KR20180102306A - A polyester protective film for polarizer and polarizer using it - Google Patents

Abstract

The present invention relates to a polyester protective film for a polarizing plate and a polarizing plate using the same. More specifically, a polyester resin is produced by biaxial stretching. So, it has a planar orientation coefficient of 0.161 to 0.166, has a thin thickness where a plane orientation coefficient deviation in the width direction is 0.005 or less on the basis of the entire width, and has excellent optical properties and no rainbow stain.

Description

TECHNICAL FIELD [0001] The present invention relates to a protective film for a polarizer and a polarizer using the same.

The present invention relates to a polyester protective film for a polarizing plate and a polarizing plate using the same, and more particularly, to a polarizing plate for a polarizing plate, which is produced by biaxially stretching a polyester resin and has a planar orientation coefficient of 0.161 to 0.166, And a polarizing plate using the same. The present invention relates to a polyester protective film for producing a polarizing plate having a thin thickness with a deviation of 0.005 or less, excellent optical properties and no rainbow stains.

Recently, the demand for liquid crystal displays (LCDs) applied to these devices is rapidly increasing, as electronic products and various display coupling devices are increasing. The polarizing plate applied to such an LCD is an essential component used for providing a certain transmitted light and changing the color tone of transmitted light, and has a function of polarizing natural light incident thereon while oscillating in various directions as light oscillating in only one direction .

Particularly, in a reflection type liquid crystal display device, a circular polarizer is used in which a polarizing plate and a? / 4 retardation film are joined to convert linearly polarized light to circularly polarized light and circularly polarized light to linearly polarized light. By using such a circular polarizer, it is possible to prevent reflection by external light, thereby helping to improve outdoor visibility. In recent years, a circular polarizer is also applied to an organic electroluminescent device (OLED) for the purpose of improving outdoor visibility.

Such a polarizing plate has a structure in which a protective film is laminated on the upper and lower portions of the polarizer with an adhesive. The protective film serves to protect and support the polarizer from the outside, and films formed by various materials and methods for such protective films have been developed. As the polarizer used here, polyvinyl alcohol (PVA) is mainly used.

As described above, the polarizing plate has a basic structure of a protective film / PVA / protective film or a protective film / PVA, and triacetyl cellulose (TAC) is widely used as a protective film of the PVA polarizer. However, protective films of such materials are vulnerable to moisture, and cyclic olefin polymers (COP), acrylic films, and polyester films have recently been applied. Particularly, in recent years, adoption of polyester films has been expanding to maximize anisotropy.

As a prior art example, Japanese Patent Application Laid-Open No. 2011-532061 proposes a technique of using a polyester film produced by stretching a polyester film four or more times in the transverse direction as a polarizer protective film. There is a problem in quality due to uneven stretching in the width / length direction during the manufacturing process. In particular, as the thickness becomes thinner, transverse stretching (TD) in the transverse direction must be applied to cause retardation. And there is a limit to the thinning of the film. In addition, the machine direction longitudinal stretching (MD) process was not included, and there was a restriction in improving the processability and the yield.

On the other hand, Japanese Patent Laid-Open Publication No. 2010-118509 discloses a polarizing plate structure using a polyester-based biaxial (TD / MD) stretched film. However, in this case, when the biaxial stretching is carried out, since the retardation in the thickness direction is too large, there is a problem that it is not suitable to be practically applied to the polarizing plate protection.

Thus, there is a need for a polyester protective film for polarizing plate which has a thin thickness of 60 탆 or less, excellent optical properties with a low retardation, and does not cause rainbow stains.

1. Japanese Patent Application Laid-Open No. 2011-532061 2. Japanese Patent Laid-Open No. 2010-118509

In order to solve the problems of the prior art as described above, it has been studied for a long time, and as a result, it has been found that the process for biaxially stretching the polyester film during the production of the polarizing plate protective film is adjusted to have a plane orientation coefficient of 0.161 to 0.166, A high quality polyester which has a haze of 3% or less, a heat shrinkage ratio of 85% of 1% or less, a thin thickness of 60 탆 or less, excellent physical properties and no unevenness when the surface orientation coefficient deviation in the width direction is 0.005 or less A protective film can be prepared, and thus the present invention has been completed.

Therefore, an object of the present invention is to provide a polyester protective film for producing a high-quality flat plate, which has a thin film having a plane orientation coefficient of 0.161 to 0.166, a variation in surface orientation coefficient in the width direction of not more than 0.005, .

Another object of the present invention is to provide a method for producing a polyester film for a polarizer protective film of high quality through biaxial stretching or addition of polyethylene naphthalate under a stretching condition of a specific range of a polyester film.

It is still another object of the present invention to provide a polarizing plate to which the above-described high quality polyester film is applied as a protective film.

In order to accomplish the object of the present invention, the biaxially oriented polyester protective film according to the present invention is characterized in that the plane orientation coefficient of the following formula (1) is 0.161 to 0.166, Wherein the polarizing plate has an orientation coefficient deviation of 0.005 or less.

The present invention also relates to a method for producing an unstretched sheet, comprising the steps of: extruding a polyester resin to produce an unstretched sheet; Stretching the polyester film in the longitudinal stretching (MD) direction; Stretching the polyester film in the transverse direction (TD) direction simultaneously with or after the longitudinally stretching step; And thermally fixing the biaxially stretched polyester sheet to produce a polyester film. The present invention also provides a process for producing a polyester protective film for polarizing plate.

The present invention also provides a polarizing element comprising: a polarizer layer; And a protective layer on which the polyester protective film is attached as a protective film on at least one side of the polarizer.

Further, the present invention provides a display panel comprising: a display panel; And a display device in which a polarizing plate having the polyester protective film is disposed on at least one of an upper surface and a lower surface of the display panel.

The polyester protective film for manufacturing a polarizing plate according to the present invention has a plane orientation coefficient of 0.161 to 0.166 and a surface orientation coefficient deviation in the width direction of 0.005 or less on the basis of the entire width. The polyester protective film has high transmittance, high hydrolysis resistance and high Heat resistance.

In addition, the polyester protective film for producing a polarizing plate according to the present invention can be produced by biaxial stretching under specific conditions, so that a high-quality polarizing plate protected with a protective film having a small thickness and a small retardation can be produced.

Further, polyethylene naphthalate (PEN) is additionally added to the polyester resin to reduce crystallization, to significantly reduce the retardation in the width direction, in particular to increase the retardation in the thickness direction, and when observed from above the side, It has improved optical properties and can be applied to an optimal polarizing plate. In addition, when polyethylene naphthalate (PEN) is additionally added, the UV-cut function can be imparted and the economical efficiency can be increased.

In addition, the polarizing plate produced by attaching the polyester protective film according to the present invention has an effect of exhibiting excellent physical properties in which rainbow stains do not appear even in a large area.

In addition, the polyester protective film according to the present invention can be easily thinned in the manufacturing process due to biaxial stretching by setting favorable conditions, thereby improving the process of manufacturing the polarizing plate.

1 is a cross-sectional view of a polyester protective film according to an embodiment of the present invention.
2 is a cross-sectional view illustrating a polarizer plate to which a polyester protective film according to an embodiment of the present invention is applied.
3 is a schematic cross-sectional view illustrating an embodiment of a liquid crystal display device including a polarizing plate to which a polyester protective film according to an embodiment of the present invention is applied.

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

In the case where each film, film, panel, layer or the like described in the present invention is described as being formed 'on' or 'under' of each film, film, panel, The terms " on " and " under " include both 'directly' and 'indirectly formed'. In addition, the criteria for the top and bottom of each component are described with reference to the attached drawings. The size of each component in the drawings may be exaggerated for the sake of explanation and does not mean the size actually applied.

The present invention relates to a polarizing plate protective film produced by biaxially stretching a stretching condition of a polyester film in a specific range during the production of a polarizing plate protective film and having a plane orientation coefficient of 0.161 to 0.166 in the following formula 1, And a surface orientation coefficient deviation of 0.005 or less.

[Equation 1]

0.161?? P? 0.166

DELTA P = (nx + ny) / 2-nz where nx, ny, and nz are the refractive index in the longitudinal direction, the refractive index in the width direction, and the refractive index in the thickness direction, respectively.

In addition, the protective film according to the present invention has an in-plane retardation of 350 nm or less, a haze of 3% or less, and a heat shrinkage of 85% or less. The protective film according to the present invention is a protective film having an in-plane retardation (Ro) of 350 nm or less and a thickness direction retardation (Rth) of 6,500 nm or more and can be used for producing a polarizing plate. According to a more preferred embodiment of the present invention, the in-plane retardation may be 300 nm or less and the thickness direction retardation (Rth) may be 7,000 nm or more.

At this time, the protective film according to the present invention has a plane orientation coefficient falling within the above-mentioned range, and if the above condition is satisfied, it is possible to reduce the optical distortion phenomenon such as rainbow disorder.

The protective film satisfying these conditions may have a haze of 3% or less and more specifically 1% or less. Further, the heat shrinkage ratio of 85 is 1% or less, and iridescent blotting does not appear, and it has improved optical properties and can be used attached to at least one side or both sides of the polarizer.

The protective film can be obtained by, for example, a method of melt-extruding the above-mentioned polyester resin into a film form and then cooling and solidifying it with a casting drum to form a film.

In the present invention, a stretched polyester film or a sequential biaxially stretched polyester film can be used from the viewpoint of imparting crystallinity to the polyester film and achieving the above characteristics. Incidentally, in the case of using the aromatic polyester as the main component as the first protective film, the film may contain a resin other than the aromatic polyester, an additive, or the like.

The protective film may be a stretched film, and may be biaxially stretched. For example, in order to produce the protective film, longitudinal and transverse sequential biaxial stretching, longitudinal and transverse simultaneous biaxial stretching, and the like can be employed. The stretching means can be produced by any suitable stretching machine such as a roll stretching machine, a tenter stretcher, a biaxial stretching machine of pantograph or linear motor type, and the like.

The protective film may further include an ultraviolet absorber such as a benzotriazole-based ultraviolet absorber, a penzophenone-based ultraviolet absorber, or an acrylonitrile-based ultraviolet absorber when applied to the polarizer layer for protecting the polarizer layer.

Further, the protective film may have a structure of two or more layers. For example, the protective film may include a base film comprising the polyester resin and a coating layer comprising the ultraviolet absorber. Further, the protective film may be subjected to a corona treatment, a coating treatment, a flame treatment, or the like in order to improve the adhesion with the polarizer layer.

In order to improve the adhesion to the polarizer layer, at least one surface of the protective film is coated with at least one primer selected from the group consisting of AG (Anti Glare), scratch and low refractive layer (LR) the primer can be treated.

According to a preferred embodiment of the present invention, it may be a PVA polarizer protective film having a thickness of 60 탆 or less. More preferably 40 占 퐉 or less.

According to a preferred embodiment of the present invention, the polyester protective film may be a polarizer protective film satisfying the following formula (2).

&Quot; (2) "

25? Rth / Ro

Here, Rth is the retardation in the thickness direction of the protective film, and Ro is the in-plane retardation of the protective film.

More specifically, Rth / Ro in Equation (1) may be 30 or more.

Further, according to a preferred embodiment of the present invention, the polyester protective film may be a polarizer protective film satisfying the following formula (3).

&Quot; (3) "

1.0? TD / MD? 1.2

Here, MD is the stretching ratio in the longitudinal stretching direction, and TD is the stretching ratio in the transverse stretching direction.

According to a preferred embodiment of the present invention, the transmittance of the protective film may be 91% or more. More specifically, the transmittance of the protective film may be 92% or more.

Since the protective film according to the present invention includes a polyester resin, it can have a high transmittance, high hydrolysis resistance and high heat resistance, and can be used as a UV-cut function by including polyethylene naphthalate (PEN) It is possible to increase the economic efficiency. For reference, an aromatic polyester is preferable, and polyethylene naphthalate (PEN) is particularly preferably used in consideration of the fact that the polyester exhibits crystallinity. And preferably 2 to 10% by weight of polyethylene naphthalate (PEN). If the polyethylene naphthalate content is less than 2% by weight, ultraviolet ray cut (UV-cut) is limited. If it exceeds 10% by weight, surface hardness and economical efficiency are limited.

Further, when the polyethylene naphthalate (PEN) is added, the protective film of the present invention can significantly reduce the deviation in the width direction of the in-plane retardation and increase the retardation in the thickness direction, and when observed from above the side, Do not. Accordingly, the protective film according to the present invention has improved optical properties, and thus can be optimally applied as a protective film for a polarizing plate.

Particularly, when the protective film has a retardation in plane and thickness in the in-plane retardation and thickness direction as described above, the protective film may have optimal optical characteristics necessary for a polarizing plate.

The polyester protective film according to the present invention can be produced by the following process.

The present invention is a preferred embodiment for producing the above polyester film,

Extruding a polyester resin to produce an unstretched sheet;

Biaxially stretching the unstretched sheet; And

And a step of heat-fixing the biaxially stretched sheet to produce a polyester film, wherein the polyester film has a plane orientation coefficient of 0.161 to 0.166 and a surface orientation coefficient deviation in the width direction of 0.005 or less based on the entire width, Wherein the in-plane retardation is 350 nm or less, the retardation in the thickness direction is 6,500 nm or more, the haze is 3% or less, the heat shrinkage ratio at 85 is 1% or less, and the ultraviolet light blocking ratio at 380 nm is 5% .

First, the polyester resin is prepared. According to the present invention, the polyester resin is melt-extruded and cooled to produce an unoriented sheet. Thereafter, the unstretched sheet is stretched in the longitudinal stretching direction and the transverse stretching direction, and is heat-set, so that the protective film can be produced.

The melt extrusion is preferably performed at a temperature of Tm + 30 to Tm + 60. When the temperature of the extruder is lower than Tm + 30 in the melt extrusion process, the melt is not smoothly melted and the viscosity of the extrudate is increased to lower the productivity. Conversely, when the temperature exceeds Tm + 60, the molecular weight of the resin decreases due to depolymerization due to thermal decomposition, Problems can arise. Further, the cooling is preferably performed at a temperature of 30 or less, more preferably 15 to 30.

The unstretched sheet can be stretched by biaxial stretching.

According to the present invention, as another embodiment, the unstretched sheet can be stretched at a stretching ratio similar to the first direction and the second direction. For example, the unstretched sheet may be stretched three to four times in the first direction and three to four times in the second direction.

The first direction and the second direction may be perpendicular to each other. The first direction may be a machine direction, and the second direction may be a tenter direction. Conversely, the first direction may be the tenter direction, and the second direction may be the machine direction.

According to a preferred embodiment of the present invention, the non-stretched sheet is stretched three to four times in the longitudinal stretching direction, stretched three to four times in the transverse stretching direction, Can be manufactured.

In addition, according to a preferred embodiment of the present invention, an unstretched sheet can be produced at a stretching ratio satisfying the following formula (3).

&Quot; (3) "

1.0? TD / MD? 1.2

Here, MD is the stretching ratio in the longitudinal stretching direction, and TD is the stretching ratio in the transverse stretching direction.

According to a preferred embodiment of the present invention, the stretching speed in the longitudinal stretching direction is from 60 m / min to 100 m / min, more preferably from 60 m / min to 80 m / min. According to a preferred embodiment of the present invention, the stretching speed in the transverse stretching direction is from 60 m / min to 100 m / min, more preferably from 60 m / min to 80 m / min.

According to the embodiment of the present invention, the orientation properties desired in the present invention can be maintained by appropriately adjusting the stretching speeds in the longitudinal stretching direction and the transverse stretching direction, and the stretching speed in the longitudinal stretching direction and the transverse stretching direction, Accordingly, appropriate optical properties can be realized in the polarizing plate.

According to a preferred embodiment of the present invention, the stretching temperature is preferably in the range of Tg + 5 to Tg + 50, and the lower the Tg, the better the stretchability, but the break may occur. In particular, a stretching temperature range of Tg + 10 to Tg + 40 is preferable for improving the brittleness.

According to the present invention, after initiation of heat setting after stretching, the film relaxes in longitudinal stretching direction and / or transverse stretching direction.

According to a preferred embodiment of the present invention, the heat-setting temperature in the heat-setting step is 180 to 260, more preferably 200 to 250. Here, the process time of the heat fixation step may be 5 seconds to 1 minute. More specifically, the process time of the heat setting process may be from 10 seconds to about 45 minutes.

According to the present invention, when a polyester protective film for polarizing plate production is produced by the above-described production method, a protective film having a planar orientation coefficient of 0.161 to 0.166 and a thin thickness and no color unevenness can be produced.

In addition, the protective film of the present invention can contain various additives such as ordinary electrostatic charge, antistatic, antiblocking agent and other inorganic lubricant within a range that does not impair the effect of the present embodiment.

The protective film according to the present invention may have improved optical and mechanical properties. In addition, since the protective film formed by the above process has low heat shrinkage, the polarizer layer can be efficiently protected.

On the other hand, the present invention provides a polarizer layer comprising: a polarizer layer; And

Wherein the protective film comprises a polyester resin and has a plane orientation coefficient of 0.161 to 0.166, an in-plane retardation of 350 nm or less, a thickness direction of the polarizer layer , A retardation of 6,500 nm or more, a haze of 3% or less, a heat shrinkage of 85% or less, and a UV blocking ratio of 5% or less at 380 nm.

According to a preferred embodiment of the present invention, in the polarizing plate, the protective film for protecting the polarizer has a thickness of 60 탆 or less, satisfies the above-mentioned expressions (1) and (2) and is stretched three to four times in the longitudinal stretching direction , And 3 to 4 times in the transverse stretching direction.

According to a preferred embodiment of the present invention, a display panel; And a polarizer disposed on at least one of an upper surface and a lower surface of the display panel, wherein the polarizer comprises a polarizer layer; And a polyester protective film adjacent to at least one of the upper surface and the lower surface of the polarizer layer, wherein the protective film comprises a polyester resin, has a plane orientation coefficient of 0.161 to 0.166 and an in- , A retardation in the thickness direction of 6,500 nm or more and a surface orientation coefficient deviation in the width direction of 0.005 or less on the basis of the entire width, a haze of 3% or less, a heat shrinkage of 85% or less and a UV cut- And 5% or less.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIG.

1 is a cross-sectional view of a polyester protective film according to an embodiment of the present invention.

Referring to FIG. 1, the protective film 310 may be manufactured with a structure including a pair of primers P1 and P2.

2 is a cross-sectional view illustrating a polarizer according to an embodiment of the present invention.

Referring to FIG. 2, the polarizing plate 11 according to the present invention may be manufactured with a structure including a polarizer layer 220, and one or a pair of protective films 310 and 320.

The polarizer layer 220 performs a polarization function. The polarizer layer 220 may be a polyvinyl alcohol layer stained with iodine or the like. At this time, the polyvinyl alcohol molecules contained in the polyvinyl alcohol layer may be aligned in one direction. The protective films 310 and 320 are polyester films having a plane orientation coefficient of 0.161 to 0.166.

As described above, the protective film according to the present invention has improved optical and mechanical properties and has a low heat shrinkage. Therefore, when the protective film is used as a protective film, the polarizer layer can be efficiently protected.

Thus, the polarizer according to the present invention can have improved optical, mechanical and thermal properties.

The polarizing plate may be applied to a display device such as a liquid crystal display device or an organic light emitting display device.

The polarizing plate to which the protective film according to the present invention is applied can be used for manufacturing a liquid crystal display (LCD).

3 is a cross-sectional view schematically showing one embodiment of a liquid crystal display device according to the present invention.

Referring to FIG. 3, a liquid crystal display device according to an embodiment of the present invention includes a liquid crystal panel and a backlight unit 20.

The backlight unit 20 emits light to the liquid crystal panel. The liquid crystal panel displays an image using light from the backlight unit 20. [ In more detail, the liquid crystal panel displays an image by adjusting the intensity of light emitted in units of pixels using light from the backlight unit 20. [

The liquid crystal panel includes an upper polarizer 11, a color filter substrate 13, a liquid crystal layer 14, a TFT substrate 15, and a lower polarizer plate 12.

The TFT substrate 15 and the color filter substrate 13 are opposed to each other. The TFT substrate 15 includes a plurality of electrodes corresponding to each pixel, thin film transistors connected to the pixel electrodes, a plurality of gate lines for applying driving signals to the thin film transistors, And a plurality of data lines for applying a data signal to the pixel electrodes.

The color filter substrate 13 includes a plurality of color filters corresponding to respective pixels. The color filters may filter transmitted light to achieve red, green, and blue, respectively. In addition, the color filter substrate 13 may include a common electrode facing the pixel electrodes.

The liquid crystal layer 14 is interposed between the TFT substrate 15 and the color filter substrate 13. The liquid crystal layer 14 may be driven by the TFT substrate 15. More specifically, the liquid crystal layer 14 may be driven by an electric field formed between the pixel electrodes and the common electrode. The liquid crystal layer 14 can adjust the polarization direction of light passing through the lower polarizer 12. That is, the TFT substrate 15 can control a potential difference applied between the pixel electrodes and the common electrode in pixel units. Accordingly, the liquid crystal layer 14 can be driven to have different optical characteristics in pixel units.

At least one of the upper polarizer 11 and the lower polarizer 12 may have substantially the same configuration as the polarizer of the above-described manufacturing method.

The lower polarizer plate 12 is disposed below the TFT substrate 15. The lower polarizer plate 12 may be adhered to the lower surface of the TFT substrate 15.

The upper polarizer 11 is disposed on the color filter substrate 13. The upper polarizer 11 may be adhered to the upper surface of the color filter substrate 13.

The polarization directions of the upper polarizer 11 and the lower polarizer 12 may be the same or perpendicular to each other.

As described above, the upper polarizer 11 and / or the lower polarizer 12 include a protective film having an improved performance. Accordingly, the liquid crystal display device according to the embodiment of the present invention can have improved brightness, image quality, and durability.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are illustrative of the present invention, and the contents of the present invention are not limited to the following examples.

Example  1-4

Polyethylene terephthalate resin (product of SKC) was used as a protective film material, and the polyethylene terephthalate resin was extruded through an extruder at a temperature of about 285 and cast in a casting roll of about 30 to prepare an unstretched sheet. These unstretched sheets were stretched in the longitudinal stretching direction and the transverse stretching direction at the stretching ratios shown in Table 1 below at the temperatures of 82 and 145 after the preheating. Thereafter, the stretched sheet was heat set for about 30 seconds to prepare a polyester protective film. At this time, the thermal fixation relaxation rate was about 3%.

Comparative Example  1-4

An unoriented sheet was produced using the same polyethylene terephthalate resin as in Example 1 except that a protective film was prepared in the same manner as in Example 1, stretched at the stretching ratio shown in Table 1, Respectively.

division thickness
(탆) Stretching cost casting
speed
(m / min) Elongation speed
TD
(m / min) Stretching temperature
(° C) Stretching temperature
(° C) Heat setting temperature
(° C) MD TD TD / MD Example 1 40 3.3 3.47 1.05 20 69 82 145 190 Example 2 38 3 3.4 1.13 22 79 82 145 200 Example 3 42 3.3 3.5 1.06 19 66 82 145 190 Example 4 44 3.2 3.53 1.10 23 77 82 147 200 Comparative Example 1 40 3.2 3.9 1.22 35 118 81 150 210 Comparative Example 2 43 3.4 4.3 1.26 32 114 82 152 240 Comparative Example 3 38 3.1 4.1 1.32 32 104 80 145 230 Comparative Example 4 40 3.2 4.2 1.31 30 101 80 147 220

Experimental Example

The properties were evaluated for Examples 1 to 4 and Comparative Examples 1 to 4, and the results are shown in Table 2 below. Here, each property evaluation was carried out as follows.

(1) Measurement of refractive index

Using Abbe's refractometer and sodium D line (589 nm) as a light source, the refractive index in the thickness direction of the film was measured.

(2) In-plane retardation (Ro)

The in-plane retardation is a parameter defined by a product (NxyXd) of anisotropy (Nxy = | Nx-Ny |) of a refractive index of an orthogonal biaxial film on the film and a film thickness d (nm), and is a measure for optical anisotropy and anisotropy. The anisotropy (Nxy) of the refractive index of the biaxial axis was obtained by the following method. Using two polarizing plates, the direction of the orientation axis of the film was determined, and a rectangle of 4 cm x 2 cm was cut out so that the orientation axis direction was orthogonal to obtain a measurement sample. The refractive index (Nx, Ny) and the refractive index (Nz) in the thickness direction orthogonal to the biaxial axis were determined by Abbe's refractive index meter (NAR-4T manufactured by Atago Corporation, measurement wavelength: 589 nm) The absolute value of the difference (| Nx-Ny |) is defined as the anisotropy (Nxy) of the refractive index. The thickness d (nm) of the film was measured using an electric micrometer (Millitron 1245D, manufactured by Pahrung Paste), and the unit was converted to nm. The retardation (Re) was determined from the product (NxyXd) of the anisotropy (Nxy) of the refractive index and the thickness d (nm) of the film.

(3) Plane orientation coefficient (? P)

The refractive index obtained by the above method was calculated to obtain the plane orientation coefficient (AP).

(4) Surface orientation coefficient deviation

The plane orientation coefficients were measured at 10 cm intervals of the full width standard, and the deviation was defined as the largest difference from the average plane orientation coefficient.

(5) Rainbow stain observation

A polyester film produced by a method described later on one side of a polarizer made of PVA and iodine was stuck to the polarizer so that the absorption axis of the polarizer and the main axis of alignment of the film were perpendicular to each other, and a TAC film (manufactured by Fuji Film Co., Thickness: 80 mu m) was attached thereto to prepare a polarizing plate. The obtained polarizing plate was set so that the polyester film was on the visible light side of a light emitting side of a liquid crystal display device in which a white LED as a light emitting element in combination with a blue light emitting diode and a yttrium aluminum garnet yellow phosphor was used as a light source (Nichia Corporation, NSPW500CS) . This liquid crystal display device has a polarizing plate that uses two TAC films as a polarizer protective film on the incident light side of the liquid crystal cell. The front and the oblique directions of the polarizing plate of the liquid crystal display device were visually observed to determine whether rainbow color unevenness occurred or not as follows.

⊚: No rainbow color spots occur in any direction.

?: When observed in the oblique direction, some very light rainbow irregularities are observed.

X: When observed in the oblique direction, an iridescent color unevenness is clearly observed.

division Refractive index In-plane retardation Plane orientation coefficient Plane orientation coefficient
Deviation Rainbow stain nx ny nz Example 1 1.655 1.658 1.494 120 0.1625 0.0015 ◎ Example 2 1.654 1.656 1.495 76 0.1615 0.002 ○ Example 3 1.656 1.658 1.493 84 0.1635 0.002 ◎ Example 4 1.657 1.6573 1.491 13.2 0.164 0.0022 ◎ Comparative Example 1 1.634 1.695 1.468 2000 0.1745 0.008 X Comparative Example 2 1.63 1.73 1.46 4300 0.207 0.0155 X Comparative Example 3 1.617 1.72 1.47 3914 0.1645 0.012 X Comparative Example 4 1.625 1.715 1.467 3600 0.1835 0.0098 X

The results of Table 2 show that, in the case of the embodiment according to the present invention, since the irregular smear is not observed when the side orientation is observed while satisfying the plane orientation coefficient of 0.161 to 0.166, it has improved optical characteristics, Can be applied. In addition, the physical properties such as haze, heat shrinkage, ultraviolet light blocking ratio and hardness are excellent It is widely applicable as a polarizer protective film of a polarizing plate.

In addition, the present invention can be applied to a display device such as a liquid crystal display device, an organic electroluminescent display device, and the like, as long as the polarizing plate to which the polyester protective film according to the present invention is applied can be applied to a display device.

11, 12 - polarizer
220 - Polarizer layer (PVA)
310, 320 - protective film
13 - Color filter substrate
14 - liquid crystal layer
15-TFT substrate
20 - Backlight unit

Claims (17)

The polyester protective film according to claim 1, wherein the biaxially oriented polyester protective film has a plane orientation coefficient of 0.161 to 0.166 and a surface orientation coefficient deviation of 0.005 or less on the basis of the entire width.
[Equation 1]
0.161?? P? 0.166
DELTA P = (nx + ny) / 2-nz where nx, ny and nz are the refractive index in the longitudinal direction, the refractive index in the width direction, and the refractive index in the thickness direction, respectively.
The polyester protective film according to claim 1, wherein the polyester protective film has a thickness of 60 탆 or less.
The polyester protective film according to claim 1, which satisfies the following formula (2):
&Quot; (2) "
25? Rth / Ro
Here, Rth is the retardation in the thickness direction of the protective film, and Ro is the in-plane retardation of the protective film.
The polyester protective film according to claim 1, wherein the polyester protective film is stretched three to four times in the longitudinal stretching direction and three to four times in the transverse stretching direction.
The polyester protective film according to claim 1, which satisfies the following formula (3).
&Quot; (3) "
1.0? TD / MD? 1.2
Here, MD is the stretching ratio in the longitudinal stretching direction, and TD is the stretching ratio in the transverse stretching direction.
The polyester protective film of claim 1, wherein the polyester protective film further comprises polyethylene naphthalate (PEN).
The film according to any one of claims 1 to 6, wherein the film has an in-plane retardation of 350 nm or less, a retardation in the thickness direction of 6,500 nm or more, a haze of 3% or less, a heat shrinkage ratio of 85% lt; RTI ID = 0.0 > nm. < / RTI >
The polyester protective film according to any one of claims 1 to 6, which is a polyvinyl alcohol (PVA) polarizer protective film.
Extruding a polyester resin to produce an unstretched sheet;
Stretching the polyester film in the longitudinal stretching (MD) direction;
Stretching the polyester film in the transverse direction (TD) direction simultaneously with or after the longitudinally stretching step;
Thermally fixing the biaxially stretched polyester sheet to produce a polyester film;
≪ / RTI > wherein the polyester protective film is a polyester film.
The method for producing a polyester protective film according to claim 9, which satisfies the following formula (1)
[Equation 1]
0.161?? P? 0.166
DELTA P = (nx + ny) / 2-nz where nx, ny and nz are the refractive index in the longitudinal direction, the refractive index in the width direction, and the refractive index in the thickness direction, respectively.
The method for producing a polyester protective film according to claim 9, wherein the polyester protective film satisfies the following formula (2)
&Quot; (2) "
25? Rth / Ro
Here, Rth is the retardation in the thickness direction of the protective film, and Ro is the in-plane retardation of the protective film.
[12] The method of producing a polyester protective film according to claim 9, wherein the polyester protective film is stretched three to four times in the longitudinal stretching direction and three to four times in the transverse stretching direction.
The method of producing a polyester protective film according to claim 9, which satisfies the following formula (3).
&Quot; (3) "
1.0? TD / MD? 1.2
Here, MD is the stretching ratio in the longitudinal stretching direction, and TD is the stretching ratio in the transverse stretching direction.
[12] The method of producing a polyester protective film according to claim 9, wherein the heat fixing temperature in the heat fixing step is 180 to 260 and the heat setting time is 5 seconds to 1 minute.
The method of producing a polyester protective film according to claim 9, wherein the polyester resin further comprises polyethylene naphthalate (PEN).
A polarizer layer; And
And a protective film adjacent to at least one of the upper surface and the lower surface of the polarizer layer,
Wherein the protective film is a polyester protective film according to any one of claims 1 to 7.
17. The polarizer of claim 16, wherein the polarizer layer is a polyvinyl alcohol (PVA) polarizer.

Images