Measuring and testing – With fluid pressure – Porosity or permeability
Reexamination Certificate
2003-05-06
2004-12-28
Larkin, Daniel S. (Department: 2856)
Measuring and testing
With fluid pressure
Porosity or permeability
Reexamination Certificate
active
06834532
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of measuring the gas transmission rate of a plastic film and a measuring apparatus for the method, which measure the transmission rates of various gases which are transmitted through plastic films.
2. Description of the Related Art
Plastic films have been used in a wide range of applications including food storage containers, and new materials for such films have been developed one after another. Gas permeability is an important property in understanding the performance and quality of these films, and hence measuring apparatuses based on various schemes have been developed and commercialized in various countries.
There are three known methods of measuring gas transmission rates for general gases: the differential pressure method, the isobaric method, and the small bag method. For water vapor, the cap method, the moisture sensor method, the infrared sensor method, and the dish method are known.
The gas transmission rates of films are general measured by using the differential pressure method or the isobaric method defined in JIS (Japanese Industrial Standard) (Testing method for gas transmission rate through plastic film and sheeting: JIS K 7126, testing methods for water vapor transmission rate of plastic film and sheeting; JIS K 7129, method of permeability test for moisture proof packing case; and JIS Z 02222, and testing methods for determination of the water vapor transmission rate of moisture-proof packaging materials: JIS Z 0208).
In the differential pressure method, one of the two portions separated by a test piece is kept in a vacuum, and a test gas is introduced into the other portion, thereby obtaining a gas transmission rate on the basis of an increase in pressure on the low-pressure side. In the isobaric method, a test gas is supplied to one of the two portions separated by a test piece while a carrier gas is flowed in the other portion at equal pressure, and the amount of gas transmitted is measured by some kind of gas detector or gas chromatograph. Measuring apparatuses based on the differential pressure method and the isobaric method have been developed and commercialized for a long time. In either of the methods, the surrounding of a test piece attached to a measuring portion must completely be sealed, and measuring apparatuses themselves are complicated.
The measuring method based on the small bag method was made public (Toshio Inoue and Takasuke Ishitani, “Changes in Oxygen Concentration and Volume over Time in Gas Purge Packaging”, Packaging Study Vol. 11, No. 1 (1990), pp. 21-27). According to this method, a change in gas concentration in the bag and a change in the volume of the bag are checked. When a film subjected to gas transmission rate measurement is to be actually used as a product, the film is often processed into a bag-like airtight container and, for example, food is sealed into the container. The small bag method allows tests and evaluations in accordance with actual usage including the structures of bags, and hence is considered to have a wide range of applications.
In this method, however, both a change in gas concentration and a change in bag volume must be measured. A volume change is obtained from, for example, an increase in water level upon sinking a bag into the water, whereas a concentration change is obtained by using, for example, a gas chromatograph. There is therefore no merit in directly measuring an airtight bag, and no measuring apparatus based on this method has been commercialized.
Either of the cap method and the dish method which use no gas sensor is a method of measuring an increase in the weight of a hygroscopic material due to water vapor that is transmitted into a container or bag; measurement is limited to water vapor.
As described above, the conventional methods of measuring the gas transmission rates of plastic films demand complicated procedures and complicated measuring apparatuses.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to provide a method of measuring the gas transmission rate of a plastic film, which requires only simple measurement preparations and procedures and exhibits very high measurement precision as compared with the conventional techniques, a measuring apparatus used for the measuring method, and a gas transmission rate measuring program using the measuring method.
In order to achieve the above object, according to the present invention, there is provided a method of measuring a gas transmission rate of a plastic film, comprising sealing a gas X into a test film bag which is formed by processing a test plastic film into a bag and has a known mass and surface area, measuring a mass of the test film bag in which the gas is sealed, a plurality of numbers of times on the time series, while keeping a temperature constant in a temperature-controlled airtight vessel which is filled with a gas Y different from the gas X so as to make a pressure in the vessel equal to an internal pressure of the test film bag, and obtaining a transmission rate (a value representing the number of moles of a gas transmitted through a test piece with a unit area in a unit time at a unit partial pressure difference) associated with the gas X from a relationship between the measurement results, the mass of the test film bag alone, and the surface area.
More specifically, this method is executed by program processing by an arithmetic processing apparatus on the basis of the following techniques:
(1) A method of measuring a gas transmission rate of a plastic film, in which when a transmission rate (a value representing the number of moles of a gas transmitted through a test piece with a unit area in a unit time at a unit partial pressure difference) k
x
[mol/m
2
sPa] of a gas X is known, a transmission rate k
y
[mol/m
2
sPa] of a gas Y through a test plastic film is measured, comprising:
preparing a test film bag by processing the test plastic film into a bag, and measuring a mass m
f
[kg] of the test film bag alone and a total surface area A [m
2
] associated with gas transmission in advance;
sealing the gas X into the test film bag at a density &rgr;
x
, and measuring masses m
0
[kg], m
1
[kg], and m
2
[kg] of the test film bag in which the gas is sealed at least at times t
0
[s], t
1
[s], and t
2
[s] in an airtight vessel which is filled with the gas Y at a density &rgr;
y
so as to set a pressure P [Pa] equal to an internal pressure of the test film bag and in which a temperature is kept constant at a measurement temperature T [K];
obtaining volumes V
x0
, V
x1
, and V
x2
of the gas X in the test film bag at times t
0
, t
1
, and t
2
from
V
x0
=(
m
0
−m
f
)/(&rgr;
x
−&rgr;
y
)
V
x1
=(
m
1
−m
f
)/(&rgr;
x
−&rgr;
y
)
V
x2
=(
m
2
−m
f
)/(&rgr;
x
−&rgr;
y
)
obtaining &lgr;
x
by substituting the obtained results into the following equation for obtaining &lgr;
x
:
&lgr;
x
={a
(
t
1
−t
0
)−
b
(
t
2
−t
0
)}/(
aV
x1
−bV
x2
−cV
x0
)
for
a
=log
V
x0
−log
V
x2
b
=log
V
x0
−log
V
x1
c
=log
V
x1
−log
V
x2
and
computing
k
y
=(&lgr;
x
K
x
2
+K
x
)/(
RTA
)
where R is a gas constant and K
x
=k
x
RTA
thereby obtaining the transmission rate k
y
of the gas Y when the transmission rate k
x
is known.
(2) A method of measuring a gas transmission rate of a plastic film, in which when a transmission rate (a value representing the number of moles of a gas transmitted through a test piece with a unit area in a unit time at a unit partial pressure difference) k
y
[mol/m
2
sPa] of a gas Y is known, a transmission rate k
x
[mol/m
2
sPa] of a gas X through a test plastic film is measured, comprising:
preparing a test film bag by processing the test plastic film i
Izutsu Naoki
Yajima Nobuyuki
Japan Aerospace Exploration Agency, an Independent Administrativ
Larkin Daniel S.
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