Durable and scratch-resistant anti-reflective articles
Embodiments of durable, anti-reflective articles are described. In one or more embodiments, the article includes a substrate and an optical coating disposed on the major surface. The optical coating includes an anti-reflective coating and a scratch-resistant coating forming an anti-reflective surface. The article exhibits a maximum hardness of 12 GPa or greater, as measured on the anti-reflective surface by a Berkovich Indenter Hardness Test along an indentation depth of about 100 nm or greater. The articles of some embodiments exhibit a single side average light reflectance measured at the anti-reflective surface of about 8% or less over an optical wavelength regime in the range from about 400 nm to about 800 nm and a reference point color shift in transmittance or reflectance of less than about 2. In some embodiments, the article exhibits an angular color shift of about 5 or less at all angles from normal incidence to an incident illumination angle that is 20 degrees or greater.
1. An article comprising:
a substrate having a major surface; and
an optical coating disposed on the major surface and forming an anti-reflective surface, the optical coating comprising an anti-reflective coating,
the article exhibiting a maximum hardness of about 12 GPa or greater as measured on the anti-reflective surface by a Berkovich Indenter Hardness Test along an indentation depth of about 100 nm or greater;
wherein the article exhibits a single side average light reflectance measured at the anti-reflective surface of about 8% or less over an optical wavelength regime in the range from about 400 nm to about 800 nm and either one or both of:
article transmittance color coordinates in the (L*, a*, b*) colorimetry system at normal incidence under an International Commission on Illumination illuminant exhibiting a reference point color shift of less than about 2 from a reference point as measured at the anti-reflective surface, the reference point comprising at least one of the color coordinates (a*=0, b*=0) and the transmittance color coordinates of the substrate, and
article reflectance color coordinates in the (L*, a*, b*) colorimetry system at normal incidence under an International Commission on Illumination illuminant exhibiting a reference point color shift of less than about 5 from a reference point as measured at the anti-reflective surface, the reference point comprising at least one of the color coordinates (a*=0, b*=0), the color coordinates (a*=−2, b*=−2), and the reflectance color coordinates of the substrate,
wherein, when the reference point is the color coordinates (a*=0, b*=0), the color shift is defined by √((a* article ) 2 +(b* article ) 2 ),
wherein, when the reference point is the color coordinates (a*=−2, b*=−2), the color shift is defined by √((a* article +2) 2 +(b* article +2) 2 ), and
wherein, when the reference point is the color coordinates of the substrate, the color shift is defined by √((a* article −a* substrate ) 2 +(b* article −b* substrate ) 2 ).
2. The article of claim 1 , wherein the article exhibits an angular color shift of about 5 or less at an incident illumination angle that is 20 degrees or greater, referenced to normal incidence, under an International Commission on Illumination illuminant selected from the group consisting of A series illuminants, B series illuminants, C series illuminants, D series illuminants, and F series illuminants, wherein angular color shift is calculated using the equation √((a* 2 −a* 1 ) 2 +(b* 2 −b* 1 ) 2 ), with a* 1 , and b* 1 representing the coordinates of the article when viewed at normal incidence and a* 2 , and b* 2 representing the coordinates of the article when viewed at the incident illumination angle.
3. The article of claim 2 , wherein the article exhibits an angular color shift of about 5 or less at all incident illumination angles in the range from about 20 degrees to about 60 degrees.
4. The article of claim 2 , wherein the substrate has a hardness less than the maximum hardness of the article.
5. The article of claim 1 , wherein the article exhibits an abrasion resistance after a 500-cycle abrasion using a Taber Test on the anti-reflective surface comprising any one or more of
about 1% haze or less, as measured using a hazemeter having an aperture, wherein the aperture has a diameter of about 8 mm,
an average roughness Ra, as measured by atomic force microscopy, of about 12 nm or less,
a scattered light intensity of about 0.05 (in units of 1/steradian) or less, at a polar scattering angle of about 40 degrees or less, as measured at normal incidence in transmission using an imaging sphere for scatter measurements, with a 2 mm aperture at 600 nm wavelength, and
a scattered light intensity of about 0.1 (in units of 1/steradian) or less, at a polar scattering angle of about 20 degrees or less, as measured at normal incidence in transmission using an imaging sphere for scatter measurements, with a 2 mm aperture at 600 nm wavelength.
6. The article of claim 1 , wherein the anti-reflective coating comprises a plurality of layers, wherein the plurality of layers comprises a first low RI layer, and a second high RI layer.
7. The article of claim 6 , wherein the anti-reflective coating comprises a plurality of periods such that the first low RI layer and the second high RI layer alternate.
8. The article of claim 7 , wherein the anti-reflective coating comprises up to about 10 periods.
9. The article of claim 1 , wherein the single side average light reflectance is about 2% or less over the optical wavelength regime at a viewing angle in the range from about 6 degrees to about 40 degrees.
10. The article of claim 1 , wherein the substrate comprises an amorphous substrate or a crystalline substrate.
11. The article of claim 10 , wherein the amorphous substrate comprises a glass selected from the group consisting of soda lime glass, alkali aluminosilicate glass, alkali containing borosilicate glass and alkali aluminoborosilicate glass.
12. The article of claim 11 , wherein the glass is chemically strengthened and comprises a compressive stress (CS) layer with a surface CS of at least 250 MPa extending within the chemically strengthened glass from a surface of the chemically strengthened glass to a depth of layer (DOL) of at least about 10 μm.
13. The article of claim 1 , further comprising an easy-to-clean coating, a diamond-like coating or a scratch-resistant coating disposed on the optical coating.
14. The article of claim 1 , wherein the optical coating comprises a scratch resistant layer having a thickness in the range from about 1 micrometer to about 3 micrometers.
15. The article of claim 14 , wherein the anti-reflective coating is disposed between scratch resistant layer and the substrate.
16. The article of claim 14 , wherein the scratch resistant layer is disposed between the substrate and the anti-reflective coating.
17. The article of claim 14 , wherein the anti-reflective coating comprises a first portion and a second portion, and wherein the scratch resistant layer is disposed between the first portion and the second portion.