UV-curable Inks Research Articles

High value-added use of waste photosensitive polyimide to develop low-shrinkage UV-curable inks for digital light projection technology

In the mass industrial production process of polyimide photoresists, waste generation is inevitable due to unqualified molecular weights, inappropriate ionic content of resins, or storage expiration. Consequently, the recycling and reuse of waste photosensitive polyimide (w-PSPI) is a growing concern in both scientific and industrial communities. In this work, w-PSPI was explored to prepare photocurable, fully crosslinked inks for digital light projection technology (DLP). For this purpose, suitable photoactive solvents and crosslinking agents were first screened to overcome the issue of large shrinkage caused by solvent volatilization. The formation of cross-linked network structures during DLP processing and subsequent imidization was also investigated. As a result, a polyimide DLP ink with minimum size shrinkage (less than 5 %) was proposed. For a given active solvent, the mechanical behavior and heat resistance of DLP-formed objects were significantly influenced by the ratio of short-chain and long-chain crosslinkers and the imidization temperature. By optimizing ink composition and imidization temperature, the DLP-formed objects showed high heat resistance (Td5 > 385 °C, Tg > 150 °C) and balanced mechanical properties of strength and toughness (Modulus ≥1 GPa, elongation at break >5 %). This w-PSPI ink has been successfully utilized to manufacture several complex 3D structures and vertical 3D microarrays with 100-µm on a limited-resolution DLP printer. This study not only points the direction for the high-added utilization of w-PSPI but also demonstrates the potential for expanding PSPI application from 2D lithography to 3D micro-manufacturing.

Probabilistic risk assessment of dietary exposure to benzophenone derivatives in cereals in Taiwan.

Benzophenone (BP) and BP derivatives (BPDs) are widely used as ultraviolet (UV) stabilizers in food packaging materials and as photoinitiators in UV-curable inks for printing on food-contact materials. However, our knowledge regarding the sources and risks of dietary exposure to BP and BPDs in cereals remains limited, which prompted us to conduct this study. We measured the levels of BP and nine BPDs-BP-1, BP-2, BP-3, BP-8, 2-hydroxybenzophenone, 4-hydroxybenzophenone, 4-methylbenzophenone (4-MBP), methyl-2-benzoylbenzoate, and 4-benzoylbiphenyl-in three types of cereals (rice flour, oatmeal, and cornflakes; 180 samples in total). A Bayesian Markov-chain Monte Carlo (MC) simulation approach was used for deriving the posterior distributions of BP and BPD residues. This approach helped in addressing the uncertainty in probabilistic distribution for the sampled data under the detection limit. Through an MC simulation, we calculated the daily exposure levels of dietary BP and BPDs and corresponding health risks. The results revealed the ubiquitous presence of BP, BP-3, and 4-MBP in cereals. Older adults (aged>65 years) had the highest (97.5 percentile) lifetime carcinogenic risk for BP exposure through cereals (9.41 × 10-7), whereas children aged 0-3 years had the highest (97.5 percentile) hazard indices for BPD exposure through cereals (2.5 × 10-2). Nevertheless, across age groups, the lifetime carcinogenic risks of BP exposure through cereals were acceptable, and the hazard indices for BPD exposure through cereals were<1. Therefore, BPD exposure through cereals may not be a health concern for individuals in Taiwan.

Evaluation of Recycled Paperboard Properties and Characteristics

Paperboard boxes represent a sought-after class of packaging products, where the use of recycled fibers offers a cost-effective and environmentally friendly alternative to virgin fibers. The presence of a significant proportion of recycled fibers in the paperboard leads to a number of limitations associated with the deterioration of its characteristics. In this study, the properties of coated and uncoated paperboards containing recycled fibers, wood pulp, and virgin cellulose fibers were investigated using a laboratory sample of paperboard produced from 100% recycled fibers without any chemical additives for comparison. Properties such as smoothness, bulk density, absorbency, and tensile strength, as well as colorimetric characteristics, were determined for the recycled paperboards; for the latter test, charts were printed using inkjet printing and UV-curable inks. Whiteness was calculated by three formulae (CIE, Berger, and Stensby), and all the paperboards had a relatively low whiteness (not exceeding 90 CIE), with a yellowish tint due to recycled fibers and mechanical pulp in the composition. The absence of optical brightening agents in the paperboards was experimentally confirmed. The color gamuts of the paperboards were in direct ratio to their whiteness, with the highest ones demonstrated by the coated paperboards. Color reproduction, according to the tone value increase curves, also depended on the whiteness. Uncoated paperboards demonstrated smaller color shifts than the coated ones, with the greatest increase in tone for yellow color. Coated recycled paperboards are suitable for packaging printing under the same conditions as virgin fiber boards, while uncoated boards are the recommended choice for digital printing with UV inks.

Preparation and wear resistance of water-based UV curable ink

ABSTRACT UV water-based inks have disadvantages such as slow curing speed and low degree of crosslinking. In this paper, the copolymer P(MMA-r-HEMA) was prepared by traditional free radical polymerization using methyl methacrylate (MMA) and hydroxyethyl methacrylate (HEMA) as monomers, and the copolymer P(MMA-r-HEMA) was modified by acrylic acid (AA) to synthesis completely water-soluble acrylic prepolymer P(MMA-r-HEMA)-g-AA. Triethylenetetramine reacted with glycidyl methacrylate (GMA) to yield a multifunctional reactive diluent TGMA. Secondly, acrylic prepolymer P(MMA-r-HEMA)-g-AA, multifunctional reactive diluent TGMA and photoinitiator were used to prepare water-based UV curable ink. The influence of the type and quality of photoinitiator, the relative molecular weight and mass fraction of P(MMA-r-HEMA)-g-AA, the number of functional groups and mass fraction of TGMA on the UV ink curing speed and the wear resistance of the ink film were discussed. When the mass fraction of the photoinitiator TPO was 1%, the number-average relative molecular mass of the prepolymer was 1.67 × 104 g/mol and the mass fraction was 60%, the number of functional groups of the reactive diluent was 6 and the mass fraction was 40%, the light curing of UV water-based ink was completed in 0.1 s, and the mass loss after 50 times abrasion was 0.2–0.4%.

Characterizing VOCs emissions of five packaging and printing enterprises in China and the emission reduction potential of this industry

The packaging and printing industry has become an important source of industrial volatile organic compounds (VOCs) emissions in China, due to the abundant consumption of organic materials. Effective control measures must be developed which rely on a comprehensive understanding of both current emission characteristics and future emission projections. However, representative VOCs source profiles and updated EFs of packaging and printing industry in China are still lacking. In order to fully explore the VOCs emissions characteristics of packaging and printing industry, field measurements including 17 processes in five packaging and printing factories were conducted in this study. The emission factors (EFs), VOCs source profiles, ozone formation potential (OFP) and secondary organic aerosols potential (SOAP) of 110 VOCs species were acquired. Speciated VOCs emission inventory of packaging and printing industry was compiled based on the activity data in 2020. The future reduction perspectives of packaging and printing industry in China were projected. The VOCs EFs of different materials were estimated, including solvent-based ink (287 g/kg), water-based ink (117 g/kg), soybean oil ink (44 g/kg), UV curing ink (22 g/kg), solvent-based adhesive (420 g/kg), and water-based adhesive (139 g/kg). The VOCs EFs of products were 35.58 kg/t for plastic wrapper, 7.28 g/m2 for soft package plastic, 0.083 g/piece for carton, 0.54 g/piece for tin case, and 0.14 g/piece for aluminum can. The total VOCs emissions in Chinese packaging and printing industry was estimated to 634.32 Gg in 2020. Guangdong, Zhejiang, Jiangsu, Fujian, Shandong, and Sichuan contributed 73% to total VOCs emissions. Printing workshop was the main contributor to both primary emission and secondary pollutant generation. OVOCs was the most abundant specie in three sub-industries. The key VOCs species in PF were ethylacetate, ethanol, 2-pentanone, methyl ethyl ketone, and i-propanol. I-propanol, ethanol, m-tolualdehyde, and dichloromethane were dominated in PP. Ethanol, m/p-xylene, i-propanol, o-xylene, and acetaldehyde were the key species in MC. The key VOCs species to OFP and SOAP were ethanol, methyl ethyl ketone, 2-pentanone, ethyl methacrylate, acetaldehyde, toluene, and xylene, which should be prioritized. The VOCs emissions would be reduced by 46.5% in 2025 and 66.4% in 2030 with stringent control measures. Increasing the usage proportion of low-VOCs-contained raw material and improving treatment efficiency are the key technologies to reduce the VOCs emissions in the packaging and printing industry.

Occurrence, Fate, Human Exposure, and Toxicity of Commercial Photoinitiators.

Photoinitiators (PIs) are a family of anthropogenic chemicals used in polymerization systems that generate active substances to initiate polymerization reactions under certain radiations. Although polymerization is considered a green method, its wide application in various commercial products, such as UV-curable inks, paints, and varnishes, has led to ubiquitous environmental issues caused by PIs. In this study, we present an overview of the current knowledge on the environmental occurrence, human exposure, and toxicity of PIs and provide suggestions for future research based on numerous available studies. The residual concentrations of PIs in commercial products, such as food packaging materials, are at microgram per gram levels. The migration of PIs from food packaging materials to foodstuffs has been confirmed by more than 100 reports of food contamination caused by PIs. Furthermore, more than 20 PIs have been detected in water, sediment, sewage sludge, and indoor dust collected from Asia, the United States, and Europe. Human internal exposure was also confirmed by the detection of PIs in serum. In addition, PIs were present in human breast milk, indicating that breastfeeding is an exposure pathway for infants. Among the most available studies, benzophenone is the dominant congener detected in the environment and humans. Toxicity studies of PIs reveal multiple toxic end points, such as carcinogenicity and endocrine-disrupting effects. Future investigations should focus on synergistic/antagonistic toxicity effects caused by PIs coexposure and metabolism/transformation pathways of newly identified PIs. Furthermore, future research should aim to develop "greener" PIs with high efficiency, low migration, and low toxicity.

Control of UV-Curing Ink Splashing and Line Quality during DC-Pulse-Modulated Electrohydrodynamic Printing for Textile-Based Electronics

The DC pulse-modulated electrohydrodynamic (EHD) printing technique enables one-step formability of electronic components of electronic textiles. However, the common fabrics as a kind of insulating substrate inevitably come into serious ink splashing behavior during printing, which will severely deteriorate the quality of printed patterns. To solve this problem, the reason for ink splashing on the polyester woven fabric was experimentally clarified, and then a facile solution, that is, the mature antistatic finishing technique in the textile industry, was used to dissipate residual charges emerging on insulating fabric substrates. The relationship between the ink splashing behavior and the electrostatic half-life of fabric was investigated. Also, the feasibility of antistatic finishing for overcoming ink splashing was evaluated. Results show that ink splashing is solved, and the standard deviation of line width is within 3% at a half-life of less than 0.2 s. Moreover, there is no significant effect of antistatic finishing on electrical resistance and adhesion performance of printed lines, and the finishing even with a dilution ratio of 1:100 did not disturb the port impedance of the printed antenna. This strategy is expected to promote the practice of the EHD printing technique in the large-scale and low-cost fabrication of wearable electronic textiles compatible with most of the common fabric substrates.

Low Dielectric Constant Photocurable Fluorinated Poly (Phthalazinone Ether) Ink with Excellent Mechanical Properties and Heat Resistance

The photosensitive resins for 3D printing technology have been widely applied throughout the advanced communication field due to their merits of high molding accuracy and fast processing speed. Regardless, they, in particular, should have better mechanical properties, heat resistance, and dielectric properties. Herein, photocurable fluorinated poly (phthalazinone ether) (FSt-FPPE) was utilized as a prepolymer to improve the performance of photosensitive resin. A series of UV-curable inks named FST/DPGs were prepared with FSt-FPPE and acrylic diluents of different mass fractions. The FST/DPGs were cured into films by UV curing and post-treatment. After curing, their properties were characterized in detail. In terms of heat resistance, glass transition temperature (Tg) could reach 233 °C and the 5% thermal decomposition temperature (Td5%) was 371 °C. The tensile strength surprisingly reached 61.5 MPa, and the dielectric constant (Dk) could be significantly reduced to 2.75. Additionally, FST/DPGs were successfully employed in UV-assisted direct writing (DIW) to print 3D objects that benefited from their commendable fluidity and rapid curing speed. A stiff cylinder sample with a smooth surface and distinct pattern was ultimately obtained, indicating their remarkable 3D printing adaptation. Such photosensitive resin for UV-assisted DIW exhibits tremendous potential in the electronic industry.

Material jetting for advanced applications: A state-of-the-art review, gaps and future directions

The proven ability of additive manufacturing (AM, also known as 3D printing) to fabricate complex components with substantial reductions in material wastage and reduced lead times has made it a key enabling technology for numerous important industrial applications. Of current AM processes, material jetting (MJ) is demonstrating considerable potential for producing multi-material, intricate, 3D components and systems with integrated functionality, with the additional benefit that the process can be easily integrated with other manufacturing procedures. However, material jetting of functional materials to produce advanced applications still poses numerous technological challenges which hinder its full industrial exploitation. These extend from the limited range of high-performance materials with consistent properties usable for MJ, through the need to enhance the process itself by optimizing the droplet formation process, tuning waveforms for specific processes, modification of substrate and substrate/jetted material interactions, the complexities of curing and post-processing procedures, and the challenge of characterizing the 3D printed parts. In this context, this article attempts to provide a comprehensive discussion of the principles and characteristics of the most recent material jetting technology and review the state-of-the-art research and development being conducted. This review identifies existing gaps with regards to high-performance UV-curable inks, printing behavior of non-Newtonian fluids, optimum jetting and curing strategies and effective measures for achieving high-precision MJ. Future work should bridge the aforementioned gaps in order to improve the performance of the technology, thereby making it more attractive for large-scale adoption by industry and increasing market acceptance and penetration of material jetting for advanced applications.

Bacterial cellulose nanofibers modification with 3-(trimethoxysilyl)propyl methacrylate as a crosslinking and reinforcing agent for 3D printable UV-curable inks

Bacterial cellulose nanofibers modification with 3-(trimethoxysilyl)propyl methacrylate as a crosslinking and reinforcing agent for 3D printable UV-curable inks

14.4: Inkjet Printing Patterned Quantum Dot Microarrays

14.4: Inkjet Printing Patterned Quantum Dot Microarrays

Effects of Non-Wood Fibres in Printed Paper Substrate on Barrier and Migration Properties

Nowadays, there is a strong initiative to use recycled or biodegradable materials in all aspects of production including the graphic industry. In this study, paper was used as a material fulfilling the two of mentioned properties. Under laboratory conditions, papers were made of 70% pulp from recycled wood fibres with an addition of 30% straw pulp (wheat, barley or triticale). Considering the importance of the possibility of printing such media based on their end use, the influence of fibre type on vapour barrier properties was studied and overall migration to hydrophilic and fatty food simulants was measured. Analyses were performed on digital, flexographic, and offset prints obtained by printing laboratory papers with UV-curable black ink. It was found that prints produced using the offset technique, in which the ink remains on the surface of the paper, had lower overall levels of migration compared to other printing techniques. The paper produced appears to have the potential to be used as a secondary food packaging material.

Improvement of UV-curable ink adhesion onto melamine faced board using dual silane treatments

ABSTRACT The application of UV digital inkjet printing onto melamine-faced board (MF) has attracted increasing attention as an efficient and environmentally benign surface decoration method. However, the interface bonding between UV coating and melamine-formaldehyde surface is weak, resulting in poor printing durability. In this study, the MF surface is grafted with 3-(triethoxysilyl) propyl isocyanate (ICPTES) via a urea cross-linking process, and then condensed with γ-methacryloxypropyl trimethoxy silane (KH570) to improve its compatibility with the polyacrylate-based UV ink. A combination of physical (surface polishing) and chemical (dual-silane treatments) activations of MF surface enhances its interface bonding strength with UV coating up to 2.24 MPa, 966.7% and 119.6% higher than those of the untreated and the conventional adhesion promotor treated surface, respectively. FTIR results confirm that effectual chemical bonds are established between MF surface and UV coating by the ICPTES and KH570 dual-silane treatments. SEM imaging shows that a seamless connection between MF and UV coating forms. Thus, MF surface modified by silane is a facile and effective strategy to enhance the adhesion of UV digital ink and this printing method shows enormous potentials in a wide range of applications.

CHEMICAL AND MECHANICAL PRINT STABILITY OF SUBSTRATES CONTAINING ALTERNATIVE NON-WOOD FIBRES

The aim of this research has been to demonstrate the use and applicability of substrates containing non-wood fibres in the printing industry, with an emphasis on flexographic printing for packaging. To obtain such substrates, laboratory papers were produced with the addition of 30% non-wood fibres (wheat, barley and triticale), in combination with recycled wood pulp. These substrates were tested for chemical and mechanical resistance after flexographic printing with conventional and ultraviolet curing inks. The results showed that all laboratory papers with the addition of 30% non-wood fibres, printed with water-based inks, had fairly good chemical and mechanical resistance, except for the prints treated with sodium hydroxide. Thus, such papers should not be used as packaging materials for alkaline products. UV-curable inks on these substrates showed low chemical resistance, thus should only be used on substrates intended for secondary packaging. The mechanical resistance of UV prints was very good, thus papers containing straw pulp could be used for various applications.

Fabrication of a Human Skin Mockup with a Multilayered Concentration Map of Pigment Components Using a UV Printer.

In this paper, we propose a pipeline that reproduces human skin mockups using a UV printer by obtaining the spatial concentration map of pigments from an RGB image of human skin. The pigment concentration distributions were obtained by a separating method of skin pigment components with independent component analysis from the skin image. This method can extract the concentration of melanin and hemoglobin components, which are the main pigments that make up skin tone. Based on this concentration, we developed a procedure to reproduce a skin mockup with a multi-layered structure that is determined by mapping the absorbance of melanin and hemoglobin to CMYK (Cyan, Magenta, Yellow, Black) subtractive color mixing. In our proposed method, the multi-layered structure with different pigments in each layer contributes greatly to the accurate reproduction of skin tones. We use a UV printer because the printer is capable of layered fabrication by using UV-curable inks. As the result, subjective evaluation showed that the artificial skin reproduced by our method has a more skin-like appearance than that produced using conventional printing.

Application of ATR-IR measurements to predict the deinking efficiency of UV-cured inks

In recent years, ultraviolet (UV)-curable ink has been developed and widely used in various printing applications. However, using UV-printed products (UV prints) in recovered paper recycling causes end-product dirt specks and quality issues. A new method was developed that can distinguish UV prints from other prints by means of attenuated total reflectance infrared (ATR-IR) spectroscopy. Application of this method could allow more efficient use of UV prints as raw materials for paper recycling. First, a mill trial was performed using UV prints alone as raw materials in a deinked pulp (DIP) process. Second, test prints were made with four types of UV inks: a conventional UV ink and three different highly-sensitive UV inks. Each print sample had four levels of four-color ink coverage patterns (100%, 75%, 50%, and 25%). Next, drinkability of all prints was evaluated by laboratory experiments. Finally, each print was measured using the ATR-IR method, and the relationship between the IR spectra and deinkability was investigated. Mill trial results showed that UV prints caused more than 20 times as many dirt specks as those printed with conventional oil-based ink. There were variations in recycling performance among UV prints taken from bales used for the mill trial. Lab tests clearly revealed that not all UV-printed products lead to dirt specks. In order to clarify the factors that affected deinkability of UV prints, the print samples were investigated by lab experiments. Key findings from lab experiments include: • The number of dirt specks larger than 250 μm in diameter increased as the ink coverage increased. • Higher ink coverage area showed stronger intensity of ATR-IR spectral bands associated with inks. These results indicate that deinkability of UV prints could be predicted by analysis of ATR-IR spectra. • Finally, the method was applied for assessment of recovered paper from commercial printing presses. It was confirmed that this method made it possible to distinguish easily deinkable UV prints from other UV prints. Based on these findings, we concluded that the ATR-IR method is applicable for inspection of incoming recovered paper.

Measurement the Durability of UV-curable inks compared to solvent-based inks for Surface printing on transparent polypropylene

Measurement the Durability of UV-curable inks compared to solvent-based inks for Surface printing on transparent polypropylene

Influence of procedural noise on the glossiness of 2.5D printed patches

Perlin noise, a type of procedural noise, was used for the design of elevation files for 2.5D printing. This printing method uses elevation data from a height map to create physical relief by superimposing layers of ink. In this experiment, the grayscale values of noise functions were used as elevation values to build different surface structures in UV curable ink by 2.5D printing. Printed samples with varying levels of Perlin noise were created and their reflectance properties were studied by measuring the values of specular gloss. The roughness and specular gloss of the printed surfaces were effectively influenced when varying the persistence and octaves of the noise functions. The aim of implementing the procedural approach to a high-resolution printing method has been to explore the reflectance properties of custom noise functions when transferred to the physical realm. This might contribute to better understand the effect of surface structure on the appearance of materials. Potentially, this approach will enable the use of relief printing to produce structures with a more natural appearance and a desired gloss value by using a low-cost computing process.

Color Reproduction Study on the Corrugated Packaging Using UV Wide-format Inkjet Printer

Packaging is one of the fastest growing segments in the print industry, specifically the digital packaging arena. Color digital printing for corrugated is essentially all inkjet and has existed for at least 20 years. High quality packaging prototyping allows for greater client choice and more short-run finished corrugated products. To exam the color reproduction capability on the corrugated packaging using UV wide-format inkjet printer, a Roland VersaUV LEJ-640 UV LED printer with Eco UV-curable inks was employed in this study. Four print settings were tested on the selected B-flute corrugated boards. The main purposes of this experimental study are to (1) identify the most important factors that influence color reproduction on the corrugated packaging using UV wide-format inkjet printing, (2) exam the process capability of tested print settings, and (3) establish optimum print setting so that the maximum yield of optical density and print contrast could be obtained. It was found that the use of white ink is the most important factor and has a significant effect on the optical density. The print setting of standard mode with white ink is suggested to achieve the maximum yield of optical density and print contrast.

Formulation of UV curable nano-silver conductive ink for direct screen-printing on common fabric substrates for wearable electronic applications

One-step printing of electrically conductive inks on textiles is one of the simplest and most prospective methods to manufacture functional wearable electronics. However, the high surface roughness and porous structure as well as poor temperature endurance of most textiles have become the major challenges for the realization of printed electronic textiles (E-textiles). To solve these issues, the UV curable conductive ink with fast curing and low temperature characteristics was formulated to fabricate the flexible fabric-based conductive patterns using screen printing method. The specific focus was spent on investigating the effect of ink composition on curing speed, film forming ability, morphological characteristics and electrical properties of conductive patterns directly printed on fabric substrates. Firstly, we determined the necessity of defoamer for the formation of uniform and continuous printed textile-based patterns, and optimized the film forming ability of UV-curing ink by exploring the defoamer performance. Then, the ink curing speed was found heavily depending on the different types and contents of photoinitiators. Finally, the nano-silver loading showed critical influence to the screen-printability and the electrical properties of printed patterns. An ink formulation with 60 wt% nano-silver, 4 wt% photoinitiator (1173), and 0.2 wt% defoamer (BYK-555) showed satisfactory screen printability, and the conductive patterns with 1.0 mm width exhibited a remarkably low resistivity of 4.04 × 10−5 Ω cm. Moreover, the high performance of the conductive pattern screen-printed on four different fabrics by the formulated UV curable conductive ink further demonstrated its application potential. The results showed that uniformity and electrical properties of printed patterns were directlyrelated to the weaving method, texture characteristic, and roughness of thetextiles. We believe these results will provide basic guidance for the formulation design of conductive ink and facilitate the utility of textiles-based wearable electronics.