KR20130135669A - Optical film having improved stability at a high temperature and a polarizing plate comprising the same - Google Patents

Abstract

The present invention relates to an optical film having excellent stability at a high temperature and a polarizing plate including the same and, more specifically, to an acrylic optical film having a moisture ratio of 0.8-2.4 wt% and a thermal expansion coefficient of 10-70 ppm/K at a temperature of 40-90°C and a polarizing plate including the same. The optical film according of the present invention has a moisture ratio and a thermal expansion coefficient of a specific range at a high temperature. Therefore, in case that the optical film of the present invention is used, curl can be mitigated which can be generated during the heating and drying process of the manufacturing process of the polarizing plate. Thus, the optical film can be used in a polarizing plate having excellent curl characteristics and an information electronic device like a display device including the same.

Description

OPTICAL FILM HAVING IMPROVED STABILITY AT A HIGH TEMPERATURE AND A POLARIZING PLATE COMPRISING THE SAME

The present invention relates to an optical film having excellent high temperature stability and a polarizing plate including the same, and more particularly to an optical film having excellent heat resistance and optical properties, and particularly excellent at high temperature and a polarizing plate including 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, polymer films based on acrylic or polycarbonate such as polystyrene, methyl methacrylate, have been proposed. These polymer films have an advantage of excellent heat resistance, but in the case of polystyrene or polycarbonate films, since they have an aromatic ring in the polymer, birefringence occurs during orientation, which adversely affects optical properties, and methyl methacrylate. In the case of the phase difference value is relatively small compared to polystyrene or polycarbonate, but it is not enough to be applied to an optical material such as a liquid crystal device that high precision is required.

In order to be applied as a polarizer protective film, the retardation of the film after film formation and stretching should have a value close to zero. For this purpose, a monomer or polymer having a positive birefringence as a material for a polymer film having excellent heat resistance and a low retardation value, A method of copolymerizing or blending monomers or polymers with negative birefringence has been proposed. Typical examples of these methods include copolymers of benzyl methacrylate and methyl methacrylate.

On the other hand, when manufacturing a polarizing plate by laminating an optical film with a polarizer, an aqueous adhesive is generally used. At this time, if the components of the optical film laminated on one side of the polarizer and the optical film laminated on the other side are different in the process of heating and drying the water of the water-based adhesive, curl may occur due to the difference in dimensional change between them. There is a problem that occurs. For example, when the TAC-based film is laminated on one surface of the polarizer and the acrylic film is laminated on the other surface, curling may occur in the manufacturing process of the polarizing plate due to the difference in the dimensional change thereof, and the dimensional change may cause thermal expansion coefficients of the two films. And the difference in moisture content.

Accordingly, there is a need for an optical film having excellent stability at high temperature and a polarizing plate having reduced curl generation therewith.

The present invention is to solve the above problems, and provides an optical film having excellent optical properties and heat resistance and excellent high temperature stability and a polarizing plate including the same.

According to one aspect of the present invention, there is provided an acrylic optical film having a thermal expansion coefficient of 10 to 70 ppm / K and a moisture content of 0.8 to 2.4 wt% at a temperature of 40 to 90 ° C.

The optical film is an alkyl (meth) acrylate unit; Benzyl (meth) acrylate units; (Meth) acrylic acid units; And a copolymer comprising a unit represented by the following formula (I).

 (I)

In Formula 1, X is NR ₃ or O, wherein R _1, R ₂ and R ₃ are each independently hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl.

It is preferable that the sum of the content of the (meth) acrylic acid unit and the unit represented by the formula (I) per 100 parts by weight of the copolymer is 4 to 25 parts by weight.

The copolymer comprises 55 to 93 parts by weight of alkyl (meth) acrylate units; 2 to 20 parts by weight of benzyl (meth) acrylate units; 1 to 10 parts by weight of (meth) acrylic acid units; And 3 to 15 parts by weight of the unit represented by the formula (I).

The alkyl (meth) acrylate unit is preferably selected from the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate.

It is preferable that the said benzyl (meth) acrylate unit is benzyl methacrylate.

The (meth) acrylic acid unit is preferably selected from the group consisting of acrylic acid, methacrylic acid, methylacrylic acid, methylmethacrylic acid, ethyl acrylic acid, ethyl methacrylic acid, butylacrylic acid and butyl methacrylic acid.

The unit represented by the formula (I) is preferably glutaric anhydride.

It is preferable that the said optical film is a polarizing plate protective film.

According to another aspect of the present invention, an alkyl (meth) acrylate-based unit; Benzyl (meth) acrylate type units; (Meth) acrylic acid units; And preparing an acrylic copolymer comprising a unit represented by Formula I; Extruding the acrylic copolymer resin to prepare a film; And it comprises a step of stretching the film, there is provided a method for producing an acrylic optical film having a thermal expansion coefficient of 10 ~ 70ppm / K and a moisture content of 0.8 ~ 2.4 wt% at a temperature of 40 ~ 90 ℃.

The stretching step is preferably performed 1.5 to 2.7 times in the longitudinal direction (MD), 1.5 to 2.7 times in the lateral direction (TD) biaxial stretching.

The stretching step is preferably performed at a temperature of Tg to Tg + 20 ℃.

According to still another aspect of the present invention, a polarizer; And an acrylic optical film of the present invention attached to at least one surface of the polarizer.

The optical film attached to the other surface of the polarizer may be a TAC (Tri-acetyl-cellulose) optical film.

The optical film according to the present invention has a specific range of coefficient of thermal expansion and moisture at high temperature, and accordingly, when using the optical film of the present invention, curls that may occur in the process of heating and drying during the manufacturing process of the polarizing plate are alleviated and curled. A polarizing plate having excellent characteristics can be obtained and used in various information electronic devices such as a display device including the same.

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

The inventors of the present invention have been studied to develop a resin composition for an optical film having excellent optical properties and heat resistance and excellent high temperature stability, the thermal expansion coefficient of 10 ~ 70ppm / K and 0.8 ~ 2.4 at a temperature of 40 ~ 90 ℃ An acrylic optical film having a moisture content of wt% was prepared.

In the present specification, the temperature of 40 to 90 ℃ is referred to as 'high temperature', such a range of temperature is generally used in the optical film in the process of heating and drying the moisture of the water-based adhesive when manufacturing a polarizing plate using the water-based adhesive Temperature applied.

The optical film of the present invention has a thermal expansion coefficient of 10 ~ 70ppm / K and a moisture content of 0.8 ~ 2.4 wt% at a temperature of 40 ~ 90 ℃, more preferably, the optical film of the present invention 35 at a temperature of 40 ~ 90 ℃ It has a coefficient of thermal expansion of ˜65 ppm / K and a moisture content of 0.8-2.0 wt%.

If the coefficient of thermal expansion is less than 10 ppm / K, there is a problem that the (+) curl of the concave form of the TAC film side of the polarizing plate is severe, if the exceeding 70 ppm / K, the curl direction is switched to concave the acrylic film side There is a problem that the negative (-) curl gets worse. In addition, when the moisture content is less than 0.8 wt%, there is a problem that the (-) curl is severe, and when it exceeds 2.4 wt%, there is a problem that the (+) curl is severe.

In particular, the thermal expansion coefficient is preferably a thermal expansion coefficient in the transverse direction (TD, Transverse Direction). Curls according to the dimensional change in the machine direction (MD) can be improved to some extent by lamination conditions such as the angle and tension when the optical film is laminated to the polarizer, but the curl in the TD direction is difficult to improve. Therefore, improvement through controlling the properties of the optical film is required.

The dimensional change of the optical film at high temperature is greatly influenced by the coefficient of thermal expansion and moisture content among the physical properties of the optical film. In particular, the moisture content of the optical film is determined by the composition of the optical film, the thermal expansion coefficient of the optical film can be further adjusted by the stretching conditions of the optical film, that is, the draw ratio and the stretching temperature in addition to the composition of the optical film.

The optical film of the present invention is an alkyl (meth) acrylate unit; Benzyl (meth) acrylate units; (Meth) acrylic acid units; And it is preferable that it is an acrylic optical film containing the copolymer containing the unit represented by following formula (I).

 (I)

In Formula 1, X is NR ₃ or O,

Wherein R _1, R ₂ and R ₃ are each independently hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl group.

When a four-component resin composition containing an alkyl (meth) acrylate unit, a benzyl (meth) acrylate unit, a (meth) acrylic acid unit, and the unit represented by the formula (I) is used, the retardation value is small and the glass transition temperature is only high. In addition, an excellent optical film having a low coefficient of thermal expansion can be produced.

In particular, the sum of the content of the (meth) acrylic acid unit and the unit represented by the formula (I) per 100 parts by weight of the copolymer is preferably 4 to 24 parts by weight, and the sum is less than 4 parts by weight per 100 parts by weight of the copolymer. In this case, there is a problem that the coefficient of thermal expansion is increased and out of the allowable range, and if it exceeds 24 parts by weight, the transparency of the film is lowered, and the film is easily broken, and thus it is difficult to apply to the polarizing plate.

In the resin composition of the present invention, the alkyl (meth) acrylate unit 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 the said 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.

More specifically, the alkyl (meth) acrylate unit is preferably selected from the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate. .

On the other hand, the content of the alkyl (meth) acrylate unit is preferably about 55 to 94 parts by weight, more preferably 60 to 90 parts by weight, most preferably 70 to 90 with respect to 100 parts by weight of the total resin composition. It may be part by weight. This is because excellent retardation characteristics and optical characteristics can be obtained when the content of the alkyl (meth) acrylate units is in the above range.

In the resin composition of the present invention, the benzyl (meth) acrylate unit is to impart a suitable phase difference value to the optical film of the present invention and to impart compatibility between alkyl (meth) acrylate and (meth) acrylic acid. , Benzyl methacrylate or benzyl acrylate, especially benzyl methacrylate.

Meanwhile, the content of the benzyl (meth) acrylate unit may be about 2 to 20 parts by weight, and more preferably 2 to 18 parts by weight based on 100 parts by weight of the total resin composition. This is because the desired retardation characteristics can be obtained when the content of benzyl (meth) acrylate is within the above range.

On the other hand, in the resin composition of the present invention, the (meth) acrylic acid unit serves to improve the heat resistance and to lower the coefficient of thermal expansion by introducing a polar group, for example, acrylic acid, methacrylic acid, methylacrylic acid, methyl meta It may be methacrylic acid, ethylacrylic acid, ethyl methacrylic acid, butylacrylic acid or butyl methacrylic acid, with methacrylic acid being particularly preferred.

On the other hand, the content of the (meth) acrylic acid unit is preferably about 1 to 10 parts by weight, more preferably 1 to 5 parts by weight, even more preferably 1 to 3 parts by weight based on 100 parts by weight of the total resin composition. Parts, most preferably 1 to 2 parts by weight. This is because when the content of the (meth) acrylic acid unit is in the above range, desirable heat resistance characteristics can be obtained. In particular, when the content of (meth) acrylic acid is 2 parts by weight or less, there is an additional advantage that can significantly reduce the generation of bubbles in the film forming process.

In addition, the resin composition of the present invention includes a unit represented by the following formula (1).

(I)

In Formula 1, X is NR ₃ or O, wherein R _1, R ₂ and R ₃ are each independently hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl group.

The unit represented by Formula 1 serves to lower the coefficient of thermal expansion of the resin composition. When a bulky functional group that inhibits polymer chain rotation 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, when using the compound represented by the formula (1) as in the present invention, it is possible to effectively lower the coefficient of thermal expansion without adversely affecting the optical properties.

Specific examples of the unit represented by the formula (1) include glutaric anhydride, glutaric acid imide, and the like, and glutaric anhydride is particularly preferable. On the other hand, the content of the unit represented by the formula (1) is preferably about 3 to 15 parts by weight based on 100 parts by weight of the total resin composition. When the content of the unit represented by the formula (1) is within the above range, it is possible to implement a low coefficient of thermal expansion without compromising the retardation characteristics.

In the optical film of the present invention including the above components, the glass transition temperature is preferably about 120 ° C to 500 ° C, more preferably 125 ° C to 500 ° C, and most preferably 125 ° C to 200 ° C. In addition, in terms of processability, heat resistance and productivity, the weight average molecular weight is preferably 50,000 to 500,000, more preferably about 50,000 to 200,000. In addition, the yellow index value is preferably about 0.3 to 2.0. If the value is out of the above, the display color may change.

It is preferable that the said optical film is a polarizing plate protective film. Since the optical film of this invention has a low thermal expansion coefficient compared with the conventional acryl-type film, and since the thermal expansion coefficient is low in this way, curling can be suppressed when the optical film of this invention is applied to a polarizing plate.

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.

According to another aspect of the present invention, an alkyl (meth) acrylate-based unit; Benzyl (meth) acrylate type units; (Meth) acrylic acid units; And preparing an acrylic copolymer comprising a unit represented by Formula I:

 (I)

(In Formula 1, X is NR ₃ or O, wherein R _1, R ₂ and R ₃ are each independently hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl);

Extruding the acrylic copolymer resin to prepare a film; And it comprises a step of stretching the film, there is provided a method for producing an acrylic optical film having a thermal expansion coefficient of 10 ~ 70ppm / K and a moisture content of 0.8 ~ 2.4 wt% at a temperature of 40 ~ 90 ℃.

Components of the optical film is as described above, the step of preparing the acrylic copolymer may be prepared according to a copolymer production method well known in the art. For example, the monomer of each component of the present invention may be mixed and then prepared by solution polymerization, bulk polymerization, suspension polymerization or emulsion polymerization.

On the other hand, when the component of the formula (1) of the optical film of the present invention is glutaric anhydride, without addition of the component of the formula (1), of the alkyl (meth) acrylate, (meth) acrylic acid and benzyl (meth) acrylate The resin composition of this invention can also be manufactured by the method of bulk-polymerizing three components, or carrying out suspension polymerization and heat-processing. In this case, the alkyl (meth) acrylate and / or benzyl (meth) acrylate and (meth) acrylic acid are hydrolyzed by heat to form glutaric anhydride while forming a quaternary copolymer.

Extrusion of the acrylic copolymer resin to prepare a film may be prepared in the form of a film according to an extrusion method well known in the art resin composition comprising the copolymer. 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.

When the optical film is manufactured by the above step, the film is subsequently stretched, and the biaxial stretching is performed by 1.5 to 2.7 times in the longitudinal direction (MD) and 1.5 to 2.7 times in the transverse direction (TD). It is preferable. When the longitudinal or transverse stretching is less than 1.5 times, there is a problem that the longitudinal or transverse coefficient of thermal expansion of the film exceeds the allowable value, and when the longitudinal or transverse stretching exceeds 2.7 times, stable film production may occur due to the breakage of the film during the stretching process. There is an impossible problem.

However, the stretching step may be performed in the longitudinal direction (MD) stretching, transverse direction (TD) stretching, or both may be performed. 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 rolls can be performed, and in the case of transverse stretching, tenter can be used. The time of railing of the tenter is usually within 10 degrees, thereby suppressing the bowing phenomenon occurring in the transverse direction drawing and controlling 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 is preferably performed at a temperature of Tg to Tg + 20 ℃ when the glass transition temperature of the resin composition for producing the optical film is Tg. When the temperature is less than Tg, there is a problem in that stable production is not possible due to frequent breakage of the film, and when the temperature is greater than Tg + 20 ° C., the thermal expansion coefficient of the film exceeds the allowable value. The glass transition temperature of the resin composition can be measured by a differential scanning calorimeter (DSC).

The stretching speed is preferably in the range of 1 to 100 min / min for a universal testing machine (Zwick Z010) and within the range of 0.1 to 2 m / min for a pilot stretching machine. Do.

Through the stretching process as described above it is possible to adjust the thermal expansion coefficient and phase difference characteristics of the optical film.

On the other hand, the optical film of the present invention prepared by the above method has a plane direction phase value (R _in ) of 0 to 10nm, thickness direction phase difference value (R _th ) of about -5 to 10nm at a wavelength of 580nm. Here, the plane 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 ) x d

&Quot; (2) "

R _th = (n _z -n _y ) x 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 a refractive index, n _z is a refractive index of a thickness direction, and d is a thickness of a film.

In another aspect, the present invention relates to a polarizer comprising a polarizer and an acrylic optical film according to the present invention provided as a protective film on at least one surface of the polarizer.

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, a tri-acetyl-cellulose (TAC) film, PET film, COP film, PC A film, a norbornene-based film, and the like may be provided, and among these, in consideration of economics and the like, a TAC film is particularly preferable. 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. As the adhesive, adhesives used in the related art, for example, a polyvinyl alcohol adhesive, a polyurethane adhesive, an acrylic adhesive and the like may be used without limitation.

The polarizing plate of the present invention prepared as described above preferably has an inner curl and an outer curl of -25 to 25 mm on the basis of the size of 200 × 200 mm. The curl is divided into the outer curl and the inner curl as described above, the outer curl means the curl in the finished state of the polarizing plate consisting of a laminate of a protective film, a polarizing plate, pressure-sensitive adhesive, release film, the inner curl is a state in which the release film is removed from the finished polarizing plate It means the curl measured by.

In general, the outer curl can be relatively easily improved by adjusting the tension, lamination angle, etc. when laminating the adhesive / release film and the protective film on the polarizing plate, but in the case of the inner curl, the adjustment is not easy. Therefore, in the present patent, after the outer curl was made to almost zero through lamination condition adjustment, the release film was removed to measure the inner curl.

The current allowable curl level is ± 15mm based on the 32-inch size for TV, but experimental results of the curl according to the size of the specimens indicate that it is required to satisfy ± 25mm based on the 200 × 200mm size. This is because the smaller the size of the specimen, the less curl reduction caused by the weight of the specimen itself. On the other hand, when the outer curl is less than -25 mm and more than 25 mm, when attaching the polarizing plate and the liquid crystal panel using an adhesive, there is a problem in that external air flows into the polarizing plate curl part to deteriorate the appearance quality of the liquid crystal panel.

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 more specifically by way of specific examples. The following examples are given for the purpose of helping to understand 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. Resin composition: measured using C13-NMR.

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

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

4. Phase difference: It measured using Elli-SE by Ellipso Tech.

5. Haze: It measured according to ASTM1003 method.

6. Coefficient of thermal expansion (CTE): measured using Pyris 6 DCS of Perkin Elmer.

7. Moisture content: Measure the initial weight (W1) after storing the film specimen cut into 100 × 100mm at 24 ℃ and 50% RH for 3 days or more and drying the film in 80 ℃ hot air drying oven for 3 days. After measuring (W2), it was calculated using the following formula.

Moisture Content (%) = (W1-W2) / W1 × 100

8. Polarizer curl amount: Store the polarizer specimen cut to 200 × 200mm size on a horizontal table at 24 ° C and 50% RH with the concave side facing up for 1 hour and store the four corners of the specimen. The height heard from the height was measured using a ruler and the maximum value was defined as the amount of curl. At this time, the case where the protective film side was concave was defined as (+) curl, on the contrary, when the release film side was concave as (-) curl.

Example 1

87 weight part of methyl methacrylate monomer, 8 weight part of benzyl methacrylate monomer, and 5 weight part of methacrylic acid monomer are mixed with toluene which is a polymerization solvent, and 0.03 weight part of dicumyl peroxide which is an initiator with respect to 100 weight part of this mixed solution. , 0.5 parts by weight of t-dodecyl mercaptan as a molecular weight regulator, 0.2 parts by weight of Irganox 245 as an antioxidant to prepare a polymerization solution.

The polymerization solution was polymerized at 145 ° C. for 2 hours by continuous bulk polymerization, followed by devolatilization of unreacted monomers and solvents in a volatilization tank at 250 ° C. and a vacuum of 20 torr, followed by methyl methacrylate unit, benzyl methacrylate unit, and methacrylic acid. A resin comprising a unit and a glutaric anhydride unit was prepared in a pellet state. The weight average molecular weight and glass transition temperature of the prepared resin were measured, and the results are shown in Table 1.

The resin was prepared using a T-die extruder to produce a film having a thickness of 185 μm, and then biaxially stretched at a ratio of 1.9 times the MD and TD directions at a temperature of 10 ° C. higher than the glass transition temperature of the resin. An optical film was prepared. The retardation value, haze, thermal expansion coefficient and moisture content of the prepared film were measured, and the results are shown in Table 1.

Using the optical film of the present invention prepared above was prepared a polarizing plate as follows. First, the acrylic film is placed on one side of a 25 μm thick PVA polarizer, and a 60 μm thick TAC film (Fuji, UZ TAC) is placed on the other side, and a modified PVA water-based adhesive is injected therebetween, using a compression roll. After pressing, hot air was dried at a temperature of 80 ° C. for 5 minutes to prepare a semi-polarizing plate. After the corona treatment was performed on the acrylic film surface of the manufactured semi-finished polarizing plate under the condition of 50 W / m ² · min, a polyester film having a release layer coated with a 20 μm thick adhesive was laminated using a roll laminator, On the other side of the TAC film surface, a polyester-based protective film having an adhesive layer was laminated to prepare a finished polarizing plate. The curl characteristics of the polarizers thus prepared were compared, and the results are shown in Table 1.

Example 2

A resin, a film, and a polarizing plate were manufactured in the same manner as in Example 1, except that 82 parts by weight of methyl methacrylate monomer, 8 parts by weight of benzyl methacrylate monomer, and 10 parts by weight of methacrylic acid monomer were used. Their main physical properties were measured and the results are shown in Table 1.

Example 3

A resin, a film, and a polarizing plate were manufactured in the same manner as in Example 1, except that 74 parts by weight of methyl methacrylate monomer, 8 parts by weight of benzyl methacrylate monomer, and 18 parts by weight of methacrylic acid monomer were used. Their main physical properties were measured and the results are shown in Table 1.

Example 4

A resin, a film, and a polarizing plate were prepared in the same manner as in Example 2 except that the film thickness before the stretching was 150 μm and the stretching ratio was 1.7 times. Their main physical properties were measured and the results are shown in Table 1.

Example 5

A resin, a film, and a polarizing plate were prepared in the same manner as in Example 2 except that the film thickness before stretching was 225 μm and the draw ratio was 2.1 times. Their main physical properties were measured and the results are shown in Table 1.

Example 6

A resin, a film, and a polarizing plate were manufactured in the same manner as in Example 2, except that the resin was stretched at a temperature higher than the glass transition temperature of the resin by 5 ° C. Their main physical properties were measured and the results are shown in Table 2.

Example 7

A resin, a film, and a polarizing plate were manufactured in the same manner as in Example 2, except that the resin was stretched at a temperature higher than the glass transition temperature of the resin by 15 ° C. Their main physical properties were measured and the results are shown in Table 2.

Example 8

A resin, a film, and a polarizing plate were prepared in the same manner as in Example 7, except that the film before stretching was 295 μm and the draw ratio was 2.5 times. Their main physical properties were measured and the results are shown in Table 2.

division Example 1 Example 2 Example 3 Example 4 Example 5 Copolymer polymerization solution MMA 87 82 74 82 82 BzMA 8 8 8 8 8 MAA 5 10 18 10 10 Final copolymer components MMA 87.3 82.2 74.1 82.2 82.2 BzMA 8.2 8.1 8.1 8.1 8.1 MAA 1.4 2.0 3.6 2.0 2.0 G / A 4.1 7.7 14.2 7.7 7.7 Resin properties Weight average molecular weight (Mw * 10 ⁴ ) 12.3 11.9 8.3 11.9 11.9 Tg (占 폚) 121 124 136 124 124 Extruded Film Thickness (㎛) 185 185 185 150 225 Drawing condition Stretching temperature (占 폚) Tg + 10 Tg + 10 Tg + 10 Tg + 10 Tg + 10 Stretch ratio (fold), (TD / MD) 1.9 / 1.9 1.9 / 1.9 1.9 / 1.9 1.7 / 1.7 2.1 / 2.1 Stretched Film Properties Thickness (㎛) 50 50 51 49 50 Rin / Rth 1.4 / -1.3 2.3 / -1.6 3.1 / -2.5 1.8 / -0.9 2.9 / -2.1 Haze (%) 0.2 0.2 0.4 0.2 0.2 Coefficient of thermal expansion (ppm / K) 63 59 53 64 55 Moisture content (wt%) 0.83 1.07 1.27 1.10 1.04 Polarizer Properties Outer curl (mm) 0 0 0 0 0 Inner curl (mm) -21 -12 -3 -18 -10

BzMA: benzyl methacrylate

MMA: methyl methacrylate

MAA: methacrylic acid

G / A: glutaric anhydride

division Example 6 Example 7 Example 8 Copolymer polymerization solution MMA 82 82 82 BzMA 8 8 8 MAA 10 10 10 Final copolymer components MMA 82.2 82.2 82.2 BzMA 8.1 8.1 8.1 MAA 2.0 2.0 2.0 G / A 7.7 7.7 7.7 Resin properties Weight average molecular weight (Mw * 10 ⁴ ) 11.9 11.9 11.9 Tg (占 폚) 124 124 124 Extruded Film Thickness (㎛) 185 185 295 Drawing condition Stretching temperature (占 폚) Tg + 5 Tg + 15 Tg + 15 Stretching ratio (fold),
(TD / MD) 1.9 / 1.9 1.9 / 1.9 2.5 / 2.5 Stretched Film Properties Thickness (㎛) 48 53 50 Rin / Rth 2.5 / -1.8 1.7 / -1.0 2.7 / -2.1 Haze (%) 0.2 0.2 0.2 Coefficient of thermal expansion (ppm / K) 54 65 49 Moisture content (wt%) 1.02 1.07 0.98 Polarizer Properties Outer curl (mm) 0 0 0 Inner curl (mm) -11 -16 -7

BzMA: benzyl methacrylate

MMA: methyl methacrylate

MAA: methacrylic acid

G / A: glutaric anhydride

Comparative Example 1

A resin, a film, and a polarizing plate were each prepared in the same manner as in Example 1 except that 92 parts by weight of methyl methacrylate monomer and 8 parts by weight of benzyl methacrylate monomer were used. Their main physical properties were measured and the results are shown in Table 3.

Comparative Example 2

A resin, a film, and a polarizing plate were each prepared in the same manner as in Example 1 except that 67 parts by weight of methyl methacrylate monomer, 8 parts by weight of benzyl methacrylate monomer, and 25 parts by weight of methacrylic acid monomer were used. Their main physical properties were measured and the results are shown in Table 3.

Comparative Example 3

A resin, a film, and a polarizing plate were prepared in the same manner as in Cell Se Example 2, except that the resin was stretched at a temperature higher than 25 ° C. above the resin glass transition temperature. Their main physical properties were measured and the results are shown in Table 3.

Comparative Example 4

Resin, film, and polarizing plate were each prepared in the same manner as in Example 6 except that the film before stretching was 115 μm and the draw ratio was 1.4 times. Their main physical properties were measured and the results are shown in Table 3.

division Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Copolymer polymerization solution MMA 92 67 82 82 BzMA 8 8 8 8 MAA 0 25 10 10 Final copolymer components MMA 91.9 67.3 82.2 82.2 BzMA 8.1 7.8 8.1 8.1 MAA 0 5.6 2.0 2.0 G / A 0 19.2 7.7 7.7 Resin properties Weight average molecular weight (Mw * 10 ⁴ ) 124 67 11.9 11.9 Tg (占 폚) 104 139 124 124 Extruded Film Thickness (㎛) 185 185 185 115 Drawing condition Stretching temperature (占 폚) Tg + 10 Tg + 10 Tg + 25 Tg + 5 Stretching ratio (fold),
(TD / MD) 1.9 / 1.9 1.9 / 1.9 1.9 / 1.9 1.4 / 1.4 Stretched Film Properties Thickness (㎛) 50 50 58 49 Rin / Rth 1.0 / 1.6 5.9 / -7.3 0.9 / -0.5 1.3 / -1.0 Haze (%) 0.2 3.3 0.2 0.2 Coefficient of thermal expansion (ppm / K) 83 45 86 72 Moisture content (wt%) 0.74 1.34 1.12 1.06 Polarizer Properties Outer curl (mm) -2 0 -One -One Inner curl (mm) -37 0 -29 -25

BzMA: benzyl methacrylate

MMA: methyl methacrylate

MAA: methacrylic acid

G / A: glutaric anhydride

Claims (16)

An acrylic optical film having a thermal expansion coefficient of 10 to 70 ppm / K and a water content of 0.8 to 2.4 wt% at a temperature of 40 to 90 ° C.
The method of claim 1, wherein the optical film is an alkyl (meth) acrylate unit; Benzyl (meth) acrylate units; (Meth) acrylic acid units; And an acrylic optical film comprising a copolymer comprising a unit represented by the formula (I):
(I)

In Formula 1, X is NR ₃ or O,
Wherein R _1, R ₂ and R ₃ are each independently hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl.
The acrylic optical film according to claim 2, wherein the sum of the content of the (meth) acrylic acid unit and the unit represented by the formula (I) per 100 parts by weight of the copolymer is 4 to 24 parts by weight.
The method of claim 2, wherein the copolymer
55 to 93 parts by weight of alkyl (meth) acrylate units;
2 to 20 parts by weight of benzyl (meth) acrylate units;
1 to 10 parts by weight of (meth) acrylic acid units; And
Acrylic optical film containing 3 to 15 parts by weight of the unit represented by the formula (I).
The method of claim 2, wherein the alkyl (meth) acrylate unit is selected from the group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate Optical film.
The acrylic optical film of claim 2, wherein the benzyl (meth) acrylate unit is benzyl methacrylate.
The acrylic optical system of claim 2, wherein the (meth) acrylic acid unit is selected from the group consisting of acrylic acid, methacrylic acid, methylacrylic acid, methylmethacrylic acid, ethylacrylic acid, ethylmethacrylic acid, butylacrylic acid and butyl methacrylic acid. film.
The acrylic optical film of claim 2, wherein the unit represented by Chemical Formula I is glutaric anhydride.
The acrylic optical film of claim 1, wherein the optical film is a polarizing plate protective film.
Alkyl (meth) acrylate-based units; Benzyl (meth) acrylate type units; (Meth) acrylic acid units; And preparing an acrylic copolymer comprising a unit represented by the following formula (I):
(I)

(In Formula 1, X is NR ₃ or O,
Wherein R _1, R ₂ and R ₃ are each independently hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl);
Extruding the acrylic copolymer resin to prepare a film; And
Stretching the film;
A method for producing an acrylic optical film having a thermal expansion coefficient of 10 to 70 ppm / K and a water content of 0.8 to 2.4 wt% at a temperature of 40 to 90 ° C.
The method for producing an acrylic optical film according to claim 10, wherein the sum of the content of the (meth) acrylic acid and the unit represented by the formula (I) per 100 parts by weight of the copolymer is 4 to 24 parts by weight.
The method of claim 10, wherein the copolymer
55 to 93 parts by weight of alkyl (meth) acrylate units;
2 to 20 parts by weight of benzyl (meth) acrylate units;
1 to 10 parts by weight of (meth) acrylic acid units; And
A method for producing an acrylic optical film comprising 3 to 15 parts by weight of the unit represented by the formula (I).
The method of claim 10, wherein the stretching is performed 1.5 to 2.7 times in the longitudinal direction (MD) and 1.5 to 2.7 times in the lateral direction (TD).
The method of claim 10, wherein the stretching is performed at a glass transition temperature (Tg) to a glass transition temperature (Tg) + 20 ° C. 12.
A polarizer; And
A polarizing plate comprising the acrylic optical film of any one of claims 1 to 9 attached to at least one surface of the polarizer.
The polarizing plate of claim 15, wherein the optical film attached to the other surface of the polarizer is a TAC (Tri-acetyl-cellulose) optical film.