JP2005239806A - Carbon fiber-reinforced thermoplastic resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To a provide carbon fiber-reinforced thermoplastic resin molding which exhibits excellent bending strength and small anisotropy in strength. <P>SOLUTION: The molding is composed at least of a thermoplastic resin and a carbon fiber, whose fiber length distribution satisfies the features as described below. The molding has a generally flat part, and bending strength according to ASTM D790 of the generally flat part of the molding has an S<SB>Max</SB>/S<SB>Min</SB>value of 1.3 or less, wherein S<SB>Max</SB>is the bending strength in the direction showing the maximum value in the substantially same section and S<SB>Min</SB>is the bending strength in the direction showing the minimum value. Fiber length distribution: the number of carbon fibers having a length of from 1.0 to less than 2.0 mm is 10% or more of the total number of carbon fibers, and the number of carbon fibers having a length of 2.0 mm or more is 5% or more of the total number of carbon fibers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement of a carbon fiber reinforced thermoplastic resin molded article. More specifically, the present invention relates to a molded article having improved strength by improving the fiber length and fiber distribution of carbon fibers in the molded article, reducing the strength anisotropy of the molded article.

  Conventionally, a fiber reinforced composite material composed of a reinforced fiber and a matrix resin is lightweight and has excellent mechanical properties, and thus has been widely used in sports equipment applications, aerospace applications, and general industrial applications.

  Reinforcing fibers used in these fiber-reinforced composite materials reinforce molded products in various forms depending on the intended use. These reinforcing fibers include metal fibers such as aluminum fibers and stainless fibers, organic fibers such as aramid fibers and PBO fibers, inorganic fibers such as silicon carbide fibers, and carbon fibers. From the viewpoint of balance of lightness, carbon fiber, and among them, polyacrylonitrile-based carbon fiber is preferably used because it can realize low cost. These fibers reinforce the molded product in a continuous or discontinuous state, but discontinuous fiber reinforced molded products have good production means such as injection molding, such as electrical / electronic equipment and structural members. Is used. In the discontinuous fiber reinforced molded product, the reinforcement direction of the reinforcing fiber is important. If the orientation direction of the reinforcing fiber is biased, the strength of the molded product is biased, and the molded product is difficult to apply to structural members. .

  In recent years, fiber reinforced composite materials have been used in various fields, and improvement of their mechanical properties has become essential. In particular, for use in structural members such as automobiles, not only strength but also low anisotropy of strength and productivity have been demanded.

  Therefore, conventionally, a technique has been proposed in which the aspect ratio of the reinforced carbon fiber in the molded product is reduced to reduce the anisotropy of the orientation of the carbon fiber in the molded product (see, for example, Patent Document 1). In order to reduce the aspect ratio, the strength is disadvantageously reduced.

Furthermore, although the technique which prescribes | regulates the orientation of a reinforced glass fiber and improves intensity | strength anisotropy and dimensional stability is proposed (for example, refer patent document 2), since a reinforced fiber is a glass fiber, It is more disadvantageous than the carbon fiber reinforced molded product in terms of strength and rigidity of the molded product.
Japanese Patent Laid-Open No. 4-8759 (first page) JP-A-6-114869 (2nd page)

  Carbon fiber is brittle compared to glass fiber and easily breaks when kneaded, so that it has been difficult to make long fibers. If the fiber length of the carbon fiber reinforced molded product can be increased, it can be used as a structural material by utilizing the high mechanical properties of the carbon fiber.

  In view of the background of such conventional technology, the present invention aims to improve the fiber length and fiber distribution of carbon fibers in a molded product, lower the strength anisotropy of the molded product, and provide a molded product having excellent strength. And

In order to achieve the above object, the present invention employs the following configuration. That is,
(1) It consists of at least a thermoplastic resin and carbon fiber, the fiber length distribution of the carbon fiber satisfies the following characteristics, and the bending strength based on ASTM D790 of the substantially flat portion of the molded product is substantially the bending strength in the direction showing the maximum value at the same site as the S _Max, when the flexural strength in the direction indicated by the minimum value set to S _Min, substantially flat value of S _Max / S _Min is 1.3 or less A molded product characterized by having a part.

  Fiber length distribution: The number of carbon fibers of 1.0 mm or more and less than 2.0 mm is 10% or more of the total number of carbon fibers, and the number of carbon fibers of 2.0 mm or more is 5% or more of the total number of carbon fibers.

(2) The molded product according to (1), wherein the substantially flat portion having a value of S _Max / S _Min of 1.3 or less occupies an area of 30% or more of the substantially flat portion of the molded product. .

  (3) The molded article according to any one of (1) to (2) above, wherein the weight average fiber length of carbon fibers in the molded article is 1.5 to 5 mm.

(4) The molded product according to any one of (1) to (3), wherein S _Min is 300 MPa or more.

  (5) The molded product according to any one of (1) to (4), wherein the degree of orientation of the carbon fiber at the center thickness of the substantially planar portion is 45 to 90 °.

  (6) The molded article according to any one of (1) to (5) above, comprising both fibers of carbon fiber and glass fiber.

  (7) The thermoplastic resin is applied to pellets obtained by melting and coating a thermoplastic resin on the surface of the long fibrous carbon fiber and cutting the strand having a core-sheath structure into a predetermined length, or chopped yarn obtained by cutting the carbon fiber. The molded product according to any one of (1) to (6) above, wherein a pellet obtained by melting, kneading, and cutting into a predetermined length is injection molded to obtain a molded product having a predetermined shape Production method.

  (8) A method for producing a molded product, characterized in that the molded product according to any one of claims 1 to 6 is produced by supplying carbon fiber and a matrix resin directly to a molding machine and performing injection molding.

  (9) The molded article according to any one of (1) to (6), wherein the use is a part or member of an automobile, an aircraft, a two-wheeled vehicle, or a bicycle.

  The molded article of the present invention can be a carbon fiber reinforced thermoplastic resin molded article that exhibits excellent bending strength and has low strength anisotropy.

  Hereinafter, the present invention will be described in more detail.

  Examples of the carbon fiber used in the present invention include a PAN system using polyacrylonitrile fiber as a raw material, a pitch system using coal tar or petroleum pitch as a raw material (isotropic, mesophase, etc. depending on the internal structure), and viscose rayon. There are a cellulosic system using cellulose or cellulose acetate as a raw material and a vapor phase growth system using hydrocarbon as a raw material. These graphite fibers may also be used. Further, these are coated with at least one layer of a metal such as nickel, ytterbium, gold, silver, or copper by a plating method (electrolysis or electroless), a CVD method, a PVD method, an ion plating method, an evaporation method, or the like. Metal-coated carbon fiber may be used. Two or more of these may be blended. Among these, PAN-based carbon fibers that are excellent in balance between mechanical properties such as strength and elastic modulus and cost are particularly preferable.

  Further, the carbon fibers in the molded product have a fiber length distribution, the number of carbon fibers of 1.0 mm or more and less than 2.0 mm is 10% or more of the total number of carbon fibers, and the number of carbon fibers of 2.0 mm or more is all carbon fibers. It is characterized by being 5% or more of the number. The number of carbon fibers having a fiber length of 1.0 mm or more and less than 2.0 mm is more preferably 12% or more, and still more preferably 15% or more of the total number of carbon fibers. The upper limit of the number of carbon fibers having a fiber length of 1.0 mm or more and less than 2.0 mm is less than 90%. When the number of carbon fibers having a fiber length of 1.0 mm or more and 2.0 mm is 90% or more, the appearance of the surface of the molded product may be poor due to the fiber's surface. The number of carbon fibers having a fiber length of 2.0 mm or more is more preferably 8% or more of the total number of carbon fibers, and further preferably 14% or more. The upper limit of the number of carbon fibers having a fiber length of 2.0 mm or more is less than 90%. When the number of carbon fibers having a fiber length of 2.0 mm or more is 90% or more, a surface appearance defect of a molded product due to fiber scum or the like may occur. The upper limit of the carbon fiber of 2.0 mm or more is not particularly limited, but if it is 10 mm or less, the effect of the present invention can be exhibited. When the number of carbon fibers of 1.0 mm or more and less than 2.0 mm is less than 10% of the total number of carbon fibers, a portion having a low reinforcing effect is generated, and the strength anisotropy is increased. Similarly, when the number of carbon fibers of 2.0 mm or more is less than 5% of the total number of carbon fibers, the strength anisotropy is increased and the strength cannot be sufficiently exhibited.

Further, the bending strength based on ASTM D790 of the substantially flat portion of the molded product is defined as S _Max in the direction showing the maximum value in the substantially same part, and the bending strength in the direction indicating the minimum value is S _Min. Then, it has the substantially plane part whose value of S _Max / S _Min is 1.3 or less. More preferably, the value of S _Max / S _Min is 1.25 or less, and further preferably, the value of S _Max / S _Min is 1.15 or less. When the value of S _Max / S _Min exceeds 1.3, anisotropy appears strongly in the strength of the molded product, which causes problems such as limited use as a molded product. In addition, the minimum value of the value of S _Max / S _Min is 1.0, and in this case, there is no anisotropy of strength, which is preferable as a molded product.

Here, the bending strength at substantially the same portion of the substantially flat portion of the molded product is evaluated by one of the two methods [Evaluation A] and [Evaluation B] described below. . In addition, the substantially flat portion of the molded product means, for example, a flat portion having a uniform thickness on the back and front of the molded product, and the flat surface having a uniform thickness on the back and front of the molded product. If the part does not exist, select an arbitrary part of the molded product, and if the surface irregularity of the part is 1/10 or less of the thickness of the molded product, it is regarded as a flat part, and that part is Say. For example, in an injection-molded product, in the case of a molded product having an uneven surface such as a boss and a rib on the back surface, the unevenness of the boss and rib is 1/10 or less of the thickness of the molded product of the portion. When it is, it becomes a substantially flat part. In addition, the substantially same part is a part that can be regarded as having the same level of characteristics such as shape, specific gravity, fiber orientation, and mechanical characteristics in a molded product. For example, in an injection molded product, a target molding for a gate. It is a product part.
[Evaluation A]
A plurality of substantially the same molded products are produced by the same method, and at least five test pieces are cut out at different angles from the same part. The bending strength of the obtained test piece is evaluated, and the average value obtained by excluding the two lowest values is defined as the bending strength of the test piece.

The same method here is a routine method in which the shape, weight, specific gravity, fiber orientation, mechanical characteristics, and other characteristics of the obtained molded product are extremely constant. For example, using the same material, the same method is used. Injection molding, press molding, autoclave molding, RTM molding, etc. performed under conditions. In addition, the same part here means that when a test piece is taken out from the first molded product at an arbitrary angle θ1 with respect to a molded product that can be regarded as having the same feature formed by a plurality of the same methods, 2 The first molded product is the same location as the first molded product, and the test piece is cut out at an angle θ2 different from the angle θ1 at this location. [Evaluation A] is an evaluation method applied when at least 5 or more of the same molded product can be used.
[Evaluation B]
From the same molded article, the target part with respect to the gate is regarded as substantially the same part on the molded article. However, the weld part is excluded. The angle is changed from the part, and at least five test pieces are cut out. The bending strength of the obtained test piece is evaluated, and the average value obtained by excluding the two lowest values is defined as the bending strength of the test piece. [Evaluation B] is an evaluation method applied when only 4 or less molded articles can be used. Further, the molded product of the present invention has an anisotropic property as long as the substantially flat portion having a value of S _Max / S _Min of 1.3 or less occupies an area of 30% or more of the substantially planar portion of the molded product. It is preferable as a molded product having low properties. More preferably, it is 50% or more, More preferably, it is 70% or more. There is no restriction | limiting in particular as an upper limit of the said area which the substantially plane part whose value of _SMax / _Smin is 1.3 or less occupies. If it is 100%, it is preferable as a molded article having extremely low anisotropy. Furthermore, if the weight average fiber length of the carbon fiber is 1.5 to 5 mm, the molded product in the present invention is preferable because the molded product has good appearance and low strength anisotropy. More preferably, it is 2.0-4.5 mm.

Here, the method for measuring the weight average fiber length is to randomly extract at least 400 carbon fibers in the molded product at random and measure the length with an optical microscope or a scanning electron microscope up to 1 μm unit. This is done by calculating the average length. As a method for extracting the carbon fiber, a part of the molded product is cut out, the matrix resin is sufficiently dissolved with a solvent for dissolving the matrix resin, and then separated from the carbon fiber by a known operation such as filtration. When there is no solvent that dissolves the matrix resin, a method can be used in which a part of the molded product is cut out and the matrix resin is removed by incineration in a heating furnace to extract the carbon fibers. In addition, if the number of measured carbon fibers extracted at random is 400 or more, the calculated value of the weight average fiber length of the carbon fibers hardly changes. Also preferred for the value of S _Min of the molded article becomes level that can be used as a structural member as long as more than 300 MPa. More preferably, it is 320 MPa or more, More preferably, it is 350 MPa or more. The upper limit of the value of Smin is not particularly limited, but if it is 500 MPa or less, the effect of the present invention can be sufficiently exerted. Furthermore, in the molded product of the present invention, the degree of orientation of the carbon fibers at the center thickness of the substantially flat portion of the molded product is preferably 45 to 90 °.

  Here, the degree of orientation is a parameter based on the orientation angle of the carbon fibers in the molded product, and is evaluated by the following method. A part of a substantially flat surface of the molded product is cut out and polished to prepare an observation test piece. The test piece obtained by polishing a depth portion of 200 μm or less from the surface is observed with an optical microscope, and 400 carbon fibers are randomly selected. A reference straight line as an angle reference is arbitrarily set, and all angles formed by the carbon fibers selected with respect to the reference straight line are measured. The angle is measured at a portion forming an acute angle with respect to the reference straight line. An average value of angles formed by 400 selected carbon fibers is defined as P. The difference between P and Q when the average value of the angle between the reference straight line and the carbon fiber measured in the same manner when the same specimen for observation was further polished and polished to about half the depth of the molded product was Q Is the orientation degree at the center thickness.

  From the viewpoint of reducing anisotropy, the orientation degree of the center thickness is preferably 45 to 90 °. More preferably, it is 60 to 90 °. If the orientation degree of the center thickness is close to 90 °, the fibers are oriented in a direction different from the orientation of the carbon fibers on the surface, which is considered to reduce the strength anisotropy.

  The molded product of the present invention can be reinforced by hybridizing carbon fibers with metal fibers such as aluminum fibers and stainless fibers, organic fibers such as aramid fibers and PBO fibers, inorganic fibers such as silicon carbide fibers, glass fibers, and hemp. I do not care. In particular, since glass fiber is advantageous in terms of cost, it can be mixed and used if the strength and rigidity are within the target range.

  Examples of the thermoplastic resin of the present invention include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyester such as liquid crystal polyester, PE), polypropylene (PP), polyolefins such as polybutylene, styrene resins, polyoxymethylene (POM), polyamide (PA), polycarbonate (PC), polymethylene methacrylate (PMMA), polyvinyl chloride (PVC), Polyphenylene sulfide (PPS), polyphenylene ether (PPE), polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polysulfone (PSU), polyethersulfone , Polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK), polyarylate (PAR), polyethernitrile (PEN), phenolphenoxy resin (such as novolac type), fluororesin, and polystyrene , Polyolefin-based, polyurethane-based, polyester-based, polyamide-based, polybutadiene-based, polyisoprene-based, fluorine-based thermoplastic elastomers, copolymers, modified products, or resins blended in two or more types. Also good. Further, in order to further improve the impact resistance, a resin obtained by adding another elastomer or a rubber component to the thermoplastic resin may be used. In particular, at least one selected from a styrene resin, a polycarbonate resin, a polyphenylene ether resin, a polyamide resin, a polyester resin, a polyphenylene sulfide resin, a polyolefin resin, a liquid crystal resin, and a phenol resin can be employed as a preferable thermoplastic resin. . More preferably, a polyamide resin is used, and the strength of the molded product can be increased.

  The molded product of the present invention is preferably molded by injection molding. Injection molding is a technique that can achieve high productivity and low cost from the advantageous aspect of molding cycle or molding of complex shapes.

  Furthermore, in order to effectively develop the strength of the molded article of the present invention, it is preferable to use a carbon long fiber molding material. Here, the carbon long fiber molding material is obtained by impregnating a continuous carbon fiber bundle while passing through a molten bath of a matrix resin, taking it out, and then cutting it, and the material length becomes the fiber length as it is. . On the other hand, the carbon short fiber molding material is obtained by melting and kneading a chopped carbon fiber having a length of about 3 to 12 mm in a matrix resin and an extruder, extruding it in a strand shape, and cutting it. The fiber length is about 0.3 mm. When the carbon long fiber molding material is formed into a molded product as compared with the carbon short fiber molding material, the carbon fiber length can be increased.

  As a technique for increasing the fiber length in the molded article, a technique (direct molding) in which carbon fibers and a matrix resin are directly supplied to a molding machine and injection molded can be used. In injection molding, the carbon short fiber molding material and carbon long fiber molding material are usually supplied to the molding machine, but the fiber breakage is minimized by supplying the carbon fiber and matrix resin directly to the molding machine. Can be suppressed. Moreover, it does not go through an intermediate process for producing a molding material, which leads to cost reduction.

  Moreover, when producing the molded article of this invention by injection molding, it is preferable to carry out on the conditions which make fiber length as long as possible as follows. The screw is usually composed of a supply unit, a compression unit, and a metering unit, and is preferably a full flight shape that makes the degree of kneading the lightest, and may be used by adjusting the level of kneading by partially including a kneading part. Absent. In order to keep the fiber length long, fiber breakage can be suppressed by molding using a screw with as few kneading parts as possible. In addition, the clearance between the cylinder and the screw greatly affects the fiber length. By increasing the clearance, kneading can be lightened and fiber breakage can be suppressed. Further, the size of the nozzle diameter also affects the fiber length. When the nozzle diameter is small, high shear is applied when the molten molding material passes, and the fiber is broken. The fiber length can also be increased by increasing the nozzle diameter. Moreover, shearing can be suppressed by enlarging the mold runner, and the fiber length can be increased. Furthermore, by making it a hot runner or adjusting the temperature of the mold appropriately, the viscosity of the fluidized resin can be lowered and fiber breakage can be suppressed.

  As for molding conditions, it is preferable to set the cylinder temperature to a high temperature within a range where the matrix resin does not decompose, to set the screw rotation speed low, to shorten the measuring time, and to set the back pressure low. By raising the cylinder temperature, the viscosity of the molten resin is reduced, the shearing force applied to the fibers is reduced, and breakage can be suppressed. Also, if the screw speed is set low, the metering time is shortened, and the back pressure is set low, molding can be performed with as little kneading and shearing as possible, resulting in a molded product with a long fiber length, low anisotropy and high strength. High molded product. The strength anisotropy of the molded product is low because if the fiber length is long (1 mm or more), the fiber resists the resin flow inside the molded product and is oriented in the vertical direction, and is instantly cooled and solidified by the mold. On the surface of the molded product, the fibers are oriented in the resin flow direction. As a result, the fiber is not reinforced in one direction but in a reinforced form in each direction, and the anisotropy of the molded product is low. It seems to be.

  Further, the molded product of the present invention may further comprise (mica, talc, kaolin, sericite, bentonite, zonotolite, sepiolite, smectite, montmorillonite, wollastonite, silica, calcium carbonate, glass beads, glass flakes, glass Microballoon, clay, molybdenum disulfide, titanium oxide, zinc oxide, antimony oxide, calcium polyphosphate, graphite, barium sulfate, magnesium sulfate, zinc borate, calcium borate, aluminum borate whisker, potassium titanate whisker, polymer Such as fillers, conductivity-imparting materials (such as metal, metal oxide, carbon black, graphite powder), halogenated flame retardants (such as brominated resins), antimony trioxide, antimony pentoxide, etc. ) Antimony Flame retardants, phosphorus flame retardants (such as ammonium polyphosphate, aromatic phosphate, red phosphorus), organic acid metal salt flame retardants (such as metal salts with borate, metal carboxylates, and aromatic sulfonimide metals), Inorganic flame retardants (such as zinc borate, zinc, zinc oxide, zirconium compounds), nitrogen-based flame retardants (such as cyanuric acid, isocyanuric acid, melamine, melamine cyanurate, melamine phosphate, and nitrogenated guanidine), such as PTFE ) Fluorine flame retardants, silicone flame retardants (such as polyorganosiloxane), metal hydroxide flame retardants (such as aluminum hydroxide and magnesium hydroxide), and other flame retardants (cadmium oxide, zinc oxide, Cuprous oxide, cupric oxide, ferrous oxide, ferric oxide, cobalt oxide, manganese oxide, molybdenum oxide, tin oxide Flame retardant aids (such as titanium oxide), pigments, dyes, lubricants, mold release agents, compatibilizers, dispersants, crystal nucleating agents (such as mica, talc, kaolin), plasticizers (such as phosphate esters) , Heat stabilizers, antioxidants, anti-coloring agents, UV absorbers, fluidity modifiers, foaming agents, antibacterial agents, vibration control agents, deodorants, sliding property modifiers (such as polyetheresteramides) ) An antistatic agent or the like may be added.

  Moreover, since the molded article of the present invention has low strength anisotropy and high strength, it can be suitably used for structural members that require high strength and low anisotropy. In particular, it can be suitably used for parts and members of automobiles, aircraft, motorcycles, bicycles and the like. Specifically, motor parts, alternator terminals, alternator connectors, IC regulators, light meter potentiometer bases, suspension parts, various valves such as exhaust gas valves, fuel-related, various exhaust system or intake system pipes, air intake nozzle snorkel, intake Manifold, various arms, various frames, various hinges, various bearings, fuel pump, gasoline tank, CNG tank, engine cooling water joint, carburetor main body, carburetor spacer, exhaust gas sensor, cooling water sensor, oil temperature sensor, brake pad wear Sensor, throttle position sensor, crankshaft position sensor, air flow meter, brake butt wear sensor, air conditioner service Stat base, Heating hot air flow control valve, Radiator motor brush holder, Water pump impeller, Turbine vane, Wiper motor related parts, Distributor, Starter switch, Starter relay, Transmission wire harness, Window washer nozzle, Air conditioner panel Switch board, coil for fuel related electromagnetic valve, connector for fuse, battery tray, AT bracket, head lamp support, pedal housing, handle, door beam, protector, chassis, frame, armrest, horn terminal, step motor rotor, lamp socket, lamp Reflector, lamp housing, brake piston, noise shield, radiator support, spare Ear cover, seat shell, solenoid bobbin, engine oil filter, igniter case, under cover, scuff plate, pillar trim, propeller shaft, wheel, fender, fascia, bumper, bumper beam, bonnet, aero parts, platform, cowl louver, roof, Cars, motorcycle-related parts such as instrument panels, spoilers and various modules, parts and skins, landing gear pods, winglets, spoilers, edges, ladders, elevators, failings, ribs and other aircraft-related parts, parts and skins It is.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, the following Example does not restrict | limit this invention. Polyamide 6 resin is used as a matrix.
[Sample preparation / measurement / evaluation method]
(1) Long fiber molding material (A) Yasuhara Chemical Co., Ltd., which was made by opening a continuous carbon fiber bundle of “Torayca” (registered trademark) T700SC / 12K manufactured by Toray Industries, Inc. Manufactured Terpenphenol YP · 902 was partially or wholly weighed with a gear pump and applied to a carbon fiber bundle using a coater. Further, the carbon fiber bundle was passed between 10 rolls (φ50 mm) alternately arranged on the top and bottom on a straight line heated to 180 ° C., and the carbon fiber bundle was sufficiently impregnated with the terpene phenol. Subsequently, the polyamide 6 resin was extruded with a single screw extruder in a sufficiently kneaded state in a crosshead die attached to the tip of the polyamide 6 resin, and at the same time, the continuous yarn of the carbon fiber bundle subjected to the above operation was also contained in the crosshead die. Was continuously fed to coat the surface of the carbon fiber bundle with molten polyamide 6 resin. The strand obtained by the above-described method was cooled and then cut into a length of 7 mm with a cutter to obtain a core-sheath carbon long fiber molding material.

(B) A long glass fiber molding material was obtained in the same manner as described above using an E-glass fiber bundle having an average diameter of 13 μm and 650 tex.
(2) Short fiber molding material “Torayca” (registered trademark) manufactured by Toray Industries, Inc. using a JSW TEX / 30α type twin screw extruder (screw diameter 30 mm, die diameter 5 mm, barrel temperature 280 ° C., rotation speed 150 rpm) ) A chopped yarn obtained by cutting a continuous carbon fiber bundle of T700SC / 12K into a length of 6 mm was sufficiently dried to a moisture content of 0.05% or less, and then introduced from a side hopper, and polyamide 6 as a thermoplastic resin. Resin is put in from the main hopper, and guts containing discontinuous carbon fibers are continuously extruded in a state where they are sufficiently kneaded, and after cooling this, it is cut into a length of 5 mm with a cutter to obtain a carbon short fiber molding material. Obtained.
(3) Carbon fiber chopped yarn for direct molding ε-caprolactam 30% by weight and bisaminopropyl polyethylene glycol obtained from polyethylene glycol having a number average molecular weight of 800 to adipic acid in a ratio of 70% by weight of salt with a molar ratio of 1 The mixture was charged into a liter polymerization can, and the interior was purged with nitrogen, followed by polymerization for 2 hours with stirring at 250 ° C. under a pressure of 1 MPa to complete the reaction. After completion of the polymerization, the heating was stopped, and the polymer discharged from the lower portion of the polymerization can was formed into a sheet shape and cut to about 5 mm square. The polymer thus obtained was prepared in an aqueous solution having a concentration of 6% by weight and adhered to “Torayca” (registered trademark) T700SC · 12K manufactured by Toray Industries, Inc. It was cut into a length of 6 mm and then dried with a hot air dryer at 190 ° C. for 5 minutes to obtain a carbon fiber chopped yarn for direct forming.
(4) Molded product preparation After the above molding material was dried in vacuum at 80 ° C for 5 hours or more, it was molded under various conditions using a JSW J350ELIII injection molding machine with a screw shape of full flight. A box-shaped container molded product having a thickness of 3 mm, a length of 100 mm, a width of 250 mm, and a height of 70 mm was obtained. The molded product is shown in the perspective view of FIG.
(4) Bending test A test piece for evaluating bending strength based on ASTM D790 was cut out from the substantially flat surface portion (FIG. 1) of the box-shaped container molded product, and evaluated using Evaluation Method A. As the excision site, two sites (1) and (2) shown in FIG. 2 were selected. For each test piece, four molded products were used. For example, if it is a part (1), the cutting direction of the bending test piece is 1 to 4 directions shown in the figure, and if it is the part (2), the bending test piece is cut out. Four directions were prepared by changing the direction by 45 ° at substantially the same site such as the directions 5 to 8 shown in the figure. Among the four types of test pieces, the highest bending strength was S _Max and the lowest bending strength was S _Min, and the value of S _Max / S _Min was calculated.
(5) Fiber length and fiber length distribution A part of the molded product was cut out, the polyamide 6 resin was sufficiently dissolved with formic acid that dissolves the polyamide 6 resin, and then the carbon fibers were separated by filtration. At least 400 separated carbon fibers were randomly extracted, the length was measured with an optical microscope up to 1 μm unit, and the weight average fiber length was calculated from the following formula. Two cutout sites, site (1) and site (2), were selected (FIG. 2).

Weight average fiber length = Σ (Li × Wi / 100)
Li: measured fiber length (i = 1, 2, 3,... N)
Wi: Fiber weight fraction of fiber length Li If the number of measured carbon fibers to be randomly extracted is 400 or more, the calculated value of the weight average fiber length of the carbon fibers is almost unchanged.
(6) Degree of fiber orientation A part of a substantially flat surface of a molded product having a thickness of 3 mm was cut out and polished to prepare an observation test piece. A 200 μm deep portion from the surface of the test piece was observed with an optical microscope, and 400 carbon fibers were randomly selected. A reference straight line as an angle reference was arbitrarily set, and an angle formed by carbon fibers selected with respect to the reference straight line was measured. The angle was determined by measuring a portion forming an acute angle with respect to the reference straight line. The average value of the angles formed by the selected 400 carbon fibers was calculated as P. The average value similarly measured at a depth of 1.5 mm from the surface was defined as Q, and the absolute value of the difference between P and Q was defined as the degree of orientation at the center thickness.
[Examples 1 and 2]
The long fiber molding material was supplied to an injection molding machine, and the molding conditions were changed as shown in Table 1 to produce a molded product.
[Example 3]
Instead of the long fiber molding material, a 6 mm long carbon fiber chopped yarn for direct molding and polyamide 6 resin pellets were directly supplied to an injection molding machine to produce a molded product.
[Example 4]
A molded article was prepared in the same manner as in Example 1 except that a molding material mixed at a carbon long fiber molding material / glass long fiber molding material = 9/1 (weight ratio) was used.
[Comparative Examples 1-2]
Using a carbon long fiber molding material, the molding conditions were set so that the fiber length was shorter than in Examples 1 and 2, and a molded product was produced.
[Comparative Example 3]
A molded product was prepared in the same manner as in Example 1 except that the above short fiber molding material was used.
[Comparative Example 4]
A molded product was produced in the same manner as in Example 1 except that the above long glass fiber molding material was used.

  The following molding conditions and evaluation results are summarized in Tables 1 to 3 below.

The following is clear from the examples and comparative examples in Tables 1 to 3.
In Examples 1 to 4, the bending strength anisotropy of the molded product is extremely reduced, and a molded product having a bending strength of 300 MPa or more is obtained even at the lowest value. In Example 3 in which the carbon fiber chopped yarn for direct molding was directly fed to the injection molding machine and molded, the strength anisotropy of the molded product was reduced, and the effect of the long fiber was obtained. Understand. Any molded product can be used as a structural member as it is because of its characteristics. The anisotropy is low in both the cut-out sites (1) and (2). On the other hand, in Comparative Examples 1-3, the anisotropy of the strength of the molded product is strong, so that it is difficult to apply to the structural member as it is. Furthermore, the anisotropy is high in both the cutout portions (1) and (2).

  By comparing the examples 1 and 2 and the comparative examples 1 and 2, the fiber length distribution and bending strength anisotropy of the molded product are increased. When the screw rotation speed is increased, fiber breakage occurs, and the strength anisotropy of the molded product is strong. It has become. Further, increasing the back pressure also causes fiber breakage, which has an effect on anisotropy. It can be seen that the strength anisotropy is reduced under the shaping conditions of the embodiment.

  From the comparison between Example 1 and Comparative Example 3, it can be seen that by using a long fiber molding material, the fiber length distribution and fiber length of the molded product are kept long, and the bending strength anisotropy is reduced.

  Further, it can be seen from Comparative Example 4 that the strength of the molded product is inferior to that of the carbon fiber reinforced molded product only by glass fiber reinforcement.

It is a perspective view of the molded article used in the Example of this invention. It is a figure which shows the cutout direction of the bending test piece on the molded article of FIG.

Explanation of symbols

Site (1)
1: Cutting direction of bending test piece 1
2: Cutting direction 2 of bending test piece
3: Bending test piece cutting direction 3
4: Cutting direction of bending test piece 4
Site (2)
5: Cutting direction of bending test piece 5
6: Cutting direction of bending test piece 6
7: Cutting direction of bending test piece 7
8: Cutting direction of bending test piece 8

Claims (9)

It consists of at least a thermoplastic resin and carbon fibers, the fiber length distribution of the carbon fibers satisfies the following conditions, and the bending strength based on ASTM D790 of the substantially flat portion of the molded product is at the substantially same site. the bending strength in the direction showing the maximum value is set to S _Max, when the flexural strength in the direction indicated by the minimum value set to S _Min, the value of S _Max / S _Min has a substantially flat portion is 1.3 or less A molded product characterized by that.
Fiber length distribution: The number of carbon fibers of 1.0 mm or more and less than 2.0 mm is 10% or more of the total number of carbon fibers, and the number of carbon fibers of 2.0 mm or more is 5% or more of the total number of carbon fibers. 2. The molded product according to claim 1, wherein the substantially planar portion having a value of S _Max / S _Min of 1.3 or less occupies an area of 30% or more of the substantially planar portion of the molded product. The molded article according to any one of claims 1 to 2, wherein the weight average fiber length of the carbon fibers in the molded article is 1.5 to 5 mm. The molded product according to any one of claims 1 to 3, wherein S _Min is 300 MPa or more. The molded product according to any one of claims 1 to 4, wherein the degree of orientation of the carbon fibers at the center thickness of the substantially planar portion is 45 to 90 °. The molded article according to any one of claims 1 to 5, comprising both fibers of carbon fiber and glass fiber. The thermoplastic resin is melted on the surface of the long fibrous carbon fiber, melted and coated, pellets obtained by cutting the core-sheathed strand into a predetermined length, or chopped yarn obtained by cutting the carbon fiber, The method for producing a molded product according to any one of claims 1 to 6, wherein the pellet obtained by kneading and cutting into a predetermined length is injection-molded to obtain a molded product having a predetermined shape. A method for producing a molded product, characterized in that the molded product according to any one of claims 1 to 6 is produced by supplying carbon fiber and a matrix resin directly to a molding machine and performing injection molding. The molded product according to any one of claims 1 to 6, wherein the use is a part or a member of an automobile, an aircraft, a two-wheeled vehicle, a bicycle.

Images