WATERBASED POLYESTER COATINGS FOR CHLORINATED POLYOLEFIN PRIMED
POLYPROPYLENE
UNIVERSITY OF MISSOURI- ROLLA
W. L. Dechent
J. M. Land
J. O. Stoffer
email to Jim Stoffer (jstoffer@umr.edu)
Other questions requiring Eastman personal, please direct to
Jonathan Lawniczak, Coatings Laboratory, 615.229.5762
THE SLIDES PRESENTED AT THE 1994 WATERBORNE SYMPOSIUM ARE SHOWN BELOW
- - Title Slide
The purpose of this part of the research project was to develop a
waterborne coating system that would adhere to CPO, and to test
the adhesion mechanism.
- - Outline
- - What is CPO?
CPO is prepared by chlorinating polypropylene, to about a chlorine
every four repeat groups, and then maleating it to add anhydride
functionality.
- - Why paint plastic?
The auto industry has increased the number of plastic parts on a
vehicle to reduce the weight. This results in better gas mileage.
- - Surface Energy Considerations
A low energy fluid will wet a high energy solid, but a high energy
fluid will bead up on a low energy solid. Polypropylene, a pure
hydrocarbon, has a low surface energy.
- - Methods of Improving Adhesion
A list of the different techniques used to make polypropylene and
other polyolefins paintable.
- - Why do we need CPO?
Paint on polypropylene shows negligible adhesion. CPO will still to
polypropylene, and paint will stick to CPO.
- - The Peel Test
A cartoon of an Instron pulling a cloth away from a piece of plastic. The
cloth had been soaked in the paint and was placed on the plastic to
dry. The cloth is pulled away from the plastic as the upper Instron
clamp moves upward at a constant speed. The Instron sends a signal of the
strength required for the pull to an X-Y recorder, and a Stress vs. Strain
plot is reduced. Stress refers to the force required for the pull,
and Strain refers to dimensional change as a cloth is pulled.
- - Different Cloth Peel Tests
- Paint/CPO/Plastic- A paint soaked cloth is placed on CPO treated
plastic
- CPO/Plastic- A CPO soaked cloth is placed on plastic
- Paint/Paint- Two cloths are soaked in paint and put
together
- CPO/CPO- Two cloths are soaked in CPO and put
together
- - Failure of High Strength Samples
There are five possible modes of failure, two of which are adhesive, and three
of which are cohesive. Acording to Bikermann, a sample formed by good wetting
will always show cohesive failure. Other adhesion experts have been able to
create systems that show adhesive failure.
- - Effects of Heat Cycle
After determining that a heat cycle improves peel strength, it is
necessary to determine the cause of the improvement.
- A heat cycle could increase the diffusion between two polymer phases,
leading to stronger adhesion.
- A heat cycle could decrease the free volume of a polymer phase,
leading to stronger cohesion.
- If there is a chemical reaction to form covalent bonds between
two phases, the heat cycle could increase the number of covalent
bonds between the two phases.
- - Possible Paint/CPO Interactions
- Interphase Formation
- Interphase Formation and Covalent Bonding
- Covalent Bonding
- - Time Temperature Superposition,
WLF Theory Applied to Heat Cycle
- The idea here is that a superposition exists between the time of a
heat cycle, and the temperature of a heat cycle.
- Peel strength vs. either time or temperature produces the same
function.
- This function indicates diffusion is a part of the mechanism that
leads to higher peel strength, but that is another slide.
- - Materials- materials used for previous research
A materials slide covering materials tested before we started work with a
waterborne polyester.
- - Materials- materials used for UPE
This slide lists the materials used for the research involving the
unsaturated polyester.
- - Components of the Unsaturated Polyester
- Trimellitic Anhydride-
- Maleic Anhydride-
- Adipic Acid-
- Isophthallic Acid-
- Trimethylolpropane-
- B E P D-
- - CPO Soaked Cloth/ TPO Systems
- Waterborne CPO soaked cloths were placed on thermoplastic olefin
and left to dry, then heat cycled.
- The time of the heat cycle was held constant, and the temperature
of the heat cycle was varied.
- The result function shows a linear increase over the temperature
range through which polymer diffusion increases the peel peel strength
if diffusion is a part of the mechanism that improves adhesion.
- - Diffusion could be CPO into plastic or CPO/CPO annealing
This slide explains why a test of the heat cycle effect on CPO cohesive
strength must be carried out.
- - CPO/CPO Two Cloth Peel Test
- Two waterborne CPO soaked cloths were placed together and left to dry.
- The time of the heat cycle was held constant, and the temperature
of the heat cycle was varied.
- The resulting function indicates that diffusion occurs
as a result of the heat cycle which improves the peel strength.
- - Observed Modes of Failure
We have never observed adhesive failure (statement applies to research
reported up to the time of the talk only.)
- - Effect of Anhydride Functionality
Eastman supplied us with two special CPOs to see if hydrolysis of
the anhydride functionality would change the peel strength.
- - IR Test of Covalent Bonding
- Samples were prepared by mixing CPO, polyisocyanate, and dibutyl tin
dilaurate catalyst.
- Films were pressed between teflon and infrared spectra taken with
a specific interest in the peak at 2280 cm(^-1) corresponding to
an isocyanate stretch.
- Control samples used CPO without anhydride functionality. The
other samples used CPO with anhydride functionality.
- All films were cast from acetate solvents
- Samples were subjected to a 20 minute, 100 C heat cycle.
- Lack of isocyanate peak change for the control samples indicated no
reaction took place for samples with CPO lacking anhydride functionality.
- If there had been a major peak disappearance, we would suspect hydrolysis
from atmospheric water.
- But there wasn't
- Loss of the isocyanate peak for samples with functionalized CPO indicates
that the isocyanate reacted with the anhydride functionality.
- - Infrared Spectra
This slide shows the results of the IR experiment to confirm
covalent bonding between isocyanate and CPO.
- - Acetone UPE/ CP 310w/ TPO SEM
A scanning electrom microscope micrograph shows there are three
distinct phases, paint, CPO, and thermoplastic olefin, when an
acetone borne unsaturated polyester is placed on thermoplastic
olefin treated with waterborne CPO.
- - Acid vs. Anhydride
Eastman Chemical synthesized two speciality CPOs, where the variable
was the "closed vs. open" content of the anhydride functionality.
The anhydride functionality of the CPO can be hydrolyzed. If 75%
of the anhydride functionality has been hydrolyzed, the CPO is
referred to as 75% "open."
- - Effect of Acid Content
Peel tests show no significant variance in peel strength between the
commercial CPO, and a CPO with a high "open" content, and a CPO with
a high "closed" content.
- - Effect of Heat Cycle on Cohesive Paint Strength,
Unsaturated Polyester
One goal of the waterborne unsaturated polyester project was develop a
strong paint that would stick to CPO. This test demonstrates that
the heat cycle increases the cohesive strength of the unsaturated
polyester paint.
- - Peel Strength vs. Peel Speed
- A two cloth peel test of acetone borne unsaturated polyester
- Peel speed varied
- A 20 minute/100 deg C heat cycle used
- A peel speed dependence (i.e. the slower you peel, the lower the
peel strength) indicates that chain pullout is a part of the failure
mechanism.
- - WUPE vs. ABUPE Peel Strength
- This graph compares results using acetone vs. water for the continuous
phase.
- For acetone systems, the results show the effect of the heat
cycle.
- For water systems, it wasn't possible to do a no-heat sample,
since the blocked isocyanate needed 140 deg C temperatures to
deblock.
- The excess concentration of isocyanate was cut from 50%
to 15% for waterborne comparison.
- - Conclusions
first of two slides with conclusions
- - Second Conclusions Slide
second of two slides with conclusions
- -We're on the web
- - Thanks to Missouri Department of Economic Development
This research was supported in part by a grant from the Missouri Department
of Economic Development.
- - Special Thanks to the Eastman Chemical Company
Slide Thirteen- 2nd Heat Cycle Restores CPO COHESIVE STRENGTH
- This slide was not included in the presentation for the amount
of time required to explain it.
- For solvent borne polyesters, the peel strength values were
so low (~50 to 100 g/cm) that it was as if the CPO/plastic samples
had not been given a heat cycle.
- The paint/CPO/plastic samples were given a second heat cycle.
Definition of first heat cycle
- Note: the first heat cycle was of the CPO/plastic system
Definition of second heat cycle
- The second heat cycle was for the paint/CPO/plastic system
There are several twists to the low numbers
- This gets really complicated because it would be easy to say
"Oh, acrylics can ambient cure
so they don't need a second heat cycle, but your polyester systems
needs the heat cycle to facilitate the cure"
the 2nd heat cycle cured two phases
- And it is true that the second heat cycle improved the cohesive
strength of the paint,
- The failure of the solvent polyester/CPO/TPO systems was cohesive
CPO failure at ~50 g/cm
Focus on CPO cohesive strength
- We know from previous tests that the cohesive CPO strength
after the heat cycle can be as high as 1000 g/cm.
The results
- The application of the paint lowered the cohesive strength of the
CPO.
The conclusion
- We conclude that the heat cycle strengths both the paint and the CPO.
Future work
- If the paint solvents can go through the CPO, is it possible that
the cohesive failure of TPO might occur at a higher peel strength if
there are no solvents used in either the CPO or the paint.