The Use of Environment-friendly Water-based UV Ink in Outdoor Large-scale Advertising Screen Printing (Part Two)


Third, the water-based UV ink screen printing of the adaptability and process requirements

Water-based UV ink is an ink that cures instantaneously by ultraviolet irradiation and can form a good ink film layer. In screen printing, the materials and technical requirements applicable to water-based UV inks (such as the HU000 series) are as follows:

1. Substrate

Substrates suitable for water-based UV ink screen printing include synthetic paper (such as YUPO), PS, hard PVC, polyethylene materials, paper and cardboard. However, in different substrates, there is also a small amount of water-based UV ink adhesion, scratch resistance, poor flexibility; ink adhesion properties of different substrates are also different, so we must ensure that the ink and substrate printing Good fitness is very important. In particular, synthetic paper and plastics, etc., have a wide variety of products and must be tested for adhesion and other properties before use. Even if the substrates are all paper, the phenomenon of poor adhesion may occur due to the difference in the type of paper and ink and the difference in curing conditions. Therefore, attention should be paid to prepress testing.

2. Screen selection and stretching requirements

Generally choose 140 ~ 150 mesh monofilament wide opening polyester mesh is more appropriate, stretching tension should be controlled at 20N/cm or more. Polyurethane scrapers with a hardness of 70-90 Shore are available for printing, requiring edge sharpening. Since the monomer contained in the ink will cause the swell of the blade, it is necessary to pay attention to checking the use of the blade during use, and to grind or reverse the damaged blade to ensure the quality of the printed matter.

3. The selection of screen photosensitive materials

Can choose solvent-resistant photosensitive adhesive or thin capillary photosensitive film, such as indirect five-star red photosensitive film. When photosensitive emulsion plate is used, the thickness of the photosensitive layer should be controlled at about 4 μm in addition to the yellow polyester mesh, and the surface roughness should be less than 5 μm to improve the sharpness of the dots.

The main points of quality control in screen making are:

1 In order to ensure that small screen dots are not lost during the use of the screen, the screen must be roughened and degreased before the screen is applied and pasted to make the photosensitive adhesive and the screen securely attached, and the small dots are not lost. To ensure that the shades of color are too natural.

2 The color screens used for printing must ensure that the tension is uniform and uniform, otherwise it will cause four-color overprinting, inconvenience, and other ills. Moreover, after screen printing and sticking the photo-resist film, the screen must be completely dried before exposure. Otherwise, in the process of developing or printing, the small dots will be lost in advance and the service life of the screen will be reduced.

3 During exposure, the under-exposure and over-exposure of the photosensitive layer on the screen cannot produce the best screen, so the exposure time of the photosensitive layer must be strictly controlled in the screen production (the optimal exposure time is measured by the exposure scale. ), to ensure that the screen on the small network (printed on the high-profile outlets) can be washed through, the screen on a small network of photosensitive adhesives (printing dark spot) can be attached to the screen.

4 After the exposure of the screen version of the development of quality is very important, the mesh screen version must use a combination of comprehensive development and local development methods, because the small screen is not easy to penetrate the screen, after full-scale printing, if small The outlets have not yet rushed out, and the local “water column” type fill-in for small outlets should be implemented so that the small outlets will be washed through and the high-profile outlets of printed products will not be lost.

After the 5th version of the graphic is developed, it is necessary to check the color separation film and determine the correctness of the screen after the second exposure to improve the service life of the screen.

4. Curing light source

A medium-pressure mercury lamp with a light-concentrating cover is used. The power is 200 W, and the curing transmission speed is about 20 m/min.

5. Pay attention to the use of ink

When mixing inks, try not to mix them with oily inks. If you really need to mix with other types of inks, you must first confirm the fluidity, adhesion, printability, and gelity of the mixed inks. In general, yellow and red water-based UV inks have strong light transmittance to ultraviolet rays, and blue and black (especially black) are weak. Therefore, it is not possible to increase the printing density too much in order to increase the printing effect. Otherwise, the ink may be poorly cured. Easy to wipe off, poor adhesion, and even cause back-side sticky and other faults.

6. Additives and printing techniques

The HU000 series of water-based UV inks are best used with the same series of HU000 product additives, such as HU 1800 thinner, HU 193 regulating paste, HU349 thinning agent, HU350 spot oil and so on. The HU000 series water-based UV inks have a high color density and are best suited for the printing of backlit advertising. When you want to reduce the color density, you can add HU350 spot oil; if you need to adjust the viscosity and leveling, you can add about 8% HU193 conditioning paste or about 2% of HU180 thinner, but before printing it must be with water The base UV ink is fully stirred. In the printing process, if the ink layer is found to be still not thin enough to cause dot gain, the HU349 thinning agent can be added to the first color and the second color ink. Under the same printing conditions, since the water-based UV ink is thicker than the solvent-based ink ink layer, the dot on the negative film can be adjusted before screen printing. When screen printing is performed, select a higher-order number of filaments. Thin screens or single-sided flattened screens that use special UV inks can also be controlled by controlling the thickness of the screened photosensitive layer. Water-based UV inks should avoid direct sunlight during the printing process or screen cleaning process.

7 to control the indoor temperature and humidity when printing

The viscosity of water-based UV inks has the property of undergoing a dramatic change with changes in temperature, and this viscosity change has a great influence on printability and print film thickness. In general, when the ink temperature decreases, the viscosity increases and the film thickness increases. If the viscosity of the ink becomes too high, the permeability of the screen becomes weak, and many printing quality problems such as foaming and blowholes occur after printing. Keep the room temperature constant during printing. Generally 18 ~ 25 °C is appropriate. If the relative humidity in the printing shop is high, some water-based UV screen printing inks will absorb moisture, causing problems such as stickiness and gels. At this time, air conditioners or dehumidifiers can be used to solve the problem.


Source: Screen Printing Industry Author: Qi into