KR20090089968A - Optical film, back light unit and liquid crystal displayhaving the same - Google Patents

Abstract

An optical film, a backlight unit and a liquid crystal display device having the same are provided to prevent a moire phenomenon by controlling a pattern pitch of a first film and a second film of the optical film. A liquid crystal display device includes a liquid crystal display panel, a backlight unit(10) and an optical film(20). The optical film is formed between the liquid crystal display panel and the backlight unit. The optical film is comprised of a first film(22) and a second film(21). The first film has a prism pattern in the upper surface. The second film is arranged in the bottom of the first film and includes the cylindrical pattern in the top.

Description

Optical film, backlight unit and liquid crystal display device having the same {OPTICAL FILM, BACK LIGHT UNIT AND LIQUID CRYSTAL DISPLAYHAVING THE SAME}

The present invention relates to an optical film, a backlight unit and a liquid crystal display device having the same, and more particularly, to adjust a pattern pitch of the first film and the second film of the optical film to prevent moiré phenomenon, One backlight unit and a liquid crystal display device are provided.

In general, a liquid crystal display device is an electronic device that transmits various electrical information generated by various devices to visual information by using a change in liquid crystal transmittance according to an applied voltage. The LCD has attracted attention as an alternative means of overcoming the shortcomings of the Cathode Ray Tube (CRT), which has been widely used since it has advantages such as miniaturization, light weight, and low power consumption. This is installed in almost all information processing equipment. Such liquid crystal displays generally apply a voltage to a liquid crystal having a specific molecular array and change it to another molecular array, and optical properties such as birefringence, photoreactivity, dichroism, and light scattering characteristics of the liquid crystal generated by the change of the molecular array. It is a display device that uses the modulation of light by liquid crystal to convert the change of the light into a visual change. A liquid crystal display device, which is a light-receiving element without a self-luminous source, requires a separate light source device capable of illuminating the entire screen of the device from the back side. Such an illumination device for a liquid crystal display device is commonly referred to as a backlight unit.

In general, the backlight unit is classified into an edge-light method and a direct lighting method according to a method of disposing a light emitting light source. Among them, the edge-light method is a method in which a light emitting light source is disposed on a side of a light guide plate for guiding light generated from the light emitting light source, and is applied to a relatively small liquid crystal display device such as a desktop computer or a laptop monitor, and has uniformity of light. This is good, excellent in durability, and advantageous for thinning the device. On the other hand, the direct method has been developed for use in medium and large display devices of 20 inches or more, and a method of directly illuminating the front of the liquid crystal panel by arranging a plurality of light sources under the liquid crystal panel.

Currently, the liquid crystal display uses an optical film to improve the brightness and viewing angle by diffusing and condensing light incident from the light source. At this time, the widely used optical film contains a diffusing agent therein, so that the bright line of the lamp is not visible by scattering by the diffusing agent. On the other hand, the optical film is composed of a flat-shaped light diffusing film containing a prism-shaped film on the top and a diffusing agent on the bottom to diffuse and condense the light emitted from the light source through the light-diffusion film and then enter through the prism film The light being refracted appropriately. However, due to the recent thinning of LCDs and backlight units, an optical film in which a lenticular type is convex on the surface is adopted instead of a flat light diffusing film containing a diffusing agent to prevent the visible light of the lamp. However, since the lenticular diffuser plate has a periodic shape, a prism-shaped optical film and moire phenomenon, which also have a periodic pattern, occur.

In order to solve this problem of moiré shape, US Patent No. 6,091,547 (3M Innovative Properties Company) discloses a brightness control film having a prism pitch of 30 μm or less. However, when the pitch of the prism is 30 µm or less, not only the luminance is lowered relatively, but also the manufacturing process is very complicated. Furthermore, in terms of thermal and mechanical properties, the moiré phenomenon is partially generated when the lenticular shape, especially the cylindrical film, is positioned as the second film.

The present invention has been made to solve the above problems, an object of the present invention is to provide an optical film that can prevent the moiré phenomenon by appropriately adjusting the pattern pitch of the first film and the second film of the optical film. .

Another object of the present invention is to provide a backlight unit and a liquid crystal display device employing the optical film.

The optical film of the present invention for achieving the above object is composed of a first film including a prism-shaped pattern on the upper surface, a second film located on the lower surface of the first film and including a cylindrical pattern on the upper surface. The pattern pitch of the first film and the pattern pitch of the second film satisfy Equation 1 below.

[Equation 1]

0.3≤ (P1 / P2) -N ≤ 0.7

      However, P1 is the pattern pitch of the first film, P2: the pattern pitch of the second film, and N means an integer greater than or equal to a decimal point among P1 / P2 values.

The lower surface of the first film and the second film is preferably a flat surface, a polymer film, the haze of 5 to 90% can be used.

The patterns of the first film and the second film are preferably arranged in parallel and adjacent to each other along one direction.

The prism shape is preferably a linear prism shape, the vertical cross section with respect to the axial direction thereof is a triangle, the triangle has a vertex opposite to the lower surface of 80 to 110 ° and the pitch of the prism is 10 to 300 mu m.

The thickness of the first film is preferably 0.1 to 5 mm.

The cylindrical shape of the second film is preferably arcuate in a vertical cross section with respect to the axial direction.

The second film preferably has a ratio of pitch to height of 0.2 to 0.5.

The backlight unit of the present invention includes the above-described optical film, and the liquid crystal display includes such a backlight unit.

The terms used herein are briefly described.

As used herein, the cylinder type refers to a type in which a column having a semicircular cross section is arranged in 11 characters as shown in 21 in FIG. 1.

As used herein, the pitch is the distance between the mountain which is the highest part of the convex portions protruding from the repeating pattern part and the immediately adjacent mountain. For example, the pitch of the prism sheet is t in FIG. 2, and the pitch of the cylinder sheet is e in FIG. 2.

According to the present invention, by properly adjusting the pattern pitch of the first film and the second film in the optical film used in the liquid crystal display panel, it is possible to maintain the high brightness while improving the light collecting efficiency and to improve the moiré phenomenon.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

1 is a perspective view schematically showing an optical film according to an embodiment of the present invention. Referring to FIG. 1, the liquid crystal display of the present invention includes a liquid crystal display panel (not shown) in which an image is implemented, a backlight unit 10 serving as a light source of the liquid crystal display panel, these liquid crystal display panels, and a backlight unit 10. It includes an optical film 20 formed between).

First, the backlight unit 10 will be described.

The backlight unit 10 is positioned at the rear of the liquid crystal panel and the optical film 20 and provides light, for example, white light, to the liquid crystal panel. The backlight unit 10 receives a light source 11 that provides light for illuminating the liquid crystal panel, a light source reflector (not shown) disposed outside the light source 11, and light provided from the light source 11. It includes a light guide plate (not shown) for providing to and an optical film 20 disposed between the light guide plate and the liquid crystal panel. In the present invention, the light source 11 of the backlight unit 10 is preferably driven in a direct type, but is not limited thereto.

In the present invention, the light source 11 includes a linear light such as a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) that generates light having a predetermined wavelength, for example, white light. A light source is used. However, only the linear light source as described above is not used for the light source 11.

In another embodiment of the present invention, the light source 11 may use a point light source such as a light emitting diode (LED). In this case, the number of light emitting diodes used as the light source 11 may be appropriately selected according to the size of the liquid crystal panel to be illuminated. In addition, the light emitting diode used as the light source 11 is not limited, and one white light emitting diode is used or a combination of three light emitting diodes generating colors of red (R), green (G), and blue (B). It is also possible to use.

The light source reflector 160 may be disposed outside the light source 11. The light source reflector (not shown) may be made of metal or plastic, and the inner wall may be coated with a material capable of reflecting light to reflect the light emitted from the light source 11 to the side of the light guide plate.

The light generated from the light source 11 is incident on the light guide plate through the side of the light guide plate, that is, the light incident surface. The light source reflector reflects the light generated from the light source 11 toward the light guide plate to improve the efficiency of light incident on the light guide plate. . The light guide plate transmits the light incident through the light incident surface disposed on its side to equalize it while transmitting in a direction substantially parallel to the viewing plane of the liquid crystal panel disposed thereon using the principle of total internal reflection. do. The front surface of the light guide plate is a light emitting surface for emitting light in the direction in which the liquid crystal panel is arranged.

In order for the light incident on the light guide plate to be emitted in the direction of the liquid crystal panel, total reflection must be diffused inside the light guide plate. To this end, a light scattering pattern (not shown) as shown by dot-printing for printing white ink may be formed on the back surface of the light guide plate opposite to the light exit surface.

On the other hand, a non-printing light guide plate that does not go through the printing process may be used. U. S. Patent No. 6,123, 431 discloses a non-printing light guide plate in which a light scattering pattern is formed by forming grooves on the surface of the light guide plate. U. S. Patent No. 5,881, 201 discloses a light guide plate by dispersing inorganic or organic particles having a different refractive index from a basic resin in the light guide plate. Disclosed is a non-printing light guide plate which also serves as a diffuser plate function by having a scattering function due to a refractive index difference within. For reference, the light guide plate may be made of a transparent acrylic resin such as poly methyl methacrylate (PMMA).

The reflective sheet (not shown) is preferably disposed on the bottom surface of the light guide plate and serves to reflect the light exiting to the bottom surface of the light guide plate and reenter the light guide plate. The reflective sheet 180 may be manufactured by coating silver (Ag) on a sheet made of SUS, brass, aluminum, PET, and the like, and titanium coating to prevent deformation due to endotherm for a long time even if heat is generated minutely. In addition, the reflective sheet may be produced by dispersing bubbles for scattering light on a sheet made of synthetic resin such as PET.

Next, the optical film 20 is the core of the present invention.

The backlight unit 10 includes at least one optical film 20 disposed between the light guide plate and the liquid crystal panel. The optical film 20 improves luminance by effectively injecting light emitted from the light guide plate into the visible surface of the liquid crystal panel, and serves to make the entire surface of the visible surface have a uniform luminance distribution by making light incident on the liquid crystal panel uniform. To perform.

To this end, the optical film 20 of the present invention is composed of a first film 22 and a second film 21. As described above, in the conventional optical film 20 composed of two layers, a prism-shaped sheet is used as the first film and a planar sheet containing a light diffusing agent is used as the second film 21. However, in recent years, the thin film of the liquid crystal display panel is required to replace the planar second film with a lenticular shape. However, the light irradiated from the light source 11 is incident on the incident surface of the lenticular second film and then emitted through the exit surface and irradiated onto the prism-shaped film which is the first film. In this case, since the pattern pitch of the first film and the second film is different, the moiré phenomenon occurs as a result of interference of light.

Accordingly, in the present invention, the first film 22 including the prism-shaped pattern on the upper surface, and the optical film including the second film 21 located on the lower surface of the first film 22 and the cylindrical pattern on the upper surface thereof. In (20), it was confirmed that the moiré phenomenon does not occur when the pattern pitch of the first film 22 and the pattern pitch of the second film 22 satisfy the following Equation 1.

[Equation 1]

0.3≤ (P1 / P2) -N ≤ 0.7

      However, P1 is the pattern pitch of the first film, P2: the pattern pitch of the second film, and N means an integer greater than or equal to a decimal point among P1 / P2 values.

It is not confirmed whether the moiré phenomenon does not improve when the equation 1 is satisfied through some mechanism. However, as the value of (P1 / P2) -N approaches 0.5, the median of the numerical range, the moiré phenomenon is significantly lowered. I could confirm that.

Hereinafter, the first film 22 and the second film 21 constituting the optical film 20 will be described.

First, the second film is disposed in parallel with the light exit surface at the upper portion of the backlight unit 10, and scatters the light emitted from the light guide plate to make the luminance uniform throughout the visible surface of the liquid crystal panel. The second film 21 may include a protective layer that has a high haze effect and a high transmittance, and diffuses and condenses the light emitted from the light guide plate to make the luminance uniform. In addition, the light is transmitted in the direction of the first prism-shaped first film 22 to be described later disposed on the upper side to improve the viewing angle.

It serves to widen and conceal the pattern formed on the light guide plate.

The second film 21 used in the present invention is a material and thickness of the film is enough to be used in a conventional light diffusing film, preferably the material is a thermoplastic resin having a good balance of heat resistance and electrical properties, for example, It may be made of a resin alone or mixed with two or more from polyester, polyvinyl chloride, polycarbonate, polymethyl methacrylate, polystyrene, polyester sulfone, polybutadiene, polyether ketone and the like. Preferably, it may be composed of a resin alone or mixed with two or more kinds from polycarbonate, polymethylmethacrylate, polystyrene and polybutadiene. In the case of thickness, preferably 0.5 to 3 mm.

On the other hand, referring to Figure 2, the second film 21 used in the present invention is advantageous in that the shape of the cross-section is close to the hemispherical or arcuate shape, the pattern is preferably adjacent to each other along one direction Arranged in parallel. In other words, when a cylindrical pattern is formed in one axial direction, the stripe shape is formed in parallel so that the stripe shape has the same pattern pitch in parallel to it.

On the other hand, the pattern pitch (e) of the second film 21 is preferably 50 μm to 1 mm. In addition, the second film preferably has a ratio of pitch to height of 0.2 to 0.7. If the pitch-to-height ratio is less than 0.2, there is a problem in that the light condensing effect is lowered, and the luminance is lowered.

The first film 22 for improving light efficiency and brightness is disposed on the second film 21. In this case, the first film 22 includes a prism-shaped pattern on an upper surface thereof, and the patterns are arranged in parallel with each other along one direction in the same manner as the pattern of the second film 21.

The prism shape is a linear prism shape, preferably the vertical cross section with respect to the axial direction is a triangle, and the triangle preferably has a vertex (a in FIG. 2) facing the lower surface of 80 to 110 °. If the vertex opposite to the lower surface is less than 80 ° or more than 110 °, the condensing effect of the prism is lowered and the luminance increase effect is lowered.

Preferably, from the point of view of luminance, an isosceles triangle whose angle (a) of the vertex facing the lower surface is 90 ° and the magnitude of the angle (b) and the angle (c) is preferable, but from the viewpoint of the viewing angle, It is preferable that an isosceles triangle in which (a) is 90 degrees or more and angles (b) and (c) have different sizes. That is, when high luminance is important, it is preferable to design an isosceles triangle whose angle a is 90 degrees, and to enlarge the viewing angle, it is designed to be an isosceles triangle whose angle a is 90 degrees or more. It is desirable to.

 On the other hand, the pitch of the prism is preferably 10 ~ 300㎛. If it is less than 10㎛ may cause a problem that the angle is not good, if it exceeds 300㎛ may cause a problem in visibility. The thickness of the first film is preferably 0.1 to 5 mm. If it is less than 0.1 mm, shape stability may be degraded, and a problem may occur in reliability. If it exceeds 5 mm, it is disposed to face slimmer and thinner.

The material of the first film 22 is a thermoplastic resin having a good balance of heat resistance and electrical properties, for example, polyester, polyvinyl chloride, polycarbonate, polymethyl methacrylate, polystyrene, polyester sulfone, polybutadiene, poly It may consist of a resin alone or in mixture of two or more from the ether ketone. Preferably, it may be composed of a resin alone or mixed with two or more kinds from polycarbonate, polymethylmethacrylate, polystyrene and polybutadiene.

Preferably, the first film 22 and the second film 21 preferably have the same pattern direction, but the pattern directions of the first film 22 and the second film 21 to satisfy the mathematical formula 1 are satisfied. This may also apply if there is a mismatch. Further, the first film 22 and the second film 21 are preferably separated without being in close contact, and the separation distance thereof is preferably 20 to 100 µm.

Meanwhile, a protective film (not shown) may be further added to the upper portion of the first film 22 in order to improve heat resistance of the first film 22.

Hereinafter, the present invention will be described in detail by way of examples. The following examples are merely illustrative of the present invention, but the scope of the present invention is not limited to the following examples.

< Example  1>

A second film having a thickness of 1.2 mm was obtained by repeating a cylindrical shape having a pattern pitch of 200 μm formed by extruding a polycarbonate-based polymer. After that, the polycarbonate-based polymer was extruded on the upper part of the second film, so that an isosceles triangular prism having a pattern pitch of 150 µm and an angle of 90 degrees opposite to the lower surface was repeated to form a first film having a thickness of 0.5 mm. An optical film was prepared.

Then, the optical film was mounted on the LTA400WS-L04 produced by Hansol LCD, a BLU manufacturer, and the luminance was measured at a distance of 50cm from a stage equipped with TOPCON BM-7 under the conditions of CCFL voltage of 16.5V and dimming value of 2.8V. The results are shown in Table 1. In addition, the moiré phenomenon is expressed in four stages: strong, medium, weak, and weak.

If the thickness of the bands represented by the interference phenomenon is 2mm or more, it is classified into steel level, 1.0mm or more, medium level, 0.5mm or more, about weak level, and 0.1mm or more.

< Example  2>

The pattern pitch of the second film An optical film was prepared in the same manner as in Example 1 except that the pitch pitch of 300 μm and the pattern pitch of the first film were 190 μm.

< Example  3>

An optical film was manufactured in the same manner as in Example 1, except that the pattern pitch of the first film was 70 μm.

< Comparative example  1>

An optical film was prepared in the same manner as in Example 1 except that the pattern pitch of the first film was 190 μm.

< Comparative example  2>

An optical film was prepared in the same manner as in Example 1 except that the pattern pitch of the second film was 300 μm.

 < Comparative example  3>

An optical film was prepared in the same manner as in Example 1 except that the pattern pitch of the first film was 100 μm.

TABLE 1

division P2 [Μm] P1 [Μm] ( P1 Of P2 ) -N Moire Luminance [ nit ] Example 1  150 200 0.333 weak 10,510 Example 2 190 300 0.579 weak 10,500 Example 3 70 100 0.428 weak 10,505 Comparative Example 1 190 200 0.053 River 10,495 Comparative Example 2 150 300 0 River 10,500 Comparative Example 3 100 100 0 River 10,495 Comparative Example 4 165 200 0.212 about 10,490 Comparative Example 5 110 200 0.818 about 10,495

As can be seen in Table 1, the optical film of Examples 1 to 3 satisfying Equation 1 of the present invention does not reduce the brightness as compared to the optical films of Comparative Examples 1 to 5 that do not satisfy the moiré phenomenon. It was confirmed that the remarkable improvement.

The optical film of the present invention can be effectively used in the liquid crystal display panel because the moiré phenomenon is improved.

Although the present invention has been described in detail only with respect to the embodiments described, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical spirit of the present invention, and such modifications and variations belong to the appended claims. .

1 is a perspective view of an optical film according to an embodiment of the present invention.

2 is a front view of an optical film according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10: backlight 11: light source

20: optical film 21: second film

22: first film

Claims (15)

A first film including a prism-shaped pattern on an upper surface thereof, and a second film disposed opposite to a lower surface of the first film and including a cylindrical pattern on an upper surface thereof, wherein the pattern pitch of the first film and the second film Optical film, characterized in that the pattern pitch of the film satisfies the following formula (1). [Equation 1] 0.3≤ (P1 / P2) -N ≤ 0.7       (In the above, P1 is the pattern pitch of the first film, P2 is the pattern pitch of the second film, and N is an integer greater than or equal to a decimal point among P1 / P2 values.) The optical film of claim 1, wherein the lower surfaces of the first film and the second film are flat. The optical film of claim 1, wherein the first film and the second film are polymer films. The optical film of claim 4, wherein the polymer film has a haze of 5 to 90%. The optical film as claimed in claim 1, wherein the patterns of the first film and the second film are arranged adjacent to each other in parallel in one direction. The optical film of claim 1, wherein the prism shape is a linear prism shape. The optical film as claimed in claim 1, wherein the prism of the first film has a pitch of about 10 μm to about 300 μm. The optical film of claim 6, wherein the linear prism shape has a triangular cross-sectional shape in a direction perpendicular to the lower surface of the first film. The optical film of claim 1, wherein the first film has a thickness of about 0.1 mm to about 5 mm. The optical film of claim 7, wherein the triangle has a vertex opposite to a lower surface of 80 to 110 °. The optical film of claim 1, wherein the cylindrical shape has an arcuate cross section perpendicular to the axial direction. The optical film of claim 1, wherein the second film has a pitch-to-height ratio of 0.2 to 0.5 in a cylinder pattern. The optical film of claim 1, wherein the second film has a thickness of 0.5 to 3 mm. A backlight unit comprising the optical film of claim 1. A liquid crystal display comprising the backlight unit of claim 14.

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