ULTRASONIC SEALING TOOL DESIGN FOR THIN FILM PLASTICS
Miranda Marcus and Olivia Prior, EWI, 1250 Arthur E. Adams Dr., Columbus OH 43221
Abstract
Thin film packaging is used for a wide range of
products including packaging of food, medical tools,
electronics, and toys. Each of these applications requires a
different type of film, from thin and brittle, to composite
film including a foil layer, to biodegradable films. These
films can be adhesively bonded, heat sealed, impulse
welded, and increasingly, ultrasonically welded. Ultrasonic
welding offers many benefits to thin film sealing such as
faster cycle times, reduction in film usage due to narrower
bond widths, elimination of adhesive layers, improved
hermeticity for increased shelf life, and less sensitivity to
contaminants in the seal area.
However, tool design can have a significant effect
on weld strength. Optimum tool design depends not just on
the thickness of the material to be welded, but also the type
of polymer to be joined, and seal requirements (such as
hermeticity and peel strength). In this study, we seek to
provide starting guidelines with the goal of lowering the
cost and duration of the tooling development process by
investigating the achievable peel strength of a wide variety
of film types with twenty-five horn and anvil design
combinations.
Tool designs studied include male knurl, female knurl,
single ridge, five ridge, and flat, both on horn and anvil,
sized for films with a thickness of about 3-6 mil, although
some thicker materials were used. Films studied include
foil films, biodegradable films, film coated paper, multicolor films, and films for produce packaging.
Literature Review
Ultrasonic welding can present many advantages
over traditional sealing techniques. Compared to heat
sealing, ultrasonic sealing offers shorter processing times,
especially for thick materials, reduced exposure of the
packaging contents to heat, and the ability to cool the
welded film under pressure [1]. Compared to induction and
infrared sealing, ultrasonic sealing offers consistent seal
quality and shorter sealing times [2].
Previous experimentation has shown that weld
quality depends significantly on the strength of the film
being welded [1,3]. A 2014 study by Ward and Kazakov
concluded that polyethylene sealing layers are favorable
for maintaining integrity within the weld area due to their
broad molecular weight distribution, high toughness, and
low zero shear viscosity [4].
Experimentation
Introduction
Traditionally, bag sealing has been accomplished
via thermal welding techniques. However, using
ultrasonics offers a cost savings due to the ability to use
less film in the package by having a narrower bond width
as well as eliminating the need for an adhesive layer. For
large-scale manufacturers this can add up to hundreds of
thousands of dollars, if not millions, in savings a year.
However, identifying the optimum tooling design for an
application can be a time consuming and expensive
process.
Typical film sealing designs include the use of a
male or female knurl or a rounded ridge pattern. The
sealing pattern can be placed on the horn or anvil, or
multiple patterns can be used together, for example, a
female knurl can be placed on both the horn and anvil.
Additionally, the knurl or rounded ridge can come in a
wide variety of dimensions, allowing for thousands of
possible tooling variations.
Equipment
A Branson 2000X 20 kHz ultrasonic welding
machine with a 4000 W generator and 7.6-cm diameter
pneumatic cylinder was used with the supporting Branson
X-Port Program for this investigation, as shown in Figure
1. At maximum shop pressure of 690 kPa, the maximum
force that the Branson 2000X welder can apply is 3.15 kN.
Carbon paper was used to check the parallelism of
the horn to the anvil. This procedure was performed after
every tooling change, and was monitored throughout each
set of welding trials.
The objective of this study is to determine
achievable weld strength with a comprehensive sub-set of
different combinations of tool design and film material.
SPE ANTEC™ Indianapolis 2016 / 1336
Tooling
Four common film sealing details were selected
for these trials, in addition to a flat face horn and anvil.
These details were initially intended to be used for films 36 mil thick and were designed for that size. However,
thicker and thinner films were used. EWI designed the
sealing details, and the horns and anvils were
manufactured by Dukane.
The five 50.8-mm long sealing details selected
include a 6.35mm wide medium male knurl, a 6.35-mm
wide medium female knurl, a single 1.27-mm full round
ridge, five 1.27-mm full round ridges, and a 6.35-mm wide
flat. All non-flat details are shown in Figures 4-7. These
details were placed on five titanium horns and five
stainless steel anvils to be used in a variety of
combinations.
Figure 1: Branson 2000X Welder (20 kHz)
A Chatillon Digital Force Gauge was used with
the Chatillon TCM 201 motorized force tester to measure
the peel strength of each weld. After early peel tests
resulted in slipping of the film in the tool with selftightening and mechanical grips, the pneumatic grips
shown in Figure 3 were selected for the peel testing trials.
Peel tests were run at 50 mm/ min and the peak value (N)
was recorded.
Figure 4: Female Knurl Horn Schematics
Figure 5: Male Knurl Horn Schematics
Figure 3: Pneumatic Grips
SPE ANTEC™ Indianapolis 2016 / 1337
Figure 9: Flat Anvil Schematic
Figure 6: Single Ridge Horn Schematics
Materials
Twelve unique materials were used in the
preliminary trials, welding with every anvil detail and the
flat faced horn. A description of each material used and its
nominal thickness are described in Table 1. The twelve
materials were divided into five groups for comparison. A
description of the defining aspect of each group is shown
in Table 2. All films are represented just once, with the
exception of material 9, which was included in both Group
III and IV. Materials 1-10 were provided by Glenroy Inc.,
while 11-12 were supplied by Bemis Company.
Table 1: Summary of Material, Thickness, and Group
Figure 7: Five Ridge Horn Schematics
Figure 8 shows the basic horn design. The horn
design provides an approximate gain of 2.5. When used
with a 1.5 booster, the total amplitude was about 75
micrometers. This falls within the recommended amplitude
range for most polymers, usually around 40-90
micrometers for amorphous polymer and 50-125
micrometers for semi-crystalline polymers.
#
Paper/Foil/Coex
Paper//PLA (thick)
Paper//PLA (thin)
PET//LLDPE (white)
PET//LLDPE (clear)
PET//Foil//LEL Coex
PET//Foil/EMAA
PET//Foil//LLDPE
Thickness
(mm)
0.38
0.53
0.21
0.14
0.14
0.10
0.07
0.09
PET//Foil//ACN
0.09
Paper//Foil//ACN
OPP/PE Coex
PE Coex
0.13
0.05
0.03
Group
1
2
3
4
5
6
7
8
9
10
11
12
I
II
III
III &
IV
IV
V
Material
Table 2: Material Groups
Figure 8: Flat Horn Schematic
The anvils were designed to be interchangeable
on an aluminum leveling plate, using pins for locating.
Each individual anvil has four leveling screws to enable
leveling of the anvil to each horn, as shown in Figure 9.
The same sealing details that were used on the horns, as
shown in Figure 1, were also used on the anvils. In this
way every sealing detail could be paired with every other
sealing detail, with either one being on the horn or anvil.
Group
I
II
III
IV
V
Description:
Films with fibreform paper layer
Films with Nylon and LDPE (white and clear)
interlayers
Films with an Aluminum foil interlayer and
varying materials on the weld side
Films with ACN (Acrylonitrile) sealing layer
Films with an ink and anti-fog varnish layer
(packaging films)
SPE ANTEC™ Indianapolis 2016 / 1338
Prior to welding, all film was cut down into 50x64
mm rectangular pieces. Two identical pieces of film were
welded together; care was taken to ensure the correct film
orientation for welding (symmetric interfaces, where the
same polymer exists on both sides of the interface). All
materials are described with the sealing layer noted last.
For example, the sealing layer of PET//Foil//LLDPE is
LLDPE.
For the preliminary trial, all five anvil designs were
tested in combination with the flat face horn on each of the
twelve types of film material. Afterwards, a down selection
was made on the films resulting in three materials for
continuation into the in-depth trial where all twenty-five
tooling combinations were tested. The three films selected
for the in-depth trials were chosen to provide a variety of
film types which are widely used. The three films chosen
were:
 Material 1, Paper/Foil/Coex
 Material 2, Paper//PLA (thick)
 Material 12, PE Coex.
Layer diagrams of each of these selected films are
shown in Figures 10-12.
Figure 12: Material 12, PE Coex. Figure taken from Bemis
Product Data Sheet A214.
Preliminary Weld Trials
During the preliminary weld trials, the female
knurl anvil was used first with the flat horn. Using this
initial tooling combination, baseline welding parameters
were developed for each film type through varying Weld
Energy, Pressure, Trigger Force, Amplitude, and Hold
Time. This was done by comparing the weld strength
(visually and via peel test) at various welding settings.
These initial settings are shown in Table 3.
Table 3: Initial Parameter Settings
Parameter
Weld Energy (J)
Pressure (KPa)
Trigger Force (N)
Amplitude (%)
Hold Time (sec)
Figure 10: Material 1, Paper/Foil/Coex. Figure taken from
Glenroy Product Data Sheet AAFS 001-001. [1mil= 0.025mm]
Initial Setting
See Table 4
276
222
100
1
It was decided to minimize the variables that
would be adjusted during trials in order to ensure
comparability between weld strength results on the
different materials. Therefore, only weld energy was
varied between the film types to optimize strength in the
preliminary weld trials. The initial weld energy settings
used are show in Table 4.
Table 4: Summary of Baseline Weld Energy Settings
Figure 11: Material 2, Paper//PLA (thick). Figure taken from
Glenroy Product Data Sheet AAO 006-001.
#
1
2
3
4
5
6
7
8
9
10
11
12
Material
Paper/Foil/Coex
Paper//PLA (thick)
Paper//PLA (thin)
PET//LLDPE (white)
PET//LLDPE (clear)
PET//Foil//LEL Coex
PET//Foil/EMAA
PET//Foil//LLDPE
PET//Foil//ACN
Paper//Foil//ACN
OPP/PE Coex
PE Coex
Weld Energy (J)
100
100
80
100
60
100
200
200
200
350
100
100
SPE ANTEC™ Indianapolis 2016 / 1339
For some of the tooling combinations, however,
adjusting energy alone could not result in a good bond. In
these cases, the trigger force and/or pressure were adjusted
next. Amplitude and hold time were not changed during
any of the trials. Weld cycle time is a result of the
previously mentioned variables and would generally be
between 0.1 and 0.2 seconds.
For each material type, three welds were peel
tested for each tooling combination set, excepting certain
tooling/material combinations that did not generate
acceptable welds were not taken for further testing. In all
the following tables, the peel strengths shown are the
average of three samples welded at the same welding
parameters.
For the preliminary trials, using just the flat horn
with all five anvil types and all twelve materials, three
welds at each of the fifty-eight weld material and tooling
combinations were made and peel tested, one hundred and
seventy-four welds in total. For the welding of three
selected materials with all twenty-five tooling
combinations, three welds at each of the sixty-one weld
material and tooling combinations were made and peel
tested, one hundred and eighty-three welds in total. All
welding and peel testing was completed by one operator.
Results and Discussion
Anvil Effect with Flat Horn
During the preliminary trials, the flat faced horn
was used with all five anvil types. Some trends were noted
for all the materials. All the materials welded with the flat
horn and flat anvil combinations were weak, even when
weld energy was increased. This was expected due to the
wide surface area to be bonded. Additionally, slipping of
all materials between the flat surfaces was noted.
With the small surface area provided by the single
ridge anvil, weld settings had to be adjusted to prevent
cutting of the materials. For all of the films, some mix of
reduced energy input, decreased pressured, and lower
trigger force was required. The male knurl anvil required
no change in weld parameters from the female knurl anvil.
This may be due to both anvils providing the same surface
area. Energy input had to be reduced for two materials,
PET//Foil/EMAA and Paper//PLA (thick), when the fiveridge anvil was used.
Peel Strength Results for Flat Horn Trials
Table 5 shows the average peel strength (N) for
Group I materials using the flat horn with all five anvil
types. The only difference between the two PLA materials
is the thickness. Despite this difference in thickness, the
peel strength values are very similar for the female and five
ridge anvils. The film with the foil layer showed the
greatest peel strength with all anvil types.
Table 2: Group 1 Average Peel Strength Results (N)
Group I
Paper//PLA
(thin)
Paper//PLA
(thick)
Paper/Foil/C
oex
Female
Five
Flat
Male
Single
57.9
57.9
53.0
41.2
54.9
63.7
59.8
62.8
68.6
31.4
85.3
102.0
81.4
83.4
93.2
Table 6 shows the average peel strength (N) for
Group II materials using the flat horn with all five anvil
types. These two very similar materials have similar force
values when using the single ridge and five ridge anvils,
but were unweldable with the flat horn and anvil
combination. Interestingly, the clear material required less
energy input (60J) than the white material (100J), yet was
much stronger when welded with the female and male
anvils.
Table 3: Group II Average Peel Strength Results (N)
Group II
PET//LLDPE
(clear)
PET//LLDPE
(white)
Female
Five
102.0
38.2
Flat
Male
Single
108.7
87.3
105.9
106.9
45.1
97.1
Table 7 shows the average peel strength (N) for
Group III materials using the flat horn with all five anvil
types. The material located at the weld interface in this
group had a significant effect on which anvil is most
suitable. The LLDPE material demonstrated the greatest
peel strength, using the male knurl anvil. The LEL Coex
showed the second greatest peel strength, using the five
ridge anvil.
Table 4: Group III Average Peel Strength Results (N)
Group III
PET//Foil//L
EL Coex
PET//Foil/
EMAA
PET//Foil//L
LDPE
PET//Foil//
ACN
Female
Five
Flat
Male
Single
60.8
84.3
59.8
53.9
37.3
64.7
51.0
28.4
59.8
60.8
50.0
34.3
92.2
66.7
55.9
40.2
20.6
44.1
3.5
Table 8 shows the average peel strength (N) for
Group IV materials using the flat horn with all five anvil
types. Both films in this group welded best using the
female and male anvils. However, weld strength varied
greatly for the other three anvil styles. This may be due to
the difference in thickness between the two materials. It is
not unexpected that the thicker material performed better
SPE ANTEC™ Indianapolis 2016 / 1340
Group IV
PET//Foil//
ACN
Paper//Foil//
ACN
Female
Five
Flat
Male
60.8
27.5
46.1
55.9
55.9
40.2
20.6
44.1
Single
34.3
Table 9 shows the average peel strength (N) for
Group V materials using the flat horn with all five anvil
types. The OPP/PE Coex film was designed to peel at a
constant value due to the delamination strength of the
layers, which it did with three of the four anvil styles.
However, using the single ridge anvil provided a
significant increase in peel strength.
Table 6: Group V Average Peel Strength Results (N)
Group V
OPP/PE Coex
PE Coex
Female
24.5
43.1
Five
26.5
Flat
Male
18.6
37.3
Single
42.2
36.3
Three Films Welded with All Tool Combinations
Table 10 shows the average peel strength (N) for
the Paper/Foil/Coex material with all twenty-five tooling
combinations. One of the interesting results from welding
with all combinations of horn and anvil is the difference in
strength when the sealing detail is placed on the horn
instead of the anvil. For most of the tooling combinations
with this material, the strength was the same regardless of
the orientation of the details. However, when welding with
the male knurl and flat combination, weld strength was
greater when the knurl was on the horn as opposed to the
anvil. In fact, the male knurl horn detail with flat anvil
detail provided the greatest strength of any combination.
There was also a difference in strength when the
single ridge and five ridge combination where greater
strength was achieved when the five ridge detail was on the
horn. However, this difference may be attributed to
alignment of the small features.
Table 7: Summary for Paper/Foil/Coex
Horn
Paper/Foil/
Coex
Female
Five
Flat
Male
Single
Female
107.9
103.0
85.3
99.0
96.1
Anvil
Five
Flat Male
99.0 90.2 99.0
82.4 99.0 91.2
102.0 81.4 83.4
86.3 109.8 103.0
47.1 93.2 103.0
Single
91.2
77.5
93.2
91.2
36.3
Table 8: Summary for Paper//PLA (thick)
Paper//PLA
(thick)
Horn
Table 5: Group IV Average Peel Strength Results (N)
Table 11 shows the average peel strength (N) for
the Paper//Paper (thick) material with all 25 tooling
combinations. With this material almost every detail
combination showed a difference in strength depending on
the placement of the sealing detail on the horn or anvil.
The most distinct result is that the lowest peel strengths
were achieved with the single ridge detail, whether it was
placed on the horn or the anvil. The greatest peel strength
was achieved when the male knurl was both on the horn
and anvil.
Female
Five
Flat
Male
Single
Female
80.4
83.4
63.7
86.3
31.4
Five
69.6
62.8
59.8
77.5
61.8
Anvil
Flat
72.6
79.4
62.8
85.3
40.2
Male
84.3
92.2
68.6
98.1
43.1
Single
49.0
55.9
31.4
50.0
40.2
Table 12 shows the average peel strength (N) for
the PE Coex material with all 25 tooling combinations. The
male and single ridge horns were not used with this thin
material due to easy puncture and cutting despite low weld
energy, pressure and trigger force. Additionally, early trials
with these horns resulted in some damage to the sealing
detail, so their use was discontinued.
With this material, peel strength was much greater
when the five ridge anvil was used with the female knurl
horn than when the female knurl was on the anvil and the
five ridge detail was on the horn. In the former case, with
the female knurl on the horn, the weld strength was among
the highest for all the tooling combinations. However, in
the latter case, where the female knurl was on the anvil, the
peel strength was the lowest of all tooling combinations, by
a significant factor.
Table 9: Summary for PE Coex
PE Coex
Horn
with the single and five ridge anvils while the thinner
material performed better with the flat anvil. The thicker
material would benefit from the smaller surface areas,
while the thinner material would be more likely to be
damaged when using those anvils.
Female
Five
Flat
Female
44.1
26.5
43.1
Five
42.2
37.3
Anvil
Flat
35.3
39.2
Male
37.3
Single
45.1
37.3
36.3
Conclusions
This fundamental exploration into ultrasonic
tooling designs and combinations for thin films has
highlighted the importance of proper tooling selection for a
given thin film material. Additionally, optimization of
welding parameters is essential to achieve maximum bond
strength.
SPE ANTEC™ Indianapolis 2016 / 1341
These trials have resulted in a number of significant
findings.
•
•
•
•
•
Seal layer material plays a significant role in bond
strength and tooling selection.
The process window is individually dependent on
the film composition.
Colorant has a definite impact on peel strength.
In most cases, the sealing detail can be placed on
the horn or anvil. However, when there was a
difference, greater strength was generally
achieved when the male or female knurl was
placed on the horn.
Obtaining a wide process window is highly
dependent on careful material vs. tooling
selection.
Acknowledgments
A great deal of thanks goes to Glenroy, Inc. and
Bemis Company for generous donation of the films used to
do this research.
References
1.
2.
3.
4.
S. Bach, K. Thurling, and J. Majschak, IAPRI
Symposium, Berlin, Germany (2011).
H. Yeh and A. Benatar, Tappi Journal, 80, 197 (1997).
N. Stoehr, B. Baudrit, E. Haberstroh, N. Michael, P.
Heidemeyer, and M. Bastian, Journal of Applied
Polymer Science, DOI: 10.1002 / APP.41351 (2015).
D. Ward and A. Kazakov, PLACE Conference (2014).
SPE ANTEC™ Indianapolis 2016 / 1342