JP7645511B2 - Polyimide Fiber Paper - Google Patents

Description

This application forms the basis of a domestic priority application to be filed at a later date.
The present invention relates to a polyimide fiber paper using a non-thermoplastic polyimide resin.

Polyimide film is a material with excellent electrical insulation, heat resistance, cold resistance, flame retardancy, chemical resistance, and mechanical properties, and is 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 film as an insulating material in spacecraft, which requires weight reduction and space saving, and as a thermal management material in power devices and heaters, which operate at high temperatures. However, polyimide film does not fully meet the requirements for a thermal management material in terms of insulation performance and gas and liquid permeability, and there was a demand for the development of a new polyimide material with improved properties.

One example of a polyimide material that meets the requirements for a thermal management material is polyimide fiber paper, which is made by fiberizing polyimide and processing it into a paper-like material. For example, there are technologies shown in Patent Document 1 and Patent Document 2.

Patent Publication 2009-97117 Patent Publication No. 2019-35157

Prior Art Document 1 shows a method for producing a non-thermoplastic nonwoven fabric made of polyimide resin. The method involves spinning a precursor solution of non-thermoplastic polyimide, collecting it 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 in the case of a wide sheet product, and the cost is high.

Also, a method for producing polyimide fiber paper made of non-thermoplastic polyimide is shown in Prior Art Document 2. The production method in Prior Art Document 2 is, first, to produce a temporary paper of polyimide fiber paper by 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-laid papermaking, and second, to obtain polyimide fiber paper by dispersing a polyimide precursor solution in the temporary paper and then heating the polyimide precursor solution to imidize it. However, according to the inventors' studies, this production method has a problem that when heated at a temperature range required for imidization, the water-soluble polymer remains and inhibits the product from acquiring flame retardancy, and further, 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.

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

That is, the present invention relates to the following inventions. As a first invention, we provide 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.

Next, as a second invention, we provide a polyimide fiber paper that contains 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 of the fibers made of a non-thermoplastic polyimide resin and the syrup-like structural portion made of a non-thermoplastic polyimide resin.

Next, as a third invention, we provide a polyimide fiber paper in which, 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 at 200°C is reduced by 5% from the reference point is 450°C or higher.

Next, as a fourth invention, we provide polyimide fiber paper whose thermal conductivity measured by a steady-state method is 0.10 W/m·K or less and 0.001 W/m·K or more.

Next, as a fifth invention, we provide polyimide fiber paper whose thermal conductivity measured by a steady-state method is 0.04 W/m·K or less and 0.001 W/m·K or more.

Next, as a sixth invention, we provide polyimide fiber paper that has a thickness in the range of 0.05 mm to 1.0 mm and meets 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.

Next, as a seventh invention, we provide polyimide fiber paper with a thickness of 0.1 mm to 0.5 mm.

The eighth invention provides a method for producing polyimide fiber paper, which is characterized by being obtained 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 having an oxygen ratio of 0.0 to 1.0% by volume at a temperature of 360°C to 450°C.

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.

Next, as a tenth invention, we provide a polyimide fiber paper characterized in that the total amount of decomposition gas components derived from the residue 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.

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 components 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 an 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.

Optical microscope image showing the structure of polyimide fiber paper 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 an eighth embodiment. 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. 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. 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 in a superheated steam furnace is heat-treated in a ninth embodiment.

Hereinafter, 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 spirit of the present invention.
<Embodiment 1>

This embodiment mainly relates to claim 1.
<Overview of First Embodiment>

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 First Embodiment>

In the polyimide fiber paper of this embodiment, by using the 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 shape, which is usually difficult, and obtain fiber paper having sufficient strength for practical use as a paper-like structure, as shown in Figure 1. Furthermore, by performing intersection bonding between polyimide fibers with the 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>

This embodiment mainly relates to claim 2.
<Overview of Second Embodiment>

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 Second Embodiment>

In this embodiment, if the amount of the syrup-like structural portion 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 portion 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>

This embodiment mainly relates to claim 3.
<Overview of Third Embodiment>

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 Third Embodiment>

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 is 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>

This embodiment mainly relates to claim 4.
<Outline of Fourth Embodiment>

The polyimide fiber paper of this embodiment is characterized in that 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.
<Configuration of Third Embodiment>

If the thermal conductivity of the polyimide fiber paper measured by the steady-state method exceeds 0.10 W/mK, the resulting polyimide fiber paper may not exhibit the expected insulating performance when used as an insulating material. In order to obtain the desired insulating performance, it may become necessary, for example, to stack multiple sheets of polyimide fiber paper. In that case, not only will the insulating layer be expensive, but the insulating layer will also become thick, making it unsuitable for use in electronic devices and the like where space saving is required.
<Embodiment 5>

This embodiment mainly relates to claim 5.
<Outline of Fifth Embodiment>

The polyimide fiber paper of this embodiment is characterized in that the thermal conductivity measured by a steady-state method is 0.04 W/m·K or less and 0.001 W/m·K or more.
<Configuration of Fifth Embodiment>

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 within 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 polyimide film has superior insulation performance and light weight compared to polyimide films, and the polyimide film can be suitably used as an insulation material or thermal management material in spacecraft, electronic devices, and heater applications.
<Embodiment 6>

This embodiment mainly relates to claim 6.
<Overview of Sixth Embodiment>

The polyimide fiber paper of this embodiment has a thickness in the range of 0.05 mm to 1.0 mm, and is characterized by 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 Sixth Embodiment>

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 the UL94V flammability test based on the UL94 (6th 2018-05-30) V flammability test.
By satisfying the flame retardancy UL-94 standard V-0, the material can be suitably used as a heat insulating material or a heat management material for controlling the flow of generated heat in electronic devices.
<Embodiment 7>

This embodiment mainly relates to claim 7.
<Overview of Seventh Embodiment>

The polyimide fiber paper of this embodiment is characterized by having a thickness of 0.1 mm to 0.5 mm.
Seventh embodiment: Configuration

The polyimide fiber paper of this 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 electronic devices is reduced and the material can be suitably used as a heat insulating material or a heat management material in electronic devices with limited space.
<Embodiment 8>

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

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 a non-thermoplastic polyimide, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of the polyimide, in a heating furnace in an environment 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. or more and 450° C. or less.
<Configuration of embodiment 8>

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.

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

In this structural formula, R represents _OCH3 , and X represents O, _CH2 , or _SO2 . Examples 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, which may be used alone or in combination of two or more.

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.

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

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, and 4,4'-oxydiphthalic anhydride. These may be used alone or in combination of two or more.

A polyimide temporary paper consisting of shaved fibers of a non-thermoplastic polyimide, a polyimide precursor solution, and a water-soluble polymer whose decomposition temperature is lower than the glass transition temperature of the 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>

As shown in FIG. 2, the "polyimide temporary paper heat treatment process (heat treatment step (0202))" is a process in which 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, is heat-treated at a temperature of 360°C to 450°C in a heating furnace under an atmosphere of 1 atmosphere where the oxygen ratio to the volume is 0.0 to 1.0% by volume, to obtain polyimide fiber paper. By performing heat treatment in the above temperature range, as shown in FIG. 3, an imidization 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 FIG. 4, a second reaction (0403) occurs in which the water-soluble polymer (0401) decomposes at a temperature lower than the glass transition temperature of polyimide. By removing this water-soluble polymer (0401), it is possible to obtain polyimide fiber paper with high heat resistance due to the imidized component (0404), which is the starch syrup-like structure of the polyimide precursor solution.

The heat treatment step in the preceding paragraph is preferably carried out in a heating furnace with an oxygen ratio of 0.0 to 1.0 % by volume. If the oxygen ratio in the heating furnace exceeds this range, oxidation of the surface of the polyimide fiber paper, which is originally ochre-colored, progresses and the paper turns black, which makes it difficult to detect defects such as foreign matter in the inspection process, which is not preferable. By keeping 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, and in order to proceed with the reaction more quickly and quantitatively, the heating temperature is more preferably 300° C. or higher, 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>

This embodiment mainly relates to claim 9.
<Overview of 9th embodiment>

The invention in this embodiment is a method for producing polyimide fiber paper by heat treating a polyimide temporary paper made 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% by volume at a temperature of 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>

As shown in FIG. 5, the "polyimide temporary paper heat treatment process in a superheated steam furnace (heated steam treatment step (0502))" is a process in which the polyimide temporary paper, which is made of the shaved fibers of non-thermoplastic polyimide 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, is heat-treated 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 imidization 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 FIG. 4, a second reaction (0403) occurs in which the water-soluble polymer (0401) decomposes at a temperature lower than the glass transition temperature of polyimide. By removing this water-soluble polymer (0401), it is possible to obtain polyimide fiber paper with high heat resistance due to the imidized component (0404), which is the starch syrup-like structure of the polyimide precursor solution.

The heat treatment using a superheated steam furnace is preferably at 200°C or higher, since both the first and second reactions in the previous section occur at 200°C or higher, and more preferably at 300°C or higher to allow the reactions to proceed more quickly and quantitatively, with 360°C or higher being particularly preferred. On the other hand, heat treatment at high temperatures can cause thermal decomposition of the polyimide material, so a temperature of 500°C or lower is preferred, with 450°C or lower being even more preferred.

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>

This embodiment mainly relates to claim 10.
<Outline of embodiment 10>

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>

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 having a temperature lower than the glass transition temperature of 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 the polyimide fiber paper is heated at a high temperature, if the total amount of decomposition gas components derived from the residue of the 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 satisfy the flame retardancy of the UL94V standard, and cannot be used suitably for 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 in spacecraft applications that require low outgassing.

The present invention includes various combinations of the above configurations within the technical scope of the present invention, as long as the effects of the present invention are achieved.

Next, the present invention will be explained 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.

The characteristics in the examples were evaluated by the following methods.
(1) 5% weight loss temperature: In a TGA chart obtained by measurement using an instrument: TGA-50 (product name, manufactured by Shimadzu Corporation) under conditions of a measurement temperature range of 25 to 700° C. and a heating rate of 3° C./min, the temperature at which the weight at 200° C. was reduced by 5% from the reference point was determined, and this value was defined as the 5% weight loss temperature.
(2) Thermal Conductivity: The thermal conductivity was measured by a steady-state method using a device: KES-F7 Thermo Lab (trade name, manufactured by Katotex).
(3) Thickness: Measured using a dial thickness gauge.
(4) Tensile strength The tensile strength of sample pieces of 15 mm × 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 In accordance with UL94 ( ^6th 2018-05-30) "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 judgment criteria was recorded 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.

[Example 1]
A roll of polyimide temporary paper made 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, 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.

[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 generating 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.

[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.

[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.

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)

The polyimide fiber paper of the present invention has excellent flame retardancy, heat resistance, and low outgassing properties derived from the polyimide material, and is also superior in heat insulation performance, breathability, and flexibility to polyimide films, which are common polyimide materials. Therefore, it can be suitably used as an insulation material for spacecraft, as an insulation material for power devices that operate at high temperatures, and as a thermal management material for electronic devices.

0202 Heat treatment step 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 Heated steam treatment step

Claims (10)

Polyimide fiber paper in which fibers made of non-thermoplastic polyimide resin are bonded to each other by a syrup-like structure also made of non-thermoplastic polyimide resin. The polyimide fiber paper according to claim 1 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. The polyimide fiber paper according to claim 1 or 2, in which, in a thermogravimetric analysis, 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 rise rate is 3°C/min, and the temperature at which the weight at 200°C is reduced by 5% from the reference point is 450°C or higher. The polyimide fiber paper according to any one of claims 1 to 3, which has 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. The polyimide fiber paper according to any one of claims 1 to 4, which has 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. A 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 retardancy standard in a UL94V flammability test based on the UL94 (6th 2018-05-30) V flammability test. The polyimide fiber paper according to claim 6, which has a thickness of 0.1 mm to 0.5 mm. The method for producing polyimide fiber paper according to any one of claims 1 to 7, characterized in that the polyimide temporary paper is obtained 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 having an oxygen ratio of 0.0 to 1.0% by volume at a temperature of 360°C to 450°C. The method for producing polyimide fiber paper according to claim 8, characterized in that the heat treatment of the polyimide temporary paper is carried out in a superheated steam furnace at a temperature of 360°C or higher and 450°C or lower. The polyimide fiber paper according to any one of claims 1 to 7, characterized in that the total amount of decomposition gas components derived from the residue 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.

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