U.S. patent application number 11/785749 was filed with the patent office on 2008-10-23 for integrally blow-moulded bag-in-container comprising an inner layer and an outer layer comprising energy absorbing additives, and preform for making it.
This patent application is currently assigned to INBEV S.A.. Invention is credited to Daniel Peirsman, Sarah Van Hove, Rudi Verpoorten.
Application Number | 20080258356 11/785749 |
Document ID | / |
Family ID | 39619001 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080258356 |
Kind Code |
A1 |
Van Hove; Sarah ; et
al. |
October 23, 2008 |
Integrally blow-moulded bag-in-container comprising an inner layer
and an outer layer comprising energy absorbing additives, and
preform for making it
Abstract
The present invention relates to an integrally blow-moulded
bag-in-container and preform for blow-moulding the
bag-in-container. An inner layer and an outer layer are used,
wherein the preform forms a two-layer container upon blow-moulding,
and wherein the obtained inner layer of said container releases
from the thus obtained outer layer upon introduction of a gas at a
point of interface between the two layers. At least one of the
inner and outer layers includes at least one additive allowing both
inner and outer layers to reach their respective blow-moulding
temperatures substantially simultaneously.
Inventors: |
Van Hove; Sarah; (Boutersem,
BE) ; Peirsman; Daniel; (Bornem, BE) ;
Verpoorten; Rudi; (Lommel, BE) |
Correspondence
Address: |
Levy & Grandinetti
P.O . Box 18385
Washington
DC
20036
US
|
Assignee: |
INBEV S.A.
Leuven
BE
|
Family ID: |
39619001 |
Appl. No.: |
11/785749 |
Filed: |
April 19, 2007 |
Current U.S.
Class: |
264/535 ;
425/392 |
Current CPC
Class: |
B29K 2023/12 20130101;
B29C 49/22 20130101; B29K 2023/086 20130101; Y10T 428/1352
20150115; B29B 2911/14326 20130101; B29B 11/14 20130101; B29C
49/4273 20130101; B29K 2105/0032 20130101; B29L 2031/712 20130101;
B29B 2911/14066 20130101; B65D 83/0055 20130101; B29C 2045/1601
20130101; B29K 2023/06 20130101; B29C 49/221 20130101; B29K 2077/00
20130101; B29B 2911/14646 20130101; B29C 45/1684 20130101; B29C
49/06 20130101; B29K 2105/258 20130101; B29K 2067/00 20130101; B29B
2911/14333 20130101; B29B 2911/14113 20130101; B29B 2911/1444
20130101; B29K 2105/005 20130101; B29B 2911/14093 20130101; B29C
2035/0822 20130101; B29C 49/6418 20130101; B29B 11/08 20130101;
B29B 2911/14053 20130101; B29K 2067/046 20130101; B29C 35/0805
20130101; B65D 23/02 20130101; B29K 2023/065 20130101; B29B
2911/1414 20130101; B29B 2911/1408 20130101 |
Class at
Publication: |
264/535 ;
425/392 |
International
Class: |
B29C 49/00 20060101
B29C049/00; B28B 21/00 20060101 B28B021/00 |
Claims
1. A preform for blow-moulding a bag-in-container, comprising: an
inner layer and an outer layer, wherein said preform forms a two
layer container upon blow-moulding, and wherein the obtained inner
layer of said container releases from the obtained outer layer upon
introduction of a gas at a point of interface between said two
layers; and at least one of said inner and outer layers includes at
least one additive allowing both inner and outer layers to reach
their respective blow-moulding temperatures substantially
simultaneously upon heating them together in a single oven.
2. The preform according to claim 1, wherein the at least one
additive is selected from the group of energy absorbing additives
and colorants.
3. The preform according to claim 2, wherein the energy absorbing
additive is a member being selected from the group consisting of
carbon black, graphite, diamond dust, diazonium salts, sulphonium
salts, sulfoxonium salts, and iodonium salts.
4. The preform according to claim 1, wherein the inner and outer
layers consist of a different materials each selected from PET,
PEN, PTT, PA, PP, PE, HDPE, EVOH, PGAc, PLA, and copolymers or
blends thereof.
5. The preform according to claim 1, wherein the at least one point
of interface is a vent in the shape of a wedge with the broad side
at the level of the opening thereof and getting thinner as it
penetrates deeper into the vessel, until the inner and outer layers
meet to form an interface.
6. The preform according to claim 1, wherein more than one vent is
distributed around the lip of the preform's mouth.
7. The preform according to claim 1, wherein the inner and outer
layers of the preform are connected by an interface throughout
substantially the whole inner surface of the outer layer.
8. The preform according to claim 1, wherein the inner and outer
layers of the preform are separated over a substantial area of the
preform's body by a gap containing air and which is in fluid
communication with at least one interface vent.
9. The preform according to claim 1, consisting of an assembly of
two separate inner and outer preforms fitted into one another.
10. The preform according to claim 1, including an integral preform
obtained by injection moulding one layer on top of the other.
11. A process for producing a bag-in-container comprising the
following steps: providing a polymer preform having an inner layer
and an outer layer, wherein said preform forms a two layer
container upon blow-moulding, and wherein the obtained inner layer
of said container releases from the obtained outer layer upon
introduction of a gas at a point of interface between said two
layers; and at least one of said inner and outer layers includes at
least one additive allowing both inner and outer layers to reach
their respective blow-moulding temperatures substantially
simultaneously upon heating them together in a single oven heating
said preform to blow-moulding temperature in a single oven; and
blow-moulding the thus heated preform to form a bag-in-container;
wherein the type and amount of additives in at least one of the
inner and outer layers of said preform are such that said two
layers reach their respective blow-moulding temperatures
substantially simultaneously.
12. The process according to claim 11, wherein the at least one
additive is selected from the group of energy absorbing additives
and colorants.
13. The process according to claim 12, wherein the energy absorbing
additive is a ember being selected from the group of consistently
carbon black, graphite, diamond dust, diazonium salts, sulphonium
salts, sulfoxonium salts, and iodonium salts.
14. The process according to claim 11, wherein the inner and outer
layers include the same or different materials each selected from
PET, PEN, PTT, PA, PP, PE, HDPE, EVOH, PGAc, PLA, and copolymers or
blends thereof.
15. The process according to claim 11, wherein the oven comprises
infrared lamps.
16. A bag-in-container made by the process comprising: providing a
polymer preform having an inner layer and an outer layer, wherein
said preform forms a two layer container upon blow-moulding, and
wherein the obtained inner layer of said container releases from
the obtained outer layer upon introduction of a gas at a point of
interface between said two layers; and at least one of said inner
and outer layers includes at least one additive allowing both inner
and outer layers to reach their respective blow-moulding
temperatures substantially simultaneously upon heating them
together in a single oven heating said preform to blow-moulding
temperature in a single oven; and blow-moulding the thus heated
preform to form a bag-in-container; wherein the type and amount of
additives in at least one of the inner and outer layers of said
preform are such that said two layers reach their respective
blow-moulding temperatures substantially simultaneously.
17. A process comprising using energy absorbing additives or
colorants for the substantially simultaneous heating to the
respective blow-moulding temperatures of the inner and outer layers
of a preform for blow-moulding a bag-in-container.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to new developments
in dispensing bag-in-containers and, in particular, to integrally
blow-moulded bag-in-containers made of different materials. It also
relates to a method for producing the bag-in-containers and, in
particular, to preforms used for their production, as well as a
method for producing said preform.
BACKGROUND OF THE INVENTION
[0002] Bag-in-containers, also referred to as bag-in-bottles or
bag-in-boxes depending on the geometry of the outer vessel, all
terms considered herein as being comprised within the meaning of
the term bag-in-container, are a family of liquid dispensing
packaging consisting of an outer container comprising an opening to
the atmosphere--the mouth--and which contains a collapsible inner
bag joined to said container and opening to the atmosphere at the
region of said mouth. The system must comprise at least one vent
fluidly connecting the atmosphere to the region between the inner
bag and the outer container in order to control the pressure in
said region to squeeze the inner bag and thus dispense the liquid
contained therein.
[0003] Traditionally, bag-in-containers were--and still
are--produced by independently producing an inner bag provided with
a specific neck closure assembly and a structural container
(usually in the form of a bottle). The bag is inserted into the
fully formed bottle opening and fixed thereto by means of the neck
closure assembly, which comprises one opening to the interior of
the bag and vents fluidly connecting the space between bag and
bottle to the atmosphere. Examples of such constructions can be
found inter alia in U.S. Pat. No. 3,484,011, U.S. Pat. No.
3,450,254, U.S. Pat. No. 4,330,066, and U.S. Pat. No. 4,892,230.
These types of bag-in-containers have the advantage of being
reusable, but they are very expensive and labour-intensive to
produce.
[0004] More recent developments focused on the production of
"integrally blow-moulded bag-in-containers" thus avoiding the
labour intensive step of assembling the bag into the container, by
blow-moulding a polymeric multilayer preform into a container
comprising an inner layer and an outer layer, such that the
adhesion between the inner and the outer layers of the thus
produced container is sufficiently weak to readily delaminate upon
introduction of a gas at the interface. The "inner layer" and
"outer layer" may each consist of a single layer or a plurality of
layers, but can in any case readily be identified, at least upon
delamination. Said technology involves many challenges and many
alternative solutions were proposed.
[0005] The multilayer preform may be extruded or injection moulded
(cf. U.S. Pat. No. 6,238,201, JPA-10128833, JPA11010719,
JPA9208688, U.S. Pat. No. 6,649,121. When the former method is
advantageous in terms of productivity, the latter is preferable
when wall thickness accuracy is required, typically in containers
for dispensing beverage.
[0006] The formation of the vents fluidly connecting the space or
interface between bag and bottle to the atmosphere remains a
critical step in integrally blow-moulded bag-in-containers and
several solutions were proposed in e.g., U.S. Pat. No. 5,301,838,
U.S. Pat. No. 5,407,629, JPA5213373, JPA-8001761, EPA1356915, U.S.
Pat. No. 6,649,121, JPA10180853.
[0007] One redundant problem with integrally blow-moulded
bag-in-containers is the choice of materials for the inner and
outer layers which must be selected according to strict criteria of
compatibility in terms of processing on the one hand and, on the
other hand, of incompatibility in terms of adhesion. These criteria
are sometimes difficult to fulfil in combination as illustrated
below. This problem does not arise in the field of blow-moulding
co-layer plastic containers, wherein the adhesion between layers is
maximized in order to avoid delamination, because best adhesion is
obtained with similar materials, which generally have similar
thermal properties. Consequently, finding materials being
compatible in terms of both processing and adhesion as for the
fabrication of co-layer containers is generally less problematic
than finding materials being compatible in terms of processing and
incompatible in terms of adhesion as for the fabrication of
bag-in-containers.
[0008] Addressing processing compatibility, EPA1356915 and U.S.
Pat. No. 6,649,121 proposed that the melting temperature of the
outer layer should be higher than the one of the inner layer in
order to allow production of integral preforms by injection
moulding the outer layer first, followed by injecting thereover the
inner layer. Examples of materials for the outer layer given by the
authors include PET and EVOH, whilst polyethylene is given as an
example for the inner layer. Though this materials selection could
result advantageous for the injection moulding production of the
preforms, it is far from optimal for the blow-moulding step since
polyethylene and PET are characterized by quite different
blow-moulding temperatures. Again, in U.S. Pat. No. 6,238,201 a
method is described including co-extruding a two layer parison
followed by blow-moulding said parison into a bag-in-container
wherein the outer layer preferably comprises an olefin and the
inner layer an amorphous polyamide.
[0009] Concerning the materials choice for a weak interfacial
adhesion required for ensuring proper delamination of the inner
layer from the outer layer upon use, mention is made in
JPA-2005047172 of "mutually non-adhesive synthetic resins." In the
review of the background art in U.S. Pat. No. 5,921,416 the use of
release layers interleaved between inner and outer layers, forming
three- or five-layer structures is mentioned. An example of such
construction is described in U.S. Pat. No. 5,301,838 which
discloses a complex five layer preform comprising three PET layers
interleafed by two thin layers of a material selected from the
group of EVOH, PP, PE, PA6. Here again, beside the complexity
involved with the production of such preforms, substantial
differences in blow-moulding temperatures characterize these
different materials.
[0010] Alternatively and surprisingly it has been discovered that
excellent delamination results between the inner and outer layers
can be obtained also with preforms wherein both inner and outer
layers consist of the same material. Similar results were obtained
both with preform assemblies as well as with integral preforms. In
the case of integral, over-moulded preforms, it is generally
believed that better results are obtained with semi-crystalline
polymers.
[0011] The same polymer is considered in contact on either side of
the interface between the inner and outer layers in the following
cases: [0012] inner and outer layers consist of the same material
(e.g., PET.sub.innerPET.sub.outer, regardless of the specific grade
of each PET); or [0013] the inner and outer layers consist of a
blend or copolymer having at least one polymer in common, provided
said polymer in common is at the interface, whilst the differing
polymer is substantially absent of said interface (e.g., (0.85
PET+0.15 PA6).sub.inner-(0.8 PET+0.2 PE).sub.outer. The presence in
a layer of low amounts of additives is not regarded as rendering
the material different, so far as they do not alter the interface
substantially.
[0014] Although in case the same material is used for the inner and
outer layers, there is no difference in blow-moulding temperature
between layers, the heating rate of the two layers can be
substantially different due to the wide difference in thicknesses
between the inner and outer layers. Moreover, the inner layer is
sheltered by the thick, outer layer from the IR-radiation of the
IR-oven usually used to bring the preform to blow-moulding
temperature. It follows that even for materials having little or no
difference in blow-moulding temperature, there can be a problem to
heat up simultaneously both layers to their process
temperatures.
[0015] In order to overcome the problem of different blow-moulding
temperatures or heating rates of the materials forming the inner
and outer layers of blow-moulded multilayer containers, the
different preform components may be heated separately in different
ovens to heat them at their respective blow-moulding temperature
(cf. e.g., JPA57174221). This solution, however, is expensive in
terms of equipment and space and does not apply to integral
preforms, which inner and outer layers cannot be separated.
[0016] The use of energy absorbing additives in preforms for
blow-moulding monolayer containers has been proposed for shortening
the heating stage and thus saving energy in, e.g., U.S. Pat. No.
5,925,710, U.S. Pat. No. 6,503,586, U.S. Pat. No. 6,034,167, U.S.
Pat. No. 4,250,078, U.S. Pat. No. 6,197,851, U.S. Pat. No.
4,476,272, U.S. Pat. No. 5,529,744, and the likes. The use of
energy absorbing additives has also been proposed in the inner
layer of blow-moulded co-layer containers (i.e., not meant to
delaminate) to compensate for the greater strain undergone by the
inner layer compared with the outer layer during blow-moulding
operation. In co-layer containers it is very important that the
inner layer is allowed to stretch sufficiently to contact and
adhere to the outer layer over substantially the whole of their
interface. The inner layer containing the energy absorbing
additives is thus heated to a higher temperature than the outer
layer and can be stretched further to adhere to the outer
layer.
[0017] The above considerations do not apply in the field of
bag-in-containers, since a good adhesion between the inner and
outer layers is exactly what is to be avoided. Furthermore,
preforms for the production of integrally blow-moulded
bag-in-containers clearly differ from preforms for the production
of blow-moulded co-layered containers, wherein the various layers
of the container are not meant to delaminate, in the thickness of
the layers. A bag-in-container is comprised of an outer structural
envelope containing a flexible, collapsible bag. It follows that
the outer layer of the container is substantially thicker than the
inner bag. This same relationship can of course be found in the
preforms as well, which are characterized by an outer layer being
substantially thicker than the inner layer. This has a detrimental
effect on the heating efficacy of IR-lamps on heating the inner
layer, since the latter is separated from the IR-lamps by the thick
wall of the outer layer.
[0018] It follows from the foregoing that there remains a need in
the art for solutions for compensating the difference in
blow-moulding temperatures and heating rates between the "mutually
non-adhesive synthetic resins" (cf. JP2005047172) of the inner and
outer layers of a preform for the production of integrally
blow-moulded bag-in-containers.
SUMMARY OF THE INVENTION
[0019] The present invention is defined in the appended independent
claims. Preferred embodiments are defined in the dependent claims.
In particular the present invention relates to a preform for
blow-moulding a bag-in-container. An inner layer and an outer layer
are used, wherein said preform forms a two layer container upon
blow-moulding, and wherein the obtained inner layer of the
container releases from the thus obtained outer layer upon
introduction of a gas at a point of interface between said two
layers. At least one of the inner and outer layers includes at
least one additive allowing both inner and outer layers to reach
their respective blow-moulding temperatures substantially
simultaneously when heated together in a single oven.
[0020] It also concerns a process for producing a bag-in-container
from the above preform and a bag-in-container thus obtained.
Finally the present invention relates to the use of energy
absorbing additives for the substantially simultaneous heating to
the respective blow-moulding temperatures of the inner and outer
layers of a preform for blow-moulding a bag-in-container.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1A is a schematic cross-sectional representation of a
first embodiment of a preform according to the present invention
and the bag-in-container obtained after blow-moulding thereof.
[0022] FIG. 1B is a schematic cross-sectional representation of a
second embodiment of a preform according to the present invention
and the bag-in-container obtained after blow-moulding thereof.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Referring now to appended FIGS. 1A and 1B, there is
illustrated an integrally blow-moulded bag-in-container (2) and a
preform (1)&(1') for its manufacturing. The preform (1)
comprises an inner layer (11) and an outer layer (12) joined at
least at the level of the neck region (6) by an interface (shown on
the right hand side). The region between inner and outer layers
(11) and (12) may either consist of an interface (14) wherein the
two layers are substantially contacting each other, or comprise a
gap (14') in fluid communication with at least one vent (3) opening
to the atmosphere in (4).
[0024] Many vent geometries have been disclosed, and it is not
critical which geometry is selected. It is preferred, however, that
the vent be located adjacent to, and oriented coaxially with said
preform's mouth (5) as illustrated in FIG. 1. More preferably, the
vents have the shape of a wedge with the broad side at the level of
the opening (4) thereof and getting thinner as it penetrates deeper
into the vessel, until the two layers meet to form an interface
(14) at least at the level of the neck region. This geometry allows
for a more efficient and reproducible delamination of the inner bag
upon use of the bag-in-container. The container may comprise one or
several vents evenly distributed around the lip of the
bag-in-container's mouth. Several vents are advantageous as they
permit the interface of the inner and outer layers (21) and (22) of
the bag-in-container (2) to release more evenly upon blowing
pressurized gas through said vents. Preferably, the preform
comprises two vents opening at the vessel's mouth lip at
diametrically opposed positions. More preferably, three, and most
preferably, at least four vents open at regular intervals of the
mouth lip.
[0025] The preform may consists of an assembly of two separate
preforms (11) and (12) produced independently from one another and
thereafter assembled such that the inner preform (11) fits into the
outer preform (12). This solution allows for greater freedom in the
design of the neck and vents. Alternatively, it can be an integral
preform obtained by injection moulding one layer on top of the
other. The latter embodiment is advantageous over the assembled
preform in that it comprises no assembly step and one production
station only is required for the preform fabrication. On the other
hand, the design of the vents in particular is restricted by this
process.
[0026] A preform for the production of a typical 8 liter
bag-in-container for dispensing beer has an outer layer (12) about
210 mm thick, preferably 36 mm, most preferably 45 mm thick, whilst
the inner layer generally is about 0.33 mm thick, preferably 0.31.5
mm, most preferably 0.51 mm thick
[0027] Preferred materials for the inner and outer layers of the
preform and bag-in-container of the present invention are pairs of
different materials selected from the group of polyesters like PET,
PEN, PTT, PTN; polyamides like PA6, PA66, PA11, PA12; polyolefins
like PE, PP; EVOH; biodegradable polymers like polyglycol acetate
(PGAc), polylactic acid (PLA); and copolymers and blends thereof.
Materials like PET or PEN should optimally be heated before
blow-moulding, whilst polyolefins and polyamides should be heated.
In order to allow for the substantially simultaneous heating to the
respective process temperatures of the resins of the inner and
outer layers of the preform using a single oven, energy absorbing
additives are added to the resin having highest process
temperature. It is, however, also possible that both layers
comprise energy absorbing additives of different nature and/or in
different amounts, as long as the time required to arrive at the
respective process temperatures of the materials of the inner and
outer layers is substantially the same.
[0028] The additives useful in the present invention The additives
that can be used in the present invention may be any compound that
selectively absorbs radiation in the wavelength region of 500 to
2000 nm and which is preferably sufficiently fine not to be visible
to the eye. They comprise energy absorbing additives and colorants.
Examples of energy absorbing additives include but are not limited
to carbon black, graphite, diamond dust, diazonium salts,
sulphonium salts (e.g., triphenylsulphonium bromide), sulfoxonium
salts, odonium salts, etc.
[0029] The amount of additive present in a layer depends on the
additive itself and on the resins used for the inner and outer
layers. A larger amount may impair stretchability of the
layers.
[0030] The two layers (11) and (12) of the preform may be connected
by an interface (14) throughout substantially the whole inner
surface of the outer layer. Inversely, they may be separated over a
substantial area of the preform's body by a gap (14) containing air
and which is in fluid communication with at least one interface
vent (3). The latter embodiment is easier to realize when using a
preform assembly designed such that the inner preform is firmly
fixed to the outer preform at the neck region (6) and a substantial
gap (14) may thus be formed between inner and outer layers (11) and
(12).
[0031] The bag-in-container (2) of the present invention can be
obtained by providing a preform as described above, at least one
layer of which comprising energy absorbing additives; bringing each
layer of said preform to their respective blow-moulding
temperatures; fixing the thus heated preform at the level of the
neck region with fixing means in the blow-moulding tool; and
blow-moulding the thus heated preform to form a bag-in-container,
wherein, the type and amount of energy absorbing additives
comprised in at least one of the inner and outer layers of said
preform are such that said two layers reach their respective
blow-moulding temperatures substantially simultaneously.
[0032] The inner and outer layers (21) and (22) of the thus
obtained bag-in-container are connected to one another by an
interface (24) over substantially the whole of the inner surface of
the outer layer. Said interface (24) is in fluid communication with
the atmosphere through the vents (3), which maintained their
original geometry through the blow-moulding process since the neck
region of the preform where the vents are located is held firm by
the fixing means and is not stretched during blowing.
[0033] It is essential that the interface (24) between inner and
outer layers (21) and (22) releases upon blowing pressurized gas
through the vents in a consistent and reproducible manner. The
success of said operation depends on a number of parameters, in
particular, on the interfacial adhesive strength, the number,
geometry, and distribution of the vents, and on the pressure of the
gas injected. The interfacial strength is of course a key issue and
can be modulated by the choice of the material for the inner and
outer layers, and by the process parameters during blow-moulding.
The pressure-time-temperature window used is of course of prime
importance and greatly depends on the materials selected for the
inner and outer layers.
[0034] Excellent results can be obtained if the blow-moulding
process is carried out on a preform as described above, of the type
wherein a gap containing air separates the inner and outer layers
over a substantial area of the preform's body and wherein said gap
is in fluid communication with at least one interface vent and
wherein, [0035] in a first stage, a gas is blown into the space
defined by the inner layer to stretch the preform, whilst the air
in the gap separating the preform inner and outer layers is
prevented from being evacuated by closing said at least one preform
interface vent with a valve located in the fixing means; and [0036]
in a second stage, when the air pressure building up in said gap
reaches a preset value, the valve opens thus allowing evacuation of
the air enclosed in the gap.
[0037] By this method, the inner layer is prevented from entering
into contact with the outer layer by the air cushion enclosed
within the gap separating the two layers when their respective
temperatures are the highest. As stretching proceeds, the gap
becomes thinner and air pressure within the gap increases. When the
pressure reaches a preset value, the valve closing the vent opening
releases, the air is ejected, and the inner layer is permitted to
contact the outer layer and form an interface therewith at a stage
where their respective temperatures have dropped to a level where
adhesion between the layers cannot build up to any substantial
level.
EXPERIMENTAL EXAMPLES
[0038] The following examples demonstrate the benefits of the
present invention. Preforms comprising an inner and outer layers
made of different materials were heated in an oven comprising six
IR lamps. The heating conditions were maintained constant for all
the tests. The temperatures, T.sub.inner and T.sub.outer, of the
inner and outer layers were measured after residence in the oven
and the preforms were then blow-moulded with a blow pressure of 10
bar in a mould set a temperature of 83.degree. C. Table 1 below
lists the measured temperatures of the inner and outer layers,
comments on blow-mouldability, and indicates the values of the
delamination pressure.
[0039] The delamination pressure was determined as follows. The
interface vents of an empty bag-in-container obtained as described
above are connected to a source of pressurized air. Air is injected
through the vents at a constant pressure and the interface between
inner and outer layers is observed; the pressure is increased until
delamination pressure is reached. Delamination pressure is defined
as the pressure at which the inner bag separates from the outer
layer over the whole of their interface and collapses. The surfaces
of the thus separated layers are examined for traces of bonding.
Preferred results are a low delamination pressure, of the order of
above 0.3 to 0.9 bar overpressure, with no traces of bonding.
* * * * *