Continued Studies of the Effects of Metallic Pigment Dispersions on the Physical
Properties of Thermoplastics
Jeffrey S. Drusda, Silberline Manufacturing Co., Inc., Tamaqua, PA
Abstract
Metallic pigments continue to serve an important part
in the coloration and function of thermoplastics. In
particular, aluminum flake pigments play a prominent role
in expanding plastics markets such as automotive,
electronics, and appliances. The use of in-mold and inprocess coloration for paint replacement is growing as
result of market drivers that require low volatile organic
content (VOC) coloration, lower process costs, and
reduced manufacturing times.
As the amount of plastic used for high-profile
applications increases, the need for physical property
trends becomes more useful. Impact strength and tensile
properties of polymers play an important part of material
selection, and the addition of colorants and additives
affect those properties. Previous studies1,2 involving
aluminum flake-pigmented polycarbonate (PC) and
acrylonitrile-styrene-acrylate (ASA) noted the effect of
carrier types, flake particle size, geometries, and
concentration levels on impact and tensile properties. As
a result, physical property trends for additional polymer
types are of interest.
Introduction
This study will serve as a continuing effort to examine
the property effects of aluminum flake pigments and
respective carrier types on different polymers.
In
addition, an investigation using a surface-treated
aluminum flake will be included to determine whether the
flake can be enhanced to influence impact strength and
tensile properties. The results will serve the reviewer as a
guide for trends that involve metallic flake products and
polymer selection.
Materials
The materials used in this experiment set consisted of
three polymers: polypropylene (PP) manufactured by
ENTEC and classified as a 12 MFI random copolymer;
polymethylmethacrylate (PMMA) manufactured by
Arkema and classified as a 15 MFI acrylic; and
acrylonitrile-butadiene-styrene polymer manufactured by
SABIC-IP and classified as a 10 MFI terpolymer.
Aluminum pigments are identified by D50 particle
size measurement in microns (µm). For this study, 14 µm
and 45 µm flake types are used. The role of this size
distinction is to determine whether particle size continues
to have influence on physical properties as noted in The
Effect of Metallic Pigment Dispersions on Physical
Properties of Engineering Thermoplastics (Sanchez, SPEANTEC Papers, 2005).
The aluminum flake products used are dispersed at
high concentrations in select carrier mediums:
polyethylene wax (PE wax) or acrylic. The concentration
of aluminum pigment is between 70-80% (by weight) as
is cited in each experimental table. For the sake of
compatibility, acrylic carrier is not used with
polypropylene trails due to incompatibility and inadequate
part consistency.
Additionally, one surface-treated aluminum flake is
used in trials with PP and ABS. This flake is a 45 micron
flake that is first encapsulated with a proprietary
technology, and then dispersed in a PE wax carrier for
safer processing.
Each polymer will be examined separately.
Aluminum pigments will be compounded prior to
molding into ASTM test parts. Refer to Tables 1, 2, and 3
for individual trials descriptions.
Table 1: Polypropylene Trials
PP
Trial
1*
2
3
4
5
6
7
8
9
10
11
Aluminum Flake
Clear PP
Clear PP
PP + PE Wax
PP + PE Wax
PP + PE Wax
14 µm/ PE Wax
14 µm / PE Wax
14 µm / PE Wax
45 µm / PE Wax
45 µm / PE Wax
45 µm / PE Wax
Treated 45 µm
12
/PE Wax
Treated 45 µm
13
/PE Wax
Treated 45 µm
14
/PE Wax
*one heat history
%
Al
%
Carrier
0.0
0.0
0.0
0.0
0.0
1.0
3.0
5.0
1.0
3.0
5.0
0
0
0.42
1.28
2.14
0.42
1.28
2.14
0.42
1.28
2.14
%
Product
Loading
0
0
0
0
0
1.42
4.28
7.28
1.42
4.28
7.28
1.0
0.42
1.42
3.0
1.28
4.28
5.0
2.14
7.28
SPE ANTEC™ Indianapolis 2016 / 273
Table 2: PMMA Trials
PMMA
Trial
Aluminum Flake
1*
PMMA
2
PMMA
3
PMMA + PE Wax
4
PMMA + PE Wax
5
PMMA + Acrylic
6
PMMA + Acrylic
7
14 µm/ PE Wax
8
14 µm / PE Wax
9
45 µm / PE Wax
10
45 µm / PE Wax
11
14 µm / Acrylic
12
14 µm / Acrylic
13
45 µm / Acrylic
14
45 µm / Acrylic
*one heat history
%Al
%
Carrier
0.00
0.00
0.00
0.00
0.00
0.00
1.00
3.00
1.00
3.00
1.00
3.00
1.00
3.00
0
0
0.42
1.28
0.25
0.75
0.42
1.28
0.42
1.28
0.25
0.75
0.25
0.75
%
Product
Loading
0
0
0
0
0
0
1.42
4.28
1.42
4.28
1.25
3.75
1.25
3.75
Table 3: ABS Trials
ABS
Trial
1*
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Grade
Clear ABS
Clear ABS
ABS + PE Wax
ABS + PE Wax
ABS + PE Wax
ABS + Acrylic
ABS + Acrylic
ABS + Acrylic
14 µm/ PE Wax
14 µm/ PE Wax
14 µm/ PE Wax
45 µm/ PE Wax
45 µm/ PE Wax
45 µm/ PE Wax
14 µm/ Acrylic
14 µm/ Acrylic
14 µm/ Acrylic
45 µm/ Acrylic
45 µm/ Acrylic
45 µm/ Acrylic
Treated 45 µm/PE
21
Wax
Treated 45 µm/PE
22
Wax
Treated 45 µm
23
/PE Wax
*one heat history
%Al
%
Carrier
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.50
1.50
3.00
0.50
1.50
3.00
0.50
1.50
3.00
0.50
1.50
3.00
0
0
0.21
0.64
1.28
0.125
0.375
0.75
0.21
0.64
1.28
0.21
0.64
1.28
0.125
0.375
0.75
0.125
0.375
0.75
%
Product
Loading
0
0
0
0
0
0
0
0
0.71
2.14
4.28
0.71
2.14
4.28
0.63
1.88
3.75
0.63
1.88
3.75
0.50
0.21
0.71
1.50
0.64
2.14
3.00
1.28
4.28
Experimental
The experiment is divided into three sets. All materials
are compounded with the either PP, PMMA, or ABS
according to the levels listed in Tables 1,2, and 3. For PP,
no trials with acrylic resin were performed.
Compounding is performed through a 1 1/4 inch
single-screw extruder (25:1 LOD). The result compounds
are molded into ASTM parts using a 55 ton injection
molder.
Additionally, a surface-treated aluminum flake (or
treated aluminum flake) product is included with PP and
ABS trials. The treated flake is surface-encapsulated with
a proprietary and carried in a PE wax dispersion. The
testing of this treated flake with a polyolefin is based on
the complete dispersion of the flake in the plastic.
Samples from each polymer experimental trial are
tested for Charpy energy (Joules, J), tensile strength
(megapascals, MPa), and percent tensile elongation.
Charpy bars are notched after proper cure, and standard
dog-bone tensile bars are used for tensile tests. Five
samples from each experiment set are measured,
averaged, and recorded with the respective trial. These
data are evaluated to determine trends for each polymer.
Results
For the polypropylene trials, there are effects noticed
with both aluminum flake and carrier addition. Referring
to the data in Table 4, the results for impact energy
required to break the Charpy bar are mixed. Both slight
increases and decreases in impact energy are observed
when compared to unfilled PP. Particle size appears to be
factor, with 14 µm product addition showing less effect
than 45 µm product. Increased product loading is also a
factor in some trials.
Tensile strength at break data shows results not seen
in previous studies2. Aluminum-pigmented PP offers a
slight increase in tensile strength compared to unfilled PP,
as opposed to noticeable decreases observed with
polycarbonate trails2.
Tensile elongation results in the most notable
differences, mainly decreases when compared to unfilled
PP. The effect is seen at the point of addition, and the
decreases become larger with increased aluminum flake
addition.
Regarding the addition of surface-treated aluminum
flake, very little change in impact energy is observed.
Tensile strength shows only a slight decrease. Tensile
SPE ANTEC™ Indianapolis 2016 / 274
elongation, however, shows large changes compared to
untreated flake and clear PP.
Last, carrier addition appears to play a role with
decreasing impact energy and tensile elongation.
Table 4: Physical Property Test Data for Aluminum
Flake-Pigmented Polypropylene
Tensile
Impact
Tensile
PP
Strength
Grade
Energy
Elongation
Trial
at Break
(J)
(%)
(MPa)
0.40
32.2
55%
1*
Clear PP
0.40
32.0
54%
2
Clear PP
PP + PE
0.35
32.5
52%
3
Wax
PP + PE
0.36
32.1
52%
4
Wax
PP + PE
0.36
32.2
52%
5
Wax
1% 14
0.33
33.0
50%
µm/PE
6
Wax
3% 14
0.38
33.3
35%
µm/PE
7
Wax
5% 14
0.38
33.4
31%
µm/PE
8
Wax
1% 45
0.38
33.4
48%
µm/PE
9
Wax
3% 45
0.36
32.6
38%
µm/PE
10
Wax
5% 45
0.36
33.0
50%
µm/PE
11
Wax
1%Treated
0.40
31.3
33%
45 µm/PE
12
Wax
3%Treated
0.40
31.8
26%
45 µm/PE
13
Wax
5%Treated
0.38
31.4
21%
45 µm/PE
14
Wax
*one heat history
For the PMMA trials, PE Wax carrier addition shows
a gradual rise in the impact energy of PMMA resin with
increased carrier levels compared to unfilled PMMA.
Acrylic carrier only shows slight changes. Refer to the
data listed in Table 5.
14 µm products show steady increase in impact
energy change, up to 33% for each grade over unfilled
PMMA. Addition of 45 µm products yield increases in
impact energy for each increase in product addition, also.
In most cases, increases in tensile strength, at break,
were observed, ranging from 2% - 5%. Only at the low
loading of 14 µm/acrylic product and the higher loading
of acrylic arrier were decreases in tensile strength seen.
Regarding the effect of carrier addition on elongation
of PMMA, PE Wax and acrylic carrier addition do not
appear to have an appreciable effect on the tensile
elongation of PMMA. Only the addition of 14 µm
product at a higher loading shows an increase of ~2%
over that of clear PMMA. All other materials display no
more than 1% difference above or below clear PMMA.
Table 5: Physical Property Test Data for Aluminum
Flake-Pigmented PMMA
Tensile
Impact
Tensile
PMMA
Strength
Grade
Energy
Elongation
Trial
at Break
(J)
(%)
(MPa)
1*
PMMA
0.12
69.83
2.85%
2
PMMA
0.12
68.44
3.05%
PMMA +
3
PE Wax
0.13
72.06
3.86%
PMMA +
4
PE Wax
0.15
71.83
3.46%
PMMA +
5
Acrylic
0.15
73.10
3.05%
PMMA +
6
Acrylic
0.12
67.71
2.64%
1% 14 µm/
7
PE Wax
0.16
74.93
4.88%
3% 14 µm/
8
PE Wax
0.16
75.05
4.67%
1% 45 µm/
9
PE Wax
0.17
74.05
3.05%
3% 45 µm/
10
PE Wax
0.16
72.42
3.86%
1% 14 µm/
11
Acrylic
0.14
66.24
2.85%
3% 14 µm/
12
Acrylic
0.16
70.45
3.05%
1% 45 µm/
13
Acrylic
0.15
70.36
2.44%
3% 45 µm/
14
Acrylic
0.14
70.62
2.85%
*one heat history
For the ABS trials, carrier loading for both PE Wax
and acrylic types does not appear to pose a significant
change in the impact energy of ABS resin. All results are
very close to the original values obtained for the clear
ABS resins. Refer to the data listed in Table 6.
SPE ANTEC™ Indianapolis 2016 / 275
14 µm products show the most amount of impact
energy change, especially at higher loadings. 45 µm
products display very little change in impact energy at
lower levels of addition.
Tensile strength properties are show decreases in all
cases, as product and carrier addition cause varying
decreases to tensile strength compared to clear ABS.
For carrier addition effects on elongation, PE Wax
carrier addition has an appreciable effect on the tensile
elongation of ABS at lower loadings and a slight decrease
at the higher amount. The acrylic carrier shows modified
elongation at the initial loading followed by a slight
decrease at the higher additions.
Product additions show mixed results with tensile
elongation. The most noticeable change is that of 14
µm/PE wax product at higher levels, where it offers
higher elongation values over clear ABS. 14 µm /acrylic
product shows higher elongation only at the higher
loading. 45 µm/PE Wax product addition gives increased
elongation only at the lower addition. 45 µm/acrylic
product additions results in decreases of elongation at
each addition.
The addition of surface-treated aluminum flake shows
only slight effect on impact energy and tensile strength.
However, tensile elongation results in sizeable increases
with the addition of this product.
Table 6: Physical Property Test Data for Aluminum
Flake-Pigmented PMMA
ABS
Trial
1*
2
Grade
Clear ABS
Clear ABS
ABS + PE
3
Wax
ABS + PE
4
Wax
ABS + PE
5
Wax
ABS +
6
Acrylic
ABS +
7
Acrylic
ABS +
8
Acrylic
1% 14 µm/ PE
9
Wax
3% 14 µm /
10
PE Wax
5% 14 µm /
11
PE Wax
1% 45 µm /
12
PE Wax
3% 45 µm /
13
PE Wax
5% 45 µm /
14
PE Wax
1% 14 µm/
15
Acrylic
3% 14 µm/
16
Acrylic
5% 14 µm/
17
Acrylic
1% 45 µm/
18
Acrylic
3% 45 µm/
19
Acrylic
5% 45 µm/
20
Acrylic
1% Treated 45
21
µm/PE Wax
3% Treated 45
22
µm/PE Wax
5% Treated 45
23
µm /PE Wax
*one heat history
Impact
Energy (J)
Tensile
Strength
at Break
(MPa)
Tensile
Elongation
(%)
0.49
0.48
44.45
45.27
3.86%
6.71%
0.48
44.81
9.35%
0.50
45.09
11.18%
0.49
44.40
4.88%
0.47
44.90
10.16%
0.49
45.04
5.89%
0.46
44.92
5.89%
0.36
44.72
5.69%
0.37
44.30
9.55%
0.29
44.32
9.55%
0.46
43.96
7.72%
0.46
44.47
7.11%
0.42
43.29
5.08%
0.41
44.82
4.47%
0.38
45.04
6.10%
0.34
44.50
4.47%
0.46
44.07
5.28%
0.43
44.56
6.71%
0.40
43.25
7.52%
0.43
42.4
12%
0.37
42.5
11%
0.30
41.4
10%
SPE ANTEC™ Indianapolis 2016 / 276
Conclusions
As observed in previous physical property studies, a
few trends regarding loading levels and particle size are
repeated. As loading increases, some properties decrease,
with a few exceptions. Additionally, larger particle sizes
tend to create decreases in impact energy and tensile
strength compared to smaller particle sizes.
Of particular interest is the increase in the physical
properties for PMMA.
This is a contrast in the
observations of ABS and prior PC trails. Additionally,
there is relative maintenance of impact and tensile
strength properties after product addition to PP. These
features reveal that aluminum flake is not always a
detriment to physical properties.
While many patterns are repeated, this trial series
indicates the need for testing each polymer type when
coloring with aluminum pigments. No assumption or
general rule can be made to indicate an overall behavior
regarding these qualities.
Additional studies may be made to examine whether
melt index plays any correlation within a polymer type.
This feature may be of interest to determine if this
variable is correlated with other physical property
behaviors of aluminum-pigmented products. Also, further
exploration of polyolefins is warranted, given the results
of the polypropylene trials.
References
1.
2.
Wheeler, Ian R., Metallic Pigments in Polymers,
©1999, Rapra Technology, LTD., United Kingdom
Sanchez, Michael J., The Effect of Metallic Pigment
Dispersions on Physical Properties of Engineering
Thermoplastics, SPE-CAD RETEC® Papers, Color
and Appearance Division of SPE, Charlotte, NC,
September 2005.
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