JP2008153106A - Plane light source element and image display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plane light source element and an image display device which can efficiently deflect light from a light source in a front direction and can give high luminance in the front direction. <P>SOLUTION: The plane light source element is provided with a light source, a light guide plate and an emitting light controlling plate for emitting light in a front direction. Convex portions are optically adhered tightly with the light guide plate and a cross-section of the convex portion satisfies a predetermined formula. And, the image display device is provided with the plane light source element. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image display device such as a surface light source element and a liquid crystal display device including the surface light source element, and a personal computer, a computer monitor, a video camera, a television receiver, a car navigation system, and the like provided with the image display device as a display module. The present invention relates to a display device.

  2. Description of the Related Art A transmissive image display device typified by a liquid crystal display device includes a surface light source element (backlight) that emits light in a planar shape and a transmissive display element in which pixels are arranged in a dot shape. Characters, images, and the like are displayed by controlling the light transmittance from the surface light source element in each pixel of the element. As a surface light source element, a halogen lamp, a reflector, a lens, etc. are combined to control the luminance distribution of the emitted light. A fluorescent tube is provided on the end surface of the light guide plate, and light from the fluorescent tube is perpendicular to the end surface. The light emitted from a flat surface, the one provided with a fluorescent tube directly under the light guide plate (direct type), and the like. A surface light source element using a halogen lamp is mainly used in a liquid crystal projector that requires high luminance.

  On the other hand, since a surface light source element using a light guide plate can be thinned, it is often used for a direct-view liquid crystal TV, a display of a personal computer, and the like. In these surface light source elements using the light guide plate, a prism sheet or a diffusion sheet is usually provided on the exit surface side of the light guide plate for the purpose of improving the front luminance and the viewing angle characteristics of the emitted light. As such, an outgoing light control plate having the functions of these sheets is effective. These outgoing light control plates have a convex portion having a shape determined in accordance with a desired viewing angle characteristic on the incident surface, and the light guide plate and the outgoing light control plate are arranged in parallel and through a fixed layer. Thus, it is possible to control the light emitted from the emission surface of the outgoing light control plate by optically contacting the light guide plate (see Patent Document 1).

JP 2001-338507 A

  However, in recent years, there has been an increasing demand for luminance enhancement in the front direction with respect to these surface light source elements. On the other hand, it is desired to efficiently deflect light in the front direction from the viewpoint of energy saving. The ratio of deflecting light in the front direction depends on the cross-sectional shape of the convex portion, and the cross-sectional shape must be changed according to the refractive index of the light guide plate and the refractive index of the material forming the convex portion. However, the knowledge about the cross-sectional shape for efficiently increasing the luminance in the front direction has been insufficient.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a surface light source element and an image display device having high brightness in the front direction by efficiently deflecting light from the light source in the front direction. To do.

The invention described in claim 1
A light guide plate having a light source, an incident surface that is at least one end surface that receives light from the light source, and an output surface that is one of main surfaces substantially perpendicular to the incident surface, and an output surface of the light guide plate A surface light source element including an outgoing light control plate that receives the light from the convex portion on the incident surface and emits the light from the outgoing surface in the front direction, and the convex portion is in optical contact with the light guide plate, The plane perpendicular to the exit surface including the shortest path between the arbitrary projection and the light source nearest to the projection and the line of intersection of the exit surface is the X axis, and the center of the optical contact portion of the projection The cross-sectional shape of the portion that is not optically in close contact in the X-axis direction has N slopes expressed by the following formulas (1) to (14), where the axis that passes through and is orthogonal to the exit surface is the Y-axis. The surface light source element is characterized in that the different regions satisfy the following expression (15).

The invention described in claim 2
The cross-sectional shape of the convex portion in the X-axis direction is a shape obtained by approximating the shape of at least one pair of two adjacent regions by a curve among N different regions forming the convex portion. It is a surface light source element illuminating device of Claim 1.

The invention described in claim 3
An image display device comprising a transmissive display element on the exit surface side of the surface light source element according to claim 1.

  According to the present invention, in the surface light source element in which the exit surface of the light guide plate and the entrance surface of the exit light control plate are optically adhered, the directivity is strong by controlling the cross-sectional shape of the convex portion of the exit light control plate. A surface light source element having high brightness in the front direction can be obtained. In addition, by providing a transmissive display element on the surface light source element of the present invention, an image display device having high directivity and high luminance in the front direction can be obtained. The convex portion has the largest amount of energy of light incident from the nearest light source. Therefore, by optimizing the cross-sectional shape in the X-axis direction, the luminance in the front direction can be increased most efficiently.

  In the surface light source element of the present invention, the light source plate and the convex portion are controlled by the cross section of the convex portion that connects the light source closest to the outgoing light control plate and the convex portion and is perpendicular to the outgoing surface. The light deflection direction depends on the incident position of the optical contact portion. Therefore, by defining the cross-sectional shape in the plane passing through the center of the optical contact portion between the light guide plate and the convex portion, the deviation from the target light beam control direction is reduced, and the target light beam direction control can be performed efficiently. It becomes.

  In the formula (1), the ratio b of the portion W that is not optically adhered is divided into N parts. What is necessary is just to make inclination in each point so that the light which injected into each divided | segmented point radiate | emits efficiently to a front direction. Here, the ratio b needs to be in the range of 0.85 to 1. If b is less than 0.85, there will be a wall surface on which light does not enter, leading to a reduction in efficiency.

As shown in FIG. 5, the expression (2) is the maximum angle with respect to the normal direction of the end face when light incident from the end face 1 of the light guide plate is refracted. Moreover, (3) Formula is an incident angle to the convex part of the said light ray, (4) Formula represents the angle made with the light guide plate output surface normal direction inside a convex part. Further, equation (5) represents an angle formed from the light guide plate exit surface. Equation (6) is a refraction angle inside the convex portion when incident on the convex portion at an angle π / 2. However, in the case of n ₂ <n ₁ , total reflection occurs, so this light ray does not occur. Therefore, the minimum angle formed with the exit plane inside the convex portion is obtained by equation (7). That is, as shown in FIG. 5, the light incident from the end face of the light guide plate repeatedly propagates the total reflection in the light guide plate, and when the convex portion enters the convex portion from the portion that is in optical contact with the light guide plate, The light of the convex portion is limited to an angle of A ′ or more and B ′ ″ or less from the light guide plate exit surface.

  Equations (8) and (9) give initial values of shapes to be obtained as polygons. Equations (10) and (11) indicate the x coordinate of each region when the convex contact portion and the optical contact portion of the light guide plate are equally divided into (M + 1).

The inclination of light traveling from each region shown in FIG. 1 to the slope (X _i , Y _i ) of the convex portion is expressed by equation (12). If this slope is less than A ′ or greater than B ′ ″, this means that this light does not exist (13). Therefore, (14) represents the average of the inclination of the incident light on the slope (X _i , Y _i ).

In order for light having an inclination of θ _i to be totally reflected on the wall surface and to be directed substantially in the front direction, the inclination α _i in (X _i , Y _i ) only needs to satisfy the expression (15). α _i may be appropriately selected according to a desired viewing angle characteristic. To obtain high brightness in the front direction,
| 2α _i −θ _i −π / 2 | ≦ π / 20 (16)
Is desirable,
| 2α _i −θ _i −π / 2 | ≦ π / 30 (17)
Is more desirable.

From the coordinates (X _i , Y _i ) and the inclination at that point, the next coordinates (X _{i + 1} , Y _{i + 1} ) can be obtained by equation (18).
Y _{i + 1} = (X _i + Δ) × tan α _i + Y _i (18)

  Light incident from the optically close portion of the convex portion having this shape is efficiently emitted in the substantially front direction, and a surface light source element having high luminance in the front direction can be obtained.

  The invention according to claim 2 is the surface light source element according to claim 1, wherein the cross-sectional shape of the convex portion in the X-axis direction is at least one set out of N different regions forming the convex portion. The surface light source element is characterized in that the shape of two adjacent areas is approximated by a curve. In the main surface light source element, the distribution of light output intensity in the front direction and the distribution of light output angles can be made smooth. In addition, since it is easier to form, it is advantageous when producing the outgoing light control plate. Furthermore, it is also desirable that the bonded portion of the region is not easily broken because it is not a sharp shape. The breakage of the joint is undesirable because it may cause a change in the light emission direction and unnecessary scattering.

  The invention described in claim 3 is an image display device characterized in that a transmissive display element is provided on the light exit surface side of the surface light source element of claim 1 or 2. Since the surface light source element has high brightness in the front direction, it can be used as a preferred image display device by providing a transmission type display element on the exit surface side. Here, the image display device refers to a display module in which a surface light source element and a transmissive display element are combined, and a device having at least an image display function such as a television and a personal computer monitor using the display module.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 6 is a schematic sectional view showing a partial section of the surface light source element according to the embodiment of the present invention. The surface light source element includes a light guide plate 3 provided with a light source 2 on the left and right end faces 1 side, and an outgoing light control plate 4 that controls the distribution of the outgoing angles of light emitted from the light guide plate 3. The outgoing light control plate 4 is disposed on the light guide plate 3, and light incident on the incident surface 5 is emitted from the outgoing surface. A large number of convex portions 7 are formed on the incident surface 5 of the outgoing light control plate 4 in order to direct light from the outgoing surface 6 of the light guide plate 3 in the front direction through the outgoing light control plate 4. The top of the projection 7 is in optical contact with the light exit surface 6 of the light guide plate 3. A reflector that reflects light traveling in the opposite direction to the incident surface 1 side of the light guide plate and travels to the incident surface 1 side of the light guide plate may be provided around the light source 2.

  Light incident on the incident surface 1 of the light guide plate from the light source 2 propagates through the light guide plate 3 repeatedly with total reflection. The propagating light is taken into the outgoing light control plate 4 from the interface with the top of the convex portion 7 of the outgoing light control plate 4. Thereby, the light propagating in the light guide plate 3 and the fixed layer 9 is sequentially extracted from the interface to the outgoing light control plate 4, and the extracted light is totally reflected in the convex portion 7 of the outgoing light control plate 4. Emitted.

  As the light guide plate used in the surface light source element of the present invention, an acrylic resin such as polymethyl methacrylate (PMMA), a polycarbonate resin (PC), a polystyrene resin (PS), a resin having excellent transparency such as a cycloolefin polymer, or glass is used. What was processed into the predetermined shape can be used. Of these, it is preferable to use PMMA in terms of lightness and transparency. As a processing method, a method of cutting out from an extruded plate or a cast plate or a melt molding method such as a hot press or injection molding is preferably used, but is not limited thereto.

  In order to optically adhere the light guide plate and the outgoing light control plate, a fixed layer may be provided between the light guide plate and the outgoing light control plate. Examples of the fixing layer include an adhesive, a pressure-sensitive adhesive, an adhesive, a photocurable resin, and the like. A photocurable adhesive is preferably used from the viewpoints of handleability and productivity. Examples of the pressure-sensitive adhesive include those based on an appropriate polymer such as rubber, acrylic, vinyl alkyl ether, silicone, polyester, polyurethane, polyether, polyamide, and styrene. Among these, acrylic pressure-sensitive adhesives based on polymers mainly composed of alkyl esters of acrylic acid or methacrylic acid are preferred because they are excellent in transparency, weather resistance and heat resistance. In addition, the adhesive may be appropriately selected from conductive inorganic particles such as silica, alumina, titania and zirconia, tin oxide and indium oxide, cadmium oxide and nonmony oxide, and organic particles such as a crosslinked or uncrosslinked polymer. One kind or two or more kinds of transparent particles may be contained to obtain a light diffusion type.

When the stationary phase is provided, the tip of the convex portion may be buried. In this case, as shown in FIG. 4, the surface of the fixed layer may be the light exit surface 6 of the light guide, and the width embedded in the stationary phase may be 2a. Further, when the refractive index of the stationary phase was n ₃ is
n ₁ ≦ n ₃ ≦ n ₂ (19)
It is preferable that When the refractive index satisfies the equation (19), light propagating in the light guide plate can be efficiently taken into the convex portion, and high brightness can be easily achieved.

  Furthermore, the surface modification of the light guide plate and the self-adhesiveness of the material that forms the convex part of the outgoing light control plate allow the light guide plate and the outgoing light control plate to be optically adhered without a stationary phase. You may let them. In this case, it is preferable to provide a flat portion 2a at the tip of the convex portion. When the flat portion is in close contact, the width of the optical close contact portion can be obtained with high accuracy.

  Further, the surface shape of the outgoing light control plate is formed on a transparent substrate by using a stamper or a female die or the like by a hot press method, a 2P method by ultraviolet curing, a casting method by thermal curing, an injection molding method, or the like. be able to. As the transparent substrate, resin such as acrylic resin, polycarbonate resin, polystyrene resin, cycloolefin polymer, or glass is used. In the present invention, it is preferable to transfer the shape with a photocurable resin onto a transparent substrate using an acrylic resin.

  The photocurable resin used when transferring to the substrate determines the optical performance of the produced outgoing light control plate, and is preferably selected as appropriate according to the desired performance. As a component of the photo-curable resin, a monomer or oligomer capable of radical polymerization is used alone or in combination of two or more, but usually two or more are preferably used, and the mechanical strength required for the outgoing light control plate is used. , Impact resistance, heat resistance, surface hardness and the like can be imparted. Specific examples of the component include an ester type (meth) acrylate obtained by a condensation reaction of an aliphatic, alicyclic, or aromatic mono- or polyalcohol with acrylic acid or methacrylic acid, or two or more in the molecule. Urethane poly (meth) acrylate obtained by urethanization reaction of isocyanate compound having isocyanate group and (meth) acrylate containing hydroxyl group or thiol group and compound having at least two epoxy groups in the molecule and acrylic acid or Epoxy poly (meth) acrylate obtained by glycidyl group ring-opening reaction with methacrylic acid, polyester (meth) acrylate obtained by condensation reaction with saturated or unsaturated polyvalent carboxylic acid, polyhydric alcohol and (meth) acrylic acid (Meth) acryloyl functional monomers or oligomers such as Ren, chlorostyrene, bromostyrene, dibromostyrene, and vinyl compounds such as divinylbenzene, diethylene glycol bis allyl carbonate, diallyl phthalate, (meth) allyl compounds such as diallyl biphenylene rate and the like. These monomers may be used individually by 1 type, and may mix 2 or more types.

  For example, a stamper used for manufacturing the emission light control plate is coated with a negative or positive photosensitive resin on a glass substrate, and the photosensitive resin is exposed through a photomask or exposed by a laser drawing apparatus. It can be produced by electroforming after development, or it can be produced by cutting.

  The suitable thickness of the outgoing light control plate is 0.05 mm to 3 mm, and particularly the film shape of 0.1 mm to 0.5 mm reduces the thickness of the device, reduces the weight, and reduces the stress that leads to reduced adhesion. An effect is acquired and it is preferable. If it is less than 0.05 mm, it is not preferable because of wrinkles at the time of fixing to the light guide plate and a decrease in physical strength. On the other hand, if it exceeds 3 mm, the apparatus becomes undesirably heavy.

  Further, the convex portion provided in the outgoing light control plate in the present invention may be a two-dimensionally arranged lens array type shown in FIG. 2 or 3 in addition to a pattern such as a one-dimensionally arranged lenticular lens. When a linear fluorescent tube is used as the light source, a lenticular lens type or a lens array type can be used. When a point light source typified by an LED is used, it is preferably a lens array type. In the case of a lens array, it is preferable that the lens array is rotationally symmetric with respect to the center of the unit lens so that light incident on the convex portion from a light source other than the nearest can be emitted in the front direction.

  Fine surface irregularities may be directly transferred to the light emission surface of the emission light control plate, or a diffusion layer may be provided by applying a diffusing agent liquid mixed with light-transmitting fine particles. A viewing angle characteristic becomes gentle by the diffusion layer, and good quality can be obtained.

  2 (a + w), which is the size of the unit convex portion, is preferably 10 μm or more and 300 μm or less. More desirably, it is 15 μm or more and 200 μm or less. If it is smaller than 10 μm, coloring occurs due to diffraction phenomenon, and the quality of the screen is lowered. On the other hand, if it is larger than 300 μm, the projection itself is visually recognized, so that the quality of the screen is lowered.

  N is preferably in the range of 5-10. If it becomes smaller than this, sufficient performance cannot be obtained. Further, the difficulty in producing the convex shape increases.

  The approximation method to the curve is not particularly limited, and a generally well-known least square method, spline interpolation method, Lagrange interpolation method, or the like can be used. As the points used for approximation, at least one point is selected from the approximated region. Usually more than the number of approximated areas. For example, it is possible to select both ends of a plurality of continuous regions and contact points of each region. In addition, the midpoint of each region can be used for approximation.

  Examples of the light source used in the present invention include a cold cathode tube, a linear light source such as between hot cathodes, and a point light source such as an LED. In the case of a linear light source, one or a plurality of light sources may be arranged on one end face of the light guide plate or on opposite end faces. When the number of linear light sources increases, the amount of light incident on the light guide plate increases, and high brightness can be achieved. In the case of a point light source, one or more may be used. In this case, it is preferable to arrange the point light sources symmetrically with respect to the center of the side surface of the light guide plate where the point light sources are arranged. With this arrangement, the in-plane distribution can be targeted and the appearance quality can be improved. On the other hand, when using two or more, it is desirable to arrange | position so that the space | interval of a point light source may become equal. As a result, unevenness between the vicinity of the point light source and the point light source can be minimized.

  Hereinafter, the effects of the present invention will be described more specifically by way of examples. In each example and comparative example, the front luminance of the surface light source element configured as shown in FIG. 6 was measured to confirm the effect. In any case, three white LEDs were disposed as light sources on the short side surface of the light guide plate to obtain a surface light source element. The distance between the light emission centers of the LEDs was 10 mm, and one at the center was arranged at the center of the side surface of the light guide plate. The central part of the surface light source element was measured with a luminance meter (BM-7Fast, manufactured by Topcon Technohouse) from a distance of 500 mm perpendicular to the light emitting surface.

(Example 1)
In Example 1, as the light guide plate 3, a flat PMMA having a size of 30 mm × 40 mm and a thickness of 1 mm was used, and the emission surface and the opposing surface were flat surfaces. The emission light control plate 4 was prepared by using a PMMA film having a thickness of 0.1 mm as a base material and transferring the photo-curing resin applied to the stamper to the base material by UV curing. The refractive index of the light guide plate was 1.49, and the refractive index of the photocurable resin after curing was 1.54. The outgoing light control plate was bonded to the outgoing surface of the light guide plate.

(Example 2)
In Example 2, as the light guide plate 3, a flat PMMA having a size of 30 mm × 40 mm and a thickness of 1 mm was used, and the emission surface and the opposite surface were flat surfaces. The emission light control plate 4 was prepared by using a PMMA film having a thickness of 0.1 mm as a base material and transferring the photo-curing resin applied to the stamper to the base material by UV curing. The refractive index of the light guide plate was 1.49, and the refractive index of the photocurable resin after curing was 1.54. The outgoing light control plate was bonded to the outgoing surface of the light guide plate.

(Example 3)
In Example 3, a flat plate PC having a size of 30 mm × 40 mm and a thickness of 1 mm was used as the light guide plate 3, and the emission surface and the opposing surface were flat surfaces. The emission light control plate 4 was prepared by using a PC film having a thickness of 0.1 mm as a base material and transferring a photocurable resin applied to a stamper to the base material by ultraviolet curing. The refractive index of the light guide plate was 1.59, and the refractive index of the photocurable resin after curing was 1.59. The outgoing light control plate was bonded to the outgoing surface of the light guide plate.

(Comparative Example 1)
In Comparative Example 1, a flat-plate PC having a size of 30 mm × 40 mm and a thickness of 1 mm was used, and the emission surface and the opposing surface were flat surfaces. The emission light control plate 4 was prepared by using a PC film having a thickness of 0.1 mm as a base material and transferring a photocurable resin applied to a stamper to the base material by ultraviolet curing. The refractive index of the light guide plate was 1.59, and the refractive index of the photocurable resin after curing was 1.59. The outgoing light control plate was bonded to the outgoing surface of the light guide plate.
Table 1 shows the evaluation results of the front luminance of the above examples and comparative examples.

FIG. 7 shows the (X _i , Y _i ) coordinates of the convex section shape in Example 1. The unit of X _i and Y _i is mm.

ＸおよびＹの単位はｍｍである。実施例２および３の（２０）式における各パラメータをそれぞれ図８、図９に示す。 The convex section sectional shapes of Examples 2 and 3 are approximated by the following polynomial.

The unit of X and Y is mm. The respective parameters in the expression (20) of Examples 2 and 3 are shown in FIGS. 8 and 9, respectively.

It is a schematic sectional drawing which shows the principle of this invention. It is the schematic of the convex part shape which can be used for this invention. 1 is a schematic diagram of a rotationally symmetrical convex shape that can be used in the present invention. It is a schematic sectional drawing at the time of using a stationary phase between a convex part and a light-guide plate. It is explanatory drawing of the symbol used for description of this invention. It is a schematic sectional drawing which shows the partial cross section of the surface light source element of this invention. 3 is a table showing (X _i , Y _i ) coordinates of a convex section sectional shape according to Example 1. It is a table | surface which shows the parameter which concerns on Example 2 in (20) Formula which shows a convex part cross-sectional shape. It is a table | surface which shows the parameter which concerns on Example 3 in (20) Formula which shows a convex part cross-sectional shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... End surface, 2 ... Light source, 3 ... Light guide plate, 4 ... Output light control board, 5 ... Incident surface 6 ... Output surface, 7 ... Convex part, 9 * ..Fixed layer, 10 ... reflector

Claims (3)

A light guide plate having a light source, an incident surface that is at least one end surface that receives light from the light source, and an output surface that is one of main surfaces substantially perpendicular to the incident surface, and an output surface of the light guide plate A surface light source element including an outgoing light control plate that receives the light from the convex portion on the incident surface and emits the light from the outgoing surface in the front direction, and the convex portion is in optical contact with the light guide plate, The plane perpendicular to the exit surface including the shortest path between the arbitrary projection and the light source nearest to the projection and the line of intersection of the exit surface is the X axis, and the center of the optical contact portion of the projection The cross-sectional shape of the portion that is not optically in close contact in the X-axis direction has N slopes expressed by the following formulas (1) to (14), where the axis that passes through and is orthogonal to the exit surface is the Y-axis A surface light source element characterized in that different regions satisfy the following expression (15).

  The cross-sectional shape of the convex portion in the X-axis direction is a shape obtained by approximating the shape of at least one pair of two adjacent regions by a curve among N different regions forming the convex portion. The surface light source element according to claim 1.   An image display device comprising a transmissive display element provided on the light exit surface side of the surface light source element according to claim 1.

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