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IMECE2007-43516

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Proceedings of IMECE2007
2007 ASME International Mechanical Engineering Congress and Exposition
November 11-15, 2007, Seattle, Washington, USA
IMECE2007-43516
EFFECT OF SIZE AND SPATIAL DISTRIBUTION OF TITANIA PIGMENTS IN
INJECTION MOLDED PARTS ON SURFACE REFLECTANCE
B.R. Dantal
Mechanical Engineering Department
Tufts University, Medford, MA 02155
United States of America
barish.dantal@tufts.edu
A. Saigal
Mechanical Engineering Department
Tufts University, Medford, MA 02155
United States of America
anil.saigal@tufts.edu
M.A. Zimmerman
Mechanical Engineering Department,
Tufts University, Medford, MA 02155,
United States of America
mzimmerman@qlpkg.com
ABSTRACT
Titania pigments are used in molding compounds as a
means to improve opacity by increasing the scattering
efficiency of the medium and to develop new applications
such as liquid crystal displays (LCD) and light emitting
diodes (LED).
The characteristics of the injection molded products
are a function of molding parameters such as gate
location and shear rate. In this study, quantitative
measures of the particle distribution of titania pigments in
polymer
composites
have
been
experimentally
determined, including area fraction, average diameter,
and diameter volume. A 2 x 3 x 3 ANOVA test has been
conducted to assess the statistical significance of these
parameters.
This study deals with the size and spatial distribution
of the particles. The important parameters calculated
based on the Feret’s diameter are diameter-volume (dv),
diameter-number (dn), and area fraction (AF). The term
diameter-volume (dv) has been used to give greater
significance to the large particles and thus ‘large’
indicates more and/or larger particles. The parameters
have been calculated by using Image-J image processing
software.
MINITAB has been used to assess the statistical
significance of these parameters. The results show that
titania particles are not uniformly distributed within the
final molded parts and they vary along the molding
(longitudinal) and transverse directions of plastic flow.
The difference of pigment area fraction and diameter
volume at different locations within a final molded part
has a significant effect on the percentage reflectance of
the surface.
INTRODUCTION
During the past decade, inorganic/polymer hybrid
materials have been the focus of research for their
excellent electrical, optical, magnetic, optoelectronic, and
enhanced mechanical properties. These hybrid materials
combine the advantages of the organic polymers
(lightweight, flexibility, relatively high impact resistance,
and reasonable processability) and inorganic materials
(strong chemical resistance, high thermal stability, and
1
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high brittleness). Optical, mechanical, and thermal
properties of the hybrid materials are a function of the
relative weight percent of each constituent in the
composite material. Recently, the development of
inorganic/polymer hybrid materials with high refractive
index have attracted significant interest for electronic
applications [1, 2].
The properties and distribution of pigment particles
affect dielectric and optical properties of the final injection
molded part. The interplay between the molding
parameters, pigment concentration, gate location, particle
size distribution, and spatial distribution must be
examined in a structured manner to understand their
effects on the final properties of the part.
The material is used in electronic packaging
applications where it encapsulates the light emitting
diode. Light emitted by diode is reflected by the
surrounding walls of the material. Reflectance of light is a
function of the amount and distribution of titania particles
on the surface. This study quantitatively measures the
particle distribution, including area fraction, average
diameter, and diameter volume of titania pigments in
injection molded parts with the ultimate goal of optimizing
them to maximize surface reflectance of light. This study
also investigates the relationship between gate location
and how different measures vary at different locations.
The variation of reflectance caused by uneven particle
distribution has been assessed.
and 270 deg.) minimizes measurement
associated with directionality [2].
variation
Input particle size distribution for the pigment (Titania
particles) is received from the manufacturer. Pigment
particles on the surface of the injection molded have been
characterized using Field Emission Scanning Electron
Microscope (FESEM - LEO B Make: Zeiss). The LEO
Field Emission Scanning Electron Microscope (FESEM)
allows surface examination down to nanometer scales.
FESEM uses a low to moderate energy (0.2 to 30 keV)
electron beam to image a sample in high vacuum with
resolutions down to 1 nanometer at 30 keV.
All surface images are taken at 5 keV. FESEM was
capable of identifying pigment particles with sufficient
clearness. As shown in Fig. 1, molded parts have been
A
-1
B
0
1
1
7
8
9
0
4
5
6
-1
1
2
3
TEST MATERIALS
Injection molded plaques, provided by Quantum Leap
Packaging, Inc., are analyzed in this study. These
plaques are composites of liquid crystal polymer and
titania particles. The titania pigment particle concentration
varies from 22 wt.%. to 40 wt.%. The particles are
approximately normally distributed with a mean of 0.2 μm
and standard deviation 0.08 μm. Parts obtained are
rectangular in shape (5 in. X 3 in. X 0.12 in.).
EXPERIMENTAL PROCEDURE
All the plaques were received from the provider
without further treatment. Gate location was marked for
sample preparation purpose. As shown in Figure 1,
plaques were cut into nine small square pieces of 1 in.
side. Gate location is at 2. To investigate how particle size
and spatial distribution change with respect to gate
location, parts have been marked as A (-1 0 1)
horizontally and B (-1 0 1) vertically.
A HunterLab ColorQuest XE spectrophotometer has
been used to measure the reflectance of the plaques.
Averaging readings at different rotation angles (0, 90, 180
Gate Location
Fig. 1: Different locations on the molded part.
cut into nine small squares 1 inch on each side.
These small squares were then coated with the help of
a sputter coater (Make: Cressington, Model: 208HR).
Since samples are non-conductive, a Platinum/Palladium
target was used to coat the samples. There are a total of
nine images for each sample. The images have been
enhanced by using common imaging tools and were
analyzed using the Image-J software.
The pigment particles have a wide range of particle
sizes. Images 9.66 μm X 9.06 μm at 10,000 X have been
used in this study. Macros incorporated into the Image-J
software have been used to locate the particles, calculate
the average particle diameter, obtain the area fraction,
and calculate the diameter volume. A thresholding feature
has been applied to remove all of the particles smaller
than 0.1 μm, also considered as noise in the image.
2
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The size distribution and spatial distribution of the
particles are of interest in this study. The important
parameters included diameter-volume, diameter-number
(average diameter) and area fraction (AF).
Equations (1) and (2) have been used to calculate
d v and d n [3, 4]. Figure 2 shows the image obtained
with the help of FESEM and Figure 3 shows the binary
image acquired after the image processing.
dn =
∑d
N
i
K(2)
where d i is the Feret’s diameter of the ith particle and N is
the particle count. Here, d n is the average diameter of
the pigment particles. The purpose of introducing d v is to
give more significance to the large particles where ‘large’
thus indicates more and/or larger particles. Area fraction
approximates the weight fraction and normally will be
smaller than the weight fraction.
RESULTS AND DISCUSSIONS
Figure 4 shows the average reflectance for samples
measured with a colorquest spectrometer. Reflectances
obtained on the front and back sides of the sample are
similar and do not show significant differences. Overall,
reflectance for sample with 22 wt.% TiO2 is higher than
pure LCP (0 wt.% TiO2) and the sample with 40 wt.%
TiO2. Reflectance has been measured at nine different
locations and the average reflectance is plotted in Figure
4 for all the samples. Adding 22 wt.% titania particles to
the pure LCP materials increases the surface reflectance.
However, increasing the amount of titania further to 40
wt.% does not lead to further increase in reflectance.
Fig. 2: Image obtained from FESEM.
85
75
% Reflectance
65
55
22 wt.l% Titania Pigments
45
40 wt.% Titania Pigments
35
0 wt.% Titania Pigment (Pure LCP)
25
15
400
450
500
550
600
650
700
Wavelength (nm)
Fig. 4: Average reflectance for samples
measured with ColorQuest XE spectrometer
Fig. 3: Binary image obtained after image
processing (Black spots, TiO2 Particles)
dv
∑d
=
∑d
4
i
3
i
K (1)
3
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Results obtained by using the Image-J software are
tabulated in Table 1. Values for percent reflectance are
recorded at 500 nm wavelength for all the samples at
three different points. Finally, for each sample the
average AF, d v , d n , and N values are calculated [5].
Table. 1: Results from Image-J Image analysis
wt.% TiO2 as compared to those with 40 wt.% TiO2. The
effect of particle concentration on reflectivity of the
material obtained here is similar to those obtained by
other investigators [6, 7].
Regression plots in Figure 6, show that values of AF, d v
and d n decrease as Titania pigment wt.% increases.
12
Loc
1
2
3
4
5
6
7
8
9
B
-1
-1
-1
0
0
0
1
1
1
A
-1
0
1
-1
0
1
-1
0
1
N
44
109
139
160
89
113
116
124
85
% Refl.
70.56
71.67
71.38
71.84
71.96
72.37
71.48
71.9
71.56
N
127
67
223
149
162
143
201
203
207
% Refl.
76.77
76.78
77.97
77.24
78.63
77.69
76.77
78.15
77.33
Figure 5 shows the linear regression plot for percent
reflectance versus TiO2 wt.% for both the samples. There
is significant increase in reflectance for samples with 22
Variable
AF
dv
dn
10
AF
A
-1
0
1
-1
0
1
-1
0
1
8
6
dv
B
-1
-1
-1
0
0
0
1
1
1
4
2
dn
Loc
1
2
3
4
5
6
7
8
9
40 wt.% TiO2 Sample
AF
dv
dn
3.98
0.37
0.21
2
0.83
0.20
4.2
0.65
0.23
7.11
0.76
0.21
3.5
0.73
0.28
5
0.69
0.29
3.39
1.08
0.23
3.89
1.07
0.22
4.09
0.90
0.22
22 wt.% TiO2 Sample
AF
dv
dn
10.29
0.59
0.21
10.76
1.63
0.22
10.53
1.9
0.3
5.74
1.29
0.3
7.08
1.25
0.28
3.51
2.33
0.23
9.3
3.51
0.61
6.01
3.85
0.44
6.17
1.33
0.26
0
22
TiO2 wt.%
40
Fig. 6: Regression plots of area fraction (AF),
diameter volume ( d v ), and average diameter ( d n ),
versus TiO2 wt.%.
Figure 7 shows that the number of particles on the
surface of the injection molded part also decreases as
TiO2 wt.% increase.
This shows that as the weight percent increases, the
tendency for agglomeration of particles increases.
225
79
200
78
175
150
76
N
% Reflectance
77
75
125
74
100
73
75
72
50
71
22
70
22
TiO2 wt. %
40
TiO2 wt. %
40
Fig. 7: Regression plot of number of particles versus
TiO2 wt.%.
Fig. 5: Regression plot of % reflectance versus
TiO2 wt.%.
B
4
B
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Agglomerated particles larger than half the wavelength of
the incident light in size, do not scatter the light effectively
which leads to poor refraction [6, 7].
A
-1
% Reflectance
Figure 8 shows the molding and transverse direction of
the plastic flow and the locations with high and low
reflectances.
Molding Direction
0
1
B
Transverse
Direction
7
8
9
1
4
5
6
0
1
2
3
-1
Gate Location
High Reflectance
Low Reflectance
Fig. 10: Reflectance vs. locations
40 wt.% sample.
TiO2 have higher area fraction, diameter volume, number
of particles and average diameter. All these measures
lead to higher reflectivity of the material. Higher
reflectance has been observed at locations 4, 5, 6, and 8
as shown in Figure 8.
A similar trend is observed for both the samples.
Figures 9 and 10 show the surface plots of % reflectance
and variations along the molding and transverse
directions for samples containing 22 and 40 wt.% titania,
respectively.
CONCLUSIONS
% Reflectance
Fig. 8: High and Low reflectance locations on
sample.
Fig. 9: Reflectance vs. locations
22 wt.% sample.
Larger particles migrate more than the smaller
particles to the surface of the part. Samples with 22%
Two samples with different molding parameters have
been studied; one contains 22% weight fraction pigment
particles and the other contains 40% weight fraction
pigment particles. Images obtained from cross sections at
various locations have been analyzed for the particle
distribution. The measures used to assess the particle
distribution include average diameter ( d n ), diameter
volume ( d v ), and area fraction (AF), as these measures
are known to affect material properties. MINITAB was
used to to assess the statistical significance of these
measures. The results show that the pigment particles
are not uniformly distributed within the sample. It has
been observed that these measures vary along the
molding and transverse directions.
It was expected that for samples with higher TiO2 wt.%
higher reflectance will be obtained but for samples with
higher wt.% lower reflectance has been observed. Since
surface reflectance measured on both the front and back
of the sample are similar, this indicates that most of the
particles are settled in the center of the sample. Thus,
particle size and spatial distribution across the thickness
5
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of the sample and as a function of injection molding
parameters and gate location needs further investigation.
ACKNOWLEDGMENTS
We would like to gratefully acknowledge the support
from Quantum Leap Packaging, Inc. for providing
samples and funding the project. The authors would like
to thank Dave Lange, CNS, Harvard University, for his
help in sample preparations.
REFERENCES
[1] E. Mcneil and R. H. French, “Multiple Scattering
from Rutile TiO2 Particles,” Acta Materialia, 48(18-19),
pp. 4571–4576, 2000.
[2] http://www.hunterlab.com/measurementmethods/
solid3.html.
[3] Y. Huang, D. Bigio, and M.G. Pecht,
“Investigation of the Size and Spatial Distribution of
Fillers in Mold Compounds after Device Packaging,”
IEEE Transactions on Components and Packaging
Technologies 29 (2), pp. 364-370, 2006.
[4] P. Elkouss, R. Mudalamane, Y. Huang, K.
Broadwater, and D. Bigio, “Impact Modification of
Nylon 6,6—An Experimental Study,” in Antec, 2001.
[5] Image-J 1.36b, National Institute of Health, USA,
http://rsb.info.nih.gov/ij/Java 1.5.0_06.
[6] S. Fitzwater and J. W. Hook, “Dependent
Scattering Theory: A New Approach to Determine
Scattering in Paints,” Journal of Coating Technology,
57(721), pp. 39-47, 1985.
[7] E. Allen, “Prediction of Optical Properties of
Paints from Theory (with special reference to
Microvoid Paints),” Journal of Paint Technology,
45(584), pp. 65-72, 1973.
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