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Before World War I, felt products were difficult to print using general printing methods. This period was the first time that such templates were used to print felt products. The role of stencils in screen printing is the same as that of gravure in the gravure printing technology. The printing plate in the screen printing industry has greater advantages than other printing plates: it can reach thousands of printings; it can be used by hand. , etched or made with light and chemical methods; area can be large and fine; field lines or halftones can be printed; both manual and mechanical printing can be done; printing can be done at manual printing speed, if needed It can print at mechanical speeds up to 5,000 prints/hour.
There are about 40 different types of printing plates in screen printing, but all types are either handmade or made by photography. Hand-made printing plates can be divided into direct production and indirect production. Usually, manual preparation of the screen plate has the following three aspects: knife carving, design, cleaning or increasing the resistance to printing force. Photographic screen printing plates are made with the help of light and chemical methods. It mainly has three types:
(1) Direct photo. That is, the emulsion is directly coated on the screen of the printing plate.
(2) Direct-indirect types. That is, the product containing the stencil and the emulsion, or the emulsion is directly applied to the screen.
(3) Indirect or transit type. That is, the sensitizer is first prepared on a temporary surface and then transferred to the screen cloth. Photographic screen printing and knife engraving are the two most commonly used types at present. However, because the knife-engraving template is not only the most practical in business, but also the earliest method, we first explain it in detail.
On a knife-printing stencil, the print area is cut away, leaving the part that sticks to the screen. Therefore, the screen printing plate consists of a portion adhered to the screen plate and a screen. The ink will pass under pressure through those portions of the stencil that have been cut off. The uncut portion of the stencil will prevent the ink from passing through, so that the desired pattern is obtained. All knife-cut stencils have the same characteristics and are all carved with a knife or other sharp tool. These stencils mainly include plain paper knife stencils, shellac papers, lacquered papers, lacquer decals, insect-coated decals, thin plastic papers, and commercial screen-printing stencils.
1. Commercial knife stencils Commercial knife stencils contain a transparent or translucent thin plastic paper with a special pre-made film that is semi-permanently stuck to it. In general, the stencil is made by using a sticker on the back of the plastic paper, and then spraying a few layers of paint, shellac or sticking the prepared film to a paper with a sticker coating. Commercial templates are generally coated three to eight layers under controlled conditions and then attached to paper or plastic. The sticker sticks with the stencil before it is transferred to the printing plate and can be removed at any time. You can cut out a part of the area or point of the stencil, and then strip away the unwanted part, but the back support paper must remain intact.
The stencils adhered to the back support paper have different transparent colors, have different film thicknesses, and undergo different roughening or gloss treatments. The color of the template is usually amber, green, gray blue, and red. The reason why the template selects the transparent color is because the transparent color can reveal other color components when it is matched with other colors. Another advantage is that it is easy to separate the colors. Just put the packaging machine' target=_blank> transparent film on the pattern to distinguish them without marking each color template. The stencil that the support is a plastic paper has greater transparency than the paper-based stencil, and the pattern can be observed in more detail. The plastic back does not resemble a paper-based back and it does not absorb moisture. No moisture is a big advantage when slicing large-format printing plates, because the large-format printing plates tend to stretch before they are applied.
Commercial knife-cut stencils on the market today have features that meet the needs of screen printing: wear resistance, good flexibility, easy knife-cutting, easy peeling, easy adhesion to screens, easy removal from screens, and storage in normal Under the air conditions for a long time. In fact, it was at the manufacturer's ability to produce products with these characteristics that the development of screen printing became a reality because it almost eliminated all the previous methods of preparing a screen version.
The templates can be classified into four levels by thickness: thin, medium, thick, and extra thick. Each level has its own applicable object for each level, generally using a medium-level template. When the width of the printed area or line is approximately one-half inch, the thinner the stencil, the thinner the ink layer; the thicker the stencil, the thicker the ink layer. However, the thickness of the ink layer is also related to the thickness of the screen. Thin stencils are used when multiple transparent overlays are needed, or if ink is to be saved. Thick stencils are conducive to accentuating dominant colors; are conducive to printing text outlines; are useful for printing woolen products and other similar materials; are conducive to the use of thick wire mesh or metal meshes; and are conducive to the printing of metals, wood products, glass products, and wool products; Thick templates are also used when emphasising slight color changes. The production of the template must also be able to meet the needs of various inks such as oil inks, water-based inks, and varnish inks.
2. Preparation of the stencil When using the stencil, the stencil is stuck to the pattern. The stencil is on the top and the part to be printed is cut off by hand with a sharp tool. Be careful when cutting, do not cut to the back of the paper base. Although this process is very simple, there are also some basic technologies that help printers. The most important possibility is to choose the sharpest knife. Only a sharp cutting knife can cut a good printed screen stencil. It is like using a good pencil and ruler to draw a good technical pattern. However, for the average printer, it is recommended to invest in the following tools: a knife; a good metal or glass ruler; a 30-60 degree triangle ruler and a 45-degree triangle ruler (all 8 Inch height); curved plate; circular cutter; adjustable double cutter; compass cutter; rotary cutter;
Although the cutter shown in Figure 48 can be simply made with some drawing tools, it is recommended that you purchase the finished product. Because commercial tools are not expensive, and they are made of medical surgical tool steel; they have the sharpness of a razor, they can stay sharp for a long time; when they begin to become blunt, they can be reground on a sharpening stone. Very sharp. The two types of blades shown in Figures 49 and 50 are not fixed and adjustable. They are used to cut parallel lines and parallel curves. The knife size for the fixed double cutter can be easily removed from about 1/32 to 1/2 inch (0.08 to 1.27 centimeter) cutter heads, and can be changed to different sized cutter heads if desired, with the holder unchanged. The adjustable double-knife has only one cutter head, but the blade spacing can be adjusted. The parallel distance can be 1/16 to 3/4 inch (0.16 to 1.87 cm).
The circular cutter shown in Figure 51 is designed to be round. It has double blades that can be cut left or right. It can cut a diameter of 1/16 to 4 inches (0.16 to 10.2 cm). The compass cutter shown in Figure 52 can also be tangential, but its cutting diameter is 3/4 to 27 inches (1.87 to 68.58 cm). Both circular cutters and compass cutters can cut both single and double lines, depending on whether the cutter head is single or double.
In addition to the above-mentioned types of guillotines, the cutting knife should also have a rotating knife. The rotary cutter has a rotatable blade for cutting curves. When cutting, the blade can be freely rotated or fixed in a certain position. All of the above cutters can also be used for cutting, cellophane, and stencil plates.
Before using the template, it must be ensured that it is not stored for a long time. Because long-term stencils are difficult to cut, dark in color, and difficult to apply. Although better-produced stencils can be stored under standard air conditions for about one year, they will remain intact, but they are best stored in an environment that is neither moisture nor too cold or too hot. Any stencil paper that has not been used should remain in the original cylinder and the stencil sheet should be oriented outwards to prevent it from separating from the paper base.
Experts in the die-cutting field generally open the film roll for cutting at night, which can give the film a time to adapt to the indoor environment.
When preparing the film, fasten the pattern to a flat table. Cut a stencil 2 to 4 inches larger than the pattern and stick it to the pattern. Then begin to cut the membrane. Care must be taken when cutting the membrane. The cutter can only penetrate the membrane and cannot pass through the paper base. If you cut through the paper base, you have difficulty in the mucous membrane. Therefore, the cutter must be sharp and the membrane can be cut off under slight pressure. If you are a beginner, it's best to practice the tangent lines, curves, or circles first. You can cut some simple patterns during practice.
If the printer wants to cut fine details, it is recommended to use a magnifying glass. The magnifier is not expensive, but it can also be rotated to different viewing angles and positions. At the same time, you can also empty your hands (Figure 53). If you need continuous details of the cut, it is best to have a magnifying glass that can be worn on the eye. Any magnifier can be magnified two to three times. If you need a better light, it is recommended that you place the light in front of the work at a distance of about 6 inches to 1 foot (15.2 to 30.5 cm). This will reduce the reflection of the template and make it easier to see the cut line.
When cutting the membrane, cut through the intersection slightly (Figure 54), otherwise the membrane layer will not peel off easily. After the kerfs were completed, all pattern films were peeled off (Figure 55). If a large area of ​​the film is peeled off, a long strip of paper can be cut in this area, which is good for sticking the template to the screen and also preventing the paper base from bending during filming.
When it is necessary to make a rush, especially when a pattern is too large and a person is difficult to complete in a short period of time, many die-cutting people cut the entire template together with the paper base and the pattern, and separate them by different people. cut. When cutting, no uniform segmentation is used, which is beneficial for the film to be combined together to form a complete pattern.
3. There are generally two types of stencils for a film: a stencil or a stencil that can be softened and dissolved by a paint solvent, a water-soluble stencil or a stencil that is only dissolved by water or an aqueous solution. There are two ways to apply the film: solvent method and heating method. Solvent method is the most commonly used method. This method is to moisten the stencil enough to soften it so that it sticks to the screen. The heating method uses a heated soldering iron to stick the stencil to the screen.
Make sure the screen is clean before applying the film. If the screen used is new, it is recommended to clean it with water or soapy water. The benefit of cleaning is that any material on the screen can be removed. Nylon, polyester or wire mesh can be cleaned and degreasing by the supplier's method. Also wet the screen with a damp cloth to remove any dust and particles that may be present. These substances may affect the effect of the film.
Before starting the filming operation, a base layer should be built under the film so that it can make good contact with the wire mesh. The substrate can be cardboard, laminated wood, plastic sheets, or a piece of glass that is a half inch smaller than the screen plate. Place the substrate on a flat surface and place the prepared template in the centered position with the membrane facing upwards. The screen plate is then pressed against the stencil, ensuring that the screen is in intimate contact with the film. Put some pressure on the frame, you can also clamp the base layer and the screen plate with a C clamp.
The adhesive used to apply the film must be a screen printing product recommended by the stencil manufacturer. Commonly used adhesives are paint thinners, amyl acetate, naphtha solvents, acetone, mixtures of acetone and amyl acetate, alcohol and commercial adhesives. Improper use of adhesives will prevent the correct film from flashing and may even dissolve the template. A good way to test the adhesive is to use a little bit of adhesive on your fingers and put your fingers in contact with the stencil. The stencil should stick to your fingers immediately. The excellent adhesive not only has fast bonding speed but also has fast evaporation speed. One thing to be reminded is that acetone should not be used for stencils with plastic substrates. Water-soluble film is generally used as an adhesive with water or water and isopropyl alcohol solution. The printing plate produced by this template should be printed using paint ink
Screen printing knife engraving template
The screen printing stencil is composed of a pre-made sheet with a pattern. One of the earliest stencils was a stencil with a knife-engraving pattern. This ancient copy-patterning process consisted of placing a stencil on a flat surface, then applying ink, pressing it on top of the substrate, and getting a sheet after uncovering it. printed matter. This process was first discovered in Egypt's 12th dynasty, about 2300 BC.