KR20150002511A - Polyester film and manufacturing method thereof - Google Patents

Abstract

The present invention relates to an oligomer-blocking polyester film which controls the thermal contraction rate, blocks the migration of an oligomer while being heated, and has the low rate of haze change after being heated, thereby can be used in an insulation film for protecting ITO. The polyester film in the present invention comprises a polyester base film consisting of a polyester resin; and a primer layer formed by having a water-dispersion resin composition with the oligomer blocking properties coated on one side or both sides.

Description

[0001] POLYESTER FILM AND MANUFACTURING METHOD THEREOF [0002]

The present invention relates to an oligomer-blocked polyester film which is controlled in thermal shrinkage and blocks oligomer migration during heating and has a low haze change rate after heating, and is applicable to heat-resistant films for protecting ITO.

The optical film is used as an optical member for a display, and is used as an optical material of an LCD BLU or an optical member for surface protection of various displays such as an LCD, a PDP, and a touch panel.

In particular, in ITO films used in touch screen panel (TSP) products, quality problems have arisen related to oligomer outflow of polyester films used as base films. This is because migration of oligomers from inside the polyester film occurs as a result of applying a high temperature in a post-processing step such as a curing step and an aging step after adhesive coating to a polyester film, resulting in defects in the expensive ITO film, The optical characteristics of the light emitting diode are deteriorated.

Japanese Patent Application Laid-Open No. 2007-253511 (2007.10.04) (Patent Document 1) discloses a polyester film having a laminated film on at least one side thereof, and a method of forming a laminated film on the polyester film, Having an average size of 10 탆 ² or less in terms of an area and a number of 100 or less in a field of view of 100 탆 x 100 탆 is described in a laminated polyester film in which the average size of oligomer particles precipitated on a laminated film when heated at 150 캜 for 60 minutes is not more than 100 in terms of area. This invention attempts to control the outflow of oligomers but does not completely block them.

In addition to the problem of blocking oligomer migration, touch screen panel products are also required to have fairness in post-processing. In addition to the ITO film, the touch screen panel product uses three or more films laminated such as a heat-resistant film for ITO protection and a hard-coated polyester film coated with rainbow-reduced primer on both sides. If the heat shrinkage ratio among the three or more films is not equal to each other, problems such as curling and wrinkling may occur due to inconsistency of heat shrinkage in a post-processing process performed at a high temperature, resulting in degradation of product quality.

Therefore, it is also essential to improve process conditions that can ensure various heat shrinkages (high heat shrinkage, low heat shrinkage) that meet customer's process conditions.

Japanese Patent Laid-Open No. 2007-253511 (2007.10.04)

In order to solve the above problems, it is an object of the present invention to provide a polyester film on both sides of a substrate layer made of a polyester resin, in which the oligomer-blocking primer layer is coated to completely block the outflow of oligomers.

It is also an object of the present invention to provide an oligomer-blocked polyester film which is controlled in heat shrinkage and is suitable for a post-process.

An object of the present invention is to provide an optical film comprising the polyester film.

The present invention also provides a method for producing a polyester film capable of blocking the migration of oligomers after heating while controlling the heat shrinkage ratio.

In order to achieve the above object, the present invention provides a polyester base film comprising a polyester base film and a primer layer formed by applying a water dispersible resin composition having oligomer blocking properties on one or both sides thereof, To the polyester film satisfying the following formulas (1) to (4).

0? Smd? 1.0 [Formula 1]

0? Std? 0.5 [Formula 2]

- 0.2? Vmd? 0.2 [Formula 3]

- 0.2? Vtd? 0.2 [Formula 4]

Smd, Std, Vmd, and Vtd mean the heat shrinkage (%) of a film measured according to JIS C-2318 standard after holding a polyester film having a size of 10 cm in width and 10 cm in 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 denotes the shrinkage percentage (%) of the film in the machine direction (MD), Std denotes the shrinkage percentage (%) of the film in the width direction (TD), Vmd denotes the number of samples (%) Of the heat shrinkage ratio in the machine direction, and Vtd means a deviation (%) of the heat shrinkage ratio in the width direction of 10 samples selected at intervals of 50 cm on the basis of the film full width.

The polyester film may include those satisfying the following formulas (5) to (7).

0? S (45)? 1.0 [Formula 5]

0? S (135)? 1.0 [Formula 6]

S (135) -S (45) < / = 0.2 [Equation 7]

(%) Of the film measured according to JIS C-2318 standard after keeping the polyester film having a size of 10 cm in width and 10 cm in length at 150 ° C for 30 minutes, and S (45) (%) = (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. S (45) means a diagonal shrinkage ratio (%) of 45 degrees in the clockwise direction with respect to the width direction (TD) of the film, and S (135) Means a diagonal contraction ratio (%) of an angle of 135 deg.

In the present invention, the primer layer may have a T _g of 60 ° C or more, a swelling ratio of 30% or less, a gel fraction of 95% or more, and a density of 1.3 to 1.4.

In the present invention, the polyester film may have a haze change rate (H) according to the following formula (8): 0.1% or less.

[Equation 8]

H (%) = Hf - Hi

(Where Hf is the haze of the film after holding for 60 minutes at 150 DEG C, and Hi is the haze of the film before heating).

In the present invention, the water-dispersible resin composition preferably has a solid content weight ratio (A) / (B) of 20 to 100 parts by weight of the acrylic resin (A) and the water-dispersible polyester resin (B) copolymerized with the glycidyl group-containing radically polymerizable unsaturated monomer. 80/80 ~ 20.

In the present invention, the water-dispersible resin composition may have a solid content of 0.5 to 10% by weight of the binder resin.

In the present invention, the water-dispersible resin composition may further comprise a silicone-based wetting agent.

In the present invention, the water-dispersible polyester resin may be a copolymer of a dicarboxylic acid component containing a sulfonic acid alkali metal salt compound and a glycol component containing diethylene glycol.

In the present invention, the water-dispersible polyester resin may contain 20 to 80 mol% of diethylene glycol in the total glycol component.

In the present invention, the water-dispersible polyester resin may contain an alkali metal sulfonate compound in an amount of 6 to 20 mol% of the total acid components.

In the present invention, the acrylic resin may be a copolymerized monomer containing 20 to 80 mol% of a glycidyl group-containing radically polymerizable unsaturated monomer as a whole monomer component.

In the present invention, the polyester base film may be a polyethylene terephthalate film.

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

In the present invention, the primer layer may have a dry coating thickness of 20 to 150 nm.

Also included in the scope of the present invention is an optical film 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 a polyester film according to the present invention.

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

a) preparing a uniaxially stretched polyester base film in the machine direction;

b) forming a primer layer by applying a water dispersible resin composition having oligomer blocking properties to one side or both sides of the uniaxially stretched polyester base film;

c) biaxially stretching the uniaxially stretched polyester base film having the primer layer formed thereon in the transverse direction (TD); And

d) thermally fixing the biaxially stretched film and performing relaxation in the machine direction (MD) to a range satisfying the following expression (9);

1.1 ≤ relaxation ratio (%) ≤ 2.5 [

(In the above formula, the relaxation ratio (%) = (running speed of the film in the relaxation processing section-running speed of the entire film in the relaxation processing section) / running speed of the entire film in the relaxation processing section × 100)

.

In the present invention, in the step d), the relaxation of the machine direction (MD) may be performed in a temperature range satisfying the following expression (10).

Stretching temperature (占 폚)? Relaxation temperature (占 폚)? Heat fixing temperature (占 폚)

In the present invention, the water-dispersible resin composition preferably has a solid content weight ratio (A) / (B) of 20 to 100 parts by weight of the acrylic resin (A) and the water-dispersible polyester resin (B) copolymerized with the glycidyl group-containing radically polymerizable unsaturated monomer. 80/80 ~ 20.

The polyester film according to the present invention has an effect of completely blocking the outflow of oligomer at high temperature.

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.

The present invention relates to a polyester base film comprising a polyester resin and a primer layer formed by applying a water dispersible resin composition having an oligomer blocking property on one or both sides thereof and has a heat shrinkage percentage (4). ≪ / RTI >

0? Smd? 1.0 [Formula 1]

0? Std? 0.5 [Formula 2]

- 0.2? Vmd? 0.2 [Formula 3]

- 0.2? Vtd? 0.2 [Formula 4]

Smd, Std, Vmd, and Vtd mean the heat shrinkage (%) of the film measured according to JIS C-2318 standard after maintaining a polyester film having a size of 10 cm in width and 10 cm in length at 150 ° C for 30 minutes, The heat shrinkage percentage (%) = (length of film before heat treatment - length of film after holding at 150 캜 for 30 minutes) / length of film before heat treatment 占 100,

Smd denotes the shrinkage percentage (%) of the film in the machine direction (MD), Std denotes the shrinkage percentage (%) of the film in the width direction (TD), Vmd denotes the number of samples (%) Of the heat shrinkage rate in the machine direction, and Vtd means a deviation (%) of the heat shrinkage ratio in the width direction of 10 samples selected at intervals of 50 cm on the basis of the film full width.

It is ideal when the thermal shrinkage percentage (%) of the film in the machine direction (MD) is 0 to 1.0%. When the film shrinkage ratio is less than 0%, the film is expanded and the possibility of curling in the subsequent process is increased. The machine direction shrinkage in the process becomes large, and the likelihood of curling may also increase. And more preferably 0 to 0.9%.

The film is most ideal when the heat shrinkage ratio (%) in the width direction (TD) is 0 to 0.5%. When it is less than 0%, expansion of the film occurs in the width direction. This large-scale control can be difficult. More preferably, it is 0 to 0.4%.

The polyester film may include those satisfying the following formulas (5) to (7).

0? S (45)? 1.0 [Formula 5]

0? S (135)? 1.0 [Formula 6]

S (135) -S (45) < / = 0.2 [Equation 7]

In the above formula, S (45) and S (135) mean the heat shrinkage (%) of a film measured according to JIS C-2318 standard after holding a polyester film of 10 cm in width and 10 cm in 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. S (45) means a diagonal shrinkage ratio (%) of 45 degrees in the clockwise direction with respect to the width direction (TD) of the film, and S (135) Means a diagonal shrinkage ratio (%) of an angle of 135 deg.

In the present invention, the heat shrinkage of the polyester film in the diagonal direction may be controlled within the above range, thereby maximizing the migration blocking property of the oligomer at high temperature. In addition, a synergistic effect of physical properties including the optical characteristics of the polyester film can be realized. The heat shrinkage rate at a 45 ° angle in the clockwise direction with respect to the width direction (TD) of the film which is the diagonal direction of the polyester film and at 135 ° clockwise with respect to the width direction (TD) of the film is preferably 0 To 1.0%. At the same time, the absolute value of the heat shrinkage difference in the two diagonal directions may preferably be 0.2% or less. When the absolute value of the difference in the diagonal heat shrinkage ratio exceeds 0.2%, a twisted curl may be generated as the balance to be shrunk in the diagonal direction is broken.

Further, uniformity of heat shrinkage can be ensured within a range of ± 0.2% of the variation of the heat shrinkage ratio with respect to the full width of the film, and curl control can be facilitated.

The present inventors have studied to develop a film having a low heat shrinkage ratio while controlling the migration of oligomers at the time of producing a polyester film, and found that a primer layer has a T _g of 60 ° C or higher, a swelling ratio of 30% A primer layer having physical properties of 95% or more in a gel fraction and a density of 1.3 to 1.4 was formed and relaxed under specific conditions in a heat fixation step in the production of a film to form haze ) Change is 0.1% or less, and that the heat shrinkage ratios of the above formulas (1) to (7) can all be satisfied. In addition, it was confirmed that a film having a degree of oligomer migration satisfying the above range did not show a diamond mark and whitening phenomenon.

That is, the physical properties of the primer layer, T _g is at least 60 ℃, Swelling ratio is 30%, the gel fraction (Gel fraction) a haze change rate according to the following formula 8 in the range that satisfies the physical properties of 95% or more and a density of 1.3 or more (? H) of 0.1% or less can be satisfied.

H (%) = Hf - Hi [Expression 8]

In the above equation, Hf is the haze of the film after being maintained at 150 DEG C for 60 minutes, and Hi is the haze of the film before heating.

Specifically, the physical properties of the primer layer T _g is less than 60 ℃, and more specifically less than 60 ℃ and the upper limit is not limited, Swelling ratio is 30% or less, and more specifically, 0% ~ 30%, Gel fraction 95 The structural densities of the coating film and the mobility of the primer layer are lowered in the range satisfying the physical properties of the density of 1.3 or more, more specifically 95 to 100%, of 1.3 or more, more specifically 1.3 to 1.4, And it was confirmed that the oligomer inside the polyester film could not migrate to the surface even when the pressure was applied.

In the polyester film of the present invention, the primer layer may be formed by applying a water dispersible resin composition having an oligomer blocking property.

In one embodiment of the present invention, a water-dispersible resin composition comprising an acrylic resin copolymerized with a glycidyl group-containing radically polymerizable unsaturated monomer and a water-dispersible polyester resin is used as the water-dispersible resin composition for forming the primer layer .

In one embodiment of the present invention, the water-dispersible resin composition contains (A) / (B) a solid weight ratio of the acrylic resin (A) and the water-dispersible polyester resin (B) in which the glycidyl group-containing radically polymerizable unsaturated monomer is copolymerized. = 20 ~ 80/80 ~ 20. More preferably from 40 to 60/60 to 40 by weight. When the solid content of the water-dispersible polyester resin (B) is less than 20% by weight and the solid content of the acrylic resin (A) copolymerized with the glycidyl group-containing radically polymerizable unsaturated monomer exceeds 80% by weight, As the particle size increases, unevenness occurs in in-line coating, the adhesion to the polyester base film and transparency deteriorate, the solid content of the water-dispersible polyester resin (B) exceeds 80% by weight, When the solids content of the acrylic resin (A) copolymerized with a radical-polymerizable unsaturated monomer containing a silyl group is less than 20% by weight, sufficient oligomer blocking effect can not be exhibited.

The water-dispersible resin composition of the present invention can be produced by mixing a water-dispersible polyester resin (B) with a binder resin obtained by mixing an acrylic resin (A) copolymerized with a glycidyl group-containing radically polymerizable unsaturated monomer and water, It is also possible to produce a radically polymerizable unsaturated monomer containing a glycidyl group alone or a radically polymerizable unsaturated monomer copolymerizable with a glycidyl group-containing radically polymerizable unsaturated monomer in an aqueous dispersion of the water-dispersible polyester resin (B). In this case, a surfactant and a polymerization initiator can be used. The surfactant and the polymerization initiator can be used without limitation as long as they are commonly used in emulsion polymerization. Specifically, for example, an anionic surfactant, a nonionic surfactant, or a non-reactive surfactant may be used as the surfactant, and they may be used in combination. As the polymerization initiator, a radical polymerization initiator, a peroxide initiator or a nitrogen compound such as azobisisobutyronitrile may be used.

The water dispersion composition of the present invention may further contain a defoaming agent, a wetting agent, a surfactant, a thickener, a plasticizer, an antioxidant, an ultraviolet absorber, a preservative, a crosslinking agent and the like as necessary.

In the water-dispersible composition of the present invention, the water-dispersible polyester resin (B) may be a copolymer of a dicarboxylic acid component containing a sulfonic acid alkali metal salt compound and a glycol component containing diethylene glycol.

More specifically, as the dicarboxylic acid component, an aromatic dicarboxylic acid and an alkali metal salt compound of sulfonic acid may be used, and the sulfonic acid alkali metal salt compound may be contained in an amount of 6 to 20 mol% of the total acid component.

The dicarboxylic acid component may be an aromatic dicarboxylic acid such as phthalic acid, terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, 2,5-dimethyl terephthalic acid, 2,6-naphthalene dicarboxylic acid, Aliphatic dicarboxylic acids such as acetic acid, adipic acid and sebacic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.

Specific examples of the sulfonic acid alkali metal salt compound include alkali metal salts such as sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfoisophthalic acid and 4-sulfonaphthalic acid-2,7-dicarboxylic acid. , And 6 to 20 mol%. When it is used in an amount less than 6 mol%, the dispersion time of the resin to water becomes long and the dispersibility is low, and when it is used in excess of 20 mol%, the water resistance may be lowered.

As the glycol component, diethylene glycol and aliphatic or alicyclic glycols having 2 to 8 carbon atoms and 6 to 12 carbon atoms may be used. Specifically, there may be mentioned, for example, ethylene glycol, 1,3-propanediol, 1,2-propylene glycol, neopentyl glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, , 1,2-cyclohexanedimethanol, 1,6-hexanediol, P-xylene glycol, triethylene glycol, and the like. It is preferable that diethylene glycol is contained in 20 to 80 mol% of the total glycol component.

The number average molecular weight of the water dispersible polyester resin (B) is preferably 1,000 to 50,000, more preferably 2,000 to 30,000. When the number average molecular weight is less than 1000, the oligomer blocking effect is insignificant. When the number average molecular weight is more than 50000, water dispersibility may be difficult.

The water-dispersible polyester resin (B) is prepared by uniformly dispersing the water-soluble polyester resin (B) in water or water containing an aqueous solvent at 50 to 90 캜 with stirring. The water dispersion thus prepared preferably has a solid concentration of 30% by weight or less, more preferably 10 to 30% by weight for uniform dispersion. Examples of the aqueous solvent include alcohols such as methanol, ethanol and propanol, and polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and glycerin.

Next, the acrylic resin (A) copolymerized with the glycidyl group-containing radically polymerizable unsaturated monomer will be described.

The acrylic resin (A) in which the glycidyl group-containing radically polymerizable unsaturated monomer is copolymerized may be a homopolymer of the glycidyl group-containing radically polymerizable unsaturated monomer or another radically polymerizable unsaturated monomer capable of copolymerizing with the glycidyl group-containing radically polymerizable unsaturated monomer And is a copolymerized resin.

The acrylic resin may be a copolymerized monomer containing 20 to 80% by mole of a glycidyl group-containing radically polymerizable unsaturated monomer in the whole monomer component. The glycidyl group-containing radically polymerizable unsaturated monomer improves the strength of the coating film of the primer layer by cross-linking reaction and increases the cross-link density, so that the outflow of the oligomer can be blocked. Specific examples thereof include glycidyl ethers such as glycidyl acrylate, glycidyl methacrylate, and aryl glycidyl ether.

Radically polymerizable unsaturated monomers copolymerizable with the glycidyl group-containing radically polymerizable unsaturated monomer include vinyl esters, unsaturated carboxylic acid esters, unsaturated carboxylic acid amides, unsaturated nitriles, unsaturated carboxylic acids, allyl compounds, nitrogen-containing vinyl monomers, hydrocarbon vinyl monomers Or a vinyl silane compound. As the vinyl ester, vinyl propionate, vinyl stearate, vinyl chloride, and the like can be used. Examples of the unsaturated carboxylic acid ester include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, butyl methacrylate, butyl maleate, octyl maleate, butyl fumarate, octyl fumarate, Hydroxypropyl acrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, and the like. As the unsaturated carboxylic acid amide, acrylamide, methacrylamide, methylacrylamide, butoxymethylol acrylamide and the like can be used. As the unsaturated nitrile, acrylonitrile and the like can be used. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic acid ester, fumaric acid acid ester, itaconic acid acid ester and the like. Examples of the allyl compound include allyl acetate, allyl methacrylate, allyl acrylate, allyl itaconate, diallyl itaconate, and the like. As the nitrogen-containing vinyl monomer, vinyl pyridine, vinyl imidazole and the like can be used. Examples of the hydrocarbon vinyl monomer include ethylene, propylene, hexene, octene, styrene, vinyltoluene, and butadiene. Examples of the vinylsilane compound include dimethylvinylmethoxysilane, dimethylvinylethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, gamma-methacryloxypropyltrimethoxysilane, gamma-methacryloxypropyldimethoxysilane, etc. Can be used.

The water-dispersible resin composition according to one aspect of the present invention is characterized in that the acrylic resin (A) and the water-dispersible polyester resin (B) in which the glycidyl group-containing radically polymerizable unsaturated monomer is copolymerized have a solid content of 0.5 to 10% It is preferably an acidic or water-soluble composition. More specifically, the solid content of the acrylic resin (A) and the water-dispersible polyester resin (B) in which the glycidyl group-containing radically polymerizable unsaturated monomer is copolymerized is 0.5 to 10% by weight and the remainder is water, A wetting agent, a dispersing agent, and the like. The wetting agent is used for improving the coating property. Specifically, for example, a modified silicone based wetting agent such as Q2-5212 of Dow Corning, TEGO WET 250 of ENBODIC, and BYK 348 of BYK CHEMIE can be used. However, It is not. The wetting agent is preferably used in an amount of 0.1 to 0.5% by weight, and the intended coating property can be improved within the above range.

In the present invention, the primer layer may have a dry coating thickness of 20 to 150 nm. When the thickness of the dried coating is less than 20 nm, the oligomer blocking properties may not be sufficiently exhibited. When the thickness exceeds 150 nm, coating unevenness appears, and there is a high possibility that a blocking phenomenon occurs in which the primer layers stick together after the film is wound.

In the present invention, the polyethylene terephthalate film may be a polyethylene terephthalate film. The thickness of the polyethylene terephthalate film is preferably 25 to 250 μm, more preferably 50 to 188 μm. When the thickness is less than 25 mu m, mechanical properties suitable for the optical film are not realized. When the thickness is more than 250 mu m, the thickness of the film becomes too thick, which may cause a problem that the display device is not suitable for thinning.

In the present invention, the water-dispersible resin composition may be applied by an inline coating method during a polyester film production process. In other words, it can be produced by applying an in-line coating method before stretching in the manufacture of a polyester base film or a second stretching method after the first stretching, and then stretching the film. By heating in the second stretching and heat setting process, water evaporates, Layer may be formed. The application method is not limited as long as it is a known application method.

More specifically, the process for producing the polyester film of the present invention comprises

a) preparing a uniaxially stretched polyester base film in the machine direction;

b) forming a primer layer by applying a water dispersible resin composition having oligomer blocking properties to one side or both sides of the uniaxially stretched polyester base film;

c) biaxially stretching the uniaxially stretched polyester base film having the primer layer formed thereon in the transverse direction (TD); And

d) thermally fixing the biaxially stretched film and performing relaxation in the machine direction (MD) to a range satisfying the following expression (9);

1.1 ≤ relaxation ratio (%) ≤ 2.5 [

(In the above formula, the relaxation ratio (%) = (running speed of the film in the relaxation processing section-running speed of the entire film in the relaxation processing section) / running speed of the entire film in the relaxation processing section × 100)

.

In the present invention, in the step d), the relaxation of the machine direction (MD) may be performed in a temperature range satisfying the following expression (10).

Stretching temperature (占 폚)? Relaxation temperature (占 폚)? Heat fixing temperature (占 폚)

In the present invention, after stretching as described above, heat fixing and relaxation in the machine direction are performed, and relaxation is carried out under conditions satisfying the above formulas 9 and 10, whereby the oligomer is not migrated at high temperature, And therefore, a film favorable for the post-process can be produced.

More specifically, in the polyester production method of the present invention, in the step (a) of the present invention, the polyester chips are put into an extruder, melt-extruded, quenched and hardened with a casting drum to produce a polyester sheet, In the direction (MD). At this time, the stretching ratio is preferably 2 to 4 times.

In the step b), the uniaxially stretched polyester base film may be coated with the water dispersible resin composition, and may be coated using a method known to a person skilled in the art.

In the step c), the polyester base film having the primer coating layer formed thereon is subjected to biaxial stretching in the transverse direction (TD), and is preferably stretched to 2 to 4 times at 110 to 150 ° C.

The step d) may be a step of performing heat fixing and relaxation, and the step d) may be performed in a tenter. The heat fixing temperature may be performed at 200 to 240 ° C, and the relaxation temperature may preferably be within a range satisfying the following formula (9).

Stretching temperature (占 폚)? Relaxation temperature (占 폚)? Heat fixing temperature (占 폚)

The relaxation may be performed using the MD Relax facility in the machine direction (MD direction), or may be performed with the Passing path different from the Clip in the width direction (TD direction). The MD Relax facility can control the shrinkage performance in the MD direction by setting a speed difference of 1.1 ~ 2.5% between 9 rails after the heat treatment period. Preferably 1.2 to 2.0%, and more preferably 1.25 to 2.0%. The heat shrinkage ratio in the MD direction under the condition of 150 占 폚 for 30 minutes under the condition of the MD Relax ratio is in the range of 0 to 1.0%, more preferably in the range of 0.3 to 0.9%. The heat shrinkage ratio in the TD direction under the above conditions is in the range of 0 to 0.5%, more preferably in the range of 0.0 to 0.4%. It is also preferable that the deviation of the heat shrinkage ratio in the full width of the master roll is within ± 0.2% in the MD / TD direction.

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) Heat shrinkage

After cutting the film to a size of 10 cm in width and 10 cm in length, the dimensional change after being left in a hot air oven maintained at 150 캜 for 30 minutes is measured according to JIS C-2318. However, the film is measured at an interval of 50 cm for a full width roll, and the dimensional change is measured for the MD direction, the TD direction, the TD direction, and the 45 degree clockwise direction and the 135 degree direction, respectively.

Heat shrinkage ratio (%) = (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

2) Haze change rate (? H)

In order to measure the migration of the surface of the oligomer in the film, the film was placed in a box having a height of 3 cm, a width of 21 cm and a height of 27 cm, which was open at the top, followed by heat treatment at 150 ° C. for 60 minutes to migrate the oligomer to the film surface, The value was measured using a haze meter (Nipon denshoku, Model NDH 5000) according to JIS K 715 standard.

The haze change amount was calculated according to the following equation (8).

H (%) = Hf - Hi [Expression 8]

(Where Hf is the haze of the film after holding for 60 minutes at 150 DEG C, and Hi is the haze of the film before heating).

3) Dry coating thickness of primer layer

The cross-section of the film was measured with an SEM (Hitachi S-4300), and the film width of the base film coated with the coating composition was measured at 5 points in 1m intervals in the machine direction (TD) The average value was calculated after measuring 30 points.

4) Swelling Ratio, Gel Fraction and Tg measurement

15 g of the water dispersible resin composition prepared in Examples and Comparative Examples was placed in a bowl having a diameter of 80 mm and a height of 15 mm and then dried at 80 ° C for 24 hours and then at 120 ° C for 3 hours and then aged at 180 ° C for 1 hour. From this, 1 g of the dried coating film was taken and Tg was measured. The dried film was immersed in 50 g of distilled water and left at 70 캜 for 24 hours. And the swelling ratio was measured. The dried film was dried at 120 ° C for 3 hours, and the weight was recorded to measure the gel fraction.

(1) Swelling Ratio

Approximately 1 g of the dried coating film was immersed in 50 g of distilled water, and then left at 70 ° C. for 24 hours to take out the coated film and record the weight.

Swelling Ratio = (weight after leaving - initial weight) / initial weight × 100

(2) Gel fraction

The dried coating was dried at 120 ° C for 3 hours and then the weight was recorded.

Gel Fraction = (weight after drying / initial weight) × 100

(3) Tg measurement

DSC (using PerkinElmer DSC 7) Using the instrument, measure in 2nd Run mode. 10 to 11 mg of the dried coating film is measured using a PerkinElmer DSC7.

1st Run. = 0 to 200 DEG C and 200 DEG C / min,

Holding Time After maintaining the temperature at 200 ° C for 3 minutes,

The temperature was lowered at a rate of 200 ° C to -40 ° C and 200 ° C / min,

Holding Time Keep the temperature at -40 ° C for 5min.

2nd Run. = -40 占 폚 to 200 占 폚, and 20 占 폚 / min.

5) Whether curl is generated or not

The hard-coated film and evaluation film were laminated at a rate of 3 mpm at 150 캜, and then cut into a size of A4 size (width 29.7 cm, length 21.0 cm) in the width direction. Then, the dimensional change after standing for 12 hours in a hot air oven maintained at 80 ° C is measured. The dimensional changes are measured for the four corners of the A4 film at the height apart from the floor.

Curl occurrence was judged to be no curl when the height from the bottom to the corner of the film was 3 mm or less.

The binder resins used in the following Examples and Comparative Examples are as follows.

1) KLX-007 binder

(A) / (B) = 50/50 in the weight ratio of the acrylic resin (A) copolymerized with the radically polymerizable unsaturated monomer containing a glycidyl group and the water-dispersible polyester resin (B)

The acrylic resin contains 50% by mole of a glycidyl group-containing radically polymerizable unsaturated monomer as a copolymerizable monomer,

The water-dispersible polyester resin contains 50 mol% of diethylene glycol as the total glycol component and 10 mol% of the sulfonic acid alkali metal salt compound as a whole acid component.

2) P3208 binder

(Rohm & Haas), which contains 40% by weight of methyl methacrylate, 40% by weight of ethyl acrylate and 20% by weight of melamine.

[Example 1]

1) Preparation of water-dispersible resin composition (1)

0.3 wt% of silicone based wetting agent (Dow Corning, polyester siloxane copolymer, Q2-5212) and 0.3 wt% of colloidal silica particles having an average particle diameter of 140 nm were added to 16 wt% of a KLX-007 binder (25% And the mixture was stirred for 2 hours to prepare a water dispersible resin composition (1) having a total solid content of 4.6% by weight.

2) Production of Heat Shrinkage Controlled Oligomer Blocking Polyester Film

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (1) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was performed at 235 占 폚 in a 5-stage tenter, heat relaxed by 10% in the width direction at 200 占 폚, and the Relax ratio of the MD Relax equipment was adjusted to 1.25%, thereby obtaining a 125 占 퐉- .

The dry coating thickness of the primer coating layer of the composition was 80 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Example 2]

1) Preparation of water-dispersible resin composition (2)

0.3% by weight of a silicone based wetting agent (Dow Corning, polyester siloxane copolymer, Q2-5212) and 0.3% by weight of colloidal silica particles having an average particle diameter of 140 nm were added to 8% by weight of a KLX-007 binder (25% And the mixture was stirred for 2 hours to prepare a water dispersible resin composition (2) having a total solid content of 2.6% by weight.

2) Production of Heat Shrinkage Controlled Oligomer Blocking Polyester Film

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (2) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was performed at 235 占 폚 in a 5-stage tenter, heat relaxed by 10% in the width direction at 200 占 폚, and the Relax ratio of the MD Relax equipment was adjusted to 1.25%, thereby obtaining a 125 占 퐉- .

The dry coating thickness of the primer coating layer of the composition was 40 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Example 3]

1) Preparation of water-dispersible resin composition (3)

0.3 wt% of silicone based wetting agent (Dow Corning, polyester siloxane copolymer, Q2-5212) and 0.3 wt% of colloidal silica particles having an average particle diameter of 140 nm were added to 24 wt% of a KLX-007 binder (25% And the mixture was stirred for 2 hours to prepare a water dispersible resin composition (3) having a total solid content of 6.6% by weight.

2) Production of Heat Shrinkage Controlled Oligomer Blocking Polyester Film

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (3) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, preheated and dried, and 3.5 times Lt; / RTI > Thereafter, heat treatment was performed at 235 占 폚 in a 5-stage tenter, heat relaxed by 10% in the width direction at 200 占 폚, and the Relax ratio of the MD Relax equipment was adjusted to 1.25%, thereby obtaining a 125 占 퐉- .

The dry coating thickness of the primer coating layer of the composition was 160 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Example 4]

1) Preparation of heat shrinkage controlled oligomer-blocked polyester film

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (1) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was performed at 245 ° C in a 5-stage tenter, and heat relaxed by 10% in the width direction at 200 ° C. After that, the Relax ratio of the MD Relax equipment was adjusted to 1.25% .

The dry coating thickness of the primer coating layer of the composition was 80 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Example 5]

1) Preparation of heat shrinkage controlled oligomer-blocked polyester film

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (1) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was carried out at 237 ° C in a 5-stage tenter, heat relaxed by 10% in the transverse direction at 200 ° C, and the Relax ratio of the MD Relax equipment was adjusted to 2.0% .

The dry coating thickness of the primer coating layer of the composition was 80 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Example 6]

1) Preparation of heat shrinkage controlled oligomer-blocked polyester film

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (1) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was performed at 244 占 폚 in a 5-stage tenter, and heat relaxed by 10% in the transverse direction at 200 占 폚. After heat fixation, the Relax ratio of the MD Relax equipment was adjusted to 2.0% .

The dry coating thickness of the primer coating layer of the composition was 80 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Comparative Example 1]

1) Preparation of water-dispersible resin composition (4)

0.3 wt% of P-3208 Binder, 9.1 wt% (solid content 44% water dispersion composition), silicone based wetting agent (Dow Corning, polyester siloxane copolymer, Q2-5212), 0.3 wt% colloidal silica particles having an average particle diameter of 140 nm And the mixture was stirred for 2 hours to prepare a water dispersible resin composition (4) having a total solid content of 4.6% by weight.

2) Production of Heat Shrinkage Controlled Oligomer Blocking Polyester Film

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The water-dispersible resin composition (4) thus prepared was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was performed at 235 占 폚 in a 5-stage tenter, heat relaxed by 10% in the width direction at 200 占 폚, and the Relax ratio of the MD Relax equipment was adjusted to 1.25%, thereby obtaining a 125 占 퐉- .

The dry coating thickness of the primer coating layer of the composition was 80 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Comparative Example 2]

1) Preparation of oligomer-blocked polyester film without heat shrinkage

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (1) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was performed at 235 占 폚 in a 5-stage tenter, heat relaxed by 10% in the transverse direction at 200 占 폚, and the Relax ratio of the MD Relax equipment was adjusted to 1.00%, thereby obtaining a 125 占 퐉 biaxially stretched film coated on both surfaces .

The dry coating thickness of the primer coating layer of the composition was 80 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Comparative Example 3]

1) Preparation of oligomer-blocked polyester film without heat shrinkage

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (1) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was carried out at 235 ° C in a 5-stage tenter, heat relaxed by 10% in the width direction at 200 ° C, and then the Relax ratio of the MD Relax equipment was adjusted to 3.00% .

The dry coating thickness of the primer coating layer of the composition was 80 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

[Comparative Example 4]

1) Preparation of oligomer-blocked polyester film without controlled heat shrinkage

The water-removed polyethylene terephthalate chip was put in an extruder, melt extruded, and quenched and solidified by a casting drum having a surface temperature of 20 ° C to prepare a polyethylene terephthalate sheet having a thickness of 1500 μm. The prepared polyethylene terephthalate sheet was stretched 3.5 times at 80 DEG C in the machine direction (MD), and then cooled to room temperature. The resulting water-dispersible resin composition (1) was coated on both sides by a bar coating method, then heated to 110 to 150 ° C at a rate of 1 ° C per second, pre-heated and dried to obtain 3.5 times Lt; / RTI > Thereafter, heat treatment was carried out at 235 ° C in a 5-stage tenter, heat relaxed by 10% in the transverse direction at 200 ° C, and the Relax ratio of the MD Relax equipment was adjusted to 0%, thereby obtaining a 125 μm- .

The dry coating thickness of the primer coating layer of the composition was 80 nm. The physical properties of the polyester film thus obtained are shown in Tables 1 and 2 below.

As shown in Table 1, it was found that the polyester film according to the present invention exhibits excellent characteristics as an optical film because the haze change rate before and after the heat treatment is small. On the other hand, it can be confirmed that Comparative Example 1 affects the rate of haze change depending on the composition of the primer coating layer. That is, it can be confirmed that a difference in the degree of oligomer blocking performance may occur due to the selection of the composition of the coating layer.

In addition, as shown in Table 2, the target heat shrinkage ratio can be uniformly maintained over the entire width of the steel sheet by the heat treatment temperature and the mechanical relaxation (MD) ratio. This confirmed that the curl problem of the product can be controlled. On the other hand, in Comparative Example 2, it was found that it is difficult to secure a desired heat shrinkage ratio only by using existing facilities with an MD Relax rate of 1.0%, and the uniformity is also lowered. Also, in Comparative Example 3, film formation was impossible when the MD Relax rate was set to 3.0%.

In Comparative Example 4, although the heat shrinkage rate deviation in the MD direction and the TD direction was 0.2%, good results were confirmed, but it was confirmed that the problem of curling occurred at 3.5 mm. In this case, the shape of the curl generated is a twist curl in which curling is generated only at two corners in the diagonal direction among four corners, which is caused by a difference in diagonal heat shrinkage ratio. As shown in Table 3, it can be seen that the diagonal heat shrinkage difference occurs due to the difference in the conditions of the film forming process, and this difference causes the twist curl to occur during the laminating process. That is, in the case of the comparative example 4, although the heat shrinkage rate deviation in the MD direction and the TD direction is good with respect to the full width of the film, the diagonal heat shrinkage difference is not uniform, Is 0.2% or more, curl control is not possible due to the occurrence of twist curl.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Accordingly, the above description should not be construed as limiting the scope of the present invention defined by the limits of the following claims.

Claims (22)

A polyester base film comprising a polyester resin and a primer layer formed by applying a water dispersible resin composition having an oligomer blocking property on one or both sides thereof, wherein a heat shrinkage ratio (%) satisfies the following formulas 1 to 4 Lt; / RTI >
0? Smd? 1.0 [Formula 1]
0? Std? 0.5 [Formula 2]
- 0.2? Vmd? 0.2 [Formula 3]
- 0.2? Vtd? 0.2 [Formula 4]
Smd, Std, Vmd, and Vtd mean the heat shrinkage (%) of a film measured according to JIS C-2318 standard after holding a polyester film having a size of 10 cm in width and 10 cm in 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 denotes the shrinkage percentage (%) of the film in the machine direction (MD), Std denotes the shrinkage percentage (%) of the film in the width direction (TD), Vmd denotes the number of samples (%) Of the heat shrinkage ratio in the machine direction, and Vtd means a deviation (%) of the heat shrinkage ratio in the width direction of 10 samples selected at intervals of 50 cm on the basis of the film full width. The method according to claim 1,
Wherein the polyester film further satisfies the following formulas (5) to (7).
0? S (45)? 1.0 [Formula 5]
0? S (135)? 1.0 [Formula 6]
S (135) -S (45) < / = 0.2 [Equation 7]
(%) Of the film measured according to JIS C-2318 standard after keeping the polyester film having a size of 10 cm in width and 10 cm in length at 150 ° C for 30 minutes, and S (45) (%) = (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. S (45) means a diagonal shrinkage ratio (%) of 45 degrees in the clockwise direction with respect to the width direction (TD) of the film, and S (135) Means a diagonal contraction ratio (%) of an angle of 135 deg. The method according to claim 1,
The primer layer has a T _g above 60 ℃, swelling ratio (Swelling ratio) is 30%, the gel fraction (Gel fraction) is 95% or more and a density of 1.3 ~ 1.4 is a polyester film. The method according to claim 1,
Wherein the polyester film has a haze change ratio (? H) according to the following formula (8): 0.1% or less.
[Equation 8]
H (%) = Hf - Hi
(Where Hf is the haze of the film after holding for 60 minutes at 150 DEG C, and Hi is the haze of the film before heating). The method according to claim 1,
The water-dispersible resin composition contains a binder resin composed of an acrylic resin (A) and a water-dispersible polyester resin (B) in which a glycidyl group-containing radically polymerizable unsaturated monomer is copolymerized, and the glycidyl group-containing radically polymerizable unsaturated (A) / (B) = 20 to 80/80 to 20 of the acrylic resin (A) copolymerized with a monomer and the water-dispersible polyester resin (B). 6. The method of claim 5,
The water dispersible resin composition is a polyester film having a solid content of 0.5 to 10% by weight of a binder resin. 6. The method of claim 5,
Wherein the water-dispersible resin composition further comprises a silicone-based wetting agent. 6. The method of claim 5,
Wherein the water dispersible polyester resin is a polyester film obtained by copolymerizing a dicarboxylic acid component containing a sulfonic acid alkali metal salt compound and a glycol component containing diethylene glycol. 6. The method of claim 5,
Wherein the water dispersible polyester resin contains 20 to 80 mol% of diethylene glycol in the total glycol component. 6. The method of claim 5,
Wherein the water dispersible polyester resin contains 6 to 20 mol% of an alkali metal sulfonate compound in the total acid component. 6. The method of claim 5,
Wherein the acryl-based resin contains 20 to 80 mol% of a glycidyl group-containing radically polymerizable unsaturated monomer as a copolymerizable monomer in the total monomer components. The method according to claim 1,
Wherein the polyester base film is a polyethylene terephthalate film. The method according to claim 1,
The polyester base film is a polyester film having a thickness of 25 to 250 탆. The method according to claim 1,
Wherein the primer layer has a dry coating thickness of 20 to 150 nm. 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 film of any one of claims 1 to 14. a) preparing a uniaxially stretched polyester base film in the machine direction;
b) forming a primer layer by applying a water dispersible resin composition having oligomer blocking properties to one side or both sides of the uniaxially stretched polyester base film;
c) biaxially stretching the uniaxially stretched polyester base film having the primer layer formed thereon in the transverse direction (TD); And
d) thermally fixing the biaxially stretched film and performing relaxation in the machine direction (MD) to a range satisfying the following expression (9);
1.1 ≤ relaxation ratio (%) ≤ 2.5 [
(In the above formula, the relaxation ratio (%) = (running speed of the film in the relaxation processing section-running speed of the entire film in the relaxation processing section) / running speed of the entire film in the relaxation processing section × 100)
≪ / RTI > 17. The method of claim 16,
Wherein in the step d), relaxation in the machine direction (MD) is performed in a temperature range satisfying the following formula (10).
Stretching temperature (占 폚)? Relaxation temperature (占 폚)? Heat fixing temperature (占 폚) 17. The method of claim 16,
The water-dispersible resin composition contains a binder resin composed of an acrylic resin (A) and a water-dispersible polyester resin (B) in which a glycidyl group-containing radically polymerizable unsaturated monomer is copolymerized, and the glycidyl group-containing radically polymerizable unsaturated (A) / (B) = 20 to 80/80 to 20 in terms of solid content ratio of the acrylic resin (A) copolymerized with the monomer and the water-dispersible polyester resin (B). 17. The method of claim 16,
Wherein the polyester film satisfies the following formulas (1) to (4) in heat shrinkage percentage (%).
0? Smd? 1.0 [Formula 1]
0? Std? 0.5 [Formula 2]
- 0.2? Vmd? 0.2 [Formula 3]
- 0.2? Vtd? 0.2 [Formula 4]
Smd, Std, Vmd, and Vtd mean the heat shrinkage (%) of a film measured according to JIS C-2318 standard after holding a polyester film having a size of 10 cm in width and 10 cm in 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 denotes the shrinkage percentage (%) of the film in the machine direction (MD), Std denotes the shrinkage percentage (%) of the film in the width direction (TD), Vmd denotes the number of samples (%) Of the heat shrinkage ratio in the machine direction, and Vtd means a deviation (%) of the heat shrinkage ratio in the width direction of 10 samples selected at intervals of 50 cm on the basis of the film full width. 17. The method of claim 16,
Wherein the polyester film further satisfies the following formulas (5) to (7).
0? S (45)? 1.0 [Formula 5]
0? S (135)? 1.0 [Formula 6]
S (135) -S (45) < / = 0.2 [Equation 7]
(%) Of the film measured according to JIS C-2318 standard after keeping the polyester film having a size of 10 cm in width and 10 cm in length at 150 ° C for 30 minutes, and S (45) (%) = (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. S (45) means a diagonal shrinkage ratio (%) of 45 degrees in the clockwise direction with respect to the width direction (TD) of the film, and S (135) Means a diagonal contraction ratio (%) of an angle of 135 deg. 17. The method of claim 16,
Wherein the primer layer has a T _g of 60 ° C or more, a swelling ratio of 30% or less, a gel fraction of 95% or more, and a density of 1.3 to 1.4. 17. The method of claim 16,
Wherein the polyester film has a haze change rate (? H) according to the following formula (8): 0.1% or less.
[Equation 8]
H (%) = Hf - Hi
(Where Hf is the haze of the film after holding for 60 minutes at 150 DEG C, and Hi is the haze of the film before heating).