I. INTRODUCTION In the last 20 years, the development of Flexographic in packaging printing is obvious to all, especially in the printing of corrugated boxes, which is not considered by the second person except flexo printing. Its printing is convenient and exquisite, which is of great help to the promotion of the product. The reason why Flexo Printing can achieve current results is related to the improvement of preprint, ink, flexo printing, and printing materials. However, the progress and development of photographic flexographic plates in the past 20 years cannot be ignored.
At present, the printing of corrugated boxes has gradually shifted from traditional hand-carved rubber plates to photosensitive flexo plates, but the vast majority of them are solid photosensitive flexo plates, and only a few use liquid photopolymer plates. However, in Europe, the United States, Japan and Australia, liquid photosensitive resin plates account for more than 50% of the market in corrugated box printing, and there is a continued trend of growth.
I would like to borrow a little space here today to make a report on the characteristics and recent developments of the liquid photosensitive resin plate for reference.
Second, development and performance of the liquid photosensitive resin plate The liquid photosensitive resin plate and the solid photosensitive plate began to develop around 1970. At the time, the UV Light Sensitizer and initiator and monomer were just on the market. The advanced chemical companies such as Dupont, GRACE, Uniroyal and Hercules from the United States, Asahi from Japan, and BASF from Germany immediately Use this new product to develop printing plates. (Currently, the graphic arts divisions of GRACE, Uniroyal, and Hercules in the United States have merged to become Medtech Graphic Arts, MacDermid Graphic Arts)
By 1975, based on the chemical properties and market demand, two different types of plates were developed, the so-called liquid resin plates and solid plates. The principle of imaging of these two types of plates is the same:
1. Absorption of UV light by photosensitizers immediately produces activated red (Free Redical)
2. Free radicals react with monomers and then chain reaction occurs (Chain Recation)
3. The chain lock reaction combines monomer and polymer rubbers or resins into a permanently solidified font or image. The difference between the solid and liquid versions of a printing plate can be attributed to their physical properties and process of plate making:
1. The solid plate is mainly made of Thermal Plastic Block Copolymer which is solid but not yet cured, while the liquid plate is mainly made of High Viscosity Photo Sensitive Resin.
2. Solid plate manufacturers rely on customer specifications to make plates of various sizes and thicknesses and send them to platemaking manufacturers. Plate makers simply place the plates on the plate, and use the plates for exposure imaging. The supplier of the liquid plate material transports the drum-loaded photosensitive resin to various plate-making manufacturers. The plate-making company uses a specific machine to make the liquid resin into a plate of a desired size and thickness, and then exposes and images on the plate of the plate-making machine.
3. The main component of the solid plate is rubber, and most require the use of organic solvents to wash the image. (Recently, both Medela and Dupont have come out with a solid version of water washing, which is currently not suitable for corrugated carton printing due to high hardness). The uncured part of the liquid version is a highly viscous, water-soluble resin that can be easily removed by physical methods (extrusion and air blow) at high temperatures and rinsed clean with water.
4. Solid version is based on rubber, so it has good ink resistance to alcohol ink and water-based ink. The liquid version is based on polarizing polyurethane, so it is not suitable for alcohol ink, and it is only suitable for water-based inks. (If the printing manufacturer still uses oil ink or "water washable ink", the liquid version is mainly compared to the solid version)
Third, the advantages of the liquid version in the corrugated box printing From the plate-making process and ink resistance performance, the solid plate seems to have a slight advantage, but why foreign liquid photosensitive resin plate will be used by a large number of corrugated box manufacturers? The main reason is as follows 1. Solid bottom printing ink transmission is excellent. In the past ten years, water-based inks have made great breakthroughs in flexographic printing. In addition to vivid colors and uniform gloss, physical properties such as abrasion resistance, water soaking and adhesion to corrugated paper have Significant improvements. Although the ink has been improved, but the thickness of the corrugated version of the paper, and the uneven level of corrugated, in the solid cover at the time of printing is still quite difficult. Liquid plates have unexpected advantages in this regard, mainly related to the properties of the plates.
The resin of the liquid plate is a highly polarizable photosensitive acrylic (Acrylatc Polyurethane). The surface tension of the plate is 4-5 dynes/cm higher than the solid plate (liquid plate: 36-38 dynes/cm; solid plate: 32-33 dynes/cm), so the same anilox roller is used (an lox), the liquid plate material has a 10-20% higher ink content than the solid plate material. At the same time, the liquid plate material has a low modulus, and has a large degree of compliance during printing and is relatively coarse. Table paper or corrugated paper also has a good surface contact, so the effect of solid coverage is better.
It is more economical to make a version: the cost of raw materials for liquid and solid versions is almost the same, but the liquid version saves time and money in the process of plate making. As we said before, the main component of the solid version is a non-mobile (physically cured) rubber that, when it is printed through the negative, undergoes a chemical chain lock reaction to become permanently cured rubber. The non-exposed parts are dissolved with organic solvents, and the solidified font is highlighted on the plate for printing. In general, the solvent for washing plates can only be dissolved at most 4-6% of the rubber, otherwise the solvent developing ability will be weakened. Therefore, 1 gallon of tetrachloroethene/butanol solvent can only dissolve 200g of rubber. By analogy, averaging a 1 square meter 6.50 millimeter (mm) thickness solid version with a font height of 3.2 mm requires 7-8 gallons of solvent. Although the solvent can be recovered, there is a lot of loss due to volatilization in the plate cleaner, residue in the solvent recovery, or removal by the plate material during plate cleaning (absorption of the plate material). If we can achieve a 60% solvent recovery, we still need to consume more than 3 gallons of tetrachloroethylene/butanol solvent per square meter. At the same time, the plate absorbs a large amount of solvent during washing, and generally needs to be dried in a dryer at 65 degrees Celsius for 2-3 hours, and the plate can be restored to the original thickness. Thicker plates require longer drying times.
However, in the case of liquid plates, when the photosensitive resin is exposed through a negative film, the non-exposed portion is still a flowing resin after the characters have been cured by a brilliance bond reaction. More than 80% of uncured resin can be recycled by physical means (extrusion or high-pressure air blowing). A small amount of residual resin on the plate can be washed with water solvent, so the liquid plate is on the plate making material and the process It is much more economical than the solid version. In the process of washing plates, the plate material only absorbs a very small amount of water solvent, and the thickness can be said to have no increase. Therefore, it usually takes only 10 to 20 minutes to dry, so that the entire plate making process can be exposed, rinsed, dried, and then exposed. The time is reduced by more than 50%.
Japan's flexographic community has also used the characteristics of liquid media to develop an "island plate making method" for thicker versions of corrugated cartons. The general flexo back exposure is a full back exposure that cures to form a base layer with a certain thickness. However, the island plate-making method uses partial back exposure, that is, back exposure only in areas where there are fonts and graphics. This part of the base layer and font graphics, formed on the bottom of the polyester film as a separate block of islands distributed on the plate, the resin is not cured on the whole recovery. The benefit of this version is not only to increase the proportion of photosensitive resin recycling, but also to make the entire plate lighter and more obtrusive, easier to install, and less prone to warping.
In the printing of corrugated boxes on solid plates, the "island plate making method" is not appropriate. Because it is necessary to wash the solid plate to the underlying polyester film, it takes longer to wash the plate, consumes more solvent, and the plate expands even more. Not to mention that the washed plates can not be recycled. Why waste solvent? So this method only applies to liquid plates.
Based on the above advantages, liquid plates are popular in corrugated box printing in Europe, the United States, Japan and Australia. Especially in countries that focus on conservation and environmental protection, such as Japan, the liquid version of the plate recycling and the water solvent washing version monopolize the corrugated box printing market.
IV. The development of liquid plates in recent years There were several obvious shortcomings in the early days of liquid plates, but they have recently been improved step by step.
1. The surface of the plate is too viscous Because the raw material of the liquid plate is a highly rigid polyurethane, it is inevitable that the surface is still sticky after curing. In order to solve this problem, both early Medela and Asahi were dissolved in the resin with low-solubility fatty acids, and the principle of solubility change after curing caused the separation of fatty acids, and formed a thin layer of fatty acid on the surface of the plate. Reduce viscosity. However, this method is only a temporary solution. When printing, ink will gradually take away this layer of acid cream, and then the surface of the plate becomes sticky again.
In recent years, UVC (short-wavelength) lamps have gradually become popular, and a variety of new sensitizers and polymer monomers have been introduced to the market. If a suitable formulation is used, a very good detackification effect can be achieved using short UV exposure. The TF2 photosensitive resin plate recently launched by Medtech has been exposed after short-UV de-bonding. The surface of the plate is smoother than the normal solid plate, making it ideal for printing in corrugated boxes.
2. Expanding of cable lines The plates used for corrugated carton printing are mostly hand-engraved rubber plates or laminating rubber plates. It is difficult to print fine prints and accurate dots. When photosensitive resin plates or photosensitive solid plates come out, the requirements for corrugated box printing are getting higher and higher. Foreign corrugated carton manufacturers gradually found that the liquid version of the font looks very fine, anti-white and deep, but the effect of printing out is not as solid as the media. Because of the expansion ratio of dots and lines, it is higher than the solid version. After our detailed study, we found that this phenomenon is related to the physical properties of the plate. When the plate is cured by UV irradiation, the liquid plate has a lower degree of fine line and dot curing than the solid plate. After shredding and post-exposure treatment, the Shore A hardness of the liquid plate is lower by 3-5 degrees than the wide solid part, so when a higher pressure corrugated box is printed, The expansion rate of thin lines and outlets is relatively high. Based on this understanding, Medtech first proposed a method for making a composite liquid plate. Before coating ordinary photosensitive resin, first apply a layer of (0.16-0.20mm) photosensitive resin with a higher hardness than the bottom layer on the thin film and halftone film, and then apply a normal liquid material. The hardness of the surface layer of the complex version of the thin lines and dots is higher than that of the rest, and printing reduces the dot gain.
In this way, the liquid composite material can enjoy high ink transmission without excessive dot enlargement, and is most suitable for the color printing of corrugated cartons.
3. Plates are not strong enough The development of early liquid plates has paid more attention to the ability of plate photographic imaging, ink resistance and printing effects. After the market was expanded, it was found that the liquid plate's resistance to printing and the shelf life of the plate were not as good as those of the solid plate. Over the past five years, through continuous improvement, the Abrasion Resistance, Elongation, Toughness, and shelf life of liquid media have been greatly improved. This is almost the same as a solid plate, but It is a solid plate or liquid plate and cannot be directly illuminated by strong light during storage. Because there are many activators in the plate material, these strong light will make the activator react continuously, destroying the network structure of the plate curing molecules and making the plate material fragile.
Due to the unique nature of liquid plates and the growth of the market, there are currently two companies in Europe that produce liquid plates in addition to the United States's Medtech and Japan's Asahi. Platemakers also have a variety of different line sizes (from 16" x 24" to 52" x 80") for manufacturers to choose from. (Dr. Yang Wenjian, Business Development Manager, German America, Inc.)
At present, the printing of corrugated boxes has gradually shifted from traditional hand-carved rubber plates to photosensitive flexo plates, but the vast majority of them are solid photosensitive flexo plates, and only a few use liquid photopolymer plates. However, in Europe, the United States, Japan and Australia, liquid photosensitive resin plates account for more than 50% of the market in corrugated box printing, and there is a continued trend of growth.
I would like to borrow a little space here today to make a report on the characteristics and recent developments of the liquid photosensitive resin plate for reference.
Second, development and performance of the liquid photosensitive resin plate The liquid photosensitive resin plate and the solid photosensitive plate began to develop around 1970. At the time, the UV Light Sensitizer and initiator and monomer were just on the market. The advanced chemical companies such as Dupont, GRACE, Uniroyal and Hercules from the United States, Asahi from Japan, and BASF from Germany immediately Use this new product to develop printing plates. (Currently, the graphic arts divisions of GRACE, Uniroyal, and Hercules in the United States have merged to become Medtech Graphic Arts, MacDermid Graphic Arts)
By 1975, based on the chemical properties and market demand, two different types of plates were developed, the so-called liquid resin plates and solid plates. The principle of imaging of these two types of plates is the same:
1. Absorption of UV light by photosensitizers immediately produces activated red (Free Redical)
2. Free radicals react with monomers and then chain reaction occurs (Chain Recation)
3. The chain lock reaction combines monomer and polymer rubbers or resins into a permanently solidified font or image. The difference between the solid and liquid versions of a printing plate can be attributed to their physical properties and process of plate making:
1. The solid plate is mainly made of Thermal Plastic Block Copolymer which is solid but not yet cured, while the liquid plate is mainly made of High Viscosity Photo Sensitive Resin.
2. Solid plate manufacturers rely on customer specifications to make plates of various sizes and thicknesses and send them to platemaking manufacturers. Plate makers simply place the plates on the plate, and use the plates for exposure imaging. The supplier of the liquid plate material transports the drum-loaded photosensitive resin to various plate-making manufacturers. The plate-making company uses a specific machine to make the liquid resin into a plate of a desired size and thickness, and then exposes and images on the plate of the plate-making machine.
3. The main component of the solid plate is rubber, and most require the use of organic solvents to wash the image. (Recently, both Medela and Dupont have come out with a solid version of water washing, which is currently not suitable for corrugated carton printing due to high hardness). The uncured part of the liquid version is a highly viscous, water-soluble resin that can be easily removed by physical methods (extrusion and air blow) at high temperatures and rinsed clean with water.
4. Solid version is based on rubber, so it has good ink resistance to alcohol ink and water-based ink. The liquid version is based on polarizing polyurethane, so it is not suitable for alcohol ink, and it is only suitable for water-based inks. (If the printing manufacturer still uses oil ink or "water washable ink", the liquid version is mainly compared to the solid version)
Third, the advantages of the liquid version in the corrugated box printing From the plate-making process and ink resistance performance, the solid plate seems to have a slight advantage, but why foreign liquid photosensitive resin plate will be used by a large number of corrugated box manufacturers? The main reason is as follows 1. Solid bottom printing ink transmission is excellent. In the past ten years, water-based inks have made great breakthroughs in flexographic printing. In addition to vivid colors and uniform gloss, physical properties such as abrasion resistance, water soaking and adhesion to corrugated paper have Significant improvements. Although the ink has been improved, but the thickness of the corrugated version of the paper, and the uneven level of corrugated, in the solid cover at the time of printing is still quite difficult. Liquid plates have unexpected advantages in this regard, mainly related to the properties of the plates.
The resin of the liquid plate is a highly polarizable photosensitive acrylic (Acrylatc Polyurethane). The surface tension of the plate is 4-5 dynes/cm higher than the solid plate (liquid plate: 36-38 dynes/cm; solid plate: 32-33 dynes/cm), so the same anilox roller is used (an lox), the liquid plate material has a 10-20% higher ink content than the solid plate material. At the same time, the liquid plate material has a low modulus, and has a large degree of compliance during printing and is relatively coarse. Table paper or corrugated paper also has a good surface contact, so the effect of solid coverage is better.
It is more economical to make a version: the cost of raw materials for liquid and solid versions is almost the same, but the liquid version saves time and money in the process of plate making. As we said before, the main component of the solid version is a non-mobile (physically cured) rubber that, when it is printed through the negative, undergoes a chemical chain lock reaction to become permanently cured rubber. The non-exposed parts are dissolved with organic solvents, and the solidified font is highlighted on the plate for printing. In general, the solvent for washing plates can only be dissolved at most 4-6% of the rubber, otherwise the solvent developing ability will be weakened. Therefore, 1 gallon of tetrachloroethene/butanol solvent can only dissolve 200g of rubber. By analogy, averaging a 1 square meter 6.50 millimeter (mm) thickness solid version with a font height of 3.2 mm requires 7-8 gallons of solvent. Although the solvent can be recovered, there is a lot of loss due to volatilization in the plate cleaner, residue in the solvent recovery, or removal by the plate material during plate cleaning (absorption of the plate material). If we can achieve a 60% solvent recovery, we still need to consume more than 3 gallons of tetrachloroethylene/butanol solvent per square meter. At the same time, the plate absorbs a large amount of solvent during washing, and generally needs to be dried in a dryer at 65 degrees Celsius for 2-3 hours, and the plate can be restored to the original thickness. Thicker plates require longer drying times.
However, in the case of liquid plates, when the photosensitive resin is exposed through a negative film, the non-exposed portion is still a flowing resin after the characters have been cured by a brilliance bond reaction. More than 80% of uncured resin can be recycled by physical means (extrusion or high-pressure air blowing). A small amount of residual resin on the plate can be washed with water solvent, so the liquid plate is on the plate making material and the process It is much more economical than the solid version. In the process of washing plates, the plate material only absorbs a very small amount of water solvent, and the thickness can be said to have no increase. Therefore, it usually takes only 10 to 20 minutes to dry, so that the entire plate making process can be exposed, rinsed, dried, and then exposed. The time is reduced by more than 50%.
Japan's flexographic community has also used the characteristics of liquid media to develop an "island plate making method" for thicker versions of corrugated cartons. The general flexo back exposure is a full back exposure that cures to form a base layer with a certain thickness. However, the island plate-making method uses partial back exposure, that is, back exposure only in areas where there are fonts and graphics. This part of the base layer and font graphics, formed on the bottom of the polyester film as a separate block of islands distributed on the plate, the resin is not cured on the whole recovery. The benefit of this version is not only to increase the proportion of photosensitive resin recycling, but also to make the entire plate lighter and more obtrusive, easier to install, and less prone to warping.
In the printing of corrugated boxes on solid plates, the "island plate making method" is not appropriate. Because it is necessary to wash the solid plate to the underlying polyester film, it takes longer to wash the plate, consumes more solvent, and the plate expands even more. Not to mention that the washed plates can not be recycled. Why waste solvent? So this method only applies to liquid plates.
Based on the above advantages, liquid plates are popular in corrugated box printing in Europe, the United States, Japan and Australia. Especially in countries that focus on conservation and environmental protection, such as Japan, the liquid version of the plate recycling and the water solvent washing version monopolize the corrugated box printing market.
IV. The development of liquid plates in recent years There were several obvious shortcomings in the early days of liquid plates, but they have recently been improved step by step.
1. The surface of the plate is too viscous Because the raw material of the liquid plate is a highly rigid polyurethane, it is inevitable that the surface is still sticky after curing. In order to solve this problem, both early Medela and Asahi were dissolved in the resin with low-solubility fatty acids, and the principle of solubility change after curing caused the separation of fatty acids, and formed a thin layer of fatty acid on the surface of the plate. Reduce viscosity. However, this method is only a temporary solution. When printing, ink will gradually take away this layer of acid cream, and then the surface of the plate becomes sticky again.
In recent years, UVC (short-wavelength) lamps have gradually become popular, and a variety of new sensitizers and polymer monomers have been introduced to the market. If a suitable formulation is used, a very good detackification effect can be achieved using short UV exposure. The TF2 photosensitive resin plate recently launched by Medtech has been exposed after short-UV de-bonding. The surface of the plate is smoother than the normal solid plate, making it ideal for printing in corrugated boxes.
2. Expanding of cable lines The plates used for corrugated carton printing are mostly hand-engraved rubber plates or laminating rubber plates. It is difficult to print fine prints and accurate dots. When photosensitive resin plates or photosensitive solid plates come out, the requirements for corrugated box printing are getting higher and higher. Foreign corrugated carton manufacturers gradually found that the liquid version of the font looks very fine, anti-white and deep, but the effect of printing out is not as solid as the media. Because of the expansion ratio of dots and lines, it is higher than the solid version. After our detailed study, we found that this phenomenon is related to the physical properties of the plate. When the plate is cured by UV irradiation, the liquid plate has a lower degree of fine line and dot curing than the solid plate. After shredding and post-exposure treatment, the Shore A hardness of the liquid plate is lower by 3-5 degrees than the wide solid part, so when a higher pressure corrugated box is printed, The expansion rate of thin lines and outlets is relatively high. Based on this understanding, Medtech first proposed a method for making a composite liquid plate. Before coating ordinary photosensitive resin, first apply a layer of (0.16-0.20mm) photosensitive resin with a higher hardness than the bottom layer on the thin film and halftone film, and then apply a normal liquid material. The hardness of the surface layer of the complex version of the thin lines and dots is higher than that of the rest, and printing reduces the dot gain.
In this way, the liquid composite material can enjoy high ink transmission without excessive dot enlargement, and is most suitable for the color printing of corrugated cartons.
3. Plates are not strong enough The development of early liquid plates has paid more attention to the ability of plate photographic imaging, ink resistance and printing effects. After the market was expanded, it was found that the liquid plate's resistance to printing and the shelf life of the plate were not as good as those of the solid plate. Over the past five years, through continuous improvement, the Abrasion Resistance, Elongation, Toughness, and shelf life of liquid media have been greatly improved. This is almost the same as a solid plate, but It is a solid plate or liquid plate and cannot be directly illuminated by strong light during storage. Because there are many activators in the plate material, these strong light will make the activator react continuously, destroying the network structure of the plate curing molecules and making the plate material fragile.
Due to the unique nature of liquid plates and the growth of the market, there are currently two companies in Europe that produce liquid plates in addition to the United States's Medtech and Japan's Asahi. Platemakers also have a variety of different line sizes (from 16" x 24" to 52" x 80") for manufacturers to choose from. (Dr. Yang Wenjian, Business Development Manager, German America, Inc.)
Muffin Pan,Cupcake Pan,Square Cupcake Pan,Cupcake And Muffin Pans
Xiongyang Household Co., Ltd , https://www.yjkitchen-manage.com