Flat-section glass fiber, glass fiber reinforced resin composition and glass fiber reinforced resin molded articles

Abstract

This invention provides a flat-section glass fiber that, compared to oblong-section glass fibers, offers superior spinnability and chopped strand productivity. The invention comprises a plurality of flat-section glass filaments with a long diameter of 15.0–25.0 μm, a short diameter of 8.0–12.0 μm, and an aspect ratio R of 1.5–3.0 for the ratio of long diameter to short diameter (long diameter / short diameter). The fiber is characterized by a fill power P of 80.1–89.9% for the cross-sectional area of ​​the flat-section glass filaments relative to the area of ​​the rectangle circumscribed around the cross-section of the flat-section glass filaments, where the aspect ratio R and fill power P satisfy the following formula (1).

Description

Flat cross-section glass fiber, glass fiber reinforced resin composition, and glass fiber reinforced resin molded product The present invention relates to flat cross-section glass fibers, glass fiber reinforced resin compositions, and glass fiber reinforced resin molded products. Conventionally, there is known a glass fiber reinforced resin molded product containing glass fibers including a plurality of flat-cross-section glass fibers having a flat cross-section (hereinafter sometimes referred to as flat-cross-section glass fibers) (see, for example, Patent Document 1). In particular, glass fiber reinforced resin molded articles containing glass fibers (hereinafter sometimes referred to as oblong cross-section glass fibers) including a plurality of flat cross-section glass fibers (hereinafter sometimes referred to as oblong cross-section glass fibers) having an oblong cross-section (where the short sides of each rectangle are replaced with a semicircle having the short sides as the diameter) are used in thin and short parts such as portable electronic device casings because they suppress the occurrence of warping, have excellent dimensional stability, and further have excellent mechanical properties such as tensile strength, compared to glass fiber reinforced resin molded articles containing glass fibers including a plurality of circular cross-section glass fibers. [Prior Art Literature] [Patent Literature] [Patent Document 1] International Publication No. 2020 / 137004 [Problems to be solved by the invention] However, compared with circular cross-section glass fibers, oblong cross-section glass fibers have a problem in that the yarns are cut more often during spinning, resulting in poor spinnability. Furthermore, when the aforementioned oblong cross-sectional glass fibers (glass strands) comprising a plurality of oblong cross-sectional glass fibers are cut into a specified length and processed into chopped strands, the cutting blades are more easily worn than in the case of the aforementioned circular cross-sectional glass fibers, so the number of times the cutting blades need to be replaced increases, which leads to a problem of deterioration in the productivity of the chopped strands. The present invention aims to provide a flat cross-section glass fiber that, when used as a glass fiber-reinforced resin molded article, maintains comparable mechanical properties such as dimensional stability and tensile strength compared to the aforementioned oblong cross-section glass fiber, while resolving the aforementioned problems and achieving superior spinnability and chopped strand productivity compared to the oblong cross-section glass fiber. [Means for Solving the Problem] To achieve this object, the present invention provides a glass fiber comprising a plurality of flat-section glass fibers having a flat cross-sectional shape, wherein the major diameter of the cross section is in the range of 15.0 to 25.0 μm, the minor diameter is in the range of 8.0 to 12.0 μm, and the profile ratio R of the ratio of the major diameter to the minor diameter (major diameter / minor diameter) is in the range of 1.5 to 3.0. The glass fiber is characterized in that the filling rate P of the ratio of the cross-sectional area of ​​the flat-section glass fibers to the area of ​​a rectangle circumscribed with the cross-sectional area of ​​the flat-section glass fibers (cross-sectional area of ​​the flat-section glass fibers / area of ​​the rectangle circumscribed with the cross-sectional area of ​​the flat-section glass fibers) is in the range of 80.1 to 89.9%, and the profile ratio R and the filling rate P satisfy the following formula (1). Furthermore, the flat cross-section glass fiber of the present invention preferably has the aforementioned profile ratio R and the aforementioned filling ratio P satisfying the following formula (2). Furthermore, the glass fiber reinforced resin composition of the present invention is characterized in that the flat cross-section glass fiber of the present invention is contained in the resin composition. Furthermore, the glass fiber reinforced resin molded article of the present invention is characterized in that it is composed of the glass fiber reinforced resin composition of the present invention. According to the flat cross-section glass fiber of the present invention, which satisfies the above-mentioned formula (1) according to the above-mentioned profile ratio R and the above-mentioned filling rate P, the glass fiber reinforced molded product of the present invention maintains the same mechanical properties such as dimensional stability and tensile strength as those of glass fiber reinforced resin molded products containing oblong cross-section glass fibers, and can also obtain excellent spinnability and short strand productivity compared with oblong cross-section glass fibers. Here, maintaining equivalent dimensional stability compared to glass fiber-reinforced resin molded articles containing oblong glass fibers means that the warpage of the glass fiber-reinforced resin molded articles, as measured by the measurement method described below, is 10.0 mm or less. Furthermore, maintaining equivalent mechanical properties compared to glass fiber-reinforced resin molded articles containing oblong glass fibers means that the tensile strength, as measured by the measurement method described below, is 230 MPa or greater. Furthermore, the phrase "excellent spinnability" means that the number of spinning cuts measured by the measurement method described below is less than 10. Furthermore, the phrase "excellent chopped yarn productivity" means that the number of cutter exchanges measured by the measurement method described below is less than 30. Furthermore, the flat cross-section glass fiber of the present invention satisfies the above formula (2) by virtue of the aforementioned profile ratio R and the aforementioned filling rate P. In the glass fiber reinforced molded product of the present invention, compared with the glass fiber reinforced resin molded product containing the oblong cross-section glass fiber, excellent mechanical properties such as dimensional stability and tensile strength can be obtained, and compared with the oblong cross-section glass fiber, more excellent spinnability and short-cut yarn productivity can be obtained. Here, "excellent dimensional stability compared to fiber-reinforced resin molded articles containing oblong-cross-section glass fibers" means that the warpage of the glass-fiber-reinforced resin molded articles, as measured by the method described below, is 7.5 mm or less. Furthermore, "excellent mechanical properties compared to fiber-reinforced resin molded articles containing oblong-cross-section glass fibers" means that the tensile strength, as measured by the method described below, is 240 MPa or greater. Furthermore, the phrase "more excellent spinnability" means that the number of spinning cuts, as measured by the method described below, is less than 9. Furthermore, the phrase "more excellent chopped yarn productivity" means that the number of cutter exchanges, as measured by the method described below, is less than 20. Furthermore, the glass fiber reinforced resin molded article according to the present invention can maintain equivalent mechanical properties such as dimensional stability and tensile strength as those of glass fiber reinforced resin molded articles containing glass fibers having an oblong cross-section. Here, the maintenance of mechanical properties such as dimensional stability and tensile strength equivalent to those of glass fiber reinforced resin molded articles containing oblong cross-section glass fibers has the same meaning as described above. Next, embodiments of the present invention will be described in further detail. The flat-cross-section glass fiber of this embodiment comprises a plurality of flat-cross-section glass fibers having a flat cross-section. The flat-cross-section glass fibers have a major diameter in the range of 15.0 to 25.0 μm, a minor diameter in the range of 8.0 to 12.0 μm, and an aspect ratio (R) in the range of 1.5 to 3.0. Here, the "cross-section" of the flat-cross-section glass fibers refers to a transverse cross-section perpendicular to the longitudinal direction of the flat-cross-section glass fibers, and the aspect ratio (R) is the ratio of the major diameter to the minor diameter (major diameter / minor diameter). In addition, the flat cross-section glass fiber filling rate P of this embodiment is in the range of 80.1 to 89.9%, and the aforementioned profile ratio R and the aforementioned filling rate P satisfy the following formula (1), preferably satisfying the following formula (2). Here, the filling rate P is the ratio of the cross-sectional area of ​​the flat cross-sectional glass filament to the area of ​​the rectangle circumscribing the cross-sectional area of ​​the flat cross-sectional glass filament (cross-sectional area of ​​the flat cross-sectional glass filament / area of ​​the rectangle circumscribing the cross-sectional area of ​​the flat cross-sectional glass filament). The flat-cross-section glass fibers of this embodiment can be produced, for example, by the following method. First, glass raw materials (batch glass) prepared to a predetermined glass composition are supplied to a melting furnace and melted at a temperature ranging from, for example, 1450°C to 1550°C. The melted batch glass (molten glass) is then drawn from 10 to 30,000 nozzle tips in a bushing that controls the melted glass at a predetermined temperature and rapidly cooled. By setting the nozzle tips to a non-circular shape, for example, one corresponding to the cross-sectional shape of the flat-cross-section glass fibers and including protrusions or notches for rapidly cooling the molten glass, and controlling the temperature conditions, flat-cross-section glass fibers can be obtained. Next, a bundling agent or adhesive is applied using an applicator of a coating device. Using a bundling shoe, 10 to 30,000 flat-cross-section glass filaments are bundled together. These filaments are then wound onto a tube at high speed using a winder, thereby producing the flat-cross-section glass fiber of this embodiment. Furthermore, in the flat-cross-section glass fiber of this embodiment, more than 50% of the glass filaments comprising the flat-cross-section glass fiber are the aforementioned flat-cross-section glass filaments, preferably at least 80%, more preferably at least 90%, and even more preferably 100%. The flat cross-section glass fibers of this embodiment can have their minor and major diameters adjusted by adjusting the major and minor diameters of the nozzle tip, the winding speed, and temperature conditions. For example, increasing the winding speed can reduce the minor and major diameters, while decreasing the winding speed can increase the minor and major diameters. The glass composition of the glass forming the flat cross-section glass fiber of this embodiment is not particularly limited, and can be, for example, the most commonly used glass composition, the E-glass composition. The E-glass composition contains SiO in the range of 52.0 to 56.0 mass % relative to the total amount of the glass fiber. 2. With Al in the range of 12.0~16.0 mass% 2O 3. With a total of 20.0-25.0% by mass of MgO and CaO, and 5.0-10.0% by mass of B 2O 3 composition. Examples of the flat cross-section glass fibers include glass yarn, glass chopped strands, glass roving, glass powder, and glass mat. Furthermore, the glass fibers may be in the form of glass yarn, glass cloth composed of lath roving, or chopped strand mat composed of glass chopped strands. Furthermore, the glass fibers may be dispersed in a glass fiber-reinforced resin molded article. For example, when the flat-cross-section glass fibers of this embodiment are chopped strands, the number of glass filaments constituting the flat-cross-section glass fibers is, for example, 10 to 20,000, preferably 50 to 10,000, and more preferably 1,000 to 8,000. Furthermore, the length of the chopped strands of the flat-cross-section glass fibers of this embodiment is, for example, 1.0 to 100.0 mm, preferably 1.2 to 51.0 mm, more preferably 1.5 to 30.0 mm, even more preferably 2.0 to 15.0 mm, and particularly preferably 2.3 to 7.8 mm. Here, the aforementioned short chopped strands can be obtained by cutting the flat cross-section glass fiber produced by the aforementioned method into the aforementioned specified length by feeding the glass fibers (strands) between a knife roller with cutters (cutting blades) installed radially at equal intervals and a rubber roller equipped with rubber on the outer circumference that contacts and rotates, and cutting the long fiber cutting device. When the flat cross-section glass fiber of this embodiment is a roving, the number of glass filaments constituting the flat cross-section glass fiber is, for example, 200 to 30,000. Furthermore, the flat cross-section glass fiber roving of this embodiment has a mass per unit area of ​​35 to 10,000 tex (g / km). When the flat-cross-section glass fiber of this embodiment is a glass powder (sometimes also referred to as cut fiber), the number of glass filaments constituting the flat-cross-section glass fiber is, for example, 10 to 20,000. Furthermore, the length of the glass powder of the flat-cross-section glass fiber of this embodiment is, for example, 0.001 to 0.900 mm. The glass powder can be obtained by pulverizing the flat-cross-section glass fiber produced by the aforementioned method using a known method such as a ball mill or Henschel mixer to the aforementioned specified length. In the flat cross-section glass fiber of the present embodiment, the major axis and minor axis of the cross section can be measured, for example, as follows. First, when the flat-cross-section glass fiber of this embodiment is not contained in a glass fiber-reinforced resin molded article, the flat-cross-section glass fiber is embedded in a resin such as an epoxy resin, the resin is cured, the cured resin is cut, and the cross-section is polished. The cross-section of the cured resin is then observed using an electron microscope. Furthermore, for all or 200 or more of the flat-cross-section glass fibers constituting the flat-cross-section glass fiber exposed in the cross-section of the cured resin, the lengths of the individual fibers are measured, with the longest side passing through the thick center of the flat-cross-section glass fiber as the major axis and the side perpendicular to the thick center of the flat-cross-section glass fiber as the minor axis. Furthermore, when the flat-cross-section glass fibers are contained in a glass fiber-reinforced resin molded article, the glass fiber-reinforced resin molded article is cut, the cross section is polished, and the cross section of the resin is then observed using an electron microscope. Furthermore, for the 200 or more flat-cross-section glass fibers constituting the flat-cross-section glass fibers exposed in the cross section of the resin, the lengths of the individual fibers are measured, with the longest side passing through the thick center of the flat-cross-section glass fibers being the major axis and the side perpendicular to the thick center of the flat-cross-section glass fibers being the minor axis. Here, even in either the case where the flat cross-section glass fibers are not included in the glass fiber reinforced resin molded product or are included in the glass fiber reinforced resin molded product, the major axis and minor axis of the cross-section can be measured by processing the image obtained by an electron microscope using an automatic analysis device. The flat-cross-section glass fiber of the present invention is the aforementioned flat-cross-section glass fiber, wherein the major diameter of the cross section is in the range of 15.0 to 25.0 μm, preferably in the range of 16.1 to 23.9 μm, and more preferably in the range of 17.1 to 22.4 μm. The flat-cross-section glass fiber of the present invention is the flat-cross-section glass fiber described above, wherein the short diameter of the cross section is in the range of 8.0 to 12.0 μm, preferably in the range of 8.6 to 11.4 μm, and more preferably in the range of 9.1 to 11.0 μm. The above-mentioned irregularity ratio R can be calculated as the ratio of the major diameter to the minor diameter (major diameter / minor diameter) from the major diameter and minor diameter of the aforementioned cross section measured as described above. In addition, the area of ​​the rectangle circumscribed with the cross section of the flat cross-section glass fiber can be calculated from the major diameter and minor diameter of the aforementioned cross section measured as described above, as the product of the minor diameter and the major diameter (minor diameter × major diameter). When measuring the major diameter and minor diameter of the cross-sectional area of ​​the aforementioned flat cross-section glass fiber, the measurement can be performed using well-known image analysis software such as "A-Image" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.). Moreover, the aforementioned filling rate P can be calculated from the area of ​​the aforementioned rectangle circumscribed with the cross-section of the flat-section glass fiber and the cross-sectional area of ​​the aforementioned flat-section glass fiber, as the ratio of the cross-sectional area of ​​the flat-section glass fiber to the area of ​​the rectangle circumscribed with the cross-section of the flat-section glass fiber (cross-sectional area of ​​the flat-section glass fiber / area of ​​the rectangle circumscribed with the cross-section of the flat-section glass fiber). If the profile ratio R of the flat cross-section glass fiber of this embodiment exceeds 3.0, the spinnability and chopped strand productivity are reduced, and if it is less than 1.5, sufficient mechanical properties such as dimensional stability and tensile strength cannot be obtained in the glass fiber reinforced resin molded article of the present invention. In the flat glass fiber of this embodiment, the profile ratio R is preferably in the range of 1.6 to 2.8, more preferably in the range of 1.7 to 2.5, and even more preferably in the range of 1.8 to 2.3. Furthermore, when the filling ratio P of the flat cross-section glass fiber of the present invention exceeds 89.9%, the cross-sectional shape becomes too close to a rectangle, thereby reducing the spinnability and chopped strand productivity. Furthermore, when the filling ratio P is less than 80.1%, the cross-sectional shape becomes too close to an ellipse, and sufficient mechanical properties such as tensile strength cannot be obtained in the glass fiber-reinforced resin molded article of the present invention. In the flat cross-section glass fiber of this embodiment, the filling rate P is preferably in the range of 86.4% or less, more preferably in the range of 84.9% or less, further preferably in the range of 80.6 to 84.4%, and particularly preferably in the range of 81.6 to 83.9%. The flat cross-section glass fiber of this embodiment preferably has a cross-sectional shape that is approximately symmetrical with respect to the longest side passing through the thick center of the flat cross-section glass fiber. In the flat cross-section glass fiber of this embodiment, while the effect of improving tensile strength and warpage increases with increasing filling ratio P, there is a tendency for spinnability and chopped strand production to deteriorate. On the other hand, while the effect of improving tensile strength and warpage increases with increasing profile ratio R, spinnability and chopped strand production deteriorate. It is believed that formula (1) represents this balance. According to the flat cross-section glass fiber of this embodiment, since the aforementioned profile ratio R and the aforementioned filling rate P satisfy the aforementioned formula (1), the glass fiber-reinforced resin molded article of this embodiment containing the flat cross-section glass fiber can maintain the same mechanical properties such as dimensional stability and tensile strength as those of the glass fiber-reinforced resin molded article containing the oblong cross-section glass fiber, while achieving excellent spinnability and chopped strand productivity compared to the oblong cross-section glass fiber. Here, maintaining equivalent dimensional stability compared to glass fiber-reinforced resin molded articles containing oblong glass fibers means that the warpage of the glass fiber-reinforced resin molded articles, as measured by the measurement method described below, is 10.0 mm or less. Furthermore, maintaining equivalent mechanical properties compared to glass fiber-reinforced resin molded articles containing oblong glass fibers means that the tensile strength, as measured by the measurement method described below, is 230 MPa or greater. Furthermore, the phrase "excellent spinnability" means that the number of spinning cuts measured by the measurement method described below is less than 10. Furthermore, the phrase "excellent chopped yarn productivity" means that the number of cutter exchanges measured by the measurement method described below is less than 30. [Method for Measuring Warpage of Glass Fiber-Reinforced Resin Molded Articles] First, the surface of the flat-cross-section glass fiber was coated with a composition containing a silane coupling agent and cut into 3 mm lengths to prepare chopped strands. Next, the chopped strands were kneaded with polyamide 6 resin (manufactured by Ube Industries, Ltd., trade name: UBE1015B) in a twin-screw kneader (manufactured by Shibaura Machine Co., Ltd., trade name: TEM-26SS) at 270°C, with the screw speed set at 100 rpm, to produce resin pellets containing 50% by mass of glass fiber. Next, the resin pellets were injection molded using an injection molding machine (NEX80, manufactured by Nissei Plastics Co., Ltd.) at a mold temperature of 80°C and an injection temperature of 270°C to form flat warp test pieces measuring 80 mm long, 60 mm wide, and 1 mm thick. When one corner of the warp test piece was grounded to a flat surface, the distance between the corner that was grounded to the flat surface and the corner at the opposite corner was measured with a vernier caliper. The distances were measured when each of the four corners of the warp test piece was grounded to a flat surface, and the average of the measured values ​​was determined as the warp value. [Method for Determining the Tensile Strength of Glass Fiber-Reinforced Resin Molded Products] First, the aforementioned resin pellets were injection molded using an injection molding machine (manufactured by Nissei Plastics Co., Ltd., trade name: NEX80) at a mold temperature of 80°C and an injection temperature of 270°C to form Type A dumbbell test pieces (4 mm thick) in accordance with JIS K 7165:2008. The Type A dumbbell test pieces were then subjected to a static tensile test in accordance with JIS K 7165:2008 at a test temperature of 23°C using a precision universal testing machine (manufactured by Shimadzu Corporation, trade name: Autograph AG-5000B) to determine their tensile strength. [Method for Measuring Spinning Cutoffs] During the 30-day production of the flat-cross-section glass fiber, the number of times the flat-cross-section glass fibers constituting the flat-cross-section glass fiber were cut was measured between shifts, each shift being 8 hours. The average number of cutoffs per shift, with each shift being 8 hours, was taken as the spinning cutoff. [Method for measuring chopped strand productivity] Strands of the flat cross-section glass fiber coated with a composition containing a silane coupling agent are mounted at equal intervals on radial blade rollers. The strands are fed into a long fiber cutting device between rollers equipped with rubber on the outer circumference and rotating in contact with the blade rollers. The strands are cut into 3 mm lengths and the number of cutter changes during 240 hours of chopped strand production is measured. Furthermore, the flat cross-section glass fiber of this embodiment satisfies the above formula (2) by virtue of the aforementioned profile ratio R and the aforementioned filling rate P. In the glass fiber reinforced molded product of the present invention, compared with the glass fiber reinforced resin molded product containing the oblong cross-section glass fiber, excellent mechanical properties such as dimensional stability and tensile strength can be obtained, and compared with the oblong cross-section glass fiber, more excellent spinnability can be obtained. Here, "excellent dimensional stability compared to fiber-reinforced resin molded articles containing oblong-cross-section glass fibers" means that the warpage of the glass-fiber-reinforced resin molded articles, as measured by the aforementioned method, is 7.5 mm or less. Furthermore, "excellent mechanical properties compared to fiber-reinforced resin molded articles containing oblong-cross-section glass fibers" means that the tensile strength, as measured by the aforementioned method, is 240 MPa or greater. Furthermore, the phrase "more excellent spinnability can be achieved" means that the number of spinning cuts measured by the aforementioned method is less than 9. Furthermore, the phrase "more excellent chopped yarn productivity can be achieved" means that the number of cutter exchanges measured by the aforementioned method is less than 20. Next, the glass fiber reinforced resin composition of this embodiment contains the flat cross-section glass fiber of this embodiment in the resin composition. Next, the glass fiber reinforced resin molded article of this embodiment is composed of the glass fiber reinforced resin composition of this embodiment. The glass fiber reinforced resin molded article of this embodiment maintains comparable mechanical properties such as dimensional stability and tensile strength to glass fiber reinforced resin molded articles containing oblong cross-section glass fibers. Here, the maintenance of mechanical properties such as dimensional stability and tensile strength equivalent to those of glass fiber reinforced resin molded articles containing oblong cross-section glass fibers has the same meaning as described above. Examples of the aforementioned resin composition constituting the glass fiber reinforced resin composition of the present embodiment include resin compositions containing thermoplastic resins or thermosetting resins. Examples of the thermoplastic resin include polyethylene, polypropylene, polystyrene, styrene / maleic anhydride resin, styrene / maleimide resin, polyacrylonitrile, acrylonitrile / styrene (AS) resin, acrylonitrile / butadiene / styrene (ABS) resin, chlorinated polyethylene / acrylonitrile / styrene (ACS) resin, acrylonitrile / ethylene / styrene (AES) resin, acrylonitrile / styrene / methyl acrylate (ASA) resin, styrene / acrylonitrile (SAN) resin, methacrylic resin, polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyamide, polyacetal, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polycarbonate, polyarylene sulfide, polyether sulfide (PES), polyphenylene sulfide (PPSU), polyphenylene ether (PPE), modified polyphenylene ether (PTT), and polyurethane elastomer. ether)(m-PPE), polyaryletherketone, liquid crystal polymer (LCP), fluororesin, polyetherimide (PEI), polyarylate (PAR), polysulfone (PSF), polyamide imide (PAI), polyaminobismaleimide (PABM), thermoplastic polyimide (TPI), polyethylene naphthalate (PEN), ethylene / vinyl acetate (EVA) resin, ionomer (IO) resin, polybutadiene, styrene / butadiene resin, polybutene, polymethylpentene, olefin / vinyl alcohol resin, cyclic olefin resin, cellulose resin, polylactic acid, etc. Examples of the polyethylene include high-density polyethylene (HDPE), medium-density polyethylene, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ultra-high molecular weight polyethylene. Examples of the polypropylene include isotactic polypropylene, atactic polypropylene, syndiotactic polypropylene, and mixtures thereof. Examples of the polystyrene include general-purpose polystyrene (GPPS) having an atactic structure, high-impact polystyrene (HIPS) having a rubber component added to GPPS, and syndiotactic polystyrene having a syndiotactic structure. Examples of the methacrylic resin include single polymers of acrylic acid, methacrylic acid, styrene, methyl acrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, and fatty acid vinyl esters, or copolymers of two or more thereof. Examples of the polyvinyl chloride include single vinyl chloride polymers polymerized by conventionally known methods such as emulsion polymerization, suspension polymerization, microsuspension polymerization, and bulk polymerization, copolymers of monomers copolymerizable with vinyl chloride monomers, and graft copolymers obtained by grafting vinyl chloride monomers onto polymers. Examples of the polyamides include polycaproamide (polyamide 6), polyhexamethylene adipamide (polyamide 66), polytetramethylene adipamide (polyamide 46), polytetramethylene decanediamide (polyamide 410), polypentamethylene adipamide (polyamide 56), polypentamethylene decanediamide (polyamide 510), polyhexamethylene decanediamide (polyamide 610), polyhexamethylene dodecanediamide (polyamide 612), polydecamethylene adipamide (polyamide 106), polydecamethylene decanediamide (polyamide 410), and polyhexamethylene dodecanediamide (polyamide 612). Polyamide (Polyamide 1010), Polydecamethylene dodecamethylene (Polyamide 1012), Polyundecamethylene (Polyamide 11), Polyundecamethylene adipamide (Polyamide 116), Polydodecylamide (Polyamide 12), Polyxylene adipamide (Polyamide XD6), Polyxylene decamethylene (Polyamide XD10), Polymethylene (m-xylylene) adipamide (Polyamide MXD6), Polyp-xylylene adipamide (Polyamide PXD6), Polytetramethylene Polyphenylenediamine (Polyamide 4T), Polypentamethylene-p-phenylenediamine (Polyamide 5T), Polyhexamethylene-p-phenylenediamine (Polyamide 6T), Polyhexamethylene-m-phenylenediamine (Polyamide 6I), Polynonamethylene-p-phenylenediamine (Polyamide 9T), Polydecamethylene-p-phenylenediamine (Polyamide 10T), Polyundecamethylene-p-phenylenediamine (Polyamide 11T), Polydodecamethylene-p-phenylenediamine (Polyamide 12T), Polytetramethylene-m-phenylenediamine (Polyamide 4I) ), polybis(3-methyl-4-aminohexyl)methane p-xylylenediamide (polyamide PACMT), polybis(3-methyl-4-aminohexyl)methane m-xylylenediamide (polyamide PACMI), polybis(3-methyl-4-aminohexyl)methane dodecanamide (polyamide PACM12), polybis(3-methyl-4-aminohexyl)methane tetradecylamide (polyamide PACM14), or a copolymer or a mixture thereof. Examples of the polyacetal include a single polymer containing oxymethylene units as main repeating units and a copolymer mainly composed of oxymethylene units and having oxyalkylene units having 2 to 8 adjacent carbon atoms in the main chain. Examples of the polyethylene terephthalate include polymers obtained by polycondensation of terephthalic acid or its derivatives and ethylene glycol. Examples of the polybutylene terephthalate include polymers obtained by polycondensing terephthalic acid or a derivative thereof with 1,4-butanediol. Examples of the polytrimethylene terephthalate include polymers obtained by polycondensation of terephthalic acid or a derivative thereof and 1,3-propylene glycol. Examples of the polycarbonate include polymers obtained by a transesterification method in which a dihydroxydiaryl compound is reacted with a carbonate such as diphenyl carbonate in a molten state, and polymers obtained by a phosgene method in which a dihydroxydiaryl compound is reacted with phosgene. Examples of the polyarylene sulfide include linear polyphenylene sulfide, cross-linked polyphenylene sulfide having a high molecular weight due to a curing reaction after polymerization, polyphenylene sulfide sulfone, polyphenylene sulfide ether, and polyphenylene sulfide ketone. Examples of the modified polyphenylene ether include polymer alloys of poly(2,6-dimethyl-1,4-phenylene) ether and polystyrene, polymer alloys of poly(2,6-dimethyl-1,4-phenylene) ether and styrene / butadiene copolymer, polymer alloys of poly(2,6-dimethyl-1,4-phenylene) ether and styrene / maleic anhydride copolymer, polymer alloys of poly(2,6-dimethyl-1,4-phenylene) ether and polyamide, and polymer alloys of poly(2,6-dimethyl-1,4-phenylene) ether and styrene / butadiene / acrylonitrile copolymer. Examples of the polyaryletherketone include polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polyetheretherketoneketone (PEEKK). Examples of the aforementioned liquid crystal polymer (LCP) include (co)polymers composed of one or more structural units selected from aromatic hydroxycarbonyl units, aromatic dihydroxy units, aromatic dicarbonyl units, aliphatic dihydroxy units, aliphatic dicarbonyl units, etc. selected from thermotropic liquid crystal polyesters. Examples of the fluororesin include polytetrafluoroethylene (PTFE), perfluoroalkoxy resin (PFA), fluorinated ethylene propylene resin (FEP), fluorinated ethylene tetrafluoroethylene resin (ETFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), and ethylene / chlorotrifluoroethylene resin (ECTFE). Examples of the ionomer (IO) resin include copolymers of olefins or styrene and unsaturated carboxylic acids, and polymers in which a portion of the carboxyl groups is neutralized with metal ions. Examples of the olefin / vinyl alcohol resin include ethylene / vinyl alcohol copolymers, propylene / vinyl alcohol copolymers, ethylene / vinyl acetate copolymer saponified products, and propylene / vinyl acetate copolymer saponified products. Examples of the cyclic olefin resin include monocyclic compounds such as cyclohexene, polycyclic compounds such as tetracyclopentadiene, and polymers of cyclic olefin monomers. Examples of the polylactic acid include poly-L-lactic acid which is a single polymer of the L-isomer, poly-D-lactic acid which is a single polymer of the D-isomer, and stereocomplex-type polylactic acid which is a mixture thereof. Examples of the cellulose resin include methyl cellulose, ethyl cellulose, hydroxy cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, cellulose propionate, and cellulose butyrate. In addition, examples of the aforementioned thermosetting resin include unsaturated polyester resin, vinyl ester resin, epoxy (EP) resin, melamine (MF) resin, phenol resin (PF), urethane resin (PU), polyisocyanate, polyisocyanurate, polyimide (PI), urea (UF) resin, polysilicone (SI) resin, furan (FR) resin, benzoguanamine (BR) resin, alkyd resin, xylene resin, bismaleimide tris (BT) resin, diallyl phthalate resin (PDAP), etc. Furthermore, in the flat-cross-section glass fiber of this embodiment, the flat-cross-section glass filaments constituting the flat-cross-section glass fiber may be in contact with each other or separated. When the flat-cross-section glass filaments are separated, a surface treatment agent or a resin composition constituting a glass fiber-reinforced resin molded article may be present between the flat-cross-section glass filaments. Examples of the surface treatment agent include urethane resins, epoxy resins, vinyl acetate resins, acrylic resins, modified polypropylene, especially carboxylic acid-modified polypropylene, copolymers of (poly)carboxylic acids, especially maleic acid, and unsaturated monomers, and silane coupling agents. Furthermore, the flat cross-section glass fiber of this embodiment may be coated with a composition containing, in addition to such resins or silane coupling agents, a lubricant, a surfactant, etc. Such a composition is coated on the flat cross-section glass fiber at a ratio of 0.1 to 2.0% by mass, based on the mass of the flat cross-section glass fiber in a state not coated with the composition. Alternatively, the flat-cross-section glass fiber may be coated with an organic material. For example, during the manufacturing process of the flat-cross-section glass fiber, a solution containing the resin, the silane coupling agent, or the composition may be applied to the flat-cross-section glass fiber using a known method such as a roller applicator. The flat-cross-section glass fiber coated with the solution of the resin, the silane coupling agent, or the composition may then be dried. Here, examples of the silane coupling agent include aminosilane, chlorosilane, epoxysilane, mercaptosilane, vinylsilane, acrylsilane, and cationic silane. These silane coupling agents may be used alone or in combination of two or more. Examples of aminosilanes include γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-N'-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-anilinopropyltrimethoxysilane. Examples of the chlorosilane include γ-chloropropyltrimethoxysilane and the like. Examples of epoxysilane include γ-glycidoxypropyltrimethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Examples of the mercaptosilane include γ-mercaptotrimethoxysilane and the like. Examples of the vinylsilane include vinyltrimethoxysilane and N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane. Examples of the acrylsilane include γ-methacryloxypropyltrimethoxysilane and the like. Examples of the cationic silane include N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride and N-phenyl-3-aminopropyltrimethoxysilane hydrochloride. Examples of lubricants include modified silicone oils, animal oils and their hydrogenated derivatives, vegetable oils and their hydrogenated derivatives, animal waxes, vegetable waxes, mineral waxes, condensates of higher saturated fatty acids and higher saturated alcohols, polyethyleneimine, polyalkylpolyamine / alkylamide derivatives, fatty acid amides, and quaternary ammonium salts. These lubricants may be used alone or in combination of two or more. Examples of animal oils include beef tallow and the like. Examples of the vegetable oil include soybean oil, coconut oil, rapeseed oil, palm oil, and castor oil. Examples of animal waxes include beeswax and lanolin. Examples of the vegetable wax include candelilla wax and carnauba wax. Examples of the mineral wax include paraffin wax and montan wax. Examples of the condensation product of a higher saturated fatty acid and a higher saturated alcohol include stearic acid esters such as lauryl stearate. Examples of the fatty acid amide include dehydration condensates of polyethylene polyamines such as diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, and fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid. Examples of the fourth-stage ammonium salt include alkyltrimethylammonium salts such as lauryltrimethylammonium chloride. Examples of the surfactant include nonionic surfactants, cationic surfactants, anionic surfactants, and amphoteric surfactants. These surfactants may be used alone or in combination of two or more. Examples of the nonionic surfactant include ethylene oxide propylene oxide alkyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene-polyoxypropylene-block copolymers, alkyl polyoxyethylene-polyoxypropylene-block copolymer ethers, polyoxyethylene fatty acid esters, polyoxyethylene fatty acid monoesters, polyoxyethylene fatty acid diesters, polyoxyethylene sorbitol fatty acid esters, glycerol fatty acid ester ethylene oxide adducts, polyoxyethylene castor oil ethers, hydrogenated castor oil ethylene oxide adducts, alkylamine ethylene oxide adducts, fatty acid amide ethylene oxide adducts, glycerol fatty acid esters, polyglycerol (Glycerine) fatty acid esters, pentaerythritol fatty acid esters, sorbitol fatty acid esters, sorbitol fatty acid esters, sucrose fatty acid esters, polyol alkyl ethers, fatty acid alkanolamides, acetylene glycol, acetylene alcohol, ethylene oxide adducts of acetylene glycol, and ethylene oxide adducts of acetylene alcohol. Examples of the cationic surfactant include alkyldimethylbenzylammonium chloride, alkyltrimethylammonium chloride, alkyldimethylethylammonium ethylsulfate, higher alkylamine acetates, higher alkylamine hydrochlorides, ethylene oxide adducts of higher alkylamines, condensates of higher fatty acids and polyalkylenepolyamines, salts of esters of higher fatty acids and alkanolamines, salts of higher fatty acid amides, imidazoline-type cationic surfactants, and alkylpyridinium salts. Examples of the anionic surfactant include higher alcohol sulfates, higher alkyl ether sulfates, α-olefin sulfates, alkylbenzenesulfonates, α-olefinsulfonates, reaction products of fatty acid halides and N-methyltaurine, dialkyl sulfosuccinates, higher alcohol phosphates, and phosphates of higher alcohol ethylene oxide adducts. Examples of the amphoteric surfactant include amino acid-type amphoteric surfactants such as alkali metal salts of alkylaminopropionic acid, and betaine-type and imidazoline-type amphoteric surfactants such as alkyldimethylbetaine. Examples of molding methods for obtaining the glass fiber reinforced resin molded article of this embodiment include injection molding, injection compression molding, two-color molding, hollow molding, foam molding (including those using supercritical fluids), insert molding, in-mold coating, extrusion, sheet molding, thermoforming, rotational molding, lamination, press molding, blow molding, stamping, injection molding, hand lamination, spraying, resin transfer molding, sheet molding compound, bulk molding compound, pultrusion, and filament winding. Among these methods, injection molding is preferred due to its excellent production efficiency. Next, examples of the present invention and comparative examples are shown. [Examples 1 to 4, Comparative Examples 1 to 4, Reference Example 1] First, glass raw materials (glass batch material) prepared in a manner to become an E-glass composition are supplied to a melting furnace and melted at a temperature in the range of 1450 to 1550°C. The resulting molten glass is pulled out from a bushing having 200 nozzle tips to obtain a plurality of flat cross-section glass fibers having a short diameter, a long diameter, a profile ratio R and a filling rate P shown in Table 1. The plurality of flat cross-section glass fibers are bundled to produce flat cross-section glass fibers. In this case, the nozzle tip may include a hole portion having a flat cross-sectional shape with a major diameter of a predetermined length and a minor diameter of a predetermined length, and a wall portion having a notch for cooling the molten glass. The length of the minor diameter of the hole portion is adjusted within a range of 0.2 to 2.5 mm, and the ratio of the major diameter to the minor diameter of the hole portion is adjusted within a range of 2.0 to 6.5. The amount of molten glass passing through the nozzle tip per portion is adjusted within a range of 0.1 to 3.0 g / min, thereby obtaining the flat cross-sectional glass fibers of Examples 1 to 4 and Comparative Examples 1 to 4. The flat cross-sectional glass fibers of Comparative Example 4 are oval cross-sectional glass fibers having an oval cross-sectional shape, and the flat cross-sectional glass fibers of Comparative Example 4 are oval cross-sectional glass fibers comprising a plurality of oval cross-sectional glass fibers. Furthermore, by determining that the nozzle tip has a hole portion having a true circular cross-sectional shape, a circular cross-sectional glass fiber of Reference Example 1 was obtained. Next, the flat cross-section glass fibers of Examples 1 to 4, Comparative Examples 1 to 4, and the round cross-section glass fibers of Reference Example 1 were subjected to the following procedures to measure the number of spinning cuts and evaluate the chopped strand productivity. [Determination of Spinning Cutoffs] 30 days after the production of the flat-cross-section glass fibers of Examples 1 to 4 and Comparative Examples 1 to 4, and the round-cross-section glass fibers of Reference Example 1, the number of cuts caused by the flat-cross-section glass fibers of Examples 1 to 4 and Comparative Examples 1 to 4, or the round-cross-section glass fibers of the round-cross-section glass fibers of Reference Example 1, was measured. One shift was defined as 8 hours, and the average number of cuts per shift was defined as the spinning cutoffs. A spinning cutoff of less than 9 times per shift was designated "A," a spinning cutoff of 9 or more but less than 10 times per shift was designated "B," and a spinning cutoff of 10 or more times per shift was designated "C." [Evaluation of Chopped Strand Productivity] Strands obtained by coating the surfaces of the flat-cross-section glass fibers of Examples 1-4, Comparative Examples 1-4, and the round-cross-section glass fibers of Reference Example 1 with a composition containing a silane coupling agent were fed into a long-fiber cutting apparatus between a cutter roll with radially mounted cutters (cutting blades) at equal intervals and a rubber roller equipped with a rubber outer surface that rotates in contact with the cutter roll. The strands were cut into 3 mm lengths. When the chopped strands were produced for 240 hours, the number of cutter replacements was measured. A cutter replacement of less than 20 times was rated "A," a cutter replacement of 20 or more but less than 30 times was rated "B," and a cutter replacement of 30 or more times was rated "C." Next, the flat cross-section glass fibers of Examples 1-4 and Comparative Examples 1-4, and the round cross-section glass fibers of Reference Example 1 were coated with a composition containing a silane coupling agent and cut into 3 mm lengths to obtain chopped strands of Examples 1-4, Comparative Examples 1-4, and Reference Example 1. Subsequently, the chopped strands were kneaded with polyamide 6 resin (manufactured by Ube Industries, Ltd., trade name: UBE1015B) in a twin-screw kneader (manufactured by Shibaura Machine Co., Ltd., trade name: TEM-26SS) at 270° C. with the screw speed set to 100 rpm to produce resin pellets of Examples 1-4, Comparative Examples 1-4, and Reference Example 1 having a glass fiber content of 50% by mass. Next, each resin pellet was injection molded using an injection molding machine (manufactured by Nissei Plastic Industry Co., Ltd., trade name: NEX80) at a mold temperature of 80°C and an injection temperature of 270°C to form a flat plate warpage measurement test piece with dimensions of 80 mm long × 60 mm wide × 1 mm thick, and a type A dumbbell test piece (thickness 4 mm) in accordance with JIS K 7165:2008. Next, the secondary warpage of each warpage test piece from Examples 1-4, Comparative Examples 1-4, and Reference Example 1 was measured as follows. Furthermore, the tensile strength of each A-type dumbbell test piece from Examples 1-4, Comparative Examples 1-4, and Reference Example 1 was measured as follows. The results are shown in Table 1. [Warp Measurement] When one corner of the warp test piece is grounded to a flat surface, the distance between the corner that is grounded to the flat surface and the corner at the opposite corner is measured with a vernier caliper. When each of the four corners of the warp test piece is grounded to a flat surface, the distances are measured. The average of the measured distances is designated "A" if it is 7.5 mm or less, "B" if it exceeds 7.5 mm and is 10.0 mm or less, and "C" if it exceeds 10.0 mm. [Determination of Tensile Strength] The aforementioned A-type dumbbell test pieces were subjected to a static tensile test in accordance with JIS K 7165:2008 using a precision universal testing machine (manufactured by Shimadzu Corporation, trade name: Autograph AG-5000B) at a test temperature of 23°C to determine their tensile strength. A tensile strength of 240 MPa or greater was designated "A," a tensile strength of 230 MPa or greater but less than 240 MPa was designated "B," and a tensile strength of less than 230 MPa was designated "C." Table 1 shows that the flat cross-section glass fibers of Examples 1-4, compared to the oblong cross-section glass fibers of Comparative Example 4, maintain comparable dimensional stability (warpage) and mechanical properties (tensile strength) in glass fiber-reinforced resin molded articles while exhibiting superior spinnability (number of spinning cuts) and chopped strand productivity. On the other hand, it was found that the flat cross-section glass fibers of Comparative Example 1, in which the filling ratio P was less than 80.1% and the profile ratio R and the filling ratio P did not satisfy the aforementioned formula (1) (less than 337.6), deteriorated in dimensional stability (warpage) and mechanical properties (tensile strength) when used as glass fiber reinforced resin molded products. It was found that the flat cross-section glass fibers of Comparative Examples 2 and 3, in which the profile ratio R and the filling ratio P did not satisfy the aforementioned formula (1) (exceeding 421.2 or less than 337.6), deteriorated in dimensional stability (warpage) when used as glass fiber reinforced resin molded products or deteriorated in spinnability (number of spinning cuts).

Claims

1. A flat-section glass fiber comprising a plurality of flat-section glass filaments having a flat cross-sectional shape, wherein the long diameter of the cross-section is in the range of 15.0~25.0 μm, the short diameter is in the range of 8.0~12.0 μm, and the irregularity ratio R of the ratio of the long diameter to the short diameter (long diameter / short diameter) is in the range of 1.5~3.0, characterized in that the filling rate P of the ratio of the cross-sectional area of ​​the flat-section glass filament to the area of ​​the rectangle circumscribed with the cross-section of the flat-section glass filament (cross-sectional area of ​​the flat-section glass filament / area of ​​the rectangle circumscribed with the cross-section of the flat-section glass filament) is in the range of 80.1~89.9%, wherein the aforementioned irregularity ratio R and the aforementioned filling rate P satisfy the following formula (1), .

2. As in claim 1, a flat-section glass fiber, wherein, The aforementioned irregularity ratio R and the aforementioned filling rate P satisfy the following equation (2).

3. A glass fiber reinforced resin composition, characterized in that the resin composition contains flat-section glass fibers as claimed in claim 1 or 2.

4. A glass fiber reinforced resin molded article, characterized in that it is composed of the glass fiber reinforced resin composition as claimed in claim 3.