Description:
Hyperbranched products, such as CN2302 and CN2304, are highly
branched three-dimensional materials that differ structurally
from the linear or lightly branched products typically used
in radiation-cured systems. Because of the approximately spherical
or globular morphology, the properties of hyperbranched polymers
differ from traditional linear polymers in that they have relatively
low molecular volume for a given molecular weight and have a
high concentration of end groups. In addition, the end group
concentration remains relatively constant as molecular weight
increases.
The unique structure
of hyperbranched materials offers uncommon
and advantageous characteristics that include: low viscosity
at a given molecular weight, high end-group concentration, low
shrinkage on cure and fast development of physical properties.
The structure and properties of two hyperbranched polyester
acrylates will be discussed in terms of their application to
radiation curable inks and coatings. The figure below illustrates
the structure of the hyperbranched materials and presents a
summary of related characteristics.
High functionality
acrylates are used in radiation-cured systems because of the
enhancements they can bring in properties, such as cure speed,
hardness, scratch resistance and chemical resistance. Use of
traditional high functionality materials, such as dipentaerythritol
hexaacrylate (DPHA) or high functionality urethane acrylates,
require a tradeoff with less desirable properties, such as high
viscosity, high film shrinkage on cure and brittleness. The
unique structural features of hyperbranched polyester acrylates
like CN2302 and CN2304 may make it possible to break these paradigms.
The tables below show
the features and typical properties of CN2302 and CN2304. As
shown, DPHA is considerably more viscous than the hyperbranched
products, although its acrylate functionality is only six. DPHA
also shrinks to a much greater degree and produces brittle films.
Weatherability
Testing:
The hyperbranched products demonstrate excellent weathering
resistance compared to an aliphatic urethane acrylate with superior
weatherability (passed 2.5 year outdoor Florida exposure). Changes
in yellowness index and 60° gloss during accelerated weathering
testing are shown below based on the following cure and test
conditions. Performance for the hyperbranched products was comparable
to the aliphatic urethane acrylate control.
Cure Conditions
A formulation comprised of 97 wt.% oligomer and 3 wt.%
TPO (2,4,6 trimethyl benzoyl diphenyl phosphine oxide) was applied
at a film thickness of 35-45 micrometers to cold-rolled steel
with E. coat primer and white base coat. Curing followed a two-step
process. Step one used a 600 watt/inch Fusion V lamp with a
cure speed of 25 fpm in air. Step two employed a 600 watt/inch
Fusion H lamp with a cure speed of 25 fpm in nitrogen. Total
UV energy was 4.5 J/cm2.
The hyperbranched
products are also tough and durable materials. To demonstrate
this scratch resistance was tested by measuring 60° gloss
values versus the number of passes with 000 steel wool under
a 1kg load. As shown below, CN2304 performs very well in that
it loses only 12% of its initial gloss after 200 passes. As
noted above, DPHA could not be tested due to embrittlement.
The listed properties
are illustrative only, and not product specifications.
Sartomer Company disclaims any liability in connection with
the use of the information, and does not warrant against infringement
by reason of the use of its products
in connection with other materials or in any process.
Sartomer Company,
Inc.
502 Thomas Jones Way
Exton, PA 19341
U.S.A.
1-800-SARTOMER
610-363-4100
www.sartomer.com
