Three-dimensional printing is a branch of the printing process. It is a combination of raster stereoscopic imaging technology and special printing technology, which enables the flat-printed image to exhibit a strange visual experience of stereoscopic vision and alien animation. The company where the author is also engaged in three-dimensional printing, so here to talk about their own experience with their own production practice experience.
Stereo printing There are two general methods of printing:
The first is to print on the surface of paper or synthetic paper with a common machine. After the ink on the surface of the paper is dried, the lenticular sheet matching the image is used to face the paper. In general, when printing on paper using solvent-based inks, the ink is dried by osmotic and oxidative conjunctiva. The number of screens required for three-dimensional printing is high. In general, the network expansion is inversely proportional to the perimeter of the network. In other words, the higher the number of screen lines, the smaller the network points, and the more serious the network points are expanded during the printing process and drying process. Therefore, when a high number of lines is printed on the paper, the dark portion of the image is prone to stencil printing, resulting in the loss of image darkness levels. At the same time, the grating is generally manually operated. Since the matching of materials and images is very demanding in the three-dimensional printing, if the process control is improper, the product rejection rate is high.
The second method is to print directly on the back of the grating. Since the material of the grating is a polymer material, it is a non-absorbent surface, and ordinary ink printed on the grating material will not be permeated and dry. Therefore, we use a UV ink printer to directly print on the back of the grating. ,Using UV drying principle to make the photochemical reaction of ink, instantaneous drying. At the same time, it should be noted that when the film is discharged, the film surface is facing upwards, which is the opposite of the film film surface of the first method.
UV curing means that under the irradiation of ultraviolet light, the photoinitiator absorbs ultraviolet radiation and then splits into free radicals, causing the prepolymer to polymerize, cross-linking the grafts, and solidifying into a three-dimensional network in a very short time. High-molecular polymers give cured films, which essentially achieve chemical drying through the formation of chemical bonds. The three-dimensional printing adopts the technology of direct printing on the back of the grating. UV curing can effectively control the loss of fine dots and improve the ink transfer rate of the color registration.
(1) Different types of substrates should be selected for different inks. The light transmittance, the curing rate, the hiding of the ink, and the glossiness of the surface of the ink should be taken into consideration. The ink balance is a well-known principle, specifically: the pH of the water is the same as the pH of the ink, otherwise it is not a water-colored oil, it is an oil-colored water (herein for offset printing), and the ink emulsification phenomenon is formed, leading to the UV ink The ink film is opaque and directly affects the pass rate of ultraviolet light energy. This will slow down the drying time of the film, and even though it is solid, there is still moisture in the ink film. Once it is rubbed or stuck with an adhesive tape, the ink film will be pulled off. At the same time, we must strictly control the temperature and humidity of the UV ink warehouse and printing shop. Prevents long-term exposure of the ink to natural light. Because ultraviolet light contains a small amount of ultraviolet light, if it is exposed for a long time, dry crusts may occur on the surface of the UV ink, affecting the use, and even causing printing accidents. At the same time, the impurities of the ink and the deposition of dust during the production process will weaken the effect of the light intensity in the ultraviolet region, thereby greatly reducing the drying time of the light-curing ink. Generally, it is required to clean the dust and cover the ink tank (bucket) in time. The company where the author is working in the production of grating products uses Gao's RAP series inks. This type of ink has good printability.
(2) Photo-curing inks generally strictly stipulate the order of printing, that is, the color sequence. UV printing ink is strictly according to its wavelength. Otherwise it is difficult to achieve consistent drying after light curing, especially the hue balance of the hue. In color printing, the ability of various pigments to absorb UV photons is different, and its transmittance is from high to low as yellow, black (MYC, K), so the curing degree of each color ink is also different. The transmittance directly affects the photon's excitation energy of the photoinitiator. Since the yellow (Y) has the lowest visual stimulus to the human eye, the printing color sequence should be ranked as black cyan, magenta, and yellow (KCM, Y). The ink with poor light transmission absorbs as many photons as possible, enhancing its curing effect.
(3) The use of the alcohol dampening system can reduce the surface tension of the ink and promote the curing effect. In the printing process, the dampening area (blank portion) of the printing plate can be intensified with a fountain solution to ensure that the lipophilic area is adequate. Intimate ink, the hydrophilic area does not ink.
Improvement of the ink formulation and the addition of the corresponding additives can increase the hydrophobicity of the ink, but the excessive hydrophobicity will cause the ink on the edge of the image to shrink, the loss of fine levels, and the unclear dot boundary affect the quality of the print. Participating in UV inks and catalytic drying (curing) are photosensitizers and initiating crosslinkers. Usually people only pay attention to the pigment wavelength and ignore the different viscosity, different purity of the printing ink, scientific choice of different photoinitiators or crosslinking agents. For example, benzoin is different from benzophenone because it is both a photosensitizer and an initiator.
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