Antifogging member
An antifogging member has an concave-convex surface defined by convex portions and concave portions, a Fourier-transformed image obtained by applying two-dimensional fast-Fourier transform processing to an observation image of the concave-convex surface exhibits a circular or annular pattern having an origin for which the absolute value of the wave number is 0 μm −1 as the substantial center thereof, the convex portions and the concave portions extend in random directions in plan view, the average pitch of the concave portions and convex portions of the concave-convex surface is in the range of 50-250 nm, and the water contact angle on a smooth surface formed from the material constituting the concave-convex surface is 90 degrees or less. The antifogging member has high abrasion resistance, minimal haze, and a small difference in chromaticity and transmittance when viewed from oblique and perpendicular directions, and the transmittance and chromaticity thereof are not azimuth dependent.
1. An antifogging member having a concave and convex surface defined from a convex portion and a concave portion, wherein
a Fourier-transformed image obtained by performing a two-dimensional fast Fourier-transform processing on an observation image of the concave and convex surface shows a circular or annular pattern substantially centered at an origin at which an absolute value of wavenumber is 0 μm −1 ,
the convex portion and the concave portion extend in random directions as viewed in plan view,
an average pitch of concavities and convexities in the concave and convex surface is in a range of 50 to 250 nm,
a contact angle of water on a flat and smooth surface formed from a material forming the concave and convex surface is not more than 90°,
the concave and convex surface is defined from a plurality of convex portions and a concave portion surrounding the plurality of convex portions, and
a total of perimeters of convex portions included in the plurality of convex portions and having a perimeter of not more than seven times the average pitch of the concavities and convexities is not more than 10% of a total of perimeters of the plurality of convex portions.
2. The antifogging member according to claim 1 , wherein an average depth of the concavities and convexities in the concave and convex surface is in a range of 15 to 500 nm.
3. The antifogging member according to claim 1 , wherein the concave and convex surface is defined from a plurality of concave portions and a convex portion surrounding the plurality of concave portions.
4. The antifogging member according to claim 1 , wherein a width of the convex portion at a position lower than a top of the convex portion by D (depth of concavities and convexities)/2 is in a range of 20 to 95% of the average pitch of the concavities and convexities.
5. The antifogging member according to claim 4 , wherein the width of the convex portion at the position lower than the top of the convex portion by D (depth of concavities and convexities)/2 is in a range of 50 to 95% of the average pitch of the concavities and convexities.