JPS6021658B2 - molding material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a molding material obtained by mixing and thoroughly kneading polyvinyl chloride (hereinafter referred to as PVC) pitch and graphite powder (scaly graphite).

In general, the materials used to form diaphragms for audio equipment, especially speaker diaphragms, are lightweight and rigid so that when formed into a thin diaphragm plate, they reproduce efficiently and faithfully over a wide frequency range. It is required that the ratio E/p of Young's double E and the density p be large. Conventionally, wood pulp, synthetic resin, aluminum, titanium, etc. have been used from these points of view, but it is difficult to say that any of them has sufficient properties.

In addition, an example of using carbon-based materials is a composite material of carbon fiber and synthetic resin, but due to the lubricity of the surface of the carbon fiber itself, the bonding of the carbon fibers by the synthetic resin is insufficient. Also, due to the large anisotropy of carbon fiber, it is not possible to obtain large rigidity as a surface like a diaphragm. Therefore, the inventor focused on carbon as a material that is lightweight, has high rigidity, and has a large ratio E/p of Young's B modulus to density p, and developed a diaphragm obtained by first carbonizing or graphitizing a synthetic resin material. However, it was confirmed that the material shrinks and deforms significantly during the carbonization or graphite process of synthetic resins, causing cracks and other problems. In view of these points, an object of the present invention is to manufacture a diaphragm for audio equipment by carbonizing or graphitizing it, which is lightweight, has high rigidity, and has a large Young's modulus to density ratio E/p. It is an object of the present invention to provide a molding material from which a diaphragm for an audio device can be obtained, and which does not cause deformation of the material that occurs during the carbonization or graphitization process.

That is, the present invention provides a molding material obtained by making PVC into a pitch shape and kneading it with graphite powder.

In order to obtain a carbon material with a large Young's modulus and high mechanical strength, it is necessary to carbonize the material using a raw material with a high carbon yield.

If polyvinyl chloride is carbonized as is, the carbon yield is about 20-30%, and the properties after carbonization are Young's modulus of 3000.
Mechanical strength is low at ~4000k9/fence. By forming polyvinyl chloride into pitch, the carbon yield increases to around 80%. However, when PVC pitch is molded singly into the shape of a diaphragm and then carbonized, it is difficult to carbonize while maintaining the shape of the diaphragm. Furthermore, unless tension is applied during carbonization, the orientation will not be high and a highly elastic carbon material will not be obtained. Therefore, when using PVC pitch alone,
It is necessary to add solid powder because deformation tends to occur when forming into the shape of a diaphragm and carbonizing it.

The most preferred solid powder is graphite powder.
In this way, by adding graphite powder to a molding material made by adding graphite powder to PVC pitch, it is possible to prevent shrinkage and deformation that occur during pre-firing and carbonization; When forming into a plate shape, the graphite powder is oriented, which improves the elastic modulus and mechanical strength.When the paste is carbonized, the graphite powder becomes a crystal nucleus, resulting in carbon with good crystallinity. Effects such as improved elastic modulus and mechanical strength can be expected. Generally, materials added during carbonization include carbon materials such as carbon black and carbon fiber.
Carbon black has poor crystallinity, so it cannot be used as a good crystal nucleus.Also, graphitized carbon fiber is preferable, and if it can be cut into lengths of several meters or less, it will become a good crystal nucleus. Although it is possible, it is difficult to cut a size of less than a few French meters, and even if it were possible, it would be extremely expensive and impractical. The molding material of the present invention will be explained below.

The molding material of the present invention first obtains a PVC pitch by heating PVC in a non-oxidizing atmosphere such as nitrogen or argon gas to about 400 particles, and then adds 0.1 to 50 particles of particle size to the PVC pitch. It is obtained by adding and mixing graphite powder (scaly graphite) of m and kneading with a kneader or roller while heating to 200 to 300°C.

PVC can be pitched by simply heating it. Another method for obtaining pitch-like PVC is PVC.
It is also possible to use VC with a plasticizer or a solvent.
To facilitate cross-contamination of graphite powder, use a solvent to
C. Pitch is made into a liquid with appropriate viscosity at room temperature and kneaded without heating. However, in this method, the solvent shrinks when it evaporates, so care must be taken to avoid this. The amount of graphite powder added is in the range of 10 to 9 t%, but 40 t%
Good results are obtained with ~7 skin t%.

The particle size of the graphite powder varies depending on the size and shape of the diaphragm to be formed, but in general, the smaller the particle size, the better.
It is desirable that the particle size is about 0 French m (the average particle diameter is preferably 5 m or less). A method for manufacturing a diaphragm using the molding material obtained in this way will be described below. Molding process The molding material is first molded into the desired shape of the diaphragm, such as a dome shape or a cone shape.

The thickness of the molded product to be molded into a diaphragm varies depending on the size and shape of the diaphragm. When the molding material is obtained by mixing (kneading) while heating, a press mold formed into the desired shape and size of the diaphragm is heated to about 200 to 300 oo, and the press Mold.

When the molding material is obtained by mixing (kneading) a solvent, it is press-molded at room temperature and thoroughly dried to remove the solvent. The molded product obtained in the molding step, which is the pre-baking step, is heated in air (in an oxidizing atmosphere) to 250 to 30 psi to oxidize at least the surface of the molded product, and then during the next step, carbonization. It is made infusible to prevent deformation.

Note that this infusibility may be oxidized in ozone at a temperature of about 50 to 8,000 ℃ for 4 to 8 hours, and then further carried out in air at the above-mentioned temperature. In addition, in the infusibility process, heating may cause the molded product to deform, so a wire mesh or punched thin metal plate may be placed on a jig formed into the shape of a diaphragm, or it may be clamped. .

Further, good results can be obtained by setting the heating time to 1q hours or more.

Carbonization Step The molded product that has undergone the preliminary firing step is carbonized by heating to 1000 to 150 psi in a non-oxidizing atmosphere such as nitrogen or argon gas.

This carbonization process requires a slow initial overflow rate. That is, it is preferable to increase the temperature up to 40,000 at a heating rate of 1 to 20° C./hour, and to increase the temperature to 40,000 or higher, at a heating rate of 10 to 10 degrees C/hour. A carbide with better properties can be obtained by decreasing the heating rate. This is because if the initial heating rate is increased, the carbon material will have a rough structure and both Young's modulus and mechanical strength will decrease.
When the temperature is 0o○ or more, it is performed at an appropriately fast speed in consideration of economical efficiency.
Since the molded product is deformed during carbonization, it is preferable to carry out carbonization by placing or holding the molded product on a jig made of carbon or high-melting point metal, etc., and formed into the shape of a diaphragm.

The carbonized molded product can be used as a diaphragm as is, or it can be further processed as desired (deburring, drilling, etc.)
is applied to complete the diaphragm. Examples of the present invention will be described below.

Example: Added 50% graphite with particle size 〆m, and made PVC pitch 250.
A molding material was obtained by cross-wiring while heating to qo.

To form a diaphragm using this material, first press mold it into a dome shape with 250 mm, and then press the molded product at 300°C for 2 hours.
M Terama Oxidize in air, then 3 in nitrogen gas atmosphere
Heating at a temperature increase rate of 3°C/hour between 0000 and 500 o 0, and 20 qo/hour between 500 qo and 1250 o ○.
A speaker diaphragm was obtained which was carbonized by heating at a temperature increase rate of 1 hour. The Young's modulus of the diaphragm thus obtained was 16
000k9/fence, density was 1.6/m.

The table below shows a comparison between a diaphragm made of the molding material of the present invention and a diaphragm made of other materials. As shown in the table, the diaphragm using the molding material mixed with the PVC pitch graphite powder of the present invention has a specific elastic modulus E/about 5 times that of aluminum.
p, which is slightly inferior to beryllium.

Furthermore, the internal loss of the diaphragm obtained using the material of the present invention is about 1q louder than that of beryllium, and its frequency characteristics are second to none.
As shown in the figure, the resonant frequency of the same-shaped beryllium diaphragm indicated by the dotted line is almost the same as that of the Rabe Takagi diaphragm, and the characteristics are flat, and the frequency characteristics in the high frequency range are good, making it extremely excellent. It becomes something. As explained above, a molding material obtained by mixing PVC pitch and flaky graphite with an average particle size of 0.1 to 50 fm is molded and then carbonized to form a diaphragm. , it is possible to manufacture a diaphragm that has a large specific modulus of elasticity, a large internal loss, and is also inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a process diagram illustrating a method for manufacturing a diaphragm using the molding material of the present invention, and FIG. 2 is a comparison diagram showing the frequency characteristics of a diaphragm made of the material of the present invention and a beryllium diaphragm. Figure lFigure 2

Claims (1)

[Claims] 1. A molding material obtained by forming polyvinyl chloride into a pitch, mixing and kneading flaky graphite with an average particle size of 0.1 to 50 μm.