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 using a compression molding method.

The CF-SMC is a type of carbon fiber prepreg, 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) (<CIT>).

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 (<CIT>).

There is an example in which chopped carbon fiber bundles having a fiber length of <NUM> cut out from a continuous carbon fiber bundle having a filament number of <NUM> are brought into contact with a striking mechanism, divided into a plurality of pieces, and thereafter, used for forming a carbon fiber mat (<CIT>).

The main purpose of the present invention is to provide a useful improvement in a method for manufacturing a CF-SMC from a continuous carbon fiber bundle having a large filament number, typically such as a large tow.

A manufacturing method of an SMC of the present invention includes the features of claim <NUM>. Embodiments are named in the dependent claims.

According to the present invention, there is provided a useful improvement in a manufacturing method of a CF-SMC from a continuous carbon fiber bundle having a large filament number, typically such as a large tow.

One embodiment of the invention relates to an SMC manufacturing method.

The SMC manufacturing method of the present embodiment comprises the following steps (i) to (iv).

<FIG> represents a conceptual diagram of the SMC manufacturing apparatus that can be preferably used in the SMC manufacturing method comprising the above-described steps (i) to (iv).

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 the 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.

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, so that chopped carbon fiber bundles <NUM> having constant fiber lengths 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 direction of a rotation axis of each roll provided in the rotary cutter <NUM>, that is, a direction of a rotation axis of the cutter roll <NUM>. 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 by 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>, a guide plate <NUM> and a pair of pin rollers (first pin roller 163a and second pin roller 163b) which are disposed inside the cover. The first pin roller 163a and the second pin roller 163b are disposed side by side, have substantially the same axial lengths, 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 163a and the second pin roller 163b are parallel to the rotation axis direction of the rotary cutter <NUM>.

Referring to <FIG>, the first pin roller 163a has a cylinder 164a, and a plurality of pins 165a having the same shapes and the same dimensions are disposed on the surface thereof. Both the cylinder 164a and the pin 165a are rigid bodies, and are formed of metal, for example.

A diameter of the cylinder 164a is not limited to, but can be <NUM> to <NUM>, for example.

The pins 165a extend to be perpendicular to the rotation axis of the first pin roller 163a. Although not limited, the pins 165a have columnar shapes, for example. A boundary between an end surface and a circumferential surface may be chamfered in the pin 165a.

The diameter of the pin 165a is not limited to, but can be, for example, <NUM> to <NUM>.

The length of the pin 165a, that is, the distance from the tip to the root of the pin is not limited to, but can be, for example, <NUM> to <NUM>.

It is preferable that the pin 165a has a circular cross section to prevent fuzzing of the chopped carbon fiber bundles <NUM> processed by the fragmentation-processing apparatus <NUM>. The pin 165a may have a shape of a cone or a truncated cone whose diameter decreases toward the tip.

It is preferable that disposition of the pins 165a on the circumferential surface of the cylinder 164a overlaps the 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 pin roller 163a represented in <FIG>, when the circumferential surface of the cylinder 164a is plane-developed, the pin 165a is disposed at each vertex of an equilateral triangle (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 pins 165a represented in <FIG> overlaps the original disposition when shifted by <NUM> in the axial direction and approximately <NUM> in the circumferential direction.

All with regard to the first pin roller 163a described above are also applied to the second pin roller 163b.

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 a maximum radius, a cylinder diameter, and shapes, dimensions, a number and a disposition of pins, designs and specifications of the first pin roller 163a and the second pin roller 163b coincide with each other.

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.

Referring to <FIG>, the sum of a maximum radius rM1 of the first pin roller 163a and a maximum radius rM2 of the second pin roller 163b 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 163a and a radius rC2 of the cylinder 164b 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 163b and a radius rC1 of the cylinder 164a 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 a sum of the maximum radius rM1 of the first pin roller 163a and the maximum radius rM2 of the second pin roller 163b and the distance d<NUM> between the rotation axes is not limited to, but may be <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less.

The first pin roller 163a and the second pin roller 163b are rotationally driven by a drive mechanism (not represented). Rotation speeds of the first pin roller 163a and the second pin roller 163b may be independently controllable.

There is no limitation on the rotation directions of the first pin roller 163a and the second pin roller 163b. Therefore, the rotation direction of the first pin roller 163a and the rotation direction of the second pin roller 163b may be the same or opposite.

When the first pin roller 163a and the second pin roller 163b rotate in mutually opposite directions, the rotation mode may be inward rotation or outward rotation. The inward rotation means a mode in which each pin roller rotates such that its pins move downward from above on its side facing the other pin roller. On the other hand, the outward rotation means a mode in which each pin roller rotate such that its pins move upward from below on its side facing the other pin roller.

Rotating both the first pin roller 163a and the second pin roller 163b is advantageous in preventing the chopped carbon fiber bundles <NUM> from being clogged between the two pin rolls.

In a modified embodiment, in the fragmentation-processing apparatus <NUM>, the sum of a maximum radius rM1 of the first pin roller 163a and a maximum radius rM2 of the second pin roller 163b 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>, the sum of the maximum radius rM1 of the first pin roller 163a and the maximum radius rM2 of the second pin roller 163b may be slightly smaller than the distance d<NUM> between the rotation axes of the two pin rollers, in which a difference {d<NUM> - (rM1 + rM2)} therebetween is preferably <NUM> or less, and is more preferably <NUM> or less.

In another embodiment, the number of pin rollers provided in the fragmentation-processing apparatus may be one, or may be three or more.

In still another embodiment, the fragmentation-processing apparatus may be provided a rotating body other than a pin roller. An example of the rotating body other than a pin roller is a rotating body having a structure in which a pair of disks are connected by a plurality of wires or rods as represented in <FIG>.

In the SMC manufacturing method of the present embodiment, the continuous carbon fiber bundle having the filament number of NK is used as a carbon fiber raw material.

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

The filament number of the continuous carbon fiber bundle used as a raw material in the SMC manufacturing method of the present embodiment is at least <NUM>, preferably <NUM> or more, more preferably <NUM> or more, and is much more preferably <NUM> or more.

The filament number of the continuous carbon fiber bundle used as a raw material in the SMC manufacturing method of the present embodiment is not limited to, but is usually <NUM> or less, and may be <NUM> or less, or <NUM> or less, <NUM> or less.

The abovementioned upper limits and lower limits can be arbitrarily combined. For example, the filament number of the continuous carbon fiber bundle used as a raw material in the SMC manufacturing method of the present embodiment is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, much more preferably <NUM> to <NUM>, and is particularly preferably <NUM> to <NUM>.

Preferably, the continuous carbon fiber bundle used as a raw material in the SMC manufacturing method of the present embodiment is a continuous carbon fiber bundle partially split into the n-number (where, n is an integer of <NUM> or more) of sub-bundles such that N/n is <NUM> to <NUM>. N/n is preferably <NUM> to <NUM>, and is more preferably <NUM> to <NUM>.

When it is said that the 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 the division into n parts is called the sub-bundle.

Although not limited, partially splitting of the continuous carbon fiber bundle can be conducted by using a split device represented in a conceptual diagram in <FIG>, for example.

Referring to <FIG>, the split device <NUM> comprises a spread section <NUM> and a split 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 B1 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>. Mechanism for these configurations 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 to, but can be typically <NUM> when the filament number is <NUM>.

The spread section <NUM> may be omitted, when the continuous carbon fiber bundle <NUM> is sufficiently flat in a stage where 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>.

A rotation axis of the rotary blade <NUM> is parallel to a width direction of the continuous carbon fiber bundle <NUM> traveling in 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 an inter-slit gap length can be controlled by adjusting a traveling speed of the continuous carbon fiber bundle <NUM>, a circumferential speed of the rotary blade <NUM>, and/or an interval between the blade parts <NUM>.

The traveling speed of the continuous carbon fiber bundle <NUM> is controlled by a plurality of godet rolls <NUM>.

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

As an example, <FIG> and <FIG> represent the continuous carbon fiber bundle <NUM> when n=<NUM>, that is, when partially divided into five parts by four rotary blades <NUM>.

For convenience, when the fiber direction (longitudinal direction) of the continuous carbon fiber bundle <NUM> 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 in the z-direction, and <FIG> represents a cross section perpendicular to the x-direction (a cross section when cut by a yz-plane) of the continuous carbon fiber bundle <NUM>.

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

The first slit row Asi 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 Ass 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.

The slit length Ls and the 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 Asi, 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.

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 a cutting length when the continuous carbon fiber bundle <NUM> is cut to manufacture the 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, or more than <NUM> and <NUM> or less.

The inter-slit gap length LG is not limited to, but for example, is <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 Asi and the second slit row AS2. The same applies to between the second slit row AS2 and the third slit row Ass, and between the third slit row Ass 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 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.

What is described above about the slit length Ls, the inter-slit gap length LG, a ratio Ls/(L S+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 is not limited to a case of n=<NUM>, that is, 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.

Referring to <FIG> again, the continuous carbon fiber bundle <NUM> partially split into n parts in the split section <NUM> is wound on a take-up bobbin B2 to form a package, and thereafter, the package is used in the SMC manufacturing method according to the present embodiment. That is, the split device <NUM> is offline from the SMC manufacturing apparatus <NUM>.

In another embodiment, the split device <NUM> may be connected inline to the SMC manufacturing apparatus <NUM>. That is, the continuous carbon fiber bundle <NUM> partially split into the n parts by the split device <NUM> may be supplied to the chopping section <NUM> of the SMC manufacturing apparatus <NUM> without being wound on the bobbin even once.

When the continuous carbon fiber bundle <NUM> does not contain a sufficient amount of sizing agent, fuzzing is likely to occur when the continuous carbon fiber bundle <NUM> is partially split, and, in addition to that, the sub-bundles <NUM> formed by splitting tend to be fixed to each other. When the sub-bundles <NUM> are fixed to each other, an advantageous effect obtained by splitting the continuous carbon fiber bundle <NUM> is impaired, therefore, in such a case, before being partially split for example, it is desirable to supplement the sizing agent contained in the continuous carbon fiber bundle <NUM>.

Supplementing the sizing agent in this stage is also effective in preventing generation of a large amount of excessively fine fragments when the fragmentation-processing is performed on the chopped carbon fiber bundle in a later step.

The partially split 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 predetermined fiber lengths. 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 to, but can be <NUM> to <NUM>, preferably <NUM> to <NUM>, for example, and can be typically approximately <NUM> (<NUM> inches), approximately <NUM> (<NUM> inch), or approximately <NUM> (<NUM> inches).

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 163a and the second pin roller 163b and are each 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. The chopped carbon fiber bundle having an excessively small filament number has low straightness, and does not have a sufficient reinforcing effect. The carbon fiber bundle having the filament number exceeding <NUM> easily maintains straightness, and has a relatively high reinforcing effect.

In the fragmentation-processing apparatus <NUM>, the rotation direction of the first pin roller 163a and the second pin roller 163b and the circumferential speed at each pin tip are set so that a content of the chopped carbon fiber bundle having the filament number of <NUM> or less in the carbon fiber deposited on the first carrier film <NUM> is preferably less than <NUM>% by weight.

When other conditions are the same, and when the first pin roller 163a and the second pin roller 163b are each rotationally driven such that its pins move downward from above on its side facing the other pin roller (inward rotation mode), the generation amount of fragments having the filament number of <NUM> or less decreases, compared to a case of adopting another rotation mode.

When other conditions are the same, as the circumferential speed is lower at the pin tips of each of the first pin roller 163a and the second pin roller 163b, the generation amount of fragments having the filament number of <NUM> or less decreases.

In a preferred example, the rotation directions of the first pin roller 163a and the second pin roller 163b and the circumferential speed at each pin tip may be set so that the content of the chopped carbon fiber bundle having the filament number of <NUM> or less in the carbon fibers deposited on the first carrier film <NUM> is less than <NUM>% by weight if the continuous carbon fiber bundle <NUM> were supplied without being partially split.

The content of the sizing agent of the continuous carbon fiber bundle <NUM> may be increased to reduce the generation amount of fragments having a filament number of <NUM> or less and fuzz.

In the inward rotation mode in which the first pin roller 163a and the second pin roller 163b are each rotationally driven such that its pins move downward from above on its side facing the other pin roller, substantially all of the chopped carbon fiber bundles <NUM> produced in the chopping section <NUM> are fallen to the deposition section through between the cylinder 164a of the first pin roller 163a and the cylinder 164b of the second pin roller 163b. As a result, 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 bundle <NUM> is wide, there is an advantage in that the carbon fiber mat <NUM> is likely to be uniform along the thickness direction.

The first resin layer <NUM> formed on the first carrier film <NUM> using the first applicator <NUM>, and the second resin layer <NUM> formed on the second carrier film <NUM> using the second applicator <NUM> are comprised of the same thermosetting resin composition <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.

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 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.

In the SMC manufactured by the SMC manufacturing method of the present embodiment, even when a starting material is the continuous carbon fiber bundle classified as a large tow, the CFRP obtained by curing the same shows a favorable elastic modulus. The favorable elastic modulus here means an elastic modulus equivalent to an elastic modulus of a CFRP obtained by curing an SMC manufactured by using a continuous carbon fiber bundle having a less filament number as a starting material.

In the SMC manufactured by the SMC manufacturing method of the present embodiment, furthermore, when the continuous carbon fiber bundle having a filament number of NK serving as the starting material is partially split into n sub-bundles, the CFRP obtained by curing the same shows high strength. The high strength here means strength equivalent to strength of a CFRP obtained by curing an SMC manufactured by using a continuous carbon fiber bundle having a less filament number as a starting material.

In a preferred embodiment, N/n is <NUM> or more and <NUM> or less. For example, this means that n is <NUM> to <NUM> when N is <NUM>, n is <NUM> to <NUM> when N is <NUM>, and n is <NUM> to <NUM> when N is <NUM>. In the preferred embodiment, the number of slit rows that have to be formed in the continuous carbon fiber bundle serving as the starting material is pretty small. This means that not only that the slits are easily formed, but also that the amount of fuzz generated along with the formation of the slits is small. The small amount of fuzz is advantageous in that impregnation defects are less likely to occur, and is also preferable in preventing deterioration of appearance of the CFRP molded from the manufactured SMC.

An SMC was prepared by using an SMC manufacturing apparatus having a similar configuration as the SMC manufacturing apparatus represented in <FIG>.

A configuration of a fragmentation-processing apparatus was similar to that included in the SMC manufacturing apparatus represented in <FIG>. Two pin rollers were both formed of metal and had the same configuration. Diameters and lengths of pins disposed on a cylinder circumferential surface of each pin roller were respectively <NUM> and <NUM>. The disposition of the pins on the cylinder circumferential surface 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. A sum of maximum radii of the two pin rollers was <NUM> larger than a distance between rotation axes of the two pin rollers.

A continuous carbon fiber bundle (TRW40 <NUM> manufactured by Mitsubishi Chemical Corporation) having the filament number of <NUM> was dipped in an aqueous dispersion of an epoxy acrylate-based sizing agent, dried, and then used as a carbon fiber raw material. After the sizing process, the content of the sizing agent in the carbon fiber bundle was <NUM> wt%.

A thermosetting resin composition was prepared by blending a thickener, a polymerization inhibitor, a polymerization initiator, and an internal mold release agent with a mixture of a vinyl ester resin, an unsaturated polyester resin, and styrene.

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

The two pin rollers of the fragmentation-processing apparatus were both rotated such that the circumferential speeds at a tip of the pin were <NUM>/min. The rotation directions were set to be opposite to each other, and each pin roller was rotated such that its pins moved downward from above on its side facing the other pin roller.

The chopped carbon fiber bundles fragmentation-processed by the fragmentation-processing apparatus were fallen onto a polyethylene carrier film traveling at a linear speed of <NUM>/min. The fallen chopped carbon fiber bundles were deposited on the thermosetting resin composition applied to the carrier film in advance in a separate step, thereby forming a carbon fiber mat.

The carrier film loaded with the deposited carbon fiber mat was laminated with another polyethylene carrier film with the same thermosetting resin composition applied to one surface, and thereafter, pressurized with the impregnation machine, so that the carbon fiber mat was impregnated with the thermosetting resin composition.

After the impregnation, the laminate was placed at <NUM> for <NUM> hours (<NUM> days) to thicken the thermosetting resin composition, thereby completing the SMC. The content of the carbon fiber in the obtained SMC was approximately <NUM>% by weight, and an areal weight of the carbon fiber was approximately <NUM>,<NUM>/m<NUM>.

The obtained SMC was cut into <NUM> × <NUM> and cured by using a press molding machine under conditions of a temperature of <NUM>, a pressure of <NUM> MPa, and a pressurization time of <NUM> minutes, thereby forming a <NUM> square CFRP plate having a thickness of <NUM>.

A bending test piece having a length of <NUM> and a width of <NUM> was cut out from the CFRP plate, and a three-point bending test was performed by using a <NUM> kN Instron type universal tester at L/D=<NUM> and a crosshead speed of <NUM>/min. As a result, bending strength was approximately <NUM> MPa, and a bending elastic modulus was approximately <NUM> GPa.

In order to examine filament numbers of the chopped carbon fiber bundles included in the SMC prepared as described above, a dry carbon fiber mat was deposited on a carrier film by following a similar procedure except that the thermosetting resin composition was not applied to the carrier film.

A region of approximately <NUM> × <NUM> deposited near a center line of the carrier film was selected from the carbon fiber mat, and the filament numbers of all of the chopped carbon fiber bundles (<NUM> pieces or more) having widths of <NUM> or more included in the region were examined by conversion from weights. As a result, the content of a component with the filament number of more than <NUM> was <NUM>% by weight, and the content of a component with the filament number of <NUM> or less was less than <NUM>% by weight.

An SMC having the content of carbon fibers of approximately <NUM>% by weight and an areal weight of carbon fibers of approximately <NUM>/m<NUM> was produced in a similar manner to Experiment <NUM> except that the continuous carbon fiber bundle having a filament number of <NUM> was used after being widened to an approximate <NUM> width and partially split into four sub-bundles having a width of approximately <NUM>. Furthermore, a CFPR plate was prepared from the SMC and the bending test was performed.

The partial split was performed by forming three slit rows each with a slit length of <NUM> and an inter-slit gap length of <NUM> in the continuous carbon fiber bundle. Positions of the inter-slit gaps in the fiber direction were the same among the three slit rows.

As a result of the bending test, the bending strength was approximately <NUM> Mpa, and the bending elastic modulus was approximately <NUM> GPa.

Furthermore, the dry carbon fiber mat was deposited on the carrier film by following a similar procedure except that the thermosetting resin composition was not applied to the carrier film, and the filament numbers of the chopped carbon fiber bundles included therein was examined in the same manner as that in Experiment <NUM>. As a result, the content of the component with the filament number of more than <NUM> was <NUM>% by weight, and the content of the component with the filament number of <NUM> or less was less than <NUM>% by weight.

An SMC having the content of carbon fibers of approximately <NUM>% by weight and an areal weight of carbon fibers of approximately <NUM>/m<NUM> was produced in a similar manner to Experiment <NUM> except that a continuous carbon fiber bundle having the content of sizing agent of <NUM> wt% and a filament number of <NUM> (TR50S <NUM> manufactured by Mitsubishi Chemical Corporation) was used in place of the continuous carbon fiber bundle having a filament number of <NUM>, and that the fragmentation-processing apparatus was not used. Furthermore, a CFPR plate was prepared from the SMC and the bending test was performed.

Comparing the CFRPs prepared in Experiments <NUM> to <NUM> with each other, whereas the bending elastic moduli were comparable, the bending strengths were not on a level. Specifically, the bending strength of the CFRP prepared in Experiment <NUM> was lower than that of the CFRP prepared in Experiments <NUM> and <NUM>. On the other hand, the bending strength of the CFRP prepared in Experiment <NUM> and the bending strength of the CFRP prepared in Experiment <NUM> were comparable each other.

Claim 1:
A manufacturing method of an SMC, comprising:
(i) forming chopped carbon fiber bundles (<NUM>) by chopping a continuous carbon fiber bundle (<NUM>) having a filament number of NK with a rotary cutter (<NUM>);
(ii) fragmentation-processing the chopped carbon fiber bundles (<NUM>) by using a fragmentation-processing apparatus (<NUM>) comprising a rotating body;
(iii) forming a carbon fiber mat (<NUM>) by depositing the fragmentation-processed chopped carbon fiber bundles on a carrier film traveling below the rotary cutter (<NUM>); and
(iv) impregnating the carbon fiber mat (<NUM>) with a thermosetting resin composition,
characterized in that the continuous carbon fiber bundle (<NUM>) is a continuous carbon fiber bundle partially split into n sub-bundles (<NUM>) (where, n is an integer of <NUM> or more) such that N/n is <NUM> to <NUM>.