JP4494177B2 - Light guide for surface light source device, surface light source device and method for manufacturing mold member - Google Patents

Description

  The present invention relates to an edge light type surface light source device and a light guide used therefor, and more particularly to a surface light source device intended to reduce the visibility of luminance unevenness and a light guide used therefor. The surface light source device of the present invention is, for example, a backlight of a liquid crystal display device used as a display unit of a monitor such as a portable notebook personal computer or a liquid crystal television or a video integrated liquid crystal television, or a portable type such as a mobile phone. For backlights of relatively small liquid crystal display devices used as display panels for electronic devices and indicators of various devices, or for backlights of liquid crystal display devices used as information display boards and signs in stations and public facilities Alternatively, it is suitable for a backlight of a liquid crystal display device used as a marking device such as a traffic sign on a highway or a general road.

  Liquid crystal display devices have been widely used as monitors for portable notebook personal computers or the like, as display units for liquid crystal televisions and video integrated liquid crystal televisions, and in various other fields. A liquid crystal display device basically includes a backlight and a liquid crystal display element. As the backlight, an edge light type is often used from the viewpoint of making the liquid crystal display device compact. Conventionally, as an edge light type backlight, at least one end face of a rectangular plate-shaped light guide is used as a light incident end face, and a linear or rod-like shape such as a straight tube fluorescent lamp is provided along the light incident end face. A primary light source is disposed, light emitted from the primary light source is introduced from the light incident end surface of the light guide into the light guide, and the light exit surface is one of the two main surfaces of the light guide. What is emitted from the projector is widely used.

  In such a backlight, the luminance distribution on the light emitting surface may be non-uniform (decrease in luminance uniformity) due to the propagation form of light emitted from the primary light source and emitted through the light guide. One form of this reduction in brightness uniformity is that the brightness in the area close to the primary light source is higher than in other areas.

  As methods for preventing such a decrease in luminance uniformity, for example, Japanese Utility Model Publication No. 40-26083 (Patent Document 1), Japanese Utility Model Application Publication No. 60-60788 (Patent Document 2) and Japanese Utility Model Application Publication No. 62-154422. The gazette (Patent Document 3) discloses disposing a light-absorbing film or a light-adjusting film for suppressing light transmission at a position near the primary light source of the light exit surface of the light guide. This method is merely a small distance from the primary light source as a countermeasure against the fact that the intensity of light emitted from the light guide light exit surface in the region near the primary light source is larger than the intensity of light emitted in the region far from the primary light source. This is intended to limit the light emission from the light emission surface area.

  Incidentally, in recent years, liquid crystal display devices are required to increase the display efficiency by increasing the ratio of the display screen dimensions to the external dimensions as much as possible. Therefore, also in the surface light source device, the ratio of the light emitting surface dimension to the outer dimension is made as large as possible, that is, the size of the structural part (sometimes referred to as a “frame”) existing in a frame shape around the light emitting surface is made as small as possible. Is required to do.

  On the other hand, the surface light source device is also required to be thin, and in order to meet this demand, it is necessary to reduce the thickness of the light guide. As the light guide becomes thinner (for example, about 0.5 mm to 3 mm in thickness), a light emission surface close to (for example, about 2 mm) the light incident end surface of the light guide as a special form of the above-described decrease in luminance uniformity. Corresponding to the position, a streaky bright portion (bright line) brighter than the surroundings may be observed in parallel with the light incident end face. That is, the effect of the light emitted from the primary light source functioning as a secondary light source at the ridge line of the light guide that forms the boundary between the light incident end surface and the light exit surface of the light guide is affected by the light emitting surface of the surface light source device. Appears in brightness. This effect is noticeable mainly in a region near the light incident end face. This phenomenon is not particularly a problem in practice when the frame width is large, but in the surface light source device having the small frame width as described above, the luminance unevenness due to this influence is particularly easily recognized.

  When the technique as in Patent Documents 1 to 3 is employed to prevent the luminance uniformity from being reduced by the bright line, there arises a problem that the brightness of not only the bright line but also the entire periphery thereof tends to decrease.

  On the other hand, with the generation of the bright lines as described above, streaky dark portions (dark lines) darker than the surroundings may be observed between the adjacent bright lines in parallel with the light incident end face.

  In JP-A-8-227074 (Patent Document 4), as a technique for preventing the occurrence of such dark lines, light having a light absorption pattern in which the light absorption rate gradually decreases as the distance from the light incident end face increases. It is disclosed to form an absorbent layer.

  In the method of Patent Document 4 described above, a pattern such as a dot pattern is adopted as the light absorption pattern. In this case, there is a region that does not partially absorb light, and light shielding in this region is insufficient. Therefore, there are problems such as bright lines being observed.

  As described above, as one form of the ease of visually recognizing the luminance unevenness of the light emitting surface, in a region close to the light incident end surface, a portion with high luminance (bright line or bright band) and a portion with low luminance (dark line or dark band). ) Occur at specific intervals and are visually recognized as a plurality of bright and dark lines extending substantially parallel to the light incident end face.

  As a technique for preventing such luminance unevenness in the vicinity of the light incident end face, for example, in Japanese Patent Laid-Open No. 10-153778 (Patent Document 5), an area adjacent to the light incident end face of the light emitting face is placed adjacent to the area. It is disclosed that a band-like light diffusion region having a higher light scattering property is provided. In order to achieve the same object, for example, Japanese Patent Application Laid-Open No. 2002-216530 (Patent Document 6) describes the average inclination angle of the surface of the light exit surface in the vicinity of the light incident end face as another region of the light exit surface. Making it larger is disclosed.

According to the methods of Patent Document 5 and Patent Document 6, the light scattering property or the light diffusing property in the region near the light incident end surface of the light emitting surface is strengthened, and the amount of emitted light in this region is increased. The band is made inconspicuous to reduce brightness unevenness.
Japanese Utility Model Publication No. 40-26083 Japanese Utility Model Publication No. 60-60788 Japanese Utility Model Publication No. 62-154422 JP-A-8-227074 JP-A-10-153778 JP 2002-216530 A

  According to the present invention, a surface light source device and a light source used for the surface light source device in which it is difficult to visually recognize luminance unevenness, particularly in the vicinity of the light guide light incident end surface due to thinning of the light guide, by a method different from Patent Document 5 and Patent Document 6 described above. An object is to provide a light body.

According to the present invention, as a solution to the above problems,
A light source for a surface light source device that is used to configure a surface light source device in combination with a primary light source and guides light emitted from the primary light source,
A light incident end surface on which light emitted from the primary light source is incident, a light emitting surface from which guided light is emitted, and a back surface opposite to the light emitting surface;
A plurality of prism rows extending in a direction crossing the light incident end face and arranged in parallel to each other are formed on the back surface,
Each apex of each of the prism rows has at least a partial region in the extending direction thereof, a first portion having a first radius of curvature in a cross-sectional shape and a second portion having a second radius of curvature smaller than the first radius of curvature. A light guide for a surface light source device, comprising:
Is provided.

  In one aspect of the present invention, there is a ratio change region in which a ratio of the length of the first portion to the sum of the length of the first portion and the length of the second portion changes in the extending direction. In one aspect of the present invention, the ratio constant region where the ratio is constant on the side near the light incident end surface and / or on the side far from the light incident end surface in the extending direction, adjacent to the ratio changing region. Is present. In one aspect of the present invention, in the ratio change region, the ratio continuously changes monotonously with respect to the extending direction. In one aspect of the present invention, a plurality of the ratio change regions are provided. In an aspect of the present invention, the ratio is continuous over all the ratio change areas and all the constant ratio areas. In one aspect of the present invention, the position of the boundary between the ratio change region and the constant ratio region is not all the same among the four or more prism rows that are continuously located in the arrangement direction of the prism rows. Thus, the arrangement direction of the prism row is changed. In one aspect of the present invention, the distribution of the ratio in the extending direction is different between the central region in the arrangement direction of the prism rows on the back surface and the regions on both sides thereof.

  According to the present invention, in order to solve the above problems, the surface light source is characterized in that the primary light source is disposed facing the light incident end surface of the light guide for the surface light source device described above. An apparatus is provided.

  In one aspect of the present invention, the surface light source device is further disposed on the light exit surface of the light guide, and the light entrance surface on which light emitted from the light exit surface of the light guide enters, and the light entrance surface An optical deflection element having a light exit surface on the opposite side is provided. In one aspect of the present invention, the light deflection element includes a plurality of prism rows that extend along the light incident end surface of the light guide and are arranged in parallel to each other on the light incident surface. Each has a first prism surface on which light from the light exit surface of the light guide is incident and a second prism surface on which the incident light is internally reflected.

  According to the present invention as described above, the tops of the plurality of prism rows formed on the back surface of the light guide for the surface light source device extending in the direction crossing the light incident end surface and arranged in parallel with each other, Because at least a part of the region in the extending direction includes a first portion having a first radius of curvature in a cross-sectional shape and a second portion having a second radius of curvature smaller than the first radius of curvature. In addition, it is easy to provide a surface light source device in which luminance unevenness, in particular, luminance unevenness in the vicinity of the light guide light incident end surface associated with the thinning of the light guide is less visible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic perspective view showing one embodiment of a surface light source device according to the present invention, and FIG. 2 is a partial sectional view thereof. As shown in the drawing, the surface light source device of the present embodiment includes a light guide 3 having at least one side end surface as a light incident end surface 31 and a light exit surface 33 as one surface substantially orthogonal thereto. A linear primary light source 1 disposed facing the light incident end surface 31 of the light guide 3 and covered with the light source reflector 2, a light deflection element 4 disposed on the light exit surface of the light guide 3, and a light guide The light reflecting element 5 is disposed so as to face the back surface 34 opposite to the light emitting surface 33 of the light body 3.

  The light guide 3 is arranged in parallel with the XY plane and has a rectangular plate shape as a whole. The light guide 3 has four side end surfaces, and at least one of the pair of side end surfaces parallel to the YZ plane is a light incident end surface 31. The light incident end face 31 is disposed to face the primary light source 1, and the light emitted from the primary light source 1 enters the light incident end face 31 and is introduced into the light guide 3. In the present invention, for example, the light source may be disposed opposite to another side end face such as the side end face 32 opposite to the light incident end face 31.

  Two main surfaces that are substantially orthogonal to the light incident end surface 31 of the light guide 3 are respectively positioned substantially parallel to the XY plane, and one of the surfaces (the upper surface in the drawing) serves as the light emitting surface 33. By providing the light emitting surface 33 with a directional light emitting mechanism composed of a rough surface, light incident from the light incident end surface 31 is guided through the light guide 3 and the light incident end surface 31 and the light incident end surface 31. Light having directivity is emitted in a plane (XZ plane) orthogonal to the light emitting surface 33. The angle between the peak direction (peak light) of the emitted light luminous intensity distribution in the XZ in-plane distribution and the light emitting surface 33 is defined as α. The angle α is, for example, 10 to 40 degrees, and the full width at half maximum of the emitted light luminous intensity distribution is, for example, 10 to 40 degrees.

  The rough surface and the lens array formed on the surface of the light guide 3 have a luminance within the light emitting surface 33 that the average inclination angle θa according to ISO 4287 / 1-1984 is in the range of 0.5 to 15 degrees. It is preferable from the point of aiming at the degree of uniformity. The average inclination angle θa is more preferably in the range of 1 to 12 degrees, and more preferably in the range of 1.5 to 11 degrees. The average inclination angle θa is preferably set in an optimum range by a ratio (L / t) between the thickness (t) of the light guide 3 and the length (L) in the direction in which the incident light propagates. That is, when the light guide 3 having a L / t of about 20 to 200 is used, the average inclination angle θa is preferably 0.5 to 7.5 degrees, more preferably 1 to 5 degrees. It is a range, More preferably, it is the range of 1.5-4 degree | times. When the light guide 3 having L / t of about 20 or less is used, the average inclination angle θa is preferably 7 to 12 degrees, and more preferably 8 to 11 degrees.

The average inclination angle θa of the rough surface formed on the light guide 3 is obtained by measuring the rough surface shape using a stylus type surface roughness meter in accordance with ISO 4287 / 1-1984 and setting the coordinate in the measurement direction as x. From the obtained gradient function f (x), the following equations (1) and (2)
Δa = (1 / L) ∫ ₀ ^L | (d / dx) f (x) | dx (1)
θa = tan ⁻¹ (Δa) (2)
Can be obtained using Here, L is the measurement length, and Δa is the tangent of the average inclination angle θa.

  Further, the light guide 3 preferably has a light emission rate in the range of 0.5 to 5%, and more preferably in the range of 1 to 3%. This is because when the light emission rate is smaller than 0.5%, the amount of light emitted from the light guide 3 tends to be small and sufficient luminance cannot be obtained. When the light emission rate is larger than 5%, the vicinity of the primary light source 1 is present. This is because a large amount of light is emitted, the attenuation of the emitted light in the X direction within the light emitting surface 33 becomes significant, and the luminance uniformity on the light emitting surface 33 tends to decrease. Thus, by setting the light emission rate of the light guide 3 to 0.5 to 5%, the angle of the peak light in the emission light intensity distribution (in the XZ plane) of the light emitted from the light emission surface is the same as that of the light emission surface. The full width at half maximum of the emitted light luminous intensity distribution (in the XZ plane) in the XZ plane that is in the range of 50 to 80 degrees with respect to the normal and is perpendicular to both the light incident end face and the light emitting face is 10 to 40 degrees. Provided is a surface light source device that can emit light having a high directivity from the light guide 3 and can efficiently deflect the emission direction by the light deflection element 4 and has high luminance. it can.

In the present invention, the light emission rate from the light guide 3 is defined as follows. The relationship between the light intensity (I ₀ ) of the emitted light at the edge on the light incident end face 31 side of the light emitting face 33 and the emitted light intensity (I) at a distance L from the edge on the light incident end face 31 side is When the thickness (dimension in the Z direction) of the light guide 3 is t, the following formula (3)
I = I ₀ (α / 100) [1- (α / 100))] ^{L / t} (3)
Satisfying such a relationship. Here, the constant α is the light output rate, and the light guide 3 per unit length (a length corresponding to the light guide thickness t) in the X direction orthogonal to the light incident end surface 31 on the light output surface 33. It is the ratio (percentage:%) at which the light is emitted from. The light emission rate α is obtained from the gradient by plotting the relationship between the logarithm of the light intensity of the light emitted from the light exit surface 23 on the vertical axis and (L / t) on the horizontal axis. be able to.

  In the present invention, instead of forming the light emitting mechanism on the light emitting surface 33 as described above, or in combination with this, the light diffusing fine particles are mixed and dispersed in the light guide so as to emit directional light. A mechanism may be added.

  Moreover, in order to control the directivity in the surface (YZ surface) parallel to the primary light source 1 of the emitted light from the back surface 34 which is the main surface to which the directional light emitting mechanism is not provided, It is a prism row forming surface in which a large number of prism rows are arranged in a direction crossing the light incident end surface 31, more specifically in a direction substantially perpendicular to the light incident end surface 31 (X direction).

  In the present invention, the prism row on the back surface 34 of the light guide 3 has the following features in the cross-sectional shape at the top.

  FIG. 3 shows a plan view of the light guide 3 and an A-A ′ cross-sectional view of the prism row portion. FIG. 3 shows a state of the back surface 34 seen through from the light emitting surface side. The prism row 34a has a portion including a curve whose cross-sectional shape is convex outward at the top thereof, and has three regions which are distinguished by the form of the top. That is, the prism row 34a has three regions RC1, RV1, and RC2 that are sequentially located from the light incident end face 31 side in the extending direction (X direction).

  FIG. 4 shows a cross-sectional shape of a portion of the prism row 34a in each of the regions RC1, RV1, and RC2. The prism row 34a has prism inclined surfaces 34a1 and 34a2 each formed of a flat surface except for the top. In region RC1, the curve of the top cross-sectional shape has a first radius of curvature R1 (eg, 25 μm as shown). In region RC2, the curve of the top cross-sectional shape has a second radius of curvature R2 (eg, 10 μm as shown) that is smaller than R1. In region RV1, the curve of the top cross-sectional shape has two first portions LR1 having a first radius of curvature R1 and a second portion LR2 having a second radius of curvature R2 located between them. The first radius of curvature R1 can be, for example, 23 to 27 μm, and the second radius of curvature R2 can be, for example, 5 to 15 μm.

  The ratio of the length of the first portion LR1 to the sum of the length of the first portion LR1 (the total length of the two first portions) and the length of the second portion LR2 in the cross-sectional shape is the extension of the prism row 34a. The direction has changed. That is, the ratio is 100% at the boundary with the region RC1, and the ratio is 0% at the boundary with the region RC2, and the ratio continuously and monotonously changes between them. Here, monotonous change refers to monotonous increase or monotonic decrease. Therefore, the ratio change is not limited to the one that changes linearly at a constant change rate over the entire region RV1 as shown in the figure. For example, at least the vicinity of the boundary with the region RC1 and the vicinity of the boundary with the region RC2 It is also possible that the rate of change gradually decreases and the rate of change at the boundary becomes zero. By doing in this way, the discontinuity visibility of the brightness | luminance in a boundary part can be reduced. Thus, the region RV1 is a ratio change region in which the ratio changes with respect to the extending direction of the prism row 34a, while the regions RC1 and RC2 have a constant ratio constant region with respect to the extending direction of the prism row 34a. is there. The region RC1 can be omitted. The two portions between the first portion LR1 and the second portion LR2 can be inclined substantially equal to the prism inclined surfaces 34a1 and 34a2, respectively (that is, substantially parallel to the prism inclined surfaces 34a1 and 34a2, respectively). .

  3 and 4 illustrate the dimensions of each part in the light guide 3. Here, 50 μm is exemplified as the arrangement pitch of the prism rows 34 a, but in the present invention, the arrangement pitch of the prism rows 34 a can be set in the range of, for example, 10 to 100 μm, and preferably in the range of 30 to 60 μm. Here, 100 ° is exemplified as the angle formed between the prism inclined surfaces 34a1 and 34a2, but in the present invention, the angle formed between the prism inclined surfaces 34a1 and 34a2 can be set within a range of, for example, 85 to 110 degrees. . This is because, by setting this angle within this range, the light emitted from the light guide 3 can be collected appropriately, and the luminance of the surface light source device can be improved. It is in the range of 90 to 100 degrees.

  The light guide 3 is not limited to the shape shown in FIG. 1, and various shapes such as a rust shape with a thicker light incident end face can be used.

  The light guide 3 as described above includes a first mold member having a first transfer surface for transferring and forming the light emitting surface 33 and a second mold member having a second transfer surface for transferring and forming the back surface 34. It can manufacture by shape | molding translucent synthetic resin using. Here, when forming the second transfer surface for transfer formation of the back surface 34, the prism row corresponding portion of the second mold member corresponding to the prism row 34a is the first tip having the first curvature radius R1. It can be formed by performing a first step of cutting using one cutting tool and a second step of cutting using a second cutting tool having a tip shape having a second curvature radius R2. In forming the ratio change area corresponding portion of the second mold member corresponding to the ratio change area RV1, the depth of cut of the second bite is changed in a desired manner in the second step. The second step is preferably performed after the first step.

  The light deflection element 4 is disposed on the light emitting surface 33 of the light guide 3. The two main surfaces 41 and 42 of the light deflection element 4 are arranged in parallel with each other as a whole, and are located in parallel with the XY plane as a whole. One of the main surfaces 41 and 42 (the main surface located on the light emitting surface 33 side of the light guide 3) is a light incident surface 41, and the other is a light emitting surface 42. The light exit surface 42 is a flat surface parallel to the light exit surface 33 of the light guide 3. The light incident surface 41 is a prism row forming surface in which a large number of prism rows extending in the Y direction are arranged in parallel to each other. The prism row forming surface may be provided with a bottom flat portion having a relatively narrow width between adjacent prism rows (for example, a flat portion having a width equal to or smaller than the dimension in the X direction of the prism row). It is preferable to arrange the prism rows continuously in the X direction without providing a flat bottom portion in order to improve the utilization efficiency of the prism.

  FIG. 11 schematically shows a state of light deflection by the light deflection element 4. This figure shows an example of the traveling direction of the peak light (light corresponding to the peak of the outgoing light distribution) from the light guide 3 in the XZ plane. The peak light emitted obliquely at an angle α from the light emitting surface 33 of the light guide 3 is incident on the first prism surface of the prism row and is totally reflected by the second prism surface so as to be substantially equal to the light emitting surface 42 method. Emits in the direction of the line. Further, in the YZ plane, the luminance in the direction of the normal line of the light exit surface 42 can be sufficiently improved in a wide area by the action of the prism row on the light guide back surface 34 as described above.

  The shape of the prism surface of the prism row of the light deflection element 4 is not limited to a single plane, and can be, for example, a convex polygonal shape or a convex curved surface shape, thereby achieving high brightness and narrow field of view. it can.

  In the light deflection element 4, a prism array is formed for the purpose of accurately producing a desired prism shape, obtaining stable optical performance, and suppressing wear and deformation of the prism top during assembly work and use as a light source device. A top flat portion or a top curved surface portion may be formed on the top of the top. In this case, the width of the top flat part or the top curved surface part is preferably 3 μm or less from the viewpoint of suppressing the occurrence of a non-uniform luminance pattern due to a decrease in luminance or a sticking phenomenon as the surface light source device. The width of the top flat part or the top curved part is 2 μm or less, more preferably 1 μm or less.

  The primary light source 1 is a linear light source extending in the Y direction. As the primary light source 1, for example, a fluorescent lamp or a cold cathode tube can be used. In this case, as shown in FIG. 1, the primary light source 1 is not only installed to face one side end face of the light guide 3, but is further placed on the opposite side end face as necessary. You can also

  The light source reflector 2 guides the light from the primary light source 1 to the light guide 3 with little loss. As the material, for example, a plastic film having a metal-deposited reflective layer on the surface can be used. As shown in the figure, the light source reflector 2 avoids the light deflecting element 4 and passes from the outer surface of the light reflecting element 5 to the light emitting surface edge of the light guide 3 through the outer surface of the primary light source 1. It is wrapped around. On the other hand, the light source reflector 2 can be wound from the outer surface of the light reflecting element 5 to the light emitting surface edge of the light deflecting element 4 through the outer surface of the primary light source 1. A reflection member similar to the light source reflector 2 can be attached to the side end face other than the light incident end face 31 of the light guide 3.

  As the light reflecting element 5, for example, a plastic sheet having a metal vapor deposition reflecting layer on the surface can be used. In the present invention, it is also possible to use a light reflecting layer or the like formed by metal vapor deposition or the like on the back surface 34 of the light guide 3 instead of the reflecting sheet as the light reflecting element 5.

  The light guide 3 and the light deflection element 4 of the present invention can be made of a synthetic resin having a high light transmittance. Examples of such synthetic resins include methacrylic resins, acrylic resins, polycarbonate resins, polyester resins, and vinyl chloride resins. In particular, methacrylic resins are optimal because of their high light transmittance, heat resistance, mechanical properties, and molding processability. Such a methacrylic resin is a resin mainly composed of methyl methacrylate, and preferably has a methyl methacrylate content of 80% by weight or more. When forming a surface structure such as a rough surface of the light guide 3 and the light deflecting element 4 or a surface structure such as a prism array or a lenticular lens array, the transparent synthetic resin plate is heated using a mold member having a desired surface structure. You may form by pressing, and you may give a shape simultaneously with shaping | molding by screen printing, extrusion molding, injection molding, etc. The structural surface can also be formed using heat or a photocurable resin. Furthermore, the surface of a transparent substrate such as a polyester resin, acrylic resin, polycarbonate resin, vinyl chloride resin, polymethacrylamide resin, or the like, or a rough surface made of an active energy ray curable resin is used. A structure or a lens array arrangement structure may be formed, or such a sheet may be bonded and integrated on a separate transparent substrate by a method such as adhesion or fusion. As the active energy ray-curable resin, polyfunctional (meth) acrylic compounds, vinyl compounds, (meth) acrylic acid esters, allyl compounds, (meth) acrylic acid metal salts, and the like can be used.

  On the light emitting surface (the light exit surface 42 of the light deflection element 5) of the surface light source device including the primary light source 1, the light source reflector 2, the light guide 3, the light deflection element 4, and the light reflection element 5 as described above, By disposing the transmissive liquid crystal display element 8 as shown in FIG. 2, a liquid crystal display device using the surface light source device of the present invention as a backlight is configured. The liquid crystal display device is observed by an observer from above in FIG.

  In the present embodiment, the prism row 34a formed on the back surface 34 of the light guide has a second portion LR1 having a first curvature radius R1 and a second curvature radius R2 whose top cross-sectional shape curve has a first curvature radius R1. Since the region having the portion LR2 is included, by appropriately setting the ratio of the length of the first portion LR1 to the sum of the length of the first portion LR1 and the length of the second portion LR2 in this region, the prism row 34a The form of internal reflection of light can be set as appropriate. In particular, by setting the region having the first portion LR1 and the second portion LR2 as the ratio change region RV1, luminance unevenness due to bright lines and dark lines in the vicinity of the light incident end face is hardly visible. Further, constant ratio regions RC1 and RC2 are arranged adjacent to the ratio change region RV1, the ratio of the region RC1 is made larger than the ratio of the region RC2, and the ratio continuously and monotonously changes in the prism row extending direction in the region RV1. In addition, since the ratio is continuous in the prism row extending direction over all the regions RC1, RV1, and RC2, the luminance unevenness is further less easily recognized.

  FIG. 5 shows a plan view of a light guide in another embodiment of the surface light source device according to the present invention and an A-A ′ cross-sectional view of the prism row portion thereof. FIG. 6 shows a cross-sectional shape of a prism row portion in each region. In these drawings, the same members or portions as those in the embodiment of FIGS. 1 to 4 are denoted by the same reference numerals.

  In the present embodiment, a constant ratio region RC3, a ratio change region RV2, a constant ratio region RC4, and a ratio change region RV3 are arranged in this order from the ratio change region RV1 side between the ratio change region RV1 and the constant ratio region RC2. ing. As shown in FIGS. 5 and 6, the constant ratio region RC4 has the same cross-sectional shape as the constant ratio region RC1, and the constant ratio region RC3 has the same cross-sectional shape as the constant ratio region RC2. Further, as shown in FIG. 5, the ratio change region RV3 is monotonically changed from 100% to 0% from the light incident end face side to the opposite side as in the ratio change region RV1. Conversely, the ratio change region RV2 is monotonically changed from% to 100% from the light incident end face side to the opposite side. Further, the ratio is continuous in the prism row extending direction over all of the regions RC1 to RC4 and the regions RV1 to RV3.

  In the present embodiment, since a plurality of ratio change regions are provided and the ratio is changed a plurality of times with respect to the prism row extending direction, the surface light source device in addition to the same functions and effects as those of the embodiments of FIGS. It is possible to further improve the brightness uniformity on the light emitting surface.

  FIG. 7 shows a plan view of a light guide in a further embodiment of the surface light source device according to the present invention and a cross-sectional view taken along line A-A ′ of the prism row portion thereof. FIG. 8 shows a cross-sectional shape of the prism row portion in each region. In these drawings, the same members or portions as those in the embodiment of FIGS. 1 to 4 are denoted by the same reference numerals.

  In the present embodiment, the distribution form of the ratio in the prism row extending direction is different between the central region M in the arrangement direction (Y direction) of the prism row on the back surface of the light guide and the two regions N on both sides thereof. Yes. The width (dimension in the Y direction) of the region N can be set to, for example, 20 to 50 mm as illustrated in FIG. In the ratio change region RV1 ′, in the portion belonging to the region N, the ratio is monotonously changed from 100% to 0% as in the above-described embodiments of FIGS. The ratio monotonously changes from 100% to 20%. Then, in the region RCV adjacent to the ratio change region RV1 ′, the ratio belonging to the region N is set to 0% as in the embodiment of FIGS. 1 to 4 above, but in the portion belonging to the region M, The ratio is 20%. That is, the region RCV is a constant ratio region, but the constant ratio value changes in the Y direction.

  In the present embodiment, in the region RCV, the ratio of the portion belonging to the region N is smaller than the portion belonging to the region M. Therefore, in addition to the same functions and effects as those of the embodiment of FIGS. A decrease in luminance at N can be intensively suppressed.

  FIG. 9 shows a partial plan view of a light guide in yet another embodiment of the surface light source device according to the present invention. In this figure, the same code | symbol is attached | subjected to the member or part similar to in the embodiment of the said FIGS. 1-4.

  In the present embodiment, the boundary between the ratio change region RV1 and the constant ratio regions RC1 and RC2 changes sequentially with respect to the arrangement direction (Y direction) of the prism rows. By making the boundary of the region deviate from the straight line in this way, it is possible to further suppress the visibility of the discontinuity in luminance at the boundary portion. Such a function can be similarly realized in the embodiment of FIGS. 5 to 6 and the embodiment of FIGS.

  FIG. 10 shows a modification of the embodiment of FIG. In this modification, the boundary between the ratio change region RV1 and the constant ratio region RC1 and further, although not shown, the boundary between the ratio change region RV1 and the constant ratio region RC2 is discontinuous with respect to the arrangement direction (Y direction) of the prism rows. To change. The period of this change is made not to be the same between the four or more prism rows 34a that are continuously located in the arrangement direction of the prism rows, thereby suppressing the visibility of the discontinuity of the luminance at the boundary portion. From the viewpoint of In FIG. 10, the boundary is changed for each of the three prism rows 34 a that are continuously located in the arrangement direction of the prism rows.

It is a typical perspective view which shows embodiment of the surface light source device by this invention. It is a fragmentary sectional view of the surface light source device of FIG. It is the top view of a light guide, and A-A 'sectional drawing of the prism row | line | column part. It is a figure which shows the cross-sectional shape of the part of the prism row | line | column in each area | region. It is the top view of a light guide, and A-A 'sectional drawing of the prism row | line | column part. It is a figure which shows the cross-sectional shape of the part of the prism row | line | column in each area | region. It is a top view of a light guide, and A-A 'and B-B' sectional drawing of the prism row part. It is a figure which shows the cross-sectional shape of the part of the prism row | line | column in each area | region. It is a fragmentary top view of the light guide in embodiment of the surface light source device by this invention. It is a figure which shows the modification of embodiment of FIG. It is a figure which shows typically the mode of the optical deflection by an optical deflection element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary light source 2 Light source reflector 3 Light guide 31 Light incident end surface 32 Side end surface 33 Light emitting surface 34 Back surface 34a Prism row 34a1, 34a2 Prism slope 4 Light deflecting element 41 Light incident surface 42 Light emitting surface 5 Light reflecting element 8 Liquid crystal display element

Claims (6)

A light source for a surface light source device that is used to configure a surface light source device in combination with a primary light source and guides light emitted from the primary light source,
A light incident end surface on which light emitted from the primary light source is incident, a light emitting surface from which the guided light is emitted, and a back surface opposite to the light emitting surface,
A plurality of prism rows extending in a direction crossing the light incident end face and arranged parallel to each other are formed on the light exit surface and / or the back surface,
Each apex of each of the prism rows has at least a partial region in the extending direction thereof, a first portion having a first radius of curvature in a cross-sectional shape and a second portion having a second radius of curvature smaller than the first radius of curvature. It comprises a door,
There is a ratio change region in which a ratio of the length of the first portion to the sum of the length of the first portion and the length of the second portion varies with respect to the extending direction. Light body. The light guide for a surface light source device according to claim 1, wherein a height of the prism row changes in the extension direction in the ratio change region. The light guide for a surface light source device according to claim 1, wherein in the ratio change region, the ratio changes monotonously continuously in the extending direction. The light guide for a surface light source device according to claim 1, wherein a plurality of the ratio change regions are provided. The primary light source is disposed so as to face the light incident end surface of the light guide for the surface light source device according to claim 1,
And a light deflection element disposed on the light exit surface of the light guide and having a light entrance surface on which light emitted from the light exit surface of the light guide enters and a light exit surface on the opposite side. A surface light source device. A method for producing a mold member having a transfer surface for transferring and forming a surface on which the plurality of prism rows of the light guide for a surface light source device according to claim 1 are formed,
In forming the transfer surface, the prism row corresponding unit corresponding to each of the prism rows, a first step of cutting with the first byte with the first radius of curvature of the tip shape, the second A method of manufacturing a mold member, wherein the second step of cutting using a second cutting tool having a tip having a radius of curvature is sequentially formed .

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