Photocured Materials: Fabrication of Functional Nanoshells: Volume 13 - Rilegato

Rilegato

ISBN 10: 178262001X ISBN 13: 9781782620013

Casa editrice: Royal Society of Chemistry, 2014

Riassunto

Traditionally, most synthetically developed materials are hardened by heating them to an elevated temperature, a process requiring large amounts of energy and space. Interest in photo cured materials using UV-light is growing due to simplifications in manufacturing and growing environmental concerns; it is expected photocuring could reduce electricity consumption by 90% compared to traditional curing. Photocured materials also reduce evaporation of volatile organic components, curing time and waste, thereby enhancing productivity and reducing work space.

The materials technologies based on photocuring are gaining momentum, and this will be the first book to provide an in-depth focus on the subject. This book summarises the fundamentals required to understand the field, characterises the use of novel materials and the development of synthetic aspects, and discusses the future of the technology.

The comprehensive review chapters are suitable for a broad readership from diverse backgrounds including chemistry, physics, materials science and engineering, medical science, pharmacy, biotechnology and biomedical engineering. Photocured Materials will be of interest to students, researchers, scientists, engineers and professors.

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Dalla quarta di copertina

Traditionally, most synthetically developed materials are hardened by heating them to an elevated temperature, a process requiring large amounts of energy and space. Interest in photocured materials using UV and visible light is growing due to simplifications in manufacturing and growing environmental concerns; it is expected photocuring could reduce electricity consumption by up to 90% compared to traditional curing. Photocured materials also reduce evaporation of volatile organic compounds, curing time and waste, thereby enhancing productivity and reducing work space.

The materials technologies based on photocuring are gaining momentum, and this will be the first book to provide an in-depth focus on the subject. This book summarises the fundamentals required to understand the field, characterises the use of novel materials and the development of synthetic aspects, and discusses the future of the technology.

The comprehensive review chapters are suitable for a broad readership from diverse backgrounds including chemistry, physics, materials science and engineering, medical science, pharmacy, biotechnology and biomedical engineering. Photocured Materials will be of interest to students, researchers, scientists, engineers and professors.

Dal risvolto di copertina interno

Traditionally, most synthetically developed materials are hardened by heating them to an elevated temperature, a process requiring large amounts of energy and space. Interest in photocured materials using UV and visible light is growing due to simplifications in manufacturing and growing environmental concerns; it is expected photocuring could reduce electricity consumption by up to 90% compared to traditional curing. Photocured materials also reduce evaporation of volatile organic compounds, curing time and waste, thereby enhancing productivity and reducing work space.

The materials technologies based on photocuring are gaining momentum, and this will be the first book to provide an in-depth focus on the subject. This book summarises the fundamentals required to understand the field, characterises the use of novel materials and the development of synthetic aspects, and discusses the future of the technology.

The comprehensive review chapters are suitable for a broad readership from diverse backgrounds including chemistry, physics, materials science and engineering, medical science, pharmacy, biotechnology and biomedical engineering. Photocured Materials will be of interest to students, researchers, scientists, engineers and professors.

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Photocured Materials

By Atul Tiwari, Alexander Polykarpov

The Royal Society of Chemistry

Copyright © 2015 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-78262-001-3

Contents

Chapter 1 Photocured Materials: A General Perspective Alexander Polykarpov and Atul Tiwari, 1, 
Chapter 2 UV-Curable Coating Technologies Mark D. Soucek and Xiaofeng Ren, 15, 
Chapter 3 Newly Synthesized Photocrosslinkable Liquid-Crystalline Polymers and their Properties G. Kumar and K. Subramanian, 49, 
Chapter 4 Efficient Photoinitiators for Two-Photon Polymerization Jan Torgersen, 75, 
Chapter 5 Inhomogeneous Photopolymerization in Multicomponent Media A. Veltri, A. V. Sukhov, R. Caputo, L. De Sio, M. Infusino and C. P. Umeton, 87, 
Chapter 6 Microfabrication Processes and Applications of Liquid Photosensitive Materials Chin-Tai Chen, 103, 
Chapter 7 UV-Cured Functional Coatings M. Sangermano, I. Roppolo and M. Messori, 121, 
Chapter 8 Photoreactive Polymers For Microarray Chips Di Zhou, Ponnurengam Malliappan Sivakumar, Tae Il Son and Yoshihiro Ito, 134, 
Chapter 9 Boron/Phosphorus-Containing Flame-Retardant Photocurable Coatings Emrah Çakmakçi and Memet Vezir Kahraman, 150, 
Chapter 10 Lamellar and Circular Constructs Containing Self-Aligned Liquid Crystals Luciano De Sio, Nelson Tabiryan and Timothy Bunning, 188, 
Chapter 11 POLICRYPS: A Multipurpose, Application-Oriented Platform R. Caputo, M. Infusino, A. Veltri, L. De Sio, A. V. Sukhov and C. P. Umeton, 200, 
Chapter 12 SU-8 for Microsystem Fabrication Yi Chiu and Yu-Ting Cheng, 220, 
Chapter 13 UV-Based Dual Mechanism for Crosslinking and Stabilization of PAN-Based Carbon-Fiber Precursors Marlon S. Morales and Amod A. Ogale, 256, 
Chapter 14 Analytical Methods for Determining Photoinitiators in Food-Contact Materials M. A. Lago, R. Sendón and A. Rodríguez-Bernaldo de Quirós, 290, 
Chapter 15 Methacrylate and Epoxy Resins Photocured by Means of Visible Light-Emitting Diodes (LEDs) Claudia I. Vallo and Silvana V. Asmussen, 321, 
Chapter 16 Waste Materials Cured and Modified by Irradiating and their Use in Concrete Gonzalo Martínez-Barrera and Osman Gencel, 347, 
Subject Index, 360, 

CHAPTER 1

Photocured Materials: A General Perspective

ALEXANDER POLYKARPOV AND ATUL TIWARI

1.1 Current Trends and Future Avenues

1.1.1 Photocured Applications

Photocured materials are obtained by photoinduced hardening or cross-linking of various monomer-, oligomer-, and polymer-based compositions. Most commonly these materials are cured by UV, visible light, and electron beam (EB). A wide range of inexpensive UV photoinitiators coupled with the compactness, simplicity, and relatively low cost of UV equipment allows UV-cured materials to be used much more often and the interest in photocured materials has continued to grow in recent years.

Photocured materials are commonly used as coatings, inks and adhesives. The global consumption of photocurable coatings, inks and ad-hesives was 868 million pounds in 2012 worth $4.94 billion, according to a recent study from Kusumgar, Nerlfi & Growney Inc. Photocured materials have also been the mainstay of photolithographic applications playing an important role in the creation of microchips and printed circuit boards. Due to the very rapid and low-temperature cure these single-component systems also found uses in biomedical applications from nail polish and dental restorations to providing scaffolds for tissue and organ regeneration. Increasing demands for higher productivity and lower emissions of volatile organic chemicals (VOC) continue to support the expansion of photocured materials into various areas of human activities.

1.1.2 Graphic Arts

As the printing market declined due to reduced use of newspapers, magazines, and paper books the growth in the UV and electron beam (EB)-curable printing inks and coatings continued to be in the packaging applications. Especially attractive has been the use in food packaging where there is a continued need for safer, faster, and cheaper inks, functional coatings, and overprint varnishes.

Recent research in the photocurable inks area has been focused on replacing mercury-vapor-based UV lamps with UV LED cure sources and developing better performing systems with low migration and low odor for use in food packaging. Acrylate oligomers developed for use in UV/EB curable inks have to be fast curing, disperse multiple pigments well, and provide suitable rheology to the ink formulations. Most commonly these are polyester acrylates, though aliphatic epoxy acrylates and polyurethane acrylates are also used. Various special effect inks continue to be developed.

UV inkjet inks are being used to make packaging labels and typically suffer from fewer delamination issues than conventional inks. These inks also allow for easy inline processing such as hot stamping, die cutting, embossing and others. Plastic films are well suited for UV inkjet printing.

EB cure often provides a viable alternative to UV for inks and overprint varnishes. EB cure has been found to be especially effective in food-packaging applications where it leads to higher conversions of photocurable materials, while also removing the need for migrating photoinitiators and cure accelerators. Being an ionizing radiation with higher depth of penetration EB allows for much better through cure of pigmented coatings and inks. EB also enables cure through opaque to UV and visible-light multilayered substrates. EB coatings can be sufficiently durable to replace more expensive film lamination in paper-bag packaging.

1.1.3 Adhesives and Sealants

Photocured materials are being used in laminating and pressure-sensitive adhesives and even as structural adhesives. However, they still face a tough competition with the often less expensive on the per weight unit basis solvent, waterborne, and 100% solids two-component systems. Providing a low migration bonding layer for substrates used in food packaging presents an additional level of challenge due to the lower functionality of the oligomers and monomers used in adhesives than in coatings. This is often coupled with the difficulties in curing through opaque bonded substrates. EB-curable adhesives have recently seen better growth due to superior properties and better process control of EB cure.

Due to the speed of cure and ease of application UV-curable sealants found use in manufacturing of ammunition rounds. In this application UV-curable sealant is applied to the joint between the brass casing and the projectile of the ammunition cartridge after the cartridge has been fully assembled and crimped. The sealant penetrates into the joint by capillary action and is then UV cured to form a waterproof joint. A specially designed LED UV source is used to obtain a narrow strip of UV exposure with well-controlled uniformity.

UV-curable hot melt adhesives continue to be developed and often have superior properties to the conventional systems. UV-cured hot melt adhesives find uses in specialty pressure sensitive tapes, construction, and medical applications.

1.1.4 Barrier Coatings

Films and plastic containers with gas barrier coatings found multiple uses in food packaging where protection of flavor and extension of the life of packaged food and beverages is of great importance. Photopolymerizable thiolene systems were shown to form films with oxygen permeability that can be dialed from very low to very high depending on the glass-transition temperature of the created polymer network. Modification of these networks with amine functional groups was found to create very good oxygen barrier films. Surface modification of clays with acrylate or thiol-functional groups coupled with the selection of suitable exfoliating surfactants was shown to lead to UV-curable formulations with improved mechanical properties. Such formulations were also shown to result in better gas and water barrier properties.

Various other barrier and sensor applications became possible via printing of the functional components using UV- and EB-cure processes. The opportunity in gas and especially oxygen barrier coatings remains to be open for photocured coatings with high flexibility and adhesion to various plastic substrates.

1.1.5 Release Coatings

Release coatings are usually applied either on film or paper substrates and used as removable liners for pressure-sensitive adhesive films or as protective films for various displays. Modern UV-curable release coatings are based on acrylated or epoxy functional polysiloxanes.

1.1.6 UV Powder Coatings

UV powders are typically based on methacrylates and unsaturated polyesters. These formulations are applied by electrostatic spray to a substrate followed by melting of the powder in an oven and UV cure of the melt. The temperature required for melting is lower than what is required for thermally cured powder coatings and is typically around 120 °C. UV powder coatings are used on a variety of substrates such as metals, medium density fiber-board (MDF), structural foams, plastics, composites and other heat-sensitive materials. Creating cost-effective photocurable polymer powders with better resistance to sintering during storage and shipment remains an industry challenge.

1.1.7 Corrosion-Protection Coatings

UV-cure technology capabilities have been extended to the high-performance corrosion protection of steel and aluminum surfaces in industrial applications. Thinner and faster to cure UV coatings were shown to have corrosion protection similar to solvent based two-component urethane and epoxy systems. Adhesion is often a challenge for UV-cured protective coatings on metal and some materials were suggested to address this issue. Very large commercial opportunities for coatings with corrosion protection for metal remain in marine, automotive and aerospace uses, where there is a strong desire to move to rapidly curing, solvent-free and isocyanate-free systems. One of the key challenges remains to be the need for a well-working system that would combine exceptional durability and weatherability of the cured coatings with easy to use and relatively inexpensive curing and application devices. Recent developments in robotic UV systems have been made that allow precision application and cure of UV coatings on surfaces with various curvature and complexity including large vertically positioned surfaces.

UV-curable coatings based on halogenated phenyl acrylates were shown to inhibit biofouling and biocorrosion on plastic panels immersed in waste water.

1.1.8 Automotive Refinish

UV coatings are slowly making way into the automotive refinish area. Among the challenges is the need to cure around corners and in cracks. Dual cure and photolatent catalyst approaches have been used to address these issues. Recent advances in UV LED resulted in creation of hand-held cure devices that do not emit in the UVB and UVC range of the spectrum and do not generate ozone, which is expected to accelerate the adoption of the UV-cure technology by the automotive refinish and other applications where the materials are field applied and cured.

1.1.9 Aircraft Coatings

UV coatings have found uses in aircraft exterior applications where faster process flow for coatings is often sought. Since the aircraft exterior finishing takes place at the end of the build process the urgency to avoid delivery delays while holding a very expensive inventory pushes the manufacturers to selection of faster curing coatings and UV is one of the options being considered. UV coatings are also being considered as replacement for thermally cured coatings for the exhaust vent areas, where the coatings can be subjected to temperatures as high as 150 °C. Recent developments in UVA LED cure sources and matching photoinitiating systems resulted in increased interest in field repair and stencil coatings for aircraft. These UVA-curable coatings have been shown to have performance that rivals that of the conventional 2K urethane systems.

The idea of creating shark-skin-inspired microscale patterns on the surface of aircraft to improve fuel economy by reducing drag was recently tested using UV-curable materials.

1.1.10 Coatings for Plastics

Creation of stable dispersions based on submicrometer scale particles of alumina and silica along with the improvements in polyurethane acrylates led to creation of a new generation of scratch-resistant coatings with exceptional wear resistance. More recent developments in functionalized silicas, hybrid alkoxysilane-epoxy and acrylate systems, and waterborne polyurethane acrylates made UV-curable coatings especially useful for such easy to scratch plastics like polycarbonate, which is widely used in automotive headlamps. Various consumer electronics devices, optical discs, eye glasses, and even vinyl flooring have also benefited from UV-cured scratch-and abrasion-resistant coatings.

Photocured coatings are typically praised for their high gloss. Matte finish or low gloss photocured coatings have been less common due to the challenges in their formulation. Recently, there has been an increased interest in matte UV coatings driven in part by the increasing demand for matte finishes in plastic packaging. There is also a need, particularly for the automotive and consumer electronics markets, for 'soft touch' rapidly cured at low-temperature coatings where despite multiple attempts the balance of the soft to touch, velvety texture with high chemical resistance has not yet been attained.

UV-cured coatings are also used as base and top coats for metallization of substrates using physical vapor deposition techniques. The 'chrome look' has found uses in automotive, cosmetics and home-appliances markets.

1.1.11 Can Coatings

UV coatings found use in protection of beverage can rims from abrasion damage. The coating also allows for easier movement of the cans on conveyors during manufacturing and filling. UV inks are also used in metal container decoration, although to a smaller extent than solvent-based inks.

1.1.12 Wood Coatings

Modern coatings for parquet flooring are based on UV-curable formulations. These coatings are multilayered systems consisting of the bottom layer, which is typically a water borne UV-curable formulation, followed by 100% solids UV-curable formulations layers to provide the necessary abrasion and scratch resistance. UV-cured coatings are still used in multiple furniture and kitchen cabinetry applications. 100% solids UV lacquer was found to be the best alternative from an environmental point of view as a surface coating for wood furniture.

1.1.13 Concrete Coatings

UV-curable formulations have been developed for coating concrete floors. While these coatings provide almost instantaneous cure and are zero to low VOC they continue to face tough competition with the two-component rapid-cure technologies. Repair of rail seat abrasions on concrete ties has been shown to be very effective when using UV-cured materials.

1.1.14 Alkyd Paints

Alkyd paints are based on oxidative drying of the unsaturated fatty acid esters and are used in households to paint doors, trim, and cabinets. Cobalt salts are typically used to accelerate the drying that otherwise can take more than 24 h. Recent studies showed that cobalt salts could be linked to adverse health and environmental effects, which forced the paint industry to seek alternatives to cobalt-based accelerators of the drying. A photochemical system was shown to be a viable candidate for a photoassisted autoxidation drying process in alkyds.

1.1.15 Photochromic and Imaging Materials

A full-color imaging system based on photopolymerizable pressure-sensitive microcapsules was invented in 1984 for use in color copying. The system was later developed into a visible light and pressure-sensitive single-sheet full-color printing medium. More recent systems were developed to color irreversibly directly upon the exposure of photopolymerizable materials to UV and even EB without requiring secondary mechanisms such as heat or pressure for color development. These systems found uses as cure indicators in photopolymerizable systems, as sensors and dosimeters for UV and EB radiometry, and presented an opportunity for various photocured formulations to develop color as part of the curing process. Photocurable color imaging systems based on structural color using magnetically tunable photonic crystals are also being developed.

Photocured materials can also be used as parts of the image forming or transferring devices. UV-curable formulations containing carbon nanotubes found uses in electrostatographic devices as transfer belts. Such formulations were shown to have better control over the uniformity of electrical resistivity and superior mechanical properties to solvent-based thermoplastic and thermosetting systems.

1.1.16 Photoresists

Photocure can be used to prepare negative-tone photoresists, where photo-polymerization or crosslinking can be used to render the material insoluble in the developer. Positive-tone photoresists, where the polymer is rendered soluble in the developer after the exposure, are typically not prepared by photopolymerization and can be classified as photosensitive, rather than photocurable materials.

Relatively simple photopolymerizable systems can be used to make low-resolution stencils and masks for etching glass and ceramics. Flexography is based on the use of the printing plates prepared from photocurable materials image wise exposed by UV. Stencils for screen printing can also be prepared using photoresists.

High-resolution nanolithography and patterning is obtained using immersion 193 nm systems in making microchips. EUV (extreme UV), EB, X-ray, and other imaging technologies are under different stages of evaluation and development for fabricating even smaller nanometer scale patterns for next-generation microchips.

(Continues...)

Excerpted from Photocured Materials by Atul Tiwari, Alexander Polykarpov. Copyright © 2015 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Dettagli dell'edizione

• Editore: Royal Society of Chemistry
• Data di pubblicazione: 2014
• Lingua: Inglese
• ISBN 10: 178262001X
• ISBN 13: 9781782620013
• Rilegatura: Copertina rigida
• Numero di pagine: 370
• Redattore: Tiwari Atul, Polykarpov Alexander
• Contatto del produttore: non disponibile
• Persona responsabile: non disponibile