WO2014204168A1 - Multilayer optical film, method for preparing same and polarizing plate comprising same - Google Patents

Abstract

The present invention relates to a multilayer optical film, a method for preparing same, and a polarizing plate comprising same, wherein the multilayer optical film comprises: a first film layer formed of a thermoplastic acryl-based resin composition including 0.01 to 2.0 parts by weight of a triazine-based ultraviolet ray absorbing agent based on 100 parts by weight of a thermoplastic acryl-based resin composition; a second film layer formed of a thermoplastic acryl-based resin composition including 0.1 to 5.0 parts by weight of one or more ultraviolet ray absorbing agent(s) selected from the group consisting of triazole-based, benzophenon-based, oxanilide-based and cyanoacryl-based ultraviolet ray absorbing agents; and a third film layer formed of a thermoplastic acryl-based resin composition including 0.01 to 2.0 parts by weight of triazine-based ultraviolet ray absorbing agent.

Description

Multi-layered optical film, manufacturing method thereof and polarizing plate comprising the same

The present invention relates to a multilayer optical film, a method of manufacturing the same, 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.

On the other hand, polarizing plates used in image display apparatuses such as liquid crystal display devices generally use a triacetyl cellulose film (hereinafter, TAC film) as a protective film for protecting a polyvinyl alcohol polarizer. However, the TAC film does not have sufficient heat and moisture resistance, and when used under high temperature or high humidity, the TAC film has a problem in that polarization plate characteristics such as polarization degree and color are degraded due to film deformation. Therefore, in recent years, a method of using a transparent acrylic resin film having excellent moisture resistance and heat resistance instead of the TAC film has been proposed as a material of the polarizer protective film.

Moreover, the technique which prevents a polarizer from being degraded by an ultraviolet-ray by adding a ultraviolet absorber to such an acryl-type film to have ultraviolet absorption performance was also proposed. In the case of such a conventional acrylic film, a benzotriazol compound, a benzophenone compound, a benzotriazine compound, a cyano acrylate compound, or a salicylic acid type as a ultraviolet absorber It is known that compounds and the like can be used.

However, since the UV absorbers are mostly decomposed during high temperature processing, not only the UV absorbing ability is lowered, but also the yellowing of the resin and the film is caused by thermal decomposition of the UV absorber.

In particular, the benzotriazine-based compound has a high ultraviolet B region (315 nm ~ 280 nm) absorption capacity, but the ultraviolet A region (400 nm ~ 315 nm) absorption ability is low, so added in excess in order to increase the ultraviolet A region absorption capacity Should be. However, when the excess UV absorber is added, the acrylic resin melted under the high temperature and pressure of the extruder during the acrylic film manufacturing process passes through the T-die and passes through the casting roll. When the sudden cooling in the UV absorber decomposes out of the film as the phenomenon of migration to the casting roll was severe, as a result of the thermal decomposition of the UV absorber is also buried in the film has a problem that the appearance of the film is poor.

Furthermore, since the known ultraviolet absorbers have a low molecular weight and a glass transition temperature, when a large amount of the ultraviolet absorber is added to the acrylic resin, the glass transition temperature of the resin composition is greatly lowered, thereby lowering heat resistance or adversely affecting optical properties of the optical film.

Accordingly, there is a need for the development of a technology capable of manufacturing an optical film having excellent UV absorption performance but having a high glass transition temperature (Tg) value and preventing coloring and contamination problems.

The present invention is to provide a multilayer optical film having excellent heat resistance, excellent ultraviolet absorption performance and high economical efficiency, a method of manufacturing the same, and a polarizing plate including the same.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, in one aspect, this invention is a 1st film layer formed from the thermoplastic acrylic resin composition containing 0.01 weight part-2.0 weight part of triazine type ultraviolet absorbers with respect to 100 weight part of thermoplastic acrylic resin compositions. ; 0.1 to 5.0 parts by weight of at least one ultraviolet absorber selected from the group consisting of triazole-based, benzophenon-based, oxanilide-based and cyanoacryl-based ultraviolet absorbers A second film layer formed of a thermoplastic acrylic resin composition; And a third film layer formed of a thermoplastic acrylic resin composition including 0.01 parts by weight to 2.0 parts by weight of a triazine ultraviolet absorber.

In another aspect, the present invention provides a method for manufacturing a multilayer optical film comprising coextruding a first film layer, a second film layer and a third film layer as described above, and stretching the coextruded film. to provide.

In another aspect, the present invention, a polarizer comprising a polarizer and a protective film provided on at least one surface of the polarizer, at least one of the protective film is the first film layer, the second film layer and the third film layer It provides a polarizing plate which is a multilayer optical film containing.

The multilayer optical film according to the present invention is excellent in heat resistance and excellent in ultraviolet absorption performance, but has high economical efficiency.

In addition, according to the manufacturing method of the multilayer optical film according to the present invention, since the film manufacturing process and the stretching process can be configured continuously, the productivity is improved, and the optical film production having the desired UV transmittance without any additional process Since it is easy, there is high economical efficiency, and the optical film manufactured by this is very excellent in mechanical strength and impact strength.

In addition, the polarizing plate of the present invention includes a polarizer and a protective film provided on at least one surface of the polarizer, wherein at least one of the protective film comprises the first film layer, the second film layer and the third film layer. It is an optical film and is excellent in durability.

1 is a view showing a multilayer optical film according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. 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. Shape and size of the elements in the drawings may be exaggerated for more clear description.

The inventors of the present invention, as a result of research to develop an optical film that is excellent in UV blocking effect and also excellent in physical properties such as transparency, color and heat resistance, and has high UV absorption performance and excellent economy, A multilayer optical film has been developed.

That is, the inventors of the present invention, by producing an optical film in a multi-layer, and selectively using the type and components of the ultraviolet absorber of each film layer, according to the present invention having excellent ultraviolet absorption performance, but having high economic efficiency and thermal stability The multilayer optical film was completed.

In one aspect, the present invention, the first film layer formed of a thermoplastic acrylic resin composition containing 0.01 parts by weight to 2.0 parts by weight of the triazine-based ultraviolet absorber with respect to 100 parts by weight of the thermoplastic acrylic resin composition; 0.1 to 5.0 parts by weight of at least one ultraviolet absorber selected from the group consisting of triazole-based, benzophenon-based, oxanilide-based and cyanoacryl-based ultraviolet absorbers A second film layer formed of a thermoplastic acrylic resin composition; And a third film layer formed of a thermoplastic acrylic resin composition including 0.01 parts by weight to 2.0 parts by weight of a triazine ultraviolet absorber.

1, an embodiment of a multilayer optical film of the present invention is disclosed. As shown in FIG. 1, the multilayer optical film according to the present invention has a multilayer structure of the first film layer 10, the second film layer 20, and the third film layer 30. The optical film of the multilayer structure as described above has an advantage that can be produced by changing the configuration of each film layer. That is, the first film layer and the third film layer include a triazine-based ultraviolet absorbent having excellent heat resistance, and the second film layer has a triazole-based, benzophenon-based, and oxanilide having excellent ultraviolet absorption performance. By including at least one ultraviolet absorber selected from the group consisting of (Oxanilide) and cyanoacryl-based ultraviolet absorbers, an optical film excellent in both heat resistance and ultraviolet absorbing performance can be produced. In particular, even if a very expensive triazine-based UV absorber is used in a small amount only in some layers of the multilayer optical film as described above, an optical film having excellent heat resistance can be obtained, thereby lowering the production cost of the optical film, which is very advantageous in terms of economy. There is an advantage.

On the other hand, the thermoplastic acrylic resin composition forming the first film layer and the third film layer, the content of the triazine-based UV absorber may be in the range of 0.01 parts by weight to 2.0 parts by weight based on 100 parts by weight of the thermoplastic acrylic resin composition. . When the content of the triazine-based UV absorber included in the first film layer and the third film layer satisfies the numerical range, the acrylic resin melted under high temperature and pressure in the extruder during the manufacturing of the multilayer optical film is When suddenly cooled in the process of passing through the die and passing through the T-die, the UV absorber decomposes and escapes from the film. Can be prevented. As a result, a multilayer optical film having excellent appearance characteristics and excellent ultraviolet absorption performance can be obtained. In addition, since an optical film having excellent heat resistance can be obtained even by adding a small amount of an expensive triazine-based ultraviolet absorber, manufacturing cost can be lowered and productivity can be improved.

In addition, the thermoplastic acrylic resin composition forming the second film layer is composed of a triazole, benzophenon, oxanilide, and cyanoacryl ultraviolet absorbers. The content of the at least one ultraviolet absorber selected from the group may range from 0.1 parts by weight to 5.0 parts by weight based on 100 parts by weight of the thermoplastic acrylic resin composition. When the content of the ultraviolet absorber included in the second film layer satisfies the numerical range, the glass transition temperature of the resin composition can be prevented from being greatly reduced, and the multilayer optical film of the present invention has heat resistance characteristics and ultraviolet absorption performance. This is very excellent.

In particular, in the present invention, the amount of the ultraviolet absorber included in the first film layer and the third film layer is added in excess of the numerical range, or the content of the ultraviolet absorber included in the second film layer is the upper numerical range. When the excess amount is added in excess, the melt viscosity difference between the thermoplastic resin composition forming the first film layer and the second film layer or between the thermoplastic acrylic resin composition forming the third film layer and the second film layer is severe. In this case, a wave pattern may occur at each interface of the multilayer optical film, thereby causing a problem of poor appearance characteristics of the film.

On the other hand, in the multilayer optical film according to the present invention, the triazine-based UV absorber included in the first film layer and the third film layer is particularly limited as long as the ultraviolet absorption performance is in the range of 10% to 80% in the wavelength range of 280nm to 400nm. For example, the benzotriazine-based compound including a hydroxy group and the benzotriazine-based compound including one or more organic residues having 1 to 20 carbon atoms may be used. As described above, when the benzotriazine-based compound contains at least one hydroxyl group or an organic moiety having 1 to 20 carbon atoms, the maximum absorption wavelength (λmax) of the triazine-based ultraviolet absorber moves to a long wavelength region near the 380 nm wavelength band. Because it works, there is a very advantageous effect in terms of minimizing the content of the ultraviolet absorber included in the film.

In particular, the triazine-based ultraviolet absorber included in the thermoplastic resin composition forming the first film layer and the third film layer has a weight molecular weight of 300 to 2,000. When the weight molecular weight of the triazine-based UV absorber satisfies the above numerical range, it has excellent compatibility with the ultraviolet absorber and the thermoplastic acrylic resin composition, and has excellent mechanical and thermal properties of the formed first and third film layers. There is this.

On the other hand, in the multilayer optical film according to the present invention, the first film layer and the third film layer, when measured in terms of the thickness of the optical film 60㎛, the linear light transmittance of 10% to 30% at 380nm wavelength Can be. In the case of the 380nm wavelength, it is called a UVA region, which is not absorbed by the ozone layer, and because the intensity is also very high, it must be blocked. Therefore, when the straight light transmittance of the first film layer and the third film layer in the above conditions satisfy the above numerical range, it is possible to obtain an optical film excellent in the ultraviolet absorption performance, in particular the ultraviolet absorption performance of the UVA region.

In addition, the first film layer and the third film layer, when measured in terms of the thickness of the optical film 60㎛, the linear light transmittance may be 3% to 12% at 290nm wavelength. The 290nm wavelength is called the UVB region, which is mostly absorbed by the ozone layer, but because the energy is strong as the wavelength is short, it needs to be blocked even if the amount reaching the surface is small. Therefore, under the above conditions, when the linear light transmittance of the first film layer and the third film layer satisfies the numerical range, it is possible to obtain an optical film having excellent ultraviolet absorption performance, in particular, the ultraviolet absorption performance of the UVB region.

In the multilayer optical film according to the present invention, the ultraviolet absorber of the second film layer is not particularly limited as long as the ultraviolet absorbing performance is in the range of 10% to 80% in the wavelength range of 280nm to 400nm, for example, triazole ( Triazole), benzophenone (Benzophenon), oxanilide (Oxanilide) and may be one or more selected from the group consisting of cyanoacryl (Cyanoacryl) ultraviolet absorber. In particular, the ultraviolet absorber included in the second film layer in the present invention comprises a triazole compound containing a hydroxy group, an acrylonitrile group and a chlorine element, and a triazole compound including one or more organic residues having 1 to 20 carbon atoms. At least one selected from the group is more preferable because an optical film having a desired ultraviolet absorbing performance can be obtained while minimizing the content of the ultraviolet absorbing performance of the optical film, that is, the content of the ultraviolet absorbent.

In addition, the ultraviolet absorber included in the thermoplastic resin composition forming the second film layer, the weight average molecular weight is preferably 100 to 1000 or 200 to 800. When the weight average molecular weight of the ultraviolet absorber included in the second film layer satisfies the above numerical range, the thermal stability of the ultraviolet absorbent is excellent, the thermal stability of the resin composition is also excellent, and the boiling point is high, and it is easy to control the addition amount of the ultraviolet absorbent. This is because the mechanical and thermal properties of the formed second film layer are excellent.

Meanwhile, in the multilayer optical film according to the present invention, the second film layer may have a linear light transmittance of 1% to 15% at a wavelength of 380 nm when measured in terms of a thickness of 60 μm of the optical film. When the linear light transmittance of the second film layer satisfies the numerical range under the above conditions, the degeneration of the polarizer by the ultraviolet rays, in particular the UVA region, may be prevented. It can be prevented from adversely affecting.

In addition, the second film layer may have a linear light transmittance of 0.1% to 7% at a wavelength of 290 nm when measured in terms of a thickness of 60 μm of the optical film. Under the above conditions, when the linear light transmittance of the second film layer satisfies the numerical range, it is possible to prevent denaturation of the polarizer due to ultraviolet rays, particularly ultraviolet rays in the UVB region. It can be prevented from adversely affecting.

In addition, the said thermoplastic acrylic resin contains the copolymer containing the (a) alkyl (meth) acrylate type unit and (b) styrene type unit. In addition, the thermoplastic acrylic resin may further include an aromatic resin having a carbonate portion in the main chain.

In the present invention, the alkyl (meth) acrylate-based unit gives a negative in-plane retardation (Rin) and a negative thickness direction retardation (Rth) to the film in the stretching process to a weak degree, the styrene-based unit is a strong negative surface The internal phase difference Rin and the negative thickness direction phase difference Rth can be provided. On the other hand, the aromatic resin having a carbonate portion in the main chain can provide positive in-plane retardation (Rin) characteristics and positive thickness direction retardation (Rth) characteristics.

Here, the negative in-plane retardation means that the refractive index is greatest in the direction perpendicular to the stretching direction, and the positive in-plane retardation means that the refractive index is greatest in the stretching direction, and the negative thickness retardation means that the refractive index in the thickness direction is the plane. It means larger than the direction average refractive index, and a positive thickness direction retardation means that in-plane average refractive index is larger than thickness direction refractive index.

By the characteristics of each unit described above, 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, the composition and the extending | stretching method of each said component can be adjusted, and especially the multilayer optical film which can be used as a zero retardation film, ie, a protective film, can be manufactured.

Meanwhile, the copolymer in the present specification means that an element referred to as a 'unit' in the present specification is polymerized into a monomer to be included as a repeating unit in the copolymer resin, and in the present specification, the copolymer is a block copolymer or It may be a random copolymer, but the copolymer form is not limited thereto.

In addition, the term "alkyl (meth) acrylate-based unit" in the present specification includes both 'alkyl acrylate-based unit' and 'alkyl methacrylate-based unit', but is not limited thereto, optical transparency, commercial In view of the properties, processability and productivity, the alkyl moiety of the alkyl (meth) acrylate-based unit preferably has 1 to 10 carbon atoms, more preferably 1 to 4 carbon atoms, and is a methyl group or an ethyl group. More preferred. More specifically, the alkyl (meth) acrylate units are methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, hydroxyethyl methacrylate , Isobonyl methacrylate and cyclohexyl methacrylate may be at least one selected from the group consisting of, but is not limited thereto.

In this case, the alkyl (meth) acrylate-based unit includes 70 parts by weight to 98 parts by weight based on 100 parts by weight of the copolymer, more preferably contains 82 parts by weight to 97 parts by weight. When the content satisfies the above range, a film having excellent transmittance and heat resistance of the optical film may be obtained, and the birefringence generated during stretching may be minimized.

Next, in the present invention, the (b) styrene-based unit can improve the polymerization efficiency between the monomers, the film produced by the resin composition comprising the same can easily control the stretching phase difference more excellent birefringence A zero retardation film having a property can be obtained.

In this case, the (b) styrene-based unit 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 part by weight to about 10 parts by weight based on 100 parts by weight of the copolymer, and more preferably about 0.5 parts by weight to about 5 parts by weight. If the content of the styrene monomer meets the above range, it is because the stretching phase difference of the film can be easily adjusted to obtain a more preferable effect in terms of the optical properties of the film.

On the other hand, in the present invention, it is preferable that the aromatic resin having a carbonate portion in the main chain contains 5 to 10,000 at least one unit represented by the following [Formula I].

[Formula I]

Wherein X is a divalent group comprising at least one benzene ring. More specifically, X is preferably a divalent group selected from the group consisting of the following structural formulas.

On the other hand, the aromatic resin having a carbonate part in the main chain is added to the phase difference control may be included in an amount of 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the total thermoplastic acrylic resin composition, 1 part by weight to 5 It is more preferable to be included in about a weight part. When the aromatic resin having a carbonate portion in the main chain is contained in a smaller amount than this, there is a problem that the thickness direction retardation of the stretched film is increased in a positive direction, and when included in an amount exceeding this, the thickness direction retardation of the stretched film is negative. There is a problem that increases in the direction of. Moreover, when it exceeds 10 weight part, compatibility with a thermoplastic acrylic resin composition falls, and there exists a problem that a whitening phenomenon generate | occur | produces. Therefore, when the content of the aromatic resin having a carbonate moiety in the main chain satisfies the numerical range, the absolute value of the surface direction phase difference R _in defined by the following [Formula 1] and the thickness direction defined by the following [Formula 2] The absolute value of the retardation (R _th ) may be added by adjusting the content so as to be 5 nm, preferably 3 nm, and more preferably 0, respectively.

[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.

In this case, the resin composition of the present invention including the copolymer resin and the aromatic resin having a carbonate portion in the main chain may be prepared using a method well known in the art, such as, for example, a compounding method.

Further, the copolymer comprising the (a) alkyl (meth) acrylate unit and (b) styrene unit is (c) at least one in terms of providing excellent heat resistance to the film produced using the same. It is preferable to further include a 3-membered to 6-membered heterocyclic unit substituted with a carbonyl group, wherein the heterocyclic unit is selected from the group consisting of maleic anhydride, maleimide, glutaric anhydride, glutalimide, lactone and lactam Can be. In addition, when the (c) 3- to 6-membered heterocyclic unit substituted with at least one carbonyl group and the (a) alkyl (meth) acrylate-based unit constitute a copolymer, the copolymer resin and the main chain have a carbonate moiety. Compatibility with the aromatic resin can be improved.

On the other hand, the (c) three- to six-membered heterocyclic unit substituted with at least one carbonyl group, more specifically, for example, ethyl maleimide, n-butyl maleimide, t-butyl maleimide, cyclohexyl maleimide It is preferable that it is a maleimide derivative like a phenyl maleimide etc., and it is especially preferable that it is a phenyl maleimide type unit. The phenyl maleimide unit has a uniform chemical structure under the influence of a substituted phenyl group, thus making it easy to form copolymers with (a) alkyl (meth) acrylate units and (b) styrene units and improve heat resistance. This is because there is an advantage that the polymerization time is relatively short.

On the other hand, specific examples of the phenyl maleimide-based unit is a group consisting of phenyl maleimide, nitrophenyl maleimide, monochlorophenyl maleimide, dichlorophenyl maleimide, monomethylphenyl maleimide, dimethylphenyl maleimide, and ethylmethylphenyl maleimide It is preferably at least one selected from.

At this time, the (c) at least one member of the three to six-membered heterocyclic unit substituted with a carbonyl group is preferably included in an amount of 0.1 parts by weight to 10 parts by weight with respect to 100 parts by weight of the copolymer resin. When the content of the three to six-membered heterocyclic unit substituted with the at least one carbonyl group satisfies the numerical range, the optical film is excellent in heat resistance, and the resin properties become unstable, resulting in breakage of the optical film. It can prevent an easy state.

Meanwhile, in the present invention, the thermoplastic acrylic copolymer may further include an alkyl acrylate unit in order to impart polymerization stability and thermal stability to the resin composition and toughness to the stretched film. By introducing this structural unit, it is possible to obtain a composition having excellent heat resistance such as molding processability such as mold release property and preventing weight loss due to heat during the process.

In this case, the alkyl moiety of the alkyl acrylate monomer may be a cycloalkyl group or a substituted alkyl group, preferably has 1 to 10 carbon atoms, more preferably 1 to 6, and is a methyl group or an ethyl group. Most preferred. 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 alkyl acrylate-based unit may include about 0.1 parts by weight to about 5 parts by weight based on 100 parts by weight of the thermoplastic acrylic copolymer, and more preferably about 0.5 parts by weight to about 3.0 parts by weight. When the content of the alkyl acrylate-based unit is in the above range, the polymerization between the (a) alkyl (meth) acrylate-based unit and (c) at least one carbonyl group substituted with at least one carbonyl group at the time of copolymerization It is easy, it is possible to overcome the thermal decomposition phenomenon that can occur in the resin melting process, it is very advantageous because it has the effect that the stretching process is easily carried out by giving toughness when stretching the film.

On the other hand, the thermoplastic acrylic resin used in the embodiment of the present invention can be suitably used as long as the glass transition temperature is 70 ° C or higher. In order to further suppress the moisture absorption of the pellets, the glass transition temperature of the thermoplastic acrylic resin is preferably 110 ° C. or higher, for example, 115 ° C. or higher, 120 ° C. or higher, or 125 ° C. or higher. The higher the glass transition temperature of the thermoplastic acrylic resin, the higher the temperature at which the fusion of the pellets occurs, so that pellets can be manufactured at a higher temperature, and as a result, a thermoplastic acrylic resin pellet having a lower water content can be produced.

Next, the ultraviolet absorber is not particularly limited in shape, but may be, for example, powder, granule, flake, liquid, or the like.

In the multilayer optical film according to the present invention, the glass transition temperature difference of the films constituting each film layer may be 2 ° C or less. When the glass transition temperature difference of the films constituting each film layer satisfies the numerical range, the bending and curling phenomenon may be prevented from occurring in the multilayer optical film due to the difference in the coefficient of thermal expansion of each film layer. Can be.

The multilayer optical film according to the present invention may have a UV transmittance in the range of 1% to 10% at a wavelength of 380 nm. When the ultraviolet transmittance at the wavelength of 380 nm satisfies the above numerical range, this indicates that the ultraviolet light absorbing ability is excellent in the visible light region of 400 nm to 800 nm, especially in the vicinity of the 400 nm wavelength band, thereby preventing the decrease in light transmittance in the vicinity. The durability of the polarizing plate to which such a multilayer optical film is applied can be improved. In this regard, when the UV transmittance near the 400 nm wavelength band becomes high, that is, when the light transmittance decreases, the reddish reddish light becomes more intense, resulting in a yellowing phenomenon in which the film turns yellow. This is because the color change and the polarization of the polarization element may occur.

In the multilayer optical film according to the present invention, the first film layer, the second film layer, and the third film layer may be coextruded. When the multilayer optical film is manufactured by the co-extrusion process as described above, it is possible to manufacture an optical film having a desired ultraviolet absorption performance without any additional process, there is an advantage that it is easy to control the thickness of each layer and the content of the ultraviolet absorber.

In the multilayer optical film according to the present invention, when measured in terms of a thickness of 60 μm of the optical film, the linear light transmittance may be 80% or more at a wavelength of 550 nm, and more specifically, may be 85% to 100%. When the multilayer optical film is converted to a thickness of 60 μm of the optical film and the linear light transmittance measured at the wavelength of 550 nm satisfies the numerical range, the transmittance of the polarizing plate is improved to improve visibility, prevent color change, and contrast. The contrast ratio (CR) is reduced, so that the clarity of the liquid crystal panel is excellent.

In addition, the multilayer optical film may have a straight light transmittance of 0.1% to 15%, more preferably 0.1% to 10% at a wavelength of 380 nm when measured in terms of a thickness of 60 μm of the optical film. When the multilayer film is converted to a thickness of 60 μm of the optical film and the linear light transmittance measured at the wavelength of 380 nm satisfies the numerical range, the optical film has excellent ultraviolet absorption performance, particularly ultraviolet absorption performance in the UVA region. When it is applied to the polarizing plate, it is possible to prevent denaturation of the polarizing element due to ultraviolet rays in the UVA region.

Furthermore, the multilayer optical film may have a linear light transmittance of 0.01% to 5%, more preferably 0.01% to 4% at a wavelength of 290 nm when measured in terms of a thickness of 60 μm of the optical film. When the multilayer film is converted into a thickness of 60 µm of the optical film and the linear light transmittance measured at the wavelength of 290 nm satisfies the numerical range, the optical film has excellent ultraviolet absorption performance, particularly ultraviolet absorption performance in the UVB region. When applied to the polarizing plate, it is possible to prevent denaturation of the polarizing element due to ultraviolet rays in the UVB region.

In the multilayer optical film according to the present invention, the components of the ultraviolet absorber of the first film layer and the third film layer are the same, and the components of the ultraviolet absorber of each film layer are changed in such a manner that the ultraviolet components of the second film layer are different. By using selectively, there is an advantage of excellent ultraviolet absorption performance, but also having high economy and thermal stability.

Next, the manufacturing method of the multilayer optical film which concerns on this invention is demonstrated.

In another aspect, the present invention, the first film layer, the second film layer and the third film layer by co-extrusion; And it provides a method for producing a multilayer optical film comprising the step of stretching the coextruded film.

In the manufacturing method of the optical film according to the present invention, the step of co-extrusion of the first film layer, the second film layer and the third film layer is to obtain a multilayer optical film in a continuous process, it is performed by co-extrusion Can be. More specifically, for example, it may be performed by a coextrusion T die method, a coextrusion inflation method, a coextrusion lamination method, but is not limited thereto.

In particular, the co-extrusion of the first film layer, the second film layer and the third film layer may be performed by a co-extrusion T die method. For example, the thermoplastic acrylic resin composition forming the second film layer may be extruded using a biaxial first extruder having a diameter of 32φ and an L / D of 40, and the first film layer and The thermoplastic resin composition forming the third film layer may be extruded using a second uniaxial extruder having a diameter of 30φ and an L / D of 28. The resin melted in the first extruder and the second extruder are respectively joined in a feed block unit after the extruder to form a melt flow layer, and then formed into a multilayer film through a T-die. Can be. Here, L / D means a value obtained by dividing the entire length of the screw by the screw diameter.

On the other hand, the extrusion temperature during the co-extrusion is appropriately selected so that the resin is a melt viscosity suitable for extrusion film forming, the first film layer, the second film layer and the third film layer all 220 ℃ to 290 ℃ or 240 ℃ to May be 280 ° C. Further, in the multilayer optical film, the temperature difference between the first film layer and the second film layer or the extrusion temperature difference between the third film layer and the second film layer may be such that the resin of each film layer is in a T die or in a feed block. When contacted, the melt viscosity may be excessively changed by temperature change, and may be within 30 ° C. or within 20 ° C. so that moldability does not deteriorate.

The melt viscosity of the thermoplastic acrylic resin composition forming the first film layer, the second film layer, and the third film layer is 200 Pa · s to 900 Pa · under conditions of a melting temperature of 265 ° C. and a shear rate of 100 l / s. It may be s, wherein the difference in melt viscosity between the thermoplastic acrylic resin composition forming the first film layer and the second film layer or the difference in melt viscosity between the thermoplastic acrylic resin composition forming the third film layer and the second film layer, It may be within 300 Pa.s, preferably 50 Pa.s to 200 Pa.s, in order to ensure moldability, in particular the uniformity of the thickness of each layer. This is because when the viscosity difference of the molten resin constituting each film layer exceeds 300 Pa · s, the appearance quality of the film is deteriorated due to the generation of wave patterns due to the difference in shear rate at each film layer interface.

The thermoplastic acrylic resin used for the multilayer optical film of the present invention can obtain sufficient adhesion strength in a state where the first film layer, the second film layer, and the third film layer are in direct contact with each other by thermal fusion by coextrusion. . Moreover, even after extending | stretching process, the adhesiveness of the said 1st film layer, the 2nd film layer, and the 3rd film layer is maintained favorable.

On the other hand, in the manufacturing method of the multilayer optical film, not all film layers are limited to being manufactured by co-extrusion, the first film layer or the third film layer, for example, may be formed by coating and curing. .

Next, the step of stretching the coextruded film will be described.

In the manufacturing method of the optical film according to the present invention, the stretching step in the step of stretching the co-extruded film may be performed in the longitudinal direction (MD) stretching, transverse direction (TD) stretching, respectively, or both. have. In addition, in the case where both longitudinal stretching and transverse stretching are performed, either stretching may be performed first and then stretched in the other direction, or both directions may be stretched simultaneously. In addition, the stretching may be performed in one step or may be performed in multiple steps. In the case of longitudinal stretching, stretching by the speed difference between the rolls can be performed, and in the case of transverse stretching, a tenter can be used. The rail starting angle of the tenter is usually within 10 ° to suppress the bowing phenomenon occurring during the lateral stretching and to control the angle of the optical axis regularly. Even when the transverse stretching is carried out in multiple stages, the anti-boeing effect can be obtained. Through the stretching process as described above it is possible to adjust the phase difference characteristics of the film.

In the manufacturing method of the optical film according to the present invention, the stretching ratio in the step of stretching the coextruded film, 1.3 times to 3.5 times, 1.5 times to 3.0 times or 1.7 times to 2.7 times in the longitudinal direction (MD) Can be. When the longitudinal stretch magnification satisfies the numerical range, the film is excellent in handleability, and breakage of the stretched film can be prevented. In the present specification, the longitudinal direction (MD, Machine Direction) refers to the film advancing direction.

In addition, the draw ratio in the stretching of the coextruded film may be 1.3 times to 3.5 times, 1.5 times to 3.0 times, or 1.7 times to 2.7 times in the transverse direction (TD). When the lateral stretch magnification satisfies the numerical range, the film is excellent in handleability, and breakage of the stretched film can be prevented. In the present specification, the longitudinal direction (MD, Machine Direction) refers to the film advancing direction. In the present specification, the transverse direction (MD, Machine Direction) means a direction perpendicular to the film advancing direction.

On the other hand, in the stretching step in the method for producing an optical film according to the present invention, it is preferable to determine the stretching temperature based on the glass transition temperature of the film of each film layer of the multilayer optical film in adjusting the phase difference. Specifically, the glass transition temperature of the film having the highest glass transition temperature among the film layers of the multilayer optical film may be a temperature within +30 ℃ or +20 ℃. When the stretching temperature satisfies the numerical range, the mechanical properties of the optical film may be excellent, and the problem of film breakage may be prevented during stretching.

At this time, it is preferable that all the glass transition temperatures of the film of each film layer of the said multilayer optical film are 110 degreeC or more, In particular, in order to ensure thermal stability and stretchability, the glass transition temperature of the film of each film layer is 110 degreeC. It is preferable that they are -180 degreeC or 120 degreeC-150 degreeC.

In the optical film manufacturing method according to the present invention, since the film manufacturing process and the stretching process can be continuously configured, the productivity is improved, and since it is easy to manufacture the optical film having the desired UV transmittance without any additional process, the high It is economical, and the optical film produced thereby has a significant increase in mechanical strength and impact strength.

According to a third aspect of the present invention, there is provided a polarizer and a protective film provided on at least one surface of the polarizer, wherein at least one of the protective films includes a first film layer, a second film layer, and a third film layer. It provides a polarizing plate which is the multilayer optical film.

The multilayer optical film according to the present invention can be used as a polarizer protective film. In this case, the surface may be modified to improve adhesion. Modification methods include a method of treating the surface of the protective film by corona treatment, plasma treatment, UV treatment, and the like to form a primer layer on the surface of the protective film, and the above two methods may be used at the same time. Although the kind of primer is not specifically limited, It is preferable to use the compound which has a reactive functional group like a silane coupling agent.

Polarizing plate comprising a multilayer optical film according to the present invention as a protective film, the polarizer and a protective film provided on at least one side of the polarizer, at least one of the protective film is a structure of the multilayer optical film according to the present invention described above It can have

On the other hand, in the polarizing plate according to the present invention, as the polarizer can be used without limitation known in the art, for example, a film made of polyvinyl alcohol (PVA) containing iodine or dichroic dye can be used. have. 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 the present specification, the polarizer means a state not including a protective film, and the polarizing plate means a state including a polarizer and a protective film.

Adhesion of the polarizer and the protective film may be performed using an adhesive layer. The adhesive that can be used when laminating the protective film and the polarizing plate is not particularly limited as long as it is known in the art. For example, a one-component or two-component polyvinyl alcohol (PVA) adhesive, a polyurethane adhesive, an epoxy adhesive, a styrene butadiene rubber (SBR) adhesive, or a hot melt adhesive can be used.

Further, the adhesion of the polarizer and the protective film is first coated with an adhesive using a roll coater, gravure coater, bar coater, knife coater, or capillary coater on the surface of the polarizer protective film or PVA film that is a polarizer, Before the adhesive is completely dried, the protective film and the polarizing film may be carried out by a method of laminating by heat pressing at room temperature or pressing at room temperature. In the case of using a hot melt adhesive, a heat press roll should be used.

In addition, an adhesive may also be used as long as it can exert sufficient adhesive force. The adhesive is preferably hardened by heat or ultraviolet rays after lamination, and thus the mechanical strength is improved to the level of the adhesive. The adhesive strength is also large, and thus the adhesive strength is such that it does not peel off without breaking of either film to which the adhesive is attached. It is preferable.

In particular, examples of the pressure-sensitive adhesive that can be used include natural rubber, synthetic rubber or elastomer, vinyl chloride / vinyl acetate copolymer, polyvinyl alkyl ether, polyacrylate, modified polyolefin-based pressure-sensitive adhesive having excellent optical transparency, and a curing agent such as isocyanate is added thereto. One curable adhesive can be mentioned.

The polarizing plate according to the present invention manufactured as described above may be used in various applications. Specifically, it can be preferably used for an image display device including a polarizing plate for liquid crystal display (LCD), an anti-reflective polarizing plate of an organic EL display device, and the like. In addition, the polarizing plate according to the present invention combines various optical layers such as retardation plates, light diffusing plates, viewing angle expanding plates, brightness enhancing plates, reflecting plates such as various functional films, for example, λ / 4 plates, λ / 2 plates, and the like. It can be applied to one composite polarizer.

The polarizing plate may be provided with an adhesive layer on at least one surface so as to be easily applied to an image display device. In addition, a release film may be further provided on the pressure-sensitive adhesive layer to protect the pressure-sensitive adhesive layer until the polarizing plate is applied to an image display device or the like.

The polarizing plate according to the present invention includes a polarizer and a protective film provided on at least one surface of the polarizer, wherein at least one of the protective films includes the first film layer, the second film layer, and the third film layer. The polarizing plate which is an optical film is excellent in durability.

Preparation Example 1

(1) Preparation of resin composition

1000 g of a monomer mixture consisting of 92 parts by weight of methyl methacrylate, 5 parts by weight of N-phenylmaleimide, 2 parts by weight of α-methyl styrene and 1 part by weight of methacrylate was prepared, and 2000 g of distilled water and 5% polyvinyl chloride were prepared in a 5 liter reactor. 8.4 g of alcohol solution (POVAL PVA217, Kuraray), 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.

Next, the primary polymerization was carried out at 80 ° C., and after the suspension reached 80 ° C., it was confirmed that a polymerization peak was generated after about 60 minutes, and the temperature was raised to 115 ° C. to carry out secondary polymerization for about 40 minutes. After the second polymerization as described above, the suspension was cooled to 30 ° C. to obtain a resin composition in the form of polymerized particles. The resin composition was used after washing with distilled water and dehydrating and drying.

At this time, the resin composition showed a spherical particle form having an average diameter of 250㎛ as confirmed using an optical microscope (LV100P, Nikon).

(2) Production of raw material pellets

Next, 1 part by weight of a triazine-based UV absorber (Tinuvin-1577, BASF) was added to 100 parts by weight of the resin composition, followed by mixing for 2 minutes in a solid mixer, and then the raw material mixture was prepared from a raw material hopper. Up to two extruders were supplied to a second extruder of 24 φ which was nitrogen-substituted and melted at 260 ° C. to prepare raw pellets.

At this time, the prepared resin was measured for glass transition temperature (Tg) by using a DSC (DSC823, Mettler Toledo) at 10 ℃ / min temperature rising conditions.

Preparation Example 2

In Production Example 1, a resin composition was produced with the same composition and method.

Next, the raw material pellets were manufactured in the same manner as in Preparation Example 1, except that 3 parts by weight of a triazole UV absorber (TINUVIN 326, BASF) was used based on 100 parts by weight of the resin composition using the resin composition.

Preparation Example 3

In Production Example 1, a resin composition was produced with the same composition and method.

Next, the raw material pellets were manufactured in the same manner as in Production Example 1 except that the ultraviolet absorbent was not used using the resin composition.

Preparation Example 4

In Production Example 1, a resin composition was produced with the same composition and method.

Next, the raw material pellets were manufactured in the same manner as in Production Example 1, except that 2 parts by weight of the ultraviolet absorbent was used based on 100 parts by weight of the resin composition using the resin composition.

Preparation Example 5

In Production Example 2, a resin composition was produced with the same composition and method.

Next, the raw material pellets were manufactured in the same manner as in Production Example 2, except that 6 parts by weight of the ultraviolet absorber was used based on 100 parts by weight of the resin composition using the resin composition.

Preparation Example 6

In Production Example 1, a resin composition was prepared in the same manner except that acrylonitrile and styrene copolymer resin pellets (82TR, LG Chem.) Were used.

Next, a raw material pellet was manufactured in the same manner as in Production Example 1, except that 1 part by weight of a triazine-based ultraviolet absorber (Tinuvin-1577, BASF) was used based on 100 parts by weight of the resin composition.

Preparation Example 7

In Production Example 1, a resin composition was prepared in the same manner except that polycarbonate resin pellets (LUPOY, LG Chem.) Were used.

Next, a raw material pellet was manufactured in the same manner as in Production Example 1, except that 1 part by weight of a triazine-based ultraviolet absorber (Tinuvin-1577, BASF) was used based on 100 parts by weight of the resin composition.

Preparation Example 8

In Production Example 1, a resin composition was produced with the same composition and method.

Next, except that 1 part by weight of a triazine-based UV absorber (Tinuvin-1577, BASF) and 3 parts by weight of a triazole-based UV absorber (TINUVIN 326, BASF) were used based on 100 parts by weight of the resin composition. , The raw material pellets were prepared in the same manner as in Preparation Example 1.

The type, molecular weight and content of the ultraviolet absorber added to the raw material pellets prepared according to Preparation Examples 1 to 8 are shown in the following [Table 1].

Table 1

division	UV absorbers	UV absorber molecular weight	UV absorber content (wt%)	Tg (℃)
Preparation Example 1	Triazine system	425	1.0	125
Preparation Example 2	Triazole type	316	3.0	124
Preparation Example 3	-	-	-	125
Preparation Example 4	Triazine system	425	2.0	123
Preparation Example 5	Triazole type	316	6.0	122
Preparation Example 6	Triazine system	425	1.0	116
Preparation Example 7	Triazine system	425	1.0	143
Preparation Example 8	Triazine and Triazole	Triazine system: 425 Triazole system: 316	Triazine system: 1.0 Triazole system: 3.0	123

Example 1

The raw material pellets prepared according to Preparation Example 1 were hot-air dried at 80 ° C. for 6 hours and melted with a second extruder at 260 ° C. to form a first film layer and a third film layer. In addition, the raw material pellets prepared according to Preparation Example 2 were hot air dried at 80 ° C. for 6 hours, and melted with a first extruder at 265 ° C. to form a second film layer.

Next, the first film layer, the second film layer and the third film layer is passed through a coat hanger type T-die (T-die), and the optical of 210㎛ thickness through a chrome plating casting roll, drying roll, etc. A film was prepared. At this time, the thickness of the prepared film was measured using a contact thickness meter (m-hite, TEAS, Swiss).

Thereafter, the film was oriented in the longitudinal direction (MD) and in the transverse direction (200 mm / min) at 131 ° C. to 135 ° C. under conditions of 10 ° C. higher than the glass transition temperature (Tg) of each film layer using an experimental film stretching equipment. TD) was stretched 100% each to prepare a multilayer optical film having a thickness of 52 μm.

Comparative Example 1

In Example 1, the first film layer and the third film layer is formed using the raw material pellets prepared in Preparation Example 2, and the second film layer is formed using the raw material pellets prepared in Preparation Example 1 A multilayer optical film having a thickness of 54 µm was prepared in the same manner as the above.

Comparative Example 2

In Example 1, the first film layer and the third film layer was formed using the raw material pellets prepared in Preparation Example 1, and the second film layer was formed using the raw material pellets prepared in Preparation Example 3. A multilayer optical film having a thickness of 55 µm was manufactured in the same manner as the above.

Comparative Example 3

In Example 1, the first film layer and the third film layer is formed using the raw material pellets prepared in Preparation Example 1, and the second film layer is formed using the raw material pellets prepared in Preparation Example 5. A multilayer optical film having a thickness of 58 μm was prepared in the same manner except as described above.

Comparative Example 4

In Example 1, the first film layer and the third film layer is formed using the raw material pellets prepared in Preparation Example 2, and the second film layer is formed using the raw material pellets prepared in Preparation Example 3 A multilayer optical film having a thickness of 53 μm was prepared in the same manner except the above.

Comparative Example 5

In Example 1, the first film layer and the third film layer was formed using the raw material pellets prepared in Preparation Example 2, and the second film layer was formed using the raw material pellets prepared in Preparation Example 4. A multilayer optical film having a thickness of 54 µm was prepared in the same manner as the above.

Comparative Example 6

In Example 1, a multilayer optical film having a thickness of 57 μm was manufactured in the same manner except that the first film layer and the third film layer were formed using the raw material pellets prepared in Preparation Example 4.

Comparative Example 7

In Example 1, a multilayer optical film having a thickness of 54 μm was manufactured in the same manner except that the first film layer and the third film layer were formed using the raw material pellets prepared in Preparation Example 6.

Comparative Example 8

In Example 1, a 52-micrometer-thick multilayer optical film was produced by the same method except having formed the 1st film layer and the 3rd film layer using the raw material pellet manufactured according to manufacture example 7.

Comparative Example 9

In Example 1, the multilayer optical film of 52 micrometers in thickness was produced by the same method except having formed all the 1st film layer-the 3rd film layer using the raw material pellet manufactured by the manufacture example 2.

Comparative Example 10

In Example 1, a single-layer optical film having a thickness of 51 μm was manufactured in the same manner except that the raw material pellets prepared in Preparation Example 8 were formed using a first extruder.

<Measuring roll contamination>

In the manufacturing process of the multilayer optical film according to Example 1 and Comparative Examples 1 to 10 by measuring the contamination of the roll is shown in Table 2 below. Roll contamination was measured by observing the surface of the casting roll 1 hour after film forming to visually confirm the degree of contamination by the ultraviolet absorbent. At this time, the degree of contamination of the casting roll was expressed as "○" when the cloudy surface was observed with the naked eye, and "x" when maintaining the clean state as the glass surface.

<Measure the appearance of film defects>

In the manufacturing process of the multilayer optical film according to Example 1 and Comparative Examples 1 to 10 by measuring the appearance of the film is poor, the results are shown in the following [Table 2]. Measurement of the appearance defect of the film was performed by a method of confirming whether the appearance defect of the film through visual observation of the optical film passed through the casting roll. At this time, when there was a wave pattern defect between each layer of the film formed, it was indicated by "x", and when maintaining a clean state, such as a glass surface, it was indicated by "○".

<Measurement of Straight Light Transmittance of Optical Film>

With respect to the optical film prepared according to Example 1 and Comparative Examples 1 to 10, the linear light transmittance was measured and the results are shown in the following [Table 2]. At this time, the linear light transmittance of the optical film was measured using a UV-Visible Spectrophotomer (U-3310, Hitachi, Japan) without the integrating sphere.

<Measurement of Impact Strength of Optical Film>

For the optical film prepared according to Example 1 and Comparative Examples 1 to 10, the impact strength of the film was measured and the results are shown in the following [Table 2]. At this time, the impact strength is measured by dropping a metal ball of a predetermined weight by using a Drop Impact Tester equipment to measure the height of the film break, and convert the potential energy corresponding to the measured height into the unit volume of the film to the impact strength Converted.

TABLE 2

division	Film thickness (㎛)	Whether the roll is dirty	Film appearance	Straight light transmittance (%)		Impact Strength of Film (Unit: kPa)
				290 nm	380nm
Example 1	52	X	O	0.02	2.08	558
Comparative Example 1	54	O	O	0.02	10.37	568
Comparative Example 2	55	X	O	4.91	80.26	487
Comparative Example 3	58	X	X	0	0.05	541
Comparative Example 4	53	O	O	5.86	14.92	494
Comparative Example 5	54	O	O	0	7.26	4878
Comparative Example 6	57	O	O	0	1.74	506
Comparative Example 7	54	X	X	0.03	2.47	420
Comparative Example 8	52	X	X	0.02	2.31	1122
Comparative Example 9	52	O	O	0.01	1.08	537
Comparative Example 10	51	O	X	0.02	2.34	340

As shown in the above [Table 2], in the case of Example 1, a multilayer optical film was obtained in which no roll contamination occurred, the external appearance property of the film was excellent, and the straight light transmittance and the impact strength were also excellent.

However, in the case of the optical film according to Comparative Example 1 and Comparative Examples 4 to 6, there was a problem that the roll is contaminated and the straight light transmittance is also not good. In addition, in the case of the optical films according to Comparative Examples 2 and 4 it can be seen that the straight light transmittance is not very good.

On the other hand, in the optical film according to Comparative Example 3, due to the large amount of ultraviolet absorber included in the second film layer, the melt viscosity imbalance with the first film layer and the third film layer occurred, resulting in a wave pattern on the interface of the film layer Was observed. Furthermore, in the case of the optical films according to Comparative Examples 7 and 8, the resin composition forming the second film layer and the resin composition having a large difference in glass transition temperature were used as the first film layer and the third film layer. Similarly, there was a problem of unbalanced melt viscosity with the second film layer, and as a result, a wave pattern was observed at the interface of each film layer. Moreover, when forming an optical film in a single layer like the comparative example 10, it turned out that impact strength falls remarkably.

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.

[Description of the code]

10: first film layer

20: second film layer

30: third film layer

Claims (20)

1. To 100 parts by weight of the thermoplastic acrylic resin composition,

   A first film layer formed of a thermoplastic acrylic resin composition comprising 0.01 parts by weight to 2.0 parts by weight of a triazine ultraviolet absorber;

   0.1 to 5.0 parts by weight of at least one ultraviolet absorber selected from the group consisting of triazole-based, benzophenon-based, oxanilide-based and cyanoacryl-based ultraviolet absorbers A second film layer formed of a thermoplastic acrylic resin composition; And

   A multilayer optical film comprising a third film layer formed of a thermoplastic acrylic resin composition comprising 0.01 parts by weight to 2.0 parts by weight of a triazine ultraviolet absorber.
2. The method of claim 1,

   The ultraviolet absorber of the first film layer and the third film layer is a multilayer optical film having a weight average molecular weight of 300 to 2000.
3. The method of claim 1,

   The first film layer and the third film layer is a multilayer optical film having a linear light transmittance of 10% to 30% at a wavelength of 380nm when measured in terms of a thickness of 60㎛ of the optical film.
4. The method of claim 1,

   The first film layer and the third film layer is a multilayer optical film having a linear light transmittance of 3% to 12% at a wavelength of 290nm when measured in terms of a thickness of 60㎛ of the optical film.
5. The method of claim 1,

   The ultraviolet absorber of the second film layer is a multilayer optical film having a weight average molecular weight of 100 to 1000.
6. The method of claim 1,

   The second film layer is a multilayer optical film having a linear light transmittance of 1% to 15% at a wavelength of 380 nm when measured in terms of a thickness of 60 μm of the optical film.
7. The method of claim 1,

   The second film layer is a multilayer optical film having a linear light transmittance of 0.1% to 7% at a wavelength of 290nm when measured in terms of a thickness of 60㎛ of the optical film.
8. The method of claim 1,

   The thermoplastic acrylic resin composition is a multilayer optical film wherein the thermoplastic acrylic resin comprises a copolymer comprising an alkyl (meth) acrylate unit and a styrene unit.
9. The method of claim 8,

   The thermoplastic acrylic resin composition is a multilayer optical film that the thermoplastic acrylic resin further comprises an aromatic resin having a carbonate portion in the main chain.
10. The method of claim 1,

    The multilayer optical film whose glass transition temperature difference of the thermoplastic acrylic resin composition which comprises each film layer is 2 degrees C or less.
11. The method of claim 1,

    The multilayer optical film has a UV transmittance of 0.1% to 10% at a wavelength of 380nm.
12. The method of claim 1,

    The said multilayer optical film is a multilayer optical film which coextruded the 1st film layer, the 2nd film layer, and the 3rd film layer.
13. The method of claim 1,

    The multilayer optical film has a straight light transmittance of 85% to 100% at a wavelength of 550 nm when measured in terms of a thickness of 60 μm of the optical film.
14. The method of claim 1,

    The multilayer optical film has a linear light transmittance of 0.1% to 15% at a wavelength of 380 nm when measured in terms of a thickness of 60 μm of the optical film.
15. The method of claim 1,

    The multilayer optical film has a linear light transmittance of 0.01% to 5% at 290 nm wavelength when measured in terms of a thickness of 60 μm of the optical film.
16. To 100 parts by weight of the thermoplastic acrylic resin composition,

    A first film layer formed of a thermoplastic acrylic resin composition comprising 0.01 parts by weight to 2.0 parts by weight of a triazine ultraviolet absorber;

    0.1 to 5.0 parts by weight of at least one ultraviolet absorber selected from the group consisting of triazole-based, benzophenon-based, oxanilide-based and cyanoacryl-based ultraviolet absorbers A second film layer formed of a thermoplastic acrylic resin composition; And

    Co-extruding a third film layer formed of a thermoplastic acrylic resin composition comprising 0.01 parts by weight to 2.0 parts by weight of a triazine ultraviolet absorber, and

    Stretching the coextruded film.
17. The method of claim 16,

    The stretching step is a 1.3 to 3.5 times the stretching of the coextruded film in the longitudinal direction (MD) method for producing a multilayer optical film.
18. The method of claim 16,

    The stretching step is a 1.3 to 3.5 times the stretching of the co-extruded film in the transverse direction (TD) manufacturing method of the multilayer optical film.
19. The method of claim 16,

    The stretching may include stretching at a temperature within + 30 ° C. of the glass transition temperature of the film having the highest glass transition temperature among the film layers of the multilayer optical film.
20. Polarizer; And

    A polarizing plate comprising a protective film provided on at least one surface of the polarizer, wherein at least one of the protective film is a multilayer optical film of any one of claims 1 to 15.

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