Analysis of three-dimensional printing process
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In today's world packaging market, China's packaging industry is growing faster and faster. Packaging pays attention to the visual impact effect, especially some high-end packaging products, but also pursues a variety of unique artistic effects, in order to be unique in the market. Special printing has attracted the attention of the printing industry and the industry with its unique and exquisite printing effect, changing printing process and wide application range. In today's packaging and decoration, anti-counterfeiting printing, special printing technology has shown its unique advantages, creating an unprecedented added value for a wide variety of packaging products with unique shapes and special effects in the commodity market.
The effect of special printing is not available in general printed matter, and the elements that have an influence on the human feeling are injected into the printed matter, and the performance effect is enhanced, and the additional function as a printed matter can be better exhibited. In other words, it is a means of increasing the extra value of print.
As one of the special printing, three-dimensional printing can reproduce objects realistically and has a strong three-dimensional effect. The surface of the printed product is covered with a lenticular lenticular grating plate, which can directly view the stereoscopic effect of the panoramic picture. In recent years, the domestic three-dimensional printing market has been greatly developed, but the overall technological and product innovation is lacking. With the continuous development of commodity economy and printing science and technology, three-dimensional printing will show strong vitality and broad development prospects. The three-dimensional reproduction of the stereo image of the object - three-dimensional printing, has become an important content in the field of printing, the following will talk about the technical characteristics of this.
First, the definition and principle of three-dimensional printing
1. Definition of three-dimensional printing
Stereoscopic printing refers to a printing method in which the visual effect of the product has a three-dimensional effect. The image of the ordinary printed matter is generally displayed in two dimensions, and the three-dimensional printed matter can reflect the three-dimensional effect of the three-dimensional space. By simulating the distance between the two eyes, the left and right pixels are recorded on the photosensitive material when viewed from different angles. 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 stereo printing. .
2. The principle of making stereo images
Since the distance between the eyes of the person is about 6 cm, a stereoscopic effect can be produced when viewing the same object. The surface of the three-dimensional printed matter is covered with a plastic cylindrical mirror plate with a pitch of about 0.6 cm, which is equivalent to a cylindrical grating plate. There are generally 48 concave and convex lines per centimeter, and there are 6 pixels under each strip. The grating plays the role of mapping the pixels into the left and right eyes respectively, and sees the corresponding images. Since the left and right eyes have different viewing angles, the coincident images produce a stereoscopic image through the optic nerve. This printing method is also called a grating. Board method.
Second, the three-dimensional printing process and points
The main process flow of three-dimensional printing is: taking stereo photos → color separation and screen making → printing → grating plate bonding type.
1. Stereo photo shooting
For three-dimensional printing, stereo photography must be performed using a stereo photo as a manuscript. In stereo photography, a cylindrical grating plate is directly attached to the front of the photosensitive sheet of the camera, and the camera is moved in a certain field of view to continuously capture the subject. Accurate calculation of the position, angle, center point, and spacing of the grating plates before shooting.
At present, there are two methods for photographing a three-dimensional printed original: a circular motion photography method and a shutter movement method.
Arc motion shooting: Take a point on the subject as the center of the subject, and use the distance from the camera to the radius of the camera as the arc. The camera moves along this arc to shoot continuously or intermittently. That is, the cylindrical lens plate is directly attached to the front side of the photosensitive film, and is photographed by one camera, and the optical axis of the camera is always directed at the center of the subject. The grating plate in front of the camera is randomly synchronized with the photosensitive film, and the total distance of the camera motion is determined to meet the requirements of the reproduced image, and is generally controlled within an angle range of 3° to 10°. Each exposure during shooting is focused into one pixel under each half cylinder of the grating plate. When the predetermined distance is taken, the pixels will fill the entire pitch and a stereo photo will be obtained after rinsing.
Shutter movement shooting: When shooting, the distance from the one end of the lens to the other end is 6cm, which is equivalent to the distance between the eyes of the two people. At the same time, the grid in front of the photosensitive sheet moves accordingly, and the moving distance is a pitch, that is, 0.6mm.
Note when shooting: The camera uses a single-lens or multi-lens machine, which requires the camera to have high precision, avoid vibration and cause errors, and accurately adjust the focal length, angle and moving distance of the grating.
2. Separation and screen printing
2.1 selection of screen lines
Separate the stereo photos, add screens and make four plates to make the same platemaking process and the same. When copying the positive image, a line of the same width as the pitch should be used between the negative film and the photosensitive film; the printing plate should use a PS plate with better level of expression.
The cylindrical grating plate has a magnifying effect, so it is necessary to use a high-dot line number plate making plate. When the color separation is performed by an electronic color separation machine, the number of scanning lines is 400 lines/cm or more. Due to the small size of the stereo image and the amplification of the lenticular grating, the number of plate-making lines must be above 120 lines/cm. Improve the accuracy of color separation and copying, and ensure that the 300-line dot is strong and the image of the scene remains rich.
2.2 screening angle selection
The cylindrical grating plate is a parallel straight line, which is easy to produce a flashing halo with the dot. Therefore, avoid using the 45° and 90° dot angles and change the mesh angle according to the grating plate pitch. The three-dimensional printing and the ordinary color printing have different angles, and the cyan and black versions use the same mesh angle.
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 combined. Therefore, when selecting the angle of the network cable, in addition to considering the moiré formed between the screens, attention should also be paid to the screens. The moiré formed between the angle and the pixel line and the column plate line. Stereo printing should not be selected as 0°, because the horizontal network cable is the most obvious, and 0° is orthogonal to the pixel line and the cylindrical line, which will interfere with the sharpness and depth of the image. In addition, the stereo printing has the same angle as the black version and the black version, which is determined by its own characteristics.
2.3 combination of the number of screen lines and the angle of the screen
Three-dimensional printing of different pitches, yellow, magenta, cyan, black four-block version need to choose a combination of different network lines and angles to avoid interference fringes. There are three combinations of the most used network cables and screen angles at home and abroad.
Table 1. Combination of screen line number and screen angle
2.4 printing control
Because the three-dimensional printed matter is finally combined with the plastic plate, the cylindrical mirror plate mostly has a certain gray scale; at the same time, the three-dimensional printing uses a very fine 300 line/cm screen, and only needs to be dried to 8.5% when printing. 9 into the network, otherwise it is easy to cause paste when printing, so the three-dimensional printing to achieve the effect of 9 to 9.5 into the dot, the need to increase the amount of ink in the dark area, so the three-dimensional printing is higher than the color density of the four-color printing.
When the three-color ink is overprinted and close to the neutral gray, in order to reduce the error of the fourth overprint, the black version is often no longer printed, so the black version and the green version can be taken at the same angle for flexibility.
When the small-format is exposed to the sun, the temperature of the exposure light source will cause the film to shrink, causing the change of the pitch of the front and back webs, which affects the accuracy of the printing orientation. Therefore, the color separation film can be connected into a whole negative film for printing, and the effect is ideal.
3. Choice of printing methods
The printing method selected for three-dimensional printing should ensure that the three-dimensional feeling is not lost, the overprinting precision is good, and the printing is suitable in large quantities. The following several printing methods are used to compare the three-dimensional printing.
Offset offset printing: plate making, printing overprinting precision, and printing durability are better. The printed product has a strong stereoscopic effect, stable plate making, and can be mass produced.
Photogravure: plate making, printing overprinting accuracy is poor, printing durability is good, printing stereo effect is good, but multi-color printing is not good.
The plate making modulation is unstable, the printing durability is low, the printing precision of the printed products is good, and the stereoscopic effect is strong, but it is not suitable for mass production.
It can be seen from the comparison that the three-dimensional printing is preferably printed by the lithographic offset printing process, and the quality of the three-dimensional printing has a significant influence on the visual effect of the stereoscopic image. In addition, to improve the quality of the finished product in the three-dimensional printing process, you should also pay attention to a few points:
3.1 The grating has focusing and obstructing functions. Therefore, the network cable is required to be clear and the overprinting is accurate. The color registration error is not more than 0.02 mm, and strictly speaking, it should be less than 0.01 mm.
3.2 requires that the ink is not faded, the printing ink does not use foaming ink, because any visible degree of foaming will affect the clarity and three-dimensional effect of the image.
3.3 Printing with high-precision four-color printing press, the rule line must be strictly met.
3.4 sets of color printing must be completed in a short time according to the plan, to avoid paper stretching, resulting in inaccurate overprinting.
3.5 Printing is printed on a tightly coated, smooth, flat, and stretchable coated paper or cardboard, otherwise it will affect the sharpness and three-dimensionality of the image.
3.6 The printing workshop should maintain constant temperature and constant humidity conditions.
4. Grating plate paste type
The combination of cylindrical grating plates and printed matter is a key process for three-dimensional printing. The spacing and angle of the grid should have higher precision, and the composite molding requires accurate positioning; the transparency of the hard plastic material and the soft plastic material used for the grating plate is better.
There are two ways to make a cylindrical grating plate:
One is a cylindrical grating plate process, coating a layer of bright glue on the printed finished product, heating and softening the highly transparent thermoplastic material, pressing into a cylindrical grating plate, and fitting the plate to the printed finished product. On the top, the raster lines and the raster lines on the printed matter are precisely aligned to show a stereoscopic effect.
In another method, the formed grating plate is first prepared, and then a layer of adhesive glue is coated on the printed product, and the grating plate and the printed matter are accurately aligned and combined to display a stereoscopic effect.
Third, the characteristics and effects of three-dimensional printing
1. The main features of three-dimensional printing
1.1 The three-dimensional printed originals are mostly made of modeling design or scenery, and choose high-quality coated paper and high-temperature ink printing, so the printed products have good gloss, bright colors and are not easy to fade.
1.2 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.
1.3 can reproduce objects realistically, with a strong three-dimensional sense. The product image is clear, the level is rich, the image is realistic, and the artistic conception is deep.
2. Several common effects of three-dimensional printing
2.1.3D stereo effect: divided into flat 3D (Layer 3D) and true 3D (True 3D).
2.1.1 Planar 3D: Use the layering function of the drawing software such as Photoshop to layer the image and generate the front and rear displacement images. After the printed image is attached to the grating plate, the resulting image has different effects before and after the layer and depth. The effect is a layer of discontinuous depth, so it is called plane 3D.
2.1.2 True 3D: Using a professional stereo camera to simultaneously capture different angle images, or using 3D animation software to simulate multiple images of different angles, the professional stereoscopic production software synthesizes the front and rear displacement images, and the printed image is combined with the grating plate. The image has layers before and after, because the effect is one layer and one layer of continuous depth, so it is called true 3D.
2.2. Variable image effect: 2 to 3 images are placed into the professional synthesis production software, and the images produced after printing on the grating plate enable the viewer to see different image effects at different angles.
2.3. Dynamic effect: shooting multiple continuous images or 3D animation software to produce multiple images, using professional synthetic production software to generate new images, images produced after printing on the grating plate, so that viewers can see the continuous dynamic effect of the images. .
2.4. Larger and smaller effect: Use Photoshop and other drawing software to scale the image according to the same scale. Generally, 5 to 6 images are synthesized by professional synthesis software to synthesize new images, and the images produced after printing on the grating plate make the observer The images you see are getting bigger and smaller.
2.5.Morph (similar to the progressive way of changing face): It is made by selecting two similar images to be deformed by the designer or using professional software to generate multiple images, and a new image is produced by professional synthesis software, which is printed on the grating plate. The regenerated image allows the viewer to see the image progressively transition from one image to another, with a continuous effect.
2.6. Folding effect: After special image processing, the image background will produce some geometric images, so that the image has different depth and depth effects or irregular dynamic changes, which can be used as anti-counterfeiting design.
Combining the above various effects, it can be designed on the same print according to actual needs, showing unique effects.
Fourth, the application and prospects of three-dimensional printing
As one of the special printing technologies, three-dimensional printing has several times higher added value than the processing profit of flat printing, and has a broad market prospect. At present, it has been widely used in various fields such as packaging and decoration products, commercial advertisements, anti-counterfeiting marks, trademark tags, mouse pads, and various credit cards. Three-dimensional printing is prone to inaccurate color overprinting, large cumulative error in the plate making process, and inconsistent bonding of printed matter and lenticular grating sheets, resulting in high scrap rate and high printing cost.
With the development of digital information technology, stereo photography has entered the digital age, and stereoscopic image synthesis uses computer software. In addition, CTP technology, FM screening, high-precision printing equipment applications, greatly simplify the process, speed up the publishing cycle, improve product quality, not only reduce costs, but also ensure the quality of three-dimensional printing. The three-dimensional printing technology has been continuously optimized and updated, and the process is gradually improved, which will have a place in the market development. Three-dimensional printing has been effectively developed in China's printing industry, and the domestic three-dimensional printing market has great potential and broad development space.