NIR‐Dyes for Photopolymers and Laser Drying in the Graphic Industry

Strehmel, Bernd; Brömme, Thomas; Schmitz, Christian; Reiner, Knut; Ernst, Steffen; Keil, Dietmar

doi:10.1002/9781119006671.ch7

Cited by 35 publications

(37 citation statements)

References 31 publications

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“…Photopolymerizations can be initiated in various ways, such as through radical, cationic, or even anionic processes. Many photoinitiating systems that act at a UV, visible, or even near IR region have been developed. Since UV wavelengths require higher energy and can cause skin and eye damage, there is a great deal of interest in extending the photoactivation of polymerizations to the visible range.…”

Section: Introductionmentioning

confidence: 99%

Visible Light Induced Cationic Polymerization of Epoxides by Using Multiwalled Carbon Nanotubes

Sangermano

Rodriguez

González

et al. 2018

Macromol. Rapid Commun.

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The visible light induced cationic polymerization of epoxides can be achieved by means of multiwalled carbon nanotubes (MWCNTs), which act as visible light photoinitiators via a radical-induced cationic photopolymerization process. When MWCNTs are irradiated with longer wavelengths (above 400 nm), they generate carbon radicals, by means of hydrogen abstraction from the epoxy monomer; these radicals are oxidized in the presence of iodonium salt to a carbocation that is sufficiently reactive to start the cationic ring-opening polymerization of an epoxy monomer. These mechanisms have been supported by electron paramagnetic resonance analysis.

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Section: Introductionmentioning

confidence: 99%

Visible Light Induced Cationic Polymerization of Epoxides by Using Multiwalled Carbon Nanotubes

Sangermano

Rodriguez

González

et al. 2018

Macromol. Rapid Commun.

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“…The line length can exceed up to several meters depending on the power while the width in the focus is between a few micrometers and a millimeter. This was already successfully tested for physical drying of offset printing inks using a NIR absorber that selectively uptakes radiation [13]. These NIR absorbers possess a high quantum yield of non-radiative deactivation while the efficiency to release fluorescence remains relatively low.…”

Section: Introductionmentioning

confidence: 99%

Advances of Near Infrared Sensitized Radical and Cationic Photopolymerization: from Graphic Industry to Traditional Coatings

Strehmel

Schmitz

Brömme

et al. 2016

J. Photopol. Sci. Technol.

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This contribution summarizes recent progress in the field of near-infrared (NIR) initiated photopolymerization. The photoinitiator system consists of a cyanine as sensitizer (Sens) and an iodonium salt with distinct structural pattern of both the cation and anion as radical initiator. Both, photonic and thermal events are discussed as the main source for formation of initiating species. Electron transfer between the excited state of Sens (Sens*) and the iodonium salt can be seen as the main source for formation of initiating species such as radicals and protons/electrophiles. Furthermore, the ion mobility as probed by the electric conductivity possesses a major function to tune the reactivity of the photopolymer system. The reactivity of these systems was studied in different applications such as Computer to Plate (CtP), LED curing, photonic baking, and curing of powder coatings with NIR lasers exhibiting line shape focus.

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“…[9] Semiconductor lasers with emission in the NIR (l = 808 nm, 980 nm) and line-shaped focus lasers were first applied for physicald rying of offset-printing inks using temperature-sensitive paper as substrate. [10] This technique, which was developed 10 years ago by small and medium enterprises (SMEs), [11] requires only to move the substrate in one direction while the laser system generates one continuous shining line up to al ength of at least 60 cm with similar intensity. [12] The embedded absorber compound in the coating uptakes 980 nm NIR laser irradiation, with no damageo ft he paper occurring.…”

Section: Introductionmentioning

confidence: 99%

“…[6] Afew attempts have been reported using NIR irradiation for chemical curing of coatings. [9,10] Our NIR photoinitiator system comprises cyanines operating as absorbera nd sensitizer to generate heat, and initiating radicals for radical polymerization, respectively.T he materials used in this contribution absorb, depending on the structure,l aser irradiation at either l = 808 nm or 980 nm. This contribution demonstrates arevolutionary technique based on photonic methods to cure VOCfree coatings with line-shape-focused NIR lasers.…”

Section: Introductionmentioning

confidence: 99%

Photochemical Treatment of Powder Coatings and VOC‐Free Coatings with NIR Lasers Exhibiting Line‐Shaped Focus: Physical and Chemical Solidification

Schmitz

Strehmel

2016

ChemPhotoChem

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NIR‐sensitized (NIR=near‐infrared) radical photopolymerization can be employed to chemically cure VOC‐free coatings; that is, either a powder coating or liquid monomer coating system with no significant components of volatile organic compounds (VOC). A NIR laser with line‐shaped focus was applied to cure the coatings. This system operated in multi‐wavelength mode where preferentially the emission wavelengths λ=808 nm and 980 nm of the laser system could be employed to solidify and crosslink the starting components as a transparent film; that is, chemical drying by photonic events. Cyanines absorbing at λ=980 nm and 808 nm functioned as heat generators to melt the powder and as sensitizers (Sens) to generate initiating radicals in combination with a radical initiator (RI). The radical initiator was either the iodonium salt RI‐1 ([(t‐C4H9‐Ph)2I+][(CF3SO2)2N−]) or triazine A (RI‐2). Photoinduced electron transfer between the excited states of Sens and RI was found to control the efficiency of initiating radicals. Line‐shape‐focused laser experiments demonstrated that both liquid VOC‐free coatings and solid powder coatings can be cured. Curing of solid powder coatings occurs with a curing rate of 3.6 m min−1, opening the possibility to introduce NIR laser curing as a new technology in coating sciences. Finally, rheological measurements and differential scanning calorimetry (DSC) were applied to characterize the flow properties of the molten powder and the glass transition temperatures of the crosslinked materials, respectively. The molten powder coating behaved like a liquid up to 160 °C as concluded from the complex shear modulus (G*), while the phase shift (∂) documents crosslinking above this temperature.

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NIR‐Dyes for Photopolymers and Laser Drying in the Graphic Industry

Cited by 35 publications

References 31 publications

Visible Light Induced Cationic Polymerization of Epoxides by Using Multiwalled Carbon Nanotubes

Visible Light Induced Cationic Polymerization of Epoxides by Using Multiwalled Carbon Nanotubes

Advances of Near Infrared Sensitized Radical and Cationic Photopolymerization: from Graphic Industry to Traditional Coatings

Photochemical Treatment of Powder Coatings and VOC‐Free Coatings with NIR Lasers Exhibiting Line‐Shaped Focus: Physical and Chemical Solidification

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