KR101042477B1 - A transparent composition with high heat resistance and an optical isotropic film prepared by the same - Google Patents

Abstract

Disclosed is an optical isotropic film excellent in transparency and heat resistance. The optically isotropic film according to the present invention is made of a transparent resin composition comprising a polymethyl (meth) acrylate polymer, a styrene-maleic anhydride copolymer and a rubber. This optically isotropic film is used as a protective film of the polarizer. According to the present invention, an optically isotropic film excellent in transparency and heat resistance can be manufactured at low cost, and in particular, the optically isotropic film according to the present invention is excellent in heat resistance and transparency and can be protected without degrading the optical properties of the polarizer. This can be suitably used for the liquid crystal display device of various modes.

Isotropic, polymethyl (meth) acrylate, styrene-maleic anhydride copolymer, transparency, heat resistance, rubber, protective film, liquid crystal display

Description

Transparent resin composition excellent in heat resistance and an optically isotropic film manufactured by the same {A TRANSPARENT COMPOSITION WITH HIGH HEAT RESISTANCE AND AN OPTICAL ISOTROPIC FILM PREPARED BY THE SAME}

1 is a cross-sectional view of one embodiment of a conventional polarizing plate including an optically isotropic film as a protective film of a polarizer.

2 is a cross-sectional view of one embodiment of a conventional liquid crystal display device structure.

* Explanation of code for main part of drawing

1: release protective film 2: adhesive layer

3: wide viewing angle retardation film 4: polarizer protective film

5: polarizer (PVA film) 6: polarizer protective film

7: protective film for polarizing film 10: liquid crystal

12: molecular alignment film 14: transparent electrode

16: glass substrate 18: polarizing plate

The present invention relates to an optically isotropic film having excellent transparency and heat resistance, and more particularly, to an optically isotropic film made of a transparent resin composition comprising a polymethyl (meth) acrylate polymer, a styrene-maleic anhydride copolymer, and rubber. And it relates to a polarizing plate and a liquid crystal display device comprising the same.

BACKGROUND ART Liquid crystal displays have a lower power consumption, smaller volume, and lighter weight than portable cathode ray tube displays. In general, the liquid crystal display has a basic configuration in which polarizers are provided on both sides of the liquid crystal cell, and the orientation of the liquid crystal cell is changed depending on whether an electric field is applied to the driving circuit, thereby changing the characteristics of the transmitted light emitted through the polarizer. Visualization takes place.

Generally, as shown in FIG. 1, the polarizing plate 8 consists of several components, The polarizer protective films 4 and 6 which become its protective film are attached to both surfaces of the polarizer 5 via an adhesive agent first. . The polarizing film protective film 7 is attached to one side of the polarizing film 4 + 5 + 6 through an adhesive, and the other side of the polarizing film 4 + 5 + 6 is bonded to the wide viewing angle retardation film 3 and the adhesive layer 2 thereon. Through the release protective film 1 is attached.

As the polarizer 5, an iodine or a dichroic dye is adsorbed onto a hydrophilic polymer such as polyvinyl alcohol (PVA) and stretched aligned. Polarizer protective films 4 and 6 are used to increase the durability and mechanical properties of the polarizer 5, and it is important for the protective film to maintain optical characteristics such as polarization characteristics of the polarizer. Therefore, the polarizer protective film requires optical transparency and isotropy, and the heat resistance and adhesion to the adhesive / adhesive act as an important factor.

Currently, a triacetyl cellulose (TAC) film is mainly used as a polarizer protective film, and a cyclic olefin polymer having excellent heat resistance and moisture resistance is applied to some products. As for the wide viewing angle retardation film 3, in order to ensure clear image quality and a wide wide viewing angle in a liquid crystal display, the stretched film which has optical transparency and anisotropy, the film orientated by liquid crystal coating, etc. are mainly used.

The polarizer, the polarizer protective film, the release protective film, the wide viewing angle retardation film, etc. in the polarizing plate are attached to each other with an adhesive or a pressure-sensitive adhesive, the adhesive force between each component film acts as an important factor for the optical properties and durability of the polarizing plate.

As the polarizer protective film, a cellulose-based film such as triacetyl cellulose, a polyester-based film, a polyacrylate-based film, a polycarbonate-based film, a cyclic olefin-based film, a norbornene-based film, etc. may be applied based on the required characteristics. In particular, triacetyl cellulose-based film is most widely used.

However, the triacetyl cellulose-based film is small in-plane retardation value, but the retardation value in the thickness direction is relatively large, there is a problem that the retardation value due to the action of the external stress is expressed. In particular, the triacetyl cellulose-based film has a large hydrophilic functional group in the molecular chain structure, so that the moisture permeability is increased, which results in deformation of the protective film under heat / humidity conditions or dissociation of iodine ions in the polarizer, thereby improving polarization performance of the polarizer. There is a problem of deterioration. In particular, during the high temperature and high humidity test of the liquid crystal display device, deformation of the triacetyl cellulose film causes uneven optical anisotropy in the film, and as a result, problems such as light leakage occur.

In order to solve this problem, Japanese Laid-Open Patent Publication No. 2001-343528 discloses a technique for controlling moisture permeability by adding a hydrophobic plasticizer to a triacetyl cellulose film, and Japanese Laid-Open Patent Publication No. 2004-93906 reduces the moisture permeability. A method of installing a barrier layer is presented. However, the method has a limitation in effectively controlling moisture permeability, and in particular, when a film having a barrier layer is applied as a polarizer protective film, there is a problem in that adhesion with the polarizer is difficult in a conventional polarizing plate processing process.

On the other hand, Japanese Patent Application Laid-Open No. 2001-324616 discloses a technique of applying a cyclic olefin-based film having excellent moisture and heat resistance as a polarizer protective film. There is a disadvantage in that the productivity is difficult to dry. Therefore, in order to use as a polarizer protective film, the water vapor transmission rate is higher than that of the cyclic olefin film and lower than the triacetyl cellulose film material can be said. In addition, the above materials have a problem that the price is also expensive, there is a need for a transparent film of a low-cost material having optical isotropy and excellent moisture and heat resistance.

As a material excellent in transparency and optical isotropy, acrylic resins such as polymethyl (meth) acrylate are also known. However, acrylic resins are susceptible to external shock, and are brittle and have low heat resistance, thereby deteriorating polarization performance of the polarizer under high temperature and high humidity conditions.

In order to solve the above problem, Japanese Laid-Open Patent Publication No. 2006-284882 adds a soft acrylic resin and an acrylic rubber to an acrylic resin to increase the flexibility of the acrylic film, thereby manufacturing a polarizer protective film. However, the polarizer protective film prepared by the above composition still exhibits low heat resistance (glass transition temperature = 113 ° C.), thereby deteriorating the durability of the polarizing plate.

On the other hand, Japanese Laid-Open Patent Publication No. 2006-337493 introduced a maleimide-based comonomer to an acrylic resin to improve the heat resistance of the acrylic resin, from which a high heat-resistant transparent film having a glass transition temperature of 120 ° C. or higher could be produced. However, the film is difficult to apply as a polarizer protective film due to the low flexibility and impact resistance of the acrylic resin.

The present invention is to solve the problems of the prior art as described above. Accordingly, it is an object of the present invention to provide a transparent resin composition having low manufacturing cost and excellent heat resistance and optical isotropy.

It is also an object of the present invention to provide an optically isotropic film produced by the resin composition, having excellent transparency, heat resistance and optical isotropy to the extent that can be used as a protective film of the polarizer.

It is also an object of the present invention to provide a polarizing plate comprising the optically isotropic film formed on the polarizer and the polarizer as its protective film.

Another object of the present invention is to provide a liquid crystal display device including the polarizing plate.

The present invention provides a styrene-maleic anhydride-based copolymer and a rubber comprising a polymethyl (meth) acrylate polymer, a styrene compound repeating unit and a maleic anhydride or imidized maleic anhydride repeating unit. It provides a resin composition comprising.

In addition, the present invention provides an optically isotropic film produced by the resin composition, excellent in properties such as heat resistance, transparency and optical isotropy, a polarizing plate including such an optical isotropic film, and a liquid crystal display device including the polarizing plate.

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

The polymethyl (meth) acrylate polymers referred to herein are polymerized with only methyl (meth) acrylate monomers, as well as methyl (meth) acrylate monomers and methyls, unless otherwise noted, as described in detail below. It is to be understood that the copolymer includes a copolymer of a (meth) acrylate monomer and a polymerizable unsaturated monomer.

As used herein, the styrene-maleic acid anhydride copolymer refers to a copolymer formed by copolymerization of a styrene compound monomer and a maleic anhydride compound or an imidized maleic anhydride compound monomer, wherein styrene It is to be understood that the system compound includes not only styrene but also substituted styrene compounds, and the maleic anhydride compound includes not only maleic anhydride but also a substituted maleic anhydride compound, which is further applied to the imidized maleic anhydride compound. The same applies to.

The resin composition according to the present invention comprises 10 to 95% by weight of polymethyl (meth) acrylate polymer, preferably 50 to 80% by weight, styrene compound repeating unit and maleic anhydride or imidized maleic anhydride compound repeating unit. 4 to 60% by weight of styrene-maleic anhydride copolymer, preferably 17 to 35% by weight and 1 to 30% by weight of rubber as the impact modifier, preferably 3 to 15% by weight. By such a resin composition, the optically isotropic film of this invention is manufactured.

When the content of the styrene-maleic anhydride-based copolymer exceeds 60% by weight and thus the content of the polymethyl (meth) acrylate polymer and the impact modifier is less than 40% by weight, the optical isotropy of the transparent film is inhibited. If the content of the polymethyl (meth) acrylate polymer is more than 95% by weight and thus the content of styrene-maleic anhydride-based copolymer and impact modifier is less than 5% by weight, the heat resistance and impact strength of the transparent film There is a disadvantage that is lowered. In particular, rubber, an impact reinforcing material, is an important factor controlling transparency, impact resistance, and optical isotropy of the optically isotropic film. If the rubber content is less than 1% by weight, the optical film may exhibit birefringence (anisotropy) and sufficient resistance. It is difficult to obtain impact properties, and when the rubber content is 30% by weight or more, there is a problem that the transparency of the optical film is lowered.

In the resin composition for optically isotropic film production of the present invention, the polymethyl (meth) acrylate polymer may be a polymer obtained by polymerizing (meth) acrylic acid methyl ester alone, or (meth) acrylic acid The copolymer which copolymerized methyl ester and the unsaturated monomer copolymerizable with this may be sufficient. In addition, when the polymethyl (meth) acrylate polymer is a copolymer, it is preferable to include (meth) acrylic acid methyl ester at least 50% by weight, preferably 50 to 90% by weight, in view of transparency and heat resistance of the optically isotropic film. . Moreover, as said polymethyl (meth) acrylate polymer, the polymethyl methacrylate polymer formed by superposing | polymerizing only with the methyl methacrylate monomer is more preferable.

In the above, the unsaturated monomer copolymerizable with the (meth) acrylic acid methyl ester is, for example, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate. (phenyl methacrylate), benzyl methacrylate, 2-ethylhexyl methacrylate or 2-hydroxyethyl methacrylate, or substituted with a hydroxy group; unsubstituted alicyclic or aliphatic C _{1 -12} alkyl methacrylate or C _{6 -12} aryl methacrylate; Methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate (2-ethylhexyl acrylate) or 2-hydroxyethyl acrylate (2-hydroxyethyl acrylate), such as, hydroxyl group substituted or unsubstituted alicyclic or aliphatic C _{1 -12} alkyl acrylate or C _6-12 aryl acrylates; Such as for example styrene or α- methylstyrene, C _{1 -4} alkyl or halogen-substituted styrene or unsubstituted styrene compounds such as; Acrylonitrile; And for example, such as cyclohexyl maleimide (cyclohexyl maleimide) or phenylmaleimide (phenyl maleimide), consisting of maleimide compounds, such as substituted or unsubstituted alicyclic or aliphatic C _{1 -12} alkyl or C _{6 -12} aryl-maleimide It is preferable that it is at least 1 type selected from the group.

In the resin composition for producing an optically isotropic film of the present invention, the styrene-maleic anhydride copolymer is used to compensate for the insufficient heat resistance of the polymethyl (meth) acrylate polymer, and is a styrene monomer and a maleic anhydride monomer or already. It may be prepared by copolymerizing imidized maleic anhydride monomer.

The styrene-based monomers include C _{1 -4} alkyl, or substituted with halogen or may be a unsubstituted styrene compounds, and more preferably styrene, α- methylstyrene (α-methyl styrene), bromostyrene p- (p -bromo styrene), p-methyl styrene (r-methyl styrene), and one or more selected from the group consisting of p-chloro styrene (p-chloro styrene) can be used.

The styrene-maleic anhydride copolymer is preferably prepared by copolymerizing 50 to 96 wt% of a styrene monomer and 4 to 50 wt% of a maleic anhydride monomer or an imidized maleic anhydride monomer, preferably a styrene monomer 70 To 90% by weight and 10 to 30% by weight of maleic anhydride monomer or imidated maleic anhydride monomer are prepared by copolymerizing. When the amount of the maleic anhydride monomer or the imidated maleic anhydride monomer used in the production of the styrene-maleic anhydride-based copolymer is less than 4% by weight, the heat resistance of the optically isotropic film may be insufficient, and it is more than 50% by weight. In this case, there is a problem that the impact strength of the optically isotropic film is lowered.

In the resin composition for optically isotropic film production of the present invention, the impact modifier rubber is to improve the low impact resistance and optical isotropy of the two-component blend composed of a polymethyl (meth) acrylate polymer and a styrene-maleic anhydride copolymer As used, methacrylonitrile-butadiene-styrene (MBS) system, acrylonitrile-butadiene-styrene (ABS) system, acrylonitrile-ethylene-propylene-diene copolymer-styrene (AES) system, acrylonitrile Styrene-butyl acrylate (ASA), ethylene-propylene-diene terpolymer (EPDM), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-butadiene (SB) Type, styrene-isoprene type rubber, ethylene-vinyl acetate (EVA) type, ethylene-ethyl acrylate (EEA) type, ethylene-vinyl alcohol (EVOH) copolymer, ethylene chloride (CPE) type resin, silicone rubber, It may be any one selected from the group consisting of acrylic-silicone rubber, PBT-based elastomer, PET-based elastomer and nylon-based elastomer. In particular, in order to maintain the high transmittance of the optically isotropic film made of the three-component transparent resin composition, a two-component transparent blend made of a polymethyl (meth) acrylate polymer and a styrene-maleic anhydride copolymer and a rubber of an impact reinforcing material It is important to control the refractive index difference of within 0.01, preferably within 0.005.

In addition to the above components, the resin composition of the present invention, at least one additive selected from the group consisting of antioxidants, heat stabilizers, plasticizers, antistatic agents, nucleating agents, flame retardants, weather stabilizers and lubricants, and release agents, achieves the object of the present invention. It may be further added within the range possible. In particular, in including the ultraviolet absorber in the optically isotropic film, in order to increase the weather resistance of the polarizer protective film, it is preferable to add at least one ultraviolet absorber so as to have ultraviolet absorbing ability over a wide wavelength range. As the ultraviolet absorber, 2- (2H-benzotriazole-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol, 2,4-di benzotriazole-based ultraviolet absorbers, such as -t-butyl-6- (5-chlorobenzotriazole-2-yl) phenol, 2- (4,6-diphenyl) Triazin-based ultraviolet absorbers, such as (diphenyl) -1,3,5-triazin-2-yl) -5- (hexyloxy) phenol, 2-hydroxy benzophenone-based ultraviolet absorbers such as (hydroxyl) -4-octoxybenzophenone, salicylic acid-based ultraviolet absorbers such as p-octylphenyl salicylate, and the like. Benzoate-based light stabilizers such as di-t-butylphenyl-3,5-di-t-butyl-4-hydroxy benzoate, or bis; (2,2,6,6-tetramethyl-4-piperidyl) sebacate, etc. Light stabilizers, such as a hindered amine light stabilizer, can also be used.

By the resin composition of this invention, the optically isotropic film of this invention is manufactured.

In the method for producing the optically isotropic film of the present invention, a three-component transparent resin composition composed of a polymethyl (meth) acrylate polymer, a styrene-maleic anhydride copolymer, and a rubber which is an impact modifier is an injection molding method which is a method for producing a general film. , An extrusion molding method, an inflation molding method, a solution casting method, or the like, which is processed into a film, and the obtained film can be stretched or can be used as the unstretched film itself. In particular, when the optical film is manufactured using the stretching process, the stretching process should be performed within a range that does not impair the optical isotropy of the film, and the biaxial stretching such as uniaxial stretching such as free width stretching or constant stretching, or sequential stretching or simultaneous stretching It is possible to use.

The stretching process of the optically isotropic film is preferably carried out in the temperature range of T _g -30 ^o C to T _g +30 ^o C based on the glass transition temperature (T _g ) of the three-component transparent resin composition, in particular It is more preferable to carry out in the temperature range of T _g -10 ^o C to T _g +20 ^o C. In addition, the drawing speed and the drawing rate can be appropriately adjusted within the range of achieving the object of the present invention. There is no restriction | limiting in particular in the apparatus used for an extending process, Any apparatus which can extend | stretch a polymer film can be used, including well-known stretching apparatuses, such as a roll stretching machine or a tender type stretching machine.

The optically isotropic film of the present invention prepared as above has excellent optical isotropy, heat resistance, transparency and the like.

First, in the optically isotropic film of the present invention, the degree of optical isotropy may be determined by the phase difference value R _e in the plane direction and the phase difference value R _{th in the} thickness direction represented by Equations 1 and 2, respectively. have.

R _e = (n _x -n _y ) x d ... (1)

R _th = (n _z -n _y ) x d ... (2)

In Equations 1 and 2, n _x represents a refractive index in a slow axis (x-axis) direction in a plane measured at a wavelength of 550 nm, and n _y represents a fast axis in a plane measured at a wavelength of 550 nm. axis: the refractive index in the y-axis) direction, and n _z represents the refractive index in the thickness (z-axis) direction, and d represents the thickness of the film.

As R _e and R _th represented by Equations 1 and 2 are closer to 0, it may be said that the optical isotropy is excellent.

In the optically isotropic film of the present invention, when the film thickness is 30 to 200 micrometers, the retardation value R _{th in the} thickness direction and the retardation value R _{e in the} plane direction are each preferably 20 nm or less, more preferably 10 It is characterized by being less than nm. In the present invention, when the film having a phase difference value R _{th in} the thickness direction and a phase difference value R _{e in the} plane direction is 20 nm or more as a polarizer protective film, problems such as contrast decrease in the liquid crystal display device. Occurs and is not preferred.

The optically isotropic film of the present invention is also advantageously small in absolute value of the photoelastic coefficient, preferably 10 x 10 ^-12 m ² / N or less, more preferably 5 x 10 ^-12 m ² / N or less. If the absolute value of the photoelastic coefficient of the optically isotropic film is more than 10 x 10 ^-12 m ² / N, there is a problem that the optical distortion due to the stress occurs at high temperature and high humidity conditions, thereby causing light leakage phenomenon. The photoelastic coefficient (c) is defined as the degree of birefringence (Δn) with respect to the stress (ΔF) applied to the isotropic solid, as shown in Equation 3 below.

c = △ n / △ F .............. (3)

It is preferable that glass transition temperature of the optically isotropic film of this invention is 105 degreeC or more, and it is more preferable that it is 115 degreeC or more. If the glass transition temperature of the optically isotropic film is 105 ℃ or less, there is a problem that the heat resistance is insufficient to easily deform the film under high temperature and high humidity conditions, thereby distorting the polarization characteristics of the polarizing film.

The optically isotropic film of the present invention further preferably has a straight transmittance of at least 85% at 400 to 800 nm, more preferably at least 90%. In addition, the haze of the optically isotropic film is preferably 2% or less, and more preferably 1% or less. If the linear transmittance and turbidity of the optically isotropic film are less than 85% and 2% or more, respectively, the transparency of the polarizing film is lowered, thereby reducing the luminance of the LCD.

In addition, the optically isotropic film of the present invention has excellent adhesion to a material such as polyvinyl alcohol and can be attached to a polyvinyl alcohol polarizer, and, if necessary, corona discharge treatment, glow discharge treatment, flame treatment, and acid treatment. Transparency, isotropy, etc. do not deteriorate even when used with at least one surface treatment selected from the group consisting of alkali treatment, ultraviolet irradiation treatment and coating treatment.

According to another aspect of the present invention, the present invention provides a polarizing plate comprising the heat-resistant optical isotropic film as a protective film of a polyvinyl alcohol polarizer, and a liquid crystal display device including such a polarizing plate.

Hereinafter, a polarizing plate including the optical isotropic film of the present invention as a protective film of a polyvinyl alcohol polarizer and a liquid crystal display device including the polarizing plate will be described in detail with reference to the drawings.

1 is a cross-sectional view of one embodiment of a conventional polarizing plate including an optically isotropic film as a protective film of a polarizer, and FIG. 2 is a cross-sectional view of one embodiment of a structure of a conventional liquid crystal display device.

The polarizing plate of the liquid crystal display device will be described in more detail with reference to FIG. 1. The polarizing plate 8 consists of several components as shown in FIG. 1, First, the polarizer protective films 4 and 6 which become its protective film are attached to both surfaces of the polarizer 5 via an adhesive agent. As the polarizer protective film, the optically isotropic film of the present invention described above is used. The polarizing film protective film 7 is attached to one side of the polarizing film 4 + 5 + 6 through an adhesive, and the other side of the polarizing film 4 + 5 + 6 is adhered to the wide viewing angle retardation film 3 and the adhesive layer is formed thereon. 2) through the release protective film (1) is attached. The polarizing plate 8 configured as described above transmits only natural light having a vibration plane in a 360 ° direction and transmits light having a vibration plane in a predetermined direction, and absorbs the remaining light to provide polarized light.

Meanwhile, referring to FIG. 2, in the conventional liquid crystal display device, the liquid crystal 10 is disposed between two molecular alignment films 12. A transparent electrode 14 is formed on each molecular alignment film 12, a glass substrate 16 is formed on the transparent electrode 14, and a polarizing plate 18 is formed on the glass substrate 16. In this case, the glass substrate may be replaced with a polymer substrate formed of a polymer resin having properties similar to those of glass. As the polarizing plate 18, the polarizing plate 8 according to the present invention as shown in FIG. 1 described above may be applied. In this case, the release protective film 1 of the polarizing plate 8 illustrated in FIG. It is disposed to the outside of the display device.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

[Example]

Example 1

75% by weight of polymethyl methacrylate polymer (brand name HP202, manufactured by LG MMA) and 20% by weight of styrene-maleic anhydride copolymer (brand name Dylark 332, 15% by weight maleic anhydride monomer content, manufactured by NOVA Chemical), ABS impact modifier (Core-shell structure, rubber content 40%, manufactured by LG Chemical) After dry blending the three-component resin composition composed of 5%, a coaxial twin screw extruder (screw diameter 27mm, L / D = 48, manufactured by Leistritz) was used. A heat resistant blend in pellet form was prepared. After drying the prepared pellets, an unstretched extruded film having a thickness of 80 μm was prepared using an extruder including a T-die. The properties of the film thus prepared were measured in the following manner.

(1) Glass transition temperature (T _g )

: It measured at the temperature increase rate of 10 degree-C / min using the differential scanning calorimeter (brand name DSC 2010, TA instrument make).

(2) straight transmittance and turbidity

: Straight transmittance and haze were measured for transparency evaluation, straight transmittance was measured over a wavelength range of 200 to 900 nm, and haze was measured with a transmittance meter (model HR-100, manufactured by Murakami Color Research Laboratory).

(3) optical isotropic

: Refractive index (n) was measured using an Abbe refractometer, and the phase difference value (R _e ) in the surface direction was measured using a sample inclination type automatic birefringence meter (model name KOBRA-21 ADH, manufactured by Prince Measuring Instrument). And the phase difference value ( _Rθ ) when the angle between the incident light and the film surface was 50 ^° , and the phase difference value (R _th ) in the film thickness direction was obtained according to the following equation.

In the above equation, θ _f is an internal angle.

(4) photoelastic coefficient

: After cutting the film into the size of 6 cm x 1 cm, it was measured using a polarization spectrophotometer at 20 ℃, 60% relative humidity conditions. To this end, after fixing both ends of the film as a support, the birefringence was measured according to the load change and the photoelastic coefficient was calculated from the slope.

[Example 2]

65% by weight of the same polymethyl methacrylate polymer as in Example 1 and 30% by weight of styrene-maleic anhydride copolymer, 5% by weight of MBS-based impact modifier (core-shell structure, rubber content 65%, manufactured by LG Chemical) A non-stretched extruded film was prepared in the same manner as in Example 1 except that a composition was used, and the same properties as in Example 1 were measured for the prepared non-stretched extruded film, and the results are shown in Tables. 1 is shown.

Example 3

45% by weight of the same polymethyl methacrylate polymer as in Example 1, 50% by weight of styrene-maleic anhydride copolymer, 5% by weight of ABS-based impact modifier (core-shell structure, rubber content 65%, manufactured by LG Chemical) A non-stretched extruded film was prepared in the same manner as in Example 1 except that a composition was used, and the same properties as in Example 1 were measured for the prepared non-stretched extruded film, and the results are shown in Tables. 1 is shown.

Example 4

A heat-resistant blend in pellet form was prepared in the same manner as in Example 1 (three-component resin composition composed of 75 wt% polymethyl methacrylate, 20 wt% styrene-maleic anhydride copolymer, and 5 wt% ABS impact modifier). Then, it was dissolved in methylene chloride solvent to prepare a resin solution of about 35%. The resulting solution was coated / dried on a clean glass plate to prepare an 80 탆 thick unstretched casting film, and the same properties as in Example 1 were measured for the resulting unstretched casting film, and the results are shown in Table 1 below. Shown in

Example 5

A non-stretched extruded film was prepared in the same manner as in Example 1 (three-component resin composition composed of 75 wt% polymethyl methacrylate, 20 wt% styrene-maleic anhydride copolymer, and 5 wt% ABS-based impact modifier) A 30% uniaxially stretched film was prepared at 117 ° C. through a roll drawing machine for the prepared unstretched film. The same properties as in Example 1 were measured for the prepared stretched film, and the results are shown in Table 1 below.

Comparative Example 1

The same properties as in Example 1 were measured for the unstretched TAC film (thickness 80 µm, manufactured by Fujifilm), and the results are shown in Table 1 below.

Comparative Example 2

A non-stretched extruded film was prepared in the same manner as in Example 1, except that only the same polymethyl methacrylate polymer as in Example 1 was used, and the same properties as in Example 1 were applied to the prepared non-stretched extruded film in the same manner. The results are shown in Table 1 below.

Comparative Example 3

Extruded non-stretched film was prepared in the same manner as in Example 2, except that a two-component resin composition composed of 79 wt% of the same polymethyl methacrylate polymer and 21 wt% of the styrene-maleic anhydride copolymer was used. The same properties as in Example 1 were measured for the prepared unstretched film by the same method, and the results are shown in Table 1 below.

[Comparative Example 4]

For a non-stretched film prepared by the same method as in Comparative Example 3 (two-component resin composition composed of 79 wt% polymethyl methacrylate polymer and 21 wt% styrene-maleic anhydride copolymer) at 117 ° C. through a roll drawing machine. A 30% uniaxially stretched film was prepared. The same properties as in Example 1 were measured for the prepared stretched film, and the results are shown in Table 1 below.

As can be seen in Table 1, the film (Examples 1 to 5) made of a three-component transparent resin composition composed of a polymethyl (meth) acrylate polymer, a styrene-maleic anhydride-based copolymer, and an impact modifier rubber It was found that the retardation value in the thickness direction or the plane direction was very good within 5 nm, and the heat resistance was also superior to that of the polymethyl (meth) acrylate polymer (Comparative Example 2). In particular, by varying the content of the styrene-maleic anhydride copolymer in the three-component transparent resin composition (Examples 1 to 3), optically isotropic films having different glass transition temperatures could be prepared. As a result of the film manufacturing method being different from the extrusion molding method and the solution casting method (Examples 1 and 4), all of them showed excellent isotropy regardless of the manufacturing method, and especially the casting film showed somewhat better transparency than the extruded film. On the other hand, as a result of examining the optical properties according to the stretching of the film (Examples 1 and 5), optical anisotropy did not appear according to the uniaxial stretching, Comparative Example 1 as the absolute photoelastic coefficient is about 2 x 10 ^-12 N / m ² Very low values compared to the TAC film. In addition, the optically isotropic film of Example 5 has a water vapor transmission rate of 38 g / m ² · day at 38 ° C., which is higher than that of the nonpolar cyclic olefin film and is much lower than that of the TAC film. It could be inferred that there is.

On the other hand, the TAC film of Comparative Example 1 exhibited optical anisotropy having a large absolute value of retardation value in the thickness direction and high photoelastic coefficient value. The polymethyl methacrylate polymer alone film of Comparative Example 2 was excellent in optical isotropy, but was not suitable for use as a polarizer protective film due to poor heat resistance and mechanical properties. In addition, the non-stretched extruded film made of the two-component transparent resin composition composed of the polymethyl methacrylate polymer and the styrene-maleic anhydride copolymer of Comparative Example 3 has a disadvantage in that it is excellent in heat resistance but weak in mechanical properties (impact resistance). As a result of uniaxial stretching of the unstretched film (Comparative Example 4), optical anisotropy was expressed, which was not suitable for use as a polarizer protective film.

Although the present invention has been described in detail with reference to the described embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical scope of the present invention, and such modifications and modifications fall within the scope of the appended claims. It is natural.

As described above, according to the present invention, an optically isotropic film excellent in transparency and heat resistance can be manufactured at low cost, and in particular, the optically isotropic film prepared according to the present invention is suitable for liquid crystal display as a polarizer protective film having excellent moisture and heat resistance. Can be used.

Claims (27)

10 to 95% by weight polymethyl (meth) acrylate polymer, 4 to 60% by weight styrene-maleic anhydride copolymer comprising styrene compound repeating unit and maleic anhydride or imide maleic anhydride compound repeating unit and rubber 1 to Resin composition comprising 30% by weight. The method of claim 1, The content of the polymethyl (meth) acrylate polymer is 50 to 80% by weight, the content of the styrene-maleic anhydride copolymer is 17 to 35% by weight, the content of the rubber is 3 to 15% by weight Resin composition made into. The method of claim 1, The polymethyl (meth) acrylate polymer is a resin composition, characterized in that the polymer formed by the polymerization of only the methyl (meth) acrylate monomer. The method of claim 1, The polymethyl (meth) acrylate polymer is a copolymer formed by copolymerizing 50 to 90% by weight of a methyl (meth) acrylate monomer and an unsaturated monomer copolymerizable with the methyl (meth) acrylate monomer, and the methyl (meth) Unsaturated monomers copolymerizable with acrylate monomers include alicyclic or aliphatic C1-12 alkyl methacrylates, unsubstituted or substituted with hydroxy groups, alicyclic or aliphatic C1-12 alkyl acrylates, unsubstituted or substituted with hydroxy groups C6-12 aryl methacrylate, optionally substituted with an oxy group, C6-12 aryl acrylate, optionally substituted with a hydroxy group, a styrene compound optionally substituted with C1-4 alkyl or halogen, acrylonitrile, and Substituted or unsubstituted alicyclic or aliphatic C1-12 alkyl or C6-12 aryl A resin composition, characterized in that it is selected from the group consisting of maleimide compounds. delete The method of claim 1, The styrene-maleic anhydride-based copolymer is a resin composition, characterized in that formed by the copolymerization of 50 to 96% by weight of styrene monomer and 4 to 50% by weight of maleic anhydride monomer or imide maleic anhydride monomer. The method of claim 6, The styrene monomer is a resin composition, characterized in that at least one selected from the group consisting of styrene, α-methylstyrene, p-bromostyrene, p-methyl styrene and p-chlorostyrene. The method of claim 1, The rubber is methacrylonitrile-butadiene-styrene (MBS), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-ethylene-propylene-diene copolymer-styrene (AES), acrylonitrile- Styrene-butylacrylate (ASA) system, ethylene-propylene-diene terpolymer (EPDM) system, styrene-butadiene-styrene (SBS) system, styrene-isoprene-styrene (SIS) system, styrene-butadiene (SB) system , Styrene-isoprene rubber, ethylene-vinyl acetate (EVA), ethylene-ethyl acrylate (EEA), ethylene-vinyl alcohol (EVOH) copolymer, ethylene chloride (CPE) resin, silicone rubber, acrylic-silicone The resin composition, characterized in that at least one selected from the group consisting of rubber, PBT-based elastomer, PET-based elastomer and nylon-based elastomer. The method of claim 1, A resin composition further comprising at least one additive from the group consisting of antioxidants, heat stabilizers, plasticizers, antistatic agents, nucleating agents, flame retardants, weather stabilizers, mold release agents, ultraviolet absorbers, light stabilizers and lubricants. The method of claim 1, The resin composition is a resin composition, characterized in that it has a glass transition temperature of 115 ℃ or more. The method of claim 1, Resin composition characterized in that the refractive index difference between the two-component transparent blend consisting of the polymethyl (meth) acrylate polymer and the styrene-maleic anhydride copolymer and the rubber is within 0.01. 10 to 95% by weight polymethyl (meth) acrylate polymer, 4 to 60% by weight styrene-maleic anhydride copolymer comprising styrene compound repeating unit and maleic anhydride or imide maleic anhydride compound repeating unit and rubber 1 to Optically isotropic film prepared from a resin composition comprising 30% by weight The method of claim 12, Optical isotropic film, characterized in that the optical isotropic film is used as a polarizer protective film. The method of claim 12, When the film thickness is 30 to 200 micrometers, the optically isotropic film, characterized in that the phase difference values (R _e and R _th ) in the plane direction and the thickness direction represented by the following equations are 20 nm or less. R _e = (n _x -n _y ) xd R _th = (n _z -n _y ) xd In the above equation, n _x , n _y and n _z represent the refractive index in the low speed axial direction, the refractive index in the high speed axial direction, and the refractive direction in the thickness direction, respectively, measured at a wavelength of 550 nm, and d represents the thickness of the film. The method of claim 12, The polymethyl (meth) acrylate polymer is an optical isotropic film, characterized in that the polymer formed by the polymerization of only the methyl (meth) acrylate monomer. The method of claim 12, The polymethyl (meth) acrylate polymer is a copolymer formed by copolymerizing 50 to 90% by weight of a methyl (meth) acrylate monomer and an unsaturated monomer copolymerizable with the methyl (meth) acrylate monomer, and the methyl (meth) Unsaturated monomers copolymerizable with acrylate monomers include alicyclic or aliphatic C1-12 alkyl methacrylic acid, optionally substituted with a hydroxy group, alicyclic or aliphatic C1-12 alkyl acrylic acid, hydroxy, optionally substituted with a hydroxy group C6-12 aryl methacrylic acid, optionally substituted with a group, C6-12 aryl acrylic acid, optionally substituted with a hydroxy group, styrene compound optionally substituted with C1-4 alkyl or halogen, acrylonitrile, and substituted or Unsubstituted alicyclic or aliphatic C1-12 alkyl or C6-12 aryl maleimide compound An optically isotropic film, characterized in that selected from the group consisting of. delete The method of claim 12, The styrene-maleic anhydride-based copolymer is an optically isotropic film, characterized in that formed by copolymerization of 50 to 96% by weight of styrene monomer and 4 to 50% by weight of maleic anhydride monomer or imide maleic anhydride monomer. The method of claim 18, The styrene monomer is an optically isotropic film, characterized in that one or more selected from the group consisting of styrene, α-methylstyrene, p-bromostyrene, p-methylstyrene and p-chlorostyrene. The method of claim 12, The rubber is methacrylonitrile-butadiene-styrene (MBS), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-ethylene-propylene-diene copolymer-styrene (AES), acrylonitrile- Styrene-butylacrylate (ASA) system, ethylene-propylene-diene terpolymer (EPDM) system, styrene-butadiene-styrene (SBS) system, styrene-isoprene-styrene (SIS) system, styrene-butadiene (SB) system , Styrene-isoprene rubber, ethylene-vinyl acetate (EVA), ethylene-ethyl acrylate (EEA), ethylene-vinyl alcohol (EVOH) copolymer, ethylene chloride (CPE) resin, silicone rubber, acrylic-silicone Optical isotropic film, characterized in that at least one selected from the group consisting of rubber, PBT-based elastomer, PET-based elastomer and nylon-based elastomer. The method of claim 12, The optically isotropic film, wherein the refractive index difference between the polymethyl (meth) acrylate polymer and the styrene-maleic anhydride copolymer and the rubber is within 0.01. The method of claim 12, The resin composition has an optical isotropic film, characterized in that having a glass transition temperature of 115 ℃ or more. 13. The optically isotropic film of claim 12, wherein the photoelastic coefficient of the optically isotropic film is 10 x 10 ^-12 m ² / N or less. The method of claim 12, The optically isotropic film has a light transmittance of 85% or more at a light wavelength of 400 to 800 nm. A polarizing plate comprising a polarizer and an optically isotropic film according to any one of claims 12 to 16 or 18 to 24 formed on at least one surface of the polarizer film as the polarizer protective film. The method of claim 25, The optically isotropic film is formed on both sides of the polarizer, the polarizing plate further comprises a retardation film formed on at least one of the optically isotropic films. A liquid crystal display device comprising at least one polarizing plate according to claim 25.

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