JP2022090766A - Speaker diaphragm and manufacturing method thereof - Google Patents

Abstract

To provide a high quality speaker diaphragm.SOLUTION: A speaker diaphragm includes a cellulose fiber and aramid nanofibers made of para-type total aromatic polyamide with an average fiber diameter of 100 nm or less, and the content ratio of the aramid nanofiber is 2 pts.wt. to 20 pts.wt. with respect to 100 pts.wt. of the cellulose fiber.SELECTED DRAWING: None

Description

The present invention relates to a speaker diaphragm containing aramid nanofibers and a method for manufacturing the same.

Generally, the characteristics required for a speaker diaphragm include high strength, high air density, high Young's modulus (elastic modulus, rigidity), and large internal loss (tan δ). .. In order to meet such demands, the material and structure of the speaker diaphragm are continuously studied.
However, the reproduced sound quality is not limited only by Young's modulus, internal loss, and the speed of sound calculated from Young's modulus and specific gravity, but is required to have a good balance from bass to treble.

Those with a high Young's modulus are less likely to distort the bass because the diaphragm is less deformed, those with a high internal loss do not produce the sound peculiar to the material, so the original sound reproduction is faithful, and those with a high sound velocity reproduce the treble region. Is said to be good. On the other hand, in order to suppress the deformation of the diaphragm, the sound quality that is reproduced differs depending on the desired sound quality, such as a non-pressed papermaking cone that has high bending rigidity and light weight by intentionally reducing the density and increasing the thickness. Judgment by the sensitivity test.

According to Patent Document 1, sound quality is improved by adding cellulose nanofibers produced by TEMPO oxidation treatment and miniaturization treatment to a speaker cone using cellulose pulp. Further, according to Patent Document 2, it is disclosed that the Young's modulus can be improved by adding the TEMPO oxidation treatment and the cellulosic nanofibers obtained by miniaturization.

However, these documents aim to homogenize the paper structure by filling the branched structure of pulp with nanofibers to reduce the unequal vibration caused by the non-uniformity of the voids and improve the reproduced sound. However, since the nanofibers and cellulose pulp produced by miniaturization have the same structure in which the cellulose molecules are oriented as the plant grows, the crystal structure is the same even if the shape is different, and the sound quality that they exhibit is the same. The improvement effect is due to an increase in the density of the obtained paper, and although the sound quality in the treble region is improved, the improvement effect is not recognized in the bass region.

Japanese Unexamined Patent Publication No. 2013-42405 Japanese Unexamined Patent Publication No. 2017-118334

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a speaker diaphragm having high sound quality.

As a result of diligent studies, the present inventors have found that a speaker vibrating plate having high sound quality can be obtained by using a specific amount of aramid nanofibers made of para-type total aromatic polyamide having a specific fiber diameter. Reached.

That is, according to the present invention, the following configurations (1) to (3) are provided.
(1) Includes cellulose fibers and aramid nanofibers made of para-type total aromatic polyamide having an average fiber diameter of 100 nm or less.
A speaker diaphragm characterized in that the content ratio of aramid nanofibers is 2 parts by weight to 20 parts by weight with respect to 100 parts by weight of the cellulose fibers.
(2) The speaker diaphragm according to the previous item (1), wherein the para-type total aromatic polyamide is poly-p-phenylene terephthalamide.
(3) Amid nanofibers having an average fiber diameter of 100 nm or less obtained by adding a strongly basic substance to cellulose fibers and para-type total aromatic polyamide fibers or pulp under an aprotic polar solvent to form nanofibers. The method for manufacturing a speaker vibrating plate according to the preceding item (1) or (2), which is obtained by mixing, mixing and molding.

According to the present invention, it is possible to provide a speaker diaphragm having excellent sound quality in the entire sound range by containing a specific amount of aramid nanofibers made of para-type total aromatic polyamide having a specific fiber diameter.

It is an example which showed the structure observation image of the aramid nanofiber of this invention. This is an example showing an enlarged structure observation image of FIG. 1 for calculating the average fiber diameter. It is explanatory drawing about the calculation method of the average fiber diameter.

Hereinafter, the details of the present invention will be described.
<Speaker diaphragm>
The speaker vibrating plate of the present invention contains cellulose fibers and aramid nanofibers made of para-type total aromatic polyamide having an average fiber diameter of 100 nm or less, and the content ratio of the aramid nanofibers is 100 parts by weight of the cellulose fibers. It contains 2 parts by weight to 20 parts by weight. By doing so, it is possible to obtain a speaker diaphragm having good sound quality in the entire range.

Further, in the speaker vibrating plate of the present invention, the content ratio of the aramid nanofibers is 2 parts by weight to 20 parts by weight, preferably 3 parts by weight to 15 parts by weight, more preferably 3 parts by weight, based on 100 parts by weight of the cellulose fibers. It is preferably 5 parts by weight to 10 parts by weight. Within such a range, a speaker diaphragm having excellent sound quality can be obtained in the entire range. When the content ratio of the aramid nanofibers exceeds 20% by weight, the manufacturing efficiency of the speaker diaphragm becomes long and the manufacturing efficiency may be significantly reduced. Further, nanofibers are not preferable because they have a large specific surface area, prolong the drying time, and form a film due to the drying of the surface layer, which may cause swelling and rupture due to the expansion of water inside.

Further, the cellulose fiber used for the speaker vibrating plate of the present invention may be, for example, wood pulp made of coniferous tree or broadleaf tree, or non-wood pulp made of kenaf or the like, but the fiber length is long. Pulp of coniferous wood, which is relatively long and has high rigidity, is preferable because it is easy to handle as a speaker vibration plate.

The speaker diaphragm of the present invention may further contain other fibers, if necessary. Other fibers can be appropriately selected according to the purpose. For example, for the purpose of improving mechanical strength, high-strength fibers may be mixed. Further, fibers depending on the purpose (for example, heat-dissipating fibers) can be mixed.

The speaker diaphragm of the present invention may contain other components, if necessary. Specific other components include, for example, semiconductor materials such as silicon, silicon carbide (SiC), and germanium, and nitrides such as silicon nitride (silicon nitride), aluminum nitride (aluminum nitride), and boron nitride (boron nitride). Examples thereof include inorganic substances such as compounds, carbon black, diamond, graphene, fullerene, carbon nanotubes, carbon nanofibers, and carbon materials such as graphite. Further, mineral fine particles such as kaolin, talc, clay, hydrotalcite, and diatomaceous earth can also be used. In addition to the particles listed above, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide, and alumina , Mica, zeolite, glass and the like can also be used. The high specific surface area of the aramid nanofibers works effectively, and it is also possible to function as a gripping material for the components.

The density of the speaker diaphragm of the present invention is preferably 0.3 g / cc or more and 0.5 g / cc or more. If it is 0.3 g / cc or less, it is not preferable because the increase in the voids causes the composting at medium to high temperatures. Further, at 0.5 g / cc or more, the high temperature reproduction ability is improved, but if the weight is the same, the sound pressure may be reduced due to the decrease in bending rigidity due to the thinning, and if the thickness is the same, the sound pressure may be decreased due to the increase in weight.

The speaker diaphragm of the present invention can be manufactured by any suitable manufacturing method. A typical production method is to use cellulose fiber (wood pulp) as a main component, mix a predetermined amount of aramid nanofiber with the cellulose fiber (wood pulp), and make a mixed extract. Any suitable method can be adopted as the mixed extraction method and the molding method. Specific examples of the molding method include three-dimensional papermaking + hot press molding.

The speaker diaphragm of the present invention may have an arbitrary appropriate shape depending on the purpose. For example, the speaker diaphragm of the present invention may have a cone shape, a dome shape, or any other shape.

The speaker diaphragm of the present invention can be applied to a speaker for all purposes. For example, the speaker using the diaphragm of the present invention may be an in-vehicle speaker, a portable electronic device (for example, a mobile phone, a portable music player), or a stationary speaker. Further, for example, the speaker using the diaphragm of the present invention may have a large diameter (25 cm or more), a medium diameter (20 to 10 cm), or a small diameter (5 cm or less). .. It is preferably used for medium to small diameter speakers.

<Aramid nanofiber>
The aramid nanofibers used in the speaker diaphragm sheet of the present invention have an average fiber diameter of 100 nm or less, preferably 50 nm or less, and more preferably 25 nm or less. The lower limit of the average diameter is preferably 1 nm or more, preferably 3 nm or more. Further, it is preferable that the aramid nanofibers do not have a diameter of 500 nm or more. When the average fiber diameter exceeds 100 nm, the hydrogen-bonding interaction density between the aramid nanofibers becomes low, and a high Young's modulus and a high internal loss (tan δ) are less likely to occur. As a result, acoustic characteristics such as high sound velocity and sharp sound interruption cannot be obtained, which is not preferable.

The aramid nanofiber in the present invention has an aspect ratio represented by fiber length / fiber diameter of preferably 10 or more and 1,000 or less, more preferably 10 or more and 500 or less, and further preferably 10 or more and 100 or less. .. If the aspect ratio is less than 10, the entangled structure of the fibers is difficult to develop, and therefore the expected characteristics may be difficult to develop.

Further, the aramid nanofiber in the present invention is a para-type total aromatic polyamide. As the para-type total aromatic polyamide, poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-amide hydrazide, poly-p-phenylene terephthalamide-3,4-diphenylether terephthalamide and the like are preferable. It is preferably a poly-p-phenylene terephthalamide fiber having crystallinity (forming a domain of a liquid crystal structure in a spinning solution).

As fibers using para-type total aromatic polyamide, poly-p-phenylene terephthalamide fiber (commercially available products are "Twaron" (trade name) manufactured by Teijin Limited and "Kevlar" manufactured by Toray DuPont Co., Ltd. ("Kevlar" (commercially available). (Trade name), etc.) and coparaphenylene 3,4'oxydiphenylene terephthalamide fiber (commercially available products include "Technora" (trade name) manufactured by Teijin Limited).

<Manufacturing of aramid nanofibers>
The production of the aramid nanofiber in the present invention uses a para-type aromatic polyamide fiber as a raw material, soaks and swells the fiber in a solvent having a high affinity, and further adds a strong basic substance to cut the hydrogen bond portion. And it is generated as a result. The para-type total aromatic polyamide that can be preferably used in the present invention is a polymer in which one or more divalent aromatic groups are linked by an amide bond, and two or more aromatic groups are linked. An aromatic ring may be present, and the aromatic ring may be directly bonded or may be bonded via oxygen or sulfur. Further, the hydrogen atom of the divalent aromatic group may be substituted with a halide, a lower alkyl group or a phenyl group. The solvent used for producing the aramid nanofibers is preferably an aprotic polar solvent, and specific examples thereof include dimethyl sulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone. Examples of the strong base substance used for producing aramid nanofibers include potassium hydroxide, sodium hydroxide, barium hydroxide, calcium hydroxide and the like.

The production of aramid nanofibers in the present invention can be specifically produced by immersing para-type total aromatic polyamide (for example, poly-p-phenylene terephthalamide) fiber or pulp in dimethyl sulfoxide prepared to be alkaline. can.

The para-type total aromatic polyamide (for example, poly-p-phenylene terephthalamide) is obtained by forming a domain of a liquid crystal structure in a spinning solution, discharging it from a capillary, and then washing the spinning solvent with water. The obtained fiber is cleaved by the above method to break the weak bond between the liquid crystal domains constituting the fiber under alkaline conditions, and then the obtained fiber is liberated in a highly compatible solvent to cut the obtained fiber with high elasticity and high strength. The fiber can be obtained. Next, the aramid nanofibers can be isolated by putting the obtained cut fibers into a poor solvent (water, alcohol, acetone, etc.) which is a dispersion solvent.

All para-types obtained by cutting para-type total aromatic polyamide (for example, poly-p-phenylene terephthalamide) fibers having a diameter of 10 to 20 μm into several mm and performing a refiner treatment in which mutual shearing is applied in water. Aromatic polyamide (eg, poly-p-phenylene terephthalamide) pulp can be obtained. In such a refiner treatment, the fibers finely divided from the fiber surface due to shear fracture at the liquid crystal interface are in a branched state without being completely separated, and the diameter of the finely divided fibers is 100 to 1000 nm, and the central portion of the raw material fibers is formed. The diameter is several μm. The refined pulp can also be made into aramid nanofibers by the above treatment.

As another method for refining the aramid material, a method of applying a mechanical shearing force instead of the above-mentioned chemical treatment can be considered, but this method partially obtains a fibril structure having a fiber diameter of nano-order. Only be done. Therefore, since a micro-order structure that has not been fibrillated is also included, a homogeneous confounding structure in the nano-order cannot be obtained and the expected physical properties are not exhibited. In the present invention, it is preferable to form an entangled structure with homogeneously nanonized fibers instead of partially nanonized.

In the present invention, cellulose fibers and para-type total aromatic polyamide fibers or pulp are nanofibers obtained by adding a strongly basic substance under an aprotic polar solvent to form an amide nano having an average fiber diameter of 100 nm or less. A method of manufacturing a speaker vibrating plate by mixing, mixing and molding with fibers is particularly preferable.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to the following Examples and Comparative Examples. In addition, each characteristic value in an Example was measured by the following method.

<Sound quality evaluation>
A cone having an inner diameter of 35 mm and an outer diameter of 135 mm was prepared, and an aluminum piece provided with a screw hole for joining to the vibrator in the center of the cone was adhered and fixed to the vibrator via a screw.
Female vocals (band accompaniment) and piano solo songs were used as sound sources, and 8 males and 3 females in their 20s to 50s were judged by hearing. The test subject did not know the composition of the corn.

High-pitched area: 5 for bright, clear and stretchy, 1 for unclear mid-range: 5 for stretchy and glossy vocal voice, 1 for unclear and muffled bass : The bass drum with a sharp rise was set to 5, and the one with distortion was set to 1.
In each case, the coniferous BKP corn was used as a reference, and the scores were given by repeated auditioning.

<Evaluation of drainage time>
With a 25 cm square tappi paper machine, solid content was added so that the basis weight of the paper was 100 g / m ² , and the drainage time when filtering water (normal pressure) after adding 15 L of water was measured. ..
The judgment criteria are as follows.
〇: Drainage time is less than 30 seconds Δ: Drainage time is 30 seconds or more and less than 60 seconds ×: Drainage time is 60 seconds or more

<Drying evaluation>
After making a 25 cm square paper, the sample was sandwiched between filter papers, passed through a rotary dryer whose surface temperature was set to 140 ° C. three times, and then dried in a 60 ° C. dryer for 3 hours. Subsequent papermaking samples were observed to determine whether the dry condition was good or bad.
The judgment criteria are as follows.
〇: There is no swelling or rupture point due to the expansion of the internal moisture △: There is one swelling or rupture point due to the expansion of the internal moisture ×: There are two or more swelling or rupture points due to the expansion of the internal moisture

<Average fiber diameter>
The structure of the sample was observed using a scanning electron microscope (manufactured by JEOL Ltd., product board: JSM-6330F). From the image observed at a magnification of 50,000 times, an image area of 1,800 nm to 2,000 nm in width and 1,200 nm to 1,500 nm in length is selected, and the image area is further divided into 4 in the vertical direction and 4 in the horizontal direction. A total of 16 grid areas A1-D4 obtained by division are defined, one sample existing in each grid area is selected, and the average value obtained by measuring the fiber diameter of the selected sample on the image is the average fiber diameter. (Fig. 2).

[Example 1]
<Making aramid nanofibers>
-Aramid pulp: 10 g (10 g of fiber obtained by cutting 6 mm of Twaron 1000 manufactured by Teijin Aramid Co., Ltd. was boiled and washed with 1000 g of boiling water for 30 minutes, cooled, washed with water, and dried).
・ Tokyo Chemical Industry Co., Ltd. Dimethyl sulfoxide (DMSO)> 99% 80g,
・ Tokyo Ohka Kogyo Co., Ltd. Potassium hydroxide (KOH) 10g

The above was put into a planetary mixer and stirred at 70 ° C. for 2 hours. After stirring, the aramid pulp lost its shape and a red translucent high-viscosity solution was obtained.
The obtained red translucent solution containing nanofibers was diluted with 3 times the amount of DMSO and gradually added to 20 liters of water with stirring to precipitate poly-p-phenylene terephthalamide nanofibers. At this time, the solution was a yellow-red slurry, in which sulfuric acid was added in an amount required for KOH neutralization, and poly-p-phenylene terephthalamide nanofibers were collected by filtration.

Subsequently, the solvent and salt were removed by washing and stretching dehydration 3 to 5 times using distilled water or ion-exchanged water. Distilled water was added to the obtained poly-p-phenylene terephthalamide nanofiber-containing aqueous solid material so that the solid content concentration was 1%, and Masuyuki Sangyo Co., Ltd. stone mill type crushing and kneader (Super Mascoroider). Was used to obtain a poly-p-phenylene terephthalamide nanofiber dispersed aqueous solution. The obtained poly-p-phenylene terephthalamide nanofiber dispersion was diluted with isopropyl alcohol, added dropwise to the preparation, dried, and confirmed to have an average fiber diameter of 20 nm.

<Manufacturing of diaphragm for speaker>
Two parts by weight of the aramid nanofibers obtained above were mixed with 100 parts by weight of BKP (beating degree 500 cc) derived from coniferous trees, and cone-shaped three-dimensional papermaking was performed. The paper-made cone paper was dried by pressing a three-dimensional hot plate heater at 190 ° C for 1 minute at 0.5 MP. When the thickness was adjusted to 0.4 mm at this time, the weight of the cone paper was 3.0 g. Met.

[Example 2]
The procedure was the same as in Example 1 except that the blending amount of the aramid nanofiber was 3 parts by weight. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 3.0 g.

[Example 3]
The procedure was the same as in Example 1 except that the blending amount of the aramid nanofiber was 5 parts by weight. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 2.9 g.

[Example 4]
The procedure was the same as in Example 1 except that the blending amount of the aramid nanofiber was 10 parts by weight. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 2.8 g.

[Example 5]
The procedure was the same as in Example 1 except that the blending amount of the aramid nanofiber was 20 parts by weight. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 2.7 g.

[Comparative Example 1]
The same procedure as in Example 1 was carried out except that 100 parts by weight of BKP derived from coniferous trees was used without using aramid nanofibers (0 part by weight). When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 3.0 g.

[Comparative Example 2]
The procedure was the same as in Example 1 except that the blending amount of the aramid nanofiber was 1 part by weight. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 3.0 g.

[Comparative Example 3]
The same procedure as in Example 1 was carried out except that the cellulose nanofibers (manufactured by Chuetsu Pulp, 20 nm) were replaced with aramid nanofibers in an amount of 5 parts by weight. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 3.0 g.

[Comparative Example 4]
The same procedure as in Example 1 was carried out except that the cellulose nanofibers (manufactured by Chuetsu Pulp, 20 nm) were replaced with 10 parts by weight instead of the aramid nanofibers. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 3.0 g.

[Comparative Example 5]
The same procedure as in Example 1 was carried out except that the carbon fiber (STS-40 (6 mm) manufactured by Teijin Limited) was replaced with 10 parts by weight instead of the aramid nanofiber. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 3.1 g.

[Comparative Example 6]
The same procedure as in Example 1 was carried out except that the aramid fiber (Teijin Aramid BV Twaron 1000 (6 mm)) was replaced with 10 parts by weight instead of the aramid nanofiber. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 2.8 g.

[Comparative Example 7]
The same procedure as in Example 1 was carried out except that the amount of aramid pulp (Teijin Aramid BV Twaron pulp 1094) was changed to 10 parts by weight instead of aramid nanofibers. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 2.8 g.

[Comparative Example 8]
The same procedure as in Example 1 was carried out except that PPTA fine pulp (Tiara manufactured by Daicel Chemical Co., Ltd.) was used in an amount of 10 parts by weight instead of aramid nanofibers. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 2.8 g.

[Comparative Example 9]
The same procedure as in Example 1 was carried out except that the amount of cellulose fine pulp (Cerish manufactured by Daicel Chemical Co., Ltd.) was changed to 10 parts by weight instead of aramid nanofibers. When the thickness at this time was adjusted to be 0.4 mm, the weight of the cone paper was 3.0 g.

Since the speaker diaphragm of the present invention has high sound quality, it is extremely useful as a diaphragm for a small micro speaker used in a portable device or the like.

Claims (3)

Includes cellulose fibers and aramid nanofibers made of para-type total aromatic polyamide with an average fiber diameter of 100 nm or less.
A speaker diaphragm characterized in that the content ratio of aramid nanofibers is 2 parts by weight to 20 parts by weight with respect to 100 parts by weight of the cellulose fibers. The speaker diaphragm according to claim 1, wherein the para-type total aromatic polyamide is poly-p-phenylene terephthalamide. Cellulose fibers and para-type total aromatic polyamide fibers or pulps are mixed with amide nanofibers having an average fiber diameter of 100 nm or less obtained by adding a strongly basic substance under an aprotic polar solvent to form nanofibers. The method for manufacturing a speaker vibrating plate according to claim 1 or 2, which is obtained by mixing and molding.

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