COMPOSITION OF POLY-ARYLENE ETHER KETONE KETONE POWDERS SUITABLE FOR LASER SINTERING

Abstract

The present invention relates to a composition comprising at least one poly(arylene ether ketone) powder suitable for laser sintering and also to the process which makes it possible to obtain it, minimizing the amount by weight of remaining non-sintered powder after production of the part by sintering.

Claims

1. A composition comprising a PEKK powder, the tapped density of which is less than 340 kg/m.sup.3, limit included, measured according to ISO 1068-1975 (F), and the flowability of which exhibits a passage time in a 12 mm funnel of less than 50 s, limit included, or a passage time in a 17 mm funnel of less than 30 s.

2. The composition as claimed in claim 1, wherein the PEKK exhibits a percentage by weight of terephthalic unit with respect to the sum of the terephthalic and isophthalic units of between 55% and 85%.

3. The composition as claimed in claim 1, comprising, in addition to the PEKK powder, a PEK, PEEKEK, PEEK or PEKEKK powder, the PEKK powder representing more than 50% by weight, limit included.

4. The composition as claimed in claim 1, additionally comprising a filler.

5. The composition as claimed in claim 1, additionally comprising at least one additive.

6. A heat treatment process for preparing a PEKK powder the tapped density of which is less than 340 kg/m.sup.3, limit included, measured according to ISO 1068-1975 (F), and the flowability of which exhibits a passage time in a 12 mm funnel of less than 50 s, limit included, or a passage time in a 17 mm funnel of less than 30 s, the process comprising the following stages: arranging a PEKK powder in a ventilated chamber in a static or dynamic device; heating the PEKK powder at a temperature between T10 C. and T+10 C., where T=3.75*A+37.5, expressed in C., A representing the percentage by weight of terephthalic unit with respect to the sum of the terephthalic and isophthalic units and is between 55% and 85%, for a time sufficient to reduce the tapped density to less than 340 kg/m.sup.3.

7. A method, comprising sintering a composition as claimed in claim 1 in a laser sintering device.

8. A method, comprising sintering a composition as claimed in claim 2 under a laser beam.

Description

DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 illustrates, in schematic form, a funnel.

[0022] FIG. 2 is a scanning electron microscope image of a PEKK powder before heat treatment.

[0023] FIG. 3 is a scanning electron microscope image of a PEKK powder after heat treatment.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The poly(arylene ether ketone)s used in the invention comprise units of formula IA, of formula IB and their mixture.

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[0025] In a more general context, the poly(arylene ether ketone)s corresponding to the generic names PEK, PEEKEK, PEEK or PEKEKK (where E denotes an ether functional group and K a ketone functional group) cannot be excluded, in particular when their use takes place in a way combined with that of PEKK in proportions by weight where the PEKK represents more than 50% as proportion by weight and preferably more than 80% as proportion by weight, limits included.

[0026] Preferably, the poly(arylene ether ketone)s are poly(ether ketone ketone)s comprising a mixture of IA and IB units, so that the percentage by weight of terephthalic units with respect to the sum of the terephthalic and isophthalic units is between 55% and 85% and preferably between 55% and 70%, ideally 60%. Terephthalic and isophthalic unit is understood to mean the formula of terephthalic acid and isophthalic acid respectively.

[0027] These poly(arylene ether ketone)s are provided in the form of powders which may have been prepared by milling or precipitation.

[0028] They exist, after the heat treatment process of the invention, in the form of a powder, the tapped density of which is less than 400 kg/m.sup.3, limit included, preferably less than 370 kg/m.sup.3 and more preferably less than 340 kg/m.sup.3, this density being measured according to the standard ISO 1068-1975 (F), a flowability in a 12 mm funnel of less than 50 s and preferably of less than 40 s or a flowability in a 17 mm funnel of less than 30 and preferably of less than 25 s.

[0029] The powders or mixtures of powders used in the process can be obtained, for example, by a milling process described in the application FR 1160258. They can, if appropriate, be additivated with or contain different compounds, such as reinforcing fillers, in particular inorganic fillers, such as carbon black, nanotubes, which may or may not be of carbon, fibres, which may or may not be ground, 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 or additives.

[0030] The process for the treatment of such powders in accordance with the invention and which makes it possible to obtain the powders in accordance with the invention consists in causing the powder to reside in a static or dynamic device, typically a ventilated chamber held at temperature, typically between a temperature T10 C. and T+10 C., where T=3.75*A+37.5, expressed in C. (A, representing the percentage by weight of terephthalic unit with respect to the sum of the terephthalic and isophthalic units, is between 55% and 85%), preferably between T5 C. and T+5 C. and more preferably between T3 C. and T+3 C., ideally T, for times which can vary according to the type of heating chamber used, typically greater than 2 minutes. Mention may be made, among the types of heating chambers under consideration, without limitation, of ventilated ovens, fluidized beds, flash dryers, vane dryers, vertical shaft dryers, rotary ovens or also tunnels heated using infrared lamps. It would not be departing from the scope of the invention to carry out several successive heat treatments (at the same temperature or at two different temperatures of between T10 C. and T+10 C., where T=3.75*A+37.5, expressed in C., A representing the percentage by weight of terephthalic unit with respect to the sum of the terephthalic and isophthalic units). In the latter case, the temperature of the 2.sup.nd treatment is greater than the temperature of the 1.sup.st treatment.

[0031] The powder resulting from this heat treatment is subsequently used in a device for sintering powders under a laser beam in order to make possible the manufacture of an object.

[0032] Whereas, in this process for the manufacture of an object, it is not rare to find that only 10% by weight of the powder is actually sintered, the remainder having to be recycled, the use of the powders which are a subject matter of the invention and which are treated by the process of the invention makes it possible to obtain, starting from low density (that is to say, <400 kg/m.sup.3) powder, a sintered part with a typical density of 1290 kg/m.sup.3 plus or minus 20 kg/m.sup.3 with a residual porosity of the sintered part of less than or equal to 2%. The proportion by weight of non-sintered powder remaining to be reused is thus lower with the powder of the invention (density <400 kg/m.sup.3) than with the powders obtained according to the prior art, this resulting in a spectacular increase in productivity by minimizing major handling operations, contamination, indeed even detrimental changes in the quality of the recycled part, in order to obtain objects exhibiting fewer defects.

EXAMPLES

Example 1: Measurement of the Density

[0033] The tapped and bulk densities are measured according to the standard ISO 1068-1975 (F) in the following way:

[0034] Tapped and Bulk Densities [0035] The balance is tared with the empty measuring cylinder cleaned and dried beforehand. [0036] A volume of powder is introduced into an accurate graduated 250 ml glass measuring cylinder. [0037] If necessary, the free surface of the powder is levelled, without tapping it, and the volume V.sub.0 is recorded. [0038] The measuring cylinder with the powder is weighed with a balance accurate to 0.1 g. [0039] The measuring cylinder is placed on the plate of the STAV 2003 tapping device. [0040] Tapping is carried out with 1250 drops and V.sub.1 is recorded. [0041] Tapping is carried out with 1250 drops and V.sub.2 is recorded. [0042] The tapping operation is repeated until two equivalent volumes Vi are obtained. V.sub.f is recorded.

[0043] The bulk density is the weight of powder introduced divided by V.sub.0.

[0044] The tapped density is the weight of powder introduced divided by V.sub.f.

[0045] It is expressed in kg/m.sup.3.

Example 2: Measurement of the Flowability

[0046] The flowability of these powders was carried out in glass funnels in the following way: [0047] Glass funnels with an orifice of 17 or 12 mm (FIG. 1) are filled with the powder up to 5 mm from the edge. The orifice of the bottom is blocked with the finger.

[0048] With for the 12 mm funnel:

[0049] d.sub.e=39.2 mm

[0050] d.sub.o=12 mm

[0051] h=106 mm

[0052] h.sub.1=83 mm

[0053] and for the 17 mm funnel:

[0054] d.sub.e=42.0 mm

[0055] d.sub.o=17 mm

[0056] h=112 mm

[0057] h.sub.1=67 mm [0058] The flow time of the powder is measured with a stopwatch. [0059] If flow does not take place, the funnel is tapped using a spatula. The operation is repeated, if required. [0060] The flow time and the number of tapped blows using the spatula are recorded.

Example 3

[0061] A Kepstan 6003 powder from Arkema, containing 60% of terephthalic units with respect to the sum of the terephthalic and isophthalic units, the particle size of which exhibits a dv50 of 50 m plus or minus 5 m, with a bulk density of 235 kg/m.sup.3 and with a tapped density of 355 kg/m.sup.3, is subjected to different heat treatments in a crystallizing dish in a ventilated oven. The powder is arranged in a crystallizing dish so that the thickness of the powder bed is between 1 and 1.5 cm.

[0062] The Dv50 is also referred to here as median diameter by volume, which corresponds to the value of the particle size which divides the population of particles examined exactly into two. The Dv50 is measured according to the standard ISO 9276parts 1 to 6. In the present description, a Malvern particle sizer, Mastersizer 2000, is used and the measurement is carried out by the liquid route by laser diffraction on the powder.

[0063] After treatment, the powders were sieved on a 250 m vibrating sieve in order to deagglomerate them.

[0064] The results are given in table 1 for residence times of 16 h.

TABLE-US-00001 TABLE 1 16 h at 16 h at 19 h at T = 0 200 C. 260 C. 285 C. Bulk density (Kg/m.sup.3) 235 238 235 205 Tapped density (Kg/m.sup.3) 355 350 335 315 Flowability, Time (s) 95 55 30 50 12 mm funnel Number of multi multi 25 multi blows Flowability, Time (s) 50 40 10 40 17 mm funnel Number of 40 30 4 27 blows Moisture content 0.45% 0.16% 0.23% 0.23%

[0065] The results clearly show that a treatment at 260 C. very significantly improves the flowability while reducing the tapped density.

[0066] The effect of the heat treatment on the morphology of the powders can be viewed with a scanning electron microscope in FIG. 2 (before heat treatment) and in FIG. 3 (after heat treatment). It is apparent, on these same powder particles observed before and after the heat treatment, that the temperature treatment according to the invention results in a roughness of the powder particles.