CA2373304A1

CA2373304A1 - Film, especially for packaging purposes, and packaging

Info

Publication number: CA2373304A1
Application number: CA002373304A
Authority: CA
Inventors: Horst-Ditmar Grone
Original assignee: Individual
Current assignee: J and T Co
Priority date: 1999-05-14
Filing date: 2000-05-11
Publication date: 2000-11-23
Also published as: MXPA01011717A; DE19922065A1; AU5065400A; BR0010523A; WO2000069750A1

Abstract

The invention relates to a film, especially for packaging purposes, which essentially consists of a hardened foam that is at least partially provided with an open-pored structure. Liquid can be stored in the pores of said foam.
According to the invention, the pore size of the foam increases at least in sections and with an increasing distance from a first surface (8) of the film and a second surface (10) of the film, whereby said second surface is opposite the first surface.

Description

NOV-13-2001 10~59 Wells St.lohn RobertsETAL 509 838 3424 P.04i1'7 Film, ~sp~ecially for packaging purposes, aad pack The present invention relates to a Li''~m, especially for packaging purposes. which essentially consists of a hardened foam that is at least partially provided with an open-cell structure, in thp cells of which a liquid can be stored, and to a pack, in particular for foods containing liquid such as meat or the like, which essentially comprises a container 7.0 thermoformed pr molded from a film for receiving a product.
Films of this type serve as a starting mate vial for the production of packs in tray form for the storage of ~oodsr in particular those which contain.
relatively large proportions of liquid. Packs o~ this type are envisaged for relatively small portions, intended for final consumers, of meat, fish, poultry and the like which contain high proportions of blood and water, which collect in the pack after packing_ Since mixtures of blood and water of this type adversely influence the entire appearance of the packed product, packs which - at least partially -- absorb mixtures of this type have been proposed..
In the case of a known pa c:kaging tray, a paper lining is arranged between two Layers of plastic, fox .instance polystyrene. Through a plurality of holes in the inner layer of plastic, facing the packed product, the Liquid, for instance the previously mentioned mixture of blood and water, can get between the two layers and be absorbed by the paper lining. This pack achieves results which are satisfactory in principle, but is relatively complicated and consequently expensive tv produce.
A further known pack comprises a liqu:id absorbent foam of plastic, which has on the product side an open-cell structure and on the our_er side.
fac~.ng away from the px'oduct, a closed-cell structure or ~.s provided with a covering film which is liquid impermeable, so that l~.quid cannot escape fnom the i NOV-13-2001 10:59 Wells St. John RobertsOTRL 509 838 3424 P.05i1'7 - 2 -- PCT/=-P00/0a25o pack. Liquid can k~e stored in the cells or the foam.
Such a pack is made by thermoforming from a film produced by extrusion.
A special method of producing such a =11m as a starting rnateria.L for the pack makes it possii~l° to achieve a cell structure which is distinguis?'~ed by the fact that the Size of the cell-s decreases from the outer surface of the fiim, 1..e. relatively large cells are formed in the region of the sur=ace and to increasingly smaller cells are formed as the distance from the surface increases. In the case of_ the known pack, the surface with the large cells is arranged on the znside of the pack, on the product side. In the region of the large cells, the Liquid storage capacity of the hardened foam ~or the take-up of liquid is greater than in the region of smaller cells.
Consequently, in the case of the known pack, liquid is stored to a far greater extent on the product side, or to put it another way on the inner side of the pack, 2o than in regions of the pack further away from the surface.
On account of the structure of the pack described above, a further problem arises, In particular in the case of re.l.atively large stored amounts of Liquid, the liquid stored in the film is often visible to a viewer from the inner side of the pack, which der_racts considerably from the overall esthetic appearance of the pack, especially if the liquid is a dark mixture of water and blood. To reduce this adverse esthetic effect. it has been proposed to produce particularly thick-walled packs or to choose dark colors for the packaging materials. However, dark colors are used for the packaging materials only in the case of approximately 30$ of all packs, while light 3s colors are desirable, and axe accordingly also used, in the case of 70b of packs of the type in question; in the case of the light packaging materials primarily used, the problem described above is consequently of great significance.

NOU-14-2001 09:15 Wells St. John Roberts~TRL 509 838 344 P.03~15 Translation into English - Your ref.: JT3-g42 -2a-... relatively large volumes of stored fluid .... are visible on the inside of the packaging to a viewer, which considerably impairs the overall aesthetic impression created by the packaging. particularly when the fluid is a dark mixture of wafer and blood.
In order to mitigate this negative aesthetic effect, it is proposed to manufacture packaging with a particularly thick wall, or to chpose dark colors for the packaging materials.
However, dark colors are used for the packaging materia4s in only about 30% of all packaging, whereas light colors are desirablE and accordingly used in about ~0% of the kind of packaging under consideration here; the problem described in the foregoing is therefore of major importance in the case of these prevalently used, light-colored packaging materials.
)n order to increase the fluid uptake capacity, it has also been proposed that a particularly thick film be provided as the initial material for the packaging. However, the ratio of uptake capacities to volumes of packaging material can be improved upon.

NOU-14-2001 09:115 Wells St. John RobertsETAL 509 838 344 P.04~15 2b -FR 2041 488 describes a thermoplastic material having an open-pored cell structure in the open pores of which fluid can be received and stored. The material may have such a structure that the density at the surface is greater than the density inside the material.
GB 2 322 100 discloses packaging materials with open-pored and closed-pore cells. In a closed-pore structure, the size of the pores filled with gas or gaseous mixtures increases with increasing distance from the opposite surfaces of the structure.
US 5,591,486 describes a method for manufacturing composite sheet materials by means of an extrusion process. Two laminae are formed by separate extruders and bonded together after extrusion.
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NOU-14-2001 09:15 Wells St. John RobertsETRL 509 838 3424 P.05i15 The technical problem of the invention, therefore, is t4 provide a film and packaging that avoid the disadvantages of the prior art, have a high fluid storage capacity and also ensure a pleasing optical impression, particularly when dark fluids or large volumes of fluid are stored.
The invention achieves this purpose, a packaging of the kind referred to at the outset. by virtue of the pore size of the foam increasing at least portion-wise with increasing distance from a first surface of the film, and by the pore size of the foam increasing, also at least portion-wise, with increasing distance from a second surface of the film opposite said first surface, and by virtue of the film being comprised of two layers that are seated, welded or bonded to each other.

i NOU-14-2081 09:15 Wells St. John RobertsETRL 509 838 3424 P.06~15 The film and packaging according to the invention has a high fluid uptake capacity and ensures that received fluid is not visible or only slightly visible from outside, even when the fluid has a relatively dark color compared to the color of the packaging material. According to the invention, the size of the pores increases with increasing distance from the two outer surfaces, whereas the size of the pores near the surfaces is relatively small.
In this way. the fluid is essentially stored inside the film and not in the outer portions, since the fluid uptake capacity is greater where the pores are of greater me~dn size than in the portion where the pore sizes are smaller. Due to the greater fluid storage inside the film, an external viewer cannot see, or only to a negligible extent, that fluid is collected inside the pores of the foam.
Even in the case of dark fluids and a light-colored foam, an external viewer cannot see, or to a minimal extent only, that fluid is present in the film. This is a major advantage compared to notorious types of packaging- The film according to the invention has a very high specific fluid uptake capacity ~ relative to its mass - and ensures that fluid is collected at a distance from the outer surface of the film and hence primarily in the inner portion of the film.
According to the invention, the film comprises two layers that are preferably seated, welded or bonded to each other such that they are symmetrically mirrored. This results in a major advantage for manufacturing, in that two separate layers can first be produced that are subsequently and permanently bonded to each other. The separate layers can be manufactured, for example to make the pore stnrcture according to the invention, by extruding through an extruder nozzle a fluid plastic constituting the initial material, expanding the plastic to form cells or open-pored structures, and subsequently cooling the plastic from one side, such as the outer side of a tubular strip of film, such that pores of very small size .~.- ._-.....
,... . ...._....... __....-...w..

NOV-14-2001 09:15 ~Je~ls St. John RobertsETAL 509 838 3424 P.O'7~15 ensue at the cooled surface, or even that a portion without pores is formed, while pores of targe diameter are formed on the opposite, inner side of the film.
A particularly preferred embodiment of the film according to the invention is characterized in that the film is essentially impervious to fluids at the first and second surfaces_ The imperviousness to fluid at the surfaces ensures, firstly, that received fluid cannot escape from the film, in other words that it cannot escape from paGcaging made with the film according to the invention. Secondly, received fluid will not flow b8ck into the interior of the packaging.
The fluid moves from the interior of the packaging into the film by virtue of the fact that -pursuant to a particularly preferred development of the invention - openings are provided at the first or second surface in the portion that is impervious to fluid, through which openings the fluid can move into the portion with an open-pored structure. Furthermore, the portions that are impervious to fluid also form an "optical barrier" such that fluid stored in tie film cannot be seen from outside, and does not shine through the film in a further alternative embodiment of the invention, a cover film is attached onto the first surface andlor the second surface. The cover film may be a thin film, consisting of a different material, that is then sealed, bonded or welded onto the film according to the invention_ Tt,is results in additional imperviousness of the film to gases and fluids, as well as an improvement in the overall optical impression of the packaging, because dark fluids, in particular, are not visible from the outside.
The invention is described in the following with reference to the attached drawings, on the basis of an embodiment and a manufacturing method. The drawings show:
Fig. 1 a schematic diagram of ...
._.._..~.~._..~~...y._. .....~_._.._. _._.._._..~.....M..~~..~.--.n._.--_. _ .____.__.._..~,....

NOV-13-2001 11:00 Wells St. John RobertsETRL 509 838 3424 P.09i17 wp 00/69750 - 6 - I?CT/EP00/04~~0 far producing a foam. The film is the starting material for the production of a pack according to the invention in the form of a gray representing a container, in the space inside which foods such as meat er the like are placed and which, is sea:ied with a covering film in ~~n airtight. and '_i.qu.id-impermeable manner. The film can, however, also be used for other purposes.
The film according to the invention is composed of two identical layers 2, 4, which in the exemplary embodiment are sealed to each other, but alternatively may also be welded, adhesz.vel.y bonded or fastened to each other in some other way. The f»lm is formed essentially mixror--symmetrically with respect to a 1~ contact surface 6 between the layers 2, 9. Both layers 2, 4 are essentially liquid-impermeable in the region of their surfaces B and 10, which respectively form a first surface 8 and an opposite second surface 10 of the composed film. rn the region of the surfaces 8, 10 ZO there i_s an essentially closed structure without cells, which results from the production process explained in more detail below. With increasing distance X from the surfaces 8, 10, the average size of the cells 3 of the hardened foam increases, as revealed by the 25 representation.
Figure 2 schematically illustrates the liquid take-up capacity of the film according to the invention by the spacings of the depicted lines 12, 14, measured along the straight lines running parallel to the 30 surface 8 and 10, respectively. In the outer region 16 of the layer 2 and outer region 18 of the layer 4, neighboring the surfaces 8 and 10, respectively, the film is liquid-impermeable and there is no liquid take-up capacity. With increasz,ng distance X from the s5 surface 8 or 10, the liquid take-up capacity increases on account of the increasing sizes of the cells 3 approximatel.y linearly - up to a maximum in the region near the center of the film and the contact region 6 between the two layers 2, 4. Then the liquid take-up NOV-13-:2001 11:01 I,JeI is St. Tohn l2obertsET~IL 509 838 3424 P. 1017 WO 00/69750 - ~ - PCT/EP00/04255 capacity decreases greatly a5 the distance X =rom the surface 8 or IO increases further and the distance from the contact region 6 decreases. T.,iauid taken up by the film is accordingly stored essentially in the interior of the film. From the outside, the liquid stored in the cells of the film cannot be perceived, or only slightly.
T he alternative exemplary embodiment of the film ac~:ording to the invention represented in figux-e 3 to has an open-cell structure similar i:n principle to the exemplary embodiment described above; the same parts ox structures are provided with they same reference numerals and, to avoid repetit~.on, reference is made to the descriptior_s above. Tn addition, a covering film 22, 24 is adhesively bonded to they layers 2 and 4, respectively. in the region of the caurfaces 8 and i0.
The covering films 22, 24 consist of a la.quid-impermeable plastic. The two layers 2, 4 are welded to each other in the contact region ~~. zn a way not 2o represented, only one layer 2 could be jozned to a covering film instead of both layer:> 2, 4; a covering film increases the strength of the film and consequently of the pack.
Once the Film has been produced, in the case of z5 the two exemplary embodiments described above, apertures through which Liquid can pass from outside into the cells of the open---cell foam in order to be stored in the cells, are formed i.n the region of the surface $ or 1U facing the space inside the later pack.
3o These apertures are for example punched in. In the case of the first exemplary embodiment (figures 7. and 2), the apertures pass completely through the outer region 16. In the case of the eaernplary embodiment aoCording to figure 3, the apertures pass completely 35 through both the covering film 22 and the neighboring region 26 of t_he layer 2, so that liquid can get into the cells 3 through the apertures.
A method and a device for producing a film according to the invention is described below on the NOV-13-2001 11.:01 I,Jells St.,Tohn RobertsETRL 509 E338 3424 P.11i17 WO 00/0'9750 - 8 - PCT/EP00/04250 basis of figures 4 and 5.
Figure 4 schematically illustrates the joining of two layers 2, 4 by welding or adhesive bonding. For welding, a heating device (not represented.) for heating the inner sides of the layers 2, A is arranged in relation to the layers 2, 4 in such a way that the inner sides of the layers 2, 4 are heated such that they are subsequently joined together by welding.
Alternatively, an adhesive application device may be lc provided for applying adhesive to the inner sides of the layers 2 and 4. After the heating or application of adhesive, the two layers 2 and 4 are pressed against each other by mechanical devzces not represented, for example roller guides, so that they are permanently 15 jo~.ned to each other.
l:'igure 5 illustrates a device and also the method for producing a film according to the invention.
Liquid plastic, for instance polystyrene, emerges under high pressure from an annular extrusion die of a 2c; fixedly mounted extruding device 30 and, a.s it does so, expands and forms a tubular web 32. During the expansion, a foam is formed with an essentially open-cell structure. Arranged outside the tubular web 32 is an air cooling device (not represented), which has a 2:i plurality of air outlet nozzles, from which air streams emerge for cooling the tubular web 32. on account of the air streams, more intense cooling of the tubulax web 32 occurs in the region of the outer surface of the latter than on the inner surface thereof, where cooling 3c) in the ambient air takes place. Ori account of this uneven cooling of the tubular web 32, a cEall structure, described above with reference to figures 1 to 3, forms in the hardening foam.
The tubular web 32 is conveyed along the outer 3~ surface of what is known as a cooling mandrel 34, which is continuously cooled from inside with a liquid, for example water. During the contact of t_h~e tubular web 32 with the outer surface of the cooling mandrel 34, the web 32 continues to cool down.

NOU-13-2001 11~01 Wells St. John RobertsETAL 509 838 3424 P.12~17 wo 00/9750 - 9 ~ PC;/SP00/04256 A cutting device 3& with tw,~ rotating cutting blades is fastened downstream on tile cooling mandrel 34 and severs the tubular web 32 at twc opposite locat_=ons in a central plane, 5o that two separate webs or layers S 2, 4 are produced from the tubular web 32 (cf. figures above), whioh are "laid flat", or transformed into planar layers 2. 4, on account of xestr.icr.ed guidance with the aid of two cylindrical rolls 38 i.n total. The rolls 38 are rotatably mounted or. a frame 40.
1U With the aid of the rolls 38 rotatably mounted on the frame 40, the layers 2, 4 are deflected and pressed against each other with the aid of the rollers 42.
Two radiators 44, fastened to the frame 40 in a 15 way not represented, heat the respective inner side of the layers 2, 4 (cf_ f~_qure 4) witty radiant heat, so that the surface of the layers ?, 4 is brought into a flowable state. Sealing of the two ~_ayers 2, 4 subsequently takes place ~n the contact region 6 2Q between the layers 2, 4 by using tae rollers 42.
Subsequently, the finished film aCCOrding to the invention is wound up in a way not represented.
After cooling down completely, the film is unwound and thermoformed for the production of a packaging 25 according to the invention, and is ~subsequent7.y cut up into separate packs, which in each case have a tray-shaped contai.ner_

Claims

1. A film, in particular a film for packaging, essentially comprised of a hardened foam having an open-pored structure, at least in part, in the pores of which foam a fluid can be stored, characterized in that the pore size of the foam increases at least portion-wise with increasing distance from a first surface (8) of the film and that the pore size of the foam increases at least portion wise with increasing distance from a second surface (10) of the film opposite said first surface (8), and that the film is a composite of two layers (2, 4) that are sealed. welded or bonded to each other.

2. Film according to claim 1, characterized in that the film is essentially impervious to fluid at the first and second surface (8, 10).

3. Film according to claim 2, characterized in that the film has openings at the portion (16) that is impervious to fluid, through which openings the fluid can penetrate into the portion with the open-pored structure.

4. Film according to claim 2 or 3, characterized in that a cover film (22, 24) is attached at the first surface (8) and/or the second surface (10).

5. Packaging, in particular for food containing fluid, such as meat or the like, consisting essentially of a container that is deep-drawn or molded from a film for receiving a good, characterized by a film according to at least one of the above claims.