JP2013079345A - Highly transparent polyimide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide precursor which gives a polyimide molding having sufficient transparency, a small CTE, a small elastic modulus, and a small birefringence.SOLUTION: The polyimide precursor is a copolymer having structural units represented by formula (I) and (II), wherein the molar ratio of (I) and (II) is (I):(II)=95:5-85:15.

Description

  The present invention includes a polyimide precursor, a resin composition containing the same, a polyimide comprising the same, a method for producing a polyimide molded article, a polyimide molded article obtained from the production method, a transparent substrate comprising the same, a protective film, and an electronic component having the same, The present invention relates to a display device and a solar cell module.

  Polyimide resins have electrical and mechanical properties with excellent insulating properties in addition to high heat resistance. Because of having such characteristics, polyimide resin is used as a surface protective film and an interlayer insulating film of a semiconductor device.

  On the other hand, in recent years, in the field of display devices, replacement of a transparent substrate such as a glass substrate or a cover glass with a transparent substrate using a resin has been studied in order to improve breakage resistance, reduce the weight, and reduce the thickness. Yes. A display device refers to a liquid crystal display, an organic electroluminescence display, electronic paper, or the like. In particular, display devices for mobile information communication devices such as portable information terminals such as mobile phones, electronic notebooks, laptop computers, and the like have a strong demand for transparent substrates using resin instead of conventional glass substrates.

  A transparent substrate used for a display device is required to have high transparency and low birefringence from the viewpoint of high visibility in addition to heat resistance and mechanical properties. Furthermore, the transparent substrate used in the display device has a small coefficient of thermal expansion (hereinafter referred to as CTE (Coefficient Of Thermal Expansion)) in order to prevent deterioration in alignment accuracy due to heating when forming a TFT (Thin Film Transistor). Is required.

  In general, a polyimide resin is colored yellowish brown due to intramolecular conjugation and formation of a charge transfer complex. Therefore, there has been proposed a method for inhibiting the formation of a charge transfer complex and introducing transparency by introducing fluorine into the polyimide resin, imparting flexibility to the main chain, introducing bulky side chains, etc. (Non-Patent Document 1). In addition, a method of expressing transparency by using a semi-alicyclic or fully alicyclic polyimide resin that does not form a charge transfer complex has been proposed (Patent Documents 1 and 2).

However, when a transparent substrate is formed using these polyimide resins, since the CTE is large (for example, 50 × 10 ⁻⁶ K ⁻¹ ), there is a problem that the alignment accuracy deteriorates. Therefore, polyimide formed from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and trans-1,4-diaminocyclohexane as a polyimide resin having excellent transparency and small CTE (Patent Document 3) ) Has been proposed.

JP 2002-348374 A JP 2005-015629 A JP 2002-161136 A

Polymer (USA), vol. 47, p. 2337-2348, 2006

However, when the polyimide resin of Patent Document 3 is used, although the CTE is small (for example, 20 × 10 ⁻⁶ K ⁻¹ ), the elastic modulus (tensile elastic modulus) is large and the birefringence is large. It was difficult to use as a transparent substrate or a protective film.

  An object of the present invention is to provide a polyimide precursor that has a sufficient transparency, has a low CTE, a low elastic modulus, and a polyimide molded body having a low birefringence.

  According to the present invention, the following polyimide precursors and the like are provided.

The polyimide precursor of the present invention is a copolymer having structural units represented by the following formulas (I) and (II), and the ratio of (I) and (II) is (I) :( II) = 95: 5 to 85:15.

  The present invention provides a resin composition having the polyimide precursor. The resin composition of the present invention preferably contains (b) an organic solvent. Moreover, it is preferable to use the polyimide precursor or resin composition of this invention for the transparent substrate formation of a display apparatus.

  The present invention provides a polyimide obtained by heating the polyimide precursor.

  The present invention includes a process for forming a resin film by applying and drying the resin composition on a substrate, and a process for heat-treating the resin film after the drying. Provide a method. Moreover, the polyimide molded body obtained by the said manufacturing method is provided.

  Furthermore, this invention provides the transparent substrate and protective film which consist of the said polyimide molded object. Moreover, this invention provides the electronic component, display apparatus, and solar cell module which have this transparent substrate and this protective film.

  ADVANTAGE OF THE INVENTION According to this invention, the polyimide precursor which has sufficient transparency, a CTE is small, an elasticity modulus is small, and gives a polyimide molded body with small birefringence can be provided.

  Below, the polyimide precursor of this invention, the resin composition, the polyimide molded object, its manufacturing method, and embodiment of an electronic component are described in detail. In addition, this invention is not limited by this embodiment.

構造単位（Ｉ）と（II）のモル比は、得られる硬化物のＣＴＥ，弾性率の観点から（Ｉ）：（II）＝９５：５〜９０：１０が好ましい。 [(A) Polyimide precursor]
The polyimide precursor of the present invention is a copolymer having structural units represented by the following formulas (I) and (II), and the molar ratio of (I) and (II) is (I) :( II) = 95. : 5 to 85:15.

The molar ratio between the structural units (I) and (II) is preferably (I) :( II) = 95: 5 to 90:10 from the viewpoint of CTE and elastic modulus of the obtained cured product.

  The polyimide precursor of the present invention is obtained by synthesizing 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 1,4-diaminocyclohexane, 2,2′-bis (trifluoromethyl) benzidine. It is done.

Use 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (acid dianhydride obtained by heating 3,3 ′, 4,4′-biphenyltetracarboxylic acid and dehydrating and ring-closing) Thus, it is considered that the obtained cured product exhibits good heat resistance and can reduce CTE.
In addition, as said raw material tetracarboxylic acid (3,3 ', 4,4'-biphenyltetracarboxylic acid), although an acid anhydride is normally used, the acid itself or another derivative can also be used.

  By using 1,4-diaminocyclohexane, it is considered that the obtained cured product can exhibit good transparency and chemical resistance. From the viewpoint of expressing good transparency and heat resistance and reducing CTE, it is preferable to use trans 1,4-diaminocyclohexane. When trans 1,4-diaminocyclohexane is used, it is preferable that the steric structures of the two amino groups bonded to the cyclohexane ring are both in an equatorial configuration.

  Moreover, it is thought that birefringence of the obtained cured product can be reduced by using 2,2'-bis (trifluoromethyl) benzidine.

In addition, the molar ratio of the formula (I) and (II) which is a structural unit of a copolymer can be adjusted by changing the ratio of tetracarboxylic acid and diamine.
For example, 1,4-diaminocyclohexane and 2,2′-bis (trifluoromethyl) benzidine are used in an amount of 95: 5 to 85:15 (molar ratio), and an appropriate amount (over and short of the above diamines). In the amount of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, the molar ratio of structural units (I) to (II) is 95: 5 to 85:15. A polyimide precursor can be obtained.

In addition, the molar ratio of Formula (I) and (II) can be calculated | required by measuring a < ¹ > HNMR spectrum, for example. The copolymer may be a block copolymer or a random copolymer.

The molecular weight of the polyamic acid (polyimide precursor) of the present invention is preferably 10,000 to 500,000, more preferably 10,000 to 300,000, and particularly preferably 20,000 to 200,000 in terms of weight average molecular weight.
When the weight average molecular weight is less than 10,000, it is difficult to form a resin film in the step of heating the applied resin composition, and even if it can be formed, the mechanical properties are poor. When the weight average molecular weight is larger than 500,000, it is difficult to control the molecular weight during the synthesis of polyamic acid, and it becomes difficult to obtain a resin composition having an appropriate viscosity.

  A weight average molecular weight can be calculated | required by standard polystyrene conversion using the gel permeation chromatography method (GPC, for example, apparatus is L4000 UV made from Hitachi, Ltd., and a column is the Hitachi Chemical Co., Ltd. gel pack).

  The polyamic acid (polyimide precursor) of the present invention can be synthesized by a conventionally known synthesis method. For example, after a predetermined amount of diamines (1,4-diaminocyclohexane and 2,2′-bis (trifluoromethyl) benzidine) are dissolved in a solvent, tetracarboxylic acid (3,3) is added to the obtained diamine solution. A predetermined amount of tetracarboxylic dianhydride obtained by heating (3 ′, 4,4′-biphenyltetracarboxylic acid) in a dryer at 160 ° C. for 24 hours to perform dehydration and cyclization is added and stirred.

When dissolving each monomer component, you may heat as needed.
The reaction temperature is preferably from -30 to 200 ° C, more preferably from 20 to 180 ° C, particularly preferably from 30 to 100 ° C. Stirring is continued as it is at room temperature (20 to 25 ° C.) or at an appropriate reaction temperature, and the time when the viscosity of the polyamic acid becomes constant is taken as the end point of the reaction. The viscosity can be measured at 25 ° C. using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd.).
The above reaction can usually be completed in 3 to 100 hours.

The solvent for the above reaction is not particularly limited as long as it is a solvent capable of dissolving diamines, tetracarboxylic acid, and generated polyamic acid.
Specific examples of such solvents include aprotic solvents, phenol solvents, ethers and glycol solvents. Specifically, as the aprotic solvent, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, tetramethyl Amide solvents such as urea; Lactone solvents such as γ-butyrolactone and γ-valerolactone; Phosphorus-containing amide solvents such as hexamethylphosphoric amide and hexamethylphosphine triamide; dimethylsulfone, dimethylsulfoxide, sulfolane Sulfur-containing solvents; ketone solvents such as cyclohexanone and methylcyclohexanone; tertiary amine solvents such as picoline and pyridine; ester solvents such as acetic acid (2-methoxy-1-methylethyl). Examples of phenol solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol and the like can be mentioned. As ether and glycol solvents, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, bis [2- (2-methoxyethoxy) ethyl] ether , Tetrahydrofuran, 1,4-dioxane and the like. Of these, N-methyl-2-pyrrolidone is preferable from the viewpoint of solubility and coating film formation. These reaction solvents may be used alone or in combination of two or more.

The polyimide precursor (polyamic acid) of the present invention is usually obtained as a solution using the reaction solvent as a solvent (hereinafter referred to as a polyamic acid solution).
The polyamic acid component (resin non-volatile content: hereinafter referred to as solute) relative to the total amount of the obtained polyamic acid solution is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, from the viewpoint of coating film formation. 40% by mass is particularly preferred.

  The ratio of the solute is determined by measuring the mass (the mass of the metal petri dish and the polyamic acid, hereinafter referred to as the mass before heating) after taking the polyamic acid solution (about 1 g as a guide) into a metal petri dish whose mass is known in advance. Measure the mass after heating for 2 hours on a hot plate at 0 ° C. (the mass of the metal petri dish and the solute, hereinafter referred to as the mass after heating), and (the mass after heating−the mass of the metal petri dish) ) ÷ (mass before heating−mass of metal petri dish) × 100.

  The solution viscosity of the polyamic acid solution is preferably 500 to 200,000 mPa · s at 25 ° C., more preferably 2000 to 100,000 mPa · s, and particularly preferably 5000 to 30000 mPa · s. The solution viscosity can be measured using an E-type viscometer (VISCONIC EHD manufactured by Toki Sangyo Co., Ltd.).

  When the solution viscosity is lower than 500 mPa · s, it is difficult to apply the film during film formation, and when it is higher than 200000 mPa · s, there is a problem that stirring during synthesis becomes difficult. However, even if the solution becomes highly viscous during the synthesis of the polyamic acid, it is possible to obtain a polyamic acid solution with a good handleability by adding a solvent after the reaction and stirring.

  The polyimide of this invention is obtained by heating the said polyimide precursor and carrying out dehydration ring closure.

[Resin composition]
The resin composition of the present invention contains the above (a) polyimide precursor, preferably (b) an organic solvent.
[(B) Organic solvent]
The resin composition of the present invention preferably uses (b) an organic solvent as necessary.
The (b) organic solvent is not particularly limited as long as it can dissolve the polyimide precursor (polyamide acid) of the present invention. As such (b) organic solvent, (a) a polyimide precursor (polyamide acid) is used. A solvent that can be used at the time of synthesis can be used. (B) The organic solvent may be the same as or different from the solvent used in the synthesis of (a) polyamic acid.
The component (b) is preferably added so that the viscosity at 25 ° C. of the resin composition is 0.5 Pa · s to 100 Pa · s.

Moreover, 60-210 degreeC is preferable, the boiling point in the normal pressure of (b) organic solvent has more preferable 100-205 degreeC, and its 140-180 degreeC is especially preferable.
When the boiling point is higher than 210 ° C., a drying process is required for a long time. When the boiling point is lower than 60 ° C., the surface of the resin film is roughened in the drying process or bubbles are generated in the resin film, so that a uniform film is obtained. It may not be possible.

[Other ingredients]
The resin composition of the present invention may contain (1) adhesion imparting, (2) a surfactant or a leveling agent, in addition to the components (a) and (b).

[Other components: (1) Adhesiveness imparting agent]
The resin composition of the present invention may contain (1) an adhesion-imparting agent such as an organic silane compound and an aluminum chelate compound in order to enhance the adhesion of the cured film to the substrate.

  Examples of the organic silane compound include vinyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, urea propyltriethoxysilane, methylphenylsilanediol, ethylphenylsilanediol, n- Propylphenylsilanediol, isopropylphenylsilanediol, n-butylphenylsilanediol, isobutylphenylsilanediol, tert-butylphenylsilanediol, diphenylsilanediol, ethylmethylphenylsilanol, n-propylmethylphenylsilanol, isopropylmethylphenylsilanol, n-butylmethylphenylsilanol, isobutylmethylphenylsilanol, tert-butylmethylphenylsilanol Ethyl n-propylphenylsilanol, ethylisopropylphenylsilanol, n-butylethylphenylsilanol, isobutylethylphenylsilanol, tert-butylethylphenylsilanol, methyldiphenylsilanol, ethyldiphenylsilanol, n-propyldiphenylsilanol, isopropyldiphenylsilanol, n-butyldiphenylsilanol, isobutyldiphenylsilanol, tert-butyldiphenylsilanol, phenylsilanetriol, 1,4-bis (trihydroxysilyl) benzene, 1,4-bis (methyldihydroxysilyl) benzene, 1,4-bis ( Ethyldihydroxysilyl) benzene, 1,4-bis (propyldihydroxysilyl) benzene, 1,4-bis (butyldihi Loxysilyl) benzene, 1,4-bis (dimethylhydroxysilyl) benzene, 1,4-bis (diethylhydroxysilyl) benzene, 1,4-bis (dipropylhydroxysilyl) benzene, 1,4-bis (dibutylhydroxysilyl) ) Benzene and the like.

  Examples of the aluminum chelate compound include tris (acetylacetonate) aluminum, acetylacetate aluminum diisopropylate, and the like.

  When these (1) adhesion imparting agents are used, it is preferable to contain 0.1 to 20 parts by mass, and more preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of component (a). preferable.

[Other components: (2) Surfactant or leveling agent]
Moreover, the resin composition of this invention may contain (2) surfactant or a leveling agent from a viewpoint of applicability | paintability, for example, a viewpoint which prevents striation (film thickness nonuniformity).

  Examples of the surfactant or leveling agent include polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octylphenol ether, and the like.

  Commercially available products include Megafax F171, F173, R-08 (trade name, manufactured by Dainippon Ink & Chemicals, Inc. (DIC Corporation)), Florard FC430, FC431 (trade name, manufactured by Sumitomo 3M Limited), organosiloxane Examples thereof include polymers KP341, KBM303, KBM403, and KBM803 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.).

  The viscosity at 25 ° C. of the resin composition of the present invention is preferably 0.5 to 100 Pa · s, more preferably 1 to 30 Pa · s from the viewpoint of workability in the coating process, although it depends on the intended use and purpose. 5-20 Pa. s is particularly preferred. Here, the viscosity can be measured using an E-type viscometer (VISCONIC EHD manufactured by Toki Sangyo Co., Ltd.).

The method for producing the resin composition of the present invention is not particularly limited. For example, when the solvent used when synthesizing (a) polyamic acid and (b) the organic solvent are the same, the resin composition was synthesized. A polyamic acid solution can be used as a resin composition. Moreover, you may add and stir and mix a (b) component and another additive in the temperature range of room temperature (25 degreeC)-80 degreeC as needed.
For this stirring and mixing, an apparatus such as a three-one motor (manufactured by Shinto Chemical Co., Ltd.) equipped with a stirring blade, a rotation and revolution mixer, or the like can be used. Moreover, you may add a 40-100 degreeC heat | fever as needed.

  When (a) the solvent used when synthesizing the polyamic acid is different from (b) the organic solvent, the solvent in the synthesized polyamic acid solution is removed by reprecipitation or solvent distillation, a) After obtaining the polyamic acid, in the temperature range of room temperature to 80 ° C., (b) an organic solvent and other additives as necessary may be added and stirred and mixed.

The resin composition of the present invention can be used to form a transparent substrate of a display device such as a liquid crystal display, an organic electroluminescence display, a field emission display, or electronic paper.
Specifically, it can be used for forming a thin film transistor (TFT) substrate, a color filter substrate, a transparent conductive film (ITO, Indium Thin Oxide) substrate, and the like.

[Polyimide molded product]
The polyimide molded body of the present invention can be obtained by forming a resin film obtained by applying the resin composition of the present invention to a substrate and drying it, followed by heat treatment (imidization). Moreover, this polyimide molded object can be used as forms, such as a film form, a film form, and a sheet form, according to a use use / purpose.
Since the polyimide molded body of the present invention is excellent in transparency, low birefringence, low thermal expansion coefficient and low elastic modulus, it can be suitably used as a display substrate, a protective film and the like.

  The method for producing a polyimide molded body is preferably (1) a step of applying the resin composition of the present invention on a substrate to form a resin film, and (2) drying the applied resin film with heat at 80 to 200 ° C. And (3) a step of heat-treating the resin film after drying, and a step of imidizing the polyimide precursor in the resin composition by heating at 300 ° C. or higher.

  (1) There is no restriction | limiting in particular in the application | coating method used at an application | coating process, According to the desired application | coating thickness, the viscosity of a resin composition, etc., it can select and use a well-known application | coating method suitably. Specifically, doctor blade knife coater, air knife coater, roll coater, rotary coater, flow coater, die coater, bar coater and other coating methods, spin coating, spray coating, dip coating and other coating methods, screen printing and gravure printing It is also possible to apply printing techniques represented by the above.

  The substrate on which the resin composition is applied is not particularly limited as long as it has heat resistance at the drying temperature in the subsequent steps and has good peelability. Examples thereof include a substrate made of glass, a silicon wafer or the like, and a support made of PET (polyethylene terephthalate), OPP (stretched polypropylene) or the like. In addition, in the case of a film-like polyimide molded body, a coating object made of glass, silicon wafer or the like can be mentioned. In the case of a film-like or sheet-like polyimide molded body, a support made of PET (polyethylene terephthalate), OPP (stretched polypropylene) or the like. Is mentioned.

  Other substrates include glass substrates, metal substrates such as stainless steel, alumina, copper, nickel, polyethylene glycol terephthalate, polyethylene glycol naphthalate, polycarbonate, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polyethersulfone, A resin substrate such as polyphenylene sulfone or polyphenylene sulfide is used.

  The coating thickness of the resin composition of the present invention is appropriately adjusted depending on the thickness of the target molded article and the ratio of the resin non-volatile component in the resin composition, but is usually about 1 to 1000 μm. A resin non-volatile component is calculated | required by the above-mentioned measuring method. The coating step is usually performed at room temperature, but may be performed by heating the resin composition in the range of 40 to 80 ° C. for the purpose of reducing viscosity and improving workability.

  Following the coating process, (2) a drying process is performed. The drying step is performed for the purpose of removing the organic solvent. A drying process can utilize apparatuses, such as a hotplate, a box-type dryer, and a conveyor type dryer, It is preferable to carry out at 80-200 degreeC, and it is more preferable to carry out at 100-150 degreeC.

Subsequently, (3) a heating step is performed. This heating step is a step of (2) removing the organic solvent remaining in the resin film in the drying step and advancing the imidization reaction of the polyamic acid in the resin composition to obtain a cured film. The heating process is performed using an inert gas oven, a hot plate, a box-type dryer, a conveyor-type dryer or the like. Further, this step may be performed simultaneously with (2) the drying step or sequentially.
(3) The heating process may be performed in an air atmosphere, but it is recommended that the heating process be performed in an inert gas atmosphere from the viewpoint of safety and prevention of oxidation. Examples of the inert gas include nitrogen and argon. Although heating temperature is based also on the kind of (b) organic solvent, 250 to 400 degreeC is preferable and 300 to 350 degreeC is more preferable. If it is lower than 250 ° C., imidization becomes insufficient, and if it is higher than 400 ° C., the transparency of the polyimide molded body may be lowered or the heat resistance may be deteriorated. The heating time is usually about 0.5 to 3 hours.

  In addition, depending on the intended use and purpose of the polyimide molded body, (4) a peeling step for peeling the cured film from the substrate is required after the heating step. This peeling process is implemented after cooling the molded object on a base material to room temperature-about 50 degreeC. In order to easily perform the peeling operation, a release agent may be applied to the substrate as necessary before applying the resin composition of the present invention. Examples of the release agent include vegetable oil-based, silicon-based, fluorine-based, and alkyd-based release agents.

  The obtained polyimide molded body can also form a pattern by a resist process according to a use. In the resist process, for example, after (3) the heating step or (4) the peeling step, a resist is applied, and a pattern is formed by exposure and development. The resist material and the material used for etching are not particularly limited as long as they are used in a normal resist process. For example, generally well-known etching solutions include hydrazine hydrate, potassium hydroxide aqueous solution, sodium hydroxide aqueous solution and the like. In addition to these wet etchings, dry methods such as oxygen plasma etching and oxygen sputter etching can also be employed. After pattern formation, the resist is peeled off from the polyimide molded body using an organic solvent. Examples of the organic solvent include ethanolamine, NMP, DMSO and the like, and a mixture thereof can also be used.

  The manufacturing method of the polyimide molded body of this invention is useful when manufacturing a polyimide molded body with a film thickness of 1-500 micrometers. In particular, it is preferable to produce a polyimide molded body having a thickness of 1 to 100 μm in order to further improve the effects of the present invention.

  The amount of the remaining organic solvent in the polyimide molded body after the heating step (3) of the present invention is preferably 2% by mass or less, more preferably 1% by mass or less, and further preferably 0.5% by mass or less. The amount of residual organic solvent in the polyimide molded body can be measured by simultaneous differential thermogravimetric measurement (TG-DTA) and gas chromatograph mass spectrometry (GC-MS).

The transparency of the polyimide molded body of the present invention is such that the light transmittance at a wavelength of 400 nm or more is preferably 70% or more, more preferably 75% or more at a film thickness of 10 μm.
The birefringence of the polyimide molded body of the present invention is preferably 0.12 or less, and more preferably 0.08 or less. This value is regarded as having sufficient transparency and low birefringence as a polyimide molded body used in the fields of optical communication and display devices.

  The CTE (thermal expansion coefficient) of the polyimide molded body of the present invention is preferably 1 to 45 ppm, more preferably 5 to 45 ppm, and still more preferably 5 to 30 ppm in both the width direction and the operation direction. When the polyimide molded body is used in a state of being integrated with the substrate (coating object), the linear thermal expansion coefficient of the polyimide molded body is preferably adjusted to be approximately the same as that of the coating object.

  250-400 degreeC is preferable and, as for the glass transition temperature (Tg) of the polyimide molded body of this invention, 300-400 degreeC is more preferable. This value is regarded as having sufficient heat resistance as a polyimide molded body used in the fields of optical communication and display devices. The glass transition temperature is a value obtained by the method described in Examples described later.

  CTE and glass transition temperature (Tg) are obtained by TMA measurement using TMA / SS6000 manufactured by Seiko Instruments Inc.

As for the mechanical properties of the polyimide molded body of the present invention, the elastic modulus (tensile elastic modulus) is preferably 1.5 GPa to 6.0 GPa in both the width direction and the operation direction, more preferably 1.7 to 6.0 GPa, and more preferably 1.7. -5.5 GPa is more preferred. If the elastic modulus is greater than 6.0 GPa, the substrate tends to warp after curing.
The tensile strength (breaking strength) is preferably 150 to 300 MPa, and more preferably 150 to 200 MPa. When the tensile strength is less than 150 MPa, the film is fragile and becomes difficult to handle when used as a substrate.
The elongation at break is preferably 5% or more, and more preferably 10% or more. If the elongation at break is less than 5%, the bending stress when the polyimide molded body is used as a substrate is weak, and the reliability of the substrate is lowered.

  All of these mechanical properties can be obtained by a tensile test using a tensile test apparatus. If the polyimide molded body has these mechanical properties, it is considered to have sufficient toughness as a polyimide molded body used in the fields of optical communication and display devices, and can be used practically.

[Transparent substrate / Protective film / Electronic components]
The transparent substrate and protective film of the present invention are characterized by comprising the polyimide molded body. As the manufacturing method, a conventionally known manufacturing method can be used. For example, the resin composition of the present invention can be applied to a temporarily fixed substrate, dried and heated, then subjected to the resist process according to the application, and used as a transparent substrate. In addition, the resin composition of the present invention can be applied to a temporarily fixed substrate, dried and heated, peeled from the temporarily fixed substrate, and used as a protective film.

  Since the transparent substrate and protective film of the present invention have sufficient transparency, CTE is small, elastic modulus is small, and birefringence is small, such as liquid crystal display, organic electroluminescence display, field emission display, electronic paper, etc. Can be used for display devices.

  Specifically, the transparent substrate of the present invention includes a substrate for forming a thin film transistor (TFT), a substrate for forming a color filter, a substrate for forming a transparent conductive film (ITO, Indium Thin Oxide), etc. Can be used as When the transparent substrate of the present invention is used, it is considered that breakage resistance, which is a problem of the conventional glass substrate, can be improved, and that the substrate can be reduced in weight and thickness. Furthermore, since the CTE of the transparent substrate of the present invention is small, it is possible to prevent deterioration in alignment accuracy in the heating process at the time of TFT formation, and the transparency is high and the birefringence is small, so that the visibility is excellent. Moreover, since the transparent substrate of the present invention has a low elastic modulus, it can also be used as a substrate for a flexible display.

  The protective film of the present invention can also be used as a flexible display substrate, a color filter protective film, and the like. The protective film of the present invention can also be used as a surface protective film for solar cells.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples.

Example 1
In a 0.2 liter flask equipped with a stirrer and a thermometer, 56 g (564 mmol) of N-methylpyrrolidone, 3.25 g (28.5 mmol) of 1,4-diaminocyclohexane and 2,2′-bis (trifluoromethyl) ) 0.48 g (1.5 mmol) of benzidine was charged, immersed in a water bath at 60 ° C., stirred, and then heated with a dryer (160 ° C./24 h) to cause dehydration and ring closure 3,3 ′, 4,4′− Biphenyltetracarboxylic anhydride 8.83 g (30 mmol) was added, and the mixture was heated and stirred for 10 minutes in a water bath at 80 ° C. to completely dissolve it. Thereafter, the mixture was stirred for about 70 hours until the molecular weight became constant to obtain a polyamic acid solution (molar ratio of structural units (I) :( II) = 95: 5).

  The weight average molecular weight and dispersion degree of the obtained polyamic acid were calculated | required by gel permeation chromatography (GPC) standard polystyrene conversion. The weight average molecular weight was 31,000, and the degree of dispersion was 2.2.

The measurement conditions for the weight average molecular weight and the degree of dispersion are shown below.
Measuring device: Detector L4000 UV manufactured by Hitachi, Ltd.
Pump: Hitachi Ltd. L6000
C-R4A Chromatopac made by Shimadzu Corporation
Measurement conditions: Column Gelpack GL-S300MDT-5 × 2 eluent: THF / DMF = 1/1 (volume ratio)
LiBr (0.03 mol / l), H ₃ PO ₄ (0.06 mol / l)
Flow rate: 1.0 ml / min, detector: UV 270 nm
The measurement was performed using a solution of 1 ml of a solvent [THF / DMF = 1/1 (volume ratio)] with respect to 0.5 mg of the polymer.

  The obtained polyamic acid solution (resin composition) was diluted with NMP to a viscosity that was easy to apply, and the residual solid content (NV) was measured to be 14%. Here, the residual solid content is the ratio of the resin non-volatile content in the resin composition, and was determined by the method of measuring the resin non-volatile content described above.

  This was filtered using a 5 μm filter (Millipore, SLLS025NS). The obtained resin composition was spin coated on a silicon wafer and dried at 120 ° C. for 3 minutes to form a resin film having a film thickness of 14 to 18 μm. This was further heated under a nitrogen atmosphere using an inert gas oven to obtain a cured film having a thickness of 10 μm.

The conditions for the heating step (full cure) using an inert gas oven are as follows.
Apparatus: Inert gas oven manufactured by Koyo Thermo Systems Co., Ltd. Conditions: Temperature rise Room temperature to 200 ° C (5 ° C / min)
Hold 200 ° C (20 minutes)
200 ° C to 300 ° C (5 ° C / min)
Hold 300 ° C (60 minutes)
Cooling 300 ° C to room temperature (60 minutes)

The following evaluation was performed about the obtained cured film.
(Evaluation of birefringence)
Birefringence was measured using the cured film attached to the substrate obtained by the method described above. For birefringence measurement, a metricon 2010 model manufactured by Seki Technotron Co., Ltd. was used, and the refractive index in the Y polarization at a wavelength of 1300 nm: TE and the refractive index in the X polarization: TM were measured. (Equation 1) The birefringence was determined by
Birefringence = TE-TM (Formula 1)

  A birefringence of 0.08 or less was designated as A (particularly good), a value greater than 0.08 and 0.12 or less was designated as B (good), and a value greater than 0.12 was designated as C (not good).

(Evaluation of transmittance, CTE, glass transition temperature, and mechanical strength)
Next, using 4.9 mass% hydrofluoric acid aqueous solution, the obtained cured film was peeled from the silicon wafer, washed with water, dried, and then evaluated for transmittance, CTE, glass transition temperature (Tg), and mechanical strength. It was.

  The light transmittance was determined by measuring the light transmittance at a wavelength of 400 nm or more using U-3310 (Spectrophotometer manufactured by Hitachi, Ltd.), and obtaining a value converted to 10 μm using Lambert-Beer's law.

  CTE was measured using a TMA / SS6000 thermomechanical measuring device manufactured by Seiko. Specifically, the cured film is cut into 2 mm × 3 cm, and TMA / SS6000 thermomechanical measuring device manufactured by Seiko Co., Ltd. is applied to 30 to 420 ° C. while applying a load of 10 g / min (temperature increase rate 5 ° C./min. ) Heated. CTE was measured by measuring the slope of the elongation of the cured film between 100 and 200 ° C. The case where CTE was 30 ppm / K or less was designated as A (particularly good), the case where it was greater than 30 ppm / K and 45 ppm / K or less was designated as B (good), and the case where it was greater than 45 ppm / K was designated as C (not good).

  The glass transition temperature was determined from the inflection point of the coefficient of thermal expansion using a TMA / SS6000 manufactured by Seiko Instruments Inc. at a heating rate of 5 ° C./min.

  Mechanical strength (elastic modulus, breaking elongation and breaking strength) was determined from a tensile test using an autograph AGS-100NH manufactured by Shimadzu Corporation. An elastic modulus of 5.5 GPa or less was designated as A (particularly good), a value greater than 5.5 GPa and 6.0 GPa or less was designated as B, and a value greater than 6.0 GPa was designated as C (not good).

Examples 2, 3 and Comparative Examples 1-5
A polyamic acid was synthesized in the same manner as in Example 1 except that the amount of amine, acid and the amount thereof was changed as shown in Table 1, and a resin composition and a cured film were prepared, and these were evaluated.
Amine 1,2 and acid 1,2 are as follows.
Amine 1: 1,4-diaminocyclohexaneamine 2: 2,2′-bis (trifluoromethyl) benzidine acid 1: 3,3 ′, 4,4′-biphenyltetracarboxylic acid 2: 3,3 ′, 4 , 4'-Tetracarboxydiphenyl ether

The cured films obtained in Examples 1 to 3 exhibited good transmittance, low CTE, low birefringence, and low elastic modulus even after heat treatment at 300 ° C. or higher. It has been found that the polyimide precursor of the present invention provides a cured film that satisfies all of transparency, CTE, and mechanical strength.
On the other hand, when 2,2′-bis (trifluoromethyl) benzidine was not included as in Comparative Example 1, the elastic modulus and birefringence were high. Further, when the amount of 2,2′-bis (trifluoromethyl) benzidine was large as in Comparative Examples 2, 3, and 5, the transmittance was deteriorated. When 3,3 ′, 4,4′-biphenyltetracarboxylic acid was not used as in Comparative Example 4, CTE and mechanical strength deteriorated.

  The polyimide molded body of the present invention can be used as a display substrate, a protective film and the like.

Claims (12)

It is a copolymer having structural units represented by the following formulas (I) and (II), and the molar ratio of (I) and (II) is (I) :( II) = 95: 5 to 85:15 Polyimide precursor.

  A resin composition comprising the polyimide precursor according to claim 1.   The resin composition according to claim 2 containing an organic solvent.   The resin composition according to claim 2 or 3 for forming a transparent substrate of a display device.   A polyimide obtained by heating the polyimide precursor according to claim 1.   A polyimide molded body comprising a step of applying a resin composition according to any one of claims 2 to 4 on a substrate and drying to form a resin film, and a step of heat-treating the resin film after drying. Production method.   A polyimide molded body obtained by the production method according to claim 6.   A transparent substrate comprising the polyimide molded body according to claim 7.   A protective film comprising the polyimide molded body according to claim 7.   An electronic component having the transparent substrate according to claim 8 or the protective film according to claim 9.   A display device comprising the transparent substrate according to claim 8 or the protective film according to claim 9.   A solar cell module having the transparent substrate according to claim 8 or the protective film according to claim 9.