MXPA97007349A - Surface coating for insulating materials, method of obtaining it and its application to protect boxes isolated - Google Patents

Abstract

A surface coating on a substrate of insulating material, which ensures protection against electromagnetic interference in corrosive media, comprises two stacked metallic layers, the first layer, in contact with the substrate, is a layer of nickel-based alloy containing approximately 2% to 10% by weight of an element of group VB of the periodic table of the elements, the second is a surface layer of silver or one of its alloys, the applications include boxes of insulating material for electrical or electronic components, including a protection consisting of a surface coating of this ti

Description

SURFACE COATING FOR INSULATING MATERIALS, METHOD OF OBTAINING IT AND ITS APPLICATION TO PROTECT INSULATING BOXES CfíriPO DE Lñ INVENCIÓN The present invention relates to a surface coating of insulating material. More precisely, the invention relates to a surface coating for parts of insulating material designed to ensure protection against electromagnetic interference in a corrosive environment. Said insulating materials include polymeric materials and mixed materials of the type including, but not limited to, a resin based on polyrnepene rnatepal with reinforcing fibers. An application of the invention and the invention is the production of electromagnetic protection for boxes of electrical or electronic components made of polirnepc or mixed materials. Therefore, the invention also refers to said protected boxes of polyurethane or mixed material for electrical or electronic components. Another application of the present invention is the production of a protective layer for severely constrained subject parts, such as corrosion, which require the presence of a protective metal layer with superior adhesion, regardless of external constraints.

BACKGROUND OF THE INVENTION The industrial processes for metallizing parts of polyester material, in particular the so-called "wet process" and the so-called "vacuum evaporation" process, and the application of paint loaded with metal particles, are already known per se. In general terms, the wet process consists of properly preparing the surface, including steps of satin finishing and activation, followed by depositing a copper layer in two steps, the first using chemical conversion, the second using electrolysis. The vacuum evaporation process, used very widely in decorative techniques, consists of applying a very thin film of metal, generally aluminum, to the part to be coated by evaporation in a vacuum. Because it is thin, this film is very fragile. For this reason, it is often protected with a varnish. In some cases, the metallization is sometimes preceded by an activation treatment using an atmospheric plasma or a vacuum. Finally, conductive paints consisting of resins with metal particles, for example copper, aluminum, silver, etc., are sometimes used, but have high resistivities and the coating thickness is not controlled with great accuracy. The technical advances and the increasingly demanding requirements for performance indicate that current solutions have reached their limits and can not be used in many cases. In particular, the new applications of electronics are leading to the use of portable equipment and more and more varied conditions, in particular exterior structures that introduce a new restriction, especially resistance to different forms of corrosion. This phenomenon may deteriorate or even destroy the metallic layer, as in the case of aluminum and copper, and may also deteriorate the interface between the polymer substrate and the metal coating, leading to partial or total separation of the latter. In both cases, the electromagnetic protection of the components is no longer secure. An object of the present invention is to provide a surface coating which, while having excellent adhesion to plastic and mixed materials, together with a remarkable resistance to corrosion, especially salt corrosion, provides high quality protection against interference electromagnetic, and the adhesion of which is not affected by exposure to a corrosive atmosphere. The applicant has developed a surface coating composition for a substrate of insulating material that satisfies the above object by ensuring durable electromagnetic protection, even in corrosive atmospheres.

BRIEF DESCRIPTION OF THE INVENTION The invention consists of surface coating on a substrate of insulating material, adapted to ensure protection against electromagnetic interference in corrosive media, comprising two stacked layers of metal, the first, in contact with said substrate, is an alloy layer nickel base containing approximately 80% to 98% by weight of nickel, the second, is a surface layer based on metallic silver or one of its alloys. In a preferred embodiment of the invention, the nickel-based alloy contains at least one metal of group VB of the periodic table of the elements, the most usual being vanadium, in an amount of between about 2% and 20% by weight . The amount of metal of group V B of the periodic table of the elements in the nickel-based alloy is advantageously between about 5% and 10% by weight. In a way that has yet to be explained, the simultaneous properties of protection against electromagnetic interference, corrosion resistance and adhesion, are optimal when the nickel-based alloy layer and the metallic silver base layer have thicknesses between 0.02 urn and 1 μm and between 0.2 μ and 2 μ, respectively. These qualities can deteriorate if the thickness is greater than indicated.

For smaller thicknesses, the adhesion is excellent but the resistance to corrosion and electromagnetic protection are insufficient. The expert is well aware that silver-based alloys have a greater resistivity than metallic silver. Consequently, in the case of a silver-based alloy, the thickness of the layer must be multiplied by the ratio between the resistivity of said silver-based alloy and the resistivity of metallic silver. The surface coating of the present invention is particularly advantageous and performs particularly well because simultaneously: it provides high quality protection against electromagnetic interference due to its excellent electrical conductivity. -It has excellent adhesion to plastic and mixed materials. -It has excellent resistance to corrosion, especially salt corrosion. -their adhesion is not affected at all by exposure to the corrosive atmosphere. The two-layer surface coating of the invention can be applied by any suitable surface treatment method or technology without its properties being affected thereby. However, in a preferred but not exclusive embodiment, the coating of the invention is applied by means of a vacuum deposition technology, obtaining the best results with the electronic cathode deposit technique. The surface coatings of the present invention have an application in cases of protection of electrical or electronic components, in particular boxes of portable telephones.

DETAILED DESCRIPTION OF THE INVENTION The non-limiting examples described below illustrate the invention.

EXAMPLES In all of the following examples, polymer test pieces were coated. First the surface resistivity R [], also known as the resistance per unit area, was measured and is representative of the protection against electromagnetic interference, and the adhesion of the coating was determined using the normal test of detachment that includes the application of a Adhesive tape after scratched with crossed lines. The test pieces were then subjected for 48 hours to the accelerated corrosion test known as the "salt spray" test, carried out in accordance with French Standard NF C 20-711. After washing and drying the test pieces, they were subjected again to the surface resistivity and adhesion tests, using the release test of the French Standard NF T 30-038; The final result indicated the level of protection produced by the coating and its durability.

EXAMPLE 1 (Comparative) A layer of aluminum of 3 μm was deposited on a batch of five pieces by activation of oxygen plasma followed by deposit by evaporation in vacuum. Before the corrosion test, the mean resistivity, REI, was 60 mOCJ. The adhesion was excellent (there was no detachment in the tensile test). After exposure to the salt spray, the RCJ resistivity was 150 rnOCl at the measurement points, confirmed by visual observation: the coating had become, at least on the surface, insulating alumina, with a greater or lesser degree of hydration . At the same time, the adhesion became very weak, the. Coating is easily peeled off on the adhesive tape.

EXAMPLE 2 (Comparative) A copper deposit of 5 μm thickness was applied to a second batch of five test pieces by means of the conventional aqueous phase technique: satin finish, activation, copper chemical deposit, copper electrolytic deposit. Before the corrosion test, the mean resistivity RE] was 10 mOH and the adhesion was excellent. After exposure to the sa spray, the appearance of the coating indicated the abundant presence of verdigris, the resistivity H was between 20 mOE3 and 80 mOH and the adhesion could not be measured due to the partial separation and desquamation of the coating at many points on the test pieces.

EXAMPLE 3 (Comparative) A conductive paint sold by BECKER INDUSTRIE, under its reference 599-Y 2000, was applied to a third batch of test pieces and then polished according to the manufacturer's recommendations. The average thickness of the film was 35 μm ± 10 μrn. Before the corrosion test, the average resistivity R? it was 50 mOil and the adhesion was excellent since the tensile test did not cause any detachment. After corrosion, the appearance of the coating had changed little and the resistivity RE 3 was between 320 rnOE3 and 450 rnOC3. Adhesion was partially degraded as the test showed detachment at a few points.

EXAMPLE 4 A fourth batch of 15 test pieces was divided into three groups, A, B and C, each of five test pieces. Afterwards, each batch received a first layer of nickel alloy including 9% vanadium (the layer in contact with the substrate) followed by a layer of metallic silver (surface layer), the two layers were successively deposited by electronic deposit of cathode in a vacuum. The respective thickness of the layers deposited on the test pieces of the three groups were as indicated in Table 1 below: TABLE 1 The results of surface resistivity and adhesion tests, before and after corrosion, are indicated in Table 2 below: TABLE 2 Note that none of the test pieces of the three groups changed in appearance after corrosion. Adhesion was excellent, since the test showed no peel points for groups A and B and only a few peel points for group C, where the thickness of the coating, probably too large, did not produce a perfect quality skin. . The resistivity RE] was remarkably stable. The very low values of RE] measured for groups B and C indicated an excellent level of protection, -the values of RE] measured for group A, although they are acceptable, represented a slightly lower level of performance, probably associated with the small thickness of the layers. The person skilled in the art will understand that although the invention has been described and shown by a specific embodiment, many variants may be contemplated without departing from the scope of the invention defined in the appended claims.

Claims (12)

NOVELTY OF THE INVENTION CLAIMS

1. - A surface coating on a substrate of insulating material, adapted to ensure protection against electromagnetic interference in corrosive media, comprising two layers of stacked metal, the first, in contact with said substrate, is a layer of nickel-based alloy which it contains approximately 80% to 98% by weight of nickel, the second is a surface layer based on metallic silver or one of its alloys.

2. The coating according to claim 1, further characterized in that said nickel-based alloy contains between about 2% and 20% by weight of at least one metal of group V B of the periodic table of the elements.

3. The surface coating according to claim 2, further characterized in that the concentration in the nickel-based alloy of said element of group VB of the periodic table of the elements, is between approximately 5% and 10% in weight.

4. The surface coating according to claim 2, further characterized in that said element of group V B of the periodic table of the elements is vanadium.

5. - The surface coating according to claim 1, further characterized in that the thickness of said layer of nickel-based alloy is between 0.02 μ and 1 μm.

6. The surface coating according to claim 1, further characterized in that said surface layer is made of metallic silver and the thickness of said layer based on metallic silver is between 0.2 μm and 2 μm.

7. The surface coating according to claim 1, further characterized in that said surface layer is a silver-based alloy and the thickness of said layer based on silver alloy is between nx 0.2 μm and nx 2 μm, where "n" is the value of the relationship between the resistivity of said silver-based alloy and the resistivity of metallic silver.

8. The surface coating according to claim 1, further characterized in that said insulating material is chosen from polymeric materials and mixed materials.

9. The surface coating according to claim 8, further characterized in that said mixed material comprises a polymer and reinforcing fibers.

10. The surface coating according to claim 1, further characterized in that said nickel-based alloy layers and said silver-based surface layer are applied by vacuum deposition technology.

11. The surface coating according to claim 10, further characterized in that said vacuum deposition technology is electronic cathode deposit.

12. A box of protected insulating material for electrical or electronic components, wherein the protection is a surface coating according to any of claims 1 to 11.