Technical Paper

Productivity Advantages of Lightweight Injection Molded
Thermoplastics Enabled by 3M™ Glass Bubbles
Andrea C. Charif, Steve E. Amos, Erik LaBelle, Kelly Denman, 3M Company
Shannon Bollin, Megan Shewey, Patricia Tibbenham, Ford Motor Company

ABSTRACT
Hollow glass microspheres from 3M can offer multiple advantages in injection molded plastics, including
lightweighting, processing improvements, and dimensional stability. In this study, formulations with hollow glass
microspheres were created to meet the specifications of existing materials and determine the effect on cycle time,processing conditions and mechanical properties using a research tool developed by Ford Research containingpressure and temperature transducers. Both polypropylene and polyamide formulations were evaluated frommultiple material suppliers. Ford in conjunction with 3M found savings and improvements in both cycle time andprocessing conditions with mechanical properties meeting existing specifications.
INTRODUCTION
3M™ Glass Bubbles are low density, free-flowing
powders consisting of thin-walled unicellular glass
spheres. When used with other reinforcing fillers, in an
optimized formulation, they can provide excellent
weight reduction, performance, processing anddimensional stability characteristics. Glass Bubbles canalso reduce mold cycle times by causing thethermoplastic parts to cool faster in the mold.1
The cooling time of molten plastic in the injection
molding process can be estimated by calculating
thermal diffusivity (𝛼). This material property is themeasure of a material’s ability to transmit heat relative
to its ability to store heat (Equation 1).
Equation 1. Thermal diffusivity𝛼=𝛼 = Thermal diffusivity
𝑘 = Thermal conductivity𝑘𝜌𝐶𝑝𝜌 = Density
𝐶𝑝 = Specific heat capacity

All process parameters kept constant, materials withhigher thermal diffusivity require shorter cooling times(Equation 2). Glass bubbles increase the thermal

diffusivity by decreasing the density and composite
heat capacity, thus increasing cooling rates.
Equation 2. Theoretical Cooling Time for an Injection Molded
Plate

𝑡𝑐 =
𝑡𝑐 = Cooling timeℎ = Part thicknessℎ2
4 𝑇𝑚𝑒𝑙𝑡 − 𝑇𝑚𝑜𝑙𝑑
ln (
)
𝜋 2𝛼
𝜋 𝑇𝑒𝑗𝑒𝑐𝑡 − 𝑇𝑚𝑜𝑙𝑑
𝛼 = Thermal diffusivity
𝑇 = Temperature

Initial work at 3M on PP tensile bars showed decreased
part temperature with increased glass bubble content.
Reducing cooling times by as much as 37% in unfilled
PP at 20wt% GB loading. In glass fiber filledformulations, cooling time reduction was as high as
25%. The smallest cooling time reductions were seen informulations containing talc.2 Additional work by 3M
and SKZ Institute showed variability in cycle time
reduction depending on base resin and additional fillers
as well. The focus of this paper is to present a cycle
time study using commercially available thermoplastic
compounds on a larger part with advanced processcharacterization instrumentation to help further
understand the effect of glass bubbles on cycle timeand processing improvements.

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Productivity Advantages of Lightweight Injection Molded Thermoplastics Enabled by 3M™ Glass Bubbles

EXPERIMENTAL
Materials
The glass bubbles used for this study were 3M™ Glass
Bubbles iM16K, which have a density of 0.46 g/cc andan isostatic crush strength of 16,000 psi.
All of polypropylene and polyamide 6,6 materials werecompounded by commercial suppliers.
Formulations
The formulations evaluated in the study are summarizedin Table 1.

Temperature Monitoring
Temperature images of the molded samples were takenusing a Thermal FlirONE camera and analyzed by FLIR
Tools. Images were always taken at precisely 18
seconds after ejection; this interval included moldopening time, part ejection and placement of theejected part in front of the camera in a marked location,
as shown in Figure 2. This ensured that all parts
experienced the same cooling history before their
thermal images were taken.

Table 1. Experimental Formulations
Incumbent
Replacement
FillerFiller
20% T
5% GF
5% GB
PP
20% GF 10% M
20% GF
10% GB
PA66
8% GF
10% M
7% GF
10% GB
3% M
T: Talc; GF: Glass Fiber; GB: Glass Bubbles; M: Mineral
PolymerTool
The tool used in this study, shown in Figure 1, was a
Ford Research Beam Tool that contains a 14” beam, atensile bar, a flex bar, 2 pressure transducers and 5
thermocouples.

Figure 1. Ford Research Beam Tool

Processing conditions
Processing conditions for both the incumbent and GB
materials for each formulation are summarized in tables
3, 6 and 9.
Nozzle and tool temperatures recommended bymaterial supplier are referred to as Standard conditions.
Lower nozzle and tool temperatures, to simulate acondition that might be run at a supplier to maximize
output, are referred as Optimized conditions.
After process stabilization a minimum of 10 parts weresequentially collected and evaluated for each
formulation and under each set of process conditions.

Figure 2. Thermal Image of Ford Research Beam Tool as itcools 18 seconds after ejection

Mechanical Properties
Mechanical properties of the injection-moldedcomposites were measured using ISO standard test
methods. A Micromeritics AccuPyc™ 1330 Helium Gas
Pycnometer was used to measure density for all
samples. An MTS frame with a 5000 lbf load cell andtensile and 3-point bending grips were used for tensileand flexural properties, respectively. A Tinius Olsenmodel IT503 impact tester and its specimen notcher
were used to measure Notched Charpy impact strengthof the molded parts. A Phenom Pro Desktop SEM wasused to collect images of cold fractures of the molded
parts.
Dimensional Stability
Digital Image Correlation (DIC) was used for thedimensional stability analysis of the different
formulations. Multiple cameras used the high contrast
random speckle pattern of the coated samples (Figure
3, top) to create a 3D mesh of the object as seen in
Figure 3, bottom. With subsequent analysis of the 3D
objects a cross-section profile is plotted and compared
between the different formulations.

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Productivity Advantages of Lightweight Injection Molded Thermoplastics Enabled by 3M™ Glass Bubbles

Table 2. Mechanical properties of PPT20 and PP GF5/GB5under Standard and Optimized processing conditions
Component
Polypropylene
Glass Bubble iM16k
Talc
Glass Fiber
TS @ RT (MPa)
TM @ RT (MPa)Strain at Break (%)
NCI @ RT (kJ/m2)
NCI @ -40oC (kJ/m2)

PPT20

PPT20

PP GF5/GB5Standard

Optimized

Standard

PP GF5/GB5
Optimized

wt %

vol%

wt %

vol%

wt %

vol%

wt %

vol%

80
0
20
0

92
0
8
0

80
0
20
0

92
0
8
0

90
5
0
5

89
10
0
2

90
5
0
5

89
10
0
2

33.6
3.3
16.7
2.9
2.3

33.7
3.4
23.3
2.5
1.7

36.0
2.6
5.8
3.0
1.5

35.7
2.8
6.3
2.5
1.7

Processing conditions for PP T20 and PP GF5/GB5 aresummarized in Table 3.
Table 3. Processing conditions, cooling and holding time for
PPT20 and PP GF5/GB5
Figure 3. 3D mesh of beam tool for dimensional stability
analysis (bottom) generated from coated samples (top)RESULTS
Case Study I
20% Talc + Polypropylene (PP T20) to 5% Glass Fiber+ 5% Glass Bubbles (PP GF5/GB5)
In the first case study a talc filled polypropylene (PPT20) was reformulated to a 5% glass fiber and 5% glass
bubble filled polypropylene (PP GF5/GB5). SEM
images in Figure 4 show uniform dispersion and highsurvival rates of glass bubbles.

Molding
Condition
Standard
Optimized

BarrelTemp (oF)
430
390

Mold
Temp (oF)80
80

CoolingTime (s)
15
15

Hold
Time (s)15
10Despite the decrease in post gate temperature
measured in mold, the average part temperature did notshow much difference between the two materials. Parts
in the PP GF5/GB5 materials molded in the standard
condition were 2oC cooler out of the mold than thebaseline material. The cooling time was reduced by 2
seconds for the PP 5GF/5GB material for a 5%
reduction in cycle time (Figure 5). Faster cycle times
have been observed in the molding of larger parts.

Figure 4. SEM Left - PP T20, Right - PP GF5/GB5

Table 2 shows the mechanical properties of PP T20 and
PP GF5/GB5 processed under standard and optimized
conditions. The part weight was reduced from 133 g to
115 g (-14%). The tensile strength increased 6% whiletensile modulus decreased 20%. Notched Charpy
impact shows negligible effect of changing material
formulation at both room temperature and -40oC.

Figure 5. Average part temperature and cycle time PPT20 and
PP GF5/GB5 under Standard and Optimized processing
conditions

The maximum injection pressure dropped up to 18%
depending on the molding conditions, this represents a

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Productivity Advantages of Lightweight Injection Molded Thermoplastics Enabled by 3M™ Glass Bubbles

potential opportunity to use a smaller press. The
maximum post gate temperature dropped 5oF withglass bubble materials, which represents a possibility
for faster cycle times.
Table 4. Maximum injection pressure and post gate
temperature of PPT20 and PP GF5/GB5 under Standard andOptimized processing conditions
Material
PP T20
PP GF5/GB5
PP T20
PP GF5/GB5

Molding
Condition
Standard
Optimized

Max Injection
Pressure (psi)
8345
7390
9862
8099

↓11%
↓18%

Max Post Gate
Temperature
(oF)
171
↓3%
166
168
↓4%
162

Case Study II
20% Glass Fiber + 10% Mineral + Polypropylene (PPGF20/M10) to 20% Glass Fiber + 10% Glass Bubbles +Polypropylene (PP GF20/GB10)
In the second case study a 20% glass fiber and 10%
mineral filled polypropylene (PP GF20/M10) was
reformulated to a 20% glass fiber and 10% glass bubble
filled polypropylene (PP GF20/GB10). SEM images in
Figure 7 show uniform dispersion and high survival
rates of glass bubbles.

Cross-sections through the middle of the beam (Figure6) show similar behaviors between the two materials.
As expected, optimized conditions show more warp
than the standard conditions.
Figure 7. SEM Left - PP GF20/M10, Right - PP GF20/GB10

Table 5 shows the mechanical properties of bothmaterials processed under standard and optimized
conditions. The part weight was reduced from 143 g to
124 g (-13%). The tensile strength decreased 10% whiletensile modulus decreased 8%. Notched Charpy impact
shows a 20% decrease at room temperature and a 15%
decrease at -40oC.
Table 5. Mechanical properties of PP GF20/M10 and PP
GF20/GB10 under Standard and Optimized processing
conditions
Component
Polypropylene
Glass Bubble iM16k
Glass Fiber
Mineral
TS @ RT (MPa)
TM @ RT (MPa)Strain at Break (%)
NCI @ RT (kJ/m2)
NCI @ -40oC (kJ/m2)

PP
GF20/M10
Standard

PP
GF20/M10
Optimized

wt %

vol%

wt %

vol%

wt %

vol%

wt %

vol%

70
0
20
10

87
0
9
4

70
0
20
10

87
0
9
4

70
10
20
0

73
20
7
0

70
10
20
0

73
20
7
0

69.9
6.2
3.1
6.4
4.9

65.4
6.2
3.1
5.8
4.4

GF20/GB10
Standard

64.8
5.8
2.1
5
4.1

Processing conditions for PP GF20/M10 and PP
GF20/GB10 are summarized in Table 6.
Figure 6. Cross-sections through the middle of the beam
PPT20 and PP GF5/GB5 under Standard and Optimized
processing conditions

GF20/GB10
Optimized

58
5.6
2.1
4.7
3.9

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Productivity Advantages of Lightweight Injection Molded Thermoplastics Enabled by 3M™ Glass Bubbles

Table 6. Processing conditions, cooling and holding time for
PP GF20/M10 and PP GF20/GB10
Molding
Condition
Standard
Optimized

BarrelTemp (oF)
430
430

Mold
Temp (oF)
140
105

CoolingTime (s)
15
15

Hold
Time (s)158

As in Case Study I the cross-sections through the
middle of the beam show similar behaviors between thetwo materials. As expected, optimized conditions
showed more warp than the standard conditions.
Case Study III

Significant cycle time savings were realized for both thestandard and optimized processes. Parts in the PP
GF20/GB10 material were 6oC cooler out of the moldthan the baseline material. Standard molding conditions
achieved a 4 second cycle time saving (8% reduction).
Optimized molding conditions achieved a 5 second
cycle time saving (11% reduction) (Figure 8).

Figure 8. Average part temperature and cycle time for PP
GF20/M10 and PP GF20/GB10 under Standard and Optimized
processing conditions

The maximum injection pressure dropped 27%, apotential opportunity to use smaller press. The
maximum post gate temperature dropped up to 14 oF
with glass bubble materials, a possibility for faster cycle
times. Hold pressure were also able to be reduced from400 psi to 300 psi for glass bubbles materials (25%reduction).
Table 7. Maximum injection pressure and post gate
temperature of PP GF20/M10 and PP GF20/GB10 underStandard and Optimized processing conditions
Material
PP GF20/M10
PP GF20/GB510
PP GF20/M10
PP GF20/GB510

Molding
Condition
Standard
Optimized

Max Injection
Pressure (psi)
8783
6392
8429
6170

↓27%
↓27%

Max Post
Gate
Temperature
(oF)
214
↓7%
200
187
↓2%
184

8% Glass Fiber + 10% Mineral + PA66 (PA66 GF8/M10)
to 7% Glass Fiber + 3% Mineral + 10% Glass Bubbles +PA66 (PA66 GF7/M3/GB10)
In the last case study, an 8% glass fiber and 10%
mineral filled polyamide 66 (PA66 GF8/M10) was
reformulated to a 7% glass fiber, 3% mineral and 10%
glass bubble filled PA66 (PA66 GF7/M3/GB10). SEM
images Figure 9 show uniform dispersion and highsurvival rates of glass bubbles.

Figure 9. SEM Left - PA66 GF8/M10, Right - PA66
GF7/M3/GB10

Table 8 shows the mechanical properties of bothmaterials processed under optimized conditions. The
part weight was reduced from 160 g to 134 g (-16%).
The tensile strength increased 17% while tensile
modulus decreased 10%. Notched Charpy impact
shows 25% decrease at RT and 10% decrease at -40oC.
Table 8. Mechanical properties of PA66 GF8/M10 and PA66
GF7/M3/GB10 under Standard processing conditions
PA66 GF8/M10
Component
Polypropylene
Glass Bubble iM16k
Glass Fiber
Mineral
TS @ RT (MPa)
TM @ RT (MPa)Strain at Break (%)
NCI @ RT (kJ/m2)
NCI @ -40oC (kJ/m2)

Standard
wt %
vol%
81
91
0
0
9
5
10
4
61.7
4.8
2.5
4.4
2.6

PA66
GF7/M3/GB10
Optimized
wt %
vol%
77
69
12
27
8
3
3
1
72.2
4.3
3.3
3.3
2.3

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Productivity Advantages of Lightweight Injection Molded Thermoplastics Enabled by 3M™ Glass Bubbles

Processing conditions for of PA66 GF8/M10 and PA66
GF7/M3/GB10 are summarized in Table 9.
Table 9. Processing conditions, cooling and hold time for PA66
GF8/M10 and PA66 GF7/M3/GB10
Molding
Condition
Standard

BarrelTemp (oF)
518

Mold Temp(oF)
160

CoolingTime (s)15

HoldTime (s)10Parts in the P66 GF7/M3/GB10 material were 7oC
cooler out of the mold than the baseline material.
Standard molding conditions achieved a 3 second cycle
time saving (6%). Further savings may possibly berealized with more process optimization (Figure 10).

CONCLUSIONS
The addition of glass bubbles to material formulations
resulted in cooler parts out of the mold and cycle timesavings up to 11%. Different factors like glass bubble
loading level, processing conditions and parts volume
influence cycle time savings. Increasing glass bubble
volume increased the cycle time savings. Savings could
possibly increase with larger parts/more material
volume. Materials developed are drop in (same shrink)for incumbent materials.
The presence of glass bubbles reduced the density of
the injection molded parts while allowing the productproperties to be retained to a large extent. Glass
bubbles offered weight savings of ~15% depending on
formulation. Also depending on the formulation
Notched Charpy impact properties may be reduced.
Future work includes formulation development for
improved impact properties.
REFERENCES

Figure 10. Average part temperature and cycle time for PA66
GF8/M10 and PA66 GF7/M3/GB10 under Standard
processing conditions

In this case the maximum injection pressures increased
significantly (74%), the GB material was rheology
modified to have a higher viscosity than the baselinematerial at the request of end use customer. The
maximum post gate temperatures drop up to 14oF (7%)
with glass bubbles materials, a possibility for faster
cycle times.
Table 10. Maximum injection pressure and post gate
temperature of PA66 GF8/M10 and PA66 GF7/M3/GB10
under Standard processing conditions.
Material

Molding
Condition

Max Injection
Pressure (psi)PA66 GF8/M10
PA66 GF7/M3/GB10

Standard

7386
12847

↑74%

Max Post
Gate
Temperature
(oF)
214
↓7%
200

Cross sections through the middle of the beam show
similar behavior between the two materials.

1. Baris Yalcin et al. “3MTM Glass Bubbles iM16K for
Reinforced Thermoplastics.” Technical Paper Issued by
3M Company.
2. Baris Yalcin et al. “Productivity Benefits of 3M Glass
Bubbles in Injection Molded Thermoplastics via
Increased Cooling Rates”. Technical Paper Issued by
3M Company.

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Phone 1-800-367-8905
www.3M.com/autoglassbubbles© 3M 2019. All rights reserved.
Issued: 08/2019