3D Printing
3D printing, also known as stereoscopic printing, typically refers to stereolithography printing. It employs a principle that simulates the spatial difference perceived by human eyes, recording pixels of different angles and depths on photosensitive materials. With the combination of grating materials, it presents a three-dimensional effect or even a virtual reality on a two-dimensional surface image. Through this method, people can experience the wonderful pleasure of viewing three-dimensional images directly with their eyes, without the need for any tools. Like three-dimensional stereograms, 3D printed materials do not exhibit a three-dimensional effect when viewed on a computer screen. However, after printing, due to the special properties of the grating material, a three-dimensional effect can be seen without the need for stereoscopic glasses.
Early images were presented in black and white (monochrome) and later evolved into color. Currently, there is a greater emphasis on 3D printing and even virtual reality. The technology for converting flat images into three dimensions was introduced over 30 years ago but was limited by materials and unresolved key technologies. As a result, it could only be applied to small areas and could achieve no more than four layers of pseudo-3D (3D printing), such as commonly seen in animations created using image displacement techniques.
To display depth in thin-sheet printing or create magical animation effects, grating sheets are currently used for printing. Holographic laser film cannot reproduce true colors. Currently, the most widely used grating internationally is PET columnar grating. PET has advantages such as high transparency, moderate hardness, and environmental degradability, making it more suitable for folding boxes and providing clearer images compared to PP. To achieve the desired image accuracy, typically, a grating of 100 lines to 161 lines (the number of grating stripes per inch) is used. Packaging boxes usually use a 75-line grating.
Grating printing requires high standards for publishing and printing equipment, as well as considerable professional experience from factory personnel to design and print clear and aesthetically pleasing three-dimensional images or animated pictures.
Currently, three-dimensional packaging boxes, three-dimensional plastic sheets, and three-dimensional grating sheets made from non-toxic, harmless, recyclable, and environmentally friendly PET materials are widely used for three-dimensional anti-counterfeiting and aesthetically pleasing packaging of products such as cigarettes, alcohol, cosmetics, and medicines. They are also used in various fields such as promotional advertisements, posters, wedding photography, stationery, calendars, various cards, postcards, hanging tags, and tote bags. 3D technology can adapt to various fields such as politics, economics, military affairs, science, culture, and art, meeting the extensive needs of the global economy and society.
3D Stereoscopic Embossing Technology
3D stereoscopic embossing technology is a novel three-dimensional printing technology that creates special three-dimensional effects with a series of stripes, icons, trademarks, and other patterns. The depth of field can be controlled arbitrarily, and even super-depth images can be created.
Due to the structural characteristics of the three-dimensional columnar grating, no matter how advanced traditional three-dimensional printing technology and printing equipment are, it cannot overcome the phenomenon of abrupt changes in the three-dimensional image. Even with precise control of three-dimensional printing technology, there may still be 2 to 6 abrupt changes in the image. If the three-dimensional printing technology is not up to standard, the flickering points will move around the image, which is the fundamental reason why many people feel dizzy when viewing three-dimensional images.
Regardless of how exquisite the printed image is, if it causes discomfort to consumers due to three-dimensional printing technology, it will affect the product image to some extent. Now, with the use of 3D stereoscopic embossing technology, not only is dizziness eliminated, but the product grade is also improved, attracting consumers and serving as a certain anti-counterfeiting measure.
The biggest difference between 3D stereoscopic embossing technology and traditional three-dimensional printing technology lies in the absence of abrupt changes and flickering in the three-dimensional effect. The image has a three-dimensional effect from any angle, but there are no flickering points. In other words, viewing from any angle is comfortable without flickering, which cannot be achieved by traditional three-dimensional printing technology.
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.
The main difference between the materials used in three-dimensional printing and those used in flat printing is the use of grating materials. Grating sheet materials mainly include hard plastic three-dimensional grating sheets and soft plastic three-dimensional grating sheets. Hard plastic three-dimensional grating sheets are made of polystyrene raw materials processed by injection molding to form concave-convex cylindrical grating sheets. Polystyrene is colorless and transparent (transparency reaches 88%-92%), with a refractive index of 1.59-1.6. It is non-stretchable and flammable. Its high refractive index gives it a good gloss. Processing transparent plastics produces birefringent stress—optical effects. Its tensile strength is 3.52-6.33 MPa, bending strength is 6.12-9.84 MPa, and heat distortion temperature is 70°C-98°C. Polystyrene's chemical properties include resistance to certain mineral oils, organic acids, alkalis, salts, low-level alcohols, and their aqueous solutions. It softens after being attacked by hydrocarbons, ketones, and higher fatty esters and dissolves in aromatic hydrocarbons and monomers such as toluene, xylene, and styrene. In some cases, the degree of attack by chemical reagents on polystyrene can be reduced by annealing and stress relief measures. Soft plastic three-dimensional grating sheets mainly use polyvinyl chloride substrates pressed into soft plastic three-dimensional grating sheets by metal grating drums or grating plates. Polyvinyl chloride is a polymer compound made by polymerizing chloroethylene and is difficult to burn. Although both polyvinyl chloride and polyethylene are milky white, polyvinyl chloride can be made into colorless, transparent, glossy films and films of various softnesses according to the content of plasticizers. This material is also highly resistant to pulse heat sealing, high-frequency heat sealing, and bonding. Polyvinyl chloride's chemical properties include good resistance to chemical corrosion, but poor thermal stability and light resistance. It begins to decompose hydrogen chloride at 140°C, so stabilizers need to be added during manufacturing. The chlorine content of polyvinyl chloride is 56%-58%, and low molecular weight polyvinyl chloride is soluble in ketones, esters, and chlorinated hydrocarbon solvents. High molecular weight polyvinyl chloride is less soluble.
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