KR101638666B1 - Method for manufacturing optical film having a good surface property and heat-resistance and optical film produced by using the same - Google Patents

Abstract

The present invention relates to a method for producing an optical film comprising molding an acrylic resin by a melt extrusion method using a film production apparatus including an extruder, a polymer filter and a die, wherein the viscosity of the acrylic resin in the extruder is η _E , the viscosity of the acrylic resin in the polymer filter is eta _P , and the viscosity of the acrylic resin in the die is eta _D , the molding step is performed so as to satisfy the following formulas (1) and (2) The present invention also provides a method for producing an optical film.
0.5?? _P /? _E ? 2.5
0.8?? _P /? _D ? 2.0

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing an optical film having excellent surface properties and heat resistance, and an optical film produced using the optical film.

More particularly, the present invention relates to a method for producing an optical film which is easy to produce when an optical film is produced by using an acrylic resin composition having high heat resistance and is less likely to cause optical defects due to bubbles or the like .

Recently, various thin display devices such as a plasma display, a liquid crystal display, and an organic light emitting diode display have been proposed and commercialized based on the development of optical technology. These thin display devices are thinner, lighter, and have less energy consumption than conventional CRTs.

On the other hand, these thin display devices generally have a polarizing plate for providing a specific polarized light to the display panel, and the polarizing plate usually comprises a polarizer and a protective film attached to one or both sides of the polarizer to protect the polarizer . Conventionally, triacetyl cellulose (TAC) films have been mainly used as the protective film. However, in the case of a cellulose-based film, since the hydrophilic functional groups are large in the molecular chain structure, the moisture permeability is high, There is a problem that the film is deformed to cause light leakage, or dissociation of iodide ions occurs in the polarizer, resulting in deterioration of the polarization performance of the polarizer.

Protective films using an acrylic resin such as polyMethylMethacrylate (PMMMA) or the like and a cycloolefin polymer (COP) resin having low moisture permeability have been proposed. Among them, the acrylic resin is excellent in transparency and optical isotropy and has attracted attention as a material suitable for an optical film. However, in the case of polymethyl methacrylate, it is easily broken due to external impact, and the polarizing performance of the polarizing plate may deteriorate under high temperature and high humidity conditions due to low heat resistance, which is not suitable as an optical film for display. Accordingly, a method of producing an optical film by using an acrylic resin prepared by copolymerizing monomers having high heat resistance such as a styrene monomer, a lactone ring monomer, and / or an imide monomer, for example, with an acrylic monomer has been proposed. However, in the case of such an acrylic copolymer resin, there is a problem that it is difficult to process the film due to high viscosity, and bubbles are generated during the processing, and optical defects are likely to occur in the appearance of the film.

Disclosure of the Invention The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for producing an optical film which is easy to process and has little optical defects due to bubbles when an optical film is produced using a high heat- .

To this end, the present invention is, in one aspect, a process for producing an optical film comprising molding an acrylic resin by a melt extrusion method using a film production apparatus comprising an extruder, a polymer filter and a die, (1) and (2), when the viscosity of the acrylic resin in the die is η _E , the viscosity of the acrylic resin in the polymer filter is η _P and the viscosity of the acrylic resin in the die is η _D , ) Of the optical film is satisfied.

0.5?? _P /? _E ? 2.5

0.8?? _P /? _D ? 2.0

In another aspect, the present invention relates to an optical film produced by the optical film production method of the present invention, wherein the thickness deviation in the MD and TD directions of the film is as small as 2 m or less and the heat resistance is excellent, And an optical film excellent in surface characteristics.

In another aspect, the present invention provides a polarizing plate and a display device comprising the optical film of the present invention.

The optical film produced according to the optical film production method of the present invention has high heat resistance characteristics, is easy to process, has little optical defects due to bubbles, and has excellent surface properties.

1 is a view showing an embodiment of an optical film production apparatus of the present invention.
Fig. 2 is a graph showing the apparent shear viscosity according to apparent shear rates of the resins of Production Examples 1 and 2. Fig.

Hereinafter, the present invention will be described more specifically with reference to the drawings.

The present inventors have conducted extensive studies to develop a high heat-resistant acrylic optical film having excellent surface properties. As a result, when the acrylic resin is melt-extruded, the viscosity ratio of the acrylic resin is adjusted to a specific range according to the section, Heat-resistant acrylic optical film can be produced, and the present invention has been completed.

More specifically, the method for producing an optical film of the present invention comprises a step of melt-extruding an acrylic resin using an optical film production apparatus equipped with an extruder, a polymer filter and a die and molding the same, (1) and (2) satisfy the following expressions (1) and (2) when the viscosity of the acrylic resin is η _s , the viscosity of the acrylic resin in the polymer filter is η _P and the viscosity of the acrylic resin in the die is η _D. .

(1): 0.5?? _P /? _S ? 2.5

(2): 0.8?? _P /? _D ? 2.0

In the present invention, the viscosity of the acrylic resin is defined as a ratio of an apparent shear stress (τ _ap ) to an apparent shear rate (r _ap ) as shown in the following formula (3) The apparent shear viscosity (r _ap ) and apparent shear stress (τ _ap ) are defined by the equations (4) and (5), respectively.

(3): apparent viscosity (η) = apparent shear stress (τ _ap ) / apparent shear rate (r _ap )

(4): Apparent shear stress (τ _ap ) = {(pd) / (4L)} × 10 ⁵ (Pa)

Expression (5): apparent shear rate (r _ap ) = (4V) / πR ³ (s ^-1 )

Where V is the volume flow rate of the acrylic resin, R is the pipe radius of the measuring device, p is the melt pressure, d is the diameter of the pipe of the measuring device, Means the pipe length of the device. In the present invention, the apparent shear viscosity, apparent shear stress and apparent shear rate of an acrylic resin were measured using a Capillary Rheometer (Rheograph 20, Geottfert) using a capillary rheometer . 1 mm and L / D 32 capillaries at 260-290 ° C and shear rate of 1 ~ 2000 1 / s. Based on these measurements, extruder and polymer filter, T-die flow rate and pressure were measured Apparent shear rate and apparent shear viscosity were determined.

According to the studies of the present inventors, it has been found that, in the case of an optical film using a high heat-resistant acrylic resin composition, the surface characteristics of the optical film can be improved by controlling the viscosity ratio to a specific range for each section in the film-

The surface properties of the optical film show a tendency to depend on the flow stability of the molten resin and the flow stability must be maintained as the molten resin passes through the polymer filter and the T-die in the extruder. On the other hand, in order to maintain the flow stability, it is advantageous to have a higher viscosity in the order of extruder, polymer filter, and T-die. In this case, the pressure is increased to pass through each part of the equipment, and only a certain level of the increased pressure passes through the equipment, so that a certain level of pressure can be formed. For example, if the viscosity of the extruder is higher than the polymer filter, the molten resin is less likely to form unstable flows through the polymer filter, which may be the same for polymer filters and T-die . If the flow of the molten resin is unstable, intermittent thickness deviation occurs in the MD direction of the film, resulting in poor film appearance, and wrinkle defects such as gauge band in the produced roll product may occur. This part may be similar in the polymer filter, T-die section. Particularly, in the polymer filter and T-die section, since the flow is generated only by the melt pressure without the shearing force applying device such as the extruder, the viscosity change rate may be slightly smaller than the extruder and polymer filter section.

Hereinafter, this will be described in more detail with reference to FIG. Fig. 1 shows an embodiment of a film production apparatus used for producing the optical film of the present invention. 1, the film production apparatus 1 used in the present invention includes an extruder 10, a polymer filter 20, and a die 30.

The extruder 10 is for melting an acrylic resin which is a raw material of an optical film, and various extruders used in the art can be used without limitation. For example, the extruder 10 usable in the present invention is not limited to this, but may be configured as a raw material supply unit 13, a screw 12, a barrel 14, etc. as shown in Fig. . At this time, the screw 12 is rotatably disposed in the barrel 14, and melts the raw resin supplied through the raw material supply part 13. [ On the other hand, as the screw 12, a one-axis screw, a two-axis screw, a BUSS co-reader or the like may be used, but a one-axis screw is particularly preferable. One-axis screw is advantageous in that a certain amount of resin can be supplied in comparison with a two-screw screw and a bus cone nut, which require a separate feeding device, because the raw material feeding part depends on the screw volume. The extruder 10 may further include a vent portion 16 for removing volatile components, a temperature adjusting portion 18, and the like, if necessary.

The acrylic resin of the present invention is supplied to the barrel 14 through the raw material supply portion 13 and discharged to the front of the extruder 10 in a molten state by the rotation of the screw 12. [ The discharged molten resin is conveyed along the pipe to the polymer filter (20). The polymer filter 20 removes impurities from the molten acrylic resin. The polymer filter 20 may be a polymer filter well known in the art such as a leaf disk type polymer filter, a pack disk filter, a cylindrical filter, Type filter and the like can be used without limitation.

Meanwhile, the polymer filter used in the present invention may be a leaf disc type in which the opening size may be 5 to 10 탆 and 30 to 60 can be used.

On the other hand, in the present invention, the ratio of η _P on the viscosity of the acrylic resin in the extruder (10), η _s, when the viscosity of the acrylic resin η _P d at the polymer filter (20), wherein η _s , That is,? _P /? _S is preferably 0.5 to 2.5. At this time, the viscosity of the acrylic resin in the extruder is a value obtained through the pressure value and the flow rate measured at the outlet of the extruder, and the viscosity of the acrylic resin in the polymer filter is a value obtained through the pressure value measured in the polymer filter and the flow rate .

When the viscosity of the acrylic resin in the extruder-polymer filter section is out of the above range, the appearance of the film to be formed may become uneven due to flow instability. That is, when the section ratio is less than 0.5, the viscosity of the extrusion section is very high, so that the polymer filter can pass through the polymer filter at a high flow rate to generate an unstable flow. When the ratio exceeds 2.5, the viscosity of the polymer filter section is very high, do.

Next, the acrylic resin having passed through the polymer filter 20 is discharged through the die 30 to be formed into a film. The die 30 is not particularly limited and may be formed of materials known to those skilled in the art, for example, a T-die, a manifold die, a coat hanger die, or the like. The molten resin discharged through the die 30 is formed into a film shape through a cooling device such as a casting drum (not shown).

At this time, when the viscosity of the acrylic resin in the polymer filter 20 considered η _P, of the acrylic resin in the die viscosity η _D, the ratio of η _P for the η _D, that is, η _P / η _D 0.8 To about 2.0.

When the viscosity of the acrylic resin in the polymer filter to the die section is out of the above range, the appearance of the film to be formed may become uneven due to flow instability as in the extruder to polymer filter section described above. That is, when the section ratio is less than 0.8, the viscosity of the T-die section is very high, making it difficult to cause a smooth melt flow. When the ratio exceeds 2.0, the viscosity of the polymer filter section becomes very high, The film thickness may become very poor.

The viscosity ratio described above is a value depending on the shear rate for each extrusion section, but it is preferable that appropriate extrusion temperature setting is performed because it also depends on the extrusion temperature. If the extrusion temperature is very low or high, the viscosity of the molten resin may be very high or low, which may cause unstable melt flow.

On the other hand, the optical film producing apparatus of the present invention may further include a gear pump 40, if necessary. If a gear pump is included in the extrusion section, pressure can be applied to pass through the polymer filter, and flow instability caused by unstable factors such as temperature change and discharge amount fluctuation can be relieved during the extrusion process to induce stable melt flow There may be advantages to be able to.

On the other hand, in the present invention, the acrylic resin to be a raw material may be a resin containing an alkyl (meth) acrylate unit and its composition is not particularly limited.

Examples of the acrylic resin usable in the present invention include a copolymer (A) comprising an alkyl (meth) acrylate-based unit, (b) a styrene-based unit, and an aromatic resin (B) having a carbonate- And the like.

In the present invention, the alkyl (meth) acrylate-based unit imparts a negative in-plane retardation (Rin) and a negative thickness direction retardation (Rth) to a weak degree in a stretching process, and the styrene- It is possible to impart the in-phase difference Rin and the negative thickness direction retardation Rth. On the other hand, an aromatic resin having a carbonate moiety in the main chain can impart a positive in-plane retardation (Rin) characteristic and a positive thickness direction retardation (Rth) characteristic.

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

Depending on the characteristics of each unit described above, the retardation characteristics of the optical film produced therefrom may vary depending on the composition of each component, the stretching direction, the stretching ratio, and the stretching method. Accordingly, in the present invention, it is possible to produce an optical film which can be used as a zero-phase retardation film, that is, a protective film by adjusting the composition of each component and the stretching method.

As used herein, the term "copolymer" means that an element referred to herein as "unit" is polymerized as a monomer and contained as a repeating unit in the copolymer resin. In the present specification, the copolymer is a block copolymer or a random copolymer But the type of copolymerization is not limited thereto.

As used herein, the term 'alkyl (meth) acrylate-based unit' means that it can include both an 'alkyl acrylate-based unit' and an 'alkyl methacrylate-based unit'. The alkyl moiety of the alkyl (meth) acrylate-based unit preferably has 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group. The alkyl methacrylate-based unit is more preferably methyl methacrylate, but is not limited thereto.

In the present invention, the styrene unit (b) may be an unsubstituted styrene unit, but styrene substituted with at least one substituent selected from the group consisting of aliphatic hydrocarbon and heteroatom in the benzene ring or vinyl group of styrene may be used including and, more particularly, C _{1 - 4} may be used for the units substituted with alkyl or halogen, more preferably from the group consisting of α- methyl styrene, p- bromo styrene, p- methyl styrene and p- chlorostyrene May be used. And most preferably substituted by at least one substituent selected from the group consisting of styrene? -Methylstyrene, and p-methylstyrene.

In the present invention, it is preferable that the aromatic resin (B) having a carbonate moiety in the main chain contains 5 to 10,000 units of at least one kind represented by the following formula (I).

 (I)

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

The copolymer preferably comprises (a) 80 to 99.9 parts by weight of an alkyl (meth) acrylate-based unit and (b) 0.1 to 20 parts by weight of a styrene-based unit relative to 100 parts by weight of the copolymer. When the content of the acrylate unit is less than 80 parts by weight, there is a problem that the transmittance of the optical film is deteriorated. When the content exceeds 99.9 parts by weight, there is a problem in the heat resistance of the optical film. On the other hand, when the content of the styrenic unit is less than 0.1 part by weight, there is a problem in retardation control of the optical film, and when it exceeds 20 parts by weight, there is a problem in compatibility with the aromatic resin (B).

The copolymer and the aromatic resin are preferably mixed at a weight ratio of 90:10 to 99.5: 0.5, more preferably 95: 5 to 99: 1. When the copolymer is contained in a smaller amount than the above range, there is a problem in controlling the retardation of the optical film. When the copolymer is contained in an amount exceeding the above range, there is a problem in compatibility with the copolymer and the aromatic resin, .

Furthermore, the copolymer (A) may further comprise (c) a 3- to 6-membered heterocyclic unit substituted with at least one carbonyl group. The 3 to 6 membered heterocyclic unit may be selected from the group consisting of, for example, maleic anhydride, maleimide, glutaric anhydride, glutarimide, lactone and lactam. The 3- to 6-membered heterocyclic unit substituted with at least one carbonyl group can provide excellent heat resistance to the film produced by the resin composition. In addition, the units listed above exhibit excellent compatibility with the aromatic resin. When the (c) units listed above and (a) the alkyl (meth) acrylate-based units constitute a copolymer, compatibility of the copolymer with the aromatic resin Can be improved.

(c) the copolymer further comprising 3- to 6-membered heterocyclic units substituted with at least one carbonyl group is selected from a) 80 to 99.9 parts by weight of an alkyl (meth) acrylate based on 100 parts by weight of the copolymer, b) 0.1 to 10 parts by weight of a styrene-based unit, and (c) 0.1 to 10 parts by weight of a 3- to 6-membered heterocyclic unit substituted with at least one carbonyl group.

When the alkyl (meth) acrylate-based unit is contained in an amount of less than 80 parts by weight, there is a problem of deteriorating the transmittance of the optical film. When the amount of the alkyl (meth) acrylate-based unit is more than 99.9 parts by weight, If the content of the styrenic unit is less than 0.1 part by weight, there is a problem in controlling the retardation of the optical film. If the styrenic unit is contained in an amount exceeding 10 parts by weight, there is a problem in compatibility with the aromatic resin and a haze . When the amount of the 3- to 6-membered heterocyclic unit substituted with at least one carbonyl group is less than 0.1 part by weight, there is a problem that the heat resistance of the optical film is deteriorated. When the amount is more than 10 parts by weight, the resin characteristics are brittle And the optical film thus produced can easily break.

(c) the copolymer further comprising a 3- to 6-membered heterocyclic unit substituted with at least one carbonyl group and the aromatic resin are mixed at a weight ratio of 90:10 to 99.5: 0.5, When it is contained in a small amount, there is a problem in controlling the retardation of the optical film, and when it is contained in an amount exceeding the above range, there is a problem in compatibility with the aromatic resin.

Other examples of the acrylic resin usable in the present invention include alkyl (meth) acrylate units, benzyl (meth) acrylate units, (meth) acrylic acid units; And a unit represented by the following formula (II). 55 to 94 parts by weight of an alkyl (meth) acrylate unit; 2 to 20 parts by weight of a benzyl (meth) acrylate unit; 1 to 10 parts by weight of (meth) acrylic acid units; And 3 to 15 parts by weight of a unit represented by the following formula (II).

≪ RTI ID = 0.0 &

In Formula II, Y is NR ₃ or O, R ₁ and R ₂ Are each hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl group.

Meanwhile, in the acrylic resin composition, the alkyl (meth) acrylate unit means both an alkyl acrylate and an alkyl methacrylate. However, considering the optical transparency, compatibility, processability, and productivity, , The alkyl group of the alkyl (meth) acrylate preferably has about 1 to about 10 carbon atoms, more preferably about 1 to about 4 carbon atoms, and most preferably a methyl group or an ethyl group. The content of the alkyl (meth) acrylate unit is preferably 55 to 94 parts by weight, more preferably 60 to 90 parts by weight, and most preferably 70 to 90 parts by weight based on 100 parts by weight of the total resin composition. Weight portion. When the content of the alkyl (meth) acrylate unit is within the above range, excellent retardation and optical characteristics can be obtained.

On the other hand, the benzyl (meth) acrylate unit is used for imparting a proper retardation value to the optical film of the present invention and for imparting compatibility between alkyl (meth) acrylate and (meth) acrylic acid, and benzyl methacrylate Benzyl acrylate, and benzyl methacrylate is particularly preferable. On the other hand, the content of the benzyl (meth) acrylate unit is preferably about 2 to 20 parts by weight, more preferably about 2 to 18 parts by weight, based on 100 parts by weight of the total resin composition. When the content of benzyl (meth) acrylate is within the above range, desired retardation characteristics can be obtained.

Next, the (meth) acrylic acid unit improves the heat resistance and lowers the coefficient of thermal expansion by introducing a polar group, and examples thereof include acrylic acid, methacrylic acid, methyl acrylic acid, methyl methacrylic acid, Methacrylic acid, butyl acrylic acid or butyl methacrylic acid, and particularly preferably methacrylic acid. The content of the (meth) acrylic acid unit is preferably about 1 to 10 parts by weight, more preferably 1 to 5 parts by weight, and even more preferably 1 to 3 parts by weight based on 100 parts by weight of the total resin composition Part, and most preferably 1 to 2 parts by weight. When the content of the (meth) acrylic acid unit is within the above range, preferable heat resistance characteristics can be obtained. Particularly, when the content of (meth) acrylic acid is 2 parts by weight or less, bubbles can be remarkably reduced in the film forming process.

In addition, the acrylic resin composition of the present invention includes a unit represented by the following formula (II).

≪ RTI ID = 0.0 &

In Formula II, Y is NR < ₃ > or O,

R ₁ and R ₂ are each hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl group.

The unit represented by the above formula (II) is intended to lower the thermal expansion coefficient of the resin composition. When a bulk functional group inhibiting polymer chain conformation is introduced into the polymer backbone, the coefficient of thermal expansion of the polymer can be lowered. However, for example, when polymers including bulky functional groups such as styrene and polycarbonate are used, the thermal expansion coefficient can be lowered, but birefringence is exhibited by stretching, which may cause problems in optical characteristics. However, when the unit represented by the general formula (II) is contained as in the present invention, the thermal expansion coefficient can be effectively lowered without adversely affecting the optical properties. Specific examples of the unit represented by the following formula (II) include glutaric acid anhydride, glutaric acid imide and the like, among which glutaric acid anhydride is particularly preferable. On the other hand, the content of the unit represented by the formula (II) is preferably about 3 to 15 parts by weight based on 100 parts by weight of the total resin composition. When the content of the unit represented by the general formula (II) is within the above range, a low thermal expansion coefficient can be realized without deteriorating the retardation characteristics.

The acrylic resin composition containing the above components preferably has a glass transition temperature of 120 to 500 ° C, more preferably 125 to 500 ° C, and most preferably 125 to 200 ° C. In terms of processability, heat resistance and productivity, the weight average molecular weight is preferably from 50,000 to 500,000, and more preferably from 50,000 to 200,000. The transparency (haze) is preferably about 0.1 to 3%, and the light transmittance is preferably 90% or more. It is also preferable that the yellow index value is about 0.3 to 2.0. If the value is out of the above range, the color of the display may be changed.

On the other hand, the acrylic resin composition as described above can be manufactured according to a method for producing a copolymer resin or a method for producing a blend resin well known in the art. For example, the acrylic resin composition may be formed by mixing monomers of respective components, followed by solution polymerization, bulk polymerization, suspension polymerization, or emulsion polymerization, or a monomer or homopolymer resin of each component or a copolymer resin of two or more components And then blended.

On the other hand, the inventors of the present invention have found that when the component (II) of the resin composition of the present invention is glutaric anhydride, the component (II) is not added and alkyl (meth) And benzyl (meth) acrylate are polymerized by a specific method to produce the four-component resin composition of the present invention.

More specifically, the four-component acrylic resin composition can be produced, for example, by copolymerizing alkyl (meth) acrylate, (meth) acrylic acid and benzyl (meth) acrylate by a continuous mass polymerization method. In the case of continuous bulk polymerization, unlike solution polymerization or suspension polymerization, a high exotherm occurs in the polymerization process, and by the exotherm resulting from the polymerization process, alkyl (meth) acrylate and / or benzyl (meth) ) Acrylic acid undergoes hydrolytic condensation reaction to form glutaric anhydride.

The four-component acrylic resin composition may be prepared by, for example, polymerizing alkyl (meth) acrylate, (meth) acrylic acid and benzyl (meth) acrylate by a suspension polymerization method and then heat- have. In this case, in the heat treatment process, hydrolytic condensation reaction of alkyl (meth) acrylate and / or benzyl (meth) acrylate with (meth) acrylic acid leads to formation of glutaric anhydride. As a result, .

In the case of forming the resin composition of the present invention by the heat treatment after the continuous bulk polymerization or suspension polymerization as described above, the four-component resin composition of the present invention can be formed without adding glutaric anhydride, , The thermal expansion coefficient of the resin composition is lowered by the formed glutaric anhydride and a film of superior quality can be produced compared with the three component resin of alkyl (meth) acrylate, benzyl (meth) acrylate and (meth) acrylic acid .

When an acrylic copolymer resin containing the above four components is used, an optical film having a small retardation value, a high glass transition temperature and a low thermal expansion coefficient can be produced.

The acrylic resin composition according to the present invention can be prepared by blending the above-described components according to a method well known in the art such as compounding. Melting and mixing of the components can be performed using an extruder or the like.

Further, the acrylic resin composition may contain 0.01 to 1.0 part by weight of additives commonly known in the art, such as lubricants, antioxidants, UV stabilizers, and heat stabilizers, which are generally used.

After obtaining the resin composition having the above composition, the optical film may be produced through the film forming step as described above, and if necessary, the step of uniaxially or biaxially stretching the molded film may be further included .

The optical film formed using the resin composition of the present invention preferably has a thickness of 5 to 300 μm, but is not limited thereto. The optical film may have a light transmittance of 90% or more, a haze of 2.5% Or less, preferably 1% or less, more preferably 0.5% or less. When the transmittance of the optical film is less than 90% and the haze is more than 2.5%, the luminance of a liquid crystal display device using such an optical film can be reduced.

The glass transition temperature of the optical film according to the present invention is preferably 110 DEG C or higher, more preferably 120 DEG C or higher. The glass transition temperature of the resin composition may be 200 DEG C or lower, but is not limited thereto. If the glass transition temperature is less than 110 캜, the film may be deformed under high temperature and high humidity conditions due to insufficient heat resistance, resulting in non-uniform compensation characteristics of the film.

The weight average molecular weight of the resin composition is preferably from 50,000 to 500,000 in terms of heat resistance, processability, and productivity.

The optical film of the present invention produced by the above method has not only excellent heat resistance but also excellent surface properties. More specifically, the optical film produced by the production method of the present invention has excellent thickness uniformity within 2 占 퐉 in the thickness deviation in the MD direction and the TD direction, and the stretch uniformity is increased, and uneven thermal deformation is reduced The overall heat resistance is increased. At this time, the thickness deviation means the maximum thickness-minimum thickness value of the film.

In the optical film of the present invention, the retardation (Rin) in the plane direction represented by the following formula (6) is about 0 to 5 nm and the retardation (Rth) in the thickness direction represented by the following formula (7) It is preferably about 15 to 15 nm.

(6) Rin = (nx-ny) xd

(7) Rth = (nz-ny) xd

In the above formulas (6) and (7)

nx is the largest refractive index among the in-plane refractive indices of the optical film,

ny is a refractive index in a direction perpendicular to nx of the in-plane refractive index of the optical film,

nz is the refractive index in the thickness direction of the optical film,

d is the thickness of the film.

The optical film according to the present invention having the above characteristics can be preferably used as a protective film for a polarizing plate.

In another aspect, 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. The optical film according to the present invention may be provided on both sides of the polarizer, or may be provided on one side only. When the optical film of the present invention is provided on one side of the polarizer, a polarizer protective film such as a TAC film, a PET film, a COP film, a PC film, a norbornene-based film, etc. well known in the art Among them, a TAC film is particularly preferable in view of economical efficiency and the like.

On the other hand, the attachment of the polarizer and the optical film and / or protective film of the present invention can be carried out by coating an adhesive on the surface of the film or polarizer using a roll coater, a gravure coater, a bar coater, a knife coater or a capillary coater , A method in which the protective film and the polarizer are laminated by heating with a joint roll or by pressing at room temperature. As the adhesive, adhesives used in the related art, for example, a polyvinyl alcohol adhesive, a polyurethane adhesive, an acrylic adhesive and the like may be used without limitation.

In another aspect, the present invention relates to an image display device including the polarizing plate of the present invention. The image display device may be, for example, a liquid crystal display (LCD), a plasma display (PDP), an electroluminescent device (LED), or the like.

Hereinafter, the present invention will be described more specifically by way of specific examples. The following examples are given for the purpose of helping to understand the present invention, but the scope of the present invention is not limited thereto.

Manufacturing example  1 - Resin A

1000 g of a monomer mixture comprising 92 parts by weight of methyl methacrylate monomer, 6 parts by weight of N-cyclohexylmaleimide monomer and 2 parts by weight of? -Methylstyrene monomer was prepared and 2000 g of distilled water, 5% polyvinyl alcohol solution (POVAL PVA217, manufactured by Kuraray Co.), 0.1 g of boric acid, 2.5 g of n-octyl mercaptan and 1.5 g of 2,2'-azobisisobutyronitrile, and dispersed in water phase while stirring at 400 rpm to prepare a suspension.

Next, the suspension was heated to 80 DEG C, and polymerization was carried out for 90 minutes. Then, the suspension was cooled to 30 DEG C, washed with distilled water, dehydrated and dried to obtain an acrylic copolymer resin composition.

98 parts by weight of the acrylic copolymer resin composition and 2 parts by weight of the polycarbonate resin were mixed and fed from a hopper hopper of a raw material hopper to an extruder (Leistritz, L / D = 36) The raw material pellets were obtained by melting.

Manufacturing example  2 - Resin B

Pellets of a (meth) acrylate resin (product name: AX1-MR1000, Japan Catalyst Company) containing a lactone ring structure were used.

The shear rate and shear viscosity of Resins A and B prepared as described above were measured using a capillary rheometer. The measurement results are shown in FIG.

Example  1 to 3 and Comparative Example  1-3

The resin A and the resin B were melt-extruded using a film-making apparatus including an extruder, a polymer filter and a die to produce a film. The types of resins used in the examples and comparative examples were as shown in Table 1, and the temperature, shear rate and viscosity in the melt extrusion process were adjusted as shown in Table 1 below. Then, the appearance characteristics of the produced film were measured. The appearance of the produced film was continuously measured by the in-line thickness meter in the MD and TD directions. The case where the thickness deviation in the MD and TD directions is within ± 1 μm is represented by O and the case where the thickness deviation in the MD and TD directions exceeds ± 1 μm is represented by X. The measurement results are shown in Table 1.

division Suzy Extruder Polymer filter T-die η _P / η _E η _P / η _D film
Exterior Temperature
(° C) shear
speed
(1 / s) shear
Viscosity
(Pa.s) Temperature
(° C) Shear rate
(1 / s) shear
Viscosity
(Pa.s) Temperature
(° C) shear
speed
(1 / s) shear
Viscosity
(Pa.s) Example 1 A 260 100 748.26 270 10 808.57 260 50 1010.20 1.08 0.80 O Example 2 A 260 100 748.26 270 10 808.57 270 50 646.73 1.08 1.25 O Example 3 A 270 100 515.58 270 10 808.57 260 50 1010.20 1.57 0.80 O Comparative Example 1 A 270 100 515.58 260 10 1535.95 270 50 646.73 2.98 2.37 X Comparative Example 2 B 270 100 558.95 290 10 424.09 270 50 731.39 0.76 0.58 X Comparative Example 3 B 290 100 266.93 290 10 424.09 290 50 306.81 1.59 1.38 X

1: Film manufacturing apparatus
10: extruder
20: Polymer filter
30: Die
40: Gear pump

Claims (21)

A process for producing an optical film comprising a step of molding an acrylic resin by a melt extrusion method using a film production apparatus including an extruder, a polymer filter and a die,
(1) and (2), when the viscosity of the acrylic resin in the extruder is eta _E , the viscosity of the acrylic resin in the polymer filter is eta _P , and the viscosity of the acrylic resin in the die is eta _D , (2). ≪ / RTI >
0.5?? _P /? _E ? 2.5
0.8?? _P /? _D ? 2.0
The method according to claim 1,
Wherein the acrylic resin comprises a copolymer comprising an alkyl (meth) acrylate-based unit and a styrene-based unit, and an aromatic resin having a carbonate moiety in the main chain.
3. The method of claim 2,
Wherein the alkyl moiety of the alkyl (meth) acrylate-based unit is a methyl group or an ethyl group.
3. The method of claim 2,
The styrene-based unit is a benzene ring or C ₁ groups of the vinyl _styrene-The method of producing the optical film comprises a styrene substituted with one or more substituents selected from the group comprising a _4-alkyl or halogen.
3. The method of claim 2,
Wherein the aromatic resin having a carbonate moiety in the main chain comprises 5 to 10,000 at least one kind of unit represented by the following formula (I).
(I)

In the above formula (I), X is a divalent group comprising at least one benzene ring.
The method for producing an optical film according to claim 5, wherein X is a divalent group selected from the group consisting of the following structural formulas.

3. The method of claim 2,
Wherein the copolymer comprises 80 to 99.9 parts by weight of an alkyl (meth) acrylate-based unit and 0.1 to 20 parts by weight of a styrene-based unit based on 100 parts by weight of the copolymer.
3. The method of claim 2,
Wherein the copolymer further comprises a 3- to 6-membered heterocyclic unit substituted with at least one carbonyl group.
9. The method of claim 8,
Wherein said heterocyclic unit is selected from the group consisting of maleic anhydride, maleimide, glutaric anhydride, glutarimide, lactone and lactam.
9. The method of claim 8,
Wherein the copolymer comprises 80 to 99.9 parts by weight of an alkyl (meth) acrylate unit, 0.1 to 10 parts by weight of a styrene unit, and 0.1 to 10 parts by weight of a 3- to 6-membered heterocyclic unit substituted with at least one carbonyl group, based on 100 parts by weight of the copolymer. 10 parts by weight.
3. The method of claim 2,
Wherein the copolymer and the aromatic resin are mixed at a weight ratio of 90:10 to 99.5: 0.5.
The method according to claim 1,
The above-
Alkyl (meth) acrylate units;
Benzyl (meth) acrylate units;
(Meth) acrylic acid units; And
And a unit represented by the following formula (II).
≪ RTI ID = 0.0 &

In Formula II, Y is NR < ₃ > or O,
R ₁ and R ₂ are each hydrogen, C _{1 ~ 10} alkyl, C _{3 ~ 20} cycloalkyl or C _{3 ~ 20} aryl.
13. The method of claim 12,
The above-
55 to 94 parts by weight of an alkyl (meth) acrylate unit;
2 to 20 parts by weight of a benzyl (meth) acrylate unit;
1 to 10 parts by weight of (meth) acrylic acid units; And
And 3 to 15 parts by weight of a unit represented by the above formula (II).
13. The method of claim 12,
Wherein the alkyl (meth) acrylate unit is methyl methacrylate.
13. The method of claim 12,
Wherein the benzyl (meth) acrylate unit is benzyl methacrylate.
13. The method of claim 12,
Wherein the (meth) acrylic acid unit is selected from the group consisting of acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate and butyl methacrylate.
13. The method of claim 12,
Wherein the unit represented by the formula (II) is glutaric anhydride.
An optical film produced by the manufacturing method according to any one of claims 1 to 17,
The thickness deviation in the MD and TD directions of the film is within 2 占 퐉,
An optical film having a retardation in the plane direction represented by the following formula (6) of 0 to 5 nm and a retardation in the thickness direction represented by the following formula (7): -15 to 15 nm:
(6) Rin = (nx-ny) xd
(7) Rth = (nz-ny) xd
In the above formulas (6) and (7)
nx is the largest refractive index among the in-plane refractive indices of the optical film,
ny is a refractive index in a direction perpendicular to nx of the in-plane refractive index of the optical film,
nz is the refractive index in the thickness direction of the optical film,
d is the thickness of the film.
delete A polarizing plate comprising the optical film of claim 18.
A display device comprising the optical film of claim 18.

Images