Patent Application
20080049330
The invention may be more completely understood and appreciated in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, where the drawings are not to scale and in which:
a is a schematic side-view of another film laminate;
The present invention is applicable to displays, such as liquid crystal displays (LCDs), and is believed to be particularly useful for hand-held LCD devices where it is desirable for the device to be thin, have high gain, and have a display area free of visible defects.
In the specification, a same reference numeral used in multiple figures refers to the same or similar elements having the same or similar properties and functionalities.
Display unit 12 could be a liquid crystal display (LCD) panel, which is typically sandwiched between two glass layers. Display unit 12 may include absorbing polarizers above and below the LCD panel to provide polarization contrast typically required for producing a polarization-based image. Control unit 13 controls the image displayed on display unit 12.
Back light assembly 14 is typically used for providing light through display unit 12 when there is insufficient ambient light for the user to view the image formed by display unit 12. Light guide 18 directs the light from light source 16 up through system 10 towards the display unit. Light source 16 may be any suitable type of light source. In many cases, light source 16 includes one or more fluorescent lamps.
Light management film stack 22 includes a first diffuser film 24, light directing films 26 and 28, and a reflective polarizer film 34. First diffuser film 24 is configured to make uniform the intensity of the light passing up through film stack 22.
Light directing films 26 and 28 may be structured films, as shown in
Films 26 and 28 may be arranged, relative to each other, such that their arrays of structured elements 27 and 29 run parallel, or more typically, non-parallel. In the embodiment of
Structured elements 27 of film 26 may include a pattern of tall prisms separated by short prisms, as shown in
Film 26 may be adhered to film 28 via an adhesive layer 32, as shown in
It should be noted that, depending on a system design, some of the elements represented in film stack 22 may be missing, added to, or substituted with other functional elements. Since it is often important to reduce the thickness of stack 22 to reduce overall display thickness, individual films in film stack 22 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, for example, during manufacture. Bundling various optical film layers may improve handling and final system assembly efficiency. In addition, the bundling of films may improve stiffness and result in films that are more mechanically stable.
One method of bundling optical films includes inserting an adhesive layer between each of the films to form a film laminate. The adhesive layer may lie across the entire stack from edge to edge, may be positioned along one or more edges of the stack, or may be patterned over the area of some or all of the film layers.
Structured surface 48 includes a plurality of tall structures 58 which are separated by a plurality of short structures 60. Each tall structure 58 has a first side surface 62a and a second side surface 62b, which intersect at their top edges to form a top 64. Each short structure 60 has a first side surface 66a and a second side surface 66b, which intersect to form a top 68. Adjoining structures, whether tall or short, intersect at their bottom edges to form grooves 70, which may or may not lie in the same plane relative to one another. It is useful to define a common reference plane 72 disposed between surfaces 48 and 50 and located closest to second major surface 50 of first film 42. Reference plane 72 may also be defined as a plane located below and closest to structured surface 48 without passing through any of tall structures 58 or short structures 60. Location of the common reference plane is, at least in part, determined by a lowest groove among grooves 70.
Each tall structure 58 has a height Hi measured from top 64 to common reference plane 72. Similarly, each short structure 60 has a height H2 measured from top 68 to reference plane 72. As shown in
In the exemplary embodiment of
Tops 64 of neighboring tall structures 58 are separated by a distance D. In the embodiment of
Each tall prism has an inclusion or apex angle α and each short prism has an inclusion angle β. In some cases, at least two tall prisms have different inclusion angles, although in some other applications, all tall prisms have the same inclusion angle. In some applications, at least two short prisms have different inclusion angles, although in some other applications, all short prisms have the same inclusion angle. In some applications, at least one tall prism has a different inclusion angle than at least one short prism. In some cases, tall and short prisms have the same inclusion angle.
Base film portion 52 has a thickness TB measured from reference plane 72 to second major surface 50. Thickness TB of base film portion 52 may vary depending on, for example, the particular display system in which film laminate 40 is intended to be used. In some applications, such as a display system for a television, thickness TB may have a large acceptable range of values, as compared to hand-held applications, in which thickness TB may be minimal. A general range for thickness TB is about 1 to 510 microns. For hand-held applications, a suitable range for thickness TB is about 25 to 52 microns. In some other cases, a range for thickness TB can be about 1 to 15 microns. For larger display systems, a suitable range for thickness TB is less than about 510 microns. In some applications, a suitable range for thickness TB is from about 380 to 510 microns.
In some cases, first film 42 may be disposed on a substrate having a thickness ranging from about 25 to 510 microns, or about 25 to 52 microns, or about 1 to 15 microns. In cases where first film 42 is disposed on a substrate, thickness TB in first film 42 may be minimal, including zero microns.
Structured surface 48 of first film 42 is shown in
In
Full face adhesion can generate moire and more pronounced wet out patterns. Wet out occurs when prism tips become optically coupled to an adjacent material. Wet out can reduce gain.
An advantage of the present invention is improved adhesion because of full face adhesion between adjacent films. Another advantage of the invention is that distance D is chosen so that the visibility of a wet out pattern is reduced or eliminated. Furthermore, D is selected so that any optical coupling between the two films due to adhesive layer 46 results in little or no reduction in gain.
As shown in
Furthermore, the short structures can have any suitable shape capable of directing light in an application.
In some applications, thickness TA of adhesive layer 46 may range from about 1 to 2.5 microns, depending, for example, on a composition of adhesive layer 46, distance D, and the differential between height H1 and height H2. In some applications, TA can be smaller than 1 micron or larger than 2.5 microns.
In some cases, one or both of films 42 and 44 may include other layers not shown explicitly in
a is a schematic side-view of a film laminate 140 including a first film 142 and a second film 144. First film 142 includes a structured surface 148, an opposing second major surface 150, and a base film portion 152 disposed between structured surface 148 and second major surface 150. Second film 144 includes a first major surface 154 and an opposing second major surface 156. An adhesive layer 146 is disposed between second major surface 156 of second film 144 and structured surface 148 of first film 142.
Structured surface 148 includes a plurality of tall structures 158, such as tall structures 158a, 158b and 158c, which are separated by a plurality of short structures 160, such as short structures 160a-160j. A distance D is defined as a spacing between neighboring tall structures 158, where D can, in general, be different for different neighboring tall structures. Adjoining structures, tall and short alike, are separated by grooves 170, which, as shown in the embodiment of
Tall structures 158 have heights H1, such as heights H1a-H1c, and widths W1, such as widths W1a-W1c, as shown in
Similarly, as shown in
Each tall structure 258 has a first side surface 262a and a second side surface 262b, which intersect at their top edges to form a top 264. Each short structure 260 has a first side surface 266a and a second side surface 266b, which intersect to form a top 268. Adjoining structures, tall or short, intersect at their bottom edges to form grooves 270. Common reference plane 272 is defined as a plane disposed between surfaces 248 and 250. In some applications, plane 272 is located closest to second major surface 250. In some cases, common reference plane 272 may be defined as a plane located below and closest to structured surface 248 without passing through any of structures 258 or 260.
Each tall structure 258 has a height H1 measured from top 264 to common reference plane 272; each short structure 260 has a height H2 measured from top 268 to common reference plane 272. Each tall structure 258 has a width W1 and each short structure 260 has a width W2, where widths W1 and W2 are defined as the smallest lateral distance between the two side surfaces of the structure in a plane that includes at least one of the two grooves associated with that structure.
In the exemplary embodiment shown in
A suitable range of values for widths W1 and W2 is about 10 to 60 microns. A suitable range of values for heights H1 and H2 is about 5 to 30 microns. It is recognized that widths W1 and W2, as well as heights H1 and H2, may be any value within a wide range. The dimensions of the structures may typically be affected by such factors as the type of display, the desired thickness of the film stack, and the thickness of the adhesive.
Each structure 255 of second film 244 has a first side surface 274a and second side surface 274b which intersect at their top edges to form a top 276. Adjoining structures 255 intersect at their bottom edges to form grooves 278. In the exemplary embodiment of
Each structure 255 has a height H3 measured from top 276 to common reference plane 280 and a width W3. In the exemplary embodiment shown in
In the exemplary embodiment shown in
As shown in
In the embodiment shown in
In the embodiment shown in
As stated above, the present invention relates to an optimal range for distance D, where D is equal to a distance between tops of neighboring tall structures 258. In some cases, distance D may vary within structured surface 248 of film 242 (see, for example,
A height differential between tall structures 258 and short structures 260 can be in a range from about 1 micron to 10 microns. In some applications, thickness TA is in a range from about 1.0 to about 1.75 microns.
Forming a repeating pattern of tall structures and short structures increases gain and reduces wet out by reducing the contact area between films 242 and 244. The repeating pattern of film 242 of
In the table below, distance D is the distance between neighboring tall structures. For each test pattern, a laminate was prepared by adhering the test pattern film to a second structured film having all prisms with an apex angle of 90 degrees and a spacing of 24 microns between adjacent prisms. Film laminate 240, as shown in
Based upon data presented above, a suitable range for distance D is between about 50 and 250 microns. In some applications, a suitable range for distance D is between about 50 and 150 microns. For D greater than 250 microns, a film laminate tends to have relatively low adhesion and visible wet out patterns. For D less than about 50 microns, gain tends to be relatively low. In some applications, distance D is between about 90 and 150 microns to optimize both gain and adhesion, while minimizing or reducing visible wet out.
In addition to using patterns of tall and short structures, wet out may also be reduced by adjusting the adhesive properties of the adhesive layer. Incorporating stiffer, thinner adhesives into the design of the film laminates can further reduce wet out, while maintaining sufficient adhesion. The visibility of the wet out pattern is partly governed by the depth of penetration. Depth of penetration is a distance a tall prism penetrates the adhesive plus any distance the adhesive might have flowed along a side of the tall prism. For a soft adhesive, depth of penetration can be larger than the adhesive thickness as the adhesive may flow, for example, during assembly or with time, along the sides of a tall prism. In some applications, a stiffer and/or thinner adhesive may be used, in which case a depth of penetration may be essentially equal to the distance the prism penetrates the adhesive. In some applications, a thicker adhesive may be used, in which case a tall prism may only partially penetrate the adhesive layer.
In some cases, third film 302 may be designed to have a function other than brightness enhancement. For example, third film 302 may be an optical diffuser, in which case, structures 305 of structured surface 304 may function as spacers between third film 302 and first film 242.
The structured films described above are manufactured using various methods, including embossing, extrusion, casting and curing, compression molding and injection molding. One method of embossing is described in U.S. Pat. No. 6,322,236, which includes diamond turning techniques to form a patterned roll which is then used for embossing a structured surface onto a film. A similar method may be used to form the films described above having patterns of tall and short structures.
Other approaches may be followed for producing a film having a structured surface with a repeating pattern. For example, the film may be injection molded using a mold having a particular pattern thereon. The resulting injection molded film has a surface that is the complement of the pattern in the mold. In another approach, the film may be compression molded.
As used herein, terms such as “vertical”, “horizontal”, “above”, “below”, “left” and “right”, and other similar terms, refer to relative positions as shown in the figures. In general, a physical embodiment can have a different orientation, and in that case the terms are intended to refer to relative positions modified to the actual orientation of the device. For example, even if the construction in
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
