Not only did the scraper not be respected, but it also blamed many problems that were not caused by it. If streaks appear on the print, blame is placed on the scraper. Similarly, if the ink on the print is uneven, it also pushes the responsibility to the scraper. Whether the printing ink is too light or dark, and whether the dots are too small or too big, the scraper is inevitably the scapegoat.
It is undeniable that the scraper is in a dirty and dirty environment. But as the old saying goes: "There must be someone doing it." And the fact is that the squeegee may cause any of the above problems or all of the problems. However, the question is: How far can you let the scraper take on all the accidents? More importantly, no matter what causes these problems, what can you do to correct these problems?
In order to determine where the failure occurred, everything that was taken was often an easy test. Unfortunately, there are very few printing manufacturers applying this test. Whenever you encounter a printing failure, the first step you should take is to perform this test, rotating the squeegee on the press and printing several patterns without adjusting any other parameters. Because this is not the same thing as thoroughly testing a new screed, it is automatically changing a few other parameters.
If a standard squeegee with two blades at each end is used, the printed image may or may not change when the blade corresponding to the blade is printed. If the image changes, whether it is good or bad, then the problem encountered must be caused by the blade in front of the squeegee because it is almost impossible to get the same streaks or defects with two different squeegee blades in the same position. . On the other hand, if the rotating squeegee has no effect and the image shows the same problem in the same position as before, there is no reason to blame the squeegee (unless, of course, it makes you feel good).
There are many boring explanations about the root cause of image defects. The explanations seem to be that the sensation is, and the effect is like a scraper blade problem, although they are not. In the presence of streaks, the stripes appear as unneeded fine parallel lines on the print, in the order of arrogance and smallness of the appearance of stripes, due to:
â— There is a gap in the ink plate.
The scraper drags debris and ink particles and embeds them in the screen.
â— The emulsion is not coated and the screen is damaged and streaks are produced.
â— The ink plate dripped the ink in front of the scraper (especially in the location, the color density changed, the possible causes are:
â— The printing platform is uneven, high or low.
â— uneven blade pressure.
â— Failed to evenly place the scraper in the scraper clamp (not vertical along its length).
â— Uneven screen tension.
The solution to these imaginary squeegee problems is obvious. Do not sand the squeegee as soon as you see it. Use common sense methods to avoid problems. This method should include the following points:
â— Clean the ink pad and store it well. At the same time, the corners of the flushing chamber are not suitable for storing scrapers or ink plates.
â— Keep the workshop clean and tidy, use a clean ink container.
â— Clean the screen and clean the edges of the coating tank. Do not use scratched ink or squeegee printing even if the image looks good. The template does not help when there is a problem with the image.
â— Avoid applying ink and squeegee wet.
â— Adjust the corrective of the printer: "non-uniformity" issues.
You must be able to avoid and control the difference between these stripes and colors, because when they occur with the scraper blade problems, you will spend a few days and hours to solve them. This is why rotating the squeegee is a simple and important step.
To further distinguish the real blade problem (Figure 1) and other reasons, keep in mind the following rules:
(1) The characteristics of the streaks due to the jagged or notched edges of the scraper blade;
• In contrast to the predominantly dark stripe caused by the cracking of the inked panel, alternating light and dark ink streaks are exhibited.
Continuation of the stripe along the entire length of the squeegee
• Straight and parallel to each other (and if printing is done automatically by the machine, parallel to the screen frame in the squeegee direction).
(2) Caused by the scraper blade (because the scraper blade is worn or the height of the squeegee is uneven) The color unevenness has the following characteristics:
â— The dark, slender part that continues throughout the entire length of the squeegee.
â— If the squeegee blade is not straight, multiple parallel sections appear.
In general, the solution to these problems is to sharpen the squeegee so that the worn, saw-toothed or nicked blade is worn off and the squeegee blade is straightened to remove the uneven parts. Unfortunately, grinding scrapers is not as straightforward as it sounds.
As in every other screen printing operation, there are a large number of parameters that may enhance or hinder the sharpening process. The most important of these parameters are:
â— The squeegee's physical properties.
â— The compatibility of squeegee and printing ink.
â— The state of the squeegee before sharpening.
â— Have a squeegee ready for printing.
Scraper physical properties
Hardness, wear resistance and chemical resistance determine the main physical properties of the squeegee. In theory, none of these features affect the method of squeegeeing or squeegeeing. In reality, however, all three features affect both the squeegee blade and the sharpening method.
The hardness indicates the hardness and elasticity of the squeegee, which affects the number of blades to be ground to obtain a straight and uniform blade. In general, when grinding the cutting edge instead of cutting off a part of the cutting edge, grinding out a little bit of the cutting edge will make the cutting edge straight. If you cut a part of the edge, the part that must be cut off will become large, and the hardness will decrease.
Abrasion resistance is a feature that prolongs the use time of the squeegee. This benefit, if taken together, becomes like this: The wear-resistant scraper is difficult to grind, so it is also ground again with a grinding device. The sharpening of the highly wear-resistant squeegee is mainly limited to the knife cutting equipment.
The chemical resistance itself does not affect the grinding, but it affects the polished blade. The higher the chemical resistance of the squeegee blade, the sharper the squeegee blade may be without worrying about the previous blade breakage.
Each of these physical properties means that you must carefully evaluate the squeegee in order to ensure that it suits your needs. It must be compatible with grinding (the number of times a uniform printed image is ground), grinding equipment (grinding or cutting), and the type of ink required for the printed product.
Ink compatibility
Although most inks do not seriously affect polyurethane squeegees, there are still some corrosive UV inks for vinyl and crude polyester and some solvent-based inks affect the squeegee. Symptoms of squeegee deterioration due to corrosive inks include the following:
• The squeegee is ready to use at the beginning, but the print quality rapidly drops (in the case of a few hundred prints or less) as the squeegee begins to leave streaks.
â— The squeegee blade will become soft and sticky, especially if it does not allow sufficient rest time in the middle of two uses. The squeegee will also wear faster after each print schedule.
â— Especially if the squeegee is ground before the proper rest time, the squeegee blade will break and lose a few large pieces. Such damaged squeegees usually leave dark streaks.
If you suspect that there is a problem with the compatibility between the ink and the squeegee, you should further determine your suspicions before making major changes to the production process. First of all, the squeegee should be given as much as possible for a period of 6-12 hours of rest between prints, and they should be ground only after the rest time. At the same time, it is ensured that there are several squeegees on hand for each printing, and they are often changed during printing. Finally, the squeegee blade is polished with very fine sandpaper (particle size 500-600) or a device that is specifically used to polish the squeegee blade. Removing a thin layer and a sharp edge (and any irregular part) from the squeegee will make the blade more durable and less likely to break. If none of these steps solve the problem, you must find a different ink and squeegee combination that is best suited to your production.
Problems related to aging
All polyurethane squeegees age quickly, depending on their composition and maintenance conditions, and their service life is typically one year or less. In general, a low hardness squeegee will soften over time, while a medium or high hardness squeegee will harden. In either case, its resilience, stretchability, abrasion resistance and heat resistance are reduced. Although printing with a squeegee will accelerate the aging process, they will also be quickly damaged if unused squeegees are exposed to high temperatures, heat and ultraviolet light (sun).
The aged squeegee has two symptoms that are easily noticeable: (1) Hardness change reduces resilience, and (2) Squeegee grinds. The resiliency change presents a permanent fixed curvature of the squeegee and it is difficult to cut the pressure of the squeegee. When you try to sharpen the squeegee by grinding, you will see that it is difficult to maintain a sharp broken edge. The squeegee blade also becomes soft during grinding. If a knife is used to sharpen the squeegee, although you may notice that you may not notice the difference in cutting, there are problems with clamping the squeegee due to the breakage of the cutting edge and loss of resilience.
If you suspect that the squeegee is too old, you can easily test its resiliency. In most cases, it is a good indicator of the age of the squeegee. Take a piece of material and clamp it in a corner 1/2 inch by 1/2 inch (1 cm by 1 cm). The squeegee was flattened by bench (or tiger) forceps until it was 1/3 of its original thickness, about 0.125 inch (3 mm), and the standard thickness was 0.375 inch (9.5 mm). Flatten the blade for 15 seconds and release it. If the squeegee does not return to its original shape and size within 15 seconds, it has aged. The length of time the squeegee regains its shape (at whatever point) is a good indicator of its age.
If you find the squeegee condition is unknown, try grinding it. If you can grind it very successfully, you can use it for unimportant print jobs. But don't expect the edge above it to be of good quality. To extend the service life of unmounted squeegees, they should be placed in a cool, dark place. The squeegee attached to the fixture should rely on the fixture instead of the squeegee.
The state of the squeegee before grinding
The state of the squeegee before grinding largely determines the quality of the grinding edge. First, the squeegee must be of good quality and the surface must be smooth and free from scratches and bubbles. If the surface is not smooth, the cutting edge will not be smooth. Take two smooth ends to form a smooth edge, and grind only one of them.
Second, the squeegee to be ground must be clean and dry without solvents and plasticizers. To achieve this condition, it must be placed between the two printing schedules for 6-12 hours and stored properly to avoid nicks and scratches. Do not grind the squeegee with dust, solvent, and poor condition. Such a squeegee not only has a low quality edge, but also slops the grinding equipment. If the squeegee is required to be responsible for you, you should treat them like babies - keep them clean, dry, solvent-free, and rested.
Printing method
The type of image and ink viscosity also determine how the squeegee is used in production. Low viscosity inks or low thixotropic inks can easily pass through the mesh and quickly flatten (flow out) on the substrate. Such an ink, that is, a poorly prepared squeegee squeegee, is less likely to cause squeegee bar marks as long as the thickness of the ink layer is sufficient for the ink to flow.
However, if the ink layer is thin and the ink is transparent, the readiness of the blade is noticeable in view of the occurrence of streak. If a thin, high-viscosity clear ink layer is to be printed (for example with UV ink), streaks will also be printed even with a well-prepared edge. E.g:
It is undeniable that the scraper is in a dirty and dirty environment. But as the old saying goes: "There must be someone doing it." And the fact is that the squeegee may cause any of the above problems or all of the problems. However, the question is: How far can you let the scraper take on all the accidents? More importantly, no matter what causes these problems, what can you do to correct these problems?
In order to determine where the failure occurred, everything that was taken was often an easy test. Unfortunately, there are very few printing manufacturers applying this test. Whenever you encounter a printing failure, the first step you should take is to perform this test, rotating the squeegee on the press and printing several patterns without adjusting any other parameters. Because this is not the same thing as thoroughly testing a new screed, it is automatically changing a few other parameters.
If a standard squeegee with two blades at each end is used, the printed image may or may not change when the blade corresponding to the blade is printed. If the image changes, whether it is good or bad, then the problem encountered must be caused by the blade in front of the squeegee because it is almost impossible to get the same streaks or defects with two different squeegee blades in the same position. . On the other hand, if the rotating squeegee has no effect and the image shows the same problem in the same position as before, there is no reason to blame the squeegee (unless, of course, it makes you feel good).
There are many boring explanations about the root cause of image defects. The explanations seem to be that the sensation is, and the effect is like a scraper blade problem, although they are not. In the presence of streaks, the stripes appear as unneeded fine parallel lines on the print, in the order of arrogance and smallness of the appearance of stripes, due to:
â— There is a gap in the ink plate.
The scraper drags debris and ink particles and embeds them in the screen.
â— The emulsion is not coated and the screen is damaged and streaks are produced.
â— The ink plate dripped the ink in front of the scraper (especially in the location, the color density changed, the possible causes are:
â— The printing platform is uneven, high or low.
â— uneven blade pressure.
â— Failed to evenly place the scraper in the scraper clamp (not vertical along its length).
â— Uneven screen tension.
The solution to these imaginary squeegee problems is obvious. Do not sand the squeegee as soon as you see it. Use common sense methods to avoid problems. This method should include the following points:
â— Clean the ink pad and store it well. At the same time, the corners of the flushing chamber are not suitable for storing scrapers or ink plates.
â— Keep the workshop clean and tidy, use a clean ink container.
â— Clean the screen and clean the edges of the coating tank. Do not use scratched ink or squeegee printing even if the image looks good. The template does not help when there is a problem with the image.
â— Avoid applying ink and squeegee wet.
â— Adjust the corrective of the printer: "non-uniformity" issues.
You must be able to avoid and control the difference between these stripes and colors, because when they occur with the scraper blade problems, you will spend a few days and hours to solve them. This is why rotating the squeegee is a simple and important step.
To further distinguish the real blade problem (Figure 1) and other reasons, keep in mind the following rules:
(1) The characteristics of the streaks due to the jagged or notched edges of the scraper blade;
• In contrast to the predominantly dark stripe caused by the cracking of the inked panel, alternating light and dark ink streaks are exhibited.
Continuation of the stripe along the entire length of the squeegee
• Straight and parallel to each other (and if printing is done automatically by the machine, parallel to the screen frame in the squeegee direction).
(2) Caused by the scraper blade (because the scraper blade is worn or the height of the squeegee is uneven) The color unevenness has the following characteristics:
â— The dark, slender part that continues throughout the entire length of the squeegee.
â— If the squeegee blade is not straight, multiple parallel sections appear.
In general, the solution to these problems is to sharpen the squeegee so that the worn, saw-toothed or nicked blade is worn off and the squeegee blade is straightened to remove the uneven parts. Unfortunately, grinding scrapers is not as straightforward as it sounds.
As in every other screen printing operation, there are a large number of parameters that may enhance or hinder the sharpening process. The most important of these parameters are:
â— The squeegee's physical properties.
â— The compatibility of squeegee and printing ink.
â— The state of the squeegee before sharpening.
â— Have a squeegee ready for printing.
Scraper physical properties
Hardness, wear resistance and chemical resistance determine the main physical properties of the squeegee. In theory, none of these features affect the method of squeegeeing or squeegeeing. In reality, however, all three features affect both the squeegee blade and the sharpening method.
The hardness indicates the hardness and elasticity of the squeegee, which affects the number of blades to be ground to obtain a straight and uniform blade. In general, when grinding the cutting edge instead of cutting off a part of the cutting edge, grinding out a little bit of the cutting edge will make the cutting edge straight. If you cut a part of the edge, the part that must be cut off will become large, and the hardness will decrease.
Abrasion resistance is a feature that prolongs the use time of the squeegee. This benefit, if taken together, becomes like this: The wear-resistant scraper is difficult to grind, so it is also ground again with a grinding device. The sharpening of the highly wear-resistant squeegee is mainly limited to the knife cutting equipment.
The chemical resistance itself does not affect the grinding, but it affects the polished blade. The higher the chemical resistance of the squeegee blade, the sharper the squeegee blade may be without worrying about the previous blade breakage.
Each of these physical properties means that you must carefully evaluate the squeegee in order to ensure that it suits your needs. It must be compatible with grinding (the number of times a uniform printed image is ground), grinding equipment (grinding or cutting), and the type of ink required for the printed product.
Ink compatibility
Although most inks do not seriously affect polyurethane squeegees, there are still some corrosive UV inks for vinyl and crude polyester and some solvent-based inks affect the squeegee. Symptoms of squeegee deterioration due to corrosive inks include the following:
• The squeegee is ready to use at the beginning, but the print quality rapidly drops (in the case of a few hundred prints or less) as the squeegee begins to leave streaks.
â— The squeegee blade will become soft and sticky, especially if it does not allow sufficient rest time in the middle of two uses. The squeegee will also wear faster after each print schedule.
â— Especially if the squeegee is ground before the proper rest time, the squeegee blade will break and lose a few large pieces. Such damaged squeegees usually leave dark streaks.
If you suspect that there is a problem with the compatibility between the ink and the squeegee, you should further determine your suspicions before making major changes to the production process. First of all, the squeegee should be given as much as possible for a period of 6-12 hours of rest between prints, and they should be ground only after the rest time. At the same time, it is ensured that there are several squeegees on hand for each printing, and they are often changed during printing. Finally, the squeegee blade is polished with very fine sandpaper (particle size 500-600) or a device that is specifically used to polish the squeegee blade. Removing a thin layer and a sharp edge (and any irregular part) from the squeegee will make the blade more durable and less likely to break. If none of these steps solve the problem, you must find a different ink and squeegee combination that is best suited to your production.
Problems related to aging
All polyurethane squeegees age quickly, depending on their composition and maintenance conditions, and their service life is typically one year or less. In general, a low hardness squeegee will soften over time, while a medium or high hardness squeegee will harden. In either case, its resilience, stretchability, abrasion resistance and heat resistance are reduced. Although printing with a squeegee will accelerate the aging process, they will also be quickly damaged if unused squeegees are exposed to high temperatures, heat and ultraviolet light (sun).
The aged squeegee has two symptoms that are easily noticeable: (1) Hardness change reduces resilience, and (2) Squeegee grinds. The resiliency change presents a permanent fixed curvature of the squeegee and it is difficult to cut the pressure of the squeegee. When you try to sharpen the squeegee by grinding, you will see that it is difficult to maintain a sharp broken edge. The squeegee blade also becomes soft during grinding. If a knife is used to sharpen the squeegee, although you may notice that you may not notice the difference in cutting, there are problems with clamping the squeegee due to the breakage of the cutting edge and loss of resilience.
If you suspect that the squeegee is too old, you can easily test its resiliency. In most cases, it is a good indicator of the age of the squeegee. Take a piece of material and clamp it in a corner 1/2 inch by 1/2 inch (1 cm by 1 cm). The squeegee was flattened by bench (or tiger) forceps until it was 1/3 of its original thickness, about 0.125 inch (3 mm), and the standard thickness was 0.375 inch (9.5 mm). Flatten the blade for 15 seconds and release it. If the squeegee does not return to its original shape and size within 15 seconds, it has aged. The length of time the squeegee regains its shape (at whatever point) is a good indicator of its age.
If you find the squeegee condition is unknown, try grinding it. If you can grind it very successfully, you can use it for unimportant print jobs. But don't expect the edge above it to be of good quality. To extend the service life of unmounted squeegees, they should be placed in a cool, dark place. The squeegee attached to the fixture should rely on the fixture instead of the squeegee.
The state of the squeegee before grinding
The state of the squeegee before grinding largely determines the quality of the grinding edge. First, the squeegee must be of good quality and the surface must be smooth and free from scratches and bubbles. If the surface is not smooth, the cutting edge will not be smooth. Take two smooth ends to form a smooth edge, and grind only one of them.
Second, the squeegee to be ground must be clean and dry without solvents and plasticizers. To achieve this condition, it must be placed between the two printing schedules for 6-12 hours and stored properly to avoid nicks and scratches. Do not grind the squeegee with dust, solvent, and poor condition. Such a squeegee not only has a low quality edge, but also slops the grinding equipment. If the squeegee is required to be responsible for you, you should treat them like babies - keep them clean, dry, solvent-free, and rested.
Printing method
The type of image and ink viscosity also determine how the squeegee is used in production. Low viscosity inks or low thixotropic inks can easily pass through the mesh and quickly flatten (flow out) on the substrate. Such an ink, that is, a poorly prepared squeegee squeegee, is less likely to cause squeegee bar marks as long as the thickness of the ink layer is sufficient for the ink to flow.
However, if the ink layer is thin and the ink is transparent, the readiness of the blade is noticeable in view of the occurrence of streak. If a thin, high-viscosity clear ink layer is to be printed (for example with UV ink), streaks will also be printed even with a well-prepared edge. E.g:
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