JPS5986994A - Diaphragm for loudspeaker - Google Patents

Abstract

PURPOSE:To make a specific elastic modulus of a titled diaphragm high and to make its flexural rigidity large by both mica and flaky graphite as a reinforcing material to a base material consisting of a mixture of 4-methylpenten polymer and other olefin compound polymer. CONSTITUTION:As for 4-methylpenten polymer, ite melting temperature is low in case of a simple substance, its film forming property and forming property are bad, and its glass transition temperature is in the vicinity of a room temperature, therefore, a tone quality is varied by a variation of an elastic modulus and an internal loss due to a temperature, but by mixing other olefin compound polymer, the film forming property and forming property are improved, and a sudden change of the elastic modulus and the internal loss at a glass transition temperature can be suppressed. By mixing mica and flaky graphite as a reinforcing material, the elastic modulus is raised, and the flexural rigidity can be enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a thermoformable speaker diaphragm having flat frequency characteristics, low distortion, and excellent water resistance over a wide reproduction frequency band.

Conventional structure and its problems Paper cones have traditionally been used as a material for speaker diaphragms, but this is because paper has a low density, moderate elastic modulus, internal loss, and high bending rigidity. It is. These physical properties are greatly related to efficiency, reproduction band, frequency characteristic flatness, and input resistance in terms of acoustic characteristics. However, since paper cones cannot be thermoformed, the manufacturing process is complicated, as it is necessary to make each sheet into a cone shape, and as a result, the quality during manufacturing is unstable.
Poor water resistance and moisture resistance 0 Attempts have been made to use materials to replace paper and polymeric materials such as polypropylene and polyethylene, but while metal materials have a high specific modulus, internal loss is extremely high. It has the disadvantage of having a low frequency characteristic and a sharp peak in the high range.

Therefore, it is mainly used for tweeters. On the other hand, in the case of polymeric materials, although they have high internal loss and are excellent in moldability, water resistance, and moisture resistance, they have the drawbacks of low specific modulus of elasticity and low bending rigidity.

OBJECTS OF THE INVENTION The present invention aims to improve the low specific elastic modulus and low rigidity, which are disadvantages of polymer diaphragms, and to achieve a wider band and higher input resistance.

Structure of the Invention The speaker diaphragm of the present invention is made of 4-
The base material is a blend of methylpentene polymer and other olefin polymers such as polyethylene and polypropylene that have excellent moldability, and this base material is composited with both mica and graphite scales as reinforcing materials. This diaphragm has high internal loss, high specific modulus, and high rigidity, and also has excellent mass productivity, reliability, and quality stability. 4-Methylpentene polymer alone has the disadvantage of low melt viscosity, poor film-forming properties and poor moldability, and has a glass transition temperature near room temperature (29
~60"C), which causes large changes in elastic modulus and internal loss due to temperature, resulting in changes in sound quality. However, by using a blend of 4-methylpentene polymer and other olefin polymers as a base material, Improved film formability and formability,
It has the advantage of suppressing rapid changes in elastic modulus and internal loss at the glass transition temperature. Other olefin polymers mentioned here include polyethylene, polypropylene,
Refers to polybutylene, etc. Since 4-methylpentene polymer is an olefin-based polymer and is non-polar, it cannot be blended with polar polymers, and is effective when blended with olefin-based polymers.

When mica alone is mixed as a reinforcing material, the specific gravity of mica is as high as 2.7, which is disadvantageous in terms of bending rigidity, and also has the disadvantage of being weak against repeated fatigue. On the other hand, when graphite scales are mixed alone, the modulus of elasticity does not increase by 9%, and when the content is increased, it becomes conductive, which has the disadvantage that it cannot be used in indirect lead type diaphragms. However, by mixing scaly graphite and mica, the elastic modulus was improved and the bending rigidity was also improved. This is thought to be because mica promotes cleavage of flaky graphite during crosstalk, since mica has a hardness of 3, whereas flaky graphite has a hardness of approximately 1. Regarding the elastic modulus when scale-like materials are used as reinforcing materials, Halp
It is well known that the elastic modulus of a composite material is expressed by the following equation, which has been studied in detail by In-Tsai and N1elser et al.

El 1-Bv2 A = 2 W / t 1 Subscript 1.2 represents the base material and reinforcing material, respectively, E is the elastic modulus,
(2) represents the volume fraction, W represents the diameter of the scales, and t represents the thickness. As the opening progresses, t becomes smaller and A becomes larger. FIG. 1 shows the relationship between the value of and E, and it can be seen that as the value of A increases, E also increases.

On the other hand, the internal loss was due to two factors: the contribution of the polymer resin itself and the contribution of the loss between the layers of the scale-like material, and no decrease was observed even in the state of advanced cleavage. Table 1 shows the physical properties of various sheets, and it can be seen that as a base material, 4-methylpentene polymer is superior to other resins in terms of density, internal loss, and bending rigidity. On the other hand, as a reinforcing material, a mixed system of scaly graphite and mica is excellent. A diaphragm using a composite sheet made of 4-methylpentene polymer and other olefin polymers as a base material and reinforced with scaly graphite and mica has flat frequency characteristics and a wide reproduction frequency band. It has excellent characteristics such as low distortion, water resistance, mass production, and quality stability.

Description of Examples Example 1 4-Methylpentene Polymer (Mikata Petrochemical Co., Ltd. TPX)
)50wt%, polypropylene (Ube Industries, Ltd. F2O
31) 2swt% as a base material, scale graphite (average particle size 1o
μm) 22wt%, mica (average particle size 4oμm) 3wt
% as reinforcement in a twin screw extruder (extrusion temperature 26
Mix well using 0″C) to make master pellets,
Next, the pellets were pre-dried at 110"C for 10 hours, and then
A composite sheet with a thickness of 160 μm was drawn using a T-die. Next, heat this 7-t with far infrared rays (about 7 to 8 seconds)
After softening, vacuum forming was performed.

The physical properties of this sheet are shown in Table 1, and it was superior in terms of elastic modulus, specific elastic modulus, and bending rigidity to a composite of scaly graphite and mica alone. The frequency characteristics of a 12FFI speaker diaphragm using these sheets are shown in FIG. 2, and it was observed that the distortion was lower and the reproduction band was wider than that of a polypropylene diaphragm. In FIG. 2, the solid line a is the sound pressure frequency characteristic of this embodiment, the solid line is the second-order distortion characteristic, the broken line C is the sound pressure frequency characteristic of the polypropylene diaphragm, and the broken line d is the second-order distortion characteristic.

Example 2 35wt% 4-methylpentene and 45w polypropylene
t% as a base material, scaly graphite 5wt%, mica 15wt%
A thickness of 10,071 m was prepared using the same method as in Example 1 using reinforcing material.
A composite sheet was prepared. Next, sandwich this sheet between Teflon-coated hot plates (220″C) for a few seconds.
Once the sheet had softened, cold press forming was performed. Table 1 shows the physical properties of the sheet. Although the bending rigidity was lower than that of the sheet of Example 1, the internal loss was higher. A dome tweeter with a diameter of 4 ohm x b was made from this sheet, and compared to one using a conventional polypropylene sheet, the distortion was lower and the upper limit frequency was extended by about 2 k)h.

Effects of the Invention As described above, according to the present invention, a blend of 4-methylpentene polymer and other olefin polymer is used as a base material, and mica and flake graphite are used as reinforcing materials. It has a high elastic modulus and high bending stiffness, so it has flat frequency characteristics, low distortion, and can have acoustic characteristics over a wide reproduction frequency band, and is water resistant, weather resistant, and mass-producible.

It also has the advantage of excellent quality stability.

[Brief explanation of the drawing]

FIG. 1 is a curve diagram showing the relationship between the volume fraction of the reinforcing material and the elastic modulus, and FIG. 2 is a comparative characteristic diagram showing the frequency characteristics of a speaker diaphragm according to an embodiment of the present invention and a conventional example. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 5 Rice integral rate (xtO) in East Ihioo

Claims (1)

[Claims] A diaphragm for a speaker, characterized in that the base material is a blend of 4-methylpentene polymer and other olefin polymer, and this base material is composited with both mica and scaly graphite as reinforcing materials.