JPH06284496A - Acoustic diaphragm - Google Patents

Abstract

PURPOSE:To provide the acoustic diaphragm which has specific density an modulus of elasticity ans is superior in moisture proofness and acoustic characteristic by forming the acoustic diaphragm of the thermoplastic resin composition containing a specific amount of infinitesimal hollow particles having a specific density. CONSTITUTION:The thermoplastic resin composition consisting of a polypropylene, a poly 4-methyl pentene-1, etc., is allowed to contain a ratio of 30 to 40wt.% inorganic infinitesimal hollow particles having <=0.8g/cm<3> density. A single screw extrusion molding machine is used to extrude this composition after melting and kneading, thus producing the acoustic diaphragm like a sheet. This diaphragm has <=0.9g/cm<3> density and >18000kg/cm<3> modulus of elasticity. Glass balloons, 'SHIRASU' (volcanic glass) balloons, or the like are used in infinitesimal hollow particles made to contain in the resin composition and if the density of these particles is higher than 0.8g/cm<3>, it is difficult that the diaphragm has a low density. The acoustic diaphragm produced in this manner has a large internal loss, a high modulus of elasticity, and excellent moisture proofness and acoustic characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic diaphragm used for speaker cones and the like. In particular, the invention is
The present invention relates to an acoustic diaphragm having low density, high elastic modulus (rigidity), large internal loss, and extremely excellent acoustic characteristics.

[0002]

2. Description of the Related Art An acoustic diaphragm used for a speaker cone or the like is required to have a large internal loss, a small density, and a high elastic modulus in terms of acoustic characteristics. Conventionally, acoustic diaphragms made of various kinds of materials have been known, and typical examples of the material for the acoustic diaphragms used therefor include cone paper, plastic such as polypropylene, beryllium alloy and titanium alloy. .

Cone paper is suitable as an acoustic diaphragm because it has moderate internal loss and elastic modulus, and has a very low density of generally 0.4 to 0.6 g / cm ³ , but it has insufficient moisture resistance. Without humidity, its acoustic characteristics are easily affected, and the quality of paper is easily affected by the manufacturing process of cone paper,
It has a drawback that it is difficult to obtain a diaphragm having constant acoustic characteristics.

Further, the acoustic diaphragm made of plastic is superior to the cone paper in that it is excellent in moisture resistance and that it is easy to obtain one having a constant quality. However, although polypropylene has a density of 0.91 g / cm ³ and belongs to the lighter class of resins, it still has a higher density than cone paper and has the characteristics of sufficiently low density required for an acoustic diaphragm. Not prepared. Therefore, it has been proposed to use a polypropylene foam having a low density as an acoustic diaphragm (JP-A-57-41096 and JP-A-58).
No. 25797 and Japanese Patent Laid-Open No. 58-131896), the density is improved in this case, but the elastic modulus (rigidity) is lowered and the acoustic characteristics are not sufficiently satisfactory. On the other hand, it has been attempted to add a filler such as mica, talc, and carbon fiber to polypropylene to manufacture an acoustic diaphragm in order to increase the elastic modulus, but the density increases and the conversion efficiency decreases, resulting in a noise reduction. It has the drawback of reducing pressure.

Further, the acoustic diaphragm made of a metal material as described above has a high limit frequency for high frequency reconstruction and tends to produce high-pitched sound, but has a drawback that it has a high limit frequency for low-frequency reconstruction and low bass. In addition, the peak dip appears remarkably in the high range, and a faithful reproduced sound cannot be obtained.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a good and stable sound having a high internal loss and a high elastic modulus required for an acoustic diaphragm, a low density and an excellent moisture resistance. An object is to provide an acoustic diaphragm having characteristics and durability.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present inventors have made various studies from the viewpoint of the material and manufacturing of the acoustic diaphragm. As a result, it has been found that the above object can be achieved by forming an acoustic diaphragm from a specific thermoplastic resin composition in which a thermoplastic resin contains fine hollow particles having a density of 0.8 g / cm ³ or less. Completed the invention.

Therefore, the present invention has a density of 0.8 g /
It is made of a thermoplastic resin composition containing 30 to 60% by weight of minute hollow particles of ³ cm ³ or less, and has a density of 0.9 g.
/ Cm ³ or less and an elastic modulus of 18,000 kg / cm ² or more.

In the present invention, the kind of thermoplastic resin constituting the acoustic diaphragm is not particularly limited, and any thermoplastic resin which can be molded into the acoustic diaphragm such as a film or a sheet can be used. Moreover, the thermoplastic resin is not particularly limited by physical properties such as the degree of polymerization, the average molecular weight, and the melt flow rate. Examples of thermoplastic resins include polypropylene,
Examples include olefin resins such as poly-4-methylpentene-1, ethylene-propylene copolymers, polyester resins such as polyethylene terephthalate, and the like. Even if only one kind of thermoplastic resin is used, two or more kinds are mixed. You may use it. Among them, olefin-based resins, particularly polypropylene having a glass transition point near room temperature and having large internal loss and low density, and poly-4-methylpentene-1 having large internal loss and low density.
Is preferred.

The fine hollow particles to be contained in the thermoplastic resin must have a density of 0.8 g / cm ³ or less. If the density is higher than 0.8 g / cm ^3. It becomes difficult to reduce the density of the acoustic diaphragm, and it is necessary to contain a large amount of fine hollow particles in order to reduce the density of the acoustic diaphragm. The fine hollow particles have a density of 0.8 g / cm ³ or less, and are not broken or melted by the heat or pressure when molding and processing the thermoplastic resin composition into an acoustic vibration plate The type is not limited as long as it can maintain a hollow state. As the fine hollow particles, both inorganic fine hollow particles and organic fine hollow particles can be used, for example, glass balun,
Examples thereof include inorganic fine hollow particles such as silas balun, fly ash balun, perlite and carbon balun, and organic fine hollow particles such as phenol resin balun, epoxy resin balun and sarang baln. Among these fine hollow particles, the inorganic fine hollow particles are preferably used in terms of uniformity, handleability, and the like.

[0011] The smaller the density of the fine hollow particles, the smaller the amount of addition, the smaller the density of the acoustic diaphragm.
Generally, the smaller the hollow particles, the thinner the wall thickness,
Since the thermoplastic resin composition is easily melted and kneaded during the production of an acoustic diaphragm during molding and processing, the density of the hollow microparticles of 0.8 g / cm ₃ or less is 0.1% or less. ˜0.65 g / cm ³ is preferred and 0.
It is more preferably 5 to 0.65 g / cm ³ . Glass balun and silas balun are particularly preferable in that they have a low density and are durable and are not easily broken.

The particle size of the fine hollow particles is not particularly limited as long as the thermoplastic resin containing the fine hollow particles can be molded and processed into an acoustic diaphragm, but generally the particle size is about 50 μm.
It is preferable to use m or less from the viewpoints of ease of molding and processing into an acoustic diaphragm, appearance of the obtained acoustic diaphragm, acoustic characteristics, etc. Moldability and processability of the contained thermoplastic resin composition into an acoustic diaphragm are facilitated and the appearance of the acoustic diaphragm is improved.

The content of the hollow microparticles in the acoustic diaphragm may vary depending on the requirements such as the density of the hollow hollow particles and the final density of the desired acoustic diaphragm, but is 3 based on the total weight of the acoustic diaphragm. The range is from 60 to 60% by weight, preferably from 5 to 40% by weight. If the content of the micro hollow particles is less than 3% by weight, it becomes difficult to reduce the density of the acoustic diaphragm.
On the other hand, when it exceeds 60% by weight, it becomes difficult to knead with the thermoplastic resin when manufacturing the acoustic diaphragm.

In addition to the above-mentioned thermoplastic resin and fine hollow particles, the acoustic vibration plate of the present invention may, if necessary,
It may contain an inorganic filler such as mica, talc, carbon fiber or glass fiber in order to increase the elastic modulus, and further, a plasticizer, a lubricant, an antioxidant, an ultraviolet stabilizer, a dye or pigment, a flame retardant, etc. It may contain other additives.

A thermoplastic resin composition containing a thermoplastic resin as a raw material for producing an acoustic diaphragm and fine hollow particles can be prepared by any method, for example, a single-screw extruder, a twin-screw extruder, a kneader, It can be prepared using a Banbury mixer or the like, and it is preferable to select the mixing and kneading conditions so that the fine hollow particles are not destroyed and are uniformly dispersed in the thermoplastic resin.

The method for producing the acoustic diaphragm of the present invention is not particularly limited and can be produced by any method. For example, the above-mentioned thermoplastic resin composition containing a thermoplastic resin and fine hollow particles is used for injection. Molding, injection compression molding, press molding,
It can be performed by methods such as vacuum forming and compression forming,
Also in this case, it is preferable that the fine hollow particles are not destroyed. Among them, in the case of injection compression molding, the pressure applied to the thermoplastic resin is small, and it is possible to effectively prevent breakage of the fine hollow particles contained in the thermoplastic resin.

The acoustic diaphragm of the present invention has a density of 0.9.
It is necessary to adjust the combination of the types of the thermoplastic resin and the minute hollow particles, the content of the minute hollow particles, the ratio of other components, etc. so that the elastic modulus is g / cm ³ or less and the elastic modulus is 18000 kg / cm ² or more. The density of the acoustic diaphragm is 0.9g / cm
^When the elastic modulus is more than ³ and the elastic modulus is less than 18,000 kg / cm ^{2, the} requirements required for the acoustic diaphragm cannot be sufficiently satisfied, which is not preferable.

The acoustic diaphragm of the present invention is a speaker cone,
It can be used as an acoustic diaphragm in various acoustic products such as caps, and its shape, depending on the type, shape, size, etc. of the acoustic product to which it is finally attached,
It is good to decide the dimensions.

The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. The abbreviations of the components used in the following Examples and Comparative Examples are shown in Table 1 below. Moreover, the density, elastic modulus and internal loss of the acoustic diaphragms (sheets) obtained in the following Examples and Comparative Examples were measured by the following methods.

[0020]

[Table 1] Code: Content PP: Propylene homopolymer [melt flow rate 0.8 g / 10 minutes (230 ° C., 2.16 kg)] PMP: poly-4-methylpentene-1 [melt flow rate 8 g / 10 minutes (260 ° C., 5 kg)] GB: Glass balun (density 0.6 g / cm ³ ; average particle size 30 μm) MC: Mica powder (weight average flake diameter 40 μm, aspect ratio 30)

Density of acoustic diaphragm : JIS K7112A
Obtained in compliance with the law. Elastic Modulus and Internal Loss of Acoustic Diaphragm: Orientec Co., Ltd. "Reo Vibron DDV-III" was used to measure frequency 1
The measurement was performed under the conditions of 10 Hz and a measurement temperature of −150 to 200 ° C., and the elastic modulus and internal loss at 23 ° C. were obtained.

<< Examples 1 to 4 and Comparative Examples 1 to 3 >> Thermoplastic resin compositions having the formulations shown in Table 2 below were melt-kneaded using a single-screw extruder and then extruded to obtain a thickness. A 300 μm sheet-shaped acoustic diaphragm was manufactured (PP compounding was extruded by melting and kneading at 250 ° C .; PMP
The composition using was kneaded at 315 ° C and extruded). The density, elastic modulus and internal loss of the acoustic diaphragm obtained in each example were measured by the above-mentioned methods and were as shown in Table 2 below. For reference, the density is 0.85g
The elastic modulus of an acoustic diaphragm made of a commercially available polypropylene foam sheet having a density of / cm ³ was measured in the same manner.
It was as shown in Table 2.

[0023]

[Table 2]  Example Comparative example Foam 1 2 3 4 1 2 3 PP(Commercially available) Component (% by weight) PP 80 70 100 70 PMP 90 70 100 GB 20 10 20 20 MC 10 10 30Acoustic diaphragm physical properties Density (g / cm³) 0.82 0.80 0.88 0.83 0.91 0.83 1.14 0.85 Modulus of elasticity (kg / cm²) 19000 18000 23000 23000 17000 17000 41000 7000 Internal loss 0.06 0.042 0.05 0.03 0.07 0.047 0.05 0.06

From the results shown in Table 2 above, the acoustic diaphragms of Examples 1 to 4 produced from the resin compositions containing fine hollow particles in polypropylene or poly-4-methylpentene-1 all had a density of 0. It is required to have excellent characteristics required for an acoustic diaphragm, which is low, less than 0.90 g / cm ³ , and has a large elastic modulus of 18000 kg / cm ² or more, large internal loss.

On the other hand, the acoustic diaphragm of Comparative Example 1 produced only from polypropylene has a high density of 0.91 g / cm ³ and a small elastic modulus of 17,000 kg / cm ² .
Comparative Example 2 consisting only of poly-4-methylpentene-1
The acoustic diaphragm of No. ³ has a small density of 0.83 g / cm ³ , but has a small elastic modulus of 17,000 kg / cm ^2, and the acoustic diaphragm of Comparative Example 3 in which polypropylene contains mica powder has an elastic modulus of 41,000 kg / cm 2. The density is as high as ^{2, which} is as high as 1.14 g / cm ^3, and it does not have the characteristics of low density and high elastic modulus required for an acoustic diaphragm, and the commercially available acoustic diaphragm made of expanded polypropylene has a high density. Small as 0.85 g / cm ³ , but elastic modulus of 900
It is as extremely low as 0 kg / cm ^2, and it can be seen that neither satisfies the requirements required for the acoustic diaphragm.

[0026]

The acoustic diaphragm of the present invention has a high internal loss, a high elastic modulus, a low density and an excellent moisture resistance, and therefore has extremely excellent acoustic characteristics. Such excellent acoustic characteristics are stable and hardly affected by humidity, etc., and are highly durable.

Claims (2)

[Claims] 1. A thermoplastic resin composition containing 30 to 60% by weight of fine hollow particles having a density of 0.8 g / cm ³ or less, a density of 0.9 g / cm ³ or less, and an elastic modulus. Is 18000 kg / cm ² or more, an acoustic diaphragm. 2. The thermoplastic resin is polypropylene or poly4.
-The acoustic diaphragm of claim 1, which is methylpentene-1 or a mixture thereof.