Flexo is one of the commonly used production processes for printing of packaging products. It is easier to make plates, easier for plate loading, has wide print adaptability, high production efficiency, low equipment investment, low production cost, and is increasingly obtained in the packaging and printing industry. The more widely used. Like any kind of printing process, some printing failure problems are inevitable in the flexographic printing process, which affects the printing quality of the product. Therefore, understanding and mastering the problems that are easily occurred in the flexographic printing can be achieved through the implementation of preventive and corrective measures. To reduce or avoid the occurrence of printing quality failures, achieve normal production, and improve the printing quality of products.
Ink color is not uniform and there are flowers or paste phenomenon
In the flexographic printing process, sometimes the ink on the layout of the printed product will appear uneven, hair growth or stencil printing. The main causes and corresponding solutions are as follows:
1, the thickness of the printing plate is inconsistent or the hardness is too low. Plates are required to be selected from plates of the same thickness. For the coexistence of solid and small texts, a thin layer of tape can be added on the back of the field plate. If the plate is of poor quality, consider using a quality plate. Plate making.
2, the ink dried solid caused on the plate. Ink solidification on the printing plate will cause poor ink transmission. Therefore, any machine that needs a long period of shutdown during the printing process should be cleaned in time. If the ink drying speed is too fast, an appropriate amount of slow drying agent may be used to adjust the ink dryness.
3, the poor accuracy of the anilox roller or the contact pressure with the printing plate is too large or too small. For the wear and looseness of the axial roller head, appropriate repair measures shall be taken to eliminate it; if the structure of the traction roller for separating and closing is unstable, the cause shall be ascertained and treated to ensure that the anilox roller is pressed. No pulsation occurs; if the roller pressure on both sides is inconsistent and the roller pressure is too large or too small, accurate adjustments should be made.
4, caused by the instability of the pressure roller. Two-color flexographic printing machine directly printed on corrugated board, if it is the bending or deformation of the pressure roller shaft, looseness, should take appropriate measures to repair; if the pressure roller position is too high or too low, it should pass Adjust the proper position of the pressure roller so that the gap between the pressure roller and the plate cylinder adapts to the thickness of the cardboard to ensure that the ink on the printing plate remains stable.
5, caused by poor rubber roller. If the rubber roll is aged and deformed, the head of the roll shaft will be loose and beating, which will cause the ink supply to be unstable and affect the quality of the ink. In this regard, new rubber rollers should be replaced, and corresponding repair measures should be taken to eliminate loosening and bouncing of the rubber roller shaft head.
6, caused by bad squeegee. At present, some flexographic printing press ink delivery systems do not use rubber ink rollers, and the anilox roll is directly immersed in the ink tank. When rotating, excess ink on the roller surface is scraped off by a squeegee. This structure of the machine, if there is wear and deformation or the squeegee blade there is loose, beating phenomenon, will also cause the ink supply instability and affect the quality of printing ink color, can wear and deformation of the squeegee knife grinding, so that its working site remains flat Straight and straight state; to repair loose and beating parts, take repair measures to eliminate them.
7, ink viscosity caused by discomfort. If the viscosity of the ink is too large or too small, the ink on the plate surface of the printing product may easily cause the occurrence of blooming or stencil printing. Usually, the viscosity of printing inks on the netting and form printing plates should be appropriately lower, while the viscosity of the inks should be slightly larger when printing solid plates and plates. The viscosity of the water-based ink is generally controlled between 40 and 50S. However, since the temperature varies from place to place when using ink, this will affect the viscosity of the ink and the printing effect. Therefore, it is necessary to scientifically grasp and adjust actual conditions according to the printing environment.
8, caused by poor ink fineness. If fine dots of ink are used to print dots, then due to the coarse pigment particles in the ink, the layout of the printing plate will be prone to stencil and hair spots, and the printing rate of the printing plate will also be reduced. Therefore, printing dot products should be printed with fine ink. The fine ink with good density has a high concentration and can make the dots of printed products clear and plump.
9, caused by improper use of adhesive tape. Improper use of sticky tape will also make it appear that the printed ink appears to be blooming. Therefore, the tape should be reasonably selected according to the characteristics of the printing plate. Low-density adhesive tape should be used for printing fine lines and screens. For printing text lines and field versions, medium-density tapes can be used; the entire layout is printed on the ground. High-density tapes can be used.
Phantoms appear on prints
When the substrate is paper, a cloud-like phantom appears on the ink layer of the printing plate, or a large area of ​​the field part sees a shadow of another part of the picture, and a blank convex shape appears in the field, and the printing of the cellophane is a hazy fog. Phantom phenomenon. The reason is that the ink is not uniformly coated; the amount of ink is too small, the ink flowability is poor, and the anilox roller is not clean.
The solution is to: change the diameter of the plate cylinder and the different speeds of the anilox roller; thoroughly wash the anilox roller and plate with solvent; replace the ink and use the correct solvent formulation; use a slow drying agent as appropriate Appropriate increase in the amount of ink, to ensure that the anilox roller to obtain a certain amount of ink, increase the anilox roller soaked area; printed glass paper can be appropriate to reduce the solvent; control the ink drying.
Fine dots in the ink layer of the printed product
Fine point-like holes appear in the ink layer of the flexographic product, and the printing industry is accustomed to image it as "pinhole". There are two performance situations for “pinholes†in flexographic products. One is that there are many traces of holes on the prints, and there is no regular distribution, but the size of the “pinholes†is also not the same. Usually called “pinholesâ€. Chemical pinholes, which are commonly found on cellophane and overprinted products. Another type of "pinhole" is a "pinhole" trace that appears on a large area of ​​ink in a printed product. The size of the pinhole is relatively uniform and is often referred to as "mechanical pinhole." There are many reasons for the “pinhole†in the flexographic printing ink layer, and corresponding solutions should be adopted according to the problems that arise, so as to better eliminate the malfunction and ensure the printing quality of the product. In the production process, "pinholes" appear in the ink of India, and there are several situations as follows:
If the printing surface tension is unfavorable, an adjustment of about 1.5% of the aqueous ink surface tension adjuster may be added.
If the wettability between the ink and the surface of the print is so poor that the ink layer on the print shrinks to produce a “pinhole†mark, consider adding some improvements in wettability and leveling to the ink. Agent.
If the temperature of the printing shop is low or the humidity is too high, and the viscosity of the ink is too low or the drying is too slow to allow the ink to completely wet the surface of the print, the viscosity of the ink can be adjusted by increasing the temperature of the printing shop and reducing the humidity. Or add some additives to improve the ink compatibility, if the ink adjustment is invalid, consider replacing the ink type to solve.
If the ink is too thin or the printing ink layer is too thin, the ink viscosity should be adjusted and the printing ink supply volume should be appropriately increased.
If the ink is in the conjunctiva, because the air enters and creates a bubble-like void, and does not form a uniform ink layer on the surface of the print, some ink additives may be added to improve the fluidity of the ink.
If the printing ink dries quickly on the anilox roller, causing ink transfer and ink coating unevenness, the slow-drying agent can be used for adjustment. If it takes a long time to stop printing, the machine should be cleaned in time.
If the network is blocked or the anilox roller is worn out so that the amount of ink is reduced, the anilox roller should be cleaned or a new anilox roller should be replaced to ensure the ink supply and to maintain a proper printing ink layer thickness.
If the surface of the printed product is rough and the ink layer is difficult to keep in close contact with the depressed surface of the printed sheet, the printing pressure, the amount of ink applied, or the overprinting of the on-site layout should be appropriately increased twice.
If the surface of the plate is worn to form rough marks, or if the plate is slightly corrosive due to poor acid resistance, a new plate should be replaced.
If there is dirt on the impression cylinder, the impression cylinder should be cleaned.
If the printing pressure is too light to cause the ink layer on the printing plate to be transferred badly, the printing pressure should be appropriately increased.
If impurities adhere to the plate or sheet, measures should be taken to prevent dust, dust and paper particles from remaining on the plate surface and the print surface.
Loss or distortion of flexographic printing
In the printing production process, if the production process is not properly controlled, quality problems such as dot loss and deformation are prone to occur. For example, small dots in the highlights of the layout are easily lost, and dark dot sites are prone to be enlarged and become paste-like. Therefore, the flexographic printing process is difficult to express the dots below 5%, and more than 95% of the dots are easily lumped into a ball. The intermediate tone and shadow tone parts are easily lost. At the same time, due to the ductility of the flexographic plate, the accuracy of the overlay printing is also difficult to increase. Due to the expanded distortion of outlets, the printing layout lacks a sense of hierarchy, and the quality of printing and copying is significantly reduced. It can be seen that the printing plate is soft and elastic, which is the main reason why the quality of the flexographic printing dots is prone to occur. Process analysis shows that in the flexographic printing process, under the effect of pressure, the graphic size of the printing plate becomes larger, so that the dot area also becomes larger, and the fine dots are easily lost due to wear or uneven pressure. On the other hand, due to the use of low-viscosity inks for flexographic printing, when the contact pressure between the surface of the printing plate and the print is slightly larger, the ink on the printing plate spreads outwards, making the ink dot in the middle of the expanded dots thin and marginal. The ink layer is thick, forming a hollow-like point. When the observation is made with a magnifying glass, the edge of the dot can be seen to be smeared out. This is the basic feature of the increase of the flexographic printing dots. The production process also shows that the higher the dot number of the flexographic plate, the larger the dot gain value; the coarser the ink particles used, the larger the dot gain; the larger the ink volume on the plate or the ink is too thin, and the dot gain is also large. The larger the printing pressure and the pressure of the anilox roller, the larger the dot enlargement. The softer the substrate, the rubber roller, the pad, or the flexible plate, the bigger the dot enlargement; the worse the accuracy is due to the aging of the machine. The bigger it is. In addition, the thickness of the printing plate is inconsistent and it is easy to make the printing dot enlarge or lose. Therefore, to prevent the emergence of flexographic printing quality problems, a better solution is to not only pay attention to the maintenance of the equipment, select good quality, high-precision plate materials and high-quality ink, but also pay attention to the good operation technology. Off and printing process technology, when the printing unit has excess, when printing the screen version of the cable version and the field version, it should consider separating the cable version from the on-site version and print them separately, which is not only conducive to accurate printing pressure. The control is also conducive to the uniform application of ink and improve the printing quality of flexographic products.
Marks of ink marks appear on the print ink layer
When the thickness of the plate is uneven or there is a wrinkle on the bottom double-sided tape, the old version should be replaced. Use a high-quality plate with high precision or reattach the double-sided tape on the back of the plate to eliminate wrinkles.
When the spindle shaft or gear and other key parts are worn out, the fluttering or sliding phenomenon is likely to occur during the printing process, so that the print layout horizontal bars appear, and the area of ​​the screen area expands, so you should pay attention to the equipment Lubrication work prevents this problem from occurring.
When the squeegee is improperly installed or the fastening device is loosened, the squeegee should be reinstalled and the squeegee should be re-tightened to prevent the squeegee from taking place. The tightening adjustment should not be carried out in time, and careful adjustment should be made gradually.
When the ink fountain roller and the anilox roller partially exhibit partial wear, the new ink fountain roller and the anilox roller should be replaced. In normal operation, care should be taken to prevent dry friction of the roller body. The amount of ink must be sufficient. In the absence of ink, do not allow the squeegee or ink fountain roller to make intimate contact with the anilox roller.
When the ink in the local cells of the anilox roller is dry, the anilox roller must be thoroughly cleaned, so that the accumulated ink in the cells can be effectively removed.
Ink color is not uniform and there are flowers or paste phenomenon
In the flexographic printing process, sometimes the ink on the layout of the printed product will appear uneven, hair growth or stencil printing. The main causes and corresponding solutions are as follows:
1, the thickness of the printing plate is inconsistent or the hardness is too low. Plates are required to be selected from plates of the same thickness. For the coexistence of solid and small texts, a thin layer of tape can be added on the back of the field plate. If the plate is of poor quality, consider using a quality plate. Plate making.
2, the ink dried solid caused on the plate. Ink solidification on the printing plate will cause poor ink transmission. Therefore, any machine that needs a long period of shutdown during the printing process should be cleaned in time. If the ink drying speed is too fast, an appropriate amount of slow drying agent may be used to adjust the ink dryness.
3, the poor accuracy of the anilox roller or the contact pressure with the printing plate is too large or too small. For the wear and looseness of the axial roller head, appropriate repair measures shall be taken to eliminate it; if the structure of the traction roller for separating and closing is unstable, the cause shall be ascertained and treated to ensure that the anilox roller is pressed. No pulsation occurs; if the roller pressure on both sides is inconsistent and the roller pressure is too large or too small, accurate adjustments should be made.
4, caused by the instability of the pressure roller. Two-color flexographic printing machine directly printed on corrugated board, if it is the bending or deformation of the pressure roller shaft, looseness, should take appropriate measures to repair; if the pressure roller position is too high or too low, it should pass Adjust the proper position of the pressure roller so that the gap between the pressure roller and the plate cylinder adapts to the thickness of the cardboard to ensure that the ink on the printing plate remains stable.
5, caused by poor rubber roller. If the rubber roll is aged and deformed, the head of the roll shaft will be loose and beating, which will cause the ink supply to be unstable and affect the quality of the ink. In this regard, new rubber rollers should be replaced, and corresponding repair measures should be taken to eliminate loosening and bouncing of the rubber roller shaft head.
6, caused by bad squeegee. At present, some flexographic printing press ink delivery systems do not use rubber ink rollers, and the anilox roll is directly immersed in the ink tank. When rotating, excess ink on the roller surface is scraped off by a squeegee. This structure of the machine, if there is wear and deformation or the squeegee blade there is loose, beating phenomenon, will also cause the ink supply instability and affect the quality of printing ink color, can wear and deformation of the squeegee knife grinding, so that its working site remains flat Straight and straight state; to repair loose and beating parts, take repair measures to eliminate them.
7, ink viscosity caused by discomfort. If the viscosity of the ink is too large or too small, the ink on the plate surface of the printing product may easily cause the occurrence of blooming or stencil printing. Usually, the viscosity of printing inks on the netting and form printing plates should be appropriately lower, while the viscosity of the inks should be slightly larger when printing solid plates and plates. The viscosity of the water-based ink is generally controlled between 40 and 50S. However, since the temperature varies from place to place when using ink, this will affect the viscosity of the ink and the printing effect. Therefore, it is necessary to scientifically grasp and adjust actual conditions according to the printing environment.
8, caused by poor ink fineness. If fine dots of ink are used to print dots, then due to the coarse pigment particles in the ink, the layout of the printing plate will be prone to stencil and hair spots, and the printing rate of the printing plate will also be reduced. Therefore, printing dot products should be printed with fine ink. The fine ink with good density has a high concentration and can make the dots of printed products clear and plump.
9, caused by improper use of adhesive tape. Improper use of sticky tape will also make it appear that the printed ink appears to be blooming. Therefore, the tape should be reasonably selected according to the characteristics of the printing plate. Low-density adhesive tape should be used for printing fine lines and screens. For printing text lines and field versions, medium-density tapes can be used; the entire layout is printed on the ground. High-density tapes can be used.
Phantoms appear on prints
When the substrate is paper, a cloud-like phantom appears on the ink layer of the printing plate, or a large area of ​​the field part sees a shadow of another part of the picture, and a blank convex shape appears in the field, and the printing of the cellophane is a hazy fog. Phantom phenomenon. The reason is that the ink is not uniformly coated; the amount of ink is too small, the ink flowability is poor, and the anilox roller is not clean.
The solution is to: change the diameter of the plate cylinder and the different speeds of the anilox roller; thoroughly wash the anilox roller and plate with solvent; replace the ink and use the correct solvent formulation; use a slow drying agent as appropriate Appropriate increase in the amount of ink, to ensure that the anilox roller to obtain a certain amount of ink, increase the anilox roller soaked area; printed glass paper can be appropriate to reduce the solvent; control the ink drying.
Fine dots in the ink layer of the printed product
Fine point-like holes appear in the ink layer of the flexographic product, and the printing industry is accustomed to image it as "pinhole". There are two performance situations for “pinholes†in flexographic products. One is that there are many traces of holes on the prints, and there is no regular distribution, but the size of the “pinholes†is also not the same. Usually called “pinholesâ€. Chemical pinholes, which are commonly found on cellophane and overprinted products. Another type of "pinhole" is a "pinhole" trace that appears on a large area of ​​ink in a printed product. The size of the pinhole is relatively uniform and is often referred to as "mechanical pinhole." There are many reasons for the “pinhole†in the flexographic printing ink layer, and corresponding solutions should be adopted according to the problems that arise, so as to better eliminate the malfunction and ensure the printing quality of the product. In the production process, "pinholes" appear in the ink of India, and there are several situations as follows:
If the printing surface tension is unfavorable, an adjustment of about 1.5% of the aqueous ink surface tension adjuster may be added.
If the wettability between the ink and the surface of the print is so poor that the ink layer on the print shrinks to produce a “pinhole†mark, consider adding some improvements in wettability and leveling to the ink. Agent.
If the temperature of the printing shop is low or the humidity is too high, and the viscosity of the ink is too low or the drying is too slow to allow the ink to completely wet the surface of the print, the viscosity of the ink can be adjusted by increasing the temperature of the printing shop and reducing the humidity. Or add some additives to improve the ink compatibility, if the ink adjustment is invalid, consider replacing the ink type to solve.
If the ink is too thin or the printing ink layer is too thin, the ink viscosity should be adjusted and the printing ink supply volume should be appropriately increased.
If the ink is in the conjunctiva, because the air enters and creates a bubble-like void, and does not form a uniform ink layer on the surface of the print, some ink additives may be added to improve the fluidity of the ink.
If the printing ink dries quickly on the anilox roller, causing ink transfer and ink coating unevenness, the slow-drying agent can be used for adjustment. If it takes a long time to stop printing, the machine should be cleaned in time.
If the network is blocked or the anilox roller is worn out so that the amount of ink is reduced, the anilox roller should be cleaned or a new anilox roller should be replaced to ensure the ink supply and to maintain a proper printing ink layer thickness.
If the surface of the printed product is rough and the ink layer is difficult to keep in close contact with the depressed surface of the printed sheet, the printing pressure, the amount of ink applied, or the overprinting of the on-site layout should be appropriately increased twice.
If the surface of the plate is worn to form rough marks, or if the plate is slightly corrosive due to poor acid resistance, a new plate should be replaced.
If there is dirt on the impression cylinder, the impression cylinder should be cleaned.
If the printing pressure is too light to cause the ink layer on the printing plate to be transferred badly, the printing pressure should be appropriately increased.
If impurities adhere to the plate or sheet, measures should be taken to prevent dust, dust and paper particles from remaining on the plate surface and the print surface.
Loss or distortion of flexographic printing
In the printing production process, if the production process is not properly controlled, quality problems such as dot loss and deformation are prone to occur. For example, small dots in the highlights of the layout are easily lost, and dark dot sites are prone to be enlarged and become paste-like. Therefore, the flexographic printing process is difficult to express the dots below 5%, and more than 95% of the dots are easily lumped into a ball. The intermediate tone and shadow tone parts are easily lost. At the same time, due to the ductility of the flexographic plate, the accuracy of the overlay printing is also difficult to increase. Due to the expanded distortion of outlets, the printing layout lacks a sense of hierarchy, and the quality of printing and copying is significantly reduced. It can be seen that the printing plate is soft and elastic, which is the main reason why the quality of the flexographic printing dots is prone to occur. Process analysis shows that in the flexographic printing process, under the effect of pressure, the graphic size of the printing plate becomes larger, so that the dot area also becomes larger, and the fine dots are easily lost due to wear or uneven pressure. On the other hand, due to the use of low-viscosity inks for flexographic printing, when the contact pressure between the surface of the printing plate and the print is slightly larger, the ink on the printing plate spreads outwards, making the ink dot in the middle of the expanded dots thin and marginal. The ink layer is thick, forming a hollow-like point. When the observation is made with a magnifying glass, the edge of the dot can be seen to be smeared out. This is the basic feature of the increase of the flexographic printing dots. The production process also shows that the higher the dot number of the flexographic plate, the larger the dot gain value; the coarser the ink particles used, the larger the dot gain; the larger the ink volume on the plate or the ink is too thin, and the dot gain is also large. The larger the printing pressure and the pressure of the anilox roller, the larger the dot enlargement. The softer the substrate, the rubber roller, the pad, or the flexible plate, the bigger the dot enlargement; the worse the accuracy is due to the aging of the machine. The bigger it is. In addition, the thickness of the printing plate is inconsistent and it is easy to make the printing dot enlarge or lose. Therefore, to prevent the emergence of flexographic printing quality problems, a better solution is to not only pay attention to the maintenance of the equipment, select good quality, high-precision plate materials and high-quality ink, but also pay attention to the good operation technology. Off and printing process technology, when the printing unit has excess, when printing the screen version of the cable version and the field version, it should consider separating the cable version from the on-site version and print them separately, which is not only conducive to accurate printing pressure. The control is also conducive to the uniform application of ink and improve the printing quality of flexographic products.
Marks of ink marks appear on the print ink layer
When the thickness of the plate is uneven or there is a wrinkle on the bottom double-sided tape, the old version should be replaced. Use a high-quality plate with high precision or reattach the double-sided tape on the back of the plate to eliminate wrinkles.
When the spindle shaft or gear and other key parts are worn out, the fluttering or sliding phenomenon is likely to occur during the printing process, so that the print layout horizontal bars appear, and the area of ​​the screen area expands, so you should pay attention to the equipment Lubrication work prevents this problem from occurring.
When the squeegee is improperly installed or the fastening device is loosened, the squeegee should be reinstalled and the squeegee should be re-tightened to prevent the squeegee from taking place. The tightening adjustment should not be carried out in time, and careful adjustment should be made gradually.
When the ink fountain roller and the anilox roller partially exhibit partial wear, the new ink fountain roller and the anilox roller should be replaced. In normal operation, care should be taken to prevent dry friction of the roller body. The amount of ink must be sufficient. In the absence of ink, do not allow the squeegee or ink fountain roller to make intimate contact with the anilox roller.
When the ink in the local cells of the anilox roller is dry, the anilox roller must be thoroughly cleaned, so that the accumulated ink in the cells can be effectively removed.
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