CA2006904A1 - Fine-grained polyether-ketone powder, process for the manufacture thereof, and the use thereof - Google Patents

Abstract

Abstract of the disclosure Fine-grained polyether-ketone powder, process for the manufacture thereof, and the use thereof A fine-grained polyether-ketone powder, having a particle size with a d50 value smaller than or equal to 40 µm and a grain size distribution range smaller than or equal to 55 µm, is obtained by cold-grinding of coarse-grained polyether-ketone in a fluid-bed opposed-jets mill, which is provided with a grinding chamber (2) subjected to gas jets, a grinding material-charging device, a screening device (5) for separating coarse material (11) and fine material (10), and a bottom (3) underneath the grinding chamber fox added material to be ground and coarse material flowing back from the screening device, the material to be ground and the coarse material flowing back from the screening device being cooled by means of a cryogenic refrigerant.

The powders obtained in this way are used for producing surface coatings or composites.

Description

HOEC~ST ~TIENGESELLSC~L~FT HOE 88tF 385 Dr. ~R~9 Description Fine-grained pol~ether-ketone lpowder~ pro~e~ iEor the 3nanuiEa~cture thereof r ~d th~ u~5e ~hereof .

The invention relates to a fine~grained polyether-ketone, to the manufacture thereof in a fluid-bed opposed-~ets mill and to the use of ~he powder especi~lly or produc-ing surface coatings.

Polye~her-Xetones are polymers which are obtained by nucleophilic or electrophilic condensation. They have been described axtensively in an extremely large numher of variations both with respect to their structure, their preparation and their properties and possible applica-tions. The polyether-ketones are highly esteemed by those skilled in the art~ in particular because of their outstanding property pattern. They are high t~mperature-resistant, have very good mechanical propertieY and are extremely resistant to chemical and environmental in-fluences. They have the disadvantage, however, that it is difficult to obtain them as a finely grained powder.
It is therefore also impossible to obtain crack-free, uniform and, in particular, smooth coatings, for example coatings on metal surfaces, hy means of flame-coating.
However, the known polyether-ketone powders or ~xains are frequently also insufficiently fine for other pxocesses and purpose~ such as, for example, electrostatic ~pray-coating, whirl-sintering, ram e~trusion, the production of pressed composites and the like. Some of the known powders are also acicular and therefore tend to felting.

Recently, a process for pulverizing PEE~ has been dis-closed, which is said to allow the production of powders having a 97 ~ content of grain sizes of less than 20 ~m ("Plastics Engineering", 44 (1988) issue No. 9~ page 63).
Our owql tests have shown, however, that the data giYen therein are insufficient for repeating the process or ~O~g~

obtaining a powder of this fineness.
The commercially available polyether-ketones ~U~:CTREX
PEEK 150 and VICTRBX PE~K 450 PF have grain 8iZQ8 of about 100 ~m. Howe~er, ~he si~e of the grain and the relatively wide grain size distribution of these products are disadvantageous. No sati~factory results are there-fore obtained in the powder-coating of metal~ or in sintering processes.

It is the ob~ect of the invention to overcome the di~ad-~antage~ mentioned and ~o provide a fine-grained poly-ether-ketone powder having enhanced ~phericity an~d a process for the manufacture thereof.

A fur~her ob~ect is to obtain a granulated polyether-ketone powder which i8 largely free of abrasion by the grinding device. ~hi~ is particularly important for a faultlesY surface quality of the coatings.

The invention rela~es ~ a fine-grained polyether-ketone powder which has a mean grain ~ize ~d50 v~lue) ~maller than or equal ~o 40 ~m, preferably smaller than or equal to 30 ~m and especially ~maller than or equal to 20~m.
Further data which are important for characterizing the powder are the d90 value which i~ smaller than or equal to 70 ~m, preferably smaller than or equal to 50 ~m, and the dlo value which is smaller than or equal to 15 ~m, prefer-ably smaller than or equal to 10 ym. This give~ thedistribution range, which can be calculated from the difference d30 minus dlo- It has values of smaller than or equal to 55 ~m, preferably smaller than or equal to 40 ~m and especially smailer than or equal to 20 ~m. The distribution range defines the range of the grain size distribution in the powders; the smaller the value, the better is the processability and hence the structure of the molding obtained.

The term polyether-Xetones includes all polymers which have recurring units ~ ~ - O - ~ and ( ~ - CO - ). These 2~

units are mutually linked in ~arious ways, in general in the p-position. Accord.ing to g~neral parlance, thP first unit i5 designa~ed as E' (ether) and the second unit a~
~K (ketone). Thus, ~he abovemen~ioned polye~her-Xetone is de6cribed as PEER. Pre~erred polyether-ketones accordin~ to the invention are those of the PER and PERK
type~, and PEEK~ is particularly preferred. However, these polymers can al~o con~ain other recurring units as copolymer constituents, æelected from the group compri-10 ~ing E~EE~, EÆR, EEKR, and EXR, but as a rule in quan-tities of not more than 40 %, preferably not more than 20 % and particularly preferably not more than 5 mol ~.

With a view to the ver~atile applicability of the poly-ether-ketone powder according to the present invention, the powders can h~ve a melt index MFI from 400 to 1.0 g, measured at 400C in 10 minutes ~ASTM D 1238). Their melting point is in general above 250C, preferably above 300C and especially above 350C, and their softening point is in general above 130C.

Moreover, the invention also re.lates to a process for producing the ~ine-grained polyethex-ketone powder%, in which coarse-grain polyether-ketone i5 cold-ground in a fluid-bed opposed-~ets mill having a grinding chamber t2) sub~ected to gas ~ets, a grinding material-charging device, a ~creening device (5) for separating cn~r~e material (11) and fine material (lO) t and a bottom (3) underneath the grinding chamber for added material to be ground and coa.rse material flowing back from the screen-ing device, the material to be ground and the coarse material ~lowing back from the screening device being cooled by means of a cryogenic refrigerant~

Jet mills are comminuting machines known for a long time, in which the particles to be comminuted are accelerated by gas streams and comminuted by mutual Lmpingement.
' There are a number of different ~et mill designs. They differ in the type of ga6 flow, in the type of impingement of the particles on one another or on an impingement ~urface and in whether ~he par~icles to be comminuted are carri~d along in the gas ~t or whe her the gas ~e~ ~npinges upon the particles and en~rains S them. ~he grinding g~s use~ is normally air or ~uper-heat~d steam.

In the fluid-bed opposed-jet~ mill, freely expanding gas jet~ impact upon one another in a grindinq chamber which contains the grinding material in the form of a fluid bedO Grinding ~akes place here virtually exclusively by mutual impingement of the grinding material particles upon one another, and grinding is therefore almost free of wear. The fluid-bed opposed-jets mill i8 associated with a screening device in which the fines obtained are ~eparated off from the coaræe material which ha~ not yet heen sufficiently comminuted. The coarse material is returned into the gxinding chamber.

Many materials, for example, plastics, can be ground to fine grain sizes only with difiEiculty or not at all, becau~e of their toughnes~. The grinding properties of ~uch tough materials can be improved by cooling, which results in an embrittlement of the material~. The propellant gas ~tream in jet mills i~ therefore cooledt as is described, for example, in German O~fenlegungs-schrift 2,133,019. Cooling of the propellant gas ~tream allows materials to be ground which will not be grindable in ~et mills under normal conditions. In spite of intensive cooling, for e~ample with liguid nitrogen, and in spite of the cooling of the pxopellant gas stream itself due t~ its exp~n~ion, the achievable Lmprovement in grindability ~till, however, leave~ m~ch to be desired. Fine grain sizes can admittedly be reached, but only with extremely high Gonsumption of tLme and enexgy.

The proce s according to the invention therefore achieves ' the object of allowing super-fine grinding of polyether-ketones to hitherto virtually unattainable very fine - 5 ~ i9~'~
grain sizes with a substantial increa~e in throughput, coupled with a low consumption of eneryy and refrigerant.
In this case, it is no~ the propellan~ gas stream, but the circulating coars~ matexial which is cooled by a cryogenic refrigerant. The measure according ko the invention has the efect of a step change in ~mproving the results of grinding, as can be ~een from the re~ults listed in the table.

By means of the process according to the inven ion, a considerable increase in throughput as compared with grinding under normal conditions can be achieved in fluid-bed opposed-~ets mills. Particles of highest fineness with a corre6ponding increase in surface area and a smooth curface structure can be produced ~-ith polyether-ketones. The end product becomes readily flowable and has a high bulk density and tap density.

The refrigerants used can above all be liquefied gases, in particular nitrogen, but also carbon dioxicle. In the simplest and frequently most appropriate case, these can be fed directly into the bot~om o~E the mill. Of course, indirect cooling of the coarse material is also possible.
Indirect cooling can also be effected by other refriger-ants, for example brine baths.

A few illustrative examples of the invenkion will be explained by reference to the attached drawings, in which:
Figure 1 shows a fluid-bed opposed-jets mill in a diagrammatic fonm, Figure 2 shows the coolinq of the bottom of the fluid-bed opposed-~ets mill of Figure 1, Figure 3 shows a mixed f~rm of direct and indirect cooling of the bottom, Figure 4 show~ an embodiment similar to Figure 3, but exclusively with direct cooling, 5 ~ Figure 5 shows direct cooling of the coarse material flowing back outside of the bottom of the mill/

and Figure 6 ~hows indirect cooling of the coar~e material flowing back outside o the bottom of the mill.

In the description which follows, the same reference symbols ha~e been used in all figures for the s~me parts.

Figure 1 shows th~ fluid-bed opposed-jets mill in a diagra~ma~ic form. The mill comprises a housing 1 which contains the grinding chamber 2 and the bottom 3. The propellant gas enters the grinding chamber 2 through the nozzles 4. The hou~ing 1 i5 ad~oined by the ~creening ~evice 5. The coarse material to be ground is in the form of a fluid bed 6 in the yrinding chamber. The grinding material is fed in through the lock 7. The fines 10 separated off in the screening device 5 are withdrawn through the fines outlet 8, as indicated ~y the arrow 9, and fed to the filter unit 15. The latter possesses a branch 16 for the exit gas and a discharge lock 17 for the fines 10 produced. The coar~e material 11 flows from the screening device 5 baclc into the grinding chamber 2. The propellant gas charged to the nozzles 4 is introduced through t.he feed line 14.

According to the invention, the l~oarse material present in the bottom 3 of the mill is cooled down by liquid nitrogen. The lat~er is introduced through ~he line 12 and the porou~ charging body 13. Porous charging bodies are particularly suit~ble for ~mall mills. ~or mills of larger diameters, other charging systems, for e~mple nozzle plates, are to be preferred, in order to enable the nitrogen to be introduced a~ finely di~ided a~
possible. The nitrogen feed through the line 12 and the porous charging body 13 takes place as a function of the temperature control 18. The charging of the grinding material t~rough the lvck 7 can also take place direc~ly in~o the bottom 3. The fines fraction of the fine ~ material 10 is determined by the spQed of rotation of the screening device 5. The coar~e material 11 flowing back 9~'~

from the ~creening device 5 together with the grinding material entering from the lock 7 forms the fluid bed 6.
The liquid nitrogen entering through the porous charging body 13 vaporizes and cools the bottom of the mill, i.e.
the coaræe material 11 flowing back from the screening device 5 and any freshly charged grinding material. The vaporized cold ni~rogen flows of upwards thxough the material and enters ~he grinding zone. Cold gas, coarse material and grinding material form a first fluid-bed zone underneath the grinding ch~mber 2 in the bottom 3.

Figure 2 shows the lower part of the fluid-bed opposed-jets mill of Figure 1 in a diagrammatic ~orm, but with the lock 7 for the grinding material located directly on the bottom 3. The arrows 19 clearly indi~te the mixture of cold gas, propellant gas, coarse material and fine material flowing upwards to the screening device.

Figure 3 ~hows a variant with indirect and direct heat exchange between the nitrogen feed and grindîng material.
The liguid nitrogen i~ fed through the lines 20 and 21.
The liquid nitrogen entering through line 21 passe~ into a double-walled pipe 22 closed at the end faces. Thi~
double-walled pipe 22 has inward-E)ointing outlet orifices 23. The entire lower part of the mill housing is like-wise constructed as a double-walled chamber 24. The line 20 leads into the latter. The chamber 24 has outlet orifices 25, arranged in the bottom 3, for the nitrogen fed through the line 20. The coarse material 11 flowing back from the screening device is thexefore first cooled indirectly in the region between the doubled-walled tube 22 and the chamber 24. Subseguently, direc~ cooling taXes place by the nitrogen isæuing from the outlet orifice~ 23 and 25.

Depending on the mode of operation, this nitrogen can be still liquid or already gaseous.

Figure 4 show~ another embodLment similar to Figure 2, oo but with an ex~ended bottom 3. A certain type o flow is here impressed upon the coarsP material 11 and the cold ga~ by a pipe-shaped apron 26. The apron 26 separ-ates the grinding chamber into a central shaft 37, where the grinding process takes place, and an annular shaft 38 for the coarse material flowing back. Liquid nitrogen feed takes place at two points, namely through line 12a directly into the bottom 3 and through line 12b into a spray system 39 in the annular shaft 3B. Accordingly~
the nitrogen introduced through line 12b directly cools the coarse material flowing back from the screening device.

Figure 5 shQws a Yariant with direct but extPrnal heat exchange between refrigerant and coarse material. The coarse material separated off in the externally arranged ~creening device 5 passes through the line 27 into the filter 28. The exit gas escapes through line 29, while th2 coarse material together with any grinding material added through the line 30 enters a helical screw 31.
Liguid nitrogen entering through the line 32 i8 fed to the helical ~crew 31. The mixture of cooled c~arse material and vaporized nitrogen flows through line 33 into the bottom 3.

Figure 6 shows a variant of the embodiment according ~o Figure 5. The coarse material from the filter 28 and any grinding material fr~m the line 30 here enter a heat ex~h~nger 35. From there, they pass indirectly cooled into the bottom 3. The cooling is effected by liquid nitrogen which i8 introduced through line 34 in~o the h~at exchanger 35. Vapori2ed ga~eous nitrogen then passes as cold gas through the line 36 likewise into the bottom 3, where subsequent fur~her direct cooling takes place.

There are still numexou~ further possibilities for ' cooling the coarse material flowing back from he screening device by a refrigerant. For example, a - 9 ~
plurality of grinding zones with a bottom can be arranged in series in the form of a cascade. In this case, the mix~ure of fines and coarse material leaving the grindiny zone is separated from ~he exit ga~ in the filter and fed to the ne~t grinding zone. The bo~tom located underneath sach grinding zone i6 here cooled according to the invention. A screening device is associated onl~ wi h the last staye.

The fine-grained polyether ketones according ~o the invention can advantageously be used for coating sur-faces, for example by flame-coating, electrostatic spray-coating, whirl-sintering or ram extrusion. Furthermsre, they are outstandinyly suitable for sintering processes, for example for producing pressed composites.

Examples:

As the start~ng point for the tests, a polyether-ether-ketone-ketone (PEEKK) having a melt index MPI of 15 g ~400C/10 min) was used. The particle sizes of this starting material are listed in t]he table. Moreover, two commercially available polyether-ketones from ICI under the names ~Victrex PEEK 150 P and Victrex PEEK 450 PF (Vl and V4 and V5 respectively) were used as a comparison.
Examples 2 and 3 represent ex~mples according to the invention.

The particle size analysi6 was carried out on a suspen-sion of solid, water and wetting agent ~a~ed on nonylphenol polyglycol ether, using a commercially available laser granulometer (Manufacturer: Cilas, 91460 Marcousse, France). The dlo, d50 and d~o values were chosen as repres~ntative value6. For example, the dlo value of ~.4 ~m in Example 2 means that 10 ~ of the end produc~
have a particle size of 6.~ ~m. Examples 2 and 3 differ in this respect to the speed of rotation of the screening -' device and the product throughput rate.

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The table ~hows that ~he distl-ibution range decreases when the ~peed o rotation of the screening devics increases and the product throughput decreases, i.e. a product having a uniform particle size properties is obtained in Example 2. A further advantage of these polyether~ketone powders i8 the l~rgely spheroidal form of the PE~ paxticles. The increased sphericity of the particles leads to an improved flowability as compared with the hitherto known processes. The flowability is important for uniform application in use, for example in metal coating. Due to the agglomeration tendency of the known powders, non-uniform ~urfaces can result from the hitherto known grinding proce6ses. However, a uniform suxface is a prerequisite for ~he quality of ~he surface.
Hitherto, only crazed surfaces were obtainable, wherea~
smooth suxfaces are obtained with the polyether-ketone powders ac:cording to the invention.

Claims (16)

1. A fine-grained polyether-ketone powder, wherein the grain size has a d50 value smaller than or equal to 40 µm and the grain size distribution range is smaller than or equal to 55 µm.

2. A polyether-ketone powder as claimed in claim 1, wherein the polyether-ketone has a melt index from 400 to 1.0 g (400°C/10 min).

3. A polyether-ketone powder as claimed in claim 1, wherein the polyether-ketone is selected from the group comprising PEK, PEEK, PEEKK, PEKK or a mixture thereof.

4. A polyether-ketone powder as claimed in claim 1 or 2 or 3, wherein the d50 value is smaller than or equal to 30 µm, and the grain size distribution range is smaller than or equal to 40 µm.

5. A polyether-ketone powder as claimed in claim 1 or 2 or 3, wherein both the d50 value and the grain size distribution range are smaller than or equal to 20 µm.

6. A polyether-ketone powder as claimed in claim 3, wherein the polyether-ketones are co-condensates which contain up to 40 mol % of the other units selected from the group comprising EKEEK, EEK, EEKK, and EKK.

7. A process for cold-grinding coarse-grained polyether-ketone which comprises grinding said polyetherketone in a fluid-bed opposed-jets mill having a grinding chamber (2) subjected to gas jets, a grinding material-charging device, a screening device (5) for separating coarse material (11) and fine material (10), and a bottom (3) underneath the grinding chamber for added material to be ground and coarse material flowing back from the screening device, and cooling the material the screening device by means of a cryogenic refrigerant.

8. The process as claimed in claim 7, wherein the cryogenic refrigerant is contacted in a finely divided form with the coarse material.

9. The process as claimed in claim 7, wherein liquid nitrogen or carbon dioxide is used as the cryogenic refrigerant.

10. The process as claimed in claim 7 or 8 or 8, wherein the cryogenic refrigerant is introduced into the bottom.

11. The process as claimed in claim 7 or 8 or 9, wherein the coarse material is cooled directly by the cryogenic refrigerant.

12. The process as claimed in claim 7 or 8 or 9, wherein the coarse material is cooled indirectly.

13. A surface coating, produced from the powder as claimed in claim 1.

14. A composite, produced from the powder as claimed in claim 1.

15. The fine-grained polyether-ketone powder as claimed in claim 1, and substantially as described herein.

16. The fine-grained polyether-ketone powder as claimed in claim t 1 and substantially as described herein.