Erschienen in:Zeitschrift für Physikalische Chemie
Sprache:
Englisch
DOI:
10.1515/zpch-2014-0451
ISSN:
0942-9352;
2196-7156
Entstehung:
Anmerkungen:
Beschreibung:
<jats:title>Abstract</jats:title>
<jats:p>This contribution discusses photoinitiated crosslinking of
multifunctional acrylic esters in polymeric binders based on digital
imaging using the Computer to Plate (CtP) technology applying laser
exposure at 830 nm in the near infrared (NIR). All coating
components (NIR photoinitiator system, monomers, binder, adhesion
promoter, contrast dye, and oxygen barrier material) were applied as
thin double layer film (1–2 μm dry film thickness)
on Al-plates with an anodized surface. Materials exposed exhibit
a sensitivity between 30–200 mJ/cm<jats:sup>2</jats:sup> depending on the
NIR-photoinitiator composition. This was processed in a weak aqueous
alkaline bath to obtain the image. Generation of initiating radicals
occurs by electron transfer from the excited state of the
NIR-sensitizer to the radical generator; that is either an onium salt
or neutral electron deficient compound. Redox potentials were
determined for the NIR-sensitizers and the radical generator. These
data allow a rough estimate regarding the free energy of electron
transfer of the excited state of the sensitizer and radical generator
in NIR-photosensitive imaging material. Photoinduced electron transfer
plays a major function to generate initiating radicals by a sensitized
mechanism but thermal events also influence sensitivity of the
coating. Particular the non-radiative deactivation of the
NIR-sensitizer possesses a major function to release selectively the
heat. Absorption data of many NIR-sensitizers used exhibit molar
extinction coefficient of more than
200000 M<jats:sup>
<jats:italic>–</jats:italic>1</jats:sup> cm<jats:sup>
<jats:italic>–</jats:italic>1</jats:sup>.</jats:p>