EXTRUDED PLASTIC FILM FILLED WITH METAL PARTICLES, METHOD OF PRODUCTION AND USES THEREOF

Abstract

The present invention relates to a plastic film obtained by (co)extrusion or by a multilayer extrusion process.

The purpose of the invention is to supply a plastic film having useful properties, in particular of thermal behaviour, adhesion, linear tearability, and having a reduced production cost.

This film contains lamellar particles based on at least one metal and/or at least one metal oxide. It is obtained by the extrusion of a raw material constituted entirely or partly by a ground material from at least one coated film comprising at least one polyester and/or polyolefin film and at least one coating film based on at least one metal and/or at least one metal oxide.

The invention also relates to a method of manufacture of the raw material of the plastic film according to the invention, a method of manufacture of said plastic film as well as the uses of said film.

Application in the field of packaging, decoration and heat treatments.

Claims

1-14. (canceled)

15. A polymeric film comprising a first layer and a second layer, the first layer comprising ground material, the ground material being a blend of (a) a polyester or a polyolefin, and (b) a metal and/or a metal oxide, the second layer being a non-polymeric layer and comprising a metal and/or a metal oxide.

16. The polymeric film of claim 15, wherein the first layer consists entirely of ground material.

17. The polymeric film of claim 15, wherein the first layer includes polyester.

18. The polymeric film of claim 16, wherein the polyester is polyethylene terephthalate.

19. The polymeric film of claim 15, wherein the first layer includes a polyolefin.

20. The polymeric film of claim 15, wherein the first layer has from 20 wt. % to 100 wt. % ground material.

21. The polymeric film of claim 15, wherein the first layer has from 1 wt. % to 20 wt. % ground material.

22. The polymeric film of claim 15, wherein the thickness of the film is from 3 to 350 m.

23. The polymeric film of claim 22, wherein the thickness of the film is from 8 to 50 m.

24. The polymeric film of claim 15, wherein the optical density of the film is from 0.1 to 0.5.

25. The polymeric film of claim 15, wherein the ground material includes the metal, the metal being aluminum, copper, nickel, gold, silver, or alloys thereof.

26. The polymeric film of claim 15, wherein the ground material includes the metal oxide, the metal oxide being oxides of any selected metal, oxides of silicon, and mixtures thereof.

27. The polymeric film of claim 15, wherein the first layer includes lamellar particles based on at least one of a metal and a metal oxide, the lamellar particles correspond to a form factor (F=L/e) defined as the ratio of the largest dimension (L) in the plane of the particle to its thickness (e), wherein 10F1000.

28. The polymeric film of claim 27, wherein the lamellar particles correspond to a form factor (F=L/e) defined as the ratio of the largest dimension (L) in the plane of the particle to its thickness (e), wherein 50F5000.

29. The polymeric film of claim 28, wherein the first layer includes lamellar particles based on at least one of a metal and a metal oxide, a content Tx (in wt. %) of lamellar particles being 0.001Tx<10.

30. A polymeric film comprising a first layer and a second non-polymeric layer, the first layer comprising ground material, the ground material being a blend of (a) a polyester or a polyolefin, and (b) a metal, the second layer being a non-polymeric layer and comprising a metal.

31. The polymeric film of claim 30, wherein the metal of the ground material includes aluminum.

32. A method of forming a polymeric film, the method comprising: providing a first layer, the first layer comprising ground material, the ground material being a blend of (a) a polyester or a polyolefin, and (b) a metal and/or a metal oxide; providing a second non-polymeric layer, the second layer comprising a metal and/or a metal oxide; and placing the second non-polymeric layer on the first layer by coextrusion, coating, varnishing, extrusion coating, hot-melt coating, vacuum evaporation or vacuum deposition.

33. The method of claim 32, wherein the ground material includes the metal, the metal being aluminum, copper, nickel, gold, silver, or alloys thereof.

Description

DESCRIPTION OF THE DRAWINGS

[0156] FIGS. 1a to 1e show four photographs of the film according to the invention

[0157] FIG. 1a: view with a transmission light microscope (magnification 1100) in the XY plane;

[0158] FIG. 1b, 1c, 1d: transverse sections (Z plane), viewed with a transmission electron microscope (magnification 5600, 24000, 84000 respectively);

[0159] FIG. 1e: view with a transmission electron microscope in the XY plane of a metal particle after dissolution of the polyester.

[0160] FIG. 2 is a graph showing the aluminium content (Al), in wt. %, measured from the ash content and the content of aluminium oxide (Al.sub.2O.sub.3), in wt. %, measured by X-ray fluorescence as a function of the concentration of ground material (Qb, in wt. %) contained in the films.

[0161] FIG. 3 is a graph showing measurement of optical density as a function of the concentration of ground material (Qb, in wt. %) contained in the films.

[0162] FIG. 4 is a graph showing measurement of haze as a function of the concentration of ground material (Qb, in wt. %) contained in the films.

[0163] The FIGS. 5a and 5b are graphs showing respectively the whiteness index and L* as a function of the concentration of ground material (Qb, in wt. %) contained in the films.

[0164] FIG. 6 is a graph showing the measurement of gloss as a function of the concentration of ground material (Qb, in wt. %) contained in the films.

[0165] FIG. 7 is a graph showing the melt resistivity (M.Math.m) as a function of the concentration of ground material (Qb, in wt. %) contained in the films.

EXAMPLES

[0166] IMethod of Production of PET Films Filled with Lamellar Particles of Aluminium

[0167] 1. Method of Preparation of the Ground Material Based on Metallized Polyester

After being ground in an ALPINE grinding mill from HOSOKAWA (stage A), PET films metallized with aluminium (CLARYL range from TORAY) are processed on a machine of the VACUREMA type from EREMA.
Next, the films reduced to flakes are compacted and agglomerated in a compactor at 172 C. (stage B). Then the agglomerates are melted at 280 C. (stage C). The molten mass is then cooled and solidified in a stream of water at ambient temperature (stage D) by means of equipment associated with the VACUREMA machine, with the brand-name RIETER. Said cooled mass is cut at ambient temperature into granules by the device downstream of the RIETER equipment (stage E).
The characteristics and operating conditions of grinding, agglomeration and extrusion (stages A-E) are as follows:

Characteristics and Operating Conditions of the Compactor

[0168] Motor power: 71 KW
Compacting speed: 145 rpm
Machine loading: 61%
Level of vacuum: 36 mbar
Temperature of the granules in the compactor: 172 C.
Temperature of the zone at the level of the filling hole of the extruder: 196 C.

Condition of Vacuum Extrusion

[0169] Flow rate: 946 kg/hour
Screw speed: 64 rpm
Machine loading: 55%
Level of vacuum: 20 mbar
Filtration is ensured by 4 metal filters with a cut-off of 35 microns. Neither filter clogging nor deposits are found on dismantling.
The ground material that is to be used for making the films as described above is analysed by X-ray fluorescence according to an in-house method usually used for the characterization of PET. The measurements prove that aluminium is present in the re-granulated material (see Table 1). The viscosity index is measured according to ISO 1628-5 and the results are given in Table 1.

TABLE-US-00001 TABLE 1 Characterization of the various batches of re-granulated metallized PET. PET Aluminium Granules VI X-ray Fluorescence (ppm) Tests (dl/g) Ca P Sb Mg SiO.sub.2 Ti Al 1 0.559 41 46 165 53 727 1 8066 2 0.558 28 48 167 50 706 1 7016 3 0.562 32 48 165 44 723 1 7833 4 0.57 42 49 167 37 745 1 8024 5 0.569 42 47 163 48 754 1 8040

[0170] 2. Preparation of PET Films Containing Said Ground Material

Next, the granules thus obtained, called ground material above, are extruded mixed with other polymers in the film-making machine (stage F) in order to produce new films of polyester filled with lamellar particles of aluminium with percentages of ground material Qb less than or equal to 100 (in wt. %).
The various mixtures based on PET and ground material are homogenized in the granulated state and are then extruded in the molten state through a slot die as a thick film, which is cooled by electrostatic applying to a cooling drum at 20 C. (stage G), so as to form an amorphous film.

[0171] 3. Preparation of Biaxially Oriented PET Films Containing Said Ground Material

Biaxially oriented PET films containing ground material are produced according to the conditions for preparation of the film usually used in the field of packaging. For reasons of processability, inorganic fillers are incorporated at a concentration usually below 0.1%. In these examples, the percentages of ground material Qb incorporated vary in the mass of the films comprising an extruded layer. In these examples, a polyethylene terephthalate PET is used that has a viscosity index of 0.64 dl/g (measured according to standard ISO 1628-5) and contains 0.1 wt. % of a filler constituted by particles of silica having a median diameter by volume d.sub.50 of approximately 3.5 m. In these examples, the ground material used has a viscosity index (measured according to the same standard mentioned above) of 0.56 dl/g. The ground material is in this case derived from a method of recycling of films of the CLARYL type comprising a PET film coated on one side with a thin coating film of aluminium obtained by vacuum evaporation.
The various mixtures based on PET and ground material are homogenized in the granulated state and are then extruded in the molten state through a slot die as a thick film, which is cooled by electrostatic applying to a cooling drum at 20 C. (stage G), so as to form an amorphous film. The film thus obtained is then subjected to longitudinal stretching MD (degree LS 3.0) followed by transverse stretching (degree TS 3.5) (stage H). The degree of planar stretching (defined as the product of the degree of longitudinal stretching and the degree of transverse stretching, regardless of the order thereof) is 10.5. The biaxially stretched film (having a thickness of 12 m in all the examples) is then subjected to heat-setting at a temperature above 215 C. (stage I). Finally the films are subjected to various assessments.

[0172] 4. Form, Distribution and Dimensions of the Particles in the Biaxially Oriented Filled FilmsObservations with the Microscope.

As shown in FIGS. 1a, 1b, 1c, 1d, and 1e, the aluminium particles, denoted by reference 1, are in the form of lamellae, predominantly roughly rectangular (cf. FIG. 1e), embedded in the PET 2 matrix and arranged as several lamellae parallel to faces 3 and 4 of film 5 (cf. FIG. 1b).
The distribution of the particles in the various films as well as their size are estimated by optical measurements using a light microscope of the NIKON type. The aluminium particles are randomly distributed in the plane of the PET film prepared by the addition of ground material derived from recycled metallized polymer films. The form factor (F), defined as the ratio of the largest dimension in the plane of the particle (L) to its thickness (e), is in this example approximately 100 (see FIG. 1d: F=1250 nm/12.5 nm).

[0173] 5. Determination of the Aluminium Filler in the Films

The presence of aluminium is quantified by X-ray fluorescence measurements. The content of aluminium oxide, for example Al.sub.2O.sub.3, is then calculated, the values obtained being in agreement with theoretical expectations (see FIG. 2).
The presence of aluminium is demonstrated by so-called ash content measurements. The ash content is measured after complete combustion for various films containing ground material. For a film that only contains PET filled with silica particles, the value of 0.11% corresponds to the quantity of silica used. For a film that contains 80% ground material the total ash content (aluminium and silica) is 1.11%, leading to a percentage of aluminium of 1% (see FIG. 2).

[0174] 6. Specific Optical Properties of Biaxially Oriented Filled PET Films

The optical properties of PET films containing ground material are highly dependent on the concentration of the incorporated product. A satin-grey appearance is obtained at high concentrations (60% as an example) whereas an appearance identical to a standard PET film is obtained for a concentration below a known threshold.

[0175] 6.1. Optical Density

The optical density OD is measured using a densitometer of the MACBETH type according to ASTM D-1003, an apparatus for measuring the luminous intensity (orthochromatic source, wavelength range from 350 to 650 nm) transmitted through a film. For a biaxially stretched film with a thickness of approximately 12 m, the optical density increases from 0.04 for 0% of ground material to 0.45 for 100% of ground material in the bulk of the film (see FIG. 3).

[0176] 6.2. Haze

Haze is measured using a hazemeter of the BYK GARDNER type according to ASTM D-1003. Haze is determined by the fillers within the film, by the void created around the fillers during stretching, by the surface roughness and by the ground material incorporated. As an example, a biaxially stretched film that contains 80% ground material with a thickness of 12 m, has a very high haze (60%, see FIG. 4) relative to a PET film without addition of ground material (haze 3%).

[0177] 6.3. Colorimetry

The colorimetric measurements of the type L*, a*, b*, and the whiteness index WI ASTM E-313 are carried out using a spectrophotometer of the KONICA-MINOLTA type. On increasing the quantity of ground material incorporated in the biaxially stretched film, the luminosity and the whiteness index decrease, and the films become increasingly grey (see FIGS. 5a and 5b).

[0178] 6.4. Gloss

Gloss is measured using a reflectometer of the GARDNER MIRROR-TRI-GLOSS type according to ASTM D-2457. The surface of the sample is subjected to a light beam at a defined angle (here 20 and 60) and the light reflected is measured photoelectrically. A PET film with 60% of ground material is appreciably less glossy than a film with 40% of ground material (see FIG. 6).

[0179] 7. Specific Surface Properties of Biaxially Oriented Filled PET Films

[0180] 7.1. Surface Tension/Wettability

Surface tension is measured using calibrated inks according to test method ASTM D-2578. A film containing 80% of ground material has a surface tension of 54 mN/m, which is higher than the surface tension of a standard PET (48 mN/m). This can determine better printability depending on the case.

[0181] 7.2. Coefficient of Friction/Slip

The coefficient of friction is measured using apparatus of the INSTRON type according to ASTM D-1894. The addition of ground material improves the slip of the film and consequently its machinability.

[0182] 8. Electrical Behaviour of Biaxially Oriented Filled PET Films

The various films considered in these examples are not antistatic, as the surface resistivity measured according to ASTM D-257 with a resistivity meter of the KEITHLEY type (electrometer) is greater than 10.sup.15 /square.
The melt resistivity measured according to the method described below increases if the percentage of ground material increases (see FIG. 7).

Measurement of the Resistivity of Polymers in the Molten State

[0183] The field of application of this method of measurement only includes molten polymers. The principle is measurement of the intensity of the current passing through a sheet defined by approximately ten granules of polymer in the molten state, after stoving under vacuum, on subjecting them to a defined voltage.
The instrument is based on the following equations from physics:

U=RI

R=rho*L/S

[0184] Therefore rho=R*S/L=(U/I)*(S/L)

Where Q=cross-section of the polymer sheet [0185] L=length of the polymer sheet [0186] E=thickness of the dielectric [0187] S=area of polymer analysed [0188] U=voltage (V) [0189] I=current intensity (A)

Moreover, S=Q*E

[0190] We therefore have: rho=K/I

[0191] Where K=U*S/L

The following procedure is used for the measurement: [0192] dry 100 g of polymer granules in a stove under vacuum, 2 hours at 140 C., [0193] prepare the heating unit of the electrometer 1 hour beforehand, at 278 C., [0194] leave the 10 polymer granules taken from the 100 grams of dry granules, for at most 5 minutes in the measuring cell, but wait long enough for melting to be effective, [0195] apply the voltage and measure the current.
Based on the design of the electrometer, it is found that:

[0196] Rho=0.142/Intensity recorded in M.Math.metre

[0197] 9. Behaviour of Biaxially Oriented Filled PET Films with Respect to Adhesion of a Thin Metallic Layer

[0198] 9.1. A PET film containing 60% of ground material in its bulk is metallized by vacuum evaporation (thickness of the metallic layer 20 nm). The adhesion strength of the metal (in this case aluminium) on polyester film is measured according to the AIMCAL recommendations TP-105-92 (Metallizing Technical Reference published by the Association of Industrial Metallizers, Coaters and Laminators). The adhesion strength between the metallic layer and the PET film is 0.2 N/38 mm. The adhesion strength between one and the same type of metallic layer and a standard PET film is approximately 0.05 N/38 mm. The adhesion strength between the same type of metallic layer and a plasma-treated PET film is approximately 0.15 N/38 mm.

[0199] 9.2. A PET film containing 60% of ground material in a coextruded layer is metallized by vacuum evaporation (thickness of the metallic layer 20 nm). The adhesion strength of the metal (in this case aluminium) on polyester film is measured according to the test method described above. The adhesion strength between the metallic layer and the PET film is 0.2 N/38 mm. The adhesion strength between the same type of metallic layer and a plasma-treated PET film is approximately 0.15 N/38 mm. The adhesion strength between the same metallic layer and a standard PET film is approximately 0.05 N/38 mm.

[0200] 10. Behaviour of Biaxially Oriented Filled PET Films with Respect to Surface Treatment

[0201] 10.1. The surface of a film containing 60% ground material is treated with an electric discharge of the corona type. The treatment conditions are: atmospheric pressure (1 bar), treatment gas ambient air, film-electrode gap 1 mm, dose 15 Wmin/m.sup.2. Then the surface tension of the film is measured using calibrated test inks according to test method ASTM D-2578. The surface tension of the film increases from 52 mN/m to 58 mN/m.

[0202] 10.2. The surface of a film containing 60% ground material is treated with a plasma of the magnetron type under vacuum. The pressure is 510.sup.2 mbar, the treatment gas is a mixture of Ar and O.sub.2, the film-electrode gap is approximately 20 cm and the speed of movement of the film is 600 m/min. Then the surface energy of the film is measured using calibrated test inks according to ASTM D-2578. The surface energy of the film increases from 52 mN/m to more than 60 mN/m.

[0203] 10.3. The surface of a film containing 60% ground material is treated with a dielectric barrier discharge plasma. The pressure is atmospheric pressure (1 bar), the treatment gas is a nitrogen-based mixture, the film-electrode gap is approximately 1 mm, the dose is 20 Wmin/m.sup.2. Then the surface energy of the film is measured using calibrated test inks according to ASTM D-2578. The surface energy of the film increases from 52 mN/m to more than 60 mN/m, demonstrating a change in the physicochemical nature of the surface of the film.

[0204] 11. Particular Mechanical Properties (Ease of Linear Propagation of Tearing) of the Biaxially Oriented Filled PET Films

Measurements of MD/TD breaking strength (TD corresponding to the transverse direction and MD corresponding to the machine direction) and of MD/TD elongation at break are carried out according to ASTM D-882 using an instrument of the INSTRON type and show that the mechanical properties in the two directions are lower than in the case of a PET without the addition of ground material. Measurements of puncture resistance are in agreement. Measurements of oriented tearing carried out using an instrument of the ELMENDORF type show that the incorporation of ground material (particles) facilitates linear propagation of tearing.

[0205] 12. Oxygen and Water Vapour Barrier Properties of the Biaxially Oriented Filled PET Films

The values of permeability to oxygen measured according to ASTM D-3985 and to water vapour measured according to ASTM F-1249 are not in any way degraded relative to a standard PET for the same thickness.

[0206] 13. Fire Resistance of the Biaxially Oriented Filled PET Films

Biaxially oriented PET films containing said ground material and having a thickness of 23 m are evaluated with respect to their fire resistance according to standard UL94. A film filled with ground material (Qb) at 80 wt. % does not ignite and does not drip.

[0207] 14. Microwave Cooking Test in the Presence of a Filled Film

Cooking tests are carried out on various food products to evaluate whether packaging that includes films containing said ground material have the necessary properties for applications of the susceptor type, for which there is considerable demand in the field of active packaging. The equipment used is a microwave oven of the DAEWOO type, which has an output power of approximately 900 W and operates at the standard industrial frequency of 2.45 GHz. The cooking time is adjusted depending on the type of food and packaging. For example, a PET film containing 80% of ground material (Qb) proves particularly suitable for cooking poultry, obtaining browning corresponding to conventional cooking. It is also significant that the behaviour of films filled with metal particles in the bulk is clearly improved during a longer time of exposure to microwaves compared with the behaviour of surface-metallized films of comparable optical density (films of the susceptor type that are usually used).

TABLE-US-00002 TABLE 2 Microwave cooking test in the presence of a film containing ground material. Appearance and texture Box Bag Reference film Hamburger Nuggets Chicken Nuggets PET LUMIRROR X X control PET with 80% of X ground material (Qb) X: poor : correct : good
IIExamples of the Production of Films of Polypropylene Filled with Lamellar Particles of Aluminium.

[0208] 1. Preparation of the Ground Material Based on Metallized Polypropylene

After being ground in an ALPINE grinding mill from HOSOKAWA (stage A), PET films metallized with aluminium (CLARYL range from TORAY) are processed on a machine of the VACUREMA type from EREMA.
Next, the films reduced to flakes are compacted and agglomerated in a compactor at 133 C. (stage B). Then the agglomerates are melted at 190 C. (stage C). The molten mass is then cooled and solidified in a stream of water at ambient temperature (stage D) by means of equipment associated with the VACUREMA machine, with the brand name RIETER. Said cooled mass is cut at ambient temperature into granules by the device downstream of the RIETER equipment (stage E).
The characteristics and operating conditions of grinding, agglomeration and extrusion (stages A-E) are as follows:

Characteristics and Operating Conditions of the Compactor

[0209] Motor power: 60 KW
Compacting speed: 145 rpm
Machine loading: 51%
Level of vacuum: 36 mbar
Temperature of the granules in the compactor: 133 C.
Temperature of the zone at the level of the filling hole of the extruder: 155 C.

Conditions of Vacuum Extrusion

[0210] Flow rate: 946 kg/hour
Screw speed: 64 rpm
Machine loading: 48%
Level of vacuum: 20 mbar
Filtration is ensured by 4 metal filters with a cut-off of 35 microns. Neither filter clogging nor deposits are found on dismantling.

[0211] 2. Preparation of Polypropylene Films Containing Said Ground Material

Next, the granules obtained as above, called ground material, are extruded mixed with other polymers in the film-making machine (stage F) in order to develop new films of polypropylene filled with lamellar particles of aluminium with percentages of ground material Qb less than or equal to 100.
The various mixtures based on polypropylene and ground material are homogenized in the granulated state and are then extruded in the molten state through a slot die as a thick film, which is cooled on a succession of three drums cooled to a temperature of approximately 20 C. (stage G) so as to form an amorphous film.

[0212] 3. Preparation of Biaxially Oriented Polypropylene Films Containing Said Ground Material

The amorphous film thus obtained is then subjected to longitudinal stretching MD (degree LS 4.0) followed by transverse stretching (degree TS 4.5) (stage H). The degree of planar stretching (defined as the product of the degree of longitudinal stretching and the degree of transverse stretching, regardless of the order thereof) is 18. The biaxially stretched film, with a thickness of 18 m, is then subjected to heat-setting at a temperature above 130 C. (stage I).