JP2010262827A - Surface light source device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device capable of preventing unevenness of luminance in the vicinity of a light source due to light leakage from a stepped part of a light guide without lowering luminance, and to provide a liquid crystal display device using the surface light source device. <P>SOLUTION: The surface light source device includes a primary light source consisting of a light-emitting diode row, at least one light incident surface facing the light source, and the light guide having a light emission surface nearly crossing the light incident surface, as well as a lens sheet arranged so as a lens layer to be faced to the light emission surface of the light guide. A thickness of the light incident surface of the light guide is thicker than that of the light emission surface, and a step is provided between the light incident surface and the light emission surface. The lens sheet includes a lens layer with a lens row formed on a first side of a sheet-like translucent base material which has a first and a second sides, and a light diffusion layer is formed on the second side. A thickness of the sheet-like translucent base material is to be ≤75 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a surface light source device and a liquid crystal display device.

The liquid crystal display device includes a backlight unit (surface light source device) and a liquid crystal display surface (liquid crystal panel). As the surface light source device, there are a direct type device in which a light source is arranged directly below a liquid crystal display surface and an edge light type device in which a light source is arranged on a side surface of a light guide. Edge light-type devices are often used for applications such as notebook personal computers and mobile phones where importance is placed on the lightweight and thin liquid crystal display devices.
In a liquid crystal display device using an edge light type surface light source device, light is incident on the side surface of the light guide from the light source, the surface of the light guide is emitted, emitted to the liquid crystal display surface, and surface emission is performed. In such a liquid crystal display device, in order to more efficiently use the light obtained from the light source, a lens sheet for concentrating and emitting the light from the surface light source in a specific direction is used.

  In such a lens sheet, a lens array such as a prism array is formed on one surface, and the light is aligned in a certain direction by the lens array. Then, light is diffused within a viewing angle range according to the use of the liquid crystal display device by a light diffusion layer provided on the surface opposite to the lens array.

  On the other hand, in recent years, light emitting diodes (LEDs) are increasingly used as light sources in notebook personal computers where portability is important. This is because the use of an LED has advantages such as a reduction in power consumption, an improvement in luminance, and a reduction in the thickness of the light guide as compared with a cold cathode tube. However, since there is a lower limit to the thickness of a light source such as an LED, the thickness of the light exit surface is made thinner than the thickness of the light entrance surface, and the thickness gradually decreases between the light entrance surface and the light exit surface. Increasing the weight and thickness of the backlight portion by using a light guide having a stepped portion is increasing (for example, Patent Document 1).

  On the other hand, by using the light guide having a step portion between the light incident surface and the light exit surface as described above, leakage from the periphery of the step portion of the light guide is disclosed in Patent Document 1. There is a problem that light is generated, and bright lines are generated non-uniformly only in the vicinity of the LED light source, resulting in uneven brightness and degrading the quality of the liquid crystal display device.

JP 2007-27002 A

  The luminance unevenness near the light source will be described with reference to FIG. FIG. 1 is a perspective view of a surface light source device using a light source having a stepped portion between a light incident surface and a light output surface using a plurality of point light sources 20 arranged as a primary light source. A light source 20 is arranged close to the light incident surface of the light guide 10 and spaced from each other. The light guide 10 has a stepped portion 13, and a lens sheet 30 is installed in the vicinity of the stepped portion 13. The luminance unevenness is generated in such a manner that light lines extend from the light source in a direction perpendicular to the light source array.

  In order to prevent such unevenness, conventionally, in the light diffusion layer provided on the light emitting surface side of the lens sheet, a refractive index difference is provided between the light-transmitting resin and the light diffusion material constituting the light diffusion layer, By forming an interface having a different refractive index inside the diffusion layer, when the light beam guided through the lens sheet 30 passes through the light diffusion layer, it reaches the surface of the light diffusion layer (that is, the interface with air) and reflects it. Before being performed, the brightness unevenness was prevented by scattering the light rays.

  However, in the prior art, the difference in refractive index between the light diffusing material and the translucent resin is large, and part of the light that should be used for light emission of the liquid crystal display device is scattered in an unintended and unnecessary direction. There was a problem that caused a decrease in. Accordingly, an object of the present invention is to provide a surface light source device and a liquid crystal display device that can prevent the luminance unevenness without causing a decrease in luminance.

  FIG. 2 is a partial cross-sectional view of the surface light source device as shown in FIG. A step portion 13 is provided between the light incident surface 11 and the light emitting surface 12 of the light guide 10, and the lens sheet 30 has a lens so that the lens layer 32 faces the light guide light emitting surface 12. The sheet end portion 31 is disposed close to the light guide step portion 13. Further, the reflection sheet 40 is disposed in contact with the surface on the back side of the light emitting surface 12 of the light guide 10, and the light source reflection sheet 21 is disposed so as to cover other than the irradiation surface of the light source 20.

  Although the cause of the brightness unevenness has not been elucidated in detail, the present inventors have found that the leaked light emitted from the step portion 13 of the light guide is the end of the lens sheet as shown in FIG. Incoming from 31, guided through the lens sheet 30, exited after guiding a certain distance from the end of the lens sheet, and the amount of emitted light increases only at that part, so that it is visually recognized as uneven brightness I found.

  In the present invention, a primary light source composed of a plurality of point light sources, at least one light incident surface facing the primary light source, and light that is substantially orthogonal to the light incident surface and incident from the light incident surface is emitted. A light guide having a light exit surface, and a lens layer in which a plurality of lens rows are arranged substantially in parallel on the first surface of the sheet-like light-transmitting substrate, And a lens sheet in which a light diffusion layer is formed on the surface of the light guide, wherein the light guide has a thickness of the light guide on the light incident surface of the light guide on the light exit surface. Thicker than the thickness, and between the light incident surface and the light exit surface, has a step portion where the thickness of the light guide gradually decreases, the lens sheet, the light exit surface of the light guide, The lens layer of the lens sheet is disposed so as to face the light diffusion layer. The total haze is 5% or more and 60% or less, the ratio of the internal haze to the total haze is 50% or less, and the thickness of the sheet-like translucent substrate is 100 μm or less. A light source device is provided.

  In this way, by setting the thickness of the sheet-like translucent base material to 75 μm or less, it is possible to reduce the light incident from the end of the lens sheet, so that the internal haze of the diffusion layer is set to 50% or less. It is possible to prevent a defect such as luminance unevenness from occurring while suppressing a decrease in luminance due to internal diffusion of the transparent member.

  In another aspect of the present invention, the pitch of the lens rows of the lens sheet is 20 μm or less.

  By adopting the configuration as described above, even if luminance unevenness occurs, the luminance unevenness can be shortened. For example, in a surface light source device, a portion where the luminance unevenness occurs can be outside the effective region. , Brightness unevenness can be made inconspicuous.

  In another aspect of the present invention, the light diffusing layer contains a light diffusing material in a translucent resin, and the content of the light diffusing material in the translucent resin is It is 1 mass% or more and 20 mass% or less. In another aspect of the present invention, the light diffusing material has an average particle diameter of 1 μm or more and 20 μm or less, and a refractive index difference from the translucent resin of 0.00 or more and 0.06 or less. . By setting it as such a structure, the total haze of a light-diffusion layer can be 5% or more and 60% or less, and the ratio of the internal haze to all the haze can be 50% or less.

  According to the surface light source device of the present invention, it is possible to prevent luminance unevenness in the vicinity of the light source due to leakage light from the step portion of the light guide without reducing the luminance.

It is the perspective view which showed the surface light source device of the state which the brightness nonuniformity generate | occur | produced. It is sectional drawing of the surface light source device shown in detail about generation | occurrence | production of the brightness nonuniformity in a surface light source device. It is a perspective view which shows the surface light source device concerning embodiment of this invention. It is sectional drawing of the surface light source device concerning embodiment of this invention.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the attached drawings and the following description, and various modifications may be added as necessary.

  An example of an embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a perspective view showing a surface light source device using the lens sheet 30 of the present invention. 4 is a partial cross-sectional view of the surface light source device shown in FIG.

As shown in FIG. 3, the surface light source device includes a primary light source in which a plurality of point light sources 20 such as LEDs are arranged, a reflection sheet 40, a light guide 10, and a lens sheet 30. The light source 20 is disposed so as to face the light incident surface 11 of the light guide 10. A reflective sheet 40 is disposed below the light guide 10. The lens sheet 30 is disposed such that the surface on which the lens layer is formed faces the light emitting surface 12 of the light guide 10.
<Light guide>
Although the thickness of the light incident surface 11 of the light guide 10 is approximately the same as that of the light source 20, the step 13 is provided between the light incident surface 11 and the light output surface 12 of the light guide to guide the light on the light output surface. The thickness of the light body is smaller than the thickness of the light guide on the light incident surface. The thickness of the light guide on the light incident surface 11 is usually about 0.5 mm to 2 mm, and the thickness of the light guide on the light exit surface is usually about 0.1 to 1.5 mm. Further, the shape of the step portion 13 is various such as a slope shape or a step shape. The height of the stepped portion (that is, the difference between the thickness of the light incident surface 11 and the thickness of the light guide on the light emitting surface 12) is usually about 0.05 to 1 mm. In addition, the width (that is, the depth) of the step when having the sloped or stepped shape is usually about 0.3 to 5.0 mm.

The light guide 10 is made of a highly transparent synthetic resin. Examples of such synthetic resins include methacrylic resins, acrylic resins, polycarbonate resins, polyolefin resins having a cyclic or norbornene structure, polyester resins, and vinyl chloride resins. In particular, a methacrylic resin is preferably used from the viewpoints of high light transmittance, heat resistance, mechanical properties, and moldability. As the methacrylic resin, a resin containing methyl methacrylate as a main component is preferable, and one having 80% by mass or more of methyl methacrylate is more preferable.
<Lens sheet>
An example of a lens sheet used in the surface light source device of the present invention will be described with reference to FIG.

FIG. 4 is a cross-sectional view of the surface light source device of the present invention including the lens sheet 30. In the lens sheet 30, a light diffusing layer 34 including a translucent resin 35 and a light diffusing material 36 is provided on one surface of a sheet-like translucent base material 33. In addition, a lens layer 32 in which a prism row with apex angle θ and pitch P is formed is provided on the other surface of the sheet translucent substrate 33. A light beam emitted from the light guide 10 at an angle α is totally reflected by the prism row and is emitted in the normal direction of the surface light source device.
<Light diffusion layer>
The light diffusion layer 34 preferably has a total haze (H1 + H2) of 5% or more and 60% or less, with a surface haze of H1 and an internal haze of H2. If it is less than 5%, incident light from the end of the sheet-like translucent substrate 32 cannot be efficiently diffused, and it tends to be difficult to prevent luminance unevenness. On the other hand, if it exceeds 60%, the luminance of the liquid crystal display device using the surface light source device tends to be low. A more preferable value of the total haze is 10% or more and 55% or less, and particularly preferably 15% or more and 50% or less. The haze is a value defined according to JIS-K7136 by using a haze meter (for example, product name: HM-150, manufactured by Murakami Color Research Laboratory) so that the light diffusion layer 34 faces the light receiving side. It is.

  Further, the ratio of the internal haze H2 to the total haze (H1 + H2) is preferably 50% or less. When the ratio of the internal haze H2 exceeds 50%, the occurrence of luminance unevenness is suppressed, but unnecessary scattering occurs in an unintended direction, and the luminance and luminance half-value angle of the surface light source device are reduced. There is a tendency to decrease. For this reason, luminance reduction can be prevented by setting the ratio of the internal haze H2 in the light diffusion layer 32 to 50% or less.

  The structure of the light diffusing layer 34 is not particularly limited as long as the ratio of the internal haze H2 is 50% or less. However, a paint including the light transmissive resin 35 and the light diffusing material 36 is applied on the sheet-like light transmissive substrate 33. It can form by apply | coating to. Moreover, the coating material which contains 2 or more types of resin components and forms uneven | corrugated shape by the effect | action of phase separation can also be used.

  Furthermore, as another method of forming the light diffusion layer 34, a light diffusion layer obtained by transferring and curing a mold having a concavo-convex shape on the surface onto a transparent substrate 33 using an ultraviolet curable resin, By pressing the transparent base material 33 that has been softened by heating to a mold having an uneven shape, it is possible to use a light diffusion layer that has been thermally transferred to the uneven shape.

  A method for forming the light diffusing layer by applying a paint containing the light transmissive resin 35 and the light diffusing material 36 on the sheet-like light transmissive substrate 32 will be described below.

  The translucent resin 35 can be used without particular limitation as long as it can disperse the light diffusing material 36, has high translucency, and has desired heat resistance, scratch resistance, elasticity, and the like. Such translucent resins include polyamide resins, polyurethane resins, polyester resins, acrylic resins, and other thermoplastic resins, thermosetting resins, active energy ray curable resins (ionizing radiation curable resins), etc. Of these, it is preferable to select appropriately in consideration of the adhesiveness to the sheet-like translucent base material 33 and the light diffusing material 36, etc. Among them, the use of an acrylic resin having a high transmittance is particularly preferable. . As the acrylic resin, polymers such as hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, and acrylic acid are preferable. In particular, an acrylic polyol containing hydroxyalkyl (meth) acrylate as a monomer unit is dissolved in a solvent such as toluene or methyl ethyl ketone, and an isocyanate bifunctional monomer or an isocyanate compound such as isocyanurate or melamine, etc. An acrylic resin obtained by mixing with a cross-linking agent, coating, and curing is preferable in terms of strength and adhesion to a sheet-like translucent substrate. Moreover, from a heat resistant viewpoint, the thing whose glass transition point is 60 degreeC or more is preferable.

  In addition, a leveling agent, a thixotropic agent, a slip agent, an antifoaming agent, an antistatic agent, an ultraviolet absorber, and the like can be added and contained in the translucent resin 35. Among these, by incorporating a leveling agent, aggregation of the light diffusing material 36 can be suppressed and irregularities due to the light diffusing material 36 can be easily formed. Moreover, the damage at the time of friction with the liquid crystal panel surface can be prevented by adding a slip agent. As the slip agent, commercially available products such as silicon-based, fluorine-based, paraffin-based, and mixtures thereof can be used without particular limitation, and examples thereof include BYK series manufactured by Big Chemie Japan Co., Ltd.

  Examples of the light diffusing material 36 include inorganic particles such as glass, silica, talc, and barium sulfate. Examples of organic particles include crosslinked organic fine particles such as polymethyl methacrylate, polystyrene, polyurethane, acrylic-styrene copolymer, benzoguanamine, and melamine, fine particles of silicone resin, acrylic rubber, butadiene, styrene-butadiene, acrylonitrile-butadiene-styrene (ABS). ) And the like, and silicone rubber. The light diffusing material 36 may be a commercially available one or one obtained by suspension polymerization or emulsion polymerization. For example, methacrylates such as methyl methacrylate and octyl methacrylate, acrylates such as methyl acrylate and butyl acrylate, vinyl aromatic compounds such as styrene, α-methyl styrene, chlorostyrene and vinyl toluene, vinyl nitriles such as acrylonitrile and methacrylonitrile, ethylene Acrylic crosslinked particles obtained by suspension polymerization or emulsion polymerization of propylene, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl propionate, alkyl fumarate, and other ethylenically unsaturated compounds be able to.

  As an example of the said acrylic type crosslinked particle, the polymethyl methacrylate crosslinked particle containing 20-50 mass% of crosslinking agents is mentioned. As a commercial item, Sekisui Plastics Co., Ltd. Techpolymer SSX-series etc. are mentioned.

  The flexible rubber particles are effective for preventing damage to the liquid crystal panel surface, particularly when the liquid crystal panel surface is a smooth surface. For example, silicone composite powder KMP-600 series manufactured by Shin-Etsu Chemical Co., Ltd., Techpolymer BMX series, ARX series manufactured by Sekisui Plastics Co., Ltd. may be mentioned.

  The shape of the light diffusing material 36 can be appropriately selected and used regardless of the shape such as a spherical shape, an indeterminate shape, a bowl shape, a spheroid shape, or a needle shape.

  The configuration of the light diffusing material 36 is not particularly limited as long as the ratio of the internal haze H2 is 50% or less. However, the refractive index difference represented by the following formula between the refractive index N1 of the translucent resin 35 ( (Absolute value) It is preferable that Δn has a refractive index N2 of 0.00 to 0.06, preferably 0.00 to 0.04. This is because if Δn exceeds 0.06, scattering at the interface between the light diffusing material 36 and the translucent resin 35 becomes strong, and the ratio of the internal haze H2 tends to exceed 50%.

Δn = | N1-N2 | (1)
The light diffusing material is preferably contained in the light diffusing layer in the range of 1% by mass to 20% by mass. More preferably, they are 2 mass% or more and 15 mass% or less, More preferably, they are 4 mass% or more and 10 mass% or less. When the content of the light diffusing material is less than 1% by mass, the total haze (H1 + H2) of the light diffusing layer tends to be less than 5% and it becomes difficult to prevent luminance unevenness. When H1 + H2) exceeds 60%, the luminance of the surface light source device tends to decrease.

  It is preferable to use a light diffusing material having an average particle diameter of 1 μm to 20 μm, more preferably an average particle diameter of 1.5 μm to 15 μm, and still more preferably an average particle diameter of 2 μm to 10 μm. A light diffusing material is used. When the average particle diameter is less than 1 μm, the concealing property of the light diffusion layer is lowered and the transmitted light tends to be colored. On the other hand, when the average particle diameter exceeds 20 μm, the glare phenomenon tends to be remarkably deteriorated.

The thickness of the light diffusion layer 34 is not particularly limited, and is preferably determined in the range of 1 to 20 μm, for example. If it is less than 1 μm, production tends to be difficult, and if it exceeds 20 μm, luminance unevenness tends to deteriorate.
<Sheet-like translucent substrate>
In the present invention, the sheet-like translucent base material 33 is a sheet-like material having a thickness of 100 μm or less. The sheet-like translucent base material 33 has a thickness within this range, thereby reducing the total haze of the light diffusing layer of the lens sheet and suppressing the decrease in luminance, while preventing luminance unevenness due to the leaked light of the stepped portion. Can be prevented. This is because the amount of leakage light incident from the end 31 of the lens sheet is smaller than when a sheet-like translucent substrate thicker than 100 μm is used, and the incident leakage light is also guided in the lens sheet. In this case, the thickness of the lens sheet is thin, so that the number of reflections inside the lens sheet increases, and the light is emitted out of the lens sheet at a location close to the light source, so that luminance unevenness is less noticeable. The thickness of the sheet-like translucent substrate 33 is more preferably 85 μm or less, and even more preferably 75 μm or less.

  On the other hand, the lower limit of the thickness of the sheet-like translucent substrate 33 is preferably 10 μm or more, and more preferably 25 μm or more. If the thickness is less than 10 μm, the strength of the lens sheet tends to decrease and the handleability tends to deteriorate.

  The material of the sheet-like translucent base material 33 is not particularly limited, but is preferably one that transmits active energy rays, for example, an acrylic resin such as polymethyl methacrylate, a polycarbonate resin, a polyester resin such as polyethylene terephthalate and polyethylene naphthalate, Cellulose resins such as diacetyl cellulose and triacetyl cellulose, styrene resins such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, and olefin resins such as ethylene / propylene copolymers, Films, sheets, plates and the like made of polyamide resins such as nylon and aromatic polyamide, vinyl chloride resins, polymethacrylimide resins and the like can be used. In addition, other treatments such as antistatic, antireflection, and adhesion prevention between substrates can be performed.

Further, the sheet-like translucent substrate 33 may have a surface treatment portion for improving the adhesion with the lens layer 32. Examples of the surface treatment include those having easy adhesion made of polyester resin, acrylic resin, urethane resin, and the like. Moreover, what roughened the surface of the sheet-like translucent base material 33 may be used. Furthermore, an antistatic agent may be contained in the easy-adhesion layer as necessary, and the antistatic performance can be imparted to the lens sheet 30. Thereby, the workability at the time of assembling the liquid crystal display device can be improved, and the adsorption of foreign matters due to static electricity can be prevented.
<Lens layer>
The material of the lens layer 32 is not particularly limited, and is made of, for example, an active energy ray curable resin, and the refractive index is about 1.50 to 1.6. The active energy ray curable resin is not particularly limited as long as it is cured with active energy rays such as ultraviolet rays and electron beams. For example, polyesters, epoxy resins, polyester (meth) acrylates, epoxy Examples include (meth) acrylate resins such as (meth) acrylate and urethane (meth) acrylate. Among these, urethane (meth) acrylate resins are particularly preferable from the viewpoint of optical characteristics and the like. These may be used alone or as a mixture of two or more, and usually contain a photopolymerization initiator by active energy rays.

  The lens array formed in the lens layer 32 is not limited to a substantially triangular prism as shown in FIG. 4 and can be determined according to the application. For example, a lenticular lens, a polygonal pyramid, a conical lens, and the like can be mentioned. A prism having a substantially triangular cross section is particularly preferable.

  When the lens array is a prism, the apex angle of the prism is not particularly limited, but is preferably in the range of about 40 to 75 °, more preferably in the range of 45 to 70 °.

The pitch for arranging the lens rows is not particularly limited, but from the viewpoint of suppressing the occurrence of luminance unevenness, the arrangement pitch of the lens rows is preferably 20 μm or less. This is because, compared with a lens sheet having a pitch larger than 20 μm, a light beam that enters from the end 31 of the lens sheet and guides the inside of the lens sheet enters the lens array while guiding a certain distance inside the lens sheet. This is because the number of times increases, and the light is emitted out of the lens sheet 30 by refraction and reflection at a location closer to the lens sheet end portion 31, and as a result, the length of luminance unevenness is shortened. Therefore, even if luminance unevenness occurs, the length can be shortened, so that the luminance unevenness can be made inconspicuous.
<Light source and reflection sheet for light source>
The light source 20 is not particularly limited as long as it is a point light source such as an LED, and can be determined according to a desired surface light source device or liquid crystal display device. For example, a pseudo-white light emitting diode or a light emitting diode that emits white light using a red / green / blue light emitting diode chip as one light source can be used.

The light source reflection sheet 21 that covers the light source 20 is not particularly limited as long as it can reduce the loss of light from the light source 20 and can be guided to the light guide 10, and is a plastic film having a metal-deposited reflective layer on its surface, a refractive index. A multilayer film composed of a plurality of different resin layers, a light diffusing material-containing plastic film, and the like can be used.
<Reflection sheet>
The reflection sheet 40 is not particularly limited as long as it reflects light emitted from the back surface of the light emitting surface 12 of the light guide 10 and makes it incident on the light guide 10 again. Examples thereof include polyethylene terephthalate (PET), polycarbonate, polystyrene, and polyolefin. Of these, polyethylene terephthalate is preferable. Moreover, it is preferable that the reflection sheet 40 is a white sheet containing a pigment or a fine void. Examples of the pigment include titanium oxide, barium sulfate, calcium carbonate, and magnesium carbonate. Instead of the reflective sheet 40, a reflective layer may be formed on the light guide 10 side surface on the reflective sheet 40 side by metal vapor deposition or the like.

The thickness of the reflection sheet 40 is not specifically limited, For example, it is preferable to determine in the range of 30-300 micrometers.
<LCD panel>
The liquid crystal panel is not particularly limited, and any of an active matrix driving TFT liquid crystal display element and a simple matrix driving STN liquid crystal display element can be used. In the TFT type liquid crystal display element, various active elements such as polysilicon, amorphous silicon, metal insulator, and metal can be used as the element.
<Manufacturing method>
Below, an example of the manufacturing method of the lens sheet 30 is demonstrated.

  First, the light diffusing material 36, the translucent resin 35, and other additives are added to and mixed with the dispersion medium to form a coating liquid, and the coating liquid is applied to one surface of the sheet-like translucent substrate 33. As the dispersion medium, it is preferable to select a dispersion medium having good dispersion of the light diffusing material 36 and good dissolution of the translucent resin 35, and determined according to the type of the light dispersion material 36 and the translucent resin 35. Can do. Examples thereof include methyl ethyl ketone, methyl isobutyl ketone, toluene, ethyl acetate, butyl acetate, isopropyl alcohol, ethanol and the like.

  Although content of the light-diffusion material 36 in the said coating liquid is not specifically limited, It is preferable that it is 2-40 mass%. If it is within the above range, the application of the coating solution and the volatilization of the solvent are good, and the operation becomes easy.

  The coating method of the coating liquid is not particularly limited, and examples thereof include existing coating methods such as a screen printing method, a die coating method, a gravure coating method, a spin coating method, a dip coating method, a bar coating method, and a spray coating method. .

The coating amount of the coating solution may be an amount that can obtain the light diffusion layer 33 having a desired thickness, and is preferably about ² to 100 g / m ² , for example.

  The method for volatilizing the dispersion medium is not particularly limited as long as the performance of the lens sheet 30 is not deteriorated. For example, the dispersion medium can be volatilized by heat treatment at 80 to 180 ° C.

  Next, the lens layer 32 is formed on the surface of the sheet-like translucent substrate 33 opposite to the surface on which the light diffusion layer 34 is formed. The method for forming the lens layer 32 is not particularly limited, and an existing method can be used. For example, a known heat press method or a roll-shaped mold engraved with the shape of a lens array is filled with an active energy ray-curable resin, and then covered with a sheet-like translucent substrate 33 via a resin liquid. The sheet-like translucent base material 33 provided with the lens layer 32 is continuously produced by irradiating the resin layer, the resin liquid is poured into a mold corresponding to the shape of the lens array, and the sheet-form translucent The method of manufacturing the sheet-like translucent base material 33 provided with the lens layer 32 by a batch method by laminating the conductive base material 33 is exemplified.

  In this way, the lens sheet 30 can be obtained. In addition, the manufacturing method of the lens sheet 30 is not limited to the above. For example, after the lens layer 32 is formed on one surface of the sheet-like translucent substrate 33, the lens sheet 30 is formed on the other surface of the sheet-like translucent substrate 33. The light diffusion layer 33 may be formed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, it is not limited to an Example.

The evaluation methods used in the examples are described below.
<All haze (H1 + H2)>
Using a haze meter (trade name: HM-150, manufactured by Murakami Color Research Laboratory), the light diffusion layer was attached so as to face the light receiving side, and the total haze (JIS-K7136) was measured.
<Internal haze (H2)>
After spreading a transparent UV curable resin having a refractive index after curing of 1.52 on the light diffusion layer, there is no easy-adhesion coat of PET film (product name: A4100, manufactured by Toyobo Co., Ltd.) having a thickness of 188 μm Overlay the surface on the UV curable resin, remove the excess resin by rubbing with a rubber roll, cure by irradiating with UV from the PET film side, then release the PET film, UV cured after curing A PET film having a light diffusion layer with a resin thickness of 15 μm and a smooth surface was prepared, and the haze of this film was measured in the same manner as the total haze.
<Ratio of internal haze (H2) to total haze (H1 + H2)>
The internal haze (H2) measured above was obtained by dividing by the total haze (H1 + H2).
<Luminance and half-value angle>
A luminance meter (trade name: BM-7, manufactured by Topcon Co., Ltd.) is placed at a position 50 cm away from the center of the surface light source device in the normal direction without placing the liquid crystal panel on the surface light source device. Was turned on, and the normal luminance and half-value angle were measured using the center of the effective screen as the luminance measurement region.
<Luminance unevenness>
On the lens sheet of the surface light source device, the length of the luminance unevenness from the end of the lens sheet was visually measured. The direction of visual observation was divided into the following two types for evaluation.
(Vertical direction) The maximum length of luminance unevenness that can be confirmed when the line of sight is moved in a direction perpendicular to the direction in which the light source array of the surface light source device is arranged was measured and determined as follows.

Less than 1.0 cm: ○
1.0 cm or more: ×
(Slant direction) The line of sight was moved in the direction other than the vertical direction, and the luminance unevenness of the maximum length that could be confirmed was measured and determined as follows.

Less than 1.5cm: ○
1.5 cm or more: ×
The compounds used in the examples are abbreviated as follows.

Methyl ethyl ketone: MEK
Methyl methacrylate: MMA
Ethyl acrylate: EA
2-Hydroxyethyl methacrylate: HEMA
Acrylic acid: MAA
Azobisisobutyronitrile: AIBN
(Preparation Example 1) Production of translucent resin In a 2 L separable flask of a polymerization reaction vessel, 106 parts by mass of toluene, 71 parts by mass of MEK, 69 parts by mass of MMA, 25 parts by mass of EA, 5 parts by mass of HEMA, and 1 part by mass of MAA were weighed. While stirring with a stirring blade, bubbling with nitrogen was performed for 30 minutes. Thereafter, 0.45 parts by mass of AIBN was added as a radical polymerization initiator, and then the reaction vessel was heated to 90 ° C. and kept in that state for 5 hours. Further, 1 part by mass of AIBN was added and the reaction vessel was held for 4 hours, and then cooled to room temperature to complete the reaction, whereby an acrylic resin A solution was obtained. The molecular weight of the acrylic resin A is MW = 75,100, the hydroxyl value is 21.6 mgKOH / g, the acid value is 2.1 mgKOH / g, Tg is 61 ° C., and the heating residue of the acrylic resin A solution is 36.0% by mass. there were.

Example 1
A lens sheet, a surface light source device, and a liquid crystal display device similar to those shown in FIGS. 2 to 3 were produced as follows.

  As the sheet-like translucent substrate, a PET film having a thickness of 75 μm (manufactured by Toyobo Co., Ltd., trade name: Cosmo Shine A4300) was used.

  Acrylic resin A having a refractive index of 1.49 obtained in Preparation Example 1, resin fine particles having a refractive index of 1.49 and a volume average particle diameter of 5 μm as a light diffusing material (Techpolymer SSX-105, manufactured by Sekisui Plastics Co., Ltd.) And resin fine particles having a refractive index of 1.49 and a volume average particle diameter of 8 μm (manufactured by Sekisui Plastics Co., Ltd., Techpolymer SSX-108), Duranate TPA-100 (manufactured by Asahi Kasei Chemicals Co., Ltd.) as a crosslinking agent, and a diluent solvent MEK and toluene were weighed in a container and stirred with a stirring blade to prepare a coating liquid A for forming a light diffusion layer in which the light diffusion material was uniformly dispersed.

  Using the reverse gravure coating method, the coating liquid A was applied onto the PET film so that the average thickness after solvent drying was 7 μm and dried. Thereby, the laminated body A which has a light-diffusion layer in the single side | surface of PET film was obtained.

  The appearance of the obtained laminate A was very good with no generation of coating spots such as streaks. Regarding the light diffusion layer, the total haze (H1 + H2) was 32.0%, and the ratio of the internal haze (H2) to the total haze (H1 + H2) was 5.9%. The results are shown in Table 2.

  On the other hand, a shape transfer surface corresponding to the shape of the prism row forming surface was formed on the surface of three types of JIS brass thin plates having a thickness of 1.0 mm and 400 mm × 690 mm to obtain a mold member. Here, the target prism array forming surface has a shape in which a large number of prism arrays having a pitch P = 50 μm and an apex angle of 65 ° are arranged in parallel.

  Next, a stainless steel cylindrical roll having a diameter of 220 mm and a length of 450 mm was prepared, and a mold member was wound around and fixed to the outer peripheral surface to obtain a roll-shaped mold (roll mold). The laminate A was supplied along the roll mold between the roll mold and the rubber roll, and the sheet-like translucent substrate was nipped between the rubber roll and the roll mold by a pneumatic cylinder connected to the rubber roll.

  The viscosity was adjusted to 300 mPa · S / 25 ° C. using an ultraviolet curable composition having the following composition.

Phenoxyethyl acrylate (Biscoat # 192, manufactured by Osaka Organic Chemical Industry Co., Ltd.): 50 parts by mass Bisphenol A-diepoxy-acrylate (epoxy ester 3000A, manufactured by Kyoeisha Chemical Co., Ltd.): 50 parts by mass 2-hydroxy-2-methyl-1 -Phenyl-propan-1-one (Darocur 1173, manufactured by Ciba Geigy Corporation of Japan): 1.5 parts by mass
This ultraviolet curable composition was supplied to the surface of the sheet-like translucent base material niped into a roll mold by a rubber roll, on the side opposite to the surface provided with the light diffusion layer. While rotating the roll mold, the ultraviolet curable composition is sandwiched between the roll mold and the sheet-like translucent substrate and irradiated with ultraviolet rays from an ultraviolet irradiation device to polymerize and cure the ultraviolet curable composition. The prism array pattern on the roll-shaped shape transfer surface was transferred. Then, it released from the roll type | mold and the prism sheet A was obtained.

  The obtained prism sheet is cut into a 11.1 inch W (wide) size, and this is shown in FIG. 3 on the light exit surface of a 11.1 W inch (wide) size light guide having a light source disposed on the side surface. As described above, the surface of the prism array was placed so as to face the resinous light guide, and the other side surface and back surface were covered with a reflection sheet to obtain a surface light source device. The light incident surface of the light guide has a thickness of 0.75 m, and the light guide has a thickness of 0.60 mm on the light exit surface. That is, the height of the stepped portion is 0.163 mm. The step portion has a stepped shape with a width of 2.5 mm in which 25 steps with a height of 0.0065 mm and a width of 0.1 mm are formed at equal intervals.

  The obtained surface light source device was evaluated for luminance, half-value angle, and luminance unevenness in accordance with the above evaluation method, and the results are shown in Table 2.

(Comparative Example 1)
A laminate B was prepared in the same manner as in Example 1 except that a 125 μm thick PET film (manufactured by Toyobo Co., Ltd., trade name: Cosmo Shine A4300) was used as the sheet-like translucent substrate. In the same manner as in Example 1, a prism sheet B was obtained using a mold member having a pitch P = 50 μm. The luminance, half-value angle, and luminance unevenness were evaluated, and the results are shown in Table 2.

(Example 2)
In Example 1, the lens array is formed on the surface opposite to the light diffusion layer of the layered product A in the same manner as in Example 1, except that the mold member for forming the prism array uses a mold member having a pitch P = 18 μm. The prism sheet C was obtained. The luminance, half-value angle, and luminance unevenness were evaluated, and the results are shown in Table 2.

(Example 3)
A laminate C was prepared in the same manner as in Example 2 except that a 50 μm thick PET film (manufactured by Toyobo Co., Ltd., trade name: Cosmo Shine A4300) was used as the sheet-like translucent substrate. In the same manner as in Example 2, a prism sheet D was obtained using a mold member having a pitch P = 18 μm. The luminance, half-value angle, and luminance unevenness were evaluated, and the results are shown in Table 2.

(Comparative Example 2)
Polyester resin solution with a refractive index of 1.55 (trade name: Byron 20S, manufactured by Toyobo Co., Ltd.) as a translucent resin, and resin fine particles (Sekisui Plastics) with a refractive index of 1.49 and a volume average particle size of 5 μm as a light diffusing material Industrial Co., Ltd., Techpolymer SSX-105), and resin fine particles having a refractive index of 1.49 and a volume average particle diameter of 8 μm (manufactured by Sekisui Plastics Co., Ltd., Techpolymer SSX-108), Takenate D-110N as a crosslinking agent (Mitsui Chemical Polyurethane Co., Ltd.), MEK and toluene as diluent solvents are weighed in a container and stirred with a stirring blade to form a light diffusing layer in which the light diffusing material is uniformly dispersed. A coating liquid B was prepared.

  A laminate D was prepared in the same manner as in Example 1 using a 125 μm-thick PET film (trade name: Cosmo Shine A4300, manufactured by Toyobo Co., Ltd.) as the sheet-like translucent substrate. Similarly, a prism sheet E was obtained using a mold member having a pitch P = 50 μm. The luminance, half-value angle, and luminance unevenness were evaluated, and the results are shown in Table 2.

As shown in Table 2, in Examples 1 to 3, in which the ratio of the internal haze to the total haze of the light diffusion layer is 50% or less and the thickness of the sheet-like translucent substrate is 75 μm or less, the luminance unevenness The length of can be reduced to a range where there is no problem. Furthermore, since the luminance was maintained at 11572 cd / m ² or more and the half-value angle was 18.4 ° or more, the luminance necessary for the liquid crystal display device was maintained and a wide viewing angle was obtained. understood.

  On the other hand, in Comparative Example 1 using a sheet-like translucent substrate having a thickness of 125 μm, the length of the luminance unevenness is large, and also within the effective screen of the liquid crystal display device manufactured by mounting the liquid crystal panel on the surface light source device. The brightness unevenness was visually recognized, and the quality of the liquid crystal screen was not good.

Further, in Comparative Example 2 using the light diffusion layer in which the ratio of the internal haze to the total haze exceeds 50%, although the luminance unevenness and the half-value angle are not a problem, the luminance is 11353 cd / m ² , which is approximately that of Examples 1 to 3. Reduced by 200 cd / m ² .

DESCRIPTION OF SYMBOLS 10 Light guide 11 Light incident surface 12 Light output surface 13 Step part 20 Light source 21 Light source reflection sheet 30 Lens sheet 31 End part 32 Lens layer 33 Sheet-like translucent base material 34 Light diffusion layer 35 Translucent resin 36 Light Diffuser 40 Reflective sheet

Claims (5)

A primary light source composed of a plurality of point light sources;
A light guide having at least one light incident surface facing the primary light source, and a light emitting surface that is substantially orthogonal to the light incident surface and from which light incident from the light incident surface is emitted;
A lens layer in which a plurality of lens rows are arranged substantially in parallel is formed on the first surface of the sheet-like translucent substrate, and a light diffusion layer is formed on the second surface of the sheet-like translucent substrate. A surface light source device having a lens sheet,
In the light guide, the thickness of the light guide on the light incident surface is larger than the thickness of the light guide on the light output surface, and the light guide is between the light incident surface and the light output surface. Has a stepped portion that gradually decreases in thickness,
In the lens sheet, the light exit surface of the light guide and the lens layer of the lens sheet are arranged to face each other, and the total haze of the light diffusion layer is 5% or more and 60% or less, A surface light source device, wherein the ratio of internal haze to total haze is 50% or less, and the thickness of the sheet-like translucent substrate is 100 μm or less. The surface light source device according to claim 1, wherein a pitch of the lens rows is 20 μm or less. The light diffusing layer contains a light diffusing material in a translucent resin, and the content of the light diffusing material in the translucent resin is from 1% by mass to 20% by mass. The surface light source device according to claim 1, wherein the surface light source device is a feature. 4. The light diffusing material according to claim 3, wherein the light diffusing material has an average particle diameter of 1 μm or more and 20 μm or less, and a refractive index difference from the translucent resin of 0.00 or more and 0.06 or less. Surface light source device. A liquid crystal display device comprising the surface light source device according to claim 1.