KR101985469B1 - Polyester multi-layer film and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a polyester multilayer film which is excellent in thickness uniformity and transparency, prevents oligomers from migrating upon heating, has little change in haze after heating, and can be used in optical applications and a method for producing the same.

Description

[0001] POLYESTER MULTI-LAYER FILM AND MANUFACTURING METHOD THEREOF [0002]

The present invention relates to a polyester multilayer film which is excellent in thickness uniformity and transparency, prevents oligomers from migrating upon heating, has little change in haze after heating, and can be used in optical applications and a method for producing the same.

Optical films are films used as optical members for displays and are used as optical materials for LCD BLUs or as optical members for surface protection of various displays such as LCDs, PDPs, and touch panels.

Particularly, in the ITO film used in the touch screen panel (TSP), quality problems related to ITO contamination due to oligomer migration of a polyester film used as a base film are occurring. This is because oligomers are migrated inside the polyester film due to the application of high temperature in the post-processing step such as the curing process and the aging process after the adhesive coating to the polyester film, so that defects are generated in the expensive ITO film, .

The touch screen panel is a panel that does not use an input device such as a keyboard or a mouse but detects a character or a specific position of a human hand or object when the touch is detected and processes a specific function. Such touch screens, ITO base films, and ITO process films are subject to high temperature heat treatment in the post-processing process. In this high temperature process, oligomers of the polyester film are migrated to the surface, causing whitening of the film surface, A problem such as curling occurs.

Attempts have been made to prevent migration of the oligomer of such a polyester film. Japanese Patent Application Laid-Open No. 2007-253511 (Oct. 4, 2007) discloses a technique for controlling the outflow of oligomers by forming a laminated film on a polyester film. Is a polyester film having a laminated film on at least one side thereof. When the film is heated at 150 占 폚 for 60 minutes, the average size of oligomer particles precipitated in the laminated film is 10 占 퐉 ² or less in area conversion, Lt; RTI ID = 0.0 > 100 < / RTI > This invention attempts to control the outflow of oligomers but does not completely block them. The polyester film may be aged at a high temperature or a high heat-resistant polymer such as polyethylene naphthalate (PEN) or polyimide (PI) may be used. However, when the polyester film is aged at a high temperature, the production yield of the film is not sufficient and there is a problem that deformation due to moisture and the like occurs. When the high heat resistant polymer is used, heat resistance is remarkably excellent and there is no oligomer migration, There is a problem that the preparation cost is considerably high and it is difficult to postproduce.

Japanese Patent Laid-Open No. 2007-253511 (2007.10.04) Japanese Patent Application Laid-Open No. 2009-279923 (2009.12.03) Japanese Patent Laid-Open No. 2010-171151 (Aug. 5, 2010) Japanese Patent Application Laid-Open No. 2002-331575 (Nov. 19, 2002)

In order to solve the above problems, it is an object of the present invention to provide a polyester multilayer film having a high heat resistance characteristic, an excellent post-processing characteristic and a small heat shrinkage in a post-process.

It is another object of the present invention to provide a polyester multilayer film suitable for ITO process, base film for ITO and base film for hard coating for touch panel.

In order to achieve the above object, the inventors of the present invention have studied and found that, by controlling the oligomer content and the diethylene glycol content of the resin used for the skin layer and the skin layer containing two or more skin layers, It is possible to provide a film satisfying desired physical properties by controlling the intrinsic viscosity of an ester resin and by loosening in the transverse direction at the time of heat fixation, thereby completing the present invention.

Specifically, the present invention provides a polyester multilayer film comprising three or more layers including a base layer and a skin layer having at least two layers laminated on both sides of the base layer,

Wherein the polyester resin constituting the skin layer has an oligomer content of 0.3 to 0.6% by weight, a diethylene glycol content of 0.1 to 1.1% by weight,

Wherein the heat shrinkage ratio of the multilayered film satisfies the following formulas 1 to 2, the plane orientation coefficient ns satisfies the following formula 3, the haze (Hi) of the film before heating is less than 1.5% The haze of the film satisfies the following formula (4).

0.2? Smd? 1.5 [Formula 1]

0? Std? 1.0 [Formula 2]

0.1590? Ns [Formula 3]

Hf? Hi? 2.5 [Formula 4]

(%) Of the film measured in accordance with JIS C-2318 standard after keeping the film having a size of 200 mm width and 200 mm length at 150 캜 for 30 minutes, and the heat shrinkage (% ) = (Length of film before heat treatment - length of film after holding at 150 占 폚 for 30 minutes) / length of film before heat treatment 占 100, Smd means shrinkage (%) in the longitudinal direction (MD) Means the shrinkage percentage (%) in the width direction (TD) of the film,

(The refractive index in the longitudinal direction + the refractive index in the thickness direction in the width direction) / 2}, and the surface orientation coefficient ns = {(longitudinal refractive index + lateral refractive index) / 2}

Hf is the haze of the film after being held at 150 DEG C for 30 minutes, and Hi is the haze of the film before heating.

In the present invention, the multilayered film may have a surface roughness (Ra) of 10 nm or less.

In the present invention, the polyester base film is obtained by co-extruding a base layer and a skin layer, and may have an intrinsic viscosity satisfying the following formula (5).

1 < Ns / Nc < / = 1.2 [Formula 5]

(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer)

In the polyester multilayer film of the present invention, the polyester resin constituting the substrate layer may have an intrinsic viscosity of 0.5 to 1.0, and the polyester resin constituting the skin layer may have an intrinsic viscosity of 0.6 to 1.0.

In the present invention, the base layer may be 70 to 90% by weight and the skin layer may be 10 to 30% by weight.

In the present invention, the polyester multilayer film may have a total thickness of 25 to 250 탆.

In the present invention, the skin layer may contain 100 ppm or less of inorganic particles.

In the present invention, the inorganic particles may have an average particle diameter of less than 3 mu m.

In the present invention, the inorganic particles may be any one or a mixture of two or more selected from silica, zeolite, and kaolin.

The present invention also encompasses optical films in which at least one functional coating layer selected from a hard coating layer, a pressure-sensitive adhesive layer, a light diffusion layer, an ITO layer and a printing layer is formed on the polyester multilayer film.

Further, the method for producing the polyester multilayer film of the present invention

a) a skin layer composition comprising a first polyester resin having an intrinsic viscosity satisfying the following formula 5, an oligomer content of the polyester resin being 0.3 to 0.6% by weight and a diethylene glycol content of 0.1 to 1.2% by weight, and Extruding a second polyester resin for a substrate layer having an intrinsic viscosity satisfying the following formula (5) and pneumatically delivering the second polyester resin;

1 < Ns / Nc < / = 1.2 [Formula 5]

(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer)

b) uniaxially or biaxially stretching the coextruded sheet to produce a film;

c) heat-setting the stretched film and performing relaxation in the transverse direction (TD) in a range satisfying the following expression (6);

2? TDr (%)? 11.5 [Formula 6]

TDr represents the relaxation ratio in the width direction (TD), and the relaxation ratio (%) = {(maximum width in the width direction of the entire relaxation processing section- ) / The maximum width of the entire film in the relaxation section} × 100.

.

In the manufacturing method of the present invention, the skin layer composition in step (a) may contain not more than 100 ppm of inorganic particles.

In the production method of the present invention, the inorganic particles may have an average particle size of less than 3 mu m.

In the production method of the present invention, it is preferable that the multilayered film has a surface roughness Ra of 10 nm or less, a heat shrinkage ratio satisfies the following formulas 1 to 2, a plane orientation coefficient ns satisfies the following formula 3, After holding for 30 minutes, the haze of the film may satisfy the following expression (4).

0.2? Smd? 1.5 [Formula 1]

0? Std? 1.0 [Formula 2]

0.1590? Ns [Formula 3]

Hf? Hi? 2.5 [Formula 4]

(%) Of the film measured in accordance with JIS C-2318 standard after keeping the film having a size of 200 mm width and 200 mm length at 150 캜 for 30 minutes, and the heat shrinkage (% ) = (Length of film before heat treatment - length of film after holding at 150 占 폚 for 30 minutes) / length of film before heat treatment 占 100, Smd means shrinkage (%) in the longitudinal direction (MD) Means the shrinkage percentage (%) in the width direction (TD) of the film,

(The refractive index in the longitudinal direction + the refractive index in the thickness direction in the width direction) / 2}, and the surface orientation coefficient ns = {(longitudinal refractive index + lateral refractive index) / 2}

Hf is the haze of the film after being held at 150 DEG C for 30 minutes, and Hi is the haze of the film before heating.

In the production process of the present invention, the polyester base film may be one obtained by co-extruding a base layer and a skin layer, and has an intrinsic viscosity satisfying the following formula (5).

1 < Ns / Nc < / = 1.2 [Formula 5]

(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer)

In the manufacturing method of the present invention, in the case of relaxing in the step c), it is possible to perform the relaxation in the widthwise direction and the relaxation in the longitudinal direction within the range satisfying the following expression (7).

0.3? MDr (%)? 2.5 [Formula 7]

(%) = (Running speed of film in relaxation section - running speed of entire film in relaxation section) / running speed of all films in relaxation section x 100.)

The polyester film according to the present invention has an effect of preventing the oligomer from flowing out under high temperature conditions.

In addition, the polyester film according to the present invention has optical properties suitable for use in a heat-resistant film for ITO protection in a touch panel film, and the heat shrinkage ratio with respect to the full width of the film is controlled, It is easy to secure the processability in the lamination process of three or more films such as an interference fringe polyester film.

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

In the present invention, the oligomer means a dimer, a trimer, a tetramer or the like having a weight average molecular weight of about 500 to about 10,000.

According to an aspect of the present invention, there is provided a polyester multi-layer film comprising three or more layers including a base layer and a skin layer having at least two layers laminated on both sides of the base layer,

Wherein the polyester resin constituting the skin layer has an oligomer content of 0.3 to 0.6% by weight, a diethylene glycol content of 0.1 to 1.1% by weight,

Wherein the heat shrinkage ratio of the multilayered film satisfies the following formulas 1 to 2, the plane orientation coefficient ns satisfies the following formula 3, the haze (Hi) of the film before heating is less than 1.5% The haze of the film satisfies the following formula (4).

0.2? Smd? 1.5 [Formula 1]

0? Std? 1.0 [Formula 2]

0.1590? Ns [Formula 3]

Hf? Hi? 2.5 [Formula 4]

(%) Of the film measured in accordance with JIS C-2318 standard after keeping the film having a size of 200 mm width and 200 mm length at 150 캜 for 30 minutes, and the heat shrinkage (% ) = (Length of film before heat treatment - length of film after holding at 150 占 폚 for 30 minutes) / length of film before heat treatment 占 100, Smd means shrinkage (%) in the longitudinal direction (MD) Means the shrinkage percentage (%) in the width direction (TD) of the film,

(The refractive index in the longitudinal direction + the refractive index in the thickness direction in the width direction) / 2}, and the surface orientation coefficient ns = {(longitudinal refractive index + lateral refractive index) / 2}

Hf is the haze of the film after being held at 150 DEG C for 30 minutes, and Hi is the haze of the film before heating.

When the thermal shrinkage (%) in the longitudinal direction (MD) of the film is less than 0.2%, it is most ideal but it is difficult to achieve in the film forming process. When the thermal shrinkage occurs in the subsequent process, So that after hard coating or ITO sputtering, curling or heat wrinkling may occur during post-processing. More preferably, it is 0.3 to 0.8%.

In the case where the heat shrinkage ratio (%) in the width direction (TD) is 0%, it is most ideal. When the thermal shrinkage ratio is more than 1.0%, heat shrinkage occurs in the subsequent process, Or ITO sputtering may cause curling or heat wrinkling. More preferably, it is 0.1 to 0.4%.

The film preferably has a planar orientation coefficient of 0.1590 or more, more specifically 0.1590 to 0.1610. When the plane orientation coefficient is less than 0.1590, the surface structure of the film is not precise and the surface migration of the oligomer can easily occur.

The haze is used to determine the outflow of oligomer under high temperature conditions. If the range is out of the above range, the outflow of oligomer means that the deep haze is reduced. Since the post-processability is not greatly affected in the range satisfying the haze range, it has properties suitable for use as an optical film.

In the present invention, the polyester multi-layer film may be composed of three or more layers including a base layer and a skin layer in which at least two layers are laminated on both sides of the base layer, or may be formed by coextrusion.

The total thickness of the polyester multilayered film is preferably 25 to 250 mu m, more preferably 50 to 188 mu m. When the thickness is less than 25 탆, the optical film does not have proper physical properties. When the thickness exceeds 250 탆, the thickness of the film becomes too thick, which may result in a problem that the display device is not suitable for thinning.

It is preferable that the content of the base layer is 70 to 90% by weight of the whole film and the content of the skin layer is 10 to 30% by weight, more preferably the content of the base layer is 70 to 80% Is 20 to 30% by weight, which is effective since it has excellent interfacial stability during the co-extrusion and excellent barrier property against oligomers.

It is preferable that the substrate layer made of the polyester resin is made of a polyethylene terephthalate (PET) resin alone. The polyethylene terephthalate resin used herein preferably has an intrinsic viscosity of 0.5 to 1.0, more preferably 0.60 to 0.80. If the intrinsic viscosity of the base layer polyethylene terephthalate resin is less than 0.5, the heat resistance may be reduced. If the intrinsic viscosity is more than 1.0, the workability of the raw material may not be easy and the workability may be decreased.

The skin layer formed by co-extruding at least two layers on both sides of the polyester base layer has an oligomer content of 0.3 to 0.6% by weight, more preferably 0.4 to 0.6% by weight, based on the total weight of the film, and diethylene glycol (DEG ) Is preferably from 0.1 to 1.1% by weight, more preferably from 0.7 to 1.1% by weight. When the content of the oligomer and diethylene glycol in the polyester resin of the skin layer is in the above range, the haze value of the initial film is increased and the haze change rate is increased rapidly when the heat treatment is performed, Problems that can not be achieved arise.

The oligomer content of the polyester resin constituting the core layer is preferably 0.6 to 1.5%, and the content of diethylene glycol is preferably 0.8 to 1.5%.

The polyester resin of the skin layer can be produced by a synthesis method which is obvious in the technical field in order to have the content of oligomer and diethylene glycol within the above range, but in particular, those produced by solid phase polymerization are oligomers and diethylene glycol Which is effective to reduce the content of

The intrinsic viscosity of the polyester resin in the skin layer is preferably 0.6 to 1.0, more preferably 0.65 to 0.85. Skin layer If the intrinsic viscosity of the polyethylene terephthalate resin is less than 0.6, the heat resistance may be decreased. If the intrinsic viscosity is more than 1.0, the workability may be decreased because the raw material processing is not easy.

It is preferable that the following formula (5) is satisfied in order to improve workability when the base layer and the skin layer are co-extruded.

1 < Ns / Nc < / = 1.2 [Formula 5]

(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer)

When the intrinsic viscosity ratio of the skin layer and the base layer is more than 1.2, the problem of interfacial unstability occurs in the co-extrusion, so that a multilayered structure may not be formed. Therefore, the range is preferably in the range of 1.0 to 1.05 Is effective for improving workability.

In the present invention, the skin layer may contain inorganic particles, and it is preferable to use the film so that the initial haze of the film satisfies a haze of less than 1.5%. It is also preferable that the surface roughness of the film is 10 nm or less. If the surface roughness exceeds 10 nm, the problem of smoothness of the final product may occur after hard coating.

 More specifically, it is preferable to use particles having an average particle diameter of less than 3 占 퐉 at 100 ppm or less. As the inorganic particles, particles used in a film such as silica, zeolite, and kaolin are all possible. These inorganic particles come out to the surface of the film through a stretching process to improve slipperiness and windability of the film.

If the particle size is 3 m or more, even if the content of the particles is 100 ppm or less, the transparency of the film is greatly decreased, and the smoothness is lowered because the roughness Ra is 10 nm or more.

In addition, when the particle content is 100 ppm or more, the transparency of the film is lowered, which is not suitable for a touch panel. In addition, when the haze is 1.5% or more, transparency drops sharply when used for optical and touch panels, light transmittance is greatly decreased, and it is difficult to judge defects visually in BLU evaluation, making it difficult to use for optical use.

The production of the polyester multilayer film including the base layer and the skin layer of the present invention is not limited, but may be obtained by casting after extrusion melt-extrusion in at least two melt extruders and by biaxial stretching. More specifically, the polyester is extruded from one extruder, and the additives such as polyester and inorganic particles such as silica, kaolin, and zeolite are melt-extruded at the same time in another extruder, and then the respective melts meet in the feed block, Cast, cooled, and subsequently biaxially stretched.

More specifically, the polyester multilayer film of the present invention comprises

a) a skin layer composition comprising a first polyester resin having an intrinsic viscosity satisfying the following formula 5, an oligomer content of the polyester resin being 0.3 to 0.6% by weight and a diethylene glycol content of 0.1 to 1.2% by weight, and Extruding a second polyester resin for a substrate layer having an intrinsic viscosity satisfying the following formula (5) and pneumatically delivering the second polyester resin;

1 < Ns / Nc < / = 1.2 [Formula 5]

(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer)

b) uniaxially or biaxially stretching the coextruded sheet to produce a film;

c) heat-setting the stretched film and performing relaxation in the transverse direction (TD) in a range satisfying the following expression (6);

2? TDr (%)? 11.5 [Formula 6]

TDr represents the relaxation ratio in the width direction (TD), and the relaxation ratio (%) = {(maximum width in the width direction of the entire relaxation processing section- ) / The maximum width of the entire film in the relaxation section} × 100.

.

In the present invention, after stretching as described above, heat fixing and relaxation in the longitudinal direction are performed, and relaxation is carried out under the condition satisfying the formula (6) at the time of relaxation, oligomers are not migrated under high temperature conditions, It is possible to produce a film favorable for the post-process.

More specifically, in the polyester production method of the present invention, the step a) is a step of co-extruding a polyester resin constituting the base layer and the skin layer, followed by quenching and solidifying with a casting drum to produce a polyester sheet, It is preferable that the intrinsic viscosity of the polyester resin used for the layer and the substrate layer is in a range satisfying the following formula (5).

1 < Ns / Nc < / = 1.2 [Formula 5]

(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer)

Next, step b) is a step of stretching the coextruded sheet to produce a film, which may be uniaxially or biaxially stretched, and preferably biaxially stretched. In the case of biaxial stretching, uniaxial stretching is performed in the longitudinal direction (MD) at 80 to 100 ° C, and the stretching ratio is preferably 2 to 4 times. Next, the biaxial stretching is performed in the transverse direction (TD), and it is preferable to perform stretching at 2 to 4 times at 110 to 150 ° C.

The step c) may be a step of performing heat fixing and relaxation, and the step d) may be performed in a tenter. The heat setting temperature may be performed at 200 to 240 ° C, and the heat shrinkage ratio may be controlled by performing the relaxation ratio in the width direction upon relaxation so as to satisfy Equation (6).

2? TDr (%)? 11.5 [Formula 6]

TDr represents the relaxation ratio in the width direction (TD), and the relaxation ratio (%) = {(maximum width in the width direction of the entire relaxation processing section- ) / The maximum width of the entire film in the relaxation section} × 100.

Further, if necessary, it is possible to perform relaxation in the longitudinal direction within a range satisfying the following expression (7) simultaneously with the width direction.

0.3? MDr (%)? 2.5 [Formula 7]

(%) = (Running speed of film in relaxation section - running speed of entire film in relaxation section) / running speed of all films in relaxation section x 100.)

By performing relaxation in a range that satisfies the above-mentioned equations 6 and 7, the shrinkage ratio of the film after holding at 150 DEG C for 30 minutes can satisfy the equations 1 and 2. [

A hard coating layer, a pressure-sensitive adhesive layer, a light diffusion layer, an ITO layer, a printing layer, and the like may be formed on the polyester film of the present invention. Even if heating is performed after forming the functional coating layer, the oligomer is prevented from flowing, So that the polyester film of the present invention is suitable for use as an optical film.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples.

The following physical properties were measured by the following measurement methods.

1) Intrinsic viscosity

0.4 g of PET pellet (sample) was added to 100 ml of a reagent in which phenol and 1,1,2,2-tetrachloroethanol were mixed at a weight ratio of 6: 4, and the mixture was transferred to a Ubero's viscometer. For 10 minutes, and the falling seconds of the solution was determined using a viscometer and an aspirator. The number of drops of the solvent was also determined by the same method, and RV and IV values were calculated by the following equations (1) and (2).

In the following equation, C represents the concentration of the sample.

[Equation 1]

&Quot; (2) "

2) Oligomer content (%)

Oligomer Chloroform is added to the sample solvent HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) by quantitative method and dissolved at room temperature, and then acetonitrile is precipitated as a polymer. Then, a calibration curve of the reference material (cyclic oligomer) is prepared using LC analysis equipment, and the cyclic oligomer purity is determined through sample analysis. Analytical instruments were liquid chromatography (LC) and Agilent 1100 series.

3) Content of DEG (Diethylene glycol) (%)

The content of diethylene glycol (DEG, Diethylene Glycol) was measured by placing 1 g of the sample in a 50 mL container, adding 3 mL of monoethanolamine and heating by using a hot plate to completely dissolve the sample, , And a solution of 0.005 g of 6-hexanediol dissolved in 20 mL of methanol was added, and 10 g of terephthalic acid was added to neutralize the solution. The resulting neutralized solution was filtered using a funnel and a filter paper, and the filtrate was subjected to gas chromatography to measure the DEG content (wt%). The GC analysis was carried out using a Shimadzu GC analyzer and according to the Shimadzu GC manual.

4) Hayes

The specimen of the film thus formed was measured according to JIS K 715 using a haze meter (model name: Nipon denshoku, Model NDH 5000).

5) Haze change

The film was placed in a box having a height of 3 cm, a width of 21 cm and a length of 27 cm and heat-treated at 150 ° C., 10 min, 20 min and 30 min to migrate the oligomer to the film surface and allowed to stand for 5 minutes. The haze value was measured according to JIS K 715 And measured using a haze meter (Nipon denshoku, Model NDH 5000) according to the standard.

 6) Surface roughness (Ra)

Equipment used: 3D non-contact surface roughness tester (NT 2000, WYCO)

Ra (centerline average roughness) was measured using the above apparatus.

7) Plane orientation coefficient

The index of refraction in the longitudinal direction, the width direction and the thickness direction is measured using an Abbe refractometer (ATOGO) and calculated by the following equation.

(Refractive index in the longitudinal direction + refractive index in the thickness direction in the lateral direction) / 2} < EMI ID = 1.0 >

8) Shrinkage measurement

After measuring the length and width of the film, the length and width of the film were measured after heating in a hot air oven at 150 ° C for 30 minutes.

Shrinkage (%) = (length before heat treatment - length after heat treatment) / length before heat treatment × 100

[Example 1]

A PET chip having an intrinsic viscosity of 0.65, a diethylene glycol (DEG) content of 1.2% and an oligomer content of 1.4% was used as the substrate layer, and the skin layer had an intrinsic viscosity of 0.67, a DEG content of 0.8, and an oligomer content of 0.5% Solid-polymerized PET chips were used and co-extrusion casting was carried out using 30 ppm of particles having a particle size of 0.7 mu m. Thereafter, the films were sequentially stretched in the longitudinal and transverse directions at 3.2 times and 3.2 times, respectively, and heat-treated at 230 占 폚 to give a widthwise relaxation of 3% to prepare a multilayer film of 125 占 퐉. In this case, the relaxation in the widthwise direction relaxes the three zones of the heat treatment zone in the tenter at the maximum width after stretching, and the width is reduced by 3% of the maximum width direction.

The composition and content of the skin layer are shown in Table 1.

The oligomer surface migration, surface roughness, haze, planar orientation coefficient, shrinkage percentage of the film after the preparation were measured with the base layer of the multi-layer film as 80% of the total film weight and the skin layer as 20% of the total film weight.

≪ Examples 2 and 3 >

The procedure of Example 1 was repeated except that the DEG content of the raw material of the skin layer was changed as shown in Table 1 below.

On the obtained film, oligomer surface migration, surface roughness, haze, plane orientation coefficient, shrinkage ratio of the film were measured.

≪ Examples 4 and 5 >

The procedure of Example 1 was repeated except that the oligomer content of the raw material of the skin layer was changed as shown in Table 1 below.

On the obtained film, oligomer surface migration, surface roughness, haze, plane orientation coefficient, shrinkage ratio of the film were measured.

≪ Examples 6 and 7 >

The procedure of Example 1 was repeated except that the weight of the skin layer was changed as shown in Table 1 below.

≪ Examples 8 and 9 >

The procedure of Example 1 was repeated except that the particle content of the skin layer was changed as shown in Table 1 below.

≪ Example 10 >

The same procedure as in Example 1 was carried out, and the same procedure as in Example 1 was carried out with 1.5% relaxation in the longitudinal direction simultaneously with the relaxation in the width direction.

≪ Comparative Example 1 &

The same procedure as in Example 1 was carried out except that the skin layer had an intrinsic viscosity of 0.65 and an oligomer content of 1.4% alone, and the oligomer surface migration, surface roughness, haze , Plane orientation coefficient, and shrinkage were measured.

≪ Comparative Examples 2 and 3 >

The procedure of Example 1 was repeated except that the DEG content of the skin layer was changed as shown in Table 1.

On the obtained film, oligomer surface migration, surface roughness, haze, plane orientation coefficient, shrinkage ratio of the film were measured.

≪ Comparative Examples 4 and 5 >

The procedure of Example 1 was repeated except that the oligomer content of the skin layer was changed as shown in Table 1. The oligomer surface migration, surface roughness, haze, plane orientation coefficient and shrinkage ratio of the film were measured for the resulting film.

≪ Comparative Examples 6 and 7 >

The procedure of Example 1 was repeated except that the weight of the skin layer was changed as shown in Table 1 below.

≪ Comparative Examples 8 and 9 &

The procedure of Example 1 was repeated except that the particle content of the skin layer was changed as shown in Table 1 below.

≪ Comparative Examples 10 and 11 >

The composition was the same as that of Example 1 except that the heat treatment was carried out at a temperature of 200 ° C and a temperature of 210 ° C and a widthwise relaxation of 1% and 1.5%, respectively.

 [Table 1]

* Co-extruded with A / B / A. (The skin layer thickness is the total amount of both A layers)

 [Table 2]

As shown in Table 2, the embodiment of the present invention is characterized in that, after holding at 150 ° C for 30 minutes, the heat shrinkage rate of the film is as low as satisfying the formulas 1 and 2, the surface orientation coefficient is 0.1590 or more, And the haze (Hi) of the film before heating was less than 1.5%. After holding for 30 minutes at 150 占 폚, it was confirmed that the haze of the film satisfies all of the equations (4).

Claims (16)

A polyester multilayer film comprising three or more layers including a base layer and a skin layer having at least two layers laminated on both sides of the base layer,
Wherein the polyester resin constituting the skin layer has an oligomer content of 0.3 to 0.6% by weight, a diethylene glycol content of 0.1 to 1.1% by weight,
Wherein the heat shrinkage ratio of the multilayered film satisfies the following formulas 1 to 2, the plane orientation coefficient ns satisfies the following formula 3, the haze (Hi) of the film before heating is less than 1.5% And the haze of the film satisfies the following formula (4).
0.2? Smd? 1.5 [Formula 1]
0? Std? 1.0 [Formula 2]
0.1590? Ns [Formula 3]
Hf? Hi? 2.5 [Formula 4]
Smd and Std mean the heat shrinkage (%) of the film measured in accordance with JIS C-2318 standard after holding a film having a size of 200 mm width and 200 mm length at 150 ° C for 30 minutes, ) = (Length of film before heat treatment - length of film after holding at 150 占 폚 for 30 minutes) / length of film before heat treatment 占 100, Smd means shrinkage (%) in the longitudinal direction (MD) Means the shrinkage percentage (%) in the width direction (TD) of the film,
(The refractive index in the longitudinal direction + the refractive index in the thickness direction in the width direction) / 2}, and the surface orientation coefficient ns = {(longitudinal refractive index + lateral refractive index) / 2}
Hf is the haze of the film after being held at 150 DEG C for 30 minutes, and Hi is the haze of the film before heating. The method according to claim 1,
Wherein the multilayered film has a surface roughness (Ra) of 10 nm or less. The method according to claim 1,
The polyester base film is obtained by co-extruding a base layer and a skin layer, and has an intrinsic viscosity satisfying the following formula (5).
1 < Ns / Nc < / = 1.2 [Formula 5]
(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer) 3. The method of claim 2,
Wherein the polyester multilayer film has an intrinsic viscosity of 0.5 to 1.0 and a polyester resin forming the skin layer has an intrinsic viscosity of 0.6 to 1.0. The method according to claim 1,
Wherein the base layer is 70 to 90% by weight and the skin layer is 10 to 30% by weight. The method according to claim 1,
Wherein the polyester multilayer film has a total thickness of 25 to 250 탆. The method according to claim 1,
Wherein the skin layer contains inorganic particles in an amount of 100 ppm or less. 8. The method of claim 7,
Wherein the inorganic particles have an average particle diameter of less than 3 mu m. 8. The method of claim 7,
Wherein the inorganic particles are any one or a mixture of two or more selected from silica, zeolite, and kaolin. An optical film in which at least one functional coating layer selected from a hard coating layer, a pressure-sensitive adhesive layer, a light-diffusing layer, an ITO layer and a printing layer is formed on the polyester multi-layer film of any one of claims 1 to 9. a) a skin layer composition comprising a first polyester resin having an intrinsic viscosity satisfying the following formula 5, an oligomer content of the polyester resin being 0.3 to 0.6% by weight and a diethylene glycol content of 0.1 to 1.2% by weight, and Extruding a second polyester resin for a substrate layer having an intrinsic viscosity satisfying the following formula (5) and pneumatically delivering the second polyester resin;
1 < Ns / Nc < / = 1.2 [Formula 5]
(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer)
b) uniaxially or biaxially stretching the coextruded sheet to produce a film;
c) heat-setting the stretched film and performing relaxation in the transverse direction (TD) in a range satisfying the following expression (6);
2? TDr (%)? 11.5 [Formula 6]
TDr represents the relaxation ratio in the width direction (TD), and the relaxation ratio (%) = {(maximum width in the width direction of the entire relaxation processing section- ) / The maximum width of the entire film in the relaxation section} × 100.
≪ / RTI > 12. The method of claim 11,
Wherein the skin layer composition in step (a) contains inorganic particles in an amount of 100 ppm or less. 13. The method of claim 12,
Wherein the inorganic particles have an average particle diameter of less than 3 占 퐉. 12. The method of claim 11,
Wherein the multilayered film has a surface roughness (Ra) of 10 nm or less, a heat shrinkage ratio satisfying the following formulas 1 to 2, a surface orientation coefficient (ns) satisfying the following formula (3) Wherein the haze satisfies the following formula (4).
0.2? Smd? 1.5 [Formula 1]
0? Std? 1.0 [Formula 2]
0.1590? Ns [Formula 3]
Hf? Hi? 2.5 [Formula 4]
(%) Of the film measured in accordance with JIS C-2318 standard after keeping the film having a size of 200 mm width and 200 mm length at 150 캜 for 30 minutes, and the heat shrinkage (% ) = (Length of film before heat treatment - length of film after holding at 150 占 폚 for 30 minutes) / length of film before heat treatment 占 100, Smd means shrinkage (%) in the longitudinal direction (MD) Means the shrinkage percentage (%) in the width direction (TD) of the film,
(The refractive index in the longitudinal direction + the refractive index in the thickness direction in the width direction) / 2}, and the surface orientation coefficient ns = {(longitudinal refractive index + lateral refractive index) / 2}
Hf is the haze of the film after being held at 150 DEG C for 30 minutes, and Hi is the haze of the film before heating. 12. The method of claim 11,
Wherein the polyester base film is obtained by co-extruding a base layer and a skin layer, and has an intrinsic viscosity satisfying the following formula (5).
1 < Ns / Nc < / = 1.2 [Formula 5]
(Where Ns is the intrinsic viscosity of the polyester resin constituting the skin layer and Nc is the intrinsic viscosity of the polyester resin constituting the base layer) 12. The method of claim 11,
Wherein relaxation in the longitudinal direction is performed within a range satisfying the following expression (7) simultaneously with relaxation in the transverse direction upon relaxation in the step (c).
0.3? MDr (%)? 2.5 [Formula 7]
(%) = (Running speed of film in relaxation section - running speed of entire film in relaxation section) / running speed of all films in relaxation section x 100.]