JP2004273465A - Surface light source element and light transmission body used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light transmission body for a surface light source element, having high luminance and uniform luminance distribution in a light emitting surface without applying any uniformizing process such as a dot pattern. <P>SOLUTION: The surface light source element comprises at least one side surface as a light incident surface, and one surface approximately orthogonal to the light incident surface as a light emitting surface. A plurality of lens arrays having an inclined surface of an average inclination angle of 0.5-6°, arranged on at least one surface of the light emitting surface and its back surface, extending in a direction parallel with the light incident surface. The light emission from the light emitting surface has a directivity of 60-80° with respect to the normal line of the the light emitting surface. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device used for a notebook personal computer, a liquid crystal television, etc., a display device such as a signboard or a large signboard at a station or a public facility, and various guide signs and traffic signs on an expressway or a general road. The present invention relates to a surface light source element constituting a display device such as a traffic display device, and a light guide used for the surface light source element.

  In recent years, color liquid crystal display devices have been widely used in various fields such as notebook personal computers, liquid crystal televisions, and video-integrated liquid crystal televisions. This liquid crystal display device basically includes a backlight section and a liquid crystal display element section. As the backlight unit, there are a direct type in which a light source is provided immediately below a liquid crystal display element and an edge light type in which a light source is provided on a side surface of a light guide. I have. The edge light type is a backlight of a type in which a light source is disposed on a side surface of a plate-shaped light guide to emit light on the entire surface of the light guide, and is a so-called surface light source element.

  In such a surface light source element, a plate-shaped transparent material such as an acrylic resin plate is used as a light guide, and light from a light source disposed at one end is made to enter the light guide from a light incident surface, and the incident light is reflected. By providing a light emitting function such as a light scattering portion formed on the front surface (light emitting surface) or the back surface of the light guide, light is emitted from the light emitting surface in a planar manner. However, when the light emitting function is formed uniformly on the front surface or the back surface of the light guide, the brightness of the emitted light decreases as the distance from the light source increases, and the brightness in the light emitting surface becomes non-uniform. It could not be obtained. Such a tendency becomes conspicuous as the size of the liquid crystal display element increases, and is not practical for a large-sized liquid crystal display device of 10 inches or more. In particular, with the recent increase in the size of liquid crystal screens, very high uniformity of the luminance distribution within the screen is required for liquid crystal display devices used for notebook computers, liquid crystal televisions, and the like.

  In addition, display devices such as guide signs and large signboards, and traffic display devices such as guide signs and traffic signs on expressways and general roads, require an internal lighting system and an external lighting system to enhance visibility and legibility at night. Two illumination systems, illumination systems, have been employed. In the internal lighting system, characters, figures, photographs, etc. are formed on a translucent plastic plate such as a methacryl plate by cutting or printing to form a display plate, and a light source serving as a backlight is arranged inside the display plate. The display panel is illuminated by a light source, and a straight tube or annular fluorescent lamp is generally used as the light source. In the external illumination system, a light source is disposed above, below, or on the front side of a display panel on which display contents are formed, and the light source illuminates the entire surface of the display panel. Tube-shaped fluorescent lamps are commonly used.

  In such a display device, the luminance distribution over the entire surface of the display panel, that is, the maximum value / minimum value of the luminance becomes extremely large, and in such a method, the display device having a small luminance distribution and uniform brightness. It was difficult to get. This tendency was particularly remarkable in the external lighting system. In addition, the internal illumination system has a problem that a see-through phenomenon in which a fluorescent lamp or the like used as a light source can be seen through a sign plate easily occurs. Therefore, in these display devices, an attempt is being made to adopt an edge-light type backlight that arranges a light source on the side surface of a plate-shaped light guide and emits light over the entire surface of the light guide. However, such a display device requires a large surface light source element, and has a problem that sufficient uniformity of luminance on the light emitting surface cannot be achieved as in the case of the liquid crystal display device.

  Various proposals have been made in order to solve the problem of uneven brightness of the surface light source element. For example, Japanese Patent Application Laid-Open No. 1-24522 (Patent Literature 1) discloses a light emitting function in which a light diffusing substance is applied or adhered densely to a back surface opposite to a light emitting surface of a light guide as the distance from the light incident surface increases. A provided surface light source element has been proposed. Also, Japanese Patent Application Laid-Open No. 1-107406 (Patent Document 2) proposes that a light guide is formed by laminating a plurality of transparent plates on the surface of which fine spots made of a light scattering substance are formed in various patterns. Have been. In such a surface light source element, since a white pigment such as titanium oxide or barium sulfate is used as a light scattering substance, light loss such as light absorption occurs when light hitting the light scattering substance is scattered. This is not preferable because it causes a decrease in the luminance of the emitted light.

  Japanese Patent Application Laid-Open Nos. 1-244490 (Patent Literature 3) and 1-225933 (Patent Literature 4) disclose a light reflection pattern corresponding to the reciprocal of the emission light distribution on the light emission surface of the light guide. There has been proposed a surface light source element in which an emission light adjusting member and a light diffusion plate having the same are arranged. However, even in such a surface light source element, since the light reflected by the emission light adjusting member or the light diffusion plate cannot be reused, light loss occurs, and the luminance of the emission light is reduced.

  Further, JP-A Nos. 2-17 (Patent Document 5) and 2-84618 (Patent Document 6) disclose a light emitting surface of a light guide and at least one of its back surface as a matte surface. A surface light source element has been proposed in which a large number of lens units are formed, and a prism sheet is mounted on a light exit surface. However, although such a surface light source element can obtain extremely high luminance, it has not been satisfactory in terms of uniformity on a light emitting surface.

On the other hand, as for a surface light source element that increases the luminance by reducing the light loss while making the luminance of the emitted light uniform, as disclosed in JP-A-6-18879 (Patent Document 7), A large number of lens units are formed on the light emitting surface or a matte surface is formed, and a rough surface portion and a smooth portion are formed on the back surface so that the ratio of the rough surface portion increases as the distance from the light source increases. A surface light source element on which a prism sheet is mounted has been proposed.
JP-A-1-24522 JP-A-1-107406 JP-A-1-244490 JP-A-1-252933 JP-A No. 2-17 JP-A-2-84618 JP-A-6-18879

  However, in the surface light source element as described in Patent Document 7, although the luminance of emitted light can be made uniform and the loss of light can be reduced, when used as a display device such as a liquid crystal display device, the liquid crystal display element or the display A pattern formed by a rough surface portion and a smooth portion formed on the back surface of the light guide through the plate was observed, which hindered image observation. Also, providing such a uniform light emitting function to the light guide surface is not preferable from the viewpoint of productivity of the light guide.

  Therefore, the present invention provides a light guide for a surface light source element and a surface light source element which have high luminance and can obtain high uniformity of luminance on a light emitting surface without performing a uniform processing of a speckle pattern or the like. The purpose is to do.

  That is, the light guide for a surface light source element of the present invention has at least one side end surface as a light incident surface, one surface substantially orthogonal to the light incident surface as a light exit surface, and the light exit surface and the back surface thereof. At least one surface is formed of a large number of lens arrays formed of inclined surfaces extending in a direction parallel to the light incident surface and having an average inclination angle of 0.5 to 6 °. The light is emitted with directivity at an angle of 60 to 80 ° with respect to the normal line of the emission surface.

  Further, the surface light source element of the present invention comprises a light source, a light guide having at least one side end face facing the light source as a light incident surface, and one surface substantially orthogonal to the light incident surface as a light exit surface. A prism sheet in which a number of prism rows are formed in parallel on at least one surface provided on the light exit surface side of the light guide, and at least one of the light exit surface of the light guide and the back surface thereof Surface extends in a direction parallel to the light incident surface, and is composed of a large number of lens rows including inclined planes having an average inclination angle of 0.5 to 6 °, and the prism sheet is provided on the light exit surface. The light emitting surface of the light guide is directed at an angle of 60 to 80 ° with respect to a normal line of the light emitting surface. Emitted by the prism sheet, and the emitted light is deflected by the prism sheet in a substantially normal direction. It is characterized in.

  According to the present invention, at least one of the light emitting surface of the light guide and the back surface facing the light emitting surface is formed with a large number of lens rows each having an inclined surface having an average inclination angle (θa) of 0.5 to 6 °. As a result, the emission rate of the light emitted from the light exit surface of the light guide can be reduced, and a uniform luminance distribution can be obtained in the light exit surface without performing a uniform processing such as a speckle pattern. A light is emitted from the light exit surface of the light body with directivity at an angle of 60 to 80 ° with respect to the normal line, and the emitted light is changed in the direction of the normal line by a prism sheet. A surface light source that can increase brightness and is suitable as a liquid crystal display device used for notebook computers, liquid crystal televisions, etc., as a display device for information signs and traffic signs, etc. Can provide elements is there.

  The light guide for a surface light source element of the present invention is composed of a transparent substrate having at least one side end surface as a light incident surface and one surface substantially orthogonal to the light incident surface as a light emitting surface. In such a light guide, the light incident on the light guide propagates through the light guide with light having a distribution within the critical angle repeatedly reflected on the surface of the light guide. When a rough surface portion is formed on the surface of the light guide, light exceeding the critical angle with respect to the rough surface out of the light reaching the rough surface portion is refracted and emitted out of the light guide, and the critical angle The light within is reflected and propagates through the light guide. This is because the traveling direction of light is determined by the refractive index of the medium and the angle of incidence of the light with respect to the normal to the incident surface according to Snell's law.

  FIG. 1 schematically shows the refraction and reflection of light on the surface of a light guide having an uneven shape. The light A incident on the slope of the uneven portion at an incident angle i exceeding the critical angle is out of the light guide at an emission angle i 'that satisfies the relationship of nsini = sini' (n is the refractive index of the light guide) according to Snell's law. Out. On the other hand, light B incident at an incident angle k that is within the critical angle is reflected at an angle k ′ (k ′ = k) and propagates in the light guide. The light once incident on the concave and convex portion and reflected therefrom has a sharp incident angle when the light is next incident on the concave and convex portion, so that the light easily exceeds the critical angle and easily exits the light guide.

The inventors of the present invention have found that the relationship between the light emission intensity (I) at a certain point and the light emission intensity (I ₀ ) at the end of the light incident surface in the light guide for a surface light source element is the emission rate (a). It was found experimentally that the following formula (1) was used depending on the distance (L ') from the end of the light emitting surface and the thickness (t) of the light guide.

From the equation (1), it can be seen that if the length (L) and the thickness (t) of the light guide are determined, the uniformity of luminance in the light emission surface is determined by the emission rate (a). The emission rate (a) of the light guide having a thickness of tmm was measured at intervals of 20 mm from the light incident surface end of the light guide, and the distance (l) from the light incident surface end and the logarithm of the luminance were measured. The gradient (K (mm ⁻¹ )) is obtained from the graph, and is obtained by the following equation (2).

In the present invention, the uniformity of luminance in the light guide for a surface light source element is evaluated and examined using the degree of variation (R%) represented by the following equation (3) as a measure of the uniformity of luminance. went. For the degree of variation (R%), the luminance was measured at intervals of 20 mm in a range from a point 5 mm away from the end of the light incident surface to the opposite end in the approximate center of the light guide, and the maximum value of the measured luminance (I _max ), the minimum value of the measured luminance (I _min ), and the average value of the measured luminance (I _av ), and are calculated by the following equation (3).

  As a result, it was found that the emission rate (a) and the degree of variation (R%) had a specific relationship depending on the length (L) and the thickness (t) of the light guide. When (a) increases, the degree of variation (R%) increases accordingly, and when the emission rate (a) is constant, the ratio (L / t) of the length (L) to the thickness (t) of the light guide is obtained. ) Increases, the degree of variation (R%) also increases. In other words, in a light guide having a certain size, the uniformity of luminance (degree of variation) in the light exit surface of the light guide depends on the emission rate (a) from the light guide. It can be seen that uniformity of luminance can be achieved by controlling the emission ratio (a).

  On the other hand, the present inventors, when forming a large number of lens rows extending in the direction parallel to the light incident surface on the surface of the light guide, depending on the gradient of the inclined surface forming such a lens row, It has been found that the emission direction and the emission rate of the light emitted from the light guide change. Here, the average inclination angle (θa) specified by ISO4287 / 1-1987 can be used as the gradient. That is, when the average inclination angle (θa) increases, the light emitted from the light guide has a smaller emission angle and becomes closer to the normal direction. Further, as the average inclination angle (θa) increases, the emission rate from the light guide increases accordingly. From this, the uniformity of the luminance in the light emitting surface of the surface light source element can be improved by lowering the emission rate from the light guide, and the uniformity can be achieved by reducing the average inclination angle (θa). I found that I could do it. The uniformity of the brightness of the light guide varies depending on the application, but in a large display device such as a signboard, a large signboard, a sign or a traffic sign, the degree of variation (R%) is preferably 250% or less. Is not more than 200%. Further, a surface light source element used in a liquid crystal display device such as a notebook computer or a liquid crystal television is required to have extremely high uniformity, and the degree of variation (R%) is 25% or less, preferably 20% or less. .

  In order to make the brightness uniform within the light exit surface of such a light guide for a surface light source element, an average inclination angle (θa) is required on at least one of the light exit surface and the back surface of the light guide. It is necessary to form a large number of lens rows each having a smooth slope of 0.5 to 6 ° so as to extend in a direction parallel to the light incident surface of the light guide. This is because when the average inclination angle (θa) of the smooth slopes constituting the lens array is less than 0.5 °, the emission angle of the light emitted from the light emission surface (the angle with respect to the normal to the light emission surface) is large. This is because it becomes impossible to sufficiently direct the emitted light in the normal direction even if a variable-angle member such as a prism sheet described later is used. Conversely, when the average inclination angle (θa) of the smooth inclined surfaces constituting the lens array exceeds 6 °, the exit angle of the light emitted from the light exit surface (the angle with respect to the normal line of the light exit surface) becomes smaller. This is because the directivity of the emitted light also decreases, the luminance as the surface light source element decreases, and the emission rate from the light guide increases, thereby deteriorating the uniformity of luminance as the surface light source element. Preferably, the average inclination angle (θa) is in the range of 2 to 5 °. A large number of lens arrays each having a smooth inclined surface having an average inclination angle (θa) of 0.5 to 6 ° may be formed on the light emitting surface of the light guide from the viewpoint of uniform luminance and high luminance. preferable. Also, by forming a large number of lens rows each having a smooth inclined surface having such an average inclination angle (θa) so as to extend in a direction parallel to the light incident surface of the light guide, the light exit surface of the light guide is formed. Can be emitted with high directivity at an angle of 60 to 80 degrees with respect to the normal line.

  The size of the light guide for a surface light source element of the present invention is not particularly limited, but the length (L) and the thickness of the light guide are required in order to exert the effect of the present invention more remarkably. It is preferable to use it as a light guide having a ratio (L / t) of 150 or less to (t). When L / t exceeds 150, even if the average inclination angle (θa) of the light guide is reduced, there is a tendency that uniformity of luminance on the light emitting surface cannot be sufficiently achieved. It is in the range of 130 or less, more preferably 80 or less.

  In the present invention, as the light guide, a transparent plate such as glass or synthetic resin can be used. As the synthetic resin, for example, various synthetic resins having high transparency such as acrylic resin, polycarbonate resin, vinyl chloride resin and the like can be used, and this resin can be extruded by a normal molding method such as injection molding. The light guide can be manufactured by molding into a plate-like body. In particular, methacrylic resin is excellent in light transmittance, heat resistance, mechanical properties, and moldability, and is most suitable as a light guide material. Such a methacrylic resin is a resin containing methyl methacrylate as a main component, and preferably has a methyl methacrylate content of 80% by weight or more. Further, a light diffusing agent, fine particles and the like may be mixed in the light guide as needed.

  As shown in FIG. 3 or FIG. 4, as the number of lens rows formed on the surface of the light guide, a lens row composed of a smooth inclined surface having an average tilt angle (θa) within the above range can be used. It is not particularly limited, and examples thereof include a lenticular lens array having an arc-shaped cross section, a prism array having a serrated cross section, and a concavo-convex array having a continuous cross section having a waveform. Among them, a prism row and a lenticular lens row whose cross sections are symmetrical are particularly preferable. Further, such a lens row is formed so that the lens row extends in a direction parallel to the light incident surface of the light guide, and preferably, each lens row is formed continuously in parallel. The pitch of the lens rows is appropriately selected depending on the application, but is usually preferably in the range of 20 μm to 5 mm.

  The processing method for forming a large number of lens arrays composed of smooth inclined surfaces having a specific average inclination angle (θa) on the surface of the light guide is not particularly limited as long as the average inclination angle (θa) falls within a specific range. Although it is not a thing, for example, using a mold or the like on which a lens pattern is formed by chemical etching, bead cutting, laser processing, etc., the transparent substrate is heated and pressed, or the active energy ray-curable resin is placed on the transparent substrate. A method of transferring a lens pattern by applying and curing by application of active energy rays to transfer a lens pattern, a method of forming by injection molding, and a method of directly processing a light guide by etching, cutting with a tool, laser processing, or the like are included.

  As shown in FIG. 2, the surface light source element of the present invention has a light source 2 such as a fluorescent lamp disposed at one end of the light guide 1 as described above, and has a back surface facing the light emitting surface. The reflection layer 4 is formed by a reflection film or the like. In order to effectively introduce light from the light source 2 to the light guide 1, the light incident surfaces of the light source 2 and the light guide 1 are configured to be covered with a case or film coated with a reflective agent on the inside. Further, as the light guide 1, various shapes such as a plate shape, a wedge shape, and a boat shape can be used.

  In the surface light source element of the present invention, the emission direction of the emitted light from the light guide 1 is generally a direction deviated from the normal direction. It is preferable that the output light be deflected in the normal direction by taking measures such as placing the lens sheet 3 on the light guide 1. In this case, the lens sheet 3 used has a lens surface in which a large number of lens units are formed in parallel on at least one surface. As the lens shape to be formed, various shapes are used depending on the purpose, and examples thereof include a prism shape, a lenticular lens shape, and a corrugated shape. The lens unit pitch of the lens sheet 3 is preferably about 20 μm to 5 mm. When a prism sheet is used, the prism apex angle is appropriately selected according to the emission angle of the light emitted from the light guide. Generally, it is preferable to be in the range of 50 to 120 °. Also, the orientation of the prism sheet is appropriately selected according to the emission angle of the light emitted from the light guide, and may be mounted so that the lens surface is on the light guide side, or may be mounted in the opposite direction. Good. When a large number of lens arrays composed of smooth inclined surfaces having an average inclination angle (θa) of 0.5 to 6 ° are formed on the light emitting surface of the light guide, light emitted from the light emitting surface has a normal line. A prism sheet having a prism array having a prism apex angle of about 55 to 70 ° is formed on a prism sheet to emit light with a relatively large angle of high directivity of about 80 to 60 °. The light emitted from the light guide is efficiently deflected substantially in the normal direction, and the luminance in the normal direction can be improved.

  The lens sheet 3 of the present invention is preferably manufactured using a material having a high visible light transmittance and a relatively high refractive index. For example, acrylic resin, polycarbonate resin, vinyl chloride resin, active energy ray curing Mold resin and the like. Among them, an active energy ray-curable resin is preferable from the viewpoints of scratch resistance, handleability, productivity and the like of the lens sheet. Further, additives such as an antioxidant, an ultraviolet absorber, a yellowing inhibitor, a bluing agent, a pigment, and a diffusing agent can be added to the lens sheet as needed. As a method for producing the lens sheet, a usual molding method such as extrusion molding, injection molding or the like can be used. When manufacturing a lens sheet using an active energy ray-curable resin, the lens sheet is made of a transparent resin such as a polyester resin, an acrylic resin, a polycarbonate resin, a vinyl chloride resin, a polymethacrylimide resin, and a polyolefin resin. A lens portion is formed on a transparent substrate such as a transparent film or sheet by using an active energy ray-curable resin. First, an active energy ray-curable resin liquid is injected into a lens mold having a predetermined lens pattern formed thereon, and a transparent substrate is overlaid. Next, an active energy ray such as an ultraviolet ray or an electron beam is irradiated through the transparent base material, and the active energy ray-curable resin liquid is polymerized and cured, and is separated from the lens mold to obtain a lens sheet.

In the surface light source device of the present invention, in addition to the lens sheet as described above, various types of optical sheet such as a diffusion sheet, a color filter, a polarizing film, and the like that optically change, converge, and diffuse light or change its optical characteristics. Can be used.
The surface light source element of the present invention is a notebook personal computer using a liquid crystal display element, a backlight of a color liquid crystal display device such as a liquid crystal television or a video integrated liquid crystal television, a character by cutting out or printing on a translucent plastic plate, and the like. It is suitable as a backlight of a display device such as a guide signboard or a large signboard using a display board formed with figures, photographs, or the like, or a guide sign or a traffic sign on an expressway or a general road.

Hereinafter, the present invention will be specifically described with reference to examples.
Measurement of brightness The cold cathode tube of the light guide was connected to a DC power supply via an inverter (CXA-M10L manufactured by TDK), and was lit by applying DC 12V. Place the surface light source device on the measuring table and adjust the measurement distance so that the surface light source device is perpendicular to the center line of the luminance meter (Minolta nt-1 ゜) and the measurement circle has a diameter of 8 to 9 mm. did. Next, after aging the cold cathode tubes for 30 minutes or more, the luminance was measured. For the measurement, the part excluding 5 mm near the light source was divided into 20 mm x 20 mm areas, the center of the measurement circle of the luminance meter was matched with the center of each area, and the brightness of each area was measured. The luminance in the normal direction was used. In the case of a large-sized display device, the measurement was performed by turning on a 30 W fluorescent lamp instead of a cold cathode tube.

Variation (R%)
From the measured value of the luminance in each region from the light source side at the center of the surface light source element to the other end surface,
It was calculated based on equation (3).
Emission rate (a)
From the measured value of the luminance in each region from the light source side at the center of the surface light source element to the other end surface,
It was calculated based on equation (2).

Average tilt angle (θa)
It was determined according to ISO4287 / 1-1984. Using a stylus type surface roughness meter (Surfcom 570A, manufactured by Tokyo Seiki Co., Ltd.) using E-DT-S04A (1 μmR, 55 ° cone, diamond) as a stylus, the surface roughness of the rough surface was adjusted to a drive speed of 0. It was measured at 03 mm / sec. The inclination was corrected by subtracting the average line from the measured average line, and was calculated by the following equations (4) and (5).

Example 1
Using a diamond tool on a brass plate, using a mold in which a prism pattern in which a number of prism rows with a vertical angle of 172 ° and a pitch of 50 μm are continuous in parallel as shown in FIG. The prism surface was transferred to one surface of the transparent acrylic resin plate by thermal transfer to obtain a light guide. On the surface of the obtained light guide, a prism pattern was formed in which a large number of prism rows composed of smooth inclined surfaces continued in parallel, and the average inclination angle (θa) was 4.2 °. A silver-deposited PET film was adhered to two end faces of 165 mm and the other end face of the obtained light guide by adhesion processing, and a silver-deposited PET film was formed on the back face opposite to the light emission face serving as the prism face. The tape was fixed to form a reflective surface. A cold cathode tube (KC230T4E, 4 mmφ × 230 mm, manufactured by Matsushita Electric Co., Ltd., 4 mmφ × 230 mm) is wound around a PET film on which silver is vapor-deposited on the other end surface of the light guide, and the light guide is installed as a light source lamp. A prism sheet having a large number of parallel prism rows with a vertical angle of 63 ° and a pitch of 50 μm made of an acrylic ultraviolet curable resin having a refractive index of 1.53 is placed so that the prism surface faces the light emitting surface side of the light guide. To provide a surface light source element. The normal luminance and the degree of variation (R%) of the obtained surface light source element were determined and are shown in Table 1.

  On the other hand, using a transparent acrylic resin plate of 3 mm × 90 mm × 300 mm, a light guide was produced in the same procedure. A surface light source element was prepared in the same manner as described above, except that a PET film on which silver was vapor-deposited was adhered to two end faces of 90 mm of the obtained light guide, and the resulting film was adhered. The emission ratio was determined and is shown in Table 1.

Example 2
4 mm × 210 mm × 165 mm transparent acrylic resin plate using a mold in which a large number of lenticular lens rows having a pitch of 50 μm as shown in FIG. The lens surface was transferred to one surface of the substrate by thermal transfer to form a light guide. On the surface of the obtained light guide, a lens pattern was formed in which a large number of lens rows composed of smooth slopes were continuous in parallel, and the average tilt angle (θa) was 4.3 °. A silver-deposited PET film was attached to two end faces of 165 mm and the other end face of the obtained light guide by adhesive processing, and a silver-deposited PET film was deposited on the back face opposite to the light emission face serving as the prism face. The tape was fixed to form a reflective surface. A cold cathode tube (KC230T4E, 4 mmφ × 230 mm, manufactured by Matsushita Electric Co., Ltd., 4 mmφ × 230 mm) is wound around a PET film on which silver is vapor-deposited on the other end surface of the light guide, and the light guide is installed as a light source lamp. A prism sheet is formed by forming a large number of parallel prism rows with a vertical angle of 63 [deg.] And a pitch of 50 [mu] m using an acrylic UV curable resin having a refractive index of 1.53 so that the prism surface faces the light emitting surface side of the light guide. To provide a surface light source element. Table 1 shows the normal luminance and the degree of variation (R%) of the obtained surface light source element.

  On the other hand, using a transparent acrylic resin plate of 3 mm × 90 mm × 300 mm, a light guide was produced in the same procedure. A surface light source element was prepared in the same manner as described above, except that a PET film on which silver was vapor-deposited was adhered to two end faces of 90 mm of the obtained light guide, and the resulting film was adhered. The emission ratio was determined and is shown in Table 1.

Comparative Examples 1-2
After the surface of the glass plate is subjected to chemical etching by performing a fluorine treatment after performing a sandblasting treatment, the thickness is 3 mm × 210 mm × 165 mm and 4 mm × 210 mm × using an electroforming mold obtained by taking a replica mold by electroforming. The rough surface was transferred by heat transfer to one surface of two types of transparent acrylic resin plates of 165 mm to form a light guide. A rough surface having an average inclination angle (θa) of 8.4 ° was formed on the surface of the obtained light guide. A silver-deposited PET film was adhered to two end surfaces of 165 mm and the other end surface of the obtained light guide by adhesive processing, and a silver-deposited PET film was formed on the back surface opposite to the roughened light emission surface. The tape was fixed to form a reflective surface. A cold cathode tube (KC130T4E72, 4 mmφ × 130 mm, manufactured by Matsushita Electric Industrial Co., Ltd., 4 mmφ × 130 mm) is wound around a PET film on which silver is vapor-deposited on the other end surface of the light guide, and the light guide is installed as a light source lamp. A prism sheet is formed by forming a large number of parallel prism rows with a vertical angle of 63 [deg.] And a pitch of 50 [mu] m using an acrylic UV curable resin having a refractive index of 1.53 so that the prism surface faces the light emitting surface side of the light guide. To provide a surface light source element. Table 1 shows the normal luminance and the degree of variation (R%) of the obtained surface light source element.

  On the other hand, using a transparent acrylic resin plate of 3 mm × 90 mm × 300 mm, the light guide 1 was produced in the same procedure. A surface light source device was prepared in the same manner as described above, except that a PET film on which silver was vapor-deposited was adhered to two 90 mm end surfaces of the obtained light guide 1, and the obtained surface light source device was obtained. Table 1 shows the emission rates of the samples.

Comparative Example 3
Using a diamond tool on a brass plate, using a mold having a prism pattern in which a number of prism rows having a vertical angle of 164 ° and a pitch of 50 μm are formed in parallel and continuous as shown in FIG. 5, a 4 mm × 210 mm × 165 mm The prism surface was transferred to one surface of the transparent acrylic resin plate by thermal transfer to obtain a light guide. On the surface of the obtained light guide, a prism pattern was formed in which a large number of prism rows composed of smooth inclined surfaces continued in parallel, and the average inclination angle (θa) was 8.2 °. A silver-deposited PET film was attached to two end faces of 165 mm and the other end face of the obtained light guide by adhesive processing, and a silver-deposited PET film was deposited on the back face opposite to the light emission face serving as the prism face. The tape was fixed to form a reflective surface. A cold cathode tube (KC230T4E, 4 mmφ × 230 mm, manufactured by Matsushita Electric Co., Ltd., 4 mmφ × 230 mm) is wound around a PET film on which silver is vapor-deposited on the other end surface of the light guide, and the light guide is installed as a light source lamp. A prism sheet is formed by forming a large number of parallel prism rows with a vertical angle of 63 [deg.] And a pitch of 50 [mu] m using an acrylic UV curable resin having a refractive index of 1.53 so that the prism surface faces the light emitting surface side of the light guide. To provide a surface light source element. Table 1 shows the normal luminance and the degree of variation (R%) of the obtained surface light source element.

  On the other hand, using a transparent acrylic resin plate of 3 mm × 90 mm × 300 mm, a light guide was produced in the same procedure. A surface light source element was prepared in the same manner as described above, except that a PET film on which silver was vapor-deposited was adhered to two end faces of 90 mm of the obtained light guide, and the resulting film was adhered. The emission ratio was determined and is shown in Table 1.

Comparative Example 4
A transparent acrylic resin plate of 4 mm × 210 mm × 165 mm using a mold in which a lens pattern in which a large number of lenticular lens rows with a pitch of 50 μm as shown in FIG. The lens surface was transferred to one surface of the substrate by thermal transfer to form a light guide. On the surface of the obtained light guide, a lens pattern was formed in which a large number of lens rows each formed of a smooth inclined surface continued in parallel, and the average inclination angle (θa) was 8.3 °. A silver-deposited PET film was attached to two end faces of 165 mm and the other end face of the obtained light guide by adhesive processing, and a silver-deposited PET film was deposited on the back face opposite to the light emission face serving as the prism face. The tape was fixed to form a reflective surface. A cold cathode tube (KC230T4E, 4 mmφ × 230 mm, manufactured by Matsushita Electric Industrial Co., Ltd., 4 mmφ × 230 mm) is wound around a PET film on which silver is vapor-deposited on the other end surface of the light guide, and is set as a light source lamp. A prism sheet is formed by forming a large number of parallel prism rows with a vertical angle of 63 [deg.] And a pitch of 50 [mu] m using an acrylic UV curable resin having a refractive index of 1.53 so that the prism surface faces the light emitting surface side of the light guide. To provide a surface light source element. Table 1 shows the normal luminance and the degree of variation (R%) of the obtained surface light source element.

On the other hand, using a transparent acrylic resin plate of 3 mm × 90 mm × 300 mm, a light guide was produced in the same procedure. A surface light source element was prepared in the same manner as described above, except that a PET film on which silver was vapor-deposited was adhered to two end faces of 90 mm of the obtained light guide, and the resulting film was adhered. The emission ratio was determined and is shown in Table 1.

  As is clear from Table 1, in the surface light source devices of Examples 1 to 4 of the present invention, the degree of variation (R%) of the luminance in the light emitting surface is excellent at 20% or less and excellent in uniformity. The device was sufficiently practicable as a surface light source element for an apparatus. On the other hand, in the surface light source elements of Comparative Examples 1 to 4, the degree of luminance variation (R%) in the light emitting surface exceeds 100%, and the uniformity of luminance is not sufficiently obtained. Was.

Example 3
A 10 mm × 600 mm × 1250 mm mold was used, in which a diamond pattern was used as a brass plate and a prism pattern in which a number of prism rows having a vertical angle of 172 ° and a pitch of 50 μm were formed in parallel and continuous as shown in FIG. 3 was formed. The prism surface was transferred to one surface of the transparent acrylic resin plate by thermal transfer to obtain a light guide. On the surface of the obtained light guide, a prism pattern was formed in which a large number of prism rows composed of smooth inclined surfaces were continuous in parallel, and the average inclination angle (θa) was 4.2 °. A silver-evaporated PET film was adhered to two end faces of 1250 mm and the other end face of the obtained light guide, and the silver-evaporated PET film was adhered to the back face opposite to the light emission face as the prism face. The tape was fixed to form a reflective surface. A 30 W fluorescent lamp (FSL30T6 manufactured by Matsushita Electric Co., Ltd.) was wound around a PET film on which silver was deposited on the other end face of the light guide, and the light guide was installed as a light source lamp. A prism sheet made of 1.53 acrylic ultraviolet curable resin and having a large number of parallel prism rows with a vertical angle of 63 ° and a pitch of 50 μm is placed so that the prism surface faces the light exit surface side of the light guide. A surface light source element was used. The normal line luminance and the degree of variation (R%) of the obtained surface light source element were determined and are shown in Table 2.

  On the other hand, using a transparent acrylic resin plate of 10 mm × 600 mm × 1250 mm, a light guide was produced in the same procedure. A surface light source element was prepared in the same manner as described above, except that a silver-evaporated PET film was adhered to two end faces of 1250 mm of the obtained light guide, and the resulting film was adhered. The emission ratio was determined and is shown in Table 2.

Example 4
A transparent acrylic resin plate of 10 mm × 600 mm × 1250 mm using a mold in which a lens pattern in which a large number of lenticular lens rows with a pitch of 50 μm are continuous in parallel as shown in FIG. The lens surface was transferred to one surface of the substrate by thermal transfer to form a light guide. On the surface of the obtained light guide, a lens pattern was formed in which a large number of lens rows each formed of a smooth inclined surface continued in parallel, and the average inclination angle (θa) was 4.3 °. A silver-evaporated PET film was adhered to two end faces of 1250 mm and the other end face of the obtained light guide, and the silver-evaporated PET film was adhered to the back face opposite to the light emission face as the prism face. The tape was fixed to form a reflective surface. A 30 W fluorescent lamp (FSL30T6 manufactured by Matsushita Electric Co., Ltd.) was wound around a PET film on which silver was deposited on the other end face of the light guide, and the light guide was installed as a light source lamp. A prism sheet made of 1.53 acrylic ultraviolet curable resin and having a large number of parallelly arranged prism rows with a vertical angle of 63 ° and a pitch of 50 μm is placed so that the prism surface faces the light emitting surface side of the light guide. A surface light source element was used. The normal line luminance and the degree of variation (R%) of the obtained surface light source element were determined and are shown in Table 2.

  On the other hand, using a transparent acrylic resin plate of 10 mm × 600 mm × 1250 mm, a light guide was produced in the same procedure. A surface light source element was prepared in the same manner as described above, except that a silver-evaporated PET film was adhered to two end faces of 1250 mm of the obtained light guide, and the resulting film was adhered. The emission ratio was determined and is shown in Table 2.

Comparative Example 5
Using a diamond tool on a brass plate, a 10 mm × 600 mm × 1250 mm mold was used in which a prism pattern in which a number of prism rows having a vertical angle of 164 ° and a pitch of 50 μm were continuously formed in parallel as shown in FIG. 5 was formed. The prism surface was transferred to one surface of the transparent acrylic resin plate by thermal transfer to obtain a light guide. On the surface of the obtained light guide, a prism pattern was formed in which a large number of prism rows composed of smooth inclined surfaces continued in parallel, and the average inclination angle (θa) was 8.2 °. A silver-evaporated PET film was adhered to two end faces of 1250 mm and the other end face of the obtained light guide, and the silver-evaporated PET film was adhered to the back face opposite to the light emission face as the prism face. The tape was fixed to form a reflective surface. A 30 W fluorescent lamp (FSL30T6 manufactured by Matsushita Electric Co., Ltd.) was wound around a PET film on which silver was deposited on the other end face of the light guide, and the light guide was installed as a light source lamp. A prism sheet made of 1.53 acrylic ultraviolet curable resin and having a large number of parallelly arranged prism rows with a vertical angle of 63 ° and a pitch of 50 μm is placed so that the prism surface faces the light emitting surface side of the light guide. A surface light source element was used. The normal line luminance and the degree of variation (R%) of the obtained surface light source element were determined and are shown in Table 2.

  On the other hand, using a transparent acrylic resin plate of 10 mm × 600 mm × 1250 mm, a light guide was produced in the same procedure. A surface light source element was prepared in the same manner as described above, except that a silver-evaporated PET film was adhered to two end faces of 1250 mm of the obtained light guide, and the resulting film was adhered. The emission ratio was determined and is shown in Table 2.

Comparative Example 6
A transparent acrylic resin plate of 10 mm × 600 mm × 1250 mm using a mold having a lens pattern in which a large number of lenticular lens rows with a pitch of 50 μm as shown in FIG. The lens surface was transferred to one surface of the substrate by thermal transfer to form a light guide. On the surface of the obtained light guide, a lens pattern was formed in which a large number of lens rows each formed of a smooth inclined surface continued in parallel, and the average inclination angle (θa) was 8.3 °. A silver-evaporated PET film was adhered to two end faces of 1250 mm and the other end face of the obtained light guide, and the silver-evaporated PET film was adhered to the back face opposite to the light emission face as the prism face. The tape was fixed to form a reflective surface. A 30 W fluorescent lamp (FSL30T6 manufactured by Matsushita Electric Industrial Co., Ltd.) was wound around a PET film on which silver was deposited on the other end surface of the light guide, and the light guide was installed as a light source lamp. A prism sheet made of 1.53 acrylic ultraviolet curable resin and having a large number of parallel prism rows with a vertical angle of 63 ° and a pitch of 50 μm is placed so that the prism surface faces the light exit surface side of the light guide. A surface light source element was used. The normal line luminance and the degree of variation (R%) of the obtained surface light source element were determined and are shown in Table 2.

On the other hand, using a transparent acrylic resin plate of 10 mm × 600 mm × 1250 mm, a light guide was produced in the same procedure. A surface light source element was prepared in the same manner as described above, except that a silver-evaporated PET film was adhered to two end faces of 1250 mm of the obtained light guide, and the resulting film was adhered. The emission ratio was determined and is shown in Table 2.

  As is clear from Table 2, in the surface light source devices of Examples 3 and 4 of the present invention, the degree of variation (R%) of the luminance in the light emission surface is 200% or less, which is excellent in uniformity, and large display. The device was sufficiently practicable as a surface light source element for an apparatus. On the other hand, in the surface light source elements of Comparative Examples 5 to 6, the degree of variation in luminance (R%) in the light emitting surface exceeds 600%, and the uniformity of luminance is not sufficiently obtained. Was.

It is the schematic which shows the optical path of the light in the lens surface of the light guide of this invention. FIG. 2 is a partial perspective view showing a surface light source element of the present invention. FIG. 4 is a partial cross-sectional view illustrating a prism surface of a light guide according to an example. FIG. 3 is a partial cross-sectional view illustrating a lenticular lens surface of a light guide according to an example. It is a partial sectional view showing the prism surface of the light guide of a comparative example. It is a partial sectional view showing the lenticular lens surface of the light guide of a comparative example.

Explanation of reference numerals

Reference Signs List 1 light guide 2 light source 3 lens sheet 4 reflection layer

Claims (2)

  At least one side end surface is a light incident surface, and one surface substantially orthogonal to the light incident surface is a light emitting surface, and at least one of the light emitting surface and the back surface thereof is in a direction parallel to the light incident surface. And an average inclination angle is comprised of a number of lens rows composed of inclined surfaces having an angle of 0.5 to 6 °, and the light emitted from the light exit surface has an angle of 60 to 80 ° with respect to the normal line of the light exit surface. A light guide for a surface light source element, wherein the light guide emits light with directivity. A light source, a light guide having at least one side end surface facing the light source as a light incident surface, and a light exit surface as one surface substantially orthogonal to the light incident surface; and a light exit surface side of the light guide. A prism sheet in which a number of prism rows are formed in parallel on at least one surface of the light guide, and at least one of the light exit surface and the back surface of the light guide is parallel to the light entrance surface. And a plurality of lens rows each having an inclined surface having an average inclination angle of 0.5 to 6 °, and the prism sheet is configured such that a surface on which the prism rows are formed on the light exit surface is the light exit surface. The light emitted from the light exit surface of the light guide emits light with directivity at an angle of 60 to 80 ° with respect to the normal to the light exit surface, and the emitted light is A surface light source element characterized in that the angle is changed in a substantially normal direction by a prism sheet.

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