Compilation of UV ink questions
1. Advantages and disadvantages of UV inks versus ordinary inks? Analysis of ingredients, principles!
Advantages: The many advantages of UV inks are due to their near-100% curing system and instant curing characteristics. The biggest advantages are increased production efficiency, no dry spraying and low VOCs. Other advantages include abrasion resistance, solvent resistance, high overprint rates, low dot expansion, etc.
Disadvantages: 1) special UV consumables are needed; 2) the price is more than 3 times that of ordinary offset printing; 3) UV mercury lamps consume electricity, have ozone and have a heavy smell (consider LED-UV cold light source curing systems); 4) Ink-water balance control is more difficult than offset printing.
Ingredients: UV - polyester acrylic resin, acrylate monomer, initiator, inhibitor, filler, pigment, other auxiliaries, etc. General Offset - modified rosin resin, vegetable oil, mineral oil, pigments, antioxidants, drying agents, other auxiliaries, etc.
Principle: UV irradiation - initiator excitation - double bond crosslinking. Oily - paper penetration and solvent absorption, solvent volatilisation and thickening, resin oxidation and conjugation.
The difference: ordinary offset printing liquidity is very good, the body and bone to maintain also better, especially in the machine printing, ordinary offset printing with the roller temperature, viscosity change trend more moderate, UV more significant, resulting in water and ink balance and emulsification differences.
2. Is the sunlight resistance level of UV inks the same as that of ordinary inks? Same colour comparison.
The sunlight resistance rating is most dependent on the pigment, with only the degree of yellowing varying in the resin.
The main difference between the four colours is in the yellow ink, which can be up to grade 5 for UV and only grade 3+ for normal yellow ink. If the same pigments are used, the sunlight resistance will be closer. Of course UV will be slightly better than ordinary offset inks due to its better water resistance after curing and the presence of photosensitizers.
3. UV fluorescent inks with a sunlight resistance rating and the principle of why they are not sunlight resistant
Fluorescent ink is generally 1-3 levels of sunlight resistance, the principle of fluorescence itself is the absorption of ultraviolet light is easy to produce electron leap and caused, that is, the phosphor is unstable, so in the high intensity of ultraviolet radiation, after the leap is not easy to recover, resulting in decomposition. The temperature resistance of phosphor is also relatively poor, generally the decomposition temperature is below 120℃, while the general pigment is at least 150℃, sunlight resistant ink can reach 180℃ or more. Inorganic pigments are the best in terms of heat resistance, with carbon black and white having the highest resistance to sunlight, and of course the yellowing effect of the resin should also be considered.
4. What information do we need to confirm with the customer if they require sunlight resistance? How does it correspond to the Hang Hua sunlight resistance test results?
1) provide the material; 2) confirm the process: whether varnished or laminated; 3) conditions of use and sunlight resistance requirements; 4) colour range and intensity, preferably with a colour palette.
Please refer to our sunlight resistance information for further details. For outdoor labels, which generally require 1-2 years or more without fading, the highest grade of red and yellow ink "UV 161 SR Series" should be used. For labels requiring less than 1 year, with a red to yellow ratio or concentration of 50% or more, consider "UV 161 Super Lightfast Series".
5. Why do UV inks print dark (compared to normal inks)? How can it be improved?
The main reason for UV printing darkness is caused by printing transferability problems, but of course due to insufficient levelling time and relatively low gloss, it will also feel darker.
The first thing is to improve the transferability of the ink, you can choose the UV HY-BD series which has a relatively slow curing speed and is not suitable for dry rollers, which has better print transferability and gloss to show better printing results. However, the screen expansion of this series will be slightly larger than the 161 series, for example.
Secondly, special UV printing equipment and consumables are used to enhance the gloss by lengthening the distance from the ink set to the UV lamp, air pressure and varnish.
6. Why are UV inks prone to uneven printing when printing? How can it be improved?
You need to improve the wetting of the ink and rubber rollers and improve the transferability of the ink to enhance. The first step is to ensure that the rollers and blankets are correctly selected and have been adequately wetted. The ink type can be selected from a relatively soft range of products, such as the UV HY-BD series for packaging printing and the UV GP-LED series for commercial printing.
7. What are the limitations of matching UV metallic inks to post-processes?
The gold and silver ink can only float to the surface to show the metallic lustre, but it will cause problems such as floating silver and copper, and the surface is prone to non-abrasion, sticky flowers and other problems. It is not suitable for post-processing such as coding and laminating, and if varnished, the metallic lustre will be significantly reduced.
8. If a printer does not have drying equipment when colour matching UV inks, it is not possible to make accurate colour predictions for the colours requested by the customer. How does your company carry out colour confirmation of ink blending?
We are cured to confirm the colour phase, the regular colour is generally close before and after curing, there are changes mainly involving peach, golden red, light blue and special black, etc., with surface light changes in the colour. If 161 series products are used, we have over 1700 spot colour formulas for reference.
9. UV ink residues of harmful substances or the effects of penetration or migration, if the customer packaging is in direct or indirect contact with the product (without foil pouches), what are the recommendations?
National laws and regulations for food contact materials have been enacted, the composition of substances that do not comply with GB9685 must not come into direct contact with food etc. UV inks must be printed on the outer surface of materials with a barrier layer.
The relevant standards for food packaging printing inks are being developed, involving UV inks are mainly partly restricted monomers, initiators, o-benzene and other substances, mainly with reference to Europe, the United States, Nestlé and other relevant standards.
Therefore, printing involving materials with non-barrier layers will not comply with the relevant national standards for food contact materials, and boxes must have a barrier layer inside (aluminium foil bags, plastic bags, etc.). With a barrier layer, the printing process needs to be strictly controlled to avoid back-stick residues and frictional ink loss, and finally by migration testing, requiring specific migration of less than 10ppb and total migration of less than 10mg/dm2 .
If no barrier is available, the appropriate raw materials are selected and used in accordance with the relevant customer requirements and a letter of guarantee is provided. The relevant responsibility is borne by the company itself.
10. What is food-grade UV ink? What are the requirements and testing methods for food grade UV inks?
True food-grade inks are inks that can be eaten, including printing inks for logo text on pills, designs on sweets, cakes, etc.
Food-grade inks for packaging printing should be low migration inks. In addition to the list of components meeting the relevant legal and regulatory requirements, a barrier layer needs to be ensured and then pass the GB4806.X test and the relevant migration tests.
11. Under the same UV drying conditions, why does K ink dry less thoroughly and slower than other colour inks? Reasons and improvement methods.
UV rays are absorbed by the darker black ink, especially if the ink layer is thicker and UV rays do not penetrate the ink layer, or the bottom absorbs very little UV rays. To improve this, a faster curing speed and a higher concentration of special black products are generally used. The curing system uses a combination of LED-UV and normal UV, as LED-UV has stronger penetration and normal UV has better surface curing properties.
12. Why can't I use alcohol-free fountain solution for UV inks?
This is not absolute, a suitable alcohol-free fountain solution can also improve UV printing performance. Offset printing is mainly a matter of water-ink balance and the ink needs the right emulsification to improve printing stability. If alcohol is not added, UV inks are hard when they are first put on the machine, the ink is hard, the emulsification rate is low, and it is more difficult to clean dirty plate situations with IPA-free fountain solutions, and operators tend to keep increasing the fountain water supply. As the machine temperature increases, UV ink viscosity decreases, the body and bones become soft, the emulsification rate will change from low to high, and constantly upwards causing paste version until over emulsification.
The right proportion of IPA can be added to allow a faster emulsification at the beginning stage, so that the water-ink balance is completed quickly, instead of easily causing the situation of big ink and big water. The ratio varies according to the brand of the fountain solution, but it is generally recommended that the IPA is added at around 5%, the fountain solution process PH value is controlled at around 5, and the conductivity is 800-1500.
13. Why is LED-UV more environmentally friendly?
LED-UV lamps are single-band UV lamps, but of course they also have an infrared part, which still has a certain amount of heat. The UV band is mainly in the 365-395nm range, with our main focus on the 385nm high power lamp, which has an electrical power conversion rate of nearly 50%. The ultraviolet light in this wavelength range is the far ultraviolet part, which is not harmful to human beings, animals and plants by direct irradiation, and only causes skin darkening. It does not produce ozone either. Because the ozone excitation band is around 250nm, the deep ultraviolet light within 300nm of ordinary mercury lamps is very strong and therefore ozone is significant and causes direct harm to humans, animals and plants. The UV conversion rate of ordinary UV lamps is only 20% or less, and the life span is only one tenth of that of LED-UV lamps. Mercury is a heavy metal, which is disposed of freely, pollutes soil and water and cannot be degraded. The use of mercury is expected to be completely banned by 2022, so LED-UV lamps are an inevitable trend. Comprehensive advantages.
1) Ozone-free, low heat, very good workshop environment; 2) Long life, very low maintenance costs; 3) Power consumption saving, only 20%~50% of ordinary mercury lamps; 4) Can be lit in areas according to paper size, further energy saving; 5) Modular partial replacement available, further extending life and reducing renewal costs.
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