Adhesive stacking for multiple optical films Number:7,520,654 from the United States Patent and Trademark Office (PTO) owispatent In a new packaging method for light management films in displays, such as liquid crystal displays, a stack of two or more optical films is held together before insertion into the display frame. The stack includes at least two of the films that are adhered together using adhesive positioned outside the viewing area of the films. In some embodiments, the adhesive is provided at one or more tabs provided around the periphery of the film stack.<H multiple, stacking, Adhesive, stacki, 7520654.html, Patent, pto, 7520654

Title: Adhesive stacking for multiple optical films

Abstract: In a new packaging method for light management films in displays, such as liquid crystal displays, a stack of two or more optical films is held together before insertion into the display frame. The stack includes at least two of the films that are adhered together using adhesive positioned outside the viewing area of the films. In some embodiments, the adhesive is provided at one or more tabs provided around the periphery of the film stack.

Patent Number: 7,520,654 Issued on 04/21/2009 to Freking, et al.

Inventors: Freking; Anthony J. (Vadnais Heights, MN), Kotchick; Keith M. (St. Paul, MN)
Assignee: 3M Innovative Properties Company (Saint Paul, MN)

Appl. No.: 12/168,372

Filed: July 7, 2008

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
10652998	Aug., 2003	7413336

Current U.S. Class: 362/627 ; 362/561; 362/606

Current International Class: F21V 7/04 (20060101)

Field of Search: 362/601,606,615,620,622,624,627,633,561 349/115,112

References Cited [Referenced By]

U.S. Patent Documents


3531358	September 1970	Rost et al.
3754813	August 1973	DePalma
3765281	October 1973	Wolfe
3788171	January 1974	Hoadley
3851093	November 1974	Sunstein
RE29091	December 1976	DePalma
4542449	September 1985	Whitehead
4576850	March 1986	Martens
4713273	December 1987	Freedman
4791540	December 1988	Dreyer, Jr.
4804253	February 1989	Stewart
4906070	March 1990	Cobb, Jr.
4971719	November 1990	Vaz et al.
4984144	January 1991	Cobb, Jr. et al.
5005108	April 1991	Pristash
5076668	December 1991	Dalisa
5128783	July 1992	Abileah
5146415	September 1992	Faris
5161041	November 1992	Abileah
5190370	March 1993	Miller
5207493	May 1993	Murase et al.
5247390	September 1993	Hed
5268782	December 1993	Wenz et al.
5280371	January 1994	McCartney, Jr.
5394255	February 1995	Yokota
5435963	July 1995	Rackovan et al.
5467208	November 1995	Kokawa
5492590	February 1996	Kakai et al.
5521797	May 1996	Kashima
5550657	August 1996	Tanaka
5552907	September 1996	Yokota
5592332	January 1997	Nishio
5596429	January 1997	Kokawa
5598280	January 1997	Nishio
5600455	February 1997	Ishikawa
5600462	February 1997	Suzuki
5627926	May 1997	Nakamura
5659408	August 1997	Wenyon
5748269	May 1998	Harris
5767931	June 1998	Paczkowski
5771328	June 1998	Wortman
5828488	October 1998	Ouderkirk et al.
5868892	February 1999	Kilma, Jr.
5919551	July 1999	Cobb, Jr.
5997964	December 1999	Klima, Jr.
6052164	April 2000	Cobb, Jr.
6079840	June 2000	Ono et al.
6104854	August 2000	Masaki
6185043	February 2001	Imamura
6191833	February 2001	Hirakata
6219127	April 2001	Hirakata et al.
6305812	October 2001	Kim et al.
6322236	November 2001	Campbell
6364497	April 2002	Park et al.
6411353	June 2002	Yarita et al.
6462794	October 2002	Yoshikawa et al.
6502945	January 2003	Kim et al.
6538709	March 2003	Kurihara
RE38243	September 2003	Oe et al.
6613421	September 2003	Jonza et al.
6626550	September 2003	Choi
6661482	December 2003	Hara
6661487	December 2003	Takahashi et al.
6685795	February 2004	Braun
6708595	March 2004	Chaussade et al.
6846089	January 2005	Stevenson et al.
6847417	January 2005	Kim
6891580	May 2005	Jang et al.
6913365	July 2005	Masaki et al.
7147358	December 2006	Freking et al.
7339635	March 2008	Freking et al.
2002/0080598	June 2002	Parker et al.
2002/0124950	September 2002	Klima et al.
2002/0149712	October 2002	Kitamura et al.
2002/0196397	December 2002	Takahashi et al.
2003/0063251	April 2003	Murata et al.
2003/0133207	July 2003	Minami et al.
2004/0141103	July 2004	Kotchick
2004/0150874	August 2004	Suzuki
2005/0238852	October 2005	Nakayama et al.
2006/0108050	May 2006	Satake et al.

Foreign Patent Documents


3 407 431	Aug., 1985	DE
0 395 957	Nov., 1990	EP
0 531 939	Mar., 1993	EP
0 770 899	May., 1997	EP
1 134 068	Sep., 2001	EP
1 168 282	Jan., 2002	EP
1 220 014	Jul., 2002	EP
1 302 922	Apr., 2003	EP
06-18707	Jan., 1994	JP
06-342106	Dec., 1994	JP
07-043713	Feb., 1995	JP
07-078254	Mar., 1995	JP
08-248209	Mar., 1995	JP
09-127309	May., 1997	JP
09-267424	Oct., 1997	JP
11-259021	Sep., 1999	JP
2001-301104	Oct., 2001	JP
2002-304254	Oct., 2002	JP
2003-207767	Jul., 2003	JP
10-1997-0007399	Feb., 1997	KR
WO 95/27919	Oct., 1995	WO
WO 96/27757	Sep., 1996	WO
WO 97/28468	Aug., 1997	WO
WO 01/50160	Jul., 2001	WO
WO 02/21167	Mar., 2002	WO
WO 03/010569	Feb., 2003	WO
WO 03/042747	May., 2003	WO

Other References

US 2001/0013282 A1, 08/2001, LaBelle et al. (withdrawn) cited by other.

Primary Examiner: Choi; Jacob Y

Parent Case Text

This application is a divisional of U.S. application Ser. No. 10/652,998 filed Aug. 29, 2003 now U.S. Pat. No. 7,413,336.

Claims

We claim:

1. A display system, comprising: an illumination unit; a display unit; and a light management unit disposed between the illumination unit and the display unit to manage light passing from the illumination unit to the display unit, the light management unit comprising a stack of at least first and second optical films each of the at least first and second optical films having at least one peripheral tab, the at least one peripheral tabs of the at least first and second optical films being in relative alignment, and a layer of adhesive disposed between the at least one peripheral tabs of the at least first and second optical films to adhere at least the first and second optical films to each other.

2. A system as recited in claim 1, further comprising a control unit coupled to the display unit to control an image displayed by the display unit.

3. A system as recited in claim 1, wherein the display unit includes a liquid crystal display layer.

4. A system as recited in claim 3, further comprising an absorbing polarizer layer on a viewing side of the liquid crystal display layers and an absorbing polarizer on an illumination unit side of the liquid crystal display layer.

5. A system as recited in claim 1, wherein the illumination unit includes one or more light sources illuminating a light guide panel, light from the one or more light sources entering the light guide panel and passing through a face of the light guide panel to the light management unit.

6. A system as recited in claim 1, further comprising a frame holding the illumination unit, the light management unit and the display unit.

7. A display system, comprising: an illumination unit; a display unit; and a light management unit disposed between the illumination unit and the display unit to manage light passing from the illumination unit to the display unit, the light management unit comprising a stack of at least first and second optical films, the first optical film having a first peripheral edge, at least one first peripheral tab disposed on the first peripheral edge, the second optical film being disposed over the first optical film and having a second peripheral edge, at least one second peripheral tab disposed on the second peripheral edge, the at least one second peripheral tab being aligned with the at least one first peripheral tab, the at least one second peripheral tab being adhered to the at least one first peripheral tab with an adhesive.

8. A system as recited in claim 7, further comprising a control unit coupled to the display unit to control an image displayed by the display unit.

9. A system as recited in claim 7, wherein the display unit includes a liquid crystal display layer.

10. A system as recited in claim 9, further comprising an absorbing polarizer layer on a viewing side of the liquid crystal display layers and an absorbing polarizer on a light source side of the liquid crystal display layer.

11. A system as recited in claim 7, wherein the illumination unit includes one or more light sources illuminating a light guide panel, light from the one or more light sources entering the light guide panel and passing through a surface of the light guide panel to the light management unit.

12. A system as recited in claim 7, further comprising a frame holding the illumination unit, the light management unit and the display unit.

13. A system as recited in claim 12, wherein at least the first and second optical films of the light management unit include one or more peripheral alignment tabs for locating the light management unit within the frame, the one or more peripheral alignment tabs being attached together with adhesive.

Description

FIELD OF THE INVENTION

The present invention is directed to optical displays, and more particularly to an approach for packaging light management optical films used in optical displays.

BACKGROUND

Optical displays, such as liquid crystal displays (LCDs) are becoming increasingly commonplace, finding use, for example in mobile telephones, hand-held computer devices ranging from personal digital assistants (PDAs) to electronic games, to larger devices such as laptop computers, and LCD monitors and television screens. The incorporation of light management films into optical display devices results in improved display performance. Different types of films, including prismatically structured films, reflective polarizers and diffuser films are useful for improving display parameters such as output luminance, illumination uniformity, viewing angle, and overall system efficiency. Such improved operating characteristics make the device easier to use and may also increase battery life.

The light management films are stacked, one by one, into the display frame between a backlight assembly and the flat panel display. The stack of films can be optimized to obtain a particular desired optical performance. From a manufacturing perspective, however, several issues can arise from the handling and assembly of several discrete film pieces. These problems include, inter alia, the excess time required to remove protective liners from individual optical films, along with the increased chance of damaging a film when removing the liner. In addition, the insertion of multiple individual sheets to the display frame is time consuming and the stacking of individual films provides further opportunity for the films to be damaged. All of these problems can contribute to diminished overall throughput or to reduced yield, which leads to higher system cost.

SUMMARY OF THE INVENTION

In view of the problems listed above, the present invention is directed to a new packaging method in which two or more optical films are held together in a stack together before insertion into the display frame. This makes handling of the films easier, reduces the number of steps required for assembly of the display device, reduces the chance of damaging the films and increases yields.

Generally, the present invention relates to packaging stacks of two or more light management films, where at least two of the films are adhered together using adhesive positioned outside the viewing area of the films. In some embodiments, the adhesive is provided at one or more tabs provided around the periphery of the film stack.

In one embodiment, the invention is directed to a light management film package for managing light within a display. The package comprises a stack of at least first and second optical films. Each of the at least first and second optical films has at least one peripheral tab. The at least one peripheral tabs of the at least first and second optical films are in relative alignment. A layer of adhesive is disposed between the at least one peripheral tabs to adhere the at least first and second optical films to each other.

Another embodiment of the invention is directed to a display system that includes an illumination unit, a display unit; and a light management unit disposed between the illumination unit and the display unit to manage light passing from the illumination unit to the display unit. The light management unit comprises a stack of at least first and second optical films. Each of the at least first and second optical films has at least one peripheral tab. The at least one peripheral tabs of the at least first and second optical films are in relative alignment. A layer of adhesive is disposed between the at least one peripheral tabs to adhere the at least first and second optical films to each other.

Another embodiment of the invention is directed to a method for stacking optical films for an optical display. The method includes adhering, with an adhesive layer, a first optical film to a second optical film at portions of the first and second optical films corresponding to peripheral optical tabs. The first and second optical films are cut to produce respective first and second optical film segments having respective peripheral tabs. The first and second optical films form a film stack having aligned and adhered peripheral tabs.

Another embodiment of the invention is directed to a light management film package for managing light within a display. The package comprises a first optical film having a first peripheral edge, with at least one first peripheral tab disposed on the first peripheral edge. A second optical film is disposed over the first optical film. The second optical film has a second peripheral edge, with at least one second peripheral tab disposed on the second peripheral edge. The at least one second peripheral tab is aligned with the at least one first peripheral tab. The at least one second peripheral tab is adhered to the at least one first peripheral tab with an adhesive.

Another embodiment of the invention is directed to a display system that has an illumination unit, a display unit and a light management unit disposed between the illumination unit and the display unit. The light management unit manages light passing from the illumination unit to the display unit. The light management unit comprises a stack of at least first and second optical films. The first optical film has a first peripheral edge, with at least one first peripheral tab disposed on the first peripheral edge. The second optical film is disposed over the first optical film. The second optical film has a second peripheral edge, with at least one second peripheral tab disposed on the second peripheral edge. The at least one second peripheral tab is aligned with the at least one first peripheral tab. The at least one second peripheral tab is adhered to the at least one first peripheral tab with an adhesive.

The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 schematically illustrates a display unit;

FIG. 2A schematically illustrates a light management film unit according to an embodiment of the present invention;

FIG. 2B schematically illustrates a light management film unit according to another embodiment of the present invention;

FIGS. 3A-3C schematically illustrate top view of different embodiments of a light management film unit according to principles of the present invention;

FIG. 4 schematically presents a perspective view of a display unit according to an embodiment of the present invention;

FIG. 5 schematically illustrates an embodiment of a display unit according to principles of the present invention;

FIG. 6 schematically illustrates steps in a system useful for manufacturing a light management film unit according to principles of the present invention;

FIG. 7 schematically illustrates another embodiment of a system for manufacturing a film stack according to principles of the present invention;

FIG. 8 schematically illustrates an embodiment of a film stack with a liner according to principles of the present invention; and

FIG. 9 schematically illustrates an embodiment of a system useful for generating a film stack with a liner as shown in FIG. 8, according to principles of the present invention.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention is applicable to displays, such as liquid crystal displays, and is particularly useful for reducing the number of steps required for making such a display.

A display system 100 is schematically shown in FIG. 1. The system includes in electronic display element 102, such as a liquid crystal display (LCD) panel, which is typically sandwiched between two glass layers. Furthermore, the display element 102 may include absorbing polarizers above and below the LCD panel to provide the polarization contrast typically required for producing a polarization-based image.

A backlight assembly 104 may be used as the primary light source for the display element 102, or may be used for providing light through the display element 102 when there is insufficient ambient light for the user to view the image formed by the display element 102. In one particular embodiment, backlight assembly 104 may include several elements such as a light source 106, a light guide 108, and one or more reflector layers 110. An important feature of the display system 100 in many applications is that the total thickness of the system 100 be small. Accordingly, the light source 106 is commonly positioned to the side of the light guide 108, and the light guide 108 directs the light from the light source 106 up through the system 100 towards the display element. The light source 106 may be any suitable type of light source. In many applications, it is desirable to illuminate the display 100 with white light, in which case the light source 106 may be a fluorescent lamp, an array of light emitting diodes whose colors are mixed to produce white light, or the like.

In the illustrated embodiment, the light guide 108 is provided with diffusely reflecting regions 112 that direct light from the light guide 108 towards the display element 102. The light guide 108 may include other types of elements for directing light towards the display element 102, such as light extraction regions on the upper surface of the light guide 108 facing the display element. Light extraction features may also be provided on both the upper and lower surfaces of the light guide 108. It will be appreciated that the light guide 108 may be in the form of a slab, as illustrated, but may also be in another geometry, for example a wedge. Also, other devices may be used to transmit light from the light towards the display element 102.

Other embodiments of backlight assembly may also be used, for example, the backlight assembly may be formed with an array of lamps positioned in a suitable reflective cavity. While there are several other options for the design of backlight assembly, it should be appreciated that the specific design of the backlight assembly is not important for the present invention.

A number of light management films are typically interposed between the backlight assembly 104 and the display element 102 in a light management film stack 114. The light management film stack 114 typically contains a number of films to control various optical characteristics of the light incident on the display element 102. For example, the light management film stack may include a first diffuser film 116. The first diffuser film may be used to help homogenize the intensity of the light passing up through the film stack 114.

Films 118 and 120 may be structured films, each having a row of prism-shaped ribs 119 running across its upper surface. The prism-shaped ribs help to direct the light towards the optical axis 130 of the system 100. The ribs 119 of the film 118 redirect the light in a direction parallel to the plane of the figure. The ribs of the film 120 are typically arranged non-parallel to those of the film 118. The ribs of the film 120 may be perpendicular to the ribs 119 of the film 118 so that the ribs of the film 120 redirect the light in a direction perpendicular to the plane of the figure. This may be referred to as a crossed-structure configuration. In another embodiment (not shown), the layers 118 and 120 may be substituted with a single structured optical film that redirects light received from the backlight assembly 104.

The stack 114 may also include a reflective polarizer layer 122. This layer is useful for recycling light from the backlight assembly 104 that is in the wrong polarization state for transmission through the display element 102 as image light. The light reflected by the reflective polarizer 122 may be diffusely reflected by the reflector 110, with some polarization mixing, so that at least a portion of the reflected light makes it through to the display element 102 with the correct polarization state for use as image light. In addition, a polarization converter, for example a quarter wave retarder layer may be used to convert the polarization of the light reflected from the reflective polarizer 122. The reflective polarizer 122 may be any suitable type of reflective polarizer, for example a multi-polymer layer film, a cholesteric polarizer or a wire-grid polarizer.

The stack 114 may also include another sheet 124, often referred to as a "cover sheet". The cover sheet 124 may be a relatively weak diffuser. The diffuser sheets 116 and 124 may be useful for making the illumination of the display element 102 uniform to the viewer. The cover sheet 124 may also include a shading frame, which is a mask to define the viewing area of the film stack 114, or to mask edge effects of the backlight 104 or of the stack 114. It should be noted that depending on the actual system design, some of the elements represented by layers 116-124 may be missing, added to, or substituted with other functional elements.

With such a film stack 114, each of the discrete optical film layers 116-124 must be individually inserted to the display frame during manufacture. Since it is often important to reduce the thickness of the films 116-124, to reduce overall display thickness, the individual films 116-124 may be made very thin. As a result, the individual film stiffness may be low, which can result in increased difficulty in handling, processing, and assembly during manufacture. Also, because these film layers often have precise optical functionality, the introduction of surface defects, such as scratches or debris may compromise total system performance. Often, each film layer is provided with dual side protective liners, which must be removed prior to insertion into the backlight assembly. The action of liner removal and the resulting insertion into the backlight assembly can expose the delicate film to a host of potential modes of defect introduction. Examples of such defects include scratching, lint and other debris attracted to the film surfaces due to the build up of static electricity. In addition, the removal of the liners requires additional fabrication steps, and so the reduction in the number of liners to be removed results in fewer manufacturing steps, with concomitant savings in manufacturing costs. When multiple film layers are incorporated into the backlight assembly, the probability of creating/introducing a defect can grow ever higher, which can result in slower manufacturing throughput due to excessive re-work and higher unit costs.

This invention is directed to approaches to holding together various optical film layers and/or components in a stack in order to improve handling and final backlight/system assembly efficiency.

One method of holding at least two optical layers together in a stack includes inserting an adhesive layer between peripheral tab portions of the layers. Such adhesive bonding can accomplish multiple film adhesion, but each adhesive layer may add an incremental thickness, typically of the order of 30 .mu.m. In certain circumstances, such an increase in the overall thickness of the film stack may be acceptable in the final construction. Also, where the adhesive layer is limited to the periphery of the optical film, outside the viewing area of the film, the adhesive layer does not result in deterioration in the refractive properties of any structured film surface that may be present. Thus, the technique may be used for stacking films that have a structured refractive surface, such films as the prismatic films 118 and 120.

One approach to forming an adhered film stack 200 according to the present invention is schematically illustrated in FIG. 2A. Layers 216-224 represent different optical layers as may be found in a light management film stack in a display system. For example, layer 216 may be a diffuser layer, and layers 218 and 220 may be prismatically structured films for directing light, the orientation of layer 220 being crossed with respect to layer 218. Layer 222 may be a reflective polarizer layer while layer 224 may be a diffuser layer.

The adhesive 230 represents a layer of adhesive that secures adjacent film layers together. Adhesive 230 is limited in extent so as to that permit the presence of an air gap between unadhered portions of the film layers, for example where the surface of one of the films contains structure. Such an air gap may be useful in maintaining the efficient operation of certain optical films, such as structured optical films 218 and 220, for redirecting light towards the axis 232 of the stack 214. Adhesive 230 is typically located along an edge of the film layers, or on one or more side tabs of the layers 216-224. Such tabs may also serve as registration elements for mounting the stack 200 into the display frame.

Another embodiment of a film stack is schematically illustrated in FIG. 2B, in this case showing an adhesive layer 230 between a prismatically structured film 266 and another film 270. One or both of the films 266 and 270 may be indented to receive the adhesive 230. The height of the indent(s) 268 and 272 may be sufficient to accept the layer of adhesive while adding little or no extra height to the stack of films 266 and 270. The air gap 274 between the films 266 and 270 permits the prismatically structured film to redirect the light passing therethrough, but does not add to the thickness of the film stack.

Different approaches may be used to reduce or prevent the degradation of the optical quality of the stacked films. For example, care is taken to reduce the presence of contaminant particles between the films that may lead to Newton's rings. Further, one or both of the surfaces that touch together may be provided with small height variations to reduce wet-out, for example as is discussed in U.S. Pat. No. 6,322,236, incorporated herein by reference. Also, a prismatically structured film may be provided with a variable height structured surface, as described in U.S. Pat. No. 5,771,328, incorporated herein by reference.

Different types of adhesive 230 may be used, for example a pressure sensitive adhesive (PSA), a radiation cured resin, a hot melt glue, or an epoxy system. The adhesive may be applied as a transfer adhesive via a dry lamination process or wet coated adhesive using such techniques as screen printing or gravure coating.

A top view of a stack 300 of films is schematically presented in FIG. 3, showing only the topmost film sheet 302. The films in the stack have one or more peripheral tabs 304. The tabs 304 may take on many different shapes, number, and location depending on the specific design of the final backlight/system assembly. In the illustrated embodiment, the shaded areas 306 correspond to areas provided with adhesive to adhere to the layer below.

The tabs 304 may provide a convenient area to hold the stack 300 during assembly or inspection, and may also be used for registering the film stack when mounting the stack with the display. In addition, the tabs 304 may be provided in a non-symmetric pattern around the film. This helps an assembler to immediately identify which side of the film stack is uppermost, thus enabling quicker assembly of the display unit, and reducing errors from incorrectly inserting a film in an inverted position.

The portions of the films, through which the light passes to the display element and to the viewer, are referred to as viewing areas. The viewing area of the topmost film 302 is shown schematically as the area enclosed within the dashed lines 310. In order to reduce the size of the film package, the viewing area preferably takes up as much of the film area as possible. The viewing area may extend, in some cases therefore, to the edge of the film. Furthermore, it is important to maintain high optical quality in the viewing area. Since some adhering techniques change the optical qualities of the film, it is important in many circumstances to place the adhesive outside the viewing area. Thus, the adhesive 312 may be disposed on at least a portion of the peripheral edge 314 of the film itself, for example as schematically illustrated in FIG. 3B.

Another embodiment of a film stack is schematically illustrated in FIG. 3C. In this embodiment, there are tabs 304 provided on two sides of the stack, and the peripheral edge on which some adhesive 306 is disposed is also an edge that has tabs 304. It will be appreciated that many different combinations and placements of tabs are possible, and that different sides of the stack may receive adhesive.

The choice of an adhesive layer for use in adhesively stacking optical films may be similar to those described in Table I.

TABLE-US-00001 TABLE I Example Adhesives and Characteristic Thicknesses Adhesive Properties Total Adhesive Thickness PET Carrier Adhesive (Including Carrier) Thickness Choice [mils] [mils] Teraoka 1.1 N/A 707 3M 9019 1.1 0.5 3M 9313 1.1 0.5 3M 9009 1.9 0.5 3M 467 2.3 None MP 3M 4597 2.4 0.6 3M 9492 2.5 0.5

An exploded view of an embodiment of a display 400 is presented in FIG. 4, showing how the different parts of a display may be assembled to form the display. In this particular embodiment, the display 400 uses a frame 402 to contain the other components. The frame 402 may contain one or more slots 404, or other alignment features, for example pins or the like, for aligning the films in the light management film stack.

The backlight assembly 406 is the first component placed within the frame 402. The backlight assembly 406 includes one or more light sources 408 that illuminate the edge of the light guide 410. The light management film stack 412 is then positioned above the backlight assembly 406. The light management film stack 412 includes two or more light management films 414 that are adhered together using an adhesive 416. In the illustrated embodiment, the adhesive 416 is located on the alignment tab 418 that aligns the film stack 412 with the alignment slot 404. The display element 420, for example a liquid crystal display element, including polarizers, is positioned above the light management film stack 412.

It will be appreciated that the light sources 408 and the display element have electrical connections to receive electrical power and control signals. The electrical connections are not shown.

The light management film stack may also be attached directly to one of the display elements. One example of such a display is schematically illustrated in FIG. 5. In this particular embodiment, a film stack 514 is formed from a stack of adhered films 516-524. In the illustrated embodiment, films 518 and 520 are prismatically structured films. Film 516 may be a diffuser or may be a light turning film, for example a prismatically structured film with the prismatically structured surface facing towards the backlight assembly 504.

The display also includes a display element 502 and a backlight assembly 504, having a light source 506, a light guide 508, and a lower reflector 510. The optical film stack 514 contains at least two films adhered together using one of aforementioned methods. The film stack is then anchored to another element of the display unit, such as the display element 502 and/or the backlight assembly 504.

In the illustrated embodiment, the film stack 514 is attached to the backlight assembly 504, for example using adhesive around the edges of film 516 and the light guide 508. In another embodiment, the optical film stack 514 may be anchored to the display element 502 or to the frame (not illustrated). This approach may be advantageous as it may be performed automatically, thereby avoiding manual insertion of the optical film stack. In this way, the introduction of defects may be minimized and manufacturing throughput and unit costs can be improved.

In some embodiments, the lower film 516 may extend beyond the right edge of the stack 514 and the overhanging portion of the film 516 may be used as a base on which to mount the light source 506.

A controller 530, for example a processor or the like, is typically coupled to the display element 502 to control the image seen by the viewer.

The use of an adhered film stack in such devices as flat panel displays offers several advantages. Many of the light management films used in a display are very thin. For example the prismatically structured films may each have a thickness of about 62 .mu.m, while a reflective polarizer may have a thickness in the range of about 1 .mu.m to 100's of .mu.m. Light management films used in displays also tend to be very flexible, which may cause problems during assembly of the display. Holding multiple thin, flexible films together in a stack, on the other hand, creates a stiffer film pack, which can ease assembly issues. Eliminating the sequential stacking of discrete layers when assembling the display also minimizes the probability of defect introduction and ultimate yield loss. Additionally, since films are usually delivered by the manufacturer to the display integrator with protective linings on either side, the number of protective liners that the display integrator has to remove is reduced when the films are held together in a stack. This further optimizes yield and manufacturing unit costs.

Also, the stacking of optical films may improve final inspection and quality yield versus the separate examination of each discrete film layer. This can be easily considered when using structured optical films, which may tend to distort and camouflage defects in underlying or other film layers that would otherwise be detected if these layers were inspected individually.

It will be appreciated that the film stack may, in addition to including at least two films that are adhered between peripheral tabs, also include a bond between other films that is not adhesive between peripheral tabs.

Optical films are often fabricated in large sheets, in some cases on a roll. The individual film pieces that are assembled in a display are cut from the large sheet, usually by a die. Several different approaches may be used for forming film stacks. For example, the films may be die-cut to the appropriate shape and then aligned in a stack and adhered. In other approaches, the films may be adhered at the same time as being die cut, or may be adhered even before being die cut. Furthermore, stacks may be formed of two or more adhered films. It should be appreciated that a stack that includes three or more films may be formed using one or more adhering steps. For example, the first two optical films may be laminated together to form the basis of the stack, and then one or more additional films laminated to the stack. In another example, three or more optical films may be laminated together in a single lamination operation.

Some methods may be more advantageous for manufacturing large numbers of film stacks. One such method, referred to as a 90.degree. indexing process, is now described with reference to FIG. 6. This process is particularly useful for adhering two films together that each have structure, where the structure of the first film is oriented perpendicular to the other film. One example of such films is the prismatic brightness enhancing film often found in liquid crystal displays. Such a film is typically formed by forming the prismatic pattern using a cylindrical roller, so that the prismatic structures lie along the web of the film. This process may also be used where the two films being adhered to each other have no preferred orientation.

The 90.degree. indexing process takes two input rolls 602 and 604, each with a downweb structure, and unwinds them at 90.degree. to each other. As the material from the first input roll 602 is unwound, adhesive strips 606 are laminated in a laminator 608 to the top surface of the first roll 602. Material from the second input roll 604 is unwound, cut into sheets, and placed on the top of the adhesive strips at the sheet cutting station 610. The two layers of film are now adhered to each other in a stack, with the surface structures of the two films oriented perpendicular to each other.

The stacked material proceeds to a die cutting station 612. A finished product carrier 614, or liner, is fed into the die cutting station. At the die cutting station 612, tabbed parts are cut out of the stacked material and transferred to the finished product carrier. Any suitable type of die may be used in the die cutting station, for example a flatbed die, a matched metal die or rotary dies. The process indexes and the liner with the finished part indexes out of the die for the next cut and transfer. A finished product winder 616 extracts the finished product from the die cutter, while a waste winder 618 extracts the waste material from the die cutter. The finished product and waste material winders 616 and 618 may be oriented at 90.degree. from each other.

Another embodiment of a process for forming an adhered stack is now is described with reference to FIG. 7. This process is particularly useful where the films being adhered have no particular orientation, or the structures on the films are such that the two films can be stacked from parallel rolls. A first film roll 702 contains a roll of film that has a liner on at least one side. The liner 704 is stripped by a stripping roll 706. A second film roll 708 may also contain a roll of film that has a liner on at least one side. The liner 710 is stripped by a second stripping roll 712. The stripped films 714 and 716 pass towards a lamination station 718 having a pair of rollers roller 720 and 722. Adhesive 724 is fed in between the stripped films 714 and 716 from an adhesive roll 726. The adhesive 724 may be shaped to include clear areas that correspond to the viewing area of the subsequent film stack. The two films 714 and 716 are laminated together in the lamination station 718 to form a laminated stack 728.

The laminated stack 728 is fed to a die cutting station 730, where a die cuts the stack shape, including the peripheral tabs. Any suitable type of die may be used in the die cutting station, for example a flatbed die, a matched metal die or rotary dies. The die is preferably phased to the clear areas of the adhesive so that the stack is cut out at those locations where there is no adhesive in the viewing area of the stack. In one particular embodiment, the die may kiss cut through the laminated stack 728 to a controlled depth, to the lower liner of the lower film. The peripheral weed 732, may then be stripped away, leaving an array of film stacks 734 on the lower liner layer 736. The lower liner layer 736 may then be received on a collection roller 738.

The two films 714 and 716 that may be any light management films. For example the first film 714 may be a prismatically structured film with the ribs oriented across the web of the film 714, while the second film 716 is a prismatically structured film with the ribs oriented along the web of the film 716. The first and second films 714 and 716 may also be other types of light management films, such as a diffuser or a reflective polarizer film.

In another method of adhering film to form an adhered stack, different films may be fed in directions at right angles to each other. For example, two roll