JP4834111B2 - Light guide sheet and electronic device using the same - Google Patents

Description

  The present invention relates to a light guide sheet useful for illumination of operation keys or an operation panel of, for example, a mobile phone, a personal digital assistant (PDA), and a calculator, and an electronic device using the same.

  For portable electronic devices such as a mobile phone, a personal digital assistant (PDA), and a calculator, operation keys or operation panel lighting is necessary to enable use in the night or in a dark place. On the other hand, these portable electronic devices preferably have less illumination power for the operation keys in order to prevent battery consumption. For this reason, using a light emitting diode (LED) as an illumination source has been proposed (Patent Documents 1 and 2). These documents disclose a device having a structure in which one LED is arranged for one switch.

However, the above apparatus has a problem that power consumption is large because a large number of LEDs are required. Furthermore, since the LEDs are arranged below each switch, there is a problem that the thickness of the device increases and it is difficult to reduce the size of the device.
Japanese Utility Model Publication No. 7-10701 Japanese Utility Model Publication No. 6-36162

  In order to solve the above problem, the present invention provides a light guide sheet that can reduce the number of LEDs in an electronic device and can be downsized, and an electronic device using the same.

The light guide sheet of the present invention includes a reflective film, a plurality of print mark portions printed on the front surface of the reflective film, and a front surface of the reflective film, and the print mark portion is embedded in the reflective film. integrated with a film, comprising a transparent sheet, wherein it is visible light transmittance of the transparent sheet is 99% or less than 80%, the transparent sheet, the light can be incident light to the inside of the transparent sheet on its end face An incident portion is included, and light incident on the inside of the transparent sheet from the light incident portion is reflected by the print mark portion, and the light guide sheet is reflected from the surface opposite to the reflective film side of the transparent sheet. a light guiding sheet which can be derived to the outside, the transparent sheet is a silicone rubber sheet was cured by heating the thermosetting liquid rubber, the print mark portion, is dispersed in a base material wherein the base material And a light irregularly reflected particles, the base material is characterized in that is obtained by heat curing an ink comprising a heat-curable liquid silicone rubber.

  The electronic device of the present invention includes a light guide sheet of the present invention, a light source disposed adjacent to the light incident portion, a key switch disposed on the opposite side of the transparent film to the reflective film side, and the reflection The wiring board arrange | positioned on the opposite side to the said transparent light sheet side of a film, The metal dome arrange | positioned between the said light guide sheet and the said wiring board is included.

FIG. 1 is a plan view of an example of the light guide sheet of the present invention. 2 is a cross-sectional view taken along the line II of FIG. FIG. 3 is a cross-sectional view of an example of a mobile phone using an example of the light guide sheet of the present invention. FIG. 4 is an explanatory diagram for explaining the conditions for measuring the luminance of the light guide sheets of Examples and Comparative Examples.

(1) Reflective film The reflective film may be a single metal film such as aluminum, silver, or gold, and is disposed in contact with one main surface of the resin base film and the resin base film. It may be a film including a metal layer formed by a method such as vapor deposition. From the viewpoint of cost reduction and high strength, it is preferable to use a film in which a metal such as aluminum, silver, or gold is deposited on one main surface of a polyethylene terephthalate (PET) base film. 10-100 micrometers is preferable and, as for the thickness of a resin base film, 20-80 micrometers is more preferable. A preferable thickness of the metal layer is 10 to 100 nm, and more preferably 20 to 50 nm. Such a reflective film is commercially available.

(2) Print mark portion A desired print mark portion is printed on the reflective surface of the reflective film. Light incident on the transparent sheet from a light incident portion of the transparent sheet described later propagates in the transparent sheet. The light exceeding the critical angle by being reflected by the print mark portion is led out of the transparent sheet from the opposite surface of the transparent sheet on the reflective film side. More specifically, each print mark portion includes a base material and fine particles dispersed in the base material. The base material contains as a main component a material having the same or similar refractive index value as the material of the transparent sheet. When the transparent sheet is a silicone rubber sheet, the base material preferably contains silicone rubber as a main component. Although there is no restriction | limiting in particular about the printing method, Print printing is preferable.

  When the transparent sheet is a silicone rubber sheet, examples of a suitable printing ink for forming the print mark portion include a silicone-based ink containing the fine particles. The silicone-based ink includes, for example, the fine particles and silicone rubber such as heat curable liquid rubber. The silicone-based ink may further contain additives such as a heat-resistant agent, a flame retardant, an antibacterial agent, and an antifungal agent as long as the object of the present invention is not impaired. The printing ink is used after being mixed with a curing agent, for example. Examples of the fine particles include titanium oxide fine particles, calcium carbonate fine particles, and barium sulfate fine particles. The printing ink and the printing mark part may contain only one kind of these fine particles, but may contain two or more kinds. The average particle diameter of the fine particles is not particularly limited as long as it can reflect the light that has passed through the transparent sheet and entered the print mark portion. For example, 20 μm or less is appropriate, and good printing can be performed. It is preferable that it is 1 micrometer-10 micrometers. The amount of fine particles added to the silicone rubber varies depending on the type and average particle diameter, but may be appropriately determined within a range in which a reflection effect is obtained and the rubber elasticity of the printed mark portion is not impaired.

  Examples of commercially available printing inks include silicone printing ink (manufactured by Toray Dow Corning Co., Ltd., product name, “PRK-3 WHITE”). To 100 parts by weight of this silicone printing ink, 10 parts by weight of a curing agent (for example, product name, “PRK-3 WHITE CAT-A” manufactured by Toray Dow Corning Co., Ltd.) is uniformly stirred and mixed. These mixtures are sufficiently degassed with a vacuum deaerator. Screen printing is performed on a predetermined position of the transparent sheet using the mixture after defoaming. For screen printing, for example, a screen having dot-shaped holes is used. Next, in order to cure the silicone printing ink, the printed ink is heated and cured for 30 minutes in a hot air circulation oven at 150 ° C., for example.

In order to improve the uniformity of the brightness of light emitted from the light emitting surface of the light guide sheet (opposite surface of the transparent sheet on the reflective film side), the plurality of printed mark portions include the following (a) to (c): It is preferable that at least one of them is formed.
(A) About several printing mark parts, the shielding area is so large that the distance from the light-incidence part is a printing mark part. Here, the shielding area refers to a contact area between each print mark portion and the silicone rubber sheet.
(B) About several printing mark parts, the thickness is so thick that the printing mark part where the distance from a light incident part is far.
(C) For a plurality of print mark portions, the concentration of light irregular reflection particles contained in the print mark is higher as the print mark portion is farther from the light incident portion.

  Each print mark portion may be composed of a single mark, but may be composed of, for example, a plurality of dot shape marks. When each print mark part is composed of a plurality of dot shape marks, for example, with respect to one print mark part, the area from the light incident part is larger than the area of the dot shape mark at a location near the distance from the light incident part. For example, the area of the dot-shaped mark at a long distance can be increased. In this case, it is easy to perform control for increasing the uniformity of the luminance of light emitted from the light emitting surface of the light guide sheet, which is preferable.

(3) Transparent sheet As a transparent sheet having a visible light transmittance of 80% or more and 99% or less, a transparent resin sheet containing polymethacrylate resin (PMMA) or the like, or polyurethane (U) (U is classified according to ASTM D1419, and so on) ), Polybutadiene (BR), styrene / butadiene copolymer (SBR), butadiene / acrylonitrile copolymer (NBR), polyisoprene (IR), polychloroprene (CR), isobutylene / isoprene copolymer (IIR), ethylene Propylene copolymer (EPM), ethylene / propylene terpolymer (EPDM), chlorosulfonated polyethylene (CSM), organic polysulfide (T), organic polysiloxane (Q), propylene hexafluoride / vinylidene fluoride Copolymer (FKM) acrylic ester copolymer (ACM / ANM) comprises a resilient material selected from organic synthetic rubber such as a transparent sheet having rubber-like elasticity can be used. A suitable material for the transparent sheet is organic polysiloxane (Q), and the transparent sheet is preferably formed from a material that becomes a rubber elastic body by being cured, such as a commercially available silicone rubber compound or silicone rubber.

  Hereinafter, a preferred example of the transparent rubber sheet will be described. Examples of the silicone rubber used for forming the silicone rubber sheet include heat curable millable rubber, heat curable liquid rubber, and silicone gel. Of these, heat curable liquid rubber is preferable. Examples of the crosslinking mechanism of silicone rubber include organic peroxide crosslinking and addition reaction crosslinking, and addition reaction crosslinking is preferred. Regarding the physical properties after crosslinking of the silicone rubber, the hardness (JIS-K6253 compliant A-type hardness) is 20 to 95 degrees, the tensile strength (JIS-K6251) is 2 MPa or more, and the elongation (JIS-K6251) is 20% or more. Preferably there is.

  For forming a silicone rubber sheet having a visible light transmittance of 80% or more and 99% or less, for example, a transparent rubber material containing no filler is used. However, the transparent rubber material may contain additives such as a heat-resistant agent, a flame retardant, an antibacterial agent, and an antifungal agent in addition to the silicone rubber as long as the object of the present invention is not impaired. An example of a method for forming a silicone rubber sheet will be described below.

  First, on a resin film such as a polyethylene terephthalate (PET) film, a film obtained by uniformly mixing a silicone rubber raw material and a crosslinking agent is cast to form a film. Next, a PET film is placed on the film. Next, after rolling the film sandwiched between two PET films to a predetermined thickness as necessary, for example, by heating at 120 ° C. for 20 minutes to crosslink the silicone rubber raw material, A silicone rubber sheet is used. The average thickness of the silicone rubber sheet is not particularly limited as long as the visible light transmittance is 80% or more and 99% or less, but is preferably 0.10 to 1.00 mm, and preferably 0.20 to 0.80 mm. And more preferred.

  Thus, a transparent sheet is laminated on the reflective film, and a laminated sheet in which the reflective film and the transparent sheet are integrated can be obtained. The laminated sheet is cut into a predetermined shape according to the application. A printed mark is formed on the front surface of the reflective film, but the reflective film and the transparent sheet are integrated so that air is not contained inside the laminated sheet in which the reflective film and the transparent sheet are integrated. Is done. These peelings cannot be easily performed. For this reason, dust or the like does not enter between the reflective film and the transparent sheet, and the interface between the reflective film and the transparent sheet can be kept clean, so that it is possible to prevent a change in optical characteristics due to contamination of the interface.

  Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of an example of the light guide sheet of the present invention. One end face of the light guide sheet 10 has portions that are recessed toward the center as light incident portions 2a and 2b. In an electronic device using the light guide sheet 10, a light source such as an LED is disposed adjacent to the light incident portions 2a and 2b. The light incident portions 2a and 2b can be easily formed by a method such as cutting.

  2 is a cross-sectional view taken along the line II of FIG. In the example shown in FIG. 2, the reflective film 6 is comprised from the resin base film 6a and the metal layer 6b. Print mark portions 3a to 3i having a desired shape are printed on the metal layer 6b of the reflective film 6 (see FIG. 1). The printing method is preferably print printing. As the printing ink, for example, an ink containing titanium oxide fine particles is used. Light emitted from a light source such as the LED 4 enters the transparent sheet 1 from the light incident portion 2 a and propagates through the transparent sheet 1. The light that exceeds the critical angle by being reflected by the print mark portions 3a to 3d is led out of the transparent sheet 1 from the surface opposite to the surface on the reflective film 6 side of the transparent sheet 1, and is indicated by, for example, arrows 5a to 5d. Light can be extracted from the light guide sheet 10.

  If, for example, an operation panel of a mobile phone is disposed above the print mark portions 3a to 3i, a push button on the operation panel can be illuminated brightly. In the example shown in FIG. 1, all the push buttons can be illuminated brightly by using only two LEDs for one operation panel, and the power consumption can be kept low.

  FIG. 3 is a cross-sectional view of an example of a cellular phone using the light guide sheet of the present invention. The light emitting diode (LED) 4 is disposed adjacent to the light incident portion 2a of the light guide sheet. The light of the LED 4 is incident on the transparent sheet 1, and the light incident on the transparent sheet 1 propagates through the transparent sheet 1. Light that exceeds the critical angle by being reflected by the print mark portions 3a to 3d is led out of the transparent sheet 1 from the opposite surface of the transparent sheet 1 on the reflective film 6 side. The light extracted from the light guide sheet is irradiated toward the back surface of the key switch 14 disposed on the side opposite to the reflective film 6 side of the transparent sheet 1, and brightly illuminates the numerical values and symbols attached to the key switch 14. .

  As shown in FIG. 3, a wiring board 13 (for example, a printed wiring board) is disposed on the side opposite to the transparent light sheet 1 side of the reflective film 6, and a metal dome 8 is interposed between the light guide sheet and the wiring board 13. Has been placed. That is, the pressure-sensitive adhesive layer 7, the metal dome 8, and the wiring board 13 are arranged in this order on the opposite side of the reflective film layer 6 to the transparent sheet 1 side. The wiring substrate 13 includes, for example, a substrate 12 and wiring layers 9 and 11 formed on the substrate 12. When the key switch 14 is pressed, this force is transmitted to the metal dome 8 through the light guide sheet, and the metal dome 8 is crushed and the metal layer forming the metal dome 8 contacts the wiring layer 9 of the printed wiring board 13. This gives an input signal to the electronic device.

  As described above, in the light guide sheet of the present invention, a transparent sheet having a high visible light transmittance is used, and light can be incident on the inside from the end face of the transparent sheet. The plurality of print mark portions printed on the front surface of the reflective film can reflect the light that has entered the transparent sheet, and can be led out from the opposite surface of the surface of the transparent sheet on the reflective film side. Therefore, in the electronic device including the light guide sheet of the present invention, the number of LEDs can be reduced, and the uniformity of the luminance of light emitted from the light emitting surface of the light guide sheet can be improved. In addition, the thickness of the light emitting portion of the electronic device can be reduced. As a result, electronic devices such as mobile phones can be miniaturized. Furthermore, since the reflective film and the transparent sheet are integrated, dust or the like does not enter between the reflective film and the transparent sheet, and these interfaces can be kept clean. Therefore, it is possible to prevent the change in optical characteristics due to the contamination of the interface.

  Hereinafter, it demonstrates more concretely using an Example.

(1) Formation of print mark on reflective film Silicone printing ink (manufactured by Toray Dow Corning Co., Ltd., product name, “PRK-3 WHITE”) 100 parts by weight of curing agent (manufactured by Toray Dow Corning Co., Ltd., product name) , "PRK-3 WHITE CAT-A") 10 parts by weight was uniformly stirred and mixed. Thereafter, the obtained mixture was sufficiently degassed with a vacuum deaerator. Next, screen printing was performed on a predetermined position of the reflective film using the defoamed mixture. The printing thickness (dry thickness) was set to 20 μm ± 5 μm. As the reflective film, a film composed of a polyethylene terephthalate (PET) base film and a metal layer formed by depositing aluminum on one main surface thereof was used. The print mark part was printed on the metal layer. Next, the printed ink was heat-cured for 30 minutes in a hot air circulation oven at 150 ° C. For screen printing, a screen obtained by forming a plurality of openings by pasting a polyester screen (250 mesh) coated with an emulsifier on an aluminum frame and peeling the emulsifier into dots at a plurality of locations, respectively. Using. The dot-shaped opening of the screen is smaller as it is closer to the light incident part of the silicone rubber sheet, and is larger as it is farther away.

(2) Lamination of transparent sheet Two liquids of liquid silicone rubber (manufactured by Shin-Etsu Chemical Co., Ltd., trade names “KE1935A” and “KE1935B”: two-liquid mixed type) are mixed and stirred at a weight part ratio of 1: 1, The mixture was fully degassed with a vacuum deaerator. The defoamed mixed solution was cast on the surface on which the print mark portion of the reflective film was formed. On top of that, a film separator “No. 042” (manufactured by Teraoka Seisakusho, product name silicone adhesive separator, base material: polyester film # 50) was placed, and then the reflective film and film separator No. The mixture sandwiched between 042 "was rolled to a predetermined thickness with a constant speed roll. Next, the uncured sheet obtained by rolling the mixture was heated and cured in a 120 ° C hot air circulating oven for 20 minutes. Thereafter, the film separator No. 042 "was peeled off from the cured sheet to obtain a sheet having an average thickness of 0.30 mm.

  Further, a transparent sheet (silicone rubber sheet) was separately prepared as described below, and its physical characteristics were measured.

  Two liquids of liquid silicone rubber (manufactured by Shin-Etsu Chemical Co., Ltd., trade names “KE1935A” and “KE1935B”: two-component mixed type) are mixed and stirred at a weight ratio of 1: 1, and then the mixture is subjected to a vacuum defoamer. Fully vacuum degassed. The defoamed mixture was cast on a film separator “No. 042” (manufactured by Teraoka Seisakusho, product name silicone adhesive separator, substrate: polyester film # 50). After another film separator “No. 042” was placed thereon, the mixture sandwiched between the two film separators was rolled to a predetermined thickness with a constant speed roll. Next, the uncured sheet formed by rolling the mixture was heated and cured in a 120 ° C. hot air circulating oven for 20 minutes, and then the upper and lower film separators were peeled off from the cured sheet to obtain a thickness of 0. A 25 mm cured silicone rubber sheet was obtained.

  The properties of the obtained silicone rubber sheet (transparent sheet) are: visible light transmittance 90% (transmittance is 90% for light of any wavelength in the wavelength range 380 nm to 780 nm), hardness (according to JIS-K6253, type A) Hardness meter) was 55 degrees, tensile strength (based on JIS-K6251) 6 MPa, elongation (based on JIS-K6251) 350%.

In addition, the thickness (after drying) of the print mark portions a _{1 to} c ₄ is 17 to 25 μm, the thickness of the metal layer 6 b is 20 to 30 nm, the thickness of the resin base film 6 a is 50 μm, and the thickness of the adhesive layer 8. The thickness was 30 to 40 μm (see FIG. 3).

  In addition, the average thickness of the silicone rubber sheet with a reflective layer and the silicone rubber sheet 1 is a value obtained by measuring five points using a micrometer as defined in JIS B 7502 and averaging them.

As shown in FIG. 4, LED distance L ₁ was 20 mm. The dimensions of the light guide sheet obtained as described above are as follows: L ₂ : 10 mm, L ₃ : 5 mm, L ₄ : 5 mm, L ₅ : 5 mm, L ₆ : 10 mm, L ₇ : 50 mm, L ₈ : 50 mm It was. Table 1 shows the print states of the print mark portions a _{1 to} c ₄ . The numerical values in Table 1 indicate the shielding area ratio by dot printing per unit area (1 cm ² ) of the print mark portions a _{1 to} c ₄ in FIG.

Light was irradiated into the light guide sheet from two LEDs (Nichia Corporation, trade name NSSW020A type white LED), and brightness was measured with a luminance meter (trade name “CA-2000”, manufactured by Konica Minolta, Inc.). However, the luminance was measured in the range of 38 to 47 cd / m ^{2. In} addition, the luminance was measured by making the light-receiving surface of the luminance meter face the transparent sheet, and sequentially scanning above the print mark portions a _{1 to} c ₄ with the luminance meter, The luminance of light emitted from the light emitting surface of the light guide sheet was measured, and the distance between the light receiving surface of the luminance meter and the transparent sheet was 250 mm (the same applies to Example 2 and Comparative Example 1).

  Next, as shown in FIG. 3, the light guide sheet was incorporated into the mobile phone. As a result, it was possible to brighten the full push button only by using two LEDs, and to keep power consumption low.

(Example 2)
A light guide sheet was obtained in the same manner as in Example 1 except that the visible light transmittance of the silicone rubber sheet 1 (average thickness 0.25 mm) was 80%. When the luminance was measured in the same manner as in Example 1, it was 25 to 45 cd / m ² .

(Comparative Example 1)
A light guide sheet was obtained in the same manner as in Example 1 except that the visible light transmittance of the silicone rubber sheet 1 (average thickness 0.25 mm) was 78%. When the luminance was measured in the same manner as in Example 1, it was 8 to 40 cd / m ² .

  The above results are summarized in Table 2.

  From the above experimental results, it was confirmed that the uniformity of the luminance of light emitted from the light emitting surface of the light guide sheet was significantly improved when the visible light transmittance of the transparent sheet was 80% or more. Furthermore, it has confirmed that the uniformity of the brightness | luminance of the light radiated | emitted from the light emission surface of a light guide sheet improved further that the visible light transmittance | permeability of a transparent sheet is 90% or more.

Industrial applicability

  ADVANTAGE OF THE INVENTION According to this invention, the light guide sheet which can reduce the number of LED in an electronic device, and can also reduce the size of an electronic device, and an electronic device using the same can be provided.

Claims (13)

A reflective film;
A plurality of print mark portions printed on the front surface of the reflective film;
Laminated on the front surface of the reflective film, the print mark portion is embedded therein, and integrated with the reflective film , including a transparent sheet,
The visible light transmittance of the transparent sheet is 80% or more and 99% or less,
The transparent sheet has a light incident part that allows light to enter the inside of the transparent sheet on an end surface thereof,
Light that is incident on the inside of the transparent sheet from the light incident part is reflected by the print mark part, and can be led out of the light guide sheet from the surface opposite to the surface on the reflective film side of the transparent sheet. Light sheet ,
The transparent sheet is a silicone rubber sheet obtained by heat-curing a heat-curable liquid rubber,
The printed mark portion includes a base material and light diffused reflection particles dispersed in the base material, and the base material is obtained by heat-curing an ink containing a heat-curable liquid silicone rubber. Light guide sheet.   The light guide sheet according to claim 1, wherein the transparent sheet has a visible light transmittance of 90% or more.   The light guide sheet according to claim 1, wherein the transparent sheet has an average thickness of 0.10 to 1.00 mm. The light guide sheet according to claim 1, wherein the silicone rubber sheet is heat-cured by addition reaction crosslinking. The physical properties of the silicone rubber sheet after crosslinking are as follows: hardness (JIS-K6253 compliant A-type hardness) is 20 to 95 degrees, tensile strength (JIS-K6251) is 2 MPa or more, and elongation (JIS-K6251) is 20% or more. The light guide sheet according to claim 1.   The light guide sheet according to claim 1, wherein each print mark portion includes a plurality of dot shape marks. When the contact area between each printed mark part and the silicone rubber sheet is a shielding area,
The light guide sheet according to claim 1, wherein the shielding area of the plurality of print mark portions is larger as the print mark portion is farther from the light incident portion. The light guide sheet according to claim 1, wherein the plurality of print mark portions are thicker as the print mark portion is farther from the light incident portion. Wherein the plurality of printing marks section, the light guide sheet according to claim 1 the concentration of the light irregularly reflected particles higher contained in the distance the print mark farther print mark from the light incident portion.   The light guide sheet according to claim 1, wherein the incident light incident on the inside of the silicone rubber sheet from the light incident portion is light from a light emitting diode (LED).   The light guide sheet according to claim 1, wherein the reflective film includes a resin base film and a metal layer disposed in contact with one main surface of the resin base film. A light guide sheet according to any one of claims 1 to 11
A light source disposed adjacent to the light incident portion;
A key switch disposed on the opposite side of the transparent film to the reflective film side;
A wiring board disposed on the opposite side of the reflective film from the transparent light sheet side;
An electronic device including the light guide sheet and a metal dome disposed between the wiring boards. The electronic device according to claim 12 , wherein the light source is a light emitting diode (LED).

Images