JP2014145048A - Carbon fiber reinforced thermoplastic resin prepreg sheet or molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a molded article high in strength and elastic modulus, further high in dimensional accuracy and dimensional stability from a long fiber reinforced thermoplastic resin composite material.SOLUTION: There is provided a carbon fiber reinforced thermoplastic resin prepreg sheet or a molded article containing a thermoplastic resin of 25 to 50 mass% and a carbon fiber having a length of 7.5 mm to 100 mm of 50 to 75v mass%, and having linear expansion coefficients in optional orthogonal two directions in-plane each in the range of -0.5×10to 0.5×10cm/cm/K.

Description

  The present invention relates to a prepreg sheet or molded article made of a carbon fiber reinforced thermoplastic resin. Specifically, the strength and elastic modulus are very high, the linear expansion coefficient in each direction in the molded product surface is isotropic, and its absolute value is very small. It relates to a prepreg sheet or molded product having high dimensional stability.

  In recent years, long fiber reinforced thermoplastic resins developed for structural materials (see, for example, Non-Patent Document 1) have been used as plate-like or beam-like structural materials because of their high strength and rigidity. When used as a structural material, not only high strength and rigidity are required, but also high dimensional accuracy is required against environmental changes such as temperature and humidity. In particular, a molded product used in a plate shape is required to have a small dimensional change in any direction and a small anisotropy of the dimensional change depending on the direction. The long fiber reinforced thermoplastic resin has a very small linear expansion coefficient in the axial direction of the fiber, but the effect of suppressing the linear expansion coefficient of the fiber is not utilized in the direction orthogonal to the longitudinal axis of the fiber. It is common for the linear expansion coefficient to be higher than the linear expansion coefficient. As a result, the difference in linear expansion coefficient between the longitudinal direction of the fiber and the direction orthogonal thereto is very large and exhibits great anisotropy. The dimensional difference due to the anisotropy of the linear expansion coefficient causes a large variation in the dimensions of the molded product, and warping or twisting of the molded product. Also, the tensile effect in the direction perpendicular to the fiber axis does not utilize the reinforcing effect of the fiber, so the strength and rigidity in the direction perpendicular to the fiber axis direction are low, and therefore the mechanical properties of the molded product. Anisotropy is very large, and improvement of reliability as a structural material has been an issue in practical use.

  So far, Japanese Patent Application Laid-Open No. 2004-231697 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2006-291076 (Patent Document 2) have disclosed materials having anisotropy of linear expansion coefficient of 1.0 to 2.5. ing. However, the absolute value of the linear expansion coefficient is not limited to a low value, and the anisotropy of the linear expansion coefficient is not limited to around 1.0, and the disclosed material has high dimensional accuracy for precision parts and It did not match the requirements for dimensional stability. Moreover, the precision which mix | blended Unexamined-Japanese-Patent No. 6-9888 (patent document 3) the glass fiber of average length 0.05-13mm, the carbon fiber of average length 0.05mm-15mm, and potassium titanate of average length 5-120micrometer. A molding composition is disclosed. However, this composition did not meet the purpose of the present invention, because there was a great difference in the anisotropy of the linear expansion coefficient and the required value of the absolute value. Japanese Unexamined Patent Application Publication No. 2009-149823 (Patent Document 4) discloses a composition in which 0.5 to 20% by weight of carbon fiber is blended with a polypropylene resin. However, there is still a great difference from the aim of the present invention in the level of strength, dimensional accuracy and dimensional stability, and it was not used for precision members.

  Further, as disclosed in JP 2010-18724 A (Patent Document 5), a nonwoven fabric-like reinforcing fiber having a small anisotropy is used as the reinforcing fiber, and the distance is such that the reinforcing fiber is cut and the mold is transferred. It is disclosed that a prepreg sheet is produced by impregnating a resin into a randomly arranged chopped strand mat as disclosed in Japanese Patent Application Laid-Open No. 2007-262360 (Patent Document 6). In order to obtain a composite effect, high impregnation is necessary, but impregnation becomes difficult when the fiber content becomes high, so a molded product with high fiber content cannot be obtained, and the high strength targeted by the present invention No molded product was obtained. Further, since the fiber reinforcing effect of the obtained composite material is small, it is insufficient to suppress the large thermal expansion of the resin, and the strength and the elastic modulus are not sufficiently met with the requirements as a structural material. In addition, in order to obtain an isotropic composite material, it has been disclosed that the length of the fiber is shortened so that the fiber is not easily oriented by flow resistance, but if the fiber is short, a reinforcing effect cannot be obtained and physical properties are required. It was not achieved. Further, as disclosed in JP-A-2005-324340 (Patent Document 7), it has been disclosed to combine a discontinuous fiber reinforced layer that flows and a continuous fiber reinforced layer that hardly flows. However, since the continuous fiber layer does not flow in the direction perpendicular to the fiber axis, the molded product may be thinned, or the discontinuous fiber reinforced layer that has flowed in may have defects that do not meet the requirements in terms of strength. It was easy and there was a problem in quality in cases other than special molded products, and it was not common.

As in International Publication No. WO2007 / 20910 (Patent Document 8), tapes obtained by orienting long fibers in the length direction and impregnated are cut into strips, laminated randomly, and anisotropic. A method for producing a small sheet-shaped preform was proposed. Prior to re-molding, the fiber orientation was dispersed in a pseudo-random state, so that a molded product with low anisotropy can be obtained by reducing the area ratio between the prepreg and the re-molded product. However, because it shows a dimensional change corresponding to the linear expansion coefficient with respect to changes in the operating environment temperature, internal stress is likely to appear at the dimensional change and interface, and in precision parts for applications where the operating environment changes greatly, There are many cases where dimensional accuracy and shape accuracy due to dimensional change differences are problematic and cannot be applied. Japanese Unexamined Patent Application Publication No. 2011-189747 (Patent Document 9) discloses that physical properties such as a linear expansion coefficient are made isotropic by combining reinforcing fibers having different length distributions. A short fiber aims at the effect that it is hard to orient by flow. However, as is well known in the art for short fiber reinforced thermoplastic resins for injection molding, a prepreg made of reinforcing fibers having a length / fiber diameter of 100 or more that can provide a fiber reinforcing effect was flowed. In this case, it is still susceptible to flow resistance, the fibers are oriented, and even if the length of the fibers is short, the effect of disturbance of orientation due to flow is very small. It was insufficient. Further, as disclosed in Japanese Patent Application Laid-Open No. 2011-11362 (Patent Document 10), it is possible to arrange a plurality of unidirectionally oriented fibers and arrange them orthogonally, for example, to maintain pseudo-isotropicity. It is disclosed. However, in this case, the resin reinforced with fiber in the axial direction of the fiber hardly flows, the transferability of the mold is poor, and it is difficult to apply to a molded product having a large projected area.
On the other hand, thermoplastic composites reinforced with long fibers have high strength and rigidity per unit weight, so there is a strong desire in the market to use for automobile weight reduction, isotropic and high fluidity, Even when molding is possible with a molding machine having a small capacity, and there is a great change in usage environment, there has been a strong demand for development of a structural material with small dimensional change and internal stress and a molding method for obtaining the structural material.

Japanese Patent Laid-Open No. 2004-231697 JP 2006-291076 A JP-A-6-9888 JP 2009-149823 A JP 2010-18724 A JP 2007-262360 A JP 2005-324340 A International Publication No. WO2007 / 20910 JP 2011-189747 A JP 2011-11362 A

Industrial materials, 37 (1), 53-57 (1989)

  The aim of the present invention is to be used as a plate-like or beam-like structural material that requires dimensional stability, has high strength and rigidity, has little dimensional change with respect to environmental changes such as temperature, and depends on the direction. It is to provide a composite material with small dimensional change anisotropy and high dimensional accuracy.

As a result of intensive studies to obtain a molded product having high strength and rigidity, high dimensional accuracy and dimensional stability, regardless of the deformation direction and location, the present inventors have obtained the following results in the long fiber reinforced thermoplastic resin composite material. It has been found that the above-mentioned problems can be solved by the means shown in the above, and the present invention has been achieved.
That is, this invention consists of the following structures.
1. A prepreg sheet or molded product containing 25 to 50% by mass of a thermoplastic resin and 50 to 75% by mass of carbon fibers having a length of 7.5 to 100 mm, and is orthogonal to each other in the plane of the prepreg sheet or molded product Carbon fiber reinforced thermoplastic resin prepreg sheet or molded product characterized in that linear expansion coefficients in both directions are in the range of −0.5 × 10 ^{−5 to} 0.5 × 10 ⁻⁵ cm / cm / K. .
2. In the cross section (1 mm × 1 mm) in the thickness direction of the prepreg sheet or molded product, the ellipticity n / m represented by the ratio of the short axis n to the long axis m in the cross section of the carbon fiber is the formula (1), (2) 1. A fiber bundle region containing 100 or more single fibers oriented in different directions respectively satisfying the formula (1) and the formula (3). The carbon fiber reinforced thermoplastic resin prepreg sheet or molded article described in 1.
0.8 ≦ n / m ≦ 1.0 (1)
0.4 ≦ n / m ≦ 0.6 (2)
0.01 ≦ n / m ≦ 0.2 (3)
3. The thermoplastic resin is composed of one or more resins selected from polyolefin resins, polyamide resins, and polyphenylene sulfide resins. Or 2. The described fiber-reinforced thermoplastic resin prepreg sheet or molded article is a preferred embodiment.

  It is not yet clear why the aim of the present invention that achieves both the high fiber reinforcing effect and the contradictory physical properties of dimensional stability has been achieved, but (1) a carbon fiber having a minimal or negative linear expansion coefficient as a reinforcing fiber. (2) The fiber content was very high and the thermoplastic resin fraction was able to be composited in a very low state, (3) The carbon fiber length axis was locally highly oriented and the fiber bundle state (4) The distribution of the length axis of the carbon fiber can be averaged in the thickness axis direction or in the in-plane multiaxial direction, and can be pseudo-randomized. All the conditions will be considered due to the fulfilled effect.

  Since the absolute value of the linear expansion coefficient of the prepreg or molded product of the present invention is very small, the dimensional change due to a change in environmental temperature is extremely small, and the dimensional stability is excellent. Further, since the difference depending on the direction of the linear expansion coefficient is small, the deformation of the molded product and the generation of warp due to the environmental temperature change are extremely suppressed, and the shape stability is excellent. According to the present invention, it is possible to provide a molded product having a stable dimension and shape against environmental temperature changes, and a structural material and a precision industrial part with high dimensional accuracy can be obtained.

  It is a model figure of a molded article sectional photograph. Depending on the orientation of the fiber length axis, the ellipticity of the carbon fiber cross section varies. The aggregated state showing the same ellipticity in the cross section indicates that the carbon fibers form a fiber bundle and the length axis is oriented.

The model figure of the molded article cross-sectional photograph of this invention is shown.

The present invention is described in detail below.
The linear expansion coefficient in the sheet or molded product of the present invention refers to the surface of the molded product that has the maximum area among the projected areas of the plane, elevation, and side surfaces of the sheet or molded product, and is near the center of gravity of the surface. This is represented by a portion having an area of 1 cm ² or more and a uniform thickness, and means the average value of the linear expansion coefficient between 20 ° C. and 120 ° C. for a test piece taken therefrom.
Carbon fiber is used in the present invention. The carbon fiber used in the present invention is not particularly limited, but a carbon fiber having a negative linear expansion coefficient, more preferably a linear expansion coefficient whose absolute value is 1.0 × 10 ⁻⁶ cm / cm / K or less is preferable. . When the linear expansion coefficient of the carbon fiber is positive, it is not preferable because it is combined with the linear expansion coefficient of the resin and the dimensional stability is lowered. The carbon fiber used in the present invention is not particularly limited by its precursor and production method, but after treating fibers such as polyacrylonitrile fiber and cellulose fiber in air at 200 to 300 ° C., in an inert gas Carbon fibers having a tensile strength of 20 t / cm ² or more and a tensile modulus of 200 GPa or more that are calcined and produced by carbonization at 1000 to 3000 ° C. are preferable. The diameter of the single fiber used in the present invention is not particularly limited, but is preferably 3 to 20 μm, particularly preferably 4 to 15 μm, from the production line step of the composite. If it is less than 3 μm, impregnation and defoaming are difficult, and if it exceeds 20 μm, the specific surface area becomes small, and the effect of compounding becomes unfavorable. The carbon fiber used in the present invention is preferably treated for improving adhesion by wet oxidation with air or nitric acid, dry oxidation, heat cleaning, whiskerizing, or the like. Moreover, it is preferable that the carbon fiber used for composite material manufacture of this invention is converged by the sizing agent which softens at 120 degrees C or less from the handleability of a work process. Although there is no restriction | limiting in particular in the number of converging filaments, 1000-30000 filaments, Preferably 5000-25000 filaments are preferable.

  The present invention is a prepreg sheet (preliminary molded article) or molded article containing carbon fibers having a length of 7.5 mm to 100 mm, preferably 25 mm to 75 mm. If the length of the carbon fiber is less than 7.5 mm, the reinforcing effect is small and a high strength cannot be obtained, which is not suitable for the purpose of the present invention. Moreover, when it exceeds 100 mm, the flow resistance in a metal mold | die is high, and it is unpreferable on a shaping | molding. The present invention also relates to a prepreg sheet (preliminary molded article) or molded article containing 50 to 75% by mass, preferably 55 to 70% by mass of carbon fiber. If it is less than 50% by mass, high strength as a structural material cannot be obtained, and this does not meet the object of the present invention. On the other hand, if it exceeds 75% by mass, entanglement between fibers tends to occur with resin flow, and the moldability is lowered, which is not preferable.

In the present invention, in a 1 mm × 1 mm cross section in the thickness direction of a molded product obtained by compression molding, in the carbon fiber cross section, m is the major axis of the fiber cross section, and n is the minor axis, the ellipticity is n / m. Each having a region of 0.8 to 1.0, a region of 0.4 to 0.6, and a region of 0.01 to 0.2, more preferably 100 or more, more preferably It is a preferable embodiment that 200 or more, particularly 500 or more have a fiber bundle region containing adjacent single fibers. A region can also be viewed as a layer. The ellipticity of a single fiber in cross section is a measure of the orientation of the single fiber axis. When the ellipticity is 1, it means that the single fiber is oriented perpendicular to the cross section of the molded product. Further, the smaller the ellipticity is, the substantially less than 0.1 means that the single fibers are oriented parallel to the cross section of the molded product. The case of 0.14 means 45 degrees with respect to the cross section of the molded product, and the case of 0.5 means that it is oriented at 60 degrees with respect to the cross section of the molded product. It is a preferable aspect that a single fiber bundle group in which the length axes of fibers having an ellipticity difference between adjacent single fibers is equal to or less than 10% of the average ellipticity forms a region. If the number of single fibers contained in each region is less than 100, fluidity and rigidity as a fiber bundle are not exhibited, which is not preferable for the present invention. In addition, there is a fiber bundle region in which the ellipticity is greatly different within a cross section of 1 mm × 1 mm in the thickness direction of the molded product. It means to become.
The short axis n of the cross section of the carbon fiber of the present invention is 4 to 10 μm, and preferably 5 to 9 μm. If the thickness is less than 4 μm, the rigidity of the single fiber is low, and the fiber axis tends to be bent, which is not preferable. On the other hand, if it exceeds 10 μm, the strength of the fiber is low, the effect of the present invention is small, and it is not preferable. The reason for this is not clear yet, but the present invention is easily achieved when the periphery of adjacent fiber bundles in which the directions of the fiber axes are aligned is covered with a resin layer. This is considered to be an effect of suppressing the entanglement and cutting of the carbon fiber during the flow during molding. This effect is presumed from the experimental data that the thickness of the resin layer needs to be twice or more the single fiber diameter. On the other hand, in order to obtain high strength and high rigidity, a high fiber fraction and a low resin fraction are required. Therefore, the thickness of the resin layer covering the fiber bundle is 8 to 30 μm, preferably 10 to 20 μm. is there. Therefore, in the present invention, a carbon fiber having a single fiber diameter of 5 to 10 μm is a preferable embodiment for achieving the present invention.

In this invention, 25-50 mass% of thermoplastic resins, Preferably, 30-45 mass% is contained. If it exceeds 50% by mass, the carbon fiber content will be low, and the targeted strength and elastic modulus of the composite structural material will not be achieved. If it is less than 25%, carbon fiber impregnation is insufficient, and the reinforcing effect of the fiber is not exhibited, which is not preferable.
The thermoplastic resin used in the present invention is not particularly limited as long as it has a small linear expansion coefficient, preferably 10 × 10 ⁻⁵ cm / cm / K or less. For example, polypropylene, polymethylpentene, polyamide 6, polyamide 66, polyamide MXD6, polyamide 12, polyamide 11, polyamide 6T copolymer, polyphenylene sulfide, syndiotactic polystyrene, polybutylene terephthalate, polyethylene terephthalate, polyketone and their co-polymers Examples include coalescence and polymer alloy. Among these, preferred are a polyolefin resin such as polypropylene and polymethylpentene containing a crystal part, a polyamide resin such as polyamide 6, polyamide 66, polyamide MXD6, and polyamide 6T copolymer, and a polyphenylene sulfide resin. When the linear expansion coefficient of the thermoplastic resin constituting the matrix is high, the dimensional stability in a certain direction of the composite material is locally lowered, the local dimensional variation is increased, and internal stress is generated, which is not preferable.

  In addition, the thermoplastic resin used in the present invention preferably contains a chemically reactive group or a polar group with an active group on the surface of the carbon fiber in order to enhance the adhesion to the carbon fiber. For example, in the case of polypropylene, polymethylpentene or syndiotactic polystyrene having no polar group, those modified with an unsaturated acid such as maleic anhydride or itaconic acid or an unsaturated epoxy such as glycidyl methacrylate are preferred.

  More specifically, isotactic polypropylene homotype, block type, syndiotactic polypropylene and the like are used as polypropylene. Atactic polypropylene having low crystallinity is not preferable for the present invention because it is inferior in molding processability of the composite material. A block type polypropylene obtained by block copolymerization of other polyolefin such as polyethylene and polybutene with polypropylene is also used in the present invention. In particular, this is a preferred embodiment for structural composite materials that require impact resistance. In the composite material of the present invention, the object of the present invention can also be achieved by further blending unmodified polypropylene. In particular, when the melt flow rate of the maleic anhydride-modified polypropylene used exceeds 100 g / 10 min, the melt flow rate of the mixture is preferably 30 to 120 g / 10 min by blending higher molecular weight unmodified polypropylene. Is preferably adjusted to 40 to 100 g / 10 min. This is an industrially preferred embodiment. The maleic anhydride modification amount is 0.01 to 4% by mass, preferably 0.02 to 3% by mass, based on the total mass of the modified product and the unmodified product. 4: 6 to 0.5: 9.5 is more preferably 2: 8 to 0.7: 9.3. If the ratio of the unmodified product to the modified product is less than 4: 6, the economic effect is small, and if it exceeds 0.5: 9.5, the modified product is insufficient with respect to the interface between the carbon fiber and the polypropylene, resulting in a defect point. Is not preferable.

  The thermoplastic resin used in the present invention preferably has a melt flow rate under a 21.2N load at a temperature 30 ° C. higher than the melting point of 30 to 150 g / 10 min, particularly preferably 50 to 140 g / 10 min. If it is less than 30 g / 10 min, the impregnation property to the fiber is low, and the porosity is high, which is not preferable. Moreover, when it exceeds 150 g / 10min, at the time of the melt processing of a composite material, it is easy to isolate | separate resin and fiber, and is not preferable.

The method for combining the thermoplastic resin and the carbon fiber is not particularly limited. A method of laminating a carbon fiber bundle and a thermoplastic resin film, heating and melting the film to impregnate the carbon fiber bundle, and arranging the opened carbon fiber bundle together on the surface and supplying the molten resin from the die head of the extruder And the method etc. which are made into a prepreg tape or a prepreg strand by carrying out pressure impregnation are illustrated.
Strips and pellets obtained by cutting a prepreg tape or prepreg strand to 7.5 mm to 100 mm are randomly dispersed in a flat plate mold, heated and compressed to form a prepreg sheet. The thermoplastic fiber film is laminated on the chopped strand mat obtained by cutting the carbon fiber bundle to 7.5 mm to 100 mm in advance and randomly dispersing the chopped strands on a flat surface and partially melting the sizing agent. The method of cooling and solidifying after heat compression and impregnation, the method of supplying a thermoplastic resin heated and melted by an extruder or kneader to the chopped strand mat surface, and pressurizing and impregnating to a prepreg sheet, etc. .
A prepreg sheet layer, a prepreg tape, and a prepreg strand may be combined and laminated in a uniaxial direction or a perpendicular direction and a multi-axial layer or a woven layer.

  The prepreg sheet (preliminary molded body) and composite material of the present invention have a structure in which infrared heating or high-frequency heating is performed, the resin is heated and melted, supplied to a mold of a compression molding machine, and is removed after shaping cooling. A material part (molded product) is formed. The molding conditions are not particularly limited. For example, the preform is heated to a melting point or softening point of the parent phase or higher, preferably 30 ° C. or higher, preferably 40 ° C. or higher from the temperature. A preferred embodiment is a method in which the mixture is supplied to a compression mold at a temperature of ℃ or less, preferably 40 ℃ or less, and is cooled and solidified. Also, a preform with a melting point lower than the melting point of the matrix phase is supplied to a mold heated to a temperature higher than the melting point. After the preform is heated by heat transfer from the mold and compression molding is performed, the mold is cooled to below the melting point and molded. Goods can be taken out. In any method, the effect of the present invention is exhibited.

Since the prepreg sheet according to the present invention has isotropic high fluidity, the shape of the blank before molding is not particularly limited, and a high degree of freedom is also one of the features of the present invention. In order to effectively achieve the aim of the present invention, the horizontal projection area of the prepreg sheet is 0.7 to 0.99 times, preferably 0.85 to 0.99 times the horizontal projection area of the target molded product. Is preferred. In particular, 0.90 to 0.99 is preferable. If it is less than 0.7 times, the flow distance in the mold becomes long, and anisotropy may be manifested by orienting the longitudinal direction of the carbon fiber, which is not preferable. On the other hand, if it exceeds 0.99, the molding pressure rises rapidly during molding, and internal homogenization is difficult to proceed. In addition, in a molded product having a rib or boss or a standing surface, it is preferable to add a prepreg sheet in the vicinity thereof.
The thickness of the prepreg sheet is 1 mm to 10 mm, preferably 1.2 to 7 mm. If it is less than 1 mm, the flow resistance is unfavorably large. On the other hand, if it exceeds 10 mm, when preheating is performed before molding, the temperature difference between the inside and the surface layer is large, and the flow tends to be nonuniform, which is not preferable.

  In addition to the above essential components, the prepreg sheet of the present invention has a crystal nucleating agent / mold releasing agent, a lubricant, an antioxidant, a flame retardant, a light resistance agent, a weather resistance, for the purpose of improving physical properties, moldability, and durability. Agents can be added.

  Molded parts obtained from the prepreg sheet (preliminary molded product) or composite material of the present invention can be used for parts that require high strength and rigidity, such as automobile frames, motorcycle frames, agricultural equipment frames, OA equipment frames, and machine parts. Used.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples.

[1] Method for observing ellipticity of single fiber cut surface of molded product cross section Fiber distribution state and fiber axis orientation state of the cross section of molded product are cut out to a size of 10 × 10 mm from the center of the molded product of 300 × 300 × 3 mm Then, the cross section in the thickness direction was set so as to be horizontal, and embedded in an epoxy resin (Epon 812 manufactured by Shell Chemical Co., Ltd.). After the epoxy resin was cured, the upper surface was polished with a rotating grindstone using an APU138 type manufactured by Refine Tech Co., Ltd. to smooth the cross section. Using the digital microscope VH-Z100R type (manufactured by Keyence Corporation), the obtained smooth surface was magnified 400 times by epi-illumination, and the cross section was linearly traced in the thickness direction and photographed. A range in which the single fiber cross-sections have approximately the same ellipticity was sorted, counted as one layer, and counted whether there were 100 or more in one layer. For each layer, the short diameter and long diameter of 100 or more single fibers were measured, the ellipticity (short diameter / long diameter) of each single fiber was determined, and the average was defined as the ellipticity of the fiber bundle. The presence or absence of fiber bundles or the number of fiber bundles (number of layers) corresponding to the average ellipticity in the formulas (1) to (3) were counted.

[2] Linear expansion coefficient measurement About 8 mm in the vertical direction × about 8 mm in the horizontal direction was cut from the center of the prepreg sheet or molded product. Each molded product was polished with sand sand No. 1000 so that both the vertical and horizontal cross sections thereof were parallel to each other, and a test piece for measuring the linear expansion coefficient was obtained.
The cut specimen is stored for 48 hours in a desiccator in a test room whose temperature is adjusted to 23 ° C., and then on a 1 mmφ probe using a thermal physical testing machine TMA manufactured by Rigaku Corporation in accordance with test standard ISO11359-2. A load of 3 g was applied to the sample, cooled to 0 ° C., heated to 120 ° C. at 10 ° C./min, and the probe displacement was measured.
The coefficient of linear expansion was calculated from the displacement between 20 ° C. and 100 ° C. by the following equation: β = (X ₁₂₀ −X ₂₀ ) / (120−20) / L
Here, β: linear expansion coefficient, L: test piece height, X ₁₂₀ : probe position at 120 ° C., X ₂₀ : probe position at 20 ° C.

Example 1
A roving made of 6000 carbon fibers (Toho Tenax Co., Ltd. IMS40) was expanded and opened at a rate of 4 kg / H and supplied to the die head of the impregnation table. Modified polypropylene resin MAH003 (230 ° C, melt flow rate under 21.2N load 50g / 10min) is put into the hopper of a screw-type extruder adjusted to 260 ° C, and the molten resin is weighed 2kg / H with a gear pump. Then, it was supplied to the die head of the impregnation table. After pressure impregnation and defoaming on an impregnation stand, the tape-like prepreg coated with impregnation was extruded from a die having a width of 10 mm and a height of 0.2 mm, air-cooled and solidified, and then wound on a basket. (55% carbon fiber, 45% resin)
The obtained prepreg tape was cut into 35 mm, and the strip-shaped prepreg tape was randomly distributed and supplied into a plate-shaped mold of 300 mm × 300 mm. The mold was heated to 280 ° C., compressed, held for 3 minutes, and then the mold was cooled to a low temperature of 120 ° C. to obtain a prepreg sheet in which carbon fibers were randomly oriented.
A blank of 290 mm × 290 mm was cut from the center of a prepreg sheet having a thickness of 3.1 mm in which reinforcing materials were randomly oriented. This blank is preheated to 250 ° C. with a far-infrared heater in advance, attached to a compression molding machine (manufactured by Shinfuji Metal Industry Co., Ltd., 50 t), and supplied to a mold having a 300 mm × 300 mm cavity whose temperature is adjusted to 150 ° C. And compression molding at 30 MPa for 3 minutes to obtain a 300 × 300 × 3 mm flat plate molded product.
About 10 mm in the vertical direction and about 8 mm in the horizontal direction were cut from the center of each of the 10 flat molded articles obtained by compression molding. The molded product was polished with sandpaper No. 1000 so that both the vertical and horizontal cross-sections of each molded product were parallel to obtain a test piece for evaluating the linear expansion coefficient.
According to the above [1], the ellipticity of the short fibers of the cross section was obtained, and it was confirmed that the fiber bundle of each layer had 100 or more short fibers, and the presence or absence of the corresponding ellipticity and the number of each layer were counted. Further, the linear expansion coefficient was obtained from the displacement between 20 ° C. and 100 ° C. by the following equation according to [2].
The linear expansion coefficients of the two orthogonal directions of the molded product are −0.03 × 10 ⁻⁵ cm / cm / K and −0.04 × 10 ⁻⁵ cm / cm / K, which are close to 0, 20 ° C. and 120 ° C. The dimensions in degrees Celsius were almost unchanged.

Examples 2-7
Composition of the thickness direction of the orientation of the fiber axis on each laminated surface of the molded product obtained by laminating and molding the prepreg thermoplastic resin for the prepreg and the prepreg sheet or prepreg strand (random: surface In Table 1, the fiber axes are randomly oriented, orthogonal: the fibers of the other layer are orthogonal to the fiber axis of one layer, and one direction: the fiber axes of each layer are in the same direction. A prepreg was produced in the same manner as in Example 1 except that the flat molded product was formed. A test piece was cut from a flat molded product in the same manner as in Example 1, and after polishing the surface, the linear expansion coefficient was measured in the same manner as in Example 1 and shown in Table 1.
The linear expansion coefficients in two orthogonal directions in the molded product were all in the range of −0.11 to −0.44 × 10 ⁻⁵ cm / cm / K.

Comparative Examples 1-7
A prepreg tape was obtained in the same manner as in Example 1 except that glass fiber was used as the reinforcing fiber and the fiber fraction was changed. The prepreg tape and the uniaxial, orthogonal or multiaxially oriented product of the reinforcing fiber are combined with the prepreg tape and molded in exactly the same manner as in Example 1 to obtain a flat molded product. Similarly, the linear expansion coefficient is measured, and Table 2 shows Indicated.
In Comparative Examples 1 and 2, when the carbon fiber was changed to glass fiber, the orthogonal linear expansion coefficients both exceeded 0.5 × 10 ⁻⁵ cm / cm / K, and the dimensional change was large. In Comparative Example 3, when the resin fraction was 55% by mass, the linear expansion coefficients were as high as 0.64 × 10 ⁻⁵ cm / cm / K and 0.67 × 10 ⁻⁵ cm / cm / K. Further, in Comparative Example 4, when the resin fraction was 20% by mass, it was −0.60 × 10 ⁻⁵ cm / cm / K or more, indicating a large shrinkage. In Comparative Example 5, in the case of unidirectional lamination, the fiber direction is −0.78 × 10 ⁻⁵ cm / cm / K, and the perpendicular direction is 5.57 × 10 ⁻⁵ cm / cm / K, which is a high positive and negative line. It showed an expansion coefficient and a large anisotropy. In the case of non-strengthening, the linear expansion coefficient was as high as 8 × 10 ⁻⁵ cm / cm / K or more in both orthogonal directions.

Raw materials and symbols used in the experiment:
T802: Polyamide resin PA6 (manufactured by Toyobo Co., Ltd., MFR at 250 ° C. 73 g / 10 min, melting point 227 ° C.)
MAH003: Polypropylene W101 (manufactured by Sumitomo Chemical Co., Ltd.) 98.5 parts by mass, dicumyl peroxide (Nippon Yushi Co., Ltd. Park Mill D) 0.5 parts by mass, powdered maleic anhydride (manufactured by Nacalai Tesque) 2 parts by mass An anhydrous maleate obtained by cooling and solidifying a strand obtained by melting and reacting with a screw at a speed of 80 revolutions / minute by feeding to a hopper of a twin screw extruder whose temperature is adjusted to 190 ° C. Acid-modified polypropylene (MFR 50 g / min), melting point 165 ° C.
EMC700: Polybutylene terephthalate (Toyobo Co., Ltd., MFR 60 g / 10 min at 250 ° C., melting point 225 ° C.)
TS001: Polyphenylene sulfide (manufactured by Toyobo Co., Ltd., MFR 78 g / 10 min at 300 ° C., melting point 284 ° C.)
GF-R: Glass fiber roving (manufactured by Nippon Electric Glass Co., Ltd., AR2500H-103, 31 strands)
CF-R: carbon fiber, Toho Tenax IMS40 manufactured by Teijin Ltd. (single fiber diameter 6.4 μm, 6000 filament)

  According to the present invention, in spite of having high strength and elastic modulus, the in-plane linear expansion coefficient is isotropic, the absolute value is extremely small, and high strength molded product having high dimensional accuracy and dimensional stability against heat. Is provided. Accordingly, it has become possible to convert metal precision mechanical parts and structural members that have not been possible until now.

Claims (3)

A prepreg sheet or molded product containing 25 to 50% by mass of a thermoplastic resin and 50 to 75% by mass of carbon fibers having a length of 7.5 to 100 mm, and is orthogonal to each other in the plane of the prepreg sheet or molded product Carbon fiber reinforced thermoplastic resin prepreg sheet or molded product characterized in that linear expansion coefficients in both directions are in the range of −0.5 × 10 ^{−5 to} 0.5 × 10 ⁻⁵ cm / cm / K. . In the cross section (1 mm × 1 mm) in the thickness direction of the prepreg sheet or molded product, the ellipticity n / m represented by the ratio of the short axis n to the long axis m in the cross section of the carbon fiber is the formula (1), (2) The carbon fiber reinforced thermoplastic resin prepreg sheet according to claim 1, comprising a fiber bundle region containing 100 or more single fibers oriented in different directions respectively satisfying the formula (3) and the formula (3) Molding.
0.8 ≦ n / m ≦ 1.0 (1)
0.4 ≦ n / m ≦ 0.6 (2)
0.01 ≦ n / m ≦ 0.2 (3) The carbon fiber reinforced thermoplastic resin prepreg sheet or molded article according to claim 1 or 2, wherein the thermoplastic resin comprises one or more resins selected from polyolefin resins, polyamide resins, and polyphenylene sulfide resins. .