DE1694349B2 - Impermeable packaging film - Google Patents

Description

Packaging films made of polyolefins, such as polyethylene, have been known for a long time and can be found in widely used, but they are suitable for certain purposes because of their permeability not suitable for gases and vapors. There are already various proposals for reducing it The permeability has been made, including, among other things, equipping the films with a impermeable coating or lamination belongs, but this requires a considerable additional effort in time and cost.

It has now surprisingly been found that the permeability of polyolefin films for gases and Vapors, e.g. B. for use as packaging films, can be reduced quite significantly if the films are made from a polymer that has a platelet-shaped filler with certain Contains particle dimensions.

The invention accordingly provides an impermeable packaging film based on filler-containing material Polyethylene, polypropylene, polystyrene or more than 50% ethylene as a monomer containing copolymers, which is characterized in that the filler is in the form of platelet-shaped Particles with an aspect ratio between 20: 1 and 300: 1 and a length of at most 30 μΐη is present.

It is already known from US Pat. No. 3,157,614, the dielectric properties of rubber-like To improve polymers including rubbery olefin polymers in that a certain form of talc is incorporated as a filler, which is known as »mistron talc«, preferably, though not necessarily, a product of the platelet type acts. The same filler can also be used for molding compounds that are not elastomeric Contain polyolefins or thermosetting resins such as those used in the manufacture of laminates and tubing Find use. The dielectric constant, however, is a property common to packaging films is of no importance. In contrast, it was surprising that by adding Platelet-shaped fillers with a very specific particle size reduce the gas permeability of polyolefin films can reduce quite considerably.

The packaging films according to the invention preferably contain about 0.5 to 50 percent by weight Filler. The foils usually have a thickness between 0.01 and 1.25 mm.

It has been found that practically every substance of mineral, inorganic or organic nature, which is in the form of platelets or platelet-like particles of the size described above and in which polymer is practically insoluble, can be used as a filler with good results. The term “filler” is understood here to mean a substance with a platelet-shaped structure, which is used in the Incorporation into the polymer system, the films made from it are practically impermeable to gases like oxygen, nitrogen, air, water vapor or carbon dioxide does. The mineral fillers can consist of naturally occurring or synthetically or chemically modified minerals. Suitable fillers are, for example, platelet-shaped clays, mica, vermiculite, kaolinite, Montmorillonite or platelet-shaped talc, platelets made of metals or metal alloys such as aluminum and bronze flakes and, among organic substances, N-benzoylacetamide flakes. These fillers can be treated with aluminum ions or cations of transition elements, d. H. Elements with ordinal numbers 21 to 32, 39 to 51 or 57 to 83 can be modified. in the In general, such a modification is carried out by treatment with iron (III), chromium (III) or zirconium (IV) ions carried out.

This treatment makes the filler less sensitive to hydrating and damaging Effect of atmospheric water vapor, making the filler-containing polymer film even more impermeable power. Other platelet-shaped fillers are known or can be easily found by the person skilled in the art.

For the preparation of impermeable films of the invention all known Polyäthylenarten can as the branched-chain products of low density (ie, about 0.910 to 0.925 g / cm ³⁾ having a melting point in the range of 90 to 110 ⁰ C, medium density products and by the Ziegler process ( TiCL ^ aluminum alkyl catalyst) or the Phillips process (chromium (VI) oxide on silicon oxide / aluminum oxide carrier) manufactured products of high density (about 0.950 to 0.980 g / cm ³ ) with a melting point in the range from 120 to 137 ⁰ C can be used. Ethylene-containing copolymers such as ethylene-butene-1, ethylene-vinyl acetate, ethylene-ethyl acrylate or ethylene-methyl or ethylene methacrylate can also be used. The copolymer component preferably consists of an aliphatic, ethylenically unsaturated monomer having 2 to 12 carbon atoms. Mixtures of two or more of the polymers mentioned can also be used, for example a mixture of high-density and low-density polyethylene.

The impermeable, filler-containing polyethylene, polypropylene, ethylene copolymer and polystyrene films of the invention can be used for a wide variety of packaging purposes. So can they are used, for example, to package foods such as cereal flakes and potato chips that must be protected from air and moisture to keep them crisp.

For the preparation of mixtures from which films of the invention are obtained, the components can lie temperature that the polymers and the filler, for example about 1 to 10 minutes at a about 10 to 30 ⁰ C above the Scftmelzpunkt of the polymers in a Brabender plastograph , a Banbury mixer, or a two-roll mixer. It is also possible to mix the filler and the polymer, preferably in particulate form, at a temperature below the melting point of the polymer, for example 25 ° C., and then to mix the mixture over the to form a homogeneous mass containing the filler in the molten polymer To heat the melting point of the polymer. A dispersant or plasticizer can be used to facilitate incorporation of the filler into the polymer.

The homogeneous mixture is then shaped into a film. In the laboratory, especially for test purposes, it can be used, for example, in a plate press at a temperature at which the poly-

mere is melted, pressed under a pressure of 35 to 1400 kg / cm ² . One method of industrial production consists in adding the polymer and the filler in the desired ratio to the feed hopper of an extruder, mixing the components in the barrel of the extruder at a temperature above the melting point of the polymer to form a homogeneous melt mixture and then mixing the mixture at a Temperature above the melting point of the polymer extruded through the extruder die to form a film.

The invention is illustrated by the following examples, unless otherwise noted - all quantities are based on weight.

The melt index of the polymer was in all cases below that given in ASTM D 1238-52T Conditions were measured and the density of the polymer was determined according to those given in ASTM D 1505-57T Conditions determined.

Oxygen permeability is the speed at which oxygen passes through a unit of volume of the material per unit of pressure difference and time. The provision was so in all cases carried out that a pressure difference was generated between both sides of the film and the in Amount of gas diffusing through the film at a given time was measured. The following units were used to indicate the oxygen permeability:

cm ³ = cm ³ _{acid r} mil diffused through the film

atm
m ²

material,

Thickness of the polymer film in mil

(0.0254 mm),

Pressure difference in atmospheres,

Foil areas in m ² ,

Time in days.

3850

cm ³ mil
atm · m ² · t

Chen polyethylene without the addition of fillers has an oxygen permeability from

The oxygen permeability was measured under the conditions given in ASTM D 1434-63 and was calculated on a film thickness of 0.0254 mm.

The determination of the water vapor permeability was carried out according to the ASTM E 96-63 T under »Procedure Α «given conditions, but with a relative humidity of 75% outside the shell was adhered to. The muscovite mica used had a composition analogous to the formula HjKAySiO ^, a specific gravity of 2.8 to 3, a refractive index of 1.58, a particle size of about 325 mesh, and a moisture content less than 0.25%.

E.g. 1 1

In a Brabender plastograph, 80 parts of commercially available polyethylene with a density of 0.92 and a melt index of 2.1 and 20 parts of stearate-treated muscowite mica were mixed for about 20 minutes at 140 ° C. to form a homogeneous mass. The mass was transferred from the Brabender Plastograph in a platen press and pressed there for 5 minutes at 140 ⁰ C lower than 1400 kg / cm ² pressure to a 0.127 mm thick film. The film had an oxygen permeability of

9000

cm ³ mil
atm m ² t '

When the example is repeated using 80 parts of commercially available polystyrene in place A film was obtained from polyethylene, the oxygen permeability of which is lower than that of only one was made from the polystyrene film.

Were at a repetition, in which 80 parts of commercially available polypropylene having a density of 0.905 and a melting point of 168 ° C was used instead of polyethylene, and the mixing and pressing took place at a temperature of 180 ⁰ C, a film with a lower oxygen permeability than Using the same polypropylene obtained without filler.

Example 2

The same procedure was used as in Example 1, but now 70 parts were used of the polyethylene mixed with 30 parts of the muskowite mica. The obtained film had an oxygen permeability from

2110

cm ³ ■ mil
atm · m ² · t

B e i s ρ i e 1 3

The same procedure was used as in Example 1, except that 80 parts were commercially available Polyethylene with a melt index of 12 and a density of 0.92 with 20 parts of the Muscovite mica mixed. The film had an oxygen permeability of

3240

cm ³ mil
atm · m ² · t

A corresponding film made of unfilled polymer, on the other hand, had an oxygen permeability of

6580

cm ³ mil

atm ■ m ² ■ t '

Example 4

Example 3 was repeated, but in this case 30 parts of the muskowite mica were included 70 parts of the polyethylene of Example 3 mixed. The film had an oxygen permeability of

mil

1920

cm

atm · m ² · t

B e i s ρ i e 1 5

Example 4 was repeated, but 70 parts of polyethylene with a melt index of 22 and a density of 0.92 mixed with 30 parts of the muscovite mica. The film had an oxygen permeability from

In contrast, a slide made from the glei-1270

cm ³ ■ mil
atm · m ² · t

A corresponding film without filler had an oxygen permeability of

10 700

cm ³ mil

atm ■ m ² t '

B e i s ρ i e 1 6

The procedure of Example 1 was repeated, but the mixture consisted of 91.42 parts of the Low density polyethylene according to Example 1 and 8.58 parts of muscovite mica. The slide had an oxygen permeability of

4460

cm ³ ■ mil

atm ■ m ² ■ t
and a water vapor permeability of

g mm

0.084

t ■ m ² cmHG '

0.20

g mm

t · m ² · cmHg

Example 8

Oxygen permeability of

35

Example 7

The procedure of Example 1 was repeated, but 80 parts of polyethylene and 20 parts commercial bentonite clay used. The film had a lower oxygen permeability than a corresponding film made of unfilled polyethylene. The same result was obtained using a other commercially available bentonite clays.

Example 1 was also used of 60 parts of polyethylene and 40 parts of feinteiligeih vermiculite repeated, with a film with lower Oxygen permeability than obtained using unfilled polyethylene.

1.65 · 10 ³

cm ³ ■ mil atm · m ² ■ t

would have. A corresponding film made from a mixture of 99.75 parts of copolymer .unä 0.25 parts of filler had an oxygen permeability of

45 1.50; 10 ³

cm ³ mil atm m ² t

and a film made from a mixture of 99.5 parts Copolymer and 0.5 part filler! an oxygen permeability of

1.53 ■ 10 ³

cm ³ ■ mil atm · m ² · t

The corresponding J film without the addition of fillers had an oxygen permeability of

The water vapor permeability of a corresponding film without the addition of fillers was 1.98 · 10 ³

cm ³ ■ mil

atm · m

Example 10

90 parts of commercially available ethylene-vinyl acetate copolymer with a vinyl acetate content of 33 percent by weight and 10 parts of organically treated bentonite clay were ^{mixed in a Brabender plastograph for 20 minutes at 140 °} C. to form a homogeneous mixture. The molten mixture was pressed in a platen press at 140 ° C. and 1400 kg / cm ^{2 for} 5 minutes into 0.127 mm thick film which had an oxygen permeability of

2.49 ■ 10 ⁴

cm ³ mil atm m ² t

In a Brabender plastograph, 95 parts of commercially available polyethylene with a density of 0.96 and a melt index of 0.05 and 5 parts of the muscovite mica were mixed thoroughly for 20 minutes at 155 ° C. to form a homogeneous molten mixture. The molten mixture was pressed in a platen press at 175 ° C. and 1400 kg / cm ² to give a 0.127 mm thick film which had a lower oxygen permeability than a corresponding film made of filler-free polymer.

would have.

Two similar films made from this ethylene-vinyl acetate copolymer and bentonite in a proportion of 80:20 and 70:30, respectively, had oxygen permeability of 1.69 or of

1.22 · 10 ⁴

cm ³ mil atm m ² t

In contrast, the oxygen permeability of a corresponding film without filler was

3.5 · 10 ⁴

cm ³ mil atm m ² t

Example 9

99.9 parts of commercially available ethylene-butene-1 copolymer with a density of 0.950 and a melt index of 0.4 and 0.1 part of muscovite mica were mixed in a Brabender plastograph for 20 minutes at 155.degree. C. to form a homogeneous mixture. The molten mixture was added in a platen press at 175 ° C and 1400 kg / cm ²

60

65 B e i s ρ i e 1 11

In a Brabender plastograph, 100 parts of a mixture of 66.6 parts of the ethylene Vinyl acetate copolymers according to Example 10, 16.6 parts of paraffin wax and 16.6 parts of bentonite Mixed for 20 minutes at 140 ° C to form a homogeneous mixture. The melted mixture was in

a 0.127 mm thick film is pressed, which a plate press at 140 ° C and 1400 kg / cm ² to

a 0.127 mm thick film, which has an oxygen permeability of

7.49 · 10 ³

cm ³ mil
atm · m ² · t

would have. A corresponding film made from 100 parts of a mixture of 80 parts of the ethylene-vinyl acetate copolymer according to Example 10 and 20 parts of paraffin wax without the addition of fillers, however, had a Oxygen permeability of

30.8 ■ 10 ³

cm

mil

atm ■ m · f

The films according to the invention can also be of various types which are customary in the plastic film industry Treatments are subjected. For example, they can improve their physical Properties are crosslinked chemically or by irradiation and / or to achieve from shrink films. "Oriented in the usual way will.

Claims (2)

Patent claims: 1. Impermeable packaging film based on lamellar filler containing Polyethylene, polypropylene, polystyrene or a monomer containing more than 50% ethylene 'Copolymers, characterized in that the filler is in the form of platelet-shaped particles with an aspect ratio between 20: 1 and 300: 1 and with a length of at most 30 μm is present in an amount of 0.1 to 50 percent by weight. 2. Packaging film according to claim 1, characterized in that it is used as a platelet-shaped filler, mica platelets, vermiculite or contains bentonite clay. 109544/379