WO2010021896A1

WO2010021896A1 - Light guides including laser-processed light extractors and methods

Info

Publication number: WO2010021896A1
Application number: PCT/US2009/053635
Authority: WO
Inventors: Craig R. Sykora; Robert T. Krasa
Original assignee: 3M Innovative Properties Company
Priority date: 2008-08-22
Filing date: 2009-08-13
Publication date: 2010-02-25
Also published as: EP2331868A1

Abstract

This disclosure relates to light guides that include light extractors and methods for making the same. More specifically, this disclosure relates to light guides that include laser-processed light extractors that can be useful in display or switching devices.

Description

LIGHT GUIDES INCLUDING LASER-PROCESSED LIGHT EXTRACTORS AND METHODS

Field

Background

A variety of devices has been proposed for illuminating electronic displays and input devices such as keypads. These devices include backlighting panels, front lighting panels, concentrators, reflectors, structured-surface films, and other optical devices for redirecting, collimating, distributing, or otherwise manipulating light. Passive optical components (for example, lenses, prisms, mirrors, and light extraction structures) are well- known and are used in optical systems to collect, distribute, or modify optical radiation. Efficient use of light is particularly important in battery powered electronic displays and keypads such as those used in cell phones, personal digital assistants, MP3 players, and laptop computers. By improving lighting efficiency, battery life can be increased, power can be diverted to other electronic components, and/or battery sizes can be reduced, which are increasingly important as devices decrease in size and increase in functionality and complexity. Prismatic films are commonly used to improve lighting efficiency and enhance the apparent brightness of a backlit liquid crystal display, and multiple light sources (for example, light emitting diodes (LEDs)) are commonly used for this purpose in keypads.

Lighting quality is also an important consideration in electronic displays and keypads. One measure of lighting quality for a backlit display or keypad is brightness uniformity. Because displays (and, to a somewhat lesser extent, keypads) are typically studied closely or used for extended periods of time, relatively small differences in the brightness can easily be perceived. These types of variances in brightness can be distracting or annoying to a user. To soften or mask non-uniformities, a light scattering element (for example, a diffuser) can sometimes be used. However, such scattering elements can negatively affect the overall brightness of a display or keypad and add cost and complexity to the final device. Alternatively, multiple light sources can be used to achieve brightness uniformity, but this approach has the associated disadvantage of reduced battery life. Thus, there has been some attention to the development of various means of effectively distributing the light from a more limited number of light sources, including the development of light guides comprising a plurality of light extraction structures. Such light extraction structures, as well as light extraction structure arrays, have been made by a number of different techniques including microreplication, hand stamping, and/or lithographic processes. Most of these processes involve multiple steps and can take time for making the tooling and masters required for production.

Summary

There is a need for a fast, low-cost process to make light guides that include light extractors. There is also a need for a process that can tailor make the individual light extractors included in a light guide in order to increase uniformity of the light that is delivered to, for example, a lighted display or keypad on an electronic device. In one aspect, a method is provided of making a light guide that includes providing a substantially transparent material, positioning the transparent material in the path of a laser beam having sufficient energy and intensity to ablate the transparent material, and ablating at least a portion of the transparent material with said beam to create at least one light extractor. In another aspect, a light guide is provided that is made from a process that includes providing a substantially transparent material, positioning the transparent material in the path of a laser beam having sufficient energy and intensity to ablate the material, and ablating at least a portion of the transparent material with said beam to create at least one light extractor.

In some embodiments, the substantially transparent material is an organic polymer that can be flexible. In other embodiments the organic polymer can include a UV curable resin such as a silicone, an acrylate, a urethane, a urethane-acrylate, or a combination thereof. In yet other embodiments, the transparent material can be positioned in the path of the laser beam automatically using a computer. In some embodiments, the size and shape of the light extractors can be controlled by controlling properties of the laser beam such as pulse length, intensity, and focal width.

The disclosed methods and light guides made from processes that include these methods can rapidly provide low-cost light guides that include extractors that can be useful as, for example, keypads on electronic devices such as mobile phones, keyless entry systems, displays such as automotive instrument panel displays, or backlighting for liquid crystal displays (LCDs).

The above summary is not intended to describe each disclosed embodiment of every implementation of the present invention. The brief description of the drawing and the detailed description which follows more particularly exemplify illustrative embodiments.

Brief Description of the Drawings

FIG. 1 is a perspective view of a flexible light guide including a plurality of light extraction structure arrays.

FIGS. 2A-I are cross-sectional views of a variety of light extraction structures. FIG. 3 is a cross-sectional view illustrating a light guide used in a cell phone keypad assembly.

Detailed Description

In the following description, reference is made to the accompanying set of drawings that form a part of the description hereof and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

In general, the current disclosure is directed to a method of making light guides that include at least one light extractor. The light guides are suitable for use in environments which require, for example, flexibility, durability, or a combination thereof. One such environment includes input devices, and more specifically, keypads for cell phones, computers, MP3 players, and the like. Light guides suitable for use in these and similar applications preferably possess certain physical properties that do not detract from desirable tactile feedback during depression and/or release of a key, optical properties that allow the effective transmission of light, and sufficient durability to ensure both the tactile feedback and optical properties are substantially constant for the lifetime of the device. FIG. 1 is a perspective view illustrating a system 10 including a flexible light guide

12 and a light source 16. Flexible light guide 12 includes a plurality of light extraction structure arrays 14, each of which includes at least one light extraction structure. Flexible light guide 12 may be sufficiently flexible conform to a curved surface, such as a curved display screen or keypad. The flexibility of flexible light guide 12 may be affected by the properties of the materials that are used to form flexible light guide 12, including glass transition temperature (T_g) and tensile modulus, and by the thickness of flexible light guide 12.

Flexible light guide 12 preferably provides substantially homogeneous illumination in a direction substantially normal to surface 18a or 18b at each light extraction structure array 14. That is, in the case of a keypad, each key is illuminated substantially equally. This may be accomplished by combining geometries and fill factors such as those described hereinafter. Flexible light guide 12 preferably possesses substantially no birefringence and is substantially optically clear, so little visible light is lost to scattering or absorption. The combination of these properties may provide efficient use of light" from light source 16.

Flexible light guide 12 directs light from at least one light source 16 and distributes the light through the flexible light guide 12 and emits the light via the light extraction structure arrays 14. The plurality of light extraction structure arrays 14 may reflect or refract light to direct light out of at least one of surfaces 18a, 18b of flexible light guide 12. Light extraction structure arrays 14 may be positioned continuously or intermittently throughout flexible light guide 12, depending on the desired illumination pattern. For example, when it is desired that only the keys on a cellular telephone keypad are illuminated, light extraction structure arrays 14 may be formed as islands on or in flexible light guide 12 which correspond to the locations of the keys, or which correspond to the shape of the respective numbers, letters, or symbols. In some embodiments, light extraction structure arrays 14 may be located on a single major surface 18a or 18b of flexible light guide 12, or on both major surfaces 18a, 18b. Each individual light extraction structure 30 within light extraction structure arrays 14 may include depressions or protrusions, or both. For example, as shown in FIGS. 2A-2H, light extraction structures 30 may include a wide variety of geometries, including pyramid or cone shaped depressions 30a or protrusions 30b (FIGS. 2A and 2B), a repeating pattern of grooves 30c (FIG. 2C), Fresnel lenses 30d (FIG. 2D), prolate hemispheroid depressions 30e and protrusions 3Of (FIGS. 2E and 2F), prolate hemispheroids with truncated ends 30g, 30h (FIGS. 2G and 2H), and the like.

In addition to the geometries shown in FIGS. 2A-2H, other geometries may be utilized. The configurations can be complex (for example, combining segments of multiple shapes in a single structure, such as a stacked combination of a cone and a pyramid or of a cone and a "Phillips head" shape). Geometric configurations can comprise such structural elements as a base, one or more faces (for example, that form a side wall), and a top (which can be, for example, a planar surface or even a point). Such elements can be of essentially any shape (for example, bases, faces, and tops can be circular, elliptical, or polygonal (regular or irregular), and the resulting side walls can be characterized by a vertical cross section (taken perpendicular to the base) that is parabolic, hyperbolic, or linear in nature, or a combination thereof). Typically, the side wall is not perpendicular to the base of the structure (for example, angles of from about 10 degrees to about 80 degrees, from about 20 degrees to about 70 degrees; or even from about 30 degrees to about 60 degrees can be useful). The light extraction structure can have a principal axis connecting the center of its top with the center of its base. Tilt angles (the angle between the principal axis and the base) of up to about 80 degrees (typically, up to about 25 degrees) can be achieved, depending upon the desired brightness and field of view.

Alternatively to the geometric construction of light extraction structures 30, light extraction structures 3Oi may be printed onto or into flexible light guides 12 of the current disclosure, as in the example shown in FIG. 21. For example, highly refractive or reflective inks may be printed onto flexible light guide 12, and the inks will cause light to refract or reflect similarly to encountering a geometrically formed surface between two materials of different refractive indices.

Individual light extraction structures 30 may have heights in the range of from about 5 microns to about 300 microns (typically from about 25 to about 200; or from about 50 to about 100) and/or maximum lengths and/or maximum widths in the range of from about 5 microns to about 500 microns (typically, from about 50 to about 300; or from about 100 to about 300). Light extraction structure arrays 14, such as those illustrated in FIG. 1, may have a substantially homogeneous construction, i.e., all structures within a single array are similarly sized and shaped, or the size and shape of the light extraction structures 30 may vary substantially continuously or, alternatively, non-continuous Iy, throughout a single light extraction structure array 14. Additionally, the fill factor of light extraction structures 30 (e.g. the number of light extraction structures per unit area) within a single light extraction structure array 14 may be substantially constant, or the fill factor may change throughout the light extraction structure array 14. For many applications, fill factors of about 1 percent to 100 percent (typically from about 5 percent to about 50 percent) can be useful. Similarly, light extraction structure 30 sizes, shapes, and fill factors may be substantially similar between light extraction structure arrays 14, or may vary either substantially continuously or non-continuously between light extraction structure arrays 14. Preferably, light extraction structure arrays 14 located further away from a light source 16 have light extraction structures 30 that are taller, have higher fill factors, or both, compared to light extraction structure arrays 14 closer to the light source 16.

As described briefly above, flexible light guide 12 is preferably substantially optically clear, and possesses substantially no birefringence, preferably no birefringence. Desired optical clarity may be determined to a sufficient accuracy by a theoretical calculation of a material's absorbance, and a measurement of the refractive index of the flexible light guide 12.

For example, the absorbance of the flexible light guide 12 may be calculated using Beer's law:

I / Io = e^"αx or α = - In(I / I₀) / x

where I is the final intensity, Io is the incident intensity, α is the absorbance in cm^"1, and x is equal to the propagating path length, based on the dimensions of the light guide. To calculate the desired absorbance, a desired value of 1/I₀, which relates the final intensity to the incident intensity is chosen, and the required absorbance to achieve this value (for a known path length) is calculated. Suitable flexible light guide 12 materials can be transparent organic polymers that have an absorbance of less than about 0.0279 cm^"1, typically less than about 0.0203 cm^"1, or less than about 0.0132 cm^"1, which corresponds to a 20% loss of light intensity, a 15% loss of light intensity or a 10% loss of light intensity, respectively, over a path length of about 8 cm. Suitable flexible light guide 12 materials have a refractive index ranging from about 1.35 to about 1.65, typically from about 1.40 to about 1.55, or from about 1.45 to about 1.53 within the visible spectrum (approximately 400 nm to 700 nm).

Flexible light guide 12 also preferably transmits force effectively so that tactile feedback is possible. For example, a common keypad construction includes metallic popples that deform when a key is pressed. The metallic popples (otherwise known as dome switches) make contact with an underlying circuit, which causes a processor to register a key press. Additionally, the popples give tactile and/or audible feedback when deformed, as the popple "pops" nearly inside-out. Flexible light guide 12 is typically located between the keypad and the popple layer, so any force applied to a key must be transmitted through the flexible light guide 12 to the popple. Thus, the flexible light guide 12 may be sufficiently flexible to allow deformation under loads typically applied by a user to a key, and yet sufficiently rigid to transmit this force to the popple and the tactile response of the popple back to the key.

Flexible light guide 12 also preferably deforms substantially elastically under the loads applied to it. Specifically, both the individual light extraction structures 30 and the flexible light guide 12 preferably deform substantially elastically. It is important for durability and long life that flexible light guide 12 retains its original shape after deformation, particularly when flexible light guide 12 is utilized in an input device. Typical flexible light guides have a dynamic bending modulus of from about 40 to about 2500 MPa as measured at 23⁰C by dynamic mechanical analysis. In addition to elastic deformation, other features may be included in the flexible light guide 12 to promote durability. For example, the individual light extraction structures 30 may be constructed as depressions. Light extraction structures 30 constructed in this manner may experience less deformation compared to light extraction structures 30 formed as protrusions when a key is depressed. Thus, flexible light guides 12 with depressed structures may exhibit enhanced durability.

As described briefly above, flexible light guides 12 of the current disclosure may be used in a system to provide backlight to an input device. FIG. 3 is a cross-sectional view illustrating an embodiment of the flexible light guide being utilized in a cellular telephone keypad assembly 60. Flexible light guide 12 is located between a plurality of keys 62 and domesheet 64, with one end adjacent a side-emitting LED 7. Flexible light guide 12 also includes a plurality of light extraction structure arrays 14, each of which includes a plurality of light extraction structures 30. Each light extraction structure array 14 is located underneath a corresponding key 62, and directs light to the key 62. Dome sheet 64 covers conductive popples 66 and spacer adhesives 68. When a user depresses a key 62 (arrow 80), the corresponding protrusion 78 is also pushed down and contacts a portion of flexible light guide 12 adjacent protrusion 78. As the user continues to further depress key 62, the flexible light guide 12 deforms and contacts the dome sheet 64, which also deforms. Dome sheet 64 contacts the adjacent popple 66, which is deformed and "pops" when at least a portion of popple 66 is pushed inside out. This causes the tactile feedback, and also causes at least a portion of popple 66 to contact at least a portion of electrical contacts 70. This contact closes the electronic circuit and is interpreted as a key press. Thus, as described above, the preferred flexible light guide 12 transmits the force applied to key 62 effectively to popple 66 so that popple 66 "pops" and makes electrical contact with electrical contacts 70. The method of making light guides that include at least one light extractor includes providing a transparent material. Suitable transparent materials for use in the disclosed light guides may vary widely, and essentially any polymeric material may be used, whether pre-polymerized and thermally formable, or polymerized thermally or radiation cured in contact with the mold. In some embodiments, thermally formable materials may be subsequently post-processed and crosslinked by a variety of processes such as, for example, e-beam or chemical curing. Exemplary materials include, but are not limited to, acrylates, urethanes, silicones, urethane acrylates, epoxies, thermoplastic materials, elastomers and the like. Materials may be chosen to accomplish one or more of the desired characteristics discussed above, such as flexibility (typically a function of T_g, tensile modulus, and thickness of the light guide), optical clarity (related to absorption and refractive index), and durability. Useful transparent materials are disclosed, for example, in U.S. Provisional Application No.

60/967,633, filed September 25, 2007. The substantially transparent material may be provided as a sheet or a roll. The material may be in contact with a release liner for handling purposes. Typical release liners include polyesters, silicone coated polyesters, and the like. The transparent material can be produced by coating a mixture of precursors to the organic polymer onto the liner and then curing (thermally or by exposure to UV radiation). Alternatively the precursors to the organic polymer can be placed in a flat mold and cured. Typically, the thickness of the organic polymer can be between about 50 μm and about 700 μm. Alternatively the transparent material may be extruded through a coating die onto the liner and then cured. The cured substantially transparent material is then positioned in the path of a laser beam having sufficient energy and intensity to ablate at least a portion of the transparent material to create at least one light extractor. Useful lasers are lasers that have sufficient absorption by the material to cause erosion, melting, vaporization, or evaporation of the material, and include, for example gas and solid state lasers such as CO₂ lasers, Nd-YAG, Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, and Yb:CaF2 lasers, all forms of Fiber lasers, as well as doubled, tripled, or quadrupled solid state lasers that produce wavelengths of radiation that are shorter than the fundamental wavelength of the laser.. The size, depth, and resolution of ablated areas can be altered by controlling at least one property of the laser such as pulse length, intensity, focal point width, pulses per area or total exposer time, and/or the location of and pattern of exposure. A computer can be used to vary any of these properties or a combination thereof. In this way it is possible to create at least two or more light extractors in a light guide that have different light extraction properties such as intensity, uniformity, or angle of illumination.

The transparent material can be positioned manually or automatically. Either the material can be positioned in the path of a stationary laser beam or the material can be stationary and the laser beam can be positioned, or a combination thereof. The positioning can be computer-controlled and the material can be handled as a sheet using, for example, a FLEXPRO laser converting machine, available from Preco, Somerset, WI. The transparent material can be on a roll using, for example, a WEBPRO laser converting machine, available from Preco, Somerset, WI. In another aspect a light guide is provided from a process that includes providing a transparent material, positioning the transparent material in the path of a laser beam having sufficient energy and intensity to ablate the material, and ablating at least a portion of the transparent material with said beam to create at least one light extractor. The light guide can be useful in display devices such as, for example, displays on mobile phones, personal digital assistants, MP3 players, laptop computers, as well as game controllers and/or consoles.

The light guide can further comprise an adhesive in contact with the transparent material. The adhesive can be an optically clear pressure sensitive adhesive. Adhesives useful in the provided light guides are any optically clear pressure sensitive adhesives. Exemplary adhesive include the (meth)acrylate block copolymer pressure sensitive adhesives disclosed in U. S. Pat. No. 7,255,920 (Everaerts et al.) and adhesive blends disclosed in U. S. Pat. Publ. No. 2004/0202879 (Xia et al.). The light guide can also include a dome sheet that is in contact with the transparent material as shown in the illustrations described above and can be held to the dome sheet by an adhesive. The light guide can be used as a tool for creating a patterned film. The tool can be used directly as a mold to form light guides by adding an unformed resin to the mold by, for example, extrusion or any known coating method and then either curing the material if it is a thermosetting material or cooling the material if it is thermoplastic. The unformed resin can be uncured polymer precursors such as, for example, acrylates, silicones, or urethanes. It can be advantageous to coat the mold with a release material for easy removal of the produced part from the mold. Appropriate release materials are well known to those of skill in the art and include, silicones, fluoropolymers, fluorosilicones, and the like.

An additional embodiment is a roll-to-roll system, which allows for roll-to-roll material handling, enabling high speed laser ablation. The process is done in a step-wise fashion or on the fly. This type of processing (either in sheets or rolls) additionally offers the opportunity to have a broad range of material. Defects such as air bubbles can also be reduced because the process is be done without a microreplication tool which can introduce air bubbles during processing. The materials options also allow greater flexibility in choosing final properties of the light guide, including the force required to remove them from their carrier liner.

Another embodiment is one where the light guide created from the process can be used as a tool in a coating or extrusion process to create a patterned mold that can be used to make the light guides. Additional embodiments include in-line lamination of additional layers, such as dome sheets and/or adhesives. These layers can be converted in a prior process, or even in-line with the light guide converting. Other features can include online inspection and tracking of individual parts. A final operation can include weeding (to remove the waste material) and if necessary slitting to create a reel with the parts arranged for easy handling at the manufacturing assembly site for the customer.

Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.

Examples

Materials

CN9009 is an aliphatic urethane acrylate oligomer available from Sartomer Company, Inc., Exton, PA. CN965 is an aliphatic polyester-based urethane diacrylate available from Sartomer.

SR256 is 2-(2-ethoxyethoxy)ethyl acrylate and is available from Sartomer. SR230 is diethylene glycol diacrylate and is available from Sartomer. SR306F is tripropylene glycol diacrylate and is available from Sartomer. TPO-L is a phosphine oxide photoinitiator available from BASF, Florham Park, NJ.

Irganox 1076 is an antioxidant available from CIBA, Tarrytown, NJ. Preparation of Urethane Acrylate Films Formulation 1

85 parts (by weight) CN9009, 9 parts SR956, 6 parts SR230, 0.3 parts TPO-I, and 0.15 parts Irganox 1076.

Formulation 2 42.5 parts CN965, 42.5 parts CN9009, 12.0 parts SR256, 3.0 parts SR306F, 0.3 parts TPO-L, and 0.15 parts Irganox 1076

The formulations were prepared by mixing appropriate amounts of each component in a Hauschild DAC 400FV(Z) (available from FlackTek Inc., Landrum SC) for two 4 minute mixing cycles at 2200 rpm. Each of the formulations was then degassed under a vacuum at about 70⁰C for about 30 minutes, and were then used to prepare films.

Example 1.

A mechanical file describing a 2-Dimensional shape was loaded into the computer software that is used to drive the galvo-scanned laser on a Preco FLEXPRO laser converting machine, available from Preco, Somerset, WI. A digital pattern consisting of approximately 500 features was put into one of the 3 fields where light extraction was required in the lightguide design file. The pattern was regular, hexagonally packed features. Using a manual process, several rows of features were deleted creating a pattern with lower density features closest to the LED and higher density features far from the LED. This pattern was copied into the other 2 fields. A lightguide was produced with this pattern where the pattern was ablated and the lightguide shape was cut through the sheet of transparent material, wherein the film consisted of the same film used in the microreplication production of Custom Planar Lightguides. The film was nominally 0.200 mm thick. The film used was made from Formulation 1 by casting a 0.200 mm thick layer of Formulation 1 between to layers of polyethylene terephthalate (PET) film to eliminate air and exposing it to UV light using a Fusion Systems F300S with a mercury "H" bulb and LC-6 benchtop conveyor (Fusion UV Systems, Inc., Gaithersburg, MD). The film was placed on the conveyor belt at a speed of about 0.35 ft/sec (10.7 cm/sec) and passed under the lamp twice on each side of the laminate. After exposure, the cured film and PET cover sheet were removed and a release coated PET sheet was applied to the exposed light guide surface for protection. The films were used for forming lightguides as described above.

The resultant lightguide was placed into a cellular phone that was designed for the lightguide shape. The lightguide was placed on top of a capacitive touch sensor and the top "A-Cover" was placed on the phone. The lighting uniformity was poor, with the brightest location (of the 3) being closest to the LED, and falling off as the light was further from the LED .

Laser energy was reduced for the pattern location closest to the LED by lowering the pulse duration to 10 ms. The pulse duration was reduced to 25 ms for the middle key, and the farthest key was split into 2 sub-units, with the pulse duration being 35 ms for the sub-unit closest to LED and 50 ms for the sub-unit farther from the LED. The resultant lightguide appeared more uniform, but still was not acceptable when observed by eye.

The pulse duration was reduced to 7 ms for the first key (closest to the LED), 15 ms for the second key (middle key), and increased to 60 ms for the sub-unit of the third key farthest from the LED. The resultant lightguide had poor pattern appearance closest to the LED and had a hole burned through the sub-unit created with 60 ms, suggesting the laser energy was too high. The next attempt used 50 ms for sub-unit farthest from the LED, 35 ms for the other sub-unit of key 3, 13 ms for the middle key, and 10 ms for the first key. The resultant lightguide looked very good, but the sub-unit furthest from the LED appeared dark, like it was shadowed by the first sub-unit. The key closest to the LED also appeared too bright near the LED. To adjust for this, some of the extractors in horizontal rows of the first sub-unit were deleted in the computer laser marking software, and also in the first key. The resultant lightguide looked acceptable by eye when under the cover of the phone. The farthest sub-unit continued to have a shadow appearance, but it was not visible through the cover. The total time for the design effort was 2.5 hrs. The total time to create one lightguide with the resultant pattern was 4.3 seconds including the pattern of extractors and the lightguide shape. Twenty additional lightguides with adhesive were then produced by first cutting holes in a pressure sensitive adhesive sheet. That sheet was then laminated to a film, followed by laser patterning of the extractors in the regions where there were holes, followed by the laser converting step to cut the lightguides. The "weed" was then removed, leaving the individual lightguides with adhesive.

For comparison, a lightguide was produced using a computer design process that required 2 design cycles, each cycle requiring >1.5 weeks. The resultant design was patterned using a Two Photon process as described, for example, in PCT Pat. Publ. No. 2007/0137102 (Marttila et al.) with a mercury "H" bulb and LC-6 benchtop conveyor (Fusion UV Systems, Inc., Gaithersburg, MD). Each laminate was placed on the conveyor belt at a speed of about 0.35 ft/sec (10.7 cm/sec) and passed under the lamp twice on each side of the laminate. After exposure, the light guide and PET cover sheet were removed from the PP mold as a laminate, and a release coated PET sheet was applied to the exposed light guide surface for protection. Individual light guide samples were then trimmed from the six-sample cluster using a CO₂ laser, leaving both PET films intact, with a mercury "H" bulb and LC-6 benchtop conveyor (Fusion UV Systems, Inc., Gaithersburg, MD). Each laminate was placed on the conveyor belt at a speed of about 0.35 ft/sec (10.7 cm/sec) and passed under the lamp twice on each side of the laminate. After exposure, the light guide and PET cover sheet were removed from the PP mold as a laminate, and a release coated PET sheet was applied to the exposed light guide surface for protection. Individual light guide samples were then trimmed from the six-sample cluster using a CO₂ laser, leaving both PET films intact followed by creating a hand- stamped tool. The tool was used to make a lightguide with six different light extractor shapes placed in the same macroscopic regions as the lightguide of Example 1. The light extracted for each light extractor for the comparative example (tool formed by two-photon process) and the direct laser ablation (Example 1) was measured using a Topcon model BM-7 luminance colorimeter available from Hoffman Engineering in Stamford, CT.

Table I

While the process described above was a manual one, it is envisioned that it could be combined with a luminance meter (available from Topcon or Minolta) or a camera- based system (such as a SpectraScan from Radiant Imaging). The camera-based system allows image-based analysis which offers a way of viewing the entire part in one image while being able to resolve individual areas with high resolution. In this system, the laser can pattern the part until the requirements meet a target value for efficiency and uniformity. The envisioned system could use an algorithm that could be derived from experimental results to provide a logic-based control process to create the pattern. The envisioned process and the process used in example 1 both offer the advantage that the resultant pattern can easily be replicated if stored in a controller.

Example 2

A mechanical file describing a 2-Dimensional shape was loaded into the computer software that is used to drive the galvo-scanned laser on a Preco FLEXPRO laser converting machine, available from Preco, Somerset, WI. A digital pattern consisting of approximately 500 features was put into the location farthest from a LED of the 3 fields where light extraction was required in the lightguide design file. The pattern was regular, hexagonally packed features. This pattern was copied into the middle field, and the field closest to the LED was left unpatterned because the LED provided a high amount of light to the closest region because the LED was taller than the relative thickness of the lightguide, resulting in uncoupled light being available to illuminate that region. A secondary optic of a partial mirror (also known as a "deflector") was created by cutting a diagonal line in the part to reflect light from the LED to the 2 patterned extractor regions, as the LED was mounted such that the LED was pointed in an axis approximately orthogonal to the axis of the extraction regions. The diagonal line was cut above the LED coupling region such that it would reflect light to the middle and farthest region. A lightguide was produced with this pattern where the pattern was ablated and the lightguide shape was cut through the sheet of transparent material of Formulation 2, wherein the film was nominally 0.200 mm.

The resultant lightguide was placed into a cellular phone that was designed for the resultant lightguide shape. The lighting uniformity was acceptable by observation. The laser energy for the pattern farthest from the LED was managed by setting the pulse duration to 20 ms and the laser energy for the middle extraction region was established by a pulse duration of 16 ms.

The partial mirror was adjusted such that the line was moved farther from the LED coupling edge by 0.200 mm. Another lightguide was patterned and cut by the laser using this condition. The resultant lightguide appeared to be brighter than the previous lightguide, the result of a more efficient partial reflection of the LED light. The partial mirror was adjusted by moving it an additional 0.200 mm and another lightguide was patterned and cut by the laser using this design. The resultant lightguide appeared to be less bright as the result of a less efficient partial reflection of the light from the LED. The total time for the design effort was 20 minutes. The total time to create one lightguide with the resultant pattern was 1.27 seconds including the pattern of extractors and the lightguide shape. Thirty additional lightguides were then produced by replicating the 2^nd design of the 3 designs that were created.

Example 3

A mechanical file describing a 2-Dimensional shape was loaded into the computer software that is used to drive the galvo-scanned laser on a Preco FLEXPRO laser converting machine, available from Preco, Somerset, WI. A digital pattern consisting of approximately 1000 features was put into the regions representing the locations of the numerical key regions of a "flip" style cellular phone. The pattern was regular, hexagonally packed features. This pattern was copied into the navigation and menu key regions of the phone, which were smaller in area than the numerical key regions. The total number of unique extraction regions was 23. The laser energy for the extractors was set by setting the pulse duration at 13 ms. The LEDs in the cellular phone were mounted such that their emission was pointed in the opposite direction of two of the menu buttons, requiring the lightguide to have voids in it to accommodate the LEDs. A lightguide was produced with this pattern where the pattern was ablated and the lightguide shape was cut through the sheet of transparent material nominally 0.200 mm thick. The total time for the design was approximately 3 hours, and the time to pattern the final part was approximately 10 seconds. The film used to make the lightgiude was the same film used in Example 2 and was made from Formulation 2. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows. All references cited herein are hereby incorporated by reference in their entirety.

Claims

What is claimed is:

1. A method of making a light guide comprising: providing a substantially transparent material; positioning the transparent material in the path of a laser beam having sufficient energy and intensity to ablate the transparent material; and ablating at least a portion of the transparent material with said beam to create at least one light extractor.

2. A method according to claim 1 wherein the transparent material comprises an organic polymer.

3. A method according to claim 2 wherein the organic polymer is flexible.

4. A method according to claim 3 wherein the organic polymer comprises a UV curable resin.

5. A method according to claim 4 wherein the resin comprises a silicone, an acrylate, a urethane, a urethane-acrylate, or a combination thereof.

6. A method according to claim 1 wherein the positioning is automatic, step-wise or continuous.

7. A method according to claim 6 wherein the positioning is computer-controlled.

8. A method according to claim 1 wherein the laser is an infrared laser.

9. A method according to claim 1 further comprising controlling at least one property of the laser selected from pulse length, intensity, and focal point width.

10. A method according to claim 9 wherein at least two light extractors, each of which has different light extraction properties are created.

11. A method according to claim 1 wherein the transparent material is on a roll.

12. A light guide made from a process comprising: providing a substantially transparent material; positioning the transparent material in the path of a laser beam having sufficient energy and intensity to ablate the material; and ablating at least a portion of the transparent material with said beam to create at least one light extractor.

13. A light guide according to claim 12 wherein the process further comprises adapting the transparent material to form a light guide article useful in display devices.

14. A light guide according to claim 12 comprising an adhesive in contact with the transparent material.

15. A light guide according to claim 12 comprising a sheet comprising a dome sheet in contact with the transparent material.

16. An electronic display device comprising the light guide according to claim 12.

17. A light guide according to claim 12 wherein the light guide is used as a tool for creating a patterned film.

18. A light guide according to claim 17 wherein the patterned film is made by extrusion.

19. A light guide according to claim 17 wherein the patterned film is made by coating.