METHOD FOR EVALUATING THE SENSITIVITY OF A GLAZING TO FORMING QUENCH MARKS

Abstract

A method for evaluating the sensitivity of a glazing to forming quench marks depending on its anisotropy, the sensitivity being evaluated by computing parameter σ.sub.v, the quench marks resulting from different optical phase shifts in different regions of the glazing for a vision in transmission or reflection and from either side of the glazing, the method including computing a transmission parameter T1, T2 through face 1 or 2 or a reflection parameter R1, R2 from face 1 or 2, this computation being done for a region of the glazing without optical phase shift and for a region of the glazing inducing an optical phase shift δ; computing a parameter ΔE(δ) corresponding to the color difference between said regions, based on at least one of T1, T2, R1, R2, and computing σ.sub.v by applying a function G dependent on computed ΔE(δ) and where appropriate on the one or more corresponding δ.

Claims

1. A method for evaluating a sensitivity of a glazing to forming quench marks depending on its anisotropy, said sensitivity being evaluated by computing a parameter σ.sub.v, said glazing comprising a face 1 and a face 2, both making contact with an exterior environment, said quench marks resulting from different optical phase shifts in different regions of the glazing for a vision in transmission or in reflection and from either side of the glazing, said method comprising a computer-implemented step of computing at least one parameter of transmission through face 1 or through face 2, called T1 or T2, or at least one parameter of reflection from face 1 or from face 2, called R1 and R2, said computation being carried out for a region of the glazing inducing no optical phase shift and for a region of the glazing having birefringence axes oriented at a given angle with respect to a plane of incidence and inducing an optical phase shift δ in a light ray in a given optical phase-shift domain, for a given polarization of the light ray and for a given angle of incidence of the light ray; a computer-implemented step of computing at least one parameter ΔE(δ) corresponding to a color difference between the region of the glazing inducing no optical phase shift and the region of the glazing inducing the optical phase shift δ, on the basis of at least one of the parameters T1, T2, R1, R2, then computing the parameter σ.sub.v by applying a function G dependent on the one or more computed ΔE(δ) and where appropriate on the one or more corresponding optical phase shifts δ.

2. The method as claimed in claim 1, wherein the function G is equal to an arbitrary function F2 depending only on a σ.sub.δ determined for a given δ or on a plurality of σ.sub.δ each determined for a different δ, each σ.sub.δ being equal to the a quotient of ΔE(δ) divided by a function F1(δ) dependent only on the corresponding δ.

3. The method as claimed in claim 2 wherein the function F2 is a polynomial function of the one or more σ.sub.δ.

4. The method as claimed in claim 1, wherein the function F1(δ) delivers for each δ in question a value comprised between (sin.sup.2δ)-1 and (sin.sup.2δ)+1.

5. The method as claimed in claim 4, wherein the function F1(δ) delivers for each δ in question a value comprised between (sin.sup.2δ)-0.5 and (sin.sup.2δ)+0.5.

6. The method as claimed in claim 5, wherein the function F1(δ) is equal to sin.sup.2δ.

7. The method as claimed in claim 1, wherein the one or more optical phase shifts δ are comprised in an optical phase-shift domain ranging from 0 to π/2.

8. The method as claimed in claim 7, wherein the one or more optical phase shifts δ are comprised in an optical phase-shift domain ranging from 0 to π/15.

9. The method as claimed in claim 8, wherein the one or more optical phase shifts δ are comprised in an optical phase-shift domain ranging from 0 to π/30.

10. The method as claimed in claim 2, wherein the one or more σ.sub.δ used for the computation of σ.sub.v are chosen for a domain of the optical phase shift δ in which σ.sub.δ varies by less than 0.5 and when δ passes from the limit of ΔE/F1(δ) when δ tends toward 0 to the highest value in this domain.

11. The method as claimed in claim 2, wherein σ.sub.v=F2(lim.sub.δ.fwdarw.0ΔE/F1(δ)).

12. The method as claimed in claim 11, wherein σ.sub.v=lim.sub.δ.fwdarw.0ΔE/F1(δ).

13. The method as claimed in claim 12, wherein σ.sub.v=lim.sub.δ.fwdarw.0ΔE/sin.sup.2(δ).

14. The method as claimed in claim 1, wherein the method is applied to two different glazing substrates V1 and V2 to be compared on a same measurement scale, leading to two parameters σ.sub.v denoted σ.sub.v1 and σ.sub.v2, respectively.

15. The method as claimed in claim 14, wherein the glazing substrate V1 is identical to the glazing substrate V2 except that the glazing substrate V1 further comprises a coating system comprising a thin layer or a stack of thin layers on one or both of its two main faces.

16. A process for manufacturing a glazing comprising carrying out the method, which is applied to said glazing, as claimed in claim 1, followed by production of the glazing.

17. A process for manufacturing the glazing V1, comprising carrying out the method of claim 15, then producing the coating system.

18. (canceled)

19. A non-transitory computer-readable storage medium on which a computer program comprising program-code instructions or instruction segments for executing at least one computer-implemented computing step of the method of claim 1 is stored.

20. The method as claimed in claim 10, wherein the one or more σ.sub.δ used for the computation of σ.sub.v are chosen for a domain of the optical phase shift δ in which σ.sub.δ varies by less than 0.2 when δ passes from the limit of ΔE/F1(δ) when δ tends toward 0 to the highest value in this domain.

Description

Example 1

[0069] It is proposed to determine the influence of a stack of thin layers comprising, in particular, a layer of 8 nm of silver on the quench marks of a glass sheet of Planiclear trademark (sold by Saint-Gobain Glass France) of 10 mm thickness.

[0070] To do this, values of σ.sub.δ are determined for various values of the optical phase shift δ=π/n, with n ranging from 2 to 50, for an angle of incidence of 65°, for the four spectra of the configurations T1, T2, R1 and R2, and for the coated glass sheet (see FIG. 1) and for the uncoated glass sheet (see FIG. 2).

[0071] It may be seen in FIGS. 1 and 2 that the smaller the optical phase shift δ, the more σ.sub.δ is independent of the optical phase shift δ. For this reason, the relevant optical phase-shift domain in the context of the invention is preferably close to zero and starts at zero. In particular, the limit of σ.sub.δ when δ tends toward 0 is a good value for characterizing a glazing.

[0072] In the case of the uncoated glass sheet (FIG. 2), as the glazing is symmetric, face 1 being identical to face 2, the values of σ.sub.δ in T1 and in T2 are identical, and the values of σ.sub.δ in R1 and in R2 are also identical. These values are here the Fresnel coefficients.

[0073] Comparing FIGS. 1 and 2 shows that the values of σ.sub.δ in configurations T1 and T2 are hardly influenced by the coating. In contrast, for an identical optical phase shift, the values of σ.sub.δ in configurations R1 and R2 are much lower in the presence of the coating. The coating will therefore have, for an angle of incidence of 65°, an effect that will, with respect to the bare glazing substrate, conceal quench marks in configurations R1 and R2.

[0074] The limiting value of σ.sub.δ when δ tends toward 0 has moreover been calculated, but for an angle of incidence varying from 45 to 85°. FIG. 3 shows the results for Planiclear coated with the coating and FIG. 4 shows the results for bare Planiclear.

[0075] The maximum sensitivity in the exterior reflection (R2) for the coated glass is from 17.5 to 51° whereas it is from 41 to 62° for the bare glass. On the whole, the coating will therefore have, with respect to the bare glazing substrate, an effect of concealing quench marks.

Example 2

[0076] The process was the same as for example 1 except that the coating comprises a stack of thin layers comprising two silver layers of 12 and 22 nm thickness, respectively, deposited on face 1 of a Planiclear glass sheet of 10 mm thickness. FIG. 5 shows the results. Here again, the smaller the optical phase shift δ, the more σ.sub.δ is independent of the optical phase shift δ. It is also possible to state that the coating will have, with respect to the bare glazing substrate, a concealing effect at 65° on quench marks in configurations R1 and R2 (compare with FIG. 2). The value of σ.sub.δ when δ tends toward 0 has moreover been calculated, but for an angle of incidence varying from 45 to 85°. FIG. 6 shows the results. Here as well, the maximum sensitivity is lower with the coating than with the bare glass (compare with FIG. 4) and it may be stated that the coating attenuates the visibility of quench marks.