KR20230040179A - Multi-layered film having high hardness and bendability - Google Patents

Abstract

The present invention provides a multi-layered polyimide film which can be used as a cover window of a display by exhibiting excellent optical properties while exhibiting different mechanical properties and bending properties, such as high surface hardness and high bending properties. The present invention relates to a multi-layered film of at least two layers including a first layer and a second layer, wherein the first layer has modulus of 5 GPa or more measured according to ASTM D882 and yield strain (Y/S) of less than 2.0 %, and the second layer has modulus of less than 5 GPa measured according to ASTM D882 and yield strain (Y/S) of 2.0 % or more.

Description

Multi-layer film having excellent hardness and bending properties {MULTI-LAYERED FILM HAVING HIGH HARDNESS AND BENDABILITY}

The present invention relates to a multilayer polyimide film that exhibits excellent transparency, high surface hardness and high flexural properties and can be used as a cover window for a display.

A cover window for protecting a panel is applied to a surface of a display device such as a liquid crystal display (LCD) or an organic light emitting display (OLED). As a material of a conventional cover window, tempered glass having excellent flatness, heat resistance, chemical resistance, and barrier performance against moisture or gas, a low coefficient of linear expansion (CTE), and high light transmittance has been mainly used.

Meanwhile, flexible displays such as curved displays and in-folding displays are being developed. In order to be applied to such a flexible display, the cover window must also have flexibility, but a conventional glass cover window is generally heavy and easy to break, and is not suitable for a flexible display due to poor flexibility.

In order to solve the above problems, recently, cover windows using a plastic material having relatively free formability have been proposed. A cover window made of a plastic material has the advantage of being light, hard to break, and capable of implementing various designs. Currently, as a plastic material for a cover window, polycarbonate, polyethylene terephthalate, and polymethyl methacrylate having excellent transparency are mainly used. While these materials have excellent transparency, their glass transition temperature (Tg) is less than 150° C., and their application is limited due to poor heat resistance, poor chemical resistance and mechanical strength. In order to compensate for this, a thick hard coating layer or the like is sometimes introduced into the plastic material described above, but in this case, cracks occur in the hard coating layer during molding or flexibility is significantly reduced. In addition, since the total thickness of the cover window becomes thick, it is difficult to apply it to a flexible display.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a multi-layered film that can be applied as a cover window with excellent surface hardness, mechanical strength, high flexibility, transparency, and other physical properties. .

Other objects and advantages of the present invention can be more clearly described by the following detailed description and claims.

In order to achieve the above object, the present invention is a multilayer film of at least two layers including a first layer and a second layer, wherein the first layer has a modulus of 5 GPa or more measured according to ASTM D882, and a yield strain (Yield Strain, Y/S) is less than 2.0%, the modulus of the second layer is less than 5 GPa, the yield strain (Y/S) is 2.0% or more, and the first layer and the second layer have a modulus measured according to ASTM D882. Each of the layers includes at least one type of diamine; and a polyimide or polyamideimide film copolymerized with at least one acid dianhydride.

For one embodiment of the present invention, the modulus of the first layer is 5 to 7 GPa, the yield strain (Y/S) is 1.0 to 1.99%, the modulus of the second layer is 3 to 4.99 GPa, and the yield strain (Y/S) is 1.0 to 1.99%. The strain (Y/S) may be between 2.0 and 3.0%.

For one embodiment of the present invention, the pencil hardness of the first layer measured by the ASTM D3363 standard may be greater than H, and the pencil hardness of the second layer may be less than H.

For one embodiment of the present invention, when each of the first layer and the second layer is bent with a radius of curvature of 1 to 5 mm, the number of bends until breakage may be 200,000 or more.

For one embodiment of the present invention, each of the first layer and the second layer may have a light transmittance of 85% or more at a wavelength of 550 nm at a thickness of 30 to 100 μm and a yellowness of 5 or less according to the ASTM E313 standard.

For one embodiment of the present invention, each of the at least one type of diamine constituting the first layer is fluorinated aromatic diamine; and at least one of non-fluorinated aromatic diamines.

In one embodiment of the present invention, at least one type of diamine constituting the first layer is para-phenylenediamine (p-PDA), 4,4′-diaminobenzanilide (DABA), 4,4 With '-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFDB), 2,2'-dimethylbenzidine (m-Tol), and 3,3'-dimethylbenzidine (o-Tol) One or more selected from the group consisting of may be included.

For one embodiment of the present invention, at least one type of acid dianhydride constituting the first layer is a fluorinated aromatic acid dianhydride; non-fluorinated aromatic acid dianhydrides; And it may include one or more selected from the group consisting of alicyclic acid dianhydrides.

In one embodiment of the present invention, at least one acid dianhydride constituting the first layer is 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (S-BPDA), pyromellitic acid dianhydride Water (PMDA), 2,3,3,4-biphenyltetracarboxylic dianhydride (a-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 1,2,3 ,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA), 2 ,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane (6FDA), bicyclo[2,2,2]-7-octene-2, It may include at least one selected from the group consisting of 3,5,6-tetracarboxylic dianhydride (BOTA), and 4-(trifluoromethyl)pyromellitic dianhydride.

For one embodiment of the present invention, at least one type of diamine constituting the second layer may include fluorinated aromatic diamine; and at least one of non-fluorinated aromatic diamines.

In one embodiment of the present invention, at least one type of diamine constituting the second layer is 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (Bis-AP-AF) , para-phenylenediamine (p-PDA), 4,4′-diaminobenzanilide (DABA), 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl (TFDB) ), 2,2'-bis (trifluoromethyl) -4,3'-diaminobiphenyl (FODA), 2,2'-bis (trifluoromethyl) -4,4'-diaminophenyl ether (6FAPB), 2,2'-bis (4-aminophenoxyphenyl) propane (HFBAPP), 3,3'-sulfonyldianiline (3,3-DDS), 4,4'-sulfonyldianiline (4, 4-DDS), 4,4-bis (3-aminophenoxy) diphenyl sulfone (m-BAPS), and 1 species selected from the group consisting of 4,4'-oxydianiline (4,4-ODA) may contain more than

For one embodiment of the present invention, at least one acid dianhydride constituting the second layer is a non-fluorinated aromatic acid dianhydride; And it may include at least one or more of fluorinated acid dianhydride.

In one embodiment of the present invention, at least one acid dianhydride constituting the second layer is 4,4′-(4,4′-isopropylidenediphenoxy) bisphthalic dianhydride (BPADA), 3,3′,4,4′-diphenylether carboxylic acid dianhydride (ODPA), 3,3′,4,4′-diphenylsulfotetracarboxylic acid dianhydride (DSDA), bis(3,4- composed of dicarboxyphenyl)dimethylsilane acid dianhydride (SiDA) and 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane (6FDA) It may contain one or more selected from the group.

For one embodiment of the present invention, the content of the non-fluorinated aromatic acid dianhydride or the fluorinated acid dianhydride may be 10 to 100 mol% based on 100 mol% of the total acid dianhydride constituting the second layer.

In one embodiment of the present invention, the ratio (a/b) of the number of moles of the diamine (a) and the acid dianhydride (b) constituting the first layer or the second layer may be in the range of 0.7 to 1.3.

In one embodiment of the present invention, the thickness ratio of the first layer and the second layer may be 10: 90 to 90: 10 based on the total thickness of the sum of the thicknesses of the first layer and the second layer. .

For one embodiment of the present invention, at least one of the first layer and the second layer may further include at least one selected from the group consisting of a colorant for compensating optical properties and an inorganic filler.

For one embodiment of the present invention, the multi-layer film includes a first adhesive layer formed between a first layer and a second layer in which a first layer and a second layer are sequentially stacked and disposed opposite to each other; and a second adhesive layer formed on any one surface of the non-opposite first layer and the second layer. At least one of them may be further included.

For one embodiment of the present invention, the first adhesive layer or the second adhesive layer may include an optically clear adhesive (OCA).

For one embodiment of the present invention, the present invention also provides a multilayer film used as a cover window or protective film of a display device.

In one embodiment of the present invention, one of the first layer and the second layer provided in the multi-layer film is attached to one surface of the display device through a second adhesive layer, and the other is disposed on the outermost surface of the display device. can

For one embodiment of the present invention, the outermost surface of the multilayer film attached to the display device may further include at least one of a hard coating layer, an anti-fingerprint layer, and a protective film layer.

According to an embodiment of the present invention, a multilayer having a first layer having excellent surface hardness and modulus characteristics and a second layer having flexibility and bendability using polyimide compositions exhibiting different physical properties. film can be provided.

Such a multi-layer film can be freely applied as a cover window having a desired surface hardness property or a cover window having a high bending property by changing the arrangement structure of the first layer and the second layer or adjusting the ratio of the polyimide composition to be applied. can do.

In addition, in the present invention, the reliability of the final product can be improved by exhibiting excellent optical properties such as high light transmittance and low yellowness.

Accordingly, the multi-layered polyimide film of the present invention can be usefully applied as a cover window for display devices, flexible displays, etc. in the related art including flat panel display panels, and other IT products, electronic products, It can also be applied to home appliances.

Effects according to the present invention are not limited by the contents exemplified above, and more diverse effects are included in the present specification.

1 is a view showing the structure of a multilayer film 100 according to an embodiment of the present invention.
2 is a view showing the structure of a multilayer film 200 according to another embodiment of the present invention.
3 is a stress-strain curve graph in which yield strain is defined in a tensile test using a multilayer film according to the present invention.

Hereinafter, the present invention will be described in detail. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art, and the following examples may be modified in various other forms, and the scope of the present invention is not limited to the following embodiments. It is not limited to examples. Here, like reference numerals designate like structures throughout this specification.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used in a meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in commonly used dictionaries are not interpreted ideally or excessively unless explicitly specifically defined.

Also, throughout the specification, when a certain part "includes" a certain component, it means that it may further include other components, not excluding other components, unless otherwise stated. In addition, throughout the specification, "above" or "on" means not only the case of being located above or below the target part, but also the case of another part in the middle thereof, and must necessarily specify the direction of gravity It does not mean that it is located above the standard. Also, terms such as "first" and "second" in the present specification do not indicate any order or importance, but are used to distinguish components from each other.

<Multilayer film>

The multilayer film according to an embodiment of the present invention is a transparent film that can be provided in a display device, and more specifically, can be used as a cover window of a flexible display.

Here, the cover window refers to a film disposed on the outermost surface of the flexible display device to protect the display device. The cover window may be a window film alone or a film having a window coating layer formed on a separate substrate made of an optically transparent resin.

On the other hand, the cover window of the display device exposed to the outside should not only have processing characteristics such as scratch resistance and flexibility in everyday life, but also have excellent optical characteristics. While abrasion resistance of a window made of a conventional plastic material increases due to an increase in crosslinking density, it is difficult to apply it as a cover window of a foldable display because cracks occur and flexibility is significantly reduced.

In contrast, the multilayer film according to the present invention comprises a first layer and a second layer having different physical properties to form a multilayer structure of at least two layers. For example, the first layer uses polyimide or polyamideimide film having high modulus and surface hardness, and the second layer is polyimide or polyamide having high yield strain (Y/S) and high flexural properties. use mid film. This multi-layer film not only secures high surface hardness and excellent bending properties compared to conventionally known plastic films or single-layer polyimide films, but also has excellent optical properties in both the first and second layers. , It may be disposed opposite to one surface of the display device and applied as a cover window. In particular, when applied to a cover window of a foldable mobile phone, a cover window or surface in which bending characteristics are important by adjusting the arrangement structure of the first layer or the second layer located on the outermost surface or the polyamic acid composition thereof within a predetermined range It can be freely applied as a cover window for which hardness and mechanical properties are important. Such a display device may be applied to any display device known in the art without limitation, and may be in particular an in-folding or out-folding type foldable display.

Meanwhile, FIGS. 1 and 2 schematically show cross-sectional structures of multilayer films 100 and 200 according to the present invention.

Referring to FIGS. 1 and 2, the multilayer films 100 and 200 have a multilayer structure of at least two layers including a first layer 110 and a second layer 120 having different physical properties, and these ( 110, 120) are each independently at least one diamine; and a polyimide film or polyamideimide film copolymerized with at least one acid dianhydride. Specifically, the first layer 110 has a modulus of 5 GPa or more and a yield strain (Y/S) of less than 2.0%, measured according to ASTM D882, and the second layer 120 is ASTM D882. The modulus measured according to D882 is less than 5 GPa, and the yield strain (Y/S) may be 2.0% or more.

In the present specification, yield strain (Y/S, 降伏變形) is a stress-strain curve of a multilayer film measured according to ASTM D882, in a specific tensile strength range (eg, 20 to 40 The x-intercept value of a predetermined threshold slope (X ₂ ≥ X ₁ × 0.8) having at least 80% of the stress-strain slope (X ₁ ) in MPa), that is, tensile strain It is defined as (see FIG. 3 below). Since the yield strain (Y/S) defined as above is a unique physical property due to the specific composition of the polyimide film, it may correspond to a physical property different from that of the conventional polyimide film. This yield strain (Y / S) can be based on the stress-strain curve (SS curve) obtained by a tensile test measured at 25 ° C, and the modulus (Young's modulus) means a value measured according to ASTM D882 .

Specifically, in the multilayer film 100 according to the present invention, the modulus of the first layer 110 is 5 to 7 GPa, the yield strain (Y / S) is 1.0 to 1.99%, and the second layer 120 The modulus may be 3 to 4.99 GPa, and the yield strain (Y/S) may be 2.0 to 3.0%. In the case of the multilayer films 100 and 200 of the present invention satisfying the above-described modulus and yield strain (Y/S) parameters, the surface hardness of the first layer 110 may be further improved to exhibit scratch resistance. In addition, by further increasing the bending resistance of the second layer 120, generation of cracks due to repeated bending fatigue may be suppressed, and excellent flexibility and bendability may be exhibited.

The aforementioned modulus and yield strain (Y/S) parameters and their values are affected by the thickness of the first layer 110, the second layer 120, and the multilayer films 100 and 200 including the same. can The values of the modulus and the yield strain (Y/S) may be measured based on the total thickness of 30 to 100 μm of the multilayer film (100, 200), for example, 30 to 90 μm, specifically 80 ± 5 μm can be

For another specific example, the pencil hardness of the first layer 110 measured by the ASTM D3363 standard in the multilayer film 100 is greater than H, and the pencil hardness of the second layer 120 is less than H can Here, the pencil hardness means a value measured according to the ASTM D3363 standard.

For another specific example, when the first layer 110 and the second layer 120 constituting the multilayer films 100 and 200 are bent with a radius of curvature of 1 to 5 mm, respectively, the number of bendings until fracture is 200,000 may be more than once. In particular, in the case of the second layer 120 having excellent bendability, the upper limit of the deformation of the number of times of bending until fracture is not particularly limited. For example, it may be 2,000,000 times or less, and may be specifically 1,500,000 times or less.

In order for the polyimide film according to the present invention to be used as a cover window of a mobile communication terminal or a tablet PC, it must simultaneously have excellent optical properties such as high transparency and light transmittance in order to increase visibility of a display screen.

For one specific example, the multilayer polyimide film has a light transmittance of 85% or more at a wavelength of 550 nm at a thickness of 30 to 100 μm, and specifically may be 88% or more. In addition, yellowness (Y.I.) according to the ASTM E313-73 standard may be 5 or less. At this time, the upper limit of the light transmittance and the lower limit of the yellowness are not particularly limited.

The above-described multilayer film 100 of the present invention has the modulus, yield strain, and pencil hardness of the final multilayer film by adjusting the unique physical properties of the first layer 110 and the second layer 12 and controlling their thickness ratio. , light transmittance, and various physical properties such as yellowness can be optimized.

For example, the multilayer polyimide film has a modulus of 5.0 to 6.5 GPa, a yield strain (Y/S) of 1.5 to 2.5%, and a modulus measured according to ASTM D882, ASTM D3363 standard. Pencil hardness (Hardness) by H or more, a light transmittance of 550 nm wavelength is 87% or more, yellowness (Y.I.) according to the ASTM E313-73 standard may be 3.0 or less. However, it is not limited thereto, and the physical properties of the final multilayer film can be freely modified as desired by the user by adjusting the unique physical properties of the first layer 110 and the second layer 12 and controlling their thickness ratio.

Each physical property limited to the multilayer film 100 according to the present invention is based on a film thickness of 10 to 100 μm, and may be specifically 30 to 80 μm, unless otherwise specified. However, it is not limited to the aforementioned thickness range, and may be appropriately adjusted within a normal thickness range known in the art.

The multilayer films 100 and 200 according to the present invention are not particularly limited to components constituting polyimide or polyamideimide resin and/or their composition, as long as they satisfy the above-described modulus and yield strain (Y/S) characteristics. . For example, the multilayer films 100 and 200 may include at least one type of diamine; and at least one acid dianhydride, and may be prepared by imidizing and heat-treating a polyamic acid composition including the above-described diamine, acid dianhydride, and, if necessary, a solvent, at a high temperature.

In general, polyimide (PI) resins or polyamideimide resins are prepared by solution polymerization of aromatic acid dianhydride and aromatic diamine or aromatic diisocyanate to prepare polyamic acid derivatives, followed by ring-closure dehydration at high temperature to imidize. heat-resistant resin. Such a polyimide resin is a polymer material containing an imide ring, and has excellent heat resistance, chemical resistance, wear resistance and electrical properties based on the chemical stability of the imide ring. The polyimide or polyamideimide resin may be in the form of a random copolymer or a block copolymer.

The diamine (a) component constituting the first layer 110 and/or the second layer 120 of the multilayer film 100 of the present invention is not limited as long as it is a compound having a diamine structure in the molecule, and is known in the art. Conventional diamine compounds can be used without limitation. For example, the diamine compound includes an aromatic, alicyclic, aliphatic compound having a diamine structure, or a combination thereof. In particular, in the present invention, the high surface hardness and mechanical properties of the first layer 110 constituting the multilayer film (100, 200); excellent yield strain (Y/S) and high flexibility of the second layer 120; Considering optical properties such as high transmittance, low Y.I, and low haze of these 110 and 120, as a diamine compound constituting the first layer 110 and the second layer 120, , Fluorinated aromatic diamine having a fluorine substituent introduced thereto, sulfone-based aromatic diamine, hydroxy-based aromatic diamine, ether-based aromatic diamine, and non-fluorinated aromatic diamine may be used alone or in a mixture of two or more by appropriately combining them. there is.

For one specific example, at least one type of diamine constituting the first layer 110 may include fluorinated aromatic diamine; and at least one of non-fluorinated aromatic diamines. . Non-limiting examples of the diamine compound constituting the first layer 110 include para-phenylenediamine (p-PDA), 4,4′-diaminobenzanilide (DABA), 4,4′-dia In the group consisting of mino-2,2'-bis(trifluoromethyl)biphenyl (TFDB), 2,2'-dimethylbenzidine (m-Tol), and 3,3'-dimethylbenzidine (o-Tol) One or more selected species may be included.

For another specific example, at least one type of diamine constituting the second layer 120 may be the same as or different from the diamine compound of the first layer 110 described above, and more specifically, fluorinated aromatic diamine; and at least one of non-fluorinated aromatic diamines. Non-limiting examples of the diamine constituting the second layer 120 include 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (Bis-AP-AF), para-phenylene Diamine (p-PDA), 4,4′-diaminobenzanilide (DABA), 4,4′-diamino-2,2′-bis(trifluoromethyl)biphenyl (TFDB), 2,2 '-bis (trifluoromethyl) -4,3'-diaminobiphenyl (FODA), 2,2'-bis (trifluoromethyl) -4,4'-diaminophenyl ether (6FAPB), 2 ,2'-bis(4-aminophenoxyphenyl) propane (HFBAPP), 3,3'-sulfonyldianiline (3,3-DDS), 4,4'-sulfonyldianiline (4,4-DDS), It may contain at least one selected from the group consisting of 4,4-bis (3-aminophenoxy) diphenyl sulfone (m-BAPS) and 4,4'-oxydianiline (4,4-ODA). there is. If necessary, it may further include conventional fluorinated aromatic diamines, non-fluorinated aromatic diamines, alicyclic aromatic diamines, sulfone-based aromatic diamines, hydroxy-based aromatic diamines, ether-based aromatic diamines, and the like known in the art without being mentioned above. can

In the diamine compound (a) constituting the above-described first layer 110 or second layer 120, fluorinated aromatic diamine; And / or the content of the non-fluorinated aromatic diamine is not particularly limited, and may be 0 to 100 mol% based on 100 mol% of the total diamine constituting the first layer 110 or the second layer 120, respectively, Specifically, it may be 10 to 90 mol%, more specifically 20 to 80 mol%. However, the content of at least one of the fluorinated aromatic diamine and the non-fluorinated aromatic diamine is included to satisfy 100 mol% of the total diamine.

For a preferred example, as the diamine (a) constituting the first layer 110 or the second layer 120, fluorinated aromatic diamine and non-fluorinated aromatic diamine may be mixed. At this time, their use ratio is not particularly limited, and may be, for example, 50 to 90: 10 to 50 mol% ratio.

The acid dianhydride (b) component constituting the first layer 110 and/or the second layer 120 of the multilayer film 100 of the present invention is not limited as long as it is a compound having a dianhydride structure in the molecule, and the related art Conventional acid dianhydride compounds known to may be used without limitation. For example, an aromatic, alicyclic, or aliphatic compound having a dianhydride structure, or a combination thereof may be used. In particular, in the present invention, the high surface hardness and mechanical properties of the first layer 110 constituting the multilayer film (100, 200); excellent yield strain (Y/S) and high flexibility of the second layer 120; Considering their optical properties, such as high transmittance, low Y.I, and low haze, the acid dianhydride compounds constituting the first layer 110 and the second layer 120 have a fluorine substituent. The introduced fluorinated aromatic acid dianhydride, non-fluorinated aromatic acid dianhydride, and sulfone-based aromatic acid dianhydride may be used alone or in a mixture of two or more of them by properly combining them.

For one specific example, the at least one acid dianhydride constituting the first layer 110 may include a fluorinated aromatic acid dianhydride; non-fluorinated aromatic acid dianhydrides; And it may include one or more selected from the group consisting of alicyclic acid dianhydrides. preferably fluorinated aromatic acid dianhydrides; non-fluorinated aromatic acid dianhydrides; and alicyclic acid dianhydrides, at least two or more, more preferably all of them. Non-limiting examples of the acid dianhydride compound constituting the first layer 110 include 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (S-BPDA) and pyromellitic acid dianhydride (PMDA). , 2,3,3,4-biphenyltetracarboxylic dianhydride (a-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 1,2,3,4-cyclo Butanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA), 2,2-bis (3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane (6FDA), bicyclo[2,2,2]-7-octene-2,3,5, It may include at least one selected from the group consisting of 6-tetracarboxylic dianhydride (BOTA) and 4-(trifluoromethyl)pyromellitic dianhydride.

In the acid dianhydride compound (a) constituting the above-described first layer 110, a fluorinated aromatic acid dianhydride; non-fluorinated aromatic acid dianhydrides; And the content of the alicyclic acid dianhydride is not particularly limited, and may be 0 to 100 mol% based on 100 mol% of the total acid dianhydride constituting the first layer 110, specifically 10 to 90 mol%, More specifically, it may be 20 to 80 mol%. However, the content of at least one of fluorinated aromatic acid dianhydride, non-fluorinated aromatic acid dianhydride, and alicyclic acid dianhydride is included to satisfy 100 mol% of the total acid dianhydride.

For one specific example, as the acid dianhydride (b) constituting the first layer 110, a fluorinated aromatic acid dianhydride; non-fluorinated aromatic acid dianhydrides; And alicyclic acid dianhydride may be used in combination. At this time, their use ratio is not particularly limited, and can be appropriately adjusted in consideration of physical properties such as surface hardness and modulus. For example, it may be 5 to 30: 5 to 20: 50 to 90 mol% ratio.

For another specific example, at least one acid dianhydride constituting the second layer 120 is different from the acid dianhydride of the first layer 110 described above, and more specifically, a non-fluorinated aromatic acid dianhydride; And it may include at least one or more of fluorinated acid dianhydride. Non-limiting examples of the acid dianhydride constituting the second layer 120 include 4,4′-(4,4′-isopropylidenediphenoxy)bisphthalic dianhydride (BPADA), 3,3′, 4,4'-diphenylether carboxylic acid dianhydride (ODPA), 3,3',4,4'-diphenylsulfotetracarboxylic acid dianhydride (DSDA), bis(3,4-dicarboxyphenyl)di 1 selected from the group consisting of methylsilane acid dianhydride (SiDA) and 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane (6FDA) May include more than one species. If necessary, a conventional non-fluorinated aromatic acid dianhydride, a fluorinated aromatic acid dianhydride, an alicyclic acid dianhydride, or a sulfone-based aromatic acid dianhydride known in the art may be further included without being mentioned above.

In addition, in the acid dianhydride compound (a) constituting the second layer 120, the content of fluorinated aromatic acid dianhydride and non-fluorinated aromatic acid dianhydride is not particularly limited. It may be 0 to 100 mol%, specifically 10 to 90 mol%, and more specifically 20 to 80 mol% based on 100 mol% of the acid dianhydride. However, the content of at least one of the fluorinated aromatic acid dianhydride and the non-fluorinated aromatic acid dianhydride is included to satisfy 100 mol% of the total diamine.

For one specific example, as the acid dianhydride (b) constituting the second layer 110, a non-fluorinated aromatic acid dianhydride; And fluorinated aromatic acid dianhydride may be mixed. At this time, the use ratio thereof is not particularly limited, and may be, for example, 10 to 90: 90 to 10 mol% ratio, and specifically 50 to 90: 50 to 10 mol% ratio.

In the polyamic acid composition constituting the first layer 110 and/or the second layer 120, the ratio (a/b) of the number of moles of the diamine component (a) to the number of moles of the acid dianhydride component (b) is 0.7 ~ 1.3, preferably 0.8 to 1.2, more preferably 0.9 to 1.1.

In the polyamic acid composition of the present invention, an organic solvent known in the art may be used as a solvent for solution polymerization of the above-described monomers without limitation. For example, m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), acetone, diethyl At least one polar solvent selected from acetate and dimethyl phthalate (DMP) may be used. In addition, a low boiling point solution such as tetrahydrofuran (THF) or chloroform or a solvent such as γ-butyrolactone may be used. At this time, the content of the solvent (first solvent for polymerization) is not particularly limited, but is preferably 50 to 95% by weight based on the total weight of the polyamic acid composition in order to obtain an appropriate molecular weight and viscosity of the polyamic acid composition (polyamic acid solution) , More preferably, it may be included in the range of 70 to 90% by weight.

The above-described polyamic acid composition may be prepared by adding at least one kind of acid dianhydride and at least one kind of diamine to an organic solvent and then reacting them. For example, to improve the physical properties of polyimide, diamine (a) and acid dianhydride (b) ) can be adjusted to an equivalence ratio of approximately 1: 1. The composition of the polyamic acid composition is not particularly limited, and for example, 2.5 to 25.0 weight of an acid dianhydride based on 100 weight% of the total weight of the polyamic acid composition constituting the first layer 110 and/or the second layer 120. %, 2.5 to 25.0% by weight of diamine, and a balance of an organic solvent that satisfies 100% by weight of the composition. Here, the content of the organic solvent may be 70 to 90% by weight. In addition, the polyamic acid composition may include 30 to 70 wt% of acid dianhydride and 30 to 70 wt% of diamine based on 100 wt% of the solid content, but is not particularly limited thereto.

The polyamic acid composition configured as described above may have a viscosity ranging from about 1,000 to 200,000 cps, preferably about 5,000 to 50,000 cps. When the viscosity of the polyamic acid composition falls within the above-mentioned range, the thickness can be easily controlled during coating of the polyamic acid composition, and the coating surface can be exhibited uniformly.

As necessary, the polyamic acid composition may contain at least one of a plasticizer, an antioxidant, a flame retardant, a dispersant, a viscosity modifier, a leveling agent, an inorganic filler, a colorant, etc. Additives may be included in small amounts.

For example, at least one of the first layer 110 and the second layer 120 may further include at least one selected from the group consisting of a colorant and an inorganic filler. These colorants, inorganic fillers, etc. are not particularly limited, and conventional colorants and inorganic filler components known in the art may be applied.

The colorant is not particularly limited, and colorants, dyes, and/or pigments used for compensating optical properties in the art may be applied without limitation. The material usable as the colorant is not particularly limited, and examples thereof include at least one material selected from the group consisting of carbon black, cobalt oxide, Fe-Mn-Bi black, iron oxide black, and mica iron oxide. In addition, depending on the type of colorant, the first layer 110 and the second layer 120 may each have a color such as black, dark gray, dark brown, or dark brown. At this time, the amount of the colorant is not particularly limited and may be appropriately adjusted within a content range known in the art. For example, the colorant may be included in an amount of 0.5 to 20% by weight based on the total weight of the first layer 110 or the second layer 120 .

Non-limiting examples of usable inorganic fillers include silica, calcium carbonate, magnesium carbonate, alumina, magnesia, clay, talc, calcium silicate, titanium oxide, antimony oxide, glass fiber, aluminum borate, barium titanate, strontium titanate, and calcium titanate. , magnesium titanate, bismuth titanate, titanium oxide, barium zirconate, calcium zirconate, boron nitride, silicon nitride, talc, mica, and the like. The amount of the inorganic filler used is not particularly limited, and may be appropriately adjusted in consideration of mechanical properties of the final multilayer film. The average particle diameter and content of the inorganic filler are not particularly limited, and may be appropriately adjusted within a conventional range known in the art, for example. For example, it may be in the range of 0.1 to 10 μm.

The multilayer film according to the present invention can be prepared according to conventional methods known in the art.

In one embodiment of manufacturing the multilayer film, after coating (casting) the polyamic acid composition constituting the first layer (or second layer) on a substrate, for example, a glass substrate, a temperature range of 30 to 350 ° C. After preparing by inducing imide ring closure reaction (Imidazation) for 0.5 to 8 hours while slowly raising the temperature in the second layer (or first layer) on the polyimide film of the prepared first layer (or second layer) ) It may be finally prepared by coating and imidizing the polyamic acid composition constituting the second layer (or first layer) to form a polyimide film.

At this time, the coating method may use a conventional method known in the art without limitation, and as an example, spin coating, dip coating, solvent casting, slot die coating, and It can be made by at least one method selected from the group consisting of spray coating. The polyamic acid composition may be coated at least once or more so that the colorless and transparent polyimide resin layer has a thickness of several hundred nm to several tens of μm.

In the polyimide film manufacturing method according to the present invention, the imidation method applied to the imidization step by casting the polymerized polyamic acid on a support is a thermal imidation method, a chemical imidation method, or a thermal imidation method and a chemical imidation method. It can be applied in combination with the imidization method.

The thermal imidation method is a method of obtaining a polyimide film by casting a polyamic acid composition (polyamic acid solution) on a support and heating it for 1 to 10 hours while slowly raising the temperature in a temperature range of 30 to 400 ° C.

In the chemical imidation method, a dehydrating agent represented by an acid anhydride such as acetic anhydride and an imidation catalyst represented by amines such as isoquinoline, β-picoline, and pyridine are added to the polyamic acid composition. When a thermal imidation method or a thermal imidation method is used in combination with the chemical imidation method, heating conditions of the polyamic acid composition may vary depending on the type of the polyamic acid composition, the thickness of the polyimide film to be produced, and the like.

In more detail, when the thermal imidation method and the chemical imidation method are used together, a dehydrating agent and an imidation catalyst are added to the polyamic acid composition, casted on a support, and then 80 to 300 ° C., preferably 150 to 250 ° C. After partially curing and drying by heating at °C to activate the dehydrating agent and the imidation catalyst, a polyimide film can be obtained.

For another example of manufacturing the multi-layer film, a conventional adhesive or pressure-sensitive adhesive known in the art may be used between the pre-prepared first layer and the second layer. This adhesive or pressure-sensitive adhesive is not particularly limited, and may be, for example, an optically transparent adhesive (OCA). Such an optically clear adhesive (OCA) may be formed not only on the opposite surface between the first layer and the second layer, but also on any one surface of the non-opposite first layer and the second layer.

The thickness of the multilayer film 100 thus formed is not particularly limited and may be appropriately adjusted depending on the applied field. For example, it may be in the range of 10 to 150 μm, preferably in the range of 30 to 100 μm. At this time, the thickness ratio of the first layer 110 and the second layer 120 constituting the multilayer film 100 is 10:90 to 90:10 based on the total thickness of the sum of the thicknesses of the first layer and the second layer. It may be, but is not particularly limited thereto.

Meanwhile, in the present invention, the structure in which the first layer 110 is laminated on the second layer 120; A structure in which the second layer 120 is stacked on the first layer 110 is exemplarily described through FIGS. 1-2. However, it is not particularly limited thereto, and it is also within the scope of the present invention to freely select and configure the number and stacking order of the polyimide or polyamideimide layers constituting the multilayer film 100 according to the purpose. For example, the order of the first layer 110 and the second layer 120 described above is changed, or by additionally introducing other common surface layers, release films, base films, protective films, etc. known in the art, 3 It may have a multilayer structure of more than one layer.

The polyimide or polyamideimide film of the present invention prepared as described above and its modifications have high surface hardness and mechanical properties; It can be usefully used in various fields requiring excellent yield strain (Y/S), high flexural properties, and excellent optical properties. For example, it may be used as a cover window or protective film of a display device. In particular, it can be applied as a cover window of a display device to prevent surface scratches and provide excellent flexibility and visibility to a flexible display device.

For example, in the multilayer film 100 or 200, a first layer 110 and a second layer 120 are sequentially stacked, and between the first layer 110 and the second layer 120 disposed opposite to each other. A first adhesive layer formed on (not shown); And a second adhesive layer (not shown) formed on any one surface of the non-opposite first layer 110 and second layer 120; At least one of them may be further included. The first adhesive layer and the second adhesive layer may be identical to or different from each other, and may include, for example, an optically clear adhesive (OCA). However, it is not limited thereto, and conventional adhesive and/or pressure-sensitive adhesive components known in the art may be used.

In addition, one of the first layer 110 and the second layer 120 provided in the multilayer film 100, 200 of the present invention is attached to one surface of the display device through the second adhesive layer, and the other is attached to the outermost surface. can be placed. At this time, when the first layer 110 having high modulus, surface hardness and mechanical properties is disposed as one component of the multilayer films 100 and 200 disposed on the outermost surface, a cover window film for which surface hardness is important It can be applied to improve the scratch resistance and reliability of the display. And when the second layer 120 having high yield strain (Y/S) and foldability is used as one component of the multilayer films 100 and 200 disposed on the outermost surface, a cover window in which bendability is important (Cover Window) By being applied to the film, crack generation due to repeated bending fatigue can be suppressed due to excellent flexibility and excellent flexibility can be exhibited.

For one specific example, the outermost surface of the multilayer film 100 or 200 attached to the display device may further include at least one of a hard coating layer, an anti-fingerprint layer, and a protective film layer. The hard coating layer, the anti-fingerprint layer, and the protective film layer are not particularly limited, and conventional configurations known in the art may be applied.

In the present invention, a display device refers to a flexible display device or a non-flexible display device that displays an image, and includes a flat panel display device (FPD) as well as a curved display device, a foldable display device, and a foldable display device. It includes a foldable display device, a flexible display device, a foldable mobile phone, a smart phone, a mobile communication terminal, a tablet PC, and the like. Specifically, the display device includes a liquid crystal display, an electrophoretic display, an organic light emitting display, an inorganic light emitting display, and a field emission display. It may be a field emission display, a surface-conduction electron-emitter display, a plasma display, a cathode ray display, electronic paper, and the like. For example, it may be a flat panel display panel such as LCD, PDP, OLED. Not limited to the above-described uses, the multilayer film of the present invention can be applied to conventional display devices known in the art, and can also be used as a substrate or protective film for other flexible displays.

One specific example of a display device having the above-described multilayer film includes a display unit, a polarizing plate, a touch screen panel, a cover window, and a protective film, and the cover window comprises a multilayer film according to an embodiment of the present invention. can include Here, each component constituting the display device is not particularly limited, and may include conventional components known in the art.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are merely examples to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

[Examples 1 to 9. Manufacture of polyamic acid and polyimide multilayer film]

Polyamic acids of Preparation Examples 1 to 4 were prepared using compositions including diamine and acid dianhydride shown in Table 1 below.

Thereafter, in order to prepare the second layer film 120, the polyamic acid composition described in Table 2 below was spin-coated on the glass for LCD, and then in a nitrogen atmosphere convection oven at 80 ° C. for 30 minutes, at 150 ° C. for 30 minutes, 200 ° C. Drying and imidazation were carried out while slowly raising the temperature stepwise at °C for 1 hour and 300 °C for 1 hour. Accordingly, a second layer polyimide film 120 having an imidation rate of 85% or more and a film thickness of 5 to 75 μm was manufactured.

After spin-coating the polyamic acid composition of the first layer film 110 described in Tables 1 and 2 below on the second layer polyimide film 120 prepared as described above, at 80 ° C. in a convection oven in a nitrogen atmosphere. 30 minutes, 150℃ for 30 minutes, 200℃ for 1 hour, 300℃ for 1 hour, while gradually raising the temperature step by step, drying and imidazation are carried out to achieve a film thickness of 85% or more with an imidation rate of 5 to 75 Multilayer films of Examples 1 to 9 in which the first layer polyimide film 110 of μm was formed were prepared.

Diamine (mol %) Acid dianhydride (mol%) 1st monomer Second monomer 1st monomer Second monomer 3rd monomer 1st floor
(110) Preparation Example 1 TFDB (100) - BPDA (20) CBDA (70) 6FDA (10) Preparation Example 2 TFDB (90) m-Tol (10) BPDA (20) CBDA (70) 6FDA (10) 2nd floor
(120) Preparation Example 3 TFDB (90) m-Tol (10) BPADA (40) BPDA (20) ODPA (40) Production Example 4 TFDB (90) m-Tol (10) BPADA (40) BPDA (30) 6FDA (30)

structure composition 1st floor (100) 2nd floor (200) Furtherance Thickness (㎛) Furtherance Thickness (㎛) multilayer film
(1st floor - 2nd floor) Example 1 Preparation Example 1 5 Preparation Example 3 45 Example 2 Preparation Example 1 10 Preparation Example 3 40 Example 3 Preparation Example 1 20 Preparation Example 3 30 Example 4 Preparation Example 1 25 Production Example 4 75 Example 5 Preparation Example 1 25 Preparation Example 3 25 Example 6 Preparation Example 2 75 Preparation Example 3 25 Example 7 Preparation Example 1 30 Preparation Example 3 20 Example 8 Preparation Example 1 40 Preparation Example 3 10 Example 9 Preparation Example 1 45 Preparation Example 3 5 single layer
film
(1st or 2nd floor) Comparative Example 1 Preparation Example 1 50 - - Comparative Example 2 Preparation Example 2 100 - - Comparative Example 3 - - Preparation Example 3 50 Comparative Example 4 - - Production Example 4 100

[Comparative Examples 1 to 4. Production of polyamic acid composition and polyimide film]

Polyamic acids of Preparation Examples 1 to 4 were prepared using the compositions containing the diamine and acid dianhydride described in Tables 1 and 2 above.

After spin-coating the polyamic acid composition on glass for LCD, drying while slowly raising the temperature in a convection oven under a nitrogen atmosphere at 80 ° C for 30 minutes, 150 ° C for 30 minutes, 200 ° C for 1 hour, and 300 ° C for 1 hour and imide ring closure reaction (Imidazation) was performed. Accordingly, a single-layer polyimide film having a film thickness of 50 μm or 100 μm and having an imidization rate of 85% or more was prepared. Thereafter, the glass was etched with hydrofluoric acid to obtain polyimide films of Comparative Examples 1 to 4, respectively.

[Experimental Example: Evaluation of physical properties]

The physical properties of the polyimide resin films prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were evaluated in the following manner, and the results are shown in Table 3 below.

<Physical property evaluation method>

1) Measurement of light transmittance

It was measured using a UV-Vis NIR Spectrophotometer (Shimadzu, model name: UV-3150) at a wavelength of 550 nm.

2) Yellowness measurement

The yellowness at 550 nm was measured according to the ASTM E313-73 standard using a spectrophotometer (Konica Minolta, CM-3700d).

3) Thickness measurement

The thickness of the film was measured using a thickness meter (Mitutoyo, model name: 547-401).

4) Modulus measurement

Tensile strength (MPa) and modulus of elasticity (GPa) were measured according to the ASTM D882 standard using UTM (Instron, model name: 5942).

5) Measurement of Yield Strain

Using UTM (Instron, model name _: 5942), a threshold value (X ₂ Strain (x value) corresponding to ≥ X ₁ × 0.8) was measured.

6) Measurement of bending characteristics (Dynamic Folding cycle)

The bending characteristics were measured using a flat body unloaded U-folding test equipment (DLDMLS-FS, YUASA), and the folding cycle was measured by adjusting the radius of curvature to 1 mm to 5 mm.

7) Measurement of pencil hardness

In order to check the hardness of the polyimide film, the surface hardness was measured according to the ASTM D3363 standard using a pencil hardness tester [CORTECH (CT-PC2)]. The pencil (Mistubishi, Japan) used for measurement was held at 90° and the tip was abraded with sandpaper, and the surface of the polyimide film was rubbed at a constant speed while tilted at an angle of 45° while a load of 1 kg was applied in a certain direction. The highest value at which scratches did not occur was measured. The measurement was repeated three times for one test piece, and when no trace was generated more than 0 times, the hardness of the pencil used was measured as a surface hardness value. At this time, as the degree of scratching, (Soft) 9B ~ B → HB → F → H ~ 9H (Hard), that is, it is indicated by the type of pencil at maximum strength.

structure composition Characteristics of the film thickness
(μm) permeability
(%) yellowness modulus
(GPa) yield strain
(Yield strain,%) pencil
Hardness Dynamic Folding cycle (@1R) multi-layer
polyimide
(1st floor - 2nd floor) Example 1 1st floor 5 89.9 1.0 5.9 1.7 H 210K 2nd floor 45 88.5 1.8 4.9 2.2 HB 1100K final 50 89.2 1.6 5.7 2.0 H 530K Example 2 1st floor 10 89.8 1.4 5.9 1.7 H 210K 2nd floor 40 88.6 1.8 4.9 2.2 HB 1100K final 50 89.1 1.7 5.7 2.1 H 580K Example 3 1st floor 20 89.6 1.6 6.1 1.6 H 210K 2nd floor 30 88.6 1.7 4.8 2.2 B 1000K final 50 89.4 1.6 5.7 2.0 H 620K Example 4 1st floor 25 89.6 1.6 6.1 1.6 H 210K 2nd floor 75 88.2 1.9 4.9 2.1 HB 850K final 100 88.7 1.7 5.6 2.0 H 520K Example 5 1st floor 25 89.6 1.6 6.1 1.6 H 210K 2nd floor 25 88.6 1.6 4.7 2.2 B 1000K final 50 89.3 1.6 5.6 2.1 H 530K Example 6 1st floor 75 89.1 1.9 6.6 1.6 2H 250K 2nd floor 25 88.6 1.6 4.7 2.2 B 1000K final 100 88.88 1.7 6.2 2.0 H 540K Example 7 1st floor 30 89.5 1.6 6.1 1.6 H 210K 2nd floor 20 88.6 1.6 4.7 2.2 B 1000K final 50 88.7 1.6 5.8 2.0 H 510K Example 8 1st floor 40 89.5 1.7 6.2 1.6 H 200K 2nd floor 10 89.8 1.5 4.6 2.2 2B 1200K final 50 89.6 1.6 6.0 2.0 H 480K Example 9 1st floor 45 89.5 1.7 6.2 1.6 H 210K 2nd floor 5 89.9 1.5 4.6 2.2 2B 1200K final 50 89.5 1.6 6.0 2.0 H 450K single layer
polyimide Comparative Example 1 50 89.2 1.7 6.2 1.6 H 210K Comparative Example 2 100 87.1 3.4 6.7 1.6 2H 200K Comparative Example 3 50 88.6 1.8 4.9 2.2 HB 1000K Comparative Example 4 100 88.4 3.8 4.9 2.2 HB 600K

As shown in Table 3, in the case of the multilayer films of Examples 1 and 2, the yield strain (Y/S) is higher than that of the single layer film of Comparative Example 1, and there is no change even if the number of folding exceeds 1 million times. , and it was found that the modulus and pencil hardness characteristics were simultaneously improved compared to Comparative Example 3, which is a single layer structure.

In addition, Example 4 exhibited better optical properties and folding properties than Comparative Examples 2 and 4 having the same thickness. And even in the case of Example 5, it showed low yellowness and excellent folding characteristics compared to Comparative Example 1 having the same thickness, and showed characteristics of low yellowness, high modulus and pencil hardness compared to Comparative Example 3.

In addition, the multilayer film of Example 6, compared to Comparative Example 2 and Comparative Example 4, showed the possibility of improving optical characteristics and folding characteristics even under a thick thickness condition of 100 μm.

In addition, even in the case of the multilayer films of Examples 7 to 9, as compared to the comparative example having a single layer structure, the required characteristics were improved, and thus various flexible displays (Flexible display) It was seen that it is possible to appropriately respond to the required characteristics .

Accordingly, it was confirmed that the multilayer film of the present invention can be usefully applied as a cover window of a display device.

100, 200: multilayer film
110: first layer
120: second layer

Claims (23)

As a multilayer film of at least two or more layers including a first layer and a second layer,
The first layer has a modulus of 5 GPa or more, a yield strain (Y / S) of less than 2.0%, measured according to ASTM D882,
The second layer has a modulus of less than 5 GPa and a yield strain (Y / S) of 2.0% or more, measured according to ASTM D882,
Each of the first layer and the second layer includes at least one type of diamine; and a polyimide or polyamideimide film copolymerized with at least one acid dianhydride. According to claim 1,
The modulus of the first layer is 5 to 7 GPa, the yield strain (Y / S) is 1.0 to 1.99%,
The second layer has a modulus of 3 to 4.99 GPa and a yield strain (Y/S) of 2.0 to 3.0%. According to claim 1,
A multilayer film, wherein the pencil hardness of the first layer is greater than H and the pencil hardness of the second layer is less than H, as measured by the ASTM D3363 standard. According to claim 1,
The first layer and the second layer, respectively,
A multilayer film having a bending number of 200,000 or more until breaking when bending with a radius of curvature of 1 to 5 mm. According to claim 1,
The first layer and the second layer, respectively,
The transmittance of light at a wavelength of 550 nm is 85% or more at a thickness of 30 to 100 μm,
A multilayer film having a yellowness of 5 or less according to the ASTM E313 standard. According to claim 1,
At least one kind of diamine constituting the first layer is fluorinated aromatic diamine; and a non-fluorinated aromatic diamine. According to claim 6,
At least one type of diamine constituting the first layer is para-phenylenediamine (p-PDA), 4,4'-diaminobenzanilide (DABA), 4,4'-diamino-2,2' - at least one selected from the group consisting of bis(trifluoromethyl)biphenyl (TFDB), 2,2'-dimethylbenzidine (m-Tol), and 3,3'-dimethylbenzidine (o-Tol) Multi-layer film containing. According to claim 1,
The at least one type of acid dianhydride constituting the first layer may include a fluorinated aromatic acid dianhydride; non-fluorinated aromatic acid dianhydrides; And a multilayer film comprising at least one selected from the group consisting of alicyclic acid dianhydrides. According to claim 8,
At least one acid dianhydride constituting the first layer is 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (S-BPDA), pyromellitic acid dianhydride (PMDA), 2,3, 3,4-biphenyltetracarboxylic dianhydride (a-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA), 2,2-bis(3,4- Dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane (6FDA), bicyclo[2,2,2]-7-octene-2,3,5,6-tetracarboxylic A multilayer film selected from the group consisting of acid dianhydride (BOTA), and 4-(trifluoromethyl)pyromellitic dianhydride. According to claim 8,
the fluorinated aromatic acid dianhydride; non-fluorinated aromatic acid dianhydrides; and each content of the alicyclic acid dianhydride is 10 to 100 mol% based on 100 mol% of the total acid dianhydride constituting the first layer. According to claim 1,
At least one type of diamine constituting the second layer is fluorinated aromatic diamine; and a non-fluorinated aromatic diamine. According to claim 11,
At least one type of diamine constituting the second layer is 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (Bis-AP-AF), para-phenylenediamine (p- PDA), 4,4'-diaminobenzanilide (DABA), 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFDB), 2,2'-bis( Trifluoromethyl) -4,3'-diaminobiphenyl (FODA), 2,2'-bis (trifluoromethyl) -4,4'-diaminophenyl ether (6FAPB), 2,2'- Bis (4-aminophenoxyphenyl) propane (HFBAPP), 3,3'-sulfonyldianiline (3,3-DDS), 4,4'-sulfonyldianiline (4,4-DDS), 4,4- A multilayer film comprising at least one selected from the group consisting of bis (3-aminophenoxy) diphenyl sulfone (m-BAPS) and 4,4'-oxydianiline (4,4-ODA). According to claim 1,
The at least one type of acid dianhydride constituting the second layer is a non-fluorinated aromatic acid dianhydride; and a fluorinated acid dianhydride. According to claim 13,
At least one acid dianhydride constituting the second layer is 4,4'-(4,4'-isopropylidenediphenoxy) bisphthalic dianhydride (BPADA), 3,3',4,4' -Diphenyl ether carboxylic acid dianhydride (ODPA), 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride (DSDA), bis(3,4-dicarboxyphenyl)dimethylsilane acid dianhydride (SiDA), and at least one selected from the group consisting of 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane (6FDA) , multi-layer film. According to claim 13,
The content of the non-fluorinated aromatic acid dianhydride or fluorinated acid dianhydride is 10 to 100 mol% based on 100 mol% of the total acid dianhydride constituting the second layer, respectively. According to claim 1,
The ratio (a / b) of the number of moles of diamine (a) and acid dianhydride (b) constituting the first layer or the second layer is in the range of 0.7 to 1.3, respectively. According to claim 1,
The thickness ratio of the first layer and the second layer is 10: 90 to 90: 10, the multilayer film. According to claim 1,
At least one of the first layer and the second layer further comprises at least one selected from the group consisting of a colorant and an inorganic filler, the multilayer film. According to claim 1,
In the multilayer film, a first layer and a second layer are sequentially laminated,
a first adhesive layer formed between the first layer and the second layer that are disposed opposite to each other; and
a second adhesive layer formed on any one surface of the non-opposite first and second layers; A multilayer film further comprising at least one of. According to claim 19,
The multilayer film, wherein the first adhesive layer or the second adhesive layer comprises an optically clear adhesive (OCA). According to claim 1,
A multilayer film used as a cover window or protective film for display devices. According to claim 19,
Any one of the first layer and the second layer provided in the multilayer film is attached to one surface of the display device through a second adhesive layer, and the other is disposed on the outer surface of the multilayer film. According to claim 22,
The outer surface of the multilayer film attached to the display device further comprises at least one of a hard coating layer, an anti-fingerprint layer, and a protective film layer.

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