GB2272399A - Multilayer paper packaging material - Google Patents

Abstract

A packaging material comprises a multilayer structure made essentially out of paper, characterized: in that it comprises at least two layers A and B of paper, respectively an internal layer and an external layer; in that the layer A is absorbent and contains at least one chemical agent suitable for imparting wet strength thereto; and in that layer B includes at least one oleophobic additive suitable for imparting resistance thereto in particular against fats and water, said layer having an outside face treated with a hydrophobic coating agent (2). This material is particularly suitable for making trays for selling meat, that are recyclable and that absorb exudates, but without detracting from presentation. <IMAGE>

Description

2272399 1 PACKAGING MATERIAL AND PACKAGING CONSTITUTING AN APPLICATION

THEREOF The field of the present invention is that of manufacturing a packaging material that is recyclable and that is In the form of sheets from which various packaging articles can be made. For example, these articles may be trays, plates, platters, or the like and suitable, in particular, for being obtained by thermoforming.

The present invention thus relates to a packaging material of the type comprising a multilayer structure made essentially out of paper. The application that is most particularly intended is packaging foods that are liable to release or sweat out liquid exudates (blood), such as meat or fish, for example.

This property presents a problem when the food is to be packaged so as to conserve it in an acceptable state over a certain period of time, and so as to present it for sale in a form that is attractive to the customer.

The materials used for manufacturing this type of packaging must satisfy a certain number of technical specifications that result from constraints specific to the intended purpose, which purpose is preferably, but not exclusively, as described herein.

In the first place, these constraints are mechanical.

Given that one of the most convenient ways of making packaging of this type is thermoforming or thermomolding, i.e. shaping while hot under pressure to impart appropriate depth and shape to the package, it is important that the material used should be capable of withstanding the stresses imposed by such transformation, and in particular that it should possess a capacity for a high degree of deformation.

In addition, it is necessary for the material to have good mechanical strength so as to retain its initial shape after the transparent protective film has been put 1 . 0 2 into place and so as to withstand the various deformations to which it may be subject during various handling operations. Good tear resistance is also desirable.

Another constraint is that the material must be capable of withstanding the liquids to which it is exposed. These liquids may be constituted firstly by any exudate or juice expelled by the fresh food during storage, and secondly by water from condensation which is a consequence of the way this type of product is stored by refrigeration. The packaging material must therefore be strong enough to avoid disintegrating soggily on contact with such liquids.

If foods that tend to sweat out liquids are to be well presented for sale, then it is necessary for exudates to be absorbed so as to avoid a food being immersed in a pool of liquid, in particular blood, since that is not -ery attractive to the customer.

Nevertheless, such absorption must not spoil the appearance of the packaging itself, i.e. the packaging must not include marks of liquid, grease, or blood on its surface since that also spoils the presentation of the product.

It is also desirable to ensure that moist food does not adhere to the packaging so as to avoid difficulties when removing the food therefrom.

The material used must naturally be food grade material.

Finally, and above all, the material must satisfy one of the major preoccupations of the present day: it must be kind to the environment. It must therefore be recyclable, so as to give rise to as little polluting waste as possible.

The prior art includes various technical proposals that attempt to satisfy the various constraints mentioned above, but without real success.

3 Thus, trays are known that are made from plastics materials, such as oriented expanded polystyrene, or from materials that associate papers with plastic materials or metals such as aluminum in multilayer structures.

Thus, French patent application No. 2 473 418 describes expanded polystyrene trays having an inside face coated with an aluminum skin and assembled by hot welding.

In a manner similar to materials that are constituted from plastics only, such plastics/metal composites have absolutely no capacity for absorbing exudates, and above all they are difficult to recycle.

This is due to the fact that systems for collecting and retreating such packages are not established or are insufficiently developed, as is the case for plastics, and/or to the fact that their very structure requires retreatment that is complex and expensive.

On the subject of composite materials comprising multiple layers of plastics and paper, such as those described in European patent applications Nos. 0 313 356 and 0 443 402, they generally seek to satisfy objects other than those of the material of the invention, in particular because they are not absorbent (EP 0 313 356) and/or because they raise severe recycling problems.

In an attempt to remedy that difficulty, manufacturers in the field in question have naturally turned their attention to materials of multilayer structure that are made essentially from paper and/or card. Such materials have the advantage of being relatively repulpable, i.e. of being easily recycled, by being ground up and put into aqueous suspension, thereby enabling a reusable paper-making pulp to be obtained.

Thus, German patent application No. 4 028 236 discloses a method and apparatus for manufacturing a packaging tray for food. The tray in question is made up of a plurality of layers of paper, namely: an internal hydrophobic layer having a plurality of perforations a 0 4 0 a 4 formed therein, an absorbent or blotting external layer, optionally covered on its outside face with a layer of recycled paper that is also absorbent, and a final outside layer that is hydrophobic.

The perforations in the internal layer enable liquid exudates to reach the internal absorbent layer.

It can be seen that the structure of that material is relatively complex. Its manufacture thus requires numerous assembly operations that are lengthy and expensive, to which there must also be added the operation of perforating the internal layer.

In addition, that material is subject to degraded mechanical strength and structural integrity after it has absorbed exudates. Furthermore, its low resistance to moisture is combined with low resistance to fats, in particular polar fats of the type contained in blood exudates from meat.

It can thus be seen that the prior art has not provided a satisfactory solution to the problem of providing a packaging material, in particular for foods that are liable to sweat out liquid exudates, such as meat, fish, or cooked dishes.

An object of the present invention is therefore to provide a packaging material that presents good mechanical properties of rigidity and of resistance to deformation and to tearing, and which is also thermoformable.

Another object of the invention is to propose a material that enables the liquid exudates from food to be absorbed, while also having qualities of withstanding the water and the polar or non-polar fats that are likely to make up such liquids.

The material must therefore not be liable to disintegrating by becoming soggy, and it must withstand the diffusion of liquids and of fats.

64 0 b 0 4 Another object of the invention is to provide a material that is not sensitive to condensation water coming from the outside.

Another object of the invention is to provide a material whose inside face does not adhere to the packaged food.

Finally, another object of the invention is to provide a packaging material that is recyclable, that is of food grade, and that is capable of beingpbtained by a manufacturing method that is simple and cheap.

These objects and others are achieved by the present invention which provides a packaging material of the type comprising a multilayer structure made essentially out of paper, characterized:

in that it comprises at least two layers A and B of paper, respectively an internal layer and an external layer; in that the layer A is absorbent and contains at least one chemical agent suitable for imparting wet strength thereto; and in that layer B includes at least one oleophobic additive suitable for imparting resistance thereto in particular against fats and water, said layer having an outside face treated with a hydrophobic coating agent.

One of the major advantages of this material stems from the capacity of paper layer A to absorb hydrolipidic liquid exudates coming from the packaged food.

Its power of absorption is such as to enable it to absorb a quantity of liquid that is not less than 20%, preferably not less than 30%, and still more preferably in the range 50% to 80% of its own weight.

This characteristic can also be measured using a test To standardized in NF Q03 014 (also known as the Cobb method), with a duration of 1,800 seconds. According to the To test, the absorption power of layer A 6 is not less than 50 grams per square meter (g/M2) and pref erably lies in the range 70 g/ml to 120 g/M2.

In practice, the absorption power depends on the weight of the paper and on its thickness.

In addition to its high absorption ability, paper layer A has very good wet strength. This makes it possible to avoid the,packaged article being contaminated with paper-making fibers after absorption has taken place, and it also makes it possible to avoid damage to said layer A by splitting.

The wet strength of paper A can be measured in terms of its ultimate tensile strength in the wet state using the T, method standardized in NF Q 03-056.

In accordance with the invention, its ultimate tensile strength in the wet state should be not less than 7 N per 15 mm in the manufacturing direction of the paper and not less than 3 N per 15 mm in the cross direction, and it should preferably be not less than 11 N in the long direction and not less than 6 N in the cross direction.

To achieve this property, paper A is filled with at least one chemical agent that provides wet strength, and that is preferably selected from the family of epichlorhydrine-treated polyamides. For example, it may be the substance sold under the trademark KYMENE 557 H by the firm Hercules.

Other chemical agents may provide the same effect. Particular mention may be made of glyoxal, for example.

The concentration of chemical agent contained in layer A, expressed as a dry weight relative to the total mass of layer A, is advantageously not less than 0.05, preferably not less than 0.01, and still more preferably lies in the range 0.2 to 1.5.

Insofar as the packaging material is intended for packaging food, the upper limit on the concentration of the chemical agent depends on the legislation that defines food grade for packaging materials.

7 The same applies to the oleophobic additive present in paper layer B, whose concentration expressed as a dry weight relative to the total mass of layer B is not less than 0.05, is preferably not less than 0.08, and 5 still more preferably lies in the range 0.1 to 1.3.

The oleophobic additive is preferably constituted by a compound or a mixture of compounds selected from the family of fluorine-containing polymers. Such compounds provide the paper with strength to withstand polar fats and water coming from the exudates of the packaged substance. More precisely, they turn out to be particularly effective against blood, preventing it from migrating through the material.

An example of a fluorine-containing polymer is the compound sold by 3M under the registered trademark SCOTCHBAN FX 845, or the compound sold by Atochem under the registered trademark FORAPERLE 321. These compounds are presented in emulsified form, which is particularly preferred in the context of the invention.

The fluorine-containing substance may be included directly in the bulk of the paper, or it may be applied to the surface thereof by any system that enables the treatment to reach at least 30% of the thickness of the paper so as to achieve a good barrier against absorbed exudates.

The layer B is characterized by a value for its resistance to penetration by water as determined by the TO test for a period of 1 minute, which value is not greater than 13, and preferably lies in the range 9 to 12. Its ability to withstand wetting as determined by a T2 test or the "contact angle" method (standard TAPPI T 458 OM-89) is not less than 1000, is preferably not less than 1050, and still more preferably lies in the range 1100 to 1250.

Such properties stem in particular from treating the outside face of layer B by means of at least one coating agent applied by impregnation or by coating, the agent 8 being constituted by a wax, a latex, or a wax-latex mixture.

It is important that the surface treatment does not affect the thermoforming and recycling qualities of the packaging material in question. Thus, the treatment is advantageously performed in such a manner as to obtain a deposition rate lying in the range 1 to 17, preferably in the range 3 to 12, and still more preferably of the order of 9 grams of dry matter per M2 of treated area.

This treatment of the outside face of layer B makes it possible to reinforce the barrier effect against liquids coming from the inside, i.e. from layer A, and against condensation water coming from the outside as a result of temperature changes that occur when the final packages are removed from the refrigerated.cabinets in which they are stored.

Furthermore, this outer coating also provides a barrier effect against gases, and in particular oxygen and water vapor. It also serves to improve the external appearance of the packaging with respect to brilliance, freshness, and printability.

In order to enable the material of the invention to be thermoformable (or thermomoldable), it is important for each of the layers A and B to comprise: firstly cellulose fibers that are long and that have an ultimate elongation value as measured using the T3 test of the AFNOR standard: NF Q03 002, that is not less than 2.8%, that is preferably not less than 3%, and that is still more preferably not less than 3.5%; and secondly cellulose fibers that are short, having an ultimate elongation value that is not less than 2%, preferably not less than 2.5t, and still more preferably not less than 3 16.

By way of example, suitable long fibers are those sold under the names COLOMBUS, KAMLOOPS, and ASPA, having respective ultimate elongations of 2.8%, 3.5%, and 3.4%. The short fibers are advantageously eucalyptus fibers 9 such as those sold under the names SOPORCEL, ARACRUZ, and SOCEL, having respective ultimate elongations of 2.3%, 2.6%, and 2.3%.

The ratio of short fibers to long fibers depends on the elongation and rigidity characteristics that it is desired to give to the material. In practice, equivalent percentages of the two types of selected fiber gives a good result.

The suitability of the packaging material of the invention for recycling is easily evaluated in terms of its repulpability.

One particularly suitable way of doing this is to defiber the paper by putting it into suspension in demineralized water at a concentration of 25 grams of dry mater per liter, at pH 2: 10, at a temperature of 800C, and for a period of 30 minutes.

The paper to be tested is cut up into 2 cm by 2 cm pieces and is then stored for 24 hours under normal atmospheric conditions (230C, relative humidity = 50%) prior to being put into suspension in the defibering medium.

The pH of this medium is set at 10 by using NaOH.

When the defibering is over, the quantity of the non-defibered mass that may possibly still remain is determined by means of a screening device of the BrechtHoll type including a plate with holes having a diameter of 0.7 mm. This quantity corresponds to a residue that can be expressed as a dry weight % relative to the total mass put into suspension.

Test pieces having a weight of 60 g/M2 are also made from the pulp that is obtained (DIN 54 358), both before and after passing through a Haindl type grinder.

These test pieces are examined visually to determine the approximate quantity of non-defibered masses, and they also serve to give an indication of the suitability of the defibered pulp for forming sheets.

4 From the results of this method, the material of the invention is thoroughly repulpable.

The quantity of residue that it leaves on the Brecht-Holl plate having holes with a diameter of 0.7 mm is not greater than about lt dry matter relative to the total mass put into suspension.

It should also be observed that the material of the invention is a noble recyclable paper, i.e. it has no mineral fillers and it is essentially constituted by fibers.

The sole figure of the accompanying drawings shows an embodiment of the material of the invention. It comprises an internal paper layer A and an external paper layer B that are pasted together so that a layer given reference 1 is formed at the interface between them.

The outside face of external layer B is coated with a hydrophobic layer 2 deposited by surface treatment and comprising the above-mentioned hydrophobic agent.

In accordance with an advantageous but non-limiting characteristic of the present invention, the inside face of the internal layer A has an anti-adhesion coating 3 obtained by a surface treatment (e. g. a roller coating treatment), using a coating agent of the type comprising a wax emulsion or a latex containing wax. The concentration of coating agent in the emulsion is selected so as to obtain a deposit of not more than 3 g/M2 of dry matter on a dry surf ace.

The anti-adhesion coating 3 is intended to make it easier for the consumer to separate packaged fresh food, 30 e.g. meat, from the packaging.

According go to the T2 test, the anti-adhesion effect of the coating 3 is characterized by a contact angle with water of not less than 900, preferably not less than 100', and still more preferably in the range 1000 to 1100.

In addition to the characteristics mentioned above, the material of the invention has a weight lying in the Z 11 range 80 g/M2 to 500 g/M2, pref erably in the range 100 g/M2 to 400 g/M2, and still more pref erably in the range 180 g/M2 to 350 g/M2.

The weights of the papers A and B are chosen as a function of the criteria that need to be enhanced for each particular type of final application: absorption, blood barrier, mechanical strength, rigidity and tearing strength, The pasting is performed conventionally.

The nature and the quantity of paste used for pasting the two papers together are selected so as to avoid affecting either the recyclability of the packaging or its suitability for packaging food.

It is thus possible to use pastes having an aqueous base such as the pastes formed using starches and/or polyvinyl alcohols, or synthetic pastes such as latex of the type sold by BASF under the trademark ACRONAL 500 D. When using a synthetic paste, precautions should be taken to ensure that the deposit is no more than 15 g/M2 of dry 20 area, with the range 8 g/M2 to 10 g/M2 being particularly preferred. The paste must withstand the thermal conditions imposed by thermoforming. In practice, the quantity of paste required is determined as a function of the porosity, the surface tension, and the roughness of each of the papers used. In accordance with the invention, various other technical dispositions may be envisaged to further improve the quality of the packaging material. 30 Particular mention may be made of applying a pigmented coating layer on the outside face of layer B. Such surface treatment improves the whiteness, the brilliance, and the printability of said outside face. It is also possible for the papers A and B to include additives of the kind used conventionally in paper-making: various adhesive agents; organic or inorganic fillers; a retention agent, a binder, a 12 conservation agent, an antimicrobial agent (of the antibiotic type or quaternary ammonium salts), a fungicide, etc.

The only constraint on such additives is naturally that the substances in question should be approved for packaging foods.

In a manner that is entirely conventional in papermaking, these substances may either be added in bulk or else on the surface of the paper.

Finally, in order to avoid discoloring meat, it should be observed that it may be particularly advantageous to add an anti-oxidizing agent on the surface and/or to the bulk of at least one of the two layers A and B. By way of example, the anti-oxidizing agent may be ascorbic acid or any other anti-oxidizing agent approved for use in the food industry and compatible with the formulation of the papers under consideration.

The recyclable packaging material of the invention is particularly suitable for thermoforming operations that enable packaging articles such as trays, plates, platters, or the like to be manufactured The following examples show various makeups and implementations for packaging material of the invention.

EXAMPLES Example 1 A packaging paper that is thermomoldable and recyclable was obtained by pasting together a paper A having a weight of 165 g/M2 and a paper B having a weight of 200 g/M2 by means of 10 g/M2 of ACRONAL 500D paste (BASF).

Paper A had the following characteristics:

Fiber composition:

1 13 Pulp Ultimate elongation in pulp COLOMBUS 2.8% 375% SOPORCEL 2.3% 63% Absorption:

Wet strength agent: Hercules KYMENE 557 H at 0.2% dry weight relative to dry paper. Absorption, as measured using the Totest or Cobb 1800 test, was 70 g/m2, thus constituting a blood absorption capacity of about 42% relative to the weight of the paper.

Using the T, test, the wet strength of the paper made in this way was 12 N for 15 mm in the long direction and 9 N in the cross direction.

Paper A was coated using a pasting press having separate circuits and using the following solutions:

face 1 that comes into contact meat: MOBILCER C (Mobil) at 5% commercial product relative to coating bath; face for pasting: starch at 10% dry matter.

Paper B had the following characteristics:

Fiber composition:

Pulp Ultimate elongation in pulp (test T3) COLOMBUS 2.8% 47% ARACRUZ 2.6% 53% 0.6-0o dry matter relative to the weight of the paper of SCOTCHBAN FX 845 as sold by 3M was incorporated in the bulk of the paper. The paper contained no filler, no adhesion agent, and no retention agent. The paper was coated in a pasting press in different manners on its two faces: face for pasting: starch at 10% dry matter; and 14 outside face 2: a solution of AQUAMOL 67 latex as sold by Bim Kemi, at a concentration of 30 commercial product relative to the coating bath.

The packaging paper manufactured in this way complied with legislation in France for being used in direct contact with meat.

The repulpability of this product is good, as determined by the method described above. The quantity of Brecht-Holl residue was practically zero.

Thermomolding performed in a Peerless press presented no problem.

Anti-adhesion as measured using the contact angle method (test T2) gave the following results:

inside face: 115' outside face: 125'.

Trays containing meat were closed by means of a plastic film in the usual way for this type of packaging.

Example 2

Papers A and B had the same characteristics, the paste was identical to that in Example 1, but the faces of papers A and B for pasting were treated using water instead of a starch solution.

Example 3

Papers A and B were identical to those of Example 1 and the paste used was a starch paste at 15 g/M2 dry weight.

Thermomolding was still possible, the recyclability of the product was even better than in Examples 1 and 2 because of the ease with which the paste can be dissolved in water.

Example 4

The paper A differed from that of Example 1 in its weight, which was 255 g/M2' thereby giving it greater blood absorption capacity, the Cobb 1,800 (test TO) test b.: ".:

RI on said paper gave result of 80 g/M2, i.e. 31% absorption relative to the weight of the paper A.

Paper B was identical to that in Example 1, except that its weight was 150 g/M2.

The quantity of starch paste used was 12 g/M2 dry matter, giving rise to a packaging material whose final weight was 417 g/M2.

The surface treatments performed on papers A and B were identical to those of,Example 2.

Example 5

This example differed from Example 1 by the paper B being bulk treated with SCOTCHBAN FX 845 at 0.3 in terms of dry matter relative to the weight of the paper. Its characteristics were little changed: only the barrier was a little less good, said packaging being more particularly suitable for white meat that gives rise to less juice.

Example 6

This example differed from Example 1 by the way in which paste 2 of paper B was treated (outside face) in the pasting press: the following composition expressed in grams per liter of coating bath was deposited on the paper:

latex UKADUR 9533 from Schill Seilacher: 300 g PASILEX from Degussa: 70 g.

Because of the mineral pigment present in this composition, the printability of the paper was better and the paper was whiter, this treatment making it possible to enhance the packaging by means of colored printing, thereby making the food more attractive.

16

Claims (20)

1. CLAIMS 1/ Packaging material of the type comprising a multilayer structure

   made essentially out of paper, characterized: in that it comprises at least two layers A and B of paper, respectively an internal layer and an external layer; in that the layer A is absorbent and contains at least one chemical agent suitable for imparting wet strength thereto; and in that layer B includes at least one oleophobic additive suitable for imparting resistance thereto in particular against fats and water, said layer having an outside face treated with a hydrophobic coating agent.
2. 2/ A material according to claim 1, characterized in that paper layer A possesses absorption power enabling it to absorb a quantity of liquid that is not less than 20%, preferably not less than 30%, and still more preferably lies in the range 50% to 80% of its own weight.
3. 3/ A material according to claim 1 or claim 2, characterized in that layer A has wet strength as measured using the T1 test that is not less than 7 N per 15 mm in the paper manufacturing direction and not less than 3 N per 15 mm in the cross direction, and that is preferably not less than 11 N in the long direction and not less than 6 N in the cross direction.
4. 4/ A material according to any one of claims 1 to 3, characterized in that the chemical agent contained in layer A is present at a concentration expressed in terms of dry weight % relative to the total mass of layer A, that is not less than 0.05, that is preferably not less than 0.1, and that still more preferably lies in the range 0.2 to 1.
5. 5.

   7 17 5/ A material according to any one of claims 1 to 4, characterized in that the concentration of oleophobic additive in layer B, expressed in terms of dry weight relative to the total mass of layer B, is not less than 0.05, is preferably not less than 0.08, and still more preferably lies in the range 0.1 to 0.3.
6. 6/ A material according to claim 5, characterized in that the oleophobic additive is a compound or a mixture of compounds selected from fluorine-containing polymers.
7. 7/ A material according to any one of claims 1 to 6, characterized in that the resistance of layer B to penetration by water as expressed using test TO for a period of 1 minute, is no greater than 13, and preferably lies in the range 9 to 12, and in that the resistance to wetting of layer B as specified in a test T2 that measures its contact angle with water, is not less than 100', is preferably not less than 1050, and still more preferably lies in the range 1100 to 1250.
8. 8/ A material according to any one of claims 1 to 7, characterized: in that the coating agent ig a liquid composition based on a substance or a mixture of substance selected from the family of waxes and/or latexes; and in that it is deposited at a rate lying in the range 1 to 17, preferably in the range 3 to 12, and still more preferably about 9 grams of dry mater per M2.
9. 9/ A material according to any one of claims 1 to 8, characterized in that it is thermoformable, and in that each of layers A and B includes both long cellulose fibers having an ultimate elongation value as measured using test T3 that is not less than 2. 8%, that is preferably not less than 3%, and that is still more preferably not less than 3.5%, and also short cellulose 18 f ibres having an ultimate elongation value that is not less than 2%.
10. 10. A material according to claim 9, wherein the ultimate elongation value is at least 2.5%.
11. 11. A material according to claim 9, wherein the ultimate elongation value is at least 3%.
12. 12. A material according to any of claims 1 to 11, wherein the layers A and B are pasted together.
13. 13. A material according to any of claims 1 to 12, wherein 10 the internal f ace of layer A has been treated with a coating agent applied at a concentration of not more than 3 g dry matter per m 2, so that its anti-adhesion, as measured by the T2 test' is not less than 900.
14. 14. A material according to claim 13, wherein the anti- is adhesion is at least 1000.
15. 15. A material according to claim 13, wherein the antiadhesion is 1000 to 1100.
16. 16. A material according to any of claims 1 to 15, wherein its outside face includes a pigmented coating.
17. 17. A material according to claim 1, substantially as exemplified herein.
18. 18. A material according to claim 1, substantially as described here with reference to the accompanying drawing.
19. 19. Packaging of a material according to any of claims 1 to 18.
20. 20. Packaging according to claim 19,, in the form of a tray, plate or platter.