JP7809535B2 - Speaker diaphragm and manufacturing method thereof - Google Patents

Description

This disclosure relates to a speaker diaphragm and a method for manufacturing the same.

Generally, many speaker diaphragm materials have been proposed, including those made from short fibers such as pulp, those molded from thin metal sheets, and those injection-molded from thermoplastic resins such as polypropylene.

In recent years, speaker systems have become more powerful, requiring heat resistance and rigidity to withstand the heat generated by the coil 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, 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).

Such FRP diaphragms have a sufficiently high elastic modulus, but extremely low internal loss (tan δ). As a result, a steep peak occurs at Fh (high-frequency resonance frequency), which significantly colores the tone.

Patent No. 4049179 Special Publication No. 7-32511

One of the objectives of this disclosure is to provide a speaker diaphragm that suppresses the occurrence of valleys in frequency characteristics, and a method for manufacturing the same.

Means for solving the problem and effects of the invention

According to a first aspect of the present invention, the speaker diaphragm includes reinforcing fibers including first fibers, second fibers, and a matrix resin, 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 suppress the occurrence of a steep drop in frequency characteristics.

Furthermore, according to the speaker diaphragm of the second aspect of the present invention, the frequency characteristics exhibit no drop of 10 dB/20 μPa or more in either a range of +250 Hz or -250 Hz of a specific frequency of 12,500 Hz or less.

Furthermore, according to the speaker diaphragm according to the third aspect of the present invention, the second fibers are contained in an amount of 5 to 13 vol% in any of the above aspects.

Furthermore, according to the fourth aspect of the present invention, in the speaker diaphragm of any of the above aspects, the reinforcing fibers contain 20% to 50% by volume of the second fibers.

Furthermore, according to a fifth aspect of the present invention, the loudspeaker diaphragm of any of the above aspects contains 20 to 30 vol% of the reinforcing fibers. This configuration makes it possible to obtain a loudspeaker diaphragm that suppresses the occurrence of valleys in the frequency characteristics without changing the internal loss.

Furthermore, according to the speaker diaphragm according to the sixth aspect of the present invention, in any of the above aspects, the storage modulus is 7.1 GPa or more.

Furthermore, according to the seventh aspect of the present invention, in the speaker diaphragm of any of the above aspects, the matrix resin is a thermoplastic resin.

Furthermore, according to the speaker diaphragm of an eighth 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.

Furthermore, a method for manufacturing a speaker diaphragm according to a ninth aspect of the present invention includes the steps of forming a substrate containing a nonwoven or woven fabric composed of first fibers, second fibers, and a matrix resin as reinforcing fibers, and heating and pressurizing 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. This makes it possible to suppress the occurrence of a steep drop in frequency characteristics.

1 is a graph showing equal loudness curves. 10 is a graph showing characteristics in which a drop of more than 10 dB/20 μPa occurs in the range of ±250 Hz of a specific frequency a. 4 is a graph showing frequency characteristics of the speaker diaphragm according to Example 1. 10 is a graph showing frequency characteristics of a speaker diaphragm according to Example 2. 10 is a graph showing frequency characteristics of the speaker diaphragm according to Example 3. 10 is a graph showing frequency characteristics of a speaker diaphragm according to Example 4. 10 is a graph showing frequency characteristics of a speaker diaphragm according to Example 5. 10 is a graph showing frequency characteristics of the speaker diaphragm according to Comparative Example 1. 10 is a graph showing frequency characteristics of a speaker diaphragm according to Comparative Example 2. 10 is a graph showing frequency characteristics of a speaker diaphragm according to Comparative Example 3. 10 is a graph showing frequency characteristics of speaker diaphragms according to Example 4 and Comparative Example 2 superimposed on each other. 10 is a graph showing the relationship between the blending amount of the second fiber and the ratio.

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 to these. Furthermore, this specification in no way specifies the components set forth in the claims as components of the embodiments. Unless otherwise specified, the dimensions, materials, shapes, and relative locations of the components described in the embodiments are not intended to limit the scope of the present invention, and are merely illustrative examples. Note that 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 components that are identical or of similar quality, and detailed description will be omitted as appropriate. Furthermore, the elements constituting the present invention may be configured with the same components, with one component serving multiple functions, or conversely, the function of one component may be shared by multiple components.

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, elasticity, and light weight (low specific gravity) to withstand the heat generated by the coil and large driving forces. In response to this, 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 it (see, for example, Patent Document 1).

However, while such FRP diaphragms have an excellent elastic modulus, they suffer from the problem of producing a steep peak at high resonance frequencies, which has a significant impact on the sound. In particular, there is a problem in that certain frequency ranges of sound are not output sufficiently in the frequency characteristics, creating valleys, so to speak, which means that sounds across a wide frequency range cannot be accurately reproduced.

Figure 1 shows equal loudness curves, which represent the frequency characteristics of loudness (the perception of loudness). (Source: "Precise Determination of Two-Dimensional Equal Loudness Curves for the Whole Listening Range" <https://www.nedo.go.jp/content/100084730.pdf>) As shown in this figure, ISO 226: Two-Dimensional Equal Loudness Curves 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, valleys appear in the curves in the high-frequency range. When speakers are actually made using FRP diaphragms, the frequency characteristics change depending on the FRP diaphragm used, and these drops at specific frequencies become steeper, affecting sound reproduction. Generally, speaker diaphragm materials are required to have excellent specific elastic modulus E/ρ and internal loss tanδ. A higher specific elastic modulus results in a more favorable piston motion range, while a higher internal loss is expected to flatten the playback frequency characteristics. However, in terms of material properties, materials with a high specific modulus of elasticity have low internal loss, or the opposite characteristic, with these two properties being in a trade-off relationship. Previously, attempts have been made to reduce this drop by adjusting the internal loss of speaker diaphragms. However, because internal loss is a unique value depending on the material that makes up the speaker diaphragm, it is difficult to adjust and has not yet been completely eliminated.

The inventors of the present application therefore conducted various studies to find ways to reduce this sagging, and discovered that adding specific fibers to the reinforcing fibers that make up speaker diaphragms made of fiber-reinforced resin, such as FRP diaphragms, or adjusting the amount of reinforcing fibers, could suppress this sagging, leading to the creation of the present invention. This is explained below.

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 in which, in the frequency range below 12,500 Hz, there is no 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 corresponds to the minimum value as shown in Figure 2.

A speaker diaphragm according to an 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, woven fabric, or nonwoven fabric.

It is preferable to include 20 to 30 vol% of reinforcing fibers. This can suppress the occurrence of valleys without increasing internal loss.

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

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)

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

The reinforcing fibers include first fibers and second fibers. The second fibers preferably account for 20% to 50% by volume when the total reinforcing fibers are taken as 100%.

The first fiber can be carbon fiber. For example, PAN-based carbon fiber, pitch-based carbon fiber, high-modulus carbon fiber, etc. can be used. Alternatively, 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 can also be used. 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.

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 for details of aramid fibrids). 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 softer than the first fiber, often contain finely divided (fibrillated) fibers, and have an apparent modulus of elasticity of generally less than 50 GPa. These fibers may be commercially available products or fibers recycled from scraps. Furthermore, the organic synthetic fiber may be produced from biomass materials. In this way, by adding the second fiber, it is possible to suppress the occurrence of a steep drop in the frequency characteristics. Aramid pulp is particularly preferable because it can suppress the occurrence of a steep drop in sound pressure level over a wide frequency band.
(matrix resin)

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.
[Method of manufacturing speaker diaphragms]
(Base material formation process)

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]

Speaker diaphragms were produced in Examples 1 to 5 and Comparative Examples 1 to 3. PET was used as the matrix resin in all Examples and Comparative Examples.

The frequency characteristics of the speaker diaphragms obtained in each example and comparative example were measured. Frequency measurements were performed using a portable acoustic vibration multi-analysis device in accordance with JIS C5532:2014.

Furthermore, the density of each sample was measured. Density measurements were performed in accordance with JIS P8118:2014.

Furthermore, the storage modulus (GPa) and internal loss (tan δ) 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%.

The measurement results of the frequency characteristics of each sample are shown in Figures 3 to 11. In these figures, Figure 3 shows a graph of the frequency characteristics of each speaker diaphragm for Example 1, Figure 4 for Example 2, Figure 5 for Example 3, Figure 6 for Example 4, Figure 7 for Example 5, Figure 8 for Comparative Example 1, Figure 9 for Comparative Example 2, and Figure 10 for 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.

In Example 1, 12.5 vol% carbon fiber with a fiber length of 6 mm was used as the first fiber, and 12.5 vol% aramid pulp was used as the second fiber. The valley of the frequency characteristics of the resulting speaker diaphragm is 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, with the latter exhibiting excellent characteristics with no drop of more than 10 dB/20 μPa, in other words, no steep valleys.

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 resulting 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 frequencies were 8 dB and 13 dB, respectively, with the former showing characteristics without a drop of more than 10 dB/20 μPa.

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

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

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. As shown in Figure 7, the valley of the frequency characteristics of the resulting speaker diaphragm showed a minimum frequency of 80 dB at 1600 Hz, 94 dB at -250 Hz, and 84 dB at +250 Hz. The differences from the minimum frequencies were 14 dB and 4 dB, respectively, with the latter showing characteristics without a drop of more than 10 dB/20 μPa.

In contrast, in Comparative Example 1, the reinforcing fiber consisted solely of 15 vol% carbon fiber, with no secondary fiber added. As shown in Figure 8, the valleys in the frequency characteristics of the resulting speaker diaphragm showed a minimum frequency of 64 dB at 10,400 Hz, 78 dB at -250 Hz, and 74 dB at +250 Hz. The differences from the minimum frequencies were 14 dB and 10 dB, respectively, and both showed characteristics with a drop of more than 10 dB/20 μPa.

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

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. As shown in Figure 10, the valley of the frequency characteristics of the resulting speaker diaphragm showed a minimum frequency of 81 dB at 1700 Hz, 93 dB at -250 Hz, and 95 dB at +250 Hz. The differences from the minimum frequencies were 12 dB and 14 dB, respectively, and both showed characteristics with a drop of more than 10 dB/20 μPa.

Figure 11 shows a graph overlaying the frequency characteristics of speaker diaphragms according to Example 4 and Comparative Example 2, both of which contain 20 vol% reinforcing fiber. As shown in this figure, a large valley occurs near 8,100 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.

Table 1 shows the results of measuring the composition and properties (density, storage modulus, and internal loss) of each example and comparative example. Figure 12 also shows the relationship between the amount of second fiber blended and the ratio of second fiber to the total reinforcing fiber, i.e., the value obtained by dividing the amount of second fiber blended by the total reinforcing fiber. In this figure, examples are plotted with a circle and comparative examples with an x.

Comparing Example 4 and Comparative Example 1, both contain 20 vol% reinforcing fiber, 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 then 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.

On the other hand, in Comparative Example 3, in which 15 vol% aramid pulp was added as the second fiber, the storage modulus was lower than in Example 4, in which 5 vol% aramid pulp was added. This demonstrates that adding too much aramid pulp reduces the storage modulus. Therefore, from the perspective of increasing the storage modulus, it is preferable to use less second fiber than first fiber. In the examples, a good storage modulus was obtained when the second fiber was 25% to 50% of the first fiber.

The speaker diaphragm and manufacturing method thereof according to the present invention can be suitably used for any suitable speaker, such as an in-car speaker, a speaker for outdoor use such as a PA speaker, or a speaker for earphones.

Claims (8)

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;
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 . The speaker diaphragm according to claim 1 ,
A speaker diaphragm containing the second fibers in an amount of 5 to 13 vol %. The speaker diaphragm according to claim 2 ,
The speaker diaphragm comprises the reinforcing fibers containing the second fibers in an amount of 20% to 50% by volume. The speaker diaphragm according to claim 2 or 3 ,
A speaker diaphragm containing 20 to 30 vol % of the reinforcing fibers. 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. The speaker diaphragm according to any one of claims 1 to 5 ,
The speaker diaphragm, wherein the matrix resin is a thermoplastic resin. 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. 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;
A method for manufacturing a speaker diaphragm that exhibits frequency characteristics 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 within a range of +250 Hz or -250 Hz of the specific frequency.