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Technology basics

Cationic curing is a photoinitiated, acid catalysed ring opening polymerisation of epoxy resins using onium salts.


On exposure to UV light energy and in the presence of a hydrogen donor (typically the resin components of a formulation) cationic photoinitiators produce a long lived acidic species. This species ring opens an epoxy group to form a carbocation which goes on to react with other epoxy groups producing a crosslinked network.


The principle is similar to free radical polymerisation, with initiation, propagation and chain transfer steps. However, only the initiation phase is dependant on the use of a UV light source. All other stages of the polymerisation reaction are thermally driven. The acid generated remains active after the removal of UV light energy until it is consumed and the entire film is cured. This is known as dark cure.

Formulations typically consist of 3 materials:

 

  • Photoinitator onium salts supplied under the SpeedCure name.
  • Cycloaliphatic epoxide resins supplied under the UviCure name.
  • Oxetane resins supplied under the UviCure name.

 

Logo Speedcure Uvicure.png

Polymerisation steps:

1. Initiation – Photoinduced reaction

On exposure to UV light energy onium salt photoinitators produce a strong Brønsted acid which goes on to propagate the polymerisation reaction.

chemical-equation-1.png

 

2. Propagation - Thermally driven reaction

The strong acid ring opens an epoxy and/or oxetane

chemical-equation-2.png

Cationic curing benefits

Cationic curing technology offers several benefits to help you achieve high performance properties for your project

UviCure cationic resins

Epoxy resins
Name
Structure
Properties
UVICURE S105 UviCure S105.jpg
  • Low shrinkage
  • Viscosity (ca. 300 mPa.s @25° C)
  • Hard polymers
  • High crosslink density and high Tg
UVICURE 128

UviCure S128.jpg

  • Low shrinkage
  • Viscosity (ca. 600 mPa.s @25° C)
  • Increased flexibility over UviCure S105
Oxetane diluent resins
Name
Structure
Properties
UVICURE S130 UviCure S130.jpg
  • Improved adhesion
  • Improved flexibility
  • Increases reactivity
UVICURE140

UviCure S140.jpg

  • Improved adhesion
  • Improved flexibility

 

 

Oxetane property modifier resins
Name
Structure
Properties

UVICURE S150

UviCure S150.jpg
  • Improved adhesion

  • Improved flexibility

  • Increased toughness

  • Increased thermal stability

UVICURE S160

UviCure S160.jpg
  • Improved adhesion

  • Improved hardness

  • Increased chemical resistance

  • Increased thermal stability

UVICURE S170

UviCure S170.jpg
  • Hybrid oxetane/methacrylate functionality

  • Reduced phase separation in hybrid systems

  • Adhesion promotion in free radical systems

 

SpeedCure cationic photoinitiators

Iodonium salts
Name Structure Properties

SpeedCure 937



 

       SpeedCure 937.png
  • Benzene free
  • Good reactivity
  • Low yellowing
  • Cost efficient sensitization 
 

SpeedCure 938

SpeedCure 938.png
  • Benzene free
  • Good reactivity
  • Produces long lived acid species
  • Low yellowing
  • Cost efficient sensitization

 

SpeedCure 939

SpeedCure 939.png
  • Benzene free
  • Very high reactivity in silicone epoxy systems
  • Produces long lived acid species
  • Low yellowing

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sulfonium salts
Name Structure Properties

SpeedCure 976

SpeedCure 976.png
  • Very high reactivity
  • Produces long lived acid species
  • Low yellowing
  • Expensive to sensitize
 

SpeedCure 992

SpeedCure 992.png
  • High reactivity
  • Produces long lived acid species
  • Low yellowing
  • Expensive to sensitize

 

 

 

 

 

 

 

 

 

 

 

Discover our solutions for cationic curing

Cationic resins                  CATIONIC PHOTOINITIATORS

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