JP7083272B2 - Optical film - Google Patents

Description

The present invention relates to an optical film used as a front plate or the like of an image display device.

Image display devices such as liquid crystal displays and organic EL display devices are widely used in various applications such as mobile phones and smart watches. Glass has been used as the front plate of such an image display device. Glass has high transparency and can exhibit high hardness depending on the type of glass, but it is very rigid and easily broken, so that it is difficult to use it as a front plate material for a flexible display. Therefore, the use of polymer materials as an alternative material to glass is being considered. Since the front plate made of a polymer material easily exhibits flexible properties, it can be expected to be used for various purposes. Various resins have bending resistance, and one of them is a polyamide-imide resin. Polyamideimide resins are used in various applications from the viewpoint of transparency and heat resistance (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-207955

However, according to the study of the present inventor, an optical film in which silica particles are added to a polyamide-imide resin can improve the elastic modulus while maintaining bending resistance, but for example, the haze and yellowness of the optical film. It was found that the optical characteristics may be deteriorated by increasing the amount of.

Therefore, an object of the present invention is to provide an optical film capable of achieving both a high elastic modulus and excellent optical properties.

［式（２ａ）中、Ｒ^３～Ｒ^６は、それぞれ独立に、水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、Ｒ^３～Ｒ^６に含まれる水素原子は、それぞれ独立に、ハロゲン原子で置換されていてもよく、ｍは１～４の整数であり、＊は結合手を表す］
で表される基を有する構成単位の含有量は、カルボン酸化合物由来の全構成単位の総モル数に対して０～８０モル％である、［１］～［３］のいずれかに記載の光学フィルム。
［５］ポリアミドイミド樹脂を構成するカルボン酸化合物由来の構成単位に含まれるジカルボン酸化合物由来の構成単位のうち、式（２ｂ）

［式（２ｂ）中、Ｒ^７～Ｒ^１４は、それぞれ独立に、水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、Ｒ^７～Ｒ^１４に含まれる水素原子は、それぞれ独立にハロゲン原子で置換されていてもよく、ｍ^１は１～４の整数であり、ｍ^２は０又は１であり、Ａ^１及びＡ^２はそれぞれ独立に－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－Ｓ－、－ＳＯ_２－、－ＣＯ－又は－ＮＲ^１５－を表し、Ｒ^１５は水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、＊は結合手を表す］
で表される基を有する構成単位の含有量は、カルボン酸化合物由来の全構成単位の総モル数に対して３～７０モル％である、［１］～［４］のいずれかに記載の光学フィルム。
［６］ポリアミドイミド樹脂を構成するカルボン酸化合物由来の構成単位に含まれるテトラカルボン酸化合物由来の構成単位の含有量は、カルボン酸化合物由来の全構成単位の総モル数に対して１０～６０モル％である、［１］～［５］のいずれかに記載の光学フィルム。
［７］ポリアミドイミド樹脂の重量平均分子量は８００，０００以下である、［１］～［６］のいずれかに記載の光学フィルム。 As a result of diligent studies to solve the above problems, the present inventor has found that in an optical film containing a polyamide-imide resin having a weight average molecular weight of 210,000 or more and silica particles, the content of the silica particles is the same as that of the optical film. It has been found that the above object is achieved when the content is 3 to 70% by mass with respect to the mass, and the present invention has been completed. That is, the present invention includes the following.
[1] An optical film containing a polyamide-imide resin having a weight average molecular weight of 210,000 or more and silica particles, and the content of the silica particles is 3 to 70% by mass with respect to the mass of the optical film. , Optical film.
[2] The optical film according to [1], wherein the content of silica particles is 5 to 70% by mass with respect to the mass of the optical film.
[3] The content of the constituent unit derived from the dicarboxylic acid compound contained in the constituent unit derived from the carboxylic acid compound constituting the polyamide-imide resin is 20 to 90 mol with respect to the total number of moles of all the constituent units derived from the carboxylic acid compound. %, The optical film according to [1] or [2].
[4] Among the structural units derived from the dicarboxylic acid compound contained in the structural units derived from the carboxylic acid compound constituting the polyamide-imide resin, the formula (2a)

[In the formula (2a), R ³ to R ⁶ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and hydrogen contained in R ³ to R ⁶ is represented. Each atom may be independently substituted with a halogen atom, m is an integer of 1 to 4, and * represents a bond.]
The content of the structural unit having a group represented by is 0 to 80 mol% with respect to the total number of moles of all the structural units derived from the carboxylic acid compound, according to any one of [1] to [3]. Optical film.
[5] Among the structural units derived from the dicarboxylic acid compound contained in the structural units derived from the carboxylic acid compound constituting the polyamide-imide resin, the formula (2b)

[In the formula (2b), R ⁷ to R ¹⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and hydrogen contained in R ⁷ to R ¹⁴ . The atoms may be independently substituted with halogen atoms, m ¹ is an integer of 1 to 4, m ² is 0 or 1, and A ¹ and A ² are independently -O- and-, respectively. CH _2- , -CH ₂ -CH _2- , -CH (CH ₃ )-, -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -S-, -SO _2- , -CO- Or -NR ^15- , R ¹⁵ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and * represents a bond.]
The content of the structural unit having a group represented by is 3 to 70 mol% with respect to the total number of moles of all the structural units derived from the carboxylic acid compound, according to any one of [1] to [4]. Optical film.
[6] The content of the constituent unit derived from the tetracarboxylic acid compound contained in the constituent unit derived from the carboxylic acid compound constituting the polyamide-imide resin is 10 to 60 with respect to the total number of moles of all the constituent units derived from the carboxylic acid compound. The optical film according to any one of [1] to [5], which is mol%.
[7] The optical film according to any one of [1] to [6], wherein the polyamide-imide resin has a weight average molecular weight of 800,000 or less.

The optical film of the present invention has a high elastic modulus and excellent optical properties.

The optical film of the present invention contains a polyamide-imide resin and silica particles.

<Polyamide-imide resin>
As used herein, the polyamide-imide resin represents a polymer containing both a repeating structural unit containing an imide group and a repeating structural unit containing an amide group. The polyamide-imide resin is preferably a resin obtained by copolymerizing a carboxylic acid compound containing a dicarboxylic acid compound, a tetracarboxylic acid compound, and if necessary, a tricarboxylic acid compound, and a diamine compound. Therefore, the polyamide-imide resin of the present invention contains a structural unit derived from a dicarboxylic acid compound, a structural unit derived from a tetracarboxylic acid compound, and, if necessary, a structural unit derived from a tricarboxylic acid compound, and a diamine. Includes building blocks derived from compounds. In addition, in this specification, a "compound-derived structural unit" may be simply referred to as a "unit". For example, the dicarboxylic acid "constituent unit derived from a compound" is referred to as a dicarboxylic acid "unit", the tetracarboxylic acid "constituent unit derived from a compound" is referred to as a tetracarboxylic acid "unit", and the diamine "constituent unit derived from a compound" is diamine. It may be called a "unit".

で表される化合物由来の構成単位（ジカルボン酸化合物（１）由来の構成単位と称する場合がある）を含むことが好ましい。ここで、本発明のポリアミドイミド樹脂において、ジカルボン酸化合物（１）由来の構成単位は、ジアミン化合物由来の構成単位とＷの両側に形成されたアミド基を介して結合し得る。ジカルボン酸単位として、ジカルボン酸化合物（１）由来の構成単位が１種類又は２種類以上含まれていてもよく、２種類以上含まれる場合、それぞれのジカルボン酸化合物（１）由来の構成単位においてＷの種類が異なる。
式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、－ＯＨ、－ＯＭｅ、－ＯＥｔ、－ＯＰｒ、－ＯＢｕ又は－Ｃｌであり、好ましくは－Ｃｌである。 The dicarboxylic acid compound shows a dicarboxylic acid or a dicarboxylic acid derivative, and examples of the dicarboxylic acid derivative include an acid chloride and an ester of the dicarboxylic acid. The dicarboxylic acid unit is the formula (1).

It is preferable to contain a structural unit derived from the compound represented by (may be referred to as a structural unit derived from the dicarboxylic acid compound (1)). Here, in the polyamide-imide resin of the present invention, the structural unit derived from the dicarboxylic acid compound (1) can be bonded to the structural unit derived from the diamine compound via the amide groups formed on both sides of W. As the dicarboxylic acid unit, one kind or two or more kinds of constituent units derived from the dicarboxylic acid compound (1) may be contained, and when two or more kinds are contained, the constituent unit derived from each dicarboxylic acid compound (1) is W. The type of is different.
In formula (1), R ¹ and R ² are independently -OH, -OME, -OEt, -OPr, -OBu or -Cl, and are preferably -Cl.

［式（２ａ）中、Ｒ^３～Ｒ^６は、それぞれ独立に、水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、Ｒ^３～Ｒ^６に含まれる水素原子は、それぞれ独立に、ハロゲン原子で置換されていてもよく、ｍは１～４の整数であり、＊は結合手を表す］ In the formula (1), W represents a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms. The organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, in which case the hydrocarbon group and the fluorine-substituted hydrocarbon group preferably have 1 to 8 carbon atoms. As W, the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28) or the formula. Examples of the group represented by (29) include a group in which two non-adjacent groups are replaced with hydrogen atoms, a group represented by the formula (2a), and a divalent chain hydrocarbon group having 6 or less carbon atoms. Will be done. A structural unit derived from a compound in which W in the formula (1) contains a group represented by the formula (2a) may be referred to as a structural unit derived from the aromatic dicarboxylic acid compound (A).

[In the formula (2a), R ³ to R ⁶ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and hydrogen contained in R ³ to R ⁶ is represented. Each atom may be independently substituted with a halogen atom, m is an integer of 1 to 4, and * represents a bond.]

In the embodiment of the present invention, from the viewpoint of improving the optical characteristics of the obtained optical film, for example, easily reducing the yellowness, the formula (20), the formula (21), the formula (22), the formula (23), and the formula (24). ), The group represented by the formula (25), the formula (26) or the formula (27), the group in which two non-adjacent ones are replaced with hydrogen atoms; and the group represented by the formula (2a) are preferable. .. In the present specification, the optical characteristics of the optical film indicate, for example, haze (sometimes referred to as Haze), yellowness (sometimes referred to as YI value), total light transmittance, and the like of the optical film. The improvement of the optical characteristics of the optical film means that the haze, yellowness, and the like are reduced, and that the total light transmittance is increased.

In a preferred embodiment of the present invention, from the viewpoint of improving the mechanical strength of the obtained optical film, for example, easily increasing the elastic coefficient, the polyamide-imide resin has a dicarboxylic acid unit in which W in the formula (1) is described later. (26), a group represented by a group in which two non-adjacent groups are replaced with hydrogen atoms among the bonds of the groups represented by the formula (28) or the formula (29); and a group represented by the formula (2a). It is preferable to contain the group represented by the formula (2a), and it is more preferable to contain the group represented by the formula (2a). From the viewpoint of availability of raw materials and good solubility in organic solvents, m in the formula (2a) is more preferably 1 to 2, and m is even more preferably 1. Further, when all of R ³ to R ⁶ in the formula (2a) are hydrogen atoms, it is more advantageous in terms of improving the elastic modulus.

In a preferred embodiment of the present invention, from the viewpoint of easily exhibiting good bending resistance, the polyamideimide resin has two or more aromatic hydrocarbon rings as a dicarboxylic acid unit excluding a single bond and an aromatic group. Includes building blocks derived from aromatic dicarboxylic acid compounds linked by valence groups. Examples of the aromatic hydrocarbon ring include a monocyclic hydrocarbon ring such as a benzene ring; a fused bicyclic hydrocarbon ring such as naphthalene, and a polycyclic hydrocarbon ring such as a ring-assembled hydrocarbon ring such as biphenyl. , Preferably a benzene ring.

［式（２ｂ）中、Ｒ^７～Ｒ^１４は、それぞれ独立に、水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、Ｒ^７～Ｒ^１４に含まれる水素原子は、それぞれ独立にハロゲン原子で置換されていてもよく、ｍ^１は１～４の整数であり、ｍ^２は０又は１であり、Ａ^１及びＡ^２はそれぞれ独立に－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－Ｓ－、－ＳＯ_２－、－ＣＯ－又は－ＮＲ^１５－を表し、Ｒ^１５は水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、＊は結合手を表す］
で表される基であることが好ましい。なお、式（１）中のＷが式（２ｂ）で表される基を含む化合物由来の構成単位を芳香族ジカルボン酸化合物（Ｂ）由来の構成単位と称する場合がある。 Specifically, the structural unit derived from an aromatic dicarboxylic acid compound in which two or more aromatic hydrocarbon rings are linked by a single bond or a divalent group excluding an aromatic group has W in the formula (1). , Equation (2b)

[In the formula (2b), R ⁷ to R ¹⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and hydrogen contained in R ⁷ to R ¹⁴ . The atoms may be independently substituted with halogen atoms, m ¹ is an integer of 1 to 4, m ² is 0 or 1, and A ¹ and A ² are independently -O- and-, respectively. CH _2- , -CH ₂ -CH _2- , -CH (CH ₃ )-, -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -S-, -SO _2- , -CO- Or -NR ^15- , R ¹⁵ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and * represents a bond.]
It is preferably a group represented by. A structural unit derived from a compound in which W in the formula (1) contains a group represented by the formula (2b) may be referred to as a structural unit derived from the aromatic dicarboxylic acid compound (B).

In the formula (2b), A ¹ and A ² are independently, preferably -O- and -CH ₂ , respectively, from the viewpoint that the drying temperature can be easily lowered and an optical film having good bending resistance can be easily obtained. -, -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -S- or -SO _2- , and more preferably -O-, -CH _2- , -C (CH ₃ ) ₂ . -Or -SO _2- , more preferably -O-. R ⁷ to R ¹⁴ preferably represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and more preferably a hydrogen atom or an alkyl having 1 to 3 carbon atoms, from the viewpoint of good raw material availability and mechanical strength. It represents a group, more preferably a hydrogen atom. Here, the hydrogen atoms contained in R ⁷ to R ¹⁴ may be independently substituted with halogen atoms. Further, m ¹ is preferably 1 or 2, and more preferably 1. m ² is preferably 0.

で表される。ジカルボン酸単位として、式（１）中のＷが式（２ｂ’）で表される化合物由来の構成単位を含有するポリアミドイミド樹脂を含んでなる光学フィルムは、より機械的強度（例えば、弾性率や耐屈曲性）を向上しやすい。 In a more preferred embodiment of the invention, the formula (2b) is the formula (2b') :.

It is represented by. An optical film containing a polyamide-imide resin containing a constitutional unit derived from a compound in which W in the formula (1) is represented by the formula (2b') as a dicarboxylic acid unit has higher mechanical strength (for example, elastic modulus). And bending resistance) are easy to improve.

Specific examples of the dicarboxylic acid compound constituting the dicarboxylic acid unit include, for example, 4,4'-oxybis benzoic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and 3,3'-biphenyl. Aromas such as dicarboxylic acid, a single bond of two benzoic acids, -CH _2- , -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -SO _2- or a compound linked by a phenylene group. Dicarboxylic acids and their derivatives (eg, acid chlorides, acid anhydrides); aliphatic dicarboxylic acids such as dicarboxylic acid compounds of chain hydrocarbons having 8 or less carbon atoms and their derivatives (eg, acid chlorides, esters) and the like. Can be mentioned. These dicarboxylic acid compounds can be used alone or in combination of two or more. Among these, in order to achieve both the elasticity and the bending resistance of the optical film, the dicarboxylic acid compound and the aromatic dicarboxylic acid compound (B) constituting the structural unit derived from the aromatic dicarboxylic acid compound (A) are used. It is preferable to use a dicarboxylic acid compound constituting the derived structural unit in combination. Specifically, the combined use of 4,4'-oxybis (benzoyl chloride) and terephthaloyl chloride can be mentioned as a preferable example.

The content of the dicarboxylic acid unit contained in the carboxylic acid unit constituting the polyamide imide resin is preferably 20 mol% or more, more preferably 30 mol% or more, based on the total number of moles of all the constituent units of the carboxylic acid unit. It is more preferably 40 mol% or more, particularly preferably 50 mol% or more, most preferably 60 mol% or more, preferably 90 mol% or less, more preferably 85 mol% or less, still more preferably 80 mol% or less. .. When the content of the dicarboxylic acid unit is at least the above lower limit value, the mechanical strength (for example, elastic modulus) of the optical film can be improved by the hydrogen bond between the amide bonds derived from the dicarboxylic acid unit. Further, when the content of the dicarboxylic acid unit is not more than the above upper limit value, the viscosity of the polyamide-imide varnish described later can be suppressed by suppressing the thickening due to the hydrogen bond between the amide bonds derived from the dicarboxylic acid unit. It is possible to facilitate the processing of the optical film.

Among the dicarboxylic acid units contained in the carboxylic acid unit constituting the polyamideimide resin, the content of the structural unit having a group represented by the formula (2a), for example, the structural unit derived from the aromatic dicarboxylic acid compound (A) is With respect to the total number of moles of the carboxylic acid unit, it is preferably 0 mol% or more, more preferably 20 mol% or more, further preferably 30 mol% or more, particularly preferably 40 mol% or more, and most preferably 50 mol% or more. Yes, preferably 80 mol% or less, more preferably 75 mol% or less, still more preferably 70 mol% or less. When the content of the structural unit having a group represented by the formula (2a) is equal to or higher than the above lower limit value, the optical film has structural rigidity derived from the structural unit having a group represented by the formula (2a). Mechanical strength (eg elastic modulus) can be improved. Further, when it is not more than the above upper limit value, the viscosity of the polyamide-imide varnish is suppressed by suppressing the thickening due to the hydrogen bond between the amide bonds derived from the structural unit having the group represented by the formula (2a). It can facilitate the processing of the optical film.

Among the dicarboxylic acid units contained in the carboxylic acid units constituting the polyamideimide resin, the content of the structural unit having a group represented by the formula (2a), for example, the structural unit derived from the aromatic dicarboxylic acid compound (A) is With respect to the total number of moles of the dicarboxylic acid unit, it is preferably 0 mol% or more, more preferably 30 mol% or more, still more preferably 50 mol% or more, particularly preferably 70 mol% or more, and preferably 95 mol% or less. , More preferably 90 mol% or less. When the content of the structural unit having a group represented by the formula (2a) is equal to or higher than the above lower limit value, the optical film has structural rigidity derived from the structural unit having a group represented by the formula (2a). The mechanical strength (for example, elastic modulus) can be improved, and when it is not more than the above upper limit value, the bending resistance of the optical film tends to be good.

Among the dicarboxylic acid units contained in the carboxylic acid unit constituting the polyamideimide resin, the content of the structural unit having a group represented by the formula (2b), for example, the structural unit derived from the aromatic dicarboxylic acid compound (B) is With respect to the total number of moles of the carboxylic acid unit, it is preferably 3 mol% or more, more preferably 5 mol% or more, further preferably 7 mol% or more, particularly preferably 10 mol% or more, and preferably 70 mol% or less. , More preferably 65 mol% or less, still more preferably 60 mol% or less. When the content of the structural unit having a group represented by the formula (2b) is equal to or higher than the above lower limit value, the structural flexibility derived from the structural unit having a group represented by the formula (2b) makes the optical film. Flexibility tends to improve, and if it is below the above upper limit, thickening due to hydrogen bonds between amide bonds derived from the structural unit having a group represented by the formula (2b) is suppressed, which will be described later. The viscosity of the polyamide-imide varnish can be suppressed, and the processing of the optical film can be facilitated.

Among the dicarboxylic acid units contained in the carboxylic acid units constituting the polyamideimide resin, the content of the structural unit having a group represented by the formula (2b), for example, the structural unit derived from the aromatic dicarboxylic acid compound (B) is With respect to the total number of moles of the dicarboxylic acid unit, it is preferably 3 mol% or more, more preferably 5 mol% or more, further preferably 7 mol% or more, particularly preferably 10 mol% or more, and preferably 100 mol% or less. Is. When the content of the structural unit having a group represented by the formula (2b) is at least the above lower limit value, the bending resistance of the optical film tends to be improved. The content of the dicarboxylic acid unit, the content of the structural unit having a group represented by the formula (2a), the content of the structural unit having a group represented by the formula (2b), etc. are, for example, ¹ H-NMR. It can be measured using it, or it can be calculated from the charging ratio of raw materials.

で表される化合物由来の構成単位（テトラカルボン酸化合物（３）由来の構成単位と称する場合がある）を含むことが好ましい。ここで、本発明のポリアミドイミド樹脂において、テトラカルボン酸化合物（３）由来の構成単位は、ジアミン化合物由来の構成単位とＹの両側に形成されたイミド基を介して結合し得る。テトラカルボン酸単位として、テトラカルボン酸化合物（３）由来の構成単位が１種類又は２種類以上含まれていてもよく、２種類以上含まれる場合、それぞれのテトラカルボン酸化合物（３）由来の構成単位においてＹの種類が異なる。 The tetracarboxylic acid compound indicates a tetracarboxylic acid or a tetracarboxylic acid derivative, and examples of the tetracarboxylic acid derivative include an anhydride of tetracarboxylic acid. The tetracarboxylic acid unit is the formula (3).

It is preferable to contain a structural unit derived from the compound represented by (may be referred to as a structural unit derived from the tetracarboxylic acid compound (3)). Here, in the polyamide-imide resin of the present invention, the structural unit derived from the tetracarboxylic acid compound (3) can be bonded to the structural unit derived from the diamine compound via the imide groups formed on both sides of Y. As the tetracarboxylic acid unit, one kind or two or more kinds of constituent units derived from the tetracarboxylic acid compound (3) may be contained, and when two or more kinds are contained, the constituent units derived from the respective tetracarboxylic acid compound (3) are contained. The type of Y is different in the unit.

In the formula (3), Y independently represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms. In the organic group, the hydrogen atom in the organic group may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine, in which case the carbon number of the hydrocarbon group and the hydrocarbon group substituted with fluorine is preferable. Is 1-8. As Y, the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28), or the formula (28), or the formula (28). A group represented by the formula (29); a group in which a hydrogen atom in the group represented by those formulas is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a tetravalent carbon number of 6 or less. The chain hydrocarbon group of is exemplified.

In equations (20) to (29),
* Represents a bond
W ¹ is a single bond, -O-, -CH _{2-, -CH 2 -} CH _2- , -CH (CH ₃ )-, -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -Ar-, -SO _2- , -CO-, -O-Ar-O-, -Ar-O-Ar-, -Ar-CH ₂ -Ar-, -Ar-C (CH ₃ ) ₂ -Ar- Or, it represents -Ar-SO ₂ -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a phenylene group. From the viewpoint of easily improving the elastic modulus of the obtained optical film, in the formula (3), Y is preferably a group represented by the formulas (26), (28) and (29). Further, from the viewpoint of easily reducing the yellowness of the optical film, in the formula (3), Y is the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), and the formula ( 25), a group represented by the formula (26) or the formula (27); and a group in which the hydrogen atom in the group is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group is preferable. In addition, W ¹ is independently single-bonded, -O-, -CH _{2-, -CH 2 -} CH _2- , -CH (CH ₃ ), respectively, from the viewpoint of easily suppressing the yellowness of the optical film. -, -C (CH ₃ ) ₂ -or-C (CF ₃ ) ₂ -preferably, single bond, -O-, -CH _2- , -C (CH ₃ ) _2- or -C (CF). ₃ ) It is more preferably ₂ -C (CH ₃ ) _2- or -C (CF ₃ ) _2- , and particularly preferably -C (CF ₃ ) _2- .

［式（４）中、Ｒ^１６～Ｒ^２３は、それぞれ独立に、水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、Ｒ^１６～Ｒ^２３に含まれる水素原子は、それぞれ独立に、ハロゲン原子で置換されていてもよく、＊は結合手を表す］
で表される。 In a preferred embodiment of the present invention, Y in the formula (3) is the formula (4).

[In the formula (4), R ¹⁶ to R ²³ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and hydrogen contained in R ¹⁶ to R ²³ . Atoms may be independently substituted with halogen atoms, where * represents a bond.]
It is represented by.

In the formula (4), R ¹⁶ to R ²¹ are preferably hydrogen atoms, R ²² and R ²³ are hydrogen atoms or alkyl groups having 1 to 6 carbon atoms, and more preferably R ¹⁶ to R ²¹ are hydrogen atoms and R. ²² and R ²³ are hydrogen atoms or alkyl groups having 1 to 3 carbon atoms, where the hydrogen atoms contained in R ²² and R ²³ may be independently substituted with halogen atoms. R ²² and R ²³ are each independently more preferably a methyl group, a fluoro group, or a chloro group from the viewpoint that the elastic coefficient of the optical film can be easily improved and the optical characteristics can be easily improved, for example, the yellowness can be easily reduced. Alternatively, it is a trifluoromethyl group, and particularly preferably a methyl group or a trifluoromethyl group.

で表される。テトラカルボン酸単位として、式（３）中のＹが式（４’）で表される化合物由来の構成単位を含有するポリアミドイミド樹脂を含んでなる光学フィルムは、ヘイズが低減されるとともに、全光線透過率を高めることができるため、優れた透明性を有する。さらにフッ素元素を含有する骨格によりポリアミドイミド樹脂の溶媒への溶解性を向上し、ポリアミドイミドワニスの粘度を低く抑制することができ、また光学フィルムの製造が容易となる。 In a preferred embodiment of the invention, formula (4) is represented by formula (4') :.

It is represented by. An optical film containing a polyamide-imide resin containing a constitutional unit derived from a compound in which Y in the formula (3) is represented by the formula (4') as a tetracarboxylic acid unit has reduced haze and is totally present. Since the light transmittance can be increased, it has excellent transparency. Further, the skeleton containing a fluorine element improves the solubility of the polyamide-imide resin in a solvent, suppresses the viscosity of the polyamide-imide varnish to be low, and facilitates the production of an optical film.

Examples of the tetracarboxylic acid compound constituting the tetracarboxylic acid unit include aromatic tetracarboxylic acid and its anhydride, preferably an aromatic tetracarboxylic acid compound such as a dianhydride thereof; an aliphatic tetracarboxylic acid and its anhydride, preferably. Examples thereof include aliphatic tetracarboxylic acid compounds such as the dianhydride. The tetracarboxylic acid compound may be a derivative of a tetracarboxylic acid compound such as an acid chloride as well as an anhydride, and these may be used alone or in combination of two or more.

Specific examples of the aromatic tetracarboxylic acid dianhydride include a non-condensed polycyclic aromatic tetracarboxylic acid dianhydride, a monocyclic aromatic tetracarboxylic acid dianhydride, and a condensed polycyclic aromatic tetra. Carboxylic acid dianhydride can be mentioned. Examples of the non-condensed polycyclic aromatic tetracarboxylic acid dianhydride include 4,4'-oxydiphthalic acid dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, 2,2'. , 3,3'-benzophenone tetracarboxylic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride, 3,3', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) Phenyl) Propane dianhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4'-(hexafluoroisopropylidene) diphthalic acid dianhydride (also referred to as 6FDA) Yes), 1,2-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4) -Dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3-) Examples thereof include dicarboxyphenyl) methane dianhydride, 4,4'-(p-phenylenedioxy) diphthalic acid dianhydride and 4,4'-(m-phenylenedioxy) diphthalic acid dianhydride. Examples of the monocyclic aromatic tetracarboxylic acid dianhydride include 1,2,4,5-benzenetetracarboxylic acid dianhydride, and the condensed polycyclic aromatic tetracarboxylic acid dianhydride is used. Includes 2,3,6,7-naphthalenetetracarboxylic acid dianhydride.
Among these, preferably 4,4'-oxydiphthalic acid dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, 2,2', 3,3'-benzophenone tetracarboxylic acid dihydride. Anhydrous, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride, 3,3', 4,4'-diphenyl Sulfonite tetracarboxylic acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2- Bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4'-(hexafluoroisopropylidene) diphthalic acid dianhydride, 1,2-bis (2,3-dicarboxyphenyl) ethane dianhydride 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-) Dicarboxyphenyl) ethane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 4,4'-(p-phenylenedioxy) ) Diphthalic acid dianhydride and 4,4'-(m-phenylenedioxy) diphthalic acid dianhydride, more preferably 4,4'-oxydiphthalic acid dianhydride, 3,3', 4,4. '-Biphenyltetracarboxylic acid dianhydride, 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride, 4,4'-(hexafluoroisopropylidene) diphthalic acid dianhydride, bis (3,4) -Dicarboxyphenyl) methane dianhydride and 4,4'-(p-phenylenedioxy) diphthalic acid dianhydride can be mentioned. These can be used alone or in combination of two or more.

Examples of the aliphatic tetracarboxylic acid dianhydride include cyclic or acyclic aliphatic tetracarboxylic acid dianhydride. The cyclic aliphatic tetracarboxylic acid dianhydride is a tetracarboxylic acid dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride. , 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, cycloalkhantetracarboxylic acid dianhydride such as 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride, Bicyclo [2.2] .2] Oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, dicyclohexyl3,3'-4,4'-tetracarboxylic acid dianhydride and their positional isomers can be mentioned. .. These can be used alone or in combination of two or more. Specific examples of the acyclic aliphatic tetracarboxylic acid dianhydride include 1,2,3,4-butanetetracarboxylic acid dianhydride, 1,2,3,4-pentanetetracarboxylic acid dianhydride and the like. These can be used alone or in combination of two or more. Further, a cyclic aliphatic tetracarboxylic acid dianhydride and an acyclic aliphatic tetracarboxylic acid dianhydride may be used in combination.

Among the tetracarboxylic acid compounds, the alicyclic tetracarboxylic acid dianhydride or the non-condensation polycyclic aromatic tetracarboxylic acid is preferable from the viewpoint of easily improving the elasticity, bending resistance, and optical properties of the optical film. Acid dianhydride can be mentioned. Specific examples include 4,4'-oxydiphthalic acid dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride. , 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride, 3,3', 4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 2,2-bis (3,4-di) Carboxyphenyl) propane dianhydride, 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride and mixtures thereof are preferred, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride and 4 , 4'-(hexafluoroisopropyridene) diphthalic acid dianhydride and mixtures thereof are more preferred, and 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride is even more preferred.

The content of the tetracarboxylic acid unit contained in the carboxylic acid unit constituting the polyamide imide resin is preferably 10 mol% or more, more preferably 20 mol% or more, and preferably 20 mol% or more, based on the total number of moles of the carboxylic acid unit. Is 60 mol% or less, more preferably 50 mol% or less, still more preferably 40 mol% or less. When the content of the tetracarboxylic acid unit is not more than the above upper limit value, the mechanical strength (for example, elastic modulus) tends to be improved, and when it is more than the above lower limit value, the solubility in a solvent or optics tends to be improved. It tends to be able to improve its properties (eg, reduce haze and yellowness).

Among the tetracarboxylic acid units contained in the carboxylic acid units constituting the polyamide imide resin, the structural unit having a group represented by the formula (4), for example, Y in the formula (3) is represented by the formula (4). The content of the constituent unit derived from the compound is preferably 10 mol% or more, more preferably 20 mol% or more, preferably 60 mol% or less, more preferably 50 mol, based on the total number of moles of the carboxylic acid unit. % Or less, more preferably 40 mol% or less. Further, among the tetracarboxylic acid units contained in the carboxylic acid units constituting the polyamide imide resin, the content of the structural unit having a group represented by the formula (4) is based on the total number of moles of the tetracarboxylic acid units. It is preferably 50 mol% or more, more preferably 60 mol% or more, still more preferably 70 mol% or more, and preferably 100 mol% or less. When the content of the structural unit having a group represented by the formula (4) is in the above range, the yellowness of the optical film can be reduced and the optical characteristics can be improved. Further, the solubility of the polyamide-imide resin in a solvent is further improved, the viscosity of the polyamide-imide varnish can be suppressed to a lower level, and the production of an optical film becomes easy. The content of the tetracarboxylic acid unit and the content of the structural unit having a group represented by the formula (4) can be measured by using, for example, ¹ H-NMR, or from the charging ratio of the raw materials. It can also be calculated.

In the carboxylic acid unit contained in the polyamide imide resin, the content of the structural unit derived from the dicarboxylic acid compound (1) is preferably 0.1 mol with respect to 1 mol of the structural unit derived from the tetracarboxylic acid compound (3). As described above, it is more preferably 1 mol or more, further preferably 2 mol or more, preferably 5 mol or less, more preferably 4 mol or less, still more preferably 3 mol or less. When the content of the structural unit derived from the dicarboxylic acid compound (1) is at least the above lower limit value, the optical film containing the polyamide-imide resin tends to have high mechanical strength (for example, elastic coefficient), and the above upper limit value. When it is less than the value, the thickening due to the hydrogen bond between the amide bonds in the constituent unit derived from the dicarboxylic acid compound (1) can be suppressed, the viscosity of the polyamide-imide varnish can be reduced, and the optical film can be easily manufactured. Become.

で表される化合物由来の構成単位（テトラカルボン酸化合物（５）由来の構成単位と称する場合がある）、及び／又はトリカルボン酸化合物由来の構成単位を含むことができる。
本発明のポリアミドイミド樹脂が、テトラカルボン酸化合物（５）由来の構成単位を含む場合、テトラカルボン酸化合物（５）由来の構成単位は、ジアミン化合物由来の構成単位とＹ^１の両側に形成されたイミド基又はアミド基を介して結合し得る。テトラカルボン酸単位として、テトラカルボン酸化合物（５）由来の構成単位が１種類又は２種類以上含まれていてもよく、２種類以上含まれる場合、それぞれのテトラカルボン酸化合物（５）由来の構成単位においてＹ^１の種類が異なる。 The polyamide-imide resin has the formula (5) as long as it does not impair various physical properties of the optical film containing the polyamide-imide resin.

It may contain a structural unit derived from the compound represented by (may be referred to as a structural unit derived from the tetracarboxylic acid compound (5)) and / or a structural unit derived from the tricarboxylic acid compound.
When the polyamide-imide resin of the present invention contains a structural unit derived from the tetracarboxylic acid compound (5), the structural unit derived from the tetracarboxylic acid compound ( ⁵ ) is formed on both sides of the structural unit derived from the diamine compound and Y1. It can be attached via an imide group or an amide group. As the tetracarboxylic acid unit, one kind or two or more kinds of constituent units derived from the tetracarboxylic acid compound (5) may be contained, and when two or more kinds are contained, the constituent units derived from the respective tetracarboxylic acid compound (5) are contained. ^The type of Y1 is different in the unit.

In the formula (5), Y ¹ is a tetravalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As Y ¹ , the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28) or Examples thereof include a group represented by the formula (29) and a chain hydrocarbon group having a tetravalent carbon number of 6 or less. Further, R ²⁴ and R ²⁵ are independently of -OH, -OMe, -OEt, -OPr, -OBu or -Cl, and are preferably -Cl.

The tricarboxylic acid compound constituting the structural unit derived from the tricarboxylic acid compound indicates a tricarboxylic acid or a tricarboxylic acid derivative, and examples of the tricarboxylic acid derivative include an acid chloride and an ester of tricarboxylic acid.

で表される化合物由来の構成単位（トリカルボン酸化合物（６）由来の構成単位と称する場合がある）を含むことが好ましい。本発明のポリアミドイミド樹脂が、トリカルボン酸化合物（６）由来の構成単位を含む場合、トリカルボン酸化合物（６）由来の構成単位は、ジアミン化合物由来の構成単位とＹ^２の両側に形成されたイミド基又はアミド基を介して結合し得る。トリカルボン酸単位として、トリカルボン酸化合物（６）由来の構成単位が１種類又は２種類以上含まれていてもよく、２種類以上含まれる場合、それぞれのトリカルボン酸化合物（６）由来の構成単位においてＹ^２の種類が異なる。また、Ｒ^２６は、－ＯＨ、－ＯＭｅ、－ＯＥｔ、－ＯＰｒ、－ＯＢｕ又は－Ｃｌであり、好ましくは－Ｃｌである。 The tricarboxylic acid unit is the formula (6).

It is preferable to contain a structural unit derived from the compound represented by (may be referred to as a structural unit derived from the tricarboxylic acid compound (6)). When the polyamide-imide resin of the present invention contains a structural unit derived from the tricarboxylic acid compound (6), the structural unit derived from the tricarboxylic acid compound (6) is an imide formed on both sides of the structural unit derived from the diamine compound and Y ² . It can be attached via a group or an amide group. As the tricarboxylic acid unit, one kind or two or more kinds of constituent units derived from the tricarboxylic acid compound (6) may be contained, and when two or more kinds are contained, Y in each constituent unit derived from the tricarboxylic acid compound (6). The ^two types are different. Further, R26 is -OH, ^-OME , -OEt, -OPr, -OBu or -Cl, and is preferably -Cl.

In the formula (6), Y ² is a trivalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine. As Y ² , the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28) or Examples thereof include a group in which any one of the bonds of the group represented by the formula (29) is replaced with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or less carbon atoms.

When the polyamideimide resin of the present invention contains a tricarboxylic acid unit, the tricarboxylic acid compound constituting the tricarboxylic acid unit includes aromatic tricarboxylic acid, aliphatic tricarboxylic acid and derivatives thereof (for example, acid chloride, acid anhydride, etc.). As a specific example thereof, 1,2,4-benzenetricarboxylic acid anhydride; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydrous; phthalic acid anhydride and benzoic acid are simply used. Examples include the binding, -O-, -CH _2- , -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -SO _2- or a compound linked with a phenylene group. These tricarboxylic acid compounds can be used alone or in combination of two or more.

In a preferred embodiment of the present invention, the carboxylic acid unit contained in the polyamide-imide resin is a structural unit derived from the dicarboxylic acid compound (1), a structural unit derived from the tetracarboxylic acid compound (3), and optionally a tricarboxylic acid compound ( 6) It consists of the constituent units derived from it. Further, from the viewpoint of improving the optical properties of the optical film containing the polyamideimide resin, for example, reducing the yellowness, the total number of moles of the dicarboxylic acid unit and the tetracarboxylic acid unit among the carboxylic acid units contained in the polyamideimide resin is , Preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% or more, still more preferably, relative to the total number of moles of the dicarboxylic acid unit and the tetracarboxylic acid unit, and optionally the tricarboxylic acid unit. Is 98 mol% or more, and may be 100 mol%. Further, the dicarboxylic acid unit and the tetracarboxylic acid unit are usually 100 mol% or less with respect to the total number of moles of the dicarboxylic acid unit, the tetracarboxylic acid unit and, in some cases, the tricarboxylic acid unit. The content can be measured by, for example, ¹ H-NMR, or can be calculated from the charging ratio of raw materials.

で表される化合物由来の構成単位（ジアミン化合物（７）由来の構成単位）を含むことが好ましい。ジアミン単位として、ジアミン化合物（７）由来の構成単位が１種類又は２種類以上含まれていてもよく、２種類以上含まれる場合、それぞれのジアミン化合物（７）由来の構成単位においてＸの種類が異なる。ここで、本発明のポリアミドイミド樹脂において、ジアミン化合物（７）由来の構成単位は、ジカルボン酸化合物（１）由来の構成単位とＸの両側に形成されたアミド基を介して結合でき、テトラカルボン酸化合物（３）由来の構成単位とＸの両側に形成されたイミド基を介して結合でき、テトラカルボン酸化合物（５）由来の構成単位とＸの両側に形成されたイミド基又はアミド基を介して結合でき、トリカルボン酸化合物（６）由来の構成単位とＸの両側に形成されたイミド基又はアミド基を介して結合できる。 The diamine compound has the formula (7).

It is preferable to include a structural unit derived from the compound represented by (diamine compound (7)). As the diamine unit, one kind or two or more kinds of constitutional units derived from the diamine compound (7) may be contained, and when two or more kinds are contained, the kind of X is included in each constitutional unit derived from the diamine compound (7). different. Here, in the polyamide imide resin of the present invention, the structural unit derived from the diamine compound (7) can be bonded to the structural unit derived from the dicarboxylic acid compound (1) via the amide groups formed on both sides of X, and is tetracarboxylic. A structural unit derived from the acid compound (3) and an imide group or an amide group formed on both sides of the tetracarboxylic acid compound (5) can be bonded via an imide group formed on both sides of X. It can be bonded via an imide group or an amide group formed on both sides of the structural unit derived from the tricarboxylic acid compound (6).

In the formula (7), X represents a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms. In the organic group, the hydrogen atom in the organic group may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine, in which case the carbon number of the hydrocarbon group and the hydrocarbon group substituted with fluorine is preferable. Is 1-8. X is represented by the formula (10), the formula (11), the formula (12), the formula (13), the formula (14), the formula (15), the formula (16), the formula (17) or the formula (18). Groups in which the hydrogen atom in the groups represented by these formulas is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms are exemplified. To.

* In equations (10) to (18) represents a bond, and V ¹ , V ² and V ³ are independent, single bond, -O-, -CH _{2-, -CH 2 -} CH, respectively. _2- , -CH (CH ₃ )-, -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -S-, -SO _2- or -CO-. It is preferable that V ¹ and V ² and V ² and V ³ are respectively located at the meta-position or the para-position with respect to each ring.

A group represented by the formula (10), the formula (11), the formula (12), the formula (13), the formula (14), the formula (15), the formula (16), the formula (17) or the formula (18). Above all, from the viewpoint of easily improving the elastic modulus of the optical film containing the polyamide-imide resin, the group represented by the formula (13), the formula (14), the formula (15), the formula (16) or the formula (17). Is preferable, and the group represented by the formula (14), the formula (15) or the formula (16) is more preferable. Further, V ¹ , V ² and V ³ may be single-bonded, —O— or —S— independently from the viewpoint of easily improving the elastic modulus of the optical film containing the polyamide-imide resin. It is preferably single-bonded or —O—, and even more preferably single-bonded.

［式（８）中、Ｒ^２７～Ｒ^３４は、それぞれ独立に、水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、Ｒ^２７～Ｒ^３４に含まれる水素原子は、それぞれ独立に、ハロゲン原子で置換されていてもよく、＊は結合手を表す］
で表される。ポリアミドイミド樹脂に含まれるジアミン単位として、式（７）中のＸが式（８）で表される化合物由来の構成単位を含むと、ポリアミドイミド樹脂を含んでなる光学フィルムは、高い弾性率及び優れた光学特性を両立しやすい。 In a preferred embodiment of the present invention, X in the formula (7) is the formula (8) :.

[In the formula (8), R ²⁷ to R ³⁴ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and hydrogen contained in R ²⁷ to R ³⁴ . Each atom may be independently substituted with a halogen atom, where * represents a bond].
It is represented by. When X in the formula (7) contains a structural unit derived from the compound represented by the formula (8) as the diamine unit contained in the polyamide-imide resin, the optical film containing the polyamide-imide resin has a high elastic modulus and It is easy to achieve both excellent optical characteristics.

In the formula (7), R ²⁷ to R ³⁴ are preferably R ²⁷ to R ³² being a hydrogen atom, R ³³ and R ³⁴ being a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and more preferably R ²⁷ to R 27. R ³² represents a hydrogen atom, R ³³ and R ³⁴ represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, where the hydrogen atoms contained in R ³³ and R ³⁴ are independently substituted with halogen atoms, respectively. May be. Each of R ²⁷ to R ³⁴ is more preferably a methyl group or a trifluoromethyl group, and particularly preferably, from the viewpoint of easily obtaining an optical film having excellent optical properties, for example, low haze and low yellowness. It is a trifluoromethyl group.

で表される。ジアミン単位として、式（８）中のＸが式（８’）で表される化合物由来の構成単位を含有するポリアミドイミド樹脂を含んでなる光学フィルムは、ヘイズが低減されるとともに、黄色度を低減することができるため、優れた光学特性を有することができる。さらにフッ素元素を含有する骨格によりポリアミドイミド樹脂の溶媒への溶解性を向上し、ポリアミドイミドワニスの粘度を低く抑制することができ、また光学フィルムの製造が容易となる。 In a preferred embodiment of the invention, formula (8) is represented by formula (8') :.

It is represented by. An optical film containing a polyamide-imide resin containing a constitutional unit derived from a compound in which X in the formula (8) is represented by the formula (8') as a diamine unit has reduced haze and yellowness. Since it can be reduced, it can have excellent optical characteristics. Further, the skeleton containing a fluorine element improves the solubility of the polyamide-imide resin in a solvent, suppresses the viscosity of the polyamide-imide varnish to be low, and facilitates the production of an optical film.

Examples of the diamine constituting the diamine unit include aliphatic diamines, aromatic diamines and mixtures thereof. In addition, in this embodiment, "aromatic diamine" represents a diamine in which an amino group is directly bonded to an aromatic ring, and an aliphatic group or another substituent may be contained in a part of the structure thereof. The aromatic ring may be a monocyclic ring or a condensed ring, and examples thereof include, but are not limited to, a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring. Among these, a benzene ring is preferable. Further, the "aliphatic diamine" represents a diamine in which an amino group is directly bonded to an aliphatic group, and an aromatic ring or other substituent may be contained as a part of the structure thereof.

Specific examples of the aliphatic diamine include acyclic aliphatic diamines such as hexamethylenediamine; 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, norbornanediamine, 4,4. '-Cycholic aliphatic diamines such as diaminodicyclohexylmethane can be mentioned. These can be used alone or in combination of two or more.

Specific examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylene diamine, p-xylylene diamine, 1,5-diaminonaphthalene, and 2,6-diamino. Aromatic diamines having one aromatic ring, such as naphthalene; 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3 '-Diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-Aminophenoxy) benzene, 4,4'-diaminodiphenyl sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-Aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2'-dimethylbenzidine, 2,2'-bis (trifluoromethyl) -4,4'-Diaminodiphenyl (sometimes referred to as TFMB) 4,4'-bis (4-aminophenoxy) biphenyl, 9,9-bis (4-aminophenyl) fluorene, 9,9-bis ( 2 aromatic rings such as 4-amino-3-methylphenyl) fluorene, 9,9-bis (4-amino-3-chlorophenyl) fluorene, 9,9-bis (4-amino-3-fluorophenyl) fluorene, etc. Examples include aromatic diamines having one or more. These can be used alone or in combination of two or more.

The aromatic diamine preferably includes 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, and the like. 3,3'-Diaminodiphenyl sulfone, 1,4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2'-dimethylbenzidine, 2,2'-bis (Trifluoromethyl) -4,4'-diaminodiphenyl, 4,4'-bis (4-aminophenoxy) biphenyl, more preferably 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-Diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 1,4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, 2,2-bis [ 4- (4-Aminophenoxy) phenyl] propane, 2,2'-dimethylbenzidine, 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl, 4,4'-bis (4-amino) Phenoxy) Biphenyl. These can be used alone or in combination of two or more.

Among the above diamine compounds, one or more selected from the group consisting of aromatic diamines having a biphenyl structure should be used from the viewpoint of easily improving the elastic modulus of the optical film and improving the optical properties, for example, easily reducing the haze. Is preferable. From 2,2'-dimethylbenzidine, 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl, 4,4'-bis (4-aminophenoxy) biphenyl and 4,4'-diaminodiphenyl ether It is more preferable to use one or more selected from the group, and it is even more preferable to use 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl.

Among the diamine units constituting the polyamide-imide resin, the content of the structural unit having a group represented by the formula (8), for example, the structural unit derived from the compound in which X in the formula (7) is represented by the formula (8). Is preferably 30 mol% or more, more preferably 50 mol% or more, still more preferably 60 mol% or more, still more preferably 70 mol% or more, and particularly preferably 80 mol%, based on the total number of moles of the diamine unit. The above is preferably 100 mol% or less. When the content of the structural unit having a group represented by the formula (8) is in the above range, the obtained optical film has reduced haze and can have higher transparency, and the production of the optical film can be performed. It will be easy. The content of the structural unit having a group represented by the formula (8) can be measured by using, for example, ¹ H-NMR, or can be calculated from the charging ratio of the raw materials.

In a preferred embodiment of the present invention, the polyamide-imide resin may contain halogen atoms as described above. Specific examples of the fluorine-containing substituent include a fluoro group and a trifluoromethyl group. When the polyamide-imide resin contains a halogen atom, it may be possible to improve the optical characteristics of the optical film containing the polyamide-imide resin, for example, to reduce haze and yellowness. Further, the halogen atom is preferably a fluorine atom from the viewpoint of further improving the optical properties, elastic modulus and bending resistance of the optical film.

The content of the halogen atom in the polyamide-imide resin is preferably 1 to 40% by mass, more preferably 3 to 35% by mass, and further, based on the mass of the polyamide-imide resin, from the viewpoint of further improving the optical properties of the optical film. It is preferably 5 to 32% by mass.

As described above, the polyamide-imide resin of the present invention is, for example, a reaction between a carboxylic acid compound containing the dicarboxylic acid compound, the tetracarboxylic acid compound, and, if necessary, the tricarboxylic acid compound, and the diamine compound, for example. Manufactured by polycondensation. In one embodiment of the present invention, an imidization catalyst may be present in the synthesis of the polyamide-imide resin. Examples of the imidization catalyst include aliphatic amines such as tripropylamine, dibutylpropylamine and ethyldibutylamine; N-ethylpiperidine, N-propylpiperidine, N-butylpyrolidin, N-butylpiperidine, and N-propylhexahydro. Alicyclic amines such as azepine (monocyclic); azabicyclo [2.2.1] heptane, azabicyclo [3.2.1] octane, azabicyclo [2.2.2] octane, and azabicyclo [3.2. 2] Alicyclic amines such as nonane (polycyclic); and pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2, Aromatic amines such as 4-dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8-tetrahydroisoquinoline, and isoquinoline can be mentioned.

In the production of the polyamide-imide resin, the reaction temperature is not particularly limited, but is, for example, 50 to 350 ° C. The reaction time is also not particularly limited, but is, for example, about 30 minutes to 10 hours. If necessary, the reaction may be carried out under conditions of an inert atmosphere or reduced pressure. The reaction may be carried out in a solvent, and examples of the solvent include a solvent used for preparing a polyamide-imide varnish, which will be described later.

The polyamide-imide resin has a standard polystyrene-equivalent weight average molecular weight of 210,000 or more, preferably 3,000,000 or more, more preferably 350,000 or more, preferably 800,000 or less, and more preferably 750,000 or less. , More preferably 600,000 or less, preferably 500,000 or less. When the weight average molecular weight of the polyamide-imide resin is at least the above lower limit value, the elastic modulus and bending resistance of the optical film containing the polyamide-imide resin can be improved, and the optical properties can be improved, for example, haze can be reduced. Further, when the weight average molecular weight of the polyamide-imide resin is not more than the above upper limit value, the viscosity of the polyamide-imide varnish can be suppressed to be low, and the optical film can be easily stretched, so that the processability is good. In the present specification, the weight average molecular weight can be obtained by, for example, GPC measurement and converted to standard polystyrene, and specifically, can be obtained by the method described in Examples.

In the optical film, the content of the polyamide-imide resin is preferably 30 to 99% by mass, more preferably 35 to 90% by mass, still more preferably 40 to 80% by mass, and particularly preferably 40, based on the mass of the optical film. It is about 70% by mass. Within the above range, it is easy to obtain an optical film having a high elastic modulus and excellent optical properties.

More specifically, the polyamide-imide resin according to a preferred embodiment of the present invention has a repeating structural unit represented by the formula (31) and a repeating structural unit represented by the formula (34). In the polyamide-imide resin according to the present embodiment, the strength of the film is such that the repeating structural unit represented by the formula (31) and the repeating structural unit represented by the formula (34) are the main structural units of the polyamide-imide resin. And is preferable from the viewpoint of transparency. The total of the repeating constituent units represented by the formula (31) and the repeating constituent units represented by the formula (34) is preferably 40 mol% or more, more preferably, with respect to all the repeating constituent units of the polyamide-imide resin. Is 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more, and particularly preferably 98 mol% or more. The total of the repeating building blocks represented by the formula (31) and the repeating building blocks represented by the formula (34) may be 100 mol%.

Further, in the polyamide-imide resin according to the present embodiment, the repeating structural unit represented by the formula (34) is a repeating structural unit represented by the formula (31) and a repeating structural unit represented by the formula (34). With respect to the total, it is preferably 20 mol% or more, more preferably 30 mol% or more, still more preferably 40 mol% or more, particularly preferably 50 mol% or more, and most preferably 60 mol% or more. Further, it is preferably 90 mol% or less, more preferably 85 mol% or less, and further preferably 80 mol% or less. When the repeating structural unit represented by the formula (34) is in the above range, it is preferable from the viewpoint of good film forming property by improving the elastic modulus of the optical film and the solubility of the resin.

Further, the polyamide-imide resin according to the preferred embodiment of the present invention is repeatedly represented by any of the formula (32) and the formula (33) as long as the various physical properties of the obtained polyamide-imide polymer film are not impaired. It may contain any one or more of the structural units. Further, the polyamide-imide resin may contain two or more kinds of repeating structural units represented by the formula (31), the formula (32), the formula (33) or the formula (34).

In the repeating structural unit represented by the formula (31) and the repeating structural unit represented by the formula (32), the tetracarboxylic acid compound (3) or the tetracarboxylic acid compound (5) reacts with the diamine compound (7). A structural unit derived from the tetracarboxylic acid compound (3) or the tetracarboxylic acid compound (5) and a structural unit derived from the diamine compound (7). The repeating structural unit represented by the formula (33) is a structural unit formed by reacting the tricarboxylic acid compound (6) and the diamine compound (7), and is a structural unit derived from the tricarboxylic acid compound (6) and a diamine. It is a structural unit including both a structural unit derived from the compound (7). The repeating structural unit represented by the formula (34) is a structural unit formed by reacting the dicarboxylic acid compound (1) and the diamine compound (7), and is a structural unit derived from the dicarboxylic acid compound (1) and a diamine. It is a structural unit including both a structural unit derived from the compound (7).

Therefore, in each of the formula (31), the formula (32), the formula (32) or (34), G ¹ and G ² are Y in the formula (3) or Y ¹ and G ³ in the formula (5) are. Y ² and G ⁴ in the formula (6) are the same as W in the formula (1), and X ¹ to X ⁴ in the formula (31), the formula (32), the formula (33) and (34) are respectively. It is the same as X in the formula (7), and X ¹ to X ⁴ may be the same or different, respectively.

<Silica particles>
The optical film of the present invention contains silica particles. The average primary particle diameter of the silica particles is preferably 10 nm or more, more preferably 15 nm or more, further preferably 20 nm or more, preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less, and particularly preferably 40 nm or less. Particularly preferably, it is 30 nm or less. When the average primary particle diameter of the silica particles is in the above range, aggregation of the silica particles can be suppressed, the optical characteristics of the optical film can be improved, for example, haze can be reduced. In the present invention, the average primary particle size can be measured by the BET method.

The content of the silica particles contained in the optical film of the present invention is 3 to 70% by mass with respect to the mass (100% by mass) of the optical film. The optical film of the present invention has a high elastic modulus and excellent optical properties, for example, by containing the polyamide-imide resin having a weight average molecular weight of 210,000 or more and the silica particles having a weight average molecular weight of 3 to 70% by mass. It has low haze, low yellowness (YI value), and high total light transmittance.

The content of the silica particles contained in the optical film of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 30% by mass or more, and preferably 60% by mass or less. When the content of the silica particles is at least the above lower limit value, the elastic modulus is more likely to be improved, and when the content of the silica particles is at least the above upper limit value, the optical characteristics are improved, for example, haze is reduced. However, it is easy to improve the durability (flexibility) in the bending test.

In one embodiment of the present invention, when the weight average molecular weight of the polyamide-imide resin contained in the optical film is relatively large and the content of silica particles is relatively small, for example, haze increases, and other optical characteristics are obtained. May decrease. Therefore, when the weight average molecular weight of the polyamide-imide resin is relatively large, it is preferable to increase the content of silica particles relatively. For example, when the weight average molecular weight of the polyamide imide resin is 210,000 or more, the content of the silica particles is preferably 3% by mass or more, more preferably 5% by mass or more, based on the mass (100% by mass) of the optical film. It is more preferably 10% by mass or more, particularly preferably 30% by mass or more, and the content of silica particles is 70% by mass or less. By adjusting the content of the silica particles to a predetermined amount or more in this way, high elastic modulus and excellent optical properties can be exhibited even if the optical film contains a high molecular weight polyamide-imide resin.

<Optical film>
Since the optical film of the present invention contains a polyamide-imide resin having a weight average molecular weight of 210,000 or more and silica particles of 3 to 70 parts by mass with respect to the mass of the optical film, it has a high elastic modulus and is excellent. Has optical properties. The optical film of the present invention is also excellent in bending resistance. Therefore, the optical film of the present invention can be used as a member of an image display device, particularly a front plate (window film) of a flexible display. The front plate has a function of protecting the image display element in the flexible display. Examples of the image display device include a television, a smartphone, a mobile phone, a car navigation system, a tablet PC, a portable game machine, electronic paper, an indicator, a bulletin board, a clock, a wearable device such as a smart watch, and the like. Examples of the flexible display include an image display device having flexible characteristics, such as a television, a smartphone, a mobile phone, a car navigation system, a tablet PC, a portable game machine, electronic paper, an indicator, a bulletin board, a clock, and a wearable device.

The optical film of the present invention may further contain an ultraviolet absorber. Examples of the ultraviolet absorber include a triazine derivative (triazine ultraviolet absorber) such as a benzotriazole derivative (benzotriazole ultraviolet absorber), a 1,3,5-triphenyltriazine derivative, and a benzophenone derivative (benzophenone ultraviolet absorber). ), And a salicylate derivative (salicylate-based ultraviolet absorber), and at least one selected from the group consisting of these can be used. Since it has a good ultraviolet absorbing ability, it is preferable to use at least one selected from the group consisting of a benzotriazole-based ultraviolet absorber and a triazine-based ultraviolet absorber, and a benzotriazole-based ultraviolet absorber is more preferable.

Specific examples of the benzotriazole-based ultraviolet absorber include a compound represented by the formula (9), which can be used alone or in combination of two or more. Specific examples of the compound represented by the formula (9) include trade names of Sumisorb 200 (2- (2-hydroxy-5-methylphenyl) benzotriazole) and Sumisorb 300 (2- (2- (2- (2- (2-hydroxy-5-methylphenyl) benzotriazole)) manufactured by Sumitomo Chemical Co., Ltd. 3-tert-Butyl-2-hydroxy-5-methylphenyl) -5-chlorobenzotriazole), Sumisorb 340 (2- (2-hydroxy-5-tert-octylphenyl) benzotriazole), Sumisorb 350 (2- (2- (2- (2-) 2-Hydroxy 3,5-di-tert-pentylphenyl) benzotriazole).

In formula (9), T is a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 5 carbon atoms or an alkoxy group having 1 to 5 carbon atoms, and R ³⁵ and R ³⁶ are independent hydrogen atoms. Alternatively, it is a hydrocarbon group having 1 to 20 carbon atoms, and at least one of R ³⁵ and R ³⁶ is a hydrocarbon group having 1 to 20 carbon atoms.

The alkyl groups having 1 to 5 carbon atoms in T include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group and 2-methyl. -Butyl group, 3-methylbutyl group, 2-ethyl-propyl group and the like can be mentioned.
Examples of the alkoxy group having 1 to 5 carbon atoms in T include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a sec-butoxy group, a tert-butoxy group, and an n-pentyloxy group, 2. -Methyl-butoxy group, 3-methylbutoxy group, 2-ethyl-propoxy group and the like can be mentioned.
T is preferably a hydrogen atom, a fluorine atom, a chlorine atom or a methyl group, and more preferably a hydrogen atom, a fluorine atom or a chlorine atom.

R ³⁵ and R ³⁶ are hydrogen atoms or hydrocarbon groups having 1 to 20 carbon atoms, respectively, and at least one of R ³⁵ and R ³⁶ is a hydrocarbon group. When each of R ³⁵ and R ³⁶ is a hydrocarbon group, it is preferably a hydrocarbon group having 1 to 12 carbon atoms, and more preferably a hydrocarbon group having 1 to 8 carbon atoms. Specific examples thereof include a methyl group, a tert-butyl group, a tert-pentyl group and a tert-octyl group.

In the optical film, the content of the ultraviolet absorber is preferably 0.01 to 10 parts by mass, more preferably 1 to 8 parts by mass, still more preferably, with respect to 100 parts by mass of the total mass of the polyamide-imide resin and the silica particles. Is 3 to 7 parts by mass. When the content of the ultraviolet absorber is at least the above lower limit, the ultraviolet absorption can be improved. When the content of the ultraviolet absorber is not more than the above upper limit value, the decomposition of the ultraviolet absorber due to heat during the production of the optical film can be suppressed, and the optical characteristics can be improved, for example, haze can be reduced.

The optical film of the present invention may contain additives other than the polyamide-imide resin, silica particles and the ultraviolet absorber. Examples of other additives include resins other than polyamide-imide resins, antioxidants, mold release agents, stabilizers, colorants such as brewing agents, flame retardants, lubricants, and leveling agents. When the optical film contains an additive, the content of the additive is preferably 0.01 to 20% by mass, more preferably 0.1 to 10% by mass, based on the mass of the optical film.

The other resins are not particularly limited, and conventional resins such as polyolefin resins, cellulose resins, polyester resins, polycarbonate resins, (meth) acrylic resins, polystyrene resins, polyether ether ketone resins, and polysulfones are used. Examples thereof include based resins and polyimide resins. Other resins can be used alone or in combination of two or more.

The thickness of the optical film is appropriately adjusted depending on the intended use, but is usually 10 to 200 μm, preferably 20 to 100 μm, more preferably 25 to 80 μm, and further preferably 30 to 50 μm. When the thickness of the optical film is within the above range, the optical characteristics and bending resistance are good. In the present invention, the thickness of the optical film can be measured by, for example, the method described in Examples.

The haze of the optical film of the present invention is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less. The transparency of the optical film whose haze is equal to or less than the above upper limit value becomes good, and it can contribute to high visibility when used for the front plate of an image display device. The lower limit of haze is usually 0.01%. The haze can be measured by the method described in Examples.

The yellowness of the optical film of the present invention is preferably 8 or less, more preferably 5 or less, still more preferably 3 or less. The transparency of the optical film in which the yellowness of the optical film is equal to or less than the above upper limit value becomes good, and it can contribute to high visibility when used for the front plate of an image display device. The yellowness is usually −5 or higher, preferably −2 or higher. The yellowness can be measured by the method described in Examples.

In the optical film of the present invention, the total light transmittance at a thickness of 50 μm is preferably 80% or more, more preferably 85% or more, further preferably 90% or more, particularly preferably 91% or more, and most preferably 92% or more. be. An optical film having a total light transmittance of not more than the above lower limit value has good transparency and can contribute to high visibility when used as a front plate of an image display device. The upper limit of the total light transmittance is usually 99.99%. The total light transmittance can be measured by the method described in Examples.

The elastic modulus of the optical film of the present invention is preferably 3 GPa or more, more preferably 4 GPa or more, further preferably 5 GPa or more, particularly preferably 6 GPa or more, preferably 10 GPa or less, more preferably 8 GPa or less, still more preferably 7 GPa or more. It is as follows.
When the elastic modulus of the optical film is within the above range, the bending resistance is likely to be improved. The elastic modulus can be measured by the method described in Examples.

The method for producing the optical film is not particularly limited, but for example, the following steps:
(A) A step of preparing a liquid containing a polyamide-imide resin and silica particles (sometimes referred to as a polyamide-imide varnish) (polyamide-imide varnish preparation step).
(B) A step of applying a polyamide-imide varnish to a substrate to form a coating film (coating step), and (c) a step of drying the applied liquid (coating film) to form an optical film (optical film). Formation process)
It can be manufactured by a method including.

In the polyamide-imide varnish preparation step, for the preparation of the polyamide-imide varnish, the dicarboxylic acid compound, the tetracarboxylic acid compound, the diamine compound, and if necessary, a tricarboxylic acid compound, a tertiary acting as an imidization catalyst. Other components such as amines and dehydrating agents are mixed and reacted to prepare a polyamide-imide resin mixed solution. Examples of the tertiary amine include the above-mentioned aromatic amine and aliphatic amine. Examples of the dehydrating agent include acetic anhydride, propionic anhydride, isobutyric acid anhydride, pivalic acid anhydride, butyric acid anhydride, isovaleric acid anhydride and the like. A poor solvent is added to this polyamide-imide resin mixed solution to precipitate the polyamide-imide resin by a reprecipitation method, and the mixture is dried to take out the precipitate. If necessary, the precipitate is washed with a solvent such as methanol and dried to obtain a polyamide-imide resin. Next, the polyamide-imide resin is dissolved in a solvent, and the silica particles and, if necessary, an ultraviolet absorber or other additives are added and stirred to prepare a polyamide-imide varnish. A silica sol in which the dispersion medium of the silica sol containing silica particles is replaced with a solvent capable of dissolving the polyamide-imide resin, for example, the solvent used for preparing the following polyamide-imide varnish may be added to the polyamide-imide resin.

The solvent used for preparing the polyamide-imide varnish is not particularly limited as long as it can dissolve the polyamide-imide resin. Examples of such a solvent include amide solvents such as N, N-dimethylacetamide and N, N-dimethylformamide; lactone solvents such as γ-butyrolactone and γ-valerolactone; sulfur-containing solvents such as dimethyl sulfoxide, dimethyl sulfoxide and sulfolane. Solvents; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof (mixed solvents) can be mentioned. Among these solvents, lactone-based solvents such as γ-butyrolactone and γ-valerolactone are preferable for preparing the varnish to which silica sol is added. Further, the polyamide-imide varnish may contain water, an alcohol solvent, a ketone solvent, an acyclic ester solvent, an ether solvent and the like.

In the coating step, a polyamide-imide varnish is applied onto the substrate by a known coating method to form a coating film. Known coating methods include, for example, wire bar coating method, reverse coating, roll coating method such as gravure coating, die coating method, comma coating method, lip coating method, spin coating method, screen coating method, fountain coating method, dipping method, and the like. Examples include a spray method and a salivation forming method.

In the optical film forming step, the optical film can be formed by drying the coating film and peeling it from the substrate. After peeling, a drying step of further drying the optical film may be performed. The coating film can be dried at a temperature of usually 50 to 350 ° C. If necessary, the coating film may be dried under conditions of an inert atmosphere or reduced pressure.

Examples of the base material include PET film, PEN film, polyimide film, polyamide-imide film and the like. Among them, PET film, PEN film, polyimide film, and other polyamide-imide film are preferable from the viewpoint of excellent heat resistance. Further, the PET film is more preferable from the viewpoint of adhesion to the optical film and cost.

It is also possible to form a laminated film in which a functional layer such as a hard coat layer, an adhesive layer, and a hue adjusting layer is added to the optical film of the present invention. Further, a protective film may be attached to the surface of the optical film.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. "%" And "parts" in the examples mean mass% and parts by mass unless otherwise specified. First, the measurement and evaluation methods will be described.

<Haze>
The optical films obtained in Examples and Comparative Examples were cut into a size of 30 mm × 30 mm, and haze (%) was measured using a haze computer (“HGM-2DP” manufactured by Suga Test Instruments Co., Ltd.).
<Yellowness (YI value)>
The optical films obtained in Examples and Comparative Examples were cut into a size of 30 mm × 30 mm, and a tristimulus value (X) was used using an ultraviolet-visible near-infrared spectrophotometer (V-670 manufactured by JASCO Corporation). , Y, Z) was obtained and substituted into the following formula to calculate the YI value.
YI = 100 × (1.2769X-1.592Z) / Y
The evaluation was judged based on the following criteria.
<Evaluation method>
◎… YI ≦ 3.5
○… 3.5 <YI ≦ 5
× ... 5 <YI

<Total light transmittance>
The optical films obtained in Examples and Comparative Examples were cut into a size of 30 mm × 30 mm, and using a haze computer (“HGM-2DP” manufactured by Suga Test Instruments Co., Ltd.), the entire optical film at a thickness of 50 μm was used. The light transmittance (%) was measured.

<Elastic modulus>
The optical films obtained in Examples and Comparative Examples were cut into strips of 10 mm × 100 mm using a dumbbell cutter to obtain samples. The elastic modulus of this sample was measured using an autograph AG-IS manufactured by Shimadzu Corporation under the conditions of a chuck distance of 500 mm and a tensile speed of 20 mm / min, and the SS curve was measured, and the elastic modulus of the optical film was calculated from the inclination.

<Weight average molecular weight (Mw)>
Gel Permeation Chromatography (GPC) Measurement / Pretreatment Method Add DMF eluent (10 mM lithium bromide solution) to the polyamide-imide resin obtained in Examples and Comparative Examples at a concentration of 2 mg / mL, and at 80 ° C. The solution was heated with stirring for 30 minutes, cooled, and then filtered through a 0.45 μm membrane filter to obtain a measurement solution.
-Measurement conditions Column: TSKgel SuperAWM-H x 2 + SuperAW2500 x 1 (6.0 mm ID x 150 mm x 3)
Eluent: DMF (10 mM lithium bromide added)
Flow rate: 1.0 mL / min.
Detector: RI detector Column temperature: 40 ° C
Injection volume: 100 μL
Molecular weight standard: Standard polystyrene

<Thickness of optical film>
The optical films obtained in Examples and Comparative Examples were measured for the thickness of the optical film using an ABS digital indicator (“ID-C112BS” manufactured by Mitutoyo Co., Ltd.).

(Preparation of silica sol)
Amorphous silica sol with different BET diameter (average particle size measured by BET method) produced by the sol-gel method is used as a raw material, and γ-butyrolactone (hereinafter, also referred to as GBL) substituted silica sol is obtained by solvent substitution. Prepared. The obtained sol was filtered through a membrane filter having an opening of 10 μm to obtain a GBL-substituted silica sol. The obtained GBL-substituted silica sol contained 30 to 32% by mass of silica particles. As shown in Table 1, as the amorphous silica sol, either 23 nm or 27 nm BET diameter was used in Examples and Comparative Examples.

(Preparation of polyamide-imide resin)
1. 1. Synthesis example 1
45 g (140.52 mmol) of 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl (TFMB) and N, N-dimethyl in a 1 L separable flask equipped with a stirring blade under a nitrogen gas atmosphere. 770.40 g of acetamide (DMAc) was added and TFMB was dissolved in DMAc with stirring at room temperature. Next, 19.01 g (42.80 mmol) of 4,4'-(hexafluoroisopropylidene) diphthalic acid dianhydride (6FDA) was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 4.21 g (14.27 mmol) of 4,4'-oxybis (benzoyl chloride) (OBBC) and then 17.38 g (85.60 mmol) of terephthaloyl chloride (TPC) were added to the flask and stirred at room temperature for 1 hour. did. Next, 4.65 g (49.93 mmol) of 4-methylpyridine and 13.11 g (128.39 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 250,000.

2. 2. Synthesis example 2
Under a nitrogen gas atmosphere, 45 g (140.52 mmol) of TFMB and 768.55 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 18.92 g (42.58 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 4.19 g (14.19 mmol) of OBBC and then 17.29 g (85.16 mmol) of terephthaloyl chloride (TPC) were added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 4.63 g (49.68 mmol) of 4-methylpyridine and 13.04 g (127.75 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 355,000.

3. 3. Synthesis example 3
Under a nitrogen gas atmosphere, 40 g (124.91 mmol) of TFMB and 682.51 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 16.78 g (37.77 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 3.72 g (12.59 mmol) of OBBC and then 15.34 g (75.55 mmol) of terephthaloyl chloride (TPC) were added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 8.21 g (88.14 mmol) of 4-methylpyridine and 15.43 g (151.10 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 400,000.

4. Synthesis example 4
Under a nitrogen gas atmosphere, 40 g (124.91 mmol) of TFMB and 682.18 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 16.76 g (37.74 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 3.71 g (12.58 mmol) of OBBC and then 15.32 g (75.47 mmol) of terephthaloyl chloride (TPC) were added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 8.20 g (88.05 mmol) of 4-methylpyridine and 15.41 g (150.95 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 475,000.

5. Synthesis example 5
Under a nitrogen gas atmosphere, 40 g (124.91 mmol) of TFMB and 681.21 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 16.71 g (37.62 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 3.70 g (12.54 mmol) of OBBC and then 15.28 g (75.25 mmol) of terephthaloyl chloride (TPC) were added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 8.18 g (87.79 mmol) of 4-methylpyridine and 15.36 g (150.49 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 602,000.

6. Synthesis example 6
Under a nitrogen gas atmosphere, 40 g (124.91 mmol) of TFMB and 680.57 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 16.68 g (37.55 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 3.69 g (12.52 mmol) of OBBC and then 15.25 g (75.09 mmol) of terephthaloyl chloride (TPC) were added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 8.16 g (87.61 mmol) of 4-methylpyridine and 15.33 g (150.19 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 750,000.

7. Synthesis example 7
Under a nitrogen gas atmosphere, 65 g (202.97 mmol) of TFMB and 834.69 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 27.09 g (60.98 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 12.00 g (40.66 mmol) of OBBC and then 20.63 g (101.64 mmol) of terephthaloyl chloride (TPC) were added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 6.63 g (71.15 mmol) of 4-methylpyridine and 18.68 g (182.95 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 310,000.

8. Synthesis example 8
Under a nitrogen gas atmosphere, 50 g (156.13 mmol) of TFMB and 642.07 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 20.84 g (46.91 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 9.23 g (31.27 mmol) of OBBC and then 15.87 g (78.18 mmol) of terephthaloyl chloride (TPC) were added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 9.89 g (106.17 mmol) of 4-methylpyridine and 14.37 g (140.73 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 400,000.

9. Synthesis example 9
Under a nitrogen gas atmosphere, 45 g (140.52 mmol) of TFMB and 635.28 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 25.01 g (56.29 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 24.92 g (84.44 mmol) of OBBC was added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 9.97 g (126.01 mmol) of pyridine and 22.99 g (225.17 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes, heated to 70 ° C. using an oil bath, and further 3 hours. The mixture was stirred to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 320,000.

10. Synthesis example 10
Under a nitrogen gas atmosphere, 45 g (140.52 mmol) of TFMB and 574.25 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 19.11 g (43.02 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 4.23 g (14.34 mmol) of OBBC and then 17.47 g (86.03 mmol) of terephthaloyl chloride (TPC) were added to the flask, and the mixture was stirred at room temperature for 1 hour. Next, 9.35 g (100.37 mmol) of 4-methylpyridine and 17.57 g (172.07 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at room temperature for 30 minutes and then heated to 70 ° C. using an oil bath. The mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin. The weight average molecular weight (Mw) of the polyamide-imide resin was 205,000.

(Optical film)
1. 1. Examples 1-12, 14-19, 20, and Comparative Example 1.
The polyamide-imide resins of Synthesis Examples 1 to 5 and 7 to 10 are dissolved in GBL, the above GBL-substituted silica sol is added, and the mixture is sufficiently mixed to obtain a polyamide-imide resin / silica particle mixed varnish having the composition shown in Table 1. (Hereinafter, sometimes referred to as mixed varnish) was obtained. At that time, a mixed varnish was prepared so that the polyamide-imide resin / silica particle concentration (concentration with respect to the total mass of the resin and the silica particles) was 9 to 13% by mass.
After filtering the obtained mixed varnish with a filter having an opening of 10 micrometers, the thickness of the self-supporting film is 55 μm on the smooth surface of the polyester base material (manufactured by Toyobo Co., Ltd., trade name “A4100”). After coating with an applicator and drying at 50 ° C. for 30 minutes and then at 140 ° C. for 15 minutes, the polyester substrate was peeled off to obtain a self-supporting film. The obtained self-supporting film was fixed to a gold frame and dried at 200 ° C. to obtain an optical film having a film thickness of 50 μm. In Table 1, the content of the silica particles is based on the mass of the optical film (total mass of the polyamide-imide resin and the silica particles).

2. 2. Example 13
An ultraviolet absorber (manufactured by Sumika Chemtex Co., Ltd., product name "Sumisorb 340") is dissolved in GBP, the polyamide-imide resin of Synthesis Example 6 and the above-mentioned GBL-substituted silica sol are added, and the mixture is sufficiently dissolved in GBP. As a result, a resin / silica particle mixed varnish was obtained. At that time, the charging ratio of the raw materials is such that the ultraviolet absorber is 4 parts by mass with respect to 100 parts by mass of the total mass of the polyamideimide resin and the silica particles, and the resin / silica particle concentration (total mass of the resin and the silica particles). The mixed varnish was prepared so that (concentration with respect to) was 11% by mass.
After filtering the obtained mixed varnish with a filter having an opening of 10 micrometers, the thickness of the self-supporting film is 55 μm on the smooth surface of the polyester base material (manufactured by Toyobo Co., Ltd., trade name “A4100”). After coating with an applicator and drying at 50 ° C. for 30 minutes and then at 140 ° C. for 15 minutes, the polyester substrate was peeled off to obtain a self-supporting film. The obtained self-supporting film was fixed to a gold frame and dried at 200 ° C. to obtain an optical film having a film thickness of 50 μm.

3. 3. Example 21
The polyamide-imide resin of Synthesis Example 9 was dissolved in GBL, a GBL-substituted silica sol was added, and the mixture was sufficiently mixed to obtain a resin / silica particle mixed varnish having the composition shown in Table 1. At that time, a mixed varnish was prepared so that the concentration of the resin and the silica particles was 16% by mass. After filtering the obtained mixed varnish with a filter having an opening of 10 micrometers, the thickness of the self-supporting film is 55 μm on the smooth surface of the polyester base material (manufactured by Toyobo Co., Ltd., trade name “A4100”). After coating with an applicator and drying at 50 ° C. for 30 minutes and then at 140 ° C. for 15 minutes, the polyester substrate was peeled off to obtain a self-supporting film. The obtained self-supporting film was fixed to a gold frame and dried at 200 ° C. to obtain a film having a film thickness of 50 μm.

Table 1 shows the haze, yellowness (YI value), elastic modulus, and total light transmittance of the optical films obtained in Examples 1 to 21 and Comparative Example 1. In Table 1, the ratio of the constituent units constituting the polyamide-imide resin represents the ratio (mol%) of the constituent units derived from TPC / the constituent units derived from 6FDA / the constituent units derived from OBBC / the constituent units derived from TFMB.

The optical films of Examples 1 to 21 have lower haze and yellowness, have an excellent elastic modulus, and have a higher total light transmittance as compared with Comparative Example 1. Therefore, the optical films of Examples 1 to 21 can have both a high elastic modulus and excellent optical characteristics.

Claims (6)

An optical film containing a polyamide-imide resin having a weight average molecular weight of 210,000 or more and silica particles, the content of the silica particles is 3 to 70% by mass with respect to the mass of the optical film.
The polyamide-imide resin contains a structural unit derived from a carboxylic acid compound containing a structural unit derived from a dicarboxylic acid compound and a structural unit derived from a tetracarboxylic acid compound.
The structural unit derived from the dicarboxylic acid compound is the formula (2a).

[In the formula (2a), R ³ to R ⁶ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and hydrogen contained in R ³ to R ⁶ is represented. Each atom may be independently substituted with a halogen atom, m is an integer of 1 to 4, and * represents a bond.]
The content of the structural unit having a group represented by the formula (2a) is 30 to 95 mol% with respect to the total number of moles of the structural unit derived from the dicarboxylic acid compound. There is an optical film. The optical film according to claim 1, wherein the content of the silica particles is 5 to 70% by mass with respect to the mass of the optical film. The optical film according to claim 1 or 2, wherein the content of the structural unit derived from the dicarboxylic acid compound is 20 to 90 mol% with respect to the total number of moles of all the structural units derived from the carboxylic acid compound. Among the structural units derived from the dicarboxylic acid compound, the formula (2b)

[In the formula (2b), R ⁷ to R ¹⁴ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and hydrogen contained in R ⁷ to R ¹⁴ . The atoms may be independently substituted with halogen atoms, m ¹ is an integer of 1 to 4, m ² is 0 or 1, and A ¹ and A ² are independently -O- and-, respectively. CH _2- , -CH ₂ -CH _2- , -CH (CH ₃ )-, -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -S-, -SO _2- , -CO- Or -NR ^15- , R ¹⁵ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and * represents a bond.]
The optical film according to any one of claims 1 to 3 , wherein the content of the structural unit having a group represented by is 3 to 70 mol% with respect to the total number of moles of all the structural units derived from the carboxylic acid compound. .. The optical film according to any one of claims 1 to 4 , wherein the content of the structural unit derived from the tetracarboxylic acid compound is 10 to 60 mol% with respect to the total number of moles of all the structural units derived from the carboxylic acid compound. .. The optical film according to any one of claims 1 to 5 , wherein the polyamide-imide resin has a weight average molecular weight of 800,000 or less.