Three-dimensional printing is a special printing that has been popular in recent years. Three-dimensional printing is to simulate the distance between human eyes and shoot from different angles. 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. The principle of pixels is printed. It can reproduce objects realistically and has a strong three-dimensional sense. The product image is clear, rich in layers, vivid in image, and has a deep artistic conception. The printed matter has good gloss, bright colors, and is not easy to fade. Because the surface of the printed product is covered with a layer of concave and convex cylindrical mirror grating, you can directly watch the stereoscopic effect of the panoramic picture. Three-dimensional printing usually prints three-dimensional images on paper, plastic and other substrates. Common three-dimensional printing, holographic three-dimensional printing, three-dimensional printing of fabrics, etc. are widely used in the fields of packaging printing, anti-counterfeiting printing and textile printing. In addition, three-dimensional printing is also widely used in the printing of the manufacturing casting industry, such as the three-dimensional printing (3DP) process, which can be used to manufacture ceramic shells and cores for casting. With the continuous development of screen printing technology and the increasing demand for the novelty of fabric printing, this special printing has also played an important role in fabric printing. Textile screen printing has opened up a new development direction.
Printing pictures and texts on textiles has always followed the traditional flat printing process. The printing technician can print anything imagined, but designers can only design flat objects, with the exception of foaming ink. Although foaming ink can produce a three-dimensional effect, the degree of foaming is difficult to control. Even the best printers, when printing with foaming ink, are difficult to accurately reproduce the fine layers of the image.
In recent years, a new type of T-shirt screen printing ink has been developed in the United States. The thickness of the ink layer can reach more than 600 μm. At the same time, the protrusion of the ink layer can be effectively controlled. Compared with previous conventional printed products, the thickest ink layer of ordinary printed products is usually the ink layer of metal decorative ink printed on the transfer paper. At present, the thickness of the ink layer on a plane with good inking performance and a non-porous printing material can only be up to 250μm. However, the thickness of the ink layer is not the most significant feature of three-dimensional printing of fabrics. The most striking is its high resolution and Clarity. Three-dimensional printing can make the edges of the ink layer very clear and smooth, and it looks like it has been die-cut or laser engraved. The three-dimensional printing ink film is not like the transfer of high hiding power ink, sports shirt printing and plastic ink printing, the edge of the image is often very thin, no matter how high the resolution of the template, the printed image is easy to be smeared; nor Like foaming ink, although a thick ink layer can be printed, the edges are not clear and irregular after curing. The three-dimensional print is very clear and regular, and looks almost like mechanical engraving. Since the 1980s, with the gradual systemization of the textile four-color printing process, some people have been committed to three-dimensional printing to reform the T-shirt decoration process. However, due to translation and other reasons, 3D printing is often called "high density printing". In fact, the density of the ink film for 3D printing is not too high, but it is higher than the density of the conventional cured foam ink, and there is no high hiding power. The density of the white plastic ink is higher.
The characteristics of 3D image printing are far more than the use of a different ink or emulsion. Successful 3D printing requires a different operating procedure than ordinary printing. Compared with standard printing procedures, although it is not difficult, it is very different, and It must be well integrated with many integrated systems before 3D printing can have a new and huge impact.
We know that screen printing is the most commonly used printing method for textile printing. On the silk screen, the three-dimensional printing uses a 24 wire / cm screen, stretched on the reproducible screen frame, the tension is at least 30N / cm. This screen currently has 5 wire diameters, the range of which is 120 ～ 145μm , Practice has proved that it is better to use the finest wire mesh, because the fine wire mesh can fill the openings of the same version with as much ink as possible; in addition, it is best to use dyed wire mesh, because three-dimensional The emulsion used in the printing process requires a longer exposure time, and the dyed screen reduces the light scattering performance. On the stencil, screen printing technicians know that the thickness of the stencil is the main factor affecting the thickness of the ink film, and the same is true in three-dimensional printing. The thickness of the stencil is directly related to the thickness of the ink film after curing. Practice has proved that if every operation process is guaranteed to be correct, the cured ink film can reach 90% of the thickness of the template. In three-dimensional printing, a 200 μm stencil is usually used.
At present, there are three main types of thick template production, each with advantages and disadvantages. Although the choice of emulsion for each coating method is slightly different, it is necessary to use rapid exposure to compensate for the extra thick emulsion layer. Fast exposure type SBQ photosensitive emulsion or pure photosensitive resin emulsion (liquid or diaphragm) is best to choose diazo or dual curing type. For screen three-dimensional printing, not only to understand how thick the template is for printing, but more importantly, you must be familiar with the method of making a thick template. Let's talk about the selection and use of materials in the three-dimensional printing of fabrics.
1. The most basic method of liquid emulsion is to apply liquid emulsion repeatedly on the screen, which needs to be applied 15 to 20 times on the printing surface of the screen to make the stencil reach the required thickness. First apply the first layer of emulsion to the printed side of the screen, and then dry it thoroughly. In order to shorten the drying time, the drying room should be equipped with a dehumidifier to keep the humidity between 40% and 45%. After the first layer of emulsion is applied and dried, tape is applied around the image on the same printing surface to quickly increase the thickness of the stencil. Apply a second layer of emulsion and apply a layer of tape after drying. Repeat steps 2 and 3 until the required stencil thickness is reached. The advantage of this method is that it can be operated with familiar techniques. The disadvantage is that it takes too long (at least a few days), and the thickness of the emulsion layer is not easy to control. The most difficult thing is that due to the irregular coating method, it is likely that the total number of coatings that have been applied is missed.
2. Capillary photosensitive film is a method of making ultra-thick template quickly. The capillary photosensitive film is attached to the silk screen. The most ideal material is a thickest pure photosensitive resin capillary film. Direct capillaries of 150 μm are currently on the market, and membranes of 200 to 250 μm will soon be available.
When pasting the capillary photosensitive film, you should first prepare a flat plate, which is smaller than the inner size of the screen frame, larger than the outer size of the image, 1mm thick, and the surface should be absolutely smooth. It is recommended to use a glass plate with smooth edges and four corners, and ensure that the screen and the film are in full contact; then put a capillary photosensitive film on the flat plate with the emulsion side up; then put the screen on the capillary photosensitive film On the film, the printed side is facing down. Pour a thin layer of liquid emulsion on the screen along the side of the capillary photosensitive film, and disperse the liquid emulsion on the entire screen, contact with the capillary photosensitive film, and paste the die; finally dry the emulsion layer. However, it must be noted that a liquid emulsion compatible with the capillary photosensitive film must be used, that is, the sensitizer of the liquid emulsion used is the same as that of the capillary photosensitive film, and has the same basic chemical properties. Most emulsion manufacturers are able to provide compatible emulsions and capillary photosensitive films. To increase the thickness of the stencil, after the capillary photosensitive film / direct emulsion layer is dried, tear off the polyester base from the film and continue to paste another layer of capillary photosensitive film on it.
The operation is as follows: First, the coating solution is prepared with a ratio of 1 part liquid emulsion to 15 parts water, and tape is applied to the opening of the screen printing surface. Then, hold the screen vertically against the side of the cleaning tank, and coat the capillary photosensitive film that has been pasted on the screen with the coating solution. Paste another layer of capillary photosensitive film on the film just soaked with liquid emulsion. The emulsion is laminated with the emulsion layer. Dry this layer of film, and then tear off the polyester base film. To continuously increase the emulsion layer, you can repeatedly hold the screen vertically against the side of the cleaning tank, and coat the capillary photosensitive film that has been pasted on the screen with the coating solution. Repeat the operation until the desired emulsion thickness is reached. The advantage of this method is that the thickness of the stencil can be increased as needed, the surface of the stencil is smooth, and the emulsion layer is well controlled. The disadvantage is that the operating procedure is slow, and certainly not as slow as liquid emulsion application.
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