KR101285159B1 - Acryl-based copolymers, and an optical film comprising the same - Google Patents

Abstract

The present invention is an alkyl (meth) acrylate monomer; (Meth) acrylate monomers containing an aromatic ring; And it relates to an acrylic copolymer comprising a maleimide monomer, a resin composition comprising the same and an optical film produced using the same.

Description

ACRYL-BASED COPOLYMERS, AND AN OPTICAL FILM COMPRISING THE SAME

The present invention relates to an acrylic copolymer and an optical film comprising the same.

Recently, a display technology using various methods such as a plasma display panel (PDP), a liquid crystal display (LCD) and the like replacing a conventional cathode ray tube has been proposed and marketed on the market. Polymer materials for such displays have further improved their required properties. For example, in the case of a liquid crystal display, thinning, weight reduction, and enlargement of the screen area are promoted, which is a particularly important problem in view of wide viewing angle, high contrast, suppression of image tone change according to viewing angle, and uniform display.

Accordingly, various polymer films are used for polarizing films, polarizer protective films, retardation films, plastic substrates, light guide plates, etc., and as liquid crystals, twisted nematic (TN), super twisted nematic (STN), and vertical Various modes of liquid crystal display using alignment (VA), in-plane switching (IPS) liquid crystal cells, and the like have been developed. All of these liquid crystal cells have a unique liquid crystal arrangement and have inherent optical anisotropy. To compensate for this optical anisotropy, a film imparting a retardation function by stretching various kinds of polymers has been proposed.

Specifically, since the liquid crystal display uses high birefringence characteristics and orientations of the liquid crystal molecules, the refractive index varies according to the viewing angle, and thus the color and brightness of the screen change. For example, since most liquid crystal molecules used in the vertical alignment method have a positive phase difference in the thickness direction of the liquid crystal display surface, a compensation film having a negative phase difference in the thickness direction is required to compensate for this. In addition, the front of the two polarizers orthogonal to each other do not pass light, but when the angle is inclined, the optical axis of the two polarizers are not orthogonal to cause light leakage. In addition, the display device using the liquid crystal requires both phase difference compensation in the thickness direction and plane direction difference compensation in order to widen the viewing angle.

As a requirement for the retardation compensation film, birefringence must be easily controlled. However, the birefringence of the film is not only due to the fundamental birefringence of the material but also by the orientation of the polymer chains in the film. The orientation of the polymer chain is mostly forcibly caused by the force externally applied, or due to the intrinsic properties of the substance, and the method for orienting molecules by external force is to uniaxially or biaxially stretch the polymer film.

In order to solve the viewing angle problem of LCDs due to the inherent birefringence characteristics of the liquid crystals, N-TAC, V-TAC, and COP films have recently been used as compensation films or retardation films. However, these films have a problem of high cost and complicated manufacturing process.

In order to solve the problems of the prior art as described above, an object of the present invention is to provide an acrylic copolymer having excellent heat resistance than conventional while maintaining transparency.

Another object of the present invention is to provide an acrylic copolymer resin having excellent compatibility with a resin containing one or two selected from aromatic rings and aliphatic rings in the main chain contained in the compounding resin for optical films.

Still another object of the present invention is to provide a resin composition comprising a resin containing one or two of the aromatic copolymer and the aliphatic ring in the acrylic copolymer resin and the main chain.

Still another object of the present invention is to provide an optical film excellent in heat resistance and optical transparency containing the resin composition, and a liquid crystal display device including the optical film.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art,

1) alkyl (meth) acrylate monomers;

2) a (meth) acrylate monomer containing an aromatic ring; And

3) to provide an acrylic copolymer containing a maleimide monomer.

The present invention also provides a compounding resin in which the acrylic copolymer of the present invention and a main chain are mixed with a resin containing one or two of an aromatic ring and an aliphatic ring.

Moreover, it provides the optical film containing the said compounding resin of this invention.

Moreover, it provides the liquid crystal display device containing the said optical film of this invention.

The acrylic copolymer according to the present invention is excellent in heat resistance while maintaining transparency. In addition, the acrylic copolymer is excellent in compatibility with the resin containing one or two selected from the aromatic ring and aliphatic ring in the main chain contained in the compounding resin for optical films. The optical film including the compounding resin including the acrylic copolymer has excellent transparency and heat resistance, and is excellent in workability, adhesion, retardation characteristics, and durability.

Hereinafter, the present invention will be described in detail.

One aspect of the invention, the alkyl (meth) acrylate monomers; (Meth) acrylate monomers containing an aromatic ring; And it relates to an acrylic copolymer comprising a maleimide monomer.

In the present specification, the copolymer resin containing a monomer means that the monomer is polymerized and included as a repeating unit in the copolymer resin.

As used herein, the term "(meth) acrylate monomer" includes "acrylate monomer" or "methacrylate monomer."

The acrylic copolymer may be a block copolymer or a random copolymer, but the copolymer form is not limited thereto.

In the acrylic copolymer resin, the alkyl (meth) acrylate-based monomer means both an alkyl acrylate-based monomer and an alkyl methacrylate-based monomer. It is preferable that the alkyl group of the said alkyl (meth) acrylate type monomer is C1-C10, It is more preferable that it is C1-C4, It is still more preferable that it is a methyl group or an ethyl group. The alkyl methacrylate monomer is more preferably methyl methacrylate, but is not limited thereto.

The content of the alkyl (meth) acrylate monomer is preferably 50 to 98.9 parts by weight, more preferably 50 to 90 parts by weight based on the total content of the acrylic copolymer. When the content of the acrylate-based monomer is in the above range, it may be excellent in transparency and heat resistance.

In the acrylic copolymer resin, the (meth) acrylate-based monomer containing an aromatic ring serves to increase the compatibility of one or two of the aromatic ring and aliphatic ring in the main chain.

The (meth) acrylate monomer containing the aromatic ring preferably includes an aromatic ring having 6 to 12 carbon atoms, specifically, may be a phenyl (meth) acrylate monomer, and more preferably phenyl methacrylate. Do.

In the acrylic copolymer resin, the content of the (meth) acrylate monomer containing the aromatic ring is preferably more than 0 parts by weight and less than 50 parts by weight, more than 5 parts by weight and 30 parts by weight with respect to the total content of the acrylic copolymer. It is more preferable that it is below a part. When the content of the (meth) acrylate monomer containing the aromatic ring is within the above range, compatibility with the resin containing an aromatic ring and / or an aliphatic ring in the main chain may be sufficiently secured.

In the acrylic copolymer resin, the maleimide monomer serves to make the copolymer of the present invention exhibit higher heat resistance and strength. The maleimide monomer is preferably a maleimide monomer substituted with an alkyl group having 1 to 10 carbon atoms or a maleimide monomer substituted with an aryl group having 6 to 12 carbon atoms, more preferably cyclohexyl maleimide or phenyl maleimide. Do.

The maleimide monomer is preferably included in an amount of 0.1 to 10 parts by weight based on the total content of the acrylic copolymer.

The weight average molecular weight of the acrylic copolymer is preferably 50,000 to 500,000.

In addition, the weight average molecular weight of the acrylic copolymer resin is preferably 50,000 to 500,000 in terms of heat resistance, processability and productivity.

The second aspect of the present invention relates to the acrylic copolymer of the first aspect of the present invention, and a compounding resin in which a resin containing one or two of aromatic rings and aliphatic rings in a main chain is mixed.

In the above resin composition, as the resin containing one or two kinds of aromatic rings and aliphatic rings in the main chain, for example, polycarbonate resin, polyarylate resin, polynaphthalene resin, polynorbornene resin, etc. Although it is more preferable that it is polycarbonate resin, it is not limited only to this.

It is preferable that the said resin composition is 60-99.9: 0.1-40, and the weight ratio of acrylic copolymer resin and resin which contains 1 type (s) or 2 or more types in an aromatic ring and an aliphatic ring in a main chain is 70-99: 1-30 More preferably.

The resin composition may be prepared by blending the acrylic copolymer resin and a resin including one or two of aromatic rings and aliphatic rings in the main chain according to methods well known in the art, such as compounding, colorants, Additives well known in the art such as flame retardants, reinforcing agents, fillers, UV stabilizers, antioxidants, etc. may comprise 0.001 to 50 parts by weight based on 100 parts by weight of the resin composition.

It is preferable that it is 110 degreeC or more, and, as for the glass transition temperature of the said resin composition, it is more preferable that it is 120 degreeC or more. Although the glass transition temperature of the said resin composition is not specifically limited, It may be 200 degrees C or less.

Moreover, it is preferable that the weight average molecular weights of the said resin composition are 50,000-200,000 from a viewpoint of heat resistance, sufficient workability, productivity, etc.

A third aspect of the invention relates to an optical film comprising the compounding resin.

The optical film according to the present invention may have different retardation values depending on the content of the resin containing one or two of the aromatic rings and aliphatic rings in the main chain, and thus may be used as a retardation compensation film or a protective film.

The retardation compensation film may be used in the VA mode type or the TN mode type according to the retardation value. The optical film according to the present invention may have a plane direction retardation value (R _in ) of 20 nm to 100 nm and a thickness direction retardation value (R _th ) of -50 nm to -400 nm, in which case as a VA mode type retardation compensation film. Can be used. Further, the optical film of the present invention may have a plane direction retardation value Rin of 0 nm to 10 nm, preferably 0 nm to 5 nm, more preferably about 0 nm, and a thickness direction retardation value R _th . May be -10 nm to 10 nm, preferably -5 nm to 5 nm. In this case, the optical film of the present invention can be usefully used for applications in which isotropy is required, for example, a polarizer protective film.

On the other hand, in the present invention, the retardation value of the optical film can be adjusted by appropriately adjusting the content of a resin containing one or two of the aromatic ring and aliphatic ring in the main chain.

As an example, when the content of the resin containing one or two of the aromatic and aliphatic rings in the main chain is 10% by weight to 40% by weight, the plane direction retardation value R _in of the optical film is 20 nm. The thickness direction retardation value (R _th ) may be -50nm to -400nm. In this case, the optical film according to the present invention can be used as a VA mode type retardation compensation film.

As another example, when the content of the resin containing one or two of the aromatic and aliphatic rings in the main chain is 0.1% to 10% by weight, more preferably 1% to 5% by weight, the optical film The plane direction retardation value R _in may be 0 nm to 10 nm, preferably 0 nm to 5 nm, more preferably about 0 nm, and the thickness direction retardation value R _th is −10 nm to 10 nm. Nm, preferably -5 nm to 5 nm, more preferably about 0 nm. In this case, the optical film according to the present invention can be used as a polarizer protective film.

The 3) optical film may be prepared into a film according to a method well known in the art, such as 2) the resin composition of the solution caster method or extrusion method, of which the solution caster method is preferred.

It may further comprise the step of uniaxially or biaxially stretching the film prepared as described above, may be prepared by adding a modifier in some cases.

When the film is uniaxially or biaxially stretched, the stretching step may be performed in the longitudinal direction (MD) stretching or in the transverse direction (TD) stretching, or both. When extending | stretching both a longitudinal direction and a lateral direction, after extending | stretching either one, you can extend in another direction and you may extend | stretch both directions simultaneously. The stretching can be performed in one step or in multiple steps. When stretching in the longitudinal direction, stretching can be performed by the speed difference between the rolls, and in the case of stretching in the transverse direction, tenter can be used. The time of railing of the tenter is within 10 degrees of the total, suppressing the bowing phenomenon occurring in the transverse direction drawing, and controlling the angle of the optical axis regularly. It is also possible to obtain the same bowing suppression effect by setting the transverse stretching in multiple stages.

The stretching may be performed at a temperature of (Tg-20 ° C) to (Tg + 30 ° C) when the glass transition temperature of the resin composition is Tg. The glass transition temperature refers to a range from a temperature where the storage elastic modulus of the resin composition begins to decrease and a loss elastic modulus becomes larger than a storage elastic modulus to a temperature at which the orientation of the polymer chain is relaxed and disappears. The glass transition temperature can be measured by a differential scanning calorimeter (DSC). The temperature at the time of the stretching step is more preferably the glass transition temperature of the film.

The drawing speed is preferably in the range of 1 to 100 mm / min in the case of a universal drawing machine (Zwick Z010) and in the range of 0.1 to 2 m / min in the case of a pilot drawing machine. It is preferable to stretch the film by applying an elongation of 5 to 300%.

The optical film according to the present invention can be uniaxially or biaxially stretched by the above-described method, thereby adjusting the phase difference characteristics.

In the optical film manufactured as described above, it is preferable that the plane direction retardation value represented by the following equation (1) is 0 nm to 200 nm, and the thickness direction retardation value represented by the following equation (2) is 10 nm to -400 nm. desirable.

&Quot; (1) "

R _in = (n _x -n _y ) × d

&Quot; (2) "

R _th = (n _z -n _y ) × d

In Equations 1 and 2,

n _x is a refractive index of the direction of the largest refractive index in the plane direction of the film,

n _y is a refractive index in the vertical direction in the n _x direction in the plane direction of the film,

n _z is the refractive index in the thickness direction,

d is the thickness of the film.

In the optical film according to the present invention, the surface direction retardation value and the thickness direction retardation value may be adjusted according to the content of the resin including one or two kinds of aromatic rings and aliphatic rings in the main chain. For example, the planar retardation value R _in of the optical film according to the present invention may be 20 nm to 100 nm, and the thickness direction retardation value R _th may be -50 nm to -400 nm. In this case, the optical film according to the present invention can be used as a VA mode type retardation compensation film.

Further, the plane direction retardation value R _in of the optical film according to the present invention may be 0 nm to 10 nm, preferably 0 nm to 5 nm, more preferably about 0 nm, and the thickness direction retardation value R _th ) may be -10 nm to 10 nm, preferably -5 nm to 5 nm, and more preferably about 0 nm. In this case, the optical film according to the present invention can be used as a polarizer protective film.

When the optical film according to the present invention is applied to the liquid crystal display device, it may be provided on only one side of the liquid crystal panel (one sheet type), or may be provided on both sides of the liquid crystal panel (two sheets type).

When the optical film according to the present invention is provided only on one side of the liquid crystal panel, the plane direction retardation value R _in of the optical film is 30 nm to 80 nm, preferably 35 nm to 70 nm, more preferably about 40 It is preferable that they are nm-60 nm, and it is preferable that thickness direction retardation value R _in is -270 nm or less, ie, an absolute value whose thickness direction retardation value is 270 or more.

When the optical film according to the present invention is provided on both sides of the liquid crystal panel, respectively, the plane direction retardation value R _in of the optical film is 30 nm to 80 nm, preferably 35 nm to 70 nm, more preferably about It is preferable that they are 40 nm-60 nm, and it is preferable that thickness direction retardation value R _in is -100 nm or less, ie, absolute value whose thickness direction retardation value is 100 or more.

The brittleness of the optical film according to the present invention can be measured by dropping a steel sphere having a particle diameter of 15.9 mm and a weight of 16.3 g on a test film to measure a height at which a hole is formed in the film, and the optical film according to the present invention has the height Preferably it is 600 mm or more, More preferably, it is 700 nm or more.

It is preferable that the haze value of the optical film which concerns on this invention is 1% or less, It is more preferable that it is 0.5% or less, It is further more preferable that it is 0.1% or less.

Hereinafter, preferred examples will be described to aid in understanding the present invention. The following examples are merely to illustrate the invention, but are not intended to limit the scope of the invention to this.

Example

The physical property evaluation method in the Example of this invention is as follows.

1. Weight average molecular weight (Mw): The prepared resin was dissolved in tetrahydrofuran and measured by gel osmosis chromatography (GPC).

2. Tg (glass transition temperature): Measured using a DSC (Differential Scanning Calorimeter) from TA Instrument.

3. Retardation value (Rin / Rth): After stretching at the glass transition temperature of the film was measured using AxoScan from Axometrics.

4. Transparency Measurement: Measured according to ASTM 1003 method.

Example  One

An acrylic copolymer resin was prepared from 91 parts by weight of methyl methacrylate, 5 parts by weight of phenyl methacrylate, and 4 parts by weight of phenyl maleimide monomer. As a result of measuring the glass transition temperature and molecular weight of the produced resin, the resin with a glass transition temperature of 125 degreeC and a weight average molecular weight of 110,000 was obtained. 90 parts by weight of this resin was prepared by compounding with 10 parts by weight of polycarbonate to prepare a final resin composition. After producing this resin composition into the film by the solution casting method, extending | stretching was performed at the glass transition temperature and the phase difference value of the film was measured. As a result, the plane retardation value / thickness retardation value was 30 / -80.

Example  2

Acrylic copolymer resin was prepared from 86 parts by weight of methyl methacrylate, 10 parts by weight of phenyl methacrylate, and 4 parts by weight of phenyl maleimide monomer. As a result of measuring the glass transition temperature and molecular weight of the produced resin, the resin with a glass transition temperature of 126 degreeC and a weight average molecular weight of 115,000 was obtained. 85 parts by weight of this resin was prepared by compounding with 15 parts by weight of polycarbonate to prepare a final resin composition. After producing this resin composition into the film by the solution casting method, extending | stretching was performed at the glass transition temperature and the phase difference value of the film was measured. As a result, the plane retardation value / thickness retardation value was 45 / -120.

Example  3

Acrylic copolymer resin was prepared from 76 parts by weight of methyl methacrylate, 20 parts by weight of phenyl methacrylate, and 4 parts by weight of phenyl maleimide monomer. As a result of measuring the glass transition temperature and molecular weight of the produced resin, a resin having a glass transition temperature of 128 ° C. and a weight average molecular weight of 115,000 was obtained. 80 parts by weight of the resin was compounded with 20 parts by weight of polycarbonate to prepare a final compounding resin. After producing this compounding resin into a film by the solution casting method, extending | stretching was performed at the glass transition temperature and the phase difference value of the film was measured. As a result, the plane retardation value / thickness retardation value was 60 / -280.

Example  4

Acrylic copolymer resin was prepared from 76 parts by weight of methyl methacrylate, 20 parts by weight of phenyl methacrylate, and 4 parts by weight of phenyl maleimide monomer. As a result of measuring the glass transition temperature and molecular weight of the produced resin, a resin having a glass transition temperature of 128 ° C. and a weight average molecular weight of 115,000 was obtained. 75 parts by weight of the resin was compounded with 25 parts by weight of polycarbonate to prepare a final compounding resin. After producing this compounding resin into a film by the solution casting method, extending | stretching was performed at the glass transition temperature and the phase difference value of the film was measured. As a result, the plane retardation value / thickness retardation value was 70 / -330.

Example  5

An acrylic copolymer resin was prepared from 76 parts by weight of methyl methacrylate, 20 parts by weight of phenyl methacrylate, and 4 parts by weight of cyclohexyl maleimide monomer. As a result of measuring the glass transition temperature and molecular weight of the produced resin, a resin having a glass transition temperature of 130 ° C. and a weight average molecular weight of 120,000 was obtained. 75 parts by weight of the resin was compounded with 25 parts by weight of polycarbonate to prepare a final compounding resin. After producing this compounding resin into a film by the solution casting method, extending | stretching was performed at the glass transition temperature and the phase difference value of the film was measured. As a result, the plane retardation value / thickness retardation value was 80 / -370.

Comparative example  One

An acrylic copolymer resin was prepared from 91 parts by weight of methyl methacrylate, 5 parts by weight of cyclohexyl methacrylate, and 4 parts by weight of phenyl maleimide monomer. As a result of measuring the glass transition temperature and molecular weight of the produced resin, the resin with a glass transition temperature of 124 degreeC and a weight average molecular weight of 115,000 was obtained. 80 parts by weight of the resin was compounded with 20 parts by weight of polycarbonate to prepare a final compounding resin. After producing this compounding resin into a film by the solution casting method, it extended | stretched at the glass transition temperature and manufactured the film. However, haze of the film occurred and the retardation value was measured, but not measured.

Comparative example  2

An acrylic copolymer resin was prepared from 76 parts by weight of methyl methacrylate, 20 parts of cyclohexyl methacrylate, and 4 parts by weight of cyclohexyl maleimide monomer. As a result of measuring the glass transition temperature and molecular weight of the produced resin, the resin with a glass transition temperature of 126 degreeC and a weight average molecular weight of 115,000 was obtained. 80 parts by weight of the resin was compounded with 20 parts by weight of polycarbonate to prepare a final compounding resin. After producing this compounding resin into a film by the solution casting method, it extended | stretched at the glass transition temperature and manufactured the film. However, haze of the film occurred and the retardation value was measured, but not measured.

Hereinafter, Table 1 shows the results of measuring the components and contents of the polymers of Examples 1 to 5, Comparative Examples 1 and 2, the glass transition temperature and the weight average molecular weight.

Monomer (parts by weight) Glass transition temperature
(℃) Weight average molecular weight MMA PhMA / CHMA PMI / CHMI Example 1 91 5/0 4/0 125 110,000 Example 2 86 10/0 4/0 126 115,000 Example 3 76 20/0 4/0 128 115,000 Example 4 76 20/0 4/0 128 115,000 Example 5 76 20/0 0/4 130 120,000 Comparative Example 1 91 0/5 4/0 124 115,000 Comparative Example 2 76 0/20 0/4 126 115,000

MMA: Methyl methacrylate PhMA: Phenyl methacrylate

CHMA: cyclohexyl methacrylate PMI: phenylmaleimide

CHMI: cyclohexylmaleimide

Compounding Resin (parts by weight) transparency
Haze (%) R _in
(Nm) R _th
(Nm) Acrylic Copolymer PC Example 1 90 10 ○ 30 -80 Example 2 85 15 ○ 45 -120 Example 3 80 20 ○ 60 -280 Example 4 75 25 ○ 70 -330 Example 5 75 25 ○ 80 -370 Comparative Example 1 80 20 △ Not measurable Not measurable Comparative Example 2 80 20 △ Not measurable Not measurable

As shown in Table 2, it can be seen that the transparency and retardation of the optical film using the acrylic copolymer of the present invention is superior to the comparative example.

Claims (19)

60 to 99.9 wt% of an acrylic copolymer comprising an alkyl (meth) acrylate monomer, an (meth) acrylate monomer including an aromatic ring, and a maleimide monomer; And
Compounding resin mixed with 0.1 to 40% by weight of polycarbonate. The method according to claim 1,
The acrylic copolymer is based on 100 parts by weight of the acrylic copolymer,
50 to 98.9 parts by weight of an alkyl (meth) acrylate monomer;
0.1 to 50 parts by weight of a (meth) acrylate monomer containing an aromatic ring; And
Compounding resin containing 0.1 to 10 parts by weight of the maleimide monomer. The method according to claim 1,
Compounding resin, characterized in that the alkyl (meth) acrylate monomer is methyl (meth) acrylate. The method according to claim 1,
Compounding resin, characterized in that the (meth) acrylate monomer containing an aromatic ring is phenyl (meth) acrylate. The method according to claim 1,
The maleimide monomer is a compounding resin, characterized in that the maleimide monomer substituted with an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 12 carbon atoms. The method according to claim 1,
Compounding resin, characterized in that the weight average molecular weight of the acrylic copolymer is 50,000 ~ 500,000. delete delete delete An optical film comprising the compounding resin of claim 1. The method of claim 10,
The optical film is an optical film, characterized in that the retardation compensation film or protective film. The method of claim 11,
The retardation compensation film is an optical film, characterized in that for VA mode liquid crystal display device or TN mode liquid crystal display device. The method of claim 10,
The optical film is an optical film, characterized in that the plane direction retardation value represented by the following equation 1 is 0nm to 200nm:
&Quot; (1) "
R _in = (n _x -n _y ) × d
In the above equation (1)
n _x is a refractive index of the direction of the largest refractive index in the plane direction of the film,
n _y is a refractive index in the vertical direction in the n _x direction in the plane direction of the film,
d is the thickness of the film. The method of claim 10,
The optical film is an optical film, characterized in that the thickness direction retardation value represented by the following formula (2) is -400nm to 10nm:
&Quot; (2) "
R _th = (n _z -n _y ) × d
In Equation (2)
n _x is a refractive index of the direction of the largest refractive index in the plane direction of the film,
n _y is a refractive index in the vertical direction in the n _x direction in the plane direction of the film,
n _z is the refractive index in the thickness direction,
d is the thickness of the film. The method of claim 10,
The optical film is an optical film, characterized in that the surface direction retardation value represented by the following equation 1 is 20nm to 100nm, the thickness direction retardation value represented by the following equation (2) is -50nm to -400nm.
&Quot; (1) "
R _in = (n _x -n _y ) × d
&Quot; (2) "
R _th = (n _z -n _y ) × d
In Equations 1 and 2,
n _x is a refractive index of the direction of the largest refractive index in the plane direction of the film,
n _y is a refractive index in the vertical direction in the n _x direction in the plane direction of the film,
n _z is the refractive index in the thickness direction,
d is the thickness of the film. The method of claim 10,
The optical film is an optical film, characterized in that the surface direction retardation value represented by the following equation (1) is 0nm to 10nm, the thickness direction retardation value represented by the following equation (2) is -10nm to 10nm.
&Quot; (1) "
R _in = (n _x -n _y ) × d
&Quot; (2) "
R _th = (n _z -n _y ) × d
In Equations 1 and 2,
n _x is a refractive index of the direction of the largest refractive index in the plane direction of the film,
n _y is a refractive index in the vertical direction in the n _x direction in the plane direction of the film,
n _z is the refractive index in the thickness direction,
d is the thickness of the film. delete A liquid crystal display device comprising the optical film of claim 10. 19. The liquid crystal display device according to claim 18, wherein the liquid crystal display device is in VA mode.