WO2022029022A1

WO2022029022A1 - Process for the production of packaging for the preservation of food products consisting of a cellulosic support coated with a polymer resin layer in which anionic clays are dispersed intercalated with active molecules, and packaging thus obtained

Info

Publication number: WO2022029022A1
Application number: PCT/EP2021/071377
Authority: WO
Inventors: Vittoria Vittoria; Valeria Bugatti; Giovanni Fuganti; Federica ZUPPARDI
Original assignee: Nice Filler S.R.L.
Priority date: 2020-08-05
Filing date: 2021-07-30
Publication date: 2022-02-10
Also published as: EP4193017A1; IT202000019378A1

Abstract

The present invention concerns a process for the production of packaging for the preservation of food products, the packaging thus obtained consisting of a cellulosic support such as, for example, paper or cardboard, coated with a layer of preferably acrylic or styrene/acrylic polymer resin, in which anionic clays are dispersed, preferably hydrotalcite, intercalated with active molecules.

Description

PROCESS FOR THE PRODUCTION OF PACKAGING FOR THE PRESERVATION OF FOOD PRODUCTS CONSISTING OF A CELLULOSIC SUPPORT COATED WITH A

POLYMER RESIN LAYER IN WHICH ANIONIC CLAYS ARE DISPERSED INTERCALATED WITH ACTIVE MOLECULES, AND PACKAGING THUS OBTAINED DESCRIPTION

The present invention concerns a process for the production of packaging for the preservation of food products and the packaging thus obtained. More particularly, the packaging according to the invention consists of a cellulosic support such as, for example, paper or cardboard, coated with a polymer resin layer in which anionic clays are dispersed, intercalated with active molecules.

Polymer resins comprising particular additives - here defined as “active molecules” - capable of interacting positively with substances present in the environment are used in various sectors of application, for example in the sector of food packaging, where they are also designated as “active functional packaging”.

An active functional packaging, in addition to performing the function of containing a product - for example a food product - also performs other functions, such as the function of improving conservation of the product, extending the period of freshness. An active packaging is therefore able to interact positively with a biologically active product, generally a food with which it is in contact or exposed, in order to obtain performances that would be impossible with a conventional packaging. The positive interaction of the active packaging consists, for example, in removing undesired volatile substances from the food, or substances that accelerate the deterioration thereof, or by immobilizing or releasing substances with antimicrobial and/or anti-oxidant properties.

Substances with anti-oxidant or antimicrobial properties are often added to foods or to their packages or to the packaging materials. In particular, widely used anti-oxidant substances are, for example, ascorbic acid and relative salts, tocopherols, gallates, butylated hydroxyanisole (BHA), butylhydroxytoluene (BHT), lactic, citric and tartaric acids and relative salts. Widely used antimicrobial substances are, for example, sorbic, benzoic, acetic, propionic acids and relative salts, ethyl, propyl and methyl p-hydroxybenzoates and relative salts, sulphur dioxide, biphenyl, 2-phenylphenol, sodium or potassium nitrites and nitrates.

Paper and cardboard, in terms of type of material, are already among the products most widely used in the food packaging sector. However, the demand for paper and cardboard suitable for contact with food is destined to further increase, especially for a packaging industry in search of new opportunities and innovation. The reasons for the appeal of paper and cardboard for packaging are clear; they are lightweight materials, they come from renewable sources and are recyclable and compostable. In fact, according to the specifications of ATICELCA, the Italian association of paper manufacturers, paper waste can be classified into 3 different categories, A B and C, to allow correct disposal of the objects once they have reached the end of their working life.

Categories A and B are currently considered by all municipalities in Italy as paper waste disposable and recyclable as paper whereas not all municipalities in Italy are equipped to recycle category C.

The categories are differentiated according to the quantity of plastic material contained in/on the paper. In particular, category A must contain 0% (zero) of plastic material, category B can contain up to 20% of plastic material out of the total weight of the paper and category C can contain 20 to 40% of plastic material out of the total weight of the paper.

This means that at strategic level, paper and cardboard will become increasingly competitive, in particular with respect to plastic. Today these materials are able to compete easily with alternative materials in terms of efficiency and life cycle, but with new emerging technologies (barrier, antimicrobial, smart. . .etc.) paper and cardboard will become the material of choice for almost all packaging solutions.

However, the essential condition for the use of paper and cardboard in food packaging is that it must function safely and effectively in contact with the food. In fact, exposure to water, humidity and grease is highly destructive for this material, hence, currently, various techniques are adopted to improve the properties, in particular mechanical and surface properties, of cardboard.

Cardboard packaging is often made of multiple layers of different materials, each of which provides a functional benefit. For example, a cardboard container, in order to maintain its shape, can be combined with a resin-coated sheet to protect the freshness of the product, acting as a barrier to humidity or air. Cardboard sheets are sometimes laminated with aluminium and/or polymer sheets to prevent contact with water. This technique, however, limits recycling of the paper material.

Alternatively, fine plastic coatings are also used to improve the gas barrier and water repellence.

The introduction of lignin or fine layers of nano-cellulose are used to improve gas permeability and water repellence. Combinations of different approaches are sometimes used. However, the commonest technique is to provide the cardboard with a covering (paint or coating) which acts as a barrier and improves its mechanical properties. Paint compositions in general contain four classes of components. A transport medium, a resin precursor in the form of a monomer or a polymer, pigments and additives.

The transport medium is a liquid component that serves to dissolve (or disperse) and transport all the other components. It generally evaporates when the paint precursor solidifies, forming the coating, and dries on the surface. In paint for paper, it is generally water, whereas in oilbased paint it is an organic solvent.

Pigments are solid particles that provide various aesthetic qualities such as colour, opacity and duration. Many additives can be included in the paint composition and contribute to various properties of the paint, such as viscosity, stability, and aesthetic qualities.

The resin precursors are multiple and can be chosen from numerous different classes based on their nature and use, as will be illustrated below.

The interest in functionally active packaging able to contain food products, maintaining their freshness and nutritional and organoleptic characteristics, has stimulated the search for increasingly performing materials, i.e. capable of extending as far as possible the shelf-life of the food.

It would therefore be desirable to have a food packaging able to extend the product shelf-life which is made of a natural material as far as possible, so that it can be recycled or composted. It would also be desirable to have a process for the production of said packaging able to provide an effective lasting packaging, which is industrially sustainable.

One object of the present invention is therefore to provide a process for producing food packaging capable of extending the shelf-life of the food, and able to provide a stable, effective and environment-friendly packaging.

A further object of the present invention is to provide an easily repeatable and industrially economic process.

A further object of the present invention is to provide a food packaging comprising additives that are able to extend the product shelf-life and which is recyclable or compostable and allows a reduction in plastic waste.

Last but not least, a further object of the present invention is to provide a method for inhibiting bacterial growth on food products which uses recyclable or compostable articles and which respects both the environment and human health.

One aspect of the present invention therefore consists of a process for the production of packaging for the preservation of food products comprising the following steps: a) providing a cellulosic support suitable for use as food packaging; b) coating said cellulosic support with a layer having thickness ranging from 3 to 10 p of a resin selected from the group consisting of: polyurethane, silicone, acrylic, styrene/acrylic, thermoplastic polyester, polyolefin resins, if necessary cross-linked, for example with aliphatic isocyanates, quinones and silanes, or mixtures thereof; in which anionic or cationic clays are dispersed in a quantity ranging from 1 to 50% by weight of the total weight of the resin, intercalated with active molecules; wherein said resin has a viscosity, measured at 25°C according to the DIN 53211 standard, ranging from 30 to 90 seconds Ford 4 and a pH higher than 7.

In this way it is possible to obtain a natural packaging that maintains the freshness and nutritional and organoleptic characteristics of the food preserved therein, extending the shelflife of the food.

By the term cellulosic support according to the present invention we mean any support of natural origin derived from cellulose such as, for example, paper, wood, cardboard and similar.

It has surprisingly been found that the thickness of the coating resin of the cellulosic support plays an important role in obtaining a food packaging with the desired characteristics, in fact if it is too fine it does not allow the active molecules to perform their action on the food, whereas if the layer is too thick it compromises the workability of the support, limiting the use thereof and forming in the desired container.

It has also surprisingly been found that also the viscosity of the resin when applied on the cellulosic support influences the functioning and effectiveness of the packaging. In fact, if the density is too low it allows the resin to be absorbed by the cellulosic support and to penetrate deeper into the fibres, and this translates into a lower effectiveness of the active molecules which, being absorbed in the support, do not correctly perform their action on the food.

When the density is too high, on the other hand, it does not allow correct application of the resin, compromising the integrity of the packaging and at the same time preventing the active molecules from migrating outside the resin to perform their action.

According to the present invention, the viscosity is measured according to the DIN 53211 standard at 25 °C.

According to the present invention, the clay (or filler) is dispersed in quantities ranging from 5 to 40% by weight of the total weight of the resin, preferably in quantities ranging from 8 to 20 % % by weight of the total weight of the resin. In this way the coating resin incorporates inside it a quantity of material sufficient for the active molecules intercalated in the clay to perform their action, increasing the shelf-life of the food.

It has surprisingly been found that coarse dispersions of filler in the resin do not allow the active molecules to perform their action in the best way.

In view of the above consideration, the clay dispersed in the resin has dimensions ranging from 1 to 50 p, preferably 2 to 30 p, even more preferably 3 to 20 p.

In this way a uniform dispersion of the filler in the resin is obtained, which allows a continuous and effective layer of resin to be obtained on the support.

The dispersion can occur by means of common dispersion means including mixing, stirring, milling, or combinations thereof.

The filler can be micronized before being dispersed in the resin or can be micronized directly during dispersion in the resin based on preparation requirements and the nature of the components.

Preferably the active molecule is present in a quantity ranging from 1 to 50% by weight, more preferably 20 to 50%, even more preferably approximately 40 to 50% of the weight of the clay. This percentage is naturally linked to the molecular weight of the active molecule.

The choice of the active molecule depends on the application, ranging between antimicrobials, antioxidants and antifungals.

Antimicrobial preservatives, E200-E299

• E200 Sorbic acid (preservative)

• E201 Sodium sorbate (preservative)

• E202 Potassium sorbate (preservative)

• E203 Calcium sorbate (preservative)

• E214 Ethyl parahydroxybenzoate (preservative)

• E215 Sodium salt of ethyl parahydroxybenzoate ("ethylparaben") (preservative)

• E216 Propyl parahydroxybenzoate (preservative)

• E217 Sodium salt of propyl parahydroxybenzoate ("propylparaben") (preservative)

• E218 Methyl parahydroxybenzoate (preservative)

• E219 Sodium salt of methyl parahydroxybenzoate ("methylparaben") (preservative)

• E231 2-Phenylphenol (preservative)

• E232 Sodium salt of 2-phenylphenol (preservative)

• E233 Tiabendazole (preservative)

• E234 Nisin (preservative) • E235 Natamycin, Pimaracin (preservative)

• E236 Formic acid (preservative) .

• E237 Sodium formate (preservative)

• E238 Calcium formate (preservative)

• E239 Hexamethylenetetramine, hexamine (preservative)

• E242 Dimethyl dicarbonate (preservative)

• E249 Potassium nitrite (preservative)

E260 Acetic acid (preservative)

• E261 Potassium acetate (preservative)

• E262 Sodium acetate and Sodium diacetate (preservative)

• E263 Calcium acetate (preservative)

• E264 Ammonium acetate (preservative)

• E270 Lactic acid (preservative) (acid) (antioxidant)

• E280 Propionic acid (preservative)

• E281 Sodium propionate (preservative)

• E282 Calcium propionate (preservative)

• E283 Potassium propionate (preservative)

• E284 Boric acid (preservative)

• E285 Borax, sodium tetraborate (preservative)

• Sodium salicylate (preservative)

Antioxidants: E300-E399

• E300 Ascorbic acid (Vitamin C) (antioxidant)

• E301 Sodium ascorbate (antioxidant)

• E302 Calcium ascorbate (antioxidant)

• E303 Potassium ascorbate (antioxidant)

• E304 Esters of fatty acids of ascorbic acid (i) Ascorbyl palmitate (ii)

• Ascorbyl stearate (antioxidant)

• E306 Natural extracts rich in tocopherol (antioxidant)

• E307 a-tocopherol (synthetic) (antioxidant)

• E308 y-tocopherol (synthetic) (antioxidant)

• E309 6-tocopherol (synthetic) (antioxidant)

• E310 Propyl gallate (antioxidant)

• E311 Octyl gallate (antioxidant)

• E312 Dodecyl gallate (antioxidant) • E315 Erithorbic acid (antioxidant)

• E316 Sodium erythorbate (antioxidant)

• E320 Butylated hydroxy anisole (BHA) (antioxidant)

• E321 Butylated hydroxytoluene (BHT) (antioxidant)

• E325 Sodium lactate (antioxidant)

• E326 Potassium lactate (antioxidant)

• E327 Calcium lactate (antioxidant)

• E329 Magnesium lactate (antioxidant)

• E330 Citric acid (antioxidant)

• E331 Sodium citrates: (i) Monosodium citrate (ii) Disodium citrate (iii) Trisodium citrate (antioxidant)

• E332 Potassium citrates: (i) Monopotassium citrate (ii) Tripotassium citrate (antioxidant)

• E334 Tartaric acid (L (+/-) (acid) (antioxidant)

• E335 Sodium tartrates: (i) Monosodium tartrate (ii) Disodium tartrate (antioxidant)

• E336 Potassium tartrates: (i) Monopotassium tartrate (cream of tartar) (ii) Dipotassium tartrate (antioxidant)

• E337 Sodium and potassium tartrate (antioxidant)

• E338 Phosphoric acid (antioxidant)

• E339 Sodium phosphates: (i) Monosodium phosphate (ii) Disodium phosphate (iii) Trisodium phosphate (antioxidant)

• E340 Potassium phosphates: (i) Monopotassium phosphate (ii) Dipotassium phosphate (iii) Tripotassium phosphate (antioxidant)

• Lipoic aid

• Sulphur-containing amino acids (cystine, methionine, cysteine, taurine, cisteic acid)

• Beta-carotene or provitamin A (carotenoid)

• Bioflavonoids

• Coenzyme Q10

• E.D.T.A. (ethylenediaminetetraacetic acid)

• Glutathione

• Lycopene (carotenoid)

• Lutein (carotenoid)

• Melatonin

• Methionine

• MSM • NAC or N-Acetyl-Cysteine

• Pycnogenol

• Potassium

• Copper

• Resveratrol

• Selenium

• Vitamin A

• Vitamin C

• Vitamin E

• Zeaxanthin

• Zinc

• Chlorophyll

• Anthocyanins

• Lycopene

Antifungals

• Metronidazole (benzoate)

• Doxycycline

• Aciclovir

• Famciclovir

• Methisoprinol

• Valaciclovir (hydrochloride)

According to the present invention, the application of the resin, or the phase of coating the cellulosic support, can be conducted with any means suitable for applying a liquid on a surface, such as rotogravure, flexography, spray, etc. Preferably it is carried out by means of a flexographic coating (flexography) or rotogravure system.

In this way a uniform layer of resin is obtained on the support using known and well-tested industrial processes.

Preferably said cellulosic support is paper, paperboard or cardboard. By the term paper we mean a flat support weighing between 10 and 150 g/m² and with thickness ranging from 0.03 to 0.3 mm; by the term paperboard we mean a flat support weighing between 150 and 450 g/m² and with thickness ranging from 0.3 to 1 mm and by the term cardboard we mean a flat support weighing between 450 and 1,200 g/m² and with thickness greater than 1 mm.

According to the present invention examples of cationic clays that can be dispersed in the resin are: montmorillonite, smectite, bentonite. According to the present invention, examples of anionic clays that can be dispersed in the resin are: hydrotalcites with different ratio between M(II) and M(III).

Preferably the clay dispersed in the resin is an anionic clay, even more preferably a synthetic hydrotalcite, with ratio M(III) to M(II) between 0.2 and 0.4.

The synthetic hydrotalcite is a layered solid consisting substantially of positively charged planes, the charge of which is balanced by exchangeable anions found in the interlayer region. The anion can therefore be an active molecule which is stored and conserved and which can in some cases be released subsequently into the environment to interact positively with it.

In particular the hydrotalcites are layered solids, the planes of which, consisting substantially of layered double hydroxides (LDHs), have positive charges balanced by anions that are found in the interlayer region and are exchangeable.

In an absolutely preferred embodiment, the hydrotalcite intercalated with active molecules according to the invention is a hydrotalcite having the following formula (I)

[M(II)i-xM(III)x(0H)2]^x+[Aⁿ-x/n]^x- mS (I) wherein:

M(II) = Mg, Zn, Cu, Mn, Co, Fe, Ni;

M(III) = Al, Mn, Fe, Co, Ni, Cr, Ga; x = 0.2-0.4;

Aⁿ" is the intercalated anion of the active molecule with charge n-; m = number of molecules of cointercalated solvent (S);

S = cointercalated solvent.

Preferably in said hydrotalcite having general formula (I) M(II) = Mg o Zn, M(III) = Al, S = H2O.

The above-mentioned hydrotalcite having formula (I) can advantageously be prepared in one single stage by reaction in a solution of salts of the metals M(II) and M(III) with a solution containing the anion Aⁿ" of the active molecule A, at a temperature ranging from 10 to 60°C and at a pressure ranging from 90 to 110 KPa.

In particular it can be prepared according to the method described in the European Patent EP 2771396 Bl.

The hydrotalcites intercalated with functionally active molecules prepared in one single reaction stage by co-precipitation from the salts of the metals M(II) and M(III) in the presence of the active molecule Aⁿ", and subsequently dispersed in a polymer matrix, allow the functionally active molecule to perform an improved long-term action

Preferably said coating resin of the cellulosic support according to the present invention is an acrylic or styrene/acrylic resin in water emulsion.

The acrylic resins are obtained by polmerization of acrylic or methacrylic monomers (e.g. ethyl and methyl esters of acrylic acid and methacrylic acid. The acrylic resins are therefore polymers or copolymers with chemical structure of the repetitive unit generically described as follows:

[... CH2— C(R1)COO(R2)— CH2. . . ]n

By varying the chemical nature of the substituents R1 and R2 it is possible to produce a very large number of resins with different characteristics. The family further increases if we consider the possible products that are obtained by copolymerization of the various monomers.

Acrylic polymers, copolymers or terpolymers are used as dispersions, emulsions or water- soluble adhesives. They are used mainly, but not only, for packaging of dry food products or for secondary/tertiary packaging, applied on different substrates, for paper, cardboard or polymer films.

Another aspect of the present invention consists of a packaging for the preservation of food products comprising a cellulosic support coated with a layer having thickness ranging from 3 to 10 micron of a resin selected from the group consisting of: phenolic, amide, epoxy, polyurethane, unsaturated polyester, cyanoacrylic, silicone, alkyl, acrylic, styrene/acrylic, polycarbonate, thermoplastic polyester, vinylester, polyvinyl fluoride and polyolefin resins, in which anionic clays are dispersed in quantities ranging from 1 to 50% by weight of the total weight of the resin, intercalated with active molecules.

Preferably the clay is dispersed in quantities ranging from 5 to 40% by weight of the total weight of the resin, preferably in quantities ranging from 8 to 20% % by weight of the total weight of the resin.

Preferably the clay has dimensions ranging from 1 to 50 p, preferably from 2 to 30 p, even more preferably from 32 to 0 p.

Preferably the active molecules are present in quantities as previously reported for the preparation process, and are selected from the group consisting of antimicrobials, antioxidants and antifungals, as listed above.

Preferably the cellulosic support consists of paper, paperboard or cardboard. Preferably the clay dispersed in the resin is an anionic clay as previously described, in particular it is the hydrotalcite intercalated with active molecules reported above.

Preferably the resin with which the cellulosic support is coated constituting the food packaging according to the invention is an acrylic or styrene/acrylic resin.

The coatings for the Packaging according to the invention, are prepared by grinding the filler in a vehicle of a polymeric nature. Said vehicle can be water-based or solvent-based, depending on the application system.

Usually, in the paper converting companies that do not have solvent abatement systems and that only use flexographic technology, water-based coatings must be used.

The binder is an acrylic or styrene/acrylic emulsion. Acrylic systems, which have a low viscosity, have good adhesion on treated polyolefin films or on polymeric films with high polarity (such as polyester). Styrene/acrylic emulsions, on the other hand, have much higher viscosities above 90 seconds Ford 4.

For paper and cardboard, the resins according to the invention are acrylic or styrene acrylic emulsions. Given that the filler behaves like a thickener, in order to bring them up to a preferred viscosity of 60 seconds (which is optimal from the point of view of application), a certain percentage of water should be added, in addition to stabilizing and anti-foaming additives. Viscosity influences the transfer of the coating from the anilox to the gum and from the gum to the paper substrate.

A further aspect of the present invention concerns a method for the inhibition of bacterial growth on food products, which comprises the packing of food products in a packaging as described previously. Said packaging is advantageously produced by a process as previously described.

EXAMPLES

The methods for the preparation of packaging for the preservation of food according to the process subject of the present invention are described below.

Preparation of the clay-active molecule intercalate

Hydrotalcite powders intercalated with active molecule were prepared using the hydrotalcite preparation method described in the European patent EP 2771396 Bl.

Example 1

Synthesis [ZnAl(OH)2]-sal (LDHsal)

A solution containing Zn(NO3)2*6H2O (12.9g) / A1(NO3)3*9H2O (8.14g) is added to the solution containing sodium salicylate (5.9g) under stirring and under nitrogen flow. The pH slowly reaches the value of 7.5 with the addition of NaOH IM (approximately 24 hours). At the end, it is filtered and washed repeatedly with water and left in a vacuum oven at 50°C. It is left for a further 5h at 100°C. 8g of [ZnAl(OH)2]-salicylate (LDHsal) are obtained.

Table 1

As can be seen from table 1, 0.0434 moles of Zn(NO3)2*6H2O were mixed with 0.0217 moles of A1(NO3)3*9H2O in 30 mL of water and 0.0368 moles of sodium salicylate were added in the presence of 127 mL of NaOH IM. 8 grams of [ZnAl(OH)2]-salicylate (LDHsal) were obtained.

Example 2

Synthesis [ZnAl(OH)2]-pOHBz (LDHpOHBz)

A solution containing Zn(NO3)2*6H2O (12.9g) / A1(NO3)3*9H2O (8.14g) is added to the solution containing sodium parahydroxybenzoate (5.9g) under stirring and under nitrogen flow. The pH slowly reaches the value of 7.5 with the addition of NaOH IM (approximately 24 hours). At the end it is filtered and washed repeatedly with water and left in a vacuum oven at 50°C. It is left for a further 5h at 100°C. 8g of [ZnAl(OH)2]-pOHbenzoate (LDHpOHBz) are obtained.

Table 2

As can be seen from table 2, 0.0434 moles of Zn(NO3)2*6H2O were mixed with 0.0217 moles of A1(NO3)3*9H2O in 30 mL of water and 0.0368 moles of sodium p-hydroxybenzoate were added in the presence of 127 mL of NaOH IM. 8 grams of [ZnAl(OH)2]-salicylate (LDHsal) were obtained. 9 g of [ZnAl(OH)2]-pOHbenzoate (LDHpOHBz) are obtained.

Resin characterization

The resins used are acrylic or styrene acrylic emulsions such as, for example, Joncryl® ECO 2124-E. They were diluted with water until obtaining a viscosity of 50 seconds Ford, and hydrotalcites functionalized with molecules such as [ZnAl(OH)2]-pOHbenzoate (LDHpOHBz) or [ZnAl(OH)2]-salicylate were added.

Dispersion of the filler intercalated with active molecules in the resin

Hydrocalcites were added to the resins previously described according to examples 1 and 2 in order to evaluate the dispersibility of the filler in the resin.

Example 3

12 grams of hydrotalcite [ZnAl(OH)2]-salicylate (LDHsal) which has mean dimensions of 5- 600 micron were mixed with 88 grams of a series of acrylic and styrene/acrylic resins having density ranging from 1.04 to 1.08 g/cc.

A poor dispersion was noted with large powder agglomerations, visible to the naked eye. The known methods of dispersion of the hybrid solid in the water-based resin were used: mechanical mixing, milling, sonication. It was noted that uniform dispersion is possible only below a dimensional threshold value of the compound powders. This value was 5 microns. The resin with the hybrid powder then underwent one of the processes listed above, until the dimension of the powders was brought from 600 micron, as obtained by the synthesis process, to 3 microns. With these dimensions as upper limit, the dispersion in the resin was very good, and it was possible to proceed with spreading of the paint on the cardboard.

Paint deposition process

To transfer the functional paint onto the cardboard, a rotogravure system was used. In this case printing is by direct contact, from the support matrix: the web of the reel passes between the matrix cylinder and a second pressure cylinder so that the ink present in the grooves is absorbed by the paper. For this purpose, the ink used is generally very liquid and the paper is very porous, with gram weight between I CK I 50 g/m² for paper, 150^450 g/m² for paperboard and 450-4,200 g/m² for cardboard. The functional hybrid concentration varies between 0.542.0 g/ m².

Example 4 An acrylic resin with density 1.04 g/cc, with 10% filler [ZnAl(0H)2]-salicylate (LDHsal), according to example 1, was deposited on flat paperboard weighing 250 g/m² with thickness of 0.6 mm. The thickness of the coating was 8 microns.

Example 5

A second styrene-acrylic resin with density 1.08 g/cc with 12% filler [ZnAl(OH)2]-pOHBz (LDHpOHBz), prepared according to example 2, was deposited on cardboard weighing 450 g/m² and having thickness of 1.5 mm. The thickness of the coating was 10 microns.

Response to packaging bacteria

The bactericidal capacities of the packaging according to the invention were tested in order to evaluate the effectiveness of the active molecules present in the coating.

Example 6

An acrylic resin Joncryl® ECO 2124-E, density 1.04 g/cc, with 10% filler [ZnAl(OH)2]- salicylate (LDHsal), according to example 1 and 4, was deposited on flat paperboard weighing 250 g/m² with thickness of 0.6 mm. The thickness of the coating was 8 microns. A series of bacteria were inoculated, reported in the Table, on a square measuring 2x2 cm and the bacterial growth was evaluated by microscope count. The paperboard in which no growth is observed in the first 24 hours, according to table 3, is considered effective.

Table 3

Bacterial count and effect on food shelf-life The packaging produced according to the invention was tested in order to evaluate the actual effectiveness on food in terms of both bacterial count and extension of the shelf-life.

Example 7

500g of white grapes were packaged in punnets weighing 250 g/m² with thickness of 0.6 mm, on which a paint with thickness of 8 micron had been deposited containing [ZnAl(OH)2]- salicylate (LDHsal), according to example 1 and 4, and kept at both 5°C and 25°C. The same quantity of grapes was packaged in control punnets without filler and kept in the same conditions as those with filler.

Table 4

As can be seen from table 4, at 7 days at 5°C no difference is noted for total coliforms, moulds and yeasts, while the total mesophile count is much higher in the control (2800 Ufc/g) than in the punnet with the filler (500 Ufc/g). At the temperature of 25°C the values of the punnet with filler are always considerably lower than the control.

Example 8

200 g of fresh strawberries were packaged in punnets weighing 250 g/m² with thickness of 0.6 mm, on which a paint with thickness of 8 micron containing [ZnAl (OH)2]-salicylate (LDHsal) had been deposited, according to example 1 and 4, and kept at both 5°C and 25°C. The same quantity of strawberries was packaged in control punnets without filler and kept in the same conditions as those with filler. Table 5

As can be seen from table 5, at 7 days at 5°C no difference is noted for total coliforms whereas for moulds and yeasts and total mesophile count the value is much higher in the control than in the punnet with the filler. At the temperature of 25°C the values of the punnet with the filler are always considerably lower than the control.

Example 9

500g of fresh cherry tomatoes were packaged in punnets weighing 250 g/m² with thickness of 0.6 mm, on which a paint with thickness of 8 micron containing [ZnAl(OH)2]-salicylate (LDHsal) had been deposited, according to example 1 and 4, kept at both 5°C and 25°C. The same quantity of fresh cherry tomatoes was packaged in control punnets without filler and kept in the same conditions as those with the filler.

Table 6

As can be seen from table 6, at 7 days at 5°C no difference is noted for total coliforms whereas for moulds and yeasts and total mesophile count the value is much higher in the control than in the punnet with filler. At the temperature of 25°C the values of the punnet with filler are similar for the total coliforms but always stay considerably lower than the control for total mesophile count and moulds and yeasts.

Example 10

The shelf-life of the food in the containers treated with NF compared to the control was obtained from the data of the bacterial count at various temperatures and at various times and after evaluation of the organoleptic properties (colour, flavour, fragrance).

Table 7

As can be seen from table 7, the shelf-life of the white grapes increases by 4 days, for the fresh strawberries by 6 days and for the tomatoes by 5 days.

Example 11

Thickness of the paint layer deposited on the paper.

Hydrotalcite from Example 1, with a size of 3 microns, was mixed in a styrene/acrylic resin with a concentration of 8%. This is the maximum concentration to have a homogeneous dispersion without precipitating the solid. The resin with the filler was transferred to the paper substrate with a thickness of 2 microns. The dry residue of the paint has an amount of filler less than 0.6 g/m2, which is the minimum amount for the purpose of protecting the food.

It was therefore deduced that a thickness of 2 microns is not sufficient, and greater thicknesses must be deposited. The same procedure was followed by deposing the resin with a much higher thickness of 15 microns. It was noticed that deposing such a thickness the workability of the substrate and the forming of the container was affected.

Claims

CLAIMS Process for the production of packaging for the preservation of food products comprising the following steps:

(a) providing a cellulosic support suitable for use as food packaging;

(b) coating said cellulosic support with a thickness layer from 3 to 10 p of a resin selected from the group consisting of: polyurethane, silicone, acrylic, styrene/acrylic, thermoplastic polyesters, polyolefins eventually cross-linked with aliphatic isocyanates, quinones and silanes, or mixtures thereof; in which anionic or cationic clays are dispersed in quantities between 1 and 50% by weight of the total weight of the resin, intercalated with active molecules; wherein said resin has a viscosity, measured at 25°C according to DIN 53211, between 30 and 90 seconds Ford 4 and a pH greater than 7. Process according to claim 1, characterized in that said clay is dispersed in an amount from 5 to 40 % by weight of the total weight of the resin, preferably in an amount from 8 to 20 % by weight of the total weight of the resin. Process according to one or more of the preceding claims, characterized in that said clay is from 1 to 50 p in size, preferably from 2 to 30 p, and even more preferably from 3 to 20 p. Process according to one or more of the preceding claims, characterized in that said active molecules are selected from the group consisting of antimicrobials, antioxidants, antifungals. Process according to one or more previous claims, characterized in that said active molecules are present in an amount from 1 to 50% by weight of the weight of said clay. Process according to one or more of the preceding claims, characterized in that said coating step is carried out by means of a flexographic or rotogravure coating system. Process according to one or more of the preceding claims, characterized in that said cellulosic support is paper, paperboard or cardboard. Process according to one or more of the preceding claims, characterized in that an anionic clay is dispersed in said resin. Process according to claim 8, characterized in that said anionic clay is a hydrotalcite intercalated with active molecules, having the formula (I)

[M(II)i-xM(III)x(0H)2]^x+[Aⁿ-x/n]^x- mS (I) wherein:

M(II) = Mg, Zn, Cu, Mn, Co, Fe, Ni;

M(III) = Al, Mn, Fe, Co, Ni, Cr, Ga; x = 0,2-0, 4;

Aⁿ" is the intercalated anion of the active molecule with charge n-; m = number of cointercalised solvent molecules (S);

S = co-integrated solvent. Process according to one or more of the preceding claims, characterized in that in said hydrotalcite of general formula (I) M(II) = Mg or Zn, M(III) = Al, S = H2O. Process according to one or more of the preceding claims, characterized in that said resin is a water emulsion acrylic or styrene/acrylic resin. Packaging for the preservation of food products comprising a cellulosic support coated with thickness layer from 3 to 10 p of a resin selected from the group consisting of: polyurethane, silicone, acrylic, styrene/acrylic, thermoplastic polyesters, polyolefins eventually cross-linked with aliphatic isocyanates, quinones and silanes, or mixtures thereof; wherein an anionic or cationic clay intercalated with active molecules are dispersed in an amount from 1 to 50% by weight of the total weight of the resin. Packaging according to claim 12, characterized in that said clay is dispersed in an amount from 5 to 40 % by weight of the total weight of the resin, preferably in an amount from 8 to 20 % by weight of the total weight of the resin. Packaging according to one or more of the claims 12 or 13, characterized in that said clay is from 1 to 50 p in size, preferably from 2 to 30 p, and even more preferably from 3 to 20 p. Packing according to one or more of the claims from 12 to 14, characterized in that said active molecules are selected from the group consisting of antimicrobials, antioxidants, antifungals. Packaging according to one or more of the claims from 12 to 15, characterized in that said active molecules are present in an amount from 1 to 50% by weight of the weight of said clay. Packing according to one or more of the claims from 12 to 16, characterized in that said cellulosic support is paper, paperboard or cardboard. Packing according to one or more of the claims from 12 to 17, characterized in that an anionic clay is dispersed in said resin. Packing according to one or more of the claims 12 to 18, characterized in that said anionic clay is a hydrotalcite intercalated with active molecules, having a general formula (I)

[M(II)i-xM(III)x(0H)2]^x+[Aⁿ-x/n]^x- mS (I) wherein:

M(II) = Mg, Zn, Cu, Mn, Co, Fe, Ni;

M(III) = Al, Mn, Fe, Co, Ni, Cr, Ga; x = 0,2-0, 4;

S = co-integrated solvent Packing according to one or more of the claims from 12 to 19, characterized in that in said hydrotalcite of general formula (I) M(II) = Mg or Zn, M(III) = Al, S = H2O. Packing according to one or more of the claims from 12 to 20, characterized in that said resin is a water emulsion acrylic or styrene/acrylic resin. Method for inhibiting bacterial growth on food products comprising the packaging of food products in a packaging according to one or more of claims from 12 to 21.