Light curing resin systems

Specialized Light Curing Resin Systems for Fabrication of Inflatable Rigidizable Structures... 

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. 

Calcium hydroxide can be used as a supersaturated solution, as chelate cements and as a light-cured resin (in UDMA systems). 

The resin matrix of dental materials has important influence on the chemical and physical properties of light cure resins. The organic formulations also include photoiniti-ating systems that absorb light. From there free radicals start the conversion of the oligomer blend to a polymeric cross-linked network. Camphorquinone (CQ) is widely used in dental resin mixed with an amine. However, CQ is a solid, yellow compound with an unbleachable chromophore. 

Other cycloaliphatic diamines such as isophorone diamine, bis-p-aminocyclohexylmethane and 1,2-diaminocyclohexane are used as epoxy resin curing agents for both ambient and heat cured epoxy resin systems. While they have advantages, such as light color and good chemical resistance, they provide rather sluggish cure rates at low temperatures. 

This paper discusses our analyses of two such specialized resin systems and the development of models that will allow us to predict the time required to cure given a particular set of light intensity and temperature conditions. 

The cure of the free radical resin systems was conducted using high intensity UV LEDs. To ensure safety of the analysis system and to improve reproducibility of the data, our DSC system was modified further with respect to the experiments described above. Ideally, the modified system would be flexible to evaluation of many different light sources (1), and such that the light sources could be positioned reproducibly relative to the sample pans in the instrument (2). 

The area of ultra-violet curable resins has undergone considerable growth during the last 15 to 20 years. Useful resin systems which can be cured by ultra-violet light initiated free radical mechanisms can be classified as follows ... 

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. 

B. Ozturk, A.N. Ozturk, A. Usumez, S. Usumez, F. Omer, Temperature rise during adhesive and resin composite photopolymerization with various light curing systems. Open Dent. 29 (2004) 325-332. 

The reason that the designation resin-modified is preferred to light-cured (or light-curable ) is that these latter terms incorrectly imply that the characteristic acid-base reaction is initiated by irradiation with light. It should be noted, however, that unfortunately this term has been widely used for these materials, including in the first two scientific papers describing the properties of the first commercially successful formulation [3,4]. The option dual-cure is rendered inappropriate because of the possibility of tri-cure formulations, where the monomer is polymerized both by photo-initiators and two-component free radical initiators, both of which complement the acid-base cure process. Consequently, it is possible in principle to have a dual-cure material in which there is no acid-base reaction, and the system is not a giass-ionomer at all. 

For light-cured materials, the initiator system can be based on camphorquinone, so that cements can be cured with a conventional dental cure lamp emitting at a maximum wavelength around 470nm. Unlike formulations of composite resin, these materials cannot deploy amines as activators, because they would react with the carboxylic acid groups on the polymer, forming salts. Instead, a substance such as sodium p-toluene sulfinide is used as the activator. In addition, a photo-accelerator such as ethyl 4-NJ -dimethylamino benzoate is included [10]. 

In addition to its role as a photoreductant in light activated dental resin systems, 4EDMAB is also a microviscosity sensitive fluorescent probe. Its fluorescence emission spectra is strongly quenched by the uncured, polar liquid resin. After fully curing the resin the fluorescence intensity of 4EDMAB increases dramatically (over 20 fold after 1 hour). The relationship between fluorescence intensity changes and DC indicates a monotonically increasing but nonlinear function. 

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