JP7689505B2 - Fiber-reinforced resin molding and its manufacturing method - Google Patents

Description

The present invention relates to a fiber-reinforced resin molding that can be widely used as a structural material and a method for manufacturing the same.

Fiber-reinforced resins are as lightweight as general resins, but some have tensile strength in the fiber direction that is comparable to that of metal materials. Due to these excellent characteristics, molded products made from fiber-reinforced resins are used in a wide range of fields today, including industrial materials such as machines, aircraft, vehicles, and building materials, as well as leisure equipment, medical equipment, and space industry materials.
In particular, those using thermoplastic resins as the matrix resin have superior elasticity and impact resistance compared to those using thermosetting resins, and can be solidified in a short time by cooling, making them useful from both a physical property and an economical standpoint.

One method for manufacturing fiber-reinforced resin moldings using thermoplastic resin as the matrix resin is to laminate multiple prepregs made by impregnating reinforcing fibers that have been aligned in one direction and spread with matrix resin and forming them into sheets, and then molding them into a desired shape using a heat press. With this method, the fiber length of the reinforcing fibers can be made longer, resulting in higher strength, compared to injection molding, which uses short fibers as a filler.

Previously, the applicant of the present application has made further improvements to the manufacturing method using the prepreg, and has filed a patent application for a manufacturing method for a fiber-reinforced plastic molded product (corresponding to the above-mentioned fiber-reinforced plastic molded body) that can increase the degree of freedom in the shape of the molded product while enjoying the favorable reinforcing effect of the reinforcing fibers (see Patent Document 1).
Patent Document 1 filed by the applicant of the present application discloses a manufacturing technique in which a sheet-like base material (corresponding to the prepreg) made of a thermoplastic matrix resin impregnated with a large number of reinforcing fibers is cut in a predetermined pattern, and the base material is stacked with the fiber directions alternating, and then pressed.

As shown in FIG. 21, the predetermined pattern in the base material 800 has a plurality of parallel perforated vertical cut lines 801, 801... and a plurality of parallel horizontal cut lines 802, 802.... The adjacent vertical cut lines 801, 801... are slightly offset from one another, and the horizontal cut lines 802, 802... cross the vertical cut lines 801, 801... in a straight line so as to connect each end 803, 803... of each vertical cut line 801, 801... every other vertical cut line. The horizontal cut lines 802, 802... are provided for each of the vertical cut lines 801, 801... that are continuous in a perforated manner. However, since none of the cuts reach the outer periphery 804 of the base material 800, the base material 800 does not separate. Due to these cuts, the remaining part zigzags in the direction perpendicular to the fibers, and these cuts are arranged in parallel in the fiber direction.

In the technology described in the above Patent Document 1, the horizontal cut lines cut the reinforcing fibers, shortening the fiber length and reducing the degree to which the reinforcing fibers hinder the flow of the resin, thereby improving the ease of deformation of the base material that tries to deform to follow the shape of the press die.
On the other hand, although vertical cut lines do not cut the reinforcing fibers, they do reduce the integrity of the substrate.
These vertical and horizontal cut lines have the effect of promoting the flow of resin during press working, thereby increasing the degree of freedom in the shape of the molded product.

As another method for producing the fiber-reinforced resin molding, a chopped prepreg is produced by cutting a sheet-like prepreg into small strips, and a plurality of chopped prepregs are spread out into a sheet and laminated. A chopped prepreg sheet is also known in which the matrix resin is melted and solidified again.
In this manufacturing method, the chopped prepregs are shaken off and stacked so that the fiber direction of each chopped prepreg is oriented in a random direction, so that the fiber direction of the chopped prepreg sheet as a whole becomes pseudo-isotropic. When the fiber direction is pseudo-isotropic, physical properties such as tensile strength and flexural modulus become pseudo-isotropic, so that a molded article using the chopped prepreg sheet can be given a uniform strength that is not dependent on the directionality.

Previously, the applicant of the present application made further improvements to the manufacturing method using the chopped prepreg and filed a patent application for a technology for efficiently molding a thick fiber reinforced composite material (corresponding to the chopped prepreg sheet) as a whole (see Patent Document 2).
Patent Document 2 filed by the applicant of the present application discloses a fiber-reinforced composite material having a thickness of 1 mm or more and including a plurality of chopped materials (corresponding to the chopped prepreg) stacked and solidified in the thickness direction, and a manufacturing method for a resin molded product (corresponding to the fiber-reinforced resin molded body) using the same.

The fiber-reinforced composite material of Patent Document 2 is composed of chopped material containing a thermoplastic matrix resin and a large number of reinforcing fibers. The reinforcing fibers are impregnated in the matrix resin while being oriented in the same direction. The chopped material is laminated so that the basis weight of the reinforcing fibers in the fiber-reinforced composite material to be produced is 700 g/ ^m2 or more and the volume content of the reinforcing fibers is 20% or more and 70% or less.
The resin molded product using the fiber-reinforced composite material is manufactured using a press mold including a punch and a die. The resin molded product can be manufactured by a method in which a plurality of fiber-reinforced composite materials are placed in the die of the press mold, and the fiber-reinforced composite materials are heated while the punch is pressed into the die, thereby deforming the fiber-reinforced composite materials into a shape corresponding to the molding space between the punch and the die.

In the technology described in Patent Document 2, the basis weight of the reinforcing fibers in the fiber-reinforced composite material is 700 g/ ^m2 or more, and the volume content of the reinforcing fibers is 20% or more and 70% or less, so that a sufficient amount of reinforcing fibers is contained, and a sufficient reinforcing effect can be obtained. In addition, since the thickness of the fiber-reinforced composite material is 1 mm or more, the number of sheets of fiber-reinforced composite material required to achieve a predetermined thickness can be reduced compared to when the thickness is less than 1 mm. Therefore, the number of times that the fiber-reinforced composite material is stacked in a mold for hot press processing can be reduced.
These advantages make it possible to efficiently produce thick, high-strength resin molded products.

On the other hand, regarding the configuration of the fiber-reinforced resin molded body itself, there are known techniques that can improve the strength by forming a predetermined shape and structure. In particular, there is known a technique that forms a hollow structure in a part of the fiber-reinforced resin molded body to obtain a fiber-reinforced resin molded body that is lightweight yet has excellent strength and rigidity.
For example, Patent Document 3 discloses a technique relating to a fiber-reinforced resin molded body having a hollow structure that is resistant to destruction even when subjected to bending stress, and has excellent rigidity and light weight.

The fiber-reinforced resin molded body 900 of Patent Document 3 is a molded body in which a first member 901 and a second member 902 are integrated, as shown in FIG. 22(a). A core part 906 of the first member 901 is sandwiched between a surface layer part 905 of the first member 901 and the second member 902, thereby forming a hollow structure. The first member 901 is made of reinforcing fibers 903 and a matrix resin 904, as shown in FIG. 22(b), and is composed of a surface layer part 905 having a planar shape and a core part 906 having a protruding shape. Here, as shown in FIG. 22(b), the reinforcing fibers 903 are present across the surface layer part 905 and the core part 906. At boundary surface 907 between surface layer 905 and core 906, reinforcing fibers 903 are present at 400 fibers/ ^mm2 or more, and the number average fiber length of reinforcing fibers 903 is 1 mm or more.

In the technology described in Patent Document 3, reinforcing fibers are arranged across the boundary between the surface layer and the core material, forming a core material with a protruding shape that has a high reinforcing effect. By providing a protruding shape that has a high reinforcing effect, it is possible to reduce the number of joint surfaces that become weak when an external force is applied, or to position the weak parts closer to the central surface, which is said to have the effect of achieving high rigidity as a molded body.

International Publication No. 2021/079787 International Publication No. 2021/079786 International Publication No. 2014/103711

As mentioned above, the applicant of the present application has been engaged in many developments related to fiber-reinforced plastic molded bodies having pseudo-isotropy. One of the objectives of Patent Document 1 mentioned above as a specific example is to increase the degree of freedom in the shape of the molded product, while one of the objectives of Patent Document 2, also a specific example, is to efficiently mold a thick plastic molded product.
In this way, the applicant of the present application has developed basic manufacturing techniques for producing fiber-reinforced resin moldings as typified by Patent Documents 1 and 2, but the above documents did not specifically mention the configuration of the molded fiber-reinforced resin molding itself.
Therefore, it has been desired to find a fiber-reinforced resin molding having various functionalities useful as a structural material by applying basic manufacturing techniques including those described in the above-mentioned documents.

In this regard, Patent Document 3 describes a technology relating to a fiber-reinforced resin molded body having a surface layer and a core material for forming a hollow structure, and excellent in bending strength, rigidity, and light weight, as described above. However, in Patent Document 3, in lamination of fiber-reinforced resin layers before molding, the layer that will become the core material is made to have a smaller concentration parameter than the layer that will become the surface layer. According to Patent Document 3, since the concentration parameter is proportional to the basis weight and number average fiber length of the reinforcing fibers, the reinforcing fibers contained in the core material must have a smaller basis weight and shorter fiber length than the reinforcing fibers contained in the surface layer.
In this way, if the premise is that the fiber-reinforced resin layers of the surface layer and the core layer are made different by the concentration parameter to make it easier to fill the reinforcing fibers, even if the surface layer and the core layer have a high degree of homogeneity, that is, the ratio of the filling rate of the reinforcing fibers converted into weight is the same, in reality, the surface layer will be sparsely filled with long fibers, while the core layer will be densely filled with short reinforcing fibers.

In addition, in the technology of Patent Document 3, the reinforcing fibers are arranged to straddle the boundary surface between the surface layer and the core, thereby reinforcing the bottom part, which is the base of the core. Therefore, when the height of the core is high, the bottom part can be expected to be reinforced by the long reinforcing fibers of the surface layer straddling it. However, as mentioned above, the tip part of the core is filled only with reinforcing fibers with short fiber length, and it is not expected that the strength of the tip part will be improved. Therefore, in order to provide sufficient strength, the height of the core part is limited, and the fiber-reinforced resin molding must be very thin.
Furthermore, simply filling the tip of the core material with short reinforcing fibers does not increase the rigidity of the tip. If the height of the core material increases, the tip becomes more susceptible to deformation, reducing the rigidity of the fiber-reinforced resin molding.

In this way, if the strength differs between the bottom and tip of the core material, in the case of a bending direction in which tensile stress occurs on the tip side, the tip of the core material will break more easily than in the case of a bending direction in which tensile stress occurs on the bottom side.
Furthermore, if the rigidity of the fiber-reinforced resin molding is reduced, when it is used as a structural material, it will be subject to greater deflection under bending load, vibrations will be more likely to propagate, and the noise transmission loss will also be reduced.
In addition, if the fiber-reinforced resin molding is thin, various problems may arise when it is used as a structural material, such as poor insulation properties and a tendency to buckle when subjected to a load parallel to the surface direction.

The present invention was made in consideration of the above problems, and its objective is to provide a fiber-reinforced resin molding that is not only lightweight and has excellent strength and rigidity, but also has a sufficient thickness, excellent toughness regardless of the bending direction, and a high noise transmission loss, and a method for manufacturing the same.

The means adopted by the present inventors to solve the above problems will be described below.
The fiber-reinforced resin molding of the present invention is a three-dimensional fiber-reinforced resin molding comprising a matrix resin which is a thermoplastic resin and reinforcing fibers impregnated with the matrix resin, and is formed by compression molding a prepreg made of a sheet-like fiber-reinforced resin.

The fiber-reinforced resin molding of the present invention is sufficient if it comprises at least the matrix resin and the reinforcing resin, and may also contain other components such as fillers. Furthermore, the reinforcing fibers referred to here may be fibers that have properties that can impart other physical properties to the fiber-reinforced resin molding, such as improving temperature characteristics or having sound absorption properties, in addition to the property of strengthening mechanical strength. Furthermore, the manner of impregnation of the reinforcing fibers with the matrix resin includes complete impregnation in which the reinforcing fibers are completely impregnated with the matrix resin, as well as those that include some or all of the reinforcing fibers that are unimpregnated.

The fiber-reinforced resin molded article of the present invention has a basic configuration including at least a flat plate-like portion and a plurality of tubular portions provided substantially perpendicularly to the plate-like portion.
The plate-like portion is not limited to being entirely flat, but may be slightly curved or have a three-dimensional shape in part, but may be considered to be flat as a whole. In addition, a cylindrical shape refers to a shape in which a space is surrounded by a predetermined wall, but may include a part that is not surrounded in part. The cross-sectional shape of the space and the thickness of the wall are not limited, and each cylindrical portion may have a different cross-sectional shape or may include different wall thicknesses.

The multiple tubular portions have portions where the tubular portions are connected to each other, and the reinforcing fibers are filled from the bottom to the tip of the plate-like portion , and the reinforcing fibers at the tip of the plate-like portion and the tubular portion are in a state where only thin-layered reinforcing fibers are oriented in random directions at every position.
The connection between the cylindrical parts includes a case where opposing walls forming the cylindrical parts are connected by other walls, and a case where the cylindrical parts are connected by sharing a wall forming the cylindrical parts. In addition, the filling of the reinforcing fibers is not limited to a case where the fiber volume filling rate is uniform from the bottom to the tip of the plate-like part of the cylindrical part, and the fiber volume filling rate may be different between the bottom and the tip.

In the fiber-reinforced resin molded product of the present invention, by having a plurality of cylindrical parts provided on the plate-like part, the fiber-reinforced resin molded product has a large section modulus, which is an index of bending difficulty. In particular, by being cylindrical, the wall part has a form that surrounds a space, and the section modulus becomes large against bending in all directions. When the section modulus becomes large, it becomes difficult to bend for the same load, so that even when a load is applied to the fiber-reinforced resin molded product as a structural material, it becomes difficult to bend. In other words, the rigidity is improved.
Furthermore, by connecting the multiple tubular portions at least in part, the cross-sectional modulus becomes large between adjacent tubular portions, thereby preventing localized reduction in rigidity and achieving high rigidity in the cross section at all points.

On the other hand, in the fiber-reinforced resin molding of the present invention, the reinforcing fibers are filled from the bottom to the tip of the plate-shaped portion of the cylindrical portion, so that the tip has sufficiently high rigidity compared to the bottom of the cylindrical portion. In addition, the high tensile strength of the reinforcing fibers allows the fiber-reinforced resin molding to have high strength as a whole.

Here, the case where the fiber reinforced resin molded article of the present invention is compressed will be described.
When a force is applied to compress the fiber-reinforced resin molded body along the longitudinal direction of the cylindrical portion, a compressive load acts on the cylindrical portion in the longitudinal direction, and a compressive load acts on the plate-like portion in the thickness direction.

Since the plate-like portion is generally flat and has a relatively large area in a plan view, even if a compressive load acts in the thickness direction, the compressive stress generated in the cross section in the planar direction is small, and therefore it is unlikely that the plate-like portion will undergo extreme plastic deformation in the thickness direction.
However, in the case of a cylindrical portion, the cross-sectional area of the wall portion constituting each cylindrical portion is relatively small and has a certain height. When a compressive load acts on such a cylindrical portion in the longitudinal direction and compressive stress exceeds the yield stress, the cylindrical portion undergoes plastic deformation so as to be crushed in the longitudinal direction.

Viscoelastic materials such as resins generally rarely break when compressed, and continue to be compressed, causing plastic deformation into a flat shape. As the material becomes flat, its apparent cross-sectional area increases, so a large load is required to compress it further. The load at this time is proportional to the apparent cross-sectional area, but also to the Young's modulus of the material. Therefore, if the tip of the tubular section is not filled with reinforcing fibers and the Young's modulus of elasticity is small, not only will the load at the time of yielding of the tubular section be small, but if further load is continued after yielding, the deformation will be greater than when the Young's modulus of elasticity is large, assuming the same load.

In this regard, in the present invention, reinforcing fibers are filled from the bottom to the tip of the plate-shaped portion of the tubular portion, and the reinforcing fibers can provide a high Young's modulus even at the tip of the tubular portion. Therefore, even if a compressive load acts in the longitudinal direction of the tubular portion, it is unlikely to undergo plastic deformation, and even if it does undergo plastic deformation, the amount of deformation can be kept small.

Next, a case where the fiber-reinforced resin molding of the present invention is bent into a bow shape will be described.
When the fiber-reinforced resin molded body is curved into an arc so that the surface of the plate-like portion that is not in contact with the cylindrical portion bulges, tensile stress is mainly generated on the surface of the plate-like portion that is not in contact with the cylindrical portion. In addition, in the cylindrical portion, tensile stress or compressive stress is generated in each part of the wall that constitutes the cylindrical portion depending on the shape, and compressive stress is particularly likely to be generated at the tip of the cylindrical portion.

As mentioned above, resin is a viscoelastic body, so it will not break even if it is continuously compressed, but will usually break when pulled. Therefore, in the case of bending in the above-mentioned direction, it is mainly the flat plate-shaped portion that is prone to breaking due to tensile stress.

Conversely, when the fiber-reinforced resin molded body is bent in a direction such that the surface of the plate-like portion that is in contact with the cylindrical portion expands, tensile stress is generated primarily at the tip of the cylindrical portion. Also, compressive stress is generated on the surface of the plate-like portion that is not in contact with the cylindrical portion. In this case, it is primarily the tip of the cylindrical portion that is prone to break due to tensile stress.

When comparing the flat plate-like portion with the wall portion at the tip of the tubular portion, the plate-like portion has a large width and depth, and therefore the cross-sectional area in the thickness direction is also relatively large. Since the tensile stress decreases as the cross-sectional area increases, the tensile stress generated in the cross section when the surface of the plate-like portion that is not in contact with the tubular portion is bent in the direction in which it expands tends to be relatively small.
On the other hand, since the cross-sectional area of each wall portion constituting the cylindrical portion is smaller than that of the plate-like portion, the tensile stress generated in the cross section of each wall portion is likely to be large. Therefore, when the tip of the cylindrical portion is bent in the expanding direction, the tensile stress generated in the cross section tends to be relatively large.

As described above, because the plate-like portion is flat, it is unlikely to break due to tensile stress unless it is extremely thin. However, because the cross-sectional area of the tip of the tubular portion is smaller than that of the plate-like portion, it is prone to large tensile stress and breakage. Therefore, if the tip of the tubular portion is not filled with reinforcing fibers and has low strength, it will easily break when bent in the direction in which the tip of the tubular portion expands.

In this regard, in the present invention, reinforcing fibers are filled from the bottom to the tip of the plate-shaped portion of the tubular portion, and the high tensile strength of the reinforcing fibers allows the tubular portion to have excellent strength not only at the base but also at the tip. Therefore, the fiber-reinforced resin molding can have high strength regardless of the bending direction.

When sound enters a material that has no air permeability, the material vibrates and radiates sound backwards as a new sound source. This is called transmitted sound, and the ratio of the sound pressure between the incident sound and the transmitted sound, expressed in decibels, is called transmission loss. In order to improve sound insulation, this transmission loss must be increased, and it is essential to suppress the vibration of the material as much as possible.
As described above, the fiber-reinforced resin molding of the present invention has high bending elasticity even at the tip of the cylindrical portion because the reinforcing fibers are filled from the bottom of the plate-shaped portion to the tip of the cylindrical portion. Since the high bending elasticity increases the rigidity, the fiber-reinforced resin molding of the present invention is less likely to vibrate even when sound is incident, and has a high transmission loss for the incident sound. The reason why the fiber-reinforced resin molding of the present invention, which has high rigidity, exhibits high transmission loss will be described in detail below.

Sound insulation materials are often attached to a certain enclosed space in a structure such as a machine structure or a building with the outer periphery supported. When the sound insulation material is attached to the enclosed space, resonance occurs at a specific frequency in the mid-low range due to the shape and material properties of the sound insulation material. At the resonance frequency, the sound insulation material vibrates strongly and radiates a large sound to the rear, resulting in the lowest transmission loss.
Therefore, when a material with no air permeability such as a fiber-reinforced resin molding is used as a sound-proofing material, it is necessary to set the resonant frequency outside the desired frequency band as much as possible so that there is a high transmission loss in the desired frequency band.

The resonant frequency is inversely proportional to the weight of the material, so an increase in weight reduces the resonant frequency, whereas an increase in stiffness increases the resonant frequency, so that an increase in stiffness increases the resonant frequency.
In this regard, the fiber-reinforced resin molding of the present invention has a configuration in which a tubular portion having a predetermined space is provided relative to a plate-like portion, and therefore is lighter than a flat plate of the same thickness and uniform density.
In addition, the fiber-reinforced resin molding of the present invention has a portion where the cylindrical portions are connected to each other, and the cylindrical portions are filled with reinforcing fibers from the bottom portion on the plate-like portion side to the tip portion, so that the rigidity of the entire fiber-reinforced resin molding is higher than that of a molding in which the cylindrical portions are not filled with reinforcing fibers up to the tip portion.
In this way, the fiber-reinforced resin molding of the present invention is lighter than a flat plate of the same thickness and uniform density, and as described above, the fiber-reinforced resin molding has high overall rigidity. Therefore, when this is installed as a sound-proofing material in an enclosed space, the resonant frequency will shift to a higher frequency, and the transmission loss at low and mid-range frequencies, which have large amplitudes and are likely to cause noise problems, can be increased.

In addition, when the soundproofing material is flat, the surface of the plate may undulate at high frequencies, generating surface waves. When this happens, resonance occurs when a sound of a specific frequency incident obliquely matches the frequency and phase of the surface wave seen from the same oblique direction as the incident sound, and a coincidence effect may occur, which is the same effect as when the soundproofing material undergoes bending vibration and the sound is transmitted through it.

In the fiber-reinforced resin molding of the present invention, the cylindrical portion and the plate-like portion are integrated to generate bending vibration, and there is a possibility that a coincidence effect will occur.
The frequency at which the coincidence effect occurs decreases in proportion to the angle of incidence of the sound waves. The lowest frequency at which the coincidence effect occurs is when the sound waves are parallel to the soundproofing material (angle of incidence 90 degrees), and this frequency (coincidence limit frequency) decreases the greater the thickness and longitudinal elastic modulus of the soundproofing material.
However, the fiber-reinforced resin molding of the present invention has a thickness greater than that of a flat plate of the same weight because it has multiple cylindrical parts provided at approximately right angles to the plate part. It is known that, if the Young's modulus and density are the same, the increase in thickness can suppress the decrease in transmission loss caused by the coincidence effect.

In addition, when the wavelength of the frequency at which the coincidence effect occurs is longer (the frequency is lower) than the size of the fiber-reinforced resin molding, bending vibration due to the coincidence effect is less likely to occur. Since the fiber-reinforced resin molding of the present invention is thick, the frequency at which the coincidence effect occurs is lower than that of a flat plate of the same weight. Therefore, when used as a sound-proofing material, the wavelength of the bending vibration due to the coincidence effect tends to be longer than the size of the fiber-reinforced resin molding itself, making bending vibration less likely to occur.
For these reasons, the fiber-reinforced resin molding of the present invention can prevent an extreme decrease in transmission loss at a specific frequency caused by the coincidence effect.

As described above, the fiber-reinforced resin molding of the present invention has at least a flat plate-like portion and a plurality of tubular portions arranged approximately perpendicular to the plate-like portion, has a portion where the tubular portions are connected to each other, and is configured so that reinforcing fibers are filled from the bottom of the tubular portions on the plate-like portion side to the tip.
As a result, even if the overall thickness of the fiber-reinforced molding is made thick, it is possible to achieve high strength regardless of the bending direction. Furthermore, when the fiber-reinforced resin molding of the present invention is used as a sound insulation material, it is possible to achieve high transmission loss over a wide frequency range.

As a means adopted in the present invention to solve the above-mentioned problems, it is possible to use a means in which the reinforcing fibers are carbon fibers.
In addition, in a binary image analysis of the cross section at the tip of the tubular portion, the average area ratio of the carbon fibers in each tubular portion can be configured to be -5% or more relative to the fiber volume content of the prepreg before compression molding. If the fiber volume content at the tip of the tubular portion is approximately the same as the fiber volume content of the prepreg before compression molding, it can be said that the carbon fibers are sufficiently filled in the tubular portion.
In this regard, in the binary image analysis, the area analyzed per carbon fiber may differ depending on the orientation of the carbon fiber at the measurement point. Therefore, taking such errors into consideration, it is desirable to configure the average value of the area ratio of the carbon fiber in each tubular portion to be -5% or more relative to the fiber volume content of the prepreg before compression molding.

In this way, by using carbon fibers as reinforcing fibers, the fiber-reinforced resin molding as a whole can be made lightweight yet have excellent strength. In addition, by making the area ratio of the carbon fibers at the tip of the tubular portion at -5% or more of the volumetric fiber content of the prepreg, the tip of the tubular portion is filled with a large amount of carbon fibers, so that the longitudinal elastic modulus and strength of the tubular portion can be increased.

When adopting the above-mentioned means, a configuration can also be adopted in which, in the binary image analysis of the cross section at the tip of the tubular portion, the difference in the area ratio of the carbon fiber between the tubular portion located on the outermost side and the tubular portion located in the center of the entire fiber-reinforced resin molding is within 10%.
Since the difference in the ratio of carbon fiber filled between the outermost side and the center of the multiple cylindrical portions is small, the physical properties such as strength of the fiber-reinforced resin molding as a whole can be made uniform. Therefore, when used in a structure, the strength, sound insulation, and other performance can be exhibited uniformly regardless of the part.

The cylindrical portion may be formed in a honeycomb shape consisting of plane-filled regular hexagonal columns.
Plane filling refers to the filling of a plane with a figure without gaps, and in the above, it refers to the filling of a three-dimensional regular hexagonal prism in the plane direction without gaps. The honeycomb shape can have the largest area for the same perimeter length, compared to other regular polygons that can be filled on a plane, such as equilateral triangles and squares. Therefore, even if a load acts in the compression direction, which is the height direction of the regular hexagonal prism, due to bending or the like, the area of the space part can be made larger while having the same buckling load, compared to the cylindrical part of the above-mentioned regular polygon with the same perimeter length. Therefore, it has high strength against bending and compression and can be made lighter.

Furthermore, when a fiber-reinforced resin molding having a honeycomb-shaped tubular portion is used in a wall structure, loads may act not only in the thickness direction of the fiber-reinforced resin molding but also in the width direction or depth direction.
Considering a prism with a square cross section, adjacent sides of the square are at right angles and opposing sides are parallel, so when a uniform tensile load is applied in a direction parallel to any one side of the square, only tensile stress is generated in each side parallel to the load direction, making the square less likely to break.

However, when a shear load acts on the entire square tessellation in the width or depth direction, all the adjacent squares tend to deform into parallelograms, no matter how the squares are arranged in the tessellation. In other words, a bending moment is generated on each side perpendicular to the shear direction in all the adjacent squares, and the bending moment causes all the sides perpendicular to the shear direction to tilt simultaneously, deforming them into a parallelogram shape.
Therefore, in a cylindrical section having a shape formed by filling a plane of rectangular columns, when a shear load is applied, a large bending stress is generated, which easily leads to breakage.

In contrast, in the case of a honeycomb shape, adjacent sides of a regular hexagon have an angle of 120 degrees. Therefore, even if a shear load acts on the entire plane-filled regular hexagon in the width or depth direction, the direction of the shear load and the two sides that have an angle of 120 degrees through each vertex will be at an angle of 90 degrees or more, which is close to parallel. As a result, the side that is close to parallel is mainly subjected to a compressive load or a tensile load, and the occurrence of bending moment is small. Therefore, the load due to shear is resolved into a compressive load or a tensile load and is balanced.
In this way, in the case of a honeycomb shape, even if a shear load is applied to the fiber-reinforced resin molding, bending moment is unlikely to be generated, so the regular hexagon is unlikely to deform and large bending stress is unlikely to be generated, making it unlikely to break.

In the above, when the cylindrical portion has a honeycomb shape, it is preferable that the thickness of the plate-like portion is 1 mm or more, and the height of the cylindrical portion is 4 mm or more.
If the thickness of the plate-shaped portion is less than 1 mm, the plate-shaped portion is so thin that when the plate-shaped portion is bent, the tensile load caused by the bending generates tensile stress that exceeds the tensile strength of the plate-shaped portion, making it prone to breakage.
On the other hand, if the height of the cylindrical portion is less than 4 mm, the thickness of the fiber-reinforced plastic molding will be thin, and not only will the rigidity decrease and the transmission loss decrease, but the transmission loss will also decrease due to the coincidence effect. In addition, if the thickness is thin, not only will the thermal insulation properties as a structural material be limited, but the entire fiber-reinforced plastic molding will be prone to buckling when subjected to a load in the planar direction.

Meanwhile, a means may be adopted in which the reinforcing fibers are laminated in a plurality of layers so that the fiber direction in the plate-like portion and the cylindrical portion has pseudo-isotropy.
When a fiber-reinforced resin molding is constructed using a sheet-like prepreg in which reinforcing fibers are aligned in one direction, spread, and impregnated with a matrix resin, if the molding is performed with the reinforcing fibers facing in a single direction, the fiber direction will be unidirectional overall in the fiber-reinforced resin molding after molding, resulting in anisotropy, and the physical properties of the fiber-reinforced resin molding itself will also become anisotropic.

Therefore, by configuring the reinforcing fibers to be layered in multiple directions, the fiber orientation in the fiber-reinforced resin molded body after molding is also random overall, making it pseudo-isotropic, and the physical properties of the fiber-reinforced resin molded body itself are also pseudo-isotropic. Therefore, when the fiber-reinforced resin molded body is used as a structural material, it exhibits excellent strength against loads in all directions. Furthermore, when used as a sound-proofing material, it exhibits high rigidity in all directions even if sound is incident, making it difficult for vibration to occur and improving transmission loss.

When adopting a multiple-layered configuration in which the fiber direction has pseudo-isotropy, it is possible to adopt a configuration in which a plurality of chopped prepregs cut into strips are laminated on the plate-shaped portion and the tubular portion, and the direction of the reinforcing fibers has pseudo-isotropy.
Here, the chopped prepreg is made of a UD (Uni Direction) sheet material in which the reinforcing fibers that have been opened into thin layers are aligned in a single direction and impregnated with the matrix resin.
In a spread fiber bundle obtained by a general spreading method, many bundles of reinforcing fibers are laminated and become thick. Here, the thin layer spread reinforcing fibers do not limit the basis weight of the spread fiber bundle or the thickness when made into a prepreg, but refer to fibers spread in a thin layer so that the fluidity of the reinforcing fibers is high enough that the reinforcing fibers can be filled from the bottom to the tip of the plate-like portion of the tubular portion when molded into a fiber-reinforced resin molding.

The UD sheet made of the thin-layered reinforcing fibers is made into a chopped prepreg, and multiple chopped prepreg sheets are laminated to be pseudo-isotropic, so that the reinforcing fibers of the strip-shaped chopped prepregs are oriented in all directions and laminated, eliminating unevenness in strength due to direction in the fiber-reinforced resin molding. In other words, the strength is uniform against bending, twisting, pulling, and other forces in all directions.
In addition, since the thin-layered reinforcing fiber bundles are cut into strips, the reinforcing fibers are easily unraveled by the flow of the matrix resin during compression molding, and flow easily together with the molten matrix resin into a tubular portion having a specified height, making it easy for the reinforcing fibers to be filled up to the tip of the tubular portion in a pseudo-isotropic state.

On the other hand, in the fiber-reinforced resin molding of the present invention that includes the plate-like portion and the cylindrical portion, various bending strengths can be exhibited depending on the shape of the plate-like portion and the cylindrical portion, the properties of the reinforcing fibers, etc. In this regard, as described above, it is also possible to configure the cylindrical portion by filling the bottom of the plate-like portion side to the tip with reinforcing fibers, and to configure the smaller indenter load at break in a bending test in which an indenter is pressed against the center of the tip of the cylindrical portion and the smaller indenter load at break in a bending test in which an indenter is pressed against the center of the surface of the plate-like portion on which the cylindrical portion is not provided, to be 50% or more of the larger indenter load.

The bending test is performed using a bending tester equivalent to JIS K7171. The sample dimensions, test speed, distance between supports, and indenter shape can be arbitrary, but the bending test is performed under the same conditions for each bending direction. During the bending test, the load applied to the sample by the indenter when part of the sample breaks is measured and compared for each bending direction.

The above means does not directly limit the shape of the plate-like and tubular parts or the properties of the reinforcing fibers themselves to specific conditions. In other words, it is a means for arbitrarily setting and configuring the shape of the plate-like and tubular parts, focusing on the difference in bending strength for each bending direction in a bending test, on the premise that the reinforcing fibers are filled at least from the bottom to the tip of the tubular part on the plate-like side.

As described above, by configuring the difference in the indenter load at break in each of the different bending directions so that the smaller indenter load is 50% or more of the larger indenter load, when the fiber-reinforced resin molded body is used as a structural material, even if bending occurs due to a load being applied from either the front or back, it is possible to provide uniform bending elasticity and strength, and one of the bending directions will not become extremely weak.

The fiber-reinforced resin molding of the present invention described above can be produced by the following means.
First, the reinforcing fibers that have been spread into thin layers are aligned in a single direction, and the UD sheet formed by impregnating the reinforcing fibers with the matrix resin is cut into rectangular shapes to form a plurality of chopped prepregs.
Next, the plurality of chopped prepregs are laminated so that the direction of the reinforcing fibers has pseudo-isotropy, and the matrix resin is melted and solidified to form a chopped prepreg sheet.

Here, a mold based on a predetermined shape is used, and a plurality of the chopped prepreg sheets are stacked and arranged in the mold. The shape of the mold has a flat plate-like portion and a plurality of cylindrical portions provided substantially perpendicularly from the plate-like portion, and the cylindrical portions have portions where the cylindrical portions are connected to each other.
Finally, the multiple laminated chopped prepreg sheets are hot-pressed in the mold to melt the matrix resin of the multiple laminated chopped prepreg sheets, and a fiber-reinforced resin molded body is produced in which the carbon fibers are filled together with the molten matrix resin from the bottom to the tip of the plate-shaped portion of the tubular portion.

UD sheets using thin-layered reinforcing fibers are very thin, with a relatively small number of overlapping fibers in each fiber direction. Chopped prepreg sheets, which are made by cutting the thin UD sheets and laminating them so that the fibers are in a random direction, have a certain overall thickness, but the number of reinforcing fibers stacked in each fiber direction is very small.
By using such chopped prepreg sheets for hot press molding, when the matrix resin melted by heat flows through the molding space in the mold, the reinforcing fibers with little overlap in each fiber direction easily unravel and can flow freely through the molding space of the mold together with the matrix resin.
As a result, the tubular portion can be filled from the bottom to the tip on the plate-shaped portion side, and a fiber-reinforced resin molding can be produced that has sufficient rigidity and strength even at the tip of the tubular portion.

As described above, the fiber-reinforced resin molding of the present invention has at least a flat plate-like portion and a plurality of tubular portions arranged approximately perpendicular to the plate-like portion, and the plurality of tubular portions have portions where the tubular portions are connected to each other, and the reinforcing fibers are filled from the bottom to the tip on the plate-like portion side.
With this configuration, the section modulus is large in any bending direction, and the tip portion of the cylindrical portion has sufficiently high elasticity and strength compared to the bottom portion.
Therefore, not only is it lightweight and has excellent strength and rigidity, but it can also be made thicker than a flat plate of the same weight or strength, and has the effect of being excellent in terms of thermal insulation, buckling load, etc. In addition, it has the effect of being possible to obtain a fiber-reinforced resin molding that has excellent toughness regardless of the bending direction and a high transmission loss against noise.

1A and 1B are a perspective view and a cross-sectional view illustrating a fiber-reinforced resin molding of the present invention. FIG. 2 is a partial end view showing the distribution of reinforcing fibers in a fiber-reinforced resin molding of the present invention. 1 is a flowchart showing a method for producing a fiber-reinforced resin molding of the present invention. 1 is an explanatory diagram showing a method for producing a fiber-reinforced resin molding of the present invention. 1A and 1B are a front view and a plan view showing measurement points for binarized image analysis of a cross section in an embodiment of the present invention. 11 is a photograph showing the results of a comparison between an embodiment of the present invention and a comparative example in terms of binary image analysis of a cross section of a cylindrical portion on the outermost side. 13 is a photograph showing the results of a comparison between an embodiment of the present invention and a comparative example in terms of binary image analysis of a cross section at a central cylindrical portion. 1A and 1B are a front view and a plan view showing a test piece for a compression test in an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a method of a compression test in an embodiment of the present invention. 1 is a graph showing the results of a comparison of a compression test in an embodiment of the present invention with a comparative example. 1A and 1B are a front view and a plan view showing a test specimen for a bending test in an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a method of bending test in an embodiment of the present invention. 1 is a graph showing the results of a comparison of a bending test in an embodiment of the present invention with a comparative example. 1A and 1B are a front view and a plan view showing a measurement item of transmission loss using an acoustic tube in an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a transmission loss measuring device using an acoustic tube in an embodiment of the present invention. 1 is a graph showing general characteristics of measurement results of transmission loss using an acoustic tube. 1 is a graph showing a comparison result of measurement results of transmission loss using an acoustic tube in an embodiment of the present invention with a comparative example. FIG. 2 is an explanatory diagram showing a measurement device for transmission loss using a reverberation chamber and an anechoic chamber in an embodiment of the present invention. 1 is a graph showing a comparison result of measurement results of transmission loss using a reverberation chamber and an anechoic chamber in an embodiment of the present invention with a comparative example. FIG. 13 is a plan view showing a modified example of the present invention. FIG. 2 is a front view showing the base material of Patent Document 1. 1A and 1B are a schematic perspective view and a schematic cross-sectional view showing a fiber-reinforced resin molded body of Patent Document 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.
In the following description, the width direction in FIG. 1 is defined as the x direction, and the depth direction is defined as the y direction.

As shown in the perspective view of FIG. 1, the overall shape of a fiber-reinforced resin molded body 100, which is an example of an embodiment of the present invention, has a flat plate-like portion 1 and multiple tubular portions 2, 2... that are arranged approximately perpendicularly from the plate-like portion 1. Each tubular portion 2 has multiple regular hexagonal columns formed by stretching a plane-filled regular hexagon in the thickness direction, and the walls 21, 21 of adjacent tubular portions 2 are connected together as a shared connecting portion 22, giving the body a so-called honeycomb shape.

In the form shown in FIG. 1, the plate-like portion 1 is a rectangular flat plate, and the lower limit of its thickness is preferably more than 0.5 mm, and more preferably 1 mm or more, from the viewpoint of preventing cracks during molding. If the thickness is 0.5 mm or less, the plate-like portion 1 will be pulled by the burrs that occur on the outer periphery during hot press molding, causing cracks. Furthermore, the upper limit of the thickness is preferably less than 4.5 mm, more preferably 4 mm or less, and even more preferably 3 mm or less, from the viewpoint of the balance between the overall weight and the reinforcement and transmission loss. If the thickness is 4.5 mm or more, not only will the weight increase, but the effect of improving sound transmission loss will be minimal compared to the case where a simple flat plate and cylindrical portions 2, 2... of the same thickness are provided.

In the embodiment shown in FIG. 1, the cylindrical portion 2 is a regular hexagonal prism, with nine regular hexagonal prisms arranged in parallel in the x direction and nine regular hexagonal prisms arranged in a staggered pattern in the y direction. The distance between two opposing parallel sides of the regular hexagon, which is the shape of the space of the regular hexagonal prism, can be set appropriately from the perspective of balancing light weight and rigidity. The thickness of the wall portion 21, which also serves as the connecting portion 22 of the regular hexagonal prism, can also be set appropriately from the perspective of balancing light weight and rigidity.

The lower limit of the height of the cylindrical section 2 is preferably 4 mm or more, and more preferably 6 mm or more, in order to ensure sufficient bending strength. If the height is less than 4 mm, the effect of improving strength by the cylindrical section 2 will be limited, and the effect of improving sound transmission loss in terms of sound insulation will also be limited depending on the frequency. The upper limit of the height can be set appropriately based on the balance with the weight.

In the fiber-reinforced resin molded body 100 consisting of such a plate-like portion 1 and cylindrical portions 2, 2..., as shown in the cross-sectional view of FIG. 1, in both cross sections in the x direction and in the y direction, a substantially T-shaped cross section is continuous. In general, compared with a simple rectangular cross section, when a T-shaped cross section is formed with a wall perpendicular to the long side of the rectangle, the section modulus increases, and the rigidity against bending increases. In the present invention, not only are the cylindrical portions 2, 2... arranged substantially perpendicular to the plate-like portion 1, but the walls 21, 21 of the cylindrical portions 2, 2 are connected to each other by the connecting portion 22, so that in both cross sections in the x direction and in the y direction, a continuous T-shaped cross section always appears regardless of the cut position. Note that FIG. 1 shows only cross sections perpendicular to the x direction and the y direction, but the same applies to diagonal cross sections.

As shown in Fig. 2, the internal configuration of the fiber reinforced resin molding 100 includes a matrix resin 3, which is a thermoplastic resin, and reinforcing fibers 4, 4... impregnated with the matrix resin 3. Note that the distribution of the reinforcing fibers 4, 4 in Fig. 2 is shown diagrammatically for the purpose of explanation, and the thickness of each portion is exaggerated.
Here, the cylindrical portion 2 is configured by being filled with the reinforcing fibers 4 from the bottom 23 on the plate-like portion 1 side to the tip 24. As for the filling mode, the reinforcing fibers 4 are not only oriented substantially parallel to the longitudinal direction of the cylindrical portion 2, but also oriented in the depth direction and partially bent and filled. With the reinforcing fibers 4 oriented in such random directions, the fiber direction has pseudo-isotropy not only in the plate-like portion 1 but also in the cylindrical portion 2.

As the matrix resin 3, various thermoplastic resins can be used, such as PP (polypropylene), PE (polyethylene), PS (polystyrene), PA (polyamide), POM (polyacetal), PC (polycarbonate), ABS (acrylonitrile-butadiene-styrene copolymer), PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PI (polyimide), PAI (polyamide imide), PEI (polyetherimide), PESU (polyethersulfone), PPS (polyphenylene sulfide), PEK (polyether ketone), PEEK (polyether ether ketone), PEKK (polyether ketone ketone), PSF (polysulfone), PAR (polyarylate), PPSU (polyphenylsulfone), PMMI (acrylic resin), fluorine-based resin, thermoplastic epoxy resin, liquid crystal polymer, etc. Also, a polymer alloy in which two or more of these thermoplastic resins are mixed may be used.

Carbon fibers, glass fibers, aramid fibers, ceramic fibers, etc. can be used as the reinforcing fibers 4. Carbon fibers are particularly preferred from the viewpoint of light weight and strength, and in this case, pitch-based carbon fibers with excellent elasticity can be used, but PAN (polyacrylonitrile)-based carbon fibers can provide even higher strength. A mixture of multiple reinforcing fibers 4 may also be used.
Moreover, the fiber length of the reinforcing fibers 4 can be adjusted appropriately.

In the present invention, the reinforcing fibers 4, 4... are filled from the bottom 23 on the plate-shaped portion 1 side of the tubular portion 2 to the tip portion 24, so that the tip portion 24 has sufficiently high elasticity compared to the bottom 24 of the tubular portion 2.
The ratio of the fiber volume content at the bottom 23 of the tubular portion 2 to the fiber volume content at the tip portion 24 is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and ideally 100%, in terms of the balance between rigidity and strength. If it is below 50%, the strength at the tip portion 24 decreases compared to the bottom portion 23, so the tip portion 24 becomes more likely to break when bent as the height of the tubular portion 2 is increased. This makes it difficult to make the fiber-reinforced resin molding 100 sufficiently thick.

Furthermore, the fiber volume content in the tip portion 24 is preferably at least -10% of the fiber volume content of the material before molding, more preferably at least -5%, and even more preferably the same fiber volume content or more.

The fiber-reinforced resin molding 100 of the present invention as described above can be manufactured by the manufacturing method shown in FIG. 3. The specific details are described below with reference to FIG. 4 as appropriate. The alphabets at the beginning of each step in FIG. 3 correspond to the alphabets in each explanatory diagram in FIG. 4.

First, (a) the reinforcing fibers are spread into a thin layer. There are various methods for spreading the reinforcing fibers, but as an example, the reinforcing fibers can be spread into a thin layer using a fiber spreading device 5 as shown in Fig. 4(a). In this device example, a reinforcing fiber bundle 52 fed from a yarn feeding section 51 is spread in a fiber spreading processing section 53.
The mechanism of fiber spreading is as follows: the suction pump 54 is operated to suck in air, and a downward air current passes through the fiber spreading processing section 53. When the downward air current passes through the fiber spreading processing section 53, the reinforcing fiber bundle 52 becomes bent due to the flow speed of the air current. When the air current passes between the fibers of the bent reinforcing fiber bundle 52, a force is generated that moves each reinforcing fiber in the width direction of the reinforcing fiber bundle 52, and the reinforcing fiber bundle 52 is spread.

Here, the contact member 55 is rotated to contact the reinforcing fiber bundle 52, thereby performing a process of continuously tensioning and relaxing the reinforcing fiber bundle 52. By passing a descending air current through the reinforcing fiber bundle 52 during relaxation, the reinforcing fiber bundle 52 can be more efficiently spread. Although not shown, by providing the fiber spreading processing unit 53 and the contact member 55 in multiple stages, the reinforcing fiber bundle 52 can be efficiently spread into a wider and thinner layer. For example, when a carbon fiber bundle 12K (single fiber diameter about 7 um, number of fibers 12,000) is used, the reinforcing fiber bundle 52' spread by a special method such as this can be spread into a thin layer with a basis weight of about 40 g/m ² when spread to a width of 20 mm, a basis weight of about 20 g/m ² when spread to a width of 40 mm, and a basis weight of about 12.5 g/m ² when spread to a width of 64 mm. However, the thin layer spreading is not limited to the fiber type, spreading width, and basis weight, and can be said to be a thin layer spreading as long as the fluidity of the reinforcing fibers 4 is increased to such an extent that the tip portion 24 of the tubular portion 2 can be sufficiently filled in the hot press described later.

Next, the thin-layered reinforcing fiber bundles 52' are used to produce a UD sheet (b). There are various methods for producing a UD sheet, but for example, a UD sheet production apparatus 6 as shown in FIG. 4(b) can be used.
This example of the apparatus is for laminating and integrating the reinforcing fiber bundles 52' that have been opened into thin layers by the above-mentioned method and a resin sheet 61 made of a thermoplastic resin that serves as the matrix resin 2.

In the lamination and integration process, first, a plurality of reinforcing fiber bundles 52' are aligned and sent to heating rolls 62 together with a resin sheet 61. The heating rolls 62 are provided with two pairs of rolls, and each roll is heated to a high temperature to apply heat and pressure to the reinforcing fiber bundles 52' and the resin sheet 61 passing between the rolls. The resin sheet 61, which is a thermoplastic resin, melts when heated to a high temperature, and the molten resin is impregnated into the reinforcing fiber bundles 52' by applying pressure at the same time.
Next, the impregnated resin is cooled and solidified by two pairs of cooling rolls 63, 63, to obtain a UD sheet 64 in which the reinforcing fiber bundles 52', whose fibers are aligned in one direction, are impregnated with the resin sheet 61. The UD sheet 64 thus produced is wound around a take-up roll 65.

In the UD sheet manufacturing device 6, the resin sheet 61 is laminated on one side of the reinforcing fiber bundle 52', but the UD sheet 64 is not limited to this configuration. For example, it is also possible to adopt a configuration in which the reinforcing fiber bundles 52', 52' are sandwiched and laminated from both sides of the resin sheet 61, or a configuration in which the resin sheets 61, 61 are sandwiched and laminated from both sides of the reinforcing fiber bundle 52'.

Next, (c) a chopped prepreg sheet is produced using the produced UD sheet 64. There are various methods for producing a chopped prepreg sheet, but for example, a chopped sheet production apparatus 7 as shown in FIG.
This device example cuts the UD sheet 64 produced by the above-mentioned method into chopped prepreg strips, stacks a number of these, and heats them to laminate together.

In the process of producing the chopped prepreg sheet, first, the UD sheet 4 is cut into strips by a vertical cutter 71 and a horizontal cutter 72 to produce chopped prepregs 73, 73.... The dimensions of the chopped prepreg 73 can be set as appropriate, but the width is preferably 1 mm to 30 mm. If the width is smaller than 1 mm, the UD sheet 64 is likely to fluff when cut, and the fluidity is poor during the heat pressing described below. If the width is larger than 30 mm, the fiber direction is likely to be biased in one direction during lamination described below, and anisotropy in the fiber direction is likely to occur.
The length is preferably 5 mm to 100 mm. If the length is less than 5 mm, the tensile strength of the reinforcing fibers 4 decreases, and the strength of the fiber reinforced resin molding 100 itself also decreases. If the length is more than 100 mm, the lamination thickness increases, and the fluidity of the reinforcing fibers 4 during hot pressing decreases.

Next, the chopped prepregs 73, 73... obtained by cutting are dropped onto a conveyor 74. The conveyor 74 is composed of multiple conveyors 741, 742, 743, each of which is installed at a predetermined distance apart in the conveying direction. The chopped prepregs 73, 73... conveyed by the conveyor 74 fall onto the conveyor belt 75, each at a different position. At this time, the chopped prepregs 73, 73... are dropped onto the conveyors 741, 742, 743 and onto the conveyor belt 75, so that the fiber direction is randomly oriented in a two-dimensional direction.

The chopped prepregs 73, 73... dropped from the conveyor 741 have the matrix resin 2 remelted by the adhesive roll 75a consisting of a heating roll 751a and a pressing roll 752a, and are laminated and integrated. The same process is performed in the conveyor 742, but the chopped prepregs 73, 73... are dropped from the conveyor 742 on top of the chopped prepregs 73, 73... that have already been laminated and integrated by the adhesive roll 75a. The dropped chopped prepregs 73, 73... have the matrix resin 2 remelted by the adhesive roll 75b consisting of a heating roll 751b and a pressing roll 752b, and are further laminated and integrated. The same process is performed in the next conveyor 743. Finally, they are cooled by the cooling roll 76.
In this way, by dividing the chopped prepregs 73, 73... into multiple stages and stacking them together, the final chopped prepreg sheet 77 is stacked with the fibers oriented randomly in the two-dimensional direction.

Next, (d) hot press molding is performed using chopped prepreg sheet 77 obtained by laminating and integrating. Various methods can be used for hot press molding, and for example, a single press mold 8 as shown in FIG. 4(d) can be used.
The press die 8 includes a punch 81 and a die 82. The inner surface of the punch 81 has a planar shape that becomes the outer surface of the plate-like portion 1 of the fiber reinforced resin molding 100. The inner surface of the die 82 has a shape that is an inverted shape of the tubular portion 2 of the fiber reinforced resin molding 100. When the punch 81 and the die 82 are faced to each other and clamped, a molding space having approximately the same shape as the fiber reinforced resin molding 100 to be obtained is created between the punch 81 and the die 82.

In the hot press molding process, a plurality of chopped prepreg sheets 77, 77... produced by the above-mentioned method are stacked and placed on a die 82. Then, the press die 8 is heated to a high temperature, and a punch 81 is pressed into the die 82 to clamp the die.
The temperature of the mold is appropriately adjusted depending on the type of matrix resin 2 of the chopped prepreg sheet 77, and for example, the punch 81 and die 82 can be set to 280°C.

The number of chopped prepreg sheets 77 to be stacked varies depending on the thickness of the chopped prepreg sheets 77 used, but the weight of the chopped prepreg sheets 77 to be stacked is set according to the weight of the fiber reinforced resin molding to be ultimately obtained.
For example, in the embodiment of FIG. 1, the plate-like portion 1 has a width of 110 mm and a depth of 100 mm, the distance between two parallel sides of the regular hexagon, which is the shape of the space of the regular hexagonal prism in the cylindrical portion 2, is 9 mm, the thickness of the wall portion 21 of the regular hexagonal prism is 1 mm, and the height is 20 mm. PA (nylon 6) is used for the matrix resin 2, and carbon fibers with a fiber diameter of 7 um and a fiber length of 5 mm are used for the reinforcing fibers 4, and the fiber volume content Vf is 50%. Under these conditions, the plate-like portion 1 is laminated so that it weighs about 48 g when the thickness is 0.5 mm, about 57 g when the thickness is 1.0 mm, and about 66 g when the thickness is 2.0 mm. In this way, the weight of the chopped prepreg sheets 77, 77... used is the remainder filled in the molding space that becomes the cylindrical portion 2, which becomes the thickness of the plate-like portion 1.

The chopped prepreg sheets 77, 77... of the weight set as described above are stacked and clamped with a mold 8 heated to a high temperature, thereby remelting the matrix resin 2 of the chopped prepreg sheets 77, 77.... The melted matrix resin 2 flows due to the pressure of the clamping. With this flow of the matrix resin 2, the reinforcing fibers 4 with random fiber orientation also flow. The reinforcing fibers 4 are thinly spread as described above and cut to a predetermined length. Therefore, although the reinforcing fibers 4, 4... as a whole are laminated in a state where the fibers are oriented in a random direction and have a predetermined thickness, in the parts that were the individual chopped prepregs 73, 73..., there are a very small number of reinforcing fibers 4, 4... for each fiber direction. Therefore, with the flow of the matrix resin 2, the reinforcing fibers 4, 4... also flow easily, and the reinforcing fibers 4, 4... are naturally filled in the plate-shaped part 1 where the reinforcing fibers 4 are originally distributed overall, and are also filled in the tubular part 2 from the bottom 23 to the tip 24.
The pressure and time of clamping the mold should be adjusted appropriately, but in the embodiment of FIG. 1, as an example, a load of 5 kgf is applied to the cylinder of the molding machine for 20 minutes to preheat it, and then the load is switched to 30 kgf and pressed for 5 minutes to mold the molded product.

Finally, the press die 8 is held in a clamped state for a certain period of time, the matrix resin 2 is sufficiently cooled and solidified, and then the fiber reinforced resin molded body 100 is released from the die. At this time, cooling can be achieved in a shorter period of time by adopting a method in which the punch 81 and die 82 are cooled and cold pressing is performed using the same die 8. As an example, the punch 81 is not heated but is allowed to cool naturally, the die 82 is adjusted to 110°C, and a load of 40 kgf is applied to the cylinder for 7 minutes to perform cold pressing.
Furthermore, if a separate press die 8' (not shown) identical to the press die 8 is prepared, and after opening the punch 81 during cooling, another cooled punch 81' is fastened to the die 82 which is being cooled, cooling can be performed in an even shorter time, and continuous molding can be performed using multiple dies.

"Binarized image analysis of the tip of a cylindrical part"
Here, a binary image analysis performed on Example 1 and Comparative Example 1 of the fiber-reinforced resin molding 100 manufactured by applying the above-mentioned embodiment will be described. In this analysis, as shown in Fig. 5, the cross sections of the tip end 24 of the tip end of the cylindrical part 2a located on the outermost side and the cylindrical part 2b located in the center among the multiple cylindrical parts 2, 2... were photographed with a magnifying glass. Then, the images were subjected to binary image processing by a computer, and the cross-sectional ratio of the reinforcing fiber 4 to the photographed range was calculated.

Specifically, the image was processed by binary image processing so that the cross sections of the reinforcing fibers 4, 4... appeared white, and the cross sections of the matrix resin 3 and voids (air bubbles) appeared black, and the ratio of the number of white pixels to the total number of pixels was calculated. Note that there are no particular limitations on the software that performs the binary image processing, so long as it can perform binary processing based on the loaded bitmap image and calculate the ratio of white and black pixels.

The fiber-reinforced resin molded body 100 used in the test in both Example 1 and Comparative Example 1 is the fiber-reinforced resin molded body 100 shown in FIG. 1. As shown in FIG. 5, the dimensions of each part are as follows: the distance a between two opposing parallel sides of the regular hexagon that forms the shape of the space of the regular hexagonal prism in the tubular part 2 is 9 mm, the thickness of the wall part 21 of the regular hexagonal prism is 1 mm, the thickness h of the plate-like part 1 is 1 mm, and the height h of the tubular part 2 is 20 mm.

In Example 1, PA6 is used as the matrix resin 4, and a UD sheet with a fiber volume content of 53% is produced by the above-mentioned manufacturing method, which is then cut into strips to produce chopped prepregs with a fiber volume content of 50% by the above-mentioned manufacturing method, and then compression molded to form a fiber reinforced resin molding 100.
On the other hand, in Comparative Example 1, PA6 was used as the matrix resin 4, and a UD sheet with a thickness of 0.16 mm and a width of 166 mm was produced using carbon fibers that had been spread relatively thickly by a conventional known manufacturing method. This was then cut into strips to produce chopped prepregs with a fiber volume content of 49%, which were then compression molded to form a fiber-reinforced resin molding.

To photograph the cross section, the tip 24 is ground and polished as thin as possible to expose the cross section. In this embodiment, the tip is ground and polished to about 1 to 2 mm. The cross section is then photographed using an image inspection device or an optical microscope capable of capturing image data. The magnification is selected so that the cross section of the carbon fiber can be photographed with good accuracy. In this analysis, the image is photographed at 120x.
When calculating the percentage of pixels based on the binarized image, in order to reduce errors due to location, two or three arbitrary locations on the cross section are selected and the percentage is calculated for all of those pixels. In this analysis, the analysis range is 500um x 500um or 950um x 950um depending on the condition of the measurement location, and the average is calculated.

The photographed images and analysis results obtained by this analysis are shown in Figures 6 and 7. The left side of each figure is Example 1, and the right side is Comparative Example 1. Figures 6(a) and (b) show the analysis results of the cylindrical portion 2a located on the outermost side, where three locations within a 500 um x 500 um square area were analyzed in Figure 6(a), and two locations within a 950 um x 950 um square area were analyzed in Figure 6(b).
Moreover, Figures 7(a) and (b) show the analysis results of the centrally located cylindrical portion 2b, and in both Figures 7(a) and (b), the analysis was performed at two locations each within the 950 um x 950 um square area, slightly shifted from one another.
In addition, the upper side of each photograph is the RGB image at the time of shooting, and the lower side is the binarized image.

As can be seen from Figures 6 and 7, in both the outer tubular portion 2a and the central tubular portion 2b, in Example 1, the proportion of carbon fiber cross sections represented by white pixels was approximately equal to or greater than the proportion of matrix resin and voids represented by black pixels, whereas in Comparative Example 1, the proportion of carbon fiber cross sections was smaller, even though the fiber volume content of the chopped prepreg before compression molding was similar to that of this example.

A comparison of the average values of the cross-sectional proportions of these carbon fibers is shown in Table 1. In this example, the fiber volume content of both the outer circumferential tubular portion 2a and the central tubular portion 2b was greater than 50% of the chopped prepreg before compression molding.
On the other hand, in Comparative Example 1, the fiber volume content of both the outer circumferential cylindrical portion 2a and the central cylindrical portion 2b in this embodiment was smaller than the fiber volume content of 49% of the chopped prepreg before compression molding.

"Compression test"
Next, a description will be given of the results of the compression test carried out on Example 2 and Comparative Example 2. In this test, the fiber reinforced resin moldings 100 of Example 1 and Comparative Example 1 were processed into the form shown in Fig. 8 to produce fiber reinforced resin moldings 110, and a compression test was carried out for each of them with N=2, and a load-strain diagram was calculated.

The fiber-reinforced resin molding 110 used in the test was prepared by processing the fiber-reinforced resin molding 100 in the above-mentioned Example 1 and cutting it into a shape having a total of seven tubular portions 2, 2..., with one tubular portion 2 adjacent to each other, as shown in Figure 8.
This was tested in two ways using a compression testing machine equivalent to JIS K7181: as shown in Fig. 9(a), the plate-like portion 1 was fixed and the pressure plate was in contact with the cylindrical portion 2 (hereinafter referred to as "upward" in this test), and as shown in Fig. 9(b), the cylindrical portion 2 was fixed and the pressure plate was in contact with the plate-like portion 1 (hereinafter referred to as "downward" in this test). During the test, the displacement amount of the pressure plate and the load were recorded, and the records were kept until the progress of plastic deformation after the fiber-reinforced resin molding 110 yielded.

The comparison results of the load at break are shown in Table 2, and the load-strain curves are shown in Figures 10(a) and 10(b). Note that Figure 10(a) shows the upward direction, and Figure 10(b) shows the downward direction.
The load at yield of Comparative Example 2, which was obtained by machining Comparative Example 1, in which the proportion of carbon fiber in the tip 24 of the tubular portion 2 was small in the above-mentioned binary image analysis, was 3.18 kN upward and 3.16 kN downward. In contrast, in Example 2, which was obtained by machining Example 1, in which carbon fiber was sufficiently filled up to the tip 24, the load was 3.33 kN upward and 3.45 kN downward, which was a higher load than Comparative Example 2.
In addition, after yielding, Comparative Example 2 resulted in an increase in strain (stroke) even at a lower load than Example 2.

"Bending test"
Next, a description will be given of the results of bending tests carried out on the fiber reinforced resin moldings 120 produced by applying the above-mentioned embodiment in Examples 3 to 9 and Comparative Examples 3 and 4. In this example, seven types of fiber reinforced resin moldings 120 having the configuration shown in Fig. 11 were produced, and bending tests were carried out on each of them to measure the indenter load at break.

The fiber-reinforced resin molded body 120 of this embodiment used in the test has a rectangular plate-like portion 1 with a width of 110 mm and a depth of 15 mm, eight regular hexagonal prisms exhibiting a honeycomb shape are arranged in parallel with each other with a center reference, and a cylindrical portion 2 is provided with half of a regular hexagonal prism connected to both ends of the eight regular hexagonal prisms, as shown in Fig. 11. The distance a between two opposing parallel sides of the regular hexagon, which is the shape of the space of the regular hexagonal prisms in the cylindrical portion 2, is 9 mm, and the thickness of the wall portion 21 of the regular hexagonal prisms is 1 mm.
Here, the thickness h of the plate-like portion 1 is 1 mm in Examples 3 to 6 and 9, and 3 mm in Examples 7 to 8. In addition, PAN-based carbon fibers with a fiber diameter of 7 um are used as reinforcing fibers in Examples 3 to 8, and pitch-based carbon fibers with a fiber diameter of 10 um are used as reinforcing fibers in Example 9. The height H of the cylindrical portion 2 differs in each Example, and is an appropriate combination of 4 mm, 6 mm, 10 mm, and 20 mm.

On the other hand, for the comparative examples, PAN-based carbon fibers with a fiber diameter of 7 um were used to produce flat plates of the same dimensions as plate-shaped portion 1 in Examples 3 to 9. The thickness of Comparative Example 3 was 1 mm, the same as plate-shaped portion 1 in Examples 3 to 6 and 9, and the thickness of Comparative Example 4 was 4.5 mm, which resulted in the same weight as Example 6. The manufacturing conditions for Examples 3 to 9 and Comparative Examples 3 and 4 are shown below, and representative values for the specifications and weights are shown in Table 3.

(manufacturing conditions)
Matrix resin: Polyamide 6
Reinforced fiber...See Table 3. Hot press conditions...Mold temperature 280°C, preheating at 5kgf for 20 minutes, pressing at 30kgf for 5 minutes. Cold press conditions...Punch unheated, die 110°C, pressing at 40kgf for 7 minutes.

The bending test was performed using a bending tester equivalent to JIS K7171 in two directions: a bending direction in which the indenter contacted the tip 24 of the cylindrical portion 2 as shown in Figure 12(a) (hereinafter referred to as the "upward direction" in this test), and a bending direction in which the indenter contacted the outer surface of the plate-like portion 1 as shown in Figure 12(b) (hereinafter referred to as the "downward direction" in this test). The test conditions were as follows: indenter tip curvature R1: 5 mm, support distance L: 60 mm, support curvature R2: 5 mm, test speed: 3 mm/min.

The test results are shown in Table 4, and a bar graph is shown in Figure 13. In comparison with Comparative Example 1 having a plate thickness of 1 mm, Examples 3 to 6 and 9 having a plate-like portion 1 of the same thickness showed a larger indenter load at break than Comparative Example 3, regardless of the type of reinforcing fiber and whether the bending direction was upward or downward.
Furthermore, when comparing Comparative Example 4 and Example 6, which have the same weight but a difference in overall thickness of about 5 times, the indenter load was approximately the same in the upward direction, but the indenter load of Example 6 was greater in the downward direction.
Furthermore, in all of Examples 3 to 9, the smaller of the indenter loads in the upward and downward directions was 50% or more of the larger one.

"Sound transmission loss measurement using an acoustic tube"
Next, a description will be given of the sound transmission loss measurement using an acoustic tube performed on Examples 10 to 12 and Comparative Examples 5 to 10 of the fiber-reinforced resin molding 130 manufactured by applying the above-mentioned embodiment. In this test, three types of fiber-reinforced resin molding 130 having the configuration shown in Fig. 14 and six types of comparative examples were manufactured, and the sound transmission loss was measured for each.

The fiber-reinforced resin molding 130 of this embodiment used in the test has a shape including a disk-shaped plate-like portion 1 having a diameter of 100 mm and a thickness h of 1 mm, and a tubular portion 2 in which regular hexagonal prisms having a honeycomb shape are evenly packed on the plane, as shown in Figure 14.
The distance a between two opposing parallel sides of the regular hexagon, which is the shape of the space of the regular hexagonal prism in the cylindrical portion 2, is 9 mm, and the thickness of the wall portion 21 of the regular hexagonal prism is 1 mm. In addition, PAN-based carbon fibers with a fiber diameter of 7 um are used as the reinforcing fibers. In addition, the height H of the cylindrical portion 2 is 5 mm in Example 10, 10 mm in Example 11, and 20 mm in Example 12.

On the other hand, Comparative Examples 5 to 8 are flat plate materials that do not have a cylindrical portion 2. Comparative Example 9 has a structure in which plate-like portions 1, 1 are bonded to both sides of a cylindrical portion 2 that has a honeycomb shape, and the distance between two opposing parallel sides of the regular hexagon is 9 mm, which is the same as in this example, but the thickness of the wall portion of the regular hexagon is 0.2 mm.
Comparative Example 5 uses stainless steel SUS304. Comparative Example 9 uses a single material PP that does not contain reinforcing fibers. Comparative Example 10 has the same shape and dimensions as Example 12, but uses a single material PA6 that does not contain reinforcing fibers.
The plate thickness is 1 mm in Comparative Examples 5 to 7, 4.6 mm in Comparative Example 8, and 0.6 mm on one side and 0.5 mm on the other side in Comparative Example 9.
The reinforcing fibers used in Comparative Examples 7 and 8 were PAN-based carbon fibers having a fiber diameter of 7 um, while Comparative Example 6 used pitch-based carbon fibers.
Representative values of the specifications and weights of Examples 10 to 12 and Comparative Examples 5 to 10 are shown in Table 5.

For the sound transmission loss test, a simple transmission loss measuring device 9 using an acoustic tube as shown in FIG. 15 was used. In the transmission loss measuring device 9, a sine wave is generated from a speaker 92 arranged via an amplifier on one end side of an acoustic tube 91 having a diameter of 80 mm and a length of 330 mm. Then, with the other end side of the acoustic tube 91 open, the sound pressure emitted from the acoustic tube 91 is measured by a measuring microphone 93, and the sound pressure value is calculated and recorded by a calculation device 94. Next, a fiber-reinforced resin molded body 130 serving as a sample is arranged on one end side of the acoustic tube 91 so that sound does not leak, and a sine wave of the same volume is similarly generated from the speaker 92. Then, the sound pressure of the sound transmitted through the sample is measured by the measuring microphone 93, and the sound pressure value is calculated and recorded by a calculation device 94. Using the sound pressure value thus obtained, the difference in sound pressure level before and after placing the sample is recorded as the transmission loss.
In the measurement, the measurement frequency band was from 200 Hz to 4 kHz. Furthermore, the fiber reinforced resin molded body 130 serving as a sample was placed so that the plate-shaped portion 1 faced the speaker 92, which was the sound source.

For hard, non-breathable samples such as the fiber-reinforced resin molded body 130, if there is a gap between the outer periphery of the sample and the inner periphery of the sound tube 91, the test results will show an extremely low transmission loss, so it is necessary to seal the outer periphery of the sample and the inner periphery of the sound tube 91. In this example, oil clay 95 was applied to the outer periphery of the sample to achieve a seal. Glass wool 96 and sound-absorbing sponge 97 are placed around the sound tube 91 to reduce the effect of standing waves caused by the sound tube 91 on the transmitted sound and the effect of sound waves radiated to the outside through the device.

Generally, in a thin, hard, non-air permeable sample such as the acoustic tube 91, whose outer periphery is supported within an enclosed space, the transmission loss characteristics show a tendency as shown in FIG.
The region indicated by S in the low-mid frequency range is the region where sound is transmitted due to the sample's bending elasticity (rigidity) causing the sample itself to vibrate. This region is called the elasticity control region because the transmission loss characteristics can be controlled by increasing or decreasing the bending elasticity of the sample. In the elasticity control region, the phases of the incident sound and the sample vibration approach each other as the frequency increases, so the transmission loss gradually decreases in proportion to the frequency.
On the other hand, the region indicated by M in the mid-high frequency range is a region where the amplitude decreases at the same sound pressure due to the influence of the mass of the sample, i.e., the inertia of the sample, making it more difficult for the sample to vibrate at higher frequencies. This region is called the mass control region because the transmission loss characteristics can be controlled by increasing or decreasing the mass of the sample itself. In the mass control region, the so-called mass law closely approximates the actual measured value, so for a sound insulation material made of a single material with a large area, the transmission loss is proportional to the product of the surface density and frequency, and increases at about 6 dB/Oct as the frequency increases.
The boundary region between the S region and the M region includes the resonance point where the vibration becomes maximum as the acoustic impedance due to bending elasticity and the acoustic impedance due to mass cancel each other out. Since the amplitude of the resonance is determined only by mechanical resistance such as friction within the sample tissue, this region is called the resistance control region.

In this way, when a hard, non-permeable sample is attached to an enclosed space, the transmission loss characteristics vary greatly depending on the position of the resonance frequency. For the same shape, the lighter the sample is and the higher the rigidity, the higher the resonance frequency will be. When the resonance frequency is high, the elastic control region with high transmission loss can be widened. The elastic control region is a low-mid frequency region where the sound amplitude is large and can easily become a problem as noise, so under the above conditions, it is more effective to make the resonance frequency as high as possible.

Considering the general tendency of vertical transmission loss measurement using the above acoustic tube, the representative values of the transmission loss measurement results are shown in Table 6, and the transmission loss characteristics are shown in semi-logarithmic graphs in Figures 17(a), (b), and (c). Note that the frequencies where the transmission loss decreases, which is a common tendency for all samples, are excluded from the comparison because they are thought to be due to standing waves or resonance of the acoustic tube 91 itself.
17(a), a decrease in transmission loss was observed near 1 kHz in Comparative Example 5 using SUS304, near 1.6 kHz in Comparative Example 6 using 1 mm thick pitch-based carbon fiber, and near 1.2 kHz in Comparative Example 7 using 1 mm thick PAN-based carbon fiber, which is believed to be due to resonance of the flat plate. However, no extreme decrease in transmission loss was observed in Comparative Example 8 using 4.6 mm thick PAN-based carbon fiber.
As shown in Figure 17(b), in comparison example 9, which has a structure in which plate-shaped portions 1/1 are bonded to both sides of the tubular portion 2, a large decrease in transmission loss was observed from 2 kHz to 3 kHz, but in comparison example 10, which did not contain reinforcing fibers, no extreme decrease in transmission loss was observed.

17(c), in the examples, no extreme decrease in transmission loss was observed in any of the examples 10 to 12, and the tendency was similar to that of the 4.6 mm thick comparative example 8. The reason why almost no difference was observed in the degree of transmission loss in the examples is thought to be that the transmitted sound pressure was extremely small and attenuated to the level of environmental sound due to the SN ratio.
Thus, in this example, it is believed that the resonance frequency shifted to a higher frequency outside the measurement range, and the transmission loss was equal to or greater than that of Comparative Example 8, which was heavy and had a thickness of 4.6 mm, and Comparative Example 9, which had two plate-shaped parts. Also, in Comparative Example 5, which was made of SUS304 and had a similar weight, a decrease in transmission loss was observed due to resonance of the flat plate, but in this example, no decrease in transmission loss was observed even though it was of the same weight.

"Sound transmission loss measurement using reverberation and anechoic rooms"
Next, a description will be given of the measurement of sound transmission loss using a reverberation chamber and an anechoic chamber performed for Examples 13 and 14 and Comparative Examples 11 and 12 of the fiber-reinforced resin molded body manufactured by applying the above-mentioned embodiment. In this test, a fiber-reinforced resin molded body 140 having an overall size of 300 mm x 300 mm was used, and a thick metal frame was attached to its outer periphery to make a sample with an opening size of 260 mm x 260 mm. In this example, two types of fiber-reinforced resin molded body 140 and two types of comparative examples were produced, and the sound transmission loss was measured for each.

The fiber-reinforced resin molded body 140 of this embodiment used for the measurement is not shown, but has a shape similar to that of Example 1, in which a rectangular plate-like portion 1 of a predetermined thickness is arranged, and a cylindrical portion 2 in which regular hexagonal prisms of a honeycomb shape are evenly filled in the plane. The distance a between two opposing parallel sides of the regular hexagon that forms the space of the regular hexagonal prisms in the cylindrical portion 2 is 9 mm, and the thickness of the wall portion 21 of the regular hexagonal prisms is 1 mm. The thickness of the plate-like portion 1 is 1 mm in both Examples 13 and 14, and the height of the cylindrical portion 2 is 5 mm in Example 13 and 20 mm in Example 14.

On the other hand, Comparative Examples 11 and 12 are flat plate-shaped materials of 300 mm × 300 mm that do not have a cylindrical portion 2. Comparative Example 11 is a flat plate using PAN-based carbon fibers with a fiber diameter of 7 um, like Examples 13 and 14, and Comparative Example 12 is a steel plate using SS400, which is carbon steel for mechanical structures. The plate thickness was 2.3 mm in both Comparative Examples 11 and 12.
Representative weight values for Examples 13 and 14 and Comparative Examples 11 and 12 are shown in Table 7.

The sound transmission loss test was performed using a measuring device 10 based on the sound intensity method in accordance with JIS, as shown in Fig. 18. Multiple speakers 103 and microphones 104 were placed in a reverberation chamber 101, and adjustments were made so that the sound pressure level in the reverberation chamber was constant regardless of position. In this test, four speakers and five microphones were used to adjust the sound pressure level to be uniform. In addition, an acoustic intensity probe 105 was used in the anechoic chamber 102, and the sound power at multiple positions could be measured using a microphone moving device (MT) or the like.
Between the reverberation chamber 101 and the anechoic chamber 102, the above-mentioned 300 mm × 300 mm sample was placed so that no sound would leak out, with the cylindrical part 2 facing the reverberation chamber 101 side. In this state, noise with a continuous spectrum over the entire measurement frequency range was generated from the speakers 103, 103, ..., and the transmission loss in the frequency range from center frequency 400 Hz to 10 kHz for each 1/3 octave band was analyzed by the computer 106.

When measuring transmission loss using the sound intensity method, unlike the previously mentioned method using an acoustic tube, the sample size is relatively large, and it is possible to accurately reproduce the condition of an actual sound-proofing material placed in an environmental sound. Generally, in this test, the sample size is large, so it has lower rigidity than a sample attached to an acoustic tube, and so it tends to show the characteristics of the mass control region shown by M in Figure 16. On the other hand, unlike when an acoustic tube is used, sound waves generated in the reverberation chamber are incident on the sample from all directions, so the previously mentioned coincidence effect is likely to occur at high frequencies.

Considering the general tendency of the transmission loss measurement using the acoustic intensity method, the representative values of the measurement results of the transmission loss by the above method are shown in Table 8, and the measurement results of the transmission loss are shown in Figure 19. The dashed straight line is a graph of the mass law calculated from the weight. Since both Examples 13 and 14 and Comparative Examples 11 and 12 have the same slope as the slope of the mass law, it can be seen that the frequency range of this measurement result is in the above-mentioned mass control region.
In Comparative Example 11, a decrease in transmission loss due to the coincidence effect was observed near 6.3 kHz, while in Example 14, the influence of the coincidence effect was observed at a lower frequency of 4 kHz. This is because the overall thickness of Example 13 is 6 mm, which is thicker than that of Comparative Example 11, and it is considered that the frequency at which the coincidence effect occurs is lower in Example 13 as a whole. However, the frequency range in which the transmission loss decreases due to the coincidence effect drops sharply from 3.15 kHz in Comparative Example 11 and drops over a wide range up to 6.3 kHz, whereas in Example 13, it does not drop much from 2 kHz to 2.5 kHz, and drops only in a narrow range from 2.5 Hz to 4 kHz. This is presumably because the overall thickness is thickened by the cylindrical portion 2, suppressing the amplitude of the generated bending vibration. Therefore, it is considered that the frequency range affected by the coincidence effect is narrower in Example 13 than in Comparative Example 11.

In addition, in the steel plate of Comparative Example 12, the influence of the coincidence effect was observed in a wide range from 3.15 kHz to 6.3 kHz, and the amount of decrease was also large. However, in Example 14, which was 9 times thicker than Comparative Example 12, the transmission loss was larger than that of Comparative Example 12 at 4 kHz and above, and the influence of the coincidence effect was not observed in the measurement frequency range. This is presumably because the height of the cylindrical portion 2 of Example 14 was as high as 20 mm, and the wavelength at which the coincidence effect occurs was longer than the size of the sample, making it difficult for bending vibration to occur, thereby suppressing the decrease in transmission loss caused by the coincidence effect.
Incidentally, below 4 kHz, Example 14 has a lower overall transmission loss than Comparative Example 12, but this is due to the difference in weight in the first place. By adjusting the length of the tubular portion 2 and the thickness of the plate-like portion 1 of Example 14 to make the overall weight equivalent to that of Comparative Example 12, it is believed that below 4 kHz the transmission loss will be equivalent to that of Comparative Example 12, and above 4 kHz the transmission loss will also increase at 6 dB/oct, similar to the case below 4 kHz.

As described above, from Examples 1 and 2, it was found that the fiber-reinforced resin molding of the present invention is sufficiently filled with the reinforcing fibers 4 up to the tip 24 of the tubular portion 2, and has the characteristics of having higher compressive strength and being less susceptible to plastic deformation after compressive deformation compared to one in which the reinforcing fibers 4 are not sufficiently filled.
Furthermore, it was found that in Examples 3 to 9, the plates had higher bending strength than a flat plate having a similar weight, and the difference in bending strength was small regardless of the direction in which the plates were bent.
Furthermore, in Examples 10 to 12, it was found that the rigidity and energy of the plates were higher than that of flat plates of similar weight, and therefore the transmission loss could be increased without causing resonance in the low-frequency range where resonance should be avoided.
In addition, it was found from Examples 13 and 14 that the plate is less susceptible to the coincidence effect compared to a flat plate having a similar weight.

『Variations』
The present invention is not limited to the above embodiment, and other embodiments may be adopted. Therefore, a modified example of the present invention will be described with reference to Fig. 20. In the following description, the same reference numerals are used for the same parts as those in the above embodiment, and duplicated descriptions will be omitted.
The modified example shown in FIG. 20(a) differs from the embodiment in FIG. 1 in that the shape of the space in the tubular portion 2 is a truss shape in which equilateral triangles are alternately arranged.

By making the tubular section 2 an equilateral triangular prism, even if a shear load is applied to the tubular section 2, the load is dispersed as a tensile or compressive load at the vertices of each triangle, without generating bending moments that could lead to breakage on each side of each triangle. Compared to other regular polygons that can fill a plane, equilateral triangles have the greatest strength against shear loads. Therefore, although they are slightly less lightweight than regular hexagons, they can be made stronger.

In addition to the configuration in which each wall portion 21, 21... of the tubular portion 2 also serves as the connecting portions 22, 22... as in Figures 1 and 20(a), the tubular portion 2 may be provided with connecting portions 22, 22... consisting of a plurality of straight ribs in addition to the cylindrical wall portion 21 as shown in Figure 20(b).
Furthermore, the shape of the tubular portion 2 need not necessarily consist of a single polygon, but may be a combination of different types of polygons; for example, a combination of an octagon and a rectangle may be used, as shown in FIG. 20(c).
On the other hand, the tubular portion 2 does not need to be a space that is completely blocked by the walls 21, 21..., but may have unblocked portions 25, 25... in which a portion of the wall 21 is open and the opening is spatially connected to the outer periphery, as shown in Figure 20(d).

100, 110, 120, 130, 140 Fiber-reinforced resin molded body 1 Plate-shaped portion 2 Cylindrical portion
21 Wall
22 Connecting part
23 Bottom
24 Tip
25 Unblocked portion 3 Matrix resin 4 Reinforcement fiber 5 Opening device
51 Yarn feeding section
52 Reinforced fiber bundle 6 UD sheet manufacturing equipment
61 Resin sheet
62 Heating Roll
63 Cooling roll
64 UD Sheet
65 Take-up roll 7 Chopped sheet manufacturing device
71 Longitudinal cutter
72 Transverse cutter
73 Chopped prepreg
74 Conveyor
75 Adhesive Roll
76 Cooling roll
77 Chopped prepreg sheet 8 Press mold
81 Punch
82 Die 9 Simple Transmission Loss Measuring Device
91 Sound tube
92 Speakers
93 Measurement microphone
94 Computing equipment
95 Oil Clay
96 Glass wool
97 Sound absorbing sponge
10. Acoustic Intensity Method Measurement Equipment
101 Reverberation Room
102 Anechoic chamber
103 Speaker
104 Microphone
105 Sound Intensity Probe
106 Calculator

Claims (8)

A three-dimensional fiber-reinforced resin molding is provided by compression molding a prepreg made of a sheet-like fiber-reinforced resin, the prepreg comprising a matrix resin that is a thermoplastic resin and reinforcing fibers impregnated with the matrix resin,
The device has at least a flat plate-like portion and a plurality of cylindrical portions provided substantially perpendicularly to the plate-like portion,
The plurality of cylindrical portions have portions where the cylindrical portions are connected to each other, and the reinforcing fibers are filled from the bottom portion to the tip portion on the plate-shaped portion side ,
The reinforcing fibers at the tip end of the plate-like portion and the cylindrical portion are in a state in which only the reinforcing fibers that are thinly spread are oriented in a random direction at any position,
A fiber-reinforced resin molding, characterized in that, in a binary image analysis of a cross section at the tip of the tubular portion, the average area ratio of the reinforcing fibers in each tubular portion is -5% or more relative to the fiber volume content of the prepreg before compression molding . The reinforcing fibers are carbon fibers,
2. The fiber-reinforced resin molding according to claim 1, characterized in that in a binary image analysis of a cross section at the tip of the tubular portion, the difference in area ratio of the carbon fiber between the tubular portion located on the outermost side and the tubular portion located at the center in the entire fiber-reinforced resin molding is within 10%. 3. The fiber-reinforced resin molding according to claim 1 , wherein the cylindrical portion has a honeycomb shape made up of plane-packed regular hexagonal columns. 4. The fiber-reinforced resin molded product according to claim 1, wherein the plate-shaped portion has a thickness of 1 mm or more, and the tubular portion has a height of 4 mm or more. 5. The fiber-reinforced resin molding according to claim 1 , wherein the reinforcing fibers are laminated in a plurality of layers in the plate-like portion and the tubular portion so that the fiber direction has pseudo-isotropy. The plate-like portion and the cylindrical portion are formed by laminating a plurality of chopped prepregs cut into strips, and the direction of the reinforcing fibers is pseudo-isotropic,
The fiber-reinforced resin molding according to claim 5 , characterized in that the chopped prepreg is made of a UD sheet material in which the reinforcing fibers are thinly spread and aligned in a single direction, and the reinforcing fibers are impregnated with the matrix resin. an indenter load at the time of breakage in a bending test in which an indenter is pressed against the center of the tip end of the cylindrical portion;
The difference between the indenter load at the time of breakage in a bending test in which an indenter is pressed against the center of the surface of the plate-like portion on which the cylindrical portion is not provided, and the indenter load at the time of breakage in a bending test in which an indenter is pressed against the center of the surface of the plate-like portion on which the cylindrical portion is not provided,
7. The fiber-reinforced resin molding according to claim 1 , wherein the smaller indentation load is 50% or more of the larger indentation load. A method for producing a three-dimensional fiber-reinforced resin molding comprising a matrix resin which is a thermoplastic resin and reinforcing fibers impregnated with the matrix resin,
The thin-layered reinforcing fibers are aligned in a single direction, and the reinforcing fibers are impregnated with the matrix resin to form a UD sheet, which is then cut into strips to form a plurality of chopped prepregs.
The plurality of chopped prepregs are laminated so that the direction of the reinforcing fibers has pseudo-isotropy, and the matrix resin is melted and solidified to form a chopped prepreg sheet;
A plurality of the chopped prepreg sheets are laminated and arranged in a mold based on a shape having a flat plate-like portion and a plurality of cylindrical portions provided substantially perpendicularly from the plate-like portion, and the cylindrical portions have portions where the cylindrical portions are connected to each other;
The plurality of stacked chopped prepreg sheets are hot-pressed with the mold to melt the matrix resin of the plurality of stacked chopped prepreg sheets, and the reinforcing fibers and the molten matrix resin are filled from the bottom to the tip of the plate-shaped portion in the cylindrical portion,
During filling, the reinforcing fibers at the tip end of the plate-like portion and the cylindrical portion are in a state in which only the opened reinforcing fibers are oriented in a random direction at any position,
A method for producing a fiber-reinforced resin molding, characterized in that, in a binary image analysis of a cross section at the tip of the tubular portion of the fiber-reinforced resin molding after molding, the average area ratio of the reinforcing fibers in each tubular portion is -5% or more relative to the fiber volume content of the prepreg before compression molding .

Images