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Factors that influence blister resistance Technical Paper
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Date:
950 HIGHWAY 57 EAST COLLIERVILLE, TN 38017 (800) 238-7536 FAX (901) 854-1183 www.aoc-resins.com
Abstract
New low styrene unsaturated polyester resins have been de-
veloped for the filled market segment. These polyesters
maintain viscosity and thix indexes of conventional systems
while offering dramatic reduction in styrene content.
The next generation resin system has a styrene content of
30%. Although the styrene content has been dramatically
reduced, rollout and wetout remain equal to the higher sty-
rene systems. The cure profile is rapid while maintaining
low peak temperatures. Shrinkage is minimal, and physical
property test results are comparable to typical polyester resin
used in filled applications. The Heat Distortion Tempera-
ture is dramatically improved over traditional filled resin
systems that are available in the industry today, which con-
tain a much higher level of styrene.
As the new generation of resin is introduced, liquid proper-
ties and physical properties will be compared to resins typi-
cally used in the filled market sector.
Historical background in filled systems
Filler was introduced to the market in the early seventies
as a way of adding a degree of fire retardancy to a finished
part. Alumina trihydrate was the filler of choice. The rea-
son for using Alumina trihydrate was approximately 35%
water is given off upon heating to temperatures of 300C or
higher. Therefore provides fire retardant properties.
Later, filler was added similar to a diluent, that is, as a way
of extending the resin system, which lowered the cost on
the finished components produced. Additional attributes
also contributed to the use of fillers. Opacity of filled sys-
tems improved the surface cosmetics, cracks were reduced
in areas of tight radii, parts were more rigid and shrinkage
was reduced.
Early on, resin systems used were typically orthophthalic
in composition. The level of styrene in the systems aver-
aged 50%. These resin systems had filler loading of 40%-
50% using alumina trihydrate.
Low Styrene Content Filled Resin Systems
Many challenges were presented as filler was introduced
to resin systems. Some of the obstacles to overcome were
as follows; maintaining a workable viscosity for
sprayability, optimizing the thix index to prevent sliding
on horizontal surfaces, good wetout and rollout abilities,
and the ability to keep the filler from packing in the day
tanks and lines. As systems evolved, suppliers worked with
fabricators to overcome these areas of concern.
Fabricators began to blend different types of fillers. Cal-
cium carbonate was blended with alumina trihydrate. This
allowed for an even further reduction in cost on the fin-
ished parts. Calcium sulfate (Gypsum) also was used. The
Gypsum releases water molecules at 200°F when heated.
Thus, it also is flame-retardant filler.
Glass contents on resin systems before filler was introduced
were typically targeted at 25%. As the fabrication of parts
evolved using fillers, glass contents were reduced to a range
of 10 to 15%. Which again reduced the cost of the fin-
ished part.
The filled market segment of open molding has changed
dramatically over the years. New chemistries of poly-
mers were introduced. In 1980 polyester resin based on
DCPD (dicyclopentadiene) as a raw material were intro-
duced to the market. They were lower in molecular weight
than the orthophthalic resins, thus allowing for an increase
in filler loading. One of the attributes of the DCPD based
systems was processability. These systems made the roll
out and wet out of glass much less burdensome.
Figure #1 represents the evolution of filled resins systems.
It compares a traditional orthophthalic system to the newer
chemistries of resin that have evolved over the years.
Each system was thinned with styrene to a targeted filled
viscosity of 1000-1200 cps with a thix index range of 2-3.
The range is typical of specifications that most fabricators
use. Each system was filled at 47% loading.
Margie Smith-Krantz
Oct. 3-6, 2001 Technical Paper
950 HIGHWAY 57 EAST COLLIERVILLE, TN 38017 (800) 238-7536 FAX (901) 854-1183 www.aoc-resins.com
One of the reasons for the creation of a new polymer was
increasing pressures on the industry by the government to
reduce HAPS in a fabricators shop. The new polymer has
a styrene content of 30%. This is a 33% reduction in sty-
rene over traditional orthophthalic resin systems.
Introduction of New Low Styrene System
One of the problems encountered when removing styrene
from a system is that the physical properties are dramati-
cally reduced. Testing indicates that a system can become
styrene deficient, in that there is not enough styrene in a
system for the necessary crosslinking to occur. As a result,
parts are under cured and tend to be sticky. DSC results
indicate that this is indeed true and the parts will tend to
post print and distort. With this information taken into con-
sideration, a new polymer was created by careful selection
of glycol and acids at specific ratios to reduce styrene and
maintain processability of the filled resin system. The vis-
cosity and thix index are equal to that of the orthophthalic
system; however, the styrene content has been reduced by
33%.
Impact on Physical Properties
Figure #2 compares the physical properties of the different
resins used in filled systems as they have evolved over the
years.
The samples were made via the industry standard of clear
casting, non-filled, promoted with cobalt 12% and 1.25-%
MEKP. All samples were post cured.
As expected, the physical properties in a clear casting have
dropped in value. The main point of interest is that the new
system at 30% styrene has a higher HDT than any of the
other systems at much higher levels of styrene. This is im-
portant for fabricators of truck caps and tonneau covers that
are post cured and painted at higher temperatures. If the
HDT is too low, the parts will sag or droop in the middle.
The following photos (Figure #6, Figure #7) demonstrate a
part bridged in the air with no middle support. The test bars
were placed in a 90°C oven for one hour. As one can clearly
see, the new polymer maintains its integrity, the system with
the lower HDT sags dramatically in the middle.
Laminate Physical Properties
Clear cast physical properties have been accepted as an in-
dustry standard, however, they do not clearly reflect filled
laminate physical properties.The following table lists the
comparison properties of laminates on the same systems in
the previous tables. Looking at the data in the clear cast
table, one can see the reduction in some of the physical
properties. The filled laminate physical property results
portray a different picture. The drop in values are mini-
mal. A slight increase in glass content can easily overcome
any reduction in physical properties one may experience by
using a lower styrene system. Figure #3 demonstrates those
results.
The laminates were prepared in the same manner; filled at
47%, targeted 15% glass, and 21% glass on the new poly-
mer. Analytical testing was performed on the laminate itself
to determine the exact glass content of each laminate.
Cure Profile
Figure #4 lists the cure profile of filled resin systems that
have evolved over the years.
Identical formulations were used to demonstrate the differ-
ence in cure profile and hardness progression. The only
difference in the formulation is the level of styrene. Each
system was thinned with styrene to meet the 1000-1200 cps
viscosity and a thix index of 2.0 to 3.0.
As one can see by the test results, the new polymer meets
and matches the cure profile of previous systems. The hard-
ness development is improved, allowing for quicker through-
put of parts. Formulations can be tailored to meet the
customers fitness criteria on peak temperature without ad-
versely impacting the cure profile.
Impact on Shrinkage
Reducing styrene and/or adding filler to a system reduces
linear shrinkage.
Figure #5 demonstrates the differences in linear shrinkage
from the traditional orthophthalic system to the new poly-
mer. All samples were filled at 47% (contains no glass).
The samples were room temperature cured.
Results indicate that as styrene is reduced from the system,
linear shrinkage is reduced to a minimum. This translates
to dimensional stability on the finished parts. 950 HIGHWAY 57 EAST COLLIERVILLE, TN 38017 (800) 238-7536 FAX (901) 854-1183 www.aoc-resins.com
Technical Paper
Conclusion
Fabricators are looking for ways to reduce HAPS in their
process through many different avenues. A combination
of technologies may be necessary to meet desired levels
of HAPS. Non-atomizing spray equipment along with a
reduced HAP resin system that maintains filler
Figure #1
Viscosity, Thix Index and
Styrene Percent
Traditional
Orthophthalic
system
First DCPD
systems
Next
generation of
DCPD
New
Polymer
Styrene content
45%
38%
36%
30%
Viscosity, LV#3 @60
1096
1144
1148
1120
Thix Index, 6/60
2.4
2.8
2.7
3.0
Figure #2
Clear Casting
M echanical Test results
Traditional
Orthophthalic
Sy