improved cure rates.1 This is illustrated in Figures 5a and 5b, respectively.
Improved cure rates by filler addition
opens up the possibility for greater line
speeds or reduced energy requirements
simply by adding ultrafine nepheline syenite to the system.
Experimental
Previous experiments noted above confirmed that ultrafine nepheline syenite
has a positive effect on cure rate and
film hardness in UV-cure PUD systems
as opposed to unmodified systems using indirect measures. To better investigate the real-time curing behavior of
ultrafine nepheline syenite, the effects
of loading level and varying film thickness, and the potential to reduce the
required amount of costly photoinitiators, an improved analytical technique
was required.
UV-Cure PUD Test
Formulations
The particle size statistics for ultrafine
nepheline syenite ( 5 µm N.S.) used in the
experiments are found in Table 2. The
5 µm N.S. was first incorporated into a
stable resin-free pre-dispersion found in
Table 3 so it could be added directly to
test formulations. The UV-cure PUD test
formulations used in this investigation
are found in Table 4. The photoinitiator
selected for this study functions optimally
at higher UV wavelengths of 360 to 440
nm to match the energy of the LED UV
light source used for curing.
Cure Rate Determination
A Dymax DX-1000 Visicure Spot was
utilized to cure the samples during testing
in the FTIR spectrometer. This UV spot
curer has a peak wavelength of 405 nm.
The spot curer power can be set from 0 to
100% and is fed via fiber optic cable to
the area to be cured. This high-intensity
source provides virtually instantaneous
and controlled power output, making it
particularly suitable for measuring real-
time cure rates.
The test formulations were applied to
Leneta release charts (form RC-5C) with
a wire wound bar at the specified wet
thickness. The coatings were allowed
Figure 5a. Pendulum hardness with increasing
energy at 6% N.S by wt. in a UV PUD.
Figure 5b. Acrylate double bond conversion as a
function of cure time at 12% 5 µm N.S. in UV PUD
spot oven curing.
Median, µm (D50) 99% < µm (D99)
5 µm N.S. 1.5 5
Table 2. Nepheline Syenite test filler particle size.
Ingredient
DI Water 31.0
Polymeric hyper-dispersant ( 50 N.V.) 8.0
5 µm N.S. 61.0
Total Solids Content 65.0
Table 3. Stable resin-free pre-dispersion formulation.
Wt. of 5 µm N.S. on clear resin solids 0 6 12
Ingredient ( solids)
Aqueous UV-cure PUD 36. 5 67.45 67.45 67.45
Peroxide Photoinitiator 100 1.0 1.0 1.0
Non-ionic dispersant 25 0.67 0.67 0.67
Mix 5 min at 900 RPM
5 µm N.S. Pre-Dispersion 65 0.0 2.91 6. 29
DI Water 10.0 15. 15 15. 15
Surface wetting aid 0.3 0.3 0.3
Mix 10 min at 1100 RPM
Table 4. Clear aqueous UV-cure PUD formulation.
