JP2016155912A - Carbon fiber-reinforced resin molding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber-reinforced resin molding material capable of achieving desired mechanical characteristics of a molded product and desired flowability at the time of molding in a well-balanced manner.SOLUTION: A carbon fiber-reinforced resin molding material contains at least a carbon fiber base material and a matrix resin. The carbon fiber base material is formed of a chipped fiber bundle obtained by cutting a fiber bundle of continuous carbon fibers, and is opened so that the number of single fibers becomes 100 or less, in 50-85% of the chopped fiber bundle at a weight ratio of the carbon fiber base material to the total carbon fiber amount.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carbon fiber reinforced resin molding material, and more particularly to a carbon fiber reinforced resin molding material in which desirable mechanical properties of a molded product and desirable fluidity during molding are balanced.

  Carbon fiber reinforced resins reinforced with carbon fibers as reinforcing fibers include those using continuous fiber woven fabrics and unidirectional sheets as reinforcing fiber base materials, and those using short-fiber carbon fibers. . Carbon fiber reinforced resin using continuous fiber reinforced fiber base material has extremely high anisotropy such as strength characteristics, and is mainly applied to applications based on or using the anisotropy. Yes. On the other hand, in the carbon fiber reinforced resin using the reinforced fiber base material composed of short carbon fibers, this anisotropy can be reduced, but depending on the production method, a considerable degree of anisotropy remains and is expressed. There are limits to the mechanical properties such as possible strength.

  A carbon fiber reinforced resin molded by SMC (Sheet Molding Compound) is known as a typical carbon fiber reinforced resin using short carbon fibers. Carbon fibers are industrially usually produced as carbon fiber fiber bundles (strands), and the number of single yarns is usually 1,000 (1K) to 48,000 in consideration of productivity and production cost. It is manufactured as a fiber bundle up to (48K). In the SMC, such a fiber bundle of carbon fibers is used.

  In FIG. 3, the concept of the carbon fiber base material in SMC is shown. That is, in SMC, cut short fiber carbon while cutting (chopping) a fiber bundle made of continuous carbon fiber into a predetermined length on a semi-cured thermosetting resin film (sheet). By dispersing carbon fiber bundles 101 made of fibers in random directions and impregnating the resin with a hot press to form a sheet, a resin-impregnated carbon fiber substrate 100 is obtained (usually a semi-cured resin and a carbon fiber substrate). 100 prepreg form). This carbon fiber substrate 100 is generally manufactured continuously. In the SMC sheeting process, there is no process for opening and splitting the carbon fiber bundle, so that the carbon fiber bundle is substantially the same as the carbon fiber bundle 101 in the circle in the figure. In the state of being converged to the predetermined amount (1K to 48K pieces) without being separated in a regular manner (that is, in a state of strand form), and is isotropic as the orientation state of the carbon fiber. Is low. However, since it is in a strand state and has high rigidity as a fiber bundle, the straight fiber length (the cut length) can be increased. On the other hand, a fiber bundle impregnated with resin during pressure molding, which is a feature of SMC, is flowed together with low-viscosity resin by pressing pressure, and the carbon fiber is bent or bent at the curved surface, corner, corner, etc. of the molded body. The number of places to go increases. In addition, if the press pressure is forcibly increased in order to increase the volume content of the carbon fiber in order to improve the mechanical properties such as strength of the molded body, the bending of the fiber bundle may bend even in the flat part due to the bending due to the overlapping of the fiber bundles. And fiber breakage is likely to occur. When these fiber bundles are bent or broken, cracks that lead to breakage tend to progress from the site, and improvement in the mechanical properties of the carbon fiber reinforced resin cannot be expected. That is, the conventional carbon fiber reinforced resin molded by general SMC has a limit in improving mechanical properties such as strength.

  In addition, since the SMC is a carbon fiber base material in a state of a bundle of fibers in which a large number of carbon fibers are bundled, it is difficult to concentrate the carbon fiber bundles to a certain level or higher (forcibly densely by pressing pressure). If you try to do so, the above-mentioned problem becomes remarkable). For this reason, there is a limit to the improvement of mechanical properties by increasing the fiber volume content. In addition, since each carbon fiber bundle is a relatively thick fiber bundle made of single yarn of 1K or more, the resin portion between the fiber bundles becomes relatively large, and the bending of the fiber bundle or the fiber that becomes the starting point of the break as described above When the crease has occurred, the crack that leads to the breakage in the resin portion is more likely to progress. Also from this aspect, the carbon fiber reinforced resin molded by conventional SMC has a limit in improving mechanical properties such as strength.

  For such a problem, 90% or more of the fiber bundles in the carbon fiber substrate are composed of fiber bundles that are split so that the number of single yarns is 100 or less, and the number of straight fiber bundles is the total number of fiber bundles. Fibers that are 70% or more, fiber bundle orientation is two-dimensionally quasi-isotropic, and 90% or more of the fiber bundles in the base material are split so that the number of single yarns is 100 or less. The number of straight fiber bundles is 70% or more of the total number of fiber bundles, the orientation of the fiber bundles is two-dimensionally quasi-isotropic, and the volume content of carbon fibers is 35% or more. A certain carbon fiber reinforced resin is known (Patent Document 1).

  However, in the carbon fiber reinforced resin described in Patent Document 1, since the carbon fiber bundle is very highly separated (opened), mechanical properties such as strength are greatly improved. Therefore, the fluidity at the time of molding is too low, and it may not be possible to mold into a desired shape.

JP 2008-174605 A

  Therefore, the object of the present invention is to focus on the problems in the conventional SMC as described above and the problems in the carbon fiber reinforced resin described in Patent Document 1, and the desirable mechanical properties of the molded product and the desirable fluidity during molding. An object of the present invention is to provide a carbon fiber reinforced resin molding material capable of achieving both of these in a balanced manner.

  In order to solve the above problems, a carbon fiber reinforced resin molding material according to the present invention is a carbon fiber reinforced resin molding material including at least a carbon fiber base material and a matrix resin, and the carbon fiber base material is continuous carbon. It is formed from a chopped fiber bundle obtained by cutting a fiber bundle of fibers, and 50 to 85% of the chopped fiber bundle is equal to or less than 100 single yarns in a weight ratio with respect to the total amount of carbon fibers in the carbon fiber substrate. Thus, it is characterized by being opened.

  In such a carbon fiber reinforced resin molding material according to the present invention, of the chopped fiber bundles in the carbon fiber substrate, an appropriate proportion (that is, 50 to 85% by weight) of chopped fiber bundles is a single piece. Since the fiber is opened at a high level of 100 yarns or less, the degree of opening of the chopped fiber bundle is set to an appropriate range as the entire carbon fiber base material. That is, there is a problem that there is a limit in improving mechanical properties such as strength when the degree of opening is too low or the degree of opening is too low, and a problem that the fluidity at the time of molding is too low when the degree of opening is too high. Both of these are eliminated or reduced, and it is possible to balance the desired mechanical properties of the molded article with the desired fluidity during molding in a balanced manner.

  In the carbon fiber reinforced resin molding material according to the present invention, the end portion of the chopped fiber bundle may be cut in a direction orthogonal to the extending direction of the fiber bundle, It can also be configured to be cut in a non-orthogonal direction (in an oblique direction) with respect to the existing direction. In particular, in the case of the latter form, it is possible to achieve higher mechanical properties of the molded product while maintaining the desired fluidity during molding.

  In the carbon fiber reinforced resin molding material according to the present invention, the weight average fiber length of the carbon fibers in the carbon fiber substrate is preferably in the range of more than 5 mm and 40 mm or less. In such a range, it is more preferably 7 mm or more and 40 mm or less, and further preferably 12 mm or more and 40 mm or less. In contrast to this range, if the weight average fiber length of the carbon fiber is shortened, the fluidity during molding tends to be high, but the mechanical properties of the molded product tend to be reduced.If the weight average fiber length of the carbon fiber is increased, molding is performed. Although the mechanical properties of the product can be maintained relatively high, the fluidity during molding tends to decrease. As described above, the degree of opening of the chopped fiber bundle is set to an appropriate range, and the weight average fiber length of the carbon fiber is kept within a preferable range, so that the desired mechanical properties of the molded product and the molding can be more reliably performed. It is possible to balance the desired fluidity in a balanced manner.

  As described above, according to the carbon fiber reinforced resin molding material according to the present invention, an appropriate proportion of the chopped fiber bundle in the carbon fiber base material is opened at an appropriate degree. It is possible to achieve a balance between the properties and the desired fluidity at the time of molding, and both the mechanical properties and the fluidity can be realized within the target range.

It is a schematic partial top view of each carbon fiber base material ((A)-(D)) from which the opening degree of a chopped fiber bundle differs. It is a schematic comparison figure of the bending strength of the molded article using each carbon fiber base material ((A)-(D)) from which the opening degree of a chopped fiber bundle differs. It is a general | schematic fragmentary top view which shows an example of the carbon fiber base material in the conventional SMC.

Embodiments of the present invention will be described below with reference to the drawings.
The carbon fiber reinforced resin molding material according to the present invention includes at least a carbon fiber base material and a matrix resin, and the carbon fiber base material is formed from a chopped fiber bundle obtained by cutting a fiber bundle of continuous carbon fibers. The chopped fiber bundle is opened so that 50 to 85% of the chopped fiber bundle is 100 or less in number of single yarns by weight ratio with respect to the total amount of carbon fibers in the carbon fiber substrate.

Here, the method for confirming the ratio of the chopped fiber bundle that has been opened so that the number of single yarns is 100 or less is not particularly limited, but examples thereof include the following methods. That is, a 100 mm × 100 mm sample is cut out from the carbon fiber reinforced resin molding material, and the cut out sample is heated in an electric furnace for about 1 to 2 hours to burn off organic substances such as a matrix resin. The weight of the carbon fiber base material thus obtained is measured. Then, using tweezers or the like, a chopped fiber bundle in the carbon fiber substrate is collected from the carbon fiber substrate, and the weight is measured (bundle weight). At the same time, the fiber length is measured using a caliper capable of measuring up to 0.1 mm. Then, from the following equation, the number of single yarns of carbon fibers constituting the extracted chopped fiber bundle can be calculated.
(Number of single yarns) = (bundle weight) / {(fineness of carbon fiber single yarn) × (fiber length)}
The above operation is performed on all the chopped fiber bundles in the carbon fiber base material taken out, the number of single yarns is measured, and the total weight of the chopped fiber bundles exceeding 100 single yarns is calculated. From the following formula, the proportion of chopped fiber bundles having 100 or less single yarns present in the carbon fiber substrate can be calculated.
(Proportion of chopped fiber bundle having 100 single yarns or less) = {1- (total of weights of chopped fiber bundles having more than 100 single yarns) / (weight of carbon fiber substrate)} × 100

  The matrix resin in the present invention is not particularly limited, for example, epoxy resin, unsaturated polyester resin, vinyl ester resin, phenol resin, epoxy acrylate resin, urethane acrylate resin, phenoxy resin, alkyd resin, urethane resin, maleimide resin, Thermosetting resins such as cyanate resin, polyamide, polyacetal, polyacrylate, polysulfone, ABS, polyester, acrylic, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene, polypropylene, polyphenylene sulfide (PPS), Fluorine resins such as polyetheretherketone (PEEK), liquid crystal polymer, vinyl chloride, polytetrafluoroethylene, and thermoplastic resins such as silicone That.

  If the opening degree of the chopped fiber bundle in the said carbon fiber base material is shown notionally, it will come to show, for example in FIG. FIG. 1 (A) shows a schematic partial plane of an example of the carbon fiber substrate 1 according to the present invention in which a chopped fiber bundle is appropriately opened and a part of the chopped fiber bundle remains as shown in FIG. ) Shows a schematic partial plane of an example of the carbon fiber base material 100 in the above-described conventional SMC, and FIG. 1 (C) shows the degree of opening in the present invention although opening is performed compared to the conventional SMC. FIG. 1 (D) shows a schematic partial plane of an example of a carbon fiber substrate 110 that is too low as compared with the carbon fiber substrate 120 having a fiber opening degree higher than the fiber opening degree of the chopped fiber bundle defined in the present invention. Shows a schematic partial plane of an example of

  The degree of opening of such a chopped fiber bundle can be controlled by airlaid or carding, for example. However, since it is difficult to open the fiber with only airlaid, it is relatively high as defined in the present invention. In order to achieve a high degree of opening, it is preferable to use carding. Carding can be performed, for example, by putting a predetermined amount of chopped fiber bundles obtained by cutting carbon fiber strands (1K to 48K yarns) into a predetermined fiber length into a card machine used in the spinning process. When the degree of opening is lower than the target value, it can be reopened on the card machine and opened to a higher level.

  When the chopped fiber bundle is formed by cutting the carbon fiber strand into a predetermined fiber length as described above, it is usually cut so that the end of the chopped fiber bundle is perpendicular to the extending direction of the fiber bundle. Although it cut | disconnects with a blade, it can also cut | disconnect in a non-orthogonal direction with respect to the extension direction of a fiber bundle. As the non-orthogonal direction, it is possible to cut linearly in an oblique direction with respect to the extending direction of the fiber bundle, and it is also possible to cut in a curved shape. Cutting in a curved shape is possible in either the orthogonal direction or the oblique direction with respect to the extending direction of the fiber bundle. By cutting in an oblique direction, it is possible to achieve higher mechanical properties of the molded product while maintaining the desired fluidity during molding as described above.

  When the end of the chopped fiber bundle is cut by a cutting blade so that the end of the chopped fiber bundle is orthogonal to the extending direction of the fiber bundle, the length as the bundle, that is, the distance between both ends of the chopped fiber bundle, and the fiber bundle The lengths of the carbon fiber single yarns constituting the are equal. However, when cut in a non-orthogonal direction with respect to the extending direction of the fiber bundle, the length of the chopped fiber bundle may be different from the length of the carbon fiber single yarn constituting the fiber bundle.

  Here, the “fiber length” in the present invention refers not to the length as a bundle but to the length of the carbon fiber single yarn constituting the bundle. Therefore, when calculating the above-mentioned weight average fiber length, in the case of a chopped fiber bundle cut in a non-orthogonal direction, it is calculated using the length of the carbon fiber single yarn constituting the bundle. The weight average fiber length can be calculated by a known method.

  As described above, by increasing the degree of opening of the chopped fiber bundle in the carbon fiber base material, the fluidity during molding tends to decrease, but the mechanical properties of the molded product are enhanced. For example, FIG. 2 shows a schematic comparison of bending strengths of molded articles using carbon fiber base materials ((A) to (D)) having different degrees of opening of chopped fiber bundles. (B) in FIG. 2 shows the bending strength of the molded product using the carbon fiber base material in the conventional SMC corresponding to the form of FIG. 1 (B), and (C) in FIG. FIG. 2 shows the bending strength of a molded product using a carbon fiber base material corresponding to the form of (C), but the degree of opening is lower than that of the present invention although opening is performed compared to the conventional SMC. (A) has shown the bending strength of the molded article using the carbon fiber base material of the opening degree of the appropriate chopped fiber bundle prescribed | regulated by this invention, (D) in FIG. 2 shows FIG. 1 (D). The bending strength of the molded article using the carbon fiber base material in the above-mentioned patent document 1 of the opening degree higher than the opening degree of the chopped fiber bundle defined in the present invention corresponding to the form of, for example, is shown.

  As shown in FIG. 2, the mechanical properties of the molded product are enhanced as the degree of opening of the chopped fiber bundle in the carbon fiber substrate is increased. However, as described above, if the degree of opening of the chopped fiber bundle is excessively increased, the mechanical properties of the molded product are enhanced, but the fluidity during molding tends to decrease. In the carbon fiber reinforced resin molding material according to the present invention, an appropriate proportion of the chopped fiber bundle in the carbon fiber base material is opened at an appropriate degree, so that desirable mechanical properties of the molded product and desirable at the time of molding are obtained. The fluidity is satisfied as a characteristic within the target range with a good balance. This will be described below based on examples and comparative examples.

  As shown in Tables 1 and 2 (Examples 1 to 6 and Comparative Examples 1 to 3) described later, the weight average fiber length, the opening degree of the chopped fiber bundle, and the cut end of the chopped fiber bundle in the carbon fiber base material The carbon fiber base material having a different shape, the fiber bundle extending direction and the angle formed by the cut portion, vinyl ester resin (“Delaken” (registered trademark)) 100 manufactured by Dow Chemical Co., Ltd. as matrix resin [VE-1] 100 1 part by weight of tert-butyl peroxybenzoate (manufactured by NOF Corporation, “Perbutyl Z” (registered trademark)) as a curing agent, magnesium oxide (manufactured by Kyowa Chemical Industry Co., Ltd.) as a thickener A carbon fiber reinforced resin molding material impregnated with 7 parts by weight of MgO # 40 ″) was produced, and the bending strength and bending elastic modulus as the mechanical properties of the molded product and the fluidity during molding were evaluated. In addition, the evaluation method of the ratio, bending strength, and fluidity | liquidity of the chopped fiber bundle opened to 100 or less in the carbon fiber base material in a carbon fiber reinforced resin molding material is as follows.

(1) Ratio of chopped fiber bundle opened to 100 or less in carbon fiber substrate A sample of 100 mm × 100 mm was cut out from a carbon fiber reinforced resin molding material, and the cut sample was 600 ° C., 1 Heated for 5 hours to burn off the matrix resin. The weight of the carbon fiber base material thus obtained was measured, and then a chopped fiber bundle in the carbon fiber base material was collected from the carbon fiber base material using tweezers, and the weight was measured (bundle weight). . At the same time, the fiber length was measured using a caliper capable of measuring up to 0.1 mm. Then, from the following formula, the number of single yarns of carbon fibers constituting the extracted chopped fiber bundle was calculated.
(Number of single yarns) = (bundle weight) / {(fineness of carbon fiber single yarn) × (fiber length)}
Said operation was performed with respect to all the chopped fiber bundles in the carbon fiber base material taken out, the number of single yarns was measured, and the sum total of the weight of the chopped fiber bundles exceeding the number of single yarns 100 was calculated. And the ratio of the chopped fiber bundle opened to the number of single yarns of 100 or less was calculated from the following formula.
(Ratio of chopped fiber bundles opened to 100 or less single yarns) = {1- (total of weights of chopped fiber bundles exceeding 100 single yarns) / (weight of carbon fiber base material)} × 100

(2) Evaluation method of bending strength It measured based on JISK7074. About the value of the obtained bending strength, it evaluated based on the following criteria, and more than (triangle | delta) was set as the pass in this invention.
A: 400 MPa or more B: 370 to 399 MPa
Δ: 340 to 369 MPa
X: Less than 340 MPa

(3) Fluidity evaluation method A carbon fiber reinforced resin molding material is placed at a charge rate of 50% in a flat plate mold having an uneven part (thickness 1 mm) and ribs (thickness 2 mm), and molded by press molding. I got a product. The obtained molded product was evaluated based on the following criteria, and Δ or more was regarded as acceptable in the present invention.
(Double-circle): It has a smooth surface without a flesh and a wrinkle.
○: There is no thinning and some fine wrinkles exist on the surface.
Δ: Although there is no lack of meat, some wrinkles and blisters are present on the surface.
X: A missing piece is present in the molded product.

  As can be seen from Tables 1 and 2, the ratio of the chopped fiber bundle that is opened so that the number of single yarns is 100 or less is 50 to 85% in the weight ratio with respect to the total amount of carbon fibers in the carbon fiber substrate. When it is in the range (Examples 1 to 6), the desired mechanical properties of the molded product and the desired fluidity at the time of molding can be balanced with each other, and in particular, the end portion of the chopped fiber bundle is made of the fiber bundle. When cut in a direction oblique to the extending direction (Examples 3 and 4), higher mechanical properties can be achieved while maintaining good fluidity.

  On the other hand, when the ratio of the chopped fiber bundle opened so that the number of single yarns is 100 or less is less than the range of the ratio defined in the present invention in the weight ratio with respect to the total amount of carbon fibers in the carbon fiber substrate. In (Comparative Examples 1 and 2), although excellent fluidity is obtained, it is difficult to achieve high mechanical properties, and the ratio of the chopped fiber bundle that is opened so that the number of single yarns is 100 or less. When the ratio was higher than the range defined in the present invention (Comparative Example 3), it was difficult to obtain excellent fluidity although high mechanical properties could be achieved.

  The carbon fiber reinforced resin molding material according to the present invention can be applied to molding in all fields.

1, 100, 110, 120 Carbon fiber substrate 101 Carbon fiber bundle

Claims (3)

  A carbon fiber reinforced resin molding material containing at least a carbon fiber base material and a matrix resin, wherein the carbon fiber base material is formed from a chopped fiber bundle obtained by cutting a fiber bundle of continuous carbon fibers, and the carbon A carbon fiber reinforced resin molding material, wherein the fiber base material is opened so that 50 to 85% of the chopped fiber bundle has a number of single yarns of 100 or less in a weight ratio with respect to the total amount of carbon fibers in the fiber base material.   The carbon fiber reinforced resin molding material according to claim 1, wherein an end portion of the chopped fiber bundle is cut in a non-orthogonal direction with respect to the extending direction of the fiber bundle.   The carbon fiber reinforced resin molding material according to claim 1 or 2, wherein a weight average fiber length of carbon fibers in the carbon fiber substrate is in a range of more than 5 mm and 40 mm or less.

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