EP3694911A1

EP3694911A1 - Polymeric film and speaker diaphragm comprising it

Info

Publication number: EP3694911A1
Application number: EP18788851.6A
Authority: EP
Inventors: Andrew Elleray; Colin RIMMER
Original assignee: Victrex Manufacturing Ltd
Current assignee: Victrex Manufacturing Ltd
Priority date: 2017-10-12
Filing date: 2018-10-11
Publication date: 2020-08-19
Also published as: WO2019073242A1; CN111183175A; GB201716764D0; GB2567468A

Abstract

There is disclosed a polymeric film. The film comprises a polymeric material having a repeat unit of formula and a repeat unit of formula wherein Ph represents a phenylene moiety and wherein the shear viscosity, SV, of the polymeric material, measured by a Standard method as defined in ISO11443:2014, is in the range from around 400 Pa.s to around 600 Pa.s, at 340°C. Further disclosed is a speaker diaphragm and a method of making a speaker diaphragm.

Description

POLYMERIC FILMAND SPEAKER DIAPHRAGM COMPRISING IT

There is disclosed a polymeric film. In particular, there is disclosed a polymeric film suitable for a micro speaker diaphragm for use in portable devices.

As personal devices such as smartphones and smart watches get smaller and smaller, there is an ever increasing need for the miniaturisation of acoustic components that make up the devices such as speakers and receivers. However, the acoustic performance of miniaturised speakers and receivers can also be impacted. Most affected by miniaturisation in speakers and receivers is the lower frequency acoustic performance such as the bass tones.

Polymeric films are often used in such devices. Polyaryletherketones (PAEKs) typically have excellent mechanical properties and are used in portable devices. PAEKs are the materials of choice for many acoustic devices because they excellent mechanical properties. However, even when using high performance polymers such as PAEKs to make polymeric films for acoustic components, it can still be challenging to reach the performance requirements needed to further miniaturise acoustic components.

There is a need for a polymeric film suitable for use as a micro speaker diaphragm exhibiting improved low frequency acoustic performance while still providing good mechanical properties in order to provide improved fatigue performance.

BRIEF SUMMARY

In a first aspect, there is disclosed a polymeric film, the film comprising a polymeric material having a repeat unit of formula

-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety and wherein the shear viscosity, SV, of the polymeric material, measured by a Standard method as defined in ISO1 1443:2014, is in the range from around 400 Pa.s to around 600 Pa.s, at 340 °C.

It has been surprisingly found that the polymeric film recited above is particularly good for numerous applications including but not limited to acoustic devices, laminate structures and optical devices. Preferably, the SV of the polymeric material is in the range between 450 Pa.s or more and 550 Pa.s or less, at 340 °C. More preferably, SV is in the range between 480 Pa.s and 520 Pa.s, at 340 °C.

In particular, one benefit of the polymeric material is that it exhibits improved optical properties. For example, a significant reduction in the % haze was identified for the polymeric film of the present invention compared with PEEK polymer film of the same thickness. In some examples, a reduction in the measured % haze of up to 6% was measured when compared with other polymeric films having a similar thickness.

Preferably, the polymeric film of nominal thickness 6 pm has a transmission haze, as measured by ASTM D1003-2013, of less than 5%. More preferably, the polymeric film has a transmission haze of less than 2%, or less than 1 %. Most preferably, the polymeric film has a transmission haze of 0.5% or less.

Optionally, the polymeric film is in the amorphous state. It has surprisingly been found that the polymeric film in the amorphous state, when constructed into a simple speaker diaphragm, exhibits a lower resonant frequency Fothan other comparative films constructed into simple speaker diaphragms.

Alternatively, the polymeric film is in the crystalline state.

Preferably, the polymeric film has a thickness from 3pm to 100pm, and more preferably, has a thickness from 3pm to 25pm, or from 3pm to 12pm or less, or from 3pm to 9pm or less, or from 3pm to less than 5pm.

Alternatively, the polymeric film has a thickness from 50pm to 70pm, or 55pm or more to 65pm or less.

In a second aspect, there is disclosed a speaker diaphragm comprising: at least one layer of film comprising a polymeric material, the polymeric material having a repeat unit of formula

-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety and wherein the shear viscosity, SV, of the polymeric material, measured by a Standard method as defined in IS011443:2014, is in the range from around 400 Pa.s to around 600 Pa.s, at 340 °C. Surprisingly, it has been found that the speaker diaphragm, in use, exhibits a significant improvement in sound generation, especially in low frequency sound generation, resulting in an overall improved speaker performance especially at lower frequencies compared with known speaker diaphragms.

Preferably, the SV of the polymeric material is in the range between 450 Pa.s or more and 550 Pa.s or less, at 340 °C. More preferably, SV is in the range between 480 Pa.s and 520 Pa.s, at 340 °C.

Preferably, the at least one layer of film has a thickness from 3μιτι to 25μηι, and more preferably, has a thickness from 3μπι to 12μηι or less, or most preferably from 3μηι to 9μηι or less, or from 3μηι to less than 5μητ

Preferably, the speaker diaphragm provides a reduction in the measured lowest resonant frequency Fo of up to 50 Hz compared with comparative speaker diaphragms. Surprisingly, it has been found that the speaker diaphragm of the present invention exhibits a lower resonant frequency Fo compared with speaker diaphragms made with PEEK.

Preferably, the at least one layer of film is in the amorphous state. It has surprisingly been found that film in the amorphous state exhibits an even lower resonant frequency Fothan a film in an amorphous state.

In an example, the speaker diaphragm may have an improvement in the achievable lowest resonant frequency of up to 50 Hz compared to other speaker diaphragms.

Alternatively, the at least one layer of film is in a crystalline state. In this example, the speaker diaphragm may have an improvement in the achievable lowest resonant frequency of up to 20 Hz compared to other speaker diaphragms.

Optionally, the diaphragm is a laminate structure comprising a plurality of layers of material. The diaphragm may comprise layers of different polymeric material, or layers of adhesive, or backing materials.

In another aspect, there is provided a method of making a speaker diaphragm, the method comprising the steps:

(i) extruding a film comprising a polymeric material having a repeat unit of formula

-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula -O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety;

wherein the repeat units I and II are in the relative molar properties 1:11 of from 65:35 to 95:5;

(ii) thermoforming the film into a diaphragm.

The method may further comprise the step of laminating the film after step (i). The lamination process may including adding damping layers to the film.

The following features are applicable to the polymeric material:

Preferably the repeat units I and II are in the relative molar proportions 1:11 of from 65:35 to 95:5, e.g. 75:25.

Preferably, in the polymeric material, the following relationship applies:

logio (X%) > 1.50 - 0.26 MV;

wherein X% refers to the % crystallinity measured as described in Example 31 of WO2014207458A1 incorporated herein, and wherein MV refers to the melt viscosity measured using capillary rheometry operating at 340°C at a shear rate of 1000s ¹ using a circular cross-section tungsten carbide die, 0.5mm (capillary diameter) x 3.175mm (capillary length) also as described in WO2014207458A1. The MV measurement is taken 5 minutes after the polymer has fully melted, which is taken to be 5 minutes after the polymer is loaded into the barrel of the rheometer.

The phenylene moieties (Ph) in each repeat unit may independently have 1 ,4- para linkages to atoms to which they are bonded or 1 ,3- meta linkages. Where a phenylene moiety includes 1 ,3- linkages, the moiety will be in the amorphous phase of the polymer. Crystalline phases will include phenylene moieties with 1 ,4- linkages. In many applications it is preferred for the polymeric material to be highly crystalline and, accordingly, the polymeric material preferably includes high levels of phenylene moieties with 1 ,4- linkages.

In a preferred embodiment, at least 95%, preferably at least 99%, of the number of phenylene moieties (Ph) in the repeat unit of formula I have 1 ,4-linkages to moieties to which they are bonded. It is especially preferred that each phenylene moiety in the repeat unit of formula I has 1 ,4- linkages to moieties to which it is bonded.

In a preferred embodiment, at least 95%, preferably at least 99%, of the number of phenylene moieties (Ph) in the repeat unit of formula II have 1 ,4-linkages to moieties to which they are bonded. It is especially preferred that each phenylene moiety in the repeat unit of formula II has 1 ,4- linkages to moieties to which it is bonded.

Preferably, the phenylene moieties in repeat unit of formula I are unsubstituted. Preferably, the phenylene moieties in repeat unit of formula II are unsubstituted.

Said repeat unit of formula I suitably has the structure

Said repeat unit of formula II suitably has the structure

Preferred polymeric material in accordance with the invention have a crystallinity which is greater than expected from the prior art. Preferably, log™ (X%) > 1.50 - 0.23 V. More preferably log (X%) > 1.50 - 0.28 MV + 0.06 MV².

Said polymeric material may include at least 68 mol%, preferably at least 71 mol% of repeat units of formula I. Particular advantageous polymeric material may include at least 72mol%, or, especially, at least 74 mol% of repeat units of formula I. Said polymeric material may include less than 90 mole%, suitably 82mol% or less of repeat units of formula I. Said polymeric material may include 68 to 82 mol%, preferably 70 to 80 mol%, more preferably 72 to 77 mol% of units of formula I.

Said polymeric material may include at least 10mol%, preferably at least 18 mol%, of repeat units of formula II. Said polymeric material may include less than 32 mol%, preferably less than 29 mol% of repeat units of formula II. Particularly advantageous polymeric materials may include 28 mol% or less; or 26 mol% or less of repeat units of formula II. Said polymeric material may include 18 to 32mol%, preferably 20 to 30mol%, more preferably 23 to 28mol% of units of formula II.

The sum of the mol% of units of formula I and II in said polymeric material is suitably at least 95mol%, is preferably at least 98mol%, is more preferably at least 99mol% and, especially, is about 100mol%.

The ratio defined as the mol% of units of formula I divided by the mol% of units of formula II may be in the range 1 .8 to 5.6, is suitably in the range 2.3 to 4 and is preferably in the range 2.6 to 3.3. The Tm of said polymeric material (suitably measured as described herein) may be less than 330°C, is suitably less than 320°C, is preferably less than 310°C. In some embodiments, the Tm may be less than 306°C. The Tm may be greater than 280°C, or greater than 290°C, 295°C or 300°C. The Tm is preferably in the range 300°C to 310°C.

The Tg of said polymeric material (suitably measured as described herein) may be greater than 130°C, preferably greater than 135°C, more preferably 140°C or greater. The Tg may be less than 175°C, less than 165°C, less than 160°C or less than 155°C. The Tg is preferably in the range 145°C to 155°C.

The difference (Tm-Tg) between the Tm and Tg may be at least 130°C, preferably at least 140°C, more preferably at least 150°C. The difference may be less than 170°C or less than 165°C. In a preferred embodiment, the difference is in the range 145-165°C.

In a preferred embodiment, said polymeric material has a Tg in the range 145°C-155°C, a Tm in the range 300°C to 310°C and the difference between the Tm and Tg is in the range 145°C to 165°C.

Said polymeric material may have a crystallinity of around 10 to 20%, measured as described in Example 31 of WO2014207458A1 incorporated herein.

Said polymeric material suitably has a melt viscosity (MV) of at least 0.10 kNsm ², preferably has a MV of at least 0.15 kNsm ², more preferably at least 0.20 kNsm ², especially at least 0.25 kNsm ². MV is suitably measured using capillary rheometry operating at 340°C at a shear rate of 1000s ¹ using a tungsten carbide die, 0.5mm x 3.175mm. Said polymeric material may have a MV of less than 1.8 kNsm ², suitably less than 1 .2 kNsm ².

Said polymeric material may have a tensile strength, measured in accordance with IS0527 of at least 40 MPa, preferably at least 60 MPa, more preferably at least 80 MPa. The tensile strength is preferably in the range 80-1 10 MPa, more preferably in the range 80-100 MPa.

Said polymeric material may have a flexural strength, measured in accordance with IS0178 of at least 130 MPa. The flexural strength is preferably in the range 135-180 MPa, more preferably in the range 140-150 MPa.

Said polymeric material may have a flexural modulus, measured in accordance with IS0178 of at least 2 GPa, preferably at least 3GPa. The flexural modulus is preferably in the range 3.0-4.5 GPa, more preferably in the range 3.0-4.0 GPa.

Said polymeric material may be in the form of pellets or granules, wherein the pellets or granules include at least 95wt%, preferably at least 99wt%, especially about 100wt% of said polymeric material. Pellets or granules may have a maximum dimension of less than 10mm, preferably less than 7.5mm, more preferably less than 5.0mm.

In the context of the present invention, the Glass Transition Temperature (Tg), the Cold Crystallisation Temperature (Tn), the Melting Temperature (Tm) and Heat of Fusions of Nucleation (ΔΗη) and Melting (AHm) are determined using the following DSC method:

A dried sample of a polymer is compression moulded into an amorphous film, by heating 7g of polymer in a mould at 400°C under a pressure of 50bar for 2 minutes, then quenching in cold water producing a film of dimensions 120 x120mm, with a thickness in the region of 0.20mm. A 8mg plus or minus 3mg sample of each film is scanned by DSC as follows:

Step 1 Perform and record a preliminary thermal cycle by heating the sample from 30°C to 400°C at 20°C /min.

Step 2 Hold for 5 minutes.

Step 3 Cool at 20°C/min to 30°C and hold for 5mins.

Step 4 Re-heat from 30°C to 400°C at 20°C/min, recording the Tg, Tn, Tm, ΔΗη and AHm.

From the DSC trace resulting from the scan in step 4, the onset of the Tg is obtained as the intersection of the lines drawn along the pre-transition baseline and a line drawn along the greatest slope obtained during the transition. The Tn is the temperature at which the main peak of the cold crystallisation exotherm reaches a maximum. The Tm is the temperature at which the main peak of the melting endotherm reaches a maximum.

The Heats of Fusion for Nucleation (ΔΗη) and Melting (AHm) are obtained by connecting the two points at which the cold crystallisation and melting endotherm(s) deviate from the relatively straight baseline. The integrated areas under the endotherms as a function of time yield the enthalpy (mJ) of the particular transition, the mass normalised Heats of Fusion are calculated by dividing the enthalpy by the mass of the specimen (J/g).

The polymeric material

-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety, may be produced using the following processes, and described in WO2014207458A1 and incorporated herein, comprising polycondensing a mixture of at least one dihydroxybenzene compound and at least one dihydroxybiphenyl compound in the molar proportions 65:35 to 95:5 with at least one dihalobenzophenone in the presence of sodium carbonate and potassium carbonate wherein:

(i) the mole% of said potassium carbonate is at least 2.5 and less than 5, and/or

(ii) the following relationship (referred to as the "D50/mole% relationship") applies the D₅₀ of said sodium carbonate in μΐτι

mole% of potassium carbonate = < 46

The mole% of said potassium carbonate is suitably defined as: the number of moles of potassium carbonate

the total number of moles of hydroxy monomer(s)used °

The D50 of the sodium carbonate may be measured as described in .Example 29 ofW02014207458A1 incorporated herein.

the total number of moles of hydroxy monomer(s)used ^{X 0}

Under option (i), the mole% of said potassium carbonate may be at least 3 mole%, is preferably at least 3.5 mole%, is more preferably at least 3.9 mole%. The mole% of said potassium carbonate may be of said potassium carbonate is in the range 3.5 to 4.9 mole%.

The total mole% of carbonates used in the method (i.e. the total number of moles of carbonates used in method divided by the total number of moles of hydroxy monomer(s) used, expressed as a percentage) is suitably at least 100%.

The total mole% of carbonates may be greater than 100 mole%. It may be less than 105 mole%.

The mole% of sodium carbonate used in the method may be at least 90 mole%, preferably at least 92 mole%, more preferably at least 95 mole%.

The sum of the mole% (again related to the moles of hydroxy monomer(s)) of sodium carbonate and potassium carbonate used in the method is preferably at least 100 mole% and is more preferably greater than 100 mole%. It may be in the range 100-105 mole%. The mole% of carbonates (which term is intended to encompass carbonate (CO3² ) and bicarbonate (HCO3 )) other than sodium carbonate and potassium carbonate used in the method is preferably less than 5 mole%, more preferably less than 1 mole% (again related to the moles of hydroxy monomer(s)).

Preferably, the only carbonates used in the method are sodium carbonate and potassium carbonate.

Under option (ii), the D50/mole% relationship is preferably less than 44, more preferably less than 42, especially less than 40. Said relationship may be less than 30 or 26. D50 is suitably measured as described in Example 29 of WO2014207458A1 incorporated herein.

Preferably, both the relationships described in options (i) and (ii) apply.

The potassium carbonate selected for use in the method is preferably able to pass through a 500pm mesh screen.

The D50 of said sodium carbonate is suitably less than 140pm, preferably less than 125pm, more preferably less than 110pm. The D50 may be at least 50pm.

The following features are generally applicable to the present invention:

Said polymeric material may form part of a composition which may comprise said polymeric material and a filler means. Said filler means may include a fibrous filler or a non-fibrous filler. Said filler means may include both a fibrous filler and a non-fibrous filler. A said fibrous filler may be continuous or discontinuous.

A said fibrous filler may be selected from inorganic fibrous materials, non-melting and high-melting organic fibrous materials, such as aramid fibres, and carbon fibre.

A said fibrous filler may be selected from glass fibre, carbon fibre, asbestos fibre, silica fibre, alumina fibre, zirconia fibre, boron nitride fibre, silicon nitride fibre, boron fibre, fluorocarbon resin fibre and potassium titanate fibre. Preferred fibrous fillers are glass fibre and carbon fibre.

A fibrous filler may comprise nanofibres.

A said non-fibrous filler may be selected from mica, silica, talc, alumina, kaolin, calcium sulfate, calcium carbonate, titanium oxide, ferrite, clay, glass powder, zinc oxide, nickel carbonate, iron oxide, quartz powder, magnesium carbonate, fluorocarbon resin, graphite, carbon powder, nanotubes and barium sulfate. The non-fibrous fillers may be introduced in the form of powder or flaky particles. Said composition may define a composite material which could be prepared as described in Impregnation Techniques for Thermoplastic Matrix Composites. A Miller and A G Gibson, Polymer & Polymer Composites 4(7), 459 - 481 (1996), EP102158 and EP102159, the contents of which are incorporated herein by reference. Preferably, in the method, said polymeric material and said filler means are mixed at an elevated temperature, suitably at a temperature at or above the melting temperature of said polymeric material. Thus, suitably, said polymeric material and filler means are mixed whilst the polymeric material is molten. Said elevated temperature is suitably below the decomposition temperature of the polymeric material. Said elevated temperature is preferably at or above the main peak of the melting endotherm (Tm) for said polymeric material. Said elevated temperature is preferably at least 300°C. Advantageously, the molten polymeric material can readily wet the filler and/or penetrate consolidated fillers, such as fibrous mats or woven fabrics, so the composite material prepared comprises the polymeric material and filler means which is substantially uniformly dispersed throughout the polymeric material.

The composite material may be prepared in a substantially continuous process. In this case polymeric material and filler means may be constantly fed to a location wherein they are mixed and heated. An example of such a continuous process is extrusion. Another example (which may be particularly relevant wherein the filler means comprises a fibrous filler) involves causing a continuous filamentous mass to move through a melt or aqueous dispersion comprising said polymeric material. The continuous filamentous mass may comprise a continuous length of fibrous filler or, more preferably, a plurality of continuous filaments which have been consolidated at least to some extent. The continuous fibrous mass may comprise a tow, roving, braid, woven fabric or unwoven fabric. The filaments which make up the fibrous mass may be arranged substantially uniformly or randomly within the mass. A composite material could be prepared as described in PCT/GB2003/001872, US6372294 or EP1215022.

Alternatively, the composite material may be prepared in a discontinuous process. In this case, a predetermined amount of said polymeric material and a predetermined amount of said filler means may be selected and contacted and a composite material prepared by causing the polymeric material to melt and causing the polymeric material and filler means to mix to form a substantially uniform composite material.

The composite material may be formed into a particulate form for example into pellets or granules. Pellets or granules may have a maximum dimension of less than 10mm, preferably less than 7.5mm, more preferably less than 5.0mm.

Preferably, said filler means comprises one or more fillers selected from glass fibre, carbon fibre, carbon black and a fluorocarbon resin. More preferably, said filler means comprises glass fibre or carbon fibre.

In the following discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

Throughout this specification, the term "comprising" or "comprises" means including the components) specified but not to the exclusion of the presence of other components. The term "consisting essentially of or "consists essentially of" means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. Typically, when referring to compositions, a composition consisting essentially of a set of components will comprise less than 5% by weight, typically less than 3% by weight, more typically less than 1 % by weight of non-specified components.

The term "consisting of or "consists of means including the components specified but excluding other components.

References herein such as "in the range x to y" are meant to include the interpretation "from x to y" and so include the values x and y.

Whenever appropriate, depending upon the context, the use of the term "comprises" or "comprising" may also be taken to include the meaning "consists essentially of" or "consisting essentially of", and also may also be taken to include the meaning "consists of or "consisting of.

Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 illustrates a typical film extrusion process; and

Figure 2 illustrates the measurement of resonant frequency of a number of receivers. DETAILED DESCRIPTION

Polymeric film was formed using a typical sheet/film extrusion process whereby polymer granules are added to a hopper 2 and melted to form a polymer melt. The polymer melt is then guided under pressure through an extruder 4 to a die 6. The shape of the die 6 controls the width and thickness of the film 10. The film is then cooled under tension via a number of rollers or calendars 12. The rollers or calendars 12 can be arranged to stretch the film to further control the dimensions of the film, such as the thickness of the film. The film is then wound onto a film core.

Example 1 - Measurement of shear viscosity The shear viscosity, SV, was measured according to a Standard method as defined in IS011443:2014 using capillary rheometry operating at 340°C at a shear rate of 1000s ¹ using a circular cross-section tungsten carbide die, 0.5mm (capillary diameter) x 3.175mm (capillary length). The range of SV of the polymeric material selected was from around 400 Pa.s to around 600 Pa.s, at 340 °C.

Example 1 - Measurement of crystallinity of the film

Crystallinity of the polymeric films may be assessed by several methods for example by density, by infra-red spectroscopy, by X-ray diffraction or by differential scanning calorimetry (DSC). The DSC method has been used to evaluate the crystallinity that developed in the polymers using a TA Instruments DSC Q100, Q2000 or Q2500 instrument under a nitrogen flow rate of 40ml/min.

The Glass Transition Temperature (Tg), the Cold Crystallisation Temperature (Tn), the Melting Temperature (Tm) and Heat of Fusions of Nucleation (ΔΗη) and Melting (AHm) for the polymer film was determined using the following DSC method.

A sample of each polymer film is prepared by cutting pieces that fit into a standard aluminium DSC pan until a quantity between 5-10 mg has been achieved. The sample was then scanned by DSC as follows:

1 : Equilibrate at 40.00 °C

2: Isothermal for 2.00 min

3: Ramp 20.00 °C/min to 400.00 °C

5: Equilibrate at 40.00 °C

From the resulting DSC curve from the scan in step 4, the onset of the Tg was obtained as the intersection of the lines drawn along the pre-transition baseline and a line drawn along the greatest slope obtained during the transition. The Tg was determined to be around 150 °C. The Tn corresponds to the temperature at which the main peak of the cold crystallisation exotherm reaches a maximum. The Tm corresponds to the temperature at which the main peak of the melting endotherm reach maximum. Tc corresponds to the temperature at which the main peak of the crystallisation from the melt exotherm reaches a maximum.

The Heat of Fusion (ΔΗ (J/g)) may be obtained by connecting the two points at which the melting endotherm deviates from the relatively straight baseline. The integrated area under the endotherm as a function of time yields the enthalpy (mJ) of the melting transition: the mass normalised Heat of Fusion is calculated by dividing the enthalpy by the mass of the specimen (J/g). The level of crystallisation (%) is determined by dividing the Heat of Fusion of the specimen by the Heat of Fusion of a totally crystalline polymer, which for PEEK:PEDEK was assumed to be 130 J/g. Using the DSC method above, polymeric film of the present invention in the amorphous state have approximately 5% crystallinity which is less than comparative PEEK film which was found to have a crystallinity of approximately 10%. Crystalline polymeric films of the present invention were found to have a crystallinity of approximately 20%, whereas comparative PEEK film had a crystallinity of approximately 30%. However, these values are based on the assumption that the enthalpy of fusion of PEEK:PEDEK according to the invention is the same as the enthalpy of fusion of PEEK.

Example 2 - Measurement of haze

The transmission haze of the film according to the invention was determined using the Standard test method ASTM D1003. Transmission haze determines the transmitting properties of a transparent film. Light transmittance through a film can be affected by irregularities in the film. The irregularities can cause the light to scatter in different directions. When light is scattered by small irregularities the scattering behaviour is known as Wide Angle Scattering, which causes haze due to the loss of transmissive contrast. Transmission haze is therefore the amount of light that is subject to Wide Angle Scattering at an angle greater than 2.5° from normal.

Polymeric film samples were prepared using 6pm and 8pm sheets of film, and measured on 57D Hazemeter. Table 1 shows the % haze and % transmission properties. Surprisingly, it has been found that the PEEK-PEDEK film according to the present invention has a significantly lower haze compared with PEEK film prepared in the same manner.

Table 1 : Determination of haze and transmission according to ASTM D1003

One benefit of a polymeric film of the present invention is in electronic displays. The combination of low haze and good mechanical properties make this particular film suitable for flexible electronic displays.

Example 3 - Comparison of lowest resonant frequency

A polymeric film of the present invention was thermoformed into a simple speaker diaphragm and used to construct simple receivers in order to measure resonant frequencies of the speaker diaphragms. Comparative films comprising PEEK were also thermoformed into speaker diaphragms and constructed into simple receivers to provide comparative data between speaker diaphragms of the present invention and speaker diaphragms made from PEEK. The receivers were the same, only the film used to form the diaphragm was different. Receivers are a low power speaker and were used for comparative testing for their ease of testing. In order to make a receiver, the film is first thermoformed into a diaphragm and then constructed to form a receiver.

Thermoforming is a manufacturing process where a film is heated to a pliable forming temperature, formed to a specific shape in a mould, and trimmed to create a usable diaphragm. Typically, the film is placed in a tool comprising a male and female part and held under pressure. A temperature is applied to the tool in order to form the film into the shape of the tool. The temperature of the tool is set from around 130 C around 150 C to form the diaphragm. The tool temperature is increased to up to around 185 °C for a crystalline film. Samples 2, 3 and 5, correspond to the crystalline diaphragms. The films had a nominal thickness of 6μηι. Once constructed as receivers, impedance tests were performed to determine the lowest resonant frequency of the receivers.

Table 2 - Measurement of resonant frequency of speak diaphragm

Figure 2 and Table 2 show the results of the impedance measurements to determine the resonant frequency, Fo, of the receivers produced using different films. Samples 1 and 4 correspond to amorphous film samples, and samples 2 and 5 correspond to crystalline film samples that were crystallised using the thermoforming process using. Sample 3 corresponds to a crystalline film, which was crystalline prior to thermoforming. Surprisingly, receivers with diaphragms according to the present invention exhibited, in use, a lower resonant frequency compared with similar receivers made from PEEK film.

More surprisingly, receivers made using amorphous film exhibited, in use, the lowest measurable Fo. It has been found that using a speaker diaphragm of the present invention can lead to a significant improvement in the performance of micro speakers in the lower frequency ranges.

Without being bound by theory, it is thought that the polymeric film of the present invention provides for a speaker diaphragm (being thermoformed) that has a lower modulus than speaker diaphragms thermoformed from other polymeric material. The modulus of the polymeric film according to the invention is similar to that of PEEK film post extrusion, however, when the polymeric film is thermoformed into a speaker diaphragm and constructed as a simple receiver, it appears that the modulus of the polymeric film of the present invention is reduced. It is thought that because Fo is related to the modulus of the film it follows that a reduction in Fo is related to a lower modulus diaphragm.

Figure 2 shows that receivers formed using polymeric film diaphragms of the present invention provide up to a 50 Hz reduction in the lowest acoustic frequency measured.

The Tg of the polymeric material is also suitably high, thereby allowing speaker diaphragms of the present invention to experience higher temperature without failure.

A further benefit of the film is for use in laminates. Under certain processing conditions, the film provides excellent adhesion to other layers of material. Crystalline film is particularly useful in laminates.

It will be appreciated that optional features applicable to one aspect of the invention can be used in any combination, and in any number. Moreover, they can also be used with any of the other aspects of the invention in any combination and in any number. This includes, but is not limited to, the dependent claims from any claim being used as dependent claims for any other claim in the claims of this application.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A polymeric film, the film comprising a polymeric material having a repeat unit of formula

-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety and wherein the shear viscosity, SV, of the polymeric material, measured by a Standard method as defined in IS01 1443:2014, is in the range from around 400 Pa.s to around 600 Pa.s, at 340 °C.

2. A polymeric film according to claim 1 , wherein the SV is in the range between 450 Pa.s or more and 550 Pa.s or less, at 340 °C.

3. A polymeric film according to claim 1 or 2, wherein the SV is in the range between 480 Pa.s and 520 Pa s, at 340 °C.

4. A polymeric film according to any preceding claim, wherein the polymeric film has a nominal thickness of 6 pm and a transmission haze, as measured by ASTM D1003-2013, of less than 5%.

5. A polymeric film according to claim 4, wherein, the polymeric film has a transmission haze of less than 2%, or less than 1 %, or, the polymeric film has a transmission haze of 0.5% or less.

6. A polymeric film according to any preceding claim, wherein the polymeric film is in an amorphous state.

7. A polymeric film according to any one of claims 1 to 5, wherein the polymeric film is in a crystalline state.

8. A polymeric film according to any preceding claim, wherein the polymeric film has a thickness from 3pm to 100pm, or has a thickness from 3pm to 25pm, or has a thickness from 3pm to 12pm or less, or has a thickness from 3pm to 9pm or less, or has a thickness from 3pm to less than 5pm.

9. A polymeric film according to any one of claims 1 to 7, wherein the polymeric film has a thickness from 50pm to 70pm, or 55pm or more to 65pm or less.

10. A speaker diaphragm comprising: at least one layer of film comprising a polymeric material, the polymeric material having a repeat unit of formula

-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety and wherein the shear viscosity, SV, of the polymeric material, measured by a Standard method as defined in IS011443:2014, is in the range from around 400 Pa.s to around 600 Pa.s, at 340 °C.

11. A speaker diaphragm according to claim 10, wherein the SV of the polymeric material is in the range between 450 Pa.s or more and 550 Pa.s or less, at 340 °C.

12. A speaker diaphragm according to claim 10 or 11 , wherein the SV of the polymeric material is in the range between 480 Pa s and 520 Pa.s, at 340 °C.

13. A speaker diaphragm according to any of claims 10 to 12, wherein the at least one layer of film has a thickness from 3pm to 25pm; or

the at least one layer of film has a thickness from 3pm to 12pm or less; or

the at least one layer of film has a thickness from 3pm to 9pm or less; or

the at least one layer of film has a thickness from 3pm to less than 5pm.

14. A speaker diaphragm according to any of claims 10 to 13, wherein the at least one layer of film is in the amorphous state.

15. A speaker diaphragm according to any of claims 10 to 14, wherein the speaker diaphragm has an improvement in the achievable lowest resonant frequency of up to 50 Hz compared to other speaker diaphragms.

16. A speaker diaphragm according to any of claims 10 to 13, wherein the at least one layer of film is in the crystalline state.

17. A speaker diaphragm according to claim 16, wherein the speaker diaphragm has an improvement in the achievable lowest resonant frequency of up to 20 Hz compared to other speaker diaphragms.

18. A speaker diaphragm according to any of claims 10 to 17, wherein the diaphragm is a laminate structure comprising a plurality of layers of material.

19. A method of making a speaker diaphragm, the method comprising the steps:

-O-Ph-O-Ph-CO-Ph- I and a repeat unit of formula

-O-Ph-Ph-O-Ph-CO-Ph- II wherein Ph represents a phenylene moiety and wherein the shear viscosity, SV, of the polymeric material, measured by a Standard method as define in IS011443:2014, is in the range from around 400 Pa.s to around 600 Pa.s, at 340 °C;

(ii) thermoforming the film into a diaphragm.

20. A method according to claim 19, wherein the method further comprises the step of laminating the film after step (i).

21. A method according to claim 20, wherein the lamination process includes adding damping layers to the film.