Questions about UV Ink - 2019
1. What are the advantages and disadvantages of UV ink and ordinary ink? As well as composition and principle analysis!
UV advantages: The advantages of UV ink benefit from its nearly 100% curing system and instantly curing characteristics. In addition to abrasion resistance, solvent resistance, high ink trapping and low web expansion, the biggest advantage is to improve production efficiency, no need to spray powder and low VOCs.
Disadvantages: 1) Special UV consumables are required; 2) The price is more expensive than conventional offset printing ink; 3) UV mercury lamp consumes electricity, produce ozone and generate heavy odor (consider LED-UV cold light source curing system); 4) Controlling ink-water balance is more difficult than that of conventional offset printing.
Ingredients: UV-polyester acrylic resin, acrylate monomer, initiator, polymerization inhibitor, filler, pigment, other auxiliaries, etc. Conventional offset printing - modified rosin resin, vegetable oil, mineral oil, pigment, antioxidant, desiccant, other auxiliaries, etc.
Principle: UV irradiation - initiator excitation - double bond cross-linking. Oily - Paper penetrates and absorbs solvent, solvent volatilizes and thickens, and resin oxidizes conjunctiva.
Difference: The fluidity of conventional offset printing is very good, and the body of ink is well maintained. The viscosity of conventional offset printing change trend is moderate while the viscosity of UV changes more significantly with the increase of roller temperature especially when printing on the machine. The latter result in a large difference in ink-water balance and emulsification.
2. Is the light fastness grade of UV ink the same as that of conventional ink? Same color contrast.
The light fastness grade has the greatest relationship with the pigment, and the resin aspect only has differs in the degree of yellowing.
Yellow ink has the largest difference in light fastness among the four colors. UV yellow ink can reach grade 5 of light fastness, while conventional yellow ink has only grade 3+. The light fastness will be similar if the same pigment is used. Due to the good water resistance after curing and the presence of photosensitizers, the UV light fastness will be slightly better than that of conventional offset printing ink.
3. What is the light fastness grade of UV fluorescent ink, and why it’s weaker?
The light fastness grade of fluorescent ink is generally 1-3. The fluorescence itself is caused by electronic transition after absorbing ultraviolet rays, that is, the fluorescent powder is unstable. Thus, it is decomposed and not easy to recover after transition under high-intensity ultraviolet radiation. The temperature resistance of fluorescent powder is relatively poor. Generally, its decomposition temperature is lower than 120 °C while that of the general pigment is at least 150 °C or more, and that of the lightfast ink can reach 180 °C or more. Inorganic pigment has the best heat resistance, and carbon black and white have the highest light fastness. Of course, the yellowing effect of the resin should also be considered.
4. If customers require light fastness, what information do we need to confirm with the customers? How does it correspond to the results of the light fastness test of Hangzhou Toka?
1) Provide substrates; 2) Confirm the technology: whether to varnish or film laminating; 3) Application conditions and light fastness requirements; 4) Color system and concentration (It is best to provide color swatches).
For other information, please refer to our company's lightfast instructions. When it comes to outdoor labels, it is generally required that the color will not fade for 1-2 years or more. The highest grade of "UV 161 SR series" ink should be used for red and yellow. If the proportion or concentration of red and yellow is more than 50% within 1 year, "UV 161 SL series" can be used.
5. Why UV ink looks dark when printed (compared with conventional ink)? How to improve?
The main reason for the darkening of UV printing is about transferability. Moreover, insufficient leveling time also leads to low gloss.
First of all, please choose the UV HY-BD series which is relatively slow in curing speed and not easy dry on rollers to improve the transferability of ink. It has better printing transferability and gloss, and to get better printing results. However, the dot expansion of this series will be slightly larger than that of the 161 series.
Secondly, please use UV specialized printing equipment and consumables to improve the gloss by lengthening the distance from the ink set to the UV lamp, air pressure, varnishing and etc.
6. Why is it easy to print uneven when UV ink printing? How to improve?
It is necessary to improve the wettability of the ink and the rubber roller to improve the ink transfer. You should ensure that the rubber roller and blanket are selected correctly and have been fully wetted. The ink type can be selected from relatively soft series products, such as UV HY-BD series for packaging printing, and UV GP-LED series.
7. What are the limitations of UV metal inks and post-process matching.
Gold and silver ink can show metallic luster only when it floats to the surface, but it will cause problems such as floating silver, floating copper. The surface is prone to problems such as non-wear-resistant and sticky flowers. It is not suitable for post-processing such as coding and lamination and the metallic luster will be significantly reduced after varnishing.
8. If the printer does not have drying equipment when matching UV ink, it is impossible to accurately predict the color required by the customers. How does your company confirm the ink color?
Our company always confirms the color shade after curing. Regular colors are generally close to each other before and after curing except colors with surface light changes such as pink, warm red, reflex blue and conc. black. Our company can share you HHC 1700 colors' formula table for reference based on UV offset series.
9. What is the impact of residues, penetration or migration of harmful substances of UV ink? If customers directly or indirectly contact packaging products (without aluminum foil bags), what are your suggestions?
The national laws and regulations for food contact materials have been promulgated. The material components that do not meet GB9685 shall not be in direct contact with food, etc. UV ink must be printed on the outer surface of materials with a barrier layer.
Relevant standards for printing inks for food packaging are being formulated. Monomers, initiators, phthalates and other substances related to UV ink refer to relevant standards in the United States Europe and Nestle.
Therefore, it will not meet the relevant national standards for food contact materials to print non-barrier layer materials. There must be a barrier layer (aluminum foil bag, plastic bag, etc.) inside the packaging box. Under the premise of a barrier layer, the printing process needs to be strictly controlled to avoid back sticking residue and friction out of ink. Finally, the specific migration is confirmed by the migration test to be less than 10 ppb, and the total migration is less than 10mg/dm2.
Please select and use suitable raw materials according to the relevant requirements of customers and provide guarantee letter if there is no barrier layer. , The relevant responsibility shall be borne by the enterprise itself.
10. What is food-grade UV ink? Requirements and testing methods for food-grade UV inks?
Real food-grade ink is edible, including logo text on pills, patterns on candy and cakes.
Food-grade ink for packaging printing should be of low migration. In addition to the component list meeting relevant laws and regulations, it is necessary to ensure that there is a barrier layer, and then pass the test of GB4806.X and related migration tests.
11. Under the same UV curring conditions, why does K ink dry less thoroughly and slower than other color ink? The reason and how to improve it.
Ultraviolet rays are absorbed by dark black ink, especially when the ink layer is thick. The ultraviolet rays cannot penetrate the ink layer or the bottom absorbs very little ultraviolet rays. The improvement method is generally the use of special black products with faster curing speed and higher concentration. The curing system adopts a combination of LED-UV and conventional UV because that LED-UV has stronger penetration yet conventional UV has better surface curing performance.
12. Why can't UV ink use alcohol-free fountain solution?
This is not absolute. UV printing performance can be improved by a suitable alcohol-free fountain solution. Offset printing is mainly to consider the ink-water balance because that ink needs a suitable emulsification can improve printing stability.. When UV ink is just on the machine, the ink is hard at a low emulsification rate without alcohol. It is more difficult for the fountain solution without IPA to clean the dirty plate, and the operator tends to continuously add the fountain solution. The viscosity of the UV ink decreases, the body bone becomes soft with the temperature of the machine increases. The emulsification rate will increase from low to high, and it will continue to cause the greasing problem until it is over-emulsified.
When IPA is added at an appropriate ratio, emulsification occurs at the initial stage. The water-ink balance can be achieved quickly. On the contrary, it is not easy to cause a large amount of ink and water. This ratio varies in the brand of fountain solution. It is generally recommended that the IPA addition ratio is about 5%, the pH value of fountain solution is at about 5, and the conductivity is 800-1500.
13. Why is LED-UV more environmentally friendly?
The LED-UV is a single-band ultraviolet lamp including infrared part, but there is still a certain amount of heat. Its ultraviolet band is mainly in 365-395 nm. Our company mainly promotes 385 nm high-power lamps at the electric power conversion rate of about 50%. Ultraviolet rays in this band are far-ultraviolet rays. Indirect irradiation is not harmful to human body, animals and plants, merely causes skin to darken. It does not produce ozone because that the excitation band of ozone is around 250 nm. However, the deep ultraviolet rays within 300 nm of conventional mercury lamps is very strong, Therefore, ozone is significant and causes direct harm to human body, plants and animals. The ultraviolet conversion rate of conventional UV lamps is only less than 20%, and the lifespan is only one tenth of that of LED-UV lamps. Mercury is a heavy metal. If it is disposed of at will, it cannot be degraded and pollutes soil and water sources. It is expected that the application of mercury will be completely banned in the future, so LED-UV lamps are an inevitable trend. Comprehensive advantages:
1) Better workshop environment without ozone at low heat; 2) Long service life and extremely low maintenance cost; 3) The electricity consumption is only 20% - 50% of the conventional mercury lamps; 4) According to paper size, regional lighting is available for further energy saving; 5) Modular local replacement is possible to further extend service life and reduce update costs.
