KR20150100183A - Optical film, liquid crystal display including the same and method for preparing protective film applied to the same - Google Patents

Abstract

The present invention relates to an optical film, a liquid crystal display apparatus including the same, and a method for manufacturing a protective film applied to the same. The optical film of the present invention includes: a polarizer and a first protective film stacked on one surface of the polarizer. A refractive index of a slow axis of a first protective film is larger than that of the polarizer and the slow axis is at an angle of 70 to 110° from an adsorption axis of the polarizer.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical film, a liquid crystal display including the optical film, and a method of manufacturing a protective film used therefor. BACKGROUND ART [0002]

The present invention relates to an optical film, a liquid crystal display including the same, and a method for manufacturing a protective film used therefor.

In recent years, the display field has been rapidly developed, and various flat panel display devices having excellent performance such as thinning, light weight, and low power consumption have been developed and replaced with existing CRT (cathode ray tube) .

Specific examples of such a flat panel display include a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), an organic electroluminescent display Organic Electroluminescence Device).

Of these, liquid crystal displays are one of the most widely used flat panel displays. In general, a liquid crystal display has a structure in which a liquid crystal layer is sealed between a TFT (Thin Film Transistor) array substrate and a color filter substrate.

However, the liquid crystal display has a problem that the contrast ratio at the side is lowered, thereby lowering the visibility, that is, the viewing angle is poor.

Accordingly, it is an object of the present invention to provide an optical film for improving the viewing angle as described above, and to provide a liquid crystal display device including the optical film. It is another object of the present invention to provide a production method for easily producing the optical film.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing the same.

According to an aspect of the present invention, there is provided an optical film comprising a polarizer and a first protective film laminated on one surface of the polarizer, wherein the refractive index of the first protective film is greater than that of the polarizer, The slow axis may form an angle with the absorption axis of the polarizer in the range of 70 ° to 110 °.

The refractive index of the slow axis of the protective film may range from 1.55 to 1.80.

The optical film may have a contrast ratio (CR) of 80 or more at a polar angle of 60 [deg.].

The first protective film may include a polyester-based material.

The first protective film may be a polyethylene terephthalate type, a polyethylene naphthalate type, or a copolymer thereof.

The thickness of the first protective film may range from 10 [mu] m to 80 [mu] m.

And a second protective film may be further included on the other surface of the polarizing plate.

The second protective film may be made of the same material as or different from the first protective film.

The second protective film may be a different material from the first protective film, and may be a TAC, a phase difference COP, or an acrylic film.

According to an aspect of the present invention, there is provided a liquid crystal display comprising a liquid crystal cell, a backlight unit, a lower polarizer disposed between the liquid crystal cell and the backlight unit, and an upper polarizer disposed on the viewer side of the liquid crystal cell, And the upper polarizer plate may include the optical film.

The first protective film of the optical film may be positioned on the viewer side of the upper polarizer.

According to an aspect of the present invention, there is provided a method of manufacturing a protective film, comprising the steps of: preparing an unstretched polyester film; and stretching the unstretched polyester film.

The stretching may be performed by a uniaxial stretching method or a biaxial stretching method.

The details of other embodiments are included in the detailed description and drawings.

The embodiments of the present invention have at least the following effects.

That is, the optical film of the present invention can be applied to a liquid crystal display to improve the contrast ratio at the side, thereby improving the visibility.

The effects according to the present invention are not limited by the contents exemplified above, and more various effects are included in the specification.

1 is a cross-sectional view schematically showing an optical film according to an embodiment of the present invention.
2 is a cross-sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention.
3 is a cross-sectional view schematically illustrating a liquid crystal cell of a liquid crystal display according to an embodiment of the present invention.
4 is a schematic flowchart of a method of manufacturing a protective film according to an embodiment of the present invention.
5 shows the results of Black Luminance measurement of the optical film of Production Example 1. Fig.
6 is a black luminance measurement result of the optical film of Comparative Example 1. Fig.
7 is a black luminance measurement result of the optical film of Comparative Example 2. Fig.
8 is a graph showing a result of measurement of the contrast ratio in Experimental Example 1. FIG.
9 is a graph showing the results of White Luminance measurement in Experimental Example 1. FIG.
10 is a graph showing the results of Black Luminance measurement in Experimental Example 1. FIG.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

It is to be understood that elements or layers are referred to as being "on " other elements or layers, including both intervening layers or other elements directly on or in between. Like reference numerals refer to like elements throughout the specification.

Although the first, second, etc. are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used only to distinguish one component from another. Therefore, it goes without saying that the first component mentioned below may be the second component within the technical scope of the present invention.

It should also be understood that the steps constituting the manufacturing method described herein may be sequential or sequential, or one step and the other step constituting one manufacturing method may be performed in the order described in the specification It is not construed as limited. Therefore, the order of the steps of the manufacturing method can be changed within a range that can be easily understood by a person skilled in the art, and a change apparent to a person skilled in the art accompanying thereto is included in the scope of the present invention.

Optical film

Hereinafter, an optical film according to an embodiment of the present invention will be described with reference to FIG. 1 is a cross-sectional view schematically showing an optical film according to an embodiment of the present invention.

Referring to FIG. 1, an optical film 100 according to an embodiment of the present invention includes a first protective film 101 and a second protective film 103 positioned on both surfaces in a thickness direction, and a first protective film And a polarizer 102 interposed between the second protective film 103 and the second protective film 103.

In an exemplary embodiment, one of the first protective film 101 and the second protective film 103 may be omitted.

The slow axis refractive index of the first protective film 101 is larger than the refractive index of the polarizer 102 and the slow axis of the first protective film 101 forms an angle with the absorption axis of the polarizer 102 in the range of 70 ° to 110 ° .

The slow axis means an axis having the greatest refractive index at a specific wavelength in the plane of the film. In contrast to this, the phase axis, which is the axis perpendicular to the ground axis and the plane, can be mentioned. The in-plane retardation can be obtained by multiplying the value obtained by subtracting the refractive index of the phase axis from the refractive index of the slow axis by multiplying the thickness.

The slow axis refractive index of the first protective film 101 is not particularly limited as long as it is relatively large relative to the refractive index of the polarizer 102, but may be in the range of 1.55 to 1.80, for example.

The polarizer 102 is a film that can convert natural light or polarized light into arbitrary polarized light, and can generally be converted into specific linearly polarized light. As the polarizer 102, a hydrophilic polymer film such as a polyvinyl alcohol film, a partially porous polyvinyl alcohol film, or an ethylene-vinyl acetate copolymerization system partially saponified film may be formed by adsorbing a dichroic substance such as iodine or a dichroic dye, , A polyene-based oriented film such as a dehydrated product of phlyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, and the like, but the present invention is not limited to these. In the exemplary embodiment, a polyvinyl alcohol-based film having a high degree of polarization and excellent in adhesion to the protective films 101 and 103 can be cited. However, the present invention is not limited thereto.

The first protective film 101 may include a polyester-based material.

As the polyester, for example, terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5- Naphthalene dicarboxylic acid, diphenylcarboxylic acid, diphenoxyethane dicarboxylic acid, diphenylsulfone carboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,3-cyclo Hexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethyl malonic acid, succinic acid, 3,3-diethyl succinic acid, glutaric acid, 2,2 - dicarboxylic acids such as dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid and dodecadicarboxylic acid, Ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexane (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) propane, -Hydroxyphenyl) sulfone, and the like, but the present invention is not limited thereto. A homopolymer obtained by polycondensing one kind of each of the above materials or a copolymer obtained by polycondensing at least one kind of dicarboxylic acid and two or more kinds of diols or a copolymer obtained by polycondensing two or more kinds of dicarboxylic acids and one or more kinds of diols And a blend resin obtained by blending two or more of these homopolymers or copolymers. However, the present invention is not limited to these.

In an exemplary embodiment, an aromatic polyester may be used from the viewpoint that the polyester exhibits crystallinity, and examples thereof include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and copolymers thereof However, the present invention is not limited to these.

The polyester film is obtained by, for example, a method of melt-extruding the above-mentioned polyester resin into a film form and then cooling and solidifying it by a casting drum to form a film. In the present invention, a stretched polyester film can be suitably used from the viewpoint of imparting crystallinity to the polyester film and achieving the above properties. The stretching may be uniaxial stretching or biaxial stretching. In the case of using as the first protective film an aromatic polyester as a main component, such a film may contain a resin other than an aromatic polyester, an additive, or the like.

The second protective film 103 may include the same material as the first protective film 101, or may include different materials.

In the case where the second protective film 103 includes a material different from the first protective film 101, the optical isotropic material having substantially no birefringence or the birefringent birefringent material has an extremely small retardation value or an in-plane uniformity in the optical axis direction Excellent ones can be used. Further, the first protective film 101 may have a relatively low refractive index. A material having such characteristics is not particularly limited, but a transparent polymer having a uniform optical property can be used, and from the viewpoint of transparency, an amorphous polymer can be used. For example, a resin such as a cellulose resin, a cyclic polyolefin resin (norbornene resin), a polycarbonate resin, a polyarylate resin, an amorphous polyester resin, a polyvinyl alcohol resin, a polysulfone resin, Resin, and the like. However, the present invention is not limited thereto. In an exemplary embodiment, the second protective film may be, but is not limited to, a TAC series, a phase difference COP, or an acrylic film.

When the first protective film 101 is a stretched film, the stretching method is not particularly limited, and a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse biaxial stretching method, and a longitudinal and transverse simultaneous biaxial stretching method can be employed. As the stretching means, any appropriate stretching machine such as a roll stretching machine, a tenter stretching machine, or a pantograph or linear motor type biaxial stretching machine can be used.

The thicknesses of the first protective film 101 and the second protective film 103 are not particularly limited as long as they have the above-described characteristics, but they may be in the range of 10 탆 to 80 탆 for thin film formation. In an exemplary embodiment, the thickness may range from 15 [mu] m to 60 [mu] m, but is not limited thereto.

Liquid crystal display

FIG. 2 is a cross-sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention, and FIG. 3 is a schematic cross-sectional view of a liquid crystal cell included in a liquid crystal display device.

Referring to FIGS. 2 and 3 together with FIG. 1, a liquid crystal display 10 includes a liquid crystal cell 200, a backlight unit 300, a lower polarizer plate (not shown) disposed between the liquid crystal cell 200 and the backlight unit 300 And an upper polarizer 110 disposed on the viewing side of the liquid crystal cell 200. [

The liquid crystal cell 200 includes a liquid crystal panel including a first substrate 210, a second substrate 230, a liquid crystal layer 220 sealed between the first substrate 210 and the second substrate 230, , And the upper polarizer 110 may be laminated on one surface (upper surface) of the first substrate 210. The upper polarizer 110 may be composed of the optical film 100 of the present invention. In the exemplary embodiment, the first protective film of Fig. 1 may be disposed on the upper surface of the upper polarizer plate 110, i.e., on the viewer side. Therefore, the contrast ratio (CR) at the side is relatively improved, and the viewing angle can be improved.

The lower polarizer 120 may be laminated on the lower surface of the second substrate 230. When the two polarizers 110 and 120 are positioned above and below the liquid crystal cell 200, Orthogonal or parallel.

The first substrate 210 may be a color filter (CF) substrate. Although not shown in detail in FIG. 3, for example, a black matrix for preventing light leakage, a color filter for red, green, and blue, and a transparent (transparent) material such as ITO or IZO are formed on a lower surface of a substrate made of a transparent insulating material such as glass or plastic. And a common electrode which is an electric field generating electrode formed of a conductive oxide.

The second substrate 230 may be a TFT (Thin Film Transistor) substrate. Though not specifically shown in FIG. 3, for example, a thin film transistor composed of a gate electrode, a gate insulating film, a semiconductor layer, a resistive contact layer, and a source / drain electrode, and a thin film transistor formed of a transparent insulating material such as ITO Or a pixel electrode that is an electric field generating electrode formed of a transparent conductive oxide such as IZO.

The plastic substrate that can be used for the first substrate 210 and the second substrate 230 may be a plastic substrate such as PET (polyethylene terephthalate), PC (polycarbonate), PI (polyimide), PEN (polyethylene naphthalate) sulfone, PAR (polyarylate), and COC (cycloolefin copolymer). However, the present invention is not limited thereto. Also, the first substrate 210 and the second substrate 230 may be made of a flexible material.

The liquid crystal layer 220 may be a twisted nematic (TN) mode having a positive dielectric constant anisotropy, a vertically aligned (VA) mode or a horizontally aligned (IPS, FFS) mode or the like. 3, the TN mode will be described as an example.

When there is no voltage difference between the pixel electrode and the common electrode, that is, the electric field generating electrode, the electric field is not applied to the liquid crystal layer 220. As shown in Fig. 3, And is arranged parallel to the surfaces of the substrate 210 and the second substrate 230 and has a structure in which the first substrate 210 and the second substrate 230 are spirally twisted by 90 °.

The polarized light of linearly polarized light passes through the liquid crystal layer 220 and changes due to retardation due to the refractive index anisotropy of the liquid crystal. When the dielectric anisotropy (DELTA epsilon) of the liquid crystal and the chiral pitch or the thickness of the liquid crystal layer 220, i.e., the cell gap, are adjusted, the linearly polarized light direction of the light passing through the liquid crystal layer 220 is 90 °.

The backlight unit 300 may generally include a light source, a light guide plate, a reflective film, and the like. Depending on the configuration of the backlight, it can be arbitrarily divided into a direct-down system, a sidelight system, and a planar light source system.

Protective Film Manufacturing Method

4 is a schematic flowchart of a method of manufacturing a protective film according to an embodiment of the present invention.

Referring to Fig. 4 together with Fig. 1, the manufacturing method of the first protective film 101 includes a step (S10) of producing an unstretched polyester film and a step (S20) of stretching an unstretched polyester film do.

Step S10 of producing an unstretched polyester film is not particularly limited, but a melt extrusion method can be used, for example. It is possible to melt at a melting temperature of the polyester-based material or higher and discharge it out of the extrusion facility to form a non-stretched film. Hereinafter, the melt extrusion method will be described in more detail.

If the content of water present in the raw material in the melt extrusion process is above a certain level, bubble-like product defects such as orange peel may occur. Therefore, the moisture content should be controlled to a certain level or less. The shape of the dryer is not particularly limited, and examples thereof include a dehumidifying dryer, a hot air dryer, and the like, but are not limited thereto. The drying temperature can be performed below the glass transition temperature of the film raw material. However, it goes without saying that the drying temperature can be appropriately selected depending on the kind of resin used and the glass transition temperature. If the drying temperature is too low, there is no drying effect. On the contrary, if the drying temperature is higher than necessary, the characteristics of the raw material are changed and it is not appropriate. The drying time of the raw material may be in the range of 0.5 to 5 hours, but can be easily selected in consideration of the ambient humidity and the like.

The dried raw material can be supplied to the raw material storage (hopper) located at the entrance of the extrusion facility. In some cases, the filter may be routed through the filter while primarily circulating air in the reservoir to remove impurities that may be contained in the feed.

The input material is filled in the first section of the screw inside the extrusion facility. The first section serves to transfer the raw material to the extruding equipment cylinder.

Hereinafter, the second section is a section in which melting of the raw material starts, and is preferably set to a temperature higher than the glass transition temperature of the film raw material.

The third section serves to completely convert the raw material into the melt. The temperature setting can be maintained in the same range as the second section.

The fourth section increases the density of the molten material by increasing the pressure of the molten raw material, thereby securing a stable discharge amount. In this process, the temperature condition can be maintained in the same range as the second and third intervals so that the discharged melt is not cured.

In some cases, it passes through a gear pump section that transfers the melt to the tee die by a certain amount. When the raw material is fed directly to the tie die through the screw in the cylinder of the extrusion equipment, the quantity of the raw material to be transferred is irregular, so that a product of excellent quality can not be obtained. Therefore, the gear pump can store irregularly charged raw materials from the extruding equipment cylinder in a certain space, and can steadily supply a certain amount of molten material to the tie die, thereby minimizing a change in the pressure distribution.

The section through which the melt is finally discharged out of the extrusion facility is a tee section. The shape of the film and the production thickness are determined according to the shape of the Ti-die. The shape of the tee die can be classified into a "T" die, a coat hanger die, a fish tail die, and the like, but is not limited thereto. The type of tie dies can be selectively used depending on the flowability of the melt.

The step (S20) of stretching the non-stretched polyester film may use a general wet stretching method and / or dry stretching method in the related art.

Examples of the dry stretching method include inter-roll stretching method, heating roll stretching method, compression stretching method, tenter stretching method, and the like, and the wet stretching method Non-limiting examples include a tenter stretching method and a roll-to-roll stretching method.

In the case of the above wet stretching method, stretching can be performed in an alcohol, water, or boric acid aqueous solution. For example, a solvent such as methyl alcohol or propyl alcohol may be used, but not limited thereto.

In addition, the stretching step S20 may employ a vertical uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse direction biaxial stretching method, and a longitudinal and transverse simultaneous biaxial stretching method.

In the exemplary embodiment, only the slow axis refractive index can be adjusted using the uniaxial stretching method, but the present invention is not limited thereto.

The stretching ratio MD or TD of the stretching step S20 may be varied depending on the desired thickness range and the like, and is not particularly limited. For example, the stretching ratio may be in the range of 2: 1 to 10: 1.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Manufacturing example  One

Extruding process and uniaxial stretching so as to have a thickness of 40 탆 and a refractive index of 1.67 by using polyethylene terephthalate and measuring an angle between the absorption axis of the polyvinyl alcohol polarizer containing iodine and the angle? -p) were bonded at 90 ° so as to produce an optical film.

Comparative Example  One

An optical film was prepared in the same manner as in Production Example 1, except that a TAC film having a refractive index of 1.52 at the slow axis and a thickness of 40 탆 was used.

Comparative Example  2

An optical film was produced in the same manner as in Production Example 1 except that the angle (? R-p) between the absorption axis of the polarizer and the slow axis was 0 °.

Experimental Example  One

Black Luminance was measured using an LCD master using the optical film produced in Production Example 1 and Comparative Examples 1 and 2 as a simulator, and the results are shown in FIGS. 5 to 7. FIG.

Referring to Figs. 5 to 7, it can be seen that Black Luminance is the least in the optical film of Production Example 1. In the drawing, the part marked in red indicates that the black luminance is high, and the part indicated in blue indicates that the black luminance is low. 6 and 7, the black luminance was measured in red at the azimuth angles of 45 °, 135 °, 225 °, and 315 °, but in the case of FIG. 5, there is no region measured in red.

In Comparative Example 2 in which the refractive index is the same as that of Comparative Example 1, which has a relatively small refractive index, but 慮 r-p is 0, Black Luminance is not significantly different. Since the contrast ratio (CR) is calculated by White Luminance / Black Luminance, the smaller the denominator Black Luminance, the more the contrast ratio can be increased.

When the slow axis having a relatively large index of refraction is at 90 degrees to the absorption axis of the polarizer, light transmitted through the polarizer passes through the protective film in the direction of the greatest refractive index and becomes parallel to the transmission axis. In this case, the total reflection can proceed from the high refractive index medium to the low refractive index medium, and the larger the refractive index difference, the more the total reflection can occur.

Therefore, by adjusting only the refractive index in a specific direction to increase the total reflection amount and reducing the black luminance, the contrast ratio can be increased to increase the viewing angle.

Experimental Example  2

The optical films prepared in Preparation Example 1 and Comparative Example 1 were evaluated for contrast ratio, White Luminance and Black Luminance at an actual side (polar angle: fixed at 60 °, azimuthal angle of 45 ° / 135 ° / 225 ° / 315 °) And the results are shown in Table 1 and Figs. 8 to 10.

Pole: fixed at 60 °
Azimuth: 45 ° / 135 ° / 225 ° / 315 ° CR White Luminance Black Luminance Production Example 1 105/96/84/86 47/45/39/39 0.45 / 0.47 / 0.47 / 0.45 Comparative Example 1 79/76/67/68 58/56/48/49 0.74 / 0.74 / 0.71 / 0.72

Referring to Table 1 and FIG. 8 to FIG. 10, it can be confirmed that the optical film of Preparation Example 1 is superior to Comparative Example 1 in contrast ratio CR at the side. In Comparative Example 1, the contrast ratio (CR) of Comparative Example 1 was higher than that of Preparation Example 1, and the contrast ratio (CR) of Comparative Example 1 was higher than that of Production Example 1 Respectively.

Therefore, it can be seen that when the optical film of the present invention is used in the viewing direction of the display device, the side contrast ratio can be improved and the visibility can be improved.

It will be appreciated that the embodiments described above are all exemplary and that different embodiments may be applied in combination.

10: liquid crystal display device 100: optical film
101: first protective film 102: polarizer
103: second protective film 110: upper polarizer plate
120: lower polarizer plate 200: liquid crystal cell
300: backlight unit 210: first substrate
220: liquid crystal layer 230: second substrate

Claims (13)

A polarizer, and a first protective film laminated on one surface of the polarizer,
Wherein the slow axis refractive index of the first protective film is larger than the refractive index of the polarizer and the slow axis forms an angle with the absorption axis of the polarizer in the range of 70 to 110 degrees. The method according to claim 1,
Wherein the protective film has a refractive index in the range of 1.55 to 1.80. The method according to claim 1,
An optical film having a contrast ratio (CR) of at least 80 at a polar angle of 60 °. The method according to claim 1,
Wherein the first protective film comprises a polyester-based material. 5. The method of claim 4,
Wherein the first protective film is a polyethylene terephthalate-based, polyethylene naphthalate-based, or copolymer thereof containing them. The method according to claim 1,
Wherein the thickness of the first protective film ranges from 10 占 퐉 to 80 占 퐉. The method according to claim 1,
And a second protective film on the other surface of the polarizing plate. 8. The method of claim 7,
Wherein the second protective film is made of the same or different material as the first protective film. 8. The method of claim 7,
Wherein the second protective film is a material different from the first protective film and is a TAC system, a phase difference COP, or an acrylic film. Liquid crystal cell,
Backlight unit,
A lower polarizer plate disposed between the liquid crystal cell and the backlight unit, and
And an upper polarizer disposed on the viewing side of the liquid crystal cell,
Wherein the upper polarizer comprises the optical film of claim 1. 11. The method of claim 10,
Wherein a first protective film of the optical film is positioned on a visible side of the upper polarizer. Preparing a non-stretched polyester film; And
And stretching the non-stretched polyester film. 13. The method of claim 12,
Wherein the stretching is performed by a uniaxial stretching method or a biaxial stretching method.

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