JP5321193B2 - Polyamic acid solution, polyimide and optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyamic acid solution capable of providing an aromatic polyimide for optics, showing good light-transmitting properties and a refractive index and having excellent adhesiveness and heat resistance. <P>SOLUTION: The polyamic acid solution is prepared by dissolving a polyamic acid in an organic solvent, the polyamic acid having a specified 9,9-diphenyl fluorene residue and at least one non-fluorene residue selected from specified diphenyl ether residues, diphenyl thioether residues and diphenyl sulfone residues. The polyamic acid contains not less than 40 mass% of the 9,9-diphenyl fluorene residue and has an average polymerization degree of 5 to 100. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a polyamic acid solution in which a polyamic acid, which is a precursor of a polyimide material used in various optical devices for the purposes of adhesion, surface protection, optical path adjustment, hole filling, and the like, is dissolved in an organic solvent. The present invention also relates to a polyimide formed from the polyamic acid solution and an optical device in which a polyimide film is laminated on a substrate for an optical device.

  In recent years, as optical devices such as digital cameras, liquid crystal displays, and projectors have been improved in performance and reduced in size, various optical devices used in these optical devices such as solid-state imaging devices, LEDs, inorganic polarizing plates, microlens arrays, etc. Used for optical thin film materials such as moth-eye type non-reflective film, antireflection film, waveguide film, or for the purpose of adhesion, hole filling, sealing, surface protection, etc. in these optical devices Has been.

  Among optical devices, there are devices that are assumed to be used at temperatures exceeding 200 ° C. and optical devices that involve heat treatment at 350 to 400 ° C. for several hours in the manufacturing process. Therefore, the conventional optical polyimide is required to exhibit not only good translucency, adhesion and refraction, but also high heat resistance.

  By the way, as what is conventionally used as an optical polyimide, it has translucency and has an excellent refractive index and heat resistance, such as an aromatic polyimide (Patent Documents 1 and 2), and heat resistance. However, a polysiloxane composition in which inorganic fine particles of a titanium or zirconium compound having a high refractive index are blended with a polysiloxane having a relatively low refractive index has been proposed (Patent Document 3).

JP 2007-332186 A JP 2007-277399 A JP 2007-246877 A

  However, the conventional aromatic polyimides described in Patent Documents 1 and 2 are translucent, but absorb relatively large light at wavelengths near 400 nm, and the types of optical devices that can be applied are very large. There was a problem of few. Further, in the case of the polysiloxane composition, there is a problem that light scattering occurs due to the blended inorganic fine particles, and the translucency is not sufficient. There is also a problem that metal impurities in the inorganic fine particles adversely affect the performance of the optical device.

  The present invention is intended to solve the above-described problems of the prior art, and has high translucency, particularly high transmissivity of light having a wavelength near 400 nm, and relatively high without using inorganic fine particles. It is an object of the present invention to provide a polyamic acid solution that is a polyimide precursor that can provide an optical aromatic polyimide that exhibits a refractive index and is excellent in adhesion and heat resistance.

  The present inventor is the type and content ratio of the residue constituting the polyamic acid, the type and content ratio of the tetracarboxylic dianhydride component constituting the polyamic acid, and the type and content ratio of the diamine component of the resulting polyimide. As a result of studying them focusing on the fact that they have a great influence on the properties, polyamic acid is composed of a specific 9,9-diphenylfluorene residue and a specific ether residue, and 9,9-diphenyl The inventors have found that the above object can be achieved by setting the content ratio of the fluorene residue to 40% by mass or more and setting the average degree of polymerization of the polyamic acid to 5 to 100, thereby completing the present invention.

That is, the present invention relates to at least one 9,9-diphenylfluorene residue represented by the formula (1a), the formula (1a ′), the formula (1b) or the formula (1c), the formula (2a), the formula ( A polyamic acid solution in which a polyamic acid having at least one non-fluorene residue selected from a diphenyl ether residue, a diphenyl thioether residue, and a diphenyl sulfone residue represented by 2b) or formula (2c) is dissolved in an organic solvent The polyamic acid contains a 9,9-diphenylfluorene residue in an amount of 40% by mass or more, and provides a polyamic acid solution having an average degree of polymerization of 5 to 100.

  The present invention also provides an aromatic polyimide having a refractive index of 1.67 or higher and a light transmittance of 90% or higher, obtained by drying and imidizing the above-mentioned polyamic acid solution coating film.

  Furthermore, the present invention provides a refractive index of 1.67 or more and 90% or more obtained by applying the substrate for optical device and the above-mentioned polyamic acid solution to the substrate for optical device, drying and further imidizing. An optical device having an aromatic polyimide film exhibiting a light transmittance of the above is provided.

  In the polyamic acid solution of the present invention, the polyamic acid is composed of a specific 9,9-diphenylfluorene residue and a specific ether residue, and the content of the 9,9-diphenylfluorene residue is 40% by mass. The average degree of polymerization of the polyamic acid is 5 to 100. For this reason, this polyamic acid solution has high translucency, in particular, high transmissivity of light having a wavelength of around 400 nm, and exhibits a relatively high refractive index without using inorganic fine particles. In addition, it is possible to provide an aromatic polyimide for optics that is excellent in the above.

  The polyamic acid solution of the present invention comprises at least one 9,9-diphenylfluorene residue represented by formula (1a), formula (1a ′), formula (1b) or formula (1c), formula (2a), A polyamic acid in which a polyamic acid having at least one non-fluorene residue selected from a diphenyl ether residue, a diphenyl thioether residue and a diphenyl sulfone residue represented by the formula (2b) or the formula (2c) is dissolved in an organic solvent It is an acid solution.

  In the present invention, the polyamic acid contains 9,9-diphenylfluorene residue in an amount of 40% by mass or more, preferably 42 to 65% by mass. The 9,9-diphenylfluorene residue has a function of imparting good translucency, solvent solubility, high refractive property, and heat resistance to polyimide. For this reason, when the 9,9-diphenylfluorene residue is less than 40% by mass, the heat resistance of the polyimide is excessively lowered and discolored, and the translucency is less than 90%. Here, the 9,9-diphenylfluorene residue in the polyamic acid may be derived from either a tetracarboxylic dianhydride component or a diamine component. Incidentally, the 9,9-diphenylfluorene residue of formula (1a) and formula (1a ′) is derived from the tetracarboxylic dianhydride component, and the 9,9-diphenylfluorene residue of formula (1b) and formula (1c) The group is derived from a diamine component. On the other hand, among at least one non-fluorene residue selected from the diphenyl ether residue, diphenyl thioether residue and diphenyl sulfone residue represented by the formula (2a), the formula (2b) or the formula (2c), the formula (2a ) And the non-fluorene residue of formula (2b) is derived from a tetracarboxylic dianhydride component having a diphenyl ether residue or a diphenyl sulfone residue, and the non-fluorene residue of formula (2c) is a diphenyl ether residue, diphenyl It is derived from a diamine component having a thioether residue or a diphenylsulfone residue.

  As described above, the polyamic acid includes diphenyl ether residue, diphenyl thioether residue and diphenyl sulfone residue represented by the formula (2a), (2b) or (2c) in addition to the 9,9-diphenylfluorene residue. It contains at least one selected non-fluorene residue of less than 40% by weight, preferably 20 to 38% by weight. These non-fluorene residues not only provide good translucency in the initial stage of polyimide, but also have a function of improving solubility in organic solvents. Among these, use of the non-fluorene residue of the formula (2c) is preferable from the viewpoint that flexibility can be imparted to the polyimide.

Examples of tetracarboxylic dianhydrides having 9,9-diphenylfluorene residues of formulas (1a) and (1a ′) include 9,9-bis (3,4-dicarboxyphenyl) fluorene represented by formula (3). Dianhydride (BPAF), 9,9-bis [4- (3,4-dicarboxyphenoxy) phenyl] fluorene dianhydride represented by the formula (4), and the like. Examples of tetracarboxylic dianhydrides having non-fluorene residues represented by the formulas (2a) and (2b) include 4,4′-oxydiphthalic dianhydride, 3,4,3 ′, 4′-diphenylsulfone tetracarboxylic acid. An acid dianhydride etc. are mentioned.

  Examples of the diamine having a 9,9-diphenylfluorene residue of the formula (1b) and the formula (1c) include 9,9-bis (4-aminophenyl) fluorene, 9,9-bis (3-amino-4). Hydroxyphenyl) fluorene, 9,9-bis (toluidine) fluorene, 9,9-bis (4-amino-3-fluorophenyl) fluorene, and the like.

  Diamines having a non-fluorene residue of formula (2c) (ie diphenyl ether residue, diphenyl thioether or diphenyl sulfone residue) include 4,4'-diaminodiphenyl ether 3,4'-diaminodiphenyl ether, 1,3 -Bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, 3,5-bis (4-aminophenoxy) benzoic acid, bis (3-aminophenyl) sulfone, bis (4-aminophenyl) sulfone, 3,7-diamino-2,8-dimethyldibenzothiophenesulfone, bis [4 -(3-Aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) ) Phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, bis (4-aminophenyl) And sulfides.

  The average degree of polymerization n of the polyamic acid is 5 to 100, preferably 10 to 70. When the average polymerization degree is less than 5, the elastic modulus of the polyimide becomes too low, and when it exceeds 100, the viscosity of the polyamic acid solution becomes too high, which is inconvenient when applied by a spin coater. In the present invention, the average degree of polymerization means the average number of repeating units of a polymer unit composed of a tetracarboxylic dianhydride component and a diamine component. The higher the average degree of polymerization n, the higher the molecular weight of the polyamic acid.

  The average degree of polymerization n of the polyamic acid can be determined by the charged molar ratio of tetracarboxylic dianhydride and diamine. In this case, the handling depends on whether or not the end-capping agent is used.

  When the end-capping agent is not used, the molar ratio of tetracarboxylic dianhydride to diamine is preferably 1: 0.99 to 1: 0.83, more preferably 1: 0.986 to 1: 0. .90 is preferable. Thus, in the present invention, the amount of tetracarboxylic dianhydride is preferably larger than that of diamine. Thereby, the terminal of a polyamic acid molecule can be made into an acid anhydride terminal, the adhesiveness of the polyimide is improved, and even when the polyimide is thermally aged, the translucency of the polyimide can be maintained. . The terminal acid anhydride portion may be converted to free dicarboxylic acid by hydrolysis after the synthesis of polyamic acid.

  A specific relationship between the average degree of polymerization n and the molar ratio will be described below. That is, when n is 5, the molar ratio of tetracarboxylic dianhydride to diamine is 1: 0.83, and when n is 100, it corresponds to 1: 0.99.

  In the case of using an end-capping agent, the ratio of tetracarboxylic dianhydride to diamine may be either tetracarboxylic dianhydride or a large amount of diamine. When there are many dianhydrides, it is preferable to use a monofunctional amine as the terminal blocking agent, and when there are many diamines, it is preferable to use a monofunctional acid anhydride as the terminal blocking agent. The specific molar ratio is as follows.

<When there are many acid anhydrides>
Tetracarboxylic dianhydride: diamine: monofunctional amine = 1: (0.99 to 0.83): (0.02 to 0.34)
<When there are many diamines>
Tetracarboxylic dianhydride: diamine: monofunctional anhydride = (0.99 to 0.83): 1: (0.02 to 0.34)

  As end-capping agents that can be used in the present invention, generally used monofunctional amines and monofunctional acid anhydrides can be used. Moreover, the polyimide of this invention mentioned later can also be made into a crosslinkable polyimide by using the terminal blocker which has a crosslinkable functional group like an acetylene group or a maleimide group.

As a preferable embodiment of the polyamic acid described above, at least one 9,9-diphenylfluorene residue represented by the formula (1a) or the formula (1a ′) derived from the acid dianhydride component and a formula derived from the diamine component And a polyamic acid having at least one non-fluorene residue selected from a diphenyl ether residue, a diphenyl thioether residue and a diphenyl sulfone residue represented by (2c). A particularly preferred specific polyamic acid is shown in the formula (5a), and a more specific polyamic acid is shown in the formula (5b). In this case, when the average degree of polymerization n is 53 and the acid anhydride terminal structure is used, the mass% of the 9,9-diphenylfluorene residue is 43.2 mass%.

  The polyamic acid solution of the present invention is obtained by dissolving the polyamic acid described above in an organic solvent. As the organic solvent, a known solvent which is a good solvent for polyamic acid can be used. Specifically, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, triglyme and the like are preferable, among which γ-butyrolactone, N- Particularly preferred is at least one solvent selected from methyl-2-pyrrolidone, triglyme and N, N-dimethylacetamide. In addition, in order to improve the solubility with respect to these polyamic acids, PGMEA, diglyme, monoglyme, etc. can be used together.

  Moreover, the suitable solvent amount of the polyamic acid solution of this invention becomes like this. Preferably it is 70-95 mass%. If the amount is less than 70% by weight, the viscosity tends to be too high and application tends to be difficult. If the amount exceeds 95% by weight, it is difficult to form a film.

  The polyamic acid solution of the present invention can contain various additives such as a surfactant, a transparent filler, an antioxidant, an antioxidant, a radical quencher, and an adhesion promoter, as necessary.

  The polyamic acid solution of the present invention can be prepared according to a known method. For example, first, a specified amount of an organic solvent is charged into a reaction vessel, and then a specified amount of diamine is charged while stirring to dissolve it. Subsequently, a light amount of a polyamic acid solution can be obtained by adding a specified amount of tetracarboxylic dianhydride and reacting within a range of room temperature to 40 ° C. for 4 to 12 hours.

  In the polyamic acid solution of the present invention, a part of the amic acid residue in the contained polyamic acid may be imidized, and the polyamic acid solution containing the partially imidized polyamic acid is also a part of the present invention. Such a partially imidized polyamic acid has a 9,9-diphenylfluorene skeleton, a diphenyl ether skeleton, a diphenyl sulfone skeleton, a diphenylhexafluoropropane skeleton, a diphenylpropane skeleton, and the like, and is usually soluble in an organic solvent. Have

  Further, since the coating film of the partially imidized polyamic acid solution has already been partially imidized, 1) the amount of generated moisture is reduced during the complete imidization, and 2) the thickness reduction amount of the film is reduced. 3) Advantages such as reduction of stress strain due to shrinkage can be obtained. The degree of imidization can be indicated by the imidization rate, but the imidization rate of the partially imidized polyamic acid solution is preferably up to 95%. If it is this grade, it is possible to carry out partial imidation easily by the method shown below. On the other hand, if it exceeds 95%, the viscosity of the solution is excessively increased, so that the applicability of the polyamic acid solution is lowered, which is not preferable.

  That is, the method of partial imidation of polyamic acid can be performed by heating the obtained polyamic acid solution at a temperature of about 200 ° C. for several hours. As a general method, a small amount of an azeotropic solvent with water such as xylene is added to the solution and heated to reflux. The generated imidized water is excluded from the system together with the azeotropic solvent. If the solvent used is N-methyl-2-pyrrolidone or γ-butyrolactone, its boiling point is around 200 ° C., which is convenient for heating to reflux. At this time, it is not necessary to use an imidization catalyst.

  For the polyamic acid solution of the present invention (including a partially imidized polyamic acid solution), preferably, a filter treatment is performed using a filter in order to remove insoluble impurity fine particles contained in the solution. It is preferable to apply. Here, the pore size of the filter is preferably 0.1 μm or less, more preferably 0.05 μm or less. As a material for the filter, nylon or polyolefin is preferable to PTFE (polytetrafluoroethylene). This is because the pressure loss is reduced due to good affinity with the solvent. Moreover, it is preferable that the filtration pressure is low and the filtration flow rate is small.

  In addition, for the polyamic acid solution (filtrate) filtered by a filter, it is preferable to perform an ion exchange treatment using an ion exchange resin in order to remove soluble metal ion impurities dissolved in the solution. As the ion exchange resin, a commercially available particulate resin can be used. It is preferable to use an anion exchange resin and a cation exchange resin in combination.

  As specific examples of the ion exchange treatment, two types, a batch treatment method and a column treatment method, are known. In the batch treatment method, 2 to 20% by weight of ion exchange resin is impregnated as it is or impregnated with a solvent, and then poured into a polyamic acid solution. After stirring for about 6 to 36 hours, the ion exchange resin is filtered. It is a method of removing with. Although there exists an advantage which processing operation becomes easy, since there exists a fault that the processing amount per unit amount of ion-exchange resin is small, it is suitable when processing a small amount of polyamic acid solution. On the other hand, in the column processing method, a cylindrical glass column having cocks at the top and bottom is filled with an ion exchange resin, filled with an appropriate solvent, and then the polyamic acid solution is applied to the column using a pump or gravity. It is a method of passing liquid. When the viscosity is 10 to 500 mPa · s, the liquid passing speed is preferably at least 1 or less, and usually about 1/2 to 1/10 in terms of SV (space velocity) [SV value = (1 Sample flow rate per hour (volume) / volume of ion exchange resin]. Since the column processing method has an advantage that a polyamic acid solution having a volume 10 to 1000 times that of the ion exchange resin can be processed, it is suitable for mass processing.

  The polyamic acid solution that has been subjected to the ion exchange treatment is preferably subjected to a filter treatment again in order to remove dust that may be mixed during a process such as an ion exchange resin treatment. The pore size of the filter to be used is determined by the dust removal level required by the application, but is usually about 0.5 to 0.05 μm. There are no particular restrictions on the filter material, filtration pressure, filtration speed, and the like.

  The polyamic acid solution thus obtained is suitable for spin coating by adjusting the solid content to 30% by mass or less and the viscosity to 10 to 500 mPa · s.

  The polyamic acid solution described above can be preferably applied to produce polyimide. That is, a polyimide filler or a thin film can be obtained on an object by applying and drying the polyamic acid solution to the object and then heating the polyamic acid solution. The dried polyamic acid can be easily dehydrated by heating at 200 to 300 ° C. and converted to the corresponding polyimide. Furthermore, it can be expected that, by heat treatment at 300 to 400 ° C., the adhesion of polyimide to the substrate is improved and the elastic modulus of polyimide is improved.

  As a method for applying the polyamic acid solution, existing coating methods such as spin coater, knife coater, roll coater, bar coater, and screen printing can be used. In particular, a spin coater is useful when applying to an image sensor using a semiconductor element device.

  In addition, the target to which the polyamic acid solution is applied varies depending on the application, but representative examples include a ceramic substrate, a glass substrate, a sapphire substrate, and a silicon substrate. In particular, when applied to an image sensor that is a semiconductor element device, a silicon substrate is used.

  The aromatic polyimide produced from the polyamic acid solution of the present invention exhibits a refractive index of 1.67 or more and a light transmittance of 90% or more. Polyimide having such characteristics is laminated on a substrate for an optical device such as a semiconductor substrate for a solid-state imaging device, and can preferably function as a waveguide layer, an adhesive layer, an insulating layer, or an antireflection film.

  Hereinafter, the present invention will be specifically described by way of examples.

In addition, the imidation rate in polyimide can be calculated from the characteristic absorption of the IR spectrum according to the following formula, and in the following examples, the rate of increase in peak intensity at 1376 cm ⁻¹ was taken as the imidization rate.

_{Wherein, Ps 1376} is the peak intensity at 1376cm ^-1 samples to be measured (polyamic _{acid); Ps 1500} is the peak intensity at 1500 cm ^-1 of sample to be _{measured; PI 1376,} the sample Is a peak intensity at 1376 cm ⁻¹ of a polyimide obtained by heating at 400 ° C. for 3 minutes to completely imidize; PI ₁₅₀₀ is a polyimide obtained by heating the sample at 400 ° C. for 3 minutes to completely imidize. It is the peak intensity at 1500 cm ⁻¹ .

Example 1
In a 1000 ml three-necked glass reaction vessel, 9,9-bis (3,4-dicarboxyphenyl) fluorene (BPAF) (manufactured by JFE Chemical Co., Ltd .: purity 99.74%) as tetracarboxylic dianhydride is 100. 1.0 mmol (45.96 g) and 98.15 mmol (28) of 1,3-bis (3-aminophenoxy) benzene (APB-N) (manufactured by Mitsui Chemicals, Inc .: purity 99.9%) as the diamine component. 72 g), 275 g of γ-butyrolactone as an organic solvent was added, dissolved by stirring, and reacted at room temperature for 12 hours. As a result, a pale yellow polyamic acid solution having a solid content of polyimide equivalent of 20.55% and a viscosity of 450 mPa · s was obtained. The average degree of polymerization n in the design is 53. Therefore, the amount of 9,9-diphenylfluorene residue in the molecule is 44.3% by mass.

Example 2
Except that the organic solvent was changed to N, N-dimethylacetamide (DMAc), a pale yellow polyamic acid solution having a polyimide equivalent solid content of 20.55% and a viscosity of 310 mPa · s was obtained by repeating Example 1. It was. The average degree of polymerization n in the design is 53. Therefore, the amount of 9,9-diphenylfluorene residue in the molecule is 44.3% by mass.

Example 3
Except that the organic solvent was changed to N-methyl-2-pyrrolidone (NMP), a pale yellow polyamic acid solution having a polyimide equivalent solid content of 20.55% and a viscosity of 295 mPa · s was obtained by repeating Example 1. It was. The average degree of polymerization n in the design is 53. Therefore, the amount of 9,9-diphenylfluorene residue in the molecule is 44.3% by mass.

Example 4
By repeating Example 1 except that the APB-N of the diamine component was changed from 98.15 mmol to 87.50 mmol (25.61 g) and DMAc was used instead of γ-butyrolactone as a solvent, polyimide was obtained. A pale yellow polyamic acid solution having a converted solid content of 19.92% and a viscosity of 75 mPa · s was obtained. The average degree of polymerization n in the design is 7, and the amount of 9,9-diphenylfluorene residue in the molecule is 46.1% by mass. Next, 10 ml of toluene was added to 100 ml of this solution and heated at 200 ° C. for 1 hour in a 500 ml glass reaction vessel equipped with a reflux apparatus. The distillate was about 15 ml, and was a mixed solution of toluene, water and γ-butyrolactone. As a result, a light yellow partially imidized polyamic acid having a polyimide-converted solid content of 21.22% and a viscosity of 280 mPa · s was obtained in the reaction vessel. The imidation ratio was 82%.

Example 5
By repeating Example 1 except that the diamine component APB-N was changed from 98.15 mmol to 92.86 mmol (27.17 g) and DMAc was used instead of γ-butyrolactone as a solvent, a polyimide was obtained. A pale yellow polyamic acid solution having a converted solid content of 20.24% and a viscosity of 95 mPa · s was obtained. The average degree of polymerization n in the design is 13, and therefore the amount of 9,9-diphenylfluorene residue in the molecule is 45.2% by mass. Next, a partial imidization reaction was performed in the same manner as in Example 4. In that case, it heated at 180 degreeC for 1 hour. As a result, a partially imidized polyamic acid having a polyimide equivalent solid content of 22.02% and a viscosity of 315 mPa · s was obtained in the reaction vessel. The imidation ratio was 75%.

Example 6
By repeating Example 1 except that APB-N of the diamine component was changed from 98.15 mmol to 96.4 mmol (28.22 g) and DMAc was used as a solvent instead of γ-butyrolactone, polyimide was obtained. A pale yellow polyamic acid solution having a converted solid content of 20.45% and a viscosity of 175 mPa · s was obtained. The average degree of polymerization n of the design is 27. Therefore, the amount of 9,9-diphenylfluorene residue in the molecule is 44.6% by mass. Next, a partial imidization reaction was performed in the same manner as in Example 4. In that case, it heated at 170 degreeC for 1 hour. The distillate was about 12 ml. A partially imidized polyamic acid having a solid content of 21.08% in terms of polyimide and a viscosity of 415 mPa · s was obtained in the reaction vessel. The imidation ratio was 60%.

<Evaluation of translucency (LP)>
After diluting the polyamic acid of Examples 1 to 3 or the partially imidized polyamic acid of Examples 4 to 6 with γ-butyrolactone so as to have a viscosity of 200 mPa · s, a polytetrafluoroethylene membrane having a pore size of 0.2 μm Filtered with a filter. The obtained filtrate was applied onto a flat quartz plate having a thickness of 1.0 mm (3000 rpm, 120 seconds) using a spin coater (MS-A100, Mikasa Co., Ltd.) filled with nitrogen gas. A quartz plate coated with a polyamic acid solution is placed on a hot plate, dried at 150 ° C. for 3 minutes, subsequently imidized at 220 ° C. for 3 minutes and at 300 ° C. for 3 minutes to form a polyimide film having a thickness of 1 μm. Obtained on a quartz plate.

  Next, the translucency with respect to the light of the wavelength of 400 nm of the obtained polyimide film was measured with the spectrophotometer (V-560, JASCO Corporation). The obtained initial translucency results are shown in Table 1. Practically, it is desired to be 90% or more.

  Next, the quartz plate was placed on a hot plate in a nitrogen atmosphere and heat-treated at 400 ° C. for 1 hour so that the polyimide film whose translucency was measured was on top. Thereafter, the translucency of the polyimide film was again measured with a spectrophotometer. The obtained translucent result after heat treatment was compared with the initial translucent result. It shows that heat resistance is so favorable that the difference of the numerical value of translucency is small. In practice, the difference is preferably within 5%.

  The polyimide film obtained from the polyamic acid solution of Example 1 has a high translucency of 98.5% with respect to light having a wavelength of 400 nm after heat treatment at 300 ° C. and heat treatment at 400 ° C. for 1 hour. After that, it had high translucency of 95.5% with respect to light having a wavelength of 400 nm, the difference was only 3.0%, and the heat resistance related to translucency was good. The polyimide films obtained from the polyamic acid solutions of other examples were similarly tested and evaluated for translucency and heat resistance, and the results obtained are shown in Table 1.

<Evaluation of weight loss (WL) in thermogravimetric analysis>
About 50 mg of the polyamic acid solution of each example was placed in an aluminum pan and dried in an oven at 150 ° C. for 1 hour to obtain a sample for thermogravimetric analysis. The aluminum pan containing this sample was put into a thermogravimetric analyzer (TG / DTA6200, SII (Seiko Instruments Inc.)), and the change in weight was measured while heating at a heating rate of 10 ° C./min. In each sample, a weight loss of more than 10% was observed by 300 ° C. This is due to evaporation of residual solvent and imidized water by imidization. Thereafter, there was no change in weight up to 500 ° C., and it was almost constant. After reaching 500 ° C., the weight after 20 minutes was measured while maintaining the temperature, and the weight reduction rate relative to the weight when reaching 300 ° C. was determined. A smaller weight reduction rate means better heat resistance. Practically, it is desired to be within 5%.

<Adhesiveness (AD) evaluation>
The polyamic acid solution of each example was diluted with the organic solvent used in each example so that the viscosity became 200 mPa · s, and then filtered through a polytetrafluoroethylene membrane filter having a pore size of 0.2 μm. Using the obtained filtrate, a spin coater (MS-A100, Mikasa Co., Ltd.) filled with nitrogen gas, each of a flat silicon substrate having a thickness of 0.7 mm and a silicon substrate having a surface treated with silicon nitride (3000 rpm, 120 seconds). Each substrate coated with the polyamic acid solution is placed on a hot plate, dried at 150 ° C. for 3 minutes, subsequently imidized at 220 ° C. for 3 minutes and at 300 ° C. for 3 minutes to form a polyimide film having a thickness of 1 μm. Obtained on each substrate.

  The adhesion between the obtained polyimide film and the substrate was evaluated by a base eye test. First, using a cutter knife, a grid-like cut was made in the polyimide film to make 100 1 mm square squares. Next, an adhesive tape (Cellotape (registered trademark) No. 405, manufactured by Nichiban Co., Ltd.) was applied to the entire mesh, and then immediately peeled off. The number of cells remaining on the substrate side out of 100 cells was counted. The larger the number of cells remaining on the substrate side, the better the adhesion. Practically, it is desired that 80 squares or more, preferably 95 squares or more remain out of 100 squares.

<Evaluation of refractive index (RC)>
The polyamic acid solution of Example 1 was diluted with γ-butyrolactone so as to have a viscosity of 180 mPa · s, and then filtered through a polytetrafluoroethylene membrane filter having a pore size of 0.2 μm. The obtained filtrate was applied to a flat silicon substrate having a thickness of 0.7 mm (3000 rpm, 120 seconds) using a spin coater (MS-A100, Mikasa Co., Ltd.) filled with nitrogen gas. The substrate coated with the polyamic acid solution is placed on a hot plate, dried at 150 ° C. for 3 minutes, subsequently imidized at 220 ° C. for 3 minutes and at 300 ° C. for 3 minutes, and a 0.73 μm-thick polyimide film Was obtained on a substrate.

  The refractive index of the obtained polyimide film was measured using a refractive index measuring device (model 2010 prism coupler, manufactured by Metricon). As measurement light, laser beams having wavelengths of 405 nm, 633 nm, and 830 nm were used.

  Regarding this polyimide film, the refractive indexes obtained at the respective wavelengths were 1.758, 1.678 and 1.661. From this, a relational expression between the wavelength and the refractive index was obtained, and the refractive index at a wavelength of 550 nm was calculated from the relational expression, and as a result, it was 1.695. For the polyimide films obtained from the polyamic acid solutions of Examples 2 to 6, the refractive index at a wavelength of 550 nm was calculated in the same manner, and the results were almost the same as the measurement results of the polyimide film obtained in Example 1. In practice, it is desirable that the refractive index at a wavelength of 550 nm is 1.57 or more, preferably 1.67 or more.

<Evaluation of glass transition temperature (Tg)>
The glass transition temperature was measured by TMA (thermomechanical analysis) and DSC (differential scanning calorimetry). In addition, the linear expansion coefficient (LEC) was also measured. As a sample for TMA, the polyamic acid solution of each example was applied to a copper foil using a bar coater, dried at 150 ° C., and then heat-treated at 300 ° C. for 1 hour. A polyimide film having a thickness of about 25 μm obtained by etching out was obtained, and this film was cut into a size of 4 mm × 30 mm.

The glass transition temperature of the polyimide film obtained from the polyamic acid solution of Example 1 was 254 ° C. The linear expansion coefficient was 53 ppm. Moreover, the glass transition temperature by DSC was 256 degreeC. When the glass transition temperature and the linear expansion coefficient were measured in the same manner for the polyimide films obtained from the polyamic acid solutions of Examples 2 to 6, the glass transition temperature and the linear expansion coefficient were the polyimide films obtained in Example 1. The measurement results were almost the same. Practically, the glass transition temperature is desired to be 200 ° C. or higher because the use atmosphere temperature may reach 200 ° C. Also, the linear expansion coefficient is desirably 100 ppm or less in order to minimize the positional deviation in the optical device.

  As can be seen from Table 1, in the polyamic acid solutions of Examples 1 to 6, the polyamic acid is composed of specific 9,9-diphenylfluorene residues and non-fluorene residues, and 9,9-diphenyl. Since it contained 40% by mass or more of fluorene residues and the average degree of polymerization n was in the range of 5 to 100, it was excellent in translucency, heat resistance, adhesiveness and refraction.

Example 7 (Effects of filter treatment and ion exchange treatment)
The polyamic acid solution obtained in Example 1 was pumped from a pressurized tank and filtered using a filter (Protego DCR, manufactured by Entegris) having a pore size of 0.05 μm. 200 g of the obtained filtrate was put into a 500 ml fluorine plastic (PFA) bottle, and further 20 g of ion exchange resin (MSPS2-1DRY, manufactured by Oregano) and 20 g of solvent γ-butyrolactone (EL grade) were put. The mixture in the PFA bottle was stirred with a jar mill for 12 hours. Thereafter, the mixture was filtered again using a filter having a pore size of 0.05 μm (Protego DCR, manufactured by Entegris). As a result, a purified polyamic acid solution having a solid content of 18.0% in terms of polyimide and a viscosity of 200 mPa · s was obtained. The concentration of hybrid metal ions in this solution was measured by ICP analysis. Table 2 shows the IPC analysis results of the polyamic acid solution before and after performing both the filter treatment and the ion exchange treatment.

  As can be seen from Table 2, the polyamic acid solution is filtered and ion-exchanged to remove insoluble impurities having a size exceeding about 0.05 μm from the polyamic acid solution, and in the polyamic acid solution. The concentration of soluble metal ion impurities can be greatly reduced. The purified polyamic acid solution is suitable for spin coating and is suitable for application to a semiconductor device that dislikes the presence of impurity metal ions.

Example 8 (hole filling application)
Using the spin-coater (3000 rpm, 120 seconds), the purified polyamic acid solution prepared in Example 7 was a bottle-shaped via hole having a diameter of 0.5 μm and a depth of 2 μm (however, the diameter of the opening of the via hole was 0). .25 μm) is applied to the silicon substrate surface so as to have a dry thickness of μm, and dried on a hot plate at 150 ° C. for 3 minutes to form a polyamic acid film, followed by 220 ° C. for 3 minutes. Further, it was heat treated at 300 ° C. for 3 minutes to imidize to obtain a polyimide film. The obtained silicon substrate was cut so that the cross section of the via hole could be observed, and the cross section was observed with an optical microscope. As a result, it was confirmed that the via hole was filled with polyimide without a gap.

  The polyamic acid solution of the present invention has high translucency, in particular, high transmissivity of light having a wavelength of around 400 nm, exhibits a relatively high refractive index without using inorganic fine particles, and has good adhesion and heat resistance. An excellent aromatic polyimide for optical use can be provided. This aromatic polyimide for optics is useful as a waveguide layer, an adhesive layer, an insulating layer or an antireflection film.

Claims (9)

An aromatic substrate having a refractive index of 1.67 or more and a light transmittance of 90% or more obtained by applying a substrate for an optical device and a polyamic acid solution to the substrate for an optical device, drying and further imidizing. An optical device having a polyimide film,
The polyamic acid solution comprises at least one 9,9-diphenylfluorene residue represented by the formula (1a), the formula (1a ′), the formula (1b) or the formula (1c), the formula (2a), the formula ( A polyamic acid solution in which a polyamic acid having at least one non-fluorene residue selected from a diphenyl ether residue, a diphenyl thioether residue, and a diphenyl sulfone residue represented by 2b) or formula (2c) is dissolved in an organic solvent The optical device is a polyamic acid solution containing 40% by mass or more of 9,9-diphenylfluorene residue and having an average degree of polymerization of 5 to 100.

The polyamic acid is represented by the formula (2c) derived from at least one 9,9-diphenylfluorene residue represented by the formula (1a) or (1a ′) derived from the acid dianhydride component and the diamine component. The optical device according to claim 1, which is a polyamic acid having at least one non-fluorene residue selected from diphenyl ether residues, diphenyl thioether residues and diphenyl sulfone residues. The optical device according to claim 1 or 2, wherein the molecular terminal of the polyamic acid is an acid anhydride or a hydrolyzate thereof. The organic solvent constituting the polyamic acid solution is at least one selected from the group consisting of γ-butyrolactone, N-methyl-2-pyrrolidone, triglyme and N, N-dimethylacetamide, and the polyamic acid of the organic solvent Content in a solution is 70-95 mass%, The optical apparatus in any one of Claims 1-3. The optical device according to any one of claims 1 to 4, wherein the polyamic acid solution is adjusted to have a solid content of 30% by mass or less and a viscosity of 10 to 500 mPa · s. The optical device according to claim 1 , wherein the polyamic acid solution is subjected to a filter treatment and an ion exchange treatment. The optical apparatus according to claim 1 , wherein the aromatic polyimide film exhibits a refractive index of 1.67 or more and a light transmittance of 90% or more. The optical apparatus substrate, an optical device according to claim 1 is a semiconductor substrate for a solid-state imaging device. The aromatic polyimide film, the waveguide layer, the adhesive layer, optical device according to claim 1 which is an insulating layer or antireflective film.