Hollow structure, tube, energy-absorbing molded article, and method for manufacturing tube

Abstract

Provided are a hollow structure, a tube, an energy-absorbing molded article, and a method for manufacturing a tube.　A hollow structure according to the present disclosure is a tube-shaped hollow structure formed from commingled yarn, the hollow structure is a braid of strands of the commingled yarn, and the commingled yarn comprises continuous thermoplastic resin fibers and continuous reinforcing fibers.

Description

Hollow structure, tube, energy-absorbing molded article, and method for manufacturing a tube

[0001] The present invention relates to hollow structures, tubes, energy-absorbing molded articles, and methods for manufacturing tubes. In particular, it relates to hollow structures formed from blended yarns containing continuous thermoplastic resin fibers and continuous reinforcing fibers.

[0002] Continuous reinforcing fibers, such as continuous carbon fibers, are used as reinforcing materials for resins due to their excellent strength. Prepregs are known as examples of resin materials reinforced with continuous reinforcing fibers. One example of a prepreg is UD tape (Uni-directional Tape), known as a unidirectional continuous fiber reinforced resin material. Another example of a prepreg is a material in which woven continuous reinforcing fibers are impregnated with resin. Both thermosetting resins and thermoplastic resins can be used in such prepregs. In particular, thermosetting resins are used for hollow tube structures due to their strength. However, hollow structures using thermosetting resins have the problem of requiring a long curing time and being difficult to mold afterward. Therefore, Patent Document 1 describes braiding a tubular material made of a composite of carbon fiber and thermoplastic resin. Furthermore, the composite material of carbon fiber and thermoplastic resin is described as a composite tape material of unidirectional carbon fiber and thermoplastic resin. Furthermore, carbon fiber composite materials using thermosetting resins have almost no plasticity, and while epoxy-based carbon fiber composite materials exhibit high strength and elastic modulus, they have the drawback of rapid fracture progression.

[0003] International Publication No. 2020 / 226122

[0004] Here, as the fiber-reinforced resin material constituting the tube, prepregs containing thermosetting resins and carbon fiber fabrics and UD tapes containing thermosetting resins are known. However, as a result of the inventor's examination, it was found that tubes formed from these fiber-reinforced thermosetting resin materials are inferior in energy absorption. On the other hand, regarding the case of using a braided cord formed from a UD tape, which is a fiber-reinforced thermoplastic resin material, as described in Patent Document 1, it was also found that it cannot be applied to tubes having a bent structure or tubes with a varying diameter, and the degree of freedom in the shape that can be processed is low. The present invention aims to solve such problems, and provides a hollow structure capable of being formed into a desired shape and having high load resistance and energy absorption, as well as a tube, an energy absorption molded product, and a method for manufacturing a tube.

[0005] Based on the above problems, the inventors conducted research and found that the above problems can be solved by forming a tubular hollow structure, which is a braided cord, using a blended yarn containing continuous thermoplastic resin fibers and continuous reinforcing fibers. Specifically, the above problems were solved by the following means: [1] A tubular hollow structure formed from a blended yarn, wherein the hollow structure is a braided cord of blended yarn, and the blended yarn contains continuous thermoplastic resin fibers and continuous reinforcing fibers. [2] A tubular hollow structure formed from a blended yarn, wherein three or more units of blended yarn intersect at an angle greater than 0° and less than 90° according to a certain regularity, the blended yarn contains continuous thermoplastic resin fibers and continuous reinforcing fibers, and the hollow structure has no breaks in the cross-sectional direction perpendicular to the longitudinal direction. [3] The hollow structure according to [1] or [2], wherein the continuous thermoplastic resin fibers contain polyamide resin. [4] The hollow structure according to [3], wherein the polyamide resin comprises a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, wherein 70 mol% or more of the diamine-derived structural unit is a xylylenediamine-derived structural unit, and 70 mol% or more of the dicarboxylic acid-derived structural unit is a C4-C20 α,ω-dicarboxylic acid-derived structural unit. [5] The hollow structure according to any one of [1] to [4], wherein the thermoplastic resin constituting the continuous thermoplastic resin fiber has a tensile modulus of 2.0 to 5.0 GPa as measured according to ISO 527-1. [6] The hollow structure according to any one of [1] to [5], wherein the continuous reinforcing fiber comprises a continuous carbon fiber. [7] The hollow structure according to any one of [1] to [6], wherein the continuous thermoplastic resin fiber comprises a polyamide resin, the polyamide resin comprises a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, 70 mol% or more of the diamine-derived structural unit is a xylylenediamine-derived structural unit, and 70 mol% or more of the dicarboxylic acid-derived structural unit is a carbon-4 to carbon-20 α,ω-dicarboxylic acid-derived structural unit, the thermoplastic resin constituting the continuous thermoplastic resin fiber has a tensile modulus of 2.0 to 5.0 GPa as measured in accordance with ISO 527-1, and the continuous reinforcing fiber comprises a continuous carbon fiber.A tube formed from a structure containing a hollow structure as described in any one of [8] [1] to [7]. An energy-absorbing molded article formed from a structure containing a hollow structure as described in any one of [9] [1] to [7]. A method for manufacturing a tube, comprising applying pressure to the hollow portion of a structure containing a hollow structure as described in any one of [1] to [7], and applying a temperature to the hollow portion that is above the melting point of the thermoplastic resin constituting the continuous thermoplastic resin fibers.

[0006] The present invention provides a hollow structure that can be molded into a desired shape and provides a tube with high load resistance and energy absorption, as well as a tube, an energy-absorbing molded product, and a method for manufacturing a tube.

[0007] Figure 1 is a schematic diagram showing an example of a hollow structure viewed from the outside. Figure 2 is a schematic diagram showing the process of manufacturing a hollow structure using a prepreg made by impregnating a continuous reinforced fiber fabric with resin. Figure 3 is a schematic diagram showing an example of a structure including the hollow structure of this embodiment. Figure 4 is a schematic diagram showing an example of a method for manufacturing the hollow structure of this embodiment.

[0008] Hereinafter, embodiments for carrying out the present invention (hereinafter simply referred to as "these embodiments") will be described in detail. These embodiments are illustrative examples for explaining the present invention, and the present invention is not limited to these embodiments. In this specification, "~" is used to mean that the numerical values ​​before and after it include the lower and upper limits. Furthermore, the upper and lower limits of numerical values ​​in this specification are given as examples of these embodiments, regardless of the combination of the upper and lower limits. In this specification, preferred combinations of embodiments are more preferred embodiments. In this specification, all physical properties and characteristic values ​​are given at 23°C unless otherwise specified.

[0009] In this specification, unless otherwise specified, the number-average molecular weight shall be the value measured by the following method. The number-average molecular weight (Mn) shall be determined from the value converted to standard polymethyl methacrylate (PMMA) by gel permeation chromatography (GPC). Two columns packed with styrene polymer as the packing material shall be used, and hexafluoroisopropanol (HFIP) with a sodium trifluoroacetate concentration of 2 mmol / L shall be used as the solvent, with a resin concentration of 0.02% by mass, a column temperature of 40°C, a flow rate of 0.3 mL / min, and measurement shall be performed using a refractive index detector (RI). A calibration curve shall be obtained by dissolving six levels of PMMA in HFIP and measuring the values.

[0010] In this specification, the melting point (Tm) is measured using a differential scanning calorimeter (DSC). The sample amount is approximately 1 mg, nitrogen is flowed as the ambient gas at 30 mL / min, and the heating rate is 10 °C / min. The sample is heated to a temperature above the melting point expected from room temperature, and the melting point (Tm) is determined from the temperature of the peak top of the endothermic peak observed when the sample is melted. The unit is °C. The differential scanning calorimeter used is the "DSC-60" manufactured by Shimadzu Corporation.

[0011] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the intended function of the process is achieved. In this specification, ppm means mass ppm. In this specification, a tube is also called a pipe or cylinder. A tube is usually a structure that is long relative to its cross-section and has a hollow interior. If the measurement methods etc. described in the standards shown in this specification differ from year to year, unless otherwise specified, the standards as of January 1, 2024 shall apply. If the measurement methods etc. described in the standards shown in this specification have been abolished as of January 1, 2024, the standards at the time of abolition shall apply. Figures 1 to 3 may not be consistent with reality in terms of scale, etc.

[0012] The hollow structure of this embodiment is a tubular hollow structure formed from blended yarn, the hollow structure is a braid of blended yarn, and the blended yarn includes continuous thermoplastic resin fibers and continuous reinforcing fibers. Furthermore, the hollow structure of this embodiment is a tubular hollow structure formed from blended yarn, the hollow structure is formed in which three or more units of blended yarn intersect at an angle greater than 0° and less than 90° according to a certain regularity, the blended yarn includes continuous thermoplastic resin fibers and continuous reinforcing fibers, and the hollow structure has no breaks in the cross-sectional direction perpendicular to the longitudinal direction. Such a hollow structure is moldable into a desired shape and is a hollow structure that can provide a tube with high load resistance and energy absorption.

[0013] The embodiments of the present invention will be described in detail below, but the description of the constituent elements described below is merely one example of an embodiment of the present invention and is not limited to these.

[0014] The hollow structure of this embodiment is a tubular hollow structure formed from blended yarn. Here, "formed from blended yarn" means that it may be formed solely from blended yarn, or it may contain other materials without departing from the spirit of the present invention. Typically, 90% or more by mass of the material constituting the tubular hollow structure is blended yarn, preferably 95% or more by mass is blended yarn, and it may also be 99% or more by mass is blended yarn, and 100% or less by mass is blended yarn. Examples of components other than blended yarn that form the tubular hollow structure include thread-like materials other than blended yarn that can be braided together with the blended yarn, as well as consolidators and surface treatment agents. Here, in this embodiment, the hollow structure typically consists of blended yarn containing continuous thermoplastic resin fibers and continuous reinforcing fibers in its original state. In this embodiment, typically, the hollow structure or a structure containing the hollow structure described later is heat-treated so that the continuous thermoplastic resin fibers impregnate the spaces between the continuous reinforcing fibers, forming a tube.

[0015] The hollow structure of this embodiment is either a braided cord of blended yarns, or a structure in which three or more units of blended yarns intersect at an angle greater than 0° but less than 90° according to a certain regularity, and there are no breaks in the cross-sectional direction perpendicular to the longitudinal direction. An example of a structure in which three or more units of blended yarns intersect at an angle greater than 0° but less than 90° according to a certain regularity, and there are no breaks in the cross-sectional direction perpendicular to the longitudinal direction, is a braided cord.

[0016] Figure 1 is a schematic diagram showing an example of a hollow structure of this embodiment as viewed from the outside. In Figure 1, the direction of the arrow is the longitudinal direction of the hollow structure, and when viewed from a direction perpendicular to the arrow, a cross-section having an opening (hollow part) of the hollow structure can be seen. That is, an example of a hollow structure is a cylindrical braid. Here, "cylindrical" includes not only a cylinder in the geometric sense, but also those that are normally considered cylindrical in the technical field of the present invention. As shown in Figure 1, the hollow structure of this embodiment preferably consists of a braid made of blended yarn 1. That is, the hollow structure of this embodiment does not consist of a braid made of blended yarn wrapped around a tube to form a hollow structure, but rather includes a braid that is a braided body made from blended yarn with a hollow in the center. In other words, the hollow structure includes a braid that is a braided body made from blended yarn. Therefore, an example of a hollow structure is a structure that includes a single braid. The braid is preferably a cord obtained by taking a blended yarn as one unit, arranging three or more units of this, and crossing them diagonally according to a certain regularity. The number of units constituting the braided cord is preferably four or more, more preferably eight or more, preferably 200 or less, more preferably 100 or less, and even more preferably 50 or less. It may also be 20 or 10 or less. Only one type of blended yarn may be used to constitute the braided cord, or two or more types may be used. Braided cords are known to be elastic cords and are preferable because they are neither too strong nor too weak and can flexibly respond to changes in pressure applied to the hollow structure. They are also preferable because their shape changes flexibly according to the mold and internal pressure when forming the tube.

[0017] By creating a braided cord (hollow structure) with a hollow section formed from blended fibers in this way, it is possible to create a hollow structure without breaks in the cross-sectional direction perpendicular to the longitudinal direction. In contrast, if a hollow structure is made using a prepreg made by impregnating a woven fabric of continuous reinforced fibers with resin, breaks will occur. Specifically, as shown in Figure 2, a hollow structure 22 obtained by rolling a prepreg 21 made by impregnating a woven fabric of continuous reinforced fibers with resin into a cylindrical shape has a break 23 in the cross-sectional direction perpendicular to the longitudinal direction of the hollow structure. Here, 21 in Figure 2 shows a view of the prepreg made by impregnating a woven fabric of continuous reinforced fibers with resin from the surface direction. Also, 22 in Figure 2 is a view of the prepreg made by impregnating a woven fabric of continuous reinforced fibers with resin into a cylindrical shape, viewed from the thickness direction of the prepreg (cross-sectional direction perpendicular to the longitudinal direction of the cylinder).

[0018] On the other hand, in the case of braided cords formed from UD tape, the degree of freedom in shape during processing is reduced. In particular, braided cords formed from UD tape have poor shape conformability, and the friction between the UD tapes is large and difficult to move, so the angle is fixed, making it difficult to change the shape according to the mold when forming a tube. It is also conceivable to make a tubular knitted fabric from blended yarn. However, the blended yarn would become entangled in an omega shape, making it difficult to exhibit the strength inherent in continuous reinforcement fibers.

[0019] In contrast, in this embodiment, a hollow structure is made of a braided blended yarn having a hollow section, making it possible to form a desired tube shape. Furthermore, the degree of freedom in rigidity design can be increased by adjusting the angle of the braid. That is, by making the intersection angle of the braid obtuse, the hollow structure can be made softer, and by making the intersection angle acute, the hollow structure can be made rigid. When the bending strength of the hollow structure or tube is important, an acute angle of 45° or less is preferable, and when the torsional strength of the hollow structure or tube is important, an obtuse angle of 45° or more is preferable. That is, in this embodiment, three or more units of blended yarn intersect at an angle greater than 0° and less than 90° according to a certain regularity, but it is preferable that at least one unit of braid intersects at 10° or more, more preferably at 30° or more, preferably at 80° or less, and even more preferably at 60° or less.

[0020] Furthermore, along with the above-mentioned blended yarn, thread-like materials other than blended yarn, such as continuous fibers (continuous thermoplastic resin fibers, continuous reinforcing fibers) and UD tape, may be incorporated into the braid as a single unit. In other words, a braid formed from blended yarn in this embodiment may be composed of a portion other than blended yarn.

[0021] The length of the hollow structure is usually 5 cm or more, preferably 10 cm or more, and may be 50 cm or more, 1 m or more, or 100 m or more depending on the application, etc. There is no limit to the length, but it is practical to keep it at 1000 m or less, and may be 100 m or less depending on the application, etc.

[0022] The cross-sectional shape of the hollow structure is not specifically defined, but circular and polygonal shapes are examples. Perfect circles, ellipses, oblongs, odd-numbered regular polygons with five or more sides, and even-numbered regular polygons with four or more sides are preferred because they improve energy absorption performance. For odd-numbered regular polygons with five or more sides, 5 to 21 sides are preferred. Similarly, for even-numbered regular polygons with four or more sides, 4 to 22 integer regular polygons are preferred. Here, "perfect circle" includes not only a perfect circle in a geometric sense, but also shapes that can be recognized as perfect circles in the technical field of this invention. The same applies to ellipses, oblongs, and regular polygons.

[0023] The outer diameter of the cross-section of the hollow structure is preferably 3 mm or more, more preferably 5 mm or more, even more preferably 10 mm or more, and preferably 1000 mm or less, more preferably 900 mm or less, and even more preferably 800 mm or less. The inner diameter of the cross-section of the hollow structure is preferably 2 mm or more, more preferably 4 mm or more, even more preferably 9 mm or more, and preferably 900 mm or less, more preferably 800 mm or less, and even more preferably 700 mm or less. Here, the outer diameter of the cross-section of the hollow structure is the diameter of a circle having an area corresponding to the area of ​​the region formed by the outer circumference of the hollow structure. The inner diameter of the cross-section of the hollow structure is the diameter of a circle having an area corresponding to the area of ​​the region formed by the inner circumference of the hollow structure.

[0024] The thickness of the hollow structure is preferably 0.1 mm or more, more preferably 0.2 mm or more, even more preferably 0.5 mm or more, and also preferably 5 mm or less, more preferably 2 mm or less, and even more preferably 1 mm or less. If the thickness of the hollow structure is not constant, the thickness is measured at any 100 locations and the average value is taken as the thickness.

[0025] The hollow structure of this embodiment may consist of only one layer of braided cord formed from blended yarns, or it may consist of two or more layers.

[0026] Next, the blended yarn that forms the hollow structure of this embodiment will be described. The blended yarn used in this embodiment includes continuous thermoplastic resin fibers and continuous reinforcing fibers. By including continuous thermoplastic resin fibers and continuous reinforcing fibers in this way, the hollow structure is flexible before heat processing, making it easy to process into the desired shape, and after heating, the thermoplastic resin easily impregnates between the continuous reinforcing fibers.

[0027] The blended yarn used in this embodiment includes continuous thermoplastic resin fibers. By using continuous thermoplastic resin fibers, the resulting molded product, such as a tube, can be made to be a molded product that easily absorbs energy. Continuous thermoplastic resin fibers refer to thermoplastic resin fibers having an average fiber length of more than 6 mm, preferably having an average fiber length of more than 10 mm, preferably having an average fiber length of more than 12 mm, more preferably having an average fiber length of more than 30 mm, and even more preferably having an average fiber length of more than 10 cm. There are no particular restrictions on the average fiber length of the continuous thermoplastic resin fibers used in this embodiment, but from the viewpoint of improving moldability, it is preferably 1 m or more, more preferably 100 m or more, even more preferably 1,000 m or more, and also preferably 20,000 m or less, more preferably 10,000 m or less, and even more preferably 7,000 m or less.

[0028] The type of thermoplastic resin constituting the continuous thermoplastic resin fibers is not particularly specified, but it is preferably a crystalline resin, and is preferably polyethylene resin, polypropylene resin, polyamide resin, polyimide resin, polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyphenylene sulfide resin, or polyether ether ketone resin, with polyamide resin, polyimide resin, or polyphenylene sulfide resin being more preferred. Furthermore, the thermoplastic resin constituting the continuous thermoplastic resin fibers is preferably having a tensile modulus of 1.5 to 5.0 GPa as measured in accordance with ISO 527-1. Setting it above the lower limit tends to improve the strength of the tube and the energy absorption. Conversely, setting it below the upper limit tends to improve the toughness of the tube and the energy absorption. The tensile modulus of the thermoplastic resin is preferably 1.5 GPa or higher, more preferably 1.8 GPa or higher, even more preferably 2.0 GPa or higher, even more preferably 2.5 GPa or higher, even more preferably 2.7 GPa or higher, even more preferably 3.0 GPa or higher, and also preferably 5.0 GPa or lower, more preferably 4.0 GPa or lower, even more preferably 3.5 GPa or lower, and even more preferably 3.2 GPa or lower. When the continuous thermoplastic resin fiber used in this embodiment is composed of two or more types of thermoplastic resins, the tensile modulus of the thermoplastic resins is the weighted average value.

[0029] In this embodiment, the thermoplastic resin constituting the continuous thermoplastic resin fiber more preferably includes a polyamide resin, and more preferably includes a polyamide resin (hereinafter sometimes referred to as "xylylenediamine-based polyamide resin") in which 70 mol% or more of the diamine-derived structural units are xylylenediamine-derived structural units, and 70 mol% or more of the dicarboxylic acid-derived structural units are α,ω-dicarboxylic acid-derived structural units having 4 to 20 carbon atoms.

[0030] The diamine units of the xylylenediamine-based polyamide resin are preferably derived from xylylenediamine (preferably para-xylylenediamine and / or meta-xylylenediamine) in amounts of 75 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and particularly most preferably 99 mol% or more.

[0031] The xylylenediamine is preferably para-xylylenediamine and / or meta-xylylenediamine. The xylylenediamine preferably contains 0 to 100 mol% meta-xylylenediamine and 100 to 0 mol% para-xylylenediamine (provided that the total of meta-xylylenediamine and para-xylylenediamine does not exceed 100 mol%), more preferably 20 to 100 mol% meta-xylylenediamine and 80 to 0 mol% para-xylylenediamine, and even more preferably 50 to 90 mol% meta-xylylenediamine and 50 to 10 mol% para-xylylenediamine. The xylylenediamine-based polyamide resin preferably has a total of para-xylylenediamine units and meta-xylylenediamine units that account for preferably 80 mol% or more, more preferably 85 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 98 mol% or more, and even more preferably 99 mol% or more of the diamine units. The upper limit for the total amount of the aforementioned para-xylylenediamine units and meta-xylylenediamine units is 100 mol%.

[0032] Diamines other than meta-xylylenediamine and para-xylylenediamine that can be used as raw material diamine components for xylylenediamine-based polyamide resins include aliphatic diamines such as tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine, as well as 1,3-bis( Examples include alicyclic diamines such as aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, and bis(aminomethyl)tricyclodecane, as well as aromatic ring-containing diamines such as bis(4-aminophenyl) ether, paraphenylenediamine, and bis(aminomethyl)naphthalene. One or more of these can be used in combination.

[0033] On the other hand, of the xylylenediamine-based polyamide resin, the dicarboxylic acid units preferably amount to 75 mol% or more, more preferably 80 mol% or more, even more preferably 85 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and especially most preferably 99 mol% or more, are derived from α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms.

[0034] For use as a raw material dicarboxylic acid component in xylylenediamine-based polyamide resins, the preferred α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms is more preferably a constituent unit derived from an α,ω-linear aliphatic dicarboxylic acid having 6 to 14 carbon atoms. Specific examples of α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms include succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, adipic acid, sebacic acid, undecanediic acid, and dodecanediic acid. One or more of these can be used in combination, but among these, adipic acid, sebacic acid, and dodecanediic acid are preferred, with sebacic acid being particularly preferred.

[0035] Examples of dicarboxylic acid components other than the above-mentioned α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms include phthalate compounds such as isophthalic acid, terephthalic acid, and orthophthalic acid, and naphthalenedicarboxylic acids such as 1,2-naphthalenedicarboxylic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. These dicarboxylic acid components can be used individually or in combination of two or more.

[0036] It should be noted that while xylylenediamine-based polyamide resins are mainly composed of diamine units and dicarboxylic acid units, they do not completely exclude other constituent units, and may contain lactams such as ε-caprolactam and laurolactam, as well as constituent units derived from aliphatic aminocarboxylic acids such as aminocaproic acid and aminoundecanoic acid. Here, "main component" refers to the constituent unit of the xylylenediamine-based polyamide resin in which the total number of diamine units and dicarboxylic acid units is the largest among all constituent units. In this embodiment, the total of diamine units and dicarboxylic acid units in the xylylenediamine-based polyamide resin preferably accounts for 90% by mass or more of the total constituent units, more preferably 95% by mass or more, even more preferably 97% by mass or more, and even more preferably 99% by mass or more.

[0037] Xylylenediamine-based polyamide resins may also preferably use polyamide resins manufactured using biomass raw materials (biomass polyamide resins). Using biomass polyamide resins can reduce the environmental impact. Mass balance certified (ISCC PLUS) raw material monomers can also be used. Mass balance certification means that the extent to which renewable or bio-based raw materials are used in each factory or production facility, and how much of the product is produced or shipped, is quantified and guaranteed along with quality.

[0038] The melting point of the xylylenediamine-based polyamide resin is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, even more preferably 180°C or higher, and also preferably 300°C or lower, more preferably 290°C or lower, even more preferably 280°C or lower, and even more preferably 275°C or lower. The melting point is measured according to the examples described later. If the blended yarn used in this embodiment contains two or more xylylenediamine-based polyamide resins, the weighted average value of each polyamide resin is used.

[0039] The xylylenediamine-based polyamide resin preferably has a lower limit of number average molecular weight (Mn) of 6,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and more preferably 100,000 or less, and more preferably 50,000 or less. Within this range, heat resistance, elastic modulus, dimensional stability, and moldability are improved.

[0040] The continuous thermoplastic resin fiber may contain polyamide resins other than xylylenediamine-based polyamide resins. Examples of polyamide resins other than xylylenediamine-based polyamide resins include aliphatic polyamide resins and semi-aromatic polyamide resins other than xylylenediamine-based polyamide resins. Examples of aliphatic polyamide resins include polyamide 4, polyamide 46, polyamide 6, polyamide 66, polyamide 666, polyamide 610, polyamide 11, polyamide 12, etc., with polyamide 6, polyamide 66, and polyamide 666 being preferred, and polyamide 6 being more preferred. Examples of semi-aromatic polyamide resins include terephthalic acid-based polyamide resins (polyamide 6T, polyamide 9T, polyamide 10T).

[0041] The continuous thermoplastic resin fibers may contain components other than the thermoplastic resin (preferably a polyamide resin, more preferably a xylylenediamine-based polyamide resin), and the content thereof is preferably less than 10% by mass of the content of the xylylenediamine-based polyamide resin, more preferably less than 5% by mass, still more preferably less than 3% by mass, and even more preferably less than 1% by mass.

[0042] The continuous thermoplastic resin fibers may be surface-treated with a surface treatment agent. The continuous thermoplastic resin fibers may be drawn or may not be drawn. In the present embodiment, it is preferable that they are not drawn. By not being drawn, a mixed fiber yarn having better flexibility can be obtained.

[0043] Additives such as antioxidants, stabilizers such as heat stabilizers, hydrolysis resistance improvers, weather stabilizers, matting agents, ultraviolet absorbers, nucleating agents, plasticizers, dispersants, flame retardants, antistatic agents, anti-coloring agents, anti-gelling agents, coloring agents, mold release agents, etc. can be added to the continuous thermoplastic resin fibers. Details of these can be referred to the descriptions in paragraph numbers 0130 to 0155 of Japanese Patent No. 4894982 and paragraphs 0047 to 0103 of International Publication No. 2021 / 241471, and the contents of these are incorporated into this specification.

[0044] Further, the mixed fiber yarn used in the present embodiment contains continuous reinforcing fibers. The continuous reinforcing fibers refer to reinforcing fibers having an average fiber length exceeding 6 mm, preferably exceeding 10 mm, more preferably exceeding 12 mm, still more preferably exceeding 30 mm, and even more preferably exceeding 10 cm. Although there is no particular limitation on the average fiber length of the continuous reinforcing fibers used in the present embodiment, from the viewpoint of improving the molding processability, it is preferably 1 m or more, more preferably 100 m or more, still more preferably 1,000 m or more, and preferably 20,000 m or less, more preferably 10,000 m or less, and still more preferably 7,000 m or less.

[0045] Examples of continuous reinforcing fibers include inorganic fibers such as glass fibers, carbon fibers, metal fibers, boron fibers, basalt fibers, and ceramic fibers; and organic fibers such as aramid fibers, polyoxymethylene fibers, aromatic polyamide fibers, poly(p-phenylenebenzobisoxazole) fibers, and ultra-high molecular weight polyethylene fibers. Among these, it is preferable to include at least one selected from the group consisting of carbon fibers, glass fibers, and aramid fibers, with carbon fibers and / or glass fibers being more preferable, and carbon fibers (continuous carbon fibers) being even more preferable. Examples of carbon fibers include polyacrylonitrile-based carbon fibers and pitch-based carbon fibers. As glass fibers, fibers obtained by melt-spinning glass such as E-glass, C-glass, A-glass, S-glass, and alkali-resistant glass, which are generally supplied, are used.

[0046] The continuous reinforcing fibers may be surface-treated with a surface treatment agent. The cross-section of the continuous reinforcing fibers may be circular or non-circular. In addition to the above, the description in paragraph 0074 of Japanese Patent No. 7398028 may be considered as a continuous carbon fiber, and this content is incorporated herein. The continuous reinforcing fibers in this embodiment are usually oriented in one direction.

[0047] For continuous reinforcement fibers, carbon fibers preferably have a tensile strength of 1500 MPa or more, more preferably 2500 MPa or more, and even more preferably 3500 MPa or more. There is no particular upper limit, but it is practical to have a tensile strength of 8000 MPa or less. For glass fibers, the tensile strength preferably has a tensile strength of 800 MPa or more, more preferably 1800 MPa or more, and even more preferably 2800 MPa or more. There is no particular upper limit, but it is practical to have a tensile strength of 5000 MPa or less. The tensile strength of the fibers is measured according to JIS R7606.

[0048] The conjugate fiber used in this embodiment may or may not contain other components other than continuous thermoplastic resin fibers and continuous reinforcing fibers. Examples of the other components include fillers other than continuous reinforcing fibers, nucleating agents, stabilizers such as antioxidants and heat stabilizers, hydrolysis resistance improvers, weather stabilizers, matting agents, ultraviolet absorbers, nucleating agents, plasticizers, dispersants, flame retardants, antistatic agents, anti-coloring agents, anti-gelling agents, coloring agents, mold release agents, and other additives. Details of these can be referred to the descriptions in paragraphs 0130 to 0155 of Japanese Patent No. 4894982 and paragraphs 0047 to 0103 of International Publication No. 2021 / 241471, and the contents of these are incorporated into this specification. The content of these other components is preferably less than 10% by mass of the conjugate fiber, more preferably less than 5% by mass, still more preferably less than 3% by mass, and even more preferably less than 1% by mass.

[0049] The conjugate fiber used in this embodiment is usually produced using a continuous thermoplastic resin fiber bundle and a continuous reinforcing fiber bundle. It is preferable to use continuous reinforcing fibers and / or continuous thermoplastic resin fibers for the conjugate fiber that are surface-treated with a treatment agent. By adopting such a configuration, it becomes easier to obtain a conjugate fiber in which the continuous reinforcing fibers and the continuous thermoplastic resin fibers are more uniformly dispersed, and the impregnation rate of the continuous thermoplastic resin fiber component into the continuous reinforcing fibers after molding can be improved.

[0050] The blended yarn used in this embodiment typically contains 2 to 1,000 (preferably 10 to 100) continuous thermoplastic resin fibers and 3,000 to 50,000 (preferably 12,000 to 24,000) continuous reinforcing fibers per strand. Preferably, the blended yarn used in this embodiment has continuous reinforcing fibers dispersed within it, and the continuous reinforcing fibers and continuous thermoplastic resin fibers are bundled or tape-shaped. When forming them into bundles or tapes, it is preferable to use a consolidating agent or a surface treatment agent. Furthermore, in the blended yarn used in this embodiment, it is preferable that the continuous thermoplastic resin fibers are not impregnated into the continuous reinforcing fibers and maintain their fibrous state, from the viewpoint of having the flexibility necessary when manufacturing hollow structures. In addition, in the blended yarn used in this embodiment, a portion of the continuous thermoplastic resin fiber component may be impregnated into the continuous reinforcing fibers. Specifically, in the blended yarn used in this embodiment, the impregnation rate of the continuous thermoplastic resin fiber component is less than 50%, preferably less than 10%, and more preferably less than 5%. There is no specific lower limit for the impregnation rate, and it may be 0%. Furthermore, if a portion of the thermoplastic resin fiber component is impregnated into the continuous reinforcing fiber, the blended yarn may be in tape form. Partial impregnation makes the fiber less prone to fraying and provides the flexibility necessary for manufacturing hollow structures. It also maintains fray resistance and flexibility when molding the hollow structure to manufacture tubes.

[0051] <<Method for Measuring Impregnation Rate>> For the blended yarn, a cross section perpendicular to the longitudinal direction of the continuous reinforcing fibers is cut together, embedded in epoxy resin, the surface corresponding to the cross section of the blended yarn is polished, and the cross-sectional view is photographed using an ultra-deep color 3D shape measuring microscope. The cross section of the blended yarn embedded in epoxy resin is observed with a digital microscope. From the obtained cross-sectional photograph, the region in which thermoplastic resin fibers have impregnated the continuous reinforcing fibers (the region in which thermoplastic resin fibers have melted and impregnated between the continuous reinforcing fibers) is selected using the image analysis software ImageJ, and its area is measured. The impregnation rate is expressed as the region in which thermoplastic resin fibers have impregnated the continuous reinforcing fibers / cross-sectional area (unit: %). The ultra-deep color 3D shape measuring microscope used was the VK-9500 (controller unit) / VK-9510 (measurement unit) (manufactured by Keyence).

[0052] It is preferable that the blended yarn is treated with a treatment agent such as a consolidating agent or a surface treatment agent. This configuration increases the dispersion of the continuous reinforcing fibers in the blended yarn, making it easier to form into bundles or tapes. Examples of treatment agents include ester compounds, alkylene glycol compounds, polyolefin compounds, and phenyl ether compounds. Compounds that function as surfactants are particularly preferred.

[0053] Furthermore, the proportion of continuous reinforcing fibers in the blended yarn is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, particularly preferably 50% by mass or more, and can also be 55% by mass or more. The upper limit of the proportion of continuous reinforcing fibers in the blended yarn is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and can also be 65% by mass or less. The blended yarn used in this embodiment may contain only one type of continuous reinforcing fiber, or it may contain two or more types. When two or more types are included, it is preferable that the total amount is within the above range.

[0054] The proportion of continuous thermoplastic resin fibers in the blended yarn is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and can also be 35% by mass or more. The upper limit of the proportion of continuous thermoplastic resin fibers is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, even more preferably 70% by mass or less, even more preferably 60% by mass or less, particularly preferably 50% by mass or less, and can also be 45% by mass or less. The blended yarn used in this embodiment may contain only one type of continuous thermoplastic resin fiber, or it may contain two or more types. When two or more types are included, it is preferable that the total amount is within the above range.

[0055] Furthermore, in this embodiment, the blended yarn preferably contains 90% or more by mass of continuous thermoplastic resin fibers and continuous reinforcing fibers, more preferably 95% or more by mass, and may contain 99% or more by mass, or 100% or less by mass.

[0056] The degree of dispersion of continuous reinforcing fibers in the blended yarn is preferably 60-100%, more preferably 63-100%, even more preferably 68-100%, and particularly preferably 70-100%. By setting the degree of dispersion within this range, the blended yarn exhibits more uniform physical properties, and the appearance of the molded product is further improved. In addition, when molded products are manufactured using this yarn, products with superior mechanical properties can be obtained.

[0057] <<Method for Measuring Dispersion>> The blended yarn is embedded in epoxy resin, and a cross-section perpendicular to the longitudinal direction of the blended yarn is polished. The cross-sectional view is then photographed using a super-depth color 3D shape measuring microscope. In the captured image, six auxiliary lines are drawn radially at equal intervals, and the lengths of the continuous reinforcing fiber regions on each auxiliary line are measured as a1, a2, a3...ai (i=n). In addition, the lengths of the continuous thermoplastic resin fiber regions on each auxiliary line are measured as b1, b2, b3...bi (i=m). Based on these results, the dispersion is calculated using the following formula. For ultra-deep color 3D shape measuring microscopes, the VK-9500 (controller unit) / VK-9510 (measuring unit) (manufactured by Keyence) can be used.

[0058] Blended yarns are typically manufactured using continuous thermoplastic fiber bundles and continuous reinforcing fiber bundles. It is preferable to use continuous reinforcing fibers and / or continuous thermoplastic fibers that have been surface-treated with a treatment agent. This configuration makes it easier to obtain blended yarns in which the continuous reinforcing fibers and continuous thermoplastic fibers are more uniformly dispersed, and also improves the impregnation rate of the continuous thermoplastic fiber component into the continuous reinforcing fibers after molding.

[0059] Further details regarding other blended yarns and their manufacturing methods can be found in paragraphs 0018-0039 of International Publication No. 2016 / 159340 and paragraph 0051 of Japanese Patent Publication No. 2020-063342, the contents of which are incorporated herein by reference.

[0060] The hollow structure of this embodiment can be used for various applications. The hollow structure of this embodiment may be heat-processed as is, but it is preferable to heat-process it as a structure that includes the hollow structure and other materials. In the present invention, a structure that includes a hollow structure includes both a structure consisting only of a hollow structure and a structure that includes a hollow structure and other materials.

[0061] An example of a structure containing a hollow structure is a multilayer hollow structure having a hollow structure and other layers. An example of a multilayer hollow structure is one in which an outer layer 31 and / or an inner layer 32 are located on the inside and / or outside of a braided cord (hollow structure) formed from a blended yarn 1, as shown in Figure 3. Examples of the outer layer 31 and / or inner layer 32 include a thermoplastic resin layer and a UD tape layer. The outer layer 31 and / or inner layer 32 may each be an empty layer, a single layer, or two or more layers, independently of each other. Figure 3 shows a schematic diagram of the multilayer hollow structure viewed from the direction of the opening (for example, the direction perpendicular to the arrow in Figure 1).

[0062] In this embodiment, one example of a multilayer hollow structure is that the continuous reinforcing fiber-containing layer consists solely of the hollow structure (braided cord). Another example of a multilayer hollow structure is that the braided cord is the innermost layer. It is preferable that the layers other than the hollow structure (braided cord) included in the multilayer hollow structure of this embodiment are layers that can be heat-processed together with the hollow structure.

[0063] The hollow structure of this embodiment can be manufactured, for example, by drawing blended yarn from multiple bobbins 41, as shown in Figure 4(1), and braiding it into a single braided cord 42, as shown in Figure 4(2). In this embodiment, it is preferable to provide a rubber film on the inside or outside of the braided cord 42 after braiding the blended yarn to obtain the braided cord 42.

[0064] The hollow structure included in this embodiment can be used for various applications. In particular, due to its high load resistance and energy absorption properties, it is preferably used in the formation of energy-absorbing molded products. Examples of energy-absorbing molded products include tubes used in parts that can be used in the crushable zones of vehicles and the like.

[0065] The structure including the hollow structure of this embodiment is preferably used for forming tubes. The structure including the hollow structure may consist only of the hollow structure (for example, a braided blended yarn). The tube of this embodiment may be a tube formed from a multilayer hollow structure having the hollow structure and other layers. The tube of this embodiment is usually one in which the hollow structure of this embodiment has been heat-treated. The tube of this embodiment may have additional layers added after the heat treatment of the structure including the hollow structure. Details of the other layers will be described later.

[0066] The tube of this embodiment may be straight or it may have a bent portion. The bent portion preferably has a radius of curvature of 5° or more, and preferably 90° or less. Furthermore, the tube of this embodiment may have different diameters or may have circular and polygonal portions.

[0067] The length of the tube in this embodiment is usually 5 cm or more, preferably 10 cm or more, and may be 50 cm or more, 1 m or more, or 100 m or more depending on the application, and it is practical to be 10,000,000 m or less, and may be 1,000,000 m or less, 100,000 m or less, 10,000 m or less, 1,000 m or less, or 100 m or less depending on the application.

[0068] The shape of the tube's cross-section is not particularly defined, but circular and polygonal shapes are examples. Regular circles, ellipses, oblongs, odd-numbered regular polygons with five or more sides, and even-numbered regular polygons with four or more sides are preferred because they further improve energy absorption performance. The odd-numbered regular polygons with five or more sides are preferably those with 5 to 21 sides. The even-numbered regular polygons with four or more sides are preferably those with an integer number of sides from 4 to 22.

[0069] The outer diameter of the tube cross-section is preferably 3 mm or more, more preferably 5 mm or more, even more preferably 10 mm or more, and preferably 1000 mm or less, more preferably 900 mm or less, and even more preferably 800 mm or less. The inner diameter of the tube cross-section is preferably 2 mm or more, more preferably 4 mm or more, even more preferably 9 mm or more, and preferably 900 mm or less, more preferably 800 mm or less, and even more preferably 700 mm or less. Here, the outer diameter of the tube cross-section is the diameter of a circle having an area corresponding to the area of ​​the region formed by the outer circumference of the tube. The inner diameter of the tube cross-section is the diameter of a circle having an area corresponding to the area of ​​the region formed by the inner circumference of the tube.

[0070] The tube of this embodiment may also have different outer diameters depending on the part. In this embodiment, since blended yarn is used to make a braided cord, the diameter can be flexibly adjusted. For example, in the tube of this embodiment, the ratio of the widest part to the narrowest part (widest diameter / narrowest diameter) may be 1.1 times or more, 1.5 times or more, 5 times or less, or 3 times or less.

[0071] The thickness of the tube is preferably 0.1 mm or more, more preferably 0.2 mm or more, even more preferably 0.5 mm or more, and preferably 5 mm or less, more preferably 2 mm or less, and even more preferably 1 mm or less. If the thickness of the tube is not uniform, the thickness is measured at any 100 locations and the average value is taken as the thickness.

[0072] The tube of this embodiment may have an outer layer and / or an inner layer inside and / or outside the outer layer, in addition to the layer formed from the structure including the hollow structure of this embodiment. Examples of the outer layer and / or inner layer include a thermosetting resin layer, a fiber-reinforced thermosetting resin layer, a decorative layer, and the like. These outer layers and / or inner layers are usually provided after the hollow structure or multilayer hollow structure of this embodiment has been heat-treated.

[0073] The method for manufacturing the tube in this embodiment is characterized by applying pressure to the hollow portion of a structure including a hollow structure, and applying a temperature to the hollow portion that is above the melting point of the thermoplastic resin constituting the continuous thermoplastic resin fibers. By adopting this configuration, it becomes possible to form a tube of a desired shape.

[0074] The pressure applied to the hollow section is preferably 0.3 MPa or higher, more preferably 0.5 MPa or higher, and even more preferably 0.7 MPa or higher. There is no specific upper limit to the pressure, but 1 MPa or less is practical. By setting the pressure above the lower limit, the continuous thermoplastic resin fibers are impregnated into the continuous reinforcing fibers to the very end, suppressing the generation of voids and tending to further improve the physical properties.

[0075] The heating temperature of the hollow portion is preferably 15°C or higher above the melting point of the thermoplastic resin constituting the continuous thermoplastic resin fibers, more preferably 25°C or higher above the melting point, and more preferably 50°C or lower above the melting point, and more preferably 40°C or lower above the melting point. Setting the temperature above the lower limit tends to reduce the resin viscosity and further improve impregnation. Setting the temperature below the upper limit tends to suppress thermal degradation of the resin and prevent deterioration of physical properties.

[0076] Structures including hollow structures may be molded using a mold. For example, a hollow structure is set inside a mold, both ends are fixed with plugs, and then molded by pressurizing the inside or by heating while pressurizing. Preferably, the method involves pressurizing while heating. More specifically, a pressurizing film is wrapped around a rod having a diameter appropriate to the molded product, and the hollow structure of this embodiment is placed over it. After removing the rod, it is set in the mold. The mold may be linear, but in this embodiment, a mold having a bent structure is preferred. Depending on the bent structure, a mold with two or more divisions can be used. After inserting sealing plugs into both ends of the mold, pressurizing and heating are performed. Then, it is cooled. After that, it is preferable to remove the pressurizing film. It is also preferable to cut off the scrap material.

[0077] The present invention will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing content, processing procedures, etc., shown in the following examples can be modified as appropriate, as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. If the measuring instruments, etc., used in the examples are difficult to obtain due to discontinuation or other reasons, measurements can be taken using other instruments with equivalent performance.

[0078] <Raw Materials> <<Example of Synthesis of Polyamide Resin MPXD10>> After heating and dissolving sebacic acid in a reaction vessel under a nitrogen atmosphere, while stirring the contents, a mixed diamine with a molar ratio of 3:7 of paraxylylenediamine (manufactured by Mitsubishi Gas Chemical) and metaxylylenediamine (manufactured by Mitsubishi Gas Chemical) was gradually added dropwise under pressure (0.35 MPa) so that the molar ratio of the diamine to sebacic acid (manufactured by Ito Oil Chemicals Co., product name Sebaciate TA) was approximately 1:1, and the temperature was raised to 235°C. After the dropwise addition was completed, the reaction was continued for 60 minutes to adjust the amount of components with a molecular weight of 1,000 or less. After the reaction was completed, the contents were removed in strand form and pelletized in a pelletizer to obtain polyamide (MPXD10). Hereinafter referred to as "MPXD10". The melting point of MPXD10 was 215°C. The tensile modulus of the resin was 3.1 GPa.

[0079] <<Method for Measuring Tensile Modulus>> The tensile modulus of thermoplastic resin (MPXD10) was measured as follows. Tensile tests were performed using a tensile testing machine in accordance with JIS K7161 to measure the tensile modulus. The tensile tests were conducted under the following conditions: measurement temperature 23°C, humidity 50% RH, chuck distance 115.0 mm, and tensile speed 5 mm / min. Three test specimens were used, and the average value of the results was calculated. The tensile testing machine used was a Shimadzu AG-Xplus 100kN.

[0080] <<Thermosetting Prepreg Resin>> Toray's FK6241E-05K prepreg containing epoxy resin as the thermosetting resin and 12K twill weave cloth as the carbon fiber.

[0081] <<Reinforcement Fiber>> Continuous carbon fiber: Toray Industries, Ltd., T700SC-12k

[0082] Example 1 <Production of Continuous Thermoplastic Resin Fibers> The above thermoplastic resin was made into fibers according to the following method. The polyamide resin MPXD10 was melt-extruded using a single-screw extruder with a 30 mmφ screw, extruded in strand form from a 60-hole die, stretched while being wound on a roll, and a bundle of thermoplastic resin fibers was obtained by winding it onto a coiled body. The melting temperature was 280°C.

[0083] <Manufacturing of Blended Yarn> Continuous thermoplastic resin fibers and continuous carbon fibers of a length of 1 m or more were drawn from a wound material, passed through multiple guides, and opened by applying air blow. While opening the fibers, the continuous thermoplastic resin fibers and continuous carbon fibers were bundled together, and further passed through multiple guides and applied air blow to promote uniformity, and then blended to obtain a blended yarn. The impregnation rate in the obtained blended yarn was 0%, the proportion of continuous carbon fibers was 43 mass%, the proportion of continuous thermoplastic resin fibers was 57 mass%, and the dispersion of continuous reinforcing fibers was 88%.

[0084] <Manufacturing of Hollow Structures and Tubes> Using a braiding machine manufactured by Wilhelm Steeger GmbH & Co. KG, 20 units of blended yarn were prepared, and a hollow structure with an inner diameter of 50 mm was manufactured at a crossing angle of 45°. The obtained hollow structure was cut to the required length and placed on a metal pipe having a diameter corresponding to the molded product. Three more layers of hollow structure were then placed on top, resulting in a total of four layers. After this, the metal pipe was removed to obtain the hollow structure. The obtained hollow structure was set in a halved mold, and sealing plugs were set at both ends of the hollow structure. The other half of the mold was placed on top and the mold was secured with bolts. Air was introduced into the hollow structure to a pressure of 0.7 MPa and placed in an oven. While maintaining the internal pressure, the mold temperature was controlled to 240-250°C and held for 5 minutes, after which it was removed from the oven and cooled. After removing it from the mold, a tube with a length of 30 cm was obtained, in which the central 10 cm portion in the longitudinal direction (the length direction of the tube) is a hollow cylindrical shape with a cross-section having an inner diameter of 50 mm, and the 10 cm portions at both ends are hollow hexagonal prisms.

[0085] <Measurement of Energy Absorption> The tube obtained above was cut to a length of 5 cm, and a compression test was performed in the longitudinal and cross-sectional directions of a 5 cm long hollow cylinder. Specifically, using a universal testing machine (100 kN) manufactured by Shimadzu Corporation, a load was applied to the hollow cylinder at a compression speed of 10 mm / min, and the compression distance and stress were recorded. The maximum stress (MPa) of the hollow cylinder and the area shown by the curve obtained from the compression distance and stress were determined, and this area was evaluated as the absorbed energy. Note that in Example 1, the value shown in Comparative Example 1 is shown as a relative value with the value shown in Comparative Example 1 set to 1. The test results in the longitudinal direction are shown in Table 1. As a result of the compression test in the cross-sectional direction of the hollow cylinder, the tube deformed into a plate shape once, and then returned to its original hollow cylinder shape when the compression distance was returned to its original state.

[0086] <Processing and Formability> The hollow structure was placed in a mold and held at a melting point of +25°C and a pressure of 0.7 MPa for 5 minutes. The sample was then slowly cooled in air to obtain a molded product. The total time from the start of cutting the above hollow structure to the required length, to setting it in the mold, and obtaining the molded product was measured.

[0087] Comparative Example 1 <Manufacturing of Hollow Structures and Tubes (Manufacturing of Hollow Cylinders)> Prepreg (Toray FK6241E-05K) was wrapped around a cylindrical aluminum mold (A5052), and six more layers of prepreg were wrapped around it so that the ends did not overlap, resulting in a total of seven layers of prepreg. A mold was then placed on the outside. This was then molded in an autoclave molding machine (Hanyuuda Iron Works DANDELION) at 130°C for 2 hours under 0.3 MPa. After molding, the outer and inner molds were removed to obtain the molded product. The hollow cylinder obtained above was cut to a length of 5 cm, and compression tests were performed in the longitudinal and cross-sectional directions. The results of the longitudinal test are shown in Table 1. As a result of the compression test in the cross-sectional direction, the tube rapidly fractured during pressurization and could not maintain its shape. The total time from the start of cutting the above prepreg (Toray FK6241E-05K) to setting it in the mold and obtaining the molded product was measured to evaluate the moldability.

[0088] <Energy Absorption Measurement> The same evaluation method as in Example 1 was used.

[0089]

[0090] As is clear from the above results, the tube formed from the hollow structure of the present invention exhibited excellent energy absorption properties. Furthermore, it had excellent processability and moldability. In contrast, the tube of the comparative example exhibited poor energy absorption properties and poor processability and moldability.

[0091] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible without departing from the intent and scope of the invention.

[0092] 1 Blended yarn 21 Prepreg 22 Hollow structure 23 Cut 31 Outer layer 32 Inner layer 41 Bobbin 42 Braided cord

Claims

1. A tubular hollow structure formed from blended fibers, wherein the hollow structure is a braid of blended fibers, and the blended fibers include continuous thermoplastic resin fibers and continuous reinforcing fibers.

2. A tubular hollow structure formed from blended yarn, wherein three or more units of blended yarn intersect at an angle greater than 0° and less than 90° according to a certain regularity, the blended yarn includes continuous thermoplastic resin fibers and continuous reinforcing fibers, and the hollow structure is a hollow structure without breaks in the cross-sectional direction perpendicular to the longitudinal direction.

3. The hollow structure according to claim 1 or 2, wherein the continuous thermoplastic resin fibers include a polyamide resin.

4. The hollow structure according to claim 3, wherein the polyamide resin comprises a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, wherein 70 mol% or more of the diamine-derived structural unit is derived from xylylenediamine, and 70 mol% or more of the dicarboxylic acid-derived structural unit is derived from an α,ω-dicarboxylic acid having 4 to 20 carbon atoms.

5. The hollow structure according to any one of claims 1 to 4, wherein the tensile modulus of the thermoplastic resin constituting the continuous thermoplastic resin fibers is 2.0 to 5.0 GPa as measured in accordance with ISO 527-1.

6. The hollow structure according to any one of claims 1 to 5, wherein the continuous reinforcing fibers include continuous carbon fibers.

7. The hollow structure according to any one of claims 1 to 6, wherein the continuous thermoplastic resin fiber comprises a polyamide resin, the polyamide resin comprises diamine-derived structural units and dicarboxylic acid-derived structural units, 70 mol% or more of the diamine-derived structural units are xylylenediamine-derived structural units, 70 mol% or more of the dicarboxylic acid-derived structural units are α,ω-dicarboxylic acid-derived structural units having 4 to 20 carbon atoms, the tensile modulus of the thermoplastic resin constituting the continuous thermoplastic resin fiber is 2.0 to 5.0 GPa as measured according to ISO 527-1, and the continuous reinforcing fiber comprises continuous carbon fiber.

8. A tube formed from a structure including a hollow structure as described in any one of claims 1 to 7.

9. An energy-absorbing molded article formed from a structure including a hollow structure as described in any one of claims 1 to 7.

10. A method for manufacturing a tube, comprising applying pressure to the hollow portion of a structure including the hollow structure described in any one of claims 1 to 7, and applying a temperature to the hollow portion that is above the melting point of the thermoplastic resin constituting the continuous thermoplastic resin fibers.

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