JP7604802B2 - CF-SMC and method for producing CF-SMC - Google Patents

Description

The present invention relates to SMC (sheet molding compound) and a manufacturing method for SMC, and in particular to CF-SMC, which is an SMC that uses carbon fiber (CF) as a reinforcing material, and a manufacturing method thereof.

2. Description of the Related Art In recent years, CFRP (carbon fiber reinforced plastic), which is a composite material made of carbon fiber and resin, has been widely used in components for aircraft, automobiles, ships and various other types of transport equipment, as well as in sporting goods and leisure goods.
Some CFRP products are made from CF-SMC by compression molding.
CF-SMC is a type of carbon fiber prepreg, and has a structure in which a mat made of chopped carbon fiber strands is impregnated with a thermosetting resin composition.
It is known that CFRP has higher strength when reinforced with carbon fiber bundles having a smaller tow size, i.e., carbon fiber bundles having a smaller number of carbon fiber filaments (Patent Document 1).
In the production of CF-SMC, a method is known in which continuous carbon fiber bundles used as raw materials are slit to divide them into sub-bundles with fewer filaments and then chopped (Patent Document 2).

US Patent Application Publication No. US2012/0213997 International Publication No. WO2017/006989

When CF-SMC is used, the fewer the number of chopped carbon fiber bundles, the higher the strength of the cured product. However, the fluidity at the curing temperature decreases, so the shapes of molded products that can be produced using the SMC are limited.
The present invention has been made in view of the above circumstances, and has as its main object to provide a CF-SMC that has a good balance between the strength of the cured product and the fluidity during curing.
Problems that can be solved by each embodiment of the present invention may be explicitly or implicitly disclosed in this specification.

Preferred embodiments of the present invention include, but are not limited to, the following.
[1] A CF-SMC in which a mat made of chopped carbon fiber bundles having a predetermined fiber length in the range of 1 to 6 cm is impregnated with a matrix resin, the chopped carbon fiber bundles containing a component having a filament number of 1K or more and less than 4K at a ratio R ₁ , a component having a filament number of 4K or more and less than 7K at a ratio R ₂ , and a component having a filament number of 7K or more and less than 10K at a ratio R ₃ , the ratio R ₁ is 10 to 30 wt%, the ratio R ₂ is 30 to 60 wt%, the ratio R ₃ is 10 to 30 wt%, the sum of the ratios R ₂ and R ₃ is 60 wt% or more, and further, the chopped carbon fiber bundle does not contain 1 wt% or more of any of the components having a filament number of less than 1K and the components having a filament number of 16K or more.
[2] The CF-SMC according to [1], wherein the chopped carbon fiber bundle does not contain any component having a filament count of 16K or more.
[3] The CF-SMC according to [1] or [2], wherein the ratio R ₁ is 15 wt % or more or 20 wt % or more.
[4] The CF-SMC according to any one of [1] to [3], wherein the ratio R ₁ is 25 wt % or less.
[5] The CF-SMC according to any one of [1] to [4], having a fiber content of 45 to 65%.
[6] A method for producing a CF-SMC, comprising the steps of chopping a continuous carbon fiber bundle with a rotary cutter to form a chopped carbon fiber bundle, depositing the chopped carbon fiber bundle on a carrier film traveling below the rotary cutter to form a carbon fiber mat, and impregnating the carbon fiber mat with a matrix resin, in which the chopped carbon fiber bundle before being deposited on the carrier film is subjected to a fragmentation treatment using a fragmentation treatment device described below in (A):
(A) A fragmentation processing device comprising a first pin roller and a second pin roller, each of which has a rotation axis parallel to the rotation axis of the rotary cutter, wherein the sum of the maximum radius of the first pin roller and the maximum radius of the second pin roller is greater than the distance between the rotation axes of the first pin roller and the second pin roller, and the first pin roller is rotated and driven so that the pins move from top to bottom on the side facing the second pin roller, and the second pin roller is rotated and driven so that the pins move from top to bottom on the side facing the first pin roller.
[7] The manufacturing method described in [6], wherein the radius of the cylinder of each of the first pin roller and the second pin roller is equal to or greater than half of the maximum radius.
[8] The manufacturing method described in [6] or [7], wherein the peripheral speed at the tip of the pin of the first pin roller is equal to the peripheral speed at the tip of the pin of the second pin roller.
[9] The method according to any one of [6] to [8], wherein the continuous carbon fiber bundle is an unsplit continuous carbon fiber bundle having a filament count of 12K or more and less than 18K.
[10] The manufacturing method according to any one of [6] to [8], wherein the continuous carbon fiber bundle is a continuous carbon fiber bundle having a total filament number of 24K or more, the total filament number being divided into sub-bundles having a filament number of 12K or more but less than 18K by partial splitting.

According to one embodiment, a CF-SMC is provided that has a good balance between the strength of the cured product and the fluidity upon curing. According to another embodiment, a CF-SMC manufacturing method is provided that can be preferably used to manufacture a CF-SMC that has a good balance between the strength of the cured product and the fluidity upon curing.

FIG. 1 is a schematic diagram showing a continuous carbon fiber bundle partially split into five pieces, in which FIG. 1(a) is a plan view seen from the thickness direction, and FIG. 2(b) is a cross-sectional view showing a cross section perpendicular to the fiber direction. FIG. 2 is a schematic diagram of an SMC manufacturing apparatus. FIG. 3 is a schematic diagram of a rotary cutter. FIG. 4 is a schematic diagram of a fragmentation processing device. FIG. 5 is a schematic diagram of a pin roll provided in the fragmentation processing device. FIG. 6 shows a part of the peripheral surface of the pin roll developed in a plane. FIG. 7 is a schematic diagram showing the positional relationship between two pin rolls provided in the fragmentation processing device. FIG. 8 is a graph showing the results of the spiral flow length measurements of CF-SMC carried out in Experiments 1 to 4. FIG. 9 is a graph showing the results of measuring the bending strength of the cured CF-SMC products carried out in Experiments 1 to 4. FIG. 10 is a graph showing the results of measuring the flexural modulus of the cured CF-SMC products in Experiments 1 to 4.

1. CF-SMC
One embodiment of the present invention relates to a CF-SMC, that is, a sheet molding compound having a structure in which a carbon fiber mat made of chopped carbon fiber bundles having a predetermined fiber length is impregnated with a matrix resin.
The weight per unit area of the carbon fiber mat is typically, but not limited to, 500 to 2500 g/ ^m2 .
The fiber length of the chopped carbon fiber bundles is typically within the range of 1 to 6 cm, and can be, for example, about 0.5 inches (about 1.3 cm), about 1 inch (about 2.5 cm), about 1.5 inches (about 3.8 cm), about 2 inches (about 5.1 cm), and the like.

The CF-SMC according to the embodiment is characterized by the filament number configuration of the chopped carbon fiber bundle forming the carbon fiber mat. That is, when the chopped carbon fiber bundle contains a component having a filament number of 1K or more and less than 4K at a ratio R ₁ , a component having a filament number of 4K or more and less than 7K at a ratio R ₂ , and a component having a filament number of 7K or more and less than 10K at a ratio R ₃ , the ratio R ₁ is 10 to 30 wt%, the ratio R ₂ is 30 to 60 wt%, the ratio R ₃ is 10 to 30 wt%, and the sum of the ratios R ₂ and R ₃ is 60 wt% or more. In addition, the chopped carbon fiber bundle does not contain 1 wt% or more of either the component having a filament number of less than 1K or the component having a filament number of 16K or more. In particular, the chopped carbon fiber bundle may not contain any component having a filament number of 16K or more.
Here, K is a symbol meaning 1000. For example, the number of filaments in a carbon fiber bundle consisting of 3000 carbon fiber filaments is expressed as 3K, and the number of filaments in a carbon fiber bundle consisting of 12000 carbon fiber filaments is expressed as 12K.

The strength of the cured product of the CF-SMC according to the embodiment tends to increase as the ratio R ₁ increases. Therefore, from the viewpoint of improving the strength of the cured product, the ratio R ₁ is preferably 15 wt % or more, more preferably 20 wt % or more.
The fluidity of the CF-SMC during hardening according to the embodiment tends to decrease as the ratio R ₁ increases. Therefore, from the viewpoint of improving the fluidity during hardening, the ratio R ₁ is preferably 25 wt % or less.
In the CF-SMC according to the embodiment, the sum of the ratios _R2 and _R3 is 60 wt % or more, and the majority of the weight of the chopped carbon fiber bundle is made up of components having a filament count of 4K or more and less than 10K.
Typically, ratio _R2 is greater than ratio _R3 .

The fact that the chopped carbon fiber bundles do not contain 1 wt% or more of components with a filament count of 16K or more contributes favorably to increasing the strength of the cured CF-SMC according to the embodiment. This is because the fewer chopped carbon fiber bundles, which have a large tow size and are less susceptible to infiltration by matrix resin, the less likely resin-rich regions are to form in the CF-SMC. Resin-rich regions are areas where the matrix resin content is locally high, and become weak areas that are the starting points of fracture in the cured CF-SMC.

In the CF-SMC according to the embodiment, the chopped carbon fiber bundles do not contain 1 wt % or more of components with less than 1K filaments, which is not only preferable for improving the fluidity during curing, but also for improving the strength of the cured product. This is because chopped carbon fiber bundles with less than 1K filaments have low straightness. Furthermore, the low content of such chopped carbon fiber bundles makes it easier to impregnate the carbon fiber mat with the matrix resin.

The fiber content of the CF-SMC according to the embodiment, i.e., the ratio of the weight of carbon fiber to the weight of CF-SMC, is not limited, but may be 45 to 65 wt%. Considering the elastic modulus and strength of the cured product, the fiber content is preferably 50 wt% or more, more preferably 53 wt% or more. Considering the fluidity during curing, the fiber content is preferably 60 wt% or less.

The matrix resin of the CF-SMC according to the embodiment is a resin composition containing a thermosetting resin as a main component, a curing agent, and additives such as a thickener, a polymerization inhibitor, a shrinkage reducing agent, a filler, a flame retardant, etc., as required. The matrix resin is a paste having sufficient fluidity at the stage of impregnating the carbon fiber mat, and is thickened after impregnation.
The thermosetting resin used as the main component of the matrix resin is, for example, an epoxy resin, a vinyl ester resin, an unsaturated polyester resin, a polyimide resin, a maleimide resin, or a phenol resin. Two or more kinds selected from these may be mixed and used.

Preferred thermosetting resins are epoxy resins, vinyl ester resins and unsaturated polyester resins because of their excellent adhesiveness to carbon fibers. The vinyl ester resins and unsaturated polyester resins may be used in combination, or may be used in combination with a reactive diluent made of an ethylenically unsaturated compound such as styrene or (meth)acrylate.
Regarding the specific compounding composition of the matrix resin, those employed in conventional CF-SMCs can be referred to as appropriate.

2. Method for Producing CF-SMC One embodiment of the present invention relates to a method for producing CF-SMC.
The CF-SMC production method according to the embodiment includes a step of chopping continuous carbon fiber bundles with a rotary cutter to form chopped carbon fiber bundles, a step of depositing the chopped carbon fiber bundles on a carrier film traveling below the rotary cutter to form a carbon fiber mat, and a step of impregnating the carbon fiber mat with a matrix resin.
In the CF-SMC production method according to the embodiment, the chopped carbon fiber bundles before being deposited on the carrier film are further subjected to a fragmentation treatment using the fragmentation treatment device described below in (A).
(A) A fragmentation processing device comprising a first pin roller and a second pin roller, each of which has a rotation axis parallel to the rotation axis of the rotary cutter, wherein the sum of the maximum radius of the first pin roller and the maximum radius of the second pin roller is greater than the distance between the rotation axes of the first pin roller and the second pin roller, and the first pin roller is rotated and driven so that the pins move from top to bottom on the side facing the second pin roller, and the second pin roller is rotated and driven so that the pins move from top to bottom on the side facing the first pin roller.
By the fragmentation treatment using this fragmentation treatment device (A), the filament number composition of the chopped carbon fiber bundles in the carbon fiber mat deposited on the carrier film becomes different from that when the fragmentation treatment is not performed.

2.1 Continuous Carbon Fiber Bundles In the CF-SMC production method according to the embodiment, the continuous carbon fiber bundles as the raw material are not particularly limited, and for example, commercially available PAN-based carbon fiber bundles can be preferably used.
In the case of producing the CF-SMC according to the embodiment described above, a continuous carbon fiber bundle having an unsplit filament count of 12K or more and less than 18K, or a continuous carbon fiber bundle having a total filament count of 24K or more and divided into sub-bundles having an filament count of 12K or more and less than 18K by partial splitting, can be preferably used.
By using an unsplit continuous carbon fiber bundle having a filament count of less than 16K as a raw material, a CF-SMC can be easily produced in which the chopped carbon fiber bundle does not contain components having a filament count of 16K or more.

A continuous carbon fiber bundle with a total number of 24K or more filaments divided into sub-bundles with a number of filaments of 12K or more but less than 18K can be obtained by splitting a continuous carbon fiber bundle with a total number of filaments of 24K or more using a slitter roll so that each sub-bundle has a number of filaments of 12K or more but less than 18K. If a slitter roll with missing parts on each slit blade is used, the slits are formed intermittently, and a continuous carbon fiber bundle in which the sub-bundles are not completely separated from each other, i.e., in which the sub-bundles are partially split, can be obtained.

To obtain a continuous carbon fiber bundle divided into n sub-bundles, a slitter roller having (n-1) slit blades may be used. By forming (n-1) slits aligned in the width direction of the continuous carbon fiber bundle, the continuous carbon fiber bundle is divided into n sub-bundles.
As an example, a continuous carbon fiber bundle that has been partially split into five sub-bundles using a slitter roller equipped with four slitting blades, each having a notch, is shown in Figures 1(a) and (b).
For convenience, assuming that the fiber direction (longitudinal direction) of the continuous carbon fiber bundle is the x direction, the width direction is the y direction, and the thickness direction is the z direction, FIG. 1(a) is a plan view of the continuous carbon fiber bundle 10 as viewed from the z direction, and FIG. 1(b) shows a cross section of the continuous carbon fiber bundle 10 perpendicular to the x direction (a cross section when cut on the yz plane).

As shown in FIG. 1(a), four slit rows are formed in the continuous carbon fiber bundle 10: a first slit row A _S1 , a second slit row A _S2 , a third slit row A _S3 and a fourth slit row A _S4 .
The first slit row A _S1 is made up of a plurality of first slits S1 aligned in the x direction.
The second slit row A _S2 is made up of a plurality of second slits S2 aligned in the x direction.
The third slit row A _S3 is made up of a plurality of third slits S3 aligned in the x direction.
The fourth slit row A _S4 is made up of a plurality of fourth slits S4 aligned in the x direction.
These four slit rows are formed by different slit blades, and therefore are located at different positions in the y direction.

The slit length L _S and the inter-slit gap length L _G are constant within any slit row and are also common between different slit rows.
The ratio L _S /(L _S +L _G ) of the slit length L _{S to the sum of the slit length L S and} the inter-slit gap length L _G is usually 90% or more, preferably 95% or more, and may be, for example, 99%. Therefore, the continuous carbon fiber bundle 10 is split into five sub-bundles 11 in most parts, as shown in FIG. 1( b ).
The positions in the y direction of the first slit row _A , the second slit row _A , the third slit row _A , and the fourth slit row _A are set so that the widths of the five sub-bundles 11 are approximately the same. For example, when the continuous carbon fiber bundle 10 has 75K filaments, the number of filaments in each sub-bundle 11 is 15K±0.5K.

The slit length L _S is at least twice the fiber length of the chopped carbon fiber bundles cut out from the continuous carbon fiber bundle 10 in a later step, preferably 5 times or more, more preferably 10 times or more, and even more preferably 30 times or more.
The slit length L _S can be, for example, 3 m or less, 2 m or less, or 1 m or less.
The slit gap length L _G is preferably shorter than the fiber length of chopped carbon fiber bundles cut out from the continuous carbon fiber bundle 10 in a later process, and may be less than 10 mm, or may further be less than 5 mm.

1A, the positions of the inter-slit gaps G _S are shifted in the x-direction between the first slit row A _S1 and the second slit row A _S2 , as well as between the second slit row A _S2 and the third slit row A _S3 , and between the third slit row A _S3 and the fourth slit row A _S4 .
It is not essential to shift the positions of the inter-slit gaps G _S in the x direction between adjacent slit rows in this manner. In one example, the positions of the inter-slit gaps G _S may be aligned between all slit rows, or in another example, the positions of the inter-slit gaps G _S may be aligned between some of the slit rows and shifted in the x direction between some of the other slit rows _.

The above description of the slit length _L , the slit gap length _L , the ratio _L /( _L + _L ) of the slit length _L to the sum of the slit length _L and the slit gap length _L , and the position of the slit gap _G applies not only to the case where the continuous carbon fiber bundle 10 is partially split into five sub-bundles, but also to the case where the continuous carbon fiber bundle 10 is partially split into four or less or six or more sub-bundles.

2.2. SMC Manufacturing Apparatus A conceptual diagram of an SMC manufacturing apparatus that can be preferably used in the CF-SMC manufacturing method according to the embodiment is shown in FIG.
2, the SMC manufacturing apparatus 100 has a first resin coating section 110, a second resin coating section 120, a chop section 130, a deposition section 140, and an impregnation section 150. Between the chop section 130 and the deposition section 140, a fragmentation processing device 160 is disposed.

In the first resin coating section 110, a coater 111 equipped with a doctor blade is disposed to form a first resin layer 51 made of a matrix resin 50 on the first carrier film 41 pulled out from a roll.
In the second resin coating section 120, a coater 112 equipped with a doctor blade is disposed to form a second resin layer 52 made of a matrix resin 50 on the second carrier film 42 unwound from a roll.

In the chopping section 130, a rotary cutter 131 is disposed for chopping the continuous carbon fiber bundles 10 as they are pulled out of the package.
3, the rotary cutter 131 includes a guide roll 132, a pinch roll 133, and a cutter roll 134. A plurality of blades 135 are arranged at regular intervals on the outer periphery of the cutter roll 134 in the circumferential direction, and chopped carbon fiber bundles 20 having a constant fiber length can be cut out one after another from the continuous carbon fiber bundle 10.
Usually, a plurality of continuous carbon fiber bundles 10 are simultaneously supplied to the rotary cutter 131 in a state where they are aligned parallel to each other in a plane parallel to the rotation axis of the rotary cutter 131 .

The deposition section 140 is disposed below the chop section 130. The first carrier film 41 is transported from the first resin coating section 110 through the deposition section 140 to the impregnation section 150. As the first carrier film 41 travels through the deposition section 140, the chopped carbon fiber bundles 20 produced in the chop section 130 fall and deposit on the first resin layer 51 formed on its surface, forming a carbon fiber mat 30.

In the upstream portion of the impregnation section 150, the first carrier film 41 and the second carrier film 42 are bonded together so that the surface of the first carrier film 41 facing the first resin layer 51 and the surface of the second carrier film 42 facing the second resin layer 52 are opposed to each other to form a laminate.
The impregnation machine 151 arranged in the impregnation section 150 is equipped with two belt conveyors, one above the other, to sandwich the laminate between two conveyor belts from above and below and convey it, and is also equipped with rollers to sandwich the laminate together with the conveyor belts and apply pressure.

The fragmentation processing device 160 disposed between the chop section 130 and the deposition section 140 has a cover 161, and a guide plate 162 and a pair of pin rollers (a first pin roller 163a and a second pin roller 163b) disposed inside the cover, as shown in Fig. 4. The first pin roller 163a and the second pin roller 163b are located below the guide plate, have approximately the same axial length, and have rotation axes parallel to each other.
In the SMC production apparatus 100 , the fragmentation processing device 160 is disposed so that the rotation axes of the first pin roller 163 a and the second pin roller 163 b are parallel to the rotation axis of the rotary cutter 131 .

5, the first pin roller 163a has a cylinder 164a, on whose surface a plurality of pins 165a, all of which have the same shape and dimensions, are arranged. Both the cylinder 164a and the pins 165a are rigid bodies, and are made of, for example, metal.
The diameter of the cylinder 164a may be, for example, but is not limited to, 60 mm to 150 mm.

The pin 165a extends perpendicular to the rotation axis of the first pin roller 163a and has, for example, a cylindrical shape, but is not limited thereto. The boundary between the end face and the outer circumferential surface of the pin 165a may be chamfered.
The diameter of the pin 165a may be, for example, but is not limited to, 1 mm to 5 mm.
The length of the pin 165a, that is, the distance from the tip to the base of the pin, is not limited to, but may be, for example, 10 mm to 50 mm.
It is preferable that the pins 165a have a circular cross section in order to prevent fuzzing of the chopped carbon fiber bundles 10 being processed in the fragmentation processing device 160.

When the peripheral surface of cylinder 164a is developed into a plane, the arrangement of pins 165a on said peripheral surface preferably overlaps with the original arrangement when shifted 5 mm to 20 mm in the axial direction and 4 mm to 30 mm in the circumferential direction.
For example, in the case of cylinder 164a shown in Fig. 5, when the peripheral surface is developed into a plane, pins 165a are arranged at each vertex of an equilateral triangle (shown by a dashed line) that fills the plane with one side parallel to the axial direction, as shown in Fig. 6. When the length of one side of this equilateral triangle is, for example, 5 mm, the arrangement of pins 165a shown in Fig. 6 overlaps with the original arrangement when shifted by 2.5 mm in the axial direction and approximately 4.3 mm in the circumferential direction.

In this specification, the maximum radius of a pin roller is defined as the distance from its rotation axis to the tip of the pin. In the first pin roller 163a, the radius of the cylinder 164a is preferably at least half the maximum radius of the first pin roller 163a, and more preferably at least 75%. This is because the higher the ratio of the cylinder radius to the maximum radius of the pin roller, the smaller the difference in peripheral speed between the tip of the pin and the base of the pin when the pin roller is rotating.

Everything stated above regarding the first pin roller 163a also applies to the second pin roller 163b.
Without being limited thereto, in order to reduce the costs of designing, manufacturing and maintaining the fragmentation processing device 160, it is preferable to match the design and specifications of the first pin roller 163a and the second pin roller 163b in as many aspects as possible, including maximum radius, cylinder diameter, pin shape, dimensions, number and arrangement, etc.

7, in the fragmentation processing device 160, the sum of the maximum radius r _M1 of the first pin roller 163a and the maximum radius r _M2 of the second pin roller 163b is greater than the distance d ₁₂ between the rotation axes of the two pin rollers.
The sum of the maximum radius _rM1 of the first pin roller 163a and the radius _rC2 of the cylinder 164b of the second pin roller is smaller than the distance between the rotation axes of the two pin rollers _d12 . Similarly, the sum of the maximum radius _rM2 of the second pin roller 163b and the radius _rC1 of the cylinder 164a of the first pin roller is also smaller than the distance between the rotation axes of the two pin rollers _d12 .

The first pin roller 163a and the second pin roller 163b are rotationally driven by a drive mechanism (not shown).
The rotation directions of the first pin roller 163a and the second pin roller 163b are as shown by the arrows in Fig. 4. That is, the first pin roller 163a rotates such that the pins move from top to bottom on the side facing the second pin roller 163b, and the second pin roller 163b rotates such that the pins move from top to bottom on the side facing the first pin roller 163a.
Substantially all of the chopped carbon fiber bundles 20 produced in the chop section 130 fall into the deposition section through the gap between the first pin roller 163a and the second pin roller 163b.

2.3. Method for Producing SMC The method for producing an SMC according to this embodiment will be described using the SMC production apparatus described in 2.2 above as an example.
(Pulling out process)
In the drawing process, a continuous carbon fiber bundle is drawn from a package of continuous carbon fiber bundles that has been prepared in advance.
In this step, the bobbin package may be attached to a creel and the continuous carbon fiber bundle may be pulled out from the outside, or the continuous carbon fiber bundle may be pulled out from the package from which the bobbins have been removed from and the continuous carbon fiber bundle may be pulled out from the inside.

(Chopping process)
In the chopping process, the drawn continuous carbon fiber bundle 10 is supplied to a chopping section 130 and cut one after another by a rotary cutter 131 to produce chopped carbon fiber bundles 20 having a predetermined fiber length. The produced chopped carbon fiber bundles 20 fall toward a fragmentation processing device 160 installed below the rotary cutter 131.
The fiber length of the chopped carbon fiber bundles 20 is typically within the range of 1 to 6 cm, and may be, for example, about 0.5 inches (about 1.3 cm), about 1 inch (about 2.5 cm), about 1.5 inches (about 3.8 cm), about 2 inches (about 5.1 cm), and the like.

(Fragmentation process)
In the fragmentation treatment device 160, at least a part of the chopped carbon fiber bundles 20 dropping from the rotary cutter 131 comes into contact with at least one of the first pin roller 163a and the second pin roller 163b, and is fragmented into a plurality of fragments by the impact.
This fragmentation process is not intended for defibration. In other words, it is not intended to disentangle the chopped carbon fiber bundles to the extent that they become single fibers or a state close to single fibers. Preferably, the peripheral speeds at the pin tips of the first pin roller 163a and the second pin roller 163b are set so that the content of carbon fiber bundles having a filament count of less than 1K in the carbon fiber mat 30 deposited on the first carrier film 41 is less than 1 wt %.

The reason why the rotation directions of the first pin roller 163a and the second pin roller 163b are set so that the pins move from top to bottom on the sides facing the other is to prevent a strong shear force from being applied to the chopped carbon fiber bundle 20 passing between these two pin rollers. A strong shear force is considered to be a cause of fuzzing and loss of straightness of the carbon fiber bundle.
In order to achieve this objective more effectively, it is preferable to set the rotation speed (rpm) of the first pin roller 163a and the second pin roller 164b so that the difference between the peripheral speed at the tip of the pin 165a of the former and the peripheral speed at the tip of the pin 165b of the latter is equal.

(Resin coating process)
In the resin coating process, a first resin layer 51 made of matrix resin 50 is formed on a first carrier film 41 drawn from a roll using a coater 111, and a second resin layer 52 made of matrix resin 50 is formed on a second carrier film 42 drawn from another roll using a coater 212.
The matrix resin 50 is a paste containing a thermosetting resin as a main component, a curing agent, and, if necessary, additives such as a thickener, a polymerization inhibitor, a low-shrinkage agent, a filler, and a flame retardant.

(Deposition process)
In the depositing step, the chopped carbon fiber bundles 20 processed by the fragmentation treatment device 160 fall onto the first carrier film 41 carried below the device. The dropped chopped carbon fiber bundles 20 are deposited on the first resin layer 51 formed on the surface of the first carrier film 41, forming a carbon fiber mat 30.

(Impregnation process)
The first carrier film 41 carrying the carbon fiber mat 30 deposited on the first resin layer 51 is bonded to a second carrier film 42 having a second resin layer 52 formed on one surface while being transported toward the impregnation machine 151.
The laminate of the first carrier film 41 and the second carrier film 42 is pressed by an impregnation machine 151 , whereby the carbon fiber mat 30 is impregnated with the matrix resin 50 .
After the impregnation step is completed, the carbon fiber mat 30 impregnated with the matrix resin 50 is wound up on a bobbin while being sandwiched between the first carrier film 41 and the second carrier film 42, and is subjected to an aging step to become a CF-SMC product. In the aging step, the matrix resin 50 thickens and becomes in a semi-cured state.

3. Experimental Results The results of the experiments conducted by the present inventors are described below.

Experiment 1
A continuous carbon fiber bundle (TR50S15L manufactured by Mitsubishi Chemical Corporation) having 15K filaments, a width of 8 mm and a thickness of 0.1 mm was prepared.
A carbon fiber mat was produced from the continuous carbon fiber bundles using an SMC production apparatus having a configuration similar to that shown in FIG.
Specifically, a plurality of continuous carbon fiber bundles were arranged in parallel at equal intervals and fed to a rotary cutter, and each bundle was cut to a fiber length of 25.4 mm to obtain chopped carbon fiber bundles.
The chopped carbon fiber bundles were passed through a fragmentation treatment device and dropped onto a carrier film not coated with a matrix resin layer, which was running below a rotary cutter at a linear speed of 1.5 m/min.

The two pin rollers of the fragmentation processing device were both made of metal and had the same structure. The diameter and length of the pins arranged on the cylinder circumferential surface were 3 mm and 20 mm, respectively. When the cylinder circumferential surface of each pin roller was developed in a plane, the arrangement of the pins on the circumferential surface was periodic, and the arrangement overlapped with the original arrangement when shifted 7.5 mm in the axial direction and 6.5 mm in the circumferential direction.
The two pin rollers were both rotated so that the peripheral speed at the pin tips was 628 m/min and so that the pins on both sides facing the other pin roller moved from top to bottom.
The chopped carbon fiber bundles treated in the fragmentation treatment device fell and accumulated on a carrier film to form a carbon fiber mat.
Of the carbon fiber mats produced by the above procedure, 300 pieces of chopped carbon fiber bundles forming a portion deposited near the center line of the carrier film were weighed, and the filament number composition was examined.

Furthermore, using the same SMC manufacturing equipment, a carbon fiber mat was produced under the above conditions, and the carbon fiber mat was impregnated with a matrix resin to produce a CF-SMC. The matrix resin used was a thermosetting resin composition containing vinyl ester resin, unsaturated polyester resin, and styrene. The manufacturing conditions were adjusted so that the fiber content was about 53%.
The spiral flow length of the produced CF-SMC was measured in accordance with the Electrical Functional Materials Industry Association standard EIMS T901. The measurement conditions were a mold temperature of 140°C, a plunger pressing pressure of 10 MPa, a plunger pressing time of 160 seconds, and a curing time of 190 seconds. The spiral flow length is an index of the fluidity of CF-SMC during curing.
The prepared CF-SMC was cured at a temperature of 140° C. and a pressure of 8 MPa, and the bending strength and bending modulus of the cured product were measured.

3.2 Experiment 2
A carbon fiber mat was prepared in the same manner as in Experiment 1, except that the peripheral speed at the pin tips of the two pin rollers of the fragmentation treatment device was set to 785 m/min. The filament number composition of the chopped carbon fiber bundles contained therein was investigated. CF-SMC was also prepared and its spiral flow length and the bending strength and bending modulus of the cured product were measured.

3.3 Experiment 3
CF-SMC was produced in the same manner as in Experiment 1, except that no fragmentation treatment device was attached to the SMC production apparatus, and the spiral flow length thereof and the bending strength and bending modulus of elasticity of the cured product thereof were measured.

3.4 Experiment 4
A CF-SMC was produced in the same manner as in Experiment 3, except that the raw material continuous carbon fiber bundle was changed to a continuous carbon fiber bundle having a filament count of 3K, a width of 2 mm and a thickness of 0.07 mm (TR30S3L manufactured by Mitsubishi Chemical Corporation). The spiral flow length of the CF-SMC and the bending strength and bending modulus of the cured product were measured.

The results of Experiments 1 to 4 are shown in Table 1 and Figures 8 to 10.

As shown in Figure 8, the CF-SMC produced in Experiments 1 and 2 exhibited spiral flow lengths comparable to those of the CF-SMC produced in Experiment 3, which was produced using a continuous carbon fiber bundle with 15K filaments, and the cured products exhibited bending strengths comparable to those of the CF-SMC produced in Experiment 4, which was produced using a continuous carbon fiber bundle with 3K filaments, as shown in Figure 9.

The present invention has been described above with reference to specific embodiments, but each embodiment is presented as an example and does not limit the scope of the present invention. Each embodiment described in this specification can be modified in various ways without departing from the spirit of the invention, and can be combined with features described in other embodiments to the extent that they are feasible.

10 Continuous carbon fiber bundle 11 Sub-bundle 20 Chopped carbon fiber bundle 50 Matrix resin 100 SMC manufacturing apparatus 110 First resin coating section 120 Second resin coating section 130 Chop section 140 Accumulation section 150 Impregnation section 160 Fragmentation processing apparatus

Claims (10)

A CF-SMC in which a mat made of chopped carbon fiber bundles having a predetermined fiber length in the range of 1 to 6 cm is impregnated with a matrix resin, wherein the chopped carbon fiber bundles contain a component having a filament number of 1K or more and less than 4K at a ratio R ₁ , a component having a filament number of 4K or more and less than 7K at a ratio R ₂ , and a component having a filament number of 7K or more and less than 10K at a ratio R ₃ , wherein the ratio R ₁ is 10 to 30 wt %, the ratio R ₂ is 30 to 60 wt %, the ratio R ₃ is 10 to 30 wt %, and the sum of the ratios R ₂ and R ₃ is 60 wt % or more, and further, the chopped carbon fiber bundle does not contain 1 wt % or more of any of the components having a filament number of less than 1K and the components having a filament number of 16K or more. The CF-SMC according to claim 1, wherein the chopped carbon fiber bundle does not contain components with a filament count of 16K or more. CF-SMC according to claim 1 or 2, wherein the ratio R ₁ is 15 wt % or more. CF-SMC according to any one of claims 1 to 3, wherein the ratio R ₁ is 25 wt% or less. CF-SMC according to any one of claims 1 to 4, wherein the weight ratio of the carbon fibers to the weight of the CF-SMC is 45 to 65%. A method for producing CF-SMC, comprising the steps of chopping continuous carbon fiber bundles with a rotary cutter to produce chopped carbon fiber bundles, depositing the chopped carbon fiber bundles on a carrier film running below the rotary cutter to form a carbon fiber mat, and impregnating the carbon fiber mat with a matrix resin, and subjecting the chopped carbon fiber bundles before being deposited on the carrier film to a fragmentation treatment using a fragmentation treatment device as described below in (A): (A) A fragmentation treatment device comprising a first pin roller and a second pin roller, each of which has a rotation axis parallel to the rotation axis of the rotary cutter, the sum of the maximum radius of the first pin roller and the maximum radius of the second pin roller being greater than the distance between the rotation axes of the first pin roller and the second pin roller, the first pin roller being driven to rotate such that the pins move from top to bottom on the side facing the second pin roller, and the second pin roller being driven to rotate such that the pins move from top to bottom on the side facing the first pin roller. The manufacturing method according to claim 6, wherein the radius of the cylinder of each of the first pin roller and the second pin roller is equal to or greater than half the maximum radius. The manufacturing method according to claim 6 or 7, wherein the peripheral speed at the pin tip of the first pin roller is equal to the peripheral speed at the pin tip of the second pin roller. The manufacturing method according to any one of claims 6 to 8, wherein the continuous carbon fiber bundle is a continuous carbon fiber bundle having a filament count of 12K or more and less than 18K and not split. The manufacturing method according to any one of claims 6 to 8, wherein the continuous carbon fiber bundle is a continuous carbon fiber bundle having a total number of 24K or more filaments, the total number of filaments being divided by partial splitting into sub-bundles each having 12K or more but less than 18K filaments.

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