KR101231715B1 - Acryl-based copolymer, optical film and liquid crystal display comprising the same - Google Patents

Abstract

The present invention provides an acrylic copolymer resin containing an alkyl (meth) acrylate monomer, an acrylic monomer containing a benzene ring, a styrene monomer and an acid anhydride, an optical film including the acrylic copolymer resin, and the optical film. A liquid crystal display device is included. The optical film according to the present invention is excellent in heat resistance, optical transparency, and the like, and has a characteristic of retardation and photoelastic coefficient after stretching being very small.

Acrylic, Retardation, Protective Film, Liquid Crystal Display

Description

Acrylic copolymer resin, optical film and liquid crystal display including the same {ACRYL-BASED COPOLYMER, OPTICAL FILM AND LIQUID CRYSTAL DISPLAY COMPRISING THE SAME}

The present invention relates to an acrylic copolymer resin excellent in heat resistance, an optical film excellent in heat resistance and optical transparency containing the acrylic copolymer resin, and a liquid crystal display device comprising the optical film.

Recently, display technologies using various methods such as plasma display panels (PDPs) and liquid crystal displays (LCDs), which replace conventional CRTs, have been proposed and marketed based on the development of optical technologies. Polymer materials for such displays are becoming more sophisticated. For example, in the case of liquid crystal displays, as thin film thickness, light weight, and large screen area are promoted, wide viewing angles, high contrast, suppression of image color tone change according to viewing angle, and uniformity of screen display have become particularly important problems.

Accordingly, various polymer films are used for polarizing films, polarizer protective films, retardation films, plastic substrates, light guide plates, etc., and as liquid crystals, twisted nematic (TN), super twisted nematic (STN), Various modes of liquid crystal display using vertical alignment (VA), in-plane switching (IPS) liquid crystal cells, and the like have been developed. All of these liquid crystal cells have an inherent liquid crystal array, have inherent optical anisotropy, and in order to compensate for this optical anisotropy, films have been proposed in which various kinds of polymers are drawn to give a retardation function.

The polarizing plate generally has a structure in which a triacetyl cellulose film (hereinafter referred to as a TAC film) is laminated on a polarizer with an aqueous adhesive made of a polyvinyl alcohol-based aqueous solution. By the way, both the polyvinyl alcohol film used as a polarizer and the TAC film used as a protective film for polarizers do not have sufficient heat resistance and moisture resistance. Therefore, when the polarizing plate made of the above films is used for a long time in an atmosphere of high temperature or high humidity, the polarization degree is lowered, the polarizer and the protective film are separated, or the optical properties are deteriorated.

In addition, the TAC film has a large change in the in-plane retardation R _in and the thickness direction retardation R _th , which are existing according to changes in the ambient temperature / humidity environment, and _in particular, the change in the retardation with respect to incident light in the oblique direction is large. When a polarizing plate including a TAC film having such characteristics as a protective film is applied to a liquid crystal display device, there is a problem in that the viewing angle characteristic changes according to a change in the ambient temperature / humidity environment and the image quality is deteriorated. In addition, the TAC film has not only a large dimensional change ratio due to environmental temperature / humidity environment change, but also a relatively large photoelastic coefficient value, resulting in a change in phase retardation property locally after evaluation of durability in a heat- and moisture- .

Acryl-based resins are well known as a material for compensating for the disadvantages of the TAC film. However, acrylic resins do not have sufficient heat resistance, and after stretching, in-plane and thickness direction retardation are expressed and thus are not suitable for use as a protective film.

In order to solve the problems of the prior art as described above, an object of the present invention is to provide an acrylic copolymer resin that can be used as a polarizer protective film with little in-plane and thickness direction retardation, small photoelastic coefficient and excellent heat resistance even after stretching. will be.

Still another object of the present invention is to provide an optical film having excellent heat resistance and optical transparency including the acrylic copolymer resin, a polarizing plate provided with the optical film, and a liquid crystal display including the same.

One aspect of the present invention for achieving the above object is an alkyl (meth) acrylate monomer; Acrylic monomers containing a benzene ring; An acrylic copolymer resin comprising a styrene monomer and an acid anhydride is provided.

A second aspect of the present invention for achieving the above object provides an optical film comprising the acrylic copolymer resin.

A third aspect of the present invention for achieving the above object provides a polarizing plate having the optical film and a liquid crystal display having the same.

The acrylic copolymer resin according to the present invention is excellent in heat resistance while maintaining transparency. The optical film produced using the acrylic copolymer resin is excellent in transparency and heat resistance, and even after stretching, the retardation and photoelastic coefficient are very small.

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

One aspect of the invention, the alkyl (meth) acrylate monomers; Acrylic monomers containing a benzene ring; The present invention relates to an acrylic copolymer resin containing a styrene monomer and an acid anhydride.

The acrylic copolymer may be a block copolymer or a random copolymer, but the copolymer form is not limited thereto.

In the acrylic copolymer resin, the alkyl (meth) acrylate monomers; Acrylic monomers containing a benzene ring; The weight ratio of the styrene monomer and the acid anhydride is preferably 60 to 97: 1 to 30: 1 to 30: 1 to 30, and more preferably 65 to 90: 5 to 20: 1 to 10: 1 to 10. When the weight ratio is in the above range, the acrylic copolymer resin has excellent optical properties, suitable physical properties when manufactured into a film, and may exhibit particularly excellent heat resistance.

In the acrylic copolymer resin, the alkyl (meth) acrylate-based monomer means both an alkyl acrylate-based monomer and an alkyl methacrylate-based monomer. It is preferable that the alkyl group of the said alkyl (meth) acrylate type monomer is C1-C10, It is more preferable that it is 1-4, It is more preferable that it is a methyl group or an ethyl group. Examples of the alkyl (meth) acrylate-based monomers include methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, and the like. Methacrylate is preferred.

In the acrylic copolymer resin, the acrylic monomer containing a benzene ring is substituted with an aryl group having 6 to 40 carbon atoms, an arylalkyl group having 6 to 40 carbon atoms, an aryloxy group having 6 to 40 carbon atoms, or an aryloxyalkyl group having 6 to 40 carbon atoms. It is more preferable that the (meth) acrylate substituted with an arylalkyl group having 6 to 15 carbon atoms, an aryloxy group having 6 to 10 carbon atoms or an aryloxy alkyl group having 6 to 15 carbon atoms.

Preferred examples of the acrylic monomer containing the benzene ring include benzyl methacrylate, 1-phenylethyl methacrylate, 2-phenoxyethyl methacrylate, 2-phenylethyl methacrylate and 3-phenylpropyl methacrylate. , 3-phenylpropyl acrylate, 2-phenoxyethyl acrylate, and the like, of which benzyl methacrylate is preferred.

The styrene-based monomer means a monomer containing a styrene group, the styrene-based monomer may be generally represented by the following formula.

Each of R ₁ and R ₂ in the formula may be the same as or different from each other, and may be hydrogen or an alkyl group having 1 to 5 carbon atoms. Examples of styrene monomers include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, t-butyl styrene, and the like. Of these, styrene or α-methylstyrene is preferable in terms of heat resistance, but is not limited thereto.

Carboxylic anhydride can be used as said acid anhydride, and monovalent, divalent or more polyvalent carboxylic anhydride can be used. Preferably, maleic anhydride or a derivative thereof can be used, for example a compound of the formula

In which R ₇ and R ₈ each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

The matrix resin can be polymerized using a method known in the art, for example, a bulk polymerization method or a solution polymerization method can be used.

The molecular weight of the acrylic copolymer resin is preferably in the range of 50,000 to 500,000 in terms of heat resistance, processability and productivity.

Glass transition temperature (Tg) of the said acrylic copolymer resin becomes like this. Preferably it is 120 degreeC or more, More preferably, it is 130 degreeC or more.

A second aspect of the invention relates to an optical film comprising the acrylic copolymer resin.

The optical film may be prepared into a film according to a method well known in the art, such as solution caster method or extrusion method of the acrylic copolymer resin.

It may further comprise the step of uniaxially or biaxially stretching the film prepared as described above, may be prepared by adding a modifier in some cases.

In the optical film manufactured as described above, the plane direction retardation value represented by Equation 1 is -3 to 3 nm and the thickness direction retardation value represented by Equation 2 is preferably -4 to 4 nm.

[Equation 1]

R _in = (n _x -n _y ) × d

&Quot; (2) "

R _th = (n _z -n _y ) × d

In Equations 1 and 2,

n _x is a refractive index of the direction of the largest refractive index in the plane direction of the film,

n _y is a refractive index in the vertical direction in the n _x direction in the plane direction of the film,

n _z is the refractive index in the thickness direction,

d is the thickness of the film.

In addition, it is preferable that the optical film manufactured as described above has a photoelastic coefficient of -3 to 3. The photoelastic coefficient is a coefficient representing the degree of birefringence that is easily generated with respect to external stress. The photoelastic coefficient is calculated by plotting a retardation value generated by applying external stress to the film.

In addition, the optical film manufactured as described above preferably has a haze of 0.1 to 1.0%. When transparency is in the above range, when the optical film according to the present invention is used as a protective film of the polarizer, the image quality does not deteriorate.

The method for producing an optical film according to the present invention may further include the step of uniaxially or biaxially stretching the film. The stretching step may be performed in the longitudinal direction (MD) stretching or in the transverse direction (TD) stretching, or both. When extending | stretching both a longitudinal direction and a lateral direction, after extending | stretching either one, you can extend in another direction and you may extend | stretch both directions simultaneously. Stretching can be done in one step or stretched in multiple steps. When extending | stretching in a longitudinal direction, extending | stretching by the speed difference between rolls can be performed, and when extending | stretching in a lateral direction, a tenter can be used. The starting angle of the tenter is 10 degrees or less in total, suppressing the bowing phenomenon which arises at the time of a lateral stretch, and controls the angle of an optical axis regularly. The same boeing suppression effect can also be obtained by making transverse stretching into multiple stages.

The stretching may be performed at a temperature of (Tg-20 ° C) to (Tg + 30 ° C) when the glass transition temperature of the copolymer resin is Tg. The glass transition temperature refers to a region from the temperature at which the storage modulus of the copolymer resin begins to decrease, and thus the loss modulus becomes larger than the storage modulus, at which the orientation of the polymer chain is relaxed and lost. Glass transition temperatures can be measured by differential scanning calorimetry (DSC). The temperature during the stretching step is more preferably the glass transition temperature of the film.

The drawing speed is preferably in the range of 1 to 100 mm / min in the case of a universal drawing machine (Zwick Z010) and in the range of 0.1 to 2 m / min in the case of a pilot drawing machine. It is preferable to stretch the film by applying an elongation of 5 to 300%.

The optical film according to the present invention can be uniaxially or biaxially stretched by the above-described method, thereby adjusting the phase difference characteristics.

A third aspect of the present invention relates to a polarizer comprising a polarizer and an optical film according to the present invention, provided as a protective film on at least one side of the polarizer.

In addition, a fourth aspect of the present invention relates to a liquid crystal display including the polarizing plate.

For example, the present invention includes a light source, a first polarizing plate, a liquid crystal cell, and a second polarizing plate sequentially stacked, and includes the optical film according to the present invention as a protective film of at least one of the first and second polarizing plates. A liquid crystal display device is provided.

The liquid crystal cell is a liquid crystal layer; A substrate capable of supporting this; And an electrode layer for applying a voltage to the liquid crystal. At this time, the polarizing plate according to the present invention is an in-plane switching mode (IPS mode), vertically aligned (VA mode), OCB (Optically Compensated Birefringence mode), twisted nematic mode (Twisted Nematic mode) TN mode) and FFS (Fringe Field Switching mode; FFS mode).

The optical film according to the present invention may be provided on both sides of the polarizer. In addition, the optical film is provided on one side of the polarizer, the other side is provided with a polarizer protective film known in the art, such as TAC film, PET film, COP film, PC film, polynorbornene-based film, etc. It may be.

Adhesion of the polarizer and the optical film may be performed using an adhesive layer. The adhesive which can be used when laminating the optical film and the polarizing plate is not particularly limited as long as it is known in the art. For example, there is a one-component or two-component polyvinyl alcohol (PVA) adhesive, a polyurethane adhesive, an epoxy adhesive, a styrene butadiene rubber (SBR) adhesive, or a hot melt adhesive, but is not limited to these examples. Polyvinyl alcohol adhesive is more preferable among the said adhesive agents.

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

When using a polyurethane adhesive, it is preferable to use the polyurethane adhesive manufactured using the aliphatic isocyanate compound which is not yellowed by light. When using one-component or two-component dry laminate adhesives or adhesives with relatively low reactivity between isocyanates and hydroxyl groups, a solution type diluted with an acetate solvent, a ketone solvent, an ether solvent, or an aromatic solvent, etc. Adhesives can also be used. At this time, the adhesive viscosity is preferably low viscosity of 5,000 cps or less. The adhesives are excellent in storage stability and preferably have a light transmittance of 90% or more at 400 to 800 nm.

A tackifier can also be used if it can exert sufficient adhesive force. The adhesive is preferably hardened by heat or ultraviolet rays after lamination, and thus the mechanical strength is improved to the level of the adhesive. The adhesive strength is also large, and thus the adhesive strength is such that the adhesive cannot be peeled off without breaking of either film to which the adhesive is attached. It is preferable.

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

Hereinafter, preferred examples will be described to aid in understanding the present invention. The following examples are intended to illustrate the invention and are not intended to limit the scope of the invention.

The physical property evaluation method in this invention is as follows.

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

2. Tg (glass transition temperature): It was measured using DSC (Differential Scanning Calorimeter) of TA Instrument.

3. Retardation value (R _in / R _th ): After stretching at the glass transition temperature of the film was measured using AxoScan Axometrics.

4. Photoelastic coefficient: The film was made into a sample of 10 mm x 70 mm size, and the film was fixed. The R _in value that appears when the stress was applied was plotted against the applied stress to determine the slope value.

5. Haze value: measured according to ASTM 1003 method.

<Examples>

Example  One

100 parts by weight of the total monomer including 80 parts by weight of methyl methacrylate, 10 parts by weight of benzyl methacrylate, 5 parts by weight of styrene, and 5 parts by weight of maleic anhydride, respectively, as an initiator and a molecular weight regulator, respectively. 0.05 parts by weight of butylperoxy) -3,3,5-trimethylcyclohexane, 1 part by weight of t-dodecyl mercaptan and 20 parts by weight of toluene were charged to a reactor with a stirrer. The polymerization was carried out so as to convert the introduced monomer into a polymer while maintaining the reaction temperature at 120 ° C. and the retention time of 2 hours. The copolymerized resin was obtained after removing the unreacted monomer and the solvent while maintaining the polymerization reaction at a temperature of 220 ° C. and a vacuum pressure of 30 torr. The prepared copolymer resin was prepared into an extruded film having a thickness of 100 mm using an extruder equipped with a T-die, followed by 200% biaxial stretching, and then measured. The physical properties thereof are shown in Table 1 below.

Example  2

Except that 70 parts by weight of methyl methacrylate, 10 parts by weight of benzyl methacrylate, 10 parts by weight of styrene, and 10 parts by weight of maleic anhydride were tested in the same manner as in Example 1, the measurement results are shown in Table 1 below. .

Example  3

Except that 65 parts by weight of methyl methacrylate, 15 parts by weight of benzyl methacrylate, 10 parts by weight of styrene, 10 parts by weight of maleic anhydride were tested in the same manner as in Example 1, the measurement results are shown in Table 1 below. .

Comparative example  One

90 parts by weight of methyl methacrylate and 10 parts by weight of benzyl methacrylate were used in the same manner as in Example 1, and the measurement results are shown in Table 1 below.

Comparative example  2

Except for 85 parts by weight of methyl methacrylate, 15 parts by weight of benzyl methacrylate was tested in the same manner as in Example 1 and the measurement results are shown in Table 1 below.

Claims (19)

Alkyl (meth) acrylate monomers having 1 to 10 carbon atoms; Benzyl methacrylate, 1-phenylethyl methacrylate, 2-phenoxyethyl methacrylate, 2-phenylethyl methacrylate, 3-phenylpropyl methacrylate, 3-phenylpropyl acrylate and 2-phenoxyethyl Acrylic monomers containing a benzene ring selected from the group consisting of acrylates; Styrene monomers; And It is an acrylic copolymer resin containing an acid anhydride which is maleic anhydride or a derivative thereof, The alkyl (meth) acrylate monomers; Acrylic monomers containing a benzene ring; The weight ratio of the styrene monomer and the acid anhydride is 65 to 90: 5 to 20: 1 to 10: 1 to 10, acrylic copolymer resin, characterized in that. delete delete The method of claim 1, wherein the alkyl (meth) acrylate monomer is selected from the group consisting of methyl methacrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate Acrylic copolymer resin, characterized in that. delete delete delete The acrylic copolymer resin according to claim 1, wherein the acrylic monomer containing a benzene ring is benzyl methacrylate. The acrylic copolymer resin according to claim 1, wherein the styrene monomer is represented by the following formula.

Each of R ₁ and R ₂ in the above formula may be the same or different from each other, and is selected from hydrogen or an alkyl group having 1 to 5 carbon atoms. The acrylic copolymer resin according to claim 1, wherein the styrene monomer is selected from the group consisting of styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, and t-butylstyrene. delete delete The acrylic copolymer resin according to claim 1, wherein the glass transition temperature of the acrylic copolymer resin is 120 ° C or higher. The acrylic copolymer resin according to claim 1, wherein the Haze of the acrylic copolymer resin is 0.1 to 1.0%. Claims 1, 4, 8 to 10, claim 13, and the optical film comprising the acrylic copolymer of any one of claims. The method according to claim 15, wherein the optical film has a surface direction retardation value represented by the following formula (1) is -3 to 3 nm and the thickness direction retardation value represented by the following formula (2), characterized in that, Optical film: [Equation 1] R _in = (n _x -n _y ) × d &Quot; (2) &quot; R _th = (n _z -n _y ) × d In Equations 1 and 2, n _x is a refractive index of the direction of the largest refractive index in the plane direction of the film, n _y is a refractive index in the vertical direction in the n _x direction in the plane direction of the film, n _z is the refractive index in the thickness direction, d is the thickness of the film. The optical film according to claim 15, wherein the optical film has a photoelastic coefficient of -3 to 3. A polarizing plate comprising a polarizer and the optical film of claim 15 provided on at least one surface of the polarizer as a protective film. A liquid crystal display device comprising the polarizing plate of claim 18.