First, gravure ink overview
The gravure ink has a relatively small viscosity and is relatively thin. In the process of storage and standing, the sinking phenomenon always occurs due to the gravity of the solid component therein. The ink poured from the upper layer of the ink tank that has not been stirred may have a low viscosity, and the color density and hiding power may be poor; the ink removed from the lower layer may have a higher viscosity, and the ratio of the pigment to the film forming material may also be higher. Adhesion will be worse. Therefore, the ink in the barrel must be fully stirred before use. This should not be ignored and cannot be understated. First of all, in order to obtain a uniform and consistent color, the same before and after the color, there is no difference in viscosity before and after the difference and a good fluidity, usability, requiring the use of a clean wooden rod or metal rod, stir it before use. Generally, at least 3 to 5 minutes must be agitated to make it uniform from top to bottom. If the ink is stored for a long time, a longer stirring time is required. In order to suspend the lower sediments, more force is needed.
Second, it is necessary to verify whether the ink used is in accordance with the nature of the printed object. Because gravure (photogravure) inks are generally divided into paper printing inks, plastic film inks, etc., printing inks cannot be used to print plastic film products. At the same time, paper printing inks are printed with food paper ink such as general paper inks and confectionery; printing inks for plastic film are printed with polyethylene film, printed with polypropylene film, printed with polyvinyl chloride and for composite printing. and many more. Must be clear.
While checking the type, there is also a problem of adjusting the solvent used for viscosity and dryness. In the production of gravure inks, the solvents used are different depending on the solubility of the resin and the anti-toxicity requirements. If it is a benzene type solvent, it can use toluene or xylene; if it is a gasoline type, it can use a specific boiling range of gasoline; if it is water soluble, it can use non-ionized water; if it is alcohol type, it can use ethanol, butanol, Ethyl acetate and the like, such as printed plastic film inks, may be xylene, isopropanol, or esters if they are phenethyl alcohol mixed solvent type, and methyl ethyl ketone or butyl acetate may be used as the keto ester type. Only by having a solvent that is consistent with the nature of the ink can a desired adjustment be made. And to check the ink color, viscosity, dryness and other quality indicators, whether it is suitable for the requirements of the printing press, whether it meets the requirements of the printing pattern. Otherwise, it must be adjusted and deployed.
Again, due to the extremely volatile nature of this type of ink, the container must be capped and sealed in time to prevent loss and drying.
Since the printer uses a doctor blade to remove the ink, it is particularly necessary to prevent the inclusion of foreign matter or dry solid agglomerates. Otherwise, the blade will be damaged and the printing will be difficult. Since such inks contain a large amount of solvents (especially benzenes, ketones, etc.) toxic and flammable, they should be ventilated and explosion-proof when stored, and avoid over-cooled and over-heated environments. They must also have strict fire prevention measures. Can not sun, rain, water into the package rust, resulting in loss. The management of the remaining ink is particularly important because the ink contains solvents with different boiling points, especially low-boiling solvents, which constantly volatilize in the storage of the remaining ink during printing, and the solvent mix balance is destroyed, causing dry knots, deterioration of properties, and even air The moisture in the medium is also brought into the ink by the extremely cool solvent, and the static electricity can also absorb the surrounding dust into the ink. After use, the viscosity of the remaining ink is already very low, and it is easy to separate, precipitate, and agglomerate, which will cause many problems in use. Therefore, note that the remaining ink is tightly closed, marked well, kept in a cool place, and it is necessary to filter and stir while using it. People do not pay much attention to this point. In fact, most of the faults are related to this.
The problems that arise in gravure printing are the same as those in offset printing and letterpress printing. The reasons are as follows. One is caused by the ink itself, and the other is caused by the condition of the printer components (including the printing plate) and the printing object. The third is caused by the operator's proficiency and the level of operation technology. These three aspects determine the success or failure of the print job, smooth or tortuous. Therefore, when problems occur, detailed analysis must be conducted from these three aspects. For solvent-based inks, mechanical and material considerations must be taken into consideration when analyzing conditions, and in particular, attention should be paid to changes in climate, including temperature, humidity, ventilation, heat, etc., because of the solvent-based drying of inks. Make clear the situation, determine the cause, and take countermeasures. Most of the content of this article also applies to the use of rubber relief inks for reference.
Second, the gravure ink in the printing of the causes of the failure analysis and solutions
1 paste version (buried version, blocking version)
Symptoms: Printed images or small prints do not appear, even on the prints with a layer of ink, and the pattern is blurred.
Reasons: 1 ink drying speed is too fast, so that the ink is dry knotted in the net mesh hole. Or pattern nets were blocked by dry agglomerates, and new inks could not be completely re-dissolved, forming large areas piled on the prints and embossing patterns; the printing speed was too slow, and the scraper removed the non-patterned ink and arrived afterwards. Before the embossed dots, the ink has dried and does not transfer. The transfer rate of the ink in the gravure network is generally 1/2, that is, there are still 1/2 remaining on the printing plate. The viscosity of the ink is large and the drying speed is fast. Even if the roller is re-entered into the ink fountain, it is difficult to Dissolved, so repeated many times, the ink transfer rate decreased, eventually became blocked version. 2 Plate is too eroded or the dots are not clear. The gravure is obtained by etching the copper surface after chrome plating. Corrosion can not meet the requirements, the depth is not enough, the wall of the hole is not smooth, the hair is in a hairy state, the chrome plating is thick, the chromium block has filled the hole, and the burr is not polished well, all can promote the ink layer to dry quickly and cause blockage. Version. The ink is crusted due to poor storage. Paper blocks, plastic swarf and surrounding dust during printing are absorbed into the ink due to static electricity, or directly fall into the printing plate's cell, which can also cause stencil printing. During the printing process, it stops and remains in the layout. The film on the film has not been cleaned up in time, and gradually accumulated, and the dots are stuck; ink fluidity is poor, inks of different kinds and immiscible inks are mixed in, solvents are misused, and the number of true solvents in the ink is small, resulting in poor reconstitution and viscosity. Large, it is not easy to scrape off the non-graphic pattern, especially the residual dry knot at the edge of the network. It is constantly expanding and the cleaning is not timely, resulting in the network being buried.
Solution: Mainly based on the speed of the machine, that is, the time it takes for the squeegee to scrape ink at the printing pressure point, use a solvent to adjust the drying speed, and slow down the drying speed as much as possible. Consider the following time.
High Speed ​​Unit Rotary Gravure Press: 0.02~0.1s
Medium and low speed rotary gravure Printing Machine: 0.04~0.15s
High-speed single sheet platform gravure printing machine: 0.1~0.2s
Low-speed sheet-fed gravure printing machine: 0.5~0.6s
The ink can be evacuated with a slower solvent, such as a solvent with a boiling point of 120-150°C, which has a large latent heat of vaporization. When the ink is dried faster, the printing speed can be increased. After scraping the ink, the ink flow in the net is still not dried until it is still dry; check the quality of the plate etching, chrome plating, and polishing. Under normal circumstances, when other conditions are deemed appropriate, a paste version occurs, and after a scrub, if the paste version occurs soon, and the level is inconsistent from the text, it can be determined as a result of the printing plate. At this time, it is necessary to re-plate; check the blowing, heating device, whether it is due to changes in direction, hit the layout. If it is, it should be immediately corrected; the residue mixed in the ink, the foreign matter on the plate should be promptly removed, and the printing setting of the circulating pump can be filtered at the outlet of the 120 mesh steel wire; the ink viscosity should be based on the faster the speed, the need for viscosity The lower the principle, make adjustments. But also to prevent overcorrection. General gravure ink viscosity can be controlled in the 19 ~ 25s/25 °C (No. 4 viscosity cup) range.
In order to ensure the re-inking of the ink, the amount of true solvent in the ink should be guaranteed or increased according to the opinion of the ink manufacturer. At the same time, inks of different solvent types and different uses should not be mixed with each other to prevent the resin from depositing and losing the ink property.
2. Bite
Failure phenomenon: In the color printing of satellite rotary gravure printing machine or unit combined rotary gravure printing machine, especially when printing polyolefin film, the second color ink will stick out the ink of the previous color printing.
Reason: Due to the slowness of the ink of the previous color, or the poor adherence to the printed object, and the latter color (ie, the adhesion of the second color is too large, the printing pressure is too high, or the amount of resin in the ink is too small, The bite of the previous color bite off; the printing speed is too fast, the previous color is not dry, and it cannot withstand the splitting force of the second color. At the same time, when the printing is not focused on the pattern or the air volume is small, when adjusting, in the first color, There are too many solvents for the slow-drying component, so that the former color cannot be adhered and dried as required and is damaged by the second color of the adhesive tape.
Solution: For the former color, you should speed up the drying, adding low-boiling solvents; slow down the speed; increase the amount of resin, add the ink with the resin, do not use pure solvent; to block the part of the air duct to clear the wind blowing The surface of the printed pattern; when adjusted due to large viscosity, if there are too many slow-drying components, the original ink should be used for remedy.
For the second color, the distance between the plate roller and the embossing roller should be adjusted to reduce the pressure; the viscosity of the second color should be slightly smaller than the first color.
Synchronize slows down. If the previous color is not strong enough to adhere to the printed body, it should be checked whether the treatment of the film is more than 38 dy/cm. Otherwise, it should be re-treated, or a solution containing a resin such as a diluting agent should be added to the ink.
3. Dirty (sticky)
Symptoms: After the reel (paper, plastic or foil) is printed, part or all of the image of the printed product is printed on the back of the attached sheet, which is also called pasting or offset printing. One is that during the stacking process of the harvested rolls, the printed products stick to each other, and the imprinted backs cause waste, which is also called accumulation of dirt. Whether it is printing or printing, it is called rolling adhesion.
Reason: Mainly due to the residual viscosity of the ink. The reason for this situation is the presence of a large amount of residual solvent, which is often a high-boiling point solvent. During the printing process, it is not easy to evaporate. When the printed material is reeled, the resin in the ink has not yet solidified, resulting in residual stickiness.
In addition, many materials contain more plasticizers. Under certain conditions, they can swell the resin in the ink and cause stickiness.
Solution: Improve the initial dryness and dryness of the ink, strengthen the air blow and heat, make the ink film dry thoroughly, increase the cooling device in the winding section, and do not increase the tension when winding up.
4. Poor adhesion
Symptoms: When printing the polyolefin film, after the imprint is dried, the ink film is rubbed, rubbed, and peeled or partially peeled off with a transparent tape.
Cause: Misuse of ink that is not a printed film; polyolefin surface finish is not reached; improper heating; ink film is not completely dry or not heated enough.
Solution:
1 In the use of ink, adhere to the principle of special ink, different types of non-doping.
2 Self-arranged due to water, check the surface treatment of the film (Dyne water ratio see Schedule 1).
3 Printing objects, especially materials with high hygroscopicity, should not be wetted. When printing, diluents should be formulated according to the temperature and humidity at that time.
5. Whitening
Failure phenomenon: When the surface of the ink film of the solvent type gravure ink and the rubber letterpress ink is dry, moisture in the air penetrates into the ink film, causing the surface to become whitish. At this point, the prints are dull and the colors are not bright, and there seems to be a layer of fog.
Cause: Due to the relatively high temperature and relatively high relative humidity, the solvent is seriously out of regulation.
Solution: Add contrast ink resin, the higher boiling point, completely dissolve the true solvent of the resin, so that the ink delays drying.
It is very important to strengthen the heat and keep it dry. When adjusting the viscosity, pay attention to add enough real solvent to keep the resin in the ink fully dissolved.
6. Hydration
Symptoms: The solvent composition in the ink changes, so that the diluted ink produces thickening, resin precipitation, gelation, reduced concentration, poor transfer, paste plate and other problems, especially the small pattern, the amount of ink less.
Cause: Due to long-time printing, moisture in the air enters the ink, or water in the scene inadvertently enters the ink.
Remedy: Replace old ink with new ink; use moderately volatile solvent for delaying dryness; check hair, and do not face the roller.
7. Pinhole
Symptoms: Tiny holes appear in printed products, especially on large area solid patterns.
The gravure ink has a relatively small viscosity and is relatively thin. In the process of storage and standing, the sinking phenomenon always occurs due to the gravity of the solid component therein. The ink poured from the upper layer of the ink tank that has not been stirred may have a low viscosity, and the color density and hiding power may be poor; the ink removed from the lower layer may have a higher viscosity, and the ratio of the pigment to the film forming material may also be higher. Adhesion will be worse. Therefore, the ink in the barrel must be fully stirred before use. This should not be ignored and cannot be understated. First of all, in order to obtain a uniform and consistent color, the same before and after the color, there is no difference in viscosity before and after the difference and a good fluidity, usability, requiring the use of a clean wooden rod or metal rod, stir it before use. Generally, at least 3 to 5 minutes must be agitated to make it uniform from top to bottom. If the ink is stored for a long time, a longer stirring time is required. In order to suspend the lower sediments, more force is needed.
Second, it is necessary to verify whether the ink used is in accordance with the nature of the printed object. Because gravure (photogravure) inks are generally divided into paper printing inks, plastic film inks, etc., printing inks cannot be used to print plastic film products. At the same time, paper printing inks are printed with food paper ink such as general paper inks and confectionery; printing inks for plastic film are printed with polyethylene film, printed with polypropylene film, printed with polyvinyl chloride and for composite printing. and many more. Must be clear.
While checking the type, there is also a problem of adjusting the solvent used for viscosity and dryness. In the production of gravure inks, the solvents used are different depending on the solubility of the resin and the anti-toxicity requirements. If it is a benzene type solvent, it can use toluene or xylene; if it is a gasoline type, it can use a specific boiling range of gasoline; if it is water soluble, it can use non-ionized water; if it is alcohol type, it can use ethanol, butanol, Ethyl acetate and the like, such as printed plastic film inks, may be xylene, isopropanol, or esters if they are phenethyl alcohol mixed solvent type, and methyl ethyl ketone or butyl acetate may be used as the keto ester type. Only by having a solvent that is consistent with the nature of the ink can a desired adjustment be made. And to check the ink color, viscosity, dryness and other quality indicators, whether it is suitable for the requirements of the printing press, whether it meets the requirements of the printing pattern. Otherwise, it must be adjusted and deployed.
Again, due to the extremely volatile nature of this type of ink, the container must be capped and sealed in time to prevent loss and drying.
Since the printer uses a doctor blade to remove the ink, it is particularly necessary to prevent the inclusion of foreign matter or dry solid agglomerates. Otherwise, the blade will be damaged and the printing will be difficult. Since such inks contain a large amount of solvents (especially benzenes, ketones, etc.) toxic and flammable, they should be ventilated and explosion-proof when stored, and avoid over-cooled and over-heated environments. They must also have strict fire prevention measures. Can not sun, rain, water into the package rust, resulting in loss. The management of the remaining ink is particularly important because the ink contains solvents with different boiling points, especially low-boiling solvents, which constantly volatilize in the storage of the remaining ink during printing, and the solvent mix balance is destroyed, causing dry knots, deterioration of properties, and even air The moisture in the medium is also brought into the ink by the extremely cool solvent, and the static electricity can also absorb the surrounding dust into the ink. After use, the viscosity of the remaining ink is already very low, and it is easy to separate, precipitate, and agglomerate, which will cause many problems in use. Therefore, note that the remaining ink is tightly closed, marked well, kept in a cool place, and it is necessary to filter and stir while using it. People do not pay much attention to this point. In fact, most of the faults are related to this.
The problems that arise in gravure printing are the same as those in offset printing and letterpress printing. The reasons are as follows. One is caused by the ink itself, and the other is caused by the condition of the printer components (including the printing plate) and the printing object. The third is caused by the operator's proficiency and the level of operation technology. These three aspects determine the success or failure of the print job, smooth or tortuous. Therefore, when problems occur, detailed analysis must be conducted from these three aspects. For solvent-based inks, mechanical and material considerations must be taken into consideration when analyzing conditions, and in particular, attention should be paid to changes in climate, including temperature, humidity, ventilation, heat, etc., because of the solvent-based drying of inks. Make clear the situation, determine the cause, and take countermeasures. Most of the content of this article also applies to the use of rubber relief inks for reference.
Second, the gravure ink in the printing of the causes of the failure analysis and solutions
1 paste version (buried version, blocking version)
Symptoms: Printed images or small prints do not appear, even on the prints with a layer of ink, and the pattern is blurred.
Reasons: 1 ink drying speed is too fast, so that the ink is dry knotted in the net mesh hole. Or pattern nets were blocked by dry agglomerates, and new inks could not be completely re-dissolved, forming large areas piled on the prints and embossing patterns; the printing speed was too slow, and the scraper removed the non-patterned ink and arrived afterwards. Before the embossed dots, the ink has dried and does not transfer. The transfer rate of the ink in the gravure network is generally 1/2, that is, there are still 1/2 remaining on the printing plate. The viscosity of the ink is large and the drying speed is fast. Even if the roller is re-entered into the ink fountain, it is difficult to Dissolved, so repeated many times, the ink transfer rate decreased, eventually became blocked version. 2 Plate is too eroded or the dots are not clear. The gravure is obtained by etching the copper surface after chrome plating. Corrosion can not meet the requirements, the depth is not enough, the wall of the hole is not smooth, the hair is in a hairy state, the chrome plating is thick, the chromium block has filled the hole, and the burr is not polished well, all can promote the ink layer to dry quickly and cause blockage. Version. The ink is crusted due to poor storage. Paper blocks, plastic swarf and surrounding dust during printing are absorbed into the ink due to static electricity, or directly fall into the printing plate's cell, which can also cause stencil printing. During the printing process, it stops and remains in the layout. The film on the film has not been cleaned up in time, and gradually accumulated, and the dots are stuck; ink fluidity is poor, inks of different kinds and immiscible inks are mixed in, solvents are misused, and the number of true solvents in the ink is small, resulting in poor reconstitution and viscosity. Large, it is not easy to scrape off the non-graphic pattern, especially the residual dry knot at the edge of the network. It is constantly expanding and the cleaning is not timely, resulting in the network being buried.
Solution: Mainly based on the speed of the machine, that is, the time it takes for the squeegee to scrape ink at the printing pressure point, use a solvent to adjust the drying speed, and slow down the drying speed as much as possible. Consider the following time.
High Speed ​​Unit Rotary Gravure Press: 0.02~0.1s
Medium and low speed rotary gravure Printing Machine: 0.04~0.15s
High-speed single sheet platform gravure printing machine: 0.1~0.2s
Low-speed sheet-fed gravure printing machine: 0.5~0.6s
The ink can be evacuated with a slower solvent, such as a solvent with a boiling point of 120-150°C, which has a large latent heat of vaporization. When the ink is dried faster, the printing speed can be increased. After scraping the ink, the ink flow in the net is still not dried until it is still dry; check the quality of the plate etching, chrome plating, and polishing. Under normal circumstances, when other conditions are deemed appropriate, a paste version occurs, and after a scrub, if the paste version occurs soon, and the level is inconsistent from the text, it can be determined as a result of the printing plate. At this time, it is necessary to re-plate; check the blowing, heating device, whether it is due to changes in direction, hit the layout. If it is, it should be immediately corrected; the residue mixed in the ink, the foreign matter on the plate should be promptly removed, and the printing setting of the circulating pump can be filtered at the outlet of the 120 mesh steel wire; the ink viscosity should be based on the faster the speed, the need for viscosity The lower the principle, make adjustments. But also to prevent overcorrection. General gravure ink viscosity can be controlled in the 19 ~ 25s/25 °C (No. 4 viscosity cup) range.
In order to ensure the re-inking of the ink, the amount of true solvent in the ink should be guaranteed or increased according to the opinion of the ink manufacturer. At the same time, inks of different solvent types and different uses should not be mixed with each other to prevent the resin from depositing and losing the ink property.
2. Bite
Failure phenomenon: In the color printing of satellite rotary gravure printing machine or unit combined rotary gravure printing machine, especially when printing polyolefin film, the second color ink will stick out the ink of the previous color printing.
Reason: Due to the slowness of the ink of the previous color, or the poor adherence to the printed object, and the latter color (ie, the adhesion of the second color is too large, the printing pressure is too high, or the amount of resin in the ink is too small, The bite of the previous color bite off; the printing speed is too fast, the previous color is not dry, and it cannot withstand the splitting force of the second color. At the same time, when the printing is not focused on the pattern or the air volume is small, when adjusting, in the first color, There are too many solvents for the slow-drying component, so that the former color cannot be adhered and dried as required and is damaged by the second color of the adhesive tape.
Solution: For the former color, you should speed up the drying, adding low-boiling solvents; slow down the speed; increase the amount of resin, add the ink with the resin, do not use pure solvent; to block the part of the air duct to clear the wind blowing The surface of the printed pattern; when adjusted due to large viscosity, if there are too many slow-drying components, the original ink should be used for remedy.
For the second color, the distance between the plate roller and the embossing roller should be adjusted to reduce the pressure; the viscosity of the second color should be slightly smaller than the first color.
Synchronize slows down. If the previous color is not strong enough to adhere to the printed body, it should be checked whether the treatment of the film is more than 38 dy/cm. Otherwise, it should be re-treated, or a solution containing a resin such as a diluting agent should be added to the ink.
3. Dirty (sticky)
Symptoms: After the reel (paper, plastic or foil) is printed, part or all of the image of the printed product is printed on the back of the attached sheet, which is also called pasting or offset printing. One is that during the stacking process of the harvested rolls, the printed products stick to each other, and the imprinted backs cause waste, which is also called accumulation of dirt. Whether it is printing or printing, it is called rolling adhesion.
Reason: Mainly due to the residual viscosity of the ink. The reason for this situation is the presence of a large amount of residual solvent, which is often a high-boiling point solvent. During the printing process, it is not easy to evaporate. When the printed material is reeled, the resin in the ink has not yet solidified, resulting in residual stickiness.
In addition, many materials contain more plasticizers. Under certain conditions, they can swell the resin in the ink and cause stickiness.
Solution: Improve the initial dryness and dryness of the ink, strengthen the air blow and heat, make the ink film dry thoroughly, increase the cooling device in the winding section, and do not increase the tension when winding up.
4. Poor adhesion
Symptoms: When printing the polyolefin film, after the imprint is dried, the ink film is rubbed, rubbed, and peeled or partially peeled off with a transparent tape.
Cause: Misuse of ink that is not a printed film; polyolefin surface finish is not reached; improper heating; ink film is not completely dry or not heated enough.
Solution:
1 In the use of ink, adhere to the principle of special ink, different types of non-doping.
2 Self-arranged due to water, check the surface treatment of the film (Dyne water ratio see Schedule 1).
3 Printing objects, especially materials with high hygroscopicity, should not be wetted. When printing, diluents should be formulated according to the temperature and humidity at that time.
5. Whitening
Failure phenomenon: When the surface of the ink film of the solvent type gravure ink and the rubber letterpress ink is dry, moisture in the air penetrates into the ink film, causing the surface to become whitish. At this point, the prints are dull and the colors are not bright, and there seems to be a layer of fog.
Cause: Due to the relatively high temperature and relatively high relative humidity, the solvent is seriously out of regulation.
Solution: Add contrast ink resin, the higher boiling point, completely dissolve the true solvent of the resin, so that the ink delays drying.
It is very important to strengthen the heat and keep it dry. When adjusting the viscosity, pay attention to add enough real solvent to keep the resin in the ink fully dissolved.
6. Hydration
Symptoms: The solvent composition in the ink changes, so that the diluted ink produces thickening, resin precipitation, gelation, reduced concentration, poor transfer, paste plate and other problems, especially the small pattern, the amount of ink less.
Cause: Due to long-time printing, moisture in the air enters the ink, or water in the scene inadvertently enters the ink.
Remedy: Replace old ink with new ink; use moderately volatile solvent for delaying dryness; check hair, and do not face the roller.
7. Pinhole
Symptoms: Tiny holes appear in printed products, especially on large area solid patterns.
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