UV offset press configuration, material, adjustment and problem handling

The development time of UV offset printing in the domestic market is not long. Compared with foreign countries, there are many technical problems. There are many differences between paper printing and UV printing. Correct understanding of UV offset printing can save a lot of trouble in the printing process. Let's talk about the author's understanding of UV offset printing at home.
Offset configuration requirements

1. UV curing device

Generally, 2 to 3 UV lamps are installed in the middle part of the delivery chain guide rails, and an exhaust nozzle is installed at the top of the delivery section. A UV curing device can also be connected separately. The conveyor belt is connected to the delivery table section. . Obviously, the latter is limited by the speed of the conveyor belt of the UV curing device, which will affect the printing speed, and is not suitable from the perspective of the space occupied. When the first method is adopted, UV lamps can be set between the unit and the unit, and each unit can be used interchangeably. According to the different requirements of the printing products, the wet and dry printing state can be achieved.

The UV curing device can be equipped with a stepless adjustable power output. When the printer is under pressure, the output power is controlled to connect with the printer. At this time, the output power of the UV lamp is automatically reduced, which can extend the service 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 mirror to ensure that excess heat is effectively removed during printing. At present, the service life of general UV lamps is from 1000 to 1500 hours. If it is used well, it can reach 1500 to 2000 hours. Business card UV lamp. At present, domestic imports are still the mainstay, among which the German elthch company and the Japanese GSM company are more typical.

2. Special ink roller

UV inks use special ink rollers. The special ink roller's acid resistance, alkali resistance, oil resistance, and swelling resistance are all superior to those of the ordinary ink roller. Its excellent performance is specially applied to UV inks. The service life of the special ink roller is usually within 2 years, and the dampening roller is within 1 year.

In addition, it is preferable to install the ink cooling device of the ink fountain roller, which can effectively control the temperature of the ink roller and ensure that the print quality problem is not caused by the temperature change after the rubbing of the UV ink in the continuous rapid printing.

3. roller

(1) The impression cylinder

The impression roller uses a double-diameter cylinder (two revolutions of the plate cylinder correspond to one revolution of the impression cylinder) to ensure smooth and smooth transfer of the plastic film. Sheets after imprinting cylinders are imprinted. Only when it is transferred to the next roller, when the printer runs at a high speed, it is not easy to produce a fault, and the pressure and impulses that the printed sheet bears are kept at a minimum.

(2) transfer roller

The skeleton type transfer roller replaces the conventional transfer roller. A type of air blowing is adopted, and a row of air blows is installed on the transfer roller. During the transfer process, the tail of the printed sheet is blown down, and a cushion is blown to lift the printed sheet to prevent the dirty or scratched phenomenon. The other is to replace the air blow with a slide bar. Place the two slide bars on the two sides of the printed sheet to avoid contact with the printing graphic part in the middle. The slide bar can move freely and can be adjusted according to different printing formats.

4. Gripper, Feeder, Take-up

All the grippers, delivery teeth, and tines of the delivery teeth must be treated with special steel (such as chrome plating) to ensure their wear resistance, ensure the accuracy of the delivery, and prevent overprinting caused by slipping. Since the feed tooth row needs to be circulated from the UV lamp, its own metal structure must be resistant to high temperatures, otherwise once it is 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 large viscosity and poor fluidity of UV inks, the friction between the UV ink rollers is large and the load on the printer is large. Therefore, a motor that is one step higher than the main motor of an ordinary offset press of the same specification must be selected to ensure normal printing.

6. In addition to static electricity, dust removal device

Since the static electricity of PVC and other sheets is large and there is a lot of dust, it is recommended to install a static electricity removing device at the paper feeding portion and the paper receiving portion. If the conditions permit, the dust removing device may be installed at the paper feeding portion.

The UV offset printing machine must meet the requirements of the printing thickness of 0.1 to 0.85mm, trapping accuracy error ≤ 0.02mm, other features can be adjusted according to different brands of printing presses. From the point of view of domestic manufacturers of cards, the current four-boot is a typical model, of which Mitsubishi and Gaobao are the two most common brands.

printing material

1. UV ink

UV inks are light-curable absorbent inks, and since many cards require laminating, the performance of UV inks is particularly important. There are two key points: First, the need for high temperature, high pressure, in the laminator high temperature, high pressure does not change color, do not fade; Second, the bonding force with the plastic film to be large, the minimum standard required to reach 6N tension. In addition, the selection of UV ink for card printing is also quite critical. In addition to ensuring the quality of the ink itself, it must also match the wavelength of the UV lamp of the printer. Since many manufacturers use color inkjet drafts as their originals for printing, it is recommended that yellow, magenta, and blue inks of the standard hue should be selected when purchasing inks. In addition, when spot color inks are formulated, inks with low viscosity and good fluidity should be selected as far as possible. The European Ark ink is preferred.

2. Special printing plate

UV offset printing plate wear-resistant, resistant to printing, no need to protect the adhesive when the machine stops, the old version can be used again, and is very suitable for the transfer of UV ink, high reduction rate when printing, can basically reach 2% of the outlets Without losing, 98% of the outlets can be distinguished. The current Japanese version of Fuji UV is of better quality. Considering the cost of printing, the text version can be properly used for the short version of a batch with a normal version. However, the film is extremely fragile and must be printed with care.

3. Blanket and bag lining

In order to ensure the best transferability and dot reducibility of UV inks, it is best to use air-cushioned blankets, because they have good acid resistance, oil resistance, hydrophobicity, and good ink transfer performance, and can ensure that the dot distortion during the printing process is minimal. Printed graphics are clear, high-profile reproduction is good, and plate wear is low.

Eraser roller liner lining is better than neutral hard, because the surface of PVC and other sheets is rough, which can easily lead to high printing dot gain, and the use of neutral hard liner can make the dot clear, smooth and reproducible. The geometric shape of the graph changes little, and the increment of the width of the graphic and printed sheets is relatively small.

4. PVC and other sheets

Sheets such as PVC have a light surface and a matt surface, the light surface is flat. Matt surface is rough. Selecting the printing surface is very important and many print quality problems can be avoided. The matte side of the sheet such as PVC is usually used as the printing surface to ensure that the actual ink printing does not pull the hair, the network point is strong. The adhesion between the ink and the material is strong, and the ink is full and does not expose small white spots. In addition, the printing pressure is appropriately increased by 0.02 to 0.05 mm from the standard pressure.

5. Auxiliary materials

UV car wash used by the car wash water, blanket cleaning agent, cleaning fluid, etc. are best to use special products, which for the UV ink roller, UV blanket and UV printing plate is particularly important for the service life and performance. Although the cost will be higher, it can be flexibly applied according to the actual situation. Ensure that the ink roller is cleaned once a week: use a special revert agent to clean the blanket when it is stopped, which can not only ensure the elasticity of the blanket, but also guarantee the color balance and color difference when restarting.

Printing adjustment

1. Workshop environment control

Maintain humidity at 50% to 60%, summer temperature at 20～22°C, winter temperature at 22～25°C, UV printing in offset printing workshop will generate a lot of heat, control temperature and humidity is to ensure printing quality primary condition.

2. Formulation of fountain solution

At present, UV offset printing generally uses alcohol fountain solution or isopropyl alcohol fountain solution. In comparison, alcohol can be quickly volatilized, which can effectively transfer the heat generated by the printing plate running and the friction of the ink roller. It is recommended to use an alcohol fountain solution with a concentration of 10% to 12% and a temperature of 5 to 10°C.

The pH value of the fountain solution is particularly important, and the pH value should be increased as much as possible to ensure that the plate is not dirty. The UV offset printing is generally controlled at a pH of 5.6-6. If the acidity is too strong, the layout will be heavily visceral, the graphic and text will be eroded and the pattern will be eroded, the ink will be easily emulsified, the ink roller will be easily deinked, the ink will be dark and dull, and the acidity will be too small to make the ink Loss of balance, non-graphical part of the hydrophilic and oil-repellent weakened, the layout from the dirty, due to the increase in print outlets caused by paste version. Therefore, the control of the fountain solution pH plays a key role in printing.

3. Common printing failure

(1) Flying ink

UV inks have large viscosity and poor fluidity. However, when the room temperature is high or the humidity is too low, the printing press runs at high speed for a long time, which causes the ink viscosity to become smaller, the fluidity increases, and flying ink droplets to be generated. This time should be reduced. Room temperature, increased air humidity, and constant low speed printing.

(2) Lamo

When the UV printing field version is easy to produce ink pull phenomenon, the main reason is the improper choice of printing surface; cold machine open, the machine's UV ink roller temperature is too low or ink viscosity is too large. The printed surface of PVC and other sheets should be properly selected; let the machine idle and warm up, and 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, under the premise of not affecting the quality of the card, some inks with low viscosity and strong fluidity can be selected for printing.

(3) The front and back are 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 ink balance, it is also necessary to check whether the power of the UV lamp is within the effective range. The printing speed should not be too fast. Generally, a single-layer card printing is preferred at 6000 printing/hour. The ink is preferably matched to the wavelength of the UV lamp.

(4) Ink shades are uneven

Ink printing and squeezing can sometimes occur unevenly in printing. The new machine basically has no such phenomenon. The longer the printing machine is used, the more obvious the problem is. Appropriate machine adjustments will change. To effectively control the ink balance, adjust the machine's water, ink roller pressure. In addition, it is also possible to adjust the position of the ink oscillating roller, that is, the position of the initial static point in the lateral turbulence of the ink roller and the ink roller. When adjusting, it is necessary to gradually adjust the micro adjustment so as to obtain a relatively satisfactory printing effect.

(5) Failure of fountain solution

There are wavy vertical stripe and pale stripe in the printing. Under the condition that the printing roller is in good condition, the amount of IPA is often too much. In this case, the amount of IPA can be reduced and diluted with clean water. The appearance of thick vertical stripes, often with too little amount of IPA, at low IPA or no IPA, the concentration of fountain solution becomes lower, and corrugations and longitudinal stripes are most likely to occur.

Print design

For the print quality of the card, the print design is also critical. Because the UV offset printing of the printing card is more prone to dot gain than the paper printing, the manuscript with superior design effect is greatly dissimilar to the design intention after printing on the machine, and the color is gray. Dot enlargement is a key factor affecting color. An excellent designer, in addition to understanding the principle of print design, understands and grasps the extent of changes in the card's Internet site after printing is also crucial. When designing, taking into account the changes in printing, will be able to print a more beautiful card pattern, which requires the designer to continue to accumulate.

The future of UV printing

Environmentally friendly UV