Method for manufacturing flexible electronic devices

Abstract

The present invention makes it possible to reuse a provisional support substrate for the production of a flexible electronic device and thereby reduces production costs.　A production method for a flexible electronic device, the production method being characterized by including (a) a step for cleaning an inorganic substrate with an aqueous solution A, (b) a step for forming a polymer film on all or a part of at least one surface of the inorganic substrate to produce a laminate, (c) a step for forming an electronic device on the polymer film of the laminate, and (d) a step for peeling the electronic device and the polymer film off the inorganic substrate, the aqueous solution A being one of (1)–(3).　(1) The aqueous solution A is an alkaline aqueous solution that contains no more than 10 ppm of polyvalent metal ions that have a valence of two or more. (2) An alkaline aqueous solution that includes at least one compound selected from the group that consists of ammonia, urea, and organic alkali compounds. (3) An aqueous solution that includes at least one compound selected from the group that consists of perchlorate alkali metal salts and permanganate alkali metal salts.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing flexible electronic devices such as flexible displays, flexible sensor arrays, stretchable electronic devices, and the like.

[0002] Functional elements (devices) such as semiconductor elements, MEMS elements, and display elements are used as electronic components in information and communication equipment (broadcasting equipment, mobile radio, portable communication equipment, etc.), radar, high-speed information processing equipment, etc., and these have traditionally been formed or mounted on inorganic substrates such as glass, silicon wafers, and ceramic substrates. However, in recent years, with the demand for lighter, smaller, thinner, and more flexible electronic components, attempts have been made to form various functional elements on polymer films.

[0003] The ideal method for forming various functional elements on the surface of a polymer film is to use a roll-to-roll process, which takes advantage of the flexibility inherent in polymer films. However, in industries such as the semiconductor, MEMS, and display industries, processing techniques targeting rigid, planar substrates such as wafers or glass substrates have been the norm. To achieve this, various processes have been developed to form various functional elements on the surface of a polymer film using existing infrastructure. These processes involve using a rigid inorganic substrate (such as a glass plate, ceramic plate, silicon wafer, metal plate, or metal foil) as a temporary support, applying and drying a polymer solution or precursor solution to form a film, forming the desired elements (functional elements) on the film, and then peeling it off the support. Other processes involve temporarily fixing a film to an inorganic support, forming the desired elements on the film, and then peeling it off the support (Patent Documents 1 to 3).

[0004] Generally, relatively high temperatures are often used in the process of forming functional devices. For example, temperatures ranging from approximately 120 to 500°C are used in the formation of functional devices such as polysilicon and oxide semiconductors. In the fabrication of low-temperature polysilicon thin-film transistors, heating to approximately 450°C may be required for dehydrogenation. The fabrication of hydrogenated amorphous silicon thin films also requires temperatures ranging from approximately 150 to 250°C. While the temperature ranges exemplified here are not particularly high for inorganic materials, they are quite high for polymer films and adhesives commonly used to bond polymer films. In the aforementioned method of bonding a polymer film to an inorganic substrate and then peeling it off after forming functional devices, the polymer film and adhesives and pressure-sensitive adhesives used for bonding must have sufficient heat resistance. However, in reality, only limited polymer films can withstand such high temperatures. Furthermore, there are currently very few conventional bonding adhesives and pressure-sensitive adhesives with sufficient heat resistance.

[0005] The process described above, in which a polymer solution or precursor solution is applied to an inorganic support and dried to form a film, and then the desired device is formed on the film and then peeled off from the support, was devised because a heat-resistant adhesive method for temporarily attaching a polymer film to an inorganic substrate was unavailable. However, the polymer film obtained by this method is firmly adhered to the inorganic substrate, and is therefore brittle and easily tears when attempting to peel it off, often destroying the functional device. Peeling large-area devices is particularly difficult, resulting in insufficient productivity.

[0006] In view of these circumstances, the present inventors have proposed a laminate of a polymer film and a support for forming a functional element, in which a polyimide film, which is highly heat-resistant, tough, and can be thinned, is bonded to a support (inorganic layer) made of an inorganic material via a coupling agent (Patent Document 4).

[0007] Polymer films are inherently flexible materials and can withstand slight stretching, bending, and extension. However, electronic devices formed on polymer films often have fine structures that combine inorganic conductors and semiconductors in a predetermined pattern. Stress caused by minute stretching, bending, and extension can destroy these structures and impair the device's performance. Such stress is likely to occur when the electronic device, along with the polymer film, is peeled off from the inorganic substrate.

[0008] Therefore, the inventors have made further improvements and have proposed a technology in which an inorganic substrate that has been treated with a coupling agent is partially inactivated to form areas with high and low activity of the coupling agent, and when a polymer film is bonded to it, good adhesion areas that are relatively difficult to peel and easy peel areas that are relatively easy to peel are created, an electronic device is formed in the easy peel area, and an incision is made in the boundary between the easy peel area and the good adhesion area of ​​the polymer film to peel off only the easy peel area, thereby enabling peeling with reduced stress on the electronic device (Patent Document 5).

[0009] On the other hand, several proposals have been made regarding the reuse of inorganic substrates and glass substrates used in these processes. For example, a technology has been disclosed in which a polyimide film having a specific chemical structure is formed into a glass-like material, the polyimide film is peeled off from the glass substrate, and the glass substrate is then washed with an alkali, thereby enabling the reuse of glass (Patent Document 6). In addition, a technology has been proposed in which a polyimide precursor is applied to a glass substrate, and a polyimide film is formed under specific conditions. After peeling the polyimide film from the glass substrate, the glass substrate is subjected to solvent cleaning, alkaline solution cleaning, UV cleaning, ozone cleaning, ultrasonic cleaning, cleaning with a detergent, hydrofluoric acid cleaning, asher treatment, heat treatment, or puffing treatment, thereby reusing the glass (Patent Document 7). Furthermore, a technology has been proposed in which polyimide and a glass substrate are bonded together using a specific method, and the glass substrate can be reused by washing it with a 10% sodium hydroxide solution after use (Patent Document 8). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 58-91446 [Patent Document 2] Japanese Patent Application Publication No. 10-125930 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-243943 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-283262 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-010342 [Patent Document 6] Patent No. 6259028 [Patent Document 7] Japanese Patent Application Laid-Open No. 2015-199350 [Patent Document 8] Patent No. 6447135 Summary of the Invention [Problem to be solved by the invention]

[0011] According to the techniques described in Patent Documents 1 to 3 mentioned above, peeling off the polymer film is very difficult, and after peeling off the polymer film, the end of the polymer film or residues of adhesive or the like remain firmly adhered to the inorganic substrate, making it difficult to reuse the inorganic substrate. Furthermore, the laminates described in Patent Documents 4 and 5 above enable bonding of a polymer film to an inorganic substrate without using so-called adhesives or pressure-sensitive adhesives, and furthermore, the polymer film does not peel off even when exposed to the high temperatures required for fabricating thin-film devices. Therefore, the laminates can be used in processes for directly forming electronic devices on inorganic substrates such as conventional glass plates and silicon wafers. However, inorganic substrates used as temporary support substrates, so to speak, retain traces of the processes used to bond the polymer film and residues of the polymer film that have not peeled off, making them difficult to reuse.

[0012] Patent Documents 6 to 8 propose techniques for the reuse of such inorganic substrates, primarily glass substrates. Patent Document 6 claims that glass substrates can be reused by alkaline cleaning, but does not disclose specific alkaline cleaning conditions. Patent Document 7 also discloses that glass substrates can be reused by various cleaning processes, including alkaline cleaning, as well as heat treatment and buffing, but similarly does not disclose specific processing conditions. Heat treatment and ashing are also exemplified, but these processes are effective in removing organic components but are less effective in removing inorganic components. Furthermore, the organic components that were originally attached often carbonize and become firmly attached. Puffing treatments are likely to scratch the glass surface, limiting the range of reuse possible, or at least making it difficult to reuse the substrate for the same purpose. Patent Document 8 discloses a 20-hour immersion process in a 10% sodium hydroxide solution at room temperature, which is sufficient to remove organic residues. However, this level of strong alkali has the ability to dissolve the glass substrate surface and is likely to over-etch the glass surface, potentially resulting in loss of flatness. In particular, if organic or inorganic residues are present on the surface to be treated, the dissolution of the glass surface may become uneven, causing minute defects such as microcracks, which may make the glass itself more susceptible to cracking. [Means for solving the problem]

[0013] In order to solve this problem, the inventors have conducted extensive research into methods for reusing inorganic substrates that serve as temporary support substrates. As a result, they have discovered an inorganic substrate processing technology that can efficiently remove residues from previous processes remaining on the inorganic substrate and can finish the processed surface to a quality that allows it to be reused, and have completed this invention.

[0014] That is, the present invention has the following configuration. [1] (a) washing an inorganic substrate with aqueous solution A; (b) forming a polymer film on a part or all of at least one surface of the inorganic substrate to obtain a laminate; (c) forming an electronic device on the polymer film of the laminate; (d) peeling the electronic device together with the polymer film from the inorganic substrate. and the aqueous solution A is any one of the following (1) to (3): (1) Aqueous solution A is an alkaline aqueous solution, and the content of divalent or higher polyvalent metal ions contained in the alkaline aqueous solution is 10 ppm or less. (2) An alkaline aqueous solution containing one or more compounds selected from the group consisting of ammonia, urea, and organic alkaline compounds. (3) An aqueous solution containing one or more compounds selected from the group consisting of alkali metal perchlorates and alkali metal permanganates. [2] The method for producing a flexible electronic device according to [1], wherein the alkaline aqueous solution in (1) is an aqueous solution of sodium hydroxide or potassium hydroxide. [3] A method for producing a flexible electronic device according to [1] or [2], characterized in that after the step (a) of cleaning the inorganic substrate with an alkaline aqueous solution in (1), the method further comprises a step of rinsing with neutral cleaning water containing 10 ppm or less of divalent or higher polyvalent metal ions. [4] The method for producing a flexible electronic device according to any one of [1] to [3], wherein the hydroxide concentration in the alkaline aqueous solution in (1) is higher than the carbonate concentration. [5] The method for producing a flexible electronic device according to [1], wherein the organic alkali compound in (2) is an ammonium hydroxide compound represented by the general formula (4). General formula (4) {(R 1 )3-N + -R 2}·OH - [In general formula (4), R 1 is H or a C1-8 alkyl group, R 2 represents H, a C1-8 alkyl group, or a C1-8 hydroxyalkyl group, and R 1may be the same or different.] [6] The method for producing a flexible electronic device according to [1] or [5], wherein the aqueous solution A in (2) further contains an alkali metal hydroxide. [7] In the above (2), the (a) washing step is A method for producing a flexible electronic device according to [1], [5] or [6], characterized by comprising a step of placing an inorganic substrate, urea and water in a sealed container and heating the container to a temperature range of 60°C or higher and 150°C or lower. [8] After the step (d) of peeling the electronic device together with the polymer film from the inorganic substrate, (a)' washing the inorganic substrate with aqueous solution A; (b)' A step of forming a polymer film on a part or all of at least one surface of the inorganic substrate to obtain a laminate; (c)' forming an electronic device on the polymer film of the laminate; (d)' A step of peeling the electronic device together with the polymer film from the inorganic substrate. The method for producing a flexible electronic device according to any one of [1] to [7], wherein the aqueous solution A is any one of the following (1) to (3): (1) Aqueous solution A is an alkaline aqueous solution, and the content of divalent or higher polyvalent metal ions contained in the alkaline aqueous solution is 10 ppm or less. (2) An alkaline aqueous solution containing one or more compounds selected from the group consisting of ammonia, urea, and organic alkaline compounds. (3) An aqueous solution containing one or more compounds selected from the group consisting of alkali metal perchlorates and alkali metal permanganates. [9] The method for producing a flexible electronic device according to any one of [1] to [8], wherein the laminate is obtained by applying a polymer solution to an inorganic substrate and drying it to form a polymer film.

[10] The method for producing a flexible electronic device according to [9], wherein the polymer solution is a polyimide solution, and is obtained by applying the solution to an inorganic substrate and drying it to form a polyimide film.

[11] The method for producing a flexible electronic device according to any one of [1] to

[10] , characterized in that the laminate is obtained by applying a polyamic acid solution to an inorganic substrate, followed by drying and chemical reaction to form a polyimide film.

[12] The method for producing a flexible electronic device according to any one of [1] to [8], wherein the laminate is obtained by bonding a polymer film and an inorganic substrate via a silane coupling agent.

[13] The method for producing a flexible electronic device according to any one of [1] to [8], wherein the laminate is obtained by bonding a polymer film and an inorganic substrate with an adhesive.

[14] The method for producing a flexible electronic device according to any one of [1] to [8], characterized in that the laminate is obtained by adhering a film containing a solvent and polyamic acid to an inorganic substrate, followed by drying and chemical reaction to form a polyimide film.

[0015] The present invention preferably further includes the following configuration.

[15] The method for producing a flexible electronic device according to [1], wherein the organic alkaline compound in (2) is an amino alcohol.

[13] The method for producing a flexible electronic device according to [1], wherein the aqueous solution A in (2) contains at least monoaminoethanol and sodium hydroxide. [Effects of the Invention]

[0016] According to the present invention, by subjecting an inorganic substrate, preferably a glass substrate, to a predetermined treatment including cleaning with a predetermined aqueous solution A, the glass substrate can be reused repeatedly, thereby significantly reducing variable costs in the production costs of flexible electronic devices. As mentioned above, various techniques have been proposed for cleaning inorganic substrates such as glass substrates with aqueous solution A to remove organic matter remaining on the surface of the inorganic substrate and reuse the inorganic substrate. Here, cleaning with aqueous solution A hydrolyzes organic matter, particularly polymeric compounds, and converts them into water-soluble alkali salts, mainly of carboxylic acids, thereby cleaning the surface of the inorganic substrate.

[0017] However, the inventors of the present invention found that foreign matter adhered to the inner wall surface of the cleaning tank during the rinsing process after cleaning, and through analysis, they found that the adhered foreign matter was a water-insoluble substance consisting of organic matter and metals with a valence of 2 or higher. In other words, it is believed that the foreign matter was formed by polyvalent metal ions with a valence of 2 or higher present in the system forming insoluble salts with the organic matter that had been water-soluble during the alkaline cleaning treatment, and then precipitating in the tank. It is likely that when excessive strong alkali is present, these insolubilizing effects do not become apparent, or even if they do become apparent, they do not cause problems, but it is assumed that this phenomenon becomes apparent when the alkali concentration decreases due to dilution in the rinsing process after cleaning. Naturally, these foreign particles adhering to the inner walls of the cleaning tank are likely to adhere to the surface of the inorganic substrate being cleaned, causing re-contamination.

[0018] That is, in the present invention, aqueous solution A is any one of the above (1) to (3). In (1), keeping the concentration of divalent or higher cations, preferably metal ions, in the alkaline aqueous solution used in the cleaning treatment within a predetermined range has the effect of suppressing the formation of insoluble salts of such organic substances and polyvalent metals and preventing recontamination of the cleaned inorganic substrate. The polyvalent metal ions that are likely to be mixed into the system are alkaline earth metal ions, and calcium ions and magnesium ions in particular exist as impurities in alkaline compounds and must therefore be intentionally removed.

[0019] The inorganic alkaline compound used in the alkaline aqueous solution of the present invention is preferably sodium hydroxide or potassium hydroxide, which are available inexpensively as industrial raw materials.

[0020] It is generally known that aqueous solutions of these hydroxides absorb carbon dioxide in the air to produce sodium carbonate and potassium carbonate. In the present invention, in order to maintain the hydrolysis of organic matter by the alkaline aqueous solution, it is preferable to control the hydroxide concentration in the cleaning system so that it is greater than the carbonate concentration. If the carbonate concentration exceeds the hydroxide concentration, the hydrolysis action decreases, and the water-soluble organic matter is more likely to form insoluble salts with polyvalent metal ions, making the cleaned object more susceptible to recontamination. Therefore, the present invention realizes a manufacturing method for obtaining highly clean inorganic substrates by appropriately controlling the carbonate concentration, preferably together with the polyvalent metal ion concentration.

[0021] In (2), divalent or higher metal ions exist as impurities in inorganic alkali, and although it is possible to reduce their content through refining or other methods, completely removing them is difficult from a cost perspective, so a method of cleaning with an alkaline solution containing one or more compounds selected from the group consisting of ammonia, urea, and organic alkali compounds is used. This method makes it relatively easy to prevent the incorporation of divalent metal ions as impurities. That is, when a cleaning solution is prepared by combining an inorganic alkali and an organic alkali compound, it is difficult to completely prevent the inclusion of divalent metals, but the organic alkali compound has the effect of preventing the dissolved organic matter from becoming insoluble, thereby preventing recontamination. One embodiment of the present invention includes a process of placing an inorganic substrate, urea, and water in a sealed container and heating the container to a temperature between 60°C and 150°C. When heated in the presence of water, urea decomposes to form ammonia, which exhibits a strong cleaning effect. This method allows the use of odorless and harmless urea at least during the preparation process. Since the ammonia is essentially in aqueous solution during recovery, it can be neutralized with, for example, hydrochloric acid to recover a solid such as ammonium chloride. This method allows the removal of ammonia, hydrochloric acid, and ammonium chloride by evaporation or sublimation upon heating, facilitating the disposal of the substrate for reuse. Naturally, this method is significantly safer than hydrazine, which is similar in elemental composition to urea. As a result, by using an alkaline solution containing one or more compounds selected from the group consisting of ammonia, urea, and organic alkaline compounds specified in the present invention for cleaning inorganic substrates that have been used once, inorganic substrates, preferably glass substrates, can be reused repeatedly, thereby significantly reducing variable costs in the manufacturing process of flexible electronic devices. The heating temperature is preferably 70°C or higher, more preferably 80°C or higher. It is also preferably 140°C or lower, more preferably 130°C or lower.

[0022] In addition, (3) is a method of cleaning with an aqueous solution of one or more compounds selected from the group consisting of alkali metal perchlorates and alkali metal permanganates. In method (3), no precipitation of insoluble salts derived from divalent metal ions is observed. This is presumably because the strong oxidizing properties of perchlorates and permanganates decompose the organic matter to a sufficiently low molecular weight, preventing it from exerting sufficient adhesive strength to reattach to the tank wall or inorganic substrate. As a result, by using these chemical solutions specified by the present invention to clean inorganic substrates that have been used once, inorganic substrates, preferably glass substrates, can be reused, significantly reducing variable costs in the manufacturing process of flexible electronic devices. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention specifies a method for treating an inorganic substrate in a manufacturing method for obtaining a flexible electronic device by forming an electronic device on the polymer film surface of a laminate composed of a polymer film and an inorganic substrate, and then peeling the electronic device together with the polymer film from the inorganic substrate.

[0024] <Electronic Devices> The present invention relates to a method for manufacturing an electronic device. The term "electronic device" as used herein refers to a general term for an electronic circuit module or system that achieves some function by combining a single or multiple electronically active elements, such as transistors and diodes; passive elements, such as resistors, capacitors, and inductors; transducers that convert external stimuli into electrical signals or convert electrical signals into other energy; power supply elements; and storage elements. However, because the present invention relates to a method for manufacturing a flexible electronic device, it is preferable that the electronic device has a planar shape. Active elements, in particular, devices using thin-film semiconductors, such as thin-film transistors, are preferred. Furthermore, the electronic devices may be connected to each other via flexible or stretchable electrical connections. More specifically, examples of such electronic devices include flexible display elements, flexible sensor arrays, flexible photoelectric conversion elements, flexible thermoelectric conversion elements, flexible transducers, MEMS elements, computing elements, and memory elements. Flexible display devices include organic electroluminescence (EL) display devices, liquid crystal display devices, micro-light-emitting diode (LED) display devices, electrophoretic display devices, and quantum dot display devices, as well as color filter arrays and light-guiding films used in these display devices.

[0025] <Inorganic substrate> In the present invention, an inorganic substrate is used as a support for the polymer film. The inorganic substrate may be any plate-shaped substrate that can be used as a substrate made of an inorganic material, such as a glass substrate, a ceramic substrate, a semiconductor wafer, a metal plate, a metal foil, a laminate or composite of these, or a substrate containing fibers of these.

[0026] Glass substrates that can be used as inorganic substrates include quartz glass, high silica glass (96% silica), soda-lime glass, lead glass, aluminoborosilicate glass, borosilicate glass (Pyrex (registered trademark)), borosilicate glass (alkali-free), borosilicate glass (microsheet), aluminosilicate glass, etc. Among these, those with a linear expansion coefficient of 5 ppm / °C or less are desirable, and commercially available products such as liquid crystal glass "Corning (registered trademark) 7059," "Corning (registered trademark) 1737," and "EAGLE" manufactured by Corning Incorporated, "AN100" manufactured by Asahi Glass Co., Ltd., "OA10" manufactured by Nippon Electric Glass Co., Ltd., and "AF32" manufactured by SCHOTT are desirable. Furthermore, a substrate having a thin film of a metal such as chromium, nickel, nichrome, molybdenum, or tungsten, or a metal oxide, metal nitride, silicon nitride, aluminum nitride, or silicon carbide formed on the surface of such a glass substrate may also be used.

[0027] The planar portion of the inorganic substrate is preferably sufficiently flat. Specifically, the surface roughness Ra is, for example, 10 nm or less, preferably 3 nm or less, and more preferably 0.9 nm or less. The PV value of the surface roughness is, for example, 50 nm or less, preferably 20 nm or less, and more preferably 5 nm or less. If the surface is rougher than this, the adhesive strength between the polymer film and the inorganic substrate may be insufficient. The thickness of the inorganic substrate is not particularly limited, but from the viewpoint of ease of handling, it is preferably 10 mm or less, more preferably 3 mm or less, and even more preferably 1.3 mm or less. The lower limit of the thickness is not particularly limited, but for example, it is 0.07 mm or more, preferably 0.15 mm or more, and more preferably 0.3 mm or more.

[0028] The inorganic substrate in the present invention preferably has an area of ​​at least 4900 cm 2 The inorganic substrate of the present invention is preferably substantially rectangular with at least a short side of 700 mm or more. In the present invention, the area of ​​the inorganic substrate is preferably 5000 cm 2 More preferably, it is 10,000 cm 2More preferably, 18,000 cm 2 The length of the short side of the rectangular inorganic substrate in the present invention is preferably 730 mm or more, more preferably 840 mm or more, and even more preferably 1000 mm or more. Here, "substantially rectangular" means that corners of the rectangle, rounded edges, notches, orientation flats, etc. are allowed.

[0029] <Polymer film> Examples of the polymer film that can be used in the present invention include films of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, wholly aromatic polyesters, other copolymer polyesters, polymethyl methacrylate, other copolymer acrylates, polycarbonate, polyamide, polysulfone, polyethersulfone, polyether ketone, polyamideimide, polyetherimide, aromatic polyimide, alicyclic polyimide, fluorinated polyimide, cellulose acetate, cellulose nitrate, aromatic polyamide, polyvinyl chloride, polyphenols, polyarylate, polyphenylene sulfide, polyphenylene oxide, polystyrene, polybenzazole, polyimidebenzazole, and liquid crystal polymers. Of these polymer films, polymer films obtained by condensation polymerization reactions (condensation polymer films) are preferred in the present invention. Particularly effective and useful in the present invention are polymers with heat resistance of preferably 100°C or higher, more preferably 150°C or higher, i.e., so-called engineering plastic films. Here, heat resistance refers to the property of a glass transition temperature or heat distortion temperature of 100°C or higher (preferably 150°C or higher). Condensation polymerization polymer films (condensation polymer films) preferably used in the present invention include polyester, polyamide, polyamideimide, polyimide, polybenzazole, polyimidebenzazole, polyethylene naphthalate film, and liquid crystal polymer film, and more preferably polyimide film, polyethylene naphthalate film, or liquid crystal polymer film.

[0030] Polymer films preferably used in the present invention are polyimide films, polyamide films, polyamideimide films, polybenzoxazole films, and polyimidebenzoxazole films, and aromatic polyimides, alicyclic polyimides, polyamideimides, polyetherimides, etc. When the present invention is used particularly for producing flexible display elements, it is preferable to use colorless and transparent polyimide-based resin films, but this is not particularly limited when forming rear elements for reflective or self-luminous displays.

[0031] Generally, polyimide films are obtained by applying a polyamic acid (polyimide precursor) solution obtained by reacting diamines with tetracarboxylic acids in a solvent to a support for producing the polyimide film, drying the solution to form a green film (also called a "precursor film" or "polyamic acid film"), and then subjecting the green film to high-temperature heat treatment on the support for producing the polyimide film or after peeling it off from the support to cause a dehydration ring-closing reaction. Examples of polyimide films preferably used in the present invention include polyimide films obtained from polyimide resins having the following chemical compositions. Polyimide resin obtained from pyromellitic acid and diaminodiphenyl ether, Polyimide resin obtained from biphenyltetracarboxylic acid and phenylenediamine, Polyimide resin obtained from pyromellitic acid and phenylenediamine, Polyimide resins using diamine compounds having a benzoxazole skeleton as the diamine component, Polyimide resins using cyclohexyltetracarboxylic acid or cyclobutanetetracarboxylic acid, Polyimide resin made from alicyclic tetracarboxylic acid and aromatic diamine with amide bond Polyimide resins using fluorine-containing monomers, Polyimide resins made with sulfur-containing monomers These are examples of the main components of tetracarboxylic acids or diamines, respectively, but it is also possible to use polyimide resins copolymerized with a second or third component, polyimide resins that are polymer blends or polymer alloys made by combining polyimides of multiple compositions, polyimide resins into which inorganic fillers or polydimethylsiloxane components have been introduced, etc. It is also possible to use polyimide films having a structure in which polyimide resins of different compositions are laminated in the thickness direction.

[0032] In the present invention, the laminate of the present invention can be obtained by laminating a polymer film to an inorganic substrate. A known adhesive or pressure-sensitive adhesive can be used for lamination. Alternatively, the polymer film and / or the inorganic substrate can be surface-treated to bond them together to form a laminate. In the present invention, the laminate of the present invention can be obtained by applying a polymer solution or a solution of a polymer precursor to an inorganic substrate and drying it, or by heating or using a catalyst as necessary to induce a chemical reaction, thereby converting the polymer precursor into the desired polymer. Examples of the polymer precursor include polyamic acid, which is a precursor of polyimide.

[0033] Alternatively, as a compromise between the two, a method can be used in which a polymer solution or a polymer precursor solution is formed into a self-supporting semi-dry film, i.e., a film containing a solvent and a polymer, or a solvent and a polymer precursor, is adhered to an inorganic substrate, and then dried or dried and chemically reacted to form a laminate of the polymer film and the inorganic substrate.

[0034] The thickness of the polymer film is preferably 3 μm or more and 120 μm or less. To improve mechanical properties, it is preferably 4 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more. To improve transparency, it is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less.

[0035] In the laminate of the present invention, it is also preferable that the polymer film and the inorganic substrate are bonded together via a silane coupling agent or adhesive.

[0036] <Silane coupling agents (SCA)> In the present invention, a silane coupling agent refers to a compound containing 10% or more by mass of silicon (Si). Furthermore, it is preferable that the silane coupling agent has an alkoxy group in its structure. It is also desirable that the silane coupling agent does not contain a methyl group. The use of a silane coupling agent layer allows for a thin intermediate layer between the polymer film and the inorganic substrate, resulting in fewer outgassing components during heating, less leaching during wet processes, and even if leaching does occur, only a small amount. Silane coupling agents containing a large amount of silicon oxide are preferred to improve heat resistance, and those that are particularly heat resistant at temperatures around 400°C are preferred. The thickness of the silane coupling agent layer is preferably less than 0.2 μm. For flexible electronic devices, a thickness of 100 nm or less (0.1 μm or less) is preferred, more preferably 50 nm or less, and even more preferably 10 nm. Conventional fabrication results in a thickness of approximately 0.10 μm or less. Furthermore, in processes where minimal silane coupling agent is desired, even a thickness of 5 nm or less can be used. If the thickness is less than 1 nm, the peel strength may decrease or there may be areas where the film does not adhere, so it is desirable that the thickness be 1 nm or more.

[0037] The silane coupling agent in the present invention is not particularly limited, but is preferably one having an amino group or an epoxy group. Specific examples of silane coupling agents include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3- Glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatopropyltriethoxysilane, tris-(3- trimethoxysilylpropyl) isocyanurate, chloromethylphenethyltrimethoxysilane, chloromethyltrimethoxysilane, etc.Among these, preferred ones include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, aminophenyltrimethoxysilane, aminophenethyltrimethoxysilane, aminophenylaminomethylphenethyltrimethoxysilane, etc. When heat resistance is required in the process, those in which the Si and amino groups are linked by an aromatic group are desirable.

[0038] <Adhesive> The adhesive in the present invention is an adhesive used for bonding a polymer film to an inorganic substrate, and is preferably an adhesive that can withstand the process of forming an electronic device. Specific examples include epoxy-based adhesives, acrylic adhesives, phenolic resin-based adhesives, polyester-melamine adhesives, polyurethane resin-based adhesives, polyamide-based adhesives, polyimide-based adhesives, silicone-based adhesives, and fluororesin-based adhesives. Such adhesives are required to be resistant to thermal deformation at temperatures of at least 150°C, to emit no gases that would hinder the electronic device formation process, and to not leach impurities during wet processes. They are also required to be easily peeled off after the electronic device is formed. For this peeling, known techniques such as laser peeling, in which strong light is irradiated from the inorganic substrate side, can be used. Silicone-based adhesives are particularly preferred in the present invention. The thickness of the adhesive layer, when used in flexible electronic devices, is preferably greater than 100 nm (greater than 0.1 μm), more preferably greater than 0.5 μm, and even more preferably greater than 1 μm. Furthermore, the thickness is preferably less than 50 μm, more preferably less than 20 μm, and even more preferably less than 10 μm.

[0039] <Methods for manufacturing flexible electronic devices> By using the laminate of the present invention, a flexible electronic device can be produced by forming an electronic device on the polymer film of the laminate using existing equipment and processes for manufacturing electronic devices, and then peeling the polymer film off from the laminate.

[0040] <Means for Peeling Polymer Film from Inorganic Substrate> The means for peeling the polymer film from the support is not particularly limited, and any known method may be used. Examples of the method for peeling the polymer film from the laminate include a method of irradiating strong light from the inorganic substrate side to thermally decompose or photodecompose the adhesive portion between the inorganic substrate and the polymer film, a method of weakening the adhesive strength in advance and peeling the polymer film with a force less than the elastic strength limit of the polymer film, and a method of exposing the film to heated water, heated steam, or the like to weaken the bonding strength at the interface between the inorganic substrate and the polymer film to peel it off.

[0041] Other peeling methods include peeling from the edge using tweezers, sticking adhesive tape to one side of the cutout of the polymer film with the device and then peeling from the tape, vacuum-adhering one side of the cutout of the polymer film with the device and then peeling from that part, or leaving part of the polymer film unattached to the inorganic plate or allowing part of the polymer film to extend beyond the inorganic substrate to provide a gripping area.

[0042] <Cleaning> In the present invention, inorganic substrates are cleaned with aqueous solution A. Here, cleaning refers to exposing the inorganic substrate, which is the object to be cleaned, to aqueous solution A, which is the cleaning liquid, for a certain period of time or more. Exposure means bringing the inorganic substrate into direct contact with the treatment liquid, and a simple method is to immerse the inorganic substrate in the treatment liquid. A preferred embodiment is to agitate the treatment liquid appropriately while the substrate is immersed in the treatment liquid. Another preferred embodiment is to bring the treatment liquid into contact with the substrate while flowing. For example, the treatment liquid can be discharged from a discharge hole in a shower or spray form to contact the inorganic substrate with the treatment liquid.

[0043] <Aqueous solution A> The aqueous solution A in the present invention is any one of the following (1) to (3).

[0044] <Aqueous solution A(1)> First, (1) will be explained. In (1), aqueous solution A is an alkaline aqueous solution (hereinafter also referred to as simply an alkaline aqueous solution), and the content of divalent or higher polyvalent metal ions contained in the alkaline aqueous solution is 10 ppm or less (hereinafter also referred to as aqueous solution A(1)). An alkaline aqueous solution means an aqueous solution of an alkaline compound. As the alkaline compound, inorganic alkalis are preferred, and more specifically, hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide are preferred. The lower limit of the alkaline aqueous solution concentration is preferably 0.01 mol / L or more, more preferably 0.03 mol / L, and even more preferably 0.1 mol / L. The upper limit of the concentration is 2.5 mol / L, preferably 1.2 mol / L, and even more preferably 0.5 mol / L. By keeping the alkaline concentration within a predetermined range, it is possible to appropriately decompose and remove organic matter from the surface of the inorganic substrate, and it is also possible to avoid excessive etching and damage to the surface of the inorganic substrate.

[0045] <Aqueous solution A(2)> Next, (2) will be explained. In (2), aqueous solution A is an alkaline aqueous solution containing one or more compounds selected from the group consisting of ammonia, urea, and organic alkaline compounds (hereinafter also referred to as aqueous solution A(2)). The organic alkaline compound is preferably an ammonium hydroxide compound represented by general formula (4). General formula (4) {(R 1 )3-N + -R 2}·OH - In general formula (4), R 1 is preferably H (hydrogen) or an alkyl group having 1 to 8 carbon atoms. 1 The number of carbon atoms in R is more preferably 2 to 7, and even more preferably 3 to 6. 2 is preferably H (hydrogen), a C1-8 (carbon number 1-8) alkyl group, or a C1-8 (carbon number 1-8) hydroxyalkyl group. 2 The number of carbon atoms in R is more preferably 2 to 7, and even more preferably 3 to 6. 1 may be the same or different, provided that all R 1 and R 2 is never hydrogen. Examples of the ammonium hydroxide compound include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and tetraoctylammonium hydroxide. In the present invention, lower alcohol compounds having an amino group, such as monoaminoethanol, diaminoethanol, triaminoethanol, diethanolamine, and triethanolamine, can also be used as the organic alkaline compound.

[0046] Furthermore, in the present invention, an organic alkali compound and an inorganic alkali compound can be used in combination. More specifically, alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide can be used as inorganic alkali compounds. When an organic alkali compound and an inorganic alkali compound are used in combination, it is preferable to use an excess of the organic alkali compound. The preferred ratio (mass ratio) of organic alkali compound to inorganic alkali compound is organic alkali compound / inorganic alkali compound = more than 50 to less than 100 / less than 50 to more than 0, more preferably 60 to 90 / 40 to 10, and even more preferably 70 to 80 / 30 to 20. In the present invention, an alkaline solution containing monoethanolamine and sodium hydroxide can be shown as one preferred embodiment. The preferred lower limit of the alkaline solution concentration, in terms of the total alkaline compound content, is 0.01 mol / L or more, more preferably 0.03 mol / L, and even more preferably 0.1 mol / L. The preferred upper limit of the concentration is 2.5 mol / L, more preferably 1.2 mol / L, and even more preferably 0.5 mol / L. By keeping the alkaline concentration within a specified range, it is possible to appropriately decompose and remove organic matter from the surface of the inorganic substrate, and it is also possible to avoid excessive etching and damage to the surface of the inorganic substrate.

[0047] <Aqueous solution A(3)> Next, (3) will be explained. In (3), aqueous solution A contains one or more compounds selected from the group consisting of alkali metal perchlorates and alkali metal permanganates (hereinafter, also referred to as aqueous solution A(3)). In (3), an inorganic substrate is cleaned with aqueous solution A(3). The preferred lower limit of the concentration of the aqueous solution of one or more compounds selected from the group consisting of alkali metal perchlorates and alkali metal permanganates is 0.01 mol / L or more, preferably 0.03 mol / L, and more preferably 0.1 mol / L. The preferred upper limit of the concentration is 2.5 mol / L, preferably 1.2 mol / L, and more preferably 0.5 mol / L. By keeping the compound concentration within a specified range, organic matter on the surface of the inorganic substrate can be appropriately decomposed and removed, and excessive etching of the surface of the inorganic substrate can be avoided, thereby preventing damage.

[0048] An aqueous solution of alkali metal perchlorate can be obtained by electrolyzing an aqueous solution of alkali metal chlorate. Existing methods can be used to prepare an aqueous solution of alkali metal perchlorate by electrolysis, such as the techniques disclosed in Published Patent Application No. 2019-524991, Published Patent Application No. 2013-91829, and Published Patent Application No. 2011-58043. As the alkali metal salt, sodium salt is preferably used because of its high water solubility.

[0049] When an alkali metal permanganate is used, it is preferable to add sodium hydroxide or potassium hydroxide in an amount sufficient to maintain a pH of approximately 10-14 and a concentration of 90% or less of the alkali metal permanganate's saturated solubility in water. Potassium salts are preferably used as the alkali salt. One example is a mixed aqueous solution of 20 to 80 g / L of potassium permanganate and 10 to 60 g / L of sodium hydroxide.

[0050] <Polyvalent metal ions> The content of divalent or higher polyvalent metal ions contained in aqueous solution A in the present invention is preferably 10 ppm (mg / L) or less, more preferably 5 ppm (mg / L) or less. Note that there is no particular lower limit because there is a detection limit. The polyvalent metal ions are divalent to hexavalent ions of alkaline earth metals and transition metals, and examples thereof include ions of beryllium, magnesium, calcium, strontium, barium, scandium, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, arsenic, yttrium, zirconium, niobium, molybdenum, cadmium, indium, tin, antimony, tungsten, thallium, lead, and bismuth. Among these, the polyvalent ions that deserve particular attention are calcium and magnesium, which are easily carried over as impurities in water or alkali metals, and iron, nickel, chromium, vanadium, manganese, and molybdenum ions that originate from the materials used in pipes and bathtubs. The concentration of these polyvalent metal ions can be determined by centrifuging the metals that are present in the alkaline aqueous solution in a solid state without ionization (i.e., without dissolving), heating the supernatant, and then subjecting the evaporated, dried product to atomic absorption spectrometry. The polyvalent metal ion concentration in the present invention is the sum of all metals having a valence of two or more among the metal elements detected by the above analytical method.

[0051] To reduce the amount of polyvalent metal ions, for example, tap water is deionized with an ion exchange resin and then filtered through an ultrapure water column filter to produce ultrapure water, and then a high-purity alkaline compound refined to a desired concentration is added and dissolved.

[0052] The aqueous solution A of the present invention is preferably used at a temperature of 5 to 90°C. Since the treatment effect depends on the temperature, adjusting the temperature according to the line speed of the treatment step makes it possible to adjust the time between other processes. However, at high temperatures, the water volatilizes faster, which may make it difficult to control the concentration of the alkaline aqueous solution. The exposure time to the alkaline aqueous solution of the present invention is preferably about 10 seconds to 1 hour in the case of immersion cleaning, and 5 seconds to 10 minutes in the case of exposure to a flowing alkaline aqueous solution such as a spray.

[0053] <Acid neutralization> In the present invention, after washing with aqueous solution A, it is preferable to remove the alkaline aqueous solution adhering to the inorganic substrate by washing with water, then further perform a neutralization treatment with a dilute acid aqueous solution (referred to as an acid neutralization step), and then wash with water again. In particular, since aqueous solutions A(1) and A(2) are alkaline aqueous solutions, it is preferable to perform acid neutralization. As the dilute acid aqueous solution, dilute sulfuric acid, dilute hydrochloric acid, acetic acid aqueous solution, and citric acid aqueous solution can be preferably used. The dilute acid concentration is preferably 0.0001 mol / L to 0.05 mol / L.

[0054] <Rinse> In the present invention, after washing with aqueous solution A, preferably after the acid neutralization step, rinsing is preferably performed using neutral washing water containing 10 ppm or less of divalent or higher polyvalent metal ions. Even if the polyvalent metal ion concentration in the alkaline aqueous solution used in the washing step is controlled within a predetermined range, if polyvalent metal ions are present in the subsequent water-rinsing step, hydrolyzed products of organic substances that may remain on the inorganic substrate surface may be converted into insoluble salts, possibly forming deposits on the substrate surface. Therefore, the content of polyvalent metal ions is preferably 5 ppm or less. Rinsing refers to the operation of washing away the alkaline aqueous solution used in the washing step and the dilute acid aqueous solution used in the acid neutralization step (water washing). Therefore, rinsing is preferably performed after the step (a) of washing the inorganic substrate with an alkaline aqueous solution and before the step (b) of forming a polymer film on all or part of at least one surface of the inorganic substrate to obtain a laminate. The cleaning solution (rinse solution) can be prepared by deionizing tap water with an ion exchange resin and then filtering it through an ultrapure water column filter to produce an ultrapure water rinse solution. The pH of the cleaning solution is preferably 6.5 to 7.5, more preferably 6.8 to 7.2, and even more preferably 6.9 to 7.1.

[0055] <Carbonate concentration> As mentioned above, if the carbonate concentration in the alkaline aqueous solution exceeds the hydroxide concentration, the hydrolysis action decreases, and the water-soluble organic matter tends to form insoluble salts with polyvalent metal ions, making the washed items more likely to become re-contaminated. Carrying out treatment with an alkaline aqueous solution in a closed system is a preferred embodiment for suppressing the carbonate concentration, but in both immersion cleaning and spray cleaning, the object to be cleaned must be taken in and out, making it difficult to completely seal the system. Therefore, it is a preferred embodiment to periodically sample the material and control the carbonate concentration. The carbonate concentration can be determined by sequential fractional titration using potentiometric titration. The mass ratio of hydroxide concentration to carbonate concentration (hydroxide / carbonate) is preferably 100 / 0 to more than 50 / less than 50, more preferably 99.9 / 0.1 to 90 / 10, and even more preferably 99.8 / 0.2 to 99 / 1.

[0056] <Reusing inorganic substrates> The inorganic substrate of the present invention can be reused by peeling off the polymer film containing the flexible electronic device and then repeating steps (a) to (d) above. That is, by subjecting a used inorganic substrate to a cleaning treatment again, a polymer film can be formed on the same surface or the back surface of the inorganic substrate, and the inorganic substrate can be reused to manufacture a flexible electronic device. Specifically, after the step (d) of peeling the electronic device together with the polymer film from the inorganic substrate, (a)' washing the inorganic substrate with aqueous solution A; (b)' A step of forming a polymer film on a part or all of at least one surface of the inorganic substrate to obtain a laminate; (c)' forming an electronic device on the polymer film of the laminate; (d)' A step of peeling the electronic device together with the polymer film from the inorganic substrate. and the aqueous solution A is any one of the following (1) to (3), the flexible electronic device can be manufactured again. Furthermore, the inorganic substrate peeled off in the step (d)' can be reused in the same way. (1) Aqueous solution A is an alkaline aqueous solution, and the content of divalent or higher polyvalent metal ions contained in the alkaline aqueous solution is 10 ppm or less. (2) An alkaline aqueous solution containing one or more compounds selected from the group consisting of ammonia, urea, and organic alkaline compounds. (3) An aqueous solution containing one or more compounds selected from the group consisting of alkali metal perchlorates and alkali metal permanganates. [Example]

[0057] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The physical properties in the following examples were evaluated using the following methods.

[0058] <Polymer film thickness> The thickness of the polymer film was measured using a micrometer ("Militron 1245D" manufactured by Fine Leaf Co., Ltd.) and the average value of 10 points was calculated.

[0059] <Tensile modulus, tensile strength at break, and tensile elongation at break of polymer films> From the polymer film to be measured, strip-shaped test pieces measuring 100 mm x 10 mm in both the machine direction (MD) and the width direction (TD) were cut out, and the tensile modulus, tensile strength at break, and tensile elongation at break were measured in each of the MD and TD directions using a tensile testing machine (Shimadzu Corporation, "Autograph (registered trademark); model name AG-5000A") at a tensile speed of 50 mm / min and a chuck distance of 40 mm, and the average values ​​of all the measured values ​​in the MD and TD directions were obtained.

[0060] <Coefficient of linear expansion (CTE) of polymer film> The expansion / contraction rate was measured under the following conditions in the machine direction (MD) and width direction (TD) of the polymer film to be measured, and the expansion / contraction rate / temperature was measured at 15°C intervals (30°C to 45°C, 45°C to 60°C, ...). This measurement was continued up to 300°C, and the average value of all the measurements taken in the MD and TD directions was calculated as the coefficient of linear expansion (CTE). Device name: MAC Science "TMA4000S" Sample length: 20mm Sample width: 2mm Heating start temperature: 25℃ Heating end temperature: 400℃ Heating rate: 5°C / min Atmosphere: Argon Initial load; 34.5g / mm2

[0061] <Polyvalent metal ion concentration> The liquid to be measured was centrifuged in a centrifuge at 2500 rpm (900 G centrifugal acceleration) for 60 minutes, and the supernatant was removed and placed in a ceramic evaporating dish. It was then dried and solidified at 150°C for 30 minutes to prepare a sample. Quantitative analysis was performed using atomic absorption spectrometry. The detected metals were filtered out for alkali metals and silver, and the remaining metals were added together to obtain the polyvalent metal ion concentration. A calibration curve was created using AR-grade metal standard solution for atomic absorption spectrometry manufactured by Hayashi Pure Chemical Industries, Ltd. The detection limit is approximately 0.1 ppm because the peaks for the intentionally added components K and Na are excessively large. Furthermore, elements that were not detected in the raw water used to prepare the alkaline aqueous solution were excluded from the measurement.

[0062] <Hydroxide concentration, carbonate concentration> The hydroxide and carbonate concentrations were determined by sequential fractional titration using a 0.1 mol / L hydrochloric acid standard solution and an automatic titrator (Hiranuma Sangyo Co., Ltd.). When the concentration of the analyte was high, the solution was diluted with ultrapure water to 1 g / L or less before analysis.

[0063] <Appearance inspection, blister defect density> The number of blister defects of 30 μm or more in size was counted using a defect inspection device, and the number per 100 cm 2 was ranked as follows: ◎:0~1 piece / 100 square cm ○: 2 or more and 5 or less △: 6 or more and 15 or less ×: 16 or more and 100 or less ××:101 or more In addition, handling properties such as peelability of the film and appearance quality such as the presence or absence of wrinkles were observed and recorded.

[0064] <Preparation of polyamic acid (PAA) solution (varnish) Va> After replacing the atmosphere in a reaction vessel equipped with a nitrogen inlet tube, a thermometer, and a stirrer with nitrogen, 223 parts by weight of 5-amino-2-(p-aminophenyl)benzoxazole (DAMBO) and 4416 parts by weight of N,N-dimethylacetamide (DMAC) were added and completely dissolved. Next, 217 parts by weight of pyromellitic dianhydride (PMDA) and a dispersion of colloidal silica dispersed in dimethylacetamide as a lubricant (Nissan Chemical Industries, Ltd., "Snowtex (registered trademark) DMAC-ST30") were added so that the silica (lubricant) accounted for 0.09% by weight of the total polymer solids in the polyamic acid solution. The mixture was stirred at a reaction temperature of 25°C for 36 hours to obtain a brown, viscous polyamic acid (PAA) solution Va having the reduced viscosity shown in Table 1.

[0065] <Preparation of polyamic acid film GFa and polyimide film IFa> The polyamic acid solution Va obtained above was applied to the smooth surface (non-slip surface) of a long polyester film ("A-4100" manufactured by Toyobo Co., Ltd.) with a width of 800 mm using a slit die so that the final film thickness (film thickness after imidization) would be 18 μm, and the film was dried at 105° C. for 15 minutes to obtain a self-supporting polyamic acid film GFa. A portion of the polyamic acid film GFa was then wound up together with the polyester film to form a polyamic acid film roll. The remaining polyamic acid film GFa was then peeled off from the polyester film and heat-treated using a pin tenter at 150°C for 5 minutes in the first stage, 220°C for 5 minutes in the second stage, and 495°C for 10 minutes in the third stage to imidize it. The pin-held portions on both ends were slit to obtain a 645mm wide long polyimide film IF1 (1000m roll). The properties of the resulting film IFa are shown in Table 1.

[0066] <Preparation of Polyamic Acid (PAA) Solution (Varnish) Vb> After replacing the atmosphere in a reaction vessel equipped with a nitrogen inlet tube, a thermometer, and a stirrer with nitrogen, 176.5 parts by weight of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 31.0 parts by weight of 4,4'-oxydiphthalic acid (ODPA), 160.1 parts by weight of 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB), 113.6 parts by weight of 4-amino-N-(4-aminophenyl)benzamide (DABAN), and 2000 parts by weight of N,N-dimethylacetamide (DMAC) were charged into the reaction vessel under a nitrogen atmosphere and dissolved, followed by stirring at room temperature for 24 hours. The resulting mixture was then diluted with 1000 g of N,N-dimethylacetamide to obtain a polyamic acid solution (varnish) Vb with a reduced viscosity of 4.50 dL / g.

[0067] <Preparation of polyamic acid film GFb and polyimide film IFb> The polyamic acid solution Vb was applied to the smooth surface (non-slip surface) of a 1300 mm wide polyester film ("A-4100" manufactured by Toyobo Co., Ltd.), which served as a support for preparing the polyimide film, using a die coater (coating width: 1200 mm), and dried at 90 to 115°C for 10 minutes. After drying, the self-supporting polyamic acid film was peeled off from the support and both ends were cut to obtain polyamic acid film GFb. A portion of the polyamic acid film GFb was then wound up together with the polyester film to form a polyamic acid film roll. The remaining polyamic acid film GFb was then conveyed by a pin tenter so that the final pin sheet spacing was 1140 mm, and heat-treated at 170°C for 2 minutes in the first stage, 230°C for 2 minutes in the second stage, and 350°C for 6 minutes in the third stage. It was then cooled to room temperature in 2 minutes, and the poorly flat portions at both ends of the film were cut off with a slitter. The film was then wound up into a roll to obtain a 25 μm-thick polyimide film IFb. The properties of the resulting film IFb are shown in Table 1.

[0068] [Table 1]

[0069] <Preparation of alkaline aqueous solution A(1)-1 (Example)> Ultrapure water was obtained by deionizing water using an ion exchange resin and then filtering it through an ultrapure water column filter. This was placed in a polyethylene (PE) container, and purified, high-purity potassium hydroxide was added slowly and carefully, taking care not to allow the liquid temperature to exceed 50°C due to heat of hydration, to obtain a 1 mol / L aqueous potassium hydroxide solution. This is designated alkaline aqueous solution KQ1.

[0070] <Preparation of alkaline aqueous solution A(1)-2 (Comparative Example)> An alkaline aqueous solution KQ2 was obtained in the same manner as in Preparation of Alkaline Aqueous Solution A(1)-1, except that tap water that had not been subjected to ion exchange treatment or ultrapure water column treatment was used as raw water.

[0071] <Preparation of alkaline aqueous solution A(1)-3 (Comparative Example)> The alkaline aqueous solution KQ1 was transferred from the polyethylene container to a stainless steel (SUS) container, kept at 25°C for 48 hours, and then returned to the polyethylene container. This was used as alkaline aqueous solution KQ3.

[0072] <Preparation of alkaline aqueous solution A(1)-4 (Example)> An alkaline aqueous solution KQ4 was obtained in the same manner as in Preparation 1 of Alkaline Aqueous Solution, except that ultrapure water and tap water were mixed in a ratio of 5:1 (mass ratio).

[0073] <Preparation of alkaline aqueous solution A(1)-5 (Example)> An aqueous alkaline solution NQ1 was obtained in the same manner as in Preparation 1 of the aqueous alkaline solution, except that high-purity sodium hydroxide was dissolved in place of the potassium hydroxide used in Preparation 1 of the aqueous alkaline solution to a concentration of 0.2 mol / L. The analytical results of the obtained alkaline aqueous solution are shown in Table 2. Because the peaks of K and Na were excessively large, the measurement limit was approximately 0.1 ppm. The polyvalent metal ion concentration of KQ1 is a sum value for convenience. The alkaline aqueous solutions that satisfy requirement (1) of the present invention are KQ1, KQ4, and NQ1.

[0074] [Table 2]

[0075] <Preparation of alkaline solution A(2)-1 (Example)> A stock solution of ammonia water (28% by mass) manufactured by Kishida Chemical Co., Ltd. was diluted with ultrapure water to 15% by mass and used as alkaline solution A(2)-1.

[0076] <Preparation of alkaline solution A(2)-2 (Example)> A 25 mass % solution of industrial TMAH (tetramethylammonium hydroxide) manufactured by Showa Denko KK was diluted with ultrapure water to 20 mass % and used as alkaline solution A(2)-2.

[0077] <Preparation of alkaline solution A(2)-3 (Example)> An alkaline solution A(2)-3 was prepared by mixing 45 parts by mass of monoethanolamine, 25 parts by mass of sodium hydroxide, and 30 parts by mass of ultrapure water.

[0078] <Preparation of cleaning solution A(3)-1 (aqueous solution containing sodium perchlorate)> Water deionized with an ion exchange resin was further filtered through an ultrapure water column filter to obtain ultrapure water, which was used as raw water. The raw water was then placed in a polyethylene (PE) container, and purified sodium chlorate was added while controlling the bath temperature to 40°C ± 15°C, yielding a 1 mol / L aqueous sodium chlorate solution. The resulting aqueous sodium chlorate solution was transferred to an electrolytic cell equipped with platinum electrodes, and while monitoring the amount of perchlorate ions by ion chromatography, electrolysis was carried out until the perchlorate ion / chlorate ion (molar ratio) reached 1 or more, yielding a cleaning solution A(3)-1 containing sodium perchlorate.

[0079] <Preparation of cleaning solution A(3)-2 (aqueous solution containing potassium permanganate)> Water was deionized using an ion exchange resin, and then filtered through an ultrapure water column filter to obtain ultrapure water, which was used as raw water. The raw water was then placed in a polyethylene (PE) container, and purified potassium permanganate and high-purity potassium hydroxide were carefully and gradually added, taking care not to allow the liquid temperature to exceed 50°C due to heat of hydration. An aqueous solution of 0.5 mol / L potassium permanganate and 0.3 mol / L sodium hydroxide was obtained. This was designated cleaning solution A(3)-2.

[0080] Example 1: Laminate (A(1)) produced by IF lamination (First generation laminated body using the IF lamination method) A glass substrate (370 × 470 mm, 0.7 mm thick, LotusGlass manufactured by Corning Inc.) was used as the inorganic substrate. The inorganic substrate was cleaned by immersing it in alkaline aqueous solution KQ1 adjusted to 40°C and shaking for 10 minutes, then immersing it in the ultrapure water used to prepare the alkaline aqueous solution while shaking, rinsing it, immersing it in 0.05 mol / L dilute hydrochloric acid for 1 minute, rinsing (immersing) it again in ultrapure water, and then drying it with clean dry air at 120°C. The inorganic substrate after cleaning was exposed to the vapor of a silane coupling agent, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, for 5 minutes in a sealed chamber whose temperature was adjusted to 40°C, and then heated in clean nitrogen at 100°C for 15 minutes to perform surface treatment of the inorganic substrate.

[0081] One side of polyimide film IFa was subjected to atmospheric pressure plasma treatment under a nitrogen atmosphere to produce a plasma-treated film. The plasma-treated surface was then laminated to a surface-treated inorganic substrate using a hot roll laminator. After lamination, the laminate was heated at 150°C for 10 minutes to produce a first-generation laminate, MLia-KQ1-1G. The laminate production process shown here is referred to as the IF lamination method. In the IF lamination method, there is essentially no adhesive layer between the inorganic substrate and the film. Therefore, if the flatness of the substrate or film is poor, or if foreign matter is introduced between the substrate and film, blister defects, in which parts of the film are raised like tents, may occur. However, no visually detectable blister defects (10 μm or larger) were observed in the resulting laminate. As a simulation of the fabrication of electronic devices, an amorphous silicon film was formed on the film surface of the obtained laminate using a CVD device. The maximum process temperature was 320°C. After the simulation, the film on which the amorphous silicon thin film had been deposited was peeled off from the laminate by inserting a blade into the edge of the film to create a notch. No particular abnormalities were observed during the peeling process.

[0082] (Second generation laminated body using the IF lamination method) After the simulated operation of electronic device fabrication, the same operation as for the first generation was carried out, except that the glass substrate obtained by peeling the film from the first-generation laminate MLia-KQ1-1G was used instead of the virgin glass substrate used in the fabrication of the first-generation laminate, to obtain a second-generation laminate MLia-KQ1-2G. The resulting second-generation laminate was used to similarly carry out a simulated operation of electronic device fabrication.

[0083] (Third and fourth generation laminates made using the IF lamination method) Similarly, substrates obtained by peeling the film from the previous generation laminate were reused repeatedly, and the foreign matter density, quality, and handling ease of each generation were evaluated. The results are shown in Table 3. It was confirmed that substrates could be reused repeatedly up to at least the fourth generation.

[0084] <Comparative Examples 1 and 2, Examples 2 and 3> As shown in Table 3, laminates were produced using the IF lamination method on glass substrates cleaned with alkaline aqueous solutions KQ2, KQ3, KQ4, and NQ1, respectively. The same electronic device production simulation operation as in Example 1 and the reuse of the glass substrates after film peeling were repeated up to the fourth generation, and the state of the laminates was evaluated and observed. The results are shown in Table 3. In Comparative Example 1, which used an alkaline aqueous solution containing excess Ca and Mg ions, a gradual increase in blister defects was observed in the laminate. The same was true for Comparative Example 2. On the other hand, Examples 2 and 3 demonstrated that repeated reuse was possible up to at least the fourth generation.

[0085] Example 4 The recyclability of substrates up to the fourth generation was evaluated in the same manner as in Example 1, except that polyimide film IFb was used instead of polyimide film IFa. The results are shown in Table 3. As in Example 1, the results were good.

[0086] [Table 3]

[0087] <Examples 5 and 6, Comparative Example 3 Laminates produced by the varnish method> (First generation laminates using the varnish method) A glass substrate (370 × 470 mm, 0.7 mm thick, LotusGlass manufactured by Corning Inc.) was used as the inorganic substrate. The inorganic substrate was cleaned by spraying an alkaline aqueous solution NQ1 at 60°C for 5 minutes using a roller conveying spray washer, followed by spray rinsing with ultrapure water, spraying with 0.05 mol / L dilute hydrochloric acid for 1 minute, spray rinsing with ultrapure water again, and then drying with clean dry air at 80°C. Next, a polyamic acid solution (varnish) Va was applied to the substrate using a bar coater to a final film thickness of 15 μm, and the substrate was heated in an inert oven at 120°C for 7 minutes, 250°C for 5 minutes, and 450°C for 5 minutes to obtain a first-generation laminate Mva-NQ1s-1G using the varnish method. First-generation laminates Mvb-NQ1s-1G and Mvb-KQ2s-1G for varnish were obtained using the polyamic acid solutions (varnishes) and alkaline aqueous solutions used for washing shown in Table 4. When polyamic acid solution (varnish) Vb was used, the heat treatment conditions after application to the inorganic substrate were 150°C for 10 minutes in the first step and 280°C for 10 minutes in the second step. Next, each laminate was subjected to the same procedure as in Example 1, including simulating electronic device fabrication, film peeling, and substrate reuse up to the fifth generation, and the blister defect density was observed. The results are shown in Table 4. It was confirmed that in Examples 5 and 6, in which NQ1 was used for substrate cleaning, the substrates could be reused at least up to the fifth generation. However, in Comparative Example 3, in which the alkaline aqueous solution KQ2 was used, the blister density increased with each generation, resulting in numerous blister defects (X level) in the fourth generation. Furthermore, during the fifth generation, when the polymer film was laminated, the blister defect density reached the XX level (more than 101 per 100 square centimeters), and the test was discontinued. Composition analysis of foreign particles found in the blisters detected calcium carbonate and magnesium carbonate.

[0088] <Examples 7 and 8, Laminates by GF Method> First, the inorganic substrate was subjected to the same cleaning treatment as in Example 1. Next, the roll of polyamic acid film GFa, which was wound together with the polyester film, was unwound, and the inorganic substrate was placed on the polyamic acid film surface. The two were then laminated together using a roll laminator with a roll temperature of 80°C. The polyamic acid film was then cut to the same size as the polyester film substrate, and the polyester film was peeled off from the polyamic acid film to obtain a GFa laminate consisting of the inorganic substrate and the polyamic acid film. The GFa laminate was then heat-treated at 250°C for 8 minutes and then at 450°C for 8 minutes to obtain a laminate Mga-KQ1-1G using the GF method. Similarly, a polyamic acid film GFb was laminated onto a washed inorganic substrate, and after peeling off the polyester film, the laminate was heat treated in nitrogen at 150°C for 10 minutes and then at 280°C for 10 minutes to obtain a laminate Mgb-KQ1-1G by the GF method. Next, each laminate was subjected to the same procedure as in Example 1, whereby the electronic device fabrication simulation, film peeling, and substrate reuse were repeated up to the fifth generation, and the blister defect density was observed. The results are shown in Table 4. In all cases, the substrates could be reused without any problems up to the fifth generation.

[0089] [Table 4]

[0090] Example 9 Laminate (A(2)) by IF lamination (First generation laminated body by IF lamination method (A(2)1-1G)) The inorganic substrate used was a 370 × 470 mm, 0.7 mm thick LotusGlass manufactured by Corning Inc. The inorganic substrate was cleaned by immersing it in a sealed alkaline solution A(2)-1 adjusted to 30°C and shaking it for 30 minutes, then spray-rinsing it with ultrapure water, immersing it in 0.1% by mass dilute hydrochloric acid for 3 minutes, rinsing it twice more with ultrapure water sprays, and then drying it with clean dry air at 120°C. The inorganic substrate after cleaning was exposed to the vapor of a silane coupling agent, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, for 5 minutes in a sealed chamber whose temperature was adjusted to 40°C, and then heated in clean nitrogen at 100°C for 15 minutes to perform surface treatment of the inorganic substrate.

[0091] One side of polyimide film IFa was subjected to atmospheric pressure plasma treatment under a nitrogen atmosphere to produce a plasma-treated film. The plasma-treated surface was then laminated to a surface-treated inorganic substrate using a hot roll laminator. After lamination, the laminate was heated at 150°C for 10 minutes to produce a first-generation laminate A(2)1-1G. The laminate fabrication process shown here is referred to as the IF lamination method. In the IF lamination method, there is essentially no adhesive layer between the inorganic substrate and the film. Therefore, if the flatness of the substrate or film is poor, or if foreign matter is introduced between the substrate and film, blister defects, in which parts of the film are raised like tents, can occur. However, no visually detectable blister defects (larger than 10 μm) were observed in the resulting laminate. As a simulation of electronic device fabrication, an amorphous silicon film was formed on the film surface of the resulting laminate A(2)1-1G using a CVD device. The maximum process temperature was 320°C. After the simulation, the film on which the amorphous silicon thin film had been deposited was peeled off from the laminate A(2)1-1G by creating a notch on the edge of the film using a blade. No particular abnormalities were observed during peeling.

[0092] (Second generation laminates using the IF lamination method (A(2)1-2G)) After the electronic device fabrication simulation, the inorganic substrate from which the film had been peeled was used instead of the virgin glass substrate used in the fabrication of the first-generation laminate A(2)1-1G, and the same procedure was repeated to obtain a second-generation laminate A(2)1-2G. The resulting second-generation laminate A(2)1-2G was used to similarly simulate the fabrication of an electronic device.

[0093] (Third generation laminates (A(2)1-3G) and fourth generation laminates (A(2)1-4G) using the IF lamination method) Similarly, the inorganic substrates from which the film was peeled off from the previous generation laminate were repeatedly reused to produce third-generation (A(2)1-3G), fourth-generation (A(2)1-4G), and fifth-generation (A(2)1-5G) laminates, and the foreign matter density, quality, and handling properties of each generation were evaluated. As a result, the blister density was at the ◎ level in all cases, confirming that the substrates can be reused repeatedly up to at least five generations.

[0094] <Example 10 (A(2)2-1G to 5G)> The same procedure was followed as in Example 9, except that alkaline solution A(2)-1 was replaced with alkaline solution A(2)-2. A glass substrate cleaned using alkaline solution A(2)-2 was used to prepare a laminate A(2)2-1G using the IF lamination method. The same electronic device fabrication simulation procedure as in Example 9 and the reuse of the glass substrate after film peeling were repeated up to the fifth generation, and the state of the laminate was evaluated and observed. As a result, the blister density was at the ◎ level or ○ level, confirming that repeated reuse was possible up to at least the fifth generation.

[0095] <Example 11 (A(2)3-1G to 5G)> The same procedure was followed as in Example 9, except that the alkaline solution A(2)-1 was replaced with alkaline solution A(2)-3 and the temperature of the alkaline solution A(2)-3 was set to 60°C. A laminate A(2)3-1G was produced using an IF lamination method on a glass substrate cleaned with alkaline solution A(2)-3, and the same electronic device production simulation operation as in Example 9 and the reuse of the glass substrate after film peeling were repeated up to the fifth generation, and the state of the laminate was evaluated and observed. As a result, the blister density was at the ◎ level or ○ level, confirming that repeated reuse was possible up to at least the fifth generation.

[0096] <Example 12 (A(2)4-1G to 5G)> The recyclability of inorganic substrates up to the fifth generation was evaluated in the same manner as in Example 9, except that polyimide film IFb was used instead of polyimide film IFa. The blister density was at the ◎ level or ○ level for all generations, and was a good result similar to that of Example 9.

[0097] <Example 13 (A(2)5-1G to 5G)> The recyclability of inorganic substrates up to the fifth generation was evaluated in the same manner as in Example 10, except that polyimide film IFb was used instead of polyimide film IFa. The blister density was at the ⊚ level or ◯ level for all generations, and was as good as in Example 10.

[0098] <Example 14 (A(2)6-1G to 5G)> The recyclability of inorganic substrates up to the fifth generation was evaluated in the same manner as in Example 11, except that polyimide film IFb was used instead of polyimide film IFa. The blister density was at the ⊚ level or ◯ level for all generations, and was as good as in Example 11.

[0099] Example 15 Laminates by Varnish Method (A(2)7-1G to 5G) (First generation laminate by varnish method (A(2)7-1G)) The inorganic substrate used was a Corning LotusGlass measuring 370 × 470 mm and 0.7 mm thick. The inorganic substrate was cleaned by spraying alkaline solution 2 at 30°C for 5 minutes using a roller conveying spray washer, followed by two rinses with ultrapure water and drying with clean dry air at 80°C. Next, a polyamic acid solution (varnish) Va was applied to the substrate using a bar coater to a final film thickness of 15 μm, and heated in an inert oven at 120°C for 7 minutes, 250°C for 5 minutes, and 450°C for 5 minutes to obtain a first-generation laminate A(2)7-1G by the varnish method. Next, the resulting laminate A(2)7-1G was used to repeat the process of simulating the fabrication of an electronic device, peeling off the film, and reusing the substrate up to the fifth generation, and the blister defect density was observed, following the procedure of Example 11. As a result, the blister density was at the ◎ level or ○ level for all generations, and good laminates with few blister defects could be obtained for all generations, and they could be used in the operation of electronic devices in the same way.

[0100] <Example 16 GF Method (A(2)8-1G to 5G)> First, the inorganic substrate was cleaned using the same alkaline solution A(2)-1 as in Example 9. Next, the roll of polyamic acid film GFa, which was wound together with the polyester film, was unwound, and the inorganic substrate was placed on the polyamic acid film surface. The two were then laminated together using a roll laminator with a roll temperature of 80°C. The polyamic acid film and polyester film were then cut to the same size as the inorganic substrate, and the polyester film was peeled off from the polyamic acid film to obtain a GFa laminate consisting of the inorganic substrate and the polyamic acid film. The GFa laminate was then heat-treated at 250°C for 8 minutes and then at 450°C for 8 minutes to obtain a laminate A(2)8-1G using the GF method. Next, the resulting laminate A(2)8-1G was used to repeat the process of simulating the fabrication of an electronic device, peeling off the film, and reusing the substrate up to the fifth generation, and the density of blister defects was observed, in the same manner as in Example 9. As a result, good laminates with very few blister defects, rated as ⊚, were obtained in all generations, and they could be used in the operation of electronic devices in the same way.

[0101] <Example 17 (A(2)9-1G to 5G)> The same glass substrate as in Example 9, 1000 parts by mass of water, and 50 parts by mass of urea were charged into a stainless steel autoclave, which was then sealed. The temperature was raised to 121°C, and after 60 minutes of holding, the autoclave was cooled to room temperature. The autoclave was then opened under ventilation, and the glass substrate was removed. Upon opening, a strong ammonia odor was detected, suggesting that the urea had decomposed into ammonia. This process is referred to as autoclave treatment. Thereafter, the substrates were rinsed, neutralized with dilute hydrochloric acid, rinsed again, and dried in the same manner as in Example 9. Then, laminate fabrication by the varnish method and the simulated operation of electronic device fabrication were performed in the same manner as in Example 7, and the film was peeled off. The substrates were reused up to the fifth generation using the autoclave treatment of this example, and the blister defect density was observed. The blister density was at the ⊚ level or ◯ level for all generations, indicating that the substrates could be reused without any problems up to the fifth generation.

[0102] <Example 18 Laminate (A(3)) by IF lamination method> (First generation laminate by IF lamination method (A(3)1-1G)) The inorganic substrate used was a Corning LotusGlass measuring 370 × 470 mm and 0.7 mm thick. For the cleaning treatment, the inorganic substrate was immersed in cleaning solution A(3)-1 adjusted to 70°C, shaken for 10 minutes, spray-rinsed twice with ultrapure water, and then dried with clean dry air at 120°C. The inorganic substrate after cleaning was exposed to the vapor of a silane coupling agent, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, for 5 minutes in a sealed chamber whose temperature was adjusted to 40°C, and then heated in clean nitrogen at 100°C for 15 minutes to perform surface treatment of the inorganic substrate.

[0103] One side of polyimide film IFa was subjected to atmospheric pressure plasma treatment under a nitrogen atmosphere to produce a plasma-treated film. The plasma-treated surface was then laminated to a surface-treated inorganic substrate using a hot roll laminator. After lamination, the laminate was heated at 150°C for 10 minutes to produce a first-generation laminate A(3)1-1G. The laminate fabrication process shown here is referred to as the IF lamination method. In the IF lamination method, there is essentially no adhesive layer between the inorganic substrate and the film. Therefore, if the flatness of the substrate or film is poor, or if foreign matter is introduced between the substrate and film, blister defects, in which parts of the film are raised like tents, can occur. However, no visually detectable blister defects (10 μm or larger) were observed in the resulting laminate. As a simulation of the fabrication of electronic devices, an amorphous silicon film was formed on the film surface of the resulting laminate A(3)1-1G using a CVD device. The maximum process temperature was 320°C. After the simulation, the film on which the amorphous silicon thin film had been deposited was peeled off from the laminate by inserting a blade into the edge of the film to create a notch. No particular abnormalities were observed during the peeling process.

[0104] (Second generation laminated body by IF lamination method (A(3)1-2G)) After the electronic device fabrication simulation, the inorganic substrate from which the film had been peeled was used instead of the virgin glass substrate used in the first-generation laminate fabrication, and the same procedure was repeated to obtain a second-generation laminate A(3)1-2G. The resulting second-generation laminate A(3)1-2G was used to similarly simulate the fabrication of an electronic device.

[0105] (Third generation laminates (A(3)1-3G) and fourth generation laminates (A(3)1-4G) using the IF lamination method) Similarly, the inorganic substrates from which the film was peeled off from the previous generation laminate were repeatedly reused to produce third-generation (A(3)1-3G), fourth-generation (A(3)1-4G), and fifth-generation (A(3)1-5G) laminates, and the foreign matter density, quality, and handleability of each generation were evaluated. As a result, the blister density was at the ◎ level or ○ level, and it was confirmed that the substrates could be reused repeatedly up to at least five generations.

[0106] Example 19 (A(3)2-1G) The same procedure was followed as in Example 18, except that cleaning solution A(3)-1 was replaced with cleaning solution A(3)-2. A laminate was produced using the IF lamination method on a glass substrate cleaned using cleaning solution A(3)-2, and the same electronic device production simulation procedure as in Example 18 and the reuse of the glass substrate after film peeling were repeated up to the fifth generation, and the state of the laminate was evaluated and observed. As a result, the blister density was at the ◎ level or ○ level, confirming that repeated reuse was possible at least up to the fifth generation.

[0107] <Example 20 (A(3)3-1G)> The recyclability of inorganic substrates up to the fifth generation was evaluated in the same manner as in Example 18, except that polyimide film IFb was used instead of polyimide film IFa. The blister density was at the ◎ level or ○ level for all generations, and was a good result similar to that of Example 18.

[0108] <Example 21 (A(3)4-1G)> The recyclability of inorganic substrates up to the fifth generation was evaluated in the same manner as in Example 19, except that polyimide film IFb was used instead of polyimide film IFa. The blister density was at the ⊚ level or ◯ level for all generations, and was as good as in Example 19.

[0109] Example 21 Laminates by Varnish Method (A(3)5-1G to 5G) (First generation laminate by varnish method (A(3)5-1G)) The inorganic substrate used was a Corning LotusGlass measuring 370 × 470 mm and 0.7 mm thick. The inorganic substrate was cleaned by spraying cleaning solution A(3)-1 at 60°C for 5 minutes using a roller conveying spray washer, followed by two rinses with ultrapure water and drying with clean dry air at 80°C. Next, a polyamic acid solution (varnish) Va was applied to the substrate using a bar coater to a final film thickness of 15 μm, and the substrate was heated in an inert oven at 120°C for 7 minutes, 250°C for 5 minutes, and 450°C for 5 minutes to obtain a first-generation laminate (A(3)5-1G) by the varnish method. Next, the obtained laminate (A(3)5-1G) was used to repeat the process of simulating the production of an electronic device, peeling off the film, and reusing the substrate up to the fifth generation, and the blister defect density was observed, in the same manner as in Example 18. As a result, the blister density was at the ◎ level or ○ level for all generations, and good laminates with few blister defects could be obtained for all generations, and they could be used in the operation of electronic devices in the same way.

[0110] <Example 22 (A(3)6-1G to 5G)> The recyclability of inorganic substrates of the first to fifth generations was evaluated in the same manner as in Example 21, except that cleaning solution A(3)-2 was used instead of cleaning solution A(3)-1. The blister density of each generation was at the ◎ level or ○ level, and the results were as good as in Example 21.

[0111] <Example 23 GF Method (A(3)7-1G to 5G)> First, the substrate was cleaned using the same cleaning solution A(3)-2 as in Example 19. Next, the roll of polyamic acid film GFa, which was wound together with the polyester film, was unwound, and the inorganic substrate was placed on the polyamic acid film surface. The two were then laminated together using a roll laminator with a roll temperature of 80°C. The polyamic acid film and polyester film were then cut to the same size as the inorganic substrate, and the polyester film was peeled off from the polyamic acid film to obtain a GFa laminate consisting of the inorganic substrate and the polyamic acid film. The GFa laminate was then heat-treated at 250°C for 8 minutes and then at 450°C for 8 minutes to obtain a laminate A(3)7-1G using the GF method. Next, the obtained laminate was subjected to the same process as in Example 18, simulating the fabrication of an electronic device, peeling off the film, and reusing the substrate up to the fifth generation, and the density of blister defects was observed. As a result, good laminates with few blister defects (rated as ⊚ or ◯) were obtained in all generations, and they could be used in the operation of electronic devices in the same way.

[0112] <Example 24 (A(3)8-1G to 5G)> As in Example 23, the polyamic acid film GFb was laminated onto a washed inorganic substrate, and after peeling off the polyester film, the laminate was heat-treated in nitrogen at 150°C for 10 minutes and then at 280°C for 10 minutes to obtain a laminate A(3)8-1G by the GF method. Next, the resulting laminate A(3)8-1G was used in the same manner as in Example 18, and the process of simulating the production of an electronic device, peeling off the film, and reusing the inorganic substrate was repeated up to the fifth generation, and the blister defect density was observed. The blister density was at the ◎ level or ○ level for all generations, indicating that the inorganic substrate could be reused without any problems up to the fifth generation. [Industrial Applicability]

[0113] As described above, according to the manufacturing method of the present invention, by subjecting a substrate to a cleaning treatment that satisfies specific conditions, the substrate can be reused, thereby enabling a significant reduction in variable costs in the manufacture of flexible electronic devices.

Claims

1. (a) washing the inorganic substrate with aqueous solution A; (b) forming a polymer film on a part or all of at least one surface of the inorganic substrate to obtain a laminate; (c) forming an electronic device on the polymer film of the laminate; (d) peeling the electronic device together with the polymer film from the inorganic substrate. Including, the polymer film is any one of a polyimide film, a polyamide film, a polyamideimide film, a polybenzoxazole film, and a polyimidebenzoxazole film; The method for producing a flexible electronic device, wherein the aqueous solution A is the following (1): (1) The aqueous solution A is an alkaline aqueous solution, and the content of divalent or higher polyvalent metal ions contained in the alkaline aqueous solution is 0.5 ppm or more and 10 ppm or less.

2. 2. The method for producing a flexible electronic device according to claim 1, wherein the alkaline aqueous solution in (1) is an aqueous solution of sodium hydroxide or potassium hydroxide.

3. 3. The method for manufacturing a flexible electronic device according to claim 1, further comprising, after the step (a) of cleaning the inorganic substrate with an alkaline aqueous solution in (1), a step of rinsing the substrate with neutral cleaning water containing 10 ppm or less of divalent or higher polyvalent metal ions.

4. 4. The method for producing a flexible electronic device according to claim 1, wherein the hydroxide concentration in the alkaline aqueous solution in (1) is higher than the carbonate concentration.

5. After the step (d) of peeling the electronic device together with the polymer film from the inorganic substrate, (a)' a step of washing the inorganic substrate with the aqueous solution A; (b)' A step of forming a polymer film on a part or all of at least one surface of the inorganic substrate to obtain a laminate; (c)' forming an electronic device on the polymer film of the laminate; (d)' A step of peeling the electronic device together with the polymer film from the inorganic substrate.

5. The method for producing a flexible electronic device according to claim 1, further comprising:

6. 6. The method for producing a flexible electronic device according to claim 1, wherein the laminate is obtained by applying a polymer solution to an inorganic substrate and drying the solution to form a polymer film.

7. 7. The method for producing a flexible electronic device according to claim 6, wherein the polymer solution is a polyimide solution, and is obtained by applying the solution to an inorganic substrate and drying it to form a polyimide film.

8. The method for producing a flexible electronic device according to any one of claims 1 to 7, characterized in that the laminate is obtained by applying a polyamic acid solution to an inorganic substrate, followed by drying and chemical reaction to form a polyimide film.

9. 6. The method for producing a flexible electronic device according to claim 1, wherein the laminate is obtained by bonding a polymer film and an inorganic substrate via a silane coupling agent.

10. 6. The method for producing a flexible electronic device according to claim 1, wherein the laminate is obtained by bonding a polymer film and an inorganic substrate with an adhesive.

11. The method for manufacturing a flexible electronic device according to any one of claims 1 to 5, characterized in that the laminate is obtained by adhering a film containing a solvent and polyamic acid to an inorganic substrate, followed by drying and a chemical reaction to form a polyimide film.

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