JP7489754B2 - Fiber-reinforced thermoplastic resin composition, its production method, and injection molded product - Google Patents

Description

The present invention relates to a fiber-reinforced thermoplastic resin composition, a method for producing the same, and an injection-molded article made from the fiber-reinforced thermoplastic resin composition.

It is commonly known that thermoplastic resins can be improved in mechanical properties by incorporating fibrous fillers such as glass fiber and carbon fiber. In particular, polyamide resins containing carbon fiber exhibit high strength. A common method for incorporating fibrous fillers is to melt-knead the thermoplastic resin and chopped strands of fiber (short fibers) in an extruder.

In recent years, the demand for high performance plastics has been increasing, and in addition to mechanical properties equivalent to those of metals, design properties (good appearance) are also being sought. However, molded products obtained by blending the fibrous filler tend to suffer from poor surface appearance due to loss of gloss caused by floating of the fibrous filler and generation of wavy irregularities, making it difficult to achieve both mechanical properties and design properties.
In response to this, a carbon fiber reinforced polyamide resin composition (Patent Document 1) has been proposed that can give molded articles with excellent mechanical properties, appearance, and design properties, which is obtained by blending a semi-aromatic polyamide resin having a difference between its melting point and its temperature-reducing crystallization peak temperature of 0° C. or more and less than 50° C., a polyamide resin having a difference between its melting point and its temperature-reducing crystallization peak temperature of 50° C. or more and less than 90° C., and carbon fibers. Although this technology can suppress waviness and unevenness, there has been a demand for a more excellent surface appearance.

JP 2017-186496 A

The present invention aims to solve the above problems and provide a carbon fiber reinforced thermoplastic resin composition that can produce molded products with excellent mechanical properties and surface appearance.

As a result of intensive research into solving the above problems, the inventors of the present invention have found that the above problems can be solved by using carbon fibers having a larger diameter, and have completed the present invention. That is, the gist of the present invention resides in the following (1) to (7).
(1) A fiber-reinforced thermoplastic resin molding material comprising 40% by mass or more and 67% by mass or less of polyamide resin (A) and 33% by mass or more and 60% by mass or less of carbon fiber (B), wherein the mass average fiber length (Lw) of the carbon fiber (B) is 0.13 mm or more and less than 0.50 mm, and the circle equivalent diameter of the carbon fiber (B) is 7.0 to 8.5 μm.
(2) The fiber-reinforced thermoplastic resin composition according to (1) above, wherein the mass average fiber length of the carbon fiber (B) is 0.18 mm or less.
(3) The fiber-reinforced thermoplastic resin composition according to (1) or (2) above, containing 5% by mass or more and 30% by mass or less of an inorganic filler (C) other than the carbon fiber (B).
(4) The polyamide resin (A) is composed of a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, and 50 mol% or more of the diamine-derived structural units are xylylenediamine. The fiber-reinforced thermoplastic resin composition according to any one of (1) to (3).
(5) The polyamide resin (A) is a polyamide resin (A-1) having a difference between the melting point (Tm) and the cooling crystallization peak temperature (Tc) of 50 ° C. or more and less than 90 ° C., and a polyamide resin (A-2) having a difference between Tm and Tc of 0 ° C. or more and less than 50 ° C. (A-2) The fiber reinforced thermoplastic resin composition according to any one of (1) to (3) above, wherein the difference between Tm and Tc of the polyamide resin (A) is less than 40 ° C.
(6) A method for producing a thermoplastic resin composition according to any one of (1) to (5) above, which comprises kneading and extruding a polyamide resin (A) or a resin composition containing a polyamide resin (A) with carbon fibers (B) in an extruder, in which the carbon fibers (B) are added in separate portions from two or more locations in the extruder.
(7) An injection-molded article of the thermoplastic resin composition according to any one of (1) to (5) above, wherein the surface roughness Ra of the injection-molded article is less than 0.1 and the waviness Wa is less than 1.0.

The carbon fiber reinforced thermoplastic resin composition of the present invention can provide molded products with excellent mechanical properties and surface appearance.

The thermoplastic resin composition of the present invention is a fiber-reinforced thermoplastic resin molding material that contains 40% by mass or more and 67% by mass or less of polyamide resin (A) and 33% by mass or more and 60% by mass or less of carbon fiber (B), the mass average fiber length (Lw) of the carbon fiber (B) is 0.13 mm or more and less than 0.50 mm, and the equivalent circle diameter of the carbon fiber (B) is 7.0 to 8.5 μm. Polyamide resin (A) exhibits excellent mechanical properties by blending with carbon fiber (B), and by containing a certain amount of polyamide resin (A), mechanical properties such as bending strength are excellent.

The polyamide resin (A) is composed of diamine-derived structural units and dicarboxylic acid-derived structural units, and it is preferable that 50 mol% or more of the diamine-derived structural units are xylylenediamine. By having 50 mol% or more of the diamine-derived structural units be xylylenediamine, the water absorption rate is kept low and the resin exhibits high rigidity and strength. Examples of such polyamide resin (A) include PAMXD6 and PAXD10. Examples of commercially available products include MX nylon S6001, S6007, and S6121 manufactured by Mitsubishi Gas Chemical Co., Ltd. as PAMXD6, and Lexter 8000, 8500, and 8900 manufactured by Mitsubishi Gas Chemical Co., Ltd. as PAXD10.

The polyamide resin (A) preferably includes a polyamide resin (A-1) having a difference between the melting point (Tm) and the cooling crystallization peak temperature (Tc) of 50°C or more and less than 90°C, and a polyamide resin (A-2) having a difference between Tm and Tc of 0°C or more and less than 50°C. The difference between Tm and Tc of the polyamide resin (A-1) is more preferably 60°C or more and less than 80°C, and the difference between Tm and Tc of the polyamide resin (A-2) is more preferably 10°C or more and less than 45°C. The polyamide resin (A-1) in 100% by mass of the polyamide resin (A) is preferably 50% by mass or more and less than 99% by mass, more preferably 60% by mass or more and less than 95% by mass. The polyamide resin (A-2) in 100% by mass of the polyamide resin (A) is preferably 1% by mass or more and less than 50% by mass, more preferably 5% by mass or more and less than 40% by mass. By including polyamide resin (A-1), molded articles with excellent surface appearance and small surface roughness (Ra) and waviness (Wa) can be obtained. On the other hand, such polyamide resin (A-1) alone is difficult to crystallize, so crystallization during injection molding may be insufficient, resulting in poor dimensional stability. Therefore, by using polyamide resin (A-2), which is easily crystallized, in combination, molded articles with excellent surface appearance and dimensional stability can be obtained.

Examples of polyamide resins (A-1) whose difference between Tm and Tc is 50°C or more and less than 90°C include PAMXD6, PAXD10, and PA6, and examples of polyamide resins (A-2) whose difference between Tm and Tc is 0°C or more and less than 50°C include PA10T, PA9T, PA66, and PA612.

The difference between Tm and Tc derived from the polyamide resin (A) of the thermoplastic resin of the present invention is preferably less than 40°C, and more preferably 25°C or more. If the difference between Tm and Tc is too large, the dimensional stability of the injection molded product may deteriorate, and if the difference between Tm and Tc is too small, the surface appearance will deteriorate.

The melting points (Tm) of (A-1) and (A-2) in the present invention refer to the temperature at the apex of the melting endothermic peak, and refer to the melting endothermic peak temperature in the DSC curve when (A-1) or (A-2) is heated at a rate of 10°C/min and the calorific value is measured in accordance with JIS K7121 (1987). A differential scanning calorimeter, for example, EXSTAR DSC7020 manufactured by Seiko Instruments Inc., can be used to measure the melting points. When two or more melting endothermic peaks are observed, the melting endothermic peak temperature present on the higher temperature side is taken as Tm.

Meanwhile, the cooling crystallization peak temperature (Tc) of (A-1) and (A-2) in the present invention refers to the temperature at the top of the crystallization exothermic peak, and means the temperature at the top of the crystallization exothermic peak in the DSC curve when (A-1) or (A-2) is heated to a temperature about 30°C higher than the end temperature of the melting endothermic peak, and then held at this temperature for 10 minutes, and then cooled at a rate of 10°C/min to measure the calorific value, in accordance with JIS K7121 (1987). A differential scanning calorimeter, for example, EXSTAR DSC7020 manufactured by Seiko Instruments Inc., can be used to measure the cooling crystallization peak temperature. When two or more cooling crystallization peaks are observed, the crystallization exothermic peak temperature present on the higher temperature side is taken as Tc.

The Tm of the polyamide (A) in the thermoplastic resin is preferably 180°C or higher, more preferably 200°C or higher, from the viewpoint of heat resistance. From the viewpoint of suppressing decomposition during melt molding, it is preferably 300°C or lower, more preferably 250°C or lower. From the viewpoint of suppressing waviness, the Tc of the polyamide (A) is preferably 150°C or higher, more preferably 180°C or higher. From the viewpoint of further reducing surface roughness, it is preferably 280°C or lower, more preferably 250°C or lower.

The thermoplastic resin composition of the present invention may contain a thermoplastic resin other than the polyamide resin (A). From the viewpoint of suppressing molding shrinkage even at a mold temperature of 100°C or more, an amorphous resin with a glass transition temperature (Tg) of 130°C or more is preferred, and from the viewpoint of ease of melt-kneading with the polyamide resin (A), a Tg of 250°C or less is preferred. Examples of such thermoplastic resins include polyethersulfone (Tg 225°C), polyetherimide (Tg 217°C), polycarbonate (Tg 150°C), etc.

The thermoplastic resin composition of the present invention contains 33% by mass or more and 50% by mass or less of carbon fiber (B), preferably 35% by mass or more from the viewpoint of obtaining better mechanical properties, and preferably 45% by mass or less from the viewpoint of surface appearance and mechanical properties. If the amount of carbon fiber (B) is too much, it may be difficult to obtain a good surface appearance even when using the method of the present invention, and the strength may decrease.

The mass average fiber length of the carbon fiber (B) contained in the thermoplastic resin composition of the present invention is 0.13 mm or more and less than 0.50 mm. From the viewpoint of obtaining excellent mechanical properties, 0.14 mm or more is preferable. Furthermore, from the viewpoint of obtaining a better appearance with less surface roughness and waviness, it is preferably less than 0.18 mm, and more preferably less than 0.16 mm.

The mass average fiber length of the carbon fibers (B) is determined by heating the resin pellets at 600° C. for 3 hours in an air atmosphere to remove the polyamide resin (A) and the like by pyrolysis, measuring the fiber lengths of at least 100 remaining carbon fibers (B) under an optical microscope, and averaging the measured fiber lengths. The mass average fiber length is calculated by the following formula (1), where L is the fiber length.
Mass average fiber length=ΣL ² /ΣL Formula (1)

The carbon fiber (B) contained in the thermoplastic resin composition of the present invention has an equivalent circle diameter of 7.0 μm or more and less than 8.5 μm, preferably 7.2 μm or more from the viewpoint of obtaining a better appearance, and preferably less than 8.0 μm from the viewpoint of obtaining excellent mechanical properties. The thicker the carbon fiber (B), the fewer the number of carbon fibers (B) contained in the thermoplastic resin, and the better the dispersion of the carbon fiber (B) in the thermoplastic resin. On the other hand, if the carbon fiber (B) is too thick, the length relative to the equivalent circle diameter becomes small, and the reinforcing effect of the carbon fiber (B) becomes small. The carbon fiber (B) does not necessarily have to be circular as long as the equivalent circle diameter is within this range.

Here, the equivalent circle diameter (μm) of the carbon fiber (B) is calculated from the basis weight (mg/m), the number of filaments (pieces), and the density (g/cm ³ ) according to the following formula (2).
Equivalent circle diameter=(basis ^weight /number of filaments/density×1000/3.14)×2 Equation (2)

The carbon fiber (B) used in the present invention may be PAN-based carbon fiber or pitch-based carbon fiber, but from the viewpoint of mechanical properties, PAN-based carbon fiber is preferred. PAN-based carbon fiber is composed mainly of "filament fiber essentially made of carbon, which is produced by infusible and carbonizing fibers made of polyacrylonitrile-based resin polymerized with acrylonitrile as the main component."

Examples of the form of carbon fiber (B) used in the manufacturing method of the present invention include long fiber, chopped fiber, milled fiber, etc. These forms of carbon fiber (B) may be used alone or in combination of two or more. Among these forms of carbon fiber (B), chopped fiber is preferred because it is easy to handle and the mass average fiber length can be easily controlled.

Commercially available carbon fibers (B) include, for example, Pyrofil TRW40 50L (manufactured by Mitsubishi Chemical Corporation) as a continuous fiber, and Pyrofil TR06UL B5K, TR06NL B5K, and TR06QL B5K (manufactured by Mitsubishi Chemical Corporation) as chopped fibers.

In addition to the polyamide resin (A) and the carbon fiber (B), the thermoplastic resin composition of the present invention may contain various additives as necessary within the range in which the effects of the present invention can be obtained. Examples of additives include colorants, antioxidants, metal deactivators, carbon black, nucleating agents, release agents, lubricants, antistatic agents, light stabilizers, UV absorbers, inorganic fillers, impact resistance modifiers, processing aids, flame retardants, plasticizers, etc. These additives may be used alone or in combination of two or more.

When an inorganic filler is blended into the thermoplastic resin composition of the present invention, it is preferable that the inorganic filler (C) other than the carbon fiber (B) is contained in an amount of 5% by mass to 30% by mass, and more preferably 9% by mass to 15% by mass. Here, the inorganic filler other than the carbon fiber (B) is preferably a particulate, spherical, or plate-shaped filler with little anisotropy from the viewpoint of reducing the molding shrinkage rate of the resin, and is preferably a fibrous or plate-shaped filler from the viewpoint of improving rigidity. Plate-shaped fillers are particularly preferable. By using such inorganic fillers, it is possible to obtain better surface appearance and mechanical properties. Examples of inorganic fillers include talc, mica, graphite, calcium carbonate, barium sulfate, graphite, and glass fiber, and talc, mica, and calcium carbonate are preferable, and talc and mica are more preferable.

The thermoplastic resin composition of the present invention may contain a processing aid having the effect of improving melt tension. The use of a processing aid may improve the appearance around the gate of injection molding, and may also improve mechanical properties. Examples of such processing aids include PTFE-based processing aids and acrylic-based processing aids. Examples of commercially available PTFE-based processing aids include Metablen A-3000, A-3750, and A-3800 manufactured by Mitsubishi Chemical Corporation. Examples of commercially available acrylic-based processing aids include Metablen P-531A, P-530A, P-551A, P-501A, P-570A, P-700, and P-710 manufactured by Mitsubishi Chemical Corporation. From the viewpoint of improving mechanical properties and processability, PTFE-based processing aids are preferred.

The thermoplastic resin composition of the present invention may contain a colorant. Examples of colorants include carbon black, inorganic pigments, and organic dyes. From the viewpoint of obtaining a more uniform black appearance, carbon black is preferred. When carbon black is used as a colorant, the content is preferably 0.1% by mass or more and 2% by mass or less from the viewpoints of colorability and mechanical properties.

The thermoplastic resin composition of the present invention may contain a release agent. Examples of the release agent include fatty acid wax, fatty acid ester wax, polyethylene wax, polypropylene wax, oxidized polyethylene wax, and fluorine-based lubricants.

A nucleating agent may be used to adjust the crystallization of polyamide resin (A). Examples of nucleating agents include organic nucleating agents and inorganic fillers. From the viewpoint of heat resistance and nucleating effect, inorganic fillers are preferred, and talc is particularly preferred. The amount of the nucleating agent is preferably 0.1% by mass or more relative to the polyamide resin (A). If the amount is too small, the effect as a nucleating agent will be limited. When an inorganic filler is used as a nucleating agent, the upper limit is in accordance with the upper limit of the amount of inorganic filler to be blended.

The method for producing the thermoplastic resin composition of the present invention is preferably a method in which polyamide resin (A) or a resin composition containing polyamide resin (A) is kneaded with carbon fiber (B) in an extruder. By using an extruder, it is possible to continuously produce a thermoplastic resin composition with stable quality.

The mass average fiber length of carbon fiber (B) can be adjusted by controlling the melt mixing conditions such as the feeding method of carbon fiber (B), the screw rotation speed of the extruder, and the discharge amount. In order to adjust the fiber length of carbon fiber (B) within the range of the present invention, a method of side feeding part or all of carbon fiber (B) is preferable, and more preferably, a method of dividing carbon fiber (B) and feeding it from two or more places of the extruder. Most preferably, a method of feeding part of carbon fiber (B) together with polyamide resin (A) etc. from a main raw material feeder upstream of the extruder and melt kneading, and feeding the remaining part of carbon fiber (B) from a side feeder into a resin composition containing polyamide resin (A) in a molten state. In this case, it is possible to adjust the fiber length by adjusting the ratio of feeding from the main raw material feeder and the side feeder.

The molded article of the present invention contains the thermoplastic resin composition of the present invention and can be obtained by injection molding the thermoplastic resin composition of the present invention.
The injection molded product made of the thermoplastic resin composition of the present invention preferably has a surface roughness Ra of less than 0.1 μm and a waviness Wa of less than 1.0 μm. More preferably, Wa is less than 0.5 μm, and even more preferably Wa is less than 0.2 μm. The smaller the surface roughness and waviness, the better the surface smoothness and the better the appearance. There is no particular lower limit, but it is difficult to achieve Ra of less than 0.03 μm and Wa of less than 0.05 μm.

The flexural modulus of the injection molded article made of the thermoplastic resin composition of the present invention is preferably 23,000 MPa or more, more preferably 26,000 MPa or more. Also, it is preferably 35,000 MPa or less. If the flexural modulus is within this range, the injection molded article will have an excellent balance between rigidity and appearance.

The flexural strength of an injection molded article made of the thermoplastic resin composition of the present invention is preferably 330 MPa or more and 500 MPa or less, and more preferably 370 MPa or more and 470 MPa or less. If the flexural strength is within this range, the injection molded article will have an excellent balance between strength and appearance.

The thickness of the injection molded product made of the thermoplastic resin composition of the present invention is preferably 0.5 mm to 2.6 mm, more preferably 1.1 mm to 2.1 mm. If it is too thick, the surface appearance may be insufficient, and if it is too thin, the rigidity and strength of the injection molded product may be insufficient.

To explain the present invention in more detail, examples and comparative examples are given below, but the present invention is not limited to these examples.

[Melting point (Tm)]
The polyamide resin (A) or the thermoplastic resin composition was heated from 30° C. at a rate of 10° C./min according to JIS K7121 (1987) using a differential scanning calorimeter (EXSTAR DSC7020) manufactured by Seiko Instruments Inc., and the calorific value was measured, and the melting point (Tm) was determined from the melting endothermic peak temperature in the DSC curve. When two or more peaks were obtained, the melting endothermic peak temperature on the higher temperature side was taken as Tm.

[Cooling-down crystallization peak temperature (Tc)]
The polyamide resin (A) or the thermoplastic resin composition was heated from 30° C. to a temperature about 30° C. higher than the end temperature of the melting endothermic peak at a rate of 10° C./min according to JIS K7121 (1987) using a differential scanning calorimeter (EXSTAR DSC7020) manufactured by Seiko Instruments Inc., and then maintained at this temperature for 10 minutes. The temperature was then lowered at a rate of 10° C./min to measure the amount of heat, and the cooling crystallization peak temperature (Tc) was determined from the temperature of the apex of the crystallization exothermic peak in the DSC curve.

[Fiber length]
The thermoplastic resin compositions obtained in the Examples and Comparative Examples were heated at 600° C. for 3 hours in an air atmosphere to remove the polyamide (A) and the like by thermal decomposition, and the fiber lengths of any 100 or more remaining carbon fibers were measured using an optical microscope.
The weight average fiber length (Lw) and number average fiber length (Ln) were calculated according to the following formula.
Number average fiber length (Ln) = ΣL / n
Weight average fiber length (Lw) = ΣL ² /ΣL
L: fiber length of carbon fiber n: number of carbon fibers

[Bending test]
The thermoplastic resin pellets obtained in each Example and Comparative Examples 1 and 2 were dried at 150° C. for 2 hours, and then injection molded using an injection molding machine (model name "IS55", manufactured by Toshiba Machine Co., Ltd.) under conditions of a cylinder temperature of 300° C. and a mold temperature of 130° C. to obtain molded bodies (width 10 mm, length 80 mm, thickness 4 mm). The obtained molded bodies were subjected to a three-point bending test in accordance with ISO178 to measure the bending strength and bending modulus.
The thermoplastic resin pellets obtained in Comparative Example 3 had a high Tm, and the bending strength and bending modulus were measured in the same manner as in each of the Examples, except that the cylinder temperature was changed to 330° C. accordingly.

[Surface roughness Ra, surface waviness Wa]
The thermoplastic resin pellets obtained in each Example and Comparative Examples 1 and 2 were dried at 150°C for 2 hours, and then injection molding was performed using an injection molding machine (model name "Si-80V", manufactured by Toyo Machinery & Metals Co., Ltd.) under conditions of a cylinder temperature of 300°C and a mold temperature of 130°C to injection mold a square plate of 100m x 100mm x 2mm. Using this square plate, the arithmetic mean roughness (Ra) of the molded product surface was measured using a surface roughness measuring device (manufactured by ACCRTECH) under measurement conditions of an evaluation length of 8mm and a test speed of 0.6mm/sec, and the surface roughness was evaluated.

In addition, a square plate of 100 mm × 100 mm × 2 mm was used, and the arithmetic mean height (Wa) of the waviness curve on the surface of the molded article was measured using a surface roughness measuring device (manufactured by ACCRTECH) under measurement conditions of an evaluation length of 20 mm and a test speed of 0.6 mm/sec, to evaluate the surface waviness.
The thermoplastic resin pellets obtained in Comparative Example 3 had a high Tm, and the cylinder temperature was changed to 330° C. accordingly. Except for this, the surface roughness and surface waviness were measured in the same manner as in each of the Examples.

[material]
PAMXD6 (A-1): MX nylon S6007 (manufactured by Mitsubishi Gas Chemical Co., Ltd.) was used. The melting point (Tm) was 239°C, the cooling crystallization peak temperature (Tc) was 164°C, and Tm-Tc was 75°C.
PA66 (A-2-1): E2000SL (manufactured by Unitika Ltd.) was used. The melting point (Tm) was 264°C, the cooling crystallization peak temperature (Tc) was 224°C, and Tm-Tc was 40°C.
PA9T (A-2-2): N1000A (manufactured by Kuraray Co., Ltd.) was used. The melting point (Tm) was 302°C, the cooling crystallization peak temperature (Tc) was 276°C, and Tm-Tc was 26°C.

Carbon fiber (B-1): PAN-based carbon fiber TRW40 50L (filament count 50,000, basis weight 3,750 mg/m, density 1.81 g/cm ³ , equivalent circle diameter 7.3 μm, tensile strength 4.12 GPa, tensile modulus 240 GPa) manufactured by Mitsubishi Chemical Corporation was applied with a polyamide-based sizing agent and cut to 6 mm. Sizing agent adhesion amount 3.0%
Carbon fiber (B-2): PAN-based carbon fiber MR60H 24P (filament count 24,000, basis weight 960 mg/m, density 1.81 g/cm ³ , equivalent circle diameter 5.3 μm, tensile strength 5.68 GPa, tensile modulus 280 GPa) manufactured by Mitsubishi Chemical Corporation was applied with a polyamide-based sizing agent and cut to 3 mm. Sizing agent adhesion amount 3.0%
Carbon fiber (B-3): PAN-based carbon fiber TR50S 15L (filament count 15,000, basis weight 1,000 mg/m, density 1.82 g/cm ³ , equivalent circle diameter 6.8 μm, tensile strength 4.90 GPa, tensile modulus 235 GPa) manufactured by Mitsubishi Chemical Corporation was applied with a polyamide-based sizing agent and cut to 6 mm. Sizing agent adhesion amount 3.0%

Talc (C-1): Micron White #5000A (manufactured by Hayashi Kasei Co., Ltd.)
Calcium carbonate (C-2): Whiten P30 (manufactured by Shiraishi Calcium Co., Ltd.)
PES: Sumikaexcel PES 3600P (manufactured by Sumitomo Chemical Co., Ltd.)
Processing aid: Metablen A-3750 (manufactured by Mitsubishi Chemical Corporation)
Release agent: Pentaerythritol stearate Colorant: Carbon black

[Example 1]
Using a same-rotation twin-screw extruder (model name "PCM-30" (manufactured by Ikegai Co., Ltd.) having a main raw material feeder and a side feeder, 52.3 mass% of PAMXD6 (A-1), 6.0 mass% of PA66 (A-2-1), 0.6 mass% of talc (C-1), 0.8 mass% of carbon black, 0.3 mass% of release agent, and 30 mass% of carbon fiber (B-1) were fed from the main raw material feeder, and 10 mass% of carbon fiber (B-1) was fed from the side feeder. The mixture was melt-kneaded under conditions of 300 ° C. and 200 rpm, and the discharged strand was cooled in water and cut to a length of 4 mm with a strand cutter to obtain a thermoplastic resin composition. The evaluation results are shown in Table 1.

[Example 2]
The same procedure as in Example 1 was carried out, except that the raw materials fed from the main raw material feeder were changed to 43.4 mass% PAMXD6 (A-1), 5.0 mass% PA66 (A-2-1), 0.5 mass% talc (C-1), 0.8 mass% carbon black, 0.3 mass% release agent, 10 mass% calcium carbonate (C-2), and 30 mass% carbon fiber (B-1). The evaluation results are shown in Table 1.

[Example 3]
The same procedure as in Example 2 was repeated except that 10% by mass of PES was used instead of 10% by mass of calcium carbonate (C-1). The evaluation results are shown in Table 1.

[Example 4]
The same procedure as in Example 1 was carried out, except that the raw materials fed from the main raw material feeder were changed to 51.9% by mass of PAMXD6 (A-1), 6.0% by mass of PA66 (A-2-1), 0.6% by mass of talc (C-1), 0.8% by mass of carbon black, 0.3% by mass of release agent, 0.4% by mass of processing aid, and 30% by mass of carbon fiber (B-1). The evaluation results are shown in Table 1.

[Example 5]
The same procedure as in Example 3 was carried out, except that the carbon fiber (B-1) was fed in an amount of 20% by mass from the main raw material feeder and 20% by mass from the side feeder. The evaluation results are shown in Table 1.

[Example 6]
The same procedure as in Example 3 was carried out, except that the carbon fiber (B-1) was not fed from the raw material feeder, but was fed from the side feeder in an amount of 40 mass%. The evaluation results are shown in Table 1.

[Example 7]
The same procedure as in Example 1 was carried out except that the raw materials fed from the main raw material feeder were changed to 43.0% by mass of PAMXD6 (A-1), 5.0% by mass of PA66 (A-2-1), 0.5% by mass of talc (C-1), 0.8% by mass of carbon black, 0.3% by mass of release agent, 0.4% by mass of processing aid, 10% by mass of calcium carbonate (C-2), and 30% by mass of carbon fiber (B-1). The evaluation results are shown in Table 1.

[Example 8]
The same procedure as in Example 1 was carried out except that the raw materials fed from the main raw material feeder were changed to 43.0% by mass of PAMXD6 (A-1), 5.0% by mass of PA66 (A-2-1), 10.5% by mass of talc (C-1), 0.8% by mass of carbon black, 0.3% by mass of release agent, 0.4% by mass of processing aid, and 30% by mass of carbon fiber (B-1). The evaluation results are shown in Table 1.

[Comparative Example 1]
The same procedure as in Example 3 was carried out, except that the carbon fiber (B-1) was not fed from the side feeder, but was fed from the main raw material feeder in an amount of 40 mass%. The evaluation results are shown in Table 1.

[Comparative Example 2]
The same procedure as in Example 1 was repeated, except that carbon fiber (B-1) was not used, and instead, 40 mass % of carbon fiber (B-2) was fed from the side feeder. The evaluation results are shown in Table 1.

[Comparative Example 3]
With reference to the contents described in Example 13 of Patent Document 1, 12.0 mass% of PAMXD6 (A-1) and 48.0 mass% of PA9T (A-2-2) were fed from the main raw material feeder, and 40 mass% of carbon fiber (B-3) was fed from the side feeder, and the mixture was melt-kneaded under conditions of 330° C. and 200 rpm, in the same manner as in Example 1 to obtain a thermoplastic resin composition. The evaluation results are shown in Table 1.

Comparing Examples 1 to 9 with Comparative Examples 1 to 3, it can be seen that the thermoplastic resin composition of the present invention has an excellent balance between surface appearance and mechanical properties.

In Comparative Example 1, the length of the carbon fiber (B) is shorter than the range of the present invention, and therefore the mechanical properties such as bending strength and bending modulus are inferior to Examples 3, 5, and 6, which have the same composition but different fiber lengths of the carbon fiber (B). In addition, a comparison of Examples 3, 5, and 6 clearly shows that the shorter the carbon fiber (B), the better the appearance properties such as surface roughness and surface waviness, and the longer the carbon fiber (B), the better the mechanical properties such as bending strength and bending modulus.

In Comparative Example 2, the equivalent circle diameter of carbon fiber (B) is smaller than the range of the present invention. Comparison with Examples 1 and 6 reveals the effect of the equivalent circle diameter of carbon fiber (B). In Example 6, in which all carbon fibers (B) are side-fed as in Comparative Example 2, the fiber length of carbon fiber (B) is longer than in Comparative Example 2, but both the surface roughness and surface waviness are small, resulting in excellent surface appearance. Example 1, which has the same composition but a different mass average fiber length and equivalent circle diameter, has both smaller surface roughness and surface waviness than Comparative Example 2, resulting in excellent surface appearance.

Comparative Example 3 is a comparative example based on Prior Art Document 1. The purpose of this example is to obtain a molded product with excellent surface appearance by using PA9T (A-2-2), which has a small difference between Tm and Tc, PAMXD6 (A-1), which has a large difference between Tm and Tc, and carbon fiber (B-3). However, since the equivalent circle diameter of carbon fiber (B) is outside the range of the present invention, the surface roughness and surface waviness are greater than those of Examples 1 to 8.

Example 2 uses calcium carbonate (C-2) and has a higher flexural modulus and smaller surface waviness than Example 1. Example 3 uses PES and has evaluation results almost equivalent to Example 1. Example 4 uses a processing aid and has a higher elastic modulus than Example 1. Example 7 uses calcium carbonate (C-2) and a processing aid and has a higher elastic modulus than Example 2, which does not contain a processing aid, and Example 4, which does not contain calcium carbonate (C-2). Example 8 uses an increased amount of talc (C-1) instead of calcium carbonate (C-2) and has a higher elastic modulus and slightly smaller surface waviness than Example 7.

Claims (6)

A fiber-reinforced thermoplastic resin molding material comprising 40% by mass or more and 67% by mass or less of polyamide resin (A) and 33% by mass or more and 60% by mass or less of carbon fiber (B), the mass average fiber length (Lw) of the carbon fiber (B) is 0.13 mm or more and less than 0.50 mm, and the equivalent circle diameter of the carbon fiber (B) calculated by the following formula (2) is 7.2 to 8.5 μm.
Equivalent circle diameter=(basis ^weight /number of filaments/density×1000/3.14)×2 Equation (2) The fiber-reinforced thermoplastic resin molding material according to claim 1, wherein the mass average fiber length of the carbon fibers (B) is less than 0.16 mm. The fiber-reinforced thermoplastic resin molding material according to claim 1 or 2, which contains 5% by mass or more and 30% by mass or less of an inorganic filler (C) other than carbon fiber (B). The fiber-reinforced thermoplastic resin molding material according to any one of claims 1 to 3, wherein the polyamide resin (A) is composed of diamine-derived structural units and dicarboxylic acid-derived structural units, and 50 mol% or more of the diamine-derived structural units are xylylenediamine. The fiber-reinforced thermoplastic resin molding material according to any one of claims 1 to 3, wherein the polyamide resin (A) contains 50% by mass or more and 99% by mass or less of polyamide resin (A-1) having a difference between the melting point (Tm) and the cooling crystallization peak temperature (Tc) of 50°C or more and less than 90°C, and 1% by mass or more and 50% by mass or less of polyamide resin (A-2) having a difference between Tm and Tc of 0°C or more and less than 50°C, and the difference between Tm and Tc of the polyamide resin (A) is less than 40°C. An injection molded product made from the thermoplastic resin molding material according to any one of claims 1 to 5, the surface roughness Ra of the injection molded product being less than 0.1 and the waviness Wa being less than 1.0.