WO2008094085A1

WO2008094085A1 - A packaging laminate for a retortable packaging container, and a method of producing the same

Info

Publication number: WO2008094085A1
Application number: PCT/SE2007/001098
Authority: WO
Inventors: Ulrika Tornerefelt; Rune SJÖLIN
Original assignee: Tetra Laval Holdings & Finance S.A.
Priority date: 2007-01-30
Filing date: 2007-12-12
Publication date: 2008-08-07
Also published as: SE0700222L

Abstract

A packaging laminate for a retortable packaging container provided with decorative artwork in which a food may, for purposes of extending its shelf-life, be heat treated in a retort or in a tunnel during simultaneous agitation, without the risk that the decorative artwork of the packaging container is destroyed or deteriorates because of outer stresses. The packaging laminate (200) has a paper- or paperboard layer (201) and outer coatings (202 and 203) of which the one film (202) is, or includes, a film or propylene homopolymer. The film (202) has decorative artwork (204) of UV-cured printing ink and is wholly or partly coated with an outer layer (205) of UV-cured lacquer. Preferably, the layer (205) includes particles of a friction-damping material, e.g. polytetrafluoroethylene (PTFE).

Description

A packaging laminate for a retortable packaging container, and a method of producing the same

Technical field The present invention relates to a packaging laminate provided with decorative artwork for a retortable packaging container, the packaging laminate comprising a layer of paper or paperboard and outer, liquid-tight coatings of plastic, of which the one coating, for decorative and/or informative purposes, carries print of a UV-cured printing ink which is protected by a similarly UV-cured lacquer. The present invention also relates to a method of producing such a packaging laminate provided with decorative artwork for a retortable packaging container, the method comprising the steps of coating the one side of a web of paper or paperboard with a liquid-tight film of plastic, of printing, for decorative and/or informative purposes, the film with UV-curable printing ink, of coating the printed printing ink with a UV-curable protective lacquer, and irradiating the coated side of the paper- or paperboard web with UV light in order to cure said printing ink and protective lacquer.

Moreover, the present invention relates to a retortable packaging container consisting of such a packaging laminate provided with decorative artwork.

Background art

A packaging laminate of the type described above is previously known from, for example, international Patent Application carrying Publication number WO 02/22462. The prior art packaging laminate comprises a layer of paper or paperboard and outer, liquid-tight coatings of plastic, of which the one coating displays a decorative and/or informative print of a UV-cured printing ink which is protected by a similarly UV-cured lacquer.

From the prior art packaging laminate, it is possible to produce a retortable packaging container for foods which, for purposes of extending their shelf-life, are to be exposed to a heat treatment while still packed in the packaging container.

Such a heat treatment for extending shelf-life may be put into effect batchwise in a retort in which filled packaging containers are stacked on and adjacent one another before the retort is sealed. The food is heated by the supply of a heating medium which, via nozzles, is sprayed against the outer walls of the packaging containers until the food has reached a predetermined treatment temperature. The food is held at this temperature for a sufficient period of time to exterminate, deactivate or eliminate harmful microorganisms inside the packaging containers during the continued supply of heating medium, whereafter the supply of heating medium is stopped and cooling medium is instead supplied in order to cool the food, before the retort is opened and the packaging containers are removed from the retort.

A batchwise heat treatment in a retort is typically employed for such foods as pasta, soups, ready meals, beans, ravioli and tuna fish which withstand heat treatment at the elevated pressures and temperatures which are normally employed in a retort, i.e. 120-135 °C or higher, hi order to hasten the transfer of heat from the heating medium to the packed food and thereby reduce the requisite time to attain the treatment temperature, it is advantageous to carry out the heat treatment with simultaneous agitation or mixing of the packed food. Such agitation or mixing is effectively catered for by suitable mechanical means with the aid of which the packaging containers may be shaken, vibrated or rotated.

Another prior art heat treatment for the same purpose of extending shelf-life as in the foregoing may be put into effect continuously at atmospheric pressure in an open tunnel through which the filled packaging containers, in suitable stacks adjacent one another, are conveyed for heating and cooling of the food in accordance with a predetermined time/temperature scale. Since a continuous heat treatment or pasteurization is often carried out at a considerably lower treatment temperature, at most approx. 100 °C, than retorting, the continuous method is preferred for foods of a heat-sensitive type, in particular tomato products, fruits and vegetables. Also in this case, it is thus not only advantageous, but even necessary, to hasten the transfer of heat to the packed food in order to minimise the time during which the food is subjected to thermal effects. Such a hastened thermal transfer is catered for using suitable mechanical means by which the packaging containers may be shaken, vibrated or rotated. A heat treatment which is carried out batchwise in a retort or continuously in a tunnel, as described above, naturally places extremely high demands on both the mechanical and the physical properties of the packaging container. Packaging containers which are produced from a packaging laminate according to the above mentioned publication WO 02/22462 are sufficiently mechanically strong and stable to withstand such rough heat treatment without being deformed or otherwise destroyed or suffering from a deterioration in quality, as long as the heat treatment is carried out without agitation or mixing of the packed food. On the other hand, problems not seldom occur when the stacked packaging containers are also subjected to agitating shaking-, vibration or rotation movements, since immediately neighbouring packaging containers, during such movements, readily scratch, chafe and jolt against one another, with the result that not only the lacquer layer but also the subjacent decorative artwork and printing ink on the outer walls of the packaging containers are destroyed because of such frictional wear. There is thus still a need in the art for a packaging laminate which makes for the production of packaging containers in which a food may, for purposes of extending its shelf-life, be heat treated in a retort or in a tunnel during agitation or mixing of the packed food, without the appearance of the packaging container being destroyed or deteriorating because of excessive frictional wear.

Object of the invention

One object of the present invention is thus to obviate the above-described drawback in connection with the prior art packaging laminate.

A further object of the present invention is to realise an improved packaging laminate of the type described by way of introduction as a result of which the problem inherent in excessive wear to decorative artwork and printing may effectively be obviated.

Yet a further object of the present invention is to realise a packaging laminate for a packaging container in which a food may, for purposes of extending its shelf- life, be heat treated in a retort during simultaneous agitation of the packed food, without the outer decorative artwork or printing of the packaging container running the risk of being destroyed or deteriorating because of frictional wear against adjacent packaging containers.

Yet a further object of the present invention is to realise a packaging laminate for a packaging container in which a food may, for purposes of extending its shelf- life, be heat treated at atmospheric pressure in a tunnel through which the packaging container is conveyed during simultaneous agitation of the packed food, without the outer decorative artwork or printing of the packaging container running the risk of being destroyed or deteriorating as a result of frictional wear against adjacent packaging containers. Still a further object of the present invention is to realise a method of producing a packaging laminate according to the invention.

Yet a further object of the present invention is to realise a packaging container of the packaging laminate according to the invention in which a packed food may, for purposes of extending its shelf-life, be heat treated in a retort or in a tunnel during simultaneous agitation, without the outer decorative artwork or printing of the packaging container running the risk of being destroyed or deteriorating because of frictional wear against adjacent packaging containers.

These and other objects and advantages will be attained according to the present invention by means of the packaging laminate according to independent Claim 1 , by means of the method according to independent Claim 6 and by means of the packaging container according to independent Claim 13, respectively.

Expedient embodiments of the packaging laminate according to the present invention have the characterising features as set forth in appended subclaims 2-5, and expedient embodiments of the method according to the present invention have the characterising features as set forth in appended subclaims 7-12.

Brief summary of the invention

According to one aspect of the invention, there is thus realised an abrasion- resistant packaging laminate for a retortable packaging container, the packaging laminate comprising a layer of paper or paperboard and outer, liquid-tight coatings of plastic, of which the one has, for decorative and/or informative purposes, has decorative artwork consisting of UV-cured printing ink which is protected by an outer layer of UV-cured lacquer. The packaging laminate is characterised in that the plastic coating provided with decorative artwork is a film of propylene homopolymer.

By selecting, as plastic coating provided with decorative artwork, a film of propylene homopolymer, there will be attained, in addition to abrasion-resistant adhesion between printing ink and coating, also a printing surface which per se is sufficiently hard and strong to withstand impacts, jolts and similar outer stresses which may occur during, for example, a heat treatment with agitation, without the risk that the plastic coating is deformed by impressions with consequential cracking in the outer protective lacquer layer within the regions of such outer stresses.

In order further to improve the adhesion between printing ink and the film of propylene homopolymer, it is advantageous to subject the printing surface of the film to a per se known oxidation treatment prior to printing with printing ink in order thereby to increase the number of adhesion-activated seats on the printing surface of the film by means of which the printing ink is bonded to the film. One example of such a prior art oxidation treatment which may advantageously be employed in the present invention is flame treatment of the printing surface of the film immediately prior to or in connection with the film being printed with printing ink.

Preferably, the protective lacquer layer includes particles of a friction- damping material by means of which a non-wearing abrasion or rubbing between adjacent packaging containers in contact with one another is made possible. One example of a usable friction-damping material according to the invention is polytetrafluoroethylene (PTFE).

According to another aspect of the present invention, there will be provided a method of producing a packaging laminate provided with decorative artwork for a packaging container, the method comprising the steps of coating the one side of a web of paper or paperboard with a film of plastic, of printing, for decorative and/or informative purposes, the film with a UV-curable printing ink, of wholly or partly coating the printed plastic film with a UV-curable protective lacquer, and of subjecting the thus coated side of the paper- or paperboard web to UV radiation for curing of said printing ink and protective lacquer. The method according to the invention is characterised in that the one side of the paper- or paperboard web is coated with a film of propylene homopolymer.

According to one preferred embodiment of the method according to the invention, the plastic film is subjected to an oxidation treatment immediately prior to, or in connection with the film being printed with printing ink. The oxidation treatment may be a corona treatment, but is preferably a flame treatment of the plastic film.

According to yet a further preferred embodiment of the method according to the invention, the printed film of propylene homopolymer is coated with a UV- curable protective lacquer containing particles of a friction-damping material. Particles of polytetrafluoroethylene (PTFE) are preferably selected as friction- damping material.

The film of propylene homopolymer may, according to the invention, be applied on the paper- or paperboard web by extrusion, but for reasons of cost it is preferred that the film be applied by co-extrusion with a film of a copolymer of ethylene and propylene or a mixture of polyethylene and polypropylene, whereby the more expensive film of propylene homopolymer can be made thinner and the material consumption will thereby be less for this film than if it were to be applied alone by extrusion. According to still a further aspect of the present invention, there will be realised an abrasion-resistant packaging container for foods which, for purposes of extending their shelf-life, may be heat treated in the packaging container during simultaneous agitation without the packaging container being destroyed or deteriorating because of chafing, jolts or other external effects on the outer walls of the packaging container.

Further objects, advantages and details of the present invention will be apparent from the following description with reference to the accompanying Drawings.

Brief description of the accompanying Drawings

Fig. 1 is a schematic cross section of a packaging laminate provided with decorative artwork for a packaging container according to the prior art technology; Fig. 2 is a schematic cross section of a packaging laminate provided with decorative artwork according to the present invention; and

Fig. 3 schematically illustrates how the packaging laminate in Fig. 2 can be produced using the method according to the present invention.

Detailed description of embodiment and accompanying Drawings

While the present invention will be described with particular reference to the embodiment shown on the accompanying Drawings, it is not restricted exclusively to this example. To a person skilled in the art, with the guidance of the foregoing and the following description, it will be obvious that modifications and alterations are possible without departing from the scope of the inventive concept as this is defined in the appended Claims.

Thus, Fig. 1 schematically illustrates a packaging laminate provided with decorative artwork as previously known from, for example, WO 02/22462. The packaging laminate carrying generic reference numeral 100 comprises a layer 101 of paper or paperboard which, on both sides, displays outer films 102 and 103 of plastic. As disclosed in said WO publication, the plastic in both of the outer films 102 and 103 is preferably a mixture of polyethylene (PE) and polypropylene (PP) or, a copolymer of ethylene and propylene, respectively. The one of the outer films 102 is carrier of decorative artwork 104 of

UV-cured printing ink and is wholly or partly protected by an outer layer 105 of UV-cured lacquer.

Between the second film 103 and the paper- or paperboard layer 101, the packaging laminate 100 has a layer 106 serving as gas barrier, e.g. an aluminium foil, which, via a first tie layer 107, is bonded to the film 103 and, via a second tie layer 108, is bonded to the paper- or paperboard layer 101 by means of a suitable lamination layer 109.

From the prior art packaging laminate 100, there may be produced, by fold forming and therrnosealing, packaging containers for food which, for purposes of extending its shelf-life, is to be heat treated in a retort or in a tunnel, with attendant problems associated with decorative artwork of the type described above. Such problems relating to decorative artwork and printing are avoided according to the present invention by means of the packaging laminate which is illustrated schematically in Fig. 2.

The packaging laminate carrying the generic reference numeral 200 in Fig. 2 comprises a layer 201 of paper or paperboard which, on both sides, displays outer films 202 and 203 of plastic.

One of the two outer films 202 may, as shown, be a co-extruded film comprising, on the one hand, a first film 202a turned to face towards the paper- of paperboard layer 201 and, on the other hand, a second film 202b turned to face away from the paper- or paperboard layer 201. Alternatively, the outer film 202 may be a homogenous extruded film.

In the illustrated example, where the outer film 202 is a co-extruded film, the first film 202a facing towards the paper- or paperboard layer may be a film of a copolymer of ethylene and propylene or of a mixture of polyethylene (PE) and polypropylene (PP), while the second film 202b facing away from the paper- or paperboard layer 201 is a film of propylene homopolymer.

In the alternative example where the outer film 202 is a homogenous extruded film, the outer film 202 is a film of propylene homopolymer.

The second film 202b of propylene homopolymer facing away from the paper- or paperboard layer 201, or alternatively the extruded homogenous film 202 of propylene homopolymer, acts as carrier of a decorative artwork 204 of UV-cured printing ink and is wholly or partly protected by an outer layer 205 of UV-cured lacquer.

The outer layer 205 of UV-cured lacquer preferably includes particles of a friction-damping material in order to facilitate mutual sliding between adjacent packaging containers of the packaging laminate 200 when these are subjected to shaking, vibration and similar movements in connection with a heat treatment in a retort or tunnel, as explained above. One preferred example of such a friction- damping material is polytetrafluoroethylene (PTFE). The second outer plastic film 203 is preferably a thermosealable film of a copolymer of ethylene and propylene. Between the thermosealable film 203 and the paper- or paperboard web 201, the packaging laminate 200 may have a layer 206 serving as gas barrier, e.g. an aluminium foil, which, via a first tie layer 207, is bonded to the thermosealable film 203 and, via a second tie layer 208, is bonded to the paper- or paperboard layer 201 by means of a suitable lamination layer 209.

Fig. 3 schematically illustrates how the packaging laminate in Fig. 2, readily and with simple, already available means, may be produced by the method according to the invention. A web 300 of paper or paperboard (to the left in Fig. 3) which, on the one side, may, but need not necessarily be, coated with the material layers illustrated in Fig. 2, i.e. thermosealable film, first and second tie layers, gas barrier layer (e.g. aluminium foil) and lamination layer, is coated on its other uncoated side with a film 301 which is extruded or co-extruded on the web 300 by means of an extruder 302.

In the case when the film 301 is extruded on the web 300, the film 301 is a homogenous film of propylene homopolymer. In the second case when the film 301 is co-extruded on the web 300, the co-extruded film comprises two films, of which the one may be a film, facing towards the web 300, of a copolymer of ethylene and propylene, or of a mixture of polyethylene (PE) and polypropylene (PP), while the other is a film, facing away from the web 300, of propylene homopolymer. The web 300 with the extruded or co-extruded film 301 , is led through the nip between two rotary cooling rollers 303 and 304 and, via a bending roller 305, to a station at A where the extruded or co-extruded film 301 is, for purposes of promoting adhesion, subjected to an oxidation treatment. The adhesion-promoting treatment may be a corona treatment, but is preferably a flame treatment by means of which bonding sites on the surface of the exposed film 301 are activated by means of flames (shown schematically by means of broken line arrows at A) which are directed towards the web.

After the oxidation treatment at station A, the web 300 is led further in the direction of the solid-line arrows to a printing station at B where the activated plastic film 301 is, by a suitable printing method (schematically illustrated by ghosted roller pairs at B), provided with the desired decorative artwork of UV-curable printing ink. As was mentioned previously, the plastic film 301 is preferably printed immediately after or in direct association with the above mentioned oxidation treatment in order to ensure good adhesion between printing ink and plastic film 301.

The web 300 is thereafter led further to a station C where the printed plastic film 301 is wholly or partly coated (schematically illustrated by a ghosted roller pair) with a layer of UV-curable lacquer containing particles of a friction-damping material, e.g. polytetrafluoroethylene (PTFE).

After, or in connection with, the coating with the UV-curable lacquer, the plastic film is subjected to UV radiation in order, in one and the same operation, to cure both the printing ink and lacquer on the plastic film.

From the packaging laminate according to the present invention, there is produced in a per se known manner by fold forming and thermosealing a packaging container in which a packed food may, for purposes of extending its shelf-life, be heat treated in a retort or in a tunnel during simultaneous agitation, without the decorative artwork of the packaging container being destroyed or deteriorating because of abrasion and rubbing against adjacent packaging containers.

Industrial application

The packaging laminate according to the present invention is usable for producing packaging containers provided with decorative artwork in which a food may, for purposes of extending its shelf-life, be heat treated in a retort or tunnel without the risk that the decorative artwork of the packaging container be destroyed or deteriorate because of outer stresses. The packaging laminate is particularly usable for the production of such retortable packaging containers for a food which, during the shelf-life extending heat treatment, are simultaneously to be subjected to agitation or mixing by shaking, vibration or rotation of the packaging container.

Claims

What is claimed is:

1. A packaging laminate for a retortable packaging container, the packaging laminate (200) comprising a layer (201) of paper or paperboard and outer, liquid-tight films (202 and 203) of plastic, of which the one (202; 202a) has, for decorative and/or informative purposes, decorative artwork (204) of UV-cured printing ink which is protected by an outer layer (205) of UV-cured lacquer, characterised in that the film (202; 202b) provided with decorative artwork consists of propylene homopolymer.

2. The packaging laminate as claimed in Claim 1, characterised in that the film provided with decorative artwork is an extruded film (202) of propylene homopolymer.

3. The packaging laminate as claimed in Claim 1, characterised in that the film provided with decorative artwork is a co-extruded film comprising a first film (202a) facing towards the paper- or paperboard layer (201), of a copolymer of ethylene and propylene or a mixture of polyethylene (PE) and polypropylene (PP) and a second film (202b), facing away from the paper- or paperboard layer (201), of propylene homopolymer.

4. The packaging laminate as claimed in any of the preceding Claims, characterised in that the outer layer (205) of UV-cured lacquer includes particles of a friction-damping material.

5. The packaging laminate as claimed in Claim 4, characterised in that the friction-damping particles in the lacquer layer (205) consist of polytetrafluoroethylene (PTFE).

6. A method of producing a packaging laminate as claimed in Claim 1, the method comprising the steps of coating one side of a web (300) of paper or paperboard with a film (301) of plastic, providing, for decorative and/or informative purposes, the film (301) with decorative artwork of UV-curable printing ink, wholly or partly coating the printed film with a coating of UV-curable lacquer, and subjecting the coated side of the paper- or paperboard web (300) to UV radiation so as to cure both printing ink and lacquer, characterised in that the plastic film (301) consists of or includes propylene homopolymer.

7. The method as claimed in Claim 6, characterised in that the plastic film (301) of propylene homopolymer is extruded as a homogenous film on the paper- or paperboard web (300).

8. The method as claimed in Claim 6, characterised in that the plastic film (301) includes a first film, facing towards the paper- or paperboard web (300), of a copolymer of ethylene and propylene or a mixture of polyethylene (PE) and polypropylene (PP) and a second film, facing away from the paper- or paperboard web (300), of propylene homopolymer, both of said films being co-extruded on the paper- or paperboard web (300).

9. The method as claimed in any of Claims 6 to 8, characterised in that the extruded or co-extruded film (301), respectively, is subjected to an adhesion- promoting oxidation treatment immediately before or in connection with the application of printing ink.

10. The method as claimed in Claim 9, characterised in that the adhesion- promoting oxidation treatment includes flame treatment or corona treatment of the film (301).

11. The method as claimed in any of Claims 6 to 10, characterised in that the UV-curable lacquer includes particles of a friction-damping material.

12. The method as claimed in Claim 11, characterised in that the friction- damping particles consist of polytetrafluoroethylene (PTFE).

13. A packaging container which is produced by fold forming and thermosealing of a packaging laminate as claimed in any of Claims 1 to 5.