Three-Dimensional Curing

4 UV Curing of Coatings and Inks on Cylindrical-Shaped Parts 

This method is used for curing coatings and inks on plastic cups, tubs, tubes, or metal cans. The parts are placed on mandrels, which are attached to a rotating device. This device moves them through the individual stations feed, pretreat (most frequently corona or flame, for plastics), printing, curing, and take-off. The printing is done by dry offset (see Section 7.5.3). 

Compact and high-powered UV lamps are used to allow curing of the rotating cup directly on the mandrel. Curing times are in the range of 70 to 100 ms.  

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Radiometers for three-dimensional cure are used for simultaneous multipoint measurements, for setup and process verification of the lamp system. They can be used with UV lamps mounted on a fixed bank or a robotic arm. The collected exposure data (irradiance and total UV energy) are displayed on a computer for each sensor position. A SDCure radiometer is shown in Figure 9.7, and an example of a screen display from a 3D radiometer in Figure 9.8. 

Reactive groups other than epoxy rings may be present in the molecule. Hydroxyl and olefinic groups are the most common. These can affect reactivity as well as the course and sequence of the polymerization reactions. Their number and location could accelerate or retard the overall reaction rate and lead to significantly different three-dimensional cured polymeric structures. Catalytic sites (e.g., tertiary nitrogen) on the epoxy molecule can also influence the reactivity and favor certain reactions. 

Griffin Jr., O. H., Three-dimensional curing stresses in symmetric cross-ply laminates with temperature-dependent properties . Journal of Composite Materials, 17, 1983, 449 63. 

Epoxy phenoHc coatings either are made by blending of a soHd epoxy resin with a phenoHc resin or are the products of the precondensation of a mixture of two resins. A three-dimensional stmcture is formed during curing which combines the good adhesion properties of the epoxy resin with the high chemical resistance properties of the phenoHc resin. The balanced properties of epoxy phenoHc coatings have made them almost universal in their appHcation on food cans. 

The commonly used resins in the manufacture of decorative and industrial laminates ate thermosetting materials. Thermosets ate polymers that form cross-linked networks during processing. These three-dimensional molecules ate of essentially infinite size. Theoretically, the entire cured piece could be one giant molecule. The types of thermosets commonly used in laminates ate phenoHcs, amino resins (melamines), polyesters, and epoxies. 

SiHcone mbber has a three-dimensional network stmcture caused by cross-linking of polydimethyl siloxane chains. Three reaction types are predominantiy employed for the formation of siHcone networks (155) peroxide-induced free-radical processes, hydrosdylation addition cure, and condensation cure. SiHcones have also been cross-linked using radiation to produce free radicals or to induce photoinitiated reactions. 

Flexible foams are three-dimensional agglomerations of gas bubbles separated from each other by thin sections of polyurethanes and polyureas. The microstmetures observed in TDI- and MDI-based flexible foams are different. In TDI foams monodentate urea segments form after 40% conversion, foUowed by a bidentate urea phase, which is insoluble in the soft segment. As the foam cures, annealing of the precipitated discontinuous urea phase... 

The ion thus produced may itself react with another epoxy-group in a process which forms the first crosslink (Reaction 4.16). This reaction may occur at both ends of the molecule of the diglycidyl ether, so that a crosslinked stmcture can easily be built up from these substances. Reaction becomes complicated by the fact that the epoxy-group may also react with the hydroxy-groups that form as the epoxy ring opens up during cure. Thus the finished resin may contain a complicated array of structures within the three dimensional network. 

The liquid or low-melting solid monomers can be cured to the solid state by incorporating a curing catalyst and heating the mixtures below the decomposition temperature. Moreover, the cured solids are transparent and hard polymers formed of three-dimensional networks with moderate thermostability. 

Polymers fall into one of two major classes, thermoplastics, and thermosets. Despite the fact that thermosets have been around much longer, thermoplastics make up about 80% of the industry output. Thermoplastics are linear polymers that can be resoftened a number of times, usually by applying heat and pressure. They can be dissolved in solvents (suitable for that purpose). That s not true for thermosets once they re set. After they re formed or cured (by heat and/or pressure), these cross-linked three-dimensional polymers become nonmelting and insoluble. Thermosets actually decompose under heat before they melt. 

Thermosets cure into nonmelting, insoluble polymers. Frequently, the curing needs heat, pressure, or catalyst to proceed. Often the final cure, which is nothing more than completion of the cross-linking, takes place in the fabrication or molding operations. The chemistry is about the same as you saw in the thermoplastics, but there are more reactive sites per monomer. (They are polyfunctional.) Consequently, more three-dimensional cross-linking takes place. 

This reliable control of the curing process allows for stopping the polymerization after gelation, when the system has a fixed three-dimensional structure but is still mbbery and contourable. One potential application for employing the temporal control of the photopolymerization process would be in designing contourable fraction fixation plates. Figure 3(b) are the... 

Uncured resins are oligomers of relatively low molecular weight that may be a liquid or a solid. Before epoxy resins can become useful products, they must be cured, with the addition of a curing agent. Curing involves the cross-linkage by polymerization of the reactive epoxy groups into a three-dimensional matrix. 

Genomics is the complete understanding of all the locations and sequences in the tens of thousands of genes in humans. What are the functions associated with these sequences What proteins are made from these gene sequences, what are their onedimensional strings and three-dimensional architectures when folded appropriately Can we use this knowledge to diagnose diseases, and to make material to cure these diseases ... 

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