JP4617912B2 - Carbon fiber dividing method and sheet molding compound manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a reinforced fiber of a short fiber reinforced plastic that is suitably used for, for example, an automobile member, a sports equipment and the like.

  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.

Among the reinforcing fibers, carbon fibers have the highest specific strength and specific elastic modulus, and the members can be significantly reduced in weight, so that they are being put to practical use in automobile members and sports equipment used by humans. Carbon fibers are usually used in the form of strands in which tens of thousands to hundreds of thousands of carbon fiber filaments having a thickness of several microns to several tens of microns are aggregated. (Hereinafter, the number of carbon fiber filaments constituting the carbon fiber strand will be described as the number of filaments and expressed without units: in the industry, 1000 is represented as K, for example, 3000 is referred to as 3K)
In recent years, carbon fiber strands composed of 10,000 (10K) or more filaments have been put into practical use for the purpose of reducing the manufacturing cost of the carbon fiber itself and reducing the manufacturing cost of the member. Carbon fiber strands having a number of filaments of 10,000 or more are called thick strands because they increase in appearance as a result of the large number of filaments. (Hereafter, for simplification, this is referred to as a thick strand)
While the cost of the thick strands is reduced, the composite material using the thick strands as the reinforcing fibers tends to have reduced mechanical properties. For example, Non-Patent Document 1 shows that the strength and elastic modulus of a composite material obtained by sheet mold compound (SMC) molding decrease as the number of filaments of carbon fiber strands increases.

  In addition, studies have been made to divide and use thick strands. In Patent Document 1, a carbon fiber strand having the number of filaments of 48000 (48K) expressed as split tow passes through a spreading bar with a crown and a splitting bar with a groove. By doing so, an apparatus for dividing the carbon fiber strand into thin carbon fiber strands having thousands of filaments is disclosed.

Usually, the positional relationship between the carbon fiber filaments in the carbon fiber strand is not constant. In other words, when one of the carbon fiber filaments in the carbon fiber strand is traced in the longitudinal direction, the carbon fiber strand can be seen outside the carbon fiber strand, or the carbon fiber strand can be seen from outside the inside, It also swings from side to side or spirals. For this reason, as in Patent Document 1, in the method of dividing a thick strand through a grooved rod / roll, if the strand length of the carbon fiber to be continuously processed is long, the carbon fiber strand gradually rotates, Twist accumulates and the carbon fiber strand cannot be wound up, or the carbon fiber strand is cut by the twist and cannot be divided. In order to remove the accumulated twist, there was a problem that the apparatus had to be stopped and continuous production was not possible.
US Pat. No. 6,385,828 N. Tsuchiyama, “The Mechanical Properties of Carbon Fiber SMC”, Proceedings of the Fourth International Materials (ICCM-IV), 1988. 497-503

  The present invention provides a method of continuously dividing continuous carbon fiber strands into carbon fiber strands having a smaller number of filaments in view of the problems of the prior art.

The present invention employs the following means in order to solve such problems. That is,
(1) A carbon fiber strand dividing method for dividing a carbon fiber strand into a plurality of carbon fiber strands having a smaller number of filaments. The carbon fiber strand is continuously run while tension is applied to the continuous carbon fiber strand, and is arranged during the running. was, at the same time as the curvature of the convex surface radius (R) is widening the carbon fiber strands widening jig in the range of 50 to 500 mm, a carbon fiber strand of the expansion width state, parallel to the running direction of the carbon fiber strands A method for splitting carbon fiber strands, wherein a part of the carbon fiber filaments is cut with a cutting blade that rotates and has a peripheral speed 5 to 20% faster than the running speed of the carbon fiber strands.
(2) The carbon fiber strand splitting method according to (1), wherein the number of filaments of the carbon fiber strand before splitting is 10,000 (10K) to 400,000 (400K).
(3) The ratio (W2 / W1) of the width (W2) of the strand on the widening jig and the width (W1) of the running strand before widening is in the range of 2 to 10 (1) The division | segmentation method of the carbon fiber strand in any one of thru | or (2).
(4) The carbon fiber strand dividing method according to any one of (1) to (3), wherein the widening jig is a cylindrical body that rotates in a running direction of the carbon fiber.
(5) The carbon fiber strand dividing method according to any one of (1) to (4), wherein a liquid is applied to the running carbon fiber strand immediately before the cutting step.
(6) After cutting the carbon fiber strand divided by using the dividing method according to any one of (1) to (5) to form a discontinuous carbon fiber strand, the discontinuous carbon fiber strand is resinized. A method for producing a sheet molding compound, comprising a step of dispersing on a film.

  According to the present invention, it is possible to efficiently and continuously produce carbon fiber strands having a small number of filaments from carbon fiber strands having a large number of filaments, thereby reducing costs. This makes it possible to obtain the strength and rigidity of a composite that is close to the case of using a carbon fiber strand with a small number of filaments while using a carbon fiber strand with a large number of filaments as a raw material, and the weight of the member can be reduced. .

  Furthermore, as an effect of dividing a carbon fiber strand having a large number of filaments into carbon fiber strands having a small number of filaments, the form of packaging can be changed, the fiber can be easily cut into short fibers, the thickness of the product is reduced, etc. Various industrial values can be expected.

  Moreover, it becomes possible to continuously produce reinforcing fibers suitable for discontinuous fiber base materials such as SMC by continuously cutting carbon fiber strands with a small number of filaments into short fibers. Therefore, it is possible to produce SMC automobile members, sports equipment members, and the like at a light weight and low cost.

  The best mode for carrying out the present invention will be described below with reference to FIG. 1 (side view) and FIG. 2 (plan view).

  First, the present invention is a method of dividing a continuous carbon fiber strand into a plurality of carbon fiber strands having a smaller number of filaments. Continuous carbon fiber is usually handled in a package wound around a bobbin, and is used to manufacture molding base materials such as prepreg and SMC (sheet molding compound). The carbon fiber. A carbon fiber strand is an aggregate of 1000 or more carbon fiber filaments. Recently, carbon fiber strands composed of several hundred thousand carbon fiber filaments have been put into practical use in order to improve production efficiency.

  The carbon fiber is known to have 90% or more of carbon, an elastic modulus of 150 to 800 GPa, and a strength of 3 to 7 GPa. The present invention is limited to the carbon fiber. The carbon fiber has a fiber diameter as small as several μm (6 to 9 μm) as compared with the glass fiber or the like. This is because, as described in Document 1, the decrease in strength becomes significant depending on the number of fibers. In other words, it is because the problem on handling peculiar to this carbon fiber was tackled.

  The number of filaments of a general-purpose carbon fiber strand is usually 10,000 (10K) or more and is called a thick strand. If the number of filaments is too large, widening and cutting described later will be difficult, so the upper limit is about 400,000 (400K). Moreover, since it is excellent also in a mechanical physical property below 10,000 (10K), the necessity for dividing | segmenting is low. The filament number of the most preferable strand in the present invention is 24,000 to 60000 (24K to 60K). Also, the more the number is divided (to a carbon fiber strand having a smaller number of filaments), the more uniform the fiber distribution in the member is, and the mechanical properties (strength, elastic modulus) are improved and the thickness is reduced. A thick member can be manufactured, which is preferable. However, in order to divide many, the number of cutting blades to be described later increases, leading to an increase in cost, so a range of 1000 to 4000 (1 to 4K) is preferable. That is, when the number of filaments of the thick strand is 12000 (12K), it is appropriate to divide into 3 to 12 carbon fiber strands.

  In the present invention, first, it is necessary to continuously run the carbon fiber strands while applying tension. By applying tension, loosening of the strand is eliminated and the fiber can be cut with a cutting blade described later (the direction of the arrow in FIG. 1 indicates the traveling direction). Continuous running is an operation necessary for continuous production by moving continuous carbon fiber strands in a certain direction by tension. In order to run continuously, it is necessary to move the carbon fiber strand by applying a driving force by pulling it with a winder with driving force at one end of the carbon fiber strand, winding the carbon fiber strand around a rotating roll, or chucking with friction There is. At the same time, the carbon fiber strands before being divided need to be set on a creel stand or the like so that the yarn can be fed out, for example, by winding it around a bobbin (2). Preferably, the carbon fiber strand wound around the bobbin (2) is attached to a creel stand, and the strand end is wound and run by a winder installed after the cutting blade (3).

  Next, the carbon fiber strand (1) before the division is widened by the widening jig (4) disposed in the middle of traveling. By widening, the thickness of the strand is reduced and the division becomes easy. Moreover, the precision of the carbon fiber strand width | variety after a division | segmentation improves. The strand width literally refers to the maximum length in a plane perpendicular to the longitudinal direction of the carbon fiber strand, and can be measured with calipers or the like.

In the present invention, since the carbon fiber strand is cut in the longitudinal direction of the carbon fiber strand, it is necessary to widen the carbon fiber strand in a tensioned state. The widening jig (4) is like a cylindrical roller. Furthermore, it is necessary to have a convex surface (5) with respect to the longitudinal direction of the carbon fiber strand and to be in contact with the carbon fiber strand on the convex surface. Specifically, there are a round bar, a rotating roll, a stick-shaped bar-shaped body having a circular or elliptical cross section, etc., but it is necessary to have a strength that is not greatly deformed or broken by the tension acting on the carbon fiber strand. When the carbon fiber strand acting on tension comes into contact with the convex surface, a force acts in the thickness direction of the carbon fiber strand, and the carbon fiber strand spreads in the horizontal direction. Further, since the carbon fiber strand is fixed on the widening jig by tension, the carbon fiber strand does not loosen and can be cut with a cutting blade (3) described later.

Curvature of the convex surface of the widening tool radius (R) is required in the range of 5 0-500 mM. This is because within this range, the distance (section) where the carbon fiber strand is in contact with the widening jig and the time can be made sufficiently long, and cutting can be performed even if a plurality of cutting blades are installed.

  The most preferred widening jig is a rotatable cylindrical roller. When a strand with tension acts on the convex surface of the roller, a force acts in the thickness direction of the strand, and the carbon fiber strand spreads (collapses) in the horizontal direction and at the same time can be rotated. It is possible to adjust the tension by winding (to prevent the carbon fiber strands from unraveling), and since the location closest to the cutting blade, which will be described later, changes sequentially, there is no local wear on the rollers and continuous operation for a long time. This is because it becomes possible. Further, yarn breakage can be suppressed.

  The preferred material for the widening jig (4) is made of metal such as steel or aluminum, or made of Teflon (registered trademark), and the surface of the jig is subjected to nickel or fluorine coating to suppress deterioration due to friction. You can also put on a protective cover such as rubber or plastic film. Further, since the widening jig may come into contact with the cutting blade, it is also a preferable aspect to provide a protective cover that can be easily replaced.

  In addition, as a method of widening the carbon fiber strand, a technique of increasing the width of the carbon fiber strand while vibrating the widening jig (for example, JP-A-1-280040) or before the widening jig, hydraulic power or pneumatic force It is possible to apply a technique (for example, JP-A-1-321944) for expanding the width of the carbon fiber strands using a water jet method or air. However, in the case of hydraulic power or pneumatic power, the tension is relaxed to widen the fiber, so that part of the filament in the carbon fiber strand breaks and fluff is generated, or the cut filament is wound around the roller. For operation, it is preferable to take measures to remove the broken filament by blowing air or the like.

  Although the width of the expanded carbon fiber strand depends on the number of filaments in the carbon fiber strand, 0.5 to 3 mm is appropriate per 1000 (1K) of filaments. When the widening is insufficient and this range cannot be satisfied, the dividing step can be multistage. Specifically, when it is desired to divide into four, first divide into two, and then divide each of the two divided carbon fiber strands into two (in this case, three sets of dividing widening jigs and cutting blades). Required). As a standard of balanced widening, the ratio (W2 / W1) of the width (W2) of the carbon fiber strand on the widening jig and the width (W1) of the carbon fiber strand before widening (out of the bobbin) ) Is preferably within the range of 2-10. Below this range, the cutting accuracy may be insufficient. Above this range, the carbon fiber filaments in the carbon fiber strand are partially widened and broken and wound around a roller or the like. This is because it may interfere with driving. Moreover, the thickness of a preferable carbon fiber strand is the range of 0.05-1 mm. If the width is narrower than this range, part of the carbon fiber filament will break and fluff will occur. If this range is exceeded, the burden on the cutting blade will increase and blade spilling will occur, hindering continuous operation. Because there is a possibility.

  Next, the carbon fiber strand is cut in a part of the carbon fiber in the carbon fiber strand by the cutting blade (3) rotating in parallel with the traveling direction of the carbon fiber strand in a widened state, and the twist does not accumulate. As such, it is continuously divided into thinner carbon fiber strands.

By setting it in the widened state, it can be accurately divided into a predetermined number and the thickness is reduced, so that cutting with a cutting blade is facilitated. The cutting blade is a rotary cutter or the like, and since it is rotating, it is possible to reliably cut a part of the carbon fiber filament in the carbon fiber strand under tension with a dynamic force. . And since the direction of rotation is parallel to the running direction of the carbon fiber strand, a part of the carbon fiber filament in the carbon fiber strand is cut in a state where the tension is applied to the carbon fiber strand. Since the carbon fiber strands of the present invention do not loosen, the occurrence of twist due to loosening can be prevented, and therefore continuous production for a longer time becomes possible. As described above, the positional relationship of the carbon fiber filaments of the carbon fiber strand have good constant. That is, when one of the carbon fiber filaments in the carbon fiber strand is traced in the longitudinal direction, the carbon fiber strand can be seen outside the carbon fiber strand, or it can enter a portion that cannot be seen from outside the carbon fiber strand, In addition, since it swings from side to side or spirals, carbon fiber filaments on one side of the blade are not cut with a fixed blade such as a cutter blade. It becomes possible (the tension becomes extremely large) and hinders continuous operation. Further, the fixed blade has problems that the cooling efficiency of the blade is low, the wear is large, and the replacement frequency of the blade is increased. Since the carbon fiber has high strength, it is necessary to cut the carbon fiber while applying a dynamic force by rotating the cutting blade as in the present invention. In order to achieve sufficient cutting , it is effective to increase the rotation speed of the cutting blade, slow the traveling speed, and increase the tension. Specifically, the peripheral speed of the disconnect blade, it is necessary to quickly about 5-20% than the running speed of the carbon fiber strand, a normal 0.3～30M / min in absolute value. Moreover, the tension | tensile_strength of the carbon fiber strand at the time of a cutting | disconnection is 1-8 kg / strand per carbon fiber strand before a cutting | disconnection as a standard.

  If the cutting blade is sharp and the running speed and tension are appropriate, the fiber will be cut reliably, so twisting will not occur, but in order to more reliably suppress twisting, sandwich the portion where the twist is accumulated. In addition, the function of crushing the portion or passing the widening jig may be given.

  The cutting blade (3) is usually preferably a rotary cutter, but even a rotating processing tool such as a micro grinder can be used as long as it does not twist. The material of the cutting edge of the cutting blade is preferably super steel or diamond, and the thickness of the cutting edge is preferably 2 mm or less. More preferably, it is 1 mm or less. A plurality of cutting blades can be installed per widening jig. In this case, it is important to consider that the carbon fiber strands are sufficiently widened and the cutting edges of the cutting blades do not contact each other. The plurality of cutting blades may be arranged in parallel at equal intervals, non-equal intervals, or in steps. Further, depending on the situation, the cutting blade may be cooled by air cooling or a water cooling device.

  Furthermore, it is also preferable to apply a liquid to the carbon fiber strand in the entire process of the present invention. By applying the liquid, the fluffs of the carbon fiber strands that cause twisting and breakage of the yarn can be suppressed, and the width of the carbon fiber strands on the widening jig is also stabilized. In particular, immediately after cutting with a cutting blade, a part of the cut carbon fiber filament in the carbon fiber strand is lifted by the air flow, which may cause wrapping, but by applying a liquid, Winding can be prevented and operation can be continued for a longer time. In addition, if a liquid is applied before widening, the widening may be hindered depending on the liquid. Therefore, the position immediately before the cutting step is most preferable as the position where the liquid is applied. Examples of the liquid include solvents such as water, styrene, alcohol, acetone, and MEK, and viscous materials such as SMC resins, epoxy resins, polyester resins, and vinyl ester resins. If the deposited liquid is a volatile substance such as water or a low boiling point substance, it may be removed by drying after the cutting step. Further, when the adhered liquid is a non-volatile substance such as an epoxy resin, it may be removed by washing, or may be left in the composite as a matrix.

  Next, in succession to the above-described carbon fiber strand splitting process (continuously without winding up the paper tube with a winder), a length of 5 to 150 mm is perpendicular to the longitudinal direction of the split carbon fiber strand. It is also possible to produce a discontinuous carbon fiber strand. Further, discontinuous carbon fiber strands are dispersed randomly or with orientation on a paper or film coated with a resin release process (called a resin film in the industry), so-called SMC sheet. Can be manufactured (FIG. 3).

  As in Patent Document 1, once the divided carbon fiber strands are wound up around the bobbin, a paper tube is necessary, and a winder for this purpose is also required. The cost of the SMC sheet can be reduced and the cost of the member can be reduced. Furthermore, since the carbon fiber strands are in the widened state to be cut immediately after being divided in the widened state, the fiber damage is less than the state in which the carbon fiber strands are sequentially stacked and wound (the state wound on the bobbin). High strength is expressed.

  As a device for cutting the divided carbon fiber strands, a rotary cutter such as a roving cutter or a guillotine cutter device, which is attached to an SMC manufacturing device, can be used, but among these devices, A guillotine cutter. Since the carbon fiber strand to be cut is finely divided, the wear of the blade is small and the life is extended, so that continuous production more than conventional can be achieved.

The cutting device may be sprayed with a brush or air in order to drop the cut discontinuous carbon fiber strand onto the resin film (9) without adhering to the cutter. Moreover, it is preferable that the discontinuous carbon fiber strands cut to be dropped randomly are vibrated at a frequency of 10 to 50 Hertz or passed through a cage roll.

The resin of the resin film may be a thermosetting resin such as an epoxy resin, a polyester resin, a vinyl ester resin, or a phenol resin, or a thermoplastic resin such as polypropylene or preethylene, or a mixed resin thereof. There is no problem. In addition, since the carbon fiber strands of the present invention are finely divided, the discontinuous carbon fiber strands are uniformly dispersed on the resin film. Therefore, the basis weight of the sheet (weight per unit area) and the thickness of the sheet Becomes uniform, and reproducible members can be produced. Since the composite using this SMC sheet has high strength and high elastic modulus, the weight of the member can be reduced to the limit. Furthermore, it is possible to form a thin composite member that is not conventionally available.

  The carbon fiber strands produced by the production method of the present invention are thin. Therefore, when applied to the SMC production process, the strength of the SMC can be greatly improved. SMC is a manufacturing method suitable for mass production, which includes lightweight automotive components (panels such as hoods, doors and wheel houses, structural members such as chassis, beams such as bumpers, frames) and sports equipment ( For example, mass production of bicycle members such as cranks, rackets such as tennis rackets, shafts used for golf clubs, boards such as skateboards, and poles) is possible.

Example 1
A carbon fiber strand having 12,000 filaments (Toray Industries, Inc. product T700S-12K-60E: strength 5 GPa, elastic modulus 235 GPa) is unrolled from a bobbin, passed through a widening jig and a cutting blade, and wound up by a winder. I set the thread path. The widening jig was a satin roller made of aluminum alloy (surface roughness 1 μm, radius 100 mm), and the cutting blade was a rotary cutter (ultra steel blade made by Olfa) with a blade thickness of 0.3 mm and a radius of 20 mm.

  The winding speed of the wonder was adjusted, 3 kg of tension was applied to the carbon fiber strand, and winding of the yarn speed of 2 m / min was started. The width (W2) of the carbon fiber strand on the widening jig was 15 mm, and the width (W1) just before entering the widening jig was 3 mm (the ratio of the two was 5 times).

When the cutting blade was rotated in the same direction as the traveling direction of the carbon fiber strand at a peripheral speed of 2.2 m / min and started to be divided into two thin carbon fiber strands (width 8 mm), the carbon fiber strand length was 300 m. No twisting occurred even when the material was divided. However, a part of the cut fibers adhered to the winder.
(Example 2)
A carbon fiber strand having 24,000 filaments (Toray Industries, Inc. product T700S-24K-50C: strength 5 GPa, elastic modulus 235 GPa) is unwound from a bobbin, passed through a widening jig and a cutting blade, and then wound with a winder Set the road. The dividing operation was started using the same widening jig and cutting blade as in Example 1 except that distilled water was uniformly applied on the bobbin (the amount was 3% with respect to the weight of the carbon fiber).

  The width (W2) of the carbon fiber strand on the widening jig was 45 mm, and the width (W1) before entering the widening jig was 6 mm (the ratio of both was 7.5 times).

Even when the carbon fiber strand length of 800 m was divided, no twist was generated. Moreover, the taking-out of the cut | disconnected fiber in the winder vicinity seen in Example 1 was not seen.
(Comparative Example 1)
In Example 1, the same carbon fiber strand as in Example 1 was divided using a super steel fixed blade (Olfa 1 mm thick cutter blade) instead of the cutting blade. Twisting occurred just before the cutter blade at a running length of 20 m, and twisting further increased at a running length of 40 m, making continuous running no longer possible.

It is an example of the side view of the typical manufacturing method of this invention. It is an example of the top view of the typical manufacturing method of this invention. It is an example of the method of manufacturing an SMC sheet.

Explanation of symbols

1: Carbon fiber strand before division 2: Bobbin 3: Cutting blade
4: Widening jig 5: Convex surface 6: Roll 7: Divided carbon fiber strand 8: Cutting device 9: Discontinuous carbon fiber strand 10: Resin film 11: SMC sheet 12: Sheet winding roll

Claims (6)

A carbon fiber strand dividing method for dividing a carbon fiber strand into a plurality of carbon fiber strands having a smaller number of filaments, wherein the carbon fiber strand is continuously run while tension is applied to the continuous carbon fiber strand, and is arranged in the middle of the run. at the same time the radius of curvature (R) is widening the carbon fiber strands widening jig in the range of 50 to 500 mm, a carbon fiber strand of the expansion width state, parallel to the rotation and travel direction of the carbon fiber strand, A method for dividing a carbon fiber strand, comprising cutting a part of the carbon fiber filaments with a cutting blade whose peripheral speed is 5 to 20% faster than the running speed of the carbon fiber strand. The carbon fiber strand splitting method according to claim 1, wherein the number of filaments of the carbon fiber strand before splitting is 10,000 (10K) to 400,000 (400K). The ratio (W2 / W1) of the width (W2) of the strand on the widening jig and the width (W1) of the running strand before widening is in the range of 2 to 10. The division | segmentation method of the carbon fiber strand in any one. The carbon fiber strand dividing method according to any one of claims 1 to 3, wherein the widening jig is a cylindrical body that rotates in a running direction of the carbon fiber. The carbon fiber strand dividing method according to any one of claims 1 to 4, wherein a liquid is applied to the running carbon fiber strand immediately before the cutting step. A carbon fiber strand that has been divided using the dividing method according to any one of claims 1 to 5 is cut into a discontinuous carbon fiber strand, and then the discontinuous carbon fiber strand is dispersed on a resin film. A method for producing a sheet molding compound, comprising a step.

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