JP2009151225A - Optical sheet, backlight unit and display device - Google Patents

Abstract

An optical sheet in which a light diffusing member and an optical functional member are joined while maintaining an air layer without floating or peeling, and a backlight unit and a display device including the optical sheet are provided. With the goal.
A light diffusing member that diffuses and emits light, an optical function member that controls at least one of the direction, range, color, and luminance distribution of the light, and the light diffusing member. An adhesive layer 18 that joins the optical function member 17. An air layer 28 is provided between the light diffusion member 13 and the optical function member 17, and passes through the air layer 28. In the optical sheet 10 using light as illumination light for a liquid crystal display, the pressure-sensitive adhesive layer 18 is formed by dispersing fine particles 30 for flow prevention in a pressure-sensitive adhesive composition 32, and has a glass transition point Tg of more than −70 ° C. and 0 ° C. The optical sheet 10 which is less than the above can solve the above-mentioned problem.
[Selection] Figure 1

Description

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

  In recent years, a liquid crystal display device (LCD) used in a laptop computer or the like is widely used in which a light source (backlight) is built behind a display screen in order to improve visibility. Such a light source (backlight) consumes a large amount of power and occupies a considerable portion of the power consumed by the entire liquid crystal display (LCD).

On the other hand, since a portable computer such as a laptop computer uses a battery-type power supply, a liquid crystal display (LCD) with low power consumption is required. Therefore, it is required to improve the utilization efficiency of the light source.
In order to improve the light source utilization efficiency, there are means such as increasing the light emission conversion efficiency of the light source (backlight), adjusting the light source (backlight) according to the brightness of the surroundings, and further increasing the light utilization efficiency. Proposed.

  As a means for improving the light utilization efficiency, there is a wide range of methods using an optical film provided with a brightness enhancement film BEF (Brightness Enhancement Film: a registered trademark of 3M Corporation in the United States) between a light source or a light guide plate and a liquid crystal panel. Are known.

  For example, Patent Documents 1 to 3 disclose that an optical functional member having a repetitive array structure of prisms represented by BEF is used for a display such as a liquid crystal display device.

FIG. 5 is an example of a backlight unit with improved light utilization efficiency, and FIG. 6 is a perspective view of a brightness enhancement film (BEF) 185 used in the backlight unit shown in FIG.
In this backlight unit, a brightness enhancement film (hereinafter referred to as BEF: Brightness Enhancement Film) 185 is disposed on the light exit surface 190 b of the light source 190. As shown in FIG. 5, the light P from the light source 190 is finally emitted at a controlled angle φ by the refraction action x so as to increase the intensity of the light in the visual direction F of the viewer. Can be controlled.
As shown in FIGS. 5 and 6, the brightness enhancement film (BEF) 185 is a film that increases the brightness in a specific direction and emits the light. A unit prism 187 having a triangular cross section is formed on the transparent member 186 in one direction. Periodically arranged films. BEF is a registered trademark of 3M USA.

  This unit prism has a large size (pitch) compared to the wavelength of light, so that the brightness enhancement film (BEF) 185 collects the light from “off-axis”, and this Redirect or “recycle” light “on-axis” toward the viewer.

The brightness enhancement film (BEF) 185 improves the display quality of the display by reducing off-axis brightness and increasing on-axis brightness when the display is used (observation).
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 the brightness enhancement film (BEF) 185, a repetitive array structure of prisms is usually composed of an array in only one direction, and only redirection or recycling in the array direction is possible.
Therefore, in order to control the optical characteristics of display light in both the horizontal direction and the vertical direction, it is necessary to use two BEF sheets in combination so that the arrangement directions of the prism groups are substantially orthogonal to each other.

In addition, when the brightness enhancement film (BEF) 185 is used, light may be emitted in a direction that is not the viewer's visual direction, for example, in the lateral direction.
FIG. 7 is a graph showing the light intensity distribution when the visual direction is changed using the brightness enhancement film (BEF) 185. Light emitted from the optical sheet using the brightness enhancement film (BEF) 185 has the highest light intensity in the viewer's visual front direction F (visual direction 0 degree), but the light intensity is also in the vicinity of ± 90 degrees. A small sub-peak (side-lobe) is seen. That is, light is wasted in the lateral direction.

  In addition, when only the on-axis luminance of the optical sheet is excessively improved, the peak width of the luminance distribution curve is remarkably narrowed, and the viewing zone may be extremely limited. In order to broaden the peak width moderately, when a light diffusing film of a member different from the prism sheet is newly used, the number of members increases, which complicates display assembly work and decreases manufacturing efficiency. It is not preferable. Further, the increase in the number of members increases the possibility of putting dust between the optical sheets, and thus is not preferable particularly in a small or thin display.

Therefore, in recent years, an optical sheet having a simple structure in which an optical functional member and a light diffusing member are joined by an adhesive material layer has been developed. In this optical sheet, the light diffused by the light diffusing member erases the shadow of the fluorescent lamp of the backlight (light source), and at least one of the light direction, range, color, and luminance distribution by the optical functional member To control. In addition, by providing an air layer between the optical function member and the light diffusing member, it is possible to obtain light having a smooth luminance distribution with no sub-peak in the vicinity of ± 90 degrees, and to increase the axial luminance in the viewer direction. This can increase the light utilization efficiency.
Here, the air layer plays an important role of improving the central luminance by condensing the light again in the center. Specifically, the light diffused by the light diffusing member is condensed again at the center by utilizing the interface refraction between the resin member and the air layer to improve the central luminance.

Therefore, it is important to stably hold the air layer, but in the conventional optical sheet, the optical function member and the light diffusion member are bonded together with a pressure-sensitive adhesive or an adhesive (hereinafter referred to as pressure-sensitive adhesive). When the film thickness of the adhesive or the like is large, the air layer may be crushed at the time of bonding.
In addition, when the film thickness of the pressure-sensitive adhesive or the like is reduced, the adhesion is insufficient, and there is a case where the float due to the uneven shape on the surface of the light diffusion member occurs. Furthermore, in a high temperature environment, the adhesive and the like fluidized, and due to the difference in the degree of expansion and contraction due to the heat of each member, one of the base material members was warped and floated due to the adhesive or the like, and peeling might occur. .
Furthermore, when a flexible adhesive or the like was used, sufficient adhesion could be imparted. However, in a high temperature environment, for example, when the backlight (light source) was turned on, In some cases, the fluidity was increased, and the air layer was crushed due to peeling or bubbles from the fragile joint.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

  As a result of trial and error, the present inventors have found that the problem of peeling, floating or air layer crushing of the base member is the type of pressure-sensitive adhesive composition used for the pressure-sensitive adhesive layer and the type of flow-preventing fine particles, the addition of flow-preventing fine particles. It has been found that the problem can be solved by appropriately setting parameters such as the amount and the thickness of the adhesive layer.

  The present invention has been made in view of the above problems, and has an optical sheet having an adhesive material layer with high adhesion and capable of bonding a light diffusing member and an optical functional member while maintaining an air layer, and the same. The purpose is to obtain a backlight unit and a display device.

In order to achieve the above object, the present invention employs the following configuration. That is,
The optical sheet of the present invention includes a light diffusing member that diffuses and emits light, an optical functional member that controls at least one characteristic of light direction, range, color, and luminance distribution, and the light diffusing member. A pressure-sensitive adhesive layer that joins the optical function member, an air layer is provided between the light diffusion member and the optical function member, and light transmitted through the air layer is illuminated for a liquid crystal display. An optical sheet used as light, wherein the pressure-sensitive adhesive layer is formed by dispersing fine particles for flow prevention in a pressure-sensitive adhesive composition, and has a glass transition point Tg of more than −70 ° C. and less than 0 ° C.

  The optical sheet of the present invention is characterized in that a plurality of convex portions are formed on the light incident surface of the optical function member, and the periphery of the convex portions is an air layer.

  The optical sheet of the present invention is characterized in that a plurality of convex portions are formed on the light exit surface of the light diffusing member, and the periphery of the convex portions is an air layer.

  The optical sheet of the present invention is characterized in that the convex portion is made of a light reflective member.

  The optical sheet of the present invention is characterized in that an average particle diameter of the fine particles for flow prevention is 50 nm or more and 10 μm or less.

  The optical sheet of the present invention is characterized in that the pressure-sensitive adhesive layer has a thickness of 3 μm or more and 100 μm or less.

  The optical sheet of the present invention is characterized in that the addition amount of the flow preventing fine particles is 5 mass% or more and 50 mass% or less.

  The backlight unit according to the present invention includes the optical sheet described above and a light source.

  The display device of the present invention includes the above-described backlight unit and a liquid crystal display unit.

  According to the above configuration, there is provided an optical sheet having an adhesive layer capable of bonding the light diffusing member and the optical functional member together with the air layer maintained, and the backlight unit and the display device including the optical sheet. Can be provided.

Hereinafter, modes for carrying out the present invention will be described.
(Embodiment 1)
FIG. 1 is a schematic cross-sectional view illustrating an example of an optical sheet and a backlight unit according to an embodiment of the present invention.
As shown in FIG. 1, the backlight unit 40 is formed by arranging the optical sheet 10 on the light emitting surface 20 b of the light source 20.

  The optical sheet 10 includes a light diffusing member 13 that diffuses and emits light, an optical functional member 17 that controls luminance in the light emitting direction, and an adhesive layer 18 that joins the light diffusing member 13 and the optical functional member 17. Formed from. A plurality of lenses 16 are formed on the light exit surface 10 b of the optical sheet 10.

In the optical sheet 10, the light diffusion member 13 is disposed on the light source 20 side, and the optical function member 17 is disposed on the front side.
On the light incident surface 17 a of the optical function member 17, a convex portion 14 made of a light reflective member 22 is provided. The joint surface 14 a of the convex portion 14 is joined to the other surface 18 b of the adhesive material layer 18, and the periphery of the convex portion 14 is an air layer 28.

  In addition, although the cross-sectional shape of the convex part 14 is made into the rectangular shape, what kind of shape will be sufficient if it has the surface which can join the adhesive material layer 18 with high adhesiveness and can form the air layer 28 around it? But it ’s okay. For example, a semicircular shape, a trapezoidal shape, etc. can be mentioned.

  The light emitted from the light source 20 is a parallel light beam P emitted in the direction 1 perpendicular to the light emission surface 20b. The light emitted from the light source 20 and incident on the light incident surface 10a of the optical sheet 10 is first scattered inside the light diffusing member 13 and then incident on the adhesive material layer 18, and then the adhesive material layer 18. After being scattered inside, the light passes through the air layer 28 and is emitted in the front direction F from the light emitting surface 10 b of the optical sheet 10.

(Adhesive layer)
As shown in FIG. 1, the optical function member 17 and the light diffusing member 13 are joined by an adhesive material layer 18, and the adhesive material layer 18 is configured by dispersing fine particles 30 for flow prevention in an adhesive material composition 32. Has been.

As the flow preventing fine particles 30, for example, fine particles made of an inorganic oxide or a resin can be used.
Examples of the fine particles made of an inorganic oxide include particles such as silica or alumina. In addition, the fine particles made of resin include acrylic particles, styrene particles, acrylic, styrene copolymers and crosslinked products thereof, melamine-formalin condensate particles, PTEE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP. Examples thereof include fluorine-containing polymer particles such as (tetrafluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer), and silicone resin particles.
Two or more kinds of these fine particles may be mixed and used.

  The shape of the flow preventing fine particles 30 may be any shape that can prevent the fluidity of the adhesive layer 18 and improve adhesion, and the shape is not particularly defined. For example, a spherical shape, an amorphous shape, a plate shape, a needle shape, an oval shape, or the like can be used.

The flow preventing fine particles 30 preferably have an average particle size of 50 nm or more and 10 μm or less.
When the average particle size of the anti-flow fine particles 30 is included in the above range, the flow of the polymer constituting the adhesive material composition 32 is prevented by entering between the polymers constituting the adhesive material composition 32. Can do.
When the average particle diameter exceeds 10 μm, it cannot enter between the polymers constituting the pressure-sensitive adhesive composition 32, and the behavior of the material constituting the pressure-sensitive adhesive layer 18 does not include the flow preventing fine particles 30. It is not preferable because it is not different from the case.
On the other hand, when the average particle diameter is less than 50 μm, the film strength is lowered, and it is not possible to follow the warp of the base material in a high temperature environment, resulting in peeling.

  The average particle diameter of the flow preventing fine particles 30 is an average value of the diameters of the flow preventing fine particles 30 when the flow preventing fine particles 30 are spherical, and when the flow preventing fine particles 30 are spheroids. The average value of the minor axis is used. This particle diameter can be measured by, for example, a particle size distribution analyzer SD-2000 (manufactured by Sysmex Corporation).

The addition amount of the anti-flowing fine particles 30 in the adhesive layer 18 is preferably 5% by mass or more and 50% by mass or less.
By making the addition amount of the flow preventing fine particles 30 within the above range, it is possible to suppress the floating and peeling in the pressure-sensitive adhesive layer 18 under a high temperature environment.
When the addition amount exceeds 50% by mass, the adhesion is impaired, and it is peeled off in a high-temperature environment and causes floating, which is not preferable. On the contrary, when the addition amount is less than 5% by mass, the behavior under a high temperature environment is not stable and the air layer 28 is crushed, which is not preferable.

The refractive index of the flow preventing fine particles 30 is preferably adjusted to 1.35 to 2.76.
The pressure-sensitive adhesive layer 18 is also a part of the light path, and a light scattering effect is expressed by the difference in refractive index between the pressure-sensitive adhesive composition 32 of the pressure-sensitive adhesive layer 18 and the flow preventing fine particles 30. As a result, since it affects the luminance of the light emitted from the optical function member 17, it is preferable to adjust the refractive index of the flow preventing fine particles 30 to a desired value.

  The flow preventing fine particles 30 preferably have a center particle size equal to or less than the thickness of the pressure-sensitive adhesive layer 18. When the central particle size exceeds the thickness of the adhesive material layer 18, irregularities due to the flow preventing fine particles 30 are formed on one surface (light incident surface) 18a or the other surface (light exit surface) 18b of the adhesive material layer 18, This is because there is a possibility that the adhesion may be impaired.

Examples of the adhesive composition 32 include acrylic and urethane resins.
By using an acrylic resin as the adhesive material composition 32, the adhesive material layer 18 having excellent heat resistance can be formed.
A crosslinking material such as an isocyanate compound, an epoxy compound, or an aziridine compound is added to the acrylic polymer, and reacted with a carboxyl group, a hydroxyl group, an amino group, an amide group, or the like, which are crosslinking base points provided in the acrylic polymer, to crosslink.

  As the cross-linking material, an isocyanate compound or an epoxy compound is particularly preferably used because an appropriate cohesive force can be obtained.

  Examples of the isocyanate compound include aromatic isocyanates such as tolylene diisocyanate and xylene diisocyanate, alicyclic isocyanates such as isophorone diisocyanate, and aliphatic isocyanates such as hexamethylene diisocyanate.

  Examples of the epoxy compound include N, N, N ′, N′-tetraglycidyl-m-xylenediamine and 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane.

As the curing agent, these compounds may be used alone or in combination of two or more.
The adhesive material composition 32 selects a resin having an optimum adhesion in consideration of the resin components constituting the convex portion 14, the optical function member 17, and the light diffusing member 13 joined by the adhesive material layer 8.

  The adhesive material composition 32 may contain additives such as a tackifier and a tackifier. By containing these additives, the adhesive force can be increased and the adhesion can be improved.

Furthermore, by dispersing the flow preventing fine particles 30 in the pressure-sensitive adhesive composition 32, it is possible to suppress the pressure-sensitive adhesive composition 32 from fluidizing, floating and peeling off in a high temperature environment.
In addition, it is not prescribed | regulated whether the adhesive material layer 18 is a single layer.

The adhesive layer 18 preferably has a glass transition point Tg of more than −70 ° C. and less than 0 ° C.
The glass transition point Tg is a temperature at which a substance such as glass, which is a liquid at a high temperature, suddenly increases its viscosity in a certain temperature range due to a temperature drop, almost loses fluidity and becomes an amorphous solid.
If Tg is within this range, the adhesiveness can be kept high and the substrate can be caused to follow the warp of the substrate in a high temperature environment, and floating, peeling, and the like can be suppressed.
When Tg is −70 ° C. or lower, it is not preferable because the adhesiveness cannot be kept high and floats and peels off.
Moreover, when Tg is 0 ° C. or higher, fluidity is generated and the air layer 18 may be crushed.

Further, even when the anti-flow fine particles 30 are added to the adhesive material composition 32, the Tg of the adhesive material layer 18 does not change, and is preferably more than −70 ° C. and less than 0 ° C.
If Tg is within this range, the adhesion can be kept higher, it can cope with the warp of the substrate, etc., and can be prevented from floating, peeling, etc. It is possible to prevent the polymer constituting the adhesive material composition 32 from flowing between the polymers constituting the article 32.

  Tg is measured using a thermal analysis technique. The thermal analysis method is a method of measuring a certain physical property of a substance as a function of temperature while changing the temperature of the substance by a constant program. For example, a differential scanning calorimetry (DSC: differential scanning calorimetry method). ), Thermomechanical analysis (TA), dynamic mechanical analysis (DMA), and the like.

The thickness of the adhesive layer 18 is preferably 3 μm or more and 100 μm or less.
When the thickness of the pressure-sensitive adhesive layer 18 exceeds 100 μm, when the pressure-sensitive adhesive layer 18 is formed, the coating property is lowered, the fluidity of the pressure-sensitive adhesive layer 18 is increased, and the air layer 18 may be easily filled. Will occur. In addition, the air layer 28 may be crushed by a pressing force such as foreign matter or handling during loading. In addition, when the air layer 28 is crushed, the restoring function is also significantly reduced.
Conversely, when the thickness of the adhesive layer 18 is less than 3 μm, the function as a buffer material in the high temperature environment of the adhesive layer 18 is lost, and the adhesive layer 18 is easily peeled off, which is not preferable.

The surface treatment method of the surface on which the adhesive material layer 18 is not formed, that is, the light emitting surface 10b of the optical function member 17 and the light incident surface 10a of the light diffusing member 13 is not particularly specified, and is not limited to normal UV resistance treatment or charging It is possible to take a technique such as a prevention treatment or a separate surface treatment layer.
The surface treatment method for the surface on which the adhesive layer 18 is formed, that is, the joint surface 14a of the convex portion 14 and the light exit surface 13b of the light diffusing member 13 is not particularly defined, and the surface layer material such as corona treatment or plasma treatment is not limited. Processing methods that do not change can be taken.

As a specific method for producing the adhesive material layer 18, an adhesive material composition 32, which is a main raw material polymer, and various additives are mixed and stirred in an organic solvent in which the flow preventing fine particles 30 are dispersed. Then, the flow preventing fine particles 30 are dispersed in the adhesive composition 32. Further, the dispersion liquid (adhesive material solution) is mixed with a crosslinking agent, applied to a substrate, and dried to form the adhesive material layer 18.
The base material used at this time may be a film obtained by subjecting an inexpensive base material such as PET to a mold release treatment. Moreover, there is no restriction | limiting in particular as the application method to a base material, and a drying system.

In joining the optical function member 17 and the light diffusing member 13, for example, as described above, the adhesive layer 18 is applied to a base film such as PET to form a dry film, and then the dry film is converted to the light diffusing member 13. Alternatively, it is attached to one of the optical function members 17 and then attached to another member. At this time, it does not matter which member is first attached with the dry film.
There is also a bonding method in which the adhesive layer 18 is applied to either the light diffusion member 13 or the optical function member 17 and then adhered to another member. In this case, it does not matter which member is first attached with the dry film.

(Light diffusion member)
The light diffusing member 13 is a light diffusing member having a light scattering function. A generally used member having a light scattering function can be used.
For example, as shown in FIG. 1, a transparent resin 26 and transparent particles 24 dispersed in the transparent resin 26 are provided. The refractive index of the transparent resin 26 and the refractive index of the transparent particles 24 are different from each other.

The difference in refractive index between the transparent resin 26 and the transparent particles 24 is preferably 0.02 or more.
This is because sufficient light scattering performance cannot be obtained when the difference in refractive index is less than 0.02. When the refractive index difference exceeds 0.5, the light scattering performance does not change so much, so it may be less than 0.5.

  The average particle diameter of the transparent particles 24 is preferably 0.5 to 10.0 μm, and more preferably 1.0 to 5.0 μm. This is because by setting the average particle diameter of the transparent particles 24 within this range, the light incident on the light diffusion portion 13 can be transmitted without being attenuated as much as possible, and the light can be sufficiently scattered.

  Moreover, you may comprise the light-diffusion member 13 as a structure which has the fine cavity which contains air in transparent resin. This is because the light scattering function can be realized also by the refractive index difference between the cavity made of the transparent resin and fine air.

  As the transparent resin 26, for example, polycarbonate resin, acrylic resin, fluorine-based acrylic resin, silicone-based acrylic resin, epoxy acrylate resin, polystyrene resin, cycloolefin polymer, methylstyrene resin, fluorene resin, PET, polypropylene, or the like is used. Can do.

Here, the linear expansion coefficients of polycarbonate, polystyrene, methylstyrene resin and cycloolefin polymer are 6.7 × 10 ⁻⁵ (cm / cm / ° C.) and 7.0 × 10 ⁻⁵ (cm / cm / ° C.), respectively. 7.0 × 10 ⁻⁵ (cm / cm / ° C.) and 6-7 × 10 ⁻⁵ (cm / cm / ° C.). On the other hand, the linear expansion coefficient of PET is 2.7 × 10 ⁻⁵ (cm / cm / ° C.).

In the conventional optical sheet, when the optical function member 17 and the light diffusing member 13 are joined, the adhesive material layer 18 does not have the configuration as in the present invention.
Therefore, for example, when PET is used as the material of the optical function member 17 and polycarbonate is used as the material of the transparent resin 26 of the light diffusion member 13, the linear expansion coefficient of the polycarbonate (6.7 × 10 ⁻⁵ (cm / cm / ° C.)) is larger than the linear expansion coefficient of PET (2.7 × 10 ⁻⁵ (cm / cm / ° C.)), so when the optical sheet 10 is thermally deformed in a high temperature environment, the polycarbonate side, That is, warpage occurs on the light diffusion member 13 side.

As the transparent particles 24, transparent particles made of an inorganic oxide or transparent particles made of a resin can be used.
Examples of the inorganic oxide include particles such as silica or alumina. In addition, as transparent particles made of resin, acrylic particles, styrene particles, acrylic, styrene copolymers and crosslinked products thereof, melamine-formalin condensate particles, PTEE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), Examples thereof include fluorine-containing polymer particles such as FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PVDF (polyfluorovinylidene), and ETFE (ethylene-tetrafluoroethylene copolymer), and silicone resin particles.
In addition, you may use these transparent particles in mixture of 2 or more types.

The plate-like light diffusing member 13 can be manufactured by dispersing transparent particles in these transparent resins and performing extrusion molding.
The thickness of the light diffusing member 13 is preferably 1 to 5 mm.
When the thickness of the light diffusing member 13 is less than 1 mm, the light diffusing member 13 is too thin and does not have rigidity, so that there is a disadvantage that it bends. On the contrary, when it exceeds 5 mm, the light transmittance from the light source 20 decreases.

Further, fine irregularities may be formed on the surface of the light diffusion member 13. Light can be scattered by the fine irregularities on the surface.
In this case, the light diffusing member 13 can be formed by an extrusion method, a casting method, or a method using both the extrusion method and the casting method.

(Optical function member)
The optical function member 17 is a member that controls and emits at least one of the direction, range, color, and luminance distribution of the light incident on the inside. For example, the light intensity in the front direction F is improved and emitted.

A plurality of lenses 16 are formed on the light emitting surface 10 b of the optical function member 17.
These lenses 16 can be formed using, for example, an extrusion molding method. Alternatively, it can be formed by molding on a substrate such as PET using a thermoplastic resin or a UV curable resin.
As shown in FIG. 1, the lens 16 has a cylindrical shape, but may have other shapes. For example, a square pyramid, a spherical surface, a prism, and the like can be given.
The pitch of the lenses 16 may be the same pitch or a random pitch.

  On the light incident surface 17 a of the optical function member 17, a convex portion 14 composed of a plurality of light reflecting members 22 is formed, and the periphery of the convex portion 14 is an air layer 28.

The convex part 14 can be formed by using, for example, a metal oxide such as titanium oxide (TiO ₂ ) using a dry process such as a sputtering method or a wet process such as printing of titanium oxide gel. This metal oxide is used as the light reflecting member 22.

  As shown in FIG. 1, the light P emitted from the light source 20 enters the light incident surface 10 a of the optical sheet 10. Next, the light is scattered inside the light diffusing member 13 and further scattered inside the adhesive layer 18. Further, a part of the scattered light passes through the air layer 28 around the convex portion 14 and is emitted from the lens 16 in the front direction F. The emitted light is configured such that at least one of the characteristics of the direction, range, color, and luminance distribution of the light is controlled.

The light that does not pass through the air layer 28 around the convex portion 14, that is, the light reflected by the light reflecting member 22, once returns to the adhesive material layer 18 side, but again in the adhesive material layer 18 and the light diffusing member 13. Scattered. A part of the scattered light again passes through the air layer 28 around the convex portion 14 and is emitted from the lens 16 in the front direction F. Here, the light that does not pass through the air layer 28 around the convex portion 14 repeats the above steps, and most of the light is emitted in the front direction F.
In addition, it can also be set as the structure which radiate | emits all the light to the front direction F by providing a reflection board around the light source 20. FIG.

  In the optical sheet 10 according to the embodiment of the present invention, the pressure-sensitive adhesive layer 18 includes the pressure-sensitive adhesive composition 32 in which the fine particles 30 for flow prevention are dispersed. Since it is a structure, while maintaining high adhesiveness, it can be made to follow the curvature of the board | substrate in a high temperature environment, etc., and can suppress a float, peeling, etc. Further, the air layer 28 between the light diffusing member 13 and the optical function member 17 can be stably held without being crushed, and at least one of the optical characteristics of the light direction, range, color, and luminance distribution Can be controlled stably.

  In the optical sheet 10 according to the embodiment of the present invention, the pressure-sensitive adhesive layer 18 has the flow preventing fine particles 30 dispersed in the pressure-sensitive adhesive composition 32, and the flow preventing fine particles 30 are added to the pressure-sensitive adhesive composition 32. Since the Tg of the adhesive layer 18 is not changed and is more than −70 ° C. and less than 0 ° C., the adhesion can be kept high, and the substrate can be made to follow the warp of the substrate in a high temperature environment, and floats and peels off. Etc. can be suppressed.

  In the optical sheet 10 according to an embodiment of the present invention, the pressure-sensitive adhesive layer 18 includes the pressure-sensitive fine particle 30 dispersed in the pressure-sensitive adhesive composition 32, and the average particle size of the flow-proof fine particles 30 is 50 nm or more and 10 μm or less. Since it is a structure, it can penetrate between the polymers which comprise the adhesive material composition 32, and the flow of the polymer which comprises the adhesive material composition 32 can be prevented.

  Even in a high temperature environment, the occurrence of warping due to the difference in linear expansion coefficient between the light diffusing member 13 and the optical functional member 17 can be suppressed by buffering, and the air layer between the light diffusing member 13 and the optical functional member 17 can be suppressed. 28 can be stably held without being crushed, and optical property control can be stably performed.

  The optical sheet 10 according to the embodiment of the present invention has a configuration in which the thickness of the pressure-sensitive adhesive layer 18 is 3 μm or more and 100 μm or less, so that the adhesion between the light diffusing member 13 and the optical function member 17 can be kept high. The air layer 28 between the light diffusing member 13 and the optical function member 17 can be stably held without being crushed, and the optical characteristic control can be stably performed.

  In the optical sheet 10 according to an embodiment of the present invention, the pressure-sensitive adhesive layer 18 has a structure in which the flow preventing fine particles 30 are dispersed in the pressure-sensitive adhesive composition 32, and the addition amount thereof is 5 parts by mass or more and 50 parts by mass or less. In addition, floating and peeling in the pressure-sensitive adhesive layer 18 under a high temperature environment can be suppressed, and the air layer 28 between the light diffusion member 13 and the optical function member 17 can be stably held without being crushed. Optical characteristic control can be performed stably.

  In the optical sheet 10 according to the embodiment of the present invention, a plurality of convex portions 14 are formed on the light incident surface 17 a of the optical function member 17, and the joint surface 14 a of the convex portion 14 and the other surface of the adhesive layer 18. 18b is joined, and the periphery of the convex portion 14 is an air layer 28. Therefore, a refractive effect is imparted to the incident light by the air layer 28, and the optical characteristic control can be performed stably. .

  In the optical sheet 10 according to the embodiment of the present invention, the light that has not passed through the air layer 28 is reflected by the light reflective member 22 and returned to the adhesive material layer 18 and the light diffusing member 13. Since the process of emitting light in the front direction F is repeated after the light is diffused by the diffusing member 13, the light brightness can be controlled by effectively utilizing the light.

(Embodiment 2)
FIG. 2 is a schematic cross-sectional view illustrating another example of the optical sheet according to the embodiment of the present invention.
The configuration is the same as that of the first embodiment except that the light incident surface 17a of the brightness control member 17 is processed into a concavo-convex shape and a plurality of convex portions 14 are formed. In addition, the member shown with the same code | symbol shall be the same as the member shown in Embodiment 1. FIG.
The plurality of convex portions 14 are made of the same member as the brightness control member 17, and the other surface 18 b of the adhesive material layer 18 is joined to the joint surface 14 a of the convex portion 14. Note that the light reflective member 22 may be formed on the joint surface 14 a of the convex portion 14.

  Even in such a configuration, a plurality of convex portions 14 are formed on the light incident surface 17a of the luminance control member 17, and the periphery of the convex portions 14 is an air layer 28. Light can be transmitted through the air layer 28. Further, light can be reflected inside the adhesive layer 18 and the light diffusing member 13 by the joint surfaces 14 a of the plurality of convex portions 14. Further, the light reflective member 22 may be formed on the bonding surface 14a. In that case, light can be reflected more effectively.

  The convex portion 14 is formed by mechanically, chemically, or chemically mechanically processing the light incident surface 17a of the luminance control member 17 into an uneven shape.

  Further, when the luminance control member 17 is extruded, the convex portion 14 may be formed by pressing a mold onto one surface of the luminance control member 17. At this time, the lens 16 of the cylindrical lens can be simultaneously formed by pressing the cylindrical lens mold against the light emitting surface 10b of the optical sheet 10 as well.

  Furthermore, there is a method in which a convex portion 14 is formed by applying a thermoplastic resin or UV curable resin to a substrate and then pressing a mold. Examples of the thermoplastic resin and UV curable resin include polycarbonate, acrylic, polypropylene, and cycloolefin polymer.

The light reflecting member 22 can be formed by coating or transferring after forming the convex portion 14.
In addition, the light reflective member 22 can be formed by dispersing and mixing a metal oxide or the like in the resin during the extrusion molding. Furthermore, after the extrusion molding, the light reflective member 22 can be formed on the convex portion 14 by coating or transferring.

(Embodiment 3)
FIG. 3 is a schematic cross-sectional view showing still another example of the optical sheet according to the embodiment of the present invention.
The light emitting surface 13b of the light diffusing member 13 has the same configuration as that of the first embodiment except that the light emitting surface 13b is processed into a concavo-convex shape and a plurality of convex portions 14 are formed. In addition, the member shown with the same code | symbol shall be the same as the member shown in Embodiment 1. FIG.
The plurality of convex portions 14 are made of the same member as the light diffusing member 13. Note that the light reflective member 22 may be formed on the joint surface 14 a of the convex portion 14.
Moreover, the cross-sectional shape of the convex portion 14 is a semi-elliptical shape.

  Even in such a configuration, a plurality of convex portions 14 are formed on the light incident surface 17a of the optical function member 17, and the periphery of the convex portions 14 is an air layer 28. Light can be transmitted through the air layer 28. Further, by forming the light reflective member 22 on the joint surfaces 14 a of the plurality of convex portions 14, light can be reflected inside the adhesive material layer 18 and the light diffusing member 13.

  In the optical sheet 10 according to the embodiment of the present invention, a plurality of convex portions 14 are formed on the light emitting surface 13 b of the light diffusing member 13, the bonding surface 14 a of the convex portion 14, and the one surface 18 a of the adhesive layer 18. Are joined, and the periphery of the convex portion 14 is an air layer 28. Therefore, a refractive effect is imparted to the incident light by the air layer 28, and optical function control can be performed stably.

(Embodiment 4)
FIG. 4 is a schematic cross-sectional view showing an example of the display device according to the embodiment of the present invention.
As shown in FIG. 4, the display device 50 includes a display unit 45 and a backlight unit 40 disposed on the light incident surface 45 a of the display unit 45.
Further, the backlight unit 40 has the configuration shown in the first embodiment, and includes the light source 20 and the optical sheet 10.

  As the display unit 45, for example, a transmissive liquid crystal display is used. After the light from the light source 20 is incident on the optical sheet 10 and the luminance is controlled by the optical sheet 10 so as to increase the light intensity in the front direction F, the controlled light is used as the light incident surface 45a of the display unit 45. The information shown by the display unit 45 is transmitted to the observer in the front direction F.

  Since the backlight unit 40 according to the embodiment of the present invention includes the optical sheet 10 and the light source 20, the backlight unit 40 is arranged between the luminance control member 17 and the light diffusion member 13 of the backlight unit 40 even in a high temperature environment. Thus, the air layer 28 provided in the can can be stably held without being crushed, and the optical characteristics of the backlight unit 40 can be stably controlled.

  Since the display device 50 according to the embodiment of the present invention includes the backlight unit 40 and the liquid crystal display unit 45, the optical characteristics of the backlight unit 40 can be stably controlled even in a high temperature environment. In addition, the optical characteristics of the display device 50 can be stably controlled.

  Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited only to these examples.

  First, adhesive materials of Test Examples 1 to 38 were prepared, and their Tg was measured with a rheometer. Next, the optical sheets of Test Examples 1 to 38 using the adhesive material were prepared, and the three characteristics of the optical sheets of Test Examples 1 to 38, namely, high temperature adhesion, high temperature air layer retention, and air layer restoration properties. Was evaluated.

(Test Example 1)
First, the adhesive material solution which consists of an acrylic adhesive (adhesive material composition) containing an epoxy-type crosslinking agent was adjusted. This was applied to a PET film (model film) to form an adhesive material having a thickness of 10 μm. The adhesive material had a Tg of −26 ° C.
The film thickness of the adhesive material was measured with a contact-type film thickness meter, and the Tg of the adhesive material was measured with a rheometer.

Next, as an optical functional member, a lens sheet was prepared in which a cylindrical lens was formed on one side and a reflective layer (convex portion) made of titanium oxide having a height of 10 μm and a width of 60 μm was formed on the other side. In addition, the film thickness of the reflective layer was measured with a contact-type film thickness meter. Further, a 3 mm thick diffusion plate made of polystyrene was prepared as the light diffusion member.
Next, one surface of the adhesive material layer coated on the PET film (model film) was adhered to one surface of the reflective layer formed on the lens sheet, and the lens sheet and the adhesive material layer were bonded together.
Next, the PET film (release film) was peeled off to expose another surface of the adhesive material layer, the diffusion plate was bonded to this surface, and the lens sheet and the diffusion plate were bonded to each other with the adhesive material layer. The optical sheet of Test Example 1 was produced.

  Next, the optical sheet of Test Example 1 was evaluated for the three characteristics of high temperature adhesion, high temperature air layer retention, and air layer recovery.

  The evaluation method of adhesiveness under high temperature evaluated visually after 80 degreeC and 500 hours progress. The thing which did not float and peeled off was evaluated as (circle). Floating, peeling, etc. were evaluated as Δ when the opposite part was within 3 mm. Moreover, a thing with floating, peeling, etc. larger than the opposite part 3mm was evaluated as x.

  As a method for evaluating the air layer retention under high temperature, visual evaluation was performed after elapse of 500 hours at 80 ° C. A substrate having no air layer collapse due to the warpage of the substrate and the behavior of the adhesive was evaluated as ○. A case where the air layer collapse occurred only at a place where the external pressure caused by the sample holder was applied due to the warpage of the base material and the behavior of the adhesive material was evaluated as Δ. Moreover, the thing which air layer collapse generate | occur | produced in the location without external pressure etc. by the curvature of the base material and the behavior of the adhesive material was evaluated as x.

The air layer restoration property was evaluated by visually evaluating the restoration after pressing a rectangular parallelepiped aluminum plate having a height of 10 mm, a height of 50 mm, and a width of 50 mm from the lens surface side with a hydraulic press for 20 minutes under a load of 20 kgf.
Although there was a difference in the return time, those that returned to their original state were evaluated as ○. Those that did not partially restore only the part biting foreign objects were evaluated as △. The thing which has the part which is not restored | regenerated except the part which bite the foreign material etc. was evaluated as x.

  The production conditions and evaluation results of the optical sheet of Test Example 1 are summarized in Table 1.

(Test Example 2)
As the adhesive material, an acrylic resin fine particle (fine particle for flow prevention) was dispersed and mixed in an acrylic pressure-sensitive adhesive (adhesive material composition) containing an epoxy-based crosslinking agent to prepare an adhesive material solution. This was apply | coated to PET film and the adhesive material with a film thickness of 3 micrometers was formed. The adhesive material had a Tg of −26 ° C.
The optical sheet of Test Example 2 was produced in the same manner as Test Example 1. The production conditions and evaluation results of the optical sheet of Test Example 2 are summarized in Table 1.

(Test Examples 3-38)
Test Example 3 by changing the average particle diameter of the anti-flowing fine particles, the addition amount of the anti-flowing fine particles, the reflective layer thickness, the adhesive layer thickness, and the Tg of the adhesive layer as shown in Tables 1 to 5, respectively. -38 optical sheets were prepared. The production conditions and evaluation results of the optical sheets of Test Examples 3 to 38 are summarized in Tables 1 to 5.

In Test Examples 1, 9, 30, 33, and 36, the flow preventing fine particles were not used, so that the fluidity of the pressure-sensitive adhesive layer was high, and the air layer retention at high temperature and the air layer recoverability were poor.
In Test Examples 28 and 29, the average particle size of the flow preventing fine particles was too large as 15 μm, and could not be sufficiently penetrated between the polymers of the pressure-sensitive adhesive composition, adhesion at high temperature, air layer retention at high temperature None of the air layer resilience resulted in poor results.

It is a cross-sectional schematic diagram which shows an example of the optical sheet and backlight unit of this invention. It is a cross-sectional schematic diagram which shows an example of the optical sheet of this invention. It is a cross-sectional schematic diagram which shows an example of the optical sheet of this invention. It is a cross-sectional schematic diagram which shows an example of the display apparatus of this invention. It is a cross-sectional schematic diagram which shows an example of the conventional backlight unit. It is a perspective view which shows an example of BEF. It is a graph which shows distribution of light intensity at the time of changing a visual direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical sheet, 10a ... Light incident surface, 10b ... Light emission surface, 13 ... Light diffusing member, 13b ... Light emission surface, 14 ... Convex part, 14a ... Joint surface, 16 ... Lens, 17 ... Optical function member, 17a DESCRIPTION OF SYMBOLS ... Light incident surface, 18 ... Adhesive material layer, 18a ... One side, 18b ... Other side, 20 ... Backlight (light source), 22 ... Light reflection member, 24 ... Transparent particle, 26 ... Transparent resin, 28 ... Air layer, 30 Fine particles for preventing flow, 32 ... Adhesive composition, 40 ... Backlight unit, 45 ... Display unit, 45a ... Light incident surface, 45b ... Light exit surface, 50 ... Display device, 185 ... Brightness enhancement film (BEF), 186 ... base material, 187 ... prism, 190 ... backlight (light source).

Claims (9)

A light diffusing member that diffuses and emits light, an optical functional member that controls at least one of the direction, range, color, and luminance distribution of the light, and the light diffusing member and the optical functional member are joined. An adhesive material layer,
An optical sheet in which an air layer is provided between the light diffusing member and the optical function member, and light that passes through the air layer is used as illumination light for a liquid crystal display,
The pressure-sensitive adhesive layer is an optical sheet in which fine particles for flow prevention are dispersed in a pressure-sensitive adhesive composition, and has a glass transition point Tg of more than −70 ° C. and less than 0 ° C.   The optical sheet according to claim 1, wherein a plurality of convex portions are formed on a light incident surface of the optical function member, and the periphery of the convex portions is an air layer.   The optical sheet according to claim 1, wherein a plurality of convex portions are formed on a light emitting surface of the light diffusing member, and the periphery of the convex portions is an air layer.   The optical sheet according to claim 2, wherein the convex portion is made of a light reflective member.   5. The optical sheet according to claim 1, wherein an average particle size of the flow preventing fine particles is 50 nm or more and 10 μm or less.   The optical sheet according to any one of claims 1 to 5, wherein the pressure-sensitive adhesive layer has a thickness of 3 µm or more and 100 µm or less.   The optical sheet according to any one of claims 1 to 6, wherein the addition amount of the flow preventing fine particles is 5 mass% or more and 50 mass% or less.   A backlight unit comprising the optical sheet according to claim 1 and a light source.   A display device comprising: the backlight unit according to claim 8; and a liquid crystal display unit.

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