Cure response

Post-Gel Examples. In addition to affecting the pre-gel viscosity, the presence of water (or humidity during cure) can also affect the cure response and final network structure formed in urethane coatings. Using reactions R1-R4, the following kinetic scheme can be written for cure of polyol-urethane coatings in the presence of humidity ... 

The effective development of blocked isocyanate based coatings requires a complete understanding of the cure chemistry. Many materials have been identified which will improve cure response. Often these are reported as deblocking catalysts even though no direct evidence exists to support this claim. Most of these materials are well known catalysts of the cure reaction between hydroxyl and isocyanate and may be improving cure response solely by catalyzing this reaction. Effective development of catalyst systems requires a better understanding of the effect of catalysts on cure. 

In order to answer these questions, the kinetic and network structure models were used in conjunction with a nonlinear least squares optimization program (SIMPLEX) to determine cure response in "optimized ovens ". Ovens were optimized in two different ways. In the first the bake time was fixed and oven air temperatures were adjusted so that the crosslink densities were as close as possible to the optimum value. In the second, oven air temperatures were varied to minimize the bake time subject to the constraint that all parts of the car be acceptably cured. Air temperatures were optimized for each of the different paints as a function of different sets of minimum and maximum heating rate constants. 

A network structure model has been developed from which a parameter that correlates well with physical measures of paint cure can be calculated. This model together with a kinetic model of crosslinking as a function of time and temperature has been used to evaluate the cure response of enamels in automotive assembly bake ovens. It is found that cure quality (as measured by the number and severity of under and overbakes) is good for a conventional low solids enamel. These results are in agreement with physical test results. Use of paints with narrower cure windows is predicted to result in numerous, severe under and over bakes. Optimization studies using SIMPLEX revealed that narrow cure window paints can be acceptably cured only if the bake time is increased or if the minimum heating rate on the car body is increased. 

Lee, T.D.G. and Wakelin, D. (1982) The use of host strain variation to assess the significance of mucosal mast cells in the spontaneous cure response of mice to the nematode Trichuris muris. International Archives of Allergy and Applied Immunity 67, 302—305. 

This structure is similar to that of the copolymer TFE and ethylene, except that the random onentation of the methyl group from nonstereospeciftc free radical copo-lymenzation of propylene affords a noncrystalline structure [35] The relatively low fluorine content (54%) of these elastomers compared with VDF-based elas tomers (66-69 5%) makes them significantly less resistant to swelling by hydrocarbons Because of strict alternation, these elastomers have a relatively high glass transition temperature ( 2 °CJ and consequently limited low temperature properties Furthermore, they must be polymerized with a cure site monomer or receive a postpolymerization treatment to adequately activate them for vulcanization [36] To counteract the limited cure response, low-temperature flexibility, and hydrocarbon resistance, these polymers have also been modified with substantial amounts (ca 35 wt %) of VDF [37, 38] This provides some improvements but inevitably decreases the resistance to bases and polar solvents... 

Dynamic Mechanical Testing - Film properties such as impact resistance and the cure response of thermosetting resins are conveniently investigated by dynamic measurements in which an oscillatory or torsional strain is applied to the sample with the stress and phase difference between the applied strain and measured stress being determined. In the present study, a Rheovibron Viscoelastometer was used which employed a sinusoidal strain at a... 

The use of plastics in automotive applications has expanded considerably over the past 20 years. In 2001, approximately 2501b of plastics were used per automobile compared to less than 100 lb five years earlier. With the increased use of plastics, coating research has concentrated on the painting of these often difficult substrates. Among the numerous prerequisites for coatings on plastic are wetting of the substrate uniform film development a cure response below the heat distortion temperature of the plastic adhesion to the sub-... 

Plastic types are variable, ranging from flexible to rigid and from thermoplastic to thermoset. Because of these variations, the type of coating applied to them also varies, depending on cure response, solvent sensitivity, and modulus. The type of coating also depends upon the end use of the coated plastic. For example, topcoats can be applied directly to the plastic without the use of a conductive primer if two-toning or blackout areas are not part of the styling latitude. Adhesion promoters also are often utilized if a particularly difficult-to-adhere-to plastic is encountered (i.e., polypropylenes or thermoplastic polyolefins (TPOs), a blend of elastomer and olefin). 

Fig. 2. Typical comparison of cure response (mono-, di- and tri-acrylate). ...

Cure response Slow Moderate Fast Fastest... 

The general trend with these materials is high flexibility and adhesion but slow cure response. 

A low odour monomer with good cure response and adhesion characteristics. 

Triacrylate with good pigment wetting and cure response. 

The use of these materials is generally to increase cure response and film hardness. However, they generally will have an adverse impact on adhesion as well. 

This section contains information on the cure response of UV-curable and thermosetting polymers in the presence of fillers. The discussion includes ... 

The first problem is a reactivity problem. Early attempts at preparing water based systems encountered very slow reactivity of the dicyandiamide with the epoxy resin. This caused very slow line speeds for the laminator. This problem has been resolved with ED24574 and the cure response of the system is equal to organic solvent based standards. 

Technology which couples fast ultraviolet (UV) cure response with silicone performance characteristics suitable for integrated circuit protection has been developed. One-part silicones which can be cured in several seconds to provide products of excellent purity, stress relief, thermal stability, and protection against harsh environments are the result. 

Of the techniques utilized, photocalorlmetry Is the method of choice to give a quantitative measurement of percent conversion. Using photo-DSC to define a cure response/lrradlatlon time relationship makes It possible to plot mechanical or Infrared response versus percent conversion. The results are listed In Table II and Illustrated In Figure 8. 

Radiation curing technology is rapidly expanding into numerous, commercial applications. Due to their fast cure response, acrylate functional raw materials dominate the Industry. A wide range of acrylated monomers and oligomers is available in order to meet the various application requirements. 

Among the most successful of the new radiation-curable silicone coating systems are compositions Incorporating cycloaliphatic epoxyfunctional silicone polymers with compatible iodonlum salt photocatalysts (1 - S ) The syntheses, structures, UV cure response, and other properties of these materials and some of their derivatives and monomeric homologs are discussed In the balance of this chapter. Their specific application for release coatings has been described In great detail elsewhere (5.6 > and Is not the subject of this paper. 

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