WO2007102633A1

WO2007102633A1 - Light guide film comprising reflecting layer and emitting keypad having the same

Info

Publication number: WO2007102633A1
Application number: PCT/KR2006/000822
Authority: WO
Inventors: Hyun Soo Kim
Original assignee: Attocon Co., Ltd.
Priority date: 2006-03-08
Filing date: 2006-03-08
Publication date: 2007-09-13

Abstract

A light guide film for a keypad backlight is disclosed, wherein the film is disposed at a rear surface thereof with a reflecting layer and formed with a pattern on at least one surface thereof, and the film is made of polycarbonate (PC) or polyethylene terephthalate (PET), having a flexibility and elasticity, and whereby Introduction of an EL sheet is dispensed with, a direct illumination method is introduced to enable to realize a considerable slimness, introduction of a reflecting layer enables to enhance the luminance (brightness) even with a small number of light sources, and a uniform light emitting surface like that of a surface light source can be provided by forming a predetermined pattern on at least one surface.

Description

LIGHT GUIDE FILM COMPRISING REFLECTING LAYER AND EMITTING KEYPAD HAVING THE SAME

Technical Field

[I] The present invention relates to a light guide film comprising a reflecting layer and an emitting keypad having the same.

[2]

Background Art

[3] Generally, a light emitting keypad is applied to communication devices such as mobile phones for practical usage as a switch for conducting various supplemental functions including signal generation, and particularly for distinguishing characters or codes at night or in poor lighting conditions, and concomitant with accelerated efforts to slim down thickness of the mobile phones, development of super thin light emitting keypads is keeping pace therewith.

[4]

[5] FIG.1 is a cross-sectional view of a light emitting diode (LED) keypad by a direct illumination method according to the prior art, where the keypad includes a printed circuit board (PCB.100), a dome (102), a direct illumination LED (103) and a keypad (104). The PCB (100) is disposed with a predetermined contact terminal (101), and is also disposed at a front thereof with the dome and a plurality of direct illumination LEDs.

[6]

[7] A front side of the dome and the direct illumination LED are upwardly printed with numbers and characters, and downwardly disposed with a keypad formed with protrusions (105).

[8]

[9] The LED keypad of direct illumination method is operated in such a way that a direct illumination LED frontally mounted at the PCB generates light to illuminate the keypad. In other words, when the keypad is pressed by a user, the contact terminal of the PCB and the dome are connected by the protrusions of the keypad to generate a predetermined electrical signal, and the electrical signal causes the LED to generate light and to illuminate the keypad in the form of a spot light source.

[10]

[I I] Meanwhile, the LED keypad of direct illumination method is next to impossible to be manufactured with thin thickness due to its characteristic, such that the keypad is manufactured with a relatively thick width. The keypad consumes much electricity in proportion to illumination of the LED to shorten the usage time of batteries. Still another shortcoming is that light emission is not uniformly implemented relative to aligned positions of LEDs, resulting in design constraints.

[12]

[13] FIG.2 is a cross-sectional view of a conventional electroluminescent (EL) type keypad to address the above-mentioned problems, where the keypad includes a key top (110), an EL metal dome sheet (120) and a PCB (130). The EL metal dome sheet (120) comprises an EL sheet (121), a metal dome (123) and a base tape (122), to thereby enable to realize a super thin structure and low electricity consumption.

[14]

[15] Now, functional side of the metal dome keypad by the EL method will be described.

[16]

[17] When the key top (110) is depressed, fixed contact terminals at the metal dome

(123) and the PCB (130) are interconnected by a protrusion (111) disposed at a rear surface of the key top (110) and switched for operation.

[18]

[19] However, the conventional light emitting keypad of EL method thus described suffers from a number of shortcomings that make it inefficient, particularly, in reliability of the EL sheet and click feel because the EL sheet (121) is continuously depressed and pressurized by the protrusion (111), resulting in a high risk of damage to and destruction of the EL sheet. The EL sheet has a shorter life span than that of the LED due to its characteristic, producing an uncomfortable vibration noise on an LED module, resulting in degraded reliability, and requires higher production cost than that of the LED keypad.

[20]

[21]

Disclosure of Invention Technical Problem

[22] In order to solve the aforementioned shortcomings, a couple of considerations have been taken into account, which includes an LED light source provided by an indirect illumination method, and installation of an optical fiber having an excellent optical transmission for uniform supply of light to the keypad. However, these considerations still have shortcomings in that it is very difficult to slim down the silicon-based keypad and to adapt it into reality.

[23]

[24] The present invention is provided to solve the aforesaid shortcomings and it is an object of the present invention to provide a light guide film comprising a reflecting layer and an emitting keypad having the same, wherein introduction of an EL sheet is dispensed with, a direct illumination method is introduced to enable to realize a considerable slimness, introduction of a reflection layer enables to enhance the luminance (brightness) even with usage of a small number of light sources, and a uniform light emitting surface like that of a plane light source can be provided by forming a predetermined pattern on at least one surface.

[25]

[26]

Technical Solution

[27] In one general aspect, a light guide film for a keypad backlight is provided, the film disposed at a rear surface of a keypad for supplying light irradiated from a lateral light source to the keypad, wherein the light guide film is formed at a rear surface thereof with a reflecting layer.

[28]

[29] The reflecting layer of the light guide film includes one or more selected from a group consisting of Ag, TiO ZnO, BaSO ZnS, lead white, and Sb O

[30]

[31] Furthermore, at least one surface out of front and rear surfaces of the light guide film is formed with a pattern such that density increases as distanced from a light source to allow light to be uniformly supplied to the keypad, or is concentratively formed with a pattern at a particular region of the light guide film to allow the light be concentratively supplied to a particular region of the keypad.

[32]

[33] The reflecting layer contains a white pigment, for example Ag or the like. The reflecting layer is formed at a rear surface of the light guide film by an evaporation method, a coating method or a printing method. The reflecting layer is comprised of a sheet, and is formed attached at a rear surface of the light guide film using a two-sided tape. The pattern is formed by one of the processing methods of hot stamping, injection forming, micro blast and laser techniques. The pattern is formed by an ink containing a light scattering agent being silk-screened on a light guide film. The pattern density is adjusted by one of the two methods which are a pattern distance adjustment and a pattern size adjustment.

[34]

[35] In another general aspect, a light emitting keypad is provided, the keypad comprising: a key top disposed with a plurality of protrusions at a predetermined location of a bottom surface thereof; a light guide film disposed at a lower surface of the key top; a light source disposed at a distal end of the light guide film; and a substrate disposed at a lower surface of the light guide film and mounted with dome switches at locations corresponding to those of the protrusions.

[36]

[37] In still another general aspect, a light emitting keypad is provided, the keypad comprising: a light guide film disposed at a lower surface of a key top; a light source disposed at a distal end of the light guide film; a plurality of protrusions formed at a predetermined lower location of the light guide film; and a substrate disposed at a lower surface of the protrusions and mounted with dome switches at locations corresponding to those of the protrusions.

[38]

[39]

[40]

Advantageous Effects

[41] The light guide film comprising a reflecting layer and an emitting keypad having the same according to the present invention is provided to solve the problems of a keypad of EL method, whereby introduction of an EL sheet is dispensed with, a direct illumination method is introduced to enable to realize a considerable slimness, introduction of a reflecting layer enables to enhance the luminance (brightness) even with a small number of light sources, and a uniform light emitting surface like that of a surface light source can be provided by forming a predetermined pattern on at least one surface.

[42]

Brief Description of the Drawings

[43] FIG. 1 is a cross-sectional view of an LED light emitting keypad by a direct illumination method according to prior art.

[44] FIG.2 is a cross-sectional view of a light emitting keypad of EL method according to the prior art.

[45] FIGS.3 and 4 are cross-sectional views of a light guide film according to an exemplary embodiment of the present invention.

[46] FIGS.5 and 6 are cross-sectional views of a pattern of light guide film according to another exemplary embodiment of the present invention.

[47] FIGS.7 to 9 are plan views of a pattern of light guide film according to still another exemplary embodiment of the present invention.

[48] FIGS. 10 and 11 are cross-sectional views of a light emitting keypad mounted with a light guide film according to an exemplary embodiment of the present invention.

[49] FIGS. 12 and 13 are cross-sectional views of a light emitting keypad mounted with a light guide film according to still another exemplary embodiment of the present invention.

[50]

[51]

Best Mode for Carrying Out the Invention

[52] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

[53]

[54] FIGS.3 and 4 are cross-sectional views of a light guide film according to an exemplary embodiment of the present invention.

[55]

[56] Referring to FIGS.3 and 4, the light guide film for a keypad backlight is provided, the film disposed at a rear surface of the keypad for supplying light irradiated from a lateral light source to the keypad, wherein the light guide film (10) is made of polycarbonate (PC) or polyethylene terephthalate (PET) material, and is formed at a rear surface thereof with a reflecting layer (11).

[57]

[58] The material of the light guide film (10) must have an excellent light guiding capability, must be easy in forming and exhibit a good flexibility and elasticity as well, thereby enabling to provide an accurate switching performance and a stable click feel. As a result of repeated experiments, the polycarbonate (PC) and polyethylene terephthalate (PET) have been found to be the best materials to satisfy the above attributes. Particularly, the polycarbonate (PC) and polyethylene terephthalate (PET) have an excellent flexibility, such that when a particular button of a keypad is depressed, only a particular region thereof is bent to allow a particular button to switch, and because these materials are elastic or resilient to enable to provide a stable click feel, the button is restored to its original status when the depression is released.

[59]

[60] The light guide film (10) is formed at a rear surface thereof with a reflecting layer

(11) for improving the brightness of a light emitting surface of the keypad. This is to guard the light against emission and disappearance through the rear surface of the light guide film. Particularly, when the reflecting layer is formed at the rear surface of the light guide film and simultaneously a pattern (described later) is formed at the rear surface of the light guide film, light is scattered by the pattern at the rear surface, and the light is emitted to a front of the light guide film by the reflection layer to enable to obtain a uniform light emitting surface.

[61]

[62] There is no limit in using materials for reflecting light for the reflecting layer (11) as long as the material is capable of reflecting light. The white pigment may be used independently or mixed with a paste. Preferably, the reflecting layer (11) of the light guide film is used with one or more selected from, for example, Ag, TiO ZnO, BaSO ZnS, lead white, and Sb O

[63]

[64] The reflecting layer (11) may be formed on the rear surface of the light guide film by evaporation method, or by coating or printing method. The evaporation, coating and printing methods are known so that detailed description thereto will be omitted herein.

[65]

[66] More preferably, the reflecting layer (11) manufactured in sheets as shown in FIG.4 is attached to the rear surface of the light guide film (10) using a two-sided tape (13) for the sake of simple process.

[67] FIGS.5 and 6 are cross-sectional views of a pattern of light guide film for a keypad backlight according to another exemplary embodiment of the present invention.

[68]

[69] Referring to FIGS. 5 and 6, at least one surface of front and rear surfaces of the light guide film (10) is formed with a pattern for uniformly supplying light to the keypad. Although the present embodiment has described a pattern of small depressions (depressed patterns or concavities) on the light guide film, the present invention is not limited thereto but a light guide film may include, but is not limited to, a pattern of small protrusions, embossings or reliefs. The light can be refracted and scattered by the patterns to be emitted to the keypad and to enable to obtain a uniform light emitting surface.

[70]

[71] FIGS.7 to 9 are plan views of a pattern of depressed images (14) of light guide film for keypad backlight according to still another exemplary embodiment of the present invention.

[72]

[73] Referring to FIGS.7 to 9, it is preferred that the pattern be formed in such a manner that density (number) of depressed or dotted pattern increases from light sources to enable to obtain a uniform light emitting surface. In other words, the density of pattern is made to increase to allow the light to be further scattered and to bring about a uniform light emitting surface, because the amount of light supply decreases as gradually distanced from the light sources.

[74]

[75] Referring again to FIGS. 7 and 8, the distance adjustment of the depressed pattern, i.e., adjustment of distance between depressions enables the adjusted density of the pattern (FIG.7), and the size adjustment of the depressions of the pattern can also adjust the density of the pattern (FIG.8). Meanwhile, a concentrated light emitting surface may be provided by concentrating density of depressions on particular regions (i.e., character regions of the keypad) in order to supply more lights on the particular regions, apart from the uniform light emitting surface (FIG.9).

[76]

[77] The shape of the pattern (14) is not particularly limited, but may include, but is not limited to, any processed shape or printed shape on the surface of a light guide plate. Although the forming method of the pattern is not limited, but preferably, the pattern be created by one of the processes of hot stamping (where a patterned mold is heated, a light guide film is compressed and a pattern is transferred on the light guide film), injection forming, micro blast and laser patterning methods. The pattern may be formed by silk-printing the light guard film with an ink containing a light- scattering agent.

[78]

[79] Hereinafter, a light emitting keypad according to the present invention will be des cribed.

[80]

[81] FIGS. 10 and 11 are cross-sectional views of a light emitting keypad mounted with a light guide film according to an exemplary embodiment of the present invention.

[82]

[83] As illustrated in FIGS. 11 and 12, the keypad comprises: a key top (20) disposed with a plurality of protrusions (21) at a predetermined location of a bottom surface thereof; a light guide film (10) disposed at a lower surface of the key top (20); a light source (12) disposed at a distal end of the light guide film (10); and a substrate (30) disposed at a lower surface of the light guide film (10) and mounted with a dome switch (31, 32) at locations corresponding to those of the protrusions (21).

[84]

[85] Preferably, the light guard film is the one having the characteristics thus mentioned.

For example, the light guard film is preferably formed at a rear surface thereof with a reflecting layer (11). The key top (20) and the light guard film (10) may be distanced therebetween as illustrated in the drawings or joined together. Preferably, the protrusions (21) are integrally formed with the protrusions, and material thereof may include, but not limited to silicon or polymeric resin.

[86]

[87] The substrate (30) is not specifically limited. The substrate may be a PCB, and is mounted with a dome switch composed of the metal dome (32) and the contact terminal (31). When the key top (20) of the keypad is depressed by a user, a compressed region of the light guard film is elastically deformed by the compression of the protrusion to press the relevant metal dome (32) of the PCB (30), whereby the metal dome (32) contacts the contact terminal (31) for a switching operation.

[88]

[89] The light source (12) is not specifically limited but an LED is most preferred for the light source. It is because the LED can easily embody colors and is reasonable in manufacturing cost. The light source is disposed at a lateral end of the light guard film to become a lateral light source, and the lateral light that is emitted is changed to a surface light by the light guard film.

[90]

[91] FIGS. 12 and 13 are cross-sectional views of a light emitting keypad mounted at a light guide film according to still another exemplary embodiment of the present invention.

[92]

[93] Referring to FIGS.12 and 13, the keypad comprises: a light guide film (10) disposed at a lower surface of a key top (20); a light source (12) disposed at a distal end of the light guide film (10); a plurality of protrusions (21) formed at a predetermined lower location of the light guide film (10); and a substrate disposed at a lower surface of the protrusions (21) and mounted with dome switches (31, 32) at locations corresponding to those of the protrusions (21).

[94]

[95] Preferably, the light guard film is the one having the characteristics thus mentioned.

The key top is well known in the art and may be applied without limitation. Therefore detailed description thereto will be omitted herein. The key top and the light guard film may be distanced therebetween as illustrated in the drawings or joined together.

[96]

[97] The protrusions (21) may select, for example, but not limited to, silicon or polymeric resin for its material. The protrusions may be directly formed with the light guide film, or a rear surface layer formed with protrusions may be attached to a rear surface of the light guide film as one way of forming the protrusions. Liquefied silicon, film silicon or polymeric resin is pressed and formed at 100-150 degrees Celsius using a mold corresponding in shape thereof to a rear surface layer (6) and/or a protrusion (7), or the protrusions may be formed by application of a photography technique, or UV hardening or IR hardening ink may be screen-printed for formation of the protrusions.

[98]

[99] The protrusions are preferably so formed as to be positioned, not under the key top, but under the light guide film. The reason of this construction is that, if the protrusions are located under the key top, the patterns on top of the light guide film are deformed by compression to create a problem to the reliability of the key pad.

[100]

[101] Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed in detail above. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus of the present invention disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents. Furthermore, no element, component or method step is intended to be dedicated to the public regardless of whether the element, component or method step is explicitly recited in the claims.

[102]

[103]

[104]

[105]

[106]

Industrial Applicability

[107] An EL sheet is dispensed with, a direct illumination method is introduced to enable to realize a considerable slimness, introduction of a reflecting layer enables to enhance the luminance (brightness) even with usage of a small number of light sources, and a uniform light emitting surface like that of a surface light source can be provided by forming a predetermined pattern on at least one surface, such that the present invention can be effectively used for the light guide film comprising reflecting layer and emitting keypad having the same.

[108]

[109]

[HO]

[111] [112]

Claims

[I] A light guide film for a keypad backlight, the light guide film disposed at a rear surface of a keypad for supplying light irradiated from a lateral light source to the keypad, wherein the light guide film is formed at a rear surface thereof with a reflecting layer.

[2] The film as defined in claim 1, wherein the light guide film is composed of polycarbonate (PC) or polyethylene terephthalate (PET), having a flexibility and elasticity.

[3] The film as defined in claim 1, wherein, at least one surface out of front and rear surfaces of the light guide film is formed with a pattern such that density increases as distanced from a light source to allow light to be uniformly supplied to the keypad, or is concentratively formed with a pattern at a particular region of the light guide film to allow the light to be concentratively supplied to a particular region of the keypad.

[4] The film as defined in claim 1, wherein the reflecting layer comprise one or more selected from a group consisting of Ag, TiO ZnO, BaSO ZnS, lead white, and

[5] The film as defined in claim 1, wherein the reflecting layer is formed at a rear surface of the light guide film by an evaporation method, a coating method or a printing method.

[6] The film as defined in claim 1, wherein the reflecting layer is comprised of a sheet, and is formed attached at a rear surface of the light guide film using a two- sided tape.

[7] The film as defined in claim 3, wherein the pattern is formed by one of the processing methods of hot stamping, injection forming, micro blast and laser techniques.

[8] The film as defined in claim 3, wherein the pattern is formed by an ink containing a light scattering agent being silk-screened on a light guide film.

[9] The film as defined in claim 3, wherein pattern density is adjusted by one of two methods which are pattern distance adjustment and pattern size adjustment.

[10] A light emitting keypad, comprising: a key top disposed with a plurality of protrusions at a predetermined location of a bottom surface thereof; the light guide film of any one claim of 1 to 9 disposed at a lower surface of the key top; a light source disposed at a distal end of the light guide film; and a substrate disposed at a lower surface of the light guide film and mounted with dome switches at locations corresponding to those of the protrusions.

[I I] A light emitting keypad, comprising: the light guide film of any one claim of 1 to 9 disposed at a lower surface of a key top; a light source disposed at a distal end of the light guide film; a plurality of protrusions formed at a predetermined lower location of the light guide film; and a substrate disposed at a lower surface of the protrusions and mounted with dome switches at locations corresponding to those of the protrusions.