Paint Curing Research Articles

Photopolymerization reactions under visible lights: principle, mechanisms and examples of applications

A general overview of visible light photoinduced polymerization reactions is presented. Reaction mechanisms as well as practical efficiency in industrial applications are discussed. Several points are investigated in detail: photochemical reactivity of photoinitiating system (PIS), short overview of available photoinitiators (PIs) and photosensitizers (PSs), mechanisms involved in selected examples of dye sensitized polymerization reactions, examples of applications in pigmented coatings usable as paints, textile printing, glass reinforced fibers, sunlight curing of waterborne latex paints, curing of inks, laser-induced polymerization reactions, high speed photopolymers for laser imaging, PISs for computer-to-plate systems.

Multidimensional Imaging Using Combined Stray Field and Pulsed Gradients

The paper describes an advance in stray field imaging (STRAFI) whereby images of planar samples can be obtained in the stray field of a superconducting magnet without the need for sample rotation. This is achieved by using the static stray magnetic field gradient in combination with pulsed orthogonal gradients. Results of both two- and three-dimensional implementations of the experiment are presented and discussed. An extension to diffusion-weighted imaging is introduced. The technique is expected to prove particularly useful in experiments where high resolution is required in only one direction while lower resolution is acceptable in the orthogonal directions, such as in studies of the drying and curing of paints and varnishes. Arising from the work, a new method for accurately calibrating the radiofrequency pulse width in stray field is found.

Air convective drying and curing of polyurethane-based paints on sheet molding compound surfaces

In this study the kinetics and phase changes which occurred during the convective drying of a model car paint based on the polyurethane chemistry is described. The competition between the kinetics of the solvent removal and the phase changes, such as the gelation and/or the vitrification of the polyurethane, needs to be taken into account to avoid the defects in the resulting dried coating. The kinetics of polycondensation of a two-component polyurethane based on polyester triol and triisocyanate in a mixture of various solvents was studied as a 100 µm thick layer on sheet molding compound (SMC) and zinc plated steel plates. Differential scanning calorimetry (DSC) and Fourier-Transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA) during isothermal curings allowed us to determine the rate constants and the activation energies by using second and third order autocatalytic models.

Examination of the Photochemical Curing and Degradation of Oil Paints by Laser Raman Spectroscopy

In the present study, the curing and the degradation of oil paints by irradiation with ultraviolet light was investigated by laser Raman spectroscopy. At present, the curing reaction of oil paints is interpreted by several reaction schemes, although none of them is considered to be based on definite experimental evidence. The most typical examples are as follows: one is the radical termination reaction of the crosslinking type; the other, the polymerization reaction of the Diels—Alder reaction (diene reaction) type. In the present investigation, oil paint film (ZnO White and TiO2 White) was irradiated with a Xe lamp, and the time dependence of the Raman spectra of the films was examined. It is shown that the curing reaction cannot be explained by either of the above-mentioned reaction schemes. A new reaction mechanism for the curing and the degradation of paint films is proposed. It is concluded that the microscopic approach to the elucidation of the degradation mechanism of oil paint films based on Raman spectroscopy is very useful for the improvement of oil painting techniques.

Assessment of Ultraviolet Radiation Exposure in the Wood Surface Coating Industry

Abstract Ultraviolet (UV) radiation curing of paints and lacquers has rapidly increased in the furniture industry. Exposure to UV radiation involves a potential health hazard to workers in this industry and there is little information on UV radiation spectra and exposure levels under these working conditions. We have investigated the intensity and spectral distribution of UV radiation and determined the maximum permissible exposure times (MPETs) at different fixed points surrounding the UV curing units. The spectral irradiance was measured between 250 and 400 nm using a calibrated diode array spectrograph, and the intensity of the UV radiation was measured using a radiometer equipped with UVA and UVB detectors. The spectral power distribution was weighted for biological effect using Wester's approximation equations of the spectral effectiveness curve adopted from the International Radiation Protection Association/International Non-Ionizing Radiation Committee. The intensity of the UV radiation at the substrate passage level ranged from 100 to 200 mW/cm2, giving MPETs of 0.6 to 0.03 seconds, respectively. MPETs varied between 8 and 126 seconds at entrance and exit openings and between 0.5 and 2.3 hours at 0.8 m from the UV curing units. Direct UV radiation from holes and fissures in the units was detected at four of the six plants; MPETs varied from 6 seconds to 3 minutes. High intensity UV radiation was measured below the unshielded bottom of a UV curing unit at one plant (2 seconds MPET). The proportion of UV radiation in different wavelength regions varied moderately (UVA, 38 to 56%; UVB 21 to 40%; and UVC, 12 to 24%). We conclude that UV curing units must be equipped with proper radiation shields, including the holes and fissures, and routinely checked and maintained in order to afford adequate protection from high intensity UV radiation at biologically hazardous wavelengths. Adequate eye and skin protection is required for workers during maintenance of unshielded equipment in order to prevent harmful effects.

Electron beams in research and technology

Fast electrons lose their energy by inelastic collisions with electrons of target molecules forming secondary electrons and excited molecules. Coulomb interaction of secondary electrons with valence electrons of neighboring molecules leads to the formation of radical cations, thermalized electrons, excited molecular states and radicals. The primary reactive species initiate chemical reactions in the materials irradiated. Polymer modifications using accelerated electrons such as cross-linking of cable insulation, tubes, pipes and moldings, vulcanization of elastomers, grafting of polymer surfaces, processing of foamed plastics and heat shrinkable materials have gained wide industrial acceptance. A steadily growing electron beam technology is curing of paints, lacquers, printing inks and functional coatings. Electron beam processing offers high productivity, the possibility to treat the materials at normal temperature and pressure, excellent process control and clean production conditions. On an industrial scale the most important application of fast electrons is curing of 100% reactive monomer/prepolymer systems. Mainly acrylates and epoxides are used to formulate functional coatings on substrates such as paper, foil, wood, fibre board and high pressure laminates. A survey is given about the reaction mechanism of curing, the characterization of cured coatings, and of some industrial application.

A study of the curing process of paint on metal utilizing thermal stimulated current (TSC) and relaxation map analysis (RMA)

The purpose of this work is to illustrate the use of the process of thermally stimulated current (TSC) for the analysis and control of crosslinking and curing of paints on metal substrates. The study of the crosslink density and/or cure ratio for paint on metal is vital, not only in the final quality inspection of a finished part, but also in the development of new resins and processes for paints and coatings.

The use of oven heat sag to determine heat resistance in polypropylenes

AbstractHeat deflection is often the only test used to determine a materials ability to withstand exposure to elevated temperatures under load. This test has its limitations, simply because not all materials operate under loads of 1820 kPa (264 psi) or 455 kPa (66 psi). Consequently, heat deflection cannot always give a true indication of a materials high temperature capabilities. The automotive industry has used the heat sag test to measure the deformation of elastomeric materials during the paint curing process. The heat sag test measures the sag of a molded bar. One end of the bar is clamped while the other end is free to sag or deflect. Samples are tested over a range of temperatures to determine the failure deflection point. This study examines the correlation of the heat sag to heat deflection and dynamic mechanical analysis (DMA) on polypropylene resins and compounds and polystyrene.

High-performance liquid chromatographic determination of Benzil in air as in indicator of emissions derived from polyester powder coatings

A method to estimate occupational exposure to emissions from the curing of polyester powder paints was developed. The method is based on the monitoring only of a certain marker compound in workroom air in order to make the determinations easier. Benzil, reproducibly emitted from all the powders tested, was chosen as the indicator for curing (220°C)-derived emissions. A method for the air sampling and high-performance liquid chromatographic benzil is described. Aspects of the use of marker compounds are discussed.

Ultraviolet radiation curable paints

In product finishing lines, ultraviolet radiation curing of paints on prefabricated structures could be more energy efficient than curing by natural gas fired ovens, and could eliminate solvent emission. Diffuse ultraviolet light can cure paints on three dimensional metal parts. In the uv curing process, the spectral output of radiation sources must complement the absorption spectra of pigments and photoactive agents. Photosensitive compounds, such as thioxanthones, can photoinitiate unsaturated resins, such as acrylated polyurethanes, by a free radical mechanism. Newly developed cationic photoinitiators, such as sulfonium or iodonium salts (the so-called onium salts) of complex metal halide anions, can be used in polymerization of epoxy paints by ultraviolet light radiation. One-coat enamels, topcoats, and primers have been developed which can be photoinitiated to produce hard, adherent films. This process has been tested in a laboratory scale unit by spray coating these materials on three-dimensional objects and passing them through a tunnel containing uv lamps.

Rim Catalysis and Coating Interaction

Use of urethane RIM has grown to where more than onethird of cars produced in the United States have RIM front or rear fascias. DABCO catalyst has played an important role in the growth of RIM and will continue to do so in the future because of its unique advantages. Improved flowability, reduction in air entrapment, and proper green strength to allow parts to be demolded with the flash still intact and without part tearing or deformation are all key factors which contribute to efficient processability. DABCO catalyst and tin co-catalyzed RIM parts with DABCO levels as high as 0.5 php (100% active) are being produced today and are successfully coated with commercially available high solids coatings (e.g., Durethane 300) color plus clear, and water based coatings. With PPG's experimental High Solids Durethane Elastomeric Enamel, (higher solids level than Durethane 300) DABCO catalyst can be used in urethane formulations at up to .15 php (100% active) without any adverse effects on the coating. Additional reactive amine catalysts, such as DABCO T, can be added at levels of 0.5 php and greater as a co-catalyst with DABCO catalyst and tin, again without adverse effects on the High Solids coating. RIM parts catalyzed with DABCO catalyst levels greater than 0.15 php were successfully coated in our studies by either subjecting the part to a high temperature water rinse after the normal washing cycle (effective up to 0.3 php DABCO catalyst) or by adding a small amount of add to the primer. For processors who desire DABCO levels up to 1.0 php, RIM parts can be successfully coated with the experimental higher solids coating by the addi tion of an additive to the RIM formulation. The additive was mixed into the reactants which did not interfere with rates of reaction or demold times of the finished part. During the post cure heat cycle the additive reacts with the amine thereby preventing the amine from interfering with the acid catalysis of the paint curing cycle.

Electron-beam curing of paints and varnishes on wood panels

Electron-beam curing of paints and varnishes on wood panels

Paint Curing Systems of Ultraviolet Radiation

Paint Curing Systems of Ultraviolet Radiation

60 kW Electron Accelerator for a Paint-Curing Facility

Compared with radioactive isotopes, electron accelerators are very powerful sources of radiation. Due to the limited penetration depth of the electrons, these accelerators can only be applied for the radiation processing of surfaces or thin materials. Of special interest is the utilization of low-energy, high-power electron accelerators for the curing of paint coatings on wood, metal, and plastic surfaces. A paint-curing facility was built with a 600 keV electron accelerator with an output power of 60 kW. During the first year of continuous operation, important improvements were made in the entire process, particularly in developing suitable paint and maintaining a pure nitrogen atmosphere in the radiation chamber.

Radiation Curable Coatings on Plastics

Variables affecting the properties of electron beam cured acrylic and polyester coatings have been studied. The concentration of double bonds in unsaturated polymer, glass transition temperature of the coating and the choice of vinyl monomers for viscosity adjustment determine the solvent resistance and hardness of the coating. Electron beam cured coatings show excellent adhesion on ABS and untreated polypropylene. That the electron beam curing of paint on automotive plastic components is a suitable industrial process is indicated by recently announced Ford Production facility.

アミノアルキッド樹脂塗膜の膨潤および溶解度

アミノアルキッド樹脂塗膜の膨潤および溶解度

メラミン樹脂塗料の保存性におよぼす諸因子について

メラミン樹脂塗料の保存性におよぼす諸因子について