KR102097803B1 - Optical film, display device comprising the same and display apparatus comprising the same - Google Patents

Abstract

Includes a first copolymer of (meth) acrylate-based monomers, aromatic vinyl-based monomers and acid anhydride-based monomers, and a second copolymer of a monomer mixture comprising an aromatic vinyl-based monomer and a (meth) acrylate-based monomer And, the second copolymer containing 2% to 25% by weight of the optical film, the glass transition temperature is 120 ° C or more, in-plane retardation at a wavelength of 550nm is 10nm or less, the thickness direction retardation at a wavelength of 550nm -50nm to Provided is an optical film, a display device including the same, and a display device including the optical film, which is -10 nm and satisfies Expression 1 and Expression 2.

Description

Optical film, display element including the same, and display device including the same {OPTICAL FILM, DISPLAY DEVICE COMPRISING THE SAME AND DISPLAY APPARATUS COMPRISING THE SAME}

The present invention relates to an optical film, a display device including the same, and a display device including the same.

In recent years, based on the development of optical technology, display technologies using various methods such as plasma display panels (PDPs) and liquid crystal displays (LCDs) that replace conventional CRTs have been proposed and marketed. Polymer materials for such displays are further enhancing their required properties. For example, in the case of a liquid crystal display, as thinning, weight reduction, and enlargement of a screen area are promoted, wide viewing angle, high contrast, suppression of image color change according to viewing angle, and uniformity of screen display have become particularly important problems.

Accordingly, various polymer films are used for polarizing films, retardation films, plastic substrates, light guide plates, etc., and liquid crystals are twisted nematic (TN), super twisted nematic (STN), and VA (vertical alignment). ), IPS (in-plane switching) liquid crystal display devices in various modes using liquid crystal cells and the like have been developed. Since all of these liquid crystal cells have a unique liquid crystal arrangement, they have unique optical anisotropy, and films to extend various kinds of polymers and provide retardation functions have been proposed to compensate for the optical anisotropy.

For example, as an example using a polycarbonate (PC) resin, Japanese Patent Application Laid-Open No. 1997-304619 can be cited. However, when extending the polycarbonate resin as described above, it is possible to provide a sufficient retardation function as a retardation film, but there is a problem in that it is difficult to produce a film having a large retardation change rate and a more uniformly stable retardation according to the extension degree.

As a method for solving such a problem, a method using a cyclic olefin polymer (COP) has been proposed (Japanese Patent Publication No. 2001-350017, Japanese Patent Publication No. 2004-051928). However, the cyclic polyolefin resin has a problem of poor adhesion to a substrate such as another film, and has a problem of insufficient retardation as a retardation film due to a small retardation change rate due to extension.

The problem of the acrylic film is that it lacks the intrinsic properties of acrylic, such as insufficient brittleness, so that additives such as rubber are applied, and there are disadvantages such as increased cost and increased haze.

An object of the present invention is to provide an optical film having an in-plane retardation and a thickness direction retardation that satisfies a predetermined range, has excellent heat resistance, and has low haze and excellent optical transparency.

Another object of the present invention is to provide an optical film that suppresses diagonal light leakage by reducing a change in thickness direction retardation according to wavelength dispersion.

Another object of the present invention is to provide an optical film that can stably implement in-plane retardation and thickness direction retardation and has excellent film strength.

Another object of the present invention is to provide a display device and a display device including the optical film of the present invention.

The optical film of the present invention is a (meth) acrylate-based monomer, an aromatic vinyl-based monomer and an acid anhydride-based monomer of at least one first copolymer, an aromatic vinyl-based monomer and a monomer mixture comprising a (meth) acrylate monomer It contains a second copolymer, the second copolymer comprises 2% to 25% by weight of the optical film, the glass transition temperature is 120 ℃ or more, in-plane retardation at a wavelength of 550nm 10nm or less, at a wavelength of 550nm The thickness direction retardation is -50 nm to -10 nm, and the following equations 1 and 2 can be satisfied:

<Equation 1>

Rth (550)-Rth (450) ≤ 3nm,

<Equation 2>

Rth (550)-Rth (650) ≤ 3nm.

(In the above formulas 1 and 2, Rth (550), Rth (450), and Rth (650) are as defined in the detailed description of the invention below).

The display device of the present invention may include the optical film of the present invention.

The display device of the present invention may include the optical film or display element of the present invention.

The present invention provides an optical film having an in-plane retardation and a thickness direction retardation satisfying a predetermined range, having excellent heat resistance, and low haze, thereby providing excellent optical transparency.

The present invention provides an optical film that suppresses diagonal light leakage by reducing a change in thickness direction retardation according to wavelength dispersion.

The present invention provides an optical film that can stably implement in-plane retardation and thickness direction retardation and has excellent film strength.

The present invention has provided a display device and a display device comprising the optical film of the present invention.

It will be described in detail so that those of ordinary skill in the art to which the present invention pertains may be easily implemented by the attached embodiments. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. In order to clearly describe the present invention, parts not related to the description are omitted.

In this specification, "in-plane retardation (Re)" is represented by Equation A below, and "degree of biaxiality (NZ)" can be represented by Equation B below:

<Equation A>

Re = (nx-ny) x d

<Equation B>

NZ = (nx-nz) / (nx-ny)

(In the formulas A to B, nx, ny, and nz are the refractive indexes of the slow axis, the fast axis, and the thickness direction of the optical film, respectively, at a wavelength of 550 nm, and d is the thickness of the optical film (unit: nm)).

In the present specification, the “thickness phase retardation (Rth)” is represented by the following Equation C, and the thicknesswise phase difference may be measured at measurement wavelengths of 450 nm, 550 nm, and 650 nm:

<Equation C>

Rth = ((nx + ny) / 2-nz) x d

(In the above formula C, nx, ny, nz are the refractive indexes of the slow axis direction, the fast axis direction, and the thickness direction of the optical film at the measurement wavelength, respectively, and d is the thickness of the optical film (unit: nm)).

As used herein, "(meth) acrylic" means acrylic and / or methacryl.

Hereinafter, an optical film according to an embodiment of the present invention will be described in detail.

The optical film according to an embodiment of the present invention may be an optical compensation film (positive C plate film) of a uniaxial optical element in an amount in which the refractive index distribution satisfies nz> nx≥ny or nz> ny≥nx. In "nx≥ny" and "ny≥nx", "nx = ny" includes not only cases where nx and ny are completely identical, but also cases where nx and ny are substantially identical. The "when nx and ny are substantially the same" includes the case where the in-plane retardation of the optical film is 10 nm or less.

The optical film of an embodiment of the present invention may have an in-plane retardation of 10 nm or less, a thickness direction retardation of -50 nm to -10 nm, and a glass transition temperature of 120 ° C or higher. In the above range, the optical film may be stacked on a liquid crystal layer having a predetermined range of in-plane retardation and thickness direction retardation to exhibit a target in-plane retardation and thickness direction retardation, and may have good heat resistance. The optical film may satisfy Equation 1 and Equation 2 below;

<Equation 1>

Rth (550)-Rth (450) ≤ 3nm,

<Equation 2>

Rth (550)-Rth (650) ≤ 3nm.

(In Equations 1 and 2, Rth (550) is a thickness direction retardation at a wavelength of 550nm of the optical film, Rth (450) is a thickness direction retardation at a wavelength of 450nm of the optical film, and Rth (650) is a wavelength of 650nm of an optical film. Thickness direction phase difference).

Viewing from the side with respect to the front side of the display device is called diagonal observation, and when there is an observer in a diagonal observation state, a difference in visibility between the front and side screens is called diagonal light leakage. Diagonal light leakage occurs when the phase difference varies depending on the viewing angle. In order to control such diagonal light leakage, the present invention controls the thickness direction retardation at the wavelengths 450nm, 550nm, and 650nm of the optical film, and satisfies Equations 1 and 2 as the thickness direction retardation difference according to the wavelength dispersion, thereby achieving wavelength dispersion. It was possible to suppress the difference in visual sensation of diagonal light leakage by reducing the change in phase direction along the thickness.

In Equation 1, Rth (450) may be -45nm to -25nm. In Equation 2, Rth (650) may be -40 nm to -24 nm. Within this range, diagonal light leakage can be suppressed.

In one embodiment, the optical film has an in-plane retardation at a wavelength of 550 nm of 5 nm or less, 3 nm or less, specifically 0 nm to 5 nm, 0 nm to 3 nm, a thickness direction retardation at a wavelength of 550 nm of -50 nm to -20 nm, glass transition temperature of 120 ° C to 150 ° C.

In one embodiment, the optical film may be Rth (550)-Rth (450) of Formula 1 is 0 nm to 3 nm, Rth (550)-Rth (650) of Formula 2 is -3 nm to -1 nm. In the above range, it can be stacked on the liquid crystal layer to exhibit a target in-plane retardation and a thickness direction retardation, good heat resistance, little breakage, and diagonal light leakage can be suppressed.

The present invention features an in-plane retardation, a thickness direction retardation, a glass transition temperature, and an optical film satisfying the expressions 1 and 2 simultaneously.

The optical film may be an optical film to which a negative birefringent resin is applied.

The optical film is a monomer mixture comprising at least one first copolymer, an aromatic vinyl-based monomer, and a (meth) acrylate-based monomer among monomers including a (meth) acrylate-based monomer, an aromatic vinyl-based monomer, and an acid anhydride-based monomer. It comprises a second copolymer of, the second copolymer may comprise 2% to 25% by weight of the optical film, preferably 5% to 20% by weight. In the above range, it is possible to provide an optical film that satisfies Equations 1 and 2, which are the in-plane retardation, thickness direction retardation, glass transition temperature, and thickness direction retardation difference according to the wavelength of the present invention.

By including a second copolymer comprising an aromatic vinyl-based monomer and a (meth) acrylate-based monomer, the refractive index of the thickness direction may be increased to have an effect of the positive C film. Copolymers comprising an aromatic vinyl-based monomer and (meth) acrylic acid and the optical film including the first copolymer may have a problem in that haze rises and cracking of the optical film occurs. A copolymer comprising an aromatic vinyl-based monomer and an acid anhydride-based monomer and an optical film comprising the first copolymer may have problems of low transmittance and high haze. By including the second copolymer at 2% by weight to 25% by weight, preferably 5% by weight to 20% by weight, the heat resistance of the optical film and the retardation in the thickness direction of the present invention can be secured, and compatibility between the two copolymers You can lower the film haze by increasing. The optical film may have a haze of 1% or less, preferably 0.5% or less.

The first copolymer may include a homo, alternating, or block copolymer.

The first copolymer may include a (meth) acrylic copolymer comprising a (meth) acrylate monomer as a main monomer. The (meth) acrylate-based monomer may be included in the optical film to increase the transmittance. When a plurality of (meth) acrylate-based monomers are included in the first copolymer, they may be the same as or different from each other.

The (meth) acrylate-based monomer is 30% by weight or more and 100% by weight or less, preferably 70% by weight or more and 100% by weight or less, 80% by weight or more and 100% by weight or less, 75% by weight or more and 98% by weight in the first copolymer Or less, 80% by weight or more may be included in 95% by weight or less. In the above range, it may be effective to increase the transmittance while having high heat resistance.

In one embodiment, the optical film may be a first copolymer of a (meth) acrylate-based monomer as the first copolymer.

In another embodiment, the optical film may be a terpolymer of a (meth) acrylate-based monomer, an aromatic vinyl-based monomer, and an acid anhydride-based monomer as the first copolymer. When a plurality of aromatic vinyl monomers are included in the first copolymer, they may be the same or different from each other. When a plurality of acid anhydride-based monomers are included in the first copolymer, they may be identical to or different from each other.

(Meth) acrylate monomers, aromatic vinyl monomers and acid anhydride monomers have different monomer structures. The first copolymer can increase the heat resistance by increasing the glass transition temperature of the optical film by including an acid anhydride monomer, and is well mixed with an acid anhydride monomer and a (meth) acrylate monomer by containing an aromatic vinyl monomer. It can have the effect of lowering haze.

The total amount of the aromatic vinyl-based monomer and the acid anhydride-based monomer may be included in 2% to 25% by weight, preferably 5% to 20% by weight of the first copolymer. In the above-described range, the glass transition temperature may be increased to improve heat resistance and secure the equations 1 and 2, which are the phase difference in the thickness direction due to wavelength dispersion.

For example, the first copolymer may include 75% to 98% by weight of the (meth) acrylate monomer, 1% to 20% by weight of the aromatic vinyl monomer, and 1% to 15% by weight of the acid anhydride monomer. You can. Preferably, the first copolymer comprises 80% to 95% by weight of the (meth) acrylate monomer, 1% to 15% by weight of the aromatic vinyl monomer, and 1% to 10% by weight of the acid anhydride monomer. You can. More preferably, it may include 80% to 94% by weight of the (meth) acrylate-based monomer, 1% to 14% by weight of the aromatic vinyl-based monomer, and 5% to 10% by weight of the acid anhydride-based monomer. In the above range, the in-plane retardation, thickness direction retardation, glass transition temperature, thickness direction retardation difference according to wavelength dispersion of the present invention can be secured.

The first copolymer may further include a comonomer polymerizable with at least one of a (meth) acrylate-based monomer, an aromatic vinyl-based monomer, and an acid anhydride-based monomer. The comonomer is a monomer different from the (meth) acrylate-based monomer, aromatic vinyl-based monomer, and acid anhydride-based monomer, and may include a norbornene-based monomer (for example, COP). The comonomer may contain up to 10% by weight of the first copolymer.

The first copolymer may have a weight average molecular weight of 100,000 to 250,000, preferably 130,000 to 200,000. In the above range, there may be an effect of improving the cracking of the optical film.

The second copolymer may include a styrene-based copolymer containing an aromatic vinyl-based monomer as a main monomer. The aromatic vinyl-based monomer is included in the optical film to increase the refractive index in the thickness direction to produce an effect of the positive C film.

In one embodiment, the optical film of the present invention comprises a first copolymer of a (meth) acrylate-based monomer, a second copolymer comprising an aromatic vinyl-based monomer as a main monomer, and a second copolymer of 2 By including the weight% to 25% by weight, the in-plane retardation of the present invention, the thickness direction retardation, the thickness direction retardation difference according to the wavelength dispersion satisfies the expressions 1 and 2, and at the same time it was possible to represent the glass transition temperature of the present invention.

In another embodiment, the optical film of the present invention comprises a first copolymer and a second copolymer each comprising an aromatic vinyl-based monomer, the first copolymer comprises a (meth) acrylate-based monomer as a main monomer , The second copolymer comprises an aromatic vinyl-based monomer as a main monomer, and by including the second copolymer at 2% by weight to 25% by weight, in-plane retardation, thickness direction retardation, thickness direction retardation according to wavelength dispersion of the present invention The difference between Equation 1 and Equation 2 was satisfied and at the same time, the glass transition temperature of the present invention could be represented.

Aromatic vinyl-based monomer may be included in 75% to 99% by weight of the second copolymer, preferably 80% to 90% by weight. Within the above range, a retardation in the thickness direction of the optical film of the present invention can be secured.

The aromatic vinyl-based monomer may include 15% by weight or less of the first copolymer and 75% by weight or more of the second copolymer. In the above range, Equation 1, Equation 2, in-plane retardation, and thickness direction retardation of the present invention can be satisfied simultaneously.

The second copolymer may include a copolymer of a monomer mixture comprising an aromatic vinyl monomer and a (meth) acrylate monomer. The second copolymer may include a homo, alternating or block copolymer. (Meth) acrylate monomers and aromatic vinyl monomers have different monomer structures. The monomer mixture for the second copolymer does not contain acid anhydride-based monomers. When a plurality of aromatic vinyl-based monomers and (meth) acrylate-based monomers are respectively included in the second copolymer, they may be the same as or different from each other.

The second copolymer may be a copolymer of a monomer mixture comprising 75% to 99% by weight of an aromatic vinyl-based monomer and 1% to 25% by weight of a (meth) acrylate-based monomer. Preferably, it may be a binary copolymer of a monomer mixture containing 80% to 90% by weight of an aromatic vinyl-based monomer and 10% to 20% by weight of a (meth) acrylate-based monomer. Within the above range, the in-plane retardation of the present invention, the thickness direction retardation, the glass transition temperature, the thickness direction retardation difference in accordance with the wavelength dispersion can be secured the above Equation 1 and Equation 2.

The second copolymer may further include a comonomer polymerizable with at least one of a (meth) acrylate-based monomer and an aromatic vinyl-based monomer. The comonomer is a (meth) acrylate-based monomer, an aromatic vinyl-based monomer, and another monomer, and may include a norbornene-based (eg, COP) monomer. The comonomer may contain up to 10% by weight of the second copolymer.

The second copolymer may be a non-carboxylic acid-based copolymer that does not contain an unsaturated carboxylic acid monomer such as (meth) acrylic acid in the monomer mixture. When the second copolymer contains (meth) acrylic acid or the like, haze of the optical film may be increased or cracking may occur. The second copolymer may be a non-acid anhydride-based copolymer that does not contain an acid anhydride-based monomer such as maleic anhydride in the monomer mixture. When the second copolymer contains an acid anhydride-based monomer, there is a problem that the transmittance of the optical film is lowered and the haze is increased.

The second copolymer may have a weight average molecular weight of 100,000 to 200,000, preferably 130,000 to 200,000. In the above range, there may be an effect of improving the cracking of the optical film.

The content of the (meth) acrylate-based monomer in the first copolymer is higher than the content range of the (meth) acrylate-based monomer in the second copolymer. When the content of the (meth) acrylate monomer in the first copolymer is lower than the content range of the (meth) acrylate monomer in the second copolymer, the heat resistance of the film is lowered, and the first copolymer and the second copolymer When mixing, there may be a problem that the haze of the optical film is increased. The content of the (meth) acrylate monomer in the first copolymer is 30% by weight or more and 100% by weight or less, preferably 70% by weight or more and 100% by weight or less, 80% by weight or more and 100% by weight or less, in the second copolymer The content of the (meth) acrylate monomer may be 1% to 25% by weight.

The content of the aromatic vinyl monomer in the first copolymer is lower than the content range of the aromatic vinyl monomer in the second copolymer. The in-plane retardation, the thickness-direction retardation, the glass transition temperature, and the thickness-direction retardation difference according to wavelength dispersion may be obtained by Equations 1 and 2 above.

The (meth) acrylate monomer, aromatic vinyl monomer, and acid anhydride monomer included in the first copolymer and the second copolymer will be described.

The (meth) acrylate-based monomer may include one or more of a substituted or unsubstituted alkyl (meth) acrylate-based monomer, a monomer having a substituted or unsubstituted cycloaliphatic group, and a monomer represented by Formula 1 below:

<Formula 1>

(In the formula 1, R ₁ is a hydrogen atom or a methyl group;

R ₄ and R ₅ are each independently a substituted or unsubstituted linear alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted branched alkyl group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms. , A substituted or unsubstituted linear alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted branched alkoxy group having 3 to 10 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms, a halogen atom, or a substitution Or an unsubstituted aryl group having 6 to 10 carbon atoms;

m is an integer from 1 to 10; p is an integer from 0 to 4; q is an integer from 0 to 5,

X is a single bond, -C (R ₂ ) (R ₃ )-, -C (= O)-, -O-, -OC (= O)-, -OC (= O) O-, -S-, Is a divalent group selected from the group consisting of -SO-, and -SO _2- (where R ₂ and R ₃ are each independently a hydrogen atom, a linear alkyl group having 1 to 10 carbon atoms, 3 to 10 carbon atoms) A branched alkyl group, a cycloalkyl group having 3 to 10 carbon atoms, a linear alkoxy group having 1 to 10 carbon atoms, a branched alkoxy group having 3 to 10 carbon atoms, a cycloalkoxy group having 3 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms; R ₂ and R ₃ may be interconnected to form a cycloalkyl group having 3 to 10 carbon atoms together with the carbon atoms to which they are attached).

The alkyl (meth) acrylate-based monomer may include a (meth) acrylic acid alkyl ester having a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms and preferably 1 to 4 carbon atoms. The monomer having a substituted or unsubstituted alicyclic group may include one or more of a (meth) acrylic acid ester having a substituted or unsubstituted alicyclic group having 5 to 20 carbon atoms. Specifically, alkyl (meth) acrylate-based monomers are methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylic Acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, hydroxymethyl (meth) acrylate and hydroxyethyl (meth) And acrylates. Preferably, the alkyl (meth) acrylate-based monomer may include a (meth) acrylic monomer having an alkyl group, more preferably methyl methacrylate.

"Substituted" in the substituted or unsubstituted is one or more hydrogen atoms of the functional group is a hydroxyl group, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms or an arylalkyl group having 7 to 10 carbon atoms Means substituted with.

The aromatic vinyl-based monomer is a monomer in which one or more vinyl groups are bonded to an aromatic group, and the "aromatic group" refers to an unsubstituted benzene ring or a benzene ring in which one or more C1 to C5 alkyl groups or halogens are substituted in the benzene ring. Specifically, the aromatic vinyl-based monomer may be styrene, alpha-styrene, para-styrene or meta-styrene, vinyltoluene, and the like, preferably styrene.

The acid anhydride-based monomer may include anhydrides of polyunsaturated carboxylic acids or derivatives thereof. For example, the acid anhydride-based monomer may be represented by Formula 2 below. Preferably, the acid anhydride-based monomer can be maleic anhydride:

<Formula 2>

(In Formula 2, R ₁ and R ₂ are each independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms).

Each of the first copolymer and the second copolymer may be manufactured by a conventional method known to those skilled in the art using a monomer mixture, or a commercially available product. For example, polymerization may be performed by suspension polymerization of monomer mixtures, solution polymerization, interfacial polymerization, and the like.

The aromatic vinyl monomer in the optical film may be included in 10% to 25% by weight, preferably 13% to 20% by weight, and 15% to 20% by weight. Within the above range, in-plane retardation, thickness direction retardation, degree of biaxiality, and Equations 1 and 2 may be obtained.

The optical film may have a degree of biaxiality of -30 or more, preferably -30 to -5, and preferably -20 to -10. In the above range, there may be a blocking effect of diagonal light leakage.

The optical film may have a refractive index of 1.40 to 1.60, specifically 1.48 to 1.56, and preferably 1.51 to 1.53. In the above range, when the liquid crystal layer is laminated on the optical film, the transmittance is high, so it can be used as a display element, and for example, it can be used as an anti-reflection film as a display element.

The optical film may have a thickness of 5 μm to 200 μm, preferably 10 μm to 100 μm, more preferably 25 μm to 50 μm. In the above range, it can be used as an optical film.

The optical film may be a single layer film. However, the case where the optical film is a multilayer of two or more layers may also be included in the scope of the present invention. For example, the optical film may be a three-layer film in which the first layer, the second layer, and the third layer are sequentially stacked. At this time, the sum of the thicknesses of the entire first layer and the third layer is smaller than the thickness of the second layer.

The optical film may further include a conventional additive in addition to the first copolymer and the second copolymer. Additives may include, but are not limited to, antioxidants, ultraviolet absorbers, plasticizers, heat stabilizers, antistatic agents, flame retardants, antistatic agents, compatibilizers, crosslinking agent thickeners, leveling agents, antifoaming agents, corrosion inhibitors, pigments. The additive may be included in an optical film of 20% by weight or less, preferably 5% by weight or less, and more preferably 3% by weight or less. In the above range, it is possible to produce an additive effect without affecting the physical properties of the optical film.

Film molding may be appropriately selected according to the composition and type of the copolymer and the molding processing method. When the extrusion molding method is used, for example, a method in which a copolymer melted by heating at 200 ° C to 400 ° C is discharged in sheet form, and a method of gradually cooling it from a high temperature to a low temperature using a take-up roll (cooling drum) or the like may be selected. You can. It can also be produced by solvent casting.

Any suitable stretching method can be employed as the stretching. Specific examples thereof include longitudinal uniaxial stretching, transverse uniaxial stretching, longitudinal and lateral simultaneous biaxial stretching, and longitudinal and uniaxial biaxial stretching. At this time, "species" means the machine direction (MD) of the film, and "transverse" means the transverse direction (TD) of the film. As the stretching means, a roll stretching machine, a tender stretching machine, a biaxial stretching machine, or the like can be employed. The stretching temperature at the time of heat stretching may be performed from (the glass transition temperature of the film + 10 ° C) to (the glass transition temperature of the film + 20 ° C). Stretching may be performed once, or may be performed by two or more multi-stage stretching. When heated and stretched, a relaxation process may be performed. Preferably, the film can be stretched by simultaneous biaxial stretching or longitudinal and biaxial stretching biaxially. In the case of biaxial stretching, the MD stretching ratio: the TD stretching ratio may be 1: 0.5 to 1: 3, for example, 1: 1 to 1: 3. In the above range, the in-plane retardation and the thickness direction retardation can be simultaneously satisfied while satisfying the glass transition temperature and total light transmittance of the optical film of the present invention. The MD draw ratio can be 1.5 to 6.0 times, preferably 2.0 to 3.0 times, and the TD draw ratio can be 1.5 to 6.0 times, preferably 2.0 to 3.0 times. The transfer rate of the film at the time of stretching is not particularly limited, but may preferably be a speed of 50 mm / min to 300 mm / min in machine precision and stability of the stretching device.

Hereinafter, an optical film of another embodiment of the present invention will be described.

The optical film may include a liquid crystal layer formed on one or both surfaces of the above-described optical film. The optical film and the liquid crystal layer are different. The “liquid crystal layer” may include at least one of a liquid crystal film and a liquid crystal coating layer. The liquid crystal layer may be formed of a liquid crystal composition containing a liquid crystal compound. Examples of the liquid crystal compound include a nematic liquid crystal phase, a smectic liquid crystal phase, a cholesteric liquid crystal phase, and a cylindrical liquid crystal phase, but are not limited thereto. The liquid crystal composition may further include a chiral agent in addition to the liquid crystal compound to obtain a film having a desired refractive index. The liquid crystal composition may further include additives such as a leveling agent, a polymerization initiator, an alignment aid, a heat stabilizer, a lubricant, a plasticizer, and an antistatic agent. The liquid crystal layer may have a refractive index of 1.48 to 1.58, preferably 1.51 to 1.55. In the above range, it is possible to indicate the function of the display element. The liquid crystal layer may have a thickness of 0.1 μm to 30 μm, specifically 0.1 μm to 15 μm, and more specifically 0.3 μm to 5 μm. It can be used in the display device in the above range.

The liquid crystal layer may be a phase difference liquid crystal layer having a phase difference. The in-plane phase difference of the laminate of the liquid crystal layer and the optical film of the present invention may be 120 nm to 160 nm, for example, 130 nm to 145 nm. In the above range, when using an OLED product (eg, a mobile phone, a tablet, etc.), there may be an effect of blocking external light to make the screen well visible.

Hereinafter, the display element of the present invention will be described.

The display device of the present invention may include the optical film of the present invention. The display device may be used as an anti-reflection film, a polarizer protective film, and a viewing angle compensation film.

In one embodiment, the display device may include an optical film of the present invention and a liquid crystal layer formed on one or both surfaces of the optical film of the present invention. Preferably, the display device may be an antireflection film. In the prior art, an anti-reflection film was prepared by forming two layers of a liquid crystal layer having a phase difference on an optical retardation-free optical film. By doing so, the manufacturing process of the antireflection film was minimized and cost reduction was possible. An optical film may be formed on one side or both sides of the liquid crystal layer.

In the display device, the liquid crystal layer may be laminated on the optical film. The liquid crystal layer may be directly formed on the optical film. The "directly formed" means that no other adhesive layer, adhesive layer, or point adhesive layer is interposed between the liquid crystal layer and the optical film. Alternatively, the liquid crystal layer may be formed by forming an alignment layer on the optical film and then coating the liquid crystal composition and aligning the liquid crystal. Alignment film formation and liquid crystal alignment may be performed by conventional methods known to those skilled in the art.

In another embodiment, the display device may include the optical film of the present invention (hereinafter, the first optical film) and another optical film (second optical film) formed on the optical film of the present invention. The second optical film is different from the first optical film. The second optical film is a film formed of a conventional optically transparent resin, and may include a protective film, a polarizer, a polarizing plate, a retardation film, a polarizer protective film, and a viewing angle compensation film, but is not limited thereto.

Hereinafter, the polarizing plate of the present invention will be described.

The polarizing plate of the present invention may include a polarizer and the optical film of the present invention formed on one surface of the polarizer. In one embodiment, the polarizing plate is formed on one side of the polarizer and the polarizer may include a laminate of the optical film and the optical compensation film of the present invention. The optical film and the optical compensation film of the present invention are different from each other.

Hereinafter, the display device of the present invention will be described.

The display device of the present invention may include one or more of the optical film of the present invention, the display device of the present invention. In one embodiment, the display device may include a liquid crystal display device, a light emitting device display device, and preferably a light emitting device display device. The light emitting device display device includes an organic or organic light emitting device, and includes, for example, light emitting diodes (LEDs), organic light emitting diodes (OLEDs), quantum dot light emitting diodes (QLEDs), and phosphors. It may mean a light emitting device.

Hereinafter, the configuration and operation of the present invention through a preferred embodiment of the present invention will be described in more detail. However, the following examples are intended to help understanding of the present invention, and the scope of the present invention is not limited to the following examples.

Example  One

A methyl methacrylate was added as a monomer to a reaction apparatus equipped with a stirring device, a temperature sensor, a cooling tube, and a nitrogen introduction tube, toluene was added as a polymerization solvent, and the temperature was increased while adding nitrogen. After refluxing started with increasing temperature, t-amyl peroxide was added as a polymerization initiator, and polymerization was performed at about 100 ° C to 150 ° C. The obtained polymerization solution was dried under reduced pressure, and a first copolymer was prepared as a one-way copolymer of methyl methacrylate.

A second copolymer in which 20% by weight of methyl methacrylate and 80% by weight of styrene was polymerized was prepared in the same manner as in the preparation of the first copolymer.

80 parts by weight of the prepared first copolymer and 20 parts by weight of the second copolymer were mixed, put into a T-die melt extruder, melted, and then extruded to prepare a film having a thickness of 300 μm. The prepared film was stretched at a transfer rate of 100 mm / min and a stretching temperature of 130 ° C., but was biaxially stretched 2.0 times with a film MD and 2.0 times with a film TD to prepare an optical film having a thickness of 40 μm.

Example  3

To a reaction device equipped with a stirring device, a temperature sensor, a cooling tube, and a nitrogen introduction tube, methyl methacrylate, styrene, and maleic anhydride were added as a monomer, toluene was added as a polymerization solvent, and the temperature was increased while adding nitrogen. After refluxing started with increasing temperature, t-amyl peroxide was added as a polymerization initiator, and polymerization was performed at 100 ° C to 150 ° C. The obtained polymerization solution was dried under reduced pressure to prepare a first copolymer as a ternary copolymer in which 94% by weight of methyl methacrylate, 1% by weight of styrene, and 5% by weight of maleic anhydride were polymerized.

A second copolymer in which 20% by weight of methyl methacrylate and 80% by weight of styrene was polymerized was prepared in the same manner as in the preparation of the first copolymer.

80 parts by weight of the prepared first copolymer and 20 parts by weight of the second copolymer were mixed, put into a T-die melt extruder, melted, and then extruded to prepare a film having a thickness of 300 μm. The prepared film was stretched at a transfer rate of 100 mm / min and a stretching temperature of 130 ° C., but was biaxially stretched 2.0 times with a film MD and 2.0 times with a film TD to prepare an optical film having a thickness of 40 μm.

Example  2, Example  4 to Example  5

In Examples 1 and 3, except that the monomer composition of the first copolymer, the monomer composition of the second copolymer, and the respective contents of the first copolymer and the second copolymer were changed as shown in Table 1 below. An optical film was prepared in the same way. The draw ratio of the extruded film was 2.0 times the MD draw ratio, and 2.0 times the TD draw ratio.

Comparative example  1 to Comparative example  3

In Example 1 and Example 3, except for changing the monomer composition of the first copolymer, the monomer composition of the second copolymer, and the content of the second copolymer as shown in Table 1 below, an optical film was prepared in the same manner. Did. The draw ratio of the extruded film was 2.0 times the MD draw ratio, and 2.0 times the TD draw ratio.

First copolymer Second copolymer Second copolymer content
(weight%) MMA ST MA MMA ST Example 1 100 - - 20 80 20 Example 2 100 - - 10 90 20 Example 3 94 One 5 20 80 20 Example 4 80 10 10 20 80 5 Example 5 80 14 6 20 80 5 Comparative Example 1 100 - - 80 20 20 Comparative Example 2 94 One 5 80 20 20 Comparative Example 3 80 14 6 80 20 20

* MMA: methyl methacrylate, ST: styrene, MA: maleic anhydride

* 2nd copolymer content: 2nd copolymer content in optical film

The physical properties of Table 2 below were evaluated for the optical films prepared in Examples and Comparative Examples.

(1) In-plane retardation, thickness direction retardation, degree of biaxiality: The optical film was measured using a phase difference measuring device Axoscan (Axometric) at wavelengths of 550 nm, 450 nm, and 650 nm.

(2) Glass transition temperature (Tg): the optical film was measured by Discovery (TA instrument) while heating at a temperature of 20 ° C / min.

(3) Haze: Haze meter (Nippon Denshoku model NDH 5000) equipment was used. At 40 μm thickness according to ASTM (American Society for Testing and Measurement) Test Method D 1003-95 (“Standard Test for Haze and Luminous Transmittance of Transparent Plastic”) Haze was measured.

(4) Diagonal light leakage: The TAC of the upper surface of the polarizing film with the film close to the backlight on the display IPS panel was cross-attached to the examples and the comparative examples to visually confirm the difference in color of the diagonal light leakage in the dark. When the color inversion was not confirmed, it was evaluated as good, and when the color inversion occurred, it was evaluated as defective.

thickness
(㎛) Re
＠ 550nm
(nm) Rth ＠ 450
(nm) Rth ＠ 550
(nm) Rth ＠ 650
(nm) NZ Equation 1 Equation 2 Tg
(℃) Haze
(%) Diagonal light Example 1 40 2 -32 -30 -29 -15 2 -One 121 0.2 Good Example 2 40 2 -37 -35 -34 -17 2 -One 124 0.2 Good Example 3 40 2 -42 -40 -39 -20 2 -One 128 0.2 Good Example 4 40 2 -27 -25 -24 -13 2 -One 130 0.2 Good Example 5 40 2 -42 -40 -39 -20 2 -One 130 0.2 Good Comparative Example 1 40 2 -8 -6 -5 -3 2 -One 120 10 Bad Comparative Example 2 40 2 -7 -5 -4 -2 2 -One 125 6 Bad Comparative Example 3 40 2 -64 -60 -58 -30 4 -2 125 6 Bad

As shown in Table 2, the optical film of the present invention has an in-plane retardation and a thickness direction retardation that satisfies the scope of the present invention, has excellent heat resistance, and has low haze, thereby providing excellent optical transparency. In addition, the optical film of the present invention satisfies the in-plane retardation of the present invention, the thickness direction retardation, and Equations 1 and 2 at the same time, thereby suppressing the difference in visual sensation of diagonal light leakage.

Simple modifications or changes of the present invention can be easily implemented by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (16)

Includes a first copolymer of (meth) acrylate-based monomers, aromatic vinyl-based monomers and acid anhydride-based monomers, and a second copolymer of a monomer mixture comprising an aromatic vinyl-based monomer and a (meth) acrylate-based monomer It is an optical film to do,
The second copolymer contains 2% to 25% by weight of the optical film, the glass transition temperature is 120 ° C or higher, the in-plane retardation at wavelength 550nm is 10nm or less, and the thickness direction retardation at wavelength 550nm is -50nm to- 10 nm, satisfying the following expressions 1 and 2,
<Equation 1>
0nm ≤ Rth (550)-Rth (450) ≤ 3nm,
<Equation 2>
-3nm ≤ Rth (550)-Rth (650) ≤ 3nm,
(In Equations 1 and 2, Rth (550) is a thickness direction retardation at a wavelength of 550 nm of the optical film, Rth (450) is a phase difference in a thickness direction at a wavelength of 450 nm of the optical film, Rth (650) is the optical film Retardation in the thickness direction at a wavelength of 650 nm),
The optical film has a degree of biaxiality of -20 to -5 at a wavelength of 550 nm,
The first copolymer is a copolymer of only the (meth) acrylate-based monomer or 80% to 95% by weight of the (meth) acrylate-based monomer, 1% to 15% by weight of the aromatic vinyl-based monomer, and the It is a copolymer of 1% to 10% by weight of an acid anhydride-based monomer,
The second copolymer is a copolymer of a monomer mixture containing 75% to 99% by weight of the aromatic vinyl-based monomer and 1% to 25% by weight of the (meth) acrylate-based monomer.
The optical film according to claim 1, wherein in Equation 1, Rth (450) is -45 nm to -25 nm, and in Equation 2, Rth (650) is -40 nm to -24 nm.
delete delete delete The optical film of claim 1, wherein the aromatic vinyl-based monomer in the optical film is 10% to 25% by weight.
delete delete The optical film of claim 1, wherein the total amount of the aromatic vinyl-based monomer and the acid anhydride-based monomer in the first copolymer is 2% to 25% by weight.
delete delete The optical film of claim 1, wherein the monomer mixture does not include an unsaturated carboxylic acid monomer or an acid anhydride-based monomer.
The optical film of claim 1, wherein a liquid crystal layer is further formed on one surface or both surfaces of the optical film.
The optical film of claim 13, wherein the liquid crystal layer has an in-plane retardation of 120 nm to 160 nm at a wavelength of 550 nm.
A display device comprising the optical film of any one of claims 1, 2, 6, 9 or 12 to 14.
A display device comprising the display element of claim 15.