Insulating resin material, wiring board using insulating resin material, and method for manufacturing insulating resin material

Abstract

To provide an insulating resin material having sufficiently low relative dielectric constants and low thermal linear expansion coefficients and a circuit board using the same.SOLUTION: An insulating resin material comprises aramid nanofibers composed of a para-type wholly aromatic polyamide with an average fiber diameter of 100 nm or less and polytetrafluoroethylene particles, with the content of the aramid nanofibers being 1 pt.wt.-15 pts.wt. relative to 100 pts.wt. of the polytetrafluoroethylene particles. In a relative dielectric constant test defined in JISC6481: 1996, the insulating resin material has a relative dielectric constant of 2.5 or less and a linear expansion coefficient of 65 ppm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulating resin material containing aramid nanofibers, a wiring board using the insulating resin material, and a method for producing the insulating resin material. [Background technology]

[0002] With the development of electronic technology, electronic devices such as computers and mobile communication devices that use high frequency bands are on the rise. High frequency wiring boards and multilayer wiring boards used in such electronic devices generally require materials with low relative dielectric constants. Examples of low relative 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 in terms of low relative dielectric constant, low dielectric loss tangent, and heat resistance.

[0003] However, the resin material has a high coefficient of linear thermal expansion, which is significantly different from the coefficient of linear thermal expansion of the metal wiring material formed on the substrate. This causes problems such as peeling and breaking of the wiring due to the difference in coefficient of linear thermal expansion.

[0004] In order to reduce the linear thermal expansion coefficient of the resin material, there are methods such as filling with inorganic powder or using inorganic materials with low linear thermal expansion coefficients, such as glass cloth. However, since inorganic materials generally have a high relative dielectric constant, there is a problem that the relative dielectric constant of the resulting material is high.

[0005] Therefore, in Patent Documents 1 and 2, the distance is set to 3 to 25 m. 2 A technology has been proposed to obtain high mechanical properties and a low coefficient of linear thermal expansion by mixing and fixing aromatic polyamide pulp (para-aramid pulp) with a BET specific surface area of 1000 / g and fluororesin.

[0006] These are preferable in that they are a homogeneous composite of 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, which is produced by beating para-aramid fibers of 10 to 20 μm, has a branched structure with fibers of several to 10 μm in size in the center. Polytetrafluoroethylene that can be fixed to the fibrils of this para-aramid pulp generally has a BET specific surface area of 15 m 2 / g, and is affected by the water absorption rate and relative dielectric constant of the para-aramid pulp itself.In addition, metals derived from the raw materials and salts generated by neutralization remain in the unbeaten parts of the para-aramid pulp obtained by the above process, and care must be taken to remove these by washing.

[0007] Patent document 3 proposes a porous sheet obtained by using an aromatic polyamide solution composed of fibrils with a fibril diameter of 1 μm or less, casting the solution to form a sheet to precipitate fibrils, and then impregnating the sheet with resin.

[0008] However, producing 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 sheet will rust when made into a substrate.

[0009] 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.

[0010] Patent Document 4 describes a polymer containing fibrils made of polytetrafluoroethylene and having a BET specific surface area of 10 to 250 m 2 / g insulating resin material in which the fibrils are oriented in multiple directions and have a fine network structure with a porosity of 50% or more has been proposed.

[0011] However, to create polytetrafluoroethylene fibrils, polyfluoroethylene particles must be stretched while being subjected to shear, and strict control is required to obtain a stable fibril shape. Furthermore, the layered structure makes adhesion difficult and there is a risk of delamination due to bending or friction. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 11-112117 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-123737 [Patent Document 3] Japanese Patent Application Publication No. 09-324060 [Patent Document 4] Japanese Patent Application Publication No. 2017-171898 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an insulating resin material that combines an excellent low dielectric constant and a low coefficient of linear thermal expansion, which have been difficult to achieve conventionally, and a wiring board using the same. [Means for solving the problem]

[0014] As a result of extensive research, the present inventors discovered that an insulating resin material having both 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 of a para-type wholly aromatic polyamide having a specific fiber diameter, and thus arrived at the present invention.

[0015] 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 nanofibers have a fiber diameter of 3 to 50 nm. (4) The insulating resin material according to any one of the configurations (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 according to 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. [Effects of the Invention]

[0016] 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 has both a low dielectric constant and a low coefficient of linear thermal expansion, and a wiring board using the insulating resin material. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is an example showing a structural observation image of the aramid nanofiber of the present invention. [Figure 2]1 shows the appearance of a 1 wt % aqueous dispersion of the aramid nanofibers of the present invention. [Figure 3] 1 shows the appearance of a slurry of the present invention in which aramid nanofibers and polytetrafluoroethylene particles are composited. [Figure 4] FIG. 4 is an external view of the slurry of FIG. 3 after being lightly dehydrated. [Figure 5] This is the appearance of the slurry in Figure 3 after dehydration and drying of the press-molded sheet. [Figure 6] This is an SEM photograph of the surface of the press-molded sheet obtained by dehydrating the slurry shown in Figure 3 and drying it. [Figure 7] This is an SEM photograph of the cross section of the slurry in Figure 3 after dehydration and drying of the press-molded sheet. [Figure 8] This is the appearance of the molded sheet in Figure 5 after sintering at 400°C for 1 hour (in air). [Figure 9] 6 is an SEM photograph of the surface of the molded sheet of FIG. 5 after sintering at 400° C. for 1 hour (in air). [Figure 10] 6 is an SEM photograph of a cross section of the molded sheet of FIG. 5 after sintering at 400° C. for 1 hour (in air). [Figure 11] This shows the appearance of polytetrafluoroethylene microparticles (10 μm) to which aramid nanofibers have been added (from the left, aramid nanofibers have been added to polytetrafluoroethylene microparticles at 10.0 wt%, 4.0 wt%, 2.0 wt%, and 1.0 wt%, respectively). [Figure 12] 1 shows the appearance of the insulating resin material of the present invention molded into a semicircular shape. [Figure 13] This is an example of a structural observation image enlarged from Figure 1 for calculating the average fiber diameter. [Figure 14] FIG. 1 is an explanatory diagram regarding a method for calculating an average fiber diameter. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below.

[0019] <Insulating resin materials> 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. This makes it possible to obtain an insulating resin material that has both an excellent low dielectric constant and a low coefficient of linear thermal expansion.

[0020] Furthermore, the insulating resin material of the present invention 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 exhibits both an excellent low relative dielectric constant and 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 increases, while an aramid nanofiber content of less than 1 part by weight is undesirable because the coefficient of linear thermal expansion increases.

[0021] Furthermore, the insulating resin material of the present invention may further contain other fibers as necessary, provided that the purpose of the present invention is not violated. The other fibers can be appropriately selected depending on the purpose. For example, when the purpose is to enhance strength and toughness, para-type wholly aromatic polyamide pulp or refined para-type wholly aromatic polyamide pulp may be contained. When para-type wholly aromatic polyamide pulp is contained, polytetrafluoroethylene particles having an average particle size of 1 μm or more (preferably 10 μm or more) may be contained.

[0022] The insulating resin material of the present invention may have any suitable shape depending on the purpose, for example, a general sheet shape, a dome shape as shown in Fig. 12, or other shapes.

[0023] 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 state and D-48 / 50 by the measurement method specified in JIS C6481:1996. There is no particular lower limit, but the dielectric constant is preferably 1.0 or more.

[0024] Furthermore, the insulating resin material of the present invention has a dielectric loss tangent, measured by the method specified in JIS C6481:1996, of preferably 0.0050 or less, and more preferably 0.0030 or less, in normal state and D-48 / 50. There is no particular lower limit, and the dielectric loss tangent is preferably 0.0001 or more.

[0025] 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 it is preferably 1 ppm or more. The insulating resin material of the present invention can be suitably used as a material for wiring boards.

[0026] <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 equal to or 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.

[0027] The method for producing polytetrafluoroethylene particles is not particularly limited, but it is preferable that the particles are a powder obtained by separating and drying an aqueous dispersion of particles having a diameter of about 0.25 μm, which are produced by emulsion polymerization of tetrafluoroethylene, together with a dispersant, which is concentrated, and particles having a diameter of about several to 10 μm, which are produced by suspension polymerization.

[0028] The polytetrafluoroethylene particles are fixed to the aramid nanofibers by the electrical adsorption of fluorine and amide bonds, and can be fixed regardless of particle size. However, from the viewpoint of achieving a uniformly dispersed fixation in three dimensions, it is preferable that the polytetrafluoroethylene particles are obtained by the emulsion polymerization described above.

[0029] In the present invention, the polytetrafluoroethylene particles having a particle diameter of less than 1 μm are preferably contained in an amount of 1 to 60 parts by weight, more preferably 5 to 50 parts by weight, per part by weight of the aramid nanofibers.

[0030] <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 with 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.

[0031] The aspect ratio of the aramid nanofibers, expressed as fiber length / fiber diameter, is preferably 10 to 1,000, more preferably 10 to 500, and even more preferably 10 to 100. If the aspect ratio is less than 10, it is difficult to develop an entangled fiber structure and form a fine knit structure. This may make it difficult to achieve the expected properties.

[0032] The aramid nanofibers used in the present invention are para-type wholly aromatic polyamides, such as poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-amide hydrazide, and poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide, and are preferably poly-p-phenylene terephthalamide fibers having oriented crystallinity (forming domains of a liquid crystal structure in the spinning solution).

[0033] Examples of fibers using 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).

[0034] <Production of aramid nanofiber> The aramid nanofibers of the present invention are produced by using para-aromatic polyamide fibers as a raw material, immersing and swelling the fibers in a solvent with high affinity, and then adding a strong base to sever the hydrogen bonds. The para-aromatic polyamides that can be 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, and specific examples include dimethyl sulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone. Examples of strong bases used to produce the aramid nanofibers include potassium hydroxide, sodium hydroxide, barium hydroxide, and calcium hydroxide.

[0035] Specifically, the aramid nanofibers of the present invention can be produced by immersing para-type wholly aromatic polyamide (for example, poly-p-phenylene terephthalamide) fibers or pulp in alkaline dimethyl sulfoxide.

[0036] Para-type wholly aromatic polyamides (e.g., poly-p-phenylene terephthalamide) can be obtained by forming liquid crystal domains in a spinning solution, discharging the solution through 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 released into a 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.

[0037] 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 cut fibers to a reciprocal shear in water using a refiner. In this refiner treatment, 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 1000 nm, with the diameter of the core fiber being several μm. Refined pulp can also be converted into aramid nanofibers using the above treatment.

[0038] As another method for micronizing aramid materials, a method of applying mechanical shear force instead of the chemical treatment described above can be considered. However, this method only partially obtains a fibril structure with a fiber diameter on the nano-order. Therefore, since it also contains non-fibrillated micro-order structures, a uniform entangled structure on the nano-order cannot be obtained, and the expected physical properties are not exhibited. In the present invention, it is preferable to form an entangled structure from uniformly nano-sized fibers rather than partial nano-nization.

[0039] <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, resulting in aramid nanofibers with an average fiber diameter of 100 nm or less, and mix, fix, and mold the resulting aramid nanofibers with polytetrafluoroethylene particles.

[0040] <Molded products> 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 relative 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.

[0041] The dielectric loss tangent of the molded article, measured by the method specified in JIS C6481:1996, is preferably 0.0050 or less, more preferably 0.0030 or less, in the normal state and D-48 / 50. There is no particular lower limit, and 0.0001 or more is preferred.

[0042] Furthermore, 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 it is preferably 1 ppm or more. 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.

[0043] <Molded product manufacturing> 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.

[0044] 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.

[0045] 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).

[0046] The above-described 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) change shape to form fibrous aggregates fused and integrated along the aramid nanofibers (ANF), and the ANF is 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. This allows the sheet to achieve both a low dielectric constant and low linear expansion while maintaining the multidirectionally oriented fine mesh structure of the aramid nanofibers. [Example]

[0047] The present invention will be described in detail below with reference to examples and comparative examples, but the scope of the present invention is not limited to the following examples and comparative examples. The respective property values in the examples were measured by the following methods.

[0048] <Measurement of relative permittivity and dielectric loss tangent> Measurements were carried out in accordance with JISC6481:1996. Measuring device: LCR meter (Hewlett-Packard, HP-4284A) Measurement conditions: A normal condition (22°C, 60% RH for 90 hours) D-48 / 50 (immersed in 50°C water for 48 hours) Frequency: 1MHz

[0049] <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, then cooled to 10°C at 40°C / min, and further 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.

[0050] <Water contact angle measurement> Using a contact angle meter (Kyowa Interface Science Co., Ltd., product number: DMO-501), a water droplet was dropped onto the surface of the prepared sheet sample, and the angle between the droplet and the sheet surface, which was on the inner side of the liquid, was measured as the water contact angle.

[0051] <Average fiber diameter> The sample structure was observed using a scanning electron microscope (JEOL Ltd., model JSM-6330F). From the image observed at 50,000x magnification, an image region measuring 1,800 to 2,000 nm horizontally and 1,200 to 1,500 nm vertically was selected. This image region was further divided vertically and horizontally into four regions, resulting in a total of 16 grid regions, A1-D4. One sample within each grid region was selected, and the average fiber diameter of the selected sample was measured on the image. The average fiber diameter was used as the average fiber diameter (Figure 14).

[0052] [Example 1] <Creating 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, translucent, highly viscous solution was obtained.

[0053] The resulting red, translucent solution containing nanofibers was diluted with three times the volume of DMSO and gradually poured into 20 L of water while stirring to precipitate poly-p-phenylene terephthalamide nanofibers. At this point, the solution was a yellow-red slurry, to which sulfuric acid was added in an amount required for KOH neutralization, and the poly-p-phenylene terephthalamide nanofibers were collected by filtration.

[0054] The resulting solid was then washed 3 to 5 times using distilled water or ion-exchanged water and stretched 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.

[0055] <Creating molded sheets> When an aqueous dispersion of poly-p-phenylene terephthalamide nanofibers (concentration 1 wt%), which is easily mixed with a polytetrafluoroethylene particle dispersion (AD911 manufactured by AGC) 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 this solid, it was washed several times with water, sandwiched between polypropylene nonwoven fabric sheets, and lightly squeezed to obtain a PTFE-ANF hydrous composite.

[0056] The obtained PTFE-ANF hydrous composite material was sandwiched between filter papers and further press-dehydrated in a press dehydrator (Kumagaya Riki Kogyo Co., Ltd.) used for papermaking, 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. The results are shown in Table 1.

[0057] Although the surfactant contained in the PTFE dispersion had been almost completely washed away from the obtained molded sheet, the contact angle was approximately 70° due to the hydrophilicity of the aramid nanofibers and the influence of trace amounts of residual surfactant. 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.

[0058] [Example 2] <Creating molded sheets> 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.

[0059] [Example 3] <Creating sintered sheets> 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 Figure 8, which was then evaluated. The results are shown in Table 1. As shown in Figure 9, the heat treatment caused the PTFE particles to change shape into fibrous aggregates that were fused and integrated along the ANF. 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.

[0060] [Example 4] <Creating sintered sheets> The molded sheet of Example 2 was treated in an air atmosphere at 400° C. for 1 hour to produce a sintered sheet, which was then evaluated in the same manner as in Example 3. The results are shown in Table 1.

[0061] [Comparative Example 1] <Creating molded sheets> A cast film of polytetrafluoroethylene particle dispersion (diameter 0.25 μm, AD911 manufactured by AGC) alone was prepared and evaluated. The results are shown in Table 1.

[0062] Comparative Example 2 <Creating molded sheets> 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.

[0063] [Table 1] [Industrial Applicability]

[0064] The insulating resin material of the present invention can be suitably used as a material for wiring boards.

Claims

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. 2. The insulating resin material according to claim 1, wherein the para-type wholly aromatic polyamide is poly-p-phenylene terephthalamide.

3. 3. The insulating resin material according to claim 1, wherein the aramid nanofiber has a fiber diameter of 3 to 50 nm.

4. 4. The insulating resin material according to claim 1, 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 according to any one of claims 1 to 4.

6. 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.

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