OPTICAL DIFFUSING FILMS AND METHODS OF MAKING SAME

• US 20150293272A1
• Filed: 11/19/2013
• Published: 10/15/2015
• Est. Priority Date: 11/21/2012
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Pham, Tri D., Kong, Steven H., Zhang, Haiyan, Aronson, Joseph T., Boyd, Gary T., Johnson, Nicholas A., Wang, Qingbing, Leaf, Michael R.
• Granted Patent: US 10,295,710 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B29C 59/026 of layered or coated substantially flat surfaces
• CPC Class Codes: B29L 2011/00 Optical elements, e.g. lenses, prisms
• CPC Class Codes: B30B 15/06 Platens or press rams
• CPC Class Codes: B30B 15/062 Press plates
• CPC Class Codes: B30B 3/005 Roll constructions
• CPC Class Codes: B30B 5/04 wherein the pressing means is in the form of an endless band
• CPC Class Codes: C25D 3/04 of chromium
• CPC Class Codes: C25D 3/38 of copper
• CPC Class Codes: C25D 5/12 at least one layer being of nickel or chromium
• CPC Class Codes: C25D 5/605 Surface topography of the layers, e.g. rough, dendritic or nodular layers
• CPC Class Codes: C25D 5/627 Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance
• CPC Class Codes: G02B 5/021 the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
• CPC Class Codes: G02B 5/0221 the surface having an irregular structure G02B5/0226 takes precedence
• CPC Class Codes: G02B 5/0268 characterized by the fabrication or manufacturing method
• CPC Class Codes: G02B 5/0278 used in transmission
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members

Abstract

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.

Claims

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 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.

11. An optical film, comprising:

a structured major surface comprising closely-packed structures arranged such that ridges are formed between adjacent structures, the structures being limited in size along two orthogonal in-plane directions;

wherein the structured major surface has a topography characterizable by a first and second Fourier power spectrum associated with respective first and second orthogonal in-plane directions, and wherein

to the extent the first Fourier power spectrum includes one or more first frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a first baseline, any such first frequency peak has a first peak ratio of less than 0.8, the first peak ratio being equal to an area between the first frequency peak and the first baseline divided by an area beneath the first frequency peak; and

to the extent the second Fourier power spectrum includes one or more second frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a second baseline, any such second frequency peak has a second peak ratio of less than 0.8, the second peak ratio being equal to an area between the second frequency peak and the second baseline divided by an area beneath the second frequency peak; and

wherein the structured major surface is characterized by a total ridge length per unit area in plan view of less than 200 mm/mm².

12. The film of claim 11, wherein the structured major surface comprises substantially no beads.

13. An optical film, comprising:

a structured major surface comprising closely-packed structures, the structured major surface defining a reference plane and a thickness direction perpendicular to the reference plane;

wherein the structured major surface has a topography characterizable by a first and second Fourier power spectrum associated with respective first and second orthogonal in-plane directions, and wherein

to the extent the first Fourier power spectrum includes one or more first frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a first baseline, any such first frequency peak has a first peak ratio of less than 0.8, the first peak ratio being equal to an area between the first frequency peak and the first baseline divided by an area beneath the first frequency peak; and

to the extent the second Fourier power spectrum includes one or more second frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a second baseline, any such second frequency peak has a second peak ratio of less than 0.8, the second peak ratio being equal to an area between the second frequency peak and the second baseline divided by an area beneath the second frequency peak;

wherein the closely-packed structures are characterized by equivalent circular diameters (ECDs) in the reference plane and mean heights along the thickness direction, and wherein an aspect ratio of each structure equals the mean height of the structure divided by the ECD of the structure; and

wherein an average aspect ratio of the structures is less than 0.15.

14. An optical film, comprising:

a structured major surface comprising closely-packed structures having curved base surfaces;

wherein the structured major surface has a topography characterizable by a first and second Fourier power spectrum associated with respective first and second orthogonal in-plane directions, and wherein

to the extent the first Fourier power spectrum includes one or more first frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a first baseline, any such first frequency peak has a first peak ratio of less than 0.8, the first peak ratio being equal to an area between the first frequency peak and the first baseline divided by an area beneath the first frequency peak; and

to the extent the second Fourier power spectrum includes one or more second frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a second baseline, any such second frequency peak has a second peak ratio of less than 0.8, the second peak ratio being equal to an area between the second frequency peak and the second baseline divided by an area beneath the second frequency peak; and

wherein the structured major surface provides an optical haze of less than 95%.

15. An optical film, comprising:

a structured major surface comprising closely-packed structures;

wherein the structured major surface has a topography characterizable by a first and second Fourier power spectrum associated with respective first and second orthogonal in-plane directions, and wherein

to the extent the first Fourier power spectrum includes one or more first frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a first baseline, any such first frequency peak has a first peak ratio of less than 0.8, the first peak ratio being equal to an area between the first frequency peak and the first baseline divided by an area beneath the first frequency peak; and

to the extent the second Fourier power spectrum includes one or more second frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a second baseline, any such second frequency peak has a second peak ratio of less than 0.8, the second peak ratio being equal to an area between the second frequency peak and the second baseline divided by an area beneath the second frequency peak; and

wherein the structured major surface provides an optical haze in a range from 10 to 60% and an optical clarity in a range from 10 to 40%.

16. An optical film, comprising:

a structured major surface comprising larger first structures and smaller second structures, the first and second structures both being limited in size along two orthogonal in-plane directions;

wherein the first structures are non-uniformly arranged on the major surface;

wherein the second structures are closely packed and non-uniformly dispersed between the first structures; and

wherein an average size of the first structures is greater than 15 microns and an average size of the second structures is less than 15 microns.

17. The film of claim 16, wherein the structured major surface has a topography characterizable by a first and second Fourier power spectrum associated with respective first and second orthogonal in-plane directions, and wherein to the extent the first Fourier power spectrum includes one or more first frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a first baseline, any such first frequency peak has a first peak ratio of less than 0.8, the first peak ratio being equal to an area between the first frequency peak and the first baseline divided by an area beneath the first frequency peak;

and

to the extent the second Fourier power spectrum includes one or more second frequency peak not corresponding to zero frequency and being bounded by two adjacent valleys that define a second baseline, any such second frequency peak has a second peak ratio of less than 0.8, the second peak ratio being equal to an area between the second frequency peak and the second baseline divided by an area beneath the second frequency peak.