Acrylate Resins and UV Curing

The reactive diluent is required for tuning the resin formulation to the application viscosity. The nature of the diluent is partly dependent on the structure of the resin. In the case of methacrylate-functional resins, methacrylate-functional diluents are mostly used, whereas in the case of acrylate-functional resins, acrylate-functional diluents are commonly applied. 

Between acrylates and methacrylates there is a great difference in the homopolymerization rates. As a rale of thumb, it can be said that acrylates are ten times more reactive than their methacrylate analogs. Mixtures of acrylates and methacrylates are not often used, as acrylates are not able to increase the rate of a methacrylate resin. In that specific case, considering the reactivity ratios of this copolymerization, the methacrylate will dominate both the rate and the composition of the polymer formed. 

The composite resin industry is the main exception with respect to the selective choice of reactive diluents. Within this industry, styrene is used as well as reactive diluent (known in combination with unsaturated polyesters). Methacrylates are then often referred to as - chemically erroneously - vinyl esters. 

Within the acrylate-functional resins many distinctions can be made, for instance for functionality, polymerization speed, polarity, and so on. However, these distinctions generally do not result in different methods of production. The production can be divided into three main classes, from each of which a characteristic example will be given. 

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Radiation curing adhesives are generally applied as solvent-free liquids. High-solids EB and uv curing liquid adhesives have been formulated from a variety of resins and elastomers. They include epoxy acrylates, epoxies, other acrylates, polyesters, blends of acrylate monomers with elastomers, and other compositions. 

Binders for thermosetting powder coatings are often called a hardener. The hardeners are a mixture of a primary resin and a cross-linker. The major types of binders can be limited to polyester, epoxy, hybrid epoxypolyester, acrylic, and UV cure types. Polyester binders are used for good exterior durability, retention of gloss, and resistance to chalking. 

The formation of networks by addition polymerization of multifunctional monomers as minor components included with the monofunctional vinyl or acrylic monomer is industrially important in applications as diverse as dental composites and UV-cured metal coatings. The chemorheology of these systems is therefore of industrial importance and the differences between these and the step-growth networks such as amine-cured epoxy resins (Section 1.2.2) need to be understood. One of the major differences recognized has been that addition polymerization results in the formation of microgel at very low extents of conversion (<10%) compared with stepwise polymerization of epoxy resins, for which the gel point occurs at a high extent of conversion (e.g. 60%) that is consistent with the... 

Naphthalate polyester articles can be coated with polymerizable and crosslinkable compositions. The composition is made from the matrix and a large amount of benzotriazole derivatives. This class of compounds absorbs UV light. The cured compositions help protect the naphthalate polyester from UV exposure and other weathering effects [78]. The matrix consists of acrylic resins and methacrylic resins. The compositions are photopolymerizable. 

In 1980, Dixon received the first patent on FP, entitled In Depth Curing of Resins Induced by UV Radiation. He produced curing to depths of 500 mils (500/1000 in.) using a combination of a photoinitiator, thermal initiator, and multifunctional acrylate resin. The UV light caused a photopolymerization on the surface, which then triggered a propagating front. To increase the reactivity, he also added an accelerator such as a tertiary amine. 

PSA adhesives A significant use for radiation curing is the advancement or curing of pressure-sensitive adhesives. High solid EB and UV curing liquid adhesives are being formulated from a variety of resins and elastomers. Such adhesive compositions include acrylics, blends of acrylic monomers with elastomers, polyesters and other compositions. These products are primarily used as pressure-sensitive adhesives. 

IR spectroscopy is highly appropriate for the direct recording of curing rates -that is, the degree of conversion as a function of time [97,98]. Typical polymerization profiles obtained upon UV exposure of an urethane-acrylate resin and an acrylate/epoxide blend (diacryl derivative of bis-phenol A/bicycloaliphatic diepoxide) are shown in Figure 2.30. While the radical polymerization of the acrylate monomer occurred faster than the cationic polymerization of the epoxide... 

In this respect, it should be mentioned that dual-cure systems, combining UV irradiation and a thermal treatment, have been developed to address the issue of the lack of cure in shadow areas of 3D objects, as well as in thick pigmented samples." " A few centimeter thick nanocomposite materials can be produced by this two-step process which associates the photopolymerization of the acrylate resin and the thermally-induced polyaddition of isocyanate and alcohol groups ... 

A second type of uv curing chemistry is used, employing cationic curing as opposed to free-radical polymerization. This technology uses vinyl ethers and epoxy resins for the oligomers, reactive resins, and monomers. The initiators form Lewis acids upon absorption of the uv energy and the acid causes cationic polymerization. Although this chemistry has improved adhesion and flexibility and offers lower viscosity compared to the typical acrylate system, the cationic chemistry is very sensitive to humidity conditions and amine contamination. Both chemistries are used commercially. 

Transparent PVC plates were coated with a 70 pm thick film of an epoxy-acrylate resin containing 0.5 % of a benzotriazole UV absorber. They were first UV cured for one second and then exposed at 40°C to the low intensity radiations of a QUV accelerated weathering tester. The extent of the degradation was followed by Invisible spectroscopy, a very sensitive method that permits detec-... 

Draining of Consolidants Effect of Concentration. As noted in the introduction, one objective of the studies described here is to examine techniques for applying consolidants under conditions that will reduce the physical hazards to which the fabric substrate is exposed. Since the acrylic resins examined in Part II of this series (I) have outstanding resistance to degradation from UV light and heat and normally do not yellow or stiffen under adverse conditions, some of these resins were re-examined using a much less severe application technique. Milder curing procedures also were utilized. 

Additives and comonomers in thermoset, moisture, UV, and catalytically curing resins or coatings (e.g., acrylic, epoxy, melamine, and unsaturated polyester systems)... 

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