FR2611731A1 - Process for the surface treatment of a polymer-based material to be metallised, treated material in particular in film form, and metallised material or film obtained therefrom - Google Patents

Abstract

The invention relates to a method of surface treatment of a material to be metallized, especially a film, consisting of at least one polymer containing an anti-oxidant agent. THE PROCESS IS INTENDED TO CREATE AN INTERFACE FAVORABLE TO METALLIZATION AND TO CHEMICALLY BLOCK THE ANTI-OXIDIZING AGENT. IT CONSISTS OF COATING THE MATERIAL OF A MOLECULAR FILM OF BASE EPOXY RESIN, UNDER CONDITIONS SPECIFIC TO FIXING SAID FILM ON SITES OF THE MATERIAL BY OPENING THE EPOXIDE CYCLE OF THE RESIN. THE COATING MAY PARTICULARLY BE CARRIED OUT BY DIPPING THE MATERIAL IN A RESIN BATH SUCH AS DIGLYCIDYLETHER, HEATED BETWEEN 60 C AND 80 C, AND THEN CARRYING OUT SUCCESSIVE WASHES IN SOLVENT BATHS, ESPECIALLY ETHER. THE PROCESS MAY PARTICULARLY BE APPLIED TO THE TREATMENT OF POLYALCENE FILMS CONTAINING AN ANTI-OXIDIZING AGENT OF A PHENOLIC NATURE WITH A VIEW TO PROMOTING THEIR METALLIZATION AND STABILIZING THEIR ANTI-OXIDANT PROPERTIES.

Description

METHOD OF SURFACE TREATMENT OF A MATERIAL TO BE METALLIZED
WITH POLYI! ERE SHAFT, TREATED MATERIAL WEIGHING
IN SPECIFIC SPUS FILM FORM AND MATERIAL OR FILM
METALLIZED OBTAINED THEREFROM
The invention relates to a method of surface treatment of a material to be metallized, based on a polymer containing an antioxidant agent. It applies in particular to the treatment of materials in the form of films and extends to them treated materials and metallized materials obtained from the latter.

 It is known that metallized polymer films, in particular of polypropylene or polyethylene, are widely used in particular in the manufacture of capacitors, electric cables, jackets of hallon probe ... These films contain an antioxidant agent, most of the time phenolic in nature, intended to prevent their degradation by oxidation or photo-oxidation.

 However, polymer films do not lend themselves to a metal directly reading from their surface and, in order to obtain satisfactory adhesion of the metal layer, it is necessary to treat the material beforehand. This treatment currently consists in subjecting the material on the surface to electrical aromas under appropriate conditions. However, prolonged use of the materials thus treated has shown that they lose over time a fraction of their initial properties, in particular of their electrically insulating property.

In electrical applications, this alteration can have serious consequences for the electrical component and its environment (risk of fire).

 In addition, these polymer-based materials tend to lose their antioxidant additives over time by more or less slow diffusion depending on the temperature conditions to which they are subject; the treatment with an electric scent does not rule out this harmful phenomenon and, on the contrary, causes destruction on the surface of the antioxidants on the depth affected by the treatment.

 The present invention proposes to indicate a process for the surface treatment of polymer containing an antioxidant agent with labile hydrogen, with a view to both creating a favorable interface to metallization and chemically blocking the antioxidant agent.

 The invention relates to a process of a totally different nature from the known process using electric corona, which is free from the defects of this known process.

 An objective is to provide a treatment promoting metallization, while avoiding any degradation of the initial properties of the polymer material and even by improving some of them and in particular the electrical insulation properties.

 Another objective is to provide a material having stabilized antioxidant properties.

 To this end, the process according to the invention for treating a polymer-based material containing an antioxidant agent with labile hydrogen consists in coating the surface of the material with a molecular film of hase epoxy resin, in specific conditions for fixing said film on sites of the material by opening the epoxy resin cycle. The coating can be very simply obtained by soaking the material in a bath of epoxy resin and then carrying out one or more washes thereof in a bath of solvent.

 By "basic epoxy resin" is meant, in the usual way, a bifunctional liquid epoxy resin, not polycondensed or weakly polycondensed.

 The base resin used can in particular be diglycidyl ether of bisphenol A (DGEBA).

 According to a preferred embodiment, the coating is carried out by trenching the material in an epoxy resin bath heated between 600 ° C. and 80 ° C. and by performing successive washings in baths of solvent, in particular ether, heated between 20 and 50 C; the duration of the passage through the resin bath can in particular be between 0.5 and 5 minutes.

 The process of the invention leads to the creation of a very thin film of resin on the surface of the polymer. During contacting, the epoxy cycles of the epoxy molecules open, while the labile hydrogen of the antioxidant separates from its heteroatom: these phenomena simultaneously generate, on the one hand, fixation by l oxygen of the epoxide cycle, labile hydrogen of the antioxidant present on the surface, on the other hand, the fixation of the heteroatone of the antioxidant on the carbon left vacant in the epoxide cycle. In addition, similar phenomena occur at the level of the defects on the face of the po 1 y: era ionic defects, radical defects, presence of labile hydrogens of various origins, which contributes to the fixing of the resin film.

 This nolecular film is thus fixed by strong bonds to the material and causes, on the one hand, a neutralization of the surface defects (in particular, cause of deterioration of the characteristics of electrical insulation), on the other hand, a blocking with regard to the antioxidant by the bonds developed on the surface with these and by the waterproof screen that constitutes the film, finally a considerable improvement in the adhesion with respect to metals due to the polar nature of said film and of the presence of residual epoxy functionalities.

 The method of the invention can in particular be applied to the treatment of polyalkene films, in particular polypropylene or polyethylene, containing an antioxidant agent of phenolic mature. It thus avoids having to carry out a preliminary treatment of these films with electric effuuves, thereby eliminating all the harmful effects thereof and, in particular in the case of electrical applications, a degradation of their insulating properties.

 The invention extends to a polymer-based material containing an antioxidant agent, surface-treated by implementing the above-defined process, in particular polysene containing phenolic compounds. According to the present invention, this material comprises, on at least one side, a molecular film of epoxy resin chemically bonded to the material by open epoxy rings of the resin.

 Finally, the invention extends to the metallized material obtained from the aforementioned material. This material, in particular in the form of a film, consists of a polymer containing an antioxidant, provided on at least one face with a layer of metal, and is characterized in that it comprises, interposed between the material and the metal layer, an epoxy resin interface, in particular diglycidyl ether of bisphenol A (DGEBA).

The description which follows with reference to the appended drawings presents an example of implementation of the method of the invention and illustrates the advantages of the latter; on these drawings
- Figure 1 is a comparative diagram which represents the variations of an electrical property in the case of a polypropylene film having undergone the treatment of the invention (curve A) and in the case of two identical films, one having not undergone any treatment (curve B), the other having undergone an industrial treatment with electric corona (curve C),
- Figure 2 is a comparative diagram which represents the variations of an electrical property linked to the influence of the treatment on the antioxidant, in the case of a polypropylene film having undergone the treatment of the invention (curve D) and, by way of comparative reference, in the case of an identical film containing the same antioxidant, but which has not undergone any treatment (curve E),
- Figure 3 is a comparative diagram which represents the variations of an electrical property as a function of the temperature in the case of a polypropylene film having undergone the treatment of the invention (curve F) and an identical film having undergone industrial treatment with corona (curve G).

 All the diagrams above are in semi-logarithmic representation.

EXAMPLE OF TREATMENT
In the example in question, a polypropylene film, flat stretched, containing a phenolic antioxidant is treated.

 This film has a thickness of 8 microns, the treatment being carried out on the two faces of samples of approximately 20 cm in length.

A bath of prepolymer (hase resin) of bisphenol A diglycidylether (DGEBA) is heated to bring it to a temperature of 70 ° C. (resin distributed by the Company
SEC (Montpellier) under the reference "E 512"). The film is then dipped in this bath and left to remain there for about 1 minute.

 The film is then taken out of the resin bath and immediately immersed in a bath of ether (ethyl oxide) heated to reflux (340 C). This washing lasts about 30 seconds and is repeated three times under the same conditions in clean ether baths.

 At the end of the treatment, the film has increased opacity, linked to the fixing of a thin molecular film of resin on both sides.

METALLIZATION
This film is then metallized with aluminum by the known process of vacuum evaporation.

 Primary adhesion tests are carried out, on the one hand, on this film, on the other hand, on two identical films initially, one treated with electric aromas in accordance with the traditional process, the other untreated. These conventional tests, known as adhesive tape, consist in applying and bonding on the metallic layer of each film adhesive tapes of staggered adhesions, and in observing the possible tearing of the metallization.

 The metallization layer of the untreated film has almost zero adhesion, and tears off at the simple contact of a surface even very poorly adherent.

 The films treated by the invention and by effluents é 1 e ct r i q u e s have a degree of adhesion substantially identical, very good, the layer only tearing off with tapes with very high adhesive power.

The treatment of the invention therefore promotes the holding of the metallization in a manner analogous to the conventional treatment with electrical aromas.

PR @ ELECTRIOUF ISOLATION PRIETES
The tests carried out are of the type described in French patent application No. 86.16527.

Three films are tested
the above-mentioned film treated in accordance with the invention,
- an untreated analog film,
- a similar film industrially treated with electric scent on one side.

 These tests consist of placing each film on a support electrode, pouring it out so as to characterize a drop of acetic acid in aqueous solution, applying another electrode opposite the first, putting the electrodes under tension , and to measure the leakage current rate t as a function of the bias voltage V. The electrodes are made of stainless steel, the temperature being ambient temperature.

 It can be seen that the film treated in accordance with the invention (curve A in FIG. 1) is the site of very low amplitude leakage currents, whatever the polarization potential. On the other hand, the film treated with the scent is the site of strong leak cutters, even exhibiting runaway phenomena (curve C). The untreated film is the site of leakage currents of intermediate values.

 These leakage currents are directly linked to the electrical insulation characteristic of the film; the film according to the invention has a clearly improved insulation characteristic compared to the initial untreated film, while the film treated conventionally with corona has a degraded characteristic compared to that of said initial film.

INFLUENCE OF THE PROCESS WITH RESPECT TO ANTIOXIDANT
Use is made for the following test, the film according to the invention treated according to the method described above and the same film having undergone no treatment.

Initially, the two films therefore contain the same amount of antioxidant.

These films are subjected to an electrical test as described in the preceding paragraph, but by placing a drop of phinol in aqueous solution on the face to be characterized (instead of a drop of acid). As mentioned in
patent application FR 86.16527, such a test with addition
of a liquid phenol interface highlights the presence of phenolic antioxidant near the surface of the film (er, effect, the leakage currents measured are continuously linked to an electric produced by the presence of compounds of the same functionality on the film and at the liquid interface).

 It can be seen that, in the case of the film according to the invention (curve D in FIG. 2), the leakage currents remain very low whatever the polarization potential, while they are much higher and increase for the untreated film (curve E).

 This is significant of the presence of a barrier on the surface of the film of the invention, which blocks the phenolic antioxidant and prevents its diffusion (rupture of the electrical continuun highlighted by the low value of the leakage currents).

INFLUENCE OF TEMPERATURE
A test similar to the previous test, but without placing in liquid liquid (surfaces left dry) is carried out on two films, one treated in accordance with the invention, the other treated with electric aromas; the polarization potential is adjusted in this test to a fixed value of 130 volts and the leakage incubation measurements are carried out by varying the temperature between 20 and 70 C.

 The leakage currents do not vary for the film treated according to the invention (curve F in FIG. 3), whereas they increase linearly for the film treated with the fragrance (curve 6).

 Consequently, in the case of the film of the invention, the improvement in the characteristics referred to above is preserved in full when the temperature increases, whereas for a film treated in a conventional manner with electric scents, the degradation of these characteristics increases considerably with temperature.

Claims (9)

 1 / - Method for surface treatment of a material to be metallized, composed of at least one polymer containing an antioxidant agent with labile hydrogen, with a view to creating an interface favorable to metallization and to chemically block the anti agent -oxidizer, characterized in that it consists in coating the surface of the material with a molecular film of base epoxy resin, under conditions suitable for fixing said film on sites of the material by opening the epoxy ring of the resin.  2 / - Treatment method according to ia claim 1, characterized in that the coating is obtained by soaking the material in a bath of epoxy resin and then performing at least one washing thereof in a solvent bath.  3 / - Treatment process according to claim 2, characterized in that the coating is produced by soaking the material in a bath of epoxy resin heated between 60 C and 800 C and by performing successive washings in solvent baths, in particular d ether, heated between 20 and 500 C.  4 / - P r o c 4 de t r a itement according to claim 3, characterized in that the material is quenched and left in the epoxy resin bath for a time taken between n, 5 and 5 minutes.  5 / - Treatment method according to one of claims J, 2, 3 or 4, characterized in that the surface of the material is coated with a film of bisphenol A diglycidylether (OCEBA).  6 / - Process according to one of claims l, 2, 3, 4 or 5, applied to the treatment of a polyalkene film, in particular polypropylene or polyethylene, containing an antioxidant of phenolic nature.  7 / - Material in particular in the form of a film, based on a polymer, in particular polyalkene, containing an antioxidant agent, in particular of phenolic nature, characterized in that it comprises, on at least one side, a molecular film of resin epoxy chemically bonded to the material by open epoxy cycles of the resin.  8 / - Material according to claim 7, characterized in that the resin film is made of diglycidyl ether of bisphenol A (DGEBA).  9 / - metallized material in particular in the form of a film, based on a polymer, in particular a polyalkene, containing an antioxidant agent, in particular of a phnolic nature, provided on at least one face with a layer of metal, characterized in that it comprises, interposed between the material and the metal layer, an epoxy resin interface, in particular diglycidyl ether of bisphenol A (DCEBA).