Carbon fiber reinforced resin molding

Abstract

To provide a fiber reinforced resin molding in which surface irregularities resulting from a difference in linear expansion coefficient between carbon fiber and matrix resin are suppressed.SOLUTION: A carbon fiber reinforced molding of the present invention includes a fiber reinforcement layer in a matrix resin. The fiber reinforcement layer has at least a design surface formed of a spread carbon fiber sheet made of spread yarns with a flattened cross section, and the spread carbon fiber sheet is a unidirectional material with a thickness of 81 μm or more and 117 μm or less, so that a fiber reinforced resin molding with reduced surface unevenness can be provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a carbon fiber reinforced resin molded body, and more particularly to a carbon fiber reinforced resin molded body suitable for outer panels of vehicles such as bonnets and roof panels.

Background Art

[0002] In recent years, the vehicle body has been lightened and fuel consumption has been reduced by using a carbon fiber reinforced resin molded body (hereinafter sometimes simply referred to as "CFRP"). For the outer panel of a vehicle, for example, a thermosetting CFRP molded by an autoclave using a prepreg capable of precisely controlling the orientation and fiber content of carbon fibers is used.

[0003] However, in addition to the large difference in the linear expansion rate between carbon fibers and resin, since the carbon fiber sheet is composed of raw yarns with a circular cross section, unevenness inevitably occurs on the surface of the carbon fiber sheet, and this surface unevenness of the carbon fiber sheet appears as surface unevenness of the CFRP due to resin sink marks.

[0004] When such CFRP is directly used for the outer panel of a vehicle, the design property deteriorates due to the above-mentioned surface unevenness. Therefore, painting and polishing are repeatedly performed to smooth the surface of the CFRP, which is one of the causes of cost increase.

[0005] Although not aimed at preventing the occurrence of the above-mentioned surface unevenness, Patent Document 1 discloses a CFRP formed of a carbon fiber sheet using opened and flattened opened yarns obtained by opening raw yarns.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the case of the one described in Patent Document 1, since an open-carbon fiber sheet formed of flattened fibrillated fibers is used, it is expected that the surface unevenness can be suppressed more than that of a CFRP using a carbon fiber sheet composed of raw yarns having a circular cross section.

[0008] However, in the one described in Patent Document 1, since the thickness of the open-carbon fiber sheet is thin and the fibrillated fibers constituting the open-carbon fiber sheet are sparse, surface unevenness occurs due to the difference in thermal shrinkage between the carbon fiber bundle portion and the resin portion.

[0009] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a fiber-reinforced resin molded body in which surface unevenness caused by the difference in linear expansion coefficient between carbon fibers and a matrix resin is suppressed.

Means for Solving the Problems

[0010] As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by using a unidirectional material having a desired thickness formed of fibrillated fibers obtained by fibrillating and flattening raw yarns on the appearance surface serving as the design surface, and has completed the present invention.

[0011] That is, the carbon fiber-reinforced molded body of the present invention includes a fiber-reinforcing layer in a matrix resin. And, at least the design surface of the fiber-reinforcing layer is formed of an open-carbon fiber sheet formed of fibrillated fibers having a flattened cross section, The open-carbon fiber sheet is a unidirectional material having a thickness of 81 μm or more and 117 μm or less.

Effects of the Invention

[0012] According to the present invention, since a unidirectional material having a desired thickness formed of fibrillated fibers obtained by fibrillating and flattening is used for the appearance surface serving as the design surface, it is possible to provide a fiber-reinforced resin molded body in which surface unevenness caused by the difference in linear expansion coefficient between carbon fibers and a matrix resin is suppressed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0014] The carbon fiber reinforced molded body of the present invention will be described in detail. The carbon fiber reinforced molded body of the present invention includes a fiber reinforcing layer of a reinforcing sheet in a matrix resin. The fiber reinforcing layer includes an opened carbon fiber sheet formed of opened fibers with a flattened cross-section, and optionally includes a normal carbon fiber sheet.

[0015] Generally, a normal carbon fiber sheet constituting CFRP is a unidirectional material in which raw yarns bundling carbon single fibers with a diameter of about 7 to 8 μm are arranged in one direction or a cross material woven with the above raw yarns as shown in FIG. 1. Since the cross-section of the raw yarn is usually circular, even in the unidirectional material in which the raw yarns are arranged in one direction, irregularities occur in the direction in which the raw yarns are arranged.

[0016] In the present invention, an opened carbon fiber sheet is used for the appearance surface that becomes the design surface of CFRP. This opened carbon fiber sheet is formed by opening and flattening the above raw yarns by an air opening method or the like, and is formed of opened fibers that have become wide.

[0017] And, as shown in FIG. 1, the opened carbon fiber sheet of the present invention is a unidirectional material in which the flattened opened fibers are arranged in one direction. Therefore, irregularities caused by the cross-sectional shape of the raw yarn are suppressed, and the raw yarns do not cross each other like a cross material and the surface does not undulate.

[0018] Furthermore, since the thickness of the above-mentioned fibrillated carbon fiber sheet is 81 μm or more and 117 μm or less, adjacent fibrillated yarns are tightly attached to each other without gaps between the fibrillated yarns, and the density variation of the fibrillated yarns is small, the resin shrinkage becomes uniform, and surface unevenness caused by the difference in the linear expansion coefficients of the carbon fiber and the resin can also be suppressed.

[0019] If the thickness of the above-mentioned fibrillated carbon fiber sheet is less than 81 μm, the fibrillated yarns become sparse and gaps are likely to occur between the fibrillated yarns. Also, if it exceeds 117 μm, the number of fibrillated yarns in the thickness direction increases, so it becomes difficult for the fibrillated yarns to align straight in the thickness direction and they are likely to shift obliquely to form gaps, resulting in a large variation in the density of the fibrillated yarns.

[0020] More preferably, the thickness of the above-mentioned fibrillated carbon fiber sheet is 84 μm or more and 102 μm or less. Within this range, the variation in the density of the fibrillated yarns is reduced, and the occurrence of surface unevenness can be reliably suppressed.

[0021] As the above-mentioned fibrillated carbon fiber sheet, a prepreg in which a matrix resin is preliminarily impregnated between carbon fibers can be used. Examples of the above-mentioned matrix resin include thermosetting resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins, and phenolic resins.

[0022] Preferably, the coefficient of variation (Cv value) of the fiber existence ratio per unit area of the cross-section of the above-mentioned fibrillated carbon fiber sheet is 8.0 or less, and more preferably 6.0 or less.

[0023] The above coefficient of variation is an index indicating the density variation of the fibrillated yarns. When the coefficient of variation of the fibrillated carbon fiber sheet is within the above range, the appearance defects of the CFRP can be suppressed.

[0024] The above-mentioned fibrillated carbon fiber sheet has a basis weight of the carbon fiber of 70 g / m 2 or more and 110 g / m 2 or less, and more preferably 80 g / m 2 or more to 100 g / m 2 or less.

[0025] When the basis weight of the carbon fiber is within the above range, the generation of surface irregularities of high-strength CFRP with a fiber volume content (Vf) of 60 to 70% can be suppressed.

[0026] The carbon fiber reinforced resin molded body of the present invention may be obtained by laminating a plurality of opened carbon fiber sheets and performing autoclave molding. However, as shown in FIG. 2, on the back side opposite to the design surface, a fiber reinforcing layer of a normal carbon fiber sheet formed of a roving having a substantially circular cross section can be used.

[0027] Since the opened carbon fiber sheet of the present invention is thinner than a normal carbon fiber sheet, when producing a carbon fiber reinforced resin molded body with a desired thickness using only the opened carbon fiber sheet, the number of laminated sheets increases and the cost increases. However, by forming the back side with a fiber reinforcing layer of a normal carbon fiber sheet, the number of laminated sheets can be reduced and the cost can be reduced.

Example

[0028] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0029] On a normal carbon fiber sheet (resin: thermosetting epoxy resin, basis weight: 200 g / m 2 ), an opened carbon fiber sheet (resin: thermosetting epoxy resin) was laminated in a stacking configuration of [0 / 90 / 0 / 90 / 0 / 90 / 0 / 90 / 0], and carbon fiber reinforced resin molded bodies with different basis weights of the opened carbon fiber sheet were each autoclave molded under the conditions of a molding temperature of 130°C and a molding pressure of 0.5 MPa.

[0030] <Evaluation> Carbon fiber reinforced resin molded bodies with different basis weights of the opened carbon fiber sheet were evaluated under the following conditions. The evaluation results are shown in Table 1.

[0031] (Thickness of opened carbon fiber sheet) The cross-section of the carbon fiber reinforced resin molded body was imaged, and the thickness of the opened carbon fiber sheet was measured based on the interface of the resin derived from the prepreg.

[0032] (Variation coefficient of fiber density (variation coefficient)) From the cross-sectional image in the direction perpendicular to the opened fibers of the carbon fiber reinforced resin molded body, a square with the thickness of one opened carbon fiber sheet as the side length was defined as one section. For 12 sections, the cross-sectional image was binarized to obtain the occupied area of the carbon fibers, and the coefficient of variation (Cv value) was obtained by the following formula (1). Coefficient of variation (Cv value) = average value (Ave) of each fiber occupied area ÷ variance value (σ) of each fiber occupied area × 100 (%) ··· Formula (1)

[0033] (Surface roughness) The surface roughness (Ra) of the carbon fiber reinforced resin molded body was measured using a surface roughness measuring instrument (manufactured by Mitutoyo Corporation). The relationship between the basis weight and the surface roughness is shown above in Figure 3.

[0034] (Appearance) The texture of the carbon fiber reinforced resin molded body after painting was measured using a spectrophotometer and color difference meter (Rhopoint TAMS: manufactured by Konica Minolta). The relationship between the thickness of the opened carbon fiber sheet and the texture is shown below in Figure 3.

[0035]

Table 1

[0036] From Table 1 and Figure 3, it can be seen that the carbon fiber reinforced resin molded body of the present invention has a small surface roughness and can prevent the texture after painting.

Explanation of symbols

[0037] 1 Opened carbon fiber sheet 2 Normal carbon fiber sheet 3 Single fiber of carbon fiber 4 Matrix resin

Claims

1. A carbon fiber reinforced resin molded body having a fiber reinforcing layer in a matrix resin, wherein at least the design surface of the fiber reinforcing layer is formed of an open fiber carbon fiber sheet formed of open fibers having a flattened cross section, The carbon fiber reinforced resin molded body, wherein the open fiber carbon fiber sheet is a unidirectional material having a thickness of 81 μm or more and 117 μm or less.

2. The carbon fiber reinforced resin molded body according to claim 1, wherein the thickness of the open fiber carbon fiber sheet is 84 μm or more and 102 μm or less.

3. The carbon fiber reinforced resin molded body according to claim 1, wherein the open fiber carbon fiber sheet has a coefficient of variation (Cv value) of the fiber presence ratio per unit area of the cross section of 8.0 or less.

4. The carbon fiber reinforced resin molded body according to claim 1, wherein the open fiber carbon fiber sheet has a coefficient of variation (Cv value) of the fiber presence ratio per unit area of the cross section of 6.0 or less.

5. The carbon fiber reinforced resin molded body according to claim 1, wherein the open fiber carbon fiber sheet has a basis weight of carbon fiber of 70 g / m ２ or more and 110 g / m ２ or less.

6. The carbon fiber reinforced resin molded body according to claim 1, wherein the open fiber carbon fiber sheet has a basis weight of carbon fiber of 80 g / m ２ or more and 100 g / m ２ or less.

7. The carbon fiber reinforced resin molded body according to claim 1, wherein the fiber reinforcing layer has a fiber reinforcing layer of the open fiber carbon fiber sheet on the design surface side and a fiber reinforcing layer of a carbon fiber sheet formed of a raw yarn having a substantially circular cross section on the back surface side.

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