UV ink, also known as UV ink, is capable of changing the ink from a liquid state to a solid state through an instantaneous photochemical reaction at a certain wavelength of ultraviolet light. In the past ten years, UV inks have made great progress, and they have been applied to more and more industries in the field of packaging and printing. This article briefly describes the UV flexo inks used in flexo printing.
First, the composition of UV flexo ink UV flexo ink is mainly composed of pigments, oligomers, monomers, photoinitiators and other additives.
1, pigments. Pigments are colorants in UV inks, which not only determine the hue of UV flexo inks, but also have a significant impact on the performance of UV inks, such as flowability, dispersion, stability, and drying properties.
2, oligomers. Oligomers, also known as prepolymers, act as binders in UV inks and are also the main film-forming material. The properties of the oligomers play a crucial role in the performance of UV flexographic inks, such as the viscosity of the UV ink, the curing speed, and the nature of the cured film. Therefore, it is required to have a faster curing speed and good Wear resistance and chemical resistance and other properties. Structurally, all oligomers are oligomers containing a C=C unsaturated double bond. Currently, oligomers commonly used in UV inks are generally acrylic resins, such as epoxy acrylic resins and polyester acrylic resins. , polyurethane acrylic resin and so on.
3, monomer. The monomer is a compound with a larger molecular weight, and its molecular structure also contains a C=C unsaturated double bond. It has two functions: one is to adjust the viscosity of UV flexo ink as reactive diluent; the second is to participate in the cross-linking reaction of oligomers. The monomers used in current UV flexo inks are generally acrylate monomers such as trimethylolpropane triacrylate (TMPTA), tripropylene glycol dipropionate (TPGDA) and propoxylated neopentyl glycol II. Acrylates (PO-NPGDA), etc.
4, photoinitiator. Photoinitiators are compounds that generate free radicals or cations upon exposure to ultraviolet light and determine the speed of photochemical reactions. After absorbing the radiant energy of the ultraviolet light, the photoinitiator can generate free radicals or cations, which in turn cause cross-linking between the prepolymer and the monomer, and the UV flexo ink is cured from the surface to form a film. The photoinitiators commonly used in UV flexo inks are certain ketones, ethers and sulphides.
5, additives. Additives mainly include stabilizers, sensitizers, leveling agents, and waxes, which can improve the stability of ink storage and improve the printability and curing speed of UV inks.
Second, UV flexo ink can be basically divided into two categories: free radical type and cationic type. At present, the most widely used number of radical UV flexo inks, this ink curing time is very short, enabling instant rapid curing. The cationic UV flexo ink itself has a small odor and good adhesion to the substrate materials (including plastics and metal materials). Therefore, it is often used in the printing of food packaging and printing materials with poor adhesion.
The drying mechanism of UV flexo inks can be divided into two stages. First, the photoinitiator in the UV ink is excited under UV light to generate free radicals or cations to transmit energy to the pre-unsaturated bonds through collisions. The polymers and monomers initiate a series of cross-linking polymerization reactions between the monomers and the prepolymers, turning the linear resin into a network structure, thereby allowing the UV flexo ink to change from a liquid state to a solid state and form a firm ink film.
The polymerization reaction is very fast and can be completed in a short time, which means that instant curing can be achieved.
Third, the difference between UV flexo ink and general flexo ink 1. Different ink composition. Film-forming substances in UV flexo inks are photosensitive resins, while conventional solvent-based or water-based flexo inks use ordinary resins; solvents or water-based inks contain certain organic solvents or water. Used to dissolve and dilute the resin, while the UV flexo printing ink does not contain water or any organic solvent, the monomer acts as a diluent, and the monomer also participates in the curing reaction. In addition, UV flexo inks contain photoinitiators, which are not found in ordinary UV flexo inks.
2, the drying mechanism is different. Solvent-based or water-based flexo inks are primarily dried by volatilization, absorption, or oxidative conjunctiva process; UV flexo inks are chemically reacted under UV energy to achieve cross-linked drying.
3, different drying performance. Because the flexographic printing press uses a short ink supply system, the drying performance of the ink is relatively high. When using ordinary flexo printing ink, in order to ensure the smooth printing, a certain hair dryer or oven must be used. Heat drying equipment to achieve rapid drying. The UV flexo printing inks are different, and they can achieve instant curing and drying without heating, which is very suitable for flexographic printing.
Fourth, the characteristics of UV flexo ink Why UV flexo ink is so popular and able to get so widely used? The main reason is that it has the following characteristics:
1. The UV flexo ink has stable properties and good printability. Since UV inks cure only when exposed to UV light and UV inks are not volatile, the viscosity of the ink is always stable during the printing process. Even if the ink is stopped halfway, the ink will not stay on the roller and the screen. Drying on the roller ensures the smooth printing process and greatly reduces the number of cleaning plates and anilox rollers.
2, UV flexo ink print quality is higher. Due to the good printing adaptability of UV flexo inks, the reproduction of prints is better, the consistency is higher, the color is bright, the glossiness and sharpness are also higher. In addition, the UV ink is linear after the curing and drying. The structure becomes a network structure, so the cured film has excellent chemical resistance and wear resistance.
3, UV flexo ink can achieve instantaneous drying, greatly improving production efficiency, and can reduce the occurrence of many printing failures.
4, UV flexo printing ink is safer and more reliable. Because it is solvent-free and non-flammable, it is safer to store and use, and it can effectively improve the working environment.
5, UV flexo printing ink for a wide range of substrates. UV flexo ink has good adhesion on different substrates such as paper, aluminum foil, and plastic.
6, the use of UV flexo ink less, and save costs. Although the price of UV flexo ink is higher than that of ordinary flexo ink, its effective composition is high, almost 100% of it is converted into ink film, and a good printing effect can be obtained only with a very thin ink layer.
7, UV flexo ink is more conducive to environmental protection. From the point of view of environmental protection, compared with traditional solvent-based and water-based inks, UV-curable inks are more conducive to environmental protection. Not only are there no volatile substances (VOC) problems, but they also do not contain any air pollution substances (HAPs). Substances), in line with the provisions of environmental protection, but also avoid the problem of solvent recovery. This is one of the main reasons for the rapid development of UV flexo inks.
V. Safety Problems Occurred in the Use of UV Ink In fact, UV flexo inks, like other chemical substances, can also cause some harm to the health and safety of the human body. However, these harmful chemicals are not ordinary chemical substances. So serious, and in most cases tend to be ignored by people. At present, there are three problems in the use of UV flexo inks:
The first problem is the harm of UV flexo ink to human body. Acrylates in UV inks are skin irritants that cause allergic reactions after a period of exposure. In other words, maybe the human body may not have an allergic reaction at present, but if the skin is exposed to UV ink for a long time, it may cause skin allergic reactions, itching, redness and even peeling. Therefore, wear protective clothing, gloves, goggles, and masks when using UV inks to minimize the chance of UV flexo inks coming into contact with the skin. If you do not care about the skin with UV ink, first scrub clean and wash with soap and water as soon as possible.
The second issue is about the safety of UV light sources. UV inks must be dried using a UV light source. However, ultraviolet light may cause some damage to human skin and eyes. In fact, as long as the operator is not facing the UV lamp, there is no need to worry about being exposed to ultraviolet radiation. Moreover, if the UV curing system is designed and installed correctly and reasonably, the amount of UV light leakage is minimal. In addition, users can also purchase special instruments to detect the degree of UV leakage.
The third problem with UV flexo inks is the generation of ozone during the curing process. The short-wavelength UV light source interacts with oxygen (O2) to produce ozone (O3). Most manufacturers use pipes to discharge ozone. Therefore, ventilation should be strengthened.
Sixth, in the production should pay attention to some problems 1, strictly abide by the production of operating procedures established in the workshop, in the use of UV ink or other chemical substances in the process of doing the necessary protective work, such as wearing gloves, goggles and Masks, etc. If the skin is in contact with UV ink, wash it with soap and water.
2, due to UV flexo ink is sensitive to light and heat, excessive light and heat will make the ink deterioration, therefore, UV flexo ink to be stored at low temperatures, protected from light, and the shelf life should not be too long, It is usually about one year.
3. The monomer in the UV ink is similar to the monomer in the photosensitive resin plate in terms of molecular structure and is prone to molecular diffusion, resulting in swelling of the printing plate and affecting the quality of the printed matter, and even printing failure. Therefore, it is very important to choose a plate with low swelling or a special UV plate.
4, different colors of UV flexo ink curing speed is also different, this is mainly due to the different pigments on the UV absorption, reflection and refractive ability caused by the difference. For example, in a four-color printing ink, yellow and magenta are easily cured and dried, while black ink is not easily dried. Therefore, when printing a black UV ink, the printing speed must be appropriately slowed to ensure that it can be completely cured.
5, UV lamp life is generally 1,000 hours, after the aging of the light source to replace the UV lamp to prevent UV flexo ink curing is not complete and cause printing failures.
7. Summary In conclusion, since UV flexo printing inks do not have the problem of solvent evaporation, the production environment is improved, the quality of prints is improved, and environmental protection is also very beneficial. Although there are still some safety issues, it can be well controlled and resolved by formulating and strictly observing the corresponding operating procedures. With the development of science and technology, the performance of UV flexo printing inks has been continuously improved and improved. It can be foreseen that UV flexo printing inks must have a very broad development prospect. (Ma Lan) ("Chinese Printing")
First, the composition of UV flexo ink UV flexo ink is mainly composed of pigments, oligomers, monomers, photoinitiators and other additives.
1, pigments. Pigments are colorants in UV inks, which not only determine the hue of UV flexo inks, but also have a significant impact on the performance of UV inks, such as flowability, dispersion, stability, and drying properties.
2, oligomers. Oligomers, also known as prepolymers, act as binders in UV inks and are also the main film-forming material. The properties of the oligomers play a crucial role in the performance of UV flexographic inks, such as the viscosity of the UV ink, the curing speed, and the nature of the cured film. Therefore, it is required to have a faster curing speed and good Wear resistance and chemical resistance and other properties. Structurally, all oligomers are oligomers containing a C=C unsaturated double bond. Currently, oligomers commonly used in UV inks are generally acrylic resins, such as epoxy acrylic resins and polyester acrylic resins. , polyurethane acrylic resin and so on.
3, monomer. The monomer is a compound with a larger molecular weight, and its molecular structure also contains a C=C unsaturated double bond. It has two functions: one is to adjust the viscosity of UV flexo ink as reactive diluent; the second is to participate in the cross-linking reaction of oligomers. The monomers used in current UV flexo inks are generally acrylate monomers such as trimethylolpropane triacrylate (TMPTA), tripropylene glycol dipropionate (TPGDA) and propoxylated neopentyl glycol II. Acrylates (PO-NPGDA), etc.
4, photoinitiator. Photoinitiators are compounds that generate free radicals or cations upon exposure to ultraviolet light and determine the speed of photochemical reactions. After absorbing the radiant energy of the ultraviolet light, the photoinitiator can generate free radicals or cations, which in turn cause cross-linking between the prepolymer and the monomer, and the UV flexo ink is cured from the surface to form a film. The photoinitiators commonly used in UV flexo inks are certain ketones, ethers and sulphides.
5, additives. Additives mainly include stabilizers, sensitizers, leveling agents, and waxes, which can improve the stability of ink storage and improve the printability and curing speed of UV inks.
Second, UV flexo ink can be basically divided into two categories: free radical type and cationic type. At present, the most widely used number of radical UV flexo inks, this ink curing time is very short, enabling instant rapid curing. The cationic UV flexo ink itself has a small odor and good adhesion to the substrate materials (including plastics and metal materials). Therefore, it is often used in the printing of food packaging and printing materials with poor adhesion.
The drying mechanism of UV flexo inks can be divided into two stages. First, the photoinitiator in the UV ink is excited under UV light to generate free radicals or cations to transmit energy to the pre-unsaturated bonds through collisions. The polymers and monomers initiate a series of cross-linking polymerization reactions between the monomers and the prepolymers, turning the linear resin into a network structure, thereby allowing the UV flexo ink to change from a liquid state to a solid state and form a firm ink film.
The polymerization reaction is very fast and can be completed in a short time, which means that instant curing can be achieved.
Third, the difference between UV flexo ink and general flexo ink 1. Different ink composition. Film-forming substances in UV flexo inks are photosensitive resins, while conventional solvent-based or water-based flexo inks use ordinary resins; solvents or water-based inks contain certain organic solvents or water. Used to dissolve and dilute the resin, while the UV flexo printing ink does not contain water or any organic solvent, the monomer acts as a diluent, and the monomer also participates in the curing reaction. In addition, UV flexo inks contain photoinitiators, which are not found in ordinary UV flexo inks.
2, the drying mechanism is different. Solvent-based or water-based flexo inks are primarily dried by volatilization, absorption, or oxidative conjunctiva process; UV flexo inks are chemically reacted under UV energy to achieve cross-linked drying.
3, different drying performance. Because the flexographic printing press uses a short ink supply system, the drying performance of the ink is relatively high. When using ordinary flexo printing ink, in order to ensure the smooth printing, a certain hair dryer or oven must be used. Heat drying equipment to achieve rapid drying. The UV flexo printing inks are different, and they can achieve instant curing and drying without heating, which is very suitable for flexographic printing.
Fourth, the characteristics of UV flexo ink Why UV flexo ink is so popular and able to get so widely used? The main reason is that it has the following characteristics:
1. The UV flexo ink has stable properties and good printability. Since UV inks cure only when exposed to UV light and UV inks are not volatile, the viscosity of the ink is always stable during the printing process. Even if the ink is stopped halfway, the ink will not stay on the roller and the screen. Drying on the roller ensures the smooth printing process and greatly reduces the number of cleaning plates and anilox rollers.
2, UV flexo ink print quality is higher. Due to the good printing adaptability of UV flexo inks, the reproduction of prints is better, the consistency is higher, the color is bright, the glossiness and sharpness are also higher. In addition, the UV ink is linear after the curing and drying. The structure becomes a network structure, so the cured film has excellent chemical resistance and wear resistance.
3, UV flexo ink can achieve instantaneous drying, greatly improving production efficiency, and can reduce the occurrence of many printing failures.
4, UV flexo printing ink is safer and more reliable. Because it is solvent-free and non-flammable, it is safer to store and use, and it can effectively improve the working environment.
5, UV flexo printing ink for a wide range of substrates. UV flexo ink has good adhesion on different substrates such as paper, aluminum foil, and plastic.
6, the use of UV flexo ink less, and save costs. Although the price of UV flexo ink is higher than that of ordinary flexo ink, its effective composition is high, almost 100% of it is converted into ink film, and a good printing effect can be obtained only with a very thin ink layer.
7, UV flexo ink is more conducive to environmental protection. From the point of view of environmental protection, compared with traditional solvent-based and water-based inks, UV-curable inks are more conducive to environmental protection. Not only are there no volatile substances (VOC) problems, but they also do not contain any air pollution substances (HAPs). Substances), in line with the provisions of environmental protection, but also avoid the problem of solvent recovery. This is one of the main reasons for the rapid development of UV flexo inks.
V. Safety Problems Occurred in the Use of UV Ink In fact, UV flexo inks, like other chemical substances, can also cause some harm to the health and safety of the human body. However, these harmful chemicals are not ordinary chemical substances. So serious, and in most cases tend to be ignored by people. At present, there are three problems in the use of UV flexo inks:
The first problem is the harm of UV flexo ink to human body. Acrylates in UV inks are skin irritants that cause allergic reactions after a period of exposure. In other words, maybe the human body may not have an allergic reaction at present, but if the skin is exposed to UV ink for a long time, it may cause skin allergic reactions, itching, redness and even peeling. Therefore, wear protective clothing, gloves, goggles, and masks when using UV inks to minimize the chance of UV flexo inks coming into contact with the skin. If you do not care about the skin with UV ink, first scrub clean and wash with soap and water as soon as possible.
The second issue is about the safety of UV light sources. UV inks must be dried using a UV light source. However, ultraviolet light may cause some damage to human skin and eyes. In fact, as long as the operator is not facing the UV lamp, there is no need to worry about being exposed to ultraviolet radiation. Moreover, if the UV curing system is designed and installed correctly and reasonably, the amount of UV light leakage is minimal. In addition, users can also purchase special instruments to detect the degree of UV leakage.
The third problem with UV flexo inks is the generation of ozone during the curing process. The short-wavelength UV light source interacts with oxygen (O2) to produce ozone (O3). Most manufacturers use pipes to discharge ozone. Therefore, ventilation should be strengthened.
Sixth, in the production should pay attention to some problems 1, strictly abide by the production of operating procedures established in the workshop, in the use of UV ink or other chemical substances in the process of doing the necessary protective work, such as wearing gloves, goggles and Masks, etc. If the skin is in contact with UV ink, wash it with soap and water.
2, due to UV flexo ink is sensitive to light and heat, excessive light and heat will make the ink deterioration, therefore, UV flexo ink to be stored at low temperatures, protected from light, and the shelf life should not be too long, It is usually about one year.
3. The monomer in the UV ink is similar to the monomer in the photosensitive resin plate in terms of molecular structure and is prone to molecular diffusion, resulting in swelling of the printing plate and affecting the quality of the printed matter, and even printing failure. Therefore, it is very important to choose a plate with low swelling or a special UV plate.
4, different colors of UV flexo ink curing speed is also different, this is mainly due to the different pigments on the UV absorption, reflection and refractive ability caused by the difference. For example, in a four-color printing ink, yellow and magenta are easily cured and dried, while black ink is not easily dried. Therefore, when printing a black UV ink, the printing speed must be appropriately slowed to ensure that it can be completely cured.
5, UV lamp life is generally 1,000 hours, after the aging of the light source to replace the UV lamp to prevent UV flexo ink curing is not complete and cause printing failures.
7. Summary In conclusion, since UV flexo printing inks do not have the problem of solvent evaporation, the production environment is improved, the quality of prints is improved, and environmental protection is also very beneficial. Although there are still some safety issues, it can be well controlled and resolved by formulating and strictly observing the corresponding operating procedures. With the development of science and technology, the performance of UV flexo printing inks has been continuously improved and improved. It can be foreseen that UV flexo printing inks must have a very broad development prospect. (Ma Lan) ("Chinese Printing")
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