Acoustic material

Details Acoustic material Acoustic material

1989-04-14

1992-03-24

Schofer, Joseph L.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

526352, 427 40, 381184, 381202, C08F11002, C08F 700

Patent

active

050989766

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to an acoustic material employed as the diaphragm for a loudspeaker and more particularly to an arrangement for improving internal losses in the acoustic material consisting essentially of the drawn polyethylene having a high modulus of elasticity.


BACKGROUND OF ART

The acoustic material employed in the diaphragm of a loudspeaker is required to have low density, high modulus of elasticity and hence a high rate of propagation of longitudinal waves and large internal losses, for enhancing the reproduction frequency range. With this in view, evolution towards industrial application of a so-called composite diaphragm is now underway using a variety of fibers such as carbon-, aramide-, glass- or polyolefin resin fibers as the reinforcing materials.
Above all, drawn high elastic modulus polyethylene, prepared by a crystal surface growth method, gel spinning-ultradrawing method or a melt draw orientation method is thought to be suitable as the acoustic material, in that it has a lower density and a higher rate of propagation of longitudinal waves. For example, it is shown in the Japanese Patent Publication KOKAI No - 182994/1983 to use polyethylene fibers having the rate of propagation of the longitudinal waves not lower than 4000 m/sec as the acoustic material
It is noted that the aforementioned high elastic modulus polyethylene fibers compare favorably with aluminum in elastic modulus (Young's modulus), but are inferior to polyester in internal losses (tan .delta.), as shown in Table 1 indicating the physical properties thereof, such that it cannot be used directly as the acoustic material, above all, as the loudspeaker diaphragm.


TABLE 1 ______________________________________ Young's tan.delta. modulus method of preparation ______________________________________ polyethylene a 0.013 47 fibrilated crystal fibers b 0.011 82 growth, gel spinning- c 0.014 78 ultra drawing, or melt spinning orienta- tion aluminum 0.008 73 -- polyester 0.053 5 biaxially drawn film ______________________________________
The present invention has been made in view of the above described deficiencies of the prior art and is aimed to provide an acoustic material which is improved in internal losses without impairing the high modulus of elasticity proper to the drawn high elastic modulus polyethylene and which is relatively free from higher harmonic distortion or from fluctuations in the frequency response, that is, crests and valleys, caused by split vibrations, when the acoustic material is used as the diaphragm material.


DISCLOSURE OF THE INVENTION

As a result of our eager and perseverant investigations towards improving the internal losses of the drawn high elastic modulus polyethylene, the present inventors have found that it is most effective to process drawn high elastic modulus polyethylene containing paraffin wax as the damping agent with plasma.
On the basis of this finding, the present invention provides an acoustic material which is characterized in that drawn high elastic modulus polyethylene containing 1 to 5 wt. % of paraffin wax obtained by, for example, melt draw orientation, is processed with plasma, and in that at least a portion of paraffin wax contained in said drawn high elastic modulas polyethylene is not extracted with boiling n-hexane.
The drawn polyethylene, a main constituent of the acoustic material of the present invention, is prepared by medium to low pressure polymerization of ethylene either singly or with a minor quantity of other .alpha.-olefins, such as propylene, 1-butene, 4-methyl-1-pentene or 1-hexene. It has higher modulus of elasticity, such as the initial tensile elastic modulus not less than 30 GPa and preferably not less than 50 GPa and fracture elongation not higher than 6% and preferably not higher than 4%, thanks to the high degree of orientation of the polyethylene molecular chain brought about by ultra drawing. Above all the drawn polyethylene prepared from ultra high molecular weight polyethylene having an intrinsi

REFERENCES:
patent: 4338420 (1982-07-01), Arbit
patent: 4606930 (1986-08-01), Ueno et al.
patent: 4879076 (1989-11-01), Sano et al.

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