CN1275766C - A packaging laminate for a retortable packaging container - Google Patents

Abstract

A packaging laminate for a retortable packaging container of the type which is produced by fold forming and thermosealing of a web or a prefabricated blank of the packaging laminate. The packaging laminate (10) includes a base layer (11) of paper or paperboard which has been rendered hydrophobic by stock sizing. The base layer (11) is preferably rendered hydrophobic by stock sizing by means of an aqueous dispersion or emulsion of an alkyl ketene dimer or mixture of alkyl ketene dimers with a different number of carbon atoms in their respective fat tails. Most preferably, the base layer (11) is rendered hydrophobic by stock sizing by means of an aqueous dispersion or emulsion of an alkyl ketene dimer containing 18 carbon atoms in its fat tail. The quantity of alkyl ketene dimers is suitably at least approx. 0.25 weight %, preferably 0.25 - 0.4 weight %, most preferably approx. 0.4 weight %, calculated on the dry weight of the base layer (11).

Description

Packaging laminate for retortable packaging containers and retortable packaging containers made therefrom

technical field

The present invention relates to a packaging laminate for retortable packaging containers, the laminate comprising a paper or paperboard base layer.

Background technique

International Patent Application Publication No. WO 97/02140 discloses a packaging laminate of the type described above. Prior art packaging laminates have a rigid but foldable base or core of paper or paperboard, and outer layers of liquid-tight, heat-resistant plastic on either side of the base. A gas barrier layer, for example aluminum foil, may also be provided between the base layer and the outer layer of one of the two plastic outer layers, thus also rendering the packaging laminate gas, in particular oxygen, permeable.

International patent applications WO97/02181 and WO98/18680 also describe similar packaging stacks.

The final packaging container is manufactured from the prior art packaging stack using modern packaging and filling machines which utilize rolls, preforms of the packaging stack to form, fill and seal the final packaging. For example, blanks are used to manufacture packaging containers by first forming a blank into a tubular container enclosure in which the longitudinal edges of the blank are each folded in half and permanently joined to each other by heat sealing at so-called lap joints, The joint continues between the two open ends of the tubular container enclosure. A substantially planar end cap (bottom surface) is then imparted to one end of the container enclosure by fold forming and heat sealing adjacent bottom panels of the container enclosure. The resulting sealed-ended (bottom-end) container enclosure is filled with desired things such as food through the other open end, after filling, by final folding and forming of the corresponding end panels of the filled container enclosure. Heat sealing, thereby imparting a similar substantially planar end cap (top surface) to the open end.

It has long been known that heat-treated food products can extend their shelf life due to the fact that bacteria, fungi and other unwanted microorganisms present in the food product are destroyed, neutralized or reduced by sufficient heat treatment. In order to obtain a complete bactericidal effect, heat treatment must be carried out under the following conditions: all parts of the food to be treated are heated to the high temperature level and the length of time required to ensure that the microorganisms in the food are completely destroyed or inactivated.

Heat treatment to extend the shelf life of packaged foods is usually carried out in a retort, which is an apparatus comprising a closed processing chamber within which temperature and pressure can be adjusted and controlled during the heat treatment. Preferably this heat treatment or distillation may be carried out in the manner and under the conditions detailed in International Patent Application WO 98/16431 incorporated herein by reference. The filled packaging container is placed in the processing space of the retort, after which a gaseous heating medium, such as a flow of hot water steam, is brought into contact with the outer wall of the packaging container to heat the wrapped food to a predetermined processing temperature, which is usually Between 70-130°C. The wrapped food is kept at this temperature for a predetermined time long enough to ensure as complete a thermal destruction as possible of the microorganisms present in the food. Subsequently, the processed food is lowered to a temperature close to or slightly higher than ambient temperature, i.e. 25-30° C., using a cooling agent such as cold water, then the processing is stopped, and the packaging container is taken out from the still.

Different foods require different forms of treatment in order to achieve complete sterility by heat treatment in retorts. For some foods, more intense heat treatment is required, i.e. higher processing temperatures and/or are required than for other foods that require only a shorter duration and relatively lower temperatures to achieve the desired aseptic effect or longer processing times.

Packaging containers made of the above-mentioned known packaging laminates are generally sufficiently mechanically strong and can withstand relatively mild or less severe heat treatments, but, on the other hand, if it is sometimes necessary to ensure the thorough completeness of certain types of food During aseptic heat treatment at relatively high temperatures and/or relatively long processing times, prior art packaging containers tend to become damaged or destroyed, or even become completely unusable.

A problem often found in connection with this extremely severe heat treatment is that liquid or moisture tends to enter the packaging container in areas of the paper or cardboard layer where the cut edges of the paper or cardboard layer are more or less Areas prone to exposure to gaseous heating media such as hot steam. An example of such an area of the packaging container which is particularly sensitive to moisture and heat is along the freely exposed cut edge extending all the way between the two ends of the tubular container enclosure, ie between the top and bottom surfaces of the packaging container. In particularly severe cases, moisture and liquid penetration can cause the packaging walls to swell and delaminate, rendering them unattractive or completely unsuitable for further processing.

As described in International Patent Application WO 98/18680, previous attempts to solve the above-mentioned problem of moisture- and liquid-absorbing cut edges have started from either chemically protecting or mechanically by cutting and refolding. Cover these edges. While these two prior art methods solve the inherent problems of moisture and liquid penetration, they require at least one additional operation and additional equipment associated therewith during the production of the packaging laminate.

It is therefore an object of the present invention to solve the disadvantages associated with the prior art described above.

Another object of the present invention is to provide a packaging laminate for packaging containers which can reliably withstand heat treatment in a retort, even if the heat treatment is carried out in the retort at high temperatures and/or for a long treatment time, without Risk of damage due to penetration of moisture and liquids.

These and other objects are achieved according to the invention, in which the packaging stack described by way of introduction is endowed with the features of claim 1 .

Advantageous and expedient embodiments of the packaging stack of the invention are further characterized by the dependent claims.

Summary of the invention

Thus, the present invention provides a packaging laminate for a retort packaging container comprising a paper or paperboard layer which has been rendered hydrophobic by stock sizing.

The hydrophobic paper or paperboard layer within the packaging laminate of the present invention does not require additional chemical and mechanical means since the paper or paperboard layer which has initially been made hydrophobic by the application of sizing has sufficient moisture and liquid impermeability properties to protect exposed cut edges. Thus, the packaging laminate according to the invention can be produced in a simple manner using existing converting equipment, without using additional operating steps and the additional equipment associated therewith during the production of the packaging laminate.

According to the invention, a hydrophobic paper or board ply is produced by sizing with an alkylketene dimer dispersed or emulsified in an aqueous solution. In a practical embodiment, the aqueous dispersion or emulsion contains an alkyl ketene dimer having 16-22 carbon atoms at its fatty tail.

In a particularly preferred embodiment of the invention, the packaging laminate comprises a paper or paperboard layer which has been prepared using an aqueous dispersion or emulsion of an alkyl ketene dimer having a fatty tail of 18 carbon atoms. is made hydrophobic. Aqueous dispersions or emulsions of alkyl ketene dimers with 18 carbon atoms not only make it possible for the alkyl ketene dimers to have higher absorbency in pulp, so that in the produced paper or cardboard layers The pore closure is good (hydrophobic) and the required high absorption is achieved without hindering the subsequent handling and processing of the pulp in the papermaking plant.

Preferably, the paper or paperboard layer in the packaging laminate of the present invention comprises alkylketene dimer in an amount greater than about 0.25% by weight, based on the dry weight of the paper or paperboard layer. In other words, preferably the amount of alkyl ketene dimer should be greater than 2.5 kg per ton of paper or paperboard, but should not exceed about 4 kg, which is the maximum amount allowed for use in a food environment.

Brief description of the drawings

The invention is described in detail with reference to the following drawings, in which:

Figure 1 is a schematic cross-sectional view of a packaging stack in its simplest embodiment according to the invention.

Figure 2 shows a packaging stack for a preferred practical embodiment of the invention.

Detailed Description of Preferred Embodiments

Figure 1 is a schematic cross-sectional view of a packaging stack in its simplest embodiment according to the invention. The packaging stack, indicated by reference numeral 10, comprises a base or core layer 11 of paper or cardboard, and liquid-tight outer layers 12 and 13 of heat-sealable plastic on either side of the base layer 11 .

Aqueous dispersion or The emulsion performs sizing to make the base layer 11 hydrophobic. In a particularly preferred embodiment, the base layer 11 is made hydrophobic by using an aqueous dispersion or emulsion of an alkyl ketene dimer having 18 carbon atoms at its fatty tail.

The amount of alkyl ketene dimer in the base layer 11 can vary, but is preferably at least about 0.25% by weight based on the dry weight of the base layer. However, when the packaging laminate 10 of the present invention is intended to be used in food-related situations, the amount of alkyl ketene dimer should not exceed 0.4% by weight based on the dry weight of the base layer 11 . In other words, the amount of alkyl ketene dimer in the dry base layer 11 is preferably 2.5-4 kg per ton of paper or board.

The material of the two liquid-tight plastic outer layers 12 and 13 is preferably heat-sealable plastic to facilitate rational production of the final retort packaging container. Examples of such heat-sealable plastics for the two liquid-tight outer layers 12 and 13 include, but are not limited to, polyethylene (PE), polypropylene (PP), polyester (PET) and copolymers thereof. Examples of suitable polyethylene plastics may be high density polyethylene (HDPE) or low density linear polyethylene (LLDPE), and examples of suitable polyester plastics may be amorphous polyester (APET).

Figure 2 shows a cross-section of a packaging stack according to a preferred embodiment of the invention. The packaging stack designated by reference numeral 20 has a base layer 21 of paper or cardboard, and liquid-tight outer layers 22 and 23 on either side of the base layer 21 .

The packaging laminate 20 also has a gas barrier layer 24 between the base layer 21 and the layer 22 of one of the two liquid-tight outer layers.

Between the liquid-impermeable layer 22 and the gas-barrier layer 24 there is an adhesive layer 25 via which the liquid-impermeable layer 22 can be bonded to the gas-barrier layer 24 .

Between the gas barrier layer 24 and the base layer 21 there is a laminate or sealant layer 26, the inherent properties of which are such that the bond between the gas barrier layer 24 and the core layer 21 is sufficiently strong and bonded. The strength is stable enough so that the bond is not weakened or completely lost when the packaging laminate 20 is exposed to extremely high temperature stresses, ie, up to about 130° C. or higher.

The liquid-tight outer layer 23 on the other side of the base layer 21 may have a decorative artwork 27 of suitable printed ink, itself protected by a transparent layer 28 applied to the decorative artwork 27 and covered by a suitable lacquer or other agent to protect the decorative artwork 27 from external damage.

In order to make the packaging laminate 20 have better integrity, an adhesive layer 29 is provided between the gas barrier layer 24 and the laminate or sealant layer 26, by which the gas barrier layer 24 is bonded to the laminate or sealant layer 26. The sealant layers 26 are bonded together.

Aqueous dispersions or emulsions of alkyl ketene dimers or mixtures of alkyl ketene dimers with varying numbers of carbon atoms at their corresponding fatty tails and preferably between 16 and 22 carbon atoms The liquid is used for sizing to make the base layer 21 hydrophobic. In a particularly preferred embodiment, the base layer 21 is rendered hydrophobic by utilizing an aqueous dispersion or emulsion of an alkyl ketene dimer having 18 carbon atoms in its fatty tail.

The amount of alkyl ketene dimer in base layer 21 can vary, but is preferably at least about 0.25% by weight based on the dry weight of base layer 21 . However, when the packaging laminate 20 of the present invention is intended for use in food-related applications, the amount of alkyl ketene dimer should not exceed about 0.4% by weight based on the dry weight of the base layer 21 . In other words, the amount of alkyl ketene dimer in the dry base layer 21 is preferably 2.5-4 kg per ton of paper or paperboard.

The liquid-tight outer layer 23 may be a plastic selected from the group consisting essentially of polyethylene (PE), polypropylene (PP) and polyester (PET) or mixtures thereof. Examples of suitable polyethylene plastics can be high density polyethylene (HDPE) or low density linear polyethylene (LLDPE), examples of suitable polypropylene plastics can be oriented polypropylene (OPP), available polyester plastics An example would be amorphous polyester (APET).

Preferably the liquid impermeable outer layer 23 consists of a physical or mechanical blend of polyethylene (PE) and polypropylene (PP) which, in addition to being excellent liquid impermeability, also has sufficient moisture and heat barrier properties to Withstands the high humidity and high temperature stress of normal heat treatment in retorts for extended shelf life. Moreover, the outer layer 23 made of a physical or mechanical mixture of polyethylene (PE) and polypropylene (PP) not only has excellent printability, but also can pass through when the packaging laminate 20 is formed into a retort packaging container. So-called heat sealing makes possible a mechanically strong liquid-tight seal.

The liquid-tight outer layer 22 may likewise consist of a plastic selected from the group consisting essentially of polyethylene (PE), polypropylene (PP), polyester (PET) and copolymers thereof. Examples of suitable polyethylene plastics may be high density polyethylene (HDPE) or low density linear polyethylene (LLDPE), and examples of useful polyester plastics are amorphous polyester (APET).

Preferably, the liquid-impermeable outer layer 22 is composed of a copolymer of polyethylene and polypropylene having moisture and heat barrier properties sufficient to withstand the high humidity and heat associated with normal heat treatment in retorts for extended shelf life. high temperature stress. Furthermore, the copolymer layer of polyethylene and polypropylene facilitates a mechanically strong liquid-tight seal when the packaging laminate 20 is formed into a retort packaging container.

Layer 24 as a gas barrier layer may consist of inorganic or organic materials. Examples of inorganic materials that can be used are metal foils such as aluminum foils or silicon oxide layers obtained by plasma deposition, examples of suitable organic materials are so-called barrier polymers, such as copolymers of ethylene and vinyl alcohol (EVOH) .

Preferably, the gas barrier layer 24 is aluminum foil, which not only has excellent gas, especially oxygen permeation performance, but also facilitates the sealing of the packaging laminate 20 by heat sealing, a simple, fast and effective sealing technique.

By folding forming and heat sealing in the manner described above, the packaging laminate of the present invention can be made into a functional retort packaging container which can be reliably retorted in a retort under very high humidity and high temperature conditions. Heat treatment, while the packaging laminate does not delaminate, as moisture and vapor are effectively prevented from entering the already hydrophobically treated base layer through the exposed cut edges.

Claims (5)

1. A packaging laminate for retortable packaging containers produced by folding, forming and sealing a sheet or roll-shaped blank of a packaging laminate, said packaging laminate (10; 20) comprising paper or cardboard base layer (11; 21) and a liquid-tight outer layer (12, 13; 22, 23) made of heat-sealable plastic on both sides of the plastic layer (11; 21), characterized in that: Aqueous suspensions or emulsions of ketene dimers or mixtures of alkyl ketene dimers, wherein said dimers have 18 Carbon atoms, based on the dry weight of the paper, are used in an amount of 2.5 kg-4 kg of alkylketene dimer per 1000 kg of paper. 2. The packaging laminate according to claim 1, characterized in that the paper or cardboard layer (11; 21) contains said alkyl ketene dimer in an amount expressed as dry weight of the paper or cardboard layer (11; 21) At least 0.25% by weight. 3. Packaging laminate according to claim 1 or 2, characterized in that the paper or cardboard layer (11; 21) contains an amount of alkyl ketene dimer per ton of paper of the dry paper or cardboard layer (11; 21) Or 2.5-4kg of this dimer in the cardboard. 4. Use of a hydrophobically treated paper or paperboard layer (11; 21) as a base layer in a packaging laminate (10; 20) according to any one of the preceding claims. 5. A retortable packaging container composed of the packaging laminates according to any one of claims 1-3.

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