Optical film with improved creep deformation behavior.

Abstract

One embodiment of the present invention provides an optical film including a light-transmissive matrix and fillers dispersed in the light-transmissive matrix, the fillers being fibrous and having a Creep index of 0.46 or less, and a display device including such an optical film.

Description

Technical Field

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

Background Art

[0002] In recent years, due to the thinning, weight reduction, and flexibility of display devices, using an optical film instead of glass as a cover window has been considered. For an optical film to be used as a cover window of a display device, it is necessary to have excellent mechanical properties as well as excellent optical properties. For example, the optical film needs to have properties such as excellent strength, hardness, abrasion resistance, and flexibility.

[0003] In order to impart the desired physical properties to an optical film that requires various physical property characteristics, a filler may be added. The filler may vary depending on the physical properties required for the optical film.

Summary of the Invention

Problems to be Solved by the Invention

[0004] One embodiment of the present invention provides an optical film including rod-shaped or fibrous fillers dispersed in a light-transmissive matrix.

[0005] Another embodiment of the present invention provides an optical film having a Creep index of 0.46 or less.

[0006] Another embodiment of the present invention provides an optical film having a Martens hardness (HM) in the range of 200 to 300 MPa.

[0007] Another embodiment of the present invention provides an optical film having a Vickers hardness (HV) in the range of 40 to 70.

[0008] Another embodiment of the present invention provides an optical film having resistance to creep deformation. The optical film according to the present invention having resistance to creep deformation can be usefully applied to display devices.

[0009] Another embodiment of the present invention provides 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, having a Creep index of 0.46 or less.

[0011] The aforementioned Creep index can be calculated using the following formula 1.

[0012] [Formula 1] Creep index=Creep deformation rate / Creep stress

[0013] In the above formula 1, the creep deformation ratio can be calculated using the following formula 2.

[0014] [Formula 2] Creep deformation ratio = (length tensed after 3600 seconds - length tensed at 1% strain) / (measured length of the test specimen)

[0015] In the above formula 1, the creep stress can be calculated using the following formula 3.

[0016] [Formula 3] Creep stress = 1% strain tensile strength / yield tensile strength

[0017] In the above equation 3, the 1% strain tensile strength means the stress value required to deform the film by 1% strain. The yield tensile strength means the stress at the contact point generated by offsetting the Modulus (gradient) of the S-S Curve by 0.2%.

[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 an embodiment of the present invention, the filler contained in the optical film has a rod shape or a fibrous shape and can entangle the polymer chains constituting the light-transmissive matrix. As a result, the mechanical strength of the optical film can be improved. As a result, when the optical film according to an embodiment of the present invention is used in a display device, it is possible to prevent or suppress breakage during folding and improve the force resistant to deformation. Also, when an external force is continuously applied under the same conditions, the degree of deformation is small.

Brief Description of the Drawings

[0020] [Figure 1] It is a schematic diagram of an optical film according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view of a part of a display device according to another embodiment of the present invention. [Figure 3] It is an enlarged cross-sectional view of the "P" part in FIG. 2.

Modes for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments described below are merely presented for illustrative purposes to assist in a clear understanding of the present invention and do not limit the scope of the present invention.

[0022] The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are exemplary, and thus the present invention is not limited to the matters illustrated in the drawings. Throughout the specification, the same components can be referred to by the same reference numerals. When explaining the present invention, if it is determined that a specific explanation of related known technologies may unnecessarily impair the gist of the present invention, the detailed explanation thereof will be omitted.

[0023] When terms such as "comprising", "having", "forming", etc. referred to in this specification are used, other parts can be added unless the expression "only" is used. When a component is expressed in the singular, it includes a plurality unless otherwise explicitly stated. Also, when interpreting a component, it is construed to include an error range even without a separate explicit description.

[0024] In the case of an explanation of a positional relationship, for example, when the positional relationship between two parts is explained by "on", "above", "below", "beside", etc., one or more other parts may be located between the two parts unless the expressions "immediately" or "directly" are used.

[0025] Spatially relative terms such as "below", "beneath", "lower", "above", "upper", etc. can be used to easily describe the correlation between one element or component and another element or component as shown in the drawings. Spatially relative terms should be understood as terms including different directions of elements during use or operation in addition to the directions illustrated in the drawings. For example, when an element illustrated in the drawings is inverted, an element described as "below" or "beneath" another element may be placed "above" the other element. Therefore, the exemplary term "below" may include all directions of up and down. Similarly, the exemplary term "above" may include all directions of up and down.

[0026] When describing temporal relationships, for example, when a temporal sequence is described using phrases such as "after," "following," "next," or "before," it may include non-continuous events unless expressions like "immediately" or "directly" are used.

[0027] While terms such as "first," "second," etc., are used to describe various components, these components are not limited by these terms. These terms are simply used to distinguish one component from another. Therefore, the first component referred to below may be the second component within the technical concept of the present invention.

[0028] The term "at least one" should be understood to include all possible combinations of one or more related items. For example, "at least one of items 1, 2, and 3" could mean not just each of items 1, 2, or 3 individually, but all possible combinations of items that can be presented from two or more of items 1, 2, and 3.

[0029] The features of each of the various embodiments of the present invention can be combined or linked together, either partially or entirely, enabling various technical interlocking and driving mechanisms. Each embodiment may be implemented independently of the others, or they may be implemented together in relation to one another.

[0030] Figure 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 transmittance is called an optical film (100).

[0031] 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.

[0032] 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.

[0033] According to one embodiment of the present invention, the light-transmitting matrix (110) may contain at least one of imide repeating units and amide repeating units.

[0034] A light-transmitting matrix (110) according to one embodiment of the present invention can be produced, for example, from monomer components comprising a dianehydride and a diamine. Specifically, the light-transmitting matrix (110) may include imide repeating units formed by the dianehydride and the diamine.

[0035] However, the light-transmitting matrix (110) according to one embodiment of the present invention is not limited thereto, and the light-transmitting matrix (110) can be produced from monomer components containing dicarbonyl compounds in addition to dianehydrides and diamines. The light-transmitting matrix (110) according to one embodiment of the present invention may have imide repeating units and amide repeating units. An example of a light-transmitting matrix (110) having imide repeating units and amide repeating units is a polyamide-imide resin.

[0036] According to one embodiment of the present invention, the light-transmitting matrix (110) may include a polyimide polymer. Examples of polyimide polymers include polyimide polymers and polyamide-imide polymers. The light-transmitting matrix (110) according to one embodiment of the present invention can be made, for example, from a polyimide polymer resin.

[0037] The light-transmitting matrix (110) can have a thickness sufficient to protect the display panel from the optical film (100). For example, the light-transmitting matrix (110) can 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).

[0038] According to one embodiment of the present invention, the filler (120) can be rod-shaped or fibrous. Hereinafter, a shape in which the length is greater than the diameter is referred to as fibrous. A fibrous shape can also be called a filamentous shape. According to one embodiment of the present invention, the length of the filler (120) may be more than twice the diameter.

[0039] According to one embodiment of the present invention, the filler (120) is fibrous and can intertwine the polymer chains constituting the light-transmitting matrix (110). As a result, the stability and arrangement characteristics of the polymer chains are improved, the mechanical properties of the light-transmitting matrix (110) can be improved, and the mechanical properties of the optical film (100) can also be improved.

[0040] According to one embodiment of the present invention, the aspect ratio of the filler (120) may be in the range of 30 to 2,000. The aspect ratio is the ratio of the length of the filler (120) to its diameter.

[0041] If the aspect ratio of filler (120) is less than 30, the filler (120) is not long enough, and therefore its function of intertwining polymer chains with each other may not be fully realized, potentially resulting in insufficient improvement of polymer chain stability and sequence characteristics.

[0042] If the aspect ratio of the filler (120) exceeds 2,000, the length of the filler (120) becomes too long, reducing its dispersibility and potentially causing aggregation of the filler (120) within the light-transmitting matrix (110). As a result, the light transmittance of the optical film (100) may decrease, haze may increase, and the optical properties of the optical film (100) may deteriorate. Furthermore, the mechanical strength of the optical film (100) may decrease in the areas where the aggregated filler (120) occurs, potentially reducing the modulus of the optical film (100) and thus reducing its mechanical strength.

[0043] According to one embodiment of the present invention, the length of the filler (120) may be in the range of 1 to 6 μm.

[0044] If the length of filler(120) is less than 1 μm, the function of filler(120) in intertwining polymer chains may not be fully exhibited.

[0045] If the length of the filler (120) exceeds 6 μm, the dispersibility of the filler (120) may decrease, resulting in aggregation of the filler (120) within the light-transmitting matrix (110), and gelation may occur due to interaction with polymer chains. This may reduce the light transmittance of the optical film (100), increase haze, and potentially degrade the optical properties of the optical film (100).

[0046] According to one embodiment of the present invention, the diameter of the filler (120) may be in the range of 3 to 33 nm.

[0047] If the diameter of the filler (120) is less than 3 nm, the stability of the filler (120) may decrease, causing the filler to break or shatter, contaminating the optical film (100) and potentially increasing the haze of the optical film (100).

[0048] If the diameter of the filler (120) exceeds 33 nm, it may be difficult for the filler (120) to have a fibrous structure, or the function of intertwining polymer chains with each other may be reduced, potentially leading to an increase in the optical film (100) or a decrease in transmittance.

[0049] There are no particular restrictions on the type of filler (120). Any fibrous material can be used as filler (120) according to one embodiment of the present invention, without any restrictions on its type. Filler (120) may be inorganic or organic. Filler (120) may contain at least one of inorganic fibers, organic fibers, and organic-inorganic composite fibers.

[0050] More specifically, the filler (120) can be fibrous. For example, the filler (120) can be a single-stranded fibrous material, a multi-stranded fibrous material, or a structure in which multiple chains are arranged in a branch-like manner around a single central chain.

[0051] According to one embodiment of the present invention, the filler (120) may contain at least one of glass fiber, aluminum fiber, and fluoride fiber.

[0052] Glass fibers contain SiO2 and may further contain other components besides SiO2. Aluminum fibers contain Al2O3 and may further contain other components besides Al2O3. Fluorine fibers may contain at least one of PTFE (Polytetrafluoroethylene) and PVDF (Polyvinylidene Fluoride), and may further contain other components besides PTFE and PVDF.

[0053] According to one embodiment of the present invention, the filler (120) may contain at least one of alumina oxide hydroxide, SiO2, Al2O3, PTFE (Polytetrafluoroethylene), and PVDF (Polyvinylidene Fluoride).

[0054] According to one embodiment of the present invention, the filler (120) can be surface-treated. For example, fibers surface-treated with an organic compound group having an alkoxy group can be used as the filler (120).

[0055] According to one embodiment of the present invention, the aluminum fiber may contain at least one of alumina oxide hydroxide and Al2O3. Alumina oxide hydroxide is also called boehmite and can be represented as γ-AlO(OH). More specifically, the alumina oxide hydroxide may contain a structure represented by any one of the following chemical formulas 1, 2, and 3.

[0056] [Chemical formula 1] JPEG0007866649000001.jpg6099

[0057] [Chemical formula 2] JPEG0007866649000002.jpg61119

[0058] [Chemical formula 3] JPEG0007866649000003.jpg76119

[0059] Here, n is in the range of 1,000 to 20,000, m is in the range of 1,000 to 20,000, and p is in the range of 1,000 to 20,000.

[0060] To aid in understanding the structure of filler(120), extending the structures of chemical formulas 1, 2, and 3, filler(120) may also include a structure represented by any one of the following chemical formulas 4, 5, and 6.

[0061] The structure represented by chemical formula 1 can be represented, for example, by the following chemical formula 4. The following chemical formula 4 corresponds to the case where n is 3 in chemical formula 1.

[0062] [Chemical formula 4] JPEG0007866649000004.jpg70170

[0063] The structure represented by chemical formula 2 can be represented, for example, by the following chemical formula 5. The following chemical formula 5 corresponds to the case where m is 4 in chemical formula 2.

[0064] [Chemical formula 5] JPEG0007866649000005.jpg51170

[0065] The structure represented by chemical formula 3 can be represented, for example, by the following chemical formula 6. The following chemical formula 6 corresponds to the case where p is 5 in chemical formula 3.

[0066] [Chemical formula 6] JPEG0007866649000006.jpg66170

[0067] In the chemical formulas 4-6 above, "*" indicates the bond position.

[0068] According to one embodiment of the present invention, Al2O3 can have a unit structure represented by the following chemical formula 7.

[0069] [Chemical formula 7] JPEG0007866649000007.jpg27117

[0070] According to one embodiment of the present invention, SiO2 can have a unit structure represented by the following chemical formula 8.

[0071] [Chemical formula 8] JPEG0007866649000008.jpg82114

[0072] 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) can be adjusted to enhance the light scattering effect.

[0073] According to one embodiment of the present invention, the content of filler (120) may be 3 to 50 PHR. More specifically, the content of filler (120) can be adjusted to 4 to 30 PHR, or to 5 to 20 PHR.

[0074] If the filler (120) content is less than 3 PHR, the light scattering effect by the filler (120) is minimal, which may result in little to no improvement in the light transmittance of the optical film (100), and the function of the filler (120) in intertwining polymer chains may not be fully exercised.

[0075] On the other hand, if the content of filler (120) exceeds 50 PHR, the dispersibility of filler (120) decreases, which may reduce the haze of the optical film (100), causing aggregation of filler (120) due to the excess amount of filler (120). This aggregated filler (120) may block light, potentially reducing the light transmittance of the optical film (100).

[0076] Figure 2 is a cross-sectional view of a part of a display device (200) according to another embodiment of the present invention, and Figure 3 is an enlarged cross-sectional view of the "P" portion of Figure 2.

[0077] Referring to Figure 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).

[0078] Referring to Figures 2 and 3, the display panel (501) includes a substrate (510), thin-film transistors (TFTs) on the substrate (510), and organic light-emitting elements (570) connected to the thin-film transistors (TFTs). The organic light-emitting elements (570) include 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 Figures 2 and 3 is, for example, an organic light-emitting display device.

[0079] The substrate (510) can be made of glass or plastic. Specifically, the substrate (510) can be made of polyimide resin or plastic such as optical film. Although not shown, a buffer layer can be placed on the substrate (510).

[0080] The thin-film transistor (TFT) is placed on a substrate (510). The thin-film transistor (TFT) includes a semiconductor layer (520), a gate electrode (530) insulated from the semiconductor layer (520) and superimposed on at least a portion of the semiconductor layer (520), a source electrode (541) connected to the semiconductor layer (520), and a drain electrode (542) separated from the source electrode (541) and connected to the semiconductor layer (520).

[0081] Referring to Figure 3, a gate insulating film (535) is placed between the gate electrode (530) and the semiconductor layer (520). An interlayer insulating film (551) is placed on the gate electrode (530), and a source electrode (541) and a drain electrode (542) can be placed on the interlayer insulating film (551).

[0082] The planarization film (552) is placed on a thin-film transistor (TFT) and planarizes the top surface of the thin-film transistor (TFT).

[0083] The first electrode (571) is placed on the planarization film (552). The first electrode (571) is connected to a thin-film transistor (TFT) through a contact hole provided in the planarization film (552).

[0084] The bank layer (580) is positioned on a portion of the first electrode (571) and on the planarization film (552) and defines a pixel region or light-emitting region. For example, the bank layer (580) can define a pixel region by being positioned in a matrix structure in the boundary region between multiple pixels.

[0085] The organic light-emitting layer (572) is placed on the first electrode (571). The organic light-emitting layer (572) can also be placed on the bank layer (580). The organic light-emitting layer (572) may include one light-emitting layer or two light-emitting layers stacked vertically. Such an organic light-emitting layer (572) can emit light of any one of the colors red, green, and blue, or it may emit white light.

[0086] The second electrode (573) is placed on the organic light-emitting layer (572).

[0087] The first electrode (571), the organic light-emitting layer (572), and the second electrode (573) are stacked to form an organic light-emitting element (570).

[0088] Although not shown, if the organic light-emitting layer (572) emits white light, individual pixels may include color filters to filter the white light emitted from the organic light-emitting layer (572) by wavelength. The color filters are formed on the light path.

[0089] A thin film sealing layer (590) can be placed on the second electrode (573). The thin film sealing layer (590) may include at least one organic film and at least one inorganic film, and the at least one organic film and at least one inorganic film may be arranged alternately.

[0090] An optical film (100) is placed on the display panel (501) having the laminated structure described above. The optical film (100) includes a light-transmitting matrix (110) and fillers (120) dispersed in the light-transmitting matrix (110).

[0091] According to one embodiment of the present invention, the creep deformation ratio of the optical film (100) is 0.46 or less, and the creep deformation ratio is calculated by the following formula 1.

[0092] [Formula 1] Creep index=Creep deformation rate / Creep stress

[0093] In the above formula 1, the creep deformation ratio can be calculated using the following formula 2.

[0094] [Formula 2] Creep deformation ratio = (length tensed after 3600 seconds - length tensed at 1% strain) / (measured length of the test specimen)

[0095] In the above formula 1, the creep stress can be calculated using the following formula 3.

[0096] [Formula 3] Creep stress = 1% strain tensile strength / yield tensile strength

[0097] In the above equation 3, the 1% strain tensile strength means the stress value required to deform the film by 1% strain. The aforementioned yield tensile strength represents the stress at the contact point resulting from a 0.2% offset of the Modulus (slope) of the SS Curve.

[0098] If the Creep deformation ratio is 0.46 or higher, the level of deformation under external force may be greater, and the resistance to deformation may be weaker. As a result, the bending angle of the film may be larger when folded, and the film may break.

[0099] An optical film (100) according to one embodiment of the present invention may have a Martens hardness (HM) in the range of 200 to 300 MPa. More specifically, the optical film (100) may have a Martens hardness (HM) in the range of 230 to 270 MPa, or 250 to 265 MPa.

[0100] If the Martens hardness (HM) of the optical film (100) is less than 200 MPa, it may be vulnerable to external impacts. In other words, if external force is applied to the outside of the film, it may easily develop scratches or cracks.

[0101] If the Martens hardness (HM) of the optical film (100) exceeds 300 MPa, the optical film (100) may be easily damaged.

[0102] An optical film (100) according to one embodiment of the present invention may have a Vickers hardness (HV) in the range of 40 to 70. More specifically, the optical film (100) may have a Vickers hardness (HV) in the range of 43 to 56, or 46 to 53.

[0103] If the Vickers hardness (HV) of an optical film (100) is less than 40, it may be vulnerable to external impacts. In other words, if external force is applied to the outside of the film, it may easily develop scratches or cracks.

[0104] If the Vickers hardness (HV) of the optical film (100) exceeds 70, the optical film (100) may be easily damaged.

[0105] An optical film (100) according to one embodiment of the present invention may have a creep stress in the range of 0.5 to 0.65. More specifically, the optical film (100) may have a creep stress in the range of 0.55 to 0.63, or 0.57 to 0.6.

[0106] If the creep stress of the optical film (100) is less than 0.5, it means that less energy is required to deform the optical film. In other words, it has a low resistance to external forces and can easily deform due to those forces.

[0107] The following describes a method for producing an optical film (100) according to one embodiment of the present invention.

[0108] A method for producing an optical film (100) according to one embodiment of the present invention may include the steps of: first dispersing a filler (120) in a resin solution for forming a polymer matrix (110) to produce a first mixed solution; and casting the first mixed solution to produce a cast film.

[0109] According to one embodiment of the present invention, a polyimide-based resin solution can be used as the resin solution for forming the polymer matrix (110).

[0110] More specifically, a method for producing an optical film (100) according to one embodiment of the present invention may include the steps of: producing a polyimide resin powder; dissolving the polyimide resin powder in a first solvent to produce a polyimide resin solution; preparing a dispersion; and mixing the filler dispersion and the polyimide resin solution to produce a first mixed solution.

[0111] A filler dispersion can be prepared, for example, by dispersing filler (120) in a second solvent.

[0112] As the first solvent, DMAc (N,N-Dimethylacetamide) can be used. As the second solvent, DMAc (N,N-Dimethylacetamide) or methyl ethyl ketone (MEK) can be used. However, the embodiment of the present invention is not limited to these, and other known solvents can be used as the first and second solvents.

[0113] According to one embodiment of the present invention, the pH of the first mixture can be adjusted to improve the dispersibility of the filler (120). For example, the pH of the first mixture can be adjusted to a range of 5 to 7. This prevents aggregation or clumping of the filler (120).

[0114] Next, the first mixture can be cast, dried, and heat-treated to form an optical film (100). According to one embodiment of the present invention, the film formed by casting the first mixture is called a cast film, and the film produced by drying and heat-treating the cast film is called an optical film (100). The cast film can be called an uncured film.

[0115] Furthermore, convection can be prevented during the drying and heat treatment processes of the cast film formed by casting, and the filler (120) can be oriented in a certain direction.

[0116] 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, drying of the cast film can be carried out while increasing the temperature from 80°C to 120°C at a rate of 1°C / 1 minute. Once dried to a certain level or higher, the orientation of the filler (120) can be fixed.

[0117] The present invention will be described more specifically below with reference to exemplary manufacturing examples and embodiments. However, the present invention is not limited by the manufacturing examples and embodiments described below.

[0118] <Manufacturing Example 1: Production of Polyimide Polymer Solids> A 1 L reactor equipped with a stirrer, nitrogen injection device, dropping funnel, temperature controller, and condenser was filled with 719.104 g of DMAc (N,N-Dimethylacetamide) while passing nitrogen through it. After adjusting the reactor temperature to 25°C, 54.439 g (0.17 mol) of TFDB was dissolved, and this solution was maintained at 25°C. 13.505 g (0.046 mol) of BPDA was added and stirred for 3 hours to completely dissolve the BPDA. Then, 9.063 g (0.020 mol) of 6FDA was added and completely dissolved. After lowering the reactor temperature to 10°C, 21.053 g (0.104 mol) of TPC was added, and the mixture was reacted at 25°C for 12 hours to obtain a polymer solution with a solid content of 12% by weight.

[0119] To the obtained polymer solution, 11.54 g of pyridine and 14.90 g of acetic anhydride were added and stirred for 30 minutes. The temperature was then raised again to 80°C, and the mixture was stirred at the same temperature for 1 hour to allow the reaction to proceed. After cooling to room temperature, 20 L of methanol was added to the obtained polymer solution to precipitate the solids. The precipitated solids were filtered and pulverized, then washed again with 2 L of methanol, and dried under vacuum at 100°C for 6 hours or more to obtain a powdered polyimide polymer solid. The polyimide polymer solid produced here is a polyamide-imide polymer solid.

[0120] <Example 1> After filling a 1L reactor with 723.46g of DMAc (first solvent), the reactor was stirred for a certain period of time while maintaining the reactor temperature at 10°C. Then, 110g of the solid component powder polyamide-imide (polyimide resin powder) produced in Production Example 1 was added, and after stirring for 1 hour, the temperature was raised to 25°C to produce a liquid polyimide resin solution.

[0121] Subsequently, 55 g of an alumina hydrate-based filler dispersion, in which alumina hydrate-based fillers with an average particle size of 4 nm and an average length of 1500 nm are dispersed in a DMAc (N,N-dimethylacetamide) solution (second solvent) at a content of 10% by weight, was slowly added to the prepared liquid polyimide resin solution using a cylinder pump over a period of 1 hour to produce a first mixed solution in which the silica dispersion and the polyimide resin solution were mixed.

[0122] Immediately after preparing the first mixture, the pH of the first mixture is measured and found to be above 8. To improve the arrangement characteristics of the filler (120), a weak acid such as acetic acid is added to the first mixture to adjust its pH to a range of 5 to 7. The first mixture thus prepared is a polyimide resin solution in which fibrous filler (120) is dispersed.

[0123] The obtained first mixture was cast. A cast substrate is used for casting. There are no particular restrictions on the type of cast substrate. Glass substrates, stainless steel (SUS) substrates, Teflon (registered trademark) substrates, etc., can be used as cast substrates. According to one embodiment of the present invention, a glass substrate can be used as the cast substrate.

[0124] To maintain the orientation of the filler (120) during the drying process of the cast film, the film was manufactured by placing it in an 80°C hot air oven and slowly drying it to 120°C at a rate of 1°C / min for approximately 40 minutes. The manufactured film was then peeled from the glass substrate and fixed to the frame with pins.

[0125] The frame with the film fixed to it 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 the optical film. The optical film was then heat-treated again at 250°C for 5 minutes.

[0126] As a result, an optical film (100) with a thickness of 50 μm was completed, containing a light-transmitting matrix (110) and a silica-based filler (120) dispersed in the light-transmitting matrix.

[0127] <Example 2-3> Optical films (100) were manufactured in the same manner as in Example 1, according to the conditions in Table 1, and these were designated as Examples 2-3, respectively.

[0128] <Comparative Example 1-7> Optical films (100) were manufactured in the same manner as in Example 1, according to the conditions in Table 1, and these were designated as Comparative Examples 1-7.

[0129] [Table 1]

[0130] 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 15 nm. Specifically, filler 1 has a length of 1.5 μm and a diameter of 4 nm.

[0131] In Table 1, the molar ratios represent the relative molar ratios to 100 moles of the total diamine.

[0132] In Table 1, PHR stands for Per Hundred Resin, and means the weight (g) of filler per 100g (g) of light-transmitting matrix. Specifically, in one embodiment of the present invention, PHR means the weight (g) of filler added per 100g (g) of polyimide polymer solids.

[0133] The following physical properties were measured for the optical films produced in Examples 1-3 and Comparative Examples 1-7.

[0134] (1) Measurement of Martens hardness (HM) Measurements were taken using Fisher's HM-2000. -Force:12mN -Running Time: 12s -Hold Time: 5s

[0135] (2) Measurement of Vickers hardness (Hv) Measurements were taken using Fisher's HM-2000. -Force:12mN -Running Time: 12s -Hold Time: 5s

[0136] (3) Measurement of modulus The modulus of the optical film was measured using an Instron universal tensile testing machine (MODEL 5967) according to the ASTM D885 method. - Measurement standards within 3 hours after film manufacturing -Road Cell 30KN, Grip 250N. - Test specimen size 10mm x 50mm, tensile speed 25mm / min

[0137] (4) Measurement of yield tensile strength - Stress value at the point of tangency obtained by offsetting the Modulus (slope) of the SS Curve by 0.2% -Measurements were taken using an Instron universal tensile testing machine (MODEL 5967).

[0138] (5) Measurement of 1% Strain Tensile Strength Stress value when -1% Straight is reached -Measurements were taken using an Instron universal tensile testing machine (MODEL 5967).

[0139] (6) Measurement of Creep area Creep stress is calculated using the following formula 3. [Formula 3] Creep stress = 1% strain tensile strength / yield tensile strength

[0140] (7) Measurement of Creep deformation ratio Creep deformation ratio = (length tensed after 3600 seconds - length tensed at 1% strain) / (measured length of the test specimen)

[0141] (8) Measurement of Creep deformation ratio The Creep index is calculated using the following formula 1. [Formula 1] Creep index=Creep deformation rate / Creep stress

[0142] (9) Conditions for the Creep Test The creep properties of the optical film were measured using an Instron universal tensile testing machine (MODEL 5967). -Road Cell 30KN, Grip 250N. - Test specimen size 10mm x 50mm, tensile speed 25mm / min -Hold Strain:1% - Hold Time: 60 min

[0143] The measurement results are shown in Table 2 below.

[0144] [Table 2]

[0145] As disclosed 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 a Creep index of 0.46 or less. [Explanation of Symbols]

[0146] 100: Optical film 110: Light-transmitting matrix 120: Filler 200:Display device 501: Display Panel

Claims

1. Light-transmitting matrix; and The light-transmitting matrix contains a filler comprising alumina oxide hydroxide, Having a Creep index of 0.452 or higher and 0.459 or lower, The aforementioned filler has an aspect ratio of 30 to 2,000. The aspect ratio is the ratio of the length of the filler to its diameter. The content of the filler is 3 to 50 PHR per 100 weight of the light-transmitting matrix. The light-transmitting matrix is ​​an optical film comprising at least one of imide repeating units and amide repeating units: The aforementioned Creep index is calculated using the following formula 1: [Formula 1] Creep index = Creep deformation rate / Creep stress In the above formula 1, the Creep deformation ratio is calculated by the following formula 2: [Formula 2] Creep deformation ratio = (length tensed after 3600 seconds - length tensed at 1% strain) / (measured length of the test specimen) In the above equation 1, the creep stress is calculated by the following equation 3: [Formula 3] Creep stress = 1% strain tensile strength / yield tensile strength In the above equation 3, the 1% strain tensile strength means the stress value required to deform the film by 1% strain. The aforementioned yield tensile strength refers to the stress at the contact point resulting from offsetting the Modulus (slope) of the SS Curve by 0.2%.

2. The optical film according to claim 1, wherein the filler is in the shape of a rod or fibers.

3. The optical film according to claim 2, wherein the filler has a length in the range of 1 to 6 μm.

4. The optical film according to claim 2, wherein the filler has a diameter in the range of 3 to 33 nm.

5. The optical film according to claim 1, wherein the filler comprises at least one of glass fiber, aluminum fiber, and fluoride fiber.

6. The filler is alumina oxide hydroxide, SiO2. 2 , Al 2 O 3 The optical film according to claim 1, comprising at least one of PTFE (Polytetrafluoroethylene) and PVDF (Polyvinylidene Fluoride).

7. The optical film according to claim 1, having a Martens hardness (HM) in the range of 200 to 300 MPa: The Martens hardness (HM) is the Martens hardness of the optical film. The aforementioned Martens hardness (HM) is measured using an HM-2000 under the conditions of 12 mN / Running Time 12 s / Hold time 5 s.

8. The optical film according to claim 1, having a Vickers hardness (HV) in the range of 40 to 70: The Vickers hardness (HV) is the Vickers hardness of the optical film. The Vickers hardness (HV) is measured using an HM-2000 under the conditions of 12 mN / Running Time 12 s / Hold time 5 s.

9. The optical film according to claim 1, wherein the Creep stress is in the range of 0.5 to 0.

65.

10. Display panel; and A display device comprising an optical film according to any one of claims 1 to 9, disposed on the display panel;

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