UV-curing Technology Research Articles

Effects of compaction and UV exposure on performance of acrylate/glass‐fiber composites cured layer by layer

AbstractWith an aim to reducing manufacturing costs, in general and specifically to provide a solution to the thick laminate curing depth issue for composite materials, UV curing technology was combined with a fiber placement process to fabricate acrylate/glass‐fiber composites. A novel layer‐by‐layer UV in situ curing method was employed in this article and interlaminar shear strength (ILSS) tests and SEM were used to evaluate the effect of processing parameters, including compaction force and UV exposure dose, on ILSS. The SEM images from short‐beam strength test samples and the results of ILSS showed that the fibers' distribution was uniform in the cured matrix resin resulting from the compaction forces and that beneficially influenced the ILSS of the composite greatly. However, the matrix resin produced large shrinkage stresses when it reached a high degree of conversion (DC) in one‐step, which resulted in poor interlaminar adhesion. In addition, the fast curing speed of UV on the composite resulted in poor wetting between fiber and resin, and accordingly resulted in lower ILSS. To overcome these problems and obtain high ILSS value composites, an optimized compaction force and UV exposure dose were determined experimentally. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

On the UV-Induced Polymeric Behavior of Chinese Lacquer

To dry Chinese lacquer rapidly for the protection and restoration of archeological findings coated by lacquer or excavated lacquer wares and the development of new application of this lacquer, we carried out UV curing technology to improve its curing rate using a high-pressure mercury lamp as a UV source in the absence of any additional photoinitiator. The effects of mainly specific components in Chinese lacquer sap and the role of each reactive group of urushiol, namely hydroxyl groups, hydrogen on the phenyl ring, and olefins in the side chain, in the course of UV exposure were well-investigated. The UV-cured Chinese lacquer films were also characterized by FT-IR, (1)H NMR, SEM, TGA, and Py-GC/MS. The results showed that urushiol was the main component to form Chinese lacquer films, and decomposed to generate the urushiol semiquinone radicals, which sequentially induced the polymerization of Chinese lacquer by radical polymerization, as well as radical substitution under UV irradiation. In addition, the TG analysis suggested that polysaccharide and glycoproteins were integrated with the UV-cured films by covalent bonding. Furthermore, this method could be suitable to fast cure other phenol bearing long aliphatic unsaturated chain, such as CNSL.

Luminescence Enhancement of Organic Nanoparticles Induced by Photocrosslinking

Nanoparticles are interesting materials because they exhibit unique optical and chemical properties which differ from solvated molecules and the bulk solid state and can be finely tuned during synthesis. These properties make nanoparticles suitable for numerous applications such as catalysis, high-performance ceramic materials, microelectronic devices, sensing, high-density magnetic recording and photonic materials. Colloidal organic fluorescence nanoparticles (ONPs) can be described as a core–shell system in which the core built of fluorescent dye molecules is coated by a stabilizer layer (surfactants or polymers) and show very different fluorescent properties from those arising from the starting materials. Despite the ease of preparation (mild and sustainable conditions), and the range of starting materials, there is not an extensive literature on ONPs so far (in comparison with inorganic colloidal nanoparticles), most likely because their lack of stability, which limits their use in photonic applications. In fact, they are basically self-assembled nanostructures arranged through intermolecular interactions (such as hydrogen bonding, p–p stacking, and hydrophobic interactions) which can be weakened by medium changes (pH, polarity, hydrophobicity, dilution). Organic nanoparticles are usually prepared by mechanical milling of the raw material, by precipitation or condensation of the starting material. In general, in colloidal organic nanoparticles the fluorescent material is confined in a stabilizer shell ; thus additives such as polymers take over the functions to be a boundary layer and a colloidal stabilizer. Photoinduced polymerization (UV curing) of monomers or oligomers is one of the most efficient ways to prepare photocrosslinked polymer networks. In short times and selectively at the irradiated area, liquid resins can be transformed into solid polymers very resistant to heat and mechanical treatments. These effects made UV curing technology widely used in many industrial applications. Considering the ability of some polymers to undergo crosslinking processes, a robust protective shell for the prepared organic nanoparticles was created by UV curing. The caging of the ONPs in a photocrosslinked polymeric shell could result in a considerable improvement in the stability and hence in the emission properties of the colloidal nanomaterials. ONPs were first prepared by use of the reprecipitation method, following the literature procedures. Herein, (EE)-1phenyl-4-(1’-pyrenyl)-1,3-butadiene [(EE)-PyPhB, Scheme 1], synthesized as previously reported, was selected as organic dye to build up the particle cores.

Development and Study of Applications Combining Nanopowder Imprint Lithography and Array-Type UV-Curing Technology for Micro-Lens Molding

This study developed creative imprinting technology, combining nano-imprint lithography and array-type UV-curing technology. It used nanopowders as the method to transmit imprint force, and integrated technical features, such as soft lithography, light-curing resistant and gas-assisted imprint technology, in order to study the development of technological processes of micro-lens array manufacturing, and mature the application and technology of nano-imprinting. According to research results, SUS 304 stainless steel sheet with a micro-hole array could be smoothly fabricated into an original micro-lens array mold upon gas-assisted micro-hot embossing. At the same time, a micro-lens array structure with a complementary external form could be precisely remolded and reproduced by PDMS. Complete molding of micro-lens could be effectively achieved by combining imprints of gas-assisted lithography developed in this study, and even UV-NIL. The effective imprinting area and reproducibility of transfer printing could be greatly improved when a micro-lens contacts perfectly with a substrate surface. Moreover, since PDMS soft molds have short remolding times, and are easily feathered during manufacturing, production costs could be effectively reduced through features such as, low surface free energy, resistant to adhering to the mold during imprinting, and collocation of gas-assisted nanopowder imprinting of micro-structural processes.

Soy-based UV-curable thiol–ene coatings

Novel soy-based thiols and enes were synthesized and characterized. Then, soy-based thiol–ene UV-curable coatings were formulated and their coating physiochemical properties were investigated in detail. The use of biorenewable resources, combined with environmentally friendly UV-curable technology, provides a “green + green” solution to the stricter regulations in the coatings industry. Novel soy-based thiols and enes were synthesized through the Lewis acid-catalyzed ring opening reaction of epoxidized soybean oil with multifunctional thiols or hydroxyl functional allyl compounds. FTIR and NMR confirmed the formation of the target compounds. The soy-based thiols and enes were formulated with petrochemical-based enes and thiols, respectively, to make thiol–ene UV-curable coatings. Typical coating film properties, thermal properties, and photopolymerization kinetics of these coatings were studied. Soy-based thiol–ene coatings having lower functionality thiols and enes have poor UV curability and coating properties, which was attributed to the lower crosslink density. Soy-based thiols and enes with higher functionality can be UV-cured in combination with petrochemical-based enes or thiols even without the presence of free radical photoinitiators. Better coating film properties were obtained from these higher functionality thiol–ene systems that were toughened by commercial hyperbranched acrylates.

Variable solar control using thermotropic core/shell particles

Subject of our recent investigations is the utilization of a reversible thermotropic material for a self-regulating sun protection glazing that controls the solar energy input in order to avoid overheating. Based on the well-established UV curing technology for laminated glass a superior thermotropic material with tunable switching characteristics and of low material costs was developed. The polymer layer contains core/shell particles homogeneously dispersed in a UV-cured resin. The particle core in turn consists of an n-alkane mixture that is responsible for the temperature-induced clear/opaque switching. To obtain particles of well-defined size and with a narrow size distribution, the miniemulsion polymerization technique was used. The visible and solar optical properties (normal–normal, normal–hemispherical, and normal–diffuse transmittance) in the off (clear) and in the on state (opaque) were determined by UV/Vis/NIR spectroscopy. Samples containing particles of high median diameter (>800 nm) primarily scatter in the forward direction. However, with smaller particles (300–600 nm) a higher backscattering (reflection) efficiency was achieved. The largest difference in the normal–hemispherical transmittance could be found with a particle amount of 6% and a median scattering domain diameter of ∼380 nm.

Porosity generation using hydrogen plasma assisted thermal curing for ultra low k material

In this work H 2 plasma curing is studied to appreciate hydrogen species impact on porogen removal efficiency and transformation occurring within the porous SiOCH structure. The investigation is done by comparing H 2 plasma with other curing treatment (UV curing). H 2 plasma curing shows a benefit in term of porogen removal and can be considered as a fast process as only few minutes are required to decompose the C–H bonds and create the porosity. However, longer treatment reveals carbon depletion by Si–CH 3 decrease and porosity collapse through the shrinkage enhancement. Plasma treatments lead also to the creation of SiH bonds which could serve as a hydrogen radical generator when the film is electrically stressed. The leakage current and breakdown voltage values are then affected by these hydrogen radicals, which can contribute in the electrical conduction. The H 2 process allows obtaining films with a dielectric constant below 2.4. This process shows encouraging results comparing with the k = 2.35 obtained with UV curing technology.

2-Winylooksykarbonylooksymetyloantrachinon jako nowy nienasycony fotoinicjator stosowany do sieciowanych za pomocą UV samoprzylepnych klejow poliakrylanowych

Summary — Modern UV-curing technology requires efficient and very effective photoinitiators. The best technological solution is the use of unsaturated photoinitiators incorporated into the polymer chain during the synthesis of a pressure-sensitive adhesive (PSA) and being active in its UV-curing. In this work the unsaturated photoinitiator based on antraquinone [VCMA, formula (I)], in amounts from 0.1 to 2.0 wt. %, was used in the syntheses of photoreactive PSA made of 2-ethylhexylacrylate, methyl acrylate and acrylic acid. The obtained photoreactive polyacrylic adhesives, coated onto polyester films, were cured by UV lamp. Adhesion and cohesion of PSA were determined, dependently on photoinitiator concentration and UV curing time. It was found that high values of adhesion and cohesion were reached when photoinitiator concentration was about 0.5 wt. % and curing time about 2.5—3 min. Photoreactive polyacrylic adhesives, described and characterized in the article, synthesized with use of 2-vinyloxycarbonyloxymethyl antraquinone as photoinitiator, can be used in the

Challenges of UV curable ink‐jet printing inks – a formulator's perspective

UV curing technology has a number of unique advantages over the conventional curing technologies. However, until very recently, there had been few successful examples of the application of UV curing technology in ink‐jet printing. Several reasons, including the requirement of low viscosity for ink‐jet printing inks, were responsible for the lack of development of UV curable ink‐jet printing inks. This paper describes, in some details, the challenges that a formulator had to face in developing UV curable ink‐jet printing inks, together with information on the status quo of UV curable ink‐jet printing technology.

Review of basic chemistry of UV‐curing technology

The market for ultraviolet curing technology has been growing at double‐digit rates in the last 10 years. The main reason for such a rapid technological growth of UV curing is its unique process characteristic, which allow UV‐coating to be applied on virtually any substrates, including plastic, metal, composite, wood, paper, leather, vinyl, glass, magnetic recording tape and even human teeth. The original driving forces behind the commercialisation of UV‐technology were energy saving and freedom from solvents. These benefits are complemented by high productivity and subsequently higher profits that can be achieved with the increased line speed, just‐in‐time benefits and immediate “pack and ship” capabilities. This paper gives a review of the development of the UV curing technology, with emphasis placed on relevant chemistry.

Synthesis of clay nanocomposite materials by light-induced crosslinking polymerization

Different types of nanocomposite materials have been synthetized within seconds at ambient temperature, by photoinitiated crosslinking polymerization of epoxy, vinyl ether and acrylate-based resins containing a small amount (3 wt%) of an organoclay filler. The curing process was followed quantitatively by infrared spectroscopy through the decrease upon UV exposure of the IR bands characteristic of the functional groups. The silicate nanoparticles were found to have no effect on the polymerization kinetics. The UV-cured nanocomposites proved to be more flexible and impact resistant than the corresponding microcomposites. This method of synthesis of nanocomposites presents the advantages associated with the UV-curing technology, namely a solvent-free resin transformed rapidly at ambient temperature into a chemically resistant material, with a minimum consumption of energy.

Organic-modified polydimethylsiloxanes for UV-curable coatings

Because additives have been around for decades, they have never diminished from our focus in formulations. Even though additives represent a minor portion of a formulator’s paint or ink formula, without them surface defects can be significant. In particular, silicone additives bring to the coatings’ table a range of surface-modifying and enhancing properties. As a result of the increasing pressure to reduce VOCs, UV-curable technology is experiencing a significant growth in the market. This paper will look at the technological advancements of silicone additives as they have progressed through simple polyether modification, which helped overcome incompatibilities in coatings formulations. The more reactive functional modifications that silicones are heading towards still help to maintain compatibility but offer more permanent results. Typical coating film defects such as cratering and orange peel are avoided, and the negative effects of floating can be suppressed. Furthermore, these additives provide smooth surfaces as well as improving the gloss and allowing the coating to be more scratch resistant.

Ultrafast synthesis of bentonite-acrylate nanocomposite materials by UV-radiation curing

Nanocomposite materials made of silicate platelets randomly dispersed in a crosslinked polyurethane-acrylate have been readily produced by photoinitiated polymerization. The mineral filler (bentonite) was treated by an ammonium salt or an acrylated amine to make it organophilic and allow the acrylic resin containing a photoinitiator (aromatic ketone) to penetrate into the expanded organoclay galleries. The photoinitiated crosslinking polymerization reaction was followed in real time by infrared spectroscopy and shown to proceed extensively (>95% conversion) within a few seconds of UV-irradiation. The flat X-ray diffraction spectra recorded with the UV-cured material shows that the layered silicate has been completely exfoliated, thus demonstrating that a nanocomposite material has well been produced. This method of synthesis presents the distinct advantages associated with the UV-curing technology, namely, a solvent-free formulation undergoing ultrafast polymerization at ambient temperature in the presence of air.

Relationship between pigment properties and UV-curing efficiency

Due to solvent emission restrictions and rationalization in the coating industry, the UV-curing technology will play an important role in the future. One of the key success factors will be the feasibility to cure colored coatings without any major restrictions in terms of the pigments and their combination used. Colored substances are competing with their light absorption properties against the photoinitiators and the UV-absorbers. With the novel class of photoinitiators based on bis-acylphosphinoxides (BAPO), one step has been achieved to cure colored coatings effectively. But up to now there is a need that pigment manufacturers are doing research work to optimize their pigments for UV-curing efficiency. Preliminary investigations are reported herewith.

High-speed photocrosslinking of thermoplastic styrene-butadiene elastomers

Photoinitiated thiol/ene polymerization was used to crosslink a triblock styrene/butadiene/styrene (SBS) polymer of low vinyl content (8%). The crosslinking process was followed by infrared spectroscopy (loss of unsaturation), insolubilization, swelling, and hardness measurements. The photogenerated thiyl radicals react with both the vinyl and the 2-butene double bonds of the copolymer. Concentrations of less than 1 wt % in the trifunctional thiol crosslinker and in the acylphosphine oxide photoinitiator proved to be sufficient to create, within 0.5 s, a permanent chemical network in the elastomeric phase. This UV-curing technology was successfully applied to crosslink rapidly commercial SBS–Kraton® thermoplastic elastomers. It proved also effective in the case of the much less reactive triblock styrene/isoprene/styrene (SIS) polymer which contains no vinyl double bonds. The thiol/ene polymerization was shown to be a much more efficient process to crosslink SBS and SIS thermoplastic elastomers than was the copolymerization of the rubber double bonds with a diacrylate monomer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1902–1912, 2000

The use of UV irradiation in polymerization

Photoinitiation is one of the most efficient methods for achieving quasi-instantaneous polymerization, transforming a liquid molecule into a solid polymer material within less than 1s. The kinetics of such ultrafast reaction can be advantageously followed by real-time infrared spectroscopy, a technique which records directly conversion versus time curves and allows evaluation of the important kinetic parameters of cross-linking polymerization. Photoinitiation has proved to be well suited to inducing frontal polymerization and achieving a deep-through cure of thick specimens. UV technology is also capable of causing fast polymerization in solid media, despite severe mobility restrictions, because of the high initiation rate provided by intense illumination. This review presents some recent advances in the UV-curing technology, special emphasis being given to the kinetic aspect of ultrafast polymerization reactions induced by light. © 1998 SCI.

Ultraviolet Radiation Curing Treatments for Shrink-Resistant Wool Fabric

The application of uv curing and corona discharge technology to textiles is intro duced and discussed, The influence of uv photoreactive monomer on the shrinkage and mechanical properties of corona and nonpretreated 100% wool gabardine fabric is detailed. Machine washability can be achieved at low add-on by incorporating a uv curable silicone into the formulation and a post-cure steam treatment.

Achieving optimum performance with UV curable solder masks

The development of UV curing technology has introduced new solder masks which will replace the thermally‐cured masks of the past. In doing so, processing efficiency will be increased in terms of time, energy and space saving. In considering the effective use of the new technology, thought must be given to many factors which influence the optimum performance of UV cured solder masks. The thickness of deposit will most certainly be greatly influenced by the choice of screen fabric, mesh size and squeegee which will subsequently impact upon the rate and extent of cure. One must also prepare the substrate surface adequately to compensate for the minimal wet adhesion and dwell time of a solventless ink prior to cure. Other factors such as flux chemistry, solder temperature, and soldering conditions play an important part in the performance of a solder mask and are discussed in detail. This paper was originally presented at the First Printed Circuit World Convention held at the Cafe Royal, London, in June, 1978.