How much do you know about the principle and technology of three-dimensional printing?
In the field of printing, the printing of three-dimensional space to reproduce the three-dimensional image of the object-three-dimensional printing has become an important content in the special printing industry. Let's talk about the technical characteristics and development prospects in this area.
The principle and characteristics of three-dimensional printing
The principle of three-dimensional printing is to simulate the distance between human eyes, shoot from different angles, and record the left and right pixels on the photosensitive material. When viewing, the left eye sees the left pixel and the right eye sees the right pixel. The printed product made according to this principle is called For three-dimensional printing.
Three-dimensional printing has the following characteristics: (1) It can reproduce objects realistically and has a strong three-dimensional sense. The product image is clear, rich in layers, vivid in image, and deep in the mood; (2) The three-dimensional printed manuscript is often taken from the shape design or the scene. The printed matter is generally selected for high-quality coated paper and high-temperature ink, 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 concavo-convex cylindrical mirror grating plate, which can directly watch the three-dimensional effect of the panoramic picture. From the perspective of people's stereoscopic vision of objects, the stereoscopic vision of objects is mainly derived from human physiological factors, experience and psychological factors. In fact, stereoscopic vision is the stereoscopic information formed by the synthesis of these complex factors of appeal in the visual process. In terms of physiological factors, there are parallax (binocular parallax and monocular parallax), convergence, and adjustment. Specifically, binocular parallax is the fundamental factor for people to obtain stereo vision, that is, in daily life, when people observe an object, due to the angle of view between the two eyes, the image of the object seen by the left and right eyes will be different, namely Parallax, it gives people a three-dimensional sense.
The effect of the stereoscopic image must be reflected by the display technology. The stereoscopic display mentioned here refers to the reproduction of the stereoscopic information in the three-dimensional space of the 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-way display method.
(1) Two-way display method. Can be divided into three-dimensional mirror method, two-color filter method, polarized filter method and alternate division method. No matter which method is adopted, stereoscopic vision is obtained by observing the images separately with the two eyes and the left and right eyes. Stereoscopic method: The basic principle of the stereoscopic method is to use the stereoscopic mirror to observe the left and right figures to form a three-dimensional effect. This method has been widely used since the advent of the 19th century, but special stereoscopic mirrors must be used, otherwise there will be no stereoscopic vision. Two-color filter method: the left and right images are printed on the same plane with red and blue inks respectively, and the printed image is observed through the red and blue 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. Coupled with the different wavelengths of light entering the two eyes, it is easy to fatigue the eyes. Therefore, this method is generally rarely used except for making aerial maps. Polarized color filter method: the left and right images are projected on the same plane through polarized color filters that are orthogonal to each other, and the left and right eyes are also observed with the same polarized color filter. Although this method requires special glasses, it has been widely used in stereo movies and stereo televisions. Alternate segmentation method: the left and right images are alternately presented on the same plane and the unnecessary parts of the same period are masked to produce a three-dimensional sense. Since the afterimage effect causes flashes and the glasses for masking are expensive, this method has not been popularized so far.
(2) Multi-directional display method. There are parallax shielding method and cylindrical lens method. Parallax masking method: The parallax masking method, also known as the 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 the slit and expose it on the film, then develop, Exposure and printing. If it is placed at the same position as when shooting, the two eyes are also placed at the position where the image is placed, and you can see the stereoscopic image. Using the parallax slit method, if two images are synthesized, a parallax stereoscopic image can be obtained. If the aperture ratio of the slit is reduced, multiple images can be synthesized, and a parallax panoramic image can be obtained. The parallax slit method is essentially that the diminishing amount of light is inevitable. Therefore, it is generally seldom used except for photographing by the cylindrical lens method. Cylindrical lens method: Cylindrical lens can be regarded as a lens plate composed of many convex lens sheets side by side, it has a split image effect. The back of this lens coincides with the focal plane. Due to the splitting effect of the lens, the images A, B, C, D in all directions can be separated into a, b, c, d and recorded on the focal plane, as long as the left and right eyes are placed on the B and C Location, you can see the stereo image.
Three-dimensional printing process and main points
Three-dimensional printing photography method
As mentioned above, the cylindrical lens method for three-dimensional printing requires images of the illuminated object seen from all directions. Photography methods include (1) circular arc moving method. This method uses a certain point on the subject as the center of the circle, and the distance from this point to the camera as the radius to make an arc. The camera moves along this arc and shoots continuously or intermittently; (2) Parallel movement method. Move the lens parallel to the center line of the object. When shooting with this method, the accuracy is not easy to grasp; (3) Straight line shaking method. The captured image will be somewhat out of shape. But if higher accuracy is not required, this is a simple method.
In addition, the method of not using a cylindrical lens in photography is the same as a normal camera, moving while shooting, and then synthesizing images in all directions through a cylindrical lens. Therefore, images in all directions (6-9) cannot be continuous. It mainly has instant photography. Cameras with multiple (6-9) lenses are most suitable for outdoor photography, especially for moving objects, due to their ease of carrying. It is just that a stereo photo cannot be formed without post-synthesis, which has the advantage of enlargement in size during image synthesis. Ordinary camera movement method: Install the ordinary camera on the electric chute, and slide while shooting. Compared with the above-mentioned instant photography method, there are no outstanding advantages, but no special camera is needed. The method of using a cylindrical lens during photography can continuously shoot within an effective angle. You can get a three-dimensional image at a time, but it is very difficult to zoom in after shooting, and the exposure time is long, you can not shoot moving objects, and the camera is large, so it is not suitable for handling. The object movement method is the opposite of moving the camera, which is to rotate the object and move it linearly.
The center of the large turntable coincides with the center of the object to be photographed while the turntable moves. To use a dedicated indoor camera, it is not possible to shoot moving objects; camera parallel movement method: use the method of parallel moving camera to perform equidistant photography on the subject. With parallel movement, the camera is always aimed at the center of the subject. Get good images. However, the production of the camera is very difficult, and because of structural limitations, it is only used for indoor photography; the camera linear shaking method: this is a slightly simplified method than the above parallel movement method. The camera moves in a straight line to the left and right, and the lens repeatedly shakes to align the center of the subject. This method can be used for both indoor and outdoor photography; shutter movement method: this shooting method is limited to indoor close-range photography cameras. The shutter movement method uses a large-aperture lens, which can capture stereoscopic images in all directions as the shutter moves within the lens. This method has less lens movement distance and can be exposed in a short time. At the same time, close-range photography will not damage the three-dimensional sense, and is particularly suitable for portrait photography.
At present, there are two methods commonly used for photographing three-dimensional printed manuscripts, namely, the arc stereo photography method and the shutter movement method. Arc moving shooting: The cylindrical lens plate is directly attached to the front of the photosensitive film, and a camera is used for shooting. The optical axis of the camera is always facing the center of the subject. The total distance of the camera movement to meet the requirements of the reproduced image is generally controlled at an angle of 3 ° -10 °. The grating plate in front of the photosensitive sheet of the camera moves synchronously with the photosensitive sheet at random. Each exposure is focused into a pixel under each half cylinder of the grating plate. When the camera finishes shooting at a predetermined distance, pixels cover the entire grid pitch. Three-dimensional photos can be obtained after processing. Shutter moving shooting: When shooting, the distance that the shutter moves from one end of the lens to the other is 60mm, which is equivalent to the distance between the human eyes. At the same time, the grid plate immediately in front of the photosensitive sheet also moves accordingly, and the moving distance is a grid pitch of 0.6 mm.
Plate making and printing process
Due to the delicate pixels of the stereo image and the magnifying effect of the lenticular grating, the number of plate-making screen lines must be above 120 lines / cm. The screen angles of three-dimensional printing and ordinary color printing are different, and the cyan and black versions must use the same mesh angle. In addition, three-dimensional printing with different pitches should have different combinations of screen angles of four yellow, magenta, cyan, and black plates to avoid interference fringes. The screen angles used by general manufacturers at home and abroad today are: 0.6 grid pitch / cm, 100 lines / cm color separation, then the screen angle degrees are Y81, M36, C66, K66; 0.44 grid pitch / cm, 58 lines / For cm color separation, the screen angle degree is Y50, M20, C65, K65; 0.31 pitch / cm, 81 lines / cm color separation, the screen angle degree is Y66, M22, C51, K51.
Since the three-dimensional manuscript is composed of closely arranged pixels, and after the plate making and printing, the compound cylindrical lens plate is also needed, so when selecting the screen angle, in addition to considering the moire formed between the screens, pay attention to each net The moire formed by the angle of the screen, the pixel line, and the lenticular plate line.
For example, for stereo printing, it is not appropriate to select 0 degree, because the horizontal line is the most obvious, and 0 degree is orthogonal to the pixel line and the cylinder line, which interferes with the clarity and depth of the image. The three-dimensional printing has the same screen angle for the cyan and black plates, which is determined by its own characteristics. Because the three-dimensional printed matter will eventually be compounded with the plastic plate, and the cylindrical lens plate mostly has a certain grayscale, and because the three-dimensional printing uses a very fine 300-line screen, it only needs to be 8.5% or 9 when printing Into dots, otherwise it is easy to paste in printing, so you need to increase the amount of color in dark areas to achieve 9-9.5 dots. Therefore, the solid density of three-dimensional printing is higher than that of flat four-color printing. Generally: 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 printing ink is close to neutral gray after overprinting, in order to reduce the error caused by the fourth overprint, there is no need to print the black version, and the black version and the green version can be taken at the same angle for flexible control. When the small format continuous exposure, the temperature of the exposure light source will cause the negative film to shrink, resulting in the change of the front and rear width of the grid, affecting the printing orientation accuracy, so it is ideal to connect the color separation film into a complete negative film for printing.
When copying the positive picture, it is necessary to close the line between the negative film and the photosensitive film with the same width as the grid pitch. The printing plate should use the PS version with better expressive level. The printing method used for three-dimensional printing should ensure that there is no loss of three-dimensional sense due to printing, the accuracy of overprinting is good, and it should be printed in large quantities. Lithographic offset printing: plate making, printing overprint accuracy, and durability are better, the three-dimensional impression of the printed product is better, plate making is stable, and mass production is possible; gravure: plate making, printing overprinting accuracy is not good, the durability is good, the printing The three-dimensional effect of the product is good, but the multi-color printing effect is not good; Colro plate: plate-making modulation is unstable, the printing resistance is low, the printing accuracy of the printed product is better, the three-dimensional impression is better, but it is not suitable for mass production. Three-dimensional printing is generally printed by offset printing. The quality of 3D printing has a significant impact on the intuitive effect of 3D pictures. Due to the focusing and hindering effect of the grating, the network cable is required to be clear and the overprinting is accurate. The color registration error is not allowed to exceed 0.02mm, and the printing ink is clean and unfading. Printed on a high-precision four-color printing machine, the rule lines must meet strictly, and the workshop must have constant temperature and constant humidity conditions. As for the comparison of the above conditions, the stereographic printing method is usually adopted for the three-dimensional photos. The three-dimensional film negative film is separated by electronic color separation or direct screen photography.
3D printing materials and technology
(1) Paper. Printing paper is required to have the characteristics of compactness, smoothness, smoothness, and small stretchability; usually coated paper or cardboard is used.
(2) Grating material. There are mainly hard plastic stereo gratings. The polystyrene raw material is processed by injection molding to form a concave-convex cylindrical mirror grating. Polystyrene is colorless and transparent (transparency is 88% -92%), refractive index is 1.59-1.6, non-ductile and flammable. Because of such a high refractive index, it has good gloss. Processing of transparent plastics produces birefringent stresses-optical effects. Its tensile strength is 3.52-6.33MPa, its bending strength is 6.12-9.84MPa, and its thermal deformation temperature is 70 ° C-98 ° C. The chemical properties of polystyrene are resistant to certain mineral oils, organic acids, alkalis, salts, lower alcohols and their aqueous solutions. It is softened after being eroded by hydrocarbons, ketones, higher fatty esters, etc. It is soluble in aromatic hydrocarbons and toluene, ethylbenzene and styrene monomers. In some cases, the degree of erosion of polystyrene by chemical reagents can be reduced by annealing, stress relief and other measures. Soft plastic stereo grating. The main use of PVC film base through the metal grating drum or grating plate into soft plastic three-dimensional grating. Polyvinyl chloride is a polymer compound formed 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 shiny film, and can produce various softness films according to the content of plasticizer. This material is also fast after pulse heat sealing, high frequency heat sealing and adhesion. The chemical properties of PVC have good chemical resistance, but poor thermal stability and light resistance. Hydrogen chloride begins to decompose at 140 ° C, and stabilizers need to be added during manufacturing. Polyvinyl chloride has a chlorine content of 56% -58%, and it is easily soluble in ketones, esters and chlorinated hydrocarbon solvents with low molecular weight.
(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. In fact, any visible degree of foaming will affect the clarity and three-dimensional effect.
The curing temperature of 3D printing inks is within the curing range of standard plastic inks (149 ° C-171 ° C), but it must be increased to the 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 the standard plastic ink. Although 3D printing inks are not yet common, this ink is very different from the thicker plastic ink layers that people commonly see. If the operation is carried out correctly, the three-dimensional printed image will have sharp subtle levels and clear edges, the printed edges will protrude vertically from the fabric surface, and the ink wall will be very smooth. Although this ink is very thick and the ink plate is very thick, 3D printing can still print exciting subtle levels and screen prints.
(4) Adhesive. The role of the adhesive is to enable the printed matter and the grating to be firmly pasted together; secondly, it can protect the ink layer from discoloration at high temperatures.
Three-dimensional printing should pay attention to the following issues: single-lens camera or multi-lens camera is used for photography, which requires the camera to have high accuracy to avoid errors caused by vibration. And accurately adjust the focal length, angle and raster data movement spacing; improve the accuracy of color separation and copying of the plate making, 300-line dots are required to be solid, and the scene image maintains a rich level; color printing must be produced as planned to avoid The paper is stretched, resulting in inaccurate overprinting; the spacing and angle of the grating have high precision, and the composite molding requires accurate positioning. Hard plastic and soft plastic have better transparency performance.
Oven plate glass refers to a type of glass that is specifically designed to withstand high temperatures in ovens. It is commonly used as the door panel of an oven, allowing users to see the food being cooked inside while preventing heat from escaping.
Oven Plate glass
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