KR20160108075A - Backlight unit and display apparatus comprising the same - Google Patents

Abstract

The present invention relates to a backlight unit including a light guide plate and a light source provided on at least one side of the light guide plate, wherein the light guide plate has a front surface for emitting light received from the light source and a rear surface opposite to the front surface, And a backlight unit and a display device including the backlight unit.

Description

BACKLIT UNIT AND DISPLAY APPARATUS COMPRISING THE SAME [0002]

The present application relates to a backlight unit and a display device including the same. More specifically, the present application relates to a backlight unit including a color conversion film and a display device including the same.

With the large-sized TV, high-definition, slimmer, and more sophisticated functions are being performed. High-performance, high-definition OLED TVs still have a problem of price competitiveness, and the market is not yet open. Therefore, efforts to secure similar advantages of OLEDs with LCDs are continuing.

As one of the above efforts, many quantum dot related technologies and prototypes have recently been implemented. However, since the cadmium-based quantum dots have safety problems such as restriction of use, attention is focused on the manufacture of backlights using cadmium-free quantum dots without relative safety issues.

Korean Patent Application Publication No. 2000-0011622

The present application relates to a backlight unit including a color conversion film and a display device including the same. More specifically, the present application relates to a backlight unit capable of improving the uniformity of light emitted from a color conversion film and a display device including the same.

One embodiment of the present application is a backlight unit including a light guide plate and a light source provided on at least one side of the light guide plate, the light guide plate having a front surface for emitting light received from the light source and a rear surface opposite to the front surface, Is provided on the back side of the light guide plate.

According to another embodiment of the present application, a reflection plate is further provided on the opposite side of the surface of the color conversion film of the backlight unit opposite to the light guide plate.

According to another embodiment of the present application, a scattering pattern is provided on at least one of a front surface and a rear surface of the light guide plate of the backlight unit.

Another embodiment of the present application provides a display device including a backlight unit according to the above-described embodiments.

According to the embodiments described in the present application, the color conversion film is provided on the back surface of the light guide plate of the backlight unit, that is, on the opposite surface to the display panel or the screen display portion when applied to the display, So that light emitted when light of a different wavelength is emitted passes through the light guide plate again. At this time, when the light emitted from the color conversion film passes through the light guide plate again, the uniformity of light is improved. Particularly, when an organic color conversion film such as a film produced by dissolving an organic fluorescent substance in a resin matrix is used as the color conversion film, unevenness of optical properties due to coating unevenness, thickness variation, The uniformity of light emitted from the color conversion film can be improved according to the above-described embodiments of the present application. Further, when a scattering pattern is formed on the light guide plate, the uniformity of light can be further increased.

Figures 1-7 illustrate examples of backlight units according to embodiments of the present application, respectively.
8 to 11 illustrate the structure of the color conversion film included in the backlight unit according to the embodiments of the present application.
FIG. 12 is a schematic view showing a technique (comparative example) in which a color conversion film is placed on the front face of a light guide plate and a change in optical characteristics in an embodiment of the present invention in which the color conversion film is located on the rear face of the light guide plate.
Figs. 13 to 15 are diagrams showing the technique (comparative example) in which the color conversion film is placed on the front face of the light guide plate, the difference between the present invention in which the color conversion film is located on the rear face of the light guide plate, to be.

According to an embodiment of the present invention, a backlight unit includes a light guide plate and a light source provided on at least one side of the light guide plate, the light guide plate having a front surface for emitting light received from the light source and a rear surface opposite to the front surface And a color conversion film is provided on the back side of the light guide plate.

In the present specification, the front surface of the light guide plate refers to a surface that emits light received from a light source, and when the backlight unit is applied to a display, the surface facing the display panel or the screen display portion of the display.

In the present specification, the back surface of the light guide plate refers to the opposite surface of the display panel or the display, when the backlight unit is applied to the display. Fig. 1 shows a schematic diagram of the structure of the backlight unit according to the above-described embodiment. According to the above-described embodiment, a backlight unit structure known in the art can be applied, except that the color conversion film is disposed on the back side of the light guide plate. The light guide plate and the color conversion film may be laminated so as to be in direct contact with each other. If necessary, an adhesive layer or a pressure sensitive adhesive layer may be provided between the light guide plate and the color conversion film. If necessary, the light guide plate and the color conversion film may be in direct contact with each other, or an air gap may be present or another layer or film may be provided. When an air gap exists between the light guide plate and the color conversion film, it is advantageous for effective surface light emission.

According to another embodiment of the present application, a reflection plate is further provided on the opposite side of the surface of the color conversion film of the backlight unit opposite to the light guide plate. FIG. 2 illustrates a structure having a reflection plate. The reflection plate may be provided not only on one side of the color conversion film but also around the light source so that light emitted from the light source does not flow out. The material and structure of the reflector may be those known in the backlight unit field. The color conversion film and the reflection plate may be laminated in direct contact with each other, and if necessary, an adhesive layer or a pressure sensitive adhesive layer may be provided between the color conversion film and the reflection plate. If necessary, the coloring film may be directly contacted with the reflector, or an air gap may be present or another layer may be provided.

According to another embodiment of the present application, a scattering pattern is provided on at least one of a front surface and a rear surface of the light guide plate of the backlight unit. The scattering pattern may be formed on the surface opposite to the color conversion film of the light guide plate as shown in Fig. 3, or on the opposite surface of the light guide plate opposite to the color conversion film as shown in Fig. 4, Scattering patterns may be provided on both surfaces of the light guide plate. The scattering pattern is not particularly limited as long as it is a structure or material capable of emitting light. Although FIGS. 3 and 4 illustrate regular pattern shapes as scattering patterns, the pattern shapes may be regular or irregular, and may be larger or smaller such that the size of the pattern may be farther away from the light source, if necessary. The shape, material, and manufacturing method of the scattering pattern may be those known in the art. For example, the scattering pattern of the light guide plate may be a dot type, a prism type, or a combination thereof. According to a preferred example, a dot-like film may be used as a light guide plate having a scattering pattern, and may have a gradient distribution in which the distribution of dots changes according to a distance from a light source, if necessary.

According to another embodiment of the present application, the color conversion film comprises a resin matrix and an organic phosphor dispersed in the resin matrix.

The organic phosphor preferably has a maximum emission peak within a range of 510 to 680 nm when irradiated with blue light having a 450 nm wavelength, an emission peak at 450 nm, a half width of 40 nm or less, and a light emission intensity distribution of monomodal A phosphor may be used.

According to another embodiment of the present application, the color conversion film may include a 450 nm wavelength, an emission peak at 450 nm, a half width of 40 nm or less, and an emission peak at the time of blue light irradiation in which the emission intensity distribution is monomodal A half width of 60 nm or less, a quantum efficiency of 80% or more, and an extinction coefficient at a maximum absorption wavelength of 30,000 M ^-1 cm ^-1 or more.

The half width of the emission peak, the quantum efficiency, and the extinction coefficient at the maximum absorption wavelength can be obtained by coating a resin solution in which the organic fluorescent material is dissolved on a transparent substrate such as PET, and drying or curing the prism sheet or the DBEF film Lt; / RTI > Here, the prism sheet or the DBEF film is laminated for convenience, and does not affect the half width of the emission peak, the quantum efficiency, and the value of the extinction coefficient at the maximum absorption wavelength.

In the present specification, the half width of the emission peak is defined as the half-value width of the color conversion film when the color conversion film contains a 450 nm wavelength, or when the emission intensity distribution has a monomodal blue light emission with an emission peak at 450 nm and a half- Means a width of an emission peak at a half maximum height in a maximum emission peak of light emitted from a film. The half width of the emission peak in this specification is measured in the film state. The half width of the emission peak may be determined by the type and composition of components such as the organic phosphor, the resin matrix or other additives contained in the color conversion film. The half width of the emission peak of the color conversion film is preferably as small as possible.

In this specification, quantum efficiency can be measured using methods known in the art. For example, the quantum efficiency Qy is defined as [number of emitted photons] / [number of absorbed photons] when the light is irradiated on the color conversion film, where "absorbed photons" refers to the blue LED backlight (Blue photon amount after absorption) minus the photon amount absorbed through the color conversion film on the basis of the initial photon amount (initial blue photon amount) measured in the front direction by a spectroscopic radiation luminance meter (TOPCON) , "Number of photons emitted" is the amount of photons consumed in the form of green or red luminescence after the color conversion film is excited by receiving the blue photons transmitted from the backlight.

In this specification, the extinction coefficient at the maximum absorption wavelength can be measured and calculated using methods known in the art. For example, the measurement of the extinction coefficient is carried out by measuring the amount of absorbance of a fluorescent dye solution having a known concentration absorbed at a specific wavelength (generally the maximum absorption wavelength) using a UV spectrophotometer, Can be calculated by applying Law (A = εbc) to evaluate the value of ε.

The organic phosphor may include an organic phosphor that absorbs blue or green light to emit red light, an organic phosphor that absorbs blue light to emit green light, or a mixture thereof.

In this specification, blue light, green light, and red light may be defined as those known in the art, for example, blue light is light having a wavelength selected from a wavelength of 400 nm to 500 nm, green light is 500 nm to 560 nm, and the red light is light having a wavelength selected at a wavelength of 600 nm to 780 nm. In this specification, a green phosphor absorbs at least a part of blue light to emit green light, and a red phosphor absorbs at least a part of blue light or green light to emit red light. For example, the red phosphor may absorb blue light as well as light having a wavelength between 500 and 600 nm.

The color conversion film may include a color conversion layer including a resin matrix and an organic fluorescent material, and a substrate or a barrier film provided on at least one side of the color conversion layer. Fig. 8 shows a color conversion film including the base and the color conversion layer provided on the base. 9 shows a color conversion film including a color conversion layer provided on a barrier film and a barrier film. 10 shows a color conversion film comprising a substrate, a color conversion layer provided on the substrate, and a barrier film provided on the color conversion layer. 11 shows a color conversion film including a barrier film, a color conversion layer provided on the barrier film, and a barrier film provided on the color conversion layer. The substrate may function as a support in the production of the color conversion film. The kind of the substrate is not particularly limited and is not limited to the material and thickness as long as it is transparent and can function as the support. Here, transparent means that the visible light transmittance is 70% or more. For example, a PET film may be used as the substrate. As the barrier film, those known in the art can be used. For example, optical films known in the art, specifically, films such as PET, PMMA, COP, PA and PI can be used.

The content of the organic phosphor may be 0.005 to 2% by weight based on 100% of the entire color conversion film or color conversion layer.

The material of the resin matrix is preferably a thermoplastic polymer or a thermosetting polymer. Specifically, examples of the material of the resin matrix include poly (meth) acrylate, polycarbonate (PC), polystyrene (PS), polyarylene (PAR), polyurethane (TPU ), Styrene-acrylonitrile series (SAN), polyvinylidene fluoride series (PVDF), and modified polyvinylidene fluoride series (modified-PVDF).

The color conversion film or the color conversion layer according to the above-described embodiment may have a thickness of 2 to 200 micrometers. In particular, the color conversion film or the color conversion layer may exhibit high luminance even at a thickness of 2 to 20 micrometers. This is because the content of the organic fluorescent substance molecules contained in the unit volume is higher than that of the quantum dots. For example, a 5-micrometer thick color conversion film to which 0.5 wt% of the organic phosphor is applied may exhibit a luminance higher than 4000 nit based on the luminance of a blue backlight unit (blue BLU) 600 nit.

The above-mentioned color conversion film can be produced by coating a resin solution in which the organic fluorescent substance is dissolved and drying the organic fluorescent substance, or extruding the above-mentioned organic fluorescent substance together with a resin to form a film.

Since the above-mentioned organic fluorescent substance is dissolved in the resin solution, the organic fluorescent substance is homogeneously distributed in the solution. This is different from the manufacturing process of a quantum dot film requiring a separate dispersion process.

Additives may be added to the resin solution if necessary, and a light diffusion agent such as silica, titania, zirconia, and alumina powder may be added.

The resin solution in which the organic fluorescent substance is dissolved is not particularly limited if the organic fluorescent substance and the resin are dissolved in the solution.

According to an embodiment, the resin solution in which the organic fluorescent material is dissolved is prepared by preparing a first solution by dissolving the organic fluorescent material in a solvent, dissolving the resin in a solvent to prepare a second solution, mixing the first solution and the second solution ≪ / RTI > When the first solution and the second solution are mixed, it is preferable to mix them homogeneously. However, the present invention is not limited to this, but a method of dissolving an organic fluorescent substance and a resin in a solvent at the same time, a method of dissolving an organic fluorescent substance in a solvent followed by a dissolution by adding a resin, a method of dissolving a resin in a solvent, .

The organic fluorescent substance contained in the solution is as described above.

As the resin contained in the solution, the above-mentioned resin matrix material, a monomer curable with the resin matrix resin, or a mixture thereof can be used. For example, as the monomer curable with the resin matrix resin, there is a (meth) acrylic monomer, which can be formed from a resin matrix material by UV curing. In the case of using such a curable monomer, an initiator necessary for curing may be further added if necessary.

The solvent is not particularly limited and is not particularly limited as long as it can be removed by drying without adversely affecting the coating process. Non-limiting examples of the solvent include toluene, xylene, acetone, chloroform, various alcohol solvents, MEK (methyl ethyl ketone), MIBK (methyl isobutyl ketone), EA (ethyl acetate), butyl acetate, Cyclohexanone, PGMEA (propylene glycol methyl ethyl acetate), dioxane, DMF (dimethylformamide), DMAc (dimethylacetamide), DMSO (dimethylsulfoxide), NMP (N-methylpyrrolidone) And the like, and they may be used alone or in combination of two or more. When the first solution and the second solution are used, the solvent contained in each of these solutions may be the same or different. Even when different kinds of solvents are used for the first solution and the second solution, it is preferable that these solvents have compatibility so that they can be mixed with each other.

A roll-to-roll process can be used for the step of coating the resin solution on which the organic fluorescent material is dissolved on the substrate. For example, a step of dissolving a substrate from a roll on which a substrate is wound, coating a resin solution in which the organic fluorescent material is dissolved on one side of the substrate, drying the coated substrate, and then winding the coated substrate on a roll. In the case of using a roll-to-roll process, it is preferable to determine the viscosity of the resin solution within a range in which the process can be performed, and may be determined within a range of, for example, 200 to 2,000 cps.

As the coating method, various known methods can be used, for example, a die coater may be used, and various bar coating methods such as a comma coater, a reverse comma coater, and the like may be used.

After the coating, a drying process is performed. The drying process can be carried out under the conditions necessary for removing the solvent. For example, a color conversion film containing an organic phosphor of a desired thickness and concentration can be obtained on a substrate by drying the substrate in a direction in which the substrate proceeds in a coating process and in a state where the solvent is sufficiently blown in an oven located adjacent to the coater.

When a monomer curable with the resin matrix resin is used as the resin contained in the solution, curing such as UV curing may be performed before or during the drying.

When the organic fluorescent substance is extruded together with a resin to form a film, an extrusion method known in the art can be used. For example, a color conversion film can be produced by extruding an organic phosphor together with a resin such as a polycarbonate (PC), a poly (meth) acrylic, or a styrene-acrylonitrile (SAN).

According to another embodiment of the present application, as shown in FIG. 5 or 6, the light guide plate may further include an optical film provided on an opposite surface side of the light guide plate opposite to the color conversion film. The optical film may be applied to those known in the art. For example, the optical film may include at least one or at least two or more of a light-converging film, a light-diffusing film and a brightness improving film. As a specific example, the optical film may be a light-converging film. The light-converging film may include two prism sheets stacked in a direction perpendicular to each other. As the brightness enhancement film, a reflection type polarizing plate (APF), a DBEF film, or a combination thereof may be used.

Another embodiment of the present application provides a display device including a backlight unit according to the above-described embodiments. The display device may further include a display module provided on an opposite surface of the light guide plate opposite to the color conversion film. An additional optical film may be provided between the display module and the light guide plate as needed, as shown in FIG.

FIG. 12 shows a comparison of the optical characteristics in the embodiment of the present invention in which the color conversion film is placed on the front face of the light guide plate (comparative example) and the color conversion film is located on the rear face of the light guide plate.

12, the optical characteristics in the embodiment of the present invention located on the rear surface of the light guide plate are similar to each other with no significant difference compared to the technology in which the color conversion film is disposed on the front surface of the light guide plate. On the other hand, according to the embodiment of the present invention, since the color conversion film is positioned on the rear surface of the light guide plate, the uniformity of light emitted from the color conversion film can be improved by the light guide plate and, if necessary, the scattering pattern.

The above-described embodiments will be described in more detail with reference to the following embodiments. However, the following embodiments are not intended to limit the scope of the invention, which is intended to illustrate the foregoing embodiments of the invention.

Comparative Example  One

A color conversion film containing an organic phosphor was prepared and a BLU module of 160 mm x 90 mm was fabricated using a light source including Blue LED. The prepared module was laminated in order of reflector / scattering pattern / light guide plate / color conversion film / prism sheet 1 / prism sheet 2 / brightness enhancement film / polarizer plate, and 9 points were measured at the upper, And the deviation was calculated. The number of wrinkles and defects were confirmed in the dark room after the operation of BLU. G / B and R / B were calculated after measuring the intensity of light as follows.

* G / B: Green max intensity / Blue max intensity

* R / B: Red max intensity / Blue max intensity

The green max intensity, the blue max intensity and the red max intensity represent the maximum emission intensity in the green emission wavelength range, the blue emission wavelength range, and the red emission wavelength range, respectively. The green emission wavelength is 501 to 580 nm, And the red emission wavelength is in the range of 590 to 780 nm.

Comparative Example  2

Reflection plate / light guide plate / scattering pattern / color conversion film / prism sheet 1 / prism sheet 2 / brightness enhancement film / polarizer plate in this order.

Example  One

Reflection plate / color conversion film / scattering pattern / light guide plate / prism sheet 1 / prism sheet 2 / brightness enhancement film / polarizer plate were stacked in this order.

Example  2

Reflection plate / color conversion film / light guide plate / scattering pattern / prism sheet 1 / prism sheet 2 / brightness enhancement film / polarizer plate in this order.

Scatter pattern position Color conversion film location G / B average G / B deviation R / B average R / B deviation Luminance average Luminance deviation Number of bell wrinkles Number of defects Comparative Example 1 Rear of LGP LGP front 0.29 0.04 0.2 0.04 2656 45 4 4 Comparative Example 2 LGP front LGP front 0.29 0.04 0.2 0.05 2680 30 3 4 Example 1 Rear of LGP Rear of LGP 0.29 0.02 0.2 0.02 2670 11 0 2 Example 2 LGP front Rear of LGP 0.29 0.01 0.2 0.01 2660 4 0 0

Claims (9)

A backlight unit comprising a light guide plate and a light source provided on at least one side face of the light guide plate,
Wherein the light guide plate has a front surface that emits light received from a light source and a rear surface that is opposite to the front surface, and a color conversion film is provided on a rear surface side of the light guide plate. The backlight unit according to claim 1, further comprising a reflection plate on an opposite surface side of the color conversion film opposite to the light guide plate. The backlight unit according to claim 1, wherein a scattering pattern is provided on at least one of a front surface and a rear surface of the light guide plate. The backlight unit according to claim 3, wherein the scattering pattern is provided on a surface of the light guide plate opposite to the color conversion film, or is provided on the opposite surface of the light guide plate against the color conversion film. The backlight unit according to claim 1, wherein the color conversion film comprises a resin matrix and an organic phosphor dispersed in the resin matrix. The backlight unit according to claim 1, wherein a base material or a barrier film is provided on at least one side of the color conversion film. The backlight unit according to claim 1, further comprising an optical film provided on an opposite surface side of the light guide plate opposite to the color conversion film. 8. The backlight unit according to claim 7, wherein the optical film comprises at least one of a light-converging film, a light-diffusing film and a brightness enhancement film. A display device comprising a backlight unit according to any one of claims 1 to 8.

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