FR2685350A1 - New process for improving the properties of metallised polyester films - Google Patents

Abstract

Process for improving the properties of oriented polyester, in particular polyethylene terephthalate, films which are metallised on at least one of their faces, this process being characterised in that, after the vacuum metallisation of the polyester film, the film, kept under tension, is subjected to a heat treatment at a temperature which is higher than the glass transition temperature of the film. Another subject of the invention is an apparatus for making use of the process, this apparatus consisting in the arrangement, in the known metallising plants, of means for heating the polyethylene terephthalate film in the region included between the metallising region and the zone for reeling the metallised film produced. Another subject of the invention is the film thus obtained and its use as packaging, in particular packaging for an alimentary product.

Description

NEW METHOD OF IMPROVING THE PROPERTIES
OF METALLIZED POLYESTER FILMS
The present invention relates to a novel process for obtaining metallized polyester films on at least one of their faces, whose adhesion properties of the metallized layer to the polyester film and the oxygen barrier properties are improved. The invention furthermore relates to polyester films, in particular polyethylene terephthalate (PET) films, oriented and metallized on at least one of their faces obtained by means of the aforementioned process, as well as to possible applications of said metallized films, of which, other, obtaining packaging and in particular food packaging.

 It is known, among others from US-A-4,631,155 and its continuation (CIP) US-A-4,810,434 in the name of Scott Caines, to modify the surface condition of oriented thermoplastic polymer films, in particular PET, in order to increase the heat-sticking properties of said films. According to these US patents, this result is obtained by applying short pulses of electromagnetic radiation of broad spectrum and very short durations, in fact flash light pulses, produced for example by xenon tubes, to a surface of such a film. PET. According to these US patents, two faces of PET films having undergone such a treatment that is applied to one another and subjected to a treatment for their adhesion exhibit adhesion properties greater than those of two faces of films of such PET having not been subjected to said irradiation prior to the treatment intended to cause their adhesion.

It should be noted, however, that this can not produce any teaching as to the adhesion properties of a metallized layer to a PET film thus irradiated. In addition, the improvement of oxygen barrier properties is not obtained, or is at the expense of adhesion. Thus, there is a need for a method for improving adhesion as well as high oxygen barrier properties.

 The present invention therefore relates to a method for improving the adhesion of a metal layer deposited on an oriented polyester film while increasing the oxygen barrier properties.

 The object of the invention is, among other things, to obtain metallized polyester films whose oxygen barrier properties increase while the adhesion between metal and polyester is improved, this in a surprising and unpredictable way.

 Another surprising and unexpected fact to which the invention leads is that said adhesion properties between metal and polyester are excellent both in a dry environment and in a humid environment.

The invention therefore also relates to a novel material consisting of a polyethylene terephthalate film
Al-metallized whose metal adhesion properties Al to
PET remains of high quality both in a dry environment and in a humid environment.

 The invention furthermore relates to the application of the above-mentioned polyester film, in particular the PET film, to packaging, particularly for the packaging of food products. It also relates to the use of said material to obtain a PET / metallized metal / polyethylene laminate intended to serve as packaging for various products and, in particular, for food products.

 Thus, the subject of the invention is a novel process for improving the properties of oriented and metallized polyester films on at least one of their faces, this process being characterized in that, after the metallization of the polyester film, the film, maintained under tension, is subjected to a heat treatment at a temperature above the glass transition temperature of the film, preferably greater than 160 C.

 According to one embodiment of the method of the invention, the film is subjected to a heat treatment produced by circulation of a coolant, gaseous or liquid, hot in an enclosure such as a drum, in contact with said film maintained under pressure.

 According to another embodiment of the method of the invention, the film is subjected to a heat treatment produced by infrared radiation, while said film is kept under tension.

 According to yet another embodiment of the method of the invention, the film is subjected to a heat treatment produced by ultraviolet radiation, while said film is kept under tension.

 According to still another embodiment of the process of the invention, the film is subjected to a heat treatment produced by an oven at a temperature greater than 160.degree.

 According to a particular embodiment of the process of the invention, the polyester is polyethylene terephthalate and the metallization metal is aluminum.

 According to another embodiment of the method of the invention, the heat treatment is carried out immediately after metallization and before winding said film having undergone said metallization.

 According to yet another embodiment of the invention, the film prior to metallization has been subjected to orientation in a single direction.

 According to yet another embodiment of the invention, the film, prior to metallization, has been subjected to a bi-orientation treatment.

 According to one embodiment of the invention, the two faces of the film are metallized.

 Another subject of the present invention is an apparatus for carrying out the aforesaid process, this apparatus consisting in the provision, on known metallization installations, of heating means for the polyester film in the zone lying between the metallization zone. and the final winding area of the metallized film produced.

 The invention also relates to polyester films, in particular polyethylene terephthalate mono- or bi-drawn and metallized on at least one of their faces resulting from the implementation of the aforementioned method.

 Another subject of the invention is the application of the abovementioned polyethylene, especially polyethylene terephthalate, mono- or bi-stretched and metallized films on at least one of their faces in order to obtain packaging, in particular packaging for foodstuffs.

 The subject of the invention is also the packages formed of said polyester films, in particular of polyethylene terephthalate, which are mono- or bi-stretched and metallized on at least one of their faces.

It also applies to laminate materials formed of said metallized film on at least one of its faces and a film of a polyolefin, for example polyethylene, applied against a metallized face of the aforementioned metallized film.

 As will be apparent from the comparison of the implementation examples given below, it is surprising and totally unexpected that a heat treatment, subsequent to metallization, leads to adhesion properties of the metallized layer on the surface of the film. oriented PET so much higher than those to which a thermal treatment of the PET film prior to the metallization treatment is conducted. No theory can explain this surprising and unexpected fact and in no case the teaching of US-A-4,631,155 and 4,810,434 would allow to expect such a result.

 Other aims and advantages of the invention will appear on reading the examples of implementation below, given by way of illustration and in no way limiting.

Although the examples more particularly relate to the invention also applies to other metals conventionally used in metallization such as, inter alia, copper, silver, metal oxides, as well as SiOx. . In no way should the invention be limited to metallization by aluminum. Thus, the term metallization means, in the present invention, the application of a metal layer or oxide of this metal.

Those skilled in the art will appreciate, although the examples relate to polyethylene terephthalate (PET), that other polyesters, for example polyethylene isophthalate, polybutylene terephthalate, polyethylene naphthalate and their copolymers or mixtures, could be processed according to the method of invention and lead to the same results.

 The apparatus for carrying out the process according to the present invention consists of an apparatus comprising means for heating the inserted polyester film, in the production line, at a level located between the metallization and the winding of the polyester film. These heating means may be a drum comprising an exchanger in which circulates a heat transfer fluid, preferably water, a furnace with a temperature above 1600C, an IR radiation emitter, these heating means emitting a power of 20. at 80 kW / m2 of film. The thermal power exchanged with the film during the heat treatment is therefore 20 to 80 kW per m2 of film. Preferably, the heat treatment is carried out over a period of 1 second to 15 minutes (drum) depending on the aforementioned heating means. , the treatment time being a function of the temperature or power. This treatment time is generally inversely proportional to the temperature, but according to a complex relationship. The apparatus according to the invention is in no way limited to the aforementioned heating means and any other heating means can be used for the purpose of the invention.

Adhesion is determined by the peel strength which is a direct measure of the adhesion value of the metal film to the PET. The peel force is measured on specimens consisting of a sandwich formed of metal plates which serve as supports, and:
- a piece of 2.5 cm double sided tape
width;
- a piece of metallized film of the same width (poly
mother being located on the support side);
- a piece of film based on EEA (product marketed
by Dow Chemical) and consisting of ethylene / acid
acrylic of the same width;
a polyimide strip (for example sold by DuPont
under the brand name Kapton) and a metal plate.

The sandwich thus obtained is placed for 20 seconds in a heating press (T = 105 ° C. + 3 ° C. and P = 800 kg). This treatment has the effect of fixing the EAA to the metal film (superior adhesion to the metal film / PET adhesion); KaptonX prevents the second metal plate from sticking to the EAA.

The adhesion test is performed under two different conditions:
- the sample is directly subjected to the adhesion test
if we; we then measure the adhesion to the dry being;
- the sample is immersed for one minute in the water
deionized and then dried superficially with a paper
cloth before performing the adhesion test; we measure
then adhesion to the wet state.

By pulling on the EAA at 1800, the metal film of the polymer is then detached. The "force" applied during peeling is measured and gives a direct value of adhesion in N / m. These tests were performed on a machine of the type INSTRON 4301, with a take-off speed of 50 mm / min.

The test for measuring the oxygen barrier properties is carried out as follows. The oxygen barrier is determined by the value of oxygen permeability. The higher the permeability, the less the barrier is good. This permeability is measured on a device
Mocon 100 Twin Oxtran. The atmospheric pressure is measured using a mercury barometer and the oxtran values are corrected for deviations from the standard atmospheric pressure of 1013 hPa.

EXAMPLE 1
A square sample of polyethylene terephthalate film having a surface area of 330 cm 2 (15 x 22 cm) and a thickness of 12 μm is set under tension on an aluminum frame and then introduced into a furnace whose temperature is tightly controlled and which operates at atmospheric pressure. The treatment time is 5 minutes. The various temperatures at which heating is performed on the various samples are recorded in Table I.

 The oven used is the Salvis TSW 120 ED oven with programmable temperature and hot air circulation heating.

 After this heat treatment, the sample is removed from the oven and allowed to come to room temperature.

 Then said sample, maintained under tension, is subjected to a metallization with aluminum in a vacuum metallization chamber of a type conventionally used for this purpose, the metallization resulting from the vacuum evaporation of aluminum and its aluminum. deposit on the PET film. The resulting aluminum layer has a thickness of about 450.

The metallization is carried out using a Balzers BAE 370 metallizer by evaporation of aluminum under a high vacuum. The standard values of the parameters are:
. geometry of the sample ... circular,
diameter 13.5 cm
. vertical wire - distance from
the sample ................ 22.5 cm. thickness of the layer ..., ... approx. 450
. evaporation rate,. approx. 10 A / s
. pressure at the beginning of the
metallization ................ 2.10-5 hPa
The metallizer is equipped with a quadrupole mass spectrometer, which makes it possible to analyze the composition of the remaining gas for pressures below 1.10 5 hPa.

Partial pressures (corresponding to a
total pressure Ptot = 8.2 × 10 -6 hPa):
. N2 ........................... 6,1.10-6 hPa
. 02 ......................... 1,5.10 hPa
-6
HO 0.6.10 6 hPa
Table I below gives the value of adhesion as a function of the temperature at which the PET film was subjected prior to metallization with aluminum.

The results recorded in Table I were determined on the metallized PET obtained according to the method indicated above.

TABLE I

<tb><SEP><SEP> Temperature <SEP> Adhesion <SEP> (Control)
<tb><SEP> tment <SEP> thermal
<tb><SEP> of <SEP> PET <SEP> A <SEP> state <SEP> sec <SEP> A <SEP> state <SEP> wet
<tb><SEP>"C<SEP> N / m <SEP> (g / in) <SEP> N / m <SEP> (g / in)
<tb><SEP> 90 <SEP> 29.25 <SEP> (75) <SEP> O
<tb><SEP> 100 <SEP> 26.52 <SEP> (68) <SEP> O
<tb><SEP> 190 <SEP> 23.40 <SEP> (60) <SEP> O
<tb><SEP> 210 <SEP> 28.08 <SEP> (72) <SEP> O
<tb><SEP> 240 <SEP> 21.84 <SEP> (56) <SE> O
<tb><SEP> 245 <SEP> 7.80 <SEP> (20) <SEP> O
<tb><SEP> 250 <SEP> 7.80 <SEP> (20) <SEP> O
<tb><SEP> 255 <SEP> 5.85 <SEP> (15) <SEP> O
<tb><SEP> 260 <SEP> 9.75 <SEP> (25)
<Tb>
It is found that the dry adhesion varies between 30 and 10 N / m approximately when the heat treatment varies from 90 "C to 260" C, but that it is zero in the wet state, that is to say that the deposited metal film comes off without difficulty.

EXAMPLE 2
The operation is carried out under the same conditions and employs the same means (frame, furnace, cooling chamber and vacuum metallization chamber) as those employed in the process described in Example 1. The difference is that, in the case of the present for example, the PET film which is fixed under tension on the frame is introduced into the furnace only after it has been subjected to metallization by application of an aluminum layer of the same thickness, under the same conditions and in the same metallization chamber as that described above. Only after the metallization is complete, the sample is placed in the oven whose temperature is tightly controlled, used in the method of Example 1, and subjected to heat treatment. The various temperatures at which the treatment is performed on samples are reported in Table II.

 After this heat treatment, the samples are removed from the oven and allowed to return to room temperature under the same conditions as above.

 Table II below gives the value of the adhesion as a function of the temperature at which the metallized PET film with aluminum was subjected during the aforementioned heat treatment. These results are obtained on both dry and wet samples.

TABLE II

<tb><SEP><SEP> temperature processed <SEP>
<tb><SEP> tment <SEP> thermal
<tb><SEP> of <SEP> PET <SEP> A <SEP> state <SEP> sec <SEP> A <SEP> state <SEP> wet
<tb><SEP>"C<SEP> N / m <SEP> (g / in) <SEP> N / m <SEP> (g / in)
<tb><SEP> 90 <SEP> 27.30 <SEP> (70) <SE> O <SEP> () <SEP>
<tb><SEP> 100 <SEP> 28.08 <SEP> (72) <SEP> O <SEP> (O) <SEP>
<tb><SEP> 130 <SEP> 50.70 <SEP> (130) <SEP> 0 <SEP> (O) <SEP>
<tb><SEP> 150 <SEP> 78.00 <SEP> (200) <SE> O <SEP> (O) <SEP>
<tb><SEP> 170 <SEP> 50.70 <SEP> (130) <SEP> O <SEP><SEP> (O) <SEP>
<tb><SEP> 190 <SEP> 152.10 <SEP> (390) <SEP> O <SEP><SEP> (O) <SEP>
<tb><SEP> 200 <SEP> 218.40 <SEP> (560) <SEP> 7.80 <SEP> (20)
<tb><SEP> 210 <SEQ> 370.50 <SEP> (950) <SEP> 14.04 <SEP> (36)
<tb><SEP> 220 <SEP> 380.25 <SEP> (975) <SEP> 28.08 <SEP> (72)
<tb><SEP> 230 <SEQ> 417.30 <SEP> (1070) <SEP> 34.32 <SEP> (88)
<tb><SEP> 240 <SEP> 354.90 <SEP> (910) <SEP> 50.70 <SEP> (130)
<tb><SEP> 245 <SEP> 456.30 <SEP> (1170) <SEP> 57.72 <SEP> (148)
<tb><SEP> 250 <SEP> 436.80 <SEP> (1120) <SEP> 64.74 <SEP> (166)
<tb><SEP> 255 <SEP> 473.07 <SEP> (1213) <SEP> 76.05 <SEP> (195)
<Tb>
Exceptionally superior results are obtained than those obtained by operating according to the method of Example 1. In a similarly surprising way, it is found that a relatively good adhesion is maintained even when the samples are wet and that the adhesion increases as a function of the temperature in contrast to the previous example.

These results of the wet adhesion show that, even if a metallized PET film has not been stored under conditions of total "dryness" or is employed in atmospheric moisture saturation conditions, it is advisable to There are still good adhesion properties of the aluminum layer to the PET film. This is of considerable interest in the manufacture of polyester film intended for agri-food use, said manufacture being able to take place on food production sites.

 The results obtained in the dry state are extremely surprising and much higher. If, at 90 ° C, the adhesion is identical, it increases with temperature to reach values up to 15 times higher, which results in the manufacture of improved metallized films.

EXAMPLE 3
The test for measuring the oxygen barrier properties is carried out on the two preceding films treated at increasing temperatures for a period of 5 minutes. The samples are 13.5 cm diameter discs, the metallized side is placed down, the relative humidity is 50-70%. In this example, three types of films are compared: untreated blank film, treated film before metallization and film treated after metallization. The film is said to be untreated for the temperature of 40 ° C. The results are summarized in Table III below.

TABLE III

<tb><SEP> Permeability <SEP> to <SEP> Oxygen
<tb><SEP> (cm3 / cm2 / d) <SEP>
<tb> Temperature
<tb><SEP> C <SEP> Movie <SEP> No <SEP> Movie <SEP> Treats <SEP> Before <SEP> Movie <SEP> Treated <SEP> After
<tb><SEP> treated <SEP> metallization <SEP> metallization
<tb><SEP> 40 <SEP> 176
<tb><SEP> 100 <SEP> - <SEP> - <SEP> 162 <SEP> 204
<tb><SEP> 130 <SEP> ~ <SEP><SEP> 155 <SEP> 213
<tb><SEP> 10 <SEP> it <SEP> 115 <SEP> 157
<tb><SEP> 170 <SEP> ~ <SEP><SEP> 125 <SEP> 170
<tb><SEP> 190 <SEP> - <SEP> 115 <SEP> 98
<tb><SEP> 200 <SEP> - <SEP> - <SEP> 101
<tb><SEP> 210 <SEP> - <SEP> 48 <SEP> ~ <SEP><SEP> 81
<Tb>
Table III (continued)

<tb><SEP> Permeability <SEP> to <SEP> Oxygen
<tb><SEP> (cm3 / cm2 / d)
<tb> Temperature <SEP>
<tb><SEP> C <SEP> Movie <SEP> No <SEP> Movie <SEP> Processed <SEP> Before <SEP> Movie <SEP> Processed <SEP> After
<tb><SEP> treated <SEP> metallization <SEP> metallization
<tb><SEP> 220 <SEP> ~ <SEP><SEP> 45 <SEP> 78
<tb><SEP> 230 <SEP> ~ <SEP><SEP> - <SEP> 60
<tb><SEP> 240 <SEP> - <SEP> 15 <SEP> 58
<tb><SEP> 245 <SEP> - <SEP> 14
<tb><SEP> 250 <SEP> - <SEP> 14 <SEP> 38
<tb><SEP> 255 <SEP> 22 <SEP>
<tb><SEP> 260 <SEP> - <SEP> 13
<Tb>
Thus, it is remarkable to obtain such an improvement of the oxygen barrier. The results obtained with the treated film before metallization were given by way of reference: in this example, the oxygen barriers for the treated films before and after metallization are similar, that is to say improved, but the examples 1 and 2 show us that the film treated after metallization has a much higher adhesion. Thus, the film treated according to the present invention surprisingly combines, with unexpected effectiveness, the improvement of the adhesion with the improvement of the oxygen barrier.

Claims (14)

 1. A process for improving the properties of oriented and metallized polyester films on at least one of their faces, this method being characterized in that, after the metallization of the polyester film, said film, kept under tension, is subjected to a heat treatment at a temperature above the glass transition temperature of the film, preferably greater than 160 C.  2. A process according to claim 1, characterized in that the polyester is polyethylene terephthalate.  3. A process according to claim 1 or 2, characterized in that the metallization metal is aluminum.  4. A process according to any one of claims 1 to 3, characterized in that the film is subjected to heat treatment produced by circulation of a coolant in an enclosure such as a drum, in contact with said film maintained under voltage.  5. A process according to any one of claims 1 to 3, characterized in that the film is subjected to a thermal treatment produced by infrared radiation, while said film is kept under tension.  6. A process according to any one of claims 1 to 3, characterized in that the film is subjected to a heat treatment produced by ultraviolet radiation, while said film is kept under tension.  7. A process according to any one of claims 1 to 3, characterized in that the film is subjected to a heat treatment produced by an oven at a temperature of at least 160 C.  8. A process according to any one of claims 1 to 7, characterized in that the heat treatment is carried out immediately after metallization and before winding said film having undergone said metallization.  9. A process according to any one of claims 1 to 8, characterized in that the film prior to metallization has been subjected to an orientation in one direction.  10. A process according to any one of claims 1 to 8, characterized in that the film, prior to metallization, has been subjected to a bi-orientation treatment.  11. A process according to any one of claims 1 to 10, characterized in that the two faces of the film are metallized.  12. Apparatus for carrying out the process according to any one of claims 1 to 11, this apparatus consisting in the provision, on known metallization plants, means for heating the polyester film in the zone between the zone of metallization and the final winding area of the metallized film produced.  13. Metallized polyester films resulting from the implementation of the method according to any one of claims 1 to 11.  14.- Packaging formed of polyethylene laminates / metallized polyester films produced according to any one of claims 1 to 11, the metal being in contact with the polyethylene.