U.S. patent application number 11/190607 was filed with the patent office on 2005-12-01 for pet container for foods and drinks containing recycled resin and having dlc coating film formed on surface thereof.
Invention is credited to Hama, Kenichi, Kage, Tsuyoshi.
Application Number | 20050266191 11/190607 |
Document ID | / |
Family ID | 18494359 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050266191 |
Kind Code |
A1 |
Hama, Kenichi ; et
al. |
December 1, 2005 |
PET container for foods and drinks containing recycled resin and
having DLC coating film formed on surface thereof
Abstract
A PET container for foods and drinks having a DLC coating film
formed on the inner surface thereof, characterized in that the PET
container for foods and drinks is produced by the use of a molding
material comprising a mixture of a recycled resin which is
originated from a used PET container for foods and drinks and has
not subjected to a treatment for adjusting its intrinsic viscosity
with a fresh PET resin. The above PET container for foods and
drinks can provide satisfactory barrier properties against a
pollutant substance being present in a resin.
Inventors: |
Hama, Kenichi;
(Nishigotanda, JP) ; Kage, Tsuyoshi; (Tokyo,
JP) |
Correspondence
Address: |
HEDMAN & COSTIGAN P.C.
1185 AVENUE OF THE AMERICAS
NEW YORK
NY
10036
US
|
Family ID: |
18494359 |
Appl. No.: |
11/190607 |
Filed: |
July 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11190607 |
Jul 27, 2005 |
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10149336 |
Jun 6, 2002 |
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10149336 |
Jun 6, 2002 |
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PCT/JP00/09267 |
Dec 26, 2000 |
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Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
C08J 2367/02 20130101;
Y02W 30/62 20150501; Y02W 30/701 20150501; Y10T 428/1352 20150115;
C08J 11/06 20130101; B65D 1/0207 20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B65D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 1999 |
JP |
11/369414 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. A method of manufacturing a DLC film coated PET container for
foods and beverages containing recycled resin, comprising the steps
of: shredding used PET containers for foods and beverages to form
flakes, and then removing foreign material from said flakes,
washing said flakes using an alkaline washing agent and water, and
drying said flakes to obtain washed flakes; obtaining recycled
pellets which have not undergone intrinsic viscosity adjustment
from said washed flakes; molding a container containing recycled
resin using said recycled resin pellets and un used PET resin
pellets adjusted so that the compounding ratio (weight of recycled
resin pellets/weight of recycled resin pellets+weight of unused PET
resin pellets) is greater than 0 but less than 0.40; and coating
the inner surface of said container with a DLC film so that oxygen
permeability of said container is less than or equal to 0.01
ml/day/container when converted to a 500 ml volume.
5. A method of manufacturing a DLC film coated PET container for
foods and beverages containing recycled PET resin as defined in
claim 4 wherein said film coated PET container comprises from 10%
to 40% of recycled PET.
Description
[0001] This application is a divisional application of Ser. No.
10/149,336, filed Jun. 6, 2002.
TECHNICAL FIELD
[0002] The present invention is related to a plastic container
adapted for use as a food container or the like, and in particular
to a plastic container containing recycled PET resin which makes it
possible for the resin of a used PET (polyethylene terephthalate)
container for foods and beverages to be recycled and used again as
a plastic container for foods and beverages, and a manufacturing
method thereof
PRIOR ART TECHNOLOGY
[0003] Japanese Laid-Open Patent Publication No. HEI 8-53117
discloses a vapor deposition apparatus which uses CVD (Chemical
Vapor Deposition, chemical vapor growing method), in particular, a
plasma CVD method to vapor deposit a DLC (Diamond Like Carbon) film
on the inner surface of a plastic container in order to improve the
gas barrier properties and the like of containers such as
containers for carbonated beverages and high fruit juice beverages
and the like. Further, Japanese Laid-Open Patent Publication No.
HEI 10-258825 discloses a manufacturing apparatus for mass
producing a DLC film coated plastic container, and a manufacturing
method thereof. Furthermore, Japanese Laid-Open Patent Publication
No. HEI 10-226884 discloses a manufacturing apparatus which makes
it possible to apply a coating of DLC film without mottling to a
container having protrusions which protrude from the outer surface
to the outside, and a manufacturing method thereof.
[0004] A DLC film is a film called an i-carbon film or an amorphous
carbon hydride film (a-C:H), and also includes a hard carbon film.
Further, a DLC film is an amorphous-state carbon film, and includes
SP.sup.3 bonding and SP.sup.2 bonding.
[0005] Incidentally, the estimated resource recycling rate of PET
containers in Japan for 1999 was 18%, and the use thereof was 70%
for fiber products, and 20% for sheet related products used for
trays and egg packs and the like for packaging apples and pears and
the like. These fiber products and sheet related products have a
low added value, and the resource recycling rate is influenced by
the market conditions and the like of the fiber industry.
Hereafter, the PET container recycling rate is expected to improve
in view of the building of a recycling society, and there is a
demand for fundamental users of PET container recycled products.
For this reason, there is a desire to use PET containers in related
industries, namely, to build a bottle-to-bottle self-complete type
recycling system to carry out recycling of containers.
SUMMARY OF THE INVENTION
[0006] However, in the case where a used PET container is recycled
and used again as a food container, the recycled product is
required to have no problem in point of the sanitary safety of
food, and even when it is assumed that the sanitary safety of a
recycled product is the same as that of a new product, the consumer
or user of the recycled product needs to be convinced. Further,
with regard to the recycled product having no problem in point of
sanitary safety of food, the approval and the like of a related
government agency including an evaluation method thereof are
required. Accordingly, at the present time, the use of recycled
products for food containers is in a uneasy state.
[0007] A more detailed examination of the thought process of
sanitary safety when recycled PET containers are used for food
container packages is described below. Namely, in general after a
food container package is consumed/used for the original purpose,
due to contact with a foreign substance and foreign substance
mixing and the like in the use for another purpose, unexpected
misuse, or discarding/recycling process, a risk of contamination is
expected due to the unknown substance. Accordingly, in order for it
to be possible for a container to be recycled and used again as a
food container package, such unknown contaminants inside the
recycled product must be reduced by the recycling process to a
level that makes it possible to ensure sanitary safety, namely,
below the allowable reference value of contamination. In order to
make it easy for the unknown contaminants to be reduced below the
allowable reference value, {circle over (1)} the discarding source
of the reclaimed/recycled waste plastic needs to be restricted as
much as possible, and the origin thereof needs to be made clear
(source restricting) in order to prevent as much as possible the
waste plastic that forms the source material from being
contaminated by unknown substances; {circle over (2)} a method of
use needs to be devised to make it possible to ensure a safe level
at the time of use even when, for example, some contaminants remain
after recycling; {circle over (3)} a recycling performance needs to
be provided to make it possible to wash/reduce contaminants to a
safe level even when contamination occurs due to some kind of
unknown contaminants (ensuring recycling performance); {circle over
(4)} a means needs to be conceived to prevent contaminants from
eluting into the contents even when a small amount of unknown
contaminants remain; and the like need to be carried out.
[0008] With regard to {circle over (1)} described above, this is a
problem solved by the building of a societal recycling system, and
with regard to {circle over (2)}, a solution is carried out by
restricting the method of use from the viewpoint of the type of
foods, the use temperature, the use time, the contact surface area,
the use and the like. With regard to {circle over (3)}, a method
has been proposed in which used resin is first decomposed to a low
molecular level, and then polymerization is carried out again to
form a resin.
[0009] However, with regard to the system of {circle over (1)}, it
is built at the same time recycled products flow to market, and
with regard to {circle over (2)}, it is difficult to find
fundamental users of recycled products as restrictions are made to
use. With regard to {circle over (3)}, the required cost for the
process of low molecular conversion of resin is high, and becomes
disadvantageous by a cost comparison with new resin. Accordingly,
the {circle over (4)} conception of a means to prevent contaminants
from eluting into the contents even when a small amount of unknown
contaminants remain is thought to be realistic.
[0010] The means for preventing contaminants from eluting into the
contents is largely separated into two kinds. As for one of these,
for example, by sandwiching both surfaces of a recycled PET resin
layer between new PET resin layers to create a laminated structure,
the contents are prevented from making direct contact with the
recycled PET resin layer, and this forms a method for preventing
the movement of contaminants. The other means is a method in which,
after a container is molded from only a base substance which
contains recycled PET resin, the inner wall surface of the
container which makes contact with the contents is coated or the
like with a barrier layer that prevents the permeation of
contaminants. The former means is disadvantageous because a high
cost is required for molding.
[0011] The present invention is related to technology for forming
the latter barrier layer which does not have a high cost, and
because contaminants will elute into the container contents in a
container that is obtained by simply molding resin containing
recycled PET resin, it is an object thereof to make it possible to
reuse used PET containers for foods and beverages by coating the
inner surface of the containers with a DLC film to provide the
containers with contaminant elution barrier properties, and by
making it possible to reuse PET containers, placing the resin of
used PET containers for foods and beverages in a recycling route.
Additionally, it is an object of the present invention to reuse the
resin of used PET containers for foods and beverages without
requiring excessive cost, namely, without carrying out a solid
phase polymerization process on the resin of used PET
containers.
[0012] It is a second object of the present invention to provide a
DLC film coated PET container for foods and beverages containing
recycled resin having an optimal compounding ratio, with
consideration given to the balance between the utilization factor
of used PET containers for foods and beverages and the performance
of PET containers for foods and beverages containing recycled
resin. The background for considering balance comes from the
following facts: {circle over (1)} if the resin of a used PET
container for foods and beverages which does not undergo a solid
phase polymerization process has an excessive compounding ratio, it
will be difficult to maintain the container strength and ensure
moldability; and {circle over (2)} there is a demand to minimize
the effects of colored impurities contained in the resin of used
PET containers for foods and beverages.
[0013] It is a third object of the present invention to provide a
PET container for foods and beverages containing recycled resin
coated with a DLC film having sufficient contaminant elution
barrier properties and satisfactory fundamental container
properties such as gas barrier properties and the like.
[0014] It is a fourth object of the present invention to provide a
method of manufacturing DLC film coated PET containers for foods
and beverages containing recycled resin having sufficient container
strength and sufficient contaminant elution barrier properties, in
which inexpensive pelletized material is used without carrying out
a solid phase polymerization process on the resin of used PET
containers for foods and beverages, and sufficient mixing with
unused PET resin pellets is carried out to make it possible to mold
containers.
[0015] Further, the container according to the present invention
includes containers used with a cover or plug or seal, and also
containers used in an open state without the use of such sealing
members. The size of the opening is determined in accordance with
the contents. Plastic containers include plastic containers having
a prescribed thickness and moderate stiffness, and plastic
containers formed from sheet material which is not stiff. Further,
this includes the cover of the container. The contents of the
plastic container according to the present invention particularly
concern beverages such as carbonated beverages or fruit juice
beverages or soft drinks or the like.
[0016] In order to achieve the objects described above, the present
inventor discovered the following inventions. Namely, in the DLC
film coated PET container for foods and beverages containing
recycled resin of the present invention, a DLC film is formed on
the inner surface of the PET container for foods and beverages,
wherein the PET container for foods and beverages is a container
molded from a molding material comprising a mixture of recycled
resin of used PET containers for foods and beverages which has not
undergone intrinsic viscosity adjustment, and unused PET resin.
[0017] Further, in the DLC film coated PET container for foods and
beverages containing recycled resin of the present invention, the
compounding ratio (weight of recycled resin of used PET containers
for foods and beverages which has not undergone intrinsic viscosity
adjustment/(weight of recycled resin of used PET containers for
foods and beverages which has not undergone intrinsic viscosity
adjustment+weight of unused PET resin)) of said mixture is
preferably greater than 0 but less than 0.40.
[0018] Furthermore, in the DLC film coated PET container for foods
and beverages containing recycled resin of the present invention,
the oxygen permeability is preferably less than or equal to 0.010
ml/day/container when converted to a 500 ml volume.
[0019] The method of manufacturing a DLC film coated PET container
for foods and beverages containing recycled resin according to the
present invention comprises the steps of shredding used PET
containers for foods and beverages to form flakes, and after
removing foreign material from said flakes, washing said flakes
using an alkaline washing agent and water, and drying said flakes
to obtain washed flakes; obtaining recycled resin pellets which
have not undergone intrinsic viscosity adjustment from said washed
flakes; molding a container containing recycled resin using said
recycled resin pellets and unused PET resin pellets adjusted so
that the compounding ratio (weight of recycled resin
pellets/(weight of recycled resin pellets+weight of unused PET
resin pellets)) is greater than 0 but less than 0.40; and coating
the inner surface of said container with a DLC film so that the
oxygen permeability of said container is less than or equal to
0.010 ml/day/container when converted to a 500 ml volume.
[0020] The plastic container according to the present invention
means a PET container for foods and beverages, and in particular a
PET container for foods and beverages containing recycled resin.
The method of manufacturing this PET container for foods and
beverages containing recycled resin is as follows. Used PET
containers for foods and beverages are shredded to form fine
flakes, foreign material is removed, and then the flakes are washed
until clean using an alkaline washing agent and water. These washed
and dried flakes are pelletized by a pelletizer. These pellets of
the used PET resin for foods and drinks pelletized in this way are
mixed with unused PET resin, and a container is manufactured using
a molder. At the container molding time, the compounding ratio
(weight of recycled resin of used PET containers for foods and
beverages which has not undergone intrinsic viscosity
adjustment/(weight of recycled resin of used PET containers for
foods and beverages which has not undergone intrinsic viscosity
adjustment+weight of unused PET resin)) of these pellets should be
greater than 0 but less than 0.40, and preferably greater than 0
but less than or equal to 0.30. The utilization factor of used PET
for foods and beverages is preferably high, and the performance of
the PET container for foods and drinks containing recycled resin is
also preferably high, but when considering a balance of both of
these, the most preferred compounding ratio is greater than or
equal to 0.10 but less than or equal to 0.20. When the compounding
ratio is 0, it is not possible to recycle used PET container resin.
On the other hand, because the intrinsic viscosity (IV) of the
pellets of the used PET resin for foods and beverages is low in
comparison with the intrinsic viscosity of unused PET pellets, when
the compounding ratio is greater than or equal to 0.40, the
container strength goes down, and when an excessive amount of low
intrinsic viscosity PET pellets are mixed in, it is difficult to
mold PET containers. In such case, by carrying out solid phase
polymerization to raise the polymerization degree of the pellets of
the used PET resin for foods and beverages, and by adjusting the
molecular weight of the used PET resin for foods and beverages, it
is possible for a container to use 100% used PET resin for foods
and beverages. However, because a rise in manufacturing costs
accompanies the carrying out of solid phase polymerization,
container molding is preferably carried out by mixing used PET
resin which has not undergone intrinsic viscosity adjustment and
unused PET resin.
[0021] Further, the transparency/clearness of the PET container for
foods and beverages containing recycled resin is lowered by colored
impurities contained in the pellets of the used PET resin for foods
and beverages. When an overall judgment of the above facts is made,
the maximum compounding ratio should preferably not exceed
0.40.
[0022] As is understood by referring to the embodiments described
below, in the PET container for foods and beverages containing
recycled resin obtained in this way, one portion of contaminants
contained in the pellets of the used PET resin for foods and
beverages will elute into the container contents. Accordingly, PET
containers for foods and beverages containing recycled resin can
not be reused for foods and beverages in a state where only molding
is carried out.
[0023] In this regard, in the present invention, the inner surface
of the container is coated with a DLC film to prevent elution of
contaminants. The reason for choosing a DLC film is that a DLC film
has superior performance in following the expansion and contraction
of the container when compared with a SiO.sub.x film or the like,
and in particular this choice is due to the consideration given to
the case where the container is filled with beer, carbonated
beverages, fruit juices or the like which cause large expansion and
contraction of the container. Further, properties such as gas
barrier properties and the like are changed by the composition and
film thickness and the like of the DLC film. Accordingly, in the
present invention, the judgment of whether or not the DLC film has
sufficient contaminant elution barrier properties is determined by
indicating the oxygen gas barrier properties of the entire
container, and the oxygen permeability of the DLC film coated PET
container for foods and beverages containing recycled resin is
indicated as being less than or equal to 0.010 ml/day/container
when converted to a 500 ml volume. In order to more completely
prevent elution of contaminants, it is more preferred that the
oxygen permeability be less than or equal to 0.005 ml/day/container
when converted to a 500 ml volume. In order to make the oxygen
permeability less than or equal to 0.010 ml/day/container when
converted to a 500 ml volume, the characteristics of the DLC film
such as the composition and film thickness and the like may be
appropriately adjusted. However, in any case, if the oxygen
permeability is not made less than or equal to 0.010
ml/day/container when converted to a 500 ml volume, the container
will not have sufficient contaminant elution barrier
properties.
[0024] In accordance with the invention described in claim 1, by
coating the inner surface of the container with a DLC film to give
the container contaminant elution barrier properties, it is
possible to reuse used PET containers for foods and beverages.
Further, in accordance with the reuse of PET containers becoming
possible, the resin of used PET containers for foods and beverages
can be placed in a recycling route. Additionally, the resin of used
PET containers for foods and beverages is reused without requiring
excessive costs, namely, without carrying out a solid phase
polymerization process on the resin of used PET containers.
[0025] In accordance with the invention described in claim 2,
{circle over (1)} the resin of used PET containers which has not
undergone intrinsic viscosity adjustment is used in a range that
does not make it difficult to maintain container strength and
ensure moldability, and {circle over (2)} the effects of colored
impurities contained in the resin of used PET containers for foods
and beverages is minimized, and by considering the balance between
the utilization factor of used PET for foods and beverages and the
performance of PET containers for foods and beverages containing
recycled resin, it is possible to provide a DLC film coated PET
container for foods and beverages containing recycled resin having
an optimum compounding ratio.
[0026] In accordance with the invention described in claim 3, it is
possible to provide a DLC film coated PET container for foods and
beverages containing recycled resin which has sufficient
contaminant elution barrier properties, and which has sufficient
fundamental container properties such as gas barrier properties and
the like.
[0027] In accordance with the invention described in claim 4, it is
possible to provide a method of manufacturing a DLC film coated PET
container for foods and beverages containing recycled resin which
has sufficient container strength and sufficient contaminant
elution barrier properties, wherein a sufficient amount of unused
PET resin pellets is mixed in to make it possible to mold a
container using inexpensive pelletized resin of used PET containers
for foods and beverages which has not undergone a solid phase
polymerization process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a drawing showing one example of a manufacturing
apparatus for manufacturing a plastic container of the present
invention.
[0029] The applied symbols in FIG. 1 are as follows: 1 is a base,
1A is an exhaust outlet, 2 is a shoulder portion electrode, 3 is a
body portion electrode, 4 is a bottom portion electrode, 5 is a
plastic container, 6 is an insulator, 7 is an O-ring, 8 is an
interface device, 9 is a high-frequency oscillator, 10 is a housing
portion, 11 is an inner electrode, and 12 is a pipeline.
PREFERRED EMBODIMENTS OF THE INVENTION
[0030] Hereinbelow, a description will be given for the preferred
embodiments of a plastic container in which a DLC film is formed of
the present invention.
[0031] FIG. 1 is a drawing showing one example of a manufacturing
apparatus for forming a DLC film on the inner surface of a plastic
container. As shown in FIG. 1, the present apparatus is equipped
with a base 1, a shoulder portion electrode 2 and a body portion
electrode 3 mounted to the base 1, and a bottom portion electrode 4
which can be connected to and disconnected from the body portion
electrode 3. Further, the bottom portion electrode 4 isn't an
electrode for only the bottom portion of the plastic container, and
also functions as an electrode at the side portion of the lower
portion of the body. As shown in FIG. 1, the shoulder portion
electrode 2, the body portion electrode 3 and the bottom portion
electrode 4 each have inner wall surfaces shaped like the outer
shape of a plastic container 5, in which the shoulder portion
electrode 2 is arranged along the shoulder portion of the plastic
container 5, the body portion electrode 3 is arranged along the
body portion of the plastic container 5, and the bottom portion
electrode 4 is arranged along the bottom portion of the plastic
container 5. The shoulder portion electrode 2, the body portion
electrode 3 and the bottom portion electrode 4 form the outer
electrodes of the present apparatus.
[0032] When the bottom portion electrode 4 is mounted to the body
portion electrode 3, the base 1, the shoulder portion electrode 2,
the body portion electrode 3 and the bottom portion electrode 4
form a mutually airtight mounted state, and these function as a
vacuum chamber equipped with a housing portion 10 for housing the
plastic container 5. As shown in FIG. 1, an insulator 6 is provided
between the shoulder portion electrode 2 and the body portion
electrode 3, and in this way the shoulder portion electrode 2 and
the body portion electrode 3 are electrically insulated from each
other. Further, an O-ring 7 is provided between the body portion
electrode 3 and the bottom portion electrode 4, and when the bottom
portion electrode 4 is mounted, a small gap is formed between the
bottom portion electrode 4 and the body portion electrode 3. In
this way, while ensuring airtightness between the bottom portion
electrode 4 and the body portion electrode 3, electrical insulation
is carried out between both electrodes.
[0033] An inner electrode 11 is provided in the housing portion 10,
and the inner electrode 11 is inserted into the inside of the
plastic container 5 housed inside the housing portion 10. The inner
electrode 11 is electrically connected to a ground potential.
[0034] The inner electrode 11 is formed to have a hollow shape
(tube shape), and one blowout hole (not shown in the drawing) which
communicates the inside and the outside of the inner electrode 11
is formed in the lower end thereof. Further, instead of providing a
blowout hole in the lower end, a plurality of blowout holes (not
shown in the drawing) may be formed to pass through the inside and
the outside of the inner electrode 11 in the radial direction. A
pipeline 12 which communicates with the inside of the inner
electrode 11 is connected to the inner electrode 11, and this
structure makes it possible for a source gas fed into the inside of
the inner electrode 11 via the pipeline 12 to be emitted into the
inside of the plastic container 5 via the blowout hole. Further,
the pipeline 12 is made of metal and has electrical conductivity,
and as shown in FIG. 1, the pipeline 12 is used to connect the
inner electrode 11 to a ground potential. Further, the inner
electrode 11 is supported by the pipeline 12.
[0035] As shown in FIG. 1, the output terminal of a high-frequency
oscillator 9 is connected to the bottom portion electrode 4 via an
interface device 8. The high-frequency oscillator 9 generates a
high-frequency voltage between itself and the ground potential, and
in this way a high-frequency voltage is applied between the inner
electrode 11 and the bottom portion electrode 4.
[0036] Next, a description will be given for the process when a DLC
film is formed on the inner surface of the plastic container 5
using the present apparatus.
[0037] The plastic container 5 is set so that the bottom portion
thereof makes contact with the inner surface of the bottom portion
electrode 4, and by raising the bottom portion electrode 4, the
plastic container 5 is housed in the housing portion 10. At this
time, the inner electrode 11 provided in the housing portion 10 is
inserted inside the plastic container 5 through the orifice (upper
end opening) of the plastic container 5.
[0038] When the bottom portion electrode 4 is raised to a
prescribed position to hermetically seal the housing portion 10, a
state is formed in which the outer periphery of the plastic
container 5 makes contact with the inner surfaces of the shoulder
portion electrode 2, the body portion electrode 3 and the bottom
portion electrode 4. Next, the air inside the housing portion 10 is
exhausted through an exhaust outlet 1A of the base 1 by a vacuum
device not shown in the drawing. After the pressure inside the
housing portion 10 has been reduced to a required vacuum level, a
source gas (e.g., carbon source gases such as aliphatic
hydrocarbons such as acetylene and the like, aromatic hydrocarbons
and the like, and hydrocarbon gases containing Si) supplied via the
pipeline 12 is introduced into the inside of the PET container 5
from the blowout hole of the inner electrode 11.
[0039] After the concentration of the source gas reaches a
prescribed value, the high-frequency oscillator 9 (e.g., 13.56 MHz)
is activated to apply a high-frequency voltage between the inner
electrode 11 and the outer electrodes, whereby a plasma is
generated inside the plastic container 5. In this way, a DLC film
is formed on the inner surface of the plastic container 5.
[0040] Namely, the formation of a DLC film on the inner surface of
the plastic container 5 is carried out by a plasma CVD method,
wherein electrons accumulate on the inner wall surfaces of the
outer electrodes insulated by the plasma generated between the
outer electrodes and the inner electrode 11, and a prescribed fall
in potential occurs.
[0041] In this way, the carbon and the hydrogen of the hydrocarbon
that forms the source gas present in the plasma are each ionized to
positive, and these ion randomly with the inner wall surface of the
plastic container 5 running along the inner wall surfaces of the
outer electrodes, whereby an extremely fine DLC film is formed on
the inner wall surface of the plastic container 5 by the bonding
between adjacent carbon atoms and the bonding between carbon atoms
and hydrogen atoms, and by the breaking of bonds of hydrogen atoms
that have bonded once (sputtering effect).
[0042] As described above, the output terminal of the
high-frequency oscillator 9 is connected to only the bottom portion
electrode 4. Further, a gap is formed between the bottom portion
electrode 4 and the body portion electrode 3, and the bottom
portion electrode 4 and the body portion electrode 3 are
electrically insulated from each other. Furthermore, the insulator
6 is provided between the body portion electrode 3 and the shoulder
portion electrode 2, and the body portion electrode 3 and the
shoulder portion electrode 2 are electrically insulated from each
other. Accordingly, the high-frequency electric power applied to
the body portion electrode 3 and the shoulder portion electrode 2
becomes smaller than the high-frequency electric power applied to
the bottom portion electrode 4. However, because capacity coupling
is carried out through the respective gaps between the bottom
portion electrode 4 and the body portion electrode 3, and between
the body portion electrode 3 and the shoulder portion electrode 2,
a certain degree of high-frequency electric power is also applied
to the body portion electrode 3 and the shoulder portion electrode
2.
[0043] In general, the bottom portion of plastic containers such as
bottles and the like have complex shapes, and it is difficult to
form a DLC film having sufficient thickness. Further, because the
bottom portion has insufficient drawing at the time of
manufacturing, the gas barrier properties of the plastic itself
become lower at the bottom portion. For this reason, even after the
DLC film is formed, the gas barrier properties of the bottom
portion of the container are prone to lowering. However, by means
of the manufacturing apparatus shown in FIG. 1, because it is
possible to apply high-frequency electric power larger than that
for the body portion and shoulder portion to the bottom portion of
the plastic container, it is possible to form a DLC film having a
uniform thickness for the entire container, and it is possible to
form a thicker DLC film at the bottom portion where the gas barrier
properties of the plastic itself are low. Accordingly, it is
possible to effectively improve the gas barrier properties for the
entire container. In the embodiment described above, it is possible
to raise the applied electric power to 1200.about.1400 W for
example, and accordingly it is possible to plan a reduction in
manufacturing costs due to the shortening of the coating time.
[0044] In the apparatus described above, the shoulder portion
electrode 2, the body portion electrode 3 and the bottom portion
electrode 4 are constructed so as to be completely insulated
against direct current, but it is also possible to connect each of
the electrodes to each other by resistance or capacitive elements
or the like. In short, so long as it is possible to apply
high-frequency electric power having a required strength in
accordance with each portion of the container, for example, a
plurality of high-frequency oscillators may be provided to apply
high-frequency electric power separately to each of the electrodes
of the shoulder portion electrode 2, the body portion electrode 3
and the bottom portion electrode 4, or the output of a single
high-frequency oscillator may be connected to each of the
electrodes via a plurality of interface devices.
[0045] Further, in the apparatus described above, an example was
described for the case where the outer electrodes are divided into
three portions, but the outer electrodes may be divided into two
portions, or the outer electrodes may be divided into four or more
portions.
[0046] The DLC film coated plastic container of the present
invention can be used ideally as a returnable container, but can
also be used for one-way use (i.e., the use of a disposable
container which is filled with contents only one time and not
recycled).
[0047] The method of manufacturing the DLC film coated plastic
container is not limited to the method described above. In the
embodiment described above, a plasma CVD method that uses high
frequency is used, but it is also possible, for example, to use a
plasma CVD method using microwaves.
EXAMPLE EMBODIMENTS
Example Embodiment 1
[0048] A description will be given for the results of testing the
effectiveness of contaminant elution inhibition of PET containers
for foods and beverages containing recycled resin.
[0049] Because used PET in the city is found in various
contaminated states, model contaminants were mixed with unused PET
flakes to form PET flakes contaminated with model contaminants, and
pseudo used PET pellets were created, and then these pseudo used
PET pellets and unused PET pellets were used to form a container
which was then evaluated.
[0050] In general, the contaminants of plastic can be thought to
form the following four types of substances: {circle over (1)}
substances which are volatile and polar; {circle over (2)}
substances which are volatile and nonpolar; {circle over (3)}
substances which are nonvolatile and nonpolar; and {circle over
(4)} substances which are nonvolatile and polar. In this test,
{circle over (1)} toluene (C.sub.6H.sub.5 CH.sub.3, hydrocarbon,
volatile, nonpolar), {circle over (2)} chlorobenzene
(C.sub.6H.sub.5 Cl, halogenated hydrocarbon, volatile, intermediate
polarity, aggressive chemical for PET), {circle over (3)}
n-docosane (C.sub.22H.sub.46, hydrocarbon, nonvolatile, nonpolar),
and {circle over (4)} nonadecanol (CH.sub.3(CH.sub.2).sub.18OH,
alcohol, nonvolatile, having polarity) were used as the model
contaminants for each of the four types described above.
[0051] A. Manufacture of Pseudo Used PET Pellets
[0052] First, new PET containers were shredded to create unused PET
flakes. Next, the four types of model contaminants described above
were added to the unused PET flakes. Specifically, as a first
mixing operation, prescribed amounts of the four types of model
contaminants were mixed with 500 g of unused PET flakes to make PET
flakes contaminated with the model contaminants. After that, as a
second mixing operation, 500 g of the PET flakes contaminated with
the model contaminants was further mixed with 4500 g of unused PET
flakes to make 5000 g of a PET flake mixture contaminated with the
model contaminants in which prescribed amounts of the model
contaminants were mixed inside the PET. Table 1 shows the mixture
amounts of the model contaminants and the PET flakes.
1TABLE 1 Model Contaminants Contamination PET Flakes (g) Level
Contaminants (g) First Mixing Second Mixing Low 1 g Each .times. 4
= 4 g 500 4,500 Concentration Intermediate 3 g Each .times. 4 = 12
g 500 4,500 Concentration High 10 g Each .times. 4 = 40 g 500 4,500
Concentration
[0053] As shown in Table 1, mixtures were made for the three types
of concentrations of model contaminants defined as low
concentration, intermediate concentration and high concentration.
With respect to the 5000 g of PET flakes, 1 g of each of the model
contaminants for a total of 4 g for the low concentration, 3 g of
each of the model contaminants for a total of 12 g for the
intermediate concentration, and 10 g of each of the model
contaminants for a total of 40 g for the high concentration were
ultimately present in the mixtures. In the low concentration
mixture, there was 0.02 parts by weight of each of the model
contaminants with respect to 100 parts by weight of the PET flakes.
In the intermediate concentration mixture, there was 0.06 parts by
weight of each of the model contaminants with respect to 100 parts
by weight of the PET flakes. In the high concentration mixture,
there was 0.20 parts by weight of each of the model contaminants
with respect to 100 parts by weight of the PET flakes.
[0054] Next, these three types of PET flakes contaminated with the
model contaminants at the low concentration, intermediate
concentration and high concentration were held at 50.degree. C. in
a hermetically sealed container for two weeks to force the model
contaminants to adsorb onto the PET flakes. Next, the PET flakes
contaminated with the model contaminants were remelted by an
extruder to make pseudo used PET pellets. By carrying out this
remelting process, the intrinsic viscosity of the pseudo used PET
pellets were lowered. In this regard, in order to raise the
intrinsic viscosity of the pseudo used PET pellets, namely in order
to increase the molecular weight of the pseudo used PET pellets,
solid phase polymerization was carried out inside a flow of
nitrogen gas under the conditions of 230.degree. C. for three
hours.
[0055] Next, in order to examine the reduction of contaminants due
to the purification process, analysis of the contamination level
was carried out for the PET flakes (denoted as "Flakes")
contaminated with the model contaminants, the pseudo used PET
pellets (denoted as "Pellets") and the pellets after solid phase
polymerization (denoted as "After Solid Phase Polymerization").
First, 1 g samples, namely the pseudo used PET flake mixture, the
pseudo used PET pellets and the compounded PET pellets were placed
in 5 ml test tubes, and then 1 ml of 1,1,1,3,3,3,-hexafluoro-iso-p-
ropanol was added to each sample. The samples were held at
60.degree. C. for 24 hours in order to expand the PET. Then, 2 ml
of iso-propanol was added, and after being held at 60.degree. C.
for 24 hours, the contaminants were extracted. Next, the extracts
were analyzed by a gas chromatography method using a FID detector.
The gas chromatograph was a HP5890 I I, and the column used a
SE10-30 m-0.32 mm i.D.-0.32 .mu.m film thickness. The measurement
accuracy was 0.4 ppm, and detection was not possible below 0.4 ppm.
The contamination levels are shown in Table 2.
2TABLE 2 Toluene Chlorobenzene n-Docosane Nonadecanol Contamination
Volatile Volatile Nonvolatile Nonvolatile Level Process Nonpolar
Polar Nonpolar Polar Low Flakes 20 43 25 18 Concentration Pellets
Not Detected 2.0 15 4.3 After Solid Phase Not Detected Not Detected
0.8 1.3 Polymerization Intermediate Flakes 63 98 43 75
Concentration Pellets Not Detected 6.3 28 37 After Solid Phase Not
Detected Not Detected 1.5 4.0 Polymerization High Flakes 89 156 85
250 Concentration Pellets Not Detected 9.2 42 50 After Solid Phase
Not Detected Not Detected 3.5 63 Polymerization Units: ppm
[0056] As shown in Table 2, toluene which is a volatile substance
was forced out due to heating up to a temperature above the melting
point (approximately 255.degree. C.) at the time of remelting in
the extruder, and could not be detected at the pelletization step.
Further, chlorobenzene which is a volatile substance was forced out
at the solid phase polymerization step (three hours at 230.degree.
C. in a flow of nitrogen gas), and could not be detected. The
n-docosane and the nonadecanol which are nonvolatile substances
remained even after solid phase polymerization.
[0057] B. Evaluation by Container Formation
[0058] Next, a description will be given for the formation of
containers. While carrying out mixing to form 0.10, 0.20, 0.30,
0.40 and 0.60 compounding ratios (weight of pseudo used PET
pellets/(weight of pseudo used PET pellets+weight of unused PET
pellets)) of the intermediate concentration pseudo used PET pellets
before the solid phase polymerization described in A and the unused
PET pellets, trial contaminated PET containers (resin weight: 32 g)
having a 500 ml volume were created by injection molding (this case
is denoted as "I"). The molding temperature was approximately
270.degree. C. The compounding conditions of the pellets at the
container molding time are shown in Table 3.
3TABLE 3 Pellet Compounding Conditions at Container Molding Time
Amount Amount of Added of Added Obtained Pseudo Unused Container
Amount of Each Contaminant Used PET PET Molding Added Per 5000 g of
Pseudo Compounding Pellets Pellets Weight Used PET Pellets Ratio
(g) (g) (g) (g) 0.10 3.2 28.8 32 3 g Each .times. 4 .times. 0.1 =
1.2 g 0.20 6.4 25.6 32 3 g Each .times. 4 .times. 0.2 = 2.4 g 0.30
9.6 22.4 32 3 g Each .times. 4 .times. 0.3 = 3.6 g 0.40 12.8 19.2
32 3 g Each .times. 4 .times. 0.4 = 4.8 g 0.60 19.2 12.8 32 3 g
Each .times. 4 .times. 0.6 = 7.2 g
[0059] Further, these compounding ratios (weight of pseudo used PET
pellets/(weight of pseudo used PET pellets+weight of unused PET
pellets)) are compounding ratios that correspond to the compounding
ratios (weight of recycled resin of used PET containers for foods
and beverages which has not undergone intrinsic viscosity
adjustment/(weight of recycled resin of used PET containers for
foods and beverages which has not undergone intrinsic viscosity
adjustment+weight of unused PET resin)) in the case of recycling
actual used PET containers.
[0060] Next, using only the low concentration, intermediate
concentration and high concentration pellets after solid phase
polymerization as shown in Table 2 (this case is denoted as "II"),
trial contaminated PET containers (resin weight: 32 g) having a 500
ml volume were created by injection molding.
[0061] Then, using the DLC film forming apparatus described above,
a DLC film was formed on the inner wall surfaces of the
contaminated PET containers created by I and II described above to
create DLC film coated containers having a 500 ml volume.
[0062] As for the method of forming the DLC film, the method of
applying high-frequency electric power to the bottom electrode 4
was used as an electric discharging method with acetylene used as
the source gas. Namely, in the state in which the shoulder portion
electrode 2, the body portion electrode 3 and the bottom portion
electrode 4 are electrically insulated from each other,
high-frequency electric power at 13.56 MHz was applied only to the
bottom portion electrode 4. The high-frequency electric power was
1300 W, the vacuum level was 0.05 torr (6.66 Pa), and the gas flow
rate was 31 cc/min.
[0063] The average thickness of the DLC film coated containers was
approximately 0.3 mm, the film thickness of the DLC film was
200.about.300 .ANG., and the amount of oxygen permeation for an
entire DLC film coated container was 0.003 ml/day/container.
Further, the amount of oxygen permeation in the PET containers
having the same 500 ml volume but no DLC film formed therein was
0.033 ml/day/container for an entire container.
[0064] Next, a description will be given for the contaminant
elution test for the above-described "contaminated PET containers"
and the "DLC film coated containers" which are contaminated PET
containers coated with a DLC film.
[0065] Each of the contaminated containers and the DLC film coated
containers was filled with 50 ml of
1,1,1,3,3,3,-hexafluoro-iso-propanol, and then mixing by shaking
was carried out at 60.degree. C. for 24 hours to expand the PET.
Next, 100 ml of iso-propanol was added, and mixing by shaking was
carried out at 60.degree. C. for 24 hours to extract the
contaminants. Then, after concentrating the 150 ml of extracted
liquid to 20 ml, analysis was carried out by a gas
chromatograph.
[0066] Table 4 shows the analysis results of the contaminants
extracted from the contaminated containers and the DLC film coated
containers for the case of I and II. Further, in Table 4,
n-docosane is denoted by "D", and nonadecanol is denoted by
"N".
4TABLE 4 Used DLC Film Molding Contamination Compounding
Contaminated Coated Contaminant Material Level Ratio PET Container
Container D I Intermediate 0.10 50 Not Detected Concentration D I
Intermediate 0.20 97 Not Detected Concentration D I Intermediate
0.30 120 Not Detected Concentration D I Intermediate 0.40
Moldability .DELTA. Moldability .DELTA. Concentration D I
Intermediate 0.60 Moldability x Moldability x Concentration D II
Low 1.00 16 Not Detected Concentration D II Intermediate 1.00 28
Not Detected Concentration D II High 1.00 72 Not Detected
Concentration N I Intermediate 0.10 43 Not Delected Concentration N
I Intermediate 0.20 102 Not Detected Concentration N I Intermediate
0.30 153 Not Detected Concentration N I Intermediate 0.40
Moldability .DELTA. Moldability .DELTA. Concentration N I
Intermediate 0.60 Moldability x Moldability x Concentration N II
Low 1.00 24 Not Delected Concentration N II Intermediate 1.00 56
Not Detected Concentration N II High 1.00 97 Not Detected
Concentration Units: .mu.g/500 ml PET Container
[0067] The detection limit was 10 .mu.g. In the case of I, the
polymerization degree of the pseudo used PET pellets went down, and
the intrinsic viscosity was lowered. Accordingly, in the case of
the compounding ratios 0.40 and 0.60 which contain a lot of these
pseudo used PET pellets having lowered intrinsic viscosity, the
container strength is not sufficient, and the container moldability
is also poor. When a compounding ratio of 0.40 is not exceeded, the
container will have sufficient strength, and the container
moldability will also be good. As shown in Table 4, among the cases
having good container moldability, both n-docosane and nonadecanol
were detected for all the contaminated PET containers. On the other
hand, in the DLC film coated containers, there was no detection of
either n-docosane or nonadecanol for any of the contamination
levels. In this way, by forming a DLC film on the inner wall
surface of PET containers, it is possible to effectively inhibit
the elution of contaminants from the PET containers. Further, both
toluene and chlorobenzene which are volatile substances were
reduced to nondetectable levels at the contaminated PET container
step as described above, and the extraction thereof from the
contaminated containers and the DLC film coated containers was not
detected.
[0068] From the facts given above, in the case where used PET is
recycled to manufacture containers again, by carrying out solid
phase polymerization to raise the polymerization degree of used
PET, it is possible for containers to use 100% used PET. However,
because a rise in manufacturing costs will accompany the carrying
out of solid phase polymerization of used PET, preferably used PET
resin which has not undergone solid phase polymerization is mixed
with unused PET resin to carry out container molding, and as a more
preferred state, the compounding ratio (weight of recycled resin of
used PET containers for foods and beverages which has not undergone
intrinsic viscosity adjustment/(weight of recycled resin of used
PET containers for foods and beverages which has not undergone
intrinsic viscosity adjustment+weight of unused PET resin)) should
be greater than 0 but less than 0.40. Preferably, the compounding
ratio should be greater than 0 but less than or equal to 0.30. When
considering the utilization factor of used PET and the performance
of PET containers for foods and beverages containing recycled
resin, the most preferred compounding ratio is greater than or
equal to 0.10 but less than or equal to 0.20.
Example Embodiment 2
[0069] Next, with reference to the case of II of Table 4, a
description will be given for the relationship between the oxygen
permeability of the DLC containers and the amount of elution of the
contaminants.
[0070] First, using the high concentration pellets after solid
phase polymerization, a contaminated PET container (Experiment
Number 1, no DLC film coating) having a 500 ml volume was created,
and by changing the above-described vapor deposition conditions for
the inner wall surface of the contaminated PET to form a DLC film
on the inner wall surfaces of contaminated PET containers, a
plurality of DLC containers (Experiment Numbers 2.about.9) having
different oxygen permeabilities were created.
[0071] As shown in Table 5, the oxygen permeability of the
contaminated PET (Experiment Number 1) in a state where a DLC film
was not formed was 0.033 ml/day/container. Further, the oxygen
permeabilities of the DLC containers (Experiment Numbers 2.about.9)
created by changing the vapor deposition conditions were
respectively 0.020 ml/day/container (Experiment Number 2), 0.015
ml/day/container (Experiment Number 3), 0.012 ml/day/container
(Experiment Number 4), 0.010 ml/day/container (Experiment Number
5), 0.008 ml/day/container (Experiment Number 6), 0.005
ml/day/container (Experiment Number 7), 0.003 ml/day/container
(Experiment Number 8), and 0.001 ml/day/container (Experiment
Number 9). Table 5 shows the results of analyzing the amount of
elution of nonadecanol using the same method as that of Example
Embodiment 1.
5TABLE 5 Amount of Oxygen Nonadecanol Permeability Elution
Experiment ml/Day/ .mu.g/500 ml Number Container PET Container 1
Not Having DLC Process 0.033 95 2 Having DLC Process 0.020 30 3
Having DLC Process 0.015 18 4 Having DLC Process 0.012 12 5 Having
DLC Process 0.010 Not Detected 6 Having DLC Process 0.008 Not
Detected 7 Having DLC Process 0.005 Not Detected 8 Having DLC
Process 0.003 Not Detected 9 Having DLC Process 0.001 Not
Detected
[0072] As shown in Table 5, in the contaminated PET (Experiment
Number 1) which was not formed with a DLC film and in the DLC film
coated containers (Experiment Numbers 2.about.4) which have an
oxygen permeability greater than or equal to 0.012
ml/day/container, eluted nonadecanol was detected, but in the DLC
film coated containers (Experiment Numbers 5.about.9) which have an
oxygen permeability less than or equal to 0.010 ml/day/container,
nonadecanol was not detected. Accordingly, it is understood that by
coating the DLC film so that the oxygen permeability in the DLC
coated containers is less than or equal to 0.010 ml/day/container,
it is possible to almost completely prevent elution of
contaminants.
[0073] By the facts described above, in contaminated PET
containers, one portion of contaminants will elute into the
container contents. Accordingly, contaminated PET containers can
not be reused in a state where only molding is carried out. In the
present invention, the judgment of whether or not the DLC film has
sufficient contaminant elution barrier properties was determined by
indicating the oxygen gas barrier properties of the entire
container, and when the oxygen permeability of contaminated PET
containers coated with a DLC film is less than or equal to 0.010
ml/day/container when converted to a 500 ml volume, it was
discovered that it is possible to almost completely prevent elution
of contaminants. In order to more completely prevent elution of
contaminants, it is more preferred that the oxygen permeability be
less than or equal to 0.005 ml/day/container when converted to a
500 ml volume. In order to make the oxygen permeability less than
or equal to 0.010 ml/day/container when converted to a 500 ml
volume which was discovered to make such fact possible, the
characteristics of the DLC film such as the composition and film
thickness and the like may be appropriately adjusted. However, in
any case, if the oxygen permeability is not made less than or equal
to 0.010 ml/day/container when converted to a 500 ml volume, the
container will not have sufficient contaminant elution barrier
properties.
[0074] From Example Embodiment 1 and 2, the DLC film coated PET
container for foods and beverages containing recycled resin
according to the present invention is a container molded from
molding material which is a mixture of resin of used PET containers
for foods and beverages and unused PET resin, wherein the
compounding ratio of the mixture is preferably greater than 0 but
less than 0.40, and wherein the oxygen permeability of the
container converted to a 500 ml PET container is preferably less
than or equal to 0.010 ml/day/container.
[0075] Further, the containers having a compounding ratio less than
0.40 of the example embodiments received almost no effects from
contained colored impurities at the time container molding was
carried out using resin of used PET containers for foods and
beverages.
* * * * *