Laminated optical sheet for backlight unit

Abstract

The laminated optical sheet for a backlight unit, which has excellent light collection efficiency and light source concealment, comprises: a prism sheet; a transparent plate which is laminated with the prism sheet through an adhesive layer under the prism sheet and has a thickness of 1.0 mm or more; and a half mirror disposed under the transparent plate.

Description

Technical Field

[0001] The present invention relates to an optical sheet for a backlight unit mounted in a liquid crystal display device, a lighting device, etc.

[0002] More specifically, the present invention relates to a laminated optical sheet for a backlight unit mounted in a liquid crystal display device, a lighting device, etc., in which at least two optical sheets are laminated, and an optical sheet to which a conventional optical sheet can be additionally laminated. Background Art

[0003] A liquid crystal display (LCD) has a structure in which a liquid crystal material is inserted between an upper substrate formed with a color filter and a lower substrate formed with a thin film transistor. It is a device that changes the arrangement of liquid crystal molecules in various ways and adjusts the transmittance of light accordingly to display images.

[0004] Liquid crystal display devices are not self-luminous elements that emit light by themselves, so liquid crystal display devices need to be equipped with a backlight unit for providing light to the panel.

[0005] Backlight units are divided into edge-lit and direct-lit types according to the configuration of the light source. The edge-lit type is a structure in which the light source is only configured at one or both edges of the backlight unit, while the direct-lit type is a structure in which the light source is configured at a predetermined interval on the substrate of the backlight unit. Although cold cathode fluorescent lamps (CCFL) are more commonly used as light sources, light emitting diodes (LED) are also more commonly used recently.

[0006] The backlight unit includes optical sheets including a light diffusion plate, a lens array sheet, a prism sheet, etc. for hiding lamps and collecting light.

[0007] like Figure 1a As shown in the example in FIG. 1 , a general optical sheet has a simple laminated structure, wherein an air layer is interposed between the light diffuser plate 10 containing dispersed diffusion particles 15 and the prism sheet 20. The structure of the combination of optical sheets applied in practice is: two additional lens array sheets are laminated on the prism sheet 20 through the air layer. Figure 1a The light diffuser and prism sheet are located between the light diffuser and the prism sheet and on the top of the prism sheet. A representative lens array sheet is a "diffuser sheet" which is different from the light diffuser sheet in that it is a structure in which diffusion particles are coated on the surface of the PET film in a single layer. The increase in the number of such sheets not only hinders the thinning of the liquid crystal display device, but also causes the cost increase.

[0008] To overcome these shortcomings, Figure 1bAs shown in the example, a laminated structure in which the diffusion sheet 10 and the prism sheet 20 are laminated to each other through the lamination layer 30 is proposed.

[0009] Unlike laminated layers with an air layer in between, if the diffuser is laminated with the prism, there is no air layer. In this case, the light provided by the light source is totally reflected at the interface between the light diffuser and the laminated layer and cannot be reused, and the incident wide-angle incident light will cause the light-collecting effect of the prism to disappear.

[0010] In addition, a higher light transmittance is exhibited from the light source side of the backlight unit toward the exterior side, thereby reducing the hiding efficiency of the light source.

[0011] Combined with Figure 1a and Figure 1b As described above, there are various problems when laminating a sheet different from the light diffuser plate.

[0012] In addition, a laminated optical sheet is proposed in Korean Public Invention Patent KR10-2014-0069926A (published on June 10, 2014). The laminated optical sheet proposed in the document is characterized by comprising: a first prism sheet formed with a plurality of prisms; a laminate layer formed on the lower surface of the first prism sheet; a second prism sheet laminated on the lower surface of the laminate layer and formed with a first prism and a second prism, a prism insertion portion formed on the lower surface of the first prism sheet, and a prism with a higher height among the first and second prisms of the second prism sheet inserted into the prism insertion portion formed on the lower surface of the first prism sheet. Therefore, an optical sheet with improved adhesive force and without reducing brightness can be provided.

[0013] However, the document forms a groove on the lower surface of the first prism sheet and inserts the end of the prism of the second prism sheet into the groove, which makes it difficult to solve the above-mentioned problem that occurs when the light diffusion plate serving as a supporting layer of the optical sheet is laminated with the lens array sheet or the prism sheet through a lamination layer. Summary of the invention

[0014] Problem that the invention aims to solve

[0015] Problem to be Solved by the Invention To provide a laminated optical sheet for a backlight unit used in a liquid crystal display device, a lighting device, etc., which has high light collection efficiency and excellent light source concealment effect.

[0016] Means used to solve problems

[0017] An optical sheet for a backlight unit according to an embodiment of the present invention for solving the above-mentioned problem is an optical sheet for processing light provided by a light source of a backlight unit, and includes: a prism sheet; a transparent plate laminated with the prism sheet via an adhesive layer under the prism sheet and having a thickness of 1.0 mm or more; and a semi-reflective mirror arranged under the transparent plate.

[0018] The half mirror may be directly disposed on the lower surface of the transparent plate. Alternatively, a polymer film disposed with the half mirror may be laminated on the lower surface of the transparent plate via an adhesive layer.

[0019] According to another embodiment of the present invention for solving the above-mentioned problem, an optical sheet for a backlight unit is provided, which is an optical sheet for processing light provided by a light source of a backlight unit, and includes: a prism sheet; a transparent plate arranged under the prism sheet and having a thickness of 1.0 mm or more; and a semi-reflective mirror arranged between the prism sheet and the transparent plate and laminated with at least one of the prism sheet or the transparent plate by an adhesive.

[0020] The half mirror may be directly disposed on one of the prism sheet and the transparent plate and laminated on the other of the prism sheet and the transparent plate through an adhesive. Alternatively, a polymer film disposed with the half mirror may be laminated on the prism sheet and the transparent plate through an adhesive layer.

[0021] The transparent plate may include at least one of glass, polycarbonate, polystyrene, polyolefin, polymethyl methacrylate, and MS resin.

[0022] The transparent plate may contain no diffusing agent or contain 0.5 wt % or less of diffusing agent.

[0023] The half mirror may exhibit a light reflectivity of 10% to 80% and a light transmittance of 20% to 90%.

[0024] The semi-reflective mirror may be selected from the following films i) to vi):

[0025] i) Metal compound multilayer films;

[0026] ii) a metal film comprising one or more of chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy and titanium;

[0027] iii) a polymer film containing a dispersion of metal powder or fragments of one or more of chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy and titanium, such as polymethyl methacrylate, polystyrene, polycarbonate, polyethylene terephthalate (PET), polyurethane, polypropylene, polyolefin and their derivatives or copolymers;

[0028] iv) a glass film containing a dispersion of metal powder or fragments of one or more of chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy and titanium;

[0029] V) A multilayer film comprising a low-refractive layer of one or more of Al2O3, AlF3, NaF, MgF2 and SiO2 and a high-refractive layer of one or more of TiO2, Ti2O3, Nb2O5, Ta2O3, ZnS and AlN.

[0030] The invention may further include one or more intermediate sheets disposed between the transparent plate and the prism sheet or one or more upper sheets disposed on the prism sheet.

[0031] The upper part of the prism sheet may further include an upper sheet laminated with the prism sheet through an adhesive layer, and an air layer may be included between the upper sheet and the prism sheet. The upper sheet may be, for example, a lens array sheet or a prism sheet.

[0032] The adhesive layer may include one or more of an acrylic adhesive, a urethane adhesive, an epoxy adhesive, and a silicon adhesive.

[0033] Specific matters of undescribed embodiments of the laminated optical sheet for a backlight unit according to the present invention are included or implied in the detailed description and drawings.

[0034] Effects of the Invention

[0035] According to the laminated optical sheet for a backlight unit of the present invention, by including a half mirror on or under a transparent plate, it is possible to solve the problem of reduced light collection efficiency due to the absence of an air layer between the transparent plate and the prism sheet.

[0036] In addition, according to the laminated optical sheet for a backlight unit of the present invention, the thickness of the optical sheet can be reduced by laminating the optical sheets, thereby contributing to cost reduction.

[0037] The laminated optical sheet according to the present invention having the effects as described above can be applied to a backlight unit of a liquid crystal display device, and can also be applied to backlight units of various lighting devices.

[0038] The effects of the laminated optical sheet according to the present invention are not limited to the above-mentioned effects, and those skilled in the art can clearly understand other effects not mentioned from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1a An example of an optical sheet according to the related art is shown, which shows a structure in which a light diffusion plate and a prism sheet are laminated while an air layer is present between them.

[0040] Figure 1b Another example of an optical sheet according to the related art is shown, which shows a structure in which a light diffusion plate and a prism sheet are laminated through a lamination layer.

[0041] Figure 2 The optical sheet according to the embodiment of the present invention is schematically shown, wherein a half mirror is disposed under a transparent plate.

[0042] Figure 3 An optical sheet according to another embodiment of the present invention is schematically shown, in which a polymer film including a half mirror is disposed under a transparent plate.

[0043] Figure 4 An optical sheet according to still another embodiment of the present invention is schematically shown, wherein a half mirror is disposed between a prism sheet and a transparent plate.

[0044] Figure 5 An optical sheet according to still another embodiment of the present invention is schematically shown, wherein a half mirror is disposed between a prism sheet and a transparent plate.

[0045] Figure 6 An optical sheet according to still another embodiment of the present invention is schematically shown, in which a polymer film including a half mirror is disposed between a prism sheet and a transparent plate.

[0046] Figure 7 An optical sheet according to another embodiment of the present invention is schematically shown, in which an additional prism sheet is disposed on the upper portion of the prism sheet.

[0047] Figure 8 The diagram schematically shows a situation where an air layer exists between the prism sheet and the upper sheet.

[0048] Figure 9a Is has Figure 1a and Figure 1b Comparison of the vertical viewing angle evaluation results of the optical sheets with different structures.

[0049] Figure 9b Is has Figure 1a and Figure 2 Comparison of the vertical viewing angle evaluation results of the optical sheets with different structures. DETAILED DESCRIPTION

[0050] The advantages and features of the present invention and the methods for achieving them can be clearly seen through the accompanying drawings and the embodiments described in detail below. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different ways. The following embodiments are only provided to make the disclosure of the present invention more complete and to enable ordinary technicians in the technical field to fully understand the scope of the present invention, and the present invention is only defined by the scope of the attached claims.

[0051] In the entire specification including the drawings, the same reference numerals are used to indicate the same or similar components. In addition, for the clarity of the description, the size and relative size of parts and regions in the drawings may be exaggerated.

[0052] When an element or layer is referred to as being "above" or "on" different elements or layers, it includes not only the case where it is directly above other elements or layers, but also the case where different layers or other elements intervene. On the other hand, when an element or layer is "directly above" or "directly above", it means that there are no other elements or layers in between. In addition, when it comes to a certain constituent element being "connected", "combined" or "contacting" another constituent element, the constituent elements may be directly connected or in contact with each other, but it should be understood that other constituent elements may also be "interposed" between the constituent elements, or the constituent elements may be "connected", "combined" or "contacting" through other constituent elements.

[0053] As shown in the figure, spatially relative terms such as "below", "lower", "above", "upper", etc. can be used to easily describe the relationship between one component and other components. Spatially relative terms should be understood to include terms that refer to different directions of elements when in use or operation in addition to the directions shown in the drawings. For example, when the elements shown in the figure are turned over, elements described as "below" other elements can be placed "above" other elements. Therefore, the exemplary term "below" can include both below and above directions.

[0054] The terms used in this specification are only used to illustrate the embodiments and are not intended to limit the present disclosure. In this specification, unless otherwise specified, a sentence in the singular also includes a plural form. The terms "include" and / or "comprising" used in this specification specify the existence of the constituent elements, steps, operations and / or elements described, but do not exclude the existence or addition of one or more other constituent elements, steps, operations and / or elements.

[0055] Hereinafter, preferred embodiments of a laminated optical sheet for a backlight unit according to the present invention will be described in detail with reference to the accompanying drawings.

[0056] The optical sheet according to the present invention is an optical sheet for processing light provided by a light source of a backlight unit. The optical sheet according to the present invention includes a half mirror that performs regular reflection and regular transmission of light at an upper or lower portion of a prism sheet or a transparent plate.

[0057] The backlight unit currently used generally uses 3 to 4 optical sheets. Although lamination between some films has been achieved, lamination between the light diffuser plate, which acts as a support layer, and the prism sheet on top of it has not yet been achieved. This is because even if the light diffuser plate and the prism sheet can be laminated to achieve a reduced thickness, there is still a problem of reduced light collection efficiency and lamp concealment.

[0058] The present invention proposes a laminated structure based on a transparent plate with a half-reflective mirror and a prism sheet, which can achieve the effect of reducing the thickness without causing a decrease in light collection efficiency and lamp concealment.

[0059] Figure 2 An optical sheet according to an embodiment of the present invention is schematically shown.

[0060] like Figure 2 , Figures 3 to 8 As shown, the optical sheet according to the present invention has a structure in which a prism sheet and a transparent plate are laminated via an adhesive, rather than a structure in which a prism sheet and a transparent plate are simply laminated with an air layer interposed therebetween.

[0061] Reference Figure 2 , the illustrated optical sheet has a structure in which a prism sheet 110 and a transparent plate 120 are laminated via an adhesive layer 130 .

[0062] Furthermore, a half mirror 140 is disposed below the transparent plate 120 .

[0063] The prism sheet 110 is a sheet including a prism pattern that refracts side light into front light to increase brightness of light provided by a backlight unit.

[0064] The transparent plate 120 serves as a support for the prism sheet. The transparent plate 120 may be, for example, a polymer or glass material including one or more of polycarbonate, polystyrene (PS), polyolefin, polymethyl methacrylate (PMMA) and MS resin (copolymer of PMMA and PS), and may have a thickness of 1.0 mm or more, preferably 1.0 mm to 3.0 mm, more preferably 1.0 mm to 2.5 mm, and most preferably 1.2 mm to 2.5 mm. The transparent plate 120 may not contain a diffusant, or may contain a diffusant of at most 0.5 wt %. The transparent plate 120 used in the present invention has a thickness of at least 1.0 mm, which is different from a film having a thickness of at most several hundred μm, and the transparent plate 120 used in the present invention does not contain a diffusant or contains a diffusant of at most 0.5 wt %, which is different from a conventional light diffuser containing about 1 wt % of a diffusant.

[0065] In addition, regardless of whether it is a half mirror, an amorphous embossed shape for preventing scratches from the lamp bracket of the backlight unit may be provided at the lower portion of the transparent plate.

[0066] The adhesive layer 130 may include one or more of an acrylic adhesive, a urethane adhesive, an epoxy adhesive, and a silicon adhesive, but is not limited thereto. Any known transparent adhesive may be used.

[0067] The half mirror 140 reflects a part of the incident light and transmits the rest of the light. A part of the light provided by the light source passes through the half mirror 140 and the transparent plate 120. If a reflector or the like is provided on the light source, the light reflected from the half mirror 140 to the light source side will be incident on the half mirror 140 again. Through such a process, a higher concealment of the lamp can be finally achieved.

[0068] The half mirror 140 may exhibit a light reflectivity of 10% to 80% and a light transmittance of 90% to 20% depending on the layer thickness, the amount of metal in the half mirror, etc. When the half mirror 140 is included as a layer in the optical sheet, the half mirror 140 may exhibit a light reflectivity of 20% to 80% and a light transmittance of 80% to 20%. When the half mirror 140 is included as a plurality of layers in the optical sheet, each half mirror 140 may exhibit a light reflectivity of 10% to 80% and a light transmittance of 90% to 20%.

[0069] The semi-reflective mirror 140 may be a metal compound, such as a metal oxide multilayer film.

[0070] In addition, the half mirror 140 may be a thin film of a metal including one or more of chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy, and titanium having excellent reflectivity.

[0071] In addition, the half-reflecting mirror 140 may be a polymer film in which metal powder or flakes of one or more selected from chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy, and titanium are dispersed. The metal powder generally has a spherical shape, and the metal flakes may have a flat shape. The polymer may include one or more selected from polymethyl methacrylate (PMMA), polystyrene, polycarbonate, polyethylene terephthalate (PET), polyurethane, polypropylene, polyolefin, or derivatives or copolymers thereof.

[0072] Alternatively, the semi-reflective mirror 140 may be a glass film in which metal powder or fragments of one or more selected from the group consisting of chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy, and titanium are dispersed.

[0073] In addition, the semi-reflective mirror 140 can be a multilayer thin film in which low-refractive layers including one or more of Al2O3, AlF3, NaF, MgF2 and SiO2 and high-refractive layers including one or more of TiO2, Ti2O3, Nb2O5, Ta2O3, ZnS and AlN are alternately arranged.

[0074] The half mirror 140 can be formed in a layer form on the transparent plate 120, the polymer film ( Figure 3 , Figure 6 210), prism sheet ( Figure 5 110) etc.

[0075] Figure 3 An optical sheet according to another embodiment of the present invention is schematically shown.

[0076] exist Figure 2 In the embodiment shown, the half mirror 140 is directly formed on the lower surface of the transparent plate 120, but Figure 3 In the illustrated embodiment, the polymer film 210 including the half mirror 140 is attached to the lower part of the transparent plate via the adhesive layer 220. At this time, the relative position of the half mirror layer to the polymer film includes all situations of above, below and inside. Similar to the adhesive layer 130, the adhesive layer 220 may include one or more of an acrylic adhesive, a urethane adhesive, an epoxy adhesive and a silicon adhesive, but is not limited thereto, and any known transparent adhesive may be used.

[0077] Figure 4An optical sheet according to still another embodiment of the present invention is schematically shown.

[0078] exist Figure 2 In the embodiment shown, the half mirror 140 is directly formed on the lower surface of the transparent plate 120, but in Figure 4 In the embodiment shown, the half mirror 140 is directly formed on the upper surface of the transparent plate 120, and the transparent plate 120 formed with the half mirror 140 is laminated with the prism sheet 110 through the adhesive layer 130. In this case, it is possible to show the same Figure 2 The illustrated embodiments have similar optical properties and can be selectively set according to manufacturing conditions.

[0079] Figure 5 An optical sheet according to still another embodiment of the present invention is schematically shown.

[0080] and Figure 4 In the embodiment shown, Figure 5 In the embodiment shown, a half mirror 140 is disposed between the prism sheet 110 and the transparent plate 120. Figure 5 In the embodiment shown, the half mirror 140 is directly formed on the lower surface of the prism sheet 110, and the prism sheet 110 formed with the half mirror 140 is laminated with the transparent plate 120 through the adhesive layer 130. In this case, it is possible to show the same Figure 2 The optical properties of the structures are similar and can be selectively set according to the fabrication conditions.

[0081] Figure 6 FIG. 2 schematically shows an optical sheet according to another embodiment of the present invention. Figure 4 and Figure 5 In the embodiment shown, Figure 6 In the illustrated embodiment, a half mirror 140 is disposed between the prism sheet 110 and the transparent plate 120. Figure 6 In the embodiment shown, the polymer film 210 including the half mirror 140 is attached to the prism sheet 110 and the transparent plate 120 through the adhesive layers 130 and 220, respectively. Figure 2 The illustrated embodiments have similar optical properties and can be selectively set according to manufacturing conditions.

[0082] In addition, an additional sheet may be laminated or stacked on the upper or lower portion of the prism sheet 110 and the upper or lower portion of the transparent plate 120. That is, in the optical sheet according to the present invention, at least one half mirror is included in the lower portion of the prism sheet (when two or more prism sheets are included, the lower portion thereof based on the uppermost prism sheet).

[0083] For example, one or more intermediate sheets may be additionally arranged between the prism sheet 110 and the transparent plate 120. As another example, one or more upper sheets may be additionally arranged on the upper portion of the prism sheet 110. The intermediate sheet may be a lens array sheet such as a diffusion sheet, a prism sheet, etc., and the upper sheet may be a lens array sheet, a prism sheet, etc. The lens array sheet includes a bead coating, a sheet embossed with a bead arrangement, and the beads may be arranged amorphously or regularly.

[0084] Figure 7 An optical sheet according to still another embodiment of the present invention is schematically shown, wherein an additional prism sheet is disposed on the upper portion of the prism sheet.

[0085] Reference Figure 7 , when the additional prism sheets 810 are laminated on the prism sheet 110 via the adhesive layer 820, the directions of the prism patterns of these prism sheets are preferably orthogonal to each other.

[0086] Figure 8 The figure schematically shows the situation where there is an air layer between the prism sheet and the upper sheet. Figure 8 As shown, when the upper sheet 910 is laminated on the upper portion of the prism sheet 110 through the adhesive layer 920 , an air layer 925 may be included between the upper sheet 910 and the prism sheet 110 .

[0087] The air layer 925 may be formed when the sheet located on the lower side has an uneven three-dimensional structure such as a lens shape or a prism shape, and may be realized when the adhesive layer 920 for laminating the upper sheet 910 is formed with a sufficiently thin thickness. More preferably, a method of making the thickness of the adhesive layer 920 smaller than the height of the prism pattern of the prism sheet 110 may be used. Such an air layer 925 can minimize the loss of the light collecting effect of the prism shape caused by lamination.

[0088] like Figures 2 to 8 As shown in FIG. 1 to FIG. 2 , the lower surface of the transparent plate can be formed flat. Figure 8 As shown in the figure, regardless of whether a half-reflecting mirror is provided at the bottom of the transparent plate, an amorphous embossed shape for preventing scratches with a lamp bracket of a backlight unit may be provided at the bottom of the transparent plate.

[0089] Figure 9a The light diffuser and prism sheets are compared in a laminated optical sheet (laminated diffuser and prism sheet) in which a light diffuser and prism sheet are simply laminated with an air layer between them. Figure 1a Structure) and a laminated optical sheet (laminated diffuser plate and prism sheet) in which a light diffuser plate and a prism sheet are laminated using an acrylic adhesive ( Figure 1b The vertical viewing angle of the structure). Figure 9aIn the figure, the x-axis is the "vertical viewing angle", which can be regarded as the angle of moving the TV in the vertical direction, for example, and the angle when observing from the front is set to 0°. Figure 9a The y-axis is brightness.

[0090] Reference Figure 9a When the x value is 0, that is, the brightness at the front, the stacked type is at the level of 65, while the laminated type is at the level of 33, which is nearly half lower. In other words, it can be considered that the light-collecting function of the prism sheet is almost eliminated due to lamination. In the case of a laminated optical sheet (laminated diffuser plate and prism sheet) in which the light diffuser plate and the prism sheet are simply laminated with an air layer in between, the incident angle of light incident on the prism pattern of the prism sheet is about -45° to 45°, while in the case of a laminated diffuser prism sheet, the incident angle of light incident on the prism sheet is about -90° to 90°, which can be considered that the light-collecting function of the prism is lost. That is, light outside the range of -45° to 45° is totally reflected between the diffuser and the air layer, thereby falling downward and facing the reflector again to be reused, whereas in contrast, in the case of lamination, light outside the range of -45° to 45° travels to the prism pattern without total reflection and with a large angle change, thereby failing to collect light and emitting light at a high angle.

[0091] Figure 9b The light diffuser and prism sheets are compared in a laminated optical sheet (laminated diffuser and prism sheet) in which a light diffuser and prism sheet are simply laminated with an air layer between them. Figure 1a Structure) and a laminated optical sheet (laminated polymer sheet and prism sheet) in which a polymer transparent plate having a half mirror formed on the lower surface and a prism sheet are laminated using an acrylic adhesive ( Figure 2 structure) of the vertical viewing angle.

[0092] Reference Figure 9b In the case of a diffusion sheet prism sheet formed by adding a half mirror and an adhesive layer and laminating them, Figure 9a In the case of the polymer plate, since there is no diffuser, light outside the range of -45° to 45° cannot exist, but due to the presence of the half mirror, it can show a reflectivity similar to that when there is a light diffuser.

[0093] The light from the light source of the backlight unit travels at an angle of about -90° to 90°, but when the light is incident on the polymer plate or the light diffuser plate, it travels in the range of about -45° to 45° according to Snell's law. In the case of the light diffuser plate, the light of -45° to 45° is diffused to the range of -90° to 90° by using a dispersed diffusing agent and travels, while in the case of the polymer transparent plate, it travels in the range of -45° to 45° without diffusion.

[0094] Table 1 shows the results of analyzing optical characteristics of optical sheets with various structures.

[0095] The diffuse light transmittance and front brightness in Table 1 were measured using the optical simulation tool "LightTools". The half mirror included in the embodiment uses a dielectric multilayer film, and the reflectivity varies depending on the refractive index and film thickness.

[0096] The meanings of the symbols in Table 1 are as follows:

[0097] PS: Polystyrene board

[0098] A: Adhesive layer

[0099] Air is the air layer

[0100] H: Half mirror

[0101] D: Diffuser (transmittance is 60% due to Mie scattering) P: Prism

[0102] L: Lens array sheet (total light transmittance: 75%), haze: 99%.

[0103] Table 1

[0104]

[0105] Referring to Table 1, it can be confirmed that Examples 1 to 13 including the half mirror exhibited front brightness equal to or higher than that of Comparative Examples 1 to 5 including the light diffuser plate instead of the half mirror, and that additional lamination was possible.

[0106] Comparing Comparative Example 1 with Comparative Example 2, it can be seen that the light collection property of the structure where the light diffusion plate and the prism sheet are laminated is much lower than that of the stacked structure, and the diffuse light transmittance, which is one of the indicators for measuring lamp concealment, is significantly reduced ( Figure 9a ).

[0107] Comparison of Comparative Example 1 with Example 1 shows that, in the case of the optical sheet of Example 1 in which a transparent plate including a half-mirror is laminated, it exhibits the same effect as the optical sheet of Comparative Example 1 in which an existing light diffusion plate and a prism sheet are simply laminated with an air layer interposed therebetween ( Figure 9b ).

[0108] In particular, when comparing Example 2 with Comparative Example 1, the optical sheet of Example 2, when equipped with a half-mirror with a reflectivity of 50%, exhibits the same front brightness as the optical sheet of Comparative Example 1 and a lower diffuse light transmittance, thereby achieving a higher light source concealing effect.

[0109] In addition, it can be seen from Examples 1, 3, and 4 that similar effects are exhibited in the example in which a plurality of half mirrors with low reflectivity are provided and in the example in which a single half mirror with high reflectivity is provided.

[0110] In addition, Comparative Examples 3 and 4 are representative optical sheet combinations of backlight sources currently in use. By comparing Examples 5 to 9 with Comparative Example 3, and Examples 10 to 13 with Comparative Example 4, it can be seen that although the light diffuser plate is omitted in the optical sheets of Examples 5 to 9 and Examples 10 to 13, they still exhibit the same effects as Comparative Examples 3 to 4.

[0111] In addition, in the case of Examples 14 and 15, the prism sheet and the transparent plate are laminated via an adhesive layer, and a half mirror is disposed on the prism sheet. For example, by comparing Comparative Example 5 with Example 15, it can be seen that when a half mirror is disposed on the prism sheet, the front brightness equal to or higher than that when no half mirror is disposed can be obtained.

[0112] Although the preferred embodiments of the present invention are described in detail above, it will be appreciated by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the scope of the present invention is not limited thereto, and various modifications and improved forms implemented by those skilled in the art using the basic concepts of the present invention defined in the attached claims belong to the scope of the present invention.

Claims

1. An optical sheet for processing light provided by a light source of a backlight unit, characterized in that: include: Prism lenses, a transparent plate laminated with the prism sheet through an adhesive layer below the prism sheet, and a semi-reflective mirror, disposed below the transparent plate; The transparent plate does not include a diffusing agent or includes a diffusing agent in an amount of 0.5 wt % or less, and has a thickness of 1.0 mm to 2.5 mm.

2. The optical sheet according to claim 1, wherein: The half mirror is directly arranged on the lower surface of the transparent plate, or The polymer film provided with the half mirror is laminated on the lower surface of the transparent plate via an adhesive layer.

3. An optical sheet for processing light provided by a light source of a backlight unit, characterized in that: include: Prism lenses, a transparent plate disposed under the prism sheet, and a half mirror disposed between the prism sheet and the transparent plate and laminated with at least one of the prism sheet or the transparent plate by an adhesive; The transparent plate does not include a diffusing agent or includes a diffusing agent in an amount of 0.5 wt % or less, and has a thickness of 1.0 mm to 2.5 mm.

4. The optical sheet according to claim 3, characterized in that: The half mirror is directly disposed on one of the prism sheet and the transparent plate and is laminated on the other of the prism sheet and the transparent plate by an adhesive, or The polymer film provided with the half mirror is laminated on the prism sheet and the transparent plate via an adhesive layer.

5. The laminated optical sheet for a backlight unit according to any one of claims 1 to 4, characterized in that: The transparent plate includes one or more of glass, polycarbonate, polystyrene, polyolefin, polymethyl methacrylate and MS resin.

6. The laminated optical sheet for a backlight unit according to any one of claims 1 to 4, characterized in that: The lower surface of the transparent plate is flat or provided with an amorphous embossed shape.

7. The laminated optical sheet for a backlight unit according to any one of claims 1 to 4, characterized in that: The half mirror exhibits a light reflectivity of 10% to 80% and a light transmittance of 20% to 90%.

8. The laminated optical sheet for a backlight unit according to any one of claims 1 to 4, characterized in that: The semi-reflective mirror is selected from the following films i) to v): i) Metal compound multilayer films; ii) a metal film comprising one or more of chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy and titanium; iii) a polymer film containing a dispersion of metal powder or fragments of one or more of chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy and titanium; iv) a glass film containing a dispersion of metal powder or fragments of one or more of chromium, nickel, copper, gold, silver, aluminum, tin, stainless steel alloy and titanium; v) A multilayer film comprising alternating low-refractive layers of one or more of Al2O3, AlF3, NaF, MgF2 and SiO2 and high-refractive layers of one or more of TiO2, Ti2O3, Nb2O5, Ta2O3, ZnS and AlN.

9. The laminated optical sheet for a backlight unit according to any one of claims 1 to 4, characterized in that: It also includes one or more intermediate sheets arranged between the transparent plate and the prism sheet or one or more upper sheets arranged on the prism sheet.

10. The laminated optical sheet for a backlight unit according to any one of claims 1 to 4, characterized in that: An upper sheet laminated with the prism sheet via an adhesive layer is further included on the prism sheet, and an air layer is included between the upper sheet and the prism sheet.

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