Decorative inks are inks that produce imitation metal etching (splatter), refraction, wrinkles, icy flowers, corals, and other decorative patterns after printing on gold, silver cardboard, and certain colored card paper. They are non-color inks. Has been used for printing cigarettes, wine, cosmetics and other packaging, but also can print greeting cards and artwork.
Decorative inks are generally UV-curable (UA) inks. Compared with solvent-based inks, UV inks are safe, low-pollution, energy-saving, and quick-drying. They contain less than 5% volatile solvents, or do not contain volatile solvents. Solvent, so it will not pollute the environment when curing, safe to use, and less harmful to the human body. Another great advantage of UV inks is fast curing and good print quality.
Common solvent-based inks, even with infrared drying, cure slowly, and water-based inks cure more slowly. The UV ink cures in 3 to 5 seconds and the drying speed is less than 1 second. Since the effects of imitating metal etching (sanding), coral, and refraction must be instantaneously cured, only UV inks can be used for printing. Although wrinkles and ice flowers cure slowly, they can only produce the desired effect by controlling UV curing conditions.
First, ordinary UV ink is not suitable for gravure printing UV ink in offset printing and screen printing has long been widely used, but due to the gravure printing speed, generally higher than 100 meters / min, up to 400 meters / min, ink layer thickness is difficult to completely Curing, and the oxygen inhibition effect of the remaining ink layer of the scraper is very prominent, and the curing speed is extremely slow. For this reason, there have not been a large number of UV gravure printing inks used for printing such as packaging, except for a small number of extremely expensive UV gravure color inks used for banknote printing and UV varnish.
I have tried to use UV decorative inks for screen printing for gravure printing. It was found in the experiment that the UV ice ink ink curing speed is very slow, it is difficult to use industrially in screen printing, gravure printing machine for high speed operation is even more impossible; UV wrinkle ink is first pre-irradiated with low pressure mercury lamp, and then Curing with a medium-pressure mercury lamp causes the surface and inner layers to shrink differently and cause wrinkles. The curing speed is also very slow. It is used for gravure printing and it is difficult to wrinkle; UV screen printing coral ink is produced by printing ink A large number of bubbles and gathered together resemble corals, but this kind of ink is used for gravure printing, it is not easy to generate air bubbles, and curing speed is too slow; UV screen printing refraction ink is used for gravure printing, not only the speed is not good, but also the printed product The pattern is blurred, the refractive effect is poor, and it cannot be used; the fastest curing speed is the UV screen imitation etching ink, but the speed can not meet the needs of gravure printing.
In addition, there are two problems that also determine the UV screen imitation etching ink can not be used in the gravure:
1. Ink particles are coarse and easy to block, so that gravure printing cannot be performed normally.
2. The printing quality is poor and high-quality decorative patterns cannot be obtained. Therefore, in order to use the gravure printing technology to print decorative patterns, it is necessary to develop a UV gravure decorative ink that has a high printing speed, good print consistency, and a thick ink layer.
Second, UV gravure ink technical difficulties Despite the gravure decorative pattern has many characteristics, but UV gravure ink has not come out, because there are many key technologies difficult to solve.
First of all, the gravure ink layer is thicker and it is difficult to completely cure the ink layer in a short time. The intensity of UV radiation at any depth of the ink layer can be calculated from the Beer-Lambert equation:
lL=loekcL
Where: lo = radiation intensity of the surface of the ink layer;
C = concentration of absorbed light material;
L = range (depth from the surface);
lL = radiation intensity at the distance L below the surface.
The curing mechanism of UV inks is that photoinitiators generate free radicals upon irradiation with ultraviolet light, causing the ink to cure, and the greater the radiation intensity, the faster the curing speed. The radiation intensity decays naturally with the thickness of the ink layer, and the thickness of the ink layer increases, and the curing speed significantly decreases. The gravure ink layer is thick and the printing speed is very fast. Therefore, it is difficult to manufacture an ink that can be used in high-speed gravure printing and can be cured well.
Second, it is difficult to overcome the oxygen inhibition effect. The ground state of the electrons in the oxygen molecule is a triplet state. Although it is relatively stable and does not have enough energy to initiate polymerization of acrylate, it is prone to combine with radicals generated by a photoinitiator that is irradiated with ultraviolet light, rendering the free radicals inactive and thus unable to Initiate UV ink curing. This effect is very significant on the surface coating. Experiments have shown that the transparent coating is exposed to air in a 1μm finish that cures 20 times slower than a 5μm coating on the surface. The residual ink layer thickness of the scraper is much less than 1 μm, and the oxygen inhibition effect is more pronounced. In order to overcome the oxygen inhibition effect, the amount of photoinitiator is often added to the formula. According to the Beer-Lambert equation, the concentration of absorbed light increases, and the radiation depth decreases in proportion. Obviously, the two are contradictory. Therefore, it is difficult to manufacture UV gravure inks using conventional UV ink technology.
Generally, the thickness of the gravure printing ink layer is 10 2020 μm, and the decorative printing requires the ink layer to have a higher thickness, sometimes exceeding 40 μm, otherwise the imitation metal etched particles are not full, and lines such as wrinkles are not quite stiff. This further increases the difficulty of curing, and it is by no means easy to use a gravure method to print such a thickness.
At present, there are many kinds of common UV gravure decorative ink formulations, the following three kinds of conventional products.
UVA-101 type, better brightness, suitable for printing products with a refraction pattern, its cost is lower, the price is lower; UVA-102, UVA-103 type of high gloss, the printed line three-dimensional strong , suitable for printing high-brightness, dynamic patterns.
UVA-201 type, which is characterized by full printing ink color, is suitable for printing products with imitation metal etching and other patterns.
UVA-301 type, which is characterized by a silky and brocade-like effect, has a higher cost and therefore a higher selling price.
It should be noted that all the decorative patterns can be printed with the above three kinds of inks, but due to the different ink performance characteristics, the resulting effects are quite different. Due to the adoption of special technology, the curing speed of the UV gravure decorative ink is improved, and the problem of UV ink curing in gravure printing is solved. As long as a medium pressure mercury lamp is used, the power density is 80 W/cm×3,120 m/. The speed of the points can be cured very well.
UV gravure decorative ink ink layer is very thick, due to the fast speed, general UV irradiation as long as the surface of the printed product is dry, you can enter the next process can be. During the storage, the ink layer will also intermittently undergo a curing reaction to fully cure the ink and achieve the desired strength. The shelf life of UV inks is generally shorter, most of them are about six months. Some imported inks, due to the long turnover time, have reached the end of their shelf life. Therefore, it is very important to improve the storage stability of UV inks. In addition to the photoinitiator, the ink also contains certain substances that can promote other chemical reactions, which have a great influence on the storage stability. The shelf life of UV gravure printing ink can reach 1 year. According to the rapid aging test, under the premise of not seeing light, it can be put in the shade for 4 to 5 years.
The safety of the use of UV inks is very important, and some UV inks will make the skin of the printing workers swollen, resulting in pimples, sticking to the ink at the pain, itching, and even blisters, which are due to the use of the ink formula with strong stimulation, easy Allergenic resins and reactive diluents. This type of ink has a low production cost and a low price, but it causes serious damage to the human body and may even cause cancer. It must be banned. Practice has proved that as long as the use of high-quality resin and low-stimulus diluent, it can completely produce a safe gravure ink that does not harm the human body and the environment. Compared with the commonly used solvent-based gravure inks, UV gravure inks do not contain organic solvents that have an impact on the human body and are flammable, explosive, and volatile. Therefore, UV gravure printing inks are very safe.
In gravure printing, the ink is transferred to the substrate through a gravure cell, and the web is transferred to the substrate. For this purpose, the arrangement and number of lines, the size, shape and depth of the cell, and the web The width of the wall has a great influence on the printing quality. It can be said that there is no good printing plate, and even the best ink cannot print a good product. The gravure decorative pattern making method is more difficult to make than the general gravure plate making. Therefore, when designing the UV gravure decorative ink printing plate design, the particularity and characteristics of the process should be taken into consideration.
Third, UV gravure printing equipment UV gravure decorative ink performance and general gravure ink is very different, in the printing may produce the following problems:
1. The scraper is difficult to scrape the ink, and the remaining ink of the scraper will affect the printing quality;
2. In order to increase the thickness of the ink layer, the cell site is made deeper during the plate making, and it is difficult for the ink to completely transfer out from the cell site during printing.
3. The ink on the plate cylinder is spread toward both ends, which will contaminate the printed matter.
For this reason, the printing machinery must carry out the necessary cooperation to ensure the smooth printing and ensure the printing quality.
Gravure printers for packaging and printing include sheet-fed gravure printers and rotogravure machines. Currently, gravure printing decorative inks for printing UV are mainly sheet-fed gravure printing machines. Shanghai Ziming Machinery Co., Ltd. cooperated with the implementation of the UV gravure decorative pattern process, and carried out a lot of improvements in gravure printing machine ink supply system, printing system, squeegee device, etc. to better solve the problem of ink scraping. And help the ink transfer from the cell site to the substrate. Such as printing UVA-201 type UV gravure decorative ink, ink layer thickness up to 45μm or more. The device is equipped with a squeegee device at the two ends of the plate cylinder, which can scrape the ink at the two ends of the plate cylinder without polluting the printed material. The device is equipped with three 80W/cm medium pressure mercury lamps, which can cure UV gravure decorative inks.
Rotary gravure printers are generally multi-color machines, printing speed, but expensive equipment, suitable for large-volume printing. To print UV gravure decorative inks, equipment must be improved. For example, the Bobst Model CH-820 from Switzerland only installed a UV curing device in the last printing unit. It is mainly used to cure UV gravure coatings and protective coatings. The device can also be used to cure UV gravure decorative inks. The UV curing device consists of a medium-pressure mercury lamp, a reflector and a protective cover. The working pressure of the medium-pressure mercury lamp is 133×102 Pa. In the emission spectrum, the proportions of the 365 nm and 366.5 nm lines are relatively high. Most photoinitiation systems have strong absorption in this line region, which is favorable for ink curing. The medium-pressure mercury lamp used has a power density of 80-240 W/cm, and the actual luminous area of ​​the lamp is slightly larger than the maximum width of the cured area. If 80W/cm is selected, at least 3 must be installed; if it is greater than 120W/cm, at least 2 must be installed. In actual use, the greater the power density, the deeper the UV penetration and the better the curing effect. Two 120W/cm and three 80W/cm, the total power density is the same, but the former's curing effect is better than the latter.
The following points should be noted when installing the UV curing device:
1) To install reflectors, reflectors should be made of bright aluminum, stainless steel materials can not be used;
2) Pay attention to protection against UV light and discharge ozone outside;
3) UV lamp must be cooled, otherwise it will affect the service life of UV lamp;
4) Pay attention to explosion protection. Although UV gravure decorative inks are not flammable and explosive, the first few printing units of the rotary machines generally use solvent-based gravure printing inks and contain a large amount of inflammable and explosive solvents. These solvents will volatilize when the ink is dry, which will make The solvent concentration is very high and must be explosion proof to ensure safety. All electrical switches used in UV devices should be explosion-proof components. In addition, during operation, the temperature of the lamp should be as high as 600-800°C. Besides cooling it, it is better to form a fresh air layer to isolate the volatile gas from the air to ensure safety;
5) The currently imported rotary machines only install UV devices on the last printing unit. Nowadays, advanced decorating printing processes often require two UV curing processes. It is preferable to install UV curing devices on the latter two printing units.
Fourth, UV decorative gravure note matters 1) When the medium-pressure mercury lamp is used to heat the electron emission through the two ends of the filament, the metal tungsten will evaporate and deposit on the tube wall, a long time the lamp will gradually ink, weaken the UV The intensity of light, decay to a certain extent, will affect the curing speed, making the ink harder to dry. Generally use 1000 hours to drop to 75%. If you do not cool well, the lamp temperature is too high, and the service life is only 500 hours. Therefore, you should use a probe-type UV light meter to measure the light source periodically. If you find cure
Decorative inks are generally UV-curable (UA) inks. Compared with solvent-based inks, UV inks are safe, low-pollution, energy-saving, and quick-drying. They contain less than 5% volatile solvents, or do not contain volatile solvents. Solvent, so it will not pollute the environment when curing, safe to use, and less harmful to the human body. Another great advantage of UV inks is fast curing and good print quality.
Common solvent-based inks, even with infrared drying, cure slowly, and water-based inks cure more slowly. The UV ink cures in 3 to 5 seconds and the drying speed is less than 1 second. Since the effects of imitating metal etching (sanding), coral, and refraction must be instantaneously cured, only UV inks can be used for printing. Although wrinkles and ice flowers cure slowly, they can only produce the desired effect by controlling UV curing conditions.
First, ordinary UV ink is not suitable for gravure printing UV ink in offset printing and screen printing has long been widely used, but due to the gravure printing speed, generally higher than 100 meters / min, up to 400 meters / min, ink layer thickness is difficult to completely Curing, and the oxygen inhibition effect of the remaining ink layer of the scraper is very prominent, and the curing speed is extremely slow. For this reason, there have not been a large number of UV gravure printing inks used for printing such as packaging, except for a small number of extremely expensive UV gravure color inks used for banknote printing and UV varnish.
I have tried to use UV decorative inks for screen printing for gravure printing. It was found in the experiment that the UV ice ink ink curing speed is very slow, it is difficult to use industrially in screen printing, gravure printing machine for high speed operation is even more impossible; UV wrinkle ink is first pre-irradiated with low pressure mercury lamp, and then Curing with a medium-pressure mercury lamp causes the surface and inner layers to shrink differently and cause wrinkles. The curing speed is also very slow. It is used for gravure printing and it is difficult to wrinkle; UV screen printing coral ink is produced by printing ink A large number of bubbles and gathered together resemble corals, but this kind of ink is used for gravure printing, it is not easy to generate air bubbles, and curing speed is too slow; UV screen printing refraction ink is used for gravure printing, not only the speed is not good, but also the printed product The pattern is blurred, the refractive effect is poor, and it cannot be used; the fastest curing speed is the UV screen imitation etching ink, but the speed can not meet the needs of gravure printing.
In addition, there are two problems that also determine the UV screen imitation etching ink can not be used in the gravure:
1. Ink particles are coarse and easy to block, so that gravure printing cannot be performed normally.
2. The printing quality is poor and high-quality decorative patterns cannot be obtained. Therefore, in order to use the gravure printing technology to print decorative patterns, it is necessary to develop a UV gravure decorative ink that has a high printing speed, good print consistency, and a thick ink layer.
Second, UV gravure ink technical difficulties Despite the gravure decorative pattern has many characteristics, but UV gravure ink has not come out, because there are many key technologies difficult to solve.
First of all, the gravure ink layer is thicker and it is difficult to completely cure the ink layer in a short time. The intensity of UV radiation at any depth of the ink layer can be calculated from the Beer-Lambert equation:
lL=loekcL
Where: lo = radiation intensity of the surface of the ink layer;
C = concentration of absorbed light material;
L = range (depth from the surface);
lL = radiation intensity at the distance L below the surface.
The curing mechanism of UV inks is that photoinitiators generate free radicals upon irradiation with ultraviolet light, causing the ink to cure, and the greater the radiation intensity, the faster the curing speed. The radiation intensity decays naturally with the thickness of the ink layer, and the thickness of the ink layer increases, and the curing speed significantly decreases. The gravure ink layer is thick and the printing speed is very fast. Therefore, it is difficult to manufacture an ink that can be used in high-speed gravure printing and can be cured well.
Second, it is difficult to overcome the oxygen inhibition effect. The ground state of the electrons in the oxygen molecule is a triplet state. Although it is relatively stable and does not have enough energy to initiate polymerization of acrylate, it is prone to combine with radicals generated by a photoinitiator that is irradiated with ultraviolet light, rendering the free radicals inactive and thus unable to Initiate UV ink curing. This effect is very significant on the surface coating. Experiments have shown that the transparent coating is exposed to air in a 1μm finish that cures 20 times slower than a 5μm coating on the surface. The residual ink layer thickness of the scraper is much less than 1 μm, and the oxygen inhibition effect is more pronounced. In order to overcome the oxygen inhibition effect, the amount of photoinitiator is often added to the formula. According to the Beer-Lambert equation, the concentration of absorbed light increases, and the radiation depth decreases in proportion. Obviously, the two are contradictory. Therefore, it is difficult to manufacture UV gravure inks using conventional UV ink technology.
Generally, the thickness of the gravure printing ink layer is 10 2020 μm, and the decorative printing requires the ink layer to have a higher thickness, sometimes exceeding 40 μm, otherwise the imitation metal etched particles are not full, and lines such as wrinkles are not quite stiff. This further increases the difficulty of curing, and it is by no means easy to use a gravure method to print such a thickness.
At present, there are many kinds of common UV gravure decorative ink formulations, the following three kinds of conventional products.
UVA-101 type, better brightness, suitable for printing products with a refraction pattern, its cost is lower, the price is lower; UVA-102, UVA-103 type of high gloss, the printed line three-dimensional strong , suitable for printing high-brightness, dynamic patterns.
UVA-201 type, which is characterized by full printing ink color, is suitable for printing products with imitation metal etching and other patterns.
UVA-301 type, which is characterized by a silky and brocade-like effect, has a higher cost and therefore a higher selling price.
It should be noted that all the decorative patterns can be printed with the above three kinds of inks, but due to the different ink performance characteristics, the resulting effects are quite different. Due to the adoption of special technology, the curing speed of the UV gravure decorative ink is improved, and the problem of UV ink curing in gravure printing is solved. As long as a medium pressure mercury lamp is used, the power density is 80 W/cm×3,120 m/. The speed of the points can be cured very well.
UV gravure decorative ink ink layer is very thick, due to the fast speed, general UV irradiation as long as the surface of the printed product is dry, you can enter the next process can be. During the storage, the ink layer will also intermittently undergo a curing reaction to fully cure the ink and achieve the desired strength. The shelf life of UV inks is generally shorter, most of them are about six months. Some imported inks, due to the long turnover time, have reached the end of their shelf life. Therefore, it is very important to improve the storage stability of UV inks. In addition to the photoinitiator, the ink also contains certain substances that can promote other chemical reactions, which have a great influence on the storage stability. The shelf life of UV gravure printing ink can reach 1 year. According to the rapid aging test, under the premise of not seeing light, it can be put in the shade for 4 to 5 years.
The safety of the use of UV inks is very important, and some UV inks will make the skin of the printing workers swollen, resulting in pimples, sticking to the ink at the pain, itching, and even blisters, which are due to the use of the ink formula with strong stimulation, easy Allergenic resins and reactive diluents. This type of ink has a low production cost and a low price, but it causes serious damage to the human body and may even cause cancer. It must be banned. Practice has proved that as long as the use of high-quality resin and low-stimulus diluent, it can completely produce a safe gravure ink that does not harm the human body and the environment. Compared with the commonly used solvent-based gravure inks, UV gravure inks do not contain organic solvents that have an impact on the human body and are flammable, explosive, and volatile. Therefore, UV gravure printing inks are very safe.
In gravure printing, the ink is transferred to the substrate through a gravure cell, and the web is transferred to the substrate. For this purpose, the arrangement and number of lines, the size, shape and depth of the cell, and the web The width of the wall has a great influence on the printing quality. It can be said that there is no good printing plate, and even the best ink cannot print a good product. The gravure decorative pattern making method is more difficult to make than the general gravure plate making. Therefore, when designing the UV gravure decorative ink printing plate design, the particularity and characteristics of the process should be taken into consideration.
Third, UV gravure printing equipment UV gravure decorative ink performance and general gravure ink is very different, in the printing may produce the following problems:
1. The scraper is difficult to scrape the ink, and the remaining ink of the scraper will affect the printing quality;
2. In order to increase the thickness of the ink layer, the cell site is made deeper during the plate making, and it is difficult for the ink to completely transfer out from the cell site during printing.
3. The ink on the plate cylinder is spread toward both ends, which will contaminate the printed matter.
For this reason, the printing machinery must carry out the necessary cooperation to ensure the smooth printing and ensure the printing quality.
Gravure printers for packaging and printing include sheet-fed gravure printers and rotogravure machines. Currently, gravure printing decorative inks for printing UV are mainly sheet-fed gravure printing machines. Shanghai Ziming Machinery Co., Ltd. cooperated with the implementation of the UV gravure decorative pattern process, and carried out a lot of improvements in gravure printing machine ink supply system, printing system, squeegee device, etc. to better solve the problem of ink scraping. And help the ink transfer from the cell site to the substrate. Such as printing UVA-201 type UV gravure decorative ink, ink layer thickness up to 45μm or more. The device is equipped with a squeegee device at the two ends of the plate cylinder, which can scrape the ink at the two ends of the plate cylinder without polluting the printed material. The device is equipped with three 80W/cm medium pressure mercury lamps, which can cure UV gravure decorative inks.
Rotary gravure printers are generally multi-color machines, printing speed, but expensive equipment, suitable for large-volume printing. To print UV gravure decorative inks, equipment must be improved. For example, the Bobst Model CH-820 from Switzerland only installed a UV curing device in the last printing unit. It is mainly used to cure UV gravure coatings and protective coatings. The device can also be used to cure UV gravure decorative inks. The UV curing device consists of a medium-pressure mercury lamp, a reflector and a protective cover. The working pressure of the medium-pressure mercury lamp is 133×102 Pa. In the emission spectrum, the proportions of the 365 nm and 366.5 nm lines are relatively high. Most photoinitiation systems have strong absorption in this line region, which is favorable for ink curing. The medium-pressure mercury lamp used has a power density of 80-240 W/cm, and the actual luminous area of ​​the lamp is slightly larger than the maximum width of the cured area. If 80W/cm is selected, at least 3 must be installed; if it is greater than 120W/cm, at least 2 must be installed. In actual use, the greater the power density, the deeper the UV penetration and the better the curing effect. Two 120W/cm and three 80W/cm, the total power density is the same, but the former's curing effect is better than the latter.
The following points should be noted when installing the UV curing device:
1) To install reflectors, reflectors should be made of bright aluminum, stainless steel materials can not be used;
2) Pay attention to protection against UV light and discharge ozone outside;
3) UV lamp must be cooled, otherwise it will affect the service life of UV lamp;
4) Pay attention to explosion protection. Although UV gravure decorative inks are not flammable and explosive, the first few printing units of the rotary machines generally use solvent-based gravure printing inks and contain a large amount of inflammable and explosive solvents. These solvents will volatilize when the ink is dry, which will make The solvent concentration is very high and must be explosion proof to ensure safety. All electrical switches used in UV devices should be explosion-proof components. In addition, during operation, the temperature of the lamp should be as high as 600-800°C. Besides cooling it, it is better to form a fresh air layer to isolate the volatile gas from the air to ensure safety;
5) The currently imported rotary machines only install UV devices on the last printing unit. Nowadays, advanced decorating printing processes often require two UV curing processes. It is preferable to install UV curing devices on the latter two printing units.
Fourth, UV decorative gravure note matters 1) When the medium-pressure mercury lamp is used to heat the electron emission through the two ends of the filament, the metal tungsten will evaporate and deposit on the tube wall, a long time the lamp will gradually ink, weaken the UV The intensity of light, decay to a certain extent, will affect the curing speed, making the ink harder to dry. Generally use 1000 hours to drop to 75%. If you do not cool well, the lamp temperature is too high, and the service life is only 500 hours. Therefore, you should use a probe-type UV light meter to measure the light source periodically. If you find cure
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