Powder composition of polyarylene ether ketone ketones
allowing an excellent castability/coalescence balance
suitable for laser sintering
5 The present invention relates to a composition comprising
from 99.6% to 99.99% by weight of at least one powder of at
least one polyarylene ether ketone and 0.01% to 0.4% by
weight of a hydrophilic flow agent. This hydrophilic flow
agent is characterized by a gain in mass (amount of water
10 absorbed), after 5 days of conditioning at a relative
humidity of 95%, of greater than 0.5%. This gain in mass of
the f1or.1 agent is determined by Karl Fischer measurement
after desorption of the water via a 15-minute treatment at
170°C. This composition is suitable for laser sintering. It
15 in particular allows an excellent castability/coalescence
compromise for the powder.
Polyarylene. ...e ther ketones and more particularly polyether
ketone ketones (PEKK) are highly efficient materials. They
20 are used for applications with temperature constraints
and/or mechanical or even chemical constraints. These
polymers are found in fields as varied as aeronautics,
offshore drilling and medical implants. They may be used by
molding, extrusion, compression, spinning or laser
25 sintering, especially. However, their use in the latter
process requires powder preparation conditions that ensure
good flowability allowing implementation in the laser
sintering process as described below.
30 The technology of powder sintering under a laser beam
serves to manufacture objects in three dimensions such as
prototypes and models, but also functional parts,
especially in the motor vehicle, nautical, aeronautic,
aerospace, medical (prostheses, auditive systems, cell
35 tissues, etc.), textile, clothing, fashion and decorative
fields, casings for electronics, telephony, home automation,
information technology and lighting.
A thin layer of powder is deposited on a horizontal plate
5 maintained in a chamber heated to a certain temperature.
The laser supplies the energy required to sinter the powder
particles at various points in the layer of powder in a
geometry corresponding to the object, for example with the
aid of a computer having the shape of the object in its
10 memory and rendering this shape in the form of slices. Next,
the horizontal plate is lowered by a value corresponding to
the thickness of a layer of powder (for example between
0.05 and 2 mm and generally about 0.1 mm) and a new layer
of powder is then deposited. The laser supplies the energy
15 required to sinter the powder particles in a geometry
corresponding to this new slice of the object, and so on.
The procedure is repeated until the entire object has been
manufactured- . .
20 In this process of powder sintering under a laser beam, it
is imperative to have available powders that have good
flowability, which allows good layering of said powders.
Moreover, good coalescence of the powder is necessary after
melting induced by the laser, so that the mechanical
25 properties of the manufactured objects are maximized.
Powders are thus sought which have, firstly, good
flowability and, secondly, good coalescence during the
sintering process.
30
In the field of laser sintering, it is common practice to
add floia~ agents to improve the floiiability of powders.
US 2004/0 204 531 describes the advantage in polyamide of
35 hydrophobic silicas versus hydrophilic silicas.
Specifically, the flowability is deteriorated after
moisture uptake in the case of using hydrophilic silicas,
whereas it is unchanged in the case of using hydrophobic
silicas.
5 In the field of polyarylene ether ketones (PAEK), the
flowability is known to be improved by using a suitable
heat treatment.
US 7 847 057 relates to a process for the heat treatment of
10 polyarylene ether ketone powders, which consists in
exposing the powder to a heat treatment for over 30 minutes
at a temperature 20°C above the glass transition
temperature of the polymer.
15 This treatment applied to polyether ether ketones (PEEK)
makes it possible to obtain powders whose flowability is
acceptable for the laser sintering process. The coalescence
aspect is ... ng.t discussed in said patent, and in particular
no example demonstrates that the coalescence is effective,
20 modified or even improved by the heat treatment.'
WO 2012/047 613 also describes a heat treatment applied
more particularly to polyether ketone ketone (PEKK) powders,
which consists in exposing the powder to a heat treatment
25 for several hours between the transition temperatures of
the various crystalline phases, more particularly by
approaching the melting point of the polymer, corresponding
to the crystalline form having transition at the highest
temperature. The flowability of the powder is thereby
30 improved and the crystallinity resulting from this
treatment is conserved during the sintering process, giving
the sintered object certain advantageous physical
properties, but appearing insufficient for certain
applications. The coalescence aspect is not discussed in
35 said patent, and in particular no example demonstrates that
the coalescence is effective, modified or even improved by
the heat treatment.
To satisfy the requirements of having available powders
5 with good florsrability and good coalescence, the Applicant
conducted a series of tests demonstrating that, for
polyarylene ether ketones, the addition of a hydrophilic
flow agent firstly alloris good flowability, and secondly
that this flowability is conserved even after residence in
10 a humid atmosphere. The latter result appears unexpected
and very surprising with regard to the prior art (US 2004/0
204 531).
In addition, the Applicant found that, for such
15 compositions, the coalescence of these polyarylene ether
ketone powders supplemented with hydrophilic flow agent is
superior to that of polyarylene ether ketone powders
supplemented.with hydrophobic flow agent.
20 Summary of the invention:
The invention relates to a composition comprising from
99.6% to 99.99% by weight of at least one powder of at
least one polyarylene ether ketone and 0.01% to 0.4% by.
25 weight of a hydrophilic flow agent, preferably from 0.01%
to 0.2% by weight of a hydrophilic flow agent and, more
particularly, preferably from 0.01% to 0.1% by weight of a
hydrophilic flow agent. This hydrophilic flow agent is
characterized by a gain in mass (amount of water absorbed),
30 after 5 days of conditioning at a relative humidity of 95%,
of greater than 0.5%, preferably greater than 0.8%. This
gain in mass of the flow agent is determined by Karl
Fischer measurement after desorption of the water by a 15-
minute treatment at 170°C.
The invention also relates to the use of the compositions
of the invention and also to the objects manufactured with
the aid of these compositions, in particular with the aid
of a laser sintering process.
5
Detailed description:
The polyarylene ether ketones (PAEK) used in the invention
comprise units having the following formulae:
10 (-Ar-X-) and (-Arl-Y-)
in which:
Ar and Arl each denote a divalent aromatic radical;
a minor proportion (< 10%) of these units may be
replaced with radicals with a valency of greater
15 than 2 to introduce branches.
Ar and Arl may preferably be chosen from 1,3-
phenylene, 1,4-phenylene, 4,4'-biphenylene, 1,4-
naphthyl.en.e, 1,5-naphthylene and 2,6-naphthylene;
X denotes an electron-withdrawing group; it may
20 preferably be chosen from the carbonyl group and
the sulfonyl group,
Y denotes a group chosen from an oxygen atom, a
sulfur atom, an alkylene group, such as -CH2- and
isopropylidene.
25
In these units X and Y, at least 50%, preferably at
least 70% and more particularly at least 80% of the
groups X are a carbonyl group, and at least 50%,
preferably at least 70% and more particularly at
30 least 80% of the groups Y represent an oxygen atom.
According to a preferred embodiment, 100% of the
groups X denote a carbonyl group and 100% of the
groups Y represent an oxygen atom.
More preferentially, the polyarylene ether ketone
(PAEK) may be chosen from:
- a polyether ether ketone, also known as PEEK,
comprising units of formula I:
5
Formula I
The sequences may be totally para (Formula I), but
10 it would not constitute a departure from the
context of the invention to introduce, partially or
totally, meta sequences. Two examples (nonlimiting
list) are given below:
15 or:
- a polyether ketone, also known as PEK,
comprising units of formula 11:
Similarly, the sequences may be totally para
(Formula 11), but it would not constitute a
departure from the context of the invention to
introduce, partially or totally, meta sequences:
- a polyether ketone ketone, also known as PEKK,
10 comprising units of formula IIIA, of formula IIIB
and a mixture thereof:
Formula IIIA
Formula IIIB
- and a polyether ether ketone ketone, also
known as PEEKK, comprising units of formula IV:
Formula IV
Similarly, meta sequences may be introduced into
this structure without departing from the invention.
10 Other arrangements of the carbonyl group and of the
oxygen atom are also possible. It would therefore
not constitute a departure from the context of the
invention to use them.
15 It is also possible to incorporate into the
structure a divalent radical of .. the phthalazinone
type having the following formula:
20
The polyarylene ether ketone that may be used
according to the invention may be semicrystalline
or amorphous. Preferably, the polyarylene ether
ketones are polyether ketone ketones comprising a
25 mixture of units IIIA and IIIB such that the mass
percentage of terephthalic units relative to the
sum of the terephthalic and isophthalic units is
between 55% and 85% and preferably between 55% and
70%, ideally 60%. The terms "terephthalic unit" and
"isophthalic unit" mean the formula of terephthalic
acid and isophthalic acid, respectively.
These polyarylene ether ketones are in the form of
5 powders that may be prepared by grinding or
precipitation.
Mixtures of various polyarylene ether ketone
powders are not excluded in the context of the
10 invention. According to a preference, the mixtures
of various polyarylene ether ketone powders
comprise a polyether ketone ketone combined with
another polyarylene ether ketone or a mixture of
two PEKKs of different chemical structure. Thus, a
15 polyarylene ether ketone will be combined with a
PEK, PEEKEK, PEEK, PEKEKK or PEKK. According to a
preferred form, the PEKK will be combined with PEK,
PEEKEK, PEEK or PEKEKK or a PEKK of different
chemical formula, the PEKK representing more than
20 50% by mass, limit inclusive.
The hydrophilic flow agents used in the context of
the invention may be inorganic pigments preferably
chosen from silicas and aluminas.
25
The hydrophilic silicas used in the context of the
invention are constituted of silicon oxide. They
are fumed silicas without any specific treatment,
unlike the hydrophobic silicas, which are fumed
30 si~licas that have undergone a chemical treatment
such as grafting with dimethylchlorosilane. It
would not constitute a departure from the context
of the invention to use silicas synthesized via
another manufacturing method
The silicas commonly used are commercial products
whose trade name is Aerosil' (supplied by Evonik) or
Cab-0-Silo (supplied by Cabot).
5 These silicas are composed of nanometric primary
particles (typically between 5 and 50 nm for fumed
silicas). These primary particles are combined to
form aggregates. In use as flow agent, silicas are
found in various forms (elementary particles and
10 aggregates) .
The powders or powder mixtures comprising
hydrophilic flow agents used in the context of the
invention may, where appropriate, be supplemented
15 or contain various compounds. Among these compounds,
mention is made of reinforcing fillers, especially
mineral fillers such as carbon black, nanotubes,
which may or may not be carbon-based, fibers (glass,
carbon, etc. fibers), which may or may not be
20 ground, stabilizers (light stabilizers, ,in
particular UV stabilizers, and heat stabilizers),
optical brighteners, colorants, pigments, energyabsorbing
additives (including UV absorbers) or a
combination of these fillers or additives.
25
Examples:
Measurement of the flowability:
30 The flowability of these powders was determined in
glass funnels in the following manner:
- Fill glass funnels with a 17 or 12 mm orifice (Figure
1) with the powder up to 5 mm from the rim. Stopper
the bottom orifice with the finger.
35 With, for a 12 mm funnel:
d,= 39.2 mm
do = 12 mm
h = 106 nun
hl= 83 mm
5
and for a 17 mm funnel:
d, = 42.0 mm
do= 17 mm
h = 112 nun
10 hl = 67 mm
- Measure with a chronometer the flow time of the powder.
- If flow does not take place, tap the funnel using a
spatula. Repeat the operation if necessary.
- Note the flow time and the number of taps given with
15 the spatula.
Estimation of the coalescence:
The coalescence of the powders is estimated by means of the
20 following protocol:
- deposition of powder onto a steel plate
- baking, at 340°C for 15 minutes, of the plate coated
with powder
- observation of the coated plate after cooling after
25 removal from the oven
The coalescence will be judged to be proportionately better
the more invisible the steel plate has become following the
coalescence/film formation of the powder
30
Example 1:
A KepstanB 6003 PL powder from the company Arkema,
containing 60% of terephthalic units relative to the sum of
35 the terephthalic and isophthalic units, whose particle size
has a Dv50 of 50 pm plus or minus 5 pm, was supplemented
with 0.4% of Cab-0-SilB TS-610 silica in a Magimix kitchen
blender at high speed for 100 seconds.
The Dv50 is also known as the volume median diameter, which
5 corresponds to the particle size value which divides the
population of particles examined exactly into two. The Dv50
is measured according to standard IS0 9276 - parts 1 to 6.
In the present description, a Malvern Mastersizer 2000
particle size analyzer is used, and the measurement is
10 taken in the liquid route by laser diffraction on the
powder.
The silica Cab-0-SilB TS-610 is a fumed silica that has
been made hydrophobic by treatment with
15 dimethylchlorosilane. It will be referred to hereinbelow as
"TS-610".
The powder. has excellent flowability (time < 10 s, 0 taps
for a 17 mm funnel), but the coalescence, estimated as
20 described above, is very poor, the steel plate still being
clearly visible.
The silica may thus be an anti-coalescer at a high content.
25 Example 2:
A KepstanB 6003 PL powder from the company Arkema,
containing 60% of terephthalic units relative to the sum of
the terephthalic and isophthalic units, whose particle size
30 has a Dv50 of 50 pm plus or minus 5 pm, was supplemented
with Cab-0-SilB TS-610 silica in a Magimix kitchen blender
at high speed for 100 seconds.
A second sample of the same Kepstan powder is supplemented
35 with Cab-0-SilB M-5 silica according to the same protocol.
The silica Cab-0-Sil@ M-5 is a hydrophilic fumed silica
that has not undergone any specific treatment. It will be
referred to hereinbelow as "M-5".
The flowability results for the two supplemented powders
5 are given in Table 1 in comparison with the silica-free
powder.
Table 1
10
The term "multi" is used when the funnel is tapped
continuously.
It is found that the two types of silica improve the
15 flowability and they are thus both potential flow agents
for PEKK.
Example 3:
20 Another Kepstanm 6003PL powder from the company Arkema is
supplemented in the Magimix blender either with 0.05% Cab-
0-Silm TS-610 silica or with 0.05% Cab-0-SilB M-5 silica.
These powders are, on the one hand, stored at 23°C and 50%
25 relative humidity up to moisture saturation (in the case,
for example, of storage of the powder before machine use).
The moisture content is measured by the Karl Fischer method
(desorption of water from the Kepstanm powder by treatment
for 20 minutes at 250°C). On the other hand, the powders
are dried overnight at 140°C. The moisture content is also
measured by the Karl Fischer method (same protocol as
above) .
5
The flowability results for the two supplemented powders
with different moisture contents are given in Table 2.
Table 2
10
The moisture contents of 0.5% and 0.53% correspond to the
state of the material saturated with moisture at 23°C and
50% relative humidity.
15
The moisture contents of 0.25% correspond to the state of
the material after drying at 140°C overnight.
The moisture contents are not affected by the nature of the
20 silica.
It emerges that, irrespective of the silica used, the
flowability is not affected by the moisture content. In
particular, no deterioration of the flowability is observed
25 for powders saturated with moisture (23'C, 50% relative
humidity), even in the case of using a hydrophilic silica
as flow agent.
Example 4:
30
Three samples of Example 2 (not supplemented, supplemented
with 0.2% of hydrophobic silica (TS-610), supplemented with
0.2% of hydrophilic silica (M-5) ) are deposited on three
steel plates.
5
These coated plates are placed in an oven maintained at
340°C for 15 minutes.
They are then cooled, and the PEKK coating at the surface
10 of the plates is then observed (Figures 2 and 3), visually
and under binoculars (Stemi SVll from Zeiss).
Visually (Figure 2), a much smoother surface is observed
when the hydrophilic silica (M-5) is used, demonstrating
15 the good coalescence of the powder during the oven
treatment. Without silica and with the TS-610 silica, the
coating is not continuous and, consequently, the steel
plate remains locally visible.
20 The binocular images (Figure 3) confirm the preceding
observations: there are areas where locally the steel plate
can still be seen in the case of the non-supplemented
powder and of the powder supplemented with 0.2% of TS-610
silica, whereas, in the case of the por.rder supplemented
25 with M-5 silica, the steel plate is no longer visible. This
confirms the better coalescence of the povrder supplemented
with M-5 during the oven treatment.
Claims
1. A composition comprising from 99.6% to 99.99% by
weight of at least one powder of at least one polyarylene
5 ether ketone and 0.01% to 0.4% by weight of a hydrophilic
flow agent, said hydrophilic flow agent being characterized
by a gain in mass (amount of water absorbed), after 5 days
of conditioning at a relative humidity of 95%, of greater
than 0.5%, said gain in mass of the flow agent being
10 determined by Karl Fischer measurement after desorption of
the water by a 15-minute treatment at 170°C.
2. The composition as claimed in claim 1, in which the
hydrophilic flow agent is a hydrophilic silica.
15
3. The composition as claimed in claim 1, in which at
least one polyarylene ether ketone is PEKK.
4. The composition as claimed in claim 3, in which the
20 PEKK has a mass percentage of terephthalic units relative
to the sum of the terephthalic and isophthalic units of
between 55% and 85%.
5. The composition as claimed in claim 3, in which,
25 in addition to the PEKK, a PEK, PEEKEK, PEEK,
PEKEKK or PEKK powder of different chemical
structure is added, the PEKK representing more than
50% by mass, limit inclusive.
30 6. The composition as claimed in claim 1,
containing a filler.
7. The composition as claimed in claim 1,
containing at least one additive.
8. The use of a composition as claimed in one of
claims 1 to 7 in a laser sintering process. .
9. An object obtained using a composition as
5 claimed in one of claims 1 to 7.