WO2012165918A2

WO2012165918A2 - Resin composition for optical film and optical film using the same

Info

Publication number: WO2012165918A2
Application number: PCT/KR2012/004370
Authority: WO
Inventors: 강병일; 한창훈; 이대우; 서재범; 김범석; 최은정; 김준식; 이남정; 김수경; 성다은
Original assignee: 주식회사 엘지화학
Priority date: 2011-06-01
Filing date: 2012-06-01
Publication date: 2012-12-06
Also published as: WO2012165918A3

Abstract

The present invention relates to an optical film and a composition for the optical film which includes a copolymer including an alkyl (meth)acrylate unit, a (meth)acrylate unit including a benzene ring, and a (meth)acrylic acid, wherein residual monomer content in the resin composition is lower than 2000ppm.

Description

Resin composition for optical film and optical film using same

The present invention relates to a resin composition for an optical film and an optical film using the same, and more particularly, to a resin composition for an optical film having a low dimensional change rate due to optical properties, heat resistance and temperature change, and an optical film using the same.

Recently, with the development of optical technology, various display technologies, such as plasma display (PDP), liquid crystal display (LCD), organic EL display (LED), etc., replacing conventional CRTs, have been proposed and marketed. Meanwhile, various polymer films, such as polarizing films, polarizer protective films, retardation films, light guide plates, and plastic substrates, are used in these display devices, and the display polymer material has a trend of being further advanced.

Currently, the most widely used polymer film for display is a triacetyl cellulose film (TAC), which is used as a polarizer protective film, and the TAC film has a low polarization degree when used for a long time in a high temperature or high humidity atmosphere. There is a problem that the film is separated or the optical properties are degraded. In order to solve this problem, as an alternative to the TAC film, polystyrene, acrylic such as methyl methacrylate, or polycarbonate-based polymer films having excellent heat resistance have been proposed. These polymer films have an advantage of excellent heat resistance, but when applied to a display device because birefringence occurs during film formation, there is a problem that the optical properties of the display device are lowered by the film birefringence.

In order to solve such a problem, a method of copolymerizing or blending a monomer or polymer having a positive birefringence with a monomer or a polymer having a negative birefringence as a material for a polymer film having excellent heat resistance and low retardation value has been proposed. Typical examples of these methods include copolymers of benzyl methacrylate and methyl methacrylate. However, in the case of benzyl methacrylate and methyl methacrylate, the retardation value is close to 0, which is excellent in optical properties.However, due to the high dimensional change rate due to temperature change, that is, the coefficient of thermal expansion, the curl phenomenon that is severely bent or warped after laminating with the polarizing film There is a problem that this occurs. When such a polarizing plate curl phenomenon occurs, light leakage occurs in the polarizing plate, and the quality of the display is not only degraded, but also the liquid crystal in the display panel may be damaged.

The present invention is to solve the above problems, and provides a resin composition for an optical film and an optical film using the same as well as excellent optical properties and heat resistance, low dimensional change rate due to temperature changes.

In one aspect, the present invention includes an alkyl (meth) acrylate unit, a (meth) acrylate unit containing a benzene ring, a (meth) acrylic acid unit as an essential component, and optionally, a unit represented by the following formula (I) A resin composition for an optical film comprising a copolymer further comprising a, wherein the residual monomer content in the resin composition provides a resin composition for an optical film of 2000 ppm or less.

[Formula I]

[Revision 20.09.2012 under Rule 26]

In Formula 1, X is N or O,

R ₁ and R ₂ are each hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl group.

In another aspect, the present invention provides an optical film made of the resin composition for an optical film and a polarizing plate including the optical film as a protective film.

The optical film using the resin composition for optical films according to the present invention is not only excellent in optical properties and heat resistance, but also has a low coefficient of thermal expansion and is suitable for use as a polarizing plate protective film.

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

The inventors of the present invention, in order to develop a material for an optical film not only excellent in optical properties and heat resistance, but also have a low coefficient of thermal expansion, have been studied. As a result, (meth) acryl containing an alkyl (meth) acrylate and a benzene ring When the residual monomer content in the resin composition copolymerized with the rate and the (meth) acrylic acid monomer was adjusted to a specific content, it was found that an optical film having excellent thermal resistance and low thermal expansion coefficient could be formed with a phase difference value close to zero. The present invention has been completed.

The resin composition for an optical film of the present invention includes an alkyl (meth) acrylate unit, a (meth) acrylate unit containing a benzene ring, and a (meth) acrylic acid unit as essential components, and is optionally represented by the following Chemical Formula 1 It includes a copolymer containing a unit which becomes.

[Formula 1]

[Revision 20.09.2012 under Rule 26]

In this case, in Formula 1, X is N or O, R ₁ and R ₂ are each hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl group.

In the resin composition of the present invention, the alkyl (meth) acrylate means both alkyl acrylate and alkyl methacrylate, but is not limited thereto, in view of optical transparency, compatibility, processability and productivity, It is preferable that carbon number of the alkyl group of alkyl (meth) acrylate is about 1-10, It is more preferable that it is about 1-4 carbon atoms, It is most preferable that it is a methyl group or an ethyl group.

On the other hand, the (meth) acrylate containing the benzene ring is to impart a suitable retardation value to the optical film of the present invention and at the same time to impart compatibility between alkyl (meth) acrylate and (meth) acrylic acid, for example Benzyl methacrylate, benzyl acrylate, 1-phenylethyl methacrylate, 2-phenoxyethyl methacrylate, 2-phenylethyl methacrylate, 3-phenylpropyl methacrylate, 3-phenylpropyl acrylate and It may be one or more selected from the group consisting of 2-phenoxyethyl acrylate, but is not limited thereto. Among these, benzyl methacrylate, benzyl acrylate, and the like are particularly preferable, and benzyl methacrylate is most preferable.

On the other hand, the (meth) acrylic acid improves heat resistance and serves to lower the coefficient of thermal expansion by introducing a polar group, for example, acrylic acid, methacrylic acid, methylacrylic acid, methylmethacrylic acid, ethylacrylic acid, ethyl methacryl Acid, butylacrylic acid or butyl methacrylic acid, particularly methacrylic acid.

The unit represented by the formula (1) is to improve the phase difference value and the coefficient of thermal expansion more, for example, glutaric anhydride, glutaric acid imide and the like. Among these, glutaric anhydride is especially preferable. In general, when a bulky functional group that inhibits polymer chain conformation is introduced into the polymer backbone, the coefficient of thermal expansion of the polymer can be lowered. However, for example, when using polymers containing bulky functional groups such as styrene or polycarbonate, the coefficient of thermal expansion may be lowered, but birefringence may be exhibited by stretching, which may cause problems in optical properties. However, the results of the present inventors, the copolymer containing the unit represented by the formula (1), it was shown that the coefficient of thermal expansion can be effectively lowered without adversely affecting the optical properties.

On the other hand, when the resin composition of the present invention is a ternary copolymer resin composed of an alkyl (meth) acrylate unit, a (meth) acrylate unit containing a benzene ring, and a (meth) acrylic acid unit, the alkyl (meth) in the copolymer The content ratio of the acrylate unit, the (meth) acrylate unit containing the benzene ring, and the (meth) acrylic acid unit is preferably 70 to 95: 2 to 10: 3 to 20 by weight ratio. This is because a preferable retardation value, glass transition temperature and coefficient of thermal expansion can be obtained when the content ratio of each component is within the above range.

On the other hand, when the resin composition of the present invention is a quaternary copolymer resin composed of an alkyl (meth) acrylate unit, a (meth) acrylate unit containing a benzene ring, a (meth) acrylic acid unit and a unit of formula (1), The content ratio of the alkyl (meth) acrylate unit, the (meth) acrylate unit including the benzene ring, the (meth) acrylic acid unit and the unit represented by the formula (1) in the copolymer is 60 to 90: 2 to 10 by weight ratio: It is preferable that it is 3-10: about 5-20. This is because a preferable retardation value, glass transition temperature and coefficient of thermal expansion can be obtained when the content ratio of each component is within the above range.

In addition, the resin composition of the present invention is characterized in that the content of the unreacted residual monomer in the composition is 2000 ppm or less, preferably 1500 ppm or less, and most preferably 1000 ppm or less. The inventors of the present invention found that when the content of the unreacted residual monomer in the composition exceeds 2000 ppm, the glass transition temperature of the resin composition is lowered, thereby lowering the heat resistance, It has been found that contamination and / or bubbles are likely to occur, thereby degrading optical properties. More specifically, in the film produced by the melt extrusion method, when the content of the residual monomer in the resin composition as a raw material is high, there is a problem that the extruder vacuum vent portion is easily clogged, and the residual monomers are generally in the monomer or oligomer state. Due to its low thermal stability, bubbles are generated during film formation, making product production difficult. On the other hand, such bubble generation tends to be somewhat alleviated when the film forming temperature is lowered. However, when the film is formed at a low temperature, the pressure in the extruder is increased, so that the ejection is not smooth and the productivity is sharply worsened. There is a problem that the stain is not generated enough does not appear on the film appearance.

Therefore, in order to maintain excellent optical properties, i.e., a phase difference value close to zero, good heat resistance, and a low coefficient of thermal expansion, the content of residual monomers should be kept below a specific content. In particular, when the content of the residual monomer is 1000ppm or less, there is an advantage that the generation of bubbles significantly during film film formation.

Meanwhile, the resin composition of the present invention having a low content of residual monomers as described above may be prepared by mixing the monomers of each component and polymerizing them, followed by drying the product for a specific time in a specific temperature range. More specifically, the method for producing a resin composition of the present invention comprises the steps of: (1) copolymerizing an alkyl (meth) acrylate monomer, a (meth) acrylate monomer containing a benzene ring and a (meth) acrylic acid monomer, and (2) And drying the copolymerization reaction product at 240 ° C. to 270 ° C. for 30 minutes to 2 hours. In this case, the copolymerization step may be used a copolymerization method well known in the art, for example, solution polymerization, bulk polymerization, suspension polymerization or emulsion polymerization method, and among these, it is particularly preferred to be made by a bulk polymerization method. Once the copolymerization reaction is complete, a drying step is carried out to control the residual monomer content in the resin product. At this time, it is preferable that drying temperature is about 240 degreeC-270 degreeC, and it is preferable that drying time is about 30 minutes-about 2 hours. If the drying temperature is less than 240 ℃ volatilization of the residual monomer does not occur properly, it is difficult to control the content of the residual monomer, and if it exceeds 270 ℃, it may cause thermal deformation of the resin composition due to high temperature. In addition, if the drying time is less than 30 minutes, volatilization of the residual monomer does not occur properly, and it is difficult to control the content of the residual monomer, and if it exceeds 2 hours, thermal deformation, thermal decomposition, etc. of the resin occur and serious productivity decreases. Because it can cause.

On the other hand, the discharge amount in the drying step is preferably about 3kg / hr to 6kg / hr based on a 20 liter pilot reactor. If the discharge amount is less than 3 kg / hr, the resin is deteriorated to cause a decrease in transparency, and when the discharge amount is less than 6 kg / hr, a large amount of residue is contained without sufficient drying.

The resin composition of the present invention prepared by the above method is about 120 ° C to 500 ° C, preferably 125 ° C to 500 ° C, more preferably 125 ° C to 200 ° C, and most preferably 130 ° C to 200 ° C It has a transition temperature. In addition, in terms of processability, heat resistance and productivity, the weight average molecular weight of the resin composition of the present invention is preferably 50,000 to 500,000, more preferably about 100,000 to 500,000.

In addition, the resin composition of the present invention has excellent optical properties with a haze value of about 0.1 to 3%, a light transmittance of 90% or more, and a yellow index of 4 or less on an injection specimen having a thickness of 3 mm.

In another aspect, the present invention relates to an optical film comprising the resin composition of the present invention.

The optical film may be prepared in the form of a film according to a method well known in the art, such as a solution caster method or an extrusion method. In view of economics, it is more preferable to use an extrusion method. In some cases, during the film production process, an additive such as a modifier may be further added within a range that does not impair the physical properties of the film, and a uniaxial or biaxial stretching step may be further performed.

The stretching step may be performed in the longitudinal direction (MD) stretching or in the transverse direction (TD) stretching, or both. In addition, in the case where both longitudinal stretching and transverse stretching are performed, either stretching may be performed first and then stretched in the other direction, or both directions may be stretched simultaneously. In addition, the stretching may be performed in one step or may be performed in multiple steps. In the case of longitudinal stretching, stretching by the speed difference between the rolls can be performed, and in the case of transverse stretching, a tenter can be used. The starting angle of the tenter is usually within 10 degrees to suppress the bowing phenomenon occurring during the lateral stretching, and to control the angle of the optical axis regularly. Even when the transverse stretching is carried out in multiple stages, the anti-boeing effect can be obtained.

On the other hand, the stretching, when the glass transition temperature of the resin composition is Tg, it is preferably carried out in the temperature range of (Tg-20 ° C) ~ (Tg + 30 ° C), the temperature range is the storage elastic modulus is lowered And thus the temperature ranges from the temperature at which the loss modulus becomes greater than the storage modulus to the temperature at which the orientation of the polymer chain is relaxed and lost. The glass transition temperature of the resin composition 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 resin composition.

The stretching speed is preferably in the range of 1 to 100 mm / min for the universal testing machine (Zwick Z010) and within the range of 0.1 to 2 m / min for the pilot stretching equipment. The drawing ratio is preferably about 5 to 300%.

On the other hand, the optical film of the present invention prepared by the above method has a surface direction phase value (R _in ) of about 0 to 10nm, preferably 0 to 5nm at a wavelength of 580nm, thickness direction retardation value (R _th ) is About -5 to 10 nm, preferably -5 to 5 nm. Here, the surface direction retardation value refers to a value defined by Equation 1 below, and the thickness direction retardation value refers to a value defined by Equation 2 below.

[Equation 1]

R _in = (n _x -n _y ) × d

[Equation 2]

R _th = (n _z -n _y ) × d

In [Equation 1] and [Equation 2], n _x is the refractive index of the direction of the largest refractive index in the plane direction of the film, n _y is the vertical direction of the n _x direction in the plane direction of the film It is refractive index, n _z is a refractive index of the thickness direction, d is the thickness of a film.

Moreover, the thermal expansion coefficient of the optical film containing the resin composition of this invention is about 40-80 ppm / K, Preferably it is about 50-65 ppm / K. As such, since the optical film of the present invention has a low coefficient of thermal expansion, curling may be minimized when the optical film of the present invention is used as a polarizing plate protective film.

Moreover, the optical film of this invention is 20-200 micrometers, Preferably it is 40-120 micrometers, It is preferable that transparency is about 0.1 to 3%, and light transmittance is 90% or more. It is because it is suitable to be used as a polarizing plate protective film when the thickness, transparency, and transmittance of a film exist in the said range.

Moreover, it is preferable that the content of the residual monomer in the film of the optical film of this invention is 700 ppm or less. When the residual monomer content in the film exceeds 700ppm, not only defects such as fish eyes are likely to occur due to the residual monomer, but also residual monomers may be migrated in the lamination process with a polarizer requiring high temperature (80 to 90 degrees). migration) to degrade the adhesiveness to the polarizer, and may cause defects such as bubbles generated between the polarizer and the optical film.

In another aspect, the present invention relates to a polarizer comprising a polarizer and an optical film according to the present invention provided on at least one surface of the polarizer as a protective film. The optical film according to the present invention may be provided on both sides of the polarizer, or may be provided only on one surface. When the optical film of the present invention is provided on one side of the polarizer, on the other side, a polarizer protective film well known in the art, for example, TAC film, PET film, COP film, PC film, norbornene-based film, etc. Among them, in consideration of economics and the like, TAC film is particularly preferred. Since the coefficient of thermal expansion of the optical film of the present invention is similar to that of the TAC film, when the TAC film is attached to one side of the polarizer and the optical film of the present invention is attached to the other side, the curl phenomenon caused by the difference in coefficient of thermal expansion is minimized. Can be.

On the other hand, the attachment of the polarizer and the optical film and / or protective film of the present invention, after coating the adhesive on the surface of the film or polarizer using a roll coater, gravure coater, bar coater, knife coater or capillary coater, etc. , The protective film and the polarizer may be carried out by laminating by heating with a lamination roll, or laminating by pressing at room temperature. On the other hand, as the adhesive, adhesives used in the art, for example, polyvinyl alcohol-based adhesives, polyurethane-based adhesives, acrylic adhesives and the like can be used without limitation.

In another aspect, the present invention relates to an image display device including the polarizing plate of the present invention. In this case, the image display device may be, for example, a liquid crystal display (LCD), a plasma display (PDP), an electroluminescent device (LED), or the like.

Hereinafter, the present invention will be described in more detail with reference to specific examples. The following examples are merely examples to help understanding of the present invention, but the scope of the present invention is not limited thereto.

In the present invention, the physical property evaluation method is as follows.

1. Glass transition temperature (Tg): Measured using a differential scanning calorimeter (DSC) of TA Instrument.

2. Retardation value (Rin, Rth): The film was stretched at the glass transition temperature, and then measured using Axoscan, Axometrics.

3. Coefficient of thermal expansion (ppm / ° C.): The film was biaxially stretched by (stretching ratio substrate), and then measured by TMA, a TA instrument, a linear coefficient of thermal expansion measurement.

4. Yellowness (Yellow Index, ASTM D 1925): The yellowness of the injection specimen with a thickness of 3 mm was measured by a colorimeter.

5. Residual monomer content: 5 g of the sample was dissolved in acetone and then precipitated with methanol and measured by GC / FID (device name EQC-0248).

After mixing 85 weight part of methyl methacrylate monomers, 10 weight part of methacrylic acid monomers, and 5 weight part of benzyl methacrylate monomers with toluene which is a polymerization solvent, after adding a polymerization initiator, antioxidant, and a molecular weight modifier, continuous block polymerization is carried out. Polymerized by the method. Then, the product produced by the polymerization reaction was dried in a drying reactor at the temperature, time and discharge amount shown in the following [Table 1] and [Table 2] to prepare a resin composition. The glass transition temperature, residual monomer content and yellowness of the prepared resin were measured and shown in [Table 1] and [Table 2].

Then, the resin was prepared into an optical film using a T-die extruder, and then the retardation value, thermal expansion coefficient and residual monomer content of the prepared optical film were measured. The measurement results are shown in [Table 1] and [Table 2].

Table 1

		Example 1	Example 2	Example 3	Example 4	Example 5
Drying condition	Drying temperature (℃)	270	270	270	240	240
	Drying time (hr)	2	1.5	One	2	One
	Discharge amount (kg / hr)	3.2	3.8	4.4	3.2	4.4
Resin properties	Tg (℃)	132	132	131	130	130
	YI	4.0	3.4	2.4	2.8	1.4
	Residual Monomer (ppm)	400	550	950	1050	1350
Film properties	Phase difference (Rin / Rth)	0.1 / -2.1	0.3 / -1.8	0.2 / -1.0	0.2 / -1.4	0.6 / -1.0
	Thermal expansion coefficient (ppm / ℃)	60	60	60	60	61
	Residual monomer (ppm)	200	230	330	430	520

TABLE 2

		Example 6	Example 7	Example 8	Example 9	Example 10
Drying condition	Drying temperature (℃)	240	250	260	270	260
	Drying time (hr)	0.5	One	One	0.5	1.5
	Discharge amount (kg / hr)	5.0	4.4	4.4	5	3.8
Resin properties	Tg (℃)	129	130	130	130	130
	YI	0.8	1.7	2.0	1.5	3.1
	Residual Monomer (ppm)	1950	1250	1050	1450	810
Film properties	Phase difference (Rin / Rth)	0.2 / 2.0	0.5 / 1.0	0.3 / -1.1	0.2 / -1.0	0.6 / -1.0
	Thermal expansion coefficient (ppm / ℃)	64	62	60	62	61
	Residual monomer (ppm)	630	500	460	600	520

After mixing 85 weight part of methyl methacrylate monomers, 10 weight part of methacrylic acid monomers, and 5 weight part of benzyl methacrylate monomers with toluene which is a polymerization solvent, after adding a polymerization initiator, antioxidant, and a molecular weight modifier, continuous block polymerization is carried out. Polymerized by the method. Then, the product produced by the polymerization reaction was dried in a drying reactor at the temperature, time and discharge amount shown in the following [Table 3] to prepare a resin composition. The glass transition temperature, residual monomer content and yellowness of the prepared resin were measured and shown in [Table 3].

Then, the resin was prepared into an optical film using a T-die extruder, and then the retardation value, thermal expansion coefficient and residual monomer content of the prepared optical film were measured. The measurement results are shown in [Table 3].

TABLE 3

		Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4	Comparative Example 5	Comparative Example 6
Drying condition	Drying temperature (℃)	270	240	250	270	280	230
	Drying time (hr)	2.5	0.3	3.0	3.0	2.0	0.3
	Discharge amount (kg / hr)	2.3	5.3	5.3	1.6	3.2	5.3
Resin properties	Tg (℃)	130	117	126	118	114	111
	YI	6.4	0.4	4.6	8.0	8.5	1.2
	Residual Monomer (ppm)	2850	3750	3450	4300	8310	7250
Film properties	Phase difference (Rin / Rth)	2.2 / -3.0	2.8 / 4.0	1.4 / -3.4	0.2 / -6.0	0.6 / -8.1	0.4 / 1.4
	Thermal expansion coefficient (ppm / ℃)	69	85	64	65	93	88
	Residual monomer (ppm)	1380	1980	1960	2010	3130	3940

[Table 1] to [Table 3], when the content of the residual monomer in the resin composition exceeds 2000ppm, it can be seen that the characteristics of any one of the heat resistance, yellowness and coefficient of thermal expansion is inferior. In addition, if the drying temperature is less than 240 degrees, or the residence time is short, the content of the residual monomer is high, if the drying temperature exceeds 270 degrees, or the residence time is long, the glass transition temperature, the coefficient of thermal expansion and the yellow index are inferior It can be seen.

Claims

Alkyl (meth) acrylate units;

(Meth) acrylate units containing a benzene ring; And

The resin composition for optical films containing the copolymer containing a (meth) acrylic acid unit, The resin composition for optical films whose residual monomer content in the said resin composition is 2000 ppm or less.
[Revision 25.07.2012 under Rule 26]

The method of claim 1,

The copolymer is a resin composition for an optical film, further comprising a unit represented by the following formula (I).

[Formula I]

In Formula 1, X is N or O,

R 1 and R 2 are each hydrogen, C 1 ~ 10 alkyl, C 3 ~ 20 cycloalkyl or C 3 ~ 20 aryl.
The method of claim 1,

The content ratio of the alkyl (meth) acrylate unit, the (meth) acrylate unit containing the benzene ring and the (meth) acrylic acid unit in the copolymer is 70 to 95: 2 to 10: 3 to 20 by weight ratio. Resin composition.
The method of claim 2,

The content ratio of the alkyl (meth) acrylate unit, the (meth) acrylate unit including the benzene ring, the (meth) acrylic acid unit and the unit represented by the formula (1) in the copolymer is 60 to 90: 2 to 10 by weight ratio. : 3-10: Resin composition for optical films which is 5-20.
The method of claim 1,

The alkyl group of the said alkyl (meth) acrylate has a C1-C10 resin composition for optical films.
The method of claim 5,

Resin composition for optical films whose said alkyl (meth) acrylate unit is methyl methacrylate.
The method of claim 1,

The (meth) acrylate unit containing the benzene ring is benzyl methacrylate, benzyl acrylate, 1-phenylethyl methacrylate, 2-phenoxyethyl methacrylate, 2-phenylethyl methacrylate, 3-phenyl A resin composition for an optical film, which is at least one member selected from the group consisting of propyl methacrylate, 3-phenylpropyl acrylate and 2-phenoxyethyl acrylate.
The method of claim 1,

The (meth) acrylic acid is an optical film resin composition selected from the group consisting of acrylic acid, methacrylic acid, methyl acrylic acid, methyl methacrylic acid, ethyl acrylic acid, ethyl methacrylic acid, butyl acrylic acid and butyl methacrylic acid.
The method of claim 2,

The compound represented by the formula (I) is a resin composition for an optical film, which is glutaric anhydride.
The method of claim 1,

The resin for an optical film has a glass transition temperature of 120 ° C to 500 ° C.
The method of claim 1,

The resin for an optical film has a weight average molecular weight of 10 to 500,000 resin composition for an optical film.
The method of claim 1,

The resin composition for an optical film is a resin composition for an optical film having a yellow index of 4 or less in an injection specimen having a thickness of 3 mm.
The optical film containing the resin composition for optical films of any one of Claims 1-12.
The method of claim 13,

The optical film has an optical direction retardation value of 0 to 5 nm represented by the following Equation 1 at a wavelength of 580 nm, and an optical film having a thickness direction retardation value represented by the following Equation 2 to −5 to 5 nm.

[Equation 1]

R in = (n x -n y ) × d

[Equation 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 13,

The optical film has a linear thermal expansion coefficient of 40 ~ 80ppm / ℃.
The method of claim 13,

An optical film having a content of residual monomer in the optical film of 700 ppm or less.
The method of claim 13,

The optical film has a surface direction retardation value represented by the following Equation 1 at a wavelength 580 nm of 0 to 5 nm, a thickness direction retardation value represented by the following Equation 2 at −5 to 5 nm, and a thermal expansion coefficient of 50 to 65 ppm / ° C. And an amount of residual monomer in the film is 700 ppm or less.

[Equation 1]

R in = (n x -n y ) × d

[Equation 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.
A polarizer and a polarizing plate comprising the optical film of claim 13 as a protective film on at least one surface of the polarizer.
(1) copolymerizing an alkyl (meth) acrylate monomer, a (meth) acrylate monomer comprising a benzene ring and a (meth) acrylic acid monomer; And

(2) A method for producing a resin composition for an optical film, comprising the step of drying the copolymerization reaction product at 240 ° C to 270 ° C for 30 minutes to 2 hours.
The method of claim 19,

The discharge amount in the drying step is a method for producing a resin composition for an optical film of 3kg / hr to 6kg / hr based on a 20 liter pilot reactor.