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The present invention relates to an acoustic diaphragm made of a film containing at least one
unstretched or at least one uniaxially stretched polyester film layer containing 50 to t% or more
of a polybutylene terephthalate component. It is a thing. (The prior art and the problem to be
solved by the invention) As a speaker unit of headphones, a lightweight film diaphragm obtained
by thermoforming a polyethylene terephthalate film conventionally and a rare earth-based high
magnef are used. Because of its high rigidity and lack of internal loss, the mid-range response is
poor and the tone becomes hard. The object of the present invention is to solve the abovementioned drawbacks of the conventional polyethylene terephthalate diaphragm, and to make
the plastic diaphragm light in weight and high in rigidity and having high efficiency and high
reproduction frequency limit, and little acoustic distortion with almost no morphological
distortion. It is to provide. (Means for Solving the Problems) As a result of intensive studies on
these problems, the inventors of the present invention have invented a second acoustic
diaphragm as follows. That is, in the present invention, polybutylene terephthalate (hereinafter
referred to as PBT) is a main component. A film with a Young's modulus lower than that of
polyethylene terephthalate is selected as the diaphragm material, but in order to maintain its
compatibility and characteristics as a PBT, it is desirable that the PBT component is 50-t% or
more, preferably 60 wt% or more . The PBT resin used in the present invention is mainly
composed of PBT polymerized from terephthalic acid and 1,4-butanediol, and represents a
copolymer with another polyester and / or a blend thereof. The acid component as the
copolymerization component or the blend component may be terephthalic acid, isophthalic acid,
naphthalenedicarboxylic acid, 4.4′-diphenoxyethanedicarboxylic acid, acid, adipic acid, sebacic
acid, cyclohexanedicarboxylic acid, etc. Examples of the acid and diol components include
ethylene glycol, trimethylene glycol, 1,4-butanediol, hexamethylene glycol, polytetramethylene
glycol, bisphenol A, copolyglycol of polyethylene glycol and polypropylene glycol, and the like. Of
course, these PBT resins may be used alone or in combination of two or more. Further, as the
polyester as a blend component, a polyester formed by polymerizing the above-mentioned acid
component and diol component is used.
Preferably, crystalline thermoplastic polyester having PBT or butylene terephthalate repeating
units of 50 wt% or more is used. Further, these PBT may contain an antistatic agent, a lubricant,
an antifogging agent, a stabilizer, a dye, a pigment and the like. The intrinsic viscosity (a value
measured at 30 ° C. using a mixed solvent of phenol / tetrachloroethane (weight ratio 1/1)) of
the PBT-based resin is usually 1 to 0.5 to 3. Odj! /g。 Preferably, 1.0 to 2. Qdj! It is in
the range of / g. When the intrinsic viscosity is less than 0.5 dffi / g, the properties of the
obtained resin are hard and brittle, and breakage may occur during deep drawing. In addition,
the intrinsic viscosity is 3. Obtaining resins larger than Oi / g is difficult with current PBT
standard preparation methods. The PBT-based resin film can be used in an unstretched state, but
is preferably at least uniaxially stretched. The draw ratio is suitably 1.1 times or more, preferably
1.3 times or more. Further, better results can be obtained when biaxially stretched. The draw
ratio in this case is suitably 1.1 times or more, preferably 1.5 times or more, respectively in the
y1 side. The stretching method is not particularly limited, but in the case of uniaxial stretching, a
roll stretching method or tenter stretching method with two rolls is passed, and in the case of
biaxial stretching method, simultaneous biaxial stretching method is preferable. Although these
PBT resin films can sufficiently exhibit their characteristics even in a single layer, other resin
films can be laminated and used as needed. (Operation) Generally, in order to expand the
reproduction zone of the speaker, although a lightweight and high rigidity material is preferable
as a moving plate material, when it is made thin to reduce weight, it is used as a diaphragm.
There is a defect that the characteristic as a polymer material that Q is low and the peak at fh is
suppressed disappears and internal loss becomes small. The large internal loss is important for
damping the resonance when the diaphragm splits, PBT has a lower Young's modulus and an
appropriate internal loss compared to PET, and the PBT component By changing it, its rigidity
can be freely changed, and it becomes possible to select the loss passed through each diaphragm,
so that it is possible to use it even if the thickness of the diaphragm is made relatively thin in
order to reduce the weight. There is an advantage that it is possible to prevent the upper
resonance. Furthermore, PBT is easy to deep-draw on PETEQ and is not restricted by the
diaphragm shape. The present invention will be described in more detail by way of the following
Example 1 A polybutylene terephthalate and polyethylene terephthalate were heated and melted
by an extruder at a ratio of 7: 3 (weight ratio) and extruded from a T-die to form an unstretched
film with a thickness of 100 μm. The unstretched film was biaxially stretched at 100 ° to make
a 10 μm-thick stretched film. Vacuum forming the stretched film. The acoustic characteristics
were measured using a cone-shaped diaphragm having a diameter of 20 mm, and the values
were good as shown in Table 2 and there was no resonance. Table 1 (Effects of the Invention)
Adoption of such a diaphragm significantly improved acoustically important distortion and
power linearity in the midrange as compared with those of the conventional film film moving
plate. Of course, the film diaphragm according to the present invention can be used not only for
headphones but also as various diaphragms including dome-shaped speakers.
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