Explain and use
When the sales of screen-printed garments fall to some extent, designers will be more committed to finding a new visual sensation that can draw consumers' attention. Perhaps high density printing is what they are looking for.
This method can print a variety of different colors, and with a little time and effort, an attentive printer can master high-density printing. Below, we will make a general discussion on the details of this new method, including the entire process of design selection, plate making, ink processing, printing and drying. Like other new things, this new scheme also needs to be tested or even mistaken to adapt to different printing factories. So don't be afraid of mistakes.
Pattern selection
This is the first and perhaps most important consideration step you need. Line thickness and pattern size are also decisive factors for the success of the high-density printing process. For example, after the printing process is finished, the thin lines will look better than the large area. The small-area printing design, especially the right angle, makes it easier for the ink to hang on the mesh when printing. In general, you must be very familiar with the types of patterns that are suitable for high-density printing, and you must eliminate the use of this technique for inappropriate patterns. There are many tricks if you use 3D processing will greatly enhance the visual experience. You need to use these to your advantage.
Plate making
The screen determines the thickness of the ink layer by the thickness of the mesh yarn and the thickness of the screen. Platemaking can be done by direct emulsion coating, direct/indirect methods, or by capillary coating methods, which are described below.
For most thick plates, 60-110 mesh (per inch) may be commonly used. You may want to use a lower than normal mesh tension, such as 14-20 Newton. Thicker and thicker ink deposits require more web spacing, perhaps with increased tension. With this concept in mind, don't think about your print pattern too high. If you think so, you will make the screen distance too close, and make the appropriate network distance become impossible.
In any case, you need to prepare a suitable degreasing agent to clean the mesh. After sufficient drying time, apply the coating or patch (indirect film).
The direct emulsion film is achieved by repeating the coating on the printed surface until the desired coating thickness is achieved. This will take a day or longer. Because each coating requires drying to a moisture content of less than 4% (30 minutes to 1 hour, depending on the emulsion and drying conditions you use) to apply a layer. After all the coatings have been completed, you will need to allow the stencils to be further dried (for example, overnight) before exposure, because the screens that are not fully dried will not have a good exposure.
How to choose the appropriate emulsion is also a study of the next effort. The best choice is high solids content. The higher the solid content, the less likely it is to shrink when dried. In addition, use a quick exposure to my emulsion to minimize the exposure time. It took quite a while for me to expose the 400-1000 micron film layer.
â— The single-component light-sensitive polymeric emulsion has a high solid content and a fast exposure speed;
â— The diazo-based photopolymer has a high solid content, but the exposure speed is not fast enough;
â— Diazo-based emulsions are also low in solids and have the slowest exposure rate. (The higher the solid content of the diazo-based emulsion, the slower the exposure speed)
Any one of them is available, but I suggest using a photopolymer because it has the fastest exposure speed and good shrink control.
The first step is to do wet coating on both sides of the screen, and then apply a little more force on the ink surface. This allows the emulsion to "settle" on the printed surface. Place the screen on a horizontal shelf with the printed side facing down.
After a certain period of time has dried, it enters the thickening stage:
Thickening can be achieved in several different ways:
1, the standard coating: the use of a round scraper, from the bottom to the top coated with two layers of coating (the middle is not dry), flip the screen in the printing surface from the opposite direction twice for wet coating. Call this coating 1 . Marking the coating helps you to know exactly how many times you have applied the coating. Now let it dry and repeat the above action until the expected thickness is reached. Allow time for each coating to dry. Depending on your thickness requirements, eight, ten, or more layers may be required. When painting the third and fourth layers, it may happen that the middle of the screen is thicker than the edge. If this is the case, you will need to paint the edges one or more times to make the thickness of the stencil consistent. You can pour a small amount of cream around without going down. Repeat twice in each direction to make the standard coating, which will allow the emulsion to stay only around the screen. When the eighth or more layers are achieved, it needs to be repeated many times to make the thickness uniform. After the coating is complete, allow enough drying time. My suggestion is overnight.
2. Assist the adhesive tape application: Stick the tape along the outside of the frame, but the width between the tapes should not exceed the width of the scraper. This will help lift the distance between the scraper and the screen, and allow thicker emulsion build-up for each operation. Calculate how many layers of tape to use based on the base thickness. For example, if your tape thickness is 3 mil (1 mil = 25 microns), for a 300 micron thick film layer, you will need 4 layers. To achieve the required thickness of the screen, you may need to laminate the tape to take into account the shrinkage factor. Apply the coating twice in each direction, and carefully keep the scraper "riding" on the tape. Remove the tape before drying to avoid tearing off the dried emulsion. Then place the screen on a horizontal shelf with the printed side facing up. For thicker screens, they can be re-operated as needed, that is, after each coating is completed, new tapes are layered and the next cycle is performed. Allow enough time for drying in the middle of the coating and allow enough time after completion. My advice is still overnight.
3. Blade Coating: This method requires a support plate to provide a flat surface with the screen printing ink facing down. Correspondingly, this board is smaller than the inner edge of the basket, but higher than the height of the frame, so that it can be more closely connected with the mesh. Stick the tape along the outer edge of the screen, but make sure that the width between the tapes does not exceed that of the coated knife and the support. The tapes are stacked together (as before) to achieve a thickness that completes the coating at one time (consider shrinkage). At the end of the tape, where the squeegee starts and stops, an extra width is left for removal of the unwanted emulsion to keep the screen clean. Now pour photographic emulsion on one end of the screen, place the squeegee down the tape at the same end, and slowly and steadily push the squeegee. When finished, place the screen printing face up on a horizontal shelf. Then allow it to dry for a sufficient time - at least overnight. One disadvantage of this method is that because this time coating a thick layer may cause unevenness on the surface. The reason is that the air bubbles rise from the emulsion, or are surrounded by dry emulsion near the surface. But this is not the problem itself. What would be the effect of exposing it with a bottom plate containing bubbles? Also, if you do this, you'd better put the emulsion long enough to allow the bubbles to escape before coating, and to ensure that your technology does not introduce new bubbles in the next steps. This is similar to the direct/indirect method of using a capillary film patch, which is a film film that is pre-coated with a sensitive emulsion, then placed on the table with the film facing up, and the screen printing surface is attached to the film. On top of this, a squeegee was used to apply the emulsion to the surface of the ink. After drying, the protective film on the back side was peeled off. This method considerably improves the firmness between the film and the mesh.