Offset UV ink composition and application (2)

3. Precautions when using ultraviolet (UV) ink for offset printing

1 When blending UV inks, the photocurable inks can be blended with each other, but cannot be mixed with ordinary inks. When printing, when ordinary ink is changed into ultraviolet ink, it is necessary to use a special cleaning agent to thoroughly clean the printing part of the machine, otherwise there will be poor ink drying and bad ink.

2 UV ink auxiliary materials are mainly remover, driers, hardeners, thinners and so on. The main function of the dissolving agent is to reduce the viscosity of the ink. The amount of the dissolving agent is generally 5% of the ink. Too much will cause the ink adhesion to decrease. The role of the driers is to accelerate the curing speed of the ink. The amount of the ink is generally ink. 2%, the role of hardener is to enhance the wear resistance of the ink, the amount of ink is generally 5% to 10%; the role of the diluent is to increase the flow of the ink, the amount of ink is generally 3% to 5%, the amount of Too much will cause poor drying of the ink film.

3 ink is full of the test method: the back of the print should be clean, no dirty, hand touch ink film is not sticky; with the thumb pressure under the pressure of 50N pressure, ink film no indentation, not broken; with nails hard strokes Ink film, no scratches.

4. Offset UV (UV) ink printing process requirements

1 color sequence arrangement: UV offset color arrangement problem is more complex, due to different colors of ultraviolet photon absorption is different, so the drying rate of different inks are not the same. Magenta ink has the best UV transmittance, followed by yellow ink, blue ink, and black ink. Since the black ink is a physics full absorption spectrum, white ink is a total reflection spectrum, all affect the absorption of ultraviolet light by the photosensitizer, thus affecting the drying speed, so its color arrangement should be white, black, cyan, yellow, product The red ink absorbs as many photons as possible in the light with poor light transmittance and enhances its curing effect. Such color arrangement is particularly effective in monochrome or two-color printing. Because this is equivalent to adding a photo-curing opportunity to white ink and black ink, the drying effect is naturally good; in multi-color printing presses with multiple sets of UV lamp drying devices, this color sequence arrangement is also reasonable; In the case of color printing, the line or text version should be printed first. The dark inked, small-size field version should be printed first, and the large-area field version should be printed. This arrangement can achieve the highest ink volume and fuller color, and it can also avoid large prints. The ink film of the area was smeared and scratched.
2 fountain solution: multi-color offset printing machine with alcohol dampening device, to replace the bucket fluid to a special UV bucket fluid, alcohol does not change. In monochrome offset printing, alcohol can be added to the water to reduce the amount of water, reduce the emulsification of the ink, reduce the surface tension of the ink, and increase the drying speed of the ink. The cleaning should be cleaned with a special UV car wash water. If there is no special UV car wash water, the effect will be good with absolute ethanol or xylene.

3 printing plate: As UV ink and UV car wash water corrosive, ordinary PS version of the printing force is very low, generally around 1000 to 2000 India, so use a special UVPS version or baked ordinary PS version. In the case of a temperature of 250° C., a conventional PS plate dried according to a conventional method needs to be baked for 10 to 15 minutes, and a CTP plate also needs to be baked for 10 to 15 minutes.

Selection of 4UV lamps: experiments proved that when the printing speed is 300 rpm, three 8KW UV lamps are used; when the printing speed is 6000 to 8000 rpm, six 8KW UV lamps can be used to complete the print dry. When the drying effect is not ideal, a photosensitizer may be added as appropriate, and the amount added depends on the degree of drying. UV curing has an effective wavelength range of 200 to 400 nm. The wavelengths of some light sources in the pressroom are also within this range, which can cause the surface of the ink to slightly cure. Therefore, the effect of ambient light on the drying of UV inks should be taken into account.

Due to the special drying method of UV ink, it is suitable for printing absorptive and non-absorbing materials and other special materials, and the printing effect is excellent, and the printing performance is stable. With the resolution of UV printing technology, the future UV offset printing will be Have more room for development.