Molded products

Abstract

To provide a resin composition which has high moldability to a member having a complicated shape by injection molding, and enables manufacture of a molded article excellent in flexural elastic modulus.SOLUTION: A molding material contains a carbon fiber having a number average fiber length of 0.3 mm or less and a thermoplastic resin, wherein a single fiber diameter of the carbon fiber is 6.5-8.5 μm, and a crystallization parameter Iv1 / Ig1 by Raman spectroscopy satisfies 0.25-0.60.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a molding material containing carbon fibers suitable for injection molding, which is capable of molding components of complex shapes and has a high flexural modulus, and to a molded product using the same. [Background technology]

[0002] Carbon fiber composite materials, especially carbon fiber reinforced plastics, have been widely used in recent years as lightweight alternatives to components that previously required light metals such as aluminum due to their excellent mechanical properties. However, to achieve these excellent mechanical properties, carbon fiber reinforced plastics are often used in the form of continuous or discontinuous fibers with lengths of several millimeters or more, which poses a problem of difficulty in molding them into complex shapes. On the other hand, when injection molding, which excels in molding complex shapes, is applied to thermoplastic resins containing carbon fiber, the molded products generally have low flexural modulus, which means that their mechanical properties are not satisfactory for replacing light metals.

[0003] The most common ways to increase the flexural modulus of injection-molded thermoplastic resins containing carbon fiber are to increase the carbon fiber content, to mold the carbon fiber so that it remains long, or to increase the tensile modulus of the carbon fiber. These methods each produce almost independent effects, and research is currently underway on each of them.

[0004] Increasing the tensile modulus of carbon fiber has involved simply selecting a commercially available carbon fiber with a high tensile modulus. For example, by combining carbon fiber with a tensile modulus of 295 to 390 GPa with a specific aromatic amide, the flexural modulus of a molded product was increased to 39 GPa when the carbon fiber content was 40% by mass (Patent Document 1). Another method has been proposed for increasing the tensile modulus of carbon fiber from the general 240 GPa range to 290 GPa when combined with a specific polyamide resin (Patent Document 2). Furthermore, by using polyphenylene sulfide resin and carbon fiber with a tensile modulus of 390 to 450 GPa, the flexural modulus of a molded product was increased to 37 GPa when the carbon fiber content was 31% by mass (Patent Document 3). Another technique has been proposed in which pitch-based carbon fiber with a tensile modulus of 860 GPa is combined with polyacrylonitrile-based carbon fiber (Patent Document 4). Unless otherwise specified, the term "molded product" used in this specification refers to an injection-molded product. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-1965 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-145292 [Patent Document 3] Japanese Patent Application Publication No. 2017-190426 [Patent Document 4] Japanese Patent Application Publication No. 2019-26808 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the background art has the following problems.

[0007] Although Patent Document 1 shows an effect of improving the flexural modulus of molded articles, the flexural modulus of the molded articles was only 32 GPa when using general-purpose carbon fiber with a tensile modulus of 240 GPa. Even if the tensile modulus of the carbon fiber was increased by 1.6 times, the flexural modulus of the molded articles only improved by 1.2 times, resulting in a very small effect. Furthermore, when carbon fiber with a tensile modulus of 375 GPa was used, the flexural modulus of the molded articles was only 39 GPa, resulting in a small effect, possibly due to the small crystallization parameter measured by Raman spectroscopy (high carbonization temperature) and the small single fiber diameter. In Patent Document 2, the tensile modulus of the carbon fiber was low, and the flexural modulus of the molded articles improved only from 33 GPa to 35 GPa when the carbon fiber content was 45% by mass. In Patent Document 3, the flexural modulus of the molded articles was not satisfactory not only when the carbon fiber content was 31% by mass, but also when it was increased to 56% by mass, possibly due to the small crystallization parameter measured by Raman spectroscopy (high carbonization temperature) and the small single fiber diameter. In Patent Document 4, even when only pitch-based carbon fibers with a high tensile modulus were used, the flexural modulus of the molded product was at most 29 GPa, which was not a satisfactory result.

[0008] As described above, in the prior art, there was an idea of ​​using general-purpose carbon fibers with a high tensile modulus in molding materials containing carbon fibers and thermoplastic resins, but there was no suggestion whatsoever about carbon fibers suitable for injection molding. [Means for solving the problem]

[0009] In order to solve the above problems, the molding material of the present invention is a molding material containing carbon fibers having a number average fiber length of 0.3 mm or less and a thermoplastic resin, characterized in that the carbon fibers have a single fiber diameter of 6.5 to 8.5 μm and a crystallization parameter Iv1 / Ig1 measured by Raman spectroscopy of 0.25 to 0.60. [Effects of the Invention]

[0010] The molding material of the present invention has high moldability for injection molding into parts with complex shapes, and the molded articles obtained have excellent flexural modulus. DETAILED DESCRIPTION OF THE INVENTION

[0011] The molding material of the present invention contains carbon fiber and a thermoplastic resin.

[0012] First, the carbon fiber used in the molding material of the present invention will be described.

[0013] The carbon fibers used in the molding material of the present invention have a single fiber diameter of 6.5 to 8.5 μm. The single fiber diameter is preferably 6.5 to 8.0 μm, and more preferably 6.7 to 7.5 μm. The larger the single fiber diameter, the more likely it is that the fiber will remain long during injection molding, increasing the flexural modulus. A single fiber diameter of 6.5 μm or greater increases the flexural modulus of the molded product. Because a single fiber diameter that is too large can reduce the tensile modulus of the carbon fiber, it is preferable that the single fiber diameter be 8.5 μm or less. The single fiber diameter can be evaluated as described below. It can be calculated from the density, basis weight, and number of filaments of the carbon fiber used as the raw material, or it can be determined by isolating the carbon fibers in the molding material using a known method and observing them under a microscope. Methods for isolating carbon fibers from molding materials include dissolving and removing the resin components using a solvent or burning them off, and these methods can be selected appropriately depending on the type of resin. In these methods, it is necessary to find conditions that minimize the thermal weight loss of the carbon fiber while minimizing the resin residue. However, if the conditions are found as is commonly done by those skilled in the art, results equivalent to the single fiber diameter of the carbon fiber as the raw material can be obtained. The evaluation method in the present invention will be described in detail later. The single fiber diameter of the carbon fiber can be adjusted by the single fiber fineness of the carbon fiber precursor fiber.

[0014] The carbon fibers used in the molding material of the present invention preferably have a coefficient of variation of single fiber diameter of 3 to 7%, more preferably 4 to 6%. The coefficient of variation of single fiber diameter is defined as the standard deviation / average value of the diameters of the single fibers contained in the molding material. When the coefficient of variation of single fiber diameter is 3 to 7%, it is easy to obtain a molding material with a homogeneous internal structure.

[0015] The crystallization parameter Iv1 / Ig1 of the carbon fiber used in the molding material of the present invention, as determined by Raman spectroscopy, is 0.25 to 0.60. It is also preferably 0.30 to 0.55, more preferably 0.30 to 0.50, and even more preferably 0.35 to 0.50. The crystallization parameter Iv1 / Ig1 of the molding material of the present invention, as determined by Raman spectroscopy, is evaluated by analyzing the Raman spectrum obtained from the cross section of a single fiber of the carbon fiber. The detailed evaluation method will be described later. The Raman spectrum obtained from the cross section of a single fiber of the carbon fiber has a peak at 1,580 cm -1 Nearby G band, 1,360cm -1 Nearby D band, 1,480cm -1 A valley appears between these bands near the peak intensity of the G band. -1 The portion of the carbon fiber where the spectral intensity is weakest is designated as Iv1, and the ratio serves as an index showing the degree of crystallization of the internal structure of the carbon fiber. For commercially available carbon fibers, according to the measurement method of the present invention described below, those with a tensile modulus of around 380 GPa have an Iv1 / Ig1 ratio of less than 0.20, and those with a tensile modulus of 230 to 290 GPa have an Iv1 / Ig1 ratio of 0.70 or greater. When Iv1 / Ig1 is 0.65 or less, crystallization is sufficiently advanced, and the tensile modulus of the carbon fiber is high. When Iv1 / Ig1 is 0.25 or greater, crystallization within the carbon fiber is not excessive, making the carbon fiber less likely to break during injection molding and improving the physical properties of the molded product. These parameters can be adjusted by adjusting the maximum carbonization temperature during carbon fiber production.

[0016] The number-average fiber length of the carbon fibers contained in the molding material of the present invention is 0.3 mm or less. Furthermore, the number-average fiber length of the carbon fibers is preferably 0.05 to 0.25 mm. By setting the number-average fiber length within this range, the reinforcing effect of the carbon fibers can be enhanced, and the mechanical properties of the molded article can be sufficiently improved. Here, a method for measuring the number-average fiber length in a molded article will be described. For example, the number-average fiber length of the carbon fibers contained in a molded article can be measured by removing the resin components contained in the molded article using a dissolution method or a burn-off method, filtering out the remaining carbon fibers, and then measuring the number-average fiber length by microscopic observation. For the measurement, 400 carbon fibers are randomly selected, their lengths are measured to the nearest 1 μm using an optical microscope, and the total fiber length is calculated by dividing the total fiber length by the number of fibers. Controlling the number-average fiber length within the above range can be achieved by using carbon fibers that are less likely to break during injection molding, as described above.

[0017] The carbon fibers used in the molding material of the present invention preferably have a ratio (a / b) of the crystallization parameter Iv1 / Ig1 (= a) at the center to the crystallization parameter Iv2 / Ig2 (= b) at the outer periphery, where the inner side of a cross section perpendicular to the fiber axis of the carbon fiber is the center and the outer side is the outer periphery. The ratio is preferably 0.80 to 1.05, more preferably 0.85 to 1.05, and even more preferably 0.90 to 1.05. The smaller the difference in the crystallization parameters between the center and outer periphery, the smaller the degree of crystallization in the internal structure of the carbon fiber. This tends to increase the flexural modulus of the molded article, even when the carbon fiber single fiber diameter is large. When the ratio (a / b) of the crystallization parameters between the center and outer periphery is 0.80 or higher, the difference in the internal crystalline structure of the carbon fiber is small, making it less likely to break, and the flexural modulus of the molded article is likely to be improved. The crystallization parameters of the center and outer periphery are evaluated by Raman spectroscopy, as described above. Detailed evaluation methods are described below. These parameters can be adjusted by the maximum carbonization temperature and the draw ratio during carbonization when producing the carbon fiber. Hereinafter, the crystallization parameter Iv1 / Ig1 (= a) of the center portion in a cross section perpendicular to the fiber axis of the carbon fiber may be simply referred to as Iv1 / Ig1 or a, and the crystallization parameter Iv2 / Ig2 (= b) of the outer periphery in a cross section perpendicular to the fiber axis of the carbon fiber may be simply referred to as Iv2 / Ig2 or b.

[0018] The carbon fiber used in the molding material of the present invention preferably has a tensile modulus E of 350 to 500 GPa, more preferably 370 to 480 GPa, and even more preferably 380 to 450 GPa. The higher the tensile modulus of the carbon fiber, the higher the flexural modulus of the molded article tends to be. A tensile modulus of 350 GPa or more can significantly increase the flexural modulus of the molded article, making it of great industrial value in applications where rigidity is important. From the perspective of increasing the flexural modulus of the molded article, a high tensile modulus of the carbon fiber is preferable, but if it is too high, the effect of improving the flexural modulus of the molded article is weakened, so the tensile modulus should be 500 GPa or less. The tensile modulus of the carbon fiber can be evaluated according to the tensile test of a resin-impregnated strand described in JIS R7608:2004. The method for evaluating the strand modulus will be described in detail below.

[0019] The carbon fibers used in the molding material of the present invention are preferably carbon fibers whose crystallization parameter Iv1 / Ig1 and tensile modulus E (GPa) satisfy the relationship of formula (1). E≧-100×Iv1 / Ig1+400...Equation (1).

[0020] The constant term in formula (1) is more preferably 410, and even more preferably 420. Formula (1) is a relationship indicating that the tensile modulus is high despite the carbon fiber not being highly crystallized, and indicates that the carbon fiber can achieve both high breakage resistance and high tensile modulus during injection molding. In the present invention, by using specific carbon fibers that have a large crystallization parameter Iv1 / Ig1 and satisfy the relationship of formula (1) above, even if the tensile modulus of the carbon fiber is increased, the flexural modulus of the molded product can be effectively increased. If the constant term is 400 or more, a sufficient tensile modulus is expressed relative to the crystallization parameter of the carbon fiber, and it is easy to achieve both high breakage resistance and high tensile modulus during injection molding. This relationship can be adjusted by the maximum carbonization temperature and the draw ratio during carbonization during carbon fiber production.

[0021] The carbon fibers used in the molding material of the present invention are preferably carbon fibers whose crystallization parameter Iv1 / Ig1 and tensile modulus E (GPa) satisfy the relationship of formula (2). E≧290×(Iv1 / Ig1) -0.23 ...Equation (2).

[0022] The coefficient in formula (2) is preferably 300. Generally, the smaller the crystallization parameter Iv1 / Ig1, the more advanced the crystallization and the higher the tensile modulus of the carbon fiber, and a power-law relationship is generally observed between these two parameters. The more crystallized the carbon fiber, the more likely it is to break due to bending forces during injection molding. Therefore, the inventors' investigations revealed that carbon fibers that satisfy formula (2) can maintain a high level of tensile modulus and resistance to breakage. The physical meaning of formula (2) is that it is best to use carbon fibers that are not highly crystallized despite their high tensile modulus. By using specific carbon fibers that satisfy the relationship of formula (2), the flexural modulus of the molded product can be effectively increased.

[0023] The thermoplastic resin used in the molding material of the present invention is preferably at least one thermoplastic resin selected from the group consisting of polyolefins, polyamides, polyesters, polycarbonates, polyarylene sulfides, polyoxymethylene, polyetherimides, polyether ketones, and polyether ether ketones. From the viewpoint of the flexural modulus of the resulting molded article, polyamides and polyarylene sulfides are more preferred, and polyarylene sulfides are even more preferred. By combining the carbon fibers used in the present invention with the thermoplastic resin, the type of thermoplastic resin is not limited, and the mechanical properties such as the flexural modulus of the resulting molded article can be improved. Therefore, a wide range of thermoplastic resins can be selected, but the effects of the present invention can be easily achieved by selecting a thermoplastic resin that is likely to improve the mechanical properties of the molded article, specifically a thermoplastic resin that exhibits a high tensile yield stress.

[0024] Examples of polyolefins include homopolymers of propylene and copolymers of propylene with at least one α-olefin, conjugated diene, non-conjugated diene, and the like.

[0025] Examples of polyamides include polymers whose main chain is composed of repeating amide groups, such as polyamide 6, polyamide 66, polyamide 11, polyamide 610, polyamide 612, polyamide 6T and 6I, and polyamide 9T. Mixtures of these or copolymers of multiple types of polyamides may also be used.

[0026] Examples of polyarylene sulfides include those having, as their constituent units, p-phenylene sulfide units, m-phenylene sulfide units, o-phenylene sulfide units, phenylene sulfone units, phenylene sulfide ketone units, phenylene sulfide ether units, diphenylene sulfide units, phenylene sulfide units containing a substituent, and phenylene sulfide units containing a branched structure, with poly-p-phenylene sulfide being particularly preferred.

[0027] The molding material of the present invention may contain additives within the range that does not impair the effects of the present invention. Specific examples of additives include antioxidants, heat stabilizers, weathering agents, mold release agents, lubricants, pigments, dyes, plasticizers, antistatic agents, and flame retardants.

[0028] A preferred embodiment of the method for producing the molding material of the present invention involves mixing the above components simultaneously or in any order using a mixer such as a tumbler, V-type blender, Nauta mixer, Banbury mixer, kneading roll, or extruder, and more preferably melt-kneading using a twin-screw extruder. The extruder preferably has a vent that can remove moisture from the raw materials and volatile gases generated from the melt-kneaded resin. A vacuum pump is preferably installed in the vent to efficiently discharge the generated moisture and volatile gases outside the extruder. A screen for removing foreign matter mixed into the extrusion raw materials can also be installed in the zone before the extruder die to remove foreign matter from the resin composition. Examples of such a screen include wire mesh, a screen changer, and a sintered metal plate. In this case, it is preferable to continuously feed the carbon fiber, and more preferably to feed the carbon fiber after melt-kneading the thermoplastic resin.

[0029] After the carbon fibers are integrated with the thermoplastic resin, they may be cut into a fixed length of, for example, 1 to 50 mm using a device such as a pelletizer or strand cutter. This cutting process may be performed continuously after the thermoplastic resin placement process. If the molding material is flat or in sheet form, it may be slit into elongated pieces and then cut. A sheet pelletizer that simultaneously performs slitting and cutting may also be used.

[0030] The molding material of the present invention preferably has a flexural modulus (FM) of 30 to 55 GPa, more preferably 35 to 55 GPa, and even more preferably 39 to 55 GPa. The flexural modulus is measured according to ISO 178 and is a major factor in the rigidity of a component, indicating its resistance to bending. A higher flexural modulus allows the component to maintain its resistance to bending even when less molding material is used, leading to a lighter component. A flexural modulus of 30 GPa or more is comparable to that of magnesium alloys, a representative lightweight metal, and is a satisfactory result. While a higher flexural modulus is always better, a flexural modulus of 55 GPa or less is sufficient to replace magnesium alloys. The key to controlling the flexural modulus within the above range is to use the carbon fibers described above.

[0031] The molding material of the present invention preferably contains 15 to 55 mass % of carbon fiber, more preferably 25 to 50 mass %. The mass content Wf of carbon fiber in the molding material can be adjusted depending on the application and the desired physical properties, and if only the flexural modulus of the molded product is considered, it is preferable to increase the mass content. If the mass content of carbon fiber is 15 mass % or more, the flexural modulus of the molded product will be high, and if it is 55 mass % or less, moldability during injection can be maintained. The mass content of carbon fiber can be calculated from the ratio of the added carbon fiber to the thermoplastic resin and other additive components. Alternatively, after measuring the mass of the molding material, the resin component can be burned off in air using a known method, or the resin component can be removed with a solvent. can be calculated from the ratio of the mass of the remaining carbon fiber to the mass of the remaining carbon fiber.

[0032] In the molding material of the present invention, the flexural modulus FM (GPa) of the molded article, the mass content Wf (%) of carbon fiber in the resin composition, and the crystallization parameter Iv1 / Ig1 preferably satisfy the relationship of formula (3). FM / Wf 0.5 ≧-0.5×Iv1 / Ig1+6.5...Equation (3).

[0033] The flexural modulus depends on the mass content Wf of carbon fiber, but is not proportional to Wf, so it is empirically normalized by the 0.5 power of Wf. Although Iv1 / Ig1 is high, FM / Wf 0.5 The fact that FM / Wf is large indicates that, even though the crystallization of the carbon fiber is not advanced, the carbon fiber has a significant effect of improving the bending modulus relative to the mass content of the carbon fiber. 0.5 Controlling Iv1 / Ig1 so that it falls within the range of the present invention means that the fiber length in the molded article remains long, but the present inventors have confirmed that conventional carbon fibers do not satisfy formula (3), as in the examples described in the examples of the above-mentioned Patent Documents 1 to 3. In order to control so that formula (3) is satisfied, it is necessary to select the carbon fiber used in the present invention.

[0034] The molded article of the present invention preferably has a flexural modulus FM (GPa), specific gravity γ, carbon fiber mass content Wf (%), and carbon fiber single fiber diameter d (μm) that satisfy the relationship of formula (4). FM / γ≧Wf 1.2 / d 1.3 ...Equation (4).

[0035] It is generally recognized that adjusting the formulation of a molding material to increase the flexural modulus of a molded product tends to decrease its fluidity. For example, reducing the carbon fiber diameter or increasing the carbon fiber content increases the flexural modulus of the molded product, but both tend to decrease the fluidity of the molding material. Regarding the left side of equation (4), the flexural modulus is affected by the type of resin used in the molding material. Using a resin with a higher specific gravity tends to result in a higher flexural modulus. Therefore, dividing the flexural modulus by the specific gravity of the molded product (FM / γ) cancels out the effect of the resin type and allows for a more consistent comparison of flexural moduli. Regarding the right side, the following applies: A higher carbon fiber mass content (Wf) (%) increases the carbon fiber filling rate in the molding material, thereby decreasing the fluidity of the molding material. Furthermore, a smaller carbon fiber diameter (d (μm)) increases the number of single fibers for a given mass content (Wf) (%), resulting in a smaller average fiber spacing and therefore a decrease in the fluidity of the molding material. Although a molded article satisfying formula (4) cannot be obtained from commercially available injection materials, a molded article satisfying formula (4) can be obtained by using the carbon fiber of the present invention.

[0036] <Tensile modulus of carbon fiber> The tensile modulus of carbon fiber was determined according to the following procedure in accordance with the resin-impregnated strand test method of JIS R7608:2004. However, if the carbon fiber bundle had twists, they were untwisted by twisting the bundle in the opposite direction the same number of times as the twists. The resin formulation used was "Celloxide (registered trademark)" 2021P (manufactured by Daicel Chemical Industries, Ltd.) / boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / acetone = 100 / 3 / 4 (parts by mass), and the curing conditions were atmospheric pressure, 125°C, and 30 minutes. Ten carbon fiber strands were measured, and the average values ​​were used as the strand strength and strand modulus. The strain range for calculating the strand modulus was 0.1 to 0.6%.

[0037] <Carbon fiber single fiber diameter and its coefficient of variation> The formed material was heated in air at a temperature of 500 °C for 30 minutes using an electric furnace to sufficiently incinerate and remove the thermoplastic resin and separate the carbon fibers. For polyether ether ketone (PEEK) with a high thermal decomposition temperature, trifluoroacetic acid was used as the solvent to dissolve the resin in the formed material and separate the carbon fibers. The side surface of the remaining carbon fibers was observed at a total magnification of 1000 times using an objective lens with a magnification of 100 times of an optical microscope. A microscopic image of the side surface of the carbon fibers was obtained, and for locations where the single fibers did not overlap and could be identified as individual fibers, the thickness of the single fibers was measured as the single fiber diameter using the image analysis software ImageJ. The number of samples N for calculating the single fiber diameter was set to 50, and the average value was adopted.

[0038] The coefficient of variation of the single fiber diameter of the carbon fibers was calculated by dividing the standard deviation of the single fiber diameter by the average value and then multiplying by 100.

[0039] Note that an optical microscope "Leica DM2700M" manufactured by Leica Microsystems was used as the optical microscope.

[0040] <Crystallization parameters Iv1 / Ig1, Iv2 / Ig2 by Raman spectroscopy> The resin composition was embedded in resin and polished to expose the cross section of a single carbon fiber. To avoid the impact of polishing damage on the Raman spectrum, a final polishing step was performed using an abrasive with a diameter of approximately 0.05 μm. When the cross section of the carbon fiber perpendicular to the fiber axis was approximately circular, the center and outer periphery were identified and measured as follows. That is, concentric circles with a radius approximately half that of the original cross section were visually estimated, and the inside of these concentric circles was designated as the center and the outside as the outer periphery. When visual determination was difficult, the following procedure was performed. The area of ​​the cross section perpendicular to the fiber axis of the carbon fiber was measured, and the radius r of a perfect circle with one-quarter of that area was calculated. Ten points were selected evenly on the periphery of the cross section, and normals were drawn from each point. A point was placed a distance r from the periphery into the fiber. These points were smoothly connected to obtain a contour similar to the periphery of the cross section, which was designated as the boundary line. The inside of this boundary line was designated as the center, and the outside of this boundary line was designated as the outer periphery. Five points on the cross section of a single carbon fiber were randomly selected, and Raman spectra of the central and peripheral parts of the cross section of the single fiber were obtained using a micro-Raman spectrometer to calculate Iv1 / Ig1 and Iv2 / Ig2. During the measurement, the center of the laser was irradiated 1 μm away from the boundary line to prevent mixing of information from the central and peripheral parts. The excitation wavelength was 532 nm, the laser intensity was 1 mW, and the measurement range was 900–2,000 cm. -1 The laser beam was focused to a diameter of 2 μm using a 100x objective lens, and the measurement time was 60 seconds x 3 times. The baseline of the obtained spectrum was set at 1,000 cm -1 and 1,800 cm -1 The scattering intensity is offset using a linear function so that it becomes 0, and the height of the G band is set to Ig1, Ig2, 1,480 cm -1 The heights of the valley bottoms near the G band were used to calculate the crystallization parameters Iv1 / Ig1 and Iv2 / Ig2. To minimize the influence of errors, Ig1 and Ig2 were calculated within ±10 cm from the visual peak of the G band. -1 The range was approximated by a quadratic function using the least squares method, and the peak top intensities of the fitting function were determined as Ig1 and Ig2. -1The height was determined in the same manner for the vicinity of the valley near the center. Regarding the ratio of the crystallization parameters inside and outside the carbon fiber, the ratio (a / b) of the crystallization parameters inside and outside the carbon fiber was calculated by dividing Iv1 / Ig1 (= a) at the center by Iv2 / Ig2 (= b) at the outer periphery within the same single fiber. In the present invention, the average values ​​of Iv1 / Ig1 and Iv2 / Ig2 at five points were used.

[0041] In the examples, the embedding resin used was "EpoKwick" (registered trademark) FC (manufactured by Buehler), and the polishing machine was "AutoMet" (registered trademark) 250Pro (manufactured by Buehler). After rough polishing using #320, #500, and #700 polishing pads, the polishing was performed using "MasterTex" (manufactured by Buehler) as the polishing cloth and a 0.05 μm diameter alumina suspension as the abrasive. To check for polishing damage, a "TORAYCA" (registered trademark) M40J-12000-50E (manufactured by Toray Industries, Inc.) was always used as a blank when embedding the resin composition in resin, and was simultaneously embedded with the fiber axis perpendicular to the polished surface. If the Iv1 / Ig1 ratio evaluated using the above method for the M40J was 0.18 ± 0.02, polishing damage was minimized. If this was not the case, polishing was repeated.

[0042] <Bending test of molded products> For ISO dumbbell test specimens, flexural strength was measured in accordance with ISO 178 (2010) using a three-point bending test jig (indenter radius 5 mm) with a support distance of 64 mm and a test speed of 2 mm / min. The test specimens were left in a constant temperature and humidity chamber adjusted to a temperature of 23°C and 50% RH for 24 hours before undergoing characteristic evaluation tests. Measurements were performed on six molded products, and the flexural modulus was calculated as the average value.

[0043] In the examples and comparative examples described below, an "Instron (registered trademark)" universal testing machine Model 4201 (manufactured by Instron Corporation) was used as the testing machine.

[0044] <Number average fiber length of carbon fibers contained in molding material> The molding material was heated in air in an electric furnace at 500°C for 30 minutes, thoroughly burning off the thermoplastic resin and separating the carbon fibers. For polyetheretherketone (PEEK), which has a high thermal decomposition temperature, trifluoroacetic acid was used as a solvent to dissolve the resin in the molding material and separate the carbon fibers. Four hundred of the separated carbon fibers were randomly selected, and their lengths were measured to the nearest 1 μm using an optical microscope. The number-average fiber length (Ln) was calculated using the following formula: Number average fiber length (Ln) = (ΣLi) / Nf · Li: measured fiber length (i = 1, 2, 3, . . . , n) Nf: The total number of fibers whose length was measured.

[0045] <Evaluation of specific gravity of molded products> Measurements were performed in accordance with Method A (water displacement method) described in JIS K 7112 (1999) Section 5. A 1 cm x 1 cm test piece was cut out from the molded product and placed in a heat-resistant glass container. The container was vacuum dried at 80°C for 12 hours, and then cooled to room temperature in a desiccator to prevent moisture absorption before being used for measurement. Ethanol was used as the immersion liquid. [Example]

[0046] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples, and the type of thermoplastic resin is not limited thereto.

[0047] [Examples 1 and 2] A spinning solution containing a polyacrylonitrile copolymer composed of acrylonitrile and itaconic acid was obtained. The resulting spinning solution was discharged into the air from a spinneret and introduced into a coagulation bath containing an aqueous solution of dimethyl sulfoxide to obtain coagulated yarns by a dry-wet spinning method. The coagulated yarns were then washed with water, stretched in warm water at 90°C at a draw ratio of 3, further treated with silicone oil, dried using a roller heated to 160°C, and then subjected to pressurized steam stretching at a draw ratio of 4 to obtain carbon fiber precursor fiber bundles with a single fiber fineness of 1.1 dtex. The resulting precursor fiber bundles were then doubled to a total of 24,000 single fibers, and heat-treated in an oven at 230-280°C in an air atmosphere at a draw ratio of 1 to convert them into flame-resistant fiber bundles. The obtained flame-resistant fiber bundle was subjected to a twisting treatment to impart a twist of 25 turns / m, and then subjected to a pre-carbonization treatment in a nitrogen atmosphere at a temperature of 300 to 800°C with a draw ratio of 1.0 to obtain a pre-carbonized fiber bundle. Next, the pre-carbonized fiber bundle was subjected to a carbonization treatment under conditions of a draw ratio of 1.02 and a carbonization temperature of 1,900°C, and then subjected to an electrolysis treatment in a sulfuric acid aqueous solution to obtain a carbon fiber of 30 c / g without applying a sizing agent.

[0048] A twin-screw extruder (TEX-30α, manufactured by The Japan Steel Works, Ltd., L / D=31.5) was used to melt-knead the components, with polyphenylene sulfide (PPS) resin as the main feed and the same carbon fiber as in Example 1 as the side feed. The melt-kneading was performed at a cylinder temperature of 290°C, a screw rotation speed of 150 rpm, and a discharge rate of 10 kg / hour. The discharged material was cooled in a water-cooled bath while being withdrawn to form strands, and the guts were cut into pellets with a length of 5 mm. The mass content of the carbon fiber contained in the pellets was 30 mass% in Example 1 and 45 mass% in Example 2, and the number average fiber length was 0.16 mm in Example 1 and 0.10 mm in Example 2.

[0049] The pellets were injection molded using an injection molding machine (J150EII-P manufactured by The Japan Steel Works, Ltd.) to prepare test specimens for various evaluations. Injection molding was performed at a cylinder temperature of 320°C and a mold temperature of 150°C. The obtained test specimens were annealed at 150°C for 2 hours, then air-cooled and used for each test.

[0050] [Example 3] The same treatment as in Example 1 was carried out and the test was carried out, except that the draw ratio of the carbon fiber was finely adjusted, nylon 66 (PA66) resin was used as the matrix resin, the mass content of the carbon fiber contained in the pellet was 20 mass%, and the cylinder temperature during injection molding was 290°C.

[0051] [Examples 4 and 5] The carbon fiber draw ratio was finely adjusted and electrolytic treatment was performed to make it 120 c / g. Polyether ether ketone (PEEK) was used as the matrix resin. The melt-kneading temperature during pellet production was 340°C. The mass content of the carbon fiber contained in the pellets in Example 5 was 40 mass%, and the injection temperature during injection molding was 370°C. The same treatment as in Example 1 was performed and the test was performed.

[0052] [Examples 6 and 7] The carbon fiber draw ratio was finely adjusted, the mass content was changed to 40 mass%, and Example 7 was subjected to electrolytic treatment so that the mass content was 120 c / g. Except for this, the treatment was carried out in the same manner as Example 1, and the test was carried out.

[0053] [Example 8] The same treatment as in Example 1 was carried out and the test was carried out, except that the draw ratio of the carbon fiber was finely adjusted, nylon 610 (PA610) resin was used as the matrix resin, melt mixing during pellet production was carried out at a cylinder temperature of 245°C, the mass content of carbon fiber contained in the pellets was 45 mass%, and the cylinder temperature during injection molding was 270°C.

[0054] [Example 9] The carbon fiber draw ratio was finely adjusted, polyamide 9T (PA9T) resin was used as the matrix resin, melt mixing during pellet production was performed at a cylinder temperature of 320°C, and the cylinder temperature during injection molding was also 320°C. Except for this, the processing was carried out in the same manner as in Example 8, and the test was conducted.

[0055] [Comparative Example 1] The same treatment as in Example 1 was carried out, except that "Torayca (registered trademark)" T700SC-24000-50E manufactured by Toray Industries, Inc. was used, and the test was carried out.

[0056] Comparative Example 2 The carbon fiber reinforced thermoplastic resin "TORAYCA (registered trademark)" 3101T-30V manufactured by Toray Industries, Inc. was used in the test.

[0057] Comparative Example 3 The same treatment as in Example 1 was carried out, except that "TORAYCA (registered trademark)" M40JB-12000-50A manufactured by Toray Industries, Inc. was used, and the test was carried out.

[0058] Comparative Example 4 The same treatment as in Example 3 was carried out, except that "TORAYCA (registered trademark)" T700SC-24000-50E manufactured by Toray Industries, Inc. was used, and the test was carried out.

[0059] As shown in the examples and comparative examples, molded articles obtained from the molding materials of the present invention exhibited excellent mechanical properties regardless of the type of thermoplastic resin.

[0060] [Reference example 1] Comparison was made with reference to the values ​​in Example 2 of JP-A-2006-1965.

[0061] [Reference example 2] Comparison was made with reference to the values ​​in Example 2 of JP 2017-190426 A.

[0062] [Reference example 3] The test was conducted using "KyronMAX (registered trademark)" manufactured by Mitsubishi Chemical Advanced Materials Co., Ltd. The number average fiber length of the carbon fibers contained in the molding material was 0.14 mm, and the coefficient of variation of the single fiber diameter was 9.0%.

[0063] [Table 1]

[0064] Table 2

Claims

1. A molding material comprising carbon fibers having a number average fiber length of 0.3 mm or less and at least one thermoplastic resin selected from polyamide and polyether ether ketone, wherein the carbon fibers have a single fiber diameter of 6.5 to 8.5 μm and a crystallization parameter Iv measured by Raman spectroscopy. １ / Ig １ The crystallization parameter Iv 1 / Ig 1 and the tensile modulus E (GPa) of the carbon fiber satisfy the relationship of formula (2), and the specific gravity γ is 1.44 or less, and the flexural modulus FM (GPa), specific gravity γ, mass content Wf (%) of the carbon fiber, and single fiber diameter d (μm) of the carbon fiber satisfy the relationship of formula (4). E≧290×(Iv 1 / Ig 1 ) −0.23 ...Formula (2) FM / γ≧Wf １．２ / d １．３ ...Form (4)

2. The crystallization parameter Iv １ / Ig １ and the tensile modulus E (GPa) of the carbon fiber satisfy the relationship of formula (1). E≧-100×IV １ / Ig １ +400 ・・・Form (1)

3. The flexural modulus FM (GPa) of the molded product, the mass content Wf (%) of the carbon fiber in the molding material, and the crystallization parameter Iv １ / Ig １ The molded article according to claim 1 or 2, wherein the relationship of formula (3) is satisfied. FM / Wf ０．５ ≧-0.5×Iv １ / Ig １ +6.5 ・・・Formula (3)

4. The molded product according to any one of claims 1 to 3, wherein the coefficient of variation of the single fiber diameter of the carbon fiber is 3 to 7%.

5. The crystallization parameter Iv of the center of the cross section perpendicular to the fiber axis of the carbon fiber １ / Ig １ (= a) and the crystallization parameter Iv of the outer periphery in a cross section perpendicular to the fiber axis of the carbon fiber ２ / Ig ２ The molded article according to any one of claims 1 to 4, wherein the ratio (a / b) of (=b) is 0.80 to 1.05.

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