UV Polishing - Materials and Process Indicators (below)

The three-roll coating principle is shown in the figure. The UV varnish flows into the vinegar tank formed by the rollers M and R, and is uniformly pressed by the M-R, and the varnish adheres to the R. The R and M presses apply the oil on the R to the paper. The scraper scrapes the excess lacquer on the embossing roller M into the lower sump and reuses it. The amount of coating is determined by the pressure between M and R. This machine is characterized by fast glazing speed, simple machine structure, low price, and low operating technology. The disadvantage is that it is not suitable for thin paper because the thin paper tends to adhere to the roller R and rewind it. In some designs, the air knife can peel the paper from the roller R so that the thin paper is not taken away by the roller R, but it is not ideal for use. Then, the coating amount is not easy to control, the coating is too thick, the coating amount of varnish is not easy to adjust, and the coating thickness can only be controlled by heating oil or adding thinner.
The principle of fang-type polishing mechanism.

The principle of the dental glazing mechanism is shown in the figure. The ink stick M brings the oil from the oil tank to the platen roller R, and R presses against the pick-up platen L to transfer the varnish to the paper for coating. Advantages: Thick and thick paper are suitable, generally 80g/m2 single-sided copper paper to 450g/m2 whiteboard paper can be. Simple operation, simple structure and easy maintenance. Since the pressure between the rollers R and L is large, the ink distribution effect is better than the three-roller type. Disadvantages: slow speed, generally 2500 / hour; operators, at least 4 people; coating amount is not easy to control.
Four-roll anilox roller coater structure.

The structure of the four-roll anilox roller coater is shown in the figure. Comparison of three-roll coater, four-roller an anilox roller (metering roller), corresponding to a more scraper. The purpose of adding an anilox roller is to quantitatively control the amount of coating and to ensure the consistency of the thickness of the film on the product. General long version packaging with this type of machine, such as cigarettes, wine, soap, toothpaste, film and other product boxes need to quantitatively control the quality of products to ensure the consistency of product quality. Another example is a brand of soap box produced at different times, but placed in the same counter, if the use of three-roller polishing machine will appear different brightness of the surface of the box, and with anilox roller coating machine coating, it is not clear which Batch production of products.

Polished with an offset press.
The method of using the offset printing machine and its features are as follows:
1 Varnish is placed in a sink and coated with a water roller.
2 Remove the water fleece sleeve of the water roller and spread the oil with the rubber roller so as to reduce the oil transfer amount.
3 Adjust the amount of water on the roller, that is, adjust the amount of oil.
4 Widen the sink so that all ink rollers are above the sink. Because of the low viscosity of the varnish, the oil on the water roller drops downward on the underlying paper.
5 The cutting blanket is the same or slightly smaller than the width of the print.
6 can be coated with UV oil, water-based gloss oil, but can not be coated with solvent-based thermal drying Varnish, or sticky roll.
7 Use ordinary PS plate and ordinary blanket.
8 The thickness of the coating oil layer should not be too large, otherwise there will be pitting.
9 Can not be partially glazing because of the separation properties of UV inks on the PS plate.
10 It is easy to apply light locally by cutting the blanket.
11 When the coating is thin, the ink tank can be used for polishing.
If the shop temperature is below 20°C, the coating thickness can be adjusted by adding thinner.

Sixth, the correct use of UV Varnish

UV oils are inconsequential, just as edible oils do not deposit a dry film on the air. UV oil sees UV light, such as sunlight, arc welding, and curing light immediately. General fluorescent lamps, incandescent lamps, sodium lamps and other lighting sources do not cause curing. UV oil contains photoinitiators and thinners, which have a certain stimulating effect on human skin.
In view of the above characteristics of UV oil, the following points should be taken into account when using it:
1 Normal use temperature of UV oil is 50°C~55°C. When it is used, the oil is circulated and heated with a constant temperature water bath to make the viscosity meet the design requirements, which is beneficial for leveling and rapid curing.
2 UV oil irradiation area through the UV lamp, the temperature is 50 °C ~ 60 °C, curing fast, strong adhesion. However, it is not the lower the UV lamp temperature, the better.
3 The polishing machine is placed in a location where the sun cannot reach directly, otherwise the UV varnish is solidified on the applicator roller. If it is not possible to avoid direct sunlight, red and black curtains are used to block the light.
4 When varnishing, UV oil will disperse the ink on the varnish material into UV oil to make the varnish colored. It can be used after filtration and precipitation, and it need not be discarded.
5 When applying the UV oil to the skin, immediately wash it off with soapy water, otherwise skin redness and blistering will occur.
6 The viscosity of UV oil varies depending on the type of glazing machine. Special varnishes should be selected according to the model. If you do not reach the required viscosity of the glazing machine, you can reduce the viscosity of the thinner or stick it with a tackifier. This method will lose UV light oil curing speed, brightness, adhesion and so on.
7 When UV oil flows to the rotating part of the drive shaft, it will stick to the shaft at high temperatures, affecting the transmission, so pay attention to cleaning the shaft head.
According to the nature of the surface of the substrate, choose a special light oil, such as gold cardboard oil, PET oil.

Seven, UV curing time

Theoretically, it can be rigorously calculated how many photons the UV curing material needs to be cured per unit volume, and the photochemical reaction speed does not take much time. However, the addition of a polymerization inhibitor to the UV oil or ink delays the polymerization time (ie, the curing time) after the photochemical reaction has a direct relationship with the photoinitiator and the polymerization inhibitor.
For general UV varnish or ink formulations, the curing time is selected within 0.1~0.2s. However, the specific time after the formula is determined depends on the following factors:
1 coating thickness. The surface of the coating cures quickly, but the surface layer cures and absorbs ultraviolet light strongly. The intensity of the ultraviolet radiation decays exponentially, lowering the curing speed. Therefore, the coating is cured quickly and slowly.
2 UV intensity. When the intensity is high, the curing time is short, and vice versa.
3 Add solvent. Diluents, such as ethanol, in the UV varnish reduce the curing speed.
4 Ambient temperature. The coating temperature of 50 °C ~ 70 °C is the ideal ambient temperature. UV mercury lamps contain a large amount of visible and infrared components, providing the coating surface with ambient temperature. Therefore, designing the curing machine is not as good as the surface temperature of the material.
5 Oxygen cures faster. Oxygen has a strong absorption of ultraviolet rays, and nitrogen filling the coating surface will accelerate the curing speed.
The selection of the specific curing time is related to the following aspects:
According to the characteristics of the coating machine, such as screen printing machine, printing speed of about 600 ~ 2000 / hour, coated with 350 mesh UV Varnish, with a power density of 80W/cm lamp to meet the requirements. Four-color offset printing machine used to print UV offset ink, with three power density 80W/cm lamp, printing speed of 7000 / hour. The flexo printing machine and gravure printing machine are coated with UV varnish. The number of screen lines is 165 line anilox rollers, and one set of 120W/cm lamps has a curing speed of 80W/min. Generally choose to cure faster than the coating speed.
According to the print material temperature resistance. The non-temperature resistant material has a faster curing speed so as to avoid deformation of the material, such as a plastic film, and the coating is cured just after the surface is exposed to light, but the temperature does not reach below and the light is left, so that the material base layer is not deformed. White paper is easy to dehydrate, and it also needs to be cured quickly.

Eight, UV coating viscosity adjustment UV Varnish content is generally required in 92% to 98%, of which few solvents. From the formula to solve the problem of improper viscosity, the high viscosity is easy to achieve, only adding tackifiers, on the contrary is more difficult. The viscosity can also be adjusted by changing the ambient temperature. Generally, the roller and the storage tank are heated to 55 degrees to reduce the viscosity. Another method is to add a diluent, but this approach is not ideal, the thinner hinders the curing, affects the brightness of the film, and the intermediate does not participate in the curing, and is ultimately wasted causing environmental pollution.

Nine, the general UV coating thickness:
Film thickness is related to the following aspects:
1. It is related to the gloss and density of the paper surface. Paper bright, high density, non-permeability need thinner film thickness instead.
2. It is related to the customer's requirements. If you only need to cover the ink, you must be thin. If you want a three-dimensional effect, you need to be thicker.
3. With the polishing machine. It cannot be too thick with an offset press or a convex printer, because the pressure is large, and coating with a three-roller coating machine is not possible because the pressure is small, and the coating can be quantitatively adjusted with a gravure printer or a flexo printer. .
4. It depends on the running speed of the coating machine. Such as flexo, gravure printing machine when the speed is high, oil thin, anilox roller mesh high coating film is thin. If a low mesh is used, the viscous oil cures without leveling and the glazing layer is spot-like and not a film.
Adjust the film thickness according to the above factors. General copper paper surface ink is 1 ~ 4g / square meter, film thickness 1 ~ 4 microns; white version of paper surface with ink 3 ~ 12g / square meter, thickness 3 ~ 12 microns.

X. UV Varnish Consumption The amount of UV Varnish can be determined based on the following factors:
1. Polishing machine structure. For example, the most simple three-roller coating machine, because the roller pressure is small, no uniform ink roller, so the coating amount of varnish is relatively large, and often the coating amount far exceeds the required amount, and the general coating amount is more than 6g/m2. The use of anilox roller coating, the coating amount of 2 g/m2 or less. The amount of enamel coating machine coating 2 ~ 8g/m2. The amount of coating on the screen machine can hit 50 g/m2. General local three-dimensional art glazing, glazing film thickness of about 0.5mm, three-dimensional touch by hand. Glue and convex printing machine coating gloss 1 ~ 3 g/m2.
2. Paper surface brightness. UV glazing should be said to be the icing on the cake, but it is only suitable for paper with high surface brightness, or materials with poor surface absorbability to varnish. If the surface of the material is rough, immediately after the varnish is applied, it will seep into the lower layer, and a bright film will not be formed on the surface, so there is no sense of glossing. The only material on the paper surface is coated paper and white paper can be coated with UV oil. The copper card (glass card) has a very good effect with an oil content of 2 to 3 g/m2. The coated paper is generally coated with about 3 to 5 g/m2 of oil, and the white board is coated with about 5 to 12 g/m2 of oil.





Source: Bison