Optical film with improved elastic hysteresis

Abstract

One embodiment of the present invention provides an 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, and a display device comprising such an optical film.

Description

[Technical Field]

[0001] The present invention relates to an optical film and a display device including the same, and more particularly to an optical film having excellent mechanical properties. [Background technology]

[0002] In recent years, as display devices have become thinner, lighter, and more flexible, the use of optical films as cover windows instead of glass has been considered. To be used as cover windows for display devices, optical films must have excellent mechanical properties in addition to excellent optical properties. For example, optical films must have excellent properties such as strength, hardness, abrasion resistance, and flexibility.

[0003] In order to impart desired physical properties to optical films that require various physical properties, fillers may be added. The fillers may vary depending on the physical properties required of the optical film. Summary of the Invention [Problem to be solved by the invention]

[0004] One embodiment of the present invention is directed to providing an optical film comprising fibrous or filamentary fillers dispersed within a light-transmitting matrix.

[0005] Another embodiment of the present invention aims to provide an optical film having an S / S index of 0.6 or more.

[0006] Another embodiment of the present invention aims to provide an optical film having a yield tensile strength in the range of 90 to 160 MPa.

[0007] Another embodiment of the present invention aims to provide an optical film having a modulus in the range of 4.0 to 15 GPa.

[0008] Another embodiment of the present invention provides an optical film having excellent restoring force. The optical film having excellent restoring force according to one embodiment of the present invention can be effectively applied to display devices.

[0009] Another embodiment of the present invention aims to provide a display device including the optical film. [Means for solving the problem]

[0010] One embodiment of the present invention provides an 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.

[0011] The S / S index can be calculated using the following formula 1.

[0012] [Formula 1] S / S index = [(stress hysteresis) / (strain hysteresis)] 2

[0013] In the above formula 1, the stress hysteresis can be calculated by the following formula 2.

[0014] [Formula 2] Stress hysteresis = [Maximum compressive load / Total load] x 100

[0015] The strain hysteresis can be calculated using the following equation 3.

[0016] [Formula 3] Strain hysteresis = [Strain 2 - Strain 1] x 100

[0017] In the formula 2, the maximum compressive load means the maximum value of the compressive load applied when the material tries to return to its original state after being stretched, The total load (N) is the sum of the tensile load and the compressive load, Here, the tensile load means a load required to be pulled to a specific strain, The compressive load means a load applied when the material tries to return to its original state after being stretched. The strain 1 is the strain of the optical film before deformation, The strain 2 is the strain of the optical film after deformation.

[0018] Another embodiment of the present invention provides a display device including a display panel and the optical film disposed on the display panel. [Effects of the Invention]

[0019] According to one embodiment of the present invention, the filler contained in the optical film has a fibrous or filamentous shape, which can improve the mechanical strength of the optical film, particularly the yield tensile strength, and can improve the elastic hysteresis. As a result, when the optical film according to one embodiment of the present invention is used in a display device, the restoring force can be improved.

[0020] According to one embodiment of the present invention, a high S / S index of an optical film improves hysteresis, and when the hysteresis is improved, when the optical film is folded, there is less trace left and when the film is pressed with the same force, the force of returning to its original shape is large. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic diagram of an optical film according to one embodiment of the present invention. [Figure 2] FIG. 10 is a cross-sectional view showing a part of a display device according to another embodiment of the present invention. [Figure 3] FIG. 3 is an enlarged cross-sectional view of part "P" in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments described below are presented for illustrative purposes to help a clear understanding of the present invention, and are not intended to limit the scope of the present invention.

[0023] The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for illustrating embodiments of the present invention are merely illustrative, and the present invention is not limited to the details shown in the drawings. The same components may be designated by the same reference numerals throughout the specification. In describing the present invention, if a detailed description of related publicly known technology is deemed to unnecessarily obscure the gist of the present invention, such a detailed description will be omitted.

[0024] When terms such as "comprise," "have," and "consist of" are used in this specification, other parts may be added unless the expression "only" is used. When a constituent feature is expressed in the singular, it includes the plural unless otherwise expressly stated. In addition, when interpreting a constituent feature, it is interpreted as including a margin of error, even if there is no other explicit statement.

[0025] When describing the positional relationship between two parts, for example, "on top of," "below," or "next to," one or more other parts may be located between the two parts unless the words "immediately" or "directly" are used.

[0026] Spatially relative terms such as "below," "beneath," "lower," "above," and "upper" can be used to easily describe the relationship of one element or component to another element or component as illustrated in the drawings. Spatially relative terms should be understood to include different orientations of the elements in use or operation in addition to the orientation depicted in the drawings. For example, if an element depicted in the drawings were turned over, an element described as "below" or "beneath" another element would be positioned "above" the other element. Thus, the exemplary term "below" can encompass both an orientation of below and above. Similarly, the exemplary terms "above" or "upper" can encompass both an orientation of above and below.

[0027] When describing a temporal relationship, for example, when describing a temporal precedence relationship such as "after", "following", "next to", or "before", it can also include cases where the relationship is not consecutive, unless the words "immediately" or "directly" are used.

[0028] Although terms such as "first," "second," and the like are used to describe various components, these components are not limited by these terms. These terms are used merely to distinguish one component from another. Therefore, the first component referred to below may be the second component within the scope of the technical concept of the present invention.

[0029] The term "at least one" should be understood to include all possible combinations of one or more associated items. For example, "at least one of the first, second, and third items" means not only the first, second, or third item, but also all possible combinations of items that can be present from two or more of the first, second, and third items.

[0030] The features of the various embodiments of the present invention can be partially or fully combined or combined with each other, and various technical interlocking and driving mechanisms are possible, and the respective embodiments can be implemented independently of each other or can be implemented together in a linked relationship.

[0031] 1 is a schematic diagram of an optical film (100) according to one embodiment of the present invention. According to one embodiment of the present invention, a film having light transmissivity is referred to as an optical film (100).

[0032] An optical film (100) according to one embodiment of the present invention comprises a light-transmitting matrix (110) and a filler (120) dispersed in the light-transmitting matrix.

[0033] The light-transmitting matrix (110) has light-transmitting properties. According to one embodiment of the present invention, the light-transmitting matrix (110) can have flexible properties. For example, the light-transmitting matrix (110) can have bending properties, folding properties, or rollable properties. As a result, the optical film (100) according to one embodiment of the present invention has light-transmitting properties and can have bending properties, folding properties, or rollable properties.

[0034] According to one embodiment of the present invention, the light-transmitting matrix (110) may include at least one of imide repeat units and amide repeat units.

[0035] The light-transmitting matrix (110) according to one embodiment of the present invention can be made from monomer components including, for example, a dianhydride and a diamine. Specifically, the light-transmitting matrix (110) can include imide repeat units formed by the dianhydride and the diamine.

[0036] However, the light-transmitting matrix (110) according to one embodiment of the present invention is not limited thereto, and the light-transmitting matrix (110) may be manufactured from monomer components including dicarbonyl compounds in addition to dianhydrides and diamines. The light-transmitting matrix (110) according to one embodiment of the present invention may have imide repeat units and amide repeat units. Examples of the light-transmitting matrix (110) having imide repeat units and amide repeat units include polyamideimide resins.

[0037] According to one embodiment of the present invention, the light-transmitting matrix (110) may include a polyimide-based polymer. Examples of polyimide-based polymers include polyimide polymers and polyamide-imide polymers. The light-transmitting matrix (110) according to one embodiment of the present invention may be made of, for example, a polyimide-based polymer resin.

[0038] The light-transmitting matrix (110) may have a thickness sufficient to allow the optical film (100) to protect the display panel. For example, the light-transmitting matrix (110) may have a thickness of 10 to 100 μm. The thickness of the light-transmitting matrix (110) may be the same as the thickness of the optical film (100).

[0039] According to one embodiment of the present invention, the aspect ratio of the filler (120) may be in the range of 5 to 2500. The aspect ratio is the ratio of the length to the diameter of the filler (120).

[0040] If the aspect ratio of the filler (120) is less than 5, the filler (120) is not long enough, and therefore the function of interweaving the polymer chains with each other is not fully exerted, and the effect of improving the stability and alignment characteristics of the polymer chains may not be fully exerted.

[0041] If the aspect ratio of the filler (120) exceeds 2,500, the length of the filler (120) becomes too long, reducing the dispersibility of the filler (120), which may result in aggregation of the filler (120) within the light-transmitting matrix (110). As a result, the light transmittance of the optical film (100) may decrease, the haze may increase, and the optical properties of the optical film (100) may deteriorate. In addition, the mechanical strength of the optical film (100) may decrease in the areas where the filler (120) aggregates, which may result in a decrease in the modulus of the optical film (100), reducing the mechanical strength of the optical film (100).

[0042] According to one embodiment of the present invention, the length of the filler (120) may be in the range of 0.1 to 5 μm.

[0043] If the length (L1) of the filler (120) is less than 0.1 μm, the filler (120) may not be able to fully exert its function of interweaving polymer chains.

[0044] If the length of the filler (120) exceeds 5 μm, the dispersibility of the filler (120) decreases, which may result in aggregation of the filler (120) within the light-transmitting matrix (110), and gelation may occur due to interaction with the polymer chains. This may result in a decrease in the light transmittance of the optical film (100) and an increase in haze, which may degrade the optical properties of the optical film (100).

[0045] According to one embodiment of the present invention, the diameter of the filler (120) may be in the range of 2 to 20 nm, the diameter being measured in a direction perpendicular to the longitudinal direction.

[0046] If the diameter of the filler (120) is less than 2 nm, the stability of the filler (120) may decrease, and the filler may break or crumble, contaminating the optical film (100) and increasing the haze of the optical film (100).

[0047] If the diameter of the filler (120) exceeds 20 nm, it may be difficult for the filler (120) to have a wire shape or the function of entangling the polymer chains with each other may be reduced, which may result in an increase in the optical film (100) or a decrease in transmittance.

[0048] There is no particular limitation on the type of filler (120). Any fibrous material may be used as the filler (120) according to an embodiment of the present invention. The filler (120) may be inorganic or organic. The filler (120) may include at least one of inorganic fibers, organic fibers, and organic-inorganic composite fibers.

[0049] More specifically, the filler 120 may have the shape of a fiber or a filament. For example, the filler 120 may have the shape of a fiber consisting of a single strand (single chain), may have the shape of a fiber consisting of multiple strands (chains), or may have the shape of a single central strand (chain) with multiple strands (chains) arranged in a branch-like pattern.

[0050] According to one embodiment of the present invention, the filler (120) may include at least one of glass fiber, aluminum fiber, and fluoride fiber.

[0051] The glass fiber contains SiO2 and may further contain other components in addition to SiO2. The aluminum fiber contains Al2O3 and may further contain other components in addition to Al2O3. The fluorine fiber may contain at least one of PTFE (Polytetrafluoroethylene) and PVDF (Polyvinylidene Fluoride) and may further contain other components in addition to PTFE and PVDF.

[0052] According to one embodiment of the present invention, the filler (120) may include at least one of aluminum oxide hydroxide, SiO2, Al2O3, PTFE (Polytetrafluoroethylene), and PVDF (Polyvinylidene Fluoride).

[0053] According to one embodiment of the present invention, the filler 120 may be surface-treated. For example, fibers surface-treated with an organic compound group having an alkoxy group may be used as the filler 120.

[0054] According to one embodiment of the present invention, the aluminum fiber may contain at least one of aluminum oxide hydroxide and Al2O3. Alumina hydrate is also called boehmite and can be represented by γ-AlO(OH). More specifically, alumina hydrate may include a structure represented by any one of the following chemical formulas 1, 2, and 3.

[0055] [Chemical formula 1] JPEG2025532088000002.jpg69140

[0056] [Chemical formula 2] JPEG2025532088000003.jpg60140

[0057] [Chemical formula 3] JPEG2025532088000004.jpg77140

[0058] Here, 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.

[0059] To aid in understanding the structure of filler (120), the structures of chemical formulas 1, 2, and 3 can be expanded to include structures represented by any of chemical formulas 4, 5, and 6 below.

[0060] The structure represented by Chemical Formula 1 can be represented, for example, by the following Chemical Formula 4. Chemical Formula 4 below corresponds to the case where n in Chemical Formula 1 is 3.

[0061] [Chemical formula 4] JPEG2025532088000005.jpg67167

[0062] The structure represented by Chemical Formula 2 can be represented, for example, by the following Chemical Formula 5. Chemical Formula 5 below corresponds to the case where m in Chemical Formula 2 is 4.

[0063] [Chemical formula 5] JPEG2025532088000006.jpg49167

[0064] The structure represented by Chemical Formula 3 can be represented, for example, by the following Chemical Formula 6. Chemical Formula 6 below corresponds to the case where p in Chemical Formula 3 is 5.

[0065] [Chemical formula 6] JPEG2025532088000007.jpg67167

[0066] In the above chemical formulas 4 to 6, "*" indicates a bonding position.

[0067] According to one embodiment of the present invention, Al2O3 may have a unit structure represented by the following chemical formula 7:

[0068] [Chemical formula 7] JPEG2025532088000008.jpg24142

[0069] According to one embodiment of the present invention, SiO2 may have a unit structure represented by the following chemical formula 8:

[0070] [Chemical formula 8] JPEG2025532088000009.jpg91170

[0071] According to one embodiment of the present invention, when a filler (120) is added, the filler (120) causes appropriate light scattering, which can improve the optical properties of the optical film (100). The content of the filler (120) contained in the optical film (100) may be adjusted to enhance the light scattering effect.

[0072] According to one embodiment of the present invention, the content of the filler (120) may be 3 to 50 PHR per 100 weight percent of the light-transmitting matrix (110). More specifically, the content of the filler (120) may be adjusted to 4 to 30 PHR, or 5 to 20 PHR per 100 weight percent of the light-transmitting matrix (110).

[0073] If the content of the filler (120) is less than 3 PHR per 100 weight percent of the light-transmitting matrix (110), the light scattering effect of the filler (120) is negligible, and the effect of improving the light transmittance of the optical film (100) may be almost insignificant, and the filler (120) may not fully function to intertwine the polymer chains with each other.

[0074] On the other hand, if the content of the filler (120) exceeds 50 PHR per 100 weight percent of the light-transmitting matrix (110), the dispersibility of the filler (120) may decrease, the haze of the optical film (100) may decrease, or the brittleness may increase. In addition, the excess filler (120) may cause the filler (120) to agglomerate, which may block light and reduce the light transmittance of the optical film (100).

[0075] FIG. 2 is a cross-sectional view of a part of a display device (200) according to another embodiment of the present invention, and FIG. 3 is an enlarged cross-sectional view of the "P" portion of FIG.

[0076] Referring to FIG. 2, a display device (200) according to another embodiment of the present invention includes a display panel (501) and an optical film (100) on the display panel (501).

[0077] 2 and 3, the display panel 501 includes a substrate 510, a thin film transistor (TFT) on the substrate 510, and an organic light emitting element 570 connected to the thin film transistor (TFT). The organic light emitting element 570 includes a first electrode 571, an organic light emitting layer 572 on the first electrode 571, and a second electrode 573 on the organic light emitting layer 572. The display device 200 disclosed in FIGS. 2 and 3 is, for example, an organic light emitting display device.

[0078] The substrate 510 can be made of glass or plastic. Specifically, the substrate 510 can be made of plastic such as polyimide resin or optical film. Although not shown, a buffer layer may be disposed on the substrate 510.

[0079] 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 insulated from the semiconductor layer 520 and overlapping at least a portion of the semiconductor layer 520, a source electrode 541 connected to the semiconductor layer 520, and a drain electrode 542 spaced apart from the source electrode 541 and connected to the semiconductor layer 520.

[0080] 3, a gate insulating layer 535 is disposed between a gate electrode 530 and a 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.

[0081] The planarization film (552) is disposed on the thin film transistor (TFT) and flattens the top of the thin film transistor (TFT).

[0082] The first electrode 571 is disposed on the planarization film 552. The first electrode 571 is connected to the thin film transistor (TFT) through a contact hole formed in the planarization film 552.

[0083] The bank layer (580) is disposed on a part of the first electrode (571) and the planarization film (552) to define a pixel region or a light-emitting region. For example, the bank layer (580) is disposed in a matrix structure in the boundary region between multiple pixels, so that the pixel region can be defined by the bank layer (580).

[0084] 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 light-emitting layers stacked one above the other. Such an organic light-emitting layer (572) may emit light having any one of red, green, and blue colors, or may emit white light.

[0085] A second electrode (573) is disposed on the organic light-emitting layer (572).

[0086] The first electrode 571, the organic light emitting layer 572, and the second electrode 573 may be stacked to form the organic light emitting device 270.

[0087] 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 by wavelength. The color filter is formed on the path of light.

[0088] A thin film encapsulation layer (590) can be disposed on the second electrode (573). The thin film encapsulation layer (590) can include at least one organic film and at least one inorganic film, and the at least one organic film and the at least one inorganic film can be alternately disposed.

[0089] An optical film 100 is disposed on the display panel 501 having the above-described laminated structure. The optical film 100 includes a light-transmitting matrix 110 and a filler 120 dispersed in the light-transmitting matrix 110.

[0090] According to one embodiment of the present invention, the S / S index of the optical film (100) is 0.6 or more, and the S / S index is calculated by the following formula 1:

[0091] [Formula 1] S / S index = [(stress hysteresis) / (strain hysteresis)] 2

[0092] In the above formula 1, the stress hysteresis can be calculated by the following formula 2.

[0093] [Formula 2] Stress hysteresis = [Maximum compressive load / Total load] x 100

[0094] The strain hysteresis can be calculated using the following equation 3.

[0095] [Formula 3] Strain hysteresis = [Strain 2 - Strain 1] x 100

[0096] In the formula 2, the maximum compressive load means the maximum value of the compressive load applied when the material tries to return to its original state after being stretched, The total load (N) is the sum of the tensile load and the compressive load, Here, the tensile load means a load required to be pulled to a specific strain, The compressive load means a load applied when the material tries to return to its original state after being stretched. The strain 1 is the strain of the optical film before deformation, The strain 2 is the strain of the optical film after deformation.

[0097] If the S / S index is less than 0.6, the hysteresis of the optical film may not be improved, which may result in traces being left when the optical film is folded, and the force required to return to its original state when the film is pressed with the same force may be reduced.

[0098] The optical film (100) according to one embodiment of the present invention has a yield tensile strength in the range of 90 to 160 MPa. More specifically, the optical film (100) may have a yield tensile strength in the range of 100 to 150 MPa, or may have a yield tensile strength of 120 to 145 MPa.

[0099] If the yield tensile strength of the optical film (100) is less than 90 MPa, the yield point is low and the energy in the elastic region is low, so the film may be vulnerable to deformation, and therefore the recovery force when folded or pressed may be weak.

[0100] The optical film (100) according to one embodiment of the present invention may have a modulus in the range of 4.0 to 15 GPa. More specifically, the optical film (100) may have a modulus in the range of 6 to 13 GPa, or may have a modulus in the range of 8 to 12 GPa.

[0101] If the modulus of the optical film (100) is less than 4.0 GPa, the hardness is weak and the film may be easily damaged or deformed by external forces. Also, the yield point is low, so the energy in the elastic region is low and the film may be vulnerable to deformation. Therefore, the recovery force when the film is folded or pressed may be weak.

[0102] If the modulus of the optical film (100) exceeds 15 GPa, it may be easily deformed by an external force, causing warping of the optical film (100). In addition, the difference in resistance between the optical film (100) and other materials increases, which may result in separation or folding between the optical film (100) and other materials when the display device (200) is folded.

[0103] A method for producing the optical film 100 according to one embodiment of the present invention will now be described.

[0104] A method for manufacturing an optical film (100) according to one embodiment of the present invention may include the steps of primarily dispersing a filler (120) in a resin solution for forming a polymer matrix (110) to prepare a first mixture, and casting the first mixture to prepare a cast film.

[0105] According to one embodiment of the present invention, a polyimide resin solution may be used as the resin solution for forming the polymer matrix (110).

[0106] More specifically, a method for manufacturing an optical film (100) according to an embodiment of the present invention may include the steps of preparing a polyimide resin powder, dissolving the polyimide resin powder in a first solvent to prepare a polyimide resin solution, preparing a filler dispersion, and mixing the filler dispersion and the polyimide resin solution to prepare a first mixture.

[0107] The filler dispersion can be produced, for example, by dispersing the filler (120) in the second solvent.

[0108] The first solvent may be N,N-dimethylacetamide (DMAc). The second solvent may be N,N-dimethylacetamide (DMAc) or methyl ethyl ketone (MEK). However, one embodiment of the present invention is not limited thereto, and other known solvents may be used as the first and second solvents.

[0109] According to one embodiment of the present invention, the pH of the first mixture may be adjusted to improve the dispersibility of the filler 120. For example, the pH of the first mixture may be adjusted to a range of 5 to 7. This can prevent the filler 120 from aggregating or forming agglomerates.

[0110] The first mixture can then be cast, dried, and heat-treated to form an optical film 100. According to one embodiment of the present invention, a film formed by casting the first mixture can be called a cast film, and a film produced by drying and heat-treating the cast film can be called an optical film 100. The cast film can be called an uncured film.

[0111] In addition, convection can be prevented during the drying and heat treatment of the cast film formed by casting, and the filler 120 can be oriented in a certain direction.

[0112] Specifically, when drying a cast film using heat, if convection occurs inside, the orientation of the filler (120) may decrease. Therefore, to prevent convection, the cast film can be dried slowly. For example, the cast film may be dried while increasing the temperature from 80°C to 120°C at a rate of 1°C / minute (1 degree / minute). When the film is dried to a certain level, the orientation of the filler (120) is fixed.

[0113] The present invention will be described in more detail below with reference to illustrative production examples and examples, although the present invention is not limited to the production examples and examples described below.

[0114] <Production Example 1: Production of Polyimide Polymer Solids> A 1 L reactor equipped with a stirrer, nitrogen injector, dropping funnel, temperature controller, and condenser was charged with 719.104 g of DMAc (N,N-dimethylacetamide) while nitrogen was being passed through. The reactor temperature was then adjusted to 25°C, and 54.439 g (0.17 mol) of TFDB was dissolved and the solution was maintained at 25°C. 13.505 g (0.046 mol) of BPDA was added and stirred for 3 hours until the BPDA was completely dissolved. 9.063 g (0.020 mol) of 6FDA was then added and completely dissolved. The reactor temperature was then lowered to 10°C, and 21.053 g (0.104 mol) of TPC was added. The mixture was allowed to react at 25°C for 12 hours to yield a polymer solution with a solids concentration of 12 wt%.

[0115] To the resulting polymer solution, 11.54 g of pyridine and 14.90 g of acetic anhydride were added and stirred for 30 minutes, then the temperature was raised again to 80°C and the mixture was stirred at the same temperature for 1 hour to allow the reaction to proceed, after which it was cooled to room temperature. 20 L of methanol was added to the resulting polymer solution to precipitate a solid, which was then filtered and pulverized, washed again with 2 L of methanol, and dried in a vacuum at 100°C for at least 6 hours to obtain a powdery polyimide-based polymer solid. The polyimide-based polymer solid produced here was a polyamideimide-based polymer solid.

[0116] Example 1 723.46 g of DMAc (first solvent) was placed in a 1 L reactor, and the mixture was stirred for a certain period of time while maintaining the temperature of the reactor at 10° C. Then, 110 g of the solid powder polyamideimide (polyimide resin powder) prepared in Preparation Example 1 was added, and the mixture was stirred for 1 hour, and then the temperature was raised to 25° C. to prepare a liquid polyimide resin solution.

[0117] Thereafter, 55 g of an alumina hydrate filler dispersion, in which an alumina hydrate filler having an average particle size of 4 nm and an average length of 1500 nm was dispersed in a DMAc (N,N-dimethylacetamide) solution (second solvent) at a content of 10 wt %, was slowly added to the liquid polyimide resin solution prepared above using a cylinder pump for 1 hour to prepare a first mixture in which the silica dispersion and the polyimide resin solution were mixed.

[0118] When the pH of the first mixture is measured immediately after preparation, it is found to be 8 or higher. In order to improve the alignment characteristics of the filler (120), a weak acid such as acetic acid is added to the first mixture to adjust the pH of the first mixture to a range of 5 to 7. The first mixture prepared in this manner is a polyimide resin solution in which the fibrous filler (120) is dispersed.

[0119] The obtained first mixed liquid was cast. A cast substrate was used for casting. There are no particular limitations on the type of cast substrate. As the cast substrate, a glass substrate, a stainless steel (SUS) substrate, a Teflon (registered trademark) substrate, etc. may be used. According to one embodiment of the present invention, a glass substrate may be used as the cast substrate.

[0120] In order to maintain the orientation of the filler (120) during the drying process of the cast film, the film was produced by placing it in a hot air oven at 80°C and slowly drying it at a rate of 1°C / min up to 120°C for about 40 minutes, and the produced film was peeled off from the glass substrate and fixed to a frame with pins.

[0121] The frame with the film attached was placed in a vacuum oven and slowly heated from 100°C to 280°C for 2 hours, then gradually cooled and separated from the frame to obtain an optical film. The optical film was then heat-treated again at 250°C for 5 minutes.

[0122] As a result, an optical film (100) having a thickness of 50 μm was completed, which contained a light-transmitting matrix (110) and a silica-based filler (120) dispersed in the light-transmitting matrix.

[0123] <Example 2-3> Optical films (100) were produced in the same manner as in Example 1 according to the conditions in Table 1, and designated as Examples 2 to 4, respectively.

[0124] <Comparative Example 1-4> Optical films (100) were produced in the same manner as in Example 1 under the conditions in Table 1, and these were designated as Comparative Examples 1 to 4, respectively.

[0125] [Table 1]

[0126] In Table 1, Filler 1 is a nanowire with an aspect ratio of 375, and Filler 2 is a nanoparticle with a particle size of 20 nm. Specifically, Filler 1 is 1.5 μm long and 4 nm in diameter.

[0127] The molar ratios in Table 1 indicate relative molar ratios based on 100 moles of total diamine. PHR in Table 1 stands for Per Hundred Resin, and refers to the weight (g) of filler per 100 weight (g) of light-transmitting matrix. Specifically, PHR according to one embodiment of the present invention refers to the weight (g) of filler added per 100 parts by weight (g) of polyimide-based polymer solid content.

[0128] The optical films produced in Examples 1 to 3 and Comparative Examples 1 to 4 were measured for the following physical properties.

[0129] (1) Measurement of modulus The modulus of the optical film was measured using an Instron universal testing machine (Model 5967) according to the ASTM D885 method.

[0130] -Measurement criteria within 3 hours of film production -Load cell 30kN, grip 250N - Test piece size: 10mm x 50mm, tension speed: 25mm / min

[0131] (2) Measurement of yield tensile strength -SS The stress value at the contact point is obtained by offsetting the modulus (slope) of the curve by 0.2%. -Measurements were made using an Instron universal testing machine (MODEL 5967).

[0132] (3) Measurement of tensile load Stress value when reaching -1% strain -Measurements were made using an Instron universal testing machine (MODEL 5967).

[0133] (4) Measurement of compressive load Stress value when the grip returns to the initial position after reaching -1% strain -Measurements were made using an Instron universal testing machine (MODEL 5967).

[0134] (5) Measurement of strain 2 -Strain deformation value (%) of the test piece after 5 cycles -Measurements were made using an Instron universal testing machine (MODEL 5967).

[0135] (6) Measurement of recovery rate (Cycle Test) The recovery rate of the optical film after repeated tension-compression was measured using an Instron universal testing machine (MODEL 5967).

[0136] -Load cell 30kN, grip 250N - Test piece size 10mm x 50mm, cycle strain 1%, cycle speed 30% strain / min, number of cycles (tension-compression) 5 times

[0137] The measurement results are shown in Table 2 below.

[0138] [Table 2]

[0139] As shown in the measurement results in Table 2, it can be confirmed that the optical film (100) according to the embodiment of the present invention has an S / S index of 0.6 or more.

Claims

1. a light-transmitting matrix, and a filler dispersed in the optically transparent matrix; An optical film having an S / S index of 0.6 or more: The S / S index is calculated by the following formula 1: [Formula 1] S / S index = [(stress hysteresis) / (strain hysteresis)] 2 In the above formula 1, the stress hysteresis is calculated by the following formula 2: [Formula 2] Stress hysteresis = [maximum compressive load / total load] x 100 The strain hysteresis is calculated by the following equation 3: [Formula 3] Strain hysteresis = [Strain 2 - Strain 1] x 100 In the formula 2, the maximum compressive load means the maximum value of the compressive load applied when the material tries to return to its original state after being stretched, The total load (N) is the sum of the tensile load and the compressive load, Here, the tensile load means a load required to be pulled to a specific strain, The compressive load means a load applied when the material tries to return to its original state after being stretched. The strain 1 is the strain of the optical film before deformation, The strain 2 is the strain of the optical film after deformation.

2. 2. The optical film according to claim 1, wherein the filler has a fibrous or filamentous shape.

3. The optical film according to claim 1, wherein the filler has an aspect ratio in the range of 5 to 2,500. The aspect ratio is the ratio of the length to the diameter of the filler.

4. 2. The optical film according to claim 1, wherein the filler has a length in the range of 0.1 to 5 μm.

5. 2. The optical film according to claim 1, wherein the filler has a diameter in the range of 2 to 20 nm.

6. 2. The optical film according to claim 1, wherein the filler has a content of 3 to 50 parts by weight per 100 parts by weight of the light-transmitting matrix.

7. 2. The optical film according to claim 1, having a yield tensile strength in the range of 90 to 160 MPa.

8. 2. The optical film according to claim 1, having a modulus in the range of 4.0 to 15 Gpa.

9. 2. The optical film according to claim 1, wherein the light-transmitting matrix contains at least one of an imide repeating unit and an amide repeating unit.

10. a display panel, and The optical film according to any one of claims 1 to 9, disposed on the display panel. A display device comprising:

Images