JP2022120772A - Polyimide film having excellent optical properties - Google Patents

Abstract

To provide a novel polyimide film that can keep simultaneously, all of low thickness-direction phase difference (Rth), an in-plane-direction phase difference (Rin), and an in-plane-direction average refractive index at low levels and also has excellent properties such as transparency, flexibility, and mechanical properties, the polyimide film applicable to a cover window.SOLUTION: This polyimide film is a copolymerized one including at least one diamine and at least one acid dianhydride. At least one of the diamine and the acid dianhydride includes an alicyclic compound. With respect to a film thickness 40 μm, a thickness-direction phase difference (Rth) at a wavelength 550 nm is 300-1,200 nm.SELECTED DRAWING: Figure 1

Description

The present invention relates to a polyimide film, and more particularly, a thickness direction retardation (R _th ), an in-plane direction retardation (R _in ), and an in-plane direction average refractive index are adjusted to be low at the same time. The present invention relates to a polyimide film that can be used as a cover window of a display while preventing screen distortion by a compensation effect and ensuring excellent visibility.

A cover window is applied to the surface of a display device such as a liquid crystal display (LCD) or an organic light emitting display (OLED) to protect the panel. Conventionally, tempered glass, which has excellent flatness, heat resistance, chemical resistance, and barrier performance against moisture and gas, has a small coefficient of linear expansion (CTE), and has high light transmittance, is mainly used as the material for cover windows. It is

In recent years, flexible displays such as curved displays and in-folding displays have been developed. In order to be applied to such a flexible display, the cover window also needs to be flexible. is not suitable.

In order to solve the above-mentioned problems, recently, a cover window using a plastic material having relatively good moldability has been proposed. A cover window made of a plastic material has the advantage of being lightweight, hard to crack, and capable of implementing various designs. At present, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, etc., which are excellent in transparency, are mainly used as plastic materials for cover windows. Such materials have the advantage of having excellent transparency, but their glass transition temperature (Tg) is 150° C. or less, and their application is limited due to their poor heat resistance, low chemical resistance, and low mechanical strength. There is In addition, the cover window is disposed on the outermost shell of the flexible display device, and if the above-mentioned material is applied and it is continuously exposed to external ultraviolet rays, a yellowing phenomenon may occur, which may affect the visibility of the display. adversely affect.

In particular, a cover window made of a polyimide-based resin has high optical anisotropy (birefringence value) even with a small orientation effect because the polyimide has a content of benzene rings with high polarization. . Thus, when a material with a high birefringence value and inhomogeneity is applied to a device such as a display by a general film processing process, the transmitted stress affects the orientation of the polymer chains. As a result, the optical design of the display is disturbed, which causes the problem of distortion of the display screen and deterioration of visibility.

The present invention has been devised to solve the above problems, and has low thickness direction retardation (R _th ), in-plane direction retardation (R _in ), and in-plane direction average refractive index. It is a technical problem to provide a novel polyimide film applicable to a cover window, which simultaneously secures the above properties and has excellent physical properties such as transparency, flexibility and mechanical properties.

Other objects and advantages of the present invention will become more apparent from the detailed description and claims that follow.

In order to achieve the above technical problems, the present invention provides a polyimide film comprising at least one diamine and at least one acid dianhydride, comprising: At least one of the objects includes an alicyclic compound, and provides a polyimide film having a thickness direction retardation (R _th ) of 300 to 1,200 nm at a wavelength of 550 nm based on a film thickness of 40 μm. do.

In one embodiment of the present invention, the polyimide film has an in-plane direction retardation (R _in ) at a wavelength of 550 nm with a film thickness of 40 μm as a reference, and an in-plane direction average refractive index (n ) can be less than or equal to 1.60.

In one embodiment of the present invention, the polyimide film has a transmittance of 85% or more at a wavelength of 550 nm at a thickness of 30 to 100 μm, and has a yellowness index (YI) according to ASTM E313-73 standard. can be 5 or less.

In one embodiment of the present invention, the polyimide film has an average coefficient of linear expansion (CTE) measured at 50 to 250° C. of 100 ppm/° C. or less, and a Young's Modulus of 3 to 8 GPa. can be.

In one embodiment of the present invention, the alicyclic compound includes at least one of an alicyclic diamine and an alicyclic dianhydride, and the total mol % of the diamine and the dianhydride is is contained at a rate of 10 to 100 mol%.

In one embodiment of the present invention, the alicyclic acid dianhydride is contained in a proportion of 10 to 100 mol % with respect to the total mol % of the acid dianhydride.

In one embodiment of the present invention, the at least one dianhydride comprises a fluorinated aromatic primary dianhydride, a non-fluorinated aromatic secondary dianhydride, and a sulfonic aromatic secondary dianhydride. It may further include one or more aromatic dianhydrides selected from the group consisting of 3 dianhydrides.

In one embodiment of the invention, the at least one diamine can comprise an aromatic diamine, a cycloaliphatic diamine, or a combination of an aromatic and a cycloaliphatic diamine.

In one embodiment of the present invention, the aromatic diamine and the alicyclic diamine are contained in a ratio of 0-100:100-0 mol % with respect to 100 mol % of the total diamine.

In one embodiment of the present invention, the aromatic diamines are a fluorinated first diamine, a sulfone-based second diamine, a hydroxy-based tertiary diamine, an ether-based fourth diamine, and a non-fluorinated fifth diamine. It can contain one or more selected from the group consisting of

In one embodiment of the present invention, the molar ratio (a/b) of the diamine (a) and the acid dianhydride (b) may range from 0.7 to 1.3.

In one embodiment of the present invention, the polyimide film can be used as a cover window of a display device.

According to an embodiment of the present invention, by adopting predetermined components constituting the polyimide film and adjusting the content thereof, the thickness direction retardation (R _th ) and the in-plane direction retardation are low. (R _in ) and the in-plane direction average refractive index are secured at the same time, and the viewing angle compensation effect prevents screen distortion and provides excellent visibility. Along with this, it is possible to continuously exhibit optical properties such as high light transmittance and low yellowness.

In addition, the present invention exhibits excellent modulus and low coefficient of linear expansion (CTE), and can improve the workability and reliability of the final product.

Therefore, the polyimide film of the present invention can be usefully applied to display devices in the field including flat display panels, cover windows such as flexible displays, and other IT products, electronic products, and home appliances known in the field. It can also be applied to products and the like.

The effects of the present invention are not limited by the above exemplifications, and various more effects are included in this specification.

FIG. 1 is a diagram schematically showing an in-plane direction retardation (R _in ) and a thickness direction retardation (R _th ).

The present invention will be described in detail below. The embodiments of the present invention are provided so that those of ordinary skill in the art may understand the invention more fully, and the following embodiments may be practiced with various modifications. However, the scope of the invention is not limited by these examples. In this specification, the same reference numerals refer to the same structure.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the meaning commonly understood by one of ordinary skill in the art to which this invention belongs. . Also, terms defined in commonly used dictionaries should not be interpreted ideally or unduly unless specifically defined.

In addition, throughout the specification, when a part "includes" another component, it does not mean that the other component is excluded, but that the other component can be further included, unless otherwise specified. means In addition, in the specification as a whole, "above" or "above" means not only the case where the target part is located above or below, but also the case where there is another part in the middle. It does not mean that it is located above the direction of gravity. In this specification, terms such as "first" and "second" are used to distinguish between constituent elements, rather than to indicate any arbitrary order or degree of importance.

<Polyimide film>
A polyimide resin film according to an embodiment of the present invention is a transparent film provided in a display device, and more specifically, it is used as a cover window of a flexible display.

Here, the cover window refers to a film disposed on the outermost shell of the flexible display device to protect the display device. Such a cover window may be a window film alone or a film in which an adhesive layer and a window coating layer are formed on another substrate film made of an optically transparent resin.

On the other hand, the cover window of the display that is exposed to the outside needs to have processing characteristics such as flexibility and excellent optical characteristics in daily life. It must also have optical properties that can add or cancel out the phase retardation that occurs.

A phase difference (Ratardation) means a phase difference between two electric field components generated by a velocity difference in a medium between two orthogonal electric field components in an electromagnetic wave traveling through a medium. Such retardation characteristics include the retardation characteristics at the front and the retardation characteristics at a predetermined angle. are different from each other, and it is important to have uniform retardation characteristics not only at the front but also at an oblique angle, that is, at a viewing angle. Here, the phase retardation value at the front is called an in-plane retardation (In-Plane Retardation, R _in ), and a value that can represent the phase retardation value that obliquely incident light undergoes is the thickness direction retardation ( Out-Of-Plane Retardation, R _th ).

In the present invention, the thickness direction retardation (R _th ), the in-plane direction retardation (R _in ), and the in-plane direction average refractive index (n) are each reduced within a specific range compared to conventional polyimide films. It is characterized by adjusting Accordingly, when the polyimide film is applied to the cover window of the display device, it can prevent distortion of the display screen due to external force, exhibit a wide viewing angle, and provide excellent visibility and high reliability. Any display device known in the art can be applied to such a display device without limitation. display).

In one embodiment of the present invention, said polyimide film comprises at least one diamine and at least one dianhydride, wherein at least one of said diamine and said dianhydride is an alicyclic The thickness direction retardation (R _th ) at a wavelength of 550 nm may be 300 to 1,200 nm based on a film thickness of 40 μm. .
In addition, the thickness direction retardation (R _th ) may be defined by Equation 1 below.

式中、ｎ_ｘは、当該フィルムの面内の任意の方向軸（ｘ軸）の屈折率であり、ｎ_ｙは、前記ｘ軸に垂直な方向（ｙ軸）の屈折率であり、ｎ_ｚは、前記ｘ軸及び前記ｙ軸に垂直な厚さ方向軸（ｚ軸）の屈折率であり、ｄは、フィルムの厚さである。具体的に、厚さ方向位相差（Ｒ_ｔｈ）は、フィルムの長手方向軸をＸ軸、前記Ｘ軸に垂直なフィルムの幅手方向の軸をＹ軸、前記Ｘ軸及び前記Ｙ軸に垂直なフィルム厚さ方向軸をＺ軸とし、それぞれの軸方向屈折率をｎｘ、ｎｙ、ｎｚとする時、平面屈折率の平均値と、厚さ方向への屈折率の値であるｎｚ値との差に、フィルムの厚さを乗じて得られるものを意味する。

In the formula, nx is the refractive index of an arbitrary direction axis ( _x -axis) in the plane of the film, ny is the refractive index of the direction perpendicular to the x-axis ( _y -axis), and _nz is the refractive index of the thickness direction axis (z-axis) perpendicular to the x-axis and the y-axis, and d is the thickness of the film. Specifically, the thickness direction retardation (R _th ) is defined as follows: the longitudinal axis of the film is the X axis, the lateral axis of the film perpendicular to the X axis is the Y axis, and the X axis and the Y axis are perpendicular to When the film thickness direction axis is the Z axis and the refractive indices in the respective axial directions are nx, ny, and nz, the average value of the plane refractive indices and the nz value, which is the value of the refractive index in the thickness direction, It means the difference obtained by multiplying the thickness of the film.

In another embodiment of the present invention, the polyimide film may have an in-plane retardation (R _in ) of 0 to 200 nm at a wavelength of 550 nm based on a film thickness of 40 μm.
Note that the in-plane direction retardation (R _in ) can be defined by Equation 2 below.

[Formula 2]
R _in =(n _x −n _y )*d
(Wherein, n _x , n _y and d are the same as defined in Formula 1 above.)

Specifically, the in-plane retardation (R _in ) means that the longitudinal axis of the film is the X axis, the width direction axis of the film perpendicular to the X axis is the Y axis, and the refractive index in each axial direction is nx , ny means the front phase retardation value obtained by multiplying the difference of the refractive index values on the plane by the thickness of the film.

In still another specific example of the present invention, the polyimide film may have an in-plane average refractive index (n) of 1.60 or less measured at a wavelength of 550 nm.

In the present invention, the thickness direction retardation (R _th ), the in-plane direction retardation (R _in ), and the in-plane direction average refractive index (n) can be affected by the thickness of the film. . Such thickness direction retardation (R _th ), in-plane direction retardation (R _in ), and in-plane direction average refractive index (n) are each based on a thickness of 40 μm of the polyimide film. However, it is not limited to this, and for example, when converting what is measured under the conditions of a film thickness of 30 to 100 μm, specifically 30 to 80 μm, more specifically 40±5 μm, it is also within the scope of the present invention. included.

As one specific example, the polyimide film according to the present invention may have a thickness direction retardation (R _th ) of 350 to 1,200 nm, specifically 400 to 1,150 nm. Also, the in-plane direction retardation (R _in ) may be 0 to 200 nm, specifically 50 to 150 nm. Also, the in-plane direction refractive index (n) can be 1.5 to 1.6, specifically 1.53 to 1.59. At this time, the thickness direction retardation (R _th ), the in-plane direction retardation (R _in ), and the in-plane direction refractive index (n) are based on a film thickness of 40 nm and a measurement wavelength of 550 nm. If the standards are different from each other, some of the physical property values may vary. The thickness direction retardation (R _th ), the in-plane direction retardation (R _in ), the refractive index parameters and the polyimide film of the present invention having these numerical values, even under severe environments, display distortion due to the viewing angle compensation effect is prevented, the viewing angle is extended, and excellent visibility can be secured.

In order for the polyimide film according to the present invention to be used for cover windows of mobile communication terminals, tablet PCs, etc., in addition to the retardation properties described above, excellent optical properties such as high transparency and light transmittance and mechanical properties are required. It is preferable that the material has the following properties at the same time.

In another specific example of the present invention, the polyimide film has a light transmittance of 85% or more, specifically 89% or more, and more specifically 90% or more at a wavelength of 550 nm at a thickness of 30 to 100 μm. It can be 99%. Also, the yellowness index (Y.I.) according to the ASTM E313 standard can be 5 or less, specifically 4.7 or less, more specifically 4.5 or less.

In another embodiment of the present invention, the polyimide film may have a Young's Modulus of 3-8 GPa, specifically 3-6 GPa. It can be 4 to 6 GPa from the point of view of exhibiting mechanical hardness and excellent flexibility at the same time. The Young's modulus means a value measured according to ISO 527-3. If the ratio is smaller than the above numerical value, it is difficult to exhibit sufficient hardness, and if it is larger than the above numerical value, flexibility and foldability may be reduced.

In another specific example of the present invention, the polyimide film may have an average linear expansion coefficient (CTE) of 100 ppm/° C. or less measured at 50 to 250° C. at a thickness of 30 to 100 μm. 70 ppm/°C or less, more specifically 30 to 65 ppm/°C.

If the polyimide film according to the present invention satisfies the thickness direction retardation (R _th ), in-plane direction retardation (R _in ), and refractive index characteristics, components constituting the polyimide resin and / or its composition is not particularly limited.

As one specific example, the polyimide film contains at least one diamine and at least one acid dianhydride, and at least one of the diamine and the acid dianhydride is an alicyclic compound (alicyclic compound).

In the present invention, the alicyclic compound can include at least one of alicyclic diamines and alicyclic acid dianhydrides well known in the art. Such alicyclic diamines and alicyclic acid dianhydrides are not particularly limited as long as they contain at least one alicyclic ring in the molecular structure. , an alicyclic acid dianhydride component. Specifically, the alicyclic compound is an alicyclic acid dianhydride, and more specifically, it is preferable to use an alicyclic acid dianhydride represented by chemical formula (1) or chemical formula (2). . Such an alicyclic compound is the total mol% of the diamine and the acid dianhydride together, for example, 200 mol% of the total of 100 mol% of the diamine and 100 mol% of the acid dianhydride, It can be contained in a proportion of 10 to 100 mol %, specifically in a proportion of 50 to 90 mol %.

The diamine (a) component constituting the polyimide film of the present invention is not particularly limited as long as it is a compound having a diamine structure in the molecule, and diamine compounds known in the art can be used without limitation. For example, an aromatic, alicyclic, or aliphatic compound having a diamine structure, or a combination thereof can be used.

In particular, in the present invention, the polyimide film has low reflectance, high transmittance, and low Y.E. Considering the optical properties such as I, at least one alicyclic diamine can be used alone, or at least one aromatic diamine can be used, or the aromatic diamine and the alicyclic diamine can be used in combination. can.

Specific examples of the aromatic diamine include fluorine-based, sulfone-based, hydroxyl-based, ether-based, and non-fluorinated diamines each having a fluorinated substituent, Alternatively, one or more of them can be used in an appropriate combination. As a result, in the present invention, the diamine compound is a fluorinated aromatic first diamine into which a fluorine substituent has been introduced, a sulfone-based aromatic second diamine, a hydroxy-based aromatic third diamine, an ether-based aromatic third diamine, 4 diamine and the non-fluorinated aromatic fifth diamine can be used alone or in combination of two or more thereof.

Usable diamine monomers (a) include, for example, oxydianiline (ODA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (2,2′-TFDB), 2,2′-bis(trifluoromethyl)-4,3′-diaminobiphenyl (2,2′-bis(trifluoromethyl)-4,3′-diaminobiphenyl), 2,2′-bis(trifluoromethyl)- 5,5′-diaminobiphenyl (2,2′-bis(trifluoromethyl)-5,5′-diaminobiphenyl), 2,2′-bis(trifluoromethyl)-4,4′-diaminophenyl ether (2,2 '-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether: 6-FODA), bisaminohydroxyphenylhexafluoropropane (DBOH), bisaminophenoxyphenylhexafluoropropane (4BDAF), bisaminophenoxyphenylpropane (6HMDA) , bisaminophenoxydiphenylsulfone (DBSDA), bis(4-aminophenyl)sulfone (4,4'-DDS), bis(3-aminophenyl)sulfone (3,3'-DDS), sulfonyldiphthalic anhydride (SO2DPA), 4,4'-oxydianiline (4,4'-ODA), or a mixed form of one or more of these, but not limited thereto.

Considering the high transparency, high glass transition temperature, and low yellowness of polyimide films, 2,2'-bis(trifluoro methyl)-4,4'-diaminobiphenyl (2,2'-TFDB), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6-FAPB) can be used. Bis(4-aminophenyl)sulfone (4,4'-DDS) or 3,3'-DDS can be used as the sulfone-based second diamine. Further, as the hydroxy-based third diamine, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane: BIS-AP -AF) can be used. Further, as the ether type fourth diamine, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6-FODA) or oxydianiline (ODA) can be used. . In addition, as the non-fluorine-based fifth diamine, 2,2-bis(3-amino-4-methylphenyl)-hexafluoropropane (2,2-bis(3-amino-4-methylphenyl)-hexafluoropropane: BIS -AT-AF), m-tolidine, or p-phenylenediamine (p-PDA) can be used.

In the diamine monomer (a) of the present invention, the fluorinated aromatic first diamine, the sulfone-based aromatic second diamine, the hydroxy-based aromatic third diamine, the ether-based aromatic fourth diamine, the non- The content of the fluorine-based aromatic fifth diamine is not particularly limited, but can be 0 to 100 mol%, specifically 10 to 90 mol%, based on 100 mol% of the total diamine. More specifically, it is 20 to 80 mol %. However, the content of any one of the first to fifth diamines is included so as to satisfy 100 mol % of all diamines.

Usable alicyclic diamines include, for example, 2,2-bis(3-amino-4-hydroxycyclohexyl)hexafluoropropane, 3 ,3′-dimethyl-4,4′-diaminodicyclohexylmethane (MACM), 4,4′-methylenebicyclohexylamine (PACM), 1,3-bis(aminomethyl)cyclohexane (1,3-BAC), 1 ,4-bis(aminomethyl)cyclohexane (1,4-BAC), cis-1,2-cyclohexanedimethanamine, trans-1,2-cyclohexanedimethanamine, 1,4-cyclohexyldiamine (1,4- cyclohexyldiamine (CHDA), bis(4-aminocyclohexyl) ether, or mixtures thereof and the like can be used, but are not limited thereto.

In the diamine monomer (a) of the present invention, the mixing ratio of the aromatic diamine and the alicyclic diamine is 0 to 100:100 to 0 mol% with respect to 100 mol% of the total diamine. Specifically, the ratio is 10-90:90-10 mol %.

As the acid dianhydride (b) monomer constituting the polyimide film of the present invention, compounds known in the art having an acid dianhydride structure in the molecule can be used without limitation. For example, an aromatic, alicyclic, or aliphatic compound having a dianhydride structure, or a combination thereof can be used. Anhydrides can be used, or at least one aromatic dianhydride can be used, or a mixture of said aromatic and alicyclic dianhydrides can be used.

The alicyclic acid dianhydride is not particularly limited as long as it is a compound having a non-aromatic alicyclic ring and an acid dianhydride structure. Specifically, it is preferable to use an alicyclic acid dianhydride represented by the following chemical formula (1) or chemical formula (2).

In the chemical formulas (1) and (2),
A to C are the same or different from each other and are each independently a cyclic alicyclic organic group having 4 to 20 carbon atoms,
X is -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -(CH ₂ ) _p - (where 1≤p≤ 10), from -(CF ₂ ) _q - (where 1 ≤ q ≤ 10), -C(CH ₃ ) ₂ C-, -(CF ₃ ) ₂ C-, and -C(=O)NH- selected from the group of
n is 0-2.

As a preferred specific example of Chemical Formula 1 or Chemical Formula 2, A to C are the same or different from each other and each independently may be a cyclic alicyclic organic group having 4 to 8 carbon atoms, and X is -CH ₂ -, -(CH ₃ ) ₂ C-, -SO ₂ -, -(CF ₃ ) ₂ C-, -CO-, and -CONH-, n is 0 or 1; be.

Usable alicyclic acid dianhydrides include, for example, cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), bicyclo[2, 2,2]-7-octene-2,3,5,6-tetracarboxylic dianhydride (BCDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4 -tetrahydronaphthalene-1,2-dicarboxylic dianhydride (TDA), 1,1'-bicyclohexane-3,3',4,4'-tetracarboxylic dianhydride (H-BPDA), 1,2 , 4,5-cyclohexane-tetracarboxylic dianhydride (H-PMDA), cyclopentanone bis-spironorbornane (cpODA), bicyclo[2.2.2]octane-2,3,5 ,6-tetracarboxy 2,3:5,6-acid dianhydrides (7CI, 8CI), or mixtures of one or more thereof, and the like, but are not limited thereto. The content of the alicyclic acid dianhydride is not particularly limited, and can be appropriately adjusted in consideration of the mechanical properties and retardation properties of the polyimide film. For example, the content of the alicyclic acid dianhydride is contained at a rate of 10 to 100 mol%, specifically 20 to 90 mol%, relative to the total mol% of the acid dianhydride. , more specifically in a proportion of 30 to 80 mol %.

Further, as one specific example of the aromatic acid dianhydride, a fluorinated aromatic first acid dianhydride, a non-fluorinated aromatic second acid dianhydride, a sulfone-based aromatic third acid dianhydride Each of the substances can be used alone, or can be a combination form in which at least two or more of these are mixed.

The fluorinated first acid dianhydride monomer is not particularly limited as long as it is an aromatic acid dianhydride into which a fluorine substituent has been introduced. Usable fluorinated first acid dianhydrides include, for example, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropanoic dianhydride (2,2-bis(3,4-dicarboxyphenyl ) hexafluoropropane dianhydride: 6-FDA), 4-(trifluoromethyl)pyromellitic dianhydride (4-(trifluoromethyl)pyromellitic dianhydride: 4-TFPMDA) and the like, but are not limited thereto. These can be used alone or in combination of two or more. Among fluorinated acid dianhydrides, 6-FDA is a compound suitable for transparency because it has a very strong property of limiting the formation of charge transfer complexes (CTC) between and within molecular chains. is.

Also, the non-fluorinated second acid dianhydride monomer is not particularly limited as long as it is a non-fluorinated aromatic acid dianhydride to which no fluorine substituent has been introduced. Usable non-fluorinated third acid dianhydride monomers include, for example, pyromellitic dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride. substance (3,3′,4,4′-Biphenyl tetracarboxylic acid dianhydride: BPDA), benzophenonetetracarboxylic acid dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), 4,4-(4,4-isopropyl Reddendiphenoxy)bis(phthalic anhydride) (BPDA), bis(carboxyphenyl)dimethylsilane dianhydride (bis(3,4dicarboxyphenyl)dimethylsilane dianhydride: SiDA), and the like, but are not limited thereto. These can be used singly or in combination of two or more thereof.

Further, the sulfone-based third acid dianhydride monomer is not particularly limited as long as it is an acid dianhydride in which a sulfone group is introduced. For example, 3,3′,4,4′-diphenylsulfone Tetracarboxylic dianhydride (3,3′,4,4′-diphenylsulfonetetracarboxylic dinhydride: DSDA) can be mentioned.

In the acid dianhydride monomer (b) of the present invention, the fluorinated aromatic first acid dianhydride, the non-fluorinated aromatic second acid dianhydride, the sulfone-based aromatic third acid dianhydride, The content of the anhydride and the like is not particularly limited. For example, each of these may be contained in the range of 0 to 100 mol%, specifically 10 to 90 mol%, more specifically 20 to 80 mol%, relative to 100 mol% of the total acid dianhydride. in mol %. However, the content of at least one of the first acid dianhydride to the third acid dianhydride is contained so as to satisfy 100 mol % of the total acid dianhydride.

In the acid dianhydride monomer (b) of the present invention, the mixing ratio of the aromatic dianhydride and the alicyclic acid dianhydride is 0 to 90 with respect to 100 mol% of the total acid dianhydride. : 10 to 100 mol %, specifically 90 to 10: 10 to 90 mol %, more specifically 80 to 10: 20 to 90 mol %.

In the polyamic acid composition constituting the polyimide film of the present invention, the ratio (a/b) of the number of moles of the diamine component (a) and the number of moles of the acid dianhydride component (b) is 0.7. ~1.3, preferably 0.8 to 1.2, and more preferably in the range 0.9 to 1.1.

The polyimide film of the present invention constructed as described above contains at least one diamine and at least one acid dianhydride, of which at least one alicyclic diamine or alicyclic acid Including repeating units obtained by including a dianhydride. When a predetermined alicyclic repeating unit obtained from such an alicyclic diamine/acid dianhydride is included, low retardation properties can be exhibited and excellent visibility can be ensured. Specifically, the higher the content ratio of the cycloaliphatic structure in the main chain of the polyimide containing the aromatic diamine/acid dianhydride and the alicyclic diamine/acid dianhydride, the higher the thickness direction. It was confirmed that the retardation (R _th ) property is lowered, and especially when an alicyclic acid dianhydride is used, the thickness direction retardation (R _th ) property is lowered and the mechanical property is improved. It is possible to optimize optical and mechanical properties, including visibility, by (see Tables 1 and 2 below).

In the polyamic acid composition of the present invention, any organic solvent known in the art can be used without limitation as a solvent for solution polymerization reaction of the monomers as described above. Solvents that can be used include, for example, m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), acetone, diethylacetate, and dimethylphthalate. (DMP) can be used. Alternatively, low boiling solutions such as tetrahydrofuran (THF), chloroform, or solvents such as γ-butyrolactone can be used. At this time, the content of the solvent (first solvent for polymerization) is not particularly limited, but in order to obtain an appropriate molecular weight and viscosity of the polyamic acid composition (polyamic acid solution) 50 to 95% by weight, more preferably 70 to 90% by weight.

The polyimide according to the present invention is produced by solution polymerization using the diamine, acid dianhydride, and if necessary a solvent to produce a polyamic acid composition (polyamic acid derivative), followed by ring closure dehydration at high temperature, and imide It can be a highly heat-resistant resin produced by curing. The polyamic acid composition can be prepared by adding at least one acid dianhydride and at least one diamine to an organic solvent and then reacting them. (a) and dianhydride (b) can be adjusted in an equivalent ratio of approximately 1:1. The composition of such a polyamic acid composition is not particularly limited. ˜25.0% by weight, and the balance in 100% of the composition can comprise an organic solvent. Here, the content of the organic solvent can be 70-90% by weight. Also, the polyamic acid composition may contain 30 to 70% by weight of acid dianhydride and 30 to 70% by weight of diamine with respect to 100% by weight of the solid content, but is not limited thereto.

Polyamic acid compositions constructed as described above may have viscosities ranging from about 1,000 to 200,000 cps, preferably from about 5,000 to 50,000 cps. When the viscosity of the polyamic acid composition is within the above range, the thickness can be easily controlled and a uniform coating surface can be obtained when the polyamic acid composition is coated.

If necessary, the polyamic acid composition contains at least one of a plasticizer, an antioxidant, a flame retardant, a dispersant, a viscosity modifier, a leveling agent, and the like, as long as the objects and effects of the present invention are not impaired. Additives can be included in small amounts.

The polyimide resin film according to the present invention can be produced according to a conventional method well known in the art, for example, after coating (casting) the polyamic acid composition on a substrate such as a glass substrate , while gradually increasing the temperature in the range of 30 to 350° C. for 0.5 to 8 hours to induce an imide ring closure reaction (imidazation).

As for the coating method, any conventional method known in the art can be used without limitation, for example, spin coating method, dip coating method, solvent casting method, slot die coating method. It can be carried out by at least one method selected from the group consisting of a coating (slot die coating) method and a spray coating method. The polyamic acid composition may be coated at least once so that the colorless and transparent polyimide resin layer has a thickness of several hundred nm to several tens of μm.

In the method for producing a polyimide film according to the present invention, the imidization method applied to the step of casting the polymerized polyamic acid onto the support for imidization includes a thermal imidization method, a chemical imidization method, or a thermal imidization method. The chemical imidization method and the chemical imidization method can be used in combination.

In the thermal imidization method, a polyamic acid composition (polyamic acid solution) is cast on a support and gradually heated in a temperature range of 3 to 400 ° C. for 1 to 10 hours to obtain a polyimide film. The method.

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

Specifically, the method of using both the thermal imidization method and the chemical imidization method is described. Preferably, the polyimide film can be obtained after partial curing and drying by activating the dehydrating agent and the imidization catalyst by heating at 150 to 250°C.

The polyimide resin thus formed is a polymer containing imide rings, and has excellent heat resistance, chemical resistance, abrasion resistance and electrical properties based on the chemical stability of the imide rings. there is The polyimide resin may be in the form of a random copolymer or a block copolymer. The thickness of the polyimide film is not particularly limited and can be appropriately adjusted according to the field of application. For example, it can range from 10 to 150 μm, preferably from 30 to 100 μm.

The polyimide film of the present invention manufactured as described above and its modifications can be usefully used in various fields requiring excellent optical properties such as low retardation and high transmittance and high mechanical properties. . In particular, when applied to a cover window of a display device, surface abrasion can be prevented, and excellent flexibility and visibility can be imparted to the flexible display device.

In the present invention, the display device refers to a flexible display device or a non-flexible display device for displaying images, and includes not only a flat panel display device (FPD), but also a curved display device, a folding 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 are included. Specifically, the display device includes a liquid crystal display, an electrophoretic display, an organic light emitting display, an inorganic EL display, an electric field Field emission display, surface-conduction electron-emitter display, plasma display, cathode ray display, electronic paper, etc. can be done. One specific example is a flat panel display such as LCD, PDP, OLED. The polyimide film of the present invention is not limited to the above applications, and can be applied to display devices well known in the art, and can also be used as substrates for flexible displays and protective films.

A specific example of the display device including the polyimide film includes a display unit, a polarizing plate, a touch screen panel, a cover window, and a protective film, and the cover window includes the polyimide film according to an embodiment of the present invention. can contain. Here, each component constituting the display device is not particularly limited, and may include components known in the art.

The present invention will be described in detail below based on specific examples. The examples described below are merely illustrations for helping understanding of the present invention, and the scope of the present invention is not limited to these examples.

[Examples 1 to 9. Production of polyimide film]
A polyamic acid composition was produced using a composition containing a diamine and an acid dianhydride shown in Table 1 below.

After spin-coating the polyamic acid composition onto the LCD glass, it is placed in a convection oven in a nitrogen atmosphere for 30 minutes at 80°C, 30 minutes at 150°C, 1 hour at 200°C, and 1 hour at 300°C step by step. Drying and imide ring closure reaction (Imidazation) were carried out while gradually increasing the temperature. As a result, a 40 μm-thick polyimide film having an imidization rate of 85% or more was obtained. Next, the polyimide film was peeled off from the glass.

[Comparative Examples 1 to 5. Production of polyimide film]
Polyimide films of Comparative Examples 1 to 5 were produced in the same manner as in Examples 1 to 9, except that the compositions shown in Table 1 were used.

[Experimental example. Evaluation of the physical properties]
The physical properties of the polyimide resin films produced in Examples 1-9 and Comparative Examples 1-5 were evaluated by the methods described below, and the results are shown in Table 2 below. Each physical property in Table 2 below is based on a polyimide film thickness of 40 μm.

<Physical property evaluation method>
1) Measurement of light transmittance Measurement was performed using a UV-Vis NIR spectrophotometer (manufactured by Shimadzu, model number: uv-3150) at a wavelength of 550 nm.

2) Measurement of Yellowness Using a spectrophotometer (Konica Minolta, model number: CM-3700d), yellowness at 500 nm was measured according to ASTM E131-73 standard.

3) Measurement of thickness The thickness of the film was measured using a thickness gauge (manufactured by Mitutoyo, model number: 293-140).

4) Measurement of coefficient of thermal expansion (CTE) Measured by IPC-TM-650 2.4.24.5 method using TMA (manufactured by TA Instruments, Q400).

5) Measurement of Modulus UTM (manufactured by Instron, model number: 5942) was used to measure tensile strength (MPa) and elastic modulus (GPa) according to ISO 527-3 standards.

6) Measurement of in-plane direction average refractive index (n) The in-plane direction average refractive index was measured using a refractive index measurement device (refractive index/birefringence analyzer, manufactured by Metricon, 2010/M). The size of the sample was a square with a length and width of 5 cm, and the test piece was mounted on a holder and measured.

7) Measurement of In-plane Retardation (R _in ) Measured using a birefringence measuring device (RETarder, manufactured by Otsuka, RETs-100). The size of the sample was a square with a width and length of 5 cm each, and the test piece was mounted on a sample holder and fixed at 500 nm using a monochromator. In-plane birefringence (R _in ) was measured at an incident angle of 0°.

8) Measurement of Thickness Direction Retardation (R _th ) Measured using a birefringence measuring device (Retarder, manufactured by Otsuka, RETs-100). The size of the sample was a square with a width and length of 5 cm, and the test piece was mounted on a sample holder and fixed at 550 nm using a monochromator. Thickness direction birefringence (R _th ) was measured at an incident angle of 45°.

As shown in Table 2, the polyimide film according to the present invention has excellent thickness direction retardation (R _th ), in-plane direction retardation (R _in ), and in-plane direction average It has been found that having a refractive index (n) characteristic prevents screen distortion and ensures excellent visibility. In particular, the in-plane direction retardation (R _in ) of the polyimide films obtained in Examples 1 to 9 may be similar to that of the comparative example depending on the property adjustment at the time of production. It was confirmed that the retardation (R _th ) was significantly lower than that of the comparative example. It was also found to have excellent transparency, mechanical properties and coefficient of thermal expansion.

Therefore, it was confirmed that the polyimide film of the present invention can be usefully applied to the cover window of the display device.

Claims (13)

A polyimide film copolymerized containing at least one diamine and at least one dianhydride,
at least one of the diamine and the acid dianhydride comprises an alicyclic compound;
A polyimide film having a thickness retardation (R _th ) of 300 to 1,200 nm at a wavelength of 550 nm based on a film thickness of 40 μm. Based on a film thickness of 40 μm, the in-plane direction retardation (R _in ) at a wavelength of 550 nm is 0 to 200 nm, and the in-plane direction average refractive index (n) is 1.60 or less. Claim 1 Polyimide film according to. At a thickness of 30 to 100 μm,
Transmittance at a wavelength of 550 nm is 85% or more,
2. The polyimide film according to claim 1, which has a yellowness index of 5 or less according to ASTM E313-73 standard. The average coefficient of linear expansion (CTE) measured at 50 to 250 ° C. is 100 ppm / ° C. or less,
2. The polyimide film according to claim 1, which has a Young's Modulus of 3 to 8 GPa. The alicyclic compound includes at least one of an alicyclic diamine and an alicyclic acid dianhydride,
The polyimide film according to claim 1, which is contained in a ratio of 10 to 100 mol% with respect to the total mol% of the diamine and the acid dianhydride. The polyimide film according to claim 5, wherein the alicyclic acid dianhydride is a compound represented by the following chemical formula (1) or chemical formula (2).

(In the above chemical formulas (1) and (2),
A to C are the same or different from each other and are each independently a cyclic alicyclic organic group having 4 to 20 carbon atoms,
X is -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -(CH ₂ ) _p - (where 1≤p≤ 10), from -(CF ₂ ) _q - (where 1 ≤ q ≤ 10), -C(CH ₃ ) ₂ C-, -(CF ₃ ) ₂ C-, and -C(=O)NH- selected from the group of
n is 0-2. ) The polyimide film according to claim 5, wherein the alicyclic acid dianhydride is contained in a ratio of 10 to 100 mol% with respect to the total mol% of the acid dianhydride. The at least one dianhydride comprises a fluorinated aromatic first dianhydride, a non-fluorinated aromatic second dianhydride, and a sulfonic aromatic tertiary dianhydride. 2. The polyimide film of claim 1, further comprising one or more aromatic dianhydrides selected from the group. 3. The polyimide film of claim 1, wherein the at least one diamine comprises an aromatic diamine, a cycloaliphatic diamine, or a combination of an aromatic and a cycloaliphatic diamine. The polyimide film according to claim 9, wherein the aromatic diamine and the alicyclic diamine are contained in a ratio of 0 to 100:100 to 0 mol% with respect to 100 mol% of the total diamine. The aromatic diamine is selected from the group consisting of a fluorinated first diamine, a sulfone-based second diamine, a hydroxyl-based third diamine, an ether-based fourth diamine, and a non-fluorine-based fifth diamine. 10. The polyimide film of claim 9, comprising at least one species. The polyimide film according to claim 1, wherein the molar ratio (a/b) of the diamine (a) and the acid dianhydride (b) is in the range of 0.7 to 1.3. The polyimide film according to claim 1, which is used for a cover window of a display device.

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