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

Abstract

A flat-section glass fiber is provided, which offers superior stranding productivity compared to oblong-section glass filaments. The present invention comprises a plurality of flat-section glass filaments having a flat cross-section shape. The flat-section glass filaments have the following characteristics: a major diameter of 20.0–35.0 μm, a minor diameter of 5.0–10.0 μm, an aspect ratio R (the ratio of the major diameter to the minor diameter) greater than 3.0 and less than 5.0, and a fill factor P (the ratio of the cross-sectional area of ​​the flat-section glass filament to the area of ​​the rectangle circumscribed in the cross-section of the flat-section glass filament) of 77.0–92.0%. The aspect ratio R and the fill factor P satisfy the following formula (1), and contain 52.0–62.0% by mass of SiO2 relative to the total amount of the flat-section glass fiber. 2. 10.0~20.0% by mass of Al 2O 3. and 16.7~28.1% by mass of CaO.

Description

Flat cross-section glass fiber, glass fiber reinforced resin composition, and glass fiber reinforced resin molded article The present invention relates to a flat cross-section glass fiber, a glass fiber reinforced resin composition, and a glass fiber reinforced resin molded article. Conventionally, a glass fiber reinforced resin molded article containing glass fibers has been known. Such glass fibers (hereinafter, sometimes referred to as "flat cross-section glass fibers") include a plurality of flat cross-section glass filaments having a flat cross-sectional shape (see, for example, Patent Document 1). In particular, a glass fiber reinforced resin molded article containing glass fibers (hereinafter, sometimes referred to as "oval cross-section glass fibers") including a plurality of flat cross-section glass filaments having an oval cross-sectional shape (a shape obtained by replacing the short side portions of a rectangle with semi-circles having the short side as the diameter) has excellent dimensional stability and mechanical properties such as tensile strength and bending strength compared to a glass fiber reinforced resin molded article containing glass fibers (hereinafter, sometimes referred to as "circular cross-section glass fibers") including a plurality of glass filaments having a circular cross-sectional shape. Therefore, it is used for thin, light, short, and small parts such as mobile electronic device casings. [Prior Art Documents] [Patent Documents] Patent Document 1: International Publication No. 2020 / 137004 [Problems to be Solved by the Invention] However, when cutting the oval cross-section glass fibers into a specified length and processing them into chopped strands, the cutting blades of the oval cross-section glass fibers are more likely to wear compared to the case of the circular cross-section glass fibers, and the number of times of replacing the cutting blades needs to be increased. Therefore, there is a problem of poor chopped strand productivity. Also, depending on the glass composition of the glass constituting the glass fiber, the oval cross-section glass fibers also have the above-mentioned problem of deteriorated chopped strand productivity. An object of the present invention is to provide a flat cross-section glass fiber that can achieve: maintaining the same level of dimensional stability and mechanical properties such as bending strength when forming a glass fiber reinforced resin molded article compared to the above-mentioned oval cross-section glass fibers, solving the above-mentioned problems, and having excellent chopped strand productivity compared to oval cross-section glass filaments. [Means for Solving the Problems] In order to achieve such an object, the present invention is characterized in that it includes glass fibers composed of a plurality of flat-section glass filaments having a flat cross-sectional shape. The flat-section glass filaments are such that the major axis of the cross-section is in the range of 20.0 to 35.0 μm, the minor axis is in the range of 5.0 to 10.0 μm, the profile ratio R as the ratio of the major axis to the minor axis (major axis / minor axis) is in the range of greater than 3.0 and 5.0 or less, and the filling rate P as the ratio of the cross-sectional area of the flat-section glass filament to the area of the rectangle circumscribing the cross-section of the flat-section glass filament (cross-sectional area of the flat-section glass filament / area of the rectangle circumscribing the cross-section of the flat-section glass filament) is in the range of 77.0 to 92.0%. The aforementioned profile ratio R and the aforementioned filling rate P satisfy the following formula (1). Relative to the total amount of the flat-section glass fibers, it includes SiO in the range of 52.0 to 62.0% by mass 2 , Al in the range of 10.0 to 20.0% by mass 2 O 3 , and CaO in the range of 16.7 to 28.1% by mass. Furthermore, for the flat-section glass fibers of the present invention, the aforementioned profile ratio R and the aforementioned filling rate P preferably satisfy the following formula (2). Moreover, the glass fiber-reinforced resin composition of the present invention is characterized in that the resin composition contains the flat-section glass fibers of the present invention. Furthermore, the glass fiber-reinforced resin molded product of the present invention is characterized in that it is composed of the glass fiber-reinforced resin composition of the present invention. By virtue of the aforementioned profile ratio R and the aforementioned filling rate P satisfying the aforementioned formula (1), and including SiO in the aforementioned range relative to the total amount of the flat-section glass fibers 2 , Al 2 O 3 , and CaO, in the glass fiber-reinforced molded product of the present invention, compared with the glass fiber-reinforced resin molded product containing oval-section glass fibers, it can maintain mechanical properties such as the same level of dimensional stability and bending strength, and can obtain excellent strand cutting productivity compared with oval-section glass fibers. Furthermore, for the flat-section glass fibers of the present invention, when the content of CaO relative to the total amount of the flat-section glass fibers exceeds 28.1% by mass, sufficient mechanical properties such as bending strength cannot be obtained in the glass fiber-reinforced resin molded product of the present invention. When the content of CaO relative to the total amount of the flat-section glass fibers is less than 16.7% by mass, the strand cutting productivity will decrease. Herein, the so-called "able to maintain the same level of dimensional stability compared to a glass fiber reinforced resin molded product containing glass fibers with an oval cross-section" means that the warpage of the glass fiber reinforced resin molded product measured by the measurement method described below is 5.0 mm or less. Also, the so-called "able to maintain the same level of mechanical properties compared to a glass fiber reinforced resin molded product containing glass fibers with an oval cross-section" means that the flexural strength measured by the measurement method described below is 390 MPa or more. Also, the so-called "able to obtain excellent strand cutting productivity" means that the number of cutter exchanges measured by the measurement method described below is less than 30 times. Furthermore, the flat cross-section glass fibers of the present invention, by having the above-mentioned profile ratio R and the above-mentioned filling rate P satisfying the above-mentioned formula (2), can obtain more excellent strand cutting productivity compared to glass filaments with an oval cross-section. Herein, the so-called "able to obtain more excellent strand cutting productivity" means that the number of cutter exchanges measured by the method described below is less than 20 times. Also, with the glass fiber reinforced resin molded product of the present invention, compared to a glass fiber reinforced resin molded product containing glass fibers with an oval cross-section, it can maintain the same level of dimensional stability and mechanical properties such as flexural strength. Herein, the so-called "able to maintain the same level of dimensional stability and mechanical properties such as flexural strength compared to a glass fiber reinforced resin molded product containing glass fibers with an oval cross-section" has the same meaning as described above. [Embodiments of the Invention] Next, the embodiments of the present invention will be described in more detail. The flat cross-section glass fibers of the present embodiment include a plurality of flat cross-section glass filaments having a flat cross-sectional shape. The major axis of the cross-section of the flat cross-section glass filaments is in the range of 20.0 to 35.0 μm, the minor axis is in the range of 5.0 to 10.0 μm, and the profile ratio R is in the range greater than 3.0 and 5.0 or less, thereby having a flat cross-sectional shape. Herein, the so-called "cross-section of the flat cross-section glass filament" refers to a cross-section perpendicular to the length direction of the flat cross-section glass filament, and the above-mentioned profile ratio R is the ratio of the major axis to the minor axis (major axis / minor axis). In the flat cross-section glass fibers of the present embodiment, the above-mentioned profile ratio R is preferably in the range of 3.1 to 4.6, more preferably in the range of 3.4 to 4.4, and even more preferably in the range of 3.7 to 4.2. For the flat cross-section glass fibers of the present embodiment, if the above-mentioned profile ratio R exceeds 5.0, the strand cutting productivity will decrease, and if it is 3.0 or less, the glass fiber reinforced resin molded product of the present invention will not be able to obtain sufficient dimensional stability and mechanical properties such as flexural strength. Further, for the flat cross-section glass fiber of the present embodiment, the filling rate P is in the range of 77.0 to 92.0%, and the above-mentioned aspect ratio R and the above-mentioned filling rate P satisfy the following formula (1), preferably satisfy the following formula (2). Relative to the total amount of the flat cross-section glass fiber, it contains SiO in the range of 52.0 to 62.0% by mass 2 , Al in the range of 10.0 to 20.0% by mass 2 O 3 , and CaO in the range of 16.7 to 28.1% by mass. Here, the above-mentioned filling rate P is the ratio of the cross-sectional area of the flat cross-section glass filament to the area of the rectangle circumscribing the cross-section of the flat cross-section glass filament (cross-sectional area of the flat cross-section glass filament / area of the rectangle circumscribing the cross-section of the flat cross-section glass filament). In the flat cross-section glass filament of the present embodiment, the above-mentioned filling rate P is preferably in the range of 79.5 to 89.8%, more preferably in the range of 80.1 to 84.9%, still more preferably in the range of 80.1 to 84.4%, particularly preferably in the range of 81.8 to 84.4%, and most preferably in the range of 82.0 to 84.0%. Further, for the flat cross-section glass fiber of the present embodiment, when the above-mentioned filling rate P exceeds 92.0%, the cross-sectional shape will be overly approximated to a rectangle, so the strand cutting productivity will decrease; when the above-mentioned filling rate P is less than 77.0%, the cross-sectional shape will be overly approximated to an ellipse, and the glass fiber reinforced resin molded product of the present invention will not be able to obtain sufficient mechanical properties such as bending strength. The glass composition of the glass forming the flat cross-section glass fiber of the present embodiment, relative to the total amount of the flat cross-section glass fiber, contains SiO in the range of 52.0 to 62.0% by mass 2 , Al in the range of 10.0 to 20.0% by mass 2 O 3 , and CaO in the range of 16.7 to 28.1% by mass. The above-mentioned glass composition is preferably the following composition: relative to the total amount of the glass fiber, it contains SiO in the range of 52.0 to 56.0% by mass 2 , Al in the range of 12.0 to 16.0% by mass 2 O 3 , CaO in the range of 20.0 to 25.0% by mass, and B in the range of 0.0 to 10.0% by mass 2 O 3 ; Preferably, it has the following composition: relative to the total amount of glass fibers, it contains SiO in the range of 53.0 to 55.0% by mass 2 、Al in the range of 13.0 to 15.0% by mass 2 O 3 、CaO in the range of 21.0 to 24.0% by mass, and B in the range of 5.0 to 10.0% by mass 2 O 3 , for example, relative to the total amount of flat-section glass fibers, it contains 54.6% by mass of SiO 2 、14.1% of Al 2 O 3 、22.4% of CaO, 6.1% by mass of B 2 O 3 、1.2% by mass of MgO, 0.3% of TiO 2 、a total of 0.5% by mass of Na 2 O, K 2 O, Li 2 O, 0.6% by mass of F 2 、and 0.2% by mass of Fe 2 O 3 (hereinafter, there is a case called "Composition A"). In the flat-section glass fibers of this embodiment, for the determination of the content of each of the foregoing components, for Li, which is a light element, an ICP emission spectroscopic analysis device can be used, and for other elements, a wavelength-dispersive fluorescent X-ray analysis device can be used. As a measurement method, specifically, first, glass raw materials (mixed and blended glass raw materials) or the flat cross-section glass fibers of the present embodiment (when there are organic substances attached to the surface of the flat cross-section glass fibers, or when the flat cross-section glass fibers are mainly contained as a reinforcing material in an organic substance (resin), for example, in a muffle furnace at 300 to 600 °C, heated for about 2 to 24 hours, etc., after removing the organic substances, they are used) are placed in a platinum crucible, and in an electric furnace, maintained at a temperature of 1550 °C for 6 hours, while being stirred to melt them to obtain homogeneous molten glass. Next, the obtained molten glass is poured onto a carbon plate to produce cullet, and after being crushed to form a powder, it is used as glass powder. For the light element Li, the aforementioned glass powder is decomposed by heating with an acid, and then quantitatively analyzed using an ICP emission spectroscopic analyzer. For other elements, the quantitative analysis is carried out as follows: After forming the aforementioned glass powder into a disc shape using a press, a wavelength-dispersive fluorescent X-ray analyzer is used and quantitatively analyzed by the fundamental-parameters method. The quantitative analysis results of these are converted into oxides, and the content and total amount of each component are calculated. From these values, the content (mass %) of each of the aforementioned components can be obtained. The flat cross-section glass fibers of the present embodiment can be manufactured, for example, by the following method. First, the blended glass raw materials (glass batch) are supplied to a melting furnace so as to have a specified glass composition (for example, the aforementioned Composition A), and melted in a temperature range of, for example, 1450 to 1550 °C. Next, the melted glass raw materials (glass batch) are drawn out from 10 to 30,000 nozzle tips of a bushing controlled at a specified temperature. When performing rapid cooling, the aforementioned nozzle tips are set to have a non-circular shape (for example, a shape corresponding to the cross-sectional shape of the aforementioned flat cross-section glass filaments), and have a protrusion or cut portion for rapidly cooling the molten glass. By controlling the temperature conditions, flat cross-section glass filaments can be obtained. Next, a sizing agent or an adhesive is applied using an applicator of a coating device, and while bundling 10 to 30,000 flat cross-section glass filaments using a bundling boot, a winder is used to wind them onto a tube at high speed, and thus the flat cross-section glass fibers of the present embodiment can be manufactured. Also, in the flat cross-section glass fibers of the present embodiment, more than 50% of the glass filaments constituting the flat cross-section glass fibers are the aforementioned flat cross-section glass filaments, preferably 80% or more are the aforementioned flat cross-section glass filaments, more preferably 90% or more are the aforementioned flat cross-section glass filaments, and most preferably 100% are the aforementioned flat cross-section glass filaments. In the glass filaments contained in the flat cross-section glass fiber of the present embodiment, the minor axis and major axis can be adjusted by adjusting the major axis and minor axis of the nozzle head, the winding speed, the temperature conditions, etc. For example, by increasing the winding speed, the minor axis and major axis can be reduced, and by decreasing the winding speed, the minor axis and major axis can be increased. As the form of the aforementioned flat cross-section glass fiber, examples include glass yarn, glass cut strands, glass rovings, glass powder, and glass filament mats. Further, the aforementioned glass fiber can also be in the state of a glass cloth composed of glass yarn or glass rovings, a chopped strand mat composed of glass cut strands, or in a state where glass filaments are dispersed in a glass fiber reinforced resin molded product. For example, when the flat cross-section glass fiber of the present embodiment is in the form of cut strands, the number of flat cross-section glass filaments constituting the aforementioned flat cross-section glass fiber is, for example, 10 to 20,000, preferably 50 to 10,000, and more preferably 1,000 to 8,000. Also, the length of the cut strands of the flat cross-section glass fiber of the present 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 cut strands can be obtained by cutting the flat cross-section glass fiber manufactured by the aforementioned method into the aforementioned specified length using a well-known device such as a long fiber cutting device: the long fiber cutting device includes a cutter roll equipped with cutters (cutting blades) installed at equal intervals and radially, and a rubber roll with rubber installed on the outer peripheral surface in contact with and rotating with the cutter roll, and the glass strands (flat cross-section glass fiber) are fed between the cutter roll and the rubber roll for cutting. When the flat cross-section glass fiber of the present embodiment is in the form of rovings, the number of glass filaments constituting the aforementioned flat cross-section glass fiber is, for example, 200 to 30,000. Also, the roving of the flat cross-section glass fiber of the present embodiment has a mass per unit area of 35 to 10,000 tex (g / km). When the flat cross-section glass fiber of the present embodiment is in the form of glass powder (also referred to as "chopped fiber" in some cases), the number of glass filaments constituting the aforementioned flat cross-section glass fiber is, for example, 10 to 20,000. Also, the length of the glass powder of the flat cross-section glass fiber of the present embodiment is, for example, 0.001 to 0.900 mm. Here, the aforementioned glass powder can be obtained by pulverizing the flat cross-section glass fiber manufactured by the aforementioned method into the aforementioned specified length using a well-known method such as a ball mill or a Henschel mixer. In the flat cross-section glass fiber of the present embodiment, the major axis and minor axis of the aforementioned cross-section can be measured by the following operations, for example. First, when the glass fiber reinforced resin molded product does not contain the flat cross-section glass fibers of the present embodiment, the flat cross-section glass fibers are embedded in a resin such as epoxy resin, the resin is hardened, the hardened resin is cut, the cross-section is polished, and then the cross-section of the hardened resin is observed using an electron microscope. Then, for all or 200 or more of the flat cross-section glass filaments constituting the flat cross-section glass fibers exposed on the cross-section of the hardened resin, the longest side passing through the approximate center of the flat cross-section glass filament is used as the major axis, and the side orthogonal to the longest side and the approximate center of the flat cross-section glass filament is used as the minor axis, and the respective lengths are measured. Also, when the glass fiber reinforced resin molded product contains the flat cross-section glass fibers, the glass fiber reinforced resin molded product is cut and the cross-section is polished, and then the cross-section of the resin is observed using an electron microscope. Then, for 200 or more of the flat cross-section glass filaments constituting the flat cross-section glass fibers exposed on the cross-section of the resin, the longest side passing through the approximate center of the flat cross-section glass filament is used as the major axis, and the side orthogonal to the longest side and the approximate center of the flat cross-section glass filament is used as the minor axis, and the respective lengths are measured. Here, whether the glass fiber reinforced resin molded product does not contain the flat cross-section glass filaments or the glass fiber reinforced resin molded product contains the flat cross-section glass filaments, the major axis and minor axis of the cross-section can be measured by performing image processing on the image obtained by the electron microscope using an automatic analysis device. For the flat cross-section glass fibers of the present invention, the major axis of the cross-section of the flat cross-section glass filaments is in the range of 20.0 to 35.0 μm, preferably in the range of 22.3 to 32.8 μm, more preferably in the range of 24.1 to 31.4 μm, still more preferably in the range of 26.5 to 29.9 μm, and particularly preferably in the range of 27.0 to 28.8 μm. For the flat cross-section glass fibers of the present invention, the minor axis of the cross-section of the flat cross-section glass filaments is in the range of 5.0 to 10.0 μm, preferably in the range of 5.5 to 9.0 μm, more preferably in the range of 6.1 to 8.4 μm, still more preferably in the range of 6.5 to 7.9 μm, and particularly preferably in the range of 6.8 to 7.4 μm. The above-mentioned shape ratio R can be calculated by using the ratio of the major axis to the minor axis (major axis / minor axis) of the cross-section measured by the above-mentioned operations. Furthermore, the area of the rectangle circumscribing the cross-section of the flat cross-section glass filament can be calculated by multiplying the major axis and minor axis of the aforementioned cross-section measured by the aforementioned operation, i.e., (minor axis × major axis). When measuring the major axis and minor axis of the aforementioned cross-section, well-known image analysis software such as "A-Image-kun" (registered trademark, manufactured by Asahi Kasei Engineering Co., Ltd.) can be used to measure the cross-sectional area of the flat cross-section glass filament. Then, the filling rate P can be calculated by dividing the cross-sectional area of the flat cross-section glass filament by the area of the rectangle circumscribing the cross-section of the flat cross-section glass filament, i.e., (cross-sectional area of the flat cross-section glass filament / area of the rectangle circumscribing the cross-section of the flat cross-section glass filament). The flat cross-section glass fiber of the present embodiment preferably has a cross-sectional shape that is substantially symmetric with respect to the longest side passing through the approximate center of the flat cross-section glass filament. In the flat cross-section glass fiber of the present embodiment, the greater the filling rate P, the greater the improvement effect on the flexural strength and warpage of the glass fiber reinforced resin molded product of the present embodiment, but the spinnability and strand cutting manufacturability tend to deteriorate. On the other hand, the greater the profile ratio R, the greater the improvement effect on the strength and warpage of the glass fiber reinforced resin molded product of the present embodiment, but the strand cutting productivity deteriorates. It is considered that Equation (1) represents such a balance. With the flat cross-section glass fiber of the present embodiment, by making the profile ratio R and the filling rate P satisfy the aforementioned Equation (1), among the glass fiber reinforced resin molded products of the present embodiment containing the flat cross-section glass fiber, compared with the glass fiber reinforced resin molded products containing oval cross-section glass fibers, the mechanical properties such as dimensional stability and flexural strength of the same grade can be maintained, and excellent strand cutting productivity can be obtained compared with the oval cross-section glass fibers. Furthermore, with the flat cross-section glass fiber of the present embodiment, when the profile ratio R and the filling rate P satisfy the aforementioned Equation (1) and the filling rate P is in the range of 80.1% to 84.9%, among the glass fiber reinforced resin molded products of the present embodiment, compared with the glass fiber reinforced resin molded products containing oval cross-section glass fibers, the dimensional stability of the same grade can be maintained, and more excellent strand cutting productivity can be obtained compared with the oval cross-section glass filaments. Furthermore, by using the flat-profile glass fiber of the present embodiment, when the above-mentioned shape ratio R and the above-mentioned filling rate P satisfy the above-mentioned formula (1) and the above-mentioned filling rate P is in the range of 81.8 to 84.4%, in the glass fiber-reinforced resin molded product of the present embodiment, compared with the glass fiber-reinforced resin molded product containing the oblong-profile glass fiber, the same level of dimensional stability can be maintained, excellent mechanical properties can be obtained, and compared with the oblong-profile glass fiber, more excellent strand cutting productivity can be obtained. Here, the so-called "compared with the glass fiber-reinforced resin molded product containing the oblong-profile glass fiber, the same level of dimensional stability can be maintained" means that the warpage of the glass fiber-reinforced resin molded product measured by the measurement method described below is 5.0 mm or less. Furthermore, the so-called "compared with the glass fiber-reinforced resin molded product containing the oblong-profile glass fiber, the same level of mechanical properties can be maintained" means that the flexural strength measured by the measurement method described below is 390 MPa or more; the so-called "compared with the glass fiber-reinforced resin molded product containing the oblong-profile glass fiber, excellent mechanical properties can be obtained" means that the flexural strength measured by the measurement method described below is 400 MPa or more. Furthermore, the so-called "excellent strand cutting productivity can be obtained" means that the number of cutter replacements measured by the measurement method described below is less than 30 times; the so-called "more excellent strand cutting productivity can be obtained" means that the number of cutter replacements measured by the measurement method described below is less than 20 times. [Measurement method for warpage of glass fiber-reinforced resin molded product] First, the surface of the above-mentioned flat-profile glass fiber is coated with a composition containing a silane coupling agent, cut into lengths of 3 mm to form strands. Next, using a twin-screw kneader (manufactured by Shibaura Machine Co., Ltd., product name: TEM-26SS) with a screw rotation speed of 100 rpm, the above-mentioned strands and polyamide 6 resin (manufactured by Ube Industries, Ltd., product name: UBE1015B) are kneaded at a temperature of 270°C to produce resin pellets with a glass fiber content of 50% by mass. Next, using the above-mentioned resin pellets, injection molding is performed using an injection molding machine (manufactured by Nissei Plastic Industrial Co., Ltd., product name: NEX80) at a mold temperature of 80°C and an injection temperature of 270°C, and molded into a flat plate with dimensions of 80 mm in length × 60 mm in width × 1 mm in thickness as a test piece for warpage measurement. When one corner of the above-mentioned warpage measurement test piece is grounded on a flat surface, the distance between the corner diagonally opposite to the corner grounded on the flat surface and the flat surface is measured using a vernier caliper. For the case where the four corners of the above-mentioned warpage measurement test piece are respectively grounded on the flat surface, the above-mentioned distance is measured, and the average value of each measured value is defined as the warpage value. [Method for Measuring Bending Strength of Glass Fiber Reinforced Resin Molded Product] First, using the aforementioned resin particles, injection molding is performed with an injection molding machine (manufactured by Nissei Plastic Industrial Co., Ltd., product name: NEX80) at a mold temperature of 80°C and an injection temperature of 270°C, and molded into a Type A dumbbell specimen (4 mm thick) according to JIS K 7165:2008. For the aforementioned Type A dumbbell specimen, under the condition of a test temperature of 23°C, a static bending test is performed using a precision universal testing machine (manufactured by Shimadzu Corporation, product name: Autograph AG-5000B) according to JIS K 7171:2016 to measure the bending strength. [Method for Measuring Strand Cutting Productivity] The surface of the aforementioned flat cross-section glass fiber is coated with a composition containing a silane coupling agent to obtain a glass strand. By means of a long fiber cutting device equipped with a cutter roll having equally spaced and radially installed cutting blades (cutting edges) and a rubber roll having rubber installed on its outer peripheral surface in contact with the cutter roll and rotating, the glass strand is fed between the cutter roll and the rubber roll for cutting, thereby cutting into a length of 3 mm, and the number of cutter replacements during strand cutting for 240 hours of manufacturing is measured. Furthermore, for the flat cross-section glass fiber of the present embodiment, by making the aforementioned shape ratio R and the aforementioned filling rate P satisfy the aforementioned formula (2), in the glass fiber reinforced molded product of the present invention, compared with the glass fiber reinforced resin molded product containing long circular cross-section glass fibers, the same level of dimensional stability can be maintained, and more excellent strand cutting productivity can be obtained compared with long circular cross-section glass fibers. Here, the so-called "compared with the glass fiber reinforced resin molded product containing long circular cross-section glass fibers, the same level of dimensional stability can be maintained", and "more excellent strand cutting productivity can be obtained compared with long circular cross-section glass fibers" have the same meaning as the foregoing. Next, the glass fiber reinforced resin composition of the present embodiment contains the flat cross-section glass fiber of the present embodiment in the resin composition. Next, the glass fiber reinforced resin molded product of the present embodiment is composed of the glass fiber reinforced resin composition of the present embodiment. By the glass fiber reinforced resin molded product of the present embodiment, compared with the glass fiber reinforced resin molded product containing long circular cross-section glass fibers, the same level of dimensional stability and mechanical properties can be maintained. Here, the so-called "compared with the glass fiber reinforced resin molded product containing long circular cross-section glass fibers, the same level of dimensional stability and mechanical properties can be maintained" has the same meaning as the foregoing. As the aforementioned resin composition constituting the glass fiber reinforced resin composition of the present embodiment, a resin composition containing a thermoplastic resin or a thermosetting resin can be cited. Examples of the aforementioned thermoplastic resins 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, polyethersulfone (PES), polyphenylsulfone (PPSU), polyphenylene ether (PPE), modified polyphenylene ether (m-PPE), polyaryletherketone, liquid crystal polymer (LCP), fluororesin, polyetherimide (PEI), polyarylate (PAR), polysulfone (PSF), polyamideimide (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, and the like. Examples of the aforementioned polyethylene include high-density polyethylene (HDPE), medium-density polyethylene, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ultra-high molecular weight polyethylene, and the like. Examples of the aforementioned polypropylene include isotactic polypropylene, atactic polypropylene, syndiotactic polypropylene, and mixtures thereof. Examples of the aforementioned polystyrene include general-purpose polystyrene (GPPS) which is an atactic polystyrene having an atactic structure, high-impact polystyrene (HIPS) obtained by adding a rubber component to GPPS, syndiotactic polystyrene having a syndiotactic structure, and the like. Examples of the aforementioned methacrylic resin include polymers obtained by homopolymerizing one of acrylic acid, methacrylic acid, styrene, methyl acrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, and vinyl fatty acid ester, or copolymers obtained by copolymerizing two or more of them. Examples of the aforementioned polyvinyl chloride include vinyl chloride homopolymers polymerized by methods such as the well-known emulsion polymerization method, suspension polymerization method, minisuspension polymerization method, and bulk polymerization method, copolymers obtained by copolymerizing monomers copolymerizable with vinyl chloride monomer, and graft copolymers obtained by graft-polymerizing vinyl chloride monomer onto a polymer. Examples of the aforementioned polyamide include polycaproamide (polyamide 6), polyhexamethylene adipamide (polyamide 66), polytetramethylene adipamide (polyamide 46), polytetramethylene sebacamide (polyamide 410), polypentamethylene adipamide (polyamide 56), polypentamethylene sebacamide (polyamide 510), polyhexamethylene sebacamide (polyamide 610), polyhexamethylene dodecanediamide (polyamide 612), polydecamethylene adipamide (polyamide 106), polydecamethylene sebacamide (polyamide 1010), polydecamethylene dodecanediamide (polyamide 1012), polyundecanamide (polyamide 11), polyundecamethylene adipamide (polyamide 116), polydodecanamide (polyamide 12), polyxylene adipamide (polyamide XD6), polyxylene sebacamide (polyamide XD10), polymetaxylylene adipamide (polyamide MXD6), polyparaxylylene adipamide (polyamide PXD6), polytetramethylene terephthalamide (polyamide 4T), polypentamethylene terephthalamide (polyamide 5T), polyhexamethylene terephthalamide (polyamide 6T), polyhexamethylene isophthalamide (polyamide 6I), polynonamethylene terephthalamide (polyamide 9T), polydecamethylene terephthalamide (polyamide 10T), polyundecamethylene terephthalamide (polyamide 11T), polydodecamethylene terephthalamide (polyamide 12T), polytetramethylene isophthalamide (polyamide 4I), polybis(3-methyl-4-aminohexyl)methane terephthalamide (polyamide PACMT), polybis(3-methyl-4-aminohexyl)methane isophthalamide (polyamide PACMI), polybis(3-methyl-4-aminohexyl)methane dodecanediamide (polyamide PACM12), polybis(3-methyl-4-aminohexyl)methane tetradecanediamide (polyamide PACM14), etc., or a copolymer formed by combining two or more of the above components, or a mixture thereof, etc. Examples of the aforementioned polyacetal include homopolymers having an oxy-methylene unit as a main repeating unit, and copolymers mainly formed of an oxy-methylene unit and having an oxyalkylene unit with 2 to 8 adjacent carbon atoms in the main chain, etc. Examples of the aforementioned polyethylene terephthalate include polymers obtained by polycondensing terephthalic acid or its derivatives with ethylene glycol, etc. Examples of the aforementioned polybutylene terephthalate include polymers obtained by polycondensing terephthalic acid or its derivatives with 1,4-butanediol, etc. Examples of the aforementioned polypropylene terephthalate include polymers obtained by polycondensing terephthalic acid or its derivatives with 1,3-propanediol, etc. As the aforementioned polycarbonate, examples include polymers obtained by the transesterification method of reacting a dihydroxy diaryl compound with a carbonate such as diphenyl carbonate in a molten state, or polymers obtained by the phosgene method of reacting a dihydroxy aryl compound with phosgene. As the aforementioned polyphenylene sulfide, examples include linear polyphenylene sulfide, crosslinked polyphenylene sulfide that is polymerized and then undergoes a hardening reaction to increase its molecular weight, polyphenylene sulfide sulfone, polyphenylene sulfide ether, polyphenylene sulfide ketone, etc. As the aforementioned modified polyphenylene ether, examples 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, polymer alloys of poly(2,6-dimethyl-1,4-phenylene) ether and styrene / butadiene / acrylonitrile copolymer, etc. As the aforementioned polyaryl ether ketone, examples include polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), etc. As the aforementioned liquid crystal polymer (LCP), examples 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., which are thermotropic liquid crystal polyesters. As the aforementioned fluororesin, examples include polytetrafluoroethylene (PTFE), perfluoroalkoxy resin (PFA), fluorinated ethylene propylene resin (FEP), fluorinated ethylene tetrafluoroethylene resin (ETFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene resin (ECTFE), etc. As the aforementioned ionomer (IO) resin, examples include copolymers of olefins or styrene and unsaturated carboxylic acids, and polymers in which a part of the carboxyl groups are neutralized with metal ions. As the aforementioned olefin / vinyl alcohol resin, examples include ethylene / vinyl alcohol copolymer, propylene / vinyl alcohol copolymer, saponified ethylene / vinyl acetate copolymer, saponified propylene / vinyl acetate copolymer, etc. As the aforementioned cyclic olefin resin, examples include monocyclic monomers such as cyclohexene, polycyclic monomers such as tetracyclopentadiene, polymers of cyclic olefin monomers, etc. As the aforementioned polylactic acid, examples include poly-L-lactic acid as an L-type homopolymer, poly-D-lactic acid as a D-type homopolymer, or stereocomplex poly lactic acid as a mixture thereof. Examples of the cellulose resin include methyl cellulose, ethyl cellulose, hydroxy cellulose, hydroxy methyl cellulose, hydroxy ethyl cellulose, hydroxy ethyl methyl cellulose, hydroxy propyl methyl cellulose, cellulose acetate, cellulose propionate, cellulose butyrate, and the like. Examples of the thermosetting resin include unsaturated polyester resin, vinyl ester resin, epoxy (EP) resin, melamine (MF) resin, phenolic resin (PF), urethane resin (PU), polyisocyanate, polyisocyanurate, polyimide (PI), urea (UF) resin, polysiloxane (SI) resin, furan (FR) resin, benzoguanamine (BR) resin, alkyd resin, xylene resin, bismaleimide triazine (BT) resin, diallyl phthalate resin (PDAP), and the like. In the flat cross-section glass fiber of the present embodiment, the flat cross-section glass filaments constituting the flat cross-section glass fiber may be in contact with each other or separated from each other. When the flat cross-section glass filaments are separated from each other, a surface treatment agent or a resin composition constituting the glass fiber reinforced resin molded article may also be present between the flat cross-section glass filaments. Examples of the surface treatment agent include resins such as urethane resin, epoxy resin, vinyl acetate resin, acrylic resin, modified polypropylene (especially carboxylic acid modified polypropylene), copolymers of (poly) carboxylic acid (especially maleic acid) and unsaturated monomers, or silane coupling agents. Further, the flat cross-section glass fiber of the present embodiment can also be coated with a composition containing a lubricant, a surfactant, and the like in addition to these resins or silane coupling agents. Based on the mass of the flat cross-section glass fiber in the state of not being coated with the composition, the flat cross-section glass fiber is coated with such a composition in a proportion of 0.1 to 2.0% by mass. In addition, the coating of the flat cross-section glass fiber with an organic substance, for example, in the manufacturing step of the flat cross-section glass fiber, a sizing agent or an adhesive containing a solution of the resin, the silane coupling agent, or the composition is applied to the flat cross-section glass fiber by a well-known method such as a roll coater, and then the flat cross-section glass fiber coated with the solution of the resin, the silane coupling agent, or the composition is dried, whereby the coating can be carried out. Here, examples of the silane coupling agent include amino silane, chloro silane, epoxy silane, mercapto silane, vinyl silane, acryloyl silane, and cationic silane. These compounds of the silane coupling agent can be used alone or in combination of two or more kinds. Examples of the aminosilane include γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-N’-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-anilinopropyltrimethoxysilane, and the like. Examples of the chlorosilane include γ-chloropropyltrimethoxysilane and the like. Examples of the epoxy silane include γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and the like. Examples of the mercapto silane include γ-mercaptopropyltrimethoxysilane and the like. Examples of the vinyl silane include vinyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane, and the like. Examples of the acryloyl silane include γ-methacryloxypropyltrimethoxysilane and the like. Examples of the cationic silane include N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, N-phenyl-3-aminopropyltrimethoxysilane hydrochloride, and the like. Examples of the lubricant include modified silicone oil, animal oil and its hydride, vegetable oil and its hydride, animal wax, vegetable wax, mineral wax, condensate of higher saturated fatty acid and higher saturated alcohol, polyethyleneimine, polyalkyl polyamine alkylamide derivative, fatty acid amide, quaternary ammonium salt. The above lubricants can be used alone or in combination of two or more kinds. Examples of the animal oil include beef tallow and the like. Examples of the vegetable oil include soybean oil, coconut oil, mustard oil, palm oil, castor oil, and the like. Examples of the animal wax include beeswax, lanolin, and the like. Examples of the vegetable wax include carnauba wax, brazil wax, and the like. Examples of the mineral wax include paraffin wax, montan wax, and the like. Examples of the condensate of higher saturated fatty acid and higher saturated alcohol include stearic acid esters such as lauryl stearate and the like. Examples of the fatty acid amide include dehydration condensates of polyalkylene polyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and the like and fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and the like. Examples of the quaternary ammonium salt include alkyltrimethylammonium salts such as lauryltrimethylammonium chloride and the like. Examples of the surfactant include nonionic surfactant, cationic surfactant, anionic surfactant, amphoteric surfactant. The above surfactants can be used alone or in combination of two or more kinds. Examples of nonionic surfactants include ethylene oxide-propylene oxide alkyl ethers, polyethylene oxide alkyl ethers, polyethylene oxide-polypropylene oxide block copolymers, alkyl polyethylene oxide-polypropylene oxide block copolymer ethers, polyethylene oxide fatty acid esters, polyethylene oxide fatty acid monoesters, polyethylene oxide fatty acid diesters, polyethylene sorbitan fatty acid esters, ethylene oxide adducts of glycerol fatty acid esters, polyethylene oxide castor oil ethers, ethylene oxide adducts of hydrogenated castor oil, ethylene oxide adducts of alkylamines, ethylene oxide adducts of fatty acid amides, glycerol fatty acid esters, polyglycerol fatty acid esters, pentaerythritol fatty acid esters, sorbitol fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, polyol alkyl ethers, fatty acid alkanolamides, acetylene glycols, acetylene alcohols, ethylene oxide adducts of acetylene glycols, ethylene oxide adducts of acetylene alcohols, and the like. Examples of cationic surfactants include alkyldimethylbenzylammonium chlorides, alkyltrimethylammonium chlorides, alkyldimethylethylammonium ethyl sulfates, higher alkylamine acetates, higher alkylamine hydrochlorides, ethylene oxide adducts of higher alkylamines, condensates of higher fatty acids and polyalkylene polyamines, salts of esters of higher fatty acids and alkanolamines, salts of higher fatty acid amides, imidazoline-type cationic surfactants, alkylpyridinium salts, and the like. Examples of anionic surfactants include higher alcohol sulfates, higher alkyl ether sulfates, α-olefin sulfates, alkylbenzene sulfonates, α-olefin sulfonates, reaction products of fatty acid halides and N-methyltaurine, dialkyl ester salts of thiosuccinic acid, higher alcohol phosphates, phosphates of ethylene oxide adducts of higher alcohols, and the like. Examples of amphoteric surfactants include amino acid-type amphoteric surfactants such as alkali metal salts of alkylaminopropionic acids, betaine-type amphoteric surfactants such as alkyldimethylbetaines, imidazoline-type amphoteric surfactants, and the like. As a molding method for obtaining the glass fiber-reinforced resin molded product of the present embodiment, examples thereof include an injection molding method, an injection compression molding method, a two-color molding method, a hollow molding method, a foam molding method (including a foam molding method using a supercritical fluid), an insert molding method, an in-mold coating molding method, an extrusion molding method, a sheet molding method, a thermoforming method, a rotational molding method, a lamination molding method, a compression molding method, a blow molding method, a stamping molding method, an infusion method, a hand lay-up method, a spray-up method, a resin transfer molding method, a sheet molding compound, a bulk molding compound, a pultrusion method, a filament winding method, etc. Among these methods, the injection molding method is preferred because of its excellent manufacturing efficiency. Next, examples and comparative examples of the present invention will be shown. [Examples] [Examples 1 to 4, Comparative Examples 1 to 7, Reference Example 1] First, a glass raw material (glass raw material) prepared to have any one of Compositions A to C shown in Table 1 is supplied to a melting furnace and melted at a temperature in the range of 1450 to 1550 °C. The obtained molten glass is drawn out from a bushing having 200 nozzle heads to obtain a plurality of flat cross-section glass filaments, and the plurality of flat cross-section glass filaments are bundled to manufacture flat cross-section glass fibers. At this time, the nozzle head has: a hole portion having a flat cross-section shape (having a flat cross-section shape) with a major axis of a specified length and a minor axis of a specified length, and a wall portion having a notch for cooling the molten glass. The length of the minor axis of the hole portion is adjusted to be in the range of 0.2 to 2.0 mm, the ratio of the length of the major axis of the hole portion to the length of the minor axis is adjusted to be in the range of 2.0 to 8.0, and the amount of molten glass passing through each of the aforementioned nozzle heads is adjusted to be in the range of 0.1 to 3.0 g / minute to obtain the flat cross-section glass fibers of Examples 1 to 4 and Comparative Examples 1 to 7. Incidentally, the flat cross-section glass filaments of Comparative Example 5 are oval cross-section glass filaments having an oval cross-section shape, and the flat cross-section glass fibers of Comparative Example 5 are oval cross-section glass fibers including a plurality of oval cross-section glass filaments. Further, the nozzle head is set to have a hole portion having a true circular cross-section shape, whereby the circular cross-section glass fibers of Reference Example 1 are obtained. . The minor axis, major axis, shape ratio R, filling rate P, and P / R of each flat cross-section glass filament of Examples 1 to 4 1 / 4The values are as shown in Table 2. Also, the minor axis, major axis, shape ratio R, filling rate P, and P / R of each flat cross-section glass filament of Comparative Examples 1 to 7 and the circular cross-section glass filament of Reference Example 1 1 / 4 The values are as shown in Table 3. Next, for each flat cross-section glass fiber of Examples 1 to 4 and Comparative Examples 1 to 7 and the circular cross-section glass fiber of Reference Example 1, the spinning cut-off frequency and strand cutting productivity were determined as follows. The spinning cut-off frequency and strand cutting productivity of each flat cross-section fiber of Examples 1 to 4 are shown in Table 2. Also, the spinning cut-off frequency and strand cutting productivity of each flat cross-section glass fiber of Comparative Examples 1 to 7 and the circular cross-section glass fiber of Reference Example 1 are shown in Table 3. [Spinning cut-off frequency] For 30 days, each flat cross-section glass fiber of Examples 1 to 4 and Comparative Examples 1 to 7 and the circular cross-section glass fiber of Reference Example 1 were manufactured, and the number of times the flat cross-section glass filaments constituting each flat cross-section glass fiber of Examples 1 to 4 and Comparative Examples 1 to 4 or the circular cross-section glass filaments constituting the circular cross-section glass fiber of Reference Example 1 were cut during this period was measured. One shift was set to 8 hours, and the average cut-off frequency per shift was defined as the spinning cut-off frequency. When the spinning cut-off frequency per shift was less than 9 times, it was determined as "A"; when the spinning cut-off frequency per shift was 9 times or more and less than 10 times, it was determined as "B"; when the spinning cut-off frequency per shift was 10 times or more, it was determined as "C". [Strand cutting productivity] The surfaces of each flat cross-section glass fiber of Examples 1 to 4 and Comparative Examples 1 to 7 and the circular cross-section glass fiber of Reference Example 1 were respectively coated with a composition containing a silane coupling agent to obtain glass strands. By using a long fiber cutting device with a cutter roll equipped with equally spaced and radially installed cutters (cutting blades) and a rubber roll with rubber installed on the outer peripheral surface in contact with the cutter roll and rotating, the glass strands were fed between the cutter roll and the rubber roll for cutting, thereby cutting them into a length of 3 mm. The number of times the cutter was replaced during the strand cutting for 240 hours was measured. When it was less than 20 times, it was determined as "A"; when it was 20 times or more and less than 30 times, it was determined as "B"; when it was 30 times or more, it was determined as "C". Next, each of the flat-profile glass fibers of Examples 1 to 4, Comparative Examples 1 to 7, and the circular-profile glass fiber of Reference Example 1 was coated with a composition containing a silane coupling agent and cut into lengths of 3 mm, thereby obtaining cut strands of Examples 1 to 4, Comparative Examples 1 to 7, and Reference Example 1. Next, using a twin-screw kneader (manufactured by Shibaura Machine Co., Ltd., trade name: TEM-26SS) with a screw rotation speed set to 100 rpm, at a temperature of 270°C, the above-mentioned cut strands were kneaded with polyamide 6 resin (manufactured by Ube Industries, Ltd., trade name: UBE1015B) to produce resin pellets of Examples 1 to 4, Comparative Examples 1 to 7, and Reference Example 1 with a glass fiber content of 50% by mass. Next, using each resin pellet, injection molding was performed using an injection molding machine (manufactured by Nissei Plastic Industrial Co., Ltd., trade name: NEX80) at a mold temperature of 80°C and an injection temperature of 270°C to form test pieces for measuring warpage of flat plates with dimensions of 80 mm in length × 60 mm in width × 1 mm in thickness respectively as glass fiber-reinforced resin molded products, and Type A dumbbell test pieces (4 mm thick) according to JIS K 7165:2008. Next, for each of the test pieces for measuring warpage of Examples 1 to 4, Comparative Examples 1 to 7, and Reference Example 1, warpage was measured as follows. Also, for each of the Type A dumbbell test pieces of Examples 1 to 4, Comparative Examples 1 to 7, and Reference Example 1, tensile strength and flexural strength were measured as follows. The warpage, tensile strength, and flexural strength of the glass fiber-reinforced resin molded products of Examples 1 to 4 are shown in Table 2. Also, the warpage, tensile strength, and flexural strength of the glass fiber-reinforced resin molded products of Comparative Examples 1 to 7 and Reference Example 1 are shown in Table 3. [Warpage] When one corner of the above-mentioned test piece for measuring warpage was grounded on a flat surface, the distance generated between a corner diagonally opposite to the corner grounded on the flat surface and the flat surface was measured using a vernier caliper. For the case where the four corners of the test piece for measuring warpage were respectively grounded on the flat surface, the above-mentioned distance was measured, and when the average value of each measured value was 5.0 mm or less, it was determined as "OK"; when it exceeded 5.0 mm, it was determined as "NG". [Tensile Strength] For the above-mentioned Type A dumbbell test piece, under the condition of a test temperature of 23°C, a static tensile test was performed using a precision universal testing machine (manufactured by Shimadzu Corporation, trade name: Autograph AG-5000B) according to JIS K 7165:2008 to measure the tensile strength. When it was 240 MPa or more, it was determined as "A"; when it was less than 240 MPa, it was determined as "B". [Flexural Strength] For the aforementioned dumbbell-shaped test pieces of type A, under the condition of a test temperature of 23°C, using a precision universal testing machine (manufactured by Shimadzu Corporation, product name: Autograph AG-5000B), a static bending test was conducted in accordance with JIS K 7171:2016 to measure the flexural strength. When the flexural strength is 400 MPa or more, it is judged as "A"; when it is 390 MPa or more and less than 400 MPa, it is judged as "B"; when it is less than 390 MPa, it is judged as "C". . . It can be clearly seen from Table 2 and Table 3 that for the flat-section glass fibers of Examples 1 to 4, compared with the long-round-section glass fibers of Comparative Example 5, in the glass fiber reinforced resin molded product, the same level of dimensional stability (warpage) and mechanical properties (flexural strength) can be maintained, and excellent strand cutting productivity can be obtained. On the other hand, it can be clearly seen that by P / R 1 / 4 For the flat-section glass fibers of Comparative Examples 1, 4, and 5, where the value of is outside the range of the aforementioned formula (1) and exceeds 63.0, the strand cutting productivity is poor; by P / R 1 / 4 For the flat-section glass fibers of Comparative Examples 2 and 3, where the value of is outside the range of the aforementioned formula (1) and is less than 55.9, the dimensional stability is poor or the strand cutting productivity is poor in the glass fiber reinforced resin molded product. It can also be clearly seen that although the aforementioned shape ratio R and the aforementioned filling rate P satisfy the aforementioned formula (1), for the flat-section glass fibers of Comparative Examples 6 and 7, where the content of CaO relative to the total amount of flat-section glass fibers is less than 16.7% by mass, the strand cutting productivity is poor or the mechanical properties are poor.

Claims

1. A flat-section glass fiber, characterized in that it comprises a plurality of flat-section glass filaments having a flat cross-section shape, wherein the flat-section glass filaments have the following characteristics: the major diameter of the cross-section is in the range of 20.0 to 35.0 μm, the minor diameter is in the range of 5.0 to 10.0 μm, the profile ratio R (the ratio of the major diameter to the minor diameter) is in the range of greater than 3.0 and less than 5.0, and the filling rate P (the ratio of the cross-sectional area of ​​the flat-section glass filament to the area of ​​the rectangle circumscribed in the cross-section of the flat-section glass filament) is in the range of 77.0 to 92.0%, wherein the aforementioned profile ratio R and the aforementioned filling rate P satisfy the following formula (1), and the flat-section glass filament contains 52.0 to 62.0% by mass of SiO2 relative to the total amount of the flat-section glass fiber.

2. Al₂O₃ in the range of 10.0–20.0% by mass; 3. CaO in the range of 16.7–28.1% by mass.

2. As in claim 1, a flat-section glass fiber, wherein, The aforementioned irregularity ratio R and the aforementioned fill rate P satisfy the following equation (2), 3. A glass fiber reinforced resin composition, characterized in that the resin composition contains the flat-section glass fibers of 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 of claim 3.