At the drupa exhibition last year, the maximum speed of sheet-fed offset printing presses has reached 20,000 sheets / hour, and the maximum speed of rotary newspaper printing presses has reached 100,000 copies / hour. The customers who favor these high-speed machines are China Printers, especially cigarette and newspaper printing factories. It can be said that increasing the printing speed has great potential for the printing press itself, but the drying speed of the ink is the bottleneck of development. Therefore, in recent years, research on ink UV curing, heat drying and quick drying ink is very active. This article mainly discusses the latest development of ink UV curing, thermal drying light source and device design based on the ink drying principle.
Ink drying and curing principle
The drying of printing ink mainly includes oxidized conjunctiva drying, penetration drying, volatile drying and radiation drying.
1. Dry oxidized conjunctiva
The ink contains dry oil. The unsaturated fatty acid in the molecular structure of the oil reacts with oxygen in the air, and the small molecule linear structure is polymerized into a macromolecular network structure to form a solid substance. This chemical reaction process is called The oxidized conjunctiva dries.
2. Penetration drying
The ink binder contains more mineral oil, such as gasoline, high boiling point kerosene, etc. When the mineral oil in the ink penetrates into the porous paper fibers, the pigment is fixed on the surface of the paper to form a solid film, called infiltration drying.
3. Volatile drying
The ink contains a large amount of volatile substances, such as aliphatic hydrocarbon rosin esters, aromatic hydrocarbon solvents, alcohols, ketones, ester solvents, etc. After the ink is transferred to the surface of the printing material, the solvent volatilizes and the pigment is fixed to form a solid film, which is called volatile drying.
4. Radiation curing
Radiation curing is a chemical reaction in which chemical monomers cross-link into a polymer network structure to form a solid, and the curing speed is fast, and the formed film layer is hard and bright, but the adhesion is not good. There are currently three types of radiation curing methods commonly used.
(1) Infrared radiation drying. The ink contains a chelating agent, which can be irradiated with medium-wave infrared light with a wavelength of 3 to 30 μm to accelerate the polymerization reaction, and the heat generated at the same time promotes the evaporation of the solvent and accelerates the drying of the ink. Short-wave and long-wave infrared are not conducive to the drying of ink.
(2) Ultraviolet (UV) radiation curing. The ink contains photoinitiators, such as benzophenone (absorption wavelength 240-340nm), 2-chlorinated thioxanthone (absorption wavelength 200-400nm) and other derivatives. The photoinitiator is in the wavelength range of 250-420nm Under the irradiation of UV light, the unsaturated double bond can be quickly opened in less than 0.1 seconds to initiate the resin, such as polyurethane, epoxy acrylate, etc., cross-linking and curing to a solid and drying. UV-curable inks are essentially free of solvents.
(3) Electron beam (EB) radiation curing. Thermionic cathode tube emits a high-energy radiation electron beam, and the radiation wavelength is selected by adjusting the cathode tube emitter, so there is no visible light and infrared radiation, and it is completely a cold light source. The effective radiation intensity of the electron beam is very high, which can directly induce the polymerization of the resin into a solid. Therefore, the photoinitiator may not be used in the EB ink. The photoinitiator in the UV ink can be removed or added in a small amount to act as an electron beam curing ink.
Generally, the drying of printing ink is not a single drying method, but several kinds of drying occur simultaneously. For example, the drying of offset printing ink is caused by oxidative conjunctiva, penetration, and volatilization. The drying of oxidative conjunctiva is the main method; the drying of newspaper printing ink is the permeation drying; the gravure printing ink is mainly volatile drying.
Commonly used ink drying and curing equipment
Ink drying is often compound drying, so what drying equipment is used and how to set the parameters to maximize drying efficiency while saving energy is the most concern of the printer.
1. Infrared drying equipment
(1) Light source. For the drying of ink, the effect of mid-wave infrared is the best. There are three types of infrared light sources commonly used.
The first is the heating wire radiation source, the common is the non-closed resistance wire jacket quartz lamp. The distribution of the heat radiation intensity of this lamp tube with the light wavelength can not be controlled, the efficiency is low, the price is low, and the service life is about 2000-3000 hours.
The second type of light source is to place the resistance wire in a closed quartz tube, and fill the lamp tube with different gases to change the wavelength distribution characteristics of the radiated light, and at the same time isolate the lamp wire from oxygen in the air, and the radiation efficiency is high. Most imported printing presses are now equipped with this kind of light source, with a life span of 5000 to 10000 hours, but a large part of their radiant energy is still distributed in the visible light and near and far infrared sections, and the mid-wave infrared is not very rich.
The third type is electric heating semiconductor light-emitting tube. The outer shape is coated with red or gray matte semiconductor material on the outside of the ceramic tube, and the inner wall of the tube is wound with a resistance wire. Relying on electroheat to cause the semiconductor material to emit light, the light is dark red or black when the lamp is lit. By selecting the semiconductor material, the wavelength distribution of the radiant energy can be changed, and the radiation efficiency is extremely high.
(2) Infrared light reflector. At present, there are two common types. One is a gold-plated reflector, which is coated with a metal film at a 180 ° range around the lamp tube. The metal film reflects infrared efficiency up to 90%; the other is an oval or figured shape pressed by an aluminum plate or aluminum plate Reflector, as shown in Figure 2, the closer the lamp tube is to the lamp cover, the higher the reflection efficiency, and the highest reflectivity can reach 85%.
(3) Heat dissipation of infrared lamps. The infrared lamp tube surface can be cooled by the blowing method, and the air volume does not affect the infrared power output of the lamp. Because only about 1% of the energy radiated by the infrared lamp is absorbed by the paper and ink, and the rest of the energy is completely converted into heat, causing the temperature around the machine to heat up, it needs to be exhausted to the outside or recycled by the suction device.
(4) Scope of application. Infrared lamps are used to dry infrared inks, and the drying efficiency of non-special infrared inks is very low, and they do not even work for some inks. Infrared has penetrating power, can dry the upper and lower layers of the ink film at the same time, accelerate ink penetration, and promote oxidative conjunctiva, especially for thick ink layer printing and drying of varnish. It has good drying effect on offset printing, relief printing, screen printing, printing ink, flexographic printing ink and water-based varnish with low solvent content.
2. Hot air drying equipment
(1) Heat source. There are three kinds of heat sources for generating hot air: electric hot air pipes, such as stainless steel, quartz glass, ceramic shell hot air pipes; high temperature oil pipes, high temperature engine oil heating air through pipes to generate hot air; high temperature steam pipes, generating high temperature steam through boilers to generate hot air .
(2) Hot air device. The air around the heat source is heated by the fan and blown to the surface of the ink. Adjusting the direction of the hot air and the paper running angle can improve the efficiency of hot air drying.
The higher the speed of the hot air relative to the paper, the more beneficial it is to reduce the vapor pressure on the surface of the paper and increase the solvent volatilization speed; adjust the wind direction so that the wind direction forms an additive effect on the paper running speed, and it is more beneficial to drying. The air speed of the hot air pipe can not be lower than the required speed, otherwise, the poor heat dissipation on the surface of the air pipe will burn the lamp tube. The wind speed should not be too high, because some energy will be lost during the wind cycle, and the optimal drying effect can be achieved by selecting the fan pressure and air volume appropriately.
(3) Scope of application. It is suitable for drying plastic gravure and flexographic printing inks and solvent-based varnishes, and can also accelerate the drying of water-based inks and varnishes.
3. UV curing equipment
(1) Light source. Commonly used high-pressure mercury lamps and metal halogen lamps, high-pressure mercury lamps are mercury atoms excited to form a continuous spectrum, adjust the mercury content in the lamp tube, so that the radiation wavelength in the curing section of 254 ~ 420nm, rich in ultraviolet light. Metal halide lamps add metal halides such as gallium and iron to mercury lamps, and excite them to generate radiation under mercury excitation conditions. Different metals can be added according to the difference in the absorption spectrum of the ink to make the UV lamp radiate more of the ink absorption. Lightwave, improve curing efficiency.
The content of impurities in the metal halogen lamp tube is extremely small, and the purity of the electrode material is high. Therefore, the manufacturing process is complicated, difficult, and expensive. At present, domestic high-quality, high-power metal halogen lamps cannot be produced in the country. American Fusion, German IST, The products of Japan Yanqi and other companies. The lamp life of the lamp with a power density of 160W / cm can reach 2000 hours and the lamp head is not black. It can still reach 50% emissivity after 4000 hours.
(2) Cold UV light source. When the UV lamp is lit, its internal temperature should reach 600 ～ 1000 ℃. If the temperature in the lamp is too low or the wind speed is too high, the headlight will go out, so the "cold light source" does not actually exist, but the cooling system of the lamp can be used.
(3) Microwave UV lamp. This is a new product from Fusion. The tube is 6 inches long and has no metal electrodes at both ends. It uses microwaves to excite the substances in the tube that absorb microwaves to generate heat at high speed, and then excite substances such as mercury and metal halides to emit light. Aluminum is a good material for reflecting microwaves. The microwave source emits microwaves onto an elliptical aluminum lampshade, focusing on the electrodeless lamp to excite mercury or metal halide to emit light.
The characteristics of microwave lamps are:
â‘ The distribution characteristics of the radiant light intensity with the wavelength can be adjusted to select the best radiation wavelength, so that the ink can achieve the desired curing effect.
â‘¡Because the lamp tube has no electrode, the service life can reach 5000 hours when the power density is 300W / cm, and multiple switch does not affect the lamp life.
â‘¢Because the microwave source is easy to control, the microwave lamp can be started quickly and frequently, but the microwave also has a standby state (maintaining the working state), and it can only be started quickly in this state. This function is suitable for supporting the use of optical discs and adhesive printing machines, because screen printing optical discs and adhesive printing are mostly intermittent printing.
â‘£The UV curing section of the microwave lamp has a rich spectrum and less infrared band, so the microwave radiation temperature is lower.
⑤Since the microwave lamp has no electrodes, it is very convenient to change the lamp tube, and no wiring is required.
â‘¥Because no electrode is released, the two ends of the lamp will never be black.
⑦ Due to the limitation of the microwave transmission method, the maximum length of the microwave lamp tube is 6 inches. The placement of the lamp tube can increase the curing width. Due to the small gap of the lamp tube, the butt joint will not affect the curing effect.
⑧The price of microwave lamps is relatively high. A 6-inch curing device is about 50,000 yuan. At present, the domestic market is mainly used for curing UV inks matched with inkjet printers such as CD printing, cables, pipes, flexible packaging and so on.
⑨The luminescent material of microwave lamp is the same as that of ordinary UV lamp, and the radiation wavelength distribution is also the same, so no special ink is needed.
(4) UV lamp reflector design. Scientifically selecting reflective materials and rationally designing the structure of the reflector can increase the curing effect by multiples and save energy. The aluminum crystal formed by acid oxidation of pure aluminum has a UV light reflectivity of 90%, while the aluminum plate without oxidation treatment has a UV light efficiency of less than 60%; the stainless steel has a UV light reflectance of less than 60%; the semiconductor coating reflects UV light The rate reaches 94%, but the cost is higher. At the same time, infrared and visible light can reach the surface of the reflector through the plating layer and disperse after cooling device.
The development trend of reflector design is the change of opening and height, that is, the cross-sectional area becomes smaller to shorten the reflected optical path and reduce the loss of light intensity due to the long optical path. In addition, the top of the reflecting cover and the reflecting plate change the design of the original opening at the top, so that the radiation energy at the top of the lamp tube can be reflected to the paper surface, as shown in Figure 4. Due to the small cross-sectional area of ​​the lampshade, the distance between the lamp tube wall and the reflective surface is close, so the temperature of the reflector plate is too high, and the wind resistance of the top reflector plate will affect the heat dissipation of the lampshade. The solution is to cool the lampshade with water or increase the amount of heat dissipation air, and design the heat dissipation air path reasonably.
Introduction of advanced curing equipment
1. Microwave UV curing equipment
The characteristic of this equipment is that due to the need of microwave transmission channel, the size of the lamp is large, so it is not suitable to be installed in the paper receiving channel of the sheet-fed offset printing machine. The machine is used in combination, and the CD and inkjet printing systems are also suitable for this equipment, but due to the high price, the printing factory rarely uses it at present.
2. High power density UV curing equipment
The power density of the electrode-made UV lamp produced in Japan can reach 240 ～ 300 W / cm, which can be used for the curing of the UV silver paste covered by the rotary screen printing in the form printing unit; It has reached 400W / cm and curing speed is 150m / min; the power density of Fusion's microwave lamp reaches 400W / cm.
The high power density UV curing equipment not only accelerates the curing speed, but also facilitates the complete curing of the thick UV ink layer and the bottom layer of UV ink on rough paper. In addition, increasing the power density of the UV lamp can correspondingly reduce the sensitivity of the UV ink and reduce the content of the photoinitiator, thereby improving the stability and sensitivity of the UV ink, easy to store and transport, and also reducing the price.
3. Water cooling UV curing system
Due to the development of the design concept of the printing equipment structure, the structure of the printing machine is more compact and beautiful, and the larger UV curing air cooling channel can no longer meet the requirements, so this type of printing machine generally uses water-cooled UV curing equipment. For example, the UV drying systems of imported multi-color offset printing machines are all water-cooled, and the satellite-type adhesive printing machines are also equipped with water-cooled UV systems.
I often find in printing houses that there are many unreasonable phenomena in the drying and curing process of ink, which causes a large waste of electric energy. For example, some curing equipment is unscientific in design, although the price is cheap, but the efficiency is very low. The speed of a split glazing machine is less than 3000 sheets / hour. Three 10kW UV lamps are used. One 12kW tube is sufficient. As another example, the power configuration of the curing system of the front and rear unit of the unit type printing machine is unreasonable, which causes the printing speed to go up. And many manufacturers only consider the cost of equipment, ignoring the cost of electricity. In response to the above problems, it is recommended that printing companies consider various aspects when selecting curing equipment.
Nail Brush...WHICH BRUSHES FOR WHAT MATERIAL TO CHOOSE CORRECTLY? GEL - for gel modeling we choose brushes suitable for scooping UV / LED gel, so it is necessary to use a flat brush with which you can easily apply UV / LED gel on your nails and shape it into the right shape. There are several hair sizes and types. Furthermore, 2 shapes are used for gel modeling, either flat straight or flat oval. SAMINA Nails offers several types, which you can find HERE.
POLY GEL - a special brush is used on the poly gel, which has a spatula at one end to gain mass and a brush at the other end for shaping. We also offer a device that has a silicone tip at the ends, which can be used to shape the poly gel. We offer a poly gel brush HERE.
NAIL ART - there are a lot of brushes for nail art and decorating. The most important brush that no one should miss is the detailer, or extra thin brush, which is suitable for detailed work around the cuticle and nail walls. You can also paint a French manicure or thin lines with it. It's simply a brush you have to have. Another very popular is, for example, a brush for ombré, or a gradual transition of colors, for glitter and many others. You can find our offer HERE.
BRUSH CARE
If we want the brush to last us as long as possible, it is also necessary to take good care of it.
Never leave the brush in the water or detergent for too long - the brush head may come loose or the sleeve may start to rust
Clean the brush thoroughly - head and sleeve
Dry the moisture with a clean cloth or napkin
Place the brush upside down to dry
Dry at room temperature
Clean the brushes you use on UVLED gels properly and store them in a dark place. This will prevent direct light from curing the remnants of the gel left on the brush.
Nail Art Design Brush, Nail Art Brush for Nail Beauty , Hand Beauty tool
SAMINA FORAM (SHENZHEN) CO., LIMITED. , https://www.saminabrush.com