GB2536387A

GB2536387A - Polymer method, particles and intermediates

Info

Publication number: GB2536387A
Application number: GB1611279.9A
Authority: GB
Inventors: Ainsworth Richard
Original assignee: Victrex Manufacturing Ltd
Current assignee: Victrex Manufacturing Ltd
Priority date: 2016-06-29
Filing date: 2016-06-29
Publication date: 2016-09-14
Anticipated expiration: 2036-06-29
Also published as: GB201611279D0; GB2536387B

Abstract

A process for preparing phosphate stabilised polyetheretherketone (PEEK) particles includes the addition of a blend in a ratio of 2.5-3.5 parts monosodium dihydrogen orthophosphate and 2 parts disodium hydrogen phosphate as additives prior to drying the PEEK. The process provides a stabilised PEEK, comprising a content of 0.10-0.35% by weight monosodium dihydrogen orthophosphate and 0.08-0.25% by weight disodium hydrogen phosphate. The phosphate stabilised PEEK has high resistance to thermal degradation when maintained at temperatures above its melting point. Also disclosed are particles, granules, rod, tube, film, tape or other intermediate products including the stabilised PEEK, with or without a filler.

Description

Polymer Method, Particles and Intermediates

Field

The present invention relates to a method for preparing polyetheretherketone (PEEK), and the resulting PEEK, as well as intermediate products prepared using the PEEK. The PEEK of the invention, when used as raw material for melt processing to form intermediates or articles by moulding methods, for instance by injection or compression moulding, provides the resulting polymer melt with high resistance to degradation whilst the PEEK is held in a molten state.

Background to the invention

Polyaryletherketones (PAEKs) such as PEEK may be manufactured by nucleophilic polycondensation of bisphenols with organic dihalide compounds in a suitable solvent using alkali metal carbonates or alkaline earth metal carbonates as catalysts. This process is set out, for example, in EP-A-0001879, EP-A-0182648 and EP-A-0244167. Following polycondensation, the reaction mixture is typically washed to remove the polymerisation solvent and reaction by-products such as inorganic salts and residual monomers from the polymer. Diphenyl sulfone is typically used as solvent and the organic dihalides are typically difluoro-compounds.

In order to separate the PAEK from the by-products and the solvent, a two-step wash or leaching process may be used. In the first wash step, an organic solvent such as ethanol or acetone, the solvent preferably being at least partially miscible with water, is used to leach the diphenyl sulfone from the reaction mixture. In the second wash step, water is used to remove inorganic salts such as NaF and KF.

PEEK is typically prepared by reaction of benzene-1,4-diol (hydroquinone) as the bisphenol with 4,4'-difluorobenzophenone in diphenyl sulfone in the presence of alkali metal carbonates under an inert atmosphere such as nitrogen at temperatures approaching the melting point of the polymer (say greater than 300°C). A slight excess of 4,4'-difluorobenzophenone may be employed and/or the polymer may be end-capped at the end of polymerisation by means of addition of a suitable end-capping compound to the reaction mixture.

PEEK for commercial moulding typically has a melt viscosity (MV) at 400°C, measured as set out below, of about 90 to 700 Pa.s (0.09 to 0.70 kNsm-2), with a melting point of about 343°C. A problem with PEEK is that when it is maintained in a molten state, it may be prone to degradation. However, because of its high melting point, it is undesirable from an environmental perspective to cool the material, once melted, as this wastes energy.

Summary of the Invention

It is one aim of the present invention to stabilise PEEK so that it can be held in a molten state for long periods, for instance continuously so that it may be used in moulding processes, without suffering excessive degradation that could lead to a need to scrap the PEEK. It is another aim of the invention to avoid any need for repeated heating and cooling of PEEK in order to reduce thermal degradation, thus avoiding repeated heating and cooling of vessels which may result in wasted energy.

A first aspect of the invention provides a process for preparing stabilised polyetheretherketone (PEEK), the process comprising: a) reacting benzene-1,4-diol with 4,4'-difluorobenzophenone as monomers in the presence of sodium carbonate and potassium carbonate in diphenyl sulfone to polymerise to form polyetheretherketone, then b) solidifying the reaction mixture and comminuting the solidified reaction mixture to form particles of PEEK, then c) washing the PEEK particles with acetone, and then d) washing the PEEK particles with water to remove acetone, and sodium and potassium salts, optionally repeating steps (c) and (d), to generate an aqueous slurry comprising the PEEK particles and residual wash water, such that the PEEK particles comprise less than 0.1% by weight of diphenyl sulfone, less than 10ppm by weight of K and less than 40 ppm by weight of Na, then e) mixing monosodium dihydrogen orthophosphate and disodium hydrogen phosphate into the slurry, optionally with further water, in a ratio of from 2.5 to 3.5 parts monosodium dihydrogen orthophosphate to 2 parts disodium hydrogen phosphate by weight; and 0 drying the slurry to remove water to provide stabilised PEEK particles having a water content of less than 0.25% by weight and comprising 0.10 to 0.35% by weight of monosodium dihydrogen orthophosphate and 0.08 to 0.25% by weight of disodium hydrogen phosphate. 30 A second aspect of the invention provides particles, granules, pellets, rod, tube, film, tape or other intermediate product consisting essentially of, or consisting of, the stabilised PEEK obtained by the process of the first aspect of the invention, or comprising the stabilised PEEK obtained by the process of the first aspect of the invention as sole source of PEEK polymer in the particles, granules, pellets, rod, film, tube, tape or other intermediate product.

The third aspect of the invention provides stabilised polyetheretherketone (PEEK) comprising: from 0.10 to 0.35% by weight of monosodium dihydrogen orthophosphate, expressed as anhydrous salt, and from 0.08 to 0.25% by weight of disodium hydrogen phosphate, expressed as anhydrous salt, wherein the monosodium dihydrogen orthophosphate and disodium hydrogen phosphate are present in a ratio of from 2.5 to 3.5 parts monosodium dihydrogen orthophosphate to 2 parts disodium hydrogen phosphate by weight, less than 0.25% by weight of water, less than 10ppm by weight of K by elemental analysis, from 100 to 180 ppm by weight of Na by elemental analysis, including Na present from the monosodium dihydrogen orthophosphate and disodium hydrogen phosphate, less than 0.1% by weight of diphenyl sulfone, and at least 99% by weight of polyetheretherketone polymer.

A fourth aspect of the invention provides particles, granules, pellets, rod, tube, film, tape or other intermediate product consisting essentially of, or consisting of, the stabilised PEEK of the third aspect of the invention, or comprising the stabilised PEEK of the third aspect of the invention as sole source of PEEK polymer in the particles, granules, pellets, rod, film, tube, tape or other intermediate product.

The various aspects of the invention are as set out in the independent claims.

Other features of the invention will be apparent from the description that follows and the dependent claims.

Detailed Description of the Invention

Throughout this specification, the term "comprising" or "comprises" means including the component(s) 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, such as colourants, preservatives and the like.

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

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'.

Typically, the term "consisting essentially of will mean that components other than those specified are present at a level less than 5% by weight such as less than 2% by weight, for instance less than 1% by weight.

The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention, as set out herein are also applicable to all other aspects or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or exemplary embodiment of the invention as interchangeable and combinable between different aspects and exemplary embodiments.

The first aspect of the invention provides a process for preparing stabilised polyetheretherketone (PEEK). The process has, as a first step, reacting benzene-1,4-diol with 4,4'-difluorobenzophenone as monomers in the presence of sodium carbonate and potassium carbonate in diphenyl sulfone to polymerise to form polyetheretherketone. Typically, the monomers are present at about equimolar ratio, although either may be present in excess, with the amount of sodium carbonate being sufficient to provide at least 1 mole of sodium carbonate per mole of benzene-1,4-diol. The potassium carbonate is typically present such that the molar ratio K:Na is from 0.01 to 0.06. Optionally, further monomer addition may take place as the reaction proceeds, and it may be desirable to add a compound at the end of reaction to act as as an end-cap for the polymer. Typically, the progress of polymerisation may be monitored by measuring the power or torque required for stirring and using this to estimate the reaction progress. The viscosity of the reaction mixture will typically increase as reaction proceeds, as the PEEK molecular weight increases.

When reaction is deemed complete to give a desired PEEK molecular weight, in step (b) the reaction mixture is solidified and the solidified reaction mixture comminuted to form particles of PEEK. The solidification is by cooling, for instance by depositing the reaction mixture onto a cooled conveyor belt from where it may be transferred to a milling apparatus for comminution.

The solidified reaction mix may be comminuted into particles typically having a particle size (maximum dimension) of 20mm or less.

In the next step (c) the PEEK particles are washed with acetone, and then in a following step (d) the PEEK particles are washed with water to remove acetone left over from the previous wash and sodium and potassium salts (typically fluorides but there may be residual carbonates), formed as by-products of the polymerisation reaction.

Optionally (c) and (d) may be repeated sequentially to generate an aqueous slurry comprising the PEEK particles and residual wash water, such that the PEEK particles comprise less than 0.1% by weight of diphenyl sulphone, less than 10ppm of K and less than 40 ppm of Na. This may be checked by conventional analysis of the PEEK particles as the wash progresses, or the washing requirement may be established using prior trials. The washes will typically be effected in a leaching column.

In step (e), further water may be added to the aqueous slurry, as well as monosodium dihydrogen orthophosphate and disodium hydrogen phosphate, in a ratio of from 2.5 to 3.5 parts monosodium dihydrogen orthophosphate to 2 parts disodium hydrogen phosphate by weight.

In the next step (f), the slurry is dried to remove water to provide the stabilised PEEK particles of the invention having a water content of less than 0.25% by weight and comprising 0.10 to 0.35% by weight of monosodium dihydrogen orthophosphate and 0.08 to 0.25% by weight of disodium hydrogen phosphate. The drying may be effected, for instance, by oven drying. The amounts of monosodium dihydrogen orthophosphate and disodium hydrogen phosphate used in step (e) are chosen to provide the required levels in the dried PEEK.

Most preferably, the stabilised PEEK comprises 0.15 to 0.35% monosodium dihydrogen orthophosphate, and preferably 0.10 to 0.25% of disodium hydrogen phosphate.

Without wishing to be bound by any theory, it is believed that the presence of the residual monosodium dihydrogen orthophosphate and disodium hydrogen phosphate present in a ratio of from 2.5 to 3.5 parts monosodium dihydrogen orthophosphate to 2 parts disodium hydrogen phosphate by weight leads to improved stability of the PEEK in terms of resistance to thermal degradation when the stabilised PEEK containing the monosodium dihydrogen orthophosphate and disodium hydrogen phosphate is maintained in a molten state. In other words, the stabilised PEEK of the invention is a composition including PEEK polymer, low levels of reaction by-products and monosodium dihydrogen orthophosphate and disodium hydrogen phosphate present in proportions to give a melt stabilisation effect.

The process of the first aspect of the invention may further comprise forming the stabilised PEEK particles into granules or pellets by melt granulation, the resulting granules or pellets comprising, consisting essentially of, or consisting of, the stabilised PEEK. The stabilised PEEK particles may be blended with a filler prior to, or during, melt granulation to provide granules or pellets comprising the stabilised PEEK and the filler. The process may further comprise forming the stabilised PEEK particles or granules into intermediate products such as rod or tube by melt extrusion, the resulting rod or tube comprising, consisting essentially of, or consisting of the stabilised PEEK. The process may further comprise forming the stabilised PEEK particles or granules into film or tape, the resulting film or tape comprising, consisting of, the stabilised PEEK. The tape may be a filled tape.

Suitable fillers include, for example, reinforcing or wear enhancing fillers or fibres or bioactive fillers such as bioglasses or soluble glasses. When a filler is included in the granules or pellets, it may suitably be included to improve the mechanical properties and/or bonding characteristics and/or biological acceptability of the composition. Fillers may be inorganic fibres, particles or platelets. Particularly preferred fillers are carbon fibres or glass fibres.

A second aspect of the invention provides intermediate products such as particles, granules, pellets, rod, tube, tape, film or other intermediate products consisting essentially of, or consisting of, the stabilised PEEK obtained by the process of the first aspect of the invention, or comprising the stabilised PEEK obtained by the process of the first aspect of the invention as sole source of PEEK polymer in the particles, granules, pellets, rod, tube, tape or film or other intermediate product. In other words, the stabilised PEEK is the only PEEK polymer in the particles, granules, pellets, rod, tube, tape or film or other intermediate product, but may be blended with other polymers that are not PEEK.

In preferred intermediate products, such as particles, granules, pellets, rod, tube, tape, film, or other intermediate product, the stabilised PEEK obtained by the process of the first aspect of the invention is the sole source of polymer in the particles, granules, pellets, rod, tube tape or film or other intermediate product. In other words, no other polymer is present.

The intermediate products such as granules, pellets, rod, tube, tape, film or other intermediate products according to the second aspect of the invention may comprise from 30 to 100% by weight of the stabilised PEEK obtained by the process of the first aspect of the invention and up to 70% by weight of filler. The filler may be as mentioned above, particularly glass fibre or carbon fibre.

A third aspect of the invention provides stabilised polyetheretherketone (PEEK) comprising: from 0.10 to 0.35% by weight of monosodium dihydrogen orthophosphate, expressed as anhydrous salt, and from 0.08 to 0.25% by weight of disodium hydrogen phosphate, expressed as anhydrous salt, wherein the monosodium dihydrogen orthophosphate and disodium hydrogen phosphate are present in a ratio of from 2.5 to 3.5 parts monosodium dihydrogen orthophosphate to 2 parts disodium hydrogen phosphate by weight, less than 0.25% by weight of water, less than 10ppm by weight of K by elemental analysis, from 100 to 180 ppm by weight of Na by elemental analysis, including Na present from the monosodium dihydrogen orthophosphate and disodium hydrogen phosphate, less than 0.1% by weight of diphenyl sulfone, and at least 99% by weight of polyetheretherketone polymer.

The only other significant impurities present will typically be trace metals at less than 20ppm by weight, measured by elemental analysis, and residual, unreacted monomer, typically present as less then 0.1% by weight as measured by gas chromatography. The stabilised PEEK of the invention includes as essential components PEEK polymer in addition to both monosodium dihydrogen orthophosphate and disodium hydrogen phosphate in the proportions specified above. The components K, water and residual diphenyl sulfone, mentioned above, are not essential to the invention and are preferably present at the lowest level achievable, with their tolerable levels as set out above, but they may be completely absent.

The water content may be measured by weight loss at 140°C, or by chemical analysis such as Karl Fischer titration.

Diphenyl sulphone content may be suitably measured by extraction with acetone and gas chromatography analysis.

The stabilised PEEK of the third aspect of the invention may suitably be prepared by the process of the first aspect of the invention, or by other means.

A fourth aspect of the invention provides intermediate products such as particles, granules, pellets, rod, tube, film, tape or other intermediate product consisting essentially of, or consisting of, the stabilised PEEK of the third aspect of the invention, or comprising the stabilised PEEK of the third aspect of the invention as sole source of PEEK polymer in the particles, granules, pellets, rod, film, tube tape or other intermediate product.

The stabilised PEEK of the third aspect of the invention may be the sole source of polymer in the particles, granules, pellets, rod, tube, tape, film or other intermediate of this fourth aspect of the invention.

The granules, pellets, rod, tube, film, tape or other intermediate of the fourth aspect of the invention may comprise from 30 to 100% by weight of the stabilised PEEK of the third aspect of the invention and up to 70% by weight of filler.

The stabilised PEEK of the invention may have a Notched Izod Impact Strength (specimen 80mm x 10mm x 4mm with a cut 0.25mm notch (Type A), tested at 23°C, in accordance with IS0180) of at least 4KJrn2, preferably at least 51C1m-2, more preferably at least 6K.fin-2. The Notched Izod Impact Strength may be less than 10KJrn2, suitably less than 8KJrn2. The Notched Izod Impact Strength may be at least 3KJm-2, suitably at least 4KJm2, preferably at least 5KJrn2. The impact strength may be less than 50 KJrn2, suitably less than 30KJrn2.

The stabilised PEEK of the invention suitably has a melt viscosity (MV) of at least 0.06 kNsm2, preferably has a MV of at least 0.09 kNsm2, more preferably at least 0.12 kNsm2, or at least 0.15 kNsm2. Advantageously, the MV may be at least 0.25 kNsm2 and/or at least 0.30 kNsm-2 The polymeric material may have a MV of less than 1.00 kNsm2, preferably less than 0.70 kNsm-2. An MV of about 0.45 kNsm2 has been found to be particularly advantageous in the manufacture of accurately moulded, strong components.

The stabilised PEEK of the invention may have an MV from 0.09 to 0.70 kNsm-2, preferably from 0.14 to 0.60 kNsm2, more preferably from 0.30 to 0.50 kNsm2.

MV is suitably measured using capillary rheometry operating with the PEEK at 400°C extruded at a shear rate of 1000s-1 through a cylindrical tungsten carbide die, 0.5mm in diameter by 3.175mm in length.

Examples

Experiments were carried out to demonstrate the effect of the level of the stabilisers on the MV stability of the resulting PEEK.

The process as set out above as the first aspect of the invention was used to prepare PEEK having an MV of 0.45 kNsm2 with the particles comminuted to a size less than 20mm in step (b). However, the amounts of phosphate salts mixed into the slurry in step (e) were varied to give phosphate levels inside and outside the range specified in step (f). All other steps were unchanged.

Washing step (c) used acetone at 40°C over 3.5 hours with step (d) using water at 50°C over 7 hours. No repetition of steps (c) or (d) was required to achieve the desired purity for the PEEK particles after step (d).

Water was added to the wet PEEK drained after step (d) sufficient to dissolve the phosphate salts (monosodium dihydrogen orthophosphate and disodium hydrogen phosphate added at ratio of 3 parts by weight monosodium dihydrogen orthophosphate to 2 parts by weight disodium hydrogen phosphate, expressed as anhydrous salts) and blended for 20 minutes at 50°C as step (e). The resulting slurry was then oven dried to less than 0.25% by weight water content at 140°C.

The particles thus obtained contained NaH2PO4 and Na2HPO4 in a 3:2 ratio by weight, with the sole difference between each example being the total phosphate salt level.

Five Examples were prepared in this way, each having a different total salt content as set out in Table 1. Example (A) had no phosphate salt added.

Table 1

Example A B C D E

NaH2PO4 0 0.15% 0.30% 0.45% 0.60% Na2HPO4 0 0.10% 0.20% 0.30% 0.40% MV Stability (%) +1.63 -0.17 -0.74 -2.09 -1.85 MV stability (%) was measured as a percentage change in melt viscosity after 60 minutes at 400°C. The MV is measured by capillary rheometry as explained above. The MV typically remains stable for an initial period of time, and then falls or rises after 60 minutes, with the MV stability being the percentage change in MV, after 60 minutes, from the initial, stable value.

The data in Table 1 demonstrate that MV is most stable for samples B and C.

Claims

CLAIMS1. A process for preparing stabilised polyetheretherketone (PEEK), the process comprising: a) reacting benzene-1,4-diol with 4,4'-difluorobenzophenone as monomers in the presence of sodium carbonate and potassium carbonate in diphenyl sulfone to polymerise to form polyetheretherketone, then b) solidifying the reaction mixture and comminuting the solidified reaction mixture to form particles of PEEK, then c) washing the PEEK particles with acetone, and then d) washing the PEEK particles with water to remove acetone, and sodium and potassium salts, optionally repeating steps (c) and (d), to generate an aqueous slurry comprising the PEEK particles and residual wash water, such that the PEEK particles comprise less than 0.1% by weight of diphenyl sulfone, less than 10ppm by weight of K and less than 40 ppm by weight of Na, then e) mixing monosodium dihydrogen orthophosphate and disodium hydrogen phosphate into the slurry, optionally with further water, in a ratio of from 2.5 to 3.5 pads monosodium dihydrogen orthophosphate to 2 pads disodium hydrogen phosphate by weight; and f) drying the slurry to remove water to provide stabilised PEEK particles having a water content of less than 0.25% by weight and comprising 0.10 to 0.35% by weight of monosodium dihydrogen orthophosphate and 0.08 to 0.25% by weight of disodium hydrogen phosphate.
2. The process of claim 1 further comprising forming the stabilised PEEK particles into granules or pellets by melt granulation, the resulting granules or pellets comprising, consisting essentially of, or consisting of, the stabilised PEEK.
3. The process of claim 2 wherein the stabilised PEEK particles are blended with a filler prior to, or during, melt granulation to provide granules or pellets comprising the stabilised PEEK and the filler.
4. Particles, granules, pellets, rod, tube, film, tape or other intermediate product consisting essentially of, or consisting of, the stabilised PEEK obtained by the process of claim 1, or comprising the stabilised PEEK obtained by the process of claim 1 as sole source of PEEK polymer in the particles, granules, pellets, rod, film, tube or tape or other intermediate product.
5. Particles, granules, pellets, rods, tubes, film, tape or other intermediate product according to claim 4 wherein the stabilised PEEK obtained by the process of claim 1 is the sole source of polymer in the particles, granules, pellets, rod, film, tube, tape or other intermediate product.
6. Particles, granules, pellets, rod, film, tube, tape or other intermediate product according to claim 4 or claim 5 comprising 30 to 100% by weight of the stabilised PEEK obtained by the process of claim 1 and up to 70% by weight of filler.
7. Stabilised polyetheretherketone (PEEK) comprising: from 0.10 to 0.35% by weight of monosodium dihydrogen orthophosphate, expressed as anhydrous salt, and from 0.08 to 0.25% by weight of disodium hydrogen phosphate, expressed as anhydrous salt, wherein the monosodium dihydrogen orthophosphate and disodium hydrogen phosphate are present in a ratio of from 2.5 to 3.5 parts monosodium dihydrogen orthophosphate to 2 parts disodium hydrogen phosphate by weight, less than 0.25% by weight of water, less than 10ppm by weight of K by elemental analysis, from 100 to 180 ppm by weight of Na by elemental analysis, including Na present from the monosodium dihydrogen orthophosphate and disodium hydrogen phosphate, less than 0.1% by weight of diphenyl sulfone, and at least 99% by weight of polyetheretherketone polymer.
8. Particles, granules, pellets, rod, tube, film tape or other intermediate product consisting essentially of, or consisting of, the stabilised PEEK of claim 7, or comprising the stabilised PEEK of claim 7 as sole source of PEEK polymer in the particles, granules, pellets, rod, film, tube, tape or other intermediate product.
9. Particles, granules, pellets, rod, tube, film, tape or other intermediate product according to claim 8 wherein the stabilised PEEK of claim 7 is the sole source of polymer in the particles, granules, pellets, rod, tube, film, tape or other intermediate product.
10. Granules, pellets, rod, tube, film tape or other intermediate product according to claim 8 or claim 9 comprising 30 to 100% by weight of the stabilised PEEK of claim 7 and up to 70% by weight of filler.
11. A process for preparing stabilised polyetheretherketone (PEEK) substantially as described herein.
12. Stabilised polyetheretherketone (PEEK) substantially as described herein.
13. Granules, pellets, rods, tube, film, tape or other intermediate product substantially as described herein.