The key technology of three-dimensional printing and its application analysis (2)

Third, the development and prospects of three-dimensional printing

Three-dimensional printing is a new type of special printing. It has broad prospects for development. Now, in addition to conventional paper and plastic materials, it is also showing signs in other aspects. For example:

1, three-dimensional cartoon printing

Three-dimensional printing products, there is a kind of called animation. Stereo photo printing is mainly used to group six kinds of images in one unit of a lenticular sheet; whereas in the case of animation, two images are mostly and three are rarely. After using the lenticular lenticular film for cartoon printing, not only three-dimensional pictures but also moving animations can be obtained by changing the screen angle. We know that the right eye and the left eye observe different pixel lines, and hundreds of different pixel lines under the corrugated transparent plate are combined. Since the two eyes observe different angles, a stereoscopic image of the entire screen can be obtained. In addition, the observed picture can acquire three-dimensionality when viewed from any angle, and 1, 2, 3,... pixel lines can be accumulated under each corrugated unit of the corrugated transparent sheet, and the positions of the left and right eyes can be moved. At this time, the pixel lines 1 and 2, 2 and 3, 3 and 4... are combined in pairs so that they can be seen continuously after being enlarged by the transparent sheet. In the case of animation, the texture of the translucent transparencies is made horizontally horizontally, and the lines of the pixels 1 , 2, 3,... Are observed together. These pixels are in each cylinder unit with a pitch of 0.6 mm. 18, and then made into cartoons by printing. Can also be said to be attached to the original painting (equivalent to the film of the 18-frame continuous two sides) stored in a photo, on which a raster transparent film across, from the front to the back, it is equivalent to a movie in a second The action can be displayed within. In addition, there is an animation that makes different shifts in several sections on the same screen. This dynamic three-dimensional picture production process is as follows:

First of all: to prepare an unusual animated picture, it is to use a series of 18 video frames in order to overlay into a photo. Use this photo as a document, and apply a thin, transparent plastic plate to the front of the camera's photosensitive sheet, and place a one-inch, 300-line screen at an appropriate distance before the plastic sheet. Then, the reflected light of the photograph reaches the photosensitive sheet through the screen and the plastic plate, and a photographic negative film formed by decomposing continuous images of pixels is made. With this lithography, you can create a dynamic picture. However, this picture is so obscure that the contours of the image cannot be seen, and it is also necessary to attach transparent lenticular lenses on both sides in order to achieve direct viewing with the naked eye. If the printed three-dimensional prints are called three-dimensional space prints, then the dynamic factors will be added, so that a combination of three-dimensional sense and animation can produce a new four-dimensional space print.

2, printing three-dimensional pattern on the fabric

Printing graphics on textiles has always followed traditional graphic printing processes. Printing technicians can print anything they imagine, 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. Even the best printing workers use foaming inks to print, it is difficult to accurately reproduce the fine level of the image.

Recently, in the United States, a research team has developed a new type of T-shirt screen printing ink with an ink layer thickness of 600 μm or more, and at the same time, it can effectively control the bulging of the ink layer. In contrast to the previous situation, the thickest ink layer of ordinary prints is usually the ink layer of metal decorative ink printed on transfer paper. According to reports, the thickness of the ink layer on the flat and non-porous printing materials with good ink receptivity is 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 noticeable is its high resolution and sharpness. Three-dimensional printing makes the edge of the ink layer very clear and smooth, and it looks like it is die-cut or laser-engraved. Unlike inks with high hiding power, sweatshirt printing, and plastic ink printing, the three-dimensional printed ink film is often thin at the edges. No matter how high the resolution of the template is, the printed image can be easily stained. Like foaming inks, although a very thick ink layer can be printed, the cured edges are not clear and regular. The three-dimensional prints are clear and clean. Since the 1980s, with the gradual systematization of textile four-color printing processes, some people have been committed to three-dimensional printing to reform T-shirt decoration technology. However, due to translation and other reasons, 3D printing is often called "high-density printing." In fact, the three-dimensional printing ink film is only slightly higher than the density of the conventionally solidified foaming ink, and there is no high hiding power. The density of the white plastic ink is high.

The characteristics of three-dimensional image printing are more than just the use of a different ink or emulsion. Successful three-dimensional printing requires mastering different operating procedures and standard printing procedures than ordinary printing. Although not difficult, it is very different and must be With many well-integrated systems, 3D printing can have new and dramatic effects.

We know that the printing of textiles is screen-printed, and screen printing is used as an example here. On the screen, three-dimensional printing uses a 24 thread/cm screen, stretched on a re-stretchable screen frame with a tension of at least 30 N/cm. This type of wire mesh currently has 5 kinds of wire diameters and its range is 120-145μm. It has been proved that the wire mesh with the finest wire diameter is better, because the thin wire mesh can make the opening of the same plate fill as much as possible. More ink; In addition, it is preferable to use a dyed silk screen because the emulsion used in the three-dimensional printing process requires a longer exposure time, and the dyed screen can reduce the light scattering performance. On the stencil, the screen printing technician knows that the stencil thickness is the main factor that affects the thickness of the ink film, and in the three-dimensional printing, the thickness of the stencil is directly related to the thickness of the cured ink film. Practice has proved that if every operation process is guaranteed to be correct, the cured ink film can reach 90% of the stencil thickness. In three-dimensional printing, a 200 μm stencil is generally used. The current problem is not only to understand how thick the three-dimensional printing needs of the template, but more important is to understand the method of making thick templates. The following will introduce three kinds of thick template production methods, and discuss their advantages and disadvantages. Although each of the coating methods described below uses a slightly different selection of emulsions, they must all be compensated by rapid exposure to thicker emulsion layers. Fast-exposure SBQ emulsions or pure photosensitive emulsions (liquids or films) are preferably diazo or dual-cure.

(1) Liquid emulsions. The most basic method is to use liquid emulsion repeatedly coated on the screen, need to apply 15-20 times in the printing surface of the screen, so that the stencil to achieve the required thickness. The first layer of emulsion was first applied to the printing surface of the screen and then thoroughly dried. In order to shorten the drying time, the drying room should be equipped with a dehumidifier to keep the humidity at 40%-45%. After the first emulsion has been applied and dried, tape is applied around the image on the same printed surface to quickly increase the thickness of the stencil. Apply the second emulsion, dry it, and apply a layer of tape. Repeat steps 2 and 3 until the desired stencil thickness is reached. The advantage of this method is that it can be operated with familiar technology. The disadvantage is that it takes a long time (at least a few days) while the thickness of the emulsion layer is not well controlled. The most difficult is that because of this irregular coating method, it is likely that the total number of coated layers will be missed.

(2) Capillary photosensitive film. A method for quickly making thick templates. It is to paste the capillary photosensitive film on the screen. The most ideal material is a thickest film of pure photosensitive resin. Current 150 μm direct capillary chips are already on the market, and 200-250 μm diaphragms will soon be available. When pasting the capillary photosensitive film, a flat plate should be prepared, which is smaller than the inner frame size, larger than the outer size of the image, and 1 mm thick. 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 film; then place a capillary photosensitive film on the plate with the emulsion facing upwards; then place the screen on the capillary photosensitive film. , printing surface down. A thin layer of liquid emulsion is poured on the screen along one side of the capillary photosensitive film, and the liquid emulsion is dispersed on the entire screen. The film is contacted with the capillary photosensitive film to adhere the film. Finally, the emulsion layer is dried. However, it should be noted that it is necessary to use a liquid emulsion compatible with the capillary photosensitive film, that is to say that 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 sensitizers.

To increase the thickness of the stencil, after drying the capillary sensitized film/direct emulsion layer, remove the polyester substrate from the film and continue pasting another capillary sensitization film. The operation is as follows: First, the coating solution is prepared in a ratio of 1 part liquid emulsion to 15 parts water, and an adhesive tape is applied to the opening part of the screen printing surface. The screen is then placed perpendicular to the cleaning pool, and the capillary photosensitive film already attached to the screen is coated with a coating solution. A further layer of capillary photosensitive film is pasted on a film that has just been wetted with a liquid emulsion, and the emulsion laminates the emulsion layer. The film was dried and then the polyester base film was peeled off. To continuously increase the emulsion layer, the screen plate can be repeatedly leaned against the cleaning pool, and the capillary photosensitive film already attached to the screen can be coated with the coating solution. Repeat until you reach the desired emulsion thickness. 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 and certainly not as slow as the liquid emulsion coating.

(3) Thick film manufacturing method. The fastest way to make thick emulsion layers is to use as thick a film as possible. Its thickness range is 100-700μm. They are not capillary photosensitive films and require a special process. The first step is to choose a film of the desired thickness, which is 6-10mm larger than the size of the image on the stencil. The plastic protective film was peeled off from one side of the film, and the emulsion was faced up and placed on a flat plate (the flat plate was the same as the plate for the above-mentioned capillary photosensitive film).

Place the printed surface of the screen face down on the membrane on the plate. Then dilute the liquid emulsion and mix it with 2 parts of emulsion and 1 part of water. Dilute the diluted liquid from one side of the diaphragm. The emulsion on the surface of the patch was leveled and covered uniformly. Brush off excess emulsion and dry the same plate. After the screen was thoroughly dried, the screen's squeegee was coated with a bucket coater filled with 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 produce a three-dimensional printing template, but the supply of such template materials is limited.

As for the screen exposure, since the emulsion type, thickness, coating technology, and exposure equipment all affect the exposure time, in general, the exposure can be grasped as follows: If the exposure light source is a 50kw metal halide lamp, 16cm from the template, the printing plate The cloth thickness is 700 μm and the exposure time should be 7.5-8 mln. After exposure, soak both sides of the screen, allow the emulsion to soak for a few minutes, and then rinse again. The cleaning process can not be rushed, soaking, rinsing until all the images appear. If the positive picture used is very clear and the density is high, the finer levels after development will be clear. The cleaning time of the screen is longer than that of the ordinary screen, so it must take great patience.

As for the press commissioning, three-dimensional printed matter can be easily printed on a fully automatic screen printing machine. This is because the screen pitch can be well controlled and the screen pitch is a key factor in printing. Automatic screen printing machine operating instructions should pay attention to the following points: The screen installed on the press, the minimum distance modulation; coating speed is slightly slower than normal, using constant pressure on the ink plate. If the angle of the ink pad is adjustable, the angle between the ink pad and the screen can be minimized, and the ink can be overlaid on the screen plate; use a 75°-80° medium hardness scraper to adjust the scraper 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 usual, and the printing speed is preferably slower than usual. For better results, the printing stroke is as clean and smooth as possible, and scraping the ink twice will make the print dirty. Of course, it can also be used