KR102723414B1 - Filter sheet using photopolymer and back lighit unit - Google Patents

Abstract

The present invention provides a filter sheet for improving color reproducibility and a backlight unit including the same. By recording a central wavelength to be filtered in the filter sheet using the principle of holography, the central wavelength width and full width at half maximum of red light, green light, and blue light of the spectrum emitted from the backlight unit can be controlled.

Description

Filter sheet using photopolymer and backlight unit including same {FILTER SHEET USING PHOTOPOLYMER AND BACK LIGHIT UNIT}

The present invention relates to a filter sheet for improving the color reproducibility (color gamut) of a display device and a backlight unit using the same.

As the information society develops, the demand for display devices is also increasing in various forms. In response to this, various types of display devices are used recently, such as liquid crystal displays (LCDs), plasma display panel devices (PDPs), electroluminescence display devices (ELDs), and organic electroluminescence display devices.

Here, the liquid crystal display device displays an image by controlling the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display device includes a liquid crystal display panel having a liquid crystal cell between a thin film transistor substrate and a color filter substrate, a backlight unit that irradiates light onto the liquid crystal display panel, and a driving circuit for driving the backlight unit and the liquid crystal display panel.

Since liquid crystal displays do not emit light on their own, they include a backlight unit that provides light to the bottom of the liquid crystal display panel.

Backlight units use light-emitting diodes, CCFLs, HCFLs, and external electrode emitting lamps (EEFLs) as light sources. Recently, LED light sources are increasingly being applied due to their advantages of faster response speed, superior color expression, and environmental friendliness compared to CCFLs.

Figure 1 is a configuration diagram showing a backlight unit to which a high-color reproducibility LED is applied.

The high-color reproducibility LED used as a light source (10) is mainly a white LED that emits white light, and uses a blue chip (12), a red phosphor (24), and a green phosphor (26) to emit white light.

A blue chip (12), which is a nitride semiconductor element, is mounted on a substrate (11), and this blue chip (12) is embedded in a polymer layer (20), and a red fluorescent substance (24) and a green fluorescent substance (26) are contained on the polymer layer.

As a result, white light is realized by mixing the blue light emitted from the blue chip (12) and the red and green light emitted by the red phosphor (24) and green phosphor (26) applied to the polymer material, which absorb some of the blue light and emit it.

White light emitted from a light source (10) is guided by a light guide plate (GP) and emitted as surface light, and the surface light emitted from the light guide plate (GP) is controlled through a plurality of optical sheets (OS) and then emitted.

However, backlight units with this structure have limitations in that new fluorescent materials must be developed to control the central wavelength or half-width of red and green light.

Figure 2 is a configuration diagram showing a backlight unit to which a quantum dot sheet is applied for color reproduction.

Referring to Fig. 2, a blue LED (30) emitting blue light is used as a light source, and a quantum dot sheet (40) in which red light-emitting nanoparticles (44) and green light-emitting nanoparticles (46) are mixed and cured is laminated on the upper part of the light guide plate.

Blue light emitted from the LED (30) generates white light as it passes through the quantum dot sheet (40) containing a mixture of red light-emitting nanoparticles (44) and green light-emitting nanoparticles (46).

The above luminescent nanoparticles (44, 46) are particles of a certain size that have a quantum confinement effect, and are also called quantum dots.

Here, quantum dots are one of the nano materials that have recently been attracting attention as a result of research on 'nano' elements, which refer to tiny particles one billionth of a meter in size.

Quantum dots have various properties that other materials do not have. First, they produce strong fluorescence in a narrow wavelength range. The light emitted by quantum dots is generated when electrons in an unstable (excited) state move from the conduction band to the valence band.

At this time, the fluorescence that occurs has a very special property in that the smaller the quantum dot particle, the shorter the wavelength light is generated, and the larger the particle, the longer the wavelength light is generated. Therefore, by adjusting the size of the quantum dot, light in the visible light range of the desired wavelength can be emitted.

In these liquid crystal displays, blue light emitted from a light source (30) is guided through a light guide plate (GP) and emitted as surface light, and a portion of the blue surface light emitted from the light guide plate is converted into red light and green light through red light-emitting nanoparticles (44) and green light-emitting nanoparticles (46) in a quantum dot sheet (40), and mixed and emitted as white light from the quantum dot sheet (40).

Meanwhile, in order to improve the color reproducibility of the liquid crystal display and implement wide color reproducibility, the center wavelength positions and half-width of the red, green, and blue lights of the backlight unit must be adjusted.

As described in Fig. 1, a backlight unit that implements white light using a blue chip, a green phosphor, and a red phosphor had a limitation that a new phosphor material had to be developed in order to control the center wavelength or half-width of the red light or green light.

In addition, as described in Fig. 2, even in the case of a backlight unit that implements white light using a blue LED and a quantum dot sheet, there was a limitation that the size of the quantum dots had to be precisely controlled in order to control the central wavelength or half-maximum width of the red and green light.

The present invention provides a filter sheet capable of filtering a specific wavelength by utilizing the principle of holography.

Figure 3 is a conceptual diagram explaining the principle of holography.

A hologram is made by splitting a laser beam into a reference beam (RB) and an object beam (OB) using a beam splitter, and the reference beam (RB) is directed directly to the recording target film (HF) on which the hologram is to be recorded, while the object beam (OB) is reflected from the surface of the object and then directed to the recording target film (HF).

The reference light and object light incident on the recording target film (HF) record an interference pattern on the recording target film through the interference phenomenon of light.

The interference pattern recorded on the film (HF) contains information about the shape of the object, and when light of the same wavelength and phase as the reference light is irradiated on the film (HF) to reproduce the interference pattern, a holographic image is reproduced.

The present invention uses the recording principle of such a hologram to record wavelength information of light rather than a three-dimensional shape image of an object on a recording target film, thereby improving the color reproducibility of a display device by using the wavelength information recording film as a filter.

The purpose of the present invention is to provide a filter sheet using a photopolymer capable of improving the color reproducibility of a display device.

Another object of the present invention is to provide a backlight unit having a wide color reproducibility spectrum by including a filter sheet using a photopolymer.

Another object of the present invention is to provide a display device having excellent color reproducibility.

The present invention provides a filter sheet capable of selectively filtering a specific wavelength using a photopolymer, and a backlight unit using the same.

The filter sheet according to the present invention records a filtering wavelength in a photopolymerizable monomer using the holographic principle, and can arbitrarily select and record a filtering wavelength within a wavelength range of 360 nm to 820 nm, which is the wavelength range of visible light.

By using these filter sheets, the center wavelength and full width at half maximum of the red, blue, and green light emitted from the backlight unit can be adjusted. This allows a backlight unit capable of high color reproducibility to be implemented.

A filter sheet using a photopolymer according to the present invention has the effect of allowing the backlight unit to adjust the full width at half maximum relative to the center wavelength of each of the red, green, and blue spectrums by filtering a specific wavelength range.

In addition, the backlight unit according to the present invention has the effect of providing a spectrum capable of color reproducibility by adjusting the center wavelength and full width at half maximum (FWHM) of red, green, and blue wavelengths.

Using these backlight units has the effect of improving the color reproducibility of the display device.

Figure 1 is a configuration diagram showing a backlight unit to which a high-color reproducibility LED is applied.
Figure 2 is a configuration diagram showing a backlight unit to which a quantum dot sheet is applied for color reproduction.
Figure 3 is a conceptual diagram explaining the principle of holography.
Figure 4 is a configuration diagram showing a filter sheet using a photopolymer according to an embodiment of the present invention.
Figure 5 is a drawing for explaining the manufacturing principle of a photopolymer layer of a filter sheet according to another embodiment of the present invention.
Figure 6 is a drawing schematically showing an evaluation device for a filter sheet according to the present invention.
Figure 7 is a graph showing the spectrum of light emitted from the backlight unit used in the experiment.
Figure 8 is a graph showing the filtering spectrum of a filter sheet according to an embodiment of the present invention.
FIG. 9 is a graph showing the spectrum of light emitted from a backlight unit to which a filter sheet according to an embodiment of the present invention is applied.
Figure 10 is a configuration diagram showing a backlight unit according to an embodiment of the present invention.
Figure 11 is a schematic diagram showing a backlight unit according to another embodiment of the present invention.

Hereinafter, a filter sheet using a photopolymer according to the present invention and a high-color reproducibility backlight unit including the same will be described with reference to the drawings.

Terms including ordinal numbers such as first, second, etc. may be used to describe various components, but the components are not limited by such terms. These terms are used only to distinguish one component from another.

In addition, in the present invention, the term "on" may not only mean that a part is directly above another part while in contact with the other part, but may also mean that a part is not in contact with the other part or is above the other part while a third part is formed in the middle.

Figure 4 is a configuration diagram showing a filter sheet using a photopolymer according to an embodiment of the present invention.

As illustrated, a filter sheet (100) according to an embodiment of the present invention includes a protective layer (110) on both sides and a photopolymer layer (120) disposed between the protective layers (110).

The photopolymer layer (120) performs the function of filtering a specific wavelength and includes a photopolymer in which a photopolymerizable monomer is polymerized by a specific wavelength. Here, the specific wavelength is preferably a wavelength of 360 nm or more and 820 nm or less, which is the wavelength range of visible light.

The filter sheet (100) according to the present invention is for implementing high color reproducibility. By controlling the full width at half maximum (FWHM) of blue light, red light, and green light in the visible light wavelength range, the color distinction between colors can be clearly made or a specific wavelength can be implemented sharply, thereby improving the color reproducibility.

For example, in the case of a filter sheet for clearly distinguishing between blue light and green light, it is desirable for the filtering center wavelength to be within the range of 454 nm to 555 nm.

Additionally, in the case of filter sheets for clearly distinguishing between green light and red light, it is desirable for the filtering center wavelength to be within the range of 555 nm to 656 nm.

Photopolymers have the characteristic of changing their refractive index through polymerization.

The above photopolymer layer (120) is optically formed by laminating materials with different refractive indices, and thus performs the function of filtering specific wavelengths.

At this time, the width of the filtering wavelength can be adjusted by changing the thickness of each layer with a different refractive index.

For example, as the thickness of each layer with different refractive indices increases, the width of the filtering wavelength increases.

Here, the photopolymer layer (120) performs the function of filtering a specific wavelength using the principle of holography. At this time, the wavelength to be filtered is the wavelength recorded in the photopolymer layer (120) when manufacturing the photopolymer layer (120).

Below, a method of recording wavelengths in a photopolymer layer (120) will be examined.

Figure 5 is a drawing for explaining the manufacturing principle of a photopolymer layer of a filter sheet according to another embodiment of the present invention.

As shown, first, a polymer compound having a matrix structure is prepared using photopolymerizable monomers.

The above polymer compound is irradiated with light of a wavelength to be filtered so that the filtering wavelength is recorded. The recording of the filtering wavelength is accomplished by a photoinitiator included in the polymer compound.

By irradiating light of a specific wavelength, the center wavelength to be filtered and the filtering wavelength width can be adjusted. At this time, the filtering center wavelength and the filtering wavelength width can be adjusted by adjusting the center wavelength and wavelength width of the irradiated light itself, and the filtering center wavelength and the filtering wavelength width can also be adjusted by adjusting the angle of the irradiated light.

Additionally, in order to filter multiple wavelength bands, light having different center wavelengths and wavelength widths may be recorded through multiple light sources.

Through a development process in a photoinitiated polymer compound, only the portion where the wavelength is recorded is activated, and then the activated monomers undergo a polymerization process, after which the monomers diffuse so that only the polymerized photopolymer remains, and then the photopolymer is fixed by curing. Curing is performed by irradiating UV to a UV-curable resin included in the polymer compound.

This method uses the principle of holography production.

The principle of holography is to record an interference pattern on a photopolymer by utilizing the interference phenomenon of light. In the case of the present invention, a filter sheet that filters a specific wavelength band is manufactured by recording the wavelength to be filtered.

< Example >

Using laser light with a central wavelength of 590 nm, filter sheets with filtering widths of 30 nm and 40 nm were manufactured.

Figure 6 is a drawing schematically showing an evaluation device for a filter sheet according to the present invention.

As shown, the performance of the manufactured filter sheet was evaluated using a backlight unit including a light guide plate, a prism sheet, and a diffusion film.

The filter sheet (100) is laminated on top of the prism sheet (PS) so that light passing through the prism sheet (PS) and focused toward the center passes through the filter sheet.

The light passing through the filter sheet (100) was measured by a measuring instrument (PR) to evaluate the overlap ratio and s-RGB area ratio. A white LED with a blue chip coated with a red phosphor and a green phosphor was used as a light source (10).

Table 1 shows the performance evaluation results of a filter sheet according to an embodiment of the present invention, FIG. 7 is a graph showing the spectrum of light emitted from a backlight unit used in an experiment, FIG. 8 is a graph showing the filtering spectrum of a filter sheet according to an embodiment of the present invention, and FIG. 9 is a graph showing the spectrum of light emitted from a backlight unit to which a filter sheet according to an embodiment of the present invention is applied.

First, looking at Figure 7, the light emitted from the white LED has peaks in the blue, green, and red light regions, but the green and red light exhibited characteristics in which the peaks were not sharp.

For these spectra, green light and red light cannot be separated, which limits the ability to improve color reproducibility.

In order to improve color reproducibility in a spectrum such as Fig. 7, the half-width of green light and red light must be reduced. To do so, it is desirable to filter wavelengths between green light and red light.

Figure 8 shows the filtering spectrum of a filter sheet having a center wavelength of 590 nm and filtering widths of 30 nm and 40 nm, respectively.

This shows the results of measuring the filtering spectrum after manufacturing a filter sheet with a center wavelength of 590 nm and filtering widths of 30 nm and 40 nm recorded on photopolymer to filter wavelengths between green light and red light.

Looking at Figure 8, it can be confirmed that the wavelength in the 590 nm portion has been selectively removed.

Figure 9 shows the results of laminating a filter sheet on a backlight unit and measuring the spectrum.

As shown, compared to the spectrum before the filter sheet (100) is applied, it can be confirmed that the 590 nm wavelength portion is selectively removed, the half-width of green light and red light is reduced, and the peaks of green light and red light are sharply implemented.

division Color reproducibility DCI(overlap) s-RGB(area ratio) Comparative example 80% 101% Example 1 (filtering width 30 nm) 90% 112% Example 1 (filtering width 40 nm) 93% 117%

The comparative example evaluates the overlap ratio and s-RGB area ratio of light emitted from a backlight unit without stacking filter sheets.

Example 1 is a case where filter sheets having a center wavelength of 590 nm and a filtering width of 30 nm were laminated, and the overlap ratio of the shipped light and the s-RGB area ratio were evaluated.

Example 2 laminated filter sheets having a center wavelength of 590 nm and a filtering width of 40 nm, and evaluated the overlap ratio and s-RGB area ratio of the shipped light.

Looking at the results, it can be confirmed that when the filter sheet (100) according to the present invention is applied, the overlap ratio and S-RGB area ratio are improved, thereby improving the color reproducibility of the display device.

Figure 10 is a configuration diagram showing a backlight unit according to an embodiment of the present invention.

As described above, a backlight unit according to an embodiment of the present invention includes a light source (10), a light guide plate (GP) that guides light emitted from the light source (10), a prism sheet (PS) that refracts and collects light emitted from the light guide plate (GP), and a filter sheet (100) that filters a specific wavelength band of light emitted from the prism sheet (PS).

By laminating a filter sheet (100) on top of a prism sheet (PS), light collected by the prism sheet (PS) must pass through the filter sheet (100), so that the filter sheet can filter a more accurate wavelength range.

Since the filter sheet (100) is formed by laminating materials having optically different refractive indices, the wavelength being filtered changes depending on the angle of incidence.

The light source includes a blue chip (12) that emits blue light, and a polymer layer (20) that embeds the blue chip (12) and includes a red fluorescent substance (24) and a green fluorescent substance (26).

Some of the blue light emitted from the blue chip enters the light guide plate as is, some is converted into red light by the red phosphor (24) and enters the light guide plate, and some is converted into green light by the green phosphor (26) and enters the light guide plate.

In the light guide plate (GP), blue, red, and green light are mixed and emitted as white surface light, which passes through a prism sheet and is then focused, then passes through a filter sheet and has its wavelength selectively filtered before being emitted as white light capable of color reproduction.

Accordingly, even without developing a new material phosphor, by analyzing the spectrum of light emitted from the backlight unit and manufacturing and applying a filter sheet that filters a specific wavelength range, the center wavelength and half-maximum width of red light, green light, and blue light can be adjusted, thereby providing a backlight unit capable of high color reproducibility.

Figure 11 is a configuration diagram showing a backlight unit according to another embodiment of the present invention.

This embodiment uses a blue LED (30) as a light source, and is configured by laminating a quantum dot sheet (40) in which red light-emitting nanoparticles (44) and green light-emitting nanoparticles (46) are mixed and cured on top of a light guide plate (GP).

A prism sheet (PS) for light collection is laminated on top of the quantum dot sheet (40), and a filter sheet (100) for selective filtering of wavelengths is laminated on top of the prism sheet (PS).

Blue light emitted from a blue LED (30) passes through a quantum dot sheet (40) containing a mixture of red light-emitting nanoparticles (44) and green light-emitting nanoparticles (46) to implement white light. The white light passes through a prism sheet (PS) and is collected, then passes through a filter sheet (100) and is emitted with the center wavelength and half-width adjusted.

Accordingly, even without adjusting the size of the quantum dots, by analyzing the spectrum of light emitted from the backlight unit and manufacturing and applying a filter sheet that filters a specific wavelength range, the center wavelength and half-maximum width of red light, green light, and blue light can be adjusted, thereby providing a backlight unit capable of high color reproducibility.

Although the above description focuses on the embodiments of the present invention, various changes or modifications can be made at the level of a person skilled in the art. Accordingly, it will be understood that such changes and modifications are included within the scope of the present invention as long as they do not depart from the scope of the present invention.

10 : Light source
12 : Blue Chip
20: Polymer layer
24: Red phosphor
26 : Green Phosphor
30 : Blue LED
40: Quantum dot sheet
44: Red luminescent nanoparticles
46: Green luminescent nanoparticles
100 : Filter Sheet
110 : Protective layer
120 : Photopolymer layer
GP : Light guide plate
OS: Optical Sheet
PS: Prism sheet

Claims (7)

A photopolymer layer comprising a photopolymer polymerized by a photopolymerizable monomer having a wavelength of 360 nm to 820 nm;
A first protective layer disposed on one side of the photopolymer layer and receiving white light mixed with blue light, green light, and red light as incident light; and
A second protective layer is disposed on the other side of the photopolymer layer and white light transmitted through the photopolymer layer is emitted to the outside as light.
The above photopolymer layer has a structure in which layers having different optical refractive indices are laminated,
The photopolymer layer transmits white light having a wavelength excluding a first boundary wavelength portion, which is a wavelength between at least a first wavelength in the wavelength range of the green light and a second wavelength in the wavelength range of the red light, of the white light incident on the first protective layer toward the second protective layer, or transmits white light having a wavelength excluding a second boundary wavelength portion, which is a wavelength between the first wavelength in the wavelength range of the green light and the third wavelength in the wavelength range of the blue light, toward the second protective layer,
A filter sheet wherein the first boundary wavelength is a wavelength whose filtering center wavelength is 555 nm to 656 nm, and the second boundary wavelength is a wavelength whose filtering center wavelength is 454 nm to 555 nm.
In paragraph 1,
The above photopolymer
A filter sheet in which a photopolymerizable monomer is polymerized by a wavelength of 454 nm or more and 555 nm or less so that the filtering center wavelength, which is the second boundary wavelength portion that is not emitted to the outside of the second protective layer of the photopolymer layer from the white light incident on the first protective layer, is between the third wavelength, which is the wavelength range of the blue light, and the first wavelength, which is the wavelength range of the green light.
In paragraph 1,
The above photopolymer
A filter sheet in which a photopolymerizable monomer is polymerized by a wavelength of 555 nm or more and 656 nm or less so that the filtering center wavelength, which is the first boundary wavelength portion that is not emitted to the outside of the second protective layer of the photopolymer layer from the white light incident on the first protective layer, is between the first wavelength, which is the wavelength range of the green light, and the second wavelength, which is the wavelength range of the red light.
light source;
A light guide plate that guides light emitted from the light source to emit a surface light of white light mixed with blue light, green light, and red light;
A prism sheet positioned on the upper portion of the light guide plate and collecting light emitted from the light guide plate; and
Including the filter sheet of claim 1, which is laminated on top of the prism sheet and selectively filters the wavelength of light collected and emitted by the prism sheet,
The above filter sheet is a backlight unit that transmits white light having a wavelength excluding the first boundary wavelength portion, which is a wavelength between the first wavelength, which is the wavelength range of the green light, and the second wavelength, which is the wavelength range of the red light, or the second boundary wavelength portion, which is a wavelength between the first wavelength, which is the wavelength range of the green light, and the third wavelength, which is the wavelength range of the blue light.
In paragraph 4,
The above light source is
A blue chip that emits blue light,
A backlight unit comprising a polymer layer embedding the above blue chip and including a red phosphor and a green phosphor.
In paragraph 4,
The above light source includes a blue light-emitting diode,
Further comprising a quantum dot sheet cured by mixing red light-emitting nanoparticles and green light-emitting nanoparticles laminated on the above light guide plate,
The above quantum dot sheet is a backlight unit placed under the prism sheet.
A display panel that outputs images,
A display device comprising a backlight unit according to any one of claims 4 to 6.

Images