GB2115645A

GB2115645A - Speaker diaphragm

Info

Publication number: GB2115645A
Application number: GB08221939A
Authority: GB
Inventors: Tsunehiro Tsukagoshi; Shinichi Yokozeki; Sumio Hagiwara; Toshikazu Yoshino; Yasuyuki Arai
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1981-07-31
Filing date: 1982-07-29
Publication date: 1983-09-07
Also published as: FR2510857B1; DE3228592C2; JPS639798B2; DE3228592A1; GB2115645B; JPS5821997A; FR2510857A1

Abstract

A speaker diaphragm shaped from a mixture of graphite flakes and a synthetic resin is disclosed. The graphite flakes are used in an amount of from 50 to 200 parts by weight and the synthetic resin consists of 40 to 80 parts by weight of polyvinyl chloride or post chlorinated polyvinyl chloride and 60 to 20 parts by weight of an ABS resin. The speaker has improved heat resistance, high Young's modulus and a reasonably high internal loss.

Description

SPECIFICATION Speaker diaphragm The present invention relates to a speaker diaphragm, and more particularly, to a speaker diaphragm having improved heat resistance.

Speaker diaphragms must have a small mass, great Young's modulus and reasonably great internal loss. In addition, certain types of speakers must possess high heat resistance. For instance, speakers installed in automobiles or used for portable radio cassettes become very hot if they are subjected to direct sunlight or if the doors of the car are left closed for a long period. The temperature of a parked car on a sunny midsummer day, with the doors closed for many hours can become as high as 70-800C.

Accordingly, a speaker using a carbon-base diaphragm can become as hot as 1 000C or more.

In such extreme heat the diaphragm can be deformed causing the speaker to emit distorted sound.

According to a first aspect of the invention a speaker diaphragm is formed from a dispersion comprising graphite flakes; a polyvinyl chloride; and an ABS resin.

According to a second aspect of the invention a speaker diaphragm is formed from a dispersion comprising graphite flakes; a post chlorinated polyvinyl chloride; and an ABS resin.

Such speaker diaphragms have a high Young's modulus and reasonably great internal loss and characteristics which are fairly easy to control.

The accompanying drawing shows the Young's modulus vs. temperature characteristic curve for the diaphragms prepared in the following described Examples 1 to 3 as compared with a conventional product.

Graphite, particularly, flaky graphite crystal, has a very high Young's modulus. However, an article as large as a speaker diaphragm cannot be shaped completely from pure graphite crystal.

Therefore, fine flakes of graphite crystal of a size of 1 to 5 y are dispersed in a resin binder to form an article having high Young's modulus. Materials comprising graphite mixed with phenolic resins and polyvinyl chloride are known. However, a diaphragm made from these materials has an internal loss (tan ) of only about 0.02 which is not suitable for practical applications. A diaphragm made from materials comprising graphite mixed with polyvinyl chloride and polyvinyl chloride has an internal loss as great as 0.05. However, the Young's modulus of such material is decreased significantly at room temperature or elevated temperature and is not suitable for use in a speaker installed in automobiles because the speaker would often be subjected to high temperatures.

The speaker diaphragm of the present invention is designed to retain the desired property of graphite and achieve greater internal loss without having its Young's modulus reduced or experience any great change in its physical properties even if placed under elevated temperature. To this end, the speaker diaphragm of the present invention is formed from graphite that is mixed with a combination of polyvinyl chloride and copolymer comprised of acrylonitrile, butadiene and styrene, (hereinafter ABS resin). The polyvinyl chloride is used as a binder for graphite flakes and the ABS resin is used to achieve greater heat resistance and formability so that a diaphragm having a higher heat deformation temperature is produced. In a preferred embodiment, a post chlorinated polyvinyl chloride may also be used to achieve even higher heat resistance.

When the polyvinyl chloride and ABS resin are combined together the polyvinyl chloride is preferably present in an amount of 80 to 40 parts weight based on the weight of the mixture of these two components combined with the graphite.

The ABS resin is preferably present in an amount of 20 to 60 parts by weight (based on the weight of all three components). The combination of the polyvinyl chloride and the ABS resin are generally present in an amount of about 100 parts by weight based on the weight of all three components. The graphite is combined with those two components to form a dispersion and the graphite is present in the dispersion in an amount of 50 to 200 parts by weight, preferably 50 to 100 parts by weight based on the weight of the dispersion.

The graphite is generally in the form of flakes having a density of about 2.3 and an average size of about 5y. The polyvinyl chloride used has a glass transition temperature of about 500C to about 80"C and the ABS resin used has a glass transition temperature of about 1 000C to about 1 00C. It is also possible to use a post chlorinated polyvinyl chloride in combination with the polyvinyl chloride.

The present invention is now described in greater detail by reference to the following examples to which the invention is by no means limited.

Example 1 Components Parts by weight Polyvinyl chloride 60 ABS resin 40 Lead stearate (both as a heat stabilizer for the polyvinyl chloride and as a lubricant for mixing) 2 Graphite flakes 200 The components listed above were mixed with a mixing roll, internal mixer or an extruder, and the resulting mixture was passed through a roll mix several times to form a sheet wherein the flat surfaces of the graphite flakes were parallel to the rolled sheet. The sheet has the following characteristics at 300C.

Density 1 .7 x103 kg/m3 Young's modulus 5.7x10'0 N/m2 Internal loss (tan ar) 0.02 The sheet was then formed by vacuum forming, pressure forming or any other suitable method into a diaphragm of a desired shape. The Young's modulus vs. temperature profile of the diaphragm is shown in the accompanying drawing in comparison with a conventional product prepared from the following formulation.

Comparative Example Components Parts by weight Polyvinyl chloride 100 Lead stearate 2 Graphite flakes 200 Example 2 Components Parts by weight Polyvinyl chloride 30 Post chlorinated polyvinyl chloride 30 ABS resin 40 Lead stearate 2 Graphite flakes 200 These components were mixed and treated as in Example 1 to form a sheet having the following characteristics.

Density 1 .7x 103 kg/m3 Young's modulus 5.5x 1010 N/m2 Internal loss (tan a) 0.2 A diaphragm formed from this sheet has a heat deformation temperature of about 1 000C which was 300C higher than that of the conventional product. If much less than 30 parts of the post chlorinated polyvinyl chloride is used, the heat deformation temperature of the sheet is decreased but its formability is improved. If much more than 30 parts of the post chlorinated polyvinyl chloride is used, the heat deformation temperature is increased but the formability is impaired. It is therefore necessary to control the amount of the post chlorinated polyvinyl chloride depending upon the specific use of the speaker.

Example 3 Components Parts by weight Post chlorinated polyvinyl chloride 60 ABS resin 40 Lead stearate 2 Graphite flakes 200 These components were mixed and treated as in Example 1 to form a sheet having the following characteristics.

Density 1 .7x 103 Kg/m3 Young's modulus 5.3x 1010 N/m2 Internal loss (tan a) 0.02 A diaphragm formed from this sheet has a heat deformation temperature of 1 200C that was about 500C higher than that of the conventional product.

The above data shows that the speaker diaphragm of the present invention experiences only a small drop in Young's modulus due to heat and hence is suitable for use in elevated temperatures.

Claims 1. A speaker diaphragm formed from a dispersion comprising graphite flakes; a polyvinyl chloride; and an ABS resin.

2. A speaker diaphragm as claimed in claim 1, wherein the dispersion is comprised of 40 to 80 parts by weight of the polyvinyl chloride and 60 to 20 parts by weight of the ABS resin based on the weight of the dispersion.

3. A speaker diaphragm as claimed in any of claims 1 or 2, wherein the polyvinyl chloride and ABS resin combined are present in an amount of 100 parts by weight based on the dispersion.

4. A speaker diaphragm as claimed in claim 1, wherein the dispersion is further comprised of a post chlorinated polyvinyl chloride.

5. A speaker diaphragm as claimed in claim 4, wherein the post chlorinated polyvinyl chloride is present in an amount of about 30 parts by weight based on the weight of the dispersion.

6. A speaker diaphragm as claimed in any of claims 1 or 2, wherein the graphite flakes are present in an amount of about 50 or 200 parts by weight based on the weight of the dispersion.

7. A speaker diaphragm as claimed in claim 6, wherein the graphite flakes are present in an amount of 50 to 100 parts by weight of the dispersion.

8. A speaker diaphragm as claimed in claim 7, wherein the graphite flakes have a density of substantially 2.3 and an average size of substantially 4,u.

9. A speaker diaphragm as claimed in claim 8, wherein the polyvinyl chloride has a glass transition temperature of substantially 500C to 800C and the ABS resin has a glass transition temperature of substantially 1000Cto 1 1 OOC.

10. A speaker diaphragm formed from a dispersion comprising graphite flakes; a post chlorinated polyvinyl chloride; and an ABS resin.

11. A speaker diaphragm as claimed in claim 10, wherein the post chlorinated polyvinyl chloride and ABS resin are present in an amount of 100 parts by weight based on the weight of the dispersion.

12. A speaker diaphragm as claimed in claim 11 or claim 12, wherein the graphite flakes are present in an amount of 50 to 200 parts by weight based on the weight of the dispersion.

1 3. A speaker diaphragm as claimed in claim 10, wherein the dispersion is comprised of 40 to 80 parts by weight of the post chlorinated polyvinyl chloride and 60 to 20 parts by weight of the ABS resin based on the weight of the dispersion.

14. A speaker diaphragm as claimed in claim 10, wherein the dispersion is comprised of 40 to 80 parts by weight of the post chlorinated polyvinyl chloride, 60 to 20 parts by weight of the

Claims

ABS resin, and 50 to 200 parts by weight of the graphite flakes based on the weight of the dispersion.

1 5. A speaker diaphragm as claimed in claim 14, wherein the graphite flakes have a density of substantially 2.3 and an average size of substantially 4,u.

1 6. A speaker diaphragm according to claim 1, substantially as described with reference to Example 1 or Example 2.

1 7. A speaker diaphragm according to claim 11, substantially as described with reference to Example 3.

New claims or amendments to claims filed on Tst Dex 1982 Superseded claims 2, 3, 5, 6, 11, 12, 13, 14 New or amended claims: 2. A speaker diaphragm as claimed in claim 1, wherein the dispersion is comprised of 40 to 80 parts by weight of the polyvinyl chloride and 60 to

20 parts by weight of the ABS resin.

3. A speaker diaphragm as claimed in any of claims 1 or 2, wherein the polyvinyl chloride and ABS resin combined are present in an amount of 100 parts by weight.

5. A speaker diaphragm as claimed in claim 4, wherein the post chlorinated polyvinyl chloride is present in an amount of about 30 parts by weight.

6. A speaker diaphragm as claimed in any of claims 1 or 2, wherein tne graphite flakes are present in an amount of about 5Q to 200 parts.

11. A speaker diaphragm as claimed in claim 10, wherein the post chlorinated polyvinyl chloride and ABS resin are present in an amount of 100 parts by weight.

12. A speaker diaphragm as claimed in claim 11 or claim 12, wherein the graphite flakes are present in an amount of 50 to 200 parts by weight.

13. A speaker diaphragm as claimed in claim 10, wherein the dispersion is comprised of 40 to 80 parts by weight of the post chlorinated polyvinyl chloride and 60 to 20 parts by weight of the ABS resin.

14. A speaker diaphragm as claimed in claim 10, wherein the dispersion is comprised of 40 to 80 parts by weight of the post chlorinated polyvinyl chloride, 60 to 20 parts by weight of the ABS resin, and 50 to 200 parts by weight of the graphite flakes.