KR102413633B1 - Polyester film and flexible display apparatus comprising same - Google Patents

Abstract

When the polyester film according to an embodiment is exposed to UV light, transmittance for a specific wavelength and strain with respect to a tensile load are adjusted to a certain range, so that UV durability and flexibility can be improved at the same time. Therefore, the polyester film is applied to a cover of a flexible display device, particularly a foldable display device, so that it is possible to prevent deterioration in appearance, deformation or device defects during exposure to UV light and repeated folding due to long-term use. .

Description

Polyester film and flexible display device including the same

The embodiment relates to a polyester film having improved UV durability and flexibility, and a flexible display device including the same.

The display technology is being developed again and again due to the demand according to the development of IT devices, and technologies such as a curved display and a bent display have already been commercialized. Recently, in the field of mobile devices that require both a large screen and portability, a flexible display device that can be flexibly bent or folded according to an external force is preferred. In particular, a foldable display device is a great advantage that it can be folded down when not in use to increase portability, and when not in use, it can be unfolded to realize a large screen.

These flexible display devices mainly use a transparent polyimide film or ultra-thin glass (UTG) as a cover window, but transparent polyimide is vulnerable from external scratches and ultra-thin glass has a weak scattering prevention property. This applies. A film applied to a foldable display device continues to apply a tensile load to the film in a folded state. In this state, when the film is deformed, peeling between the constituent layers may occur.

In order to prevent this, a flexible material that does not easily deform even when a constant load is maintained for a long time, for example, an elastomer-based polymer film may be used as a protective film. However, elastomer-based polymers are difficult to control in process due to their easy-to-stick properties, and it is difficult to manufacture a flawless transparent film due to the generation of gel, which causes a sense of heterogeneity with the cover window. There is a problem that it is easily deformed due to the impact of

In addition, display devices used in mobile devices, such as mobile phones, are likely to be exposed to UV light, so a protective film is required to prevent deformation of internal components.

Korean Patent Publication No. 2017-0109746

Recently, a polyethylene terephthalate (PET) film has been considered as a protective film applied to a cover of a flexible display device, but such a polyester film has a weak problem in flexibility required for flexible display applications, that is, elastic recovery ability. In addition, since a general polyester film does not have UV durability, when it is used as a protective film for a display device, yellowing may occur or the performance of the display panel may be impaired by UV light.

On the other hand, if a large amount of a UV blocking agent is added or modified to simply increase the flexibility of the film to solve this problem, the mechanical properties and appearance properties or fairness of the polyester film may be impaired.

Accordingly, as a result of the research conducted by the present inventors, it was possible to realize a polyester film with improved UV durability and flexibility at the same time by controlling the transmittance for a specific wavelength and the strain with respect to a tensile load to a certain range when exposed to UV light.

Accordingly, an object of the embodiment is to provide a polyester film in which deformation is suppressed even after exposure to UV light and repeated folding, and a flexible display device including the same.

According to one embodiment, the total light transmittance for light having a wavelength of 370 nm is 5% or less, and after 24 hours of irradiation with UV-B light, the final tensile rate when lasting for 1 hour with a load of N2% in the in-plane first direction is A polyester film of 3% or less is provided. Here, the load of N2% is a load that stretches the film by 2% compared to the initial direction in the first direction, and the UV-B light has a peak wavelength within 310 nm to 315 nm, and the irradiance at 310 nm wavelength. ) is 0.66 W/m ² , and the total irradiation amount in the 250 nm to 400 nm wavelength band is 31.62 W/m ² .

According to another embodiment, a flexible display panel; and the polyester film disposed on the flexible display panel, a flexible display device is provided.

According to the embodiment, it is possible to provide a polyester film with improved UV durability and flexibility at the same time by controlling the transmittance for a specific wavelength and the strain for tensile load in a certain range when exposed to UV light. Therefore, the polyester film is applied to a cover of a flexible display device, particularly a foldable display device, so that it is possible to prevent deterioration in appearance, deformation or device defects during exposure to UV light and repeated folding due to long-term use. .

1A and 1B show an example of an in-folding type and an out-folding type display apparatus, respectively.
2A is an exploded perspective view of a cover from the display device;
2B shows an example of a cross-sectional view of a cover of the display device.
3 shows a spectrum of transmittance for each wavelength of light in Examples and Comparative Examples.
4 shows a method of durability testing for repeated folding.
5 shows a method of tensile testing of a polyester film.
6 shows a curve of the tensile rate according to the load applied to the polyester film.
7 and 8 show the curves of the tensile percentage (%) according to time (s) under a constant load condition after UV irradiation of the polyester films of Examples and Comparative Examples, respectively.
9 shows an example of a cross-sectional view of an organic light emitting display device.

In the description of the embodiments below, when one component is described as being formed on or below another component, one component is directly above or below another component, or another component is interposed It includes everything that is formed indirectly by

The size of each component in the drawings may be exaggerated for explanation, and may be different from the size actually applied.

In the present specification, "including" any component means that other components may be further included, rather than excluding other components, unless otherwise stated.

In addition, it should be understood that all numerical ranges indicating physical property values, dimensions, etc. of the components described in the present specification are modified by the term "about" in all cases unless otherwise specified.

In the present specification, unless otherwise specified, the expression “a” is interpreted as meaning including “a” or “plural” as interpreted in context.

Recently, foldable display devices, as shown in FIGS. 1A and 1B , are being developed into an in-folding type (1a) and an out-folding type (1b), and the polyester film applied to the cover 10 of these display devices is heated at room temperature. Since the modulus is large, deformation may occur near the repeatedly folding points p1 and p2. In addition, a general polyester film does not have UV durability, so as shown in FIG. 2a , when it is applied to the cover 10 of the display device, UV light is absorbed by the display panel 20 inside during long-term use, causing a problem in driving. can

Embodiments described below provide a polyester film with improved UV durability and flexibility by controlling the transmittance for a specific wavelength and the strain with respect to tensile load in a certain range when exposed to UV light, and a flexible display device including the same .

Characteristics of polyester film

The polyester film according to one embodiment is advantageous in preventing deformation by being applied to the cover of the display device to protect the internal components from UV light.

3 shows a spectrum of transmittance for each wavelength of light in Examples and Comparative Examples. As shown in FIG. 3 , both the Example and the comparative example show generally low transmittance in the UV wavelength band, but it can be seen that there is a difference in the curves of the Example and the comparative example in terms of transmittance at a specific wavelength.

Specifically, the curve of the example maintains a very low transmittance until the end of the UV region (370 nm), and then the transmittance rapidly increases from the boundary point (eg 380 nm), so that it is already at a significant level at the beginning of the visible light region (eg 390 nm). shows the transmittance of On the other hand, the curve of the comparative example shows a level of transmittance at the boundary point (eg 380 nm) as the transmittance gradually increases from before the end of the UV region (eg 370 nm), and up to the beginning of the visible light region (eg 390 nm). It shows a gradual rise.

As such, the polyester film may exhibit a transmittance of a specific value or less at wavelengths of 370 nm and 380 nm, and may exhibit a transmittance of a specific value or more at a visible light wavelength such as 390 nm.

For example, the polyester film may have a total light transmittance of 10% or less, 7% or less, 5.5% or less, 5% or less, 4.5% or less, or 4% or less for light having a wavelength of 370 nm. The polyester film according to an embodiment has a total light transmittance of 5% or less for light having a wavelength of 370 nm.

In addition, the polyester film may have a total light transmittance of 30% or less, 25% or less, 22% or less, 20% or less, 15% or less, or 10% or less for light having a wavelength of 380 nm. Specifically, the polyester film may have a total light transmittance of 20% or less for light having a wavelength of 380 nm.

In addition, the polyester film may have a total light transmittance of 45% or more, 50% or more, 55% or more, 60% or more, or 65% or more for light having a wavelength of 390 nm. For example, the polyester film may have a total light transmittance of 50% to 90%, 55% to 85%, or 60% to 80% for light having a wavelength of 390 nm. In addition, the polyester film may have a total light transmittance of 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more for light having a wavelength of 550 nm. As a specific example, the polyester film may have a total light transmittance of 55% or more for light of a wavelength of 390 nm, and a total light transmittance of 85% or more for light of a wavelength of 550 nm.

As a specific example, the polyester film has a total light transmittance of 2% to 5.5% for light of a wavelength of 370 nm, a total light transmittance of 9.5% to 22% for light of a wavelength of 380 nm, 65% with respect to light of a wavelength of 390 nm It may have a total light transmittance of 85% to 85%, and a total light transmittance of 85% to 95% for light having a wavelength of 550 nm.

The polyester film may have an average rate of change of total light transmittance (%) at a wavelength of 370 nm to 375 nm of 0.1%/nm to 1%/nm, and total light transmittance (%) at a wavelength of 385 nm to 390 nm The rate of change may be an average of 3%/nm to 10%/nm.

In addition, in the polyester film according to the embodiment, the strain with respect to the tensile load is controlled in a certain range even after exposure to UV light. Accordingly, the polyester film may be applied to the cover of the flexible display device to maintain original characteristics during repeated folding even when exposed to external UV light. The UV light may be, for example, UV-B light, and a specific wavelength range of the UV-B light may be about 280 nm to 315 nm. Specifically, the UV-B light has a peak wavelength of 310 nm to 315 nm, and an irradiance at a wavelength of 310 nm is about 0.66 W/m ² (eg, 0.6 to 0.7 W/m ² ), 250 The total irradiation amount in the nm to 400 nm wavelength band is about 31.62 W/m ² (eg, 31.6 to 31.7 W/m ² ).

The polyester film according to the embodiment, after 24 hours of irradiation with UV-B light, has a final tensile rate of 3% or less for 1 hour under a load of N2% in the first direction in-plane, wherein the load of N2% is a load that stretches the film in the first direction by 2% compared to the initial amount. Specifically, the tensile rate may be measured at room temperature with an initial dimension of 50 mm (initial distance between points to which a tensile load is applied) of the film in the first direction and a dimension of 15 mm in a direction perpendicular thereto.

More specifically, the polyester film (1) a film having an initial dimension of 50 mm in a first direction in plane and a dimension of 15 mm in a direction perpendicular thereto is stretched in the first direction by 2% compared to the initial dimension After first measuring the load (N2%) at the time, (2) when the load (N2%) is continuously applied in the first direction of the film for 1 hour, the ratio of the increased dimension to the initial dimension of the film, that is, the final tensile rate is less than 3%.

As an example, the polyester film may have a final tensile rate of 3% or less, 2.7% or less, 2.5% or less, or 2.3% or less after 24 hours of irradiation of UV-B light with a load of N2% for 1 hour. For example, the polyester film has a final tensile rate for 1 hour under a load of N2% after 24 hours of irradiation with UV-B light, 1.5% to each of the first and second directions perpendicular to each other in-plane 3%, 2% to 3%, 2.3% to 3%, 2% to 2.7%, or 2% to 2.5%. Specifically, the polyester film has a final tensile rate when lasting for 1 hour with a load of N2% after 24 hours of irradiation with UV-B light, 2% to 3 for each of the first and second directions perpendicular to each other in-plane It can be %.

As another example, the polyester film may have a final tensile rate of 2% or less when irradiated with UV-B light for 24 hours under a load of N1% in the in-plane first direction for 1 hour. Here, the N1% load is a load that stretches the film in the first direction by 1% compared to the initial load. For example, the polyester film may have a final tensile rate of 1.7% or less, 1.5% or less, or 1.3% or less when irradiated with UV-B light for 24 hours and maintained for 1 hour under the load of N1%. Specifically, the polyester film has a final tensile rate when lasting for 1 hour with a load of N1% after 24 hours of irradiation with UV-B light, 1.1% to 2, respectively, for the first and second directions perpendicular to each other in-plane %, 1.3% to 2%, 1.5% to 2%, 1.1% to 1.7%, or 1.1% to 1.5%. The tensile rate may be measured at room temperature with an initial dimension of 50 mm in the first direction and 15 mm in a direction perpendicular thereto.

As another example, the polyester film may have a final tensile rate of 7% or less when irradiated with UV-B light for 24 hours under a load of N3% in the in-plane first direction for 1 hour. Here, the N3% load is a load that stretches the film in the first direction by 3% compared to the initial load. For example, the polyester film has a final tensile rate of 6.7% or less, 6.5% or less, 6.3% or less, 6% or less, or 5.7% or less. Specifically, the polyester film has a final tensile rate when lasting for 1 hour with a load of N3% after 24 hours of irradiation with UV-B light, 3% to 7, respectively, for the first and second directions perpendicular to each other in-plane %, 5% to 7%, 5% to 6%, 5.5% to 6.5%, or 6% to 7%. The tensile rate may be measured at room temperature with an initial dimension of 50 mm in the first direction and a dimension of 15 mm in a direction perpendicular thereto.

As a specific example, after the polyester film is irradiated with UV-B light for 24 hours, the final tensile rate is 2% or less at a time of 1 hour under a load of N1% in the in-plane first direction, and the in-plane first direction is The final tensile rate may be 7% or less when the N3% load lasts for 1 hour. Here, the loads of N1% and N3% are loads that stretch the film by 1% and 3%, respectively, in the first direction compared to the initial load.

The first direction may be any direction in-plane of the polyester film, and the second direction may be determined as a direction perpendicular to the first direction and in-plane. For example, the first direction may be a longitudinal direction (MD) or a width direction (TD) of the film, and the second direction may be a width direction (TD) or a longitudinal direction (MD) perpendicular thereto. Specifically, the first direction may be a longitudinal direction (MD) of the film, and the second direction may be a width direction (TD) of the film.

6 shows a curve of the tensile rate (%) according to the load (N) applied to the polyester film. The loads of N1%, N2%, and N3% may be determined from the tensile rate curve according to the load, respectively. Specifically, in the polyester film, the load of N1% may be 28 N to 32 N, the load of N2% may be 50 N to 55 N, and the load of N3% may be 64 N to 68 N. can

7 and 8 show the curves of the tensile percentage (%) according to time (s) under a constant load condition after UV irradiation of the polyester films of Examples and Comparative Examples, respectively. As such, the polyester film of the embodiment has a final tensile rate of 2% or less when the N1% load is applied for 1 hour, and a final tensile rate of 3% or less when the N2% load is applied for 1 hour or less, and the N3 While the final tensile rate at a time duration of 1 hour with a load of % was 7% or less, the polyester film of Comparative Example was out of the above tensile property range.

A ratio of the N2% load and the N1% load may be 1.6:1 to 2.1:1. Specifically, the ratio of the N2% load and the N1% load may be 1.75:1 to 1.95:1. In addition, the ratio of the N3% load and the N2% load may be 1.2:1 to 1.5:1. Specifically, the ratio of the N3% load and the N2% load may be 1.20:1 to 1.35:1.

In addition, since the polyester film has excellent UV blocking properties, when two overlapping sheets are irradiated with UV-B light on the surface of one film for 24 hours, the physical properties of the other film disposed below it may not be reduced .

As an example, after overlapping two polyester films and irradiating UV-B light on one film for 24 hours, the final tensile rate when the load of N2% is maintained for 1 hour with respect to the first in-plane direction of the other film This may be 3% or less.

As another example, after overlapping two sheets of the polyester film and irradiating UV-B light on one film for 24 hours, the breaking elongation of the other film may be 80% or more, for example 85% or more, 100% or more , 120% or more, 125% or more, or 135% or more, and specifically 80% to 200%, 100% to 180%, or 135% to 160%. More specifically, after overlapping two layers of the polyester film and irradiating UV-B light on one film for 24 hours, the elongation at break in the longitudinal direction (MD) of the other film is 125% or more, and the transverse direction (TD) ) may have an elongation at break of 85% or more. Here, the elongation at break means a tensile rate at break of the film at room temperature, and the tensile rate may be measured at room temperature with an initial dimension of 50 mm in a tensile direction of the film and a dimension of 15 mm in a direction perpendicular thereto.

In addition, the polyester film has a number of repeated folding under the condition of a curvature radius of 1.5 mm until whitening or cracking after 24 hours of irradiation with UV-B light, 100 or more, 1000 or more, 10,000 or more, 50,000 or more, It may be 100,000 or more, 150,000 or more, or 200,000 or more. Specifically, in the polyester film, the number of repeated folding until whitening or cracking may be 200,000 or more. When it is within the above range, even when exposed to UV light, deformation does not occur in repeated folding, so that it is advantageously applied to a flexible display device. Due to these characteristics, the protective film may be applied to a cover of a flexible display device, particularly a cover of a foldable display device, and deterioration of properties due to repeated folding may be prevented even when exposed to UV light.

The polyester film is preferably biaxially stretched in terms of flexibility and elastic recovery. In this case, the ratio between the respective draw ratios for the biaxial may be 1:0.5 to 1:1.5, 1:0.7 to 1:1.3, or 1:0.8 to 1:1.2. Specifically, the polyester film may be biaxially stretched, and a ratio between the respective draw ratios for the biaxiality may be 1:0.8 to 1:1.2. When the draw ratio is within the range, it may be more advantageous to have flexibility in which deformation does not occur even when a constant load is continued for a long time.

The polyester film may be biaxially stretched in a first in-plane direction and in a second in-plane direction perpendicular to the first direction. In this case, the first direction stretching ratio may be 2.0 to 5.0, specifically 2.8 to 3.5, or 3.3 to 3.5. In addition, the stretch ratio in the second direction may be 2.0 to 5.0, specifically 2.9 to 3.7, or 3.5 to 3.8. Specifically, the polyester film may be biaxially stretched with a longitudinal stretch ratio of 3.3 to 3.5, and a transverse stretch ratio of 3.5 to 3.8. In addition, the ratio (d2/d1) of the second direction draw ratio (d2) to the first direction draw ratio (d1) may be 1.2 or less, for example, 1.0 to 1.2, 1.0 to 1.1, 1.0 to 1.15, or 1.05 to It can be 1.1.

The thickness of the polyester film is 10 μm to 500 μm, 10 μm to 300 μm, 10 μm to 100 μm, 10 μm to 80 μm, 20 μm to 80 μm, 30 μm to 80 μm, 40 μm to 60 μm, or It may be 10 μm to 30 μm. For example, when the polyester film is applied as a protective film to the cover of the display device, it may have a thickness of 10 μm to 80 μm. As an example, when the polyester film is applied as a front protective film of the cover, it may have a thickness of 20 μm to 80 μm. As another example, when the polyester film is applied as a back protection film of a transparent substrate, it may have a thickness of 30 μm or less, specifically 10 μm to 30 μm.

Composition of polyester film

The polyester film includes a polyester resin.

The polyester resin may be a homopolymer resin or a copolymer resin in which dicarboxylic acid and diol are polycondensed. In addition, the polyester resin may be a blend resin in which the homopolymer resin or copolymer resin is mixed.

Examples of the dicarboxylic acid 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-cyclo Hexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2 ,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid trimethyladipic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, dodecadicarboxylic acid, and the like.

In addition, examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, and the like.

Preferably, the polyester resin may be an aromatic polyester resin having excellent crystallinity, and for example, a polyethylene terephthalate (PET) resin may be a main component.

As an example, the polyester film may include about 85% by weight or more of a polyester resin, specifically, a PET resin, and more specifically, 90% by weight or more, 95% by weight or more, or 99% by weight or more. As another example, the polyester film may further include another polyester resin in addition to the PET resin. Specifically, the polyester film may further include a polyethylene naphthalate (PEN) resin in an amount of about 15% by weight or less. More specifically, the polyester film may further include about 0.1 wt% to 10 wt%, or about 0.1 wt% to 5 wt% of PEN resin.

According to the composition, the degree of crystallinity may increase in a manufacturing process in which the polyester film undergoes heating, stretching, etc., and mechanical properties such as tensile strength may be improved.

The polyester film according to an embodiment includes a UV blocking agent.

The content of the UV blocking agent in the polyester film may be 0.5 parts by weight or more, 0.7 parts by weight or more, 0.9 parts by weight or more, 1.1 parts by weight or more, or 1.3 parts by weight or more, based on 100 parts by weight of the polyester resin. In addition, the content of the UV blocking agent in the polyester film may be 2.4 parts by weight or less, 2.2 parts by weight or less, 2.0 parts by weight or less, 1.8 parts by weight or less, or 1.6 parts by weight or less, based on 100 parts by weight of the polyester resin.

As an example, the polyester film may include 100 parts by weight of a polyester resin; and 0.7 parts by weight to 2.0 parts by weight of a UV blocker. When it is within the above range, it is advantageous in preventing the problem of poor appearance due to migration of the UV additive to the surface during or after the manufacturing process or manufacturing of the film while having blocking performance for the UV region.

On the other hand, if the UV blocking agent does not have sufficient heat resistance, it may be mixed into the polyester resin and decomposed in a significant amount during extrusion at high temperature, which may adversely affect the UV blocking property of the film. Accordingly, it is preferable that the UV blocking agent has a weight reduction rate of the polyester resin at a melting temperature of a certain level or less. For example, the UV blocking agent is maintained for 1 hour in an air atmosphere at 280 ° C. The weight loss may be 20% or less, 15% or less, or 10% or less. Specifically remind The UV blocking agent may have a weight reduction rate of 15% or less after maintaining for 1 hour in an air atmosphere at 280° C. under isothermal conditions of a thermogravimetric analyzer (TGA). More specifically, the weight reduction rate may be 1% to 15%, 5% to 15%, or 10% to 15%.

The specific type of the UV blocking agent is not particularly limited, but for example, at least one UV blocking agent selected from the group consisting of benzophenone-based, benzotriazole-based, triazine-based, malonic acid ester-based, benzoate-based and benzoxazinone-based UV blocking agents can be the best

As an example, the UV blocker may be a benzoxazinone-based UV blocker, and specifically, may have one or more benzoxazinone groups, and more specifically, two benzoxazinones linked through an unsaturated hydrocarbon chain or an aromatic ring. You can have groups.

As an example, the UV blocking agent may be one or more compounds having a structure of Formula 1 below:

[Formula 1]

In the above formula, R ₁ and R ₂ are each independently hydrogen, alkyl, or alkenyl, and L is a single bond or a hydrocarbon chain, hydrocarbon ring or heterocycle having one or more unsaturated bonds.

The alkyl may be an alkyl having 1 to 6 carbon atoms, and the alkenyl may be an alkenyl having 2 to 6 carbon atoms. The hydrocarbon chain may have 2 to 10 carbon atoms, the hydrocarbon ring may have 6 to 20 carbon atoms, and the hetero ring is a 5 to 20 membered ring containing one or more heteroatoms selected from N, S and O can be In addition, the hydrocarbon ring or hetero ring may be an aromatic ring, for example, the hydrocarbon ring may be a benzene ring, the hetero ring may be a pyridine ring.

The L may be a group forming a conjugation structure with two benzooxazinone groups connected thereto.

Method for producing polyester film

Such a polyester film, using a resin composition in which a UV blocking agent is mixed, can be manufactured by a process including biaxial stretching with a controlled stretch ratio and heat treatment at a specific temperature. In particular, the method for producing the polyester film includes a step of forming a film with a resin composition, biaxially stretching and heat-treating, and obtaining a film having a final tensile rate of 3% or less when lasting 1 hour under a load of N2%. At this time, the composition and process conditions are adjusted so that the polyester film finally manufactured by the above method satisfies the tensile properties described above. Specifically, in order for the final polyester film to satisfy the above properties, the extrusion and casting temperature of the polyester resin is adjusted, the preheating temperature during stretching, the stretching ratio for each direction, the stretching temperature, the moving speed, etc. are adjusted, or after stretching It is possible to control the heat treatment temperature and relaxation rate while performing heat treatment and relaxation.

Hereinafter, each step will be described in more detail.

First, a resin composition is prepared by adding a UV blocking agent to the polyester resin. At this time, the composition of the polyester resin, the type and amount of the UV blocking agent are as exemplified above. Thereafter, the resin composition is melted and extruded to be cast into a film. The extrusion may be performed at a temperature of 230°C to 300°C, or 250°C to 280°C.

The film may be preheated at a predetermined temperature before stretching. The range of the preheating temperature satisfies the range of Tg+5℃ to Tg+50℃ based on the glass transition temperature (Tg) of the polyester resin, and at the same time, it is determined to be a range that satisfies the range of 70℃ to 90℃ can When it is within the above range, it is possible to effectively prevent the film from breaking during stretching while securing flexibility for easy stretching of the film.

The stretching is carried out by biaxial stretching, for example, it can be stretched biaxially in the longitudinal direction (i.e. machine direction) (MD) and in the width direction (i.e. tenter direction) (TD) through a simultaneous biaxial stretching method or a sequential biaxial stretching method. have. Preferably, a sequential biaxial stretching method of stretching in one direction first and then stretching in a direction perpendicular to the direction may be performed. The stretching speed may be 6.5 m/min to 8.5 m/min, but is not particularly limited.

The lengthwise stretch ratio may be 2.0 to 5.0, specifically 2.8 to 3.5, or 3.3 to 3.5. In addition, the width direction stretch ratio may be 2.0 to 5.0, specifically 2.9 to 3.7, or 3.5 to 3.8. When it is within the above preferred range, it may be more advantageous to uniform the thickness. In addition, it is preferable to adjust the load applied during stretching in each direction so that the difference in refractive index in each direction is minimized while measuring the refractive index in order to balance the longitudinal direction MD and the width direction TD. In addition, the ratio (d2/d1) of the stretch ratio in the width direction (d2) to the stretch ratio in the longitudinal direction (d1) may be 1.2 or less, for example, 1.0 to 1.2, 1.0 to 1.1, 1.0 to 1.15, or 1.05 to 1.1. have. The said draw ratios (d1, d2) are ratios which show the length after extending|stretching, when the length before extending|stretching is made into 1.0.

Thereafter, the stretched film is subjected to a heat treatment step. The heat treatment may be performed at a temperature of 180 °C or higher, specifically 195 °C or higher, and more specifically 195 °C to 230 °C. The heat treatment may be performed for 0.2 minutes to 1 minute, and more specifically, may be performed for 0.4 minutes to 0.7 minutes.

In addition, after starting the heat treatment, the film may be relaxed in the longitudinal direction and/or the width direction, and the temperature range at this time may be 150°C to 250°C. The relaxation may be performed at a relaxation rate of 1% to 10%, 2% to 7%, or 3% to 5%. In addition, the relaxation may be performed for 1 second to 1 minute, 2 seconds to 30 seconds, or 3 seconds to 10 seconds.

In addition, the film may be cooled after the heat treatment, and the cooling may be performed at a temperature lower than 50° C. to 150° C. compared to the heat treatment temperature.

laminated sheet

2B shows an example of a cross-sectional view of a cover of the display device. Referring to FIG. 2B , protective films 100a and 100b are laminated on both sides of the transparent substrate 200 in the cover 10 of the display device through the adhesive layer 300 , respectively. As the cover 10 of such a display device, a sheet in which a polyester film is laminated on both sides of a transparent substrate may be used.

A laminated sheet according to an embodiment includes a transparent substrate; a first polyester film disposed on one surface of the transparent substrate; and a second polyester film disposed on the other surface of the transparent substrate. In the laminated sheet, the first polyester film includes a UV blocking agent, and the second polyester film includes or does not include a UV blocking agent.

Since the laminated sheet includes the above-described UV-blocking polyester film, it may have an equivalent to similar UV-blocking property.

For example, the laminated sheet may have a total light transmittance of 10% or less, 7% or less, 5% or less, 4.5% or less, or 4% or less for light having a wavelength of 370 nm. In addition, the laminated sheet may have a total light transmittance of 30% or less, 25% or less, 20% or less, 15% or less, or 10% or less with respect to light having a wavelength of 380 nm. As a specific example, the laminated sheet may have a total light transmittance of 5% or less with respect to light of a wavelength of 370 nm and a total light transmittance of 20% or less of light of a wavelength of 380 nm. When within the above range, the laminated sheet is advantageous in preventing deformation by protecting internal components from UV light as a cover of the display device.

In addition, the laminated sheet may have a total light transmittance of 45% or more, 50% or more, 55% or more, 60% or more, or 65% or more with respect to light having a wavelength of 390 nm. For example, the laminated sheet may have a total light transmittance of 50% to 90%, 55% to 85%, or 60% to 80% for light having a wavelength of 390 nm. In addition, the laminated sheet may have a total light transmittance of 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more with respect to light having a wavelength of 550 nm. As a specific example, the laminated sheet may have a total light transmittance of 55% or more with respect to light having a wavelength of 390 nm and a total light transmittance of 85% or more with respect to light of a wavelength of 550 nm.

In addition, after irradiating the laminated sheet with UV-B light for 24 hours, the number of repeated folding under the condition of a curvature radius of 1.5 mm until delamination occurs is 100 or more, 1000 or more, 10,000 or more, 50,000 or more, 100,000 times or more. or more, 150,000 or more, or 200,000 or more. Specifically, in the polyester film, the number of repeated folding until delamination occurs may be 200,000 or more. When it is within the above range, even when exposed to UV light, deformation does not occur in repeated folding, so that it is advantageously applied to a flexible display device.

In addition, the total content of the UV blocking agent in the laminated sheet is 0.5 parts by weight or more, 0.7 parts by weight or more, 0.9 parts by weight or more, 1.1 parts by weight or more, or 1.3 parts by weight, based on 100 parts by weight of the polyester resin included in the laminated sheet. It can be more than wealth. In addition, the total content of the UV blocking agent in the laminated sheet is 2.4 parts by weight or less, 2.2 parts by weight or less, 2.0 parts by weight or less, 1.8 parts by weight or less, or 1.6 parts by weight or less, based on 100 parts by weight of the polyester resin included in the laminated sheet. It may be less than or equal to parts by weight. Specifically, the total content of the UV blocking agent included in the first polyester film and the second polyester film is 0.7 relative to the total of 100 parts by weight of the polyester resin in the first polyester film and the second polyester film It may be in an amount of from 2.0 parts by weight to 2.0 parts by weight.

As an example, both the first polyester film and the second polyester film may include a UV blocking agent. In this case, the content of the UV blocking agent in the first polyester film or the second polyester film is 0.5 parts by weight or more, 0.7 parts by weight or more, 0.9 parts by weight, based on 100 parts by weight of the polyester resin included in each polyester film. parts by weight or more, 1.1 parts by weight or more, or 1.3 parts by weight or more. In addition, the content of the UV blocking agent in the first polyester film or the second polyester film is 2.4 parts by weight or less, 2.2 parts by weight or less, 2.0 parts by weight or less, relative to 100 parts by weight of the polyester resin included in each polyester film parts by weight or less, 1.8 parts by weight or less, or 1.6 parts by weight or less. As another example, the second polyester film may include no or a trace amount of a UV blocker, in which case the content of the UV blocker in the second polyester film is 100 of the polyester resin included in the second polyester film. It may be less than 0.5 parts by weight, or less than 0.1 parts by weight relative to parts by weight.

The thickness of the first polyester film and the second polyester film is each 10 μm to 500 μm, 10 μm to 300 μm, 10 μm to 100 μm, 10 μm to 80 μm, 20 μm to 80 μm, 40 μm to 60 μm, or 10 μm to 30 μm. For example, the first polyester film may have a thickness of 20 μm to 80 μm, and the second polyester film may have a thickness of 30 μm or less.

The transparent substrate may be a cover window of the display device. The transparent substrate may be a polymer film or a glass substrate. Specifically, the transparent substrate may be a transparent polyimide film or ultra-thin glass (UTG).

As an example, the transparent substrate may include a polyimide-based resin. Specifically, the transparent cover may be a polyimide-based film.

The polyimide-based film includes a polyimide-based polymer, and the polyimide-based polymer is formed by polymerizing a diamine compound, a dianhydride compound, and optionally a dicarbonyl compound.

The polyimide-based polymer is a polymer including an imide repeating unit. In addition, the polyimide-based polymer may optionally include an amide repeating unit. The polyimide-based polymer may be formed by simultaneously or sequentially reacting reactants including a diamine compound and a dianhydride compound. Specifically, the polyimide-based polymer is formed by polymerization of a diamine compound and a dianhydride compound. Alternatively, the polyimide-based polymer may be formed by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound. In this case, the polyimide-based polymer includes an imide repeating unit derived from polymerization of a diamine compound and a dianhydride compound and an amide repeating unit derived from polymerization of the diamine compound and a dicarbonyl compound.

The diamine compound may be, for example, an aromatic diamine compound having an aromatic structure. Specifically, the diamine compound may include 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), but is not limited thereto.

The dianhydride compound may be an aromatic dianhydride compound having an aromatic structure or an alicyclic dianhydride compound having an alicyclic structure. Specifically, the dianhydride compound may include 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), but is not limited thereto.

The dicarbonyl compound may be an aromatic dicarbonyl compound having an aromatic structure. The dicarbonyl compound may include terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), isophthaloyl chloride (IPC), or a combination thereof. However, the present invention is not limited thereto.

The diamine compound and the dianhydride compound may be polymerized to produce a polyamic acid. Subsequently, the polyamic acid may be converted into polyimide through a dehydration reaction, and the polyimide includes an imide repeating unit.

For example, the polyimide may include a repeating unit represented by the following Chemical Formula A-1, but is not limited thereto.

<Formula A-1>

In Formula A-1, n is, for example, an integer of 1 to 400.

In addition, the diamine compound and the dicarbonyl compound may be polymerized to form an amide repeating unit represented by Formulas B-1 to B-3.

<Formula B-1>

In Formula B-1, x is, for example, an integer of 1 to 400.

<Formula B-2>

In Formula B-2, y is, for example, an integer of 1 to 400.

<Formula B-3>

In Formula B-3, y is, for example, an integer of 1 to 400.

The thickness of the transparent substrate may be 20 μm to 500 μm, 30 μm to 300 μm, or 40 μm to 100 μm.

The transparent substrate may have a surface hardness of HB or more and a light transmittance of 80% or more at a wavelength of 550 nm. In addition, the transparent substrate may have a yellowness of 5 or less and a haze of 2% or less based on a thickness of 50 μm.

The laminated sheet may further include an adhesive layer between the transparent substrate and the first polyester film, and between the transparent substrate and the second polyester film. The thickness of the adhesive layer may be 1 μm to 50 μm, 3 μm to 30 μm, 5 μm to 20 μm, 5 μm to 15 μm, 7 μm to 12 μm, or 8 μm to 12 μm. The adhesive layer may include an adhesive resin, and may further include a curing agent and/or a photoinitiator. The adhesive resin is not particularly limited, but may be, for example, a resin that can be cured by UV light irradiation, and thus the adhesive layer may be manufactured through UV curing. In addition, the adhesive resin may be a resin that is not yellowed by UV light and has good dispersibility of the UV absorber. For example, the adhesive resin may include a polyester resin, an acrylic resin, an alkyd resin, and an amino resin. The adhesive resin may be used alone, or two or more types of copolymers or mixtures may be used. Among them, an acrylic resin excellent in optical properties, weather resistance, adhesion to a substrate, and the like is preferable. In addition, the adhesive resin may be an optical clear adhesive (OCA).

In addition, the laminated sheet may further include one or more coating layers disposed on the first polyester film or the second polyester film. The coating layer may be disposed between the polyester film and the transparent substrate, or disposed on the outer surface of the protective film. The coating layer may be a functional coating layer for hardness improvement, antistatic, scattering prevention, refractive index control, surface protection, and the like.

flexible display device

The flexible display device according to an embodiment includes the polyester film or the laminated sheet described above in a cover.

A flexible display apparatus according to an embodiment includes a flexible display panel; and the polyester film disposed on the flexible display panel. A flexible display device according to another embodiment includes a flexible display panel; and the laminated sheet disposed on the flexible display panel.

The polyester film or laminated sheet included in the flexible display device has substantially the same configuration and characteristics as the polyester film or laminated sheet described above.

The flexible display device may be a foldable display device. Specifically, the foldable display device may be an in-folding type or an out-folding type according to a folding direction. Referring to FIGS. 1A and 1B , the foldable display device may be of an in-folding type (1a) in which the screen is located inside the folding direction, and an out-folding type (1b) in which the screen is located outside in the folding direction. have.

In a material applied to a flexible display device, a property that is as important as flexibility is that the original property does not deteriorate even after frequent bending or folding. Since it is almost impossible to return to the original shape due to the fact that common materials are completely folded and then unfolded, it is necessary to have specificity to overcome these limitations in the development of materials applied to flexible display devices.

Specifically, with reference to FIG. 1A , in the case of the in-folding type 1a, due to the deformation due to the load applied to the inward folding point p1, and also referring to FIG. 1B, in the case of the out-folding type 1b Whitening or cracks may occur in the cover 10 due to deformation due to a load occurring at the outwardly folding point p2, and thus properties may be easily deteriorated. Such whitening and cracking can be generally solved when the modulus of the protective film is low at room temperature, but a conventional polyester film generally has a large modulus at room temperature, so whitening and cracking easily occur when applied to a flexible display device. there is

However, the polyester film according to the embodiment can implement the properties required for the cover of the flexible display by controlling the strain with respect to the tensile load during UV irradiation to a specific range, and as a result, the polyester film according to the embodiment and the same The laminated sheet may be applied to the cover of the flexible display device to maintain its original properties even during multiple repeated folding in a UV exposure environment.

In the flexible display device, the flexible display panel may be, specifically, an organic light emitting display (OLED) panel. 9 is a cross-sectional view schematically illustrating an example of an organic light emitting display device 1 ′ including an organic light emitting display panel 20 - 2 . Referring to FIG. 9 , the organic light emitting display device 1 ′ includes a front polarizing plate 20 - 1 and an organic light emitting display panel 20 - 2 . The front polarizing plate may be disposed on the front surface of the organic light emitting display panel. More specifically, the front polarizing plate may be adhered to a surface on which an image is displayed in the organic light emitting display panel. The organic light emitting display panel displays an image by self-luminescence in units of pixels. The organic light emitting display panel includes an organic light emitting substrate and a driving substrate. The organic light emitting substrate includes a plurality of organic light emitting units respectively corresponding to pixels. Each of the organic light emitting units includes a cathode, an electron transport layer, a light emitting layer, a hole transport layer, and an anode. The driving substrate is drivably coupled to the organic light emitting substrate. That is, the driving substrate may be coupled to apply a driving signal such as a driving current to the organic light emitting substrate. More specifically, the driving substrate may apply a current to each of the organic light emitting units to drive the organic light emitting substrate.

Hereinafter, more specific embodiments will be described, but the scope of implementation is not limited thereto.

Evaluation example of UV blocker

Thermogravimetric analyzer (TGA) evaluation was performed to select a UV blocker with excellent processing efficiency even at the processing temperature of polyethylene terephthalate (PET) resin. The suitability of the UV blocker was judged as PASS if the weight loss did not exceed 15% after maintaining for 1 hour under an isothermal condition of 280° C. under an air atmosphere using Q500 equipment from TA Instruments, and FAIL otherwise.

division designation TGA evaluation result UV Blocker 1 Benzophenone-3 FAIL UV Blocker 2 Phenol, 2-(2H-benzotriazol-2-yl)-4-methyl FAIL UV Blocker 3 2,2'-(1,4-Phenylene)bis(4H-3,1-benzoxazin-4-one) PASS

Preparation example of polyester film

A composition in which a UV blocking agent as shown in the following table was added to a polyethylene terephthalate (PET) resin as shown in Table 2 below was extruded at 280° C. and then cast in a film shape through a T-die. The cast film was preheated at 100° C. and stretched 3.0 times in the longitudinal direction (MD) and 3.3 times in the transverse direction (TD). At this time, the extending|stretching temperature was made into 130 degreeC. Thereafter, the stretched film was heat-set at 200° C., relaxed by 3%, and then cooled to prepare a polyester film having a thickness of 60 μm. In addition, as a comparative example, a polyester film was prepared in the same manner as before without adding a UV blocking agent.

division PET resin composition Types of UV Blockers UV blocker content (parts by weight) film A1 Comparative Example 1 - - film A2 Comparative Example 2 UV Blocker 1 1.3 film B1 Example 1 UV Blocker 3 1.1 film B2 Example 2 UV Blocker 3 1.6 film B3 Example 3 UV Blocker 3 0.9 film B4 Example 4 UV Blocker 3 0.8 film B5 Example 5 UV Blocker 3 0.8 * UV blocker content: parts by weight of solid content of UV blocker added per 100 parts by weight of PET resin

Experimental example of total light transmittance

The total transmittance was measured for the polyester film sample as follows.

- Measuring equipment: Hunterlab's Ultrascan pro Colorimeter

- Measurement procedure: ASTM D1003

- Light source: D65/10

- Diffusion angle: 8°

The results are shown in the table below.

division Total light transmittance (%) 370 nm 380 nm 390 nm 550 nm film A1 Comparative Example 1 75 81 87.8 93.2 film A2 Comparative Example 2 5.8 18.5 72.1 92.9 film B1 Example 1 3.81 11.5 70.7 93.2 film B2 Example 2 3.5 9.7 71.3 92.9 film B3 Example 3 3.9 16.5 68.7 92.9 film B4 Example 4 3.98 19.1 70.9 93.1 film B5 Example 5 3.97 19.6 71.1 93.2

Experimental example of tensile rate

The tensile rate was measured for the polyester film. Referring to FIG. 5 , four rectangular specimens 101 adjacent to each other at a distance w of 15 mm in the polyester film 100 are cut, and the specimen 101 is placed on the jig 21 of the test equipment 2 . ) was fixed at both ends. Thereafter, the tensile rate was measured according to the following conditions and procedures.

- initial dimension in tension direction 50 mm

- dimension in the direction perpendicular to the direction of tension 15 mm

- Test temperature: room temperature (25℃)

- Test equipment: Instron's UTM 5566A

- Tensile speed: 50 mm/min

- Tensile direction: length direction (MD) or width direction (TD) of the polyester film

(1) Measurement of load by initial tensile rate

First, each load that stretches the specimen by 1%, 2%, or 3% relative to its initial dimension was first measured.

(2) Measurement of the final tensile rate under continuous load

Then, after maintaining the previously measured load to be applied to the specimen uniformly for 1 hour, the final tensile rate (%) compared to the initial specimen dimension was measured.

(3) The procedure of (1) and (2) above was performed for 4 specimens, and the average value was taken. The results are summarized in the table below.

Experimental example of tensile rate after UV irradiation

The tensile rate was measured after UV irradiation under the following conditions.

(a) UV irradiation

- UV equipment: Q-lab's QUV Tester

- UV lamp: UVB-313

- UV dose: 0.66 W/m ² @310 nm

- UV total dose: 31.62 W/m ² @250-400 nm

- UV irradiation time: 24 hours

(b) The tensile rate of the UV-irradiated specimen was measured in the same manner as before.

The results are summarized in the table below.

Experimental example of elongation at break after UV irradiation by laminating two sheets

Two sheets of the same polyester film were laminated, and after UV irradiation toward one side of the film, the elongation at break of the film located on the opposite side was measured. At this time, UV irradiation was performed in the same manner as before, and the elongation at break was measured while the specimen was stretched with the same equipment and conditions as the previous measurement of tensile rate. The results are summarized in the table below.

division Early
tensile rate
(%) Tensile rate (%) after 1 hour stacking two
After UV-B irradiation
Elongation at break (%) Before UV-B irradiation After UV-B irradiation MD TD MD TD MD TD film A1 Comparative Example 1 One 1.2 1.21 1.67 2.11 7 8 2 2.4 2.38 3.1 3.57 3 5.80 5.91 7.13 7.9 film A2 Comparative Example 2 One 1.33 1.41 1.71 1.99 132 83 2 2.15 2.67 2.81 3.21 3 4.97 5.93 6.37 7.13 film B1 Example 1 One 1.11 1.15 1.17 1.21 141 97 2 2.37 2.69 2.38 2.66 3 5.11 6.7 5.36 6.91 film B2 Example 2 One 1.31 1.32 1.31 1.35 138 101 2 2.48 2.91 2.49 2.91 3 5.31 6.72 5.33 6.71 film B3 Example 3 One 1.16 1.17 1.23 1.25 140 96 2 2.31 2.67 2.47 2.82 3 4.09 5.11 4.66 5.93 film B4 Example 4 One 1.16 1.23 1.19 1.24 129 89 2 2.3 2.35 2.53 2.78 3 4.6 5.7 5.21 6.37 film B5 Example 5 One 1.11 1.18 1.21 1.67 139 93 2 2.2 2.45 2.57 2.91 3 5.31 6.21 6.27 6.91

Manufacturing example of laminated sheet

A film having a thickness of 60 μm prepared in the same manner as in the polyester films A1 to B5 was prepared, respectively, and was used as a first polyester film. In addition, a film having a thickness of 15 to 20 μm was prepared without including a UV blocker prepared in the same manner as in film A1, and was used as a second polyester film. An optically clear adhesive (OCA) was coated on one side of the first polyester film and one side of the second polyester film to a thickness of 10 μm, respectively, and laminated on both sides of the cover window. A transparent polyimide film (see Preparation Example below) having a thickness of 50 μm was used as the cover window. As a result, the laminated sheet which has the structure of 1st polyester film/OCA layer/cover window/OCA layer/2nd polyester film was obtained.

division first polyester film 2nd polyester film Manufacturing method UV blocker
content Thickness (㎛) UV blocker
content Thickness (㎛) sheet A1 Comparative Example 1 film A1 0 60 0 20 sheet A2 Comparative Example 2 film A2 1.3 60 0 20 sheet B1 Example 1 film B1 1.1 60 0 20 sheet B2 Example 2 film B2 1.6 60 0 15 sheet B3 Example 3 film B3 0.9 60 0 15 sheet B4 Example 4 film B4 0.8 60 0 17 sheet B5 Example 5 film B5 0.8 60 0 17 * UV blocker content: parts by weight of solid content of UV blocker added per 100 parts by weight of PET resin

Preparation example of polyimide film

After filling 563.3 g of dimethylacetamide (DMAc) as an organic solvent in a nitrogen atmosphere at 20°C in a double-jacketed 1L glass reactor with temperature control, 2,2'-bis(trifluoromethyl)-4,4 '-Diaminophenyl (TFMB) and 4,4'-oxydianiline (ODA) were added and dissolved. Then, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6-FDA) was slowly added and stirred for 2 hours. Then, isophthaloyl chloride (IPC) was added and stirred for 2 hours, terephthaloyl chloride (TPC) was added and stirred for 3 hours to prepare a polymer solution.

After apply|coating the obtained polymer solution to a glass plate, it dried with hot air at 80 degreeC for 30 minutes. Thereafter, the dried gel sheet was fixed to the pin frame while being stretched 1.01 times in the first direction, and was fixed to the pin frame while being stretched 1.03 times in the second direction perpendicular to the first direction. Thereafter, the dried gel sheet was cured in an atmosphere in which the temperature was raised at a rate of 2° C./min in a temperature range of 80° C. to 300° C. while being fixed to the pin frame. Thereafter, a polyimide film having a thickness of 50 μm was obtained through a cooling step.

Folding properties after UV irradiation

After manufacturing a display module by attaching the laminated sheet prepared above on one surface of the display panel, a folding durability test was performed as shown in FIG. 4 after UV irradiation as follows.

(1) UV irradiation

- UV equipment: Q-lab's QUV Tester

- UV lamp: UVB-313

- UV dose: 0.66 W/m ² @310 nm

- UV total dose: 31.62 W/m ² @250-400 nm

- UV irradiation time: 24 hours

(2) Folding test

- Test equipment: Toyoseiki's MIT-D0A

- radius of curvature (R): 1.5 mm

- Folding test procedure: MIT folding test according to ASTM D 2176 and TAPPI T 511

- Criteria: If delamination, driving error, whitening, or other defects were confirmed after repeated folding for 200,000 times, X was set, and O was set if not confirmed.

The results are summarized in the table below.

division Folding Durability sheet A1 Comparative Example 1 X sheet A2 Comparative Example 2 X sheet B1 Example 1 O sheet B2 Example 2 O sheet B3 Example 3 O sheet B4 Example 4 O sheet B5 Example 5 O

As shown in the table above, the display module including sheets A1 or A2 had a defect during repeated folding of more than 200,000 times after UV irradiation, but the display module including sheets B1 to B5 had defects during repeated folding of more than 200,000 times after UV irradiation. Defects such as delamination, driving error, and whitening were not observed, confirming excellent UV durability and flexibility.

1: flexible display device;
1': organic light emitting display device,
1a: an in-folding type flexible display device,
1b: an out-folding type flexible display device,
2: test equipment
10: cover, 11: psalm,
20: display panel;
20-1: front polarizer, 20-2: organic light emitting display panel,
30: frame,
21: jig, 22: load cell,
100: polyester film, 101: specimen,
100a: front protection film, 100b: back protection film,
200: cover window, 300: adhesive layer;
A, A': cutting line, p1, p2: folding point,
R: curvature, w: spacing.

Claims (10)

a total light transmittance of 5% or less for light having a wavelength of 370 nm;
It is a polyester film having a final tensile rate of 3% or less when irradiated with UV-B light for 24 hours and lasting for 1 hour under a load of N2% in the first direction in-plane,
After overlapping two polyester films and irradiating UV-B light on one film for 24 hours, the elongation at break in the longitudinal direction (MD) of the other film is 125% or more, and the elongation at break in the width direction (TD) of the other film is Elongation of at least 85%, polyester film:
Here, the load of N2% is a load that stretches the film by 2% compared to the initial direction in the first direction, and the UV-B light has a peak wavelength within 310 nm to 315 nm, and the irradiance at 310 nm wavelength. ) is 0.66 W/m ² , and the total irradiation amount in the 250 nm to 400 nm wavelength band is 31.62 W/m ² .
The method of claim 1,
The polyester film having a total light transmittance of 20% or less with respect to light of a wavelength of 380 nm.
The method of claim 1,
the polyester film
100 parts by weight of polyester resin; and
A polyester film comprising 0.7 parts by weight to 2.0 parts by weight of a UV blocker.
4. The method of claim 3,
The polyester film, wherein the weight reduction rate is 15% or less after the UV blocking agent is maintained for 1 hour in an air atmosphere of 280°C under isothermal conditions of a thermogravimetric analyzer (TGA).
4. The method of claim 3,
The UV blocker is at least one UV blocker selected from the group consisting of benzophenone-based, benzotriazole-based, triazine-based, malonic acid ester-based, benzoate-based and benzoxazinone-based UV blockers, polyester film.
The method of claim 1,
The polyester film has a thickness of 10 μm to 80 μm, a polyester film.
The method of claim 1,
After the polyester film is irradiated with UV-B light for 24 hours, the final tensile rate is 2% or less when a load of N1% in the in-plane first direction is maintained for 1 hour, and a load of N3% in the first in-plane direction Polyester film having a final tensile rate of 7% or less at 1 hour duration:
Here, the loads of N1% and N3% are loads for stretching the film by 1% and 3%, respectively, in the first direction compared to the initial stage.
delete The method of claim 1,
After irradiating the polyester film with UV-B light for 24 hours, the number of repeated folding under the condition of a curvature radius of 1.5 mm until whitening or cracking occurs 200,000 times or more, a polyester film.
flexible display panel; and
A flexible display device comprising the polyester film of claim 1 disposed on the flexible display panel.

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