the images A, B, C, and D in each direction can be separated into a, b, c, and d and recorded on the focal plane, as long as the left and right eyes are placed in B and C. Position, you can see the stereo image.
Three-dimensional printing process and points
Three-dimensional printing method
As described above, cylindrical lens method embossing requires an image of an object to be seen from various directions. The photography method has (1) circular motion method. This method takes a point on the object as the center of the scene, and the distance from the point to the camera is a radius of the arc, and the camera moves along the arc to shoot continuously or intermittently; (2) Parallel movement method. Move the lens parallel around the centerline of the object. When shooting by this method, the accuracy is not easy to grasp; (3) Straight line shaking method. The image will be a little out of shape. But if you don't require higher precision, this is an easy way.
In addition, the method of using a cylindrical lens is not used in photography, and like a normal camera, photography is performed while moving, and then images in various directions are synthesized by a cylindrical lens. Thus the images in all directions (6-9 sheets) cannot be continuous. It mainly has instant photography. Cameras with multiple (6-9) lenses are ideal for outdoor photography, especially for moving objects, because of their portability. It is only that the stereoscopic photograph cannot be formed without post-synthesis, and has the advantage of being scalable when the image is synthesized. Ordinary camera movement method: Mount the ordinary camera on the electric chute and slide while shooting. Compared with the above-mentioned instant photography method, there is no outstanding advantage, but no special camera is needed. The method of using a cylindrical lens for photographing can continuously photograph within an effective angle. A stereo image can be obtained at one time, but it is very difficult to enlarge after photography, and the exposure time is long, the moving object cannot be photographed, and the camera is large in size and unsuitable for handling. The subject movement method is the opposite of moving the camera to rotate the object and move it linearly.
The center of the large turntable coincides with the center of the subject, and the turntable moves while taking pictures. To use an indoor dedicated camera, you cannot shoot a moving object; the camera parallel movement method: equidistant photography of a subject by a parallel moving camera, and the camera always aligns with the center of the subject as it moves in parallel, Get good images. However, the production of the camera is very difficult, and due to structural limitations, it is only used for indoor photography; the camera is linearly shaken: this is a slightly simplified method than the parallel movement method described above. The camera moves straight to the left and right, and the lens is repeatedly shaken to the center of the subject. This method can be used indoors and outdoors; shutter movement method: This shooting method is limited to indoor close-range photography cameras. The shutter movement method uses a large-diameter lens, and stereoscopic images in all directions can be taken as the shutter moves inside the lens. In this way, the lens has a small moving distance and can be exposed in a short time, and the close-range photography does not damage the stereoscopic effect, and is particularly suitable for portrait photography.
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.
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 moire formed between the screens, attention should also be paid to the nets. The screen angle and the moire line formed by the pixel line and the column mirror line.
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 line with the same width as the pitch between the negative film and the photosensitive sheet. 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 screen photography.
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 erosion 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.
(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 color separation of the plate-making, the accuracy of the copy, the 300-line dot requirements are solid, the image of the scene remains rich; the color printing must be carried out according to the plan to avoid production Paper stretches, causing overprinting; grating spacing and angle are high accuracy, composite molding requires accurate positioning. The transparency of soft plastic and soft plastic is better.