Ultraviolet cure materials

Storage stability can be further improved by addition of "stabilizers" which inhibit the dark reaction without retarding rate of cure. Materials fitting the description of Lewis Bases or electron-donor compounds are generally effective in inhibiting the dark reaction. Many compounds of this type, however, tend to quench the cationic reaction completely, so that curing does not occur even on exposure to ultraviolet radiation. 

Ultraviolet processing has been restricted to lab-scale studies however, many authors have examined kinetic cure modelling of these systems during the development of new UV-cure materials. 

Reiaforced plastics may also iaclude fillers (qv), which are iaexpeasive materials such as calcium carboaate used to displace resia and reduce cost curing agents (catalysts), promoters, inhibitors, and accelerators, which affect thermosetting resia cure colorants release agents (qv) to faciUtate removal from the mold and other additives which can impart a wide variety of properties to the finished part, such as fire resistance, electrical conductivity, static dissipation, and ultraviolet resistance. 

Composite resins can be cured using a variety of methods. Intraoral curing can be done by chemical means, where amine—peroxide initiators are blended in the material to start the free-radical reaction. Visible light in the blue (470—490 nm) spectmm is used to intraoraHy cure systems containing amine—quin one initiators (247). Ultraviolet systems were used in some early materials but are no longer available (248). Laboratory curing of indirect restorations can be done by the above methods as well as the additional appHcation of heat and pressure (249,250). 

In most applications, polyester and vinyl ester resins are used as the matrix materials. Epoxies are also used, although they require longer cure times and do not release easily from the pultrusion dies. Hence, thermosetting resins are most commonly used with pultrusion, although some high-performance thermoplastics such as PEEK and polysulfone can also be accommodated. In addition to the resin, the resin bath may contain a curing agent (initiator, cf. Section 3.3.1.2), colorants, ultraviolet stabilizer, and fire retardant. 

Thermoset A polymeric material that undergoes irreversible chemical changes when cured with heat, catalysts or ultraviolet light. 

It is difficult to specify Ihe increased cost of thse ultraviolet light-cured inks with any accuracy. For example, in one case, the cost of the ink was estimated to be 30-50% higher (7), but an estimate made in 1971 cannot be expected to apply today when raw material costs are increased on a monthly or even we ly basis. In anolher case, the overall cost of... 

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