JP2017091892A - Light guide sheet, edge light type backlight unit and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide sheet in which utilization efficiency of light rays is high and which can suppress luminance unevenness when using an edge light type backlight unit having an LED light source.SOLUTION: A light guide sheet is a substantially rectangular light guide sheet for LED light source having an incident end surface where light rays enter and an opposite end surface. The opposite end surface includes one or a plurality of first reflection surfaces inclining to one side, and one or a plurality of second reflection surfaces inclining to the other side, based on a virtual surface substantially in parallel with the incident end face. It is preferable that the opposite end surface alternately includes a first reflection surface group in which the plurality of first reflection surfaces continue, and a second reflection surface group in which the plurality of second reflection surfaces continue. It is preferable that the first reflection surface group and the second reflection surface group adjacent to it constitute a linear Fresnel lens in which the axial direction is the thickness direction. It is preferable that a focal distance of the linear Fresnel lens substantially coincides with an average interval of the incident end surfaces and the opposite end surfaces.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a light guide sheet, an edge light type backlight unit, and a liquid crystal display device.

  A known liquid crystal display device includes a liquid crystal panel and an edge light type backlight unit disposed on the back side of the liquid crystal panel (see Japanese Patent Application Laid-Open No. 2015-173131). As shown in FIG. 16, the edge light side backlight unit includes a substantially rectangular light guide sheet 102 having an incident end face, and a plurality of LED light sources 103 arranged along the incident end face of the light guide sheet 102. Have.

  In the edge light type backlight unit 101, a light beam from the LED light source 103 is incident on the light guide sheet 102 from an incident end surface, and the light beam incident on the light guide sheet 102 propagates in the light guide sheet 102. Further, a part of the light beam propagating in the light guide sheet 102 is emitted from the surface of the light guide sheet 102 toward the liquid crystal panel.

See JP2015-173131A

  In recent years, the brightness of LED light sources has been improved, and when such a high-brightness LED light source is used in a conventional edge light type backlight unit, the light use efficiency is not sufficient, and luminance unevenness occurs. The inventor found out. The light emitted from the high-luminance LED light source has high directivity. For this reason, among the light rays propagating in the light guide sheet, the amount emitted from the surface of the light guide sheet is small, and the amount reaching the end face (opposing end face) on the opposite side of the incident end face increases, and reaches this opposing end face. A part of the light beam is emitted from the light guide sheet as it is and becomes stray light. As a result, it is considered that the light beam utilization efficiency is lowered. In addition, since a part of the light beam that has reached the opposite end surface of the light guide sheet is reflected in a random direction, the amount of light beam that propagates in the region near the light output axis of the LED light source of the light guide sheet is relatively large. Although a large amount of light is emitted from the surface of the light guide sheet, there are portions where the amount of light propagating is small in other regions, particularly in the region between the light output axes of the plurality of LED light sources. In a portion where the amount is small, the amount of light emitted from the surface of the light guide sheet is small, and this portion is considered to be a dark spot.

  The present invention has been made in view of such circumstances, and an object of the present invention is to have high light utilization efficiency and suppress uneven brightness when used in an edge light type backlight unit having an LED light source. It is in providing the light guide sheet which can do. Another object of the present invention is to provide an edge-light type backlight unit and a liquid crystal display device in which the light use efficiency is high and luminance unevenness is suppressed.

  The light guide sheet according to the present invention, which has been made to solve the above problems, is a light guide sheet for an LED light source having an incident end face on which light is incident and an opposing end face, and the opposing end face is an incident end face. 1 or a plurality of first reflecting surfaces inclined to one side and one or a plurality of second reflecting surfaces inclined to the other side.

  In the light guide sheet, a light beam from the LED light source is incident from an incident end face, the incident light beam propagates in the light guide sheet, and a part of the light beam propagated in the light guide sheet is emitted from the surface. The Since the light guide sheet includes a first reflection surface and a second reflection surface that are inclined with respect to a virtual plane substantially parallel to the incident end surface at the opposite end surface, the light guide sheet is incident from the incident end surface and propagates through the light guide sheet. Since the light beam that has reached up to is reflected in the light guide sheet by the first reflection surface and the second reflection surface, the utilization efficiency of the light beam can be improved. Further, the light reflected by the first reflecting surface and the second reflecting surface propagates in a region other than the region in the vicinity of the light output axis of the LED light source (hereinafter also referred to as “region outside the light output axis”), thereby guiding the light. The sheet can secure the amount of light emitted in the region outside the light output axis, and can suppress the occurrence of dark spots.

  It is preferable that the opposing end surface includes alternately a first reflection surface group in which a plurality of the first reflection surfaces are continuous and a second reflection surface group in which the plurality of the second reflection surfaces are continuous. Thus, by providing the first reflecting surface group and the second reflecting surface group alternately, it is easy to reflect the light beam to the off-axis region by each of the first reflecting surface group and the second reflecting surface group. Thereby, the occurrence of dark spots can be effectively suppressed, so that the effect of suppressing luminance unevenness is enhanced.

  The first reflective surface group and the second reflective surface group adjacent thereto may constitute a linear Fresnel lens whose axial direction is the thickness direction. As described above, the first reflecting surface group and the second reflecting surface group adjacent to the first reflecting surface group constitute a linear Fresnel lens, so that the light beams reflected by the first reflecting surface group and the second reflecting surface group can be appropriately moderated. The light can be condensed or diffused, and the generation of dark spots can be further effectively suppressed.

  The first reflecting surface group and the second reflecting surface group adjacent to the first reflecting surface group may constitute a Fresnel lens whose center is located at the middle point in the thickness direction. As described above, the first reflecting surface group and the second reflecting surface group adjacent to the first reflecting surface group constitute a Fresnel lens, so that the light beams reflected by the first reflecting surface group and the second reflecting surface group are collected appropriately. Light or diffusion can be achieved, and the generation of dark spots can be more effectively suppressed. Moreover, according to this structure, since a light beam is easily reflected in the surface direction or a back surface direction, it is easy to emit a light beam from the surface side.

  The focal length of the linear Fresnel lens or the Fresnel lens may be substantially equal to the average distance between the incident end surface and the opposed end surface. Thus, by making the focal length substantially coincide with the average interval between the incident end face and the opposed end face, the generation of dark spots near the incident end face can be more reliably suppressed.

  It is good to further provide the white pigment layer or metal vapor deposition layer laminated | stacked on the said opposing end surface. Thus, the reflective property of a reflective surface can be improved by providing the white pigment layer or metal vapor deposition layer laminated | stacked on the said opposing end surface.

  As arithmetic mean roughness Ra of a 1st reflective surface and a 2nd reflective surface, 0.04 micrometer or more and 0.3 micrometer or less are preferable. As described above, by setting the arithmetic average roughness Ra of the first reflecting surface and the second reflecting surface within the above range, the reflected light reflected by the first reflecting surface and the second reflecting surface can be appropriately scattered. Therefore, the effect of suppressing the occurrence of dark spots can be improved.

  An edge light type backlight unit according to the present invention, which has been made to solve the above-mentioned problems, is disposed along an incident end face of the light guide sheet and a substantially rectangular light guide sheet having an incident end face and an opposite end face. An edge light type backlight unit comprising a plurality of LED light sources, wherein the light guide sheet is used as the light guide sheet.

  Since the edge light type backlight unit includes the light guide sheet, the light use efficiency is high as described above, and luminance unevenness can be suppressed.

  As the light guide sheet, the first reflecting surface group and the second reflecting surface group adjacent thereto constitute a linear Fresnel lens or a Fresnel lens, and the focal length of the linear Fresnel lens or the Fresnel lens is the incident end surface and the opposed end surface. The linear Fresnel lens facing the gap between one facing part with one LED light source on the incident end face and the other facing part adjacent to the facing part, using the light guide sheet that substantially matches the average spacing of Alternatively, the focal point of the Fresnel lens may be substantially located between the one facing portion and the other facing portion. Thus, the focal point of the linear Fresnel lens or the Fresnel lens facing between the one facing part of the LED light source at the incident end face and the other facing part adjacent to the facing part is the one facing part. Since the light beam reflected by the first reflecting surface and the second reflecting surface can be surely propagated to the off-axis region by being substantially located between the region and the other facing region, the generation of dark spots Can be more effectively suppressed.

  The liquid crystal display device according to the present invention, which has been made to solve the above problems, includes the edge light type backlight unit having the above configuration in a liquid crystal display unit.

  Since the liquid crystal display device includes the edge light type backlight unit, as described above, the light use efficiency is high and luminance unevenness can be suppressed.

  In the present invention, the term “substantially square” is not limited to a perfect square, and for example, a corner is chamfered, and a concave incident region for incident light from an LED light source is formed on the incident end face. Also includes other shapes. The “average interval between the incident end surface and the opposed end surface” refers to the interval between the average interface between the incident end surface and the average interface between the opposed end surfaces. Further, “substantially coincides with the average distance between the incident end face and the opposite end face” means that the difference from the average distance is 5% or less of the average distance, and preferably 3% or less. “Arithmetic mean roughness (Ra) is a value with a cutoff λc of 2.5 mm and an evaluation length of 12.5 mm in accordance with JIS-B0601: 2001. Between a facing part with one focal point and another facing part. “Substantially located” means that the focal point does not necessarily have to be located on a line including one facing portion and the other facing portion. In addition, “the focal point is located substantially between one facing part and another facing part” preferably means that the distance from the midpoint between one facing part and the other facing part to the focal point is one. The distance from the LED to the intermediate point is equal to or less than that, and more preferably, the distance from the intermediate point to the focal point is equal to or less than ½ of the distance between one LED and the intermediate point.

  As described above, the light guide sheet, the edge light type backlight unit, and the liquid crystal display device according to the present invention have high light utilization efficiency and can suppress uneven brightness.

It is a typical end view showing an edge light type backlight unit according to an embodiment of the present invention. FIG. 2 is a schematic plan view showing a light source and a light guide sheet of the edge light type backlight unit of FIG. 1. It is a typical enlarged plan view which shows the opposing end surface of the light guide sheet of the edge light type backlight unit of FIG. It is a typical enlarged view side view which shows the opposing end surface of the light guide sheet of the edge light type backlight unit of FIG. It is a typical top view which shows the light guide sheet which concerns on embodiment different from the light guide sheet of the edge light type backlight unit of FIG. It is a typical top view which shows the light guide sheet which concerns on embodiment different from the light guide sheet of FIG.1 and FIG.5. It is a typical enlarged plan view which shows the opposing end surface of the light-guide sheet | seat of FIG. It is a typical enlarged view side view which shows the opposing end surface of the light-guide sheet | seat of FIG. It is a typical top view which shows the positional relationship of the light guide sheet | seat of a backlight unit provided with the light guide sheet | seat of FIG. 6, and an LED light source. It is a typical top view which shows the light guide sheet which concerns on embodiment different from the light guide sheet of FIG.1, FIG5 and FIG.6. It is a typical enlarged plan view which shows the opposing end surface of the light guide sheet of FIG. It is a typical enlarged view side view which shows the opposing end surface of the light-guide sheet | seat of FIG. It is typical sectional drawing which shows the internal structure of a liquid crystal display device provided with the edge light type backlight unit of FIG. It is a typical top view which shows the light guide sheet which concerns on embodiment different from the light guide sheet of FIG.1, FIG.5, FIG.6 and FIG. It is a schematic plan view which shows the incident end surface of the light guide sheet which concerns on other embodiment of this invention. It is a typical perspective view which shows the conventional edge light type backlight unit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[First embodiment]
<Edge light type backlight unit>
An edge light type backlight unit 1 (hereinafter, also simply referred to as “backlight unit 1”) in FIG. 1 includes a light guide sheet 2 having a substantially rectangular shape having an incident end face and an opposite end face facing the incident end face, and a light guide. This is a one-side edge-light type backlight unit including a plurality of LED light sources 3 arranged along the incident end face of the sheet 2. The backlight unit 1 includes an optical sheet 4 disposed on the front surface side of the light guide sheet 2 and a reflection sheet 5 disposed on the back surface side of the light guide sheet 2.

(LED light source)
As shown in FIG. 2, the plurality of LED light sources 3 are arranged with a gap therebetween, and the light emission directions are substantially parallel to each other. The LED light source 3 is disposed such that a light output portion that emits light rays faces (or abuts) the incident end surface of the light guide sheet 2, and emits light rays toward the incident end surface of the light guide sheet 2.

  The plurality of LED light sources 3 are arranged at substantially equal intervals P. Although it does not specifically limit as the pitch P of the LED light source 3, For example, it is 7 mm or more and 12 mm or less. If the pitch P of the LED light sources 3 is less than the above lower limit, the number of the LED light sources 3 is increased too much, and the power consumption may be excessively increased. Conversely, if the pitch P of the LED light sources 3 exceeds the above upper limit, there is a possibility that the luminance necessary for the backlight unit 1 cannot be secured. Moreover, it does not specifically limit as a shape and magnitude | size of the light emission part of the LED light source 3, For example, it can be set as the circular shape of diameter 3mm or more and 4mm or less.

(Light guide sheet)
The light guide sheet 2 is a substantially rectangular light guide sheet for an LED light source having an incident end face on which light is incident and an opposing end face facing the incident end face. The light guide sheet 2 is formed in a non-wedge shape and a plate shape. Further, the incident end surface is configured as a flat surface, and thus the output axis Z of the light beam incident from the plurality of LED light sources 3 is configured to be substantially perpendicular to a virtual plane substantially parallel to the incident end surface. Yes. Furthermore, the light guide sheet 2 has a plurality of reflective dots 15 on the back surface. The “non-wedge shape” is not a wedge shape in which the thickness gradually increases or decreases from the incident end surface to the opposing end surface, but means that the incident end surface and the opposing end surface have substantially the same thickness.

  As a minimum of average thickness of light guide sheet 2, 50 micrometers is preferred, 150 micrometers is more preferred, and 200 micrometers is still more preferred. On the other hand, the upper limit of the average thickness of the light guide sheet 2 is preferably 600 μm, more preferably 580 μm, and further preferably 550 μm. If the average thickness of the light guide sheet 2 is less than the lower limit, the strength of the light guide sheet 2 may be insufficient, and the light from the LED light source 3 may not be sufficiently incident. . Conversely, if the average thickness of the light guide sheet 2 exceeds the above upper limit, it cannot be used as a thin light guide film and may be difficult to use for an ultra-thin portable terminal. The “average thickness of the light guide sheet” refers to the average thickness on a flat surface where the plurality of reflective dots 15 are not present.

  The lower limit of the average distance L between the incident end face and the opposing end face in the light guide sheet 2 is preferably 6 cm, more preferably 7 cm, and even more preferably 9 cm. On the other hand, the upper limit of the average distance L is preferably 45 cm, more preferably 20 cm, and even more preferably 12 cm. If the average interval L is less than the lower limit, it may not be usable for large terminals other than small mobile terminals. On the other hand, when the average interval exceeds the above upper limit, when used as a light guide film of a thin film having an average thickness of 600 μm or less, bending tends to occur, and sufficient light guide properties may not be obtained.

  The lower limit of the average width of the light guide sheet 2 (average width between a pair of side surfaces substantially perpendicular to the incident end face and the opposing end face) is preferably 6 cm, more preferably 7 cm, and even more preferably 9 cm. On the other hand, the upper limit of the average width of the light guide sheet 2 is preferably 45 cm, more preferably 20 cm, and even more preferably 12 cm. If the average width is less than the lower limit, it may not be usable for large terminals other than small mobile terminals. On the other hand, when the average width exceeds the above upper limit, when used as a thin light guide film having an average thickness of 600 μm or less, bending tends to occur, and sufficient light guide properties may not be obtained.

As a minimum of the surface area of light guide sheet 2, 30 cm ² is preferred, 50 cm ² is more preferred, and 80 cm ² is still more preferred. On the other hand, as an upper limit of the surface area of the light guide sheet 2, 1000 cm ² is preferable, 500 cm ² is more preferable, and 150 cm ² is more preferable. If the surface area of the light guide sheet 2 is less than the lower limit, it may not be usable for large terminals other than small mobile terminals. On the contrary, when the surface area of the light guide sheet 2 exceeds the above upper limit, the light guide sheet 2 is likely to be bent when used as a thin light guide film having an average thickness of 600 μm or less, and sufficient light guide properties may not be obtained. is there.

  The light guide sheet 2 has a plurality of first reflecting surfaces 11 inclined to one side and a plurality of second reflecting surfaces 12 inclined to the other side with reference to a virtual surface whose opposing end surface is substantially parallel to the incident end surface. Is provided. Specifically, as shown in FIG. 3, the opposing surface includes a plurality of first reflecting surfaces 11 inclined to one side in the width direction and the incident end surface side with respect to the virtual surface, and the other side in the width direction, and The plurality of second reflecting surfaces 12 are inclined to the incident end face side. The 1st reflective surface 11 and the 2nd reflective surface 12 are respectively comprised so that the light ray radiate | emitted from the LED light source 3 can be reflected in the incident end surface side. As shown in FIG. 4, the plurality of first reflection surfaces 11 and the plurality of second reflection surfaces 12 are each formed as a rectangular flat surface whose longitudinal direction is the thickness direction, and the thickness of the light guide sheet 2. And the lengths in the longitudinal direction of the first reflecting surfaces 11 and the second reflecting surfaces 12 coincide with each other.

  The opposing end surface is alternately provided with a first reflection surface group 13 in which a plurality of first reflection surfaces 11 are continuous and a second reflection surface group 14 in which a plurality of second reflection surfaces 12 are continuous. Specifically, the first reflecting surface group 13 has a plurality of first reflecting surfaces 11 and connecting surfaces that are connected to adjacent edges of the plurality of first reflecting surfaces 11, and has a saw blade shape in a plan view. It is configured. The second reflecting surface group 14 has a plurality of second reflecting surfaces 12 and connecting surfaces that are respectively connected to adjacent edges of the plurality of second reflecting surfaces 12, and is configured in a saw blade shape in plan view. Yes. The light guide sheet 2 is alternately provided with the first reflection surface group 13 in which the plurality of first reflection surfaces 11 are continuous and the second reflection surface group 14 in which the plurality of second reflection surfaces 12 are continuous. As a result, it is possible to prevent the length of the first reflecting surface 11 and the one second reflecting surface 12 in the direction of the light output axis Z from being increased, thereby achieving flattening of the opposing end surface as a whole, and thus the liquid crystal. The area of the display surface can be increased to increase the screen size of the liquid crystal display device. In addition, the light guide sheet 2 includes the first reflecting surface group 13 and the second reflecting surface group 14 alternately, thereby emitting light rays in the first reflecting surface group 13 and the second reflecting surface group 14 respectively. Therefore, the occurrence of dark spots can be effectively suppressed, and the effect of suppressing luminance unevenness of the liquid crystal display device can be enhanced.

  The light guide sheet 2 is disposed such that the connecting portions of the first reflecting surface group 13 and the second reflecting surface group 14 substantially coincide with the light output axis Z of the LED light source 3. Specifically, the connecting portion between the end side of the first reflecting surface 11 on the incident end surface side and the end side of the second reflecting surface 12 on the incident end surface side is disposed so as to substantially coincide with the light output axis Z of the LED light source 3. Has been. Thereby, the said light guide sheet 2 makes the reflected light reflected by the 1st reflective surface 11 the LED light source 3 corresponding to the said connection part in the said light guide sheet 2, and the other adjacent to this LED light source 3 side. It is easy to reflect the dark spot between the LED light sources 3. In addition, the light guide sheet 2 reflects the reflected light reflected by the second reflecting surface 12 in the LED light source 3 corresponding to the connecting portion position in the light guide sheet 2 and the other side adjacent to the other side of the LED light source 3. It is easy to reflect the dark spots between the LED light sources 3.

  Each first reflection surface 11 and each second reflection surface 12 are formed in a planar shape. The inclination angles of the first reflecting surfaces 11 constituting the first reflecting surface groups 13 with respect to the virtual surfaces are different from each other, and the virtual surfaces of the second reflecting surfaces 12 constituting the second reflecting surface groups 14 are different. The inclination angle with respect to the surface is different. Thus, the reflection angles of the light rays reflected by each first reflection surface 11 and each second reflection surface 12 are adjusted by the inclination angles of each first reflection surface 11 and each second reflection surface 12 being different. Easy to do. Therefore, the light guide sheet 2 reflects the reflected light reflected by each first reflecting surface 11 to the light output axis Z of the LED light source 3 corresponding to the connecting portion in the light guide sheet 2 and one side of the LED light source 3. It is easy to reflect in the dark spot between the light emission axes Z of the other LED light sources 3 adjacent to. Further, the light guide sheet 2 reflects the reflected light reflected by each second reflecting surface 12 with the light output axis Z of the LED light source 3 corresponding to the connecting portion position in the light guide sheet 2 and the other side of the LED light source 3. It is easy to reflect in the dark spot between the light emission axes Z of the other LED light sources 3 adjacent to.

  The inclination angles of the plurality of first reflection surfaces 11 in each first reflection surface group 13 and the inclination angles of the plurality of second reflection surfaces 12 in each second reflection surface group 14 may gradually become smaller from the connection portion. preferable. In this way, the light guide sheet 2 has the inclination angles of the plurality of first reflection surfaces 11 in each first reflection surface group 13 and the inclination angles of the plurality of second reflection surfaces 12 in each second reflection surface group 14 as follows. By gradually decreasing from the connecting portion, the reflected light reflected by the plurality of first reflecting surfaces 11 and the reflected light reflected by the plurality of second reflecting surfaces 12 are emitted from the LED light source 3 corresponding to the connecting portion. It is easy to reflect the dark spot between the axis Z and the light output axis Z of the pair of LED light sources 3 adjacent to both sides of the LED light source 3.

  The inclination angle of the first reflection surface 11 on the light output axis Z side of the LED light source 3 in each first reflection surface group 13 and the second reflection surface 12 on the light output axis Z side of the LED light source 3 in each second reflection surface group 14. The lower limit of the tilt angle is preferably 0.2 °, more preferably 0.5 °, and even more preferably 1 °. On the other hand, the upper limit of the tilt angle is preferably 5 °, more preferably 4 °, and even more preferably 3 °. When the tilt angle is out of the above range, the light output axis Z of the LED light source 3 and the LED light source corresponding to the connection portion are reflected in the reflection direction of the light beam reflected by the first reflecting surface group 13 and the second reflecting surface group 14. 3 may be difficult to control to dark spots between the light output axes Z of the pair of LED light sources 3 adjacent to both sides of the LED 3.

In the light guide sheet 2, the inclination angle of the first reflection surface 11 on the light output axis Z side of the LED light source 3 in each first reflection surface group 13 is α, and the light output axis Z of the LED light source 3 in each second reflection surface group 14. When the inclination angle of the second reflection surface 12 on the side is β, the average distance between the incident end surface and the opposite end surface of the light guide sheet 2 is L, and the pitch of the LED light sources 3 is P, the following formulas (1) and (2) It is preferable to satisfy. The light guide sheet 2 satisfies the following formulas (1) and (2), thereby reflecting the reflected light reflected by the plurality of first reflecting surfaces 11 and the reflected light reflected by the plurality of second reflecting surfaces 12 above. It is easy to reflect the light output axis Z of the LED light source 3 corresponding to the connecting portion and the dark spot between the light output axes Z of the pair of LED light sources 3 adjacent to both sides of the LED light source 3.
1 / 4P <L × tan α <3 / 4P (1)
1 / 4P <L × tan β <3 / 4P (2)

  As a minimum of the average width of each 1st reflective surface 11 and each 2nd reflective surface 12, 0.5 mm is preferred, 1 mm is more preferred, and 1.5 mm is still more preferred. On the other hand, the upper limit of each average width is preferably 4.5 mm, more preferably 3.5 mm, and even more preferably 2.5 mm. If the average width is less than the lower limit, it may be difficult to form the plurality of first reflection surfaces 11 and the plurality of second reflection surfaces 12, and a connection surface that connects the plurality of first reflection surfaces 11 and There is a possibility that it becomes difficult to control reflected light due to an increase in the number of connecting surfaces that connect the plurality of second reflecting surfaces 12. Conversely, if the average width exceeds the upper limit, it may be difficult to accurately reflect the light beam to the dark spot.

  The lower limit of the number of first reflecting surfaces 11 in each first reflecting surface group 13 and the number of second reflecting surfaces 12 in each second reflecting surface group 14 is preferably two, and more preferably three. On the other hand, the upper limit of the number is preferably 6, and more preferably 5. If the number is less than the lower limit, it may be difficult to accurately reflect the light beam to the dark spot. On the contrary, if the number exceeds the upper limit, it may be difficult to form the plurality of reflecting surfaces 11 and the plurality of reflecting surfaces 12, and the connecting surface that connects the plurality of first reflecting surfaces 11 and the plurality of first reflecting surfaces may be formed. There is a possibility that it becomes difficult to control the reflected light due to an increase in the number of connecting surfaces that connect the two reflecting surfaces 12.

  As a lower limit of the width of each first reflecting surface group 13 and each second reflecting surface group 14 (the shortest distance from one end to the other end in the width direction of each first reflecting surface group 13 and each second reflecting surface group 14) 2 mm is preferable, 3 mm is more preferable, and 4 mm is more preferable. On the other hand, the upper limit of the width is preferably 9 mm, more preferably 7 mm, and even more preferably 6 mm. If the width is less than the lower limit, fine control of the reflected light by each first reflecting surface group 13 and each second reflecting surface group 14 may be difficult. Conversely, if the width exceeds the upper limit, it may be difficult to dispose the first reflecting surface group 13 and the second reflecting surface group 14 corresponding to the plurality of LED light sources 3.

  The lower limit of the arithmetic average roughness Ra of the plurality of first reflection surfaces 11 and the plurality of second reflection surfaces 12 is preferably 0.04 μm, and more preferably 0.07 μm. On the other hand, the upper limit of the arithmetic average roughness Ra is preferably 0.3 μm, and more preferably 0.15 μm. If the arithmetic average roughness Ra is less than the lower limit, the reflected light cannot be scattered appropriately, and it may be difficult to emit the reflected light toward the entire area of the dark spot. Conversely, when the arithmetic average roughness Ra exceeds the upper limit, it is difficult to control the reflection angle, and it may be difficult to emit the reflected light toward the dark spot.

  Further, as described above, the light guide sheet 2 has a plurality of reflective dots 15 on the back surface. The light guide sheet 2 can scatter light incident on the light guide sheet 2 to the surface side by the reflective dots 15.

  The shape of the reflective dot 15 is not particularly limited. For example, the shape of the reflective dot 15 may be a shape having a concave portion recessed to the front surface side and a raised portion that exists around the concave portion and protrudes to the back surface side. . By making the reflective dots 15 have such a shape, it is possible to scatter incident light by the concave portions and to prevent the back surface of the light guide sheet 2 and the reflective sheet 5 from coming into close contact with each other by the raised portions.

  The concave portions of the reflective dots 15 are formed in a substantially circular shape in plan view, and are formed so as to gradually reduce the diameter toward the surface side. The three-dimensional shape of the recess is not particularly limited, and may be hemispherical, conical, cylindrical, or the like. Especially, as a three-dimensional shape of the said recessed part, a hemisphere is preferable. By making the three-dimensional shape of the concave portion hemispherical, the moldability of the concave portion can be improved, and light incident on the concave portion can be suitably scattered.

  The raised portions of the reflective dots 15 are integrally formed on the back surface of the light guide sheet 2. The raised portion protrudes from the lower surface side so as to extend from the lower end of the concave portion of the reflective dot 15, and is formed so as to surround the concave portion in an annular shape in plan view. The shape of the raised portion in plan view can be defined, for example, corresponding to the outer peripheral shape of the recess, and can be an annular shape, a polygonal shape, or the like.

  The reflective dots 15 are preferably arranged so that the density gradually decreases from the opposing end surface of the light guide sheet 2 to the incident end surface. Further, it is preferable that the number of the reflective dots 15 is small in the vicinity of the light output axis Z, and a large number is provided between the light output axis Z and the adjacent light output axis Z. By disposing the reflective dots 15 in this manner, incident light can be easily incident on a desired region of the opposing end surface, and light incident on the opposing end surface can be easily reflected toward a dark spot.

  As a minimum of the average depth from the back surface average interface of the crevice of reflective dot 15, 1 micrometer is preferred, 2 micrometers is more preferred, and 4 micrometers is still more preferred. On the other hand, as an upper limit of the average depth from the back surface average interface of the said recessed part, 10 micrometers is preferable, 9 micrometers is more preferable, and 7 micrometers is more preferable. If the average depth from the back surface average interface of the said recessed part is less than the said minimum, there exists a possibility that a light-scattering effect may not fully be acquired. On the contrary, when the average depth from the back surface average interface of the said recessed part exceeds the said upper limit, there exists a possibility of producing a brightness nonuniformity. The “average depth of the recesses” refers to the average depth of the recesses from the back surface average interface of the light guide sheet, and any 20 recesses are extracted, of which 5 from the largest depth and The average value of 10 depths, excluding 5 from those having a small depth. The “back surface average interface of the light guide sheet” refers to an interface of a flat surface in which a plurality of concave portions and a plurality of raised portions do not exist.

  As a minimum of the average diameter of the above-mentioned crevice in the back average interface, 10 micrometers is preferred, 12 micrometers is more preferred, and 15 micrometers is still more preferred. On the other hand, the upper limit of the average diameter of the recesses at the back average interface is preferably 50 μm, more preferably 40 μm, and even more preferably 30 μm. If the average diameter of the recesses at the back average interface is less than the lower limit, the light scattering effect may not be sufficiently obtained. On the other hand, if the average diameter of the recesses at the back average interface exceeds the upper limit, there is a risk of uneven brightness. The “diameter of the concave portion” means an intermediate value between the maximum diameter of the concave portion and the diameter in the direction orthogonal to the maximum radial direction. The “average diameter of the recesses” refers to an average value of 10 diameters obtained by extracting 20 arbitrary recesses and excluding 5 from those having a larger diameter and 5 from those having a smaller diameter. .

  As a minimum of average height from the back average interface of the protruding part of reflective dot 15, 0.1 micrometers is preferred, 0.3 micrometers is more preferred, and 0.5 micrometers is still more preferred. On the other hand, the upper limit of the average height from the back average interface of the raised portion is preferably 6 μm, more preferably 5 μm, and further preferably 4 μm. If the average height from the back average interface of the raised portion is less than the lower limit, sticking may not be prevented accurately. Conversely, when the average height from the back average interface of the raised portion exceeds the upper limit, the surface of the reflective sheet 5 disposed on the back side is damaged due to contact with the raised portion. There is a fear. The “average height of the raised portions” refers to the average value of the heights of any ten raised portions.

  The lower limit of the average width of the raised portions at the back average interface is preferably 1 μm, more preferably 3 μm, and even more preferably 5 μm. On the other hand, the upper limit of the average width of the raised portions at the back average interface is preferably 15 μm, more preferably 12 μm, and even more preferably 10 μm. If the average width of the raised portion at the back average interface is less than the lower limit, the surface of the reflective sheet 5 disposed on the back side may be damaged due to contact with the raised portion. On the contrary, when the average width of the raised portion at the back average interface exceeds the upper limit, the area where the raised portion is in contact with the reflection sheet 5 is increased, which may cause uneven brightness. The “width of the raised portion” refers to the difference between the outer radius and the inner radius of the raised portion. The width of the raised portion can be obtained, for example, by subtracting a value of ½ of the inner diameter from a value of ½ of the outer diameter at a portion where the outer diameter of the raised portion is maximum. The “average width of the raised portion” refers to an average value of the widths of any ten raised portions.

  Since the light guide sheet 2 needs to transmit light, the light guide sheet 2 is formed mainly of a transparent, particularly colorless and transparent synthetic resin. The main components of the light guide sheet 2 are polycarbonate, acrylic resin, polyethylene terephthalate, polyethylene naphthalate, polystyrene, methyl (meth) acrylate-styrene copolymer, polyolefin, cycloolefin polymer, cycloolefin copolymer, cellulose acetate, poly Examples include arylate, weather-resistant vinyl chloride, and active energy ray-curable resin. Especially, as a main component of the light guide sheet 2, a polycarbonate and an acrylic resin are preferable. Polycarbonate is excellent in transparency and has a high refractive index. Therefore, when the main component of the light guide sheet 2 is polycarbonate, total reflection is likely to occur on the front and back surfaces of the light guide sheet 2, and light can be propagated efficiently. it can. Moreover, since polycarbonate has heat resistance, the LED light source 3 is unlikely to deteriorate due to heat generation. Furthermore, since polycarbonate has less water absorption than acrylic resin, dimensional stability is high. Therefore, deterioration over time can be suppressed by using polycarbonate as the main component of the light guide sheet 2. On the other hand, since acrylic resin has high transparency, it is possible to reduce light wear in the light guide sheet 2. As a minimum of content of the above-mentioned main ingredient of light guide sheet 2, 80 mass% is preferred, 90 mass% is more preferred, and 98 mass% is still more preferred. Moreover, as an upper limit of content of the said main component of the light-guide sheet 2, it can be 100 mass%.

  It does not specifically limit as said polycarbonate, A linear polycarbonate and a branched polycarbonate can be mentioned. The polycarbonate may be a polycarbonate containing both a linear polycarbonate and a branched polycarbonate.

  As the linear polycarbonate, there is a linear aromatic polycarbonate produced by a known phosgene method or a melting method, and it comprises a carbonate component and a diphenol component. Examples of the precursor for introducing the carbonate component include phosgene and diphenyl carbonate. Examples of the diphenol include 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (3,5-dimethyl-4-hydroxyphenyl) propane, and 1,1-bis (4-hydroxyphenyl). ) Cyclohexane, 1,1-bis (3,5-dimethyl-4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) decane, 1,1-bis (4-hydroxyphenyl) cyclodecane, 1-bis (4-hydroxyphenyl) propane, 1,1-bis (3,5-dimethyl-4-hydroxyphenyl) cyclododecane, 4,4′-dihydroxydiphenyl ether, 4,4′-thiodiphenol, 4, Examples include 4′-dihydroxy-3,3-dichlorodiphenyl ether. These can be used alone or in combination of two or more.

  Examples of the branched polycarbonate include polycarbonate produced using a branching agent. Examples of the branching agent include phloroglucin, trimellitic acid, 1,1,1-tris (4-hydroxyphenyl) ethane, and 1,1,2-tris. (4-hydroxyphenyl) ethane, 1,1,2-tris (4-hydroxyphenyl) propane, 1,1,1-tris (4-hydroxyphenyl) methane, 1,1,1-tris (4-hydroxyphenyl) ) Propane, 1,1,1-tris (2-methyl-4-hydroxyphenyl) methane, 1,1,1-tris (2-methyl-4-hydroxyphenyl) ethane, 1,1,1-tris (3 -Methyl-4-hydroxyphenyl) methane, 1,1,1-tris (3-methyl-4-hydroxyphenyl) ethane, 1,1,1-tri (3,5-dimethyl-4-hydroxyphenyl) methane, 1,1,1-tris (3,5-dimethyl-4-hydroxyphenyl) ethane, 1,1,1-tris (3-chloro-4-hydroxy Phenyl) methane, 1,1,1-tris (3-chloro-4-hydroxyphenyl) ethane, 1,1,1-tris (3,5-dichloro-4-hydroxyphenyl) methane, 1,1,1- Tris (3,5-dichloro-4-hydroxyphenyl) ethane, 1,1,1-tris (3-bromo-4-hydroxyphenyl) methane, 1,1,1-tris (3-bromo-4-hydroxyphenyl) ) Ethane, 1,1,1-tris (3,5-dibromo-4-hydroxyphenyl) methane, 1,1,1-tris (3,5-dibromo-4-hydroxyphenyl) ethane, 4,4 - dihydroxy-2,5-dihydroxydiphenyl ether, and the like.

  The acrylic resin is a resin having a skeleton derived from acrylic acid or methacrylic acid. Although it does not specifically limit as said acrylic resin, Poly (meth) acrylic acid ester, such as polymethyl methacrylate, Methyl methacrylate- (meth) acrylic acid copolymer, Methyl methacrylate- (meth) acrylic acid ester copolymer Polymer, methyl methacrylate-acrylic ester- (meth) acrylic acid copolymer, methyl (meth) acrylate-styrene copolymer, polymer having alicyclic hydrocarbon group (for example, methyl methacrylate-methacrylic acid Cyclohexyl copolymer, methyl methacrylate- (meth) acrylate norbornyl copolymer) and the like. Among these acrylic resins, poly (meth) acrylate C1-6 alkyl such as poly (meth) methyl acrylate is preferable, and methyl methacrylate resin is more preferable.

  Examples of the active energy ray curable resin include an active energy ray curable acrylic resin and an active energy ray curable epoxy resin. As said active energy ray hardening-type resin, what contains at least 1 sort (s) among a photopolymerizable prepolymer, an oligomer, and a monomer, a photopolymerizable initiator, etc. is used, for example.

  Examples of the prepolymer and oligomer in the active energy ray-curable acrylic resin include epoxy (meth) acrylate, urethane (meth) acrylate, polyester (meth) acrylate, and polyether (meth) acrylate.

  Examples of the monomer in the active energy ray-curable acrylic resin include methyl (meth) acrylate, lauryl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, and phenoxyethyl (meth). Monofunctional acrylates such as acrylate, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxy (meth) acrylate , Neopentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentae Thritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, Multifunctional acrylates such as tripentaerythritol tri (meth) acrylate, tripentaerythritol hexa (meth) triacrylate, trimethylolpropane (meth) acrylic acid benzoate, trimethylolpropane benzoate, glycerin di (meth) acrylate hexa Urethane acrylics such as methylene diisocyanate and pentaerythritol tri (meth) acrylate hexamethylene diisocyanate Over doors and the like.

  Examples of the photopolymerizable initiator include acetophenone, 2,2-diethoxyacetophenone, p-dimethylacetophenone, p-dimethylaminopropiophenone, benzophenone, benzyl, 2-chlorobenzophenone, 4,4′-dichlorobenzophenone, 4,4′-bisdiethylaminobenzophenone, Michler's ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, methyl benzoylformate, p-isopropyl-α-hydroxyisobutylphenone, α-hydroxyisobutylphenone, 2,2- Carbonyl compounds such as dimethoxy-2-phenylacetophenone and 1-hydroxycyclohexyl phenyl ketone, tetramethylthiuram monosulfide, tetramethylthio And sulfur compounds such as uranium disulfide, thioxanthone, 2-chlorothioxanthone, and 2-methylthioxanthone. These photopolymerization initiators may be used alone or in combination of two or more.

  The light guide sheet 2 is composed of an ultraviolet absorber, a flame retardant, a stabilizer, a lubricant, a processing aid, a plasticizer, an impact resistance aid, a phase difference reducing agent, a matting agent, an antibacterial agent, an antifungal agent, and an antioxidant. Further, optional components such as a release agent and an antistatic agent may be included.

  As a minimum of a refractive index of light guide sheet 2, 1.53 is preferred and 1.55 is more preferred. On the other hand, the upper limit of the refractive index of the light guide sheet 2 is preferably 1.68, more preferably 1.66. If the refractive index of the light guide sheet 2 is less than the lower limit, the light propagation in the light guide sheet 2 may be reduced. On the other hand, when the refractive index of the light guide sheet 2 exceeds the above upper limit, the light beam reflected from the reflective sheet 5 may not easily enter the light guide sheet 2.

(Optical sheet)
The optical sheet 4 has optical functions such as diffusion and refraction with respect to light incident from the back side. Examples of the optical sheet 4 include a light diffusing sheet having a light diffusing function and a prism sheet having a refracting function toward the normal direction. These sheets may be used alone or in combination of two or more. Can be used.

(Reflective sheet)
The reflection sheet 5 is disposed on the back side of the light guide sheet 2 and reflects the light emitted from the back side of the light guide sheet 2 to the front side. As the reflective sheet 5, regular reflection is enhanced by depositing a metal such as aluminum or silver on the surface of a white sheet obtained by dispersing a filler in a base material layer resin such as polyester or a film formed from polyester. The mirror surface sheet etc. which were obtained are mentioned.

<Advantages>
In the light guide sheet 2, a light beam from the LED light source 3 is incident from an incident end face, the incident light beam propagates in the light guide sheet 2, and a part of the light beam propagated in the light guide sheet 2 is obtained. Emitted from the surface. Since the light guide sheet 2 includes the first reflection surface 11 and the second reflection surface 12 that are inclined with respect to a virtual plane substantially parallel to the incident end surface at the opposing end surface, the light guide sheet 2 is incident from the incident end surface and passes through the light guide sheet 2. Since the light beam that has propagated and reached the opposing end surface is reflected by the first reflection surface 11 and the second reflection surface 12 into the light guide sheet 2, the use efficiency of the light beam can be improved. In addition, the light guide sheet 2 can ensure the amount of light emitted from the light output off-axis region by allowing the light reflected by the first reflection surface 11 and the second reflection surface 12 to propagate through the light output off-axis region. The occurrence of dark spots can be suppressed.

  Since the backlight unit 1 includes the light guide sheet 2 and a plurality of LED light sources 3 disposed along the incident end face of the light guide sheet 2, the backlight unit 1 is emitted from the plurality of LED light sources 3 and the light guide sheet 2. Can be reflected toward the dark spot. Therefore, the backlight unit 1 has high light utilization efficiency and can suppress uneven brightness.

<Method for producing light guide sheet>
The manufacturing method of the light guide sheet 2 includes a step of forming a sheet body having a plurality of reflective dots on one surface (sheet body forming step), and a first reflecting surface and a second reflecting surface are formed on the sheet body. A step (reflection surface forming step).

(Sheet formation process)
The said sheet body formation process can be performed with the following method, for example.
(A) An injection molding method in which a molten light guide sheet forming material is injected into a mold having a plurality of recesses and a reversal shape of a plurality of raised portions present around the recesses,
(B) A method of re-heating a sheet body made of a light guide sheet forming material and sandwiching it between a mold having the above inverted shape and a metal plate or roll to transfer the shape,
(C) supplying a molten light guide sheet forming material to a T die and extruding the forming material from the extruder and the T die to form a sheet body; A method using an extrusion method in which a shape is transferred by pressing between metal plates or rolls,
(D) A casting method (solution casting method) in which a solution (dope) in which a light guide sheet forming material is melted in a solvent to have fluidity is poured into a mold having the above inverted shape, and then the solvent is evaporated (solution casting method).
(E) A method of filling an uncured active energy ray-curable resin into a mold having the above inverted shape and irradiating active energy rays such as ultraviolet rays,
(F) Using a mold having only the inverted shape of the plurality of recesses, and forming the plurality of recesses on one surface of the sheet body by the same method as in the above (a) to (e), A method of forming a plurality of raised portions using a photolithography method and an etching method around a plurality of concave portions on one surface;
(G) Forming a plurality of concave portions and a plurality of raised portions present around the concave portions by cutting using a cemented carbide bite, a diamond bite, an end mill or the like on one surface of a sheet body made of a light guide sheet forming material. Method

(Reflection surface formation process)
The reflective surface forming step can be performed, for example, by cutting the sheet body formed by the sheet body forming step in the thickness direction. Specifically, when the sheet body formed in the sheet body forming step is cut in the thickness direction with a cutting machine, the blade shape of the cutting machine is changed to a plurality of first reflection surfaces and a plurality of second reflection surfaces. A reflective surface can be formed on the sheet by setting the shape to correspond.

  In addition, the manufacturing method of the said light guide sheet is further provided with the process (incident surface formation process) of forming the incident end surface facing the opposing end surface in which the 1st reflective surface and the 2nd reflective surface were formed, This incident surface The forming step can also be performed by cutting the sheet body in the thickness direction. However, since the incident surface formed in the incident surface forming step is preferably a flat surface, the blade is different from the blade used in the reflecting surface forming step.

<Advantages>
The light guide sheet manufacturing method can easily and surely manufacture the light guide sheet 2 described above, which has high light use efficiency and can suppress luminance unevenness.

[Second Embodiment]
<Light guide sheet>
A light guide sheet 21 in FIG. 5 is used in the backlight unit 1 instead of the light guide sheet 2 in FIG. 1. The light guide sheet 21 of FIG. 5 includes a main body 22 having an incident end face and an opposite end face facing the incident end face, and a reflective layer 23 laminated on the opposite end face of the main body 22. The main body 22 includes a plurality of first reflecting surfaces 11 inclined to one side and a plurality of second reflecting surfaces 12 inclined to the other side with reference to a virtual surface substantially parallel to the incident end surface. In detail, it is comprised similarly to the light guide sheet 2 of FIG.

(Reflective layer)
The reflective layer 23 covers the entire area of the opposing end face that faces the incident end face of the main body 22. The reflection layer 23 is configured as a white pigment layer in which a white pigment is dispersed in a binder or a metal vapor deposition layer formed by vapor deposition of a metal.

  When the reflective layer 23 is configured as the white pigment layer, the binder is not particularly limited. For example, acrylic resin, polyurethane, polyester, fluororesin, silicone resin, polyamideimide, epoxy resin, ultraviolet curable type Resin etc. are mentioned, These can be used 1 type or in mixture of 2 or more types. In addition, the white pigment is not particularly limited, and examples thereof include titanium oxide (titanium white), zinc oxide (zinc white), lead carbonate (lead white), barium sulfate, calcium carbonate (white chalk), and the like. .

  The lower limit of the average particle size of the white pigment is preferably 100 nm, more preferably 200 nm, and even more preferably 300 nm. On the other hand, the upper limit of the average particle diameter of the white pigment is preferably 30 μm, more preferably 20 μm, and even more preferably 10 μm. If the average particle size of the white pigment is less than the lower limit, sufficient reflectivity may not be obtained. Conversely, when the average particle diameter of the white pigment exceeds the upper limit, the thickness of the white pigment layer (the thickness of the white pigment layer in the direction perpendicular to the thickness direction of the light guide sheet 21) becomes unnecessarily large. There is a fear. The “average particle diameter” means the average of the particle diameters of 30 particles randomly extracted from particles observed with an electron microscope with a magnification of 1000 times. The particle diameter is the Ferret diameter (parallel lines in a certain direction). And the interval when the projection image is sandwiched between them).

  As a minimum of content of the white pigment, 3 mass% is preferred, 5 mass% is more preferred, and 7 mass% is still more preferred. On the other hand, as an upper limit of content of the said white pigment, 30 mass% is preferable, 25 mass% is more preferable, and 20 mass% is further more preferable. If the content of the white pigment is less than the lower limit, sufficient reflectivity may not be obtained. Conversely, if the content of the white pigment exceeds the upper limit, the adhesion between the main body 22 and the reflective layer 23 may not be sufficiently obtained.

  The lower limit of the average thickness of the white pigment layer (the average thickness of the white pigment layer in the direction perpendicular to the thickness direction of the light guide sheet 21) is preferably 20 μm, more preferably 50 μm, and even more preferably 75 μm. On the other hand, the upper limit of the average thickness of the white pigment layer is preferably 250 μm, more preferably 200 μm, and even more preferably 150 μm. If the average thickness of the white pigment layer is less than the lower limit, the adhesion with the main body 22 may be insufficient, and the white pigment may be removed from the white pigment layer. On the other hand, if the average thickness of the white pigment layer exceeds the upper limit, the liquid crystal display device may be required to be downsized.

  The white pigment layer is composed of an ultraviolet absorber, a flame retardant, a stabilizer, a lubricant, a processing aid, a plasticizer, an impact aid, a phase difference reducing agent, a matting agent, an antibacterial agent, an antifungal agent, and an antioxidant. Further, optional components such as a release agent and an antistatic agent may be included.

  In the case where the reflective layer 23 is configured as the metal deposition layer, the metal is not particularly limited. For example, a metal such as gold, silver, zinc, aluminum, copper, nickel, chromium, iron, titanium, and zirconium A simple substance, these alloys, an oxide, etc. are mentioned.

  As a minimum of the average thickness of the above-mentioned metal vapor deposition layer, 20 nm is preferred and 30 nm is more preferred. On the other hand, as an upper limit of the average thickness of the said metal vapor deposition layer, 1000 nm is preferable and 500 nm is more preferable. If the average thickness of the metal vapor deposition layer is less than the lower limit, sufficient reflectivity may not be obtained. Conversely, when the average thickness of the metal vapor deposition layer exceeds the upper limit, the production cost may increase.

<Method for producing light guide sheet>
The manufacturing method of the light guide sheet 21 includes a step of laminating the reflective layer 23 on the facing end surface (reflective layer stacking step) in addition to the sheet body forming step and the reflective surface forming step of the above-described method of manufacturing the light guide sheet 2. .

(Reflective layer lamination process)
When the reflective layer 23 is a white pigment layer, the reflective layer laminating step can be performed by, for example, a coating method in which a coating liquid containing a binder and a white pigment is applied to the opposing end surface of the main body 22 and dried. In addition, when the reflective layer 23 is a metal vapor deposition layer, for example, (a) physical vapor deposition method (Physical Vapor Deposition method; PVD method) such as vacuum vapor deposition method, sputtering method, ion plating method, ion cluster beam method, (B) A chemical vapor deposition method (chemical vapor deposition method; CVD method) such as a plasma chemical vapor deposition method, a thermal chemical vapor deposition method, or a photochemical vapor deposition method can be used.

<Advantages>
Since the light guide sheet 21 includes the reflective layer 23 laminated on the facing end surface, the reflectivity of the plurality of first reflection surfaces 11 and the plurality of second reflection surfaces 12 can be improved.

  When the reflection layer 23 is configured as a white pigment layer, the light guide sheet 21 can appropriately scatter the reflected light and is incident on the plurality of first reflection surfaces 11 and the plurality of second reflection surfaces 12. It is easy to reflect light toward the entire area of the dark spot. On the other hand, when the reflective layer 23 is configured as a metal vapor deposition layer, the light guide sheet 21 can easily control the reflection direction of the reflected light.

[Third embodiment]
<Light guide sheet>
A light guide sheet 31 in FIG. 6 is used in the backlight unit 1 in place of the light guide sheets 2 and 21 in FIGS. The light guide sheet 31 in FIG. 6 is a substantially square light guide sheet for an LED light source having an incident end face on which light enters and an opposing end face facing the incident end face. The light guide sheet 31 is formed in a non-wedge shape and a plate shape. Further, the incident end surface is configured as a flat surface, and thereby, the light output axis Z of light incident from a plurality of LED light sources is configured to be substantially perpendicular to a virtual plane substantially parallel to the incident end surface. . Furthermore, the light guide sheet 31 has a plurality of reflective dots 15 on the back surface. About the some reflective dot 15, since it is the same as that of the light guide sheet 2 of FIG. 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The opposed end surface includes a plurality of first reflecting surfaces 32 inclined to one side and a plurality of second reflecting surfaces 33 inclined to the other side with reference to a virtual surface substantially parallel to the incident end surface. Each of the first reflecting surface 32 and the second reflecting surface 33 is configured to be able to reflect the light emitted from the LED light source toward the incident end surface. As shown in FIG. 7, the plurality of first reflection surfaces 32 and the plurality of second reflection surfaces 33 are each formed in a partial arc shape in which the light emission directions of the plurality of LED light sources are radial in plan view. Further, as shown in FIG. 8, the plurality of first reflecting surfaces 32 and the plurality of second reflecting surfaces 33 are each formed in a rectangular shape having a thickness direction as a longitudinal direction in a side view, and the light guide sheet 31. And the thicknesses of the first reflecting surface 32 and the second reflecting surface 33 coincide with each other.

  The opposed end surface is alternately provided with a first reflecting surface group 34 in which a plurality of first reflecting surfaces 32 are continuous and a second reflecting surface group 35 in which a plurality of second reflecting surfaces 33 are continued. The first reflecting surface group 34 and the second reflecting surface group 35 adjacent thereto constitute a linear Fresnel lens 36 whose axial direction is the thickness direction. Specifically, one first reflecting surface group 34 and one second reflecting surface group 35 are disposed between the light output axes Z of a pair of adjacent LED light sources. The two reflecting surface groups 35 constitute one linear Fresnel lens 36 having a predetermined focal point. In the light guide sheet 31, a plurality of linear Fresnel lenses 36 are continuously provided in the width direction of the facing end surface, and the pitch of the linear Fresnel lenses 36 is equal to the pitch of the LED light sources. Further, the end of each linear Fresnel lens 36 in the width direction coincides with the light output axis Z of the LED light source. In the light guide sheet 31, the first reflecting surface group 34 and the second reflecting surface group 35 are formed by the first reflecting surface group 34 and the second reflecting surface group 35 adjacent thereto constituting a linear Fresnel lens. It is possible to appropriately collect or diffuse the light beams reflected by the light source, and to effectively suppress the generation of dark spots.

  The focal length of the linear Fresnel lens 36 is preferably substantially the same as the average distance L between the incident end face and the opposed end face. In this way, the light guide sheet 31 has the focal length of the linear Fresnel lens 36 substantially equal to the average distance L between the incident end face and the opposite end face, thereby converting the light incident on the opposite end face into a dark spot near the incident end face. Easy to reflect toward. Therefore, the light guide sheet 31 can more reliably suppress the generation of dark spots near the incident end face.

Further, as shown in FIG. 9, the linear Fresnel where the facing portion X ₁ facing the one LED light source 3 on the incident end face and the other facing portion X ₂ adjacent to the _one facing portion X ₁ are opposed to each other. focal point F of the lens 36 is preferably substantially located between the first face portion X ₁ and other face sites X _2. As a result, the light guide sheet 31 can reliably propagate the light beams reflected by the first reflection surface 32 and the second reflection surface 33 to the region outside the light output axis, thereby more effectively generating dark spots. Can be suppressed.

  The size and main component of the light guide sheet 31 can be the same as those of the light guide sheet 2 in FIG. Further, the inclination angle of the first reflection surface 32 on the light output axis Z side of the LED light source in each first reflection surface group 34 and the inclination of the second reflection surface 33 on the light output axis Z side of the LED light source in each second reflection surface group 35. The angle of inclination of the first reflecting surface 32 on the light output axis Z side of the LED light source in each first reflecting surface group 34 is α, and the second reflecting surface 33 on the light output axis Z side of the LED light source in each second reflecting surface group 35. Is the preferred angle of inclination when the average angle between the incident end face and the opposing end face of the light guide sheet 31 is L, and the pitch of the LED light sources 3 is P, the first reflecting faces 32 and the second reflecting faces 33. , The number of first reflecting surfaces 32 and second reflecting surfaces 33 in each first reflecting surface group 34 and each second reflecting surface group 35, and the number of first reflecting surface groups 34 and each second reflecting surface group 35. As the arithmetic mean roughness Ra of the width, the plurality of first reflecting surfaces 32 and the plurality of second reflecting surfaces 33, It can be the same as the light guide sheet 2 of FIG. The inclination angle of the first reflecting surface 32 in the light guide sheet 31 is an inclination between a straight line passing through both ends in the width direction of the first reflecting surface 32 at the middle point in the thickness direction of the light guide sheet 31 and the virtual surface. The inclination angle of the second reflection surface 33 refers to the inclination angle between a straight line passing through both ends in the width direction of the second reflection surface 33 at the middle point in the thickness direction of the light guide sheet 31 and the virtual surface. .

<Advantages>
In the light guide sheet 31, as described above, the first reflecting surface group 34 and the second reflecting surface group 35 adjacent to the first reflecting surface group 34 constitute a linear Fresnel lens. can do.

[Fourth embodiment]
<Light guide sheet>
A light guide sheet 41 of FIG. 10 is used in the backlight unit 1 in place of the light guide sheets 2, 21, and 31 of FIGS. The light guide sheet 41 in FIG. 10 is a substantially rectangular light guide sheet for an LED light source having an incident end face on which light enters and an opposing end face facing the incident end face. The light guide sheet 41 is formed in a non-wedge shape and a plate shape. Further, the incident end surface is configured as a flat surface, and thereby, the light output axis Z of light incident from a plurality of LED light sources is configured to be substantially perpendicular to a virtual plane substantially parallel to the incident end surface. . Furthermore, the light guide sheet 41 has a plurality of reflective dots 15 on the back surface. About the some reflective dot 15, since it is the same as that of the light guide sheet 2 of FIG. 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 11, the opposed end surfaces are a plurality of first reflecting surfaces 42 inclined to one side and a plurality of second reflecting surfaces 43 inclined to the other side with reference to a virtual surface substantially parallel to the incident end surface. With. Each of the first reflecting surface 42 and the second reflecting surface 43 is configured to be able to reflect the light emitted from the LED light source toward the incident end face.

  The opposed end surfaces are alternately provided with first reflective surface groups 44 in which a plurality of first reflective surfaces 42 are continuous and second reflective surface groups 45 in which a plurality of second reflective surfaces 43 are continuous. Further, as shown in FIG. 12, the first reflecting surface group 44 and the second reflecting surface group 45 adjacent thereto constitute a Fresnel lens 46 whose center is located at the middle point in the thickness direction. Specifically, each of the first reflecting surface group 44 and the second reflecting surface group 45 is disposed between the light output axes Z of a pair of adjacent LED light sources. The two reflecting surface groups 45 constitute one Fresnel lens 46. In the light guide sheet 41, a plurality of Fresnel lenses 46 are continuously provided in the width direction of the facing end face, and the pitch of the Fresnel lenses 46 is equal to the pitch of the LED light sources. Moreover, the edge part of the width direction of each Fresnel lens 46 corresponds with the light emission axis Z of a LED light source. In this light guide sheet 41, the first reflecting surface group 44 and the second reflecting surface group 45 are constituted by the first reflecting surface group 44 and the second reflecting surface group 45 adjacent thereto constituting the Fresnel lens 46. It is possible to appropriately collect or diffuse the light beams reflected by the light source, and to effectively suppress the generation of dark spots. Further, the light guide sheet 41 is configured such that the first reflecting surface group 44 and the second reflecting surface group 45 adjacent to the first reflecting surface group 44 constitute a Fresnel lens 46, so that the light beam can be easily reflected in the front surface direction or the back surface direction. Can be easily emitted from the surface side.

  The focal length of the Fresnel lens 46 is preferably substantially the same as the average distance between the incident end surface and the opposed end surface, like the linear Fresnel lens 36 of the light guide sheet 31 of FIG. Further, the focal point of the Fresnel lens 46 facing between the one facing portion with one LED light source on the incident end surface and the other facing portion adjacent to the one facing portion is the focus of the light guide sheet 31 of FIG. Similar to the linear Fresnel lens 36, it is preferably located substantially between one facing portion and the other facing portion.

  The size and main component of the light guide sheet 41 can be the same as those of the light guide sheet 2 in FIG. Further, the inclination angle of the first reflection surface 42 on the light output axis Z side of the LED light source in each first reflection surface group 44 and the inclination of the second reflection surface 43 on the light output axis Z side of the LED light source in each second reflection surface group 45. The angle of inclination of the first reflection surface 42 on the light output axis Z side of the LED light source in each first reflection surface group 44 is α, and the second reflection surface 43 on the light output axis Z side of the LED light source in each second reflection surface group 45. Is the preferred inclination angle when the average angle between the incident end face and the opposing end face of the light guide sheet 41 is L, and the pitch of the LED light source is P, the first reflecting face 42 and the second reflecting face 43. Average width, number of first reflecting surfaces 42 and second reflecting surfaces 43 in each first reflecting surface group 44 and each second reflecting surface group 45, width of each first reflecting surface group 44 and each second reflecting surface group 45 As the arithmetic average roughness Ra of the plurality of first reflecting surfaces 42 and the plurality of second reflecting surfaces 43, 1 light guide sheet 2.

<Advantages>
In the light guide sheet 41, as described above, since the first reflecting surface group 44 and the second reflecting surface group 45 adjacent thereto constitute a linear Fresnel lens, generation of dark spots is further effectively suppressed. can do.

[Fifth embodiment]
<Liquid crystal display device>
A liquid crystal display device 51 of FIG. 13 includes the edge light type backlight unit 1 of FIG. 1 and a liquid crystal panel 52 disposed on the surface side of the optical sheet 4 of the backlight unit 1. The liquid crystal display device 51 is configured as a mobile phone terminal such as a smartphone.

(LCD panel)
The liquid crystal panel 52 includes a front-side polarizing plate 53 and a back-side polarizing plate 54 that are disposed substantially in parallel and at a predetermined interval, and a liquid crystal cell 55 that is disposed therebetween. The front-side polarizing plate 53 and the back-side polarizing plate 54 are composed of, for example, a polarizer such as an iodine-based polarizer, a dye-based polarizer, and a polyene-based polarizer, and a pair of transparent protective films disposed on both sides thereof. The transmission axis directions of the front-side polarizing plate 53 and the back-side polarizing plate 54 are orthogonal to each other.

  The liquid crystal cell 55 has a function of controlling the amount of transmitted light, and various known ones are employed. The liquid crystal cell 55 is generally a laminated structure including a substrate, a color filter, a counter electrode, a liquid crystal layer, a pixel electrode, a substrate, and the like. A transparent conductive film such as ITO is used for the pixel electrode. As the display mode of the liquid crystal cell, for example, TN (Twisted Nematic), VA (Virtual Alignment), IPS (In-Placed Liquid Crystal, FLC), AFLC (Anti-ferroelectric Critical Lithium). Bend), STN (Super Twisted Nematic), HAN (Hybrid Aligned Nematic), etc. can be used.

<Advantages>
Since the liquid crystal display device 51 includes the edge light type backlight unit 1, the use efficiency of light rays is high and luminance unevenness can be suppressed.

[Other Embodiments]
The light guide sheet, the edge light type backlight unit and the liquid crystal display device according to the present invention can be implemented in various modified and improved modes in addition to the above mode. For example, the facing end surface of the light guide sheet is not limited to the configuration of the above-described embodiment, and for example, the configuration shown in FIG. 14 may be employed.

  The opposing end surface of the light guide sheet 61 in FIG. 14 has a plurality of first reflecting surfaces 62 inclined to one side and a plurality of second reflecting surfaces 63 inclined to the other side with reference to a virtual surface substantially parallel to the incident end surface. With. In the light guide sheet 61, the connecting portions of the first reflecting surface 62 and the second reflecting surface 63 are substantially aligned with the light output axis Z of the LED light beam. Specifically, the connecting portion between the end side of the first reflecting surface 62 on the incident end surface side and the end side of the second reflecting surface 63 on the incident end surface side substantially coincides with the light output axis Z of the LED light source. In addition, the light guide sheet 61 is connected to the first reflecting surface 62 and the second reflecting surface 63 by a third reflecting surface 64 whose ends opposite to the light output direction of the LED light source are substantially parallel to the virtual surface. . Further, the center in the width direction of the third reflecting surface 64 is substantially coincident with the center between the light output axes Z of the adjacent LED light sources. Since the light guide sheet 61 has such a configuration, the light guide sheet 61 transmits light incident on the first reflection surface 63 and the second reflection surface 64 to the first reflection surface 63 and the second reflection surface 4. It is easy to reflect in the dark spot between the light emission axes Z of the LED light source containing. The light guide sheet 61 does not have a first reflecting surface group in which a plurality of first reflecting surfaces 62 are continuous and a second reflecting surface group in which a plurality of second reflecting surfaces 63 are continuous, but each first reflecting surface group is not included. A first reflecting surface group may be provided in place of the surface 62, and a second reflecting surface group may be provided in place of each second reflecting surface 62.

  In addition, the 1st reflective surface 62, the 2nd reflective surface 63, and the 3rd reflective surface 64 of the light guide sheet 61 of FIG. 14 may be comprised by planar shape, and may be comprised as a curved surface. Further, the size and main component of the light guide sheet 61 can be the same as those of the light guide sheet 2 of FIG. Further, the inclination angle of the plurality of first reflection surfaces 62, the inclination angle of the plurality of second reflection surfaces 63, the average inclination angle of the first reflection surface 62 is α, the average inclination angle of the second reflection surface 63 is β, and the light is guided. A preferred inclination angle when the average interval between the incident end face and the opposite end face of the sheet 61 is L, and the pitch of the LED light sources is P, and the arithmetic average roughness Ra of the plurality of first reflecting faces 62 and the plurality of second reflecting faces 63 Can be the same as the light guide sheet 2 of FIG.

  A plurality of the first reflection surface and the second reflection surface are not necessarily formed, and only one of each may be formed.

  The opposing end face is preferably laminated with the reflective layer from the viewpoint of increasing the reflection efficiency. For example, the light guide sheets 21, 31, 41, and 61 shown in FIGS. It may be.

  Even when the first reflecting surface group and the second reflecting surface group constitute a linear Fresnel lens or a Fresnel lens, the focal lengths of these lenses do not necessarily coincide with the average distance between the incident end surface and the opposed end surface. May be. Further, the linear Fresnel lens or the focal point of the Fresnel lens facing each other between one facing part with one LED light source at the incident end face and another facing part adjacent to this one facing part is not necessarily one facing part. And it does not need to be substantially located between other facing parts.

  In the third embodiment, a linear Fresnel lens in which a cylindrical lens is applied to a Fresnel lens has been described. However, the linear Fresnel lens in the light guide sheet is not necessarily limited to such a configuration. For example, the linear Fresnel lens is used. Each 1st reflective surface and 2nd reflective surface which comprise may each be comprised as a flat surface. Further, each of the first reflecting surface and the second reflecting surface constituting the Fresnel lens does not necessarily have a partial spherical shape in a strict sense.

  The light guide sheet does not necessarily have the reflective dots. Further, even when the light guide sheet has reflective dots, the specific configuration of the reflective dots is not limited to the configuration of the above-described embodiment. For example, the light guide sheet includes a plurality of convex portions formed by applying and drying ink. There may be a plurality of recesses formed from the back surface to the front surface side.

  The light guide sheet is not necessarily formed so that the entire incident end surface is a flat surface, and the configuration shown in FIG. 15 can also be adopted. In the light guide sheet 71 of FIG. 15, a plurality of light incident portions 72 where light from the LED light source 3 is incident are formed on the incident end face. In the light guide sheet 71, the virtual plane substantially parallel to the incident end face is configured as a plane substantially parallel to the plurality of light incident portions 72. In other words, “substantially parallel to the incident end face” means that, when a light incident part for incident light from the LED light source is defined on the incident end face, it is substantially parallel to the light incident part.

  The light guide sheet may have another layer on the front surface side or the back surface side. Examples of such other layers include a hard coat layer. Further, the light guide sheet may have a lenticular shape or the like on the surface so that the emitted light can be controlled.

  The edge light type backlight unit does not necessarily have a reflection sheet disposed on the back side of the light guide sheet. For example, the surface of the top plate disposed on the back side of the light guide sheet is polished. The reflecting surface may be used instead of the reflecting sheet. The edge light type backlight unit can promote thinning by forming the top plate surface as the backmost surface of the backlight unit in this way, except for the reflection sheet.

  The liquid crystal display device does not necessarily include the light guide sheet 2 of the first embodiment. As the light guide sheet provided in the liquid crystal display device, for example, the light guide sheets 21, 31, 41, and 61 shown in FIGS.

  The liquid crystal display device adopts various configurations such as a portable terminal such as a laptop computer and a tablet terminal, a portable terminal such as a laptop computer, a tablet terminal, a desktop computer, and a thin TV, in addition to the above-described mobile phone terminal such as a smartphone. be able to.

  As described above, the light guide sheet, the edge light type backlight unit and the liquid crystal display device according to the present invention have high light utilization efficiency and can suppress luminance unevenness, and thus are suitable for high quality liquid crystal display devices. ing.

DESCRIPTION OF SYMBOLS 1 Edge light type backlight unit, backlight unit 2, 21, 31, 41, 61, 71 Light guide sheet 3 LED light source 4 Optical sheet 5 Reflective sheet 11, 32, 42, 62 First reflective surface 12, 33, 43 , 63 Second reflective surface 13, 34, 44 First reflective surface group 14, 35, 45 Second reflective surface group 15 Reflective dot 22 Main body 23 Reflective layer 36 Linear Fresnel lens 46 Fresnel lens 51 Liquid crystal display device 52 Liquid crystal panel 53 Surface side polarizing plate 54 back face side-polarizing plate 55 liquid crystal cell 64 a third reflecting surface 72 the light incident portion 101 an edge light type backlight unit 102 light guiding sheet 103 LED light source F focus X _{1, X 2} facing portions Z Idemitsu axis

Claims (10)

A light guide sheet for an LED light source having an incident end face on which light enters and an opposite end face,
The opposing end surface includes one or more first reflecting surfaces that are inclined to one side and one or more second reflecting surfaces that are inclined to the other side with reference to a virtual surface substantially parallel to the incident end surface. A light guide sheet characterized.   The said opposing end surface is equipped with the 1st reflective surface group in which several said 1st reflective surfaces continue, and the 2nd reflective surface group in which several said 2nd reflective surfaces continue alternately. Light guide sheet.   The light guide sheet according to claim 2, wherein the first reflecting surface group and the second reflecting surface group adjacent thereto constitute a linear Fresnel lens whose axial direction is the thickness direction.   The light guide sheet according to claim 2, wherein the first reflecting surface group and the second reflecting surface group adjacent to the first reflecting surface group constitute a Fresnel lens whose center is located at a midpoint in the thickness direction.   The light guide sheet according to claim 3 or 4, wherein a focal length of the linear Fresnel lens or the Fresnel lens substantially coincides with an average interval between the incident end surface and the opposed end surface.   The light guide sheet according to any one of claims 1 to 5, further comprising a white pigment layer or a metal vapor deposition layer laminated on the facing end surface.   The light guide sheet according to any one of claims 1 to 6, wherein an arithmetic average roughness Ra of the first reflecting surface and the second reflecting surface is 0.04 µm or more and 0.3 µm or less. A substantially rectangular light guide sheet having an incident end face and an opposite end face;
An edge light type backlight unit comprising a plurality of LED light sources disposed along the incident end face of the light guide sheet,
An edge light type backlight unit using the light guide sheet according to any one of claims 1 to 7 as the light guide sheet. Using the light guide sheet according to claim 5 as the light guide sheet,
The focal point of the linear Fresnel lens or the Fresnel lens facing between one facing part with one LED light source on the incident end face and another facing part adjacent to the facing part is the one facing part and the other. The edge-light-type backlight unit according to claim 8, which is substantially located between the facing portions.   A liquid crystal display device comprising the edge light type backlight unit according to claim 8.

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