RUPTURE OF BOTTLENECK SEAL OF LIQUID PACKAGING BAGS
Akira SHIMAMOTO1 , Hiroyuki AOKI2 and Katsunori FUTASE2
1
Department of Mechanical Engineering, Saitama Institute of Technology,
1690, Fusaiji, Fukayashi, Saitama, Japan
2
Taisei Lamick Co.,Ltd. 873-1, Shimo-Ohsaki, Shiraoka-Cho, Minamisaitama-Gun,
Saitama, Japan
ABSTRACT
In this chapter, I evaluated the effects of impact tensile speed and the shape of the heat seal section for multilayer laminate
films used for liquid packaging bags on impact tensile strength. The impact tensile strength decreased with increasing impact
tensile speed. If the heat seal radius of the bottle-neck seal is 15 mm or larger, the impact tensile strength is equivalent to that
obtained with the flat seal, even if impact tensile speed changes.
Moreover, the shape of the bottle-neck seal greatly affected the impact rupture strength of the liquid packaging bags against
dropping impact. The impact rupture strength decreased as the heat seal radius of the bottle-neck seal decreased. When the
heat sealed radius of the bottle-neck seal was 15 mm or larger, the impact rupture strength was equivalent to that obtained
with a flat seal.
From these results, the impact tensile strength and impact rupture strength are greatly affected by the shape of the bottle-neck
seal. The experimental results for impact tensile strength and impact rupture strength tend to be similar.
Introduction
The shapes and types of containers for foods, drugs and medicines, and cosmetics and detergent refills are diverse: glass
bottles, cans, PET bottles and laminate-film liquid packaging bags are examples.
In recent years, to increase the ease of pouring out the contents of laminate-film liquid packaging bags, the shape of the heat
seal has been changed from a flat seal to a bottleneck seal. However, the large number of bottleneck seal ruptures of liquid
packaging bags due to impact load during the transport, loading and unloading of packaged products has been a problem. In
our previous study [1-10], we investigated impact tensile strength in the heat-sealed area of a laminate film; however, the
effects of the bottleneck seal shape and heat-sealed area width on impact tensile strength and rupture occurrence have not
yet been clarified.
In this study, experiments were carried out to clarify the effects of the flat and bottleneck seal shapes, as well as heal-sealed
area width, on impact tensile strength and bag rupture occurrence. The following two films were used: (1) a multilayered
laminate film with barrier characteristics against oxygen and water vapor, which is frequently used for liquid packaging bags
owing to its high efficacy in food quality preservation, and (2) a multilayered laminate film without barrier characteristics. On the
basis of the results obtained, we established, for the first time, a new standard regarding bottleneck seal shape and heatsealed area width.
Specimens and Experimental Method
Specimens
The samples used in this study include (a) the laminate film NY/XA-S [nylon (NY) + linear low-density polyethylene (LLDPE) +
linear low-density modified polyethylene (LLDPE-II)]without barrier characteristics for oxygen and water vapor, which is
generally used for liquid packaging bags, and the multilayered laminate films with barrier characteristics (b) NY/AE-PET/XAS[nylon (NY) + aluminum-evaporated PET (AE-PET) + linear low-density polyethylene (LLDPE) + linear low-density modified
polyethylene (LLDPE-II)] and (c) NY/AL/XA-S[nylon (NY) + aluminum (AL) + linear low-density polyethylene (LLDPE) + linear
low-density modified polyethylene (LLDPE-II)]. Figures 1(a)-1(c) show the structures of the three films. When a liquid
packaging bag is formed using a laminate film composed of 3-4 layers, (1) NY is the outermost layer on which the product
name and other information are printed, (2) AE-PET and AL layers, which block oxygen, vapor and light, are between NY and
XA-S layers, and (3) XA-S is the innermost layer with which the liquid content comes into contact. The thicknesses of the films
are as follows: NY 0.015 mm; AE-PET 0.012 mm; AL 0.007 mm; XA-S (LLDPE 0.025 mm + LLDPE-II 0.025 mm) 0.050 mm.
For heat sealing, a sealing apparatus is used to fold two laminate films and then tuck them so that the XA-S layers of the two
NY 0.015
NY 0.015
NY 0.015
LLDPE 0.025
AE-PET 0.012
AL 0.007
LLDPE-Ⅱ0.025
LLDPE 0.025
LLDPE 0.025
LLDPE-Ⅱ0.025
LLDPE-Ⅱ0.025
unit:mm
unit:mm
(a) NY/XA-S
NY 0.015
LLDPE 0.025
C=Heat-sealed length
(a) NY/XA-S
(C) NY/AL/XA-S
NY 0.015
AL 0.007
LLDPE 0.025
LLDPE-Ⅱ 0.025
NY 0.015
AE-PET 0.012
LLDPE 0.025
LLDPE-Ⅱ 0.025
LLDPE-Ⅱ0.025
C=0.30，0.50，1.20，2.00，10.0
unit:mm
(b) NY/AE-PET/XA-S
Figure 1. Laminate films
C=Heat-sealed length
C=Heat-sealed length
unit:mm
C=0.30，0.50，1.20，2.00，10.0
unit:mm
C=0.30，0.50，1.20，2.00，10.0
(b) NY/AE-PET/XA-S
Figure 2. Impact tensile specimens (Heat-sealed forms)
unit:mm
(C) NY/AL/XA-S
films face each other between two sealing sheets, which are heated to 160oC at a heat sealing pressure of 0.196 MPa for a
heat sealing time of 1 sec, in accordance with the test method for food-packaging plastic film.
The values of the heat-sealed area radius, which is a parameter of the bottleneck seal shape, are r = 5, 7.5, 15, 20 mm, and
∞ (the normal flat seal is indicated by ∞ in this study). The heat-sealed area widths are changed in 5 steps, i.e., C = 0.30,
0.50, 1.20, 2.00, and 10.00 mm. Each liquid packaging bags is filled with 13-15 cc of water at 23oC to adjust the bag thickness
to 10 mm. Figures 2(a)-2(c), 3 and 4 indicate the dimensions of the liquid packaging bags used in this experiment. The
specimens shown in Figures 2(a)-2(c) and 3 are used in impact tensile tests, and those shown in Figure 4 are used in impact
A
A
A
NY
bag rupture tests.
NY
NY
AE-PET
LLDPE
LLDPE-Ⅱ
Ｂ
Ｂ
AL
LLDPE
LLDPE-Ⅱ
Ｂ
LLDPE
LLDPE-Ⅱ
C=0.3，0.5，1.2，
2.0，10.0mm
C
C=0.3，0.5，1.2，
2.0，10.0mm
Flat seal
Flat seal
A=15mm B=50mm
r=5，7.5，15，20mm
C
Bottleneck
seal
r
Bottleneck seal
Liquid packaging bag
Liquid packaging bag
Figure 3. Impact tensile specimens (Heat-sealed forms)
Experimental method
Figure 5 shows the structure of the rotary impact tensile apparatus we developed. Its upper chuck is integrated with the face
area. The upper part of the specimen is fixed at the face area and the lower part of the specimen is fixed with a specialized
hook. The impact tensile test was carried out for five heat-sealed area radii (r = 5, 7.5, 15, 20 mm and ∞ (flat seal)) at four
impact tensile speeds (V = 1.20, 1.40, 1.60, and 1.98 m/s), while the heat-sealed area width and ambient temperature were
o
kept constant at 10.00 mm and 23 C, respectively.
In addition, to clarify the effect of heat-sealed area width on impact tensile strength, the impact tensile tests were carried out at
five heat-sealed area widths (C = 0.30, 0.50, 1.20, 2.00, and 10.00 mm) for five heat-sealed area radii (r = 5, 7.5, 15, 20 mm,
o
and ∞), while impact tensile speed and ambient temperature were kept constant at V = 1.40 m/s and 23 C, respectively. The
o
heat-sealed area of the two films of a specimen is opened to an angle of 180 , as shown in Figure 3, during the impact tensile
30
C
C
Flat seal
C
C
C
C
Bottleneck seal
r=5，7.5，15，20
C
Flat seal
Heat-sealed
C
70
C
Heat-sealed
C=Heat-sealed
length
C
70
C
ｒ
C=Heat-sealed length
C=0.30，0.50，0.10，1.20，10.00
C=0.30，0.50，0.10，1.20，10.00
C
Unit : mm
Figure 4. Specimen (Liquid packaging bag)
test. The maximum load was assumed to be the impact tensile strength; [11] ten specimens were measured under each set of
conditions and the standard deviation of the impact tensile strength [12] was found to be 0.3 or less.
Considering that general liquid packaging bags have dimensions of approximately 50 mm x 50 mm, the distance between the
chuck and the hook was set at 50 mm. The impact tensile strength of the specimen was measured as follows. The impact
waveforms of the force applied to the chuck were detected using load cells with frequency responses of 10 kHz, 21 kHz and
100 MHz, a load amplifier and a digital storage scope, and the peaks of the waveforms were measured.
In the impact bag rupture test, we used a new apparatus (Figure 6) that we developed with reference to a falling-weight impact
examination apparatus [13]. We first confirmed that sufficient bag rupture force is obtainable, by dropping a heavy weight
(weight: 10 kg) from a height of 100 mm onto a liquid packaging bags specimen (Figure 4) under a constant ambient
temperature of 23oC. The impact bag rupture test was then carried out to measure the impact rupture strength. Ten liquid
packaging bags were used in the impact bag rupture test under each set of conditions. The impact rupture strength was
measured using load cells, a load amplifier and a digital storage scope; the impact rupture strength was detected and recorded,
and the peak of each waveform was measured.
Load Cell
Cable
Load Amplifier
Face
Digital Storage Scope
Chuck
Stainless Belt
Pinch Roll
Fly Wheel
Specimen
Stainless Belt
Hook
Figure 5. Rotary impact tensile apparatus
Digital Storage Scope
Weight
10ｋｇ
Load Amplifier
Specimen
(Liquid packaging bag)
Load Cell
Cable
Figure 6. Falling-weight impact examination apparatus
Results and Discussion
Effect of impact tensile speed and bottleneck seal shape on impact tensile strength
To clarify the effects of impact tensile speed and bottleneck seal shape on the impact tensile strength of the three films, impact
tensile strength was measured at four impact tensile speeds (V = 1.20, 1.40, 1.60, and 1.98 m/s) for five heat-sealed area radii
(r = 5, 7.5, 15, 20 mm, and ∞). The results are shown in Figures 7-10. Figure 7 shows the relationship between sampling
time and the impact tensile strength of the flat seal for NY/XA-S, NY/AE-PET/XA-S and NY/AL/XA-S. Figures 8, 9 and 10
show the relationship between heat-sealed area radius and impact tensile strength for NY/XA-S, NY/AE-PET/XA-S and
NY/AL/XA-S, respectively.
As shown in Figure 7, impact tensile strength sharply increases immediately after starting the experiment, and at 50 ms, it
reaches 53 N for NY/XA-S, 75 N for NY/AE-PET/XA-S and 56 N for NY/AL/XA-S. After that, the bag specimens break at 100
ms.
100
100
100
V=1.40m/s
60
40
20
0
-20
V=1.40m/s
80
Impact tensile strength [N]
80
Impact tensile strength [N]
Impact tensile strength [N]
V=1.40m/s
60
40
20
0
-20
-50
0
50
100
150
60
40
20
0
-20
-50
Sampling time [ms]
80
0
50
100
150
-50
Sampling time [ms]
0
50
100
150
Sampling time [ms]
NY/XA-S
NY/AE-PET/XA-S
NY/AL/XA-S
Figure 7. Relationship between impact tensile strength and sampling time
As shown in Figures 8-10, the impact tensile strength decreases with increasing impact tensile speed. In particular, the impact
tensile strength obtained at the highest impact tensile speed, V = 1.98 m/s, is lower than that obtained at the lowest impact
tensile speed, V = 1.20 m/s, by 34.0%, 21.9% and 27.8% for NY/XA-S, NY/AE-PET/XA-S and NY/AL/XA-S, respectively.
Impact tensile strength [N]
100
80
60
40
20
1.20m/s
1.40m/s
1.60m/s
1.98m/s
ＮＹ／ＸＡ－Ｓ
∬
0
5
10
15
25
∞
20
Heat-sealed radius [mm]
Figure 8. Relationship between impact tensile strength
and heat-sealed radius
Impact tensile strength [N]
100
80
60
40
20
1.20m/s
1.40m/s
1.60m/s
1.98m/s
ＮＹ／ＡＥ－ＰＥＴ／ＸＡ－Ｓ
∬
0
5
10
15
20
25
∞
Heat-sealed radius [mm]
Figure 9. Relationship between impact tensile strength
and heat-sealed radius
Impact tensile strength [N]
100
80
60
40
20
1.20m/s
1.40m/s
1.60m/s
1.98m/s
ＮＹ／ＡＬ／ＸＡ－Ｓ
∬
0
5
10
15
25
∞
20
Heat-sealed radius [mm]
Figure 10. Relationship between impact tensile strength
and heat-sealed radius
The above finding clarified that the effect of a change in the impact tensile speed on the impact tensile strength is small for
NY/AE-PET/XA-S compared with the cases of NY/XA-S and NY/AL/XA-S. It is considered that NY/AE-PET/XA-S has a higher
impact tensile strength than NY/XA-S and NY/AL/XA-S because of its two-layered structure, which is prepared by stretching
NY and AE-PET films. As a result, the impact tensile strength of NY/AE-PET/XA-S is negligibly affected by the change in
impact tensile speed. It was also confirmed that the tendency of the decrease in the impact tensile strength with increasing
impact tensile speed is similar regardless of the heat-sealed area radius (r = 5, 7.5, 15, 20 mm, and∞ ). When the heatsealed area radius is 15 mm or larger, an impact tensile strength comparable to that obtained with a flat seal can be obtained
regardless of the heat-sealed area radius.
Effect of bottleneck seal shape and heat-sealed area width on impact tensile strength
To clarify the effects of heat-sealed area radius and width on the impact tensile strength of the three films, impact tensile tests
were carried out at a constant impact tensile speed of 1.40 m/s for five heat-sealed area radii (r = 5, 7.5, 15, 20 mm, and ∞)
and five heat-sealed area widths (C = 0.30, 0.50, 1.20, 2.00, and 10.00 mm). The results are shown in Figures 11-13.
Impact tensile strength [N]
100
80
0.30mm
0.50mm
1.20mm
2.00mm
10.00mm
ＮＹ／ＸＡ－Ｓ
60
40
20
∬
0
5
10
15
25
∞
20
Heat-sealed radius [mm]
Figure 11. Relationship between impact tensile strength
and heat-sealed radius
Impact tensile strength [N]
100
80
60
40
0.30mm
0.50mm
1.20mm
2.00mm
10.00mm
ＮＹ／ＡＥ－ＰＥＴ／ＸＡ－Ｓ
20
∬
0
5
10
15
20
25
∞
Heat-sealed radius [mm]
Figure 12. Relationship between impact tensile strength
and heat-sealed radius
Impact tensile strength [N]
100
80
0.30mm
0.50mm
1.20mm
2.00mm
10.00mm
ＮＹ／ＡＬ／ＸＡ－Ｓ
60
40
20
∬
0
5
10
15
25
∞
20
Heat-sealed radius [mm]
Figure 13. Relationship between impact tensile strength
and heat-sealed radius
The impact tensile strengths of the three films remain constant at the highest impact tensile strength obtained with increasing
heat-sealed area width for values of 1.20 mm or larger. In contrast, when the heat-sealed area width is smaller than 1.20 mm,
the impact tensile strength decreases with decreasing heat-sealed area width and reaches its lowest value when the heatsealed area width is 0.30 mm.
The impact tensile strength is affected by heat-sealed area width; however, when the heat-sealed area radius is 15 mm or
larger, an impact tensile strength comparable to that obtained with a flat seal can be obtained regardless of heat-sealed area
radius.
Effect of bottleneck seal shape and heat-sealed area width on impact rupture strength
To clarify the effects of heat-sealed area radius and width on the impact rupture strength of the three films, impact bag rupture
tests were carried out for five heat-sealed area radii (r = 5, 7.5, 15, 20 mm, and ∞ ) and five heat-sealed area widths (C = 0.30,
0.50, 1.20, 2.00, and 10.00 mm). The results are shown in Figures 14-16.
Impact rupture strength［N］
500
400
300
200
0.30mm
0.50mm
1.20mm
2.00mm
10.00mm
NY/XA-S
100
∬
0
5
10
15
20
25
∞
Heat-sealed radius［mm］
Figure 14. Relationship between impact rupture strength
and heat-sealed radius
Impact rupture strength［N］
500
400
300
200
0.30mm
0.50mm
1.20mm
2.00mm
10.00mm
NY/AE-PET/XA-S
100
∬
0
5
10
15
20
25
∞
Heat-sealed radius［mm］
Figure 15. Relationship between impact rupture strength
and heat-sealed radius
Impact rupture strength［N］
500
400
300
200
0.30mm
0.50mm
1.20mm
2.00mm
10.00mm
NY/AL/XA-S
100
∬
0
5
10
15
20
25
∞
Heat-sealed radius［mm］
Figure 16. Relationship between impact rupture strength
and heat-sealed radius
The impact rupture strength shows the highest values, i.e., 272 N for NY/XA-S, 413 N for NY/AE-PET/XA-S and 272 N for
NY/AL/XA-S, when the heat-sealed area radius is 15 mm or larger; these values are comparable to the impact rupture strength
obtained with a flat seal. In contrast, when the heat-sealed area radius is smaller than 15 mm, impact rupture strength
decreases and reaches its lowest value at the heat-sealed area radius of 5 mm. In particular, we confirmed that specimens of
NY/AE-PET/XA-S do not rupture until a very high impact load is applied, compared with the cases of NY/XA-S and NY/AL/XAS.
The impact rupture strengths of the three films remain constant at the highest impact rupture strength obtained with increasing
heat-sealed area width for values of 1.20 mm or larger. However, when the heat-sealed area width is smaller than 1.20 mm,
the impact rupture strength decreases with decreasing heat-sealed area width and reaches its lowest value at the heat-sealed
area width of 0.30 mm.
On the basis of the results obtained, we found that an average heat-sealed area width as large as 10.00-15.00 mm is not
necessary; a minimum heat-sealed area width of 1.20 mm and a minimum heat-sealed area radius of 15.00 mm are adequate
for obtaining sufficient impact tensile strength and impact rupture strength. We demonstrated that the conservation of
resources can be realized by reducing the sealing width.
Photographs of the liquid packaging bag of NY/XA-S with a heat-sealed area radius of 7.5 mm before and after bag rupture,
taken using a high-speed camera, are shown in Figures 17(a) and 17(b).
Figure 17(a) shows the state immediately before an impact load of a perpendicularly falling heavy weight is applied to the
packaging bag. Figure 17(b) shows the state immediately after the application of impact load, due to which the bag breaks
and the liquid content is ejected.
Figures 18(a) and 18(b) show cross sections of the broken laminate films of NY/XA-S for a heat-sealed area radius of 5 mm
(impact rupture strength: 244, 357, 244 N) and a flat seal (272, 413, 272 N), respectively, observed under a microscope.
As shown in Figure 18, stress is found to be concentrated at the edge of the bottleneck seal, due to which the film is locally
elongated, thinned, and broken; as a result, bag rupture occurs. In other words, bag rupture is due to the local concentration
of impact stress at the seal edge.
On the basis of the results obtained, we established, for the first time, new standards for bottleneck seal shape and heatsealed area width, considering both the conservation of resources and the reduction in the number of ruptures.
Weight
Liquid packaging bag
(a)Before liquid packaging bag has broken
Weight
Jet of water due to explosion
Liquid packaging bag
(b) Just after breaking of liquid packaging bag
Figure 17. Moment when liquid packaging bag that high speed camera caught breaks
Bottleneck seal
(r=5mm)
Flat seal (r=∞)
Heat-sealed edge
Heat-sealed edge
Heat-sealed edge
Heat-sealed edge
Liquid packaging bag
Liquid packaging bag
(a) Breaking cross section of laminate film
(b) Breaking cross section of laminate film
Bottleneck seal (r=5mm)
Flat seal (r=∞)
Figure 18. Heat-sealed edge of broken liquid packaging bag (NY/XA-S)
Conclusions
The effects of impact tensile speed and bottleneck seal shape on impact tensile strength for (a) NY/XA-S laminate films, which
is generally used for liquid packaging bags, and multilayered laminate films (b) NY/AE-PET/XA-S and (c) NY/AL/XA-S were
examined. Liquid packaging bags with flat seals and bottleneck seals, which actually contained liquids, were prepared in order
to examine the effects of bottleneck seal shape and heat-sealed area width on impact rupture strength. We obtained the
following conclusions.
(1)The impact tensile strengths of NY/XA-S, NY/AE-PET/XA-S and NY/AL/XA-S decrease with increasing impact tensile speed.
However, the impact tensile strength of NY/AE-PET/XA-S is less affected by the change in impact tensile speed than those of
NY/XA-S and NY/AL/XA-S.
(2)It was confirmed that stress is concentrated at the edge of the bottleneck seal, which leads to breakage of the film; as a
result, bag rupture occurs.
(3)When the heat-sealed area radius is 15 mm or larger and the heat-sealed area width is 1.20 mm or larger, the impact
tensile strength and impact rupture strength are not affected by the bottleneck seal shape and heat-sealed area width,
showing constant values comparable to those obtained with a flat seal.
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