KR20100118807A - Optical film with improved brightness in the frontal direction and light diffusing, back light unit having the optical film and liquid crystal display device having the back light unit - Google Patents

Abstract

PURPOSE: An optical film with improved brightness in the frontal direction and light diffusing, a back light unit having the optical film and, a liquid crystal display device having the back light unit are provided to increase the light collection efficiency by including the light diffusion unit arranged on a gap between a plurality of prisms. CONSTITUTION: A light guide plate(130) guides the light generated by a light source(110) to the optical film(140). An optical film comprises a transparent substrate(141), a plurality of prisms(142) and a light diffusion part(143). The transparent substrate plays the role of transmitting the light which enters.

Description

Optical film with improved brightness in the frontal direction and light diffusing, back light unit having the optical film and liquid crystal display device having the back light unit}

Disclosed are an optical film, a backlight unit employing the optical film, and a liquid crystal display device having the backlight unit. More specifically, an optical film including a plurality of prisms and at least one light diffusing unit disposed in a valley between the prisms, a backlight unit employing the same, and a liquid crystal display device having the backlight unit are disclosed.

The light guide plate generally includes a transparent plastic plate and reflective ink printed in dot form on one surface of the plate. Since there is a certain limit in reducing the dot size of the reflective ink printed on the light guide plate, when viewing the liquid crystal display device employing the light guide plate, there is a problem that the dot of the reflective ink is visually recognized at a distance of a general user. Therefore, in the related art, an additional diffusion sheet is disposed on the light guide plate so that the dots of the reflective ink are not visually recognized, and an additional prism sheet is further disposed on the diffusion sheet to increase the front luminance to efficiently light the light emitted from the light source. Used. In addition, a protective sheet having a diffusion function is further disposed on the prism sheet to protect the end portion of the prism sheet.

In addition, a light guide plate made by imprinting fine irregularities of several micrometers or less on a surface without printing reflective ink dots has been developed and used.

On the other hand, a reverse prism sheet technology has been developed that can improve the brightness by facing the surface of the prism pattern toward the light guide plate without disposing a diffusion sheet on the light guide plate. However, when the inverted prism sheet is used alone in the liquid crystal display device, there is a problem in that a nonuniform pattern on the light guide plate is recognized. To prevent this, the inverted prism sheet is used together with a separate diffusion sheet or the inverse prism sheet. In some cases, the beads are coated on the opposite side together with a binder to impart diffusibility.

In addition, a prism sheet having a pattern of square pyramids has also been developed, but the prism sheet has excellent diffusivity so as not to use a separate diffusion sheet, but has a problem in that the front luminance is not higher than that of the inverse prism sheet.

An embodiment of the present invention provides an optical film including a plurality of prisms and at least one light diffusion unit disposed in a valley between the prisms.

Another embodiment of the present invention provides a backlight unit employing the optical film.

Another embodiment of the present invention provides a liquid crystal display device having the backlight unit.

One aspect of the invention,

Transparent substrate;

A plurality of prisms disposed on one surface of the transparent substrate; And

It provides an optical film including at least one light diffusing portion disposed in the valley between the prism.

The height h of the light diffusing part may be 0.05 to 0.55 times the pitch p of the prism.

Each of the light diffusion units may be a polygon, a fan, or a modified polygon having at least one curved edge.

Each of the light diffusion units may have a three-dimensional shape having a polygonal pyramid, a cone, or at least one curved surface.

The optical film may have two or more kinds of light diffusion parts having different end faces in an alternate manner along a longitudinal direction.

The light diffusion unit may be discontinuously disposed along the length direction of the prism.

Another aspect of the invention,

Light source;

A light guide plate for guiding light emitted from the light source; And

The optical film disposed on the light guide plate;

The optical film provides a backlight unit in which a prism included therein faces the light guide plate.

Another aspect of the invention,

A liquid crystal display device employing the backlight unit is provided.

According to an embodiment of the present invention, a plurality of prisms and at least one light diffusing portion disposed in the valley between the prism by including a high front brightness and light diffusing optical film, a backlight unit employing the same, and the backlight unit A liquid crystal display device may be provided.

Next, an optical film and a backlight unit having the optical film according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of an edge-type backlight unit having an optical film according to an embodiment of the present invention.

Referring to FIG. 1, the backlight unit 100 according to an exemplary embodiment of the present invention may include a light source 110, a light guide plate 130 for guiding light emitted from the light source 110, and a light guide plate 130. It is provided with an optical film 140 disposed on the top. The backlight unit 100 may include a light source cover 120 disposed outside the light source 110, and may further include a reflective sheet (not shown) disposed under the light guide plate 130.

In addition, although not shown here, a liquid crystal display panel, an antireflection layer, and the like are sequentially stacked on the backlight unit 100 to form a liquid crystal display device.

The light source 110 generates light, and various light sources such as a line light source lamp, CCFL, or LED may be used.

The light guide plate 130 serves to guide the light (arrow) generated by the light source 110 to the optical film 140.

The optical film 140 includes a transparent substrate 141, a plurality of prisms 142, and at least one light diffuser 143.

The transparent substrate 141 is formed of a material such as a polyester resin to serve to transmit light incident thereto.

The prisms 142 are disposed on one surface of the transparent substrate 141, that is, on the side of the light guide plate 130, so that light incident from the light guide plate 130 may be incident on the plane of the liquid crystal display panel (not shown) of the liquid crystal display device (not shown). Serves to condense. The prisms 142 may be formed of a photocurable resin or a thermosetting resin. The refractive indices of the prisms 142 may be 1.45 to 1.65. When the refractive indices of the prisms 142 are 1.45 to 1.65, manufacturing may be easy and high brightness may be maintained.

The light diffuser 143 is disposed in the valley between the prisms 142. The light diffuser 143 may be formed of the same or similar material as that of the prism 142.

The light diffusion unit 143 reduces the phenomenon that the reflective ink dot printed on the light guide plate 130 or the pattern of the fine irregularities imprinted on the light guide plate 130 is visually recognized by the observer, thereby employing the backlight unit 100. It serves to improve the quality of the image of the device (not shown). Therefore, since the optical film 140 including the light diffusing unit 143 does not have to have a separate diffusion sheet, the optical film 140 may be economically thin and thin. In addition, since the light diffusing unit 143 and the prism 142 are respectively disposed on one surface of the transparent substrate 141, together with the transparent substrate 141, the optical film 140 is integrally formed. It improves workability during manufacturing and simplifies the manufacturing process, and reduces manufacturing cost, and also eliminates the possibility of interface phenomenon between optical films that occur when two or more optical films are overlapped such as wet-out phenomenon. Can be.

Hereinafter, the specific configuration, operation and effects of the optical film 140 will be described in detail.

FIG. 2 is a cross-sectional view illustrating a propagation path of light transmitted and reflected by a prism and a light diffusion unit included in the optical film of FIG. 1.

First, the relationship between the height h of the light diffusing portion 143 and the prism pitch p will be described.

Referring to FIG. 2, since light such as L ₁ emitted from the light guide plate 130 of FIG. 1 is incident only to the L portion of the incident surface of the prism 142, the other incident surface except the L portion may emit light in a desired direction. It does not help to progress. In addition, the light incident on the l part is refracted by the incident surface of the prism 142 and is incident on the m part of the exit surface. Like the above, the exit surface except for the m part does not help to propagate the light in the desired direction. Therefore, the light diffusing unit 143 disposed in the remaining portions except for the l or m portion may improve the light diffusing property while maintaining the front luminance of the optical film 140 high, which will be described later.

Meanwhile, when light L ₁ is incident on the optical film 140 at an angle of θ ₀ , ℓ and m may be defined as in the following equations, respectively.

In the above formula, n means the refractive index of the prism 142.

Since θ ₃ = θ ₀ + θ ₂ , both l and m are the pitch p of the prism 142, the incident angle (θ ₀ ) of the light L ₁ , the vertex angle (θ ₁ ) of the prism 142, and the prism 142. And the refractive index n of the prism 142 and the angle θ ₂ of the incident surface.

Although the incidence angle θ ₀ of the light L ₁ emitted from the light guide plate 130 is generally 5 to 20 degrees, the incidence angle θ ₀ may be adjusted to 5 to 10 degrees by appropriately changing the design of the light guide plate 130. have.

In addition, the vertex angle θ _{1 of the} prism 142 may be 60 to 90 degrees, and the angle θ ₂ of the incident surface of the prism 142 may be 45 to 60 degrees. The refractive index n of the prism 142 may be 1.45 to 1.65 as described above. In this case, when the range of l and m is calculated by the above equations, l may be 0.1 to 0.38 times the pitch p of the prism 142, and m is the prism 142 when the refractive index n of the prism is 1.45. If the refractive index n of the prism is 1.65, and the pitch (p) of the prism ()) may be 0.16 ~ 0.82 times the pitch (p) of the prism 142.

Since m is longer than l, forming the light diffusing unit 143 out of the range of m can provide diffusion while minimizing the influence on luminance.

When the vertex angle θ ₁ of the prism 142 is 90 °, the length of one inclined surface of the prism 142 is about 0.7 times the prism pitch p, so when the incident angle θ ₀ exceeds 20 °, m becomes the prism ( One slope of 142 may be completely included. Of course, when the incident angle θ ₀ decreases, m is limited to a portion of one inclined surface of the prism 142. However, when the vertex angle θ ₁ is 60 °, the length of one inclined surface of the prism 142 is 1.0 times the prism pitch p. In this case, when the refractive index n of the prism is 1.45, m is At an angle θ ₀ where light L ₁ is incident at 20 °, it is 0.73 times the prism pitch p, at 15 ° it is 0.55 times the prism pitch p, and at 10 ° the prism pitch ( 0.38 times p).

As described above, the light diffusing portion 143 may be formed at a portion other than m. When the vertex angle θ ₁ is 60 °, the height of the prism 142 is (√3) / 2 of the prism pitch p. It corresponds to the ship, and the refractive index of the prism (n) is calculated when the height of the portion other than the height corresponding to the height of the prism 142 in the case il 1.45 m, the angle of incidence (θ ₀₎ to increase the 20˚, 15˚ , 10 °, respectively, 0.22 times, 0.38 times, and 0.53 times the prism pitch p. Therefore, the light L ₁ emitted from the light guide plate 130 is formed in consideration of the refractive index n of the prism when the maximum angle θ ₀ incident to the prism 142 is 10 ° to 20 °. The height h of the light diffusing portion 143 may be 0.20 to 0.55 times the prism pitch p. It is also possible that the height h of the light diffusion portion 143 is smaller than 0.20 times the prism pitch p. However, if the height h is less than 0.05 times the pitch p of the prism 142, the diffusion effect is achieved. Is insignificant. In addition, when the height h exceeds 0.55 times the pitch p of the prism 142, the front luminance decreases. Therefore, the height h of the light diffusing portion 143 is preferably 0.05 to 0.55 times the prism pitch p.

On the other hand, since the l or m part is not reduced due to the arrangement of the light diffusion part 143, the original function of the prism 142 is not reduced at all. Therefore, the optical film 140 may exhibit high front luminance.

Hereinafter, the principle of the light diffusing property of the optical film 140 by the light diffusing unit 143 will be described.

That is, as shown in FIG. 2, a plurality of lights (L ₂ to L _6, etc.) are incident in a direction perpendicular to the smooth surface of the transparent substrate 141 along a straight line parallel to the longitudinal direction of the prism 142. Assume that In this case, it is also assumed that five or more light diffusion parts 143 having different shapes are alternately arranged along the longitudinal direction of the prism 142.

Incident angles of the lights L ₂ to L ₆ incident to the light diffusing parts 143 may be varied due to the shape differences of the light diffusing parts 143, and thus the light L ₂ to L ₆ is emitted. The angles can vary, resulting in increased light diffusivity.

3A to 3D are cross-sectional views illustrating optical films according to various other embodiments of the present invention.

Hereinafter, the same reference numerals as in the above-described drawings indicate the same member or parts of the same member.

3A to 3D, each of the light diffusion units 143 may be a polygon, a fan, or a modified polygon having at least one curved edge.

In addition, each of the light diffusion units 143 may be, for example, a three-dimensional shape having a polygonal pyramid, a cone, or at least one curved surface.

On the other hand, the prism 142 of FIGS. 1 and 2 has one end shape symmetrically, whereas the prisms 142 of FIGS. 3A to 3D have one end shape asymmetry. When light is incident in both directions of the prism 142, the shape of one end surface of the prism 142 is symmetrically preferable to improve the front luminance, and when the light is incident only in one direction of the prism 142, the prism It is preferable for the front luminance to improve that the shape of one end face of 142 is asymmetric.

4 is a perspective view showing an extract of a prism and a light diffusing unit in an optical film according to another embodiment of the present invention.

Referring to FIG. 4, the light diffusing unit 143 is disposed discontinuously along the longitudinal direction of the prism 142. 4 illustrates a plurality of light diffusing parts 143 having the same shape, the present invention is not limited thereto, and two or more light diffusing parts 143 having different shapes may be formed in a length direction of the prism 142. It may be arranged discontinuously alternately along. In addition, two or more light diffusion parts 143 having the same or different shapes may be continuously disposed along the longitudinal direction of the prism 142.

Although the preferred embodiment according to the present invention has been described above with reference to the drawings, this is merely illustrative, and those skilled in the art can understand that various modifications and equivalent other embodiments are possible. There will be. Therefore, the protection scope of the present invention should be defined by the appended claims.

1 is a cross-sectional view of an edge-type backlight unit having an optical film according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a propagation path of light transmitted and reflected by a prism and a light diffusion unit included in the optical film of FIG. 1.

3A to 3D are cross-sectional views illustrating optical films according to various other embodiments of the present invention.

4 is a perspective view showing an extract of a prism and a light diffusing unit in an optical film according to another embodiment of the present invention.

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

100: backlight unit 110: light source

120: light source cover 130: light guide plate

140: optical film 141: transparent substrate

142: prism 143: light diffusion unit

h: height of light diffusion portion p: pitch of prism

L ₁ ~ L ₆ : light

Claims (8)

Transparent substrate; A plurality of prisms disposed on one surface of the transparent substrate; And Optical film including at least one light diffusing portion disposed in the valley between the prism. The method of claim 1, The height (h) of the light diffusion part is 0.05 to 0.55 times the pitch (p) of the prism. The method of claim 1, Each of the light diffusion parts is an optical film having one end shape of a polygon, a fan shape, or a modified polygon having at least one curved edge. The method of claim 3, Each of the light diffusion parts has a three-dimensional shape having a polygonal pyramid, a cone or at least one curved surface. The method of claim 3, Two or more kinds of light diffusion parts having different end faces are alternately arranged along the longitudinal direction of the prism. The method of claim 1, The light diffusing unit is discontinuously disposed along the longitudinal direction of the prism. Light source; A light guide plate for guiding light emitted from the light source; And An optical film according to any one of claims 1 to 6 disposed on the light guide plate, The optical film is a backlight unit disposed so that the prism included therein facing the light guide plate. A liquid crystal display device employing the backlight unit according to claim 7.

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