JP2011190549A - Fiber-mixed mat-shaped molded product and fiber-reinforced molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber reinforced molded product having excellent mechanical characteristics and thermal conductivity by improving breakage of pitch-based carbon fiber and a fiber mixed mat-shaped molded product for molding the same. <P>SOLUTION: In the fiber mixed mat-shaped molded product composed of short fiber of pitch-based carbon fiber and short fiber of thermoplastic resin fiber, the carbon fiber is a pitch-based carbon fiber having a tensile elastic modulus in the fiber axis direction of not less than 400 GPa, a thermal conductivity in the fiber axis direction of not less than 60 W/mK, and a weight-average fiber length of not less than 3 mm. The fiber-reinforced molded product is obtained by press-molding the fiber-mixed mat-shaped molded product at a flow starting temperature of the thermoplastic resin fiber of the fiber-mixed mat-shaped molded product or above. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fiber-mixed mat-like molded body composed of pitch-based carbon fibers and thermoplastic resin fibers, and a fiber-reinforced molded body obtained by hot press molding the fiber-mixed mat-shaped molded body.

  Since fiber reinforced plastics (FRP) has excellent strength and elastic modulus per unit weight, application development centering on metal substitution is rapidly progressing. In particular, a carbon fiber reinforced resin molded body formed by combining carbon fiber and resin has strength and elastic modulus comparable to metal materials, but has a specific gravity smaller than that of metal materials. Moreover, since there is no problem of rusting, the use in the transportation field such as aircraft and automobiles for the purpose of reducing fuel consumption is steadily increasing.

  Among these, carbon fiber reinforced resin moldings using pitch-based carbon fibers are, for example, large glass substrates in the manufacturing process of liquid crystal displays, taking advantage of the advantages of ultra-high elasticity, high thermal conductivity, and low thermal expansion that are characteristic of pitch-based carbon fibers. It is applied to the robot hand that transports the paper, the shaft roll used in the papermaking process and the film manufacturing process, etc., and contributes to the increase in the length of the member and the speeding up by the weight reduction.

  However, the carbon fiber reinforced resin molded body is a highly anisotropic material in which the properties such as the elastic modulus, thermal conductivity, and thermal expansibility are greatly different between the direction in which the carbon fibers are oriented and the direction orthogonal thereto. For this reason, it is very difficult to use it and only a limited number of designers can handle it.

  In addition, in the case of a member that requires a high characteristic in the length direction, such as the robot hand and the shaft roll described above, the carbon fiber is designed and manufactured to be oriented in the length direction. Thus, the excellent characteristics of the carbon fiber can be effectively exhibited, but in the case of a planar member such as a panel, the anisotropy is often inconvenient. That is, in a planar member, it is desirable that the elastic modulus and thermal conductivity are equal in any direction in the plane, that is, isotropic.

  For example, Patent Document 1 describes the content of producing a thermoplastic prepreg sheet by a method of pressing and forming a sheet after arranging prepreg tapes in which a fiber bundle is impregnated with a thermoplastic resin. However, since high rigidity is required even in the state of a prepreg sheet at the same time to exhibit high rigidity at room temperature, the sheet is poor in flexibility, and bending or breaking after winding, laminating, and shaping are performed. There was a problem that it was likely to occur. In addition, in order to prevent distortion and warpage of the molded body, since it is laminated so as to be symmetrical in the thickness direction with respect to the central surface portion in the thickness direction, for example, the surface layer of one surface of the obtained molded body When a part is processed and ground, the symmetry is lost and distortion and warpage occur. Furthermore, since it is an aggregate of long fibers or continuous fibers aligned in one direction, it is difficult to follow a complicated uneven shape, and it is difficult to form a three-dimensional curved shape. In addition, since the raw material sheet is produced by further processing the long fiber or continuous fiber, there is a problem that the cost becomes high.

  Patent Document 2 describes a deformed fiber reinforced plastic in which carbon fibers having a length of 10 to 100 mm are two-dimensionally and irregularly distributed in a matrix made of a thermosetting resin. Such a method can solve such a problem, but the fiber length is short, and the fiber is damaged by the sheeting or pelletizing process, which further shortens the fiber length. It is not possible to achieve the same characteristics as metal materials. In particular, carbon fibers with higher elasticity and higher thermal conductivity are more brittle and more likely to break, making it difficult to exert their effects, and their handling is extremely difficult.

  In patent document 3, after making pitch fiber into a nonwoven fabric, the carbon fiber nonwoven fabric is produced by insolubilizing and carbonizing, and the resin is impregnated after that. In the above method, since the nonwoven fabric is formed first, the resin needs to be impregnated from the surface of the nonwoven fabric in the resin impregnation step. At this time, the impregnation property is easily influenced by the resin viscosity and the thickness (weight of the nonwoven fabric), and in order to produce a molded body with few voids by pressing, there are limitations such as a thin nonwoven fabric and a particularly low resin viscosity. In order to form a thicker plate, the resin impregnation speed and the heating temperature are important, and the adjustment of the pressurizing speed and heating conditions during pressing becomes complicated.

  Patent Document 4 describes a molding material using an opened single-fiber carbon fiber and a thermoplastic resin fiber, and a fiber-reinforced thermoplastic resin molded body molded by a compression molding method. Although a pitch system is also exemplified as the carbon fiber, there is no example in which the pitch system is used in the examples because the PAN system is preferable.

Japanese Patent Application Laid-Open No. 08-041220 Japanese Patent Laid-Open No. 03-106619 JP 2007-84649 A WO2007 / 097436 republication gazette

  The present invention provides a fiber reinforced molded article excellent in mechanical properties and thermal conductivity by improving breakage of pitch-based carbon fibers, and a fiber mixed mat-like molded article for molding the fiber reinforced molded article. With the goal.

  As a result of intensive studies, the present inventors have obtained a fiber mixture obtained by mixing a pitch-based carbon fiber having a predetermined tensile modulus, thermal conductivity, and weight average fiber length and a thermoplastic resin fiber. It has been found that the above problems can be solved, and the present invention has been completed.

  The fiber-mixed mat-shaped molded product of the present invention is a fiber-mixed mat-shaped molded product composed of short fibers of pitch-based carbon fibers and short fibers of thermoplastic resin fibers, and the carbon fibers have a tensile modulus in the fiber axis direction of 400 GPa. Thus, the thermal conductivity in the fiber axis direction is 60 W / mK or more, and the weight average fiber length is 3 mm or more.

  The fiber-mixed mat molded body preferably has a carbon fiber content of 15 to 75 wt% and a thermoplastic resin fiber content of 85 to 25 wt%.

  In this fiber-mixed mat-like molded body, the carbon fibers preferably have a fiber length distribution of 50 wt% or more within a weight average fiber length of ± 1 mm.

  In this fiber-mixed mat-like molded body, it is preferable that short fibers of carbon fibers and short fibers of thermoplastic resin are in a two-dimensional random dispersion state.

  This fiber-mixed mat-like molded body is preferably produced by a dry method.

That the basis weight of fiber mixed mats shaped body is ^{250g / m 2 ~1500g / m 2} , ^particularly preferably in ^{500g / m 2 ~1200g / m 2} .

  The fiber reinforced molded product of the present invention is obtained by laminating one or a plurality of the fiber mixed mat-shaped molded products, and press-molding at or above the flow start temperature of the thermoplastic resin fibers in the fiber mixed mat-shaped molded product. It will be.

  The thermal conductivity in the in-plane direction of the fiber reinforced molded body is preferably 20 W / mK or more.

  This fiber-reinforced molded body has a thickness of 0.2 to 10 mm, and has a bending elastic modulus of 20 GPa or more in the in-plane direction and a bending strength of 100 MPa or more measured according to JIS K7074 under the conditions of a load cell of 100 kN and a crosshead speed of 2 mm / min. Preferably there is.

  According to the present invention, it is possible to obtain a fiber-mixed mat-like molded body in which short fiber breakage is small and resin impregnation is easy. In addition, a fiber-reinforced molded body having excellent mechanical properties and functionality can be obtained by hot press molding this fiber-mixed mat-shaped molded body.

  Hereinafter, embodiments of the fiber-mixed mat-like molded body and fiber-reinforced molded body of the present invention will be specifically described, but the present invention is not limited to the following embodiments and is within the scope of the gist thereof. It can be implemented with various modifications.

[Pitch-based carbon fiber]
The pitch-based carbon fiber in the present invention is obtained by bundling single fibers with a sizing agent, and preferably 100 to 50000 monofilaments having a thickness of 3 to 25 μm are used. As the sizing agent, an epoxy resin or the like that is usually a thermosetting resin is used. However, in the present invention, it is necessary to select it according to the thermoplastic resin fiber to be used, and generally the melting temperature of the thermoplastic resin fiber is used. To make it easy to impregnate into continuous fibers. Therefore, it is preferable to use a sizing agent whose main component is the same kind of resin as the thermoplastic resin fiber.

  The carbonaceous raw material for pitch-based carbon fibers is not particularly limited as long as molecular species that are easily oriented are formed and optically anisotropic carbon fibers are provided. For example, coal-based coal tar, coal tar pitch, coal liquefied product, petroleum-based heavy oil, tar, pitch, or a polymerization reaction product by a catalytic reaction of naphthalene or anthracene can be used. These carbonaceous raw materials contain impurities such as free carbon, undissolved coal, ash, nitrogen, sulfur, and catalysts. These impurities can be filtered, centrifuged, or statically used in a solvent. It is desirable to remove it in advance by a known method such as settling separation.

  Further, the carbonaceous raw material is subjected to a pretreatment by, for example, a method in which a soluble component is extracted with a specific solvent after heat treatment, or a method in which a hydrogenation treatment is performed in the presence of a hydrogen donating solvent or hydrogen gas. You can go there.

  The fiber diameter of the carbon fiber used in the present invention is preferably 3 to 20 μm, particularly preferably 5 to 12 μm. If the fiber diameter of the carbon fiber is too thin, the handleability is inferior, and the ultrafine carbon fiber is generally high in cost, which increases the product cost. If the fiber diameter of the carbon fiber is too thick, the fiber strength is lowered and the fiber is easily broken, which is not preferable.

  Here, the fiber diameter of the carbon fiber is obtained by measuring 20 to 30 fiber diameters with a microscopic observation of the carbon fiber or a laser measuring instrument, and obtaining the average value of the measured values. In addition, the tensile modulus and thermal conductivity in the fiber axis direction of the carbon fiber are composite values obtained by preparing a unidirectional material of carbon fiber and epoxy resin and measuring the tensile modulus and thermal conductivity in the fiber axis direction. According to the law, the physical properties of the fiber itself are obtained by dividing the volume content of the carbon fiber. More specifically, the tensile elastic modulus is a calculated value from a value measured with a universal testing machine in accordance with JIS K7073. The thermal conductivity is a calculated value from a value measured with a laser flash method thermal constant measuring device “TC-3000” manufactured by Vacuum Riko Co., Ltd. in accordance with JIS R1611. The same applies to the embodiments described later.

  The length of the short fiber of the carbon fiber is preferably 50 mm or less, particularly 1 to 50 mm, particularly 3 to 20 mm. If the length of the fiber is too short, the fibers will not be entangled, making it difficult to form a nonwoven fabric, and the resulting molded article may not be able to sufficiently increase the bending elastic modulus and thermal conductivity. On the other hand, if the length of the raw fiber is too long, the fibers tend to be entangled or poorly opened, and the mixing of the thermoplastic resin fiber and the carbon fiber may be uneven.

  In the fiber-mixed mat-shaped molded body of the present invention, the carbon fiber used for production is often broken in the production process, and thus the used carbon fiber length is often not maintained as it is. For this reason, in the present invention, the weight average fiber length of carbon fibers is an important factor in the final fiber-mixed mat-like molded body. The weight average fiber length indicates the abundance as a weight. In the case of the same type of fiber, the length of the fiber is related to the weight, so that the weight average fiber length is greatly reduced when there are few long fibers. When the fiber length is short, the reinforcing effect is reduced with respect to the characteristics involved in the formation of paths such as heat conduction and electric conduction. The weight average fiber length is preferably 3 mm or more, particularly preferably 3 to 30 mm, and preferably has a fiber length distribution of 50 wt% or more, preferably 50 to 90 wt% within the weight average fiber length ± 1 mm.

  The number average fiber length is preferably 1 mm or more, particularly 1 to 20 mm. The number average fiber length is a value indicating the number of fibers present, and a small value indicates that there are more short fibers or a certain number of fibers are extremely short. In general, it is known that the fiber length affects the mechanical properties such as strength and elastic modulus in the fiber reinforced material. When there are many extremely short fibers, the reinforcing effect of these fibers is reduced.

  In addition, the number average fiber length and the weight average fiber length in the present invention were measured by extracting only fibers of 0.1 mm or more from photographs observed with an optical microscope, an electron microscope, or the like.

  The tensile modulus of elasticity of the carbon fiber used in the present invention in the fiber axis direction is 400 GPa or more, preferably 440 GPa or more, for example, 500 to 900 GPa, and the thermal conductivity in the fiber axis direction is 60 W / mK or more, preferably 110 W / mK. For example, 120 to 600 W / mK.

  Thus, by using carbon fibers having high tensile elastic modulus and high thermal conductivity, the bending elastic modulus and thermal conductivity of the obtained carbon fiber reinforced resin sheet and carbon fiber reinforced resin molded product can be increased. it can.

  It is known that the carbon fiber is graphitized to improve the tensile elastic modulus and thermal conductivity. Therefore, the carbon fiber nonwoven fabric according to the present invention may use graphitized carbon fiber, After making non-graphitized carbon fiber with low elastic modulus and low thermal conductivity into a non-woven fabric, it is graphitized before it is combined with the resin, and the tensile modulus and thermal conductivity in the fiber axis direction of the carbon fiber are measured. You may make it raise.

[Thermoplastic resin fiber]
Examples of the thermoplastic resin fiber of the present invention include generally well-known thermoplastic resins. For example, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, nylon 6, nylon 66, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyphenylene oxide, polyacetal, polysulfone, polyethersulfone, polyarylate, polyphenylene sulfide, polyether Examples thereof include ether ketone, liquid crystal aromatic polyester, polyimide and the like, copolymers and modified products thereof, and blends of two or more of the above. As the blended fiber, it is possible to use resin fibers having various structures such as a mixed single mixed resin fiber, a core-sheath structure fiber, and a composite fiber such as a side-by-side fiber.

  Especially, when the thermoplastic resin fiber used by this invention obtains a fiber mixed-mat mat-shaped molded object by a dry method, it becomes important that the crystal melting temperature or the flow start temperature contains a resin component below 200 degreeC. This is because, as an element of the present invention, the thermoplastic resin fiber is a matrix resin, and in the dry method in which a binder is not normally used, the function of the thermal bonding binder in thermal bonding is achieved. In the present invention, by having a thermoplastic resin component having a crystal melting temperature or flow start temperature of 200 ° C. or less, this portion is melt-bonded to other resin fibers or carbon fibers by passing through a steam or oil heater. As a result, it is possible to form a strongly bonded mixed mat-like molded body. If the crystal melting temperature or flow start temperature is 180 ° C. or lower, it is possible to reduce the amount of heat at the time of thermal bonding, which is further preferable in terms of high-speed molding and energy saving.

  Moreover, you may add a well-known additive, a modifier, a filler, etc. in a thermoplastic resin fiber.

  The melt viscosity of the thermoplastic resin greatly affects the wettability of the resin with the carbon fiber and the impregnation property of the thermoplastic resin into the unopened carbon fiber bundle. When the melt viscosity of the thermoplastic resin fiber is high, the wettability between the carbon fiber and the resin in the fiber reinforced molded article is poor, and the impregnation of the resin into the unopened carbon fiber bundle becomes difficult, so that the thermoplastic becomes the carbon fiber and the matrix. Interfacial peeling from the resin is likely to occur, and insufficient mechanical properties are likely to occur. Moreover, it becomes difficult to obtain a composite sheet integrated without peeling. On the other hand, when the melt viscosity is too low, the molecular weight of the resin is basically low, and mechanical properties such as impact resistance in the fiber-reinforced molded product may be deteriorated. The melt viscosity of the thermoplastic resin fiber in the present invention at a temperature not higher than the thermal decomposition start temperature is preferably 10 to 1000 Pa · s, and more preferably 20 Pa · s to 500 Pa · s. The melt viscosity of the thermoplastic resin fiber is the melt value that is the highest value and the lowest value in the temperature range under the condition that the weight loss is less than 1 wt% and the like in the dry thermoplastic resin fiber under the condition that the weight loss does not decompose. Viscosity is shown.

  The method for producing the thermoplastic resin fiber used in the present invention is not particularly limited as long as the effect of the present invention is not significantly inhibited, but a known method such as a single screw extruder or a twin screw extruder is used. Various methods such as melt spinning using a multifilament die or monofilament die, melt blowing method, flash spinning method, polymer blending method, electrospinning method, sea-island composite spinning method, split fiber composite spinning method, etc. are used. The fiber diameter is usually about 0.1 μm to 500 μm.

  The length of the thermoplastic resin short fibers is preferably 50 mm or less, particularly 1 to 50 mm, particularly 3 to 20 mm. When the length of the fiber is too short, the entanglement between the fibers becomes insufficient, and it becomes difficult to form and maintain the shape of the mat-shaped molded body. On the other hand, if the length of the raw fiber is too long, the fibers tend to be entangled or poorly opened, and the mixing of the thermoplastic resin fiber and the carbon fiber may be uneven.

[Production method of fiber-mixed mat-like molded product]
The fiber-mixed mat-like molded product of the present invention is called a nonwoven fabric, and the above-mentioned thermoplastic resin fibers and carbon fibers are cut into a predetermined length by cutting them into a predetermined length, and they are made into a planar shape (two-dimensional). It can be produced by randomly dispersing it into a sheet form. Hereinafter, in the present specification, the “fiber mixed mat-like molded product” may be simply referred to as “nonwoven fabric”.

  There are various methods for producing a fiber-mixed mat-shaped molded body from short fibers. For example, a method for producing a fiber-mixed mat-shaped molded body by a dry method includes passing a fiber between rolls with needles and irregularities. For example, there are a card method in which a sheet is beaten and defibrated to form a sheet, or an air lay method in which fibers are floated and defibrated in an air current and then sucked onto a screen to form a sheet. Specific examples include a spun bond method, a needle punch method, a thermal bond method, a resin bond method, a chemical bond method, and a melt blow method.

  In addition, as a preparation method by a wet method, fibers are dispersed in a solvent, defibrated using a device such as a beater or a pulper used in the paper industry, then drawn on a net, and the attached solvent is dried. There is a so-called wet papermaking method in which it is removed to form a sheet.

  In the production of the fiber-mixed paper mat-like molded body by the wet papermaking method, water is preferably used as a solvent for uniformly dispersing the short carbon fibers. Since carbon short fibers are normally dispersible by the sizing agent present on the surface of the carbon fibers, a thickening / dispersing agent such as sodium cellulose glycolate, polyvinyl alcohol, or hydroxycellulose is generally used. However, when it is formed into a fiber-mixed mat-like molded article, it becomes an impurity having poor compatibility and thermal stability and tends to cause deterioration in physical properties. In addition, since this thickening / dispersing agent is a water-soluble material, it is inferior in hygroscopicity, and it may be difficult to maintain its shape by re-dissolution by contact with moisture. In addition, in the wet process, breakage is generally likely to occur, and when a fiber-mixed mat-like molded body is formed, a fine carbon fiber powder with a small reinforcing effect is carried, which may contribute to an increase in weight.

  On the other hand, in the case of the dry process, it is not necessary to introduce unnecessary materials such as a thickener, and since air is used for mixing, the fiber length can be easily maintained (breakage reduction) compared to the wet process. Furthermore, the drying process can be omitted, and no waste water treatment is required. From these things, it is preferable that the nonwoven fabric of this invention is produced with a dry process.

  For example, carbon short fibers and thermoplastic resin fibers are preliminarily stored in, for example, a bag or a container, and lightly stirred up and down, left and right for about 1 minute, and then a Henschel mixer, a twin-screw mixing stirrer After pre-mixing, etc., in a device using a dry mixer such as an airlaid device, the fiber is stirred with an air stream, then stirred and mixed by hitting with a rotating bar, etc. It is preferable to form a non-woven fabric by suction lamination on the belt from below the belt.

The basis weight, that is, the fiber weight per unit area (Fiber Areal Weight, hereinafter may be referred to as FAW) in the fiber-mixed mat-shaped molded body of the present invention is preferably 250 to 2000 g / m ² , and 500 to 1500 g / m ^2. It is more preferable that Those having a small FAW are difficult to handle due to insufficient strength of the fiber-mixed mat-like molded product itself, and in order to obtain a molded product having a desired thickness, a nonwoven fabric and / or a carbon fiber reinforced resin sheet is formed in the molding process described later. It is necessary to increase the number of stacked layers, and the manufacturing process becomes complicated. On the other hand, when the FAW is too large, the thickness after molding becomes thick and it is difficult to mold a thin material, and the thickness fluctuation is large.

{Content ratio of carbon fiber and thermoplastic resin fiber}
In the fiber-mixed mat-shaped molded body of the present invention, the ratio of the short carbon fibers to the total of the short carbon fibers and the short thermoplastic resin fibers is 85 wt% or less, particularly 15 to 75 wt%, particularly 45 to 70 wt%. preferable. That is, a / (a + b) is preferably 0.85 or less, particularly 0.15 to 0, where a is the weight of short carbon fibers in the fiber-mixed mat-like molded body and b is the weight of thermoplastic short fibers. .75, especially 0.45 to 0.7 is desirable.

  If the carbon short fiber content in the fiber-mixed mat-like molded product is excessively low, the physical properties of the resulting molded product may deteriorate, and the desired thermal conductivity and flexural modulus may not be achieved. On the other hand, if the carbon short fiber content is excessively high, it is necessary to increase the pressure during molding, which is not practical.

[Method for producing fiber-reinforced molded product from fiber-mixed mat-like molded product]
A fiber-reinforced molded body is manufactured by press-molding the above-mentioned fiber-mixed mat-shaped molded body at a temperature higher than the flow start temperature (Tf) of the short fibers of the thermoplastic resin in the mixed-paper mat-shaped molded body.

  The temperature at the time of press molding is preferably 10 to 100 ° C., particularly about 20 to 50 ° C. higher than the flow start temperature Tf. The pressure at the time of press molding is preferably about 1 to 20 MPa, particularly about 3 to 10 MPa, and the pressing time is preferably about 1 to 30 minutes, particularly about 3 to 20 minutes. In this press molding, only one layer may be pressed without stacking the fiber-mixed mat-shaped molded body, or two or more layers may be stacked and multilayer press-molded. According to this multilayer press molding, a fiber-reinforced molded body having a large thickness can be produced.

This fiber-reinforced resin molded body preferably has a thickness of 0.2 to 10 mm. Further, the bulk density is preferably 1.8 g / cm ³ or less, the in-plane bending elastic modulus measured by JIS K7074 under a load cell of 100 kN and a crosshead speed of 2 mm / min is 20 GPa or more, and the bending strength is The thermal conductivity in the in-plane direction is 20 W / mK or more, and the linear expansion coefficient in the in-plane direction is 3 × 10 ⁻⁶ / ° C. or less.

  The bulk density of the molded body is calculated by measuring the dimensions and weight of the molded body, calculating the volume from the measured dimensions, and then dividing the measured weight value by the calculated volume value. The bending elastic modulus, thermal conductivity, and linear expansion coefficient in the in-plane direction of the molded body are all measured by the methods described in the Examples section described later.

  When the bending elastic modulus in the in-plane direction of the molded body of the present invention is less than 20 GPa, it is difficult to apply the high-rigidity member such as metal, which is the object of the present invention, to the substitute. Therefore, the bending elastic modulus of the molded body is preferably 20 GPa or more as described above, more preferably 30 GPa or more, and further preferably 40 GPa or more. The upper limit of the flexural modulus is not particularly specified, but is usually about 100 GPa when considering the cost for improving the flexural modulus.

  If the thermal conductivity in the in-plane direction of the molded body of the present invention is less than 20 W / mK, it is unsuitable for replacement of a high thermal conductivity member such as metal, which is the object of the present invention. Accordingly, the thermal conductivity of the molded body is 20 W / mK or more, preferably 30 W / mK or more. The upper limit of the thermal conductivity is not particularly specified, but is usually about 100 W / mK when the cost for improving the thermal conductivity is taken into consideration.

The linear expansion coefficient in the in-plane direction of the molded body of the present invention is not particularly specified, but as a member having excellent dimensional stability as long as it falls below the standard around 1 × 10 ⁻⁵ / ° C. with a metal or ceramic material. Be utilized. In the molded product of the present invention, the linear expansion coefficient can be further reduced as compared with the above value, and the absolute value is 5 × 10 ⁻⁶ / ° C. or less, further 3 × 10 ⁻⁶ / ° C. or less. Can also be realized. The lower limit of the linear expansion coefficient is not particularly specified, but when considering the cost for reducing the linear expansion coefficient, the absolute value is about 1 × 10 ⁻⁷ / ° C.

  The fiber-mixed mat-like molded body of the present invention is isotropic in the in-plane direction of the molded body (this in-plane direction is the nonwoven fabric surface direction of the nonwoven fabric contained in the molded body). That is, when the flexural modulus, thermal conductivity, and linear expansion coefficient of this molded product were measured, the difference in the average value for each direction of the measured values was within 15% regardless of the direction in the in-plane direction. It is. In order to accurately grasp this isotropic property, it is necessary to evaluate each characteristic value with respect to 360 ° in all directions in the in-plane direction of the molded body. By comparing the measured value for and the measured value in the direction orthogonal to this direction, it is possible to evaluate the rough isotropic property.

  The fiber reinforced resin molded product of the present invention is so isotropic in the in-plane direction that the nonwoven fabric of the present invention in which carbon short fibers and thermoplastic resin short fibers are randomly dispersed is used. by.

Examples and Comparative Examples will be described below, but the present invention is not limited by these.
First, the fiber length, bending characteristics, and thermal conductivity measuring methods employed in the examples and comparative examples will be described.

(1) Fiber length measurement The number average fiber length and the weight average fiber length of carbon fibers are obtained by dissolving a resin mixed mat-shaped molded article or compound pellet (in the case of Comparative Example 4) with a solvent using a solvent. It measured by observing with an optical microscope, after moving on a white sheet and making it dry. At this time, the remaining resin material is not observed by the white sheet, and as a result, only black fibers made of carbon fibers are observed. 1,000 carbon fibers were selected at random, and the fiber length was measured and then identified by making a histogram.

(2) Measurement of crystal melting temperature (Tm) and flow start temperature Using Pyris1 DSC manufactured by PerkinElmer Co., Ltd., 10 mg of resin fiber used was increased to 200 ° C. at a heating rate of 10 ° C./min according to JIS K7121. After heating and holding at 200 ° C. for 5 minutes, the crystal melting temperature Tm (° C.) was determined from the thermogram measured when the temperature was lowered to room temperature at a cooling rate of 10 ° C./min.
Moreover, the flow start temperature of the resin fiber in the present invention was measured using a flow tester (CFT-500C, manufactured by Shimadzu Corporation) with a nozzle size of φ1 × L2 mm, a temperature increase rate of 3 ° C./min, and a load of 40 kgf. As an evaluation method, the following judgment was performed from the measurement results of the crystal melting temperature and the flow start temperature.
○: Crystal melting temperature or flow start temperature is 200 ° C. or less ×: Crystal melting temperature or flow start temperature exceeds 200 ° C.

(3) Bending properties The bending strength and flexural modulus of the molded body in the present invention are obtained by using a universal material testing machine (UH-10, manufactured by Shimadzu Corporation), and a plate-shaped molded body having a thickness of 2 mm with the continuous fiber arrangement direction as the longitudinal direction. After the production, it was produced by cutting out to a length of 100 mm and a width of 15 mm in the random direction of the plane. The measuring method was measured according to JIS-K7074 with a load cell of 100 kN and a crosshead speed of 2 mm / min.

(4) Thermal conductivity The thermal conductivity measurement of the molded body in the present invention is to produce a 10 mm thick plate by bonding 4-5 sheets of 2 mm and 3 mm thick plates and bonding them, and from that as a measurement sample A cylindrical test piece having a diameter of 10 mm and a thickness of 2 mm having a thickness of 10 mm was prepared and measured. The thermal conductivity was measured using a laser flash method thermal constant measuring device (TC3000) manufactured by Vacuum Riko in accordance with JIS R1611.

[Example 1]
Pitch-based carbon fiber (trade name “DIALEAD (registered trademark) 6371T”, manufactured by Mitsubishi Plastics, Inc., average fiber diameter 11 μm, tensile modulus 640 GPa, thermal conductivity 140 W / mK in the fiber axis direction, 6 mm cut fiber) 60 As a thermoplastic resin fiber, 40% by weight of core / sheath polyester fiber (trade name “Melty 4080”, manufactured by Unitika Fiber, core component flow start temperature 250 ° C., sheath component crystal melting temperature 130 ° C., 5 mm cut fiber) is used. It was. These fibers are introduced into the paper bag, and the paper bag is lightly shaken up and down and stirred for about 1 minute, and then premixed, and then rotated at 100 rpm using a biaxial full flight type side screw feed device (manufactured by Labotech Engineering). The mixture was further mixed and opened to obtain a fiber mixture. Thereafter, the fiber mixture was obtained using a mat former II manufactured by Ikegami Kikai Co., Ltd. to obtain a fiber mixture having a basis weight of 1000 g / m ² . This fiber mixed body was heated at 180 ° C. with an electrothermal air heat-through device and thermally bonded to obtain a fiber mixed mat-like formed body. The evaluation results of this fiber mixed mat-like molded product are shown in Table 1.

  In addition, a two-mm thick press-molded body (fiber reinforced molded body) is manufactured by laminating two of these fiber-mixed mat-shaped molded bodies and melt-press-molding them at a temperature of 270 ° C., a pressure of 5 MPa, and a pressure holding time of 5 minutes. did. The evaluation results of this press-formed product are also shown in Table 1.

[Example 2]
Example 1 except that a core-sheath nylon fiber (trade name “Unimelt UL80”, manufactured by Unitika Fiber, core component flow start temperature 254 ° C., sheath component crystal melting temperature 140 ° C., 5 mm cut fiber) was used as the resin fiber. Under these conditions, a fiber-mixed mat-like molded product and a press-formed product were produced. Table 1 shows the evaluation results of this fiber-mixed mat-like molded product and press-formed product.

[Example 3]
Except for using resin fibers produced by spinning polycarbonate resin (trade name “Iupilon® M7020AD2” manufactured by Mitsubishi Engineering Plastics Co., Ltd., flow start temperature 188 ° C.) as a resin fiber by a melt spinning method. A fiber-mixed mat-like molded body and a press-molded body were produced under the same conditions as in Example 1. Table 1 shows the evaluation results of this fiber-mixed mat-like molded product and press-formed product.

[Example 4]
Example 1 except that a polypropylene resin (trade name “NOVATEC PP FY6C”, manufactured by Nippon Polypro Co., Ltd., flow start temperature: 168 ° C.) was used as a resin fiber produced by spinning by a melt spinning method. A fiber-mixed mat-like molded body and a press-molded body were produced under the same conditions. Table 1 shows the evaluation results of this fiber-mixed mat-like molded product and press-formed product.

[Comparative Example 1]
The same “Dialead (registered trademark) 6371T” used in Example 1 as pitch-based carbon fiber, 60% by weight of 6 mm cut fiber, and polyester fiber (trade name “Tetron (registered trademark) TA04N) as the thermoplastic resin fiber. 40% by weight of Teijin Fibers Ltd., flow start temperature 254 ° C., 5 mm cut fiber). These two types of fibers are introduced into a paper bag, premixed in the same manner as in Example 1, and further mixed and opened at a rotational speed of 100 rpm using the same biaxial full flight side screw feed device as described above. A fiber mixture was obtained. Thereafter, the fiber mixture was obtained using a mat former II manufactured by Ikegami Kikai Co., Ltd. to obtain a fiber mixture having a basis weight of 1000 g / m ² . This fiber mixture was heated at 180 ° C. with an electrothermal air heat-through device to perform thermal bonding. However, since the resin fiber has a high flow start temperature, a mat-like molded product can be obtained without bonding the resin fibers. could not.

[Comparative Example 2]
Using the same fibers as in Example 1, only carbon fibers are first opened at 100 rpm with a biaxial full flight screw feed device, then resin fibers are introduced, and fibers are further opened and mixed at 100 rpm. A mixture was obtained. Thereafter, the fiber mixture was made into a mixed paper mat-shaped molded body having a basis weight of 1000 g / m ² using a mat former II manufactured by Ikegami Kikai. The evaluation results of this mixed paper mat-like molded body are shown in Table 1. As shown in Table 1, in this fiber-mixed mat-like molded body, the weight average fiber length is 2.8 mm, which is smaller than 3 mm.

  Further, two of the mixed mat-like molded bodies were laminated and melt-press molded at a temperature of 270 ° C., a pressure of 5 MPa, and a pressure holding time of 5 minutes to prepare a press molded body having a thickness of 2 mm. The evaluation results of this molded body are also shown in Table 1.

[Comparative Example 3]
Using the same material as in Example 1, the paper was mixed using a Ford linear wet papermaking machine to produce a mat-like molded body. A press-molded body was produced from this mat-shaped molded body under the same conditions as in Example 1. Table 1 shows the evaluation results of the mat-like molded product and the press-formed product. As shown in Table 1, the fiber-mixed mat-like molded body has a weight average fiber length of 0.25 mm, which is smaller than 3 mm.

[Comparative Example 3]
A mixed mat-like molded body and a press-molded body were produced under the same conditions as in Comparative Example 1 except that the same resin fibers as in Example 3 were used as the resin fibers. Table 1 shows the evaluation results of the mat-like molded product and the press-formed product.

[Comparative Example 4]
Using the same DIALEAD (registered trademark) 6371T 60 parts by weight as the pitch-based carbon fiber used in Example 1, polycarbonate resin (trade name “Iupilon S2000”, manufactured by Mitsubishi Engineering Plastics Co., Ltd., started flow) 40 parts by weight were used. These were supplied to a twin-screw kneading extruder (manufactured by Labotech Engineering) having the same direction of 26 mm, and kneaded at a cylinder temperature of 260 ° C. with a full flight screw to produce compound pellets. Various test pieces were produced by injection molding of the compound pellets using an injection molding machine, and evaluation was performed. The evaluation results are shown in Table 1.

[Comparative Example 5]
PAN-based carbon fiber (trade name “Pyrofil (registered trademark) TR50S”, manufactured by Mitsubishi Rayon Co., Ltd., average fiber diameter 7 μm, tensile elastic modulus 230 GPa, thermal conductivity 10 W / mK in the fiber axis direction, 6 mm cut fiber as carbon fiber The mixed fiber mat-like molded body and press-molded body were produced under the same conditions as in Example 1 except that the above was changed. Table 1 shows the evaluation results of this fiber-mixed mat-like molded product and press-formed product.

  From Table 1, all of the fiber-mixed mat-like molded bodies of Examples 1 to 4 have a weight average fiber length of carbon fibers of 3 mm or more. This short carbon fiber has a fiber length of 3 mm ± 1 mm and 50 wt% or more. The number average fiber length is 1 mm or more. Any of the fiber reinforced molded products using such a fiber-mixed mat-shaped molded product has a bending elastic modulus of 20 GPa or more, a bending strength of 100 MPa or more, and a thermal conductivity of 20 W / m · K or more. On the other hand, in Comparative Example 1, the mixed paper mat-like molded body itself could not be obtained. In the mixed mat-like molded articles of Comparative Examples 2 to 4, the carbon fibers had a weight average fiber length outside the range defined by the present invention, and the properties of the molded fiber reinforced molded articles were insufficient. Further, in Comparative Example 5 using PAN-based carbon fibers, the properties of the fiber-reinforced molded body were similarly insufficient.

Claims (15)

  In a fiber-mixed mat-like molded article comprising short fibers of pitch-based carbon fibers and short fibers of thermoplastic resin fibers, the carbon fibers have a tensile elastic modulus in the fiber axis direction of 400 GPa or more, and the thermal conductivity in the fiber axis direction. A fiber-mixed mat-like shaped product having a weight average fiber length of 3 mm or more.   The number average fiber length of the carbon fibers is 1 mm or more.   The fiber-mixed mat molded article according to claim 1 or 2, wherein the carbon fiber content is 15 to 75 wt%, and the thermoplastic resin fiber content is 85 to 25 wt%.   The fiber-mixed mat-like molded article according to any one of claims 1 to 3, wherein the carbon fiber has a fiber length distribution of 50 wt% or more within a weight average fiber length ± 1 mm.   The fiber-mixed mat-like molded article according to any one of claims 1 to 4, wherein the short fibers of carbon fibers and the short fibers of thermoplastic resin are in a two-dimensional random dispersion state.   The fiber-mixed mat-like molded article according to any one of claims 1 to 4, wherein the resin fiber is made of a thermoplastic resin having a crystal melting temperature (Tm) or a flow start temperature of 200 ° C or lower.   The fiber-mixed mat-shaped molded body according to any one of claims 1 to 6, wherein the fiber-mixed mat-shaped molded body is produced by a dry method.   The resin fiber is a composite fiber of two or more kinds of resins, and a resin fiber in which a thermoplastic resin having a crystal melting temperature (Tm) or a flow start temperature of 200 ° C. or less exists at least outside the resin fiber is used. The fiber-mixed mat-shaped molded article according to any one of claims 1 to 4, characterized in that it is characterized in that: Fiber mixed mats shaped molded body according to any one of claims 1 to 8 basis weight of fiber mixed mats shaped molded body is a ^{250g / m 2 ~1500g / m 2} . Fiber mixed mats shaped molded body according to any one of claims 1-9 basis weight of fiber mixed mats shaped molded body is a ^{500g / m 2 ~1200g / m 2} .   The fiber-mixed mat-shaped molded body according to any one of claims 1 to 10, wherein the resin fibers in the fiber-mixed mat-shaped molded body or resin fibers and carbon fibers are melt-bonded.   A fiber-reinforced molded body obtained by press-molding the fiber-mixed mat-shaped molded body according to any one of claims 1 to 10 at a temperature higher than a flow start temperature of a thermoplastic resin fiber in the fiber-mixed mat-shaped molded body.   A laminate obtained by laminating a plurality of the fiber-mixed mat-shaped molded bodies according to any one of claims 1 to 12 at a temperature higher than the flow start temperature of the thermoplastic resin fibers in the fiber-mixed mat-shaped molded bodies. A fiber-reinforced molded product formed by press molding.   The fiber-reinforced molded body according to claim 12 or 13, wherein the thermal conductivity in the in-plane direction of the fiber-reinforced molded body is 20 W / mK or more.   The thickness of the fiber reinforced molded product is 0.2 to 10 mm, the bending elastic modulus in the in-plane direction measured by JIS K7074 under a load cell of 100 kN and a crosshead speed of 2 mm / min is 20 GPa or more, and the bending strength is 100 MPa. It is the above, The fiber reinforcement molded object of any one of Claims 12-14.