WO2006102942A1

WO2006102942A1 - Multilayer bioriented film having antiseptic and improved stiffness features

Info

Publication number: WO2006102942A1
Application number: PCT/EP2005/051477
Authority: WO
Inventors: Saleh Bayazian Benis; Selma ÇAMBER
Original assignee: Polfilm Co.
Priority date: 2005-04-01
Filing date: 2005-04-01
Publication date: 2006-10-05

Abstract

An improved biaxially oriented multilayer film structure having at least three layers is disclosed. Said laminated film exhibits superior stiffness, migration and antiseptic features intended for use particularly in the packaging of fatty foodstuffs. The film proposed by the present invention comprises at least an outermost layer having the composition of preferably 95-100% of a terpolymer or copolymer and 0-5% of organic or inorganic antiblocking agent; at least one high crystalline layer having the composition of; preferably 40-60% of a homopolymer, 5-20% of a filler material comprising CaCO3, BaSO4, TiO2 or talc, 5-15% of color pigment and 20-35% of high crystalline polypropylene where all figures are by weight. An anti-microbial agent is admixed to at least one layer of the lamination for inhibiting any microbial contamination, which considerably extends the shelf life of the packed foodstuffs.

Description

MULTILAYER BIORIENTED FILM HAVING ANTISEPTIC AND IMPROVED

STIFFNESS FEATURES

Technical Field of the Invention The present invention relates to a high barrier multilayer BOPP film structure having improved stiffness properties and deadfold characteristics, which particularly enables safe and convenient usage in especially wrapping up medical materials and foodstuffs, particularly margarines and fat containing foods. The film structure of the present invention provides a number of advantages in the foldability, cuttability and moisture & oxygen barrier properties particularly in packaging of margarine and butter like fat containing products. Proposed film of the present invention comprises at least three layers, each having a composition comprising mainly polypropylene homopolymer, high crystalline polypropylene, anti-microbial agents, copolymers, terpolymers and antiblocking agents depending on the desired features in the final product.

Background of the Invention / Prior Art

The present invention relates to a multilayer film structure having improved stiffness and also no hazardous substances migrating into foods highly migration resistant composition. Use of high crystalline polypropylene contributes the improvement of these features as well as providing excellent stiffness and deadfold characteristics of packaging material.

Parallel to the tremendously high amount of application areas in daily life, polymeric film materials take an important role to constitute part in various types of packaging purposes particularly for covering foodstuff in a hygienic manner. However, conventional films cannot be considered as totally safe for the public health although they inhibit the contact of food staff with the external conditions, due to the fact that migration of hazardous substances in the film composition through sensitive products such as food and medicine is a critical parameter as already well known in the art. Therefore, mono or multilayer packaging films should be carefully examined prior to use for these purposes. Furthermore, stiffness of the packaging material has mostly been a desired feature particularly for packaging operations of margarine and butter like foods. Disorders in packaging of these kinds of foodstuffs due to lack of foldability is undesirable as exact closure and isolation hardly happen and as such, microorganisms on foods may readily contaminate even causing fatal consequences.

Several multilayer film compositions including biaxially oriented ones are widely studied in the prior art with various combinations in their compositions. These compositions vary according to the purpose of intended use.

WO 03/046058 discloses a multilayer foldable BOPP film with improved barrier and dead-fold characteristics particularly for packaging margarine, butter or the like. The base layer and one of the outer layers contain a homopolymer, a filler and a hydrocarbon resin whereas one of the inner layers contains a homopolymer, a filler, a resin and a coloring agent, the other inner layer contains a homopolymer and a resin and the second outer layer contains a polymer mixture and an anti blocking agent. Said homopolymer is preferred to be polypropylene as indicated in this international application. However the polypropylene material used in certain layers is not high crystalline form resulting that film structure still lacks stiffness and also deadfold property. Hydrocarbon resins do readily penetrate through fatty foods when they are brought into contact with same. Therefore, the biaxially oriented multilayer film of this application does not foresee preventing migration through fatty foods. Likewise, preventing bacteria contamination is not disclosed therein.

A similar multilayer laminated and biaxially oriented film is disclosed by WO 03/072353. The bioriented film of this application mainly comprises a high crystalline propylene homopolymer resin layer of greater than about 93% isotactic content having a first surface and a second surface; a polyolefin resin layer having a discharge-treated surface; a metal layer having an optical density of at least about 2.6 deposited on the discharge-treated surface of said polyolefin resin layer; and a heat sealable layer or a winding layer disposed on the second surface. The objects of this application appear to be the elimination of the well known issue of leaky bags associated with conventional metallized film packaging as well as improving the moisture and gas barrier properties of laminate films. However, the film proposed of this application does not provide the features of good stiffness, deadfold, antimicrobial property, which are key features in packaging butter and margarine like fatty foods. GB 1441178 discloses a laminated film structure having a base layer of a biaxially stretched polymer film layer having a crystallinity of at least 60 % by weight with an inert filler; a grease-proof layer, laminated to at least one side of the thermoplastic film base layer which is selected from high density polyethylene, polypropylene (having a crystallinity of at least 60 % by weight) and ethylene based resin; also the laminate may include a heat sealable layer suitably applied by coating. The laminated film structure of this patent fails to provide enough stiffness for packaging fatty foods and also does not prevent migration and contamination through the foodstuffs.

US 2002/0182426 presents a polypropylene composite film, which comprises a crystalline polypropylene layer and a propylene- 1-butene random copolymer layer laminated on at least one surface of the crystalline polypropylene layer. As in the case of previous references, the film proposed by this document fails to provide the features of adequate stiffness and barrier body, particularly for wrapping up the margarine like foodstuffs.

Objects of the Invention

One of the objects of the present invention is to provide a multilayer foldable film having improved stiffness, improved barrier properties as well as high resistance to migration through the packed foodstuff.

Another object of the present invention is to provide novel coextruded film, which enables preventing contamination of the microorganisms, particularly in the case of packaging margarine like fatty goods.

Still a further object of the present invention is to provide a multilayer BOPP film having extremely good deadfold property for packing use with regular or irregular geometrical shaped fatty foods.

Summary of the Invention

The objects of the invention are achieved through use of a number of layers having different chemical content in a biaxially oriented polypropylene film (BOPP). Different layers, which form the film, are intended to provide different properties including high stiffness, oxygen & moisture barrier and also prevention of contamination by means of anti-microbial agents.

High crystalline polypropylene is a material widely used in conventional films both for oriented and non-oriented film bodies. Admixing said homopolymers in a film composition enhances the stiffness of the final product, which is quite an important feature during packaging of e.g. fatty foods. Furthermore, polypropylene having high isotactic content does not cause considerable migration while the hydrocarbon resins, in the contrary, cause migration through the foodstuffs. It has been found that using hydrocarbon resins in a layer that is in contact with the packaged food readily causes migration in the fatty foods. Present invention eliminates this problem by avoiding use of hydrocarbon resins at least in the layer that is in contact with the fatty food. Using high crystalline polypropylene instead of hydrocarbon resins in coextruded layers greatly improves the stiffness quality and migration features of the packaging film. At least one layer, preferentially the bottom layer, comprises an antimicrobial agent for safe consumption of the nutriments even after a long shelf life time. The top layer of the film structure comprising terpolymers or copolymers with antiblocking agents provides the adhesion for metallization and heat seal characteristics. Metallized top layer provides the decrease in oxygen and moisture permeability.

With the features mentioned briefly above, final multilayer film product of the present invention provides excellent properties convenient for packaging fatty goods such as margarine, butter, cheese and the like.

Detailed Description of the Invention

Mono or multilayer films designed for packaging contains a number of different compositions according to the purpose of use. Present invention provides a film structure particularly suitable for packing the fatty foodstuffs. To this end, the chemical composition of the same is modified to provide aforementioned desired features as well as eliminating the common disadvantages found in the prior art.

Stiffness is one of the key features during wrapping of fatty goods and the operational packaging process in which the uniform packaging machines corrugate the film containing cover sheet for isolating the foodstuffs. Crease retention of the film structure is directly proportional with the molecular regularity of polymeric substances and therefore polypropylene in high crystalline form is used in more than one layer in the chemical content. Polypropylene molecules are modified in a manner such that stereo regularity is greater than 95% and more preferably around 99%. Providing such a multilayer film without hydrocarbon resins considerably prevents the migration.

Fatty acids of foods, particularly those available in margarine and butter like commodities are mostly hydrophobic e.g. like hydrocarbon resins. Furthermore, numerous references are available in the art, which address the fact that the lower molecular weight polymers promote the migration through the food structure much more than polymers having higher molecular weight. The migration issue is an undesirable occurrence, which may cause serious health damages. Therefore, film structure proposed by the present invention does not include a layer containing hydrocarbon resins, eventually providing elimination of migration. Accordingly, at least one layer of the biaxially oriented polypropylene film structure comprises a composition of: 25-80% of homopolymers, 5-20% of filler material, 5-15% of color pigments, 10-40% of high crystalline polypropylene having the isotactic content of over 95%, more preferably of over 99%. Said filler material may be selected from the group of CaCO₃, BaSO4, TiO2 and talc.

A top layer of the film is designed to provide high barrier properties more particularly for improved isolation against moisture and oxygen. Needless to mention, this is again a key feature in particularly packing foodstuffs and medicinary commodities. This blocking layer comprises mainly; 85-100%, more preferably 95-100% of terpolymers or copolymers, 0-15%, more preferably 0-5% of organic or inorganic antiblocking agents. The terpolymer and the copolymer may comprise ethylene, propylene or butylenes whereas homopolymer may be polypropylene or polyethylene. Prefeσed antiblocking agents may be selected from one or more of aluminum silicate, magnesium silicate, silicon dioxide, calcium phosphate and polyamide.

The biaxially oriented polypropylene film structure of the present invention comprises at least three layers consisting of the above-mentioned layers in various combinations. An anti-microbial agent may also be admixed to at least one layer defined above, preferably to the bottom layer where the packaging material is in contact with the foodstuff. Said anti-microbial agents may exhibit desired bactericidal, fungicidal and/or viricidal features and greatly inhibit the contamination while increasing the shelf life of the product. Polypropylene based ready to use masterbatches containing Ag (silver) ions or silver nitrate ions as the antiseptic agents may be used in at least one layer of the BOPP films according to the present invention.

The film of the present invention may also comprise a metallized layer coated preferably with aluminum in a vacuum medium. The vacuum applied in the chamber is adjusted to about 5x10^"4 milibar where raw aluminum is at around 99.9% purity. Aluminum in vapor phase is phase transformed and condensed on the film surface in order to form the desired surface characteristics.

The multilayer and biaxially oriented polypropylene film of the present invention is produced according to a process comprising the steps of coextruding of the film layers through a die, stretching the film bi-axially, cooling, corona or flame treatment and winding the same thereafter. Resulting film may consist of several layers depending on purpose of use whereas for the present case three or five layers are preferred for the bioriented film structure.

Example 1

A bioriented film having three layers (I, II, III) particularly for wrapping up margarines where an outer top layer (I), a core layer (II) and a bottom contact layer (III) is disclosed. Compositions of each individual layer are as follows:

Layer (I); 97% of ethylene-propylene copolymer

3% of silicates

Layer (II); 50% of PP homopolymer 10% Of CaCO₃

5% of color pigments (color pigment is TiO₂) 35% of high crystalline polypropylene having an isotactic index over 99% Layer (III); 47% of PP homopolymer 8% of CaCO₃ 2% of color pigments 40% of high crystalline polypropylene having an isotactic index over 99% %3 silver ions

As evident in the compositions given above, hydrocarbon (HC) resins are not employed in defined compositions of these layers. Furthermore, an anti-microbial agent is admixed to the outermost layer (III), which gets in touch with the external conditions. In accordance with the present invention, compositions of the layers

(I, IUII) are coextruded through a die, biaxially stretched at a machine, formed molten composition is cooled down for solidification, applied a corona or flame treatment and a winding operation thereafter. Consequent product is a three-layer bioriented film having excellent stiffness, antiseptic, cuttability and barrier features as well as high resistance to migration.

Example 2 A biaxially oriented film having five layers (I, II, III, IV₁V) convenient for packaging margarine or butter like fatty foods wherein an outer top blocking layer (I), a core layer (II), intermediate layers (11,IV) and a bottom contact layer (V) are proposed. Compositions of the each layer are as follows:

Layer (I); 97% of ethylene-propylene copolymer

3% of silicates

Layer (II); 50% of PP homopolymer

10% of CaCO₃ 5% of color pigments

35% of high crystalline polypropylene having an isotactic index over 99%

Layer (III); 50% of PP homopolymer 8% of CaCO₃ 2% of color pigments (preferably TiO₂)

40% of high crystalline polypropylene having an isotactic index over 99%

Layer (IV); 50% of PP homopolymer

10% of CaCO₃

5% of color pigments

35% of high crystalline polypropylene having an isotactic index over 99%

Layer (V); 47% of PP homopolymer

10% of CaCO₃

5% of color pigments

35% of high crystalline polypropylene having an isotactic index over 99%

% 3 silver ions polypropylene base masterbatch

In accordance with the present invention, compositions of the layers (1,1I₁III₁IV₁V) are coextruded through a die, biaxially stretched at a machine, formed molten composition is cooled down for solidification, applied a corona treatment and a winding operation thereafter. Consequent product is a five-layer bioriented film having excellent stiffness, cuttability and barrier features as well as high resistance to migration.

Further variations of the number and content of the layers on the basis of the present invention are apparent for those skilled in the art in the light of the information given herewith. Accordingly, the number of layers and use of antimicrobial agents can readily be adjusted depending on the purpose of use. As per mentioned previously, all layers and/or outermost blocking layer of the film comprises high crystalline polypropylene for providing better deadfold property on the final product. Furthermore, an anti-microbial agent which might be selected depending on the intended use of the final product and which might inhibit growth of microorganisms can readily be admixed into the composition of one or more of the layers.

Claims

1. A biaxially oriented multilayer film having at least three layers characterized in that said film comprises at least one outermost blocking layer having the composition of:

85-100%, more preferably 95-100% by weight of a terpolymer or copolymer 0-15%, more preferably 0-5% by weight of synthetic, organic or inorganic anti-blocking agent, and at least one high crystalline layer having the composition of: i) 25-80% and more preferably 40-60% by weight of a homopolymer, ii) 5-20% by weight of a filler, iii) 5-15% by weight of a color pigment, and iv) 10-40% and more preferably 20-35% by weight of high crystalline polypropylene whose isotactic content is more than 95%.

2. A bioriented multilayer film according to claim 1 wherein an anti-microbial agent is admixed into at least one of the layers forming the BOPP film.

3. A bioriented multilayer film according to claim 1 wherein resulting multilayer BOPP film is metallized with aluminum in a vacuum medium.

4. A bioriented multilayer film according to claim 1 wherein said high crystalline polypropylene has an isotactic content which is equal to or more than 99%.

5. A bioriented multilayer film according to claim 1 wherein said terpolymer preferably consists of ethylene, propylene and butylene whereas said copolymer preferably consists of ethylene and propylene.

6. A bioriented multilayer film according to claim 1 wherein said antiblocking agent is selected from the group consisting of aluminum silicate, magnesium silicate, silicon dioxide, calcium phosphate and polyamide.

7. A bioriented multilayer film according to claim 6 wherein said homopolymer is polypropylene or polyethylene and color pigment is preferably TiO₂.

8. A bioriented multilayer film according to claim 2 wherein the anti-microbial agent of the masterbatch comprises silver ions or silver nitrate ions.

9. A bioriented multilayer film according to claim 1 wherein the filler material is selected from the group consisting of CaCO₃, BaSO4, TiO2 and talc.