Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05F—STATIC ELECTRICITY; NATURALLY-OCCURRING ELECTRICITY
  • H05F3/00—Carrying-off electrostatic charges
  • H05F3/02—Carrying-off electrostatic charges by means of earthing connections

Definitions

• the invention relates to an article having a surface electrical resistance of less than 10 9 Ohms per square, in particular for combating the effects of static electricity.
• the accumulation of electrostatic charges on the surface of an article made of dielectric material can be detrimental to the functioning of electronic devices or equipment by creating electrical discharges generating electromagnetic disturbances (parasites) or destroying electronic components.
• thermo-optical characteristics such as the solar absorption coefficient or the infrared emissivity factor, well determined.
• the Applicant in patent FR-B-2 770 230, proposes a solar reflector for the thermal control of a spacecraft whose coating is of a lower cost than OSR or SSM.
• the surface layer of this coating is a polysiloxane layer about 50 ⁇ m thick applied on a metallized substrate.
• This protective layer is however not electrically conductive so that the problem associated with static electricity remains.
• thermo-optical properties A means which would make it possible to confer antistatic properties to the solar reflectors of FR-B-2 770 230, without significantly degrading their thermo-optical properties, would therefore be very useful.
• electrostatic charges can be created on the surface of electrically insulating materials by friction of the air (trioboelectric effect) or by friction with other insulating materials . As in space, the accumulation of these electrostatic charges can create harmful electric discharges for electronic equipment.
• Various means for eliminating these charges are known, such as the use of conductive materials in the volume (for example polymeric materials charged with conductive particles) or the application of a layer of electrically conductive paint.
• conductive materials in the volume for example polymeric materials charged with conductive particles
• a layer of electrically conductive paint for transparent articles, such as aircraft windows, there is no suitable antistatic treatment.
• the invention aims to satisfy these needs. More specifically, the invention relates to an article whose surface has a surface electrical resistance less than or equal to 10 9 Ohms per square, characterized in that it comprises a plurality of electrically conductive particles adhering to its surface and distributed over the latter. A surface electrical resistance of 10 9 ⁇ / D is considered to be the maximum admissible resistance for an acceptable antistatic effect.
• the particles adhere to the surface of a hardened layer of resin or varnish applied to the article.
• the electrically conductive particles should be less than 0.4 ⁇ m. If transparency is not an essential criterion, larger particles can be used.
• the electroconductive particles can be doped metal oxides such as
• - doped tin oxide for example with chlorine, fluorine, antimony oxide, indium oxide or bismuth oxide,
• - doped indium oxide for example with tin oxide, antimony oxide, bismuth oxide, titanium oxide or lead oxide; or
• the salts of the oxide to be doped and of the dopant are dissolved in water or an appropriate solvent and then co-precipitated slowly by the action of an organic acid in solution.
• organic acids are, for example, oxalic acid, citric acid, tartaric acid, malonic acid, maleic acid and the like.
• the precipitate After filtration and drying in an oven, the precipitate is calcined at 500-600 ° C and then the whole is doped by calcination at a temperature which depends on the type of oxide and dopant.
• the quantity of electroconductive particles adhering to the surface of the article is advantageously the lowest possible quantity which makes it possible to obtain an appropriate surface electrical resistance, that is to say ⁇ 10 9 ⁇ / square, while not degrading not notably the thermo-optical properties of the article, when the latter factor is important. For information and not limitation, it has been found that quantity of particles distributed over the surface of the article with an interparticle distance of the order of 10 to 20 ⁇ m usually gives satisfactory results.
• This distribution of the particles corresponds substantially to a surface concentration of 0.5 to 5 mg of particles per m 2 of surface when the particles consist of a doped oxide, and of 2 to 20 mg of particles per m 2 of surface when the particles are made of a metal.
• the invention also relates to a method for imparting to an article a surface electrical resistance less than or equal to 10 9 Ohms per square, characterized in that it comprises the application, on a soft and sticky surface of said article, of a plurality electrically conductive particles distributed over said surface, followed by hardening of said surface.
• a surface layer based on a hardenable resin is applied to said article, incompletely hardened so as to be soft and sticky, prior to the application of said electrically conductive particles.
• its thickness is between 5 and 50 ⁇ m.
• the layer of polymerizable or crosslinkable resin could be replaced by a varnish composition, for example consisting of a solution in a solvent of a polymeric material.
• the surface of said article is treated with a solvent for the material constituting said surface in order to generate said soft and sticky surface.
• the particles can be applied to the surface to be treated in the dry powder state using a pneumatic or electrostatic powder gun, like those sold by the company KREMLIN, or else in the form of a suspension in a medium. liquid, for example using a paint spray gun.
• a pneumatic or electrostatic powder gun like those sold by the company KREMLIN
• a suspension in a medium. liquid for example using a paint spray gun.
• Other modes of application of the particles will be obvious to a person skilled in the art.
• the resin can be chosen, by way of illustration and without limitation, from polysiloxane, epoxy, polyurethane, polyesters, acrylic resins, etc.
• the softening must be carried out using an appropriate solvent chosen according to the material to be softened.
• To soften methacrylate resins use is made, for example, of benzene, toluene, xylene, methylene chloride, chloroform, ethylene chloride, chlorobenzene, dioxane , methyl ethyl ketone, diisopropyl ketone, cyclohexanone, methyl formate or ethyl acetate.
• To soften polycarbonate resins for example, benzene, chloroform, acetone, methylene chloride, m-cresol, dioxane, cyclohexanone, pyridine or DMF are used.
• chloroform formic acid or dichloroethylene
• methyl ethyl ketone cyclopentanone
• cyclohexanone DMF
• nitrobenzene or DMSO are used, for example.
• FIG. 1 is a schematic view, in section, of an article made electrically conductive by incorporation of electrically conductive particles in its volume, according to the prior art.
• - Figure 2 is a schematic sectional view of an article according to the present invention, the surface of which has been softened before application of the electrically conductive particles.
• - Figure 3 is a schematic sectional view of another article, according to the present invention, to the surface of which a surface layer of resin has been applied.
• identical notations are used for analogous or identical elements.
• FIG. 1 shows, in section, an article A made of a material 1 charged, in its volume, with electrically conductive particles 2.
• the material 1 is thus made electrically conductive and does not accumulate electrostatic charges.
• FIG. 2 illustrates an article A made of a material 1 having the property of being able to be made, on the surface, soft and sticky. Electrically conductive particles 2 are applied and adhered to the surface of article A.
• the material 1 is transparent, for example if the article A is an airplane window, for example made of polycarbonate, its thermo-optical properties are little modified by the application of the particles 2 to its surface.
• FIG. 3 illustrates an article A, the surface of which has been successively covered with a metallized film 3 and then with a layer 4 of transparent crosslinkable resin.
• the combination of film 3 and layer 4 is intended to ensure effective thermooptic control.
• the film 3 is not an essential element of the present invention and could be omitted, for example, if the surface layer 4 itself possessed the desired thermo-optical characteristics or in applications where these thermo-optical properties would be unimportant .
• Electrically conductive particles 2 cover the external surface of the surface layer 4.
• the embodiment of the invention illustrated in Figure 3 is particularly suited to the field of space.
• the electrically conductive particles 2 have little or no effect on the thermo-optical properties of the surface layer 4.
• the embodiment according to FIG. 2 before application of the particles
• the material 1 is a polymer
• its surface can be dissolved superficially by means of an appropriate solvent, as described above.
• the particles 2 are applied to the surface of the resin before it is cross-linked or completely cured.
• the viscosity of the surface of the substrate that is to say of the material 1 (FIG. 2) or of the surface layer 4 (FIG. 3), must make it possible, when applying the electrically conductive particles 2, to maintain them on the surface by preventing them from penetrating deep.
• the surface is hardened, for example by crosslinking or total polymerization of the polymer or by evaporation of the solvent.
• the surface fixes the electrically conductive particles 2 and becomes electrically conductive or semi-conductive.
• the particles 2 are firmly fixed in the "gangue" that constitutes the substrate after it has hardened.
• the surface of the substrate comprising the electrically conductive particles 2 thus exhibits good mechanical characteristics, which is an advantage compared to the coatings of the SSM or OSR type mentioned above.
• This gangue also protects the electrically conductive particles 2 from humidity, which improves the stability of the surface electrical resistance over time.
• tin powder doped with antimony oxide the particles of which are less than 0.4 ⁇ m, suspended in a 50/50 diacetate mixture.
• ethylene glycol / polyethylene glycol (PM 400) with a concentration of 5% by mass, on a 50 ⁇ m thick layer of polysilsesquioxane with non-crosslinked hydroxyl functional groups, previously applied on a polished aluminum support of 30 ⁇ m thick.
• the amount of powder applied is 1 mg / m 2 of surface.
• the layer is crosslinked at 225 ° C for 1 hour.
• the amount of powder applied is 1 mg / m 2 of surface.
• the layer is cured at 225 ° C for 1 hour.
• tin powder doped with antimony oxide whose particles are less than 0.4 ⁇ m, suspended in a 50/50 diacetate mixture.
• ethylene glycol / polyethylene glycol (MW 400) with a concentration of 10% by mass, on a 50 ⁇ m thick layer of an incompletely crosslinked mixture obtained from polydiethoxysiloxane (3 parts by weight), polydimethylsiloxane with silanol endings (4 parts by weight), tetramethyldiethoxydisiloxane (4 parts by weight) and dibutyltin diacetate (0.014 parts by weight) previously applied to a polished aluminum support 30 micrometers thick.
• the amount of powder applied is 1 mg / m 2 of surface.
• Silver powder is sprayed with an air pistol, the particles of which have nanometric dimensions and are suspended with a concentration of 10% by mass in a 50/50 diacetate mixture.
• the amount of powder applied is 2 mg / m 2 of surface.
• the layer is cured at 225 ° C for 1 hour.
• EXAMPLE 5 Using an air pistol, sprayed tin oxide powder doped with antimony oxide suspended in a 50/50 mixture of ethylene glycol diacetate / polyethylene glycol ( PM ⁇ 400) with a concentration of 5% by mass, the particles of which are less than 0.4 ⁇ m on Plexiglas 8 , the surface of which has been previously softened under the action of trichlorethylene.
• the Plexiglas 8 thus treated has a surface electrical resistance of the order of 1 M ⁇ / D for a deposit of tin oxide of approximately 2 mg / m 2 .
• Silver powder the particles 2 of which have nanometric dimensions, is sprayed using a compressed air gun, suspended in a mixture
• the PVC thus treated has a surface electrical resistance of the order of 10 k ⁇ / Q for a silver deposit of approximately 20 mg / m 2 .
• the layer thus applied is polymerized at 225 ° C for 1 hour.
• the invention is not limited to the embodiments described and shown, provided by way of illustration and not limitation. In particular the manufacture of powders of conductive particles 2, their nature, the manufacture of powders of conductive particles 2, their nature, the manufacture of powders of conductive particles 2, their nature, the manufacture of powders of conductive particles 2, their nature, the manufacture of powders of conductive particles 2, their nature, the manufacture of powders of conductive particles 2, their nature, the manufacture of powders of conductive particles 2, their nature, the manufacture of powders of conductive particles 2, their nature, the manufacture of powders of conductive particles 2, their nature,
• the techniques for applying the powder or the nature of the surface layer 4 or of the material 1 of article A may be different.

Landscapes

• Laminated Bodies (AREA)
• Paints Or Removers (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Elimination Of Static Electricity (AREA)

Applications Claiming Priority (3)

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• 2001
  • 2001-04-27 FR FR0105712A patent/FR2824230B1/fr not_active Expired - Fee Related
• 2002
  • 2002-04-25 ES ES02732838T patent/ES2294135T3/es not_active Expired - Lifetime
  • 2002-04-25 WO PCT/FR2002/001420 patent/WO2002089535A1/fr active IP Right Grant
  • 2002-04-25 EP EP02732838A patent/EP1382229B1/de not_active Expired - Lifetime
  • 2002-04-25 AT AT02732838T patent/ATE375075T1/de not_active IP Right Cessation
  • 2002-04-25 DE DE60222758T patent/DE60222758T2/de not_active Expired - Lifetime

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