JPH0254000B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing an acoustic diaphragm represented by a speaker cone or the like. (Prior technology) Traditionally, paper has been mainly used for electroacoustic transducers, especially diaphragms, but recently polyolefin polymer films have excellent acoustic properties, are easy to process, and are low cost. It has been attracting attention because it can be mass-produced (see Japanese Patent Application Laid-open Nos. 145024-1983, 45226-1983, and 46112-1983). However, in order to further improve the acoustic characteristics, it is desired to develop a diaphragm with a higher rigidity. For example, a diaphragm made of thermoplastic resin and flaky graphite is disclosed in JP-A-55-162695. On the other hand, it is also known to use mica as a material for the diaphragm. JP-A No. 53-47816 discloses a diaphragm made by dispersing and mixing cellulose fibers and mica in water and using a paper machine, and JP-A No. 54-27250 discloses a diaphragm manufactured by making mica into paper. A diaphragm made of a diaphragm and impregnated with a thermoplastic resin is disclosed.
Furthermore, Japanese Patent Application Laid-open No. 75316/1983 discloses a diaphragm made by mixing carbon fiber and mica and manufactured using a paper machine. Furthermore, it is known that a sheet obtained by mixing mica with a thermoplastic resin such as polyvinyl chloride is used as a material for a diaphragm (see Japanese Patent Application Laid-open No. 136796/1983), but the ones with good acoustic properties are Not obtained. (Problem to be Solved by the Invention) Generally, reinforcing fillers are mixed in to improve the rigidity of polymeric materials.
Diaphragms formed using fibrous reinforcing materials such as glass fibers and carbon fibers have the problem of anisotropy in the performance of the diaphragm due to the orientation of the fibers during extrusion molding. A diaphragm formed using a flake-like reinforcing material such as powder has a problem in that the effect of improving the rigidity of the diaphragm is insufficient. Furthermore, molding mica using a paper machine is difficult because mica itself does not have the property of intertwining, and it has not been put to practical use. The present invention is intended to solve the above-mentioned drawbacks, and its purpose is to provide a method for manufacturing a diaphragm that maintains the properties of polyolefin polymers, has no anisotropy, and has a higher rigidity. It is in. (Means for Solving the Problems) According to the present invention, the above objects are achieved by (a) 30 to 95% by weight of a polyolefin polymer and (b) a weight average flake diameter of 500 μm or less and a weight average aspect ratio of 10 or more. A composite sheet is formed from a composite material obtained by compounding 70 to 5% by weight of mica having a melt index of 3.5 g/10 min or less, and then molded into an arbitrary shape. This is achieved by providing a method for manufacturing an acoustic diaphragm that achieves this goal. Polyolefin polymers used in the present invention include polyethylene (especially high-density polyethylene), polypropylene (especially isotactic polypropylene), polybutene, poly(3-methylbutene-1), poly(4-methylpentene-1) Examples include polymers of aliphatic olefins such as ) and copolymers containing the constituent monomers of the above polymers as main components. Other monomers constituting the copolymer include other olefin monomers different from the main component monomer, vinyl acetate, maleic anhydride, acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, etc. The polymerizable monomer is used within a range that does not inhibit the crystallinity of the polymer (usually 20% or less). The copolymer may be not only a random copolymer but also a block or graft copolymer. Further, for the purpose of improving adhesion to mica, polyolefin modified with maleic acid, acrylic acid, methacrylic acid, etc., so-called polarized polyolefin, may be mixed with unmodified polyolefin. In the present invention, among the above-mentioned polymers, isotactic polypropylene polymers are particularly preferred because they have good moldability, are inexpensive, have excellent heat resistance, and can provide a diaphragm with a high sound velocity. As the isotactic polypropylene polymer, a copolymer having an ethylene content of 2 to 15% by weight is preferably used. Various types of mica can be used as the mica used in the present invention, such as white mica (muscovite), gold mica (phlogovite), and synthetic mica. The weighted average aspect ratio is
Must be 10 or more. In the present invention, the weight average aspect ratio and weight average flake diameter of mica are determined by the following formula. Weight average aspect ratio =D/- ₁ m ₁ +D/- ₂ m ₂ +...+D/- _o m _o /t ₁ m ₁
+t ₂ m ₂ +...+t _o m _o weight average flake diameter =D/- ₁ m ₁ +D/- ₂ m ₂ +...+D/- _o m _o /n Here, the average diameter of one mica flake,
t ₁ is the average thickness of the flake, and m ₁ is the total weight of the flake group having the _{shape of 1,1 . 2} ,
₂ , ₂ , _o , _o , and _mo also have similar meanings.
The average diameter of the flakes represented by ₁ , ₂ , ... _o is determined by the following formula. π(D/2) ² = Area of one flake When a diaphragm is formed from mica with a weight average flake diameter exceeding 500 μm, mica flakes are likely to peel off or fall off from the diaphragm surface. Furthermore, when molding a diaphragm using a melt molding method, molding is often extremely difficult. Desirably, the weight average flake diameter of mica is 300 μm or less. Further, when the diaphragm is formed from flakes having a weight average aspect ratio of less than 10, the effect of improving the rigidity is small and the acoustic characteristics are unsatisfactory. In the present invention, the mixing ratio of the polyolefin polymer and mica is 30 to 30% of the polyolefin polymer.
95% by weight, mica 5-70% by weight. If the mixing ratio of mica is less than 5% by weight, the effect of improving the rigidity is unsatisfactory, while if the mixing ratio of mica exceeds 70% by weight, moldability is difficult when forming a sheet for a diaphragm. Become. Among these, a mica mixing ratio of 10 to 60% by weight (polyolefin polymer mixing ratio of 90 to 40% by weight) is particularly preferred. In manufacturing the diaphragm in the present invention, fillers other than mica, such as talc, calcium carbonate, wollastonite, glass beads, magnesium hydroxide, silica, graphite, glass flakes, barium sulfate, alumina, potassium titanate fibers, are used. , processed mineral fibers (PMF), glass fibers, carbon fibers, aramid fibers, etc. may be used as supplementary materials. Additionally, additives (silane coupling agents, etc.), pigments, plasticizers, stabilizers, lubricants, etc. may be added as necessary to improve the interfacial adhesive strength between the polyolefin polymer and mica. Ru. In the present invention, the melt index of the composite material containing a polyolefin polymer and mica as main components is 3.5 g/10 min or less, preferably 3.0 g/10 min or less, and particularly preferably 2.0 g/10 min or less. Melt index is a value measured and determined according to ASTMD1238. For example, when the polyolefin polymer is polypropylene, the melt flow rate (unit: g/10
minutes). Melt index is 3.5g/
If the time exceeds 10 min, problems such as wrinkles are likely to occur when forming the acoustic diaphragm from the sheet (vacuum forming, press forming, stamp forming, etc.). Composite materials with a low melt index are often obtained by using polyolefin polymers with a low melt index as raw materials. In the present invention, a composite sheet is first formed from a composite material made of a polyolefin polymer and mica, and then this is formed into various shapes by vacuum forming or the like to obtain an acoustic diaphragm. The composite sheet is preferably formed by melt-mixing a polyolefin polymer and mica and extruding the mixture in a conventional manner. There is no particular limit to the thickness of the diaphragm obtained by the present invention, but 0.1 to 0.9 mm, particularly 0.2 to 0.7 mm, is useful. When it is thinner than 0.1mm, the strength of the plate is weak, and when it is thicker than 0.9mm, the weight of the diaphragm becomes too large, so an expensive and strong magnet is required to vibrate the diaphragm, which makes it economical. This is disadvantageous. (Examples) The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these Examples. In the examples, the rigidity (ie, elastic modulus) of the acoustic diaphragm was evaluated by dynamic elastic modulus. Further, the acoustic effect of a diaphragm is generally evaluated by specific elastic modulus and internal loss value. That is, the square root of the specific modulus of elasticity represents the speed of sound propagating within the diaphragm, and the higher the specific modulus, the lower the frequency of resonance. Further, the internal loss value represents a measure for lowering the degree of resonance, and the higher this value, the lower the degree of resonance. Therefore, a diaphragm with a high specific modulus of elasticity and a high internal loss value has a low degree of resonance and is excellent as an acoustic diaphragm. Example 1 Gold mica with a weight average flake diameter of 21 μm and crystalline polypropylene (PP) (MI: 1 g/
10min) using a single-screw extruder at 230°C, and the resulting pellets were melt-mixed using an extruder again at 240°C.
A polypropylene-mica composite sheet having a gold-mica mixing ratio of 60% by weight and a thickness of 300 μm was obtained by extrusion into a sheet at ℃. The weight average flake diameter of the mica contained in the sheet was 18 μm, and the weight average aspect ratio was 12. The dynamic elastic modulus E′ and internal loss value tanδ of the sheet were measured at a frequency of 110 Hz and 20°C using a Vibron DDV-2 manufactured by Toyo Baldwin.
In addition, the density ρ was measured using ethanol by the method specified in JIS K7112A method. Also Dynamic
The sound propagation speed was measured using a Modular Tester. Furthermore, from the temperature dependence of E′, E′
The temperature at which the temperature was 10 ⁹ dynes/cm ² was measured, and this value was used as the evaluation standard for heat resistance. The measurement results are shown in Table 1. Dynamic modulus, specific modulus, sound velocity and
The tan δ was high and the heat resistance was also extremely good.
Using this sheet, 20 speaker cones were molded at a temperature of 190° C. by a vacuum forming method. Vacuum formability was good, and no defective products were produced. There were no changes in the physical properties of the sheet before vacuum forming and the speaker cone after vacuum forming. Examples 2 and 3 The weight average flake diameter of the gold mica used was 40μ.
m (Example 2) and 230 μm (Example 3), and the gold-mica mixing ratio was 30% by weight (Example 2) and 10% by weight.
(Example 3) A sheet with a thickness of 500 μm was produced using the same method and conditions as in Example 1, except for
Its performance was measured. The results are shown in Table 1. Dynamic modulus, specific modulus, sound velocity and
The tan δ was high, and the heat resistance and vacuum formability were also good. Example 4 30% by weight of gold mica with a weight average flake diameter of 90 μm was mixed with a propylene-ethylene block copolymer (6% ethylene) resin with a melt index of 3.5 g/10 min, and the same method and conditions as in Example 1 were used. A sheet with a thickness of 200 μm was produced. The performance measurement results are shown in Table 1. This sheet had high dynamic elastic modulus, specific elastic modulus, sound velocity, and tan δ, and also had good heat resistance and vacuum formability. Comparative Examples 1 and 2 Polypropylene with a melt index of 5 g/10 min (Comparative Example 1) or propylene-ethylene block copolymer (6% ethylene) resin (Comparative Example 2)
30% by weight of gold mica having a weight average flake diameter of 40 μm was mixed into the sample, and a sheet with a thickness of 400 μm having the composition shown in Table 1 was obtained in the same manner as in Example 1. The performance measurement results are shown in Table 1. The performance of the sheets obtained in Comparative Example 1 and Comparative Example 2 was comparable to that of the sheet obtained in the Examples, but during heating during vacuum forming when forming these sheets into speaker cones, Sagging was observed, and when 20 speaker cones were molded for each comparative example, 5 speaker cones were obtained for the sheet obtained in Comparative Example 1, and 4 speaker cones were obtained for the sheet obtained in Comparative Example 2. wrinkles appeared on the speaker cones, and these speaker cones were determined to be defective. Comparative Examples 3 and 4 Using polypropylene with a melt index of 1 g/10 min, no mica was used at all (Comparative Example 3), or gold mica with a flake diameter of 90 μm was used.
By weight percent mixing (Comparative Example 4), sheets were prepared in the same manner as in Example 1, and their performances are shown in Table 1. These sheets had lower dynamic elastic modulus, lower specific elastic modulus, and lower sound velocity than the sheets obtained in Examples, and also had unsatisfactory heat resistance. Example 5 Weight average flake diameter on high density polyethylene (HDPE) with mercapto index 2g/10min
A sheet was obtained by mixing 50% by weight of 90 μm gold mica and performing melt mixing and sheet extrusion at 160° C. in the same manner as in Example 1, and its performance is shown in Table 1. This sheet had high dynamic elastic modulus, specific elastic modulus, sound velocity, and tan δ, and also had good heat resistance. The sheet could be easily formed into a diaphragm for a cone speaker by vacuum forming at 130°C, and its vacuum formability was extremely good. Comparative Example 5 A sheet was produced using only the high-density polyethylene shown in Example 5 without using mica, and its performance is shown in Table 1. This sheet had extremely lower dynamic elastic modulus, specific elastic modulus, and sound velocity than the sheets obtained in Examples, and was also unsatisfactory in heat resistance.

【table】

[Table] Comparative Examples 6 and 7 A resin containing polyvinyl chloride as the main component was used, and mica was mixed therein to prepare a sheet, and its performance is shown in Table 2. All of the sheets had a lower specific modulus than the sheets obtained in the examples. Comparative Example 8 Polymethyl methacrylate resin (methyl ethyl ketone: toluene = 1:
15% concentration of mixed solvent) is 20% by weight
After impregnating the product and leaving it for a day and night, it was heated to 100℃.
and dried for 10 minutes. Then at 150℃ for 10 minutes, 100Kg/cm ²
Heat pressed under the following conditions. Table 2 shows the performance of the obtained sheet. This sheet had an extremely low tan δ compared to the sheet obtained in the example. Comparative Examples 9 to 11 Sheets were produced in the same manner as in Examples 1 to 3, except that polymethyl methacrylate resin (Panapet EH, manufactured by Kyowa Gas Chemical Industry Co., Ltd.) was used as the matrix resin, and their performance was measured. did. The results are shown in Table 2. All of these sheets had a lower specific modulus than the sheets obtained in the Examples. Comparative Example 12 The performance of the paper forming the diaphragm was measured, and the results are shown in Table 2. This paper had an extremely low specific elastic modulus compared to the sheet obtained in the example.

【table】

[Table] (Effects of the Invention) According to the manufacturing method of the present invention, a desired diaphragm with good moldability can be obtained. The diaphragm obtained by the manufacturing method of the present invention has significantly higher rigidity and specific modulus than conventional diaphragms made of paper or diaphragms made only of polyolefin polymers, and is suitable for use in speaker cones, etc. It was recognized that it is an excellent diaphragm.
Furthermore, since the diaphragm obtained by the manufacturing method of the present invention has improved heat resistance, it is difficult to prevent the diaphragm from rising in the temperature of the atmosphere when the acoustic diaphragm is used, and when assembling audio equipment using the diaphragm. It is effective because the shape does not change even when the temperature rises when bonding it to the substrate.

Claims (1)

[Scope of Claims] 1 (a) 30 to 95% by weight of a polyolefin polymer and (b) a weight average flake diameter of 500 μm or less and 10
Mica 70 with a weight average aspect ratio of greater than or equal to
An acoustic diaphragm characterized by forming a composite sheet from a composite material obtained by compounding ~5% by weight and having a melt index of 3.5g/10min or less, and then molding it into an arbitrary shape. Manufacturing method.