TWI870044B - Optical film and display device - Google Patents

Abstract

Disclosed are an optical film including a light-transmitting matrix and a filler dispersed in the light-transmitting matrix, the optical film having an S/S index of 0.6 or more, and a display device including the optical film.

Description

Optical film and display device

The present disclosure relates to an optical film and a display device including the optical film, and more specifically to an optical film with excellent mechanical properties.

Recently, for the purpose of reducing thickness and weight and improving the flexibility of display devices, it has been considered to use optical films instead of glass as cover windows of display devices. In order for optical films to be used as cover windows of display devices, the optical films need to have excellent optical properties and excellent mechanical properties. For example, the optical films need to have properties such as excellent strength, hardness, wear resistance, and flexibility.

Fillers can be added to impart the desired physical properties to optical films that require various physical properties. The fillers can vary depending on the physical properties required of the optical film.

Therefore, in view of the above problems, the present disclosure is proposed, and one aspect of the present disclosure is to provide an optical film, which includes fibrous or filamentous fillers dispersed in a light-transmitting matrix.

Another aspect of the present disclosure is to provide an optical film having a stress/strain (S/S) index of 0.6 or greater.

Another aspect of the present disclosure is to provide an optical film having a yield tensile strength of 90 MPa to 160 MPa.

Another aspect of the present disclosure is to provide an optical film having a modulus of 4.0 GPa to 15 GPa.

Another aspect of the present disclosure is to provide an optical film with a restoring force. The optical film according to the present disclosure has a restoring force and can be useful for a display device.

Another aspect of the present disclosure is to provide a display device including the optical film.

According to one aspect of the present disclosure, an optical film is provided, the optical film comprising a light-transmitting matrix and a filler dispersed in the light-transmitting matrix, the optical film having an S/S index of 0.6 or greater than 0.6, wherein the S/S index is calculated according to the following equation 1: [Equation 1] S/S index = stress hysteresis / strain hysteresis

The stress hysteresis is calculated according to the following equation 2: [Equation 2] Stress hysteresis = [maximum compressive load/total load] * 100

The strain hysteresis is calculated according to the following equation 3: [Equation 3] Strain hysteresis = [Strain 2 - Strain 1] * 100

The maximum compressive load is the maximum compressive load required for the optical film to return to its original state after being stretched, and the total load (N) is the sum of the tensile load and the compressive load, wherein the tensile load is the load required for the optical film to be stretched to a specific strain, and the compressive load is the load required for the optical film to return to its original state after being stretched, Strain 1 is the strain before the optical film is deformed, and Strain 2 is the strain after the optical film is deformed.

According to another aspect of the present disclosure, a display device is provided, the display device comprising a display panel and an optical film disposed on the display panel.

According to an embodiment of the present disclosure, the filler contained in the optical film has a fiber shape or a filament shape, thereby improving the mechanical strength of the optical film, especially the yield tensile strength and elasticity. In this way, when the optical film according to the embodiment of the present disclosure is used in a display device, the rebound (recovery force) can be improved.

According to an embodiment of the present disclosure, when the S/S index of the optical film is high, hysteresis is improved, fewer marks are formed when the optical film is folded, and when the film is pressed with the same force, the film has a greater restoring force to return to its original state.

100: Optical film

110: Translucent matrix

120: Filling

200: Display device

501: Display panel

510: Substrate

520:Semiconductor layer

530: Gate electrode

535: Gate insulation layer

541: Source electrode

542: Drain electrode

551: Interlayer insulation layer

552: Planarization layer

570: Organic light-emitting device

571: First electrode

572: Organic luminescent layer

573: Second electrode

580:Embankment layer

590: Film encapsulation layer

P: Part

TFT: Thin Film Transistor

FIG1 is a schematic diagram showing an optical film according to an embodiment of the present disclosure.

FIG2 is a cross-sectional view showing a portion of a display device according to another embodiment of the present disclosure.

FIG3 is an enlarged cross-sectional view showing portion "P" in FIG2.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the following embodiments are provided illustratively only for a clear understanding of the present disclosure and do not limit the scope of the present disclosure.

The shapes, sizes, ratios, angles, and numbers disclosed in the drawings for illustrating the embodiments of the present disclosure are examples only, and the present disclosure is not limited to the details shown. Throughout this specification, the same reference numerals refer to the same elements. In the following description, when it is determined that a detailed description of the relevant well-known functions or configurations unnecessarily obscures the main points of the present disclosure, the detailed description will be omitted.

In the case where terms such as "include", "have" or "include" are used in this specification, another part may also exist unless the expression "only" is also used. Unless otherwise stated to the contrary, terms in the singular form may include plural meanings. In addition, when explaining an element, even if there is no explicit description of it, the element should be interpreted as including the error range.

When describing a positional relationship, for example, when using "on", "above", "below" or "close to" to describe a positional relationship, unless "immediately" or "directly" is used, it can include situations where there is no contact between them.

As used herein, spatially relative terms such as "below", "under", "lower", "above", and "upper" may be used to describe the relationship between a device or element as shown in the figures and another device or another element. It should be understood that in addition to the orientation shown in the figures, spatially relative terms are also intended to encompass different orientations of the device during use or operation of the device. For example, if the device in one of the figures is upside down, the elements described as being "below" or "below" other elements will now be positioned as being "above" other elements. Therefore, the exemplary terms "below" or "below" can encompass both the meanings of "below" and "above". Similarly, the exemplary terms "above" or "upper" can encompass both the meanings of "above" and "below".

When describing a time relationship, for example, when using "after", "afterwards", "next" or "before" to describe a time sequence, non-continuous relationships can be included unless "immediately" or "directly" is used.

It should be understood that although the terms "first", "second", etc. may be used in this article to describe various components, these components are not limited by these terms. These terms are only used to distinguish between various components. Therefore, within the technical concept of this disclosure, the first component can be referred to as the second component.

It should be understood that the term "at least one" includes all combinations related to one or more items. For example, "at least one of the first element, the second element, and the third element" may include all combinations of two or more elements selected from the first element, the second element, and the third element, as well as each of the first element, the second element, and the third element.

The features of the various embodiments of the present disclosure may be partially or completely integrated or combined with each other, and may interoperate and technically drive each other in different ways. The embodiments of the present disclosure may be implemented independently of each other, or may be implemented together in an interrelated manner.

FIG. 1 is a schematic diagram showing an optical film 100 according to an embodiment of the present disclosure. According to an embodiment of the present disclosure, a film having light transmittance is referred to as "optical film 100".

According to the disclosed embodiment, the optical film 100 includes a light-transmitting matrix 110 and a filler 120 dispersed in the light-transmitting matrix 110.

The light-transmitting substrate 110 may be light-transmitting. According to an embodiment of the present disclosure, the light-transmitting substrate 110 may be flexible. For example, the optical film according to an embodiment of the present disclosure may be bendable, foldable, or rollable. Therefore, the optical film 100 according to an embodiment of the present disclosure may be light-transmitting and may be bendable, foldable, or rollable.

According to the embodiments disclosed herein, the light-transmitting matrix 110 may include at least one of an imide repeating unit or an amide repeating unit.

The light-transmitting matrix 110 according to the disclosed embodiment can be produced from monomer components including dianhydride and diamine. Specifically, the light-transmitting matrix 110 can include imide repeating units formed by dianhydride and diamine.

However, the light-transmitting matrix 110 according to the disclosed embodiment is not limited thereto, and the light-transmitting matrix 110 may also be produced from monomer components including dicarbonyl compounds in addition to dianhydrides and diamines. The light-transmitting matrix 110 according to the disclosed embodiment may have imide repeating units and amide repeating units. For example, the light-transmitting matrix 110 having imide repeating units and amide repeating units may be a polyamide-imide resin.

According to an embodiment of the present disclosure, the light-transmitting matrix 110 may include a polyimide-based polymer. Examples of polyimide-based polymers may include polyimide polymers, polyamide-imide polymers, and similar materials. The light-transmitting matrix 110 according to an embodiment of the present disclosure may be produced from, for example, a polyimide-based polymer resin.

The light-transmitting substrate 110 may have a thickness sufficient for the optical film 100 to protect the display panel. For example, the light-transmitting substrate 110 may have a thickness of 10 microns to 100 microns. The thickness of the light-transmitting substrate 110 may be the same as the thickness of the optical film 100.

According to one embodiment of the present disclosure, the aspect ratio of the filler 120 may be in the range of 5 to 2,500. The aspect ratio refers to the ratio of the length of the filler 120 to the diameter.

When the aspect ratio of the filler 120 is less than 5, the filler 120 is not long enough and cannot fully perform the function of connecting the polymer chains to each other, and therefore cannot fully perform the function of improving the stability and arrangement characteristics of the polymer chains.

When the aspect ratio of the filler 120 is greater than 2,500, the filler 120 may reduce the dispersibility of the filler 120, and the filler 120 may agglomerate in the transparent matrix 110 due to the excessive length. As a result, the optical film 100 may have reduced transmittance, increased haze, and degraded optical properties. In addition, the mechanical strength of the optical film 100 may be reduced in the area where the filler 120 agglomerates, and therefore, the modulus of the optical film 100 may be reduced, and the mechanical strength of the optical film 100 may also be reduced.

According to one embodiment of the present disclosure, the length of the filler 120 may be in the range of 0.1 micrometer to 5 micrometers.

When the length of the filler 120 is less than 0.1 micrometer, the function of the filler 120 in linking the polymer chain may not be fully exerted.

When the length of the filler 120 is greater than 5 micrometers, the dispersibility of the filler 120 may be reduced, and as a result, the filler 120 may agglomerate within the light-transmitting matrix 110 and may easily gelate due to interaction with the polymer chain. Therefore, the optical film 100 may have reduced transmittance, increased haze, and deteriorated optical properties.

According to one embodiment of the present disclosure, the diameter of the filler 120 may be in the range of 2 nm to 20 nm. The diameter is measured in a direction perpendicular to the longitudinal direction.

When the diameter of the filler 120 is less than 2 nm, the stability of the filler 120 may be reduced, and the filler may be cut or broken, thereby contaminating the optical film 100 and increasing the haze of the optical film 100.

When the diameter of the filler 120 is higher than 20 nm, it is difficult for the filler 120 to have a wire shape, and the optical film 100 may have a degraded function of connecting polymer chains, increased haze, and reduced light transmittance.

There is no particular limitation on the type of filler 120. According to the embodiments of the present disclosure, any filler can be used as filler 120 without limitation as long as the filler has a fiber shape. Filler 120 can be inorganic or organic. Filler 120 can include at least one of inorganic fiber, organic fiber, or organic-inorganic hybrid fiber.

More specifically, the filler 120 may have a fiber shape or a filament shape. For example, the filler 120 may have a single-stranded fiber shape, a multi-stranded fiber shape, or a branch shape in which multiple strands are arranged in a branched form based on one central strand.

According to one embodiment of the present disclosure, the filler 120 may include at least one of glass fiber, aluminum fiber, or fluoride fiber.

Glass fiber includes SiO ₂ and may include other components besides SiO _2. Aluminum fiber includes Al ₂ O ₃ and may include other components besides Al ₂ O _3. Fluoride fiber may include at least one of polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) and may include other components besides PTFE and PVDF.

According to an embodiment of the present disclosure, the filler 120 may include at least one of hydroxyalumina, SiO ₂ , Al ₂ O ₃ , polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF).

According to an embodiment of the present disclosure, the filler 120 may be surface treated. For example, the filler 120 may be surface treated with an organic compound having an alkoxy group.

According to one embodiment of the present disclosure, the aluminum fiber may include at least one of hydroxyalumina or Al ₂ O _3. Hydroxyalumina is also called "Boehmite" and may be represented by γ-AlO(OH). More specifically, hydroxyalumina may include a structure represented by any one of the following Formulas 1, 2, and 3.

[Formula 1]

Where n is in the range of 100 to 20,000, m is in the range of 50 to 10,000, and p is in the range of 50 to 10,000.

When the structures of Formula 1, Formula 2, and Formula 3 are expanded to better understand the structure of the filler 120, the filler 120 can be represented by any one of Formula 4, Formula 5, and Formula 6.

The structure represented by Formula 1 can be represented by, for example, the following Formula 4. The following Formula 4 corresponds to the structure of Formula 1, wherein n is 3.

The structure represented by Formula 2 can be represented by, for example, the following Formula 5. The following Formula 5 corresponds to the structure of Formula 2, wherein m is 4.

The structure represented by Formula 3 can be represented by, for example, the following Formula 6. The following Formula 6 corresponds to the structure of Formula 3, where p is 5.

[Formula 6]

In Formula 4 to Formula 6, "*" indicates the binding position.

According to an embodiment of the present disclosure, _Al2O3 may have _a unit structure represented by the following Formula 7.

According to an embodiment of the present disclosure, _SiO2 may have a unit structure represented by the following Formula 8.

According to the embodiment of the present disclosure, the filler 120 can cause appropriate light scattering to improve the optical properties of the optical film 100. To enhance the light scattering effect, the content of the filler 120 in the optical film 100 can be adjusted.

According to an embodiment of the present disclosure, the content of the filler 120 can be 3 parts per hundred resin (PHR) to 50 parts per hundred resin relative to 100 grams of the light-transmitting matrix 110. More specifically, the content of the filler 120 can be adjusted to 4 parts per hundred resin to 30 parts per hundred resin, or 5 parts per hundred resin to 20 parts per hundred resin relative to 100 grams of the light-transmitting matrix 110.

When the content of filler 120 is less than 3 parts/100 parts of resin relative to 100 grams of the light-transmitting matrix 110, the light scattering effect caused by filler 120 is insufficient, and thus the effect of improving the light transmittance of optical film 100 cannot be obtained, and filler 120 cannot fully exert the function of connecting polymer chains.

On the other hand, when the content of filler 120 is higher than 50 parts/100 parts of resin relative to 100 grams of the light-transmitting base 110, the dispersibility of filler 120 may be reduced, the haze of the optical film 100 may be reduced, the brittleness may be increased, the filler 120 may be aggregated due to the excessive filler 120, and the aggregated filler 120 may block light, which may reduce the light transmittance of the optical film 100.

FIG. 2 is a cross-sectional view showing a portion of a display device 200 according to another embodiment of the present disclosure, and FIG. 3 is an enlarged cross-sectional view of “P” in FIG. 2 .

Referring to FIG. 2 , a display device 200 according to another embodiment of the present disclosure includes a display panel 501 and an optical film 100 located on the display panel 501.

2 and 3, the display panel 501 includes a substrate 510, a thin film transistor TFT located on the substrate 510, and an organic light emitting device 570 connected to the thin film transistor TFT. The organic light emitting device 570 includes a first electrode 571, an organic light emitting layer 572 located on the first electrode 571, and a second electrode 573 located on the organic light emitting layer 572. The display device 200 shown in FIG. 2 and FIG. 3 is an organic light emitting display device.

The substrate 510 may be formed of glass or plastic. Specifically, the substrate 510 may be formed of plastic such as polyimide resin or optical film. Although not shown, a buffer layer may be provided on the substrate 510.

The thin film transistor TFT is disposed on the substrate 510. The thin film transistor TFT includes: a semiconductor layer 520; a gate electrode 530, which is insulated from the semiconductor layer 520 and at least partially overlaps with the semiconductor layer 520; a source electrode 541, which is connected to the semiconductor layer 520; and a drain electrode 542, which is separated from the source electrode 541 and connected to the semiconductor layer 520.

Referring to FIG. 3 , a gate insulating layer 535 is disposed between the gate electrode 530 and the semiconductor layer 520 . An interlayer insulating layer 551 may be disposed on the gate electrode 530 , and a source electrode 541 and a drain electrode 542 may be disposed on the interlayer insulating layer 551 .

A planarization layer 552 is provided on the thin film transistor TFT to planarize the top of the thin film transistor TFT.

A first electrode 571 is disposed on the planarization layer 552. The first electrode 571 is connected to the thin film transistor TFT via a contact hole disposed in the planarization layer 552.

A bank layer 580 is disposed in a portion of the first electrode 571 on the planarization layer 552 to define a pixel region or a light-emitting region. For example, the bank layer 580 is disposed in a matrix at the boundaries between a plurality of pixels to define the corresponding pixel region.

The organic light-emitting layer 572 is disposed on the first electrode 571. The organic light-emitting layer 572 may also be disposed on the bank layer 580. The organic light-emitting layer 572 may include one light-emitting layer or two or more light-emitting layers stacked in a vertical direction. Light having any color among red, green and blue may be emitted from the organic light-emitting layer 572, and white light may be emitted from the organic light-emitting layer 572.

The second electrode 573 is disposed on the organic light-emitting layer 572.

The first electrode 571, the organic light-emitting layer 572 and the second electrode 573 can be stacked to form an organic light-emitting device 570.

Although not shown, when the organic light emitting layer 572 emits white light, each pixel may include a color filter for filtering the white light emitted from the organic light emitting layer 572 based on a specific wavelength. The color filter is formed on the light path.

A thin film encapsulation layer 590 may be disposed on the second electrode 573. The thin film encapsulation layer 590 may include at least one organic layer and at least one inorganic layer, and the at least one organic layer and the at least one inorganic layer may be alternately disposed.

The optical film 100 is disposed on the display panel 501 having the above-mentioned stacking structure. The optical film 100 includes a light-transmitting matrix 110 and a filler 120 dispersed in the light-transmitting matrix 110.

According to one embodiment of the present disclosure, the S/S index of the optical film 100 is 0.6 or greater than 0.6 and is calculated according to the following equation 1.

[Equation 1] S/S index = stress hysteresis/strain hysteresis

The stress hysteresis is calculated according to the following equation 2: [Equation 2] Stress hysteresis = [maximum compression load/total load] * 100

The strain hysteresis is calculated according to the following equation 3: [Equation 3] Strain hysteresis = [Strain 2 - Strain 1] * 100

Wherein the maximum compressive load is the maximum compressive load required for the optical film to return to its original state after being stretched, and the total load (N) is the sum of the tensile load and the compressive load, wherein the tensile load is the load required for the optical film to be stretched to a specific strain, and the compressive load is the load required for the optical film to return to its original state after being stretched, Strain 1 is the strain before the optical film is deformed, and Strain 2 is the strain after the optical film is deformed.

When the S/S index is less than 0.6, the hysteresis of the optical film may not be improved. As a result, the optical film may leave marks when it is folded, and when the film is pressed with the same force, the force to return to the original state may be reduced.

The optical film 100 according to the disclosed embodiment may have a yield tensile strength of 90 MPa to 160 MPa. More specifically, the optical film 100 may have a yield tensile strength of 100 MPa to 150 MPa, and may have a yield tensile strength of 120 MPa to 145 MPa.

When the yield tensile strength of the optical film 100 is less than 90 MPa, the optical film may be easily deformed due to the low yield point and low energy in the elastic section. As a result, the restoring force may be weak when the film is folded or pressed.

The optical film 100 according to the disclosed embodiment may have a modulus of 4.0 GPa to 15 GPa. More specifically, the optical film 100 may have a modulus of 6 GPa to 13 GPa, and may also have a modulus of 8 GPa to 12 GPa.

When the modulus of the optical film 100 is less than 4.0 GPa, the optical film 100 may be easily scratched or deformed by external force due to low hardness, and the optical film 100 may be easily deformed due to low yield point and low energy in the elastic section. As a result, the restoring force may be weak when the film is folded or pressed.

When the modulus of the optical film 100 is greater than 15 GPa, the optical film 100 may be easily deformed by an external force, which may cause the optical film 100 to bend. In addition, the drag difference between the optical film 100 and other materials increases, so when the display device 200 is folded, the optical film 100 and other materials are separated or folded.

Hereinafter, a method for manufacturing an optical film 100 according to another embodiment of the present disclosure will be described.

The method for manufacturing the optical film 100 according to the embodiment of the present disclosure includes: firstly dispersing the filler 120 in the resin solution used to form the light-transmitting matrix 110 to prepare a first mixed solution; and casting the first mixed solution to prepare a cast film.

According to an embodiment of the present disclosure, a polyimide resin solution can be used as a resin solution for forming a light-transmitting matrix 110.

More specifically, the method for manufacturing the optical film 100 according to the disclosed embodiment includes: preparing polyimide resin powder; dissolving the polyimide resin powder in a first solvent to obtain a polyimide resin solution; preparing a filler dispersion; and mixing the filler dispersion with the polyimide resin solution to prepare a first mixed solution.

The filler dispersion can be prepared, for example, by dispersing the filler 120 in a second solvent.

N,N-dimethylacetamide (DMAc) can be used as the first solvent. N,N-dimethylacetamide (DMAc) or methyl ethyl ketone (MEK) can be used as the second solvent, but an embodiment of the present disclosure is not limited thereto, and other known solvents can be used as the first solvent and the second solvent.

According to an embodiment of the present disclosure, in order to improve the dispersion of the filler 120, for example, the pH of the first mixed solution can be adjusted. For example, the pH of the first mixed solution can be adjusted to a range of 5 to 7. Therefore, aggregation or agglomeration of the filler 120 can be prevented.

Next, the first mixed solution is cast, dried and heat-treated to form the optical film 100. According to an embodiment of the present disclosure, the film formed by casting the first mixed solution may be referred to as a "cast film", and the film produced by drying and heat-treating the cast film may be referred to as an "optical film 100". The cast film may be referred to as an "uncured film".

In addition, during the drying and heat treatment of the cast film formed by casting, convection can be prevented so that the filler 120 can be oriented in a specific direction.

Specifically, when convection is generated inside the cast film that is dried using heat, the orientation of the filler 120 may be reduced. Therefore, the cast film may be dried slowly to prevent convection. For example, the cast film may be dried while the temperature is increased from 80°C to 120°C at a rate of 1°C/1 minute. When drying is performed to exceed a certain degree, the orientation of the filler 120 may be fixed.

Hereinafter, the present disclosure will be described in more detail with reference to preparation examples and examples. However, the following preparation examples and examples should not be interpreted as limiting the scope of the present disclosure.

<Preparation Example 1: Preparation of polymer-imide polymer solid>

719.104 g of N,N-dimethylacetamide (DMAc) was charged into a 1-liter reactor equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller and a cooler, and the reactor was purged with nitrogen. Then, the temperature of the reactor was adjusted to 25°C, 54.439 g (0.17 mol) of bis(trifluoromethyl)benzidine (TFDB) was dissolved therein, and the temperature of the solution was maintained at 25°C. 13.505 g (0.046 mol) of biphenyl-tetracarboxylic acid dianhydride (BPDA) was further added thereto and completely dissolved therein by stirring for 3 hours, and 9.063 g (0.020 mol) of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) was further added thereto and completely dissolved therein. The reactor temperature was lowered to 10°C, and 21.053 g (0.104 mol) of terephthaloyl chloride (TPC) was further added thereto and reacted at 25°C for 12 hours to obtain a polymer solution having a solid content of 12% by weight.

11.54 g of pyridine and 14.90 g of acetic anhydride are added to the obtained polymer solution, stirred for 30 minutes, heated at 80°C, stirred at the same temperature for 1 hour to allow the reaction to occur, and cooled to room temperature. 20 liters of methanol are added to the obtained polymer solution to precipitate the solid, and the precipitated solid is filtered, crushed, washed with 2 liters of methanol, and vacuum dried at 100°C for 6 hours or longer to prepare the polyimide polymer solid into powder. The prepared polyimide polymer solid is a polyamide-imide polymer solid.

<Example 1>

723.46 g of DMAc (first solvent) was added to a 1-liter reactor, and the reactor was stirred for a specific time period while maintaining the temperature of the reactor at 10°C. Then, 110 g of the polyamide-imide (polyimide resin powder) prepared as a solid powder in Preparation Example 1 was added to the reactor, stirred for 1 hour, and heated to 25°C to prepare a polyimide resin solution.

Then, the prepared liquid polyimide resin solution was slowly added to 55 grams of an alumina hydrate filler dispersion to prepare a first mixed solution comprising a silica dispersion and a polyimide resin solution. The alumina hydrate filler dispersion was prepared by dispersing an alumina hydrate filler 120 having an average particle size of about 4 nanometers and an average length of about 1,500 nanometers in a DMAc (N,N-dimethylacetamide, a second solvent) solution for 1 hour using a cylindrical pump.

When measured immediately after the first mixed solution is prepared, the pH of the first mixed solution is 8 or higher. In order to improve the alignment characteristics of the filler 120, a weak acid (e.g., acetic acid) is added to the first mixed solution to adjust the pH of the first mixed solution to a range of 5 to 7. The first mixed solution thus prepared is a polyimide-based resin solution in which the filler 120 having a fiber shape is dispersed.

The first mixed solution obtained by casting. A casting substrate is used for casting. At this time, there is no particular restriction on the type of the casting substrate. The casting substrate can be a glass substrate, a stainless steel (steel use stainless steel, SUS) substrate, a Teflon substrate or a similar substrate. According to an embodiment of the present disclosure, a glass substrate is used as a casting substrate.

Specifically, a cast film was produced by slowly drying at a rate of 1°C/min for about 40 minutes in a hot air oven at 80°C to up to 120°C to maintain the orientation of the filler 120. Then, the produced film was peeled off from the glass substrate and fixed to the frame using pins.

The frame with the optical film fixed thereon was slowly heated from 100°C to 280°C for 2 hours in a vacuum oven, slowly cooled and the optical film was separated from the frame to obtain the optical film. The optical film was heated again at 250°C for 5 minutes.

As a result, an optical film 100 having a thickness of 50 micrometers and including a light-transmitting matrix 110 and a silica-based filler 120 dispersed in the light-transmitting matrix 110 is completed.

<Example 2 and Example 3>

The optical films 100 were produced under the conditions of Table 1 in the same manner as in Example 1, and the optical films 100 are respectively referred to as "Example 2 and Example 3".

<Comparison Example 1 to Comparison Example 4>

The optical films 100 were produced under the conditions of Table 1 in the same manner as in Example 1, and the respective optical films 100 are referred to as "Comparative Example 1 to Comparative Example 7".

In Table 1, filler 1 refers to nanowires having an aspect ratio of 375, and filler 2 refers to nanoparticles having a particle diameter of 20 nanometers. Specifically, the length of filler 1 is 1.5 micrometers, and the diameter of filler 1 is 4 nanometers.

In Table 1, the molar ratio indicates the molar ratio of the corresponding component relative to 100 moles of the total diamine.

In Table 1, PHR means per hundred parts of resin, which means the weight (g) of filler relative to 100 (g) of the light-transmitting matrix. Specifically, the PHR according to the embodiment of the present disclosure represents the weight (g) of filler added to every 100 (g) of the polyimide polymer solid.

The physical properties of the optical films produced in Example 1 and Example 3 and Comparative Examples 1 to 4 were measured as follows.

(1)Measurement of module

The modulus of the optical film was measured using a universal tensile tester (Model 5967) from Instron Corp. according to American Society for Testing Material (ASTM) D885.

-Measurement standard within three hours after membrane production

-Load Cell is 30 kN, gripper is 250 N

-The sample size is 10 mm*50 mm, and the stretching speed is 25 mm/min

(2) Measurement of yield tensile strength

- Stress at the contact point when the modulus of the S-S curve shifts by 0.2%

-Measured using a universal tensile tester (model 5967) from Instron

(3) Measurement of tensile load

-Stress at 1% strain

-Measured using a universal tensile tester (model 5967) from Instron

(4) Measurement of compression load

-The stress when the gripper returns to the initial position after obtaining 1% strain

-Measured using a universal tensile tester (model 5967) from Instron

(5) Measurement of strain 2

-Strain change of the sample after 5 cycles (%)

-Measured using a universal tensile tester (model 5967) from Instron

(6) Measurement of recovery rate (cycle test)

The recovery rate of the optical film under repeated tension-compression was measured using a universal tensile tester (Model 5967) from Instron.

-Load cell is 30 kN, gripper is 250 N

- Sample size is 10 mm*50 mm, cycle strain is 1%, cycle speed is 30% strain/min, 5 cycles (extension-compression)

The measurement results are shown in Table 2 below.

As can be seen from the measurement results in Table 2, the optical film 100 according to the embodiment of the present disclosure has an S/S index of 0.6 or greater than 0.6.

100: Optical film

110: Translucent matrix

120: Filling

Claims (7)

An optical film comprises: a light-transmitting matrix; and a filler dispersed in the light-transmitting matrix, wherein the optical film has a stress/strain index of 0.6 or greater than 0.6, wherein the filler has a fiber shape or a filament shape, wherein the filler comprises at least one of glass fiber, aluminum fiber, or fluoride fiber, wherein the content of the filler is 3 parts/100 relative to 100 grams of the light-transmitting matrix. The invention relates to a method for preparing a light-transmitting matrix comprising: a light-transmitting matrix comprising at least one of an imide repeating unit or an amide repeating unit, wherein the stress/strain index is calculated according to the following equation 1: [Equation 1] Stress/strain index = stress hysteresis / strain hysteresis wherein the stress hysteresis is calculated according to the following equation 2: [Equation 2] Stress hysteresis = [maximum compressive load / total load] * 100 wherein the strain hysteresis is calculated according to the following equation 3: [Equation 3] Strain hysteresis = [strain 2 - strain 1] * 100 wherein the maximum compressive load is the maximum compressive load required for the optical film to return to its original state after being stretched, and the total load (N) is the sum of the tensile load and the compressive load, wherein the tensile load is the load required for the optical film to be stretched to 1% strain, and the tensile load is measured using a universal tensile tester, and the compressive load is the load required for the optical film to return to its original state after obtaining the 1% strain, and the compressive load is measured using the universal tensile tester, and the strain 1 is the strain of the optical film before deformation, and the strain 2 is the strain of the optical film after deformation after 5 cycles, and is measured using the universal tensile tester. An optical film as described in claim 1, wherein the filler has an aspect ratio of 5 to 2,500, wherein the aspect ratio is the ratio of the length of the filler to the diameter of the filler. An optical film as described in claim 1, wherein the filler has a length of 0.1 micrometer to 5 micrometers. An optical film as described in claim 1, wherein the filler has a diameter of 2 nm to 20 nm. An optical film as described in claim 1, wherein the optical film has a yield tensile strength of 90 megapascals to 160 megapascals. An optical film as described in claim 1, wherein the optical film has a modulus of 4.0 GPa to 15 GPa. A display device, comprising: a display panel; and an optical film as described in any one of claims 1 to 6, disposed on the display panel.