J O U R N A L O F M A T E R I A L S S C I E N C E 3 8 (2 0 0 3 ) 739 – 745

Changes in the gaseous H2S barrier properties

of damaged silicate coated nylon 6 films
M. KAWASAKI
Kawasaki Registed Technical Consulting Office, Kyoto 601-1334, Japan
T. TSUKAMOTO
Division of Advanced Fibro-Science, Kyoto Institute of Technology, Kyoto 606-8585, Japan
Y. KIMURA
Department of Polymer Science and Engineering, Kyoto Institute of Technology,
Kyoto 606-8585, Japan
T. IWASAKI
Cooperative Research Center, Kyoto Institute of Technology, Kyoto 606-8585, Japan
H. YAMANE
Division of Advanced Fibro-Science, Kyoto Institute of Technology, Kyoto 606-8585, Japan
E-mail: hyamane@pc.kit.ac.jp

The damage imposed on SiOx deposited nylon 6 films as a result of abrasion with a cotton
cloth and Gelboflex testing was examined by evaluating the rate at which copper plates,
which were enveloped by the damaged films, were corroded by H2 S. Abrasion with a
cotton cloth caused some micro-cracking of the SiOx layer and the permeation rate of H2 S
approached that of the uncoated nylon 6 film. Damage to the SiOx layer by twisting and
crushing progressed gradually with the number of Gelboflex test cycles and
correspondingly the corrosion rate of the copper plates increased. Comparison of the
corrosion rates of the copper plates kept in the pouches made of various commercial films
with those obtained for the damaged SiOx deposited nylon 6 films showed a clear
relationship between the H2 permeation rate of the films and the corrosion rate of the
copper plates by H2 S. C 2003 Kluwer Academic Publishers

1. Introduction resilience of so-called high barrier films when exposed

Transparent high barrier films utilized for the packag- to corrosive and poisonous gases such as hydrogen sul-
ing of foods, confectioneries, toiletries, and electronics fide H2 S. This paper will report the rate of corrosion by
have been manufactured by the coating of thin ceramic H2 S of copper plates packed in pouches made of SiOx
layer, such as SiOx and Al2 O3 , on flexible plastic films deposited nylon 6 films damaged in various deforma-
by vacuum deposition technique [1–11]. Effects of the tions. Change in H2 S permeation rate was compared
vacuum deposition condition and evaporation material with that of H2 permeation rate.
of SiOx layer on the barrier properties of SiOx deposited
nylon 6 films have been reported by the authors [2, 3].
However, the superior barrier property of plastic films 2. Experimental
coated with the ceramic layer may be deteriorated by the 2.1. Packaging films
damage accompanying abrasion, bending, twisting and SiOx deposited biaxially oriented nylon 6 film (SiOx -
stretching, which are commonly subjected to the films ON)(MOS-NO, Oike Industrial Co., Ltd.) was used as
in the converting processes and daily usage. Changes in a sample. This film was manufactured by the vacuum
the surface morphology and the barrier property of SiOx deposition of a SiOx layer on a biaxally oriented nylon
deposited nylon 6 films accompanying various defor- 6 film (EMBLEM-ON, Unitika Co., Ltd) using a heat-
mations were also investigated by the present authors ing system of an electron beam. The mixture of Si and
[4, 5]. SiO2 was used as an evaporation source. The thick-
In this study, change in the barrier property of SiOx ness of the deposited SiOx layer is about 40 nm.
deposited nylon 6 films accompanied by the damage in- This film is known as a high barrier film whose H2
troduced by abrasion and twisting were examined. Gen- and O2 permeation rates are 7.2 × 10−4 and 1.67 ×
erally the barrier property of the plastic films are exam- 10−5 m3 /m2 · day · MPa, respectively as compared with
ined by the measurements of oxygen and water vapor an undeposited nylon 6 film whose H2 and O2 perme-
permeation rates. However it is important to know the ation rates are 7.7×10−3 and 2.56×10−4 , respectively.

0022–2461 
C 2003 Kluwer Academic Publishers 739
T A B L E I H2 permeation rates through SiOx -ON and the various
commercial films utilized in this study

H2 permeation rate
(×10−4 m3 /
Specimen m2 · day · MPa) Composition (thickness)

SiOx -ON 7.2 SiOx deposited oriented nylon 6

(15 µm)/LLDPE (60 µm)
ON 77 Oriented nylon 6 (15 µm)/LLDPE
(60 µm)
PVDC-ON 41 PVDC coated oriented nylon 6
(17 µm)/LLDPE (60 µm)
PET 196 PET (12 µm)/LLDPE (60 µm)
OPP 3,400 Oriented PP (20 µm)/cast
PP (50 µm)
SiOx -PET 2.2 SiOx deposited PET (12 µm)/cast Figure 1 Schematic diagrams of Gelbotester and the mode of
PP (60 µm) deformation.

Five other kinds of commercial general purpose and motion of 440◦ in the first 90 mm of the stroke of the
high barrier films laminated with either linear low den- movable mandrel, followed by a straight horizontal mo-
sity polyethylene (LLDPE) or cast PP (CPP) were also tion of 65 mm. The motion of the machine is reciprocal
used for comparison. General purpose films include ori- with a full cycle consisting of the forward and return
ented polypropylene (OPP: Fukusuke Industrial Ltd.), strokes. The frequency of the reciprocating movement
poly(ethylene terephthalate) (PET: Unitika Co. Ltd., was 40 strokes/min.
EMBLET), and oriented nylon 6 (ON: EMBLEM-ON,
Unitika Co., Ltd). High barrier films include polyvinyli-
dene chloride coated oriented nylon 6 (PVDC-ON: 2.3. Lamination of damaged films
EMBLEM-DCR, Unitika Co., Ltd) and SiOx deposited SiOx deposited nylon films damaged in various ways
PET (SiOx -PET)(MOS-TH, Oike Industrial Co. Ltd.) were laminated with 50 µm thick linear low density
films. Detailed information and H2 permeation rates of polyethylene (LLDPE) film over SiOx deposited sur-
SiOx deposited nylon 6 and these commercial films are face with a dry lamination method. Some of SiOx
listed in Table I. deposited nylon films were laminated with LLDPE
before giving various deformation for comparison.
A polyester/polyurethane type adhesive (TM-215/
2.2. Damaging of SiOx deposited nylon film CAT-10L, Toyo Morton Co., Ltd.) was applied on SiOx
2.2.1. Abrasion deposited surface with a Meyer bar coater and dried
SiOx deposited nylon films were fixed over a smooth with hot air. Then LLDPE films (TUX-FCS, To-Cello
plastic plate in 200 mm wide and 360 mm long with Co., Ltd.) were laminated on the SiOx deposited films
a deposited surface outside. Another plastic plate in by pressing with a roll.
140 mm wide and 100 mm long weighing 230 g was
covered with a standard cotton cloth for staining of
color fastness test (JIS L0803, muslin No.3) as an abrad-
ing material. This plate covered with the cotton cloth 2.4. Sample preparation
was placed on a SiOx deposited nylon film with a nor- Rectangular pouches 30 mm long and 40 mm wide
mal load of 161 Pa. Predetermined cycles of abrasion were made of SiOx deposited nylon 6 and other lami-
were given to SiOx layer by moving the sliding plate nated films. An impulse heat sealer (Type M200-4, Fuji
in one direction at 100 mm/min. Only the part of film Impulse Co., Ltd.) which has a heater of 4 mm width
on which the sliding plate passed were used as test was used to seal three edges of the pouches. A rectan-
specimens. gular copper plate 25 mm × 15 mm in area and 1 mm
in thickness was put in each pouch and the pouches
were sealed with the sealer after removing the air in the
2.2.2. Gelboflex pouches.
Flex resistance of flexible barrier films is generally
determined by the Gelboflex tests according to the
method described in ASTM-F392-93 [12]. Gelboflex 2.5. Exposure to H2 S gas
tester used in this study is schematically illustrated in The pouches were placed in a 12 liter desiccator. After
Fig. 1. This apparatus consists of 90 mm diameter sta- the air in the desiccator was evacuated by a vacuum
tionary and movable mandrels spaced at a distance of pump, H2 S gas (>99.99%, Sumitomo Seika Chemical
180 mm apart from face to face at the starting position. Co., Ltd.) was blown into the desiccator slowly up to
The film specimen is supported by the shoulders on the the level of atmospheric pressure. The pouches were
mandrels. The motion of the movable mandrel is con- kept in the desiccator for various periods of time at
trolled by a grooved shaft designed to give a twisting 26◦ C.

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Figure 2 Appearance of copper plates packed in pouches made of various commercial films.

2.6. Evaluation Fig. 2 shows the appearance of the copper plates

The degree of permeation of H2 S gas through sample packed in the pouches made of various commercial
films was evaluated by examining the change in the films exposed to H2 S gas for various periods of time.
appearance of the copper plates and the reflectance of The brightness of the copper surface faded gradually
the copper surfaces. H2 permeation rates through the with time and the color of copper changed into tarnish,
sample films were also determined. dark, gray, blackish and finally into black. The change
in color began at an edge or section of the copper plate
and spreaded gradually over the entire surface. Fol-
2.6.1. Reflectance lowing colors correspond approximately to the respec-
The reflectance at the surface of copper plates was mea- tive wavelengths; violet 420 nm, blue 470 nm, green
sured by a spectrophotometer (Color-Eye 3100; Gretag 520 nm, yellow 580 nm, yellowish red 610 nm and
Macbeth Co., Ltd.) in a spectral range from 360 nm red 650 nm, respectively [19]. Since the color of fresh
to 740 nm with a wavelength interval of 20 nm. Mea- copper appears closely to be yellowish red or red, the
surements were carried out according to ISO-7724-1, reflectance at the wavelength from 600 to 660 nm sup-
2, 3 regulation to indicate the color by the system of posedly indicates the color of copper itself [20]. In this
CIE Lab [13–17]. The copper surfaces were illuminated report, we took a reflectance and a psychometric light-
with pulse xenon sources conditioned to illuminant D65 ness L ∗ at 620 nm as indices of the corrosion of copper
with an optical configuration at 2 degrees for an aper- by H2 S.
ture size of 5 mm × 10 mm. The color of the copper The change in the spectral reflectance at the surface
surface was indicated by the reflectance at 620 nm and of copper plate packed in a pouch of polyvinylidene
the psychometric lightness L ∗ . chloride coated nylon (PVDC-ON) exposed to H2 S gas
is shown in Fig. 3. The reflectance at the wavelength
from 600 to 660 nm decreased with the increasing expo-
2.6.2. H2 permeation rate
sure period to H2 S. These correspond to the change in
The gas barrier property of the laminated films was
color shown in Fig. 2, in which one can see the brilliant
evaluated by the measurement of the hydrogen gas per-
yellowish red gradually turned to tarnish and grayish
meation rate. The H2 permeation rate was measured
as the sulfuration proceeded.
at 22◦ C and 0% RH by the method according to
ASTM D-1434-75 with an apparatus for measuring gas
permeability (Type MC3, Toyo Machinery Corpora- 3.2. Damages of SiOx deposited nylon
tion). All values were specified in m3 /m2 · day · MPa 6 film by abrasion
for 100% H2 . Fig. 4 shows the appearance of the copper plates packed
in the pouches made of SiOx deposited nylon films
3. Results and discussion damaged by abrasion. The changes in the reflectance at
3.1. Corrosion of copper by H2 S the wavelength of 620 nm and the psychometric light-
Copper is sulfurated by H2 S gas and a layer of copper ness are plotted in Fig. 5 as functions of the period
sulfide is formed on the surface. The following chemical of exposure to H2 S. The change in the appearance of
reactions are considered to occur [18]; the copper surface occured more quickly and signifi-
cantly with the repetition of the abrasion on the film sur-
2Cu + H2 S → Cu2 S + H2 ↑ face. Furthermore, the spectral reflectance and the psy-
chometric lightness decreased more significantly when
Cu2 S + H2 S → 2CuS + H2 ↑
the copper plates were kept in the pouches of abraded
Cu + H2 S → CuS + H2 ↑ films. It seems that once SiOx layer was abraded with a
741
Figure 3 Change in the spectral reflectance at the copper surface kept in a PVDC-ON pouch.

Figure 4 Appearance of copper plates packed in pouches made of SiOx deposited nylon 6 films damaged by abrasion.

cotton cloth several times, some micro-cracks were

formed and H2 S molecules easily permeated through
the film.
The surface morphology of SiOx layer and the H2
permeation rate through the SiOx deposited nylon 6
films damaged by abrasion have been reported else-
where by the authors [4]. Abrasion by a sand paper
completely ruined the gas barrier property of the film.
Even mild rubbing with a cotton cloth several times
significantly reduced the barrier property of the film.
AFM observation revealed that there were a lot of irreg-
ular stripes to the abrasion direction on the SiOx layer
abraded with a cotton cloth more than 10 times and
some micro-cracks were also found at the thinner parts
of irregular stripes. Such change in the surface mor-
phology extended to all surface area abraded. Although
H2 permeation rate of unabraded SiOx deposited nylon
6 film is as low as 7.2 × 10−4 m3 /m2 · day · MPa, it in-
creased to 2.1 × 10−3 m3 /m2 · day · MPa by only 4 abra-
sion cycles and to about 3.4 × 10−3 m3 /m2 · day · MPa
by 10 cycles. For 60 abrasion cycles, the H2 perme-
ation rate was almost the same as that of uncoated nylon
6 film.
Although H2 permeation rate reported showed a clear
dependence on the number of cycles of abrasion [4], the
reflectance and the psychometric lightness obtained in
this study indicate that once film was abraded some
Figure 5 Changes in the reflectance at 620 nm and the psychometric micro-cracks were formed and sufficient H2 S perme-
lightness L ∗ for SiOx deposited nylon 6 films abraded with a cotton ated through the abraded film to cause severe corrosion
cloth. of the copper plate.

742
Figure 6 Appearance of copper plates packed in pouches made of SiOx deposited nylon 6 films after Gelboflex tests.

3.3. Deformation by Gelboflex flectance at 620 nm and psychometric lightness on the

The flexing action in the Gelboflex test consists of a surfaces of copper plates. As the flexing cycles and
twisting motion followed by a horizontal motion, thus, the period of exposure to H2 S, the brilliant yellowish
repeatedly twisting and crushing the film. Such flexing red of copper surface faded gradually and the color of
motion may deteriorate the barrier property of the film copper became tarnished, grayish, gray, blackish and
and pinholes may be formed in the film. finally into black. This tendency was also observed in
Fig. 6 shows the change in the appearance of copper the changes of the spectral reflectance and psychomet-
plates packed in the pouches made of SiOx deposited ric lightness where these values decreased more quickly
nylon films after Gelboflex tests. Fig. 7 shows the re- with the flexing cycles.
AFM observation of the SiOx deposited nylon 6 film
after 30 Gelboflex cycles revealed that the damage by
flexing formed locally [4]. Some of the part was filled
with micro-cracks and other part was kept undamaged.
The area and the extent of the damage seem to in-
crease with the Gelboflex cycles and the barrier prop-
erty deteriorated gradually. This is supported by the
reflectance and the psychometric lightness which de-
creased at higher rates with time as the number of Gel-
boflex cycles increased. No macroscopic pinhole was
formed within the number of Gelboflex tests carried out
in this study.
Generally SiOx deposited layer of the film is covered
with other protective films. The effect of the lamination
of LLDPE film on SiOx layer on the severity of the
damage during Gelboflex test was clearly seen in Fig. 8,
where the reflectance and the psychometric lightness
decreased more slowly with the number of Gelboflex
cycles given to the SiOx deposited film laminated with
LLDPE.

3.4. Various commercial packaging films

Fig. 9 shows the reflectance and the psychometric light-
ness L ∗ at the surface of copper plates packed in the
pouches made of undamaged SiOx deposited nylon
6 and various commercial films. There were remark-
able differences in the reflectance and the psychomet-
Figure 7 Changes in the reflectance at 620 nm and the psychometric ric lightness among these packaging materials. These
lightness L ∗ for the SiOx deposited nylon 6 films after Gelboflex tests. changes were observed to be more significant in the

743
 Figure 10 Reflectance and the psychometric lightness L ∗ of the copper
plates kept in H2 S for 30 min as functions of H2 permeation rate of the
films.

order of,
SiOx -PET < SiOx -ON < PVDC-ON < ON
< PET < OPP

It should be noted that this is exactly the same ten-

dency to that for the H2 permeation rates listed in
Table I. It may be interesting to plot the reflectance and
Figure 8 Changes in the reflectance at 620 nm and the psychometric the psychometric lightness L ∗ of the damaged SiOx de-
lightness L ∗ for the SiOx deposited nylon 6 films with Gelboflex cycles
carried out before and after lamination.
posited nylon 6 films and those of various commercial
films utilized as functions of H2 permeation rate. Such
plots are shown in Fig. 10. Both the reflectance and the
psychometric lightness decreased proportionally to the
logarithm of H2 permeation rates. These plots indicate
that when the H2 permeation rate is low, the corrosion
rate shows a strong dependence on the H2 permeation
rate.

4. Conclusions
We examined the damage imposed on the SiOx de-
posited nylon 6 films accompanying abrasion with a
cotton cloth and the Gelboflex tests. Change in the gas
barrier property with the progress of the damage was
evaluated by the corrosion rate of the copper plates kept
in the pouches made of the damaged films and exposed
to H2 S.
Abrasion with a cotton cloth gave a lot of stripes on
the SiOx layer alined to the abrasion direction. Further
some micro cracks were formed on the SiOx layer and
the corrosion rate of the copper approached that of the
copper plate kept in the pouch made of the uncoated
nylon 6 film.
Flexing by the Gelboflex tester gave twisting and
crushing deformations on the SiOx deposited nylon
6 films. Damage of SiOx layer by such deformations
progressed gradually with the number of Gelboflex cy-
cles. This tendency was clearly shown by the change in
the corrosion rate of the copper plates which increased
gradually with the number of the Gelboflex cycles. Even
Figure 9 Changes in the reflectance at 620 nm and the psychometric 30 cycles of the Gelboflex test did not make any pin-
lightness L ∗ for SiOx deposited nylon 6 and various commercial films. holes in the films.

744
 Comparisons of the corrosion rate of the copper 6. Y . G . T O R P S H A and N . G . H A R V E Y , J. Phys. Chem. B
plates kept in the pouches made of various commer- 101(13) (1997) 2259.
7. B . M . H E N R Y , A . P . R O B E R T S , C . R . M . G R O V N O R ,
cial films and those obtained for the damaged SiOx
A. P. SUTTON, G. A. D. BRIGGS, Y. TSUKAHARA,
deposited nylon 6 films showed a clear relationship be- M . T A N A K A , T . M I Y A M O T O and R . J . C H A T E R , in
tween H2 permeation rate and the corrosion rate of the Proceedings of the Society of Vacuum Coaters, 42nd Annual Tech-
copper plates by H2 S. nical Conference, 1999, p. 362.
8. A . Y U K I H A R A , Packaging Technology 4 (1999) 21.
9. I . Y O K O Y A M A , K . I S E K I , T . O H Y A , S . K O M E D A , Y .
Y A M A D A , and H . I S H I H A R A , in Proceedings of the Society of
Acknowledgments Vacuum Coaters, 41st Annual Technical Conference (1998) p. 434.
We acknowledge K. Yamazaki of Hyogo Industrial 10. Y . T O M I T A and K . M O M I I , Plastic Age 2 (2000) 87.
Technology for his help on the measurements of H2 11. K . H I R O S E , Convertec 12 (2000) 9.
permeation rate and K. Inoue and Y. Kurushima of 12. ASTM F392-93.
13. F . W . B I L L M E Y E R and H . S . F A I R M A N , Color Research
Unitika Fibers Co. Ltd for their help on the mea-
and Application 12 (1987) 27.
surements of the reflectance and the psychometric 14. ISO 7724/1,2,3, Part 2, Ist ed., 1984.
lightness. 15. ISO 10526, CIE S005, 2nd ed., 1999.
16. ASTM E308-99.
17. ASTM D2244-93.
References 18. T. INOUE, in “Culture Course Inorganic Chemistry” (Asakura
1. M . K A W A S A K I , J. Packaging Sci. Tech. 9(3) (2000) 145. Shoten, 1957) p. 52.
2. M . K A W A S A K I , Y . K I M U R A , T . I W A S A K I and 19. Japan Color Society (ed.), “New Color Science Hand Book,”
H . Y A M A N E , Sen-i Gakkaishi 54(11) (1998) 577. (Nankoudo Publication, 1998) p. 249.
3. Idem., ibid. 56(1) (2000) 26. 20. T . Y A M A N A K A , in “The Foundation of Color” (Bunka Shobou
4. M . K A W A S A K I , T . T S U K A M O T O and H . Y A M A N E , ibid. Hakubunsha, 1997) p. 23.
58(1) (2002) 29.
5. M . K A W A S A K I , Y . K I M U R A , T . I W A S A K I , T . Received 5 March
T S U K A M O T O and H . Y A M A N E , ibid. 58(1) (2002) 34. and accepted 10 October 2002

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