JP7688693B2 - Nonwoven fabric, method for producing nonwoven fabric, prepreg, printed wiring board and electronic component - Google Patents

Description

The present disclosure relates to nonwoven fabrics, methods for producing nonwoven fabrics, prepregs, printed wiring boards and electronic components.

Traditionally, nonwoven fabrics made from polyamide fibers are well known to be made from nylon 6 and nylon 66, which are considered to be highly strong, tough and durable and have been used for a variety of industrial purposes.

Nonwoven fabrics made of polyamide fibers are also required to have heat resistance depending on the application. It is known that semi-aromatic polyamides obtained by using aromatic monomers and aliphatic monomers have higher heat resistance than nylon 6, nylon 66, etc. For example, Patent Document 1 proposes a continuous fiber nonwoven fabric made of semi-aromatic polyamides consisting of an aromatic dicarboxylic acid component, an aliphatic diamine component, and a monocarboxylic acid component, characterized in that the aromatic dicarboxylic acid component is mainly terephthalic acid, the aliphatic diamine component is mainly 1,10-decanediamine, and the monocarboxylic acid component is an aliphatic monocarboxylic acid having a molecular weight of 140 or more, the melting point of the semi-aromatic polyamide is 300° C. or more, the content of the monocarboxylic acid component in the semi-aromatic polyamide is 1 to 10 mass%, the melt flow rate of the semi-aromatic polyamide (measured under conditions of a load of 1.2 kgf/cm ² and a temperature of 350° C.) is 10 to 150 g/10 min, and the average fiber diameter of the continuous fibers is 0.1 to 10 μm.

[Patent Document 1] JP 2016-98458 A

However, the inventors' investigations revealed that the semi-aromatic polyamide nonwoven fabric described in Patent Document 1 has a large difference between the tensile strength at around room temperature and the tensile strength in a high-temperature environment (e.g., 120°C), and may have poor heat resistance.

The present disclosure has been made in view of the above, and aims to provide a nonwoven fabric having excellent tensile strength in high-temperature environments, a method for producing this nonwoven fabric, and a prepreg, a printed wiring board, and an electronic component that include this nonwoven fabric.

Specific means for solving the above problems include the following aspects:

<1> A fiber containing a polyamide resin containing an acyclic structural unit derived from an aliphatic monomer, and the highest melting point of the fiber is 300° C. to 350° C.,
The polyamide resin is a nonwoven fabric, in which the sum of the carbon atoms contained in the acyclic structural units derived from the aliphatic monomers and contained in the carbon chain portion (excluding the carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin is divided by the number of the acyclic structural units derived from the aliphatic monomers, and the value obtained is less than 7.
<2> The nonwoven fabric according to <1>, wherein the difference between the thermal decomposition initiation temperature of the fibers and the melting point is 10°C or more and 80°C or less.
<3> The nonwoven fabric according to <1> or <2>, wherein the average fiber diameter of the fibers is 10.0 μm or less.
<4> The nonwoven fabric according to any one of <1> to <3>, wherein (Dd/Da)×100, which is obtained by dividing the average fiber diameter (Da) by the standard deviation (Dd) of the average fiber diameters and multiplying the result by 100, is 50 to 200.
<5> The nonwoven fabric according to any one of <1> to <4>, wherein the nonwoven fabric comprises a meltblown nonwoven fabric.
<6> The nonwoven fabric according to any one of <1> to <5>, wherein the polyamide resin contains two or more types of structural units derived from dicarboxylic acid.
<7> The nonwoven fabric according to any one of <1> to <6>, wherein the highest melting point of the fibers is 305°C to 340°C.
<8> The nonwoven fabric according to any one of <1> to <7>, wherein the polyamide resin has a value obtained by dividing the sum of carbon atoms contained in the acyclic structural units derived from the aliphatic monomer and contained in a carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting a main chain of the polyamide resin by the number of the acyclic structural units derived from the aliphatic monomer, of 4 to 6.5.
<9> A polyamide resin containing an acyclic structural unit derived from an aliphatic monomer or a resin composition containing the polyamide resin, the highest melting point being 300°C to 350°C, the polyamide resin being contained in the acyclic structural unit derived from the aliphatic monomer, and the value obtained by dividing the total number of carbon atoms contained in a carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of the acyclic structural units derived from the aliphatic monomer is less than 7, the polyamide resin or the resin composition being melt-kneaded using two or more axes to obtain a melt-kneaded product;
a spinning step of spinning the molten kneaded material together with heated air through a nozzle having a plurality of holes;
a drawing step of drawing the molten material spun in the spinning step by the heated air;
A method for producing a nonwoven fabric, comprising:
<10> The method for producing a nonwoven fabric according to <9>, wherein the melt-kneading step is a step of melt-kneading the polyamide resin or the resin composition using two or more shafts at a temperature that is 10° C. or more higher than the highest melting point of the polyamide resin or the resin composition and 5° C. or more lower than a thermal decomposition onset temperature of the polyamide resin or the resin composition.
<11> The method for producing a nonwoven fabric according to <9> or <10>, wherein in the melt-kneading step, the polyamide resin or the resin composition is melt-kneaded using two or more shafts while exhausting air by negative pressure.
<12> The nonwoven fabric according to any one of <1> to <8>,
A resin composition including at least one of a thermosetting resin and a thermoplastic resin;
A prepreg comprising:
<13> The thermosetting resin is a thermosetting resin having a curing temperature that is 20° C. or more lower than the lowest melting point of the nonwoven fabric,
The thermoplastic resin is a thermoplastic resin having a melting point that is 20° C. or more lower than the lowest melting point in the nonwoven fabric.
The prepreg according to <12>.
<14> A printed wiring board having a conductor layer on one or both sides of the cured or solidified product of the prepreg according to <12> or <13>.
<15> An electronic component having a circuit for transmitting an electrical signal of 1 GHz or more,
An insulating layer of the electronic component comprises a cured or solidified product of the prepreg according to <12> or <13>.

The present disclosure provides a nonwoven fabric having excellent tensile strength in high-temperature environments, a method for producing the nonwoven fabric, and a prepreg, printed wiring board, and electronic component that include the nonwoven fabric.

The following describes embodiments of the present disclosure. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.
In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified.

In the numerical ranges described in this disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Also, in the numerical ranges described in this disclosure, the upper or lower limit value of the numerical range may be replaced with the value shown in the examples.

In the present disclosure, each component may contain multiple types of corresponding substances. When referring to the amount of each component in a composition in the present disclosure, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified.
In this disclosure, "short fibers" refer to fibers having an average fiber length of 200 mm or less, and "long fibers" refer to fibers having an average fiber length of more than 200 mm.
In the present disclosure, a "resin composition containing a polyamide resin" refers to a mixture containing a polyamide resin as well as other thermoplastic resins, other components, and the like as necessary.
In the present disclosure, the preferred conditions for physical properties such as the melting point, the sum of carbon atoms/structural unit described below, thermal decomposition onset temperature, the difference between the thermal decomposition onset temperature and the highest melting point, the intrinsic viscosity, and MFR in the "polyamide resin used in the production of fibers" and the "resin composition used in the production of fibers" are the same as the preferred conditions for physical properties in the "fibers of the present disclosure" or the "polyamide resin contained in the fibers".

<Nonwoven fabric>
The nonwoven fabric of the present disclosure comprises fibers containing a polyamide resin containing acyclic structural units derived from aliphatic monomers, the fibers having a highest melting point of 300°C to 350°C, and the polyamide resin having a value obtained by dividing the sum of carbon atoms contained in the acyclic structural units derived from the aliphatic monomers and contained in a carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of acyclic structural units derived from the aliphatic monomers (hereinafter also referred to as "sum of carbon atoms/structural unit") is less than 7.

The nonwoven fabric of the present disclosure has a highest melting point in the fibers of 300° C. to 350° C., and the polyamide resin contained in the fibers has a sum of carbon atoms/structural unit of less than 7, thereby suppressing a decrease in tensile strength in a high-temperature environment, for example at 120° C. The reason for this is presumed to be that a sum of carbon atoms/structural unit of less than 7 means that the length of the carbon chain portion constituting the main chain of the polyamide resin is shorter than a certain range, and the short length of the carbon chain portion suppresses a decrease in tensile strength when the nonwoven fabric is exposed to high temperatures.
However, the above speculation is not intended to limit the nonwoven fabric of the present disclosure, but is merely an example.

The nonwoven fabric of the present disclosure has a tendency to have a small difference between the tensile strength at room temperature, for example, 28°C, and the tensile strength at 120°C, because the decrease in tensile strength at high temperatures, for example, at 120°C, is suppressed. As a result, even if the nonwoven fabric is laminated to other members at room temperature, such as 28°C, and then a heat treatment such as a preheating (for example, 120°C) treatment is performed before solder reflow processing, the decrease in tensile strength due to temperature change is small, making it easy to perform continuous processing.

(Melting Point)
The highest melting point of the fibers contained in the nonwoven fabric is 300°C to 350°C, and from the viewpoints of spinning stability and heat resistance, it may be 305°C to 340°C or 310°C to 330°C.

The highest melting point of the fiber, the polyamide resin or the resin composition described below can be determined as follows.
A sample of 10 mg of fiber, polyamide resin or resin composition is (i) heated to 340°C at 100°C/min and held at 340°C for 5 minutes, (ii) cooled to 30°C at 10°C/min, and then (iii) heated to 340°C at 10°C/min. The highest endothermic peak temperature among the endothermic peak temperatures in the differential scanning calorimetry curve (DSC curve) observed in the second heating process (iii) is taken as the highest melting point of the fiber, polyamide resin or resin composition. The endothermic peak observed in the differential scanning calorimetry curve (DSC curve) in the second heating process (iii) may be a single peak, and in that case, the single endothermic peak temperature observed is taken as the highest melting point.

(Thermal decomposition start temperature)
From the viewpoint of obtaining a nonwoven fabric having superior heat resistance, the fibers contained in the nonwoven fabric preferably have a thermal decomposition onset temperature of 330°C to 410°C, more preferably 340°C to 400°C, and even more preferably 350°C to 390°C.

The thermal decomposition onset temperature of the fiber, polyamide resin or resin composition can be determined as follows.
A sample of 10 mg of fiber, polyamide resin or resin composition is subjected to differential thermal analysis (DTA) in a nitrogen atmosphere from 25° C. to 450° C. at a heating rate of 10° C./min. The temperature at which 1% of the sample mass is decomposed (1% thermal decomposition temperature) is defined as the thermal decomposition onset temperature.

(Difference between thermal decomposition starting temperature and melting point)
The fibers contained in the nonwoven fabric preferably have a difference between the thermal decomposition onset temperature and the highest melting point (= thermal decomposition onset temperature - highest melting point) of 10°C or more and 80°C or less, and from the viewpoint of obtaining a nonwoven fabric with superior heat resistance, the difference is more preferably 60°C or less, even more preferably 50°C or less, and particularly preferably 45°C or less.
For the fibers contained in the nonwoven fabric, the lower limit of the difference between the thermal decomposition onset temperature and the highest melting point (= thermal decomposition onset temperature - highest melting point) is more preferably 25°C or higher, and even more preferably 35°C or higher.

(intrinsic viscosity)
From the viewpoint of production, the fibers contained in the nonwoven fabric preferably have an intrinsic viscosity of 0.1 dl/g to 1.0 dl/g, and more preferably 0.2 dl/g to 0.9 dl/g.
The intrinsic viscosity [η] of the fiber, polyamide resin or resin composition is a value measured using decalin as a solvent at 135° C. Specifically, it is determined as follows.
20 mg of fiber is used as a sample, the sample is dissolved in 15 mL of decalin, and the specific viscosity ηsp is measured in an oil bath at 135 ° C. After diluting the decalin solution by adding 5 mL of decalin solvent, the specific viscosity ηsp is measured in the same manner. This dilution operation is repeated two more times, and the value of ηsp / C when the concentration (C) is extrapolated to 0 is calculated as the limiting viscosity (see the formula below).
[η]=lim(ηsp/C) (C→0)

(Melt Flow Rate)
From the viewpoint of making the fiber diameter smaller, the fibers contained in the nonwoven fabric preferably have a melt flow rate (MFR: ASTM D-1238, 320° C., load 2160 g) of 1 g/10 min to 1000 g/10 min, and more preferably 10 g/10 min to 500 g/10 min.

There are no particular limitations on the method for setting the melting point, thermal decomposition onset temperature, difference between the thermal decomposition onset temperature and the highest melting point, intrinsic viscosity, or MFR of the fiber within the above ranges. For example, there are methods for changing the material of the polyamide resin contained in the fiber to a material described below; methods for adjusting the weight average molecular weight of the polyamide resin; etc.

(Average fiber diameter)
The average fiber diameter of the fibers contained in the nonwoven fabric is not particularly limited, and may be, for example, 10 μm or less. When the nonwoven fabric is used for a prepreg, a printed wiring board, and an electronic component described later, from the viewpoint of reducing the thickness of the nonwoven fabric, the average fiber diameter of the fibers is preferably 7.0 μm or less, more preferably 6.0 μm or less, even more preferably 5.0 μm or less, and particularly preferably 4.5 μm or less. Furthermore, from the viewpoint of improving the balance between the impregnation property of the resin into the nonwoven fabric and the tensile strength when the nonwoven fabric is used for a prepreg described later, the average fiber diameter of the fibers is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, particularly preferably 1.0 μm or more, and extremely preferably 1.2 μm or more.

The average fiber diameter of the fibers may be, for example, 0.1 μm to 7.0 μm, 0.5 μm to 6.0 μm, 0.8 μm to 6.0 μm, 1.0 μm to 6.0 μm, 1.2 μm to 6.0 μm, 1.2 μm to 5.0 μm, or 1.2 μm to 4.5 μm.

In order to improve the balance between the resin impregnation property and the tensile strength of the nonwoven fabric when the nonwoven fabric is used for the prepreg described below, (Dd/Da) x 100 (hereinafter also referred to as "CV value"), which is the value obtained by dividing the average fiber diameter (Da) by the standard deviation of the average fiber diameter (Dd) and multiplying the result by 100, is preferably 50 to 200, more preferably 70 to 150, even more preferably 80 to 130, and particularly preferably 85 to 110.

The average fiber diameter of the fibers can be determined as follows.
The surface of the nonwoven fabric to be measured is photographed at 1000 times magnification using an electron microscope (model number: S-3500N, manufactured by Hitachi, Ltd.). From the photograph, 100 fibers (n=100) are randomly selected, and the diameters (widths) of the selected fibers are measured, and the arithmetic average value is calculated as the average fiber diameter (Da). The standard deviation (Dd) of the average fiber diameter can be calculated using the average fiber diameter (Da).

There are no particular limitations on the method for bringing the "average fiber diameter" of the fibers and "(Dd/Da) x 100, which is the value obtained by dividing the average fiber diameter (Da) by the standard deviation of the average fiber diameter (Dd) and multiplying the result by 100" within the above range, and examples include methods for controlling the spinning temperature, residence time, nozzle hole diameter, single-hole discharge amount (discharge amount per nozzle hole), heated air temperature, heated air flow rate, etc. during the production of the nonwoven fabric.

(Yellowness index)
From the viewpoint of further improving the durability during long-term use of a printed wiring board produced using a prepreg containing the nonwoven fabric, the nonwoven fabric preferably has a yellowness index of 6.0 or less, more preferably 5.0 or less, and even more preferably 4.0 or less.

The yellowness of a nonwoven fabric can be determined in accordance with ASTM D1925.

The specific method for bringing the yellowness of the nonwoven fabric into the above range is not particularly limited, and examples include a method of spinning at a temperature lower than the thermal decomposition onset temperature (preferably a method of spinning at a temperature 10°C or more lower than the decomposition temperature); etc.

(Tensile strength)
The tensile strength of the nonwoven fabric at 28°C (hereinafter also referred to as "tensile strength 1") may be 5 N/50 mm to 200 N/50 mm, 10 N/50 mm to 100 N/50 mm, or 30 N/50 mm to 100 N/50 mm.
The tensile strength of the nonwoven fabric at 120°C (hereinafter also referred to as "tensile strength 2") may be 5 N/50 mm to 200 N/50 mm, 10 N/50 mm to 100 N/50 mm, or 30 N/50 mm to 100 N/50 mm.

(Strength reduction rate)
From the viewpoint of the heat resistance of the nonwoven fabric, the strength reduction rate of the nonwoven fabric is preferably 30% or less, more preferably 20% or less, and even more preferably 10% or less. The lower limit of the strength reduction rate of the nonwoven fabric is not particularly limited, and may be, for example, 0.1% or more.

The tensile strength 1 and tensile strength 2 of the nonwoven fabric can be determined as follows.
Ten test pieces, 50 mm wide x 200 mm long, are taken from the nonwoven fabric to be measured, 5 in the machine direction (MD) and 5 in the cross direction (CD). The tensile strength of each test piece is measured using a constant-speed extension tensile tester (Shimadzu Corporation Autograph AGS-J) under conditions of a chuck distance of 100 mm, a head speed of 200 mm/min, and 28°C or 120°C, and the average value is calculated. The tensile test is performed by holding the test piece in a temperature environment of 28°C and 120°C for 5 minutes, and then maintaining the temperature conditions.
Furthermore, the strength reduction rate (%) can be calculated based on the following formula:
Strength reduction rate (%) = [(tensile strength 1 - tensile strength 2) / tensile strength 1] x 100

There are no particular limitations on the specific method for bringing the tensile strength of the nonwoven fabric within the above range, and an example of this is a method of moving the position of the collector belt that collects the spinning material closer to the nozzle.

(Moisture percentage)
The moisture content of the nonwoven fabric can be appropriately determined depending on the application, and from the viewpoint of optimizing the conductive properties when made into a prepreg described later, it is preferable that the moisture content is low, specifically, 1% or less is preferable, 0.8% or less is more preferable, and 0.5% or less is even more preferable. The lower limit of the moisture content of the nonwoven fabric is not particularly limited as long as it is 0% or more, and may be, for example, 0.1% or more.

The moisture content of the nonwoven fabric can be determined as follows.
The moisture content of the nonwoven fabric can be determined as the mass loss before and after the heat treatment. Specifically, the mass of the nonwoven fabric to be measured is measured using a balance to obtain the mass before the treatment. After that, the nonwoven fabric is heated and dried at 120° C. for 20 minutes, and the mass of the nonwoven fabric after the treatment is obtained using the same measurement method as the mass measurement before the treatment. The obtained masses before and after the treatment are compared, and the mass loss due to the treatment is determined as the moisture content.

(Xylene solubles)
From the viewpoint of long-term reliability when the nonwoven fabric is made into a printed wiring board or the like described below, the xylene soluble content is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

The xylene soluble content of the nonwoven fabric can be determined as follows.
1) Weigh out 3 g±0.2 g of the nonwoven fabric to be measured and use this as a sample. The sample is precisely weighed into a 300 mL Erlenmeyer flask, and 100 mL of xylene is added to the flask, which is then heated at 120° C. for 30 minutes while stirring to completely dissolve the sample.
2) The xylene solution containing the sample is allowed to stand at room temperature (23° C.) for 1 hour, and then allowed to stand in a thermostatic water bath at 25° C. for an additional hour.
3) The xylene solution containing the sample is filtered using a filter cloth, and the obtained filtrate is placed in a weighed aluminum dish. The solvent is evaporated to obtain a solid.
4) The aluminum dish containing the solid is vacuum dried at 110° C. for 2 hours and then allowed to cool in a desiccator.
5) The aluminum dish containing the solid is weighed to determine the amount of solid, i.e., the amount extracted.
6) Subtract the amount of the extract from the initial sample weight (weighed amount) to obtain the amount of xylene solubles.

There are no particular limitations on the specific method for bringing the xylene-soluble content in the nonwoven fabric leaching test within the above range, and an example of this is spinning at a temperature that is 10°C or more lower than the thermal decomposition onset temperature of the nonwoven fabric.

(Metsuke)
The basis weight of the nonwoven fabric can be appropriately determined depending on the application, and is preferably 0.5 g/m ² to 200 g/m ² , more preferably 1 g/m ² to 100 g/m ² , and even more preferably 1 g/m ² to 30 g/m ² .

The basis weight of a nonwoven fabric can be determined as follows.
Ten test pieces measuring 100 mm (fiber flow direction: MD) x 100 mm (direction perpendicular to the fiber flow direction (CD)) are taken from the nonwoven fabric. The test pieces are taken from 10 locations in the CD direction. Next, the mass [g] of each test piece is measured using a top-plate electronic balance (manufactured by Kensei Kogyo Co., Ltd.) to determine the average mass of each test piece. The average value obtained above is converted to mass [g] per ^m2 to determine the basis weight [g/ ^m2 ] of each nonwoven fabric.

There are no particular limitations on the method for bringing the basis weight of the nonwoven fabric into the above range, and examples include a method of changing and adjusting the collector speed during the production of the nonwoven fabric.

(Breathability)
From the viewpoint of improving the impregnation of the nonwoven fabric with a resin when the nonwoven fabric is used for a prepreg described below, the air permeability of the nonwoven fabric is preferably 1 cm ³ /cm ² ·sec to 200 ^{cm 3} /cm ² ·sec, and more preferably 3 cm ³ /cm ² ·sec to 100 cm ³ /cm ² ·sec.

The air permeability of a nonwoven fabric can be determined as follows.
A nonwoven fabric is prepared, and five test pieces of 20 cm x 20 cm are taken from the nonwoven fabric in a temperature-controlled room of 20±2°C and 65±2% humidity as specified in JIS Z8703 (standard conditions at the test location) in accordance with JIS L1096 (8.27.1A method; Frazier type method). The amount of air passing through the test pieces ( ^cm3 / ^cm2 ·sec) is measured using a Frazier type tester, and the average value is calculated.

(Thickness)
The thickness of the nonwoven fabric can be appropriately determined depending on the application, and is preferably 0.01 mm to 100 mm. For example, when used as an electronic material such as a prepreg, the thickness of the nonwoven fabric is preferably 0.01 mm to 0.5 mm.

The thickness of the nonwoven fabric can be determined as follows.
For 10 pieces of nonwoven fabric to be measured, the thickness was measured at five points, namely the center and the four corners, and the average value of the 10 points was calculated. A thickness meter with a load of 7 gf/cm ² (measuring probe diameter 50 mmφ) was used for the thickness measurement.

(length)
The length of the nonwoven fabric in the width direction can be appropriately determined depending on the application, and is preferably 50 cm or more, and more preferably 100 cm or more.

The width of the nonwoven fabric can be determined as follows.
For ten pieces of nonwoven fabric to be measured, the length is measured at three points, namely, the center and the end, of the width direction side, and the average value of the values at each point is calculated. A steel rule is used to measure the length.

[Polyamide resin]
The nonwoven fabric of the present disclosure contains a polyamide resin. The preferred conditions for the melting point of the polyamide resin, the thermal decomposition onset temperature of the polyamide resin, the difference between the thermal decomposition onset temperature of the polyamide resin and the melting point of the polyamide resin, the intrinsic viscosity of the polyamide resin, and the MFR of the polyamide resin are the same as the preferred conditions for each physical property of the fiber described above.

In the polyamide resin, the value calculated by dividing the sum of carbon atoms contained in the acyclic structural units derived from aliphatic monomers and contained in the carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of acyclic structural units derived from aliphatic monomers (hereinafter also referred to as "sum of carbon atoms/structural unit") is less than 7. The "sum of carbon atoms/structural unit" is calculated by the following steps (1) to (4).
(1) The number N of the aliphatic monomers contained in the polyamide resin is identified.
(2) The number of carbon atoms contained in each of the acyclic structural units derived from each of the identified aliphatic monomers and contained in the carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin is calculated.
(3) The sum S of the numbers of carbon atoms contained in the polyamide resin is calculated. Note that the carbon atoms of branched chains contained in the polyamide resin are not included in the sum S.
(4) The sum S is divided by the number N of the aliphatic monomers contained in the polyamide resin (S/N) to obtain the sum of carbon atoms/structural unit, where the acyclic structural unit derived from the aliphatic monomer refers only to an aliphatic monomer unit whose content relative to the total mass of the polyamide resin is 10 mass% or more.

In the nonwoven fabrics of the present disclosure, the sum of carbon atoms/structural unit may be 4 to 6.5, or 4.5 to 6.3, or 5 to 6.1, or 5.2 to 5.8.

The polyamide resin in the present disclosure contains at least an acyclic structural unit derived from an aliphatic monomer. The polyamide resin in the present disclosure may contain an amide bond and an acyclic structural unit derived from an aliphatic monomer, and may further contain a cyclic structural unit having an aromatic ring structure, an alicyclic structure, or the like, within a range in which the sum of carbon atoms/structural unit satisfies 7. From the viewpoint of heat resistance, the polyamide resin in the present disclosure preferably further contains a structural unit derived from an aromatic monomer.
The aliphatic monomer is not particularly limited as long as it is a monomer having an aliphatic group, and may be, for example, any one of a dicarboxylic acid, a diamine, or a cyclic amide described later.
The polyamide resin may contain structural units derived from a cyclic amide such as ε-caprolactam.
Examples of the acyclic structural unit derived from an aliphatic monomer include a structural unit derived from an acyclic aliphatic monomer, and a structural unit derived from a compound that becomes an acyclic structural unit by ring-opening polymerization or the like (e.g., a cyclic amide).

From the viewpoint of obtaining a nonwoven fabric with superior heat resistance, the polyamide resin is preferably a copolymer of diamine and dicarboxylic acid. The polyamide resin may be a mixture of a copolymer of diamine and dicarboxylic acid and a ring-opening polymer of a cyclic amide such as ε-caprolactam. The content of the copolymer of diamine and dicarboxylic acid contained in the polyamide resin is preferably 80% by mass to 100% by mass, and more preferably 90% by mass to 100% by mass, relative to 100% by mass of the polyamide resin.

Examples of the dicarboxylic acid include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, etc. Examples of the aliphatic dicarboxylic acid include acyclic aliphatic dicarboxylic acids and alicyclic dicarboxylic acids.
The dicarboxylic acid may be used alone or in combination of two or more. When the dicarboxylic acid has trans and cis geometric isomers, either one of the trans and cis isomers may be used as the raw material monomer, or a mixture of the trans and cis isomers in various ratios may be used.

Examples of aromatic dicarboxylic acids include aromatic dicarboxylic acids having 8 to 20 carbon atoms, which are unsubstituted or substituted with various substituents, such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, furandicarboxylic acid, and 5-sodium sulfoisophthalic acid. Examples of the various substituents include alkyl groups having 1 to 6 carbon atoms, aryl groups having 6 to 12 carbon atoms, arylalkyl groups having 7 to 20 carbon atoms, halogen groups such as chloro groups and bromo groups, alkylsilyl groups having 3 to 10 carbon atoms, and sulfonic acid groups and salts thereof such as sodium salts. Among these, dicarboxylic acids having no various substituents are preferred, and terephthalic acid and isophthalic acid are particularly preferred.

Examples of acyclic aliphatic dicarboxylic acids include linear or branched saturated aliphatic dicarboxylic acids having 3 to 20 carbon atoms, such as malonic acid, dimethylmalonic acid, succinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethylglutaric acid, 2,2-diethylsuccinic acid, 2,3-diethylglutaric acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, eicosane diacid, and diglycolic acid. The acyclic aliphatic dicarboxylic acid may be unsubstituted or substituted. From the viewpoint of obtaining a nonwoven fabric having excellent heat resistance, acyclic aliphatic dicarboxylic acids having 3 to 8 carbon atoms are preferred, acyclic aliphatic dicarboxylic acids having 3 to 6 carbon atoms are more preferred, and adipic acid is even more preferred.

Examples of alicyclic dicarboxylic acids include alicyclic dicarboxylic acids having 3 to 10 carbon atoms in the alicyclic structure, such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,3-cyclopentanedicarboxylic acid, and preferably alicyclic dicarboxylic acids having 5 to 10 carbon atoms in the alicyclic structure. The alicyclic dicarboxylic acids may be unsubstituted or substituted. Examples of the substituents include alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and t-butyl groups.

The polyamide resin may contain two or more structural units derived from dicarboxylic acids, or may contain two or less structural units derived from dicarboxylic acids. The polyamide resin may be, for example, a polyamide resin containing structural units derived from at least one aromatic dicarboxylic acid and structural units derived from at least one acyclic aliphatic dicarboxylic acid, a polyamide resin containing structural units derived from only one aromatic dicarboxylic acid and structural units derived from only one acyclic aliphatic dicarboxylic acid, or a polyamide resin containing structural units derived from two aromatic dicarboxylic acids and no structural units derived from acyclic aliphatic dicarboxylic acids.

The dicarboxylic acid may be a composition containing terephthalic acid, isophthalic acid, and an acyclic aliphatic dicarboxylic acid having 3 to 6 carbon atoms, a composition containing only one of terephthalic acid or isophthalic acid and an acyclic aliphatic dicarboxylic acid having 3 to 6 carbon atoms (preferably adipic acid), or a composition containing terephthalic acid and isophthalic acid, but not containing an acyclic aliphatic dicarboxylic acid having 3 to 6 carbon atoms (preferably adipic acid).
The total content of terephthalic acid, isophthalic acid and acyclic aliphatic dicarboxylic acid having 3 to 6 carbon atoms is preferably 95 mol % to 100 mol % based on the total number of moles of dicarboxylic acids.

Examples of the diamine include aliphatic diamines, aromatic diamines, etc. Examples of the aliphatic diamine include acyclic aliphatic diamines and alicyclic diamines.
The diamine may be used alone or in combination of two or more kinds.

The acyclic aliphatic diamine preferably contains an acyclic aliphatic diamine having 4 to 12 carbon atoms, from the viewpoint of further improving the heat resistance of the nonwoven fabric and further improving the spinning stability.
Examples of the acyclic aliphatic diamines having 4 to 12 carbon atoms include linear aliphatic diamines such as 1,4-diaminobutane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, and 1,12-diaminododecane; and branched aliphatic diamines such as 2-methyl-1,5-diaminopentane, 2-methyl-1,6-diaminohexane, 2-methyl-1,7-diaminoheptane, 2-methyl-1,8-diaminooctane, 2-methyl-1,9-diaminononane, and 2-methyl-1,10-diaminodecane.
Among the above, from the viewpoint of obtaining a nonwoven fabric having superior heat resistance, the acyclic aliphatic diamine having 4 to 12 carbon atoms preferably includes an acyclic aliphatic diamine having 4 to 8 carbon atoms, more preferably includes a linear aliphatic diamine having 4 to 6 carbon atoms, and further preferably includes 1,6-diaminohexane.

The alicyclic diamine preferably contains an alicyclic diamine having 3 to 10 carbon atoms. Examples of alicyclic diamines having 3 to 10 carbon atoms include 1,4-cyclohexanediamine and 1,3-cyclohexanediamine.

The aromatic diamine preferably contains an aromatic diamine having 6 to 20 carbon atoms. Examples of aromatic diamines having 6 to 20 carbon atoms include diaminobenzene, diaminonaphthalene, diaminobiphenyl, metaxylylenediamine, and paraxylylenediamine.

The diamine preferably contains a linear aliphatic diamine having 4 to 6 carbon atoms.
The content of the linear aliphatic diamine having 4 to 6 carbon atoms is preferably 90 mol % to 100 mol % based on the total moles of diamines, from the viewpoint of further improving the heat resistance and spinning stability of the nonwoven fabric.

From the viewpoint of further improving heat resistance and spinning stability, the polyamide resin preferably contains an acyclic aliphatic diamine having 4 to 12 carbon atoms and an aromatic dicarboxylic acid, more preferably contains an acyclic aliphatic diamine having 4 to 6 carbon atoms and an aromatic dicarboxylic acid having 8 to 20 carbon atoms, and even more preferably contains an acyclic aliphatic diamine having 4 to 12 carbon atoms and at least one of terephthalic acid and isophthalic acid.

The polyamide resin may contain structural units derived from cyclic amides. Examples of cyclic amides include α-lactam, β-lactam, γ-lactam, δ-lactam, ε-caprolactam, and laurolactam. From the viewpoint of further improving spinning stability, the content of structural units derived from cyclic amides in the polyamide resin is preferably 10 mol % or less, and more preferably 5 mol % or less, of all structural units.

The polyamide resin may contain a structural unit derived from a monocarboxylic acid. The monocarboxylic acid is not particularly limited as long as it has reactivity with an amino group, and examples thereof include aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, pivalic acid, and isobutyric acid; alicyclic monocarboxylic acids such as cyclohexane carboxylic acid; aromatic monocarboxylic acids such as benzoic acid, toluic acid, α-naphthalene carboxylic acid, β-naphthalene carboxylic acid, methylnaphthalene carboxylic acid, and phenyl acetic acid; and any mixtures thereof. Among these, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, and benzoic acid are preferred from the viewpoints of reactivity, stability of the blocked terminal, and price. The monocarboxylic acid may be used as an end blocking agent. In the polyamide resin, from the viewpoint of spinnability, the content of structural units derived from monocarboxylic acid is preferably 0.01 mol % to 10 mol %, and more preferably 0.1 mol % to 5.0 mol %, based on the total structural units.

In polyamide resins, it is preferable that the number of structural units derived from dicarboxylic acids and the number of moles of structural units derived from diamines are approximately equal. For example, the ratio of the number of structural units derived from dicarboxylic acids to the number of moles of structural units derived from diamines is preferably 0.5:1.5 to 1.5:0.5, more preferably 0.8:1.2 to 1.2:0.8, and even more preferably 0.9:1.1 to 1.1:0.9.

In polyamide resins, the total content of the number of moles of structural units derived from dicarboxylic acids and the number of moles of structural units derived from diamines is preferably 60 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more, relative to the total structural units.

Among the structural units derived from diamines in the polyamide resin, the content of structural units derived from acyclic aliphatic diamines is preferably 70 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, even more preferably 99 mol% to 100 mol%, and particularly preferably 100 mol%.
Among the structural units derived from dicarboxylic acids in the polyamide resin, the content of structural units derived from aromatic dicarboxylic acids is preferably 5 mol% to 70 mol%, more preferably 15 mol% to 60 mol%, and even more preferably 25 mol% to 40 mol%. When the content of structural units derived from aromatic dicarboxylic acids is within the above range, the heat resistance tends to be excellent.
Among the structural units derived from dicarboxylic acids in the polyamide resin, the content of structural units derived from acyclic aliphatic dicarboxylic acids is preferably 20 mol% to 80 mol%, more preferably 30 mol% to 70 mol%, and even more preferably 40 mol% to 60 mol%. When the structural units derived from acyclic aliphatic dicarboxylic acids are in the above range, spinning stability tends to be excellent.
The content of structural units derived from cyclic amide in the polyamide resin is preferably 10 mol % or less, and more preferably 5 mol % or less, based on the total structural units.

The polyamide resin is preferably any one of the following aspects 1 to 3. By being aspect 1 or 2, spinning stability and strength tend to be excellent, and by being aspect 3, strength tends to be excellent.
Aspect 1: A configuration in which, of all structural units, the sum of diamine and dicarboxylic acid is 95 mol% or more, of the structural units derived from diamine, 1,6-diaminohexane is 95 mol% or more, of the structural units derived from dicarboxylic acid, structural units derived from terephthalic acid are 15 mol% to 70 mol% (preferably 50 mol% to 70 mol%), of the structural units derived from dicarboxylic acid, structural units derived from isophthalic acid are 5 mol% to 30 mol% (preferably 5 mol% to 20 mol%), and of the structural units derived from dicarboxylic acid, structural units derived from adipic acid are 5 mol% to 30 mol% (preferably 25 mol% to 30 mol%).
Aspect 2: An aspect in which, of all structural units, the sum of diamine and dicarboxylic acid is 95 mol % or more, of the structural units derived from diamine, 1,6-diaminohexane is 30 mol % to 70 mol %, of the structural units derived from dicarboxylic acid, terephthalic acid is 15 mol % to 45 mol %, and of the structural units derived from dicarboxylic acid, adipic acid is 15 mol % to 45 mol %.
Aspect 3: An aspect in which, of all structural units, the total of diamine and dicarboxylic acid is 95 mol % or more, the structural units derived from diamine are 1,6-diaminohexane is 30 mol % to 70 mol %, the structural units derived from dicarboxylic acid are 20 mol % to 50 mol % terephthalic acid, and the structural units derived from dicarboxylic acid are 5 mol % to 40 mol % isophthalic acid.

From the viewpoint of obtaining a nonwoven fabric with superior heat resistance, it is preferable that the polyamide resin contains a structural unit having an aromatic group. The aromatic group is not particularly limited, and is preferably an aromatic group having 5 to 14 carbon atoms, more preferably an aromatic group having 6 to 10 carbon atoms, and even more preferably an aromatic group having 6 carbon atoms, such as a phenyl group.

From the viewpoint of obtaining a nonwoven fabric having superior heat resistance, the proportion of polyamide resin in the entire nonwoven fabric is preferably 95% by mass or more, more preferably 98% by mass or more, and even more preferably 99% by mass or more.

The nonwoven fabric of the present disclosure may or may not contain other thermoplastic resins other than the polyamide resin described above. Examples of other thermoplastic resins include polyacetal, polycarbonate, modified polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, syndiotactic polystyrene, cyclic polyolefin, polyphenylene sulfide, polytetrafluoroethylene, polysulfone, polyethersulfone, amorphous polyarylate, polyetheretherketone, thermoplastic polyimide, polyamideimide, and copolymers thereof. The other thermoplastic resins may be used alone or in combination of two or more.

From the viewpoint of obtaining a nonwoven fabric having superior heat resistance, the proportion of other thermoplastic resins in the entire nonwoven fabric is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less.

[Other ingredients]
The nonwoven fabric of the present disclosure may or may not contain various known additives such as antioxidants, heat stabilizers, weather stabilizers, antistatic agents, slip agents, antifogging agents, lubricants, dyes, pigments, natural oils, synthetic oils, waxes, fatty acid amides, etc., as components other than polyamide resins and other thermoplastic resins, as necessary, within a range that does not impair the heat resistance of the nonwoven fabric. When the nonwoven fabric is used for prepregs, printed wiring boards, and electronic components described below, the content of these additives in the nonwoven fabric is preferably small from the viewpoint of long-term reliability of circuit boards, etc., specifically, 0.1 mass% or less is preferable, 0.05 mass% or less is more preferable, and 0.01 mass% or less is even more preferable.

(Embodiments of nonwoven fabric)
The nonwoven fabric of the present disclosure may be either a long fiber nonwoven fabric or a short fiber nonwoven fabric. The nonwoven fabric of the present disclosure may be produced by, for example, a spunbond method, a meltblown method, a flash spinning method, a wet method, a carding method, an airlaid method, an electrostatic spinning method, or the like.

From the viewpoint of productivity, the nonwoven fabric of the present disclosure is preferably a long-fiber nonwoven fabric.
The long fiber nonwoven fabric is preferably a nonwoven fabric produced by the spunbond method (i.e., a spunbond nonwoven fabric) or a nonwoven fabric produced by the meltblown method (i.e., a meltblown nonwoven fabric). In particular, from the viewpoint of making the average fiber diameter smaller, the nonwoven fabric is preferably a meltblown nonwoven fabric. The nonwoven fabric of the present disclosure may be one type alone or two or more types in combination.

The nonwoven fabric of the present disclosure may be a single layer or a laminate in which multiple layers are laminated. As a laminate, it is sufficient that the nonwoven fabric of the present disclosure is contained in at least one layer of the laminate. For example, it may be a laminate in which multiple nonwoven fabrics manufactured by one manufacturing method are laminated, or a laminate in which multiple nonwoven fabrics manufactured by two or more manufacturing methods are laminated, and it may be laminated with a layer other than the nonwoven fabric, such as a film. Nonwoven fabrics and films other than those disclosed herein that are laminated include conventionally known nonwoven fabrics and films.

<Applications of nonwoven fabric>
The use of the nonwoven fabric of the present disclosure is not particularly limited, and it can be used for known uses of nonwoven fabrics. Specific examples of uses include prepregs, filters, masks, sanitary products, packaging materials, semiconductors, sound absorbing materials, heat insulating materials, etc. Among these, the nonwoven fabric of the present disclosure is preferably used as a prepreg because it has excellent heat resistance.

<Nonwoven fabric manufacturing method>
The method for producing a nonwoven fabric according to the present disclosure includes the steps of: a melt-kneading step of melt-kneading a polyamide resin or a resin composition containing the polyamide resin, the polyamide resin having a highest melting point of 300°C to 350°C, the polyamide resin being contained in the acyclic structural units derived from the aliphatic monomer, and the value (sum of carbon atoms/structural unit) calculated by dividing the sum of carbon atoms contained in a carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of acyclic structural units derived from the aliphatic monomer is less than 7, the polyamide resin or the resin composition being melt-kneaded using two or more shafts to obtain a molten kneaded product; a spinning step of spinning the molten kneaded product together with heated air from a nozzle having a plurality of holes; and a stretching step of stretching the molten product spun in the spinning step with the heated air.
The method for producing the nonwoven fabric of the present disclosure includes the above steps, and thereby makes it possible to produce the nonwoven fabric of the present disclosure that has excellent heat resistance.

(Melting and kneading process)
In the melt-kneading step, a polyamide resin containing an acyclic structural unit derived from an aliphatic monomer or a resin composition containing the polyamide resin, the polyamide resin having a highest melting point of 300° C. to 350° C. and a total of carbon atoms in the polyamide resin per structural unit of less than 7, is melt-kneaded using two or more axes to obtain a melt-kneaded product. In the melt-kneading step, it is preferable to use a polyamide resin or a resin composition in which the difference between the thermal decomposition onset temperature and the melting point is 80° C. or less.

In the melt-kneading step, from the viewpoint of producing a nonwoven fabric having superior heat resistance, two or more axes are used,
It is preferable that the step is a step of melt-kneading the polyamide resin or the resin composition at a temperature that is 10° C. or more higher than the highest melting point of the polyamide resin or the resin composition and 5° C. or more lower than the thermal decomposition onset temperature of the polyamide resin or the resin composition.
More preferably, the step is a step of melt-kneading the polyamide resin or the resin composition at a temperature that is 15° C. or more higher than the highest melting point of the polyamide resin or the resin composition and 5° C. or more lower than the thermal decomposition onset temperature of the polyamide resin or the resin composition,
It is further preferable that the process is a step of melt-kneading the polyamide resin or resin composition at a temperature that is 20°C or more higher than the highest melting point of the polyamide resin or resin composition and 5°C or more lower than the thermal decomposition onset temperature of the polyamide resin or resin composition.

In the melt kneading process, by using two or more axes, uneven kneading of the resin composition is less likely to occur, and it can be kneaded with precision.

The number of shafts in the melt-kneading process is 2 or more, and preferably 2 to 10. The shaft refers to a shaft used for kneading, such as a screw. The melt-kneading process may be carried out, for example, using a melt extruder equipped with two or more screws.

As the polyamide resin in the method for producing a nonwoven fabric according to the present disclosure, the same preferred embodiments as those mentioned for the polyamide resin in the nonwoven fabric according to the present disclosure can be mentioned.
A preferred embodiment of the resin composition is a mixture containing, as necessary, other thermoplastic resins and other components together with the above-mentioned polyamide resin, and the preferred embodiments of each component are as described above.

The time for melt-kneading the polyamide resin or resin composition, i.e., the residence time, can be designed appropriately depending on the production scale, etc., but is preferably 5 to 30 minutes, and more preferably 7 to 20 minutes.

From the viewpoint of suppressing fiber breakage during the spinning process, etc., it is preferable to melt-knead the polyamide resin or the resin composition using two or more shafts in the melt-kneading process while exhausting air by negative pressure. For example, an extruder equipped with a vent (exhaust port) may be used as the extruder, and the inside of the extruder may be made negative pressure and exhausted by exhausting air from the vent. As a result, even if the number of shafts in the melt-kneading process is two or more and the kneading force is increased due to the biaxial structure, and the melt-kneaded material contains a large amount of air, the air can be suitably exhausted through the vent. As a result, there is a tendency to suppress fiber breakage during the spinning process, etc., due to the inclusion of air in the melt-kneaded material.

If the extruder is provided with a vent, it is preferable that the vent be provided at a position 0.8L to 1.0L in length from the hopper side, assuming that the total length of the extruder from the hopper to the tip is L and that the hopper side is used as the standard length, and it is more preferable that no vent be provided in the nozzle connecting the extruder to the spinning die.

The negative pressure is preferably 0.5 kPa to 10.0 kPa, and more preferably 1.0 kPa to 5.0 kPa. A negative pressure of 0.5 kPa or more tends to facilitate degassing and effectively prevent thread breakage, while a negative pressure of 10.0 kPa or less tends to reduce the risk of poor degassing due to clogged vents and effectively prevent thread breakage.

(Spinning process)
In the spinning process, the molten mixture is spun together with heated air from a nozzle having a plurality of holes. Specifically, pressure is applied by an extruder to supply the molten mixture to a spinneret having a nozzle formed therein, and the molten mixture is ejected from the nozzle. The extruder is not particularly limited, and may be a single-screw extruder or a multi-screw extruder. The hole diameter of the nozzle is preferably 0.06 mm to 0.50 mm, more preferably 0.10 mm to 0.30 mm. The discharge amount per hole in the nozzle (single-hole discharge amount) is preferably 0.01 g/min to 0.50 g/min, more preferably 0.10 g/min to 0.30 g/min. The temperature of the heated air is preferably 250° C. to 350° C. The flow rate of the heated air is preferably 200 Nm ³ /h/m to 800 Nm ³ /h/m.

(Stretching process)
In the stretching step, the molten material spun in the spinning step is stretched by heated air. By setting the flow rate, temperature and flow rate of the heated air in the range of high temperature and high velocity as described above, the average fiber diameter of the melt-blown nonwoven fabric is small and the generation of resin particles is reduced.

After the drawing process, the fibers, which have been thinned by the high-temperature, high-velocity air, are collected and deposited on a collection plate (e.g., a perforated belt or perforated drum) to obtain a nonwoven fabric.

The nonwoven fabric obtained by collecting and depositing the nonwoven fabric on the collection plate may be further subjected to secondary processing, such as intertwining, pressing, gear processing, printing, coating, laminating, heating, shaping, hydrophilic processing, water repellent processing, and pressing.

Examples of interlacing processes include thermal embossing, ultrasonic fusion, water jet processing, hot air through processing, and needle punch processing.

From the viewpoint of maintaining a better balance between rigidity and breathability, it is preferable that the entanglement treatment includes a heat embossing treatment.
When the nonwoven fabric of the present disclosure is heat-pressed by heat embossing, the embossed area ratio (heat-pressed portion) is preferably in the range of 5% to 30%, and more preferably in the range of 5% to 20%. Examples of the imprint shape include a circle, an ellipse, an oval, a square, a diamond, a rectangle, a rectangle, a quilt, a lattice, a tortoiseshell, and a continuous shape based on these shapes.

From the viewpoint of controlling the thickness, rigidity, density, air permeability, etc. of the nonwoven fabric of the present disclosure, it is preferable that the secondary processing includes a pressing process. The pressing means for pressing the nonwoven fabric of the present disclosure in the pressing process is not particularly limited, and may be, for example, a pressing means for pressing by applying pressure in the thickness direction of the nonwoven fabric (in the case of a nonwoven fabric laminate, the lamination direction of the laminate). Examples of pressing processes include a method of press-molding two or more layers of nonwoven fabric (more preferably melt-blown nonwoven fabric) stacked in a sheet shape; roll molding in which the nonwoven fabric is pressed by a roll; and the like, and among these, it is preferable to include roll molding.

<Prepreg>
The prepreg of the present disclosure includes the nonwoven fabric of the present disclosure and a resin composition containing at least one of a thermosetting resin and a thermoplastic resin. Since the prepreg of the present disclosure contains the resin composition containing the nonwoven fabric of the present disclosure, the prepreg of the present disclosure has excellent heat resistance when cured or solidified.

From the viewpoint of providing a prepreg with superior heat resistance when cured or solidified, the prepreg of the present disclosure preferably has a thermal expansion coefficient of 50 ppm/°C or less at 50°C to 100°C for the cured product obtained by heating at 145°C for 10 minutes and heat curing, or for the solidified product cooled at room temperature (23°C), of 40 ppm/°C or less.

From the viewpoint of being superior when used as an insulating layer in a printed wiring board described below, the prepreg of the present disclosure preferably has a dielectric tangent value at 1 GHz when cured of 0.005 or less, and more preferably 0.001 or less.
The method for adjusting the dielectric tangent value to be within the above range is not particularly limited, and examples thereof include a method of decreasing the moisture content and a method of decreasing the fiber diameter.

The method for producing the prepreg is not particularly limited, and a known method can be applied. For example, the method for producing the prepreg includes a method including a step of impregnating a nonwoven fabric of the present disclosure with a varnish containing a resin composition to obtain an impregnated body, and a step of heating the obtained impregnated body to remove the solvent contained in the varnish and dry it.
Impregnation of the nonwoven fabric of the present disclosure with a varnish containing the above-mentioned resin composition can be carried out, for example, by applying a predetermined amount of varnish to the nonwoven fabric of the present disclosure by a known method such as spray coating, dip coating, roll coating, curtain coating, die coating, or slit coating, and if necessary, further layering a protective film on top of the varnish, and pressing from above with a roller or the like.
The method of heating the impregnated body to dry the solvent contained in the varnish is not particularly limited, and examples thereof include a batch method in which the impregnated body is dried in an air atmosphere or a nitrogen atmosphere using a blower dryer, and a continuous method in which the body is dried through a heating furnace.

Examples of thermosetting resins include epoxy resins, melamine resins, phenolic resins, unsaturated polyester resins, silicone resins, etc. Among the above, it is preferable that the thermosetting resin contains an epoxy resin. The thermosetting resin may be one type alone or two or more types in combination. From the viewpoint of forming a prepreg having excellent heat resistance when cured, it is preferable that the curable resin is a thermosetting resin having a curing temperature that is 20°C or more lower than the lowest melting point of the nonwoven fabric.

Examples of the thermoplastic resin include the same thermoplastic resins as those exemplified in the above-mentioned other thermoplastic resins. The thermoplastic resin may be a single type or a combination of two or more types. From the viewpoint of forming a prepreg having excellent heat resistance when solidified, the thermoplastic resin is preferably a thermoplastic resin having a melting point 20°C or more lower than the lowest melting point of the nonwoven fabric.

The thickness of the prepreg can be appropriately selected depending on the application.
The thickness of the prepreg is preferably 0.001 mm to 10 mm, more preferably 0.005 mm to 1 mm, and even more preferably 0.01 mm to 0.5 mm, from the viewpoint of improving, for example, the shapeability when laminating the prepregs and the mechanical strength and toughness of the cured product.

The uses of the prepreg disclosed herein are not particularly limited and can be used, for example, in printed wiring boards, as described below.

Conductor laminate
The conductor laminate of the present disclosure is a laminate in which a conductor layer is laminated on at least one surface of the prepreg of the present disclosure. The conductor laminate of the present disclosure has the above-mentioned configuration and is therefore excellent in heat resistance.
The conductor layer is not particularly limited as long as it is a layer containing a material having electrical conductivity, and a metal foil is suitable. Examples of the metal foil include copper foil, aluminum foil, nickel foil, gold foil, silver foil, stainless steel foil, etc. The metal clad laminate of the present disclosure can be manufactured by a known manufacturing method.

<Printed wiring board>
The printed wiring board of the present disclosure has a conductor layer on one or both sides of the cured product of the prepreg of the present disclosure, which has been subjected to wiring processing. The printed wiring board of the present disclosure has the above-mentioned configuration and is therefore excellent in heat resistance.

The printed wiring board may have a conductive layer with wiring processing on one or both sides of a laminate formed by stacking the cured prepreg of the present disclosure.

The printed wiring board may have a conductor layer with antenna circuit processing on one or both sides of the cured prepreg of the present disclosure.

The method for manufacturing the printed wiring board is not particularly limited, and known manufacturing methods can be applied. For example, in the method for manufacturing the printed wiring board, the prepreg manufactured by the above-mentioned method is heated and cured by a lamination press or the like to form an insulating layer. Next, a conductor layer is laminated on the obtained insulating layer by a known method to produce a laminate. Thereafter, the conductor layer in the laminate is subjected to circuit processing or the like to obtain a printed wiring board.

Metals are suitable for the conductor layer. Examples of metals that can be used include copper, aluminum, nickel, gold, silver, and stainless steel. Methods for forming the conductor layer include, for example, a method in which a conductive material such as a metal is made into a foil and heat-sealed to an insulating layer; a method in which an insulating layer and a conductor layer are bonded together using an adhesive; and a method in which a conductor layer is formed by sputtering, vapor deposition, plating, or the like. The printed wiring board may be either a single-sided board or a double-sided board.
The printed wiring board of the present disclosure can be used as an electronic component by mounting electronic components such as semiconductor elements, for example.

<Electronic Components>
The electronic component of the present disclosure has a circuit for transmitting an electrical signal of 1 GHz or more, and an insulating layer of the electronic component contains a cured product of the prepreg of the present disclosure.
The electronic components can be manufactured based on known information.
Examples of electronic components having a circuit that transmits an electric signal of 1 GHz or more include high-frequency antenna circuits, backplanes of high-speed servers and routers, and flexible substrates for high-speed transmission used in hard disks, liquid crystal displays, and the like.

The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of this disclosure. In addition, "parts" means "parts by mass" unless otherwise specified.

Synthesis Example A: Synthesis of polyamide resin 1 (PA6T6I66) 2452g (14.8 mol) of terephthalic acid, 2800g (24.1 mol) of 1,6-diaminohexane, 383g (2.3 mol) of isophthalic acid, 876g (6.0 mol) of adipic acid, 78.8g (0.65 mol) of benzoic acid, 5.3g of sodium hypophosphite monohydrate (0.08% by mass relative to the raw material) and 545g of distilled water were placed in an autoclave with a capacity of 13.6L and substituted with nitrogen. Stirring was started from 190°C, and the internal temperature of the autoclave was raised to 250°C over 3 hours. At this time, the internal pressure of the autoclave was raised to 3.03 MPa. After continuing the reaction for 1 hour, the mixture was released into the air from a spray nozzle installed at the bottom of the autoclave and the low condensate was extracted. The extracted low condensate was cooled to room temperature (23°C), pulverized to a particle size of 1.5 mm or less with a pulverizer, and dried at 110°C for 24 hours. The water content of the obtained low condensate was 4100 ppm, and the intrinsic viscosity [η] was 0.15 dl/g. Next, this low condensate was placed in a tray-type solid-phase polymerization apparatus, substituted with nitrogen, and then heated to 180°C over about 1 hour and 30 minutes. Then, the reaction was allowed to proceed for 1 hour and 30 minutes, and the temperature was lowered to room temperature (23°C). Then, the mixture was melt-polymerized in a twin-screw extruder with a screw diameter of 30 mm and L/D=36 at a barrel setting temperature of 330°C, a screw rotation speed of 200 rpm, and a resin supply rate of 10 Kg/h to obtain polyamide resin 1. The intrinsic viscosity [η] of the obtained polyamide resin 1 was 0.79 dl/g, and the melting point Tm was 322°C.
In the obtained polyamide resin 1, the value obtained by dividing the sum of the carbon atoms contained in the acyclic structural units derived from aliphatic monomers and contained in the carbon chain portion (excluding the carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of acyclic structural units derived from aliphatic monomers was 5.6, as calculated from (24.1 x 6 + 6.0 x 4) / (24.1 + 6.0).

Synthesis Example B: Synthesis of polyamide resin 2 (PA6T66) 2107g (12.7 mol) of terephthalic acid, 2800g (24.1 mol) of 1,6-diaminohexane, 1516g (10.4 mol) of adipic acid, 36.5g (0.3 mol) of benzoic acid, 5.7g of sodium hypophosphite monohydrate and 545g of distilled water were placed in an autoclave with a capacity of 13.6L and substituted with nitrogen. Stirring was started at 190°C, and the internal temperature of the autoclave was raised to 250°C over 3 hours. At this time, the internal pressure of the autoclave was raised to 3.01 MPa. After continuing the reaction for 1 hour, the low condensation product was discharged to the atmosphere from a spray nozzle installed at the bottom of the autoclave and extracted. The extracted low condensation product was cooled to room temperature (23°C), pulverized to a particle size of 1.5 mm or less with a pulverizer, and dried at 110°C for 24 hours. Next, this low condensate was placed in a tray-type solid-phase polymerization apparatus, and after replacing with nitrogen, the temperature was raised to 220°C over about 1 hour and 30 minutes. Then, the reaction was allowed to proceed for 1 hour, and the temperature was lowered to room temperature. Then, in a twin-screw extruder with a screw diameter of 30 mm and L/D=36, melt polymerization was carried out at a barrel setting temperature of 330°C, a screw rotation speed of 200 rpm, and a resin supply rate of 6 kg/h to obtain polyamide resin 2. The intrinsic viscosity [η] of the obtained polyamide resin 2 was 0.80 dl/g, and the melting point Tm was 310°C.
In the obtained polyamide resin 2, the value obtained by dividing the sum of the carbon atoms contained in the acyclic structural units derived from aliphatic monomers and contained in the carbon chain portion (excluding the carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of acyclic structural units derived from aliphatic monomers was 5.4, as calculated from (24.1 x 6 + 10.4 x 4)/(24.1 + 10.4).

Synthesis Example C: Synthesis of polyamide resin 3 (PA6T6I) 2669g (16.1 mol) of terephthalic acid, 2800g (24.1 mol) of 1,6-diaminohexane, 1144g (6.9 mol) of isophthalic acid, 36.5g (0.3 mol) of benzoic acid, 5.7g of sodium hypophosphite monohydrate and 554g of distilled water were placed in an autoclave with a capacity of 13.6L and substituted with nitrogen. Stirring was started at 190°C, and the internal temperature of the autoclave was raised to 250°C over 3 hours. At this time, the internal pressure of the autoclave was raised to 3.03 MPa. After continuing the reaction for 1 hour, the low condensation product was discharged to the atmosphere from a spray nozzle installed at the bottom of the autoclave and extracted. The extracted low condensation product was cooled to room temperature (23°C), pulverized to a particle size of 1.5 mm or less with a pulverizer, and dried at 110°C for 24 hours. Next, this low condensate was placed in a tray-type solid-phase polymerization apparatus, and after replacing with nitrogen, the temperature was raised to 220°C over about 1 hour and 30 minutes. Then, the reaction was allowed to proceed for 1 hour, and the temperature was lowered to room temperature. Then, in a twin-screw extruder with a screw diameter of 30 mm and L/D=36, melt polymerization was carried out at a barrel setting temperature of 340°C, a screw rotation speed of 200 rpm, and a resin supply rate of 6 kg/h to obtain polyamide resin 3. The intrinsic viscosity [η] of the obtained polyamide resin 3 was 0.81 dl/g, and the melting point Tm was 328°C.
In the obtained polyamide resin 3, the value obtained by dividing the sum of the carbon atoms contained in the acyclic structural units derived from aliphatic monomers and contained in the carbon chain portion (excluding the carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of acyclic structural units derived from aliphatic monomers was 6.0, as calculated from (24.1 x 6)/(24.1).

Synthesis Example D: Synthesis of polyamide resin 4 (PA6T) 397g (2.39 mol) of terephthalic acid, 278g (2.39 mol) of 1,6-diaminohexane, 3.7g (0.03 mol) of benzoic acid, 0.55g of sodium hypophosphite monohydrate, and 64g of distilled water were placed in an autoclave with a capacity of 1L and substituted with nitrogen. Stirring was started at 190°C, and the internal temperature of the autoclave was raised to 250°C over 3 hours. At this time, the internal pressure of the autoclave was raised to 3.03 MPa. After continuing the reaction for 1 hour, the internal pressure was released and cooled, and then the container was opened and the contents were taken out. The taken-out contents were pulverized to a particle size of 1.5 mm or less with a pulverizer and dried at 110°C for 24 hours. Next, the contents were placed in a tray-type solid-state polymerization apparatus, substituted with nitrogen, and then heated to 220°C over about 1 hour and 30 minutes. After one hour of reaction, the temperature was lowered to room temperature. The resulting polyamide resin 4 decomposed violently before melting, and could not be melt-polymerized and processed in an extruder.
In the obtained polyamide resin 4, the value obtained by dividing the sum of the carbon atoms contained in the acyclic structural units derived from aliphatic monomers and contained in the carbon chain portion (excluding the carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of acyclic structural units derived from aliphatic monomers was 6.0, as calculated from (2.39 x 6)/(2.39).

Synthesis Example E: Synthesis of polyamide resin 5 (PA6T6) 2572g (15.5 mol) of terephthalic acid, 1800g (15.5 mol) of 1,6-diaminohexane, 1763g (15.5 mol) of ε-caprolactam, 36.5g (0.3 mol) of benzoic acid, 5.7g of sodium hypophosphite monohydrate, and 545g of distilled water were placed in an autoclave with a capacity of 13.6L and substituted with nitrogen. Stirring was started at 190°C, and the internal temperature of the autoclave was raised to 250°C over 3 hours. At this time, the internal pressure of the autoclave was raised to 3.03MPa. After continuing the reaction for 1 hour, the low condensation product was discharged to the atmosphere from a spray nozzle installed at the bottom of the autoclave and extracted. The extracted low condensation product was cooled to room temperature (23°C), pulverized to a particle size of 1.5mm or less with a pulverizer, and dried at 110°C for 24 hours. Next, this low condensate was placed in a tray-type solid-phase polymerization apparatus, and after replacing with nitrogen, the temperature was raised to 220°C over about 1 hour and 30 minutes. Then, the reaction was allowed to proceed for 1 hour, and the temperature was lowered to room temperature. Then, in a twin-screw extruder with a screw diameter of 30 mm and L/D=36, melt polymerization was carried out at a barrel setting temperature of 340°C, a screw rotation speed of 200 rpm, and a resin supply rate of 6 kg/h to obtain polyamide resin 5. The intrinsic viscosity [η] of the obtained polyamide resin 5 was 0.76 dl/g, and the melting point Tm was 295°C.
In the obtained polyamide resin 5, the value obtained by dividing the sum of the carbon atoms contained in the acyclic structural units derived from aliphatic monomers and contained in the carbon chain portion (excluding the carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of acyclic structural units derived from aliphatic monomers was 5.5, as calculated from (15.5 x 6 + 15.5 x 5) / (15.5 + 15.5).

[Example 1]
The polyamide resin 1 obtained in Synthesis Example A was melted at 340°C using a vented twin-screw extruder, and the reduced pressure by the vent was 3 kPa. The molten polyamide resin 1 was supplied to a die, and discharged from the die at a set temperature of 300°C with a discharge rate of 0.2 g/min per spinning nozzle and a distance between small holes of 1.0 mm together with heated air (temperature Ta: 350°C, flow rate: 300 Nm3/ ^hr /m) blown out from both sides of the spinning nozzle. The diameter of the spinning nozzle of the die was 0.4 mm. The nonwoven fabric was collected on a collector while being sucked by a suction box. The basis weight of the obtained nonwoven fabric was 15 g/ ^m2 .

[Example 2]
A nonwoven fabric was prepared in the same manner as in Example 1, except that the polyamide resin 2 obtained in Synthesis Example B was used instead of the polyamide resin 1 obtained in Synthesis Example A in Example 1.

[Example 3]
A nonwoven fabric was prepared in the same manner as in Example 1, except that the polyamide resin 1 obtained in Synthesis Example A was replaced with the polyamide resin 3 obtained in Synthesis Example C.

[Example 4]
A nonwoven fabric was produced in the same manner as in Example 2, except that suction through a vent was not performed.

[Comparative Example 1]
The same operations as in Example 1 were carried out except that a vented single-screw extruder was used instead of the vented twin-screw extruder in Example 1, and suction through the vent was not performed. However, polyamide resin 1 could not be spun.

[Comparative Example 2]
A nonwoven fabric was prepared in the same manner as in Example 1, except that the polyamide resin 1 obtained in Synthesis Example A was replaced with Xecot XN400 (sum of carbon atoms/structural unit=10) manufactured by Unitika Ltd.

[Comparative Example 3]
A nonwoven fabric was produced in the same manner as in Comparative Example 2, except that a vented single-screw extruder was used instead of the vented twin-screw extruder.

[Comparative Example 4]
The same procedure as in Example 1 was carried out except that the polyamide resin 1 obtained in Synthesis Example A was replaced with the polyamide resin 4 obtained in Synthesis Example D. However, the polyamide resin 4 could not be spun.

[Comparative Example 5]
The same procedure as in Comparative Example 1 was carried out except that Polyamide Resin 4 obtained in Synthesis Example D was used instead of Polyamide Resin 1 obtained in Synthesis Example A in Comparative Example 1, but Polyamide Resin 4 could not be spun.

[Comparative Example 6]
A nonwoven fabric was prepared in the same manner as in Example 1, except that the polyamide resin 1 obtained in Synthesis Example A was replaced with the polyamide resin 5 obtained in Synthesis Example E.

[Comparative Example 7]
A nonwoven fabric was produced in the same manner as in Comparative Example 6, except that a vented single-screw extruder was used instead of the vented twin-screw extruder in Comparative Example 6, and suction through the vent was not performed.

(Spinning stability)
For each of the Examples and Comparative Examples, the spinning stability was evaluated based on the frequency of yarn breakage per die width. The evaluation criteria were as follows:
A: Thread breakage less than 0.1 times/min/m B: Thread breakage 0.1 times/min/m or more but less than 0.5 times/min/m C: Thread breakage 0.5 times/min/m or more but less than 5.5 times/min/m D: Thread breakage 5.5 times/min/m or more

The resin type, production conditions of the nonwoven fabric, evaluation results, etc. of each example and comparative example are shown in Tables 1 and 2. Note that each property in the tables was measured by the measurement method already described.
In Table 2, "ND" means that the melting point of Polyamide Resin 4 could not be measured, so no data was available.

As shown in Tables 1 and 2, the nonwoven fabrics of each embodiment had superior tensile strength at high temperatures to the comparative examples, and furthermore, the decrease in tensile strength at high temperatures relative to the tensile strength at low temperatures was suppressed.

The prepregs and copper-clad laminates were made using the following materials:
-Preparing materials-
・Polyamide resin 1
Polyamide resin 1 obtained in Synthesis Example A in Example 1
Polypropylene homopolymer: ExxonMobil, Achieve 6936G2
MFR: 1550g/10min. Glass cloth, manufactured by Nitto Boseki Co., Ltd., glass cloth for printed wiring boards, IPC spec 1017

[Example 5]
(Preparation of nonwoven fabric)
The materials shown in Table 3 were fed into a twin-screw kneading extruder through a hopper and melt-kneaded at 340°C for a residence time of 10 minutes. The melt-kneaded materials were then extruded in a fibrous form together with heated air (340°C, 300 ^Nm3 /h/m) blown out from both sides of the nozzle. The conditions were a spinning temperature of 340°C, a nozzle nozzle with a hole diameter of 0.20 mmφ, and a single hole discharge rate of 0.15 g/min. The extruded fibrous materials were then collected in a web form to obtain meltblown nonwoven fabrics of each example.

(Preparation of prepregs)
A bisphenol A type epoxy resin (product name JER828, manufactured by Mitsubishi Chemical Corporation), which is a thermosetting resin, and 1-benzyl-2-phenylimidazole (Curesol 1B2PZ, manufactured by Shikoku Kasei Corporation) were dissolved in a toluene solvent to obtain a resin varnish. Next, the nonwoven fabric of each example was impregnated with this resin varnish and dried in a blower dryer at 145°C for 10 minutes to obtain a cured prepreg having a thickness of 0.3 mm.

(Preparation of copper-clad laminate)
Eight prepregs of each example cut into 150 mm squares were stacked, and copper foil (F1-WS, manufactured by Furukawa Electric Co., Ltd.) was stacked on both ends in the stacking direction. Then, the stack was heated at 200°C for 2 hours under a pressure of 3.5 MPa in a vacuum press to produce copper-clad laminates with the copper foil adhered thereto.

[Comparative Example 8]
A cured prepreg having a thickness of 0.3 mm was obtained in the same manner as in Example 5, except that the above glass cloth was used instead of the nonwoven fabric.

[Comparative Example 9]
A cured prepreg having a thickness of 0.3 mm was obtained in the same manner as in Example 5, except that the material and manufacturing method of the nonwoven fabric were changed to the following specifications.

(Preparation of nonwoven fabric)
The materials shown in Table 3 were fed into a twin-screw kneading extruder through a hopper and melt-kneaded at 230°C for a residence time of 10 minutes. The melt-kneaded materials were then extruded into fibers together with heated air (280°C, 300 ^Nm3 /h/m) blown out from both sides of the nozzle. The conditions were a spinning temperature of 230°C, a nozzle nozzle with a hole diameter of 0.20 mmφ, and a single hole discharge rate of 0.15 g/min. The extruded fibrous materials were then collected in the form of a web to obtain meltblown nonwoven fabrics of each example.

The properties of the meltblown nonwoven fabric obtained for each example are shown in Table 3. In the table, "-" means that the material was not measurable and therefore not measured. Each property was measured using the measurement method already described.

-evaluation-
(1) Dimensional stability The dimensions of the prepreg before and after curing, that is, the dimensions S _B of the nonwoven fabric of each example that was impregnated with the resin varnish and contained the resin varnish in an uncured state in the production of the prepreg, were compared with the dimensions S _A of the prepreg after curing to determine the dimensional change rate (%) (= [S _B /S _A ] × 100). The dimensional stability was evaluated based on the dimensional change rate according to the following evaluation criteria. The results are shown in Table 3.
<Evaluation criteria>
G1: The dimensional change rate was 5% or less.
G2: The dimensional change rate was more than 5% and 15% or less.
G3: The dimensional change rate exceeded 15%.

(2) Filling Ability When preparing the prepreg, the time required for the resin varnish to be impregnated into the nonwoven fabric of each example was measured, and the filling ability was evaluated according to the following evaluation criteria. The time required for impregnation is the time required from the impregnation of the nonwoven fabric of each example with the resin varnish until no unimpregnated parts or air bubbles were visible.
G1: Less than 1 minute.
G2: 1 minute or more but less than 5 minutes.
G3: More than 5 minutes or the material was not completely saturated naturally.

(3) Voids Each copper-clad laminate was cut in the thickness direction, and the cut surface was photographed at 10 points at 1000 times magnification using a scanning electron microscope, and the presence or absence of voids was evaluated according to the following criteria.
G1: No voids were observed on the observed surface.
G2: One void was observed on the observation surface.
G3: 10 or more voids were observed on the observed surface.

(4) Processing Resistance The nonwoven fabric or glass cloth of each example was subjected to calendar processing (3 MPa, 130° C., speed 1 m/min), and the thickness of the nonwoven fabric or glass cloth of each example was measured before and after calendar processing. Then, the folding resistance was evaluated based on the following evaluation criteria.
G1: The thickness after processing is 50% or less of the thickness before processing, and no material damage was observed. G2: The thickness after processing is 50% or less of the thickness before processing, and material damage was observed. G3: The thickness after processing is more than 50% of the thickness before processing, and material damage was observed.

As shown in Table 3, the cured prepreg prepared using the nonwoven fabric of Example 5 was found to have superior heat resistance compared to the cured prepregs prepared using the nonwoven fabrics or glass cloth of each comparative example.

The disclosure of Japanese Patent Application No. 2021-37692, filed on March 9, 2021, is incorporated herein by reference in its entirety.
All publications, patent applications, and standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or standard was specifically and individually indicated to be incorporated by reference.

Claims (13)

The fiber includes a polyamide resin including an acyclic structural unit derived from an aliphatic monomer,
The highest melting point of the fiber is 300°C to 350°C;
the polyamide resin has a value obtained by dividing the sum of the carbon atoms contained in the acyclic structural units derived from the aliphatic monomers and contained in a carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of the acyclic structural units derived from the aliphatic monomers , which is less than 7;
The average fiber diameter of the fibers is 4.5 μm or less,
(Dd/Da)×100, which is a value obtained by dividing the average fiber diameter (Da) by the standard deviation (Dd) of the average fiber diameters and multiplying the result by 100, is 70 to 130;
The polyamide resin is any one of the following aspects 1 to 3, and the nonwoven fabric includes a meltblown nonwoven fabric .
Aspect 1: A configuration in which, of all structural units, the sum of diamine and dicarboxylic acid is 95 mol% or more, of the structural units derived from diamine, 1,6-diaminohexane is 95 mol% or more, of the structural units derived from dicarboxylic acid, structural units derived from terephthalic acid are 15 mol% to 70 mol% (preferably 50 mol% to 70 mol%), of the structural units derived from dicarboxylic acid, structural units derived from isophthalic acid are 5 mol% to 30 mol% (preferably 5 mol% to 20 mol%), and of the structural units derived from dicarboxylic acid, structural units derived from adipic acid are 5 mol% to 30 mol% (preferably 25 mol% to 30 mol%).
Aspect 2: An aspect in which, of all structural units, the sum of diamine and dicarboxylic acid is 95 mol % or more, of the structural units derived from diamine, 1,6-diaminohexane is 30 mol % to 70 mol %, of the structural units derived from dicarboxylic acid, terephthalic acid is 15 mol % to 45 mol %, and of the structural units derived from dicarboxylic acid, adipic acid is 15 mol % to 45 mol %.
Aspect 3: An aspect in which, of all structural units, the total of diamine and dicarboxylic acid is 95 mol % or more, the structural units derived from diamine are 1,6-diaminohexane is 30 mol % to 70 mol %, the structural units derived from dicarboxylic acid are 20 mol % to 50 mol % terephthalic acid, and the structural units derived from dicarboxylic acid are 5 mol % to 40 mol % isophthalic acid. The nonwoven fabric according to claim 1, wherein the difference between the thermal decomposition onset temperature of the fibers and the melting point is 10°C or more and 80°C or less. The nonwoven fabric according to claim 1 or 2 , wherein the polyamide resin contains two or more types of structural units derived from a dicarboxylic acid. The nonwoven fabric according to any one of claims 1 to 3 , wherein the highest melting point of the fibers is from 305°C to 340°C. The nonwoven fabric according to any one of claims 1 to 4, wherein the polyamide resin has a value obtained by dividing the sum of the carbon atoms contained in the acyclic structural units derived from the aliphatic monomers and contained in a carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of the acyclic structural units derived from the aliphatic monomers , the value being 4 to 6.5. a melt-kneading step of melt-kneading a polyamide resin or a resin composition containing the polyamide resin, the polyamide resin having a highest melting point of 300° C. to 350° C., the polyamide resin being contained in the acyclic structural units derived from the aliphatic monomer, and the value obtained by dividing the total number of carbon atoms contained in a carbon chain portion (excluding carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of the acyclic structural units derived from the aliphatic monomer is less than 7, using two or more axes to obtain a melt-kneaded product;
a spinning step of spinning the molten kneaded material together with heated air through a nozzle having a plurality of holes;
a drawing step of drawing the molten material spun in the spinning step by the heated air;
A method for producing a nonwoven fabric, comprising: 7. The method for producing a nonwoven fabric according to claim 6, wherein the melt-kneading step is a step of melt-kneading the polyamide resin or the resin composition using two or more shafts at a temperature that is 10° C. or more higher than the highest melting point of the polyamide resin or the resin composition and 5° C. or more lower than a thermal decomposition onset temperature of the polyamide resin or the resin composition. The method for producing a nonwoven fabric according to claim 6 or 7 , wherein in the melt-kneading step, the polyamide resin or the resin composition is melt-kneaded using two or more shafts while exhausting air by negative pressure. The nonwoven fabric according to any one of claims 1 to 5 ,
A resin composition including at least one of a thermosetting resin and a thermoplastic resin;
A prepreg comprising: Nonwoven fabric,
A resin composition including at least one of a thermosetting resin and a thermoplastic resin;
Including,
The nonwoven fabric comprises fibers containing a polyamide resin containing acyclic structural units derived from an aliphatic monomer,
The highest melting point of the fiber is 300°C to 350°C;
The polyamide resin is a prepreg, in which the value obtained by dividing the sum of the carbon atoms contained in the acyclic structural units derived from the aliphatic monomers and contained in the carbon chain portion (excluding the carbon atoms derived from carbonyl groups) constituting the main chain of the polyamide resin by the number of the acyclic structural units derived from the aliphatic monomers is less than 7. The thermosetting resin is a thermosetting resin having a curing temperature that is 20° C. or more lower than the lowest melting point of the nonwoven fabric,
The thermoplastic resin is a thermoplastic resin having a melting point that is 20° C. or more lower than the lowest melting point in the nonwoven fabric.
The prepreg according to claim 9 or 10 . A printed wiring board having a conductor layer on one or both sides of the cured or solidified prepreg according to any one of claims 9 to 11, which is subjected to wiring processing. An electronic component having a circuit for transmitting an electrical signal of 1 GHz or more,
An electronic component, wherein an insulating layer of the electronic component comprises a cured or solidified product of the prepreg according to any one of claims 9 to 12 .