JP2009062648A - Method for producing chopped fiber bundle, molded material, and fiber reinforced plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing chopped fiber bundles having a good flowability and moldability when using them for a molded material compounded with a matrix resin, and exhibiting an excellent dynamic characteristic when being used for a fiber-reinforced plastic. <P>SOLUTION: This method for producing the chopped fiber bundles obtained by paralleling the reinforcing fibers substantially in one direction, includes continuously traveling a plurality of continuous fiber bundles, widening the fiber bundles so as to have a ratio (W2/W1) of the width W2 of the fiber bundles after the widening to the width W1 of the fiber bundles before the widening within the range of 1.1 to 20 by using widening means arranged at a position in the middle of the travel, and then cutting the plurality of fiber bundles in the widened state simultaneously. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a chopped fiber bundle that, when used as a molding material compounded with a matrix resin, has good fluidity and molding followability and exhibits excellent mechanical properties when used as a fiber reinforced plastic. .

  Fiber reinforced plastic consisting of reinforced fiber and matrix resin is attracting attention in industrial applications because it has high specific properties, high specific modulus, excellent mechanical properties, weather resistance, chemical resistance, etc. The demand is increasing year by year.

  As a molding method of fiber reinforced plastic having high functional properties, a semi-cured intermediate base material impregnated with matrix resin is laminated on continuous reinforcing fiber called prepreg, and heated and pressurized in a high temperature and high pressure kettle. Autoclave molding in which a matrix resin is cured and a fiber reinforced plastic is molded is most commonly performed. In recent years, for the purpose of improving production efficiency, RTM (resin transfer molding) molding in which a continuous fiber base material previously shaped into a member shape is impregnated with a matrix resin and cured has been performed. The fiber reinforced plastics obtained by these molding methods have excellent mechanical properties because they are continuous fibers. In addition, since the continuous fibers are regularly arranged, it is possible to design the required mechanical characteristics by arranging the base material, and there is little variation in the mechanical characteristics. However, on the other hand, it is difficult to form a complicated shape such as a three-dimensional shape because it is a continuous fiber, and it is mainly limited to members close to a planar shape.

  As a molding method suitable for a complicated shape such as a three-dimensional shape, there is a molding using an SMC (sheet molding compound) or a stampable sheet. In the SMC molded product, for example, a sheet-like base material (SMC) in which a chopped fiber bundle cut to about 25 mm is impregnated with a matrix resin that is a thermosetting resin and made into a semi-cured state is heated and pressurized using a heating press. Can be obtained. A stampable sheet molded product is obtained by thermoplasticizing a sheet-like base material (stampable sheet) in which a thermoplastic resin is impregnated with a chopped fiber bundle cut to about 25 mm or a nonwoven mat made of continuous reinforcing fibers with an infrared heater. It is obtained by heating above the melting point of the resin, laminating on a mold at a predetermined temperature, and cooling and pressurizing. In many cases, the SMC or stampable sheet is cut smaller than the shape of the molded body before being pressed, placed on the mold, and stretched (flowed) into the shape of the molded body by pressing. Therefore, it is possible to follow a complicated shape such as a three-dimensional shape by the flow. However, in SMC and stampable sheets, uneven distribution and uneven alignment of chopped fiber bundles and nonwoven fabric mats inevitably occur in the sheeting process, so that the mechanical properties are lowered or the variation of the values is increased. End up. Further, due to the uneven distribution and uneven alignment, warpage, sink marks, and the like are likely to occur particularly in thin members.

In order to fill in the defects of the above materials, chopped fiber bundles with a reduced number of reinforcing fibers are applied to SMC, etc., and the entanglement between chopped fiber bundles is increased and densified to suppress crack generation and progress. A base material is disclosed (for example, Patent Document 1). However, in general, reducing the number of reinforcing fibers to be focused has a high cost in the process, and there is a problem that mechanical characteristics are easily lowered due to uneven distribution and uneven orientation.
JP-A-01-163218

  In view of the background of such conventional technology, the present invention does not require a reduction in the number of reinforcing fibers that are a factor of high cost, and when used as a molding material compounded with a matrix resin, has good fluidity. When a fiber reinforced plastic is used, an object of the present invention is to provide a method for efficiently producing a chopped fiber bundle that exhibits excellent mechanical properties.

The present invention employs the following means in order to solve such problems. That is,
(1) In a method for producing a chopped fiber bundle in which reinforcing fibers are substantially aligned in one direction, a plurality of continuous fiber bundles are continuously run and widened by a widening means disposed in the middle of the run. A plurality of fibers in a widened state after widening the fiber bundle so that the ratio (W2 / W1) of the width W1 of the previous fiber bundle and the width W2 of the fiber bundle after widening is in the range of 1.1 to 20. A method for producing a chopped fiber bundle, wherein the fiber bundle is simultaneously cut.

  (2) Furthermore, the ratio (W1 / t1) between the width W1 and the thickness t1 of the fiber bundle before widening is within a range of 10 to 200, and the ratio (W2 / t2) between the width W2 and the thickness t2 of the fiber bundle after widening. ) Is in the range of 70 to 1000, the method for producing a chopped fiber bundle according to (1).

  (3) The chopped fiber according to (1) or (2), wherein a sizing agent is attached to the reinforcing fiber, and the sizing adhesion amount is 0.3 to 3 parts by weight with respect to 100 parts by weight of the reinforcing fiber. A method of manufacturing a bundle.

  (4) The fiber length of the fiber bundle is in the range of 10 to 100 mm, and the moisture content is 0 to 5 parts by weight with respect to 100 parts by weight of the reinforcing fiber. The manufacturing method of the chopped fiber bundle of description.

  (5) Manufacture of the chopped fiber bundle according to any one of (1) to (4), which is cut with a cut end length of (1.1 to 30) × W2 with respect to the width W2 of the fiber bundle after widening. Method.

  (6) The method for producing a chopped fiber bundle according to any one of (1) to (5), wherein the fiber bundle is linearly cut at an angle of 2 to 30 ° with respect to the traveling direction of the continuous fiber bundle. .

  (7) A method for producing a molding material, wherein the chopped fiber bundle obtained by the production method according to any one of (1) to (6) is dispersed and integrated into a sheet shape.

  (8) The chopped fiber bundle is spread on a sheet-like matrix resin, and then sandwiched by another sheet-like matrix resin, so that the chopped fiber bundle and the matrix resin are integrated into a sheet shape. Method for producing molding material.

  (9) The method for producing a molding material according to (7) or (8), wherein the chopped fiber bundle in the molding material has a ratio of the width W3 to the thickness t3 (W3 / t3) in the range of 70 to 1000.

  (10) The molding material obtained by the manufacturing method according to any one of (7) to (9) is disposed in the cavity in a state where the molding area is smaller than the projected area of the cavity of the molding die and thicker than the cavity thickness. A method for producing a fiber reinforced plastic, wherein the molding material is clamped and the molding material is pressurized to stretch the molding material and fill the cavity with the molding material.

  (11) The ratio (W3 / t3) of the width W3 and the thickness t3 of the chopped fiber bundle in the molding material before pressing is in the range of 70 to 1000, and the width W4 and the thickness of the chopped fiber bundle in the molding material after pressing. The method for producing a fiber-reinforced plastic according to (10), wherein a ratio (W4 / t4) to t4 is in a range of 75 to 1500, and W4 is larger than W3.

  According to the present invention, when used as a molding compound compounded with a matrix resin, a chopped fiber bundle having good fluidity and exhibiting excellent mechanical properties when used as a fiber reinforced plastic is obtained. It can be obtained efficiently. Furthermore, in order to obtain a chopped fiber bundle in a state where the continuous fiber bundle is widened in the present invention, the thickness of the obtained chopped fiber bundle is reduced, and as a result, the molding material using the chopped fiber bundle is excellent in fluidity, Fiber reinforced plastics have excellent mechanical properties.

  The inventors of the present invention have a manufacturing method for obtaining a fiber-reinforced plastic that can follow the above-described problem, that is, a complicated shape such as a three-dimensional shape, has excellent mechanical properties, and has small variations in mechanical properties. As a result of intensive studies, the inventors have found that the chopped fiber bundle obtained by a specific manufacturing method is used as a reinforced fiber of fiber reinforced plastic to solve such problems all at once. In the present specification, unless otherwise specified, in the term including fiber or fiber (for example, “fiber direction” or the like), the fiber represents a reinforcing fiber. Further, in this specification, the continuous fiber bundle refers to a fiber bundle in which a plurality of reinforcing fibers having a fiber length of 100 mm or more are bundled.

  The method for manufacturing a chopped fiber bundle of the present invention is a method for manufacturing a chopped fiber bundle in which reinforcing fibers are substantially aligned in one direction. With the widening means arranged, the fiber bundle is widened so that the ratio (W2 / W1) of the width W1 of the fiber bundle before widening and the width W2 of the fiber bundle after widening is within the range of 1.1-20. Then, a plurality of fiber bundles in a widened state are cut simultaneously. Here, “substantially unidirectional” means that when a part of the fiber bundle is focused, 90% or more of the single fibers existing within a radius of 5 mm are part of the fibers with the fiber bundle. It means that it is oriented within ± 10 ° from the orientation direction.

  In the present invention, first, it is necessary to continuously run a plurality of continuous fiber bundles. Running continuously means moving a continuous fiber bundle in a certain direction by tension or the like, and is an operation necessary for continuous production. Furthermore, productivity is further improved by running a plurality of fiber bundles continuously at the same time. In order to run continuously, a continuous fiber bundle is wound around a bobbin, a plurality of sets are set on a creel stand or the like so that the yarn can be fed out, and at the same time, one side of the continuous fiber bundle is a roller-shaped widening jig, It is necessary to apply tension by a dancer roller, a nip roller, or the like, or move the fiber bundle by applying a tensile driving force to the fiber bundle with a frictional chuck or the like.

  Next, the ratio (W2 / W1) of the width W1 of the fiber bundle before the widening and the width W2 of the fiber bundle after the widening of the continuous fiber bundle before the cutting process by the widening means arranged in the middle of the travel. Widen to be within the range of 1.1-20. Among these, the range of 1.5 to 10 is preferable from the viewpoint of processability. The widening means is not particularly limited, and a known method such as a roller, vibration, or air can be used. Among them, the most preferable widening means is a rotatable cylindrical roller. When a continuous fiber bundle with tension acts on the convex surface of the roller, a force acts in the thickness direction of the fiber bundle, and the fiber bundle spreads horizontally (collapses) and at the same time the roller can rotate. This is because local wear is eliminated, and continuous operation for a long time is possible. Further, yarn breakage can be suppressed.

  Other widening means include a technique for expanding the width of one fiber bundle while vibrating the widening jig (for example, Japanese Patent Laid-Open No. 01-280040), and water jet or air using hydropower or aerodynamic force. A technique for expanding the width of the fiber bundle of the book (for example, JP-A-01-321944) can be applied. However, in water jet and air, the tension is loosened to widen the fiber bundle, so some of the fibers in the fiber bundle break and fluff is generated, or the cut fiber is wound around the roller. For continuous operation, it is preferable to take measures to remove fluff and the like by blowing air. The preferred material for the widening jig is made of metal such as steel, stainless steel or aluminum, or made of Teflon (registered trademark), etc. The surface of the jig is coated with nickel or fluorine to prevent deterioration due to friction, It does not matter if a protective cover such as a plastic film is attached.

  Regarding the ratio between the width W1 of the fiber bundle before widening and the width W2 of the fiber bundle after widening, the ratio (W2 / W1) being smaller than 1 means that W2 is larger than W1, that is, the fibers are widened by the widening jig. Since it represents that the width of the bundle is narrowed, it is excluded from the scope of the present invention. Further, even when the ratio is smaller than 1.1, the effect of flattening by widening described later is often not preferable. Normally, the fiber bundle retains its shape by the restraining force of the sizing agent or the like, but if the ratio (W2 / W1) is greater than 20, the binding force by the sizing agent or the like is weakened during the widening process, and the cutting process is performed. When a chopped fiber bundle is used, the chopped fiber bundle may be separated, which is not preferable.

  By cutting the fiber bundle widened by the above-described method in the widened state, the resulting chopped fiber bundle is also widened. The chopped fiber bundle obtained through the widening process of the present invention is widened compared to the conventional chopped fiber bundle, so the thickness of the chopped fiber bundle is also reduced, and stable when fiber reinforced plastic is used, including variations in strength. Strength can be expressed.

  More specifically, in a fiber reinforced plastic using a chopped fiber bundle, stress concentration is caused at the end of the chopped fiber bundle. And this fiber reinforced plastic will be destroyed when the peeling | exfoliation generate | occur | produced from the chopped fiber bundle end part connects. Therefore, in order to improve the strength, it is important to reduce the stress concentration at the end portion of the chopped fiber bundle and to reduce the separation occurrence stress. In the present invention, the fiber bundle is widened so that the ratio (W2 / W1) of the width W1 of the fiber bundle before widening and the width W2 of the fiber bundle after widening is within the range of 1.1-20. The reduction of stress concentration at the end of the chopped fiber bundle was realized.

  As a method of cutting a continuous fiber bundle, it can be cut using a known cutter. For example, the fiber bundle is inserted obliquely into a rotary cutter such as a roving cutter and cut, or it is cut with a guillotine cutter in which the cutting blade is installed obliquely with respect to the running direction of the continuous fiber bundle. It is also possible to use a rotary cutter (for example, FIGS. 1 b and 5) provided with a spiral cutting blade that is inclined with respect to the traveling direction of the fiber bundle. Among these, a rotary cutter is preferable from the viewpoint of high productivity.

  In the method for producing a chopped fiber bundle of the present invention, the ratio (W1 / t1) between the width W1 and the thickness t1 of the fiber bundle before widening is within a range of 10 to 200, and the width W2 and the thickness t2 of the fiber bundle after widening. The ratio (W2 / t2) is preferably in the range of 70 to 1000. The ratio (W / t) between the width W and the thickness t is referred to as the flatness. The larger the flatness, the flatter the chopped fiber bundle, and the higher the strength improvement effect when a fiber reinforced plastic is used. I can expect. However, on the other hand, as the flatness ratio increases, it may become difficult to maintain the shape of the chopped fiber bundle, and the effect of improving the strength in the case of a fiber reinforced plastic may not be obtained. More preferable flattening ratio ranges are 30 to 100 for W1 / t1 and 120 to 600 for W2 / t2.

  When the flattening ratio (W1 / t1) before widening is less than 10, even if the flattening is performed, the target flattening ratio may not be widened. On the other hand, since the fiber bundle before widening is usually wound around a bobbin or the like, if the flatness ratio (W1 / t1) is larger than 200, the handleability may be inferior. When the flattening ratio (W2 / t2) after widening is less than 70, it becomes easier to create a space in the overlapping portion between the chopped fiber bundles when the fiber reinforced plastic is used, and the matrix resin accumulates in the space. In addition to being a source of crack generation due to thermal stress, voids are likely to occur in the resin pool. On the other hand, when the flattening ratio (W2 / t2) after widening is greater than 1000, the strength improvement effect when using fiber reinforced plastic as described above may not be obtained.

  In the method for producing a chopped fiber bundle of the present invention, a sizing agent is adhered to the reinforcing fibers, and the sizing adhesion amount is preferably 0.3 to 3 parts by weight with respect to 100 parts by weight of the reinforcing fibers. More preferably, it is 0.3 to 2 parts by weight. An object of the present invention is to obtain a specific chopped fiber bundle suitable as a reinforcing fiber of a fiber reinforced plastic. When the sizing adhesion amount is less than 0.3 parts by weight, the chopped fiber bundle is cut after cutting the continuous fiber bundle. In some cases, the shape of the chopped fiber bundle cannot be maintained and the object of the present invention cannot be achieved. Therefore, it is important that the sizing adhesion amount is 0.3 parts by weight or more so that the reinforcing fibers are brought into close contact with each other and integrated as a chopped fiber bundle with a certain restraining force. On the other hand, if the amount of sizing is more than 3 parts by weight, the chopped fiber bundle is highly converging, which impedes matrix resin impregnation into the chopped fiber bundle, and causes voids or poor resin impregnation. Thus, the obtained fiber reinforced plastic may not exhibit high mechanical properties.

  In the method for producing a chopped fiber bundle of the present invention, the fiber length of the chopped fiber bundle is preferably in the range of 10 to 100 mm, and the moisture content is preferably 0 to 5 parts by weight with respect to 100 parts by weight of the reinforcing fiber. . More preferably, the fiber length is 10 to 60 mm and the moisture content is 0 to 3 parts by weight. If the fiber length is within the above range, the fiber reinforcing effect when the fiber reinforced plastic is used can be sufficiently obtained, and the molding followability to a complicated shape when producing the fiber reinforced plastic is excellent. If the moisture content is within the above range, the molding material can be produced without drying the chopped fiber bundle when producing the molding material using the chopped fiber bundle obtained as described later. On the other hand, in a method of manufacturing a chopped fiber bundle for use in injection molding having a fiber length of about 5 mm (for example, Japanese Patent Application Laid-Open No. 2001-271230), the fiber bundle is wetted in order to keep the chopped fiber bundle convergent. Disconnected. However, in the present invention, unlike the injection molding application, the fiber length is sufficiently long, so that it is possible to cut the chopped fiber bundle while maintaining the shape of the fiber bundle without wetting the fiber bundle. Examples of means for controlling the fiber length and the moisture content within the above ranges include adjusting the cutting timing with respect to the fiber length, and adjusting the moisture content by a drying step after applying the sizing agent. Etc. are exemplified.

  Here, “fiber length” refers to the length of a single fiber in a chopped fiber bundle. Although it is difficult to extract a single fiber from a chopped fiber bundle and measure its length, in the present invention, the reinforcing fibers in the fiber bundle are substantially aligned in one direction, as shown in FIG. The length L in the fiber orientation direction of the chopped fiber bundle can be regarded as the fiber length.

  In the manufacturing method of the chopped fiber bundle of this invention, it is preferable to cut | disconnect by the cutting end part length of (1.1-30) xW2 with respect to the width W2 of the fiber bundle after widening. More preferably, cutting is performed with a cutting end portion length of (2 to 10) × W2. Here, the cut end length refers to the side length of the chopped fiber bundle end as shown in FIG. That is, when the fiber bundle is linearly cut at an angle of 90 ° with respect to the traveling direction of the continuous fiber bundle as in the conventional case, the width of the fiber bundle and the length of the cut end are the same. FIG. 3 shows an example of the shape of the chopped fiber bundle obtained by the present invention. In either case, the side length of the end portion of the chopped fiber bundle is (1.1 to 30) × W2 with respect to the width W2 of the fiber bundle. Exists in the region. By making the chopped fiber bundle like this, it becomes possible to gradually release the load of the chopped fiber bundle that is the largest in the center of the chopped fiber bundle when it is made into fiber reinforced plastic. Stress concentration at the end of the fiber bundle is less likely to occur. Therefore, compared with the case where the conventional chopped fiber bundle is used, the strength of the fiber reinforced plastic is improved by orders of magnitude. Not only that, stress concentration is less likely to occur, so initial damage does not occur and cracks do not occur until just before failure. Depending on the use of the fiber reinforced plastic, there is a use that cannot be applied because sound is generated due to initial damage and anxiety is caused, and the fiber reinforced plastic can be applied to such a use. In addition, the initial damage greatly affects the fatigue strength. However, in the case of the chopped fiber bundle obtained in the present invention, since the initial damage is small, not only the static strength but also the fatigue strength is greatly improved.

  In the method for producing a chopped fiber bundle of the present invention, it is preferable to cut the fiber bundle linearly at an angle of 2 to 30 ° with respect to the running direction of the continuous fiber bundle, that is, the fiber orientation direction. When a conventional chopped fiber bundle was cut and manufactured in a direction orthogonal to the fiber orientation direction, it was cut at an angle of 2 to 30 ° with respect to the fiber orientation direction, thereby forming a fiber reinforced plastic. A chopped fiber bundle having high strength can be obtained. When the end of the chopped fiber bundle has a smaller angle with respect to the fiber orientation direction, higher strength is expected when the fiber reinforced plastic is used, and the effect is particularly remarkable at 30 ° or less. The handleability is lowered, and in the cutting process, the smaller the angle between the fiber orientation direction and the blade to be cut, the less stable it is, so an angle of 2 ° or more is preferable. Among these, an angle of 5 to 25 ° with respect to the fiber orientation direction is particularly preferable in view of increasing strength as a fiber-reinforced plastic and processability.

  Furthermore, this invention manufactures a molding material by spraying and integrating the chopped fiber bundle obtained by said manufacturing method into a sheet form. For example, after a chopped fiber bundle is spread on a sheet-like matrix resin, it is sandwiched by another sheet-like matrix resin, and the chopped fiber bundle and the matrix resin are integrated into a sheet shape, which is called SMC or stampable sheet Such a molding material is preferable. Further, the chopped fiber bundles may be dispersed and integrated in a sheet form. If the chopped fiber bundle is impregnated with a matrix resin in advance, it can be integrated without impregnating the resin again. On the other hand, even if the chopped fiber bundle is not impregnated with the matrix resin, fiber molding is performed by performing RTM (resin transfer molding) molding, which injects the matrix resin into the sheet-shaped molding material that integrates the chopped fiber bundle. It may be plastic.

  Moreover, it is preferable that the ratio (W3 / t3) of the width | variety W3 and the thickness t3 exists in the range whose chopped fiber bundle in a molding material is 70-1000. More preferably, it is in the range of 120-600. That is, the molding material can be produced while maintaining the flatness of the chopped fiber bundle obtained by the above production method. In addition, 90% or more of the chopped fiber bundles dispersed in a sheet shape in the molding material are flat in the plane direction of the sheet. Furthermore, some of the chopped fiber bundles have cracks in the fiber bundles at the time of spreading, or the flatness of the chopped fiber bundles fluctuates when folded, but if the flatness of 80% or more of the chopped fiber bundles is within the above range, this The effects of the invention can be sufficiently obtained.

  Further, according to the present invention, the molding material obtained by the above-described manufacturing method is disposed in the cavity in a state smaller than the projected area of the cavity of the molding die and thicker than the cavity thickness, and the molding die is clamped. The molding material is stretched by pressurizing the molding material, and a fiber-reinforced plastic is produced by filling the molding material in the cavity. By manufacturing fiber reinforced plastic as described above, it becomes possible to extrude voids (voids) contained in the molding material out of the mold as the molding material stretches, making the fiber reinforced with high quality and excellent mechanical properties. Plastic can be obtained. The molding means is not particularly limited. For example, if the matrix resin is a thermosetting resin, it is obtained by heating and pressurizing using a heating press, and if the matrix resin is a thermoplastic resin, a molding material is obtained. Is heated to the melting point of the resin or higher with an infrared heater and then cooled and pressurized using a press adjusted to a predetermined temperature.

  In the fiber-reinforced plastic manufacturing method of the present invention, the ratio (W3 / t3) of the width W3 and the thickness t3 of the chopped fiber bundle in the molding material before pressurization is in the range of 70 to 1000. It is preferable that the ratio (W4 / t4) between the width W4 and the thickness t4 of the chopped fiber bundle is in the range of 75 to 1500, and W4 is larger than W3. That is, in the process of producing a fiber reinforced plastic by pressurizing the molding material, it can be produced while increasing the flatness of the chopped fiber bundle. By pressing the molding material in the thickness direction during production, the chopped fiber bundle (flattened in the plane direction of the sheet) in the molding material is also pressed in the thickness direction, and the flatness ratio increases. As described above, the higher the flatness ratio, the better the strength improvement effect when using a fiber reinforced plastic. The range of the flatness ratio of the chopped fiber bundle in the molding material after pressurization is more preferably 150 to 800.

  Examples of the reinforcing fibers used in the present invention include organic fibers such as aramid fibers, polyethylene fibers, polyparaphenylene benzoxador (PBO) fibers, glass fibers, carbon fibers, silicon carbide fibers, alumina fibers, tyrano fibers, basalts. Examples thereof include inorganic fibers such as (basalt) fibers and ceramic fibers, metal fibers such as stainless fibers and steel fibers, and other reinforcing fibers using boron fibers, natural fibers, and modified natural fibers as fibers. Among them, carbon fiber is particularly lightweight among these reinforcing fibers, and has particularly excellent properties in specific strength and specific modulus, and is also excellent in heat resistance and chemical resistance. It is suitable for members such as automobile panels that are desired to be made. Among the carbon fibers, PAN-based carbon fibers from which high-strength carbon fibers can be easily obtained are preferable. The diameter of the carbon fiber single yarn is about 5 to 10 μm, and the number of reinforcing fibers that can be increased in strength at a low cost is 1,000 to 700,000 although it depends on the method for producing the carbon fiber. Preferably from 3,000 to 100,000, and more preferably from 6,000 to 50,000 to produce carbon fiber with high strength and low cost.

  In addition, the use of fiber reinforced plastic using chopped fiber bundles obtained by the present invention as reinforcing fibers is required for strength, rigidity and light weight, such as shafts and heads for sports equipment such as bicycle equipment and golf, and aircraft interiors. Materials, automobile parts such as doors and seat frames, and mechanical parts such as robot arms. In particular, the present invention can be preferably applied to automobile parts such as seat panels and seat frames that require molding followability of complicated shapes in addition to strength and light weight.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the inventions described in the examples.

<Method for measuring flatness>
The flatness of the fiber bundle, that is, the width and thickness of the fiber bundle was measured with a precision of 1/10 mm using a metal ruler for the width, and with a precision of 1/100 mm using a caliper for the thickness. . In addition, as the state of the sample, each sample (fiber bundle) was taken out from each step, and left in a flat place for measurement in a no-tension state. The number of measurements was 10 each, and the average value was used as each value.

  The width and thickness of the chopped fiber bundle in the molding material and fiber reinforced plastic are determined by heating the molding material and fiber reinforced plastic in an electric furnace to decompose the matrix resin and taking out the remaining chopped fiber bundle. It measured similarly. The heating conditions were selected according to the type of reinforcing fiber and matrix resin, and in this example, the heating conditions were set to 500 ° C. × 2 hours.

<Mechanical property evaluation method>
A tensile strength test piece having a length of 250 ± 1 mm and a width of 25 ± 0.2 mm was cut out from a flat fiber-reinforced plastic obtained by the method described in each example. According to the test method specified in JIS K-7073 (1998), the tensile strength was measured at a crosshead speed of 2.0 mm / min with a distance between the gauge points of 150 mm. In this example, an Instron (registered trademark) universal testing machine 4208 type was used as a testing machine. The number of test pieces measured was n = 5, and the average value was the tensile strength.

<Method for measuring moisture content>
The weight w1 (g) of the glass bottle into which the fiber bundle was previously placed and the lid was measured, the fiber bundle was put into this, the lid was covered, and the weight w2 (g) was measured. Next, with the fiber bundle in the glass bottle, the lid was opened and dried in a dryer at a temperature of 130 ° C. for 7,200 seconds, and then the glass bottle was covered in the dryer. The glass bottle was taken out from the dryer, cooled in a desiccator for drying for 2,400 seconds, and then the weight w3 (g) was measured. The moisture content was obtained from the following equation.
Moisture content (parts by weight) = {(w2-w3) / (w3-w1)} × 100.

Example 1
Using the chopped fiber bundle obtained according to the present invention, an SMC sheet was produced as a molding material and molded to obtain flat plate properties.

  A continuous fiber bundle (fiber single yarn diameter 7 μm, 12,000 filament, tensile strength 4.9 GPa, tensile elastic modulus 235 GPa) made of substantially untwisted unsized carbon fiber, resin component 2.0% by weight So that the sizing agent is continuously immersed in a sizing agent mother liquor diluted with dimethylformamide (DMF) so as to give a sizing agent to the carbon fiber, and a hot tension of 150 ° C. under a drying tension of 600 g / dtex. It dried with the roller and the 200 degreeC drying furnace, and removed the water | moisture content. The amount of sizing agent adhered was 1.2 parts by weight, the average width W1 of the fiber bundle was 6.3 mm, the flatness (W1 / t1) was 56, and the moisture content was 0.1 parts by weight.

  On the other hand, 100 parts by weight of vinyl ester resin (manufactured by Dow Chemical Co., Ltd., Delaken 790) as a matrix resin, 1 part by weight of tert-butyl peroxybenzoate (manufactured by NOF Corporation, Perbutyl Z) as a curing agent, 2 parts by weight of zinc stearate (manufactured by Sakai Chemical Industry Co., Ltd., SZ-2000) is used as an internal mold release agent, and 4 parts by weight of magnesium oxide (Kyowa Chemical Industry Co., Ltd., MgO # 40) is used as a thickener. Then, they were sufficiently mixed and stirred to obtain a resin paste. The resin paste was applied onto a polypropylene release film using a doctor blade.

  Next, the carbon fiber 50 bobbin is set on a creel stand, and in the process as shown in FIG. 1-a, the average width W2 of the fiber bundle is 15.2 mm (W2 / W1 is 2.4) with a widening jig. After expanding the flatness (W2 / t2) to 315, the widened fiber bundle is cut with a rotary cutter in which cutting blades are installed at intervals of 25 mm in the circumferential direction and at an angle of 90 °. This produced a chopped fiber bundle. The obtained chopped fiber bundle has a linear form in which the end portion of the chopped fiber bundle is linear at an angle of 0 ° with the fiber orientation direction of the chopped fiber bundle as shown in FIG. 2b), and the fiber length L of the reinforcing fiber is Although there was a variation of about 1% within the same chopped fiber bundle, it was 25 mm. The side length of the chopped fiber bundle end, that is, the cut end length was 15.2 mm (1 × W2).

Under the rotary cutter, a polypropylene film coated with the above resin paste is arranged, and a chopped fiber bundle is uniformly dropped and spread on the film so that the weight per unit area is 500 g / m ² . . Then, the sheet was sandwiched between the other polypropylene film coated with the resin paste with the resin paste side inward to obtain a sheet. The volume content of carbon fibers relative to the sheet (chopped fiber bundle and resin paste) was 40%. The obtained sheet was allowed to stand at 40 ° C. for 24 hours to sufficiently thicken the resin paste, and an SMC sheet as a molding material as shown in FIG. 4 was obtained. The flatness (W3 / t3) of the chopped fiber bundle in the molding material thus obtained was 320.

  This SMC sheet is cut into 250 × 250 mm, and after four sheets are stacked, the SMC sheet is placed at a substantially central portion on a flat plate mold having a cavity of 300 × 300 mm (corresponding to a charge rate of 70%), and then a heating type press molding machine Was cured under conditions of 150 ° C. × 5 minutes under a pressure of 6 MPa to obtain a plate-like fiber-reinforced plastic of 300 × 300 mm.

  The mold cavity was filled with fiber reinforced plastic, and the flowability of the molding material was good. Only when the fiber reinforced plastic was placed on a flat test table, the molded body was in contact with the entire surface of the test table, and it was judged that there was no warpage. The thickness of the fiber reinforced plastic was 2.8 mm. According to the result of the tensile test, the tensile modulus was as high as 29 GPa, and the tensile strength was as high as 260 MPa. Even compared with Comparative Example 1, the mechanical properties of 20% or more in elastic modulus and 70% or more in strength were developed. Further, when the obtained fiber reinforced plastic is cut out and the cut surface is observed, the thickness of the chopped fiber bundle running in parallel with the cut surface as shown in FIG. 5 is constant, and the end of the chopped fiber bundle is perpendicular to the thickness direction. It was cut and a resin pool was generated at the end of the end. However, since the thickness of the chopped fiber bundle is sufficiently thin and the resin pool is very small, there is almost no influence on the tensile properties, and an excellent tensile property improvement effect due to flattening of the chopped fiber bundle was obtained. Was guessed. Further, the flatness (W4 / t4) of the chopped fiber bundle in the fiber reinforced plastic was 535.

(Example 2)
In order to obtain a chopped fiber bundle by cutting a continuous fiber bundle similar to that in Example 1 in the same manner as in Example 1, cutting blades were installed at an angle of 25 mm in the circumferential direction at an angle of 20 °. A chopped fiber bundle was prepared by cutting with a rotary cutter. The obtained chopped fiber bundle has a linear shape in which the end of the chopped fiber bundle has an angle of 20 ° with the fiber orientation direction of the chopped fiber bundle as shown in FIG. 2a), and the fiber length L of the reinforcing fiber is Although there was a variation of about 1% within the same chopped fiber bundle, it was 25 mm. The side length of the chopped fiber bundle end, that is, the cut end length was 44 mm (2.9 × W2).

  The chopped fiber bundle thus obtained was prepared as an SMC sheet as a molding material in the same manner as in Example 1, and then a fiber reinforced plastic was molded. The flatness (W3 / t3) of the chopped fiber bundle in the molding material was 340. The mold cavity was filled with fiber reinforced plastic, and the flowability of the molding material was good. Only when the fiber reinforced plastic was placed on a flat test table, the molded body was in contact with the entire surface of the test table, and it was judged that there was no warpage. The thickness of the fiber reinforced plastic was 2.8 mm.

  Next, a tensile test was carried out in the same manner as in Example 1. The tensile elastic modulus was as extremely high as 34 GPa, and the tensile strength was as high as 350 MPa. Even when compared with Comparative Example 1, the mechanical properties were improved by 40% or more in elastic modulus and twice or more in strength. Further, when the obtained fiber reinforced plastic was cut out and the cut surface was observed, the chopped fiber bundle running in parallel with the cut surface as shown in FIG. 6 became thinner from the central part toward the end, unlike Example 1. It was found that the number of fibers decreased and the thickness of the chopped fiber bundle was very thin. Therefore, excellent tensile property improvement effect due to flattening of the chopped fiber bundle, and the remarkable effect of improving not only the tensile strength but also the elastic modulus, as the load transmission efficiency at the end of the chopped fiber bundle is improved. It was speculated. Further, the flatness (W4 / t4) of the chopped fiber bundle in the fiber reinforced plastic was 705.

(Example 3)
A carbon fiber bundle similar to Example 1 was obtained except that the hot roller was omitted in the sizing agent drying step. The amount of sizing agent adhered was 1.4 parts by weight, the average width W1 of the fiber bundle was 2.0 mm, the flatness (W1 / t1) was 7, and the moisture content was 0.2 parts by weight. Subsequently, in the same process as in Example 1, the fiber bundle was widened so that the average width W2 of the fiber bundle was 9.2 mm (W2 / W1 was 4.6) and the flatness ratio (W2 / t2) was 115 using a widening jig. After that, a chopped fiber bundle was produced. The obtained chopped fiber bundle has a linear shape in which the end of the chopped fiber bundle has an angle of 90 ° with the fiber orientation direction of the chopped fiber bundle as shown in Fig. 2b), and the fiber length L of the reinforcing fiber is Although there was a variation of about 2% within the same chopped fiber bundle, it was 25 mm. The side length of the chopped fiber bundle end, that is, the cut end length, was 9.2 mm (1 × W2).

  The chopped fiber bundle thus obtained was prepared as an SMC sheet as a molding material in the same manner as in Example 1, and then a fiber reinforced plastic was molded. The flatness (W3 / t3) of the chopped fiber bundle in the molding material was 115. The mold cavity was filled with fiber reinforced plastic, and the flowability of the molding material was good. Only when the fiber reinforced plastic was placed on a flat test table, the molded body was in contact with the entire surface of the test table, and it was judged that there was no warpage. The thickness of the fiber reinforced plastic was 2.8 mm.

  Next, a tensile test was carried out in the same manner as in Example 1. The tensile modulus was as high as 27 GPa and the tensile strength was as high as 230 MPa. Even when compared with Comparative Example 1, the mechanical properties were improved by 10% or more in elastic modulus and 50% or more in strength. Further, when the obtained fiber reinforced plastic is cut out and the cut surface is observed, the thickness of the chopped fiber bundle running in parallel with the cut surface as shown in FIG. 5 is constant, and the end of the chopped fiber bundle is perpendicular to the thickness direction. It was cut and a resin pool was generated at the end of the end. However, since the thickness of the chopped fiber bundle is sufficiently thin and the resin pool is very small, there is almost no influence on the tensile properties, and an excellent tensile property improvement effect due to flattening of the chopped fiber bundle was obtained. Was guessed. Further, the flatness (W4 / t4) of the chopped fiber bundle in the fiber reinforced plastic was 140.

(Comparative Example 1)
The mechanical property of SMC using the chopped fiber bundle cut without going through the widening step is obtained and used as a comparative example.

  A chopped fiber bundle was produced by the same process as in Example 1 except that the widening jig was omitted. In the obtained chopped fiber bundle, as shown in FIG. 2b), the end of the chopped fiber bundle has a linear form at an angle of 90 ° with the fiber orientation direction of the chopped fiber bundle, and the fiber lengths of the reinforcing fibers are the same. Although there was a variation of about 3% in the chopped fiber bundle, it was 25 mm. The side length of the chopped fiber bundle end, that is, the cut end length, was 6.3 mm (1 × W2).

  After producing an SMC sheet in the same manner as in Example 1, a fiber reinforced plastic was molded. The flatness (W3 / t3) of the chopped fiber bundle in the molding material was 62.

  The mold cavity was filled with fiber reinforced plastic, and the flowability of the molding material was good. There was no warp and the thickness of the fiber reinforced plastic was 2.8 mm.

  According to the results of the tensile test, the tensile modulus was 24 GPa and the tensile strength was 150 MPa. Further, when the obtained fiber reinforced plastic is cut out and the cut surface is observed, the thickness of the chopped fiber bundle running in parallel with the cut surface as shown in FIG. 5 is constant, and the end of the chopped fiber bundle is perpendicular to the thickness direction. It was cut and a resin pool was generated at the end of the end. Furthermore, a large number of resin pools were also generated in the overlapping portion between the chopped fiber bundles. Voids exist in some of these resin reservoirs, and it is considered that low tensile properties were obtained by the resin reservoirs. Further, the flatness ratio (W4 / t4) of the chopped fiber bundle in the fiber reinforced plastic was 65.

(Comparative Example 2)
A chopped fiber bundle was produced in the same manner as in Example 3 except that the widening jig was omitted. The obtained chopped fiber bundle has a linear shape in which the end of the chopped fiber bundle has an angle of 90 ° with the fiber orientation direction of the chopped fiber bundle as shown in Fig. 2b), and the fiber length L of the reinforcing fiber is Although there was a variation of about 1% within the same chopped fiber bundle, it was 25 mm. The side length of the chopped fiber bundle end, that is, the cut end length was 2 mm (1 × W2).

  After producing an SMC sheet in the same manner as in Example 1, a fiber reinforced plastic was molded. The flatness (W3 / t3) of the chopped fiber bundle in the molding material was 7.

  The mold cavity was filled with fiber reinforced plastic, and the flowability of the molding material was good. There was no warp and the thickness of the fiber reinforced plastic was 2.8 mm.

  According to the results of the tensile test, the tensile modulus was 21 GPa and the tensile strength was 120 MPa. Further, when the obtained fiber reinforced plastic is cut out and the cut surface is observed, the thickness of the chopped fiber bundle running in parallel with the cut surface as shown in FIG. 5 is constant, and the end of the chopped fiber bundle is perpendicular to the thickness direction. It was cut, and a larger resin pool than that in Comparative Example 1 was generated at the end of the end portion and at the overlapping portion of the chopped fiber bundles. Furthermore, the resin reservoir contained a plurality of voids. Further, the flatness ratio (W4 / t4) of the chopped fiber bundle in the fiber reinforced plastic was 15.

It is the schematic which shows an example of the process of manufacturing the chopped fiber bundle of this invention. It is a perspective view which shows the example of a part of process of manufacturing the chopped fiber bundle of this invention. It is a top view which shows an example of the chopped fiber bundle in this invention. It is a top view which shows several examples of the chopped fiber bundle in this invention. It is a top view which shows an example of the molding material in this invention. It is sectional drawing which shows an example of the fiber reinforced plastics in this invention. It is sectional drawing which shows an example of another form of the fiber reinforced plastics in this invention.

Explanation of symbols

1: Creel stand 2: Continuous fiber bundle 3: Roller 4: Widening jig 5: Cutting device 6: Chopped fiber bundle 7: Resin sheet 8: Molding material 9: Fiber orientation direction 10: Reinforcing fiber (single yarn)
11: End of chopped fiber bundle 12: Side length of chopped fiber bundle end (cut end length)
13: Cut-out cross section of chopped fiber bundle 13a: Cut-out cross section of chopped fiber bundle running parallel to cut surface 14: Fiber reinforced plastic thickness direction 15: Resin reservoir L: Fiber length W: Fiber bundle width t: Fiber bundle thickness

Claims (11)

In the method of manufacturing a chopped fiber bundle in which the reinforcing fibers are substantially aligned in one direction, a plurality of continuous fiber bundles are continuously run, and the fibers before widening are provided by the widening means disposed in the middle of the running. A plurality of fiber bundles in a widened state after widening the fiber bundle so that the ratio (W2 / W1) of the width W1 of the bundle to the width W2 of the fiber bundle after widening is in the range of 1.1 to 20 A method for producing a chopped fiber bundle, in which the two are simultaneously cut. Further, the ratio (W1 / t1) between the width W1 and the thickness t1 of the fiber bundle before widening is in the range of 10 to 200, and the ratio (W2 / t2) between the width W2 and the thickness t2 of the fiber bundle after widening is 70. The manufacturing method of the chopped fiber bundle of Claim 1 which exists in the range of -1000. The method for producing a chopped fiber bundle according to claim 1 or 2, wherein a sizing agent is adhered to the reinforcing fibers, and the sizing adhesion amount is 0.3 to 3 parts by weight with respect to 100 parts by weight of the reinforcing fibers. The chopped fiber bundle according to any one of claims 1 to 3, wherein the fiber length of the fiber bundle is within a range of 10 to 100 mm, and the moisture content thereof is 0 to 5 parts by weight with respect to 100 parts by weight of the reinforcing fiber. Manufacturing method. The manufacturing method of the chopped fiber bundle in any one of Claims 1-4 cut | disconnected by the cutting end part length of (1.1-30) xW2 with respect to the width W2 of the fiber bundle after widening. The manufacturing method of the chopped fiber bundle in any one of Claims 1-5 which cut | disconnects this fiber bundle linearly at an angle of 2-30 degrees with respect to the running direction of the continuous fiber bundle. The manufacturing method of the molding material which spreads the chopped fiber bundle obtained by the manufacturing method in any one of Claims 1-6, and integrates it in a sheet form. The molding material according to claim 7, wherein the chopped fiber bundle is spread on a sheet-like matrix resin, and then sandwiched by another sheet-like matrix resin, so that the chopped fiber bundle and the matrix resin are integrated into a sheet shape. Manufacturing method. The method for producing a molding material according to claim 7 or 8, wherein the chopped fiber bundle in the molding material has a ratio of the width W3 to the thickness t3 (W3 / t3) in the range of 70 to 1000. The molding material obtained by the manufacturing method according to claim 7 is disposed in the cavity in a state where the molding material is smaller than the projected area of the cavity of the molding die and thicker than the cavity thickness. A method for producing fiber-reinforced plastic, wherein the molding material is stretched by clamping and pressurizing the molding material, and the molding material is filled in the cavity. The ratio (W3 / t3) of the width W3 and the thickness t3 of the chopped fiber bundle in the molding material before pressing is in the range of 70 to 1000, and the width W4 and the thickness t4 of the chopped fiber bundle in the molding material after pressing. The manufacturing method of the fiber reinforced plastics of Claim 10 whose ratio (W4 / t4) exists in the range of 75-1500, and W4 is larger than W3.

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