No matter what kind of printing method, the quality and effect of the printed matter must be reflected by ink in the end. Therefore, the ink is a fundamental factor that affects the quality of the printed matter.
Unlike paste inks used for embossing and offset printing, flexographic printing inks are very thin because only the use of low-viscosity inks results in an ideal transfer of the ink by the anilox roller.
Colorants used in flexographic printing inks include both dyes and pigments; both natural and synthetic materials. These colorants are all very finely ground particles, and they contribute to the hiding power, transparency, and gloss of the ink in addition to providing the ink with a pigment.
The fixation of the binder in the ink allows the toner particles to adhere to the surface of the substrate. The role of the solvent is to dissolve solid components in the ink and make the ink a fluid suitable for printing. In order to improve the adhesion of the ink, the softness and friction resistance of the ink film, some additives are added in the ink. The inks used in flexo printing include solvent inks, water-based inks (water-based inks), and UV-curable inks (ie, UV inks). Here's a brief introduction of the three types of inks and the issues they should pay attention to when using them.
I. Solvent-based inks The solvent inks used in early flexo printing were aniline inks, which had been eliminated due to the presence of toxins, and subsequently changed to aqueous inks and improved solvent-based inks. Solvent-based inks can be divided into solvent-based dye inks and solvent-based pigment inks depending on the colorant used.
The solvent-based dye ink has good transparency and is printed on a transparent plastic package. The packaged items can be seen through the ink layer to increase the intuitive sense of the package; the ink is printed on a metallic glossy paper (such as aluminum foil paper jam). Can give the print a special glossy color, greatly increased the impression of the bright print.
The solvent-based dye ink has good transparency and is printed on a transparent plastic package. The packaged items can be seen through the ink layer to increase the intuitive sense of the package; the ink is printed on a metallic glossy paper (such as aluminum foil paper jam). Can give the print a special glossy color, greatly increased the impression of the bright print.
Solvent-based dye inks have better rheological properties because the solubility of the dyes is relatively good, so the viscosity of the inks is relatively low and it is easy to control the drying speed. However, inks using basic dyes are generally used only for printing absorbent paper materials.
The solvent-based pigment inks have a wide range of substrates, including paper, plastic films, and aluminum foils. Since the binder in the ink plays a role of making the ink adhere to the substrate, the choice of the solvent and the resin in the binder is affected and limited by the substrate and the printing conditions. That is, the substrate is different. Resins and solvents are also different. Thus, solvent-based pigment inks can be divided into paper inks, cellulosic film inks, polyethylene film inks, polypropylene film inks, polyvinyl chloride film inks, nylon film inks, and aluminum foil inks, depending on the substrate.
Second, water-based ink Water-based ink from the water-based polymer resin, coloring agent, solvent (mainly water) and related additives by physical and chemical process mixture. Water-based inks have no volatile organic solvents, are non-flammable, and do not harm the health of ink manufacturers and print operators. In addition, when printing water-based inks, a simple, low-energy hot-air drying system can be used to reduce the cost of energy consumption. Therefore, in modern flexo printing, environmentally friendly water-based inks dominate.
Waterborne inks have many shortcomings in the early days of their introduction, such as poor adhesion, poor moisture resistance, low gloss, and slow drying, which can only be used for printing on rougher corrugated boxes; poor adhesion and poor moisture resistance make them The use of frozen food packaging is also very limited. Now water-based ink production technology has been greatly improved, making water-based ink gradually become the mainstream of high-grade color corrugated cartons, medium and high-grade paper packaging and plastic film flexo ink.
High-quality flexographic printing uses an anilox roller with a high number of screens to transfer ink, resulting in less transferred ink and thinner printing ink layers. In order to obtain a vivid print, colorants for water-based inks generally use pigments with good chemical stability and high strength.
Water-based inks are divided into three categories: water-soluble binders, alkali-soluble binders, and diffusion-type binders. At present, alkali-soluble binders are mainly used, consisting of water, resins, amines, and other organic solvents.
Resin is one of the most important components of water-based inks, which directly affects the ink transferability, adhesion, drying speed, anti-adhesiveness, glossiness, and heat resistance of aqueous inks. At present, water-based inks often use high-acid synthetic resins, such as acrylic resins, which are then neutralized with amines.
The role of the amine compound is to maintain the aqueous ink alkaline because of the speed of the acrylic resin in the alkaline environment.
Water-based inks also need to add some additives to adjust the ink's pH, dryness and so on. Commonly used adjuvants include pH stabilizers, retarders, dilute agents, defoamers, and the like.
(1) pH stabilizer: The viscosity and drying properties of water-based inks are closely related to the pH value. According to the type of substrate, the pH stabilizer is divided into ordinary type and thin film type. Special pH stabilizers are used when printing fine mesh prints. The usage of the general pH stabilizer is 1% to 2% of the total amount added every 30 to 40 minutes. pH stabilizers can both adjust the pH of aqueous inks and can also be used as diluents to reduce the viscosity of the ink.
(2) Anti-foaming agents and anti-foaming agents: used to suppress and eliminate bubbles and improve the transfer performance of aqueous inks. Generally, it is added before printing to prevent the ink from foaming due to agitation; if necessary, some amount may be added in the printing process, and the amount of each time cannot exceed 0.5% to 1% of the total amount of ink.
(3) Blocking agents are used to slow down the drying speed of water-based inks, prevent the ink from drying on the anilox roller, and reduce the stencil printing to obtain a satisfactory printing effect. The amount is generally 1% to 2% of the total amount of ink.
(4) Evacuation agent: The withdrawal agent is used to reduce the color of freshwater ink, but it has no effect on the pH value, viscosity, and drying speed of the ink. It is also a brightener that increases the brightness of the ink layer. The dosage depends on the circumstances.
(5) Diluent: After the addition of the diluent to the aqueous ink, the viscosity of the aqueous ink can be reduced without affecting the pH value. The amount used must not exceed 5% of the total amount of ink.
(6) Enhancer: The enhancer enhances the adhesion of the aqueous ink on the substrate. The amount is generally 1% to 2% of the total amount of ink.
(7) Static elimination agent: The static elimination agent can effectively prevent electrostatic accumulation. The amount is generally 0.5% to 1% of the total amount of ink.
The biggest characteristic of water-based ink is that the ink can be mixed with water before drying. Once the ink is dried, it is no longer soluble in water and ink, that is, the dried ink layer has water resistance. Therefore, special attention should be paid when printing. Do not allow the ink to dry on the anilox roller, so as not to block the cells of the anilox roller, hindering the quantitative transfer of ink and causing poor printing. In addition, the flexographic printing plate must always be wetted by the ink during the printing process in order to prevent the ink from drying on the plate.
The viscosity of water-based ink will change with the change of pH value, and the pH value will decrease, which will increase the viscosity of the ink and cause poor transferability. At the same time, the drying speed of the ink will be accelerated, and the anilox roller will be clogged. The pH value is mainly maintained by amine compounds. In the printing process to maintain the ink performance is stable, on the one hand to avoid the leakage of amines as much as possible, such as cover the cover of the ink residue; on the other hand, time to quantitatively add pH stabilizer to the ink tank. The use of a closed ink supply system and an ink temperature control system can reduce the volatilization of amines.
Since the volatilization of the solvent will cause changes in the viscosity of the aqueous ink, it is critical that excessive mechanical agitation be prevented in order to maintain the pH viscosity constant.
Production experience shows that the pH of general water-based inks is maintained between 8.5 and 9.5. When the PH value is too high, the water-based ink dries slowly, and problems such as poor adhesion of the backside of the printed product and poor ink-resistance of the ink layer are likely to occur.
Incidentally, the pH range of some special aqueous inks is different from that of ordinary water-based inks. For example, the pH value of gold ink and silver ink is 7.5-8.0, and the pH of the fluorescent ink is 7.5-8.3.
Most of the wide-format flexographic printing machines and the unit-type flexographic printing machines have various on-line processing functions such as roll feeding, printing, glazing, slitting, cross-cutting or die-cutting, and single-finished products, forming a package printing process. One-stop production lines, wherever there is a problem in the printing process, will produce a lot of waste products. The good printability of the ink is an important condition for the normal operation of the flexo printing machine and the printing of high quality products. The viscosity and dryness of the ink are more important.
There was a packaging and decoration printing factory that introduced a flexo line in 1996. It mainly printed soft cigarettes. At the time, it used the best water-based inks imported from the United States, but every time it was printed, it had five minutes. Stop using the brush to clean the dried ink residue in the mesh pocket, otherwise it will not be able to print normally, and the work efficiency is extremely low. At that time, ink experts in the United States could not do anything about it, because such failures had never happened in the United States. Later, the factory's workers and domestic printing process experts jointly searched for the cause of the failure and found that it was caused by the ink drying too quickly. The original waterborne gold ink imported from the United States was designed for printing at a printing speed of 150 revolutions per minute. In actual use, the speed of die cutting was limited due to the paper, and the speed of the flexo printing line could only reach a minute. This kind of 85 turns, plus the gold ink itself is very thick, so that the water-based gold ink dry solid plug in the anilox roller on the network. In addition, the leakage of amines during the printing process leads to a drop in the pH value, which also accelerates the drying rate of the aqueous gold ink, further exacerbating the failure. For the cause of the failure, add an appropriate amount of retarder composed of water, ethylene glycol, butyl ether, isopropyl alcohol, and 1830 emulsion to the aqueous gold ink, and regularly add ethanol, ethylene glycol amine, water, and water to the ink tank. The stabilizer of 1830 emulsion keeps the pH of the ink at about 9.5. The problem of ink drying on the anilox roll during the printing process never occurs again.
Water-based inks have two basic properties: liquid flow and fast fixation. Fast fixability makes it ideal for printing on non-absorbent substrates such as clear films, polyethylene and vinyl. In order for the water-based ink to adhere well to the plastic film, the plastic film also needs to be further improved to suit the wettability and adhesion of the aqueous ink.
In order to make the water-based ink transfer well, the ink supply and drying system of the flexo printer should also be improved accordingly. In addition, it is also necessary to provide a cleaning system so that the residual ink can be removed effectively and in time, and the service life of the anilox roller and the doctor blade can be extended.
With the increasing of flexo printing technology, waterborne inks have been successfully used in the multi-color mesh adjustment printing of corrugated boxes after undergoing development from field printing to halftone printing. This not only ensures that the hue and viscosity are basically stable. In addition, under the conditions of low viscosity and high color density, printing speeds of 200 to 300 sheets per minute can be accommodated. Aquatic inks have also achieved major breakthroughs in narrow flexo printing. With an 800-line/inch anilox roller, 200 lines/inches can be printed. The dots are clear and full of color. They are comparable to offset printing products and successfully applied to cigarettes. Printing of bags, folding cartons and various labels. New water-based inks that use special water-based resins and emulsion-based resins can also be applied to the printing of various specialty papers, aluminum foils, and plastic films.
Water-based inks need to be improved in the following areas:
(1) Improve the pH stability of aqueous inks;
(2) Under the premise of ensuring print drying and film forming, further improve the resolvability of the water-based ink to ensure that the printing system can run for a longer period of time before cleaning, minimizing or even eliminating paste printing malfunction;
(3) Continue to improve the performance on weakly absorbing or non-absorbing substrates, improve adhesion, enhance various resistances, and expand the use;
(4) Further reduce the content of volatile organic compounds and adapt to the future trend of increasing environmental protection requirements. (To be continued)
Unlike paste inks used for embossing and offset printing, flexographic printing inks are very thin because only the use of low-viscosity inks results in an ideal transfer of the ink by the anilox roller.
Colorants used in flexographic printing inks include both dyes and pigments; both natural and synthetic materials. These colorants are all very finely ground particles, and they contribute to the hiding power, transparency, and gloss of the ink in addition to providing the ink with a pigment.
The fixation of the binder in the ink allows the toner particles to adhere to the surface of the substrate. The role of the solvent is to dissolve solid components in the ink and make the ink a fluid suitable for printing. In order to improve the adhesion of the ink, the softness and friction resistance of the ink film, some additives are added in the ink. The inks used in flexo printing include solvent inks, water-based inks (water-based inks), and UV-curable inks (ie, UV inks). Here's a brief introduction of the three types of inks and the issues they should pay attention to when using them.
I. Solvent-based inks The solvent inks used in early flexo printing were aniline inks, which had been eliminated due to the presence of toxins, and subsequently changed to aqueous inks and improved solvent-based inks. Solvent-based inks can be divided into solvent-based dye inks and solvent-based pigment inks depending on the colorant used.
The solvent-based dye ink has good transparency and is printed on a transparent plastic package. The packaged items can be seen through the ink layer to increase the intuitive sense of the package; the ink is printed on a metallic glossy paper (such as aluminum foil paper jam). Can give the print a special glossy color, greatly increased the impression of the bright print.
The solvent-based dye ink has good transparency and is printed on a transparent plastic package. The packaged items can be seen through the ink layer to increase the intuitive sense of the package; the ink is printed on a metallic glossy paper (such as aluminum foil paper jam). Can give the print a special glossy color, greatly increased the impression of the bright print.
Solvent-based dye inks have better rheological properties because the solubility of the dyes is relatively good, so the viscosity of the inks is relatively low and it is easy to control the drying speed. However, inks using basic dyes are generally used only for printing absorbent paper materials.
The solvent-based pigment inks have a wide range of substrates, including paper, plastic films, and aluminum foils. Since the binder in the ink plays a role of making the ink adhere to the substrate, the choice of the solvent and the resin in the binder is affected and limited by the substrate and the printing conditions. That is, the substrate is different. Resins and solvents are also different. Thus, solvent-based pigment inks can be divided into paper inks, cellulosic film inks, polyethylene film inks, polypropylene film inks, polyvinyl chloride film inks, nylon film inks, and aluminum foil inks, depending on the substrate.
Second, water-based ink Water-based ink from the water-based polymer resin, coloring agent, solvent (mainly water) and related additives by physical and chemical process mixture. Water-based inks have no volatile organic solvents, are non-flammable, and do not harm the health of ink manufacturers and print operators. In addition, when printing water-based inks, a simple, low-energy hot-air drying system can be used to reduce the cost of energy consumption. Therefore, in modern flexo printing, environmentally friendly water-based inks dominate.
Waterborne inks have many shortcomings in the early days of their introduction, such as poor adhesion, poor moisture resistance, low gloss, and slow drying, which can only be used for printing on rougher corrugated boxes; poor adhesion and poor moisture resistance make them The use of frozen food packaging is also very limited. Now water-based ink production technology has been greatly improved, making water-based ink gradually become the mainstream of high-grade color corrugated cartons, medium and high-grade paper packaging and plastic film flexo ink.
High-quality flexographic printing uses an anilox roller with a high number of screens to transfer ink, resulting in less transferred ink and thinner printing ink layers. In order to obtain a vivid print, colorants for water-based inks generally use pigments with good chemical stability and high strength.
Water-based inks are divided into three categories: water-soluble binders, alkali-soluble binders, and diffusion-type binders. At present, alkali-soluble binders are mainly used, consisting of water, resins, amines, and other organic solvents.
Resin is one of the most important components of water-based inks, which directly affects the ink transferability, adhesion, drying speed, anti-adhesiveness, glossiness, and heat resistance of aqueous inks. At present, water-based inks often use high-acid synthetic resins, such as acrylic resins, which are then neutralized with amines.
The role of the amine compound is to maintain the aqueous ink alkaline because of the speed of the acrylic resin in the alkaline environment.
Water-based inks also need to add some additives to adjust the ink's pH, dryness and so on. Commonly used adjuvants include pH stabilizers, retarders, dilute agents, defoamers, and the like.
(1) pH stabilizer: The viscosity and drying properties of water-based inks are closely related to the pH value. According to the type of substrate, the pH stabilizer is divided into ordinary type and thin film type. Special pH stabilizers are used when printing fine mesh prints. The usage of the general pH stabilizer is 1% to 2% of the total amount added every 30 to 40 minutes. pH stabilizers can both adjust the pH of aqueous inks and can also be used as diluents to reduce the viscosity of the ink.
(2) Anti-foaming agents and anti-foaming agents: used to suppress and eliminate bubbles and improve the transfer performance of aqueous inks. Generally, it is added before printing to prevent the ink from foaming due to agitation; if necessary, some amount may be added in the printing process, and the amount of each time cannot exceed 0.5% to 1% of the total amount of ink.
(3) Blocking agents are used to slow down the drying speed of water-based inks, prevent the ink from drying on the anilox roller, and reduce the stencil printing to obtain a satisfactory printing effect. The amount is generally 1% to 2% of the total amount of ink.
(4) Evacuation agent: The withdrawal agent is used to reduce the color of freshwater ink, but it has no effect on the pH value, viscosity, and drying speed of the ink. It is also a brightener that increases the brightness of the ink layer. The dosage depends on the circumstances.
(5) Diluent: After the addition of the diluent to the aqueous ink, the viscosity of the aqueous ink can be reduced without affecting the pH value. The amount used must not exceed 5% of the total amount of ink.
(6) Enhancer: The enhancer enhances the adhesion of the aqueous ink on the substrate. The amount is generally 1% to 2% of the total amount of ink.
(7) Static elimination agent: The static elimination agent can effectively prevent electrostatic accumulation. The amount is generally 0.5% to 1% of the total amount of ink.
The biggest characteristic of water-based ink is that the ink can be mixed with water before drying. Once the ink is dried, it is no longer soluble in water and ink, that is, the dried ink layer has water resistance. Therefore, special attention should be paid when printing. Do not allow the ink to dry on the anilox roller, so as not to block the cells of the anilox roller, hindering the quantitative transfer of ink and causing poor printing. In addition, the flexographic printing plate must always be wetted by the ink during the printing process in order to prevent the ink from drying on the plate.
The viscosity of water-based ink will change with the change of pH value, and the pH value will decrease, which will increase the viscosity of the ink and cause poor transferability. At the same time, the drying speed of the ink will be accelerated, and the anilox roller will be clogged. The pH value is mainly maintained by amine compounds. In the printing process to maintain the ink performance is stable, on the one hand to avoid the leakage of amines as much as possible, such as cover the cover of the ink residue; on the other hand, time to quantitatively add pH stabilizer to the ink tank. The use of a closed ink supply system and an ink temperature control system can reduce the volatilization of amines.
Since the volatilization of the solvent will cause changes in the viscosity of the aqueous ink, it is critical that excessive mechanical agitation be prevented in order to maintain the pH viscosity constant.
Production experience shows that the pH of general water-based inks is maintained between 8.5 and 9.5. When the PH value is too high, the water-based ink dries slowly, and problems such as poor adhesion of the backside of the printed product and poor ink-resistance of the ink layer are likely to occur.
Incidentally, the pH range of some special aqueous inks is different from that of ordinary water-based inks. For example, the pH value of gold ink and silver ink is 7.5-8.0, and the pH of the fluorescent ink is 7.5-8.3.
Most of the wide-format flexographic printing machines and the unit-type flexographic printing machines have various on-line processing functions such as roll feeding, printing, glazing, slitting, cross-cutting or die-cutting, and single-finished products, forming a package printing process. One-stop production lines, wherever there is a problem in the printing process, will produce a lot of waste products. The good printability of the ink is an important condition for the normal operation of the flexo printing machine and the printing of high quality products. The viscosity and dryness of the ink are more important.
There was a packaging and decoration printing factory that introduced a flexo line in 1996. It mainly printed soft cigarettes. At the time, it used the best water-based inks imported from the United States, but every time it was printed, it had five minutes. Stop using the brush to clean the dried ink residue in the mesh pocket, otherwise it will not be able to print normally, and the work efficiency is extremely low. At that time, ink experts in the United States could not do anything about it, because such failures had never happened in the United States. Later, the factory's workers and domestic printing process experts jointly searched for the cause of the failure and found that it was caused by the ink drying too quickly. The original waterborne gold ink imported from the United States was designed for printing at a printing speed of 150 revolutions per minute. In actual use, the speed of die cutting was limited due to the paper, and the speed of the flexo printing line could only reach a minute. This kind of 85 turns, plus the gold ink itself is very thick, so that the water-based gold ink dry solid plug in the anilox roller on the network. In addition, the leakage of amines during the printing process leads to a drop in the pH value, which also accelerates the drying rate of the aqueous gold ink, further exacerbating the failure. For the cause of the failure, add an appropriate amount of retarder composed of water, ethylene glycol, butyl ether, isopropyl alcohol, and 1830 emulsion to the aqueous gold ink, and regularly add ethanol, ethylene glycol amine, water, and water to the ink tank. The stabilizer of 1830 emulsion keeps the pH of the ink at about 9.5. The problem of ink drying on the anilox roll during the printing process never occurs again.
Water-based inks have two basic properties: liquid flow and fast fixation. Fast fixability makes it ideal for printing on non-absorbent substrates such as clear films, polyethylene and vinyl. In order for the water-based ink to adhere well to the plastic film, the plastic film also needs to be further improved to suit the wettability and adhesion of the aqueous ink.
In order to make the water-based ink transfer well, the ink supply and drying system of the flexo printer should also be improved accordingly. In addition, it is also necessary to provide a cleaning system so that the residual ink can be removed effectively and in time, and the service life of the anilox roller and the doctor blade can be extended.
With the increasing of flexo printing technology, waterborne inks have been successfully used in the multi-color mesh adjustment printing of corrugated boxes after undergoing development from field printing to halftone printing. This not only ensures that the hue and viscosity are basically stable. In addition, under the conditions of low viscosity and high color density, printing speeds of 200 to 300 sheets per minute can be accommodated. Aquatic inks have also achieved major breakthroughs in narrow flexo printing. With an 800-line/inch anilox roller, 200 lines/inches can be printed. The dots are clear and full of color. They are comparable to offset printing products and successfully applied to cigarettes. Printing of bags, folding cartons and various labels. New water-based inks that use special water-based resins and emulsion-based resins can also be applied to the printing of various specialty papers, aluminum foils, and plastic films.
Water-based inks need to be improved in the following areas:
(1) Improve the pH stability of aqueous inks;
(2) Under the premise of ensuring print drying and film forming, further improve the resolvability of the water-based ink to ensure that the printing system can run for a longer period of time before cleaning, minimizing or even eliminating paste printing malfunction;
(3) Continue to improve the performance on weakly absorbing or non-absorbing substrates, improve adhesion, enhance various resistances, and expand the use;
(4) Further reduce the content of volatile organic compounds and adapt to the future trend of increasing environmental protection requirements. (To be continued)
Chocolate are the best gift to lovers. You will find in the heart-shaped box with golden linings chocolates of various shapes in the exquisite partitions. Matched with ribbons of different colors, the box can be customized with your own logo, so the box is not just a Gift Box, but one that represents the affection of the gift givers. Make such a box full of chocolates for your lover if you want to keep your affections to her forever.
Chocolate Box,Chocolate Gift Box,Box Of Chocolates,Chocolate Box Gift
ANSHAN JIASHUN ARTS AND CRAFTS CO.,LTD , http://www.jhwls.com