JPWO2018235512A1 - Fiber reinforced plastic - Google Patents

Abstract

In order to provide a fiber-reinforced plastic having a high fiber content while having a complicated shape, the present invention is a fiber-reinforced plastic containing fibers and a resin, wherein the fibers have an average length of 5 to 50 mm, When a population related to the fiber volume content in the local region (hereinafter, such fiber volume content is referred to as Vf) is obtained, the average value of is 40 to 65%, and the coefficient of variation of the population is 0.15 to 0.4. It is to be noted that, when the population is made into a histogram with a class number of 10 and a class having a frequency greater than the frequencies of adjacent classes on the left and right is set as a peak value, a fiber reinforced plastic having a plurality of peak values is used. Use as a summary. (Vf population) A value obtained by dividing the total area of the fibers contained in the local area by the area of the local area when a local area having a diameter of 100 μm was extracted from the cross-sectional image of the fiber-reinforced plastic and multiplying by 100. Is Vf. A plurality of local regions are extracted, and a set of Vf in each local region is used as a population. [Selection diagram] Figure 1

Description

  The present invention relates to a fiber reinforced plastic having a high fiber content while having a complicated shape.

  Fiber-reinforced plastics, which consist of fibers and resins, have attracted attention in industrial applications because of their high specific strength and specific elastic modulus, excellent mechanical properties, and high functional properties such as weather resistance and chemical resistance. , Spacecraft, automobiles, railroads, ships, electrical appliances, sports, etc., and the demand is increasing year by year.

  One of the intermediate base materials for producing a fiber reinforced plastic is a prepreg obtained by impregnating fibers in a densely unidirectionally oriented fiber with a resin. Since prepreg has a high fiber content, it exhibits high mechanical properties when made into fiber-reinforced plastic, but it does not stretch in the fiber orientation direction, so it is difficult to follow complex shapes, and productivity becomes an issue. There is. Then, the notch prepreg represented by patent documents 1 and 2 which inserted the notch in the prepreg is developed.

  Since the notched prepreg is capable of stretching in the fiber direction, it has better followability to complex shapes than the prepreg, and it is possible to manufacture fiber reinforced plastics that maintain a high fiber content and fiber orientation. .

JP, 2007-261141, A JP, 2008-207544, A

  However, the fiber-reinforced plastic molded using the notch prepreg is based on a relatively thin prepreg and has a laminated structure with layers of approximately the same thickness. The number of parts will be small.

  Therefore, an object of the present invention is to provide a fiber reinforced plastic having a high fiber content while having a complicated shape such as a thick wall change portion.

  The present invention provides the following fiber-reinforced plastic as a fiber-reinforced plastic having a complicated shape and a high fiber volume content in order to solve such problems. That is, a fiber reinforced plastic containing fibers and a resin, wherein the average length of the fibers is 5 to 50 mm, and a population related to the fiber volume content rate in the local region (hereinafter, such fiber volume content rate is referred to as Vf) is shown. When the population is obtained, the average value of the population is 40 to 65%, the coefficient of variation of the population is 0.15 to 0.4, and when the population is made into a histogram of rank 10, it is adjacent to the left and right. A fiber reinforced plastic having a plurality of peak values, where the peak value is a class having a frequency higher than that of the class.

  Here, the population related to Vf is obtained as follows.

  When a local region corresponding to a diameter of 100 μm is extracted from the cross-sectional image of the fiber-reinforced plastic, the total area of the fiber-rich pixels included in the local region is divided by the total area of the pixels included in the local region, The value obtained by multiplying by 100 is Vf. A plurality of the above-mentioned local areas are extracted, and a set of Vf obtained in each local area is used as a population.

  According to the present invention, it is possible to provide a fiber-reinforced plastic having a high fiber volume content even though it has a complicated shape, and a fiber-reinforced plastic having a high reinforcing effect can be obtained.

It is a conceptual diagram of the cross section of fiber reinforced plastic, and the conceptual diagram of the digital image binarized by cutting out a part thereof. It is an example of a histogram of the population. It is an example of a histogram of the population. It is an example of Vf distribution in the cross section of fiber reinforced plastic. It is an example of a conceptual diagram of a cross section of a fiber-reinforced plastic. It is the size and shape of the fiber-reinforced plastic molded in the examples.

  In order to provide a fiber-reinforced plastic having a high fiber volume content while having a thick-walled change portion, the present invention is a fiber-reinforced plastic containing fibers and a resin, wherein the average length of the fiber is The average value of the population is 40 to 65%, and the coefficient of variation of the population is 0.15 to 0.4 when the population related to the fiber volume content in the local region is obtained. Then, when the population is made into a histogram with a class number of 10, and a class having a frequency greater than the frequencies of the classes adjacent to each other on the left and right is taken as a peak value, a fiber-reinforced plastic having a plurality of peak values is obtained. This problem is solved.

  In the present invention, when the population related to Vf in the local region is obtained, it can be said that the variation in Vf inside the fiber-reinforced plastic is large when the coefficient of variation of the population is 0.15 or more.

  Here, the population related to Vf includes the total area of the fiber-rich pixels included in the local region when the local region corresponding to the diameter of 100 μm is extracted from the cross-sectional image of the fiber-reinforced plastic. A value obtained by dividing by the total area of pixels and multiplying by 100 is set as Vf, and a plurality of the above local regions are extracted, and a set of Vf obtained in each local region is set as a population.

  More specifically, first, a cross-sectional image of the fiber-reinforced plastic is captured, and a portion to be a local region is set from the captured image. Regarding the cross section to be obtained, the purpose of the present invention is to maintain the mechanical characteristics of the thick portion, so the cross section is obtained at the thickest portion in the fiber reinforced plastic. The size of the captured image includes both the upper surface and the lower surface in the thickness direction (longitudinal direction) of the fiber reinforced plastic, and is acquired with a width of 2 mm in the in-plane direction (width direction) of the fiber reinforced plastic. The picked-up image does not necessarily have to be an image acquired by a single shooting, and a plurality of images may be combined to form one large cross-sectional image. Further, in the present invention, the local area is set as a circular area having a diameter of 100 μm. In the local area, the captured image is first divided into pixels each having a size of 0.1 μm to 3.0 μm in the fiber reinforced plastic, and each pixel has a diameter of 100 μm as a size in the fiber reinforced plastic centered on the center of gravity of the pixel. The area surrounded by the circle is the local area centered on that pixel. That is, the local area is set by the number of partitioned pixels. Note that the local area cannot be set as a circle on the side of the captured image, but this does not affect the calculation of Vf, and as can be understood from the relationship between the pixel size and the local area size, the local area is It is set overlapping. The size of one pixel can be arbitrarily set within the range of 0.1 μm to 3.0 μm square as described above, but if the size of one pixel is too large, it becomes difficult to accurately measure Vf. It is set to 0 μm or less. If the size of 1 pixel is too small, the calculation time becomes long, and therefore the size of 1 pixel is larger than 0.1 μm. Depending on the diameter of the fiber used, if it is a fiber that is normally used, it is usually selected to be 2.0 μm square. Therefore, the imaging magnification needs to be sufficiently large so that the pixel size can be made to correspond to 0.1 μm to 3 μm in the fiber reinforced plastic as described above. The method for setting the pixel size is not particularly limited, and the cross-sectional image may be acquired by previously calculating the imaging magnification that satisfies the desired pixel size from the resolution of the imaging device, or after acquiring the cross-sectional image with a sufficiently large magnification. The pixel size may be set by image processing. Further, for each pixel, a binarization process is performed in order to separate a fiber-rich pixel and a resin-rich pixel by image processing. A pixel is considered to be a fiber-rich pixel when the area in which the fiber is observed for that pixel occupies more than half the area of that pixel. In this way, the captured image becomes an image in which fiber-rich pixels and resin-rich pixels are aggregated. The threshold for binarization is selected depending on the resin and fiber materials used, but the difference between the resin part contrast and the fiber part contrast (chromaticity difference, lightness difference or saturation difference) is usually clear. , These may be set to be divided (for example, an intermediate value is used). It is also possible to emphasize the contrast difference by changing the imaging condition.

  FIG. 1 is a conceptual view of a cross section of the fiber-reinforced plastic of the present invention, showing a state in which a plurality of fibers 1 are present in a resin 2. FIG. 1A is a conceptual diagram of a binarized digital image, which is a portion cut out from FIG. 1. The digital image is composed of a plurality of pixels 3, and the local area 4 is a circular area having a certain pixel at the center of a circle. Whether a certain pixel is included in the local region is included in the local region if even a part of the outer peripheral line of the circle covers the pixel.

  The Vf in the local area is calculated at a 100-percentage ratio with the total number of pixels included in the local area as the denominator and the number of pixels that are fiber-rich as the numerator. However, when the outer circumference of the circle for obtaining the local area extends from the cross-sectional image, the area that extends is not counted, and only the area within the cross-sectional image is calculated.

  Thus, when Vf is obtained for each local area, Vf is obtained by the number of pixels. In the present invention, such a Vf data group is referred to as a “population”.

  Since the fiber-reinforced plastic in the present invention has a high Vf, the average value of the population is 40 to 65%. When the average value of the population is 40 to 65%, high mechanical properties can be maintained. Further, by increasing the variation of Vf in the fiber reinforced plastic, that is, the coefficient of variation, a low Vf portion that can be freely flowed during molding is included, and a higher Vf portion is included, resulting in a thicker portion. It is possible to obtain a fiber-reinforced plastic having a high mechanical property while allowing the meat portion to smoothly follow the shape. That is, in the present invention, the average value of the population is 40 to 65%, but a portion having a higher Vf and a lower Vf than the aspect in which all local regions are controlled to about 40 to 65% in the cross section of the fiber reinforced plastic. It is possible to achieve the object of the present invention by making both of the points having the value of ## EQU1 ## exist and making the coefficient of variation within a certain range and setting the average value of the population to be 40 to 65%. When the coefficient of variation of the population is 0.15 or more, it is possible to secure a sufficient volume of low Vf for allowing the fibers and the resin to flow well. On the other hand, 0.4 is the maximum as the coefficient of variation of the population in terms of mechanical characteristics or productivity. That is, in the present invention, the coefficient of variation of the population is 0.15 to 0.4.

  The coefficient of variation is known as a parameter obtained by dividing the standard deviation by the average value.

  Further, in the present invention, the average fiber length is 5 to 50 mm. By doing so, it is possible to obtain a fiber-reinforced plastic that follows a curved surface or a concavo-convex shape even at a portion having a high Vf other than the thick-walled portion. Even if the average length of the fibers is in the range of 5 to 50 mm, the longer the average length of the fibers is, the more the mechanical properties of the fiber-reinforced plastic are improved, and the shorter the average fiber length is, the more complicated the shape of the fiber-reinforced plastic is. Can be realized. A more preferable lower limit of the average fiber length is 10 mm or more, and the upper limit thereof is 30 mm or less. In the present invention, fibers having a fiber length of less than 5 mm or fibers having a length of more than 50 mm may be included as long as the average length of the fibers is 5 to 50 mm. Since it is not realistic to calculate the average length of the fibers in the fiber-reinforced plastic by measuring the lengths of all the fibers contained in the fiber-reinforced plastic, 300 fibers arbitrarily extracted from the fiber-reinforced plastic are selected. The average length of the fiber is used. As a method of extracting fibers from the fiber-reinforced plastic, there is a method of burning off the resin at a high temperature. For example, an epoxy resin can be burnt out at 450 ° C., and the fibers in the fiber reinforced plastic can be extracted. However, when the resin of a small piece of fiber-reinforced plastic obtained by cutting the fiber-reinforced plastic is burned off, the fibers that come into contact with the cut surface may be shorter than when they were originally in the fiber-reinforced plastic. Therefore, it is excluded from the target of extraction.

  Further, the fiber-reinforced plastic of the present invention has a peak value when a class having a frequency greater than the frequencies of adjacent classes on the left and right is taken as a peak value when a population is made into a histogram with a class number of 10 as shown in FIG. It has multiple values. In the present invention, the class is set to 10 by equally dividing the range of the minimum Vf value to the maximum Vf value in the population into 10. For example, when the minimum Vf value in the population is 10% and the maximum Vf value is 60%, 10-15%, 15-20%, 20-25%, 25-30%, 30-35%. 35 to 40%, 40 to 45%, 45 to 50%, 50 to 55%, and 55 to 60%, for a total of 10 classes. Furthermore, in the present invention, the central value of at least one peak value, for example, 52.5% when the peak value is a class of fiber content of 50 to 55%, is lower than the average value of the population, and at least The central value of one peak value is preferably higher than the average value of the population. Since the fiber-reinforced plastic of the present invention has a plurality of peak values when the population is made into a histogram of rank 10, a portion of low Vf is included in an amount necessary for following the change in thickness, and a high Vf of The location can contain a sufficient amount to ensure mechanical properties. In the fiber-reinforced plastic of the present invention, when the population is made into a histogram of rank 10, the prepreg having a large fiber volume content and the prepreg having a small fiber volume content can be provided in order to have a mode having a plurality of peak values. It is possible to cite a method in which the layers are alternately laminated to form a laminate, which is cured to form a fiber-reinforced plastic.

  As an embodiment of the fiber reinforced plastic of the present invention, when the population is made into a histogram of 50 ranks, the peak value, and how to divide the class is 50 sections between the maximum Vf and the minimum Vf as above. In addition, the peak value may have the same meaning as above, and it may have three or more classes that are higher in frequency than the classes on both sides.

  In a preferred embodiment of the fiber-reinforced plastic of the present invention, both of the two regions, that is, the region having a Vf larger than the average value of the population and the region having a Vf smaller than the average value of the population are substantially linear. Existing in the form of. Here, Vf larger than the average value of the population is Vf larger than the average value between 40 and 65% by 5% or more (hereinafter, referred to as Vf1), and Vf smaller than the average value of the population. Is Vf (hereinafter referred to as Vf2) that is 5% or more smaller than the average value between 40 and 65%. The substantially linear existence means that in the captured image used for obtaining Vf, the pixel is the center of the local area where Vf is Vf1 or more and the center of the local area where Vf is Vf2 or less. When each of the pixels is marked with distinction, the length in the direction parallel to the surface of the fiber-reinforced plastic (the width direction is the width direction) and the direction perpendicular to the surface (the height direction is the height direction). In other words, a region having a length ratio (width / height) of 2 or more in the thickness direction of the fiber-reinforced plastic is a group of pixels serving as the center of a local region having Vf of Vf1 or more (such pixel). Group of pixels is referred to as a Vf1 pixel group) and a group of pixels serving as a center of a local region in which Vf is Vf2 or less (the group of such pixels is referred to as a Vf2 pixel group). Means.

  This will be specifically described with reference to FIG. FIG. 4 is an example of a diagram showing the distribution of pixels in which the pixel at the center of each local area in the cross-sectional image is color-coded by the value of Vf. In FIG. 4, a region 5 which is a Vf1 pixel group and a region 6 which is a Vf2 pixel group can be recognized.

  The observation of such a region indicates that the waviness in the thickness direction of the fiber is small, and such a fiber-reinforced plastic is preferable because it has high mechanical properties. It is preferable that all of the Vf1 pixel group and the Vf2 pixel group exist linearly in the captured image in which Vf of the local region is obtained, but even if it cannot be said that all groups exist linearly, It suffices that at least one is present linearly in each group.

  As described above, as a method for producing a fiber-reinforced plastic in which the Vf1 pixel group and the Vf2 pixel group are substantially linear, for example, a prepreg having a high fiber volume content and a small fiber volume content can be used. A method in which prepregs are alternately laminated to form a laminate, which is cured to form a fiber-reinforced plastic, can be mentioned.

  More preferably, at least one Vf1 pixel group, preferably more than half of the Vf1 pixel groups, and preferably all Vf1 pixel groups, are present on at least one surface of the fiber-reinforced plastic up to 30% of the thickness of the fiber-reinforced plastic. It is a fiber reinforced plastic that exists in the area. Further, it is preferable that the Vf1 pixel group exists linearly. The presence of the Vf1 pixel group in the region close to the surface, that is, in the surface layer portion is preferable because the bending rigidity of the fiber-reinforced plastic is particularly improved. Further, generation of surface irregularities due to variations in Vf is suppressed, and the fiber-reinforced plastic surface can be made smooth. A more preferred embodiment is the fiber-reinforced plastic in which the Vf1 pixel group is present on both surfaces of the fiber-reinforced plastic in an area up to 30% in the thickness direction from each surface.

  Preferred embodiments of the fiber-reinforced plastic of the present invention include having a layer in which the fibers are oriented substantially in one direction and a layer in which the fibers are oriented in multiple directions. Hereinafter, a layer in which fibers are substantially oriented in one direction is called a unidirectional layer, and a layer in which fibers are oriented in multiple directions is called a multidirectional layer. FIG. 5 is an example of a preferred fiber reinforced plastic of the present invention, which is a conceptual diagram of a fiber reinforced plastic having a layered structure. FIG. 5 includes layers A, B, C, D, E, and layers A, B, D, E are unidirectional layers.

  The unidirectional layer is a region (layer) that is substantially parallel to the surface of the fiber reinforced plastic in which the same fiber cross sectional shape appears in the cross section of the fiber reinforced plastic. The same fiber cross-sectional shape means a width of 2 mm in the cross-section of the fiber-reinforced plastic, and a lengthwise area of the fiber-reinforced plastic from the upper surface to the lower surface of the fiber-reinforced plastic. This means that when the major axis of 100 randomly selected fiber cross sections is measured and the average value is calculated, the major axis of 90 or more cross sections is within ± 10% of the average value. “Substantially parallel to the surface of the fiber reinforced plastic” means the case where the boundary of the aggregate and the surface of the fiber reinforced plastic are within the range of −10 ° to + 10 ° when the cross section of the fiber reinforced plastic is viewed. To do. Further, in the cross section of the fiber-reinforced plastic, the other region of the cross section can be regarded as a layer only when the unidirectional layer is present, and a region sandwiched between two unidirectional layers like the layer C or The region sandwiched between the unidirectional layer and the surface of the fiber reinforced plastic is also considered as a layer. The presence of the unidirectional layer makes it possible to efficiently improve the mechanical properties. Further, since the unidirectional layer is a layer corresponding to the Vf1 pixel group, it becomes possible to more efficiently improve the mechanical characteristics.

  Further, in the cross section of the fiber reinforced plastic, the other region of the cross section can be regarded as a layer only when a unidirectional layer is present, and a region sandwiched between two unidirectional layers like the layer C. Alternatively, when the region sandwiched between the unidirectional layer and the surface of the fiber reinforced plastic is regarded as a layer, 100 or more fiber cross sections are seen in a region of width 2 mm in the same layer in the cross section of the fiber reinforced plastic, A layer that does not satisfy the above definition of the unidirectional layer is a multidirectional layer. There are two patterns in the multidirectional layer. One is the case where there is a region in which fibers having a closer cross-sectional shape gather in the layer C, such as the layer C in FIG. The cross-sectional shape is close means a diameter when a major axis in a fiber cross section observed in a cross-sectional photograph of a fiber-reinforced plastic and a line segment corresponding to the major axis are mapped to a straight section of the fiber, that is, the fiber corresponding to the major axis. When the fiber orientation angle with the cross section as the reference plane is calculated from the actual diameter of the above, it means that the difference in orientation angle is within 10 °. The fiber orientation angle θ [°] is calculated by θ = arcsin ((fiber diameter) / (major axis of fiber cross section)) × 180 / π. Within the layer C, there are aggregates having similar fiber cross-sectional shapes, such as aggregates C1, C2, C3, and C4. Another pattern recognized as a multidirectional layer is when fibers having different cross-sectional shapes are intertwined with each other and cannot be divided into aggregates having similar cross-sectional shapes. In particular, if the layer corresponding to the Vf2 pixel group is a multidirectional layer, it will have isotropic mechanical characteristics even if the fiber length of the reinforcing fiber in the region having a small Vf is relatively long. Therefore, the selection of the unidirectional layer, which has a great influence on the mechanical properties, can be performed without limitation, which is preferable. Furthermore, it is more preferable that the multidirectional layer has a plurality of region groups having similar cross-sectional shapes, because the step of dispersing the reinforcing fiber bundle into a single yarn is not necessary in the step of manufacturing the base material, and the production cost is excellent.

  To obtain a fiber-reinforced plastic having a layer in which fibers are oriented substantially in one direction and a layer in which fibers are oriented in multiple directions, for example, a prepreg in which fibers are oriented substantially in one direction, and a fiber A method can be given in which a prepreg (for example, SMC) oriented in multiple directions is alternately laminated to form a laminate, which is cured to form a fiber-reinforced plastic.

  The fiber-reinforced plastic of the present invention contains a fiber and a resin. In the fiber-reinforced plastic of the present invention, the fiber is generally a fiber-reinforced plastic such as glass fiber, Kevlar fiber, carbon fiber, graphite fiber or boron fiber. Means a fiber used as a reinforcing material. Of these, carbon fibers are preferable from the viewpoint of specific strength and specific elastic modulus.

  In the present invention, the meaning of the fiber-reinforced plastic has the same meaning as the term generally used, that is, the resin contains a fiber, also referred to as a reinforcing fiber, and the fiber is used to The mechanical properties such as strength are improved. The resin used in the fiber-reinforced plastic of the present invention may be a thermosetting resin or a thermoplastic resin. Examples of the thermosetting resin include unsaturated polyester resin, vinyl ester resin, epoxy resin, benzoxazine resin, phenol resin, urea resin, melamine resin and polyimide resin. As the thermoplastic resin, for example, polyamide (PA), polyacetal, polyacrylate, polysulfone, ABS, polyester, acrylic, polybutylene terephthalate (PBT), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene, polypropylene, Examples thereof include polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyetherimide (PEI), polyetherketoneketone (PEKK), liquid crystal polymer, vinyl chloride, fluorine resin such as polytetrafluoroethylene, and silicone.

  The fiber-reinforced plastic of the present invention can be preferably used as a structural member in automobiles, aircrafts and the like.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention should not be construed as being limited to the invention described in Examples.

<Production of resin film>
To epoxy resin (Japan Epoxy Resin Co., Ltd. "jER (registered trademark)" 828: 35 parts by mass, "jER (registered trademark)" 1001: 30 parts by mass, "jER (registered trademark)" 154: 35 parts by mass) After heating and kneading 5 parts by mass of a thermoplastic resin polyvinyl formal (“Vinilec (registered trademark)” K manufactured by Chisso Corporation) with a kneader to uniformly dissolve polyvinyl formal, a curing agent dicyandiamide (Japan Epoxy Resins Co., Ltd. ) DICY7) 3.5 parts by mass and a curing accelerator 3- (3,4-dichlorophenyl) -1,1-dimethylurea (Hodogaya Chemical Co., Ltd.'s DCMU99) 4 parts by mass are kneaded with a kneader. To prepare an uncured epoxy resin composition. This epoxy resin composition was applied onto a silicone-coated release paper using a reverse roll coater to prepare a resin film having a basis weight of 62 g / m ² .

<Production of notch prepreg>
In order to produce a cut prepreg, the continuous fiber prepreg which is the basis of the cut prepreg is arranged in one direction so that the average fiber volume content (Vf) is 58%, and a carbon fiber having a basis weight of 250 g / m ² The resin film having a basis weight of 62 g / m ² obtained by the above procedure was placed on both surfaces of (T700S) and impregnated with the resin by heating and pressurizing. A cut prepreg A and a cut prepreg B were obtained by using a roll (rotary blade) provided with a blade on the obtained continuous fiber prepreg so that all the fibers in the continuous fiber prepreg were cut.

  The notch prepreg A has notches inserted so that all the fibers have a length of 22 mm, the angle between the notches and the fiber direction is 14 °, and the length of each notch is 1 mm. .

  The notch prepreg B has notches inserted so that all the fibers have a length of 11 mm, the angle between the notch and the fiber direction is 25 °, and the length of each notch is 3 mm. .

<Production of SMC>
A chopped prepreg obtained by cutting the continuous fiber prepreg into a width of 0.3 mm and a length of 30 mm is arranged so that the fiber directions of the chopped prepregs are randomly oriented, and the total fiber volume content (Vf) is 30%. It was manufactured by sandwiching the above-mentioned resin film so as to be, and vacuum-pressing at 70 ° C. for 1 minute.

<Press molding>
A laminate obtained by combining the cut prepreg A, the cut prepreg B, the resin film, and the SMC is solidified by press molding using a double-sided mold for molding a box shape as shown in FIG. Obtained. The obtained fiber reinforced plastic had a box shape having a width direction of 150 mm and a length direction of 200 mm, a bottom surface thickness of 3 mm, and a side surface thickness T of 2 patterns of 4 mm and 6 mm. The mold has a structure in which surplus flows out.

  As a press molding method, after placing the mold in the center of the mold which was previously heated to 130 ° C. inside the pressing machine, it was sandwiched between the upper mold and the lower mold, and held at a molding temperature of 130 ° C. and a molding pressure of 6.0 MPa for 30 minutes. . Then, the mold was removed to obtain a predetermined fiber reinforced plastic.

<Acquisition of population related to Vf>
The thickest part of the obtained fiber reinforced plastic (the side part in the present molded body) was cut out and embedded in a resin and buffed. A cross-section of the polished fiber-reinforced plastic was photographed with a digital microscope. One pixel had a size corresponding to 2 μm of the fiber-reinforced plastic, and the width parallel to the surface of the thickest part of the fiber-reinforced plastic was measured on the surface. The height (T) is the vertical direction (that is, the thickness direction), and it is composed of square pixels with a width of 2000, a height of 2000 when T = 4 mm, and a height of 3000 when T = 6 mm. A digital image of the fiber reinforced plastic cross section was obtained. Next, the digital image of the cross section was binarized to be divided into fiber-rich pixels and resin-rich pixels. A local area having a diameter of 100 μm centering on the center of gravity of each pixel is set to 2000 × 2000 when T = 4 mm and 2000 × 3000 when T = 6 mm, and Vf is calculated in each local area to be a population. . However, in the case where the outer circumference circle that demarcates the local area protrudes from the digital image, the area where the circle having a diameter of 100 μm and the digital image overlap is defined as the local area. Hereinafter, unless otherwise specified, the average value means the average value of the population, and the coefficient of variation means the coefficient of variation of the population. The measurement results in each of the reference examples, examples and comparative examples are as shown in Table 1.

<Vf distribution evaluation>
In the digital image, a pixel at the center of the local area was marked according to the value of Vf obtained in each local area to obtain a Vf distribution chart. By the method described above, the Vf1 pixel group and the Vf2 pixel group were obtained, and it was evaluated whether these observed groups were substantially linear. The maximum width / height of the Vf1 pixel group and the maximum width / height of the Vf2 pixel group are shown in the table.

<Evaluation of layer structure of fiber reinforced plastic>
From the digital image of the cross section, in the case where the fiber reinforced plastic has a layered structure, whether the fibers are substantially unidirectionally oriented layers or the fibers are multidirectionally oriented layers for each layer by the above method. evaluated.

  In Table 1, when the fiber reinforced plastic does not have a layered structure, W, when the fiber is composed of only a layer which is oriented substantially in one direction, X, and when the fiber is substantially oriented in one direction. When the fiber was composed of an oriented layer and a layer in which fibers were oriented in multiple directions, it was designated as Y.

(Reference example 1)
The cut prepreg A and the cut prepreg B are laminated in a laminated constitution of [-45 ° / 0 ° / + 45 ° / 90 °] _s with the width direction of 0 °, and two resin films are provided between the two laminated bodies. A substrate laminate having a cut prepreg A, a cut prepreg B, and a resin film, each having a size of 300 mm × 300 mm, was obtained.

  This base material laminate was press-molded with a mold of T = 4 mm so that the side surface was cut prepreg B. No defects such as voids were found in the obtained fiber reinforced plastic. On the other hand, the fibers on the side surface were greatly undulated. In press molding with a mold of T = 6 mm, molding defects such as a non-contact portion with the mold were observed, and it was speculated that the mechanical properties were deteriorated.

  When the population related to Vf of the obtained fiber reinforced plastic was acquired and the population was made into a histogram of the class number 10, the peak value, which is the class having a frequency greater than the frequency of the classes adjacent to the left and right, is one place. there were.

(Reference example 2)
Two notch prepregs A are laminated in a laminated constitution of [-45 ° / 0 ° / + 45 ° / 90 °] _s with 0 ° in the width direction, and four resin films are sandwiched between the two laminated bodies. , A 300 mm × 300 mm cut prepreg A, and a resin film were obtained.

  The fiber-reinforced plastic obtained by press-molding this substrate laminate with a mold of T = 4 mm showed no defects such as voids, and the waviness of the fibers on the side surface was smaller than that in Example 1. From the cross section, it can be seen that the fibers are greatly wavy inside the fiber reinforced plastic. In press molding with a mold of T = 6 mm, molding defects such as a non-contact portion with the mold were observed, and it was speculated that the mechanical properties were deteriorated.

  When the population related to Vf of the obtained fiber reinforced plastic was acquired and the population was made into a histogram of the class number 10, the peak value, which is the class having a frequency greater than the frequencies of the classes adjacent to the left and right, was found at one place. there were.

(Example 1)
The notch prepreg A is laminated in a laminated constitution of [-45 ° / 0 ° / + 45 ° / 90 °] _s with the width direction of 0 °, and the SMC having a thickness of 4 mm is overlaid, and the notch prepreg of 300 mm × 300 mm is formed. A base material laminate of A and SMC was obtained.

  The base laminate was press-molded in a mold of T = 6 mm so that the outer surface side of the fiber reinforced plastic was SMC. No defects such as voids were found in the obtained fiber reinforced plastic. It was felt that the side surface of the SMC was uneven to the touch. When viewed in cross section, there were layers in which the fibers were oriented substantially in one direction and layers in which the fibers were oriented in multiple directions. In the layer in which the fibers are oriented in multiple directions, there were a plurality of regions where fibers having similar cross-sectional shapes gathered together. In the layer in which the fibers were oriented in multiple directions, it was observed that the fibers were largely undulating out of the plane.

  When the population related to Vf of the obtained fiber reinforced plastic was acquired and the population was made into a histogram of class number 10, there were two peak values which were classes having frequencies greater than the frequencies of the classes adjacent to the left and right. It was

(Example 2)
Two sets of the notch prepreg A are laminated in a laminated constitution of [-45 ° / 0 ° / + 45 ° / 90 °] _s , with the width direction being 0 °, and an SMC having a thickness of 3 mm is provided between the two laminated bodies. By sandwiching, a base material laminate of cut prepreg A and SMC of 300 mm × 300 mm was obtained.

The base laminate was press-molded with a mold of T = 6 mm. No defects such as voids were found in the obtained fiber reinforced plastic. The texture of the side surface was smooth and smooth.
When the population related to Vf of the obtained fiber-reinforced plastic was acquired and the population was made into a histogram of class number 10, there were two peak values which were classes having frequencies greater than the frequencies of the classes adjacent to the left and right. It was

  When viewed in cross section, it had a layered structure, and there were a layer in which the fibers were substantially oriented in one direction and a layer in which the fibers were oriented in multiple directions. In the layer in which the fibers are oriented in multiple directions, there were a plurality of regions where fibers having similar cross-sectional shapes gathered together. In the evaluation of the distribution of Vf, there is a region that is substantially linear and has a Vf larger than the average value of the population, and a region that has a substantially linear Vf that is smaller than the average value. I was able to confirm.

  Further, a region having Vf larger than the average value of the population was present in a range smaller than 30% in the thickness direction from the surface layer.

(Comparative Example 1)
Two sets of continuous fiber prepregs are laminated in a laminated constitution of [-45 ° / 0 ° / + 45 ° / 90 °] _s with 0 ° in the width direction, and two resin films are sandwiched between them to form a 300 mm × 300 mm base. A material laminate was obtained.

  The base laminate was press-molded with a T = 4 mm mold. The obtained fiber reinforced plastic was not in good quality because most of the side surfaces did not contact the mold. Therefore, it was speculated that the mechanical properties would deteriorate.

(Comparative example 2)
Two sets of the cut prepreg A having a width direction of 0 ° and a laminated structure of [−45 ° / 0 ° / + 45 ° / 90 °] _s are laminated, and two resin films are sandwiched between them to form a 300 mm × 300 mm A substrate laminate was obtained.

  The base laminate was press-molded with a T = 4 mm mold. Although the obtained fiber reinforced plastic was improved as compared with Comparative Example 1, there was a part of the side surface that was not in contact with the mold, the quality was not good, and it was speculated that the mechanical properties were deteriorated.

(Comparative example 3)
SMCs were laminated to have a thickness of 6 mm to obtain a 300 mm × 300 mm SMC laminate.

  The base laminate was press-molded with a mold of T = 6 mm. Although the obtained fiber reinforced plastic did not have any noticeable defects, when the population related to Vf was obtained, the average value of the population was lower than that of any of the examples.

  In the table, “the number of peak values” means the number of classes observed as peaks when the population is a histogram with a class number of 10. For example, it is 2 in the mode of FIG.

This application is based on a Japanese patent application filed on Jun. 19, 2017, Japanese Patent Application No. 2017-119288, the content of which is incorporated herein by reference.

1: Fiber part 2: Resin part 3: Pixel 4: Local area 5: Vf1 pixel group 6: Vf2 pixel group

Claims (5)

A fiber-reinforced plastic containing fibers and resin,
The average length of the fibers is 5 to 50 mm,
When the population related to the fiber volume content in the local region (hereinafter, such fiber volume content is referred to as Vf) is obtained, the average value of the population is 40 to 65%, and the coefficient of variation of the population is 0.15 to 0. .4, wherein when the population is made into a histogram with a class number of 10, and a class having a frequency greater than the frequencies of the classes adjacent to the left and right is a peak value, the fiber-reinforced plastic has a plurality of peak values.
(Vf population)
When a local region corresponding to a diameter of 100 μm is extracted from the cross-sectional image of the fiber-reinforced plastic, the total area of the fiber-rich pixels included in the local region is divided by the total area of the pixels included in the local region, The value obtained by multiplying by 100 is Vf. A plurality of the local regions are extracted and a set of Vf obtained in each local region is used as a population.   The fiber according to claim 1, wherein both the region having a Vf larger than the average value of the population and the region having a Vf smaller than the average value of the population are substantially linear. Reinforced plastic.   The fiber-reinforced plastic according to claim 1 or 2, wherein the region having Vf larger than the average value of the population exists in a range smaller than 30% in the thickness direction from at least one surface layer.   The fiber-reinforced plastic according to any one of claims 1 to 3, which has a layer in which the fibers are oriented substantially in one direction and a layer in which the fibers are oriented in multiple directions.   The fiber-reinforced plastic according to claim 4, wherein a plurality of region groups having close cross-sectional shapes are present in the layer in which the fibers are oriented in multiple directions.

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