KR20100005463A - Photosensitive resin composition and optical sheet with elasticity by the use thereof - Google Patents

Abstract

PURPOSE: A photosensitive resin composition is provided to prevent the damage of a structural layer in order to avoid the influence of external shock when applied to a display and to maintain the function of a prism structure. CONSTITUTION: A photosensitive resin composition comprises a compound of chemical formula 1. In chemical formula 1, R is a hydrogen atom or C1~15 alkyl group; x, y, and z are an integer of 0 or more; a, b, and c are an integer of a+b+c>=4, when a+b+c<4, at least one of x, y, and z is 3 or more. An optical sheet comprises a structure layer that is a resin-cured layer with a structural layer.

Description

Photosensitive resin composition and optical sheet with elasticity TECHNICAL FIELD

The present invention relates to a photosensitive resin composition and an elastic optical sheet used in a liquid crystal display (hereinafter, LCD).

LCD, which is used as an optical display element, is an indirect light emission method that displays an image by controlling transmittance of an external light source, and a backlight unit, which is a light source device, is used as an important component for determining the characteristics of the LCD.

In particular, with the development of LCD panel manufacturing technology, the demand for thin and high brightness LCD displays has increased, and accordingly, various attempts have been made to increase the brightness of the backlight unit, which is used for monitors, PDAs (Personal Digital Assistants), and notebook computers. In the liquid crystal display used as, a bright ray from a small energy source can be said to be a measure of excellence. Therefore, in the case of LCD, the front brightness is very important.

LCD has a structure in which light passing through the light diffusion layer is diffused in all directions, so the light emitted to the front becomes very insufficient, and thus, efforts to display higher luminance with less power consumption continue. In addition, efforts are being made to widen the viewing angle so that a larger display can be viewed by more users.

For this purpose, increasing the power of the backlight increases power consumption and heat loss. As a result, portable displays have a larger battery capacity and shorter battery life.

Accordingly, a method of directing light to increase brightness has been proposed, and various lens sheets have been developed for this purpose. The representative sheet has a prism array, that is, a structure in which several peaks and valleys are arranged side by side in a straight line.

Herein, the prism structure has a triangular array structure having an inclined surface of about 45 ° to improve luminance in the front direction. Therefore, the upper part of the prism structure is in the shape of a mountain, and the upper part of the mountain is easily broken or worn by small external scratches, thereby causing a problem in that the prism structure is damaged. Since the angles emitted from the same type of prism structure are the same for each array, the luminance is reduced due to the difference in the light paths emitted between the damaged parts and the normal parts even by a small crush on the corners of the triangle or minute scratches on the inclined surface. It is lowered and a defect occurs. Therefore, even in the case of the production of the prism sheet, even in the case of minute defects, the front surface of the produced prism sheet may not be used depending on the position. This leads to a decrease in productivity, which in turn is a burden of cost increase. In fact, even in the assembling of the backlight module, defects due to damage to the prism structure due to scratches when handling the prism sheet become a significant problem.

In addition, when mounting on the backlight unit, a plurality of sheets and films are laminated, and in order to increase the brightness, a plurality of prism films may be mounted. In this case, the upper prism film and the upper prism film may be in contact with each other. Due to this there was a problem that the prism structure is easily damaged.

Therefore, in order to prevent damage of such a prism structure, there existed a case where the conventional protective film was laminated | stacked. However, since LCD panels are becoming thinner, there is a tendency to omit the film or to use a sheet having a composite function, and also to increase production cost, time, and physical efficiency due to the addition of a process of laminating a protective film.

In addition to the damage to the prism structure due to the handling during such manufacturing, the use of portable displays such as notebooks and PDAs is increasing, and the cases of moving the displays into bags and the like are rapidly increasing. In this case, when a shock is applied to the display due to jumping while moving or a vehicle is stopped, even if there is a protective film, the prism structure mounted in the display is damaged and a serious problem affecting the screen is generated.

Therefore, there is an urgent need for a prism structure that can flexibly cope with external shocks.

Accordingly, the present invention provides a photosensitive resin composition and an elastic optical sheet capable of preventing damage to the structural layer so as not to be affected by external impact when applied to a display.

It is another object of the present invention to provide a photosensitive resin composition and an elastic optical sheet which are easy to handle by preventing damage to the structural layer.

In another aspect, the present invention is to provide a photosensitive resin composition and an elastic optical sheet that can maintain the function of the prism structure by preventing the lowering of the brightness due to the difference in the optical path.

On the other hand, the present invention is to provide an elastic optical sheet that does not require a protective film.

In addition, the present invention is to provide a resilient optical sheet that can reduce the production rate and reduce the production cost and increase the production efficiency.

Accordingly, the present invention provides a photosensitive resin composition comprising a compound of formula 1 as a preferred embodiment.

Formula 1

In the above formula, R is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, x, y, z is an integer of 0 or more, a, b, c is an integer of a + b + c ≥ 4 or a + b + c <4 If one of x, y, z is 3 or more.

In another preferred embodiment of the present invention, the surface includes a structural layer that is a structured resin cured layer, and the material for the structural layer provides an optical sheet including the compound of Chemical Formula 1.

In the above embodiment, using a planar indenter on the upper surface of the structured surface is pressed until the maximum compressive force of 1g _f or 2g _f at a compression rate of 0.2031mN / sec, and after reaching the maximum compression force to stop for 5 seconds to compress When the compression force is released, the elastic recovery rate expressed by Equation 1 may be 85% or more.

Equation 1

In the above formula, D ₁ means the depth that is compressed by the external pressure is applied, D ₂ is the difference between the height of the optical sheet and the height of the optical sheet when the external pressure is removed when the external pressure is not applied. it means.

In the above embodiment, the elastic recovery rate expressed by Equation 1 may be 90% or more.

In the above embodiment, preferably, D ₁ may satisfy Equation 2 below, more preferably, Equation 3 below, and more preferably satisfy Equation 4 below. It may be.

Equation 2

Equation 3

Equation 4

In Equations 2 to 4, D means the height of the optical sheet in the state that no external pressure is applied.

In this embodiment, the optical sheet has a polyhedron shape having a polygonal, semi-circular or semi-elliptical cross section; Or a columnar shape whose cross section is polygonal, semicircular or semi-oval; Alternatively, the cross-section may include a structural layer having a plurality of patterns selected from one or more selected from among polygonal, semi-circular, or semi-elliptic curved columnar shapes.

The present invention can prevent damage to the structural layer even when an external impact is applied when applied to the display. Therefore, even in the case of a portable display such as a notebook, PDA, there is an effect that is not easily damaged by external shocks such as running in the bag or sudden stop by moving the vehicle.

In addition, the present invention has an effect that is easy to handle by preventing damage to the structural layer.

In addition, the present invention can prevent a decrease in luminance due to damage, and thus can maintain the function of the optical sheet.

On the other hand, the present invention does not require a protective film is a simple manufacturing process can reduce the production cost and increase the production efficiency.

In addition, the present invention is not easily damaged by the film lamination or external impact during the manufacturing process can reduce the failure rate can reduce the production cost and increase the production efficiency.

Hereinafter, the present invention will be described in more detail.

The present invention provides a photosensitive resin composition comprising a compound of formula 1 as a preferred embodiment.

Formula 1

In the above formula, R is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, x, y, z is an integer of 0 or more, a, b, c is an integer of a + b + c ≥ 4 or a + b + c <4 If one of x, y, z is 3 or more.

The compound of Formula 1 may have an elastic modulus after curing as a compound having a molecular weight of 150 to 10,000 by controlling the type and length of the flexible alkylene oxide chain in the molecular structure. And it is preferable as a material which is excellent in heat resistance and light resistance, and forms the structural layer of an optical sheet.

In another preferred embodiment of the present invention, the surface includes a structural layer that is a structured resin cured layer, and the material for the structural layer provides an optical sheet including the compound of Chemical Formula 1.

The optical sheet of the present invention is not particularly limited, but includes a base layer and a structural layer formed on one or both surfaces thereof, and the structural layer may include a plurality of three-dimensional structures as a cured resin layer having a structured surface. .

Among the plurality of three-dimensional structures, if the cross-section includes a polygonal structure, the upper portion of the optical sheet in the shape of a peak in the shape of the mountain, it can be easily damaged by external impact, even in this case the optical sheet of the present invention Easily deformed and easily restored, they are not easily damaged by external shocks.

The optical sheet of the present invention for this purpose is pressed by a planar indenter on the upper surface of the structured surface of the structural layer until the maximum compression force of 1g _f or 2g _f at a pressing speed of 0.2031mN / sec, when the maximum compression force is reached 5 When the compression force is released after the compression is stopped for a second, the elastic recovery rate represented by Equation 1 below is preferably 85% or more, and more preferably, the elastic recovery rate represented by Equation 1 below 90% or more.

Equation 1

In the above formula, D ₁ means the depth that is compressed by the external pressure is applied, D ₂ is the difference between the height of the optical sheet without the external pressure and the height of the optical sheet at the time of recovery by removing the external pressure. it means.

In the optical sheet of the present invention, when the elastic recovery rate is satisfied when the pressurized and pressurized force is removed as described above, even when an external impact is applied, the optical sheet has an elastic force that is flexible enough to cope with the impact. Can prevent damage.

On the other hand, when the optical sheet does not satisfy the elastic recovery rate when the optical sheet is pressurized as described above, the upper portion of the structural layer remains pressed when the optical sheet is in contact with another film or under load. There is a risk of malfunction.

In addition, it is preferable that the optical sheet of the present invention satisfies Equation 2 below, and more preferably, D _1, which means the depth into which the external pressure is applied, is compressed. Preferably, the following Equation 4 is satisfied.

Equation  2

Equation  3

Equation  4

In Equations 2 to 4, D means the height of the optical sheet in the state that no external pressure is applied.

That is, when the optical sheet of the present invention is flexible or has a load such that the depth into which the optical sheet is compressed due to the external pressure is 1/20 or more with respect to the height of the optical sheet without the external pressure is in contact with another film or under load The top of the structure layer may be more advantageous in maintaining the normal shape.

As a result, the optical sheet of the present invention easily enters the structural layer having a three-dimensional structure when subjected to a large load, but recovers as close as possible to the original state when the compressed state is released, so that the structural layer is not damaged even by external impact.

The present inventors have studied to provide an optical sheet that satisfies such an elastic recovery rate, and found that a molecular structure having a structure of a bifunctional monomer in which molecular flexible alkylene glycol chains are repeatedly connected may increase the elastic modulus. In particular, in the case of including the compound of Formula 1 as a structural layer material, it has been found that the optical recovery is not impaired while satisfying the elastic recovery rate.

Therefore, the optical sheet of the present invention preferably contains 5 to 80% by weight based on the total weight of the composition for forming the structural layer of the compound of Formula 1 so as to satisfy the elastic recovery rate described above. When included less than 5% by weight increase of the elastic recovery rate is insignificant, when included by more than 80% by weight may have a slight effect of increasing the brightness as an optical sheet.

In addition to the compound of Formula 1, the composition forming the structural layer may further include a conventional UV curing agent, a photoinitiator and a high refractive resin having a refractive index of 1.52 or more.

The method for producing the optical sheet of the present invention is not particularly limited, and for example, an additive such as an ultraviolet curing agent is added to the structural layer material to prepare an ultraviolet curable liquid composition, and then coated on the substrate layer and cured, thereby curing the optical sheet. It can manufacture.

On the other hand, the optical sheet of the present invention includes a structural layer having a plurality of three-dimensional structure as a surface-structured resin cured layer, the structural layer cross-section may be polygonal, semi-circular or semi-elliptic polyhedron shape, or the cross-section is polygonal, It may be a columnar shape that is semi-circular or semi-elliptical, or may be a curved columnar shape whose cross section is polygonal, semi-circular or semi-elliptic. It may also be a shape in which one or more of these patterns are mixed.

It also includes a case having a structure arranged in at least one concentric shape when viewed in plan view, and has a structure in which mountains and valleys are formed along the concentric circles.

When the cross section of the structural layer is polygonal, the characteristics of the brightness and the wide viewing angle vary greatly according to the angle of the vertex. Therefore, it may be advantageous that the angle of the vertex is 80 to 100 ° in consideration of the brightness and the wide viewing angle due to condensing. It may be more advantageous to be ˜95 °.

The base layer of the optical sheet is at least one material selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polystyrene, polymethacrylate, polymethyl methacrylate, polyacrylate, polyimide, polyamide It may be formed, and further comprising light-diffusing particles to form a structure in which the irregularities are formed.

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

1 is a schematic diagram for testing the elastic recovery rate of an optical sheet.

When a force is applied to the structural layer 10 of the optical sheet using the planar indenter 11, the upper surface of the structural layer 10 is compressed as shown in (B). At this time, the compressed depth is D ₁ . In the optical sheet of the present invention, the D ₁ is 1/20 or more, more preferably 1/19 or more, even more preferably 1/17 or more with respect to the height D of the optical sheet in a state where no external pressure is applied. It is preferable to become. That is, the optical sheet of the present invention has a flexibility to be able to enter much without damage to the external impact.

After removing the planar indenter 11 again, as shown in (C), the upper surface of the structural layer 10 is restored to its original state without damage. At this time, the difference between the height of the recovered optical sheet and the height D of the optical sheet in the state where no external pressure is applied is D ₂ .

Therefore, the greater the difference between the depth that is compressed by applying an external pressure and the height difference (D ₁ -D ₂ ) of the recovered and recovered structure, the better the elastic force, and the optical sheet of the present invention has an elastic recovery rate expressed by Equation 1 above. It satisfies 85% or more, preferably 90% or more, and D ₁ is large and (D ₁ -D ₂ ) is large, so that the elastic force is excellent, and it returns to its original state again as much as it enters the external impact.

2 is a graph showing the relationship between the force applied to the polymer material having excellent elastic recovery rate and D ₁ and D ₂ , and FIG. 3 is a graph showing the relationship between the force applied to the polymer material having low elastic recovery rate and D ₁ and D _2. to be. The higher the elastic recovery rate, the closer the value of D ₂ is to 0. In the case of a material having an ideal elasticity, D ₂ = 0 and the elastic recovery rate is 100%. Conversely, the lower the elasticity of the material, the closer the value of D ₂ is to D ₁ and (D ₁ -D ₂ ) is closer to zero.

The optical sheet of the present invention is close to the graph of FIG. 2, and the polymer material of the present invention is not limited to the curved form of the graph of FIG. 2.

FIG. 4 is a schematic view showing scratching using a scratch probe (probe) for the optical sheet 50 of the present invention, and FIG. 5 is a scratch probe (probe) for a conventional optical sheet 30. (Probe) (15) is a schematic diagram showing how to give a scratch.

Conventional optical sheet 30 can be seen that the damage due to the deformation of the upper part of the structural layer 35 due to the scratch probe 15, otherwise, the optical sheet 50 of the present invention, even if scratched It can be seen that no damage occurs on top of the structural layer 55.

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.

Preparation Example of Acrylate Oligomer

Synthesis Example

About 1 mole of HO- [CzH ₂ zO] c- [CyH ₂ yO] b- [CxH ₂ xO] aH compound to 2.2 moles of CH ₂ = CH (R) COCl using a reaction vessel in about 5 in the presence of a solvent of tetrahydrofuran Compounds of the desired structure could be synthesized by refluxing for about a time, and after the reaction, unreacted CH ₂ = CH (R) COCl and the solvent were removed by filtration and distillation under reduced pressure using a filter to synthesize the structure of Chemical Formula 1. . At this time, the variables of the compound were synthesized as in Table 1 below.

Synthesis Example HO-R-OH CH ₂ = CH (R) COCl yield(%) Viscosity (mPaS / 25 ℃) One x = 2, y, z = 0, a = 4, b, c = 0 R = H 93.5 25 2 x = 2, y, z = 0, a = 9, b, c = 0 95.8 58 3 x = 2, y, z = 0, a = 14, b, c = 0 97.0 106 4 x = 2, y, z = 0, a = 23, b, c = 0 92.8 100/40 ℃ 5 x = 2, y, z = 0, a = 4, b, c = 0 R = CH ₃ 93.5 50 6 x = 3, y, z = 0, a = 2, b, c = 0 R = H 97.5 8 7 x = 3, y, z = 0, a = 3, b, c = 0 96.3 12 8 x = 3, y, z = 0, a = 7, b, c = 0 95.2 34 9 x = 3, y, z = 0, a = 12, b, c = 0 94.6 68 10 x = 3, y, z = 0, a = 7, b, c = 0 R = CH ₃ 96.7 30 11 x, z = 2, y = 4, a, b, c = 1 R = H 95.5 10 12 x, z = 2, y = 4, a, b, c = 1 R = CH ₃ 94.6 10 13 x = 5, y, z = 0, a = 1, b, c = 0 R = H 96.5 6 14 x = 9, y, z = 0, a = 1, b, c = 0 R = H 94.5 20 * HO-R-OH is HO- [CzH ₂ zO] c- [CyH ₂ yO] b- [CxH ₂ xO] aH

Optical sheet manufacturers

Example  1 to 14

With respect to 100 weight part of total compositions, 30 weight part of acrylates produced by the said synthesis examples 1-14, 65 weight part of bisphenol-A diacrylates (M-2100, a micro yarn), a photoinitiator 2,4,6-trimethyl 1.5 parts by weight of benzoyl diphenylphosphine oxide, 1.5 parts by weight of photoinitiator methylbenzoylformate, and 2.0 parts by weight of additive bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate were mixed and mixed at 60 ° C. for 1 hour. To prepare a composition. After that, it was applied to one surface of polyethylene terephthalate (KOLON, 188㎛), which is a base layer, and placed on a frame of a prism roller at 35 ° C, and a type-D bulb was mounted on an ultraviolet irradiation device (Fusion, 600 Watt / inch ² ). The optical sheet was manufactured by irradiating 900 mJ / cm ² in the direction of the substrate layer to form a linear triangular prism having a prism vertex angle of 90 °, a pitch of 50 μm, and a height of 27 μm. (D = 215 μm)

Example 15

Using the composition of Example 3 to which the synthesis example 3 was applied, an optical sheet was manufactured by forming a lenticular lens having a semicircular cross section, a pitch of 50 μm, and a height of 27 μm.

Example 16

Using the composition of Example 3 to which the synthesis example 3 was applied, an optical sheet was manufactured by forming a linear prism having a semicircular cross section, a pitch of 50 μm, and a height of 27 μm.

Example 17

The optical sheet was manufactured by forming a linear prism having a pentagonal cross section, a vertex angle of 95 °, a pitch of 50 µm, and a height of 27 µm using the composition of Example 3 to which the synthesis example 3 was applied.

Example 18

Using the composition of Example 3 to which the synthesis example 3 was applied, an optical sheet was manufactured by forming a prism of a wavy arrangement having a semicircular cross section, a pitch of 50 μm, and a height of 27 μm.

Comparative Example 1

3M BEFIII prism film was used as an optical sheet. (D = 215 탆)

Comparative Example 2

Doosan's Brtie-200 prism film was used as the optical sheet. (D = 215 μm)

Comparative Example 3

LG's LES-T2 prism film was used as the optical sheet (D = 220 µm).

Comparative Example 4

The optical sheet was prepared by the method of Example 1 using 3EG-A (x = 2, y, z = 0, a = 3, b, c = 0) of a public company instead of the acrylate monomer of the synthesis example in the composition of Example 1. Prepared. (D = 215 μm)

In each of the above Examples and Comparative Examples, D ₁ , elastic recovery rate and scratch resistance of the optical sheet were measured as follows.

(1) D ₁ and elastic recovery rate

The optical sheets prepared in Examples and Comparative Examples were measured using a micro-compression hardness meter (Shimadzu DUH-W201S) manufactured by Shimadzu Corporation, Japan, to measure D ₁ and elastic recovery rate using the 'Load-Unload test' item. After placing the pointed portion of the mountain in the optical sheet structure layer at the center of the planar indenter having a diameter of 50 μm, D ₁ and the elastic recovery rate were repeatedly measured five times under the following conditions, and the average value was obtained. It was.

[Measurement Condition 1]

a. Maximum compressive force applied: 1g _f (= 9.807mN)

b. Compression force per hour: 0.2031mN / sec

c. Stop time at maximum compression: 5 sec

[Measurement Condition 2]

a. Maximum compressive force applied: 2g _f (= 19.614mN)

b. Compression force per hour: 0.2031mN / sec

c. Stop time at maximum compression: 5 sec

(2) scratch resistance

When a minimum pressure was applied to the optical sheets of the Examples and Comparative Examples using the basic weight of the Big Heart test apparatus of IMOTO, the scratches of the structural layer were measured, and the results are shown in Table 2 below. The degree of damage was visually judged and the criteria are as follows.

Bad scratch resistance ← × <△ <○ <◎ → Excellent scratch resistance

division D (μm) Measurement condition 1 Measurement condition 2 Scratch resistance D ₁ (μm) D ₂ (μm) Elastic recovery (%) D ₁ (μm) D ₂ (μm) Elastic recovery (%) Example 1 215 11.352 1.567 86.2 12.870 1.802 86.0 ◎ Example 2 215 11.349 1.245 89.0 12.865 1.682 86.9 ◎ Example 3 215 11.452 1.175 89.7 12.935 1.519 88.3 ◎ Example 4 215 11.449 0.894 92.6 12.938 0.979 92.4 ◎ Example 5 215 11.275 1.625 85.6 12.758 1.805 85.8 ◎ Example 6 215 11.365 1.420 87.5 12.900 1.857 85.6 ◎ Example 7 215 11.367 1.000 91.2 12.934 1.293 90.0 ◎ Example 8 215 11.370 0.909 92.0 12.942 1.138 91.2 ◎ Example 9 215 11.371 0.852 92.5 12.955 0.880 93.2 ◎ Example 10 215 11.366 1.079 90.5 12.788 1.291 89.9 ◎ Example 11 215 11.458 0.973 91.5 12.888 1.043 91.9 ◎ Example 12 215 11.399 1.151 89.9 12.785 1.214 90.5 ◎ Example 13 215 11.360 1.113 90.2 12.900 1.315 89.8 ◎ Example 14 215 11.500 0.977 91.5 12.921 1.033 92.0 ◎ Example 15 215 11.345 1.576 86.1 12.750 1.912 85.0 ◎ Example 16 215 11.350 1.452 87.2 12.850 1.670 87.0 ◎ Example 17 215 11.350 1.464 87.1 12.899 1.805 86.0 ◎ Example 18 215 11.352 1.339 88.2 12.902 1.612 87.5 ◎ Comparative Example 1 215 2.892 0.699 75.8 3.502 0.903 74.2 × Comparative Example 2 215 4.846 1.187 75.5 5.235 1.188 77.3 △ Comparative Example 3 220 4.389 1.198 72.7 5.200 1.346 74.1 △ Comparative Example 4 215 9.725 1.935 80.1 10.523 2.246 78.7 ○

As shown in Table 1, the optical sheet according to the embodiment of the present invention having an elastic recovery rate of 85% or more can be seen that the scratch resistance of the structural layer is very excellent, whereby the optical sheet of the present invention is damaged without external structure damage As you enter a lot and then recover as close to the original state as possible, you can flexibly cope with external shocks and can not be easily damaged.

1 is a schematic diagram for testing an elastic recovery rate of an optical sheet;

2 is a graph showing the relationship between the force applied to a polymer material having high elastic recovery rate and D ₁ and D ₂ ,

3 is a graph showing the relationship between forces applied to polymer materials having a low elastic recovery rate and D ₁ and D ₂ ;

Figure 4 is a schematic diagram showing a state of giving a scratch by using a scratch probe (probe, probe) to the optical sheet of the present invention,

FIG. 5 is a schematic diagram showing scratches using a scratch probe (probe, probe) in a conventional optical sheet.

Claims (8)

To the photosensitive resin composition comprising a compound of formula (1). Formula 1 In the above formula, R is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, x, y, z is an integer of 0 or more, a, b, c is an integer of a + b + c ≥ 4 or a + b + c <4 If one of x, y, z is 3 or more. The structure includes a structural layer which is a structured resin cured layer, The structural layer material is an optical sheet containing the compound of formula (1). Formula 1

In the above formula, R is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, x, y, z is an integer of 0 or more, a, b, c is an integer of a + b + c ≥ 4 or more, or a + b + c < If 4, one of x, y, z is 3 or more. The method of claim 2, When using the planar indenter on the upper surface of the structured surface, pressurize until the maximum compressive force of 1g _f or 2g _f at the pressure of 0.2031mN / sec, stop compression for 5 seconds when the maximum compressive force is reached, and then release the compressive force. , The optical sheet, characterized in that the elastic recovery rate is expressed by Equation 1 below 85%. Equation 1

In the above formula, D ₁ means the depth that is compressed by the external pressure is applied, D ₂ is the difference between the height of the optical sheet without the external pressure and the height of the optical sheet at the time of recovery by removing the external pressure. it means. The method of claim 3, wherein An optical sheet having an elastic recovery rate of 90% or more represented by Equation 1. The method according to claim 3 or 4, D ₁ satisfies the following equation (2). Equation  2

In the above formula, D means the height of the optical sheet in the state that no external pressure is applied. The method according to claim 3 or 4, D ₁ satisfies the following equation (3). Equation 3

In the above formula, D means the height of the optical sheet in the state that no external pressure is applied. The method according to claim 3 or 4, D ₁ satisfies the following equation (4). Equation 4

In the above formula, D means the height of the optical sheet in the state that no external pressure is applied. The method according to claim 3 or 4, The optical sheet has a polyhedron shape whose cross section is polygonal, semi-circular or semi-elliptic; Or a columnar shape whose cross section is polygonal, semicircular or semi-oval; Or a structural layer formed of a plurality of one or more patterns selected from among curved column shapes having a polygonal, semi-circular or semi-elliptic cross section.

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