Composite resins photoinitiation

By contrast, most modem composites cure by a light-activated process. The typical photoinitiator system used is based on camphorquinone (Fig. 3.4) with an aromatic tertiary amine as accelerator [13]. These are sensitive to blue light at 468 nm, and irradiation causes homolytic decomposition of the camphorquinone to form free radicals, which then initiate the polymerization and associated hardening of the composite resin. 

When composite resins were first introduced, their polymerization involved free radical initiation by a combination of benzoyl peroxide with tertiary amine activator, de-hvered in two different pastes, known respectively as base and catalyst. Contemporary composites are visible light-activated one-paste systems and the principal photoinitiator used is camphorquinone [70,80], It is used in conjunction with a co-initiator, typically an amine [81], This latter compound does not absorb hght, but is necessary to react with the fight-activated camphorquinone molecule to generate free radicals and hence initiate the chain polymerization. 

Y.J. Park, K.H. Chai, H.R. Rawls, Development of a new photoinitiation system for dental light-cure composite resins. Dent. Mater. 15 (1999) 120-127. 

The rigid structure of the BOSS cubes can be beneficially used in the development of low-shrinkage dental composite resins. Octafunctionalized methacrylate-based compounds were incorporated in commonly used photoinitiated dental formulations. The study showed that the shrinkage of nanocomposites decreased and the nanocomposites incorporated with BOSS showed improved mechanical properties at low BOSS content [101]. 

A typical formulation of a photocurable composite resin contains four basic components a radical-type photo initiator, an acrylate functionalized oligomer, a reactive diluent and the clay mineral filler. The photoinitiator is usually an aromatic ketone which cleaves into two radical fragments upon UV exposure. The telechelic oligomer consists of a short polymer chain (polyurethane, polyether, polyester) end-capped by the very reactive acrylate double bond. An acrylate monomer is generally used as reactive diluent to reduce the resin viscosity. Figure 7.2 shows some typical compounds used in UV-curable acrylic resins. Different types of phyllosilicates were selected as mineral filler an organophilic clay (Nanomer I-30E from Nanocor), native hydrophilic clays (montmorillonite KIO and bentonite) and a synthetic clay (beidellite). 

Materials. The radical-type photopolymerizable formulation consisted of a mixture of hexanediol diacrylate (HDDA from UCB) and a polyurethane-diacrylate (Actilane 20 from Arkros). A bis-acylphosphine oxide (BAPO from Ciba) was used as photoinitiator at a typical concentration of 1 wt %. The cationic type photopolymerizable resin consisted of a mixture of the divinylether of triethyleneglycol (RapiCure DVE-3 from ISP) and a divinylether derivative of bis-phenol A (DVE-BPA). The cationic photoinitiator (Cyracure UVI-6990 from Union Carbide) had a composition of 50 wt % of mixed triarylsulfonium hexafluorophosphate salts and 50 wt % of propylene carbonate. The BAPO initiator... 

Alkenyloxystyrene monomers such as 4-allyloxystyrene are useful components of photocured cationically polymerizable compositions. Used alone or in combination with divinyl ethers they provide low viscosity formulations, which are excellent solvents for commercial onium salt photoinitiators. Photocuring rates are comparable to vinyl ether monomers and the initially photocured alkenyloxystyrene polymers may be further heat processed to yield crosslinked phenolic type resins having outstanding thermal resistance properties. The new materials have good adhesive properties and are potentially useful where a combination of ease of processability and high performance is required. 

See also Epoxy coatings Epoxy chalcone, 10 450 12,13-Epoxy-cis-9-octadecenoic (vernolic) acid, physical properties, 5 35t Epoxy coatings, 10 436 450 17 845. See also Epoxy can coatings for corrosion protection, 7 199 markets for, 10 442-449 performance of, 10 423 waterborne, 10 439 Epoxy composites, 10 450, 451 Epoxy compounds, photoinitiated polymerization of, 23 716 Epoxy content analysis, 10 385 Epoxy cresol novolac (ECN) resins, 10 367, 369... 

On-aircraft repairs of composite using a rapid-cure resin system of composite component with UV light irradiation based on TRI patenP have been developed by the U.S. Air Force Research Laboratory. Alternating layers of the acrylate-based resin system and woven fiberglass (the widely used wet la)mp procedure) are applied to fill the hole and form a UV curable composition. The width of the patch can be up to 2 ft (0.6 m) and the depth as much as 0.2 in. (5 mm). The cure time using a 400 W UVA lamp is reported to be 20 min. Although it is essentially a depot repair, it can be done field when necessary to return an aircraft to service. Because of the necessity to cure relatively thick repair patches, Us-acylphosphine oxide was used as a photoinitiator. An example of the patented UV curable resin system used for the repairs is in Table 11.1. 

Multifunctional photoinitiators, (II), were prepared by Sommerlade et al. (2) for radiation-curable dental compositions using UV light. A Norrish Type visible-light-sensitive multifunctional ketopinic amide derivative attached to a modified amino-silanated resin, (III), was prepared by Condon et al. (3) and used as a macroinitiator in dental applications. 

The third type of composition is exemplified acrylate- and methacrylate-ester derivatives of epoxy resins combined with a photoinitiator 1. Epo prepolymers (e. g., glycidyl methacrylate-allyl glycidyl ether copolymers or Ciba ECN 1299) combined with a photosensitive aryldiazonium compound (e.g.,... 

Compositions having, upon polymerization, good adhesion and sealing properties were described by Nippon Soda [137] in 1986. The composition comprised an epoxidized polybutadiene, epoxy resin, onium salt, and sensitizer. Grace Japan [138] patented the simultaneous photopolymeriza-tion of epoxy compounds and compounds containing unsaturated groups by the use of free radical photoinitiators and sulfonium salts in 1986. 

Much has already been published concerning the composition of energy-curable resin systems for use in coatings and inks, and the basic approach to the development of such vehicles is well known (Refs. 1, 2, 3). A typical formulation contains an oligomer, which may or may not contain reactive functional groups (e.g., double bonds), a cross-linking agent, a reactive diluent (for viscosity control), and a photosensitizer or photoinitiator. 

The third type of composition is exemplified by acrylate- and methacrylate-ester derivatives of epoxy resins combined with a photoinitiator 1. Epoxy prepolymers (e. g., glycidyl methacrylate-allyl glycidyl ether copolymers or Ciba ECN 1299) combined with a photosensitive aryldiazonium compound (e.g., -nitrobenzenediazonium hexaflourophosphate) (38,39) 2. Epoxy prepolymers (e.g., a diglycidyl ether of disphenol A-(3,4-epoxycyclohexyl)-methyl-3,4-epoxycyclohex-anecarboxylate-alkyl glycidyl ether mixture) combined with a photosensitive aryldiazonium compound (e.g., -chlorobenzenediazonium hexaflourophosphate) and l-methyl-2-pyrrolidone gelation inhibitor (40) ... 

Sample Preparation. Photohardenable formulations based on TMPTA in combination with other reagents including photoinitiators (Quanticure ITX or 7-diethylamino-3-cinnamoyl coumarin, depending on the specific experiment) and colorless dye precursors developable upon contact with acidic resin coated paper were used as a test composition. 

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