WO2012038360A1

WO2012038360A1 - Surface-treated material comprising one or more polyamides

Info

Publication number: WO2012038360A1
Application number: PCT/EP2011/066172
Authority: WO
Inventors: Frédéric Moret; Marc Brassier; Alexis Chenet
Original assignee: Valeo Vision
Priority date: 2010-09-20
Filing date: 2011-09-19
Publication date: 2012-03-29
Also published as: FR2964972A1; FR2964972B1; EP2619036A1

Abstract

The invention relates to a material containing one or more polyamides, 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 said material and to the use thereof, in particular for the production of motor vehicle parts.

Description

Surface-treated polyamide material (s)

The present invention relates to a material based on polyamide (s) having a surface treatment to improve the properties of the surface of the material. The invention also relates to a process for obtaining this material and the use thereof, especially 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 role both technical and aesthetic. Furthermore, other parts, such as lamp holders, cradles or frames supporting elliptical module reflectors, fasteners (capsules) have an essentially technical function.

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 improved surface properties. The surface properties targeted by the invention relate more particularly to:

the appearance of the surface of the material, which must be satisfactory, whether for aesthetic reasons or for technical reasons such as not to disturb the beam of light emitted by the fire and / or projector, and - the permeability to the phenomenon degassing, the latter being capable of inducing the formation of condensates in the lighting device and / or signaling motor vehicle, generally waterproof.

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 on the other hand have the advantage of lightness and freedom in the forms obtained, because manufactured by injection molding techniques.

In particular, these parts can be made of polyamide (s).

Many factors can affect the surface properties of a polyamide part (s), including:

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

2. Surface defects of thermal origin such as blistering, iridescence, deformation, cracking or other. The parts are used in an environment likely to experience relatively high temperatures due to the presence of light sources, usually releasing heat. When these parts are reflective, for example by deposition of a reflective layer such as an aluminum layer, the increase in temperature may cause a phenomenon of deformation of the material, leading to blistering on the surface of the reflective layer or to an iridescence of the reflecting surface.

3. Degassing. The temperature increase of a material based on polyamide (s) causes a phenomenon of extraction of molecules with high vapor pressure (oligomers, additives, ...) which creates on the one hand aesthetic defects such as coloring or tarnishing of the material, which sometimes leads to parasitic chemical reactions and, on the other hand, when the material is in a sealed medium, which induces the formation of visible condensates of volatile compounds.

4. 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 material based on polyamide (s) having a surface thickness, that is to say on the surface, having an increased crosslinking. The polyamide-based material (s) according to the invention has in particular improved surface properties and in particular a better appearance of the surface. The.

By "polyamide (s)" is meant in particular one or more polymer (s) containing amide functions resulting from a polycondensation reaction between the functions carboxylic acid and amine, alone or in admixture. These polyamides can be homopolymers or copolymers, aliphatic (PA), semi-aromatic (polyphthalamide, PPA) or aromatic (PAA).

Preferably, these polyamides preferably have a Young's modulus at 23 ° C. of greater than 100 MPa (100 megapascals). These polymers have a particularly interesting rigidity. Moreover, they are fashionable by current methods. Preferably, these polymers have a Young's modulus at 23 ° C. of between 1000 and 15000 MPa, more particularly between 1000 and 5000 MPa.

Preferably, these polyamides will be chosen from the group consisting of the polyamides described in the table below or their mixture:

More preferably, the polyamide will be an aliphatic homopolymer, in particular PA66 or PA6.

By "based on" is meant a material comprising in volume at least 5% of polyamide (s), preferably at least 15%, more preferably at least 20%. By "increased crosslinking" is meant a degree of crosslinking greater than that of the polyamide (s) present in the rest of the material. In general, the degree of crosslinking of the polyamide (s) present in the rest of the material will correspond to the degree of crosslinking obtained under the usual conditions of polymerization of the polyamide (s), that is to say, without additional specific treatment of the polyamide (s).

For a polyamide, the degree of crosslinking D can be measured by the solubility in a solvent of the polyamide. Since the polyamide is soluble in the solvent, the crosslinked portions will be insoluble.

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

D = weight of the solvent-insoluble treated polyamide / total weight of the polyamide.

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.

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

Crosslinking of the material can also be demonstrated by differential scanning calorimetry (DSC).

The material based on polyamide (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 polyamide (s). The free volume is measurable for example by SAXS (acronym for "Small Angle X-Ray Scattering"). The fraction of free volume of a polyamide is generally between 0.6 and 0.4. On the other hand, in the material according to the invention, the thickness starting from the external surface 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 polyamide-based material (s) according to the invention can be obtained by the process comprising the step of treating the surface of the material by ion bombardment. 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 treatment by ion bombardment is applied to polyamides and will allow on the one hand, to create a three-dimensional network of polyamide (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 molecules of the polyamide (s). This gives the material a superficial thickness with increased crosslinking resulting from direct bonds between the polyamide molecules.

The ion bombardment treatment may also allow ions to be implanted in the object to treat its surface. In this case, it will make it possible to graft certain molecules of low molecular weight (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, the ion bombardment will be carried out 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 the order 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 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 through this treatment (see Example 1) without having to proceed with the deposition of a coating such as aluminization or the deposition of a layer of paint. In addition, the material also exhibits improved temperature creep resistance for semicrystalline polymers equivalent to that of a thermosetting material, and equivalent chemical, oxidation, and moisture resistance properties for a polymer. amorphous equivalent to those of a semi-crystalline polymer.

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.

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 surface of the material.

The invention also covers a method of treating the surface of a polyamide material (s) by ion bombardment. This treatment method is particularly effective for improving to improve the temperature resistance properties, the chemical resistance properties and the reflection properties (modification of the reflection coefficient) and / or to change the color of a material to polyamide base (s), for reducing the phenomena of iridescence of a polyamide-based material (s) comprising a reflective layer, preferably a metal layer, and for reducing the degassing phenomenon likely to occur in a material based on polyamide (s).

Thus the invention covers:

Process for treating a surface of a polyamide-based material by ion bombardment

A method of improving the reflection properties of a polyamide material (s) by treating a surface of the material by ion bombardment.

- A method of reducing the degassing phenomenon likely to occur in a polyamide-based material (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.

As indicated above, the material according to the invention is particularly suitable for the manufacture of parts for lighting and / or vehicle signaling devices. automotive, such as projector masks, hubcaps, pedestals, plates, reflectors, lamp holders, cradles or elliptical module frames, fasteners (capsules).

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 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.

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 high thermal load 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).

Other features and advantages of the invention will be described in the following examples with reference to Figure 1, which illustrates the system L * a * b * to describe a color. 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: in a first step, the parts are treated with Helium ion beam having a mean 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 2mm thick plate of the material to be tested is taken and put in contact by convection with a heat source up to 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 parameters of the ion bombardment 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, Coefficient of Linear Thermal

Expansion "): 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.

Claims

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

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

3. Material according to claim 2, wherein the fraction of the free volume relative to the volume of the material is less than 0.4.

4. Material based on polyamide (s) according to any one of claims 1 to 3, obtainable by the method comprising the step of: a. treat by ion bombardment a surface of the material

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 polyamide (s) having a Young's modulus at 23 ° C greater than 100 MPa.

8. A method of treating a surface of a polyamide material (s) by ion bombardment.

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

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

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

12. 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.