A METHOD OF MANUFACTURING A COATED POLYMER SUBSTRATE HAVING LOW EMISSIVITY

Abstract

The invention relates to a method of manufacturing a coated polymer substrate having low emissivity properties and a high hardness. The method comprises the steps of providing a polymer substrate; applying at least one adhesion promoting layer on one side of said polymer substrate; applying at least one silica or silica-based layer on said at least one adhesion promoting layer by a sol-gel process. The invention further relates to a coated polymer substrate having low emissivity properties, to a glass substrate provided with a coated polymer substrate and to the use of such a coated substrate as substrate having low emissivity properties.

Claims

1.-15. (canceled)

16. A method to manufacture a coated polymer substrate having an emissivity lower than 0.1 and a hardness of at least 2H pencil hardness, the method comprising: (a) providing a polymer substrate; (b) applying at least one adhesion promoting layer on one side of the polymer substrate; (c) applying at least one silica or silica-based layer on the at least one adhesion promoting layer by a sol-gel process, starting from a mixture comprising at least one partially condensed alkoxide precursor.

17. The method according to claim 16, wherein the silica or silica-based layer is obtained starting from a mixture comprising at least one partially condensed alkoxide precursor, a solvent and a catalyst.

18. The method according to claim 17, wherein the catalyst comprises at least one base or at least one acid.

19. The method according to claim 16, wherein the at least one partially condensed alkoxide precursor has a condensation degree of at least 60%.

20. The method according to claim 19, wherein the alkoxide precursor is fully condensed in the sol.

21. The method according to claim 16, wherein the alkoxide precursor is an alkoxy silane.

22. The method according to claim 21, wherein the silane is selected from the group consisting of tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), methyltriethoxysilane (MTES), vinyltrimethoxysilane (VTMS), 3-aminopropyltrimethoxysilane (APS), methacryloxypropyltrimethoxysilane (MAPTS), bis (triethoxysilyl)hexane, 1,6 bis (trimethoxysilyl) hexane or a combination thereof.

23. The method according to claim 16, wherein the silica or silica-based layer is deposited by roll coating.

24. The method according to claim 16, wherein the at least one adhesion promoting layer comprises a metal oxide selected from the group consisting of titanium oxide, indium oxide, tin oxide, zinc oxide, indium tin oxide, niobium oxide, zirconium oxide, either doped or non-doped and a mixture thereof.

25. The method according to claim 16, wherein the at least one adhesion promoting layer is deposited by sputter deposition.

26. A coated polymer substrate having low emissivity properties, the coated polymer substrate comprising: (a) a polymer substrate; (b) at least one adhesion promoting layer deposited on one side of the polymer substrate; (c) at least one silica or silica-based layer deposited on the adhesion promoting layer by a sol-gel process, starting from a mixture comprising at least one partially condensed alkoxide precursor, the coated polymer substrate having an emissivity lower than 0.1 and the at least one silica or silica-based layer having a hardness of at least 2H pencil hardness.

27. The coated polymer substrate according to claim 26, wherein the silica or silica-based layer has a thickness ranging between 0.1 m and 1 m.

28. The coated polymer substrate according to claim 26, wherein the adhesion promoting layer comprises a metal oxide, the metal oxide selected from the group consisting of titanium oxide, indium oxide, tin oxide, zinc oxide, indium tin oxide, niobium oxide, zirconium oxide, either doped or non-doped and a mixture thereof.

29. The coated polymer substrate according to claim 26, wherein the adhesion promoting layer has a thickness ranging between 0.01 m and 0.1 m.

30. A glass substrate with a coated polymer substrate according to claim 26.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0048] The invention will be further explained by means of the accompanying Figure.

[0049] The FIGURE illustrates the cross-section of a coated polymer substrate according to the present invention.

MODE(S) FOR CARRYING OUT THE INVENTION

[0050] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0051] The accompanying figure shows the cross-section of a coated polymer substrate 100 according to the present invention. The coated polymer substrate 100 comprises a polymer substrate 102, an adhesion promoting layer 104 and a silica or silica-based layer 106.

[0052] The polymer substrate 102 may comprise any polymer substrate. A preferred polymer substrate 102 comprises a polyester foil having a thickness of 75 m.

[0053] The adhesion promoting layer 104 comprises for example an oxide layer, for example a titanium oxide (TiO.sub.2) layer having a thickness ranging preferably between 0.02 m and 0.04 m. The TiO.sub.2 layer can be deposited by any technique known in the art. A preferred technique to deposit the TiO.sub.2 layer is by sputter deposition.

[0054] In a preferred preparation of the sol, ethanol was used as solvent and tetraethoxysilane (TEOS) was used as precursor. Possibly an organic linker such as bis (triethoxysilyl)hexane or 1,6 bis (trimethoxysilyl) hexane is added. Hydrochloric acid, acetic acid and formic acid were added as catalysts. The precursor was mixed under brisk stirring and added to the ethanol. Water was first acidified by mixing in the catalyst before it was added to the precursor mixture while stirring. The mixture is stirred until a clear sol was obtained. Precondensation was conducted by keeping the mixture during a certain time period at a predetermined temperature. The mixture was for example kept at 60 C. for one hour while stirring and refluxing.

[0055] The precondensation degree of said silane precursor in the sol is preferably high, i.e. higher than 60%, higher than 70%, higher than 80 or higher than 90%. In a preferred embodiment the mono-, di-, tri- and tetra substituted siloxane bonds designated respectively as Q1, Q2, Q3 and Q4 are fully condensed. The precondensation degree can be determined by NMR.

[0056] The silica or silica-based layer 106 is preferably applied on top of the adhesion promoting layer by roll coating and more preferably by gravure coating. The thickness of the applied layer is for example influenced by the speed of the substrate and the speed of the roll.

[0057] The silica or silica coating has a thickness preferably ranging between 0.25 m and 0.4 m.

[0058] A coated polymer substrate according to the present invention is subjected to a number of tests: hardness test, adhesion tests and low-e measurements. The tests are below described in more detail.

[0059] The hardness of the samples was evaluated by means of the Wolff-Wilborn method (ASTM D3363). To perform the tests an Elcometer 501 Pencil Hardness Tester is used. A coated substrate is placed on a firm horizontal surface and a pencil is held firmly against the coating, point away from the operator, at a 45 angle. The pencil is then pushed away from the operator. The hardness of the pencils is increased until one or both of the following defects mark the coating: [0060] a. Plastic deformation: a permanent indentation in the coating surface without cohesive fracture. [0061] b. Cohesive fracture: the presence of a visible scratch or rupture in the surface of the coating, material having been removed from the coating.

[0062] The degree of hardness of the pencil which damages the surface is taken as a measurement of scratch hardness e.g. 2H hardness.

[0063] The adhesion of the coating to the substrate is determined by a cross-hatch test. A cross-hatch test is a method to determine the resistance of coatings to separation from a substrate by utilizing a tool to cut a right angle lattice pattern into the coating penetrating all the way to the substrate.

[0064] In the cross-hatch test a cross-hatch pattern is made through the coating to the substrate. In a next step detached flakes of coating are removed by brushing with a soft brush. Subsequently pressure-sensitive tape is applied over the crosshatch cut. The tape is smoothed into place by using a pencil eraser over the area of the incisions. The tape is then removed by pulling it off rapidly back over itself as close to an angle of 180 . The adhesion is assessed on a 0 to 5 scale. The 0 to 5 scale is further explained in Table 1.

TABLE-US-00001 TABLE 1 0 the edges of the cuts are completely smooth, none of the squares of the lattice is detached. 1 detachment of small flakes of the coating at the intersections of the cuts. A cross-cut area not greater than 5% is affected. 2 the coating has flaked along the edges and at the intersections of the cuts. A cross-cut area greater than 5% but not greater than 15% is affected. 3 The coating has flaked along the edges of the cuts partly of wholly in large ribbons, and it has flaked partly or wholly on different parts of the squares. A cross-cut area greater than 15%, but not greater than 35% is affected. 4 The coating has flaked along the edges of the cuts in large ribbons and some squares have detached partly or wholly. A cross-cut area greater than 35% but not greater than 65% is affected. 5 Any greater degree of flaking that cannot even be classified by classification 4.

[0065] The emissivity of the samples is measured by subjecting the surface to be measured to the thermal radiation of the black body at a temperature of 100 C. for a short time. To obtain complete homogenous illumination of the measuring surface the radiator is designed in the form of a spherical half-space. A portion of the reflected radiation hits the radiation sensor through an opening in the radiator.

[0066] Determination of the emission level results from the comparison between the reflection values of the sample and the stored reference values of two calibrated standards. In the test TIR 100-2 apparatus was used, the calibrated standards were 0.010 and 0.962.

[0067] For the sample described above and illustrated in the accompanying figure the following results were obtained:

[0068] Hardness: 3 H pencil hardness

[0069] Adhesion test (cross-hatch test): class 0

[0070] Emissivity test: E=0.04