JP2013249554A - High strength-high modulus polypropylene fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polypropylene fiber that has high strength and high modulus without using a special raw material and/or special means.SOLUTION: There is provided a method for producing a polypropylene fiber including: a spinning step of a melt and extruded fiber, in which polypropylene is melt and extruded and the melt and extruded fiber is spun while it is drawn at a temperature of the glass-transition temperature of polypropylene or higher and the glass-transition temperature +20°C or lower so that the ratio of the drawing speed to the extruding speed falls in the range of 50 to 400; a temperature maintaining step for maintaining the melt and extruded fiber obtained in the spinning step of a melt and extruded fiber at a temperature of the glass-transition temperature of polypropylene or higher and the glass-transition temperature +20°C or lower; a drawing step for drawing the melt and extruded fiber after the temperature maintaining step; and a heat treating step for heat treating the fiber at a temperature of 110°C or higher and lower than 150°C while applying a stress in the range of 200 to 450 N/mmto the drawn fiber obtained in the drawing step.

Description

  The present invention relates to a high-strength and high-modulus polypropylene fiber and a method for producing the same.

Polypropylene (PP) is a thermoplastic resin obtained by polymerizing propylene. PP has the characteristics of low specific gravity, high strength, and excellent heat resistance and chemical resistance. For this reason, it is widely used in various applications such as fiber materials, packaging materials, containers and automobile parts.
PP fibers are usually produced by melt spinning PP and drawing the spun yarn.

  Patent Document 1 discloses that ultra-high molecular weight polypropylene (A) having an intrinsic viscosity [η] of at least 5 dl / g or more is 85 to 99.5 parts by weight, and polyethylene having an intrinsic viscosity [η] of at least 2 dl / g or more (B ) It is characterized by adding a fluidity improver (C) to an ultra-high molecular weight PP composition consisting of 0.5 to 15 parts by weight and melt-mixing it, then extruding it from a die and stretching the resulting extrudate. A method for producing an ultra-high molecular weight PP stretched molded product is described. The document describes that by using ultra high molecular weight PP, PP fibers having a tensile strength of at least 0.8 GPa can be obtained.

Patent Document 2 discloses melt-spun isotactic polypropylene having a melt flow index of 0.05 to 30 and a density of 0.890 g / cm ³ or more, and heat-treating the obtained unstretched fiber, followed by cold stretching and a stretching amount of 1 to 100. High-strength, high-elastic modulus, characterized in that it is stretched to more than 300% in total by performing one-stage or more thermal stretching in which the deformation rate during hot stretching exceeds 30% per minute. A method for producing polypropylene fibers is described.

  Patent Document 3 describes that an amorphous or low crystalline fibril as possible is zone-stretched at a temperature from the glass transition point to around the crystallization temperature to form an amorphous or low crystalline highly oriented fiber. A method for producing a high elastic modulus and high strength fiber, characterized by subjecting the obtained fiber to zone heat treatment at a temperature higher than the crystallization temperature while applying a high degree of tension, will be described.

  Patent document 4 is made of PP having a melt flow rate of 3 to 100 g / 10 min and an isotactic pentad fraction of 96.5% or more, and stretches an undrawn yarn having a smectic crystal ratio of 30% or more. A method for producing a PP fiber characterized by the following is described.

  As a method for producing polyhydroxyalkanoic acid (PHA) fiber, which is a thermoplastic resin similar to PP, the inventors of the present invention melt-extruded PHA to produce a melt-extruded fiber, and the melt-extruded fiber was converted to a glass transition temperature of PHA +15. Amorphous fibers are prepared by rapidly cooling to below ℃ and solidifying, and the amorphous fibers are allowed to stand at a glass transition temperature of +15 ℃ or less to produce crystallized fibers. A fiber manufacturing method (hereinafter also referred to as “microcrystalline nucleus stretching method”) characterized by heat treatment has been developed (Patent Document 5).

JP-A-6-41814 Japanese Unexamined Patent Publication No. 7-16415 JP-A-56-15430 Japanese Patent Laid-Open No. 9-701111 International Publication No. 2006/038373 Pamphlet

  In fiber-reinforced plastic applications that require high strength and rigidity, such as automotive parts, both the strength and elastic modulus of the plastic fiber that is the material are required to be high. However, the conventional method for producing PP fibers has a problem that it is difficult to obtain PP fibers having both high strength and high elastic modulus. For example, in the method described in Patent Document 3, PP fibers having a high elastic modulus are obtained by including steps of zone stretching and zone heat treatment. However, the breaking strength of the fiber is low.

  In the method described in Patent Document 1, PP fibers having high strength and high elastic modulus are obtained by using special ultra high molecular weight PP as a raw material. However, the use of such a special substance as a raw material increases the manufacturing cost.

  In the method described in Patent Document 5 developed by the present inventors, the resulting PHA fiber is obtained by a microcrystalline nucleus drawing method in which amorphous PHA fiber is allowed to stand near the glass transition temperature to produce a crystallized fiber. The strength of can be improved. The PHA fiber obtained by the method described in Patent Document 5 has a tensile strength of about 1.322 GPa and a Young's modulus of about 8.11 GPa.

  The present inventors applied the microcrystalline nucleus drawing method described in Patent Document 5 to polypropylene (PP), and the ratio of the take-off speed to the extrusion speed when spinning the melt-extruded fiber (hereinafter referred to as “melt-stretch ratio”). Has been developed to produce high-strength PP fiber without using special raw materials and / or means (PCT / JP2011 / 062346). ). PCT / JP2011 / 062346 discloses that the tensile strength of the PP fiber obtained by the method according to the application is about 1.7 GPa, but does not disclose the tensile modulus of the fiber. The present inventors investigated the tensile modulus of PP fiber obtained by the method disclosed in the application, and found that the tensile modulus was about 4.6 GPa. That is, the PP fiber obtained by the method disclosed in PCT / JP2011 / 062346 has a higher tensile strength but a lower tensile elastic modulus than the PP fiber obtained by the method described in Patent Documents 1 to 3. Therefore, there is a problem that it is necessary to further improve the tensile elastic modulus while maintaining the tensile strength of the PP fiber obtained by the method disclosed in PCT / JP2011 / 062346.

  Therefore, an object of the present invention is to provide a method for producing high-strength and high-modulus polypropylene fibers without using special raw materials and / or means.

  As a result of examining various means for solving the above problems, the present inventor performs heat treatment while applying a predetermined stress to the PP fiber after drawing in addition to the microcrystalline nucleus drawing method and optimization of the melt drawing ratio. Thus, it was found that PP fibers having high strength and high elastic modulus can be produced, and the present invention was completed.

That is, the gist of the present invention is as follows.
(1) A method for producing polypropylene fiber, comprising the following steps:
Polypropylene is melt-extruded, and the melt-extruded fiber is spun while being drawn so that the ratio of the take-off speed to the extrusion speed is in the range of 50 to 400 at a temperature not lower than the glass transition temperature of polypropylene and not higher than glass transition temperature + 20 ° C. Melt extrusion fiber spinning process;
A temperature maintaining step of maintaining the melt-extruded fiber obtained in the melt-extruded fiber spinning step at a temperature not lower than the glass transition temperature of polypropylene and not higher than the glass transition temperature + 20 ° C .;
A drawing step of drawing the melt-extruded fiber after the temperature maintaining step; and a temperature of 110 ° C. or more and less than 150 ° C. while applying a stress in the range of 200 to 450 N / mm ² to the drawn fiber obtained in the drawing step. A heat treatment step for heat treating the fiber;
Said method.
(2) Polypropylene fiber produced by the method described in (1) above.
(3) A fiber reinforced resin produced using the polypropylene fiber according to (2).

  According to the present invention, it is possible to provide a method for producing polypropylene fibers having high strength and high elastic modulus without using special raw materials and / or means.

It is process drawing which shows one Embodiment of the manufacturing method of the polypropylene fiber of this invention. FIG. 3 is a graph showing the relationship between the stress during the heat treatment step when producing the PP fibers of Example 1 and Comparative Example 1 and the tensile modulus of the resulting PP fibers. FIG. 3 is a diagram showing the relationship between the stress during the heat treatment step when producing PP fibers of Example 2 and Comparative Example 2, and the tensile modulus and tensile strength of the resulting PP fibers. A: Tensile modulus (GPa); B: Tensile strength (MPa). FIG. 3 is a view showing the tensile elastic modulus and tensile strength of the PP fibers of Example 3 and Comparative Example 3. A: Tensile modulus (GPa); B: Tensile strength (MPa).

<1. Production method of polypropylene fiber>
The present invention relates to a method for producing polypropylene fibers.
In the present specification, “polypropylene” (PP) means a polymer of propylene, so that all methyl groups have the same configuration, isotactic PP, and the configuration of adjacent methyl groups is opposite to each other. Syndiotactic PP in which the asymmetric carbon to which the methyl group is bonded is arranged, and atactic PP in which the asymmetric carbon to which the methyl group is bonded is arranged so that the configuration of the adjacent methyl group is irregular Any PP is included. The PP according to the present invention may be in the form of a single polymer selected from the PP, or may be in the form of a mixture of two or more PP selected from the PP. The PP according to the present invention includes any of the above forms. For example, the PP according to the present invention preferably has a mmmm fraction in a pentad (5-chain) stereoregularity evaluation of 0.85 or more, more preferably 0.9 or more. The mmmm fraction can be determined by ¹³ C-NMR method.

  The polypropylene according to the present invention may be in the form of a homopolymer consisting only of the above-mentioned PP units, or may be in the form of a copolymer (copolymer) with other monomers. 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.

Usually, when PP is formed into a fibrous form, PP fibers having a narrow molecular weight distribution are known to exhibit high strength. Therefore, the PP according to the present invention preferably has a weight average molecular weight (M _w ) in the range of 200,000 to 1,000,000. In addition, the ratio (M _w / M _n ) of the weight average molecular weight (M _w ) to the number average molecular weight (M _n ) is preferably 5 or less. The number average molecular weight and the weight average molecular weight can be determined by the GPC method.

  By using the polypropylene having the above characteristics in the method of the present invention, it is possible to produce polypropylene fibers having higher strength and higher elastic modulus than those of the prior art.

  FIG. 1 is a process diagram showing one embodiment of a method for producing polypropylene 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 fiber spinning process]
The method of the present invention includes a melt-extruded fiber spinning step (step S1) in which polypropylene is melt-extruded and the melt-extruded fiber is spun while being drawn at a temperature A. As will be described below, this step is performed under conditions that improve the degree of orientation of the PP resin molecules in the melt-extruded fiber.

  In this step, as a means for melt-extruding PP, a plastic fiber melt-extrusion technique that is usually used in the art may be used. Examples of the melt extrusion means include, but are not limited to, an extrusion apparatus that heats and melts the raw plastic and then presses and extrudes the melt. By using the extrusion apparatus in this step, the fiber diameter of the resulting PP fiber can be adjusted to a suitable range.

  In this step, the extrusion speed at which PP is melt-extruded may be in a range that satisfies a suitable ratio of the take-up speed to the extrusion speed described below. Further, the furnace temperature for melting and extruding PP is preferably equal to or higher than the melting point of the PP used, more preferably the melting point + 10 ° C or higher, and the temperature in the range of the melting point +15 to the melting point + 100 ° C. Is particularly preferred.

  In addition, although melting | fusing point is not limited, For example, it can determine by measuring melting | fusing point of PP used previously using a melting | fusing point measuring apparatus.

  The present inventors have found that when the method described in Patent Document 5 is applied to the production of PP fibers, the strength of PP fibers is improved in the same manner as PHA fibers. In the method described in Patent Document 5, the molten extruded fiber of PHA is rapidly cooled to a temperature in the range of not less than the glass transition temperature and not more than the glass transition temperature + 15 ° C. It is characterized by forming a microcrystal nucleus in the melt-extruded fiber by keeping it cold. 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 fiber is made into an amorphous form by rapidly cooling the melt-extruded fiber to a predetermined temperature A in this step, and this is further processed at a predetermined temperature in the temperature maintaining step described below. By maintaining at B, it is estimated that PP microcrystal nuclei can be formed in the melt-extruded fiber.

  In this step, the melt-extruded PP 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 needs to be a temperature in the range of not less than the glass transition temperature of PP and not more than the glass transition temperature + 20 ° C., and should be in the range of not less than the glass transition temperature and not more than the glass transition temperature + 10 ° C. preferable.

  In the present specification, “glass transition temperature (Tg)” means a temperature at which PP 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 fiber from the heating temperature in the melt-extrusion means to the temperature A is not particularly limited. For example, the melt-extruded fiber may be introduced into a liquid or gaseous cooling medium commonly used in the art. Examples of the cooling medium used in this step include, but are not limited to, water and ice water, air, and inert gases such as nitrogen and helium. Water or ice water is preferred. By rapidly cooling the melt-extruded fiber from the heating temperature in the melt-extrusion means to the temperature A using the above means, the PP forming the fiber can be made into an amorphous form.

  The crystal form of the obtained PP fiber is not limited, but can be determined by, for example, X-ray diffraction (XRD).

  In this step, the means for pulling the melt-extruded fiber at the temperature A is not particularly limited. For example, whether the melt-extruded fiber introduced into the cooling medium is formed into a wound winding body 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. Or, after passing through the cooling medium at a predetermined take-up speed, by forming a wound winding body on the take-up shaft at a predetermined take-up speed using a normal take-out means outside the cooling medium, The melt extruded fiber can be taken at temperature A. Alternatively, at a temperature A, the melt-extruded fiber rapidly cooled to the temperature A with the cooling medium is accommodated in a container that has been cooled to a temperature A in advance while being taken at a predetermined take-up speed using a normal take-up means. Melt extruded fibers can also be taken up. Either case is included in the embodiment of this step. Here, examples of the take-up means include, but are not limited to, a winding device and a roller that form a wound body by winding a fiber around a winding shaft such as a bobbin. Further, it is preferable that the melt-extruded fiber is recovered by the above-mentioned means while maintaining the tension state of the fiber applied by take-up, and is subjected to a temperature maintaining step described below. For example, the wound body of the melt-extruded 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. Also, the melt-extruded fiber contained 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. Thus, it is preferable to rapidly cool to temperature A.

  The inventors adjust the ratio between the extrusion speed and the take-up speed in this step, and set the ratio of the take-off speed to the extrusion speed (hereinafter also referred to as “melt stretch ratio”), which is usually set in the art. By optimizing to a range higher than 20, while spinning the melt extruded fiber at a temperature A, the strength of the resulting PP fiber is compared to that of PP fiber produced at a normal melt draw ratio. It has been found that it improves significantly. The effect is that the degree of orientation of the PP polymer molecules in the amorphous form in the melt-extruded fiber is optimized by optimizing the melt draw ratio in a higher range as compared with the prior art and quenching the melt-extruded fiber to the temperature A. This is presumed to improve and further improve the strength improvement effect by the microcrystal nuclei formed by the temperature maintaining step described below.

  In this step, the ratio of the take-off speed to the extrusion speed (melt drawing ratio) needs to be in the range of 50 to 400, and preferably in the range of 180 to 220. In this case, the take-up speed at which the melt-extruded fiber introduced into the cooling medium at temperature A is taken is preferably in the range of 50 to 2,500 mm / sec, and more preferably in the range of 200 to 2,000 mm / sec. . By adjusting the ratio of the take-off speed to the extrusion speed within the above range, the degree of orientation of the PP polymer molecules in the melt-extruded fiber can be improved, and the strength of the resulting PP fiber can be improved.

  By carrying out this step under the above conditions, it becomes possible to form a PP melt-extruded fiber having an amorphous form in which the degree of orientation of polymer molecules is improved.

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

  In this step, it is preferable that the melt-extruded fiber maintains the tension state of the fiber applied in the melt-extruded fiber spinning step. For example, in the case of a wound body of melt-extruded fiber, the temperature is preferably maintained at the temperature B so that the fiber is not substantially relaxed by a conventional method such as fixing both ends of the fiber to a winding shaft. In the case of melt-extruded fiber contained in a container, the fiber is not 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. Thus, the temperature B is preferably maintained.

  In this step, the temperature B for maintaining the melt-extruded fiber needs to be a temperature in the range of the glass transition temperature of PP and the glass transition temperature + 20 ° C. or less, and the glass transition temperature + 10 ° C. or less. It is preferable that the temperature be in the range. It is particularly preferable that the temperature A at which the melt-extruded fiber is rapidly cooled in the melt-extruded fiber spinning step and the temperature B at which the melt-extruded fiber is maintained in this step are the same. The time for maintaining the melt-extruded fiber at the temperature B is preferably in the range of 3 to 72 hours, and more preferably in the range of 12 to 48 hours. Here, as the means for maintaining the melt-extruded fiber at the temperature B, it is preferable to use the same means as 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 fiber of PP having an amorphous form obtained in the melt-extruded fiber spinning step.

[3. Stretching process]
The method of the present invention includes a drawing step (step S3) for drawing the melt-extruded fiber after the temperature maintaining step.
In this step, as a means for stretching the melt-extruded 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 a melt-extruded fiber from a 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 fiber does not break. Specifically, the draw ratio is preferably 2 times or more, and more preferably 10 times or more. Further, the temperature at which the melt-extruded fiber is stretched is preferably not less than the glass transition temperature of PP, more preferably not less than the glass transition temperature and not less than the glass transition temperature + 50 ° C., and room temperature (for example, 20 to A range of 25 ° C. is particularly preferable.

  Thereafter, the drawn fiber can be formed into a wound yarn body on a winding shaft at a predetermined drawing speed by using a usual take-up means, or can be accommodated in a container. Alternatively, the stretched fiber may be subjected to a heat treatment step to be described below as it is. Either case is included in the embodiment of this step. The drawn fiber is preferably collected by the above means while maintaining the tension state of the fiber applied by drawing, and is preferably subjected to a heat treatment step described below. For example, the wound body of drawn fiber is preferably made so that the fiber is not substantially relaxed by a conventional method such as fixing both ends of the fiber to a winding shaft. The drawn fiber contained 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 preferred that

  By carrying out this step under the above conditions, it is possible to reduce the fiber diameter of the resulting PP fiber.

[4. Heat treatment process]
The method of the present invention includes a heat treatment step (step S4) in which the fiber is heat treated at a temperature C while applying stress to the drawn fiber obtained in the drawing step.
The present inventors have found that when the fiber is heat-treated while applying stress to the drawn fiber obtained in the above step, the resulting elastic modulus of the PP fiber is improved. In the drawn fiber obtained in the above step, polymer molecules are highly oriented with a microcrystal nucleus as a starting point of drawing. By performing heat treatment while applying stress to the drawn fiber, crystals can be formed while suppressing the relaxation of highly oriented polymer molecular chains. Therefore, it is presumed that the resulting PP fiber has improved elastic modulus while maintaining high strength.

In this process, the stress applied to the drawn fiber is required to be in the range of 200 to 450 N / mm ^2, preferably in the range of ^{270~420 N / mm 2, 390 ±} 25 N / A range of mm ² is more preferable. It is preferable to heat-treat the drawn fiber while applying an initial stress in the above range and then continuously applying the stress in the above range. By heat-treating the drawn fiber while applying stress to the drawn fiber under the above conditions, crystals can be formed while suppressing relaxation of the PP polymer molecular chain.

  The stress applied to the drawn fiber can be calculated based on the respective values obtained by measuring the load applied to the drawn fiber and the cross-sectional area of the fiber, for example.

  In this step, various means known in the art can be applied as means for applying stress to the drawn fiber. There is no particular limitation as long as it is a means that can continuously apply the stress in the above range to the drawn fiber during this step. For example, by fixing one end or both ends of the drawn fiber to a load means such as a weight, a load is continuously applied to the fiber. Thereby, the initial stress of the said range can be provided to a drawn fiber, and the stress of the said range can be continuously given after that. In this case, the load by the loading means may be a substantially constant amount during the execution of this step, or may be appropriately increased or decreased according to the stress applied to the drawn fiber. Alternatively, in the case of a wound body of drawn fiber, after applying the initial stress in the above range and winding the wound fiber around the winding shaft, the both ends of the fiber are fixed to the winding shaft so that the fiber is continuously continuous. You may continue to give the stress of the said range.

  In this step, the temperature C at which the drawn fiber is heat-treated needs to be 110 ° C. or higher and lower than 150 ° C., and is preferably in the range of 120 to 140 ° C. When the temperature C is within the above range, it is preferable because the tensile elastic modulus is improved. The time for heat treating the drawn fiber at temperature C is preferably in the range of 2 to 15 minutes, and more preferably in the range of 5 to 10 minutes. By performing heat treatment under the above conditions, crystals can be formed while suppressing relaxation of the PP polymer molecular chain.

  In this step, the drawn fiber can be heated if it can be heat-treated at a temperature C over substantially the entire length of the stretched fiber to which the stress in the above range is applied (hereinafter also referred to as “stressed portion”). There is no particular limitation on the means to do. For example, the stressed portion of the drawn fiber is placed on a heating device such as a heater or a roller that is usually used in the technical field, and heat treatment is performed at a temperature C while applying the stress in the above range. Can do. Alternatively, by introducing the stress-applying portion of the drawn fiber into a liquid or gas heating medium usually used in the technical field, and heat-treating at a temperature C while applying the stress in the range in the heating medium, It can also be implemented. Examples of the heating medium include, but are not limited to, liquids such as water and silicone oil, air, and inert gases such as nitrogen and helium. The heating medium may be maintained at the temperature C by a heating device such as a constant temperature bath or a dry oven usually used in the technical field.

  By carrying out this step under the above conditions, it is possible to obtain PP fibers having high strength and high elastic modulus.

<2. Polypropylene fiber>
As described above, the melt-extruded fiber of PP obtained by the method of the present invention has a high degree of orientation of the PP polymer molecules in the fiber and has microcrystalline nuclei that serve as starting points (stretch nuclei) in the fiber. . In addition, by thermally treating the drawn fiber while applying stress to the drawn fiber in the heat treatment step, the highly oriented polymer molecular chain in the drawn fiber forms crystals without relaxing. For this reason, the PP fiber obtained by the method of the present invention is extremely high compared to the PP fiber obtained by the prior art method (usually having a tensile strength of about 0.4 GPa and a tensile modulus of about 5 GPa). Not only has strength, but also has a very high elastic modulus. For example, the tensile strength of PP fibers produced by the method of the present invention is usually in the range of 1.0 to 1.8 GPa, and typically in the range of 1.3 to 1.8 GPa. Moreover, the tensile elastic modulus of the PP fiber produced by the method of the present invention is usually in the range of 5.0 to 12 GPa, and typically in the range of 8 to 12 GPa. The tensile strength and tensile modulus can be determined based on JIS-K-6301.

<3. Fiber reinforced resin>
The PP fiber obtained by the method of the present invention has extremely high strength and elastic modulus compared to the PP fiber obtained by the prior art method. Therefore, the present invention also relates to a fiber reinforced resin produced using the PP fiber of the present invention.

  The fiber reinforced resin of the present invention contains the PP fiber of the present invention described above. Moreover, the fiber reinforced resin of the present invention may contain one or more additives such as a binder, a plasticizer, a colorant, a stabilizer, a lubricant, and a filler, if desired. By containing the additive, various functions can be imparted to the fiber reinforced resin of the present invention.

  As described above in detail, the method of the present invention can produce PP fibers having high strength and high elastic modulus without using special raw materials and / or means. In addition, since the PP fiber of the present invention has high tensile strength and tensile modulus, the reinforcing fiber resin produced using the PP fiber is not only lightweight but also has high strength and high rigidity. . Therefore, by using the fiber reinforced resin of the present invention, it is possible to reduce the weight of automobile parts and improve the strength and rigidity.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples.

<Reference example: Effect of optimization of microcrystal nucleus stretching method and melt stretching ratio>
[Production of polypropylene fibers of Reference Examples 1 and 2]
It is an example of PP fiber obtained by the method disclosed in PCT / JP2011 / 062346.
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 Example 2). 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). Then, after drawing the fiber from the wound body of the melt-extruded fiber and stretching the fiber 10 times at room temperature using a hand-drawing stretcher (stretching step), the stretched fiber having both ends of the fiber fixed to the hand-drawing machine In this state (hereinafter also referred to as “constant length method”), heat treatment was performed at 120 ° C. for 5 minutes (heat treatment step) to obtain PP fibers.

[Production of Polypropylene Fiber of 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 the take-up speed were adjusted so that the melt drawing ratio was a value (17) in the range of the prior art. The melt drawing ratio is calculated as the ratio of the take-up speed to the extrusion speed.

[Preparation of polypropylene fiber of 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 of polypropylene fiber]
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.

<Test 1: Effect of applied stress during heat treatment process>
[Production of polypropylene fiber of Example 1]
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, and 4.54 PP was melt extruded at an extrusion rate of mm / sec. Here, the melting temperature of the extrusion apparatus was set to a cylinder temperature of 160-210-240-240 ° C. and a die temperature of 240 ° C., and the nozzle of the extrusion port was a 24-hole nozzle having an inner diameter of 1.0 mm. The melt-extruded PP fiber is wound on a take-up shaft at a take-up speed of 908 mm / sec while rapidly cooling in a 9 ° C water bath, and both ends of the fiber are fixed to the take-up shaft. (Melt extrusion fiber spinning step). At this time, the ratio of the take-off speed to the extrusion speed was 200. The obtained wound body of the melt-extruded fiber was kept at 2 ° C. in a water bath and maintained at the temperature for 48 hours (temperature maintaining step). After drawing the fiber from the wound body of the melt-extruded fiber after the temperature maintaining step, the fiber is stretched 10 times at room temperature using a hand-drawing machine, and then wound on a take-up shaft to form a wound body of drawn fiber. (Stretching step). By drawing the fiber from the wound body of drawn fiber after the drawing process, fixing one end of the fiber in a dry oven at 120 ° C., and connecting various weights corresponding to a predetermined initial stress to the other end Then, heat treatment was performed at 120 ° C. for 5 minutes (heat treatment step) while applying a predetermined stress to the fibers (hereinafter also referred to as “loading method”) to obtain PP fibers of Examples 1-1 to 1-4.

[Production of polypropylene fiber of Comparative Example 1]
In the procedure of Example 1, the same procedure as described above except that the wound fiber body of the drawn fiber with both ends of the fiber fixed to the take-up shaft was heat-treated as it was (hereinafter also referred to as “constant length method”). Thus, a PP fiber of Comparative Example 1 was obtained. The PP fiber production method of Comparative Example 1 corresponds to the method disclosed in PCT / JP2011 / 062346. The initial stress applied to the PP fiber by the constant length method corresponds to 53 N / mm ² .

[Production of Polypropylene Fiber of Example 2]
PP fibers of Examples 2-1 to 2-7 were obtained in the same procedure as described above except that the temperature of the heat treatment step was changed to 140 ° C. and the time was changed to 10 minutes in the procedure of Example 1.

[Production of polypropylene fiber of Comparative Example 2]
In the procedure of Example 2, the wound fiber body of the drawn fiber having both ends of the fiber fixed to the take-up shaft was heat-treated as it was, and the PP fiber of Comparative Example 2 was obtained in the same procedure as described above. . The PP fiber production method of Comparative Example 2 corresponds to the method disclosed in PCT / JP2011 / 062346. The initial stress applied to the PP fiber by the constant length method corresponds to 53 N / mm ² .

[Performance test of polypropylene fiber]
The tensile modulus and tensile strength of the obtained PP fiber were 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 2. FIG. 2 shows the relationship between the stress during the heat treatment step in producing the PP fibers of Example 1 and Comparative Example 1 and the tensile modulus of the resulting PP fibers.

As shown in Table 2, in the heat treatment step, the PP fibers of Examples 1-1 to 1-3 heat-treated by the load method are given in comparison with the PP fiber of Comparative Example 1 heat-treated by the constant length method. The higher the stress, the higher the tensile modulus. In the case of Example 1-3 having an initial stress of 368 N / mm ² , the tensile elastic modulus was 7.3 GPa. In Example 1-4 where the initial stress was 526 N / mm ² , the fiber broke during the heat treatment step (FIG. 2).

  A similar tendency was confirmed in Example 2 in which the temperature of the heat treatment step was changed to 140 ° C. FIG. 3 shows the relationship between the stress during the heat treatment step when producing the PP fibers of Example 2 and Comparative Example 2, and the tensile modulus and tensile strength of the resulting PP fibers.

<Test 2: Effect of temperature and time during the heat treatment process>
[Production of polypropylene fiber]
In the procedure of Example 1, the temperature of the heat treatment step was changed to 120 or 140 ° C., the time was changed to 5 or 10 minutes, and the initial stress was changed to 368 N / mm ^2. 1-3-4 PP fibers were obtained.

In the procedure of Example 3, a PP fiber of Comparative Example 3 was obtained in the same procedure as above except that the drawn fiber wound body in which both ends of the fiber were fixed to the winding shaft was heat-treated as it was. . The PP fiber production method of Comparative Example 3 corresponds to the method disclosed in PCT / JP2011 / 062346. The initial stress applied to the PP fiber by the constant length method corresponds to 53 N / mm ² .

[Performance test of polypropylene fiber]
In the same procedure as in Test 1, the tensile modulus and tensile strength of the obtained PP fiber were measured. The results are shown in Table 3. FIG. 4 shows the tensile elastic modulus and tensile strength of the PP fibers of Examples 3-1 to 3-4 and Comparative Example 3.

  As shown in FIG. 4A, the tensile modulus increased as the temperature and / or time of the heat treatment during the heat treatment step increased. In addition, as shown in FIG. 4B, the PP fibers of Examples 3-1 to 3-4 that were subjected to the heat treatment step while applying stress to the drawn fiber were the PPs of Comparative Example 3 that were subjected to the heat treatment step by a constant length method. Compared with the fiber, the tensile strength substantially equivalent was maintained.

<Test 3: Effect of temperature and applied stress during the heat treatment process>
[Production of polypropylene fiber]
In the procedure of Example 1, the temperature of the heat treatment step was changed to 100, 110, 120, 140, or 150 ° C., the time was changed to 10 minutes, and the initial stress was changed to 406 N / mm ² . PP fibers of Examples 4-1 to 4-5 were obtained.

[Performance test of polypropylene fiber]
In the same procedure as in Test 1, the tensile modulus and tensile strength of the obtained PP fiber were measured. The results are shown in Table 4.

  As shown in Table 4, when the temperature of the heat treatment during the heat treatment step was 100 ° C. or less (Example 4-1), the tensile modulus was not improved even when stress was applied. On the other hand, when the temperature of the heat treatment during the heat treatment step was 110 ° C. or higher and lower than 150 ° C. (Examples 4-2 to 4-4), the tensile modulus increased as the temperature increased. However, in Example 4-5 in which the heat treatment process was performed at 150 ° C., the fiber broke during the heat treatment process.

  This result is considered to be due to the difference in the rate of crystallization of PP in the PP fiber that proceeds in the heat treatment step. When the temperature of the heat treatment during the heat treatment process is 100 ° C. or lower, the crystallization of PP proceeds slowly, so that the heat treatment for 10 minutes results in insufficient crystal alignment, and as a result, the improvement in tensile modulus could not be confirmed. It is done. On the other hand, when the temperature of the heat treatment during the heat treatment step is 150 ° C. or higher, the PP fiber cannot be obtained because the fiber breaks during the heat treatment step.

  From the above, in order to produce PP fiber with a high elastic modulus, the temperature of the heat treatment during the heat treatment step is preferably 110 ° C. or more and less than 150 ° C., and the temperature is in the range of 120 to 140 ° C. Is more preferable.

Claims (3)

A method for producing polypropylene fiber comprising the following steps:
Polypropylene is melt-extruded, and the melt-extruded fiber is spun while being drawn so that the ratio of the take-off speed to the extrusion speed is in the range of 50 to 400 at a temperature not lower than the glass transition temperature of polypropylene and not higher than glass transition temperature + 20 ° C. Melt extrusion fiber spinning process;
A temperature maintaining step of maintaining the melt-extruded fiber obtained in the melt-extruded fiber spinning step at a temperature not lower than the glass transition temperature of polypropylene and not higher than the glass transition temperature + 20 ° C .;
A drawing step of drawing the melt-extruded fiber after the temperature maintaining step; and a temperature of 110 ° C. or more and less than 150 ° C. while applying a stress in the range of 200 to 450 N / mm ² to the drawn fiber obtained in the drawing step. A heat treatment step for heat treating the fiber;
Said method.   2. A polypropylene fiber produced by the method according to claim 1.   A fiber-reinforced resin produced using the polypropylene fiber according to claim 2.

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