sintering.
[0005] In the family of PAEKs, the poly(ether ether ketone) (PEEK) is particularly used
in the context of the abovementioned applications. However, it exhibits the
disadvantage of crystallizing very rapidly, which can generate large internal stresses in
the manufactured parts based on this material during the cooling thereof. In some
cases, such as PEEK coatings of metal parts or in the case of bulk PEEK parts, these
internal stresses can result in splitting of the material. A subsequent annealing stage,
followed by slow cooling, is generally necessary in order to remove or at least reduce
these internal stresses. In point of fact, such a stage proves to be lengthy and thus
involves a not insignificant additional expenditure for the parts thus manufactured.
[0006] Furthermore, in the specific case of laser sintering, the rapid kinetics of
crystallization can result in deformation of the part. Such deformation is also known as
"curling". Consequently, in this case, the geometry of the part is not optimal.
[0007] Finally, even if the PEEKs already have good mechanical properties, it can be
advantageous, for some applications, to further improve the mechanical properties of
objects obtained by different types of processes such as moulding, injection moulding,
extrusion or laser sintering. Thus, it can be advantageous to increase the yield point
stress in order to be able to work a PEEK-based material under higher stresses without
irreversibly deforming it but without, however, causing a deterioration in the other
mechanical properties, such as elongation at break, for example. This is because an
increase in the yield point stress conventionally amounts to lowering the value of the
elongation at break of a material. In point of fact, for some applications, it can be
important to retain a ductile material with a high elongation at break. It is thus generally
advisable to find a compromise between the elongation at break and the yield point, in
order to have a plastic material exhibiting mechanical properties suitable for the
application for which it is dedicated.
[0008] A polymer alloy comprising between 60 and 98% by weight of a semicrystalline
PAEK and between 40 and 2% by weight of an amorphous PAEK is known from the
document US 5 342 664. Such an alloy exhibits a higher elongation at break and a
reduced viscosity in comparison with the semicrystalline PAEK alone. However, this
document remains silent with regard to the rate of crystallization which generates the
problems of deformations of parts or requires a lengthy and expensive postannealing
stage in order to eliminate the internal stresses which have appeared in the part as a
result of excessively rapid crystallization kinetics. Neither is mention made of the yield
point of the alloy.
[0009] The paper entitled "Blends of two PAEK" which appeared in the review
POLYMER, 1988, Vol. 29, June, pp. 101 7-1 020, describes the preparation of an alloy
based on PEEK and on PEK, two polymers of the family of the PAEKs which have the
distinguishing feature of both crystallizing quickly. This paper studies the crystallization
of the two compounds of the alloy and their behaviour. On the other hand, this
document studies neither the rate of crystallization and its influence on the appearance
of internal stresses and on the deformation of the parts obtained nor the mechanical
properties of the alloy.
[001 0] The paper entitled "Dynamic study of crystallization and melting-induced phase
separation in PEEK/PEKK blends", Journal of the American Chemical Society, 1997,
30, pp.4544-4550, describes an alloy of PEEK and PEKK, the T/l ratio of which of the
terephthalic units (T) to the isophthalic units (I) is 30/70. This document demonstrates
the incorporation of 30/70 PEKK in PEEK, in proportions by weight equal to 50/50,
makes it possible to slow down the crystallization of the PEEK as a result of an
interdiffusion of the two compounds of the alloy. This document does not study the
mechanical properties of such an alloy.
[Technical problem]
[001 1] It is thus an aim of the invention to overcome at least one of the disadvantages
of the prior art. In particular, it is an aim of the invention to provide a PEEK-based
composition, at least one property of which is improved, and a process for improving at
least one property of such a PEEK-based composition, so as to make possible the
preparation of parts from such a composition which exhibit a significant reduction in the
internal stresses so that it is possible to dispense with the additional postannealing
stage, which are not deformed and which exhibit enhanced mechanical properties.
[Brief description of the invention]
[001 2] Surprisingly, it has been discovered that a composition based on poly(ether
ether ketone) (PEEK) comprising poly(ether ketone ketone) (PEKK), characterized in
that the poly(ether ketone ketone) (PEKK) comprises a mixture of terephthalic and
isophthalic units, the percentage by weight of terephthalic units, with respect to the sum
of the terephthalic and isophthalic units, being between 55 and 85%, limits included,
and preferably between 55 and 70%, the said composition comprising between 1 and
40%, limits included, preferably between 5 and 40% and more preferably still between
10 and 30% by weight of PEKK, with respect to the total weight of the composition,
exhibits not only slowing in the kinetics of crystallization, in comparison with that of a
pure PEEK, but also a gain with regard to two, generally antagonistic, mechanical
properties, since the yield point stress and the elongation at break are both increased,
in comparison with a pure PEEK.
[001 3] According to other optional characteristics of the composition:
- the PEEK can be replaced with PEK or PEKEKK,
- the PEKK can be a PEKK blend, each PEKK exhibiting a percentage by weight
of terephthalic units, with respect to the sum of the terephthalic and isophthalic
units, of between 55 and 85%, limits included, and preferably between 55 and
70%,
- the composition additionally comprises at least one filler and/or at least one
additive,
- the proportion by weight of PEEK in the composition comprises from 60 to 99%,
limits included, preferably between 60 and 95% and more preferably still
between 70 and 90%, with respect to the total weight of the composition.
[0014] Another subject-matter of the invention is a process for improving at least one
property of a PEEK-based composition, the said process consisting in incorporating
PEKK in the said PEEK-based composition, the said process being characterized in
that the PEKK comprises a mixture of terephthalic and isophthalic units, the percentage
by weight of terephthalic units, with respect to the sum of the terephthalic and
isophthalic units, being between 55 and 85%, limits included, and preferably between
55 and 70%, and in that the PEKK is incorporated in the said composition in proportions
of between 1 and 40%, limits included, preferably between 5 and 40% and more
preferably still between 10 and 30% by weight, with respect to the total weight of the
composition.
[001 5] Finally, the invention relates to an object manufactured from a composition as
described above by a technology chosen from laser sintering, moulding, injection
moulding or extrusion.
[001 6] Other advantages and characteristics of the invention will become apparent on
reading the following description, given as illustrative and nonlimiting example, with
reference to the appended figures, which represent:
• Figure 1, the change in the heat flow of seven PEEK-based compositions as a
function of temperature,
• Figure 2, the change in the degree of crystallization of four PEEK-based
compositions with respect to time.
[Description of the invention]
[001 7] The composition which is a subject-matter of the invention is based on PEEK.
The constituent PEEK matrix of the composition can also be replaced by PEK or
PEKEKK. In the abbreviations used, E denotes an ether functional group and K denotes
a ketone functional group.
[001 8] The presence of PEKK, possessing terephthalic and isophthalic units, in the
PEEK-based composition makes it possible to slow down the kinetics of crystallization
of the PEEK, and thus to limit the internal stresses which may result in splits during the
cooling of the material, and to obtain nondeformed parts, the geometry of which meets
expectations. Terephthalic and isophthalic unit is understood to mean the formula of
terephthalic acid and isophthalic acid respectively.
[001 9] Preferably, the PEKK incorporated in the PEEK-based composition comprises
a percentage by weight of terephthalic units, with respect to the sum of the terephthalic
and isophthalic units, of between 55 and 85%, limits included, more preferably still
between 55 and 70% and more preferably still of the order of 60%. Such a PEKK with
approximately 60% of terephthalic units is a material having very slow crystallization,
typically 20 minutes during an isothermal crystallization at temperatures of between
240 and 260°C, and exhibiting a glass transition temperature Tg of the order of 160°C
and a melting point of the order of 305°C.
[0020] In particular, the variation in the proportions of terephthalic and isophthalic units
of the PEKK, within the abovementioned range of proportions, makes it possible to
adjust the said kinetics of crystallization of the PEEK. The kinetics of crystallization will
be studied either under anisothermal conditions, that is to say during the cooling via a
temperature gradient, or under isothermal conditions, that is to say that the degree of
crystallization will be monitored at a given temperature. In the case of the study of the
crystallization under anisothermal conditions, the lower the crystallization temperature,
the slower the kinetics of crystallization. It is consequently possible to obtain a range of
compositions based on PEEK and on PEKK, for which the rate of crystallization is
known for each composition and is adapted according to the subsequent application of
the said compositions.
[0021] Preferably, the composition comprises between 60 and 99%, limits included,
preferably between 60 and 95% and more preferably still between 70 and 90% by
weight of PEEK, with respect to the total weight of the composition, and between 1 and
40%, limits included, preferably between 5 and 40% and more preferably still between
10 and 30% by weight of PEKK, with respect to the total weight of the composition.
[0022] Such a composition advantageously makes it possible to improve two,
generally antagonistic, mechanical properties of the PEEK. This is because the addition
of PEKK possessing terephthalic and isophthalic units, in the abovementioned
proportions, with a percentage by weight of between 1 and 40%, preferably between 5
and 40% and more preferably still between 10 and 30%, with respect to the total weight
of the composition, makes it possible to obtain a gain of between 5 and 15% in the yield
point and an elongation at break improved by a factor which can range up to 3 .
[0023] The composition can in addition comprise one or more additives or contain
different compounds, such as fillers, in particular inorganic fillers, such as carbon black,
nanotubes, short (glass or carbon) fibres, long fibres, ground or nonground fibres,
stabilizing agents (light, in particular UV, and heat stabilizing agents), glidants, such as
silica, or also optical brighteners, dyes, pigments or a combination of these fillers and/or
additives.
[0024] The composition which has just been described consists of a PEEK-based
matrix. In an alternative form, the PEEK matrix can be replaced with a PEK or PEKEKK
matrix.
[0025] In addition, the PEKK incorporated in the PEEK-based composition, or PEKbased
or PEKEKK-based composition, can be a PEKK blend, provided that each PEKK
exhibits a percentage by weight of terephthalic units, with respect to the sum of the
terephthalic and isophthalic units, of between 55 and 85%, preferably between 55 and
70% and more preferably still of the order of 60%.
[0026] In addition, the invention relates to a process for improving at least one property
of a PEEK-based composition, the said process consisting in incorporating PEKK in
the said PEEK-based composition. The incorporated PEKK comprises a mixture of
terephthalic and isophthalic units, the percentage by weight of terephthalic units, with
respect to the sum of the terephthalic and isophthalic units, being between 55 and 85%
and preferably between 55 and 70% and more preferably still of the order of 60%.
Advantageously, the PEKK is incorporated in the said composition in proportions of
between 1 and 40%, preferably between 5 and 40% and more preferably still between
10 and 30% by weight, with respect to the total weight of the composition.
[0027] Such an incorporation of PEKK in the PEEK-based composition makes it
possible not only to adjust the kinetics of crystallization of the PEEK but in addition to
improve two mechanical properties of the PEEK which are generally antagonistic,
namely the yield point and the elongation at break.
[0028] The composition based on PEEK and on PEKK as defined above can be
prepared by any known method which makes it possible to obtain a homogeneous
blend containing the composition according to the invention and optionally other
additives, fillers or other polymers. Such a method can be chosen from melt extrusion,
compacting or also mixing techniques, for example using a roll mill.
[0029] More particularly, the composition according to the invention is prepared by
melt blending all its components, in particular in a "direct" process.
[0030] In the case of laser sintering, the composition can also be obtained by a dry
blending of powders.
[0031] Advantageously, the composition can be obtained in the form of granules by
compounding on a device known to a person skilled in the art, such as a twin-screw
extruder, a cokneader or an internal mixer.
[0032] The composition thus prepared can subsequently be converted, for a
subsequent conversion or use known to a person skilled in the art, using devices such
as an injection moulding machine, an extruder, and the like.
[0033] The process for the preparation of the composition according to the invention
can also use a twin-screw extruder feeding, without intermediate granulation, an
injection moulding machine or an extruder according to a processing arrangement
known to a person skilled in the art.
[0034] It is possible, starting from the composition obtained, which can be either
granules or powders, to manufacture different objects by a laser sintering or injection
moulding or extrusion technique, for example.
[0035] The following examples illustrate, without implied limitation, the scope of the
invention:
Example 1: Compounding of several compositions exhibiting different formulations
[0036] The compounding is a process which makes it possible to blend, by melting,
plastics and/or additives and/or fillers.
[0037] In order to manufacture each composition, the starting materials, which are
provided in the form of granules, are placed in a corotating twin-screw extruder. The
feed zone of the extruder is heated to a temperature of the order of 300°C.
[0038] The blending of the materials takes place under molten conditions at a
temperature of the order of 360°C, with a rotational speed of 300 revolutions/minute
and a throughput of 2.5 kg/h.
[0039] The different compositions which were manufactured by compounding in order
to be compared all comprise PEEK and PEKK in different proportions by wieght. The
PEKK incorporated in the composition is a PEKK comprising terephthalic (T) and
isophthalic (I) units, the T/l ratio of which is equal to 60/40. Two different grades of
PEKK were used. These two grades comprise the same proportions of terephthalic
units. They differ from one another essentially in their viscosity. Thus, a first PEKK,
referenced K 1 in Table I and I I below and sold by Arkema under the commercial
reference Kepstan ® 6001 , exhibits a viscosity number of 0.95 dl/g, whereas the second
PEKK, referenced K3 in the table I below and sold by Arkema under the commercial
reference Kepstan ® 6003, exhibits a viscosity number of 0.82 dl/g. The viscosity
number is measured according to Standard ISO 307, in solution at 25°C in 96%
sulphuric acid.
[0040] In these comparative examples, the proportion by weight of PEKK in the
composition varies between 10 and 30% of the total weight of the composition for table
I and from 5 to 50% for table II. The compositions based on PEEK and on PEKK are
intended to be compared with a control composition, referenced CC (table I),
comprising solely pure PEEK, sold by Victrex under the commercial reference Victrex
450G, and referenced CT (table II), comprising solely pure PEEK, sold by Victrex
under the commercial reference Victrex 150G.
[0041] The different compositions produced are combined in Table I and I I below. The
amounts of the different constituents of the composition, that is to say of PEEK and of
PEKK, are expressed as percentage by weight, with respect to the total weight of the
composition.
Table I
Table I I
Example 2 : Study of the kinetics of crystallization of the compositions obtained on
conclusion of the compounding process of Example 1
[0042] A crystallization study was carried out on the control sample of PEEK,
referenced CC in Table I above, and on the six samples of compositions referenced C 1
to C6 in Table I above.
[0043] The crystallization study is carried out by differential scanning calorimetry,
denoted DSC. DSC is a thermal analysis technique which makes it possible to measure
the differences in the heat exchanges between a sample to be analyzed and a
reference.
[0044] Use was made, in order to carry out this crystallization study, of the Q 2000
device from TA Instruments. The study was carried out under anisothermal and
isothermal crystallization conditions.
Anisothermal crystallization
[0045] The protocol for DSC under anisothermal conditions, on the different samples
CC and C 1 to C6 resulting from Example 1, consists, in a first step, in stabilizing the
temperature at 20°C. The temperature is subsequently gradually increased, along a
gradient of 20°C per minute, up to 400°C and then it is again gradually decreased down
to 20°C, along a reverse gradient of 20°C per minute.
[0046] The crystallization is studied during the cooling stage. The heat flow is
measured as a function of temperature and a curve representing the change in the heat
flow as a function of temperature is obtained for each composition studied. These
curves are represented in Figure 1. The crystallization temperature, denoted Tc and
expressed in degrees Celsius, is subsequently determined for each composition by
projecting the maximum of the corresponding curve onto the axis of the abscissae. This
determination is carried out directly by the DSC equipment used.
[0047] The crystallization temperatures Tc of each sample analyzed are combined in
Table I I below.
Table I I
[0048] The curve of the control composition CC (pure PEEK), which does not comprise
PEKK, is the curve located furthest to the right in the graph of Figure 1. This control
composition exhibits a crystallization temperature Tccc which is the highest, equal to
291 .3°C.
[0049] These curves demonstrate that, the higher the fraction by weight of PEKK in
the composition, the lower the crystallization temperature and thus the more the
crystallization is delayed. The addition of PEKK to the PEEK according to the invention
thus makes it possible to delay the crystallization of the PEEK.
Isothermal crystallization
[0050] DSC under isothermal conditions was carried out for a sample of control
composition CC and samples of the compositions C 1, C2 and C3 respectively
comprising 10%, 20% and 30% by weight of PEKK. The protocol of the isothermal DSC
comprises the following three stages: a first stage consists, in a first step, in stabilizing
the temperature at 20°C, a second stage subsequently consists in gradually increasing
the temperature, along a gradient of 20°C per minute, up to 400°C. Finally, the
temperature is reduced from 400°C down to 315°C, along a gradient of 20°C per
minute, and then it is stabilized at 315°C for one hour.
[0051] During the hour of stabilization of the temperature at 3 15°C, the fraction by
weight of PEEK crystallized as a function of time t is measured. The measurements are
carried out on the compositions C 1, C2 and C3, in comparison with the control
composition CC. The four curves obtained are represented in the graph of Figure 2 .
[0052] It results from the curve corresponding to the control sample CC that the
crystallization half time is approximately 6 minutes. The crystallization half time of a
polymer is the time necessary for the crystallization of 50% of this polymer. On the
curves of Figure 2, it is determined by being placed at the value of 50% on the axis of
the ordinates (% of crystallized PEEK) and by projecting this value onto the axis of the
abscissae (Time).
[0053] The curve corresponding to the composition C3 is offset to the right by
approximately 4 minutes, with respect to the curve of the control composition CC. The
crystallization half time on this curve is approximately 10 minutes. The curves
corresponding to the compositions C 1 and C2 are offset to the right by approximately
3 minutes, with respect to the curve of the control composition CC, the crystallization
half time of the composition C 1 being approximately 9 minutes and that of the
composition C2 being virtually 10 minutes.
[0054] It results from these curves that, surprisingly, the delay in crystallization is not
proportional to the content of PEKK incorporated in the composition. Contrary to what
might have been expected, the change in crystallization kinetics is not linear as a
function of the content of PEKK incorporated. Consequently, it is preferable to
incorporate a content of PEKK of less than or equal to 40% by weight, with respect to
the total weight of the composition, in order to prevent the appearance of a
phenomenon of phase separation in the composition.
[0055] The addition of PEKK in a proportion of 1 to 40% by weight, preferably between
5 and 40% by weight and more preferably still between 10 and 30% by weight, with
respect to the total weight of the PEEK-based composition according to the invention,
thus makes it possible to delay the crystallization of the PEEK, while avoiding a
phenomenon of phase separation.
Example 3 : Measurement of the yield point stress and of the elongation at break of
injection-moulded parts based on the compositions obtained on conclusion of the
compounding process of Example 1
[0056] In order to be able to carry out measurements of yield point stress and of
elongation at break, test specimens of samples were produced in a first step. For this,
an injection moulding machine is used. In this example, the injection moulding machine
used is a Battenfeld 80T moulding machine. The feed temperature of the moulding
machine is regulated at 350°C, the temperature of the injection nozzle is regulated at
390°C and the temperature of the mould is set at 230°C.
[0057] Test specimens appropriate for tensile tests of 1BA type according to Standard
ISO 527 are then obtained.
[0058] For the comparative tests of measurement of yield point stress and of
elongation at break, two test specimens were produced according to Standard ISO 527
1BA. A first test specimen of the control composition CC is compared with a second
test specimen of the composition C3 of Example 1, comprising 30% by weight of PEKK,
and the same procedure was repeated for controle composition CT compared with
specimen C 10 to C5a.
[0059] The measurements of stress were carried out on each test specimen using a
tensile testing device coupled to an optical extensometer, making possible the
recording of the curves of stress as a function of the strain of the test specimens
subjected to a tensile stress. The tensile testing device used for these tests is more
particularly a tensile testing device from Zwick sold under the reference Zwick 1455.
[0060] The measurements are carried out at 23°C, at a relative humidity of 50% RH
and at a pull rate of 25 mm/min.
[0061] The tensile force necessary as a function of the elongation is then measured
and the yield point stress and the elongation at break are determined. The results
obtained are combined in Table III and IV below.
Table IV
[0062] The addition of 30% by weight of PEKK to PEEK makes it possible to change
the yield point stress from 92.5 MPa to 10 1 MPa, i.e. an increase of 7.5% in results
from table III. Furthermore, this addition makes it possible to increase the elongation at
break from 40% to 100%, i.e. an increase by a factor of 2.5.
From Table IV, same conclusion can be formulated for elongation at break. Additionally,
50% composition (C5a) which is out of the claimed compositions shows that maximum
of PEKK to be advantageously mixed with PEEK should be 40%, not more.
[0063] Thus, the incorporation of PEKK in a PEEK-based composition brings about an
increase in the yield point stress and also an increase in the elongation at break and
thus an increase in two mechanical properties which are generally antagonistic.
[0064] The composition according to the invention exhibits not only the advantage of
slowing down the kinetics of crystallization of PEEK, and thereby of reducing the
internal stresses of the material, of thus dispensing with a lengthy and expensive post
annealing stage and of obtaining non deformed parts having the desired optimum
geometry, but it exhibits in addition the advantage of having exceptional mechanical
properties with a gain in the yield point and in the elongation at break, which were until
now known to be antagonistic mechanical properties.

CLAIMS
1. Composition based on one of the following polymers: poly(ether ether ketone)
(PEEK), poly(ether ketone) (PEK) or poly(ether ketone ether ketone ketone)
(PEKEKK), and comprising poly(ether ketone ketone) (PEKK), characterized in that the
poly(ether ketone ketone) (PEKK) comprises a mixture of terephthalic and isophthalic
units, the percentage by weight of terephthalic units, with respect to the sum of the
terephthalic and isophthalic units, being between 55 and 85%, limits included, and
preferably between 55 and 70%, the said composition comprising between 1 and 40%,
limits included, preferably between 5 and 40% and more preferably still between 10
and 30% by weight of PEKK, with respect to the total weight of the composition.
2 . The composition according to Claim 1, characterized in that the PEKK can be a
PEKK blend, each PEKK exhibiting a percentage by weight of terephthalic units, with
respect to the sum of the terephthalic and isophthalic units, of between 55 and 85%,
limits included, and preferably between 55 and 70%.
3. Composition according to Claims 1 and 2, characterized in that it comprises at least
one filler and/or at least one additive.
4 . Composition according to any one of Claims 1, 2 and 3, characterized in that the
proportion by weight of PEEK in the composition is between 60 and 99%, limits
included, preferably between 60 and 95% and more preferably still between 70 and
90%, with respect to the total weight of the composition.
5. Process for improving the yield point and/or the elongation at break of a composition
based on one of the following polymers: poly(ether ether ketone) (PEEK), poly(ether
ketone) (PEK) or poly(ether ketone ether ketone ketone) (PEKEKK), the said process
consisting in incorporating PEKK in the said composition, the said process being
characterized in that the PEKK comprises a mixture of terephthalic and isophthalic
units, the percentage by weight of terephthalic units, with respect to the sum of the
terephthalic and isophthalic units, being between 55 and 85%, limits included, and
preferably between 55 and 70%, and in that the PEKK is incorporated in the said
composition in proportions of between 1 and 40%, limits included, preferably between
5 and 40% and more preferably still between 10 and 30% by weight, with respect to the
total weight of the composition.
6. Object manufactured from a composition according to one of Claims 1 to 4 by a
technology chosen from laser sintering, moulding, injection moulding or extrusion.