Diaphragm for electroacoustic transducer

Abstract

[Problem] To provide an electro-acoustic transducer diaphragm which maintains a high Young's modulus and realizes moderate internal loss. [Solution] An electro-acoustic transducer diaphragm 1 includes a substrate 10 which is constituted of a fiber material based on cellulose, and which has formed therein a mixture layer 11 of a fiber material 20 and silk nanofibers 21.

Description

Technical Field

[0001] The present invention relates to a diaphragm for an electroacoustic transducer used in speakers, microphones, and the like.

Background Art

[0002] In diaphragms for electroacoustic transducers, it is required to have low density, high Young's modulus, appropriate internal loss, etc., and a material having optimal physical properties is appropriately selected according to the applications of speakers and microphones. There are various materials for diaphragms, and cellulose fibers (mainly pulp) are often used from the viewpoints of performance, cost, etc., but there are cases where desired physical properties cannot be obtained.

[0003] Therefore, in such diaphragms, another material is applied to the surface layer of a base material made of cellulose fibers to compensate for the above physical properties. For example, Patent Document 1 describes a diaphragm in which cellulose nanofibers are applied to the surface layer of a base material layer formed by papermaking cellulose fibers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Patent Document 1, although cellulose nanofibers are coated on the surface layer of the base material layer, in this case, there is a problem that the internal loss (tanδ) decreases.

[0006] The present invention has been proposed in view of the above, and an object thereof is to provide a diaphragm for an electroacoustic transducer that realizes an appropriate Young's modulus and internal loss with respect to the physical property values of the base material.

Means for Solving the Problems

[0007] In order to achieve the above object, in the diaphragm for an electroacoustic transducer according to the present invention, in the base material composed of a fiber material mainly containing cellulose fibers, a mixed layer in which the fiber material and silk nanofibers are mixed is formed.

[0008] Further, in the diaphragm for an electroacoustic transducer, the mixed layer may be formed on the surface layer side of the base material.

[0009] Further, in the diaphragm for an electroacoustic transducer, the average fiber length of the silk nanofibers may be 10 μm or less.

[0010] Further, in the diaphragm for an electroacoustic transducer, the mixed layer may be formed by spraying a suspension containing the silk nanofibers onto the other surface of the base material while sucking and dehydrating from one surface side of the base material.

[0011] Further, in the diaphragm for an electroacoustic transducer, a reinforcing layer in which the fiber material, the silk nanofibers, and a reinforcing material are mixed may be further formed on the surface layer of the base material.

[0012] Further, in the diaphragm for an electroacoustic transducer, the reinforcing material may be made of a material containing mica.

[0013] Further, in the diaphragm for an electroacoustic transducer, the reinforcing material may be made of a material containing cellulose nanofibers.

[0014] Further, in the diaphragm for an electroacoustic transducer, the reinforcing layer may be formed in the mixed layer by spraying a suspension containing the reinforcing material and the silk nanofibers onto the other surface of the base material while sucking and dehydrating from one surface side of the base material.

Advantages of the Invention

[0015] According to the present invention as described above, it is possible to provide a diaphragm for an electroacoustic transducer that realizes an appropriate Young's modulus and internal loss with respect to the physical property values of the base material.

Brief Description of the Drawings

[0016]

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Modes for Carrying Out the Invention

[0017] Hereinafter, a diaphragm for an electroacoustic transducer according to an embodiment of the present invention (hereinafter, may also be abbreviated as a diaphragm) will be described.

[0018] Figure 1 is a cross-sectional view of a diaphragm for an electroacoustic transducer according to an embodiment of the present invention. Further, Figure 2 is a schematic diagram of a cross-section of the diaphragm according to Example A1 of the present invention described later, and Figure 3 is an enlarged image of the cross-section of the diaphragm taken with a microscope. Further, Figure 4 is a schematic diagram of a cross-section of the diaphragm according to Example A3 of the present invention described later, and Figure 5 is an enlarged image of the cross-section of the diaphragm taken with a microscope.

[0019] The diaphragm 1 (diaphragm for an electroacoustic transducer) shown in Figure 1 is a diaphragm for a speaker according to an embodiment of the present invention and has a conical shape (frustum of a cone). The smaller-diameter opening side of the diaphragm 1 is attached to a vibration source of a speaker such as a voice coil (not shown). The inner surface of the conical portion of the diaphragm 1 becomes the sound radiation surface (front surface) and the surface visible from the outside. On the other hand, various devices of the speaker (not shown) are arranged on the outer surface (back surface) side of the conical portion of the diaphragm 1.

[0020] First, the configuration of the diaphragm 1 according to the present invention will be described with reference to Figures 2 and 3 according to Example A1 of the present invention. The diaphragm 1 has a mixed layer 11 in which the fiber material and silk nanofibers 21 are mixed on a base material 10 made of a fiber material mainly composed of cellulose fibers 20. Note that the diaphragms according to Example A1 and Example A3 described later have a reinforcing layer 12 in which the fiber material, silk nanofibers 21, and mica 22 as a reinforcing material are mixed on the surface layer on the front surface side of the base material 10.

[0021] Here, the base material 10 is obtained by preparing a cellulose fiber 20 (fiber material) beaten at a beating degree of 10°SR or more and 85°SR or less and forming a sheet in a diaphragm shape. The cellulose fiber 20 of the present embodiment is a mixture of wood pulp made from coniferous trees and non-wood pulp made from kenaf. As the cellulose fiber 20, other pulp such as wood pulp or non-wood pulp can be used, and a mixture of wood pulp and non-wood pulp, wood pulp alone, or non-wood pulp alone may be used. Further, the average fiber diameter (maximum width) of the cellulose fiber 20 is preferably 5 μm or more and 90 μm or less. Note that the fiber length of the cellulose fiber 20 is not particularly limited, and a fiber length used for general papermaking can be appropriately selected.

[0022] As shown in FIG. 2, the mixed layer 11 is a layer in which silk nanofibers 21 are mixed in the gaps between the cellulose fibers 20. The average fiber diameter of the silk nanofibers 21 is about 100 nm at the nanolevel, which is finer than the average fiber diameter of the cellulose fibers 20 and has entered between the cellulose fibers 20. In the example shown in the schematic diagram of FIG. 2, the silk nanofibers 21 are present from the outermost surface of the base material 10 to the vicinity of the central portion in the thickness direction.

[0023] As shown in FIG. 2, the reinforcing layer 12 is a layer in which silk nanofibers 21 and mica 22 as a reinforcing material are mixed in the surface layer on the front side of the base material 10. Since the particle size of the mica 22 is larger than the average fiber diameter of the silk nanofibers 21, it does not penetrate deeply into the base material 10 and remains on the surface layer of the base material 10. The mica 22 can increase the rigidity of the surface layer of the diaphragm 1 and increase the propagation speed of the diaphragm surface layer.

[0024] Note that FIG. 2 is a schematic diagram depicting the diaphragm 1. In FIG. 2, each element is shown with exaggeration compared to the actual dimensions in order to clearly show the relationship among the cellulose fiber 20, the silk nanofiber 21, and the mica 22. Actually, as shown in FIG. 3, while the thickness of the base material 10 is 0.2 mm or more and 0.25 mm or less on average, the mixed layer 11 is formed on the surface layer of the base material 10, and the thickness of the mixed layer 11 is about 0.1 mm on average, which is about half of that of the base material 10. In FIG. 3, in order to facilitate the identification of the mixed layer 11 of the base material 10, only the silk nanofiber 21 is dyed without dyeing the cellulose fiber 20 of the base material 10 to form the diaphragm 1. As shown in FIG. 3, it can be confirmed that the front side of the diaphragm 1 is colored, and the mixed layer 11 is formed on the front side of the diaphragm 1 by the silk nanofiber 21.

[0025] While suction-dewatering from the back (one side) of the paper-made base material 10, a suspension containing silk nanofibers 21 and mica 22 in water is sprayed onto the front (the other side) of the base material 10, for example, by the spray coating method, so that the silk nanofibers 21 and mica 22 can penetrate into the surface layer on the front side of the base material 10. Thereafter, through a forming and drying process such as hot pressing, the diaphragm 1 having the mixed layer 11 is produced. In this way, in a state where suction-dewatering is performed from the back side of the base material 10, the suspension of the silk nanofibers 21 and mica 22 is sprayed onto the front of the base material 10 and applied thereto, so that the arrangement of the cellulose fibers 20 of the base material 10 is not disturbed by the moisture of the suspension, and the silk nanofibers 21 and mica 22 can smoothly land on the surface layer of the base material 10, and the reinforcing layer 12 in which the cellulose fibers 20, silk nanofibers 21, and mica 22 are mixed can be thinly and uniformly formed. Also, by suction-dewatering from the back side of the paper-made base material 10, only the finer silk nanofibers 21 among the silk nanofibers 21 and mica 22 contained in the sprayed suspension can penetrate deeply between the cellulose fibers 20, and the mixed layer 11 can be formed deeper than the reinforcing layer 12. On the other hand, the particle size of the mica 22 is larger than the average fiber diameter of the silk nanofibers 21 and larger than the gap between the cellulose fibers 20. Therefore, although a part of the mica 22 enters the gap, most of the mica 22 tends to remain on the surface layer of the base material 10, and by the uniform presence of the mica 22 on the surface layer, the reinforcing layer 12 can be formed on the front side of the mixed layer 11. Note that the suspension does not necessarily have to contain the mica 22 which is a reinforcing material, and a suspension containing the silk nanofibers 21 without containing the mica 22 may be sprayed to form a mixed layer without forming a reinforcing layer on the diaphragm.

[0026] The silk nanofiber 21 is obtained by loosening silk fibers, which are raw materials of natural fibers mainly composed of proteins, with mechanical impact force and refining the average fiber diameter to the nanometer level. The silk nanofiber 21 used in the examples of the present invention has an average fiber diameter of about 100 nm and an average fiber length refined to 10 μm or less. Since the average fiber diameter of the silk nanofiber 21 used in the examples of the present invention is fine in this way, it easily penetrates between the cellulose fibers 20 and easily affects the physical properties of the base material 10. Since the silk nanofiber 21 has high dispersibility in water, it is uniformly dispersed in the suspension, and the silk nanofiber 21 can be uniformly applied onto the base material. Therefore, a diaphragm having uniform physical properties across the entire surface of the diaphragm can be formed.

[0027] If the particle size of the mica 22 is too small, it becomes difficult to identify the mica 22 on the surface of the diaphragm, and if it is too large, the texture becomes rough and there is a risk of deteriorating the decorativeness of the diaphragm 1. Further, if the particle size of the mica 22 is too small, it becomes difficult to retain the mica 22 on the surface layer of the base material 10, and if the particle size of the mica 22 is too large, it becomes difficult to arrange the mica 22 between the cellulose fibers 20. For this reason, the mica 22 preferably has a particle size of 10 μm or more and 500 μm or less. Note that the mica 22 may be natural mica or synthetic mica. Further, the mica 22 preferably has a gloss by being coated with titanium oxide, iron oxide, or the like, which improves the decorativeness of the diaphragm 1. Further, by using mica having a large particle size, the mica can be retained on the surface layer of the diaphragm to increase the rigidity of the surface layer, and the propagation speed of the surface layer of the diaphragm can be increased. Further, the average fiber diameter of the silk nanofiber 21 is finer than the particle size of the mica 22 and the average fiber diameter of the cellulose fibers 20, and it is difficult to visually confirm on the surface layer of the diaphragm. However, by mixing and spraying the silk nanofiber 21 and the mica 22, the mica 22 having a large particle size can be confirmed, and it can be visually confirmed that the silk nanofiber 21 has been surely sprayed. Therefore, the quality of the diaphragm as an industrial product can be guaranteed.

[0028] (First Embodiment) The following describes the comparison results of Young's modulus and internal loss using measurement samples of diaphragms for electroacoustic transducers of the first embodiment according to the present invention and comparative examples.

[0029] Comparative example a uses a measurement sample of a base material composed only of cellulose fibers. Examples A1 and A3 use measurement samples in which a mixed layer in which cellulose fibers and silk nanofibers are mixed is formed on a base material made of cellulose fibers, and a reinforcing layer in which cellulose fibers, silk nanofibers, and mica are mixed is formed on the surface layer of the base material. Examples A2 and A4 use measurement samples in which a mixed layer in which cellulose fibers and silk nanofibers are mixed is formed on a base material made of cellulose fibers. Since Examples A2 and A4 do not contain mica, a reinforcing layer is not formed. Table 1 shows the conditions of the measurement samples in each example (mass of silk nanofibers and mica with respect to the mass of the measurement sample: mass%).

[0030]

Table 1

[0031] Each of the prepared measurement samples has a total sample mass (basis weight) of 170 g / m 2It was manufactured to be constant and cut into a length of 40 mm and a width of 5 mm. Specifically, for the samples of Examples A1 and A3, after the cellulose fibers of the base material were formed into paper using a papermaking net, while suction-dehydrating from the back side of the base material, a suspension adjusted so that the mass ratio of silk nanofibers to mica was 95:5 was sprayed onto the front surface of the base material to form the samples. In Example A1, spraying was performed so that the mass of silk nanofibers and mica was 2.00% by mass of the total mass of the sample. The silk nanofibers were 1.90% by mass of the total mass of the sample, and mica was 0.10% by mass. Similarly, in Example A3, spraying was performed so that the mass of silk nanofibers and mica was 5.00% by mass of the total mass of the sample to form the sample. The silk nanofibers were 4.75% by mass of the total mass of the sample, and mica was 0.25% by mass. Also, for the samples of Examples A2 and A4, after the cellulose fibers of the base material were formed into paper using a papermaking net, while suction-dehydrating from the back side of the base material, a suspension of silk nanofibers was sprayed onto the front surface of the base material to form the samples. In Example A2, spraying was performed so that the mass of silk nanofibers was 2.00% by mass of the total mass of the sample, and in Example A4, spraying was performed so that the mass of silk nanofibers was 5.00% by mass of the total mass of the sample to form the sample.

[0032] Figures 4 and 5 are schematic diagrams of the cross-section of the diaphragm according to Example A3 of the present invention and enlarged images taken with a microscope, corresponding to Figures 2 and 3 of Example A1.

[0033] As shown in Figure 4, in the mixed layer 11 of Example A3, the mass of silk nanofibers is larger, being 4.75% by mass compared to 1.90% by mass in Example A1, and silk nanofibers 21 are present from the outermost surface of the base material 10 to near the back surface in the thickness direction. As shown in Figure 5, while the thickness of the base material 10 is 0.2 mm or more and 0.25 mm or less on average, the thickness of the mixed layer 11 is approximately 0.15 mm.

[0034] For the base materials of Comparative Example a and Examples A1 to A4, 50% by mass of NUKP and 50% by mass of kenaf were mixed as cellulose fibers and used after beating at a beating degree of 20° SR.

[0035] For the silk nanofibers of Examples A1 to A4, Model KCo-30005 manufactured by Sugino Machine Limited was used. The silk nanofibers were obtained by loosening silk fibers with mechanical impact force, and had an average fiber diameter of about 100 nm and an average fiber length of 10 μm or less after being refined. Also, for the mica in Examples A1 and A3, Model MS-100R manufactured by Nippon Kogaku Kogyo Co., Ltd. was used. The mica had a particle size of 20 μm to 100 μm, and was obtained by coating natural mica with titanium oxide and iron oxide to impart luster. In Examples A1 and A3, the blending ratio based on the mass of the silk nanofibers and mica was silk nanofibers: mica = 95:5.

[0036] The physical properties (Young's modulus, internal loss (tanδ)) of these Comparative Example a and the samples of Examples A1 to A4 measured by the vibration lead method will be described with reference to FIGS. 6 and 7. In FIG. 6, the measured average value (n = 10) of the Young's modulus is shown, and in FIG. 7, the measured average value (n = 10) of the internal loss is shown.

[0037] First, the Young's modulus will be described. As is clear from FIG. 6, in Examples A1 to A4 having a mixed layer in which silk nanofibers are mixed in the base material, the Young's modulus is lower than that of Comparative Example a. Also, as can be seen from the comparison between Comparative Example a and Example A1 and Example A3, and the comparison between Comparative Example a and Example A2 and Example A4, the Young's modulus decreases as the amount of silk nanofibers increases. Specifically, while the Young's modulus of Comparative Example a is 4.19 [GPa], the Young's modulus of Example A1 in which 1.90% by mass of silk nanofibers are mixed is 3.99 [GPa], and the Young's modulus of Example A3 in which 4.75% by mass of silk nanofibers are mixed is 3.94 [GPa]. The Young's modulus is about 5% lower in Example A1 and about 6% lower in Example A3 compared to Comparative Example a. Also, in Example A2 in which 2.00% by mass of silk nanofibers are mixed, the Young's modulus is 3.94 [GPa], and in Example A4 in which 5.00% by mass of silk nanofibers are mixed, the Young's modulus is 3.74 [GPa]. The Young's modulus is about 6% lower in Example A2 and about 11% lower in Example A4 compared to Comparative Example a. Also, as is clear from the comparison between Example A1 in which 0.10% by mass of mica is mixed and Example A2 in which mica is not mixed, and the comparison between Example A3 in which 0.25% by mass of mica is mixed and Example A4 in which mica is not mixed, by having a reinforcing layer in which mica is mixed, a decrease in the Young's modulus can be suppressed. In particular, in the comparison between Example A3 and Example A4, Example A3 having a reinforcing layer in which mica is mixed has a Young's modulus improved by about 5% compared to Example A4. In addition, by using cellulose nanofibers in addition to mica as a reinforcing material and forming a reinforcing layer in which mica and cellulose nanofibers are mixed in the mixed layer, a further decrease in the Young's modulus can be suppressed.

[0038] Next, the measured value tanδ representing the internal loss will be described. As is clear from FIG. 7, in Examples A1 to A4 having a mixed layer in which silk nanofibers are mixed in the base material, tanδ is larger than that of Comparative Example a. Further, as can be seen from the comparison between Comparative Example a and Example A1 and Example A3, and the comparison between Comparative Example a and Example A2 and Example A4, the larger the amount of silk nanofibers, the larger tanδ becomes. Specifically, while tanδ of Comparative Example a is 0.0287, Example A1 in which 1.90% by mass of silk nanofibers are mixed has a tanδ of 0.0295, and Example A3 in which 4.75% by mass are mixed has a tanδ of 0.0299. Tanδ is improved by about 3% in Example A1 and about 4% in Example A3 compared to Comparative Example a. Also, Example A2 in which 2.00% by mass of silk nanofibers are mixed has a tanδ of 0.0298, and Example A4 in which 5.00% by mass are mixed has a tanδ of 0.0304. Tanδ is improved by about 4% in Example A2 and about 6% in Example A4 compared to Comparative Example a. Since the silk fibers constituting the silk nanofibers have a weak bond with the cellulose fibers of the base material, when the silk nanofibers penetrate between the cellulose fibers, the bonding force between the cellulose fibers is weakened, and the damping effect can be increased, so the internal loss of the diaphragm can be increased. Therefore, a clear sound quality can be obtained with a speaker using the said diaphragm. On the other hand, although the decrease in the Young's modulus of the diaphragm is caused by the weakening of the bonding force between the cellulose fibers by the silk nanofibers, by adjusting the degree of penetration of the silk nanofibers, a decrease in the Young's modulus can be suppressed, and a diaphragm with an appropriate internal loss can be formed.

[0039] As described above, in the diaphragm for an electroacoustic transducer, by forming a mixed layer in which the fiber material and silk nanofibers are mixed in a base material composed mainly of cellulose fibers, the Young's modulus can be maintained and the physical properties of the internal loss inherent in the base material itself can be improved. Further, according to the amount of silk nanofibers mixed and the penetration degree of the mixed layer, the balance between the Young's modulus and the physical properties of the internal loss can be adjusted. In this way, by using silk nanofibers, it is possible to provide a diaphragm that realizes an appropriate Young's modulus and internal loss with respect to the physical property values of the base material. Therefore, by using the diaphragm, the acoustic characteristics of the speaker can be optimized according to the purpose of the speaker.

[0040] Further, by further forming a reinforcing layer in which a reinforcing material such as mica is mixed, a decrease in the Young's modulus can be suppressed. In this way, by using silk nanofibers and a reinforcing material in combination, the internal loss and Young's modulus of the diaphragm can be set in suitable states respectively.

[0041] Further, by spraying a suspension containing silk nanofibers onto the other surface of the base material while sucking and dewatering from one surface side of the base material, the silk nanofibers can penetrate into the inside of the base material, and the physical properties (especially the internal loss) of the base material can be improved efficiently. Since the average fiber diameter of the silk nanofibers is finer than the average fiber diameter of the cellulose fibers, even when the cellulose fibers and the silk nanofibers are mixed and adjusted to form a liquid, and then papermaking is performed, the silk nanofibers pass through between the cellulose fibers or through the mesh of the papermaking net during papermaking and flow out together with the papermaking drainage, making it difficult to retain them in the diaphragm. Therefore, by spraying silk nanofibers onto the base material after papermaking as in this embodiment, the silk nanofibers can be efficiently retained between the clogged cellulose fibers, and a diaphragm in which the silk nanofibers are mixed can be formed efficiently.

[0042] Also, by spraying the suspension to form the mixed layer 11, the amount of water used can be minimized. For example, when comparing a general single-layer papermaking diaphragm, a two-layer papermaking diaphragm in which both the base material and the surface layer are laminated by papermaking, and a second-layer spray diaphragm in which the base material is formed by papermaking and the surface layer (mixed layer) is formed by spraying as in this embodiment, both the two-layer papermaking diaphragm and the second-layer spray diaphragm are diaphragms with a two-layer structure structurally, but there is a difference in the thickness of the surface layer. For example, in the two-layer papermaking diaphragm, the surface layer accounts for 10% to 50% of the total thickness (diaphragm cross-section), while in the second-layer spray diaphragm, the surface layer can be formed with 2% to 5% of the total thickness. And as for the amount of water used, in the single-layer papermaking diaphragm, the papermaking water used for papermaking is several liters. Also, in the two-layer papermaking diaphragm, several liters are required for the base material and several liters are required for the surface layer papermaking. In contrast, the amount of water required for the second-layer spray diaphragm is the same for the base material, several liters, but several grams to several tens of grams of the suspension is sufficient, and the amount of water used can be significantly reduced compared to the two-layer papermaking diaphragm, contributing to the reduction of the drainage volume.

[0043] In the above embodiment and the first example, mica is used as the reinforcing material for explanation, but the reinforcing material is not limited to mica, and other materials with high flexural rigidity, or materials with a high Young's modulus such as carbon fiber and cellulose nanofiber may be used, or they may be used in appropriate combinations.

[0044] When using cellulose nanofiber as the reinforcing material, those with a short average fiber length are preferred. When using cellulose nanofiber with a short average fiber length, the dispersibility in the suspension of silk nanofiber and cellulose nanofiber is higher than that of cellulose nanofiber with a long average fiber length. Therefore, when spraying the suspension on the front surface of the base material, silk nanofiber and cellulose nanofiber can be sprayed uniformly, and the manufacturability is excellent.

[0045] When using cellulose nanofibers as the reinforcing material, when a suspension containing silk nanofibers and cellulose nanofibers is sprayed onto the front surface of the substrate and suction dehydration is performed from the back side of the substrate, the silk nanofibers enter deep into the substrate through the gaps between the cellulose fibers, while the cellulose nanofibers tend to remain on the surface layer of the substrate. Thereby, a reinforcing layer in which cellulose fibers, silk nanofibers, and cellulose nanofibers are mixed can be formed on the front side of the mixed layer. The Young's modulus of cellulose nanofibers is approximately twice as high as that of cellulose fibers such as pulp. Therefore, by using cellulose nanofibers, the internal loss can be increased with silk nanofibers without lowering the Young's modulus of the diaphragm as compared with the case of using only mica as the reinforcing material.

[0046] (Second Embodiment) Hereinafter, the comparison results of the Young's modulus and the internal loss using the measurement samples of the diaphragms for electroacoustic transducers of the second embodiment according to the present invention using cellulose nanofibers as the reinforcing material and the comparative examples will be described.

[0047] Comparative example b1 uses a measurement sample of a substrate made of only cellulose fibers. Comparative example b2 uses a measurement sample in which a layer in which short fiber cellulose nanofibers are mixed is formed on a substrate made of cellulose fibers, and a layer in which the cellulose fibers of the substrate, short fiber cellulose nanofibers, and mica are mixed is formed on the surface layer of the substrate. Comparative example b3 uses a measurement sample in which a layer in which long fiber cellulose nanofibers are mixed is formed on a substrate made of cellulose fibers, and a layer in which the cellulose fibers of the substrate, long fiber cellulose nanofibers, and mica are mixed is formed on the surface layer of the substrate.

[0048] Example B1 uses a measurement sample in which a mixed layer in which cellulose fibers and silk nanofibers are mixed is formed on a substrate made of cellulose fibers, and a reinforcing layer in which the cellulose fibers, silk nanofibers, and mica of the substrate are mixed is formed on the surface layer of the substrate. Example B2 uses a measurement sample in which a mixed layer in which silk nanofibers are mixed is formed on a substrate made of cellulose fibers, and a reinforcing layer in which the short fiber cellulose nanofibers, silk nanofibers, and mica of the substrate are mixed is formed on the surface layer of the substrate. Example B3 uses a measurement sample in which a mixed layer in which silk nanofibers are mixed is formed on a substrate made of cellulose fibers, and a reinforcing layer in which the long fiber cellulose nanofibers, silk nanofibers, and mica of the substrate are mixed is formed on the surface layer of the substrate.

[0049] Table 2 shows the conditions of the measurement samples in Comparative Examples b1 to b3 and Examples B1 to B3 (mass of nanofibers and mica with respect to the mass of the measurement sample: mass %).

[0050]

Table 2

[0051] Each of the prepared measurement samples was prepared so that the total sample mass (basis weight) was constant at 150 g / m 2 and cut into a length of 40 mm and a width of 5 mm. Note that the second example has different papermaking conditions (paper making conditions, pressing conditions, basis weight, etc.) from the first example, and the physical property data cannot be compared unidirectionally between the first example and the second example.

[0052] For the measurement samples of Comparative Examples b2 and b3 and Examples B1 to B3, after papermaking the cellulose fibers of the base material with a papermaking net, while suction-dehydrating from the back side of the base material, a suspension adjusted so that the mass ratio of nanofibers to mica is 95:5 was sprayed onto the front surface of the base material to form the samples. More specifically, in Comparative Example b2, the mass ratio of short-fiber cellulose nanofibers to mica is 95:5; in Comparative Example b3, the mass ratio of long-fiber cellulose nanofibers to mica is 95:5; in Example B1, the mass ratio of silk nanofibers to mica is 95:5; in Example B2, the mass ratio of short-fiber cellulose nanofibers, silk nanofibers to mica is 47.5:47.5:5; and in Example B3, the mass ratio of long-fiber cellulose nanofibers, silk nanofibers to mica is 47.5:47.5:5.

[0053] In Comparative Example b2, the mass of short-fiber cellulose nanofibers and mica was sprayed so as to be 2.00% by mass of the total mass of the sample. The short-fiber cellulose nanofibers are 1.90% by mass of the total mass of the sample, and mica is 0.10% by mass. Similarly, in Comparative Example b3, the mass of long-fiber cellulose nanofibers and mica was sprayed so as to be 2.00% by mass of the total mass of the sample. The long-fiber cellulose nanofibers are 1.90% by mass of the total mass of the sample, and mica is 0.10% by mass.

[0054] Example B1 was sprayed such that the masses of silk nanofibers and mica were 2.00% by mass of the total mass of the sample, with the silk nanofibers being 1.90% by mass of the total mass of the sample and the mica being 0.10% by mass. Example B2 was formed by spraying such that the masses of short fiber cellulose nanofibers, silk nanofibers, and mica were 2.00% by mass of the total mass of the sample, with the short fiber cellulose nanofibers and silk nanofibers each being 0.95% by mass of the total mass of the sample and the mica being 0.10% by mass. Example B3 was formed by spraying such that the masses of long fiber cellulose nanofibers, silk nanofibers, and mica were 2.00% by mass of the total mass of the sample, with the long fiber cellulose nanofibers and silk nanofibers each being 0.95% by mass of the total mass of the sample and the mica being 0.10% by mass.

[0055] For the base materials of Comparative Examples b1 - b3 and Examples B1 - B3, a mixture of 50% by mass of NUKP and 50% by mass of kenaf as cellulose fibers, beaten to a freeness of 20° SR, was used.

[0056] For the silk nanofibers of Examples B1 to B3, Model KCo-30005 manufactured by Sugino Machine Limited was used. The silk nanofibers were obtained by loosening silk fibers with mechanical impact force, and had an average fiber diameter of about 100 nm and an average fiber length of 10 μm or less after being refined. Also, for the mica of Comparative Examples b2, b3 and Examples B1 to B3, Model MS-100R manufactured by Nippon Kogaku Kogyo Co., Ltd. was used. The mica had a particle size of 20 μm to 100 μm, and was obtained by coating natural mica with titanium oxide and iron oxide to impart luster. Also, for the short fiber cellulose nanofibers of Comparative Example b2 and Example B2, Model FMa-10010 manufactured by Sugino Machine Limited was used. The short fiber cellulose nanofibers were obtained by loosening cellulose fibers with mechanical impact force, and had an average fiber diameter of about 10 to 50 nm after being refined. Also, for the long fiber cellulose nanofibers of Comparative Example b3 and Example B3, Model IMa-10005 manufactured by Sugino Machine Limited was used. The long fiber cellulose nanofibers were obtained by loosening cellulose fibers with mechanical impact force, and had an average fiber diameter of about 10 to 50 nm after being refined, and had a longer average fiber length than the short fiber cellulose nanofibers.

[0057] The physical properties (Young's modulus, internal loss (tanδ)) of these samples of Comparative Examples b1 to b3 and Examples B1 to B3 measured by the vibrating reed method will be described with reference to FIGS. 8 and 9. In FIG. 8, the measured average value (n = 10) of Young's modulus is shown, and in FIG. 9, the measured average value (n = 10) of the internal loss is shown.

[0058] First, Young's modulus will be described. As is clear from FIG. 8, in Examples B1 to B3, the Young's modulus is lower than that in Comparative Examples b2 and b3 in which only cellulose nanofibers are mixed, due to the mixing of silk nanofibers in the base material. Also, among Examples B1 to B3, Example B2 in which short fiber cellulose nanofibers and silk nanofibers are mixed has the lowest Young's modulus (3.38 [GPa]), followed by Example B2 with only silk nanofibers having a lower Young's modulus (3.43 [GPa]), and Example B3 in which long fiber cellulose nanofibers and silk nanofibers are mixed has the highest Young's modulus (3.59 [GPa]).

[0059] In Example B2, by mixing short fiber cellulose nanofibers with silk nanofibers in the base material, the short fiber cellulose nanofibers suppress the penetration of the silk nanofibers between the cellulose fibers. As a result, the silk nanofibers can be efficiently retained on the surface layer of the base material, so that the bonding force between the cellulose fibers and the cellulose nanofibers on the surface layer is weakened, and the Young's modulus of the entire diaphragm is lower compared to Comparative Examples b2 and b3.

[0060] In Example B3, by mixing long fiber cellulose nanofibers with silk nanofibers in the base material, highly dispersible silk nanofibers can be efficiently retained on the surface layer without penetrating into the interior of the diaphragm.

[0061] Next, the tanδ representing the internal loss will be described. As is clear from FIG. 9, when only cellulose nanofibers are mixed in the base material as in Comparative Example b2 and Comparative Example b3, the tanδ decreases. On the other hand, it is possible to increase the tanδ by mixing silk nanofibers.

[0062] For example, the tanδ (0.0284) of Example B2 in which short fiber cellulose nanofibers and silk nanofibers are mixed is higher than the tanδ (0.0274) of Comparative Example b2 in which only short fiber cellulose nanofibers are mixed. This is higher than the tanδ (0.0278) of Example B1 in which only silk nanofibers are mixed.

[0063] Also, the tanδ (0.0273) of Example B3 in which long fiber cellulose nanofibers and silk nanofibers are mixed is higher than the tanδ (0.0268) of Comparative Example b3 in which only long fiber cellulose nanofibers are mixed.

[0064] Silk nanofibers have a weak bond with the cellulose fibers of the base material and can enhance the damping effect, so that the internal loss of the diaphragm can be increased. Therefore, clear sound quality can be obtained with a speaker using the diaphragm.

[0065] Next, FIGS. 10 and 11 are schematic diagrams of the diaphragm cross-section according to Example B3 of the present invention and enlarged images taken with a microscope, and FIG. 12 is an enlarged image of the diaphragm surface according to Example B3 taken with a microscope. In FIG. 11, in order to make it easier to distinguish the mixed layer 11 of the base material 10 and the reinforcing layer, without dyeing the cellulose fiber 20 of the base material 10, the silk nanofiber 21 was dyed red and the cellulose nanofiber 23 was dyed black to form the diaphragm 1.

[0066] As shown in FIGS. 10 and 11, the surface of the diaphragm is darkly colored, and in Example B3, it can be seen that many long-fiber cellulose nanofibers 23 remain on the surface of the base material 10. Further, as shown in FIG. 12, shiny mica 22 is uniformly distributed on the diaphragm surface, and it can be confirmed that silk nanofibers 21, cellulose nanofibers 23, and mica 22 are arranged on the diaphragm surface. Also, in FIG. 11, the lightly colored area indicates the mixed layer in which silk nanofibers are mixed. Thus, in Example B3, it can be seen that the penetration of the silk nanofibers 21 into the base material 10 is shallower compared to the diaphragms of FIGS. 3 and 5 in which cellulose nanofibers are not mixed. By mixing the long-fiber cellulose nanofibers 23 and the silk nanofibers 21 in this way, the silk nanofibers 21 can be retained on the surface layer without penetrating to the inside of the diaphragm. Thereby, the gaps between the cellulose fibers 20 of the base material 10 can be efficiently filled in the surface layer of the diaphragm, and a diaphragm with a high surface layer density can be formed. Also, by mixing cellulose nanofibers and silk nanofibers 21, the amount of silk nanofibers 21 used can be reduced. In addition, a diaphragm with a high surface layer density suppresses ventilation and can efficiently transmit vibrations to the air, so the sound pressure can be improved.

[0067] By mixing not only mica but also cellulose nanofibers with silk nanofibers as the reinforcing material as in the second Examples B2 and B3, it is possible to manufacture a diaphragm having an excellent balance between Young's modulus and internal loss while improving the sound pressure.

[0068] In the second embodiments B1 to B3, mica is mixed in all of them. However, even when mica is not included, the same effects can be obtained for the tendency of Young's modulus and internal loss. Further, by disposing the silk nanofibers on the surface of the diaphragm, it is possible to enhance the deterioration of the weather resistance of the pulp against ultraviolet rays, and there is also an effect that fading and embrittlement of the diaphragm can be suppressed.

[0069] With the above, the description of the embodiments and examples of the present invention is completed. However, the aspects of the present invention are not limited to these embodiments and examples.

[0070] In the above embodiments and examples, the shape of the diaphragm 1 is conical. However, the shape of the diaphragm may be other shapes such as a dome shape. Further, the mixed layer and the reinforcing layer may be formed not only on the front side of the base material but also on the back side, or may be formed only on the back side.

[0071] Note that when simply referring to the diaphragm, the diaphragm as a speaker refers to a configuration including the edge, but the diaphragm in this embodiment refers to the body portion excluding the edge.

[0072] Further, the nanofibers in the suspension containing the cellulose fibers of the base material to be papermade, and silk nanofibers, etc. may be dyed with a dye or the like, or those subjected to sizing treatment or waterproof treatment may be used.

[0073] Further, in addition to cellulose fibers, other materials such as carbon fibers, fine powder of carbon powder, and bacterial cellulose may be mixed in the base material to be papermade.

Explanation of reference numerals

[0074] 1 Diaphragm for electroacoustic transducer 10 Base material 11 Mixed layer 12 Reinforcing layer 20 Cellulose fiber (fiber material) 21 Silk nanofiber 22 Mica

Claims

1. A diaphragm for an electroacoustic transducer, wherein a base material composed of a fiber material mainly containing cellulose fibers has a mixed layer in which the fiber material and silk nanofibers are mixed.

2. The diaphragm for an electroacoustic transducer according to Claim 1, wherein the mixed layer is formed on the surface layer side of the base material.

3. The diaphragm for an electroacoustic transducer according to Claim 1 or 2, wherein the average fiber length of the silk nanofibers is 10 μm or less.

4. The diaphragm for an electroacoustic transducer according to any one of Claims 1 to 3, wherein the mixed layer is formed by spraying a suspension containing the silk nanofibers onto the other surface of the base material while sucking and dehydrating from one surface side of the base material.

5. The diaphragm for an electroacoustic transducer according to any one of Claims 1 to 4, wherein a reinforcing layer in which the fiber material, the silk nanofibers, and a reinforcing material are mixed is further formed on the surface layer of the base material.

6. The diaphragm for an electroacoustic transducer according to Claim 5, wherein the reinforcing material is made of a material containing mica.

7. The diaphragm for an electroacoustic transducer according to Claim 5 or 6, wherein the reinforcing material is made of a material containing cellulose nanofibers.

8. The diaphragm for an electroacoustic transducer according to any one of Claims 5 to 7, wherein the reinforcing layer is formed in the mixed layer by spraying a suspension containing the reinforcing material and the silk nanofibers onto the other surface of the base material while sucking and dehydrating from one surface side of the base material.

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