JP6536490B2 - Transparent light guide plate and light reflecting sheet used therefor - Google Patents

Description

  The present invention relates to a transparent light guide plate and a light reflecting sheet used for the same. The transparent light guide plate of the present invention can be applied to, for example, a surface light source of a transmissive display device.

  As a transmissive display device, for example, the one disclosed in Patent Document 1 below is known. In the transmissive display device of Patent Document 1, a surface light source is used as a backlight.

  Here, for example, the surface light source supplies light to a liquid crystal plate or the like by emitting light incident from the side surface of the light guide plate in the thickness direction of the light guide plate. By using a surface light source as a back light, it is possible to reduce the thickness of the transmissive display device as compared to the case of using a fluorescent lamp, an LED array or the like.

  As a surface light source, for example, the one disclosed in Patent Document 2 below is known. In Patent Document 2, a large number of light-reflecting projections (light-reflecting dots in Cited Document 2) are formed on the back surface of the light guide plate using an inkjet printing technique. Then, the light incident from the side surface of the light guide plate is scattered in the light guide plate and a part thereof reaches the inner spherical surface of the light reflecting protrusion and is reflected to obtain the light emitted in the thickness direction of the light guide plate (Refer to FIG. 1 etc. of cited reference 2).

International Publication No. 2014/010585 JP, 2015-76124, A

  However, when forming a light reflection protrusion using an inkjet printing technique, it is difficult to control the diameter and pitch of this light reflection protrusion with high precision. For this reason, it has been difficult to manufacture a surface light source with a sufficiently uniform light quantity with high yield depending on the technique of Patent Document 2.

  Moreover, when using inkjet printing technology, the diameter of a light reflection protrusion can not be made small enough. For this reason, the conventional light guide plate has a drawback that it is difficult to obtain sufficient light quantity while the light reflecting projections can be visually recognized.

  Furthermore, in the case of using the inkjet printing technology, there is a disadvantage that the light reflecting protrusion is easily peeled off from the light guide plate. In particular, when the light guide plate is curved in order to create a transmissive display device having a curved display screen, a part of the light reflection protrusions peel off from the light guide plate, and a surface light source with a sufficiently uniform light amount. Can not get. Furthermore, it is also difficult to clean the surface of the light guide plate because the light reflecting projections are easily peeled off.

  An object of the present invention is to provide a light guide plate in which the uniformity of the emitted light amount is sufficiently high, the light reflecting protrusion is difficult to visually recognize, and the light reflecting protrusion is hardly peeled off.

  In order to solve such problems, the transparent light guide plate according to the invention of claim 1 reflects at least a portion of the light incident on the side surface from the light source by the inner spherical surface of the plurality of light reflecting projections provided on the back surface. A transparent light guide plate for emitting light from the surface and having a flat plate shape, and the light reflecting protrusion is formed by embossing and the forming surface of the light reflecting protrusion is And a flat-plate shaped light reflecting member attached to the back surface of the light guide substrate so as to be the outer side.

  In the invention according to claim 2, in addition to the configuration according to claim 1, the light reflecting member includes a plurality of light transmitting layers laminated on the back surface side of the light guide substrate, and the plurality of light transmitting members The outermost layer of the layers is a light reflecting layer in which the light reflecting protrusion is formed, and the light reflecting layer has a refractive index higher than that of the light transmitting layer in direct contact.

In the invention according to claim 3, in addition to the configuration according to claim 2, the plurality of light transmitting layers use a polyethylene terephthalate layer attached to the back surface of the light guide substrate and an ultraviolet curable resin. characterized in that it comprises a said light reflecting layer which is formed directly on the polyethylene terephthalate La over coat layer on.

  The invention according to claim 4 is characterized in that, in addition to the configuration according to any one of claims 1 to 3, the light guide substrate and the light reflection member have flexibility.

  The invention according to claim 5 is characterized in that, in addition to the configuration according to any one of claims 1 to 4, part of the light incident on the side surface from the light source is emitted from the back surface.

The light reflecting sheet according to the invention of claim 6 is a light reflecting sheet used as a light reflecting member constituting the transparent light guide plate according to any one of claims 1 to 5, and is formed in a flat plate shape and is embossed A light reflecting protrusion is formed by processing, and the light reflecting protrusion is attached to the back surface of the light guiding substrate so that the formation surface of the light reflecting protrusion is on the outside, and from the light source to the side surface of the transparent light guiding plate At least a part of the incident light is reflected by the inner spherical surface of the plurality of light reflecting protrusions attached to the back surface of the light guide substrate and emitted from the surface of the transparent light guide plate It is characterized in that it is configured .

  According to the first aspect of the invention, since the light reflecting protrusion is formed on the light reflecting member by embossing, it is easy to control the diameter and the pitch of the light reflecting protrusion with high accuracy.

  Further, by using embossing, it is possible to make the diameter of the light reflecting protrusion extremely small.

  Furthermore, the light reflecting protrusion can be made difficult to peel off by using embossing.

  According to the invention of claim 2, when the light reflecting member is formed by laminating a plurality of light transmitting layers, the refractive index of the light reflecting layer which is the outermost layer is larger than the refractive index of the light transmitting layer in direct contact. Because of this, it is possible to increase the amount of light that the transparent light guide plate irradiates the surface to be irradiated with.

  According to the invention of claim 3, since the light reflecting member is a laminate of the polyethylene terephthalate layer and the ultraviolet curable resin layer, it is possible to obtain a light reflecting member which has high durability, is easy to process, and is inexpensive.

  According to the invention of claim 4, by making the light guide substrate and the light reflecting member flexible, it becomes possible to use the transparent light guide plate of the transmissive display apparatus having a curved display screen.

According to the invention of claim 5, the transparent display device according to the invention is of a type in which the display screen and the background are superimposed and displayed by emitting a part of the light incident on the side surface from the light source from the back surface. the light guide plate may be used.

  According to the invention of claim 6, it is possible to obtain the light reflecting member for the transparent light guide plate according to the present invention.

It is sectional drawing which shows notionally the structure of the transparent light-guide plate which concerns on Embodiment 1 of this invention. It is a top view which shows notionally the structure of the transparent light guide plate which concerns on the said Embodiment 1. FIG. It is a conceptual fragmentary sectional view for demonstrating the principle of the transparent light guide plate which concerns on the said Embodiment 1. FIG. It is a conceptual top view for demonstrating the manufacturing method of the transparent light guide plate which concerns on the said Embodiment 1. FIG.

  Hereinafter, Embodiment 1 of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing the structure of the transparent light guide plate according to the first embodiment.

  As shown in FIG. 1, the transparent light guide plate 100 includes a light guide substrate 110, an adhesive layer 120, and a light reflection member 130.

  The light guide substrate 110 is a plate-like substrate having translucency. As the light guide substrate 110, a flat plate having a rectangular plan view is used. The light guide substrate 110 may be a plate having rigidity or a sheet having flexibility. As a forming material of the light guide substrate 110, for example, acrylic is preferable, but other materials may be used. The planar dimensions of the light guide substrate 110 are arbitrary, and may be determined according to the screen dimensions and the like of the transmissive display device to be used. Further, the thickness of the light guide substrate 110 is also optional, for example, about 2 mm. In the first embodiment, the refractive index n0 of the light guide substrate 110 is set to 1.49.

  As the adhesive layer 120, for example, a transparent optical adhesive film (Optical Clear Adhesive Film (OCA)) can be used. However, other types of adhesive sheets, adhesives and the like may be used as long as they have sufficient transparency and adhesion performance. The thickness of the adhesive layer 120 is, for example, 0.1 mm. In the first embodiment, the refractive index n1 of the adhesive layer 120 is set to 1.4857.

  The light reflecting member 130 is attached to the back surface of the light guide substrate 110 using the adhesive layer 120. As the light reflection member 130, for example, a flat plate having a plane dimension substantially the same as that of the light guide substrate 110 is used. The light reflecting member 130 may be a rigid plate or a flexible sheet (corresponding to the light reflecting sheet of the present invention).

  The light reflecting member 130 may have a single layer structure or a multilayer structure. In the example of FIG. 1, the light reflecting member 130 is formed by laminating the base layer 131 and the light reflecting layer 132. Each of the layers 131 and 132 is a light transmitting layer.

  Here, as a forming material of the base layer 131, for example, PET (that is, polyethylene terephthalate) can be used, but it may be formed of other materials. In the first embodiment, the refractive index n2 of the base layer 131 is set to 1.48. The thickness of the base layer 131 is, for example, 0.05 mm. Since the color temperature of the emitted light tends to increase as the base layer 131 becomes thicker, it is desirable to make the base layer 131 as thin as possible within the range where the durability and the like of the light reflection member 130 can be secured.

  For example, an ultraviolet curing resin can be used as the light reflecting layer 132, but it may be formed of another material. In the first embodiment, the refractive index n3 of the light reflecting layer 132 is set to 1.5785. The thickness of the light reflection layer 132 is, for example, 0.012 mm.

  A large number of light reflecting protrusions 132 b are formed on the side of the outer surface 132 a of the light reflecting layer 132.

  The light reflecting protrusion 132b desirably has a spherical shape. With such a shape, the inner spherical surface of the light reflecting protrusion 132b acts as a concave mirror to reflect a part of the light inserted from the light guiding substrate 110 into the light reflecting member 130, and the light guiding base It can be led to the surface side of the material 110.

  The dimensions of the light reflecting protrusion 132b are, for example, a diameter of 30 to 60 μm and a height of 3 to 5 μm (desirably 3.3 to 4.67 μm).

  As shown in the plan view of FIG. 2, these light reflecting projections 132 b are formed on the outer surface 132 a of the light reflecting layer 132 in the x and y directions (that is, the longitudinal and lateral directions of the light reflecting member 130) orthogonal to each other. It is arranged according to a predetermined arrangement pattern at a predetermined pitch in a two-dimensional direction along. In the example of FIG. 2, although the light reflection protrusion 132b is arrange | positioned at zigzag form, it may be normal matrix form. In FIG. 2, the pitch A in the vertical and horizontal directions is, for example, 0.16 to 0.24 mm, and the pitch B in the oblique direction is, for example, 0.11 to 0.17 mm. In addition, although the angles θa, θb, and θc of the triangle formed by the three adjacent light reflection protrusions 132b are arbitrary, in the first embodiment, θa = θb = θc = 60 ° (that is, an equilateral triangle). .

  Next, the optical principle of the transparent light guide plate 100 according to the first embodiment will be described with reference to a conceptual partial cross-sectional view of FIG.

  As shown in FIG. 3, light is incident on the transparent light guide plate 100 in the direction parallel to the front and back surfaces of the transparent light guide plate 100 from the side surface thereof. As described above, for example, a white LED (not shown) or the like is used as a light source of this light.

  Part of the light incident on the transparent light guide plate 100 reaches the interface 301 between the light guide substrate 110 and the adhesive layer 120. Then, part of the light is reflected at the boundary surface 301, and the remaining light is refracted to be incident on the adhesive layer 120.

  The light incident on the adhesive layer 120 reaches the interface 302 between the adhesive layer 120 and the base layer 131. Then, part of the light is reflected at the boundary surface 302, and the remaining light is refracted to be incident on the base layer 131.

  Furthermore, light incident on the base layer 131 reaches the interface 303 between the base layer 131 and the light reflection layer 132. Then, part of the light is reflected at the boundary surface 303, and the remaining light is refracted and is incident on the light reflection layer 132.

  Then, part of the light incident on the light reflecting layer 132 reaches the light reflecting protrusion 132 b and is reflected by the light reflecting protrusion 132 b.

  The light reflected by the light reflecting protrusion 132 b reaches the boundary surface 303, a part of which is reflected, and the rest is refracted and incident on the base layer 131.

  The light incident on the base layer 131 reaches the interface 302 and is partially reflected, and the rest is refracted and incident on the adhesive layer 120.

  Furthermore, the light incident on the adhesive layer 120 reaches the interface 301, a part of which is reflected, and the rest is refracted to be incident on the light guide substrate 110.

  Then, part of the light incident on the light guide substrate 110 is emitted from the surface of the light guide substrate 110 (lower side surface in FIG. 3).

  Here, as is well known, when light reaches from substance A (refraction index is na) to substance B (refraction index is nb), the reflectance R at the interface is expressed by the following formula (1) Given by (in the case of normal incidence).

R = (na-nb) ² / (na + nb) ² (1)
As this equation (1) shows, the smaller the difference between the refractive indices na and nb of the substances A and B, the smaller the reflectance R and hence the higher the transmittance of the light reaching the substance B from the substance A.

  In the first embodiment, as described above, the refractive index n0 of the light guide substrate 110 is 1.49, the refractive index n1 of the adhesive layer 120 is 1.4857, and the refractive index n2 of the base layer 131 is 1.48. The refractive index n3 of the light reflecting layer 132 is 1.5785.

  That is, in the first embodiment, the difference (0.0043) between the refractive index n0 of the light guide substrate 110 and the refractive index n1 of the adhesive layer 120 and the refractive index n1 of the adhesive layer 120 and the refractive index n2 of the base layer 131 The light transmittance is high at the boundary surfaces 301 and 302 of the respective portions 110, 120, and 131 because the difference (0.0057) between them is small. Therefore, much of the light incident from the side surface of the light guide substrate 110 reaches the base layer 131.

  On the other hand, the difference between the refractive index n3 of the light reflection layer 132 and the refractive index n2 of the base layer 131 (n3-n2 = 0.0985 is large, and hence the transmittance of light reaching the boundary surface 303 from the base layer 131 side) Is smaller than in the case of the boundary surfaces 301 and 302 (thus, the reflectance is larger than in the case of the boundary surfaces 301 and 302).

  On the other hand, since n3> n2, total reflection of light reaching the interface 303 from the base layer 131 does not occur.

  Therefore, a sufficient amount of light can be guided from the base layer 131 into the light reflecting layer 132.

  Here, as is well known, the larger the incident angle θ1 when the boundary surface 303 is reached, the higher the light reflectance. Therefore, a large amount of light having a small incident angle θ1 (that is, light having a small angle with respect to the thickness direction of the transparent light guide plate 100) is incident on the light reflecting layer 132.

  As described above, part of the light incident on the light reflecting layer 132 is reflected by the light reflecting protrusion 132 b. As described above, the refractive index n3 of the light reflecting layer 132 is 1.5785, which is sufficiently larger than the refractive index of the outside (usually air) of the light reflecting layer 132. The amount of light to be emitted is sufficiently large (see the above equation (1)).

  Then, the light reflected in the light reflection layer 132 reaches the boundary surface 303 again. As described above, the larger the incident angle when the boundary surface 303 is reached, the higher the light reflectance. Furthermore, since this light is light entering from a medium having a high refractive index (light reflection layer 132) to a low medium (base layer 131), total reflection is obtained for light having an incident angle θ2 larger than a predetermined value. Occur. Therefore, a large amount of light having a small incident angle θ2 (that is, light having a small angle with respect to the thickness direction of the transparent light guide plate 100) is incident on the base layer 131.

  At this time, a part of the light reflected by the boundary surface 303 is scattered in the light reflection layer 132 and is incident on the base layer 131 as light having a small incident angle θ2 to the boundary surface 303. Become.

  As described above, part of the light incident on the base layer 131 is transmitted through the adhesive layer 120 and the light guide substrate 110 and emitted from the surface of the light guide substrate 110 (the lower surface in FIG. 3). . As described above, since the difference (n2−n1) in the refractive index between the base layer 131 and the adhesive layer 120 and the difference (n0−n1) in the refractive index between the adhesive layer 120 and the light guide substrate 110 are small, The transmittance of is sufficiently large.

  As described above, in the first embodiment, the light reflection member 130 is configured such that the refractive index of the upper layer (that is, the light reflection layer 132) is higher. Therefore, the light reflection member 130 in the thickness direction of the transparent light guide plate 100 A large amount of light with a small angle can be extracted, which can enhance the directivity of the emitted light, and therefore the amount of light emitted from the surface to be irradiated (for example, the liquid crystal panel of the transmissive display device) can be increased.

  Next, a method of manufacturing the transparent light guide plate 100 according to the first embodiment will be described.

  First, the sheet-like light reflecting member 130 is manufactured as follows.

  First, a liquid ultraviolet curable resin is applied to the back surface of the base layer 131 (for example, PET).

  Next, the light reflection protrusion 132b is formed on the ultraviolet curable resin by embossing. The method of embossing is not limited, and a direct pressing method may be used in which a flat plate is pressed against the ultraviolet curable resin. However, in order to produce the large-area light reflecting member 130, a rotating roller type is used. It is desirable to use the roller transfer method used.

  Subsequently, the ultraviolet curable resin is cured by irradiating it with ultraviolet light.

  Thereafter, the light reflecting member 130 is cut into a desired size. The size of the light reflecting member 130 is determined based on the size of the light receiving surface (for example, the liquid crystal panel of the transmissive display device).

  Thus, the sheet-like light reflecting member 130 is completed.

  Next, the step of attaching the light reflection member 130 to the light guide substrate 110 is performed as follows.

  First, the adhesive layer 120 is formed on the back surface of the light guide substrate 110. As described above, the method of forming the adhesive layer 120 may be a method of attaching a transparent optical adhesive film (OCA), or a method of applying a liquid adhesive or the like to the back surface of the light guide substrate 110 It may be.

  Thereafter, the sheet-like light reflecting member 130 is attached to the back surface of the adhesive layer 120. At this time, as shown in the conceptual plan view of FIG. 4, the light reflection member 130 may be attached to the light guide substrate 110 in an inclined manner.

  For example, when the light reflecting member 130 is pasted so that the vertical and horizontal arrangement direction of the light reflecting projections 132b and the vertical and horizontal side surfaces of the light guide substrate 110 become parallel, the pitch and arrangement pattern of the light reflecting projections 132b In some cases, stripe-like luminance unevenness may occur in the light emitted from the transparent light guide plate 100 to cause deterioration of the image quality of the surface to be irradiated (for example, the liquid crystal panel of the transmissive display device).

  On the other hand, according to the study of the inventors of the present application, the light reflecting member 130 is attached to the transparent light guide plate 100 in an inclined manner so that the arrangement direction of the light reflecting projections 132b is the light incident direction. And the liquid crystal panel is inclined with respect to the alignment direction of the liquid crystal elements, which makes it possible to suppress or prevent such image quality deterioration.

  The inclination angle is, for example, about 3 to 5 °, although it varies depending on the pitch of the light reflection protrusions 132b, the arrangement pattern, and the like.

  Note that the light reflecting protrusion 132b may be formed so as to be inclined with respect to the vertical and horizontal side surfaces of the light reflecting member 130, instead of attaching the light reflecting member 130 so as to be inclined.

  As described above, according to the first embodiment, since the light reflecting projection 132b is formed on the light reflecting member 130 by embossing, the diameter and the pitch of the light reflecting projection 132b can be made with high accuracy. It becomes easy to control.

  Further, by using embossing, it is possible to make the diameter of the light reflecting protrusion 132 b very small.

  Furthermore, the light reflecting protrusion 132b can be made difficult to peel off by using embossing.

  In addition, the base layer 131 and the light reflecting layer 132 are stacked to constitute the light reflecting member 130 and the refractive index of the light reflecting layer 132 is made larger than the refractive index of the base layer 131. Can increase the amount of light irradiating the surface to be irradiated.

  According to the first embodiment, since the base layer 131 is formed of PET and the light reflecting layer 132 is formed of an ultraviolet curable resin, it is possible to obtain a light reflecting member having high durability, easy to process, and inexpensive. it can.

  According to the first embodiment, by making the light guide substrate 110 and the light reflection member 130 flexible, it becomes possible to use the display screen as a transparent light guide plate of a transmissive display apparatus having a curved surface.

  In the first embodiment, the case where the transparent light guide plate 100 according to the present invention is used for a liquid crystal display or the like is described as an example, but a part of the incident light is emitted from the back to display the screen and the background. It is also possible to use it for the transmissive display apparatus of the type which displays in piles. In this case, light transmitted through the light reflecting member 130 and reflected by the object on the back side is transmitted through the light reflecting member 130, the adhesive layer 120, and the light guide substrate 110.

100 Transparent light guide plate 110 Light guide substrate 120 Adhesive layer 130 Light reflecting member 131 Base layer 132 Light reflecting layer 132 a Outer surface 132 b Light reflecting protrusion 301 to 303 Boundary surface

Claims (6)

A transparent light guide plate for reflecting at least a part of light incident on the side surface from a light source by the inner spherical surface of a plurality of light reflecting projections provided on the back surface, and for emitting the light from the surface,
A translucent light guide substrate having a flat plate shape;
A flat-plate shaped light reflecting member which is pasted on the back surface of the light guide substrate such that the light reflecting protrusion is formed by embossing and the formation surface of the light reflecting protrusion is on the outside;
A transparent light guide plate comprising: The light reflecting member includes a plurality of light transmitting layers laminated on the back surface side of the light guide substrate,
The outermost layer of the plurality of light transmitting layers is a light reflecting layer in which the light reflecting protrusion is formed,
The light reflecting layer has a refractive index higher than that of the light transmitting layer in direct contact therewith,
The transparent light guide plate according to claim 1, Wherein the plurality of light-transmitting layer comprises a polyethylene terephthalate layer to be affixed to the bottom of the light guide substrate, the light-reflecting layer which is formed directly on the polyethylene terephthalate La over preparative layer using an ultraviolet curable resin The transparent light guide plate according to claim 2, characterized in that   The said light guide base material and the said light reflection member have flexibility, The transparent light guide plate in any one of the Claims 1 thru | or 3 characterized by the above-mentioned.   The transparent light guide plate according to any one of claims 1 to 4, wherein a part of the light incident on the side surface from the light source is emitted from the back surface. It is a light reflection sheet used as a light reflection member which constitutes a transparent light guide plate according to any one of claims 1 to 5 ,
It is formed in a flat plate shape, and a light reflection protrusion is formed by embossing, and is configured to be attached to the back surface of the light guide substrate such that the formation surface of the light reflection protrusion is on the outside.
At least a portion of the light incident from the light source to the side surface of the transparent light guide plate is reflected by the inner spherical surface of the plurality of light reflecting projections attached and provided on the back surface of the light guide substrate, the transparent A light reflecting sheet characterized in that the light is emitted from the surface of the light guide plate .

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