JP7613892B2 - Resin composition and molded article - Google Patents

Description

The present invention relates to a resin composition and a molded article. In particular, the present invention relates to a resin composition containing a polyamide resin.

2. Description of the Related Art Conventionally, attempts have been made to increase the strength of molded articles made of polyamide resin by blending carbon fibers with the polyamide resin.
For example, Patent Document 1 discloses a polyamide resin composition containing 100 parts by mass of a polyamide resin having a crystallization half time (ST(P)) of 20 to 500 seconds, 20 to 75 parts by mass of carbon fibers having a number average fiber length of 3 to 10 mm, and whiskers, the amount of whiskers being 20 to 210 parts by mass per 100 parts by mass of carbon fibers having a number average fiber length of 3 to 10 mm. Patent Document 2 discloses a polyamide resin composition containing 20 to 90% by mass of a polyamide resin obtained by reacting xylylenediamine with a linear aliphatic dicarboxylic acid having 6 to 12 carbon atoms, 5 to 60% by mass of carbon fibers, and 5 to 60% by mass of potassium titanate fibers.

JP 2017-210590 A Japanese Unexamined Patent Publication No. 58-198560

Polyamide resin compositions containing carbon fibers are advantageous in that they have excellent mechanical strength, but they have poor surface gloss, although there is a high demand for high surface gloss depending on the application.
The present invention has an object to solve the above problems, and to provide a resin composition and a molded article having excellent mechanical strength and high surface gloss.

In light of the above-mentioned problems, the present inventors conducted research and found that the above-mentioned problems can be solved by using at least one reinforcing material selected from whiskers and granular fillers in addition to carbon fibers in a polyamide resin and by precisely adjusting the mass ratio thereof.
Specifically, the above problems were solved by the following means.
<1> A resin composition comprising 100 parts by mass of a polyamide resin, 76 to 120 parts by mass of carbon fiber, and at least one reinforcing material selected from whiskers and a granular filler, wherein the reinforcing material is contained in a total amount of 10 to 120 parts by mass per 100 parts by mass of the carbon fiber, and the total amount of the carbon fiber and the reinforcing material accounts for 50% by mass or more of the entire resin composition.
<2> The resin composition according to <1>, wherein the whiskers have an aspect ratio of 5 to 50.
<3> The resin composition according to <1> or <2>, wherein the granular filler contains calcium carbonate.
<4> The resin composition according to any one of <1> to <3>, wherein the mass ratio of the carbon fiber to the reinforcing material, carbon fiber/reinforcing material, is 4.3 or less.
<5> The polyamide resin is composed of diamine-derived structural units and dicarboxylic acid-derived structural units, 70 mol % or more of the diamine-derived structural units are derived from at least one of meta-xylylenediamine and para-xylylenediamine, and 70 mol % or more of the dicarboxylic acid-derived structural units are derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms. The resin composition according to any one of <1> to <4>.
<6> The resin composition according to <5>, wherein the α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms includes adipic acid and/or sebacic acid.
<7> The resin composition according to <5>, wherein the α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms includes adipic acid.
<8> The resin composition according to any one of <5> to <7>, wherein the polyamide resin further contains polyamide 66.
<9> The resin composition according to any one of <1> to <8>, further comprising a black colorant.
<10> The resin composition according to any one of <1> to <9>, wherein the resin composition is molded into a plate of 100 x 100 x 2 mmt and has an L ^* value measured according to JIS K7105 of 24 or more.
<11> A molded article formed from the resin composition according to any one of <1> to <10>.

The present invention makes it possible to provide a resin composition and molded article that have excellent mechanical strength and high surface gloss.

Hereinafter, an embodiment of the present invention (hereinafter, simply referred to as the present embodiment) will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to the present embodiment.
In this specification, the word "to" is used to mean that the numerical values before and after it are included as the lower limit and upper limit.
In this specification, various physical properties and characteristic values are those at 23° C. unless otherwise specified.
In cases where the standards shown in this specification differ depending on the year and the measurement method, etc., the standards shall be those in effect at the time of filing, unless otherwise stated.

The resin composition of this embodiment is a resin composition containing 100 parts by mass of polyamide resin, 76 to 120 parts by mass of carbon fiber, and at least one reinforcing material selected from whiskers and granular fillers, and is characterized in that the reinforcing material is contained in a total of 10 to 120 parts by mass per 100 parts by mass of the carbon fiber, and the total amount of the carbon fiber, the whiskers, and the granular fillers accounts for 50% by mass or more of the entire resin composition. In this way, by blending the polyamide resin with the carbon fiber and at least one reinforcing material selected from the whiskers and granular fillers and precisely adjusting the quantitative ratio between them, a resin composition having excellent mechanical strength and high surface gloss can be obtained.

That is, when carbon fiber is blended with polyamide resin, the mechanical strength is improved. However, the surface glossiness (gloss value) is reduced. On the other hand, when the amount of carbon fiber is reduced, the surface glossiness is improved but the mechanical strength is reduced. Also, it is possible to replace carbon fiber with glass fiber or wollastonite, but the mechanical strength is reduced compared to when carbon fiber is used. In particular, glass fiber and wollastonite are known as reinforcing materials, but their high bending properties may not be sufficient depending on the application.
As a result of the inventor's investigations, it has been found that by adjusting the amount of carbon fiber and compounding at least one reinforcing material selected from whiskers and granular fillers, it is possible to maintain a high level of mechanical strength without reducing the surface gloss.

<Polyamide resin>
The resin composition of the present embodiment contains a polyamide resin.
The type of polyamide resin used in the present embodiment is not particularly limited, and may be an aliphatic polyamide resin, a semi-aromatic polyamide resin, or a blend thereof. For example, the description of the polyamide resin in paragraphs 0011 to 0013 of JP 2011-132550 A may be referred to.
Examples of the aliphatic polyamide resin include polyamide 6 and polyamide 66, with polyamide 66 being preferred.
The polyamide resin used in this embodiment preferably contains a semi-aromatic polyamide resin. For example, it is preferable that 80% by mass or more (preferably 85 to 95% by mass) of the polyamide resin contained in the resin composition of this embodiment is a semi-aromatic polyamide resin. Here, the semi-aromatic polyamide resin is composed of a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, and 20 to 80 mol% of the total structural units of the diamine-derived structural unit and the dicarboxylic acid-derived structural unit are structural units containing an aromatic ring. By using such a semi-aromatic polyamide resin, the mechanical strength of the obtained resin molded product can be increased. Examples of semi-aromatic polyamide resins include terephthalic acid-based polyamide resins (polyamide 6T, polyamide 9T, polyamide 10T) and xylylenediamine-based polyamide resins described later.

The polyamide resin used in this embodiment is composed of diamine-derived structural units and dicarboxylic acid-derived structural units, and it is preferable that 70 mol % or more of the diamine-derived structural units are derived from at least one of metaxylylenediamine and paraxylylenediamine, and 70 mol % or more of the dicarboxylic acid-derived structural units are derived from α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms. Hereinafter, such polyamide resins may be referred to as xylylenediamine-based polyamide resins. By using xylylenediamine-based polyamide resins, molded products having excellent mechanical strength can be obtained.
The diamine-derived constituent units of the xylylenediamine-based polyamide resin are more preferably 75 mol% or more, even more preferably 80 mol% or more, still more preferably 85 mol% or more, even more preferably 90 mol% or more, and still more preferably 95 mol% or more derived from metaxylylenediamine or paraxylylenediamine.
In this embodiment, the ratio of meta-xylylenediamine to para-xylylenediamine is preferably 10 to 100 mol% meta-xylylenediamine and 0 to 90 mol% para-xylylenediamine, more preferably 30 to 100 mol% meta-xylylenediamine and 0 to 70 mol% para-xylylenediamine, even more preferably 70 to 100 mol% meta-xylylenediamine and 0 to 30 mol% para-xylylenediamine, still more preferably 90 to 100 mol% meta-xylylenediamine and 0 to 10 mol% para-xylylenediamine, and even more preferably 98 to 100 mol% meta-xylylenediamine and 0 to 2 mol% para-xylylenediamine.
The dicarboxylic acid-derived constituent units of the xylylenediamine-based polyamide resin are more preferably 75 mol % or more, even more preferably 80 mol % or more, still more preferably 90 mol % or more, even more preferably 95 mol % or more, and still more preferably 98 mol % or more, of which the dicarboxylic acid-derived constituent units are derived from linear α,ω-aliphatic dicarboxylic acids having 4 to 20 carbon atoms.

Diamines other than meta-xylylenediamine and para-xylylenediamine that can be used as raw diamine components for xylylenediamine-based polyamide resins include aliphatic diamines such as tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine, 1,3-bis(a Examples of such diamines include alicyclic diamines such as bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, and bis(aminomethyl)tricyclodecane; and diamines having an aromatic ring such as bis(4-aminophenyl)ether, paraphenylenediamine, and bis(aminomethyl)naphthalene. These can be used alone or in combination of two or more.

Examples of α,ω-straight-chain aliphatic dicarboxylic acids having 4 to 20 carbon atoms that are suitable for use as the raw dicarboxylic acid component of xylylenediamine-based polyamide resins include aliphatic dicarboxylic acids such as succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, adipic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid. One or more of these can be used in combination, but among these, adipic acid and/or sebacic acid are more preferred, and adipic acid is even more preferred, since the melting point of the polyamide resin falls within a range suitable for molding.

Examples of dicarboxylic acid components other than the α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms include phthalic acid compounds such as isophthalic acid, terephthalic acid, and orthophthalic acid, and isomers of naphthalene dicarboxylic acids such as 1,2-naphthalene dicarboxylic acid, 1,3-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 1,6-naphthalene dicarboxylic acid, 1,7-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, and 2,7-naphthalene dicarboxylic acid, and these can be used alone or in combination of two or more.

In the present embodiment, the xylylenediamine-based polyamide resin is particularly preferably one in which 70 mol% or more (more preferably 75 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 98 mol% or more) of the diamine-derived structural units are derived from meta-xylylenediamine, and 70 mol% or more (more preferably 75 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 98 mol% or more) of the dicarboxylic acid-derived structural units are derived from adipic acid.

It should be noted that although the diamine-derived structural units and dicarboxylic acid-derived structural units are the main components, other structural units are not completely excluded, and it goes without saying that the resin may contain structural units derived from lactams such as ε-caprolactam and laurolactam, and aliphatic aminocarboxylic acids such as aminocaproic acid and aminoundecanoic acid. Here, the main component means that, among the structural units constituting the xylylenediamine-based polyamide resin, the total number of diamine-derived structural units and dicarboxylic acid-derived structural units is the largest among all structural units. In this embodiment, the total of diamine-derived structural units and dicarboxylic acid-derived structural units in the xylylenediamine-based polyamide resin preferably accounts for 90% or more of all structural units, and more preferably accounts for 95% or more.

In this embodiment, the polyamide resin preferably contains a xylylenediamine-based polyamide resin and polyamide 66, and more preferably contains 85 to 95% by mass of the xylylenediamine-based polyamide resin and 5 to 15% by mass of polyamide 66. However, the total of the xylylenediamine-based polyamide resin and polyamide 66 does not exceed 100% by mass, and it is preferable that the total of the xylylenediamine-based polyamide resin and polyamide 66 is 95 to 100% by mass, and it is more preferable that the total of the xylylenediamine-based polyamide resin and polyamide 66 is 98 to 100% by mass.

The content of the polyamide resin in the resin composition of the present embodiment is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and even more preferably 35% by mass or more. By making it equal to or more than the lower limit, extrudability tends to be more stable.
The content of the polyamide resin in the resin composition of the present embodiment is 50% by mass or less, preferably 45% by mass or less, and more preferably 40% by mass or less. By making the content less than the upper limit, the mechanical strength of the resin molded product tends to be further improved.
The resin composition of the present embodiment may contain only one type of polyamide resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

The resin composition of this embodiment may or may not contain a thermoplastic resin other than polyamide resin. The content of the thermoplastic resin other than polyamide resin in the resin composition of this embodiment is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less of the resin composition of this embodiment.

<Carbon fiber>
The resin composition of the present embodiment contains 76 to 120 parts by mass of carbon fiber per 100 parts by mass of polyamide resin. By containing the carbon fiber, a resin composition and a molded product having excellent mechanical strength, particularly bending properties, can be obtained.
The type of carbon fiber is not particularly limited, and either polyacrylonitrile-based carbon fiber (PAN-based fiber) or pitch-based carbon fiber using pitch is preferably used, with polyacrylonitrile-based carbon fiber (PAN-based fiber) being more preferred.

The carbon fibers are preferably chopped strands.
The carbon fibers preferably have a number average fiber length of 3 mm or more, more preferably 4 mm or more, and more preferably 10 mm or less, more preferably 8 mm or less, and even more preferably 7 mm or less.
The carbon fibers preferably have a number average fiber diameter of 3 to 20 μm, more preferably 5 to 15 μm. By using carbon fibers in such a range, the obtained molded product can have an excellent balance between mechanical strength and appearance.
The carbon fibers used may have a tensile strength of 5.0 GPa or less (preferably 3.5 to 5.0 GPa) measured at 23° C. in accordance with JIS R7601.
Specific examples of carbon fibers include Torayca manufactured by Toray Industries, Inc., Besfight Filament manufactured by Toho Tenax Co., Ltd., and Pyrofil manufactured by Mitsubishi Rayon Co., Ltd.

The content of carbon fiber in the resin composition of this embodiment is 76 parts by mass or more, preferably 78 parts by mass or more, and may be 81 parts by mass or more, relative to 100 parts by mass of polyamide resin. By making it equal to or more than the lower limit, the bending properties of the obtained molded product, particularly the bending modulus, can be effectively improved. The content of carbon fiber in the resin composition of this embodiment is also 120 parts by mass or less, preferably 110 parts by mass or less, more preferably 105 parts by mass or less, even more preferably 100 parts by mass or less, and may be 95 parts by mass or less, relative to 100 parts by mass of polyamide resin. By making it equal to or less than the upper limit, the surface gloss tends to be further improved. In addition, the moldability of the pellets tends to be improved.
The resin composition of the present embodiment may contain only one type of carbon fiber, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<At least one reinforcing material selected from whiskers and particulate fillers>
The resin composition of this embodiment contains at least one type of reinforcing material selected from whiskers and granular fillers (hereinafter, simply referred to as the "specific reinforcing material") in a total amount of 10 to 120 parts by mass per 100 parts by mass of carbon fiber, and further, the total amount of the carbon fiber and the specific reinforcing material accounts for 50% by mass or more of the entire resin composition.
By including the specific reinforcing material in the above-mentioned predetermined ratio, it is possible to increase the surface gloss while maintaining high mechanical strength of the resin composition.

In this embodiment, whiskers can be used as the specific reinforcing material. Whiskers are short fibrous or needle-like inorganic crystals.
The whiskers preferably have an aspect ratio of 5 to 50, and more preferably 10 to 40. By setting the aspect ratio within such a range, the appearance of the resulting molded article can be further improved.
The number average fiber length of the whiskers is preferably 5 to 200 μm, and more preferably 5 to 150 μm. By setting the number average fiber length in this range, the appearance of the obtained molded article can be further improved.
The whiskers preferably have a number average fiber diameter of 0.1 to 20 μm, and more preferably 0.3 to 15 μm. By setting the diameter within such a range, the appearance of the resulting molded article can be further improved.
The number-average fiber length and number-average fiber diameter of the whiskers can be measured by observing the whiskers under an electron microscope in a state where the whiskers are dispersed in a solvent such as alcohol, and are usually taken as an average value of 100 whiskers.

The whiskers preferably have a Mohs hardness of 2.5 to 5.0, and more preferably 3.0 to 4.8. By setting the hardness within such a range, wear on the barrel and screw of the extruder can be reduced, enabling stable extrusion.
The whiskers preferably have a specific gravity of 2.0 to 4.0, and more preferably 2.2 to 3.8. By using whiskers in such a range, the volume ratio of the whiskers in the molded article becomes smaller, the volume of the resin in the molded article can be increased, and the appearance of the molded article tends to be improved.

Raw materials for the whiskers include zinc oxide, potassium titanate, aluminum borate, silicon carbide, silicon nitride, magnesium oxide, magnesium borate, basic magnesium sulfate, titanium diboride, graphite, calcium sulfate, α-alumina, chrysotile, wollastonite, aluminum silicate, calcium silicate, titanium oxide, zirconium oxide, and the like. In this embodiment, wollastonite and/or potassium titanate are preferred. By using wollastonite, a molded product with higher rigidity and strength can be obtained without decreasing the surface gloss. By using potassium titanate, a molded product with higher rigidity and strength can be obtained without decreasing the surface gloss.

The whiskers used in this embodiment may be subjected to a known surface treatment (e.g., a surface treatment using a surface treatment agent such as a metal oxide, a silane coupling agent, a titanium coupling agent, an organic acid, a polyol, or silicone). By subjecting the whiskers to such a surface treatment, it may be possible to improve the compatibility and dispersibility with other components in the resin composition of this embodiment.

As the whiskers, for example, commercially available products such as "Pana-Tetra WZ-0501", "Pana-Tetra WZ-0501L", "Pana-Tetra WZ-0511", "Pana-Tetra WZ-0511L", "Pana-Tetra WZ-0531", "Pana-Tetra WZ-05E1", and "Pana-Tetra WZ-05F1" (all zinc oxide whiskers, manufactured by Amtec Co., Ltd.); "FTL-100", "FTL-110", "FTL-200", and "FTL-300" (all titanium oxide whiskers, manufactured by Ishihara Sangyo Kaisha, Ltd.); and "TOFIX-P" (titanium oxide whiskers, manufactured by Toho Titanium Co., Ltd.) can also be used.

The resin composition of the present embodiment may also use a granular filler as the specific reinforcing material. The granular filler is a filler in the form of particles, and typically has an aspect ratio of less than 5.
The granular filler preferably has an average particle size of 0.01 to 2 μm, more preferably 0.05 to 1 μm. By setting the average particle size within such a range, the appearance of the resulting molded article can be further improved. The average particle size here refers to the median diameter (D50) determined from a particle size distribution diagram measured with a laser diffraction particle size distribution measuring device.

The granular filler preferably has a Mohs hardness of 2.5 to 5.0, more preferably 2.5 to 4.5. By setting the hardness within this range, wear on the barrel and screw of the extruder can be reduced, enabling stable extrusion.
The specific gravity of the granular filler is preferably 2.0 to 4.0, and more preferably 2.2 to 3.8. By using a granular filler in such a range, the volume ratio in the molded article becomes smaller, the volume of the resin in the molded article can be increased, and the appearance of the molded article tends to be improved.

Examples of raw materials for the granular filler include calcium carbonate and kaolin, with calcium carbonate being preferred. By using calcium carbonate, it is possible to obtain a molded product with higher rigidity and strength without reducing the surface gloss.
Examples of calcium carbonate include synthetic calcium carbonate, natural calcium carbonate, and surface-treated calcium carbonate obtained by surface-treating these with silicic acid or an organic acid. For details of calcium carbonate, see paragraphs 0049 to 0054 of JP 2019-077778 A, the contents of which are incorporated herein by reference.

The content of the specific reinforcement material in the resin composition of this embodiment is preferably 10 parts by mass or more, and may be 20 parts by mass or more, relative to 100 parts by mass of polyamide resin. By making it equal to or more than the lower limit, the surface gloss tends to be further improved. The content of the carbon fiber in the resin composition of this embodiment is also preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and may be 60 parts by mass or less, or even 52 parts by mass or less, relative to 100 parts by mass of polyamide resin. By making it equal to or less than the upper limit, the surface gloss can be effectively improved.
The resin composition of the present embodiment may contain only one type of specific reinforcement material, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

<Carbon fiber and specific reinforcement material content>
In the resin composition of this embodiment, the specific reinforcement material is contained in a total of 10 to 120 parts by mass relative to 100 parts by mass of carbon fiber. By making it 10 parts by mass or more, the surface glossiness of the obtained molded article can be increased. In addition, by making it 120 parts by mass or less, the mechanical strength can be increased. The content of the specific reinforcement material is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, even more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, and even more preferably 50 parts by mass or more, relative to 100 parts by mass of carbon fiber. In addition, the content of the specific reinforcement material is preferably 110 parts by mass or less, more preferably 105 parts by mass or less, even more preferably 90 parts by mass or less, even more preferably 75 parts by mass or less, and even more preferably 65 parts by mass or less, relative to 100 parts by mass of carbon fiber.

In the resin composition of this embodiment, the mass ratio of carbon fiber to specific reinforcement, carbon fiber/specific reinforcement, is preferably 4.5 or less, more preferably 4.3 or less, even more preferably 3.5 or less, even more preferably 3.0 or less, even more preferably 2.5 or less, and even more preferably 2.0 or less. By making it below the upper limit value, the surface gloss tends to be further improved. In addition, the carbon fiber/specific reinforcement is preferably 0.9 or more, more preferably 1.0 or more, even more preferably 1.2 or more, and even more preferably 1.5 or more. By making it above the lower limit value, the elastic modulus and strength tend to be further improved.

Furthermore, in the resin composition of this embodiment, the total amount of the carbon fiber and the specific reinforcement material accounts for 50% by mass or more of the entire resin composition. By making it 50% by mass or more, the mechanical strength of the obtained molded product can be increased. The total amount of the carbon fiber and the specific reinforcement material is preferably 52% by mass or more, and more preferably 53% by mass or more. Furthermore, the total amount of the carbon fiber and the specific reinforcement material is preferably 70% by mass or less of the entire resin composition, more preferably 67% by mass or less, even more preferably 64% by mass or less, even more preferably 62% by mass or less, and even more preferably 58% by mass or less. By making it below the upper limit value, moldability tends to be further improved.

<Black colorant>
The resin composition of the present embodiment preferably contains a black colorant. By containing a black colorant, it is possible to provide a molded article having high rigidity, high elastic modulus, and excellent appearance.

The type of black colorant is not particularly limited, but examples include pigments such as carbon black and titanium black, nigrosine and aniline black, with carbon black being preferred.
In the resin composition of the present embodiment, by blending carbon black, the carbon black acts as a nucleating agent, and good moldability can be achieved even when a thin-walled molding is performed.

The carbon black used in this embodiment may be any conventionally known carbon black. Examples include furnace black, channel black, ketjen black, acetylene black, etc. Among these, it is preferable to use carbon black with excellent hiding power and DBP absorption of 30 to 300 g/100 ^cm3 , particularly furnace black, because it is possible to develop a stable color tone.

The content of the black colorant in the resin composition of this embodiment is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, relative to 100 parts by mass of the polyamide resin. By making it equal to or more than the lower limit, a more stable color tone can be obtained. In addition, the content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 4 parts by mass or less. By making it equal to or less than the upper limit, higher mechanical properties tend to be obtained.
The resin composition of the present embodiment may contain only one type of black colorant, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

<Nucleating agent>
The resin composition of the present embodiment may contain a nucleating agent to adjust the crystallization rate. The type of nucleating agent is not particularly limited, but talc, boron nitride, mica, kaolin, barium sulfate, silicon nitride, and molybdenum disulfide are preferable, talc and boron nitride are more preferable, and talc is even more preferable.
When the resin composition of the present embodiment contains a nucleating agent, the content thereof is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the polyamide resin. The upper limit of the content is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 6 parts by mass or less, and even more preferably 4 parts by mass or less.
The resin composition of the present embodiment may contain only one type of nucleating agent, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Release Agent>
The resin composition of the present embodiment may contain a release agent.
Examples of the release agent include aliphatic carboxylic acids, salts of aliphatic carboxylic acids, esters of aliphatic carboxylic acids and alcohols, aliphatic carboxylic acid amides, aliphatic hydrocarbon compounds having a number average molecular weight of 200 to 15,000, polysiloxane-based silicone oils, and waxes.
As the wax, polyolefin wax, ketone wax, amide wax, ester wax, and paraffin wax are preferable, and ketone wax is more preferable.
For details of the release agent, please refer to the descriptions in paragraphs 0034 to 0039 of JP2017-115093A and paragraphs 0068 to 0091 of JP2018-184575A, the contents of which are incorporated herein by reference.

When the resin composition of the present embodiment contains a release agent, the content thereof is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.2 parts by mass or more, relative to 100 parts by mass of the polyamide resin. The content is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less.
The resin composition of the present embodiment may contain only one type of release agent, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Other ingredients>
The resin composition of this embodiment may contain other components within the scope of this embodiment. Examples of such additives include fillers other than carbon fibers and specific reinforcement materials, light stabilizers, antioxidants, flame retardants, flame retardant assistants, ultraviolet absorbers, fluorescent brighteners, drip prevention agents, antistatic agents, antifogging agents, antiblocking agents, flowability improvers, weather resistance improvers, light resistance improvers, plasticizers, dispersants, and antibacterial agents. These components may be used alone or in combination of two or more. The content of these components is preferably in the range of 5% by mass or less of the resin composition.
In addition, the content of the polyamide resin, carbon fiber, and specific reinforcement material, as well as other additives that are blended as necessary, is adjusted so that the total of each component in the resin composition of this embodiment is 100 mass%. In the resin composition of this embodiment, the total of the polyamide resin, nucleating agent, carbon fiber, specific reinforcement material, black colorant, and release agent preferably accounts for 90 mass% or more of the resin composition, more preferably 95 mass% or more, and even more preferably 98 mass% or more.

<Characteristics of Resin Composition>
The resin composition of the present embodiment is preferably excellent in surface gloss. Specifically, the gloss (Gs60) is preferably 45 or more, more preferably 50 or more, even more preferably 54 or more, even more preferably 58 or more, and even more preferably 60 or more. The upper limit of the gloss (Gs60) is practically 100, and even if it is 80 or less, the required performance is satisfied.
The gloss value (Gs60) is measured according to the description in the Examples section described later.

The resin composition of the present embodiment is molded into a plate of 100 x 100 x 2 mmt, and the L ^* value measured according to JIS K7105 is preferably 24 or more, and more preferably 26 or more. In order to make the L ^* value 24 or more, it is preferable to use potassium titanate whiskers as the specific reinforcing material.
Furthermore, the resin composition of the present embodiment is molded into a plate of 100 x 100 x 2 mmt, and the L ^* value measured according to JIS K7105 is preferably less than 24, more preferably 20 or less, and even more preferably 16 or less. In order to make the L ^* value less than 24, it is preferable to use whiskers or calcium carbonate as the specific reinforcing material.
The L ^* value is measured as described in the Examples section below.

When the resin composition of this embodiment is molded into an ISO tensile test piece (4 mm thick) in accordance with ISO 178, the bending strength at a temperature of 23°C is preferably 360 MPa or more, more preferably 380 MPa or more, and even more preferably 395 MPa or more. The upper limit of the bending strength is not particularly set, but 550 MPa or less is practical.

The resin composition of this embodiment preferably has a flexural modulus of 32.0 GPa or more, more preferably 35.0 GPa or more, and even more preferably 38.0 GPa or more at a temperature of 23° C. when molded into an ISO tensile test piece (4 mm thick) in accordance with ISO 178. The upper limit of the flexural modulus is not particularly specified, but 55.0 GPa or less is practical, and even 50.0 GPa or less sufficiently satisfies the required performance.
The bending strength and bending modulus are measured by the method described in the examples below.

<Method of producing resin composition>
The resin composition of the present embodiment can be produced by a known method for producing a thermoplastic resin composition.
As an embodiment of the method for producing the resin composition of the present embodiment, it is preferable to mix and knead the polyamide resin with the carbon fiber and the specific reinforcing material. An example of such a resin composition is pellets.
Specifically, the polyamide resin, carbon fiber, specific reinforcing material, and other components to be blended as necessary may be premixed using various mixers such as a tumbler or a Henschel mixer, and then melt-kneaded using a mixer such as a Banbury mixer, a roll, a Brabender, a single-screw kneading extruder, a twin-screw kneading extruder, or a kneader.

In addition, for example, the resin composition of the present embodiment can be produced by premixing only some of the components (e.g., carbon fiber and a specific reinforcing material) without premixing the components, and then feeding the mixture to an extruder using a feeder and melt-kneading the mixture.
In addition, for example, some of the components (e.g., a black colorant) can be mixed in advance, fed to an extruder, and melt-kneaded to obtain a composition, which can be used as a master batch. The master batch can then be mixed again with the remaining components and melt-kneaded to produce the resin composition of the present embodiment.
In addition, for example, when mixing a component that is difficult to disperse, the dispersibility can be improved by dissolving or dispersing the component in advance in a solvent such as water or an organic solvent, and then kneading the component with the solution or dispersion.

<Molded products>
The molded article of the present embodiment is formed from the resin composition of the present embodiment.
The method for producing the molded article of the present embodiment is not particularly limited.
For example, the molded product of this embodiment may be produced by melt-kneading the components and then directly molding the components using various molding methods, or by melt-kneading the components and pelletizing them, and then melting them again and molding them using various molding methods.

The method for forming the molded product is not particularly limited, and any conventionally known molding method can be used, such as injection molding, injection compression molding, extrusion molding, profile extrusion, transfer molding, hollow molding, gas-assisted hollow molding, blow molding, extrusion blow molding, IMC (in-mold coating molding), rotational molding, multi-layer molding, two-color molding, insert molding, sandwich molding, foam molding, and pressure molding.

The shape of the molded product of this embodiment is not particularly limited and can be appropriately selected depending on the application and purpose of the molded product. Examples include plate-like, plate-like, rod-like, sheet-like, film-like, cylindrical, annular, circular, elliptical, gear-like, polygonal, irregularly shaped, hollow, frame-like, box-like, panel-like, etc.

The application field of the molded product of this embodiment is not particularly limited, and it is widely used in automobile and other transportation machinery parts, general machine parts, precision machine parts, electronic and electrical equipment parts, office equipment parts, building materials and housing related parts, medical devices, leisure sports goods, play equipment, medical products, daily necessities such as food packaging films, defense and aerospace products, etc.
In particular, the molded article of the present embodiment is preferably used in applications requiring mechanical strength and gloss.

The present invention will be described in more detail below with reference to examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.
If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be made using other instruments with equivalent performance.

1. Raw material <Polyamide resin>
MXD6: Mitsubishi Gas Chemical Company, #6000, melting point 237°C, glass transition temperature 85°C
PA66: Polyamide 66, DuPont, Zytel 101NC-10, melting point 265°C, glass transition temperature 55°C
<Nucleating agent>
Talc: Hayashi Kasei Co., Ltd., Micron White 5000A

<Carbon fiber>
Carbon fiber: polyacrylonitrile carbon fiber, manufactured by Mitsubishi Rayon Co., Ltd., Pyrofil TR06NL, tensile strength 4.9 GPa, number average fiber diameter 7 μm, number average fiber length 6 mm

<Specific reinforcement material>
Wollastonite: Tomoe Engineering Co., Ltd., wollastonite whisker, aspect ratio 17, NYGLOS8-10013, number average fiber length 136 μm, number average fiber diameter 8 μm, Mohs hardness 4.5, specific gravity 2.9
TISMO: Potassium titanate whisker, manufactured by Otsuka Chemical, TISMO D-101, aspect ratio 30, number average fiber length 15 μm, number average fiber diameter 0.5 μm, Mohs hardness 4.0, specific gravity 3.5
Calcium carbonate: granular filler, manufactured by Nitto Funka Kogyo Co., Ltd., product number: NS#100, average particle size 2.1 μm, Mohs hardness 3.0, specific gravity 2.7

<Black colorant>
Carbon black MB: Carbon black master batch, manufactured by Mitsubishi Chemical, carbon black #45 (furnace black, DBP absorption 53 g/100 cm ³ )

<Release Agent>
Release agent: Nitto Kasei Kogyo Co., Ltd., product number: CS-8CP

2. Examples 1 to 6 and Comparative Examples 1 to 4
Each component was weighed according to Table 1 (each component in Table 1 is expressed in parts by mass), and the components except for the carbon fiber and the specific reinforcement were blended in a tumbler, fed into the base of a twin-screw extruder (Shibaura Machine Co., Ltd., TEM26SS), melted, and kneaded. After kneading, the carbon fiber and the specific reinforcement were side-fed to prepare pellets (resin composition). The extruder was set at a temperature of 280°C.
The obtained pellets were used for the following evaluations. In Comparative Example 4, extrusion was difficult, and pellets could not be obtained.

<Bending properties>
The pellets were dried at 120°C for 3 hours, and then injection molded into ISO tensile test pieces (4 mm thick) using an injection molding machine (manufactured by Nissei Plastic Industrial Co., Ltd., "NEX140III") under conditions of a cylinder temperature of 280°C and a mold temperature of 130°C.
The flexural strength (unit: MPa) and flexural modulus (unit: GPa) were measured using the above ISO tensile test piece (4 mm thick) in accordance with ISO 178. The results are shown in Table 1.

<Glossiness (Gs60)>
The pellets were dried at 120°C for 3 hours, and then injection molded into a 100 x 100 x 2 mmt plate using an injection molding machine (Nissei Plastic Industrial Co., Ltd., "NEX140III") at a cylinder temperature of 280°C and a mold temperature of 130°C.
The gloss (Gs60) of the molded product at 60 degrees was measured in accordance with JIS Z8741. The results are shown in Table 1. The measuring machine used was VG8000 manufactured by Nippon Denshoku Industries Co., Ltd.

<L ^* value>
The L ^* value of the above plate was measured in accordance with JIS K7105 using a color difference meter (SE6000 manufactured by Nippon Denshoku Industries Co., Ltd.) under the following measurement conditions.
Measurement conditions: Reflection measurement, C light source/2°, field of view 30Φ

As is clear from the above results, the resin composition of the present invention had high mechanical strength, high gloss, and excellent surface gloss (Examples 1 to 6). Furthermore, by lowering the mass ratio of carbon fiber to specific reinforcement (carbon fiber/reinforcement), a molded product with high surface gloss was obtained.
On the other hand, when the amount of carbon fiber was small or not blended (Comparative Examples 1 and 2), the mechanical strength was poor. Also, when the amount of carbon fiber blended was too large (Comparative Example 4), extrusion was not possible and pellets were not obtained.
Furthermore, when at least one specific reinforcing material selected from whiskers and granular fillers was not blended (Comparative Example 3), the gloss level was low and the surface gloss was poor.

Claims (10)

A resin composition comprising 100 parts by mass of polyamide resin, 76 to 120 parts by mass of carbon fiber, and whiskers ,
The whiskers are contained in a total amount of 10 to 120 parts by mass per 100 parts by mass of the carbon fibers,
The total amount of the carbon fibers and the whiskers accounts for 53 mass% or more of the total amount of the resin composition,
80% by mass or more of the polyamide resin contained in the resin composition is a semi-aromatic polyamide resin, and the semi-aromatic polyamide resin is composed of a diamine-derived structural unit and a dicarboxylic acid-derived structural unit, and 20 to 80 mol % of the total structural units of the diamine-derived structural unit and the dicarboxylic acid-derived structural unit are structural units containing an aromatic ring.
Resin composition. The resin composition according to claim 1, wherein the whiskers have an aspect ratio of 5 to 50. The resin composition according to claim 1 or 2 , wherein a mass ratio of the carbon fibers to the whiskers , carbon fibers/ whiskers , is 4.3 or less. The polyamide resin according to any one of claims 1 to 3, which comprises a polyamide resin composed of diamine-derived structural units and dicarboxylic acid-derived structural units, in which 70 mol % or more of the diamine-derived structural units are derived from at least one of metaxylylenediamine and paraxylylenediamine, and 70 mol % or more of the dicarboxylic acid-derived structural units are derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms. The resin composition according to claim 4 , wherein the α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms includes adipic acid and/or sebacic acid. The resin composition according to claim 4 , wherein the α,ω-linear aliphatic dicarboxylic acid having 4 to 20 carbon atoms includes adipic acid. The resin composition according to claim 4 , wherein the polyamide resin further comprises polyamide 66. The resin composition according to any one of claims 1 to 7 , further comprising a black colorant. The resin composition according to any one of claims 1 to 8 , wherein the resin composition is molded into a plate of 100 x 100 x 2 mmt and has an L ^* value of 24 or more as measured according to JIS K7105. A molded article formed from the resin composition according to any one of claims 1 to 9 .