U.S. patent application number 10/545800 was filed with the patent office on 2006-11-02 for polymer packaging layer with improved release properties.
This patent application is currently assigned to Corus STaal BV. Invention is credited to Johannes Jacobus Dommershuijzen, Lene Hviid, Coenraad Jan Spaans, Cornelis Johannes Waringa.
Application Number | 20060243626 10/545800 |
Document ID | / |
Family ID | 32731574 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060243626 |
Kind Code |
A1 |
Spaans; Coenraad Jan ; et
al. |
November 2, 2006 |
Polymer packaging layer with improved release properties
Abstract
Use of a polymer material as a product contact layer in or on
packaging for a product, wherein the polymer material is made from
a blend of a polyester resin and an apolar resin such as a
polyolefin and has improved product-release properties as compared
to a polymer material made from essentially the polyester
resin.
Inventors: |
Spaans; Coenraad Jan;
(Harlingen, NL) ; Hviid; Lene; (Amsterdam, NL)
; Waringa; Cornelis Johannes; (Amsterdam, NL) ;
Dommershuijzen; Johannes Jacobus; (Santpoort, NL) |
Correspondence
Address: |
STEVENS DAVIS MILLER & MOSHER, LLP
1615 L STREET, NW
SUITE 850
WASHINGTON
DC
20036
US
|
Assignee: |
Corus STaal BV
P.O. Box 10000
Ijmuiden
NL
NL-1970CA
|
Family ID: |
32731574 |
Appl. No.: |
10/545800 |
Filed: |
February 18, 2004 |
PCT Filed: |
February 18, 2004 |
PCT NO: |
PCT/EP04/01619 |
371 Date: |
June 13, 2006 |
Current U.S.
Class: |
206/484 |
Current CPC
Class: |
C08L 23/12 20130101;
C08L 67/02 20130101; C08L 23/16 20130101; C08L 23/14 20130101; C08L
23/06 20130101; C08L 67/02 20130101; C08L 2666/06 20130101; C08L
23/147 20130101 |
Class at
Publication: |
206/484 |
International
Class: |
B65D 73/00 20060101
B65D073/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2003 |
EP |
03075471.7 |
Claims
1. A method of making packaging comprising the steps of: coating a
multi-layer system comprising at least three layers in or on a
metal substrate for packaging for a product, wherein the at least
three layers comprises a product contact layer comprising polymer
material, wherein the polymer material comprises a blend of a
polyester resin and an apolar resin to improve the product-release
properties as compared to a material made from essentially the
polyester resin.
2. The method according to claim 1, wherein the apolar resin is
selected from the group consisting of PE, PP, and a copolymer
comprising PE and PP.
3. The method according to claim 1, wherein the apolar resin is
modified polypropylene.
4. The method according to claim 3, wherein the apolar resin is
maleic acid modified polypropylene.
5. The method according to claim 1, wherein the polyester is
selected from the group consisting of PET, modified PET, PEI, PBT
and combinations thereof.
6. The method according to claim 1, wherein the polymer material is
coated onto a substrate in the form of a film before the substrate
is formed into packaging.
7. The method according to claim 1, wherein the polymer material is
directly extruded onto a substrate before the substrate is formed
into packaging.
8. The method according to claim 1, wherein the apolar resin is
EPDM.
9. The method according to claim 1, wherein said polymer material
is coated onto a packaging steel substrate.
10. The method according to claim 1, wherein the system contains an
adhesion layer between the product contact layer and the substrate,
and a bulk layer between the adhesion layer and the product contact
layer.
11. The method according to claim 10, wherein the bulk layer
consists of bottle-grade PET.
12. The method according to claim 1, wherein the polymer material
is coated onto a packaging steel substrate selected from the group
consisting of TFS/ECCS steel substrate.
13. Packaging for a product wherein the packaging comprises a metal
substrate, a multi-layer system comprising at least three layers
wherein the at least three layers comprises a polymer material as a
product contact layer which in use contacts the product, wherein
the metal substrate is coated with the polymer material wherein the
polymer material comprises a blend of a polyester resin and an
apolar resin to improve the product-release properties as compared
to a polymer material made from essentially the polyester
resin.
14. Packaging according to claim 13, wherein the apolar resin is
selected from PE, PP, and a copolymer comprising PE and PP.
15. Packaging according to claim 13, wherein the apolar resin is
modified PP.
16. Packaging according to claim 13, wherein the apolar resin is
maleic acid anhydride modified PP.
17. Packaging according to claim 13, wherein the polyester is PET
or modified PET or PEI or PBT and combinations thereof.
18. Packaging according to claim 13, wherein the wherein the
packaging comprises a packaging steel substrate coated with the
polymer material.
19. Packaging according to claim 13, wherein the apolar resin is
EPDM.
20. Packaging according to claim 18, wherein the polymer material
is coated onto at least one side of the substrate in the form of a
film, before the substrate is formed into packaging.
21. Packaging according to claim 20, wherein the polymer material
is directly extruded onto at least one side of the substrate before
the substrate is formed into packaging.
22. Packaging according to claim 13, which is retortable.
23. Packaging according to claim 13, wherein the system contains an
adhesion layer between the product contact layer and the substrate,
and a bulk layer between the adhesion layer and the product contact
layer.
24. Packaging according claim 23, wherein the bulk layer consists
of bottle-grade PET.
25. Packaging according to claim 13, wherein the polymer material
is coated onto a packaging steel substrate selected from the group
consisting of TFS/ECCS steel substrate.
26. The method according to claim 1, wherein the apolar resin
comprises a polyolefin.
27. Packaging according to claim 13, wherein the apolar resin
comprises a polyolefin.
Description
[0001] The invention relates to improved release of a product such
as for example a food product from a product contact layer of
packaging. The term packaging encompasses containers, wrappers and
the like for enclosing a product and closures such as lids for such
containers or wrappers. When emptying packaging filled with a
sticky product, the release properties of the product contact layer
play an important role in view of economy, convenience and
perception of a customer of how easily the packaging can be emptied
and how much product remains in the container or on the
wrapping.
[0002] In food packaging in metal containers, the product contact
layer that provides the release properties is conventionally a
lacquer applied to the metal, the metal being in the form of e.g.
tinplate or in some cases tin free steel designated as TFS or ECCS
(electrolytically chrome coated steel). To provide release
properties to the inside of e.g. traditional internally lacquered
fish cans, special release additives are added to the product
contact layer. Typical additives to achieve adequate release are
wax like materials, e.g. Carnauba wax.
[0003] Recently, there has been an increasing interest in using
polymer (coil) coated substrates for example polymer coated metal
strip or polymer coated paper (board) instead of packaging steel
with a layer of lacquer. This is particularly the case for food
packaging. Commonly applied resins for such polymer coating
applications are polyesters, e.g. polyethylene terephthalate (PET).
However, polyesters have poor product release properties, thereby
limiting the scope of their use in packaging especially where good
product release properties are required, such as in e.g. wide mouth
food jars or fish cans.
[0004] According to EP 1086808 which recognises this problem with
PET coatings, a wax component is to be added to such a PET coating
to obtain better "taking-out property" of stuffed food contents,
see table 1 C2, table 2 C2 and table 3 E1-E16 and C1-C3. However,
adding the waxes is expensive firstly because of the cost of such
waxes and secondly because of complications in the handling and
processing of the manufacture of the non-sticking polymer.
Furthermore, in some cases, the use of a wax must be limited in
connection with food quality and legislation issues. EP 1174457
also discloses the addition of wax compounds to polyester film for
laminating metal sheet for the production of cans.
[0005] Alternatively, according to EP 1086808, see table 1
.mu.l-E7, table 2 E1-E12, C1 and C3-C4 and table 3 C4-C5, for
better "taking-out property" a coating of an apolar resin, viz.
(mixtures of) a polypropylene (PP) and/or polyethylene (PE) or
polytetrafluorethylene (PTFE) optionally provided with an extra
layer of modified PP could be applied to the metal strip. However,
it is known that these coatings are not suitable for many packaging
applications, notably for foodstuffs that are sterillsed or
heat-treated in the packaging.
[0006] In applications where these apolar resin polymer coatings
are not suitable, and where it is also undesirable to have to add
waxes to a PET coating, an alternative is thus desired.
[0007] It is thus an objective to find a polymer material with a
new combination of acceptable and favourable properties in order to
reduce or solve the problem of stickiness of a polyester without
needing to add waxes to the polyester, and/or to obtain other
advantages.
[0008] According to the invention this objective is achieved by
using a polymer material as a product contact layer of packaging
for a product where the polymer material is made from a blend of a
polyester resin and an apolar resin such as a polyolefin.
[0009] Surprisingly, it turns out that by using such a blended
material of a polyester and an apolar resin, e.g. a apolar resin
such as PP or PE, which polyester and apolar resin are in principle
incompatible with each other, the product release properties of the
resulting polymer are greatly improved without thereby unacceptably
adversely affecting other properties such as the manufacturability
and processability of the polymer. Also, surprisingly, the
incompatibility of the two polymers does not lead to an
unacceptable loss of retort resistance and adhesion, in contrast to
what is reported in literature, where generally poor mechanical and
barrier properties are reported (see for example Dimitrova et al.,
Polymer, 41, 2000, 48174824).
[0010] In hindsight, the good product release properties or
non-stick behaviour may be related to demixing of the polymers
taking place. According to this theory the demixing results in a
morphology where apolar resins such as polyolefins are dispersed in
a polar polyester matrix, making the surface less polar and thereby
decreasing the affinity of the coating towards sticky products such
as many foodstuffs.
[0011] In all cases, the polymer material according to the
invention as compared to polyester material shows improved product
release properties as well as good retort resistance.
[0012] In an embodiment the apolar resin is PP. This has the
advantage that the resulting polymer material is relatively
cheap.
[0013] In another embodiment the apolar resin is modified PP. This
achieves an improved extrusion behaviour believed to be resulting
from a better compatibility of the resin with PET compared to
unmodified PP.
[0014] In a further embodiment the apolar resin is maleic acid
anhydride modified PP. In this way also a better interaction with
the PET is obtained.
[0015] In yet another embodiment the apolar resin is PE. By
choosing PE, a simple cheap polymer very similar to PP is used.
[0016] In another embodiment the apolar resin is a copolymer
comprising PP and PE. This achieves a more amorphous system than
the standard PP, which provides even better release
characteristics.
[0017] In yet another embodiment the apolar resin is EPDM.
[0018] In an embodiment the polyester is PET (polyethylene
terephthalate) or modified PET (e.g. glycol modification with CHDM
and/or terephthalate modification by isophthalate) or PEI
(polyethylene isophthalate) or PBT (polybutylene terephthalate) and
combinations (blends and/or copolymers) thereof.
[0019] The polymer material preferably contains a blend of 5-25% PP
in PET or more preferably 10-25% PP in PET or even more preferably
15-25% PP in PET. At higher levels of PP in PET it becomes
increasingly difficult to produce a stable polymer material.
[0020] Preferably, the polymer material according to the invention
is coated on a metal substrate or sheet. A metal substrate provided
with such a coating has the advantage that it can be used to
manufacture metal cans for sticky products, e.g. for canned salmon,
while achieving good release from the can after opening.
[0021] The polymer material can be relatively conveniently produced
by feeding the respective polyester and apolar resin granulates
directly into a feeding system of an extruder, taking care in the
feeding system not to exceed the temperature at which the apolar
resin softens or melts. The polymer material can easily be applied
to substrates, which can subsequently be formed into packaging or
can act as a wrapping itself. The polymer material of the present
invention is particularly suitable for coating at least one side of
a metal substrate, made from for example, packaging steel, which is
subsequently formed into packaging. Despite the rigorous processing
steps the substrate is subjected to in order to form the packaging,
the product release properties of the polymer material, which forms
the product contact layer of the packaging, are maintained. The
sterilisability of the coating also remains intact.
[0022] The polymer material can form a single coating layer or a
single (sub) layer of a multi layer system. For very demanding
retort applications, it is advisable to use a multi layer system
instead of a two or one layer system. In this way, the functional
layer that forms the product contact surface can be kept thin,
which is favourable for coating integrity during these retort
processes.
[0023] The present invention also relates to packaging for a
product wherein the packaging comprises a product contact layer
which in use contacts the product wherein said contact layer
comprises a polymer material made from a blend of a polyester resin
and an apolar resin such as a polyolefin. Such packaging has
improved product release properties as compared to packaging where
the contact layer comprises a polymer material made from
essentially the polymer resin, whilst the polymer also has
acceptable manufacturability and processability properties.
[0024] In an embodiment the apolar resin is PP. This has the
advantage that the resulting polymer material is relatively
cheap.
[0025] In another embodiment the apolar resin is modified PP. This
achieves an improved extrusion behaviour believed to be resulting
from a better compatibility of the resin with PET compared to
unmodified PP.
[0026] In a further embodiment the apolar resin is maleic acid
anhydride modified PP. In this way also a better interaction with
the PET is obtained.
[0027] In yet another embodiment the apolar resin is PE. By
choosing PE, a simple cheap polymer very similar to PP is used.
[0028] In another embodiment the apolar resin is a copolymer
comprising PP and PE. This achieves a more amorphous system than
the standard PP, which provides even better release
characteristics.
[0029] In yet another embodiment the apolar resin is EPDM.
[0030] In an embodiment the polyester is PET (polyethylene
terephthalate) or modified PET (e.g. glycol modification with CHDM
and/or terephthalate modification by isophthalate) or PEI
(polyethylene isophthalate) or PBT (polybutylene terephthalate) and
combinations (blends and/or copolymers) thereof.
[0031] The packaging preferably comprises a metal substrate coated
with the polymer material. The polymer material is preferably
coated onto at least one side of the metal substrate before the
substrate is formed into packaging. It has been found that the
polymer material has acceptable manufacturability and forming
properties and can thus be applied to a metal substrate before it
has been formed into packaging. The metal substrate coated with the
polymer material may be produced according to a process wherein the
polymer material is extruded, made into an extrudate or film, which
extrudate or film is applied to the metal sheet.
[0032] The packaging is preferably retortable. It has also been
found that the polymer material of the present invention has good
retort resistance as well as good product release properties and
can thus be used in retortable packaging. The polymer material may
form the product contact layer of a multi-layer system, whereby the
polymer material can be kept thin, which is favourable for coating
integrity during retort processes.
[0033] It turns out that a can made from a packaging steel coated
with said polymer material according to the invention has excellent
release-from-can-properties, in particular for fish based and fish
products, as will be shown hereafter by way of some non-limitative
examples.
EXAMPLE 1.1
[0034] A two layer polymer film consisting of an adhesion layer and
a bulk product contact layer was made by co-extrusion from a
feedblock-die system using for the bulk product contact layer a
standard bottle grade PET granulate representing as reference a
pure PET film, and a standard bottle grade PET granulate blended
with a standard PP homopolymer MFI 12 g/10 min granulate at
different blend ratios representing variants of the polymer having
improved release properties according to the invention. MFI 12 g/10
min (as measured according to ISO 1133, T=230.degree. C., 2.16 kg)
refers to the melt flow index of the PP, which indicates melt
viscosity.
[0035] The polymer extrudate was coated onto a conventional steel
substrate (TFS/ECCS) of 0.20 mm (normally designated as T57 CA) and
the resulting coated steel sheet was made into straight
(non-tapered) food cans O 65 mm and height 93 mm in a 3-step DRD
process using blanks O 198 mm. The 3-step draw and redraw (DRD)
process used was a standard process comprising cutting a blank of O
198 mm from the coated steel, drawing the blank through a die to
form a cup and redrawing the cup without thinning the sidewall to
form a can of O 65 mm and height 93 mm.
[0036] The cans were filled with fresh, bred atlantic salmon,
closed and retorted for 90 minutes in an autoclave at a temperature
of 121.degree. C. The cans were cooled in ambient air and stored at
35.degree. C. for one week.
[0037] Then the cans were opened, emptied and the amount of
remaining salmon was measured by weight (hereafter also referred to
as AR in g/can).
[0038] Furthermore, the area covered by the remaining salmon
(hereafter also referred to as AC in %) was determined as the
average of independent estimations by three different persons, in
order to simulate perception by the consumer of the "stickiness" of
the walls of the respective cans.
[0039] The results are given in table 1.1.
[0040] As follows from the results of this experiment, the blended
materials of PET with PP show superior performance compared to the
PET coated reference cans, the variant containing 10% showing
superior release behaviour.
[0041] As discussed in Taguchi (Bulletin of the Japanese Society of
Scientific Fisheries 46(3) 369 (1980)), laboratory trials like
these may suffer from reproducibility problems, which are possibly
related to "trivial" factors like the freshness of the fish. In
order to check the reproducibility of improvement of the release
behaviour if the invention is practiced a second experiment with a
different salmon lot was performed.
EXAMPLE 1.2
[0042] Example 1.1 was repeated with a different batch of salmon.
The results are as shown in table 1.2.
[0043] Although the results in example 1.2 differ from that of 1.1
the trend in the improvement of the release properties of the can
achieved by the invention is the same. It is presumed that
"trivial" effects like the inherently varying properties of the
salmon already mentioned above cause the differences.
EXAMPLE 2.1
[0044] In another experiment a three layer polymer film made by
co-extrusion from a feedblock-die system was used, comprising an
adhesion layer, a bulk layer and a top product contact layer, using
for the bulk layer a standard bottle grade PET and for the top
product contact layer a standard bottle grade PET granulate blended
with a standard PP granulate at different blend ratios, the rest of
the experiment being performed in the same way as in Examples 1.1
and 1.2.
[0045] The sterilisation performance (hereafter also referred to as
SP) of the polymer film was also considered by sterilising samples
of the substrate coated with polymer film with the different top
layer variants in salty water (saline test) for 90 minutes at
121.degree. C. in the presence of air, in order to determine
whether the invention can be used in practice for packaging
products that are retorted.
[0046] The results are given in table 2.1.
[0047] As follows from the above results, the top layers with
approx. 10% PP in PET show superior release performance and
adequate sterilisation performance.
[0048] As before, due to the nature of the experiment, the data
vary from experiment to experiment. Differences in e.g. the
freshness of the fish are found to influence the release
behaviour.
[0049] Again, in order to check the influence of different batches,
a further trial using a three-layer polymer film was performed.
EXAMPLE 2.2
[0050] Example 2.1 was repeated with a different batch of salmon.
The results are as shown in table 2.2. Again, the effect of the
addition of PP to PET on the release properties was clear.
EXAMPLE 2.3
[0051] Example 2.2 was repeated with a different batch of salmon.
The results are as shown in table 2.3. For the evaluation of the
release behaviour, the weight of the adhering salmon retained (AR)
is perceived as the most reliable indicator.
[0052] Again in this experiment, the effect of the addition of PP
to PET on the release behaviour is clearly indicated.
[0053] As follows from the results the 20% PP shows improved
release behaviour as compared to 15% PP.
[0054] This result indicates that 20% PP is a further optimization
of the release behaviour.
[0055] As release phenomena occur at the surface of the packaging
material in contact with the filling, it will be clear that the
effects of the invention are not limited to the embodiments of the
invention in the examples, in particular regarding the used
substrates. In other words the invention lies in realising a
relatively uncomplicated polymer layer with good release
properties. TABLE-US-00001 TABLE 1.1 AR (g/can) AC (%) PET
(reference) 6.9 30 PET (reference) 4.5 15 PET (reference) 7.9 35
PET (reference) 4.6 10 PET (reference) 5.8 35 2% PP in PET 6.3 25
2% PP in PET 2.5 10 2% PP in PET 3.3 15 2% PP in PET 6.8 25 2% PP
in PET 2.8 5 5% PP in PET 4.5 10 5% PP in PET 1.8 5 5% PP in PET
3.7 20 5% PP in PET 2.3 15 5% PP in PET 3.7 10 10% PP in PET 2.2 10
10% PP in PET 1.7 10 10% PP in PET 1.1 5 10% PP in PET 3 10 25% PP
in PET Stable polymer could not be produced 30% PP in PET Stable
polymer could not be produced 40% PP in PET Stable polymer could
not be produced
[0056] TABLE-US-00002 TABLE 1.2 AR (g/can) AC (%) PET (reference)
6.4 35 PET (reference) 15.8 35 PET (reference) 3.9 10 PET
(reference) 6 20 PET (reference) 7.3 35 PET (reference) 9.5 65 PET
(reference) 5.9 30 PET (reference) 7 30 PET (reference) 5.3 25 PET
(reference) 7.7 40 2% PP in PET 3.7 15 2% PP in PET 9.6 35 2% PP in
PET 4.4 10 2% PP in PET 2.6 5 2% PP in PET 3.4 15 2% PP in PET 6.4
25 2% PP in PET 3.6 25 2% PP in PET 7.5 15 2% PP in PET 5.1 20 2%
PP in PET 3.6 15 10% PP in PET 6.7 20 10% PP in PET 4.8 10 10% PP
in PET 4.2 10 10% PP in PET 7.7 15 10% PP in PET 2.7 5 10% PP in
PET 1.6 5 10% PP in PET 6.6 20 10% PP in PET 10.4 45 10% PP in PET
5.6 40 10% PP in PET 4.4 5
[0057] TABLE-US-00003 TABLE 2.1 top layer modification AR (g/can)
AC (%) SP PET (reference) 6.4 35 excellent PET (reference) 15.8 35
PET (reference) 3.9 10 PET (reference) 6 20 PET (reference) 7.3 35
PET (reference) 9.5 65 PET (reference) 5.9 30 PET (reference) 7 30
PET (reference) 5.3 25 PET (reference) 7.7 40 10% PP in PET 6.7 25
adequate 10% PP in PET 7.4 25 10% PP in PET 3.7 15 10% PP In PET
1.4 5 10% PP in PET 3.9 10 10% PP in PET 10.2 40 10% PP in PET 5.9
15 10% PP in PET 3.5 15 10% PP in PET 4 15 10% PP in PET 4.5 15
[0058] TABLE-US-00004 TABLE 2.2 top layer modification AR (g/can)
AC (%) SP PET (reference) 4.8 5 excellent PET (reference) 16.7 30
PET (reference) 2.7 5 PET (reference) 6.6 20 PET (reference) 2.8 5
PET (reference) 4.3 10 PET (reference) 3.4 10 PET (reference) 1.9 5
PET (reference) 2.9 5 PET (reference) 2.1 5 5% PP in PET 2.2 10
excellent 5% PP in PET 4.1 10 5% PP in PET 14 20 5% PP in PET 1.6 5
5% PP in PET 2.8 10 5% PP in PET 2.5 10 5% PP in PET 2 5 5% PP in
PET 5.2 15 5% PP in PET 2.4 5 5% PP in PET 1.7 5 10% PP in PET 3.7
10 adequate.sup.1 10% PP in PET 2.3 5 10% PP in PET 4.2 10 10% PP
in PET 3.8 10 10% PP in PET 8.9 25 10% PP in PET 1.8 5 10% PP in
PET 3.7 10 10% PP in PET 2.8 10 15% PP in PET 2 5 good.sup.1 15% PP
in PET 2 5 15% PP in PET 2.5 5 15% PP in PET 1.6 5 15% PP in PET
2.2 5 15% PP in PET 3.2 5 15% PP in PET 4.2 10 15% PP in PET 3.2 5
15% PP in PET 2.4 5 15% PP in PET 1.7 5 15% PP in PET 1.9 5
.sup.1Surprisingly, SP at 15% PP in PET is better than at 10% PP in
PET
[0059] TABLE-US-00005 TABLE 2.3 top layer modification AR (g/can)
AC (%) PET (reference) 2.5 5 PET (reference) 5.8 10 PET (reference)
15.4 15 PET (reference) 2.0 5 PET (reference) 5.1 10 PET
(reference) 8.4 15 PET (reference) 6.3 10 PET (reference) 7.6 15
PET (reference) 12.1 30 PET (reference) 1.5 3 15% PP in PET 1.9 2
15% PP in PET 9.4 25 15% PP in PET 0.8 2 15% PP in PET 1.3 5 15% PP
in PET 9.2 20 15% PP in PET 1.6 10 15% PP in PET 1.2 2 15% PP in
PET 3.5 10 15% PP in PET 3.9 10 20% PP in PET 0.9 2 20% PP in PET
6.1 8 20% PP in PET 1.2 1 20% PP in PET 1.1 1 20% PP in PET 1.3 5
20% PP in PET 1.1 1 20% PP in PET 2.1 3 20% PP in PET 5.0 15 20% PP
in PET 1.2 5 20% PP in PET 1.6 1
* * * * *