KR20100033664A - Optical sheet - Google Patents

Abstract

PURPOSE: An optical sheet is provided to improve the brightness of a front side by changing a light path from a structured surface. CONSTITUTION: An optical sheet comprises a high refractive layer(30) and a particle coating layer(40). A high refraction layer covers the entire surface of a pattern layer(20). The high refraction layer is formed on the structured surface while having a certain thickness. The high refractive layer has a high refractive index of 0.05-20%. A particle-coated layer is formed to be adjacent to a flat layer of high refraction layer.

Description

Optical sheet including a high refractive index layer

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

Light emitted from a backlight unit (BLU) Cold Cathode Fluorescent Lamp (CCFL), which is widely used in liquid crystal displays, passes through the light guide plate, the light diffusion plate, and the prism sheet to reach the liquid crystal panel. Let's do it. The light emitted from the light source is distributed to the front surface of the flat liquid crystal panel 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, a variety of materials including a light diffusion film, a prism film should be mounted. This multi-layered material raises the cost and lowers productivity. 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.

In addition, in the case of a conventional prism sheet, two prism sheets may be used to overlap each other, and another sheet is stacked thereon. In this case, there is a problem that a defect occurs due to the contact surface between sheets.

In addition, since the optical sheet including the optical structure surface is regular arrangement of the optical structure, when the optical sheet is combined with a constant array of liquid crystal pixels, an optical interference image such as a moire phenomenon may be generated due to an interference effect. Leave room. This is a physical phenomenon that cannot be avoided in a structure in which regularity overlaps.

It is an object of the present invention to provide an optical sheet that changes the path of light on the structured surface to improve front brightness.

Another object of the present invention is to provide an optical sheet having improved concealment and viewing angle.

Another object of the present invention is to provide an optical sheet capable of reducing scratch defects due to contact when laminated with other optical sheets.

In one embodiment of the invention there is provided a patterned layer having a structured surface on one side and made of a transparent polymer composition; An optical sheet comprising a substrate layer adjacent to a pattern layer, the optical sheet comprising: a high refractive layer formed with a predetermined thickness so as to cover the entire structured surface of the pattern layer and having a refractive index of 0.05 to 20% higher than that of the pattern layer; And it provides an optical sheet including a particle coating layer formed adjacent to the flat surface of the high refractive layer.

In the optical sheet according to the embodiment of the present invention, the maximum thickness of the high refractive layer may be equal to or greater than 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 particle coating layer may be formed from a crude liquid containing particles in a transparent binder.

In the optical sheet according to the embodiment of the present invention, the particles may have a diameter of 0.01 to 40㎛.

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 plurality of structures are formed by forming a high refractive index layer having a refractive index of 0.05 to 20% higher than that of a pattern layer with a predetermined thickness to cover the entire structured surface on the structured surface of the optical sheet having the structured surface. The light passing through the pattern layer formed adjacent to or not adjacent to each other is condensed toward the front through the high refractive layer, and consequently, the brightness can be improved.As a particle coating layer is placed on the high refractive layer, the adhesion between sheets can be prevented. It is possible to provide an optical sheet which can prevent the back and improve the concealment and the viewing angle by the diffusion effect due to the particles.

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

Typically, an optical sheet including an optical structure surface includes a substrate layer and a pattern layer, wherein the remaining non-adjacent surface of the pattern layer has a shape having a structured surface and is made 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.

3 to 4 illustrate an embodiment of the optical sheet according to the present invention, the substrate layer 10, the pattern layer 20 on the substrate layer, and the planarized high refractive layer 30 formed on the pattern layer. And a particle coating layer 40 formed on the high refractive layer 30.

3 illustrates a general prism structure in which the pattern layer 20 has a triangular cross section, and FIG. 4 illustrates a case where the columnar structure having a semicircular cross section is linearly arranged. In FIG. 3 or FIG. 4, only the case where the individual structures constituting the pattern layer 20 or 20 ′ are formed adjacent to each other is shown, but the case where they are spaced apart from each other will be within the scope of the technical idea of the present invention.

However, preferably, the light incident from the light source passes through the substrate layer 10 and first passes through the pattern layer 20 having a low refractive index, and then the light emitted therefrom passes through the high refractive layer 30 and finally exits. In the light path of the light emitted from the light guide plate and the light diffusing film of the BLU, the final exit light passing through the high refractive layer 30 may be more advantageous in that it can be focused in the front direction, so that the pattern layer 20 or 20 '. It may be more advantageous that the structures forming these are 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, except that the refractive index is increased by adding a resin component that can improve the refractive index of the polymer composition. Can be.

The high refractive index layer 30 preferably has a refractive index of about 0.05 to 20% greater than the pattern layer 20 or 20 '. If the high refractive index layer 30 has the same refractive index as the pattern layer or less than 0.05%, In this case, the path of the light exiting from the high refractive index layer 30 may be reduced from the front, and the central luminance may be reduced. If the refractive index is excessively greater than 20%, the total brightness of the high refractive layer may increase and the central luminance may also decrease. There may be a problem.

The high refractive index layer 30 is formed to a predetermined thickness such that the planarization as formed along the optical surface structure, up to the thickness (T _H) is obtained by subtracting the minimum height at the maximum height of the structure forming the pattern layer height (P of the high refractive index layer 30 _{In the} case of having a value smaller than _H ), the appearance quality may be degraded and the luminance may be decreased. If the maximum thickness T _H of the high refractive index layer 30 is too large, the absorption of the light in the high refractive index layer may increase, thereby decreasing the luminance. It can be disadvantageous in that it can.

Meanwhile, in the optical sheet of the present invention, the particle coating layer 40 is formed on the high refractive layer 30. The particle size may be a layer having monodispersed or polydisperse particle distribution having a diameter of 0.01 to 40 μm. When the particle size is within the above range, it may be advantageous in that the light diffusing effect due to the particle layer may be appropriately diffused and sheet damage due to detachment of the particles may be prevented.

The particle coating layer may be obtained from a crude liquid in which particles are dispersed in a transparent binder. The transparent binder has a good adhesiveness with the high refractive layer and is compatible with the particles, that is, the particles are uniformly dispersed in the resin and separated or precipitated. This ugly one can be used and is not limited.

Organic particles or inorganic particles may be used as the particles. Examples of the organic particles include methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylamide, metyrolacrylamide, glycidyl methacrylate and 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 acryl 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 thickness of the particle coating layer 40 may be about 0.1 to 100 μm in consideration of light diffusivity depending on the particle size and content.

Further, in the optical film having the optical structure surface of the present invention, the base layer may have a thickness of about 25 to 500 μm, and any base layer may be used as long as the base layer 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, since the optical path is changed by forming the high refractive layer 30 on the pattern layer 20 or 20 ', the pattern layer having a conventional optical structure surface as shown in FIGS. In the mountain portion of the pattern layer, the condensing effect is maximized, thereby improving 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.

However, when the high refractive index 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. do. Therefore, the effect of raising the front brightness can be obtained.

In addition, the light collected from the high refractive index layer 30 may be incident on the particle coating layer 40, thereby re-diffusion by the particles, thereby eliminating the moire phenomenon.

In addition, the particle coating layer 40 and the high refractive layer 30 may function to protect the optical structure surface of the pattern layer 20.

In general, an optical sheet having an optical structure surface may be used by stacking two or more sheets, and another optical sheet may be stacked on the optical sheet. In the case of the optical sheet to which the pattern layer 20 is exposed, scratches may occur on the contact surfaces between the sheets. The optical structure may be damaged.

However, as the high refractive index layer 30 and the particle coating layer 40 are further formed on the pattern layer 20, it is possible to prevent damage due to such scratches, and in particular, to prevent adhesion between sheets due to the particles of the particle coating layer 40. This effect can be further highlighted.

On the other hand, a slight diffusion occurs in the particles 41 included in the particle coating layer 40, which may serve to conceal the visible line by providing concealment. It also allows the viewing angle to be improved.

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 layer (thickness 188 µm), and 90% by weight of an acrylate oligomer (consisting of high refractive acrylate, 2-phenylethyl methacrylate and 1,6-hexadiol acrylate) is used as a photoinitiator. An optical sheet was formed from a prism solution consisting of 5% by weight and 5% by weight of a hindered phenolic light stabilizer, in which a pattern layer was formed such that its cross-section had a structured surface in which an isosceles triangular pattern was adjacent to each other (FIG. 1). Reference). The refractive index of the pattern layer was set to 1.50.

Comparative Example 2

A polyethylene terephthalate film is used as the base layer, and 90% by weight of acrylate oligomer (composed of high refractive acrylate, 2-phenylethyl methacrylate and 1,6-hexadiol acrylate), 5% by weight of photoinitiator and Hin An optical sheet in which a pattern layer was formed from a prism crude solution composed of 5% by weight of a phenol-based light stabilizer such that a three-dimensional pattern having a semicircular cross section has a structured surface having an adjacent shape (see FIG. 2). The refractive index of the pattern layer was set to 1.50.

<Example 1>

A polyethylene terephthalate film is used as the base layer, and 90% by weight of acrylate oligomer (composed of high refractive acrylate, 2-phenylethyl methacrylate and 1,6-hexadiol acrylate), 5% by weight of photoinitiator and Hin The pattern layer was formed from the prism crude liquid consisting of 5 weight% of the phenolic light stabilizers so that the shape of the cross section may have a structured surface of an adjacent equilateral equilateral triangle three-dimensional pattern. The refractive index of the pattern layer was set to 1.50.

90 weight percent of the acrylate oligomer (consisting of high refractive acrylate, 2-phenylethylmethacrylate and 1,6-hexadiol acrylate), then uniformly at the same thickness as the acid height of the prism on top of the prism layer, A crude liquid consisting of 5% by weight of a photoinitiator and 5% by weight of a hindered phenolic light stabilizer was applied to form a high refractive layer, but formed to have a refractive index of 0.02 higher than that of the pattern layer.

Next, on the high refractive layer, 70 parts by weight of methyl ethyl ketone and 50 parts by weight of toluene were weighed and diluted to 100 parts by weight of acrylic resin 52-666 (Aekyung Chemical Co., Ltd.) to prepare a binder resin having a refractive index of 1.50. Spherical polymethyl methacrylate particles having a refractive index of 1.50 MH20F (Kolon Co., Ltd.) were mixed to 110 parts by weight with respect to the binder resin and then cured for 120 seconds at 120 degrees using a gravure coater and dried to form a particle coating layer. An optical sheet as shown in Figure 3 was produced. At this time, the thickness of the particle coating layer was 30㎛.

<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 5% thicker than the acid height of the prism when the high refractive layer was applied.

<Examples 3 to 5>

An optical sheet was manufactured in the same manner as in Example 1, except that the high refractive layer crude liquid was adjusted to have a refractive index difference from the pattern layer as shown in Table 1 below.

<Examples 6 to 8>

An optical sheet was manufactured in the same manner as in Example 1, except that the types of particles in the particle coating layer were changed as shown in Table 1 below.

Example 9

A polyethylene terephthalate film is used as the base layer, and 90% by weight of acrylate oligomer (composed of high refractive acrylate, 2-phenylethyl methacrylate and 1,6-hexadiol acrylate), 5% by weight of photoinitiator and Hin A pattern layer was formed from a prism crude solution composed of 5% by weight of a phenolic light stabilizer such that its cross-section had a semicircular columnar structured surface. The refractive index of the pattern layer was set to 1.50.

90 weights of acrylate oligomers (consisting of high refractive acrylate, 2-phenylethyl methacrylate and 1,6-hexadiol acrylate) uniformly at the same thickness as the height of the apex of the semi-circular column on top of the prism layer %, 5% by weight of photoinitiator and 5% by weight of hindered phenolic light stabilizer was applied to form a high refractive layer, but the refractive index was as high as 0.02 compared to the pattern layer.

Then, on the high refractive layer, an optical sheet as shown in FIG. 3 was prepared by applying a crude liquid having the same composition as in Example 1 to form a particle coating layer. The thickness of the particle coating layer was 10 to 30 μm.

<Example 10>

An optical sheet was manufactured in the same manner as in Example 9, except that the high refractive layer was formed to be about 5% thicker than the top of the semi-circle pillar when the high refractive layer was applied.

<Examples 11 to 13>

An optical sheet was manufactured in the same manner as in Example 8, except that the high refractive layer crude liquid was adjusted to have a refractive index difference with the pattern layer as shown in Table 1 below.

Pattern Layer Structure High Refractive Layer Max Thickness High Refractive Index-Pattern Layer Refractive Index Particle Coating Layer Particle Size / Thickness Example 1 Cross section right angle isosceles triangle prism Same as prism 0.02 20/30 Example 2 Cross section right angle isosceles triangle prism 5% thicker than prism acid 0.02 20/30 Example 3 Cross section right angle isosceles triangle prism Same as prism 0.001 20/30 Example 4 Cross section right angle isosceles triangle prism Same as prism 0.05 20/30 Example 5 Cross section right angle isosceles triangle prism Same as prism 0.3 20/30 Example 6 Cross section right angle isosceles triangle prism Same as prism 0.02 0.1 / 2 Example 7 Cross section right angle isosceles triangle prism Same as prism 0.02 30/35 Example 8 Cross section right angle isosceles triangle prism Same as prism 0.02 100/120 Example 9 Section semicircular column Same as semicircle column vertices 0.02 20/30 Example 10 Section semicircular column 5% thicker than semi-cylindrical vertices 0.02 20/30 Example 11 Section semicircular column Same as semicircle column vertices 0.001 20/30 Example 12 Section semicircular column Same as semicircle column vertices 0.05 20/30 Example 13 Section semicircular column Same as semicircle column vertices 0.3 20/30

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 13 were evaluated for brightness, concealability, viewing angle, and optical interference, and the results are shown in Table 2 below.

Specific evaluation method is as follows.

(1) luminance

Luminance was measured using Topcon's BM-7, and the value was removed from all the sheets except the reflective sheet in the backlight unit (BLU, 26 inches). Using the combination of each chapter 1 >>, the luminance of the combination with the optical film of Comparative Example 1 was reported as 100, and the luminance value of the optical film prepared according to the Examples and Comparative Examples was measured as a comparison.

(2) viewing angle

Viewing angle was measured using Topcon's BM-7, and the value was removed except for the reflective sheet and diffuser in the backlight unit (BLU, 24 inches). 1 prism sheet "combination, in the case of the comparative example, the front of each optical sheet combination using the combination of" 1 light diffusing film / 1 (comparative example 1 or comparative example 2) / 1 protective film " (Viewing angle = 0 ° position) The viewing angle at the position having half the luminance value relative to the luminance was measured.

(3) concealability

The concealability was measured using Topcon's BM-7, and the value was removed except for the reflective sheet and diffuser plate in the backlight unit (BLU, 24 inches). 1 prism sheet "combination, in the case of the comparative example, using the combination of" 1 sheet of light diffusing film / 1 (comparative example 1 or comparative example 2) / 1 protective film ", the BLU according to each optical sheet combination The concealability of the optical film was measured by the ratio of the fluctuation value of the luminance to the maximum value of the measured luminance value using the step point measurement method in the vertical direction of.

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

= (Maximum of Wave of Luminance-Min of Wave of Luminance) / (Maximum measured luminance value) * 100

(4) Optical interference phenomenon measurement

Two optical sheets according to each of the above Examples and Comparative Examples were disposed between the plurality of glass plates, and a pressure was applied to the glass plates to observe optical interference (Wet-out, Newton's Ring) caused by excessive adhesion generated in the film. The relative evaluation was made as follows according to the degree of occurrence of each phenomenon.

Wet-out: Occurrence ← ◎-○-△-× → Occurrence

Newton's Ring: Occurrence ← ◎-○-△-× → No Occurrence

division Viewing angle (°) Concealable Luminance (%) Optical interference Wet-out Newton's ring Example 1 50 3.8 107 × × Example 2 50 3.8 109 × × Example 3 50 4 101 × × Example 4 50 4 107 × × Example 5 51 4 100 × × Example 6 48 5 110 △ △ Example 7 51 4 107 × × Example 8 53 3.2 98 × × Example 9 56 3.1 104 × × Example 10 56 3.1 107 × × Example 11 55 3.2 101 × × Example 12 55 3.2 106 × × Example 13 55 3.2 100 × × Comparative Example 1 47 5 100 ○ ○ Comparative Example 2 53 4 98 ○ ○

As a result of the physical property evaluation, it can be seen that when the high refractive index layer (Examples 1 to 13) is placed on the structured surface, the luminance is improved compared to Comparative Examples 1 to 2. When the highest thickness of the high refractive layer is formed larger than the apex of the pattern as in Example 2 or Example 10, it can be seen that the luminance is increased as compared with the same height.

On the other hand, the optical sheet according to the present invention having a particle coating layer showed improved results compared to Comparative Example 1 or 2 also in the concealability, and also showed a result that the viewing angle is wider.

In terms of concealment, it can be seen that when compared with Example 6 and other examples, when the thickness of the high refractive index layer coating layer is thick, the concealability is higher than when the particle layer is thin.

In addition, in the optical sheet according to the present invention, it can be seen that less optical interference due to excessive adhesion between sheets occurs.

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

Claims (5)

A pattern layer having a structured surface on one side and composed of a transparent polymer composition; In the optical sheet including the base layer adjacent to the pattern layer, A high refractive layer formed to a predetermined thickness to cover the entire structured surface of the pattern layer and planarized, and having a refractive index of 0.05 to 20% higher than that of the pattern layer; And An optical sheet comprising a particle coating layer formed adjacent to the flat surface of the high refractive layer. The optical sheet of claim 1, wherein the maximum thickness of the high refractive layer is greater than or equal to the maximum height minus the minimum height from the substrate layer to the structured surface. The optical sheet according to claim 1, wherein the particle coating layer is formed from a crude liquid containing particles in a transparent binder. The optical sheet according to claim 1 or 3, wherein the particles have a diameter of 0.01 to 40 µm. 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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