GB2232847A

GB2232847A - Carbonaceous diaphragm

Info

Publication number: GB2232847A
Application number: GB8912883A
Authority: GB
Inventors: Mitsuru Yoshida
Original assignee: Mitsubishi Pencil Co Ltd
Current assignee: Mitsubishi Pencil Co Ltd
Priority date: 1989-06-05
Filing date: 1989-06-05
Publication date: 1990-12-19
Also published as: GB8912883D0; DE3918774A1; FR2649275A1

Description

PROCESS FOR PRODUCING DIAP1HRAGM FOR 2 SPEAKER OF FULLY CARBONACEOUS

MATERIALS 3 4

BACKGROUND OF THE

The present invention relates to a process for producing 6 a diaphragm for a speaker of fully carbonaccous materials. More 7 particularly. the imyention relates to a process for producing a 8 diaphragm for a speaker of fully carbonaccous materials having a 9 high hardness, a high elasticity, a high strength. a light weight and a suitable internal loss as Compared with a conventional 11 12 I; 13 j! 14 i 11 li 1.

16 17 18 19 22 23 24 26 27 28 29 1 11 il il diaphragm, loss deformation by an external force, small distortion of sound, wide reproducing sound range, distinct sound quality and adapted for a digital audio age inexpensively by an industrially simple method.

It is generally required to satisfy as a diaphragm for a speaker the following conditions.

(1) large propagating velocity of sound, (2) adequately large internal loss of vibration, (3) large bending rigidity rate, and (4) stable against variation in the atmospheric conditions,'.no deformation nor change of properties.

More specifically, the material for the diaphragm is required to reproduce in high-fidelity over a broad frequency band as a diaphragm. To efficiently and distinctly produce sound quality, the material should have high rigidity, a light weight, no distortion such as creep against external stress. The conventional materials use paper, plastic ind metals. However, the paper and plastic have adequately large internal loss, but small propagating velocity of sound and unstable disadvantage against variation in the atmospheric conditions, and the metals have larger 1 1 1 1 i i 1 1 1 propagating velocity than the paper and the plastic, but are still 2 insufficient, and a disadvantage of extremely small internal loss.

3 Recently, the use of a diaphragm for a speaker of 4 carbonaceous materials has been proposed due to the excellent features of carbon materials, i.e., a light weight, a high rigidity, an 6 adequately intemal loss, and stability against variation in the 7 11 atmosphere conditions such as temperature and moisture. More 8 9 11 1 ii 11 fl I! 12 iii i! 13 il 1 14 i! 16 17 18 19 21 22 23 24 26 27 28 29 !I i.

li :1 i:1 1 specifically, plastics to be carbonized or plastics in which carbon powder is dispersed are formed in sheets, the sheets are molded in a diaphragm shape by utilizing its deformation by heating, carbonized and calcined.

The large propagating speed of sound is important among the features of the diaphragm. It is known that preferable results are obtained as a diaphragm of carbonaceous material due to a composite rule in a composite material in which carbon fiber and particularly short fiber of carbon fiber having high elastic rate, crystalline graphite powder or graphite whisker is blended as compared with the material carbonized solely with an organic binder.

However, the carbon powder and specially the powder having higher elastic rate contains a crystal structure that carbon elements are regularly arranged with very small surface energy, thereby resulting in a less affinity with the surface or an organic binder. Accordingly, the bond between the organic binder of matrix and the carbon powder is weak only by merely dispersing, mixing and kneading the mixture of the organic binder and the carbon powder, with the result that it cannot be considered that a large bonding strength exists in the boundary between the binder carbon carbonized from the organic binder and the carbon powder in the fine structure of the diaphragm obtained by the 2 i 1 1 1 1 1 1 i 1 1 1 1 carbonization. The conventional diaphragm cannot satisfy the 2 3 P 6 7 8 v 11 !i 4 5 12 13 14 16 17 18 19 23 24 26 27 28 29 30 C 'i $I i:

!l i, 21 22 I comDosite rule nor utilize the excellent characteristics of the carbon powder due to the reasons described above.

Further, it is also known that, when a filler is filled in the organic binder, the flexibility and the elongation of a preliminarily molded sheet decrease due to an increase in the viscosity of the rxiixed composition, resulting in disadvantages of less moldability than the material in which no filler is filled.

Therefore, there also arises a disadvantage that the quantity of the filler to be added is limited.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a process for industrially simply and inexpensively producing a diaphragm of fully carbonaceous materials having a high hardness, a high elasticity, a high strength, a light weight, an i 1 1 1 j 1 i 1 adequately internal loss, and thus less deformation by an external 1 force, small distortion of sound, wide reproducing sound range, distinct sound quality and adapted for a digital audio age by mixing a large quantity of carbon powder to perform excellent characteristics of the carbon powder by a composite rule by the use of a chemically bonded state or a physically bonded state in the boundary between the binder carbon and the carbon powder which cannot be obtained by a conventional process.

The inventor has undertook a study to perform the above-described object, and has thus completed by developing a process for producing a diaphragm for a speaker of fully carbonaceous materials comprising the steps of mixing carbon powder in an organic binder carbonized after calcining, kneading the mixture composition uniformly mixed and dispersed, 3 1 1 1 1 1 M fl I! 1 preliminarily molding it in a sheet shape, molding the 2 k preliminarily molded material in a diaphragm shape, 3 insolubilizing, infusibilizing the mixture and calcining the mixture 4 in an inert atmosphere, wherein the mixture composition contains a titanate coupling agent. Thus, a rigid bonding strength is provided in the boundary between the organic binder and the i 1 1 carbon powder in, the green state of the mixture composition, the mixture is calcined as it is so as to perform the above-mentioned i 1 object, thereby completing the present invention.

The present invention will be described in more detail.

11 A titanate coupling agent for use in the present invention is of an organic titanate having the following structure.

i 1 1 14 (R0)m - Ti - (- OXI - R2 - Y)N ± inorganic phase -) ± organic phase --> 16 i 1 17 Various type and derivatives of the titanate coupling 18 agent are obtained according to the types of the functional group 19 and the hydrocarbon group for determining the structure as disclosed in the above-described structural formula. In the i 1 1 1 1 present invention, it is preferable to suitably select the organic 22 phase according to the type of the organic binder to be used and 23 the inorganic phase according to the carbon powder.

24 The adding rate of the titanate coupling agent to the 1 1 mixture composition is 0.1 to 5 wtA with respect to the carbon 26 powder and more preferably 0.5 to 2 wtA according to the types 27 of the organic binder and the carbon powder to be used and the i quality and the properties of the product to be obtained.

A process for adding the titanate coupling agent to the mixture composition of the organic binder and the carbon powder 4 1 1 1! 1 2 3 4 6 7 8 9 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29 il 11 1 I! includes an integral blending method for adding the mixture by dissolving it in a plasticizer of organic binder, process oil or solvent in case of mixing and kneading the mixture, a dry pretreating method for dropping or spraying necessary quantity of titanate coupling agent directly or by dissolving it in a small amount of solvent while agitating the carbon powder, and a wet pretreating metho4 for dissolving a titanate coupling agent in a large quantity of solvent, mixing it with carbon powder by agitating, and then removing by drying the solvent or using it as it is. The present invention does not particularly limit the adding methods, but may suitably select the optimum method.

Then, the other constitution of the present invention will be described in detail.

The organic binder in the present invention selects one or more of thermoplastic resin, thermosetting resin, pitches, and natural or synthetic compound having condensate polynuclear aromatic group in a basic structure to be carbonized in an inert atmosphere.

The carbon powder used in the present invention are usable fine powder of artificial graphite, natural graphite, carbon black, cokes, carbon fiber, or "graphite whisker in a range of 10 to 90 wt.% of the mixture composition. Preferable results can be provided by selecting short fiber of carbon fiber having high elastic rate, crystalline graphite powder or graphite whisker by considering the acoustic properties of the diaphragm for a speaker of carbonaceous materials to be obtained. More preferably, the crystalline graphite powder having ideal features as a reinforcing material of a diaphragm for a speaker having 1020 GPa of theoretical elastic rate as extremely higher value than other carbon powder, platelike and flat two-dimensional 1 1 1 1 1 If 1 t 2 3 4 6 7 8 9 11 12 13 14 18 i 19 22 23 24 25 26 27 28 29 30 extensions of crystal state may be used preferably. The size of the powder particle is 50 microns or less and more preferably 20 microns or less of mean particle diameter to obtain preferable results.

In the process of the present invention, when mixing i 1 titanate coupling agent in the mixture composition or in order to raise the mixing or kneading characteristics of organic binder and carbon powder, sheeting characteristic of preliminary molding and the molding characteristics of a diaphragm shape, one or more of plasticizer, such as DOP, DBP, TCP, DOA, DOS, DAP, propylene carbonate, N-methylpyrrolidone or solvent, and/or one I or more of molding assistant, such as chlorinated polyolefin, ethylenevinyl acetate copolymer, ethyl en e- acrylic copolymer, metallic soap, fatty soap, natural wax, petroleum wax, etc. may be added in very small amounts, as required.

i i An embodiment of a process for producing a diaphragm for a speaker of fully carbonaceous materials with the materials described above according to the present invention will be described in detail.

1 First, organic binder, carbon powder, and plasticizer and/or solvent to be added as required, and/or molding assistant, carbonization regulator are measured, and the mixture is uniformly dispersed and mixed by a mixer by means of a process with titanate coupling agent according to any of the processes described above.

Then, the resultant mixture is kneaded. More preferably, in order to produce rigid chemical bond or physical bond with the organic binder and the carbon powder in the mixture composition through the titanate coupling agent, a kneader which can add high shearing force is employed. As a result, kneaded mixture in 6 i 1 ( 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29 which the binder carbonized after calcining is chemically and physically bonded to the surface of the carbon powder by means of mechanochemical reaction occurred by the mechanical energy can be provided. Particularly when the carbon powder in which the surface is relatively stable and inactive as compared with other fillers is employed, the surface formed due to the frictional pulverization or cjeavage of the powder particles by means of the high shearing force is very active with very large bonding strength with the titanate coupling agent to be effective. When carbon fiber is used as the carbon powder, it is noted that the fiber may not be excessively cut. The kneader for applying the high shearing force includes a two or three roll machine, a pressure kneader, a Banbury mixer, a biaxial screw extruder or a ball mill, etc.

Then, the kneaded mixture is sheeted in a uniform thickness by means of rolls, an extrusion molding Machine with T die disposed at the end thereof or other film forming machine.

Subsequently, the sheet is mounted in a die in which a contraction after carbonization is read out in a diaphragm shape to be obtained, and shaped in a desired diaphragm shape by means of a vacuum shaping method, a compression shaping method or a blow molding method known per se.

Then, the green molding is infusibilized and insolubilized. The infusibilizing and insolubilizing steps include, in case of producing an ordinary carbon material, a process for heat treating at 150 to 400"C in an oxidative atmosphere, such as air or ozone, a process for heat treating at 50 to 400"C in corrosive gas atmosphere, such as ammonia gas or chlorine gas, and a process for irradiating a radioactive ray. In the process of the present invention, the infusibilizing and insolubilizing steps are not 7 1 1 1 1 1 1 1 1 ( 2 3 6 Ij I 1 1 1 7 11 8 11 H 9 h II 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29 particularly limited. The infusibilizing and insolubilizing steps may be omitted according to the type of the organic binder to be used. Successively, the molding treated as described above is gradually heated from room temperature in an inert atmosphere, such as nitrogen or argon gas, heated to 700C or higher and more preferably 1000"C or higher to be carbonized, then cooled, and removed as a product. The diaphragm for a speaker thus obtained according to the process of the present invention has the following excellent features.

(1) The organic binder and the carbon powder filler of matrix are chemically and physically bonded therebetween through the titanate coupling agent in the green state to provide large bonding strength in the boundary between the binder carbon parbonized from the organic binder and the carbon powder in the fine structure of the diaphragm obtained by the carbonization. Thus, a composite rule is satisfied to utilize the excellent characteristics of the carbon powder.

(2) The viscosity of the mixture composition is reduced by the action of the titanate coupling agent. As a result, the following improvements are provided. a) Since the ratio of the carbon powder in the mixture composition can be increased as compared with the prior art, the characteristics of the diaphragm are improved. b) Even if the adding ratio of the carbon powder is the same as the prior art, the degree of freedoms of the

8 i 1 1 1 i 1 i 1 1 1 ( 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 moldability is increased to obtain more complicated shape or deeply drawn diaphragm. Even if the adding ratio of the carbon powder is the same as the prior art, the adding quantity of the plasticizer and the solvent to be added as required to provide plasticity of the mixture composition can be reduped. This advantageously acts in the infusibilizing and insolubilizing steps to be executed before calcining to save energy and cost.

ii 11 :i il 1 1:

P 11 1; !1 il II il 11 i 1 1 DESCRUMON OF THE PREFERRED EMBODUVIENTS The present invention will be described by examples of process for producing a diaphragm for a speaker of fully carbonaceous materials, but the present invention is not limited to the particular examples.

[Example 1]

Solution that 0.5 part by weight of acylating titanate coupling agent (Titacote S-181 produced by Nippon Soda Co., Ltd., Japan) was dissolved in 10 parts by weight of DBP was dropped while dispersing mixture composition having 40 parts by weight of chlorinated vinyl chloride resin having 65 wt.% of chlorination degree (Nikatemp T-742 produced by Nippon Carbide Kogyo K.K., Japan), 60 parts by weight of natural flaky graphite powder (CSP produced by Nippon Graphite Kogyo K.K., Japan) and I part by weight of stearic acid amide in a Henschel mixer, the mixture was further dispersed and mixed for 10 min., then kneaded under a heating condition by a pressure kneader, and further sufficiently kneaded by means of a three rol.Is machine. Then, the kneaded mixture was removed, and then preliminarily molded in a sheet cl 1 1 1 i 1 9 i 1 1 1 1 11 1 1 1 ( 2 3 4 6 13 14 16 17 18 19 21 22 23 7 8 9 11 12 24 25 26 27 28 29 30 having 150 microns of thickness by milling rolls. Thereafter, the sheet thus provided was molded in a dome shape having 36 mm of diameter in a vacuum molding machine in which heated metal mold was mounted. Thereafter, the molding was separated from the metal mold, charged in a heating oven heated at 200'C to be insolubilized and infusibilized, gradually heated to 1000C from room temperature, in nitrogen gas atmosphere to be carbonized, then cooled and the product was then removed.

The thus obtained diaphragm for a speaker of fully carbonaceous materials has accurately maintained a dome shape having 90 microns of thickness and 35 mm of diameter, and has exhibited the characteristics of 1.65 of specific weight, 280 GPa of Young's modulus, 13 km/sec. of sound velocity, and 0.03 of internal loss.

[Example 2]

Solution that 0.5 part by weight of monoalkoxy titanate coupling agent (Blaneact TTS produced by Ajinomoto Co., Ltd., Japan) was dissolved in 5 parts by weight of IPA was dropped while dispersing carbon powder having 25 parts by weight of natural flaky graphite powder (CSP produced by Nippon Graphite Kogyo K.K., Japan) and 5 parts by weight of PAN carbon short fiber (Toraka chopped fiber T008A produced by Toray Industries, Inc. , Japan) in a Henschel mixer, further dispersed and mixed for 10 min., and then the IPA was volatilized. 70 parts by weight of furan resin (Hitafuran VF-302 produced by Hitachi Chemical Co., Ltd., Japan) was added thereto, kneaded at room temperature for 40 min. in a Warner mixer, and then kneaded in a three roll machine for ink cooled with water. Then, the kneaded mixture was removed, 4 parts by weight of 50 wt.%-p-toluene sulfonic f 1 i 1 i i ' 1 1 1 i i i i i i 1 ( 2 3 4 0 7 8 9 11 12 13 14 15 16 17 18 19 22 23 24 25 26 27 28 29 30 !1 1 1 acid methanol solution was added thereto, reduced under pressure, and defoamed while sufficiently agitating the mixture at room temperature in a high speed homogeneous mixer. Subsequently, the mixture was sheeted 150 microns of thickness on a back sheet by a coating machine in which a drying zone was mounted with air heating. Then, the sheet thus obtained was separated from tho back sheet, and molded in a dome shape having 40 mm or diameter by means of a vacuum molding machine in which heated metal mold was mounted. Thereafter, the molding was separated from the metal mold, charged in a heating oven heated at 200"C to be insolubilized and infusibilized, then gradually heated from room temperature to 1000"C in nitrogen gas atmosphere to be carbonized, then cooled and the product was then removed.

The diaphragm thus obtained for a speaker of fully carbonaceous materials has accurately maintained a doe shape having 90 microns of thickness and 35 mm of diameter, and exhibited the characteristics of 1.50 of specific weight, 120 GPa of Young's modulus and 8.9 km/sec. of sound velocity and 0.01 of internal loss.

[Comparison Example 1] The same mixture composition as that of the Example I but except the titanate coupling agent was removed was molded under the same conditions as those in the Example 1. Then, since the flexibility and the elongation of the sheet were smaller, the top head of the stepwise dome molded was cracked, and the product could not be obtained.

Then, the mixture ratio of the organic binder and the carbon powder was altered, i.e., the sheet to be molded was 1 1 1 t 2 3 4 5 6 7 8 9 10 11 12 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 11 H adjusted by 50 parts by weight of chlorinated vinyl chloride resin and 50 parts by weight of natural flaky graphite powder, molded, and a product was then obtained. Then, a diaphragm was obtained under the same conditions as those in the Example 1.

The obtained diaphragm for a speaker of fully carbonaceous materials was accurately maintained in a dome shape having 90 inicrons of thickness and 35 mm of diameter, but exhibited 1.65 of specific weight, 100 GPa of Young's modulus, 7.8 km/sec. of sound velocity, and 0.03 of internal loss, which were deteriorated as compared with those in the Example 1.

[Comparison Example 21 The same mixture composition as that of the Example 2 but except the titanate coupling agent was removed was molded under the same conditions as those in the Example 2. Then, since the flexibility and the elongation of the sheet were smaller, the top head of the stepwise dome molded was cracked, and the product could not be obtained.

Then, the mixture ratio of the organic binder and the carbon powder was altered, i.e., the sheet to be molded was adjusted by 3 parts by weight of furan resin, 12 parts by weight of natural flaky graphite powder and 3 parts by weight of PAN carbon short fiber, molded, and a product was then obtained. Then, a diaphragm was obtained under the same conditions as those in the Example 2.

The obtained diaphragm for a speaker of fully carbonaceous materials was accurately maintained in a dome shape 90 microns of thickness and 35 mm. of diameter, but exhibited 1.50 of specific weight,.70 GPa of Young's modulus, 6.8 12 i 1 1 i 1 1 1 i i 1 1 1 1 1 1 ( 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29 1 km/sec. of sound velocity, and 0.01 of internal loss, which were deteriorated as compared with those in the Example 2.

As exhibited in the Examples described above, the process according to the present invention has enabled the diaphragm for a speaker of fully carbonaceous materials to be produced by chemically and physically bonding between the organic binder and the carbon powder filler of matrix in the green state through the titanate coupling agent different from the prior art process, resulting in a large bonding strength existed in the boundary between the binder carbon carbonized from the organic binder and the carbon powder in the fine structure of the diaphragm, thereby satisfying the composite rule, increasing the mixture ratio of the carbon powder to utilize excellent characteristics of the carbon powder.

Therefore, the diaphragm obtained according to the process of the present invention has excellent properties as the diaphragm having high hardness, high elasticity, high strength, light weight, less deformation by external force due to adequate internal loss, small distortion of sound, a wide reproducing sound range, a distinct sound quality and adapted for a digital audio age. In addition, the pro cess according to the invention is industrially simple, and advantageous for inexpensively producing the diaphragm having excellent properties as described above.

r 13 i 1 1 1

Claims

CLAIMS:

A process for producing an acoustic diaphragm comprising mixing carbon powder in an organic binder carbonized after calcining, kneading the mixture, preforming the mixture into a sheet and moulding the preform into a diaphragm shape, insolubilizing, infusibilizing the moulded mixture, and calcining the mixture in an inert atmosphere, wherein the mixture contains a titanate coupling agent.
2. A process according to claim 1, wherein the titanate coupling agent is present in an amount of 0. 1 to 5 wt.% with respect to the carbon powder.
3. A process according to claim 1 or claim 2, wherein the titanate coupling agent is added by dissolving it in a plasticizer of organic binder, process oil or solvent in case of mixing and kneading the mixture, by dry pretreating method for dropping or spraying the required amount of titanate coupling agent directly or by dissolving it in a small amount of solvent while agitating the carbon powder, or by dissolving a titanate coupling agent in a quantity of solvent, mixing it with carbon powder and then removing by drying the solvent or using it as it is.
4. A process according to any one of claims 1 to 3, wherein the organic binder comprises one or more of kI t thermco. stic resin, thermosetting resin, pitches, and natural or synthetic compound having condensate polynuclear aromatic group in a basic structure to be carbonized in an inert atmosphere.
5. A process according to any of claims 1 to 4, wherein the carbon powder comprises one or more of artificial graphite, natural graphite, carbon black, cokes, carbon fibre, or graphite whisker in a range of 10 to 90 wt.% of the mixture composition.
6. A process according to any one of claims 1 to 5, wherein the mean particle diameter of the powder is 50 microns or less.
7. A process according to claim 1, wherein one or mor plasticizer, such as DOP, DBP, TCP, DOA, DOS, DAP, propylene carbonate, N-methylpyrrolidone or solvent, and/or one or more of molding assistant, such as chlorinated polyolefin, ethylene-vinyl acetate copolymer, ethylene-acrylic coplymer, metallic soap, fatty soap, natural wax, petroleum wax is added to the mixture, as required to raise the mixing or kneading characteristics of organic binder and carbon powder, sheeting characteristics of preliminary molding and th molding characteristics of the diaphragm shape.
S. A process for producing an acoustic diaphragm substantially as hereiniefore described with reference to examples 1 and/or 2.

Published 1990atThe Patent Office. State House. 6671 High Holborn, London WClR4T?- Further copies maybe obtained from The Patent Office.

Sales Branch, St M&T7 Cray. Orpington, Kent BRS 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. I/a7 y Ululyivx wanzuques ALo, m wary uray, j&enT,, L;on. vwr