Curing photopolymers

The existence of two T2 relaxation times was also observed in the radiation cured photopolymers 99), and studies of tri- and tetra-functional network organosilicon polymers with rings at the network points 100). The effects of crystallization of poly-dimethylcarbosiloxane networks (PDMCS) I01), and water sorption and stoichio-metrical composition of the cured DGEBA/DETA resins on phase structure and mobility 102) were studied. 

The interactions between the components that make up a photopolymer are extremely important in arriving at a working formulation. Here we show that inclusion of pyrrolidone derivatives like NVP or NMP in acrylate systems enhances the ambient cure of a film. From the reactivity parameters of some simple systems we have derived an empirical scheme for the formulation of fully and/or partially reactive systems based on the molar equivalent ratios of the acrylate to pyrrolidone components. The data support the presence of a synergistic effect between NVP and the acrylate components. 

Two of the main considerations in the development of totally reactive liquid photopolymer systems are the resin(s) and the reactive diluents (monomers). The resins play a major role in determining the end properties and therefore the applications of the cured polymer. The reactive diluents are used to provide a fully reactive system with the appropriate reactivity, viscosity, coatability before cure and the desired crosslink density, chemical resistance and dielectric character once it is cured. The pho-toreactive monomers most commonly used are acrylate based derivatives because of the properties they impart, and their high reactivity and wide solubility range. 

Advantages of stereolithography are the excellent dimensional accuracy, excellent surface hnish, variable vat size and ability to use a range of materials. The disadvantages are the need for handling of liquid photopolymers and the requirement of post-processing (removal of supports) and post-curing in some cases. 

Cole et al. (2001) reviewed physical models for most stages of the microlithography process. For the curing stage, they state that there has been no recent development of cure models since the work of Dill (1975). Dill (1975) presented models that incorporate both light absorption and photopolymer cure kinetics modelling, as shown by the following equations ... 

Photopolymer Dielectrics The Characterization of Curing Behavior for Modified Acrylate Systems... 

The dual purpose of this study was to characterize the curing behavior of model acrylate photopolymer mixtures and to evaluate analytical techniques to determine which best describe the curing process. The characterization of curing behavior and its effects on the final physical, chemical and electrical properties can be a difficult task. 

Solvent extraction is a technique that can be used to evaluate the curing behavior of photopolymers and as a measure of sol fraction. The method is dependent, on the solubility of the unreacted or partially reacted components in the chosen solvent (methylene chloride). The method yields the percentage of unreacted monomers and partially reacted low molecular weight components in the cured film. This is derived from the weight differential of the film before and after extraction. 

The morphology of ruber modified epoxy photopolymers was found to depend on the cure conditions as well as the nature and concentration of rubber. The commercially available acrylonitrile-butadiene copolymer rubber modifiers with varying percentages of acrylonitrile content were used. They were polymerized using a photocationic initiator involving a UV exposure followed by a thermal cure. Transmission electron micrographs of osmium tetroxide stained specimens, coupled with dynamic mechanical measurements indicated that phase separation and particle size distribution depended not only on rubber concentration and compatibility, but also on the cure conditions. 

In another commercial application of free-radical polymerization, polymerizations may be carried out in industrial coatings in the presence of air to yield a variety of coatings and structures of commercial import. This development is possible. In part, because certain vinyl monomers, particularly the acrylates, are less sensitive to retardation by oxygen compared with other monomers. It is therefore possible to produce radiation-cured coatings. UV-cured printing inks and the photopolymers are important in imaging for printing, photoresist, and related applications. 

The Objet Quadra, recently developed by Objet Geometries Ltd., prints a photopolymer at 600 dots per inch in X and T, and uses a 20-pm layer thickness. The photopolymer is cured during printing so not postprocessing is required. A support material is also printed where required. The maximum model size is 27 cm x 30 cm x 20 cm. 

Polyester-styrene resins have a low raw material price and are used in wood finishing. Disadvantages are the presence of volatile styrene and the low cure speed. Products with methacrylic groups are used where line (cure) speed is less important, mainly in combination with acrylates in special end uses (e.g., in the electronics industry and in photopolymer printing plates) to improve adhesion or to obtain specific physical properties. Thiol- thiene mixtures can lead to very flexible cured films but their odor seriously limits their use. 

The fundamental process of SLA is the solidification process of a liquid photopolymer, for example an epoxy resin. It is interspersed with suitable photoinitiators and exposed to ultraviolet (laser-) radiation, which initiates polymerization in those areas where the resin is heated by the laser beam according to the cross-sections. The beam deflection is realized by a scanner system consisting of two movable mirrors [102]. The curing is limited in the horizontal direction by the diameter of the laser beam and in the vertical direction by the optical penetration depth of the used resin. After completion of a layer the platform moves down according to the layer thickness and new resin is coated. After finishing the build process the model requires post-processing, in which the model is cleaned, the support removed and post-cured in a UV-hght chamber. 

Uses Monomer for acrylics, adhesives (pressure sensitive, structural), coatings (glass, metal, optical, paper, PVC floor, release, textile, wood), electronics, inks, paints, and photopolymers Features Low shrinkage and fast cure... 

Chem. Descrip. Urethane actylate/SR 454 (PEG-3 trimethylolpropane triacrylate) blend, < 400 ppm MEHQ inhibitor Uses Urethane-acrylic for radiation and peroxide cured adhesives, coatings (metal, paper, PVC floor, wood), electronics (photoresists), inks, photopolymers... 

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