JP7722893B2 - Insulating resin material, wiring board using insulating resin material, and method for manufacturing insulating resin material - Google Patents

Description

The present invention relates to an insulating resin material containing aramid nanofibers, a wiring board made using the insulating resin material, and a method for manufacturing the insulating resin material.

With advances in electronic technology, there has been an increase in electronic devices, such as computers and mobile communication devices, that use high-frequency bands. The high-frequency wiring boards and multilayer wiring boards used in such electronic devices generally require materials with a low dielectric constant. Examples of low-dielectric-constant resin materials include non-polar polymer resin materials such as polyethylene, polypropylene, polystyrene, and polytetrafluoroethylene. Polytetrafluoroethylene in particular is known to be an excellent material for its low dielectric constant, low dielectric dissipation factor, and heat resistance.

However, the resin material has a high coefficient of linear thermal expansion, which differs significantly from the coefficient of linear thermal expansion of the metal wiring material formed on the substrate, posing issues such as wiring peeling and cutting due to the difference in coefficient of linear thermal expansion.

In order to reduce the coefficient of linear thermal expansion of the above-mentioned resin materials, one method is to fill them with inorganic powder or use inorganic materials with low coefficients of linear thermal expansion, such as glass cloth. However, because inorganic materials generally have a high relative dielectric constant, there is an issue that the relative dielectric constant of the resulting material is high.

Therefore, Patent Documents 1 and 2 propose a technology for obtaining high mechanical properties and a low coefficient of linear thermal expansion by mixing and fixing aromatic polyamide pulp (para-aramid pulp) having a BET specific surface area of 3 to 25 m ² /g with a fluororesin.

These are preferable in that they homogeneously combine a high-elasticity material with high water absorption but low linear expansion and PTFE with high linear expansion but low water absorption and low dielectric constant. However, para-aramid pulp produced by beating 10-20 μm para-aramid fibers has a branched structure with fibers of several to 10 μm in diameter in the center. The amount of polytetrafluoroethylene that can be fixed to the fibrils of this para-aramid pulp is generally about 1 g to 1.5 g per 15 m ² /g BET specific surface area, and is affected by the water absorption and dielectric constant of the para-aramid pulp itself. Furthermore, in the para-aramid pulp obtained by the above process, metals derived from the raw materials and salts generated by neutralization remain in the unbeaten portion during production, and care must be taken to remove these by washing.

Patent Document 3 proposes a porous sheet obtained by using an aromatic polyamide solution composed of fibrils with a diameter of 1 μm or less, casting the solution to precipitate fibrils, and then impregnating the sheet with a resin.

However, creating a sheet composed of fibrils from a polymerization solution requires precise control of conditions, and if the salts contained in the polymerization solution are not sufficiently removed, there is a concern that the substrate may rust when it is made into a substrate.

Furthermore, in order to impregnate a sheet with a microstructure composed of fibrils with a thermoplastic or thermosetting resin, it is preferable that the viscosity is low. For this purpose, if a resin diluted in a solvent or the like is used, it is undesirable because this requires a process of evaporating the diluting solvent or washing and removing it.
Furthermore, the high dielectric constant and water absorption rate due to the material properties of para-aramid fibrils are undesirable for next-generation communication substrates.

Patent Document 4 proposes an insulating resin material containing fibrils made of polytetrafluoroethylene and having a BET specific surface area of 10 to 250 ^{m 2} /g, in which the fibrils are oriented in multiple directions and have a fine mesh structure with a porosity of 50% or more.

However, creating polytetrafluoroethylene fibrils requires stretching while applying shear to the polyfluoroethylene particles, and strict control is required to consistently obtain the fibril shape. Furthermore, due to the layered structure, adhesion is difficult and there is a risk of delamination due to bending or friction.

Japanese Patent Application Publication No. 11-112117 Japanese Patent Application Laid-Open No. 2007-123737 Japanese Patent Application Publication No. 09-324060 JP 2017-171898 A

The present invention was made to solve the above-mentioned problems of the conventional technology, and its purpose is to provide an insulating resin material and a wiring board using the same that combine an excellent low dielectric constant and a low coefficient of linear thermal expansion, which have been difficult to achieve with conventional materials.

After extensive research, the inventors discovered that an insulating resin material that combines a low dielectric constant and a low coefficient of linear thermal expansion can be obtained by using a specific amount of polytetrafluoroethylene particles and aramid nanofibers made from a para-type wholly aromatic polyamide having a specific fiber diameter, and thus arrived at the present invention.

That is, according to the present invention, the following configurations (1) to (6) are provided.
(1) An insulating resin material comprising aramid nanofibers made of a para-type wholly aromatic polyamide having an average fiber diameter of 100 nm or less and polytetrafluoroethylene particles, wherein the content of the aramid nanofibers is 1 to 15 parts by weight per 100 parts by weight of the polytetrafluoroethylene particles, and wherein the insulating resin material has a relative dielectric constant of 2.5 or less and a linear expansion coefficient of 65 ppm or less in a relative dielectric constant test specified in JIS C6481:1996.
(2) The insulating resin material according to the above (1), wherein the para-type wholly aromatic polyamide is poly-p-phenylene terephthalamide.
(3) The insulating resin material according to the configuration (1) or (2), wherein the aramid nanofiber has a fiber diameter of 3 to 50 nm.
(4) The insulating resin material according to any one of (1) to (3), comprising 1 to 60 parts by weight of polytetrafluoroethylene particles having a particle diameter of less than 1 μm per part by weight of the aramid nanofibers.
(5) A wiring board made using the insulating resin material described in any one of the configurations (1) to (4).
(6) A method for producing an insulating resin material according to any one of the configurations (1) to (4), which is obtained by adding a strong basic substance to para-type wholly aromatic polyamide fibers or para-type wholly aromatic polyamide pulp in an aprotic polar solvent to form nanofibers, to give aramid nanofibers having an average fiber diameter of 100 nm or less, and mixing, fixing, and molding the resulting aramid nanofibers with polytetrafluoroethylene particles.

According to the present invention, by using a specific amount of polytetrafluoroethylene particles and aramid nanofibers made of a para-type wholly aromatic polyamide having a specific fiber diameter, it is possible to obtain an insulating resin material that combines a low dielectric constant and a low coefficient of linear thermal expansion, and a wiring board using the same.

1 is an example showing a structural observation image of the aramid nanofiber of the present invention. 1 shows the appearance of a 1 wt % aqueous dispersion of the aramid nanofibers of the present invention. 1 shows the appearance of a slurry of the present invention in which aramid nanofibers and polytetrafluoroethylene particles are composited. FIG. 4 is an external view of the slurry of FIG. 3 after being lightly dehydrated. This is the appearance of the slurry in Figure 3 after dewatering and drying the press-molded sheet. 4 is an SEM photograph of the surface of the press-molded sheet obtained by dehydrating the slurry of FIG. 3 and drying it. 4 is a SEM photograph of a cross section of the slurry of FIG. 3 after dehydration and drying of the press-molded sheet. This is the appearance of the molded sheet of FIG. 5 after sintering at 400° C. for 1 hour (in air). 6 is a SEM photograph of the surface of the molded sheet of FIG. 5 after sintering at 400° C. for 1 hour (in air). 6 is a SEM photograph of a cross section of the molded sheet of FIG. 5 after sintering at 400° C. for 1 hour (in air). This shows the appearance of polytetrafluoroethylene fine particles (10 μm) to which aramid nanofibers have been added (from the left, aramid nanofibers have been added to polytetrafluoroethylene fine particles in amounts of 10.0 wt %, 4.0 wt %, 2.0 wt %, and 1.0 wt %, respectively). 1 shows the appearance of the insulating resin material of the present invention molded into a semicircular shape. 2 is an example of a structural observation image obtained by enlarging FIG. 1 for calculating the average fiber diameter. FIG. 1 is an explanatory diagram regarding a method for calculating an average fiber diameter.

The details of the present invention are explained below.

<Insulating resin material>
The insulating resin material of the present invention contains aramid nanofibers made of para-type wholly aromatic polyamide having an average fiber diameter of 100 nm or less and polytetrafluoroethylene particles, and the content of the aramid nanofibers is 1 to 15 parts by weight per 100 parts by weight of the polytetrafluoroethylene particles. By doing so, an insulating resin material having both an excellent low dielectric constant and a low coefficient of linear thermal expansion can be obtained.

The insulating resin material of the present invention also has an aramid nanofiber content of 1 to 15 parts by weight, preferably 1.5 to 12 parts by weight, and more preferably 2 to 10 parts by weight, per 100 parts by weight of polytetrafluoroethylene particles. Within this range, an insulating resin material can be obtained that combines an excellent low dielectric constant with a low coefficient of linear thermal expansion. An aramid nanofiber content of more than 15 parts by weight is undesirable because the water absorption rate becomes high, while an aramid nanofiber content of less than 1 part by weight is undesirable because the coefficient of linear thermal expansion becomes high.

The insulating resin material of the present invention may further contain other fibers as needed, provided that this does not contradict the objectives of the present invention. The other fibers may be appropriately selected depending on the purpose. For example, to enhance strength and toughness, the insulating resin material may contain para-type wholly aromatic polyamide pulp or refined para-type wholly aromatic polyamide pulp. When para-type wholly aromatic polyamide pulp is contained, the insulating resin material may contain polytetrafluoroethylene particles with an average particle size of 1 μm or more (preferably 10 μm or more).

The insulating resin material of the present invention may have any suitable shape depending on the purpose. For example, it may be in the form of a typical sheet, a dome shape as shown in Figure 12, or any other shape.

The insulating resin material of the present invention has a relative dielectric constant of 2.5 or less, preferably 2.3 or less, measured in normal and D-48/50 conditions using the measurement method specified in JIS C6481:1996. There is no particular lower limit, but a value of 1.0 or more is preferred.

Furthermore, the insulating resin material of the present invention preferably has a dielectric loss tangent of 0.0050 or less, and more preferably 0.0030 or less, in normal and D-48/50 conditions, as measured using the measurement method specified in JIS C6481:1996. There is no particular lower limit, but 0.0001 or more is preferred.

Furthermore, the insulating resin material of the present invention has a linear expansion coefficient of 65 ppm or less, preferably 60 ppm or less, more preferably 55 ppm or less, and even more preferably 50 ppm or less. There is no particular lower limit, but a linear expansion coefficient of 1 ppm or more is preferred.
The insulating resin material of the present invention can be suitably used as a material for wiring boards.

<Polytetrafluoroethylene particles>
The particle diameter of the polytetrafluoroethylene particles of the present invention is preferably less than 1 μm, more preferably less than 0.5 μm, and even more preferably less than 0.3 μm. When the particle diameter is less than the above-mentioned numerical value, the time for surface fixation to the aramid nanofiber is short and the amount of fixation is sufficient, which is preferable. The lower limit of the particle diameter is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm. If the particle diameter is too small, there is a risk that surface fixation will take a long time or the amount of fixation will be too small.

The method for producing polytetrafluoroethylene particles is not particularly limited, but it is preferable that the particles be a powder obtained by separating and drying an aqueous dispersion of particles with a diameter of approximately 0.25 μm, produced by emulsion polymerization of tetrafluoroethylene, together with a dispersant, which is concentrated, and particles with a diameter of several to 10 μm, produced by suspension polymerization.

The polytetrafluoroethylene particles are fixed to the aramid nanofibers through the electrical adsorption of fluorine and amide bonds, and can be fixed regardless of particle size. However, from the perspective of achieving uniformly dispersed particles in three dimensions, it is preferable that the polytetrafluoroethylene particles be obtained by the emulsion polymerization described above.

In the present invention, polytetrafluoroethylene particles having a particle diameter of less than 1 μm are preferably contained in an amount of 1 to 60 parts by weight, and more preferably 5 to 50 parts by weight, per part by weight of aramid nanofiber.

<Aramid nanofiber>
The aramid nanofibers used in the insulating resin material of the present invention have an average fiber diameter of 100 nm or less, preferably 50 nm or less, and more preferably 25 nm or less. The lower limit of the average diameter is preferably 1 nm or more, more preferably 3 nm or more. Furthermore, it is preferable that the aramid nanofibers do not have diameters of 500 nm or more. If the average fiber diameter exceeds 100 nm, it becomes difficult to form a fine mesh structure, and the number of polytetrafluoroethylene particles that can be fixed to the surface of the aramid nanofiber by electrical adsorption of amide bonds and fluorine becomes relatively small. As a result, when aramid nanofibers having an average fiber diameter exceeding 100 nm are used, the proportion of aramid nanofibers in the insulating resin material increases, and the physical properties of the resin are influenced by the water absorption rate and dielectric constant of the aramid nanofibers, which is undesirable.

The aspect ratio of aramid nanofibers, expressed as fiber length/fiber diameter, is preferably 10 or more and 1,000 or less, more preferably 10 or more and 500 or less, and even more preferably 10 or more and 100 or less. If the aspect ratio is less than 10, it is difficult for the fibers to form an entangled structure and a fine knit structure. This may make it difficult to achieve the expected properties.

The aramid nanofibers used in the present invention are para-type wholly aromatic polyamides. Examples of para-type wholly aromatic polyamides include poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-amide hydrazide, and poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide, and poly-p-phenylene terephthalamide fibers with oriented crystallinity (forming domains of a liquid crystal structure in the spinning solution) are preferred.

Fibers made from para-type wholly aromatic polyamides include poly-p-phenylene terephthalamide fibers (commercially available products include "Twaron (registered trademark)" manufactured by Teijin Limited and "Kevlar (registered trademark)" manufactured by Toray DuPont Co., Ltd.) and coparaphenylene-3,4'-oxydiphenylene terephthalamide fibers (commercially available products include "Technora (registered trademark)" manufactured by Teijin Limited).

<Production of aramid nanofibers>
The aramid nanofibers of the present invention are produced by immersing and swelling para-aromatic polyamide fibers in a solvent with high affinity, followed by the addition of a strong base to sever hydrogen bonds. The para-aromatic polyamides preferably used in the present invention are polymers in which one or more divalent aromatic groups are linked by amide bonds. The aromatic groups may contain two or more aromatic rings, and the aromatic rings may be bonded directly or via oxygen or sulfur. The hydrogen atoms of the divalent aromatic groups may be substituted with halides, lower alkyl groups, or phenyl groups. The solvent used to produce the aramid nanofibers is preferably an aprotic polar solvent, such as dimethyl sulfoxide, dimethylacetamide, or N-methyl-2-pyrrolidone. Examples of strong bases used to produce the aramid nanofibers include potassium hydroxide, sodium hydroxide, barium hydroxide, and calcium hydroxide.

Specifically, the aramid nanofibers of the present invention can be produced by immersing para-type wholly aromatic polyamide (e.g., poly-p-phenylene terephthalamide) fibers or pulp in alkaline dimethyl sulfoxide.

Para-type wholly aromatic polyamides (e.g., poly-p-phenylene terephthalamide) are obtained by forming liquid crystal domains in a spinning solution, discharging the solution from a capillary, and then washing the spinning solvent with water. The resulting fibers are then subjected to alkaline conditions to sever the weak bonds between the liquid crystal domains that make up the fibers. The resulting fibers are then liberated in a highly compatible solvent, yielding high-elasticity, high-strength cut fibers. The resulting cut fibers can then be isolated by placing them in a poor solvent (water, alcohol, acetone, etc.) that serves as a dispersion medium to isolate aramid nanofibers.

In addition, para-type wholly aromatic polyamide (e.g., poly-p-phenylene terephthalamide) pulp can be obtained by cutting para-type wholly aromatic polyamide (e.g., poly-p-phenylene terephthalamide) fibers with a diameter of 10 to 20 μm into pieces of several millimeters and subjecting the fibers to a refining process in water in which shear is applied to the fibers. In this type of refining process, the fibers refined from the fiber surface due to shear fracture at the liquid crystal interface do not completely separate but remain branched, resulting in a diameter of 100 to 1,000 nm, with the diameter of the core of the raw fiber being several μm. Refined pulp can also be converted into aramid nanofibers by the above-mentioned process.

Another possible method for micronizing aramid materials is to apply mechanical shear force rather than the chemical treatment described above. However, this method only partially produces a fibril structure with nano-order fiber diameters. Therefore, since it also contains non-fibrillated micro-order structures, it does not produce a uniform entangled structure on the nano-order, and the expected physical properties are not achieved. In the present invention, it is preferable to form an entangled structure from uniformly nano-sized fibers, rather than partial nano-ization.

<Method of manufacturing insulating resin material>
A preferred method for producing the insulating resin material of the present invention is to add a strongly basic substance to para-type wholly aromatic polyamide fibers or para-type wholly aromatic polyamide pulp in an aprotic polar solvent to form nanofibers, thereby obtaining aramid nanofibers having an average fiber diameter of 100 nm or less, and mix, fix, and mold the resulting aramid nanofibers with polytetrafluoroethylene particles.

<Molded product>
The insulating resin material of the present invention can be used to obtain molded products such as sheets, and fired molded products obtained by firing such molded products.
The dielectric constant of these molded articles, measured by the measuring method specified in JIS C6481:1996, is preferably 2.5 or less, more preferably 2.3 or less, in normal state and D-48/50. There is no particular lower limit, but it is preferably 1.0 or more.

Furthermore, the dielectric loss tangent of the molded product, measured using the measurement method specified in JIS C6481:1996, is preferably 0.0050 or less, and more preferably 0.0030 or less, in the normal state and D-48/50. There is no particular lower limit, but 0.0001 or more is preferred.

The linear expansion coefficient of the molded article is preferably 65 ppm or less, more preferably 60 ppm or less. The linear expansion coefficient of the sintered molded article is preferably 50 ppm or less, more preferably 45 ppm or less. There is no particular lower limit, but a value of 1 ppm or more is preferred.
The water contact angle of the molded article is preferably 50 degrees or more, more preferably 60 degrees or more, and even more preferably 70 degrees or more.

<Production of molded products>
As a method for producing a molded product from the insulating resin material of the present invention, a preferred example of a method for producing a molded sheet and a fired sheet will be described.

The molded sheet and the fired sheet can be produced, for example, by the following method:
(1) A step of mixing and stirring an aqueous dispersion of aramid nanofibers with an aqueous dispersion of polytetrafluoroethylene particles, so that the polytetrafluoroethylene particles are fixed to the aramid nanofibers and separated from the solvent, thereby obtaining a PTFE-ANF impregnated composite material;
(2) forming the impregnated composite material to obtain a formed sheet;
(3) A step of firing the molded sheet to obtain a fired sheet.

When forming the formed sheet, for example, a press, an extrusion molding machine, a calender roll, etc. may be used, but among these, forming by a calender roll is preferred from the viewpoint of productivity.
The fired sheet can be fired by any method appropriately selected from known methods, but metal-metal firing is preferred. Sintering is preferably carried out at a temperature within the firing temperature range of polytetrafluoroethylene (e.g., 300 to 500°C).

The above method can produce the molded sheet shown in Figure 5 and the fired sheet shown in Figure 8. In the fired sheet, as shown in Figures 9 and 10, the polytetrafluoroethylene particles (PTFE particles) are transformed into fibrous aggregates fused and integrated along the aramid nanofibers (ANF), leaving the ANF coated with PTFE. This reduces the exposed surface area of the ANF, suppressing the effects of water absorption and dielectric constant due to the physical properties of para-aramid. It is possible to achieve both a low dielectric constant and low linear expansion while maintaining the multidirectionally oriented fine mesh structure of the aramid nanofibers.

The present invention will be described in detail below using examples and comparative examples, but the scope of the present invention is not limited to the following examples and comparative examples. The property values in the examples were measured using the following methods.

<Measurement of relative permittivity and dielectric loss tangent>
The measurement was carried out in accordance with JIS C6481:1996.
Measuring device: LCR meter (HP-4284A, manufactured by Hewlett-Packard)
Measurement conditions: A normal condition (kept at 22°C and 60% RH for 90 hours)
D-48/50 (immersed in 50°C water for 48 hours)
Frequency: 1 MHz

<Measurement of linear expansion coefficient>
Using a thermomechanical analyzer (manufactured by SII Nanotechnology, product name: TMA/SS6100), the sample was heated from 0°C to 400°C at 10°C/min, cooled to 10°C at 40°C/min, and then heated from 10°C to 200°C at 10°C/min for measurement. The measurement load was 29.4 mN, and the measurement atmosphere was air.

<Measurement of water contact angle>
A contact angle meter (Kyowa Interface Science Co., Ltd., product number: DMO-501) was used to measure the water contact angle, which was the angle between the droplet and the sheet surface when a water droplet was dropped on the surface of the prepared sheet sample.

<Average fiber diameter>
The structure of the sample was observed using a scanning electron microscope (JEOL Ltd., model number JSM-6330F). From an image observed at a magnification setting of 50,000x, an image region measuring 1,800 to 2,000 nm horizontally and 1,200 to 1,500 nm vertically was selected, and this image region was further divided vertically into four and horizontally into four to define a total of 16 grid regions A1-D4. One sample present within each grid region was selected, and the average fiber diameter of the selected sample was measured on the image. The average value was used as the average fiber diameter (Figure 14).

[Example 1]
<Creation of aramid nanofibers>
Aramid pulp: 10 g (10 g of Twaron (registered trademark) 1000 manufactured by Teijin Aramid Co., Ltd., cut into 6 mm pieces, was washed by boiling in 1000 g of boiling water for 30 minutes, cooled, washed with water, and dried).
Tokyo Chemical Industry Co., Ltd. Dimethyl sulfoxide (DMSO) >99% 80g
・Tokyo Ohka Kogyo Co., Ltd. Potassium hydroxide (KOH) 10g
The above was charged into a planetary mixer and stirred for 2 hours at 70° C. After stirring, the aramid pulp lost its shape, and a red, semi-transparent, highly viscous solution was obtained.

The resulting red, translucent solution containing nanofibers was diluted with three times the volume of DMSO and gradually poured into 20 liters of water while stirring, precipitating poly-p-phenylene terephthalamide nanofibers. At this point, the solution was a yellow-red slurry, to which sulfuric acid was added in the amount required for KOH neutralization, and the poly-p-phenylene terephthalamide nanofibers were collected by filtration.

Then, the mixture was washed 3 to 5 times using distilled water or ion-exchanged water and stretch-dehydrated to remove the solvent and salt. Distilled water was added to the resulting aqueous solid containing poly-p-phenylene terephthalamide nanofibers to a solids concentration of 1%, and the mixture was mixed using a stone mill-type grinding kneader (Supermass Colloider) manufactured by Masuko Sangyo Co., Ltd. to obtain an aqueous dispersion of poly-p-phenylene terephthalamide nanofibers. The resulting poly-p-phenylene terephthalamide nanofiber dispersion was diluted with isopropyl alcohol, added dropwise to a preparation, and dried, confirming that the average fiber diameter was 20 nm.

<Creating a molded sheet>
When an aqueous dispersion of poly-p-phenylene terephthalamide nanofibers (concentration 1 wt%), which is easily mixed with a polytetrafluoroethylene particle dispersion (diameter 0.25 μm, manufactured by AGC AD911), was mixed and stirred at a PTFE:ANF ratio of 100:10 (parts by weight), the PTFE and ANF settled and separated from the solvent, as shown in Figure 3. After removing the solid content, it was washed several times with water, sandwiched between polypropylene nonwoven fabric sheets, and lightly squeezed to obtain a PTFE-ANF hydrous composite material.

The resulting PTFE-ANF hydrous composite was sandwiched between filter paper and further press-dehydrated using a press dehydrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) used for papermaking, etc., and then sheeted using a metal-metal calendar at a linear pressure of 100 kg/cm, a temperature of 100°C, and a speed of 1 m/min to produce a molded sheet as shown in Figure 5, which was then evaluated. The results are shown in Table 1.

The surfactant contained in the PTFE dispersion had been almost completely washed away from the resulting molded sheet, but due to the hydrophilic nature of the aramid nanofibers and the influence of trace amounts of residual surfactant, the contact angle was approximately 70°. As shown in Figures 6 and 7, SEM observation of the surface and cross section confirmed that the PTFE particles had been fixed, captured, and agglomerated by the ANF.

[Example 2]
<Creating a molded sheet>
A molded sheet was produced and evaluated in the same manner as in Example 1, except that the PTFE:ANF ratio was 100:2 (parts by weight). The results are shown in Table 1.

[Example 3]
<Creating a sintered sheet>
The molded sheet obtained in Example 1 was treated in an air atmosphere at 400° C. for 1 hour to produce a sintered sheet as shown in Fig. 8, which was then evaluated. The results are shown in Table 1.
As a result of the heat treatment, the PTFE particles were transformed into fibrous aggregates fused and integrated along the ANF, as shown in FIG.
As a result, the water repellency improved due to a decrease in ANF on the surface (deactivation of the surfactant contained in the PTFE dispersion), and the contact angle of water became approximately 110°. This confirmed that the effect of water on ANF is extremely limited.

[Example 4]
<Creating a sintered sheet>
The molded sheet of Example 2 was treated in an air atmosphere at 400° C. for 1 hour to prepare a sintered sheet, which was then evaluated in the same manner as in Example 3. The results are shown in Table 1.

[Comparative Example 1]
<Creating a molded sheet>
A cast film of polytetrafluoroethylene particle dispersion (diameter 0.25 μm, manufactured by AGC, AD911) alone was prepared and evaluated. The results are shown in Table 1.

[Comparative Example 2]
<Creating a molded sheet>
The sheet obtained in Comparative Example 1 was treated in an air atmosphere at 400° C. for 1 hour to prepare a sintered sheet, which was then evaluated. The results are shown in Table 1.

The insulating resin material of the present invention can be suitably used as a material for wiring boards.

Claims (6)

An insulating resin material containing aramid nanofibers made of a para-type wholly aromatic polyamide having an average fiber diameter of 100 nm or less and polytetrafluoroethylene particles, with the aramid nanofiber content being 1 to 15 parts by weight per 100 parts by weight of the polytetrafluoroethylene particles, and having a relative dielectric constant of 2.5 or less and a linear expansion coefficient of 65 ppm or less in a relative dielectric constant test specified in JIS C6481:1996. The insulating resin material according to claim 1, wherein the para-type wholly aromatic polyamide is poly-p-phenylene terephthalamide. The insulating resin material according to claim 1 or 2, wherein the aramid nanofiber has a fiber diameter of 3 to 50 nm. The insulating resin material according to any one of claims 1 to 3 contains 1 to 60 parts by weight of polytetrafluoroethylene particles with a particle diameter of less than 1 μm per part by weight of aramid nanofiber. A wiring board made using the insulating resin material described in any one of claims 1 to 4. The method for producing an insulating resin material according to any one of claims 1 to 4, wherein a strongly basic substance is added to para-type wholly aromatic polyamide fibers or para-type wholly aromatic polyamide pulp in an aprotic polar solvent to form nanofibers, to give aramid nanofibers having an average fiber diameter of 100 nm or less, and polytetrafluoroethylene particles are mixed, fixed, and molded .