J. Pac .Sci. Tech.

Vol.22No.5（2013）

Original Paper～～～～～～～～～～～～～～～～～～～～～～～～～～～～

Sealant for Gable Top Cartons in Useof Chilled Distribution Mineral Water
Hiroshi FUKUI*, Tadahisa IWATA* and Akio TAKEMURA*
Current sealants for gable top skived cartons consist of laminated LDPE or L-LDPE layer which are
different from aseptic liquid packaging because flame sealing process is required. Such sealants oftencause off-odor or off-flavor to water which is thought to be a result of the migration of hydrocarbon
molecules generated during heat seal or lamination and the adsorption of flavor respectively. To addressthese problems, this study is focused on polyester sealant which is applicable for flame seal operation. It
is known some polyester pellets contain small particles such as talc to promote crystallization. While
charcoals, activated carbon, zeolite and TiOx, are not studied much. In this research, these small particles
are added into polyester and expected to be plasticizer and/or crystal core when they were laminated
together with resins on the paper board. Flame sealing process requires quick crystallization and proper
elongation of film. Polyesters which successively varied their adhesion property for flame seal were
forwarded to sensory test. They were soaked into mineral water as an inner layer of carton and tested forboth electric tongue and sensory test to evaluate correlations. Some of the polyester films were found to
be good quality for flame sealing.
Keywords: gable top skived carton, polyester sealant, flavor, charcoal, flame seal, electric tongue,
crystallization, elongation

1. INTRODUCTION
Liquid paper packaging for chilled circulation and flexible packaging materials consist of multilayer
films1) and paper board in order to add various barrier functions such as oxygen, vapor, flavor and scent.
Their sealants are mostly laminated or film type polyolefin, which is used as for heat seal with seal bar,
hot air and flame. However, polyolefin type sealant includes small molecular weight compounds where
off-odor of beverages especially mineral water is occurred. In addition, the adsorption of volatile andhydrophobic compounds in beverages sometimes deteriorates taste 2, 3). To address these problems,
polyesters are considered to be used as sealant especially for skived gable top cartons. As far as current
skived flame sealing process is concerned, only LDPE and L-LDPE are appropriate materials for sealant.
Polyester has high specific gravity and are synthesized by condensation polymerization, of which
polydispersity is lower than polyolefin’s4) which alienates wide distribution of molecular weight and goodsealability.

*Graduate School of Agricultural and Life Sciences, The University of Tokyo,
Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657－ 335 －

Sealant for Gable Top Cartons in Use of Chilled Distribution Mineral Water

In case of flame sealing process of polyester to polyester adhesion, physical property such as friction,
modulus of elasticity in tension, MFR, Tg, etc. are not satisfactory. In order to improve physical propertyof polyester, this study is focused on the various additives which improve sealability. We found charcoal
and activated carbons behave not only as plasticizer but also as crystal core in various polyesters. Films
were extruded with resins containing charcoal or activated carbon on OPP film or paper board if MFR at
190 or 210℃ was suitable value for extrusion. Their physical properties were analyzed by DMA, DSC,
WAXD, tensile and friction testing devises to predict polyester-polyester adhesion.
Polyester laminated carton boards (Fig.1) were adhered by actual flame seal machine for liquid
packaging cartons5,6) (Fig. 2).

Fig.1

Fig.2

Structure of laminated board

Conceptual diagram of flame seal machine－ 336 －

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Vol.22No.5（2013）

Then sealing property and quality were examined followed by sensory test and electric tongue which
employs similar statistical analysis methods for electric nose and tongue7,8,9) together with LDPE as acomparison.
In the case of butylene structure is rich, polyester films tend to be selected as a sealant for mineral water
packaging. However, in real operation of flame sealing, physical property of above chosen films alsosuggest a need for modification of flame seal machine itself.

2. MATERIALS AND METHODS
2.1 Materials
Pellets of LDPE were supplied by TOSOH Ltd. (Tokyo, Japan) and various polyesters VYLON 10) andSI173 as amorphous crystallized PET by TOYOBO Ltd. (Osaka, Japan). Liquid paper board (255g/m2)
was obtained from Stora Enso Oyj (Helsinki, Finland). Cider charcoal (6.5μm, d50) was synthesized in
our Laboratory. and bamboo charcoal (6.5μm, d50) was obtained by Maruto Ltd.(Shiga, Japan), activatedcarbon E153 (4μm, d50) by NIHON NORIT Ltd. (Tokyo, Japan), Carbon black by SUMIKA COLOR Ltd.
(Osaka, Japan). Zeolite ABSCENTS™ 2000 (4μm, d50) was obtained by UNION SHOWA K.K. (Tokyo,
Japan) and TiOx CR-93 by ISK Ltd (Osaka, Japan).
KayastainQ (Nippon Kayaku Ltd., Takasaki, Japan) was used for checking heat seal of polyester and
LDPE adhesion and water solution of Acid brilliant scarlet 3R dye (Hodogaya Chemical Ltd., Tokyo,
Japan) and surfactant Teepol-eight (TEEPOLservice Ltd., Odawara, Japan) was for pinhole check. PET
bottled mineral water Tennen-sui (Suntory Ltd., Osaka, Japan) was used for sensory evaluation as a blank.
2.2 Preparation of testing materials
Masterbatches for extrusion were prepared by double-screw strander (PCM-30, Ikegai Ltd.) andpelletizer (PL-60 Ishinaka Ltd.) by adding additives of 2%-10%(w/w) to various polyesters (VYLON
GM,GA). More than 1wt% of additives in base resin resulted in extreme coloring and inadequate film
formation. So the concentration of additives in base resin and masterbatch mixture was decided to be lessthan 1wt%.
Liquid packaging carton blanks for polyester-polyester flame sealing test were prepared by extruding
suitable VYLON polyesters about 35μm thickness using T-die extruder (L/D=24, dia. 32mm screw,
GT32-24A PLABOR) onto 25μm of LDPE (TOSOH P204) pre-coated paper board as a substrate at
200±30℃. Then they were cut and creased by sample cutter (CF 0907, Mimaki) for about 270mL ofliquid paper carton blanks. Polyester/LDPE layer does not show serious adhesion problem because ofthermal fusion.
Polyester films for physical analysis were casted on to OPP films or uncoated paper by T-die extrusion
with a favorable thickness, then peeled off from substrate.
About 300 cm2 films (30μm thickness) were soaked into 500mL of mineral water at 80℃ for 5 days forhuman sensory test and electric tongue. Area of the films was calculated by considering inner side contact
panel of 500mL of liquid paper cartons.
2.3 Flame sealing test
Laminated carton blanks by various type of polyester were evaluated by flame sealing machine equipped－ 337 －

Sealant for Gable Top Cartons in Use of Chilled Distribution Mineral Water

with two burners5,6) (Fig. 2) by changing operation speed of the test cartons at the same condition ofburners. Normal operation speed of mini type juice carton was counted as 1 unit (about 400m/min.). Andpolyester laminated cartons were calculated by the comparison of LDPE.
2.4 Evaluation of physical character
For DMA, DVA-200S (IT Keisoku Ltd.) was used. Test pieces were prepared to 0.5mm-1mm thickness
and 5mm width, then adjusted to 40mm length. Measurement condition were 2℃/min. of heat rate, 1Hzof frequency and 1L/min. of N2 purge.
For tensile test to calculate young’s modulus, SIMADZU Ltd. EZ test was used. Test pieces wereprepared about 50μm thickness and 5mm width then adjusted to 10mm length. Pulling rate was
20mm/min..
GM400 and charcoal containing film sample were analyzed by (wide-angle) X-ray diffractometerequipped with Ni filter, of which radiation source and output were CuKα and 40kVx40mA (RINT2000
RIGAKU Ltd.). Equatorial scan was conducted 2θ (10~40°) for comparing crystallinity.
Coefficient of dynamic friction (μ') was measured on the surface of laminated film based on JIS K7125
compliance.
For DSC (DSC220 SEIKO INSTRUMENT) analyses, 5mg of each film sample was once heated up to
250℃ then cooled down to below -100 ℃, then heated up to 250℃ again to detect Tc1 peak for relative
comparison of crystallization speed.
MFR was measured by using TOYOSEIKI MI F-F01 at 170℃ and /or 190℃ only when Tm ofpolyester resins was high enough to measure.
2.5 Evaluation of electric tongue and sensory test
Human sensory test was conducted among extract of films soaked in mineral water (shown in testingmaterial) by employing basically triangle test and pair test11). 7 samples were tested. For human sensory
test, scores of the samples were determined from 1 to 10 where 10 is perfect score and 1 is the lowest. In
this test, score of PET bottled mineral water was 9. Scores of each tested samples are shown in Table 4.
For electric tongue, αASTREE (Alpha M.O.S Japan K.K.) was employed. The 8 sensors which haveown response rate were used to examine response value12). Then the principal component analysis (PCA)
was applied as a statistical methods based on the sensor response. Principal component (PC1) andsecondary component (PC2) were determined as the total of contribution rate so as to be more than 97%.
In this experiment PC1 was 92% and PC2 was 8% which means only two sensors were enough toevaluate PCA (Fig.6). Each weight center of the sample was calculated by software and plotted as
euclidean distance from blank and plotted in Fig.7. Correlation between human sensory test and electric
tongue was calculated by PLS and plotted together with coefficient of correlation in Fig.8.

3. RESULT AND DISCUSSION
3.1 Property of extruded resins and flame seal testing
Polyester resins were chosen from VYLON with the difference in melting temperature (Tm),glass-transition temperature (Tg) and MFR with additives to control physical property. These polyesters
include butanediol and/or ethylene glycol as raw materials. For example GM400 consists of 35% of－ 338 －

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Vol.22No.5（2013）

ethylene glycol and remaining component is mostly butanediol showing partly PBT properties. GA1310
consists of 100% butanediol showing PBT properties. As for crystallization, GA1310 is much faster but
flavor barrier is lower. In addition, PBT has better properties of bend performance and water resistancethan those of PET 13).
Resins were chosen by Tm in between 107-179℃. In case Tg is below 0℃, severe adhesion to metals
and plastics were found in ambient temperature, also low Tm caused high MFR and poor formation offilms. For polyester extrusion, MFR and Tg are found to be key factors which are same as polyolefin.
Physical properties of extruded resin are shown in Table 1.
Both sides polyester laminated boards shown in Fig. 1 were processed to tens of carton blanks by using
sample cutter then tested for flame sealer shown in Fig. 2 to check polyester-polyester adhesion.
Table 1

Physical properties of various resins and films with required output unit of flame seal+activated carbon*StoraEnso’s juice carton=1(unit)

Adhesion of polyester and LDPE were examined by staining these portions by KayastainQ, which
elucidated thermal fusion.
Polyester laminated carton blanks were applied to flame sealer equipped with two burners used for real
carton production in the factory. Seal and pinhole check were judged by soaking adhesion portion into
mixture of Scarlet 3R dye and Teepole water solution in one minute and then peeled off adhesion site.
Then adhesion energy was calculated from the unit of operation speed. Tested carton blanks wereoperated by relatively low speed, which means high energy were required as shown in Table 1. As
observed during extrusion, low Tg resins adhered strongly to cartons and metals, which disturbs operationof flame sealer. On the other hand, high Tg showed poor adhesion.
It seemed carbon additives were of help to reduce the flame energy (discussed latter section). As a result,mixture of GA1310 (80%) and GM400 (20%) were the best selection from the flame sealing point ofview.

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Sealant for Gable Top Cartons in Use of Chilled Distribution Mineral Water

3.2 Relation between storage elastic modulus (E’) and Tg
To analyze adhesion properties, E’ of polyester films and films with additives at 50 and 100℃ (listed inTable 2) were plotted against local maximal value of tanδ as Tg measured by DMA (Fig.4). Arrowed line
in Fig.3 shows E’ of GM400 at 50 and 100℃. Most of the flame sealable polyesters showed around 108
Pa at 50℃ and also maximal value of tan δ at about 30℃, which indicates both value may be theregulatory factor for flame seal adhesion. In fact Tg is lower than ambient temperature, films become
sticky and E’ is higher than 108 Pa, no adhesion is expected.

Fig.3

Storage elastic modulus at 50 and 100℃ of GM400

Table 2 Storage elastic modulus at 50 and 100℃ and local maximal value of tanδDescription
Number
50℃
100℃
tanδ TEMP (℃）

Modulus(E')

GM913
ⅰ
159.0
63.4
-43.8

(Pa

x105)

GM900 GA3410 GM400+bamboo GM400+cider GM400 GM:GA=8:2 GA2310 GM:GA=5:5 GA2310+carbon GA1310
ⅱ
ⅲ
ⅳ
ⅴ
ⅵ
ⅶ
ⅷ
ⅸ
ⅹ
ⅺ
295.0 341.0
70.0
976.0
868.0 1200.0 735.0 1380.0
493.0
2180.033.9 54.2
409.0
409.0
312.0 352.0 247.0 433.0
225.0
ND-16.1 5.6
25.3
25.4
27.3 28.1
32.1 34.1
36.1
44.2

LDPE
Ref
938.0
57.7
68.1

（x10 5 )On the other hand, LDPE showed maximal value of tanδ at 68℃ and E’ was almost 108 Pa at 50℃ and
E’ at 100℃ was much lower than above mentioned polyesters because of melting temperature is around
110℃. We do not have clear explanation why the maximal value of tanδ at 68℃ of LDPE appears.

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Vol.22No.5（2013）

Fig.4 Plot of local maximal value of tanδ as Tg versus Modulus

3.3 Effect of additives to physical properties of polyesters
LDPE has generally low young’s modulus compared to polyesters in extrusion grade. In case young’s
modulus is so high, folded cartons sometimes show peel off along crease or pinholes because of the low
elongation of layer. It was observed that addition of 1wt% charcoals or TiOx to GM400 and GA2310 etc.
had potential to lower young’s modulus (Table 1).
Polyester GM400(80%)+GA1310(20%) which includes 1wt% of zeolite and LDPE co-extruded twolayer film (16μm each) showed much higher elongation (376%) compared to that of solid ones (279%) on
maximum stress. The above polyester and LDPE co-extrusion showed stable film formation where theproper melt tension of LDPE facilitated two layer formations. As zeolite does not have thick color,
application to extruder is much realistic than charcoals.
According to the DSC analysis of GM400 shown in Table 3, initiation temperature of crystallization
became lower than original one (Tc1) and also half width calculated by peak height/baseline showed
higher value if charcoals or carbons were added (Fig.5), indicating charcoals and carbons act as crystal
core and simultaneously plasticizer. WAXD also detected high crystallinity, which may result in lower
coefficient of dynamic friction (μ'), even LDPE is still low (0.16).
Mixture of GA1310 and GM400 were analyzed with zeolite. Table 3 shows Tg as detected by DMA,
Tc1, peak height/baseline calculated by DSC, and coefficient of dynamic friction. Zeolite promoted
crystallization rate, but Tg did not change to lower side, which implies charcoal and carbons are better
additives if color is not considered. TiOx wears manufacturing machine such as cutter. So, analysis is not
focused on TiOx.

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Sealant for Gable Top Cartons in Use of Chilled Distribution Mineral Water

Table 3

Effect of additives on physical properties of films

Methods

Measurement Items
GA1310
GM400(80%) + GA1310(20%)+Zeolite
GM400+Charcoal (bamboo)+Charcoal (cider)+Carbon black

Fig.5

DMA
Tg (℃ )
44
32
41
28
25
25
ND

DSC

WAXD

Tc1 (℃ ) Peak Height/Baseline Crystallinity ratio
45.9
1.7
68.5
1.2
60.9
1.6
70.3
0.5
1.0
63.8
0.8
62.8
0.8
4.0
63.1
1.0
-

μ'
0.22
0.30
0.30
0.43
0.29
0.29
ND

DSC chart of GM400 and charcoal added one

3.4 Human sensory test and electric tongue
Five polyesters and LDPE films together with PET bottled mineral water were analyzed to determine
correlation among them. GM400 (with/without 1wt% cider charcoal or zeolite), GA1310 and mixture ofeach polyester together with amorphous polyester SI173 which can be extruded by the same setting
temperature of LPDE as reference (Tg78℃, Softening temperature185℃ respectively) were evaluated by
sensory test and electric tongue.
Table 4 shows specimens and tested score of each film. According to the human sensory test result,
GM400 and mixture of GM400 and GA1310 maintained good taste. Zeolite or charcoal added samples
did not imply improvement unexpectedly and LDPE was the worst score among them.

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Table 4Vol.22No.5（2013）

Samples for human sensory test and scores

Sample(#)

SampleScore

ⅰBlank (PET bottled Mineral Water)

9

ⅱ

LDPE

1

ⅲ

GM400

6

ⅳ

GM400 (80%) + GA1310 (20%)

6ⅴ

GM400 with 1wt(%) of zeolite

7ⅵ

GM400 with 1wt(%) of cider charcoal

5ⅶ

Ref. Polyester SI173

7

Electric tongue was then used for analysis. It elucidated the shortest euclidean distance from Blank was
mixture of GM400 and GA1310 (Fig.7). Additives did not effect to shorten euclidean distance. This
result may indicate electric tongue recognizes the existence of additives rather than taste as human feels.
Fig.6 shows PCA plotting of PC1 and PC2, only two semiconductor sensors responded well to calculate
contribution rate, of which total contribution rate was 100%. The most of the samples were related to PC1.
Blank (ⅰ) and mixture of GM400 and GA1310 (ⅳ) occupied almost the same territory, which implied
similar directional quality.
Correlation between human sensory test scores and those predicted by electric tongue were analyzed andplotted by PLS statistical methods. Fig.8 indicated electric tongue was able to distinguish category ofmaterial and with/without additives easily, but as human sensory test did not reflect significant difference
whether additives were included or not, coefficient of correlation was 0.634. Therefore, electric tongue
may be suitable for detecting foreign element which human may not notice.

Fig.6

Score plot from the PCA of the electric tongue－ 343 －

Sealant for Gable Top Cartons in Use of Chilled Distribution Mineral Water

Fig.7

Fig.8

Euclidean center distance from bottled mineral water

Correlation of human sensory test and electric tongue loaded by PLS

4. CONCLUSIONSPolyesters are well known as flavors protect materials, which are not expected as polyolefins to be used
for sealant of liquid packaging. In this research, various types of polyesters which were laminated bothsides of paperboards were tested for flame sealing process. Laminated films with high Tg more than 35℃
rarely adhered. On the other hand, flame sealing operation was not unstable when Tg was less than 35℃
and storage elastic modulus at 50℃ by DMA was 108 Pa. In addition, lower value of young’s modulus－ 344 －

J. Pac .Sci. Tech.

Vol.22No.5（2013）and dynamic frictions were required for carton production process.
Additives such as charcoals, TiOx and zeolite behaved as plasticizer and crystal core and were found to
be a key factor for improving polyester physical property.
Both human sensory test and electric tongue elucidated superior property of some polyester in term offlavor protection.
In conclusion, to achieve realistic flame seal operation of gable top cartons especially for chilled
distribution, polyester sealant may be developed from material design and additives to control physicalproperties for production process.

Acknowledgements
We thank Alpha M.O.S Japan KK and other companies for advice of this research.

REFERENCES
1) Fukui, H. and Takemura, A., 17th Housougakkai Nenji Taikai, Japan, 92-93 (2008)
2) Kamishinbara, T., Harada, M. and R. Tajima : J. Pack. Sci. and Technol., 13 (3), 165-171 (2004)
3) Hayashi, K., Oomura, Y. and Takechi, H:Report of Tokushima Food Research Institute, 37,13-21(1989)
4) Murahashi, S.:“Polymer Chemistry 4”, ISBN 4-320-04292-1, Kyoritsu Publisher Ltd., 30-32 (2005)
5) Nippon Paper-Pak Co., Ltd.,: NP-PAK ism, 5, 2 (2007)
6) IPBMCO, Liquid Packaging Division, (2012),
http://www.ipbmco.com/content_page.html
7) Willing, B. L.,Brundin, A. and Lundstom, I.: Packaging. Technol. Sci., 11, 59-67 (1998).
8) Yoshida, K.:Monthly Food Chemical, 10, 31-36 (2010)9) Kovacs,T., Sipos. L., Kantor, D., Kokai, Z. and Fekete, A.:Proc. of the 13th symposium on Olfaction
and Electronic Nose., 1137, 489-492 (2009).
10) TOYOBO Ltd.:“ VYLON Amorphous co-polymer, crystalline co-polymer”, 5-6 (2006)11) Satou,S.:“Kannoukennsa Nyuumon(5)”, ISBN 4-8171-9001-9, Nikkagiren Publisher Ltd., 57-60(1986)
12) Alpha M.O.S. Japan K.K., Electric tongue, (2012)
http://www.alpha-mos.co.jp/sensory/am-astree-01.html
13) WinTech Polymer Ltd., Application of PBT resins to films, (2004)
http://www.polyplastics.com/jp/product/lines/extrusion/pbtfilm.pdf（Received 31January 2013）（Accepted 26August 2013）－ 345 －