PATENT DOCUMENT

Publication Number: US-8727593-B2
Application Number: US-201213523731-A
Country: US
Kind Code: B2

Title: Displays with rounded-tip turning films

Abstract:
An electronic device may be provided with a display having backlight structures. The backlight structures may include a light source. Light from the light source may be coupled into an edge of a light guide plate. The backlight structures may include layers such as a diffuser layer and one or more layers of brightness enhancing film. The brightness enhancing film layers may be used to collimate light scattered from the light guide plate and thereby enhance backlight efficiency. Brightness enhancing films may be formed from transparent substrates such as layers of polyester. A patterned polymer layer such as a layer of patterned cured resin may be formed on the transparent substrate of a backlight enhancing film. A roller-based manufacturing process may be used to form the patterned polymer layer on the substrate. The patterned polymer layer may include a series of parallel ridges with rounded peaks.

Claims:
What is claimed is: 
     
       1. A plurality of brightness enhancing films, comprising: a first brightness enhancing film that includes a first transparent layer having a series of parallel ridges, each ridge having a triangular cross section with a rounded peak that has a radius of curvature of at least one micron; and a second brightness enhancing film that includes a second transparent layer having a series of parallel ridges, each ridge having a triangular cross section with a rounded peak that has a radius of curvature of at least one micron, wherein the ridges of the first transparent layer extend parallel to a first axis, and wherein the ridges of the second transparent layer extend parallel to a second axis. 
     
     
       2. The plurality of brightness enhancing films defined in  claim 1  wherein each ridge is configured to exhibit a rounded peak with a radius of curvature of at least two microns. 
     
     
       3. The plurality of brightness enhancing films defined in  claim 2  wherein the first transparent layer of material comprises a patterned layer of material on a flexible substrate. 
     
     
       4. The plurality of brightness enhancing films defined in  claim 3  wherein the patterned layer of material comprises a patterned ultraviolet-light-curable resin. 
     
     
       5. The plurality of brightness enhancing films defined in  claim 4  wherein the flexible substrate comprises a transparent sheet of polymer. 
     
     
       6. The plurality of brightness enhancing films defined in  claim 5  wherein the transparent sheet of polymer comprises a polyester layer. 
     
     
       7. The plurality of brightness enhancing films defined in  claim 1  wherein the rounded peak of each ridge has a radius of curvature of at least three microns. 
     
     
       8. A display, comprising: display layers configured to generate an image; and a backlight unit configured to provide backlight for the display layers, the backlight unit including a plurality of brightness enhancing films, wherein the plurality of brightness enhancing films comprises: a first brightness enhancing film that includes a first transparent layer having a series of parallel ridges, each ridge having a rounded peak that has a radius of curvature of at least one micron, and a second brightness enhancing film that includes a second transparent layer having a series of parallel ridges, each ridge having a rounded peak that has a radius of curvature of at least one micron, wherein the ridges of the first transparent layer extend parallel to a first axis, and wherein the ridges of the second transparent layer extend parallel to a second axis. 
     
     
       9. The display defined in  claim 8  wherein the ridges have triangular cross-sectional shapes. 
     
     
       10. The display defined in  claim 9  wherein the backlight unit comprises: a light guide plate; and a light source configured to emit light into an edge of the light guide plate, wherein the plurality of brightness enhancing films overlaps the light guide plate and is configured to collimate light scattered from the light guide plate. 
     
     
       11. The display defined in  claim 10  wherein the display layers comprise a thin-film transistor layer and a color filter layer. 
     
     
       12. The display defined in  claim 8  wherein the first brightness enhancing film comprises a patterned layer of material on a transparent flexible substrate. 
     
     
       13. The display defined in  claim 12  wherein the patterned layer of material comprises a layer of cured ultraviolet-light-curable resin. 
     
     
       14. The display defined in  claim 13  wherein the transparent flexible substrate comprises polyester. 
     
     
       15. The display defined in  claim 14  wherein the display layers comprise:
 a color filter layer; and 
 a thin-film transistor layer.

Description:
BACKGROUND 
     This relates to electronic devices and, more particularly, to electronic devices with displays. 
     Electronic devices such as cellular telephones and computers are often provided with displays. To ensure that displays are visible in a wide variety of lighting conditions, displays are often provided with backlight units. A light source such as an array of light-emitting diodes may provide a backlight unit with light. A transparent light guide plate may be used to laterally distribute light from the light-emitting diodes over the display. 
     To enhance backlight efficiency and thereby ensure that a display exhibits satisfactory backlight brightness levels, brightness enhancing films are often incorporated into a display backlight unit. These films, which are sometimes referred to as prism films or turning films, help direct light escaping from the light guide plate upwards through display layers towards a user. 
     If care is not taken, the layers in a display such as prism or turning film layers may be susceptible to damage. For example, conventional prism or turning film surface features may be crushed during an impact event, leading to undesirable dark and white spots on a display. 
     It would therefore be desirable to be able to provide improved display backlight structures. 
     SUMMARY 
     An electronic device may be provided with a display having backlight structures. The backlight structures may include a light source. Light from the light source may be coupled into an edge of a light guide plate. 
     The backlight structures may include layers such as a diffuser layer and one or more layers of brightness enhancing film. The diffuser layer and brightness enhancing film structures may overlap the light guide plate. During use of a device, the brightness enhancing film layers may be used to collimate light scattered from the light guide plate and thereby enhance backlight efficiency. 
     Brightness enhancing films may be formed from transparent substrates such as layers of polyester. A patterned polymer layer such as a layer of patterned cured resin may be formed on the transparent substrate of a backlight enhancing film. A roller-based manufacturing process may be used to form the patterned polymer layer on the substrate. The patterned polymer layer may include a series of parallel ridges with rounded peaks. The ridges may have a triangular cross-sectional shape. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of an illustrative electronic device of the type that may be provided with brightness enhancing films in accordance with an embodiment of the present invention. 
         FIG. 2  is a cross-sectional side view of a display with backlight structures in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional side view of a portion of a backlight unit showing how backlight may be directed upwards using multiple layers of brightness enhancing film structures in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of a portion of an illustrative brightness enhancing film in accordance with an embodiment of the present invention. 
         FIG. 5  is a side view of equipment of the type that may be used in forming brightness enhancing films in accordance with an embodiment of the present invention. 
         FIG. 6  is a side view of a portion of a triangular ridge with a rounded tip of the type that may be used to provide a brightness enhancing film with increased mechanical robustness in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device display may include a backlight structure with one or more brightness enhancing films (sometimes referred to as turning films). The brightness enhancing films may have a series of parallel ridges to help collimate backlight for the display. The ridges may have triangular cross-sections with tips that are rounded to enhance mechanical robustness. 
       FIG. 1  is a diagram of an electronic device of the type that may be provided with a display having robust brightness enhancing films. Device  10  may be a handheld device such as a cellular telephone or media player, a tablet computer, a notebook computer, other portable computing equipment, a wearable or miniature device such as a wristwatch or pendant device, a television, a computer monitor, or other electronic equipment. 
     As shown in  FIG. 1 , electronic device  10  may include a display such as display  14 . Display  14  may be a touch screen that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components or may be a display that is not touch-sensitive. Display  14  may include an array of display pixels formed from liquid crystal display (LCD) components, an array of electrophoretic display pixels, an array of electrowetting display pixels, or display pixels based on other display technologies. Configurations in which display  14  includes display layers that form liquid crystal display (LCD) pixels may sometimes be described herein as an example. This is, however, merely illustrative. Display  14  may include display pixels formed using any suitable type of display technology. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button such as button  16  and an opening such as opening  18  may be used to form a speaker port. Device configurations without openings in display  14  may also be used for device  10 . 
     Device  10  may have a housing such as housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. 
     Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     A cross-sectional side view of display  14  is shown in  FIG. 2 . As shown in the illustrative configuration for display  14  of  FIG. 2 , display  14  may include a display module such as display module  32  and an associated backlight unit such as backlight unit  30 . Backlight unit  30  may provide backlight  28  that travels vertically upwards through the layers of display module  32  in direction Z. 
     Display module  32  may be a liquid crystal display module or display structures formed using other display technologies. In the example of  FIG. 2 , display module  32  has been implemented using liquid crystal display technology. As shown in  FIG. 2 , display module  32  in this type of configuration may include a layer of liquid crystal material such as liquid crystal layer  50  sandwiched between display layers  44  and  42 . Display layer  42  may be a thin-film transistor layer having a transparent substrate such as a layer of glass. Thin-film transistors and electrodes on layer  42  may be used in applying electric fields to liquid crystal layer  50  to present images to a user. Display layer  42  may be a color filter layer having an array of color filter elements on a transparent glass or plastic substrate for providing display  14  with the ability to display color images. Display layers  44  and  40  may be interposed between polarizer layers such as lower polarizer  40  and upper polarizer  46 . 
     Backlight unit  30  may have a light source such as light source  24  that produces light  26 . Light source  24  may include an array of light-emitting diodes or other light emitting devices. Light  26  from light source  24  may be coupled into an adjacent edge of light guide plate  22 . Light guide plate  22  may be formed from a transparent sheet of material such as a clear plastic layer. During operation, light  26  may be distributed laterally (in dimensions X and Y of  FIG. 2 ) due to the principal of total internal reflection. Reflector  20  may be used to reflect light that has scattered downwards back in upwards direction Z, thereby enhancing backlight efficiency. 
     Some of the light that is traveling in light guide plate  22  may escape through the upper surface of light guide plate to form backlight  28 . Backlight unit  30  may include backlight films such as layers  34 ,  36 , and  38  for enhancing the quality of backlight  28 . With one suitable arrangement, layer  34  may be a diffusing layer for minimizing hotspots and layers  36  and  38  may be brightness enhancing films for collimating backlight  28 . Additional layers (e.g., another diffuser layer, etc.) may be incorporated into backlight unit  30  if desired. The configuration of  FIG. 2  in which a single diffuser such as diffuser layer  34  and two brightness enhancing films such as layers  36  and  38  are used in backlight structures  30  is merely illustrative. 
       FIG. 3  is a cross-sectional side view of a portion of backlight structures  30 . Light guide plate  22  may be a planar member with opposing upper and lower surfaces. As shown in  FIG. 3 , light  26  that is propagating in light guide plate  22  may scatter out of upper surface  52 . A pattern of pits and/or bumps may be provided on the upper and/or lower surface of light guide plate  22  to enhance light scattering. 
     Light  26  typically scatters out of upper surface  52  at a relatively low angle A 1  with respect to the plane of upper surface  52  (i.e., the X-Y plane of  FIG. 3 ). 
     Brightness enhancing films such as films  36  and  38  may be used to collimate the backlight produced by structures  30 . In the example of  FIG. 3 , backlight structures  30  include a lower brightness enhancing film such as film  36  and an upper brightness enhancing film such as film  38 . If desired, fewer or more layers of brightness enhancing film may be used. The example of  FIG. 3  is merely illustrative. 
     Scattered light rays  28 A that exit surface  52  of light guide plate  22  may be characterized by a relatively low angle of A 1  with respect to surface  52  (e.g., A 1  may be less than 45°). If left uncorrected, the low angle of rays  28 A will render rays  28 A ineffective for backlighting display module  32 . Accordingly, brightness enhancing films  36  and  38  may be used to direct light  28 A upwards towards the user. In particular, brightness enhancing film  36  may direct light rays  28 A upwards at a steeper angle such as angle A 2  and brightness enhancing film  38  may direct light rays  28 B upwards at an even steeper angle such as angle A 3 . Angle A 2  may lie between 30° and 90° (as an example). Angle A 3  may be close to 90° (i.e., light  28 , which is produced by passing light  28 B through upper brightness enhancing film  38 , may propagate parallel to vertical dimension Z, with a relatively modest angular spread to provide illumination for off-axis viewing). Collimating light from light guide plate  22  in this way ensures that backlight  28  will serve as suitable illumination for display layers such as display module  32 . 
     A perspective view of a portion of the surface of a brightness enhancing film structure of the type that may be used in implementing layers  36  and  38  is shown in  FIG. 4 . As shown in  FIG. 4 , brightness enhancing film  54  (i.e., a transparent film of the type that may be used to implement layer  36  and/or layer  38 ) may have a series elongated protrusions such as ridges  56  that run parallel to each other. Each ridge  56  may have a triangular cross-section or other suitable cross-sectional shape. Ridges  56  may run parallel to ridge axis  62 . Each ridge may be characterized by a peak portion  58 . Adjacent ridges may be separated by interposed troughs  60 . Peaks  58  may be separated from each other by a pitch P of about 24 microns (e.g., a pitch from 5-50 microns or other suitable pitch size). Troughs  60  may likewise be separated from each other by a pitch P of about 24 microns (e.g., a pitch from 5-50 microns or other lateral separation). 
     Peaks  58  and troughs  60  may have elongated shapes that extend along axis  62 . In an assembled backlight unit, one brightness enhancement film (e.g., film  36 ) may have a ridge axis such as axis  62  that is oriented at one angle with respect to light  26  exiting light source  24  and another brightness enhancing film (e.g., film  38 ) may have a ridge axis such as axis that is oriented at another angle with respect to light  26  exiting light source  24 . Using different orientation angles for the ridge axis of each film may help reduce undesired Moiré effects that might otherwise result from aligning the ridges of films  36  and  38  in parallel with each other. 
     In the example of  FIG. 4 , ridges  58  have a triangular cross section with rounded peaks. This is merely illustrative. For example, ridges  58  may be configured to form sinusoidal corrugations or a series of parallel elongated protrusions with other cross-sectional shapes. 
     Brightness enhancing film  54  may be formed by embossing or otherwise processing a polymer film layer or may be formed by patterning a liquid polymer (e.g., a ultraviolet-light-cured resin) on a solid polymer substrate (e.g., a polyester film such as polyethylene terephthalate film). As an example, portion  66  of brightness enhancing film  54  may be formed from a solid polymer substrate layer such as a flexible sheet of polyethylene terephthalate and portion  64  of brightness enhancing film  64  may be formed from ultraviolet-light-cured resin. 
       FIG. 5  is a cross-sectional side view of a system of the type that may be used in forming brightness enhancing film  54  of  FIG. 4 . As shown in  FIG. 5 , system  68  may include rollers such as roller  74  and roller  82 . Roller  74  may rotate in direction  78  about rotational axis  80 . Roller  82  may rotated in direction  86  about rotational axis  84 . Resin dispensing tool  70  may dispense uncured liquid resin (e.g., liquid ultraviolet-light-curable polymer resin) on the surface of flexible polymer substrate  66 . Roller  74  may have a patterned surface with protruding features  76 . As layer  66  is passed through rollers  74  and  82  in direction  92 , resin  72  may be patterned by features  76 . Light  90  (e.g., ultraviolet light) from light source  88  may cure resin  72  on the surface of layer  66 , thereby forming patterned ridge structures  64 . 
     As shown in the cross-sectional diagram of  FIG. 6 , peaks (tips)  58  of ridges  56  may have a rounded shape. This may help make brightness enhancement film  54  robust and resistant to damage during an impact event that generates force on the surface of display  14 . 
     Conventional brightness enhancing films may have ridges with triangular cross sections and tips that are sharp (i.e., a tip shape characterized by a radius of curvature of about 0.5 microns or less). This makes the tips of conventional brightness enhancing films vulnerable to being crushed when display  14  is struck by an external object. Crushed portions of a conventional film may give rise to uneven backlighting and undesirable white or dark patches on a display. 
     In contrast, ridges  56  may have a rounded shape with a radius of curvature R of greater than 0.5 microns, and preferably greater than 1 micron, greater than 2 microns, 2-4 microns, 1-5 microns, greater than 3 microns, or greater than 4 microns. By providing peaks  58  of triangular ridges  56  or other suitable ridges  56  with sufficiently rounded shapes, the susceptibility of ridges  56  to damage during impact events on display  14  may be significantly reduced. For example, resistance to damage in a ball drop test may be enhanced by a factor of two or three in comparison to conventional sharp-tipped films. The use of rounded peaks  58  for ridges  56  may therefore make display  14  less vulnerable to damage during use of device  10  by a user. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20120614
Publication Date: 20140520
Grant Date: 20140520
Priority Date: 20120614
Inventors: DOYLE DAVID A.
WURZEL JOSHUA G.
Assignee: APPLE INC
CPC Classifications: [{"code": "G09F9/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1335", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133507", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1335", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/0231", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133507", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y10T428/2457", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1335", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09F13/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/0231", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0053", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0053", "inventive": true, "first": true, "tree": "[]"}, {"code": "Y10T428/2457", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 49755743