KR20100033663A - Optical sheet - Google Patents

Abstract

PURPOSE: An optical sheet is provided to improve visibility and concealment through a diffusion effect by a particle included in the high refractive layer. CONSTITUTION: An optical sheet including a high refractive layer includes a pattern layer(20) and a high refractive layer(30). The pattern layer is made of a transparent polymer with a structured surface. A base layer is adjacent to the pattern layer. The high reflective layer has a high reflective index higher than that of the pattern layer from 0.3 to 10 %.

Description

Optical sheet including a high refractive index layer

The present invention relates to an optical sheet having a structured surface.

The backlight unit (BLU), which is widely used in liquid crystal displays, uses light sources such as Cold Cathode Fluorescent Lamps (CCFLs) to sequentially pass through the light guide plate, the light diffusion plate, and the prism sheet to the liquid crystal panel. To reach. The light emitted from the light source is transmitted to the front surface of the liquid crystal panel in a planar shape through the light guide plate, and the light source passed through the light guide plate can obtain a uniform light intensity across the entire screen through the light diffusion plate. The optical path control function is performed to convert the light beams in various directions through the diffusion sheet into the viewing angle range suitable for the viewer to recognize the image. In addition, the lower portion of the light guide plate is provided with a reflecting plate for increasing the use efficiency of the light source by allowing the light that is not delivered to the liquid crystal panel to be reflected back out of the path and used.

In addition, many kinds of plates or films are used so that the maximum amount of light generated from the light source can reach the liquid crystal device.

The light diffusion plate achieves a uniformity of brightness of the light emitted from the light source lamp and at the same time serves as a concealing role to cover the bright line of the lamp. In addition, it serves as a support for the above various optical films. To this end, various light diffusing agents are added to the light diffusing plate, which causes light diffraction, scattering, reflection, and the like, and causes a diffusion effect.

In order to collect a large amount of light from the light diffusion plate to the front, various materials including a light diffusion film and a prism film should be mounted. have.

On the other hand, the prism sheet plays an important role in improving luminance by controlling light paths outside the viewing axis range into the viewing axis range.

The prism sheet has a structured surface formed by repeating a three-dimensional structure and a structure. For example, when a triangular cross-sectional structure is repeated to form a valley and a peak (see FIG. 1), the prism mountain maximizes the light collection effect. Front brightness can be increased. However, the light emitted from the side of the structure is not focused in the front, but partially diffused or reflected inside, which does not sufficiently improve the brightness.

In addition, as the front luminance is increased, the half-angle angle is relatively narrowed, and there is a problem in that the viewing angle characteristic is deteriorated, such as a cut-off phenomenon in which the luminance is sharply lowered at a specific viewing angle. In addition, a bright line is visible due to the pattern, and a protective film was additionally used to conceal and compensate for the viewing angle.

In consideration of this point, the structure of the structured surface may be deformed into a hemispherical column shape as shown in FIG. 2, but even in this case, even improvement in brightness, concealment, and viewing angle could not be expected.

The present invention seeks to provide an optical sheet that further improves frontal brightness by changing the path of light on the structured surface.

In another aspect, the present invention is to provide an optical sheet with improved hiding and viewing angle.

In one embodiment of the invention there is provided a patterned layer having a structured surface and composed of a transparent polymer composition; An optical film comprising a substrate layer adjacent to a pattern layer, the optical film including a high refractive layer having a refractive index of 0.3 to 10% higher than a pattern layer and having a predetermined thickness to cover the entire structured surface on the pattern layer. The overall thickness of provides a substantially uniform optical sheet over the front surface.

 In an optical sheet according to one embodiment of the invention, the maximum thickness of the high refractive layer may be greater than or equal to the maximum height minus the minimum height from the substrate layer to the structured surface.

In the optical sheet according to the embodiment of the present invention, the high refractive layer may include particles. In this case, the particles are 0.001 to 30㎛ in diameter and may be included in a 0.5 to 20% by weight relative to the total weight of the high refractive layer.

In the optical sheet according to the embodiment of the present invention, the pattern layer may have a structured surface in which a plurality of geometric structures are formed adjacent to or spaced from each other.

According to an embodiment of the present invention, a high refractive index layer having a refractive index of 0.3 to 10% higher than that of the pattern layer is formed on the structured surface of the optical sheet having the structured surface to a predetermined thickness, and the final optical By making the thickness of the sheet substantially uniform throughout the entire surface, light passing through a pattern layer formed with a plurality of structures adjacent or non-adjacent can be condensed to the front through the high refractive layer, resulting in improved luminance and included in the high refractive layer. Due to the diffusion effect by the particles, it is possible to provide an optical sheet having improved concealability and visibility.

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

Typically, an optical sheet comprising an optical structural surface consists of a base layer and a pattern layer, wherein the pattern layer has a structured surface and consists of a transparent polymer composition. In particular, the structured surface has a structure in which the three-dimensional structure and the structure are repeatedly formed without or adjacent to each other to repeat the bone and the peak.

An embodiment of the optical sheet according to the present invention is shown in FIG. 3, which is formed on the base layer 10, the pattern layer 20 on the base layer and the pattern layer, and finally the thickness of the optical sheet is substantially uniform. It includes a high refractive index layer 30 applied to one degree.

Here, the term 'substantially uniform' refers to an error range ㅁ about 5% of the thickness of the entire optical sheet in consideration of minute unevenness due to particles that may be included in the high refractive layer or an error in coating. Will be understood.

3 shows a general prism structure in which the shape of the pattern layer 20 is a triangular cross section, and FIG. 5 shows a case where the columnar structure having a semicircular cross section is linearly arranged. In FIG. 3 or FIG. 5, only the case in which the individual structures constituting the pattern layer 20 or 20 ′ are formed adjacent to each other is shown.

However, preferably, the light incident from the light source passes through the substrate layer 10 and passes through the pattern layer 20 having a low refractive index, and then the light emitted therefrom finally passes through the high refractive layer 30, The angle range of the light incident through the low refractive layer and entering the high refractive layer increases in a portion corresponding to the critical angle range of the high refractive layer, thereby reducing the amount of reflected light in the high refractive layer and increasing the range of light that can be focused. Thus, the structures forming the pattern layer 20 or 20 'may be more advantageously formed adjacent to each other.

Usually, the transparent polymer composition constituting the pattern layer 20 is not particularly limited, and known resins used in conventional prism sheets or prism films may be used. For example, the composition may include a mixture of a monomer or oligomer for ultraviolet polymerization and a photoinitiator.

The high refractive index layer 30 may have the same resin composition as the transparent polymer composition constituting the pattern layer 20, but may be a layer having an overall refractive index increased by including a certain amount of particles 31.

In this case, the size of the particles may have a monodisperse or polydisperse particle distribution having a diameter of 0.001 to 30 μm, and the content of the particles may be an amount having a proportion of 0.5 to 20 wt% based on the total weight of the high refractive layer.

When the particle size is within the above range, the particles can be positioned within the high refractive layer structure without disturbing the structure layer, can impart a diffusion function to the high refractive layer, and increase concealment due to the difference in refractive index between the high refractive layer and the particles. It may be advantageous in that it may be advantageous in that the concealability and diffusion function due to particle content when the content is within the above range is the minimum range that affects the luminance.

Organic particles or inorganic particles may be used as the particles. Examples of organic particles include methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylamide, metyrolacrylamide, glycidyl methacrylate, ethyl acrylate, Of acrylic particles of isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate homopolymer or copolymer and olefinic particles such as polyethylene, polystyrene and polypropylene, copolymer particles of acrylic and olefinic copolymer and homopolymer After forming the particles, multi-layered multi-component particles made by covering the layer with other monomers are used. Examples of the inorganic particles include silicon oxide, aluminum oxide, titanium oxide, zirconium oxide and magnesium fluoride. The organic and inorganic particles are merely exemplary and are not limited to the particles of the organic or inorganic materials listed above, and may be replaced by other known materials as long as the main object of the present invention can be achieved. Obviously, such material change is also within the scope of the technical idea of the present invention.

The high refractive index layer 30 preferably has a refractive index of about 0.3 to 10% greater than the pattern layer 20 or 20 ', and if the refractive index of the high refractive layer 30 is equal to or less than 0.3% larger than that of the pattern layer. In this case, the difference in refractive index between the low refractive index layer and the high refractive index layer is insufficient, so that the degree of condensing of light passing through the high refractive index layer having a low refractive index may be less. If the refractive index is excessively larger than 10%, the critical angle of the high refractive layer is As it narrows, the range of light angles that can be refracted and passed becomes narrow, and the amount of reflected light increases, which may cause problems in terms of light efficiency.

In addition, in the optical film having the optical structure surface of the present invention, the base layer may have a thickness of about 10 to 400 μm, and any base layer may be used as long as it is a sheet made of a transparent resin used for a conventional prism sheet or a prism film. . Examples thereof include polyethylene terephthalate film, polycarbonate film, polypropylene film, polyethylene film, polystyrene film or polyepoxy film.

In the present invention, the optical path due to the formation of the high refractive index layer 30 on the pattern layer 20 or 20 'is shown in Figure 4, the light collecting effect is usually maximized in the mountain portion of the pattern layer, thereby improving the front brightness. .

However, refraction of light occurs in the side portions of the individual structures constituting the pattern layer, and in some cases, total reflection may increase the amount of light loss.

On the other hand, when the high refractive layer 30 is formed to cover the pattern layer 20, the light refracted by the pattern layer passes through the high refractive layer 30, and the pattern of refraction is changed and collected. Therefore, the effect of raising the front brightness can be obtained.

On the other hand, a slight diffusion occurs in the particles 31 included in the high refractive index layer 30, which may serve to conceal the visible line by providing concealment. It also allows the viewing angle to be improved.

The optical sheet on which the high refractive index layer 30 is formed is substantially uniform in overall thickness, and is not the form in which the high refractive index layer 30 is applied along the structured surface of the pattern layer 20 but at least equal to or greater than the maximum height of the pattern layer. The higher refractive index layer 30 is formed to a higher thickness at a constant level so that the thickness of the entire surface of the optical sheet is substantially uniform.

However, when the highest thickness T _H of the high refractive index layer 30 is thinner than the height P _H subtracted from the highest height of the structure forming the pattern layer, the high refractive index layer does not cover all of the patterns of the low refractive index layer so that the light efficiency is increased. When the thickness of the high refractive index layer 30 becomes too thick and the maximum thickness T _H of the high refractive index layer 30 becomes too thick, the thickness of the non-structural layer becomes excessively thicker than that of the structural layer. It may be disadvantageous in terms of reducing the efficiency of the light passing through.

Although the present invention has been described with reference to the accompanying drawings, the present invention is not limited thereto, and a person skilled in the art may change the present invention without departing from the technical spirit of the present invention. Do.

Hereinafter, examples of the present invention will be described in more detail, but the scope of the present invention is not limited to these examples.

Comparative Example 1

A polyethylene terephthalate film is used as a base material layer (thickness 188 µm), and 80 parts by weight of high refractive acrylate, 15 parts by weight of 2-phenylethyl methacrylate, 3 parts by weight of 1,6-hexanediol acrylate, and BAPO system An optical sheet in which a pattern layer was formed from a prism crude solution consisting of 2 parts by weight of a photoinitiator to have a structured surface in which a right-angled isosceles triangle solid pattern was adjacent to each other (see FIG. 1) was prepared. The refractive index of the pattern layer was 1.515.

Comparative Example 2

A polyethylene terephthalate film is used as a base layer, and it is composed of 80 parts by weight of high refractive acrylate, 15 parts by weight of 2-phenylethyl methacrylate, 3 parts by weight of 1,6-hexanediol acrylate, and 2 parts by weight of a BAPO-based photoinitiator. An optical sheet in which a pattern layer was formed from a prism crude liquid such that a three-dimensional pattern having a semicircular cross section has a structured surface of an adjacent shape was prepared (see FIG. 2). The refractive index of the pattern layer was 1.515.

<Example 1>

A polyethylene terephthalate film is used as a base layer, and it is composed of 60 parts by weight of high refractive acrylate, 20 parts by weight of 2-phenylethyl methacrylate, 18 parts by weight of 1,6-hexanediol acrylate, and 2 parts by weight of a BAPO-based photoinitiator. A pattern layer was formed from the prism crude liquid such that its cross-sectional shape had an equilateral isosceles triangle solid pattern with a structured surface of an adjacent shape (refractive index 1.515).

Then, on the top of the prism layer uniformly to the same thickness as the acid height of the prism, 80 parts by weight of high refractive acrylate, 15 parts by weight of 2-phenylethyl methacrylate, 3 parts by weight of 1,6-hexanediol acrylate, BAPO A high refractive layer was formed by applying a crude liquid containing PMMA particles as a particle to a prism crude liquid composed of 2 parts by weight of a photoinitiator to prepare an optical sheet as shown in FIG. 3. At this time, the content of particles was 1 part by weight based on the total weight of the high refractive layer crude liquid.

<Example 2>

An optical sheet was manufactured in the same manner as in Example 1, except that the high refractive layer was formed to be about 10% thicker than the acid height of the prism when the high refractive layer was applied.

<Example 3>

An optical sheet was manufactured in the same manner as in Example 1, except that the high refractive layer was formed to be about 50% thicker than the acid height of the prism when the high refractive layer was applied.

<Examples 4 to 5>

An optical sheet was manufactured in the same manner as in Example 1, but the content of the particles included in the high refractive layer was varied as shown in Table 1 below.

<Example 6>

A polyethylene terephthalate film is used as a base layer, and it is composed of 60 parts by weight of high refractive acrylate, 20 parts by weight of 2-phenylethyl methacrylate, 18 parts by weight of 1,6-hexanediol acrylate, and 2 parts by weight of a BAPO-based photoinitiator. A pattern layer was formed from the prism crude liquid such that the columnar structures having a semicircular cross section had a structured surface of an adjacent shape (refractive index 1.515).

Then, 80 parts by weight of high refractive acrylate, 15 parts by weight of 2-phenylethyl methacrylate, and 3 parts by weight of 1,6-hexanediol acrylate were uniformly formed at the same thickness as the height of the apex of the semi-circular column on top of the prism layer. And a crude liquid containing PMMA particles (refractive index of 1.50, particle diameter of 20 μm) as particles to a prism crude liquid composed of 2 parts by weight of a BAPO-based photoinitiator to form a high refractive layer to prepare an optical sheet as shown in FIG. 5. At this time, the content of particles was 1 part by weight based on the total weight of the high refractive layer crude liquid.

<Example 7>

An optical sheet was manufactured in the same manner as in Example 6, except that the high refractive layer was formed to be about 10% thicker than the height of the peak of the semi-circular pillar when the high refractive layer was applied.

<Example 8>

An optical sheet was manufactured in the same manner as in Example 6, except that the high refractive layer was formed to be about 50% thicker than the height of the peak of the semi-circle pillar when the high refractive layer was applied.

<Examples 9 to 10>

An optical sheet was manufactured in the same manner as in Example 6, but the content of the particles included in the high refractive layer was varied as shown in Table 1 below.

Pattern Layer Structure High Refractive Layer Max Thickness High refractive layer particle amount (parts by weight relative to the total weight of the high refractive layer) High Refractive Index-Pattern Layer Refractive Index Example 1 Cross section right angle isosceles triangle prism Same as prism One 0.053 Example 2 Cross section right angle isosceles triangle prism 10% thicker than prism acid One 0.053 Example 3 Cross section right angle isosceles triangle prism 50% thicker than prism acid One 0.053 Example 4 Cross section right angle isosceles triangle prism Same as prism 10 0.053 Example 5 Cross section right angle isosceles triangle prism Same as prism 20 0.053 Example 6 Section semicircular column Same as semicircle column vertices One 0.053 Example 7 Section semicircular column 10% thicker than semi-cylindrical vertices One 0.053 Example 8 Section semicircular column 50% thicker than semi-cylindrical vertices One 0.053 Example 9 Section semicircular column Same as semicircle column vertices 10 0.053 Example 10 Section semicircular column Same as semicircle column vertices 20 0.053

In Table 1, the refractive index of the high refractive index layer and the pattern layer is a value measured by coating a crude liquid for forming each layer on a glass plate, UV curing, and then peeling off to obtain a film state. , Model name 1210 1T).

The optical sheets obtained according to Comparative Examples 1 to 2 and Examples 1 to 10 were evaluated for brightness, concealment, and viewing angle, and the results are shown in Table 2 below.

Specific evaluation methods are as follows.

(1) luminance

The luminance was measured using BM-7 manufactured by Topcon Corporation, and the values of all sheets except for the reflective sheet in the backlight unit were removed, and Examples 1 to 5 were compared with the optical film of Comparative Example 1 for <light diffusing film. Optical film of Example 1 + Example and Comparative Example A luminance comparison in which the luminance value of Comparative Example 1 is 100 by using each combination of one sheet + protective film> Examples 6 to 10 is the optical film of Comparative Example 2 The luminance value of the optical film was measured in the luminance comparison component of which the luminance value of Comparative Example 1 was 100 using a combination of <1 light diffusing film + 1 optical film of Example and Comparative Example>. .

(2) viewing angle

The viewing angle was measured using Topcon's BM-7, and the value was removed from all the sheets except for the reflective sheet in the backlight unit. Examples 1 to 5 were used for the combination with the optical film of Comparative Example 1 Using the combination of one sheet + one optical film of the Examples and Comparative Examples, each of the combination of the optical film of Comparative Example 2, Examples 6 to 10 is <one light diffusing film + Example for the combination with the optical film of Comparative Example 2 And each optical sheet of the comparative example >> combination, the viewing angle of the position which has the brightness value of half the brightness | luminance with respect to the front (viewing angle = 0 degree position) luminance by each optical sheet combination was measured.

(3) concealability

The concealability was measured using Topcon's BM-7, and the values were removed except for the reflective sheet in the backlight unit, and Examples 1 to 5 were compared with the optical film of Comparative Example 1 for <light diffusing film. Using the combination of one sheet + one optical film of the Examples and Comparative Examples, each of the combination of the optical film of Comparative Example 2, Examples 6 to 10 is <one light diffusing film + Example for the combination with the optical film of Comparative Example 2 And a step point measurement method in the vertical direction of the BLU according to each optical sheet combination, using each optical sheet combination of the comparative example to determine the fluctuation value of the luminance versus the maximum value of the measured luminance value. The concealability of the optical film was measured as a ratio.

Concealability (%) = (wave width of luminance) / (measured average luminance value) * 100

= (Highest value of wave of luminance-minimum value of wave of luminance) / (measured average luminance value) * 100

division Viewing angle (°) Concealable Luminance (%) Example 1 50 3 103 Example 2 50.8 2.8 103 Example 3 51.2 2.7 96 Example 4 51.8 2.5 95 Example 5 51.8 2.5 92 Example 6 52.3 3 100 Example 7 52.8 2.7 100 Example 8 52.9 2.4 96 Example 9 53.5 2.3 93 Example 10 53.9 2.2 92 Comparative Example 1 47 6 100 Comparative Example 2 51 6 98

As a result of the physical property evaluation, it can be seen that when a high refractive index layer is formed on the structured surface (Examples 1 to 10), the luminance is improved or exhibits a similar level as compared with Comparative Examples 1 to 2. When the maximum thickness of the high refractive layer is formed to be appropriately larger than the peak of the pattern as in Example 2 or Example 7, it is understood that the concealment performance and the viewing angle performance are increased while the luminance is maintained at the same level as compared with the same height. have. However, when the maximum thickness of the high refractive layer is formed too large than the peak of the pattern, as in Example 3 or Example 8, it can be seen that the concealment performance is increased, but the brightness is sharply reduced compared to the same or appropriate height. In addition, as the particle content increases, the luminance decreases slightly, but the viewing angle and the concealment performance can be seen to be excellently changed.

On the other hand, in the concealability, Examples 1 to 10 showed improved results compared to Comparative Examples 1 or 2 and also showed a wider viewing angle.

In terms of concealment, when the highest thickness of the high refractive layer is formed larger than the apex of the pattern, as in Examples 2 and 3 or Examples 7, 8, it can be seen that the concealment performance is increased as compared with the same height. In addition, as the content of the particles increases, the concealability also increases as the content of the particles changes.

1 is a cross-sectional view of an optical sheet having a conventional structured surface.

2 is another cross-sectional view of an optical sheet having a conventional structured surface.

3 is a cross-sectional view according to an embodiment of the present invention optical sheet.

Figure 4 is an enlarged cross-sectional view showing an optical path of the optical sheet of the present invention.

5 is a cross-sectional view according to another embodiment of the optical sheet of the present invention.

Claims (5)

A patterned layer having a structured surface and composed of a transparent polymer composition; In the optical film containing the base material layer adjacent to a pattern layer, It is formed to a certain thickness to cover the entire structured surface on the pattern layer and comprises a high refractive layer having a refractive index of 0.3 to 10% higher than the pattern layer, And wherein the overall thickness of the optical sheet is substantially uniform over the entire surface. The optical sheet of claim 1, wherein the maximum thickness of the high refractive index layer is greater than or equal to the maximum height minus the minimum height from the transparent substrate layer to the structured surface. The optical sheet according to claim 1, wherein the high refractive layer comprises particles. The optical sheet of claim 3, wherein the particles have a diameter of 0.001 to 30 μm and are included in a weight ratio of 0.5 to 20 weight based on the total weight of the high refractive layer. The optical sheet of claim 1, wherein the pattern layer has a structured surface in which a plurality of geometries are formed adjacent or spaced apart from each other.

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