JP2009122257A - Optical sheet, backlight unit provided with the same and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet capable of preventing the deterioration in optical characteristics and capable of preventing the stripping of a joint layer, to provide a backlight unit provided with the optical sheet, and to provide a display device comprising the backlight unit. <P>SOLUTION: The optical sheet 21 comprises: a diffusion layer 7 for diffusing light from a light source 20a; a lens part 1 which is arranged on the emission side of the diffusion layer 7 and has lenses arranged in an array shape therein; and a reflection part 5 which is formed between the diffusion layer 7 and the lens part 1 and is provided with air layers 5a for regulating incident ranges of respective lenses. The diffusion layer 7 and the reflection part 5 are integrated via the joint layer 6. The joint layer 6 has a storage modulus at 100°C of ≤1.0×10<SP>5</SP>Pa and has a thickness of the joint layer 6 set to ≥5 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical sheet, a backlight unit including the optical sheet, and a display device.

  A display device typified by a liquid crystal display device (LCD) incorporates a light source (backlight) in order to recognize information such as provided images. The power consumed by this light source occupies a considerable portion of the power consumed by the entire display device, and in recent years when there is a strong demand for reducing the total power, it is required to improve the utilization efficiency of the light source.

As means for solving this problem, a film provided with a brightness enhancement film (BEF; Brightness Enhancement Film: a registered trademark of 3M USA) is widely used.
BEF is a film in which unit prisms having a triangular cross section are periodically arranged in one direction on a transparent substrate. This prism is formed in a size (pitch) larger than the wavelength of light. BEF collects light from “off-axis” and redirects this light “on-axis” to the viewer, or “recycle”. " Therefore, when using the display (when observing), the on-axis luminance can be increased by reducing the off-axis luminance of the light emitted from the light source by BEF.
Note that “on the axis” is a direction that coincides with the visual direction of the viewer, and is generally a normal direction to the display screen.

In BEF, when a repetitive array structure of prisms is arranged in only one direction, only redirection or recycling in the arrangement direction is possible. Therefore, in order to control the luminance of the display light in the horizontal direction on the horizontal plane and in the vertical direction perpendicular thereto, the two BEFs may be used in combination so that the arrangement directions of the prism groups are substantially orthogonal to each other. . Thus, by adopting BEF, a desired on-axis brightness can be achieved while reducing power consumption.
Many patent documents disclose that a brightness control member having a repetitive array structure of prisms represented by BEF is used for an optical sheet such as a display device (see, for example, Patent Documents 1 to 3).

In an edge light type display device provided with an optical sheet using the above-described BEF as a luminance control member, for example, light from the light source is emitted from the inclined surface of the prism. The light emitted from the inclined surface of the prism is emitted as light in a certain angle range controlled by the refraction action with the axial direction as the center of the light so as to increase the intensity of light in the visual direction of the viewer. Be controlled.
However, at the same time, there is a problem in that the light component reflected from one inclined surface of the prism and refracted by the other inclined surface is emitted in the lateral direction without going in the viewer's visual direction. It was.

FIG. 3 is a diagram illustrating a luminance distribution with respect to the viewing angle in the display device, in which the vertical axis represents the light intensity and the horizontal axis represents the viewing angle of the observer centered on the on-axis.
As shown in FIG. 3, the light intensity distribution of the display device provided with the BEF optical sheet is the angle of the viewer's visual direction F (see FIG. 1: corresponding to the on-axis direction), as shown by the broken line B. Although the light intensity at 0 ° is the highest, the light intensity gradually decreases as the emission angle in the horizontal direction with respect to the visual direction F (on-axis direction) gradually changes in both side (±) directions. At an emission angle near ± 90 ° that coincides with the horizontal axis, sidelobe light deviating from the viewing direction is shown as a small light intensity peak. Since the sidelobe light deviates from the observer's field of view, there is a problem that the amount of light emitted from the lateral direction of the prism is increased.
In general, a usage pattern in which two prism sheets are used in combination so that the other prism is substantially orthogonal to the direction in which one prism is arranged in parallel is widely used. The broken line B in the graph shown in FIG. 3 represents the light intensity distribution when only one BEF optical sheet (prism sheet) is used. Therefore, the luminance distribution having the light intensity peak of the side lobe light indicated by the broken line B in FIG. 3 is not desirable, and there is no light intensity peak due to the side lobe light in the vicinity of ± 90 ° indicated by the solid line A as a substantially normal distribution curve. A smooth luminance distribution is preferred.

On the other hand, when only the on-axis luminance increases excessively, the width of the mountain in the graph becomes extremely narrow, and the viewing area is extremely limited.
Therefore, it is conceivable to provide a light diffusion member (diffusion layer) on the optical sheet in order to appropriately widen the width of the peaks in the graph. However, in this case, the number of optical members increases, resulting in a phenomenon in which luminance decreases.

In order to overcome such drawbacks, as shown in Patent Document 4, for example, a backlight unit using an optical sheet having a repetitive array structure of unit lenses instead of a prism has been proposed. This backlight unit includes a liquid crystal panel and light source means for irradiating the liquid crystal panel with light from the back side. The light source means is provided with an arrayed lens layer for guiding light from the light source to the liquid crystal panel. ing. An opening located in the vicinity of the lens layer focal plane and the light shielding sheet or a light shielding sheet having an opening outside the lens layer focal plane in a positional relationship where an image is formed inside the liquid crystal layer by the lens layer. In addition, the light shielding sheet has openings and light shielding parts alternately arranged, and the openings are configured as a low refractive index layer (air layer) between the light guide plate and the lens layer.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500 JP 2000-284268 A

By the way, in the optical sheet described in Patent Document 4 described above, a light shielding sheet in which air layers and light shielding portions are alternately arranged is bonded to a lens layer or a diffusion layer, such as an adhesive or a pressure sensitive adhesive. In some cases, they are bonded together through a bonding layer made of.
However, when the light shielding sheet and the lens layer or the diffusion layer are bonded together via the bonding layer, the thermal expansion in the light shielding sheet and the lens layer or the diffusion layer is caused by the influence of heat generated particularly when the backlight is turned on. Shear stress acts on the bonding layer due to a difference in rate. If the thermal expansion coefficient difference between the light shielding sheet and the lens layer or the diffusion layer is large, the bonding layer cannot absorb the shear stress, and the bonding layer peels off or the bonding layer is pressed and deformed. There are problems such as variations in the shape of the air layer and deterioration of optical characteristics.

  Accordingly, the present invention has been made in view of the above problems, and provides an optical sheet capable of preventing deterioration of optical characteristics and preventing peeling of a bonding layer, a backlight unit including the optical sheet, and a display device. is there.

In order to solve the above-described problems, an optical sheet of the present invention includes a diffusion layer that diffuses light from a light source, an optical element unit that is arranged on an emission side of the diffusion layer, and arrayed optical elements are arranged. And an optical sheet having an opening that is formed between the diffusion layer and the optical element part and restricts an incident range of light with respect to each of the optical elements. The storage layer has a storage elastic modulus of 1.0 × 10 ⁵ Pa or less at 100 ° C., and the thickness of the bonding layer is set to 5 μm or more.
Here, the storage elastic modulus represents an elastic property in the viscoelastic body, and is expressed by an elastic modulus having the same phase component as the displacement when the vibration is applied to the viscoelastic body. The reason why dynamic viscoelasticity is adopted is that the bonding material has a restoring force. The parameter indicating the restoring force can be controlled by the dynamic elastic modulus.
According to this configuration, the storage elastic modulus when the bonding layer is 100 ° C. is set to 1.0 × 10 ⁵ Pa or less, and the thickness of the bonding layer is set to 5 μm or more. Since the shear stress acting on the layer is easily absorbed, peeling of the bonding layer can be prevented.

Further, a diffusion layer that diffuses light from the light source, an optical element portion that is arranged on the emission side of the diffusion layer and in which arrayed optical elements are arranged, and is formed between the diffusion layer and the optical element portion And an optical sheet having an opening that regulates an incident range of light with respect to each of the optical elements, wherein the reflecting portion is bonded via a bonding layer, and the bonding layer is at 100 ° C. The storage elastic modulus at is 1.0 × 10 ⁵ Pa or more, and the thickness of the bonding layer is set to 20 μm or less.
According to this configuration, the storage elastic modulus when the bonding layer is 100 ° C. is set to 1.0 × 10 ⁵ Pa or more and the thickness of the bonding layer is set to 20 μm or less. Therefore, it is possible to prevent the opening from being deformed. As a result, good optical characteristics can be maintained.

The bonding layer has a loss elastic modulus at 100 ° C. set to 1.0 × 10 ⁴ Pa or more and 1.0 × 10 ⁵ Pa or less.
Here, the loss elastic modulus represents a viscous property in the viscoelastic body, and is expressed by an elastic modulus having the same phase component as the velocity when vibration is applied to the viscoelastic body.
According to this configuration, by setting the loss elastic modulus of the bonding layer to 1.0 × 10 ⁴ Pa or more and 1.0 × 10 ⁵ Pa or less, it becomes possible to prevent deterioration of optical characteristics and prevention of peeling of the bonding layer. .

The bonding layer is formed between the reflection portion and the diffusion layer.
According to this configuration, by forming the bonding layer between the reflection portion and the diffusion layer, the opening provided in the reflection portion can function as an air layer between the optical element portion and the bonding layer. . Therefore, formation of an air layer becomes easy.

Further, the bonding layer is formed between the optical element portion and the reflection portion.
According to this configuration, by forming the bonding layer between the optical element portion and the reflecting portion, the opening provided in the reflecting portion can function as an air layer between the diffusion layer and the bonding layer. . Therefore, formation of an air layer becomes easy.

Further, the optical element portion, the reflection portion, and the diffusion layer are integrated.
According to this configuration, by integrating the optical element portion, the reflection portion, and the diffusion layer, it is possible to improve the light utilization efficiency and suppress luminance unevenness.

In addition, a reflection type polarization separation film is provided on the exit side of the optical element section.
According to this configuration, among the light emitted from the optical element unit, the linearly polarized light in one polarization direction is transmitted and the linearly polarized light in the other polarization direction is reflected. Brightness unevenness can be suppressed.

The backlight unit of the present invention includes the optical sheet of the present invention, and a direct light source disposed on the back side of the image display element that defines a display image.
The backlight unit of the present invention includes the optical sheet of the present invention, and an area light source including an edge light type light source and a light guide plate disposed on the back side of the image display element that defines a display image. It is characterized by that.
According to this configuration, since the optical sheet that is excellent in light utilization efficiency and can suppress luminance unevenness is provided, a high-performance backlight unit can be provided.

A display device according to the present invention includes the backlight unit according to the present invention and an image display unit including a liquid crystal display element that defines a display image according to transmission / shielding in image units. And
According to this configuration, since the backlight unit that is excellent in light use efficiency and can suppress luminance unevenness is provided, a high-performance display device can be provided.

  According to the present invention, it is possible to prevent deterioration of optical characteristics and peeling of the bonding layer, and a desired refraction effect can be obtained with respect to light diffused by the diffusion layer. Light incident at an angle can be collected. Therefore, it is excellent in light utilization efficiency, and luminance unevenness can be suppressed.

Next, embodiments of the present invention will be described with reference to the drawings.
(Display device)
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a display device according to an embodiment of the present invention. In FIG. 1, the scale of each layer or each member is appropriately changed so that each layer or each member has a size that can be recognized on the drawing.

As shown in FIG. 1, a display device 100 according to this embodiment includes a liquid crystal display unit 22 in which a panel body 2 is sandwiched between reflective polarization separating films 3 and 4 on both sides thereof, and the liquid crystal display unit 22. And a backlight unit 23 for irradiating the liquid crystal display unit 22 with light from the back side. Thereby, the display apparatus 100 displays a rectangular image in plan view by emitting display light whose display is controlled by the image signal toward the upper side in the figure.
Hereinafter, based on such an arrangement, the upper direction in FIG. 1 may be simply referred to as a display screen side (ejection side), and the lower direction may be simply referred to as a back side.

The backlight unit 23 includes a light source unit 20 and an optical sheet 21.
The light source unit 20 includes a plurality of light sources 20a in which linear light emitting units extending in the depth direction of the paper are arranged at equal intervals along the horizontal direction of the paper, and a reflection that covers the light sources 20a from the back side and is opened on the display screen side. A direct type system composed of the plate 20b is adopted.
For example, a cold cathode tube or the like can be used as the light source 20a, but an LED light source in which a plurality of LED elements are arranged on a line along the depth direction of the paper surface may be employed. However, the light source unit 20 is not limited to such a configuration as long as white light can be emitted to the back side of the optical sheet 21, and any known light source unit may be employed. For example, an edge light type surface light source in which a line light source is arranged on the side surface of the light guide plate may be employed.

  The optical sheet 21 collects a part of the light emitted from the light source unit 20 to the display screen side, transmits the light to the display screen side, reflects the other light to the light source unit 20 side, and retransmits it to the light source unit 20. The diffusion layer 7, the bonding layer 6, the reflection part 5, the base sheet 4, and the lens part (optical element part) 1 are laminated in this order from the back side toward the display screen side. . That is, as will be described later, in the formation region of the air layer 5a formed by the reflecting portion 5, the bonding layer 6, the base sheet 4, and the lens portion 1 are laminated in this order.

  The diffusion layer 7 is a plate-like member provided at a position that covers the display screen side of the light source unit 20. The diffusion layer 7 includes a transparent resin and transparent particles dispersed in the transparent resin, and the refractive index of the transparent resin is different from the refractive index of the transparent particles. The diffusion layer 7 diffuses the light P emitted from the light source unit 20 to the display screen side, suppresses uneven illuminance in the horizontal direction of the figure due to the plurality of light sources 20a, and gives an appropriate viewing angle to the display light. Can be done. In addition, as transparent resin of the diffused layer 7, it is possible to use PC (polycarbonate) resin, acrylic resin, fluorine acrylic resin, silicone acrylic resin, epoxy acrylate resin, methylstyrene resin, fluorene resin, and the like. it can.

The reflection unit 5 includes an air layer 5a and a reflection layer 5b.
The reflection layer 5b has a rectangular shape in a cross-sectional view extending in the depth direction on the paper surface on the back side of the lens unit 1, and a plurality of the reflection layers 5b are arranged at regular intervals along the left-right direction on the paper surface and formed in a stripe shape. The reflection layer 5b reflects light incident on the reflection layer 5b out of the light P emitted from the light source unit 20 to the back side, and re-reflects the reflected light on the reflection plate 20b. And the light utilization efficiency can be improved by injecting the light re-reflected by the reflecting plate 20b to the display screen side again. The reflective layer 5b is made of, for example, metal particles or ink formed by dispersing or mixing high refractive index transparent particles such as titanium dioxide, or a transfer layer formed thereon, a metal foil laminated, or a metal material deposited. Can be used. The cross-sectional shape of the reflective layer is not limited to a rectangular cross section. For example, a trapezoidal cross section that is reduced in width toward the back side, a rectangular cross section, a cross-sectional shape obtained by rounding a corner on the back side of the trapezoidal cross section, or the like can be employed.

  Between each reflective layer 5b, an opening is formed, and this opening is configured as an air layer 5a between the display screen side surface of the bonding layer 6 and the back side interface of the lens unit 1. Yes. The air layer 5a regulates the incident range of light with respect to each of a plurality of lenses described later in the lens unit 1. The air layer 5a is configured to have a refractive index lower than that of the bonding layer 6 described later, and the light once diffused in the diffusion layer 7 is refracted at the interface between the bonding layer 6 and the air layer 5a. The light that passes through the lens unit 1 and enters the lens unit 1 with a large incident angle can be collected again in the center.

  As the base sheet 4, a glass plate or a plastic film having light transmittance with respect to the wavelength of light emitted from the light source unit 20 can be employed. Examples of the plastic film include polyethylene terephthalate (PET) and acrylic sheets that are well known in the art.

  The lens unit 1 collects diffused light transmitted through the air layer 5a to the display screen side, so that a plurality of optical elements, for example, lenses are arranged in an array at equal intervals so as to face different air layers 5a. It is a thing. The lens unit 1 is made of, for example, a PET resin, a PC resin, PMMA (polymethyl methacrylate), COP (cycloolefin polymer), or the like, which is well known in the technical field, such as an extrusion molding method, an injection molding method, or a hot press. It can be formed by a molding method. Alternatively, it can be molded using an ultraviolet (UV) curable resin. The lens unit 1 may be formed on the base sheet 4 or may be polymerized and bonded to the base sheet 4 by adhesion, adhesion, or the like.

The lens unit 1 is composed of a convex cylindrical lens array in which a convex cylindrical lens whose lens surface 1a formed convex on the display screen side is extended in the depth direction in the drawing is a unit lens. That is, it is configured as a lenticular lens.
As the shape of the lens surface, a well-known appropriate lens surface shape such as a spherical surface or an elliptical surface may be adopted depending on the required light collecting performance. Further, in order to improve the light collection efficiency, an aspherical shape in which an ellipsoidal surface is used as a reference surface and correction is performed using a higher order term may be used.

  A reflective polarization separation film 8 is provided on the display screen side of the lens unit 1. The reflective polarization separation film 8 is configured to transmit linearly polarized light in one polarization direction of the light emitted from the lens unit 1 and reflect linearly polarized light in the other polarization direction. As a result, the light utilization efficiency can be improved and the luminance unevenness can be suppressed. In the present embodiment, the reflective polarization separation film 8 scatters and reflects linearly polarized light in the other polarization direction. As an example of this reflection type polarization separation film 8, what consists of a birefringent multilayer film, what consists of a cholesteric liquid crystal layer and a phase difference plate, etc. are mentioned, for example. Moreover, it is good also as a structure which provides the light-diffusion layer which has a light diffusibility separately from a reflection type polarization separation film.

  Here, the bonding layer 6 is for stacking and integrating the diffusion layer 7 with the lens unit 1 provided with the reflection unit 5, and the diffusion layer 7 and the reflection unit 5 are interposed via the bonding layer 6. It is pasted. Examples of the constituent material of the bonding layer 6 include bonding materials such as a light-transmitting pressure-sensitive adhesive and adhesive. The main raw material of the bonding layer 6 of this embodiment is preferably a thermoplastic resin such as polycarbonate, acrylic, polypropylene, or cycloolefin polymer, or a UV curable resin containing additives such as a tackifier and a tackifier. . In addition, the constituent material of the bonding layer 6 is mixed with inorganic fillers such as glass and silica, beads such as organic fillers, diffusing agents such as titanium dioxide and barium sulfate, and reflective agents.

  As a specific manufacturing method of the bonding material to be the bonding layer 6, after applying the above-described thermoplastic resin or UV curable resin material on the diffusion layer 7, optical components such as beads, a diffusing agent, a filler, and a reflecting agent are used. Examples thereof include a method of directly applying the element material, and a method of dissolving the optical element material in a solvent together with a resin as a binder and directly applying the material on the diffusion layer 7.

  By the way, when the reflective layer and the diffusion layer are bonded together via the bonding layer, the reflection is caused by the difference in thermal expansion coefficient between the reflective layer and the diffusion layer, particularly due to the influence of heat generated when the light source is turned on. Shear stress acts on the bonding layer that bonds the layer and the diffusion layer. If the thermal expansion coefficient difference between the light shielding sheet and the lens layer or the diffusion layer is large, the bonding layer cannot absorb the shear stress, and the bonding layer peels off or the bonding layer is pressed and deformed. Variations in the shape of the air layer cause problems such as deterioration of optical characteristics.

  Therefore, the inventor of the present application sets the storage elastic modulus, loss elastic modulus, and thickness of the bonding material to be the bonding layer 6 described above to appropriate values, thereby preventing the bonding layer 6 from peeling and the air layer 5a. It has been found that it is possible to prevent deterioration of optical characteristics caused by deformation.

Specifically, the storage elastic modulus when the bonding material (bonding layer 6) is 100 ° C. is preferably 5.0 × 10 ⁴ Pa or more and 5.0 × 10 ⁵ Pa or less. Here, the storage elastic modulus represents an elastic property in the viscoelastic body, and is expressed by an elastic modulus having the same phase component as the displacement when the vibration is applied to the viscoelastic body. The reason why dynamic viscoelasticity is adopted is that the bonding material has a restoring force. The parameter indicating the restoring force can be controlled by the dynamic elastic modulus.

  The storage elastic modulus of the bonding material can be controlled by adjusting the amount of filler added, the degree of crosslinking, the diameter, and the material contained in the bonding material. It can also be controlled by the acid value, molecular weight, and gel fraction of the resin that is the main raw material of the bonding material.

When the storage elastic modulus of the bonding material is smaller than 5.0 × 10 ⁴ Pa, the shear stress acting on the bonding layer 6 can be absorbed, but the reflective layer 5b and the diffusion layer 7 are bonded together or deteriorate with time. Accordingly, the bonding layer 6 is pressed by the reflective layer 5b and the diffusion layer 7 and enters the air layer 5a, and the optical characteristics cannot suppress deterioration. On the other hand, when the storage elastic modulus is larger than 5.0 × 10 ⁵ Pa, the bonding layer 6 can be prevented from entering the air layer 5a, but the shear stress acting on the bonding layer 6 can be absorbed. There is a possibility that the bonding layer 6 may be peeled off.

  The thickness of the bonding layer 6 is preferably set to 5 μm or more and 20 μm or less. If the thickness of the bonding layer 6 is less than 5 μm, the shear stress acting on the bonding layer 6 cannot be absorbed, and the bonding layer 6 may be peeled off. On the other hand, if the thickness of the bonding layer 6 is greater than 20 μm, the bonding layer 6 is pressed by the reflective layer 5b and the diffusion layer 7 and enters the air layer 5a, and the optical characteristics cannot suppress deterioration.

  Here, the inventor of the present application has the same configuration as the optical sheet in the above-described embodiment, and the diffusion layer and the reflection portion are integrated through three types of bonding materials A to C having different storage elastic moduli. Various sample sheets (415 mm × 730 mm) were prepared, and lighting tests were performed using these sample sheets for a display device. The test conditions of this test were that after attaching each sample sheet formed with the thickness of the bonding materials A to C in the range of 3 to 25 μm to a display device (for example, reference numeral 100 in FIG. 1) and lighting the light source for 100 hours. The display state of the image displayed from the image display unit and peeling of the bonding layer were evaluated.

As a result of the measurement under the above conditions, the results shown in Table 1 below were obtained.
Here, the evaluation criteria of the lighting test will be described. In Table 1, peeling “◯” indicates a state in which the bonding layer is hardly peeled on the surface of the sample sheet in the above test, and “△” indicates that the bonding layer is peeled off, but the degree thereof is slight. In addition, it shows a state without progress. Moreover, peeling "x" has shown the state from which many peeling generate | occur | produces on the surface of a sample sheet, and progress is recognized.
In addition, the optical characteristic “◯” indicates that the optical characteristics (luminance, half-value angle, etc.) are hardly deteriorated over time on the surface of the sample sheet, and “△” indicates that the optical characteristics are deteriorated with time. The degree is insignificant and shows a state where it can be used without any problem in normal use. Further, the optical characteristic “x” indicates that the optical characteristic is relatively deteriorated with time on the surface of the sample sheet and cannot be used. In addition, the storage elastic modulus shown in Table 1 has shown the storage elastic modulus in case each joining material is 100 degreeC.

As shown in Table 1, when the bonding material A having the highest storage modulus (5.0 × 10 ⁵ Pa) is used, the optical characteristics are “◯” or “Δ” regardless of the thickness of the bonding material A. Although the above evaluation was obtained, the result of peeling was “x” when the thickness of the bonding material A was 20 μm or less.
This is considered to be the influence of heat generated when the light source is turned on as described above. That is, the sample sheet thermally expands due to the influence of heat generated when the light source is turned on, and shear stress acts on the bonding material A due to the difference in thermal expansion coefficient between the diffusion layer bonded by the bonding material A and the lens portion. . In this case, if the storage elastic modulus of the bonding material A is too high, it is considered that the bonding material A cannot absorb the shear stress, and as a result, the bonding layer peels off.
In addition, when the storage elastic modulus was set to 5.0 × 10 ⁵ Pa or more and the thickness was set to 25 μm or less, peeling could not be prevented. For this reason as well, the upper limit value of the storage elastic modulus is preferably set to 5.0 × 10 ⁵ Pa or less.

On the other hand, when the bonding material C having the lowest storage elastic modulus (5.0 × 10 ⁴ Pa) was used, the peeling was evaluated as “◯” or “Δ” regardless of the thickness of the bonding material A. Regarding the optical characteristics, the result was “x” when the thickness of the bonding material A was 5 μm or more.
This is because by setting the storage elastic modulus to be low, the shear stress acting on the bonding material C can be easily absorbed and the peeling of the bonding material C can be prevented. On the other hand, if the storage elastic modulus is too low, the bonding material It is conceivable that C is deformed by being pressed by the reflective layer or the like. The pressed bonding material C enters the air layer, and thereby the air layer is deformed. As a result, the light emitted from the light source unit cannot obtain a desired refraction effect in the air layer, leading to deterioration of optical characteristics.

When the bonding material B having a storage elastic modulus of 1.0 × 10 ⁵ Pa is used for these bonding materials A and C, the bonding layer peels off and the optical layer is in the range of the thickness of the bonding material B from 3 μm to 20 μm. A good result was obtained with “◯” for both characteristics.

From the above results, the storage elastic modulus of the bonding material, the relationship between the optical properties and the peeling with respect to the thickness, the storage elastic modulus when the bonding material is 100 ° C. is 5.0 × 10 ⁴ or more and 1.0 × 10 ⁵ Pa or less, Further, by setting the thickness of the bonding layer 6 to 5 μm or more, it is possible to reliably prevent the bonding layer 6 from peeling off. Further, when the storage elastic modulus is set to 1.0 × 10 ⁵ Pa or more and 5.0 × 10 ⁵ or less and the thickness of the bonding layer is set to 20 μm or less, the optical characteristics can be favorably maintained.
Furthermore, it is more preferable to set the storage elastic modulus to 1.0 × 10 ⁵ Pa and the thickness to 5 μm or more and 20 μ or less. Thereby, it is possible to achieve both prevention of deterioration of optical characteristics and prevention of peeling of the bonding layer 6.

Further, prevention of peeling of the bonding layer 6 and prevention of deterioration of optical characteristics can be achieved by setting the loss elastic modulus and loss tangent of the bonding material in addition to the above-described setting of the storage elastic modulus.
Specifically, the loss elastic modulus when the bonding layer 6 is 100 ° C. is preferably 1.0 × 10 ⁴ Pa or more and 1.0 × 10 ⁵ Pa or less. Here, the loss elastic modulus represents a viscous property in the viscoelastic body, and is expressed by an elastic modulus having the same phase component as the velocity when vibration is applied to the viscoelastic body.

Adjustment of the loss elastic modulus of the bonding material is the same as the storage elastic modulus described above, the amount of filler added to the bonding material, the degree of crosslinking, the diameter, the material, the acid value of the resin as the main raw material of the bonding material, the molecular weight, It can be controlled by the gel fraction.
If the loss elastic modulus of the bonding material is smaller than 1.0 × 10 ⁴ Pa, the shear stress acting on the bonding layer 6 can be absorbed. However, when the reflective layer 5b and the diffusion layer 7 are bonded to each other or deteriorate with time. Accordingly, the bonding layer 6 is pressed by the reflective layer 5b and the diffusion layer 7 and enters the air layer 5a, and the optical characteristics cannot suppress deterioration. On the other hand, when the loss elastic modulus is larger than 1.0 × 10 ⁵ Pa, the bonding layer 6 can be prevented from entering the air layer 5a, but the shear stress acting on the bonding layer 6 can be absorbed. There is a possibility that the bonding layer 6 may be peeled off.

The loss tangent is preferably set to 0.1 or more and 0.4 or less. Here, the loss tangent is represented by the ratio between the loss elastic modulus and the storage elastic modulus described above.
If the loss tangent of the bonding material is smaller than 0.1, the shear stress acting on the bonding layer 6 can be absorbed. However, the bonding layer 6 is bonded to the reflective layer 5b and the diffusion layer 7 or is deteriorated with time. Is pressed by the reflective layer 5b and the diffusion layer 7 to enter the air layer 5a, and the optical characteristics cannot suppress deterioration. On the other hand, if the loss tangent is larger than 0.4, the bonding layer 6 can be prevented from entering the air layer 5a, but the shear stress acting on the bonding layer 6 cannot be absorbed, and the bonding layer 6 may be peeled off.

Therefore, according to the above-described embodiment, by setting the storage elastic modulus when the bonding layer 6 is 100 ° C. to 1.0 × 10 ⁵ Pa or less and the thickness of the bonding layer 6 to 5 μm or more, the reflective layer Since the shear stress acting on the bonding layer 6 from the lens 5b or the lens portion 1 is easily absorbed, the peeling of the bonding layer 6 can be prevented.
Further, by setting the storage elastic modulus when the bonding layer 6 is 100 ° C. to 1.0 × 10 ⁵ Pa or more and the thickness of the bonding layer 6 to 20 μm or less, the bonding layer 6 is deformed, and the inside of the air layer 5a Therefore, it is possible to prevent deformation of the air layer 5a. As a result, good optical characteristics can be maintained.

  As described above, according to the present embodiment, it is possible to prevent deterioration of optical characteristics and peeling of the bonding layer 6, and a desired refractive effect can be obtained with respect to light diffused by the diffusion layer 7. Light incident on the lens unit 1 at a large incident angle can be collected. Therefore, it is excellent in light utilization efficiency, and luminance unevenness can be suppressed.

Furthermore, by setting the loss elastic modulus of the bonding layer 6 to 1.0 × 10 ⁴ Pa or more and 1.0 × 10 ⁵ Pa or less, it becomes possible to prevent deterioration of optical characteristics and prevention of peeling of the bonding layer.
Further, by setting the loss tangent of the bonding layer 6 to 0.1 or more and 0.4 or less, it becomes possible to prevent the optical characteristics from being deteriorated and to prevent the bonding layer from peeling off.

Further, by forming the bonding layer 6 between the reflecting portion 5 and the diffusion layer 7, the opening provided in the reflecting portion 5 can function as the air layer 5 a between the lens portion 1 and the bonding layer 6. Can do. Therefore, formation of the air layer 5a is facilitated.
In addition, by integrating the lens unit 1, the reflection unit 5, and the diffusion layer 7, it is possible to improve light use efficiency and suppress luminance unevenness.
As described above, in the present embodiment, the optical sheet 21 and the backlight unit 23 that are excellent in light use efficiency and can suppress luminance unevenness are provided, so that a high-performance display device 100 can be provided.

It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention.
FIG. 2 is a cross-sectional view showing another configuration of the display device according to the present invention.
In the above-described embodiment, the display device 100 (see FIG. 1) in which the reflection unit 5 and the diffusion layer 7 are bonded via the bonding layer has been described. For example, as illustrated in FIG. It is also possible to employ a display device 110 that is bonded to 5 via a bonding layer 6.

In this case, as a method of manufacturing the bonding layer, the above-described thermoplastic resin or UV curable resin material is applied to the base sheet 4 made of PET, PC (polycarbonate), or acrylic, and the optical material is optically contained in the material. After melting the element, the bonding layer is obtained by drying. Further, there is a method in which the optical element is dissolved in a solvent together with a resin serving as a binder, and applied to the base sheet 4 and dried to form the bonding layer 6. In addition, there is no restriction | limiting in particular as a coating system to the base material sheet 4, and a drying system.
Thus, by forming the bonding layer 6 between the lens unit 1 and the reflection unit 5, the opening provided in the reflection unit 5 functions as the air layer 5a between the diffusion layer 7 and the bonding layer 6. Can be made. Therefore, formation of the air layer 5a is facilitated.

In the above-described embodiments, the configuration of the color display is not particularly described as the display device. However, if a known configuration such as providing a color filter between the liquid crystal display unit and the optical sheet is added, the color display is performed. Needless to say, the present invention can also be applied to a display device.
Furthermore, the optical sheet according to the present invention is not limited to a lenticular lens sheet, and can be applied to a prism sheet and other unit lenses arranged in an array.

It is typical sectional drawing which shows schematic structure of the display apparatus in embodiment of this invention. It is typical sectional drawing which shows the other structure of the display apparatus in this invention. It is a graph which shows the light intensity distribution of the transmitted light of an optical sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lens part (optical element part) 5 ... Reflection part 5a ... Air layer (opening part) 5b ... Reflection layer 6 ... Bonding layer 7 ... Diffusion layer 8 ... Reflection type polarization separation film 20a ... Light source 23 ... Backlight unit 100, 110 ... Display device

Claims (10)

A diffusion layer for diffusing light from the light source;
An optical element portion arranged on the exit side of the diffusion layer, in which arrayed optical elements are arranged;
In an optical sheet having a reflection portion that is formed between the diffusion layer and the optical element portion and includes an opening that regulates an incident range of light with respect to each of the optical elements.
The reflective portion is bonded via a bonding layer, and the bonding layer has a storage elastic modulus of 1.0 × 10 ⁵ Pa or less at 100 ° C., and the thickness of the bonding layer is set to 5 μm or more. An optical sheet characterized by that. A diffusion layer for diffusing light from the light source;
An optical element portion arranged on the exit side of the diffusion layer, in which arrayed optical elements are arranged;
In an optical sheet having a reflection portion that is formed between the diffusion layer and the optical element portion and includes an opening that regulates an incident range of light with respect to each of the optical elements.
The reflection part is bonded through a bonding layer, and the bonding layer has a storage elastic modulus of 1.0 × 10 ⁵ Pa or more at 100 ° C., and the thickness of the bonding layer is set to 20 μm or less. An optical sheet characterized by that. 3. The optical according to claim 1, wherein the bonding layer has a loss elastic modulus at 100 ° C. set to 1.0 × 10 ⁴ Pa or more and 1.0 × 10 ⁵ Pa or less. Sheet.   The optical sheet according to any one of claims 1 to 3, wherein the bonding layer is formed between the reflection portion and the diffusion layer.   The optical sheet according to any one of claims 1 to 3, wherein the bonding layer is formed between the optical element portion and the reflecting portion.   The optical sheet according to any one of claims 1 to 5, wherein the optical element section, the reflection section, and the diffusion layer are integrated.   The optical sheet according to any one of claims 1 to 6, further comprising a reflective polarization separation film on an exit side of the optical element section. The optical sheet according to any one of claims 1 to 7,
A backlight unit, comprising: a direct light source disposed on the back side of an image display element that defines a display image. The optical sheet according to any one of claims 1 to 7,
A backlight unit comprising: an edge light type light source disposed on the back side of an image display element that defines a display image; and a surface light source including a light guide plate. The backlight unit according to claim 8 or claim 9,
An image display unit comprising a liquid crystal display element that defines a display image according to transmission / shading in image units.

Images