Patent Description:
In recent years, CFRP (carbon fiber reinforced plastic) which is a composite material comprising a carbon fiber and a resin has been widely used for components of aircraft, automobiles, ships and other various transportation equipment, sports goods, and leisure goods.

A certain type of CFRP products is molded from the CF-SMC by using a compression molding method.

The CF-SMC is a type of carbon fiber prepregs, and has a structure in which a mat comprising chopped carbon fiber bundles (also referred to as a "chopped carbon fiber tow" or a "chopped carbon fiber strand") is impregnated with a thermosetting resin composition.

The CFRP has higher strength when being reinforced with a carbon fiber bundle having a smaller filament number. On the other hand, the carbon fiber bundle requires a higher manufacturing cost when having a smaller filament number (smaller tow size) (Patent Document <NUM>).

It is proposed adding a step of partially splitting a continuous carbon fiber bundle unwound from a creel before chopping to an SMC manufacturing method in which steps are continuously performed from chopping of the continuous carbon fiber bundle to resin impregnation of a carbon fiber mat (Patent Document <NUM>).

The Patent Document D3 is considered to disclose a method for manufacturing SMC. which includes a step of providing a spraying mechanism 8a (based on the drawing, corresponding to a pin roller) directly under a cutter unit <NUM>, and dispersing fiber bundles, which is a part of the invention as in claim <NUM>.

It is expected that an SMC which can give a high-strength CFRP molded product can be manufactured at low cost by using a technique of partially splitting before use a continuous carbon fiber bundle having a large filament number, typically such as a large tow.

Because various adjustments are required in the step of partially splitting the continuous carbon fiber bundle, overall manufacturing efficiency may be improved when the step and subsequent steps are separated in manufacturing the SMC.

The present invention is made in a process of studies performed by the present inventors, based on the above-described idea, and mainly aims to provide a useful improvement in a CF-SMC manufacturing technique including a CF-SMC manufacturing method in which a continuous carbon fiber bundle is partially split before use.

In some cases, the present specification may explicitly or implicitly disclose problems which can be solved by each embodiment of the present invention.

An aspect of the present invention relates to an SMC manufacturing method as defined by the independent claim <NUM>.

According to the present invention, there is provided a useful improvement in a CF-SMC manufacturing technique including an SMC manufacturing method in which a continuous carbon fiber is partially split before use.

An SMC is a sheet-shaped carbon fiber prepreg obtainable by impregnating a carbon fiber mat comprising a chopped carbon fiber bundle with a thermosetting resin composition.

One embodiment of the present invention is an SMC manufacturing method including the following steps (i) to (iv).

In the SMC manufacturing method of the embodiment, fragmentation processing is performed so that at least some of the chopped carbon fiber bundles before being deposited on the carrier film is fragmented by being brought into contact with a rotating body. Through the fragmentation processing, a distribution of the filament numbers of the chopped carbon fiber bundles included in the carbon fiber mat formed in the step (iii) above becomes different from that when the fragmentation processing is not performed.

When necessary, a step of thickening the thermosetting resin composition is further provided after the step (iv).

In the SMC manufacturing method of the embodiment, a package of the continuous carbon fiber bundle prepared in advance is used. The continuous carbon fiber bundle has a filament number of NK and is partially split into n sub-bundles.

NK means N×<NUM>. For example, a filament number of a carbon fiber bundle comprising <NUM>,<NUM> single filaments is <NUM>, and a filament number of a carbon fiber bundle comprising <NUM>,<NUM> single filaments is <NUM>.

N is usually <NUM> or more, preferably <NUM> or more, and can be, but not limited to <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, for example.

When it is said that a continuous carbon fiber bundle is partially split into n sub-bundles, it means, in other words, that the continuous carbon fiber bundle is partially divided into n parts. Each of the n fiber bundles formed by dividing into n parts is called a sub-bundle.

The package of the partially split continuous carbon fiber bundle can be manufactured using, but not limited to a fiber package manufacturing apparatus represented in a conceptual diagram in <FIG>.

Referring to <FIG>, a fiber package manufacturing apparatus <NUM> includes a spread section <NUM>, a split section <NUM>, and a winding section <NUM>.

A continuous carbon fiber bundle <NUM> serving as a starting material and having a filament number of NK is drawn out from a supply bobbin B1.

The continuous carbon fiber bundle <NUM> drawn out from the supply bobbin B <NUM> before being split is first spread in the spread section <NUM>.

A spreader bar <NUM> provided in the spread section <NUM> may be heated and may be caused to reciprocate in a width direction of the continuous carbon fiber bundle <NUM>. Mechanisms therefor can refer to a known technique.

While the continuous carbon fiber bundle <NUM> originally has a flat shape, it is further increased in width and further decreased in thickness by being rubbed against the spreader bar <NUM>. The thickness of the continuous carbon fiber bundle <NUM> after passing through the spread section <NUM> is not limited, but can typically be <NUM> to <NUM>.

The spread section <NUM> may be omitted, when the continuous carbon fiber bundle <NUM> is sufficiently flat at a stage when the continuous carbon fiber bundle <NUM> is supplied from the supply bobbin B1. For example, a carbon fiber bundle having a bundle width of <NUM> times or more of an average thickness can be said to be sufficiently flat.

Next, the continuous carbon fiber bundle <NUM> is fed to the split section <NUM> and is partially split there.

The split section <NUM> is provided with a rotary blade <NUM> for forming a slit in the continuous carbon fiber bundle <NUM> and a plurality of godet rolls <NUM> for controlling a traveling speed of the continuous carbon fiber bundle <NUM>.

A rotation axis of the rotary blade <NUM> is parallel to a width direction of the continuous carbon fiber bundle <NUM> traveling along a fiber direction. A plurality of blade parts <NUM> are provided at a regular interval in a circumferential direction on an outer circumference of the rotary blade <NUM>, so that slits having a constant length are intermittently formed at a regular interval along the fiber direction of the continuous carbon fiber bundle <NUM>. A slit length and a gap length between the slits can be controlled by adjusting the traveling speed of the continuous carbon fiber bundle <NUM>, a circumferential speed of the rotary blade <NUM>, and/or an interval between the blade portions <NUM>.

The continuous carbon fiber bundle <NUM> is partially divided into n parts due to intermittent formation of slits along the fiber direction by (n-<NUM>)-number of the rotary blades <NUM> aligned in a direction parallel to the width direction of the traveling continuous carbon fiber bundle <NUM>.

The number n is not limited to, but preferably <NUM> or more and more preferably <NUM> or more and may be <NUM> or more.

As an example, <FIG> and <FIG> represent the continuous carbon fiber bundle <NUM> immediately after the slits extending in the fiber direction are intermittently formed by four rotary blades <NUM>.

For convenience, when in the continuous carbon fiber bundle <NUM>, the fiber direction (longitudinal direction) is defined as an x-direction, the width direction is defined as a y-direction and the thickness direction is defined as a z-direction, <FIG> is a plan view when the continuous carbon fiber bundle <NUM> is viewed from the z-direction and <FIG> represents a cross section of the continuous carbon fiber bundle <NUM> perpendicular to the x-direction (cross section when cut by an yz-plane).

As represented in <FIG>, in the continuous carbon fiber bundle <NUM>, four slit rows including a first slit row AS1, a second slit row AS2, a third slit row AS3, and a fourth slit row AS4 are formed.

The first slit row AS1 comprises a plurality of first slits S1 aligned in the x-direction.

The second slit row AS2 comprises a plurality of second slits S2 aligned in the x-direction.

The third slit row AS3 comprises a plurality of third slits S3 aligned in the x-direction.

The fourth slit row AS4 comprises a plurality of fourth slits S4 aligned in the x-direction.

The four slit rows are formed by different rotary blades and therefore are different from each other in positions in the y-direction.

A slit length Ls and an inter-slit gap length LG are constant in any of the slit rows, and are common also among different slit rows.

A ratio LS/(LS+LG) of the slit length LS to a sum of the slit length LS and the inter-slit gap length LG is usually <NUM>% or higher and preferably <NUM>% or higher and may be <NUM>% for example. Therefore, as represented in <FIG>, the continuous carbon fiber bundle <NUM> is split into five sub-bundles <NUM> in most parts.

The positions of the first slit row AS1, the second slit row AS2, the third slit row AS3, and the fourth slit row AS4 in the y-direction are set so that the widths of the five sub-bundles <NUM> are approximately the same. For example, when the filament number of the continuous carbon fiber bundle <NUM> is <NUM>, the filament number of each of the sub-bundles <NUM> is <NUM>±<NUM>.

The slit length Ls is not limited to, but preferably more than <NUM>, more preferably more than <NUM>, and much more preferably more than <NUM>. The slit length Ls can be <NUM> times or more, further <NUM> times or more, and further <NUM> times or more the cutting length when the continuous carbon fiber bundle <NUM> is cut to manufacture an SMC.

For example, the slit length Ls can be more than <NUM> and <NUM> or less, more than <NUM> and <NUM> or less, more than <NUM> and <NUM> or less, more than <NUM> and <NUM> or less, more than <NUM> and <NUM> or less, more than <NUM> and <NUM> or less, more than <NUM> and <NUM> or less, and more than <NUM> and <NUM> or less.

The inter-slit gap length LG is not limited to, but for example <NUM> to <NUM> and may be less than <NUM>.

In an example represented in <FIG>, positions of inter-slit gaps Gs are shifted in the x-direction between the first slit row AS1 and the second slit row AS2. The same applies to between the second slit row AS2 and the third slit row AS3, and between the third slit row AS3 and the fourth slit row AS4.

Such a configuration with a shifting in the positions of the inter-slit gaps Gs in the x- direction between the adjacent slit rows is not essential. In one example, the positions of the inter-slit gaps Gs may be aligned among all of the slit rows as represented in <FIG>. In another example, the positions of the inter-slit gaps Gs may be aligned among some of the slit rows and shifted in the x-direction among some other slit rows.

The slit length Ls, the inter-slit gap length LG, a ratio LS/(LS+LG) of the slit length Ls to a sum of the slit length Ls and the inter-slit gap length LG, and the position of the inter-slit gap GS as described above are not limited to a case where the continuous carbon fiber bundle <NUM> is partially split into the five sub-bundles, and the same applies to a case where the continuous carbon fiber bundle <NUM> is partially split into four sub-bundles or less or six sub-bundles or more.

Regardless of the number n, the filament number of the sub-bundle formed by splitting the continuous carbon fiber bundle <NUM> is preferably <NUM> or less, more preferably <NUM> or less, and much more preferably <NUM> or less.

Regardless of the number n, the filament number of the sub-bundle formed by splitting the continuous carbon fiber bundle <NUM> is preferably more than <NUM> and more preferably <NUM> or more. When the filament number is more than <NUM>, straightness of the carbon fiber bundle is likely to be maintained, and a reinforcing effect tends to be relatively high.

The abovementioned upper limits and lower limits can be arbitrarily combined. For example, regardless of the number n, the filament number of the sub-bundle formed by splitting the continuous carbon fiber bundle <NUM> is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM> and much more preferably <NUM> to <NUM>.

Referring to <FIG> again, the continuous carbon fiber bundle <NUM> partially split into n parts in the split section <NUM> is fed to the winding section <NUM>, and is wound on a winding bobbin B2, thereby completing the package.

For example, the winding bobbin B2 is a paper tube, but is not limited thereto. When the package is used, the winding bobbin B2 can be pulled out, and the continuous carbon fiber bundle can be unwound by internal unwinding.

The continuous carbon fiber bundle <NUM> is wound such that there is no gap between the sub-bundles <NUM>. The reason is to prevent the sub-bundles <NUM> from biting each other between a part previously wound on the bobbin B2 and a part wound later so as to overlap the previously wound part. By winding such that there is no gap between the sub-bundles <NUM>, the continuous carbon fiber bundle <NUM> can be prevented from being entangled or broken during unwinding by external unwinding or internal unwinding.

In order to wind the continuous carbon fiber bundle <NUM> on the bobbin so that there is no gap between the sub-bundles <NUM>, a total width W of the continuous carbon fiber bundle <NUM> may be made narrower than a sum of sub-bundle widths Ws as represented in <FIG>.

<FIG> is a sectional view when the continuous carbon fiber bundle <NUM> is cut perpendicular to the fiber direction, showing that the five sub-bundles <NUM> are arranged side by side without any gap in the y-direction. That is, there is no part where the adjacent sub-bundles <NUM> are away from each other, and each of the sub-bundles <NUM> overlaps the immediately adjacent sub-bundle <NUM> at an edge portion.

The width of the carbon fiber bundle can be reduced by guiding the carbon fiber bundle with a guide having a width narrower than that of the carbon fiber bundle. Therefore, in order to wind the continuous carbon fiber bundle <NUM> on the bobbin B2 in a state where the total width W is narrowed than a total sum of the sub-bundle widths Ws, for example, a grooved roll having a groove width narrower than the total sum of the sub-bundle widths may be used in guiding the continuous carbon fiber bundle after being partially split to the winding bobbin. Alternatively, the width of a fiber bundle guide of a traverse device may be narrowed than the total sum of the sub-bundle widths.

When the total width of the continuous carbon fiber bundle is narrowed by the above-described method, not only the sub-bundles may overlap each other, but also some sub-bundles may be folded in the width direction. Therefore, a manner of overlapping of the sub-bundles in the continuous carbon fiber bundle wound on the winding bobbin is not limited to the manner represented in <FIG> and can be various.

In order to ensure that there is no gap between the sub-bundles, the total width of the continuous carbon fiber bundles <NUM> when wound on the winding bobbin is preferably <NUM>% or less, more preferably <NUM>% or less of the total sum of the widths of the sub-bundles.

The total width of the continuous carbon fiber bundle when wound on the winding bobbin is preferably, but without limitation, not narrowed until the total width is equal to the width of the sub-bundle. In particular, in a case where the number n of sub-bundles is large, when the total width is excessively small, winding collapse is likely to occur.

A traverse device (not represented) is usually installed in the winding section <NUM>.

When the continuous carbon fiber bundle <NUM> is traverse-wound on the winding bobbin B2, although not limiting, a lead angle at a start of winding can be set to, for example, <NUM>° to <NUM>° and the lead angle at an end of winding can be set to, for example, <NUM>° to <NUM>°.

A winding ratio represents rotation times of the bobbin during one round trip of a traverse guide, and in other words, the winding ratio may be paraphrased as the number of turns per one traverse cycle. When a yarn is wound on a bobbin with a constant winding ratio, when the winding ratio is an integer, the yarn is wound at the same position of the bobbin in all traverse cycles, thereby causing so-called ribbon winding and a possible poor unwinding property.

When a fraction of the winding ratio after a decimal point is a multiple of <NUM>/p (p is an integer of <NUM> or more), the yarn is wound at the same position of the bobbin every p-traverse cycle, thereby causing a possible poor unwinding property particularly when p is small, as in a case where the winding ratio is an integer.

Therefore, when the continuous carbon fiber bundle <NUM> is wound on the winding bobbin B2, the winding ratio is usually not an integer, and further it is preferable that the fraction of the winding ratio after the decimal point is a multiple of none of <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM> and <NUM>/<NUM>.

<FIG> represents a conceptual diagram of an SMC manufacturing apparatus that can be preferably used in an SMC manufacturing method of the embodiment.

Referring to <FIG>, an SMC manufacturing apparatus <NUM> includes a first resin application section <NUM>, a second resin application section <NUM>, a chopping section <NUM>, a deposition section <NUM>, and an impregnation section <NUM>. A fragmentation processing apparatus <NUM> is disposed between the chopping section <NUM> and the deposition section <NUM>.

The first resin application section <NUM> is provided with a first applicator <NUM> including a doctor blade to form a first resin layer <NUM> comprising a thermosetting resin composition <NUM> on a first carrier film <NUM> drawn out from a roll.

The second resin application section <NUM> is provided with a second applicator <NUM> including a doctor blade to form a second resin layer <NUM> comprising the same thermosetting resin composition <NUM> on a second carrier film <NUM> drawn out from a roll.

The chopping section <NUM> is provided with a rotary cutter <NUM> for chopping a continuous carbon fiber bundle <NUM> drawn out from a package (the bobbin may be removed).

As represented in <FIG>, the rotary cutter <NUM> includes a guide roll <NUM>, a pinch roll <NUM>, and a cutter roll <NUM>. A plurality of blades <NUM> are disposed on an outer circumference of the cutter roll <NUM> at a regular interval in a circumferential direction, and chopped carbon fiber bundles <NUM> having a constant fiber length can be cut out one after another from the continuous carbon fiber bundle <NUM>.

Usually, a plurality of the continuous carbon fiber bundles <NUM> are aligned to be parallel to each other in a plane parallel to a rotation axis direction of the rotary cutter <NUM> and are supplied to the rotary cutter <NUM> at the same time.

The rotation axis direction of the rotary cutter <NUM> is a rotation axis direction of the rolls provided in the rotary cutter <NUM>, that is, a rotation axis direction of the cutter roll <NUM>. The directions of the rotation axes of the guide roll <NUM> and the pinch roll <NUM> are also the same as the direction of the rotation axis of the cutter roll <NUM>.

The deposition section <NUM> is disposed below the chopping section <NUM>. The first carrier film <NUM> is conveyed from the first resin application section <NUM> to the impregnation section <NUM> via the deposition section <NUM>. When the first carrier film <NUM> travels in the deposition section <NUM>, the chopped carbon fiber bundles <NUM> produced in the chopping section <NUM> are fallen and deposited on the first resin layer <NUM> formed on a surface of the first carrier film <NUM>, so that a carbon fiber mat <NUM> is formed.

A mechanism for gradually bringing the first carrier film <NUM> and the second carrier film <NUM> closer to each other is disposed in an upstream part of the impregnation section <NUM>. An impregnation machine <NUM> is disposed in a main part of the impregnation section <NUM>. In order that a laminate in which the carbon fiber mat <NUM> and the thermosetting resin composition <NUM> are sandwiched between the first carrier film <NUM> and the second carrier film <NUM> is conveyed by being sandwiched from above and below with two conveyor belts, the impregnation machine <NUM> includes two belt conveyors located above and below, and includes rollers for pressurizing the laminate by sandwiching it together with the conveyor belts.

As represented in <FIG>, the fragmentation processing apparatus <NUM> disposed between the chopping section <NUM> and the deposition section <NUM> includes a cover <NUM>, and guide plates <NUM> and a pair of pin rollers (first pin roller 263a and second pin roller 263b) which are disposed inside the cover. The first pin roller 263a and the second pin roller 263b have substantially the same axial length, and have the rotation axes parallel to each other.

In the SMC manufacturing apparatus <NUM>, the fragmentation processing apparatus <NUM> is disposed such that the rotation axes of the first pin roller 263a and the second pin roller 263b are parallel to the rotation axis direction of the rotary cutter <NUM>. The position of the fragmentation processing apparatus <NUM> is preferably right below the rotary cutter <NUM>.

Referring to <FIG>, the first pin roller 263a has a cylinder 264a, and a plurality of pins 265a having the same shapes and the same dimensions are disposed on the surface thereof. Both the cylinder 264a and the pins 265a are rigid bodies, and are formed of metal, for example.

A diameter of the cylinder 264a is not limited, but can be <NUM> to <NUM>, for example.

The pins 265a extend to be perpendicular to the rotation axis of the first pin roller 263a. Although not limited, the pin 265a has a columnar shape, for example. A boundary between an end surface and a circumferential surface may be chamfered in the pin 265a.

The diameter of the pin 265a is not limited, but can be, for example, <NUM> to <NUM>.

The length of the pin 265a, that is, the distance from the tip to the root of the pin is not limited, but can be <NUM> to <NUM>, for example.

It is preferable that the pin 265a has a circular cross section to prevent fuzzing of the chopped carbon fiber bundle <NUM> processed by the fragmentation processing apparatus <NUM>. The pin 265a may have a shape of a cone or a truncated cone whose diameter decreases toward the tip.

It is preferable that disposition of the pin 265a on the circumferential surface of the cylinder 264a overlaps original disposition when shifted by <NUM> to <NUM> in the axial direction and <NUM> to <NUM> in the circumferential direction.

For example, in a case of the cylinder 264a represented in <FIG>, when the circumferential surface is plane-developed, the pin 265a is disposed at each vertex of equilateral triangles (indicated by a broken line) tessellating such that one side is parallel to the axial direction, as represented in <FIG>. For example, when the length of one side of the equilateral triangle is <NUM>, the disposition of the pin 265a represented in <FIG> overlaps the original disposition when shifted by <NUM> in the axial direction and approximately <NUM> in the circumferential direction.

In this specification, the maximum radius of the pin roller is defined as a distance from the rotation axis to the tip of the pin. In the first pin roller 263a, the radius of the cylinder 264a is preferably half or more of the maximum radius of the first pin roller 263a, and is more preferably <NUM>% or more. The reason is that as the ratio of the cylinder radius to the maximum radius of the pin roller increases, a difference decreases between the circumferential speed at the tip of the pin and the circumferential speed at the root of the pin when the pin roller is rotated.

All with regard to the first pin roller 263a described above are also applied to the second pin roller 263b.

Although not limited, in order to reduce costs for designing, manufacturing, and maintaining the fragmentation processing apparatus <NUM>, it is preferable that in items as many as possible, including the maximum radius, the cylinder diameter and the shape, the dimension, the number and the disposition of the pins, designs and specifications of the first pin roller 263a and the second pin roller 263b coincide with each other.

Referring to <FIG>, in the fragmentation processing apparatus <NUM>, the sum of the maximum radius rM1 of the first pin roller 263a and the maximum radius rM2 of the second pin roller 263b is larger than a distance d<NUM> between the rotation axes of the two pin rollers.

The sum of the maximum radius rM1 of the first pin roller 263a and the radius rC2 of the cylinder 264b of the second pin roller is smaller than the distance d<NUM> between the rotation axes of the two pin rollers. Similarly, the sum of the maximum radius rM2 of the second pin roller 263b and the radius rC1 of the cylinder 264a of the first pin roller is also smaller than the distance d<NUM> between the rotation axes of the two pin rollers.

A difference {(rM1 + rM2)) - d<NUM>} between the sum of the maximum radius rM1 of the first pin roller 263a and the maximum radius rM2 of the second pin roller 263b and the distance d<NUM> between the rotation axes is not limited but may be <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less.

The first pin roller 263a and the second pin roller 263b are rotationally driven by a drive mechanism (not represented). Rotation speeds of the first pin roller 263a and the second pin roller 263b may be independently controllable.

Rotation directions of the first pin roller 263a and the second pin roller 263b are as indicated by arrows in <FIG>. That is, the first pin roller 263a rotates such that its pins move downward from above on its side facing the second pin roller 263b, and the second pin roller 263b rotates such that its pins move downward from above on its side facing the first pin roller 263a.

Rotating both the first pin roller 263a and the second pin roller 263b in such a way is advantageous in preventing the chopped carbon fiber bundle <NUM> from being clogged between the two pin rollers.

Substantially all of the chopped carbon fiber bundles <NUM> produced in the chop section <NUM> are fallen to the deposition section through between the cylinder 264a of the first pin roller 263a and the cylinder 264b of the second pin roller 263b. Since difference in falling positions of the chopped carbon fiber bundles <NUM> depending on bundle sizes is less likely to occur, even when a distribution of the bundle sizes of the chopped carbon fiber bundles <NUM> is wide, there is an advantage in that the carbon fiber mat <NUM> is likely to be uniform in the thickness direction.

In a modified embodiment, in the fragmentation processing apparatus <NUM>, a sum of the maximum radius rM1 of the first pin roller 263a and the maximum radius rM2 of the second pin roller 263b may be equal to the distance d<NUM> between the rotation axes of the two pin rollers.

In another modified embodiment, in the fragmentation processing apparatus <NUM>, a sum of the maximum radius rM1 of the first pin roller 263a and the maximum radius rM2 of the second pin roller 263b may be slightly smaller than the distance d<NUM> between the rotation axes of the two pin rollers, and in that case, a difference {d<NUM> - (rM1 + rM2)} therebetween is preferably <NUM> or less, and is more preferably <NUM> or less.

An SMC manufacturing method of the embodiment will be described using, as an example, a case in which the SMC manufacturing apparatus <NUM> described in <NUM> above is used.

In a drawing out step, a continuous carbon fiber bundle is drawn out from a package of the continuous carbon fiber bundle prepared in advance. The continuous carbon fiber bundle has a filament number of NK and is partially split into n sub-bundles in advance.

In this step, the continuous carbon fiber bundle may be drawn out by external unwinding from a bobbin package placed on a creel, or the continuous carbon fiber bundle may be drawn out by internal unwinding from a package from which a bobbin is removed.

As described above, when the package is manufactured, the continuous carbon fiber bundle is wound on the bobbin in a state where the adjacent sub-bundles overlap each other. Therefore, the continuous carbon fiber bundle drawn out from the package includes a part in which the sub-bundles are partially overlapped and sticked to each other.

In a chopping step, the drawn out continuous carbon fiber bundle <NUM> is supplied to the chopping section <NUM> and cut one after another by the rotary cutter <NUM>, thereby producing the chopped carbon fiber bundles <NUM> having a predetermined fiber length. The produced chopped carbon fiber bundles <NUM> fall toward the fragmentation processing apparatus <NUM> placed below the rotary cutter <NUM>.

The fiber length of the chopped carbon fiber bundle <NUM> is not limited, but can be <NUM> to <NUM>, preferably <NUM> to <NUM>, for example, and can be typically approximately <NUM>, approximately <NUM>, or approximately <NUM>.

As described above, the continuous carbon fiber bundle drawn out from the package includes a part in which the sub-bundles are partially overlapped and sticked to each other. The chopped carbon fiber bundles produced in the chopping step include to some extent a fiber bundle having a filament number of more than { (N/n)+<NUM> } K, which is generated by cutting such part of the continuous carbon fiber bundle. The fragmentation processing step aims to improve a distribution of the filament numbers of the chopped carbon fiber bundles in the carbon fiber mat formed in a deposition step (to be described later) by fragmentation of such fiber bundle with the fragmentation processing apparatus.

In the fragmentation processing apparatus <NUM>, at least some of the chopped carbon fiber bundles <NUM> falling from the rotary cutter <NUM> come into contact with at least one of the first pin roller 263a and the second pin roller 263b and are divided into a plurality of fragments by an impact.

The fragmentation processing is not intended for defibration. That is, the fragmentation processing is not to loosen the chopped carbon fiber bundle into single fiber filaments or a state close to single fiber filaments. In a preferred example, a circumferential speed at a tip of the pin of each of the first pin roller 263a and the second pin roller 263b is set so that the fragmentation processing does not generate a fiber bundle having a filament number of <NUM> or less and a single fiber filament, or even when generated, so that a content thereof in the carbon fiber deposited on the first carrier film <NUM> is lower than <NUM>% by weight.

One of reasons why the rotation directions of the first pin roller 263a and the second pin roller 263b are each set such that the pins move downward from above on the side facing the other pin roller is to prevent applying a strong shearing force to the chopped carbon fiber bundles <NUM> passing through between the two pin rollers. It is conceivable that the strong shearing force causes fuzzing or straightness deterioration of the carbon fiber bundles.

In order to more effectively achieve this object, it is preferable that rotation speeds (rpm) of the first pin roller 263a and the second pin roller 263b are set such that the circumferential speed at the tip of the former's pin 265a and the circumferential speed at the tip of the latter's pin 265b are equal to each other.

In a resin application step, the first resin layer <NUM> comprising the thermosetting resin composition <NUM> is formed on the first carrier film <NUM> drawn out from a roll using the first applicator <NUM>, and the second resin layer <NUM> comprising the same thermosetting resin composition <NUM> is formed on the second carrier film <NUM> drawn out from another roll using the second applicator <NUM>.

The thermosetting resin composition <NUM> is a fluid paste containing a thermosetting resin as a main component and in which a thickener and a curing agent are blended, and if necessary, additives such as a reactive diluent, a low shrinkage agent, a filler, and a flame retardant are blended.

Typical examples of the thermosetting resin are an epoxy resin, a vinyl ester resin, an unsaturated polyester resin, a polyimide resin, a maleimide resin and a phenol resin, and two or more types selected from these resins can be mixed and used.

Preferred thermosetting resins are the epoxy resin, the vinyl ester resin, and the unsaturated polyester resin in view of excellent adhesiveness to the carbon fiber.

With regard to a specific formulation of the thermosetting resin composition, a related art can be appropriately referred to.

In a deposition step, the chopped carbon fiber bundles <NUM> processed by the fragmentation processing apparatus <NUM> fall on the first carrier film <NUM> conveyed below the fragmentation processing apparatus <NUM>. The fallen chopped carbon fiber bundles <NUM> are deposited on the first resin layer <NUM> formed on a surface of the first carrier film <NUM>, thereby forming the carbon fiber mat <NUM>.

On the way to the impregnation machine <NUM>, the first carrier film <NUM> loaded with the carbon fiber mat <NUM> deposited on the first resin layer <NUM> is laminated with the second carrier film <NUM> with a side having the second resin layer <NUM> formed thereon facing downward.

The carbon fiber mat <NUM> is impregnated with the thermosetting resin composition <NUM> by pressurizing the laminate formed by the lamination with the impregnation machine <NUM>.

After the impregnation step is completed, the impregnated carbon fiber mat <NUM> is wound on a bobbin while sandwiched between the first carrier film <NUM> and the second carrier film <NUM> and becomes an SMC product through an aging step to be performed when necessary. In the aging step, the thermosetting resin composition <NUM> becomes highly viscous by an action of the added thickener and is brought into a semi-cured state.

According to the SMC manufacturing method described in <NUM>, the continuous carbon fiber bundle having a filament number of NK and partially split into n sub-bundles is used as a raw material. In the SMC manufacturing method according to a modified embodiment, a continuous carbon fiber bundle which has not been processed to partially split may be used as the raw material.

Therefore, the SMC manufacturing method below is also included in the embodiment of the present invention.

The manufacturing method according to [<NUM>],
wherein a sum of a maximum radius of the first pin roller and a maximum radius of the second pin roller is equal to or larger than a distance between rotation axes of the first pin roller and the second pin roller.

The manufacturing method according to [<NUM>],
wherein the sum of the maximum radius of the first pin roller and the maximum radius of the second pin roller is larger than the distance between the rotation axes of the first pin roller and the second pin roller.

The manufacturing method according to [<NUM>],
wherein a sum of a maximum radius of the first pin roller and a maximum radius of the second pin roller is smaller than a distance between rotation axes of the first pin roller and the second pin roller, and a difference therebetween is <NUM> or less.

The manufacturing method according to any one of [<NUM>] to [<NUM>],
wherein in each of the first pin roller and the second pin roller, a radius of a cylinder is equal to or larger than half of a maximum radius.

The manufacturing method according to any one of [<NUM>] to [<NUM>],
wherein a circumferential speed at a pin tip of the first pin roller is equal to a circumferential speed at a pin tip of the second pin roller.

The manufacturing method according to any one of [<NUM>] to [<NUM>],
wherein a content of a carbon fiber bundle having a filament number of more than <NUM> in the carbon fiber mat is <NUM>% by weight or more.

The manufacturing method according to any one of [<NUM>] to [<NUM>],
wherein the carbon fiber mat is pressurized together with the thermosetting resin composition to impregnate the carbon fiber mat with the thermosetting resin composition.

The manufacturing method according to any one of [<NUM>] to [<NUM>],
wherein at least a part of the thermosetting resin composition is applied to an upper surface of the carrier film before forming the carbon fiber mat by depositing the chopped carbon fiber bundles.

Hereinafter, results of experiments performed by the present inventors will be described.

As a starting material, a flat continuous carbon fiber bundle (TR50S15L manufactured by Mitsubishi Chemical Corporation) having a filament number of <NUM>, an initial width of <NUM> and a thickness of <NUM> was prepared. By forming four slit rows each having a slit length of <NUM>,<NUM> and an inter-slit gap length of <NUM> using a splitter having four rotary blades, the continuous carbon fiber bundle was partially split into five sub-bundles each having a width of <NUM>. Positions of inter-slit gaps along the fiber direction were the same among all of the slit rows.

After the partial splitting, by winding the continuous carbon fiber bundle on a paper bobbin having a diameter of <NUM> and a length of <NUM> with a traverse length of <NUM>, a square end type package was produced. By adjusting the width of a guide for guiding the fiber bundle, the total width of the continuous carbon fiber bundle during winding was made to be <NUM> or less.

A carbon fiber mat was prepared from the continuous carbon fiber bundle having a filament number of <NUM> and partially split into five sub-bundles prepared in the above-described procedure using an SMC manufacturing apparatus having the same configuration as the SMC manufacturing apparatus represented in <FIG> except that the fragmentation processing apparatus was not provided.

A plurality of the continuous carbon fiber bundles were supplied to a rotary cutter in a state of being aligned in parallel at an equal interval and were cut every <NUM>.

The chopped carbon fiber bundles were fallen onto a carrier film which travels below the rotary cutter at a line speed of <NUM>/min and was not coated with a thermosetting resin composition. The fallen chopped carbon fiber bundles were deposited on the carrier film to form a carbon fiber mat.

A region of approximately <NUM> × <NUM> deposited near a center line of the carrier film was selected from the carbon fiber mat prepared through the above-described procedure, and weights of all of the chopped carbon fiber bundles (<NUM> pieces or more) included in the region was measured. <FIG> represents a distribution of the filament numbers of the chopped carbon fiber bundles in the carbon fiber mat, which was obtained by converting the measured weights into filament numbers.

In the prepared carbon fiber mat, a content of the carbon fiber bundle having the filament number of more than <NUM> was <NUM>% by weight or more.

The carbon fiber mat was prepared using the same SMC manufacturing apparatus used in Experiment <NUM> except that the fragmentation processing apparatus was provided, and the distribution of the filament numbers thereof was measured in the same manner as in Experiment <NUM>. The procedure for preparing the carbon fiber mat was the same as that in Experiment <NUM> except that the chopped carbon fiber bundles were subjected to a fragmentation processing by the fragmentation processing apparatus before being deposited on the carrier film.

A configuration of the fragmentation processing apparatus was the same as that included in the SMC manufacturing apparatus represented in <FIG>. Both the two pin rollers were formed of metal and had the same configuration. A diameter and a length of a pin disposed on a cylinder circumferential surface were respectively <NUM> and <NUM>. The disposition of the pins on the circumferential surface of the cylinder of each pin roller was periodic, and the disposition overlapped the original disposition when shifted by <NUM> in the axial direction and <NUM> in the circumferential direction. The sum of the maximum radii of the two pin rollers was <NUM> larger than the distance between the rotation axes of the two pin rollers.

The two pin rollers were rotated such that in both pin rollers the circumferential speeds at the pin tips were <NUM>/min and in each pin rollers the pins moved downward from above on the side facing the other pin roller.

<FIG> represents the distribution of the filament numbers of the chopped carbon fiber bundles in the prepared carbon fiber mat.

The carbon fiber mat was prepared in the same manner as in Experiment <NUM> except that both the two pin rollers were rotated such that in each pin rollers the pins moved upward from below on the side facing the other pin roller, and the distribution of the filament numbers was measured.

It was found that the chopped carbon fiber bundles tend to be more finely fragmented by the fragmentation processing of Experiment <NUM> compared to that of Experiment <NUM>.

The carbon fiber mat was prepared in the same manner as in Experiment <NUM> except that the two pin rollers were rotated in the same direction, and the distribution of the filament numbers was measured.

The carbon fiber mat was prepared in the same manner as in Experiment <NUM> except that the distance between the rotation axes of the two pin rollers was the same as the sum of the maximum radii of the two pin rollers, and the distribution of the filament numbers was measured.

A square end type fiber package was produced by preparing and partially splitting a flat continuous carbon fiber bundle having the filament number of <NUM>,<NUM> (<NUM>), the initial width of <NUM> and the thickness of <NUM> and thereafter, winding the partially split continuous carbon fiber bundle on a paper bobbin having a diameter of <NUM> and a length of <NUM> with a traverse length of <NUM>. Widening with a spreader was not performed.

A splitter having four rotary blades was used for partially splitting the continuous carbon fiber bundle. By forming four slit rows each having the slit length of <NUM>,<NUM> and the inter-slit gap length of <NUM>, the continuous carbon fiber bundle was split into five sub-bundles each having the width of <NUM> and partially joined to each other. Positions of inter-slit gap in the fiber direction were the same among all of the slit rows.

In winding, the lead angle at the winding start was <NUM>°, the lead angle at the winding end was <NUM>°, the winding ratio was <NUM>, and the winding amount was <NUM>.

By adjusting a groove width of a grooved roll which the continuous carbon fiber bundle passed through after the split processing, the total width of the continuous carbon fiber bundle wound on the bobbin was made to be <NUM> which was <NUM>% of the total sum of the widths of the sub-bundles. When the bobbin was pulled out from the produced fiber package and the continuous carbon fiber bundle was drawn out by internal unwinding, no particular problem was found out.

In contrast, with a fiber package produced in the same manner, except that the total width of the continuous carbon fiber bundle wound on the bobbin was made to be <NUM> which was the same as the total sum of the widths of the sub-bundles, when the bobbin was pulled out and the continuous carbon fiber bundle was drawn out by internal unwinding, frequency of occurrence of entanglement was relatively high.

Claim 1:
An SMC manufacturing method comprising:
(i) drawing out a continuous carbon fiber bundle from a package, the continuous carbon fiber bundle having a filament number of NK and partially split into n sub-bundles in advance;
(ii) forming chopped carbon fiber bundles by chopping the continuous carbon fiber bundle drawn out from the package with a rotary cutter;
(iii) forming a carbon fiber mat by depositing the chopped carbon fiber bundles on a carrier film traveling below the rotary cutter; and
(iv) impregnating the carbon fiber mat with a thermosetting resin composition,
wherein fragmentation processing using a fragmentation processing apparatus (A) below is performed on the chopped carbon fiber bundles before being deposited on the carrier film,
the fragmentation processing apparatus (A) comprising a first pin roller and a second pin roller, each of which has a rotation axis parallel to a rotation axis direction of the rotary cutter, a sum of a maximum radius of the first pin roller and a maximum radius of the second pin roller is larger than the distance between the rotation axes of the first pin roller and the second pin roller, and the first pin roller is rotationally driven such that its pins move downward from above on its side facing the second pin roller, and the second pin roller is rotationally driven such that its pins move downward from above on its side facing the first pin roller.