WO2015047005A1 - Resin composition for optical film, optical film formed using same, and polarizing plate and image display device comprising same - Google Patents

Abstract

The present invention relates to a resin composition and an optical film formed using the same and, more specifically, to a copolymer resin composition formed by polymerizing an alkyl methacrylate based monomer, a styrene based monomer, a phenylmaleimide based monomer, and an alkylacrylate based monomer, and to an optical film formed using the same. The resin composition according to the present invention reduces a pungent smell created at the time of film extrusion, and has excellent heat resistance and thermal stability.

Description

Resin composition for an optical film, an optical film formed using the same, a polarizing plate and an image display device comprising the same

The present invention relates to a resin composition and an optical film formed using the same, and more particularly, to a copolymer formed by polymerizing an alkyl methacrylate monomer, a styrene monomer, a phenylmaleimide monomer and an alkyl acrylate monomer. It relates to a resin composition for an optical film, an optical film formed by using the same, a polarizing plate and an image display device comprising 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 polystyrene or polycarbonate films have an aromatic ring in the polymer, so that birefringence occurs during orientation, which adversely affects optical properties. In this case, the phase difference value is relatively smaller than that of polystyrene or polycarbonate, but it is not sufficient to be applied to an optical material such as a liquid crystal device requiring high precision.

In order to solve such a problem, a method of copolymerizing or blending a monomer or a polymer with a material for polymer film having excellent heat resistance and low retardation value has been proposed. As an example, a method of using a maleimide monomer in order to obtain a resin composition having excellent heat resistance has been proposed, and in practice, the frequency of using cyclohexyl maleimide is increasing. In particular, copolymers of methyl methacrylate, cyclomaleimide and alpha methyl styrene have been mainly used as heat resistant resins. However, in the case of the cyclohexyl maleimide, it is an environmentally regulated material, and in particular, the cyclohexyl maleimide remaining in the resin when the resin composition is extruded into the film generates an irritating and harmful odor, resulting in a decrease in production efficiency and a process. There was a problem of instability.

The present invention is to solve the problems as described above, to suppress the odor generated during the extrusion of the conventional resin composition, the resin composition for an optical film with improved thermal stability, and an optical film prepared using the same, a polarizing plate and the same An image display device is provided.

To this end, the present invention provides a resin composition for an optical film comprising a copolymer formed by polymerizing an alkyl methacrylate monomer, a styrene monomer, a phenylmaleimide monomer and an alkyl acrylate monomer.

In this case, the content of the unreacted phenylmaleimide monomer remaining in the resin composition is preferably 30 ppm or less with respect to the whole composition.

In this case, the resin composition may further include a polycarbonate.

In addition, the copolymer is 70 to 98 parts by weight of the alkyl methacrylate monomer, 0.1 to 10 parts by weight of the styrene monomer, 1 to 15 parts by weight of the phenylmaleimide monomer based on 100 parts by weight of the copolymer; And 0.1 to 5 parts by weight of alkyl acrylate monomers.

At this time, the weight ratio of the phenylmaleimide monomer and the alkyl acrylate monomer is preferably 2: 1 to 7: 1.

On the other hand, it is preferable that the resin composition for optical films has a glass transition temperature of 100 to 150 degreeC, and the 2% weight loss temperature measured by the thermogravimetric analyzer (TGA) is 280 degreeC or more.

In another aspect, the present invention provides an optical film comprising the resin composition for an optical film.

In still another aspect, the present invention provides a polarizing plate including the optical film and an image display device including the same.

The resin composition according to the present invention can reduce the odor generated during the film extrusion, excellent thermal stability can improve the production efficiency, can provide a film excellent in heat resistance and optical properties. Therefore, the optical film formed using the resin composition of the present invention can be used for display devices of various uses.

Hereinafter, preferred embodiments of the present invention will be described. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

First, according to one aspect of the present invention, there is provided a resin composition for an optical film comprising a copolymer formed by polymerizing an alkyl methacrylate monomer, a styrene monomer, a phenylmaleimide monomer and an alkyl acrylate monomer.

In the present specification, the copolymer means that the elements mentioned as monomers in the present specification are polymerized and included as repeating units in the copolymer resin. In the present specification, the copolymer may be a block copolymer or a random copolymer. However, the present invention is not limited thereto. In addition, the copolymer is a quaternary copolymer made of a resin composition for an optical film comprising a copolymer formed by polymerizing the above alkyl methacrylate monomer, styrene monomer, phenylmaleimide monomer and alkyl acrylate monomer. The present invention is not limited thereto and may further include other monomers as comonomers in addition to the above-mentioned monomers within a range not departing from the object of the present invention.

In addition, depending on the properties of each monomer, the retardation characteristics of the optical film produced therefrom may vary depending on the composition, the stretching direction, the stretching ratio and the stretching method of each component. Therefore, in this invention, an optical film can be manufactured by adjusting the composition and the extending | stretching method of each said component.

In the present invention, the alkyl methacrylate monomer is for imparting high transparency optical properties to the resin composition or film.

The alkyl moiety of the alkyl methacrylate monomer may be a substituted or unsubstituted alkyl group or a cycloalkyl group, wherein the alkyl moiety preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms. It is most preferable that they are a methyl group or an ethyl group. Specifically methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, hydroxyethyl methacrylate, isobornyl methacrylate and cyclohexyl methacrylate At least one selected from the group consisting of, but is not limited thereto.

The content of the alkyl methacrylate monomer is about 70 to 98 parts by weight, and more preferably about 82 to 97 parts by weight based on 100 parts by weight of the copolymer. When the content satisfies the above range, a film having excellent optical properties may be obtained, and the birefringence generated during stretching may be minimized.

Next, in the present invention, the styrene monomer can improve the polymerization efficiency between each monomer, it can be expected to reduce the residual monomer contained in the copolymer produced. In addition, the film produced by the resin composition containing the styrene monomer can more easily control the stretching retardation can provide a zero retardation film having excellent birefringence.

Meanwhile, the styrene monomer may be an unsubstituted styrene monomer or a substituted styrene monomer. The substituted styrene monomer may be styrene substituted with a substituent containing an aliphatic hydrocarbon or hetero atom in a benzene ring or vinyl group. For example, styrene, α-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 2-methyl-4-chlorostyrene, 2,4,6- Trimethylstyrene, cis-β-methylstyrene, trans-β-methylstyrene, 4-methyl-α-methylstyrene, 4-fluoro-α-methylstyrene, 4-chloro-α-methylstyrene, 4-bromo-α -Methylstyrene, 4-t-butylstyrene, 2-fluorostyrene, 3-fluorostyrene, 4-fluorostyrene, 2,4-difluorostyrene, 2,3,4,5,6-pentafluorostyrene , 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene, octachlorostyrene, 2-bromostyrene, 3-bromostyrene, 4-bromo It may be one or more selected from the group consisting of styrene, 2,4-dibromostyrene, α-bromostyrene and β-bromostyrene, but is not limited thereto. More preferably, styrene substituted with C _1-4 alkyl or halogen can be used. More specifically, the styrene monomer may be used at least one selected from the group consisting of styrene, α-methyl styrene, p-bromo styrene, p-methyl styrene and p-chloro styrene, most preferably styrene, α-methylstyrene and p-methyl styrene.

The content of the styrene monomer is preferably about 0.1 to 10 parts by weight, and more preferably about 0.5 to 5 parts by weight based on 100 parts by weight of the copolymer. When the content of the styrene-based monomer satisfies the above range, the effect of reducing the residual monomer and the glass transition temperature of the copolymer can be obtained, and the stretching retardation of the film is easily controlled, which is more preferable in terms of optical properties of the film. This is because the effect can be obtained.

In this invention, the said phenyl maleimide type monomer is for improving the thermal stability and heat resistance of a resin composition and a film, and improving compounding compatibility with a polycarbonate resin. In addition, unlike when using a conventional cyclohexyl maleimide, it is possible to suppress the generation of an irritating odor during extrusion of the resin composition.

In general, in the process, the maleimide-based residual monomer generates an irritating odor during processing, and may be easily solidified to cause appearance defects in optical film production. However, unlike the cyclohexyl maleimide monomer, the phenyl maleide monomer has a constant chemical structure due to the substitution of a phenyl group, and thus it is easy to form a copolymer with an alkyl methacrylate monomer and a styrene monomer, and is heat resistant. It can be improved, and the polymerization time is relatively short advantage. For this reason, the amount of phenylmaleimide-based monomer remaining in the resin after copolymer formation is much lower than that of the cyclohexylmaleimide-based resin, and it is possible to reduce the occurrence of odor during processing caused by the residual monomer.

Specific examples of the phenyl maleimide monomer are selected from the group consisting of phenyl maleimide, nitrophenyl maleimide, monochlorophenyl maleimide, dichlorophenyl maleimide, monomethylphenyl maleimide, dimethylphenyl maleimide, and ethylmethylphenyl maleimide It is preferable that it is at least one.

The content of the phenylmaleimide-based monomer is preferably about 1 to 15 parts by weight, more preferably about 2 to 10 parts by weight based on 100 parts by weight of the copolymer. When the content of the phenylmaleimide monomer satisfies the above range, the heat resistance of the resin composition or the film is strengthened, mixed well with the polycarbonate resin, and the film can be formed without precipitation.

In addition, in this invention, the said alkylacrylate type monomer is for providing the resin composition with the polymerization stability, thermal stability, and toughness to the stretched film. By introducing this structural unit into the copolymer, molding processability such as mold release property is improved, and a composition excellent in heat resistance is obtained, such as preventing weight loss due to heat during the process.

The alkyl moiety of the alkyl acrylate monomer may be a substituted or unsubstituted alkyl group or a cycloalkyl group, wherein the alkyl moiety preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, Most preferably, it is a methyl group or an ethyl group. Specifically, it may be methyl acrylate, ethyl acrylate, isopropyl acrylate n-butyl acrylate, t-butyl acrylate, cyclohexyl acrylate, isobornyl acrylate, hydroxymethyl acrylate or hydroxyethyl acrylate. It is not limited to this.

The content of the alkyl acrylate monomer is about 0.1 to 5 parts by weight based on 100 parts by weight of the copolymer, more preferably about 0.5 to 3.0 parts by weight. When the content satisfies the above range, it is easy to polymerize between the alkyl methacrylate monomer and the phenylmaleimide monomer at the time of copolymer formation, thereby reducing the residues of phenylmaleimide in the resin composition. It is possible to overcome the thermal decomposition phenomenon by the phenyl maleimide, there is an effect that the stretching process is easily carried out by giving toughness when stretching the film.

On the other hand, the weight ratio of the phenylmaleimide monomer and the alkyl acrylate monomer is preferably about 2: 1 to 10: 1, more preferably about 2: 1 to 7: 1. When the weight ratio of the two monomers satisfies the above range, the residual monomer of the copolymer can be reduced, and the retention stability in the extruder and the polymer filter during film processing can be improved.

On the other hand, in the resin composition of this invention, it is preferable that content of the unreacted phenylmaleimide-type monomer which remains in a resin composition is 30 ppm or less with respect to the whole composition, and it is more preferable that it is 20 ppm or less. The inventors of the present invention found that the cyclohexylmaleimide monomer mainly used as a monomer of the copolymer constituting the heat resistant resin has a relatively low degree of polymerization due to the high rotational properties of the cyclohexyl group. Therefore, not only the amount of monomer remaining in the resin after the copolymer polymerization is high, but also the cyclohexylmaleimide monomer generates an irritating and harmful odor, thereby causing a process problem. However, the phenylmaleimide monomer has an excellent degree of polymerization compared to the cyclohexyl maleimide monomer due to the stable aromatic ring, the amount of monomer remaining in the copolymer is very small, there is an advantage to improve the stability of the process.

Another aspect of the present invention relates to a resin composition comprising the copolymer and a polycarbonate.

The polycarbonate is added to adjust the phase difference is contained in an amount of about 0.1 to 10 parts by weight based on 100 parts by weight of the total resin composition, it is preferably included in about 1 to 5 parts by weight. When the polycarbonate is contained in a smaller amount than this, there is a problem in that the thickness direction retardation of the stretched film is increased in a positive direction. When the amount is exceeded, the thickness direction retardation of the stretched film is increased in a negative direction. There is. Moreover, when it exceeds 10 weight part, compatibility with an acrylic resin composition falls and there exists a problem that a whitening phenomenon generate | occur | produces. Therefore, according to the composition of the above range, the absolute value of the plane direction phase difference R _in defined by the following [Equation 1] and the absolute value of the thickness direction phase difference R _th defined by the following [Equation 2] are 5 nm, respectively. Preferably it can be added to adjust the content to 3nm, more preferably 0.

[Formula 1] R _in = (n _x -n _y ) × d,

R _th = (n _z -n _y ) × d

In [Formula 1] and [Formula 2],

n _x is the largest refractive index of the in-plane refractive index of the optical film,

n _y is the refractive index of the direction perpendicular to n _x of the in-plane refractive index of the optical film,

n _z is the refractive index in the thickness direction,

d is the thickness of the film.

On the other hand, the resin composition of the present invention containing an acrylic copolymer resin and a polycarbonate resin, for example, can be prepared using a method well known in the art, such as compounding method.

Furthermore, the resin composition may further include various additives generally used in the art, for example, lubricants, antioxidants, UV stabilizers, thermal stabilizers, and the like, as necessary. In this case, the additives may be included in an appropriate amount within a range that does not impair the physical properties of the resin composition, for example, may be included in about 0.1 to 5 parts by weight based on 100 parts by weight of the total resin composition.

On the other hand, the glass transition temperature of the resin composition according to the present invention is preferably about 100 ° C to 150 ° C, more preferably 105 ° C to 140 ° C, and most preferably 110 ° C to 130 ° C. If the glass transition temperature is less than 100 ℃, the heat resistance is insufficient to easily deform the film under high temperature and high humidity conditions, thereby causing a problem of deformation of the polarizing plate to cause non-uniformity of the liquid crystal panel. If the glass transition temperature is more than 150 ℃ resin processing properties are very low, there is a problem that the productivity is reduced due to the difficulty in forming the film due to the high viscosity during the joint processing.

On the other hand, the resin composition which concerns on this invention is excellent in thermal stability. Generally, around 260 degreeC in which resin containing alkyl methacrylate is actually shape | molded by injection molding or extrusion molding, the zipper decomposition peculiar to resin containing alkyl methacrylate occurs. It is known that the terminal double bond proceeds as a starting point. In contrast, the present invention can reduce the molding defect by suppressing thermal decomposition at around 260 ° C., and can realize the production of a stable optical article without deteriorating the color tone. In the present invention, thermal stability was evaluated using a thermogravimetric analyzer (TGA). In a nitrogen environment, the temperature at which 2% weight of the resin was reduced was measured in the process of raising the temperature from 30 ° C to 500 ° C at a rate of 10 ° C / min, and the temperature was compared to evaluate the thermal stability. The 2% weight loss temperature is preferably at least 280 ° C, more preferably at least 300 ° C, most preferably at least 320 ° C.

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

Specifically, after obtaining the resin composition, the optical film according to the present invention may be prepared, including forming a film, and may further include uniaxially or biaxially stretching the film.

In the production of the optical film according to the present invention, any method known in the art may be used, for example, a solution caster method or an extrusion method, and an example may be a melt extrusion method. Specifically, the resin composition is dried in vacuo to remove moisture and dissolved oxygen, and then fed from a raw material hopper to a single or twin extruder substituted with nitrogen, and melted at a high temperature to obtain raw material pellets. After vacuum drying, the raw material hopper to the extruder is melted with a nitrogen extruded single extruder, and then passed through a coat hanger type T-die to produce a film via a chrome plated casting roll, a drying roll, or the like. At this time, film forming temperature becomes like this. Preferably it is 150 degreeC-350 degreeC, More preferably, it is 200 degreeC-300 degreeC. On the other hand, when forming a film by the T-die method as mentioned above, a T-die is attached to the front-end | tip of a well-known single screw extruder or a twin screw extruder, the film extruded in film shape is obtained, and a roll-shaped film is obtained. Can be. Under the present circumstances, you may uniaxially stretch by adjusting the temperature of a winding roll suitably and extending | stretching in an extrusion direction. Moreover, simultaneous biaxial stretching, sequential biaxial stretching, etc. can also be performed by extending | stretching a film in the direction perpendicular | vertical to an extrusion direction.

On the other hand, when an extending process is performed, it is preferable that extending | stretching temperature is a range near the glass transition temperature of the resin composition which is a film raw material, Preferably it is (glass transition temperature -30 degreeC)-(glass transition temperature +100 degreeC) More preferably, it exists in the range of (glass transition temperature -20 degreeC)-(glass transition temperature +80 degreeC). If the stretching temperature is less than (glass transition temperature -30 ° C), there is a fear that a sufficient stretching ratio may not be obtained. On the contrary, when extending | stretching temperature exceeds (glass transition temperature +100 degreeC), the flow (flow) of a resin composition arises and there exists a possibility of not being able to perform stable extending | stretching.

The draw ratio defined by the area ratio is preferably 1.1 to 25 times, more preferably 1.3 to 10 times. If the draw ratio is less than 1.1 times, there is a fear that it does not lead to the improvement of the toughness accompanying stretching. When a draw ratio exceeds 25 times, there exists a possibility that the effect by raising a draw ratio may not be recognized.

The stretching speed is preferably 10 to 20,000% / min, more preferably 100 to 10.000% / min in one direction. If the stretching speed is less than 10% / min, it takes a long time to obtain a sufficient draw ratio, there is a fear that the manufacturing cost increases. When the stretching speed exceeds 20,000 & / min, there is a fear that breaking of the stretched film occurs.

The optical film may be subjected to heat treatment (annealing) or the like after the stretching treatment in order to stabilize its optical isotropy and mechanical properties. The heat treatment conditions are not particularly limited and may employ any suitable conditions known in the art.

Through the above method, the optical film formed by using the resin composition of the present invention preferably has a thickness of 5㎛ to 200㎛, but is not limited thereto.

As described above, the optical film manufactured by the resin composition of the present invention has a thermal expansion coefficient of 50 to 100 ppm / ° C, preferably 50 to 80 ppm / ° C, and a thermal expansion coefficient of PVA polarizing film as compared to conventional optical films. The difference of is so small that the polarizing plate dimension change can be effectively suppressed at the time of polarizing plate application.

In addition, the optical transmittance of the optical film is 90% or more, haze (haze) characteristics may be in the range of 0.6% or less, preferably 0.3% or less. It is because it is suitable to be used as a polarizing plate protective film when a transmittance and a haze exist in the said range.

On the other hand, in the case of the optical film produced using the compounding compound of the copolymer and polycarbonate, the absolute value of the surface direction phase difference represented by the following [formula 1] at a wavelength of 550 nm and the thickness direction represented by the above [formula 2] The absolute value of the retardation is about 5 nm, preferably about 3 nm, respectively, so that it can be very usefully used as a protective film for polarizing plates.

[Formula 1] R _in = (n _x -n _y ) × d,

R _th = (n _z -n _y ) × d

In the above [formula 1] and [formula 2], n _x is the largest refractive index among the in-plane refractive indexes of an optical film, n _y is the refractive index of the direction perpendicular to n _x among the in-plane refractive indexes of an optical film,

n _z is a refractive index in the thickness direction, and d is the thickness of the film.

The last aspect of the present invention relates to a polarizing plate including the optical film of the present invention and an image display device including the polarizing plate, and more specifically look as follows.

In the present specification, the polarizing plate means a state including a polarizer and a protective film, and as the polarizer, a film made of polyvinyl alcohol (PVA) containing iodine or dichroic dye may be used. The polarizer may be prepared by dyeing iodine or dichroic dye on the PVA film, but a method of manufacturing the same is not particularly limited.

In addition, the protective 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.

On the other hand, in the polarizing plate of the present invention, the protective film and the polarizer may be bonded by a method known in the art. For example, it may be made by an adhesive method using an adhesive. That is, first, an adhesive is coated on the surface of a PVA film which is a protective film or a polarizer (polarizing film) by using a roll coater, gravure coater, bar coater, knife coater or capillary coater. Before the adhesive is completely dried, the protective film and the polarizer are bonded by heating or pressing at room temperature with a paper roll. In the case of using a hot melt adhesive, a heat press roll should be used.

Adhesives that can be used when the protective film and the polarizer are laminated include, but are not limited to, PVA adhesive, polyurethane adhesive, epoxy adhesive, styrene butadiene rubber (SBR) adhesive or hot melt adhesive. When using the said polyurethane adhesive, it is preferable to use the polyurethane adhesive manufactured using the aliphatic isocyanate type compound which does not yellow by light.

In addition, the polarizing plate of the present invention preferably further has an adhesive layer in order to facilitate lamination to a liquid crystal cell or the like, and may be disposed on one side or both sides of the polarizing plate. The adhesive may be sufficiently cured by heat or ultraviolet rays after adhesion, and thus the mechanical strength may be improved to an adhesive level. The adhesive strength is also large, so that the adhesive does not peel off without breakage of either film to which the adhesive is attached. It is desirable to have.

The adhesive which can be used is excellent in optical transparency, and it is preferable to show the adhesive characteristic of moderate wettability, cohesion, or adhesiveness. As a specific example, the adhesive etc. which suitably prepared polymers, such as an acryl-type polymer, a silicone type polymer, polyester, a polyurethane, a polyether, synthetic rubber, as a base polymer, are mentioned.

On the other hand, in the case of the polarizing plate manufactured using the resin composition of this invention, it has the characteristic that curl generation is few. In the present invention, the curl means the center of the test piece and the edge of the test piece caused by the incorrectness generated when the polarizing plate test piece is placed on the horizontal table at a temperature of 24 ° C. and 50% RH with the concave surface facing up. Says the height of the car. The more curls are generated, there is a problem in that external air flows into the polarizer curl portion when the polarizer and the liquid crystal panel are attached to each other using the pressure-sensitive adhesive, thereby degrading the appearance quality of the liquid crystal panel.

In addition, the present invention provides an image display device including the polarizing plate, more preferably may be a liquid crystal display device. For example, the liquid crystal display according to the present invention is a liquid crystal display including a liquid crystal cell and a first polarizing plate and a second polarizing plate respectively provided on both surfaces of the liquid crystal cell, wherein at least one of the first polarizing plate and the second polarizing plate is It is characterized in that the polarizing plate according to the present invention. That is, one or two or more optical films according to the present invention are provided between the first polarizing plate and the liquid crystal cell, between the second polarizing plate and the liquid crystal cell, or between the first polarizing plate and the liquid crystal cell and between the second polarizing plate and the liquid crystal cell. It may be provided. It is preferable that the optical film or polarizer protective film provided in the opposite side to the liquid crystal cell of the said polarizing plate contains a UV absorber.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

Example

<Example 1>

Methyl methacrylate, alpha methyl styrene, phenylmaleimide and methyl acrylate were prepared in 1000 g of the monomer mixture in the amounts shown in [Table 1], and 2000 g of distilled water and 8.4 g of a 5% polyvinyl alcohol solution in a 5 liter reactor (POVAL). PVA217, Kuraray Co.), 0.1 g of boric acid, 2.5 g of normal octyl mercaptan and 1.5 g of 2,2'-azobis isobutyronitrile were mixed and dispersed in an aqueous phase with stirring at 400 rpm to prepare a suspension.

Next, the suspension was heated to 80 ° C. to carry out a polymerization reaction for 90 minutes. Then, the suspension was cooled to 30 ° C., washed with distilled water, dehydrated, and dried to obtain a resin composition.

The resin composition obtained as described above was subjected to polycarbonate (LUPOY 1080DVD, LG Chemicals) and antioxidant (AO60, Adeka) at a temperature of 265 ° C. under a nitrogen atmosphere using a twin screw extruder (diameter 30, L / D 40). Kneading was carried out under temperature conditions to prepare a resin pellet. The composition, weight average molecular weight, glass transition temperature, haze, light transmittance and weight change rate of the prepared resin were measured, and the residual maleimide content, which is considered to be a major cause of odor generated during film processing, was further measured. The measurement results are shown in Table 1.

Then, the resin was prepared into a 160 μm film using a T-die extruder, and biaxially stretched at a rate of 2.0 times 200 mm / min in the MD direction and 2.0 times in the TD direction at a glass transition temperature of + 10 ° C. of the film. , 40 µm thick optical film was prepared. At this time, the odor generated during the optical film manufacturing process was sensed and compared. The residual phase difference, tensile strength, and coefficient of thermal expansion of the prepared optical film were measured. The measurement results are shown in Table 1.

<Example 2>

A resin composition was prepared in the same manner as in Example 1, except that methyl methacrylate, alpha methyl styrene, phenylmaleimide, and methyl acrylate were mixed in the amounts shown in Table 1 below, and together with the physical property measurement results, It was.

Comparative Example 1

Except that the methyl methacrylate and phenylmaleimide were mixed in the amounts shown in Table 1, the resin composition was prepared in the same manner as in Example 1, and the physical property measurement results are shown together.

Comparative Example 2

A resin composition was prepared in the same manner as in Example 1, except that methyl methacrylate, alpha methyl styrene, and phenylmaleimide were mixed in the amounts shown in Table 1 below, and the physical property measurement results are also shown.

Comparative Example 3

Except that the methyl methacrylate, phenylmaleimide and methyl acrylate were mixed in the amounts shown in Table 1 below, the resin composition was prepared in the same manner as in Example 1, and the physical property measurement results are shown together.

<Comparative Example 4>

Except that the methyl methacrylate and cyclohexyl maleimide were mixed in the amounts shown in Table 1 below, the resin composition was prepared in the same manner as in Example 1, and the physical property measurement results are shown together.

Comparative Example 5

A resin composition was prepared in the same manner as in Example 1, except that methyl methacrylate, alphamethylstyrene, and cyclohexyl maleimide were mixed in the amounts shown in Table 1 below, and the measurement results of the physical properties were also shown.

Comparative Example 6

A resin composition was prepared in the same manner as in Example 1, except that methyl methacrylate, alpha methyl styrene, cyclohexyl maleimide, and methyl acrylate were mixed in the amounts shown in Table 1 below. Shown.

<Production Example-Method of Manufacturing Polarizing Plate>

Using the optical film of the present invention prepared in the same manner as in Examples 1 to 2 and Comparative Examples 1 to 6 to prepare a polarizing plate as follows. First, the film is placed on one surface of a 25 μm thick PVA polarizer, and a 60 μm thick TAC film (Fuji, UZ TAC) is placed on the other side, and then a modified PVA-based aqueous adhesive is injected therebetween, followed by a compression roll. After hot air drying at a temperature of 80 ° C. for 5 minutes, a polarizer semi-finished product was prepared. After the corona treatment was carried out 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 opposite side of the TAC film, a polyester-based protective film having an adhesive layer was laminated to prepare a finished polarizing plate. The physical properties of the polarizing plate thus prepared were measured by the method described below, and the single transmittance, orthogonal transmittance, and polarization degree of the polarizing plate in the semi-finished state, and the Curl of the polarizing plate in the finished state. The measurement results are shown in [Table 1].

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

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

2. Glass transition temperature (Tg): Measured under 10 ℃ / min temperature conditions using a differential scanning calorimeter (DSC) DSC823 from Mettler Toledo.

3. Weight change rate: It was set in the TGA (heat balance) measuring apparatus, it measured under the nitrogen stream, and heated up from 30 degreeC to 500 degreeC at the temperature increase rate of 10 degree-C / min, and measured the temperature which a 2% weight reduction generate | occur | produces. .

4. Measurement of residual maleimide component: The maleimide monomer remaining in the resin after polymerization was quantitatively measured by a gas chromatograph (GC) analyzer. More specifically, first, the prepared resin pellet is completely dissolved in a certain amount of organic solvent (chloroform), and then n-hexane solvent is added to precipitate the dissolved resin component. After taking the upper part of the solution thus obtained, GC analysis is performed, and the residual maleimide component remaining in the resin is measured in comparison with the GC analysis result of the copolymer monomer measured in advance. At this time, the maleimide monomer remaining in the resin is the main cause of the odor generated during processing.

5. Retardation: The retardation of the prepared film was measured using a birefringence measuring instrument (Axoscan, Axometrics), the measurement wavelength was carried out at 550nm.

6. Haze and light transmittance: It measured according to ASTM1003 method.

7. Tensile strength: using a universal testing machine (UTM, Zwick) was measured according to the ASTM D638 test method.

8. Thermal expansion coefficient (CTE): The thermal expansion coefficient of 40 ℃ to 80 ℃ was measured at 10 ℃ / min temperature conditions using TMA SDTA 840 of Mettler Toledo.

9. Polarizing plate optical properties: The polarization degree of the polarizing plate was confirmed by measuring the single transmittance (Ts) and the orthogonal transmittance (Tc) of the polarizing plate using a P-2000 (JASCO) measuring instrument which is a digital spectro polarimeter.

The polarization degree is defined by the following [Equation 3] by the parallel transmittance (Tp) obtained when the two polarizing plates are arranged in parallel with the absorption axis and the orthogonal transmission (Tc) obtained after orthogonal to each other so that the absorption axis is 90 °. . However, a single transmittance value may be used instead of parallel transmittance.

[Equation 3]

Polarization degree = [(Tp -Tc) / (Tp + Tc)] ^1/2

10. Curl measurement: A polarizer specimen cut to 200 mm x 200 mm is placed on a horizontal table at 24 ° C and 50% RH with the concave side facing up for 1 hour, and the four corners of the specimen lifted from the table. Was measured using a ruler and the maximum value was defined as the amount of curl.

Table 1 division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Resin composition (part by weight) MMA 92 93 96 94 95 95 93 92 AMS 2 2 - 2 - - 2 2 PMI 5 4 4 4 4 - - - CHMI - - - - - 5 5 5 MA One One - - One - - One additive PC content 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 AO content 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Resin properties Weight average molecular weight 123,000 120,000 118,000 125,000 118,000 120,000 121,000 120,000 Tg (℃) 126 124 123 125 122 123 125 124 2% weight loss temperature (℃) 335 330 315 321 322 316 331 332 Residual Maleimide (ppm) Not detected Not detected 35 32 29 124 72 63 Film properties R _in / R _th (nm) 0.8 / 1.1 0.7 / 0.6 0.9 / 0.2 1.0 / 0.7 1.2 / 0.8 0.7 / 0.7 0.8 / -0.5 0.7 / -0.4 Haze (%) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 % Light transmittance 92.4 92.5 92.4 92.3 92.5 92.5 92.4 92.4 Tensile Strength (GPa) 2.3 2.3 2.1 2.2 2.0 1.9 2.0 1.9 Thermal expansion coefficient (ppm / ℃) 64 62 74 70 76 81 78 82 Polarizer Properties Group Permeability (%) 41.9 42.3 40.7 39.8 39.9 40.5 41.1 41.4 % Polarization 99.998 99.997 99.989 99.985 99.988 99.990 99.994 99.991 Curl (mm) 1.0 1.5 6.0 6.0 6.0 8.0 8.0 8.5

MMA: Methyl methacrylate

AMS: Alphamethylstyrene

PMI: Phenylmaleimide

CHMI: cyclohexyl maleimide

MA: Methyl Acrylate

PC: Polycarbonate

AO: Antioxidant

As shown in Table 1, in contrast to Examples 1 to 2 and Comparative Examples 4 to 6, when phenyl maleimide is included instead of cyclohexyl maleimide in the copolymer, due to the high reactivity of phenyl maleimide, Since there was no maleimide, it was confirmed that the generation of odor significantly during film extrusion.

In addition, it was confirmed that the resin films according to Examples 1 to 2 had a lower coefficient of thermal expansion compared to Comparative Examples 1 to 6.

In addition, the polarizing plates according to Examples 1 to 2 were able to confirm that curl generation was remarkably small compared to Comparative Examples 1 to 6, and it was also found that the single transmittance and the polarization were also excellent.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations can be made without departing from the technical spirit of the present invention described in the claims. It will be obvious to those who have ordinary knowledge of.

Claims (18)

A resin composition for an optical film, comprising a copolymer formed by polymerizing an alkyl methacrylate monomer, a styrene monomer, a phenylmaleimide monomer and an alkyl acrylate monomer. The method of claim 1, The said resin composition is the resin composition for optical films whose content of the unreacted phenylmaleimide-type monomer which remains in a resin composition is 30 ppm or less with respect to the whole composition. The method of claim 1 The resin composition is a resin composition for an optical film, further comprising a polycarbonate. The method of claim 1, The copolymer is based on 100 parts by weight of the copolymer, 70 to 98 parts by weight of an alkyl methacrylate monomer; 0.1 to 10 parts by weight of styrene monomer; 1 to 15 parts by weight of a phenylmaleimide monomer; And Resin composition for an optical film containing 0.1 to 5 parts by weight of an alkyl acrylate monomer. The method of claim 1, The resin composition for optical films whose weight ratio of the said phenyl maleimide monomer and the alkyl acrylate monomer is 2: 1-7: 1. The method of claim 3, The content of the polycarbonate is an optical film resin composition containing 0.1 to 10 parts by weight based on 100 parts by weight of the total resin composition. The method of claim 1, The alkyl methacrylate monomers are methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, hydroxyethyl methacrylate, isobornyl methacrylate And cyclohexyl methacrylate. The resin composition for an optical film, which is at least one selected from the group consisting of cyclohexyl methacrylate. The method of claim 1, The styrene monomer is at least one selected from the group consisting of styrene, α-methyl styrene, p-bromo styrene, p-methyl styrene and p-chloro styrene resin composition for an optical film. The method of claim 1, The phenyl maleimide monomer is at least one selected from the group consisting of phenyl maleimide, nitrophenyl maleimide, monochlorophenyl maleimide, dichlorophenyl maleimide, monomethylphenyl maleimide, dimethylphenyl maleimide and ethylmethylphenyl maleimide Resin composition for optical films. The method of claim 1, The alkyl acrylate monomers are methyl acrylate, ethyl acrylate, isopropyl acrylate n-butyl acrylate, t-butyl acrylate, cyclohexyl acrylate, isobornyl acrylate, hydroxymethyl acrylate and hydroxyethyl A resin composition for an optical film, which is at least one selected from the group consisting of acrylates. The method of claim 1, The resin composition for an optical film has a glass transition temperature of 100 ° C to 150 ° C. The method of claim 1, The resin composition for optical films is a resin composition for optical films, wherein the 2% weight loss temperature measured by a thermogravimetric analyzer (TGA) is 280 ° C or more. The optical film manufactured from the resin composition for optical films of any one of Claims 1-12. The method of claim 13, The optical film has an optical expansion coefficient of 50 to 100 ppm / ℃. The method of claim 13, The optical film is an optical film having an absolute value of the plane direction phase difference R _in defined by the following [Equation 1] and a thickness direction phase difference R _th defined by the following [Equation 2] at a wavelength of 550 nm, respectively, 5 nm or less. ; [Formula 1] R _in = (n _x -n _y ) × d, R _th = (n _z -n _y ) × d In [Formula 1] and [Formula 2], n _x is the largest refractive index of the in-plane refractive index of the optical film, n _y is the refractive index of the direction perpendicular to n _x of the in-plane refractive index of the optical film, n _z is the refractive index in the thickness direction, d is the thickness of the film. The method of claim 15, The said optical film is an optical film which is a protective film for polarizing plates. Polarizer; And A polarizing plate comprising the optical film of claim 13 disposed on at least one surface of the polarizer. An image display device comprising the polarizing plate of claim 17.