Patent Description:
Carbon fiber reinforced plastic (CFRP) 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 vehicles, sports goods, and leisure goods.

Certain kinds of CFRP products are molded from a sheet molding compound (SMC) by a compression molding method.

SMC is a kind of carbon fiber prepreg and has a structure in which a mat comprising a chopped carbon fiber bundle is impregnated with a resin composition.

The CFRP has higher strength when reinforced with a carbon fiber bundle having a smaller filament number, while a carbon fiber bundle having a smaller filament number (a smaller tow size) is more expensive to manufacture (<CIT>).

In order to manufacture SMC comprising a chopped carbon fiber bundle with a small filament number at low cost, a method including preparing, as a starting material, a carbon fiber bundle with a large filament number which is classified as a large tow and using it after spreading and subsequent slitting has been proposed (<CIT>).

A main object of the present invention is to provide an improvement in a method for manufacturing a slit carbon fiber bundle, a carbon fiber package, or a method for manufacturing a carbon fiber package.

The present invention is defined by the carbon fiber package according to the features of independent claim <NUM> and the method for manufacturing a carbon fiber package according to the features of independent claim <NUM>. Optional features are recited in the dependent claims.

According to the invention, a carbon fiber package in which a slit carbon fiber bundle, which has been split into sub-bundles by partial slitting, is traverse-wound on a bobbin,.

According to a particular embodiment, the slit carbon fiber bundle is wound on the bobbin such that no gap is present between the sub-bundles.

According to a particular embodiment, the resin film is a discontinuous film.

According to a particular embodiment, a filament number of the flat carbon fiber bundle is <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, or <NUM> or more and may be <NUM> or less or <NUM> or less.

According to the previous embodiment, the filament number of the flat carbon fiber bundle is <NUM> or more.

According to a particular embodiment, when a filament number of the flat carbon fiber bundle is NK, and the number of the sub-bundles is n, N/n is <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less.

According to a particular embodiment,
N/n is <NUM> or more or <NUM> or more.

According to a particular embodiment, wherein the resin film comprises an epoxy resin.

According to the invention, a method for manufacturing a carbon fiber package, comprising:.

In a particular embodiment, the slit carbon fiber bundle is wound on the bobbin such that no gap is present between the sub-bundles.

In a particular embodiment, the resin film is a discontinuous film.

In a particular embodiment, a filament number of the flat carbon fiber bundle is <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, or <NUM> or more and may be <NUM> or less or <NUM> or less.

In a particular embodiment, when a filament number of the flat carbon fiber bundle is NK, and the number of the sub-bundles is n, N/n is <NUM> or less, <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less.

In a particular embodiment, N/n is <NUM> or more or <NUM> or more.

In a particular embodiment, the resin film comprises an epoxy resin.

According to the present invention, an improvement in a method for manufacturing a slit carbon fiber bundle, a carbon fiber package, or a method for manufacturing a carbon fiber package is provided.

A method for manufacturing a slit carbon fiber bundle according to an embodiment can be carried out by using a slitting device of which conceptual view is shown in <FIG>.

A method for manufacturing a slit carbon fiber bundle according to the embodiment will be described below using a case of using a slitting device <NUM> shown in <FIG> as an example.

A carbon fiber bundle <NUM> with a filament number of NK is used as a starting material.

NK denotes N × <NUM>. For example, <NUM> is expressed as <NUM>, and <NUM> is expressed as <NUM>.

N is usually <NUM> or more, preferably <NUM> or more, and more preferably <NUM> or more and may be <NUM> or more, <NUM> or more, or <NUM> or more. N is not limited to, but is usually <NUM> or less and may be <NUM> or less, <NUM> or less, or <NUM> or less.

The above-described upper limit and lower limit can be arbitrarily combined. For example, the filament number of a flat carbon fiber bundle used as a raw material in the manufacturing method of the present embodiment is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, still more preferably <NUM> to <NUM>, and particularly preferably <NUM> to <NUM>.

The carbon fiber bundle <NUM> is drawn out from a supply bobbin B1.

After drawn out from the supply bobbin B1, the carbon fiber bundle <NUM> is spread by being rubbed against a spreader bar <NUM>.

The spreader bar <NUM> can be heated or vibrated arbitrarily with reference to known techniques as appropriate.

The carbon fiber bundle <NUM> may be spread by using high pressure air in place of or in addition to use of the spreader bar.

The carbon fiber bundle <NUM> originally has a flat shape, and thus the width thereof is further increased and the thickness thereof is further decreased when the carbon fiber bundle is spread. The thickness of the carbon fiber bundle <NUM> after the spreading is not limited, but is typically approximately <NUM> when the filament number is <NUM>.

After the spread processing, spraying resin powder using a spray gun <NUM>, heating using a heater <NUM>, pressing using a nip roll <NUM>, and cooling using a cooling roll <NUM> are sequentially performed, thereby forming a single-sided coated carbon fiber bundle <NUM> of which cross-sectional view is shown in <FIG>.

The single-sided coated carbon fiber bundle <NUM> comprises the carbon fiber bundle <NUM> having one main surface 10a and another main surface 10b on the opposite side, and a resin film <NUM> formed on the one main surface 10b.

Heating by the heater <NUM> is performed for the purpose of melting the resin powder applied to the main surface 10b of the carbon fiber bundle.

Pressing by the nip roll <NUM> is performed for the purpose of making a resin constituting the resin film <NUM> permeate the carbon fiber bundle <NUM>.

Cooling by the cooling roll <NUM> is performed for the purpose of solidifying the resin film <NUM> before the slitting step in the subsequent stage.

The resin film <NUM> may be cooled by blowing cooling air in place of or in addition to use of the cooling roll <NUM>.

Either or both of the pressing by the nip roll <NUM> and the cooling by the cooling roll <NUM> may be omitted.

The purpose of forming the resin film on one surface of the spread carbon fiber bundle before slitting it is stabilizing the shape of the carbon fiber bundle and maintaining it in a spread state. In other words, the resin film is formed for the purpose of preventing the spread carbon fiber bundle from decrease in a bundle width and increase and uniformity reduction in a thickness during transportation to a slitter roll.

Formation of the resin film has also a purpose of stabilizing shapes of sub-bundles formed by slitting the carbon fiber bundle. There is an advantage that the sub-bundles are unlikely to be entangled with each other when the shapes of the sub-bundles are stable.

The effect of stabilizing the shape of the carbon fiber bundle by forming the resin film is particularly significant when the filament number is <NUM> or more, that is, when the carbon fiber bundle is a so-called large tow. This is because a binding effect of a sizing agent contained in the carbon fiber bundle weakens as the filament number increases.

The resin film <NUM> may be a continuous film that completely covers the main surface 10b of the carbon fiber bundle <NUM>, or may be a discontinuous film having an island structure or a network structure. When the resin film <NUM> is a discontinuous film, the main surface 10b of the carbon fiber bundle <NUM> is partially exposed.

It is advantageous that the resin film is the discontinuous film in terms of preventing occurrence of defective impregnation when the slit carbon fiber bundle manufactured from the single-sided coated carbon fiber bundle is used for manufacturing a prepreg.

The resin film <NUM> is not limited by the kind of a resin constituting the resin film <NUM>. For example, one or more resins selected from polyamide, polyester, polyurethane, polyolefin, an epoxy resin, a phenol resin, a vinyl ester resin, and a silicone resin may be comprised in the resin film <NUM>.

The resin film <NUM> may comprise a resin composition containing a component other than the resin.

The method for forming the resin film <NUM> is not limited to the method including spraying a resin powder. Various types of applicators such as a spray gun, a roll coater, and a die coater can be used when the resin film <NUM> is formed with a fusible resin.

The single-sided coated carbon fiber bundle <NUM> is fed to the slitter roll <NUM> and partially slit to form the slit carbon fiber bundle <NUM>. The slit is formed to penetrate through the single-sided coated carbon fiber bundle <NUM> in a thickness direction, that is, to penetrate through both the carbon fiber bundle <NUM> and the resin film <NUM>.

A slitting blade <NUM> provided on a circumferential surface 170a of the slitter roll <NUM> is provided with a missing part <NUM> for allowing partial slitting.

The single-sided coated carbon fiber bundle <NUM> comprising the carbon fiber bundle with a filament number of NK is partially split into n (n represents an integer of <NUM> or more) sub-bundles by partially slitting using the slitter roll <NUM> having (n-<NUM>) slitting blades <NUM> arranged along a rotation axis direction.

N/n is, for example, <NUM> or less, preferably <NUM> or less, more preferably <NUM> or less and may be <NUM> or less or <NUM> or less. N/n is preferably <NUM> or more and may be <NUM> or more. The above-described upper limit and lower limit can be arbitrarily combined. For example, N/n is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and still more preferably <NUM> to <NUM>.

An example of a slit carbon fiber bundle comprising five sub-bundles obtained by partially slitting a single-sided coated carbon fiber bundle with a slitter roll having four slitting blades is shown in <FIG> and <FIG>.

When a fiber direction (longitudinal direction) is defined as an x-direction, a width direction is defined as a y-direction, and a thickness direction is defined as a z-direction, <FIG> is a plan view when the slit carbon fiber bundle <NUM> is viewed in the z-direction, and <FIG> is a cross-sectional view showing a cross section perpendicular to the x-direction (cross section in a yz-plane) of the slit carbon fiber bundle <NUM>.

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

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

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

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

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

The four slit rows are formed by different slitting blades, and thus positions of the four slit rows in the y-direction are different from each other.

A slit length LS and an inter-slit gap length LG are constant in any of the slit rows and are common in different slit rows.

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

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 such that the widths of the five sub-bundles <NUM> are approximately the same as each other.

The slit length LS is not limited to, but is preferably more than <NUM>, more preferably more than <NUM>, and still more preferably more than <NUM>.

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 is, for example, in a range of <NUM> to <NUM>.

The slit length LS and the inter-slit gap length LG can be controlled by adjusting a feed speed of the single-sided coated carbon fiber bundle <NUM>, a circumferential speed of the slitter roll <NUM>, and lengths of the slitting blade <NUM> and the missing part <NUM> of the slitting blade in a circumferential direction.

For example, the slit length LS can be set to be greater than the length of the slitting blade <NUM> in the circumferential direction by adjusting the feed speed of the single-sided coated carbon fiber bundle <NUM> higher than the circumferential speed of the slitter roll.

In the slit carbon fiber bundle <NUM> shown in <FIG>, positions of the inter-slit gaps GS in the first slit row AS1 and the second slit row AS2 are shifted in the x-direction. The same applies 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.

The configuration in which the positions of the inter-slit gaps GS between the adjacent slit rows are shifted in the x-direction as described above is not essential. In one example, the positions of the inter-slit gaps GS in the x-direction may be aligned between all the slit rows as shown in <FIG>. In another example, the positions of the inter-slit gaps GS in the x-direction may be shifted between all the slit rows.

What has been described above about the slit length LS, the inter-slit gap length LG, the ratio LS/(LS + LG) of the slit length LS to the sum of the slit length LS and the inter-slit gap length LG, and the position of the inter-slit gap GS applies not only to the slit carbon fiber bundle comprising five sub-bundles but also to slit carbon fiber bundles comprising four or less or six or more sub-bundles.

The filament number of each sub-bundle <NUM> in the slit carbon fiber bundle <NUM> is preferably <NUM> or less, more preferably <NUM> or less, and still more preferably <NUM> or less, regardless of the number n. The filament number of each sub-bundle <NUM> in the slit carbon fiber bundle <NUM> is preferably <NUM> or more and more preferably <NUM> or more, regardless of the number n. The above-described upper limit and lower limit can be arbitrarily combined. For example, the filament number of each sub-bundle <NUM> in the slit carbon fiber bundle <NUM> is preferably in a range of <NUM> to <NUM>, more preferably in a range of <NUM> to <NUM>, and still more preferably in a range of <NUM> to <NUM>.

In the slitting of the single-sided coated carbon fiber bundle <NUM> using the slitter roll <NUM>, the single-sided coated carbon fiber bundle may be fed while sliding on the circumferential surface 170a of the slitter roll by setting the feed speed of the single-sided coated carbon fiber bundle to be higher than the circumferential speed of the slitter roll, in order to form a slit that is longer than the length of the slitting blade <NUM> in the circumferential direction. At this time, it is preferable that the single-sided coated carbon fiber bundle <NUM> contacts the circumferential surface 170a of the slitter roll on a side where the resin film <NUM> has been formed, in order to prevent fuzzing resulting from breakage of a filament in the carbon fiber bundle <NUM> due to friction with the slitter roll <NUM>. In other words, it is preferable that the slitting blade penetrates into the single-sided coated carbon fiber bundle <NUM> from the side of the resin film <NUM> not from the side of the carbon fiber bundle <NUM>.

In an experiment conducted by the present inventors using a carbon fiber bundle with a filament number of <NUM>, an amount of a resin film to fall off during slitting was smaller when a slitting blade penetrated into a single-sided coated carbon fiber bundle from the side of a resin film as compared with when the slitting blade penetrated thereinto from the side of a carbon fiber bundle. The details are not clear, but it is considered that the resin film is pressed against the carbon fiber bundle on a slitter roll in the former case.

Further, when a carbon fiber mat was prepared from the slit carbon fiber bundle prepared in the experiment and observed, an amount of fluff contained in the carbon fiber mat was different depending on a direction in which the slitting blade penetrated into the single-sided coated carbon fiber bundle in the preparation of the slit carbon fiber bundle. More specifically, when the slitting blade penetrated into the single-sided coated carbon fiber bundle from the side of the resin film in the slitting, the amount of fluff contained in the carbon fiber mat prepared by using the obtained slit carbon fiber bundle was smaller as compared with when the slitting blade penetrated thereinto from the side of the carbon fiber bundle.

In the experiment described above, a single-sided coated carbon fiber bundle was prepared by spreading a carbon fiber bundle to have a width of approximately <NUM>, coating one surface thereof with an epoxy resin using a spray gun, and making a part of the epoxy resin permeate into the carbon fiber bundle by allowing the carbon fiber bundle passing through a nip roll heated to <NUM>. The used epoxy resin was a bisphenol A type epoxy resin [jER (registered trademark) <NUM>, manufactured by Mitsubishi Chemical Corporation] having an epoxy equivalent of <NUM> to <NUM>, a number average molecular weight of approximately <NUM>, and a softening point of <NUM> (ring and ball method). The amount of the epoxy resin adhered to the carbon fiber bundle in this processing was approximately <NUM>% by weight of the single-sided coated carbon fiber bundle. A plurality of slitting blades were provided with a pitch of <NUM> in an axial direction on a circumferential surface of a slitter roll used in the slitting. Each slitting blade had one missing part on its outer circumference. In each slit row formed in the single-sided coated carbon fiber bundle by the slitting, the slit length was approximately <NUM>, and the inter-slit gap length was approximately <NUM>.

The carbon fiber mat was prepared by cutting the prepared slit carbon fiber bundle with a chopper to form a chopped carbon fiber bundle such that a fiber length thereof is <NUM>, bringing the chopped carbon fiber bundle into contact with a rotating pin roll, and subsequently dropping the chopped carbon fiber bundle on a resin film. The circumferential speed of the pin roll was approximately <NUM>/min at the tip of a pin.

The slit carbon fiber bundle <NUM> obtained by partially slitting the single-sided coated carbon fiber bundle <NUM> is wound on a bobbin B2. The bobbin B2 is, for example, a paper tube, but is not limited thereto.

It is preferable that the slit carbon fiber bundle <NUM> is traverse-wound on the bobbin B2 using a traverse device (not shown). In the traverse-winding, a lead angle at the start of the winding can be set to, for example, <NUM>° to <NUM>°, and the lead angle at the end of the winding can be set to, for example, <NUM>° to <NUM>°, but the lead angles are not limited thereto. A winding ratio in the traverse-winding is usually not set to an integer, and it is preferable that the fraction after the decimal point of the winding ratio is also not set to a multiple of <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM>, and <NUM>/<NUM>.

It is preferable that the slit carbon fiber bundle <NUM> is wound on the bobbin such that no gap is present between the sub-bundles <NUM>. The reason is to prevent the sub-bundles <NUM> from biting each other between a part wound first on the bobbin B2 and a part later wound thereon in an overlapping manner. When the winding is made such that no gap is present between the sub-bundles <NUM>, it is possible to suppress the sub-bundles from biting each other, and entanglement of the slit carbon fiber bundle <NUM> and breakage of the sub-bundles <NUM> can therefore be prevented when the slit carbon fiber bundle is unwound by external or internal unwinding.

A total width W of the slit carbon fiber bundle <NUM> may be set to be less than a sum of widths Ws of the sub-bundles as shown in <FIG>, in order to wind the slit carbon fiber bundle <NUM> on the bobbin such that no gap is present between the sub-bundles <NUM>.

<FIG> is a cross-sectional view when the slit carbon fiber bundle <NUM> on the bobbin is cut perpendicularly to the fiber direction, showing that the five sub-bundles <NUM> are arranged without any gap in the y-direction. That is, there is no part where the adjacent sub-bundles <NUM> are apart from each other, and each sub-bundle <NUM> overlaps the sub-bundle <NUM> next to it at the edge.

The slit carbon fiber bundle <NUM> can be wound on the bobbin B2 in a state where the total width W is less than the sum of the widths Ws of the sub-bundles by using a grooved roll having a groove width smaller than the sum of the widths of the sub-bundles as a guide roll or adjusting the guide width of the traverse device to be smaller than the sum of the widths of the sub-bundles.

When the total width of the slit carbon fiber bundle is decreased by these methods, not only does the sub-bundles overlap each other, but some of the sub-bundles may be folded in the width direction. Therefore, a state of mutual overlapping between the sub-bundles in the slit carbon fiber bundle wound on the winding bobbin is not limited to that shown in <FIG>, but can be various.

In order to reliably prevent a gap from being generated between the sub-bundles, the total width of the slit carbon fiber bundle when wound on the winding bobbin is set to preferably <NUM>% or less of the sum of the widths of the sub-bundles and more preferably <NUM>% or less thereof.

In the above-described experiment, the slit carbon fiber bundle, which was obtained by slitting the single-sided coated carbon fiber bundle having a width of <NUM>, was wound on a bobbin such that a total width thereof became approximately <NUM>, and the slit carbon fiber bundle was unwound and used to prepare the carbon fiber mat. When the slit carbon fiber bundle was unwound, entanglement of the slit carbon fiber bundle or breakage of the sub-bundles did not occur.

The slit carbon fiber bundle <NUM> can be preferably used as a material for SMC.

For example, an SMC manufacturing apparatus shown in <FIG> can be used for manufacturing SMC using the slit carbon fiber bundle <NUM>.

As shown in <FIG>, the SMC manufacturing apparatus includes a chopper <NUM>, a disperser <NUM>, a first applicator 3a, a second applicator 3b, and an impregnation machine <NUM>.

The slit carbon fiber bundle <NUM> is drawn out from a carbon fiber package P and sent to the chopper <NUM>.

The slit carbon fiber bundle <NUM> is cut by the chopper <NUM>, thereby forming a chopped carbon fiber bundle <NUM>.

The fiber length of the chopped carbon fiber bundle <NUM> is, for example, within a range of <NUM> to <NUM> and typically <NUM> (approximately <NUM>/<NUM> inches), <NUM> (approximately <NUM> inch), or the like.

The chopped carbon fiber bundle <NUM> falls on a first carrier film <NUM> travelling below the chopper while being dispersed by the disperser <NUM> having one or more rotating body. A carbon fiber mat <NUM> is deposited on the first carrier film <NUM>.

A pin roll 263a shown in <FIG> is an example of the rotating body of the disperser <NUM>. A structural body in which a pair of disks <NUM> are connected with a plurality of wires or rods <NUM> as shown in <FIG> is another example of the rotating body of the disperser <NUM>.

The surface of the first carrier film <NUM> is coated with a resin paste layer <NUM> comprising thermosetting resin paste <NUM> by the first applicator 3a before the deposition of the carbon fiber mat <NUM>.

The surface of a second carrier film <NUM> is also coated with a resin paste layer <NUM> comprising the thermosetting resin paste <NUM> by the second applicator 3b.

Both the first carrier film <NUM> and the second carrier film <NUM> are synthetic resin films and comprises, for example, polyolefin.

Subsequent to the formation of the carbon fiber mat <NUM>, a laminate <NUM> is formed by laminating the first carrier film <NUM> and the second carrier film <NUM> such that the resin paste layer respectively applied to the first carrier film and the second carrier film and the carbon fiber mat <NUM> are sandwiched therebetween.

The carbon fiber mat <NUM> is impregnated with the thermosetting resin paste <NUM> by pressing the laminate <NUM> with the impregnation machine <NUM>.

The laminate <NUM> having passed through the impregnation machine <NUM> is wound on a bobbin.

Processing up to this point is performed by the SMC manufacturing apparatus shown in <FIG>.

The laminate <NUM> on the bobbin is heated to a predetermined temperature and maintained for a certain period of time in order to further thicken the thermosetting resin paste <NUM> that has permeated into the carbon fiber mat <NUM>, as necessary.

Claim 1:
A carbon fiber package (P) in which a slit carbon fiber bundle (<NUM>), which has been split into sub-bundles (<NUM>) by partial slitting, is traverse-wound on a bobbin (B2),
wherein the slit carbon fiber bundle has been prepared by partially slitting a single-sided coated carbon fiber bundle (<NUM>) comprising a flat carbon fiber bundle (<NUM>) and a resin film (<NUM>) formed on one surface (10b) of the flat carbon fiber bundle;
characterized in that
a width (W) of the slit carbon fiber bundle on the bobbin is less than a sum of widths (Ws) of the sub-bundles.