U.S. patent application number 10/542755 was filed with the patent office on 2006-12-14 for heated-sealed sterilised product package packaging material for the same and use of the packaging material.
This patent application is currently assigned to Stora Enso Oyj. Invention is credited to Isto Heiskanen, Esa Koreasalo, Jurkka Kuusipalo, Erkki laiho, Tommi Lehikoinen, Kimmo Nevalainen, Tapani Penttinen, Markku Sainio, Antti Savolainen.
Application Number | 20060280941 10/542755 |
Document ID | / |
Family ID | 32910225 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060280941 |
Kind Code |
A1 |
Penttinen; Tapani ; et
al. |
December 14, 2006 |
Heated-sealed sterilised product package packaging material for the
same and use of the packaging material
Abstract
The invention relates to a polymer-coated heat-sealable
packaging material, to a heat-sterilised package formed from this
and to the use of the packaging material. The material comprises a
fibre base (4), which is e.g. a packaging board made of bleached
pulp, and polymer heat-seal layers (1, 9) located on both sides of
this. In accordance with the invention, the package comprises,
outside the fibre base, a polymer coating layer (2), which contains
white pigment for covering the fibre base from sight, and a second
coating layer (8), which contains light-absorbing pigment. A
coating layer pigmented grey inside the fibre base, for instance,
provides a light shield for the packaged product. The absorbent
black pigment may also be located outside the fibre base underneath
a white layer in order to stabilise the brightness of the material.
The package may be e.g. a food package heat-sterilised in an
autoclave, in which yellowing of the fibre-based material has been
avoided by means of a white pigment.
Inventors: |
Penttinen; Tapani;
(Huutjarvi, FI) ; Nevalainen; Kimmo; (Kotka,
FI) ; laiho; Erkki; (Porvoo, FI) ; Sainio;
Markku; (Porvoo, FI) ; Kuusipalo; Jurkka;
(Tampera, FI) ; Savolainen; Antti; (Kangasala,
FI) ; Koreasalo; Esa; (Valkeakoski, FI) ;
Heiskanen; Isto; (Imatra, FI) ; Lehikoinen;
Tommi; (Tampere, FI) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
Stora Enso Oyj
Kanavaranta 1
Helsinki
FI
FI-00160
|
Family ID: |
32910225 |
Appl. No.: |
10/542755 |
Filed: |
February 23, 2004 |
PCT Filed: |
February 23, 2004 |
PCT NO: |
PCT/FI04/00084 |
371 Date: |
July 10, 2006 |
Current U.S.
Class: |
428/375 |
Current CPC
Class: |
B65D 81/24 20130101;
B32B 27/12 20130101; B32B 2439/70 20130101; B32B 27/20 20130101;
B32B 27/34 20130101; B32B 2377/00 20130101; B32B 27/08 20130101;
Y10T 428/2933 20150115; B65D 81/30 20130101; B32B 2323/10 20130101;
B32B 2255/26 20130101; B65D 5/563 20130101; B05D 5/06 20130101;
B32B 7/12 20130101; B32B 27/32 20130101; B32B 2329/00 20130101;
B32B 2307/31 20130101 |
Class at
Publication: |
428/375 |
International
Class: |
D02G 3/00 20060101
D02G003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2003 |
FI |
20030260 |
May 22, 2003 |
FI |
20030773 |
Claims
1. A heat-sealed heat-sterilised product package made of a
fibre-based packaging material having polymer coating layers on
both sides of a bleached fibre base, characterised in that a
polymer coating layer outside the fibre base in the package
contains white pigment for toning against yellowing of the fibre
base caused by heating, and in that a second polymer coating layer
included in the packaging material contains a light-absorbing
pigment.
2. A package as defined in claim 1, characterised in that the
coating layer containing a light-absorbing pigment is located
inside the fibre base in the package.
3. A package as defined in claim 2, characterised in that the
polymer coating outside the fibre base contains only white pigment,
which hides the fibre base from sight.
4. A package as defined in claim 2, characterised in that outside
the fibre base in the package there are two successive pigmented
polymer layers, with the outer polymer layer containing 5 to 25% of
white pigment and the inner polymer layer located closer to the
fibre base containing black pigment, and that inside the fibre base
there is a polymer layer containing light-absorbing pigment to
provide a light shield for the packaged product.
5. A package as defined in claim 2, characterised in that inside
the fibre base the polymer layer has been toned grey by mixing
black and white pigments.
6. A package as defined in claim 2, characterised in that, both
outside and inside the fibre base, the pigments are located in the
innermost polymer layers covered by a transparent heat-sealable
overlay layer.
7. A package as defined in claim 1, characterised in that outside
the fibre base of the package there are two successive pigmented
polymer layers, with the outer polymer layer containing 5 to 25% of
white pigment and the inner polymer layer located closer to the
fibre base containing a light-absorbing black pigment.
8. A package as defined in claim 1, characterised in that inside
the fibre base of the package there is at least one polymer
oxygen-barrier layer.
9. A package as defined in claim 1, characterised in that the
outside of the heat-sterilised package has a brightness above 80%
ISO.
10. A package as defined in claim 1, characterised in being a food
package sterilised in an autoclave.
11. A polymer-coated heat-sealable packaging material intended for
the product package of claim 1, comprising a bleached fibre base
and polymer heat-sealable layers on both sides of the substrate,
characterised in that pigment has been incorporated in the polymer
layers on both sides of the fibre base, with white pigment on one
side of the fibre base hiding the fibre base and with a
light-absorbing pigment on the opposite side of the fibre base
forming a light shield for the product to be packaged.
12. A packaging material as defined in claim 11, characterised in
that the brightness of the material is above 80% ISO on one side of
the fibre base, where the polymer layer contains white pigment.
13. A packaging material as defined in claim 11, characterised in
that one side of the fibre base is provided with two successive
pigmented polymer layers, with the outer polymer layer containing 5
to 25% of white pigment and the inner polymer layer located closer
to the fibre base containing black pigment for stabilising the
brightness of said material side despite any change during heating,
and in that a pigmented light-shield polymer layer is provided on
the opposite side of the fibre base.
14. A packaging material as defined in claim 13, characterised in
that black and white pigments have been mixed in said inner polymer
layer and in that the outer polymer layer contains exclusively
white pigment.
15. A packaging material as defined in claim 11, characterised in
that the light shield on the opposite side of the fibre base has
been achieved by tinting the polymer layer grey with black and
white pigments.
16. A packaging material as defined in claim 11, characterised in
that on both sides of the fibre base the material comprises an
outer transparent heat-seal layer and at least one inner pigmented
polymer layer.
17. A packaging material as defined in claim 16, characterised in
that the inner pigmented layer contains the same heat-sealable
polymer as the outer layer.
18. A packaging material as defined in claim 11, characterised in
that the polymer in the heat-seal layers has a fusion point of at
least 130.degree. C.
19. A packaging material as defined in claim 18, characterised in
that the heat-seal polymer is polypropene.
20. A packaging material as defined in claim 11, characterised in
that the material comprises at least one polymer oxygen-barrier
layer.
21. A packaging material as defined in claim 20, characterised in
that the oxygen-barrier layer is located between the fibre base and
the light-shield layer.
22. A packaging material as defined in claim 21, characterised in
that the material of the oxygen-barrier layer or layers is ethylene
vinyl alcohol polymer (EVOH) or polyamide (PA).
23. A packaging material as defined in claim 11, characterised in
that the fibre base consists of bleached packaging paper or
board.
24. Use of the packaging material of claim 11 for packages to be
sterilised in an autoclave.
25. Use as defined in claim 24 for food packages to be sterilised
in an autoclave.
Description
[0001] The invention relates to a heat-sealed, heat-sterilised
product package made of a polymer-coated, fibre-based packaging
material. The invention also relates to a packaging material
suitable for such a package and to the use of the material.
[0002] There are numerous known applications of polymer-coated
fibre-based packaging materials, in which one or both sides of the
fibre base are provided with one or more successive coating layers
and which are intended for various packaging purposes. The coating
can optionally achieve a moisture, oxygen and/or light barrier,
which is intended to improve the storage life of the packaged
product and thus to extend its effective storage and/or "best
before date". The coating also provides a heat-sealable material,
enabling a tight seal of the product package. Food packages
constitute one principal field of application for such packaging
materials, which are used for instance for cartons, casings and
boxes formed of coated packaging board and pouch packages formed of
coated paper.
[0003] Heat-sterilised packages form a notable group of sealed food
packages, the packaging material of these being required to
withstand sterilising treatment conditions. Sterilisation may be
performed by irradiation or by hot pressurised steam in an
autoclave. Closed metal cans have typically been treated in
autoclaves, however, nowadays also fibre-based packaging materials
are available for autoclave applications. WO 02/28637 thus
describes a packaging material for autoclave packages, in which the
board substrate is equipped with an oxygen barrier layer, polymer
heat-sealing layers and binder layers required between these. In
this publication, the oxygen barrier layer is preferably formed of
an aluminium foil, even though EVOH is also mentioned as an
optional material. The proposed material for the binder and
heat-sealing layers is polypropene, which resists, without melting,
the temperature above 130.degree. C. prevailing in an
autoclave.
[0004] In tests of heat-sterilised fibre-based food packages, the
applicant has found the problem of bleached packaging board coated
merely with polymer oxygen-barrier and heat-sealing layers tending
to yellow due to heating. This is especially true for packages
treated in autoclaves, which are required to resist the high
autoclave temperature and pressure over the required treatment
period, about 30 minutes in general. In other words, a package made
of polymer-coated board gets another appearance during autoclave
treatment, and this is a drawback in the market, especially in
demanding applications.
[0005] The purpose of the present invention is to eliminate the
problem mentioned above and to provide a sterile package made of a
fibre-based material, whose material in addition to the fibre base
comprises only polymer coating layers, which achieve the
sealability, heat resistance and light shield required for the
product, and in which also yellowing of the material as a result of
heating treatment has been substantially avoided. The product
package of the invention is characterised by the fact that the
polymer coating layer outside the fibre base of the package
contains a white pigment and in that the second polymer coating
layer included in the packaging material contains a light-absorbing
pigment.
[0006] In the package of the invention, white pigment is used to
hide the fibre base so that yellowing caused by heating does not
significantly affect the aspect of the package, more precisely its
ISO brightness. The light absorbent pigment, in turn, which has
been placed in a coating layer different from that of the white
pigment imparting the package its brightness, shields the packaged
product from visible light. In addition, in accordance with the
invention, light-absorbing black pigment can also be used as an
agent for stabilising the light appearance of the package as
described in the following.
[0007] In accordance with the invention, without the use of an
aluminium foil, a fibre-based packaging material has thus been
achieved, which resists heat sterilisation, especially autoclave
treatment at high temperature and under vapour pressure, the
polymer coating layers in the material forming the light shield
required for the storage life of the product and which also meets
the requirements posed on the appearance of the finished package to
be marketed. The light shield can be formed with polymer layer
toned grey with a black and a white pigment, e.g. as in WO
01/76976, the polymer layer forming an inner layer that replaces
the conventional aluminium foil of the package, whereas on the
opposite side of the package, i.e. on its outer surface, merely
white pigment can be used, which affects the package appearance
substantially by covering the discoloration of the fibre base
caused by heating treatment.
[0008] An optional solution of the invention is to provide two
successive pigmented polymer layers outside the fibre base in the
package, with the outer polymer layer containing 5 to 25% of white
pigment and the inner polymer layer closer to the fibre base
containing black pigment in a small amount. These successive
pigmented layers allow the light tone of the packaging material to
be effectively stabilised despite yellowing of the subjacent fibre
base. The overall colour of the material is then white or light
grey, slightly toned grey under the effect of the black pigment
underneath the white pigment. The brightness degree depends on the
pigment amounts used and their mutual ratios, however, the idea is
to adjust the material tone as close to white as possible and to
maintain this tone during the heating treatment of the package.
[0009] A small amount of black pigment provided under a
white-pigmented layer has a slightly light-absorbing effect. This
effect may yet be inadequate in shielding the packaged product from
light penetrating the material. If desired, more effective
light-shielding pigmentation can be achieved by providing the
polymer coating inside the package with a sufficient amount of
light-absorbing pigment, e.g. by toning at least one inner coating
layer of the fibre base grey, as disclosed in the WO patent
specification 01/76976 mentioned above.
[0010] The desired material toning can be achieved with successive
pigmented layers, whose total weight is 25 to 60 g/m.sup.2, the
black pigment concentration of the inner layer being in the range
0.05 to 0.5%, preferably approx. 0.06 to 0.15%, and the white
pigment concentration in the outer layer being in the range 5 to
25%, preferably approx. 7 to 12%. Optionally, the inner layer
containing black pigment can also be admixed with white pigment so
as to get an overall light grey tone of the layer. The proportion
of white pigment in the inner layer could thus be 5 to 25%,
preferably 7 to 15%. Carbon black, for instance, is suitable as a
black pigment, and titanium dioxide as a white pigment.
[0011] In a preferred embodiment of the invention, the package
material comprises on both sides of the fibre base an outer
transparent heat-sealing layer, with the pigmented polymer layers
located inside these. This avoids the pigmented layer from getting
into direct contact with the product to be packaged, which is
prohibited by foodstuff legislation or regulations in a number of
countries. However, the inner pigmented polymer layer may contain
the same heat-sealable polymer as the outer layer and it may be
located immediately underneath this, so that these layers during
heat sealing act as a single uniform material layer forming the
seam.
[0012] In an autoclave package, the fusion point of the polymer in
the heat-sealing layer should be at least approx. 130.degree. C.,
thus avoiding fusion of the polymer in the autoclave. Polypropene
is an example of such heat-sealable polymers.
[0013] Depending on the packaged product, the package material may
further comprise one or more polymer oxygen-barrier layers, which
most advantageously are located inside the package, between the
fibre base and the pigmented light-shield layer. Especially
ethylene vinyl alcohol copolymer (EVOH) and polyamide (PA) are
suitable materials of the oxygen-barrier layer.
[0014] In the package of the invention, the fibre base of the
material may consist particularly of a packaging board made of
bleached pulp, having a weight in the range 130 to 500 g/m.sup.2,
or a packaging paper having a weight in the range 20 to 120
g/m.sup.2. These are suitable for heat-sealable casing or carton
packages or poach packages to be treated in an autoclave.
[0015] The heat-sealable packaging material of the invention, which
is suitable for sterile packages as described above, comprising a
fibre base and polymer heat-seal layers on its both sides, is
characterised by the fact that pigment has been incorporated in the
polymer layers on both sides of the fibre base, with the fibre base
being hidden with white pigment on one side of the fibre base, and
with a light-absorbing pigment forming a light shield for the
packaged product on the opposite side of the fibre base. Such a
material can be used for forming a light-shielding package for the
product, which can be sterilised without any yellowing caused by
heating substantially altering the aspect of the package.
[0016] The invention further comprises the use of the fibre-based,
polymer-coated packaging material tinted by pigmenting on both
sides in packages to be sterilised by heating. The invention
relates in particular to the use of one of the packaging materials
described in further detail above in food packages that have been
sealed by heat sealing and are intended for treatment in an
autoclave.
[0017] The invention is described in greater detail below by means
of examples and with reference to the accompanying drawings, in
which
[0018] FIGS. 1 to 10 are schematic views of ten different layered
packaging materials of the invention, and
[0019] FIG. 11 shows a package made from the packaging material of
FIG. 1 by bending and heat sealing.
[0020] The polymer-coated packaging board of FIG. 1 comprises in
the following order: an outer heat-sealing layer 1 made of
polypropene (PP), an inner polypropene heat-sealing layer 2
pigmented white with titanium dioxide, a fibre base 4 made of
bleached board, a polyamide (PA) oxygen-barrier layer 5 adhered
directly to the fibre base, an EVOH oxygen-barrier layer 6, a
polymer binder layer 7, a heat-sealable polypropene layer 8, which
has been toned grey by means of carbon black and titanium dioxide,
and a heat-sealing layer 9 made of polypropene. The successive
coating layers can be produced on different sides of the board 4 by
means of coextrusion. The material can be bent and heat-sealed to
form a closed product package preferably with the polypropene layer
2 tinted white with titanium dioxide placed on the outer surface of
the package, i.e. outside the fibre base 4, and with the
polypropene layer 8 tinted grey by means of carbon black and
titanium dioxide placed on the inner surface of the package, i.e.
inside the fibre base 4. Owing to the layer 2 containing white
pigment, the material generally preserves its brightness in a
heat-sterilising treatment of the package made from it, such as
autoclave treatment, despite any yellowing of the fibrous substrate
4. The grey layer 8 has the function of shielding the packaged
product from light.
[0021] The packaging material shown in FIG. 2 differs from the one
of FIG. 1 only in that the polypropene heat-sealing layer placed on
the outer surface of the package has been omitted and in that the
mutual order of PA and EVOH oxygen-barrier layers 5, 6 in the
material has been changed. Thus the polypropene layer 2 tinted
white with titanium dioxide is on the outer surface of the
material, where it serves alone as a heat-sealable layer.
[0022] The packaging material of FIG. 3, again, differs from the
one shown in FIG. 1 only in that the material of the pigmented
polymer layers 2, 8 on both sides of the fibre base 4 is
cyclo-olefin copolymer (COC) instead of polypropene. COC is a
polymer obtained by copolymerisation of ethene and norbornene,
which is poorly vapour-permeable and whose application in layered
packaging materials is known per se.
[0023] The package material of FIG. 4 consists of a polypropene
layer 1, a polypropene layer 2 pigmented white with titanium
dioxide, a fibre base 4, a polypropene layer 9', a binder layer 7',
a PA oxygen barrier layer 5, an EVOH oxygen barrier layer 6, a
second PA oxygen-barrier layer 5', a second binder layer 7, a
polypropene layer 8 pigmented grey with carbon black and titanium
dioxide, and a polypropene layer 9. In this multi-layer structure,
the adhesion of the oxygen-barrier layers 5, 6 to the fibre base 4
has been ensured by means of intermediate polypropene and binder
layers 9', 7', which may be necessary in demanding applications,
such as packages treated in autoclaves. This application has i.a.
the special feature of a symmetrical five-layer combination of
oxygen-barrier and binder layers 7', 5, 6, 5', 7, which is
advantageous when successive polymer layers are formed by
coextrusion. Optionally the five-layer structure of the material
consisting of polypropene, binder, EVOH and PA oxygen-barrier
layers 9', 7', 5, 6, 5' can be applied onto the board 4 as a
separately manufactured film laminate, which are commercially
available in the market. The laminate is then sealed on the board 4
at the same time as the outer polypropene layers 1, 2, 8, 9 are
incorporated in the final material by co-extrusion.
[0024] The packaging material of FIG. 5 differs from the one shown
in FIG. 4 in that the grey pigment composition is admixed in the
two binder layers 8, 8' of the structure, so that the number of
coating layers is reduced by one. The material comprises a
co-extruded seven-layer structure 9, 8', 5, 6, 5', 8, 9, which is
symmetrical relative to the central EVOH layer 6. FIG. 6 further
shows a variant of the material of FIG. 5, in which only the
innermost binder layer 8 contains grey pigment. This has the
advantage of the separately manufactured five-layer film laminate
5, 6, 5', 7, 9 mentioned above, which can be sealed to the final
layered packaging material as an integral assembly.
[0025] In the packaging materials of FIGS. 1 to 6, the fibre base 4
may consist of a packaging board containing bleached sulphate pulp,
having a weight in the range 130 to 500 g/m.sup.2, preferably 170
to 300 g/m.sup.2. If the fibre base optionally consists of bleached
paper, it may have a weight in the range 20 to 120 g/m.sup.2. The
weight of the PA and EVOH oxygen-barrier layers 5, 6 may be 3 to 15
g/m.sup.2, preferably 50 to 10 g/m.sup.2. The weight of the
transparent polypropene layers 1, 9 placed outermost in the
material can be 5 to 30 g/m.sup.2, preferably 7 to 20 g/m.sup.2,
and the inner pigmented polypropene layers 2, 8 adjacent these
outer polypropene layers may have a weight in the range 10 to 50
g/m.sup.2, preferably 25 to 40 g/m.sup.2. The titanium dioxide
concentration of the white-pigmented polypropene layer 2 may be 5
to 25%, preferably approx. 7 to 12%. The carbon black concentration
in the grey-pigmented polypropene layer 8 may be 0.05 to 0.5%,
preferably approx. 0.12 to 0.15% and the titanium dioxide
concentration accordingly 5 to 25%, preferably approx. 7 to 12%.
The binder layers 7, whose material is appropriately i.a. the
polymer marketed by the company Mitsui Chemicals under the trade
name Admer, may have a weight in the range 3 to 15 g/m.sup.2,
preferably 5 to 10 g/m.sup.2. If the polymer material of the
pigmented layers 2, 8 is COC or Admer instead of polypropene, the
layer weights and pigment concentrations of the pigmented layers
mentioned above apply to these as well.
[0026] The polymer-coated packaging board of FIG. 7 comprises in
the following order: a coating layer 2 pigmented white with
titanium dioxide, a coating layer 3 pigmented with carbon black, a
fibre base 4 made of bleached board, a light-shield layer 8 toned
grey with titanium dioxide and carbon black so as to resemble an
aluminium foil, and a transparent heat-sealing layer 9. The polymer
material of all of the coating layers 2, 3, 8, 9 is polypropene.
The successive coating layers can be formed on different sides of
the fibre base 4 by co-extrusion. The material can be bent and
heat-sealed to form a closed product package so that the
successive, pigmented polymer layers 2, 3 are place don the outer
surface of the package, i.e. outside the fibre base 4, and the grey
light-shield layer 8 and the transparent heat-sealing layer 9 are
placed on the inner surface of the package, i.e. inside the fibre
base 4. The outer successive pigmented layers 2,3 of the package
impart the package a light, almost white shade, which does not
change in a heat-sterilising treatment of the package.
[0027] FIG. 8 shows a packaging board suitable especially for food
packages treated in autoclaves, in which, compared with FIG. 7,
there are the following added layers: a transparent polypropene
heat-sealing layer 1 placed on the outer surface of the package,
polyamide and EVOH oxygen-barrier layers 5, 6 inside the fibre base
4, and a binder layer 7 adhering to the light-shield layer 8 of the
EVOH layer 6, whose material is e.g. the polymer marketed the
company Mitsui Chemicals under the trade name Admer. Consequently,
the package formed of the material is protected with pigmented
layers 2, 3 against any yellowing of the fibre base 4 occurring in
autoclave treatment, and the oxygen-barrier layers 5, 6 and the
light-shield layer 8 inside the package protect the packaged
product and extend its storage life and best before date.
[0028] FIG. 9 shows a modification of the packaging board of FIG.
8, to which a second polyamide layer 5' and polypropene and binder
layers 9', 7' have been added between the fibre base 4 and the
polyamide layer 5. The arrangement enhances the adhesion between
the oxygen-barrier layers and the fibre base. Additional features
consist of the symmetrical five-layer combination of the binder 7',
polyamide 5, EVOH 6, polyamide 5' and binder 7, which is an
advantage when coating layers are formed by co-extrusion, and the
provision for incorporating the five-layer structure of polypropene
9', binder 7', polyamide 5, EVOH 6 and polyamide 5' as a film
laminate in the material, such film laminates being commercially
available in the market. Such a finished laminate can be sealed to
the board at the same time as the other coating layers of the
material are produced by co-extrusion.
[0029] FIG. 10 shows a second modification of the packaging
material, which differs from the one shown in FIG. 9 only in that a
second grey-pigmented light-shield layer 8' has been added inside
the fibre base 4, so that the layer combination inside the fibre
base has been made symmetrical in its totality, which is and
advantage in terms of co-extrusion.
[0030] In the packaging materials of FIGS. 7 to 10, the
white-pigmented layer 2 outside the fibre base 4 may be 20 to 50
g/m.sup.2, and the layer 3 containing black pigment may have a
weight in the range 5 to 10 g/m.sup.2. The grey-pigmented
light-shield layer 8 inside the fibre base 4 may have a weight in
the range 10 to 50 g/m.sup.2, preferably 25 to 40 g/m.sup.2. The
titanium dioxide concentration in the white-pigmented coating layer
2 may be in the range 5 to 25%, preferably 7 to 12%. The carbon
black concentration in the inner coating layer 3 may be 0.05 to
0.5%, preferably 0.06 to 0.15%. If the layer 3 contains also
titanium dioxide, it may have a concentration in the range 5 to
25%, preferably 7 to 15%. In other respects, the material layer
weights are equal to those defined in conjunction with FIGS. 1 to
6.
[0031] The packaging boards intended for use: in autoclaves
illustrated in FIGS. 1 to 10 can be varied in different ways within
the scope of the invention. Adequate oxygen barrier can be provided
by means of one single EVOH layer 6, for instance, and then the
polyamide layers can be omitted. If the pigmented layers on the
outer surface of the package are used as heat-sealing layers, the
outermost transparent heat-sealing layer 1 may also be superfluous.
The innermost layer 3 containing black pigment, which is possibly
provided, may be optionally admixed with white pigment, e.g.
titanium dioxide, and then the layer gets a light grey overall
shade.
[0032] FIG. 11 shows a closed package product 10 shaped as a
rectangular prism, which has been manufactured by bending and heat
sealing blanks of the packaging material of FIG. 1. The figure
includes a partial enlargement of the package wall, showing that
the polymer layer 2 tinted white by pigmenting is placed outside
the substrate board 4 in the package, and that the grey-pigmented
polymer-layer 8 is placed inside this. Thus the outer surface of
the package is white and its inner surface is grey, resembling an
aluminium foil. At the seam points 11 of the package, the blank
edges are overlapping and the polypropene layers 1, 2, 8, 9 of the
opposite board sides are tightly heat sealed together. In addition
to the outermost transparent layers 1, 9, the pigmented polypropene
layers 2, 8 also contribute to the heat sealing. The package is
intended for sterilisation at the autoclave temperature of approx.
130.degree. C., at which the white layer 2 prevents the package
from yellowing.
[0033] The material of package 10 of FIG. 11 can be varied, for
instance by using any of the packaging materials illustrated in
FIGS. 2 to 10. In accordance with the invention, it is further
possible to exclude the light-shield layer 8 inside the package
from the materials of FIGS. 7 to 10, provided that the outer layer
3 containing black pigment gives adequate light shield for the
product. It is further possible, within the scope of the invention,
to provide sterilised heat-sealed poach packages having a fibre
base of paper and a weight in the range 20 to 120 g/m.sup.2.
[0034] The following examples comprise experiments, which have
primarily tested the effect achieved with pigments added to the
polymer coating in covering yellowing of the fibre base of the
packaging material during autoclave treatment. The examples have
also measured the protection against humidification of the fibre
base provided by polymer coatings. The autoclave treatment does not
affect the light shield achieved with pigments on the opposite side
of the fibre base, and this is why this effect has not been
tested.
EXAMPLE 1
[0035] Pieces of fibre-based packaging material were tested in an
autoclave, in which the saturated vapour had a temperature of
130.degree. C. The fibre base of the material consisted of a
packaging board made of bleached pulp having a weight of 250
g/m.sup.2. The test material 1 consisted of this material as such.
Test material 2 consisted of said board, with an aluminium foil
laminated on its other side by means of a low-density polyethene
(LDPE) layer having a weight of 20 g/m.sup.2, which acted as a
binder. Test materials 3 to 11 were layered packaging materials,
whose substrate consisted of said test material 2 and in which the
board was equipped, on the side opposite to the aluminium foil,
with one single polymer coating layer. The polymer of this layer
was polyethene (test material 3), polypropene, (test materials 4
and 5), a mixture of 70% polypropene and 30% polyethene (test
materials 6 and 7), a pigmented mixture of 92% of the mixture of
polypropene and polyethene above and 8% titanium dioxide (test
materials 8 and 9), and also cyclo-olefin copolymer (COC), which
was the product Topas 8007D, producer Ticona GmbH.
[0036] The test material pieces were heated in an autoclave for 20
minutes at room temperature to the treatment temperature of
130.degree. C., at which the pieces were maintained for 0, 20, 40
or 60 minutes. After the treatment, the autoclave was cooled within
20 minutes, resuming room temperature, at which the test pieces
were removed from the autoclave. For each test material, the
brightness (ISO %) of the polymer-coated side of the material, i.e.
opposite to the aluminium foil, was measured before the autoclave
treatment (initial brightness) and after autoclave treatments of
different durations. Accordingly, the moisture content of the
materials was measured before the autoclave treatment (initial
moisture) and after autoclave treatments of different durations.
The results are presented in the following table 1, which also
indicates the weight of the polymer-coating layer in each of the
test materials 3 to 11. TABLE-US-00001 TABLE 1 Coating Moisture
Brightness Test amount (%) (ISO %) material g/m.sup.2 Initial 0
min. 20 min. 40 min. 60 min. Initial 0 min. 20 min. 40 min. 60 min.
1 -- 4.4 -- -- -- -- 87.06 -- -- -- -- 2 0 5.0 31.8 31.9 -- --
86.07 78.46 74.46 -- -- 3 44.7 5.9 -- -- -- -- -- -- -- -- -- 4
28.0 5.8 10.0 12.6 13.5 14.0 86.05 78.52 71.92 68.10 65.12 5 53.2
5.7 8.3 10.8 11.3 11.9 85.99 79.44 72.67 68.30 65.12 6 30.7 5.7
10.1 12.0 13.2 13.6 86.01 78.68 71.61 67.55 64.97 7 57.9 5.8 8.8
10.8 12.1 12.2 86.18 79.63 72.09 68.13 65.62 8 41.9 5.8 9.3 11.7
12.5 13.0 89.68 85.98 83.55 81.91 80.89 9 30.4 5.6 10.1 12.2 13.2
13.7 89.14 84.47 81.08 79.44 78.19 10 15.4 5.6 8.7 10.9 12.3 12.8
85.61 78.40 70.66 65.49 62.75 11 23.3 5.8 7.8 9.5 11.0 11.6 85.63
77.98 69.98 65.00 62.04
[0037] The results show that regarding polymer-coated test
materials 4 to 11, the fibre base had 14% maximum moisture content
after autoclave treatment, which is still an acceptable value in
view of the autoclave treatment of a package made of this material.
In test material 3, the LDPE coating layer melted at autoclave
temperature, and this is why the moisture content of the fibre base
was not measured. Measurements of test material 2, i.e. uncoated
aluminium/LDPE/board laminate, indicate strong water soaking of the
unprotected fibre base in the autoclave.
[0038] A study of the measured brightness values before the
autoclave treatment and after various treatment durations shows a
progressive decrease in brightness as the treatment period
increases, which is due to yellowing of the fibre base, which is
not at all covered by the colourless polymer surface. With test
materials 8 and 9, in which the polymer coating layer was
pigmented, the brightness reduction was, however, substantially
less than with materials equipped with an unpigmented colourless
polymer coating. Consequently, white titanium dioxide pigment
allows the yellowing of a fibre base occurring in autoclave
treatment to be covered to a considerable extent.
EXAMPLE 2
[0039] A series of tests in conformity with example 1 was made with
materials, in which the fibre base consisted of packaging board
made of bleached pulp, having a weight of 210 g/m.sup.2(test
material 1). On one side of this board, an aluminium foil (test
material 2) had been laminated by means of an LDPE binder layer
having a weight of 20 g/m.sup.2, and the opposite side of the board
was additionally equipped with a two-layered polymer coating, whose
inner layer contained a mixture of 70% of polypropene and 30% of
polyethene, to which had been added titanium dioxide in various
amounts, and whose outer layer was pure polypropene (test materials
3 to 12). The measured moisture contents of the fibre base and the
brightness on the polymer coating side in the material before and
after the autoclave treatment are shown in table 2. The table also
contains the layer weights of the inner pigmented and the outer
unpigmented polymer layers, respectively. TABLE-US-00002 TABLE 2
Coating amount g/m.sup.2 Moisture (%) Pigmented Colourless Test
inner outer Brightness (ISO %) material layer layer Initial 0 min.
20 min. 40 min. 60 min. Initial 0 min. 20 min. 40 min. 60 min. 1 --
-- 4.6 -- -- -- 86.1 -- -- -- -- 2 0 0 4.7 -- -- -- -- 84.2 -- --
-- -- 3 12.1 23.7 -- 10.6 12.6 13.5 14.0 86.7 81.3 76.8 74.0 71.7 4
20.7 25.7 5.8 10.2 11.8 12.6 13.6 87.5 83.1 79.7 77.2 75.5 5 21.4
39.9 -- 9.7 11.2 12.1 12.8 87.5 83.3 79.9 77.6 75.7 6 10.7 25.3 --
10.5 12.7 13.5 14.4 86.9 82.9 77.5 74.9 72.8 7 19.8 26 5.6 9.9 11.9
12.8 13.5 87.6 84.2 80.0 77.6 76.0 8 19.1 32.7 -- 9.6 11.3 12.1
13.0 87.7 84.6 80.7 77.2 77.2 9 11.2 28.6 -- 10.3 12.3 13.1 13.8
87.1 82.2 78.6 75.7 74.5 10 21.2 24.9 5.6 9.7 11.4 12.3 13.1 88.0
84.4 81.6 79.6 78.7 11 19.6 31.3 -- 9.5 11.1 11.9 12.7 88.4 84.9
82.4 80.5 79.8
[0040] The results indicate a decrease in the brightness of the
material as the autoclave treatment period increases, however, a
comparison of the results with the brightness of the materials
equipped with an unpigmented polymer coating of table 1 shows the
considerable effect of the titanium dioxide pigment in covering the
yellowing of the fibre base, the effect increasing with an increase
of the pigment concentration and the weight of the pigmented layer,
i.e. the layer thickness. A still better covering effect can
obviously be achieved by further increasing the layer thickness of
the pigmented polymer layer.
EXAMPLE 3
[0041] In this example, the test series was performed with test
materials free from aluminium, whose fibre base consisted of a
packaging board made of bleached pulp, having a weight of 210
g/m.sup.2 (test material 1). On one side, the board was coated with
a polymer layer, in which polypropene was admixed with 7.5% of
titanium dioxide and having a layer weight of 58 g/m.sup.2 (test
material 2). The opposite side of the board was coated with an
unpigmented polymer coating layer (test material 3 to 6), or with a
layered structure formed of two or three successive unpigmented
polymer layers (test materials 7 to 11). The materials of the
coating layers was polypropene (test materials 3 and 4), a mixture
of 70% of polypropene and 30% of polyethene (test materials 5 and
6), a two-layered structure, whose inner layer was COC (Topas
8007D) and outer layer, said mixture of polypropene and polyethene
(test material 7), a three-layered structure, whose innermost layer
was polyamide, following layer a binder (Admer NF 912E) and
outermost layer said mixture of polypropene and polyethene (test
materials 8 and 9), or a three-layered structure, whose innermost
layer was ethyl vinyl alcohol copolymer, intermediate layer a
binder (Admer NF 912E) and outermost layer polypropene. The weights
of the polymer layer(s) on the unpigmented side of the fibre base
are indicated in the following table 3. TABLE-US-00003 TABLE 3
Brightness (ISO %) Coating Un- amounts, Pigmented pigmented
g/m.sup.2 Moisture (%) side side Test Innermost Interm. Outermost 0
30 60 60 60 material layer layer layer Initial min. min. min.
Initial min. Initial min. 1 -- -- -- -- -- -- -- -- -- -- -- 2 --
-- 0 -- -- -- -- 87.9 -- 85.8 -- 3 -- -- 69.4 -- 10.4 12.9 14.3
87.8 82.5 83.3 63.8 4 -- -- 41.7 -- 10.9 13.9 15.0 87.9 82.1 83.7
64.7 5 -- -- 62.1 -- 10.6 13.4 15.0 87.3 80.7 83.6 64.7 6 -- --
38.4 -- 11.4 14.4 15.3 88.1 82.5 83.9 65.5 7 22.5 -- 33.1 -- 10.0
12.8 13.9 87.7 80.8 83.3 62.3 8 13.2 6.3 42.0 -- 11.4 14.4 15.6
87.4 81.5 83.5 62.2 9 12.9 5.9 50.4 -- 11.4 14.2 15.4 87.8 81.9
83.4 61.5 10 10.4 5.6 42.1 -- 10.8 14.3 15.7 88.1 82.7 83.5 64.2 11
11.5 6.1 51.7 -- 10.8 13.8 15.3 82.6 82.6 83.5 63.6
[0042] The autoclave treatments of the test materials were
performed in the same manner as in examples 1 and 2, except that
the duration of the autoclave treatment at a temperature of
130.degree. C. was 0, 30 or 60 minutes, respectively and the
initial brightness of the material and brightness after a 60 minute
autoclave treatment were measured on both sides of the
material.
[0043] The results of table 3 show the crucial difference in the
change of the brightness between the fibre base sides coated with
pigmented and unpigmented coating. On the pigmented side, there was
a slight decrease in the brightness of the material, and in all the
cases, the brightness value after one hour of autoclave treatment
was above 80% ISO. On the unpigmented side of the material, the
brightness decreased notably as a result of yellowing of the fibre
base, which the colourless coating layers are unable to cover.
EXAMPLE 4 (COMPARATIVE)
[0044] A test series was performed with a packaging material, whose
fibre base consisted o a packaging board made of bleached pulp
having a weight of 210 m/m.sup.2. The board was coated on one side
with a polymer layer covering against yellowing, in which
polypropene was admixed with 7.5% of titanium dioxide and whose
layer weight was 58 g/m.sup.2. The opposite board side was coated
with an unpigmented polymer coating layer (test materials 1 to 4)
or a layer structure formed of two or three successive unpigmented
polymer layers (test materials 5 to 9). The coating layer materials
were polypropene (test materials 1 and 2), a mixture of 70% of
polypropene and 30% of polyethene (test materials 3 and 4), a
two-layered structure, whose inner layer was COC (Topas 8007D) and
outer layer said mixture of polypropene and polyethene (test
material 5), a three-layered structure, whose innermost layer was
polyamide, following layer a binder (Admer NF 912E) and outermost
layer said mixture of polypropene and polyethene (test materials 6
and 7), or a three-layered structure, whose innermost layer was
ethyl vinyl alcohol polymer, intermediate layer a binder (Admer NF
912E) and outermost layer polypropene (test materials 8 and 9).
[0045] The test material pieces were heated in an autoclave for 20
minutes at room temperature to a treatment temperature of
130.degree. C., at which the pieces were kept for 60 minutes. After
the treatment, the autoclave was cooled in 20 minutes, resuming
room temperature, at which the test pieces were removed from the
autoclave. The brightness (ISO %) on each side of each test
material was measured before the autoclave treatment (initial
brightness) and after the autoclave treatment. The results are
shown in table 4, which also indicates the weights of the
unpigmented polymer coating layers in each test material 1 to 9.
TABLE-US-00004 TABLE 4 Coating amounts, Brightness g/m.sup.2
Pigmented (ISO %) Unpigmented Test Innermost Intermediate Outermost
side 60 side 60 material layer layer layer Initial minutes Initial
minutes 1 -- -- 69.4 87.8 82.5 83.3 63.8 2 -- -- 41.7 87.9 82.1
83.7 64.7 3 -- -- 62.1 87.3 80.7 83.6 64.7 4 -- -- 38.4 88.1 82.5
83.9 65.5 5 22.5 -- 33.1 87.7 80.8 83.3 62.3 6 13.2 6.3 42.0 87.4
81.5 83.5 62.2 7 12.9 5.9 50.4 87.8 81.9 83.4 61.5 8 10.4 5.6 42.1
88.1 82.7 83.5 64.2 9 11.5 6.1 51.7 87.9 82.6 83.5 63.6
[0046] The test results of the table show the problem to be solved
with the invention, i.e. the notable decrease of brightness due to
yellowing of the fibre base, which the colourless coating layers on
the unpigmented side of the fibre base have been unable to cover.
Owing to the pigment, the initial brightness on the opposite side
of the fibre base, pigmented with titanium dioxide as in FI patent
application 20030260, was high and a slight decrease of brightness
has occurred in the autoclave treatment, however, with a final
brightness above 80% ISO in each case.
EXAMPLE 5
[0047] A test series in conformity with example 4 was carried out
with materials of the invention, in which the fibre base consisted
of a packaging board made of bleached pulp, having a weight of 250
g/m.sup.2. One side (the outer side) of this board, which is
intended to be the outer surface of the autoclave package, was
equipped with a two-layered polypropene coating, in the innermost
layer of which polypropene was admixed with carbon black and
titanium dioxide (test materials 1 to 7) or merely with carbon
black (test materials 8 to 22), and whose outermost layer comprised
polypropene admixed with titanium dioxide alone. In part of the
materials (test materials 20 to 22), the opposite board side, which
will be the inner surface in the autoclave package, was equipped
with an inner light-shield layer based on polypropene and pigmented
grey with carbon black (0.15%) and titanium dioxide (12,5%), having
a weight of 27 g/m.sup.2, and with a transparent polypropene layer
covering this, having a weight of 23 g/m.sup.2. The measured
brightness of said outer material side before and after the
autoclave treatment is shown in the following table 5. The table
also comprises the pigment concentrations of the pigmented polymer
layers on the outside of the material and the layer weights.
TABLE-US-00005 TABLE 5 Outside Pigment coating concentrations
amounts in the coating g/m.sup.2 layers (%) Outer Brightness Test
Inner Outer Inner layer layer ISO % material layer layer C
TiO.sub.2 TiO.sub.2 Initial 60 min. 1 9 19 0.15 12.5 12.5 67.7 68.2
2 9 21 0.15 12.5 12.5 70.0 70.6 3 9 28 0.15 12.5 12.5 74.8 74.6 4
12 25 0.15 12.5 12.5 74.2 72.3 5 12 30 0.15 12.5 12.5 74.6 75.9 6
12 34 0.15 12.5 12.5 71.0 72.0 7 12 41 0.15 12.5 12.5 79.9 80.1 8 6
21 0.12 -- 12.5 65.2 63.4 9 6 30 0.12 -- 12.5 76.3 75.0 10 6 25
0.09 -- 12.5 75.4 74.1 11 6 30 0.09 -- 12.5 77.4 74.5 12 9 23 0.09
-- 12.5 67.9 67.1 13 9 29 0.09 -- 12.5 74.2 73.2 14 6 26 0.06 --
12.5 76.9 75.0 15 6 30 0.06 -- 12.5 77.6 73.9 16 9 26 0.06 -- 12.5
74.6 71.0 17 9 30 0.06 -- 12.5 77.2 75.0 18 9 33 0.06 -- 12.5 80.5
78.8 19 9 40 0.06 -- 12.5 82.3 81.0 20 6 19 0.09 -- 12.5 73.3 70.9
21 6 25 0.09 -- 12.5 77.3 75.6 22 6 30 0.09 -- 12.5 82.5 81.2
[0048] The results show that the packaging material of the
invention can be toned to an optimum brightness of above 80% ISO,
which undergoes a slight, practically negligible change during
autoclave treatment. The final brightness after the treatment is
almost the same as in FI patent application 20030260, however, with
a clearly improved colour stability of the light shade during the
treatment.
* * * * *