Optical diffusing films and methods of making same
Optical diffusing films are made by microreplication from a structured surface tool. The tool is made using a 2-part electroplating process, wherein a first electroplating procedure forms a first metal layer with a first major surface, and a second electroplating procedure forms a second metal layer on the first metal layer, the second metal layer having a second major surface with a smaller average roughness than that of the first major surface. The second major surface can function as the structured surface of the tool. A replica of this surface can then be made in a major surface of an optical film to provide light diffusing properties. The structured surface and/or its constituent structures can be characterized in terms of various parameters such as optical haze, optical clarity, Fourier power spectra of the topography along orthogonal in-plane directions, ridge length per unit area, equivalent circular diameter (ECD), and/or aspect ratio.
1. A method of making a structured surface, comprising:
forming a first layer of a metal by electrodepositing the metal using a first electroplating process resulting in a first major surface of the first layer having a first average roughness; and
forming a second layer of the metal on the first major surface of the first layer by electrodepositing the metal on the first major surface using a second electroplating process, the second electroplating process including an organic grain refiner, resulting in a second major surface of the second layer having a second average roughness smaller than the first average roughness.
2. The method of claim 1 , further comprising:
providing a base surface having a base average roughness;
wherein the first layer is formed on the base surface, and wherein the first average roughness is greater than the base average roughness.
3. The method of claim 1 , wherein the metal is copper.
4. The method of claim 1 , wherein the first electroplating process uses a first electroplating solution that contains at most trace amounts of an organic leveler.
5. The method of claim 1 , wherein forming the first layer results in the first major surface comprising a plurality of non-uniformly arranged first structures.
6. The method of claim 5 , wherein forming the second layer results in the second major surface comprising a plurality of non-uniformly arranged second structures.
7. The method of claim 6 , further comprising:
forming a third layer of a second metal on the second major surface by electrodepositing the second metal using an electroplating solution of the second metal.
8. The method of claim 7 , wherein the second metal comprises chromium.
9. A microreplication tool made using a method according to claim 1 , such that the microreplication tool has a tool structured surface corresponding to the second major surface.
10. The microreplication tool of claim 9 , wherein the tool structured surface corresponds to an inverted form of the second major surface or a non-inverted form of the second major surface.