Patent ID: 8917452

Claim:
An optical diffusion film comprising a resin film structural member, the resin film structural member having, on a surface on at least one side thereof, a convex structure in which a plurality of convexities of irregular heights and sizes are continuously formed at random, without planar bottom portions between the convexities, and having tip points at highest points of the respective convexities and bottom points at lowest points at a periphery of the respective convexities, an average of vertical distances between the respective tip points and bottom points being taken as an average height (hm) and an average of horizontal distances between the respective tip points and bottom points being taken as an average distance (Sm), a gradient ratio (hm/Sm) being obtained by dividing the average height (hm) by the average distance (Sm), an average gradient angle (θm) being taken as an inverse tangent value of the gradient ratio (hm/Sm); a cross-sectional rectangular range being defined in which the average height (hm) and the average distance (Sm) are taken as one side in a vertical direction and another side in a horizontal direction, respectively; wherein: a range of the average gradient angle (θm) is from 5 degrees to 15 degrees; a standard deviation of the average gradient angle (θm) is within a range from 30% to 40% of the average gradient angle (θm); a regular reflectance of the optical diffusion film is 1% or less at a regular reflection angle with respect to incident light of an angle of 30 degrees from a normal direction of the film surface; when a total haze value, which is a sum of an internal optical haze value and an external optical haze value, is less than 10%, a diffuse reflectance at a first reflection angle that deviates by 20 degrees or more from the regular reflection angle is 0.001% or less, and a diffuse reflectance at a second reflection angle that deviates by 30 degrees or more from the regular reflection angle is 0.0001% or less; and when the total haze value is 10% or more, a diffuse reflectance at the first reflection angle is 0.05% or less and a diffuse reflectance at the second reflection angle is 0.005% or less; and within a measurement reference area of the convex structure, when a proportion that air occupies with respect to the cross-sectional rectangular range is taken as a void ratio, the void ratio is 20% or more and less than 50%.