Speaker diaphragm and manufacturing method thereof

Abstract

To provide a speaker diaphragm etc. that suppresses the occurrence of valleys in frequency characteristics. [Solution] A speaker diaphragm includes first fibers, second fibers, and a matrix resin as reinforcing fibers, the first fibers being at least one of carbon fiber, aramid chop, and glass fiber, and the second fibers being at least one of aramid fibrid, acrylic pulp, cellulose nanofiber, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fiber, bamboo, hemp, chitin nanofiber, wool, and silk. This configuration can suppress the occurrence of a steep drop in frequency characteristics.

Description

[Technical Field]

[0001] The present disclosure relates to a speaker diaphragm and a method for manufacturing the same. [Background technology]

[0002] Generally, many materials have been proposed for speaker diaphragm materials, such as those made from short fibers such as pulp, those made from molded thin metal plates, and those made by injection molding thermoplastic resins such as polypropylene.

[0003] In recent years, speaker systems have become more powerful, requiring heat resistance and rigidity that can withstand heat generated by coils and large driving forces. Among the various diaphragm materials, fiber-reinforced plastic (FRP), which is made by impregnating woven or nonwoven fabric made from synthetic or natural fibers with a thermosetting resin such as epoxy resin or unsaturated polyester resin and molding it, is relatively superior, and diaphragms made from FRP are widely used. A common FRP diaphragm is one made by impregnating a reinforced woven fabric made from carbon fiber or glass fiber with epoxy resin as a matrix resin and then heat-curing it (see, for example, Patent Document 1).

[0004] Although such FRP diaphragms have a sufficiently high elastic modulus, their internal loss (tan δ) is extremely low, resulting in a steep peak at Fh (high-frequency resonance frequency), which significantly colored the sound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4049179 [Patent Document 2] Special Publication No. 7-32511 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to provide a speaker diaphragm that suppresses the occurrence of valleys in frequency characteristics, and a method for manufacturing the same.

[0007] According to a first aspect of the present invention, the speaker diaphragm includes a first fiber, a second fiber, and a matrix resin as reinforcing fibers, the first fiber being at least one of carbon fiber, aramid fiber, liquid crystal polyester fiber, ultra-high molecular weight polyethylene fiber, PBO fiber, glass fiber, basalt fiber, and metal fiber, and the second fiber being at least one of aramid fibrid, acrylic pulp, cellulose nanofiber, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fiber, bamboo, hemp, chitin nanofiber, wool, and silk, and the speaker diaphragm may contain 5 to 13 vol% of the second fiber and 20 to 30 vol% of the reinforcing fiber. This configuration can prevent a steep drop in frequency characteristics. A speaker diaphragm according to a second aspect of the present invention includes a speaker diaphragm including first fibers, second fibers, and a matrix resin as reinforcing fibers, wherein the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers, and the second fibers are at least one of aramid fibrids, acrylic pulp, cellulose nanofibers, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fibers, bamboo, hemp, chitin nanofibers, wool, and silk, and the speaker diaphragm contains 5 to 13 vol% of the second fibers, and the reinforcing fibers contain 20 to 50% of the second fibers by volume. This configuration can prevent a steep drop in frequency characteristics. Furthermore, according to a third aspect of the present invention, there is provided a speaker diaphragm including first fibers, second fibers, and a matrix resin as reinforcing fibers, wherein the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers, and the second fibers are at least one of aramid fibrids, acrylic pulp, cellulose nanofibers, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fibers, bamboo, hemp, chitin nanofibers, wool, and silk, and the reinforcing fibers contain 20% to 50% of the second fibers by volume, and can contain 20 to 30% by volume of the reinforcing fibers. This configuration can prevent a steep drop in frequency characteristics. Furthermore, according to the speaker diaphragm relating to the fourth aspect of the present invention, in any of the above aspects, the frequency characteristics exhibit a characteristic in which, for a specific frequency that is a minimum value of 12,500 Hz or less, there is no drop of 10 dB / 20 μPa or more in either a range of +250 Hz or -250 Hz of the specific frequency. Furthermore, according to a fifth aspect of the present invention, in any one of the above aspects, the loudspeaker diaphragm has a storage modulus of 7.1 GPa or more. Furthermore, according to a sixth aspect of the present invention, in the loudspeaker diaphragm in any one of the above aspects, the matrix resin is a thermoplastic resin. Furthermore, according to a seventh aspect of the present invention, in any of the above aspects, the thermoplastic resin is at least one of polyethylene, polypropylene, polyvinyl acetate, polymethyl methacrylate, polyethylene terephthalate (PET), nylon, polyamide, polyoxymethylene, polycarbonate, polybutylene terephthalate, phenoxy, polyetherimide, polyether ketone, thermoplastic polyimide, polysulfone, polyethersulfone, polyphenylene sulfide, and polyamideimide. Furthermore, according to an eighth aspect of the present invention, a method for manufacturing a speaker diaphragm includes the steps of forming a substrate including a nonwoven or woven fabric composed of first fibers, second fibers, and a matrix resin as reinforcing fibers, and heating and pressing the substrate to form a molded body, wherein the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers, and the second fibers are at least one of aramid fibrids, acrylic pulp, cellulose nanofibers, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fibers, bamboo, hemp, chitin nanofibers, wool, and silk, and the second fibers comprise 5 to 13 vol% of the second fibers and 20 to 30 vol% of the reinforcing fibers, thereby suppressing the occurrence of a steep drop in frequency characteristics. According to another aspect of the present invention, there is provided a speaker diaphragm including first fibers, second fibers, and a matrix resin as reinforcing fibers, wherein the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers, and the second fibers are at least one of aramid fibrids, acrylic pulp, cellulose nanofibers, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fibers, bamboo, hemp, chitin nanofibers, wool, and silk. This configuration can prevent a steep drop in frequency characteristics.

[0008] Furthermore, according to another aspect of the present invention, the speaker diaphragm exhibits a frequency characteristic in which, for a specific frequency of 12,500 Hz or less, there is no drop of 10 dB / 20 μPa or more in either a range of +250 Hz or a range of −250 Hz of the specific frequency.

[0009] Furthermore, according to another aspect of the present invention, in any one of the above aspects, the loudspeaker diaphragm contains 5 to 13 vol % of the second fibers.

[0010] Furthermore, in a loudspeaker diaphragm according to another aspect of the present invention, in any one of the above aspects, the reinforcing fibers contain the second fibers in a volume ratio of 20% to 50%.

[0011] Furthermore, according to another aspect of the present invention, the loudspeaker diaphragm of any of the above aspects contains 20 to 30 vol % of the reinforcing fibers, and with this configuration, it is possible to obtain a loudspeaker diaphragm in which the occurrence of valleys in the frequency characteristics is suppressed without changing the internal loss.

[0012] Furthermore, in accordance with another aspect of the present invention, in any one of the above aspects, the speaker diaphragm has a storage modulus of 7.1 GPa or more.

[0013] Furthermore, according to another aspect of the present invention, there is provided a speaker diaphragm in any one of the above aspects, wherein the matrix resin is a thermoplastic resin.

[0014] Furthermore, according to a speaker diaphragm according to another aspect of the present invention, in any of the above aspects, the thermoplastic resin is at least one of polyethylene, polypropylene, polyvinyl acetate, polymethyl methacrylate, polyethylene terephthalate (PET), nylon, polyamide, polyoxymethylene, polycarbonate, polybutylene terephthalate, phenoxy, polyetherimide, polyetherketone, thermoplastic polyimide, polysulfone, polyethersulfone, polyphenylene sulfide, and polyamideimide.

[0015] Furthermore, according to another aspect of the present invention, a method for manufacturing a speaker diaphragm includes the steps of forming a substrate including a nonwoven or woven fabric composed of first fibers, second fibers, and a matrix resin as reinforcing fibers, and heating and pressing the substrate to produce a molded body, wherein the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers, and the second fibers are at least one of aramid fibrids, acrylic pulp, cellulose nanofibers, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fibers, bamboo, hemp, chitin nanofibers, wool, and silk, thereby suppressing the occurrence of a steep drop in frequency characteristics. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a graph showing equal loudness curves. [Figure 2] 10 is a graph showing characteristics in which a drop of more than 10 dB / 20 μPa occurs within a range of ±250 Hz of a specific frequency a. [Figure 3] 4 is a graph showing frequency characteristics of the speaker diaphragm according to Example 1. [Figure 4] 10 is a graph showing frequency characteristics of the speaker diaphragm according to Example 2. [Figure 5] 10 is a graph showing frequency characteristics of the speaker diaphragm according to Example 3. [Figure 6] 10 is a graph showing frequency characteristics of the speaker diaphragm according to Example 4. [Figure 7] 10 is a graph showing frequency characteristics of the speaker diaphragm according to Example 5. [Figure 8] 10 is a graph showing frequency characteristics of the speaker diaphragm according to Comparative Example 1. [Figure 9] 10 is a graph showing frequency characteristics of a speaker diaphragm according to Comparative Example 2. [Figure 10] 10 is a graph showing frequency characteristics of a speaker diaphragm according to Comparative Example 3. [Figure 11] 10 is a graph showing frequency characteristics of speaker diaphragms according to Example 4 and Comparative Example 2 in an overlapping manner. [Figure 12] 10 is a graph showing the relationship between the blending amount of the second fiber and the ratio. DETAILED DESCRIPTION OF THE INVENTION

[0017] Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments described below are merely examples for embodying the technical concept of the present invention, and the present invention is not limited thereto. Furthermore, this specification in no way specifies the components set forth in the claims as components of the embodiments. The dimensions, materials, shapes, and relative positions of components described in the embodiments are not intended to limit the scope of the present invention, and are merely illustrative unless otherwise specified. The size and relative positions of components shown in the drawings may be exaggerated for clarity. Furthermore, in the following description, the same names and symbols indicate identical or similar components, and detailed descriptions will be omitted as appropriate. Furthermore, the elements constituting the present invention may be configured with the same components, so that one component serves multiple functions, or conversely, the functions of one component may be shared among multiple components.

[0018] Paper has traditionally been used as the diaphragm for speakers. However, in order to increase the power of speaker systems, diaphragms are required to have heat resistance, elastic modulus, and light weight (low specific gravity) to withstand the heat generated by the coil and large driving forces. In response to this demand, FRP diaphragms are known, which are made by impregnating a reinforced fiber woven fabric such as carbon fiber with a thermosetting resin such as epoxy resin as a matrix resin and then heat-curing the impregnated material (see, for example, Patent Document 1).

[0019] However, while such FRP diaphragms have an excellent elastic modulus, they have a problem in that they produce a steep peak at high resonance frequencies, which has a significant impact on the sound. In particular, they produce valleys in the frequency response, meaning that sounds in certain frequency ranges are not output sufficiently, making it difficult to accurately reproduce sounds across a wide frequency range.

[0020] Figure 1 shows equal loudness curves, which are the frequency characteristics of the sensation of loudness (loudness) of sound (Source: "Precise determination of two-dimensional equal loudness curves across the entire listening field"<https: / / www.nedo.go.jp / content / 100084730.pdf> As shown in this figure, the ISO 226:2D equal loudness curve specifies sound pressure levels (vertical axis) in the range of 20 to 12,500 Hz (horizontal axis), which corresponds to the human audible range. As can be seen, a valley appears in the curve in the high-frequency range. When speakers are actually made using FRP diaphragms, the frequency response changes depending on the FRP diaphragm used, and this dip at specific frequencies becomes steeper, affecting sound reproduction. Generally, speaker diaphragm materials are required to have excellent specific modulus E / ρ and internal loss tanδ. A higher specific modulus results in a better piston motion range, while a higher internal loss is expected to flatten the frequency response. However, materials with a high specific modulus tend to have lower internal loss, or the opposite characteristic, resulting in a trade-off between these two characteristics. Previous attempts to reduce this dip have been made by adjusting the internal loss of speaker diaphragms. However, since internal loss is a specific value depending on the material that makes up the speaker diaphragm, it is difficult to adjust and has not yet been completely eliminated.

[0021] The inventors of the present invention have therefore conducted various studies to reduce this sagging, and have discovered that the sagging can be suppressed by adding specific fibers to the reinforcing fibers that make up the speaker diaphragm made of fiber-reinforced resin, such as an FRP diaphragm, or by adjusting the amount of reinforcing fibers, which has led to the creation of the present invention.

[0022] In this specification, in order to quantitatively express the steep drop in frequency characteristics, a speaker diaphragm without a steep valley is defined as one that does not have a drop of more than 10 dB / 20 μPa in either the range of +250 Hz or -250 Hz of a specific frequency a [Hz] that is the minimum value as shown in Figure 2, within the range of 12,500 Hz or less in the frequency characteristics.

[0023] The speaker diaphragm according to the embodiment of the present invention includes reinforcing fibers and a matrix resin. For example, the reinforcing fibers can be used as a short fiber mat, a woven fabric, or a nonwoven fabric.

[0024] The reinforcing fiber content is preferably 20 to 30 vol %, which makes it possible to suppress the occurrence of valleys without increasing the internal loss.

[0025] The fiber volume fraction Vf is defined in ASTM D 3171 by the following formula:

[0026]

number

[0027] In the above formula, Rρ is the density of the resin, Fρ is the weighted average of the densities of the first fiber and the second fiber, weighted by weight, and Wf is the fiber weight content (i.e., the proportion of the weight of the reinforcing fiber in the weight of the composite). (storage modulus)

[0028] The storage modulus of the speaker diaphragm is preferably 7.1 GPa or more. (reinforced fiber)

[0029] The reinforcing fibers include first fibers and second fibers, and the second fibers are preferably contained in an amount of 20% to 50% by volume when the entire reinforcing fibers are taken as 100%.

[0030] The first fiber can be carbon fiber. Examples include PAN-based carbon fiber, pitch-based carbon fiber, and high-modulus carbon fiber. Alternatively, it can be organic synthetic fibers such as aramid fiber, liquid crystal polyester fiber, ultra-high molecular weight polyethylene fiber, and polyparaphenylene benzobisoxazole (PBO) fiber, as well as glass fiber, basalt fiber, and metal fiber. These fibers have the high modulus of elasticity required for speakers, generally 50 GPa or higher. These fibers may be discontinuous or continuous, and may be surface-treated, for example, by plating or modification, as needed.Furthermore, they may be commercially available products, recycled fibers from scraps, etc. The carbon fibers and organic synthetic fibers may also be made from biomass raw materials.

[0031] The second fiber can be an organic synthetic fiber such as aramid fibrid or acrylic pulp. Aramid fibrids are film-like or fibrous microparticles made of aramid, and are sometimes referred to as aramid pulp or fibrillated aramid fiber (see, for example, Japanese Patent Publication Nos. 1960-11851 and 1962-5752). Furthermore, at least one of animal fibers such as chitin nanofiber, wool, and silk, and plant fibers such as cellulose nanofiber, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fiber, bamboo, and hemp can be used. These fibers are more flexible than the first fiber, often contain finely divided (fibrillated) fibers, and have an apparent modulus of elasticity generally less than 50 GPa. These fibers may be commercially available or recycled from scraps. Furthermore, the organic synthetic fiber may be made from biomass materials. Thus, the addition of the second fiber can suppress a steep drop in frequency characteristics. Aramid pulp is particularly preferred because it can suppress the occurrence of abrupt drops in sound pressure level over a wide frequency range. (matrix resin)

[0032] As the matrix resin, thermoplastic resins and uncured thermosetting resins can be used. Thermoplastic resins are particularly preferred. Examples of thermoplastic resins that can be used include polyethylene, polypropylene, polyvinyl acetate, polymethyl methacrylate, polyethylene terephthalate (PET), nylon, polyamide, polyoxymethylene, polycarbonate, polybutylene terephthalate, phenoxy, polyetherimide, polyetherketone, thermoplastic polyimide, polysulfone, polyethersulfone, polyphenylene sulfide, polyamideimide, and polyimide. Examples of thermosetting resins that can be used include epoxy, unsaturated polyester, urea, melamine, phenol, and diallyl phthalate. The matrix resin may be modified or a mixture of two or more types. It may also be made from recycled or biomass-derived materials. [Manufacturing method for speaker diaphragms] (Base material formation process)

[0033] A method for manufacturing such a speaker diaphragm includes the following steps. First, a substrate is formed containing a nonwoven or woven fabric composed of first fibers, second fibers, and a matrix resin as reinforcing fibers. The matrix resin may be blended in the form of resin fibers or particles when the substrate is formed, or may be impregnated into the reinforcing fibers, or may be impregnated after the formation of a base fabric of the reinforcing fibers. From the viewpoint of simplifying the manufacturing process, it is preferable to blend the matrix resin as resin fibers when the substrate is formed. The substrate may also contain a binder component. (molding process) To produce a speaker diaphragm, the substrate is heated and pressurized to produce a molded body. During this process, the resin blended into the substrate flows and solidifies to become a matrix resin. The molded body can be processed into the shape of a diaphragm after the heat-pressing process, or it can be pressed using a mold of the desired shape. This can prevent a steep drop in frequency characteristics. [Example]

[0034] Below, speaker diaphragms were produced according to Examples 1 to 5 and Comparative Examples 1 to 3. In all Examples and Comparative Examples, PET was used as the matrix resin.

[0035] The frequency characteristics of the speaker diaphragms obtained in each of the examples and comparative examples were measured using a portable acoustic vibration multi-analyzer in accordance with JIS C5532:2014.

[0036] Furthermore, the density of each sample was measured in accordance with JIS P8118:2014.

[0037] Furthermore, the storage modulus (GPa) and internal loss (tanδ) of Example 4 and Comparative Examples 1 to 3 were measured. The storage modulus was measured in accordance with JIS K7244-4:1999 using a dynamic viscoelasticity measuring device (METRAVIB; DMA+100) under tension mode conditions. The measurement frequency was 1 Hz, and the dynamic strain amplitude was 0.01%.

[0038] The measurement results of the frequency characteristics of each sample are shown in Figures 3 to 11. In these figures, Figure 3 shows graphs of the frequency characteristics of each speaker diaphragm according to Example 1, Figure 4 shows graphs of Example 2, Figure 5 shows graphs of Example 3, Figure 6 shows graphs of Example 4, Figure 7 shows graphs of Example 5, Figure 8 shows graphs of Comparative Example 1, Figure 9 shows graphs of Comparative Example 2, and Figure 10 shows graphs of Comparative Example 3. For comparison, Figure 11 shows a graph in which the frequency characteristics of Example 4 and Comparative Example 2 are superimposed. In Figures 8 to 10, the areas surrounded by dashed lines indicate valleys in the frequency characteristics.

[0039] In Example 1, 12.5 vol% carbon fibers with a fiber length of 6 mm were used as the first fibers, and 12.5 vol% aramid pulp was used as the second fibers. The valleys of the frequency characteristics of the obtained speaker diaphragm are shown in the area circled by a dashed line in Figure 3, with a minimum frequency of 66 dB at 10,500 Hz, 76 dB at -250 Hz (left side in Figure 3), and 74 dB at +250 Hz (right side in Figure 3). The differences from the minimum frequencies were 10 dB and 8 dB, respectively, and the latter showed excellent characteristics without a drop of more than 10 dB / 20 μPa, in other words, without a steep valley.

[0040] Similarly, in Example 2, 20 vol% carbon fiber and 10 vol% aramid pulp were used. As shown in Figure 4, the valley of the frequency characteristics of the obtained speaker diaphragm showed a minimum frequency of 80 dB at 1800 Hz, 88 dB at -250 Hz (left side in Figure 4), and 93 dB at +250 Hz (right side in Figure 4). The differences from the minimum frequency were 8 dB and 13 dB, respectively, and the former showed characteristics without a drop of more than 10 dB / 20 μPa.

[0041] Similarly, Example 3 used 20 vol% carbon fiber and 5 vol% aramid pulp. The valley of the frequency characteristics of the obtained speaker diaphragm showed a minimum frequency of 81 dB at 1800 Hz, 90 dB at -250 Hz, and 93 dB at +250 Hz, as shown in Figure 5. The differences from the minimum frequency were 9 dB and 12 dB, respectively, and the former also showed a characteristic of no drop of more than 10 dB / 20 μPa.

[0042] Furthermore, in Example 4, 15 vol% of carbon fiber and 5 vol% of aramid pulp were used. The valley of the frequency characteristics of the obtained speaker diaphragm was 84 dB at the minimum frequency of 1700 Hz, 93 dB at -250 Hz, and 92 dB at +250 Hz, as shown in Figure 6. The differences from the minimum frequency were 9 dB and 8 dB, respectively, and all showed excellent characteristics without drops of more than 10 dB / 20 μPa or steep valleys.

[0043] Furthermore, in Example 5, 15 vol% carbon fiber was used, and 5 vol% acrylic pulp was used as the second fiber instead of aramid pulp. The valley of the frequency characteristics of the obtained speaker diaphragm showed a minimum frequency of 80 dB at 1600 Hz, 94 dB at -250 Hz, and 84 dB at +250 Hz, as shown in Figure 7. The differences from the minimum frequency were 14 dB and 4 dB, respectively, and the latter showed characteristics without a drop of more than 10 dB / 20 μPa.

[0044] On the other hand, in Comparative Example 1, the reinforcing fiber consisted solely of 15 vol% carbon fiber, and no secondary fiber was added. The valley of the frequency characteristics of the obtained speaker diaphragm showed a minimum frequency of 64 dB at 10,400 Hz, 78 dB at -250 Hz, and 74 dB at +250 Hz, as shown in Figure 8. The differences from the minimum frequency were 14 dB and 10 dB, respectively, and both showed characteristics with a drop of 10 dB / 20 μPa or more.

[0045] In Comparative Example 2, only 20 vol% of carbon fiber was used as the reinforcing fiber. The valley of the frequency characteristics of the obtained speaker diaphragm was 65 dB at the minimum frequency of 8100 Hz, as shown in Figure 9, and 78 dB at -250 Hz and +250 Hz. The difference from the minimum frequency was 13 dB in both cases, indicating a drop of more than 10 dB / 20 μPa.

[0046] Finally, in Comparative Example 3, 15 vol% carbon fiber was used as the first fiber, and 15 vol% aramid pulp was used as the second fiber. The valley of the frequency characteristics of the obtained speaker diaphragm showed a minimum frequency of 81 dB at 1700 Hz, 93 dB at -250 Hz, and 95 dB at +250 Hz, as shown in Figure 10. The differences from the minimum frequency were 12 dB and 14 dB, respectively, and both showed characteristics with a drop of 10 dB / 20 μPa or more.

[0047] 11 shows a graph in which the frequency characteristics of the speaker diaphragms according to Example 4 and Comparative Example 2, both of which contain 20 vol% reinforcing fiber, are superimposed. As shown in this figure, a large valley occurs near 8100 Hz in Comparative Example 2, whereas the occurrence of such a valley is suppressed in Example 4, confirming that a speaker diaphragm with improved sound reproducibility has been obtained.

[0048] Table 1 shows the results of measuring the composition and properties (density, storage modulus, and internal loss) of each example and comparative example. FIG. 12 shows the relationship between the blending amount of the second fibers and the ratio of the second fibers to the total reinforcing fibers, i.e., the value obtained by dividing the blending amount of the second fibers by the total reinforcing fibers. In this figure, examples are plotted with ◯ and comparative examples are plotted with ×.

[0049] [Table 1]

[0050] Comparing Example 4 and Comparative Example 1, both contain 20 vol% reinforcing fibers, but Example 4, which contains less carbon fiber as the first fiber, has a higher storage modulus. Furthermore, Example 4, which contains 5 vol% aramid pulp as the second fiber, has a higher storage modulus than Comparative Example 2, which contains 15 vol% carbon fiber and 5 vol% carbon fiber added to make it 20 vol%. From the above, it was confirmed that the storage modulus can be improved without increasing the amount of carbon fiber.

[0051] On the other hand, in Comparative Example 3, in which 15 vol% of aramid pulp was added as the second fiber, the storage modulus was lower than in Example 4, in which 5 vol% of aramid pulp was added. This revealed that adding too much aramid pulp reduces the storage modulus. Therefore, from the viewpoint of increasing the storage modulus, it is preferable to use less second fibers than first fibers. According to the examples, a good storage modulus was obtained when the second fibers were 25% to 50% of the first fibers. [Industrial Applicability]

[0052] The speaker diaphragm and its manufacturing method according to the present invention can be suitably used for any appropriate speaker, such as an in-vehicle speaker, a speaker for outdoor use such as a PA speaker, or a speaker for earphones.

Claims

1. A speaker diaphragm, As reinforcing fibers, first fibers and second fibers, A matrix resin; Including, the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers; the second fiber is at least one of aramid fibrid, acrylic pulp, cellulose nanofiber, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fiber, bamboo, hemp, chitin nanofiber, wool, and silk; The second fibers are contained in an amount of 5 to 13 vol %, A speaker diaphragm containing 20 to 30 vol % of the reinforcing fibers.

2. A speaker diaphragm, As reinforcing fibers, first fibers and second fibers, A matrix resin; Including, the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers; the second fiber is at least one of aramid fibrid, acrylic pulp, cellulose nanofiber, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fiber, bamboo, hemp, chitin nanofiber, wool, and silk; The second fibers are contained in an amount of 5 to 13 vol %, The speaker diaphragm comprises the reinforcing fibers containing the second fibers in an amount of 20% to 50% by volume.

3. A speaker diaphragm, As reinforcing fibers, first fibers and second fibers, A matrix resin; Including, the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers; the second fiber is at least one of aramid fibrid, acrylic pulp, cellulose nanofiber, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fiber, bamboo, hemp, chitin nanofiber, wool, and silk; The reinforcing fibers contain the second fibers in a volume ratio of 20% to 50%; A speaker diaphragm containing 20 to 30 vol % of the reinforcing fibers.

4. The speaker diaphragm according to any one of claims 1 to 3, A speaker diaphragm that exhibits frequency characteristics in which, for a specific frequency that is a minimum value below 12,500 Hz, there is no drop of 10 dB / 20 μPa or more within a range of +250 Hz or -250 Hz of the specific frequency.

5. The speaker diaphragm according to any one of claims 1 to 4, A speaker diaphragm having a storage modulus of 7.1 GPa or more.

6. The speaker diaphragm according to any one of claims 1 to 5, The speaker diaphragm, wherein the matrix resin is a thermoplastic resin.

7. The speaker diaphragm according to claim 6, The speaker diaphragm is made of at least one of the thermoplastic resins polyethylene, polypropylene, polyvinyl acetate, polymethyl methacrylate, polyethylene terephthalate (PET), nylon, polyamide, polyoxymethylene, polycarbonate, polybutylene terephthalate, phenoxy, polyetherimide, polyetherketone, thermoplastic polyimide, polysulfone, polyethersulfone, polyphenylene sulfide, and polyamideimide.

8. A method for manufacturing a speaker diaphragm, forming a substrate including a nonwoven fabric or a woven fabric composed of first fibers, second fibers, and a matrix resin as reinforcing fibers; a step of heating and pressing the substrate to form a molded body; Including, the first fibers are at least one of carbon fibers, aramid fibers, liquid crystal polyester fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, glass fibers, basalt fibers, and metal fibers; the second fiber is at least one of aramid fibrid, acrylic pulp, cellulose nanofiber, softwood pulp, hardwood pulp, linter pulp, rayon, fruit fiber, bamboo, hemp, chitin nanofiber, wool, and silk; The second fibers are contained in an amount of 5 to 13 vol %, A method for producing a speaker diaphragm containing 20 to 30 vol % of the reinforcing fibers.

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