Curing kinetics describe how liquid photopolymer resins convert into solid polymers under light exposure.
Understanding curing kinetics is essential for predicting cure depth, exposure requirements, dimensional accuracy and printing speed in vat photopolymerization systems.
Exposure dose and polymerization
Photopolymerization occurs when photoinitiator molecules absorb photons and generate reactive species that initiate polymer chain formation.
The extent of polymerization depends primarily on the delivered exposure dose:
Exposure dose = light intensity × exposure time
If the delivered dose is insufficient, curing remains incomplete. If the dose is excessive, overcuring and dimensional inaccuracies may occur.
Penetration depth and Beer–Lambert behavior
Light intensity decreases exponentially as it penetrates the resin due to absorption and scattering phenomena.
This behavior is commonly approximated by the Beer–Lambert relationship, which describes the attenuation of light as it travels through an absorbing medium.
In photopolymer resins, penetration depth determines the effective thickness of each cured layer and therefore strongly influences dimensional accuracy.
Working curves and cure depth
The relationship between exposure dose and cured layer thickness is often described using the Jacobs working curve model.
Experimental working curves allow estimation of cure depth and calibration of exposure parameters for specific resin–printer combinations.
Engineering implications
- Layer thickness must remain smaller than cure depth
- Excessive cure depth causes dimensional drift in Z
- Optical scattering influences XY resolution
- Resin pigments and additives modify optical attenuation