In the mass production process 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 resolved one day, it will always trouble the production.
Here we mainly discuss several problems that are often encountered in production and are easily overlooked.
-, The color of the wire mesh The color of the wire mesh is white, yellow, amber, red, etc., among which the yellow wire mesh is preferred. In our production, we usually use 270 ～ 280T yellow silk screen imported from Japan or Germany. For particularly delicate printed products, we usually use 350T imported yellow silk screen.
Why use yellow wire mesh? We know that the brilliant colors in nature are all 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's visual nerves can feel, called visible light. Different colors are obtained by the selective absorption and reflection of light on the surface of an object. 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 nerves to appear colored, and other colored light is absorbed, so we see the color of the object is yellow.
Because screen printing uses ultraviolet light during exposure, purple light is a mixed reflection of cyan and magenta hues in color, that is, the lack of yellow hues in black. During the exposure, the yellow of the purple plus silk screen is superimposed into black, so the surface of the yellow silk screen (ie, the bottom of the emulsion layer) is not light-sensitive or lightly exposed, so there will be no "back exposure" phenomenon, and the resulting image has high definition , No vignetting.
What is backfat? That is, when light passes through the transparent part of the film and reaches the emulsion layer, reflections, refractions, and slow shots are generated on the surface of the white screen located in the middle or bottom of the coating layer, which is just exposed from the bottom and inside of the coating surface. This phenomenon is called "back exposure". It will cause a virtual halo during exposure and affect the reproduction of tones.
2. Coating of photosensitive emulsion Put the prepared photosensitive liquid into the stainless steel tank, and the photosensitive liquid accounts for about half of the tank. The coating tank is in contact with the lower end of the inclined screen, and while the tank is inclined to flow out the photosensitive solution, the tank is slowly and uniformly lifted up to apply along the surface of the screen. The coating speed should not be too fast, too fast will cause blistering of the photosensitive emulsion, and pinholes will occur on the film surface; too slow will cause uneven coating of the photosensitive emulsion. In order to obtain the best coating effect, it is best to apply from the side that is in contact with the substrate when printing. The coating area should be slightly smaller than the screen frame, and then apply the screen upside down and apply again. After coating the reverse side of the screen, it is dried so that the photosensitive emulsion fills the mesh. It is best to use hot air drying at 30 ～ 35 ℃, which can shorten the drying time. If the temperature is higher than 40 ℃, the screen will produce hot fog.
The sensitivity of the emulsion in the liquid stage is low, and the sensitivity increases with the drying of the coating film, and the specified sensitivity can be reached after complete drying. .
Of course, due to the different production conditions of various manufacturers, their coating methods and times are also different. The coating method adopted by our factory is once in place, that is, the front and back sides are coated three times at a time, and then concentrated and dried.
Since dust falling on the surface of the screen will cause pin holes in the screen, keep the room clean. At the same time, the poor treatment of the silk screen will also cause excessive pinning on the surface of the screen. When the photosensitive emulsion is applied, the drying place is too bright, which will cause the haze of the screen full-page image to affect the clarity and saturation of the printed matter.
The screen printing of our factory is mainly for the production of daily ceramic decals, mainly export products, supplemented by domestic products. 20 sets of tableware, noodle bowls and chef dishes exported to the United States, the United Kingdom, Canada and other countries all year round are popular among people.
3. Before printing and trimming the printing plate, you should first check whether there is any dirt or dust on the photosensitive surface of the film and the glass surface of the printing table. It is best to wipe it with cotton yarn dipped in alcohol before cleaning. The surface of the soft film with silver halide attached is the front side, and the shiny side of the film base is the reverse side. When printing, the film side of the film and the emulsion side of the screen should be closely attached, leaving a bite line for exposure. The exposure time should be determined by the type of photosensitive thorn, the coating thickness of the photosensitive film, the blackness of the positive picture and the printing requirements. The thicker the coating layer of the photosensitive film, the longer the exposure time required to make the plate film completely cured. If the black and white on the positive picture is not enough, that is, it is gray and not black, the exposure time should be shortened, and the development time should be extended accordingly, so that the unexposed part of the picture and text is completely transparent.
After the development, use a sponge or a clean absorbent paper to quickly remove the moisture on the screen surface for hot air or natural drying. If the heating temperature is too high during drying, the image on the printing plate will produce errors to varying degrees or cause the screen to relax, which will affect the accuracy of overprinting during printing.
In order to strengthen the plate strands, improve the water resistance and solvent resistance, and prevent the leakage of ink at the junction of the screen and the frame during printing, you can use a wide-width tape to encapsulate and strengthen the edges of the graphic, and block it with screen sealing glue or photosensitive emulsion Adhesives, pinholes on screens and undesirable openings. For the small stains on the pattern part and the remaining little photosensitive adhesive, you can use a wide-width adhesive tape to stick it outside, you can also gently wipe it with cyclohexanone or alcohol, or you can use a small needle to lightly dot to keep the screen. Transparent. But the action is straight and gentle, and the action is too large, which will damage the screen.
Fourth, printing The screen printing of our factory is not done by one person alone, but by many people to divide the work and cooperate and finish together. Only if the previous process is responsible for the next process, do the self-inspection and self-inspection of each process, and strictly control the quality, can we produce a screen printing product that is satisfactory to users-ceramic transfer decals. The perfect match between the screen, ink and printing is a prerequisite for a good print. The quality of the printing plate directly determines the quality of the printing quality. Printing is only a check on the quality of the plate making. However, under the premise of stable printing plate quality, the printing workers can not get the ideal printed products because of the carelessness of the printing plate. Greater waste, defective or scrap products.
Before printing in batches, the printing screen should be fixed and poured into ink for trial printing to check the level, ink color, thickness of the ink layer, specifications, registration accuracy, etc. of the graphic copy on the layout. If the registration accuracy is poor, it can be adjusted according to the fine-tuning knob on the front of the frame; if the hue of the ink is wrong, check whether the wrong ink is used and replace it immediately; if the ink is poor, use a solvent to wipe the graphic part of the plate to make the ink transparent Over performance and wettability of the substrate have been improved to some extent; if there is a big difference in the tone and level of the graphic, the printing screen should be replaced immediately. The following points must be noted during the printing process.
(1) See the rules frequently. Due to the continuous movement of the plate frame during printing, the plate and frame are subjected to collision and vibration during the round-trip operation, and a small displacement occurs between the two, and the phenomenon of inaccurate overprint occurs, which affects the appearance quality of the product. Therefore, we must diligently observe the rules, discover in time, and adjust in time.
(2) Always check the proofs. If you find that the print is short of ink, you should immediately wipe the screen with a clean cotton cloth. This situation is mostly caused by a broken plastic film sticking to the printing plate or a dry skin clogging the screen. If the ink color is uneven or becomes pale, it may be that the ink viscosity is too large. It should be stopped immediately to dilute the viscosity of the ink with a solvent, and at the same time wipe the graphic part of the layout with gasoline to prevent ink penetration or block the network, so as to facilitate continuous work.
(3) The stacking of semi-finished products should be neat. During the stacking of semi-finished products, the two sides of the paper must be hung down and stacked. Otherwise, the paper is formed into an arch shape due to its own gravity, and the two sides of the paper are upturned and not flat, which causes difficulties in paper transfer during printing, and the phenomenon of breakage often occurs. When the paper stack is uneven, it can be leveled with cardboard. At the same time, the height of the paper stack should often be adjusted with the adjustment knob of the paper separation mechanism, so that the paper transfer is smooth and the printing process goes smoothly.
(4) The blade of the drying device is damaged due to long-term use, and some places are not synchronized with the operation of the host, which often causes the printed matter on the paper holder to be disordered. At this time, you should be quick and quick, and immediately take it away from the bottom of the mess. It is best not to face the ink film to avoid sticking and causing defective products or waste products.
Therefore, only by paying attention to the links that affect the quality of printing can we print exquisite prints, improve the yield rate, reduce consumption and increase benefits, so that enterprises can be invincible in the market competition.
Here we mainly discuss several problems that are often encountered in production and are easily overlooked.
-, The color of the wire mesh The color of the wire mesh is white, yellow, amber, red, etc., among which the yellow wire mesh is preferred. In our production, we usually use 270 ～ 280T yellow silk screen imported from Japan or Germany. For particularly delicate printed products, we usually use 350T imported yellow silk screen.
Why use yellow wire mesh? We know that the brilliant colors in nature are all 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's visual nerves can feel, called visible light. Different colors are obtained by the selective absorption and reflection of light on the surface of an object. 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 nerves to appear colored, and other colored light is absorbed, so we see the color of the object is yellow.
Because screen printing uses ultraviolet light during exposure, purple light is a mixed reflection of cyan and magenta hues in color, that is, the lack of yellow hues in black. During the exposure, the yellow of the purple plus silk screen is superimposed into black, so the surface of the yellow silk screen (ie, the bottom of the emulsion layer) is not light-sensitive or lightly exposed, so there will be no "back exposure" phenomenon, and the resulting image has high definition , No vignetting.
What is backfat? That is, when light passes through the transparent part of the film and reaches the emulsion layer, reflections, refractions, and slow shots are generated on the surface of the white screen located in the middle or bottom of the coating layer, which is just exposed from the bottom and inside of the coating surface. This phenomenon is called "back exposure". It will cause a virtual halo during exposure and affect the reproduction of tones.
2. Coating of photosensitive emulsion Put the prepared photosensitive liquid into the stainless steel tank, and the photosensitive liquid accounts for about half of the tank. The coating tank is in contact with the lower end of the inclined screen, and while the tank is inclined to flow out the photosensitive solution, the tank is slowly and uniformly lifted up to apply along the surface of the screen. The coating speed should not be too fast, too fast will cause blistering of the photosensitive emulsion, and pinholes will occur on the film surface; too slow will cause uneven coating of the photosensitive emulsion. In order to obtain the best coating effect, it is best to apply from the side that is in contact with the substrate when printing. The coating area should be slightly smaller than the screen frame, and then apply the screen upside down and apply again. After coating the reverse side of the screen, it is dried so that the photosensitive emulsion fills the mesh. It is best to use hot air drying at 30 ～ 35 ℃, which can shorten the drying time. If the temperature is higher than 40 ℃, the screen will produce hot fog.
The sensitivity of the emulsion in the liquid stage is low, and the sensitivity increases with the drying of the coating film, and the specified sensitivity can be reached after complete drying. .
Of course, due to the different production conditions of various manufacturers, their coating methods and times are also different. The coating method adopted by our factory is once in place, that is, the front and back sides are coated three times at a time, and then concentrated and dried.
Since dust falling on the surface of the screen will cause pin holes in the screen, keep the room clean. At the same time, the poor treatment of the silk screen will also cause excessive pinning on the surface of the screen. When the photosensitive emulsion is applied, the drying place is too bright, which will cause the haze of the screen full-page image to affect the clarity and saturation of the printed matter.
The screen printing of our factory is mainly for the production of daily ceramic decals, mainly export products, supplemented by domestic products. 20 sets of tableware, noodle bowls and chef dishes exported to the United States, the United Kingdom, Canada and other countries all year round are popular among people.
3. Before printing and trimming the printing plate, you should first check whether there is any dirt or dust on the photosensitive surface of the film and the glass surface of the printing table. It is best to wipe it with cotton yarn dipped in alcohol before cleaning. The surface of the soft film with silver halide attached is the front side, and the shiny side of the film base is the reverse side. When printing, the film side of the film and the emulsion side of the screen should be closely attached, leaving a bite line for exposure. The exposure time should be determined by the type of photosensitive thorn, the coating thickness of the photosensitive film, the blackness of the positive picture and the printing requirements. The thicker the coating layer of the photosensitive film, the longer the exposure time required to make the plate film completely cured. If the black and white on the positive picture is not enough, that is, it is gray and not black, the exposure time should be shortened, and the development time should be extended accordingly, so that the unexposed part of the picture and text is completely transparent.
After the development, use a sponge or a clean absorbent paper to quickly remove the moisture on the screen surface for hot air or natural drying. If the heating temperature is too high during drying, the image on the printing plate will produce errors to varying degrees or cause the screen to relax, which will affect the accuracy of overprinting during printing.
In order to strengthen the plate strands, improve the water resistance and solvent resistance, and prevent the leakage of ink at the junction of the screen and the frame during printing, you can use a wide-width tape to encapsulate and strengthen the edges of the graphic, and block it with screen sealing glue or photosensitive emulsion Adhesives, pinholes on screens and undesirable openings. For the small stains on the pattern part and the remaining little photosensitive adhesive, you can use a wide-width adhesive tape to stick it outside, you can also gently wipe it with cyclohexanone or alcohol, or you can use a small needle to lightly dot to keep the screen. Transparent. But the action is straight and gentle, and the action is too large, which will damage the screen.
Fourth, printing The screen printing of our factory is not done by one person alone, but by many people to divide the work and cooperate and finish together. Only if the previous process is responsible for the next process, do the self-inspection and self-inspection of each process, and strictly control the quality, can we produce a screen printing product that is satisfactory to users-ceramic transfer decals. The perfect match between the screen, ink and printing is a prerequisite for a good print. The quality of the printing plate directly determines the quality of the printing quality. Printing is only a check on the quality of the plate making. However, under the premise of stable printing plate quality, the printing workers can not get the ideal printed products because of the carelessness of the printing plate. Greater waste, defective or scrap products.
Before printing in batches, the printing screen should be fixed and poured into ink for trial printing to check the level, ink color, thickness of the ink layer, specifications, registration accuracy, etc. of the graphic copy on the layout. If the registration accuracy is poor, it can be adjusted according to the fine-tuning knob on the front of the frame; if the hue of the ink is wrong, check whether the wrong ink is used and replace it immediately; if the ink is poor, use a solvent to wipe the graphic part of the plate to make the ink transparent Over performance and wettability of the substrate have been improved to some extent; if there is a big difference in the tone and level of the graphic, the printing screen should be replaced immediately. The following points must be noted during the printing process.
(1) See the rules frequently. Due to the continuous movement of the plate frame during printing, the plate and frame are subjected to collision and vibration during the round-trip operation, and a small displacement occurs between the two, and the phenomenon of inaccurate overprint occurs, which affects the appearance quality of the product. Therefore, we must diligently observe the rules, discover in time, and adjust in time.
(2) Always check the proofs. If you find that the print is short of ink, you should immediately wipe the screen with a clean cotton cloth. This situation is mostly caused by a broken plastic film sticking to the printing plate or a dry skin clogging the screen. If the ink color is uneven or becomes pale, it may be that the ink viscosity is too large. It should be stopped immediately to dilute the viscosity of the ink with a solvent, and at the same time wipe the graphic part of the layout with gasoline to prevent ink penetration or block the network, so as to facilitate continuous work.
(3) The stacking of semi-finished products should be neat. During the stacking of semi-finished products, the two sides of the paper must be hung down and stacked. Otherwise, the paper is formed into an arch shape due to its own gravity, and the two sides of the paper are upturned and not flat, which causes difficulties in paper transfer during printing, and the phenomenon of breakage often occurs. When the paper stack is uneven, it can be leveled with cardboard. At the same time, the height of the paper stack should often be adjusted with the adjustment knob of the paper separation mechanism, so that the paper transfer is smooth and the printing process goes smoothly.
(4) The blade of the drying device is damaged due to long-term use, and some places are not synchronized with the operation of the host, which often causes the printed matter on the paper holder to be disordered. At this time, you should be quick and quick, and immediately take it away from the bottom of the mess. It is best not to face the ink film to avoid sticking and causing defective products or waste products.
Therefore, only by paying attention to the links that affect the quality of printing can we print exquisite prints, improve the yield rate, reduce consumption and increase benefits, so that enterprises can be invincible in the market competition.
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