What is UV ink?
UV ink means that under the action of ultraviolet light, the photosensitive substances in the system react chemically to generate active fragments, which triggers the polymerization and cross-linking of the active monomers or prepolymers in the system, so that the system instantly changes from a liquid coating to a solid coating .
Composition of UV ink: It is mainly composed of prepolymer, reactive diluent, photoinitiator, organic dye and auxiliary.
What is the difference between uv ink and ordinary ink?
UV ink is ultraviolet curing solvent-free ink, its drying principle is the same as UV light oil, photosensitive materials receive ultraviolet photons to trigger the polymerization photochemical reaction of prepolymer and diluent. Its reaction time is very short, about 0.1-0.2S, the reaction after the formation of curing ink film layer on the surface. There is no volatile or permeable material during the reaction. Characterized by fast drying speed, good film gloss, friction resistance, but UV ink price is relatively high.
The drying principle of ordinary ink is oxidation, permeation, solvent volatilization within the ink, this several processes take a longer time, with 90% screen ordinary offset ink printing, it takes nearly 20 hours to dry.
Generally printing on flatbed paper presses without adsorptive substrates (such as PVC plastic surfaces, gold and silver cardboard, steel surfaces, etc.) when printing with UV ink. Because these materials if printed with ordinary ink, the previous sheet of ink not dry will rub the back of the next sheet to make the print damage.
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What are the applications of UV printing ink types used by characteristics?
1. Hard uv ink, generally used in sheet types;
2. Soft uv ink is generally used on soft materials;
3. Neutral uv ink is generally used on moderately soft and hard materials.
Some customers of PVC foam board say that it is easy to fall off after printing after buying the board. The same board is no problem when we take it back and hit it. Is it a problem with the ink used for uv printing?
The PVC pattern falls off: first check the cause of the uv ink itself, after printing, touch whether it is completely dry, if not, increase the power of the led lamp; secondly, replace the uv ink, it is recommended to use hard uv ink, which is more suitable for pvc materials; finally, plastic can be used Coating, wipe once before printing.
How to wipe off the UV ink after curing?
1. Use chemical flux to remove and check whether the ink is completely cured. The sooner the solvent is used, the better it can be cleaned.
2. If the ink has been cured completely, drop the solvent on the place where the ink needs to be removed, and wait for 24 hours or 48 hours to remove it.
UV ink formulation
1. Pigment
lType:
Organic pigments (phthalocyanine, azo) are rich in color, bright and good in color;
Inorganic pigments (titanium dioxide, carbon black) are light-resistant, heat-resistant, solvent-resistant and inexpensive;
l Performance impact: The amount of pigment added in the system is 5-20%. According to Lambert Beer’s law, when light-absorbing pigments are added to the system, the total amount of photons absorbed by the photoinitiator decreases.
2. Active monomers
Commonly used monomers:
• Hydroxyethyl methacrylate
•Isobornyl Acrylate
• 1,4-Butanediol diacrylate
• Tetraethylene glycol diacrylate
• Pentaerythritol triacrylate / PETA
• Trimethylolpropane triacrylate / TMPTA
• Ethoxylated pentaerythritol tetraacrylate
• Dipentaerythritol pentaacrylate
• Dipentaerythritol hexaacrylate
Newly developed special dilution monomers:
Dicyclopentadiene methacrylate (dual cure crosslinking)
Lauryl Acrylate (Flexibility, Low Shrinkage)
Alkoxylated tetrahydrofuran acrylates (pigment wetting, low odor, flexibility)
Tricyclodecane dimethanol diacrylate (low shrinkage, yellowing resistance)
Tris(2-hydroxyethyl)isocyanurate triacrylate (high adhesion, abrasion resistance, weather resistance)
3. Photoinitiator
The selection principle of photoinitiator is as follows:
The ultraviolet-visible spectral absorption of the photoinitiator, the emission spectrum of the light source and the minimum absorption of the pigment should match, that is, the wavelength of the strongest emission spectrum of the light source is exactly the maximum absorption of the photoinitiator and the minimum absorption of the pigment.
Cleavage type photoinitiator (type I)
Alpha-Hydroxy Ketone Derivatives
-Suitable for light and white inks
Photoinitiator 184
Photoinitiator 2959
Acylphosphine oxide
– Colored ink, basically no yellowing
Photoinitiator TPO
Photoinitiator TPL
Photoinitiator 819
Hydrogen abstraction type photoinitiator (type II)
Benzophenone and its derivatives
-cheap price
Photoinitiator BP
Photoinitiator OMBB
Thioxanthone and its derivatives
-Suitable for colored inks
Photoinitiator CTX
Coinitiator-H Donor
Photoinitiator EDB
Photoinitiator DMB
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