Polyimide fiber paper and method for producing laminate thereof

Abstract

[Problem] Conventional polyimide paper producing methods have the problem that polyimide fiber paper having a thickness close to any desired thickness cannot be obtained. The conventional methods also have the problem that a step for imidizing a polyimide precursor to be dispersed into an intermediate structure or a polyimide precursor contained in a polyimide solution is required. [Solution] Provided is a method for producing a laminate of polyimide fiber paper, comprising: a polyimide short fiber production step for producing polyimide short fibers; a polyimide short fiber slurry production step for producing a polyimide short fiber slurry comprising the polyimide short fibers and a water-soluble polymer; a polyimide short fiber single intermediate production step for producing a polyimide short fiber single intermediate by wet papermaking of the slurry; and a polyimide short fiber laminated intermediate production step for producing a polyimide short fiber laminated intermediate in which a water-soluble polymer residue remains, by stacking and hot-pressing a plurality of polyimide short fiber single intermediates.

Description

Polyimide fiber paper and its laminate manufacturing method

[0001] The present invention relates to polyimide fiber paper and a method for manufacturing the same.

[0002] Polyimide film is a material with excellent electrical insulation, heat resistance, cold resistance, heat resistance, chemical resistance, and mechanical properties, and is in high demand in a wide range of fields, from aerospace applications to automobiles and communications equipment. Taking advantage of the high functionality of polyimide, research and development has been conducted on polyimide fiber paper, a flexible sheet-like product with improved thermal insulation and gas and liquid permeability.

[0003] A method for producing polyimide fiber paper using polyimide fibers is disclosed, for example, in Patent Document 1. Patent Document 1 discloses a method for producing polyimide fiber paper by first preparing polyimide short fibers, mixing the polyimide short fibers in a water-soluble polymer solution whose decomposition temperature is lower than the glass transition point of polyimide, and then wet-laid to form a temporary paper. The method also discloses a method for producing polyimide fiber paper in which all of the water-soluble polymer in the temporary paper is removed by heat treatment, a polyimide precursor or a polyimide solution is dispersed, and then the polyimide precursor or the polyimide precursor in the polyimide solution is imidized by heating.

[0004] Patent Document 2 discloses a manufacturing method in which a polyimide fiber paper intermediate structure X, in which polyimide short fibers are temporarily fixed using a water-soluble or / and water-insoluble thermoplastic polymer whose melting point is lower than the glass transition point of polyimide, is heated to expand and increase the thickness of a polyimide fiber paper intermediate structure Y2, in which a polyimide solution and / or a polyimide precursor is dispersed to prepare a polyimide fiber paper intermediate structure Z3, and the polyimide precursor contained in the polyimide fiber paper intermediate structure Z3 is imidized.

[0005] JP 2019-035157 WO2020 / 171061

[0006] When polyimide fiber paper made of polyimide fibers (polyimide fiber paper in the prior art documents 1 and 2) is used as a heat insulating material, it is expected that the thicker it is, the better its heat insulating performance will be. Also, the higher the heat resistance, the better.

[0007] Patent Document 1 does not mention laminating polyimide fiber paper, and is considered to be a single layer, which poses the problem that polyimide fiber paper of a thickness close to any desired thickness cannot be obtained.

[0008] In Patent Document 2, an intermediate structure X, in which polyimide short fibers are temporarily fixed using a water-soluble and / or water-insoluble thermoplastic polymer, is heated, causing the intermediate structure X to expand like a balloon. The degree of expansion varies depending on the heating temperature and heating time, so the degree of expansion can be adjusted by adjusting the heating temperature and heating time according to the purpose of use. However, since the intermediate structure is originally a single layer, there is a limit to how much thickness can be increased. Furthermore, increasing the thickness by expanding the structure reduces the density, so the heat insulating properties do not improve significantly.

[0009] In addition, the polyimide fiber paper of Patent Documents 1 and 2 involves dispersing a polyimide precursor or a polyimide solution into an intermediate structure, imidizing the polyimide fibers, and bonding the short polyimide fibers together with the polyimide resin. The need to imidize the polyimide precursor or the polyimide precursor contained in the polyimide solution also creates a problem of complicated processes. Furthermore, because the short polyimide fibers are bonded together with the polyimide resin, the paper becomes hard, making it unsuitable for applications requiring cushioning properties in addition to heat resistance.

[0010] Therefore, the present invention provides a polyimide fiber paper laminate manufacturing method including a polyimide staple fiber slurry manufacturing step of manufacturing a polyimide staple fiber slurry containing polyimide staple fibers, a polyimide staple fiber monolayer intermediate manufacturing step of wet-laid papermaking the slurry to produce a polyimide staple fiber monolayer intermediate, and a polyimide staple fiber laminate intermediate manufacturing step of stacking and hot-pressing a plurality of the polyimide staple fiber monolayer intermediates to produce a polyimide staple fiber laminate intermediate with residual water-soluble polymer (two manufacturing methods are provided, depending on whether the water-soluble polymer is dispersed in the slurry or in the wet-laid polyimide staple fibers). The present invention also provides a polyimide fiber paper laminate manufacturing method including a water-soluble polymer removal step of heating the polyimide staple fiber laminate intermediate to remove the residual water-soluble polymer residue. The polyimide fiber paper laminate manufacturing method of the present invention includes stacking and hot-pressing, allowing the desired thickness to be increased (laminated) without reducing density and maintaining high thermal insulation. Furthermore, because the laminate manufacturing method of the present invention does not use a polyimide precursor or polyimide solution, the steps for dispersing the polyimide precursor or polyimide solution and the step for imidizing the polyimide precursor are unnecessary, thereby simplifying the manufacturing process. In this way, the polyimide fiber paper produced by the layered manufacturing method of the present invention does not have the polyimide short fibers fixed together with polyimide resin (or other binder resin), so the polyimide short fibers can shift when an external force is applied, resulting in soft, cushiony polyimide fiber paper.

[0011] In order to solve the above problems, the present invention provides the following polyimide fiber paper and a method for manufacturing the same.

[0012] As a first invention, there is provided a laminated manufacturing method for polyimide fiber paper, comprising: a polyimide staple fiber slurry A manufacturing step of manufacturing a polyimide staple fiber slurry A from polyimide staple fibers and a water-soluble polymer; a polyimide staple fiber single intermediate A manufacturing step of manufacturing a polyimide staple fiber single intermediate A by wet papermaking the manufactured polyimide staple fiber slurry A; and a polyimide staple fiber laminated intermediate manufacturing step A of stacking a plurality of manufactured polyimide staple fiber single intermediates A and hot pressing them to manufacture a polyimide staple fiber laminated intermediate having a water-soluble polymer residue remaining therein.

[0013] As a second invention, there is provided a laminated manufacturing method for polyimide fiber paper, comprising: a polyimide staple fiber slurry B manufacturing step of manufacturing a polyimide staple fiber slurry B from polyimide staple fibers and water; a polyimide staple fiber single intermediate B manufacturing step of wet-processing the manufactured polyimide staple fiber slurry B and sprinkling or / and spraying a water-soluble polymer powder and / or a water-soluble polymer solution onto the wet-processed polyimide staple fibers to disperse the water-soluble polymer among the polyimide staple fibers, thereby manufacturing a polyimide staple fiber single intermediate B; and a polyimide staple fiber laminated intermediate manufacturing step B of stacking and hot-pressing a plurality of manufactured polyimide staple fiber single intermediates B to manufacture a polyimide staple fiber laminated intermediate having a water-soluble polymer residue remaining therein.

[0014] As a third invention, there is provided a laminated manufacturing method for polyimide fiber paper, which includes a water-soluble polymer removal step of heating the polyimide short fiber laminated intermediate produced by either the first or second invention to remove any remaining water-soluble polymer residue.

[0015] As a fourth invention, based on either the first or second invention, there is provided a laminated manufacturing method for polyimide fiber paper, further comprising a water-soluble polymer removal step of heating the polyimide short fiber laminated intermediate to remove any remaining water-soluble polymer residue.

[0016] As a fifth invention, based on any one of the first to fourth inventions, there is provided a laminated manufacturing method for polyimide fiber paper, wherein the decomposition temperature of the water-soluble polymer is lower than the glass transition temperature of the polyimide.

[0017] As a sixth invention, based on either the first or second invention, there is provided a laminated manufacturing method for polyimide fiber paper, wherein the heat-pressing temperature is 100°C or higher and 200°C or lower, and the heat-pressing pressure is 0.001 MPa or higher and 20 MPa or lower.

[0018] As a seventh invention, based on any one of the first to sixth inventions, there is provided a laminated manufacturing method for polyimide fiber paper, wherein the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step are combinations of (temperature (°C), time (min)) within the area surrounded by dots (300°C, 20 min), (400°C, 5 min), (470°C, 4 min), (480°C, 4 min), and (480°C, 20 min) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis (including combinations of conditions on the boundary line connecting the dots).

[0019] As an eighth invention, based on any one of the first to sixth inventions, there is provided a laminated manufacturing method for polyimide fiber paper, wherein the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step are combinations of (temperature (°C), time (min)) within the area surrounded by dots (300°C, 20 min), (400°C, 5 min), (470°C, 4 min), (430°C, 10 min), and (363°C, 20 min) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis (including combinations of conditions on the boundary line connecting the dots).

[0020] As a ninth invention, based on any one of the first to sixth inventions, there is provided a laminated manufacturing method for polyimide fiber paper, wherein the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step are combinations of (temperature (°C), time (min)) within the area surrounded by dots (300°C, 20 min), (380°C, 10 min), (400°C, 5 min), (430°C, 5 min), (470°C, 4 min), (430°C, 10 min), and (380°C, 15 min) (including combinations on the boundary line connecting the dots) on a plane with temperature (°C) on the horizontal axis and time (min).

[0021] As a tenth aspect of the present invention, there is provided polyimide fiber paper having a thickness of 1 mm or more.

[0022] The present invention provides a method for producing polyimide fiber paper by laminating polyimide fiber sheets, including a polyimide staple fiber slurry production step in which a polyimide staple fiber slurry containing polyimide staple fibers is produced, a polyimide staple fiber monolayer intermediate production step in which the slurry is wet-laid to produce a polyimide staple fiber monolayer intermediate, and a polyimide staple fiber monolayer intermediate production step in which a plurality of the polyimide staple fiber monolayer intermediates are stacked and hot-pressed to produce a polyimide staple fiber monolayer intermediate with residual water-soluble polymer (two production methods are provided, depending on whether the water-soluble polymer is dispersed in the slurry or in the wet-laid polyimide staple fibers). The present invention also provides a method for producing polyimide fiber paper by laminating and hot-pressing the polyimide staple fiber monolayer intermediate to produce a polyimide staple fiber monolayer intermediate with residual water-soluble polymer. The present invention also provides a method for producing polyimide fiber paper by laminating and hot-pressing the polyimide staple fiber monolayer intermediate, which allows the polyimide fiber sheet to be increased in thickness to a desired thickness without losing density or maintaining high thermal insulation. Furthermore, since the layered manufacturing method of the present invention does not use a polyimide precursor or polyimide solution, the steps of dispersing the polyimide precursor or polyimide solution and imidizing the polyimide precursor are not necessary, and the process can be simplified. In this way, the polyimide fiber paper manufactured by the layered manufacturing method of the present invention does not have the polyimide short fibers fixed to each other with polyimide resin (or other binder resin), so the polyimide short fibers can slip when an external force is applied, resulting in soft, cushiony polyimide fiber paper.

[0023] 1. Flowchart of a laminated manufacturing method for polyimide fiber paper according to embodiment 1. An example of a heating press in the manufacturing step of polyimide short fiber laminated intermediate A according to embodiment 1. Flowchart of a laminated manufacturing method for polyimide fiber paper according to embodiment 2. Photographs of polyimide short fiber surfaces before and after the water-soluble polymer removal step according to embodiment 3. Flowchart of a laminated manufacturing method for polyimide fiber paper according to embodiment 4. Flowchart of a laminated manufacturing method for polyimide fiber paper according to embodiment 4. Manufacturing conditions and evaluation results for polyimide fiber paper according to embodiments 7 to 9. A diagram showing the range of heating temperature and heating time in the water-soluble polymer removal step according to embodiment 7. A diagram showing the results of thermogravimetric analysis (TGA) of polyimide fiber paper according to the present invention. A diagram showing the rate of change in weight retention obtained by differentiating the results of thermogravimetric analysis (TGA) in FIG. 8. A diagram showing the range of heating temperature and heating time in the water-soluble polymer removal step according to embodiment 8. A diagram showing the range of heating temperature and heating time in the water-soluble polymer removal step according to embodiment 9.

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the content of the present invention is not limited to the following examples, and various modifications can be made without departing from the scope of the present invention.

[0025] <Embodiment 1> <Outline of Embodiment 1> Mainly Claim 1 The laminated manufacturing method for polyimide fiber paper of this embodiment 1 is composed of a polyimide short fiber slurry A manufacturing step, a polyimide short fiber single intermediate A manufacturing step, and a polyimide short fiber laminated intermediate manufacturing step A.

[0026] <Embodiment 1: Configuration of the Invention> A laminated manufacturing method for polyimide fiber paper according to this embodiment 1 will be described using the flowchart in Figure 1. The flowchart comprises a polyimide staple fiber slurry A manufacturing step (S0101), a polyimide staple fiber single intermediate A manufacturing step (S0102), and a polyimide staple fiber laminated intermediate A manufacturing step (S0103).

[0027] <First Embodiment: Flowchart of Layer-by-Layer Manufacturing Method>

[0028] <Embodiment 1: Polyimide Short Fiber Slurry A Production Step (S0101)> In the "polyimide short fiber slurry A production step" (S0101), polyimide short fiber slurry A is produced from polyimide short fibers and a water-soluble polymer. When producing the polyimide short fiber slurry A, the polyimide short fibers and the water-soluble polymer are added to a solvent (e.g., water) that dissolves the water-soluble polymer but not the polyimide short fibers, to produce the slurry A. Hereinafter, water will be used as an example, but other solvents (e.g., dimethyl sulfoxide (DMSO)) may also be used.

[0029] <Embodiment 1: Polyimide Staple Fiber Slurry A Production Step: Production of Polyimide Staple Fibers: Types of Commercially Available Polyimides> In the following description of each embodiment in this specification, the description of the production of polyimide staple fibers in this embodiment 1 (from "Types of Commercially Available Polyimides" to "Size of Polyimide Fibers") is common. Commercially available resins that constitute the polyimide staple fibers used in the present invention include DuPont's "Kapton" (registered trademark) (PMDA / 4,4'-ODA), Ube Industries' "Upilex-S" (registered trademark) (BPDA / PDA), and Ube Industries' "Upilex-R" (registered trademark) (BPDA / 4,4'-ODA). In the description of each embodiment below, a resin represented by Chemical Formula 1 (Kapton) is used as a representative example. Note that the resin represented by Chemical Formula 1 does not limit the embodiments of the present invention. <Chemical Formula 1>

[0030] <Embodiment 1: Polyimide Short Fiber Production Step: Production of Polyimide Short Fiber: Imide Bond> The imide bond is a bond formed by bonding a primary amine (ammonia: NH ３ The structure is one in which the two hydrogen atoms bonded to the nitrogen atom of a cyclic alkylene compound (a general term for compounds in which one hydrogen atom is replaced with a hydrocarbon group or an aromatic atomic group) are replaced with two carbonyl groups (-C(=O)-).

[0031] <Embodiment 1: Polyimide Staple Fiber Slurry A Production Step: Polyimide Staple Fiber Production: Physical Properties> Polyimide is a general term for polymers containing imide bonds in their repeating units, and typically refers to aromatic polyimides in which aromatic compounds are linked by imide bonds (e.g., the above-mentioned Chemical Formula 1). Aromatic polyimides have a rigid and strong molecular structure due to the conjugated structure of aromatics via imide bonds, and the strong intermolecular forces of imide bonds give them the highest level of thermal, mechanical, and chemical properties of all polymers. Physical properties generally include a modulus of elasticity of 3 to 10 GPa, a tensile break strength of 200 to 600 MPa, a tensile break elongation of 40 to 90%, a linear expansion coefficient of 0 to 50 ppm / °C, a glass transition temperature of 200°C or higher (300°C or higher depending on the type of polyimide), and a thermal decomposition temperature of 500°C or higher.

[0032] Polyimides have high heat resistance for the following reasons. The characteristic cyclic structure formed by two carbonyl groups (C=O) and one secondary amine group (NH) in the imide bond in the molecule increases the rigidity of the entire molecule, and the imide bond is highly polar, resulting in a strong attractive force (intermolecular force) between molecules that strengthens the bonding force between molecular chains, resulting in a high thermal decomposition temperature. Furthermore, polyimides that contain aromatic rings in their molecular structure have improved heat resistance because the aromatic rings, which delocalize π electrons, further increase the rigidity of the molecule.

[0033] <Embodiment 1: Step of Producing Polyimide Short Fiber Slurry A: Production of Polyimide Short Fibers: Shaving Method> This refers to a method of shaving polyimide fibers by rotating a roll of polyimide film, which is a cylindrical roll of a strip-shaped polyimide film, and applying a blade to the side of the rotating polyimide film roll. By applying a blade to the polyimide film roll while it is rotating, a bundle of very fine polyimide fibers is produced that matches the thickness of the film and the fineness of the blade. Polyimide short fibers are produced by cutting this bundle of polyimide fibers.

[0034] Because polyimide fibers are obtained by shaving, the fiber thickness is uniform, making them easier to process in subsequent processes. Furthermore, by adjusting the thickness of the polyimide film constituting the polyimide film roll and the fineness of the tip of the blade used for shaving, the width of the shaved polyimide fibers can be easily varied, making it easier to produce fibers with a smaller width than those produced by spinning. Furthermore, by cutting the shaved fiber bundle, the fiber length can be freely adjusted. Because the fiber width and fiber length can be freely combined, the fiber width and fiber length can be varied to suit the application of the polyimide fiber paper, making it possible to produce polyimide fiber paper with various strengths and durability.

[0035] <Embodiment 1: Step of Producing Polyimide Short Fiber Slurry A: Production of Polyimide Short Fibers: Spinning Method> In addition to the cutting method, polyimide fibers can also be produced by the known electrospinning method. The produced polyimide fibers can be cut appropriately to obtain polyimide short fibers.

[0036] <Embodiment 1: Polyimide Short Fiber Slurry A Production Step: Polyimide Fiber Size> In addition to the above-described polyimide short fiber production method, known polyimide short fiber production methods can also be used. The length of the polyimide short fibers is preferably 1 mm or more and 10 mm or less, and more preferably 2 mm or more and 6 mm or less. If the polyimide short fibers are too short, the polyimide fibers will not be sufficiently entangled in the slurry, and even if they are woven, they will not be sufficiently entangled to form a nonwoven fabric. Therefore, even if a water-soluble polymer is used, temporary fixing will be difficult. On the other hand, if the polyimide short fibers are too long, they will be entangled in a complex and overlapping manner, and even when heated and pressurized, the surface will not be smooth, resulting in an unsatisfactory paper finish. Therefore, there is an optimum length for the polyimide short fibers.

[0037] <Embodiment 1: Step of Producing Polyimide Short Fiber Slurry A: Additives to Slurry> In the step of producing polyimide short fiber slurry A, the polyimide short fibers produced in the preceding step of producing polyimide short fiber, and a water-soluble polymer such as polyvinyl alcohol (hereinafter referred to as PVA), are mixed with water at room temperature to produce polyimide short fiber slurry A. In addition to the polyimide short fibers, the water-soluble polymer, and water, dispersants, thickeners, antifoaming agents, and the like that are commonly used as additives for papermaking may also be added.

[0038] <Embodiment 1: Polyimide Staple Fiber Slurry A Production Step: Water-Soluble Polymer> The water-soluble polymer used in the present invention functions as a binder that temporarily bonds the polyimide staple fibers in the polyimide staple fiber single intermediate A produced in the polyimide staple fiber single intermediate A production step described below. The water-soluble polymer may be selected from one or more of starch, alginic acid, carboxymethyl cellulose, casein, vinylon, polyvinyl alcohol (PVA), vinyl acetate, polyvinyl acetate, and / or their derivatives. The melting point of typical water-soluble polymers is often 200°C or below, and they often soften at temperatures above 100°C. Furthermore, their thermal decomposition temperature is often above 200°C. Water-soluble polymers are generally commercially available as aqueous solutions, granules, or powders (e.g., spherical or irregularly shaped). When using a water-soluble polymer powder, the powder should be irregularly shaped and have a diameter of 10 to 200 μm (the diameter of a sphere circumscribing the powder), preferably 30 to 70 μm. If the diameter of the water-soluble polymer is too small compared to the height and width of the approximately rectangular cross section of the polyimide short fiber, the polyimide short fiber and the water-soluble polymer will not easily become entangled. If the diameter is too large, the polyimide short fiber will take a long time to dissolve in water or will remain undissolved. If PVA powder that is too large remains undissolved, it may not be uniformly dispersed in the slurry. Therefore, the above ranges are suitable for the shape and size of the water-soluble polymer that remains undissolved in water to become entangled with the polyimide short fiber and remain between the single fibers in the step of producing the polyimide short fiber single intermediate A described below, so that the water-soluble polymer will remain between the single fibers and be wet-laid for papermaking.

[0039] The water-soluble polymer added to the slurry not only functions as the binder, but also helps the polyimide staple fibers to easily entangle when they are made into paper, aiding in the bonding between the fibers and contributing to the formation of a uniform and strong polyimide fiber paper.

[0040] The tendency of polyimide staple fibers to entangle during the papermaking process is due to the following three factors: (1) Hydrogen bonding: Water-soluble polymers have many hydrophilic groups (e.g., hydroxyl and carboxyl groups), which form strong hydrogen bonds with water molecules. These further hydrogen bond with the fiber surface, forming a hydrophilic layer on the fiber surface. For example, when PVA is used, the hydrogen atoms of the PVA's -OH groups hydrogen bond with the oxygen atoms of water. The oxygen atoms of the imide groups of polyimide molecules hydrogen bond with the hydrogen atoms of water molecules, causing the PVA molecules to adsorb to the polyimide staple fiber surface, forming a hydrophilic layer. This hydrophilic layer binds the polyimide staple fibers together, and the PVA on the surface of the polyimide staple fibers adheres them to each other when they come into contact. (2) Viscosity: When water-soluble polymers are dissolved in water, they increase the viscosity of the solution. This makes it difficult for polyimide fibers to precipitate in the slurry, making them more uniformly dispersed and more likely to entangle. (3) Surface activity: The water-soluble polymer has a surface activity, which reduces the energy of the fiber surface and promotes contact between the polyimide short fibers. The explanations regarding the water-soluble polymer in paragraphs 0038 to 0040 above are also applicable to the other embodiments described below.

[0041] <Embodiment 1: Polyimide Short Fiber Slurry A Production Step: Dissolving a Water-Soluble Polymer> When dissolving a water-soluble polymer in water to produce a slurry, the water temperature and dissolving method should be selected to suit the water-soluble polymer being used. For example, in the case of PVA with a high degree of saponification, the PVA is difficult to dissolve in water at room temperature. Therefore, after thorough stirring at room temperature to disperse the PVA, the water temperature should be raised to a temperature at which the solubility increases (e.g., 60°C or higher, 80-90°C, etc.), and the PVA should be dissolved with stirring for approximately 30 minutes. The temperature should then be lowered to the papermaking temperature before use. When a slurry is produced in which the water-soluble polymer is dissolved in water, the polyimide short fibers can be well entangled, as described above. However, if the water-soluble polymer is completely dissolved in water, there is a possibility that most of the dissolved water-soluble polymer will fall out of the wet paper during wet papermaking in the polyimide short fiber single intermediate A production step described below. In this case, it is thought that the fibers are bonded together by a layer of water-soluble polymer adsorbed on the surface of the polyimide short fibers in the wet paper, or that water-soluble polymer powder that has not completely dissolved in water is retained in the gaps between the polyimide short fibers and remains.

[0042] <Embodiment 1: Polyimide Staple Fiber Slurry A Production Step: Case Where Water-Soluble Polymer Is Not Completely Dissolved> To mix a water-soluble polymer with polyimide staple fibers during wet papermaking in the polyimide staple fiber single intermediate A production step described below, the water-soluble polymer is mixed with water at a temperature at which the water-soluble polymer does not completely dissolve in water, and then wet papermaking is performed. To achieve this, when wet papermaking is performed in the polyimide staple fiber single intermediate A production step described below, a water-soluble polymer that is not easily soluble in water at the temperature of the polyimide staple fiber slurry A (e.g., room temperature; PVA is easily soluble in water at 60°C or higher, so 50°C or lower) is preferred. This is because the water-soluble polymer is likely to remain between the polyimide staple fibers in the polyimide staple fiber single intermediate A during wet papermaking. For example, when wet papermaking is performed from polyimide staple fiber slurry A at room temperature, it is preferable to use PVA. Substances with a high degree of saponification, such as PVA, are almost insoluble in water at room temperature. To dissolve it completely, the PVA powder is mixed in water at room temperature with thorough stirring as described above, and the water is heated to 80 to 90° C. and stirred thoroughly for about 30 minutes.

[0043] <Embodiment 1: Polyimide Staple Fiber Single Intermediate A Production Step (S0102)> In the "polyimide staple fiber single intermediate A production step" (S0102), the produced polyimide staple fiber slurry A is subjected to wet papermaking to produce the polyimide staple fiber single intermediate A.

[0044] <Embodiment 1: Step for Producing a Polyimide Short Fiber Single Intermediate A: Wet Papermaking> In wet papermaking, the slurry is filtered using a known wire (e.g., a Fourdrinier or a Cylinder (Circular)) commonly used in papermaking to form a sheet, thereby forming a wet paper. If a thick sheet is to be filtered all at once, problems are likely to arise in maintaining the uniformity of the slurry, in achieving uniform drying in the drying step described below, in maintaining the uniformity of the density of the filtered sheet, and in maintaining the smoothness of the surface. Even if wet paper sheets are stacked immediately after filtering, problems may arise in the uniformity of drying in the drying step described below. Therefore, in the present invention, after drying, multiple sheets are stacked in step A for producing a polyimide short fiber laminated intermediate, which will be described below.

[0045] <Embodiment 1: Polyimide Short Fiber Single Intermediate A Production Step: Drying> The wet paper contains a large amount of water, so it is heated and dried. The heating during drying can be at the melting point of the water-soluble polymer contained in the slurry or a temperature slightly below the melting point. An example of a temperature below the melting point is 100°C to 180°C, at which the water-soluble polymers exemplified above soften. By heating to a temperature near the melting point of the water-soluble polymer, the moisture in the wet paper can be removed and the paper can be dried. At a temperature close to the melting point of the water-soluble polymer, the water-soluble polymer softens and heat-fuses adjacent polyimide short fibers together, thereby fixing them together. This can be used as a temporary fix until the water-soluble polymer is removed in the water-soluble polymer removal step described later in this embodiment. A step of squeezing and dehydrating the paper by applying pressure by sandwiching the paper between a press roll and a felt before drying can also be included.

[0046] For drying, for example, a commonly used multi-cylinder or Yankee type dryer can be used. Heating in the dryer is preferably performed at a temperature close to the melting point of the water-soluble polymer, as described above.

[0047] The dried polyimide short fiber single intermediate A has a thickness of 0.2 to 0.5 mm per sheet. The in-plane tolerance of the thickness is ±10%. A thickness greater than ±10% is likely due to uneven entanglement of the polyimide short fibers, resulting in thicker layers in some areas, or conversely, due to sparse distribution of the polyimide fibers, resulting in thinner layers. To prevent uniform pressing during the subsequent lamination and hot pressing steps described below, the intermediate product is manufactured to fall within the above range. When papermaking is performed using a conventional wire used in papermaking, the intermediate product is continuously made and wound around a roller. In this case, a film thickness distribution is likely to occur perpendicular to the direction of travel during papermaking (the direction of travel toward the winding roller). This is due to excess slurry moving in that direction during papermaking.

[0048] <Embodiment 1: Polyimide Short Fiber Laminated Intermediate Production Step A (S0103)> In "Polyimide Short Fiber Laminated Intermediate Production Step A" (S0103), a plurality of produced polyimide short fiber single intermediates A are stacked and hot-pressed to produce a polyimide short fiber laminated intermediate containing water-soluble polymer residue remaining therein.

[0049] A polyimide staple fiber single intermediate A was produced in the polyimide staple fiber single intermediate A production step. The polyimide staple fiber single intermediate A was produced by heating and drying a wet paper made by wet-processing polyimide staple fiber slurry A, softening the water-soluble polymer between the polyimide staple fibers with heat, and temporarily fixing them by heat fusion. As described above, a plurality of paper-like polyimide staple fiber single intermediates A, each 0.2 to 0.5 mm thick, were stacked in the required number of sheets to obtain the desired thickness and hot-pressed to produce a polyimide staple fiber laminated intermediate. Because the polyimide staple fiber single intermediate A is compressed in the thickness direction by hot-pressing, depending on the conditions, the thickness is not simply the sum of the thicknesses of the single layers. Similarly, the density is not simply the sum. If the in-plane standard density of the original single-layer polyimide staple fiber single intermediate A is d and its tolerance is ±20% (three times the standard deviation), the density tolerance of the polyimide laminated intermediate produced by stacking n sheets in the polyimide staple fiber laminated intermediate production step A is ±((0.2d) × (n)) 1 / 2Within this range, the variation in the degree of entanglement of the polyimide fibers is small, and the variation in thermal conductivity is also small, which is preferable. A more preferable range is ±20%.

[0050] After laminating a predetermined number of polyimide short fiber single intermediate bodies A, and before hot pressing, the polyimide short fibers between the polyimide short fiber single intermediate bodies A may be entangled by a known method such as needle punching or hydroentangling.

[0051] The heating temperature range during hot pressing is preferably, for example, below the glass transition temperature of the polyimide (generally 200°C or higher) and below the melting point of the water-soluble polymer (generally 200°C or lower), a temperature range in which the water-soluble polymer softens. A preferred temperature range is one in which 90% by weight or more of the water-soluble polymer remains after heating within this temperature range. For example, when PVA is used as the water-soluble polymer, heating is performed in the range of 100 to 200°C, since the melting point of PVA is approximately 200°C. Hot pressing is performed at a temperature and for a heating time in which 90% by weight or more of the PVA remains.

[0052] The "water-soluble polymer residue" refers to a water-soluble polymer remaining in a single polyimide staple fiber intermediate A produced by wet-laid papermaking of the polyimide staple fiber slurry A, and also includes a water-soluble polymer that has been softened by drying after wet-laid papermaking and / or by heat in the hot press in step A of producing a polyimide staple fiber laminated intermediate and thermally fused to adjacent polyimide staple fibers.

[0053] During the hot pressing, a mold may be used to mold a plurality of stacked polyimide staple fiber single intermediates A, as shown in Figure 2. The heating during hot pressing is preferably at or below the decomposition temperature of the water-soluble polymer contained in the polyimide staple fiber single intermediates A. When molding using a mold during hot pressing, the water-soluble polymer contained in the polyimide staple fiber single intermediates A makes it easier for the polyimide staple fiber single intermediates A to conform to the mold, and the water-soluble polymer reduces the frictional force acting between adjacent polyimide staple fiber single intermediates A stacked under pressure due to the pressure, making them more likely to entangle with each other. Furthermore, the combination of the pressure and heat increases the viscosity of the water-soluble polymer, ultimately resulting in the effect that, upon solidification, the polyimide staple fibers of the two intermediates are fused together via the solidified water-soluble polymer residue.

[0054] The purpose of using the water-soluble polymer is to maintain the shapes of the single polyimide staple fiber intermediate A and the laminated and hot-pressed polyimide staple fiber laminate intermediate by fixing the polyimide staple fibers together with the water-soluble polymer until the hot-pressing of the single polyimide staple fiber intermediate A formed by laminating a plurality of sheets in polyimide staple fiber laminate intermediate production step A is completed and until the water-soluble polymer is removed in the water-soluble polymer removal step described below, thereby facilitating handling during the process.

[0055] In the step A for producing a polyimide staple fiber laminated intermediate, any number of polyimide staple fiber single intermediates A and any number of polyimide staple fiber single intermediates B of the second embodiment described below may be laminated in any order, followed by hot pressing to produce a polyimide staple fiber laminated intermediate.

[0056] The polyimide staple fiber laminated intermediate manufacturing step A can be configured to further include an embossing substep using a mold. To achieve this, the following configuration (1) or (2) can be adopted. (1) The polyimide staple fiber laminated intermediate manufacturing step A further includes an embossing substep using a mold to form a polyimide staple fiber laminated intermediate. (2) The polyimide staple fiber laminated intermediate manufacturing step A further includes a stacking substep of stacking a plurality of the manufactured single polyimide staple fiber intermediates A to form a single polyimide staple fiber intermediate A laminate, and an embossing substep of hot-pressing the manufactured single polyimide staple fiber intermediate A laminate using a mold to form a polyimide staple fiber laminated intermediate.

[0057] Effect of Embodiment 1 The laminated manufacturing method for polyimide fiber paper of Embodiment 1 makes it possible to obtain polyimide fiber paper with a higher density and better heat insulation than thickened polyimide fiber paper of the prior art, with a desired thickness that is equal to or greater than the thickness of one polyimide short fiber single intermediate body A. If a mold is used when stacking and hot-pressing a plurality of polyimide short fiber single intermediate bodies A, a polyimide short fiber laminated intermediate body molded to the shape of the mold can be obtained.

[0058] <Embodiment 2> <Outline of Embodiment 2> Mainly Claim 2 The laminated manufacturing method for polyimide fiber paper of this embodiment 2 is composed of a polyimide staple fiber slurry B manufacturing step, a polyimide staple fiber single intermediate B manufacturing step, and a polyimide staple fiber laminated intermediate manufacturing step B, and is characterized in that, unlike embodiment 1, water-soluble molecules are not added to the slurry in the polyimide staple fiber slurry B manufacturing step, but a water-soluble polymer is dispersed between the polyimide staple fibers wet-made in the polyimide staple fiber single intermediate B manufacturing step.

[0059] <Embodiment 2: Configuration of the Invention> A laminated manufacturing method for polyimide fiber paper according to this embodiment 2 will be described with reference to the flowchart in Figure 3. The flowchart comprises a polyimide staple fiber slurry B manufacturing step (S0301), a polyimide staple fiber single intermediate B manufacturing step (S0302), and a polyimide staple fiber laminated intermediate B manufacturing step (S0303).

[0060] <Embodiment 2: Flowchart of Layer-by-Layer Manufacturing Method>

[0061] <Embodiment 2: Step of Producing Polyimide Short Fiber Slurry B (S0301)> In the "step of producing polyimide short fiber slurry B" (S0301), polyimide short fibers and water are used to produce polyimide short fiber slurry B. Note that instead of water, a solvent that dissolves water-soluble polymers but does not dissolve polyimide short fibers (e.g., dimethyl sulfoxide (DMSO)) may be used.

[0062] <Embodiment 2: Step of Producing Polyimide Short Fiber Slurry B: Production of Polyimide Short Fibers: Type of Polyimide Used> As the resin constituting the polyimide short fibers, the resins described in embodiment 1 can be used.

[0063] <Embodiment 2: Step of Producing Polyimide Short Fiber Slurry B: Production of Polyimide Short Fibers> The polyimide fibers and polyimide short fibers are produced in the same manner as in Embodiment 1, and therefore a description thereof will be omitted.

[0064] <Embodiment 2: Step of Producing Polyimide Short Fiber Slurry B: Additives to Slurry> In the step of producing polyimide short fiber slurry B, the polyimide short fibers produced in the preceding step of producing polyimide short fiber are mixed with, for example, water at room temperature to produce polyimide short fiber slurry B. In addition to the polyimide short fibers and water, a dispersant, thickener, antifoaming agent, or the like that is generally used as an additive for papermaking may also be added. Unlike the first embodiment, the second embodiment is characterized in that a water-soluble polymer is not dispersed in the slurry.

[0065] <Embodiment 2: Step of Producing a Polyimide Staple Fiber Single Intermediate B (S0302)> In the "step of producing a polyimide staple fiber single intermediate B" (S0302), the produced polyimide staple fiber slurry B is wet-laid into a paper sheet, and a water-soluble polymer powder and / or a water-soluble polymer solution is sprinkled or / and sprayed onto the wet-laid polyimide staple fibers to disperse the water-soluble polymer among the polyimide staple fibers, thereby producing a polyimide staple fiber single intermediate B.

[0066] In wet papermaking, the slurry is filtered using a known wire (e.g., a fourdrinier or cylinder (round) wire) commonly used in paper production to form a sheet, thereby forming a wet paper. If a thick sheet is to be filtered all at once, problems are likely to arise in maintaining the uniformity of the slurry, in achieving uniform drying in the drying step described below, in maintaining the uniform density of the filtered paper, and in maintaining the smoothness of the surface. Since stacking wet paper immediately after filtering can also cause problems with the uniformity of drying described below, in the present invention, multiple sheets are stacked in step B of producing a polyimide short fiber laminated intermediate described below.

[0067] <Embodiment 2: Step of Producing Polyimide Staple Fiber Single Intermediate B: Dispersion of Water-Soluble Polymer Before Drying> Water-soluble polymer powder and / or a water-soluble polymer solution is sprinkled or / and sprayed onto wet-laid polyimide staple fibers to disperse the water-soluble polymer among the polyimide staple fibers, thereby thermally fusing the polyimide staple fibers. The water-soluble polymer is preferably dispersed in the wet paper after wet-laid papermaking and before drying. This is because heating after dispersing the water-soluble polymer can be used for both heating during drying and drying. The water-soluble polymer is dispersed by sprinkling or spraying, for example, dried water-soluble polymer powder onto the wet paper from which polyimide staple fiber slurry B has been made. Alternatively, the water-soluble polymer may be dispersed among the polyimide staple fibers by spraying, for example, an aqueous solution of the water-soluble polymer dissolved in water or hot water.

[0068] <Embodiment 2: Step of Producing Polyimide Staple Fiber Single Intermediate B: Dispersion of Water-Soluble Polymer After Drying> After drying the wet paper, a water-soluble polymer powder and / or a water-soluble polymer solution can be sprinkled or / and sprayed onto the polyimide staple fibers and then heated to thermally fuse the water-soluble polymer between the polyimide staple fibers. When sprinkling or / and spraying onto the wet paper after drying, it is recommended to move or vibrate the polyimide staple fibers that have been made and dried so that the water-soluble polymer penetrates between the polyimide staple fibers after papermaking. The water-soluble polymer is dispersed by sprinkling or spraying the dried water-soluble polymer powder onto the wet paper made from the polyimide staple fiber slurry B or onto the dried wet paper. The water-soluble polymer can also be dispersed between the polyimide staple fibers by spraying an aqueous solution of the water-soluble polymer dissolved in water or hot water onto the polyimide staple fibers.

[0069] <Embodiment 2: Polyimide Staple Fiber Single Intermediate B Production Step: Water-Soluble Polymer> The water-soluble polymer functions as a binder to temporarily bond the polyimide staple fibers together. The water-soluble polymer may be selected from one or more of starch, alginic acid, carboxymethyl cellulose, casein, vinylon, polyvinyl alcohol (PVA), vinyl acetate, polyvinyl acetate, and / or their derivatives. Some water-soluble polymers are less soluble in water at certain temperatures (e.g., room temperature; PVA is easily soluble in water above 60°C, so it is best to sprinkle or spray the resulting aqueous solution powder onto the polyimide staple fibers.) Therefore, when dissolving the water-soluble polymer in water and sprinkling or spraying it onto the polyimide staple fibers, it is recommended to adjust the water temperature so that the water-soluble polymer dissolves. For example, when using PVA, mixing it in water heated to 80 to 90°C and stirring thoroughly will dissolve it.

[0070] Alternatively, a suspension may be prepared in which the water-soluble polymer is dispersed in water without being dissolved therein, and the suspension may be sprinkled or / and sprayed onto the wet paper or the wet paper by a spray or the like, thereby dispersing the water-soluble polymer powder in the suspension among the polyimide short fibers.

[0071] When the water-soluble polymer is dispersed after papermaking as in the second embodiment, when the single polyimide fiber intermediates B are laminated in the next step, Step B of producing a polyimide short fiber laminated intermediate, which will be described later, the water-soluble polymer heat-fused to the surface of the polyimide short fiber in the portion between the single polyimide fiber intermediates B must come into contact with the polyimide short fiber or water-soluble polymer of the adjacent single polyimide fiber intermediate B. For this purpose, the single polyimide fiber intermediate B should have a basis weight (weight per unit area) of 65 to 110 g / m. ２ It is preferable that the basis weight is in the range of 1000 to 15000. If the basis weight is too small, the intervals between the polyimide short fibers in the surface direction will be too wide, and even if a water-soluble polymer is sprinkled or sprayed on the polyimide short fibers after papermaking, it may not be entangled with the polyimide short fibers near the surface and may not adhere to them. If the basis weight is too large, a large amount of the water-soluble polymer will adhere to the surface of the polyimide short fibers, and a longer heating time will be required to remove the water-soluble polymer in the water-soluble polymer removal step described in the embodiment below, which may increase the production time and the cost.

[0072] <Embodiment 2: Polyimide Short Fiber Single Intermediate B Production Step: Drying> The wet paper thus produced contains a large amount of water, so it is heated and dried. When a water-soluble polymer is dispersed in the wet paper, the heating during drying can be performed at the melting point of the water-soluble polymer or a temperature slightly below the melting point. An example of a temperature below the melting point is 100°C to 180°C, at which the water-soluble polymer softens. By heating the wet paper to a temperature close to the melting point of the water-soluble polymer, the moisture in the wet paper can be removed and the paper can be dried. Furthermore, the water-soluble polymer softens at a temperature close to the melting point, allowing adjacent polyimide short fibers to be thermally fused and fixed together. This can be used as a temporary fixation until the water-soluble polymer is removed in the water-soluble polymer removal step described later. A step of squeezing and dehydrating the paper by clamping the paper between a press roll and a felt to apply pressure before drying can also be included.

[0073] Unlike the above example (in which the water-soluble polymer is dispersed before drying), if the water-soluble polymer powder is sprinkled or / and sprayed onto the wet paper after drying, a heating substep may be carried out after the sprinkling or / and spraying, before the polyimide staple fiber laminated intermediate production step B described below, in which the water-soluble polymer powder is heated to the melting point or a temperature slightly below the melting point (e.g., 100°C to 180°C at which the water-soluble polymer softens) of the water-soluble polymer, and adjacent polyimide staple fibers are thermally fused together by the softened water-soluble polymer. Since the heating substep increases the number of steps, the polyimide staple fibers may be thermally fused together and fixed by the water-soluble polymer during the heat-pressing step of the next polyimide staple fiber laminated intermediate production step B described below, without the heating substep. In this case, care must be taken in handling the single polyimide staple fiber intermediate B during the process, such as by supporting it with a jig, to prevent the shape of the single polyimide staple fiber intermediate B from being distorted until the heat-pressing step.

[0074] For drying, for example, a commonly used multi-cylinder or Yankee type dryer can be used. Heating in the dryer is preferably performed at a temperature close to the melting point of the water-soluble polymer, as described above.

[0075] The dried polyimide short fiber single intermediate B has a thickness of 0.2 to 0.5 mm per sheet. The in-plane tolerance of the thickness is ±10%. A thickness tolerance of ±10% or more is considered to be due to uneven entanglement of the polyimide short fibers, resulting in thicker layers in some areas, or conversely, due to sparse distribution of the polyimide fibers, resulting in thinner layers. To prevent uneven pressing during the subsequent lamination and hot pressing steps described below, the intermediate product is manufactured to fall within the above range. When papermaking is performed using a conventional wire used in papermaking, the intermediate product is made continuously and wound around a roller. In this case, it is considered that a film thickness distribution occurs perpendicular to the direction of travel during papermaking (the direction of travel to the winding roller). This is due to excess slurry moving in that direction during papermaking.

[0076] <Embodiment 2: Polyimide Short Fiber Laminated Intermediate Production Step B (S0303)> In "Polyimide Short Fiber Laminated Intermediate Production Step B" (S0303), a plurality of the produced polyimide short fiber single intermediates B are stacked and hot-pressed to produce a polyimide short fiber laminated intermediate containing water-soluble polymer residue remaining therein.

[0077] In the step of producing polyimide short fiber single intermediate B, a polyimide short fiber single intermediate B was produced. In this step, a plurality of paper-like polyimide short fiber single intermediate B, each having a thickness of 0.2 to 0.5 mm, are stacked in the predetermined number required to obtain the desired thickness and hot-pressed to produce a polyimide short fiber laminated intermediate. Because the heat-press compresses the thickness direction, the thickness does not simply equal the sum of the thicknesses of the single layers, depending on the conditions. Similarly, the density does not simply equal the sum. If the in-plane standard density of the original single-layer polyimide short fiber single intermediate B is d and its tolerance is ±20% (three times the standard deviation), the density tolerance of the polyimide laminated intermediate produced by stacking n sheets in the step of producing polyimide short fiber laminated intermediate B is ±((0.2d) × (n)) 1 / 2 Within this range, the variation in the degree of entanglement of the polyimide fibers is small, and the variation in thermal conductivity is also small, which is preferable. A more preferable range is ±20%.

[0078] An example of the polyimide staple fiber single intermediate B is obtained by heating and drying a wet paper made by wet-processing the polyimide staple fiber slurry B, and then temporarily fixing and securing the polyimide staple fibers by heat fusion with a water-soluble polymer. If the polyimide staple fibers have not been heat-fused and secured by the water-soluble polymer during the heating in the step of producing the polyimide staple fiber single intermediate B, the polyimide staple fibers are heat-fused and secured by the heating press in this step as described above.

[0079] After laminating a predetermined number of polyimide short fiber single intermediate bodies B, and before hot pressing, the polyimide short fibers between the polyimide short fiber single intermediate bodies B may be entangled by a known method such as needle punching or water jet entanglement.

[0080] The heating temperature range during hot pressing is preferably, for example, the glass transition temperature of the polyimide (generally 200° C. or higher) or lower and the melting point of the water-soluble polymer (generally 200° C. or lower), and is a temperature range in which the water-soluble polymer softens. For example, when PVA is used as the water-soluble polymer, the heating is performed in the range of 100 to 200° C., since the melting point of PVA is about 200° C.

[0081] The "water-soluble polymer residue" refers to the water-soluble polymer remaining in the polyimide staple fiber single intermediate B from the water-soluble polymer powder sprinkled or / and sprayed onto the polyimide staple fibers wet-sheeted in the step of producing the polyimide staple fiber single intermediate B. It also includes the water-soluble polymer that has thermally fused adjacent polyimide staple fibers together by the heat of the hot press in the step of producing the polyimide staple fiber laminated intermediate B.

[0082] During the hot pressing, a mold may be used to mold a plurality of stacked polyimide staple fiber single intermediate bodies B, as shown in Figure 2. The heating during hot pressing is preferably at or below the decomposition temperature of the water-soluble polymer contained in the polyimide staple fiber single intermediate body B. When molding using a mold during hot pressing, the water-soluble polymer contained in the polyimide staple fiber single intermediate body B helps the polyimide staple fiber single intermediate body B to conform to the mold, and the frictional force acting between adjacent polyimide staple fiber single intermediate bodies B stacked under the pressure of the press is reduced by the water-soluble polymer, making them more likely to entangle with each other. Furthermore, the combination of the press pressure and heat increases the viscosity of the water-soluble polymer, ultimately resulting in the effect that, upon solidification, the polyimide staple fibers of the two intermediate bodies are fused together via the solidified water-soluble polymer residue.

[0083] The purpose of using the water-soluble polymer is to maintain the shapes of the single polyimide staple fiber intermediate B and the laminated and heat-pressed polyimide staple fiber laminate intermediate by fixing the polyimide staple fibers together with the water-soluble polymer until the heat-pressing of the single polyimide staple fiber intermediate B formed by laminating a plurality of sheets in the polyimide staple fiber laminate intermediate production step B is completed and until the water-soluble polymer is removed in the water-soluble polymer removal step described below, thereby facilitating handling during the process.

[0084] In the step B of producing a polyimide staple fiber laminated intermediate, any number of polyimide staple fiber single intermediates B and the polyimide staple fiber single intermediates A of the first embodiment may be laminated in any order and then hot-pressed to produce a polyimide staple fiber laminated intermediate.

[0085] The polyimide staple fiber laminated intermediate production step B can be configured to further include an embossing substep using a mold. To achieve this, the following configuration (1) or (2) can be adopted. (1) The polyimide staple fiber laminated intermediate production step B further includes an embossing substep using a mold to heat-press and mold into a polyimide staple fiber laminated intermediate. (2) The polyimide staple fiber laminated intermediate production step B further includes a stacking substep of stacking a plurality of the produced polyimide staple fiber single intermediates B to produce a polyimide staple fiber single intermediate B laminate, and an embossing substep of heat-pressing and molded the produced polyimide staple fiber single intermediate B laminate into a polyimide staple fiber laminated intermediate.

[0086] Effect of Embodiment 2 The laminated manufacturing method for polyimide fiber paper of Embodiment 2 makes it possible to obtain polyimide fiber paper with a higher density and better heat insulation than thickened polyimide fiber paper of the prior art, with a desired thickness that is equal to or greater than the thickness of one polyimide short fiber single intermediate body B. If a mold is used when stacking and hot-pressing a plurality of polyimide short fiber single intermediate bodies B, a polyimide short fiber laminated intermediate body molded to the shape of the mold can be obtained.

[0087] <Embodiment 3> <Outline of Embodiment 3> Mainly Claim 3 The laminated manufacturing method for polyimide fiber paper of this embodiment 3 has a water-soluble polymer removal step in which the polyimide short fiber laminated intermediate produced by the laminated manufacturing method of either embodiment 1 or embodiment 2 is heated to remove any remaining water-soluble polymer residue.

[0088] <Embodiment 3: Configuration of the Invention> The laminated manufacturing method for polyimide fiber paper of this embodiment 3 is a laminated manufacturing method for polyimide fiber paper, which includes a water-soluble polymer removal step of heating a polyimide short fiber laminated intermediate manufactured by the manufacturing method of either embodiment 1 or embodiment 2 to remove any remaining water-soluble polymer residue.

[0089] <Embodiment 3: Water-Soluble Polymer Removal Step> In the "water-soluble polymer removal step," a polyimide staple fiber laminated intermediate manufactured by the manufacturing method of either embodiment 1 or embodiment 2 is heated to remove the water-soluble polymer residue remaining in the polyimide staple fiber laminated intermediate. Figure 4 shows 100x magnification surface photographs of a single polyimide staple fiber intermediate A (or a single polyimide staple fiber intermediate B) (left) and a polyimide fiber paper (right). As shown on the left in Figure 4, the syrup-like water-soluble polymer sandwiched between the polyimide staple fibers is thermally fused to the polyimide staple fibers. The water-soluble polymer residue is removed by heating. Therefore, as shown on the right in Figure 4, the polyimide fiber paper that has undergone the water-soluble polymer removal step has lost the syrup-like water-soluble polymer (present on the left in Figure 4) and retains the polyimide staple fibers that became entangled during wet papermaking and / or hot pressing.

[0090] The laminated manufacturing method for polyimide fiber paper of the third embodiment is a laminated manufacturing method for polyimide fiber paper in which a water-soluble polymer removal step is performed on a polyimide staple fiber laminated intermediate produced by the manufacturing method of either the first embodiment or the second embodiment. For example, this is a manufacturing method in which a polyimide staple fiber laminated intermediate produced outside Japan by the manufacturing method of either the first embodiment or the second embodiment is imported into Japan, and polyimide fiber paper is manufactured in Japan by a manufacturing method including the water-soluble polymer removal step.

[0091] The heating temperature in the water-soluble polymer removal step is in the range of not less than the thermal decomposition temperature of the water-soluble polymer and not more than the glass transition temperature of the polyimide, with higher temperatures being preferred within this range. For example, if PVA is used as the water-soluble polymer, the thermal decomposition temperature is about 200°C, so a temperature of not less than 300°C is preferred. The upper limit temperature on the higher temperature side is lower than the thermal decomposition temperature of the general polyimide, and is preferably less than 500°C.

[0092] Effect of Embodiment 3 Polyimide fiber paper with excellent heat resistance as well as heat insulation can be obtained by the method for producing polyimide fiber paper of Embodiment 3. Furthermore, since the polyimide short fibers produced by the method for producing polyimide fiber paper of Embodiment 3 are bonded only by entanglement, the fibers are not fixed to each other with a binder or the like and are therefore movable, making it possible to obtain soft, cushiony polyimide fiber paper.

[0093] <Embodiment 4> <Outline of Embodiment 4> Mainly Claim 4 The laminated manufacturing method for polyimide fiber paper of this embodiment 4 is characterized in that, after the laminated manufacturing method for polyimide fiber paper of either embodiment 1 or embodiment 2, it further includes a water-soluble polymer removal step in which the polyimide short fiber laminated intermediate is heated to remove any remaining water-soluble polymer residue.

[0094] <Embodiment 4: Configuration of the Invention> A laminated manufacturing method for polyimide fiber paper according to this embodiment 4, which is based on either embodiment 1 or embodiment 2, will be described using the flowcharts shown in Figures 5a and 5b. Figure 5a is a flowchart of the laminated manufacturing method for polyimide fiber paper according to this embodiment 4, which is based on embodiment 1, and Figure 5b is a flowchart of the laminated manufacturing method for polyimide fiber paper according to this embodiment 4, which is based on embodiment 2. Since the steps other than the water-soluble polymer removal step (S0504) in the flowcharts of Figures 5a and 5b have already been described in embodiment 1 or embodiment 2, respectively, their description will be omitted and only the water-soluble polymer removal step (S0504) will be described.

[0095] <Embodiment 4: Water-soluble polymer removal step (S0504)> In the "water-soluble polymer removal step" (S0504), the polyimide staple fiber laminate intermediate is heated to remove any remaining water-soluble polymer residue. As shown in the left side of Figure 4, the water-soluble polymer sandwiched between the polyimide staple fibers and heat-fused to the polyimide staple fibers is removed by heating. Once the water-soluble polymer is removed, the polyimide staple fibers that were entangled during wet papermaking and / or hot pressing remain, as shown in the right side of Figure 4.

[0096] The manufacturing method of this embodiment 4 is a laminate manufacturing method for polyimide fiber paper in which a water-soluble polymer removal step is performed following the laminate manufacturing method of embodiment 1 and the laminate manufacturing method of embodiment 2, as shown in Figures 5a and 5b.

[0097] The heating temperature in the water-soluble polymer removal step is preferably higher than the thermal decomposition temperature of the water-soluble polymer. For example, if PVA is used as the water-soluble polymer, the thermal decomposition temperature is about 200°C, so the heating temperature is preferably 300°C or higher. The upper limit temperature on the higher temperature side is lower than the thermal decomposition temperature of the general polyimide, and is preferably less than 500°C.

[0098] The water-soluble polymer removing step of this embodiment 4 may be configured to be performed simultaneously with the heating and pressing in step A of producing a polyimide short fiber laminated intermediate in embodiment 1 or step B of producing a polyimide short fiber laminated intermediate in embodiment 2. In this case, the heating temperature of the heating and pressing is the heating temperature in the water-soluble polymer removing step, and the heating and pressing time is the heating time in the water-soluble polymer removing step.

[0099] Effect of Embodiment 4 Polyimide fiber paper with excellent heat resistance as well as heat insulation can be obtained by the method for producing polyimide fiber paper of Embodiment 4. The polyimide short fibers produced by the method for producing polyimide fiber paper of Embodiment 4 are bonded only by entanglement, and therefore the fibers are not fixed to each other with a binder or the like and are movable, making it possible to obtain soft, cushiony polyimide fiber paper.

[0100] <Embodiment 5> <Embodiment 5: Overview> Mainly Claim 5 In the laminated manufacturing method for polyimide fiber paper of this embodiment 5, which is based on any one of embodiments 1 to 4, the decomposition temperature of the water-soluble polymer is lower than the glass transition temperature of the polyimide.

[0101] <Embodiment 5: Configuration of the Invention> In this embodiment 5, the decomposition temperature of the water-soluble polymer used in the laminated manufacturing method of polyimide fiber paper described in any one of embodiments 1 to 4 is configured to be lower than the glass transition temperature of the polyimide that constitutes the polyimide short fibers.

[0102] <Embodiment 5: Relationship between the decomposition temperature of a water-soluble polymer and the glass transition temperature of a polyimide> Generally, the melting point and glass transition temperature of a substance are lower than the thermal decomposition temperature of the substance. When the decomposition temperature of a water-soluble polymer is lower than the glass transition temperature of a polyimide, the decomposition temperature of the water-soluble polymer is lower than the decomposition temperature of the polyimide. The order of the temperatures is: decomposition temperature of polyimide > glass transition temperature of polyimide > decomposition temperature of the water-soluble polymer.

[0103] <Embodiment 5: Relationship between Heat-Pressing Temperature and Decomposition Temperature of Water-Soluble Polymer> When the single polyimide staple fiber intermediate A (or the single polyimide staple fiber intermediate B) formed by stacking several layers in the step of producing a polyimide staple fiber laminated intermediate is heat-pressed at a temperature higher than the melting point of the water-soluble polymer but lower than the decomposition temperature of the water-soluble polymer (i.e., lower than the glass transition temperature of the polyimide), the polyimide staple fibers do not undergo glass transition, only the water-soluble polymer is softened, and the polyimide staple fibers can be thermally bonded to each other via the water-soluble polymer. The shape of the polyimide staple fiber laminated intermediate formed by heat-pressing can be maintained until the water-soluble polymer is removed in the water-soluble polymer removal step after the heat-pressing.

[0104] Furthermore, the influence on the polyimide short fibers (thermal decomposition and glass transition) can be prevented. The influence on the polyimide short fibers is to prevent the polyimide short fibers from undergoing glass transition when heated. If the polyimide short fibers undergo glass transition, the polyimide short fibers will become soft and easily deformed, resulting in a polyimide short fiber laminate intermediate that is thinner than the desired thickness, or variations in the degree of fiber overlap will locally change the ease of deformation during hot pressing, resulting in an uneven surface of the polyimide short fiber laminate intermediate and reduced strength.

[0105] <Embodiment 5: Relationship between the Water-Soluble Polymer Removal Step and the Decomposition Temperature of the Water-Soluble Polymer> Generally, the decomposition temperature of polyimide (500°C or higher) is higher than the decomposition temperature of the water-soluble polymer. If the decomposition temperature of the water-soluble polymer is higher than the glass transition temperature of polyimide, the polyimide short fibers constituting the polyimide short fiber laminate intermediate formed in the previous hot press process will undergo glass transition and soften during the heat treatment in the water-soluble polymer removal step, potentially causing deformation and making it unable to maintain its shape. For this reason, the present invention uses a water-soluble polymer that decomposes at a temperature lower than the decomposition temperature of the polyimide constituting the polyimide short fibers used in the present invention. This allows the shape formed in the hot press to be maintained until the water-soluble polymer removal step.

[0106] <Effects of Embodiment 5> In the laminated manufacturing method of polyimide fiber paper of Embodiment 5, in the step of manufacturing a polyimide short fiber laminated intermediate, the water-soluble polymer is softened without affecting the polyimide short fibers to heat-fuse the polyimide short fibers together, and the shape formed by the hot press can be maintained until the step of removing the water-soluble polymer.

[0107] <Embodiment 6> <Embodiment 6: Overview> Mainly Claim 6 The laminated manufacturing method of polyimide fiber paper of this embodiment 6, which is based on any one of embodiments 1 to 5, is configured so that the heat press temperature is 100°C or higher and 200°C or lower, and the heat press pressure is 0.001 MPa or higher and 20 MPa or lower.

[0108] <Embodiment 6: Configuration of the Invention> The laminated manufacturing method of polyimide fiber paper of this embodiment 6, which is based on any one of embodiments 1 to 5, is configured so that the heat press temperature is 100°C or higher and 200°C or lower, and the heat press pressure is 0.001 MPa or higher and 20 MPa or lower.

[0109] <Embodiment 6: Polyimide Short Fiber Laminated Intermediate Production Step: Heat Press Temperature> The heat press temperature is 100° C. or higher and 200° C. or lower. Within this temperature range, the water-soluble polymer exemplified in Embodiment 1 or 2 can be pressed in a heated and softened state (and in a state in which the water-soluble polymer has not undergone thermal decomposition).

[0110] If the water-soluble polymer becomes soft, the polyimide short fibers that have been heat-fused with the water-soluble polymer can move within the single polyimide short fiber intermediate A (or single polyimide short fiber intermediate B) or between the stacked intermediates, allowing the stacked intermediate to deform along the mold during hot pressing and increasing the entanglement of the polyimide short fibers. Furthermore, the polyimide short fibers that have moved, deformed, or become entangled during hot pressing and the polyimide short fibers and the spaces between the polyimide short fibers are heat-fused and fixed in their new positions by the water-soluble polymer that has cooled and hardened after hot pressing.

[0111] In contrast, when the heat-pressing is performed at a temperature lower than 100°C, the water-soluble polymer does not soften sufficiently, and therefore the water-soluble polymer inhibits the movement of the polyimide short fibers during the heat-pressing, preventing them from moving to a new position, deforming along the mold, or increasing the entanglement of the polyimide short fibers.

[0112] Therefore, the heat pressing temperature is preferably higher within the above range, in the range of 130°C to 200°C. The heat pressing time is required to be 15 seconds or more to soften the water-soluble polymer, and a longer heating time is preferable as the number of laminated sheets increases, so 5 minutes or more is preferred. If the heating time is too long, the working time will be longer and production efficiency will decrease, so 20 minutes or less is preferred.

[0113] <Embodiment 6: Step of Producing a Polyimide Short Fiber Laminated Intermediate: Pressing Pressure During Heat Pressing> The pressing pressure during the heat pressing in the step of producing a polyimide short fiber laminated intermediate is 0.001 MPa or more. It is preferably 0.5 MPa or more, more preferably 3 MPa or more. The upper limit is 20 MPa or less, preferably 12 MPa or less, and more preferably 10 MPa or less. If the pressing pressure is too low, entanglement of the polyimide short fibers with adjacent layers is unlikely to occur between the laminated layers. Furthermore, when attempting to mold using a mold during pressing, the polyimide short fibers may not follow the mold well, which may result in normal molding. Conversely, if the pressing pressure is too high, the thickness will be too low and the volume of air contained in the polyimide fiber paper, which contributes to thermal insulation performance, will decrease, making it difficult to improve thermal insulation performance even if the number of sheets stacked is increased. Furthermore, manufacturing equipment with high pressing pressures requires greater strength, which makes it larger and more expensive. Therefore, it is preferable to set the pressure within the upper limit range as described above.

[0114] <Effects of Embodiment 6> The laminated manufacturing method of polyimide fiber paper of embodiment 6, which is based on any one of embodiments 1 to 5, can mold into a good shape during hot pressing, and polyimide fiber paper with excellent heat insulating performance can be obtained.

[0115] <Embodiment 7> <Embodiment 7: Overview> Mainly Claim 7 In the laminated manufacturing method for polyimide fiber paper of this embodiment 7, which is based on any one of embodiments 1 to 6, the condition range of the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step is defined as a closed polygonal area connecting the points of combinations of (temperature (°C), time (min)) on a plane with the horizontal axis being temperature (°C) and the vertical axis being time (min).

[0116] <Embodiment 7: Configuration of the invention> <Embodiment 7: Water-soluble polymer removal step> In the laminated manufacturing method for polyimide fiber paper of this embodiment 7, which is based on any one of embodiments 1 to 6, the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step are configured as combinations of (temperature (°C), time (min)) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis, within the area surrounded by dots (300°C, 20 minutes), (400°C, 5 minutes), (470°C, 4 minutes), (480°C, 4 minutes), and (480°C, 20 minutes) (including combinations of conditions on the boundary line connecting the dots).

[0117] <Embodiment 7 Water-soluble polymer removal step: heating temperature> The removal temperature in the water-soluble polymer removal step is preferably 300° C. or higher and 500° C. or lower. Since water-soluble polymers generally undergo thermal decomposition at 200° C. or higher, it is preferable to heat to a temperature of 300° C. or higher in order to remove as much of the water-soluble polymer as possible. Heating at a temperature higher than 500° C. for a long period of time is not preferable because the polyimide short fibers themselves will lose mass due to thermal decomposition, oxidation, etc., and will begin to deteriorate.

[0118] The inventors of the present invention conducted experiments to evaluate the heat resistance of samples prepared at different heating temperatures and times in order to determine the range of temperatures and heating times suitable for specific removal of water-soluble polymers. The heat resistance evaluation standard in the experiments shown in this embodiment 7 was a 5% weight loss temperature of 500°C or higher, as evaluated by thermogravimetric analysis. In the present invention, the water-soluble polymer is removed by thermal decomposition in the water-soluble polymer removal step. Therefore, ideally, the polyimide fiber paper after the water-soluble polymer removal step is composed only of polyimide staple fibers. If the paper is made only of polyimide staple fibers, a 5% weight loss temperature of 500°C or higher can easily be achieved, so heat resistance was evaluated using this standard.

[0119] FIG. 6 is a table listing the experimental conditions and results (5% weight loss temperature) for removing water-soluble polymers. The table in FIG. 6 shows the results for comparative samples prepared using conventional technology and example samples of the present invention. FIG. 7 is a graph showing the range of heating temperature and time for the water-soluble polymer removal step in this embodiment 7, with the horizontal axis representing the heating temperature (°C) during treatment and the vertical axis representing the heating time (minutes) during treatment. Hollow triangles in the figure indicate results with acceptable heat resistance (5% weight loss temperature of 500°C or higher), while solid triangles indicate results with poor heat resistance (5% weight loss temperature below 500°C). The area enclosed by the bold closed polygon in FIG. 7 represents the range of conditions suitable for removing water-soluble polymers. That is, the coordinates (temperature (°C), time (minutes)) of each vertex of the closed polygon represent conditions within the ranges of (300°C, 20 minutes), (400°C, 5 minutes), (470°C, 4 minutes), (480°C, 4 minutes), and (480°C, 20 minutes).

[0120] Under the conditions indicated as heat resistance OK in Fig. 7, the 5% weight loss temperatures are all 560°C or higher, and therefore it is considered that the 5% weight loss temperatures are almost the same in the range of 400°C to 500°C. Therefore, in this seventh embodiment, as shown in Fig. 7, the upper limit range on the high temperature side is set to (480°C, 4 minutes) to (480°C, 20 minutes).

[0121] By heating within the above-mentioned range of temperature and time for water-soluble polymer removal, the water-soluble polymer residue remaining in the polyimide short fiber laminated intermediate prior to the water-soluble polymer removal step is almost completely removed. "Almost completely" means that the result of the 5% weight loss temperature measurement is not affected, or that the water-soluble polymer residue is below the measurement limit so that it cannot be detected by analysis whether it remains in the polyimide fiber paper after the water-soluble polymer removal step.

[0122] Next, to compare the heat resistance of the prior art and the present invention, the 5% weight loss temperature of the polyimide fiber paper produced in accordance with the present invention and that produced by the prior art will be evaluated and the results will be described.

[0123] Seventh Embodiment Evaluation of Heat Resistance of Polyimide Fiber Paper: Evaluation at 5% Weight Loss Temperature FIG. 8 shows the results of thermogravimetric analysis (hereinafter referred to as TGA) of a comparative example sample in which three sheets of a polyimide intermediate structure (conditions for Comparative Example 1 in FIG. 6 : a mixed slurry of polyimide staple fibers and a water-soluble polymer (PVA) was wet-laid to form an intermediate structure in which a polyimide precursor was dispersed) prepared using a polyimide precursor according to the manufacturing method disclosed in Patent Document 1, previously filed by the applicant of the present application, were stacked and hot-pressed, and then heated at 430° C. for six minutes in the atmosphere to be imidized; and a polyimide fiber paper produced by the manufacturing method of the present application (conditions for Example 1 in FIG. 6 : a mixed slurry of polyimide staple fibers and a water-soluble polymer (PVA) was wet-laid to form an intermediate structure in which a polyimide precursor was dispersed). Three sheets were stacked and hot-pressed, and then heated at 400° C. for five minutes to remove the PVA.

[0124] TGA was performed using a TGA-50 (trade name, manufactured by Shimadzu Corporation) as an evaluation device, with a measurement temperature range of 25 to 700°C and a heating rate of 20°C / min. The heating rate was the TGA condition used by the inventors for product identification. This heating rate was adopted because the thermal decomposition proceeds rapidly, resulting in a steeper mass loss curve, making it easier to determine the onset temperature of thermal decomposition. In the TGA chart measured under the above conditions, the temperature at which the weight at 200°C was reduced by 5% by weight from the reference point was determined, and this value was defined as the 5% weight loss temperature.

[0125] The TGA results in Figure 8 are graphs showing weight retention when the temperature is gradually increased from a low temperature. In the graph in Figure 8, the horizontal axis represents temperature (°C), and the vertical axis represents weight retention when the weight at 200°C is taken as 100%. The thick solid line in the graph represents a sample (hereinafter referred to as the present sample) produced under the conditions of Example 1 in Figure 6 (water-soluble polymer removal step: 400°C for 5 minutes), and the thin solid line represents a sample (hereinafter referred to as the comparative sample) produced under the conditions of Comparative Example 1 in Figure 6. The 5% weight loss temperature (weight basis at 200°C) of each sample is shown by a vertical dotted line in the graph. The comparative sample had a temperature of 472°C, as indicated by the thin vertical dotted line, and the present sample had a temperature of 564°C, as indicated by the thick vertical dotted line. Heat resistance (5% weight loss temperature) was significantly improved compared to the prior art.

[0126] The reason for the improvement in the 5% weight loss temperature compared to the prior art is believed to be as follows.

[0127] (1) In the sample of the present application, the water-soluble polymer residue was heated at a temperature of 300°C or higher and 480°C or lower (400°C for 5 minutes), which was higher than the heating conditions of 190°C to 250°C in the complete water-soluble polymer removal step of Patent Document 1. Therefore, the amount of water-soluble polymer that was not completely removed was smaller than in Patent Document 1, and it is thought that this had less of an effect on the TGA measurement.

[0128] (2) On the other hand, in the comparative sample, the heating temperature (190 to 250°C) in the complete water-soluble polymer removal step of Patent Document 1 is a temperature at which the water-soluble polymer thermally decomposes, but it is lower than the heating temperature in the water-soluble polymer removal step of the present invention, and it is thought that the water-soluble polymer was not completely removed and some may have remained.

[0129] (3) Unlike the production method of the present invention, the production method of the comparative sample involves dispersing the polyimide precursor and then heating at 430°C for 6 minutes for imidization. However, it is thought that there is a possibility that not all of the polyimide precursor was imidized and some polyimide precursor remained.

[0130] (4) Since the molecular weight of the polyimide precursor is lower than that of the polyimide short fiber, it is thought that even if the polyimide precursor is imidized, the heat resistance may be lower than that of the polyimide short fiber.

[0131] For these reasons, it is considered that the difference in the 5% weight loss temperature was due to the decomposition of the remaining water-soluble polymer during heating in the TGA measurement, the release of water in the dehydration cycloreaction when the remaining polyimide precursor was imidized, or the decomposition of the polyimide precursor.

[0132] The polyimide fiber paper produced by the manufacturing method of Example 7 maintains its shape solely through the entanglement of the polyimide short fibers, as described above, by removing the water-soluble polymer residue that temporarily fixed and secured the polyimide short fibers together through thermal fusion. Therefore, its mechanical strength may be weaker than that of the comparative sample. However, its heat resistance (5% weight loss temperature) is improved, and lamination allows for the production of thicker polyimide fiber paper (i.e., better thermal insulation). Therefore, by supplementing the mechanical strength with other means, the excellent heat resistance and thermal insulation characteristics can be utilized. For example, the polyimide fiber paper of the present invention can be sandwiched between a circuit board carrying heat-generating electronic components and another circuit board carrying heat-sensitive components, and the paper is supported by both boards.

[0133] <Embodiment 7 Water-soluble polymer removal step: heating time> With regard to the time for removing the water-soluble polymer residue in the water-soluble polymer removal step, the time is extended under conditions close to 300°C. At 470°C or higher, sufficient heat resistance (5% reduction in heat resistance temperature of 500°C or higher) can be obtained with a minimum of 4 minutes of heating. The upper limit of the heating time was set to 20 minutes or less because productivity decreases if the treatment time is too long.

[0134] <Effects of the Seventh Embodiment> The polyimide fiber paper lamination manufacturing method of the seventh embodiment can improve heat resistance (5% weight loss temperature) compared to polyimide fiber paper of the prior art.

[0135] <Embodiment 8> <Embodiment 8: Overview> Mainly Claim 8 In the laminated manufacturing method for polyimide fiber paper of this embodiment 8, which is based on any one of embodiments 1 to 6, in addition to the heat resistance evaluation criterion of "5% weight loss temperature of 500°C or higher" in embodiment 7, thermal conductivity is added as an evaluation criterion and tensile strength is evaluated as a reference. Based on the newly added evaluation criterion, the range of the temperature when removing the water-soluble polymer residue in the water-soluble polymer removal step and the time for which said temperature is maintained is defined as a closed polygonal region connecting points of combinations of (temperature (°C), time (min)) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis.

[0136] In the laminated polyimide fiber paper manufacturing method of the present embodiment 8, which is based on any one of the embodiments 1 to 6, the temperature and the time for which the temperature is maintained during the water-soluble polymer removal step are determined by the combinations of (temperature (°C) and time (min)) within the area surrounded by the dots (300°C, 20 min), (400°C, 5 min), (470°C, 4 min), (430°C, 10 min), and (363°C, 20 min) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis (including the combinations on the boundary line connecting the dots). In the present embodiment 8, the evaluation criteria for heat resistance, as described above, are not only the 5% weight loss temperature as in the previous embodiments, but also thermal conductivity for evaluating heat insulation, and tensile strength was also evaluated as an indicator of mechanical strength for reference.

[0137] <Embodiment 8: Evaluation at Temperatures Other Than 5% Weight Loss Temperature> Fig. 6 shows the heating conditions (temperature, time; imidization conditions in Comparative Example 1) in the water-soluble polymer residue removal step and the results of the heat resistance evaluation. In the above-described embodiment 7, heat resistance was evaluated only at the 5% weight loss temperature, but in addition, the thermal conductivity and tensile strength of each sample were also measured after the water-soluble polymer removal step (after the imidization step in the case of the comparative sample), and the measurement results are shown in Fig. 6.

[0138] <Embodiment 8: Evaluations Other Than the 5% Weight Loss Temperature: Thermal Conductivity> Thermal conductivity was measured using a KES-F7 Thermolab (trade name, manufactured by Katotex) as a measuring instrument, using a steady-state method. If the thermal conductivity of the polyimide fiber paper measured using the steady-state method exceeds 0.10 W / m·K, the resulting polyimide fiber paper may not exhibit the expected thermal insulation performance when used as a thermal insulator. Therefore, the thermal conductivity judgment standard was set to 0.10 W / m·K or less, preferably 0.04 W / m·K or less. When evaluating the examples of the present invention and the comparative examples of the prior art, all were 0.04 W / m·K or less, except for Example 4 (water-soluble polymer removal step heating temperature 475°C), for which thermal conductivity could not be measured.

[0139] <Embodiment 8: Evaluations Other Than the 5% Weight Loss Temperature: Tensile Strength (Reference)> Tensile strength was evaluated by continuously pulling a 15 mm x approximately 250 mm sample piece using a tensile tester (tensile extrusion tester: SVZ-50NA model, load meter: SL-6001 model (trade name, manufactured by Imada Manufacturing Co., Ltd.)) set at 180 mm intervals until the sample broke, and measuring the maximum tensile load (tensile strength) at break. While a higher tensile strength value is preferable, a lower value can be used for applications where strength is not required and where flame retardancy and thermal insulation are prioritized, and therefore was measured for reference. The measurement results for the other samples were shown in Figure 6, excluding Example 4 of the present invention (water-soluble polymer removal step heating temperature 475°C), for which tensile strength could not be measured.

[0140] <Embodiment 8: Water-Soluble Polymer Removal Step: Heating Temperature> The polyimide fiber paper laminate manufacturing method of this embodiment 8 differs in that the upper limit of the high-temperature range for the heating temperature in the water-soluble polymer removal step is lowered from 480°C or less in the above-described embodiment 7 to 470°C or less. The sample of Example 4 in the experimental results shown in Figure 6 had a 5% weight loss temperature of 572°C under the heating conditions for the water-soluble polymer removal step (475°C, 6 minutes), resulting in excellent heat resistance. However, perhaps due to the influence of the heating conditions for the water-soluble polymer removal step, the prepared sample could not be placed in the measuring device, and thermal conductivity and tensile strength could not be measured. On the other hand, the sample of Example 6, which was heated at 470°C for 4 minutes, had a 5% weight loss temperature of 571°C, equivalent to the results of the sample of Example 4. Furthermore, thermal conductivity and tensile strength could be measured, and there were no problems with thermal conductivity.

[0141] In examining the differences between the samples of Example 4 and Example 6, reference was made to the graph of FIG. 8 showing the TGA results of the present sample (data prepared under the conditions of Example 1 in FIG. 6 ) and a comparative sample prepared using conventional technology. Among these TGA graphs, the graph of the present sample was focused on. To clarify the temperature at which the weight retention of the present sample changes during TGA, the change in weight retention (%) versus temperature was differentiated. The results of the differentiation, further smoothed using a moving average method (6 points), are shown in FIG. 9 as a graph of the weight retention change rate (% / °C) versus temperature. As shown in the graph of FIG. 9 , the weight retention change (decrease) begins near 250°C, and the increase in the weight retention change rate slows near 350°C. However, the weight retention change rate increases near 475°C. The weight retention change rate further increases near 550°C, reaching a maximum above 625°C. Further increase in temperature leads to a steady decrease in the weight retention change rate.

[0142] From the characteristics of the weight retention change rate graph in Figure 9, it is believed that the removal of the remaining water-soluble polymer residue progressed from around 250°C to around 350°C, and that the water-soluble polymer residue was almost completely removed up to a temperature range exceeding 475°C. The weight retention change rate begins to increase slightly above 475°C. It is believed that decomposition of the polyimide began gradually above 475°C, and as the temperature was further increased above 550°C, the weight retention change rate increased sharply up to a temperature slightly exceeding 625°C, indicating that the thermal decomposition of the polyimide was progressing rapidly.

[0143] As mentioned above, in the sample of Example 4 in the experimental results of Figure 6, the heating conditions for the water-soluble polymer removal step were 475°C for 6 minutes, and therefore, although it was below 500°C, heating at 475°C slightly initiated decomposition of the polyimide, and it is thought that the sample deteriorated after 6 minutes of heating, making it impossible to measure thermal conductivity and tensile strength. For the 470°C sample, the heating temperature was 5°C lower than the aforementioned 475°C, and the heating time was 4 minutes, which was shorter than the 6 minutes for heating at 475°C, so it is thought that little thermal decomposition occurred and almost no deterioration occurred.

[0144] The results of the heat resistance evaluation (5% weight loss temperature of 500°C or higher, thermal conductivity, and tensile strength) for this embodiment 8 are shown in Figure 10 (open circles indicate acceptable heat resistance, and filled circles indicate unacceptable heat resistance). In this embodiment 8, 470°C, which resulted in acceptable thermal conductivity (including tensile strength tests), was used as the upper limit temperature for the heating conditions in the water-soluble polymer removal step. However, the heating time at 470°C was set to 4 minutes (470°C, 4 minutes). The line passing through the point where the heat resistance was then acceptable (430°C, 10 minutes) was used as the high-temperature heating condition (temperature and time). Finally, the line was extended from (430°C, 10 minutes) toward the lower temperature side and the longer time length (toward the upper left in Figure 10), and the temperature at a heating time of 20 minutes was calculated, resulting in the condition (363°C, 20 minutes). The conditions of the heating temperature and time on the high temperature side have the same gradient as the line connecting (400°C, 5 minutes) and (300°C, 20 minutes) on the low temperature side, and are therefore considered to be appropriate.

[0145] Based on the above results, the heating temperature and time conditions in this embodiment 8 were (300°C, 20 minutes), (400°C, 5 minutes), (470°C, 4 minutes), (430°C, 10 minutes), and (363°C, 20 minutes). Note that the conditions other than the high-temperature side temperature are the same as those in embodiment 7, and therefore a description thereof will be omitted.

[0146] The polyimide fiber paper produced under the conditions of the water-soluble polymer removal step of this embodiment 8 possesses thermal insulation properties (low thermal conductivity) in addition to its inherent insulating properties. Therefore, it can be used for thermal insulation and insulation between heat-generating components and electronic components that are sensitive to high temperatures in locations where no force is applied, such as between the panel and circuit board of a flat display. Alternatively, it can be used as a support member to support the polyimide fiber paper of the present invention. In addition to the above examples, other possible uses of the polyimide fiber paper of the present invention include electronic devices such as flat-panel televisions, liquid crystal displays, laptops, tablet PCs, and smartphones (e.g., between the panel and electronic circuit, or between the battery and electronic circuit), thermal insulation for fuel cells, thermal insulation and insulation between light emitters (e.g., light bulbs, fluorescent lamps, LEDs) and control circuits in lighting fixtures, thermal insulation and insulation between the control circuit and engine in the engine compartment of an automobile, and thermal insulation and insulation for the electronic circuits of induction cookers.

[0147] <Effects of embodiment 8> In the laminated manufacturing method of polyimide fiber paper of embodiment 8, by lowering the high-temperature side temperature conditions of the water-soluble polymer removal step compared to embodiment 7, conditions were found that did not pose any problems in heat resistance evaluation, including thermal conductivity and tensile strength.

[0148] <Embodiment 9> <Embodiment 9: Overview> Mainly Claim 9 In the laminated manufacturing method for polyimide fiber paper of this embodiment 9, which is based on any one of embodiments 1 to 6, the range of the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step is defined as a closed polygonal area connecting the points of combinations of (temperature (°C), time (min)) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis.

[0149] In the polyimide fiber paper lamination manufacturing method of the present embodiment 9, which is based on any one of the embodiments 1 to 6, the temperature and the time for which the temperature is maintained during the water-soluble polymer removal step are determined by the combinations of (temperature (°C) and time (min)) within the area surrounded by the dots (300°C, 20 min), (380°C, 10 min), (400°C, 5 min), (430°C, 5 min), (470°C, 4 min), (430°C, 10 min), and (380°C, 15 min) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis. This includes the combinations on the boundary line connecting the dots. The difference from the embodiment 8 is that the heating conditions are limited to the area surrounded by the dots for the (temperature (°C), time (min)) that meet the heat resistance evaluation OK.

[0150] <Embodiment 9: Water-soluble polymer removal step: heating temperature> The difference in the polyimide fiber paper laminate manufacturing method of this embodiment 9 is that the heating temperature and time ranges in the water-soluble polymer removal step are specified narrower than those in embodiment 8. In the sample evaluation results (5% weight loss temperature, thermal conductivity, and tensile strength test results) after heating in the water-soluble polymer removal step shown in Figure 11, white circles indicate conditions that were evaluated as OK. Black circles indicate conditions where the 5% weight loss temperature was less than 500°C and / or the thermal conductivity and tensile strength test (reference) was not evaluated as NG. The heating temperature and heating time ranges in the water-soluble polymer removal step specified in this embodiment 9 are within a closed polygon whose vertices are the conditions that were evaluated as OK, and are the most preferable heating conditions compared to the conditions specified in embodiment 8.

[0151] <Effects of Embodiment 9> In the laminated manufacturing method for polyimide fiber paper of Embodiment 9, by narrowing the range of heating temperature and time in the water-soluble polymer removal step compared to Embodiment 8, it is possible to obtain polyimide fiber paper with excellent heat resistance over the entire range of heating conditions. <Embodiment 10> <Embodiment 10: Overview> Mainly Claim 10 The polyimide fiber paper of this embodiment 10, manufactured by the manufacturing method of any one of Embodiments 1 to 9, is configured to have a thickness of 1 mm or more.

[0152] Tenth Embodiment: Configuration of the Invention The polyimide fiber paper of the tenth embodiment is configured to have a thickness of 1 mm or more.

[0153] The polyimide fiber paper of the present invention manufactured by any one of the manufacturing methods of embodiments 1 to 9 can be thicker than a single-layer polyimide fiber paper, achieving a thickness of 1 mm or more, by stacking and hot-pressing multiple polyimide short fiber single intermediates A (or polyimide short fiber single intermediates B). Single-layer polyimide fiber paper has a thickness of less than 1 mm, approximately 0.2 to 0.5 mm. Because thermal insulation performance is also affected by the thickness of the insulating material, conventional techniques require stacking multiple sheets (e.g., three sheets) of polyimide fiber paper to achieve the same thickness. In conventional lamination techniques, lamination via adhesive or lamination using a polyimide precursor solution as an interlayer binder are considered. However, the former is undesirable from the perspective of heat resistance, and the latter is undesirable due to the complex process and loss of flexibility. Furthermore, both methods tend to increase thermal conductivity, which is undesirable. According to the present invention, highly heat-resistant polyimide fiber paper with a thickness of 1 mm or more can be obtained while maintaining flexibility without increasing thermal conductivity. Furthermore, while flat components can be easily stacked, when used to cover other components, the component must be molded into a convex shape, etc. Rather than molding multiple sheets of polyimide fiber paper, by using a mold when manufacturing the polyimide fiber paper of the present invention, it is possible to easily obtain a heat insulating component for the other component.

[0154] If the polyimide fiber paper is already formed into a desired shape and is used only for insulation, not as a structural support member, mechanical strength is not important. As shown by the thickness and thermal conductivity results in the table of Figure 6, the polyimide fiber paper of the present invention can exhibit excellent insulation performance for such applications.

[0155] <Effects of Embodiment 10> In embodiment 10, which is manufactured by any one of the manufacturing methods of embodiments 1 to 9, it is possible to obtain thick (1 mm or more) polyimide fiber paper with excellent heat insulating performance, which is integrated only by the entanglement of polyimide short fibers.

[0156] <Embodiment 11> As another embodiment, a manufacturing method will be described in which the water-soluble polymer removal step described in Embodiment 3 or 4 is simultaneously carried out during the hot pressing of Step A of manufacturing a polyimide staple fiber laminated intermediate in Embodiment 1 (or Step B of manufacturing a polyimide staple fiber laminated intermediate in Embodiment 2). The configurations corresponding to Embodiments 1 and 2 based on the method will be described in detail after the description. However, the step of manufacturing a polyimide staple fiber slurry A, the step of manufacturing a polyimide staple fiber single intermediate A, the step of manufacturing a polyimide staple fiber slurry B, and the step of manufacturing a polyimide staple fiber single intermediate B are the same as those described in the previous embodiments, and therefore their description will be omitted.

[0157] <Embodiment 11: Based on Embodiment 1> <Configuration> A laminated manufacturing method for polyimide fiber paper, comprising: a polyimide staple fiber slurry A manufacturing step of manufacturing polyimide staple fiber slurry A from polyimide staple fibers and a water-soluble polymer; a polyimide staple fiber single intermediate A manufacturing step of manufacturing a polyimide staple fiber single intermediate A by wet papermaking the manufactured polyimide staple fiber slurry A; and a polyimide fiber paper manufacturing step A of manufacturing polyimide fiber paper by stacking a plurality of manufactured polyimide staple fiber single intermediates A and pressing the stacked polyimide staple fiber single intermediates A while heating the stacked polyimide staple fiber single intermediates A to a temperature at or above which the water-soluble polymer residue remaining in the polyimide staple fiber single intermediates A thermally decomposes.

[0158] <Embodiment 11 Based on Embodiment 2> <Configuration> A laminated manufacturing method for polyimide fiber paper, comprising: a polyimide staple fiber slurry B manufacturing step of manufacturing a polyimide staple fiber slurry B from polyimide staple fibers and water; a polyimide staple fiber single intermediate B manufacturing step of wet-laid papermaking the manufactured polyimide staple fiber slurry B and sprinkling or / and spraying a water-soluble polymer powder onto the wet-laid polyimide staple fibers to disperse the water-soluble polymer among the polyimide staple fibers, thereby manufacturing a polyimide staple fiber single intermediate B; and a polyimide fiber paper manufacturing step B of stacking a plurality of manufactured polyimide staple fiber single intermediates B and pressing the stacked polyimide staple fiber single intermediates B while heating the stacked polyimide staple fiber single intermediates B to a temperature at or above which the water-soluble polymer residue remaining in the polyimide staple fiber single intermediates B thermally decomposes.

[0159] <Embodiment 11: Polyimide Fiber Paper Production Step A, Polyimide Fiber Paper Production Step B> The heating conditions during the heat pressing in the polyimide short fiber laminated intermediate production step A in embodiment 1 and the polyimide short fiber laminated intermediate production step B in embodiment 2 were set at a temperature and time that did not cause thermal decomposition of the water-soluble polymer (i.e., at least 90% by weight remained after the heat pressing). In these steps, the number of laminated sheets and the heat pressing time (15 seconds to 20 minutes) can be appropriately set to obtain the desired thickness. The heat pressing process itself is a continuous process in which each sheet is processed one by one (some devices can accommodate multiple molds, but the number of processes per run is small). On the other hand, the water-soluble polymer removal step in embodiments 1 to 9 requires heating conditions such as (300°C, 20 minutes) or (470°C, 4 minutes), which is time-consuming. Therefore, the water-soluble polymer removal step in embodiments 1 to 9 is performed as a batch process in which a certain amount of material is heat-treated at once. Therefore, if the heating press can heat to the temperature required for removing the water-soluble polymer and can maintain said temperature for the heating time in terms of productivity, the heating press and the removal of the water-soluble polymer can be performed simultaneously, as in the present embodiment 11.

[0160] <Embodiment 11: Molding Using a Mold> As described above, molding can also be performed using a mold during hot pressing. In that case, the configuration is as follows. The case based on Embodiment 1 is shown below, but the same applies to the case based on Embodiment 2. A laminated manufacturing method for polyimide fiber paper, comprising: a polyimide staple fiber slurry A manufacturing step of manufacturing a polyimide staple fiber slurry A from polyimide staple fibers and a water-soluble polymer; a polyimide staple fiber single intermediate A manufacturing step of manufacturing a polyimide staple fiber single intermediate A by wet papermaking the manufactured polyimide staple fiber slurry A; and a polyimide fiber paper manufacturing step A of manufacturing a polyimide fiber paper by stacking a plurality of manufactured polyimide staple fiber single intermediates A and pressing the stacked polyimide staple fiber single intermediates A using a mold while heating the stacked polyimide staple fiber single intermediates A to a temperature at or above the temperature at which the water-soluble polymer residue remaining in the polyimide staple fiber single intermediates A thermally decomposes.

[0161] <Effects of Eleventh Embodiment> According to the eleventh embodiment, the hot pressing and the water-soluble polymer removing step can be carried out simultaneously, so that the process can be further shortened.

[0162] <Effects> The laminate manufacturing method of the present invention provides a laminate manufacturing method for polyimide fiber paper, including a polyimide staple fiber slurry manufacturing step of manufacturing a polyimide staple fiber slurry containing polyimide staple fibers, a polyimide staple fiber single-fiber intermediate manufacturing step of wet-laid papermaking the slurry to produce a polyimide staple fiber single-fiber intermediate, and a polyimide staple fiber laminated intermediate manufacturing step of stacking and hot-pressing a plurality of the polyimide staple fiber single-fiber intermediates to produce a polyimide staple fiber laminated intermediate containing residual water-soluble polymer (two manufacturing methods are provided, depending on whether the water-soluble polymer is dispersed in the slurry or in the wet-laid polyimide staple fibers). The laminate manufacturing method of the present invention further includes a water-soluble polymer removal step of heating the polyimide staple fiber laminated intermediate to remove the residual water-soluble polymer residue. By stacking and hot-pressing the polyimide fiber paper, the laminate manufacturing method of the present invention can increase (laminate) the thickness to a desired level without reducing density and maintaining high thermal insulation. Furthermore, since the layered manufacturing method of the present invention does not use a polyimide precursor or polyimide solution, the steps of dispersing the polyimide precursor or polyimide solution and imidizing the polyimide precursor are not necessary, and the process can be simplified. In this way, the polyimide fiber paper manufactured by the layered manufacturing method of the present invention does not have the polyimide short fibers fixed to each other with polyimide resin (or other binder resin), so the polyimide short fibers can slip when an external force is applied, resulting in soft, cushiony polyimide fiber paper.

Claims

1. A method for manufacturing laminated polyimide fiber paper, comprising: a polyimide staple fiber slurry A manufacturing step in which polyimide staple fiber slurry A is manufactured from polyimide staple fibers and a water-soluble polymer; a polyimide staple fiber single intermediate A manufacturing step in which the manufactured polyimide staple fiber slurry A is subjected to wet papermaking to manufacture a polyimide staple fiber single intermediate A; and a polyimide staple fiber laminated intermediate manufacturing step A in which a plurality of manufactured polyimide staple fiber single intermediates A are stacked and hot-pressed to manufacture a polyimide staple fiber laminated intermediate in which a water-soluble polymer residue remains.

2. A method for manufacturing laminated polyimide fiber paper, comprising: a polyimide staple fiber slurry B manufacturing step of manufacturing polyimide staple fiber slurry B from polyimide staple fibers and water; a polyimide staple fiber single intermediate B manufacturing step of wet-processing the manufactured polyimide staple fiber slurry B and sprinkling or spraying a water-soluble polymer powder and / or a water-soluble polymer solution onto the wet-processed polyimide staple fibers to disperse the water-soluble polymer among the polyimide staple fibers, thereby manufacturing a polyimide staple fiber single intermediate B; and a polyimide staple fiber laminated intermediate manufacturing step B of stacking and heat-pressing a plurality of manufactured polyimide staple fiber single intermediates B to manufacture a polyimide staple fiber laminated intermediate having a water-soluble polymer residue remaining.

3. A method for manufacturing polyimide fiber paper laminates, comprising a water-soluble polymer removal step of heating the polyimide short fiber laminate intermediate manufactured according to claim 1 or 2 to remove any remaining water-soluble polymer residue.

4. A method for manufacturing a polyimide fiber paper laminate according to claim 1 or claim 2, further comprising a water-soluble polymer removal step of heating the polyimide short fiber laminate intermediate to remove any remaining water-soluble polymer residue.

5. A method for laminating polyimide fiber paper according to claim 1 or 2, wherein the decomposition temperature of the water-soluble polymer is lower than the glass transition temperature of the polyimide.

6. A method for manufacturing a laminated polyimide fiber paper according to claim 1 or claim 2, wherein the heat pressing temperature is 100°C or higher and 200°C or lower, and the heat pressing pressure is 0.001 MPa or higher and 20 MPa or lower.

7. The laminated manufacturing method for polyimide fiber paper according to claim 4, wherein the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step are combinations of (temperature (°C), time (min)) within the area surrounded by the dots (300°C, 20 min), (400°C, 5 min), (470°C, 4 min), (480°C, 4 min), (480°C, 20 min) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis (including combinations of conditions on the boundary line connecting the dots).

8. The laminated manufacturing method for polyimide fiber paper according to claim 4, wherein the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step are combinations of (temperature (°C), time (min)) within the area surrounded by the dots (300°C, 20 min), (400°C, 5 min), (470°C, 4 min), (430°C, 10 min), and (363°C, 20 min) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis (including combinations of conditions on the boundary line connecting the dots).

9. The laminated manufacturing method for polyimide fiber paper according to claim 4, wherein the temperature and the time for which said temperature is maintained when removing the water-soluble polymer residue in the water-soluble polymer removal step are combinations of (temperature (°C), time (min)) within the area surrounded by the dots (300°C, 20 min), (380°C, 10 min), (400°C, 5 min), (430°C, 5 min), (470°C, 4 min), (430°C, 10 min), and (380°C, 15 min) on a plane with temperature (°C) on the horizontal axis and time (min) on the vertical axis (including combinations of conditions on the boundary line connecting the dots).

10. Polyimide fiber paper with a thickness of 1 mm or more.

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