IMPROVED DIMENSIONAL STABILITY

FIELD OF THE INVENTION

The present invention relates to polyether ketone ketone parts exhibiting improved dimensional stability at high temperature, as well as their manufacturing process.

TECHNICAL BACKGROUND

Polyether Ketone Ketone (PEKK) is a polymer that exhibits a high melting point, excellent mechanical properties as well as very good chemical resistance.

Therefore, PEKK is a particularly interesting polymer for demanding technical fields such as for example the aerospace industry.

PEKK can contain different units, derived from terephthalic acid and isophthalic acid. Certain properties of PEKK such as its melting point or its crystallization kinetics depend on the proportion of these respective units.

The article Structure, crystallization and morphology of poly (aryl ether ketone ketone), by Gardner et al. in Polymer 33: 2483-2495 (1992) describes the existence of two crystalline forms called form 1 and form 2 for PEKK.

In certain applications, parts with good dimensional stability are sought, including at high temperature. More precisely, the parts, exposed to a high temperature, must not undergo appreciable deformations of the type warping or curvature or shrinkage or elongation.

There is therefore a need to provide parts made of thermoplastic material exhibiting high dimensional stability, including at high temperature.

SUMMARY OF THE INVENTION

The invention firstly relates to a part comprising polyether ketone ketone, in which the polyether ketone ketone is at least partly crystalline, and in which at least 50% by weight of the crystalline polyether ketone ketone is of form 1.

According to some embodiments at least 80% by weight, preferably at least 90% by weight, and more particularly preferably substantially all of the crystalline polyether ketone ketone is Form 1.

According to some embodiments, the polyether ketone ketone comprises at least 10% by weight, preferably at least 15% by weight of crystalline polyether ketone ketone.

According to certain embodiments, the polyether ketone ketone comprises terephthalic units and optionally isophthalic units, the proportion by weight of the terephthalic units relative to the sum of the terephthalic units and of the isophthalic units being from 35 to

100%, preferably 55 to 85%.

According to some embodiments, the polyether ketone ketone is at least 30% by weight, preferably at least 50% by weight, more preferably at least 70%, and most preferably at least 80% by weight of the part.

According to certain embodiments, the part also comprises one or more additional elements chosen from fillers, preferably including fibers, one or more other polyarylether ketones, additives and combinations thereof.

According to certain embodiments, the part is a part of an aerial or space locomotive vehicle, or a part of a drilling installation, or a part intended to be positioned in contact with or near a vehicle engine. or a reactor, or a part intended to be subjected to friction.

The invention also relates to the use of the above part, in an apparatus, machine or system, the part being subjected to a continuous use temperature greater than or equal to 200 ° C, or greater than or equal to 230 ° C. , or greater than or equal to 260 ° C, or greater than or equal to 280 ° C.

According to some embodiments, the use is performed in an apparatus, machine or system, the part being subjected to a maximum temperature greater than or equal to 200 ° C, or greater than or equal to 250 ° C, or greater than or equal to 300 ° C, or greater than or equal to 320 ° C.

The invention also relates to a method of manufacturing a part as described above, comprising:

- the supply of polyether ketone ketone;

- The shaping of the polyether ketone ketone, and the at least partial crystallization of the polyether ketone ketone in the form 1.

According to certain embodiments, the shaping is carried out by injection molding, by injection-compression or by extrusion.

According to some embodiments, the method comprises a heat treatment step after the shaping step.

The present invention makes it possible to meet the need expressed in the state of the art. It more particularly provides parts made of thermoplastic material exhibiting high dimensional stability, namely better resistance to creep, at high temperature. Thus, the parts can be used in a wide temperature range of use.

This is obtained by transforming the PEKK so that, in the part obtained, it is predominantly (see essentially or exclusively) crystallized in form 1.

By way of example, PEKK having a content of T units of 60% (as defined below) is a particularly advantageous grade because it allows processing by injection at approximately 320 ° C. However, its very slow crystallization conventionally makes it necessary to adjust the temperature of the mold to around 80-140 ° C, in particular 80-120 ° C (which is a level lower than the glass transition temperature, which is around 160 ° C) . This leads to amorphous parts having poor properties at a temperature above the glass transition temperature. The invention makes it possible to consolidate the properties of parts of this grade of PEKK at high temperature, and in particular between 160 ° C and 300 ° C approximately.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is now described in more detail and in a nonlimiting manner in the description which follows.

PEKK is a polymer comprising a succession of repeated units of formula I and / or of the following formula II:

In these formulas, n is an integer.

The units of formula I are units derived from isophthalic acid

(or units I), while the units of formula II are units derived from terephthalic acid (or T units).

In the PEKK used in the invention, the proportion by weight of T units relative to the sum of T and I units can vary from 0 to 5%; or from 5 to 10%; or from 10 to 15%; or from 15 to 20%; or from 20 to 25%; or from 25 to 30%; or from 30 to 35%; or from 35 to 40%; or from 40 to 45%; or from 45 to 50%; or from 50 to 55%; or from 55 to 60%; or from 60 to 65%; or from 65 to 70%; or from 70 to 75%; or from 75 to 80%; or from 80 to 85%; or from 85 to 90%; or from 90 to 95%; or 95 to 100%.

Ranges from 35 to 100%, in particular from 55 to 85% and more specifically still from 60 to 80%, are particularly suitable. In all of the ranges stated in the present application, the terminals are included unless otherwise specified.

The choice of the mass proportion of T units relative to the sum of T and I units is one of the factors which makes it possible to adjust the melting temperature of the PEKK. A given mass proportion of T units relative to the sum of T and I units can be obtained by adjusting the respective concentrations of the reagents during the polymerization, in a manner known per se.

In the solid state, PEKK can exist in amorphous or partially crystalline form. The crystalline fraction can be in particular in form 1 or in form 2. The mass proportion of PEKK in crystalline form, and more precisely in form 1 and / or in form 2, can be determined by an X-ray diffractometry analysis.

By way of example, the analysis can be carried out by wide angle X-ray scattering (WAXS), on a device of the Nano-inXider® type with the following conditions:

- Wavelength: main Ka1 line of copper (1.54 Angstrom).

- Generator power: 50 kV - 0.6 mA.

- Observation mode: transmission

- Counting time: 10 minutes.

A spectrum of the intensity diffused as a function of the diffraction angle is thus obtained. This spectrum makes it possible to identify the presence of crystals, when peaks are visible on the spectrum in addition to the amorphous halo.

This spectrum also makes it possible to identify the presence of form 1 and / or form 2 in the crystal, by identifying on the spectrum a set of peaks characteristic of both forms.

The main characteristic peaks of form 1 are located at the following angular positions (2Θ): 18.6 ° - 20.6 ° - 23.1 ° - 28.9 °.

The main characteristic peaks of form 2 are located at the following angular positions (2Θ): 15.5 ° - 17.7 ° - 22.6 ° - 28.0 °.

In the spectrum, we can measure the area of ​​the main characteristic peaks above of form 1 (denoted by A1), the area of ​​the main characteristic peaks above of form 2 (denoted by A2), and the area of amorphous halo (denoted AH).

The proportion (by mass) of crystalline PEKK in the PEKK is estimated by the ratio (A1 + A2) / (A1 + A2 + AH).

The proportion (by mass) of the crystals of form 1 in the crystalline phase of PEKK is estimated by the ratio (A1) / (A1 + A2).

The proportion (by mass) of the crystals of form 2 in the crystalline phase of PEKK is estimated by the ratio (A2) / (A1 + A2).

In the PEKK used in the invention, the proportion by mass of crystalline PEKK can in particular vary from 1 to 5%; or from 5 to 10%; or from 10 to 15%; or from 15 to 20%; or from 20 to 25%; or from 25 to 30%; or from 30 to 35%; or from 35 to 40%; or from 40 to 45%; or 45 to 50%. For example, PEKK is preferably crystalline in an amount of less than 40%, more preferably less than 30%.

It is advantageous for the crystalline PEKK content to be relatively high, for example greater than or equal to 5%, or greater than or equal to 10%, or even greater than or equal to 15%, in order to have parts having high mechanical performance.

In the PEKK used in the invention, the proportion by mass of PEKK of form 1, relative to the total crystalline PEKK, can in particular vary from 50 to 55%; or from 55 to 60%; or from 60 to 65%; or from 65 to 70%; or from 70 to 75%; or from 75 to 80%; or from 80 to 85%; or from 85 to 90%; or from 90 to 95%; or 95 to 100%. For example, this proportion by mass of form 1 can preferably be at least 80%, more preferably at least 90%. The crystalline PEKK can in particular consist essentially (or even consist) of PEKK of form 1.

The PEKK of the parts of the invention advantageously has an inherent viscosity of 0.4 to 1.5 dL / g, preferably 0.6 to 1.12 dL / g in 96% sulfuric acid, at the concentration of 0.005 g / mL.

The parts according to the invention can consist essentially, or even consist of PEKK.

Alternatively, they can comprise PEKK as described above and other components, such as in particular fillers (including fibers) and / or functional additives. Among the functional additives, it is possible in particular to include one or more surfactants, UV stabilizers, thermal stabilizers and / or biocidal agents.

PEKK can also be combined with one or more other polymers, in particular thermoplastics, whether or not belonging to the PAEK (polyarylether ketones) family. Such PAEKs can in particular include polyether-ketones (PEK), polyether-ether-ketones (PEEK), polyether-ether-ketone-ketones (PEEKK), polyether-ketone-ether-ketone-ketones (PEKEKK), polyether-ether-ketone-ether-ketones (PEEKEK), polyether-ether-ether-ketones (PEEEK), polyether-diphenyl-ether-ketones (PEDEK), their mixtures and their copolymers with each other or with others members of the PAEK family.

Preferably, the PEKK represents, by weight, at least 50%, more preferably at least 70%, or at least 80%, or at least 90% of all the polymers present.

In particular embodiments, only PEKK is present as a polymer (with the exception of possible fillers or functional additives).

The parts according to the invention can be composite parts which include fillers, and in particular reinforcing fibers. The composite parts may comprise, by weight, from 1 to 99%, preferably from 30 to 90%, in particular from 50 to 80%, and in particular also from 60 to 70% of fillers, in particular of reinforcing fibers.

The non-fibrous fillers can in particular be mineral fillers such as alumina, silica, calcium carbonate, titanium dioxide, glass beads, carbon black, graphite, graphene and carbon nanotubes.

The fibrous fillers can be so-called short fibers or reinforcing fibers (long or continuous fibers).

The fibrous fillers can in particular be glass fibers, quartz fibers, carbon fibers, graphite fibers, silica fibers, metal fibers such as steel fibers, aluminum fibers or carbon fibers. boron, ceramic fibers such as silicon carbide or boron carbide fibers, synthetic organic fibers such as aramid fibers or poly (p-phenylene benzobisoxazole) fibers, or even PAEK fibers, or else mixtures of such fibers.

Preferably, they are carbon fibers or glass fibers, and more particularly carbon fibers.

The fibers are preferably unsized. If they are sized, they are preferably sized with a thermally stable sizing (that is to say a sizing which does not generate, when subjected to temperatures exceeding 300 ° C, in particular exceeding 350 ° C. and in particular at 375 ° C., for at least 20 min, of reactive species capable of reacting significantly with PEKK).

Preferably, the reinforcing fibers are in the form of unidirectional fibers, for example in the form of threads grouping together several thousand elementary filaments (typically from 3000 to 48000) measuring, for example, from 6 to 10 m in diameter for the fibers. of carbon. This type of fiber is known by the name of rovings (in English "rovings").

The reinforcing fibers can nevertheless also be organized in a different manner, for example in the form of a mat, or alternatively of textiles obtained by weaving rovings.

The parts according to the invention can be manufactured according to a process comprising at least the supply of PEKK, and the shaping of the PEKK.

The shaping of the PEKK can be carried out according to any conventional method of shaping thermoplastics; it therefore involves a phase of melting the polymer.

The shaping can be carried out in particular by extrusion, or by injection molding, or by injection-compression, or by coating, optionally supplemented by thermoforming or machining.

The PEKK is initially supplied preferably in the form of powder, granules or flakes, and / or in the form of a dispersion, in particular an aqueous dispersion.

The additives, fillers and other optional constituents of the parts can be mixed with the PEKK when the latter is in the molten state, for example by compounding in an extruder. Alternatively, the PEKK can be mixed with additives, fillers and other optional constituents in the solid state, for example in powder form.

When a part comprises reinforcing fibers, it can be produced for example by introducing and circulating the reinforcing fibers in a bath of aqueous dispersion of PEKK (and additives or other optional constituents). The fibers impregnated with PEKK can then be taken out of the bath and freed from water, for example by drying in an infrared oven. The dried impregnated fibers can then be heated until the PEKK melts, in order to allow the fibers to be coated with the PEKK. As an alternative, the continuous fibers can also be coated by circulating them in a fluidized bed of PEKK powder and then heating the assembly until the PEKK melts. The coated fibers obtained are then, if necessary, shaped and sized, for example by calendering.

Alternatively, the objects obtained as described in the previous paragraph are used as semi-finished products, from which a part according to the invention proper is in turn prepared. This preparation can be carried out by first manufacturing a preform, in particular by placing or draping the semi-products in a mold. The composite part can be obtained by consolidation, a step during which the preform is heated, generally under pressure in an autoclave, so as to assemble the semi-products by fusion. The semi-finished products can then be assembled, for example by manual or automated lay-up or by robotic placement (“automated fiber placement”), and shaped by consolidation, to obtain the parts of the invention.

The crystalline PEKK content in the part as well as the proportion of Form 1 in the crystalline PEKK can be adjusted in particular as a function of the temperature conditions applied during the manufacturing process. For example, in the case of injection molding, adjusting the temperature of the mold is a factor to adjust the above parameters.

In some cases, a heat treatment or annealing after the actual shaping can be applied. Such a subsequent heat treatment must in particular be used when, after shaping, the PEKK is in exclusively amorphous form, or in a crystalline form comprising a high level of form 2.

In other cases, no heat treatment or annealing is applied. This makes it possible to avoid any risk of possible deformation during such a step. The choice of appropriate parameters for shaping (temperature of the mold in the case of molding for example, cooling ramp, etc.) can be adapted in order to make it possible to avoid such a heat treatment or annealing.

In general, the application of a relatively high temperature during the process (for example the temperature of the mold, in the case of injection molding) is favorable to the presence of the crystalline PEKK of Form 1 in the final part, and this whatever the nature of the crystalline forms in the PEKK before shaping.

The temperature threshold to be applied during the process in order to obtain the desired content of crystalline PEKK of form 1 depends in particular on the nature of the PEKK and more particularly on the proportion of units T relative to the sum of units T and I For example, in the case of injection molding, for a fixed mold temperature (typically greater than 200 ° C. for crystalline PEKKs), Form 1 will exist in a greater proportion if the content of T units is high.

As a guide, the approximate melting temperatures of crystalline Form 1 PEKK and crystalline Form 2 PEKK, depending on the content of T units, are shown in the following table:

These values ​​were obtained by differential scanning calorimetry (DSC) measurements on predominantly form 1 and predominantly form 2 samples.

Furthermore, the cooling rate of the part after shaping or after possible annealing can optionally be adjusted in order to promote the appearance of crystals of form 1. Indeed, slow cooling (for example at a rate less than or equal to 50 ° C / h, or less than or equal to 30 ° C / h, or less than or equal to 10 ° C / h) is favorable to the appearance crystals of form 1.

The parts according to the invention can be parts of any industrial or consumer object. In particular, they may be parts of medical devices.

In preferred embodiments, these are parts subjected to a relatively high temperature during their use. In particular, they may be parts of an aerial or space locomotion vehicle, or parts of drilling installations (for hydrocarbon fields), or any part located in contact with or near an engine ( for example of an engine of a maritime, land or air vehicle) or of a reactor, and in particular of seals, connectors, sheaths and structural parts. They may also be parts intended to be subjected to friction, that is to say parts in movable contact with one or more surfaces, in use. Such parts can in particular be supports, rings, valve seats, gears, pistons, piston rings,

In particular embodiments, the parts according to the invention are subjected, in use, to a continuous use temperature greater than or equal to 200 ° C, or greater than or equal to 230 ° C, or greater than or equal to 260 ° C, or greater than or equal to 280 ° C.

The continuous use temperature is the maximum temperature at which the part retains 50% of its initial properties after 100,000 hours. It can be determined according to UL 746 B.

In particular embodiments, the parts according to the invention are subjected, in use, to a maximum temperature greater than or equal to 200 ° C, or greater than or equal to 250 ° C, or greater than or equal to 300 ° C, or greater than or equal to 320 ° C. This maximum temperature is the highest temperature to which the part is subjected, even for a short time, during its entire use.

It should be noted that the permissible thresholds of continuous use temperature and especially of maximum temperature may depend on the melting temperature of the PEKK and therefore in particular on the proportion of units T relative to all the units T and I in the PEKK.

Thus, advantageously, the maximum temperature is less than or equal to the melting temperature of form 1 of the PEKK used minus 5 ° C, preferably less than or equal to the melting temperature of form 1 of the PEKK used minus 10 ° C, more preferably less than or equal to the melting temperature of form 1 of the PEKK used minus 20 ° C,

more preferably less than or equal to the melting temperature of form 1 of the PEKK used minus 30 ° C and more preferably less than or equal to the melting temperature of form 1 of the PEKK used minus 40 ° C.

EXAMPLES

The following examples illustrate the invention without limiting it.

Example 1

Dumbbells conforming to the ISO 527 1 BA standard are manufactured by injection from granules of PEKK reference KEPSTAN® 8002 marketed by Arkema, having a relative content of T units of 80%.

Dumbbells of two types A and B are prepared with the following parameters: injection temperature of 385 ° C, mold temperature of 273 ° C for dumbbells A and 265 ° C for dumbbells B.

The cycle time (time in the mold) is 40 seconds. After molding, the dumbbells are ejected and allowed to cool to room temperature.

In both cases, the degree of crystallinity determined by WAXS is 14%.

WAXS measurements make it possible to determine that the crystals are 100% form 1 in dumbbell A (according to the invention), and 15% form 1 and 85% form 2 in dumbbell B (comparative) .

The melting temperature of dumbbell A is measured at 365 ° C and the melting temperature of dumbbell B is measured at 359 ° C, by DSC.

A dynamic mechanical analysis (DMA) measurement does not reveal a significant difference in modulus between dumbbells A and B over the range 50 to 350 ° C.

Finally, strain monitoring (creep) measurements under stress are carried out on the two types of dumbbells, at different temperatures. To do this, a tension test is carried out by applying a given stress, and the deformation of each dumbbell is monitored at the temperature considered.

The results are summarized in the table below:

Temperature Stress Deformation Deformation

dumbbell A dumbbell B

320 ° C 1, 1 MPa 1, 5%, stable 1, 5%, stable

350 ° C 0.1 1 MPa 0.8%, stable 1.3%, stable

355 ° C 0.1 1 MPa 1.3%, stable 3.5%, stable

> 15%, no stabilization

360 ° C 0.1 1 MPa 3.4%, stable

then break

In the table below, a sample is considered to be stable when its deformation stops changing, up to a maximum duration of 20 minutes.

It is observed that the parts according to the invention (dumbbell A) resist creep better at a temperature above 320 ° C. than the comparative parts (dumbbell B).

Example 2

Dumbbells conforming to the ISO 527 1 BA standard are manufactured by injection from granules of PEKK reference KEPSTAN® 6002 marketed by Arkema, having a relative content of T units of 60%.

Dumbbells of two types A and B are prepared as follows: injection temperature of 340 ° C, mold temperature of 80 ° C for both types of dumbbells.

After injection, the dumbbells are in amorphous form. They are then subjected to a heat treatment:

- 280 ° C for 2 hours for dumbbell A.

- 225 ° C for 2 hours for dumbbell B.

In both cases, the level of crystallinity determined by WAXS is

13%.

WAXS measurements make it possible to determine that the crystals are 95% form 1 and 5% form 2 in dumbbell A (according to the invention), and 15% form 1 and 85% form 2 in dumbbell A (according to the invention). dumbbell B (comparative).

Stress strain (creep) monitoring measurements are performed on the two types of dumbbells, at different temperatures, in the same manner as in the previous example.

The results are summarized in the table below:

Temperature Stress Deformation Deformation

dumbbell A dumbbell B

240 ° C 1.1 MPa 2%, stable 2%, stable

285 ° C 0.1 1 MPa 1%, stable 3%, stable

p us emn

In the table below, a sample is considered to be stable when its deformation stops changing, up to a maximum duration of 20 minutes.

It is observed that the parts according to the invention (dumbbell A) resist creep better at a temperature greater than or equal to 285 ° C. than the comparative parts (dumbbell B
CLAIMS

Part comprising polyether ketone ketone, in which the polyether ketone ketone is at least partly crystalline, and in which at least 50% by weight of the crystalline polyether ketone ketone is of form 1, as determined according to the protocol described on page 4 line 29 - page 5 line 20 of the description.

Part according to Claim 1, in which at least 80% by weight, preferably at least 90% by weight, and more particularly preferably essentially all of the crystalline polyether ketone ketone is of form 1.

Part according to claim 1 or 2, wherein the polyether ketone ketone comprises at least 10% by weight, preferably at least 15% by weight of crystalline polyether ketone ketone.

Part according to one of claims 1 to 3, in which the polyether ketone ketone comprises terephthalic units and optionally isophthalic units, the proportion by weight of the terephthalic units relative to the sum of the terephthalic units and of the isophthalic units being from 35 to 100 %, preferably 55 to 85%.

Part according to one of claims 1 to 4, in which the polyether ketone ketone represents at least 30% by weight, preferably at least 50% by weight, more preferably at least 70%, and ideally at least 80% by weight of the room.

Part according to one of claims 1 to 5, which also comprises one or more additional elements chosen from fillers, preferably including fibers, one or more other polyarylether ketones, additives and combinations thereof.

7. Part according to one of claims 1 to 6, which is a part of an aerial or space locomotion vehicle, or a part of a

drilling installation, or a part intended to be positioned in contact with or near a vehicle engine or a reactor, or a part intended to be subjected to friction.

8. Use of the part according to one of claims 1 to 7, in an apparatus, machine or system, the part being subjected to a continuous use temperature greater than or equal to 200 ° C, or greater than or equal to 230 ° C, or greater than or equal to 260 ° C, or greater than or equal to 280 ° C.

Use of the part according to one of claims 1 to 7, in an apparatus, machine or system, the part being subjected to a maximum temperature greater than or equal to 200 ° C, or greater than or equal to 250 ° C, or greater or equal to 300 ° C, or greater than or equal to 320 ° C.

Process for manufacturing a part according to one of claims 1 to 7, comprising:

- the supply of polyether ketone ketone;

- The shaping of the polyether ketone ketone, and the at least partial crystallization of the polyether ketone ketone in the form 1.

A method according to claim 10, wherein the shaping is effected by injection molding, injection compression or extrusion.

12. The method of claim 10 or 11, comprising a heat treatment step after the shaping step.