KR100919973B1 - Prism sheet with light diffusing function, back light unit having the prism sheet, and liquid crystal display device having the back light unit - Google Patents

Abstract

A prism sheet having a light diffusion function, a backlight unit employing the same, and a liquid crystal display device having the backlight unit are disclosed. The disclosed prism sheet is disposed on a transparent substrate and the transparent substrate, the prism sheet having a longitudinal wave pattern, wherein the longitudinal wave pattern changes the height of the prism acid continuously or discontinuously along its length. And a height variation width (maximum height-minimum height) of the prism acid is 0.01 to 1 times the repetition period of the longitudinal wave pattern.

Therefore, the disclosed prism sheet has a light diffusing function and can improve its production yield, and the backlight unit and the liquid crystal display device employing the same can secure a wide viewing angle while maintaining high front brightness and prevent infiltration and moiré phenomena. can do.

Description

Prism sheet having a light diffusion function, a backlight unit employing the same, and a liquid crystal display device having the backlight unit having the prism sheet, and liquid crystal display device having the back light unit }

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism sheet, a backlight unit employing the prism sheet, and a liquid crystal display device having the backlight unit, and more particularly, the use of a diffusion sheet or a protective sheet by having a prism acid having a light diffusing function. The present invention relates to a prism sheet capable of reducing or eliminating and increasing a production yield, and a liquid crystal display capable of improving front luminance and preventing infiltration and moiré by employing the prism sheet.

Recently, as a flat panel display device used in a notebook computer, a television, or a mobile phone that requires thinning, miniaturization, and low power consumption, a plasma display panel (PDP), a field emission display device (field) An emission display device (FED), a thin film transistor liquid crystal display device (TFT-LCD), and the like have been developed, and among these, a liquid crystal display device having excellent color reproducibility and thinness is being actively researched.

Among the flat panel display devices, the PDP and the FED can emit light by themselves, but since the liquid crystal display device is not a light emitter by itself, image display is possible by irradiating light using a backlight unit which is an auxiliary light source. The backlight unit has a structure of a surface light source called an edge type or a direct type so as to meet the requirement of irradiating light but irradiating the entire screen uniformly.

1 is an exploded perspective view showing a backlight unit according to the prior art having an edge-type light source.

Referring to FIG. 1, the backlight unit 10 according to the related art having an edge type light source includes a light source 11, a light guide plate 12 for guiding light emitted from the light source 11, and a lower part of the light guide plate 12. A reflective sheet 13 disposed on the light guide plate 12, a diffusion sheet 14 disposed on the light guide plate 12, a prism sheet 15 disposed on the diffusion sheet 14, and an upper portion of the prism sheet 15. It comprises a protective sheet 16 to be. In addition, a light source cover 11a is disposed outside the light source 11 of the backlight unit. In addition, although not shown here, a liquid crystal display panel and an antireflection layer are sequentially stacked on the backlight unit 10 to form a liquid crystal display device. In addition, two polarizing plates, one for each of the upper and lower surfaces of the liquid crystal display panel, may be further disposed.

The light source 11 generates light, and various light sources such as a line light source lamp or a surface light source lamp, CCFL, or LED may be used.

The light guide plate 12 guides the light generated by the light source 11 to the diffusion sheet 14, and may be omitted when a direct type light source is adopted.

The reflective sheet 13 serves to reflect the light generated from the light source 11 and to supply the light toward the diffusion sheet 14.

The diffusion sheet 14 diffuses and scatters light incident through the light guide plate 12 to supply the prism sheet 15.

The prism sheet 15 refracts light incident through the diffusion sheet 14 to condense light onto a plane of the liquid crystal display panel (not shown). The prism sheet can be modified and combined with various design values such as the shape of the prism mountain and the angle of the mountain slope according to various design goals such as high light collecting efficiency, wide viewing angle, prevention of moiré phenomenon, and prevention of wet out with other films. , Commercially applicable. FIG. 1 illustrates a case where two prism sheets 15a and 15b each having a triangular prism acid arranged in a stripe shape on an upper surface thereof are used to be arranged to cross at right angles to each other. .

When using the prism sheet as described above, the reason for arranging the two prism sheets so that the arrangement directions of the prism mountains cross each other at an angle of 90 degrees is to further concentrate the incident light coming from all directions in the center direction. However, by using the two prism sheets in this way, the front luminance in the center direction increases, but the viewing angle decreases by about ± 10 degrees relative to the front side when using one prism, and as a result, the viewing angle decreases by about 20 degrees. There is a problem.

As a way to solve the problem of viewing angle reduction by the prism sheet 15 and to protect the prism sheet 15 as described above, it is essential that the protective sheet 16 is disposed above the prism sheet 15. That is, the protective sheet 16 serves to protect the prism sheet 15 and to widen the light collected by the prism sheet 15 to widen the viewing angle. By adding the protective sheet 16 as described above, it is difficult to reduce the thickness in manufacturing the backlight unit, to complicate the manufacturing process, and to increase the manufacturing cost.

In addition, the prism sheet 15 having the above-described configuration is often defective due to damage to the surface during manufacture or foreign matter mixed inside and outside thereof. As described above, when a defect occurs in the prism sheet 15, the user may feel that the image quality of the liquid crystal display device is bad. Therefore, the prism sheet 15 in which the defect has occurred should be discarded after confirmation. This, in turn, causes the production yield of the prism sheet 15 to be lowered.

In addition, the backlight unit according to the related art having the above configuration has a problem in that the moire phenomenon occurs because the prism acid is arranged in a stripe shape in a predetermined direction and the prism acid pattern overlaps the RGB pattern of the liquid crystal display panel.

Also, in this case, the shape of the prism acid of the prism sheet 15 is patterned in a stripe shape, so that the surface area of each prism sheet 15a, 15b in contact with the adjacent sheets 15b, 16 is increased. There is a problem that a wet-out phenomenon occurs. Here, infiltration is a phenomenon that occurs when the change in refractive index is removed when two surfaces are in optical contact with each other and light is transmitted from one film to the next. It refers to a phenomenon that is recognized as having an appearance. This infiltration phenomenon is particularly problematic when using a film having a stereoscopic surface (ie, prism acid) for the optical effect, such as the prism sheet 15.

The present invention has a light diffusing function by providing a prism acid of a longitudinal wave pattern having a predetermined repetition period and having a width (i.e., maximum height-minimum height) of the height change width of the prism acid at a predetermined ratio with respect to the repetition period. It is an object to provide a prism sheet capable of increasing the yield.

Another object of the present invention is to provide a backlight unit employing the prism sheet.

Still another object of the present invention is to provide a liquid crystal display device having the above-mentioned backlight unit to secure a wide viewing angle while maintaining high front brightness and to prevent infiltration and moiré phenomena.

The present invention to solve the above problems,

Transparent substrate; And

A prism acid having a longitudinal wave pattern disposed on the transparent substrate,

The longitudinal wave pattern is shaped such that the height of the prism peak varies continuously or discontinuously along its length,

The height variation width (maximum height-minimum height) of the prism mountain provides a prism sheet that is 0.01-1 times the repetition period of the longitudinal wave pattern.

According to one embodiment of the invention, the longitudinal wave pattern is shaped such that the width of the base of the prism acid varies continuously or discontinuously along its length.

According to another embodiment of the present invention, the width of the base of the prism mountain varies in size in proportion to the height of the prism mountain.

According to another embodiment of the invention, the cross section in the direction orthogonal to the longitudinal direction of the prism mountain is triangular, arched or semicircular in shape.

According to another embodiment of the present invention, the prism acid has a base length of more than 0 μm and less than 1 mm, and a height of more than 0 μm and less than 900 μm.

According to another embodiment of the invention, the prism acid has a vertex angle of the same size at all positions.

According to another embodiment of the present invention, the prism acid has a vertex angle of 60 to 120 °.

In addition, to solve the above problems, the present invention provides a backlight unit having a prism sheet according to any one of the embodiments.

In addition, to solve the above problems, the present invention provides a liquid crystal display device having a backlight unit according to any one of the above embodiments.

According to the present invention, the light diffusing function is provided by providing a prism peak of a longitudinal wave pattern having a predetermined repetition period and having a width of change of the prism acid at a predetermined ratio with respect to the repetition period (ie, maximum height-minimum height). And prism sheet can be provided which can increase the production yield.

In addition, according to the present invention, a backlight unit employing the prism sheet may be provided.

In addition, according to the present invention, by providing the backlight unit, a wide viewing angle can be secured while maintaining high front brightness, and a liquid crystal display device in which infiltration phenomenon and moiré phenomenon are prevented can be provided.

Next, a prism sheet according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a cross-sectional view showing a prism sheet and another optical film laminated thereto according to an embodiment of the present invention, Figure 3 is a plan view of a prism sheet according to an embodiment of the present invention.

Referring to FIG. 2, the prism sheet 25 according to the present embodiment includes a transparent substrate 25a and a prism acid 25b.

The transparent substrate 25a is formed of a material such as a polyester resin to serve to transmit light incident thereto.

The prism acid 25b is disposed on the transparent substrate 25a to condense the light incident through the transparent substrate 25a to the plane of the liquid crystal display panel (not shown) and to diffuse some of the incident light. Play a role. The prism acid 25b is preferably formed of the same material as the transparent substrate 25a, but the present invention is not limited thereto. In this embodiment, the prism mountain 25b is shaped to have a lengthwise wave pattern. Specifically, the longitudinal wave pattern is shaped such that the height of the prism peak 25b changes continuously or discontinuously along the length. At this time, as the height of the prism peak 25b changes along its length, the side portion (mountain slope) of the prism peak 25b forms a curved surface along its length, thereby having a diffusion effect on the same principle as that of the microlens. By shaping the prism peak 25b in this manner, the prism sheet 25 having the light diffusion effect can be obtained without a large loss of the front luminance. Here, the side part of the prism mountain 25b is a part except the top part and valley part of the prism mountain 25b, and refers to the mountain slope part of all directions. In addition, since the prism sheet 25 has a light diffusing function as described above, the use of the diffusion sheet or the protective sheet can be reduced or eliminated. Also, by forming the prism acid 25b as described above, the contact surface area between the other optical film 30 laminated on the prism sheet 25 and the prism acid 25b is reduced, and scratches due to incorporation of foreign matter and contact ), And the user's poor visibility can be reduced to lower the defective rate of the product as well as to prevent infiltration. This will be described in more detail later.

However, in changing the height of the prism peak 25b, when the change width Δh of the height is too small or the repetition period RP of the longitudinal wave pattern is too long, the side portion of the prism peak 25b Does not have enough curved surfaces to be effective for the optical acid, and thus a prism sheet having a light diffusion effect cannot be obtained.

In order to solve this problem, the prism peak 25b has a height variation width Δh = maximum height h _{max min} height h _{min that} is equal to the repetition period RP of the longitudinal wave pattern. It is formed to be 0.01 to 1 times. As such, when the ratio (Δh / RP) of the height change width Δh of the prism peak 25b to the repetition period RP of the longitudinal wave pattern is defined, the change width Δh of the prism peak height is The reduction of the above-mentioned light diffusion effect caused by being too small or the repetition period RP of the longitudinal wave pattern is too long can be reduced to some extent. That is, when the ratio (Δh / RP) of the height change width Δh of the prism peak 25b to the repetition period RP of the longitudinal wave pattern is greater than 0.01, the emitted light is effectively diffused as compared to the case where it is not. Since the prism sheet 25 is applied to a backlight unit or a liquid crystal display device, an optical film having both a light diffusion function and a front brightness enhancement function can be obtained as desired in the present invention. However, when the ratio Δh / RP is larger than 1, a satisfactory light diffusing effect can be obtained. However, in this case, the side portion of the prism acid 25b forms an excessive curved surface, so that the light condensing effect is weakened compared to the diffusion effect. This is not preferable because a problem occurs in which the luminance decreases rapidly.

In the present embodiment, the longitudinal wave pattern, as shown in FIG. 3, not only the height of the prism peak 25b but also the width of the base (hereinafter simply referred to as “width”) continuously or along its length. It is shaped to change discontinuously. In this case, the width of the prism mountain 25b is shaped so that its size changes in proportion to the height of the prism mountain 25b. Accordingly, the prism mountain 25b has a maximum width L _max at the position having the maximum height h _max and a minimum width L _min at the position having the minimum height h _min . In addition, the prism peak 25b has a triangular, arch or semi-circular cross section in a direction perpendicular to the longitudinal direction, and connects the ridges of the prism peak 25b (the tops of the prism peaks along the prism peak with the shortest distance). As shown in FIG. 2, a sinusoidal curve (Sine curve or Sinusoid) forms a sine curve, and thus a side portion belonging to or adjacent to the ridge portion forms a curved surface. That is, the light diffusion effect can be exerted on such curved surfaces. Also, in this embodiment, the prism peak 25b has the same vertex angle at all positions with respect to the cross section in the direction perpendicular to the longitudinal direction. As such, when the prism peak 25b has the same vertex angle at all positions, the width 25b of the base of the prism peak is automatically determined when the size of the vertex angle and the height of the prism peak 25b are determined. Here, "the vertex angle is the same" does not mean exactly the same, but is a concept that includes a range of error that can be recognized as the same in consideration of limitations in manufacturing technology in the art (for example, Vertex angle ± 1 ~ 5%). In addition, the width | variety of the prism mountain 25b means here the length of the base of the prism mountain 25b mentioned later. 3 refers to the ridge of the prism mountain 25b, and refers to the depression between the prism mountain 25b and another prism mountain 25b adjacent to it.

By forming the prism mountain 25b having the above structure, when the height of the prism mountain 25b is increased, the light collecting effect is increased and the light diffusion effect is solved. Similarly, when the height of the prism mountain 25b is lowered, the problem of decreasing the light converging effect and the light diffusing effect can also be solved. That is, as the height of the prism mountain 25b increases, the light converging effect increases while the light diffusing effect decreases. Thus, the width of the prism mountain 25b is adjusted in proportion to the height of the prism mountain 25b, and the prism mountain 25b. By forming a cross section in a direction perpendicular to the longitudinal direction of the triangle, arch or semi-circle to give a light diffusion effect, the relative magnitude of the light converging effect and the light diffusion effect can be maintained substantially constant. In addition, the infiltration phenomenon and the moiré phenomenon can be prevented.

The prism peak 25b has a base length of more than 0 µm and 1 mm or less, a height of more than 0 µm and 900 µm or less, and a vertex angle of 60 to 120 degrees. Here, the bottom side means one side of the prism mountain 25b orthogonal to the wave pattern direction (length direction) in the thickness direction cross section of the prism mountain 25b and in contact with the plane of the transparent substrate 25a. A prism facing the base when drawing a triangle by connecting each end of the base and the maximum separation point from the base (ie, the maximum height of the prism mountain) in the cross section perpendicular to the longitudinal direction of 25b. It means the angle of the acid 25b. If the cross-sectional shape, size, and vertex angle of the prism mountain 25 are out of the above ranges, the front luminance is lowered and the viewing angle is narrowed, which is not preferable. However, the present invention is not limited thereto, and the prism acid 25b may have different shapes of cross sections as long as the hill slope has a curved surface.

Hereinafter, referring to FIG. 2, the principle of the prism acid 25b having the longitudinal wave pattern increases the light diffusion effect and the production yield and prevents the infiltration phenomenon.

Referring to FIG. 2, the surface S of the prism acid 25b is in optical contact with the optical film 30 at the surface contact portion C. Here, the optical film 30 may be a film included in a polarizing plate (not shown).

In the present embodiment, the prism peak 25b is shaped in a longitudinal wave pattern such that the height varies continuously or discontinuously along the length as described above, so that the surface contact portion C of the surface S of the prism peak 25b is formed. ) Is very small compared to the non-contact part (i.e., S part except C). Therefore, most of the light L1 is emitted from the non-contact portion and then refracted at the interface between the prism sheet 25 and the air layer A and enters the optical film 30 through the air layer A. On the other hand, the remaining small amount of light (L2) is passed through the surface contact portion (C) in a state that is almost refracted, but is incident to the optical film 30, but the amount is so small that observers have a transmission characteristic of the surface contact portion (C) It is not recognized as different from the surrounding area (i.e., the air layer A), and as a result, the portion C is not recognized as an abnormal or defective part. In addition, since the prism acid 25b is shaped into a longitudinal wave pattern, the optical overlap with the RGB pattern of the liquid crystal display panel (not shown) may be reduced or eliminated, thereby reducing or preventing the moiré phenomenon.

In addition, since the surface contact portion (C) is very small compared to the non-contact portion, the amount of foreign matter mixed into the surface contact portion (C) is reduced, as well as the scratches generated at the surface contact portion (C) to reduce the overall product defect rate. In addition, since the height of the prism mountain 25b varies in various ways, the outgoing light position is diversified, so that the user cannot clearly recognize this even if there is a product defect. It can be used as it is without causing the product defect rate to be lowered.

Next, the light diffusion effect will be described. Light L3 and L4 incident on one side of the surface S of the prism mountain 25b (ie, the ridge and the adjacent portion) are refracted at the surface and diffused as shown in the drawing. As a result, the light diffusing effect is also increased when the light converging effect is increased by the prism acid 25b, thereby preventing the phenomenon in which the viewing angle is too narrowed by the prism acid 25b. In addition, although not shown here, the light diffusion effect can be exerted on the hillside located at the width direction or the like of the prism mountain 25b, that is, on the other side. As the prism sheet 25 exerts a light diffusion effect, the prism sheet 25 may replace the diffusion function of the diffusion sheet 14 and / or the protection sheet 16 of FIG. 1, and thus, a backlight unit (not shown) employing the prism sheet 25 may be used. At least one of the diffusion sheet 14 and the protective sheet 16 may not be provided. Therefore, the backlight unit and the liquid crystal display (not shown) employing the prism sheet 25 can be thinned and the manufacturing process can be simplified, thereby reducing manufacturing costs. In this case, however, as a method for protecting the prism sheet 25, a protective sheet having only a protective function may be attached onto the prism sheet of the backlight unit during transportation or storage, and then removed when the backlight unit is mounted on the liquid crystal display. The number will be.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited only to the following Examples.

Example

A prism sheet having a configuration similar to that of FIGS. 2 and 3 was prepared in the following manner, and then SEM images thereof were taken and shown in FIG. 4 (perspective view).

(Selection of transparent film)

As a transparent film, a PET film (Toyobo, A4300) having a thickness of 188 μm was used.

(Formation of prism acid)

In order to form a longitudinal wave pattern intended in the present invention on one surface of the transparent film, a pattern roll having an intaglio shape of the pattern was used. In the light diffusing prism sheet manufactured by the above method, the repetition period RP of the longitudinal wave pattern of the prism acid is 300 µm, the maximum height h _max of the prism acid is 25 µm, and the minimum height (h _min). ) Is 10 μm, the shape of the cross section perpendicular to the longitudinal direction of the prism acid is an isosceles triangle shape having a vertex angle of 90 °, the maximum width (L _max ) of the base of the prism acid is 50 μm, and the minimum width (L _min ) Was 20 µm.

The optical characteristics of the prepared light diffusing prism sheet were compared with the optical characteristics of the conventional optical film (two structures of the protective sheet (JS153H of SKC) and the prism sheet (BEFII of 3M) as a result of analysis. Compared with the prism sheet, the front luminance was 101% and the viewing angle was the same. At this time, the front luminance and viewing angle measurement was used TOP-3 SR-3.

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

1 is an exploded perspective view showing a backlight unit according to the prior art having an edge-type light source.

2 is a cross-sectional view showing a prism sheet and another optical film laminated thereto according to an embodiment of the present invention, which is a longitudinal cross-sectional view of a prism mountain.

3 is a plan view of a prism sheet according to one embodiment of the present invention.

4 is a SEM photograph of a prism sheet according to one embodiment of the present invention (perspective view).

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

10: backlight unit 11: light source

12: Light guide plate 13: Reflective sheet

14: diffusion sheet 15, 25: prism sheet

16: protective sheet 25a: transparent substrate

25b: prism acid 25c: diffuser

30: optical film L1, L2: light

RP: Repetition period of prism acid wave pattern h _max : Maximum height of prism acid

h _min : Minimum height of prism mountain A: Air layer

Claims (9)

Transparent substrate; And A prism acid having a longitudinal wave pattern disposed on the transparent substrate, The longitudinal wave pattern is shaped such that the height of the prism peak varies continuously or discontinuously along its length, The height variation width (maximum height-minimum height) of the prism peak is 0.01 to 1 times the repetition period of the longitudinal wave pattern, And the longitudinal wave pattern is shaped such that the width of the base of the prism mountain varies continuously or discontinuously along its length. delete The method of claim 1, A prism sheet, the width of the base of the prism mountain is changed in proportion to the height of the prism mountain. The method of claim 1, A prism sheet, characterized in that the cross section in the direction orthogonal to the longitudinal direction of the prism mountain has a triangular, arch or semicircular shape . The method of claim 4, wherein The prism acid has a base length of more than 0 µm and less than 1 mm, and a height of more than 0 µm and 900 µm or less. The method of claim 4, wherein And the prism acid has vertices of equal size in all positions. The method of claim 4, wherein The prism acid has a vertex angle of 60 to 120 °, characterized in that the prism sheet. A backlight unit comprising the prism sheet according to any one of claims 1 and 3. A liquid crystal display device comprising the backlight unit according to claim 8.

Images