UV Curing Ink Development Overview (2)

Third, the comparative advantage of UV ink and traditional ink

In general, UV-drying inks have greater abrasion resistance than conventional solvent-based or epoxy-based inks. The best example is the symbol on each key on the computer keyboard, which are all printed with UV ink. A well-known large company once experimented with using a mechanical “finger” to repeatedly punch a keyboard printed with a UV ink and a keyboard printed with a conventional ink. As a result, the keyboard symbol printed with a traditional ink was worn out about 100 to 2 million times. However, the keyboard symbols printed on UV inks wear out only about 13 million times. The abrasion resistance of UV inks is 1300% of that of conventional inks. Not only that, but also its drying speed is greatly improved compared to conventional inks, from the original 7 minutes to 15 seconds, saving 96% of the time.

UV inks also have extremely high solvent resistance after drying. This solvent resistance results in part from the high crosslink density (macromolecule weight) of the crosslinked dry ink layer. The higher degree of cross-linking makes it impossible for the molecules to separate and dissolve from each other under the effect of the solvent. In addition, UV inks can also be used with some solvent-resistant chemicals.

For the purpose of comparison, we look at the situation after replacing the epoxy ink with UV ink. First, do not mix the ink before use. Second, of course, it is time-saving because the epoxy-based ink needs to be dried for a long time under a certain high temperature condition, and the UV ink is almost instantaneously dried. This is accompanied by the additional advantage of reducing the damage of the ink layer caused by heating. UV inks also save a lot of dry space.

The more characteristics and comparison of UV inks and traditional inks are shown in Table 1.

Category UV ink Traditional ink (epoxy type)
Average Labor Value/Unit 0.001 USD 0.12 USD
Drying time/unit 2-4s 10 min-8h
Average power consumption (kWh/unit) 0.001 0.2
Drying site 1-3 square feet (1 square foot = 0.093 square meters) 2-20 square feet
Ink price $50/lb (1lb = 454g) $28/lb
Solvent content 30% 60%
Drying system funds 0.5-1 million US dollars 0.3-1 million US dollars

Fourth, the use of UV ink

1. Indoor temperature adjustment

UV inks have the property that their viscosity changes drastically as the temperature changes, and this viscosity change greatly affects the printability and the print film thickness. In general, when the ink temperature decreases, the viscosity increases and the film thickness increases. The viscosity of the ink becomes too high, the permeability of the screen is degraded, and the printing result of foaming and many pores is generated. Therefore, keep the room temperature as constant as possible during printing. Generally 18 ~ 25 °C is appropriate. Some inks absorb moisture when the temperature at the printing site is high, and problems such as thickening and gelation occur. At this time, air conditioners or dehumidifiers can be used.

2. When a normal colored ink is used as a screen printing plate, a plate with a thickness of 300 mesh or more and a photosensitive resist thickness of 10 μm or less is used. The ink film thickness printed under this condition is 10 to 12 μm. The printing area can reach 70-90 m2/kg. When printing is free of erotic paint, a thick mesh effect can be printed using a low-mesh version, and a screen can be used depending on the application.

3. The blade uses a polyurethane blade with a hardness of 65 to 80, and the edges are sharpened. The monomer contained in the ink causes the blade to swell, and it is necessary to carry out the necessary treatment such as grinding or reversal of the blade.

4. Viscosity adjustment After fully stirred, remove from ink tank and print directly. Depending on the application, if it is necessary to reduce the viscosity of the ink, a thinner can be added within 10%. Conversely, if it is necessary to increase the viscosity, you can mix in matt varnish (high viscosity, viscosity increase) or add JA-244, JAR-20 and other powder matting agent, after printing and use after mixing.

5. Concentration Adjustment When adjusting the concentration, you can add clear varnish or colorless concentration adjuster.

6. The effect of light During the printing process or the plate cleaning process, avoid direct sunlight on the screen printing ink. Fluorescent light, as long as the distance is not very close, generally no problem.

7. Standard Curing Conditions Each series of inks has its own standard curing conditions. Reference should be made to the ink product specification.

8. The curing conditions for the preliminary printing of the preliminary test vary depending on the printing material and the printing conditions. UV radiation from different manufacturers and models can also cause differences in curing. Therefore, it is necessary to perform preliminary tests under the same conditions as the printing line to determine the curing conditions. The procedure for preparing for the test is as follows:
a. After printing ink on printing material, pass UV irradiation machine under standard conditions;
b. Testing of remaining traces, adhesion, scratching, and flexural properties on the printed surface;
c. If the test results are not satisfactory, the conditions of the illuminator need to be adjusted until satisfactory results are obtained. During the test, it is recommended to use a UV accumulating light meter for measuring the amount of light.

9. Printing warm up

When printing on a material that does not easily adhere, the ink is preheated before it is irradiated with UV after printing, and preheating is performed for 15 to 90 seconds using near-red lines, far infrared rays, etc., and the adhesion is greatly improved.

Five, UV ink printing notes

1. For UV inks, yellow and red ultraviolet light are generally easier to transmit, and blue and black, especially black, are hardly transparent. Therefore, if the printing density is increased too much in order to increase the printing effect, poor curing, ink wiping off, poor adhesion, and even a negative-stick roller may occur. In the UV printing, special attention should be paid to the printing density of the black ink.

2. Among various base materials, there are also a small amount of base materials that are poor in adhesion to UV ink, scratch resistance, and flex resistance. Especially in the base villages of synthetic paper and plastics, there are many varieties, and some are also divided into substrate surface treated and untreated. The adhesion properties of inks to various substrates are also quite different. Therefore, it is very important to select suitable substrates for UV inks or to select inks suitable for the substrates. UV inks are used for paper and plastic, and they are also divided into several types for plastic UV inks. Be sure to test adhesion and other properties before use.

3. If no reflector is installed, approximately 80% of the UV light does not affect the substrate due to diffusion. Therefore, the UV lamp must be equipped with a reflector that reflects and focuses on the direction of the substrate. The importance of the reflector cannot be ignored. Reflectors must be clean and well maintained to maintain the same new features. Some paper dust or dust adhered to the reflector will affect the efficacy of UV light reflection. When not using a UV lamp, the UV lamp cover should be closed to prevent dust.

4. Do not mix with oily ink. If it must be mixed with other inks, you must confirm the fluidity, adhesion, printability, and degree of solidification of the ink before mixing. UV inks mixed with gold and silver inks and general UV inks will cause deterioration in fluidity, solidification, increased speed, and poor brightness. Therefore, the mixed ink should not be stored for a long time. If the ink is stored at a high temperature, solidification, hardening, etc. may occur, and the UV ink should be stored in a dark place below 25°C. In particular, gold and silver inks are more prone to coagulation and weaker brightness than normal UV inks, and therefore do not store for a long time.