MIRROR WITH IMPROVED DURABILITY

Abstract

A mirror includes a transparent substrate, at least one metallic reflecting layer and at least one protective paint layer on the back of the mirror. The mirror also includes an overlayer which is a barrier to corrosive elements, such as sulfides and/or chlorides, with a thickness of less than or equal to 6 m which is located on the protective layer. The process for the manufacture of such a mirror is also described.

Claims

1. A mirror comprising a transparent glass substrate, at least one metallic reflecting layer and at least one protective paint layer on the back of the mirror, wherein the mirror comprises an overlayer which is a barrier to corrosive elements with a thickness of less than or equal to 6 m which is located on the protective layer.

2. The mirror as claimed in claim 1, wherein the overlayer has a thickness of less than or equal to 3 m.

3. The mirror as claimed in claim 1, wherein the overlayer is the external layer of the mirror, located on the back of the mirror.

4. The mirror as claimed in claim 1, wherein the overlayer is an organic resin.

5. The mirror as claimed in claim 4, wherein the overlayer is an acrylic, vinyl, polyurethane, polyester, epoxy, alkyd or styrene resin.

6. The mirror as claimed in claim 1, wherein the overlayer is a layer of uniform thickness.

7. The mirror as claimed in claim 1, wherein the overlayer is a noncontinuous layer.

8. The mirror as claimed in claim 1, wherein the protective layer is a layer of water-based or organic paint.

9. The mirror as claimed in claim 1, wherein the thickness of the protective layer is at most 100 m.

10. The mirror as claimed in claim 1, wherein the metallic reflecting layer is a silver layer.

11. A process for the manufacture of a mirror, comprising: a. an optional stage of sensitization, b. an optional stage of activation of a surface of a transparent glass substrate to be coated, c. a stage of deposition of at least one metallic reflecting layer on the transparent glass substrate, d. a stage of deposition of at least one protective layer, e. a stage of deposition of an overlayer which is a barrier to corrosive entities with a thickness of less than 6 m, on said protective layer, making it possible to block the porosity of the latter, and f. a stage of drying said overlayer.

12. The process as claimed in claim 11, wherein the stage of deposition of overlayer is carried out by the liquid route by spraying, with a roller, by dip-coating, by curtain coating or by sprinkling, or by screen printing techniques.

13. The process as claimed in claim 12, wherein the stage of deposition of the overlayer is carried out by spraying or by curtain coating and is followed by a scraping stage, so as to obtain the thinnest possible overlayer.

14. The process as claimed in claim 12, wherein the stage of deposition of the overlayer is carried out with a roller which makes it possible to simultaneously carry out a scraping stage by rotation of the roller in the reverse direction, so as to obtain the thinnest possible overlayer.

15. The process as claimed in claim 11, wherein the drying stage is carried out under hot air, by IR curing and/or by UV curing.

16. A method comprising utilizing the mirror as claimed in claim 1 as indoor mirror.

17. The mirror as claimed in claim 1, wherein the corrosive elements include sulfides and/or chlorides.

18. The mirror as claimed in claim 1, wherein the overlayer has a thickness of less than or equal to 1 m.

19. The mirror as claimed in claim 9, wherein the thickness of the protective layer is at most 50 m.

20. The process as claimed in claim 11, wherein the corrosive elements include sulfides and/or chlorides.

Description

EXAMPLES

[0032] Samples were prepared and different tests were carried out on these samples in order to confirm their durability. A test has been developed to evaluate the resistance of the barrier layer and of the protective paint layer to the diffusion of sulfur-comprising compounds. In order to carry out this test, the percentage of light reflection is analyzed as a function of time on samples, the layer to be analyzed of which is covered with rubber. The samples on which the rubber is laid down are placed in a drying oven at 130 C. in order to accelerate the process of diffusion of the sulfur-comprising compounds present in the rubber. Light reflection measurements are subsequently carried out after 60 and 180 minutes, and the percentage of loss of light reflection is estimated with respect to a value measured at T=0 (before the positioning of the rubber).

[0033] Corrosion tests were carried out according to the standard EN ISO 9227. The measurements of thickness of layers are carried out by micrometric section measurement methods (Paint Borer 518 device from Erichsen). The resin thicknesses deposited were measured on a 2D/3D Taylor Hobson profilometer.

[0034] Measurements of adhesion of the layers are determined with the automatic cross hatch device from Erichsen (type 430) and correspond to the cross hatch test described in the standard NF ISO 2409 on paints and varnishes. This test consists in carrying out a visual interpretation of the surface of the cross hatch pattern on which flaking can be produced with a 1 mm comb. The classification takes place on a scale of 0 to 5 according to whether the layer comes off to a greater or lesser extent. A value of 0 indicates a very good adhesion of the layer.

[0035] Different mirrors with a size of 400 mm300 mm were prepared by depositing a metallic reflecting layer made of silver with a thickness of approximately 750 mg/m.sup.2 on a substrate made of glass of the Planilux type, after a stage of sensitization of the substrate using a solution based on SnCl.sub.2. The mirrors comprise a tin passivation layer deposited by the liquid route, with a thickness of approximately ten nanometers, and a silane-based tie primer layer with a thickness of approximately 10 nm located between the metallic reflecting layer made of silver and the protective paint layer.

[0036] Several samples were thus prepared by changing the paints used for the protective layer: [0037] paint 1: organic paint of alkyd type (One Coat LF3 Grey, sold by Fenzi), [0038] paint 2: water-based acrylic paint (WBLF4 LPB Blue 3025, sold by Fenzi).

[0039] Two different resins were tested to form the barrier overlayer: [0040] resin A: acrylate resin (G1000UV, sold by Henkel), [0041] resin B: melamine alkyd resin corresponding to the binder of the paint One Coat LF3 Grey sold by Fenzi.

[0042] The resins are applied with a film drawer and are then scraped. The resin B is dried by being placed in a drying oven at 180 C. for 15 minutes in order to make possible the crosslinking thereof. The resin A is crosslinked under UV radiation for 90 seconds (120 W/cm).

[0043] The sulfidizing corrosion performances of the different samples were evaluated in drying ovens at 130 C. The percentages of loss of light reflection at 60 minutes and at 180 minutes of the different samples tested are summarized in table 1 below.

TABLE-US-00001 TABLE 1 % of loss of % of loss of light reflection light reflection Sample at 60 min at 180 min Mirror 1 (not in accordance): 83 83 20 m paint 1 Mirror 2 according to the 51 80 invention: 20 m of paint 1 covered with 1 m of resin A Mirror 3 according to the 54 80 invention: 20 m of paint 1 covered with 2 m of resin B Mirror 4 (not in accordance >80 >80 with the invention): 20 m of paint 2 Mirror 5 (according to the 1 1 invention): 20 m of paint 2 covered with 6 m of resin A

[0044] On respectively comparing the mirror 1 with the mirrors 2 and 3, then the mirror 4 with the mirror 5, it is found that, after 60 min, the percentage of decrease is markedly smaller for the mirrors according to the present invention than for the mirrors not in accordance with the invention. After 180 min, the values obtained for the mirrors of the invention are lower than those for the comparative mirrors. This shows the beneficial effect of the barrier overlayer on the resistance to sulfidizing corrosion.

[0045] The results obtained for the different mirrors after a cycle in the CASS test (120 h at 50 C., aqueous solution of 50 g/l of NaCl and 0.26 g/l of anhydrous CuCl.sub.2, the pH being between 3.2 and 3.3) are summarized in table 2.

TABLE-US-00002 TABLE 2 Corrosion at Full face Sample the edges (m) corrosion Mirror 1 (not in accordance): Very high Very high 20 m paint 1 Mirror 2 according to the 200 Very slight invention: 20 m of paint 1 covered with 1 urn of resin A Mirror 3 according to the 113 Moderate invention: 20 m of paint 1 covered with 2 m of resin B Mirror 4 (not in accordance 750 Moderate with the invention): 20 m of paint 2 Mirror 5 (according to the 300 Very slight invention): 20 m of paint 2 covered with 6 m of resin A

[0046] The results obtained during the CASS tests show that the corrosion is markedly improved when a barrier overlayer of low thickness is applied to the protective paint layer. This is because the size of the region attacked on the edges of the mirror decreases when the barrier overlayer is deposited. The full face corrosion is also improved and becomes very slight or moderate for the mirrors according to the invention.

[0047] Adhesion measurements carried out in the cross hatch test for each of the samples have shown that the values obtained were 0 for all the mirrors according to the invention. The barrier overlayer layer thus adheres satisfactorily to the protective paint layers. In order to meet the specifications imposed by the standard ISO 2409, mirrors have to have a grade of less than 2 in the adhesion test.

[0048] All these measurements show a marked improvement in the durability of the mirrors according to the present invention.