JP6891084B2 - Highly transparent polyimide - Google Patents

Description

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

In addition to high heat resistance, the polyimide resin has excellent electrical and mechanical properties with excellent insulating properties. Since it has such characteristics, the 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, it has been considered to replace a transparent substrate such as a glass substrate or a cover glass with a transparent substrate using a resin in order to improve the damage resistance, reduce the weight, and reduce the thickness. There is. The display device refers to a liquid crystal display, an organic electroluminescence display, electronic paper, or the like. In particular, in display devices for mobile information and communication devices such as mobile information terminals such as mobile phones, electronic organizers, and laptop personal computers, there is a strong demand for a transparent substrate using resin instead of the conventional glass substrate.

The transparent substrate used in the 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. Further, the transparent substrate used for the display device is required to have a small coefficient of thermal expansion (hereinafter referred to as CTE (CofficientOfThermalExpansion)) in order to prevent deterioration of the alignment accuracy due to heating during the formation of a TFT (Thin Film Transistor). ..

Generally, a polyimide resin is colored yellowish brown by intramolecular conjugation and formation of a charge transfer complex. Therefore, a method has been proposed in which the formation of a charge transfer complex is inhibited and transparency is exhibited by introducing fluorine into the polyimide resin, imparting flexibility to the main chain, introducing a bulky side chain, and the like. (Non-Patent Document 1). Further, a method of expressing transparency by using a semi-alicyclic or full alicyclic polyimide resin that does not form a charge transfer complex has also been proposed (Patent Documents 1 and 2).

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

Japanese Unexamined Patent Publication No. 2002-348374 Japanese Unexamined Patent Publication No. 2005-015629 Japanese Unexamined Patent Publication No. 2002-161136

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 also large, so that the display device It was difficult to use it as a transparent substrate or protective film.
An object of the present invention is to provide a polyimide precursor that provides a polyimide molded product having sufficient transparency, a small CTE, a low elastic modulus, and a small birefringence.

The polyimide precursor of the present invention is a copolymer having structural units represented by the following formulas (I) and (II).

The present invention provides a resin composition having the polyimide precursor. Further, the resin composition of the present invention preferably contains (b) an organic solvent. Further, the polyimide precursor or resin composition of the present invention is preferably used for forming a transparent substrate of a display device.

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

The present invention comprises a step of applying the resin composition onto a substrate and drying it to form a resin film, and a step of heat-treating the dried resin film. Provide a method. Further, a polyimide molded product obtained by the above-mentioned production method is provided.

Furthermore, the present invention provides a transparent substrate and a protective film made of the polyimide molded product. The present invention also provides an electronic component, a display device, and a solar cell module having the transparent substrate and the protective film.

According to the present invention, it is possible to provide a polyimide precursor which has sufficient transparency, has a small CTE, has a low elastic modulus, and gives a polyimide molded product having a small birefringence.

Hereinafter, the polyimide precursor, the resin composition, and the polyimide molded product of the present invention, a method for producing the same, and embodiments of electronic components will be described in detail. The present invention is not limited to this embodiment.

構造単位（Ｉ）及び（II）の比は、得られる硬化物のＣＴＥ、弾性率及び複屈折の観点から（Ｉ）：（II）＝５：９５〜９５：５が好ましい。また、複屈折の観点から（Ｉ）：（II）＝３０：７０〜９５：５がより好ましく、ＣＴＥの観点から（Ｉ）：（II）＝５０：５０〜７０：３０がさらに好ましい。
また、合成中の塩形成をより抑制し、より反応を制御しやすくする観点からは、（Ｉ）：（II）＝３０：７０〜９５：５が好ましく、（Ｉ）：（II）＝５０：５０〜９５：５がより好ましい。 [(A) Polyimide precursor]
The polyimide precursor of the present invention is a copolymer having structural units represented by the following formulas (I) and (II).

The ratio of the structural units (I) and (II) is preferably (I) :( II) = 5: 95 to 95: 5 from the viewpoint of CTE, elastic modulus and birefringence of the obtained cured product. Further, from the viewpoint of birefringence, (I) :( II) = 30: 70 to 95: 5 is more preferable, and from the viewpoint of CTE, (I) :( II) = 50:50 to 70:30 is even more preferable.
Further, from the viewpoint of further suppressing salt formation during synthesis and making it easier to control the reaction, (I) :( II) = 30: 70 to 95: 5 is preferable, and (I) :( II) = 50. : 50 to 95: 5 is more preferable.

The ratio of the above formulas (I) and (II) can be obtained ^{, for example, by measuring 1 1 HNMR spectrum.} Further, the copolymer may be a block copolymer or a random copolymer.

The polyimide precursor (polyamic acid) of the present invention polymerizes 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic acid dianhydride, and 1,4-diaminocyclohexane. It can be obtained by letting it.

Use 3,3', 4,4'-biphenyltetracarboxylic dianhydride (acid dianhydride obtained by heating 3,3', 4,4'-biphenyltetracarboxylic acid and dehydrating and ring-closing it). Therefore, it is considered that the obtained cured product exhibits good heat resistance and can reduce CTE.

By using 4,4'-oxydiphthalic dianhydride (acid dianhydride obtained by heating 3,3', 4,4'-tetracarboxydiphenyl ether and dehydrating and ring-closing the ring), the obtained cured product is good. It is considered that the heat resistance and transparency can be exhibited and the birefringence can be reduced.
As the raw material tetracarboxylic acid (3,3', 4,4'-biphenyltetracarboxylic acid, 4,4'-oxydiphthalic acid), these acid anhydrides are usually used, but these acids or other acids are used. Derivatives of

Further, it is considered that the obtained cured product can exhibit good transparency and chemical resistance by using 1,4-diaminocyclohexane.
Trans 1,4-diaminocyclohexane is preferable as 1,4-diaminocyclohexane from the viewpoint of exhibiting good transparency and heat resistance and reducing CTE. When trans 1,4-diaminocyclohexane is used, it is preferable that the three-dimensional structures of the two amino groups bonded to the cyclohexane ring both have an equiatrial arrangement.

The ratio of the structural units (I) and (II) is as follows: tetracarboxylic acids (3,3', 4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic acid dianhydride) and diamine ( It can be adjusted by changing the ratio of 1,4-diaminocyclohexane).

The molecular weight of the polyamic acid (polyimide precursor) of the present invention is preferably 1000 to 500000, more preferably 1000 to 300000, and particularly preferably 2000 to 20000, in terms of weight average molecular weight.
If the weight average molecular weight is less than 10,000, it becomes 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 may be poor. If the weight average molecular weight is larger than 500,000, it may be difficult to control the weight average molecular weight during the synthesis of the polyamic acid, and it may be difficult to obtain a resin composition having an appropriate viscosity.

The weight average molecular weight can be determined by gel permeation chromatography (GPC) (for example, the device is L4000 UV manufactured by Hitachi, Ltd., and the column is gel pack manufactured by Hitachi Kasei Kogyo Co., Ltd.) in terms of standard polystyrene. ..

The polyimide precursor (polyamic acid) of the present invention can be synthesized by a conventionally known synthetic method. For example, after dissolving a predetermined amount of 1,4-diaminocyclohexane in a solvent, in the obtained diamine solution, 3,3', 4,4'-biphenyltetracarboxylic acid and 4,4'-oxydiphthalic acid, respectively. Is heated at 160 ° C. for 24 hours in a dryer to dehydrate and close the ring, and a predetermined amount of tetracarboxylic dianhydride is added and stirred.

When each monomer component is dissolved, it may be heated if necessary.
The reaction temperature is preferably -30 to 200 ° C, more preferably 20 to 180 ° C, and particularly preferably 30 to 100 ° C. Stirring is continued at room temperature (20 to 25 ° C.) or an appropriate reaction temperature as it is, and the point at which the viscosity of the polyamic acid becomes constant is defined 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 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 the diamine, tetracarboxylic acids and the generated polyamic acid.
Specific examples of such a solvent include aprotic solvents, phenolic solvents, ether and glycol solvents and the like. Specifically, as the aprotonic 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 hexamethylphosphintriamide; Sulfur-containing solvents; ketone solvents such as cyclohexanone and methylcyclohexanone; tertiary amine solvents such as picolin and pyridine; ester solvents such as acetic acid (2-methoxy-1-methylethyl) and the like can be mentioned. Examples of the phenolic solvent include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and the like. Examples thereof include 3,5-xylenol. Examples of the ether and glycol-based solvent include 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, and 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 forming property. 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 above reaction solvent as a solvent (hereinafter, referred to as a polyamic acid solution).
The ratio of the polyamic acid component (resin non-volatile content: hereinafter referred to as solute) 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 forming property. 10 to 40% by mass is particularly preferable.

For the solute ratio, take a polyamic acid solution in a metal petri dish whose mass is known in advance (about 1 g as a guide), measure the mass (mass of metal petri dish and polyamic acid, hereinafter referred to as mass before heating), and then measure. The mass after heating on a hot plate for 2 hours to sufficiently volatilize the solvent (mass of metal petri dish and solute, hereinafter referred to as mass after heating) is measured, and (mass after heating-mass of metal petri dish) ÷ It is obtained from (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 5,000 to 30,000 mPa · s. The solution viscosity can be measured using an E-type viscometer (VISCONICE HD manufactured by Toki Sangyo Co., Ltd.).

If the solution viscosity is lower than 500 mPa · s, it may be difficult to apply the film during film formation, and if it is higher than 200,000 mPa · s, it may be difficult to stir during synthesis. However, even if the solution becomes highly viscous during the synthesis of polyamic acid, it is possible to obtain a polyamic acid solution having a viscosity that is easy to handle by adding a solvent and stirring after the reaction is completed.

The polyimide of the present invention can be obtained by heating the polyimide precursor and dehydrating and ring-closing the polyimide precursor.

[Resin composition]
The resin composition of the present invention contains the above-mentioned (a) polyimide precursor, and preferably contains an organic solvent.
[(B) Organic solvent]
The (b) organic solvent is not particularly limited as long as it can dissolve the polyimide precursor (polyamic acid) of the present invention, and such (b) organic solvent includes the above-mentioned (a) polyimide precursor (polyamic acid). A solvent that can be used in the synthesis of the above 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 after adjusting the viscosity of the resin composition at 25 ° C. to 0.5 Pa · s to 100 Pa · s.

Further, (b) the boiling point of the organic solvent at normal pressure is preferably 60 to 210 ° C, more preferably 100 to 205 ° C, and particularly preferably 140 to 180 ° C.
If the boiling point is higher than 210 ° C, the drying process is required for a long time, and if it is lower than 60 ° C, the surface of the resin film is roughened or air bubbles are mixed in the resin film, resulting in a uniform film. It may not be obtained.

[Other ingredients]
In addition to the above components (a) and (b), the resin composition of the present invention may contain (1) an adhesive-imparting agent, (2) a surfactant, a leveling agent, and the like.
The composition of the present invention may be substantially composed of the above-mentioned components (a) and (b) and optionally additives such as an adhesive-imparting agent, a surfactant, and a leveling agent, and these It may consist only of the components of. "Substantially" means that the composition mainly comprises the above components (a) and (b) (for example, 90% by weight or more of the total composition), and in addition to these components, the above. Can contain the additives of.

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

Examples of the organic silane compound include vinyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, ureapropyltriethoxysilane, methylphenylsilanediol, ethylphenylsilanediol, and 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 (butyldihydroxysilyl) benzene, 1, Examples thereof include 4-bis (dimethylhydroxysilyl) benzene, 1,4-bis (diethylhydroxysilyl) benzene, 1,4-bis (dipropylhydroxysilyl) benzene, and 1,4-bis (dibutylhydroxysilyl) benzene. ..

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

When these (1) adhesiveness-imparting agents are used, it is preferably contained in an amount of 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the component (a). preferable.

[Other ingredients: (2) Surfactant or leveling agent]
Further, the resin composition of the present invention may contain (2) a surfactant or a leveling agent from the viewpoint of coatability, for example, from the viewpoint of preventing striation (unevenness of film thickness).

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

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

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

The method for producing the resin composition of the present invention is not particularly limited, but for example, when (a) the solvent used when synthesizing the polyamic acid and (b) the organic solvent are the same, the resin composition was synthesized. The polyamic acid solution can be used as the resin composition. Further, if necessary, the component (b) and other additives may be added and stirred and mixed in the temperature range of room temperature (25 ° C.) to 80 ° C.
For this stirring and mixing, a device such as a three-one motor (manufactured by Shinto Chemical Co., Ltd.) equipped with a stirring blade or a rotation / revolution mixer can be used. Further, heat of 40 to 100 ° C. may be applied if necessary.

When (a) the solvent used when synthesizing the polyamic acid and (b) the organic solvent are different, the solvent in the synthesized polyamic acid solution was removed by a method of reprecipitation or distilling off the solvent. After obtaining a) polyamic acid, (b) an organic solvent and, if necessary, other additives may be added and mixed by stirring in a temperature range of room temperature to 80 ° C.

The resin composition of the present invention can be used to form a transparent substrate for 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 to form a thin film transistor (TFT) substrate, a color filter substrate, a transparent conductive film (ITO, Indium Tin Oxide) substrate, and the like.

[Polyimide molded product]
The polyimide molded product of the present invention can be obtained by applying the resin composition of the present invention to a base material, drying it to form a resin film, and heat-treating (imidizing) the resin film. In addition, the polyimide molded product can be used in the form of a film, a film, a sheet, or the like, depending on the intended use and purpose.

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

(1) Coating Step The coating method used in the coating step is not particularly limited, and a known coating method can be appropriately selected and used according to a desired coating thickness, viscosity of the resin composition, and the like. Specifically, application methods such as doctor blade knife coater, air knife coater, roll coater, rotary coater, flow coater, die coater, bar coater, spin coat, spray coat, dip coat, etc., screen printing and gravure printing. It is also possible to apply printing technology represented by the above.

The base material to 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. For example, a base material made of glass, a silicon wafer or the like, a support made of PET (polyethylene terephthalate), OPP (stretched polypropylene) or the like can be mentioned. Further, in the film-shaped polyimide molded body, an object to be coated made of glass, a silicon wafer or the like can be mentioned, and in the film-shaped or sheet-shaped polyimide molded body, a support made of PET (polyethylene terephthalate), OPP (stretched polypropylene) or the like can be mentioned. Can be mentioned. Other substrates include glass substrates, metal substrates such as stainless steel, alumina, copper, and nickel, polyethylene glycol terephthalate, polyethylene glycol naphthalate, polycarbonate, polyimide, polyamideimide, polyetherimide, polyetheretherketone, and polyethersulfone. Resin substrates such as polyphenylene sulfone and polyphenylene sulfide are used.

The coating thickness of the resin composition of the present invention is appropriately adjusted according to the thickness of the target molded product and the ratio of the resin non-volatile component in the resin composition, but is usually about 1 to 1000 μm. The resin non-volatile component is obtained by the above-mentioned measuring method. The coating step is usually carried out at room temperature, but the resin composition may be heated in the range of 40 to 80 ° C. for the purpose of lowering the viscosity and improving workability.

Following the coating step, (2) drying step is performed. The drying step is performed for the purpose of removing the organic solvent. Equipment such as a hot plate, a box-type dryer, and a conveyor-type dryer can be used for the drying step, and the drying step is preferably performed at 80 to 200 ° C., more preferably 100 to 150 ° C.

Subsequently, (3) heating step is performed. The 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 step is performed using equipment such as an inert gas oven, a hot plate, a box-type dryer, and a conveyor-type dryer. This step may be performed at the same time as the above-mentioned (2) drying step, or may be performed sequentially.

The heating step may be performed in an air atmosphere, but from the viewpoint of safety and oxidation prevention, it is recommended to perform the heating step in an inert gas atmosphere. Examples of the inert gas include nitrogen and argon. The heating temperature (b) depends on the type of the organic solvent, but is preferably 250 ° C to 400 ° C, more preferably 300 to 350 ° C. If it is lower than 250 ° C., imidization becomes insufficient, and if it is higher than 400 ° C., the transparency of the polyimide molded product may be lowered or the heat resistance may be deteriorated. The heating time is usually about 0.5 to 3 hours.

Further, depending on the intended use and purpose of the polyimide molded product, a peeling step of (4) peeling the cured film from the base material is required after the (3) heating step. This peeling step is carried out after cooling the molded product on the base material to about room temperature to about 50 ° C. In order to easily carry out the peeling operation, a mold release agent may be applied to the base material, if necessary, before applying the resin composition of the present invention.
Examples of the mold release agent include vegetable oil-based, silicon-based, fluorine-based, and alkyd-based mold release agents.

The obtained polyimide molded product can also form a pattern by a resist process depending on the application. In the resist process, for example, after (3) heating step or (4) peeling step, resist is applied, and a pattern is formed by exposure, development, or the like.
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 sputtering etching are also possible. After forming the pattern, the resist is peeled off from the polyimide molded product 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 method for producing a polyimide molded product of the present invention is useful when producing a polyimide molded product having a thickness of 1 to 500 μm. In particular, it is preferable to produce a polyimide molded product having a film thickness of 1 to 100 μm in order to further improve the effect of the present invention.

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

Regarding the transparency of the polyimide molded product of the present invention obtained by the above production method, the light transmittance at a wavelength of 400 nm or more is preferably 70% or more at a film thickness of 10 μm, and more preferably 75% or more.
The birefringence of the polyimide molded product of the present invention is preferably 0.12 or less, more preferably 0.08 or less. It is a value that is evaluated to have sufficient transparency and low birefringence as a polyimide molded body used in the fields of optical communication and display devices.

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

The glass transition temperature (Tg) of the polyimide molded product of the present invention is preferably 250 to 400 ° C, more preferably 300 to 400 ° C. It is a value that is evaluated to have sufficient heat resistance as a polyimide molded product used in the optical communication field and the display device field.
The glass transition temperature can be measured by the method described in Examples.
The CTE and glass transition temperature (Tg) are determined by TMA measurement by TMA / SS6000 manufactured by Seiko Instruments Inc.

Regarding 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 1.7. ~ 5.5 GPa is more preferable. If the elastic modulus is larger than 6.0 GPa, the substrate tends to warp after curing.

The tensile strength (breaking strength) is preferably 150 to 300 MPa, more preferably 150 to 200 MPa. If the tensile strength is less than 150 MPa, the film is brittle and may be difficult to handle when used as a base material.
The elongation at break is preferably 5% or more, more preferably 10% or more. If the elongation at break is less than 5%, the bending stress when the polyimide molded product is used as the base material is weak, and the reliability of the base material is lowered.

All of these mechanical properties can be obtained by a tensile test of a tensile test device. If the polyimide molded product has these mechanical characteristics, it is said that the polyimide molded product has sufficient toughness as a polyimide molded product used in the fields of optical communication and display devices, and can be practically used.

[Transparent substrate / protective film / electronic components]
The transparent substrate and the protective film of the present invention are characterized by being made of the above-mentioned 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 temporary fixing base material, dried and heated, and then the resist process can be carried out according to the intended use as a transparent substrate.
Further, the resin composition of the present invention can be applied to a temporary fixing base material, dried and heated, peeled from the temporary fixing base material, and used as a protective film.

The transparent substrate and protective film of the present invention have sufficient transparency, have a small CTE, a low elastic modulus, and a small birefringence. Therefore, liquid crystal displays, organic electroluminescence displays, field emission displays, electronic papers, etc. It can be used as a display device.

Specifically, the transparent substrate of the present invention is used as 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 Tin Oxide), and the like. be able to. When the transparent substrate of the present invention is used, it is considered that the breakage resistance, which has been a problem of the conventional glass substrate, can be improved, and the weight and thickness of the substrate can be reduced.

Further, since the transparent substrate of the present invention has a small CTE, it is possible to prevent deterioration of the positioning accuracy in the heating process at the time of forming the TFT, and since it has high transparency and small birefringence, it is excellent in visibility.
Further, since the transparent substrate of the present invention has a small 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 protective film for a color filter, and the like. The protective film of the present invention can also be used as a surface protective film for a solar cell or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1
56 g (564 mmol) of N-methylpyrrolidone (NMP) and 3.43 g (30 mmol) of 1,4-diaminocyclohexane were placed in a 0.2 liter flask equipped with a stirrer and a thermometer, stirred, and then in a dryer. 8.39 g (28.5 mmol) of 3,3', 4,4'-biphenyltetracarboxylic dianhydride heated and dehydrated and ring-closed (160 ° C., 24 hours), and 4,4'-oxydiphthalic acid dianhydride 0.47 g (1.5 mmol) was added, and the mixture was completely dissolved by heating and stirring in a water bath at 70 ° C. for 10 minutes. Then, the mixture was stirred for about 70 hours until the molecular weight became constant to obtain a polyamic acid solution.

The weight average molecular weight and the degree of dispersion of the obtained polyamic acid were determined by gel permeation chromatography (GPC) method standard polystyrene conversion. The weight average molecular weight was 31,000 and the dispersity was 2.4.

The measurement conditions for the weight average molecular weight and the degree of dispersion are as follows.
Measuring device: Detector L4000UV manufactured by Hitachi, Ltd.
Pump: L6000 manufactured by Hitachi, Ltd.
C-R4A Chromatopac manufactured by Shimadzu Corporation
Measurement conditions: Column Gelpack GL-S300MDT-5 x 2 from Hitachi Kasei Kogyo Co., Ltd. Eluent: THF / DMF = 1/1 (volume ratio)
LiBr (0.03 mol / l), H ₃ PO ₄ (0.06 mol / l)
Flow velocity: 1.0 ml / min, Detector: UV270 nm
The measurement was carried out 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 at which it was easy to apply. The residual solid content (NV) of this resin composition was measured and found 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 above-mentioned method for measuring the resin non-volatile content.

This diluted solution was filtered using a 5 μm filter (SLLS025NS manufactured by Millipore), the obtained resin composition was spin-coated on a silicon wafer, dried at 120 ° C. for 3 minutes, and had a film thickness of 14 to 18 μm. A resin film was formed. This was further heated in a nitrogen atmosphere using an inert gas oven to obtain a cured film having a film thickness of 10 μm.
In addition, salt formation during the synthetic reaction was evaluated. Evaluation was performed with A as the case where no salt was formed or when the formation of the salt could be confirmed but easily dissolved in the solvent in the resin composition, and as B when the salt was formed and not easily dissolved in the solvent. The resin composition of Example 1 was B.

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

The obtained cured film was evaluated as follows.
(Evaluation of birefringence)
Using the Metricon 2010 model manufactured by Seki Technotron Co., Ltd., the values of the refractive index (TE) at Y polarization and the refractive index (TM) at X polarization at a wavelength of 1300 nm were measured, and the values were compounded by (Equation 1). I asked for refraction.
Birefringence = TE-TM (Equation 1)
A birefringence of 0.08 or less was designated as A (particularly good), a birefringence greater than 0.08 and 0.12 or less was designated as B (good), and a birefringence greater than 0.12 was designated as C (not good).

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

The light transmittance was determined by measuring the light transmittance with a wavelength of 400 nm or more using U-3310 (a spectrophotometer manufactured by Hitachi, Ltd.) and converting it to 10 μm using the Law of Lambert-Beer.

CTE was measured using a thermomechanical measuring device of TMA / SS6000 manufactured by Seiko. Specifically, the cured film was cut into a size of 2 mm × 3 cm, and the temperature was raised to 30 to 420 ° C. (heating rate 5 ° C./min) using a thermomechanical measuring device of TMA / SS6000 manufactured by Seiko Co., Ltd. while applying a load of 10 g / min. ) Heated. At that time, the slope of the elongation rate of the cured film between 100 and 200 ° C. was measured and used as CTE.
When the CTE was 30 ppm / K or less, it was designated as A (particularly good), when it was larger than 30 ppm / K and 45 ppm / K or less, it was designated as B (good), and when it was larger than 45 ppm / K, it was designated as C (not good).

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

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

(Evaluation of chemical resistance)
The obtained cured membrane was immersed in a solution of dimethyl sulfoxide: monoethanolamine = 30: 70 at 80 ° C. for 10 minutes to evaluate the chemical resistance of the cured membrane. The cured film without cracks was evaluated as A, and the cured film with cracks was evaluated as B.
In addition, the change in film thickness before and after the chemical resistance evaluation test was designated as A, the change in film thickness of ± 0.3 or more and ± 0.5 μm was designated as B, and the change in film thickness greater than ± 0.5 μm was designated as C. ..

Examples 2-8, Comparative Examples 1-5
Polyamic acids were synthesized in the same manner as in Example 1 except that amines, acids and their amounts were changed as shown in Table 1, resin compositions and cured films were prepared, and these were evaluated.
Amines 1 to 3 and acids 1 to 4 are as follows.
Amine 1: 1,4-diaminocyclohexaneamine 2: 3,3'-bis (trifluoromethyl) benzidineamine 3: p-phenylenediamine acid 1: 3,3', 4,4'-biphenyltetracarboxylic dian acid 2 : 3,3', 4,4'-tetracarboxydiphenyl etheric acid 3: cyclohexanetetracarboxylic dianhydride

The cured films obtained in Examples 1 to 8 showed good transmittance even after being heat-treated at a high temperature of 300 ° C. or higher, had a small CTE, a small birefringence, and a small elastic modulus. 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.
Furthermore, it was found that the cured films obtained in Examples 1 to 8 were all excellent in chemical resistance.

On the other hand, as in Comparative Example 1, when 3,3', 4,4'-tetracarboxydiphenyl ether was not contained, the elastic modulus and birefringence became large.
Further, as in Comparative Example 2, when 3,3', 4,4'-biphenyltetracarboxylic acid was not used, the CTE became large.

Further, as in Comparative Examples 3 to 5, obtained from a combination of 1,4-diaminocyclohexane, 3,3', 4,4'-biphenyltetracarboxylic acid and 3,3', 4,4'-tetracarboxydiphenyl ether. Without the polyimide precursors obtained, the resulting cured film could not satisfy all of transparency, CTE, mechanical properties and birefringence.

The polyimide molded product of the present invention can be used as a display base material, a protective film, or the like.

Although some embodiments and / or embodiments of the present invention have been described above in detail, those skilled in the art will be able to demonstrate these embodiments and / or embodiments without substantial departure from the novel teachings and effects of the present invention. It is easy to make many changes to the examples. Therefore, many of these modifications are within the scope of the invention.

Claims (12)

Copolymer der having a structural unit represented by the following formula (I) and (II) is, the molar ratio of the structural unit represented by the formula (I) and (II), (I) :( II) = 30: 70-80: 20 der is, a polyimide precursor having a weight average molecular weight of 10,000 to 500,000,
A polyimide precursor used for producing a molded product having a breaking strength of 150 to 300 MPa and a birefringence of 0.08 or less (however, the weight average molecular weight is 10,000 to 500,000, and the above formula ( Excluding polyimide precursors in which the molar ratio of structural units represented by I) is less than 40 mol%).

The resin composition having the polyimide precursor according to claim 1. The resin composition according to claim 2, which contains 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 product comprising a step of applying the resin composition according to any one of claims 2 to 4 onto a substrate and drying to form a resin film, and a step of heat-treating the dried resin film. It ’s a manufacturing method ,
The breaking strength of the polyimide molded product is 150 to 300 MPa, and the birefringence is 0.08 or less.
A method for manufacturing a polyimide molded product . A polyimide molded product obtained by the production method according to claim 6 .
The breaking strength is 150 to 300 MPa, and the birefringence is 0.08 or less.
Polyimide molded body . A transparent substrate made of the polyimide molded product according to claim 7. A protective film made of the polyimide molded product 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 having 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.