What is UV ink spray printing ink?
UV ink has a unique curing method, that does not rely on penetration and evaporation and rapid curing, is now widely used by UV inkjet printing. UV ink has three main characteristics: energy-saving drying, the substrate has a wide range of printability (almost all materials can be printed on), fast curing can shorten the subsequent process time.
But UV ink compared to the traditional what easy ink and screen printing process ink prices are high, the cost is too high which directly affects the printing price of UV inkjet printing.
UV printing ink is mainly composed of pre-polymer, active diluent, photosensitizer, color filler and various additives, the properties and functions of each component under.
Prepolymer or light-curing resin and UV printing ink operation suitability and quality suitability such as the transferability of the ink on the printing press, the curing speed of the printed film, the reproducibility of the printing network, the film gloss, adhesion, wear resistance and other closely related. Currently used in the ink more light-curing prepolymer has two types: one is unsaturated polyester, usually a saturated or unsaturated diol and unsaturated or saturated two far acid (anhydride) by condensation of the molecular chain with unsaturated double bond linear polymer compounds; two is the acrylic resin, such as polyester enolate, polyether acrylate, epoxy acrylate, urethane acrylate, etc..
2 reactive diluents
Active diluent in the UV printing ink composition system has both curing cross-linking and solvent dilution of the dual function, its molecules contain photosensitive radicals can be triggered and further prepolymer reflects the cross-linking of active functional groups (such as double bonds), to ensure a reasonable UV printing ink curing dry and take into account other printing quality suitability; at the same time, this type of viscous liquid compounds have a good solubility and dilution of prepolymer, UV printing ink commonly used active diluents are mainly two types, one is a monofunctional compounds, the molecular structure of such compounds contain a vinyl, such as styrene for saturated polyester; the other is a bifunctional or multifunctional compounds, the molecular structure contains two or more vinyl, mainly polyol acrylate Class compounds.
According to Einstein’s law of photochemical equivalence, the energy of photons is inversely proportional to the wavelength, ultraviolet light is usually located in the range of 200nm ~ 400nm continuous spectrum, corresponding to the photon energy of 598 ~ 299KJ/mol, in order to make the ink system in this range of fast and efficient light curing reaction, UV printing ink system in addition to prepolymer and active diluent, but also need to add easy to be light Decomposition or excitation of compounds, called photosensitizers (or sensitizers). This triggers the induction period of polymerization and improves the drying speed of the ink. Photosensitizers usually absorb longer wavelengths of light than the prepolymer and active diluent, decomposition to produce free radicals; or light excitation triggers a secondary reaction to produce free radicals, both of which trigger photopolymerization. Among them, carbonyl compounds are mainly used in UV ink photosensitizers, including ketones and benzoin and its ethers, their common feature is that the molecular structure contains carbonyl groups, and aromatic ketone group; the difference is that benzoin itself through the photochemical action, can trigger the alkene components for polymerization, so both photosensitizers, but also initiators. Benzophenones, after the photochemical action, often need to interact with other molecules to initiate the polymerization of alkene components. Therefore, strictly speaking, it is only a photosensitizer, not an ideal initiator, and must be used in conjunction with other compounds to further initiate the polymerization of alkene components. Nevertheless, the common feature of these two types of photosensitizers is that the carbonyl group in the aromatic ketone group is the first to carry out photosensitization.
4 pigment and filler
Pigment is an essential component of UV printing ink, pigment particles dispersed in the linkage material for printing ink color expression, the addition of pigments will change the rheological properties of the ink, but also on the printing film gloss will have a greater impact. UV printing ink, the addition of pigments will cause UV light absorption, reflection or scattering, and reflection and scattering will reduce the amount of UV light absorption of the ink system, reduce the photosensitizer photoinitiated efficiency, resulting in the ink curing drying speed becomes slower. UV ink commonly used color pigments are benzidine yellow, Hansa yellow, phthalo blue, phthalo green, permanent red, big red powder, etc., achromatic pigments are titanium dioxide, high pigment carbon black, etc.. For the overprinting ink requirements after the color sequence ink layer has enough UV transmittance, to ensure that the following ink layer has enough UV exposure, to avoid the appearance of the table ink dry and the bottom ink does not dry printing failure.
5 Auxiliary agent
UV printing ink in order to improve the printing suitability and quality suitability, in addition to the above-mentioned four components in the composition of the UV ink formula, but also need to add auxiliary agents. UV ink using auxiliary agents with a small amount, a variety of varieties and the characteristics of a specific and efficient. In this selection of its main varieties for overview.
① resist: in order to prevent UV printing ink cross-linking during the storage period, to improve the storage stability of the ink and the addition of auxiliary agents. Commonly used inhibitors are hydroquinone, p-methoxyphenol, p-benzoquinone, etc. These inhibitors do not inhibit the light polymerization reaction, only to prevent the thermal polymerization reaction is added.
② defoamer: this auxiliary agent is used to eliminate the ink in the manufacturing and use of the process of bubbles, mainly for the bottom viscosity of thin ink varieties, such as for gravure printing, flexible letterpress printing UV ink. Commonly used defoamers are silicone oils (F810, FN), silicone acrylate (R2500), etc.
③ leveling agent: used to improve the leveling of the ink layer, reduce the shrinkage of the printed film, and help improve the gloss of the printed film. Commonly used leveling agents are silicone acrylate (R2100, R2200), silicone (Takken 457) and so on.
④ Anti-impact agent: UV printing ink for metal coil printing, printing is completed because the print also shear, bending, stamping and other mechanical processing, printing film in the mechanical processing process is often broken off the film and other failures, in order to improve the performance of the ink against pressure processing, usually using the practice of adding anti-impact agent. UV printing ink using auxiliary agents in addition to the above listed, there are many varieties, such as in order to improve the rheology of the ink, improve the water resistance of the ink, enhance the abrasion resistance of the ink is usually added to the wax Modification, with the progress of science and technology, UV printing ink with auxiliary agents will continue to be introduced.