JP7249732B2 - Optical film and method for producing optical film - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical film containing a polyamide-imide resin and a method for producing the optical film.

2. Description of the Related Art Currently, image display devices such as liquid crystal display devices and organic EL display devices are widely used not only in televisions but also in various applications such as mobile phones and smart watches. With such expansion of applications, there is a demand for an image display device (flexible display) having a flexible characteristic. 2. Description of the Related Art An image display device is composed of a display element such as a liquid crystal display element or an organic EL display element, and constituent members such as a polarizing plate, a retardation plate and a front plate. All these components need to be flexible in order to achieve a flexible display.

Up to now, glass has been used as the front panel. Glass has high transparency and can exhibit high hardness depending on the type of glass, but it is very rigid and easily broken, so it is difficult to use it as a material for the front panel of a flexible display.

Therefore, utilization of polymeric materials is being studied as a material to replace glass. A front plate made of a polymer material can be expected to be used in various applications because it tends to exhibit flexible characteristics. Various resins are available as flexible resins, one of which is polyamide-imide resin. Polyamideimide resins are used in various applications from the viewpoint of transparency and heat resistance.

For example, Patent Document 1 describes a copolymerized polyamideimide resin having a specific logarithmic viscosity and breaking elongation, which is obtained by copolymerizing a polyoxyalkylene group-containing compound. Patent Document 2 describes a polyamideimide resin obtained by polymerizing specific monomers (a), (b1) and (b2). Patent Document 3 describes a polyamideimide resin having a predetermined number average molecular weight produced using a trivalent carboxylic acid component having an acid anhydride group and an isocyanate or a diamine.

JP-A-9-328550 JP 2008-285660 A JP 2009-286826 A

Conventionally, when a film containing a polyamide-imide resin is used as a front plate, a step of heating the film under high temperature conditions is performed for the purpose of increasing the surface hardness. However, heating under high temperature conditions may cause the film to turn yellow, or if the film contains additives (such as UV absorbers) in addition to the polyamide-imide resin, the additives may decompose. Therefore, there is a problem that the quality of the film is impaired.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical film containing a polyamide-imide resin, which is suitably used as a front plate of a flexible display, etc., and which can increase the surface hardness even under relatively low-temperature heating conditions.

In order to solve the above-described problems, the present inventors have made extensive studies on various properties of polyamide-imide resins, focusing on heating temperature and surface hardness. As a result, the inventors have found that surface hardness can be increased under relatively low-temperature heating conditions by using a polyamide-imide resin that satisfies specific requirements, and have completed the present invention.

［式（１）中、Ｒ^１～Ｒ^８は、それぞれ独立に、水素原子、炭素数１～６のアルキル基または炭素数６～１２のアリール基を表し、Ｒ^１～Ｒ^８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、
Ａは、それぞれ独立に、－Ｏ－、－Ｓ－、－ＣＯ－または－ＮＲ^９－を表し、Ｒ^９はハロゲン原子で置換されていてもよい炭素数１～１２の炭化水素基を表し、
ｍは１～４の整数であり、
＊は結合手を表す］
で表される構成単位を少なくとも有する、前記［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は、ジカルボン酸に由来する構成単位を少なくとも有する、前記［１］～［６］のいずれかに記載の光学フィルム。
［８］ポリアミドイミド樹脂は、フッ素原子含有ジアミンおよび／またはフッ素原子含有テトラカルボン酸二無水物に由来する構成単位を少なくとも有する、前記［１］～［７］のいずれかに記載の光学フィルム。
［９］３０μｍ以上の厚みを有する、前記［１］～［８］のいずれかに記載の光学フィルム。
［１０］（１）ポリアミドイミド樹脂および溶剤を少なくとも含む樹脂組成物を支持体に塗付する工程、ならびに、
（２－１）該樹脂組成物の塗膜を２４０℃以下の温度で乾燥後に支持体から剥離する工程、または、
（２－２）該樹脂組成物の塗膜を２４０℃以下の温度で乾燥後に支持体から剥離する工程、および、剥離したフィルムを２４０℃以下の温度で加熱する工程
を少なくとも含む、光学フィルムの製造方法。
［１１］樹脂組成物は光吸収機能を有する添加剤をさらに含む、前記［１０］に記載の製造方法。
［１２］溶剤はジメチルアセトアミドを含む、前記［１０］または［１１］に記載の製造方法。 That is, the present invention includes the following preferred aspects.
[1] An optical film containing a polyamide-imide resin having a tan δ peak value measured by DMA in the range of 300 to 370° C. and having a YI value of 3 or less.
[2] The optical film of [1] above, which has a pencil hardness of 3B or more as measured according to ASTM D 3363 under an illumination condition of 4000 lux.
[3] The optical film according to any one of [1] or [2] above, further comprising an additive having a light absorption function.
[4] The optical film according to any one of [1] to [3], wherein the additive having a light absorption function is selected from the group consisting of ultraviolet absorbers and bluing agents.
[5] The optical film according to any one of [1] to [4], wherein the polyamideimide resin contains a fluorine atom.
[6] Polyamideimide resin has the formula (1):

[In formula (1), R ¹ to R ⁸ 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 the hydrogen contained in R ¹ to R ⁸ each atom may be independently substituted with a halogen atom,
A each independently represents -O-, -S-, -CO- or -NR ⁹ -, R ⁹ represents a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom,
m is an integer from 1 to 4,
* represents a bond]
The optical film according to any one of [1] to [5], which has at least a structural unit represented by:
[7] The optical film according to any one of [1] to [6], wherein the polyamideimide resin has at least a structural unit derived from a dicarboxylic acid.
[8] The optical film according to any one of [1] to [7], wherein the polyamide-imide resin has at least structural units derived from a fluorine atom-containing diamine and/or a fluorine atom-containing tetracarboxylic dianhydride.
[9] The optical film according to any one of [1] to [8], which has a thickness of 30 μm or more.
[10] (1) A step of applying a resin composition containing at least a polyamideimide resin and a solvent to a support, and
(2-1) a step of drying the coating film of the resin composition at a temperature of 240° C. or less and then peeling it off from the support, or
(2-2) An optical film comprising at least a step of drying a coating film of the resin composition at a temperature of 240°C or less and then peeling it from a support, and a step of heating the peeled film at a temperature of 240°C or less. Production method.
[11] The production method according to [10] above, wherein the resin composition further contains an additive having a light absorption function.
[12] The production method according to the above [10] or [11], wherein the solvent contains dimethylacetamide.

The optical film of the present invention can increase the surface hardness under relatively low-temperature heating conditions. Therefore, the optical film of the present invention combines sufficient surface hardness with high transparency and low yellowness.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. The scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the gist of the present invention.

The optical film of the present invention contains a polyamide-imide resin having a tan δ peak value determined by DMA measurement within the range of 300 to 370°C. Hereinafter, the temperature at which the polyamide-imide resin has a tan δ peak value measured by DMA is also referred to as "tan δ peak temperature".
Note that the tan δ peak temperature of the resin is a temperature also called the glass transition temperature of the resin. The above range is lower than the tan δ peak temperature that conventional polyamideimide resins usually have. The optical film of the present invention containing a polyamide-imide resin having a peak value of tan δ at a temperature within the predetermined range can achieve sufficiently high surface hardness under relatively low-temperature heating conditions. It is believed that this is because the free volume of the resin decreases under relatively low temperature heating conditions. It should be noted that the above mechanism does not limit the present invention in any way. Since the optical film of the present invention can achieve a sufficiently high surface hardness under relatively low-temperature heating conditions, the film yellows due to heating, and the heat resistance of additives having a light-absorbing function, etc., which may be included in some cases. Decomposition of additives with a low B is suppressed, and the quality of the film can be improved. When the tan δ peak temperature of the polyamide-imide resin contained in the optical film of the present invention is lower than 300° C., the elastic modulus of the resin is lowered, so that high surface hardness tends to be difficult to develop. Moreover, when the tan δ peak temperature exceeds 370° C., high-temperature heat treatment is required to develop high surface hardness, and the optical properties of the resin may deteriorate. The tan δ peak temperature of the polyamideimide resin contained in the optical film of the present invention is preferably 305 to 365°C, more preferably 305 to 365°C. In one embodiment, the tan δ peak temperature of the polyamideimide resin contained in the optical film of the present invention is preferably 305-365°C, more preferably 320-365°C, and even more preferably 340-365°C.

The method for adjusting the tan δ peak temperature of the polyamideimide resin to the above range is not particularly limited. A method of adjusting the imidization rate in the imide resin and the like can be mentioned. Incidentally, if the amount of the structural unit represented by the formula (1) described later is increased or the imidization rate of the polyamide-imide resin is increased, tan δ tends to decrease. should be adjusted.

The tan δ peak temperature is measured by DMA measurement. Specifically, it can be evaluated according to the examples of the present specification using a DMA measuring instrument (DMA Q800 manufactured by TA Instruments).

The YI value of the optical film of the present invention is 3 or less. When the YI value exceeds 3, the yellowness of the optical film becomes too high, and sufficient visibility cannot be obtained. The YI value of the optical film of the invention is preferably 3.0 or less, more preferably 2.5 or less, still more preferably 2.0 or less. The visibility of an optical film can be made higher as a YI value is below said upper limit. In addition, the lower limit of the YI value is not particularly limited, and is usually 0 or more. YI value represents the yellowness of the film (Yellow Index: YI value), in accordance with JIS K 7373: 2006, spectrophotometer (manufactured by JASCO Corporation UV-visible near-infrared spectrophotometer V-670 ). Specifically, it is calculated based on the following formula from the tristimulus values (X, Y, Z) obtained by measuring the transmittance for light of 300 to 800 nm.

The pencil hardness (surface hardness) of the optical film of the present invention is preferably 3B or higher, more preferably 2B or higher, still more preferably B or higher, particularly preferably HB or higher, as measured according to ASTM D 3363 under an illumination condition of 4000 lux. , very preferably H or greater, most preferably 2H or greater. When the pencil hardness of the optical film of the present invention is at least the above lower limit, when it is used as a front plate (window film) of an image display device, it is easy to suppress scratches on the surface of the image display device, and the optical film shrinks. And it is preferable because it is easy to prevent expansion. The upper limit of the pencil hardness of the optical film of the invention is not particularly limited. Pencil hardness is measured according to JIS K5600-5-4:1999. Specifically, the measurement is performed with a load of 100 g and a scanning speed of 60 mm/min, and the evaluation is performed under an illumination condition of a light amount of 4000 lux. When evaluating the pencil hardness, the results may vary depending on the illuminance conditions used. Specifically, compared to the pencil hardness measured by evaluating under an illuminance condition of a light amount of 4000 lux, the pencil hardness measured by evaluating under an illuminance condition of a lower light amount is due to a lower light amount. As a result of less visible scratches on the film, it is likely that the result will be higher than it actually is. Therefore, the pencil hardness in this specification is a value obtained by evaluating under an illuminance condition of a light amount of 4000 lux.

The thickness of the optical film of the present invention is preferably 20 μm or more, more preferably 30 μm or more, and still more preferably 40 μm or more, from the viewpoint that the pencil hardness also affects the film thickness. The thickness of the optical film of the present invention is preferably 300 μm or less, more preferably 200 μm or less, still more preferably 100 μm or less, from the viewpoint of bending resistance. The thickness is measured using a contact-type digimatic indicator.

The total light transmittance (Tt) of the optical film of the present invention is preferably 70% or more, more preferably 80% or more, still more preferably 85% or more, and particularly preferably 90% or more. When the total light transmittance is at least the above lower limit, visibility is likely to be enhanced when the optical film of the present invention is incorporated into an image display device. In addition, the upper limit of the total light transmittance of the optical film of the present invention is usually 100% or less. The total light transmittance is measured in accordance with JIS K 7105:1981 using, for example, a fully automatic direct-reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd.

From the viewpoint of film flexibility, the elastic modulus of the optical film of the present invention is preferably 5.9 GPa or less, more preferably 5.5 GPa or less, even more preferably 5.2 GPa or less, particularly preferably 5.0 GPa or less, and most preferably 5.0 GPa or less. It is preferably 4.5 GPa or less. When the elastic modulus is equal to or less than the above upper limit, it is easy to suppress damage to other members due to the optical film when the flexible display is bent. Although the lower limit of the elastic modulus of the optical film of the present invention is not particularly limited, it is usually 2.0 GPa or more. The elastic modulus is obtained by measuring the SS curve of a 10 mm wide test piece under the conditions of a chuck distance of 500 mm and a tensile speed of 20 mm/min using, for example, an Autograph AG-IS manufactured by Shimadzu Corporation. can be measured.

The number of reciprocating bends of the optical film of the present invention is preferably 10,000, measured until the film breaks under the conditions of R = 1 mm, 135°, a load of 0.75 kgf, and a speed of 175 cpm, from the viewpoint of the bending resistance of the film. times or more, more preferably 20,000 times or more, still more preferably 30,000 times or more, particularly preferably 40,000 times or more, and most preferably 50,000 times or more. When the number of times of reciprocating bending of the optical film of the present invention is at least the above lower limit, it is easy to suppress wrinkles that may occur when the optical film is bent. Although the upper limit of the number of reciprocating bendings of the optical film is not particularly limited, it is sufficiently practical as long as it can be bent about 1,000,000 times or less. The number of times of reciprocating bending can be obtained by using, for example, an MIT folding fatigue tester (model 0530) manufactured by Toyo Seiki Seisakusho Co., Ltd., and a test piece cut out from an optical film having a thickness of 50 μm and a width of 10 mm as a measurement sample.

The weight average molecular weight (Mw) of the polyamideimide resin contained in the optical film of the present invention is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 50,000 or more, and particularly preferably 70,000 or more. is particularly preferably 100,000 or more, preferably 800,000 or less, more preferably 600,000 or less, even more preferably 500,000 or less, and particularly preferably 450,000 or less. When the weight average molecular weight (Mw) of the polyamide-imide resin is at least the above lower limit, the bending resistance of the optical film of the present invention can be easily increased. When the weight average molecular weight (Mw) of the polyamideimide resin is equal to or less than the above upper limit, the solubility of the polyamideimide resin in a solvent is improved, and the viscosity of the polyamideimide varnish used for producing the optical film of the present invention is reduced. Since it can be suppressed low, it becomes easy to manufacture the optical film of the present invention. In addition, since the optical film can be easily stretched, the workability is good. The weight average molecular weight (Mw) can be determined by, for example, GPC measurement and standard polystyrene conversion, and specifically can be determined by the method described in Examples.

The imidization rate of the polyamide-imide resin contained in the optical film of the present invention is preferably 90% or more, more preferably 95% or more. When the imidization rate is at least the above lower limit, high surface hardness tends to be exhibited. The upper limit of the imidization rate of the polyamide-imide resin is not particularly limited, and may be 100% or less. The imidization rate represents the ratio of the number of moles of imide bonds in the polyamideimide resin to twice the number of moles of structural units derived from the tetracarboxylic dianhydride in the polyamideimide resin, and is used in this specification. is measured by two-dimensional NMR.
The details of the two-dimensional NMR measurement conditions are as shown in Examples.

［式（１）中、Ｒ^１～Ｒ^８は、それぞれ独立に、水素原子、炭素数１～６のアルキル基または炭素数６～１２のアリール基を表し、Ｒ^１～Ｒ^８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、
Ａは、それぞれ独立に、－Ｏ－、－Ｓ－、－ＣＯ－または－ＮＲ^９－を表し、Ｒ^９はハロゲン原子で置換されていてもよい炭素数１～１２の炭化水素基を表し、
ｍは１～４の整数であり、
＊は結合手を表す。］
ポリアミドイミド樹脂が式（１）で表される構成単位を有する場合、ポリアミドイミド樹脂の主鎖に上記式中の－Ａ－で表される、フィルムとした場合に高い屈曲性を付与し得る構造が含まれることとなる。ポリアミドイミド樹脂が高い屈曲性を付与し得る構造を適度に有することにより、ポリアミドイミド樹脂のｔａｎδピーク温度を適度に低下させることができ、その結果、該ポリアミドイミド樹脂を含むフィルムの表面硬度を、比較的低温の加熱条件で高めることができる。 The polyamide-imide resin contained in the optical film of the present invention preferably has at least a structural unit represented by formula (1).

[In formula (1), R ¹ to R ⁸ 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 the hydrogen contained in R ¹ to R ⁸ each atom may be independently substituted with a halogen atom,
A each independently represents -O-, -S-, -CO- or -NR ⁹ -, R ⁹ represents a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom,
m is an integer from 1 to 4,
* represents a bond. ]
When the polyamideimide resin has a structural unit represented by the formula (1), the main chain of the polyamideimide resin is represented by -A- in the above formula, and a structure that can impart high flexibility when formed into a film. will be included. By appropriately having a structure capable of imparting high flexibility to the polyamideimide resin, the tan δ peak temperature of the polyamideimide resin can be appropriately reduced, and as a result, the surface hardness of the film containing the polyamideimide resin is reduced to It can be increased under relatively low temperature heating conditions.

Symbols in formula (1) are described below.
A each independently represents -O-, -S-, -CO- or -NR ⁹ -, where R ⁹ is a hydrocarbon group having 1 to 12 carbon atoms optionally substituted with a halogen atom represents From the viewpoint of the flexibility of the optical film of the present invention, each A preferably independently represents -O- or -S-, more preferably -O-.
R ¹ to R ⁸ 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. From the viewpoint of the flexibility and surface hardness of the optical film of the present invention, R ¹ to R ⁸ each independently preferably represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or a carbon It represents an alkyl group of numbers 1 to 3, more preferably a hydrogen atom. Here, hydrogen atoms contained in R ¹ to R ⁸ may each independently be substituted with a halogen atom.
m is an integer in the range of 1 to 4, preferably an integer in the range of 1 to 3, more preferably 1 or 2, still more preferably 1 from the viewpoint of raw material availability. When m is within the above range, the availability of raw materials is favorable, and the flexibility of the optical film of the present invention is likely to be enhanced.

In a preferred embodiment of the present invention, formula (1) is a structural unit represented by formula (1'). In this case, the optical film of the present invention tends to exhibit high surface hardness, low elastic modulus, and high flexibility.

In a preferred embodiment in which the polyamideimide resin contained in the optical film of the present invention has a structural unit represented by formula (1) or formula (1′), the amount of the structural unit is the total amount contained in the polyamideimide resin. It is preferably 3 mol % or more, more preferably 5 mol % or more, still more preferably 10 mol % or more, and particularly preferably 20 mol % or more, based on the structural units. When the amount of the structural unit represented by formula (1) or formula (1′) is at least the above lower limit, it is easy to obtain a polyamideimide resin having a tan δ peak value in the temperature range of 370° C. or less.
Further, the amount of structural units represented by formula (1) or formula (1') is preferably 45 mol% or less, more preferably 40 mol% or less, based on all structural units contained in the polyamideimide resin. More preferably, it is 30 mol % or less. When the amount of the structural unit represented by formula (1) or formula (1′) is equal to or less than the above upper limit, it is easy to obtain a polyamideimide resin having a tan δ peak value in the temperature range of 300° C. or higher.

The polyamide-imide resin contained in the optical film of the present invention can be produced using, for example, dicarboxylic acid, diamine and tetracarboxylic acid as main raw materials, and preferably has at least structural units derived from these. Here, the structural unit represented by formula (1) or formula (1') is preferably a structural unit derived from dicarboxylic acid.

From the viewpoint of pencil hardness and elastic modulus, the polyamide-imide resin contained in the optical film of the present invention preferably has at least a structural unit derived from a dicarboxylic acid. The structural unit derived from dicarboxylic acid is preferably a structural unit derived from dicarboxylic acid dichloride.

［式（２）中、Ｚは２価の有機基を表し、Ｂ^１およびＢ^２は、それぞれ独立して、ＯＨまたはハロゲン原子、好ましくは塩素原子を表す。］ Examples of dicarboxylic acids include compounds represented by formula (2). The polyamide-imide resin may have structural units derived from one type of dicarboxylic acid, or may have structural units derived from two or more types of dicarboxylic acids.

[In formula (2), Z represents a divalent organic group, and B ¹ and B ² each independently represent OH or a halogen atom, preferably a chlorine atom. ]

In a preferred embodiment, the polyamideimide resin contained in the optical film of the present invention has structural units derived from a dicarboxylic acid represented by formula (2). Based on the unit, it is preferably 5 mol % or more, more preferably 15 mol % or more, and still more preferably 20 mol % or more. When the amount of structural units derived from the dicarboxylic acid represented by formula (2) is at least the above lower limit, high surface hardness tends to be exhibited. Further, the amount of structural units derived from the dicarboxylic acid represented by formula (2) is preferably 45 mol% or less, more preferably 40 mol% or less, based on all structural units contained in the polyamideimide resin, and further Preferably, it is 30 mol % or less. When the amount of structural units derived from the dicarboxylic acid represented by formula (2) is equal to or less than the above upper limit, it is easy to obtain a polyamide-imide resin having a tan δ peak value in the temperature range of 370° C. or less.

Z in formula (2) represents a divalent 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. The divalent organic group includes groups represented by formulas (2a) and (2b); hydrogen atoms in the groups represented by formulas (2a) and (2b) are methyl groups, fluoro groups, and chloro groups. or a group substituted with a trifluoromethyl group; and a divalent chain hydrocarbon group having 6 or less carbon atoms.

[In formulas (2a) and (2b),
* represents a bond,
U 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 -Ar-SO ₂ -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, and specific examples thereof include a phenylene group. ]

Specific examples of the dicarboxylic acid represented by formula (2) include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, their analogous acid chloride compounds, and acid anhydrides. may Specific examples include dicarboxylic acid compounds of terephthalic acid; isophthalic acid; naphthalene dicarboxylic acid; 4,4′-biphenyldicarboxylic acid; 3,3′-biphenyldicarboxylic acid; A compound in which two benzoic acids are linked by a single bond, —CH ₂ —, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ —, —SO ₂ — or a phenylene group, and acid chloride compounds thereof mentioned. More preferably, the dicarboxylic acid represented by the above formula (2) contains 4,4'-oxybisbenzoic acid and/or its acid chloride compound. Specifically, it preferably contains 4,4'-oxybis(benzoyl chloride), and more preferably a combination of 4,4'-oxybis(benzoyl chloride) and terephthaloyl chloride.

In a preferred embodiment of the present invention in which the polyamideimide resin has a structural unit derived from a dicarboxylic acid, the polyamideimide resin has the formula (2 ) preferably has at least a structural unit derived from the dicarboxylic acid represented by formula (1). When the polyamideimide resin has structural units derived from two or more dicarboxylic acids, the amount of structural units derived from the dicarboxylic acid represented by formula (1) where Z in formula (2) is the surface of the optical film From the viewpoint of hardness, elastic modulus and flexibility, based on the total structural units derived from dicarboxylic acid contained in the polyamideimide resin, preferably 5 mol% or more, more preferably 7 mol% or more, more preferably 9 mol% More preferably, it is 11 mol % or more. The upper limit of the amount of structural units derived from dicarboxylic acid represented by formula (1) where Z in formula (2) is not particularly limited, based on the entire structural units derived from dicarboxylic acid contained in the polyamideimide resin It may be 100 mol % or less. The ratio of structural units derived from the dicarboxylic acid represented by formula (1) where Z in formula (2) can be measured using, for example, ¹ H-NMR, or can be calculated from the feed ratio of raw materials. can also

From the viewpoint of transparency, low hygroscopicity, and solubility in solvents, the polyamide-imide resin contained in the optical film of the present invention preferably has at least a structural unit derived from diamine.

［式（３）中、Ｘは２価の有機基を表す。］
ポリアミドイミド樹脂は、１種類のジアミンに由来する構成単位を有していてもよいし、２種以上のジアミンに由来する構成単位を有していてもよい。 Examples of diamines include compounds represented by formula (3).

[In Formula (3), X represents a divalent organic group. ]
The polyamide-imide resin may have structural units derived from one type of diamine, or may have structural units derived from two or more types of diamines.

In a preferred embodiment, the polyamideimide resin contained in the optical film of the present invention has structural units derived from the diamine represented by formula (3). based on, preferably 47.5 mol% or more, more preferably 49.0 mol% or more, still more preferably 49.5 mol% or more. When the amount of the structural unit derived from the diamine represented by formula (3) is at least the above lower limit, it is easy to obtain a polyamide-imide resin with a high molecular weight, and it is easy to develop high surface hardness. Further, the amount of structural units derived from the diamine represented by formula (3) is preferably 50.5 mol% or less, more preferably 50.0 mol%, based on all structural units contained in the polyamideimide resin. 49.99 mol % or less, more preferably 49.99 mol % or less. When the amount of structural units derived from the diamine represented by formula (3) is equal to or less than the above upper limit, high transparency and low yellowness are likely to be exhibited.

X in formula (3) represents a divalent 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. Divalent organic groups include formula (3a), formula (3b), formula (3c), formula (3d), formula (3e), formula (3f), formula (3g), formula (3h) and formula ( Groups represented by 3i); groups in which hydrogen atoms in groups represented by those formulas are substituted with methyl groups, fluoro groups, chloro groups or trifluoromethyl groups; and divalent chains having 6 or less carbon atoms Formula hydrocarbon groups are exemplified.

[In formula (3a), formula (3b), formula (3c), formula (3d), formula (3e), formula (3f), formula (3g), formula (3h) and formula (3i),
* represents a bond,
V ¹ to V ³ are each independently a single bond, —O—, —S—, —CH ₂ —, —CH ₂ —CH ₂ —, —CH(CH ₃ )—, —C(CH ₃ ) represents _2- , -C(CF ₃ ) ₂ -, -SO ₂ - or -CO-; ]
One example is V ¹ and V ³ are a single bond, -O- or -S- and V ² is -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ - or -SO ₂ -. The bonding positions of V ¹ and V ² to each ring and the bonding positions of V ² and V ³ to each ring are preferably meta-positions or para-positions with respect to each ring. It is more preferable to have

of groups represented by formula (3a), formula (3b), formula (3c), formula (3d), formula (3e), formula (3f), formula (3g), formula (3h) and formula (3i) Among them, from the viewpoint of surface hardness and flexibility of the optical film of the present invention, groups represented by formula (3d), formula (3e), formula (3f), formula (3g) or formula (3h) are preferable, and Groups represented by (3e), formula (3f) or formula (3g) are more preferable. From the viewpoint of the surface hardness and flexibility of the optical film of the present invention, V ¹ to V ³ are each independently preferably a single bond, —O— or —S—. - is more preferable.

Specific examples of diamines represented by formula (3) include aliphatic diamines, aromatic diamines, and mixtures thereof. In the present embodiment, the term "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and part of its structure may contain an aliphatic group or other substituents. This aromatic ring may be a single ring or a condensed ring, and examples include, but are not limited to, benzene ring, naphthalene ring, anthracene ring and fluorene ring. Among these, a benzene ring is preferred. The term "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and part of its structure may contain an aromatic ring or other substituents.

Aliphatic diamines include, for example, acyclic aliphatic diamines such as hexamethylenediamine, as well as 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine and 4,4' - Cycloaliphatic diamines such as diaminodicyclohexylmethane. These can be used alone or in combination of two or more.

Aromatic diamines include, for example, p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 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'-diaminodiphenylsulfone, 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) benzidine (sometimes referred to as TFMB), 4,4′-bis(4-aminophenoxy)biphenyl, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3- Aromatics having two or more aromatic rings, such as methylphenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, and 9,9-bis(4-amino-3-fluorophenyl)fluorene diamines. These can be used alone or in combination of two or more.

Preferred aromatic diamines include 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 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 singly or in combination of two or more.

Among the above diamine compounds, from the viewpoint of surface hardness, flexibility, bending resistance, transparency and yellowness of the optical film of the present invention, one or more selected from the group consisting of aromatic diamines having a biphenyl structure should be used. is preferred, selected from the group consisting of 2,2′-dimethylbenzidine, 2,2′-bis(trifluoromethyl)benzidine, 4,4′-bis(4-aminophenoxy)biphenyl and 4,4′-diaminodiphenyl ether It is more preferable to use one or more of these, and it is even more preferable to use 2,2'-bis(trifluoromethyl)benzidine.

［式（３ｅ’）中、Ｒ^１０～Ｒ^１７は、それぞれ独立に、水素原子、炭素数１～６のアルキル基または炭素数６～１２のアリール基を表し、Ｒ^１０～Ｒ^１７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。］ In a preferred embodiment of the present invention in which the polyamideimide resin has a structural unit derived from a diamine, the polyamideimide resin is represented by X preferably has at least a structural unit derived from the diamine represented by formula (3e').

[In formula (3e′), R ¹⁰ to R ¹⁷ 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 are included in R ¹⁰ to R ¹⁷ each hydrogen atom may be independently substituted with a halogen atom,
* represents a bond. ]

In formula (3e′), R ¹⁰ to R ¹⁷ 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, preferably a hydrogen atom or 1 to 1 carbon atoms. 6 alkyl group, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, wherein the hydrogen atoms contained in R ¹⁰ to R ¹⁷ are each independently substituted with a halogen atom; good too. From the viewpoint of surface hardness, flexibility and transparency of the optical film of the present invention, R ¹⁰ to R ¹⁷ are each independently more preferably a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group. and particularly preferably a hydrogen atom or a trifluoromethyl group.

［式（３ｅ”）中、＊は結合手を表す］
この場合、本発明の光学フィルムが高い透明性を有すると同時に、ポリアミドイミド樹脂がフッ素元素を含有する骨格を有することにより、ポリアミドイミド樹脂の溶剤への溶解性が向上し、本発明の光学フィルムを作製する際に使用する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るため、本発明の光学フィルムを製造しやすくなる。 In one preferred embodiment described above, the polyamide-imide resin preferably has at least a structural unit derived from a diamine represented by formula (3e″) where X in formula (3) is.

[in the formula (3e″), * represents a bond]
In this case, the optical film of the present invention has high transparency, and at the same time, the polyamideimide resin has a skeleton containing a fluorine element, so that the solubility of the polyamideimide resin in a solvent is improved, and the optical film of the present invention is obtained. Since the viscosity of the polyamide-imide varnish used in producing can be kept low, the optical film of the present invention can be easily produced.

When the polyamideimide resin has structural units derived from two or more diamines, X in formula (3) is a structural unit derived from a diamine represented by formula (3e′), preferably formula (3e″). The amount is preferably 30 mol% or more, more preferably 50 mol%, based on the total structural units derived from the diamine contained in the polyamideimide resin, from the viewpoint of improving the transparency and ease of production of the optical film. Above, more preferably 70 mol % or more.The upper limit of the amount of the structural unit derived from the diamine represented by the formula (3e′), preferably the formula (3e″) for X in the formula (3) is particularly limited. not more than 100 mol % based on the entire constituent units derived from the diamine contained in the polyamide-imide resin. The ratio of structural units derived from the diamine represented by formula (3e′) or (3e″) where X in formula (3) can be measured using, for example, ¹ H-NMR, or It can also be calculated from the preparation ratio.

The polyamide-imide resin contained in the optical film of the present invention preferably has at least structural units derived from tetracarboxylic dianhydride from the viewpoint of transparency, hygroscopic property and solubility in solvents.

［式（４）中、Ｙは、４価の有機基を表す］ Examples of tetracarboxylic dianhydrides include compounds represented by Formula (4). The polyamideimide resin may have a structural unit derived from one type of tetracarboxylic dianhydride, or may have a structural unit derived from two or more types of tetracarboxylic dianhydride. .

[In formula (4), Y represents a tetravalent organic group]

In a preferred embodiment, the polyamideimide resin contained in the optical film of the present invention has structural units derived from the tetracarboxylic dianhydride represented by formula (4). It is preferably 5 mol % or more, more preferably 10 mol % or more, and even more preferably 20 mol % or more, based on all constituent units contained. When the amount of the structural unit derived from the tetracarboxylic dianhydride represented by the formula (4) is at least the above lower limit, the ratio of the structural unit derived from the dicarboxylic acid can be suppressed, and the temperature of 370 ° C. or less It is easy to obtain a polyamide-imide resin having a tan δ peak value within the range. Further, the amount of structural units derived from the tetracarboxylic dianhydride represented by formula (4) is preferably 45 mol% or less, more preferably 40 mol, based on all structural units contained in the polyamideimide resin. % or less, more preferably 30 mol % or less. When the amount of the structural unit derived from the tetracarboxylic dianhydride represented by formula (4) is equal to or less than the above upper limit, the ratio of the structural unit derived from the dicarboxylic acid can be increased, resulting in high surface hardness. Cheap.

Y in formula (4) represents 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 the tetravalent organic group, formula (4a), formula (4b), formula (4c), formula (4d), formula (4e), formula (4f), formula (4g), formula (4h), formula ( 4i) and groups represented by formula (4j); groups in which hydrogen atoms in groups represented by those formulas are substituted with methyl, fluoro, chloro or trifluoromethyl groups; and groups having 6 or less carbon atoms is exemplified by a tetravalent chain hydrocarbon group.

[Formula (4a), Formula (4b), Formula (4c), Formula (4d), Formula (4e), Formula (4f), Formula (4g), Formula (4h), Formula (4i) and Formula (4j) During,
* 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 -Ar-SO ₂ -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, and specific examples thereof include a phenylene group. ]

In formula (4a), formula (4b), formula (4c), formula (4d), formula (4e), formula (4f), formula (4g), formula (4h), formula (4i) and formula (4j) Among the groups represented by the formula (4g), the groups represented by the formula (4g), the formula (4i), or the formula (4j) are preferable from the viewpoint of the surface hardness and flexibility of the optical film of the present invention. is more preferred. W ¹ is a single bond, —O—, —CH _{2 —, —CH 2 —CH 2 —} , —CH(CH ₃ )—, —, from the viewpoint of surface hardness and flexibility of the optical film of the present invention. C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ - is preferred, single bond, -O-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, more preferably a single bond, -O-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, -O- or -C(CF ₃ ) ₂ - is particularly preferred.

Examples of the tetracarboxylic dianhydride represented by formula (4) include aromatic tetracarboxylic dianhydride and aliphatic tetracarboxylic dianhydride. One type of tetracarboxylic dianhydride may be used, or two or more types may be used in combination.

Specific examples of aromatic tetracarboxylic dianhydrides include non-condensed polycyclic aromatic tetracarboxylic dianhydrides, monocyclic aromatic tetracarboxylic dianhydrides and condensed polycyclic aromatic tetracarboxylic dianhydrides. Carboxylic acid dianhydrides are mentioned. Specific examples of non-fused polycyclic aromatic tetracarboxylic dianhydrides include 4,4′-oxydiphthalic dianhydride (may be referred to as OPDA), 3,3′,4,4′- Benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3 ,3′-biphenyltetracarboxylic dianhydride, 3,3′,4,4′-diphenylsulfonetetracarboxylic 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 dianhydride (sometimes referred to as 6FDA), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride anhydride, 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 dianhydride and 4,4′-(m-phenylenedioxy ) diphthalic dianhydride. In addition, 1,2,4,5-benzenetetracarboxylic dianhydride is used as the monocyclic aromatic tetracarboxylic dianhydride, and 1, 2,4,5-Benzenetetracarboxylic dianhydride and condensed polycyclic aromatic tetracarboxylic dianhydride include 2,3,6,7-naphthalenetetracarboxylic dianhydride, respectively. . These can be used alone or in combination of two or more.

Among these, 4,4′-oxydiphthalic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 2,2′,3,3′-benzophenonetetracarboxylic dianhydride , 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride, 3,3′,4,4′-diphenylsulfonetetra Carboxylic 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 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-dicarboxy phenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthal Acid dianhydride and 4,4'-(m-phenylenedioxy)diphthalic dianhydride are preferred, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid More preferred are the dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride.

Aliphatic tetracarboxylic dianhydrides include cyclic or acyclic aliphatic tetracarboxylic dianhydrides. Cycloaliphatic tetracarboxylic dianhydrides include tetracarboxylic dianhydrides having an alicyclic hydrocarbon structure, specific examples of which include 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride anhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, cycloalkanetetracarboxylic dianhydride such as 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2. 2.2] oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyl 3,3′-4,4′-tetracarboxylic dianhydride and positional isomers thereof. be done. These can be used alone or in combination of two or more. Specific examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butanetetracarboxylic dianhydride and 1,2,3,4-pentanetetracarboxylic dianhydride. and these can be used alone or in combination of two or more. A cyclic aliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride may also be used in combination.

Among the above tetracarboxylic dianhydrides, 4,4'-oxydiphthalic dianhydride, 3, 3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 4,4′-(hexafluoroisopropylidene ) diphthalic dianhydride, and mixtures thereof, are preferred, including 4,4′-oxydiphthalic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-(hexa More preferred are fluoroisopropylidene)diphthalic dianhydride, and mixtures thereof, and even more preferred is 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride.

［式（４ｇ’）中、Ｒ^１８～Ｒ^２５は、それぞれ独立に、水素原子、炭素数１～６のアルキル基または炭素数６～１２のアリール基を表し、Ｒ^１８～Ｒ^２５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］
この場合、本発明の光学フィルムが高い透明性を有すると同時に、ポリアミドイミド樹脂の高い屈曲性骨格を有することにより、ポリアミドイミド樹脂の溶剤への溶解性が向上し、本発明の光学フィルムを作製する際に使用する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るため、本発明の光学フィルムを製造しやすくなる。 In a preferred embodiment of the present invention, wherein the polyamideimide resin has a structural unit derived from a tetracarboxylic dianhydride, the polyamideimide resin is a tetracarboxylic acid represented by the formula (4g') where Y in the formula (4) is It preferably has at least a structural unit derived from an acid dianhydride.

[In formula (4g′), R ¹⁸ to R ²⁵ 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 are included in R ¹⁸ to R ²⁵ each hydrogen atom may be independently substituted with a halogen atom,
* represents a bond]
In this case, since the optical film of the present invention has high transparency and at the same time has a highly flexible skeleton of the polyamideimide resin, the solubility of the polyamideimide resin in solvents is improved, and the optical film of the present invention is produced. Since the viscosity of the polyamide-imide varnish used for coating can be kept low, the optical film of the present invention can be easily produced.

In formula (4g′), R ¹⁸ to R ²⁵ 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, preferably a hydrogen atom or 6 alkyl group, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, wherein the hydrogen atoms contained in R ¹⁸ to R ²⁵ are each independently substituted with a halogen atom; good too. From the viewpoint of the surface hardness and flexibility of the optical film of the present invention, R ¹⁸ to R ²⁵ are each independently more preferably a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, particularly A hydrogen atom or a trifluoromethyl group is preferred.

［式（４ｇ”）中、＊は結合手を表す］
この場合、本発明の光学フィルムが高い透明性を有すると同時に、ポリアミドイミド樹脂がフッ素元素を含有する骨格を有することにより、ポリアミドイミド樹脂の溶剤への溶解性が向上し、本発明の光学フィルムを作製する際に使用する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るため、本発明の光学フィルムを製造しやすくなる。 In one preferred embodiment described above, the polyamide-imide resin preferably has at least a structural unit derived from a tetracarboxylic dianhydride represented by the formula (4g″) in which Y in the formula (4) is used.

[in the formula (4g″), * represents a bond]
In this case, the optical film of the present invention has high transparency, and at the same time, the polyamideimide resin has a skeleton containing a fluorine element, so that the solubility of the polyamideimide resin in a solvent is improved, and the optical film of the present invention is obtained. Since the viscosity of the polyamide-imide varnish used in producing can be kept low, the optical film of the present invention can be easily produced.

When the polyamideimide resin has structural units derived from two or more tetracarboxylic dianhydrides, Y in formula (4) is a tetracarboxylic acid represented by formula (4g′), preferably formula (4g″) The amount of structural units derived from acid dianhydride is based on the total structural units derived from tetracarboxylic dianhydride contained in the polyamide-imide resin, from the viewpoint of improving the transparency and ease of production of the optical film. is preferably 50 mol % or more, more preferably 60 mol % or more, and still more preferably 70 mol % or more. Y in formula (4) is represented by formula (4g′), preferably formula (4g″) The upper limit of the amount of structural units derived from the tetracarboxylic dianhydride is not particularly limited, based on the total structural units derived from the tetracarboxylic dianhydride contained in the polyamideimide resin 100 mol% or less Just do it. The ratio of structural units derived from the diamine represented by formula (4g′) or (4g″) where X in formula (4) can be measured using, for example, ¹ H-NMR, or It can also be calculated from the preparation ratio.

The polyamide-imide resin contained in the optical film of the present invention may further have structural units derived from tricarboxylic acid. Examples of tricarboxylic acids include aromatic tricarboxylic acids, aliphatic tricarboxylic acids and their analogues such as acid chloride compounds and acid anhydrides. One type of tricarboxylic acid may be used, or two or more types may be used in combination.
Specific examples include anhydride of 1,2,4-benzenetricarboxylic acid; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; a single bond between phthalic anhydride and benzoic acid; , —CH ₂ —, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ —, —SO ₂ —, or compounds linked by a phenylene group.

［式（５）および式（６）中、Ｘ、ＹおよびＺは前記と同義である］
式（５）および式（６）中のＸ、ＹおよびＺは、それぞれ、式（３）中のＸ、式（４）中のＹおよび式（２）中のＺと同義であり、式（２）～式（４）中のＸ、ＹおよびＺに関して上記に述べた好ましい記載が、式（５）および式（６）中のＸ、ＹおよびＺについても同様にあてはまる。式（５）で表される構成単位は、通常、ジアミンおよびテトラカルボン酸に由来する構成単位であり、式（６）で表される構成単位は、通常、ジアミンおよびジカルボン酸に由来する構成単位である。 In a preferred embodiment of the present invention, the polyamideimide resin contained in the optical film of the present invention and having a tan δ peak value by DMA measurement within the range of 300 to 370° C. is dicarboxylic acid (dicarboxylic acid analogue such as acid chloride diamine and tetracarboxylic acid (tetracarboxylic acid analogs such as acid chlorides and tetracarboxylic dianhydrides), and optionally further tricarboxylic acids (acid chloride compounds, tricarboxylic acid compound analogs such as tricarboxylic anhydrides ) is a condensation-type polymer that is a polycondensation product. In this aspect, the polyamide-imide resin has a structural unit represented by formula (5) and a structural unit represented by formula (6).

[In formulas (5) and (6), X, Y and Z have the same definitions as above]
X, Y and Z in formula (5) and formula (6) are respectively synonymous with X in formula (3), Y in formula (4) and Z in formula (2); 2) The preferred statements made above for X, Y and Z in formulas (4) also apply to X, Y and Z in formulas (5) and (6). The structural unit represented by formula (5) is usually a structural unit derived from diamine and tetracarboxylic acid, and the structural unit represented by formula (6) is usually a structural unit derived from diamine and dicarboxylic acid. is.

［式（７）中、Ｘ^１は２価の有機基を表し、Ｙ^１は４価の有機基を表し、
式（８）中、Ｘ^２は２価の有機基を表し、Ｙ^２は３価の有機基を表す］ In a preferred embodiment of the present invention, the polyamide-imide resin having a tan δ peak value by DMA measurement within the range of 300 to 370° C. contained in the optical film of the present invention is further represented by the formula (7) It may have units and/or structural units represented by formula (8).

[In formula (7), X ¹ represents a divalent organic group, Y ¹ represents a tetravalent organic group,
In formula (8), ^X2 represents a divalent organic group and ^Y2 represents a trivalent organic group]

In formula (7), each Y ¹ is independently a tetravalent organic group, preferably a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. It is an organic group. Y ¹ includes formula (4a), formula (4b), formula (4c), formula (4d), formula (4e), formula (4f), formula (4g), formula (4h), formula (4i) and A group represented by formula (4j) and a tetravalent chain hydrocarbon group having 6 or less carbon atoms are exemplified. The polyamideimide resin may have one structural unit represented by formula (7), or may have two or more types of structural units represented by formula (7) that are different from each other in Y ¹ and / or X ¹ May have units.

In formula (8), each Y ² is independently a trivalent organic group, preferably a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group It is an organic group. Y ² is represented by formula (4a), formula (4b), formula (4c), formula (4d), formula (4e), formula (4f), formula (4g), formula (4h), formula (4i) or A group represented by formula (4j) in which one of the bonds in the group is replaced with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or less carbon atoms are exemplified. The polyamideimide resin may have one structural unit represented by formula (8), or may have two or more types of structural units represented by formula (8) that are different from each other in Y ² and / or X ² May have units.

In formulas (7) and (8), X ¹ and X ² are each independently a divalent organic group, preferably a hydrocarbon group or a hydrocarbon in which a hydrogen atom in the organic group is substituted with fluorine. It is an organic group optionally substituted with a group. X ¹ and X ² include formula (3a), formula (3b), formula (3c), formula (3d), formula (3e), formula (3f), formula (3g), formula (3h) and formula ( Groups represented by 3i); groups in which hydrogen atoms in groups represented by those formulas are substituted with methyl, fluoro, chloro or trifluoromethyl groups; and chain hydrocarbons having 6 or less carbon atoms groups are exemplified.

In a preferred embodiment of the present invention, the polyamide-imide resin contained in the optical film of the present invention comprises structural units represented by formulas (5) and (6), and optionally formula (7) and/or formula ( 8) consists of structural units represented by In this aspect, from the viewpoint of easily increasing the flexibility and surface hardness of the optical film, the amount of the structural unit represented by the formula (5) and the structural unit represented by the formula (6) contained in the polyamideimide resin is (5) and formula (6), and optionally 80% or more, more preferably 90% or more, based on the total of structural units represented by formula (7) and/or formula (8), and further Preferably it is 95% or more. The upper limit of the amount of structural units represented by formulas (5) and (6) contained in the polyamideimide resin is formula (5) or formula (6), or, in some cases, formula (7) or formula Based on the total amount of structural units represented by (8), it is usually 100% or less. The above ratio can be measured, for example, using ¹ H-NMR, or can be calculated from the charging ratio of raw materials.

The polyamide-imide resin contained in the optical film of the present invention preferably contains halogen atoms, and more preferably contains fluorine atoms. Specific examples of fluorine-containing substituents include a fluoro group and a trifluoromethyl group. When the polyamide-imide resin contains a halogen atom, the yellowness index (YI value) of the optical film of the present invention can be easily reduced, and high flexibility and bending resistance can be easily achieved at the same time. The halogen atom is preferably a fluorine atom from the viewpoints of reduction in yellowness, reduction in water absorption, and flexibility of the optical film of the present invention. From the above viewpoint, the polyamide-imide resin preferably has at least structural units derived from a fluorine atom-containing diamine and/or a fluorine atom-containing tetracarboxylic dianhydride.

The content of halogen atoms in the polyamideimide resin is determined based on the mass of the polyamideimide resin contained in the optical film of the present invention from the viewpoint of reducing yellowness (improving transparency), reducing water absorption, and suppressing deformation of the optical film. based on, preferably 1 to 40% by mass, more preferably 3 to 35% by mass, even more preferably 5 to 32% by mass.

A method for producing the polyamide-imide resin contained in the optical film of the present invention will be described below. The polyamide-imide resin can be produced, for example, by using the above-described dicarboxylic acid, diamine and tetracarboxylic acid as main raw materials and optionally further polycondensing them with the above-described tricarboxylic acid.

The reaction temperature of the polycondensation reaction 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 desired, the reaction may be conducted under conditions of inert atmosphere or reduced pressure. Moreover, the reaction may be carried out in a solvent, and examples of the solvent include the solvents used in the preparation of the polyamide-imide varnish and described later.

An imidization catalyst may be used in the polycondensation reaction. Examples of imidization catalysts include aliphatic amines such as tripropylamine, dibutylpropylamine, ethyldibutylamine; N-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propylhexahydro Alicyclic amines (monocyclic) such as azepine; azabicyclo[2.2.1]heptane, azabicyclo[3.2.1]octane, azabicyclo[2.2.2]octane, and azabicyclo[3.2. 2] Alicyclic amines (polycyclic) such as nonane; Aromatic amines such as 4-dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8-tetrahydroisoquinoline, and isoquinoline.

From the viewpoint of improving the visibility and quality of the optical film of the present invention, the optical film of the present invention preferably further contains an additive having a light absorbing function in addition to the polyamide-imide resin. Additives having a light absorption function include, for example, ultraviolet absorbers, bluing agents, and the like. The additive having a light-absorbing function is preferably selected from the group consisting of an ultraviolet absorber and a bluing agent, since this facilitates improving the visibility and quality of the optical film of the present invention. The optical film of the present invention may contain one type of additive having a light absorbing function, or may contain two or more types of additives having a light absorbing function. Here, when additives having a light absorption function such as ultraviolet absorbers and bluing agents are added to films containing conventional polyamideimide resins, these additives have low heat resistance. In the process of heating the containing film under high temperature conditions, there is a problem that decomposition or the like occurs and the quality of the film deteriorates. Therefore, for example, it was necessary to add these additives to a layer separate from the layer containing the polyamide-imide resin, and to bond the layer to the polyamide film. According to the optical film of the present invention containing a polyamideimide resin having a peak value of tan δ within a predetermined temperature range, a sufficiently high surface hardness can be achieved under relatively low-temperature heating conditions. Even if an additive having a light absorption function is added to the same layer as the layer, it is possible to suppress degradation of the additive and the like, thereby suppressing deterioration of the film quality.

As the ultraviolet absorber, it may be used by appropriately selecting from those commonly used as ultraviolet absorbers in the field of resin materials. The ultraviolet absorber may contain a compound that absorbs light with a wavelength of 400 nm or less. Examples of the ultraviolet absorber include at least one compound selected from the group consisting of benzophenone-based compounds, salicylate-based compounds, benzotriazole-based compounds, and triazine-based compounds. When the optical film of the present invention contains an ultraviolet absorber, deterioration of the polyamide-imide resin is suppressed, so visibility of the optical film can be enhanced. In addition, in this specification, a "system compound" refers to the derivative of the compound to which the said "system compound" is attached. For example, a "benzophenone-based compound" refers to a compound having benzophenone as a parent skeleton and a substituent attached to the benzophenone.

When the optical film contains an ultraviolet absorber, the amount of the ultraviolet absorber to be added may be appropriately selected depending on the type of ultraviolet absorber used. Above, more preferably 2% by mass or more, still more preferably 3% by mass or more, preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 6% by mass or less. A suitable amount to be added varies depending on the ultraviolet absorber used, but adjusting the amount to be added so that the light transmittance at 400 nm is about 20 to 60% facilitates the improvement of the light resistance of the optical film of the present invention, and at the same time makes it transparent. It is preferable because it is easy to obtain an optical film having high properties.

The bluing agent may be appropriately selected from those commonly used as bluing agents in the field of resin materials. A bluing agent is an additive (dye, pigment) that absorbs light in a wavelength region such as orange to yellow in the visible light region and adjusts the hue. inorganic dyes and pigments, and organic dyes and pigments such as phthalocyanine bluing agents and condensed polycyclic bluing agents. The bluing agent is not particularly limited, but from the viewpoint of heat resistance, light resistance and solubility, a condensed polycyclic bluing agent is preferable, and an anthraquinone bluing agent is more preferable. From the viewpoint of heat resistance, the bluing agent preferably has a thermal decomposition temperature of 200°C or higher, preferably 240°C or higher. Examples of condensed polycyclic bluing agents include anthraquinone bluing agents, indigo bluing agents, and phthalocyanine bluing agents.

When the optical film contains a bluing agent, the addition amount of the bluing agent may be appropriately selected depending on the type of bluing agent used. % by mass or more, more preferably 0.02% by mass or more, still more preferably 0.03% by mass or more, preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and still more preferably 0.5% by mass or less. It is 2% by mass or less.

The optical film of the present invention may further contain an inorganic material such as inorganic particles in addition to the polyamide-imide resin. Examples of inorganic materials include inorganic particles such as titania particles, alumina particles, zirconia particles and silica particles, and silicon compounds such as quaternary alkoxysilanes such as tetraethyl orthosilicate. From the viewpoint of the stability of the polyamideimide varnish, the inorganic material is preferably inorganic particles, particularly silica particles. Inorganic particles may be bonded together by molecules having siloxane bonds (ie —SiOSi—).

The average primary particle size of the inorganic particles is preferably 10 to 100 nm, more preferably 20 to 80 nm, from the viewpoints of transparency of the optical film, mechanical properties, and inhibition of aggregation of the inorganic particles. In the present invention, the average primary particle size can be determined by measuring the 10-point average value of the unidirectional size with a transmission electron microscope.

The optical film of the present invention may contain inorganic materials. The content of the inorganic material in the optical film is preferably 0 to 90% by mass, more preferably 0.01 to 60% by mass, still more preferably 5 to 40% by mass, based on the total mass of the optical film. When the content of the inorganic material is within the above range, it tends to be easy to achieve both transparency and mechanical properties of the optical film.

The optical film of the invention may contain other additives. Other additives include, for example, antioxidants, release agents, stabilizers, flame retardants, pH adjusters, silica dispersants, lubricants, thickeners and leveling agents. The content of other additives is preferably 0% by mass or more and 20% by mass or less, more preferably 0.01% by mass or more and 10% by mass or less, based on the mass of the optical film of the present invention.

(Layer structure)
The layer structure of the optical film of the present invention is not particularly limited, and may be a single layer or multiple layers of two or more layers. When the optical film of the present invention further contains an additive such as an additive having a light absorption function, the additive and the polyamideimide resin are combined into one layer from the viewpoint of thinning of the image display device and economic efficiency. is preferably contained in In this case, the optical film of the present invention is more preferably a single layer containing the additive and the polyamideimide resin, or a laminate having at least a layer containing the additive and the polyamideimide resin. From the viewpoint of impact resistance, the optical film of the invention preferably has a multi-layer structure of two or more layers including at least a layer containing a polyamide-imide resin. When the optical film of the present invention further contains an additive such as an additive having a light absorption function, it is a laminate having at least a layer containing the additive and a polyamide-imide resin, or a layer containing the additive. , and a layer containing a polyamide-imide resin.

The optical film of the present invention may be a polyamide-imide laminate obtained by laminating one or more functional layers on the above layer. Examples of functional layers include layers having various functions such as a hard coat layer, an ultraviolet absorbing layer, an adhesive layer, a refractive index adjusting layer, and a primer layer. The optical film of the present invention may have one or more functional layers. Also, one functional layer may have multiple functions. For example, an optical film having a multilayer structure may be obtained by forming the functional layer on a film containing a polyamide-imide resin.

The optical film of the present invention is, for example,
(1) a step of applying a resin composition containing at least a polyamideimide resin and a solvent to a support, and
(2-1) a step of drying the coating film of the resin composition at a temperature of 240° C. or less and then peeling it off from the support, or
(2-2) Manufactured by a manufacturing method including at least a step of drying the coating film of the resin composition at a temperature of 240° C. or less and then peeling it from the support, and a step of heating the peeled film at a temperature of 240° C. or less. can do. The present invention also provides a method for producing the above optical film.

In order to produce a resin composition containing at least a polyamideimide resin and a solvent (also referred to herein as a "polyamideimide varnish") used in step (1), the above-described dicarboxylic acid, diamine, tetracarboxylic acid , and, if necessary, other components (a tertiary amine acting as an imidization catalyst, a dehydrating agent, etc.) are mixed and reacted to produce a polyamide-imide resin mixed solution. Examples of tertiary amines include the aforementioned aromatic amines and aliphatic amines. Examples of dehydrating agents include acetic anhydride, propionic anhydride, isobutyric anhydride, pivalic anhydride, butyric anhydride and isovaleric anhydride. A resin composition containing at least a polyamide-imide resin and a solvent is produced by adding a solvent and, if necessary, the above additives to this polyamide-imide resin mixture and stirring the mixture. A poor solvent is added to the polyamideimide mixed solution to precipitate the polyamideimide resin by a reprecipitation method, dried and taken out as a precipitate, and the taken out polyamideimide resin precipitate is dissolved in a solvent to obtain a polyamideimide mixed solution. good. Further, instead of the polyamide-imide resin mixture, a solution of a purchased polyamide-imide resin or a purchased solid polyamide-imide resin may be dissolved in a solvent and used as a solution.

The solvent used for producing the polyamide-imide varnish is not particularly limited as long as it can dissolve the polyamide-imide resin. Examples of such solvents 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 dimethylsulfone, dimethylsulfoxide and sulfolane. solvent; carbonate-based solvents such as ethylene carbonate and propylene carbonate; and combinations thereof (mixed solvents). Among these solvents, amide-based solvents or lactone-based solvents are preferred, and solvents containing dimethylacetamide are more preferred. Further, the polyamide-imide varnish may contain water, an alcohol solvent, a ketone solvent, an acyclic ester solvent, an ether solvent, and the like.

Next, for example, by a known roll-to-roll or batch method, a coating film of polyamideimide varnish is formed by applying polyamideimide varnish onto a support such as a resin substrate, SUS belt, or glass substrate. can be formed. Examples of supports include PET film, PEN film, polyimide film, polyamideimide film, and the like. Among them, PET film, PEN film, polyimide film, and other polyamideimide films are preferable from the viewpoint of excellent heat resistance. A PET film is more preferable from the viewpoints of adhesion with the optical film of the present invention and cost.

Next, in step (2-1) or step (2-2), the coating film of polyamideimide varnish is dried at a temperature of 240° C. or less, and peeled off from the support after drying. Drying of the coating film can be preferably carried out at a temperature of 50 to 240°C. Drying of the coating may be carried out under conditions of an inert atmosphere or reduced pressure, if desired. The optical film of the present invention can be obtained by peeling the coating film from the support after drying. In the production method of the present invention, as described in step (2-2), the peeled optical film is heated at 240° C. for the purpose of further increasing the surface hardness (for example, pencil hardness) of the optical film of the present invention. A step of heating at the following temperature may be further included.

At least one surface of the optical film produced as described above may be subjected to a surface treatment step. Surface treatments include, for example, UV ozone treatment, plasma treatment, and corona discharge treatment.
When the step (2-1) or the step after step (2-2) involves heating, the temperature is preferably 280° C. or lower, more preferably 240° C. or lower.

In a preferred embodiment of the present invention in which the optical film of the present invention contains an additive such as an additive having a light absorption function, the optical film of the present invention contains the polyamideimide resin and the additive in the same layer. Such a layer can be produced in the same manner as described above by using a polyamideimide varnish obtained by adding the additive to the resin composition containing at least the above polyamideimide resin and solvent. In a preferred embodiment of the present invention in which an additive such as an additive having a light absorption function and a polyamideimide resin are contained in one layer, an additive having a thermal decomposition temperature of at least 200 ° C. or higher, preferably 240 ° C. or higher is preferably used.

The optical film of the invention may further comprise a functional layer. Examples of functional layers include layers having various functions such as a hard coat layer, an ultraviolet absorbing layer, an adhesive layer, a refractive index adjusting layer, and a primer layer. The optical film of the present invention may have one or more functional layers. Also, one functional layer may have multiple functions.

The hard coat layer is preferably arranged on the viewer side surface of the optical film. The hard coat layer may have a single layer structure or a multilayer structure. The hard coat layer comprises a hard coat layer resin, and examples of the hard coat layer resin include acrylic resins, epoxy resins, urethane resins, benzyl chloride resins, vinyl resins, silicone resins, or mixtures thereof. UV curable, electron beam curable, or thermosetting resins such as resins may be used. In particular, the hard coat layer preferably contains an acrylic resin from the viewpoint of mechanical properties such as surface hardness and from an industrial point of view. In a preferred embodiment of the present invention, since the optical film of the present invention has high surface hardness, it has sufficient surface hardness to be used in image display devices and the like without a hard coat layer. Therefore, when the optical film of the present invention further has a hard coat layer, it is possible to further increase the surface hardness of the optical film.

The ultraviolet absorbing layer is a layer having a function of absorbing ultraviolet rays. It is composed of dispersed ultraviolet absorbers. By providing an ultraviolet absorption layer as a functional layer, it is possible to easily suppress a change in yellowness due to light irradiation.

The adhesive layer is a layer having an adhesive function, and has a function of adhering the optical film of the present invention to another member. Commonly known materials can be used as the material for forming the adhesive layer. For example, a thermosetting resin composition or a photocurable resin composition can be used.

The adhesive layer may be composed of a resin composition containing a component having a polymerizable functional group. In this case, strong adhesion can be achieved by further polymerizing the resin composition forming the adhesive layer after the optical film is adhered to another member. The adhesive strength between the optical film of the present invention and the adhesive layer may be 0.1 N/cm or more, or 0.5 N/cm or more.

The adhesive layer may contain a thermosetting resin composition or a photocurable resin composition as a material. In this case, the resin composition can be polymerized and cured by supplying energy afterward.

The adhesive layer may be a layer composed of an adhesive called Pressure Sensitive Adhesive (PSA), which is adhered to an object by pressing. The pressure-sensitive adhesive may be a pressure-sensitive adhesive that is "a substance that has adhesiveness at room temperature and adheres to the adherend with light pressure" (JIS K6800), and "a specific component is a protective coating (microcapsule) It may be a capsule-type adhesive that is "adhesive that can maintain stability until the coating is destroyed by appropriate means (pressure, heat, etc.)" (JIS K6800).

The hue-adjusting layer is a layer having a hue-adjusting function and capable of adjusting the hue of the optical film of the present invention to a desired hue. The hue adjusting layer is, for example, a layer containing a resin and a colorant. Examples of the coloring agent include inorganic pigments such as titanium oxide, zinc oxide, red iron oxide, titanium oxide-based calcined pigments, ultramarine blue, cobalt aluminate, and carbon black; azo-based compounds, quinacridone-based compounds, anthraquinone-based compounds, Organic pigments such as perylene compounds, isoindolinone compounds, phthalocyanine compounds, quinophthalone compounds, threne compounds, and diketopyrrolopyrrole compounds; extender pigments such as barium sulfate and calcium carbonate; and basic dyes, Dyes such as acid dyes and mordant dyes can be mentioned.

The refractive index adjusting layer is a layer having a function of adjusting the refractive index, has a refractive index different from that of the layer containing the polyamide-imide resin in the optical film of the present invention, and imparts a predetermined refractive index to the optical film of the present invention. It is a layer that can be The refractive index adjusting layer may be, for example, a resin layer containing an appropriately selected resin and optionally a pigment, or may be a metal thin film.

Pigments that adjust the refractive index include, for example, silicon oxide, aluminum oxide, antimony oxide, tin oxide, titanium oxide, zirconium oxide, and tantalum oxide. The average primary particle size of the pigment may be 0.1 μm or less. By setting the average primary particle size of the pigment to 0.1 μm or less, it is possible to prevent diffused reflection of light passing through the refractive index adjusting layer and to prevent a decrease in transparency.

Examples of metals used for the refractive index adjusting layer include metals such as titanium oxide, tantalum oxide, zirconium oxide, zinc oxide, tin oxide, silicon oxide, indium oxide, titanium oxynitride, titanium nitride, silicon oxynitride, and silicon nitride. Oxides or metal nitrides may be mentioned.

The optical film of the present invention is useful as a front panel of an image display device, particularly a front panel (that is, a window film) of a flexible display. The optical film of the present invention can be arranged as a front plate on the viewing side surface of an image display device, particularly a flexible display. This front panel has a function of protecting the image display element in the flexible display.

Image display devices include televisions, smartphones, mobile phones, car navigation systems, tablet PCs, portable game machines, electronic paper, indicators, bulletin boards, watches, and wearable devices such as smart watches. Flexible displays include image display devices such as those described above that have flexible characteristics.

The present invention will be described in more detail below with reference to examples. Unless otherwise specified, "%" and "parts" in the examples mean % by mass and parts by mass. First, the evaluation method will be explained.

<Measurement of weight average molecular weight (Mw)>
The weight-average molecular weight (Mw) of the polyamide-imide resin was determined by gel permeation chromatography (GPC) and converted to standard polystyrene. Specific measurement conditions were as follows.
(1) Pretreatment method A DMF eluent (10 mM lithium bromide solution) was added to the polyamideimide resin to a concentration of 2 mg/mL, heated at 80°C for 30 minutes with stirring, and cooled to form a 0.45 µm membrane. A solution obtained by filtering was used as a measurement solution.
(2) Measurement conditions Column: TSKgel SuperAWM-H × 2 + SuperAW2500 × 1 (6.0 mm ID × 150 mm × 3) (both manufactured by Tosoh Corporation)
Eluent: DMF (with 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

<Measurement of tan δ and tan δ peak temperature>
Using DMA Q800 manufactured by TA Instruments, measurements were made under the following samples and conditions to obtain a tan δ curve, which is the ratio of loss modulus to storage modulus. The tan δ peak temperature of the polyamide-imide resin was calculated from the highest peak of the tan δ curve.
Sample: length 5-15 mm, width 5 mm
Experimental mode: DMA Multi-Frequency-Strain
Experiment mode detailed conditions:
(1) Clamp: Tension: Film
(2) Amplitude: 5 µm
(3) Frequency: 10 Hz (no change in all temperature intervals)
(4) Preload Force: 0.01N
(5) Force Track: 125N
Temperature conditions: (1) Range of temperature rise: Normal temperature to 400°C, (2) Rate of temperature rise: 5°C/min Main collected data: (1) Storage modulus (E'), (2) Loss modulus (Loss modulus, E"), (3) tan δ(E"/E')

（前処理方法）
試料を重水素化ジメチルスルホキシド（ＤＭＳＯ－ｄ６）に溶解させて２質量％溶液としたものを測定試料とした。
（測定条件）
測定装置：Ｂｒｕｋｅｒ社製６００ＭＨｚＮＭＲ装置ＡＶＡＮＣＥ６００
試料温度：３０３Ｋ
測定手法：^１Ｈ－ＮＭＲ，ＨＳＱＣ
（ポリイミド樹脂のイミド化率の算出方法）
ポリイミド樹脂を含む溶液を測定試料として得られた^１Ｈ－ＮＭＲスペクトルにおいて、式（ＸＸＸ）中のプロトン（Ａ）に由来するシグナルの積分値をＩｎｔ_Ａ、プロトン（Ｂ）に由来するシグナルの積分値をＩｎｔ_Ｂとした。これらの値から、式（ＮＭＲ－１）によりイミド化率（％）を求めた。

（ポリアミドイミド樹脂のイミド化率の算出方法）
ポリイミド樹脂を含む溶液を測定試料として得られたＨＳＱＣスペクトルにおいて、式（ＸＸＸ）中のプロトン（Ｃ）に由来するシグナルの積分値をＩｎｔ_Ｃ、プロトン（Ｄ）およびプロトン（Ｅ）に由来するシグナルの積分値の平均値をＩｎｔ_ＤＥとした。これらの値から、式（ＮＭＲ－２）によりβ値を求めた。

次に、複数のポリイミド樹脂について、式（ＮＭＲ－２）によるβ値および式（ＮＭＲ－１）によるイミド化率（％）を求め、この結果から相関式（ＮＭＲ－３）を得た。

そして、ポリアミドイミド樹脂を含む溶液を測定試料として得られたＨＳＱＣスペクトルにおいて、上記と同様にして式（ＮＭＲ－２）によりβ値を求めた。このβ値を上記の相関式（ＮＭＲ－３）へ代入することにより、ポリアミドイミド樹脂のイミド化率（％）を得た。 <Measurement of imidization rate>
The imidization rates of the polyimide resins and polyamideimide resins used in Examples and Comparative Examples were measured by NMR, using signals derived from protons in the partial structures (A) to (E) shown in the formula (XXX). Calculated. A method for calculating the imidization ratio from the measurement conditions and the obtained results is as follows.

(Pretreatment method)
A sample was dissolved in deuterated dimethyl sulfoxide (DMSO-d6) to obtain a 2% by mass solution, which was used as a measurement sample.
(Measurement condition)
Measuring device: 600 MHz NMR device AVANCE600 manufactured by Bruker
Sample temperature: 303K
Measurement method: ¹ H-NMR, HSQC
(Calculation method of imidization rate of polyimide resin)
In the ¹ H-NMR spectrum obtained by using a solution containing a polyimide resin as a measurement sample, Int _A is the integral value of the signal derived from proton (A) in formula (XXX), and the integral of the signal derived from proton (B) The value was taken as Int _B. From these values, the imidization rate (%) was determined by the formula (NMR-1).

(Method for calculating imidization rate of polyamide-imide resin)
In the HSQC spectrum obtained by using a solution containing a polyimide resin as a measurement sample, the integral value of the signal derived from proton (C) in formula (XXX) is Int _C , the signal derived from proton (D) and proton (E) Int _DE is the average value of the integrated values of . From these values, the β value was determined by the formula (NMR-2).

Next, for a plurality of polyimide resins, the β value according to formula (NMR-2) and the imidization rate (%) according to formula (NMR-1) were determined, and from these results a correlation formula (NMR-3) was obtained.

Then, in the HSQC spectrum obtained by using the solution containing the polyamide-imide resin as the measurement sample, the β value was determined by the formula (NMR-2) in the same manner as described above. By substituting this β value into the above correlation formula (NMR-3), the imidization rate (%) of the polyamide-imide resin was obtained.

<Measurement of total light transmittance (Tt)>
The total light transmittance Tt of the sample was measured according to JIS K7105:1981 using a fully automatic direct-reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd.

<Measurement of yellowness index (YI value)>
The yellowness (Yellow Index: YI value) of the sample was measured according to JIS K 7373:2006 using an ultraviolet-visible-near-infrared spectrophotometer V-670 manufactured by JASCO Corporation. After the background measurement was performed without the sample, the sample was set in the sample holder and the transmittance was measured with respect to light of 300 to 800 nm to obtain tristimulus values (X, Y, Z). The YI value was calculated based on the following formula.

<Measurement of surface hardness>
As the surface hardness of the sample, the pencil hardness of the sample surface was measured according to JIS K5600-5-4:1999. The measurement was carried out under the conditions of a load of 100 g and a scanning speed of 60 mm/min, and the presence or absence of scratches was evaluated under an illumination condition of a light quantity of 4000 lux to determine the pencil hardness.

<Measurement of elastic modulus>
The elastic modulus of the sample was measured using Autograph AG-IS manufactured by Shimadzu Corporation. A sample cut into a width of 10 mm was used as a test piece, and an SS curve was measured under the conditions of a distance between chucks of 500 mm and a tensile speed of 20 mm/min, and the elastic modulus was calculated from the slope.

<Measurement of bending resistance>
As the bending resistance of the sample, the number of times of reciprocating bending was measured using an MIT folding endurance tester (model 0530) manufactured by Toyo Seiki Seisakusho Co., Ltd. A sample cut into a thickness of 50 μm and a width of 10 mm was used as a test piece, and the number of reciprocating bendings until the film broke was measured under the conditions of R=1 mm, 135°, a load of 0.75 kgf, and a speed of 175 cpm.

[Production Example 1: Preparation of polyamideimide resin (1)]
In a nitrogen gas atmosphere, 52 g (162.38 mmol) of 2,2′-bis(trifluoromethyl)benzidine (TFMB) and 734.10 g of N,N-dimethylacetamide (DMAc) were placed in a 1 L separable flask equipped with a stirring blade. was added and TFMB was dissolved in DMAc with stirring at room temperature. Next, 28.90 g (65.05 mmol) of 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) was added to the flask and stirred at room temperature for 3 hours. After that, 28.80 g (97.57 mmol) of 4,4′-oxybis(benzoyl chloride) (OBBC) was added to the flask and stirred at room temperature for 1 hour.
Next, 7.49 g (94.65 mmol) of pyridine and 26.56 g (260.20 mmol) of acetic anhydride were added to the flask and stirred at room temperature for 30 minutes. After stirring for hours, a reaction solution was obtained.
The resulting reaction solution was cooled to room temperature and thrown into a large amount of methanol in the form of a thread, and the deposited precipitate was taken out, immersed in methanol for 6 hours, and washed with methanol. Next, the precipitate was dried under reduced pressure at 100° C. to obtain a polyamideimide resin (1). The weight average molecular weight (Mw), tan δ peak temperature and imidization rate of the polyamide-imide resin (1) were measured according to the above measurement methods. there were.

[Example 1: Formation of polyamideimide film (1)]
DMAc was added to the polyamideimide resin (1) obtained in Production Example 1 so as to have a concentration of 15% by mass to prepare a polyamideimide varnish (1). The obtained polyamide-imide varnish (1) was applied on the smooth surface of a polyester base material (manufactured by Toyobo, trade name "A4100") using an applicator so that the film thickness of the self-supporting film was 55 μm, and was heated at 50° C. and 30° C. After drying at 140° C. for 15 minutes, the obtained coating film was peeled off from the polyester substrate to obtain a self-supporting film.
The self-supporting film was fixed to a metal frame and dried in the atmosphere at 230° C. for 30 minutes to obtain a polyamideimide film (1) having a thickness of 50 μm.

[Example 2: Formation of polyamideimide film (2)]
DMAc was added to the polyamideimide resin (1) obtained in Production Example 1 so that the concentration was 15% by mass, and an ultraviolet absorber (manufactured by Sumika Chemtex Co., Ltd., product name "Sumisorb 340") was added to polyamideimide. 4 parts by mass were mixed with 100 parts by mass of resin (1) to prepare polyamideimide varnish (2). A polyamideimide film (2) having a thickness of 50 μm was obtained in the same manner as in Example 1, except that the polyamideimide varnish (2) was used instead of the polyamideimide varnish (1).

[Example 3: Formation of polyamideimide film (3)]
DMAc was added to the polyamideimide resin (1) obtained in Production Example 1 so that the concentration was 15% by mass, and a bluing agent (manufactured by Chemiplast, product name "Violet B") was added to the polyamideimide resin (1 ) was mixed with 100 parts by mass to prepare a polyamide-imide varnish (3). A polyamideimide film (3) having a thickness of 50 μm was obtained in the same manner as in Example 1, except that the polyamideimide varnish (3) was used instead of the polyamideimide varnish (1).

[Production Example 2: Preparation of polyamideimide resin (2)]
In a nitrogen gas atmosphere, 52 g (162.38 mmol) of TFMB and 705.94 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc with stirring at room temperature. Next, 25.28 g (56.92 mmol) of 6FDA was added to the flask and stirred at room temperature for 3 hours. After that, 21.60 g (73.18 mmol) of OBBC and then 6.60 g (32.52 mmol) of terephthaloyl chloride (TPC) were added to the flask and stirred at room temperature for 1 hour. Then, 8.11 g (102.53 mmol) of pyridine and 23.24 g (227.67 mmol) of acetic anhydride were added to the flask, stirred at room temperature for 30 minutes, heated to 70° C. using an oil bath, and further stirred for 3 hours. A reaction liquid was obtained by stirring.
The resulting reaction solution was cooled to room temperature and poured into a large amount of methanol in the form of a thread, and the deposited precipitate was taken out, immersed in methanol for 6 hours, and washed with methanol. Next, the precipitate was dried under reduced pressure at 100° C. to obtain a polyamideimide resin (2). The weight average molecular weight (Mw), tan δ peak temperature and imidization rate of the polyamide-imide resin (2) were measured according to the above measurement methods. there were.

[Example 4: Formation of polyamideimide film (4)]
DMAc was added to the polyamideimide resin (2) obtained in Production Example 2 to a concentration of 15% by mass to prepare a polyamideimide varnish (4). A polyamideimide film (4) having a thickness of 50 μm was obtained in the same manner as in Example 1, except that the polyamideimide varnish (4) was used instead of the polyamideimide varnish (1).

[Example 5: Formation of polyamideimide film (5)]
DMAc is added to the polyamideimide resin (2) obtained in Production Example 2 so that the concentration is 15% by mass, and further an ultraviolet absorber (manufactured by Sumika Chemtex Co., Ltd., product name "Sumisorb 340") is added to the polyamideimide resin. (2) 4 parts by mass were mixed with 100 parts by mass to prepare polyamide-imide varnish (5). A polyamideimide film (5) having a thickness of 50 μm was obtained in the same manner as in Example 1, except that the polyamideimide varnish (5) was used instead of the polyamideimide varnish (1).

[Example 6: Formation of polyamideimide film (6)]
DMAc was added to the polyamideimide resin (2) obtained in Production Example 2 so that the concentration was 15% by mass, and a bluing agent (manufactured by Sumiplast Co., Ltd., product name "Violet B") was added to the polyamideimide resin (2 ) was mixed with 100 parts by mass to prepare polyamide-imide varnish (6). A polyamideimide film (6) having a thickness of 50 μm was obtained in the same manner as in Example 1, except that the polyamideimide varnish (6) was used instead of the polyamideimide varnish (1).

[Production Example 3: Preparation of polyamideimide resin (3)]
In a nitrogen gas atmosphere, 52 g (162.38 mmol) of TFMB and 698.10 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc with stirring at room temperature. Next, 25.28 g (56.92 mmol) of 6FDA was added to the flask and stirred at room temperature for 3 hours. After that, 20.43 g (73.18 mmol) of BPDOC and then 6.60 g (32.52 mmol) of terephthaloyl chloride (TPC) were added to the flask and stirred at room temperature for 1 hour. Then, 8.11 g (102.53 mmol) of pyridine and 23.24 g (227.67 mmol) of acetic anhydride were added to the flask, stirred at room temperature for 30 minutes, heated to 70° C. using an oil bath, and further stirred for 3 hours. A reaction liquid was obtained by stirring.
The resulting reaction solution was cooled to room temperature and poured into a large amount of methanol in the form of a thread, and the deposited precipitate was taken out, immersed in methanol for 6 hours, and washed with methanol. Next, the precipitate was dried under reduced pressure at 100° C. to obtain a polyamideimide resin (3). The weight average molecular weight (Mw), tan δ peak temperature and imidization rate of the polyamide-imide resin (3) were measured according to the above-described measurement methods. there were.

[Comparative Example 1: Film formation of polyamideimide film (7)]
DMAc was added to the polyamideimide resin (3) obtained in Production Example 3 so as to have a concentration of 15% by mass to prepare a polyamideimide varnish (7). Polyamideimide varnish (7) was used instead of polyamideimide varnish (1), and the freestanding film fixed to the metal frame was dried at 230°C for 30 minutes in the atmosphere. A polyamideimide film (7) having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the film was dried for 1 minute.

[Comparative Example 2: Film formation of polyamideimide film (8)]
A polyamideimide film (8) having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the polyamideimide varnish (7) obtained in Comparative Example 1 was used instead of the polyamideimide varnish (1). .

[Production Example 4: Preparation of polyamideimide resin (4)]
In a nitrogen gas atmosphere, 52 g (162.38 mmol) of TFMB and 655.58 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc with stirring at room temperature. Next, 23.84 g (53.67 mmol) of 6FDA was added to the flask and stirred at room temperature for 3 hours. After that, 22.12 g (108.96 mmol) of terephthaloyl chloride (TPC) was added to the flask and stirred at room temperature for 1 hour. Then, 8.36 g (105.69 mmol) of pyridine and 21.91 g (214.66 mmol) of acetic anhydride were added to the flask, stirred at room temperature for 30 minutes, heated to 70° C. using an oil bath, and further stirred for 3 hours. A reaction liquid was obtained by stirring.
The resulting reaction solution was cooled to room temperature and poured into a large amount of methanol in the form of a thread, and the deposited precipitate was taken out, immersed in methanol for 6 hours, and washed with methanol. Next, the precipitate was dried under reduced pressure at 100° C. to obtain a polyamideimide resin (4). The weight average molecular weight (Mw), tan δ peak temperature and imidization rate of the polyamide-imide resin (4) were measured according to the above measurement methods. there were.

[Comparative Example 3: Film formation of polyamideimide film (9)]
DMAc was added to the polyamideimide resin (4) obtained in Production Example 4 to a concentration of 15% by mass to prepare a polyamideimide varnish (8). Polyamideimide varnish (8) was used instead of polyamideimide varnish (1), and the self-supporting film fixed to the metal frame was dried at 230°C for 30 minutes in the atmosphere. A polyamideimide film (9) having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the film was dried for 1 minute.

[Comparative Example 4: Film formation of polyamideimide film (10)]
A polyamideimide film (10) having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the polyamideimide varnish (8) obtained in Comparative Example 3 was used instead of the polyamideimide varnish (1). .

[Comparative Example 5: Film formation of polyamideimide film (11)]
In the same manner as in Example 1, except that the self-supporting film fixed to the metal frame was dried at 230 ° C. for 30 minutes in the atmosphere, the self-supporting film was dried at 300 ° C. for 30 minutes in the atmosphere. A polyamideimide film (11) having

[Comparative Example 6: Film formation of polyamideimide film (12)]
In the same manner as in Example 2, except that the self-supporting film fixed to the metal frame was dried at 230 ° C. for 30 minutes in the air at 230 ° C., the self-supporting film was dried at 300 ° C. for 30 minutes in the air. A polyamideimide film (12) having

[Comparative Example 7: Film formation of polyamideimide film (13)]
In the same manner as in Example 4, except that the self-supporting film fixed to the metal frame was dried at 230 ° C. for 30 minutes in the atmosphere, the self-supporting film was dried at 300 ° C. for 30 minutes in the atmosphere. A polyamideimide film (13) having

[Comparative Example 8: Film formation of polyamideimide film (14)]
In the same manner as in Example 5, except that the self-supporting film fixed to the metal frame was dried at 230 ° C. for 30 minutes in the atmosphere, the self-supporting film was dried at 300 ° C. for 30 minutes in the atmosphere. A polyamideimide film (14) having

[Production Example 5: Preparation of polyimide resin (5)]
In a nitrogen gas atmosphere, 52 g (162.38 mmol) of TFMB and 831.46 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc with stirring at room temperature. Next, 72.24 g ( 162.62 mmol) of 6FDA was added to the flask and stirred at room temperature for 5 hours. Then, 9.65 g (121.97 mmol) of pyridine and 66.41 g (650.49 mmol) of acetic anhydride were added to the flask, stirred at room temperature for 30 minutes, heated to 70°C using an oil bath, and further stirred for 3 hours. A reaction liquid was obtained by stirring.
The resulting reaction solution was cooled to room temperature and poured into a large amount of methanol in the form of a thread, and the deposited precipitate was taken out, immersed in methanol for 6 hours, and washed with methanol. Next, the precipitate was dried under reduced pressure at 100° C. to obtain a polyimide resin (5). When the weight average molecular weight (Mw), tan δ peak temperature and imidization rate of the polyimide resin (5) were measured according to the above measurement methods, Mw was 220,000, the tan δ peak temperature was 350° C., and the imidization rate was 99%. rice field.

[Comparative Example 9: Film formation of polyimide film (15)]
DMAc was added to the obtained polyimide resin (5) so as to have a concentration of 15% by mass to prepare a polyimide varnish (9). A polyimide film (15) having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the polyimide varnish (9) was used instead of the polyamideimide varnish (1).

[Production Example 6: Preparation of polyamideimide resin (6)]
In a nitrogen gas atmosphere, 14.67 g (45.8 mmol) of TFMB and 233.3 g of DMAc were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc with stirring at room temperature. Next, 4.283 g (13.8 mmol) of 4,4'-oxydiphthalic dianhydride (OPDA) was added to the flask and stirred at room temperature for 16.5 hours. After that, 1.359 g (4.61 mmol) of OBBC and 5.609 g (27.6 mmol) of TPC were added to the flask and stirred at room temperature for 1 hour. Next, 4.937 g (48.35 mmol) of acetic anhydride and 1.501 g (16.12 mmol) of 4-picoline were added to the flask, stirred at room temperature for 30 minutes, heated to 70°C using an oil bath, and further After stirring for 3 hours, a reaction solution was obtained.
After cooling the resulting reaction solution to room temperature, 360 g of methanol and 170 g of ion-exchanged water were added to obtain a polyamideimide precipitate. It was soaked in methanol for 12 hours, collected by filtration and washed with methanol. Next, the precipitate was dried under reduced pressure at 100° C. to obtain a polyamideimide resin (6). The weight average molecular weight (Mw), tan δ peak temperature and imidization rate of the polyamide-imide resin (6) were measured according to the above measuring methods.

[Example 7: Formation of polyamideimide film (16)]
GBL was added to the polyamideimide resin (6) obtained in Production Example 6 to a concentration of 12% by mass to prepare a polyamideimide varnish (16). In the same manner as in Example 1, except that the polyamideimide varnish (16) was used instead of the polyamideimide varnish (1), and the self-supporting film was fixed to a metal frame and dried at 200 ° C. for 30 minutes. A thick polyamideimide film (16) was obtained.

For the polyamideimide films (1) to (14) and (16) and polyimide film (15) obtained in the above Examples and Comparative Examples, the total light transmittance (Tt), yellowness (YI value ), pencil hardness, elastic modulus and bending resistance (number of times of reciprocating bending) were measured. Table 1 shows the results obtained. Table 1 also shows the number of the polyamideimide resin or polyimide resin contained in these films.

Claims (12)

A polyamideimide resin having a peak value of tan δ by DMA measurement in the range of 300 to 370 ° C. and a YI value of 3 or less, wherein the polyamideimide resin is a structural unit represented by formula (5), and a structural unit represented by formula (6):

[Wherein, X represents a divalent organic group, Y represents a tetravalent organic group, and Z represents a divalent organic group]
has
The structural unit represented by the formula (5) is a diamine and the formula (4):

[In the formula, Y represents a tetravalent organic group]
A structural unit derived from a tetracarboxylic dianhydride represented by
The amount of structural units derived from the tetracarboxylic dianhydride represented by formula (4) is 5 to 20 mol% based on the total amount of structural units contained in the polyamideimide resin (2 , Per 1 mol of 2'-bistrifluoromethyl-4,4'-biphenyldiamine, 0.6 mol of terephthaloyl chloride, 0.2 mol of 4,4'-hexafluoroisopropylidenediphthalic anhydride and 3,3 ',4,4'-Biphenyltetracarboxylic dianhydride is used at a molar ratio of 0.2 mol, excluding polyamideimide copolymers obtained by imidization.), the weight of the polyamideimide resin An optical film having an average molecular weight of 100,000 to 600,000. 2. The optical film of claim 1, having a pencil hardness of 3B or greater measured according to ASTM D 3363 under an illumination condition of 4000 lux. 3. The optical film according to claim 1, further comprising an additive having a light absorption function. 4. The optical film according to any one of claims 1 to 3, wherein the additive having a light absorption function is selected from the group consisting of ultraviolet absorbers and bluing agents. The optical film according to any one of claims 1 to 4, wherein the polyamideimide resin contains fluorine atoms. Polyamideimide resin has the formula (1):

[In formula (1), R ¹ to R ⁸ 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 the hydrogen contained in R ¹ to R ⁸ each atom may be independently substituted with a halogen atom,
A each independently represents -O-, -S-, -CO- or -NR ⁹ -, R ⁹ represents a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom,
m is an integer from 1 to 4,
* represents a bond]
6. The optical film according to any one of claims 1 to 5, which has at least a structural unit represented by 7. The optical film according to any one of claims 1 to 6, wherein the polyamideimide resin has at least structural units derived from a fluorine atom-containing diamine and/or a fluorine atom-containing tetracarboxylic dianhydride. The optical film according to any one of claims 1 to 7, which has a thickness of 20 µm or more. The amount of the structural unit represented by the formula (5) and the structural unit represented by the formula (6) contained in the polyamideimide resin is the formula (5) and the formula (6), and optionally contained in the polyamideimide resin. Formula (7) and/or Formula (8):

[In formula (7), X ¹ represents a divalent organic group, Y ¹ represents a tetravalent organic group,
In formula (8), ^X2 represents a divalent organic group and ^Y2 represents a trivalent organic group]
9. The optical film according to any one of claims 1 to 8, which is 80% or more based on the total of structural units represented by. (1) Structural units having a tan δ peak value determined by DMA measurement in the range of 300 to 370° C., represented by formula (5), and structural units represented by formula (6):

[Wherein, X represents a divalent organic group, Y represents a tetravalent organic group, and Z represents a divalent organic group]
has
The structural unit represented by the formula (5) is a diamine and the formula (4):

[In the formula, Y represents a tetravalent organic group]
A structural unit derived from a tetracarboxylic dianhydride represented by
The amount of structural units derived from the tetracarboxylic dianhydride represented by formula (4) is 5 to 20 mol% based on the amount of all structural units contained in the polyamideimide resin, and the weight average molecular weight is A step of applying a resin composition containing at least a polyamideimide resin of 100,000 to 600,000 and a solvent to a support, and
(2-1) a step of obtaining an optical film by drying the coating film of the resin composition at a temperature of 240° C. or less and then peeling it from the support;
(2-2) at least a step of drying the coating film of the resin composition at a temperature of 240° C. or less and then peeling it from the support, and a step of heating the peeled film at a temperature of 240° C. or less to obtain an optical film. A method for producing an optical film having a YI value of 3 or less, comprising: 11. The manufacturing method according to claim 10, wherein the resin composition further contains an additive having a light absorption function. 12. The production method according to claim 10 or 11, wherein the solvent contains dimethylacetamide.