JP5661027B2 - Manufacturing method of core-sheath fiber - Google Patents

Description

  The present invention relates to a method for producing a core-sheath fiber including a core resin and a sheath resin.

  A fiber reinforced resin (FRP) composed of a fiber and a matrix resin is produced by spinning a fiber raw material to form a fiber, and then bringing the fiber and the matrix resin into contact with each other to heat the fiber reinforced resin (FRP). The fibers are bonded to each other to form an FRP. In this case, usually, a fiber and matrix resin integration step is required between the fiber formation step and the bonding step. Examples of the integration process include processes such as lamination of fibers and sheet-shaped resin, impregnation of fibers in a resin bath, and application of powder resin to the fibers.

  Non-Patent Document 1 describes an FRP in which reinforcing fibers and a matrix resin are made of the same kind of resin in order to improve recyclability. The document describes a method that includes laminating fibers and films to produce the FRP. As in this method, the integration process increases the manufacturing process of FRP, which increases the manufacturing cost.

  Non-Patent Document 2 describes a method of forming a fiber / matrix resin composite by laminating a plurality of core-sheath fibers composed of a low-melting thermoplastic resin and a high-melting thermoplastic resin and bonding them by heating and pressing. Describe. In the case of the method, in the spinning process of the core-sheath fiber, the sheath resin and the core resin, which are matrix resins, are bonded, so an integration step is not necessary, but the strength of the FRP is low because the strength of the fiber itself is low. Also lower.

  Various techniques are known for improving the strength of fibers obtained by melt spinning thermoplastic resins. Patent Document 1 is characterized in that after the crystalline polypropylene is melt-spun, the first stage of stretching is performed in the range of 50 to 70 ° C., and then the second and subsequent stages are stretched at a higher temperature than the first stage of stretching. A method for producing a high-strength polypropylene fiber is described. The document describes the strength and elongation by performing the first stage stretching at a lower temperature than the ordinary polypropylene fiber stretching temperature and the second and subsequent stages at a temperature higher than the first stage stretching temperature. Both states that they can provide high fiber.

  Patent Document 2 describes a method of drawing a fiber by irradiating a laser beam while applying a tension of 1 MPa or less to the fiber. In this document, the portion of the fiber irradiated with the laser beam is drawn by the above method to obtain an ultrafine fiber having a diameter of 5 μm or less. At this time, orientation crystallization occurs in the fiber, and crystallinity and high strength are high. It is described that a fiber is obtained.

  Patent Document 3 describes a core-sheath type composite fiber for use in resin reinforcement. The core of the composite fiber is polyester, the sheath has a lower melting point than the polyester of the core, and contains a terephthalic acid component, an ethylene glycol component, a 1,4-butanediol component, and an aliphatic lactone component. Is made of a copolyester having a temperature of 130 to 200 ° C. This document describes that the cutting strength of the composite fiber is 3.8 cN / dtex (corresponding to a tensile strength of about 520 MPa) or more and the cutting elongation is 20% or less.

  Patent Document 4 describes a method for producing polypropylene fiber, characterized in that polypropylene unstretched fiber is pre-stretched and post-stretched under specific conditions. According to this document, the polypropylene fiber obtained by the above method exhibits specific endothermic / melting characteristics in differential scanning calorimetry (DSC), has a uniform crystal structure, excellent heat resistance, and has a single fiber degree. It is described that the strength is excellent at 0.1 to 3 dtex and fiber strength of 7 cN / dtex (corresponding to a tensile strength of about 630 MPa) or more.

Japanese Patent No. 3976613 JP 2003-166115 A JP 2007-321256 A JP 2009-7727 A Japanese Patent No.4868521

Journal of Applied Polymer Science, 88, 2875-2883, 2003 Molding, Vol. 9, No. 11, p. 920-926, 1997

  In the case of FRP using carbon fiber or glass fiber, it is impossible to perform spinning integrally with the matrix resin, and therefore an additional integration process is essential.

  On the other hand, as in the method described in Non-Patent Document 2, when a core-sheath fiber composed of a low-melting point thermoplastic resin and a high-melting point thermoplastic resin is used for the production of FRP, the high-melting point thermoplastic resin constitutes the fiber. However, since the low-melting point thermoplastic resin constitutes the matrix resin, an additional integration step is unnecessary. However, the core-sheath fiber manufactured by the method described in this document has low strength, and no technique for improving the strength of the core-sheath fiber is known.

  For example, when the heating two-stage drawing technique described in Patent Document 1 or the laser beam drawing technique described in Patent Document 2 is applied to the core-sheath fiber, heating near the melting point of the core resin is required. Under such conditions, the sheath resin as the matrix resin melts, resulting in a non-uniform structure, resulting in a problem that the quality and strength of the resulting FRP deteriorate.

  Therefore, the present invention provides a method for producing a core-sheath fiber capable of producing a high-strength core-sheath fiber without using a special raw material and / or means, and production of a fiber-reinforced resin using the core-sheath fiber. It aims to provide a method.

  In the past, the present inventors have melt-extruded polyhydroxyalkanoic acid (PHA) to produce a melt-extruded fiber, and the melt-extruded fiber is rapidly cooled and solidified to a glass transition temperature of + 15 ° C. or lower to be amorphous. The fiber is characterized in that the amorphous fiber is allowed to stand at a glass transition temperature of + 15 ° C. or lower to produce a crystallized fiber, the crystallized fiber is drawn, and further subjected to tension heat treatment. A method was developed (Patent Document 5). In this way, the strength of the resulting PHA fiber can be increased by the method of producing the crystallized fiber by leaving the amorphous fiber in the vicinity of the glass transition temperature (hereinafter also referred to as “microcrystal nucleus drawing method”). Can be improved.

  Furthermore, the present inventors apply a microcrystalline nucleus drawing method to polypropylene (PP), and a ratio of a take-off speed to an extrusion speed when spinning a melt-extruded fiber (hereinafter also referred to as “melt-stretch ratio”). A method for producing PP fibers has been developed that can produce high-strength PP fibers without using special raw materials and / or means by adjusting to a specific range (PCT / JP2011 / 062346).

  As described above, optimization of the microcrystalline nucleus stretching method and the melt stretching ratio can improve the fiber strength without heating the melt-spun fiber, so without melting the sheath resin of the core-sheath fiber, It was thought that the fiber strength of the core resin could be improved.

  In light of the above findings, the present inventor has studied various means for solving the above problems, and as a result, the optimization of the microcrystalline nucleus stretching method and the melt stretching ratio is applied to the core-sheath fiber. It discovered that the core-sheath fiber which has intensity | strength can be manufactured, and completed this invention.

That is, the gist of the present invention is as follows.
(1) A method for producing a core-sheath fiber comprising a core resin P1 having a melting point T1 and a sheath resin P2 having a melting point T2, the following steps:
Resin P1 and resin P2 are melt-extruded so as to form a core-sheath fiber in which resin P1 is the core and resin P2 is the sheath, and the melt-extruded core-sheath fiber is equal to or lower than the glass transition temperature of core resin P1. A melt-extruded core-sheath fiber spinning process in which spinning is performed while pulling at a temperature;
A temperature maintaining step of maintaining the melt-extruded core-sheath fiber obtained in the melt-extruded core-sheath fiber spinning step at a temperature in the range of the glass transition temperature ± 15 ° C. of the core resin P1, and a melt-extruded core-sheath fiber after the temperature maintaining step; A stretching step of stretching
Including
The melting point T1 is a temperature higher than the melting point T2 by 50 ° C. or more,
The method, wherein the ratio of the take-off speed to the extrusion speed in the melt-extruded core-sheath fiber spinning step is in the range of 50 to 400.
(2) The method according to (1) above, wherein the core resin P1 is a resin mainly composed of polyethylene terephthalate, and the sheath resin P2 is a resin mainly composed of polypropylene.
(3) A core-sheath fiber produced by the method of (1) or (2).
(4) The core-sheath fiber assembly manufactured by the method of (1) or (2) is heated at a temperature in the range of the melting point T2 or more and the melting point T1 or less, and is adjacent in the core-sheath fiber assembly. A method for producing a fiber reinforced resin, comprising a fusion integration step of melting and integrating portions.

  It is possible to provide a method for producing a core-sheath fiber that can produce a high-strength core-sheath fiber without using special raw materials and / or means, and a method for producing a fiber-reinforced resin using the core-sheath fiber. It becomes.

It is process drawing which shows one Embodiment of the manufacturing method of the core sheath fiber of this invention. It is a schematic diagram which shows one Embodiment of the manufacturing method of the fiber reinforced resin of this invention.

<1. Manufacturing method of core-sheath fiber>
The present invention relates to a method for producing a core-sheath fiber.
In this specification, “core-sheath fiber” means a fiber composed of a fibrous core resin and a sheath resin disposed on the outer peripheral surface of the fibrous core resin. The ratio between the fiber diameter of the core-sheath fiber and the diameter of the core resin portion of the cross-section of the core-sheath fiber is preferably in the range of 0.1: 1 to 10: 1, and is preferably in the range of 0.5: 1 to 5: 1. It is more preferable.

  The fiber diameter of the core-sheath fiber, the diameter of the core resin part, and the thickness of the sheath resin part are not limited. For example, the core-sheath fiber is observed under an optical microscope, and the respective lengths are determined. It can be determined by actual measurement.

  The core-sheath fiber produced by the method of the present invention includes a core resin P1 having a melting point T1 and a glass transition temperature Tg1, and a sheath resin P2 having a melting point T2 and a glass transition temperature Tg2. Examples of the core resin P1 include, but are not limited to, resins mainly composed of polyethylene terephthalate (PET) or nylon 6 (PA6). A resin containing PET or PA6 as a main component is preferable. The sheath resin P2 is not limited, and examples thereof include a resin mainly composed of polypropylene (PP) or polyethylene (PE). A resin mainly composed of PP or PE is preferable.

  The core resin P1 and the sheath resin P2 used in the method of the present invention are preferably a combination in which the melting point T1 and the melting point T2 satisfy the conditions described below. Specifically, a combination in which the core resin P1 is a resin mainly composed of PET or PA6, and the sheath resin P2 is a resin mainly composed of PP or PE, and the core resin P1 is mainly composed of PET. A combination of resin as a component and the sheath resin P2 being a resin whose main component is PP is more preferable.

  The core resin P1 and the sheath resin P2 used in the method of the present invention may be in the form of a homopolymer consisting only of the above resin units, or in the form of a copolymer (copolymer) with other monomers. There may be. Alternatively, it may be in the form of a mixture of two or more homopolymers and / or copolymers. Copolymers can include block copolymers and random copolymers. Examples of the comonomer forming the copolymer include, but are not limited to, ethylene and 1-butene.

  Further, the core resin P1 and the sheath resin P2 used in the method of the present invention are one or more kinds of binders, plasticizers, colorants, stabilizers, lubricants, fillers, talc and sodium benzoate. An additive may be contained. Said additive can be mix | blended with each resin in the range which does not impair the resin performance of core part resin P1 and sheath part resin P2.

  As will be described below, when a fiber reinforced resin is produced using an assembly of core-sheath fibers according to the present invention, the sheath resin P2 is melt-integrated between adjacent portions in the assembly of core-sheath fibers. It functions as a matrix resin. Therefore, the core-sheath fiber manufactured by the method of the present invention includes the core resin P1 and the sheath resin P2 whose melting point T1 of the core resin P1 is higher than the melting point T2 of the sheath resin P2. Since the core resin P1 and the sheath resin P2 are melt-extruded together to spin the core-sheath fiber, the temperature difference between the melting point T1 and the melting point T2 is preferably within a certain range. Specifically, the melting point T1 is preferably 50 ° C. or more higher than the melting point T2, more preferably 50 to 200 ° C. higher than the melting point T2, and 50 to 100 ° C. higher than the melting point T2. It is particularly preferred.

  In addition, although melting | fusing point T1 and T2 are not limited, For example, it can determine by measuring beforehand melting | fusing point of core part resin P1 and sheath part resin P2 which are used using melting | fusing point measuring apparatus.

  By using the core resin P1 and the sheath resin P2 satisfying the above conditions in the method of the present invention, the resin is melt-extruded together to spin the core-sheath fiber, and the core-sheath has higher strength than the conventional technique. Fibers can be produced.

  FIG. 1 is a process diagram showing an embodiment of a method for producing a core-sheath fiber of the present invention. Hereinafter, a preferred embodiment of the method of the present invention will be described in detail with reference to FIG.

[1. Melt extrusion core sheath fiber spinning process]
In the method of the present invention, the resin P1 and the resin P2 are melt-extruded so as to form a core-sheath fiber in which the resin P1 is a core part and the resin P2 is a sheath part, and the melt-extruded core-sheath fiber is drawn at a temperature A. It includes a melt-extruded core-sheath fiber spinning step (step S1) for spinning while taking. As will be described below, this step is performed under conditions that improve the degree of molecular orientation of the core resin P1 in the melt-extruded core-sheath fiber.

  In this step, as a means for melt-extruding the core resin P1 and the sheath resin P2, a core-sheath fiber melt-extrusion technique usually used in this technical field may be used. Examples of the melt extrusion means include, but are not limited to, an extrusion apparatus that heats and melts a resin raw material and then presses and extrudes the melt at a predetermined heating temperature. By using the above-described extrusion apparatus in this step, it is possible to adjust the fiber diameter of the resulting core-sheath fiber to a suitable range.

  In this step, the extrusion speed at which the core resin P1 and the sheath resin P2 are melt-extruded may be in a range that satisfies a suitable ratio of the take-up speed to the extrusion speed described below.

  The present inventors disclosed a microcrystalline nucleus drawing method described in Patent Document 5 and PCT / JP2011 / 062346 for the production of core-sheath fibers containing PET as the core resin P1 and PP as the sheath resin P2. It has been found that when the optimization of the melt drawing ratio is applied, the strength of the PET fiber, which is the core resin P1, is improved similarly to the PHA fiber and the PP fiber. In the method described in Patent Document 5, the melt-extruded fiber is made amorphous by rapidly cooling the melt-extruded fiber of PHA to a temperature not lower than the glass transition temperature and not higher than the glass transition temperature + 15 ° C. Thus, microcrystalline nuclei are formed in the melt-extruded fiber. Since these microcrystal nuclei serve as starting points (stretch nuclei) for stretching, polymer molecules are highly oriented even in one stage of stretching, and the strength of the resulting fiber is improved. Therefore, also in the method of the present invention, the melt-extruded core-sheath fiber is made amorphous by rapidly cooling the melt-extruded core-sheath fiber to a predetermined temperature A in this step, and this is a temperature maintaining step described below. By maintaining the temperature at a predetermined temperature B, it is presumed that microcrystalline nuclei can be formed in the melt-extruded core-sheath fiber.

  In this step, the melt-extruded core-sheath fiber is rapidly cooled from the heating temperature in the melt-extrusion means to a predetermined temperature A, and is spun while being drawn at the temperature A. Here, the temperature A is preferably not higher than the glass transition temperature Tg1 of the core resin P1, and more preferably in the range of 0 ° C. or higher and Tg1 or lower.

  In the present specification, the “glass transition temperature (Tg)” means a temperature at which the resin transitions from a plastic state to a cured state, and is not limited to, for example, differential scanning calorimetry (DSC) or It can be determined by dynamic viscoelasticity measurement.

  In this step, the means for rapidly cooling the melt-extruded core-sheath fiber from the heating temperature in the melt-extrusion means to the temperature A is not particularly limited. The melt-extruded core-sheath fiber may be introduced into a liquid or gaseous cooling medium usually used in the art. Examples of the cooling medium used in this step include, but are not limited to, water and ice water, and inert gases such as air, nitrogen, and helium. Water or ice water is preferred. By rapidly cooling the molten core-sheath extruded fiber from the heating temperature in the melt extrusion means to the temperature A using these cooling media, the core resin P1 forming the fiber can be made into an amorphous form.

  The crystal forms of the core resin P1 and the sheath resin P2 in the obtained melt-extruded core-sheath fiber are not limited, but can be determined by, for example, X-ray diffraction (XRD).

  In this step, the means for pulling the melt-extruded core-sheath fiber at the temperature A is not particularly limited. For example, the melt-extruded core-sheath fiber introduced into the cooling medium is wound on the winding shaft at a predetermined take-up speed using a normal take-up means commonly used in the technical field in the cooling medium. After passing through the cooling medium at a predetermined take-up speed, a take-up yarn body is formed on the take-up shaft at a predetermined take-up speed by using a normal take-out means outside the cooling medium. Thus, the melt-extruded core-sheath fiber can be taken up at the temperature A. Alternatively, the melt-extruded core-sheath fiber rapidly cooled to the temperature A with the above-described cooling medium is accommodated in a container that has been cooled to the temperature A in advance while being taken at a predetermined take-up speed using a normal take-up means. At temperature A, the melt-extruded core-sheath fiber can be taken up. Either case is included in the embodiment of this step. Here, the take-up means is not limited, and examples thereof include a winding device and a roller that form a wound body by winding a fiber around a winding shaft such as a bobbin. In addition, the melt-extruded core-sheath fiber is preferably recovered by the above-described means while maintaining the tension state of the fiber applied by taking-up, and is preferably subjected to a temperature maintaining step described below. For example, the wound body of the melt-extruded core-sheath fiber is preferably rapidly cooled to the temperature A so that the fiber does not substantially relax by a conventional method such as fixing both ends of the fiber to the winding shaft. Further, the melt-extruded core-sheath fiber contained in the container is substantially relaxed by a conventional method such as fixing both ends of the fiber to the container, or fixing one end to the container and the other end to a weight. It is preferable to rapidly cool to temperature A.

  The inventors of the present invention have adjusted the ratio between the extrusion speed and the take-off speed in this step, and optimized the ratio of the take-off speed to the extrusion speed (melt draw ratio) to a range higher than the value normally set in the technical field. At the same time, by spinning the melt-extruded core-sheath fiber while drawing it at a temperature A, the resulting core-sheath fiber has a strength of the core-sheath fiber (usually 400 to 600 MPa, which is produced at a normal melt draw ratio). It was found that the tensile strength was significantly improved. The above effect is achieved by optimizing the melt drawing ratio in a higher range as compared with the prior art, and by rapidly cooling the melt-extruded core-sheath fiber to the temperature A, the core resin P1 constituting the melt-extruded core-sheath fiber It is presumed that the degree of orientation of the amorphous form molecules is improved, and the strength improvement effect by the microcrystal nuclei formed by the temperature maintaining process described below is further improved.

  In this step, the take-up speed at which the melt-extruded core-sheath fiber introduced into the cooling medium at temperature A is taken is preferably in the range of 10 to 10,000 m / min, and in the range of 100 to 1000 m / min. Is more preferable. Further, the ratio of the take-up speed to the extrusion speed (melt drawing ratio) is preferably in the range of 50 to 400, more preferably in the range of 100 to 300. By adjusting the ratio of the take-off speed to the extrusion speed within the above range, the degree of molecular orientation of the core resin P1 in the melt-extruded core-sheath fiber is improved, and the strength of the resulting core-sheath fiber is improved. It becomes possible.

  By carrying out this step under the above conditions, it is possible to form a melt-extruded core-sheath fiber containing the core resin P1 having an amorphous form with improved molecular orientation.

[2. Temperature maintenance process]
The method of the present invention includes a temperature maintaining step (step S2) for maintaining the melt-extruded core-sheath fiber obtained in the melt-extruded core-sheath fiber spinning step at a temperature B. In this step, the melt-extruded core-sheath fiber is maintained under conditions (temperature B) that form fine crystal nuclei in the core resin P1 in the melt-extruded core-sheath fiber.

  In this step, the melt-extruded core-sheath fiber preferably maintains the tension state of the fiber applied in the melt-extruded core-sheath fiber spinning step. For example, in the case of a wound body of melt-extruded core-sheath fiber, it is preferable to maintain the temperature B so that the fiber does not substantially relax by a conventional method such as fixing both ends of the fiber to a winding shaft. . Further, in the case of melt-extruded core-sheath fibers contained in a container, the fibers are substantially removed by a conventional method such as fixing both ends of the fibers to the container, or fixing one end to the container and the other end to a weight. It is preferable that the temperature B is maintained so as not to relax.

  In this step, the temperature B for maintaining the melt-extruded core-sheath fiber is preferably a temperature in the range of the glass transition temperature ± 15 ° C. of the core resin P1, and the range of the glass transition temperature ± 10 ° C. of the core resin P1 More preferably, the temperature is The time for maintaining the melt-extruded core-sheath fiber at the temperature B is preferably in the range of 24 to 240 hours, and more preferably in the range of 24 to 120 hours. Here, as the means for maintaining the melt-extruded core-sheath fiber at the temperature B, it is preferable to use the same means as the means for rapidly cooling to the temperature A in the previous step.

  By carrying out this step under the above conditions, it becomes possible to form fine crystal nuclei in the melt-extruded core-sheath fiber of PP having an amorphous form obtained in the melt-extruded core-sheath fiber spinning step.

[3. Stretching process]
The method of the present invention includes a drawing step (step S3) for drawing the melt-extruded core-sheath fiber after the temperature maintaining step.

  In this step, as a means for stretching the melt-extruded core-sheath fiber, a plastic fiber stretching technique usually used in the technical field may be used. Examples of the stretching means include, but are not limited to, a manual or mechanical stretching apparatus that draws the melt-extruded core-sheath fiber from the wound body and stretches it with a roller or the like.

  In this step, there is no particular upper limit to the draw ratio, and it is sufficient that the melt-extruded core-sheath fiber does not break. Specifically, the draw ratio is preferably 3 times or more, and more preferably 5 times or more. The temperature at which the melt-extruded core-sheath fiber is stretched is preferably a temperature in the range of glass transition temperature −50 ° C. or higher and glass transition temperature + 30 ° C. or lower of the core resin P1, and room temperature (for example, 20 to 25 ° C. Range) is particularly preferable.

  Thereafter, the drawn core-sheath fiber can be formed into a wound winding body on the winding shaft at a predetermined drawing speed by using a usual take-up means, or can be accommodated in a container. Either case is included in the embodiment of this step. The stretched core-sheath fiber is preferably recovered by the above means while maintaining the tension state of the fiber applied by stretching, and is preferably subjected to a heat treatment step described below. For example, it is preferable that the wound core body of the drawn core-sheath fiber is not loosened by a conventional method such as fixing both ends of the fiber to the winding shaft. In addition, the stretched core-sheath fiber accommodated in the container is not loosened by a conventional method such as fixing both ends of the fiber to the container, or fixing one end to the container and the other end to a weight. It is preferable to do so.

  By carrying out this step under the above conditions, the fiber diameter of the resulting core-sheath fiber can be reduced.

[4. Heat treatment process]
The method of the present invention optionally includes a heat treatment step (step S4) for heat-treating the drawn core-sheath fiber after the drawing step.

  In this step, the stretched core-sheath fiber can be heat-treated while maintaining the tensioned state imparted in the stretching step. Or the tension | tensile_strength state provided at the extending | stretching process is cancelled | released, and the stretched core-sheath fiber of a non-tensile state or a relaxation | loosening state can be heat-processed by heat-processing in a relaxation | loosening state. It is preferable to perform heat treatment while maintaining the tension state applied in the stretching step. For example, in the case of a wound body of drawn core-sheath fiber, it is preferable to heat-treat the fiber so as not to relax substantially by a conventional method such as fixing both ends of the fiber to a winding shaft. In the case of a drawn core-sheath fiber contained in a container, the fiber is substantially relaxed by a conventional method such as fixing both ends of the fiber to the container, or fixing one end to the container and the other end to a weight. It is preferable to perform the heat treatment in such a manner.

  In this step, as a means for heat-treating the drawn core-sheath fiber, a heating device such as a dry oven usually used in the technical field may be used. The temperature at which the stretched core-sheath fiber is heat-treated is preferably in the range from the glass transition temperature of the core resin P1 to the melting point or less, in the range of the glass transition temperature of the core resin P1 to + 20 ° C or more and the melting point to -20 ° C or less. More preferably. The time for heat treatment of the drawn core-sheath fiber is preferably in the range of 1 second to 60 minutes, and more preferably in the range of 10 seconds to 30 minutes.

  By carrying out this step under the above conditions, it is possible to obtain a high-strength core-sheath fiber.

<2. Core sheath fiber>
As already described, the melt-extruded core-sheath fiber after the temperature maintaining step in the method of the present invention has a high degree of molecular orientation of the core resin P1 in the fiber, and a starting point of stretching (stretching nucleus) in the fiber. It has a microcrystal nucleus. For this reason, the core-sheath fiber obtained by drawing the melt-extruded core-sheath fiber having the above characteristics is compared with the core-sheath fiber (usually having a tensile strength of 400 to 600 MPa) obtained by the method of the prior art. And extremely high strength. Specifically, the tensile strength of the core resin P1 produced by the method of the present invention is usually in the range of 1.0 to 1.9 GPa, and typically in the range of 1.0 to 1.6 GPa. The tensile strength (MPa) of the core resin P1 is determined by measuring the load at the time when the core resin P1 is broken by applying a load even after the sheath resin P2 is broken in the tensile test of the core-sheath fiber. It can be determined by dividing the load (N) at the time of fracture of the resin P1 by the fiber cross-sectional area (mm ² ) of the core resin P1.

  Therefore, the present invention also relates to a high-strength core-sheath fiber having the above-described tensile strength. By having such tensile strength, the core-sheath fiber of the present invention can exhibit extremely high strength.

<3. Manufacturing method of fiber reinforced resin>
The core-sheath fiber obtained by the method of the present invention has extremely high strength as compared with the core-sheath fiber obtained by the method of the prior art. For this reason, a high-strength fiber-reinforced resin can be produced by using the core-sheath fiber obtained by the method of the present invention. Therefore, the present invention also relates to a method for producing a fiber reinforced resin using the core-sheath fiber of the present invention.

  In the method for producing a fiber reinforced resin of the present invention, the aggregate of core-sheath fibers produced by the method of the present invention is heated at a temperature C, and adjacent portions in the aggregate of core-sheath fibers are fused and integrated. Includes a melt integration step.

  In this step, the length of the core-sheath fiber is not particularly limited. A core-sheath fiber in the form of a short fiber chopped to a length in the range of 10 to 1000 times the fiber diameter of the core-sheath fiber may be used, or a core-sheath fiber in the form of a continuous fiber may be used. .

  An aggregate of the core-sheath fibers of the above form is formed. The form of the aggregate of core-sheath fibers may be any form. The core-sheath fibers constituting the aggregate of core-sheath fibers may be arranged in parallel or substantially in parallel without intersecting each other in the aggregate, and may be arranged so that adjacent portions intersect each other.

  One embodiment of an assembly of core-sheath fibers used in the method of the present invention is shown in FIG. In the core-sheath fiber assembly 101 in a layered form, the core-sheath fiber 1 including the core part 2 that is the resin P1 and the sheath part 3 that is the resin P2 is parallel or adjacent to each other without crossing each other. It arrange | positions so that it may be arrange | positioned substantially parallel or adjacent parts may cross | intersect.

  The collection of core-sheath fibers may optionally contain one or more additives such as binders, plasticizers, colorants, stabilizers, lubricants, fillers, talc and sodium benzoate. By containing the above-mentioned additives, various functions can be imparted to the resulting fiber-reinforced resin of the present invention.

  By using an aggregate of core-sheath fibers having the above characteristics, a fiber reinforced resin having high strength can be produced.

  In this step, by heating the core-sheath fiber assembly 101 at a temperature C, the sheath resin 3 containing the resin P2 as a main component without substantially melting the core resin 2 containing the resin P1 as a main component. Of the core-sheath fiber assembly, the adjacent portions are fused and integrated, and the core resin 4 having the resin P1 as a main component and the matrix resin 5 having the resin P2 as a main component A fiber reinforced resin 102 can be obtained.

  The melted sheath resin P2 functions as a matrix resin for melting and integrating adjacent portions in the core-sheath fiber assembly. Therefore, the temperature C is preferably in the range of the melting point T2 or more and the melting point T1 or less, and more preferably in the range of the melting point T2 + 10 ° C. or more and the melting point T1−10 ° C.

  When the core-sheath fiber assembly is in the form of a layer, the core-sheath fiber assembly is heated at a temperature C while applying pressure from the outer peripheral surface of the core-sheath fiber layer in order to press the adjacent portions together. Also good. In this case, it is preferable to pressurize at a pressure in the range of 1 to 1000 MPa, and more preferably pressurize at a pressure in the range of 10 to 100 MPa.

  As explained in detail above, the method of the present invention can produce high-strength core-sheath fibers without using special raw materials and / or means. Moreover, since the core-sheath fiber of this invention has high tensile strength, the reinforced fiber resin manufactured using this core-sheath fiber has the characteristic of lightweight and high intensity | strength. Therefore, by using the fiber reinforced resin of the present invention, it is possible to reduce the weight and improve the strength of automobile parts.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
<1. Production of high strength polypropylene fiber>
[Reference Examples 1-3]
Commercially available polypropylene (PP) (FY6; M _w = 5.1 × 10 ⁵ ; M _n = 1.2 × 10 ⁵ ; M _w / M _n = 4.1; mmmm fraction = 0.934; Nippon Polypro Co., Ltd.) was charged into an extruder. PP was melt extruded at an extrusion speed of Here, the melting temperature of the extruder was set to a furnace temperature of 190 ° C. and a die temperature of 185 ° C., and the nozzle diameter of the extrusion port was set to 0.5 mm (Reference Example 1) or 1 mm (Reference Examples 2 and 3). The melt-extruded PP fiber is rapidly cooled to 0 ° C in an ice bath, wound around the take-up shaft at various take-up speeds at 0 ° C, and both ends of the fiber are fixed to the take-up shaft, and the melt-extruded fiber is wound. A body was formed (melt extruded fiber spinning process). The wound body of the obtained melt-extruded fiber was maintained at 0 ° C. for 48 hours in an ice bath (temperature maintaining step). Thereafter, the fiber was drawn from the wound body of the melt-extruded fiber, and the fiber was stretched 10 times at room temperature by using a hand-drawing stretcher, and then wound on a winding shaft to form a wound body of the stretched fiber ( Stretching step). A drawn fiber wound body in which both ends of the fiber were fixed to the winding shaft was heat-treated at 120 ° C. for 5 minutes (heat treatment step) to obtain the PP fiber of the present invention.

[Reference Comparative Example 1]
3 is an example of PP fiber obtained by the method described in Patent Document 5. PP fibers were obtained in the same manner as described above except that the extrusion speed and take-up speed were adjusted so that the melt drawing ratio was a value within the range of the prior art (17). The melt drawing ratio is calculated as the ratio of the take-up speed to the extrusion speed.

[Reference Comparative Example 2]
It is an example of PP fiber obtained by applying the melt drawing ratio of the present invention to the method of the prior art. PP fibers were obtained in the same manner as described above except that the extrusion speed and take-up speed were adjusted so that the melt drawing ratio was 189, the melt-extruded fibers were taken at room temperature, and the temperature maintaining step was omitted.

[Tensile strength test]
The tensile strength of the obtained PP fiber was measured. The measurement was performed using a 10 mm fiber length sample based on JIS-K-6301. The tensile speed was 20 mm / second. The results are shown in Table 1.

  As shown in Table 1, in the case of Reference Example 1 which was spun using an extrusion apparatus having a nozzle diameter of 0.5 mm, the tensile strength was improved as the melt drawing ratio was increased by adjusting the extrusion speed and take-up speed. Reference Example 1-3 having a melt draw ratio of 165 exhibited a tensile strength of 1.40 GPa. In Reference Example 2 in which spinning was performed using an extrusion apparatus having a nozzle diameter of 1.0 mm, the tensile strength decreased when the melt drawing ratio exceeded 200. Among the PP fibers of Reference Example 2, the tensile strength of Reference Example 2-4 having a melt draw ratio of 189 was the highest, and the tensile strength was 1.70 GPa.

  In contrast, Reference Comparative Example 1 prepared based on the method described in Patent Document 5 had a tensile strength of 0.82 GPa. Further, Reference Comparative Example 2 in which the same melt drawing ratio as that of Reference Example 2-4 showing the highest tensile strength in Reference Example 2 was applied and the melt-extruded fiber was taken at room temperature and the temperature maintaining step was omitted was 0.83. The tensile strength was GPa.

<Production of core-sheath fiber>
[Example]
Polyethylene terephthalate (PET) (RP560; T1 = 253 ° C; Tg1 = 69 ° C; Toyobo) as the core resin P1 and polypropylene (PP) (FY6; T2 = 168 ° C; Tg2 = 2 ° C) as the sheath resin P2. M _w = 5.1 × 10 ⁵ ; M _n = 1.2 × 10 ⁵ ; M _w / M _n = 4.1; mmmm fraction = 0.934; Nippon Polypro Co., Ltd., respectively, extrusion equipment (multifilament spinning equipment; CMF-2EIH; Chubu Machine Co., Ltd .; nozzle diameter: 0.7 mm x 12 holes), core resin P1 and sheath resin P2 at an extrusion rate of 8.5 g / min (2.1 m / min) and P1: P2 extrusion rate of 50:50 Was melt extruded. Here, the melting temperature of the extrusion apparatus was set to a temperature (gear pump temperature of 270 ° C. and die temperature of 280 ° C.) higher than the melting point T1 (253 ° C.) of the core resin P1.

  The melt-extruded core-sheath fiber is rapidly cooled to room temperature (28 ° C.), wound at a take-up shaft at various take-up speeds at that temperature, and both ends of the fiber are fixed to the take-up shaft to wind the melt-extruded core-sheath fiber. A thread was formed (melt extruded core-sheath fiber spinning step). The wound body of the obtained melt-extruded core-sheath fiber was maintained at 70 ° C. for 72 hours (temperature maintaining step). Thereafter, the fiber is drawn out from the wound body of the melt-extruded core-sheath fiber, and the fiber is drawn 9 or 12 times at room temperature (28 ° C.) using a hand-drawing machine, and then wound on a take-up shaft and drawn core. A wound body of sheath fiber was formed (stretching step). A wound body of drawn core-sheath fiber having both ends of the fiber fixed to the winding shaft was heat-treated at 140 ° C. for 15 minutes (heat treatment step) to obtain the core-sheath fiber of the present invention.

[Comparative example]
In the said Example, the core-sheath fiber was obtained by the method similar to the above except having omitted the temperature maintenance process.

[Tensile strength test]
The tensile strength of the obtained core-sheath fiber was measured as the tensile strength of the core resin P1. The measurement was performed using a 10 mm fiber length sample based on JIS-K-6301. The tensile speed was 20 mm / second. In the core-sheath fiber of the example, the sheath resin P2 was broken at the initial stage of the tensile test. After that, when a load was applied, it eventually broke. Here, since the final load at break is applied only to the core resin P1, the tensile strength (MPa) of the core resin P1 is the load (N) at break of the core resin P1. It was determined by dividing by the fiber cross-sectional area (mm ² ) of P1. That is,
Core resin P1 tensile strength (MPa) =
Load at the time of final break (N) / fiber cross-sectional area of core resin P1 (mm ² )
It is.

  In the core-sheath fiber of the comparative example, both the core resin P1 and the sheath resin P2 were broken at the initial stage of the tensile test. In this case, the final load at break is applied to the entire core resin P1 and the sheath resin P2. The tensile strength of the entire core-sheath fiber at this time is defined as σ (whole). The tensile strength (σ (core strength)) of the core resin P1 corresponds to a value obtained by subtracting the strength contribution (σ (sheath strength)) of the sheath resin P2 from σ (whole). Here, since the core-sheath fibers of the example and the comparative example both use the same PP resin as the sheath resin P2, the sheath resin of the example and the sheath resin of the comparative example have the same strength. I think that. Therefore, in the tensile test of the core-sheath fiber of the above example, the load decrease caused when the sheath resin P2 breaks is regarded as the strength contribution of the sheath resin P2, and the value is σ (sheath strength) of the comparative example. It was. And (sigma) (core part intensity | strength) was determined based on the following formula | equation.

σ (overall) = σ (sheath strength) × Vf50% (volume ratio)
+ Σ (core strength) × Vf50% (volume ratio)

The results are shown in Table 2.

  As shown in Table 2, the core-sheath fibers of Examples 1 to 3 exhibited a tensile strength of about 4 to 9 times that of the core-sheath fibers of Comparative Examples 1 to 3 in which the temperature maintaining step was omitted.

  From the above results, it became clear that by applying the fine crystal nucleation technology to the production of the core-sheath fiber, the core-sheath fiber having extremely high strength that cannot be obtained by the conventional technology can be produced.

  The method of the present invention makes it possible to produce a high-strength core-sheath fiber by a simple process. By heating a core-sheath fiber assembly obtained by cutting the high-strength core-sheath fiber of the present invention into a desired length, the adjacent portions in the core-sheath fiber assembly are fused and integrated, thereby reducing weight and weight. It becomes possible to produce a strong fiber-reinforced resin. This makes it possible to reduce the weight and improve the strength of automobile parts.

101 ... A collection of core-sheath fibers
102 ・ ・ ・ Fiber reinforced resin
1 ... Core sheath fiber
2 ... Core resin P1
3 ... Sheath resin P2
4 ... Core resin P1
5 ... Matrix resin P2

Claims (4)

A method for producing a core-sheath fiber comprising a core resin P1 having a melting point T1 and a sheath resin P2 having a melting point T2, the following steps:
Resin P1 and resin P2 are melt-extruded so as to form a core-sheath fiber in which resin P1 is the core and resin P2 is the sheath, and the melt-extruded core-sheath fiber is equal to or lower than the glass transition temperature of core resin P1. A melt-extruded core-sheath fiber spinning process in which spinning is performed while pulling at a temperature;
A temperature maintaining step of maintaining the melt-extruded core-sheath fiber obtained in the melt-extruded core-sheath fiber spinning step at a temperature in the range of the glass transition temperature ± 15 ° C. of the core resin P1, and a melt-extruded core-sheath fiber after the temperature maintaining step; A stretching step of stretching
Including
The melting point T1 is a temperature higher than the melting point T2 by 50 ° C. or more,
The method, wherein the ratio of the take-off speed to the extrusion speed in the melt-extruded core-sheath fiber spinning step is in the range of 50 to 400.   2. The method of claim 1, wherein the core resin P1 is a resin mainly composed of polyethylene terephthalate, and the sheath resin P2 is a resin mainly composed of polypropylene.   A core-sheath fiber produced by the method according to claim 1 or 2.   The assembly of core-sheath fibers produced by the method of claim 1 or 2 is heated at a temperature in the range of the melting point T2 or higher and the melting point T1 or lower, and the adjacent portions in the core-sheath fiber assembly are melted together. The manufacturing method of the fiber reinforced resin including the melt integration process to make.

Images