JP2013051117A - Plane light source device - Google Patents

Abstract

A liquid crystal display device is required to have high luminance when viewed from the front, and a surface light source device is required to have high luminance when viewed from the liquid crystal cell side (front side). An object of the present invention is to provide a novel surface light source device with high front luminance that gives a liquid crystal display device with high luminance when viewed from the front.
A surface light source device having a light guide plate provided with light deflection means, a light source, and a reflection plate, wherein the reflection plate is disposed on a surface of the light guide plate where the light deflection means is not provided, A surface light source device in which light is emitted from a surface of a light plate to which light deflecting means is applied.
[Selection] Figure 2

Description

  The present invention relates to a surface light source device used as a backlight of a liquid crystal display device used in a liquid crystal television, a liquid crystal monitor, a personal computer, or the like, or a surface light source device used as a lighting fixture.

  As a surface light source device such as a liquid crystal display device or a luminaire, for example, a light source such as an LED light source is disposed on the side of a light guide plate (referred to as “end face” or “edge”), and light from the LED light source is While guiding the inside of the light guide plate by total reflection, light deflection of the dot pattern, prism portion, etc. formed on the back side of the light guide plate (the side opposite to the direction in which light is emitted as a liquid crystal display device or lighting fixture) There is known a configuration in which light is uniformly emitted from the front surface of the light guide plate by means (for example, Patent Document 1).

  In particular, the liquid crystal display device is required to have high luminance when viewed from the front, and the surface light source device is required to have high luminance when viewed from the liquid crystal cell side (front side).

  In order to increase the luminance when viewed from the front, the surface light source device has been devised as follows. The surface light source device includes a light source, a light guide plate, and a reflection plate. A light source is disposed on the end surface of the light guide plate, and the light guide plate is a member for guiding light from the light source to the liquid crystal cell side (front side). A reflector is disposed on the back side of the light guide plate. A light deflecting means for guiding light from the light source to the front side, for example, white spot (dot) printing has been proposed on the surface on the back side of the light guide plate (Patent Document 1). The size and density of the spots are adjusted as appropriate so that the light emitted from the surface light source device is uniform in the surface.

JP 2001-266626 A

However, there is a demand for further improving the luminance when viewed from the front.
Therefore, an object of the present invention is to provide a novel surface light source device with high front luminance that can provide a liquid crystal display device with high luminance when viewed from the front.

As a result of intensive studies on the surface light source device in order to solve the above problems, the present inventor has completed the present invention.
That is, the present invention provides the following <1> to <5>.

<1> A surface light source device having a light guide plate provided with light deflecting means, a light source, and a reflective plate, wherein the light guide plate is disposed on a surface where the light deflecting means is not provided. A surface light source device in which light is emitted from the surface on which the light deflection means is applied.
<2> The value obtained by dividing the light flux F2 emitted from the surface of the light guide plate on which the light deflection means is applied by the light flux F1 emitted from the surface of the light guide plate on which the light diffusion means is not applied is 0.8 or more. The surface light source device according to <1>.
<3> The surface light source device according to <1> or <2>, in which the light deflection unit uses a light diffusion phenomenon.
<4> The surface light source device according to <1> or <2>, wherein the light deflection unit uses light reflection and refraction.
<5> The surface light source device according to any one of <1> to <4>, further including a lens sheet.
<6> The surface light source device according to <5>, wherein the lens sheet has a surface having a lens portion facing the light guide plate side.
<5> A light guide plate used in the surface light source device of <1> to <6>.

  The present invention provides a novel surface light source device that can be simply configured and can provide a liquid crystal display device having high luminance when viewed from the front, and when the surface light source device is used, Since a liquid crystal display device with high luminance can be manufactured, the present invention is extremely useful industrially.

The schematic diagram which shows the surface light source device of a prior art. The schematic diagram which shows one embodiment of the surface light source device of this invention. The schematic diagram which shows the liquid crystal display device comprised using the surface light source device of this invention. The figure which shows the structure for measuring a light beam. The figure which shows the structure for measuring the front luminance of a light-guide plate.

  The surface light source device of the present invention is a surface light source device having a light guide plate, a light source, and a reflection plate provided with light deflecting means, the light source being disposed on the end surface of the light guide plate, and the light deflecting means of the light guide plate being provided. A reflection plate is disposed on a non-exposed surface, and light is emitted from the surface of the light guide plate on which light deflecting means is applied.

  In a surface light source device having a light guide plate, a light source, and a reflection plate provided with the light deflection means, the light deflection means conventionally guides the light of the light source to the front side as shown in FIG. Was placed on the side. Of the light emitted from the light source, a part of the light directed to the back side of the light guide plate is reflected, refracted and diffused by the light deflecting means, and the light incident on the light guide plate surface not provided with the light deflecting means is The light is reflected on the surface of the light guide plate or is reflected by the reflector after being transmitted. The size and density of the light deflecting unit are appropriately adjusted so that the light emitted from the surface light source device to the front surface side is uniform within the emission surface of the surface light source device.

  A surface light source device with a reflecting plate removed from a conventional surface light source device (see FIG. 4) is prepared, and the front luminance measured on the light guide plate on which the light deflecting means is applied, that is, the back surface side, When comparing the front luminance measured on one front side, the inventor found that the front luminance on the rear side was unexpectedly high, and the present invention was completed as a surface light source device having a higher front luminance than before. It is.

  The surface light source device of the present invention can be schematically represented as shown in FIG.

  The light guide plate of the present invention is a light guide plate base material provided with light deflection means. As the light guide plate base material, one made of a transparent resin usually formed into a plate shape is used. Examples of the transparent resin include methacrylic resin (PMMA, etc.), polycarbonate resin, ABS resin (acrylonitrile-styrene-butadiene copolymer resin), MS resin (methyl methacrylate-styrene copolymer resin), polystyrene resin, AS resin ( Acrylonitrile-styrene copolymer resin), polyolefin resin (polyethylene, polypropylene, etc.), cyclic polyolefin resin, and the like.

  As a method for producing a transparent resin substrate that can be used for a light guide plate substrate by forming the transparent resin into a plate shape, the following methods can be usually used industrially.

  Melt extrusion method: Transparent resin material is melt-extruded using an extruder, and at least one side of a sheet-like material that can be discharged from a die is brought into contact with a roll or belt to form a transparent resin base material. It is a method to do.

  Cast polymerization method: Mixing a monomer composition containing a monomer component and a polymerization initiator, and then injecting the two glasses into a cell facing each other through a spacer, further heating or ultraviolet irradiation In this method, the initiator is activated by a method such as polymerization to obtain a sheet-like molded body to produce a transparent resin substrate.

  Press molding: a method for producing a transparent resin substrate by molding a transparent resin material into a plate shape using a heating press device.

  Injection molding: a method for producing a transparent resin base material by pouring a heat-melted transparent resin material into a mold having a plate-like void, and then cooling and solidifying.

  The thickness of the transparent resin substrate is set in consideration of efficiently taking in the emitted light from the light source, but is usually set to 0.5 mm or more, preferably 1 mm or more, more preferably 1.5 mm or more. . The upper limit of the thickness is set according to the structure of the liquid crystal display device or the surface light source device, but for the purpose of reducing the thickness and weight of the entire device or reducing the amount of transparent resin used, it is usually 15 mm or less, preferably It is set to 10 mm or less, more preferably 5 mm or less. Also, the entire thickness may be uniform, or the cross section is wedge-shaped and butterfly-shaped (two plates with a cross-section of trapezoid are in contact with each other so as to share the upper base (shorter bottom) of the trapezoid) A mold having a distribution of thickness, such as a mold having a changed shape, may be used.

  The light source may be either a linear light source or a point light source. For example, a cold cathode tube or a light emitting diode (LED) can be used. When the LED is used as a light source, for example, it may be one white light emitting LED provided with three LED chips that emit red, blue, and green colors, or each of red, blue, and green. The LED which connected and integrated three LED which light-emits a color may be sufficient. Further, it may be an LED that emits white light by a combination of a blue light emitting LED chip or a near ultraviolet light emitting LED chip and a phosphor. The light source is usually disposed on the end surface of the light guide plate, and may be disposed along only one side of the light guide plate, may be disposed on two opposite sides, or may be disposed on three sides or even four sides. May be.

  Light deflecting means is provided on the exit side surface of the light guide plate. Examples of the light deflecting means include a means utilizing a light diffusion phenomenon, a means utilizing light reflection and refraction, and the like. Usually, in order to obtain in-plane luminance uniformity, the in-plane distribution is given to the light deflection ability so that the luminance is uniform (the direction and degree of light deflection are changed according to the position of the surface of the light guide plate).

  As means utilizing the light diffusion phenomenon, there is usually used a white ink that is printed in the form of spots on the surface of the light guide plate by a printing method to form white spots. As the white ink, one in which a filler that expresses white is contained in a resin dissolved in a solvent is usually used. As the filler, transparent resin particles, titanium oxide, glass beads and the like can be used. As the filler, glass beads are preferable for improving the front luminance on the front side of the surface light source device.

  When the amount of filler, the size of the spots, and the occupation ratio in the plane of the light guide plate are changed, the light flux (F2) emitted from the light guide means side (front side) of the light guide plate and the opposite side The light flux (F1) of the light emitted to the surface side (the back surface side on the side where the reflecting plate is disposed) can be changed.

  Examples of the light deflection means using light reflection and refraction include means for providing a fine lens structure and forming a linear groove. When the lens structure, the depth of the groove, and the distance between the lenses or the grooves are changed, the light flux (F2) emitted from the light deflecting side (front side) of the light guide plate and the opposite surface The light flux (F1) of the light emitted to the side (the side where the reflector is disposed and the back side) can be changed.

  F2 / F1 is preferably 0.8 or more in order to improve the front luminance on the front side of the surface light source device, more preferably 1.0 or more, further preferably 1.05 or more, and 1.2 or more. Is even more preferable.

  Further, by changing the in-plane occupation ratio of the light guide plate of the light deflector or the shape of the light deflector depending on the location of the surface of the light guide plate, the unevenness of the luminance distribution in the exit surface of the surface light source device is reduced. be able to.

  The lens sheet is in a direction parallel to the side of the light emitting surface of the light guide plate (the surface on which the dots are printed) on which the light source is arranged (if all four sides are arranged, one of the two opposing sides). A plurality of prism-like lenses extending in parallel to the light exit surface of the light guide plate, and a surface perpendicular to the side where the light source of the light exit surface of the light guide plate is disposed (prism-like The cross section when the lens sheet is cut in a plane perpendicular to the direction in which the lens extends is a shape in which a tapered polygonal shape and a shape that is a part of a substantially elliptical shape are arranged side by side.

  For example, when the cross-sectional shape is a triangle, the apex angle θ of the apex that forms the ridge line among the apexes of the triangle can be appropriately determined according to the emission angle from the light guide plate and the distribution shape thereof, but is 50 to 120 degrees. It is preferable that it is the range of these. In addition, each side of the triangle may be either an equal side or an unequal side. The lens sheet may be installed either on the light guide plate side or on the liquid crystal panel side, but is usually determined in consideration of the front luminance. Also, a plurality of lens sheets can be combined and used.

  In particular, when the angle distribution of the light emitted from the light guide plate has an intensity peak in a direction away from the normal direction of the light guide plate, the effect of increasing the brightness is high if the lens structure surface is disposed on the light guide plate side. At that time, when the cross-sectional shape is substantially triangular, the apex angle is preferably in the range of 60 to 70 degrees.

  Further, the cross-sectional shape can be set in accordance with the characteristics of the emitted light from the surface light source device, and a shape other than a triangle, such as a curved line, may be used.

  Examples of the material of the prism sheet used in the surface light source device of the present invention include polycarbonate resin, ABS resin, methacrylic resin, methyl methacrylate-styrene copolymer resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene, and polypropylene. And polyolefin resins.

  The prism sheet can be produced by a known method such as a profile extrusion method, a press molding method, an injection molding method, a roll transfer method, a laser ablation method, a mechanical cutting method, a mechanical polishing method, or a photopolymer process. When using the photopolymer process, materials are synthesized from, for example, polyfunctional acrylates such as polyhydric alcohol acrylic acid or methacrylic acid ester, diisocyanate and polyhydric alcohol and acrylic acid or methacrylic acid hydroxy ester, etc. A so-called ionizing radiation curable resin such as polyfunctional urethane acrylate can be used. Each of these methods may be used alone, or two or more methods may be combined.

  The thickness of the lens sheet is usually 0.05 to 5 mm, preferably 0.1 to 2 mm. The distance between the prism-shaped lens ridge lines is usually in the range of 10 to 500 μm, and preferably in the range of 30 to 200 μm.

  The reflector is a white sheet or a resin film such as polyester that diffuses light by adding a filler to the resin film such as polyester or by providing a gap between the added filler and the base resin. Mirror-type reflectors, etc., in which the specular reflection component is strengthened by vapor-depositing a metal such as aluminum or silver on the surface, can be used. Is preferred. Examples of the mirror-type reflector include a smooth metal vapor-deposited surface that does not have a diffuse reflection component, is a regular reflection component, and has no fine irregularities.

  Since the surface light source device of the present invention having the above configuration is a surface light source device having a higher front luminance than the conventional one, a liquid crystal display device having a higher front luminance is provided.

  FIG. 3 schematically shows a liquid crystal display device provided with the surface light source device of the present invention. A liquid crystal cell 21 in which a liquid crystal layer 23 is provided between a pair of transparent substrates 22a and 22b is provided. Between the surface light source device 11 and the liquid crystal cell 21, a first polarizing plate 31, a liquid crystal cell 21, and a second polarizing plate 32 are arranged in this order from the surface light source device side (back side).

  A liquid crystal cell 21 used in a liquid crystal display device manufactured using the surface light source device of the present invention includes a pair of transparent substrates 22a and 22b arranged to face each other at a predetermined distance, and the pair of transparent substrates 22a and 22b. A liquid crystal layer 23 in which liquid crystal is sealed is provided. Although not shown in the figure, transparent electrodes and alignment films are laminated on the pair of transparent substrates 22a and 22b, respectively, and the liquid crystal is formed by applying a voltage based on display data between the transparent electrodes. Orient. As a display method of the liquid crystal cell 21, a display method such as a TN method, an IPS method, and a VA method can be adopted.

  As the polarizing plates 31 and 32, those in which a support film is bonded to both sides of a polarizer are usually used. As the polarizer, for example, a dichroic dye or iodine is adsorbed and oriented on a polarizer substrate such as a polyvinyl alcohol resin, polyvinyl acetate resin, ethylene / vinyl acetate (EVA) resin, polyamide resin, or polyester resin. And a polyvinyl alcohol / polyvinylene copolymer containing a molecular chain oriented with a dichroic dehydrated product of polyvinyl alcohol (polyvinylene) in a molecularly oriented polyvinyl alcohol film.

  As the support film for supporting and protecting the polarizer, a film made of a polymer having low birefringence and excellent in transparency, mechanical strength, thermal stability, moisture shielding property and the like is preferable. Examples of such films include cellulose acetate resins such as TAC (triacetylcellulose), acrylic resins, fluorine resins such as tetrafluoroethylene / hexafluoropropylene copolymers, polycarbonate resins, and polyethylene. Polyester resin such as terephthalate, polyimide resin, polysulfone resin, polyethersulfone resin, polystyrene resin, polyvinyl alcohol resin, polyvinyl chloride resin, polyolefin resin or polyamide resin, etc. are formed into a film. What was processed is mentioned.

  The liquid crystal display device manufactured with the surface light source device of the present invention may have an optical functional film having other functions.

  As such an optical functional film, for example, a reflective polarizing film that transmits a certain kind of polarized light and reflects polarized light that shows the opposite property; a film with a random concavo-convex shape on the surface; Examples thereof include a film with a deflection function having a concavo-convex shape such as a prism or a lenticular lens. For example, “DBEF” (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan) is a commercially available product corresponding to a reflective polarizing film that transmits certain types of polarized light and reflects polarized light that exhibits the opposite properties. Can be). As a commercial product corresponding to a film with a diffusion function, “Opulse” (manufactured by Eiwa Co., Ltd.) and the like can be mentioned. Moreover, as a commercial item corresponding to the film with a deflection function, “BEF” (manufactured by 3M, available from Sumitomo 3M Co., Ltd. in Japan) and the like can be mentioned.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

(Examples 1-7, Comparative Examples 1-7)
-Production of light guide plate original plate PMMA (polymethyl methacrylate) ("SUMIPEX EXN" manufactured by Sumitomo Chemical Co., Ltd.) is melt-kneaded with a single screw extruder having a screw diameter of 40 mm and extruded from a T die at a resin temperature of 255 ° C. A plate-like sample having a thickness of 4 mm and a width of 250 mm was produced. The obtained plate-like sample was cut into a size of 160 mm wide × 210 mm long, and its four side surfaces (end surfaces) were polished by a polishing machine (“Pura Beauty 1000” manufactured by Asahi Megaro) to obtain a light guide plate base material. A spotted pattern (light deflecting means) was applied to one surface of the obtained light guide plate base material using a screen printing method. Four types of light guide plates, A, B, C, and D with different degrees of light deflection were manufactured by adjusting the type and concentration of the filler added to the printing ink. Table 1 shows a sample of the light guide plate.

-Luminous flux measurement The white LED arranged in a line as a light source was installed on one side (160 mm side) of the light guide plate. For the remaining three sides, install a strip of paper that is black on one side and white on the other side, with the black side facing the light guide plate, preventing light leakage from sides other than the side where the light source is installed. did. The surface light source for measuring light flux (FIG. 4) thus obtained was placed in a large integrating sphere having a diameter of 1600 mm, and the light flux was measured using a spectrometer (DA-2100) manufactured by Labshpere. When measuring the light flux from the surface on which the light deflecting means is applied, install the opposite surface so that one side is black, the opposite surface is white, and the black surface is on the light guide plate side. Only the light flux from the surface on which the light deflection means was applied was measured. Further, when measuring the light flux from the opposite surface of the light deflection means, the light flux (lm) from the opposite surface of the deflection means was measured by similarly covering the surface subjected to the light deflection means. .

-Luminance measurement The light-guide plate, the reflecting plate, the lens sheet, and the light source were arrange | positioned as shown in FIG. 5, and the surface light source device for luminance measurement was produced. The luminance was measured using a luminance meter (“Eye Scale-3WS” manufactured by Eye System Co., Ltd.). That is, the camera is arranged in front of the surface light source device so that the entire front surface of the surface light source device is reflected. At this time, the distance from the front surface of the surface light source device to the camera is set to 80 cm, and the measurement conditions of the luminance meter are set to SPEED: 1/250, GAIN: 0, aperture: 16, and the central portion of the front surface of the surface light source device The luminance at each measurement spot (51 × 33 locations (total 1683 locations)) is measured by designating a 150 mm × 150 mm range centering on the average brightness (cd / M ² ).

  Table 2 shows the front luminance measurement results of Examples 1 to 7 and Comparative Examples 1 to 7. When the light deflecting means is provided on the liquid crystal cell side (front side), the lens surface (lens structure surface) of the lens sheet is on the liquid crystal cell side (front side), regardless of whether the light guide plate is AD. ) Or the light guide plate side (back side), the front luminance was higher than that of the corresponding comparative example in which the light deflecting means was provided on the reflection plate side (back side).

DESCRIPTION OF SYMBOLS 11 Surface light source device 12 Light source 13 Reflecting plate 14 Light guide plate base material 15 Light deflecting means 17 Lens sheet 21 Liquid crystal cell 22a Transparent substrate 22b Transparent substrate 23 Liquid crystal layer 31 First polarizing plate 32 Second polarizing plate

Claims (7)

  A surface light source device having a light guide plate provided with light deflecting means, a light source, and a reflective plate, wherein the light guide plate is disposed on a surface where the light deflecting means is not provided, and the light deflection of the light guide plate A surface light source device that emits light from a surface to which means is applied.   The value obtained by dividing the light flux F2 emitted from the surface of the light guide plate on which the light deflecting means is applied by the light flux F1 emitted from the surface of the light guide plate on which the light diffusion means is not applied is 0.8 or more. The surface light source device described.   The surface light source device according to claim 1, wherein the light deflecting unit uses a light diffusion phenomenon.   3. The surface light source device according to claim 1, wherein the light deflecting means uses light reflection or refraction.   Furthermore, the surface light source device of any one of Claims 1-4 which comprised the lens sheet.   The surface light source device according to claim 5, wherein a surface of the lens sheet having a lens portion faces the light guide plate side.   The light guide plate used for the surface light source device of any one of Claims 1-6.