(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(19) World Intellectual Property
`0
`Organization
`International Bureau
`
`(43) International Publication Date
`17 December 2015 (17.12.2015)
`
`WIPOI PCT
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`(10) International Publication Number
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`WO 2015/191949 A1
`
`\klll
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`(51)
`
`International Patent Classification:
`G02B 5/02 (2006.01)
`G02B 27/48 (2006.01)
`G02B 27/10 (2006.01)
`G02F 1/1335 (2006.01)
`G023 27/42 (2006.01)
`
`(21)
`
`International Application Number:
`
`PCT/US2015/035470
`
`(22)
`
`International Filing Date:
`
`Filing Language:
`
`Publication Language:
`
`12 June 2015 (12.06.2015)
`
`English
`
`English
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`(25)
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`(26)
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`(30)
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`(71)
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`(72)
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`W02015/191949A1|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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`W.; 3M Innovative Properties Company, PO. Box 33427,
`St. Paul, Minnesota 55133-3427 (US). STEINER, Mi-
`chael L.; 3M Innovative Properties Company, PO. Box
`33427, St. Paul, blinnesota 55133-3427 (US). LIU, Lan
`H.; 3M Innovative Properties Company, PO. Box 33427,
`St. Paul, Minnesota 55133-3427
`(US). GOLLIER,
`Jacques; 114 W'eston Lane, Painted Post, New York
`14870 (US). WEST, James Andrew;
`1 Chatfield Place
`East, Painted Post, New York 14870 (US). KOSIK-VVIL-
`LIAMS, Ellen Marie; 132 Davis Street, Painted Post,
`New York 14870 (US).
`
`(74)
`
`Agent: VALENTINO, Joseph; Fish & Richardson P.C.,
`PO. Box 1022, Minneapolis, Minnesota 55440-1022 (US).
`
`Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`A0, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY,
`BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM,
`DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT,
`HN, HR, HU, ID, IL, IN, IR, IS, JP, KE, KG, KN, KP, KR,
`KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, MG,
`MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM,
`PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW, SA, SC,
`SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN,
`TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`
`(84)
`
`Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`
`[Continued on next page]
`
`Priority Data:
`62/011,984
`
`13 June 2014 (13.06.2014)
`
`US
`
`(81)
`
`Applicants: 3M INNOVATIVE PROPERTIES CONI-
`PANY [US/US]; PO. Box 33427, St. Paul, Minnesota
`55133-3427
`(US). CORNING INCORPORATED
`[US/US]; One Riverfront Plaza, Corning, New York 14831
`(US).
`
`Inventors: SITTER, Brett J.; 3M INNOVATIVE PROP-
`ERTIES COMPANY, PO. Box 33427, St. Paul, Min-
`nesota 55133—3427 (US). RADCLIFFE, Marc D.; 3M In-
`novative Properties Company, PO. Box 33427, St. Paul,
`Minnesota 55133-3427 (US). HOFFEND, JR., Thomas
`R; 3M Innovative Properties Company, PO. Box 33427,
`St. Paul, Minnesota 55133-3427 (US). HENNEN, Daniel
`
`(54) Title: OPTICAL STACKS FOR SPARKLE REDUCTION
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`Fig. 3c:
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`(57) Abstract: Optical stacks including a grating st1ucture that generates diffraction in two in—plane dimensions. The optical stacks
`may include two gratings, which may be one-directional or two-directional. The optical stacks are suitable for reducing sparkle in
`displays .
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`WO 2015/191949 A1 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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`GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, sz, Published:
`TZ, UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU,
`TJ TM) European (AL AT BE BG CH CY CZ DE * With international search report (Art. 21(3))
`DK, EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, — before the expiration of the time limit for amending the
`LU, LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE,
`claims and to be republished in the event of receipt of
`SI, SK, SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA,
`amendments (Rule 48301))
`GN, GQ, GVV, KM, ML, MR, NE, SN, TD, TG).
`
`

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`WO 2015/191949
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`PCT/U82015/035470
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`OPTICAL STACKS FOR SPARKLE REDUCTION
`
`Background
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`High definition displays having anti-glare coatings, other irregular coatings, scratches or
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`marked surfaces are prone to generating sparkle which can be objectionable or distracting to the
`
`viewer. Sparkle in a display can be described as a grainy pattern that appears to move around or
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`flicker with small changes in the position of the viewer relative to the display. There is a need for
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`reducing sparkle in high definition displays.
`
`Summary
`
`In one aspect, the present description relates to an optical stack that includes a first layer,
`
`a second layer and a third layer. The second layer is disposed between the first layer and the third
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`layer. A first
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`interface between the first
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`layer and the second layer includes a first grating
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`extending substantially along a first direction and a second interface between the second layer and
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`the third layer includes a second grating extending substantially along a second direction that is
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`different from the first direction. The first layer has a refractive index n1, the second layer has a
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`refractive index n;, and the third layer has a refractive index [13. The first grating has a peak to
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`valley height of 111 and the second grating has a peak to valley height of 11;. The absolute value of
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`nl-nz multiplied by h is between about 150 nm and about 350 nm and the absolute value of 112-113
`
`multiplied by 112 is between about 150 nm and about 350 nm. The first grating has a first pitch in
`
`the range of about 2 microns to about 50 microns and the second grating has a second pitch in the
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`range of about 2 microns to about 50 microns. In some cases the first layer and the third layer
`
`include optically clear adhesives and in some cases the second layer includes a polymer or polymer
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`composite. In some cases, the second layer includes an optically clear adhesive and in some cases
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`the first layer and the third layer include polymers or polymer composites. In some cases, the first
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`direction of the first grating may be substantially orthogonal to the second direction of the second
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`grating. In some cases, an angle between the first direction and the second direction is greater
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`than about 5 degrees and less than or equal to 90 degrees. I11 some cases, the optical stack is a
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`flexible film and in some cases the optical stack includes an anti-glare layer or includes anti-glare
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`features. In some cases the anti-glare features include embedded particles.
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`In another aspect, the present description relates to an optical stack that includes a first
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`layer having a refractive index n1 and a second layer having a refractive index n2 disposed adjacent
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`to the first layer. A first interface between the first layer and the second layer includes a two—
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`directional grating having a peak to valley height of h. The absolute value of n1—n2 multiplied by
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`h is in the range of about 150 nm to about 350 nm. The grating has a first pitch in a first direction
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`in a range of about 2 microns to about 50 microns and a second pitch in a second direction in a
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`range of about 2 microns to about 50 microns. When the optical stack is illuminated with laser
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`light at normal incidence having an incident power P1 and having a wavelength of about 532 nm, a
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`plurality of diffi‘action peaks are produced with each diffi‘action peak having a power content and
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`a diffraction order. The plurality of diffraction peaks includes a set of 9 diffraction peaks having
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`lower diffraction orders than diffraction peaks not in the set of 9 diffraction peaks. The sum of the
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`power content of the diffraction peaks in the set of 9 diffraction peaks is P9 which is at least about
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`0.7 P1. The power content of each of the diffraction peaks in the set of 9 diffraction peaks is
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`greater than about 0.08 P9 and less than about 0.16 P9. In some cases, the second layer includes an
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`outer major surface that is substantially planar and in some cases the outer major surface includes
`
`anti—glare features which may include embedded particles. In some cases, P9 is at least about 0.8
`
`P1 and the power content of each of the diffraction peaks in the set of 9 diffraction peaks is
`
`approximately one ninth of P9. In some cases, the first layer includes a polymer and the second
`
`layer includes an optically Clear adhesive. In some cases, the optical stack is a flexible film. In
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`some cases,
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`the optical stack includes a third layer positioned adjacent
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`to the second layer
`
`opposite the first layer where the interface between the second layer and the third layer includes a
`
`second grating.
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`In another aspect, the present description relates to an optical stack including a first layer,
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`a second layer and a third layer where the second layer is disposed between the first layer and the
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`third layer. A first interface between the first layer and the second layer includes a first grating and
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`a second interface between the second layer and the third layer includes a second grating. The first
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`layer has a refractive index m, the second layer has a refiactive index 112, the third layer has a
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`refiactive index n3, the first grating has a peak to valley height of h, and the second grating has a
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`peak to valley height of 112. The absolute value of 111—112 multiplied by 111 is between about 150 nm
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`and about 350 nm and the absolute value of ng-ng multiplied by h; is between about 150 nm and
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`about 350 nm. At
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`least one of the first grating and the second gratings is a two-directional
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`grating. The first grating has a first pitch in the range of about 2 microns to about 50 microns and
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`the second grating has a second pitch in the range of about 2 microns to about 50 microns. In
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`some cases, the optical stack includes an anti-glare layer.
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`In another aspect, the present description relates to a display that includes an optical stack.
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`The optical stack may be any of the optical stacks described in present description. The display
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`includes pixels and the optical stack is positioned near the pixels such that when a first pixel
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`having a first color is illuminated and Viewed through the optical stack, secondary images are
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`produced, each secondary image having a lateral displacement from the first pixel. The first pixel
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`has primary neighbor pixels having the first color and secondary neighbor pixels having the first
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`color. The lateral displacement of each secondary image is such that each secondary image
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`overlaps with the primary neighbor pixels or overlaps with a space between the first pixel and the
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`primary neighbor pixels, and there is substantially no overlap of the plurality of secondary images
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`with the secondary neighbor pixels. In some cases, pixels are arranged in a pattern that repeats
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`along a display direction and the optical stack has an orientation that includes a grating orientation
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`direction and an angle between the display direction and the grating orientation direction is in a
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`range of about 5 degrees to about 85 degrees.
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`Brief Description of the Dravw'ngs
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`FIG. 1 is a cross-sectional view of an optical stack;
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`FIG. 2 is a schematic top perspective view of an optical stack;
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`FIG. 3A is a cross-sectional View of an optical stack;
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`FIG. 3B is a cross-sectional View of the optical stack of FIG. 3A along a cross-section
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`orthogonal to that shown in FIG. 3A;
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`FIG. 3C is a perspective View of the optical stack of FIGS. 3A and 3B;
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`30
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`FIG. 4 is a cross-sectional view of an optical stack;
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`FIG. 5A is a cross-sectional view of an optical stack having an anti-glare layer;
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`FIG. 5B is a cross-sectional View of an optical stack containing anti-glare features;
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`FIG. 5C is a cross-sectional view of an optical stack containing anti-glare features;
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`FIG. 5D is a cross-sectional View an optical stack containing an anti—glare layer;
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`FIG. 6A is a perspective view of a first
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`layer having a surface that includes a two—
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`directional structure;
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`FIG. 6B is a cross-sectional view of the first layer of FIG. 6A with a second layer filling in
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`the two-directional structure of the first layer.
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`FIG. 7 is a cross—sectional view of an optical stack;
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`FIG. 8 is a schematic cross—sectional view of a display incorporating an optical stack;
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`FIG. 9 is a drawing illustrating illuminating an optical stack;
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`FIG. 10 shows a diffraction pattern generated by illuminating an optical stack;
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`FIG. ll shows a diffraction pattern generated by illuminating an optical stack;
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`FIG. 12 is a plan view of a plurality of pixels; and
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`FIG. 13 a plan view of the plurality of pixels of FIG. 12 with one pixel illuminated and
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`viewed through an optical stack.
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`Detailed Description
`
`Sparkle in a display can be caused by light from a pixel interacting with a non-uniformity
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`in the in the optical path of the light, typically on the surface of a display. Light from a pixel may
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`appear to move around or flicker as the viewer moves due to the interaction of the pixel light with
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`the non-uniformity. Such non-uniformities can include structure or surface texture from a fihn or
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`other layer that might be added to a display. For example, surface texture in anti-glare films is
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`often included in order to reduce specular reflection from the surface thereby reducing glare. Non—
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`unifonnities that can generate sparkle also include fingerprints, scratches or other residue on the
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`display surface.
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`Approaches to reduce sparkle using one-directional periodic structures to generate
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`diffraction are known, however it has previously been believed that using two-directional periodic
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`structures that could produce diffraction would undesirably reduce the perceived resolution of the
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`display. Approaches to reduce sparkle including two-directional periodic structures designed to
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`minimize diffiaction are also known, however it has been previously believed that such structures
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`should be designed to produce insignificant diffraction effects so that the perceived resolution of
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`the display would not be compromised. According to the present description, it has been found
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`that a structure in a display that generates difliaction in two in—plane dimensions can be utilized
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`without
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`substantially reducing perceived resolution and with improved sparkle reduction
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`compared to the one-directional case. In particular, optical stacks having two or more one—
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`dircctional gratings or at least one two—directional grating selected to give controlled diffraction
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`can be incorporated in a display to significantly reduce sparkle while substantially maintaining
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`perceived display resolution.
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`Displays are often divided into a grid of addressable elements which may be subdivided
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`into single color regions. As used herein, “pixel” refers to the smallest addressable element of a
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`display. In displays in which single color elements are separately addressable, the single color
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`elements are herein denoted “pixels” though such a separately addressable single color element
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`may also be known as a “subpixel”. A display may include a periodic arrangement of pixels of a
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`first, second and third color. In some cases a fourth color may also be used. For example, an array
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`of red, green and blue pixels may be used in a display. Alternatively, an array of yellow, magenta
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`and cyan pixels may be used. Pixels of a first color are typically arranged in a periodic pattern with
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`spaces between the pixels of the first color where pixels having other colors are located. Sparkle
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`can be described as resulting fiom an apparent shift in the brightness or color of light from a pixel
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`as an observer’s position relative to the display is changed. According to the present description,
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`an approach to reducing sparkle is to fill in the space between an illuminated pixel of a first color
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`and its neighboring pixels of the first color with duplicate images of the illuminated pixel. In this
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`case, an observer would notice less shift in the brightness, color or apparent location of the pixel
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`since light fiom the pixel is spread over a greater area. Similarly, duplicate images of pixels of
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`other colors can be positioned in the space between similar pixels. It
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`is, however, generally
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`desired to preserve the resolution of the display and spreading duplicate images of illuminated
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`pixels over a broad area could lower the perceived resolution. It is therefore desired to control the
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`location of the duplicate images so that sparkle is reduced while the perceived resolution of the
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`display is maintained at an adequate level.
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`The present description provides for optical stacks that may be incorporated into or onto a
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`display and that can reduce sparkle without significantly compromising perceived resolution. The
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`optical stacks include two-directional gratings and/or multiple one—directional gratings. In some
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`embodiments, the optical stacks include polymeric materials and in some embodiments, the optical
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`stacks are made from polymers and/or polymer composites and/or optically Clear adhesives. In
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`some embodiments the optical stacks are flexible films. In other embodiments, the optical stacks
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`are made on glass or other substrates.
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`FIG.
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`1 shows a cross—section view of optical stack 100 that includes first
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`layer 110,
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`second layer 120, third layer 130, first grating 140 and a second grating 150. First layer 110 has a
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`first outer major surface 180 opposite second layer 120 and third layer 130 has a second outer
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`major surface 190 opposite second layer 120. First grating 140 has a peak to valley height of h
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`and second grating 150 has a peak to valley height of h. In the embodiment shown in FIG. 1, first
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`outer major surface 180 and second outer major surface 190 are substantially planar.
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`The distribution of intensity of the diffiaction peaks generated by diffraction gratings is a
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`function of the product of the index contrast across the grating (i.e., the absolute value of the
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`difference between the refractive index of the optical medium immediately on one side of the
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`grating and the refractive index of the optical medium immediately on the other side of the
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`grating) and the peak to valley height of the grating. As used herein, refractive index and index
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`contrast refers to refractive index measurements using light having a wavelength of 532 nm at 25
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`0C and atmospheric pressure unless otherwise indicated. The index contrast times the peak to
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`valley height can be adjusted so that diffraction peaks that reduce sparkle appear with a relative
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`high intensity while diffraction peaks that would degrade effective resolution appear with low
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`intensity or do not measurably appear at all. The range of useful values for the product of the
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`index contrast and the peak to valley height may depend on the shape of the grating. The gratings
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`may have any periodically repeating shape, for example a sinusoidal shape, a square wave shape,
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`or the gratings may have other periodically repeating regular or irregular shapes.
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`First layer 110 has a refractive index n1, second layer 120 has a refractive index 112, and
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`third layer 130 has a refractive index n3.
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`In some embodiments, the first layer and the third layer
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`are made fiom the same or similar materials so that 111 is equal to or approximately equal to 113. In
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`other embodiments 111 may differ from 113.
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`For any of the embodiments discussed herein, the index contrast for any grating multiplied
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`by the peak to valley height of the grating may be greater than about 100 nm, or greater than
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`about 150 nm, or greater than about 200 nm and less than about 400 nm, or less than about 350
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`nm, or less than about 300 nm. For example, in some embodiments,
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`|n1 , nzj multiplied by h is
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`between about 100 nm and about 400 nm or between about 150 nm and about 350 nm or between
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`about 200 nm and about 300 nm. In some embodiments, |n3 — 1’12' multiplied by 112 is between about
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`100 nm and about 400 nm or between about 150 nm and about 350 nm or between about 200 nm
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`and about 300 nm.
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`Optical stack 100 of FIG. 1 can be made in various ways. In some embodiments, first layer
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`110 and third layer 130 are made by machining a surface structure into layers ofa material. For
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`cxamplc, a layer having a surface structure can be made by using diamond tooling to cut a
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`structure into a layer of any of a wide variety of non-polymeric materials, such as glass, or
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`thermoplastic or crosslinked polymeric materials. Suitable materials
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`include polyethylene
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`terephthalate (PET), polycarbonate (PC), acrylics such as polymethyl methacrylate (PMMA),
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`cellulose acetate, and polyolefins such as biaxially oriented polypropylene which are commonly
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`used in various optical devices. Suitable diamond tooling is known in the art and includes the
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`diamond tooling described in US. Pat. No. 7,140,812 (Bryan et al.). Alternatively, a diamond tool
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`can be used to cut an inverted pattern into a copper micro—replication roll which can be used to
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`make the pattern on a substrate using a continuous cast and cure process utilizing a polymerizable
`
`rcsin. Continuous cast and cure proccsscs arc known in the art and are described in the following
`
`patents: US. Pat. Nos. 4,374,077 (Kerfeld); 4,576,850 (Martens); 5,175,030 (Lu et a1);
`
`5,271,968 (Coyle et a1); 5,558,740 (Bernard et a1); and 5,995,690 (Kotz et al.).
`
`Other suitable processes
`
`for producing first
`
`layer 110 include laser ablation and
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`embossing. Third layer 130 can be made using any of the techniques used to make first layer 110.
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`In some embodiments, second layer 120 is an optically clear adhesive that is used to adhere first
`
`layer 110 and third layer 130 together. In some embodiments, first layer 110 and third layer 130
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`are identical or similar parts that are adhered together with second layer 120 such that the grating
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`140 has a first direction and the grating 150 has a second direction that is different from the first
`
`direction.
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`In some embodiments, second layer 120 is prepared by machining a material so that it has
`
`a first grating 140 on a first major surface and a second grating 150 on a second major surface.
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`Such a structured layer can be prepared using any of the materials and techniques discussed
`
`elsewhere. First layer 110 may then be an optically clear adhesive or other coating that is applied
`
`to first grating 140 and third layer 130 may be an optically clear adhesive or other coating that is
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`applied to second grating 150.
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`Suitable Optically clear adhesives that could be used as first layer 110 and/or as third layer
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`130 when applied onto second layer 120 or that could be used to form second layer 120 by
`
`adhering first layer 110 to second layer 130 include Optically Clear Adhesive 817x, Optically
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`Clear Adhesive 817x, Optically Clear Adhesive 826x, Liquid Optically Clear Adhesive 2321,
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`CEF22xx, CEF28xx, all available from 3M Company (St. Paul, MN). Other suitable optically
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`clear adhesives include UV-curable acrylates, hot—melt adhesives and solvent cast adhesives.
`
`In some embodiments, first layer 110 includes a first polymer, second layer 120 includes a
`
`second polymer, which may the same or different fiom the first polymer, and third layer 130
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`includes a third polymer, which may be the same or different from the first or second polymers. In
`
`some embodiments, first layer 110 includes a first polymer or a first polymer composite, second
`
`layer 120 includes an optically clear adhesive, and third layer 130 includes a second polymer or a
`
`second polymer composite, which may be the same or different from the first polymer or first
`
`polymer composite. In some embodiments, first layer 110 includes a first optically clear adhesive,
`
`second layer 120 includes a first polymer or a first polymer composite, and third layer 130
`
`includes a second optically clear adhesive, which may be the same or different from the first
`
`optically clear adhesive. Suitable polymer composites include polymers, such as polyacrylates,
`
`having inorganic nanoparticles — such as zirconia or titania nanoparticles having a mean size in the
`
`range of about 5 nm to about 50 nm 2 included to adjust the refractive index of the polymer
`
`composite. In some embodiments, the optical stack is a flexible film. In many embodiments, the
`
`optical stack is substantially transparent to light in the visible spectrum.
`
`FIG. 2 shows a schematic top view of an optical stack having a first grating represented by
`
`element 212 extending in first direction 213 and a second grating represented by element 214
`
`extending in a second direction 215 with angle 226 between first direction 213 and second
`
`direction 215. The first grating represented by element 212 has a first pitch 232 and the second
`
`grating represented by element 214 has a second pitch 234.
`
`In many embodiments, second
`
`direction 215 is different from first direction 213. In some embodiments angle 226 is greater than
`
`0 degrees, or greater than about 5 degrees, or greater than about 10 degrees, or greater than
`
`about 20 degrees and less than or equal to 90 degrees. It will be understood than an angle greater
`
`than 90 degrees is equivalent to a complement angle less than 90 degrees. In some embodiments,
`
`first direction 213 and second direction 215 are substantially orthogonal. In some embodiments
`
`the first pitch 232 and the second pitch 234 are about equal. In other embodiments, the first pitch
`
`232 and the second pitch 234 are different.
`
`The location of the diffraction peaks generated by a grating is a function of the pitch of the
`
`grating. The pitch of the gratings appearing in various embodiments of the present description can
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`be adjusted so that diffraction peaks having a relatively high intensity will be located at regions
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`where they are effective at reducing sparkle but not in regions where the diffraction peaks would
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`degrade the effective image resolution of a display. The location of the diffraction peaks may
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`depend on the spacing between pixels and on the distance between the plane of the pixels and the
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`optical stack when it is positioned in the display. For any of the embodiments discussed herein,
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`the pitch for any grating may be greater than about 1 micron, or greater than about 2 microns, or
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`greater than about 4 microns or greater than about 6 microns and may be less than about 60
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`microns, or less than about 50 microns, or less than about 40 microns or less than about 30
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`microns. For example, in some embodiments first pitch 232 is between about 2 microns and about
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`50 microns or between about 4 microns and about 40 microns. In some embodiments, second
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`pitch 234 is between about 2 microns and about 50 microns or between about 4 microns and
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`about 40 microns.
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`First direction 213 and second direction 215 may be substantially orthogonal or may be
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`non—orthogonal. An optical stack where first direction 213 and second direction 215 are
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`substantially orthogonal is illustrated in FIGS. 3A, 3B and 3C. Optical stack 300 has first layer
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`310, second layer 320, third layer 330, first grating 340 and second grating 350. First grating 340
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`has a first pitch substantially the same as a second pitch in second grating 350. First grating 340
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`extends along a first direction (into the plane of FIG. 3B) and second grating 350 extends along a
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`second direction (into the plane of FIG. 3A) substantially orthogonal to the first direction. FIG.
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`3B is along the cross section indicated in FIG. 3A and FIG. 3A is along the cross section
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`indicated in FIG. 3B. FIG. 3C is a perspective View of optical stack 300.
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`FIG. 4 shows a cross—sectional View of optical stack 400 having first layer 410, second
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`layer 420, third layer 430, first grating 440 and a second grating 450. First layer 410 includes a
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`first outer major surface 480 opposite second layer 420 and third layer 430 includes a second
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`outer major surface 490 opposite second layer 420. First outer major surface 480 is substantially
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`level with the peaks in grating 440. First outer major surface 480 can be made by forming second
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`layer 420 using any of the methods discussed elsewhere and then applying a coating such as an
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`optically clear adhesive to second layer 420 such that the coating fills in the grating structure and
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`forms first outer major surface 480 which is a substantially planar surface. Similarly, second outer
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`major surface 490 is substantially level with the peaks in grating 450 and this can be achieved by
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`applying a coating such as an optically clear adhesive to second layer 420 opposite the first layer
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`such that the coating fills in grating 450 and forms second outer major surface 490 which is a
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`substantially planar surface. Suitable coatings include those discussed elsewhere.
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`Optical stack 400 is an alternative to the embodiment shown in FIG.
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`1 where first layer
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`110 and third layer 130 extend beyond the level of the peaks in first grating 140 and beyond the
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`level of the peaks in the second grating 150, respectively. In another embodiment, the first layer
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`410 may be substantially level with the peaks in first grating 440 while third layer 430 may extend
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`beyond the level of the peaks in second grating 450.
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`FIG. 5A shows optical stack 500 including uncoated optical stack 505, first major surface
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`581, outer major surface 582. binder 583, embedded particles 585, anti—glare layer 587 and anti—
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`glare features 588. First major surface 581 is coated with anti-glare layer 587 to produce outer
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`major surface 582 which includes anti-glare features 588. Uncoated optical stack 505 represents
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`any uncoated optical stack of the present description. For example, uncoated optical stack 505
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`may correspond with optical stack 100 of FIG.
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`in which case first major surface 581
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`corresponds with first outer major surface 180 of first layer 110. Anti-glare layer 587 includes a
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`binder 583 and embedded particles 585. Anti-glare layer 587 may be any coating containing beads
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`or other particles capable of producing an irregular surface structure for outer major surface 582.
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`Suitable embedded particles 585 include glass beads, polymeric beads,
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`silica particles or
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`agglomerates of silica particles having a mean diameter in the range of about 0.1 microns to about
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`10 microns or in the range of about 0.3 microns to about 2 microns. Binder 583 may be selected
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`from any optically clear adhesive or other clear materials such as transparent polymers. Suitable
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`materials for binder 583 include the optically clear adhesives and other coatings discussed
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`elsewhere. Other suitable materials for anti—glare layer 587 include aggregate silica particles in a
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`cured inorganic polymer matrix as described, for example, in US. Pat. No. 7,291,386 (Richter et
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`al.).
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`Alternatively or additionally, some embodiments include embedded particles in one of the
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`outermost layers of the optical stack. Embedded particles may be included in any outermost layer
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`of any optical stack of the present description. In the particular embodiment shown in FIG. 5B,
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`optical stack 501 includes first layer 510, second layer 520, third layer 530, first grating 540 and
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`second grating 550. Embedded particles 585 are included in first layer 510 in order to produce
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`outer major surface 582 which includes anti—glare features 588. Any materials suitable for use as
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`binder 583 and embedded particles 585 may also be used in first layer 510.
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`FIG. 5C shows another embodiment, where anti-glare features 588 are provided in optical
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`stack 502 by microreplieating, roughening or texturing outer major surface 582. Optical stack 502
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`can represent any optical stack of the present description. For example, optical stack 502 may be
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`obtained fiom optical stack 100 by structuring first outer major surface 180 to produce outer
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`major surface 582. Methods for structuring a surface to produce anti-glare features are known in
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`the art and are described, for example, in US. Patent No. 5,820,957 (Schroeder et al.). In some
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`embodiments, anti-glare features 588 may be obtained directly in any outer major surface of any
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`of the optical stacks of the present description by microreplication using, for example, a cut lathe
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`turning process as described in US. Pat. App. Pub. No. 2012/0064296 (Walker et al.).
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`Another approach to providing an anti—glare functionality is to add an anti—glare layer to
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`any of the optical stacks of the present disclosure. This is illustrated in FIG. 5D where second
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`optical stack 502 includes first optical stack 506, first major surface 561 and anti-glare la