Composition of UV curable inks mainly are photopolymerization prepolymer, photosensitive monomer, photopolymerization initiators, organic pigments and additives. Photoinitiators in inks is a compound vulnerable to light, after the absorption of light to stimulate free radicals, energy transferred to the light sensitive elements or photo-Crosslinking agents to make the UV ink occurs UV-curing reaction.
Different pigments have different characteristics to light absorption, reflection and scattering, so the degree of impediments to UV curing is different. Most pigments has certain transmission area in part UV light and visible range, it is called "spectral window" of this pigment. Photo-initiators in this window can fully absorption UV light radiant energy, therefore, make sure the window of location is very important to the selection of right of photo-initiators. In other words, photoinitiator should match with pigment in ink system, and it is in the range of the pigments on the weak absorption wavelength of UV light. So, the use of UV inks should careful observation the relations of pigment and UV absorption spectrum.
Prepolymer is the most important component of the UV ink, its performance on the nature of the curing process and the curing membrane plays a decisive role. Most commonly used oligomers in UV-curing inks are epoxy acrylate, urethane, polyester acrylic acid, alkali-soluble acrylic resin and so on.
Reactive diluents are also called Crosslinking monomer. It is a kind of unsaturated groups (such as the double bond) of small molecules compounds. It can cross-linked with oligomer under light and its molecular weight of about hundreds of thousands of. Add reactive diluent to viscous prepolymer is to regulate the viscosity of UV-curable inks, control curing crosslinking density of UV-curable ink and improved physical and mechanical properties of the cured film, such as flexibility and hardness. There are several commonly used diluent: triethylene glycol diacrylate (TPGDA), three shrink tetraethylene glycol dimethyl acrylate (TEGDA), trimethylol triacrylate (TMPTA).
Photo-initiator is the main component of any UV curing system, usually it breaks down into free radicals and induced polymerization and cross-linking at a wavelength of 200~400nm. Add a small amount of photopolymerization initiators in ink and exposed to UV light. UV-curable inks photoinitiator generally can be divided into crack initiator, hydrogen-initiator and cationic photoinitiators.
Inhibitor is an substance that can rapidly function with free radicals, slows or inhibits undesired chemical reaction. It used to prolong the storage period of certain monomers and resins, also known as polymerization terminator, it includes the inhibitor and the agents. The commonly used inhibitors are hydroquinone, p-methoxy phenol, etc.
Organic pigments and additives
Pigments also plays a significant role in the UV ink, it also has a direct impact on the characteristics of the ink. According to their origin and chemical composition, it is divided into organic and inorganic pigments. Ink additives are used to adjust the ink and make it suitable to different printing conditions of auxiliary materials. There are many kinds of ink additives. The commonly used are the withdraw of the adhesive, sub light agent, drying agent, anti-drier, diluent, rubbing agent, varnish oil, varnish, etc. If you have interest in UV curable inks and the commonly used chemicals, please follow us in Linkedin here or visit www.okchem.com!