Key Technology of Stereo Printing and Its Application Analysis (three)
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Third, the development and prospects of three-dimensional printing
Three-dimensional printing is a new type of special printing, which has broad prospects for development. Nowadays, in addition to conventional paper and plastic materials, it is also showing its advantages in other aspects, such as:
1, three-dimensional cartoon printing
Three-dimensional printing products, there is a kind of cartoon. Stereo photographic printing mainly consists of grouping six images in one unit of the lenticular sheet; in the case of animation, it is mainly two images, and rarely three images. After the lenticular lens is used in the cartoon printing, not only the three-dimensional picture but also the moving picture can be obtained by changing the angle of the picture. We know that the right and left eyes observe different pixel lines, and hundreds of different pixel lines under the corrugated transparent sheet are combined. Since the viewing angles of the two eyes are different, a stereoscopic image of all the pictures can be obtained. In addition, the observed picture can obtain a stereoscopic effect when viewed at any angle, and can store 1, 2, 3, ... pixel lines under each corrugated unit of the corrugated transparent sheet, when the positions of the left and right eyes move. When the pixel lines 1 and 2, 2 and 3, 3 and 4, ... are combined in pairs, they can be continuously seen through the transparent sheet. In the case of animation, the texture of the corrugated transparent sheet is formed into a horizontal horizontal position, and the pixels are observed together with the pixel lines 1, 2, 3, ..., which are in each cylindrical unit with a pitch of 0.6 mm. 18, and then made a cartoon by printing. It can also be said that the original painting (equivalent to the continuous two sides of the 18-piece movie) is stored in a photo, and a raster transparent film is placed on top of it, shaking from front to back, which is equivalent to a movie in one second. The action picture that can be displayed inside. In addition, there is an animated cartoon that changes in several parts on the same screen. The steps to create such a dynamic three-dimensional picture are as follows:
First of all: to prepare a different animated photo, it is to use 18 films to overlap and make a photo. Use this photo as the original, add a thin transparent plastic plate in front of the camera's photosensitive sheet, and then place an inch-size, 300-line screen at an appropriate distance in front of the plastic plate. Then, the reflected light of the photo passes through the screen and the plastic plate to reach the photosensitive sheet, that is, a photographic film which is formed by successive images decomposed into pixels. With this plate printing, a dynamic picture can be produced. However, this picture is so blurred, it is very vague, you can't see the outline of the image, you must also attach a transparent column lens on both sides to achieve the purpose of direct viewing with the naked eye. If the printed three-dimensional print is called a three-dimensional space print, and then the dynamic factors are added, the three-dimensional sense and animation can be combined to produce a new four-dimensional space print.
2, printing a three-dimensional pattern on the fabric
Printing on textiles has always followed the traditional graphic printing process. Printing technicians can print anything they imagined, but designers can only design flat objects, with the exception of foaming inks. Although foamed inks can produce three-dimensional effects, the degree of foaming is difficult to control, and even the best printers use foamed inks to print, it is difficult to accurately replicate the subtle levels of the image.
Recently, in the United States, a research team has developed a new T-shirt screen printing ink with an ink layer thickness of more than 600 μm, which can effectively control the protrusion of the ink layer. In contrast to the previous case, the thickest ink layer of a normal print is usually the ink layer of the metallic decorative ink printed on the transfer paper. It is reported that the thickness of the ink layer on the flat and non-porous printing materials with good ink performance is currently only up to 250 μm. However, the thickness of the ink layer is not the most prominent feature of the three-dimensional printing of the fabric, the most striking is its high resolution and clarity. Three-dimensional printing makes the edges of the ink layer very clear and smooth, and looks like die-cut or laser-engraved. The three-dimensional printing ink film is not like the high opacity ink transfer, the jersey printing, and the plastic ink printing. The edges of the image are often very thin. Regardless of the high definition of the stencil, the printed image is easily smashed; Like the foamed ink, although a thick ink layer can be printed, the edges are not clear and regular after curing. The three-dimensional print is clear and clean. Since the 1980s, with the gradual systematization of the four-color printing process of textiles, some people have been working on three-dimensional printing to reform the T-shirt decoration process. However, due to translation and other reasons, three-dimensional printing is often called "high-density printing." In fact, the three-dimensionally printed ink film is only a higher density than the conventionally cured foaming ink, and has no high hiding power. The white plastic ink has a high density.
The characteristics of 3D image printing are not just the use of a different ink or emulsion. Successful 3D printing requires mastering different operating procedures than standard printing. Although it is not difficult, it is very different, and it must be different. Combined with many integrated systems, 3D printing can have a huge new impact.
We know that the printing of textiles is screen printed, and the description here is based on screen printing. On the screen, three-dimensional printing uses a 24 wire/cm screen and is stretched onto the frame of the repeatable stretch net with a tension of at least 30 N/cm. This type of wire mesh currently has five wire diameters ranging from 120 to 145 μm. It has been proved that it is better to use the wire mesh with the finest wire diameter because the wire of the fine wire diameter can fill the opening of the same plate as much as possible. In addition, it is preferable to use a dyeing screen because the emulsion used in the three-dimensional printing process requires a long exposure time, and the dyeing screen can reduce the light scattering property. On the stencil, screen printing technicians know that the stencil thickness is the main factor affecting the thickness of the ink film, as well as 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 each operation is guaranteed to be correct, the cured ink film can reach 90% of the thickness of the stencil. In three-dimensional printing, a 200 μm stencil is usually used. The current problem is not only to understand how thick the template is for 3D printing, but more importantly, to understand how to make a thick template. The following describes the production methods of the three thick stencils and discusses their advantages and disadvantages. Although the emulsions selected for each of the coating methods described below are slightly different, rapid exposure must be used to compensate for the ultra-thick emulsion layer. A fast-exposure type SBQ emulsion or a pure photosensitive resin emulsion (liquid or film) is preferably a diazo or double cure type.
(1) Liquid emulsion. The most basic method is to repeatedly apply a liquid emulsion on the screen, and it is necessary to apply 15-20 times on the printing surface of the screen to achieve the desired thickness of the stencil. The first layer of emulsion is first applied to the printed side of the screen and then thoroughly dried. In order to shorten the drying time, the drying chamber should be equipped with a dehumidifier to keep the humidity at 40%-45%. After the first layer of emulsion is applied and dried, tape is applied around the image of the same printing surface to quickly increase the thickness of the stencil. Apply a second layer of emulsion and dry it before applying a layer of tape. Repeat steps 2 and 3 until the desired stencil thickness is achieved. 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 well controlled. The most difficult thing is that due to the irregular coating method, it is very likely that the total number of coated coatings will be missed.
(2) Capillary photosensitive film. A method of quickly making ultra-thick stencils. The capillary photosensitive film is attached to the screen, and the most ideal material is a thickest pure photosensitive resin capillary film. Currently, 150 μm direct capillary sheets are on the market, and 200-250 μm membranes will soon be available. When attaching the capillary photosensitive film, a flat plate should be prepared first, which is smaller than the inner frame size, larger than the outer size of the image, and 1 mm thick, and the surface should be absolutely smooth. It is recommended to use a glass plate with rounded edges and corners to ensure complete contact between the screen and the diaphragm; then place a capillary photographic film on the plate with the emulsion facing up; then place the screen on the capillary photographic film The printed side is facing down. A thin layer of liquid emulsion is poured onto the screen along one side of the capillary photosensitive film, and the liquid emulsion is dispersed throughout the screen, contacted with the capillary photosensitive film to adhere the film; and finally the emulsion layer is dried. It is to be noted, however, 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 photographic films.
To increase the thickness of the stencil, after the capillary photographic film/direct emulsion layer is dried, the polyester substrate is peeled off from the film and another layer of capillary photographic film is pasted on it. The operation is as follows: first, the coating solution is prepared in a ratio of 1 part of the liquid emulsion to 15 parts of water, and the tape is attached to the opening portion of the screen printing surface. The screen is then placed vertically against the side of the cleaning bath, and the capillary photosensitive film adhered to the screen is coated with the coating solution. Another layer of capillary photosensitive film is pasted onto the film that has just been wetted with the liquid emulsion, and the emulsion is laminated with the emulsion layer. The film was dried and the polyester base film was peeled off. To continuously increase the emulsion layer, the screen can be repeatedly placed vertically against the cleaning tank, and the capillary photosensitive film adhered to the screen is coated with the coating solution. Repeat 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 stencil surface is smooth, and the emulsion layer is well controlled. The disadvantage is that the operating procedure is slower, certainly not as slow as liquid emulsion coating.
(3) Method for making thick film. The quickest way to make a thick emulsion layer is to use a diaphragm that is as thick as possible. Its thickness ranges from 100 to 700 μm. They are not capillary photographic films and require a special process. First select a diaphragm of the desired thickness, the cut size is 6-10mm larger than the image size on the stencil. The plastic protective film was peeled off from one side of the film, and the emulsion was placed face up on a flat plate (the flat plate was the same as the flat plate for the above-mentioned fine photosensitive film).
Place the printed side of the screen face down on the diaphragm on the plate. The liquid emulsion is then diluted and formulated in a ratio of 2 parts emulsion to 1 part water. The thinned liquid is dripped from one side of the membrane. The emulsion on the surface of the membrane is smoothed and covered evenly. Brush off the excess emulsion and dry the same version. After the screen is completely dried, the screen surface of the screen is coated with a bucket applicator filled with an undiluted liquid emulsion. Dry the screen again, discard the second plastic protective film from the diaphragm and prepare for exposure. This method is the fastest way to make a three-dimensional printing template, but the current supply of such stencil materials is limited.
As for the exposure of the screen, since the emulsion type, thickness, coating technology and exposure equipment will affect the exposure time, in general, the exposure can be mastered as follows: if the exposure source is a 50kw metal halide lamp, the template is 16cm away from the stencil. The cloth thickness is 700 μm and the exposure time should be 7.5-8 mln. After exposure, soak both sides of the screen, soak the emulsion for a few minutes, then rinse. The cleaning process should not be urgent, soak and rinse until all the images appear. If the positive picture used is very clear and the density is high, the fine level after development will be clear. The cleaning time of the screen version is longer than that of the ordinary screen version, so it is necessary to have great patience.
As for press debugging, 3D prints are easy to print on fully automatic screen printers because of the good control of the mesh distance, which is a key factor in printing. The operation instructions of the automatic screen printing machine should pay attention to the following points: the screen is installed on the printing machine, the screen spacing modulation is the smallest; the ink filling speed is slightly slower than the ordinary one, and the constant ink-plate pressure is adopted. If the angle of the inking plate is adjustable, the angle between the inking plate and the screen can be minimized, and then the ink is applied to the screen plate; the blade is adjusted with a medium hardness of 75°-80°. The pressure makes it possible to transfer the ink on the same plate to the fabric. The speed of the squeegee is slightly slower than normal, and the printing speed is preferably slower than usual. For better results, the print stroke is as clean and smooth as possible, and scraping the ink twice will make the print dirty. Of course, a manual printing machine can also be used, but it is difficult to print a uniform product, and the thickness of the ink layer is almost impossible to reach 500 μm or more.
If you want to increase the thickness of the ink film, the best way is to increase the thickness of the emulsion layer on the screen. You can't increase the thickness of the ink layer by scraping the ink twice on a screen. Because the first time the ink layer is dried, it will block the net and it will not be scraped again. Another method of increasing the thickness of the ink layer is to make two thick screens, two screens are continuously printed, and the second template is printed on the image printed with the first stencil, and the ink layer between the two stencils is It can be dried in an instant, and the second layer of ink is applied to the first layer of ink film. As a result of this printing, the thickness of the ink layer is substantially twice that of a stencil. The three-dimensional portion of the image at the time of printing should be printed last and dried immediately after printing. If the three-dimensional ink is printed first, then printing other colored inks after drying will cause deformation near the three-dimensional portion of the three-dimensional printing ink.