U.S. patent application number 11/785747 was filed with the patent office on 2008-10-23 for integrally blow-moulded bag-in-container having interface vents opening to the atmosphere at location adjacent to bag's mouth; preform for making it; and processes for producing the preform and bag-in-container.
This patent application is currently assigned to INBEV S.A.. Invention is credited to Sarah Van Hove, Daniel Peirsman, Rudi Verpoorten.
Application Number | 20080257846 11/785747 |
Document ID | / |
Family ID | 39638573 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080257846 |
Kind Code |
A1 |
Hove; Sarah Van ; et
al. |
October 23, 2008 |
Integrally blow-moulded bag-in-container having interface vents
opening to the atmosphere at location adjacent to bag's mouth;
preform for making it; and processes for producing the preform and
bag-in-container
Abstract
The invention is an integrally blow-moulded bag-in-container (2)
and preform (1) for making it The bag-in-container (2) has an inner
layer (21) forming the bag and an outer layer (22) forming the
container, and a mouth (5) fluidly connecting the volume defined by
the bag to the atmosphere. The container further has at least one
interface vent (3) fluidly connecting the interface (14) between
inner and outer layers to the atmosphere, wherein the at least one
vent (3) runs parallel to the interface between inner and outer
layers (21) (22) and opens to the atmosphere at a location (4)
adjacent to, and oriented coaxially with the bag-in-container's
mouth (5). Processes for manufacturing a preform and a
bag-in-container as defined above are defined too.
Inventors: |
Hove; Sarah Van; (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: |
39638573 |
Appl. No.: |
11/785747 |
Filed: |
April 19, 2007 |
Current U.S.
Class: |
215/12.1 ;
264/267; 264/513 |
Current CPC
Class: |
B29B 2911/14066
20130101; B29K 2023/065 20130101; B29K 2067/046 20130101; B29B
2911/14113 20130101; B29L 2031/712 20130101; B29B 2911/14333
20130101; B29K 2105/258 20130101; B29B 2911/1408 20130101; B29K
2077/00 20130101; B29C 49/06 20130101; B65D 23/02 20130101; B29B
2911/14053 20130101; B29K 2101/12 20130101; B65D 83/0055 20130101;
B29B 2911/1442 20130101; B29C 45/1684 20130101; Y10S 215/902
20130101; B29C 2049/0089 20130101; B29B 2911/14093 20130101; B29L
2009/00 20130101; B29B 11/08 20130101; B29K 2023/086 20130101; B29K
2023/12 20130101; B29C 2035/0822 20130101; B29C 49/0073 20130101;
B29B 2911/1444 20130101; B29C 49/221 20130101; B29C 2049/222
20130101; B29K 2067/00 20130101; B29B 11/14 20130101; B29C 49/22
20130101; B29B 2911/1414 20130101; B29B 2911/14326 20130101; B29K
2023/06 20130101 |
Class at
Publication: |
215/12.1 ;
264/267; 264/513 |
International
Class: |
A47J 41/02 20060101
A47J041/02; B29C 45/14 20060101 B29C045/14; B29C 49/02 20060101
B29C049/02 |
Claims
1. An integrally blow-moulded bag-in-container (2) comprising: an
inner layer forming the bag and an outer layer forming the
container, and a mouth fluidly connecting the volume defined by the
bag to the atmosphere, said container having at least one interface
vent fluidly connecting the interface between inner and outer
layers to the atmosphere. said at least one vent runs parallel to
the interface between inner and outer layers and opens to the
atmosphere at a location adjacent to, and oriented approximately
coaxially with said bag-in-container's mouth.
2. The bag-in-container according to claim 1, wherein the inner and
outer layers are of different materials.
3. The bag-in-container according to claim 1, wherein the inner and
outer layers are of the same material.
4. The bag-in-container according to claim 1, wherein the inner and
outer layer consist of a material selected from PET, PEN, PTT, PA,
PP, PE, HDPE, EVOH, PGAc, PLA, and copolymers or blends
thereof.
5. The bag-in-container according to claim 1, wherein the at least
one vent is in 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 inner and outer layers
meet to form an interface.
6. The bag-in-container according to claim 1, wherein more than one
vent is distributed around the lip of the bag-in-container's
mouth.
7. A preform for blow-moulding a bag-in-container according to
claim 1, wherein said preform includes an inner layer and an outer
layer, and a body, a neck region, and a mouth fluidly connecting
the space defined by said inner layer to the atmosphere, wherein
said inner and outer layers are connected to one another by an
interface at least at the level of the neck region, said preform
includes at least one interface vent running parallel to said
interface and opening to the atmosphere at a location adjacent to,
and oriented coaxially with said preform's mouth.
8. The preform according to claim 7, wherein the inner and outer
layers consist of different materials.
9. The preform according to claim 7, wherein the inner and outer
layers consist of the same material.
10. The preform according to claim 7, wherein the inner and outer
layers consist of a material selected from PET, PEN, PTT, PA, PP,
PE, HDPE, EVOH, PGAc, PLA, and copolymers or blends thereof.
11. The preform according to claim 7, wherein the at least one vent
is 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.
12. The preform according to claim 7, wherein more than one vent is
distributed around the lip of the preform's mouth.
13. The preform according to claim 7, wherein the inner and outer
layers of the preform are connected by an interface throughout
substantially the whole inner surface of the outer layer.
14. The preform according to claim 7, 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.
15. The preform according to claim 7, having an assembly of two
separate inner and outer preforms fitted into one another.
16. The preform according to claim 7, having an integral preform
obtained by injection moulding one layer on top of the other.
17. A method for producing a bag-in-container having an inner layer
forming the bag and an outer layer forming the container, and a
mouth fluidly connecting the volume defined by the bag to the
atmosphere, said container having at least one interface vent
fluidly connecting the interface between inner and outer layers to
the atmosphere, said at least one vent runs parallel to the
interface between inner and outer layers and opens to the
atmosphere at a location adjacent to, and oriented approximately
coaxially with said bag-in-container's mouth, comprising the
following steps: providing a preform having an integral preform
obtained by injection moulding one layer on top of the other;
bringing said preform to blow-moulding temperature; fixing the
heated preform at the level of the neck region with fixing means in
the blow-moulding tool; and blow-moulding the heated preform to
form a bag-in-container.
18. The method according to claim 17 wherein the preform consists
of an assembly of two separate inner and outer preforms fitted into
one another.
19. The method according to claim 17, 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, and wherein the
blow-moulding operation further comprises the following two stages:
feeding a gas in a first stage 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 said fixing means; and opening said valve in a
second stage, when the air pressure building up in said gap reaches
a preset value, thus allowing evacuation of the air enclosed in the
gap.
20. A method for manufacturing a preform, having an integral
preform obtained by injection moulding one layer on top of the
other, comprising the following steps: injection moulding the
preform's inner layer onto a core; injection moulding the preform's
outer layer onto the inner layer; and extracting the thus formed
preform from the core; wherein said core is provided at the base
thereof with at least one pin suitable for forming an interface
vent running parallel to the interface between said first and
second layers and opening to the atmosphere at a location adjacent
to, and oriented approximately coaxially with the preform's
mouth.
21. The method according to claim 20, wherein the at least one pin
is in the shape of a wedge with the broad side at the level of
where it is connected to the core's base.
22. The method according to claim 20, wherein more than one pin is
distributed around the core.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to new developments
in dispensing bag-in-containers and, in particular, to the
interface vents design which allows control of the pressure at the
interface between an inner layer (the bag) and an outer layer (the
container) of said bag-in-container, in order to separate the inner
layer from the outer layer and collapse the inner bag. It also
relates to a method for producing said 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, JPA10128833, 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] 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
preform as well, which are characterized by an inner layer being
substantially thinner than the outer layer. Moreover, in some
cases, the preform already comprised vents which are never present
in preforms for the production of co-layered containers (cf.
EPA1356915).
[0007] One redundant problem with integrally blow-moulded
bag-in-containers is the formation of the interface vents. Several
solutions were proposed wherein the vent was formed after the
bag-in-container was blow-moulded, as in U.S. Pat. No. 5,301,838,
U.S. Pat. No. 5,407,629, JPA5213373, JPA8001761. This approach has
of course the disadvantages that it involves an additional
production step, and the danger of piercing the bag. Indeed these
solutions have in common the formation of a hole normal to the
outer container's wall and great accuracy is required not to
degrade the inner layer's wall.
[0008] In EPA1356915 and U.S. Pat. No. 6,649,121, the preform is
formed by injection moulding the outer layer first, followed by
injection moulding the inner layer over the outer layer. During
injection moulding of the layers, ventilation holes normal to the
outer layer's wall are formed with protruding pins, which are flush
with the inner surface of the thus obtained outer layer. The
over-injected inner layer is not affected by the pins and this
method solves the problem associated with the risk of damaging the
inner bag during vents formation. The ventilation holes must be
positioned close to the region of the container's mouth in an area
of no or little stretching during the blow-moulding operation.
[0009] The venting holes described in EPA1356915 and U.S. Pat. No.
6,649,121, however, are not suitable for being connected to a
source of pressurized gas to force delamination and squeezing of
the inner bag. Furthermore, the inner and outer layers are little
or not stretched in the region close to the container's mouth
resulting in thicker and more rigid walls in this region than in
the container's body. Consequently, a higher pressure would be
required to delaminate the inner from the outer layers by blowing
compressed air through the vents in a direction normal to the
interface, as required in beg-in-containers for dispensing beverage
like beer and sodas.
[0010] JPA10180853 discloses an integrally blow-moulded
bag-in-container, wherein the preform consists of an assembly of an
inner preform fitted into an outer preform such as to have a cavity
transverse to the outer container's wall at a location very close
to the preform assembly's mouth. Upon blow-moulding, said vent is
maintained in the thus produced bag-in-container. It should be
noted that the thickness of the preform's walls disclosed in
JPA10180853 varies locally which can lead to serious processing and
reproducibility problems of the final bag-in-container upon
blow-moulding.
[0011] In order to optimize delamination of the inner and outer
layers upon blowing pressurized gas into the vents, said vents
should preferably run parallel to the interface between the two
layers to provide a wedge effect. In the solutions proposed in the
prior art relating to integrally blow-moulded bag-in-containers
However, the vents run perpendicular to the interface and open to
the atmosphere through a hole across, and normal to the outer
container's wall, therefore providing no wedge effect and thus
reducing the efficacy and reproducibility of the delamination of
the inner bag from the outer container.
[0012] Bag-in-containers for beverage, like beer or sodas are
usually positioned in a specially designed appliance comprising a
dispensing passage to be connected to the mouth opening of the
inner bag and a source of pressurized gas (generally air) to be
connected to the vents opening(s). For reasons of compactness of
the appliance, the vents design is restricted and should preferably
open to the atmosphere at a location adjacent to the
bag-in-container's mouth and oriented along the same axis as the
latter, so as to allow all the piping to be bundled together. Such
design follows the traditional beer keg interface in this regard,
which is of course an advantage as it allows the replacement of a
traditional keg by an integrally blow-moulded bag-in-container,
without having to change the dispensing appliance.
[0013] It follows from the foregoing that there remains a need in
the art for an integrally blow-moulded bag-in-container dispense
package that allows optimization of the delamination of the inner
bag from the outer container upon injection of a pressurized gas at
the interface thereof and, at the same time, which can be used with
the existing dispensing appliances.
SUMMARY OF THE INVENTION
[0014] 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 an integrally
blow-moulded bag-in-container having an inner layer forming the bag
and an outer layer forming the container, and a mouth fluidly
connecting the volume defined by the bag to the atmosphere. The
container further includes at least one interface vent fluidly
connecting the interface between inner and outer layers to the
atmosphere, wherein the at least one vent runs parallel to the
interface between inner and outer layers and opens to the
atmosphere at a location adjacent to, and oriented approximately
coaxially with the bag-in-container's mouth.
[0015] The present invention also concerns a preform for
blow-moulding the bag-in-container of the present invention. The
preform includes an inner layer and an outer layer, and a body, a
neck region, and a mouth fluidly connecting the space defined by
the inner layer to the atmosphere, wherein the inner and outer
layers are connected to one another by an interface at least at the
level of the neck region. The preform includes at least one
interface vent running parallel to the interface and opening to the
atmosphere at a location adjacent to, and oriented coaxially with
the preform's mouth.
[0016] The inner and outer layers of the preform (and consequently
of the bag-in-container) of the present invention may consist of
different or the same materials. The two layers of the preform may
be connected by an interface 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 containing
air and which is in fluid communication with at least one interface
vent. The preform may be an assembly of two separate inner and
outer preforms or, alternatively, they may be an integral preform
obtained by injection moulding one layer on top of the other.
[0017] The vent preferably is 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 two layers meet
to form an interface. The container may comprise one or several
vents evenly distributed around the lip of the bag-in-container's
mouth.
[0018] One advantageous method to produce the bag-in-container of
the present invention comprises the following steps: [0019]
providing a preform as described above, 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;. [0020] bringing said preform to
blow-moulding temperature; [0021] fixing the thus heated preform at
the level of the neck region with fixing means in the blow-moulding
tool; [0022] blow-moulding the thus heated preform to form a
bag-in-container; wherein, [0023] 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 said fixing
means; and [0024] 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.
[0025] A particularly preferred embodiment of the preform according
to the present invention is an integral two layer preform which may
be manufactured by a process comprising the following sequential
steps: [0026] injection moulding the preform's inner layer onto a
core; [0027] injection moulding the preform's outer layer onto the
inner layer; [0028] extracting the thus formed preform from the
core, wherein said core is provided at the base thereof with at
least one pin suitable for forming an interface vent running
parallel to the interface between said first and second layers and
opening to the atmosphere at a location adjacent to, and oriented
coaxially with the preform's mouth.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] 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.
[0030] 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
[0031] 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). Said
vent (3) comprises an opening (4) located adjacent to, and oriented
coaxially with said preform's mouth (5).
[0032] The preform may consists of an assembly of two independent
preforms (I 1) 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, as well as in the choice of materials
constituting each preform component. 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 and the
respective melting temperatures of the inner and outer layers must
be carefully matched depending on which layer is injected first;
the rule of thumb being that the layer being injected first
generally requires a higher melting temperature.
[0033] The inner and outer layers of the preform (1) may consist of
different materials or the same material. In case different
materials are used, some requirements must be fulfilled depending
on the process parameters in the injection moulding of the preform
as well as in the blow-moulding of the bag-in-container. It is
important of course that both materials may be processed in a
rather similar process window and that they will not form too
strong an interface which would not satisfactorily release upon
injecting pressurized gas at the interface.
[0034] Alternatively and surprisingly, good results can be obtained
also with preforms wherein both inner and outer layers consist of
the same material. The same polymer is considered in contact on
either side of the interface between the inner and outer layers in
the following cases: [0035] 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 [0036] 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 the 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.
[0037] Preferred materials for the preform and bag-in-container of
the present invention are 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. In case
different materials are used for the inner and outer layers, their
optimal blow-moulding temperatures should not differ from one
another by more than about 70.degree. C., preferably 40.degree. C.,
most preferably 10.degree. C., and ideally should have the same
blow-moulding temperature. The layer's temperatures may be
determined by IR-measurement.
[0038] 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 (cf. (1) in FIG. 1A). 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) (cf. (1') in FIG. 1B). 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).
[0039] The at least one vent (3) preferably is in 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. 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.
[0040] The wedge shape of the vent is advantageous for the release
of the interface but also for the production of an integral
preform. A method for producing an integral preform suitable for
blow-moulding a bag-in-container according to the present invention
comprises the steps of: [0041] injection moulding the preform's
inner layer onto a core; [0042] injection moulding the preform's
outer layer onto the inner layer; [0043] extracting the thus formed
preform from the core, wherein said core is provided at the base
thereof with at least one pin suitable for forming an interface
vent running parallel to the interface between said first and
second layers and opening to the atmosphere at a location adjacent
to, and oriented coaxially with the preform's mouth. The core may
comprise a single pin, but it preferably comprises more than one
pin in order to have several vents opening around the lip of the
container's mouth. The pins preferably have the shape of a wedge
as, on the one hand, a wedge shaped vent has the advantages
discussed above and, on the other hand, it allows for easier
extraction of the thus produced integral preform from the
mouldcore. The dimensions of the pins depend on the size of the
bag-in-container and, in particular, of the mouth and lip thereof.
For a typical home beverage dispenser of a capacity of about 56
liters, the pins have a length of about 5 to 75 mm, preferably 5 to
50 mm, most preferably 10 to 20 mm and their base, forming the
vents openings, preferably are in the shape of an arc section of
length comprised between 3 and 15 mm, preferably 5 and 10 mm and of
width comprised between 0.5 and 5 mm, preferably 0.5 and 2 mm.
[0044] The bag-in-container (2) of the present invention can be
obtained by providing a preform as described above; bringing said
preform to blow-moulding temperature; 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. 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
substantially during blowing.
[0045] 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 materials 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, but it has surprisingly been discovered that 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,
[0046] 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 [0047] 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. 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.
[0048] A preform according to the present invention was produced by
injecting a melt into a first mould cavity cooled at a temperature
of T_mould.degree. C., to form the preform's inner layer (11). A
melt was injected into a second mould cavity cooled to form the
preform's outer layer (12). The two preform components were
assembled to form a preform according to the present invention.
[0049] The preform produced as explained above was heated in an
oven comprising an array of IRlamps and then fixed into a
blow-moulding mould which walls were maintained at a desired
temperature. Air was blown into the preform under pressure. The
thus produced bag-in-container was then filled with a liquid and
connected to an appliance for dispensing beverage comprising a
source of compressed air in order to determine the delamination
pressure.
[0050] The delamination pressure was determined as follows. The
interface vents of said bag-in-container were connected to the
source of compressed air. Air was injected through the vents at a
constant pressure, and the interface between inner and outer layers
was observed. The pressure was increased stepwise until
delamination pressure was 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 were examined for traces of
bonding.
[0051] The delamination pressure of the bag-in-container described
above was of about 05.+-.0.1 bar overpressure and showed little
trace of cohesive fracture between the inner and outer layers. This
example demonstrates that bag-in-containers of excellent quality
can be produced with integral preforms according to the present
invention.
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