JP2000143802A - Polyamide-imide resin and optical element made therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyamide-imide resin which can give an optical element having a low birefringence and a high light transmittance by selecting a resin comprising two types of repeating units in a specified ratio. SOLUTION: This resin ocmprises repeating units of formula I and repeating units of formula II in a I/II molar ratio in the range of 5:95 to 95:5. In formulae I and II, R1 is a 3-10C alkylene or cyclohexylene; R2 is null, CH2, CH2CH2, or C(CH3)2; and R3 is SO2, SO, S, CO, O, C6H4, a 0-12C alkylene, SO2-(CH2)t-SO2, SO-(CH2)t-SO, S-(CH2)t-S, COO-(CH2)t-COO, or CO-(CH2)t-CO; wherein t is an integer of 1-10. It is desirable that a film of this resin has a birefringence of 10 nm or below and a light transmittance (at 500 nm) of 70% or above. The polyamic acid being a precursor of the resin can be produced by a usual synthetic method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyamide-imide resin having a very small birefringence and a high light transmittance, and specifically relates to a precision optical component, a lens, a component for a liquid crystal display, an optical fiber, Optical waveguides, base materials, film materials, sealing materials used for optical devices such as optical semiconductors,
The present invention relates to a polyamideimide resin suitable for a coating material, an adhesive, and the like.

[0002]

2. Description of the Related Art Conventionally, lenses, prisms, optical disks,
Glass has been used for optical elements such as optical fibers and LCD substrates. However, in recent years, colorless and transparent plastics have come to be used due to demand for light weight and miniaturization. In these optical elements, polystyrene, polycarbonate, polymethyl methacrylate, styrene / methyl methacrylate copolymer, and the like are used as optical plastics. However, recently, an optical element is required to have extremely high precision because it is sensitive to a change in polarization characteristics due to a slight birefringence or a change in an external environment.

[0003] In recent years, studies have been made on lowering the birefringence of some resins. For example, in the case of an acrylic resin, a photoelastic coefficient of -1 × is used as the essential raw materials of a monomer from which a resin having a positive photoelastic coefficient is obtained and a monomer from which a resin having a negative photoelastic coefficient is obtained. A method of copolymerizing so as to be 10 ^-13 cm / dyne or more and + 1 × 10 ^-13 cm / dyne or less (Japanese Patent Application Laid-Open No. 60-185236), methyl methacrylate, an alkyl group having 3 to 8 carbon atoms. (JP-A-60-25010 and JP-A-61-7)
No. 6509), a method of copolymerizing methyl methacrylate, tricyclo [5.2.1.0 ^2,6 ] dec-8-yl methacrylate and styrene (JP-A-62-24691).
No. 4, JP-A-4-76013), a method of copolymerizing a compound having an unsaturated double bond having a photoelastic coefficient opposite to that of polymethyl methacrylate when formed into a homopolymer and methyl methacrylate (JP-A-4-76013) Publication), a monomer capable of forming a homopolymer having a positive birefringence (such as trifluoroethyl methacrylate and benzyl methacrylate) and a monomer capable of forming a homopolymer having a negative birefringence (such as methyl methacrylate) are copolymerized. A method (Japanese Patent Laid-Open No. 2-129211) and the like have been proposed.

In the case of a polyimide resin, a method of introducing substituents into both ortho positions on the benzene ring of the diamine (Japanese Patent Laid-Open No. 4-288331) is to introduce a diamine having an amino group at the meta position. Method (Japanese Unexamined Patent Publication No.
34211) and a method of using a polyimide film as a substrate for producing a polyimide film (Japanese Patent Application Laid-Open No. 9-15608). In the case of polycarbonate, graft polymerization with styrene (industrial materials
Vol. 44 No. 4 p. 35, 1996), (10) There is a method of forming a film by a casting method. Further, with respect to polyarylate and polyether sulfone, a low birefringence film is formed by the same method as in (10).

Although these conventional methods have been successful in alleviating the problem of birefringence, which has been a problem when using polymers for optical elements, they still have sufficient performance. Is hard to say.

The methods (1) to (4) originally have a certain effect in that the birefringence of a small acrylic resin is made smaller. However, since the acrylic resin has low heat resistance (glass transition temperature), high heat resistance is required. Cannot be applied to the optical element described above.

The methods (1) to (4) have a certain effect in that the birefringence of a very large polyimide resin is reduced, but the birefringence does not directly reduce the stress birefringence. Neither the orientation birefringence nor the stress birefringence are reduced at the same time. for that reason,
Actually, when a film is formed, there is a problem that large birefringence occurs.

[0008] The above method has achieved a certain effect in that the birefringence of the polycarbonate resin is reduced. However, due to its structural characteristics, microdomains are generated, which causes light scattering. Further, there is a problem that heat resistance, which is a characteristic of polycarbonate, is significantly reduced.

The method (10) is a method of controlling the molding method so that birefringence does not occur in a film or the like. However, the productivity is lower than that of a normal method, and the method is essentially essential. However, since the birefringence of the resin is not necessarily reduced, birefringence occurs in the molded article when a stress or the like is applied. In addition, polyarylate and polyether sulfone have higher heat resistance (glass transition temperature) than other resins, but when molding precise optical elements,
It is hard to say that it still has sufficient heat resistance (glass transition temperature).

[0010]

As described above, each of the above resins causes birefringence when an optical element such as a film is actually produced. In addition, even if birefringence is very unlikely to occur, it cannot be applied to an optical element because of insufficient heat resistance. The present invention solves these problems by using a specific resin. That is, the present invention provides a polyamideimide-based resin having low birefringence and high transmittance, which can be used as an optical element, and an optical element using the resin.

[Means for Solving the Problems]

The present invention comprises repeating units of the following general formulas (I) and (II), wherein the molar ratio of the general formula (I) to the general formula (II) ranges from 5:95 to 9:
The present invention relates to a polyamide-imide resin using a 5: 5 resin and an optical element using the same.

Embedded image

Embedded image (Where R ₁ represents an alkylene group having 3 to 10 carbon atoms or a cyclohexylene group. R ₂ has no bond, CH ₂ , C ₂
Represents H ₂ CH ₂ or C (CH ₃ ) ₂ . R ₃ is SO ₂ , SO, S,
_{CO, O, C 6 H 4} , alkylene group having a carbon number of 0 to 12, SO ₂ -
_{(CH 2) t-SO 2} , SO- (CH 2) t- SO, S- (CH 2) t- S, COO- (CH 2)
t-COO, represents a _{CO- (CH 2) t-CO} . Here, t is an integer of 1 to 10. )

In the present invention, the birefringence of the film is 1
It is preferably 0 nm or less, and the transmittance at 500 nm is preferably 70% or more.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Next, the polyamide-imide resin of the present invention and an optical element using the same will be described in detail.

The acid dianhydride used in the polyamide-imide resin of the present invention includes the following compounds, but is not limited to these compounds. Examples of the acid dianhydride used in the present invention include bis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic anhydride and bis (endo) -bicyclo (2,2,1) heptane-2 , 3-Dicarboxylic anhydride, methylene disulfonylbis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic anhydride, ethylenedisulfonylbis (exo) -bicyclo (2,2,1) Heptane-2,3-dicarboxylic anhydride, propylene isodisulfonylbis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic anhydride, thiobis (exo)-
Bicyclo (2,2,1) heptane-2,3-dicarboxylic anhydride, methylenedithiobis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic anhydride, ethylenedithiobis (exo)- Bicyclo (2
2,1) heptane-2,3-dicarboxylic anhydride, carbonylbis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic anhydride, methylenedicarbonylbis (exo) -bicyclo (2,1) 2,1) heptane-2,3-dicarboxylic anhydride, ethylenedicarbonylbis (exo) -bicyclo (2,2,1) heptane-2
3-dicarboxylic anhydride, methylenebis (3,3 ′,
4,4'-cyclohexanedicarboxylic anhydride), thiobis (3,3 ', 4,4'-cyclohexanedicarboxylic anhydride), sulfonebis (3,3', 4,4'-cyclohexanedicarboxylic anhydride) And carbonylbis (3,3 ', 4,4'-cyclohexanedicarboxylic anhydride). These acid dianhydrides may be used alone or in an appropriate combination. Among these acid dianhydrides, particularly preferred is bis (exo)-
Bicyclo (2,2,1) heptane-2,3-dicarboxylic anhydride.

The dicarboxylic acid used in the present invention is
Glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, decanedicarboxylic acid, undencandicarboxylic acid, and dodecanedicarboxylic acid are preferred. (These may be acid chlorides or esters). Among these, adipic acid, pimelic acid, suberic acid, azelaic acid, dodecanedicarboxylic acid and the like are more preferred.

As the diamine used in the present invention,
It is necessary to polymerize using a diamine having a fluorene group as a component. Examples of such a diamine include 9,9-bis (4-aminophenyl) fluorene, and a diamine in which hydrogen of an aromatic ring of the diamine is partially substituted with an alkyl group may be used. In these fluorene group-containing diamines, a methyl group or an ethyl group may be interposed between the amino and the aromatic ring. Such diamines include 9,9-bis (3-methyl-4-aminophenyl) fluorene and 9,9-bis (3-ethyl-4-
Aminophenyl) fluorene, 9,9-bis (4-aminoethylphenyl) fluorene, 9,9-bis (3-methyl-4-aminoethylphenyl) fluorene, 9,9
-Bis (3-ethyl-4-aminoethylphenyl) fluorene and the like.

The polyamic acid used as the precursor of the polyamideimide resin used in the present invention is produced by a usual synthesis method. As a more preferable production method, a method of producing a polyamic acid by reacting a dicarboxylic acid chloride or a dicarboxylic acid with an amine, previously synthesizing a polyamide, and then reacting the polyamide with an acid dianhydride, or adding an amine This is a method for producing a polyamic acid by simultaneously adding and reacting dicarboxylic acid chloride or dicarboxylic acid and an acid dianhydride in a solvent. The above-described production is preferably performed under a stream of an inert gas such as nitrogen.

The polyamic acid obtained by the above-mentioned production method is soluble in an aprotic organic solvent, and the imidization is performed by re-precipitating the polyamic acid solution obtained by the above-mentioned method as it is or in a poor solvent. After performing the above, the polyamide acid may be dissolved in an organic solvent capable of solubilizing and then heated, or a dehydrating agent may be added and room temperature or heating may be performed.

In the above production method, the reaction solvent is N
-Use high-boiling polar organic solvents such as methylpyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, etc. And an organic solvent other than the above may be used alone or in combination with the above organic solvent. The concentration of the polymerization solution is preferably from 3 to 50% by weight, and more preferably from 5 to 40% by weight in order to prevent the reaction solution from having a high viscosity.

In order to introduce an acyl group such as a benzoyl group or an acetyl group for the purpose of protecting the terminal amino group of the polyamideimide into the polyamideimide solution obtained by the above-mentioned production method, a monoacid chloride such as benzoyl chloride or the like is used. Acetic anhydride and / or acid anhydride such as pyridine /
Alternatively, the reaction may be further performed by adding a base.

In order to introduce an alkyl group such as a propyl group for the purpose of protecting a terminal acid anhydride group of the polyamideimide, an alkylamine such as propylamine is added to the polyamideimide solution obtained by the above-mentioned production method. Further reaction may be performed.

In the above-mentioned production method, a phosphorous compound such as triphenyl phosphite may be added to improve the hue.

In the above production method, an acid anhydride such as phthalic anhydride, a monocarboxylic acid, a monoamine or a monoisocyanate may be added for polymerization in order to control the molecular weight of the obtained polyamideimide.

In the present invention, the molar ratio of the general formula (I) to the general formula (II) is in the range of 5:95 to 95: 5, and the molar ratio is in the range of 10:90 to 90:10. It is preferable that it is within the range. If the molar ratio of the general formula (I) is less than 5, the adhesion to the substrate will be weak, and if the molar ratio of the general formula (II) is less than 5, the water absorption will increase.

In the present invention, the polyamideimide solution obtained by the above method may be used alone or in combination with a poor solvent such as water, methanol, acetone, hexane or cyclohexane, regardless of whether the terminal group is protected or not. Purification by reprecipitation is preferred.

In the present invention, the polyamide-imide resin film has a birefringence of 10 nm or less,
The transmittance at m is preferably 70% or more, the birefringence is 7 nm or less, and the transmittance at 500 nm is 80%.
More preferably, it is the above. Birefringence of film is 1
If it exceeds 0 nm or the transmittance at 500 nm is 7
If it is less than 0%, the optical function of the film and the transparency as a plastic lens tend to be low.

In the present invention, the film has a birefringence of 10
The method for producing a polyamideimide resin having a transmittance of not more than 70 nm and a transmittance of not less than 70% at 500 nm is as follows: the molar ratio of the general formula (I) to the general formula (II) is 5:95 to
Polyamide-imide resin obtained in the range of 95: 5,
The above polyamideimide resin such as N, N-dimethylacetamide is dissolved in a dissolvable organic solvent, and this solution is applied on a substrate using an applicator or the like.
After heating at 200 ° C. to volatilize, the film is peeled off from the substrate. By fixing the periphery of the film containing the solvent with an iron frame and heating the film at a temperature equal to or higher than the boiling point of the solvent, a polyamideimide film can be obtained.

In the present invention, a photosensitive solution may be used as the polyamic acid solution or the polyamideimide solution.

The method for producing an optical element using the polyamide-imide resin of the present invention varies depending on the shape of a target molded product. For example, when a polyimide amide film is obtained, a quartz plate, a stainless plate, a Kapton film, etc. The above-mentioned polyamic acid solution was cast on the substrate to a constant thickness, and heated stepwise to 70 to 350 ° C. (100
C / 30 min, 200 C / 30 min, 350 C / 60 min),
The polyamic acid solution can be imidized simultaneously with removal of the solvent from the polyamic acid solution by dehydration and ring closure. These steps may be performed continuously. Further, as another manufacturing method, a polyamic acid solution is cast on a glass substrate or the like, and is heated at 100 to 150 ° C. for 3 hours.
A film is formed by heating and drying for 0 to 120 minutes to form a film, and the film is immersed in a suitable organic solvent containing pyridine and acetic anhydride to perform a desolvation and imidation reaction. is there. When a film is obtained from the polyamideimide solution, the solution is cast on the substrate so as to have a constant thickness,
By heating until the solvent is completely removed in the range of 300 ° C., a polyamideimide film can be obtained. These steps may be performed under reduced pressure in an inert atmosphere. Further, these films may be patterned by a method such as wet etching, dry etching, laser ablation or the like, if necessary, and formed into a predetermined shape to form an optical element.

The thus obtained optical element such as a film or an optical component using the polyamideimide resin of the present invention has a small birefringence and is colorless and transparent. Is extremely good.

The molding using the polyamic acid solution and the polyamideimide solution is not limited to the above-mentioned films and optical parts, but can be applied to the formation of a molded article such as a plastic lens.

The molded article obtained by using the polyamide-imide resin of the present invention has a very small birefringence unlike the conventional one. The birefringence in the present invention,
The measured value of the birefringence of a film having a thickness of 30 μm was used.

Examples of the optical element using the polyamideimide resin in the present invention include a lens, a compact disk (CD, CD-ROM, etc.), a mini disk (MD), a disk substrate for DVD, a substrate for LCD, Polarizer support film, transparent resin sheet, retardation film, light diffusion film, liquid crystal element members such as liquid crystal element coupling, projector screen, optical waveguide, optical splitter, optical multiplexer, optical switching element, optical modulator , Optical filters, wavelength dividers, optical amplifiers, optical attenuators, optical wavelength converters, optical circuits, solar cell base film base materials, solar cell coating materials, flash memories, optical semiconductors such as CCD, PD, LD, etc. Optical elements such as encapsulants, adhesives, solar cells, special aerospace component coatings such as thermal control systems, etc. Computing material and the like.

As described above, the optical element using the colorless, transparent and low-birefringence polyamideimide resin according to the present invention is:
It is particularly suitable for liquid crystal element members and precision optical components. In the liquid crystal element member, for example, an LCD substrate interposed between a liquid crystal layer and a polarizing plate is an example. By forming this substrate with the polyimide resin according to the present invention, the glass optical It is possible to improve various performances of the liquid crystal device by taking advantage of the optical resin material in comparison with the material. Further, a polarizing plate for a liquid crystal element is formed by bonding a transparent resin sheet to both surfaces of a polarizer, and a film using the polyamideimide resin according to the present invention for the transparent resin sheet is preferable. Can be improved in various performances. In a precision optical component, for example, by forming an optical waveguide circuit with the polyamide-imide resin of the present invention, it is possible to obtain an optical waveguide circuit having good polarization preservation.

[0035]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 In a 300 ml flask equipped with a calcium chloride tube and a nitrogen inlet tube, N-methyl-2-pyrrolidone 157.
8 g were added and 15.230 g of 9,9-bis (4-aminophenyl) fluorene and 6.63 of triethylamine were added.
g was added and stirred well until dissolved. Then 4.00 g of adipic dichloride was added to the solution. However,
The flask was placed on an ice bath until the addition of adipic dichloride was completed. Next, bis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic acid 8.6
11 g was added, and the mixture was stirred at 25 ° C. for 1 hour under a nitrogen atmosphere. To imidize the obtained polyamic acid solution,
The mixture was stirred at 180 ° C. for 5 hours to obtain a polyamideimide solution. This solution was reprecipitated with water, and the obtained polymer was
Further, it was washed three times with water. The polymer was dried at 90 ° C. overnight, further washed with acetone, dried at 90 ° C. overnight,
Drying under reduced pressure was performed in a desiccator for 4 hours.

Example 2 Adipic acid dichloride was converted to pimelic acid dichloride 4.50
167 g of N-methyl-2-pyrrolidone instead of 0 g,
6.93 g of triethylamine, bis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic acid
A polyamideimide-based resin was produced in the same manner as in Example 1, except that 997 g and 9,9-bis (4-aminophenyl) fluorene were used as 15.914 g.

Example 3 Adipic dichloride was substituted with suberic acid dichloride 4.50
157 g of N-methyl-2-pyrrolidone instead of 0 g,
6.47 g of triethylamine, bis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic acid
A polyamideimide resin was produced in the same manner as in Example 1 except that 399 g and 9,9-bis (4-aminophenyl) fluorene were used as 14.856 g.

Example 4 Adipic dichloride was replaced with azelaic dichloride 5.7
N-methyl-2-pyrrolidone 183.
2 g, triethylamine 7.70 g, bis (exo)-
A polyamideimide-based resin was prepared in the same manner as in Example 1 except that bicyclo (2,2,1) heptane-2,3-dicarboxylic acid was used at 10.000 g and 9,9-bis (4-aminophenyl) fluorene at 17.688 g. Manufactured.

Example 5 Adipic acid dichloride was converted to dodecanoic acid dichloride 5.00
0 g, 144 g of N-methyl-2-pyrrolidone,
5.68 g of triethylamine, bis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic acid 7.
A polyamideimide-based resin was produced in the same manner as in Example 1 except that 372 g and 9,9-bis (4-aminophenyl) fluorene were 13.041 g.

Comparative Example 1 Adipic dichloride was replaced with terephthalic chloride 5.00
Instead of 0 g, N-methyl-2-pyrrolidone 180.6
g, 7.48 g of triethylamine, 9.703 g of bis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic acid, and 17.163 g of 9,9-bis (4-aminophenyl) fluorene. A polyamide-imide-based resin was produced in the same manner as in Example 1.

Comparative Example 2 Adipic chloride was converted to 1.000 g of succinic dichloride
Instead, 45.0 g of N-methyl-2-pyrrolidone, 1.96 g of triethylamine, bis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic acid 2.5
A polyamideimide resin was produced in the same manner as in Example 1 except that 42 g and 9,9-bis (4-aminophenyl) fluorene were used in an amount of 4.497 g.

Comparative Example 3 N-methyl-2-pyrrolidone was prepared in a 300 ml flask equipped with a calcium chloride tube and a nitrogen inlet tube.
8 g, and cyclohexanedicarboxylic acid 5,000
g and bis (exo) -bicyclo (2,2,1) heptane-2,3-dicarboxylic acid (11.442 g) were added, and the mixture was stirred well until dissolved. Then, 9,9-bis (4-
Aminophenyl) fluorene 20.238 g was added,
The mixture was stirred at 25 ° C. for 1 hour under a nitrogen stream. In order to imidize the obtained polyamic acid solution, the mixture was stirred at 180 ° C. for 5 hours to obtain a polyamidoimide solution. The polymer obtained by reprecipitating this solution with water was further washed three times with water.
The polymer was dried at 90 ° C. overnight, further washed with acetone, dried at 90 ° C. overnight, and dried in a desiccator under reduced pressure for 4 hours.

The resins obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were formed into films, and the results of measurement of transmittance, birefringence, and the like are shown in Table 1. The evaluation was performed by the following method. The imidation was confirmed by characteristic absorption due to symmetric and asymmetric stretching vibration of the carbonyl group in the infrared absorption spectrum. (1) Transmittance Polyamideimide resin is dissolved in a 20 wt% N, N-dimethylacetamide solution, and cast on a glass substrate with an appropriate thickness so that the thickness of the obtained film is 30 ± 5 μm. Preheated at 150 ° C for / 10 minutes. Further, the film is peeled off from the glass substrate, the periphery of the film is fixed with an iron frame, and the solvent is removed by heating at 250 ° C. for 10 minutes.
A film was obtained. The transmittance of this film at 500 nm was measured with a spectrophotometer (V-570 manufactured by JASCO Corporation). (2) Birefringence The birefringence (single pass) was measured with an ellipsometer (Shimadzu AEP-100) using a He-Ne laser. Further, the film obtained by the method (1) was sandwiched between two orthogonal polarizing plates, and the state of birefringence of the fixed portion when the film was fixed and dried (250 ° C.) was visually observed.

[0045]

[Table 1] * 1 Data for each item could not be measured because a polymer with film formability could not be obtained. The molar ratio between the acid component 1 and the acid component 2 is 1/1, and the molar ratio between the acid component and the diamine is 1/1. The chemical structures of the compounds indicated by the abbreviations are shown below.

[0046]

Embedded image HAC SO ₂ : (bis (exo) -bicyclo (2,2,
1) Heptane-2,3-dicarboxylic acid)

[0047]

Embedded image FDA: (9,9-bis (4-aminophenyl) fluorene)

[0048]

According to the present invention, a polyamideimide resin having low birefringence and high light transmittance can be obtained without being restricted by the conventional method. Further, the present invention provides an optical element utilizing the characteristics of the polyamide-imide resin.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F071 AA60 AF30Y AF31Y AH12 AH19 BC01 4J043 PA04 RA35 SA06 SB01 TA14 TA22 TB01 UA042 UA082 UA131 UA221 UA251 UB012 UB152 UB282 UB302 UB401 UB402 YA06 ZB01 ZB11 ZB02

Claims (3)

[Claims] The present invention comprises repeating units of the following general formulas (I) and (II), and the molar ratio of the general formula (I) to the general formula (II) ranges from 5:95 to 95: 5. Polyamide-imide resin using the above resin. Embedded image Embedded image (Where R ₁ represents an alkylene group having 3 to 10 carbon atoms or a cyclohexylene group. R ₂ has no bond, CH ₂ , C ₂
Represents H ₂ CH ₂ or C (CH ₃ ) ₂ . R ₃ is SO ₂ , SO, S,
_{CO, O, C 6 H 4} , alkylene group having a carbon number of 0 to 12, SO ₂ -
_{(CH 2) t-SO 2} , SO- (CH 2) t- SO, S- (CH 2) t- S, COO- (CH 2)
t-COO, represents a _{CO- (CH 2) t-CO} . Here, t is an integer of 1 to 10. ) 2. The film has a birefringence of 10 nm or less,
The polyamide-imide resin according to claim 1, wherein the transmittance at 500 nm is 70% or more. 3. An optical element using the polyamide-imide resin according to claim 1.