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Abstract: The present invention comprises at least one first and second outer layer (cover layer),
at least one first cover layer is composed of polyphenylene sulfide resin, and the halogen content
of polyphenylene sulfide resin (PPS-resin) is The invention relates to a multilayer composite for
use as a diaphragm for electroacoustic transducers, characterized in that it does not exceed 550
Multilayer composite for acoustic film
The present invention relates to a multilayer composite comprising at least one outer
polyphenylene sulfide film for use as a diaphragm (film) for an electroacoustic transducer.
Sound generation in cell phones and smart phones for the reproduction of speech, ring tones,
music etc. is performed using small electroacoustic transducers, so-called microphones.
The size of the diaphragm of such a microphone, which is also used for headphones, notebooks,
liquid crystal televisions or personal digital assistants (PDAs), typically ranges from 20 mm <2>
to 900 mm <2>.
Microphones become smaller and flatter because of the design requirements of the
corresponding electronic devices, but are operated at higher powers, so that the temperature
load on the microphone speaker, especially the temperature load on the diaphragm, is constantly
increasing ing. At the same time, the requirements for the acoustic characteristics of the speakers
increasingly used in smartphones, for example for loud music playback, should also have good
sound quality. Accordingly, the requirements for the mechanical load capacity and sound quality
of the microspeaker-diaphragm (film) have increased dramatically in recent years.
Loudspeaker diaphragms should generally be as stiff and light as possible to generate high sound
pressure and cover a wide frequency range, but on the other hand sufficiently to exhibit as
smooth a vibration as possible at the same time Should be attenuated. The characteristics of
stiffness, lightness, and sufficient damping are contradictory in design, so they can not all be
satisfied at the same time (the higher the stiffness, the lower the damping, and vice versa). It is
necessary to select the material of the diaphragm and to combine hard materials including good
damping materials, with overall adjustments regarding both the stiffness and damping of the
diaphragm). For this reason multilayer composites (especially multilayer laminates) are often
used and then they are formed into membranes (plates). In general, the multilayer composite
comprises a film-hardening or stabilization layer as well as a damping layer. The rigid films used
in currently marketed multilayer composites contribute little to the damping.
US 7,726,441 B describes a diaphragm of a multilayer composite of two rigid polymer films and
a damping adhesive layer situated between these films. US 8,189,851 B describes the use of a
soft pressure sensitive adhesive as a damping layer in a multilayer composite, mechanical as a
measure of the damping of the multilayer total membrane structure from the modulus of
elasticity E (Youngscher module) The loss factor (tangent delta tan δ) is mentioned. This is
defined as the ratio of the loss module E ′ ′ to the storage module E ′, tan δ = E ′ ′ / E ′,
and should have a minimum value in the relevant frequency interval.
Polyphenylene sulfide plastics are among others known as polymer film materials for rigid
polymer films (the outer layer of the membrane) (for the polyphenylene sulfide, the term PPS is
also used and used herein). Although the (micro) speaker manufactures a diaphragm using PPS
as a cover layer material, the acoustic distortion is usually insufficient and the acoustic signal is
lost. The quantity that quantifies the non-linear distortion of the loudspeaker and can be easily
determined by the loudspeaker is the so-called "total harmonic distortion", which is usually
referred to in English as the term "total harmony distortion" or simply "THD". Thus, this term is
also used within the scope of the present specification as it is customarily used by those skilled in
the art.
THD is defined as the ratio of the total power Ph of all harmonics to the power of the
fundamental vibration Pi and is usually expressed as a percentage: THD [%] = (Ph / P1) <*> 100
Polyetherimide (PEI), polyarylate (PAR) or polyetheretherketone (PEEK) is used as the plastic
material used to achieve the optimum acoustical properties of the loudspeaker diaphragm as a
cover material However, it is quite expensive as PPS.
The preparation of PPS for such diaphragms used for membranes of the above type is usually
from high-boiling dipolar aprotic solvents such as phenylene dihalides in N-methylpyrrolidone, in
particular dichlorobenzene and sodium sulfide The polycondensation of
Such a process is shown, for example, in US 4,910,294.
Another method is shown in EP 0 737 705 A, where the polymer is made of halogen-terminated
prepolymers. As a result, commercially available polyphenylene sulfide films have a relatively
high content of halogen, which can be quantified by conventional analytical methods. In
principle, this is chlorine.
Conventional PPS products typically have a halogen content of more than 600 ppm, usually more
than 900 ppm. The ppm correspond to milligrams of halogen per kilogram of analyzed PPS film
material used.
The relationship between the halogen content of PPS films used in acoustic diaphragms (acoustic
films) and the properties of these diaphragms for use as speakers has not yet been discussed.
US7,726,441B US8,189,851B US4,910,294
It is an object of the present invention to provide a film combination for the production of
loudspeaker membranes (acoustic diaphragms), which are cheap and thus economically
advantageously produced acoustic membranes have improved acoustical properties as compared
to commercial PPS films. It is to provide a system.
The diaphragm must not lose good properties with regard to high bending stiffness, low density
and high internal damping.
Surprisingly, this problem is solved if PPS is still used as the material of the cover film of such a
diaphragm, where PPS with a total halogen content of less than 550 ppm is selected.
The measurements showed that the loudspeaker distortion exhibited by THD when using such a
vibrating version is significantly lower than when using a membrane with a top layer consisting
of commercially available PPS. Such effects were not foreseeable to those skilled in the art.
Thus, the present invention comprises at least one first and second outer layer (hereinafter also
referred to as cover layer) and optionally an attenuation layer arranged between these top layers,
and For use as a diaphragm for an electroacoustic transducer (transducer), characterized in that
the cover layer consists of polyphenylene sulfide resin and the halogen content of the
polyphenylene sulfide resin (PPS-resin) does not exceed 550 ppm, or The invention relates to a
multilayer composite for producing
Optionally, additional layers may be disposed between the cover layers.
The multilayer composite may be a two-layer composite (only the cover layer), a three-layer
composite (in particular a cover layer, a damping layer, a cover layer) or even more than three
layers Preferably, at least one layer between the cover layers is an attenuation layer. The at least
one damping layer (in a three-layer or multilayer composite) is particularly preferably an
adhesive layer, in particular a pressure-sensitive adhesive.
Preferably, the first cover layer has a thickness of 1 to 50 μm, most preferably 1 to 5 μm.
Films suitable for use as the second cover layer include, for example, polyetheretherketone
(PEEK), commercially available polyphenylene sulfide (PPS), polyethylene naphthalate (PEN),
polyethylene terephthalate (PET), polybutylene terephthalate Films from (PBT), polyarylate
(PAR), polyimide (PI), polyetherimide (PEI), polyphenylsulfone (PPSU), polyethersulfone (PES),
polysulfone (PSU) or thermoplastic polyurethane (TPU) It is.
However, according to the preferred embodiment of the present invention, it is particularly
advantageous to also produce a second cover layer of low halogen content PPS, both cover layers
of the multilayer composite comprising polyphenylene sulfide resin, the halogen content of
which Of each should not exceed 550 ppm.
Preferably, the second cover layer also has a thickness of 1 to 50 μm, preferably 1 to 5 μm.
In a particularly advantageous form of the invention, a symmetrical multilayer composite or at
least a cover, wherein both cover layers are made of the same low-halogen PPS resin and / or the
thickness of both cover layers is identical. It is a symmetrical multilayer composite that is
symmetrical with respect to the layers.
In a variant of the embodiment, the multilayer composite according to the invention consists of
two laminated resin films, at least one film-optionally both films consisting of polyphenylene
sulfide resin, which have a halogen content of 550 ppm It does not exceed.
Such a two-layer film system is used for the diaphragm in cases where the two-layer composite
exhibits sufficient damping properties without an additional damping layer and / or where the
requirements for damping are low in the application. It can be used particularly well.
It is particularly advantageous if, during the production of the two-layer composite, one film can
be softened and / or melted to improve the adhesion to the other film.
Films made of thermoplastic polyurethane are particularly suitable for this purpose.
Thus, a particularly advantageous embodiment of a two-layer composite is one comprising a TPU
film and a film of halogen reduced PPS.
As mentioned at the outset, the diaphragm needs to be sufficiently damped to smooth the
frequency response as much as possible.
Thus, the damping layer can preferably be configured as a single layer or as a multilayer thereof
between the two outer layers of the multilayer composite.
A measure of the damping of the multi-layer full diaphragm structure is the mechanical loss
factor (tangent delta; tan δ) defined by the ratio of loss module E ′ ′ to storage module E ′:
tan δ = E ′ ′ / E ′.
It is known that adhesive compositions, in particular pressure sensitive adhesives, can meet the
requirements of damping layers and can provide high damping of multilayer composites. In a
preferred method, the damping layer comprises a single or multilayer double-sided adhesive
adhesive tape, in particular a pressure sensitive adhesive tape. In particular, the damping layer is
formed by a single-layer or multi-layer double-sided adhesive tape, in particular a pressuresensitive adhesive tape. Such pressure-sensitive adhesive tapes can, in addition to their damping
effect, effectively carry out the bonding of the layers because of their (self-) adhesive properties.
In a variant of the preferred embodiment, the damping layer itself is a single layer, so that the
multilayer composite is a three-layer composite. Preferably, the damping layer is a layer of
pressure sensitive adhesive. Most preferably, the multilayer composite has a symmetrical trilayer structure of cover layer-pressure sensitive adhesive-cover layer type, and the chemical
composition and thickness of the outer cover layer are identical.
The thickness of the (pressure-sensitive) adhesive layer in the multilayer composite is
advantageously 2 μm to 100 μm, preferably 5 μm to 50 μm, more preferably 10 μm to 30
A further variant of the invention is a symmetrical or asymmetric five-layer structure with an
inner support layer or a stabilizing layer, for example polyetheretherketone (PEEK), commercially
available polyphenylene sulfide (PPS), polyethylene na Phthalate (PEN), polyethylene
terephthalate (PET), polybutylene terephthalate (PBT), polyarylate (PAR), polyimide (PI),
polyetherimide (PEI), polyphenylsulfone (PPSU), polyethersulfone (PES), It is formed from a film
from polysulfone (PSU), a thermoplastic polyurethane (TPU) or, particularly preferably, a film of
low halogen polyphenylene sulfide (PPS), optionally with a halogen content of less than 550
In addition, (pressure sensitive) adhesive layers are provided between the inner support layers or
the stabilization layers and the outer cover layers. Preferably, both (pressure sensitive) adhesive
layers are chemically identical and / or of the same thickness. However, the (pressure-sensitive)
adhesive layers can also be selected to differ with regard to their chemical nature and / or their
The thickness of the inner support layer or the stabilization layer is preferably 1 to 50 μm,
preferably 1 to 30 μm, particularly preferably 1 to 5 μm.
The thickness of the (pressure sensitive) adhesive layer is preferably 1 to 100 μm, preferably 1
to 50 μm, and more preferably 2 to 40 μm.
In this case, it is highly preferred to have a cover layer which is identical with respect to the
respective chemical composition and their respective thickness, and an adhesive layer which is
identical with respect to the respective chemical composition and the respective thickness
(pressure sensitive) It is a symmetrical five-layer composite structure.
(Pressure sensitive) adhesives (self-adhesive compositions or PSAs, also called pressure sensitive
adhesives) are in particular polymeric substances and, where appropriate, other components, for
example suitable additives such as tackifying resins Depending on the application temperature
(unless otherwise defined, room temperature) is permanently tacky, adheres permanently,
adheres to several surfaces on contact, and in particular immediately adheres (has so-called
"tackiness" ).
They can adequately wet the already bonded substrate at the application temperature without
solvent or thermal activation, but usually by the effect of higher or lower pressure, so that for
adhesion with the substance There can be sufficient interaction on the substrate.
The operating parameters that influence this process are, inter alia, pressure and contact time.
The unique properties of pressure sensitive adhesives are due, inter alia, to their visco-elastic
Advantageously, an acrylate pressure sensitive adhesive is used for the adhesive layer. These are
polymer based adhesives consisting of polymers of acrylic acid and acrylic acid monomers
including methacrylic acid, esters of these acids and copolymers of further copolymerizable
derivatives of these acids, the acrylic acid monomers together with other monomers It can be
used in such an amount that the properties of the adhesive can be determined primarily. For
example, pressure sensitive adhesives having an acrylic monomer content (pure acrylate based)
of at least 50% by weight, at least 80% by weight or 100% by weight can be used for the
Other adhesives known to the person skilled in the art, in particular pressure-sensitive adhesives,
are also possible and can be used according to the invention, in particular those which have good
adhesion to PPS and also have good damping properties. . Thus, for example, silicone adhesives
and / or polyurethane adhesives and / or rubber adhesives, in particular silicone pressure
sensitive adhesives, polyurethane adhesives or rubber adhesives can be used.
To produce a multilayer structure, the pressure sensitive adhesive is applied directly to one of
the two cover layers at the desired layer thickness using application methods well known to the
person skilled in the art or, for example, Indirectly by applying a temporary transfer support
such as a siliconized paper or a siliconized film, laminating it with the first of two film layers, and
coating the temporary transfer support Apply The second of the two film layers can be fed
directly to the pressure sensitive surface of the laminated composite. A laminating device, which
continuously connects the material webs between rubber cylinders or steel and rubber cylinders,
is suitable for reliably achieving the adhesion of the composite and for avoiding aeration.
The manufacture of electroacoustic transducers, in particular diaphragms for loudspeaker
diaphragms (membranes), is carried out, for example, by embossing or thermoforming a
multilayer composite according to the invention, which is formed into a specific threedimensional shape. Be done. For this purpose, the multilayer composite is, for example, heated in
a thermoformed article and pressed into the form of a finished membrane by applying pressure
and / or vacuum.
The multilayer composites according to the invention can be advantageously used in processes
for producing diaphragms (films) for electroacoustic transducers, where they are subjected to the
process of multi-cavity thermoforming. In this method, the multilayer laminate is placed on a
heatable thermoformed body comprising a recess having a negative impression of the formable
membrane. Subsequently, the multilayer laminate is heated, for example by IR radiation, thereby
being softened and then pushed down from above with compressed air and pushed into the
recesses. Alternatively, the softened multilayer laminate can be pressed into the mold with a
silicone or foamed silicone stamp.
In the multilayer composites produced according to the invention, a total halogen content of less
than 400 ppm can be achieved. Thus, in addition to the improvement of the acoustical properties,
a further advantage is that the loudspeaker diaphragm (film) obtained therefrom is below the
limit normally required in the electronics industry, due to the lower total halogen content.
EXAMPLES, COMPARATIVE EXAMPLES Without intending to limit the present invention thereto,
the concept of the present invention will be described below using a plurality of examples and
comparative examples.
The halogen content was first analyzed by an external laboratory with commercially available
standard PPS film.
In this case, chlorine was found as a halogen and no other halogen was detected in significant
amounts. The measured sample had a chlorine content of 1000 ppm (1000 mg / kg) or more.
The halogen content of the halogen reduced PPS film was 532 ppm.
For THD measurement, 4 μm thick PPS film, 10 μm each acrylate or silicone-damping layer, 4
μm thick PPS film (in each case Example 1 and Comparative Example 1, and Example 2 and
Comparative Example 2 The same three-layer composites were produced in the same manner as
in (1), using halogen reduced PPS films in the examples of the invention and standard PPS films
in the comparative examples (see Table 1).
From these three-layer composites, rectangular diaphragms (films) 15 mm long and 11 mm wide
were formed by thermoforming, which were otherwise installed in the same microphone.
The THD curve is recorded using the R & S® UPV Audio Analyzer (Rohde & Schwarz) in the same
procedure, it is possible to compare the values directly.
The precise relative values of THD measurements do not depend on relative comparisons.
The resonant frequency of both loudspeakers is 450 Hz. The THD curves of loudspeakers with
multilayer composites made from halogen reduced PPS films use commercially available PPS film
membranes for both composites with acrylate damping layers and composites with silicone
damping layers 0.1 to 10 kHz lower than the THD curve of the speaker. Table 1 shows THD
values at frequencies below the resonant frequency.
Experiments have shown that the purpose according to the present invention can be achieved by
replacing a standard PPS film with a PPS film having a low halogen content (<550 ppm) in an
acoustic film (diaphragm).
The effect of the halogen content of the PPS film used for the sound quality of loudspeaker
diaphragms (films) made of such films was not expected by the person skilled in the art.
The THD values of diaphragms (films) made with PPS films with reduced halogen content
reduced below the resonance frequency were manufactured under the same commercially
available similar standard PPS films It was found to be lower than that of the comparative
example diaphragm (membrane) (equal thickness and shape, same loudspeaker).
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