Optical film with defect-reducing surface and method for making same

Abstract

An optical film has surface that reduces the occurrence of optical defects in a display using the film. In particular, the surface has randomized characteristics that reduce such defects as wet-out, Newton's rings, and Moiré effects. The film has a first surface free of regular structure, the first surface having a plurality of local height maxima, a characteristic measure of the first surface having a random value within a predetermined range. The film also has a second surface opposing the first surface. A method of making an optical film includes embossing a pattern lacking regular structure onto a first surface of a film, wherein the first surface has a plurality of local height maxima, a characteristic measure of the first surface having a random value within a predetermined range. The characteristic measure may be a difference between the actual heights and a nominal height of the film surface, average separation between the local height maxima on the surface, or slope angle of the first surface proximate a local height maximum.

We claim:  
     
         1 . An optical film comprising: 
 a first surface free of regular structure, the first surface having a plurality of local height maxima, a characteristic measure of the first surface having a random value within a predetermined range; and    a second surface opposing the first surface.    
     
     
         2 . An optical film as recited in  claim 1 , wherein the local height maxima have actual heights and the characteristic measure is a difference between the actual heights and a nominal height.  
     
     
         3 . An optical film as recited in  claim 1 , wherein the predetermined range is 5 microns.  
     
     
         4 . An optical film as recited in  claim 1 , wherein the predetermined range is 1.5 microns.  
     
     
         5 . An optical film as recited in  claim 1 , wherein the characteristic measure is an average separation between the local height maxima.  
     
     
         6 . An optical film as recited in  claim 1 , wherein the average separation between local height maxima on the first surface is in the range from 50 μm to 500 μm.  
     
     
         7 . An optical film as recited in  claim 5 , wherein an average separation between local height maxima on the first surface is in the range from 100 μm to 250 μm.  
     
     
         8 . An optical film as recited in  claim 1 , wherein the characteristic measure is slope angle of the first surface proximate a local height maximum.  
     
     
         9 . An optical film as recited in  claim 8 , wherein the characteristic measure is slope angle of the first surface proximate a local height maximum, in a direction relative to a preferred direction of a refractive structure on the second side of the film.  
     
     
         10 . An optical film as recited in  claim 1 , wherein the second surface includes a regular, refractive structure.  
     
     
         11 . An optical film as recited in  claim 10 , wherein the regular, refractive structure includes one of a brightness enhancement prismatic structure, a lenticular structure and a Fresnel lens structure.  
     
     
         12 . An optical film as recited in  claim 10 , wherein the characteristic measure is related to a preferred direction of the refractive structure on the second surface.  
     
     
         13 . An optical film as recited in  claim 1 , wherein the second surface is substantially flat and lacking in regular refractive structure.  
     
     
         14 . An optical film as recited in  claim 1 , wherein actual heights of portions of the second surface have a value different from the nominal height by an amount having a random value within the predetermined range.  
     
     
         15 . An optical film as recited in  claim 1 , wherein the film is a polarization sensitive film.  
     
     
         16 . An optical film as recited in  claim 1 , further comprising a second light management film contactable to the first surface, a light source to generate light incident on first surface and the second film, and a light gating device disposed to receive light transmitted by the first surface and the second film.  
     
     
         17 . An optical film comprising: 
 an anti-wet-out surface on a first surface having no regularly refractive structure; and    a second surface opposing the first surface.    
     
     
         18 . A film as recited in  claim 17 , wherein the anti-wet-out surface includes a number of local height maxima and local height minima, an average height difference between the local height maxima and the local height minima being less than a first value.  
     
     
         19 . A film as recited in  claim 18 , wherein the first value is less than 5 μm.  
     
     
         20 . A film as recited in  claim 19 , wherein the first value is approximately 1.5 μm.  
     
     
         21 . A film as recited in  claim 17 , wherein the second surface is also an anti-wet-out surface.  
     
     
         22 . A film as recited in  claim 17 , wherein the anti-wet-out surface includes a plurality of local height maxima, each local height maximum separated from an adjacent local height maximum by a random separation value within a preselected separation range.  
     
     
         23 . A film as recited in  claim 22 , wherein a line between the local height maximum and the adjacent local height maximum lies generally parallel to a selected direction.  
     
     
         24 . A film as recited in  claim 17 , wherein the anti-wet-out surface includes a plurality of local height maxima and portions of the first surface proximate the local height maxima have associated surface slope angles, the surface slope angles having values within a predetermined range.  
     
     
         25 . A film as recited in  claim 24 , wherein the surface slope angles measured along a specific direction lie within the predetermined range.  
     
     
         26 . A film as recited in  claim 25 , wherein the specific direction is related to a preferred direction of a regular refracting structure on the second surface of the film.  
     
     
         27 . A film as recited in  claim 17 , wherein the second surface includes a regularly structured refracting surface.  
     
     
         28 . An optical film, comprising: 
 a first surface; and    wet-out reducing means disposed on the first surface for reducing wet-out between the first surface and another optical surface.    
     
     
         29 . An optical film as recited in  claim 28 , further comprising wet-out reducing means disposed on the second surface.  
     
     
         30 . An optical film as recited in  claim 28 , further comprising regularly-structured refracting means on the second surface for refracting light passing through the second surface.  
     
     
         31 . An optical device, comprising: 
 a light source;    a film having an anti-wet-out surface on a first surface having no regularly refractive structure; and    a second optical component having a second surface opposing the first surface;    wherein light from the light source passes through the film and the second optical component.    
     
     
         32 . An optical device as recited in  claim 31 , further comprising a light guide positioned to receive light from the light source and an extractor to extract light from the light guide in a direction towards the film.  
     
     
         33 . An optical device as recited in  claim 32 , further comprising at least one brightness enhancement film disposed between the light guide and the film.  
     
     
         34 . An optical device as recited in  claim 31 , further comprising a liquid crystal display matrix disposed to modulate light passing therethrough from the light source.  
     
     
         35 . A method of making an optical film, comprising: 
 forming an anti-wet-out surface on a first surface of the optical film.    
     
     
         36 . A method as recited in  claim 35 , wherein forming the anti-wet-out surface includes embossing the first surface of the film to have local height maxima varying in height from a nominal value by a random height difference within a predetermined range.  
     
     
         37 . A method as recited in  claim 36 , wherein the predetermined range is zero to 5 μm.  
     
     
         38 . A method as recited in  claim 35 , wherein forming the anti-wet-out surface includes embossing the first surface of the film to have irregularly spaced local height maxima, where inter-maxima spacings between adjacent maxima fall into a predetermined separation range.  
     
     
         39 . A method as recited in  claim 35 , further comprising embossing a preliminary anti-wet-out pattern on the first surface and stretching the optical film in at least one direction after embossing the preliminary anti-wet-out pattern on the first surface so that, after stretching, the anti-wet-out surface includes irregularly spaced local height maxima, an average height difference between the local height maxima and local height minima being within a predetermined range.  
     
     
         40 . A method as recited in  claim 39 , wherein an average spacing between the irregularly spaced local height maxima is less than 250μm, and the predetermined range is zero to 5 μm.  
     
     
         41 . A method of making an optical film, comprising: 
 embossing a pattern lacking regular structure onto a first surface of a film, wherein the first surface has a plurality of local height maxima, a characteristic measure of the first surface having a random value within a predetermined range.    
     
     
         42 . A method as recited in  claim 41 , further comprising embossing a regular refractive structure on the second surface of the film, wherein the characteristic measure is related to a selected direction, and the selected direction is substantially parallel to a preferred direction of the regular refractive structure.  
     
     
         43 . A method as recited in  claim 41 , wherein the characteristic measure is maximum height difference between local height maxima and local height minima, and the predetermined range is zero to 5 μm.  
     
     
         44 . A method as recited in  claim 43 , wherein the predetermined range is zero to 1.5 μm.  
     
     
         45 . A method as recited in  claim 41 , wherein the characteristic measure is separation distance between adjacent local height maxima, and the predetermined range is 100 μm to 250 μm.  
     
     
         46 . A method as recited in  claim 41 , wherein embossing includes rolling the film between two drums, at least one of the drums being provided with an embossing pattern having portions whose actual heights vary by an amount from a nominal value by a random amount whose value lies in the predetermined range.  
     
     
         47 . A method as recited in  claim 46 , further comprising stretching the film by an amount in the range 2-10 times in a direction approximately perpendicular to a rolling direction for the film.  
     
     
         48 . A method as recited in  claim 47 , wherein embossing a pattern lacking regular structure results in portions of actual height on the first surface that vary by an amount from a nominal value by a random amount whose value lies within a first predetermined range selected so that, after stretching, local height maxima on the first surface have an average height difference from local minima on the first surface, the average height difference lying within a second predetermined range.  
     
     
         49 . A method as recited in  claim 48 , wherein the second predetermined range is zero to 1.5 μm.  
     
     
         50 . A method as recited in  claim 41 , further comprising embossing a pattern having regular structure onto a second surface of the film.  
     
     
         51 . A method as recited in  claim 41 , further comprising embossing a pattern lacking regular structure onto a second. surface of the film, wherein the second surface has portions of actual height that vary by an amount from a nominal value by a random amount whose value lies within the predetermined range.  
     
     
         52 . A method as recited in  claim 41 , further comprising forming a flat second surface on the film.  
     
     
         53 . A method of making a master replication drum, comprising: 
 rotating a drum around a rotation axis relative to a cutting tool;    cutting the surface of the drum with the cutting tool;    randomly varying a cutting characteristic of the cutting tool to produce characteristic variations lying randomly within a predetermined range.    
     
     
         54 . A method as recited in  claim 53 , wherein randomly varying a cutting characteristic includes varying a cutting depth within the predetermined range.  
     
     
         55 . A method as recited in  claim 54 , further comprising randomly varying a cutting characteristic includes varying the cutting depth within a range of up to 5 μm.  
     
     
         56 . A method as recited in  claim 54 , further comprising randomly varying a cutting characteristic includes varying the cutting depth within a range of up to 1.5 μm.  
     
     
         57 . A method as recited in  claim 53 , wherein cutting the surface of the drum includes thread cutting the surface of the drum.  
     
     
         58 . A method as recited in  claim 53 , wherein randomly varying the cutting characteristic includes cutting surface minima into the surface of the drum with separation distances, between successively cut minima, having values within the predetermined range.  
     
     
         59 . A method as recited in  claim 58 , wherein the separation distances have values in the range 100 μm to 250 μm.  
     
     
         60 . A method as recited in  claim 53 , wherein randomly varying the cutting depth includes generating a noise signal, filtering the noise signal and controlling the cutting characteristic using the filtered noise signal.  
     
     
         61 . A method as recited in  claim 53 , wherein randomly varying the cutting depth includes generating a randomized digital signal, and controlling the cutting characteristic using the randomized digital signal.  
     
     
         62 . A method as recited in  claim 61 , wherein generating a randomized digital signal includes recalling a stored, randomized signal from memory.  
     
     
         63 . A drum for embossing a surface on a film, comprising: 
 a surface free of regular structure, having a plurality of local height minima, a characteristic measure of the surface having a random value within a predetermined range.    
     
     
         64 . A drum as recited in  claim 63 , wherein the local height minima have actual heights and the characteristic measure is a difference between the actual heights and a nominal height.  
     
     
         65 . A drum as recited in  claim 63 , wherein the characteristic measure is an average separation between the local height minima.  
     
     
         66 . A drum as recited in  claim 63 , wherein the characteristic measure is slope angle of the surface proximate a local height minimum.  
     
     
         67 . A drum as recited in  claim 63 , wherein the characteristic measure is slope angle of the first surface proximate a local height maximum, in a direction relative to longitudinal axis through the drum.