According to the ISO9002 quality assurance system, several process quality control points must be set throughout the flexographic printing process. At each control point, it is necessary to formulate corresponding countermeasures and take effective measures against weak links in the process.
Flexible decoration printed matter, if classified by product, is generally divided into three categories: paper prints, plastic prints, and sales packaging carton prints. Because of the different printing substrates used in these three types of products, the specific process characteristics, process parameters, and quality control parameters are all different under the same premise of the printing process; on a specific printing substrate (PE or PP), Must choose the appropriate ink (alcoholic ink or water-soluble ink), with the corresponding plate (1.143mm thin version). This article plans to set up process quality control points in the plastic film flexographic printing process, and talk about some of our ideas and practices.
First, the printing substrate For the plastic film, the domestic is currently using the flexographic printing process, there are two main categories: PE and PP. Other types of films, such as PVC, PET, etc., generally use a gravure process because of their small tensile deformation. In addition, so far, there is no domestically applicable flexographic ink for such films. In the past, the author printed the relevant product on the PVC soft film, and he stopped because he could not find the flexo ink that met the standard in printing fastness. Therefore, the control of printed substrates is mainly the control of PE and PP printed films.
The PP film is divided into two kinds, CPP and OPP. The control of the CPP film is exactly the same as that of the gravure printing process, and will not be described here. The more OPP film used in flexo printing is the label film, the film density is relatively small, generally 0.6 ~ 0.7, compared with the original density of OPP film 0.90 ~ 0.91, obviously a lot smaller. The most widely used is the beverage labels used by the two major companies, Coca Cola and Pepsi. Due to the environmental protection and production costs of PVC heat-shrinkable bottles, many beverage suppliers have gradually changed their labels, and the market for OPP labels has become increasingly popular. Gravure printing dominates the label printing process, but savvy business operators have evolved to use a flexo printing process to print beverage labels that are less costly and require at least half the ink consumption compared to gravure printing. Therefore, the potential of flexo-printed OPP beverages on the market will be enormous. The OPP label film, which is to be controlled before printing, except for the same physical properties as the gravure process such as film flatness, vertical and horizontal tensile strength, surface friction coefficient, and wet tension of the film surface, we feel that the film should be emphasized. BaiDu. Because the flexible process is different from the gravure process, the OPP label films with different brightness have different effects under the same printing process parameters. The use of fixed-point film supply in control has been proven to be a simple and effective method. Of course, we must pay more attention to this issue when we use other brands of film under the requirement of continuously reducing the cost of film supply. Because, for gravure, even if the color difference of the film is larger, the depth of the printing plate can be adjusted and masked with the saturation of the color. However, the flexo printing process uses less ink and has a thin ink layer. It is difficult to achieve the purpose of masking. The whiteness of the OPP label film is directly related to the color masterbatch used in the production process of the film, and it is necessary to pay attention to this problem when feeding the film.
PE film is the leading product of flexographic printing materials. In the past, the main purpose of the PE film was to use the film as a heat resistant film and used as a composite film. Therefore, in general production companies, the product standards for the product are basically determined by the standards of the composite film. But now the situation is different. Whether it is transparent PE or milky white PE, it has gradually been used in flexo printing products. Therefore, if we continue to use the original parameters, we will not be able to meet the requirements of the flexo printing process. Two parameters are emphasized here, one is the crystal point problem of the film and the other is the printability problem of the film surface.
Crystal spots, also known as dead spots, are known in foreign professional books as "fish eyes" or "arrow heads." This is a process in which the polyethylene resin undergoes cross-linking after being oxidized during processing, thereby generating a gel. Such gel particles can form macroscopic aggregates in film articles. Our training on this issue is gradually deepening. Initially, during the printing process, we often encountered the squeezing of the flexographic printing plate due to the crystal point on the PE film. Therefore, the product that was provided to us for the printing film was put on the control before the film was blown. Replace the new filter beforehand. However, the accident continues. This prompted us to find ways to avoid such accidents and further control the cause of the crystal spot. In fact, a large crystal point may be caused by a bad filter, but a small crystal point can not be solved by changing the filter again. Of course, this belongs to the problem of film production. It cannot be solved by temperature regulation alone. The control of the crystal point of the printed film is a very important part. For a printing company, it is necessary to formulate an acceptance standard, that is, the size of a single crystal spot and the number of crystal spots per unit area. Crystal points that exceed a certain "degree" will be unacceptable, and it is directly related to the protection of the quality of printing plates and printed products.
For the printability of plastic films, it has long been specified only 38-42 dyne of surface wetting tension. Once this value is reached, it is generally considered to pass. However, we have encountered some problems in our production practice. When using a company's PE film, the production speed can only reach 150-160m/min, and then go up, you will find the pinhole phenomenon in the field printing more and more serious, in order to ensure the density of the field, we have to The speed is maintained at around 150m/min. However, the same production process (subsidiary materials and process parameters are completely the same) in the author's current company, only with a different film, the speed can be mentioned above 200m/min, our production speed is 230 ~ 250m/min, the field density Basically not affected. This prompted us to consider a problem, in addition to the condition of wetting tension on the surface of the film, there are still other factors that affect the ink transfer characteristics. These factors are collectively referred to as printability. Therefore, the printability of the film should also be one of the parameters that we must control. This is directly related to the quality of the product and also to the benefits of the company.
Second, the flexographic ink used in ink plastic film, both at home and abroad. High-grade inks are still known for their foreign inks. The flexo printing inks of the 1980s are suitable for use in printed plastic vests (also known as pouches) for primary flexo presses (such as laminated flexo presses). In the 1990s, great progress was made in the flexo printing process of plastic films. Flexographic inks adapted to high speed, fineness, and high color were successively landed in the domestic market. Ink quality control, in addition to the perception of fineness, color viscosity and other parameters, the author thinks that the color concentration should be emphasized. Flexographic inks, when printing fine flexographic plates, due to the use of high-line anilox rolls, even if the current anilox roll manufacturing process has undergone great reforms, CO2 laser engraving processes have been unambiguously named by YAG or others. With the laser replaced, the amount of strike ink has been significantly improved, but the anilox roller with a high number of screens also needs high-color ink, but it is still an indisputable fact. Many ink companies in their own production series, in addition to the general product, also specifically provide its ink, or high-density ink, is specifically designed to deal with this situation. However, if the ink used in normal production is overcharged, it exceeds a certain percentage, the resin in the ink is reduced, and the adhesion of the ink to the plastic film is inevitably reduced. Therefore, the ink is not as good as possible. To control a degree. Choosing and controlling the color intensity of flexographic inks, the author believes that it is essential in process quality control. We feel that using a density meter to measure field density is simple and effective. However, the ink sample scraped on the film by the scraper bar is still different from the actual print process conditions (such as a certain number of lines of anilox roller, a certain density of double-sided adhesive tape, a certain printing speed). This difference must also be noted when the instrument is tested. In addition, when it comes to the residual amount of solvent in printed products, it should also pay attention to the resin used in the selection of flexo ink. Polyamide, nitrocellulose, and PVB have their own strengths, which cannot be ignored. The inks produced by foreign companies for printing on plastics have also been trial-controlled in the domestic market. I have tested such inks and have good performance, but there are still some problems. It is estimated that it will take time to fully replace alcohol inks.
Third, drafting general printing companies themselves are not drafting. The sales department handed over the electronic documents submitted by the customer to the technical department and then transferred it to a special plate-making company. The plate-making company could handle it. However, we often encounter a problem that is puzzling. The plates produced by the plate-making company according to the design in the electronic file are always unsatisfactory and sometimes have to be reworked. Once there was such a thing, in the production of Coca-Cola 350ml “distribution†six cans of shrink packaging, the plates produced by the plate-making company according to the design in the electronic file were sent to Confirmation that it was rejected twice and successively reworked because the sent to the Palm was not approved by the advertising creative department. Customers do not confirm, where is the problem? After repeated analysis, we found the reason. Because of the heat-shrinkage PE film we use, the transparency is very poor and the product is printed on it. The whole feeling is not clear. In 2000, the design draft of the "Fanta" was orange-red. The emphasis was bright and lively, but now the product feels a gap. Before sending the sample for the third time, the author went to the advertising company to communicate with the design department and chose one of the two different resolution manuscripts in the electronic file. Under possible conditions, the Fen drawn icon was fine-tuned. Because the lightness of the film is not enough, we have simplified the details around the icon in the design, highlighting the white part. White is the color with the highest brightness. With this part of the color, it can effectively mask the lack of film. Of course, when we printed, we printed two layers of white, which also made up for the lack of film. During the process of laying out the orange-red version of the cable, we clearly proposed a red net plus one percent based on the characteristics of the process. The printing plate produced by the plate-making company according to our above requirements was successfully printed and was soon confirmed by the customer.
In general, for the electronic documents transmitted by various printing companies, the plate-making company needs to make some adjustments, but this adjustment is mainly based on the adjustment of the compensation curve for network expansion and the compensation for the extension of the printing plate caused by the radius of curvature of the printing plate. For other parameters, it is generally determined according to the parameters in the electronic file. At most, in terms of deduction, some proposals for plate-making companies are recommended. However, in the actual printing process, there are various problems, such as clasps, 0.1mm can be done according to the printing technology of the satellite flexographic printing machine, but if it is not the printed plastic packaging, instead of the printed paper trademark, at this time dozens of The trademarks are put together into one piece, and there are no major or minor parts. For the trademark, the main part is everywhere, so the 0.1mm buckle can not take into account the overprint accuracy of the entire layout. In the past, when I was producing Tiger Brand Aluminizer trademarks, we had to put forward a series of specific requirements for the platemaking companies according to the characteristics of our company's equipment. In some places, the fasteners should reach 0.25mm, and some places should be left blank. Never stack. The shrinkage of the PE film during the printing process is also the same. The PE film, especially the PE of 25-40 [mu]m, shrinks very much during the printing process, and some products can reach 3% to 4%. This compensation for design manuscripts is essential. This kind of parameter is unknown to the platemaking company. This requires the technical department to submit its own compensation requirements when submitting the electronic file. In addition, the adjustment of the layout is suitable for the flexographic printing process, such as the gradual change of the curve, large area on the ground. It is also necessary to take into account the separation of small plates from the plate making. In this way, product quality will be greatly guaranteed and delivery will not be delayed. Therefore, the process quality control in the production process is to understand the design in the electronic file and adjust it according to actual production conditions. It is not just an electronic file that we hand over to the plate-making company. It must be a complete set of instructions. If you do not have a bottom in your mind at the moment, you should discuss with the technicians of the plate-making company and work out a better plan. We feel that the role of the technical department should not be just a setter, but should be a headquarters.
Fourth, the plate-making for the average enterprise, the draft and the plate-making company are all completed by the plate-making company. Some of the equipment is more full-scale than the ones that own the platemaking workshops.
Flexible decoration printed matter, if classified by product, is generally divided into three categories: paper prints, plastic prints, and sales packaging carton prints. Because of the different printing substrates used in these three types of products, the specific process characteristics, process parameters, and quality control parameters are all different under the same premise of the printing process; on a specific printing substrate (PE or PP), Must choose the appropriate ink (alcoholic ink or water-soluble ink), with the corresponding plate (1.143mm thin version). This article plans to set up process quality control points in the plastic film flexographic printing process, and talk about some of our ideas and practices.
First, the printing substrate For the plastic film, the domestic is currently using the flexographic printing process, there are two main categories: PE and PP. Other types of films, such as PVC, PET, etc., generally use a gravure process because of their small tensile deformation. In addition, so far, there is no domestically applicable flexographic ink for such films. In the past, the author printed the relevant product on the PVC soft film, and he stopped because he could not find the flexo ink that met the standard in printing fastness. Therefore, the control of printed substrates is mainly the control of PE and PP printed films.
The PP film is divided into two kinds, CPP and OPP. The control of the CPP film is exactly the same as that of the gravure printing process, and will not be described here. The more OPP film used in flexo printing is the label film, the film density is relatively small, generally 0.6 ~ 0.7, compared with the original density of OPP film 0.90 ~ 0.91, obviously a lot smaller. The most widely used is the beverage labels used by the two major companies, Coca Cola and Pepsi. Due to the environmental protection and production costs of PVC heat-shrinkable bottles, many beverage suppliers have gradually changed their labels, and the market for OPP labels has become increasingly popular. Gravure printing dominates the label printing process, but savvy business operators have evolved to use a flexo printing process to print beverage labels that are less costly and require at least half the ink consumption compared to gravure printing. Therefore, the potential of flexo-printed OPP beverages on the market will be enormous. The OPP label film, which is to be controlled before printing, except for the same physical properties as the gravure process such as film flatness, vertical and horizontal tensile strength, surface friction coefficient, and wet tension of the film surface, we feel that the film should be emphasized. BaiDu. Because the flexible process is different from the gravure process, the OPP label films with different brightness have different effects under the same printing process parameters. The use of fixed-point film supply in control has been proven to be a simple and effective method. Of course, we must pay more attention to this issue when we use other brands of film under the requirement of continuously reducing the cost of film supply. Because, for gravure, even if the color difference of the film is larger, the depth of the printing plate can be adjusted and masked with the saturation of the color. However, the flexo printing process uses less ink and has a thin ink layer. It is difficult to achieve the purpose of masking. The whiteness of the OPP label film is directly related to the color masterbatch used in the production process of the film, and it is necessary to pay attention to this problem when feeding the film.
PE film is the leading product of flexographic printing materials. In the past, the main purpose of the PE film was to use the film as a heat resistant film and used as a composite film. Therefore, in general production companies, the product standards for the product are basically determined by the standards of the composite film. But now the situation is different. Whether it is transparent PE or milky white PE, it has gradually been used in flexo printing products. Therefore, if we continue to use the original parameters, we will not be able to meet the requirements of the flexo printing process. Two parameters are emphasized here, one is the crystal point problem of the film and the other is the printability problem of the film surface.
Crystal spots, also known as dead spots, are known in foreign professional books as "fish eyes" or "arrow heads." This is a process in which the polyethylene resin undergoes cross-linking after being oxidized during processing, thereby generating a gel. Such gel particles can form macroscopic aggregates in film articles. Our training on this issue is gradually deepening. Initially, during the printing process, we often encountered the squeezing of the flexographic printing plate due to the crystal point on the PE film. Therefore, the product that was provided to us for the printing film was put on the control before the film was blown. Replace the new filter beforehand. However, the accident continues. This prompted us to find ways to avoid such accidents and further control the cause of the crystal spot. In fact, a large crystal point may be caused by a bad filter, but a small crystal point can not be solved by changing the filter again. Of course, this belongs to the problem of film production. It cannot be solved by temperature regulation alone. The control of the crystal point of the printed film is a very important part. For a printing company, it is necessary to formulate an acceptance standard, that is, the size of a single crystal spot and the number of crystal spots per unit area. Crystal points that exceed a certain "degree" will be unacceptable, and it is directly related to the protection of the quality of printing plates and printed products.
For the printability of plastic films, it has long been specified only 38-42 dyne of surface wetting tension. Once this value is reached, it is generally considered to pass. However, we have encountered some problems in our production practice. When using a company's PE film, the production speed can only reach 150-160m/min, and then go up, you will find the pinhole phenomenon in the field printing more and more serious, in order to ensure the density of the field, we have to The speed is maintained at around 150m/min. However, the same production process (subsidiary materials and process parameters are completely the same) in the author's current company, only with a different film, the speed can be mentioned above 200m/min, our production speed is 230 ~ 250m/min, the field density Basically not affected. This prompted us to consider a problem, in addition to the condition of wetting tension on the surface of the film, there are still other factors that affect the ink transfer characteristics. These factors are collectively referred to as printability. Therefore, the printability of the film should also be one of the parameters that we must control. This is directly related to the quality of the product and also to the benefits of the company.
Second, the flexographic ink used in ink plastic film, both at home and abroad. High-grade inks are still known for their foreign inks. The flexo printing inks of the 1980s are suitable for use in printed plastic vests (also known as pouches) for primary flexo presses (such as laminated flexo presses). In the 1990s, great progress was made in the flexo printing process of plastic films. Flexographic inks adapted to high speed, fineness, and high color were successively landed in the domestic market. Ink quality control, in addition to the perception of fineness, color viscosity and other parameters, the author thinks that the color concentration should be emphasized. Flexographic inks, when printing fine flexographic plates, due to the use of high-line anilox rolls, even if the current anilox roll manufacturing process has undergone great reforms, CO2 laser engraving processes have been unambiguously named by YAG or others. With the laser replaced, the amount of strike ink has been significantly improved, but the anilox roller with a high number of screens also needs high-color ink, but it is still an indisputable fact. Many ink companies in their own production series, in addition to the general product, also specifically provide its ink, or high-density ink, is specifically designed to deal with this situation. However, if the ink used in normal production is overcharged, it exceeds a certain percentage, the resin in the ink is reduced, and the adhesion of the ink to the plastic film is inevitably reduced. Therefore, the ink is not as good as possible. To control a degree. Choosing and controlling the color intensity of flexographic inks, the author believes that it is essential in process quality control. We feel that using a density meter to measure field density is simple and effective. However, the ink sample scraped on the film by the scraper bar is still different from the actual print process conditions (such as a certain number of lines of anilox roller, a certain density of double-sided adhesive tape, a certain printing speed). This difference must also be noted when the instrument is tested. In addition, when it comes to the residual amount of solvent in printed products, it should also pay attention to the resin used in the selection of flexo ink. Polyamide, nitrocellulose, and PVB have their own strengths, which cannot be ignored. The inks produced by foreign companies for printing on plastics have also been trial-controlled in the domestic market. I have tested such inks and have good performance, but there are still some problems. It is estimated that it will take time to fully replace alcohol inks.
Third, drafting general printing companies themselves are not drafting. The sales department handed over the electronic documents submitted by the customer to the technical department and then transferred it to a special plate-making company. The plate-making company could handle it. However, we often encounter a problem that is puzzling. The plates produced by the plate-making company according to the design in the electronic file are always unsatisfactory and sometimes have to be reworked. Once there was such a thing, in the production of Coca-Cola 350ml “distribution†six cans of shrink packaging, the plates produced by the plate-making company according to the design in the electronic file were sent to Confirmation that it was rejected twice and successively reworked because the sent to the Palm was not approved by the advertising creative department. Customers do not confirm, where is the problem? After repeated analysis, we found the reason. Because of the heat-shrinkage PE film we use, the transparency is very poor and the product is printed on it. The whole feeling is not clear. In 2000, the design draft of the "Fanta" was orange-red. The emphasis was bright and lively, but now the product feels a gap. Before sending the sample for the third time, the author went to the advertising company to communicate with the design department and chose one of the two different resolution manuscripts in the electronic file. Under possible conditions, the Fen drawn icon was fine-tuned. Because the lightness of the film is not enough, we have simplified the details around the icon in the design, highlighting the white part. White is the color with the highest brightness. With this part of the color, it can effectively mask the lack of film. Of course, when we printed, we printed two layers of white, which also made up for the lack of film. During the process of laying out the orange-red version of the cable, we clearly proposed a red net plus one percent based on the characteristics of the process. The printing plate produced by the plate-making company according to our above requirements was successfully printed and was soon confirmed by the customer.
In general, for the electronic documents transmitted by various printing companies, the plate-making company needs to make some adjustments, but this adjustment is mainly based on the adjustment of the compensation curve for network expansion and the compensation for the extension of the printing plate caused by the radius of curvature of the printing plate. For other parameters, it is generally determined according to the parameters in the electronic file. At most, in terms of deduction, some proposals for plate-making companies are recommended. However, in the actual printing process, there are various problems, such as clasps, 0.1mm can be done according to the printing technology of the satellite flexographic printing machine, but if it is not the printed plastic packaging, instead of the printed paper trademark, at this time dozens of The trademarks are put together into one piece, and there are no major or minor parts. For the trademark, the main part is everywhere, so the 0.1mm buckle can not take into account the overprint accuracy of the entire layout. In the past, when I was producing Tiger Brand Aluminizer trademarks, we had to put forward a series of specific requirements for the platemaking companies according to the characteristics of our company's equipment. In some places, the fasteners should reach 0.25mm, and some places should be left blank. Never stack. The shrinkage of the PE film during the printing process is also the same. The PE film, especially the PE of 25-40 [mu]m, shrinks very much during the printing process, and some products can reach 3% to 4%. This compensation for design manuscripts is essential. This kind of parameter is unknown to the platemaking company. This requires the technical department to submit its own compensation requirements when submitting the electronic file. In addition, the adjustment of the layout is suitable for the flexographic printing process, such as the gradual change of the curve, large area on the ground. It is also necessary to take into account the separation of small plates from the plate making. In this way, product quality will be greatly guaranteed and delivery will not be delayed. Therefore, the process quality control in the production process is to understand the design in the electronic file and adjust it according to actual production conditions. It is not just an electronic file that we hand over to the plate-making company. It must be a complete set of instructions. If you do not have a bottom in your mind at the moment, you should discuss with the technicians of the plate-making company and work out a better plan. We feel that the role of the technical department should not be just a setter, but should be a headquarters.
Fourth, the plate-making for the average enterprise, the draft and the plate-making company are all completed by the plate-making company. Some of the equipment is more full-scale than the ones that own the platemaking workshops.
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