Polyimide Fiber Paper

Abstract

To provide a polyimide fiber paper which does not leave water-soluble polymer contained in a temporary paper and satisfies flame retardancy, low outgassing, and heat resistance.SOLUTION: In a polyimide fiber paper, fibers made of a non-thermoplastic polyimide resin are bonded together by a starch syrup-like structure made of the same non-thermoplastic polyimide resin, and 0.05 to 35 parts by mass of the starch syrup-like structure made of a non-thermoplastic polyimide resin are contained with respect to a total of 100 parts by mass of fibers made of a non-thermoplastic polyimide resin and starch syrup-like structure made of a non-thermoplastic polyimide resin.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This application forms the basis of a domestic priority application to be filed at a later date. The present invention relates to a non-thermoplastic polyimide resin. Use This invention relates to polyimide fiber paper. [Background technology]

[0002] Polyimide films are materials with excellent electrical insulation, heat resistance, cold resistance, flame retardancy, chemical resistance, and mechanical properties, and are used in a wide range of fields, from aerospace applications to automobiles and electronic devices. In recent years, there has been an increasing demand for polyimide films as insulation materials in spacecraft, which require weight reduction and space saving, and as thermal management materials in power devices and heaters, which operate at high temperatures. However, polyimide films do not fully meet the requirements for thermal management materials in terms of insulation performance and gas and liquid permeability, and there has been a demand for the development of new polyimide materials with improved properties.

[0003] Polyimide fiber paper, which is made by fiberizing polyimide and processing it into a paper-like material, can be given as a polyimide material that satisfies the characteristics required for thermal management. For example, there are techniques disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2009-97117 [Patent Document 2] Patent Publication No. 2019-35157 Summary of the Invention [Problem to be solved by the invention]

[0005] Prior Art Document 1 discloses a method for producing a non-thermoplastic nonwoven fabric made of a polyimide resin. The method involves spinning a precursor solution of a non-thermoplastic polyimide, drawing it up with a high-speed airflow, capturing it on a substrate, and then imidizing it. However, this method requires special manufacturing equipment, and there are problems in that it is difficult to obtain a uniform thickness, particularly a wide sheet product, and the cost is high.

[0006] Prior art document 2 also shows a method for producing polyimide fiber paper made of non-thermoplastic polyimide. The method in prior art document 2 involves, first, mixing shaved short fibers of non-thermoplastic polyimide into a water-soluble polymer solution, which is a material whose decomposition temperature is lower than the glass transition temperature of polyimide, and wet-processing the mixture to produce a temporary paper of polyimide fiber paper, and second, dispersing a polyimide precursor solution in the temporary paper, and then heating the solution to imidize the polyimide precursor solution, thereby obtaining polyimide fiber paper. However, according to the inventors' studies, this method has the problem that when the product is heated at a temperature range required for imidization, the water-soluble polymer remains, preventing the product from acquiring flame retardancy, and furthermore, when the product is used at high temperatures, harmful outgassing is generated due to the decomposition components of the water-soluble polymer. Furthermore, if heat treatment is carried out at a higher temperature in the production process in order to remove the water-soluble polymer, thermal decomposition due to oxidative degradation of the polyimide material simultaneously proceeds, resulting in a problem of loss of heat resistance. The present invention has been made to solve the above-mentioned problems in the conventional art, and aims to provide a polyimide fiber paper that does not leave any residual water-soluble polymer contained in the temporary fixing paper and that satisfies the heat resistance requirements of flame retardancy and low outgassing. [Means for solving the problem]

[0007] As a result of intensive research conducted by the inventors to address the above-mentioned problems, they have invented a new polyimide fiber paper, which is obtained by dispersing a polyimide precursor solution in a temporary fixing paper of polyimide fiber paper, as described in Prior Art Document 2, and then heating the paper in a superheated steam furnace at a certain temperature range. The new polyimide fiber paper does not contain any residue of the water-soluble polymer described in Prior Art Document 2, and exhibits sufficient mechanical properties, and can be suitably used as a thermal management material for power devices, heaters, etc.

[0008] That is, the present invention relates to the following inventions: As a first invention, there is provided a polyimide fiber paper in which fibers made of a non-thermoplastic polyimide resin are bonded to each other by a starch syrup-like structure also made of a non-thermoplastic polyimide resin.

[0009] Next, as a second invention, there is provided a polyimide fiber paper containing 0.05 to 35 parts by mass of a syrup-like structural portion made of a non-thermoplastic polyimide resin per 100 parts by mass in total of fibers made of a non-thermoplastic polyimide resin and a syrup-like structural portion made of a non-thermoplastic polyimide resin.

[0010] Next, as a third invention, we provide a polyimide fiber paper in which, when measured in a thermogravimetric analysis under conditions of continuously introducing nitrogen at a flow rate of 50 mL / min, a measurement temperature range of 25°C to 700°C, and a heating rate of 3°C / min, the temperature at which the weight is reduced by 5% from the reference point, based on the weight at 200°C, is 450°C or higher.

[0011] Next, as a fourth aspect of the present invention, there is provided a polyimide fiber paper having a thermal conductivity measured by a steady-state method of 0.10 W / m·K or less and 0.001 W / m·K or more.

[0012] Next, as a fifth aspect of the present invention, there is provided a polyimide fiber paper having a thermal conductivity of 0.04 W / m·K or less and 0.001 W / m·K or more, as measured by a steady-state method.

[0013] Next, as a sixth invention, we provide a polyimide fiber paper having a thickness in the range of 0.05 mm to 1.0 mm, which satisfies the V-0 level of the flame retardancy UL-94 standard in a UL94V flammability test based on the UL94 (6th 2018-05-30) V flammability test.

[0014] Next, as a seventh aspect of the present invention, there is provided a polyimide fiber paper having a thickness of 0.1 mm to 0.5 mm.

[0015] Next, as an eighth invention, we provide a method for producing polyimide fiber paper, which is characterized by heat-treating a polyimide temporary paper consisting of shaved fibers of non-thermoplastic polyimide, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide, at a temperature of 360°C or higher and 450°C or lower in a heating furnace having an oxygen ratio of 0.0 to 1.0 volume %.

[0016] Next, as a ninth invention, we provide a method for producing polyimide fiber paper, which is characterized by producing a polyimide temporary paper consisting of shaved fibers of non-thermoplastic polyimide, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide, in a superheated steam furnace at a temperature of 360°C to 450°C.

[0017] Next, as a tenth invention, we provide a polyimide fiber paper characterized in that the total amount of decomposition gas components derived from residues of water-soluble polymers with a temperature lower than the glass transition temperature of polyimide generated when heated at 300°C for 1 hour in a mixed gas consisting of 20% oxygen and 80% helium is 0.1% or less of the total mass. Effect of the Invention

[0018] The polyimide fiber paper of the present invention exhibits sufficient strength for practical use as a paper-like structure, and while retaining the heat resistance and cold resistance of polyimide resin, it is lighter, more breathable, and has better heat insulation performance than polyimide films. In addition, since the 5% weight loss temperature is 450°C or higher, the amount of outgassing during heating is suppressed, thereby reducing contamination of surrounding materials due to outgassing. Furthermore, since the amount of outgassing inhaled by the human body during handling at high temperatures is small, concerns about health damage to workers can be reduced. Due to the above characteristics, the polyimide fiber paper can be suitably used as MLI (multilayer insulation) for spacecraft applications and as a heat insulation material in enclosed spaces. Furthermore, since the polyimide fiber paper of the present invention satisfies the V-0 level of the UL-94 flame retardancy standard, it can be suitably used as a thermal management material in electronic devices that require flame retardancy in their constituent materials. [Brief description of the drawings]

[0019] [Figure 1] Optical microscope image showing the structure of polyimide fiber paper [Diagram 2] FIG. 13 is a flow chart showing an example of a method for producing polyimide fiber paper by heat-treating a polyimide temporary paper containing a water-soluble polymer and a polyimide precursor component according to embodiment 8. [Diagram 3] A schematic diagram showing the imidization reaction of a polyimide precursor solution as the first reaction in the heat treatment process of the polyimide temporary paper of the present invention. [Figure 4] A conceptual diagram showing the decomposition reaction of a water-soluble polymer, the decomposition temperature of which is lower than the glass transition temperature of polyimide, as the second reaction in the heat treatment process of the polyimide temporary paper of the present invention. [Diagram 5] FIG. 13 is a flow chart showing an example of a method for producing polyimide fiber paper in which a polyimide temporary paper containing a water-soluble polymer and a polyimide precursor component according to embodiment 9 is heat-treated in a superheated steam furnace. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, embodiment 1 corresponds to claim 1, embodiment 2 corresponds to claim 2, embodiment 3 corresponds to claim 3, embodiment 4 corresponds to claim 4, embodiment 5 corresponds to claim 5, embodiment 6 corresponds to claim 6, embodiment 7 corresponds to claim 7, embodiment 8 corresponds to claim 8, embodiment 9 corresponds to claim 9, and embodiment 10 corresponds to claim 10. Note that the present invention should not be limited to these embodiments in any way, and may be embodied in various forms without departing from the gist of the present invention. <Embodiment 1>

[0021] This embodiment mainly relates to claim 1. <Overview of embodiment 1>

[0022] The polyimide fiber paper of this embodiment is characterized in that fibers made of a non-thermoplastic polyimide resin are bonded to each other by a starch syrup-like structure also made of a non-thermoplastic polyimide resin. <Configuration of embodiment 1>

[0023] In the polyimide fiber paper of this embodiment, by using a syrup-like structure made of a non-thermoplastic polyimide resin, it is possible to bond non-thermoplastic short fibers such as polyimide together in a mesh-like pattern, which is usually difficult to achieve, and obtain fiber paper with sufficient strength for practical use as a paper-like structure, as shown in Figure 1. Furthermore, by performing intersection bonding between polyimide fibers with a syrup-like structure made of a non-thermoplastic polyimide resin, the obtained fiber paper has the heat resistance and cold resistance of polyimide resin and can be suitably used in environments where the above characteristics are required. <Embodiment 2>

[0024] This embodiment mainly relates to claim 2. <Overview of the Second Embodiment>

[0025] The polyimide fiber paper of this embodiment is characterized in that it contains 0.05 to 35 parts by mass of the syrup-like structural portion made of non-thermoplastic polyimide resin per 100 parts by mass of the fibers made of non-thermoplastic polyimide resin and the syrup-like structural portion made of non-thermoplastic polyimide resin combined. <Configuration of embodiment 2>

[0026] In this embodiment, if the amount of the syrup-like structural part made of non-thermoplastic polyimide resin contained therein is less than 0.05 parts by mass relative to a total of 100 parts by mass of the fibers made of non-thermoplastic polyimide resin and the syrup-like structural part made of non-thermoplastic polyimide resin, it is not preferable because this makes it impossible to obtain sufficient strength for practical use as a paper-like structure. On the other hand, if the amount of the syrup-like structure made of non-thermoplastic polyimide resin exceeds 35 parts by mass, the gaps between the fibers are filled, and the resulting polyimide fiber paper no longer exhibits heat insulating properties, which is not preferable. <Embodiment 3>

[0027] This embodiment mainly relates to claim 3. <Overview of the Third Embodiment>

[0028] The polyimide fiber paper of this embodiment is characterized in that, when measured in a thermogravimetric analysis under conditions of continuous introduction of nitrogen at a flow rate of 50 mL / min, a measurement temperature range of 25°C to 700°C, and a heating rate of 3°C / min, the temperature at which the weight is reduced by 5% from the reference point, based on the weight at 200°C, is 450°C or higher. <Configuration of embodiment 3>

[0029] The 5% weight loss temperature of the polyimide fiber paper of this embodiment is usually in the range of 450° C. or higher, preferably 460° C. or higher, more preferably 470° C. or higher, and even more preferably 480° C. or higher. If the 5% weight loss temperature of the polyimide fiber paper falls below 450°C, outgassing will occur when the resulting polyimide fiber paper is heated, and since the outgassing components are flammable, the paper will no longer exhibit flame retardancy, which is undesirable. By setting the 5% weight loss temperature of the polyimide fiber paper to 450°C or higher, preferably 480°C or higher, it can be suitably used as an insulating material for spacecraft, which requires low outgassing properties, or as a thermal management material for electronic devices, which require flame retardancy. <Embodiment 4>

[0030] This embodiment mainly relates to claim 4. <Overview of embodiment 4>

[0031] The polyimide fiber paper of this embodiment is characterized by having a thermal conductivity measured by a steady-state method of 0.10 W / m·K or less and 0.001 W / m·K or more. <Configuration of embodiment 3>

[0032] If the thermal conductivity of polyimide fiber paper measured by 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 insulation material. In order to obtain the desired thermal insulation performance, it may become necessary, for example, to use multiple sheets of polyimide fiber paper stacked together. In that case, not only will the thermal insulation layer be expensive, but the thickness of the thermal insulation layer will also increase, making it unsuitable for use in electronic devices and other devices where space saving is required. <Embodiment 5>

[0033] This embodiment mainly relates to claim 5. <Outline of the fifth embodiment>

[0034] The polyimide fiber paper of this embodiment is characterized by having a thermal conductivity measured by a steady-state method of 0.04 W / m·K or less and 0.001 W / m·K or more. <Configuration of embodiment 5>

[0035] The thermal conductivity of the polyimide fiber paper of this embodiment is usually in the range of 0.04 W / m·K to 0.001 W / m·K, and preferably 0.03 W / m·K to 0.001 W / m·K. By setting the thermal conductivity in the range of 0.04 W / m K or less and 0.001 W / m K or more, the high heat resistance of the polyimide material is maintained, while the insulating performance and light weight compared to polyimide film are superior. The material can be suitably used as an insulating material or thermal management material in spacecraft, electronic devices, and heaters. <Embodiment 6>

[0036] This embodiment mainly relates to claim 6. <Overview of embodiment 6>

[0037] The polyimide fiber paper of this embodiment is characterized by having a thickness in the range of 0.05 mm to 1.0 mm, and satisfying the V-0 level of the flame retardancy UL-94 standard in a UL94V flammability test based on the UL94 (6th 2018-05-30) V flammability test. <Configuration of embodiment 6>

[0038] The polyimide fiber paper of this embodiment usually has a thickness in the range of 0.05 mm to 1.0 mm and satisfies the V-0 level of the flame retardancy UL-94 standard in a UL94V flammability test based on the UL94 (6th 2018-05-30) V flammability test. By satisfying the flame retardancy V-0 of the UL-94 standard, the material can be suitably used as a heat insulating material or a thermal management material for controlling the flow of generated heat within electronic devices. <Embodiment 7>

[0039] This embodiment mainly relates to claim 7. <Overview of embodiment 7>

[0040] The polyimide fiber paper of this embodiment is characterized by having a thickness of 0.1 mm to 0.5 mm. <Configuration of embodiment 7>

[0041] The polyimide fiber paper of the present embodiment usually has a thickness in the range of 0.05 mm to 1.0 mm, preferably in the range of 0.1 mm to 0.6 mm, and particularly preferably in the range of 0.1 mm to 0.5 mm. By setting the thickness within the range of 0.05 mm to 1.0 mm, the size of the electronic device can be reduced, and the electronic device can be suitably used as a heat insulating material or a heat management material in electronic devices with limited space. <Embodiment 8>

[0042] This embodiment mainly relates to claim 8. <Overview of embodiment 8>

[0043] The invention in this embodiment is a method for producing polyimide fiber paper by heat-treating a polyimide temporary paper consisting of shaved fibers of non-thermoplastic polyimide, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide, in a heating furnace under an atmosphere of 1 atmosphere and with an oxygen ratio of 0.0 to 1.0 volume % relative to the volume, at a temperature of 360°C to 450°C. <Configuration of embodiment 8>

[0044] The non-thermoplastic polyimide is composed of an aromatic diamine component and an acid anhydride component. The aromatic diamine component contains at least one of paraphenylenediamine represented by the following formula (Chemical formula 1) and 4,4'-diaminodiphenyl ether represented by the following formula (Chemical formula 2) as a constituent element.

[0045] [ka]

[0046] [ka]

[0047] The aromatic diamine component may contain something other than paraphenylenediamine and 4,4'-diaminodiphenyl ether, for example, a group of compounds represented by the following structural formula (Chemical Formula 3).

[0048] [ka]

[0049] In this structural formula, R represents OCH3, and X represents O, CH2, or SO2. Examples of the compound include metaphenylenediamine, paraxylylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,5-diaminonaphthalene, benzidine, 3,3'-dimethoxybenzidine, and 1,3-bis(4-aminophenoxy)benzene. These compounds may be used alone or in combination of two or more.

[0050] The acid anhydride component contains at least one of pyromellitic dianhydride represented by the following formula (Chemical formula 4) and 3,3',4,4'-biphenyltetracarboxylic dianhydride represented by the following formula (Chemical formula 5) as a constituent element.

[0051] [ka]

[0052] [ka]

[0053] The acid anhydride component may contain something other than pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride, for example, a group of compounds represented by the following structural formula (Chemical Formula 6).

[0054] [ka]

[0055] In this structural formula, X represents O or CO. Examples include 2,3',3,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonecarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, and the like, and these may be used alone or in combination of two or more.

[0056] A polyimide temporary paper consisting of shaved fibers of non-thermoplastic polyimide, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide can be produced using known techniques, such as the technique disclosed in the patent document "JP 2019-35157 A." <Embodiment 8: Description of the heat treatment process of polyimide temporary paper>

[0057] As shown in FIG. 2, the "polyimide temporary paper heat treatment step (heat treatment step (0202))" is a step of obtaining polyimide fiber paper by heat treating the polyimide temporary paper, which is made of the non-thermoplastic polyimide shavings formed in the polyimide temporary paper formation step (0201), the polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide, in a heating furnace under an atmosphere of 1 atmosphere with an oxygen ratio of 0.0 to 1.0% by volume, at a temperature of 360°C to 450°C. By performing heat treatment in the above temperature range, as shown in FIG. 3, an imidized component (0304), which is a starch syrup-like structure portion, is generated by the imidization reaction of the polyimide precursor solution (0301) as the first reaction (0303), and polyimide short fibers are bonded and fixed to each other, thereby obtaining polyimide fiber paper that exhibits sufficient mechanical strength. Note that the reference symbol (0302) in FIG. 3 indicates a water-soluble polymer. Next, as shown in Figure 4, a second reaction (0403) occurs in which the water-soluble polymer (0401) decomposes, the decomposition temperature of which is lower than the glass transition temperature of polyimide. By removing this water-soluble polymer (0401), a highly heat-resistant polyimide fiber paper can be obtained due to the imidized component (0404), which is the syrup-like structural portion of the polyimide precursor solution.

[0058] The heat treatment process described above is carried out with an oxygen ratio of 0.0 to 1.0 volume. % It is preferable to treat the polyimide fiber paper in a heating furnace having an oxygen ratio of 100% or less. If the oxygen ratio in the heating furnace exceeds the above range, the surface of the polyimide fiber paper, which is originally ochre-colored, will be oxidized and turn black, which is undesirable because it becomes difficult to detect defects such as foreign matter in the inspection process. By setting the oxygen ratio in the heating furnace within the above range, it is possible to obtain polyimide fiber paper that does not blacken the surface and allows defects such as foreign matter to be easily detected in the inspection process. In addition, since both the first and second reactions in the previous paragraph occur at 200° C. or higher, the heating temperature in the heat treatment step is preferably 200° C. or higher, more preferably 300° C. or higher in order to proceed with the reaction more quickly and quantitatively, and particularly preferably 360° C. or higher. On the other hand, since heat treatment at high temperatures causes thermal decomposition of the polyimide material, the heating temperature is preferably 500° C. or lower, and more preferably 450° C. or lower. <Embodiment 9>

[0059] This embodiment mainly relates to claim 9. <Overview of embodiment 9>

[0060] The invention in this embodiment is a method for producing polyimide fiber paper by heat treating a polyimide temporary paper consisting of shaved fibers of non-thermoplastic polyimide, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide, in a superheated steam furnace under an atmosphere of 1 atmosphere and with an oxygen ratio of 0.0 to 1.0 volume % at 360°C to 450°C. The preparation of the polyimide temporary paper has already been explained in the eighth embodiment, and will not be described in this embodiment. <Embodiment 9: Description of the heat treatment process of polyimide temporary paper in a superheated steam furnace>

[0061] As shown in Fig. 5, the "polyimide temporary paper heat treatment step in a superheated steam furnace (heated steam treatment step (0502))" is a step of obtaining polyimide fiber paper by heat treating the polyimide temporary paper, which is made of the non-thermoplastic polyimide shavings formed in the polyimide temporary paper formation step (0501), the polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide, at a temperature of 360°C to 450°C in a superheated steam furnace under an atmosphere of 1 atmosphere where the oxygen ratio to the volume is 0.0 to 1.0 volume %, to obtain polyimide fiber paper. By performing heat treatment in the above temperature range, as shown in Fig. 3, an imidized component (0304), which is a starch syrup-like structure portion, is generated by the imidization reaction of the polyimide precursor solution (0301) as the first reaction (0303), and polyimide short fibers are bonded and fixed to each other, thereby obtaining polyimide fiber paper that exhibits sufficient mechanical strength. Next, as shown in Figure 4, a second reaction (0403) occurs in which the water-soluble polymer (0401) decomposes, the decomposition temperature of which is lower than the glass transition temperature of polyimide. By removing this water-soluble polymer (0401), a highly heat-resistant polyimide fiber paper can be obtained due to the imidized component (0404), which is the syrup-like structural portion of the polyimide precursor solution.

[0062] The heat treatment using a superheated steam furnace is preferably performed at 200° C. or higher since both the first and second reactions described above occur at 200° C. or higher, more preferably at 300° C. or higher in order to proceed the reactions more quickly and quantitatively, and particularly preferably at 360° C. or higher. On the other hand, since heat treatment at high temperatures causes thermal decomposition of the polyimide material, the heat treatment is preferably performed at 500° C. or lower, and more preferably at 450° C. or lower.

[0063] The treatment time for the heat treatment using a superheated steam furnace is usually 2 to 8 minutes, and more preferably 3 to 6 minutes in order to prevent decomposition due to excessive heat load on the material while obtaining a sufficient curing effect. A superheated steam furnace is a heating furnace that uses steam heated to 100°C or more, and compared to heating in air, it has high thermal efficiency because it heats with moisture, which has a larger specific heat, and the inside of the furnace is filled with steam and is in a nearly oxygen-free state, so that oxidation deterioration of the material during the heat treatment is unlikely to occur, and it can be suitably used in the manufacturing method of polyimide fiber paper in the present invention. <Embodiment 10>

[0064] This embodiment mainly relates to claim 10. <Overview of embodiment 10>

[0065] The polyimide fiber paper of this embodiment is characterized in that the total amount of decomposition gas components derived from residues of water-soluble polymers with temperatures lower than the glass transition temperature of polyimide generated when heated at 300°C for 1 hour in a mixed gas of 20% oxygen and 80% helium is 0.1% or less of the total mass. <Configuration of embodiment 10>

[0066] When the polyimide fiber paper of this embodiment is heated at 300°C for 1 hour in a mixed gas of 20% oxygen and 80% helium, the total amount of decomposition gas components derived from residues of water-soluble polymers with a temperature lower than the glass transition temperature of the polyimide, as detected by gas chromatography, is typically 0.1% or less, more preferably 0.05% or less, and particularly preferably 0.02% or less, relative to the mass of the polyimide fiber paper. When polyimide fiber paper is heated at high temperatures, if the total amount of decomposition gas components derived from the residue of water-soluble polymer exceeds 0.1% of the mass of the polyimide fiber paper, a large amount of decomposition gas is generated. Since this decomposition gas is flammable, the polyimide fiber paper will no longer meet the flame retardancy requirements of the UL94V standard, and cannot be used suitably in electronic devices that require flame retardancy. By controlling the total amount of decomposition gas components derived from the residue of the water-soluble polymer to within 0.1% of the mass of the polyimide fiber paper, the polyimide fiber paper exhibits flame retardancy and can be suitably used in electronic devices that require flame retardancy. In addition, since outgassing is unlikely to occur when heated at high temperatures, the polyimide fiber paper can be suitably used for spacecraft applications that require low outgassing.

[0067] The present invention includes various combinations of the above-described configurations within the technical scope of the present invention, as long as the effects of the present invention are achieved. EXAMPLES

[0068] Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples, and many modifications can be made by those skilled in the art within the technical concept of the present invention.

[0069] The characteristics in the examples were evaluated by the following methods. (1) 5% weight reduction temperature The equipment used was a TGA-50 (product name, manufactured by Shimadzu Corporation), and measurements were taken under conditions of a measurement temperature range of 25 to 700°C and a heating rate of 3°C / min. In the TGA chart obtained, the temperature at which the weight at 200°C decreased by 5% from the reference point was determined, and this value was defined as the 5% weight loss temperature. (2) Thermal conductivity Equipment: KES-F7 Thermo Lab (product name, manufactured by Katotex) was used to measure thermal conductivity by the steady-state method. (3) Thickness The thickness was measured using a dial thickness gauge. (4) Tensile strength The tensile strength of sample pieces of 15 mm x approximately 250 mm was measured using a tensile tester (tensile compression tester: SVZ-50NA type, load meter: SL-6001 type (product name, manufactured by Imada Seisakusho)) set at intervals of 180 mm. (5) UL94V Flammability Test UL94(6 th2018-05-30) In accordance with "STANDARD FOR SAFETY -Tests for Flammability of Plastic Materials for Parts in Devices and Appliances-", a UL94 vertical flammability test was conducted, and the flammability determined based on the criteria was marked as "V-0" for V-0 class equivalent, "V-1" for V-1 class equivalent, "V-2" for V-2 class equivalent, and "x" for failure.

[0070] [Example 1] A roll of polyimide temporary paper made of shaved non-thermoplastic polyimide fibers, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide, which was produced using a known technique (JP Patent Publication No. 2019-35157), was conveyed at a heating speed for 5 minutes in a superheated steam oven set at a steam generation temperature of 380°C under a tension of 0.5 kgf, to obtain polyimide fiber paper. This polyimide fiber paper was ochre in color.

[0071] [Example 2] The polyimide temporary paper obtained in the same manner as in Example 1 was conveyed at a heating speed for 5 minutes in a superheated steam furnace set at a steam generation temperature of 380°C under a tension of 0.5 kgf. The obtained polyimide fiber paper was pressed at a pressure of 10.4 MPa for 10 minutes to obtain a thin polyimide fiber paper. This polyimide fiber paper was ochre in color.

[0072] [Comparative Example 1] A polyimide fiber paper was obtained in the same manner as in Example 1, except that the steam generation temperature in the superheated steam furnace was set to 300° C. This polyimide fiber paper was ochre in color.

[0073] [Comparative Example 2] The polyimide temporary paper obtained in the same manner as in Example 1 was heated in the air for 6 minutes in an oven set at 420° C. to obtain a polyimide fiber paper. The obtained polyimide fiber paper was black in color.

[0074] [Table 1]

[0075] From the results of Examples 1 and 2 above, it was confirmed that the polyimide fiber paper of the present invention, when heat-treated within a specific temperature range in a superheated steam furnace, becomes a paper-like structure having sufficient strength for practical use, and is a fiber paper that exhibits excellent heat insulation performance while also achieving high heat resistance and flame retardancy. (Possibility of Industrial Applicability)

[0076] The polyimide fiber paper of the present invention has excellent flame retardancy, heat resistance, and low outgassing properties inherent to the polyimide material, and also has better insulation performance, breathability, and flexibility than polyimide film, which is a common polyimide material. Therefore, the polyimide fiber paper of the present invention can be suitably used as an insulation material for spacecraft, as an insulation material for power devices and the like which operate at high temperatures, and as a thermal management material for electronic devices. [Explanation of symbols]

[0077] 0202 Heat treatment process 0301 Polyimide precursor solution 0302 Water-soluble polymer 0304 Imide component of polyimide precursor solution 0401 Water-soluble polymer 0404 Imide component of polyimide precursor solution 0502 Heating steam processing process

Claims

1. A polyimide fiber paper in which fibers made of a non-thermoplastic polyimide resin are bonded to each other by a starch syrup-like structure also made of a non-thermoplastic polyimide resin.

2. The polyimide fiber paper according to claim 1, comprising 0.05 to 35 parts by mass of the syrup-like structure portion made of the non-thermoplastic polyimide resin per 100 parts by mass of the fibers made of the non-thermoplastic polyimide resin and the syrup-like structure portion made of the non-thermoplastic polyimide resin in total.

3. 3. The polyimide fiber paper according to claim 1 or 2, wherein, in a thermogravimetric analysis, when nitrogen is continuously introduced at a flow rate of 50 mL / min, the measurement temperature range is 25°C to 700°C, and the temperature increase rate is 3°C / min, the temperature at which the weight at 200°C is reduced by 5% from the reference point is 450°C or higher.

4. 4. The polyimide fiber paper according to claim 1, wherein the thermal conductivity measured by a steady-state method is 0.10 W / m·K or less and 0.001 W / m·K or more.

5. 5. The polyimide fiber paper according to claim 1, which has a thermal conductivity of 0.04 W / m·K or less and 0.001 W / m·K or more as measured by a steady-state method.

6. The polyimide fiber paper according to any one of claims 1 to 5, having a thickness in the range of 0.05 mm to 1.0 mm and satisfying the V-0 level of the flame retardant standard in a UL94V flammability test based on the UL94 (6th 2018-05-30) V flammability test.

7. The polyimide fiber paper according to claim 6, which has a thickness of 0.1 mm to 0.5 mm.

8. The method for producing polyimide fiber paper according to any one of claims 1 to 7, characterized in that the polyimide temporary paper, which is made of shaved non-thermoplastic polyimide fibers, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of polyimide, is heat-treated at a temperature of 360°C to 450°C in a heating furnace having an oxygen ratio of 0.0 to 1.0 volume % to the volume, to obtain the polyimide fiber paper.

9. 9. The method for producing polyimide fiber paper according to claim 8, wherein the heat treatment of the polyimide temporary paper is carried out in a superheated steam furnace at a temperature of 360° C. to 450° C.

10. 8. The polyimide fiber paper according to claim 1, wherein the total amount of decomposition gas components derived from residues of water-soluble polymers having a temperature lower than the glass transition temperature of polyimide generated when the paper is heated at 300° C. for 1 hour in a mixed gas consisting of 20% oxygen and 80% helium is 0.1% or less of the total mass.

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