The development of Business Card UV offset printing in China is not long. Compared with foreign countries, there are more technical problems. There are many differences between paper printing and UV printing. Correctly understanding the UV offset printing of card making can save a lot of trouble in the printing process. Let me talk about the author's understanding of domestic UV offset printing.
Configuration requirements for offset presses
1. UV curing device
Generally, 2 to 3 UV lamps are installed in the middle part of the paper collection chain guide, and an exhaust pipe port is installed at the top of the paper collection part. A UV curing device can also be connected separately, and the conveyor belt is connected to the paper collection table . Obviously, the latter will be affected by the speed of the conveyor belt of the UV curing device, which will affect the printing speed, which is not suitable from the perspective of space occupation. When using the first method, UV lamps can be installed between the units, and each unit can be used interchangeably, according to the different requirements of the printed products to achieve the wet and dry printing state.
The UV curing device can be equipped with infinitely adjustable power output, and the output power can be connected to the printing machine when the printing press is off pressure. At this time, the output power of the UV lamp is automatically reduced, which can extend the life of the lamp. The UV curing device is usually air-cooled and water-cooled at the same time. Each UV lamp is equipped with a reflector to ensure that the excess heat in the printing process is effectively eliminated. At present, the service life of general UV lamps is 1000-1500 hours, and if used properly, it can reach 1500-2000 hours. UV lamp for business card. At present, domestic imports are still the mainstay, and the products of German elthch and Japanese GSM are more typical.
2. Special ink roller
UV ink should use special ink roller. The special ink roller has better acid resistance, alkali resistance, oil resistance and swelling resistance than ordinary ink roller, and its high-quality performance is specially suitable for UV ink. Usually the service life of the dedicated ink roller is within 2 years, while the dampening roller is within 1 year.
In addition, it is best to install a water cooling device for the ink roller, so that the temperature of the ink roller can be effectively controlled to ensure that the quality of the printing is not caused by the temperature change after the UV ink rubs in continuous rapid printing.
3. roller
(1) Imprint cylinder
The impression cylinder uses a double-diameter cylinder (two rotations of the plate cylinder is equivalent to one rotation of the impression cylinder) to ensure the smooth and smooth transmission of the plastic film. The printed sheet is pressed by the impression cylinder. It is only transferred to the next cylinder. When the printing machine is running at high speed, it is not easy to cause failure, and the pressure and impact force on the printed sheet are kept to a minimum.
(2) Paper transfer roller
The skeleton-type paper transfer drum replaces the traditional type paper transfer drum. One type uses a blower type. A row of blowers is installed on the paper transfer cylinder. During the transfer process, the tail of the printed sheet is blown down, and an air cushion blower holds the printed sheet to prevent smearing or scratching. The other is to replace the blowing with a slide bar. Place the two slide bars on both sides of the printed sheet to avoid contact with the printed graphics in the middle. The slide bar can move freely and can be adjusted according to different printing formats.
4. Paper-handling, paper-handling, paper-receiving teeth row
The tips of all grippers, delivery teeth, and take-up teeth need special steel treatment (such as chrome plating) to ensure their wear resistance, ensure the accuracy of the delivery, and prevent slippage caused by overprinting. Since the paper collecting row needs to be circulated under the UV lamp, its metal structure must be resistant to high temperature, otherwise, once deformed, it will seriously affect the printing transfer.
5. Main motor
The main motor of the printing press is an AC motor. Because of the high viscosity and poor fluidity of the UV ink, the friction between the UV ink rollers is large, and the printing machine has a large load. Therefore, you must choose a motor that is one step higher than the power of the main motor of an ordinary offset press of the same specification to ensure normal printing.
6. Static and dust removal device
Due to the high static electricity and dust of PVC and other sheets, it is recommended to install a static removal device in the paper conveying part and the paper receiving part. If conditions permit, a dust removing device can also be installed in the paper conveying part.
The business card UV offset printing machine needs to meet the requirements. The printing thickness is 0.1-0.85mm, and the color accuracy error is ≤0.02mm. Other functions can be adjusted according to different brands of printing machines. From the point of view of various domestic card manufacturers, the current four-boot is a typical model, of which the two brands of Mitsubishi and KBA are the most common.
printing material
1. UV ink
UV ink is a light-curable absorbent ink. Since many cards require film lamination, the performance of the UV ink itself is particularly important. There are two key points: one is the need to withstand high temperature and high pressure, and it does not change color or fade under the high temperature and high pressure of the laminator; the second is that the adhesion with the plastic film is greater, and the minimum standard needs to reach 6N. In addition, the selection of UV inks for card making is also very important. In addition to ensuring the quality of the ink itself, it must also match the wavelength of the UV light of the printing press. Since many manufacturers use color inkjet manuscripts for printing, it is recommended to choose yellow, magenta, and cyan inks with standard hues when purchasing ink. In addition, when preparing spot color inks, try to choose inks with low viscosity and good fluidity. Ake ink from Europe is better.
2. Special printing plate
The special printing plate for UV offset printing is wear-resistant and durable, without the need to apply protective glue when it is stopped halfway, the old version can be used again, and it is very suitable for the transfer of UV ink. The dot reduction rate is high during printing, which can basically reach 2% of the dot No loss, 98% of the dots can be distinguished. At present, the Fuji UV version of Japan is of good quality. Considering the printing cost, for short-run jobs with small batches, the text version can be properly used as the ordinary version, but the plate film is very easy to wear, so pay more attention when printing.
3. Blanket and lining
In order to ensure the best transferability and dot reducibility of UV ink, it is best to use air cushion blanket, because it has good acid resistance, oil resistance, hydrophobicity and good ink transfer performance, which can ensure the smallest dot deformation during printing. The printed graphics are clear, the reproducibility of high-profile parts is good, and the plate wear is small.
The rubber roller lining is better to use neutral harder, because the surface of PVC and other sheets is rough, it is easy to cause a high rate of printing dots. The use of neutral hard lining can make the dots clear, smooth and reproducible. The geometric shape of the graphic changes little, and the width increment of the graphic and printed sheet is relatively small.
4. PVC and other sheets
Sheets such as PVC have a bright surface and a matte surface, the bright surface is relatively smooth. Matt surface is rough. It is very important to choose the printing surface, which can avoid many printing quality problems. The matt surface of PVC and other sheets is usually used as the printing surface to ensure that the solid ink is not roughened and the dots are strong. The adhesion between the ink and the material is strong, the ink is full and no white spots are revealed. In addition, the printing pressure is appropriately increased by 0.02 to 0.05 mm compared to the standard pressure.
5. Auxiliary materials
It is best to use special products for car wash water, blanket cleaning agent, and plate cleaner for UV offset printing. This is particularly important for the service life and performance of UV ink rollers, UV blankets, and UV printing plates. Although the cost will be higher, it can be used flexibly according to the actual situation. Ensure that the ink roller is cleaned once a week: use a special recovery agent to clean the blanket when the machine is shut down. This will not only ensure the effective elasticity of the blanket, but also ensure that the color balance is uniform and the color difference is avoided when restarting.
Printing adjustment
1. Workshop environment control
Maintain humidity at 50% to 60%, summer temperature is best at 20-22 ° C, winter temperature is best at 22-25 ° C, UV printing in offset printing workshops will generate a lot of heat, and controlling temperature and humidity guarantees printing quality primary condition.
2. Preparation of fountain solution
At present, UV offset printing generally uses alcohol dampening solution or isopropyl alcohol dampening solution. In comparison, alcohol volatilizes quickly and can effectively transfer the heat generated by the friction between the printing plate and the ink roller. It is recommended to use alcohol fountain solution, the concentration is preferably 10% -12%, and the temperature is preferably 5 ~ 10 ℃.
The control of the pH value of the fountain solution is particularly important. As long as the printing plate is not dirty, the pH value should be increased as much as possible. The pH value of the UV offset printing is generally controlled at 5.6 to 6. If the acidity is too strong, the layout will be seriously dirty. The graphic base will be eroded to cause the printing plate. The ink is easy to be emulsified, the ink roller is easy to produce deinking, and the printed ink is gray and dull; the acidity is too small, which is easy to make the ink Loss of balance, the hydrophilic and oil repellency of the non-graphic part is weakened, the plate is dirty, and the paste is caused by the increase of the printed dots. Therefore, the pH control of fountain solution plays a key role in printing.
3. Common printing faults
(1) Flying ink
The UV ink itself has high viscosity and poor fluidity. However, when the room temperature is too high or the humidity is too low, the printing machine runs at a high speed for a long time, which will reduce the viscosity of the ink, enhance the fluidity, and generate scattered ink droplets. At room temperature, increase air humidity to maintain a constant low-speed printing.
(2) Lamo
Ink printing is easy to occur during UV printing of the field version, mainly due to improper selection of the printing surface; printing is started in a cold machine, the temperature of the UV ink roller in the machine is too low, or the viscosity of the ink is too large. The printing surface of PVC and other sheets should be selected correctly; let the machine run preheated idly, and properly apply some thinner on the ink roller; in winter, pay special attention to the temperature change of the UV ink roller of the machine. In addition, some inks with low viscosity and strong fluidity can be selected for printing without affecting the quality of the card.
(3) The front and back surfaces are sticky and dirty
The main cause of stickiness is insufficient ink curing, especially black ink. In addition to effectively controlling the pH of the fountain solution and controlling the balance of water and ink, you should also check whether the power of the UV lamp is within the effective range, and the printing speed should not be too fast. Generally, the single-layer card printing is better at 6000 prints / hour. The ink preferably matches the wavelength of the UV lamp.
(4) Uneven shades of ink
The unevenness of the ink color of the mouth and the trailing edge sometimes occurs during printing. The new machine basically does not have this phenomenon. The longer the printing machine is used, the more obvious the problem. Appropriate machine adjustments will improve. To effectively control the water-ink balance, adjust the water and ink roller pressure of the machine. In addition, it is also possible to adjust the static spot position of the cross-ink roller, that is, to adjust the initial static spot position in the lateral movement of the cross-ink roller and the inking roller. When adjusting, pay attention to the micro-adjustment step by step, to adjust to obtain a relatively satisfactory printing effect is better.
(5) Malfunction of fountain solution
Wavy longitudinal stripes and light-colored stripes appear in printing. When it is determined that the water roll is in good condition, the amount of IPA is often too large. At this time, the amount of IPA can be reduced and diluted with clean water. The appearance of dark vertical stripes is often due to too little IPA. In the state of low IPA or no IPA, the concentration of the fountain solution becomes lower, and ripples and vertical stripes are most likely to occur.
Print design
For the printing quality of cards, the printing design is also critical. Because the business card UV offset printing is more prone to dot gain than paper printing, often the originals with good design effects have a large gap between the effect and the design intention after machine printing, and the colors are dark. The increase of dots is a key factor that affects color. An excellent designer, in addition to understanding the principles of print design, is also critical to understand and master the range of changes in card dots after printing. When designing, taking into account the changes in printing will print out more exquisite card patterns, which requires designers to accumulate.
The future of UV printing
Environmentally friendly UV printing is the future development trend of printing. It can achieve 100% curing, no solvent evaporation, no powder spraying, instant drying, and stable ink color. The overprint is accurate and can be processed immediately after printing. The ink has high abrasion resistance and high-strength gloss, suitable for printing non-absorbent materials. The UV curing device between the units can realize the wet press dry printing state. However, most of the current UV inks are imported products, the cost is extremely high, including its auxiliary materials, but also a problem that plagues many enterprises. With the development of new technology and new materials in the future, I believe that card printing will go to a new level.
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