Cationic curing

Discover cationic curing technology and its benefits to achieve high performance properties

Technology presentation

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 initiationpropagation 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.
 

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.

 

 

2. Propagation – Thermally driven reaction

The strong acid ring opens an epoxy and/or oxetane

 

 

 

 

Cationic curing benefits

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

 

UviCure epoxy and oxetane resins

UviCure epoxy resins

Name Structure Properties

 

UviCure S105


                

 

  • Low shrinkage
  • Viscosity (ca. 300 mPa.s @25° C)
  • Hard polymers
  • High crosslink density and high Tg

 

UviCure S128


 

  • Low shrinkage
  • Viscosity (ca. 600 mPa.s @25° C)
  • Increased flexibility over UviCure S105

UviCure oxetane diluent resins

Name Structure Properties

 

UviCure S130

 

  • Improved adhesion
  • Improved flexibility
  • Increases reactivity

 

UviCure S140

 

  • Improved adhesion
  • Improved flexibility

UviCure oxetane property modifier resins

Name Structure Properties

 

UviCure S150

 

 

  • Improved adhesion
  • Improved flexibility
  • Increased toughness
  • Increased thermal stability

UviCure S160

 

 

 

  • Improved adhesion
  • Improved hardness
  • Improved chemical resistance
  • Increased thermal stability

 

 

UviCure S170


 

  • 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


          

 

 

  • Benzene free
  • Good reactivity
  • Low yellowing
  • Cost efficient sensitization

 

 

SpeedCure 938


  • Benzene free
  • Good reactivity
  • Produces long lived acid species
  • Low yellowing
  • Cost efficient sensitization

 

 

SpeedCure 939

 

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

 

Sulfonium salts

Name Structure Properties

 

 

 

SpeedCure 976


 

 

  • Very high reactivity
  • Produces long lived acid species
  • Low yellowing
  • Expensive to sensitize

 

 

SpeedCure 992



 

  • High reactivity
  • Produces long lived acid species
  • Low yellowing
  • Expensive to sensitize
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