JP2022189909A - Polypropylene nanofiber and method of producing laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a polypropylene nanofiber using not an electric field, but a high-speed high-temperature gas.

SOLUTION: A method of producing a polypropylene nanofiber comprises: a process (A) of discharging molten polypropylene from a discharge nozzle and a process (B) of stretching the molten polypropylene by ejecting a high-speed high-temperature gas from a gas nozzle to form the nanofiber, in which a melt flow rate of the polypropylene is 300-3000 g/10 minutes at 230°C and with a load of 21.18 N.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to polypropylene nanofibers and methods of making laminates.

Prior art

Traditionally, polypropylene fibers have been produced by melt spinning. However, it is difficult to produce very fine polypropylene fibers by the melt spinning method, and it is particularly difficult to stably obtain fibers with a diameter of 20 μm or less (about 3 dtex in single fiber fineness). On the other hand, an electrospinning method is known as a method for producing ultrafine fibers. A melt electrospinning method that does not use a solvent during spinning has also been proposed (Patent Document 1: JP-A-2007-321246), and attempts have also been made to apply a propylene-based resin composition to the melt electrospinning method ( Patent Document 2: JP-A-2011-162636 and Patent Document 3: JP-A-2009-133039). However, with these methods, it is difficult to form polymer melts into ultrafine fibers due to electrolytic interference caused by high voltage. On the other hand, Patent Document 4 (Japanese Patent Laid-Open No. 2016-156114) discloses a method for producing a nanofiber sheet without using electrolysis. However, there is no specific disclosure of a method for producing nanofibers made of polypropylene alone.

JP 2007-321246 A JP 2011-162636 A JP 2009-133039 A JP 2016-156114 A

The inventors have experimentally implemented the method described in Patent Document 4 using various polypropylenes, and found that it is difficult to produce nanofibers without using a specific polypropylene. In view of such circumstances, an object of the present invention is to provide a method for producing polypropylene nanofibers using high-speed high-temperature gas without using an electric field.

The inventors have found that a polypropylene with a specific melt flow rate (MFR) solves the above problems. Therefore, the above problems are solved by the present invention described below.
[1] Step (A): A step of discharging molten polypropylene from a discharge nozzle, and Step (B): A step of discharging high-speed high-temperature gas from a gas nozzle to stretch the molten polypropylene to form nanofibers.
A method for producing polypropylene nanofibers comprising:
The production method, wherein the polypropylene has a melt flow rate (230° C., load 21.18 N) of 300 to 3000 g/10 minutes.
[2] Step (A): a step of discharging molten polypropylene from a discharge nozzle;
Step (B): A step of drawing a high-speed, high-temperature gas from a gas nozzle to stretch the molten polypropylene to form nanofibers;
Step (C): A step of providing a polypropylene nanofiber layer by attaching the polypropylene nanofibers to a base material arranged at a position facing the discharge nozzle or the gas nozzle;
A method for manufacturing a laminate comprising
The melt flow rate of the polypropylene (230 ° C., load 21.18 N) is 300 to
3000 g/10 minutes, manufacturing method.
[3] Step (D): A step of ejecting a molten polymer from a second ejection nozzle and ejecting a high-speed high-temperature gas from a second gas nozzle to stretch the molten polymer to form second nanofibers;
Step (E): A step of attaching a second nanofiber onto the polypropylene nanofiber layer formed in step (C);
The method for producing a laminate according to [2], further comprising:
[4] Step (A'): a step of discharging a molten polymer other than polypropylene from a discharge nozzle;
Step (B′): A step of discharging high-speed, high-temperature gas from a gas nozzle to stretch the molten polymer to form nanofibers;
Step (C′): a step of attaching the nanofibers to a base material arranged at a position facing the discharge nozzle or the gas nozzle to form a nanofiber layer;
Step (D'): A step of ejecting the polypropylene according to claim 1 or 2 from the second ejection nozzle, ejecting high-speed high-temperature gas from the second gas nozzle, and stretching the polypropylene to form polypropylene nanofibers. ,
Step (E'): A method for producing a laminate, comprising a step of adhering the polypropylene nanofibers formed in step (D') onto the nanofiber layer formed in step (C').
[5] The production method according to any one of [1] to [4], wherein the polypropylene supplied to the nanofiber forming step does not contain additives.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for producing polypropylene nanofibers using a high-velocity high-temperature gas without using an electric field.

Schematic diagram showing the method for producing polypropylene nanofibers of the present invention Schematic diagram showing a method for manufacturing a laminate of the present invention

The present invention will be described in detail below. In the present invention, "X to Y" includes X and Y which are end values.

1. Method for producing polypropylene nanofibers The production method includes step (A): a step of discharging molten polypropylene from a discharge nozzle, and step (B): discharging high-speed high-temperature gas from a gas nozzle to stretch the molten polypropylene to produce nanofibers. A step of forming is provided. The speed of the discharged gas is not particularly limited, but is preferably 4 to 30 Nm ³ /min/m, and the temperature is preferably in the range of 250 to 350°C.

(1) Polypropylene In the present invention, polypropylene refers to a polypropylene homopolymer, a polypropylene copolymer of propylene and less than 10 mol% of an α-olefin, a composition containing the homopolymer, or a composition containing the copolymer. say. Specifically, i) a polypropylene homopolymer, ii) a polypropylene copolymer obtained by polymerizing propylene and an α-olefin and containing less than 10 mol % of α-olefin units, i) a resin composition containing ii) ), a resin composition comprising i) and ii), a resin composition comprising i) and ii), and the like. The resin composition may contain additives described below.

The melt flow rate of the polypropylene used in the present invention measured at 230° C. and a load of 21.18 N (hereinafter simply referred to as “MFR”) is 300 to 3000 g/10 minutes. If the MFR is less than the lower limit, the polymer cannot be sufficiently stretched to the nano level. If the MFR exceeds the upper limit, fiber breakage or the like occurs. From this point of view, the MFR is preferably 500 to 3000 g/10 minutes, more preferably 1000 to 3000 g/10 minutes.

The polypropylene used in the present invention preferably has a xylene-insoluble content of 95% by weight or more, and more preferably has the following characteristics.
1) The melting peak temperature (Tm) of the xylene-insoluble matter measured by DSC (differential scanning calorimetry) is above 150°C and below 170°C.
2) The molecular weight distribution (Mw/Mn) of the xylene-insoluble matter is 2.0 to 5.0.
3) Stereoregularity (mmmm) of xylene-insoluble matter is 95.0 to 99.5%.

The xylene-insoluble component of polypropylene corresponds to the isotactic component, which is crystalline. On the other hand, the xylene-soluble component contained in polypropylene in a small amount corresponds to an amorphous atactic component, and has a lower molecular weight than the xylene-insoluble component. Therefore, the melting properties of polypropylene and the physical properties of molded articles are mainly affected by components that are insoluble in xylene.

The amount of xylene-insoluble matter in polypropylene being 95% by weight or more means that the crystalline component of polypropylene is 95% by weight or more. The amount of xylene-insoluble matter is more preferably 96% by weight or more, and even more preferably 97% by weight or more. If the crystalline component of the polypropylene is less than 95% by weight, the fibers tend to adhere to each other incorrectly, making spinning difficult.

The Tm of the crystalline component of the polypropylene is measured by DSC (Differential Scanning Calorimetry) as the melting peak temperature, preferably above 150°C and below 170°C. The lower limit of Tm is preferably 152°C or higher, more preferably 154°C or higher. The upper limit of Tm is preferably 165°C or less. When the Tm of the crystalline component of the polypropylene is less than 150°C, the heat resistance of the fiber is insufficient, and when it exceeds 170°C, crystallization at a higher temperature may result in difficulty in spinning.

The molecular weight distribution (Mw/Mn) of the crystalline component of polypropylene is preferably 2.0 to 5.0. When Mw/Mn exceeds 5.0, it may become difficult to obtain ultrafine fibers due to the ballast effect. Moreover, the stereoregularity (mmmm) of the crystalline component of the polypropylene is preferably 95.0 to 99.5%. If mmmm is less than 95.0%, the strength and heat resistance of the fiber may deteriorate.

The polypropylene used in the present invention is a catalyst comprising (a) a solid catalyst component containing magnesium, titanium, halogen and an internal electron donor compound as essential components, (b) an organoaluminum compound, and (c) an external electron donor compound. can be obtained by polymerizing a monomer using Known components can be used as these components. However, from the viewpoint of achieving a relatively high MFR, the internal electron donor compound is preferably a 1,3-diether. Alternatively, a metallocene catalyst may be used to produce the polypropylene used in the present invention.

The polypropylene used in the present invention includes oil extender, antioxidant, nucleating agent, filler, chlorine absorber, heat stabilizer, light stabilizer, ultraviolet absorber, internal lubricant, external lubricant, antiblocking agent, antistatic. olefin polymers, such as additives, antifog agents, flame retardants, organic and inorganic pigments, dyes, dispersants, copper inhibitors, neutralizers, plasticizers, blowing agents, antifoam agents, crosslinkers, peroxides, etc. may contain conventional additives and pigments commonly used in However, considering spinning, it is more preferable not to contain additives.

(2) Step (A)
This step will be described with reference to FIG. In FIG. 1, 20 is molten polypropylene, 22 is a discharge nozzle, 10 is gas, and 12 is a gas nozzle. In this step, the molten polypropylene 20 is discharged from the discharge nozzle 22 . The discharge temperature is not limited as long as it is a temperature at which polypropylene melts, but it is preferably 200 to 300°C. The nozzle diameter is also not particularly limited, and a commercially available nozzle used for ordinary meltblown spinning can be used. If the nozzle diameter is too large, a fine fiber diameter cannot be obtained. On the other hand, if the nozzle diameter is too small, it becomes difficult to machine the nozzle and the pressure loss increases.

(3) Step (B)
In this step, a high-speed high-temperature gas 10 is discharged from a gas nozzle 12 to the molten polypropylene 20 to stretch the molten polypropylene 20 to form nanofibers. A nanofiber is a fiber having an average fiber diameter of nano-order, specifically a fiber of less than 1000 nm, preferably 500 nm or less, more preferably 300 nm or less. The average fiber diameter is measured by observing the fibers with an electron microscope or the like.

It is preferable not to cool the molten polypropylene 20 excessively in this step. Therefore, the gas 10 is at a high temperature, eg, about 200-300.degree. The fiber diameter can be appropriately adjusted by the velocity of the gas 10 . Gas 10 is therefore discharged at high pressure so as to achieve the desired flow rate. The high-pressure gas is not particularly limited, but a compressed gas of 0.5 to 0.7 MPa can be used. Thus, the molten polypropylene 20 rides on the flow of the gas 10, and polypropylene nanofibers are formed in the direction of discharge of the gas 10. FIG. A shatterproof cover may be provided around the streamlines of the propylene nanofibers to prevent diffusion of the propylene nanofibers. As the gas, an inert gas such as nitrogen or air is preferable.

The polypropylene nanofiber of the present invention is useful as a raw material for laminates to be described later, as well as for medical applications such as drug carriers and cell culture media, and as a raw material for heat-insulating woven fabrics.

2. Method for Manufacturing Laminate The method will be described with reference to FIG. In FIG. 2, 24 is a polypropylene nanofiber layer, 40 is a second nanofiber, 42 is a second discharge nozzle, 30 is a second high-speed high-temperature gas, 32 is a second gas nozzle, and 50 is a substrate. The laminate of the present invention is manufactured through the step (C) of attaching the polypropylene nanofibers manufactured by the above-described method to the substrate 50 provided at a position facing the discharge nozzle 22 or the gas nozzle 12 . In FIG. 2, the base material 50 can be moved downward on the plane of the paper, so the thickness of the layer can be adjusted by its speed. A laminate having a polypropylene nanofiber layer 24 on a substrate 50 can thus be produced. The type of the base material 50 is not limited, and polymer sheets, paper, glass, metal foil, etc. can be used, for example. The discharge nozzle 22 and the gas nozzle 12 are arranged at an angle. Although the substrate 50 is arranged to face the gas nozzle 12 in FIG.

Additionally, after the polypropylene nanofiber layer 24 is formed, a second nanofiber may be formed from the second polymer 40 and attached to the polypropylene nanofiber layer 24 to form a second nanofiber 44 layer. can. Since the second nanofibers are in a high temperature state, they are heat-sealed to the polypropylene nanofiber layer 24 . That is, the polypropylene nanofiber layer 24 can be used as an adhesive layer. The second nanofibers can be formed similarly to the polypropylene nanofibers using the second discharge nozzle 42 and the second gas nozzle 32 . The second polymer may be any known polymer. Such polymers include polyesters, polyamides, polyolefins, polystyrene, polyvinyl chloride, polylactic acid, ethylene-based copolymers, polyolefin-modified resins, polyurethanes (PU), etc., or combinations thereof. However, when the polyolefin is polypropylene, the MFR of the polypropylene is 300 to 3000 g/10 minutes.

Further, by the same method, instead of the polypropylene having an MFR of 300 to 3000 g/10 min (also referred to as "specific MFR polypropylene"), the second polymer is used to form an adhesive layer of nanofibers, A nanofiber layer using polypropylene with a specific MFR can also be formed thereon.

The laminate of the present invention is useful as a filter, a separation material such as a mask, a plant culture soil, and the like.

The present invention will be further described with reference to examples below. Each analysis in the examples is as follows.
[MFR]
According to JIS K 7210, it was measured under conditions of a temperature of 230° C. and a load of 21.18 N.

[Amount of xylene-insoluble matter in polypropylene resin material]
2.5 g of polymer were dissolved in 250 ml of xylene at 135° C. with stirring. After 20 minutes the solution was cooled to 25°C with stirring and then allowed to rest for 30 minutes. The precipitate was filtered through filter paper, the solution evaporated in a stream of nitrogen and the residue dried under vacuum at 80° C. until constant weight was reached. Thus the weight percent of polymer soluble in xylene at 25°C was calculated. The amount of xylene insolubles (weight percent of polymer insoluble in xylene at 25° C.) is determined by (100-weight percent of polymer soluble) and is considered the amount of the isotactic component of the polymer.
The xylene-insoluble matter was collected by thoroughly washing the xylene remaining in the precipitate with methanol and then drying it under vacuum at 80°C.

[Melting point (Tm) of xylene-insoluble matter]
The melting point of the xylene-insoluble matter obtained by the above method was determined by holding a sample at 230°C for 5 minutes using a diamond DSC manufactured by PerkinElmer, and then cooling to 30°C at a cooling rate of 10°C/min to crystallize. After holding at 30°C for 5 minutes, it was determined from the peak position of the melting curve obtained when heating to 230°C at a heating rate of 10°C/min. In the case of low-molecular weight polypropylene, a sub-melting peak may occur on the high temperature side of the main melting peak due to melting of crystals caused by melt-recrystallization during temperature rise, but the melting point used in the present invention is the main melting peak. It was determined from the position of the melting peak.

[Molecular weight distribution (Mw/Mn) of xylene-insoluble matter]
The molecular weight distribution (Mw/Mn) of the xylene-insoluble matter obtained by the above method was measured by gel permeation chromatography (PL-GPC220 manufactured by Polymer Laboratories). In the GPC measurement in the present invention, 1,2,4-trichlorobenzene containing an antioxidant is used as the mobile phase, the same solvent as the mobile phase is used for the polymer sample solution, and the sample concentration is 1 mg / mL. , 150° C. with shaking for 2 hours to prepare the sample. 200 μL of the sample solution thus obtained was injected into the column and measured at a flow rate of 1.0 mL/min, a temperature of 140° C., and a data acquisition interval of 1 second.

[Tacticity of xylene insolubles (mmmm)]
The mmmm of the xylene-insoluble matter obtained by the above method was determined as follows. First, a sample dissolved in a mixed solvent of 1,2,4-trichlorobenzene/deuterated benzene was measured by ¹³ C-NMR method using JNM LA-400 (13 C resonance frequency 100 MHz) manufactured by JEOL Ltd. Then, from the obtained spectrum, the intensity ratio of peaks corresponding to pentads in which four meso (m) bond sequences of the propylene monomer are consecutive is calculated as A. It was determined according to the method described in Zambelli, Macromolecules, 6, 925 (1973).

[Average fiber diameter]
The spun fiber diameter is observed using JSM-6510LA (low-vacuum analytical scanning electron microscope) manufactured by JEOL Ltd., and the average fiber diameter is measured.

[Example 1]
(1) Production of Polypropylene 1 Powdery homopolypropylene: Polypropylene 1 (MFR = 1750 g/10 min, amount of xylene insolubles at 25°C = 97.7% by weight, Tm of xylene insolubles = 160°C, xylene insolubles Mw/Mn = 4.5, xylene insolubles mmmm = 98.4%).
1) Preparation of Solid Catalyst Component Component (A) (solid catalyst component) was prepared according to Example 1 of European Patent Application EP728769. Specifically, component (A) was prepared as follows.
225 ml of TiCl ₄ were introduced at 0° C. into a 500 ml reactor equipped with a porous barrier. While stirring the contents, 10.1 (54 mmol) g microspherical MgCl ₂ .2.1C ₂ H ₅ OH was added for 15 minutes under nitrogen atmosphere. A method for producing the MgCl ₂ .2.1C ₂ H ₅ OH will be described later. At the end of the addition the temperature was brought to 70° C., 9 mmoles of 9,9-bis(methoxymethyl)fluorene were added, the contents were heated to 100° C. and allowed to react at this temperature for 2 hours. TiCl ₄ was then filtered off. Another 200 ml of TiCl ₄ and 9 mmol of 9,9-bis(methoxymethyl)fluorene were added and the contents were allowed to react at 120° C. for 1 hour. Afterwards, it was filtered again, another 200 ml of TiCl ₄ was added, the contents were allowed to react at 120° C. for a further hour, then filtered and an n− Washed with heptane. The solid component was analyzed and found to contain 3.5 wt% Ti and 16.2 wt% 9,9-bis(methoxymethyl)fluorene.

Microspherical MgCl ₂ .2.1C ₂ H ₅ OH adducts were prepared as follows. 48 g of MgCl ₂ , 77 g of anhydrous C ₂ H ₅ OH and 830 ml of kerosene were introduced into a 2 liter autoclave equipped with a turbine stirrer and dip pipes at ambient temperature under inert gas atmosphere. The contents were heated to 120° C. with stirring, forming an adduct between MgCl ₂ and the alcohol. The adduct was melted and mixed with the dispersant. The inside of the autoclave was maintained at a nitrogen pressure of 15 atmospheres. The immersion pipe of the autoclave was externally heated to 120° C. by means of a heating jacket. The heating jacket had an inner diameter of 1 mm and an end-to-end length of 3 m. The mixture was circulated through the pipe at a speed of 7 m/s. The dispersion was collected with stirring in a 5 liter flask. The flask contained 2.5 liters of kerosene and was externally cooled by a jacket maintained at an initial temperature of -40°C. The final temperature of the emulsion was 0°C. The spherical solid product, which constituted the dispersed phase of the emulsion, was separated by sedimentation and filtration, then washed with heptane and dried. All the above operations were carried out in an inert atmosphere. 130 g of MgCl ₂ .3.0C ₂ H ₅ OH were obtained in the form of solid spherical particles with a maximum diameter of less than 50 microns. The product was then freed of alcohol by gradually increasing the temperature from 50°C to 100°C in a stream of nitrogen until the alcohol content was 2.1 moles _per mole of MgCl2.

2) Polymerization In a precontacting vessel, 0.56 mmol dicyclopentylmethoxysilane (DCPMS) and 7 mmol triethylaluminum (TEAL) were added to 7 mg of the solid catalyst component obtained above in 80 ml of anhydrous n-hexane. Contact was made for 20 minutes at 10°C. The resulting catalyst system was introduced into a 4 liter stainless steel autoclave equipped with a horseshoe stirrer and purged with a stream of nitrogen for 1 hour and prepolymerized by being suspended in liquid propylene at 20° C. for 10 minutes. did Subsequently, hydrogen (used for the purpose of MFR adjustment) was supplied to the liquid propylene so as to be 15000 mol ppm, and the content was polymerized at a polymerization temperature of 70°C using the obtained prepolymer. Unreacted monomer was then removed and the polymer was recovered and dried in an oven at 70° C. for 3 hours under a stream of nitrogen. Polypropylene 1 was thus produced.

(2) Production of Laminate The polypropylene is heated to 250° C. using the apparatus shown in FIG. A pressurized gas 10 heated to 250° C. is discharged from a gas nozzle 12 to stretch molten polypropylene 20 to form polypropylene nanofibers. A laminate is obtained by attaching the polypropylene nanofibers to the base material 50 . The average fiber diameter of polypropylene nanofibers is 500 nm.

[Example 2]
(1) Production of Polypropylene 2 Powdery homopolypropylene: Polypropylene 2 (MFR = 1800 g/10 min, amount of xylene insolubles at 25°C = 98.7% by weight, Tm of xylene insolubles = 154° C., xylene insolubles Mw/Mn=2.5, xylene insolubles mmmm=96.7%).
1) Preparation of catalyst components A catalyst system was prepared by the method described in PCT/EP2004/00761. However, instead of rac-dimethylsilylbis(2-methyl-4,5-benzoindenyl)zirconium dichloride, rac-dimethylsilylene prepared by the method described in US-2003/0149199 (2-methyl-4-( 4′-tert-butylphenyl)indenyl)(2-isopropyl-4-(4′-tert-butylphenyl)indenyl)zirconium dichloride was used.

2) Polymerization The catalyst system in the form of catalyst mud prepared as described above was fed into a precontacting vessel and diluted therein with about 5 (kg/h) of propane. The catalyst system was fed from the precontacting vessel to the prepolymerization loop, to which propylene was simultaneously fed. The temperature in the prepolymerization loop was 45° C. and the residence time of the catalyst was 8 minutes. The prepolymerized catalyst obtained in the prepolymerization loop is then continuously fed into the loop reactor to feed propylene and hydrogen (used for MFR adjustment purposes) to 900 mol ppm. Then, polymerization was carried out at a polymerization temperature of 70°C. The polymer was removed from the reactor, separated from unreacted monomer and dried in an oven at 70° C. for 3 hours under a stream of nitrogen.

(2) Production of laminate A laminate of polypropylene nanofibers is obtained in the same manner as in Example 1 except that polypropylene 2 is used. The average fiber diameter of polypropylene nanofibers is 300 nm.

[Comparative Example 1]
Powdered homopolypropylene 3 (MFR = 200 g/10 min, xylene-insoluble matter at 25°C A laminate is produced in the same manner as in Example 1, except that the amount of = 98.0% by weight) is used. However, in this example, the polypropylene fibers have an average fiber diameter of 1500 nm and do not become nanofibers.

[Comparative Example 2]
Instead of homopolypropylene 1, powdery homopolypropylene 4 (MFR too high to be measured) obtained in the same manner as homopolypropylene 1 except that hydrogen was supplied to 23000 mol ppm without using DCPMS. A laminate is produced in the same manner as in Example 1, except for the use. However, in this example, fiber breakage occurs and polypropylene fibers cannot be obtained.

10 gas 12 gas nozzle 20 molten polypropylene 22 discharge nozzle 24 polypropylene nanofiber layer 30 second gas 32 second gas nozzle 40 second nanofiber 42 second discharge nozzle 44 second nanofiber layer 50 substrate

Claims (5)

Step (A): A step of discharging molten polypropylene from a discharge nozzle, and Step (B): A step of discharging high-speed high-temperature gas from a gas nozzle to stretch the molten polypropylene to form nanofibers.
A method for producing polypropylene nanofibers comprising:
The production method, wherein the polypropylene has a melt flow rate (230° C., load 21.18 N) of 300 to 3000 g/10 minutes. Step (A): a step of discharging molten polypropylene from a discharge nozzle;
Step (B): A step of drawing a high-speed, high-temperature gas from a gas nozzle to stretch the molten polypropylene to form nanofibers;
Step (C): A step of providing a polypropylene nanofiber layer by attaching the polypropylene nanofibers to a base material arranged at a position facing the discharge nozzle or the gas nozzle;
A method for manufacturing a laminate comprising
The production method, wherein the polypropylene has a melt flow rate (230° C., load 21.18 N) of 300 to 3000 g/10 minutes. Step (D): A step of ejecting a molten polymer from a second ejection nozzle and ejecting a high-speed high-temperature gas from a second gas nozzle to stretch the molten polymer to form second nanofibers;
Step (E): A step of attaching a second nanofiber onto the polypropylene nanofiber layer formed in step (C);
The method for manufacturing a laminate according to claim 2, further comprising: Step (A'): a step of discharging a molten polymer other than polypropylene from a discharge nozzle;
Step (B′): A step of discharging high-speed, high-temperature gas from a gas nozzle to stretch the molten polymer to form nanofibers;
Step (C′): a step of attaching the nanofibers to a base material arranged at a position facing the discharge nozzle or the gas nozzle to form a nanofiber layer;
Step (D'): A step of ejecting the polypropylene according to claim 1 or 2 from the second ejection nozzle, ejecting high-speed high-temperature gas from the second gas nozzle, and stretching the polypropylene to form polypropylene nanofibers. ,
Step (E'): A method for producing a laminate, comprising a step of adhering the polypropylene nanofibers formed in step (D') onto the nanofiber layer formed in step (C'). The production method according to any one of claims 1 to 4, wherein the polypropylene supplied to the nanofiber forming step does not contain additives.

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