Ultraviolet radiation curing

Soybean oil derivatives epoxidized using 2-hydroxylethyl acrylate in the presence of an acid catalyst result in oligomers applicable in ultraviolet radiation cures. Castor oil consists of ricinoleic acid (12-hydroxy oleic acid) as a major fatty acid, which can be used for the production of polyamide building blocks. 

While the overall rate of increase of adhesive consumption since 1950 has been high, the growth of certain types of products has been especially dramatic. Pressure sensitive and hot melt formulations have been very rapid gainers and anaerobic adhesives too have been strong performers in recent years. Specialty adhesives, including cyanoacrylates (the so-called instant glues) and ultraviolet radiation cured products have also been favorably received. 

Ultraviolet radiation, effect on commercial polymers, 201 Ultraviolet-cured coatings hydroxy-benzotriazolc, 213 photostabilization of PVC, 213 Ultraviolet-visible spectrum,... 

But vitrification may be a problem when the cure is started at room temperature and no external heat source is provided (the only source of heat generation is the polymerization reaction). This is the case of UV (ultraviolet radiation), EB (electron beam), or X-ray curing processes. 

Curing by light irradiation can be apphed to a variety of polymers. The acrylic family is a typical example of photosensitive monomers. A well-documented review has recently been dedicated to the curing of composites by ultraviolet radiation [45], Photocuring time is much shorter than for traditional thermal curing (minutes rather than hours), leading to a significant reduction in the cycle time. 

Although the basis and end result of the radiation curing process is essentially the same using either electron or ultraviolet energy, the mechanisms are quite different. This is because the energy of electrons is about 50,000 times... 

Pacansky et al. (1987) described the fabrication of dual-layer photoreceptors by radiation curing. The layers were coated with a polymerizable acrylate monomer or oligomer as the liquid component, then cured by a 175 kV electron beam or ultraviolet exposure. These methods were used for the preparation of generation layers containing bisazo and hydroxysquaraine pigments. 

The average shore A hardness of the cured sealant is 20 to 25 but increases with ageing. Resistance to ultraviolet radiation is excellent, but this is not important for indoor applications. The maximum movement accommodation factor (MAF) can be 15% of the total joint width. Joints should be designed so that movement due to shrinkage and thermal changes does not exceed the maximum MAF, related to the joint width. Table 5.4 lists the properties in general for acrylic emulsion sealants. These properties are summarised from the commercial literature of several acrylic emulsion sealant manufacturers and should not be considered as specifications. Table 5.5 lists the standard specifications for these sealants. 

Sealants durability resistance to heat cold water, ozone and ultraviolet radiation adhesion to a variety of substrates high recovery colour stability glazing sealants construction sealants (neutral cure systems) sanitary sealants... 

Electron Beam-Cured Inks. Electron beam-cured inks are similar in principle to ultraviolet light-cured inks except that no photoinitiator is needed. Vinyl polymerizations may be initiated Iqr any form of ionizing radiation, e. g., neutrons, a-particles, y-rays, and x-rays, as well as by high-energy electrons ( 5-rays). The mechanism of initiation is more complex than that of photochemical initiation in that radiation of vinyl monomers gives cations and anions as well as free radicals however, most radiation-initiated polymerizations are radical-initiated because the cations and anions formed are not stable at the temperature of polymerization and therefore dissociate to form radicals. 

Although rickets was first described in the mid-1600s, it was not until the 1920s that deficiency of vitamin D was recognized as its cause. Despite its designation as a vitamin, dietary vitamin D is needed only if a person receives inadequate exposure to sunlight. Normally, vitamin D3 is synthesized in the skin by irradiation of 7-dehydrocholesterol (Figure 37-1). Sufficient exposure to ultraviolet radiation can cure rickets. 

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. 

There are some donor compounds which, while not completely preventing the dark reaction, will inhibit it and, at the same time, not interfere with the curing reaction. Cyclic amides (30), nitriles ( ), substituted ureas ( ) and sulfoxides (33) have been shown to promote storage stability of photosensitized epoxides without preventing rapid cure when exposed to ultraviolet radiation. 

Ultraviolet radiation is required only for the first step. The second step, while independent of UV radiation, is influenced by heat. Continuous exposure to a mercury arc to determine tack-free time can influence the course of the polymerization because of an increase in temperature of coating and substrate caused by the intense heat of the mercury arc. To avoid this complication and to maintain control of the temperature of the coating during cure, exposure to the mercury arc was generally limited to two seconds. This proved adequate to give a tack-free condition within one second following exposure for the most reactive epoxides. 

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