EP2619037A1

EP2619037A1 - Surface-treated material comprising one or more polymers

Info

Publication number: EP2619037A1
Application number: EP11757865.8A
Authority: EP
Inventors: Frédéric Moret; Marc Brassier; Alexis Chenet
Original assignee: Valeo Vision SAS
Current assignee: Valeo Vision SAS
Priority date: 2010-09-20
Filing date: 2011-09-19
Publication date: 2013-07-31
Also published as: WO2012038366A1; FR2964971A1; US20130224480A1; FR2964971B1

Abstract

The invention relates to a material containing one or more polymers, the surface of said material being treated by means of ion bombardment in order to improve the appearance thereof. The invention also relates to a method for producing the part and to the use thereof, in particular for the production of lighting and/or signalling devices.

Description

Surface-treated polymer (s) material

The present invention relates to a polymer-based material (s) having a surface treatment to improve the surface appearance of the material. The invention also relates to a process for obtaining this material and the use thereof, in particular for the manufacture of parts for a motor vehicle.

In the field of polymer-based technical materials, research often focuses on improving the mechanical properties and / or surface appearance of the shaped parts from these materials.

In the case of a lighting device and / or signaling of a motor vehicle, certain parts such as masks or hubcaps, essentially fulfill an aesthetic function. Other parts, including pedestals, plates, reflectors, can play a purely mechanical role or a role both mechanical and aesthetic.

By way of example, the function of the reflector is to reflect the light emitted by one or more light sources so that the light beam emitted by the lighting and / or signaling device respects precise photometry. The mask must be able to give an aesthetic appearance, shiny or satin for example, which is homogeneous and durable over time, as the bases and turntables, especially when they are visible from outside the projector or fire.

Whatever their function, these parts need to have certain properties, especially at the surface, whether for aesthetic reasons and / or for technical reasons such as good resistance to temperature or a surface appearance allowing do not disturb the reflection of the light emitted by the fire and / or projector.

These parts, which are important elements in a lighting and / or signaling device of a motor vehicle, may be made of metal or of a material based on polymer (s), in particular thermosetting or thermoplastic, which have the advantage the lightness and freedom in the shapes obtained, because manufactured by injection molding techniques.

However, the surface of the parts made from these polymer-based materials can be modified by many factors, among which:

1. Surface defects of thermal origin such as deformations, blistering, cracking or others. The parts are used in an environment susceptible to relatively high temperatures due to the presence of light sources, usually giving off heat. Good temperature resistance prevents any deformation (creep) of the part made of polymer-based material (s). In addition, when these parts are metallized, for example by depositing a reflective metal layer of the aluminum type, the increase in temperature causes a deformation phenomenon of the material, leading to blistering on the surface of the metal layer.

2. The resistance to abrasion. The workpiece may be subject to slight friction or abrasion during transport and handling resulting in scratches on its surface.

3. Degassing. The increase in temperature evoked in point 2 of a polymer-based material can also cause a phenomenon of extraction of molecules with high vapor pressure (oligomers, additives, etc.) which creates aesthetic defects such as coloring or tarnishing of the material, which sometimes leads to parasitic chemical reactions and / or, when the material is in a sealed medium, which induces the formation of visible condensates of volatile compounds.

4. Resistance to chemical agents. A polymer-based material is liable to degrade in the presence of various chemical compounds, such as water, oxygen, nitrous oxide, carbon dioxide or any other oxidizing agent, as well as certain compounds present in the polymer (s) and likely to react with the polymer (s) during degassing.

5. The brilliance. For some applications, it is advantageous to have materials having a glossy surface. However, it is sometimes difficult to make deposits to improve this property of the material without changing the geometry or texture of the surface of the room.

The present invention therefore relates to a polymer-based material (s) having a surface thickness, that is to say on the surface, having increased crosslinking. The polymer-based material (s) according to the invention notably has an improved surface appearance.

In the present application, the term "polymer (s)" means polymers preferably having a Young's modulus at 23 ° C. of greater than 100 MPa (100 mega Pascal). These polymers have a particularly interesting rigidity. In addition, they are customizable by current methods. Preferably, these polymers have a Young's modulus at 23 ° C. of between 1000 and 15000 MPa, more particularly between 2000 and 5000 MPa.

Preferably, these polymers are thermoplastic or thermosetting polymers, alone or in a mixture, in particular the polymers chosen from the group consisting of polycarbonates (PC), high temperature polycarbonates (PC-HT), polyamides (PA), Acrylonitrile-butadiene-styrene (ABS) copolymers, polybutylene terephthalates (PBT), polyethylene terephthalates (PET), polypropylenes (PP), unsaturated polyesters (UP), polyepoxides (EP), polymethyl methacrylates (PMMA), polysulfones (PSU), polyethersulfones (PES) and phenylene polysulfides (PPS).

Preferably, the polymer (s) will be selected from the group consisting of polycarbonates (PC), high temperature polycarbonates (PC-HT), polyamides (PA), acrylonitrile-butadiene-styrene copolymers (ABS) polybutylene terephthalates (PBT), polypropylenes (PP), unsaturated polyesters (UP-BMC) and polymethylmethacrylates (PMMA).

More preferably, the polymer (s) will be selected from the group consisting of polycarbonates (PC), high temperature polycarbonates (PC-HT), polyamides (PA), polypropylenes (PP) and polymethacrylates methyl (PMMA).

By "based on" is meant a material comprising in volume at least 5% of polymer (s), preferably at least 15%, more preferably at least 20%.

By "increased crosslinking" is meant a degree of crosslinking greater than that of the polymer (s) present in the rest of the material. In general, the degree of crosslinking of the polymer (s) present in the remainder of the material material will correspond to the degree of crosslinking obtained under the usual polymerization conditions of the polymer (s), that is to say ie, without additional specific treatment of the polymer (s).

For a given polymer group (s), the degree of crosslinking D can be measured by the solubility in a solvent of the polymer. Since the polymer is soluble in the solvent, the crosslinked portions will be insoluble.

Considering only the mass of the superficial thickness of the polymer:

D = weight of the polymer-insoluble treated polymer / total weight of the polymer.

For example, the degree of crosslinking of Polyamide 6-6 (PA66) can be measured as follows: D = weight of PA66 insoluble in metacresol or formic acid / total weight of PA66.

For PMMA, the degree of crosslinking will be calculated as follows:

D = weight of PMMA insoluble in ethyl acetate / total weight of PMMA.

Advantageously, the degree of crosslinking is 10% greater than that of the polymer (s) present in the remainder of the material, preferably 50%, more preferably, 95%.

Crosslinking of the material can also be demonstrated by DSC (differential scanning calorimetry). A comparison of the treated and untreated material shows that the increase in the degree of crosslinking of the material has the effect of eliminating the glass transition temperature "Tg" (endothermic change in heat capacity). Such a comparison is illustrated in Example 6 below.

The polymer-based material (s) according to the invention can also be characterized by the presence on the surface of a thickness having a decrease in the fraction of the free volume of the material.

The free volume is the volume of material not occupied by the polymer (s). The free volume is measurable for example by SAXS (acronym for "Small Angle X-Ray Scattering"). The fraction of free volume of a polymer is generally between 0.6 and 0.4. In contrast, in the material according to the invention, the surface thickness of the material according to the invention will have a fraction of free volume less than 0.4, preferably between 0.2 and 0.01.

The polymer-based material (s) according to the invention is obtainable by the process comprising the step of treating by ion bombardment an outer surface of the material. This ion bombardment treatment may be a treatment using at least one ion beam.

Already known in the state of the art, particularly from FR-A-2 899 242, an installation for the treatment by ion bombardment of an object.

According to the present invention, the ion bombardment treatment is applied to polymers and will allow on the one hand, to create a three-dimensional network of polymer (s) on the surface of the material by creating bridges between the macromolecular chains. Preferably, the treatment by ion bombardment will allow crosslinking resulting from direct bonds between the polymer molecules (s). This gives the material a superficial thickness with increased crosslinking resulting from direct bonds between the polymer molecules (s).

The ion bombardment treatment may also allow ions to be implanted in the object to treat its surface. In this case, it will enable certain low molecular weight molecules (oligomers or additives) present in the material. The ion bombardment treatment is carried out using a device comprising ion bombardment means such as for example those described in FR-A-2 899 242: ion generator means and applicator means. ion.

The ion applicator usually comprises means selected for example from electrostatic ion beam shaping lenses, a diaphragm, a shutter, a collimator, an ion beam analyzer and a beam controller. ions.

The ion generator usually comprises means selected for example from an ionization chamber, an electron cyclotron resonance ion source, an ion accelerator and in some cases an ion separator.

Ion bombardment is usually carried out under vacuum. For example, FR-A-2,899,242 proposes housing all the ion bombardment means (ion generator and ion applicator) as well as the object to be treated in a vacuum chamber. Vacuum means are connected to this chamber. These vacuum means must allow to obtain a relatively high vacuum in the chamber, for example of the order of 10 ^"2 mbar to ^{10" 6} mbar.

Advantageously, according to the invention, the ion bombardment will be carried out by means of ion beams derived from gases such as helium, neon, krypton, argon, xenon, dioxygen or dinitrogen, alone or in mixed. Preferably, the oxygen and / or the dinitrogen, more preferably the helium and / or the dinitrogen, will be used.

Preferably, according to the invention, the ion bombardment will take place at a pressure of between 1 mbar and 10 ^-5 mbar, preferably between 10 ^-2 mbar and 5 × 10 ^-4 mbar, and transmitting to the material an energy of in the range of 0.1 to 100 kEV, preferably 0.3 to 30 kEV.

It has been demonstrated that the material according to the invention has improved properties. Indeed, the material according to the invention has a better temperature creep resistance for semicrystalline polymers equivalent to that of a thermosetting material and chemical resistance properties (including resistance to oxidation and oxidation. moisture) equivalent for an amorphous polymer equivalent to those of a semi-crystalline polymer. In addition, the material also has greater gloss on the treated surface (see Example 1) and is less likely to be subject to the degassing phenomenon (see Example 2). It is also possible to change the color of the material or to make it reflective thanks to to this treatment (see Example 1 below) without having to proceed with the deposition of a coating such as aluminization or the deposition of a layer of paint.

These properties come from the conjunction of two phenomena:

grafting of the volatile elements present (demolding agents, oligomers, antioxidants, anti-UV, external and internal lubricants, and other additives), and creating a "barrier" on the surface of the material by crosslinking the macromolecular chains of such so that the diffusion of the volatile compounds of the material outwards or from outside to the material is blocked.

Finally, when the polymer-based material (s) is metallized by deposition of a reflective layer, the ion bombardment treatment makes it possible to avoid the blistering phenomenon described above and to avoid the formation of iridescence on the surface. metallized surface. Indeed, a part such as a reflector (or the mask), must be able to reflect the light achromatically, that is to say without iridescence or coloring effect, the color of the light beam emitted by a device lighting is a photometric constraint, both regulatory and aesthetic.

Advantageously, the thickness having a higher degree of crosslinking or a free volume fraction lower than the rest of the material is less than 5μηι, preferably less than 2 μηι, starting from the external surface of the material.

The invention also covers a method for treating a surface, especially an external surface, of a material based on polymer (s) by ion bombardment. The ion bombardment treatment method is particularly effective for improving the temperature resistance properties, the chemical resistance properties and the reflection properties (modifying the reflection coefficient) and / or for changing the color of a material. based on polymer (s), for reducing the phenomena of irisation of a polymer-based material (s) comprising a reflective layer, preferably a metal layer, and for reducing the degassing phenomenon likely to occur in a polymer-based material (s). Some of these properties are highlighted in the examples that follow.

It will be noted that the degassing phenomenon is particularly reduced when the polymer treated by ion bombardment is a polyamide (see Example 2 below) or a polypropylene (see Example 5 below).

The improvement of the reflection properties is particularly marked when the polymer treated by ion bombardment is a polypropylene or a polyamide (see Example 1 below). Particularly advantageous results in terms of temperature resistance are obtained with high temperature polycarbonates, treated by ion bombardment. In addition, when these high-temperature polycarbonates are metallized using a deposition of a metal layer, significant results are obtained in terms of reducing the phenomena of iridescence and blistering (see Example 4).

To obtain a metallized part, namely a part obtained by depositing a thin metallic layer (for example of a thickness less than 200 nm) on a polymer-based part, the results obtained in terms of reduction iridescence and blistering phenomena are identical regardless of the method used, the metallization layer was deposited on the material before or after treatment of the workpiece by ion bombardment (see Example 4 below). A metallized piece is for example a reflector, in which a polymer is coated with a reflective layer by aluminization.

As indicated above, the material according to the invention is particularly suitable for the manufacture of parts for a lighting device and / or signaling of a motor vehicle, such as projector masks, hubcaps, pedestals, plates and the reflectors.

Thus the invention covers:

a method of improving the temperature resistance properties of a polymer-based material by treating a surface of the material by ion bombardment,

a process for improving the chemical resistance properties of a polymer-based material by treating a surface of the material by ion bombardment,

a process for reducing the phenomena of irisation of a polymer-based material comprising a reflective layer on a surface of said material in which the surface of the material is treated by ion bombardment,

a method for improving the reflection properties of a polymer-based material by treating a surface of the material by ion bombardment; - a method of reducing the degassing phenomenon that can occur in a material based on of polymer (s), by treating a surface of the material by ion bombardment.

Preferably, these methods make it possible to obtain materials according to the present invention.

The invention also covers a part of a device, this part having an aesthetic, optical, chemical, electrical, thermal and / or mechanical function, this part being subjected to a strong thermal stress and comprising a material according to the invention. By way of example, this part can be a mask (aesthetic function), a reflector (optical function), a detector (chemical function), an electrical insulator (electrical function), a radiator (thermal function) and / or a part support (mechanical function).

The invention also covers a piece for a lighting and / or signaling device of a motor vehicle comprising a material according to the invention.

The invention also covers a method of treating a part of a device, in particular a lighting and / or signaling device for a motor vehicle, said method comprising the following steps:

deposition, in particular by PVD, of a layer, in particular a metal layer, on the surface of a polymer-based material, preferably PMMA, PC or high-temperature PC,

- Treatment of the material by ion bombardment, this ion bombardment processing step taking place after the deposition step.

This ion bombardment treatment may be a treatment using at least one ion beam.

This makes it possible not to reduce the adhesion between the material and the deposited layer, the ion beam treatment being carried out while the bridges between the material and the deposited layer have been made. The property modifications of the polymer-based material (s) and the advantages described above are retained. This is particularly advantageous for polymers such as PMMA, PC and high temperature PCs. It should be noted that this ionic bombardment treatment step does not necessarily take place directly after the deposition step of the layer, in particular metal, and may be preceded by other processing steps, for example a deposition step. a protective layer, such as a varnish.

The step of treating the material by ion bombardment is carried out according to a method according to the present invention.

The invention covers a device part, in particular a lighting and / or signaling device for a motor vehicle, according to a method of treating a part of a device according to the invention. This may be for example a reflector or a mask (also called hubcap) lighting device and / or signaling of a motor vehicle.

The invention also covers the use of a material according to the invention, for the manufacture of parts for a lighting device and / or signaling of a motor vehicle. Other features and advantages of the invention will be described in the following examples with reference to the figures presented below:

FIG. 1 illustrates the L * a * b * system for describing a color; FIG. 2 is a thermogram resulting from a differential scanning calorimetry analysis of PMMA sample treated according to the invention or untreated,

FIG. 3 is an infrared spectrum obtained by FTIR spectroscopy of various samples of PMMA treated according to the invention or untreated. Example 1: Treatment of Polyamide 6-6 - Effect on color and reflectance

The part is implemented by injection or by any other means of transformation. This piece is inserted into a chamber equipped with an ion bombardment apparatus, in which a vacuum of between 1 and 10 ^-4 mbar, preferably 10 ^-3 mbar, is produced.

The ion bombardment parameters are as follows:

Gas: Helium or Diazote (N ₂ )

Processing energies received by the part: 0, 1 to 30 kEV

- Working pressure (P): 5.10 ^"4 mbar <P <1.10 ^{" 2} mbar.

After treatment, the measurements performed on the part are as follows:

- Color: the measurement is made using the L * a * b * system (also called CIE Lab, model of color representation developed in 1976 by the International Commission on Illumination). This system characterizes a color using an intensity parameter corresponding to the luminance and two chrominance parameters that describe the color (see Figure 1). - Gloss: the gloss measurement is performed with an angular reflectometer according to ISO 2813.

Results:

Conclusion It is thus observed that with the treatment, the color (variation of a and b), the clarity (variation of L) and the gloss of polyamide 6-6 varied. It will be noted in particular that the brightness increases with the amount of energy received by the material. Example 2: Polyamide Treatment 6-6 - Effect on Degassing

Automotive headlight masks are treated by ion bombardment in the chamber described in Example 1 under the following conditions:

Method 1: a single helium ion beam treatment having a mean energy such that each piece receives about 1 kEV.

Method 2: during a first step, the parts are treated by ion beam

Helium having an average energy such that each piece receives about 5kEV. In a second step, a deposition of aluminum with a thickness of 50-100 nm by vacuum cathode sputtering PVD (in accordance with the acronym for "Physical Vapor Deposition") is applied to each part before a second deposition of a layer. polysiloxane thickness of 15-50nm plasma-assisted PECVD DC or AC (according to the acronym for "Plasma Enhanced Chemical Vapor Deposition") at 40 kHz (medium frequency, "MF").

Serial process (metallization): an aluminum deposit with a thickness of 50-1Omnm by vacuum cathode sputtering PVD (in accordance with the acronym for "Physical Vapor Deposition") is applied to each part before a second deposit of a Polysiloxane layer 15-50nm thick plasma-assisted PECVD DC or AC (according to the acronym for "Plasma Enhanced Chemical Vapor Deposition") at 40 kHz (medium frequency, "MF"). Absence of treatment by ion bombardment.

The measures concerning degassing (also called "fogging") are carried out by the following method:

A 2 mm thick plate of the material to be tested is taken and brought into contact by convection with a heat source up to a temperature of 200 ° C. A glass slide is disposed above the sample plate to receive gases that may form within this sample. The glass slide is itself thermostated at a temperature of 70 ° C to condense the gases formed within the sample.

The sample is subjected for 20 hours, at a temperature determined according to its resistance and the environmental conditions to which the constituent material of the sample is likely to be subjected. These temperatures are shown in the table below. The glass slide is then recovered and the transmittance (% T) of this slide is measured by UV-visible spectroscopy at 550 nm, the reference value being given by a clean and clean glass slide. The value of the transmittance is all the higher as the presence of condensates is low, and therefore the degassing is low.

Results:

Conclusion:

The treatment by ion bombardment thus makes it possible to reduce degassing. Indeed, the treated parts (1 and 2) have better transmittance values and therefore a lower outgassing than the untreated parts (3 and 4), although the latter have been subjected to lower temperatures than the treated parts. .

Example 3 Treatment of Polyamide 6

A piece of Polyamide 6 (PA 6) is inserted into the chamber described in Example 1. The ion bombardment parameters are as follows:

Gas: Helium

Processing energies received by the part: 90 kEV

Working pressure: 1.10 ^"3 mbar.

- Treatment time: 120 s

Result:

After resumption of humidity for 7 days at 95% RH (relative humidity) at 60 ° C, the recovery is 0.5% by weight for PA 6 treated against 6% by weight for untreated PA 6. The fall of the Young's modulus and the linear expansion are 20% and 0.5% respectively for PA 6 treated against 80% and 2% for PA 6 untreated.

The temperature limit of onset of degassing is 160 ° C for PA 6 treated against 110 ° C for PA 6 untreated.

Linear Expansion Coefficient (CLTE): 4.10-5 / ° C versus 7.10-5 / ° C?

Finally, the treated PA 6 has an improvement in the tensile strength of + 10% compared with the untreated PA 6.

Conclusion: These results demonstrate that the polyamide 6 treated by ion bombardment have improved mechanical and chemical properties, particularly with regard to resistance to humidity, stress and temperature. Example 4 Treatment of High Temperature Polycarbonate

The parts are prepared by injection from copolycarbonate mixture of bisphenol A (BPA) and trimethylcyclohexanonebisphenol (BPTMC), hereinafter designated "BP-TMC-180".

Two processes are implemented on these parts:

Method A

Step 1: ion bombardment treatment of helium ions with energy received by the 5kEV pieces

Step 2: glow discharge with an air pressure of 5.10 ^"2 to 10 ^{" 1} mbar for 120 s.

Step 3: Deposition of an aluminum layer with a thickness of 70 to 100 nm by PVD

Step 4: PECVD / DC or AC plasma deposition of a 35 nm thick layer of polysiloxane from a precursor such as hexamethyldisiloxane (HMDSO).

A control piece T1 is also produced with a process A * identical to process A with the exception of step 1, which has not been carried out.

Method B:

Step 1: Glow discharge with an air pressure of 8.10 ^"2 mbar

120s

Step 2: Deposition of an Aluminum Layer with a Thickness of 70 to 100 nm by PVD Step 3: Plasma PECVD / DC or AC Deposition of a 45 nm Medium-Density Polysiloxane Layer from a precursor such as HMDSO.

Step 4: Treatment by ionic bombardment of nitrogen ions with an energy received by the 10kEV pieces

A control piece T2 is also produced with a process B * identical to process B with the exception of step 4, which has not been carried out.

Result:

Reference Process Limit temperature

iridescent appearance and / or

blistering

BP-TMC-180 at 170 ° C

T1 A * 150 ° C

BP-TMC-180 B 170 ° C

T2 B * 155 ° C Conclusion:

These results demonstrate that when the part is metallized, the ion bombardment carried out on high temperature polycarbonate materials makes it possible to limit the phenomena of blistering and the appearance of iridescence. It can also be observed that, for the polycarbonates treated, the results are similar, regardless of the order in which the different process steps were performed.

Example 5 Treatment of a Polypropylene Copolymer

Polypropylene copolymer parts are treated by ion bombardment in the chamber described in Example 1 under the following conditions:

- Nitrogen ion beam treatment with an energy of 5kEV.

The measures relating to degassing are carried out as in Example 2.

Result:

- untreated part:% T = 90% for a temperature of 1 10 ° C

treated part:% T = 90% for a temperature of 130 ° C.

Conclusion:

These results demonstrate that when the polypropylene part is treated, it is less sensitive to the degassing phenomenon.

Example 6 Characterization of the Layer Treated by Ion Bombardment Example on PMMA

In order to characterize the layer treated by ion bombardment, a differential scanning calorimetry (DSC) and a Fourier transform infrared spectroscopy (FTIR) are carried out.

Several pieces are studied for comparison and samples are taken.

The reference sample is untreated PMMA.

Samples are referenced as follows

DSC analysis: Samples Nos. 2 to 4 are prepared by extraction into ethyl acetate (true solvent of thermoplastic PMMA). The presence of an insoluble fraction (deposit) is recorded in samples 2 to 4. This insoluble fraction is dried and then analyzed by DSC in comparison with the dried soluble fraction and also analyzed from the reference sample. The thermogram resulting from the DSC analysis is presented in FIG.

It is noted that the glass transition temperature (Tg) disappeared in samples 2 to 4. In addition, it was found that none of the insoluble fractions had melted at the end of the DSC analysis (observation of capsule content).

FTIR spectroscopy analysis:

Samples 2, 3 and 5 were analyzed by FTIR (Infra-Red Fourier Transform Spectroscopy). The infared spectrum resulting from this analysis is given in FIG. 3. It is noted that ion bombardment treatment does not cause a fundamental change in the chemical nature of the material. This is a PMMA for the three samples tested. On the other hand, the disappearance of a specific peak of a CH3 (surrounded by a dotted circle in the figure) and the appearance of a characteristic peak of an OH bond (indicated by an arrow in the figure) indicating the creation of bridge (COC) between chains of macromolecules.

Example 7 Demonstration of the Effects on the Adhesion of the Layer Treated by Ion Bombardment Example on PMMA

Tests were performed to determine the effect on the adhesion of the surface of an ion beam treated PMMA layer. Each sample tested was subjected to a beam of ions from helium (He +). The dose of ion received varied from sample to sample.

The adhesion of the treated layer of these samples was evaluated by measuring the polar component of the surface energy of the treated layer of the corresponding sample. The surface energy in fact comprises a dispersive component and a polar component, and it is this polar component that is correlated with the adhesion of said surface. The higher this polar component, the better the adhesion.

The polar component of surface energy was calculated by a Zisman method method. The angle of a drop of solvent deposited on the surface treated with this surface was measured. By measuring three different solvents of known surface energy, the surface energy of the treated layer and its polar and dispersive components are measured. The table below gives the results obtained for the different samples.

Considering the polar component of the surface energy of these different treated samples (samples Nos. 1 to 4) and that of the untreated sample (no. 5), the best adhesion is obtained by the sample. Treaty No. 3. However, this adhesion is very close to that of sample No. 5, namely the control sample without treatment. For all other samples, the polar component, and therefore the adhesion is significantly reduced. The further away from the dose received by the sample 3, the less this adhesion is good.

These results show that the ion beam treatment at best has no influence on the adhesion of the treated layer, and for precise parameters. For most assays, ion beam treatment decreases adhesion.

It follows that for polymers whose adhesion is already low, such as PMMA, PC and high temperature PC, it will be difficult to metallize the surface of the polymer-based material (s) treated. Thus, for such materials, when it is desired both to metallize the material and to treat it by an ion beam, it is advantageous to deposit the metal layer on the polymer-based material beforehand. perform the ion beam treatment. For example, considering Example 4, even if methods A and B both make it possible to limit the blistering phenomena and the appearance of iridescence, it may be preferred to choose the method B in order to facilitate the step of metallization of the piece ..

Claims

1. Material based on polymer (s), having a superficial thickness with increased crosslinking.

2. Material based on polymer (s) according to claim 1, comprising a surface thickness having a decrease in the fraction of the free volume of the material.

3. The material of claim 2, wherein the free volume fraction is less than 0.4.

4. Material based on polymer (s) according to any one of claims 1 to 3, obtainable by the process comprising the step of:

at. treat by ion bombardment of a material surface

the surface thickness being obtained by said method.

5. Material according to any one of claims 1 to 4, wherein said surface thickness has a crosslinking resulting from direct bonds between the polymer molecules (s).

6. Material according to any one of claims 1 to 5, wherein said surface thickness is less than 5μηι from a surface of the material.

7. Material according to any one of the preceding claims, said polymer having a Young's modulus at 23 ° C. of greater than 100 MPa.

8. Process for treating a surface of a polymer-based material (s) by ion bombardment.

9. Process according to claim 8 for improving the temperature resistance properties of a polymer-based material.

10. Process according to claim 8 for improving the chemical resistance properties of a polymer-based material (s)

1. Method according to claim 8 for reducing the phenomena of irisation of a polymer-based material (s) comprising a reflective layer on a surface of said material in which the surface of the material is treated by ion bombardment.

12. Process according to claim 8 for improving the reflection properties of a polymer-based material

13. The method of claim 8 for reducing the degassing phenomenon likely to occur in a polymer-based material (s).

14. Part of a device, the part having an aesthetic, optical, chemical, electrical, thermal and / or mechanical function, the part being subjected to a high thermal stress and comprising a material according to any one of claims 1 to 7. .

15. Part for lighting and / or signaling device of a motor vehicle comprising a material according to any one of claims 1 to 7.

16. A method of treating a part of a device, particularly a lighting and / or signaling device of a motor vehicle, said method comprising the following steps:

deposition, in particular by PVD, of a layer, in particular a metal layer, on the surface of a polymer-based material,

17. The method of claim 16, wherein the step of treating the material by ion bombardment is carried out according to a method according to one of claims 8 to 13.

18. Use of a material according to any one of claims 1 to 7 for the manufacture of parts for a lighting device and / or signaling of a motor vehicle.