Spectra Group manufactures and supplies a number of specialty photoinitiators and photoinitiator blends. These products range from off-the-shelf standard solutions to tailor-made photoinitiator packages to fit unique applications and light sources.



Photoinitiators are chemical compounds used to generate reaction intermediates after the absorption of light. In the presence of specific small molecules (liquid monomers) these intermediates are responsible for the production of solids from liquids, (i.e. polymerization).

• Type I photoinitiators produce reactive intermediates directly after light absorption
• Type II photoinitiators require a second compound, a so-called co-initiator, to produce such intermediates 

In early 90s, the scientists at Spectra Group have pioneered the development of the H-Nu photoinitiator line. H-Nu photoinitiators are capable of curing (hardening) resins of two general kinds: 
• acrylates and methacrylates, cured by free-radical processes
• epoxides, cured by cationic processes 

Spectra Group offers a patented line of unique Type II UV/visible light photoinitiators, covering the panchromatic UVA and visible spectrum (H-Nu 470, H-Nu 535, H-Nu 635).


• Acrylate and methacrylate polymerization (free-radical) initiated by H-Nu 470, H-Nu 535 and H-Nu 635 photoinitiators generally requires partners such as amine and iodonium salt co-initiators
• Epoxides (cationic) polymerization generally is carried out in combination with iodonium salt co-initiators (H-Nu 470 and H-Nu 535 cationic photoiniators). Further improvement in polymerization efficiency is possible by the use of proprietary accelerators.
H-Nu 470 and H-Nu 535 cationic photoinitiators have proved to work exceptionally well with SU-8 photoresins, making possible visible light lithography.



Benefits of the visible light H-Nu photoinitiator series in photopolymerization processes:

• High Absorptivity - low concentrations needed
• Speed of Cure - moderate to fast (depending on formulation)
• Better light utilization and reduced levels of UV photoinitiators normally required – by adding H-Nu photoinitiators to an existing UV formulation
• H-Nu photoinitiators can provide a thick cured coating after one pass - saving time and energy
• Capable of significant depth of cure – > 1 inch or more
• Enhanced adhesion/depth of cure of pigmented formulations 
• Cure through UV opaque, pigmented, colored substrates (i.e. red plastic). 
• Photoinitiator bleaching - pale or no residual color 
• Bleaching/Color change indicator of cure (exposure) with visible light (UV)

H-Nu Photoinitiators Recent Innovations

• Liquid blends targeted to match and optimize surface cure with UVA LED light sources (H-Nu 470 LT & H-Nu 470LT5)
• Further extension of the H-Nu photoinitiator line to provide cure with red and infra-red (IR) light sources (H-Nu-Blue and IR)
• Photoinitiators to provide tack-free cure (acrylates) in UVA/visible light range and capable of sensitizing both iodonium and sulfonium salts in UVA/visible range (H-Nu 470X)
• H-Nu photoinitiators liquid blends to provide for ease of addition and incorporation as well as the curing range extension to cover UV/visible range (H-Nu 400 IL, H-Nu 470 IL, H-Nu 470LT)
• Improved efficiency of UV and visible light cure (photosensitization) of iodonium salts to cure epoxides (e.g. Cycloaliphatic, Bisphenol A, Novolacs, and others) through the use of proprietary liquid blends and accelerators (H-Nu 390 and H-Nu 390HI)
• Antimony-free (H-Nu 390) and both antimony- and benzene-free (H-Nu 390HI) liquid blend cationic photoinitiators
• Liquid blends for visible light cure of water-based acrylate monomers and dispersions (H-Nu 605IL).

MSDS sheets for all H-Nu photoinitiators can be provided upon e-mail request.

At Spectra Group, we are pleased to offer photoinitiator samples as testing kits, to include all necessary co-initiators and co-solvents. The purpose of providing a kit is that you can quickly test your concept to see if our materials may be working for you. To request one of our photoinitiator kits, email us or give us a call.

Here is an example of the efficiency and depth of cure of one of our photoinitiators, H-Nu 470. H-Nu 470 photoinitiator converts a liquid resin into solid in just few seconds utilizing light from an overhead projector:

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For additional information or to order, please call us at (419) 837-9783 or
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