KR102291819B1 - 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, and more particularly, by specifying the stretching conditions during film production, has a low retardation and thin thickness, and has excellent physical properties even in a large area, so that it does not cause stains. It relates to a polyester protective film and a polarizing plate using the same.

Description

Polyester protective film for polarizing plate manufacturing and polarizing plate 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, by specifying the stretching conditions during film production, has a low retardation and thin thickness, and has excellent physical properties even in a large area, so that it does not cause stains. It relates to a polyester protective film and a polarizing plate using the same.

In recent years, as electronic products and various display combination devices have exploded, the demand for liquid crystal displays (LCDs) applied to these devices is also rapidly increasing. The polarizing plate applied to this LCD is an essential part used to provide constant transmitted light and change the color tone of the transmitted light. .

In particular, in the reflective liquid crystal display device, a circular polarizing plate is used, in which a polarizing plate and a λ/4 retardation film are bonded to convert linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light. By using such a circular polarizing plate, it is possible to prevent reflection by external light, which helps to improve outdoor visibility. Also, in recent years, circular polarizers have been applied to organic light emitting diodes (OLEDs) for the purpose of improving outdoor visibility.

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

As described above, the polarizing plate consists of a basic configuration of a protective film/PVA/protective film, and triacetyl cellulose (TAC) has been widely used as the protective film of the PVA polarizer. However, protective films made of these materials have a problem of being vulnerable to moisture, and recently, cyclic olefin polymers (COPs), acrylic films, polyester films, and the like have been applied.

As an example of the related art, Japanese Patent Laid-Open No. 2009-92769 discloses a film containing a cyclic olefin-based resin such as a norbornene-based resin as a main component, and the cyclic olefin-based resin has low specific gravity, low birefringence, and low photoelastic coefficient characteristics. It has been reported that it can be applied to large-area expansion. However, the cyclic olefin-based film has poor adhesion to polyvinyl alcohol (PVA) due to low water absorption, causing problems such as peeling of the PVA and the retardation film and curling of the polarizing plate.

In addition, Japanese Patent Application Laid-Open No. 2011-532061 proposes a technique for using a polyester film prepared by stretching a polyester film in the transverse direction by 4 times or more as a polarizer protective film, but such a protective film is not wide enough in the manufacturing process. / There is a problem in quality due to non-uniform stretching in the longitudinal direction, etc. In particular, as the thickness decreases, it is necessary to apply TD in the width direction to express retardation, but there is a problem that equipment modification is required. There is a limit to thinning the film. In addition, since the longitudinal stretching (MD) process in the machine direction was not included, there were limitations in improving processability and yield.

On the other hand, Japanese Patent Laid-Open No. 2010-118509 discloses a polarizing plate configuration using a polyester-based biaxial (TD/MD) stretched film. However, here, since the thickness direction retardation range is too large in carrying out biaxial stretching, there is a problem that it is not suitable for practically applying it for protection of a polarizing plate.

1. Japanese Patent Laid-Open No. 2009-92769 2. Japanese Patent Laid-Open No. 2011-532061 3. Japanese Patent Laid-Open No. 2010-118509

As a result of research and review for a long time to solve the problems of the prior art as described above, when biaxial stretching is performed in a specific range under the stretching conditions of the polyester film in the manufacture of a polarizing plate protective film, the retardation is low, but it has a thin thickness and a large area. The present invention was completed by finding out that it is possible to manufacture a high-quality polyester protective film that does not cause stains due to its excellent physical properties.

Accordingly, it is an object of the present invention to provide a high-quality polyester protective film for manufacturing a polarizing plate that has a low retardation, a thin thickness, and excellent physical properties even in a large area, and thus does not cause stains.

In addition, another object of the present invention is to provide a method for producing a polyester film for a polarizer protective film by biaxially stretching the stretching conditions of the polyester film in a specific range.

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

As described above, in order to create a purpose through solving the problems of the present invention, in the present invention, the polyester resin is included, the in-plane retardation is 300 nm or less, and the retardation in the thickness direction is 3,000 nm or less. A protective film is provided.

In addition, the present invention comprises the steps of extruding a polyester film to prepare an unstretched sheet; Stretching the polyester film 2.5 to 6 times in the longitudinal stretching (MD) direction; Stretching the polyester film 2.5 to 6 times in the transverse stretching (TD) direction at the same time or after the longitudinal stretching step; It provides a method for producing a polyester protective film for manufacturing a polarizing plate, comprising the step of heat-setting the biaxially stretched polyester sheet to prepare a polyester film.

In addition, the present invention is a polarizer layer; and the polyester protective film adjacent to at least one of an upper surface and a lower surface of the polarizer layer.

In addition, the present invention provides a display panel; and a display device including a polarizing plate disposed on at least one of an upper surface and a lower surface of the display panel.

As described above, the polyester protective film for manufacturing a polarizing plate according to the present invention minimizes in-plane retardation and thickness-direction retardation, and since it contains a polyester resin, it can have high transmittance, high hydrolysis resistance, and high heat resistance.

In addition, the protective film according to the present invention has a small retardation in the thickness direction and a small in-plane retardation even after the stretching process. Therefore, when observed from the upper side, since rainbow blotches and the like are not observed, it has improved optical properties and thus can be optimally applied for a polarizing plate.

As described above, the polyester protective film for manufacturing a polarizing plate according to the present invention is manufactured by biaxially stretching under stretching conditions in a specific range, thereby producing a high-quality polarizing plate protected by a protective film having a low retardation and a thin thickness.

In addition, the polarizing plate manufactured 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 has the effect of improving the process according to the manufacturing process of the polarizing plate because it is easy to reduce the thickness in the manufacturing process due to biaxial stretching by setting desirable conditions.

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

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

Where each film, membrane, panel, or layer or the like described herein is described as being formed “on” or “under” each film, membrane, panel, or layer, etc., “On” and “under” include both “directly” or “indirectly” formed through another element. In addition, the criteria for the upper / lower of each component will be described with reference to the accompanying drawings. The size of each component in the drawings may be exaggerated for explanation, and does not mean the size actually applied.

The present invention is a polyester protective film manufactured by biaxially stretching in a specific range under stretching conditions for a polarizing plate protective film, and has excellent physical properties while having little in-plane retardation and thickness-direction retardation. do.

The present invention is a protective film containing a polyester resin, having an in-plane retardation (Ro) of 300 nm or less, and a thickness direction retardation (Rth) of 3000 nm or less, and may be used for manufacturing a polarizing plate.

If the in-plane retardation is greater than 300 nm, there is a problem, and if the thickness direction retardation is greater than 3000 nm, there is a problem.

According to a preferred embodiment of the present invention, the polyester resin may be an aromatic polyester resin.

The polyester protective film of the present invention may be used by being attached to at least one or both surfaces of the polarizer.

The said protective film can be obtained, for example by the method of melt-extruding the said polyester resin in film form, cooling and solidifying with a casting drum, and forming a film, etc.

In this invention, a stretched polyester film and a sequentially biaxially stretched polyester film can be used from a viewpoint of providing crystallinity to a polyester film and achieving the said characteristic. In addition, when using what has aromatic polyester as a main component as a 1st protective film, the film may contain resin, additives, etc. other than aromatic polyester.

"It has aromatic polyester as a main component" means 50% by weight or more of aromatic polyester, preferably 60% by weight or more, more preferably 70% by weight or more, preferably 80% by weight or more with respect to the total weight of the film. means to have

The protective films may be entirely formed of a polyester resin. The polyester resin may be included in the protective films in an amount of about 90 wt % or more. More specifically, the polyester resin may be included in the protective films in an amount of about 95 wt% or more. In more detail, the polyester resin may be included in the protective films in an amount of about 99 wt% or more.

The protective film may be a stretched film, and may be formed by biaxially stretching. For example, in order to manufacture the said protective film, the longitudinal and transverse sequential biaxial stretching method, the longitudinal and transverse simultaneous biaxial stretching method, etc. can be employ|adopted. As a stretching means, it can manufacture with arbitrary suitable stretching machines, such as a roll stretching machine, a tenter stretching machine, a pantograph type, or a linear motor type biaxial stretching machine.

The polyester resin includes a diol component and a dicarboxylic acid component. In more detail, the polyester resin may be entirely composed of the diol component and the dicarboxylic acid component. In more detail, the polyester resin may include about 95 mol% or more of the diol component and the dicarboxylic acid.

The polyester resin may be formed by polymerization of the diol component and the dicarboxylic acid component after transesterification.

Examples of the polyester include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5 -Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3- Cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, Dicarboxyl such as 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid trimethyladipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, and dodecadicarboxylic acid Acid and ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, Homo obtained by polycondensing 1 type of diol such as 1,5-pentanediol, 1,6-hexadiol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone, respectively. Polymers or copolymers obtained by polycondensing one or more dicarboxylic acids and two or more diols, or copolymers obtained by polycondensing two or more dicarboxylic acids and one or more diols, and homopolymers or copolymers thereof Some polyester resins of the blend resin formed by blending more than one type are mentioned. Among them, in consideration of polyester showing crystallinity, aromatic polyester is preferable, and polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) can be particularly preferably used.

In addition, when applied to the polarizer layer to protect the polarizer layer, the protective film may further include a UV absorber such as a benzotriazole-based UV absorber, a phenzophenone-based UV absorber, or an acrylonitrile-based UV absorber.

In addition, the protective film may have a structure of two or more layers. For example, the protective film may include a base film including the polyester resin and a coating layer including the UV absorber.

In addition, the protective film may be subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve adhesion with the polarizer layer.

In addition, in order to improve the adhesiveness with the polarizer layer, an easily adhesive layer containing at least one of a polyester resin, a polyurethane resin, or a polyacrylic resin as a main component may be formed on at least one surface of the protective film.

Here, the "main component" means a component of 50 mass % or more among the solid components constituting the easily adhesive layer.

As for the coating liquid used for formation of the said easily bonding layer, the aqueous coating liquid containing at least 1 sort(s) among a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and a polyurethane resin is preferable. The aqueous coating solution may be a water-soluble or water-dispersible copolymer polyester resin solution, an acrylic resin solution, a polyurethane resin solution, and the like.

According to a preferred embodiment of the present invention, the in-plane retardation (Ro) of the protective film may be about 250 nm or less. In more detail, the in-plane retardation of the protective film may be about 200 nm or less.

According to a preferred embodiment of the present invention, it may be a PVA polarizer protective film having an in-plane retardation of 150 nm or less. In more detail, the in-plane retardation of the protective film may be about 90 nm or less. In more detail, the in-plane retardation of the protective film may be about 80 nm or less. The minimum value of the in-plane retardation of the protective film may be about 0 nm.

According to a preferred embodiment of the present invention, the thickness direction retardation (Rth) of the polyester protective film may be about 2700 nm or less. In more detail, the thickness direction retardation (Rth) of the protective film may be about 2600 nm or less. In more detail, the thickness direction retardation (Rth) of the protective film may be about 2500 nm or less.

The minimum value of the retardation in the thickness direction of the protective film may be about 1 nm. In more detail, the retardation in the thickness direction of the protective film may be about 1 nm to about 2000 nm. In more detail, the retardation in the thickness direction of the protective film may be about 1 nm to about 1500 nm.

According to a preferred embodiment of the present invention, it may be a PVA polarizer protective film having a thickness of 60 μm or less.

According to a more preferred embodiment of the present invention, it may be a PVA polarizer protective film having a thickness of 40 μm or less.

According to a more preferred embodiment of the present invention, it may be a PVA polarizer protective film having a thickness of 30 μm or less.

According to a preferred embodiment of the present invention, the lowest thickness of the protective film may be about 5㎛.

According to a preferred embodiment of the present invention, the polyester protective film may be a polarizer protective film satisfying Equation 1 below.

[Equation 1]

15≤Rth/Ro

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

More specifically, in Equation 1, Rth/Ro may be 17 or more. More specifically, Rth/Ro may be 20 or more. The maximum value of Rth/Ro may be about 3000.

According to a preferred embodiment of the present invention, the transmittance of the protective film may be 80% or more. In more detail, the transmittance of the protective film may be 85% or more. In more detail, the transmittance of the protective film may be 88% or more. In more detail, the transmittance of the protective film may be 90% or more.

According to a preferred embodiment according to the present invention, the haze of the protective film may be about 10% or less. In more detail, the haze of the protective film may be about 5% or less. In more detail, the haze of the protective film may be about 2% or less.

Since the protective film according to the present invention includes the polyester resin, it may have high transmittance, high hydrolysis resistance, and high heat resistance.

In addition, in the protective film of the present invention, both the in-plane retardation and the retardation in the thickness direction are small. Therefore, when the protective film is observed from the upper side, rainbow spots and the like are not observed. Therefore, the protective film according to the present invention has improved optical properties, and thus can be optimized and applied as a protective film for a polarizing plate.

In particular, when the protective film has the in-plane retardation and thickness direction retardation as described above, the protective film may have optimal optical properties required for a polarizing plate.

The polyester protective film according to the present invention may be manufactured by the following process.

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

Extruding a polyester resin to prepare an unstretched sheet;

biaxially stretching the unstretched sheet; and

and manufacturing a polyester film by thermally fixing the biaxially stretched sheet, wherein the polyester film has an in-plane retardation of 300 nm or less and a thickness direction retardation of 3000 nm or less.

First, the polyester resin is prepared. As described above, the polyester resin may be formed by esterification and polymerization of the diol component and the dicarboxylic acid.

According to the present invention, the polyester resin is melt-extruded and cooled to prepare an unstretched sheet. Thereafter, the unstretched sheet may be stretched in a longitudinal stretching direction and a transverse stretching direction, and heat-set to prepare the protective film.

The melt extrusion is preferably made at a temperature of Tm+30 to Tm+60°C. In the melt extrusion process, when the temperature of the extruder is less than Tm+30℃, smooth melting is not achieved and the viscosity of the extruded product is increased, resulting in decreased productivity. problems may occur due to In addition, the cooling is preferably made at a temperature of 30 ℃ or less, more preferably 15 to 30 ℃ can be made.

The unstretched sheet may be stretched by biaxial stretching.

According to another embodiment according to the present invention, the unstretched sheet may be stretched in the first direction and the second direction at a similar draw ratio. For example, the unstretched sheet may be stretched by about 2.5 times to about 6 times in the first direction and from 2.5 times to 6 times in the second direction. In more detail, the unstretched sheet may be stretched from about 3.5 times to about 6 times in the first direction and from about 3.5 times to about 6 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 a tenter direction, and the second direction may be a machine direction.

According to the present invention, the protective film may be a film stretched more in the transverse stretching direction than in the longitudinal stretching direction. In more detail, the protective film may be a film stretched by about 2.5 times to about 6 times in the longitudinal stretching direction and 2.5 times to 6 times in the transverse stretching direction. In more detail, the protective film may be a film stretched by about 3.5 times to about 6 times in the longitudinal stretching direction and from about 3.5 times to about 6 times in the transverse stretching direction.

According to a preferred embodiment of the present invention, the polyester protective film may be prepared from an unstretched sheet at a draw ratio satisfying Equation 2 below.

[Equation 2]

0.8≤TD/MD≤1.4

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

According to a more preferred embodiment of the present invention, TD/MD in Equation 2 may be about 0.9 to about 1.2. More specifically, the TD/MD may be from about 0.95 to about 1.1.

According to a preferred embodiment of the present invention, the unstretched sheet is stretched 2.5 times to 6 times in the longitudinal stretching direction, and is stretched 2.5 times to 6 times in the transverse stretching direction, as a protective film satisfying Equations 1 and 2 can be manufactured.

According to a preferred embodiment of the present invention, the stretching speed in the longitudinal stretching direction may be about 6 m / min to 10 m / min, more preferably 6.5 m / min to 8.5 m / min to prepare the protective film. More specifically, it may be 6.5 m/min to 8 m/min. More specifically, the stretching speed in the longitudinal stretching direction may be about 7 m / min to about 7.8 m / min.

According to a preferred embodiment of the present invention, the stretching speed in the transverse stretching direction may be about 6 m/min to 10 m/min, more preferably 6.5 m/min to 8.5 m/min to prepare the protective film. More specifically, it may be 6.5 m/min to 8 m/min. In more detail, the stretching speed in the transverse stretching direction may be about 7 m/min to about 7.8 m/min.

According to the present invention, when the stretching speed in the longitudinal stretching direction and the transverse stretching direction is 6 m/min to 10 m/min, the polyester film may have a low retardation in the thickness direction.

That is, according to the embodiment of the present invention, by appropriately adjusting the stretching speed in the longitudinal stretching direction and the transverse stretching direction, the orientation desired in the present invention can be maintained, and the stretching speed in the longitudinal stretching direction and the transverse stretching direction and Depending on the draw ratio, optical properties suitable for the polarizing plate may be implemented.

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

According to the present invention, after starting the heat setting after stretching, the film is relaxed in the longitudinal stretching direction and/or in the 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 ℃, most preferably 210 ℃ to 240 ℃ to the protective film can be manufactured. The heat setting temperature in the heat setting step may be, for example, 220° C. to 230° C. in more detail. When the heat setting temperature is out of the above range, the thickness direction retardation of the heat-fixed polyester film becomes large, and rainbow spots may occur.

Here, the process time of the heat setting process may be about 5 seconds to about 1 minute. In more detail, the process time of the heat setting process may be about 10 seconds to about 45 minutes.

According to the present invention, when the polyester protective film for manufacturing a polarizing plate is manufactured by the manufacturing method as described above, a protective film having an appropriate thickness, in-plane retardation and thickness direction retardation can be manufactured.

In addition, the protective film of the present invention may include various additives such as conventional antistatic agents, antistatic agents, antiblocking agents and other inorganic lubricants within the range that does not impair the effects of this 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 thermal shrinkage, it is possible to efficiently protect the polarizer layer.

On the other hand, the present invention is a polarizer layer; and

a protective film adjacent to at least one of the upper and lower surfaces of the polarizer layer, wherein the protective film includes a polarizing plate containing a polyester resin, an in-plane retardation of 300 nm or less, and a thickness direction retardation of 3000 nm or less .

According to a preferred embodiment of the present invention, in the polarizing plate, the protective film protecting the polarizer has a thickness of 30 μm or less, satisfies Equations 1 and 2, and is stretched 2.5 to 6 times in the longitudinal stretching direction, , it may be a polarizing plate applied to be prepared by stretching 2.5 to 6 times in the transverse stretching direction.

According to a preferred embodiment of the present invention,

display panel; and a polarizing plate disposed on at least one of an upper surface and a lower surface of the display panel.

Including, wherein the polarizing plate is

polarizer layer; and a polyester protective film adjacent to at least one of the upper and lower surfaces of the polarizer layer.

and a display device in which the protective film includes a polyester-based resin, an in-plane retardation of 300 nm or less, and a thickness direction retardation of 3000 nm or less.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in conjunction with the accompanying drawings illustrating embodiments thereof.

1 is a cross-sectional view illustrating a polarizing plate according to an embodiment of the present invention.

Referring to FIG. 1 , the polarizing plate 11 according to the present invention may be manufactured to have a structure including a polarizer layer 220 and 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 dyed with iodine or the like. In this case, the polyvinyl alcohol molecules included in the polyvinyl alcohol layer may be aligned in one direction. The protective films 310 and 320 include a polyester resin. For example, the protective films include a polyester resin. That is, all of the protective films may include a polyester resin. Alternatively, one of the protective films may include a polyester resin, and the other may include an acrylic resin or a triacetyl cellulose resin.

As such, the protective film according to the present invention has improved optical and mechanical properties, and has low thermal shrinkage, so that when it is applied as a protective film, the polarizer layer can be efficiently protected.

Accordingly, the polarizing plate according to the present invention may have improved optical properties, mechanical properties, 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 may be used in the manufacture of a liquid crystal display (LCD).

2 is a cross-sectional view schematically illustrating a liquid crystal display device according to the present invention as an embodiment.

Referring to FIG. 2 , a liquid crystal display according to an exemplary 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 by using the 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 by using the light from the backlight unit 20 .

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

The TFT substrate 15 and the color filter substrate 13 face 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 the thin film transistors, respectively. Through this, a plurality of data lines for applying a data signal to the pixel electrodes may be included.

The color filter substrate 13 includes a plurality of color filters corresponding to respective pixels. The color filters may implement red, green, and blue colors by filtering the transmitted light. Also, 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 . In more detail, 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 may adjust the polarization direction of the light passing through the lower polarizing plate 12 . That is, the TFT substrate 15 may control a potential difference applied between the pixel electrodes and the common electrode in units of pixels. Accordingly, the liquid crystal layer 14 may be driven to have different optical characteristics in units of pixels.

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

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

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

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

As described above, the upper polarizing plate 11 and/or the lower polarizing plate 12 include a protective film having improved performance. Accordingly, the liquid crystal display according to the embodiment of the present invention may have improved luminance, image quality, and durability.

In addition, as another embodiment according to the present invention, an organic electroluminescence display may be manufactured using the polarizing plate to which the protective film of the present invention is applied.

3 is a cross-sectional view illustrating an organic EL display device according to an embodiment of the present invention.

Referring to FIG. 3 , an organic EL display device according to an embodiment of the present invention includes a front polarizing plate 16 and an organic EL panel.

The front polarizing plate 16 may be disposed on the front surface of the organic EL panel. In more detail, the front polarizing plate 16 may be adhered to a surface on which an image is displayed in the organic EL panel. The front polarizing plate 16 may have substantially the same configuration as the polarizing plate in the above-described manufacturing method.

The organic EL panel displays an image by self-luminescence in units of pixels. The organic EL panel includes an organic EL substrate 31 and a driving substrate 32 .

The organic EL substrate 31 includes a plurality of organic electroluminescent units respectively corresponding to pixels. Each of the organic electroluminescent units includes a cathode, an electron transport layer, a light emitting layer, a hole transport layer, and an anode.

The negative electrode and the positive electrode are opposite to each other. The negative electrode and the positive electrode are spaced apart from each other. At least one of the cathode and the anode is transparent. In more detail, at least one of the negative electrode and the positive electrode may include a transparent conductive oxide.

The light emitting layer, the electron transport layer, and the hole transport layer are interposed between the cathode and the anode. The electron transport layer is adjacent to the cathode, and the hole transport layer is adjacent to the anode. The emission layer is interposed between the electron transport layer and the hole transport layer. That is, the organic electroluminescent units may be disposed in the order of the cathode, the electron transport layer, the light emitting layer, the hole transport layer, and the anode.

The anode may be transparent. Examples of the material used for the anode include indium tin oxide (ITO). In addition, the cathode may include a metal having a low work function, such as aluminum. Light may be emitted through the anode, and an image may be displayed.

The electron transport layer transports electrons from the cathode to the light emitting layer. Examples of the material used for the electron transport layer include tris(8-hydroxyquinolinato)aluminium (tris(8-hydroxyquinolinato)aluminium; Alq3).

The hole transport layer transports holes from the anode to the light emitting layer. Examples of the material used as the hole transport layer include N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine)((N,N '-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine); NPB) and the like.

The light emitting layer generates light by combining electrons from the electron transport layer and holes from the hole transport layer. The emission layer may include a host and a dopant doped into the host. Examples of the material used as the host include a carbazole-based or anthracene-based organic material. In addition, examples of the material used as the dopant include a blue, green, or red fluorescent material.

The driving substrate 32 is drivably coupled to the organic EL substrate 31 . That is, the driving substrate may be coupled to apply a driving signal such as a driving current to the organic EL substrate 31 . In more detail, the driving substrate 32 may drive the organic EL substrate 31 by applying a current to each of the organic electroluminescent units.

The driving substrate 32 may include a plurality of gate wires, a plurality of data wires, and a plurality of thin film transistors.

Since the front polarizing plate 16 has improved optical properties, mechanical properties, and thermal properties, the organic EL display device according to the present embodiment may have improved luminance, image quality, and durability.

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

Examples 1 to 5

A polyethylene terephthalate resin (manufactured by SKC) was used as a material for the protective film, and the PET resin was extruded through an extruder at a temperature of about 285° C., and cast on a casting roll at about 30° C. to prepare an unstretched sheet. After preheating, the unstretched sheet was stretched at a temperature of 125° C. at a draw ratio as shown in Table 1 below, but was stretched in a longitudinal stretch direction and a transverse stretch direction, respectively. Then, the stretched sheet was heat-set for about 30 seconds at the temperature shown in Table 1 below to prepare a polyester protective film.

Comparative Examples 1 and 2

A protective film was prepared in the same manner as in Example 1, but using the same PET resin as in Example 1, an unstretched sheet was prepared, stretched at a draw ratio as shown in Table 1 below, and then heat-fixed to prepare a protective film.

division Thickness (㎛) Longitudinal stretching (machine direction) Transverse stretching (in the tenter direction) heat setting temperature
(℃) draw ratio
(Drainage) draw speed
(m/min) draw ratio
(Drainage) draw speed
(m/min) Example 1 15 3.0 7.2 3.4 7.2 220 Example 2 18 3.2 7.5 3.4 7.5 225 Example 3 20 3.0 7.5 3.4 7.5 230 Example 4 20 3.0 8.0 3.4 8.0 180 Example 5 40 3.2 15 3.4 15 220 Comparative Example 1 80 3.0 8.0 3.4 8.0 220 Comparative Example 2 90 3.2 7.0 3.4 7.0 220

Experimental example
The physical properties of Examples 1 to 5 and Comparative Examples 1 to 2 were evaluated, and the results are shown in Table 2 below.

Here, each physical property evaluation was performed as follows.

(1) In-plane phase difference (Ro)

The in-plane retardation is a parameter defined by the product (ΔNxy × d) of the refractive index anisotropy (ΔNxy=|Nx-Ny|) of the biaxial orthogonal to the film and the film thickness d (nm), indicating optical isotropy and anisotropy. is a measure The biaxial refractive index anisotropy (ΔNxy) was determined by the following method. Using two polarizing plates, the orientation axial direction of the film was calculated|required, and the rectangle of 4 cm x 2 cm was cut out so that an orientation axial direction might be orthogonal to it, and it was set as the sample for a measurement. For this sample, the refractive indices (Nx, Ny) and the refractive index (Nz) in the thickness direction of the biaxial orthogonal to the sample were determined by an Abbe refractometer (manufactured by Atago, NAR-4T, measuring wavelength 589 nm), and the biaxial refractive index The absolute value of the difference (|Nx-Ny|) was made into the anisotropy (ΔNxy) of the refractive index. The thickness d (nm) of the film was measured using an electric micrometer (manufactured by Fine Lup Corporation, Miltron 1245D), and the unit was converted into nm. The retardation (Re) was calculated|required from the product (ΔNxy×d) of the anisotropy of the refractive index (ΔNxy) and the thickness d (nm) of the film.

(2) Thickness direction retardation (Rth)

The thickness direction retardation (retardation) is a retardation obtained by multiplying the film thickness d by two birefringence ΔNxz (= | Nx-Nz |) and ΔNyz (= | Ny-Nz |) when viewed from a cross section in the film thickness direction, respectively. This parameter represents the average of the data. The thickness direction retardation (Rth) was obtained by calculating Nx, Ny, Nz and the film thickness d (nm) in the same manner as the retardation measurement, and calculating the average value of (ΔNxz × d) and (ΔNyz × d) .

(3) Observation of rainbow color blotches

A polyester film produced by the method described later on one side of a polarizer made of PVA and iodine is affixed so that the absorption axis of the polarizer and the main axis of orientation of the film are perpendicular to each other, and a TAC film (Fujifilm Co., Ltd.) on the opposite side. The company make, 80 micrometers in thickness) was affixed, and the polarizing plate was produced. The obtained polarizing plate is used as a light source (Nicia Chemical, NSPW500CS) with a white LED, which is a light emitting device that combines a blue light emitting diode and a yttrium/aluminum/garnet-based yellow phosphor, so that the polyester film is on the viewing side on the outgoing light side of the liquid crystal display device. installed. This liquid crystal display device has a polarizing plate which uses two TAC films as a polarizer protective film on the incident light side of a liquid crystal cell. It was visually observed from the front side of the polarizing plate of a liquid crystal display device, and the oblique direction, and the presence or absence of occurrence of rainbow color unevenness was judged as follows.

(double-circle) : No generation|occurrence|production of a rainbow-colored nonuniformity in any direction.

(circle): When it observes from the diagonal direction, some very light rainbow-colored nonuniformity is observed.

x: When it observes from the diagonal direction, rainbow-colored nonuniformity is observed clearly.

division In-plane retardation (nm) Thickness direction retardation (nm) Rth/Ro Appearance (Rainbow Stains) Example 1 83 2050 28 ◎ Example 2 90 2150 24 ◎ Example 3 95 2200 23 ◎ Example 4 96 2451 26 ◎ Example 5 95 3992 42 ○ Comparative Example 1 1670 6980 4 X Comparative Example 2 2310 7540 3 X

The polyester protective film according to the present invention can be applied as a polarizer protective film of a polarizing plate.

In addition, in the present invention, the polarizing plate to which the polyester protective film according to the present invention is applied as described above can be applied to a display device, for example, it can be applied to various display devices such as a liquid crystal display device and an organic light emitting display device.

[Explanation of reference numerals]

11, 12, 16 - Polarizer

220 - polarizer layer

310, 320 - protective film

13 - color filter substrate

14 - liquid crystal layer

15 - TFT substrate

31 - organic EL substrate

32 - drive board

Claims (11)

Contains a UV absorber and a polyester resin,
The transmittance is 88% or more, the haze is 5% or less,
A polyester film having a thickness of 30 μm or less and satisfying Equation 1 below:
[Equation 1]
20≤Rth/Ro≤3000
Here, Rth is the thickness direction retardation of the polyester film, and Ro is the in-plane retardation of the polyester film.
The method according to claim 1,
The Rth is 3992 nm or less, the polyester film.
The method according to claim 1,
The UV absorber comprises a benzotriazole-based UV absorber, a phenzophenone-based UV absorber or an acrylonitrile-based UV absorber.
The method according to claim 1,
The Ro is 300 nm or less, the polyester film.
The method according to claim 1,
The polyester film whose said film is a film for polarizer protection.
Extruding a polyester resin to prepare an unstretched sheet;
biaxially stretching the unstretched sheet; and
Comprising the step of heat-setting the biaxially stretched sheet to prepare a polyester film,
The step of biaxial stretching includes stretching the unstretched sheet 2.5 to 6 times in the longitudinal stretching (MD) direction, and stretching 2.5 to 6 times in the transverse stretching (TD) direction,
The polyester film includes a UV absorber and a polyester resin,
The transmittance of the polyester film is 88% or more,
The polyester film has a haze of 5% or less,
The polyester film has a thickness of 30 μm or less and satisfies the following Equation 1, a method for producing a polyester film:
[Equation 1]
20≤Rth/Ro≤3000
Here, Rth is the thickness direction retardation of the polyester film, and Ro is the in-plane retardation of the polyester film.
7. The method of claim 6,
The stretch ratio in the transverse stretch (TD) direction is larger than the stretch ratio in the longitudinal stretch (MD) direction, the method for producing a polyester film.
7. The method of claim 6,
The stretching speed in the longitudinal stretching direction is 6m/min to 10 m/min, and the stretching speed in the transverse stretching direction is 6m/min to 10 m/min, the method for producing a polyester film.
7. The method of claim 6,
The heat setting temperature in the step of heat setting is 180 ℃ to 260 ℃, the method for producing a polyester film.
polarizer; and
a polyester film adjacent to at least one of the upper and lower surfaces of the polarizer;
The polyester film has a thickness of 30 μm or less and satisfies the following Equation 1, a polarizing plate:
[Equation 1]
20≤Rth/Ro≤3000
Here, Rth is the thickness direction retardation of the polyester film, and Ro is the in-plane retardation of the polyester film.
display panel; and
a polarizing plate disposed on at least one of an upper surface and a lower surface of the display panel;
The polarizer may include a polarizer; and
a polyester film adjacent to at least one of the upper and lower surfaces of the polarizer;
The polyester film has a thickness of 30 μm or less and satisfies Equation 1 below, a display device:
[Equation 1]
20≤Rth/Ro≤3000
Here, Rth is the thickness direction retardation of the polyester film, and Ro is the in-plane retardation of the polyester film.

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