Convective and radiant (IR) curing of bulk and waterborne epoxy coatings as thin layers. Part II: Infrared curing

In the first part of this paper, a method for studying the curing of 100-μm-thick epoxy-based layers on steel substrates was described. In this second part, we extend our study to radiative (infrared) heating conditions. A simple waterborne epoxy reactive system based on a diglycidylether of bisphenol-A prepolymer and a polyether triamine was used. The chemical kinetics during infrared heating were studied with the reaction kinetics recorded during convective heating. A second order autocatalytic model described the data. The curing mode had no significant influence on the heating kinetics but the heating rate had a significant influence on the curing kinetics. Higher heating rates can be achieved by infrared heating conditions compared with convective heating. The gelation phenomenon was changed for infrared conditions. Microdielectrometry can be used to record in situ the extent of reaction of the epoxy reactive system for thin layers during radiant heating.     

Development of high performance,waterborne coatings. Part I: Emulsification of epoxy resin

A new manufacturing process of high performance, waterborne coatings for can coating applications is developed, which includes emulsification of an epoxy resin with or without its hardener by incorporation of an acrylic resin. It becomes possible by this new process to emulsify a variety of resins with minimum effects of the surfactant acrylic resin. Thus, latitude to design formulations is widened and the performance of epoxy resin and its hardener can be fully developed.     

High performance waterborne coatings based on dispersions of a solid epoxy resin and an amine-functional curing agent

A novel, waterborne epoxy system comprised of non-ionic stabilized dispersions of a solid epoxy resin and an amine curing agent has been designed for ambient-cure coatings. The performance characteristics of coatings formulated from the new system have been compared to a standard system. The new system produced formulated coatings with robust performance over a wide range of amine-to-epoxy stoichiometries (65 to 130%). At 100% stoichiometry, the new system was found to have lower VOC, faster hardness development, better gloss, and higher impact resistance than the standard system. The new formulations also exhibited superior water and salt spray resistance, and a definitive viscosity rise at the end of potlife. Unlike the standard system, coating morphology of the new waterborne system was found to be similar to a solvent-based coating. For the new system, good coalescing solvents, as judged by gloss and gloss potlife, were found to have low solubility parameters and high boiling points. Presented at the 76th Annual Meeting of the Federation of Societies for Coatings Technology, on October 15, 1998, in New Orleans, LA. P.O. Box 1380, Houston, TX 77251-1380.     

Development of high performance,waterborne coatings. Part III: Characterization of coatings and cured film

High performance waterborne coatings were developed which could be utilized as an adhesive primer for sideseam bonded cans. The manufacturing process is unique; blending an epoxy / phenolic solution and an acrylic resin solution and dispersing the mixture in an aqueous medium by the phase transition method. The epoxy resins are neither chemically modified by grafting nor esterified by acrylic resin, which is thought to develop the excellent performance of epoxy / phenolic coatings. The morphology of the coatings and cured film was characterized and found to be quite different from the conventional waterborne coatings, i.e., the acrylic-modified epoxy resin systems. It was confirmed that acrylics and epoxy / phenolic resins exist in separate phases in the cured film, and that the epoxy / phenolic resin constitutes the continuous phase.     

Thermal scanning rheometric analysis of curing kinetic of an epoxy resin. I. An anhydride as curing agent

The curing reaction of the system diglycidyl ether of bisphenol A (DGEBA), an organic anhydride (HMTPA), as curing agent and a tertiary amine (DMP 30) as initiator has been studied by Thermal Scanning Rheometry (TSR) under isothermal conditions. The gel time, which is defined by several different criteria, has been found to be a good parameter to determine the activation energy of this curing process; on the other hand, the gel time depends on the concentration of the initiator. An empirical model has been used to predict the change in viscosity (η*) of the system with time until the gelation is reached; the first‐order kinetics, the apparent kinetic constant (k′), and the activation energy before gelation have been determined. Furthermore, these results are reported together with the reaction mechanism proposed by another authors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1239–1245, 1999     

The leveling of thermosetting waterborne coatings. Part IV: Effects of film thickness

The influence of film thickness on the leveling of a thermosetting waterborne coating (WBC) was examined. The theory of Patton has been revised to give the proper force balance and modified to include the changes in surface tension and viscosity during leveling by the evaporation of volatile components. However, the predicted leveling process by a numerical method did not coincide with the observed results. Thus, the driving force in the theory, the hydrostatic pressure gradient in the film, was considered to be insufficient to describe the leveling process of the WBC. The hydrostatic pressure gradient can be a component of the driving force to promote leveling, but the existence of an additional component is suggested.     

油脂基聚氨酯改性脂肪胺水性环氧固化剂的合成及性能

以高级脂肪醇聚氧乙烯醚（OE-6）、甲苯二异氰酸酯（TDI）为原料,物料比n(TDI)∶n(OE-6)= 1.05∶1、温度45℃、反应2.5 h合成了端异氰酸酯预聚体,再将其与多元胺按照摩尔比n (多元胺)∶n (预聚体)=1.2∶1、温度40℃、反应3 h扩链,得到油脂基聚氨酯改性脂肪胺水性环氧固化剂（UFAWECAOF）。用红外光谱、 13C-NMR表征了UFAWECAOF的结构。粒径分析表明目标产物具有乳化液体环氧树脂的功能,其与环氧树脂EPON828复配制备的双组分水性涂料涂膜固化物,柔韧性达1 mm、铅笔硬度达3 H、耐冲击性达50 kg/cm。     

The leveling of thermosetting waterborne coatings. Part III: Leveling under controlled conditions

Experiments on coated films of water borne, coatings (WBC) under controlled conditions (i.e., 25°C, 65% RH) were carried out to study the mechanism of leveling. Data in a companion paper imply that the development of the surface tension gradients plays an important role in promoting leveling. The stress due to surface tension gradients is found to be much greater than the stress introduced by hydrostatic pressure gradients in the film caused by surface tension and the free boundary curvature of the film. This reconfirms that the use of a co-solvent, which evaporates faster than water, greatly accelerates the leveling of a WBC.     

A simple imide compound as a curing agent for epoxy resin. I. Synthesis and properties

A simple imide compound, 4‐amino‐phthalimide (APH), was synthesized as a curing agent for epoxy resin. APH was prepared from the hydration of 4‐nitro‐phthalimide, which was prepared from the nitration of phthalimide. The chemical structure of APH was verified by IR and ¹H‐NMR spectra. The thermal properties and dielectric constant (ε) of a phosphorus‐containing novolac epoxy resin cured by APH were determined and compared with those of epoxy resins cured by either 4,4′‐diamino diphenyl methane (DDM) or 4,4′‐diamino diphenyl sulfone (DDS). The results indicate that the epoxy resin cured by APH showed better thermal stability and a lower ε than the polymer cured by either DDM or DDS. This was due to the introduction of the imide group of APH into the polymer structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The leveling of thermosetting waterborne coatings. Part II: Drying of coated wet films

Evaporation behavior of water/solvent blends was estimated using the universal functional activity coefficient, UNIFAC, method. The evaporation rate from a free surface of a waterborne coating, WBC, containing a co-solvent was experimentally determined. These results were used to estimate the evaporation rate from wet films of a WBC containing a variety of co-solvents with a range of initial thickness. Knowing the composition of the WBC during the drying process, the change in the viscosity and the surface tension was determined. The results strongly support the development of a surface tension gradient in the film. It is also suggested that a surface tension gradient would accelerate the leveling of the ribs if a proper co-solvent were employed.     

Organic polymeric coatings for silica fibers. I. UV-curing epoxy acrylate (V1F)

Coated optical fibers (～100 μm) were prepared exhibiting fracture strengths in excess of 750 ksi (5.3 GN/m²) for lengths up to 100 meters. To achieve this we have developed a novel coating and coating application process. The coating is an epoxy acrylate, cured by UV irradiation, which may contain a multifunctional silane coupling agent. The coating liquid was applied to the fiber prior to solidification by an applicator, which facilitates centering of the fiber in the coating. Our coating system offers advantages in that there is no solvent to remove, thereby avoiding possible surface “corrosion” of the glass fiber. The reasonably low viscosity of the coating formulation allows for the extensive wetting of the fiber surface irregularities prior to solidification.     

Development of high performance,waterborne coatings. Part II: Factors affecting adhesion performance

A new manufacturing process for high performance, waterborne coatings for can coating application was developed, which includes emulsification of an epoxy resin with or without a hardener by incorporation of an acrylic resin. It is possible by this new process to emulsify a variety of resins with minimum effects of the surfactant. (acrylic resin). The effects of surfactant and neutralizer on adhesion performance were studied. It was found that the effects of the acrylic resin amount were relatively small, and that the effects of the neutralizer were significant. It was confirmed that the usage of ammonia or amines with a branched alkyl group is required to achieve balanced dry and wet adhesion.     

Polymeric reagents: Part 1. Synthesis of polymer-anchored amines useful for curing epoxy resins

A range of polymers carrying amino-functions [NHEt, NHBuⁿ, NEt₂, NPr, N(CH₂CH₂CH₂NH₂)₂, NMeCH₂CH₂CH₂NH₂ or NEtCH₂CH₂CH₂ NH₂] has been synthesised via amination of styrene-vinylbenzyl chloride copolymers, poly(epichlorohydrin) and poly(2-chloroethyl vinyl ether), and via homopolymerisation and copolymerisation (with styrene) of (n-butyl)(vinylbenzyl)-ammonium chloride. Some of the polymers showed promise as curing agents for epoxy resins.     

Flexibility of epoxy coatings. Part 2: The relationship with the degree of cure

The flexibility of epoxy coating films, crosslinked by a phenolic resin, has been evaluated. The network structures of these films were estimated by the method proposed in the companion paper. The coating films with a higher molecular weight of network chain, M_c, showed more flexibility. This was achieved by the use of an epoxy resin with higher molecular weight or an epoxy resin with a lower content of lower molecular weight components and by control of cure.     

Moisture absorption by cyanate ester modified epoxy resin matrices. Part IV: Effect of curing schedules

The cure schedule (time and temperature) has a profound effect on the physical properties of thermosetting materials. For hydrophilic systems, it can also influence the rate of diffusion of moisture and the equilibrium concentration. The effect of post‐cure time and temperature on the moisture sorption behavior and the viscoelastic properties of cyanate ester modified epoxy resin has been investigated. Moisture absorbed at 96% R.H. (relative humidity) and 50°C under isothermal conditions was found to increase with post‐cure temperature, but the diffusion coefficient decreased in line with the crosslink density. Resins of high crosslink density and high glass transition temperature appeared to exhibit a larger reduction in glass transition temperature on plasticization by moisture in comparison to those with lower crosslink density.     

Cyclic deformation behavior of an epoxy polymer. Part I: Experimental investigation

A series of uniaxial cyclic tests were carried out on solid cylindrical specimens of an epoxy resin, Epon 826/Epi‐Cure Curing Agent 9551. The focus of the study was to investigate time‐dependent viscoelastic behavior of this thermosetting polymer material under cyclic loading and to develop a constitutive model with the capabilities to simulate the observed deformation response. The tests include stress‐controlled or strain‐controlled cyclic loading with/without mean stress or mean strain at various amplitudes and loading rates. It was found that the cyclic stress‐strain response of this material is amplitude‐dependent and rate‐dependent, and the response to axial tension is different from that in compression. The stress‐strain loops exhibit more pronounced nonlinearity with high amplitudes or low loading rates. For stress‐controlled cyclic loading with mean stress, ratcheting strain is accumulated, which is of viscoelastic nature, and this is confirmed by its full recovery after load removal. For strain‐controlled cyclic loading with mean strain, the mean stress relaxation occurs, which contributes to the observed longer life in comparison to the stress‐controlled cyclic loading with mean stress. Polym. Eng. Sci. 44:2240–2246, 2004. © 2004 Society of Plastics Engineers.     

Accelerated curing of cementitious systems by carbon dioxide: Part I. Portland cement

Treatment of portland cement mortars with carbon dioxide immediately after molding produces compressive strengths higher than samples hydrated for one day under normal conditions. The water/cement ratio is critical in that sufficient moisture must be present for carbonation to occur rapidly, but not so much as to fill pores and impede the diffusion of CO₂ into the sample. Increases in the sand/cement ratio reduced strength. Increases in compaction pressure used to mold samples, increased strength of the carbonated specimens, as did mechanical mixing. Posthydration of carbonated samples increased strength about 30 and 45 percent after one and three days respectively. Upon hydration, the strength gain of carbonated samples reached a plateau at three days while the noncarbonated samples continued to gain strength and finally exceeded the strength of carbonated samples at 14 days. Autoclave curing of carbonated samples resulted in higher strengths than with noncarbonated samples.