JP6653476B2 - Fiber aggregate and sound absorbing material - Google Patents

Description

  The present invention relates to a fiber assembly applicable to a sound absorbing material and a sound absorbing material provided with the fiber assembly.

  2. Description of the Related Art Conventionally, a sound absorbing material has been used to suppress driving noise emitted from a transportation vehicle such as an automobile. The driving source of a conventional transportation vehicle is mainly an internal combustion engine such as a gasoline engine. Since the driving noise of the internal combustion engine includes many high-frequency sounds, the sound absorbing material has been required to have high absorptivity of high-frequency sounds, particularly sounds having a frequency of 2 kHz or more.

  As such a sound absorbing material, Patent Literature 1 discloses that a fiber is made of a thermoplastic resin fiber, and the fiber has an integrated frequency of 1% or less of 5% or more and a fiber diameter of 10 μm or more of 0.1 to 5%. Are disclosed.

  In recent years, transport vehicles equipped with a drive source other than the internal combustion engine, such as electric vehicles and hybrid vehicles, have been put into practical use, and accordingly, the sound absorbing material has a medium-range sound, for example, a sound having a frequency of 500 to 1500 Hz. Sex is required.

JP 2013-147771 A

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a fiber assembly having a high sound absorbing property in a middle sound range and a sound absorbing material including the fiber assembly.

  The fiber aggregate according to one embodiment of the present invention is an aggregate of fibers including a thermoplastic resin. The fiber has at least one of a melt flow rate in a range of 1600 to 5000 g / 10 min and a melt viscosity in a range of 250 to 7000 mPa · s. The median diameter of the fibers is in the range of 0.3 μm to 0.9 μm. The number of fibers having a diameter of 8 μm or less among the fibers is 99% or more.

  A sound absorbing material according to one embodiment of the present invention includes the fiber aggregate.

  According to one embodiment of the present invention, a fiber aggregate and a sound absorbing material that can effectively absorb mid-range sounds can be obtained.

  Hereinafter, embodiments of the present invention will be described.

  In the present embodiment, the fiber aggregate is an aggregate of fibers containing a thermoplastic resin. The fiber has at least one of a melt flow rate in a range of 1600 to 5000 g / 10 min and a melt viscosity in a range of 250 to 7000 mPa · s. The median diameter of the fibers is in the range of 0.3 μm to 0.9 μm. The number of fibers having a diameter of 8 μm or less among the fibers is 99% or more.

  For this reason, the fiber assembly and the sound-absorbing material including the fiber assembly can effectively absorb mid-range sounds, particularly sounds having a frequency of 500 to 1500 Hz.

  The sound-absorbing material including the fiber aggregate is preferably for a vehicle. In particular, when the sound absorbing material is applied for suppressing driving noise in a transport vehicle having a driving source other than the internal combustion engine, such as an electric vehicle or a hybrid vehicle, the driving source can effectively absorb the driving noise.

  The fiber assembly and the sound absorbing material according to the present embodiment will be described in more detail.

  As described above, the fibers in the fiber assembly include a thermoplastic resin.

  As described above, the fiber has at least one of a melt flow rate in a range of 1600 to 5000 g / 10 min and a melt viscosity in a range of 250 to 7000 mPa · s.

  The significance of the melt flow rate and the melt viscosity of the fiber in the present embodiment will be described in detail. The inventor found through many experiments that the material of the fiber greatly affected the sound absorption of the mid-range sound, and as a result of examining the factors, the melt flow rate and melt viscosity of the fiber caused the absorption of the sound in the mid-range. It was found that there was a strong correlation with gender. Based on this finding, the inventors have attempted to improve the mid-range sound absorption by defining the melt flow rate or melt viscosity of the fiber. As a result, as described above, if the fiber has at least one of a melt flow rate in the range of 1600 to 5000 g / 10 min and a melt viscosity in the range of 250 to 7000 mPa · s, the sound of the mid-range sound is obtained. It has been found that the absorbency is greatly improved.

  Further, in particular, when the melt flow rate of the fiber is 5000 g / 10 min or less, the fiber aggregate also has high heat resistance.

  Furthermore, if the fiber has at least one of a melt flow rate in the range of 1600 to 5000 g / 10 min and a melt viscosity in the range of 250 to 7000 mPa · s, high heat resistance can be imparted to the fiber assembly. . In addition, in this specification, the high heat resistance of the fiber assembly means that even if the fiber assembly is heated, the absorption of sound in the mid-range of the fiber assembly is difficult to reduce.

  Furthermore, if the fiber has at least one of a melt flow rate in the range of 1600 to 5000 g / 10 min and a melt viscosity in the range of 250 to 7000 mPa · s, the fiber material (hereinafter referred to as a spinning material) ) Is spun to produce fibers, despite that the median diameter of the fibers is a small value in the range of 0.3 μm to 0.9 μm, the fibers can be produced stably, and the fiber aggregate It is easy to reduce body density. That is, when the fiber has at least one of a melt flow rate of 1600 g / 10 min or more and a melt viscosity of 7000 mPa · s or less, the spinning material easily flows when the spinning material is spun to produce the fiber. Therefore, it is easy to reduce the diameter of the fiber. Further, in this case, in the case where the airflow is blown during spinning as in the melt blown method, it is possible to further reduce the diameter of the fibers even in a weak airflow, and it is easy to lower the density of the fiber aggregate. It is. Therefore, if the spinning conditions are the same, when the fiber has at least one of a melt flow rate of 1600 g / 10 min or more and a melt viscosity of 7000 mPa · s or less, the diameter of the fiber is larger than in the case where it is not. It is possible to reduce the size and the density of the fiber assembly. Further, when the fiber has at least one of a melt flow rate of 5000 g / 10 min or less and a melt viscosity of 250 mPa · s or more, it is easy to form a fiber having a sufficient length by spinning. To easily produce a fiber assembly. For this reason, it becomes possible to manufacture fibers having a small diameter while suppressing the amount of airflow when spinning the spinning material, and it is possible to manufacture a fiber aggregate having a low density.

  The fibers preferably have a melt flow rate in the range of 2000-5000 g / 10 min, more preferably a melt flow rate in the range of 3500-5000 g / 10 min. When the fiber has a melt flow rate of 2000 g / 10 min or more, the diameter of the fiber can be further reduced and the density of the fiber aggregate can be lowered. When the fiber has a melt flow rate of 3500 g / 10 min or more, the diameter of the fiber can be particularly reduced, and the density of the fiber aggregate can be reduced.

  Further, the fiber preferably has a melt viscosity in the range of 250 to 3000 mPa · s, and more preferably has a melt viscosity in the range of 250 to 800 mPa · s. When the fiber has a melt viscosity of 3000 mPa · s or less, the diameter of the fiber can be further reduced and the density of the fiber aggregate can be reduced. When the fiber has a melt viscosity of 800 mPa · s or less, the diameter of the fiber can be particularly reduced, and the density of the fiber aggregate can be reduced.

  The melting point or softening point of the fiber is preferably 130 ° C. or higher. In this case, even when the fiber aggregate is heated, the absorbency of the sound in the middle sound range of the fiber aggregate is not easily reduced. It is more preferable that the melting point or softening point is 140 ° C. or higher. More preferably, the melting point or softening point is 150 ° C. or higher.

  The melt flow rate of the fiber is measured at a temperature of 230 ° C. and a load of 2.16 kg in accordance with ASTM D1238. The melt viscosity of the fiber is the melt viscosity at 230 ° C. Further, the melting point and softening point of the fiber can be determined from the peak of the heat of fusion peak obtained by the DSC method under the condition of a heating rate of 5 ° C./min.

  Further, the melt flow rate, melt viscosity, and melting point and softening point of the above fibers are values relating to the fibers in the fiber assembly, not values relating to the spinning material, and are not values relating to the components contained in the spinning material. .

  The median diameter of the fibers is in the range of 0.3 μm to 0.9 μm, and the number of fibers having a diameter of 8 μm or less of these fibers is 99% or more of the total fibers. In the present embodiment, by defining the diameters of the fibers in the fiber assembly in this way, it is possible to improve the mid-range sound absorption of the fiber assembly and the sound absorbing material.

  The improvement of the mid-range sound absorption by defining the fiber diameter will be described in detail. According to the known Biot model of the porous sound absorbing material, as the diameter of the fiber in the sound absorbing material decreases, the peak of the sound absorbing characteristic of the sound absorbing material shifts to a lower frequency region than 2 kHz. However, in practice, the mere inclusion of fibers having a small diameter does not provide sufficiently high sound absorption in the midrange. This is because if the small diameter fiber and the large diameter fiber are mixed in the sound absorbing material, the air in the sound absorbing material is likely to flow, which impairs the sound absorption of the middle sound range. The inventor speculated. Based on this presumption, the inventor tried to improve the absorbency of the mid-range sound by defining the fiber diameter. As a result, as described above, not only the median value of the fiber diameter is in the range of 0.3 μm to 0.9 μm, but also the number of fibers having a fiber diameter of 8 μm or less with respect to the entire fiber is 99% or more. The inventor has found that the absorption of the mid-range sound is greatly improved.

  It is particularly preferable that the number of fibers having a diameter of 5 μm or less among these fibers is 99% or more relative to the whole fibers. In this case, the absorbency of the sound in the midrange can be further improved.

  It is particularly preferred that the maximum diameter of the fibers is less than 10 μm. That is, it is particularly preferable that the fiber aggregate does not include a fiber having a diameter of 10 μm or more. In this case, the weight ratio of the fiber having a small diameter per unit volume of the fiber assembly increases, and therefore, the sound absorption in the middle sound range becomes particularly high.

  The length of the fibers is preferably, for example, 5 mm or more, but is not particularly limited as long as the fibers have a length that can be sufficiently entangled.

  The value of the aspect ratio of each fiber is preferably 1000 or more.

  In addition, the diameter and length of the fiber are measured by performing image processing on an image obtained by photographing the fiber with an electron microscope. The median value of the fiber diameters is a median value based on quantity calculated from the measurement results of the diameters of 200 fibers. In defining the diameter and length of the fibers in the present embodiment, the portions where the fibers are thermally fused and the portions where the fibers are not formed into fibers and are clumps are not regarded as fibers.

The fiber aggregate preferably has a density of 0.03 g / cm ³ or less. In this case, the absorptivity of the midrange sound of the fiber assembly is further improved. It is also preferable that the fiber aggregate has a density of 0.003 g / cm ³ or more. In this case, the deformation and the density change of the fiber aggregate due to its own weight are suppressed, so that the good absorbency of the fiber aggregate can be maintained for a long time.

The fiber aggregate is, for example, a sheet or a layer. When the fiber aggregate is in the form of a sheet or a layer, the basis weight of the fiber aggregate (that is, the mass per unit planar area) is preferably in the range of 100 to 1000 g / m ² , and more preferably 100 to 600 g / m 2. ² , more preferably within the range of 100 to 500 g / m ² . When the basis weight is 100 g / m ² or more, the fiber aggregate can have higher sound absorbing properties. Further, if the basis weight is 1000 g / m ² or less, the fiber assembly can be made compact and lightweight, and therefore, the degree of freedom in vehicle design increases, especially when the fiber assembly is for use in vehicles. .

  The components contained in the fiber will be described in detail.

  Thermoplastic resins include, for example, polypropylene, polyethylene, polyolefin-based thermoplastic elastomers, 1-butene polymer, 1-hexene polymer, 1-octene polymer, 1-decene polymer, 1-hexadecene polymer, and 1-heptadecene polymer. Coalescence, 1-octadecene polymer, polyester, polyethylene terephthalate, polybutylene terephthalate, polyamide, polyurethane, polybutene, polylactic acid, polyvinyl alcohol, polyphenylene sulfide, polysulfone, liquid crystal polymer, ethylene vinyl acetate copolymer, polyacrylonitrile, cyclic Contains at least one component selected from the group consisting of polyolefins and polyoxymethylene. Further, the thermoplastic resin may contain a wax-like component such as polyethylene wax, polypropylene wax, and paraffin wax. In particular, the thermoplastic resin preferably contains at least one component selected from the group consisting of polypropylene, polyethylene, a polyolefin-based thermoplastic elastomer, and paraffin. In this case, the absorbability of the middle frequency range sound of the fiber assembly becomes particularly high.

  The thermoplastic resin can contain two or more resins, in which case these resins can have at least one of a different melt flow rate and a different melt viscosity. In this case, by adjusting the amount of each resin in the thermoplastic resin, at least one of the melt flow rate and the melt viscosity of the fiber can be easily adjusted. Further, as a component of the thermoplastic resin, a component whose physical properties do not match the fiber, that is, a component whose melt flow rate is not in the range of 1600 to 5000 g / 10 min and whose melt viscosity is not in the range of 250 to 7000 mPa · s. Can be applied. Therefore, the degree of freedom in selecting the components of the thermoplastic resin is increased.

  At least some components in the thermoplastic resin (hereinafter, referred to as specific components) may be manufactured through a thermal decomposition step. The thermal decomposition step is a step of obtaining a specific component having a controlled molecular weight by thermally decomposing a raw material of the specific component (hereinafter, referred to as a specific raw material). In this case, by adjusting the molecular weight of the specific component, at least one of the melt flow rate and the melt viscosity of the fiber can be easily adjusted. In addition, it is possible to apply a component having a melt flow rate smaller than 1600 g / 10 min and a melt viscosity higher than 7000 mPa · s as the specific raw material. Therefore, the degree of freedom in selecting the raw material of the thermoplastic resin is increased. For example, when the thermoplastic resin contains two or more kinds of resins, at least one kind of the resins may be produced through a thermal decomposition step. Further, all of the thermoplastic resin may be manufactured through a thermal decomposition step.

  In order not to melt when the fiber aggregate is thermally fused to a support or the like, it is preferable that the thermoplastic resin has high crystallinity. It is also preferable that the surface tension of the thermoplastic resin is as low as possible. In this case, stable spinning is possible when spinning a spinning material containing the thermoplastic resin to produce a fiber.

  The fibers may contain a plasticizer having at least one of a lower melt flow rate than the thermoplastic resin and a lower melt viscosity than the thermoplastic resin. In this case, by adjusting the amount of the plasticizer, at least one of the melt flow rate and the melt viscosity of the fiber can be easily adjusted. Further, as the thermoplastic resin, it is possible to use a component whose melt flow rate is smaller than 1600 g / 10 min and whose melt viscosity is higher than 7000 mPa · s. Therefore, the degree of freedom in selecting the thermoplastic resin is increased.

  The plasticizer preferably has compatibility with the thermoplastic resin. In this case, bleeding out of the plasticizer from the fiber is suppressed. However, a material having no compatibility with the thermoplastic resin may be contained in the fiber as long as it is small enough to prevent bleed-out.

  The plasticizer may contain a liquid material such as oil, for example. Specifically, the plasticizer can contain, for example, one or more materials selected from the group consisting of liquid paraffin, petroleum-based lubricating oil, naphtha lubricating oil, silicone oil, synthetic oil such as fluorine-type oil, and grease.

  The plasticizer is in the range of, for example, 0.1 to 50% by mass based on the total of the thermoplastic resin and the plasticizer, but is not limited thereto.

  The melt viscosity of the resin and the plasticizer is measured using an Anton Paar Japan viscoelasticity measuring device MCR302 under a nitrogen atmosphere at 230 ° C. under a shear rate of 10 [1 / s]. Is the typical viscosity. The melt viscosity of the resin and the plasticizer is the melt viscosity at 230 ° C.

  The fibers in the fiber assembly can include an antioxidant. In this case, the heat resistance of the fiber assembly is improved. Further, when spinning a spinning material containing a base resin to produce fibers, an antioxidant may be added to the spinning material to knead the material, spin the base resin at the time of spinning, and absorb sound after spinning. Oxidation degradation of the material is suppressed.

  The antioxidant may be mixed with the raw material of the base resin when synthesizing the material such as the base resin. The antioxidant may be mixed with a base resin or the like at the time of preparing the spinning material.

  Antioxidants include, for example, phenolic antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, amine-based antioxidants, hydrazine-based antioxidants, amide-based antioxidants, and light stabilizers (HALS). At least one material selected from the group consisting of:

  In particular, when the antioxidant contains a phenolic antioxidant, long-term heat resistance of the fiber aggregate can be improved. The phenolic antioxidant may be any of a hindered type, a semi-hindered type, and a less hindered type. When the antioxidant contains at least one of a phosphorus-based antioxidant and a sulfur-based antioxidant in addition to the phenol-based antioxidant, oxidative deterioration of the base resin and the like during spinning is further suppressed.

  It is particularly preferable that the antioxidant contains both a phenolic antioxidant and a phosphorus antioxidant. By combining such two kinds of antioxidants, the heat resistance of the fiber assembly is improved and the high heat resistance is maintained for a long time. In other words, even at high temperatures, high absorption of mid-range sounds is maintained for a long period of time.

  When the fiber contains a phenolic antioxidant and a phosphorus-based antioxidant, the total percentage of the phenolic antioxidant and the phosphorus-based antioxidant to the thermoplastic resin is 0.1 to 2.0% by mass. It is preferable that it is within the range. When the percentage is 0.1% by mass or more, the oxidative deterioration of the fiber can be particularly suppressed. If the percentage is more than 2.0% by mass, the effect of suppressing the oxidative deterioration of the fiber aggregate is saturated, and the amounts of the phenolic antioxidant and the phosphorus antioxidant are unnecessarily increased. The percentage is preferably 2.0% by mass or less because of economic disadvantage. The mass ratio of the phenolic antioxidant to the phosphorus antioxidant is preferably in the range of 1.0 / 3.0 to 3.0 / 1.0. When this mass ratio is 1.0 / 3.0 or more, high heat resistance is maintained particularly for a long time. When the mass ratio is 3.0 / 1.0 or less, the heat resistance of the fiber assembly is particularly increased. Furthermore, consumption of a phenolic antioxidant when obtaining fibers by spinning can be suppressed.

  The fibers may contain additives such as weather stabilizers, light stabilizers, anti-blocking agents, lubricants, nucleating agents, pigments, softeners, hydrophilic materials, auxiliaries, water repellents, fillers, and antibacterial agents.

  The fibers can be produced, for example, by spinning a spinning material containing a thermoplastic resin, as described above.

  The composition of the spinning material is determined to match the composition of the fiber. That is, the spinning material can include a plasticizer. The spinning material can also include an antioxidant. The spinning material may contain a phenolic antioxidant and a phosphorus antioxidant. In addition, the material for spinning contains additives such as weather stabilizers, light stabilizers, antiblocking agents, lubricants, nucleating agents, pigments, softeners, hydrophilic materials, auxiliaries, water repellents, fillers, and antibacterial agents. You may.

  For preparing the spinning material, for example, the components of the spinning material may be dry-blended, or the components of the spinning material may be mixed while being heated and melted. In the case where the components of the spinning material are mixed while being heated and melted, the components may be mixed in a heating vessel in a batch system or in a continuous spin extruder. When mixing with a continuous spinning extruder, the spinning extruder may be any of a single-screw, twin-screw and multi-screw extruder.

  As a method of spinning the spinning material, a melt spinning method such as a melt blown method and an electrospinning method can be applied. In this case, the fiber can be manufactured stably.

  When producing a fiber by a melt spinning method, for example, a material for spinning is first melted by heating. When the spinning material is prepared by a continuous spinning extruder, the spinning material is prepared in a molten state. The melted spinning material is discharged from a nozzle. The spinning material may be drawn by blowing a heated airflow onto the spinning material discharged from the nozzle. The direction of the air flow may be a direction along the discharge direction of the spinning material from the nozzle, or may be a direction different from this discharge direction. The fiber may be drawn by applying a voltage to the spinning material discharged from the nozzle. Thereby, a fiber can be manufactured.

  The diameter of the fiber, depending on the composition of the spinning material, for example, heating conditions when melting the spinning material, the hole diameter of the nozzle, the discharge amount of the spinning material from the nozzle, the temperature of the airflow when blowing the airflow and It can be controlled by adjusting the flow rate and the voltage application conditions when applying the voltage.

The heating temperature for melting the material for spinning depends on the composition of the material for spinning, but is higher than the melting point or softening point of the thermoplastic resin in the material for spinning by 10 ° C. or higher and lower than the thermal decomposition temperature of the thermoplastic resin. Is preferably within the range. The discharge amount of the spinning material from the nozzle is preferably in the range of 0.05 to 0.5 g / min per one hole of the nozzle. When an air stream is blown onto the fiber during spinning, the temperature of the air stream is preferably in the range of 200 to 450 ° C. The flow rate of the air current is preferably in the range of 50 to 500 Nm ³ / hour · m.

  When producing a fiber, as described above, a fiber containing the specific component may be produced by thermally decomposing the specific raw material to obtain a specific component whose molecular weight is adjusted.

  In the thermal decomposition of the specific raw material, for example, before preparing the material for spinning, the specific raw material is preferably placed in an inert atmosphere (for example, under a nitrogen atmosphere) or under a reduced pressure at a temperature at which thermal decomposition of the specific raw material occurs. By arranging, the specific raw material is thermally decomposed. This temperature depends on the type of the specific raw material, and is, for example, 300 ° C. or more when the specific raw material is a polypropylene resin. The thermal decomposition of the specific raw material may be carried out batchwise in a heating vessel, or may be carried out continuously in a closed continuous reactor. The spinning material can be prepared by mixing the specific component obtained as described above with a component other than the specific component of the fiber. By spinning the spinning material, a fiber containing a specific component can be produced.

  A specific raw material and a component other than the specific component of the fiber are mixed to prepare a spinning material containing the specific raw material, and when the spinning material is spun to produce a fiber, the specific raw material in the spinning material is heated. By decomposing, a fiber containing a specific component may be produced. For example, when producing a fiber by melt-spinning a spinning material as described above, the temperature at which the spinning material is melted is set to a temperature at which thermal decomposition of the specific raw material occurs in the spinning material. May be thermally decomposed. However, in order to produce the fiber aggregate more stably, it is preferable to thermally decompose the specific raw material before preparing the spinning material.

  The temperature at which thermal decomposition occurs is, for example, a temperature at which the weight of the specific raw material decreases under an inert atmosphere, or a temperature at which the melt viscosity of the specific raw material decreases under an inert atmosphere.

  In the present embodiment, since the fiber has at least one of a melt flow rate in a range of 1600 to 5000 g / 10 min and a melt viscosity in a range of 250 to 7000 mPa · s, such a fiber is described above. The fiber can be manufactured stably by the melt spinning method, whereby the fiber having a diameter of 8 μm or less and the number of fibers of 99% or more can be manufactured stably.

  By assembling the fibers, a fiber aggregate is obtained. It is preferable that the fibers are intertwined in the fiber assembly. The fiber aggregate is, for example, a non-woven fabric, but is not limited thereto.

  Preferably, the fiber aggregate is subjected to an annealing treatment. For example, it is preferable to treat the fiber assembly at a heating temperature of 100 ° C. for 2 hours. The annealing promotes the crystallization of the fiber and increases the shape stability of the fiber aggregate.

  The sound absorbing material may be composed of only the fiber aggregate, or may include a fiber aggregate and a support that supports the fiber aggregate. The support is, for example, a microfiber nonwoven fabric. The sound absorbing material may include a fiber assembly and a bag containing the fiber assembly. The bag is made of, for example, a microfiber nonwoven fabric. In order to support the fiber aggregate on the support, the fiber aggregate may be thermally fused to the support by hot pressing or blowing hot air.

  The fiber aggregate preferably has a heat resistance of 120 ° C. This heat resistance is evaluated based on the vertical sound absorption coefficient of the fiber assembly after subjecting the fiber assembly to a process of exposing it to a high-temperature air atmosphere at 120 ° C. for 500 hours. If the fiber assembly after the treatment has a sound absorption of not less than 20% at 600 Hz and a sound absorption of not less than 50% at 1000 Hz, it is evaluated as having a heat resistance of 120 ° C.

  Such high heat resistance can be achieved by appropriately adjusting the composition of the fibers constituting the fiber assembly within the range described above.

(1) Production of fiber aggregates of Examples and Comparative Examples Except for Example 10, the components shown in the column of “Composition” in the table below were melted at 200 ° C. under inert conditions. , And solidified by cooling to room temperature, and further pulverized to obtain a spinning material.

  In the case of Example 10, components other than the antioxidant among the components shown in the column of “Composition” in the table below were placed in a reaction vessel under a nitrogen atmosphere to obtain a mixture. The mixture was heated to 350 ° C. while stirring the mixture in the reaction vessel, and then maintained for 10 minutes to thermally decompose the PP resin (f) in the mixture. Subsequently, the mixture was cooled to 200 ° C. Subsequently, an antioxidant was added to the mixture, and the mixture was mixed for 5 minutes. After cooling to room temperature, the mixture was solidified and further pulverized to obtain a spinning material.

  The fiber was obtained by spinning the spinning material by a melt spinning method. Specifically, after the spinning material was melted, an airflow was blown onto the spinning material while discharging the spinning material from a nozzle to obtain fibers. The conditions of the heating temperature for melting the spinning material, the discharge amount of the spinning material per one hole of the nozzle, the hole diameter of the nozzle, the temperature of the airflow, and the speed of the airflow are shown in the "Spinning conditions" column in the table. As shown in FIG. In the case of Comparative Example 3, a nozzle having a 0.25 mm diameter hole and a 1.0 mm diameter hole in a quantity ratio of 15: 1 was used. The discharge amount of the spinning material was adjusted by extruding a predetermined amount of the spinning material from an independent extruder for each value of the nozzle hole diameter.

Further, the fibers formed by cooling the spinning material discharged from the nozzles were collected on a conveyor to obtain a non-woven fiber aggregate. The feed speed of the conveyor was adjusted such that the basis weight of the fiber assembly was 400 g / m ² . In the case of Example 11, a fiber aggregate was prepared on a spunbonded nonwoven fabric having a basis weight of 20 g / m ² , and then the spunbonded nonwoven fabric and the fiber aggregate were bonded by a hot roll press.

The details of the components in the table below are as follows.
-PP resin (a): Polypropylene resin manufactured by Sun Allomer Co., product number PWH00N, weight average molecular weight 87,000, melt flow rate 1700 g / 10 min, 230 ° C melt viscosity 6000 mPa · s, melting point 166 ° C.
-PP resin (b): crystalline polypropylene resin (homopolymer) manufactured by Mitsui Chemicals, Inc., product number NP805, weight average molecular weight 35,000, melt flow rate 3500 g / 10 min, 230 ° C melt viscosity 800 mPa · s, melting point 155 ° C .
-PP resin (c): Crystalline polypropylene resin (homopolymer) manufactured by Mitsui Chemicals, Inc., product number NP500, weight average molecular weight 35,000, melt flow rate 5000 g / 10 min, 230 ° C melt viscosity 270 mPa · s, melting point 164 ° C .
-PP resin (d): crystalline polypropylene resin (homopolymer) manufactured by Mitsui Chemicals, Inc., product number NP055, weight average molecular weight 1,000,000, melt flow rate 6000 g / 10 min, 230 ° C melt viscosity 25 mPa · s, melting point 145 ° C .
PP resin (e): polypropylene resin manufactured by Total Petrochemical, product number 3962, weight average molecular weight 145,000, melt flow rate 1300 g / 10 min, 230 ° C melt viscosity 7500 mPa · s, melting point 165 ° C.
-PP resin (f): Polyimiley polypropylene resin, product number HP461X, weight average molecular weight 150,000, melt flow rate 1100 g / 10 min, 230 ° C melt viscosity 8600 mPa · s, melting point 168 ° C.
-PE resin: polyethylene wax manufactured by Mitsui Chemicals, product number 40800, melt viscosity at 230 ° C 135 mPa · s, melting point 130 ° C.
-Paraffin: Paraffin wax manufactured by Nippon Seiro Co., Ltd., product number FT115, 230 ° C melt viscosity 5 mPa · s, melting point 113 ° C.
-Thermoplastic elastomer: ExxonMobil Co., Ltd. product name VISTAMAXX, product number 6202, melt flow rate 20 g / 10 min, 230 ° C melt viscosity 196,000 mPa · s, softening point 94 ° C.
Phenolic antioxidant: Phenolic antioxidant manufactured by BASF, trade name IRGANOX 1010.
-Phosphorus antioxidant: Adeka Co., Ltd. phosphorous antioxidant, trade name ADK STAB PEP-36.

(2) Evaluation test The following evaluation tests were performed for each example and comparative example. The results are shown in the column of “Evaluation test” in the table below.

  In the case of Comparative Example 4, it was difficult to form a fiber even if the material for spinning was spun. However, only a formed body that can be regarded as a fiber was collected to produce a fiber aggregate, and the fiber assembly was evaluated. Was done.

(2-1) Melt flow rate evaluation test The melt flow rate of the fibers in the fiber assembly was measured in accordance with ASTM D-1238. The measurement conditions for the melt flow rate are determined according to the type of the thermoplastic resin in the spinning material used to produce the fiber, and the thermoplastic resin in the spinning material contains two or more resins. In this case, the determination was made according to the type of the resin having the largest mass ratio.

(2-2) Melt Viscosity Evaluation Test Using a viscoelasticity measuring device (model number MCR302) manufactured by Anton Paar Japan, the melt viscosity at 230 ° C. of the fibers in the fiber assembly was measured under a nitrogen atmosphere and a shear rate. It was measured under the condition of 10 [1 / s].

(2-3) Measurement of Fiber Diameter After attaching the fiber in the fiber assembly to a 3 mm × 3 mm area of the carbon tape, the fiber was coated with Au by evaporating Au onto the fiber for about 2 minutes. Subsequently, using a scanning electron microscope (manufactured by Keyence Corporation, model number VE-7800), an image of 3000 times the fiber was obtained. The image was subjected to image processing to measure the diameters of arbitrary 200 fibers, and the median of the diameters of the fibers was calculated from the measurement results.

  In addition, from the measurement results, the ratio of the number of fibers having a diameter of 10 μm or more, the ratio of the number of fibers having a diameter of 8 μm or less, and the ratio of the number of fibers having a diameter of 5 μm or less among the 200 fibers Was calculated.

(2-4) Weight and Density The fibrous aggregate was cut to produce ten samples having a size of 50 mm x 50 mm in plan view. The mass of the sample was measured, and the average value of the mass was calculated from the result. The weight per unit area of the fiber assembly was calculated by dividing the average value of the mass of the sample by the area of the sample in plan view.

  The thickness of the center of each of the four sides of the sample was measured with a vernier caliper, and the average value of the thickness of the sample was calculated from the measurement result. The value obtained by multiplying the area of the sample in plan view by the average value of the thickness of the sample was defined as the average value of the volume of the sample. The density of the fiber aggregate was calculated by dividing the average value of the mass of the sample by the average value of the volume of the sample.

(2-5) Sound Absorption Characteristic Test A test piece having a diameter of 29 mm in a plan view was cut out from the fiber assembly. Based on JIS A1405-2, a vertical sound absorption system equipped with an acoustic impedance tube (Model No. DS-200, manufactured by Ono Sokki Co., Ltd.) was used to determine the vertical incidence sound absorption coefficient of each of the frequencies of 600 Hz, 1000 Hz, and 1500 Hz. ).

(2-6) Heat resistance test After heating the fiber assembly at the above-mentioned sound absorption characteristic test for 500 hours at 120 ° C, the same method as in the case of the above-mentioned sound absorption characteristic test was applied to each of the frequencies of 600 Hz, 1000 Hz and 1500 Hz. The normal incidence sound absorption coefficient of the sound was measured.

Claims (9)

An aggregate of fibers containing a thermoplastic resin,
The fiber has a melt viscosity in the range of 250 to 7000 mPas,
The median value of the fiber diameter is in the range of 0.3 μm to 0.9 μm,
A fiber aggregate, wherein the number of fibers having a diameter of 8 µm or less with respect to the whole fibers is 99% or more. The fiber has a melt viscosity in the range of 250 to 3000 mPa · s,
The fiber assembly according to claim 1. Having a density of not more than 0.03 g / cm ³ ,
The fiber assembly according to claim 1. The thermoplastic resin contains two or more resins,
The resins have different melt viscosities,
The fiber aggregate according to any one of claims 1 to 3. The thermoplastic resin contains at least one component selected from the group consisting of polypropylene, polyethylene, a polyolefin-based thermoplastic elastomer and paraffin,
The fiber aggregate according to any one of claims 1 to 4. The fiber contains a plasticizer,
The plasticizer has a lower melt viscosity than the thermoplastic resin,
The fiber aggregate according to any one of claims 1 to 5. The fiber assembly according to any one of claims 1 to 6, which has a heat resistance of 120 ° C. A sound-absorbing material comprising the fiber aggregate according to any one of claims 1 to 7. The sound absorbing material according to claim 8, which is for use in a vehicle.