Application of ink in three-dimensional printing

Stereo printing is a branch of the printing process. It is a combination of raster stereoscopic imaging and special printing processes. The flat printed image presents a strange visual experience of stereoscopic vision and alien animation. The author's company is also engaged in three-dimensional printing. So here we talk about our experience with our own production practice experience.

Three-dimensional printing

Stereo Printing There are two ways to print in the usual way.

The first is to use ordinary machines to print on the surface of paper or synthetic paper. After the ink on the paper surface is dry. Use the lenticular sheet that matches the image and the paper. usually. When printing on paper using solvent-based inks, the ink is dried by penetration and oxidative conjunctiva. Three-dimensional printing requires a high number of screens. In general, outlet expansion is inversely proportional to the perimeter of outlets. In other words: The higher the number of screens, the smaller the number of points. The more serious the dot expansion 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 raster. Because the material of the grating is a polymer material, it is a non-absorbent surface, ordinary ink printed on the grating material will not be osmotic drying, so we use the uV ink printing machine to print directly on the back of the grating, using UV drying principle to make the ink produce photochemical reaction. Instantly dry. 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 refers to the photoinitiator splitting into radicals after absorbing ultraviolet radiation under the irradiation of ultraviolet light. Initiate prepolymer polymerization, cross-linking reaction. Cured into a three-dimensional mesh polymer in a very short time. Get a hard film. The essence is chemical drying through the formation of chemical bonds. The three-dimensional printing uses the technology of direct printing on the back of the raster, UV curing can effectively control the loss of small dots. Increase the ink transfer rate of the overprint.

UV offset printing three-dimensional printing matters needing attention

(1) different types of substrates should choose different inks. It is necessary to comprehensively consider the light transmittance, the curing rate, the hiding of the ink, and the glossiness of the surface of the ink. 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 oil-water (here 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 film drying time, even though the light is solid, but the ink film still has moisture, once rubbed or glued with a secure graphic. You will find that the ink film is pulled off. Simultaneously. We must strictly control the temperature and humidity of UV ink warehouses and printing plants. 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 crusting will occur on the surface of UV ink, which will affect its use. It even caused a print accident. 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 UV region, which greatly reduces the drying time of the photo-curable ink. It is generally required to clean the dust and cover the ink tank (bucket) promptly and frequently. 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) Light-curing inks generally strictly stipulate the order of printing. The color sequence. UV printing ink is strictly according to its wavelength. It is difficult to achieve consistent drying after photocuring. Especially the hue of the hue. In color printing. The ability of various pigments to absorb UV photons is different, and its transmittance from high to low is yellow, black (MYC, K). Therefore, the degree of curing of each color ink is also different. The transmittance directly affects the excitation energy of the photon to the photoinitiator, and the yellow (Y) has the lowest visual stimulus to the human eye. Therefore, it is advisable to rank the printing color sequence as black cyan, magenta, and yellow (KCM, Y) so that the ink with poor light transmission absorbs as many photons as possible. Increase 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 liquid (blank portion) of the printing plate can be intensified by using a fountain solution to ensure that the lipophilic region is sufficient. Ink. The hydrophilic area is not inked.

Improve the ink formulation and add the appropriate additives to increase the hydrophobicity of the ink. However, if the hydrophobicity is too strong, the ink on the edge of the image will be shrunk. The loss of fine levels and unclear borders will 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. It is another initiator.

(4) The three-dimensional printing has high requirements on the surface strength of the grating, the surface strength is not enough, and printing accidents with poor pitching force are prone to occur. Since the grating surface is smooth, the affinity for the ink is small, and the first color ink is easily pulled off when the second color is overprinted. Therefore, in the three-dimensional printing, the grating material with larger surface tension should be selected, and the color sequence should be reasonably arranged to adjust the relevant process parameters in the printing process so as to avoid and reduce the occurrence of the above phenomenon.

(5) Different types of inks have different drying characteristics. To fully dry the UV ink, a UV light source that matches the ink needs to be selected. The commonly used uV light sources are high-pressure mercury lamps, ozone-free lamps and metal halide lamps. The lamp cooling methods include ventilation cooling and water cooling. When choosing uV light source. It depends on the drying conditions of uV ink and uV varnish. Also compare the UV lamp irradiation efficiency. Different UV lamps have different irradiation efficiencies.

30% of uV light absorbed by the ink when dry, directly from the light source. 70% from the reflector reflection. Nowadays, aluminum reflectors are used more often. Because of the different processing technologies, the reflectivity of the reflectors varies greatly. Therefore, when detecting uV light energy, not only the lamps but also all ultraviolets including reflected light must be measured. The amount of light. In the three-dimensional printing, it is necessary to use a cold reflective plate, which reflects only the ultraviolet rays and transmits the infrared rays, so that the surface temperature of the printed matter drops by 10°C. In addition, the general life of ultraviolet lamps is about 1 000 hours. That is very limited. This also directly affects the drying and curing time of the UV ink.

(6) In addition to the positive PS version for uV inks, if other positive Ps versions are not processed by baking, the print resistance is low. Therefore, the baking treatment is required. The baking conditions are 250°C, 6-8. minute. Negative Ps version, try to use high-resistant printing plate. At the same time, there is no special fountain solution for uV ink, and excessive gum arabic should be avoided in the fountain solution during UV ink printing, because gum arabic will react with UV ink, causing the failure of the blanket blanket of ink.

(7) As domestic uV offset printing is still not very common, and there are few technical operators for the equipment, so companies need to invest considerable funds in the training of operators. This is also a difficulty in the control of Wei J in the three-dimensional printing process. weight.

Reprinted from: Print Quality and Standardization