KR101588500B1 - Optical film, method for preparing the same, polarizing plate comprising the same and liquid crystal display comprising the same - Google Patents

Abstract

The present invention is a non-liquid crystalline thermoplastic resin single film, wherein the film has an upper surface portion and a lower surface portion located on the surface in the thickness direction; And an inside of the film positioned between the upper surface portion and the lower surface portion, wherein the inside of the film is obliquely oriented in the thickness direction, and the tilt orientation angle increases from the upper surface portion to the lower surface portion, And a polarizing plate and a liquid crystal display including the optical film, a method of manufacturing the optical film, and a polarizing plate and a liquid crystal display including the optical film.

Description

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

The present invention relates to an optical film, a method for producing the same, a polarizing plate including the same, and a liquid crystal display including the same.

The liquid crystal display has a structure in which a liquid crystal cell layer is sealed between a TFT (Thin Film Transistor) substrate and a color filter substrate. When a voltage is applied to the electrodes existing on the TFT substrate and the color filter substrate, the arrangement of the liquid crystal molecules in the liquid crystal cell layer sealed therebetween is changed, and the image is displayed by using this. On the other hand, a polarizing plate is provided on the outside of the TFT substrate and the color filter substrate. The polarizer can control the polarization by selectively transmitting light in a specific direction among light incident from the backlight and light passing through the liquid crystal cell layer. The polarizer includes a polarizer capable of polarizing light in a specific direction, a protective film and a compensation film.

The liquid crystal display has a problem of viewing angle. A wide viewing angle technique such as a vertical alignment (VA) mode or a horizontal alignment mode (IPS, FFS) in which a viewing angle of a conventional TN (Twisted Nematic) mode is improved is widely employed. Conventionally, a viewing angle compensation film oriented in the thickness direction has been developed, but the contrast ratio (CR) is deteriorated. In this regard, Korean Patent Laid-Open Publication No. 2011-0113580 discloses an optical compensation film comprising a non-liquid crystal polymer arranged in an oblique orientation.

An object of the present invention is to provide an optical film capable of greatly improving a viewing angle and a contrast ratio of a liquid crystal display.

Another object of the present invention is to provide an optical film capable of improving the contrast ratio and the contrast of light generated in liquid crystal compensation.

Another object of the present invention is to provide a liquid crystal display device capable of improving the viewing angle and contrast ratio by compensating not only the liquid crystal aligned in the direction of thickness in the liquid crystal cell but also the liquid crystal cell in the in- And to provide an optical film.

An optical film as an aspect of the present invention is a single film of a non-liquid crystalline thermoplastic resin, and the film has an upper surface portion and a lower surface portion located on the surface in the thickness direction; And an inside of the film positioned between the upper surface portion and the lower surface portion, wherein the inside of the film is obliquely oriented in the thickness direction, and the tilt orientation angle increases from the upper surface portion to the lower surface portion, The inside of the film may be an optical film in which the in-plane optical axis is twisted in the thickness direction.

A polarizing plate, which is another aspect of the present invention, may include a polarizer and the optical film formed on one side of the polarizer.

Another aspect of the present invention is a liquid crystal display comprising: the optical film; A polarizer formed on one surface of the optical film; And a liquid crystal cell formed on the other surface of the optical film.

According to the present invention, it is possible to greatly improve the viewing angle and the contrast ratio by compensating not only the liquid crystal having a tilt direction in the thickness direction when a voltage is applied to the liquid crystal cell but also the liquid crystal in which the in-plane optical axis in the vicinity of the substrate or the orientation film in the liquid crystal cell is twisted Lt; / RTI > Further, according to the present invention, there is provided an optical film capable of greatly improving the viewing angle and contrast ratio of a liquid crystal display, and capable of improving light saturation and contrast ratio caused by liquid crystal compensation.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view in the thickness direction of an optical film of one embodiment of the present invention.
2 is a top perspective view of the optical film of one embodiment of the present invention.
3 is a sectional view of a TN mode liquid crystal display.
4 is a top perspective view of the liquid crystal alignment remaining in the vicinity of the alignment film in voltage driving in the TN mode.
5 is a schematic view of a profile of a tilt orientation angle on the basis of the thickness direction of the optical film of one embodiment of the present invention.
6 is a conceptual diagram of the oblique orientation angle (film beta angle).
7 schematically shows an image of a polarizing microscope image according to the rotation angle when the optical film of the present invention is placed between orthogonal Nicol polarizers and rotated 0 to 90 °.
8 is a schematic view of a process for producing a thermoplastic resin film according to one embodiment of the present invention.
Fig. 9 is a schematic diagram of oblique stretching of a thermoplastic resin film according to one embodiment of the present invention.
10 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention.
11 is a cross-sectional view schematically showing a liquid crystal display according to an embodiment of the present invention.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification. The terms " upper "and" lower "in this specification are defined with reference to the drawings, and the term" lower "

FIG. 1 is a cross-sectional view in the thickness direction of an optical film according to one embodiment of the present invention, and FIG. 2 is a top perspective view of an optical film according to an embodiment of the present invention.

1, the optical film 10 has an upper surface portion 10a and a lower surface portion 10b located on the film surface in the thickness direction of the film, and a lower surface portion 10b located between the upper surface portion 10a and the lower surface portion 10b And the inclined orientation angle is set so as to be inclined from the interface between the upper surface portion 10a and the film inside 10c to the inside of the film 10c The lower surface portion 10b is opposed to the liquid crystal cell (not shown in Fig. 1), and the upper surface portion 10a is lowered toward the interface between the upper surface portion 10a and the lower surface portion 10b, 2, the inside of the film 10c of the optical film 10 is inclined in the in-plane optical axis 50 within an angle? Within a predetermined range in the thickness direction of the film (not shown in Fig. 1) (twist). The "inflection point" is defined as the point at which the tilt orientation angle in the tilt orientation angle profile is within the film. The "in-plane optical axis" refers to the slow axis of the film.

3 is a cross-sectional view of a liquid crystal display of a TN (Twisted Nematic) mode. 3, the liquid crystal cell includes a color filter substrate 30a, a TFT substrate 30b, a first alignment film 31a formed on the lower surface of the color filter substrate 30a, a first alignment film 31b formed on the upper surface of the TFT substrate 30b, A second alignment layer 31b formed on the first alignment layer 31a and a liquid crystal 60 and 70 formed between the first alignment layer 31a and the second alignment layer 31b. In the TN mode, the liquid crystal layer has a hybrid structure in the thickness direction at the time of voltage non-driving (off), and has a structure in which the in-plane optical axis is twisted. 3, the liquid crystal 60 inside the liquid crystal cell stands vertically while the liquid crystal 70 in the vicinity of the alignment layer is in a state in which the liquid crystal is laid due to an anchoring force between the alignment film and the liquid crystal In addition, it has a structure in which the in-plane optical axis is rotated within a predetermined range (a hybrid structure in the thickness direction and a hybrid structure in the azimuth direction coexist). Fig. 4 is a top perspective view of the liquid crystal alignment remaining near the alignment film during voltage driving. Fig. Referring to FIG. 4, molecules of the liquid crystal 70 are aligned with respect to each other with respect to a direction normal to the substrate, and the absolute value of the angle? Such a liquid crystal alignment may hinder the viewing angle or front CR (contrast ratio) of the liquid crystal display.

The optical film of the present invention has the maximum tilt orientation angle on the surface facing the liquid crystal cell to compensate for the liquid crystal lying in the vicinity of the alignment film and the optical axis in the plane in the film thickness direction is also twisted, The viewing angle of the liquid crystal display and the contrast ratio can be greatly improved by compensating even the liquid crystal.

5 is a schematic view of the profile of the oblique orientation angle with reference to the thickness direction of the optical film of one embodiment of the present invention. 5, the optical film is obliquely oriented in the thickness direction. The optical film is tilted from the interface between the upper surface portion 10a and the film inside 10c to the interface between the lower surface portion 10b and the film inside 10c, Has a profile in which the angle gradually increases and reaches the inflection point (BP), has the maximum orientation angle, and decreases again after the inflection point. That is, it has a profile shape that forms a post-increase decrease curve rather than a gradually increasing type profile.

The position of the inflection point BP may be closer to the lower surface portion 10b than the upper surface portion 10a. For example, the inflection point BP may be located between the center line C of the film thickness and the upper surface of the lower surface portion 10b. As described above, the inflection point BP having the maximum oblique orientation angle is located closer to the liquid crystal cell than the polarizer, so that the liquid crystal in the vicinity of the alignment film in the TN liquid crystal, that is, the liquid crystal lying can be compensated. For example, the inflection point is located at a point 1 to 49.9% of the film thickness, for example, 5 to 45%, such as 10 to 35%, for example, 20 to 35% of the film thickness from the lower surface of the lower surface portion 10b Lt; / RTI > The viewing angle compensation effect at the above position can be excellent.

6 is a conceptual diagram of the oblique orientation angle (film beta angle). 6, the film beta angle is the same as the section orientation angle, and the angle formed between the z axis in the thickness direction and the z 'axis perpendicular to the orientation plane. The film beta angle can be obtained at an angle where the optical film is placed between the polarizers and the orthogonal Nicole transmission is observed by observing the orthogonal Nicole.

The inside of the film has different values of the film beta angle along the z axis which is the thickness direction, and has the profile of Fig. In the specific example, the inside of the film may have a film beta angle of 0.1 to 50 degrees, for example, 15 to 20 degrees, and a maximum film beta angle at an inflection point (BP) of 15 to 35 degrees, specifically 20 to 35 degrees. In the above range, the viewing angle compensation effect can be realized. On the other hand, the upper surface portion and the lower surface portion may have a film beta angle of 0 DEG, respectively. This is because the surface portion of the optical film is rapidly cooled while being in direct contact with the roll, so that shear force is not applied and it is difficult to be tilted.

An optical film can have an ideal film beta angle of 15 to 40 degrees, which can be the film beta angle at the inflection point. The viewing angle improving effect is excellent in the above range. The ratio β1 / β2 of the maximum β angle β1 and the minimum β angle β2 in the film interior 10c is 1 to 7.0, for example, 1.15 to 7.0, for example, 1.5 to 5, for example, 2 To 4.5. The viewing angle compensation is excellent in the above range. The maximum beta angle (beta 3) between the upper surface portion and the film thickness center C and the ratio beta 1 / beta 3 of the maximum beta angle beta 1 between the film thickness center C and the lower surface portion are 1.1 to 2.0 . The viewing angle compensation is excellent in the above range.

2 and 4, in the film of the optical film of the present invention, the in-plane optical axis in the film thickness direction is deviated in the opposite direction to the direction in which the liquid crystal near the liquid crystal cell is turned, and the in- the direction of the machine direction of the optical film is 0 °, and when the machine direction of the optical film is 0 °, the angle of deviation of the in-plane optical axis May be varied from more than 0 DEG to 5 DEG or less, specifically 0.001 DEG to 5 DEG or less. In the above range, the liquid crystal in the vicinity of the liquid crystal cell can also be compensated. The in-plane optical axis of the optical film is not distorted in the thickness direction of the upper surface portion and the lower surface portion of the optical film. Inside the film, the degree of misalignment of the in-plane optical axis with respect to the center line of the film thickness direction may be symmetrical.

The optical film may have an in-plane retardation value (Ro ') of the following formula 1 at a wavelength of 550 nm of 20 to 110 nm, for example, 50 to 100 nm. There is an advantage of viewing angle compensation in this range:

[Formula 1]

Ro '= (nx - ny') xd

(Where nx and ny 'are the refractive index in the x and y' axis directions of the optical film, respectively, and d is the thickness (unit: nm) of the film).

The optical film may have a thickness retardation value (Rth ') of 80 to 190 nm, for example, 120 to 180 nm, at a wavelength of 550 nm. There is an advantage of viewing angle compensation in this range:

[Formula 2]

Rth '= [(nx + ny') / 2 - nz '] xd

(Where nx, ny 'and nz' are the refractive indexes in the x-, y- and z'-axis directions of the optical film, respectively, and d is the thickness (unit: nm) of the film).

The optical film is a non-liquid crystalline thermoplastic resin single film. According to one embodiment, the non-liquid crystalline thermoplastic resin is a thermoplastic resin that is transparent and extrudable, and is a thermoplastic resin that is selected from the group consisting of a cycloolefin resin, a polycarbonate resin, a polyolefin resin, an aromatic vinyl resin, a polyamide resin, a polyimide resin, Based resin, a (meth) acrylic-based resin, and the like, which may be used alone or in combination of two or more.

The term "single film" means that the surface portion and the inside of the film are formed by extrusion without forming a separate coating layer or adhesive layer between the upper surface portion and the lower surface portion. That is, no adhesive layer or coating layer is formed between the upper surface portion and the lower surface portions 10a and 10b and the film inner portion 10c, and they are the same components, and they are conveniently distinguished depending on the orientation of the tilt angle. As such, the optical film can be improved in viewing angle and light leakage by forming the optical film different in orientation depending on the surface portion and the inside, and since the optical film can be manufactured in a single extrusion process with different inclination directions depending on the surface portion and the inside, And the manufacturing cost can be reduced.

The upper surface portion and the lower surface portion may have thicknesses t1 and t2 of from 1 to 20 mu m, for example, from 3 to 10 mu m, respectively, from the surface. An excellent viewing angle can be secured in the above range. The thickness of the upper surface portion and the lower surface portion may be 0.1 to 20% of the total film thickness, respectively. An excellent viewing angle can be secured in the above range. The thickness t3 of the film inner portion 10c may be 5-100 占 퐉, for example, 5-85 占 퐉. An excellent viewing angle can be secured in the above range. The thickness d of the film may be 1-500 占 퐉, for example, 30-110 占 퐉. In the above range, it can be used for a liquid crystal display.

7 schematically shows an image of a polarizing microscope image according to the rotation angle when the optical film of the present invention is placed between orthogonal Nicol polarizers and rotated 0 to 90 °. In the figure, the black part means that the darkest part appears on quadrature Nicol (quenching).

Referring to FIG. 7, it can be seen that the quenched zone is formed at any angle on the surface of the film, whereas the quenched zone is not present in the interior of the film and is oriented in accordance with the thickness.

The optical film of the present invention is produced by melt-extruding a non-liquid crystalline thermoplastic resin, passing the molten extruded thermoplastic resin between a first forming roll and a second forming roll to produce a thermoplastic resin film, and then obliquely stretching the thermoplastic resin film ≪ / RTI >

8 is a schematic view of a process for producing a thermoplastic resin film according to one embodiment of the present invention. 8, the thermoplastic resin 44 melt-extruded in the die 43 is passed between the first forming roll 41 and the second forming roll 42 to be made of the thermoplastic resin film 45. [

The first and second forming rolls 41 and 42 can make the running speeds different from each other. As a result, different shearing stresses are generated on the film surface and inside of the film due to the running of the first and second forming rolls, thereby giving a tilting orientation angle only to the inside of the film, and at the same time, A larger shearing force may be generated on the surface in contact with the first forming roll to have the profile. For example, the running speed of the first forming roll can be made higher than the running speed of the second forming roll. In a specific example, the running speed of the first forming roll may be 0.9 to 1.2 times, for example 1.01 to 1.2 times the running speed of the second forming roll, And the surface in contact with the second forming roll can be the upper surface portion of the film. Within this range, there may be a viewing angle compensation effect.

The surface temperature of the first and second shaping rolls 41 and 42 is set to be not higher than the glass transition temperature Tg of the thermoplastic resin for film forming, A different shearing force can be generated and a tilt orientation angle can be given only to the inside of the film. That is, when the melt extruded thermoplastic resin comes into contact with the forming roll to form a film, the inside of the film is above the Tg temperature, while the film surface is different from the Tg temperature. When the molding rolls at both ends are driven in a state in which the molding temperature difference between the film surface and the inside is generated, a different shearing force is generated on the surface and inside of the film, so that different tilt angles in the thickness direction can be realized.

In the embodiment, the surface temperature Tr of the first and second forming rolls 41 and 42 may satisfy the following formula 3:

[Formula 3]

(Where Te is the thermoplastic resin temperature immediately after melt extrusion and Tr is the surface temperature of the first and second molding rolls).

When the surface temperature of the first and second forming rolls 41 and 42 is out of the above range, the surface is not oriented and it is difficult to have a structure in which only the inside of the film is tilted.

The first and second forming rolls 41 and 42 may have different surface temperatures so that the inside of the film has different profiles of the oblique orientation angles. In a specific example, by making the surface temperature of the first forming roll lower than 50 캜, for example, 5-50 캜 lower than that of the second forming roll, the surface in contact with the first forming roll can be the lower surface portion of the film, The surface in contact with the forming roll is the upper surface portion of the film and can have the above-mentioned profile. For example, the surface temperature of the first shaping roll may be 75-130 占 폚, and the surface temperature of the second shaping roll may be 95-150 占 폚.

The first and second forming rolls 41 and 42 may have different degrees of elasticity to form various film beta-angles. For example, the first forming roll 41 may be more resilient than the second forming roll 42. In a specific example, a combination of rubber roll + FSR, FSR + FSR, steel flexible roll + FSR, metal roll + FSR, SFR + SFR, metal roll + rubber roll may be used. FSR is a roll in which a water layer and a steel layer are sequentially formed on the surface of a metal roll, and the SFR is a roll in which a rubber layer and a steel layer are sequentially formed on the surface of the metal roll.

In other embodiments, the optical film can be made into a multi-layer structure using a primary extruder and a secondary extruder. For example, the main extruder is manufactured by forming the inside of the film, the auxiliary extruder forming the surface of the film, and separately setting the extrusion temperature of the main extruder and the auxiliary extruder. In the specific example, the temperature at the surface portion coming out of the secondary extruder is set low and the temperature inside the film coming out of the main extruder is set high, so that it can be made higher when the inclination angle in the thickness direction is generated by utilizing the speed difference between rolls.

Fig. 9 is a schematic diagram of oblique stretching of a thermoplastic resin film according to one embodiment of the present invention. In FIG. 8, the thermoplastic resin film 45 having passed between the first and second forming rolls 41 and 42 is obliquely stretched. The term "warp stretching" means that the MD direction and the TD direction For example, when the MD direction of the film is 0 deg. And the TD direction is 90 deg., The stretching is performed in a range of 85 deg. To less than 90 deg. (For example, 85 deg. Deg. 89.5 DEG), or a stretching angle? Of more than 90 DEG and not more than 95 DEG (for example, 90.5 DEG to 95 DEG). In this range, it is possible to manufacture an optical film that can compensate for liquid crystal in which the in-plane optical axis near the liquid crystal cell in the TN mode is distorted. By such oblique stretching, the oblique orientation in the thickness direction can be maintained.

The stretching ratio can be elongated to 5 to 20% with respect to the oblique stretching direction. The front retardation Ro 'and the thickness direction retardation Rth' characteristics can be ensured within the above range. Preferably, the elongation can be elongated to 8 to 15% of the oblique stretching direction.

The stretching can be performed at a temperature lower than the glass transition temperature (Tg) of the non-liquid crystalline thermoplastic resin. For example, the stretching can be performed at a temperature lower than the glass transition temperature (Tg) of the non-liquid crystalline thermoplastic resin by 0.1 to 20 ° C, for example, 3 to 5 ° C. There is an advantage that the contrast ratio can be increased in the above range.

The polarizing plate of the present invention may include a polarizer and an optical film formed on one side of the polarizer. A protective film may be further formed on the other surface of the polarizer. The protective film is a transparent polymeric resin film. Examples of the protective film include a cellulose-based film including triacetylcellulose (TAC) and the like, a polyester-based film, an acrylic-based film, a cyclic polyolefin (COP )- based film, a polycarbonate- The film may be a film of one or more resins selected from the group consisting of polyether sulfone, polysulfone, polyamide, polyimide, polyolefin, polyarylate, polyvinyl alcohol, polyvinyl chloride, and polyvinylidene chloride . A polarizer may be formed on one surface of the upper surface portion of the optical film. 10 is a cross-sectional view of a polarizing plate of one embodiment of the present invention. 10, the polarizing plate may include a polarizer 21, the optical film 10 formed on the lower surface of the polarizer 21, and a protective film 22 formed on the upper surface of the polarizer 21. [

The liquid crystal display of the present invention may include an optical film, a polarizer formed on one side of the optical film, and a liquid crystal cell formed on the other side of the optical film. The lower surface portion of the optical film may be opposed to the liquid crystal cell. The liquid crystal display to which the optical film of the present invention is applied can compensate the liquid crystal in which the in-plane optical axis in the vicinity of the liquid crystal cell and the liquid crystal in the tilt direction in the thickness direction are compensated in the TN (Twisted Nematic) mode liquid crystal, It is possible to improve the contrast ratio with the light source generated by the liquid crystal compensation.

11 is a cross-sectional view schematically showing a liquid crystal display according to one embodiment of the present invention. 11, a liquid crystal panel including a liquid crystal cell layer 40 sealed between a first substrate 30a and a second substrate 30b is formed on one surface of the first and second substrates 30a, And the optical film 10 of the present invention can be laminated, respectively. In one embodiment, the first substrate 30a may be a color filter (CF) substrate (upper substrate), and the second substrate 30b may be a TFT (thin film transistor) substrate (lower substrate).

The first substrate 30a and the second substrate 30b may be the same or different, and may be a glass substrate or a plastic substrate. The plastic substrate may be made of a material selected from the group consisting of polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), polyethylene naphthalate (PEN), polyether sulfone (PES), polyarylate ), But the present invention is not limited thereto.

The optical film 10 of the present invention may be laminated on the first substrate 30a. Also, the optical film 10 of the present invention may be laminated on the lower part of the second substrate 30b.

A laminate 20 of a polarizer and a protective film may be formed on the optical film 10. At this time, the lower surface portion 10b of the optical film is opposed to the substrates 30a and 30b, and the upper surface portion 10a is opposed to the laminate 20, specifically, the polarizer.

In addition, although not shown in the drawing, a normal pressure-sensitive adhesive layer, a reflection ring layer, a hard coating layer, and the like can be further formed.

The liquid crystal cell layer 40 may be a liquid crystal cell layer containing TN (Twisted Nematic) mode liquid crystal. Normally, a TN liquid crystal display has a structure in which a liquid crystal lies vertically in a liquid crystal cell when a voltage is applied, while a liquid crystal is laid by an anchoring force of an orientation film in the vicinity of an alignment film, do. At this time, the liquid crystal alignment can narrow the viewing angle of the TN liquid crystal display. The optical film of the present invention has a structure in which the optical axis of the in-plane optical axis is different from that of the liquid crystal display, The viewing angle and the CR can be improved by compensating for the liquid crystal which has been changed in addition to the slanted alignment of the liquid crystal compensation effect.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. However, the following examples are provided to aid understanding of the present invention, and the scope of the present invention is not limited to the following examples.

Example  1 to 5

The RX4500 thermoplastic resin prepared in JSR was melt extruded at 230-280 ° C in a T die and passed between FSR and metal rolls to form a film. At this time, the ratio of the FSR speed to the metal roll speed was 1.01 to 1.03 times, and the surface temperature of the FSR and the metal roll were respectively lower than the glass transition temperature of the thermoplastic resin. The extruded thermoplastic resin film was obliquely stretched at an in-plane stretching angle shown in Table 1 at 8 to 15% of the stretching direction to produce an optical film having a thickness of 90 占 퐉. The stretching angle is defined as an angle at which stretching is performed when 0 ° is set in the MD direction and 90 ° in the TD direction.

The maximum beta angle (beta 3) between the upper surface portion and the film thickness center C and the maximum beta angle (beta 1) between the film thickness center C and the lower surface portion were changed as shown in Table 1 below. The maximum beta angle position is calculated as a percentage of the total film thickness from the lower surface of the lower surface portion. The upper surface portion and the lower surface portion are not obliquely oriented. The in-plane optical axis of the film is turned in the thickness direction, and the in-plane optical axis is not tilted in the thickness direction in the upper surface portion and the lower surface portion. The maximum absolute value of the in-plane optical axis deflection angle in the thickness direction was measured by the Cross-Nicol method. The angle at which the transmittance was increased while maintaining the lowest transmittance while twisting the film between the polarizers while crossing the polarizer was measured Angle).

The prepared optical film was subjected to epoxy molding and then microtome was made using GLASS KNIFE so that the film thickness was 90 μm and the slice thickness was 10 μm. The film slice was placed on a glass plate, the plate was sandwiched between orthogonal Nicol polarizers, and observed with a polarizing microscope to confirm the orientation according to the angle.

Comparative Example  One

An optical film was produced in the same manner as in Example 1 except that the film was stretched in the TD direction at an elongation angle of 90 °. Although the optical film is obliquely oriented in the thickness direction, the in-plane optical axis is not twisted.

Comparative Example  2

An optical film was produced in the same manner as in Example 1, except that the film was stretched in the MD direction at a stretching angle of 0 °. Although the optical film is obliquely oriented in the thickness direction, the in-plane optical axis is not twisted.

In-plane stretching angle
(°) ? 3 (max)
Top surface part ~ center (°) beta 1 (max)
Center to lower surface part (°) Ro '
(nm) Rth '
(nm) The maximum absolute value of the in-plane optical axis deflection angle in the thickness direction (°) Viewing angle
(Left / right, CR = 10, °) Viewing angle
(Up / Down, CR = 10, °) Example One 88.5 13 25 60 150 1.5 83/83 85/85 2 89 13 25 63 161 One 88/88 87/87 3 89.5 13 25 65 165 0.5 88/88 88/88 4 85 13 25 60 160 5 83/83 85/85 5 95 13 25 60 172 5 83/83 85/85 Comparative Example One 90 13 25 62 155 0 80/80 80/80 2 0 13 25 60 149 0 20/20 20/20

(1) nx, ny 'and nz' were obtained by using Axo scan for the prepared film, and values of Ro 'and Rth' (wavelength of 550 nm) were obtained by the following formulas 1 and 2, respectively.

[Formula 1]

Ro '= (nx - ny') xd

(Where nx and ny 'are the refractive index in the x and y' axis directions of the optical film, respectively, and d is the thickness of the film).

[Formula 2]

Rth '= [(nx + ny') / 2 - nz '] xd

(Where nx, ny 'and nz' are refractive indices in the x-axis, y'-axis and z'-axis directions of the optical film, respectively, and d is the thickness of the film).

(2) β angle: Axo scan. To observe the detailed thickness profile in the thickness direction, the luminance distribution of the polarizing microscope image was analyzed by angle using an image analysis program .

(3) Viewing Angle: At a polar angle of 80 °, the CR was measured as EZ contrast or SR3 in up / down / left / right and defined as the side angle of CR 10 or higher. CR (Contrast Ratio) was measured by EZ contrast as a luminance ratio of black and white on the screen in the state where the polarizing plate was attached to the liquid crystal panel.

As shown in Table 1, the optical film of the present invention was not only obliquely oriented in the thickness direction but also in-plane optical axis, so that the viewing angle was improved compared to Comparative Examples 1 and 2 in which the in-plane optical axis was not distorted. Comparative Examples 1 and 2 were tilted only in the thickness direction, and liquid crystal that was distorted could not be compensated, so that the effect of improving the viewing angle was low.

Claims (23)

Non-liquid crystalline thermoplastic resin single film,
The film has an upper surface portion and a lower surface portion located on the surface in the thickness direction; And a film inside the upper surface portion and the lower surface portion,
Wherein the inside of the film is inclined in the thickness direction and has a profile in which the angle of inclination increases from the upper surface portion to the lower surface portion and decreases after passing through the inflection point,
Wherein the inside of the film is twisted in an in-plane optical axis in a thickness direction. The optical film according to claim 1, wherein the lower surface portion is opposed to the liquid crystal cell, and the in-plane optical axis is deviated in the opposite direction to the direction in which the liquid crystal molecules in the vicinity of the liquid crystal cell are twisted. 2. The optical film according to claim 1, wherein the maximum absolute value of the angle at which the in-plane optical axis is twisted is 0 DEG or more and 5 DEG or less when the machine direction of the optical film is 0 DEG. The optical film according to claim 1, wherein the upper surface portion and the lower surface portion each have an in-plane optical axis deflection angle in the thickness direction. The optical film according to claim 1, wherein the in-plane optical axis of the film is symmetric with respect to a center line of the film thickness direction. The optical film according to claim 1, wherein the inflection point is closer to the lower surface portion than the upper surface portion. The optical film according to claim 1, wherein the inflection point is located between the center line of the film thickness and the lower surface portion. The optical film according to claim 1, wherein the inflection point is located at 1 to 49.9% of the film thickness from the lower surface of the lower surface portion. The optical film according to claim 1, wherein the upper surface portion and the lower surface portion each have a film beta angle of 0 DEG. The optical film according to claim 1, wherein the upper surface portion and the lower surface portion are respectively 1 to 20 탆 in thickness from the surface of the optical film. The optical film according to claim 1, wherein the upper surface portion and the lower surface portion are each 1 to 20% of the total film thickness. The optical film according to claim 1, wherein the film has a maximum film beta angle of 20 to 35 degrees. The optical film according to claim 1, wherein a ratio (beta 1 / beta 2) of a maximum beta angle (beta 1) to a minimum beta angle (beta 2) in the film is 1.15 to 7.0. The thermoplastic resin composition according to claim 1, wherein the thermoplastic resin is at least one selected from the group consisting of a cycloolefin resin, a polycarbonate resin, a polyolefin resin, an aromatic vinyl resin, a polyamide resin, a polyimide resin, An optical film comprising at least one. The optical film according to claim 1, wherein the optical film has an in-plane retardation value (Ro ') of 20 to 110 nm of the following formula 1 at a wavelength of 550 nm:
[Formula 1]
Ro '= (nx - ny') xd
(Where nx and ny 'are the refractive index in the x and y' axis directions of the optical film, respectively, and d is the thickness (unit: nm) of the film). The optical film according to claim 1, wherein the optical film has an optical retardation value (Rth ') in the thickness direction of 80 to 190 nm of the following formula (2) at a wavelength of 550 nm:
[Formula 2]
Rth '= [(nx + ny') / 2 - nz '] xd
(Where nx, ny 'and nz' are the refractive indexes in the x-, y- and z'-axis directions of the optical film, respectively, and d is the thickness (unit: nm) of the film). Extruding a non-liquid crystalline thermoplastic resin, passing the melt-extruded thermoplastic resin between a first forming roll and a second forming roll to produce a thermoplastic resin film, and obliquely stretching the thermoplastic resin film, The surface temperatures of the first forming roll and the second forming roll are respectively equal to or lower than the glass transition temperature of the thermoplastic resin and generate different shearing forces inside the film surface along the running of the first and second forming rolls, Wherein a tilt angle is provided to the optical film. 18. The thermoplastic resin film according to claim 17, wherein the oblique stretching is performed in the range of 85 deg. To less than 90 deg. Or more than 90 deg. Deg. To 95 deg. Deg. Deg. Or less based on the MD direction when the MD direction of the thermoplastic resin film is 0 deg. And stretching the film at a stretching angle. A polarizer comprising a polarizer, and an optical film according to any one of claims 1 to 16 formed on one surface of the polarizer. 20. The polarizer of claim 19, wherein the polarizer is opposed to the upper surface portion of the optical film. The polarizer according to claim 19, wherein a protective film is further formed on the other surface of the polarizer. An optical film according to any one of claims 1 to 16;
A polarizer formed on one surface of the optical film; And
And a liquid crystal cell formed on the other surface of the optical film. 23. The liquid crystal display according to claim 22, wherein a lower surface portion of the optical film faces the liquid crystal cell.

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