Talking about some negligible problems in screen printing
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In the process of mass production of screen printing, if a specific link is not noticed, it will bring a series of troubles to the production, and this situation will not be solved one day, it will always plague production.
Here are a few of the issues that are often encountered in production and are easily overlooked.
First, the color of the screen
The color of the screen is white, yellow, amber, red, etc., of which yellow screen is preferred. We produce 270-280T yellow wire mesh imported from Japan or Germany in our production. For special fine prints, we use 350T imported yellow wire mesh.
Why use yellow wire mesh? We know that the beautiful colors of nature are due to the effect of light. Without light, there is no color. The color of light is determined by the frequency of light waves. Red, orange, yellow, green, blue, basket, and purple are the light that people can feel by the visual nerves, called visible light. The surface of the object selectively absorbs and reflects light to give different colors. In short, any color we can see is the color of light. That is, when a beam of light hits the surface of a yellow object, only the yellow light is reflected, stimulating our optic nerve and coloring, while other colors are absorbed, so we see that the color of the object is yellow.
Since screen printing is exposed to ultraviolet light, the purple light is reflected by a mixture of two colors of cyan and magenta in color, that is, a yellow hue is absent in black. During exposure, the yellow color of the purple plus mesh is superimposed into black, so the surface of the yellow screen (ie, the bottom of the emulsion layer) is not sensitive or less exposed, so there is no "back drying" phenomenon, resulting in high image clarity. , will not produce vignette.
What is the sun? That is, when light passes through the transparent portion of the film to reach the emulsion layer, reflection, refraction, and slow motion are generated on the surface of the white screen located at the middle or bottom of the coating layer, just from the bottom and inside of the coated surface. This phenomenon is called "back drying". It causes a faint glow during exposure and affects the reproduction of the hue.
Second, the application of emulsion
The prepared photosensitive liquid is placed in a stainless steel tank, and the photosensitive liquid accounts for about half of the groove. The coating tank is in contact with the lower end of the inclined screen, and while the groove is inclined to flow out of the photosensitive liquid, the groove is slowly and uniformly lifted up and applied along the screen surface. The coating speed should not be too fast, too fast will cause the emulsion to foam, and the film surface will produce pinholes; too slow will cause uneven coating of the emulsion. In order to obtain the best coating effect, it is best to apply the coating from the side that is in contact with the substrate at the time of printing. The coating area should be slightly smaller than the screen frame, and then the screen is turned upside down and coated once again. The reverse side of the screen is coated and dried to fill the mesh with the emulsion. It is best to dry with hot air at 30 to 35 ° C, which can shorten the drying time. If the temperature is higher, the screen will produce hot fog when it exceeds 40 °C.
The sensitivity of the emulsion in the liquid phase is low, the sensitivity rises with the drying of the coating film, and the specified sensitivity is achieved after it is completely dried. Therefore, it is sufficiently dried before the printing, and the printing is completed in a short time after drying. .
Of course, due to the different production conditions of various manufacturers, the coating method and the number of times are also different.
Since the dust on the plate surface causes pinholes in the screen, keep the room clean. At the same time, the screen must be handled poorly, which will cause too much pinching on the surface of the screen. When the emulsion is coated, the dry place is too bright, which will cause the fog of the full-page image of the screen to affect the sharpness and saturation of the printed matter.
Third, printing, finishing
Before printing, check whether there is any dirty or dust on the glass surface of the film and the surface of the film. It is best to wipe it with cotton yarn and alcohol before cleaning. The surface of the film with silver halide attached is the front side, and the shiny side of the film base is the reverse side. When printing on the plate, the film surface of the film and the emulsion surface of the screen should be tightly bonded, and the bite line should be left for exposure. The exposure time should be determined according to the type of photosensitive thorn, the coating thickness of the photosensitive film, the blackness of the positive image, and the printing requirements. The thicker the coating layer of the photosensitive film, the longer the exposure time required, so that the film is completely cured. If the image on the image is not strong enough, that is, gray and not black, the exposure time should be shortened, and the development time should be extended accordingly so that the unsensed image portion is completely transparent.
After development, use a sponge or a clean, absorbent paper to quickly remove moisture from the surface of the screen for hot air or natural drying. If the heating temperature is too high during drying, the image on the printing plate may cause errors to some extent or cause the screen to be slack, which affects the overprinting accuracy during printing.
In order to strengthen the plate, improve the water resistance and solvent resistance, and prevent the ink from leaking at the joint of the screen and the frame, the edge of the image can be covered with a wide-width tape paper, and the mesh is sealed with a sealing glue or emulsion. Pinholes on the bond, screen, and undesired openings. For small stains on the pattern and a small amount of photoresist left over, you can use a wide-band tape to stick the paper, or you can gently wipe it with cyclohexanone or alcohol, or you can use a small needle to gently keep the screen. Transparent. But the action is straight and gentle, and the action is too large, which will damage the screen.
Fourth, printing
In most manufacturers, screen printing is not done by one person alone, but by many people working together. Only the previous process is responsible for the next process, and the self-inspection and self-inspection of the respective processes are carried out, and the quality is strictly controlled to produce the screen prints that the user is satisfied with. The perfect match between screen, ink and printing is a prerequisite for good prints. The quality of the printing plate directly determines the quality of the printed product. Printing is only a test of the quality of the plate making. However, under the premise of stable printing quality, the printing workers are not taken lightly, and the ideal printed matter cannot be obtained. More waste, defective or defective products.
Before batch printing, the printing screen should be fixed, pour into the ink test, check the layout of the layout and text, ink color, ink layer thickness, specifications, registration accuracy and so on. If the registration accuracy is poor, you can adjust it according to the fine adjustment knob on the front of the frame; if the hue of the ink is wrong, check if the wrong ink is used and replace it immediately. If the ink is poor, the printing plate can be wiped with solvent to improve the permeability of the ink and the wettability of the substrate. If the tone and level of the graphic are different, replace the printing immediately. Screen version. The following points must be noted during the printing process.
(1) Look at the rules. Since the frame moves continuously back and forth during printing, the plate and the frame are subjected to collision and vibration during the reciprocating operation. When a small displacement occurs between the two, an inaccurate overprinting phenomenon occurs, which affects the appearance quality of the product. Therefore, we must look at the rules, find out in time, and adjust in time.
(2) Always check the proofs. If the printed matter is found to be out of ink, the screen should be wiped with a clean cotton cloth immediately. Most of this is due to the fact that the plate is stuck with a broken plastic film or the ink crust is dry and clogged. If the ink color is found to be uneven or light, it may be that the viscosity of the ink is too large. Immediately stop the solvent to dilute the viscosity of the ink. At the same time, use the gasoline to wipe the graphic part of the layout to prevent bleeding or blocking the net for continuous operation.
(3) The stacking of semi-finished products should be neat. During the stacking process of the semi-finished products, it is necessary to stack the two sides of the paper. Otherwise, the paper forms an upper bow due to its own gravity, and the two sides of the paper are not flattened, which causes difficulty in paper transfer during printing, and often breaks. When the paper roll is not flat, the cardboard can be flattened, and the height of the paper roll should be adjusted frequently with the adjustment knob of the paper separation mechanism, so that the paper transfer is smooth and the printing process proceeds smoothly.
(4) The blades of the drying device are damaged due to long-term use, and some places are not synchronized with the operation of the main machine, which often causes the printed matter on the paper frame to be disordered. At this point, you should take your eyes and hands quickly, and immediately remove them from the bottom of the chaos. It is best not to make the ink film face opposite, so as not to cause defective or defective products.
Therefore, only by paying attention to the links that affect the quality of printing can we produce exquisite printed materials, improve the yield, reduce the consumption and increase the efficiency, and make the enterprise in an invincible position in the market competition.