Ultraviolet Curing Process Research Articles

Analysis on the ultraviolet curing process of resin‐based glass fiber composites based on finite element mesoscale model

AbstractThe resin curing process triggered by ultraviolet radiation possesses numerous advantages, including rapid speed, low cost, and minimal environmental impact. Due to the hindrance of light propagation by the medium, uneven curing or incomplete curing at the bottom may occur frequently, particularly when the material thickness is excessive. To address these issues and delve into the regularities of the light‐curing process, this study employed a modeling approach that separately represents fiber bundles and the resin matrix to construct a mesoscopic model of the resin‐based glass fiber‐reinforced composite material glass fiber reinforced polymer (GFRP). Based on the models of light propagation, light‐curing kinetics, and heat conduction, a multiphysics field decoupling model is established to simulate the light‐curing process of GFRP. Using this model, the temporal and spatial variations of the internal light field, degree of curing field, and temperature field within GFRP during the curing process are simulated. The mechanistic reasons for these variations are analyzed. Finally, in conjunction with the regular analysis based on the macroscopic model, the accuracy of the model and the obtained regularities are validated through experiments. This provides an effective analytical method for the study of light‐curing in resin‐based fiber‐reinforced composite materials.

Aerosol jet printing of nickel oxide nanoparticle ink with ultraviolet radiation curing for thin-film temperature sensors

In this study, the ultraviolet (UV) radiation curing process and furnace curing process for curing aerosol jet printed nickel oxide (NiO) nanoparticle thin films were investigated. NiO has a negative temperature coefficient and can be used to fabricate temperature sensors. Four UV power settings (for 10 min) and four furnace temperatures (for 1 h) were used to cure the aerosol jet printed sensors. The resultant sensor resistance at 100 °C and 180 °C was measured, and the sensor’s sensitivity was characterized by a B value. Confocal microscopy was performed to characterize the sensor surface. The 60% UV power setting yields the lowest resistance and the highest B value among all sensors. The analysis of variations shows that the UV power setting is not a significant factor in the resistance and B value, while the furnace temperature is a significant factor. This indicates that UV curing is a more robust method and does not need to be optimized to achieve good results. The UV curing process not only reduces the required curing time but also improves the performance of the temperature sensor.

Effect of Printing Parameters on the Tensile Properties of 3D-Printed Polylactic Acid (PLA) Based on Fused Deposition Modeling.

In order to optimize the efficiency of the Fused deposition modeling (FDM) process, this study used polylactic acid (PLA) material under different parameters (the printing angle and the raster angle) to fabricate specimens and to explore its tensile properties. The effect of the ultraviolet (UV) curing process on PLA materials was also investigated. The results showed that the printing and raster angles have a high impact on the tensile properties of PLA materials. The UV curing process enhanced the brittleness and reduced the elongation of PLA material. Different effects were observed on tensile strength and modulus of specimens printed with different parameters after UV curing. The above results will be a great help for researchers who are working to achieve sustainability of PLA materials and FDM technology.

Process Simplification on Integration of UV Cure Machine with Tape Saw Singulation

Strips that have undergone tape saw singulation will not be completed without the ultraviolet (UV) curing process. To detach the units from the tape, the singulated strips have required further assistance to be loaded for UV cure. Otherwise, hard-to-pick units will be the outcome and sticky residues were usually observed to be attached on the units. Since tape sawn strips requires UV cure, suppliers were asked to engage on upgrading their machine to equip the singulation machine with UV cure. The principle is that after sawing, the singulated strips will be washed and dry normally at the spinner. Then instead of unloading the singulated strips, the machine will pass it first to the inline UV cure machine and then unload when successfully completed the whole process. Through adding the UV curing process in the package singulation sequence, singulated strips unloaded are now ready for the next succeeding process. That way, it would be much help to lessen the handling of sawn strips from one machine to another. The introduction of inline UV cure has simplified the process by automation which increased the security of the units’ quality as well as the productivity of manpower.

UV LED Assisted Printing Platform for Fabrication of Micro-Scale Polymer Pillars

Ultraviolet (UV) assisted printing has emerged as a promising additive manufacturing (AM) technology, which puts UV light sources with focused emission in high demand. Unfortunately, current ultraviolet light-emitting diodes (UV LEDs) are not able to provide adequately focused UV emission required for printing. Thus, a UV LED package with focused UV emission was proposed and fabricated using microelectromechanical system (MEMS) technology in this study. An optical model of the UV LED package with focused UV emission was developed. Based on the designed model, a silicon reflector stacked on another was achieved. By assembling the stacked silicon reflector and hemispherical quartz lenses, the UV LED package with focused UV emission was successfully achieved. A narrow beam with a beam angle of 16° between half maximum intensity was achieved, while the intensity at 0° was greater than 1000 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the focal point. The UV LED curing system using two focused UV LED packages was successfully developed based on the optical simulation results. Polymer pillars were fabricated by instantaneous UV curing process with synchronized UV curable polymer jetting process in one shot, and micro-scale polymer pillars with a diameter of 20 μm were achieved. Thanks to the high intensity and focused UV emission, polymer pillars can be formed in as little as 100 ms. 13600 polymer pillars were printed on a silicon wafer with uniform diameter and geometry in a single dispensing cycle. The UV LED assisted printing platform was successfully demonstrated for fabrication of micro-scale 3D structures in a fast speed with smooth printing process.

An analytical model of through-thickness photopolymerisation of composites: Ultraviolet light transmission and curing kinetics

In this paper, a kinetic model able to predict the evolution of the through-thickness degree of cure of ultraviolet (UV) cured composites has been developed and validated. The kinetic model, which is based on the autocatalytic model, depends on the temperature of the composite and the absorbed intensity by the photoinitiators. This intensity is calculated by an optical model divided into discrete values of wavelength. As a result, the kinetic model considers the main factors of UV curing: the resin, reinforcement and thickness of the composite; the incident UV light spectrum; the absorbance range of photoinitiators and its consumption during the photopolymerisation. The main values of the model can be obtained by spectrometry and measuring the electric resistance of the composite during the whole UV curing process.

Distributed UV Light Sensor Probe Based on Photo-Responsive Polymer Coated Optical Fiber

A novel distributed ultraviolet (UV) light sensor based on a functional polymer-coated optical fiber is proposed. An azobenzene polymer was prepared by mixing an azobenzene compound and UV curing agent and applied as coating on a distributed strain sensor probe as optical fiber using the UV curing process. This coating was reversibly stretched by the UV light, and in the coated region, it induced tensile strains by the UV light along the fiber. This strain, measured by a distributed fiber optic sensor (DFOS) interrogator, was up to 124.5 με under a UV power of 10 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Using this method, distributed UV monitoring can be realized in conventional strain/temperature DFOS interrogators.

Layer-by-layer ultraviolet assisted extrusion-based (UAE) bioprinting of hydrogel constructs with high aspect ratio for soft tissue engineering applications.

One of the major challenges in the field of soft tissue engineering using bioprinting is fabricating complex tissue constructs with desired structure integrity and mechanical property. To accomplish such requirements, most of the reported works incorporated reinforcement materials such as poly(ϵ-caprolactone) (PCL) polymer within the 3D bioprinted constructs. Although this approach has made some progress in constructing soft tissue-engineered scaffolds, the mechanical compliance mismatch and long degradation period are not ideal for soft tissue engineering. Herein, we present a facile bioprinting strategy that combines the rapid extrusion-based bioprinting technique with an in-built ultraviolet (UV) curing system to facilitate the layer-by-layer UV curing of bioprinted photo-curable GelMA-based hydrogels to achieve soft yet stable cell-laden constructs with high aspect ratio for soft tissue engineering. GelMA is supplemented with a viscosity enhancer (gellan gum) to improve the bio-ink printability and shape fidelity while maintaining the biocompatibility before crosslinking via a layer-by-layer UV curing process. This approach could eventually fabricate soft tissue constructs with high aspect ratio (length to diameter) of ≥ 5. The effects of UV source on printing resolution and cell viability were also studied. As a proof-of-concept, small building units (3D lattice and tubular constructs) with high aspect ratio are fabricated. Furthermore, we have also demonstrated the ability to perform multi-material printing of tissue constructs with high aspect ratio along both the longitudinal and transverse directions for potential applications in tissue engineering of soft tissues. This layer-by-layer ultraviolet assisted extrusion-based (UAE) Bioprinting may provide a novel strategy to develop soft tissue constructs with desirable structure integrity.

A reactive fluorine-free, efficient superhydrophobic and flame-retardant finishing agent for cotton fabrics

A novel finishing agent, N,N-dimethyl-octadecyl phosphate acrylamide (NDOPA), was synthesized with octadecanol, phosphorous acid, formaldehyde and acrylamide, and applied to cotton fabrics by ultraviolet curing to endow cotton fabrics with superhydrophobicity and flame retardancy. Results showed that NDOPA could be grafted onto cotton fabrics through C–O–C covalent bonds during the ultraviolet curing process. The contact angle of cotton fabric treated with the 10% NDOPA agent could reach 157.5°. The treated cotton fabrics exhibited clear flame retardancy. The treated cotton retained strong hydrophobicity and flame retardancy after 30 laundering cycles, indicating that the treated cotton fabrics had excellent durability. Thermogravimetric analysis revealed that the treated samples had flame-retardant properties. The results of Fourier-transform infrared spectroscopy, energy dispersive X-ray analysis and scanning electron micrography showed that NDOPA was successfully grafted onto the cotton fabrics; X-ray diffraction analysis indicated that the crystallized structure of treated cotton fibers nearly did not change.

Synthesis of UV and thermal dual curing oligomer for solder resist ink using ink‐jet printing

ABSTRACTA novel solder resist ink for inkjet printing containing the ultraviolet (UV) and thermal dual curing oligomer is introduced in this work. Three kinds of acrylic monomers for the synthesis of the oligomer are successful prepared and their structures are determined by Fourier transfer infrared. Both UV curing process and thermostability are monitored under UV differential scanning calorimetry and thermogravimetric analysis. For the photoreaction process, the oligomer using Lauryl methacrylate as the material of copolymerization possesses the highest reactivity and conversion of carbon–carbon double bond. Besides, this kind of oligomer also owns excellent thermostability, just losing 5.9% of its weight at 288 °C. The solder resist inks containing the oligomers and jetting by the inkjet printer are tested with the adhesion, soldering resistance, and other performances, presenting the outstanding heat resistance and wide application prospects. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47428.

Highly sensitive and fast UV sensor based on fiber grating with easily producible photoreactive material

In this paper, a newly synthesized material has been proposed to improve the ultraviolet (UV) sensitivity of a non-etched fiber Bragg grating (FBG) for UV sensors, comparable to the high sensitivity of a previously reported UV sensor based on a diameter-downsized FBG. The photomechanical material was prepared simply by mixing an azobenzene compound and curing agent. An FBG was subsequently coated with the functional polymer using the UV curing process. We determined the best combination of the azobenzene compound exhibiting UV-induced mechanical stretching and the curing agent as a commercially available coating polymer to achieve the highest sensitivity in many combinations. The maximum wavelength shift of the non-etched FBG was 2.5 nm at a UV power of ∼2.5 mW/cm2. The sensitivity of the sensor was found to be related to the hardness of the coating material. In addition, we suggested a simple algorithm to determine the presence and absence of UV radiation using the change in the slope of the wavelength shift over time obtained through the first derivative of the measured data. The proposed method is very easy to use, providing the information at a glance, and our fast UV sensor is sufficiently powerful for applications such as corona discharge detection and lightning strike monitoring.

Facile fabrication of photoinduced superhydrophobic–superhydrophilic surfaces on cellulose substrate without strength loss

A novel strategy was reported on the design and fabrication of functional photosensitive hybrid sols (FPHSs) by non-alcoholic emulsification in the presence of a TiO2 nanoparticle and photoinitiator via a sol-gel process using tetraethylorthosilicate, γ-methacryloxypropyltrimethoxysilane (MPS) and hydrophobic silane coupling agents as precursors. Smart cellulose substrates with alterable superhydrophobic–superhydrophilic conversion were fabricated using FPHS via the ultraviolet (UV) curing process. The liquid FPHS was photocured into solid gel during UV irradiation for 40 s with MPSs in FPHS, which was verified via Fourier transform infrared spectra. The cellulose substrates were modified with FPHSs, and the water contact angles of the modified cellulose substrates were more than 150°. The superhydrophobicity was improved by the gathering of hydrophobic chains and particle deposition of hybrid gel on the fiber surface. Nevertheless, the water contact angles of the modified cellulose substrates were receded with UV irradiation from 158° to 0° in 200 min, due to TiO2 photoinduction. The irradiated cellulose substrates were placed in the dark, and the water contact angles were recovered to about 130°, gradually. What is more, the reversible process can be repeated more than eight times. The modified cellulose substrate presented excellent washing fastness, even suffering 10 times washing processing. The mechanical properties, including breaking strength and elongation rate, were improved after the coating and UV curing process, which considerably remedied the defects of the heating curing process on the mechanical properties.

Effect of ultraviolet curing kinetics on the mechanical properties of out of die pultruded vinyl ester composites

This paper analyses the effect of curing kinetics on the mechanical properties of composites manufactured by out of die ultraviolet (UV) cured pultrusion. Curing kinetics have been modified using two combinations of depth curing (BAPO) and surface curing (α aminoketone) photoinitiators. The rate constant of the autocatalytic model k, shows that the curing kinetics of the formulation with the higher content of BAPO and lower content of α aminoketone is faster in the studied intensity range. Spectrometry results justify the differences in curing kinetics, since the light transmission through thickness is higher during the whole UV curing process due to photobleaching effect of BAPO. Faster UV curing kinetics generates lower expansion at the exit of the pultrusion die, reducing the void content approximately 90%. Consequently, flexural and interlaminar shear strength, as well as specific energy absorption index of the fast curing resin, are higher.

Stochastic simulation of the UV curing process in nanoimprint lithography: Pattern size and shape effects in sub-50 nm lithography

The authors have performed stochastic simulations of the ultraviolet (UV) curing process of the resist in nanoimprint lithography. Chain formation between an activated monomer and a randomly selected monomer within the critical reaction radius occurred until there was no unreacted monomer within the reaction radius. A deactivation mechanism was introduced to prevent the chain reaction at the resist surface by setting a smaller maximum reaction radius at the resist surface than in the middle of the resist. By introducing the deactivation effect, the conversion ratio of the UV-cured resist decreased with decreasing resist pattern size and depended on the pattern shape. Resist pattern shrinkage after UV curing was also simulated by relaxing the structures with the molecular mechanics method.

Study on impact of UV curing process of digital light processing 3-D printer on the mechanical properties and dimensional accuracies

In the last decade, there has been an exponential increase of the scientific interest for smart additive manufacturing (AM) technology. Among the different AM techniques, the most commonly applied processes are digital light processing (DLP). DLP is a laser-based process that works with photopolymer resins, which react with the ultraviolet (UV) and is cured to form a solid in a very precise way to produce parts with high dimensional accuracy. However, because of the scattering effect when UV light passes through the transparent vat and different polymerization characteristics and curing depth of photopolymer resins, there are lots of parameters of DLP printers need to be optimized. Among these, exposure time affects the quality of the 3D printed specimen. If it is not optimized, it brings about problems such as poor mechanical properties and poor dimensional accuracy. Therefore, this study examinedoptimal exposure time. With a same specimen and layer thickness, the photopolymer resin was exposed to the UV light in different times to evaluate the influence of it. The UV mercury lamp, 240 W and wavelength of 385-650nm is used. To investigate the effect of exposure time on the mechanical strength, the tensile strength and young’s modulus were experimentally determined using universal material test machine.

Fabrication of an Anti-Biofouling Plasma-Filtration Membrane by an Electrospinning Process Using Photo-Cross-linkable Zwitterionic Phospholipid Polymers.

The goal of this study is to fabricate a stable plasma filtration membrane with antibiofouling properties via an electrospinning process. To this end, a random-type copolymer consisting of zwitterionic phosphorylcholine (PC) groups and ultraviolet (UV)-cross-linkable phenyl azide groups was synthesized. The zwitterionic PC group provides antibiofouling properties, and the phenyl azide group enables the stable maintenance of the fibrous nanostructure of hydrophilic zwitterion polymers in aqueous medium via a simple UV curing process. To demonstrate the antibiofouling nature of the PC group, a polymer without antibiofouling PC groups was also prepared for comparison. The successful synthesis of the random-type copolymers containing phenyl azide groups was proven by 1H nuclear magnetic resonance and Fourier transform infrared spectroscopy, and the fibrous structure of the prepared membranes was observed by field emission scanning electron microscopy. The antibiofouling properties were analyzed by fluorescein isothiocyanate-labeled bovine serum albumin adsorption and platelet adhesion tests. The experimental results show that membranes containing zwitterionic PC groups exhibited obvious decreases in platelet adhesion and protein adsorption. Platelet-rich plasma solution was filtered using the prepared membranes to test their filtration properties. The sequential filtration process removed 80% and almost 98% of the platelets. This finding confirmed that the membrane retained its blood-inert biomaterial surface in a complex medium that included blood plasma and platelets.

Fabrication of Patchable Organic Lasing Sheets via Soft Lithography

Here, we report a novel fabrication technique for patchable organic lasing sheet based on non-volatile liquid organic semiconductors and freestanding polymeric film with high flexibility and patchability. For this work, we have fabricated the second-order DFB grating structure, which leads to surface emission, embedded in the freestanding polymeric film. Using an ultra-violet (UV) curable polyurethaneacrylate (PUA) mixture, the periodic DFB grating structure can be easily prepared on the freestanding polymeric film via a simple UV curing process. Due to unsaturated acrylate remained in the PUA mixture after UV curing, the freestanding PUA film provides adhesive properties, which enable mounting of the patchable organic lasing sheet onto non-flat surfaces with conformal contact. To achieve laser actions in the freestanding resonator structure, a composite material of liquid 9-(2-ethylhexyl)carbazole (EHCz) and organic laser dyes was used as the laser medium. Since the degraded active materials can be easily refreshed by a simple injection of the liquid composite, such a non-volatile liquid organic semiconducting medium has degradation-free and recyclable characteristics in addition to other strong advantages including tunable optoelectronic responses, solvent-free processing, and ultimate mechanical flexibility and uniformity. Lasing properties of the patchable organic lasing sheet were also investigated after mounting onto non-flat surfaces, showing a mechanical tunability of laser emission under variable surface curvature. It is anticipated that these results will be applied to the development of various patchable optoelectronic applications for light-emitting displays, sensors and data communications.

A study on radial spreading of a resin droplet with varying viscosity under UV curing process

One-dimensional axisymmetric fluid dynamics of a resin droplet was studied when it is squeezed between two parallel plates under the influence of UV (Ultraviolet) radiation curing. The radial spreading of different level of resin viscosity and its spreading speed are developed from the previous framework for viscous fluid dynamics of Newtonian fluid with negligible capillary number and Reynolds number. Then the final equations for spreading radius and spreading speed under the influence of UV curing are related with each other for the given spreading radius, viscosity at the corresponding elapsed time. The elapsed time increment could be assessed from the incremental elapsed time calculated from the incremental radius, assuming negligible viscosity change when the incremental radius is controlled to be small enough. The spreading of resin droplet is highly restricted by rapid viscosity rise due to crosslinking polymerization from UV curing. The theory was verified through droplet spreading tests with resin samples of different initial viscosities and of the same viscosity under different UV power. The theoretical prediction was in good agreement with the experimental results for both spreading radius and spreading speed. The same theoretical approach was then applied to the prediction of spreading boundary size and time to reach to it for a slow curing resin with different UV power intensity.

Double-layer anisotropic light diffusion films fabricated using a two-step UV curing technique

We developed a novel light diffusion film with a double diffusion layer structure for high reflectivity and a wide diffusion angle range. We demonstrated that the internal layer structure of the light diffusion film is controlled by the diffusion angle of the ultraviolet (UV) light used for photopolymerization. We successfully fabricated two different diffusion layers in a single polymer film using a two-step UV curing process and achieved a wide diffusion angle range and high reflectivity normal to the film surface. Our light diffusion film can control the distribution of diffused light, and should contribute to the development of future low-power reflective displays with high reflectivity similar to the white paper.

Electron Beam Curing Technology for Very High-Throughput Manufacturing of Flexible Alternating Current Powder Electroluminescent Devices

Thick-film alternating current powder-based electroluminescent (ACPEL) succeeds on the market as mature technology for large-area light sources. An additional boost for its development may come from the radiation curing technology. Since it is totally compatible with high-speed roll-to-roll processing, radiation curing can offer multiple advantages to further lower costs and make easier the fabrication process of ACPEL devices. In this paper, the application of the electron beam (EB) curing technology to produce flexible ACPEL devices was explored for the first time. In particular, devices with emitting layer made by EB irradiation were successfully fabricated on poly(ethylene terephthalate) (PET) substrate. Device properties were evaluated and compared with those obtained using the conventional ultraviolet curing process. Smaller driving voltages and higher luminous output were observed for the EB treated samples as a consequence of a more cross-linked polymeric binder of the emitting layer generated. In addition, possible effects of EB overdose were also investigated; experiments revealed that excessively high doses can induce the degradation of both polymeric binder and emitting particles. Therefore, the feasibility of using the EB curing was proven to fabricate ACPEL devices, launching it as the next future technology for more sustainable, very fast, and one-step manufacturing of powder-based alternating current EL devices.