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, with the thinning, lightening, and flexibilization of display devices, it has been considered to use an optical film instead of glass as a cover window. In order 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 target physical properties to an optical film that requires various physical properties, 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] Still another embodiment of the present invention provides an optical film having a Martens hardness (HM) in the range of 200 to 300 MPa.

[0007] Still 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 a display device.

[0009] Another embodiment of the present invention provides a display device including the optical film.

Means for Solving the Problems

[0010] One embodiment of the present invention provides an optical film including a light-transmissive matrix and fillers dispersed in the light-transmissive matrix, and having a creep index of 0.46 or less.

[0011] The creep index can be calculated by the following formula 1.

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

[0013] In the formula 1, the creep deformation rate can be calculated by the following formula 2.

[0014] [Formula 2] Creep deformation rate = (Tensile length after 3600 s - Tensile length at 1% strain) / (Test piece measurement length)

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

[0016] [Formula 3] Creep stress = Tensile strength at 1% strain / Yield tensile strength

[0017] In the formula 3, the tensile strength at 1% strain 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.

Advantages 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

Figure 2

Figure 3

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. In explaining the present invention, when it is determined that a specific description of related known technologies may unnecessarily impair the gist of the present invention, the detailed description 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. Further, in interpreting a component, even without a separate explicit description, it is construed as including an error range.

[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 can 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] In the case of an explanation regarding the relationship of time, for example, when the temporal sequence is explained by expressions such as "after ~", "subsequent to ~", "next to ~", "before ~", etc., it may include non - consecutive cases unless the expressions "immediately" or "directly" are used.

[0027] The first, second, etc. are used to describe various components, but these components are not limited by these terms. These terms are merely used to distinguish one component from another. Therefore, the first component mentioned below can be the second component within the technical concept of the present invention.

[0028] The term "at least one" must be understood to include all combinations that can be presented from one or more related items. For example, the meaning of "at least one of the first item, the second item, and the third item" can mean not only each of the first item, the second item, or the third item alone, but also all combinations of two or more items that can be presented from among the first item, the second item, and the third item.

[0029] The respective features of the various embodiments of the present invention can be partially or wholly combined or combined with each other, various linkages and drives are technically possible, and in some cases, each embodiment can be implemented independently of each other, and in other cases, they can be implemented together as a related relationship.

[0030] FIG. 1 is a schematic diagram of an optical film (100) according to an embodiment of the present invention. According to an embodiment of the present invention, a film having light - transmissivity is referred to as an optical film (100).

[0031] An optical film (100) according to an embodiment of the present invention includes a light - transmissive matrix (110) and a filler (120) dispersed in the light - transmissive matrix.

[0032] The light-transmissive matrix (110) has light transmissivity. According to an embodiment of the present invention, the light-transmissive matrix (110) can have flexible characteristics. For example, the light-transmissive matrix (110) can have bending characteristics, folding characteristics, or rollable characteristics. As a result, the optical film (100) according to an embodiment of the present invention has light transmissivity and can have bending characteristics, folding characteristics, or rollable characteristics.

[0033] According to an embodiment of the present invention, the light-transmissive matrix (110) may include at least one of an imide repeating unit and an amide repeating unit.

[0034] The light-transmissive matrix (110) according to an embodiment of the present invention can be manufactured from monomer components including, for example, dianhydride and diamine. Specifically, the light-transmissive matrix (110) can include an imide repeating unit formed by dianhydride and diamine.

[0035] However, the light-transmissive matrix (110) according to an embodiment of the present invention is not limited thereto, and the light-transmissive matrix (110) can be manufactured from monomer components including a dicarbonyl compound in addition to dianhydride and diamine. The light-transmissive matrix (110) according to an embodiment of the present invention can have an imide repeating unit and an amide repeating unit. As the light-transmissive matrix (110) having an imide repeating unit and an amide repeating unit, for example, there is a polyamide-imide resin.

[0036] According to an embodiment of the present invention, the light-transmissive matrix (110) can include a polyimide-based polymer. Examples of the polyimide-based polymer include a polyimide polymer, a polyamide-imide polymer, and the like. The light-transmissive matrix (110) according to an embodiment of the present invention can be made of, for example, a polyimide-based polymer resin.

[0037] The light-transmissive matrix (110) can have a thickness sufficient for the optical film (100) to protect the display panel. For example, the light-transmissive matrix (110) can have a thickness of 10 to 100 μm. The thickness of the light-transmissive matrix (110) may be the same as the thickness of the optical film (100).

[0038] According to an embodiment of the present invention, the filler (120) can have a rod shape or a fibrous shape. Hereinafter, a shape in which the length is larger than the diameter is referred to as a fibrous shape. According to an embodiment of the present invention, the length of the filler (120) may be more than twice as large as the diameter.

[0039] According to an embodiment of the present invention, the filler (120) has a fibrous shape and can entangle the polymer chains constituting the light-transmissive matrix (110) with each other. As a result, the stability and arrangement characteristics of the polymer chains are improved, the mechanical properties of the light-transmissive matrix (110) can be improved, and the mechanical properties of the optical film (100) can also be improved.

[0040] According to an 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 to the diameter of the filler (120).

[0041] When the aspect ratio of the filler (120) is less than 30, since the filler (120) is not long enough, the function of entangling the polymer chains with each other may not be sufficiently exerted, and the effect of improving the stability and arrangement characteristics of the polymer chains may not be sufficiently exerted.

[0042] When the aspect ratio of the filler (120) exceeds 2,000, the length of the filler (120) is too long, the dispersibility of the filler (120) decreases, and aggregation of the filler (120) may occur 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. Also, the mechanical strength of the optical film (100) may decrease at the portion where the aggregation of the filler (120) occurs. As a result, the modulus of the optical film (100) may decrease, and the mechanical strength of the optical film (100) may decrease.

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

[0044] When the length of the filler (120) is less than 1 μm, the function of the filler (120) to entangle polymer chains with each other may not be sufficiently exerted.

[0045] When the length of the filler (120) exceeds 6 μm, the dispersibility of the filler (120) may decrease. As a result, aggregation of the filler (120) may occur within the light-transmitting matrix (110), and gelation is likely to occur due to the interaction with the polymer chains. Thereby, 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.

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

[0047] When the diameter of the filler (120) is less than 3 nm, the stability of the filler (120) may decrease, the filler may break or be crushed, contaminating the optical film (100), and the haze of the optical film (100) may increase.

[0048] When the diameter of the filler (120) exceeds 33 nm, it may be difficult for the filler (120) to have a fibrous shape, the function of entangling polymer chains with each other may decrease, the optical film (100) may increase, and the transmittance may decrease.

[0049] There is no particular limitation on the type of the filler (120). As long as it has a fibrous shape, it can be used as the filler (120) according to an embodiment of the present invention without limitation to its type. The filler (120) may be an inorganic substance or an organic substance. The filler (120) may contain at least one of inorganic fiber, organic fiber, and organic-inorganic composite fiber.

[0050] More specifically, the filler (120) can have a fibrous shape. For example, the filler (120) can have a single-stranded fibrous shape, a multi-stranded fibrous shape, or a shape in which a plurality of strands are arranged in a branch shape on a single central strand.

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

[0052] 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 fluoride 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.

[0053] According to an 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).

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

[0056] [Chemical Formula 1] JPEG2025523540000002.jpg6099

[0057] [Chemical Formula 2] JPEG2025523540000003.jpg61119

[0058] [Chemical Formula 3] JPEG2025523540000004.jpg76119

[0059] Here, n ranges from 1,000 to 20,000, m ranges from 1,000 to 20,000, and p ranges from 1,000 to 20,000.

[0060] To help understand the structure of the filler (120), when expanding the structures of Chemical Formulas 1, 2, and 3, the filler (120) may 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 by, for example, 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] JPEG2025523540000005.jpg70170

[0063] The structure represented by Chemical Formula 2 can be represented by, for example, 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] JPEG2025523540000006.jpg51170

[0065] The structure represented by Chemical Formula 3 can be represented by, for example, 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] JPEG2025523540000007.jpg66170

[0067] In the above Chemical Formulas 4 to 6, "*" indicates the bonding position.

[0068] According to an embodiment of the present invention, Al2O3 can have a unit structure represented by the following Chemical Formula 7.

[0069] [Chemical Formula 7] JPEG2025523540000008.jpg27117

[0070] According to an embodiment of the present invention, SiO2 can have a unit structure represented by the following Chemical Formula 8.

[0071] [Chemical Formula 8] JPEG2025523540000009.jpg82114

[0072] According to an embodiment of the present invention, when the filler (120) is added, appropriate light scattering is generated by the filler (120), and the optical properties of the optical film (100) can be improved. In order to enhance the light scattering effect, the content of the filler (120) contained in the optical film (100) can be adjusted.

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

[0074] When the content of the filler (120) is less than 3 PHR, since the light scattering effect by the filler (120) is negligible, the effect of improving the light transmittance of the optical film (100) may hardly appear, and the function of the filler (120) to entangle polymer chains with each other may not be fully exerted.

[0075] On the other hand, when the content of the filler (120) exceeds 50 PHR, the dispersibility of the filler (120) decreases, the haze of the optical film (100) may decrease, aggregation of the filler (120) due to the excessive filler (120) occurs, and the aggregated filler (120) like this may block light, and the light transmittance of the optical film (100) may decrease.

[0076] 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" part in FIG. 2.

[0077] 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).

[0078] Referring to FIGS. 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 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.

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

[0080] 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 part 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).

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

[0082] The planarization film (552) is disposed on the thin film transistor (TFT) to planarize the upper part of the thin film transistor (TFT).

[0083] 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 provided in the planarization film (552).

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

[0085] The organic light-emitting layer (572) is disposed on the first electrode (571). The organic light-emitting layer (572) can also be disposed on the bank layer (580). The organic light-emitting layer (572) can include one light-emitting layer, or can include two light-emitting layers stacked one on top of the other. In such an organic light-emitting layer (572), light having any one of red, green, and blue colors can be emitted, or white light can be emitted.

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

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

[0088] Although not shown, when the organic light-emitting layer (572) emits white light, an individual pixel can 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 light travel path.

[0089] 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.

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

[0091] According to an 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 formula 1, the Creep deformation rate can be calculated by the following formula 2.

[0094] [Formula 2] Creep deformation rate = (Tensile length after 3600s - Tensile length at 1% strain) / (Test piece measurement length)

[0095] In the formula 1, the Creep stress can be calculated by the following formula 3.

[0096] [Formula 3] Creep stress = Tensile strength at 1% strain / Yield tensile strength

[0097] In the formula 3, the tensile strength at 1% strain means the stress value required to deform the film by 1% strain, and 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%.

[0098] When the Creep deformation ratio is 0.46 or more, the level of deformation under an external force may be greater, and the force resisting deformation may be weak. As a result, the bending angle of the film during folding may be large, and the film may break.

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

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

[0101] If the martensite 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 an 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, and may be 46 to 53.

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

[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 an 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, and may be 0.57 to 0.6.

[0106] When the Creep stress of the optical film (100) is less than 0.5, it means that less energy is required for the deformation of the optical film. In other words, the force resisting the external force is small, and it may be easily deformed by the external force.

[0107] Hereinafter, a method for manufacturing an optical film (100) according to an embodiment of the present invention will be described.

[0108] The method for manufacturing an optical film (100) according to an embodiment of the present invention may include a step of primarily dispersing a filler (120) in a resin solution for forming a polymer matrix (110) to produce a first mixed solution, and a step of casting the first mixed solution to produce a cast film.

[0109] According to an 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, the method for manufacturing an optical film (100) according to an embodiment of the present invention may include a step of manufacturing a polyimide-based resin powder, a step of dissolving the polyimide-based resin powder in a first solvent to produce a polyimide-based resin solution, a step of preparing a dispersion liquid, and a step of mixing the filler dispersion liquid and the polyimide-based resin solution to produce a first mixed solution.

[0111] The filler dispersion liquid can be produced, for example, by dispersing the 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, an embodiment of the present invention is not limited thereto, and other known solvents can also be used as the first solvent and the second solvent.

[0113] According to an embodiment of the present invention, in order to improve the dispersibility of the filler (120), the pH of the first mixed solution can be adjusted. For example, the pH of the first mixed solution can be adjusted to the range of 5 to 7. Thereby, aggregation or lumping of the filler (120) can be prevented.

[0114] Next, the first mixed solution can be cast, dried, and heat-treated to form the optical film (100). According to an embodiment of the present invention, the film formed by casting the first mixed solution is referred to as a cast film, and the film manufactured by drying and heat-treating the cast film can be referred to as the optical film (100). The cast film can be said to be an uncured film.

[0115] Also, during the drying and heat-treatment process of the cast film formed by casting, convection can be prevented so that the filler (120) is oriented in a certain direction.

[0116] Specifically, when drying the cast film using heat, if convection occurs inside, the orientation of the filler (120) may decrease. Therefore, in order to prevent convection, the cast film can be dried slowly. For example, drying of the cast film can be carried out while raising the temperature at a rate of 1 °C / 1 minute (1 degree / 1 minute) up to 80 °C to 120 °C. When dried to a certain level or above, the orientation of the filler (120) can be fixed.

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

[0118] <Production Example 1: Production of a Polyimide-Based Polymer Solid Content> While passing nitrogen through a 1L reactor equipped with a stirrer, a nitrogen injection device, a dropping funnel, a temperature regulator, and a cooler, 719.104 g of DMAc (N,N-Dimethylacetamide) was filled. After adjusting the temperature of the reactor 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 here, and after stirring for 3 hours to completely dissolve BPDA, 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 then reacted at 25°C for 12 hours to obtain a polymer solution with a solid content concentration of 12% by weight.

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

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

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

[0122] Immediately after producing the first mixed solution, when the pH of the first mixed solution is measured, the pH is 8 or higher. In order to improve the alignment characteristics of the filler (120), a weak acid such as acetic acid is introduced into the first mixed solution and adjusted so that the pH of the first mixed solution is in the range of 5 to 7. The first mixed solution thus produced is a polyimide-based resin solution in which fibrous fillers (120) are dispersed.

[0123] The obtained first mixed solution was cast. A cast substrate is used for casting. There is no particular limitation on the type of the cast substrate. As the cast substrate, a glass substrate, a stainless steel (SUS) substrate, a Teflon (registered trademark) substrate, etc. can be used. According to an embodiment of the present invention, a glass substrate can be used as the cast substrate.

[0124] In order to maintain the orientation of the filler (120) during the drying process of the cast film, it was placed in a hot air oven at 80 °C and slowly dried to 120 degrees at a rate of 1 °C / min for about 40 minutes to produce a film. The produced film was peeled off from the glass substrate and fixed to a frame with pins.

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

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

[0127] <Example 2-3> According to the conditions in Table 1, an optical film (100) was manufactured in the same manner as in Example 1, and these were designated as Example 2-3, respectively.

[0128] <Comparative Example 1-7> According to the conditions in Table 1, an optical film (100) was manufactured in the same manner as in Example 1, and these were designated as Comparative Example 1-7, respectively.

[0129]

Table 1

[0130] In Table 1, Filler 1 is a nanowire with an aspect ratio of 375, and Filler 2 is nanoparticles with a particle size of 15 nm. Specifically, the length of Filler 1 is 1.5 μm, and the diameter is 4 nm.

[0131] In Table 1, the molar ratio indicates the relative molar ratio with respect to 100 moles of the total diamine.

[0132] In Table 1, PHR is Per Hundred Resin, and it means the weight (g) of the filler with respect to 100 weight (g) of the light-transmissive matrix. Specifically, PHR according to an embodiment of the present invention means the weight (g) of the filler added per 100 weight (g) of the polyimide-based polymer solid content.

[0133] For the optical films manufactured in Examples 1 to 3 and Comparative Examples 1 to 7, the following physical properties were measured.

[0134] (1) Measurement of Martens hardness (HM) It was measured using HM-2000 of Fisher. -Force: 12 mN - Running Time: 12s - Hold Time: 5s

[0135] (2) Measurement of Vickers hardness (Hv) It was measured using HM - 2000 of Fisher Co., Ltd. - Force: 12mN - Running Time: 12s - Hold Time: 5s

[0136] (3) Measurement of modulus In accordance with the ASTM D885 method, the modulus of the optical film was measured using an Instron universal tensile testing machine (MODEL 5967). - Measurement standard within 3 hours after film production - Road Cell 30KN, Grip 250N. - Specimen size 10mm × 50mm, tensile speed 25mm / min

[0137] (4) Measurement of yield tensile strength - Stress value at the contact point generated by offsetting the Modulus (gradient) of the S - S Curve by 0.2% - It was measured using an Instron universal tensile testing machine (MODEL 5967).

[0138] (5) Measurement of 1% Strain tensile strength - Stress value at the time of reaching 1% Strain - It was measured using an Instron universal tensile testing machine (MODEL 5967).

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

[0140] (7) Measurement of Creep deformation rate Creep deformation rate = (tensile length after 3600 s - tensile length at 1% strain) / (test piece measurement length)

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

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

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

[0144]

Table 2

[0145] As disclosed in the measurement results of Table 2, it can be confirmed that the optical film (100) according to the examples of the present invention has a Creep index of 0.46 or less.

Explanation of symbols

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

Claims

1. A light-transmissive matrix; and A filler dispersed in the light-transmissive matrix, An optical film having a Creep index of 0.46 or less: The Creep index is calculated by the following formula 1, [Formula 1] Creep index = Creep deformation rate / Creep stress In the above formula 1, the Creep deformation rate is calculated by the following formula 2, [Formula 2] Creep deformation rate = (Tensile length after 3600 s - Tensile length at 1% strain) / (Test piece measurement length) In the above formula 1, the Creep stress is calculated by the following formula 3, [Formula 3] Creep stress = Tensile strength at 1% strain / Yield tensile strength In the above formula 3, the tensile strength at 1% strain 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%.

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

3. The optical film according to claim 1, wherein the filler has an aspect ratio of 30 to 2,000: The aspect ratio is the ratio of the length to the diameter of the filler.

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

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

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

7. The filler is at least one of aluminum oxide hydroxide, SiO 2 , Al 2 O 3 , PTFE (Polytetrafluoroethylene), and PVDF (Polyvinylidene Fluoride), and the optical film according to claim 1.

8. The optical film according to claim 1, wherein the content of the filler has a content of 3 to 50 PHR with respect to 100 weights of the light-transmissive matrix.

9. 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 Martens hardness (HM) is measured using HM-2000 under the conditions of 12 mN / Running Time 12 s / Hold time 5 s.

10. 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 HM-2000 under the conditions of 12 mN / Running Time 12 s / Hold time 5 s.

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

65.

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

13. A display panel; and An optical film according to any one of claims 1 to 12, disposed on the display panel; A display device comprising:

Images