RP016 -
Dynamic Cure and Diffusion Monitoring in Thin Coatings; Micromet
Instruments, Inc., Dr. David R. Day and David D. Shepard
ABSTRACT
The recent development
of miniature microelectronic dielectric sensors enables relatively
simple drying, curing, and diffusion studies in extremely thin
films. The microdielectric sensor measures dielectric constant
and loss factor of the first 12 microns of material in contact
with the sensor. This paper discusses recent dielectric data
reproduction techniques which simplify the frequency, temperature,
and time dependent response into a single viscosity related
curve. The data resulting from an epoxy coating cure is demonstrated
and analyzed. The time required for moisture to influence the
dielectric response is used to determine diffusion rates through
thin coatings. Dielectric properties are used to analyze the
post curing properties of a latex film.
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RP101 -
Evaluation of Coil Coatings by Dielectric Analysis (DEA),
GE Appliances, Jesse Howard
ABSTRACT
Dielectric analysis
has existed for many years, however only lately has the technology
advanced to the point that its true potential is being realized.
It is felt that the information presented here offers finish
formulators and processors in the coil coating industry the
opportunity to more fully understand their products' cure kinetics
much earlier in the development cycle and to optimize cure
as it relates to performance.
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RP034 -Moisture
Diffusion Monitoring in Polymers with Microdielectronic Sensors;
Micromet Instruments, Inc., Dr. David R. Day and David D.
Shepard
ABSTRACT
With the use
of composites in space, there is always a concern for the moisture
content and the rate of moisture uptake within the structure.
For the past several years microdielectric sensors have been
used to monitor curing reactions in composites, while recent
work has shown that they can be used to monitor moisture diffusion
in a composite part after cure has taken place. Due to the
very localized measurement by the sensor, several sites within
a part can be monitored individually. This paper describes
preliminary diffusion work carried out in thin epoxy and polyimide
films as a function of ultimate cure temperature and film thickness.
This work shows
that microdielectric sensors are sensitive to moisture changes
in both polyimide and epoxy thermoset systems. The sensors
could not only monitor the curing of the structure during fabrication,
but could also be used during the life of the part to monitor
moisture uptake and moisture evolution in various regions within
the structure.
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RP109 -
A Study of the Drying and Curing Rates of Acrylic Automotive
Topcoats Using Dielectric Analysis, Micromet Instruments,
Inc. , David D. Shepard
ABSTRACT
The drying and
curing rates of acrylic automotive topcoats are critical to
the performance and appearance of the coating and the efficiency
of the manufacturing process. Typical evaluations of coatings
involve post-process tests which provide little information
as to the actual drying and curing rates during processing.
Dielectric Analysis
provides a means to study the drying and curing rates under
actual or simulated processing conditions. The coating is applied
to a planar dielectric sensor and dielectric measurements made
during the drying and curing of the coating. This provides
a continuous graph related to the rate of drying and curing
or the coating. This paper looks at the drying and curing rates
of both solvent based and water based automotive topcoats.
The effect of applying a Clearcoat over a Basecoat is also
examined.
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RP123 -
A New Dielectric Measurement System for Monitoring the Drying
and Curing of Coatings in Production Scale Conveyor Ovens,
Micromet Instruments, Inc., David D. Shepard, Huan L. Lee
ABSTRACT
The drying and
curing rates of coatings are critical to the performance and
appearance of the coating and the efficiency of the manufacturing
process. Processing of a coating often involves spraying the
coating onto the metal substrate to be coated, allowing some
of the solvents to evaporate, and then curing the coating onto
the substrate at an elevated temperature. Previous work has
shown that dielectric sensors mounted on the substrate can
be used to monitor the drying and curing process for acrylic
automotive coatings under simulated processing conditions.
In actual manufacturing,
this process is automated into a continuous process on a conveyor
system where the parts are sprayed, pass through a drying chamber,
and then into the curing oven. This paper discusses a new dielectric
maeasurement system that can travel through the process along
with the sensor. This eliminates the need for long extension
cables and enables the drying and curing behavior in production
scale processes to be monitored. Data collected with the new
dielectric measurement system is discussed.
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RP126 -
Cure Monitoring of Powder Coatings Using Dielectric Analysis,
McWhorter Technologies, Milind Sohoni, Micromet Instruments,
David D. Shepard
ABSTRACT
As dielectric
analysis has become a more accepted method of monitoring the
cure characteristics of thermoset resin systems, the applications
for this analytical technique have become more commonplace.
Traditionally, dielectric analysis has been used in the aerospace
industry to help understand cure related phenomena and determine
process parameters for advanced composite manufacturing. In
recent years dielectric analysis has seen growth in its use
for research and development, quality assurance and production
control in industries such as industrial molding, electronics,
medical and paints and coatings. The rapid growth of powder
coatings in an increasing number of applications has led to
a greater number of formulation requirements as well as the
need for a better understanding of the effect of processing
conditions on cure characteristics. This paper reviews the
theory of dielectric measurements and analyzes and discusses
dielectric data collected from various powder coating formulations
processed under different temperature conditions.
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RP042 -
Moisture Monitoring at the PI-SiO2 Interface Using Microdielectric
Sensors; Micromet Instruments, Inc., Dr. David R. Day
ABSTRACT
Reaction and
diffusion in polyimide was studied using microdielectric sensors.
Onset of imidization was observed at 135C while reaction and/or
loss of volatiles was observed up to the final temperature
of 240C. Microdielectric sensors were found to monitor moisture
concentration changes at the PI-SiO2 interface of a polyimide
film on the sensor. Data were fit with a Fickian model and
exhibited excellent agreement. Calculated diffusion coefficients
ranged from 2.2 to 4.8 x 10-9(cm2/sec). The polyimide diffusion
coefficient was found to be nearly constant with reaction temperatures
ranging from 160C to 240C.
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RP050 -Moisture
Diffusion Monitoring of Polyetheretherketone (PEEK) with
Microdielectric Sensors; Micromet Instruments, Inc., Dr.
David R. Day, David D. Shepard, and Kelly J. Craven
ABSTRACT
Classical diffusion
analysis involves weight uptake measurements as a function
of time on thin polymeric samples. The use of Microdielectrometry
to monitor the diffusion of moisture through polymers is a
relatively new technique. Sensors have been developed which
are sensitive to the small changes in permittivity (dielectric
constant) of polymeric materials as water concentration (and
thereby, mobile dipole concentration) increases. In addition,
sensors exist which can withstand the high temperatures (greater
than 350C) required for the consolidation of high temperature
thermoplastics. The diffusion coefficient can be estimated
through a simple Fickian diffusion model of the dynamic dielectric
response. The Microdielectric sensors measure a very localized
area of approximately 0.01cm into the material. This allows
monitoring diffusion properties of thin films, or of many simultaneous
and independent locations in a bulk material.
Previous work
has studied the diffusion characteristics of epoxies and polyimides
by this technique. This study examines the diffuson of water
through a thin film of polyetheretherketone (PEEK) and compares
it with published data obtained by weight uptake studies. The
diffusion rate of moisture through amorphous PEEK is shown
to be slightly faster than diffusion through more crystalline
PEEK.
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RP113 -Dielectric
Analysis for Determining the Extent of Cure for UV/EB Systems,
Thomas F. O'Malley, Sun Chemical Corporation and Nathaniel
T. Smith, Micromet Instruments, Inc.
ABSTRACT
In the past
dielectric analysis (DEA) has been used as an important measurement
component in the overall analysis of polymer resin systems.
Much of this work has been done at the research level in determining
viscosity behavior, rate of cure, and cure endpoint. In the
areas where DEA has been used in the production environment,
it has been in the low volume applications of aerospace composites.
Within the last several years there has been an expansion of
the applications were dielectric cure analysis has been used.
One of those areas is the analysis of both UV and EB curing
systems. For UV systems the reaction can be monitored during
the exposure and during post cure. For EB systems the change
in cure state is measured before and after EB exposure. Both
processes can be measured in real-time, in-situ. By monitoring
the change in electrical properties of the resin system the
rate and extent of cure can be determined. With sampling rates
down to 55 milliseconds, measurements can be taken during the
exposure process. Diffusion properties can also be monitored.
Films down to 1 micron in thickness can be measured.
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