NO860900L - PROCEDURE FOR PACKAGING GOODS. - Google Patents

Abstract

A method is described for automatically packaging articles, such as food articles (11). In the method, substantially rigid preformed containers (1) of porous material are fed by conveyor means (4) and lined with a superimposed web of plastics material (7) at a thermo-forming station (5) so that the plastics material is united with and coherently bonded to the interior of the containers and so as to connect the containers. The containers are then filled and sealed with a second web of plastics material (12) whereafter the containers are separated. The sealing of the containers is conveniently effected by a so-called modified atmosphere packaging system. The use of the preformed containers (1) enables the packaging operation to be operated more efficiently and economically and with less downtime than previously proposed automatic packaging systems.

Description

This invention relates to packaging and concerns an improved system and an improved method for the automatic packaging of items such as fresh and frozen, raw or processed foodstuffs, such as meat, fish, cheese, bakery products, fruit and vegetables, as well as for the packaging of sterile or sterilizable objects for hospitals and other uses.

According to a method for packaging e.g. fresh meat, carried out on an automatic system, a web of relatively thick plastic material such as a polyvinyl chloride/polyethylene layer is thermoformed to form containers in the form of troughs or the like to receive the items to be packaged. The containers are preferably formed in a grid pattern. The containers are then filled, e.g. with portions of fresh meat or meat products and a web or film of plastic material is fed from above onto the containers. The containers are then sealed by a form of packaging known under the term "modified atmosphere packaging" where the atmosphere that is in contact with the contents of the containers is controlled with regard to e.g. the oxygen content, although for the packaging of certain items no modification of the atmosphere is actually necessary, while in other cases the modification of the atmosphere in the packaging may take place during storage by reaction with the product being stored. The containers can then be separated by cutting.

By virtue of the properties that the resulting packaging must be able to exhibit, the range of materials that can be used to make up the packaging is limited. In practice, only thick laminates of non-plasticized polyvinyl chloride and polyethylene have been used to form the base component of the packaging. The base components are manufactured by thermoforming to form deep cup or box shaped structures which are then closed by heat sealing a membrane around the peripheral lip of the base component to form a package containing a product and a suitable gas mixture. The laminate's thick layer of polyvinyl chloride (PVC) is used to make the packaging gas-impermeable and to give the finished closed package physical rigidity as well as to ensure that the package is essentially gas-tight.

As stated above, the polyvinyl chloride must be relatively thick in order to be gas impermeable and sufficiently rigid. Although it is theoretically possible to heat seal a lid of similar PVC to a container of the material, in practice difficulties arise and it is preferred to use an adhesive or a hot melt adhesive compound to connect the lid to the container. However, such containers made of thick PVC are too expensive to be a commercially viable solution.

If you try to use thinner material, two problems arise. Firstly, if a plastic container is to be sufficiently rigid for its intended purpose, it is a fact that the side walls of the container must be vertical, otherwise the container becomes unacceptably flexible. As most shallow plastic containers are formed using deep drawing techniques, either by pressure or vacuum forming, an unacceptable thinning of the material occurs at the corners. Thus, e.g. a 0.5 mm thick sheet of plastic material, when deep drawn to form a shallow bowl could have a bottom that is approx. 0.375 mm thick, but can be 0.160 to 0.125 mm thick at the corners. At this thickness, the material is very susceptible to breakage or damage.

Secondly, when the material is made thinner, it loses its gas-impermeability, and to restore this property it becomes necessary either to use a thicker plastic sheet or to line the container with a gas-impermeable layer. However, the problems associated with thinning at the corners also occur if a gas impermeable layer is applied by deep drawing techniques.

Due to the special nature of the packaging material and the volume of the container, the modified atmosphere packaging process is limited to factory production in large quantities using expensive and complicated packaging equipment where rolls of laminate material are used to form the base components, which rolls must have a large diameter if pro - the session must be financially feasible. Consequently, the process can only be used by a few large packaging or processing companies.

However, this packaging method has several disadvantages. As the material from which the containers are made is relatively thick, coils of the material must be frequently replaced with the eventual consequent interruption of operation and significant material failure.

According to the present invention, a method for packaging objects is provided, where a number of joined together, essentially gas-impermeable containers for the objects are fed to a filling station where the objects are placed in the containers, and where the containers are then closed by connecting a web of plastic lid material to the edges of the containers, at a heat sealing station, thereby enclosing the objects in the containers with a lid of said plastic material, characterized in that a number of essentially rigid, pre-formed individual containers of porous material are fed onto a conveyor device under a path of plastic lining material which is in essentially gas-impermeable, and that the web of plastic lining material is joined and connected to the inside of the containers by means of a thermoforming operation, thereby giving the porous containers a continuous connected, essentially gas-impermeable lining and to connect the containers to each other.

In this method, the plastic material used to line the preformed containers is preferably a multi-layer film with a gas-impermeable layer and a thermoplastic layer and it is very much thinner than the material that was used when thermoforming the containers by the known process.- Fewer coil replacements therefore becomes necessary and a faster cycle time is achieved due to the use of thinner material in the thermoforming step. Furthermore, the cutting mechanism for separating the sealed containers into individual packs can be of lighter construction as it only needs to cut through two thin plastic films.

The containers are preferably made of porous fiber material such as cast fiber pulp, paper, cardboard or fiberboard produced in a conventional way by casting fibers that are deposited by papermaking techniques. Alternatively, the containers can be made of bonded chip, bonded fiber material or other suitable gas-permeable membranes. The containers can also be formed from open-cell foam plastic constructions or fibrous plastic constructions, which can contain fillers. The material from which the containers are made must be rigid and porous and must have spaces on its surface in which the thermo-plastic layer in the multi-layer lining film can become coherent.

bound.

An advantage of the container used in the present method is that it is easier to make unusual shapes by casting than by vacuum forming, so that the present method is particularly suitable for packaging unusually shaped products by adapting the packaging to the product in an economical way.

The sealing is carried out using a lid or a closing membrane which can be a multilayer film with a gas-impermeable layer and a thermoplastic layer.

If the product to be packaged, e.g. is meat or fish, it is highly desirable that a potential buyer should be able to inspect the contents. It is therefore desirable that the lid or sealing membrane has a dew-free internal surface closest to the gas-tight space, so that the lid does not become opaque due to condensation of water from the product in the event of any temperature changes.

The plastic film used for lining the preformed containers can comprise a single layer of thermoplastic plastic, such as polypropylene, or a layer of plastic material such as a polyester, e.g. polyethylene terephthalate, or an amide, such as nylon, with a layer of thermoplastic adhesive by which the liner can adhere to the container.

As indicated above, however, the plastic film used to line the preformed containers is preferably a multi-layered film of which at least some of the layers are thermoplastic.

The multi-layer film can comprise anything desired

the number of layers necessary to give the film the required thermoplasticity and gas impermeability. The film which is connected to the container is preferably a multilayer film comprising at least three layers, namely a first layer capable of forming a strong connection with the surface of the porous container to form a connection at least as strong as the inherent mechanical strength of the container, a central layer of gas impermeable polymeric material, and a third layer of polymeric material which can be connected to the thermoplastic material of the lid or closure membrane.

The multi-layer thermoplastic film can suitably comprise an ionomer polymer material such as, for example that known under the registered trademark "SURLYN", as said first and third layers, and the gas impermeable layer may be of polyvinylidene chloride, polyvinyl alcohol or an ethylene/vinyl acetate copolymer which may be partially hydrolyzed.

The lid or closing membrane can be made of a similar material to the lining material and preferably has a higher melting or softening point than the inner ionomer layer.

In order for the invention to be better understood, reference is made to the accompanying drawings which schematically and by way of example show an embodiment of the invention, and where:

Figure 1 shows a facility for packaging objects

by means of the method according to the present invention,

and

Figure 2 is a section, shown with the parts partially separated from each other, through a gasket that has been produced using the plant shown in Figure 1.

Figure 1 shows a facility where packages of fresh meat are to be formed on a vacuum package gas filling machine, such as e.g.

a "Multivac R7000" machine of the type described in U.S. patent no. 3956867 in the name of Kastulus Utz et al. Preformed containers in the form of bowls or boxes 1 of porous fiber material such as paper, cardboard, fiber board, pulp fiber, wood or fiber chips or foamed plastic material, preferably of molded pulp fiber, are retrieved from a box stack or stacks 1 by means of a destacking device indicated by the arrow 3 and are placed in rows on a conveyor 4 so that they form a closely spaced row of boxes on the conveyor. The boxes 1 are fed by means of the conveyor to a thermoforming station 5. A coil - 6 of thin plastic material 7, such as a film comprising a layer of polyvinylidene chloride sandwiched between two layers of ionomer polymer material and with a total thickness of 100 to 150 µm is mounted over the conveyor 4 and the film are joined to the boxes 1 at the thermoforming station 5 to thereby line the containers with the film and join the containers. The film is connected continuously to the container by being heated by means of a heating device 8 and by being drawn downwards by means of a vacuum which is added by a vacuum outlet 9. The film is drawn into the spaces in the

porous substrate so that the polyvinylidene chloride layer is adhered to the box. In this way, the gas-impermeable polyvinylidene chloride layer is firmly connected to the box in such a way that it is prevented from loosening and consequently being damaged with consequent deterioration or destruction of the contents of the package.

After the boxes have left the thermoforming station 5, they are taken to a filling station 10 where they are in turn filled with the meat product 11 to be packaged. A cover material 12

in the form of a non-stretchable composite web is unwound from a feed roll 14 located above the flow path of the boxes and is brought to cover them. The two webs are then united in a vacuum chamber in the vacuum package gas filling machine 15 so that the mouth of the box is covered and heat sealed to the composite web 12 using a heated sealing plate 16 and with appropriate control of the atmosphere and pressure in the chamber and gasket as is known in the art using suitable gas and vacuum inlets and outlets generally indicated at 17 and 18. 1

The containers that come out of the chamber are separated by means of a knife 19 into individual packages 20 which can be subjected to edge trimming.

It should be understood that modifications of the present method are possible and that the filling effect of the lined containers can take place in another place, the manufactured containers being fed directly to the vacuum chamber.

The advantages that the present method exhibits over the previously proposed method where the boxes are thermoformed from relatively thick PVC, lie not only in the flexibility of the present method, but also in the significant and unexpected economic advantages that arise. The price of molded fiber boxes is considerably less than the price of the relatively thick PVC for boxes of similar stiffness/and as mentioned, it is easier to obtain molded fiber boxes of complicated shape and uniform thickness than by thermoforming the plastic material.

As the coil 6 is made of thin lining material instead of relatively thick material that has to be thermoformed, the intervals between coil changes are increased considerably and since a coil change involves a stoppage of operation, production is increased by the present method and the amount of scrap is reduced. A production increase of 8-10% has been achieved with the present method compared to the previously proposed method. This increase is in addition to the fact that there never needs to be any interruption in the placement of the boxes 1 on the conveyor 4. As the thermoforming station 5 works with thin material instead of thick material, the time for heating the material and for connecting it with the box be less than the time it takes to heat and thermoform the thicker material. In this connection, a production increase of up to 25% has been achieved compared to the previously proposed method. As the plant generally works with thinner and lighter material than the relatively thick PVC, costs for tools and maintenance will also be reduced. Finally, the present method is very well suited for use with lining and/or cover materials comprising polyesters as these will be in thin layers which are significantly easier to process than thick polyester layers.

Reference is now made to Figure 2 where the gasket 20 is shown in greater detail and comprises the porous, rigid, flanged box 1, lined with the lining material 7. The lining material 7 comprises a gas-impermeable layer 21 inserted between two layers 2 2 and 23 of ionic polymer material such as what is known under the registered trademark "SURLYN". The layer 22 closest to the box 1 is softened and drawn into the spaces in the box so that it is connected continuously to the box and thus connects the lining material to the box.

The lid material 12 is also formed from three bonded layers to form a unitary structure which is flexible. The layer 24 that will make up the inside of the gasket is made of an ionic polymer material that is similar or the same as that from which the layer 23 is made, so that the layers 23 and 24 can be united with each other by a heat seal, welding or other connection operation in the machine 15. The middle layer 25 is, like the layer 21, gas-impermeable and the outer layer 26 is a support layer which has a significantly higher melting point than either of the layers 24 and 25, so that it can withstand a heat seal or the like. operation, so that the layers 23 and 24 are joined at the edges of the box 1.

It is to be understood that the material of which the box 1 is made must be able to be connected continuously to and moistened by the polymer in the layer 22 when the polymer is applied to the surface of the box at a high temperature.

As indicated above, the layers 22, 23 and 24 are made of an ionomer polymer, i.e. a polymer of the polymer class where ionized carboxyl groups form ion cross-links in the molecular structure. These crosslinks are reversibly broken at melting temperatures. The layers 22, 23 and 24 can conveniently be made of the same material, such as e.g. that which is sold under the registered trademark "SURLYN". To ensure that the ionomeric polymer obtains a satisfactory bond to the molded, porous box 1, the layer 22 can be thicker than the other two layers. The layer 21 of gas impermeable material is preferably a film of polyvinylidene chloride or a copolymer thereof. Alternatively, the gas impermeable layer 21 may be a polyvinyl alcohol or a copolymer of ethylene and vinyl acetate which may have undergone some hydrolysis.

As indicated above, the layer 24 of the lid material 12 is made of an ion-polymer material similar to the material of which the layer 23 is made, and the layer 24 must be heat-sealable or weldable to the layer 23. It is a preferred feature of the layer

24 that the surface of this layer in contact with the gas atmosphere in the space in the seal must be hydrophilic, so that when the finished seal is in use, a continuous transparent film of water can form on the surface of the layer 24 to thereby maintain visibility of the contents of the package. The lid material in the finished package thus has a dew-free internal surface close to the space that occupies the contents of the package. Made 24

can be made hydrophilic in a conventional way, e.g. by applying a surface agent in or on the layer.

If desired, the layers 23 and 24 can be pigmented with white or another desired color to make the package more attractive.

The middle layer 25 of the cover material is impermeable

for gases, such as oxygen and can, like layer 21, be made up of a vinylidene chloride polymer or copolymer of a vinyl alcohol polymer or a copolymer of ethylene and vinyl acetate which can be partially hydrolysed.

The outermost layer 26 of the lid material 12 has a significantly higher melting point than both the layer 24 and the layer 25 so that heat sealing of the layers 23 and 24 can be carried out with the help of heat which is transferred through the layers 26 and 25. The layer 26 is suitably a film of a polyester or polyamide.

If desired, the box 1 can be designed with cutouts that are separated by rods or by cross-shaped elements. The lining material 7 pulls over the recesses and it should be understood that this arrangement makes it possible to inspect the contents of the package from the underside. In this case, it may be desirable that the inner surface of the layer 23 is also hydrophilic.

The invention shall be further illustrated by the following example.

EXAMPLE

Stacks of molded pulp boxes marketed under the trademark "SHOPAK" by Keyes Fiber Company are fed by means of a take-off device onto a conveyor belt so that a number of boxes are placed across the belt in rows along the belt. The belt runs to a thermoforming station along with a first web of plastic material for lining the boxes using a vacuum forming technique. The web comprises, as shown in figure 2, a layer 22 of an ionomer polymer which is marketed under the trademark "SURLYN" and has a thickness of 75 µm. Layer 23 is of the same material but is only 40 µm thick. Layer 21 between layers 22 and 23 is a coating of polyvinylidene chloride which is applied to layer 21 at a rate of 5 g per m 2 and forms an adhesive connection with the layer 22.

A food product to be packaged is then placed in the space in the container and the lid material 12 is applied to the top of the package and heat-sealed to it after the atmosphere in the space has been regulated to the desired composition. The material 12 comprises a layer 24 of the same material as the layers 22 and 23 but with a thickness of 40 µm. The layer 25 comprises a coating of polyvinylidene chloride applied to the layer 24 at a rate of 3 g per m 2 and adhesively connected with the layer 26 which comprises a polyester layer of thickness 12.5 µm.

The packaging of the food products is carried out appropriately

in a conventional packaging machine where the atmosphere inside

in the room is controlled, as the choice of gas composition depends on the particular food product being packaged. Mixtures of carbon dioxide and oxygen are usually used for packaging fresh meat and mixtures of nitrogen and carbon dioxide are used for packaging fish products.

Claims (10)

1. Method of packaging articles, wherein a number of joined, substantially gas-impermeable containers for the articles are fed to a filling station where the articles are placed in the containers, and where the containers are then closed by connecting a web of plastic lid material to the edges of the containers, at a heat sealing station, thereby enclosing the objects in the containers with a lid of said plastic material, characterized in that a number of essentially rigid, predetermined single containers of porous material are fed onto a conveyor device under a path of plastic lining material which is essentially gas- impermeable, and that the web of plastic lining material is united and connected to the inside of the containers by means of a thermoforming operation, thereby providing the porous containers with a coherently connected, substantially gas-impermeable lining and connecting the containers to each other. 2. Method according to claim 1, characterized in that the plastic lining material is a multilayer thermoplastic film of which at least one of the layers is preferably pigmented. 3. Method according to claim 2, characterized in that the multilayer thermoplastic film connected to the containers comprises at least three layers, namely a first layer which is able to form a strong connection with the surface of the porous containers to form a connection that is at least equal to strong as the containers' inherent mechanical strength, a central layer of gas-impermeable polymeric material, and a third layer of polymeric material which can be connected to the web of the plastic lid material to form the lid of the containers. 4. Method according to claim 3, characterized in that the multi-layer thermoplastic film comprises an ionomer polymer material as the first and second layers, and that the gas-impermeable layer is of polyvinylidene chloride, polyvinyl alcohol or an ethylene/vinyl acetate copolymer which may be partly hydrolysed. 5. Method according to one of claims 1-5, characterized in that the web of plastic lid material comprises at least three layers, namely a first layer bondable to the plastic liner material connected to the box, a central layer of gas impermeable polymeric material and a third layer of polymeric material having a melting or softening point higher than the melting or softening point of the first layer. 6. Method according to claim 5, characterized in that the web of plastic cover material comprises an ionomer polymer material as the first layer and a polyester or polyamide as the third layer, and that the gas-impermeable layer is of polyvinylidene chloride, polyvinyl alcohol or an ethylene/vinyl acetate copolymer which may be partially hydrolysed. 7. Method according to one of claims 1-6, characterized in that the second web of plastic material has a dew-free surface near the space in the packaging. 8. Method according to one of claims 1-7, characterized in that the porous box is made of paper, cardboard, fibreboard, fiber pulp, wood or fiber chips or foamed plastic material, preferably molded fiber pulp. 9. Method according to one of claims 1-8, characterized in that the plastic lining material is in contact with and continuously connected to the inner surface of the containers by a vacuum forming technique at the thermoforming station. 10. Method according to one of claims 1-9, characterized in that the containers are sealed using a modified atmosphere packaging technique at the heat sealing station.