UV Curing Process Research Articles

Nanostructured hybrid materials obtained by UV curing and sol-gel processes involving alkoxysilane groups

AbstractNovel hybrid organic-inorganic coatings were obtained by photopolymerization and subsequent thermally induced condensation through solgel processes. Both radical (methacrylic) and cationic (epoxy) resins were considered as precursors of the organic phase; tetraethoxysilane (TEOS) was the precursor of the inorganic phase. The effect of the presence of a coupling agent was investigated. Real-time FT-IR analysis was used for evaluating the kinetics of photopolymerization. 29Si-NMR spectroscopy was used in order to evaluate the degree of condensation of alkoxysilane groups. The results showed the prevalence of Q3 e T2 structures indicating an incomplete condensation of the alkoxysilane groups. T1 and Q1 signals are not present, thus indicating that for each Si atom, two or more alkoxysilane groups take part to the condensation reaction. FE-SEM analyses evidenced a nanometric organization of the inorganic domains in the polymer matrix. The addition of the coupling agent was found to influence the morphology of the hybrid systems. DMTA and TGA analyses revealed an increase of the Tg values and of the thermal stability by increasing the coupling agent and TEOS content.

Development of photoluminescent powder coatings by UV curing process

The use of thermal curing powder coatings have obtained a wide acceptance, but is limited to the metal substrates applications, because they need high temperatures for the film curing. Safety sings in edifications use, generally, PVC substrates, that are unable to support typically curing temperatures (150–200 °C). In order to prepare a photoluminescent powder coating by UV curing process, an experimental technique was development and the influence of some preparative conditions were studied. To achieve the better results, photoluminescent pigment percentage, conditions of ultra-centrifugal mill and thickness of deposition coating were varied in order to increase the luminance decay time.

Preparation and optical properties of organic/inorganic nanocomposite materials by UV curing process

In this study, photo-polymerized poly(acrylic)/silica hybrid thin films were prepared from various acrylic monomers and monodispersed colloidal silica with the coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA). The silica content in the hybrid thin films varied from 0 to 50 wt.%. The experimental results show that the particle size of silica in hybrid films could be effectively controlled at 15–20 nm as the weight ratio of MSMA to colloidal silica is higher than 0.68 and 0.60 for the poly(methyl methacrylate)/silica ( US) and poly(ethylene glycol dimethacrylate-trimethylolpropane trimethacrylate)/silica ( UDT) hybrid materials, respectively. The polymerization conversion for US and UDT hybrid materials could reach to 100% and 94.5%, respectively. The comparison of surface roughness with the film thickness is less than 0.10%, indicating the excellent surface planarity of the prepared hybrid thin films. Besides, the prepared hybrid films from the crosslinked acrylic polymer moiety show much better film uniformity, thermal stability and mechanical properties than those obtained from poly(methyl methacrylate). The refractive index decreases with increasing the silica content in the hybrid films. Excellent optical transparency is obtained in the prepared hybrid films. These results show that the prepared hybrid thin films have potential applications as passive films for optical devices.

UV-cured polymer electrolytes encompassing hydrophobic room temperature ionic liquid for lithium batteries

We demonstrate herewith the application of in situ one-shot free radical photo-polymerisation (UV-curing) process to incorporate room temperature ionic liquids (RTILs) into polymer membranes which can be used as electrolytes for lithium-based batteries. The reactive formulation for the preparation of the polymer membranes was based on a dimethacrylic oligomer (BEMA). The polymer electrolyte membranes were synthesized by UV radiating a mixture of BEMA and a proper radical photo-initiator with different compositions of 1-ethyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide [EMIPFSI] and, additionally, LiTFSI as lithium source. Stable and flexible polymer films with good mechanical integrity can easily be produced with varying the EMIPFSI content by using this method. Remarkable values of ionic conductivity were obtained even at ambient temperature. Galvanostatic charge/discharge cyclability tests were performed on the polymer electrolyte membranes by constructing a cell using LiFePO 4 as cathode and Li metal as anode. The preliminary results are interesting, exhibiting good reversibility and cyclability.

Magnetochromatic Microspheres: Rotating Photonic Crystals

Magnetochromatic microspheres have been fabricated through instant assembly of superparamagnetic (SPM) colloidal particles inside emulsion droplets of UV curable resin followed by an immediate UV curing process to polymerize the droplets and fix the ordered structures. When dispersed in the liquid droplets, superparamagnetic Fe(3)O(4)@SiO(2) core/shell particles self-organize under the balanced interaction of repulsive and attractive forces to form one-dimensional chains, each of which contains periodically arranged particles diffracting visible light and displaying field-tunable colors. UV initiated polymerization of the oligomers of the resin fixes the periodic structures inside the droplet microspheres and retains the diffraction property. Because the superparamagnetic chains tend to align themselves along the field direction, it is very convenient to control the orientation of such photonic microspheres and, accordingly, their diffractive colors, by changing the orientation of the crystal lattice relative to the incident light using magnetic fields. The excellent stability together with the capability of fast on/off switching of the diffraction by magnetic fields makes the system suitable for applications such as color display, rewritable signage, and sensors. As a simple demonstration, we have fabricated a display unit that has on/off bistable states by embedding the magnetochromatic microspheres in a matrix that can thermally switch between solid and liquid phases.

Nanocomposite epoxy coatings containing rare earth ion-doped LaF 3 nanoparticles: Film preparation and characterization

New epoxy-based nanostructured materials containing lanthanide ions doped LaF 3 nanoparticles were obtained by cationic UV-induced ring-opening polymerization. The lanthanide Er 3+ and Yb 3+ ions were added as dopant to LaF 3 nanoparticles. The synthesized NPs were solubilized into cyclohexene oxide and afterwards dispersed, in the range between 3 and 20 wt.%, into CE as dicycloaliphatic epoxy resin. The cured films were completely transparent and TEM analysis showed the absence of macroscopic agglomeration. The fast UV curing process was shown to be efficient on “freezing” the good nanometric dispersion achieved in the liquid formulations. These new materials could find suitable applications in optical communication and in LASER waveguide direct writing.

UV-curable PDMS-containing PU system for hydrophobic textile surface treatment

Polydimethylsiloxane (PDMS) is a super-hydrophobic material with low surface energy. UV-curable PDMS-containing polyurethane (PU) oligomer (UV-PDMS-PU), having a PDMS moiety is designed for textile (PET and Nylon) surface treatment with a long lasting hydrophobic property. UV-PDMS-PU was prepared by an addition of 2-hydroxyethyl methacrylate (2-HEMA) to NCO-terminated PDMS-containing PU pre-polymer (NCO-PDMS-PU). NCO-PDMS-PU was obtained from an addition reaction of alkyl hydroxyl-terminated PDMS with an excess amount of isophorone diisocyanate (IPDI). UV-PDMS-PU system consisted of 1% (w/w) photo-initiator that was coated either on glass plate or textile and then cured by UV-radiation. The UV-cured PDMS-containing PU films were evaluated by the measurements of thermal and physical properties. The hydrophobic characters and silicone content were remained on textile surface after water washing cycles, which indicating that UV-curing process can help the PDMS moiety to anchor onto textile fibers.

UV Coatings: Basics, Recent Developments and New Applications

Chapter 1 Introduction to Coatings Technology Chapter 2 The UV Curing Process Chapter 3 Network Formation and Characterization Chapter 4 Raw Materials Chapter 5 Formulations Chapter 6 StructureProperty Relationships Chapter 7 Tackling the Drawbacks of UV Systems Chapter 8 Classical Applications Chapter 9 Recent Developments Chapter 10 New Applications Chapter 11 Health, Safety and Environment

UV curing kinetics and mechanism of a highly branched polycarbosilane

AbstractThe UV curing process in both air and nitrogen atmosphere for the highly branched polycarbosilane system was investigated by differential scanning photo calorimeter. The UV cured products were characterized by Fourier‐transform infrared spectrometry (FTIR). By comparison with the FTIR results of the uncured liquid mixture and the cured samples, the possible cross‐linking reactions were determined. The kinetics of the curing systems was studied. The rate constant k was calculated based on the experimental results. The activation energies in different curing conditions were obtained. According to these results, it was learned that the mechanism for the UV curing in nitrogen was controlled by the photolysis of photoinitiator. Comparably, the UV curing process in air was complicated. It was affected by not only the photolysis of photoinitiator, but also oxygen and tripropane glycol diacrylate. Copyright © 2008 John Wiley & Sons, Ltd.

Polymer electrolyte for lithium batteries based on photochemically crosslinked poly(ethylene oxide) and ionic liquid

Polymer/ionic liquid composites were investigated as solvent-free electrolytes for lithium batteries. Ternary electrolytes based upon poly(ethylene oxide), an ionic liquid and a conducting salt were UV crosslinked with benzophenone as the photoinitiator. Crosslinking leads to an increase in mechanical stability of the PEO composites. This straight-forward process provides a way to increase the content of ionic liquid and thus to raise ionic conductivity without loss of mechanical stability. Impedance measurements showed that the ionic conductivity of the composites is not affected by the UV curing process. Moreover, the UV curing process causes a decrease in the degree of crystallinity in the PEO composites which contributes to an increase in ionic conductivity. The present work is related to safety issues of lithium batteries.

Extolling the advantages of UV-curing processes

Extolling the advantages of UV-curing processes

Optical Property Changes in Low-k Films upon Ultraviolet-Assisted Curing

Ultraviolet-assisted curing (UV curing) has been applied recently to enhance the mechanical properties of low- films. Knowledge about which UV energies are most effective is still limited and the consequences of applying the UV-curing process to integrated stacks in on-chip interconnects are unknown. To clarify these open questions, we investigated the optical properties of a SiCOH low- layer by purged UV spectroscopic ellipsometry in the energy region 2–9 eV. The complex refractive index of the low- film shows an absorption edge with a superimposed absorption band at 6.4 eV that vanishes upon UV-assisted curing. A comparison with Fourier transform infrared transmission demonstrates that the absorption at 6.4 eV must be attributed to the organic porogens, which also influence the absorption edge. Further analysis reveals the redshift of the absorption edge of silica-based low- films with the presence of carbon species. The measured optical properties permit simulation of the standing wave pattern of light within the films in differently configured stacks.

Epoxy coatings containing clays and organoclays: Effect of the filler and its water content on the UV-curing process

UV-cured coatings were prepared by photoinitiated cationic ring-opening polymerisation of epoxides in the presence of natural montmorillonite and different organically modified clays (5 wt%). The curing was monitored by FTIR in real time while irradiating the formulations by UV light. Significant changes of both the rate of curing and the final conversion were found. Only in the presence of a suitable montmorillonite and after a suitable pre-treatment, the process showed the same polymerisation rate, guaranteed a higher conversion than the neat epoxide and the formation of intercalated nanostructured coatings.

Bond Structure in Porous SiOCH Low-k Film Fabricated by Ultraviolet Irradiation

Using an advanced ultraviolet irradiation (UV curing) process, a high performance porous low-k film of k=2.57, whose Young's modulus is larger than 8 GPa, now is developed to improve the mechanical properties of a film by the reconstruction of Si–O network structure from cage-like Si–O bonds, suboxide structures and Si–CH3 bonds. It was found that the UV curing process can efficiently strengthen the mechanical properties of porous low-k film, and reduce its dielectric constant value by removing hydrocarbon bonds to form porosities. As a result, the key features of this optimal SiOCH material, high elastic modulus and a low dielectric constant, provide promising properties for future integrated schemes.

Synthesis of UV crosslinkable waterborne siloxane–polyurethane dispersion PDMS-PEDA-PU and the properties of the films

A UV crosslinkable waterborne siloxane–polyurethane dispersion, PDMS-PEDA-PU, was synthesized by incorporating acrylate groups into the side chain of the polyurethane using pentaerythritol diacrylate (PEDA). Polysiloxane groups were introduced into the soft segment of the polyurethane using polydimethylsiloxane (PDMS). They formed a crosslinking structure after UV radiation. The structure of PDMS-PEDA-PU was confirmed by the use of Fourier transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) analysis indicated that the formed PDMS-PEDA-PU was amorphous. The curing rule of PDMS-PEDA-PU was investigated on the basis of the change in C=C conversion during the UV curing process. The influence of the PDMS/PEDA ratio was studied with respect to the water resistance, the thermal property, and the mechanical property of the films.

Nanophotonic crystals with chiral elements by a hot embossing process in SU-8

We report a novel nanoprocess to fabricate 2D metallic and non-metallic nanophotonic crystals on SU-8 using hot embossing combining with a UV-curing process. The fabricated photonic crystals were characterized by optical diffraction experiments. Theoretical simulation of the light diffraction through such kind of artificial crystals agrees with the measured optical property very well, indicating that the developed fabrication technique is able to produce large area nanosize photonic crystals at economic costs. The success of this work not only provides scientists with a good opportunity to pioneer novel photonic physics in metallic and non-metallic chiral as well as photonic crystal systems, but also bridges the gap between laboratory and industrial application for mass production of photonic nanostuctures.

Free-standing SU-8 subwavelength gratings fabricated by UV curing imprint

Fabrication technique for making subwavelength anti-reflective grating structures has been developed, based on nanoimprint of SU-8, for applications in the near infrared spectral range. The depth and duty cycle of the grating structures optimized for wavelengths around 1550nm were calculated using rigorous theory of diffraction. The Si mold was made by electron-beam lithography and deep reactive ion etching. The mold structures were transferred to SU-8 by imprinting and followed by UV curing process. A bilayer process using PMMA as sacrificial layer was developed to release the SU-8 layer. The optical properties of the replicated SU-8 gratings were measured over a wide range of spectral wavelength. The general shapes of the curves are in good agreement with the calculations. The reflectivity has been reduced significantly.

Effect of UV Curing on Electrical Properties of a UV‐Curable co‐Polyacrylate/Silica Nanocomposite as a Transparent Encapsulation Resin for Device Packaging

AbstractElectrical properties of UV‐curable co‐polyacrylate/silica nanocomposite resins prepared via sol‐gel process for device encapsulation were investigated. It was found that, by appropriate UV curing process and the formation of nanoscale silica particles finely dispersed in the resin matrix, the leakage current density of the nanocomposite resin films decreases from 235 to 1.3 nA · cm−2 at the applied electrical field of 10 kV · cm−1. The silica nanoparticles also restricted the motions of polar functional groups in organic matrix that the nanocomposite films with satisfactory dielectric properties [dielectric constant (ε) = 3.93 and tangent loss (tanδ = 0.0472) could be obtained. Chemical structure analyses revealed that excessive UV curing results in photooxidation and/or photodegradation in resin samples, leading to the polar groups and ionic/radical segments in organic matrix as well as the SiOSi structure in the vicinity of silica nanoparticles. These organic/inorganic functional groups generated more permeation paths for charge carrier migration and hence deteriorated the electrical properties of the nanocomposite samples. Though post‐baking treatment at 80 °C for 1 h followed by UV curing improved the rigidity of the resin sample, it brought the polar functional groups closer to each other and similarly degraded electrical properties of the nanocomposite resins.magnified image

Preparation and characterization of UV-cured epoxy nanocomposites based on o-montmorillonite modified with maleinized liquid polybutadienes

Polymeric nanocomposites based on an epoxy cycloaliphatic resin and o-montmorillonite (Cloisite 30B®) modified by reaction with maleinized liquid polybutadienes were prepared through photopolymerization. The conditions for the o-montmorillonite modification were settled. After the reaction, a strong increase of the basal spacing of the nanoclays was evidenced through XRD analysis. The modified clays were dispersed in the epoxy resin (5wt.%) and subjected to the UV-curing process. The kinetics of the photopolymerization process was evaluated by means of Real-Time FT-IR spectroscopy. The obtained nanocomposites were studied by means of XRD and TEM analyses; the formation of either intercalated or quasi-exfoliated structure was assessed. The thermal and mechanical properties of the cured films were evaluated and correlated to the morphology of the obtained nanocomposites.

New perfluoropolyether urethane methacrylates as surface modifiers: Effect of molecular weight and end group structure

The paper reports the synthesis and characterisation of two new series of perfluoropolyether methacrylates, characterised by increasing MW and different end groups. They were used as co-monomers in the polymerisation of Bisphenol A bis-ethylether diacrylate via a UV-curing process. Notwithstanding their very low concentration (<1% w/w), the fluorinated monomers caused a dramatic change of the surface properties of the copolymeric networks. They showed an excellent surface activity evidencing hydrophobic and lipophobic properties which could be modulated either by changing the MW and the end group of the fluorinated co-monomer or by controlling the curing process, in particular the time elapsing between the coating of the co-monomers mixtures onto the substrate and the irradiation of the systems.