Radiation-curing systems

Radiation curing is a technology which uses electromagnetic (mainly UV) or ionizing (mainly accelerated electrons) radiation to initiate a chain reaction in which mixtures of polyfunctional compounds are transformed into a cross-linked polymer network. 

Resin Systems. Radiation-curable resin systems can be classified as follows  

The polymerization of all these systems can be divided into initiation, propagation, and termination steps. The initiation step involves generation of a reactive species (free radical or acid). During irradiation with UV light, the reactive species are formed by chemical decomposition of a photoinitiator. In electron-beam (EB) curing, reactive species (radicals) are generated by interaction of accelerated electrons with organic compounds. 

In systems 1-4 radical polymerization takes place. Decomposition of the photoinitiator (e.g., benzoin and its derivatives) leads to formation of free radicals which react with the carbon-carbon double bonds. In system 5 acidic reactive species are formed which react with cycloaliphatic epoxy compounds and vinyl ethers to form a cross-linked network. Sulfonium, and iodonium salts are used to initiate this cationic polymerization, a typical example is PhjS PFg.  

Polyester-styrene resins have a low raw material price and are used in wood finishing. Disadvantages are the presence of volatile styrene and the low cure speed. Products with methacrylic groups are used where line (cure) speed is less important, mainly in combination with acrylates in special end uses (e.g., in the electronics industry and in photopolymer printing plates) to improve adhesion or to obtain specific physical properties. Thiol- thiene mixtures can lead to very flexible cured films but their odor seriously limits their use. 

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Radiation cure system. Other addition reaction cure systems that have emerged in recent years are the ultra-violet (UV) and electron beam (EB) radiation cure systems. The development of these systems has been prompted by the ever-increasing need for fast cure rates and low cure temperatures. The U V cure system... 

The tensile strength of NR compounds in the presence of cross-link promoters such as dichlorobenzene is increased as compared to the sulfur-accelerator and peroxide-curing systems. The retention of the maximum tensile strength at elevated temperamres is greater for radiation cured than for chemically vulcanized NR [326,327]. Also reported are a higher abrasion resistance [328] and a lower flex life in the case of radiation-cured system. Effect of phenoxy ethyl acrylate (PEA)... 

Recently, hot melt PSA systems have been introduced and radiation curable PSA systems are at the commercial development stage. High solids (50%-70% by wt.) nonaqueous dispersion acrylic PSA systems have also been reported(1). Unlike the hot melt and radiation cured systems which require new capital outlay in coating head and/or curing (drying) equipment, BFG has developed PSA systems, based on Hycar 2100R reactive acrylic liquid polymers and isocyanate terminated prepolymer, which can be processed at 80% solids (by wt.) with equipment presently used in the PSA industry, namely, the reverse roll and knife-over-roll coater. 

TABLE 16. Functional siloxane radiation cure systems... 

Cellulose acetate butyrate is beneficial in radiation-curing systems. CAB 551-0.01 with its high butyryl content and low viscosity is soluble in many vinyl monomers... 

Comprehensive information on all paint systems and binders, pigments, fillers, and additives has been given in individual chapters. Modern, low-emission paints such as high-solids paints, water-borne paints, powder paints, and radiation-curing systems are also discussed in detail. 

Uses Filler for polyolefins, silicone rubber, radiation-cured systems, road marking paints... 

Uses Monomer for prod, of thermosetting resins for protective coatings or top coatings for leather, metal, and other substrates crosslinking agent in radiation-cured systems, for photoresists, latex, sol n. coatings Features Bifunctional self-crosslinking Cylink NBMA [Cytec Ind.)... 

Uses Adhesion promoter for radiation-curing systems, many paints to metallic, mineral, and plastic substrates Properties Gardner 2 vise, liq. dens. 1.1 g/cm (23 C) vise. 8000 mPa-s-(23 C) m.p. 60 C acid no. 18-20 hyd. no. 16 50% solids in tripropylene glycol diacrylate Use Level 5-15% of binder... 

Chem. Descrip. Amorphous hydrated siiica CAS 7631-86-9 EiNECS/ELiNCS 231-545-4 Uses Matting agent in coii and can coatings (> 0.75 mii), generai indus-triai coatings, high soiids systems (> 0.75 mii), water-based coatings, radiation-cured systems (> 0.75 mii)... 

Chem. Descrip. Hexanediol diacrylate CAS 13048-33-4 EINECS/ELINCS 235-921-9 Uses Monomer, thinner for radiation-curing systems, paints, varnishes Features Reactive Laromer POEA [BASF AG]... 

Chem. Descrip. Tripropylene glycol diacrylate CAS 42978-66-5 EINECS/EEINCS 256-032-2 Uses Thinner for radiation-curing systems Features Reactive Laromin A327 [BASE AG]... 

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