WO2018056670A1 - Optical film exhibiting excellent adhesive force and polarizing plate comprising same - Google Patents

Abstract

An optical film, according to the present invention, may enable the realization of a zero phase difference even when using an acrylic resin having a main chain which does not include a cyclic structure. In addition, the optical film exhibits excellent adhesion to a PVA device which is a polarizing plate.

Description

 【Specification】

 [Name of invention]

 Optical film with excellent adhesion and polarizing plate comprising the same

 Technical Field

 Cross Citation with Related Application (s)

 This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0120104 of September 20, 2016 and Korean Patent Application No. 10-20 Γ7-0119830 of September 18, 2017, and the Korean patent application All content disclosed in these references is included as part of this specification. The present invention relates to an optical film having excellent adhesion, and a polarizing plate including the same.

 Background Art

The liquid crystal display uses polarized light, and for this purpose, a polarizing plate is used, and a PVA element is typically used. However, since a polarizing plate such as a PVA device has a weak mechanical property and is easily affected by an external environment, for example, temperature or humidity, a protective film is required to protect it. Such protective films should be excellent in optical properties and in mechanical properties. Conventionally, a TAC film (Tri-Acetyl-cel lulose Film) has been used as a protective film for a PVA device used in a polarizing plate, but recently, an acrylic film having better heat resistance and water absorption resistance than a TAC film has been used. Such a polarizing plate protective acrylic film is manufactured through stretching processing, so that the acrylic resin having a glass transition temperature of 120 ^° C. or more is generally used so that the dimensional change at high temperature and the optical properties can be stably maintained. In addition, in order to further improve the dimensional stability and optical properties of the acrylic resin, a ring structure is introduced into the main chain. The monomer of the cyclic structure which gives heat resistance is introduced. However, when introducing a monomer having a ring structure, not only the unit cost of the raw material is increased, but also a problem of processing at a higher temperature is required. On the other hand, acrylic resins, in particular polymethyl methacrylate (PMMA), have excellent transparency, which may be a protective film for polarizing plates. However, the glass transition temperature is low. have. In addition, in order to use as a polarizer protective film for IPS mode, a separate phase difference regulator must be added to realize zero phase difference value. At this time, the phase difference regulator used must have excellent compatibility with polymethyl methacrylate, and also _zero phase difference. Appropriate content should be included for implementation. In addition, when the polymethyl methacrylate is stretched and manufactured into a film, there is a problem in that the adhesive force with the PVA device, which is a polarizing plate, varies depending on the stretching conditions. Accordingly, the present inventors, while using an acrylic resin that does not contain a monomer having a ring structure in the main chain, can achieve zero phase difference, and as a result of intensive efforts to manufacture an optical film having excellent adhesion with a PVA device, which is a polarizing plate, will be described later. As described above, the biaxially stretched optical film prepared by including polycarbonate as a phase difference modifier and including a primer layer was confirmed to achieve the above, thereby completing the present invention.

 [Content of invention]

 [Problem to solve]

 The present invention is to provide a biaxially stretched optical film excellent in adhesion to the polarizing plate and can implement a zero phase difference.

 Moreover, this invention is providing the polarizing plate containing the said biaxially stretched optical film.

 [Measures of problem]

In order to solve the said subject, this invention is a biaxially stretched optical film containing a base material layer and the primer layer formed on the said base material layer, The said The base layer includes an acrylic resin and a polycarbonate, and the primer layer provides a biaxially stretched optical film including 70 to 95 parts by weight of a polyester resin and 5 to 30 parts by weight of a polyurethane resin. Acrylic resin is excellent in transparency and can be used as an optical film, especially a polarizing plate protective film. However, when the acrylic resin is made into a film, a stretching process should be used to increase the mechanical strength. Since the acrylic resin has a low glass transition temperature, the optical film prepared by stretching is released at high temperature, resulting in poor dimensional stability. there is a problem. In order to improve this, there is a method of introducing a ring structure into the main chain of the acrylic resin, but the manufacturing process is complicated, the cost of the raw material is not only high, there is a problem that must be processed at a higher temperature. In addition, when the acrylic resin is stretched, it has a negative birefringence characteristic in which the refractive index increases in a direction perpendicular to the stretching direction, and thus has a positive birefringence characteristic in which the refractive index increases in the stretching direction in order to have a _zero phase difference like a protective film of a polarizing plate. A phase difference regulator is needed. In addition, when the acrylic resin is stretched and manufactured into a film, there is a problem in that the adhesive force with the PVA element, which is a polarizing plate, varies depending on the stretching conditions. Accordingly, the present invention provides a biaxially stretched optical film having an excellent adhesive force with the polarizing plate as well as an acrylic resin and a polycarbonate as a phase difference regulator, and introducing a primer layer to introduce a primer layer. . Hereinafter, the present invention will be described in more detail. Acrylic resin

The term ¹ acrylic resin ¹ used in the present invention means a resin produced by polymerizing an acrylate monomer, and in the present invention, It is the constituent main component. In particular, the 'acrylic resin' is characterized by not including a ring structure in the main chain. Preferably, the acrylate monomer has no ring structure, methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylnuclear methacrylate, lauryl methacrylate, and benzyl Any one or more selected from the group consisting of methacrylates can be used. In addition, if necessary, the acrylic resin may further include a styrene monomer, for example, styrene, α-methylstyrene, Ρ-methylstyrene, m-methylstyrene or benzoyl styrene, or acrylonitrile. The glass transition temperature of the acrylic resin is locrc to i20 ^° c. If the glass transition temperature is less than ioo ^° c there is a problem that the thermal stability is lowered when manufactured with a film. In addition, the weight average molecular weight of the acrylic resin is 100,000 to 150,000. When the weight average molecular weight is less than 100,000, there is a problem in that the mechanical properties when the film is produced, and when the weight average molecular weight is more than 150,000, there is a problem that extrusion processing is difficult. In particular, in the present invention, methyl methacrylate and / or methyl acrylate may be used as the acrylate monomer, and preferably polymethyl methacrylate, which is a copolymer of methyl methacrylate and methyl acrylate. Preferably, the polymethyl methacrylate includes methyl methacrylate in an amount of 90 to 99% by weight, and preferably includes 1 to 10% by weight of a methyl acrylate monomer. The methyl acrylate serves to suppress decomposition of the copolymer. The polymethyl methacrylate can be produced by a known method, except that methyl acrylate is used in addition to methyl methacrylate. For example, it may be prepared by an emulsion polymerization method, an emulsion-suspension polymerization method, a suspension polymerization method, or the like. In addition, in order to introduce the methyl acrylate monomer to the terminal of the polymethyl methacrylate, the polymethyl methacrylate may be polymerized first and then the methyl acrylate monomer may be polymerized. Polycarbonate

The term 'polycarbonate' used in the present invention is formed by reacting an aromatic di compound and a carbonate precursor, and may be prepared by interfacial polymerization or solution polymerization. For example, bisphenol A and phosgene can be produced by interfacial polymerization. In particular, in the present invention, it is a component constituting the base layer together with the polymethyl methacrylate. The polycarbonate is added to control the phase difference, and as described below, the biaxially stretched optical film according to the present invention is added to implement zero phase difference. In addition, in consideration of compatibility with the acrylic resin, the weight average molecular weight of the polycarbonate is preferably from 10, 000 to 20, 000. When the weight average molecular weight of the polycarbonate is more than 20, 000, the compatibility with the acrylic resin is poor, it becomes a totally opaque composition is not preferable for use as an optical film. In addition, the polycarbonate is preferably contained in 10% by weight or less in the base layer. When the content exceeds 10% by weight, it becomes an opaque composition as a whole, and the phase difference expression property is so large that it is not preferable to implement zero phase difference. Also preferably, the polycarbonate is preferably 1% by weight or more, or 2% by weight or more in the substrate layer. Equipment

In the present invention, the base layer is made of a composition containing the above-described acrylic resin and polycarbonate. For example, the acrylic resin and the polycarbonate may be prepared by melting and kneading the composition, and then, the non-stretched film to prepare the base layer. In addition, the composition may include additives such as a ultraviolet absorber, a heat stabilizer, a lubricant, 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 composition, for example, may be included in 0.1 to 5 parts by weight based on 100 parts by weight of the total composition. In addition, as a method for producing a film from the composition, any method known in the art, for example, a solution caster method, an extrusion method, or the like can be used, and for example, a melt extrusion molding method can be used. Specifically, after drying the resin composition for optical materials to remove moisture, supply the extruder from the raw material hopper to a single or twin-screw extruder, melt at high temperature to obtain raw material pellets, drying the obtained raw material pellets, After melting from the hopper to the extruder with a single extruder, it can be passed through a coat hanger type T-die and subjected to creme plating casting, cooling, and the like to produce a film. At this time, the film forming temperature is preferably 150 ^° C to 350 ^° C, more preferably 200 ^° C to 300 ^° C. On the other hand, as described above, in the case of forming a film by the T-die method, a T-die is attached to the tip of a known single screw extruder or twin screw extruder, and the film extruded into a film shape is wound to obtain a film having a shape of. Can be. In addition, a polymer filter may be used to remove foreign substances in film forming. Primer layer

In the present invention, the primer layer is formed on the base layer If necessary, it may be formed on one surface or both surfaces of the substrate layer. In particular, the primer layer of the present invention can improve the adhesive force with a polarizing plate, for example, a PVA device, when biaxially stretched to produce an optical film as described below. The primer layer contains ₇₀ to ₉₅ parts by weight and 5 to 30 parts by weight of a polyester resin and a polyurethane resin, respectively. More preferably, the primer layer comprises 75 to 90 parts by weight and 10 to 25 parts by weight of polyester resin and polyurethane resin, respectively. The polyester-based resin refers to a resin containing an ester group formed by the reaction of carboxylic acid and alcohol in the main chain, preferably a water dispersible polyester resin, more preferably, polybasi c acid) and polyester glycols formed by reaction of polyols. At this time, as the polybasic acid component, for example, ortho-phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2, 6-naphthalenedicarboxylic acid, biphenyldi Aromatic dicarboxylic acids such as carboxylic acid and tetrahydrophthalic acid; Aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelline acid, sebacic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid and itaconic acid; Alicyclic dicarboxylic acids such as nucleated hydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclonucleic acid dicarboxylic acid, and 1,4-cyclonucleic acid dicarboxylic acid; Or semi-ungung derivatives such as acid anhydrides, alkyl esters, and acid halides thereof, and the like, but are not limited thereto, and may include one or two or more kinds from the group consisting of these. Among these, terephthalic acid, isophthalic acid, and succinic phase are particularly preferable. Moreover, when isophthalic acid substituted by sulfonic acid salt is used for salt time, it is especially preferable at the point of water dispersibility. If the said polyol has two or more hydroxyl groups in a molecule | numerator, For example, the poly olefin may be ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1'4-butanediol, neopentylglycol, pentanediol, 1,6-dicarboxylic acid, 1,8-octanediol, 1,10-decanediol, 4,4'-dihydroxyphenylpropane, 4, 4'-dihydroxymethylmethane, diethylene glycol, triethylene glycol ， Polyethylene glycol (PEG), dipropylene glycol, polytetramethylene glycol (PTMG), polypropylene glycol (PPG) ᅳ 1,4-cyclonucleodimethanol, 1,4-cyclonucleodidiol, bisphenol k, bisphenol F, glycerin , 1,1,1-trimethylolpropane, 1,2,5-nuxatriol, pentaerythritol, glucose, sucrose, and sorbitol are preferably included at least one selected from the group consisting of. Furthermore, when dimethyl containing a carboxy group as a polyol contains 1 type, or 2 or more types selected from the group which consists of alkanoic acid, dimethylol acetic acid, dimethylol propionic acid, and dimethylol butyric acid, it is especially preferable at the point of water dispersibility. The polyester glycol is polylactic time and polyol 2.5: 1 to

It is preferably formed by reacting in a molar ratio of 1: 2.5, preferably in a molar ratio of 2.3: 1 to 1: 2.3, more preferably in a molar ratio of 2: 1 to 1: 2. This is because when the salting out of the reaction time between the polysalt time and the polyol may cause odor or unsatisfactory coating. The method for producing the polyester resin is well known in the art, for example, by the method of condensation after the esterification reaction of polybasic acid and polyol, or by the method of condensation polymerization after the esterification reaction of polybasic anhydride and polyol, etc. Can be. Specifically, the methods include (1) a raw material mixing step of mixing a polymerization raw material for polymerization of polyester to obtain a raw material mixture, (2) an esterification reaction step of esterifying the raw material mixture, and (3) an ester A polycondensation step may be obtained by polycondensing the pulverized raw material mixture to obtain a polyester. On the other hand, the polyester-based resin produced through the same method may include a repeating unit represented by the following formula (1):

 [Formula 1]

 In Chemical Formula 1,

Ri and ¾ are each independently a - ₂₀ alkyl group, a C ₆ - ₂₀ aryl group, or a C ₅ -

20 cycloalkylene group,

¾ and ¾, and R4 are each a substituent substituted on ¾, each independently selected from hydrogen, carboxy, hydroxy, sulfonic acid base, d- ₂₀ alkyl, C ₆ - ₂₀ aryl, or C ₅ - ₂₀ cycloalkyl, with the proviso that, R At least one of ₃ and R4 is a carboxy, hydroxy, or sulfonate group. Preferably, ¾ or is a carboxy or sulfonate group. More preferably, the poly resin may include a repeating unit represented by the following Chemical Formula 2:

 [Formula 2]

 In Chemical Formula 2,

R, 'and R "are each independently alkylene, C ₆ - ₂₀ arylene, and four ᄋ一^20' and roal Killen, S¾Na is R" means a substituent substituted on. Meanwhile, the polyester resin may further include additional components in addition to the components within a range that does not impair the physical properties of the present specification. The polyurethane resin means a resin containing a urethane repeating unit formed by reaction of isocyanate and polyol in the main chain, wherein the isocyanate is a compound having two or more NC0 groups, and the polyol is a compound having two or more hydroxyl groups, For example, polyester-based polyols, polycarbonate-based polyols, polyether polyols and the like, but is not limited thereto. Specifically, examples of the diocyanate include toluene isocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), toldine diisocyanate (T0DI), Nucleomethylene diisocyanate (HMDI), isopron diisocyanate (IPDI), P-phenylene diisocyanate, transcyclonucleic acid, 1,4-diisocyanate, and xylene diisocyanate (XDI), but are not limited thereto, These may be those containing one kind or two or more kinds. The polyester-based polyol may be obtained by reacting a polybasic acid component and a polyol component, and examples of the polybasic acid component include ortho-phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, and 2,5-naphthalene. Aromatic dicarboxylic acids such as dicarboxylic acid, 2, 6-naphthalenedicarboxylic acid, biphenyldicarboxylic acid and tetrahydrophthalic acid; Aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelline acid, sebacic acid, linoleic acid, maleic acid, fumaric acid, mesaconic acid and itaconic acid; Alicyclic dicarboxylic acids such as nucleated hydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclonucleic acid dicarboxylic acid, and 1,4-cyclonucleic acid dicarboxylic acid; Or semi-ungung derivatives such as acid anhydrides, alkyl esters, and acid halides thereof, and the like, but are not limited thereto, and may include one or two or more kinds from the group consisting of these. In addition, the polycarbonate-based polyol may be obtained by reacting a compound having a carbonate group and a polyol component. In this case, examples of the compound having a carbonate group include diphenyl carbonate, dialkyl carbonate, alkylene carbonate, and the like. It doesn't happen. On the other hand, the polyether polyol can be obtained by ring-opening polymerization of an alkylene oxide to the polyol component. The polyol component is not particularly limited as long as it has two or more hydroxyl groups in the molecule. For example, as the polyol, ethylene glycol, 1,2-propanedi, 1, 3-propanediol, 1,3-butanediol, 1, 4-butanediol, neopentylglycol, pentanediol, 1,6- Nucleic acid diols, 1,8-octanediol, 1,10-decanediol, 4,4'-dihydroxyphenylpropane, 4,4'-dihydroxymethylmethane, diethylene glycol, triethylene glycol, polyethylene glycol ( PEG), dipropylene glycol, polytetramethylene glycol (PTMG), polypropylene glycol (PPG), 1,4-cyclonucleodimethanol, 1,4-cyclonucleodiol diol, bisphenol A, bisphenol F, glycerin, 1,1 , 1-trimethylolpropane, 1,2,5—nucleated triol, pentaerythritol, glucose, sucrose, and sorbitol. Especially, it is preferable that it is at least 1 sort (s) chosen from the group which consists of polytetramethylene glycol (PTMG), polypropylene glycol (PPG), and polyethylene glycol (PEG). On the other hand, the polyurethane-based resin may further include other polyols or chain extenders in the above components in a range that does not impair the physical properties of the present specification. Said other polyol has three hydroxyl groups, for example, sorby, glycerin, trimethyl ethane, trimethyl propane, and pentaerythritol. Polyols and the like, but is not limited thereto. The other chain extender is, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1, 3-propanediol, 1,3_butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1, 6—Glycols such as diol and propylene glycol are included, but are not limited thereto. On the other hand, the polyurethane-based resin may further include a neutralizing agent, if necessary. When it contains a neutralizing agent, the stability of the urethane resin in a crystal | crystallization improves. The neutralizing agent is selected from the group consisting of, for example, ammonia N-methylmorpholine, triethylamine, dimethylethanolamine, methyldiethanolamine, triethanolalkyne, morpholine, tripropylamine, ethanol amine, triisopropanolamine It may be one or two or more. Preparation of the polyurethane-based resin is preferably carried out in an organic solvent inert to the isocyanate and compatible with water. The organic solvent is selected from the group consisting of ester solvents such as ethyl acetate and ethyl cellosolve acetate, ketone solvents such as acetone, methane ethyl ketone and methyl isobutyl ketone, and ether solvents such as dioxane tetrahydrofuran. It may be one or two or more. In addition, the polyurethane-based resin can be prepared through a one-shot method and a multi-stage method well known in the art. Specifically, the one-shot method is a method of reacting each component at a time, and the multi-stage method is a method of reacting each component in steps. In addition, the production of the polyurethane-based resin may further include a urethane reaction catalyst. On the other hand, the present invention is not limited thereto, but in view of dispersibility and transparency, the polyurethane resin may be a carbonate-based polyurethane resin or a polyester-based polyol using a polycarbonate-based polyol as a reaction product. It is especially preferable that it is an ester type polyurethane resin to be used. In addition, the weight average molecular weight of the polyurethane-based resin is preferably from 10,000 to 1,000, 000. When the numerical range is satisfied, sufficient adhesion can be achieved, and the water dispersibility is excellent. According to one embodiment of the present specification, the polyurethane-based resin preferably includes at least one functional group selected from the group consisting of carboxy, hydroxy, sulfonate groups, and tertiary amine groups. When the functional groups are included in the polyurethane-based resin, adhesion to the adhesive layer and water dispersibility are greatly improved. On the other hand, the polyurethane-based resin containing the functional group can be prepared by using a compound containing the functional groups as poly and / or isocyanate, or by adding a chain extender containing the functional groups in the polyol and isocyanate reaction. Can be. For example, a polyurethane-based resin containing a carboxyl group or a tertiary amine group may be prepared by adding a chain extender having a free carboxyl group or a free amine group to the isocyanate reaction with the polyester polyol. At this time, examples of the chain extender having the free carboxyl group include dihydroxy carboxylic acid, dihydroxy succinic acid, and the like, but are not limited thereto. Dihydroxy carboxylic acid, for example, dimethyl is selected from the group consisting of dialkylol alkanoic acid including dimethylol alkanoic acid, such as acetic acid, dimethylol butanoic acid, dimethylol propionic acid, dimethylol butyric acid, dimethylol pentanoic acid It may be one containing two or more species. On the other hand, as a chain extender which has the said free amine group, For example, Aliphatic diamines, such as ethylenediamine, a propylene dianith, nuxa methylenediamine, 1, 4- butanediamine, aminoethylethanolamine; Alicyclic diamines such as isophorone diamine and 4, 4'-dicyclonuxylmethanediamine; Aromatic diamines such as xylylenediamine and rylenediamine, and the like, but are not limited thereto, and may include one or two or more selected from the group consisting of these. have. Meanwhile, the polyurethane resin may further include additional components in addition to the components within a range that does not impair the physical properties of the present specification. In addition, the primer layer may further include a water-soluble fine particles and a water-dispersible crosslinking agent as necessary. As the water-dispersible fine particles, one or more selected from the group consisting of silica, tania, ^' alumina, zirconia, and antimony-based fine particles can be used, and preferably silica can be used. When using silica, it is preferable to use it as colloidal silica. The diameter of the water-dispersible fine particles is 50 nm to 500 nm, preferably 70 nm to 300 nm. The primer layer may be prepared by coating a primer solution containing a polyester resin and a polyurethane resin, and the coating method is not particularly limited. For example, bar coating, microgravure coating, slot die coating, comma coating, or the like may be used. In addition, if necessary, the primer layer may have an antistatic property, and for this purpose, the primer layer may contain a surfactant, an organic salt, an inorganic salt, a conductive filler, a conductive polymer, a block copolymer, a metal oxide, or the like. It may comprise 10% by weight. In addition, if necessary, the primer layer may have ultraviolet ray blocking properties, and for this purpose, the primer layer may include 0.01 to 10 wt% of an ultraviolet absorber. The ultraviolet absorber is not particularly limited as long as it is used in an optical film. For example, a triazine-based, benzotriazole-based or benzophenol-based ultraviolet absorber can be used. In addition, if necessary, the primer layer may have ant i-blocking properties, and for this purpose, the primer layer may include organic beads or inorganic beads. When using the primer layer as described above, by giving the slip property to the base layer has the effect of ant i-block, and also has the effect of preventing the erosion of the base layer from the coating solution during coating. In addition, as described below, even in biaxial stretching of the base layer and the primer layer, the adhesive force of the primer layer can be improved while maintaining the properties of each layer.

Biaxially oriented optical film

The biaxially stretched optical film according to the present invention includes the base layer described above and a primer layer formed on the base layer. Said biaxial stretching means biaxial stretching of the unstretched film containing a base material layer and a primer layer, or after uniaxially stretching a base material layer, forming a primer layer, and extending this transversely. I mean. Specifically, forming a primer layer on the substrate layer and the substrate layer described above to prepare an unstretched film; And biaxially stretching the non-stretched film to produce a biaxially stretched optical film. Alternatively, the biaxially stretched optical film according to the present invention comprises the steps of uniaxially stretching the substrate layer described above in a longitudinal direction; Forming a primer layer on the substrate layer; And a step of stretching the substrate layer and the primer layer in the transverse direction, to prepare a biaxially stretched optical film. Preferably, the draw ratio is preferably 1.2 times to 3.0 times in the MD. Direction and 1.5 times to 4.0 times in the TD direction. The stretching is to align the polymer, affecting the properties of the biaxially stretched optical film produced according to the degree of stretching. More preferably, ratio (TD draw ratio / MD draw ratio) of the draw ratio of the said MD direction and the draw ratio of a TD direction is 1.0-2.5. In addition, the stretching temperature is preferably carried out in a temperature range of -10 ^° C to +20 ^° C based on the glass transition temperature of the acrylic resin. The stretching temperature affects the adhesion of the biaxially stretched optical film, the temperature There exists a problem that adhesive force is not enough in the range. In addition, the biaxially stretched optical film according to the present invention has excellent dimensional stability, and introduced a parameter called TTS (Temperature of Thermal Shr inkage) to evaluate the thermal dimensional stability. Denotes the temperature at which the optical film produced by the stretching process begins to shrink rapidly as the stretching history is relaxed. Specifically, when the temperature is applied to the optical film, it means the temperature at which shrinkage starts after expansion as the temperature increases. Preferably, the TTS in the MD direction and the TTS in the TD direction of the biaxially stretched optical film according to the present invention are each 95 ^° C. or more, preferably 100 ^° C. to 120 ^° C. On the other hand, the thickness of the biaxially stretched optical film according to the present invention can be appropriately adjusted, if necessary, it is preferably 10 urn to 100 Pa. Also preferably, the biaxially stretched optical film according to the present invention satisfies Equation 1 and Equation 2:

 [Equation 1]

 0 nm <Rin <10 nm (Rin = (nx-ny) x d)

 [Equation 2]

 -10 nm <Rth <10 nm (Rth = (nz-ny) d)

 In Equations 1 and 2,

 nx represents the refractive index of the direction of the largest refractive index in the plane of the optical film, ny represents the refractive index of the direction perpendicular to nx, nz represents the refractive index of the thickness direction of the optical film,

d means the thickness (nm) of an optical film. Equations 1 and 2 mean that the zero phase difference is satisfied. As described above, polycarbonate is used as the acrylic resin and the phase difference regulator. By using this, zero phase difference can be realized. Polarizer

Moreover, this invention provides the polarizing plate containing the said biaxially stretched optical film. As described above, the biaxially stretched optical film according to the present invention can be used as a protective film of a polarizing plate, thereby compensating the mechanical properties of the polarizing plate and protecting the polarizing plate from the influence of the external environment, for example, temperature or humidity. have. In this specification, a polarizing plate means the state containing a polarizer and a protective film. At this time, the primer layer of the protective film according to the present invention may be in contact with the polarizer, or the base layer of the protective film according to the present invention may be in contact with the polarizer. 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 polarizer 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, acrylic film, TAC film, PET film, COP film, PC film, norbornene-based Films and the like can be used without limitation. On the other hand, the adhesive agent which is equipped with the protective film which concerns on this invention to a polarizer can be used. It is preferable to use a non-aqueous adhesive as said adhesive agent, and it is more preferable to use an ultraviolet curing type. As an example of the said adhesive agent, Adhesive which uses radical photopolymerization reaction, such as (meth) acrylate type adhesive agent, N / thiol type adhesive agent, unsaturated polyester adhesive agent; Or an adhesive using a photo cationic polymerization reaction such as an epoxy adhesive, an oxetane adhesive, an epoxy / oxetane adhesive, or a vinyl ether adhesive, but is not limited thereto. It is not. In the case of using the non-aqueous adhesive, a non-aqueous adhesive may be applied to one surface of the polarizer or the protective film to form an adhesive layer, and then, the polarizer and the protective film may be laminated, and the adhesive layer may be cured through light irradiation. 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 sides of the liquid crystal sal, 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 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 U-polarizing plate and the liquid crystal cell and between the second polarizing plate and the liquid crystal cell. Can be. The optical film or polarizer protective film provided on the side opposite to the liquid crystal cell of the polarizing plate preferably includes a UV absorber, and may be surface coated such as AG and LR.

 【Effects of the Invention】

 As described above, the biaxially stretched optical film according to the present invention can realize zero phase difference while using polymethyl methacrylate not containing a monomer having a ring structure, and also has excellent adhesion with a PVA device, which is a polarizing plate. There is a characteristic.

 [Specific contents to carry out invention]

 Hereinafter, to help understand the present invention. To the present preferred embodiment. However, the following examples are merely provided to more easily understand the present invention, and the contents of the present invention are not limited thereto. Preparation Example 1 Polymethylmethacrylate

In a 5 liter reactor, 1000 g of a monomer mixture of 98% by weight of methyl methacrylate and 2% by weight of methyl acrylate was added, and 8.4g of distilled water and a solution of 5% polyvinyl alcohol (P0VAL PVA217, kuraray), and 0.1 g of boric acid was added as a dispersing aid and dissolved. Here, 2.5 g of n-octylmercaptan as a chain transfer agent, A suspension was prepared by adding 1.5 g of 2,2'-azobisisobutyronitrile as a polymerization initiator and dispersing it in an aqueous phase while stirring at 400 rpm. The mixture was heated to 80 ^° C. for 90 minutes, and then cooled to 3 C C. The obtained beads were washed with distilled water, dehydrated, and dried to prepare a polymethylmethacrylate resin. As a result of measuring the glass transition temperature and molecular weight of the resin thus prepared, the glass transition temperature was 115 ^° C, the weight average molecular weight was 120,000. The glass transition temperature was measured under a temperature rising condition of 10 ^° C./min using a differential scanning calorimeter (DSC) manufactured by Met Tier Toledo. Preparation Example 2 Polycarbonate

As the polycarbonate, a polycarbonate resin (IF 1004A, LG Chemical Co., Ltd.) having a glass transition temperature of 134 ^° C. and a weight average molecular weight of 16, 000 was used. Preparation Example 3 Primer Solution

 Polyester-based resin (A-645GH; Takamatsu oil &fat; total content of solids except water is 30% by weight) and polyurethane-based resin (CK-PUD-PF; light-glow paint yarn; total solids except water) 30 weight ¾ was mixed at a weight ratio of 80: 20 based on solids, and aqueous silica was mixed at 5 weight% to prepare a primer solution Preparation Example 4: Primer solution

 Prepared in the same manner as in Preparation Example 3, by mixing a polyester-based resin and a polyurethane-based resin in a weight ratio of 20: 80 on a solid basis, to prepare a primer solution. Preparation Example 5 Primer Solution

Prepared in the same manner as in Preparation Example 3, using only a polyurethane-based resin, to prepare a primer solution. Preparation Example 6 Primer Solution It was prepared in the same manner as in Preparation Example 3, a mixture of polyester resins and polyurethane-based resins in a weight ratio of 65:35 based on a solid content to prepare a primer solution. Preparation Example 7 Primer Solution

 Prepared in the same manner as in Preparation Example 3, using only a polyester resin, to prepare a primer solution. Examples 1 to 3

97.3% of the polymethyl methacrylate prepared in Preparation Example 1 and 2.7% of the polycarbonate of Preparation Example 2 were mixed, and dry blended by prescribing an antioxidant (Irganox 1010, BASF) in a content of 0.4 phr. Compounding with an extruder to prepare a resin composition. The resin composition was melted at 265 ^° C., and extrusion-cast into a sheet form through T-Die to obtain a sheet having a thickness of 180 um. After the sheet was uniaxially stretched in the MD direction, a primer layer was formed from the primer solution prepared in Preparation Example 3 using a bar coater, and then stretched in the TD direction to prepare a biaxially stretched film (Example 1) . The draw temperature and draw ratio were as shown in Table 1 below. The same as above, but biaxially stretched at the stretching temperature and the draw ratio as described in Table 1, respectively, to prepare an optical film (Examples 2 and 3). Comparative Example 1

 Prepared in the same manner as in Example 1, but biaxially stretched at the stretching temperature and draw ratio as shown in Table 1 below to prepare an optical film. Comparative Examples 2 and 3

Prepared in the same manner as in Example 1, but using 100% polymethyl methacrylate prepared in Preparation Example 1 without using the polycarbonate of Preparation Example 2 and also as described in Table 1 below An optical film was prepared by biaxial stretching at the same stretching temperature and stretching ratio. Comparative Example 4

 Prepared in the same manner as in Example 1, using the primer solution of Preparation Example 4 instead of the primer solution of Preparation Example 3, an optical film was prepared. Comparative Example 5

 Prepared in the same manner as in Example 1, using the primer solution of Preparation Example 5 instead of the primer solution of Preparation Example 3, an optical film was prepared. Comparative Example 6

 Prepared in the same manner as in Example 1, using the primer solution of Preparation Example 6 instead of the primer solution of Preparation Example 3, an optical film was prepared. Comparative Example 7

 Prepared in the same manner as in Example 1, using the primer solution of Preparation Example 7 instead of the primer solution of Preparation Example 3, an optical film was prepared. Experimental Example

 The optical film manufactured by the said Example and the comparative example was evaluated by the following method.

1) TTS Temperature of Thermal Shr inkage): After the optical film was prepared with a sample having a size of 10 4.5 瞧, it was measured using a TM Q400) equipment. Specifically, when the temperature was applied under conditions of a temperature increase rate K C / min and a load of 0.02 N, the temperature (tangential slope 0) of the inflection point at which the sample started to contract after expansion in the MD and TD directions, respectively, was taken as the value.

2) Retardation: The retardation was measured at a wavelength of 550 nm using a birefringence measuring instrument (AxoScan, Axometr ics). Refractive index (nx) in the X-axis direction and in the y-axis direction The in-plane retardation (Rin) and thickness direction retardation (Rth) values were calculated by the following equation with the measured values of the refractive index (ny) and the refractive index (nz) in the z-axis direction.

 Rin (nm) = (ηχ-ny) d

 Rth = (nz-ny) d

 In the above, nx represents the refractive index of the direction of the largest refractive index in the plane of the optical film, ny represents the refractive index of the direction perpendicular to nx, nz represents the refractive index of the thickness direction of the optical film,

d means the thickness (nm) of an optical film. 3) Adhesion (90 ^° Peel Peeling Force): Physical property analyzer (TA.XT.plus Texture

Analyser; Adhesion was measured using Stable Micro Systems. Specifically, it was laminated in the order of the general acrylic optical film / PVA device / the optical film prepared above. At this time, the primer surface of the optical film was faced to the PVA device, and the opposite surface (substrate surface) of the primer surface of the optical film to face the PVA device, two kinds were prepared. After apply | coating UV cure adhesive between each film, conditions were set so that the thickness of a final adhesive layer might be 1-2 micrometers, and the laminator passed through. Subsequently, ultraviolet rays were irradiated onto the normal acrylic optical film side. The specimen was prepared with a width of 2 cm, and the peeling force was measured by peeling an optical film from the PVA device at a speed of 300 mm / min and 90 ^° using a property analyzer. In addition, after the rest of the specimen was stored at 80 ^° C. for 500 hours, the peel force was measured in the same manner. The results are shown in Tables 1 and 2 below. In the case of Table 2, the value of Example 1 was described again for comparison.

 Table 1

기재면 접착력 (N/20 mm) 1.7 1.2 1. 1 0.3 0. 1 1.0

Base Surface Adhesion (N / 20 mm) 1.7 1.2 1.1 0.3 0.3 0.1

1) Glass transition degree of polymethyl methacrylate

[Table 2]

상기 표 1에 나타난 바와 같이， 본 발명에 따른 실시예 1 내지 3은 모두 zero 위상차를 나타내었으며， 접착력이 1 N/20 隱 이상으로 우수하였다. 반면， 비교예 1및 2은 연신은도가 너무 높아 접착력이 0.5 N/20 mm 미만으로 낮게 나타났다. 또한， 비교예 2 및 3은 위상차 조절제인 폴리카보네이트가 포함되지 않아 zero 위상차를 구현하지 못하였다. 또한， 기재면 접착시 실시예 1 내지 3은 모두 접착력 우수하나， 비교예 1 및 2 연신온도가 너무 높아 접착력이 0.5 N/20 謹 미만으로 낮게 나타났다. 또한， 상기 표 2에 나타난 바와 같이， 본 발명에 따른 실시예 1에 비하여 비교예 4 내지 7은 프라이머층의 조성이 본 발명에 만족하지 않아 효과적인 접착력이 구현되지 않음을 확인할 수 있었으며， 비교예 7의 경우에는 초기 접착력은 구현되나， 고온에 장시간 노출 후에는 접착력이 저하됨을 확인할 수 있었다. 따라서， 본 발명에 따른 광학 필름은 zero 위상차를 구현하면서도 접착력이 우수함을 확인할 수 있었다.

As shown in Table 1, Examples 1 to 3 according to the present invention all exhibited a zero phase difference, and the adhesion was excellent as 1 N / 20 kPa or more. On the other hand, Comparative Examples 1 and 2 were too high in elongation and showed a low adhesion strength of less than 0.5 N / 20 mm. In addition, Comparative Examples 2 and 3 did not include a polycarbonate as a phase difference regulator did not implement a zero phase difference. In addition, in Examples 1 to 3, all of the adhesive strength was excellent when the substrate surface adhesion, Comparative Examples 1 and 2, the drawing temperature was too high, the adhesion was lower than 0.5 N / 20 Pa. In addition, as shown in Table 2, compared with Example 1 according to the present invention, Comparative Examples 4 to 7 was confirmed that the composition of the primer layer was not satisfied with the present invention did not implement an effective adhesive force, Comparative Example 7 In the case of the initial adhesive strength is implemented, after a long time exposure to high temperature was confirmed that the adhesive strength is lowered. Therefore, the optical film according to the present invention was confirmed that the adhesion is excellent while implementing a zero phase difference.

Claims

Claims [1] A biaxially stretched optical film comprising a base layer and a primer layer formed on the base layer, wherein the base layer comprises an acrylic resin and a polycarbonate, and the primer layer is Biaxially stretched optical film containing 70-95 weight part of polyester-type resins, and 5-30 weight part of polyurethane-type resins. Claim 2 The biaxially stretched optical film of claim 1, wherein the acrylic resin does not contain a ring structure in the main chain. [Claim 3] The biaxially stretched optical film of claim U, wherein the glass transition temperature of the acrylic resin is 100 to 120 ° C. Claim 4 The biaxially stretched optical film of claim 1, wherein the weight average molecular weight of the acrylic resin is from 100, 000 to 150, 000. Claim 5 The biaxially stretched optical film of claim 1, wherein the acrylic resin is a copolymer of methyl methacrylate and methyl acrylate. [Claim 6] The biaxially stretched optical film of claim 5, wherein the acrylic resin contains methyl methacrylate at 90 to 99% by weight, and contains 1 to 10% by weight of methyl acrylate monomer. Claim 7 The biaxially stretched optical film of claim 1, wherein the polycarbonate has a weight average molecular weight of 10, 000 to 20, 000. 8. The biaxially stretched optical film of claim 1, wherein the base layer contains 10 wt% or less of the polycarbonate. [Claim 9] The biaxially stretched optical film of claim 1, wherein the primer layer comprises 75 to 90 parts by weight and 10 to 25 parts by weight of a polyester resin and a polyurethane resin, respectively. Claim 10 The biaxially stretched optical film according to claim U, wherein the magnification of the biaxial stretching is 1.2 times to 3.0 times in the MD direction and 1.5 times to 4.0 times in the TD direction. [Claim 111] The biaxially stretched optical film according to claim 10, wherein a ratio (TD draw ratio / MD draw ratio) of the draw ratio in the MD direction and the draw ratio in the TD direction is 1.0 to 2.5. 12. The biaxially stretched optical film of claim 1, wherein the biaxially stretched temperature is in a temperature range of -10 ° C to + 2CTC based on the glass transition temperature of the acrylic resin. 13. The biaxially stretched optical film of claim 1, wherein the biaxially stretched optical film satisfies the following formulas (1) and (2):  [Equation 1]  0 nm <Rin <10 nm (Rin = (nx-ny) x d)  [Equation 2]  -10 nm <Rth <10 nm (Rth = (nz-ny) X d)  In Equations 1 and 2,  nx represents the refractive index in the direction of the largest refractive index in the optical film and in-plane, ny represents the refractive index in the direction perpendicular to nx, nz represents the refractive index in the thickness direction of the optical film,  d means the thickness (nm) of an optical film. [Claim 14]  The polarizing plate containing the biaxially stretched optical film of any one of U-13.